CN1933195A

CN1933195A - Nitride semiconductor substrate and nitride semiconductor device

Info

Publication number: CN1933195A
Application number: CNA2006100999374A
Authority: CN
Inventors: 清久裕之; 中村修二; 小崎德也; 岩佐成人; 蝶蝶一幸
Original assignee: Nichia Chemical Industries Ltd
Current assignee: Nichia Chemical Industries Ltd
Priority date: 1997-04-11
Filing date: 1998-04-09
Publication date: 2007-03-21
Anticipated expiration: 2018-04-09
Also published as: CN100492687C

Abstract

A method of growing a nitride semiconductor crystal which has very few crystal defects and can be used as a substrate is disclosed. This invention includes the step of forming a first selective growth mask on a support member including a dissimilar substrate having a major surface and made of a material different from a nitride semiconductor, the first selective growth mask having a plurality of first windows for selectively exposing the upper surface of the support member, and the step of growing nitride semiconductor portions from the upper surface, of the support member, which is exposed from the windows, by using a gaseous Group 3 element source and a gaseous nitrogen source, until the nitride semiconductor portions grown in the adjacent windows combine with each other on the upper surface of the selective growth mask.

Description

Nitride semiconductor substrate and device

The present application is a divisional application of chinese patent application entitled "method for growing nitride semiconductor, nitride semiconductor substrate, and device" filed on 1998, application No. 200310118286.5, which was filed on1998, 4/9.

Technical Field

The present invention relates to a method for growing a nitride semiconductor, a nitride semiconductor substrate, and a semiconductor device, and more particularly to a method for growing a nitride semiconductor having good crystal quality using a substrate formed of a semiconductor material different from that of a nitride semiconductor, a nitride semiconductor substrate, and a nitride semiconductor device.

Background

It is generally known that when a semiconductor is grown on a substrate, a semiconductor having good crystallinity with few crystal defects can be grown when a substrate lattice-matched with the semiconductor to be grown is used. However, since there is no substrate which is lattice-matched with a nitride semiconductor, has excellent crystallinity, and on which a nitride semiconductor crystal can be stably grown, it is necessary to grow a nitride semiconductor on a substrate which is lattice-mismatched with a nitride semiconductor, such as sapphire, spinel, or silicon carbide.

On the other hand, various research institutes have attempted to produce GaN bulk crystals lattice-matched to nitride semiconductors, but no report has been made on obtaining crystals having an overall size of about several millimeters. That is, heretofore, there has not been obtained a GaN bulk crystal which is practically usable in that a plurality of wafers can be cut out from a bulk crystal and used as a substrate for growing a nitride semiconductor layer.

Thus, as a technique for producing a GaN substrate, for example, japanese unexamined patent publication No. h 7-202265 or japanese unexamined patent publication No. h 7-165498 describes a technique for forminga ZnO buffer layer on a sapphire substrate, growing a nitride semiconductor on the ZnO buffer layer, and then removing the ZnO buffer layer by dissolution. However, the ZnO buffer layer grown on the sapphire substrate is poor in crystallinity, and it is difficult to obtain a nitride semiconductor crystal of good quality even if a nitride semiconductor is grown thereon. In addition, it is also difficult to continuously grow a sufficiently thick nitride semiconductor that can be used as a substrate over the thin film ZnO buffer layer.

In the fabrication of nitride semiconductor electronic devices that can be used in various electronic devices such as Light Emitting Diode (LED) devices, Laser Diode (LD) devices, and photo-sensors, if a substrate made of a nitride semiconductor having few crystal defects can be fabricated, a new nitride semiconductor constituting a device structure can be grown thereon with few lattice defects, so that the performance of the resulting device can be dramatically improved, and a device having high performance that has not been achieved before can be realized.

Disclosure of Invention

Accordingly, an object of the present invention is to provide a method for growing a nitride semiconductor crystal excellent in crystallinity.

Specifically, a method of growing a nitride semiconductor crystal that can provide a nitride semiconductor substrate, and a nitride semiconductor substrate and a nitride semiconductor device provided on such a nitride semiconductor substrate are provided.

The 1 st aspect of the present invention can provide a method for growing a nitride semiconductor, comprising the steps of: (a) a step of forming a1 st selective growth mask having a plurality of 1 st windows for selectively exposing the surface of the underlying layer of a support, on thesupport having a main surface and composed of a different-type substrate formed of a material different from the nitride semiconductor and an underlying layer formed of a nitride semiconductor provided on a main surface of the different-type substrate, and (b) a growth step of growing a nitride semiconductor from the surface of the underlying layer exposed in the windows by using a gaseous group 3 element source and a gaseous nitrogen element source until the upper surfaces of the nitride semiconductor selective growth masks grown in the adjacent windows are united. In this case, the total surface area of the portions of the base layer covered with the 1 st selective growth mask is preferably larger than the total surface area of the portions of the base layer exposed from the 1 st window.

The invention according to claim 2 provides a method for growing a nitride semiconductor, comprising the steps of: (a) a step of forming a1 st selective growth mask having a plurality of 1 st windows partially exposing the surface of a support on the support having a main surface and including a different-type substrate formed of a material different from that of the nitride semiconductor, such that the total surface area of the portions of the support covered with the 1 st selective growth mask is larger than the total surface area of the portions of the support exposed from the 1 st windows, (b) a growth step of growing the 1 st nitride semiconductor from the surface of the support exposed from the windows using a gaseous group 3 element source and a gaseous nitrogen element source, until the nitride semiconductors grown in the adjacent windows are united on the upper surface of the selective growth mask.

In the 1 st and 2 nd aspects of the present invention, the 1 st selective growth mask is desirably formed of a plurality of individual strips extending in parallel, separated from each other, and defining the 1 st window therebetween. Furthermore, in aspects 1 and 2, the ratio of the width of each individual stripe to the width of the respective 1 st window is preferably greater than 1 and less than 20. In the 1 st and 2 nd aspects, it is particularly desirable that the dissimilar substrate is a sapphire substrate whose main surface is a (0001) plane, and each individual stripe extends in a direction perpendicular to a (1120) plane of sapphire, the dissimilar substrate is a sapphire substrate whose main surface is a (1120) plane, and each individual stripe extends in a direction perpendicular to a (1102) plane of sapphire, or that the dissimilar substrate is a spinel substrate whose main surface is a (111) plane, and each individual stripe extends in a direction perpendicular to a (110) plane of spinel.

In the methods 1 and 2, in the step (b), a1 st nitride semiconductor crystal may be grown by organometallic vapor phase epitaxy, and a 2 nd nitride semiconductor crystal may be grown on the grown 1 st nitride semiconductor crystal by halide vapor phase growth. Alternatively, the 1 st and 2 nd aspects may further include a step (c) of forming a 2 nd selective growth mask having a plurality of 2 nd windows for selectively exposing the surface of the 1 st nitride semiconductor on the 1 st nitride semiconductor crystal grown in the step (b), and a growth step (d) of growing the 2 nd nitride semiconductor from the surface of the 1 st nitride semiconductor exposed from the 2 nd windows by using a gaseous group 3 element source and a gaseous nitrogen element source until the 2 nd nitride semiconductors grown in the adjacent windows are united on the upper surface of the selective growth mask. In this case, it is preferable that the 2 nd selective growth mask has the same configuration as the 1 st selective growth mask.

Further, the present invention provides, in claim 3, a method for growing a nitride semiconductor, comprising the steps of: (a) a step of forming a nitride semiconductor layer on a support having a main surface and containing a different-type substrate formed of a material different from that of the nitride semiconductor, (b) a step of forming a plurality of recesses having a bottom surface substantially parallel to a surface of the support on the nitride semiconductor layer, (c) a step of selectively forming a1 st growth control mask on a top surface of the nitride semiconductor layer and selectively exposing the nitride semiconductor layer from side surfaces of the recesses, and (d) a step of growing the nitride semiconductor from an exposed surface of the nitride semiconductor layer using a gaseous group 3 element source and a gaseous nitrogen element source. In this case, the 1 st growth control mask is preferably configured in the same manner as the 1 st selective growth mask of the 1 st and 2 nd aspects.

The step (c) of claim 3 preferably further comprises a step of forming a 2 nd growth control mask on the bottom surface of the recess so as to selectively expose the nitride semiconductor layer from the side surface of the recess. In this case, the 1 st growth control mask is desirably constituted by a plurality of individual stripes extending in parallel, separated from each other, with the 1 st window being constituted therebetween. Further, in this case, it is particularly desirable that the different-type substrate is a sapphire substrate whose main surface is a (0001) plane, and each individual stripe extends in a direction perpendicular to a (1120) plane of sapphire, the different-type substrate is a sapphire substrate whose main surface is a (1120) plane, and each individual stripe extends in a direction perpendicular to a (1102) plane of sapphire, or that the different-type substrate is a spinel substrate whose main surface is a (111) plane, and each individual stripe extends in a direction perpendicular to a (110) plane of spinel.

In growing a nitride semiconductorcrystal using the present invention, the molar ratio of the gaseous nitrogen element source to the gaseous group 3 element source is preferably 2000 or less.

Further, according to the present invention, there can be provided a nitride semiconductor crystal having the 1 st main surfaceAnd a 2 nd main surface, the crystal defects in the region near the 1 st main surface being relatively small, and the crystal defects in the region near the 2 nd main surface being relatively large, and a nitride semiconductor substrate comprising a nitride semiconductor crystal having the 1 st main surface and the 2 nd main surface, the 1 st main surfaceThe surface region of the main surface has crystal defects of less than 1 × 10⁵/cm²The nitride semiconductor substrate of (1).

Further, according to the present invention, there can be provided a nitride semiconductor device including a nitride semiconductor device structure supported by the nitride semiconductor substrate of the present invention.

Further developments of the invention are described in the following description and in the scope of the claims.

In the present invention, the nitride semiconductor can be represented by the formula In_aAl_yGa_1-a-bN (wherein 0. ltoreq. a, 0. ltoreq. b, and a + b. ltoreq.1).

Drawings

Fig. 1A to 1C are schematic cross-sectional views illustrating the principle of the nitride semiconductor growth method according to the 1 st or 2 nd aspect of the present invention in sequence of steps.

Fig. 2 is a schematic cross-sectional view of a substrate having an inclined main surface that can be used when growing a nitride semiconductor layer according to the present invention.

Fig. 3 is a unit cell diagram showing a crystal structure of a nitride semiconductor.

Fig. 4 is a plan view of a support provided with a selective growth mask in the form of a strip.

Fig. 5A and 5B are schematic cross-sectional views illustrating a method for growing a nitride semiconductor according to another embodiment of the present invention in sequence of process steps.

Fig. 6 to 6C are schematic cross-sectional views illustrating a method for growing a nitride semiconductor according to still another embodiment of the present invention in sequence of process steps.

Fig. 7A to 7D are schematic cross-sectional views illustrating the principle of an ideal embodiment of the nitride semiconductor growth method according to the 3 rd aspect of the present invention in sequence of process steps.

Fig. 8A is a cross-sectional view schematically showing a nitride semiconductor light-emitting diode device supported by the nitride semiconductor substrate of the present invention.

Fig. 8B is a plan view of the light emitting diode device shown in fig. 8A.

Fig. 9 is a cross-sectional view schematically showing another nitride semiconductor light-emitting diode device supported by the nitride semiconductor substrate of the present invention.

Fig. 10 is a cross-sectional view schematically showing a nitride semiconductor laser diode device supported by the nitride semiconductor substrate of the present invention.

Fig. 11 is a cross-sectional view schematically showing another nitride semiconductor laser diode device supported by the nitride semiconductor substrate of the present invention.

Fig. 12 is a cross-sectional view schematically showing still another nitride semiconductor laser diode device supported by the nitride semiconductor substrate of the present invention.

Detailed Description

The following description refers to the accompanying drawings. The same or similar parts are denoted by the same reference numerals throughout the drawings.

Fig. 1A to 1C are schematic cross-sectional views sequentially illustrating the principle of the growth method of a nitride semiconductor according to aspect 1 of the present invention.

As shown in fig. 1A, first, a support 10 is prepared which is composed of a substrate (hereinafter, may be referred to as "dissimilar substrate") 11 made of a material different from that of the nitride semiconductor and a foundation layer 12 made of a nitride semiconductor provided thereon.

In the scope of the present specification and claims, the underlayer means a layer formed of a nitride semiconductor grown on the different-type substrate 11 by a normal nitride semiconductor growth method without using the growth method of the present invention. The substrate layer 12 may be a single layer structure or a multilayer structure. In fig. 1A, the base layer 12 is shown as a single buffer layer. Such a buffer layer can be relaxed on the different-type substrate 11Lattice mismatch with the nitride semiconductor crystal grown on the base layer 12 makes it possible to grow thereon a nitride semiconductor crystal having better crystallinity, typically in a thickness of about several tens of angstroms to several hundreds of angstroms at a low temperature of less than 900 ℃, typically 500 ℃ to 800 ℃. Such a low-temperature buffer layer is particularly preferably formed of undoped GaN. In the present invention, by forming the underlying layer as a multilayer structure, a nitride semiconductor crystal having fewer crystal defects can be formed thereon. For example, in the present invention, the base layer of the multilayer structure may be composed of the low-temperature buffer layer as described above and another nitride semiconductor layer formed thereon provided on the dissimilar substrate 11. A for the other nitride semiconductor layer_1xGa_1-xN (0. ltoreq. x. ltoreq.0.5) is particularly preferably formed. The thickness of the additional nitride semiconductor layer is larger than that of the low-temperature buffer layer, and is preferably 10 μm or less. SubstrateThe layer 12 can be grown by a known method unsuitable for growing a nitride semiconductor, such as Metal Organic Vapor Phase Epitaxy (MOVPE), Molecular Beam Epitaxy (MBE), or Halide Vapor Phase Epitaxy (HVPE), using a gaseous group 3 element source and a gaseous nitrogen element source.

Referring again to fig. 1A, a selective growth mask 13 having a plurality of windows 14a to 14f that partially (selectively) expose a base layer 12 is formed on the base layer 12 formed on a different type substrate 11. In fig. 1A, the selective growth mask 13 is shown as a mask made up of individual strips 13a to 13e each having a substantially rectangular cross section as an ideal solution. In fig. 1A, the spaces between the strips 13 correspond to the windows 14a to 14 f. The windows 14a to 14f are hereinafter often collectively referred to as the windows 14.

Next, as shown in fig. 1B, according to the present invention, the nitride semiconductor 15 is grown using the gaseous group 3 element source and the nitrogen element source from the surface portion of the base layer 12 which has been exposed from the windows 14a to 14f of the selective growth mask 13. In this way, when a nitride semiconductor is grown on the base layer 12 whose surface is covered with the selective growth mask 13 (or whose surface is selectively exposed), the nitride semiconductor is not grown on the entire surface of the selective growth mask 13 in the initial stage, but is selectively grown on the base layer 12 exposed from the window 14. When the nitride semiconductor is further grown to exceed the upper end face of the mask 13, the respective nitride semiconductor crystals 15, each exceeding one of the windows 14, are grown in the left and right lateral directions each on one of the selective growth masks 13. In the portion of the nitride semiconductor 15 grown in the lateral direction, unlike the nitride semiconductor grown in the longitudinal direction in the base layer 12, the crystal defects of the base layer 12 have been covered with the selective growth mask 13, so that the crystal defects of the base layer 12 are difficult to be transferred. Further, the crystal defects of the underlying layer 12 tend to stop in the middle although they spread in the lateral direction at the same time as the growth of the nitride semiconductor crystal 15 in the upper portion of the selective growth mask 13. Further, some crystal defects that are dislocated from the window 14 appear on the surface of the growing nitride semiconductor layer, but tend to stop in the middle of the growth.

When the growth of the nitride semiconductor of nitride semiconductor crystal 15 is continued as described above, adjacent nitride semiconductor crystals 15 grown in the lateral direction above selective growth mask 13 and also grown in the longitudinal direction are connected to each other, and then, as shown in fig. 1C, all crystals 15 are finally united into a unified nitride semiconductor crystal 16. Narrow and small voids 17a to 17e, which are triangular in cross section and extend in the longitudinal direction of the strips 13a to 13e, present at substantially the centers of the upper surfaces of the respective strip masks 13a to 13e, are evidence of integration of the nitride semiconductorcrystals 15 adjacent to each other by growth in the lateral direction on the selective growth mask 13 and thereafter also by growth in the longitudinal direction. (in fig. 1A and 1C, wavy lines and bent lines in the base layer 12, the nitride semiconductor crystal 15, and the nitride semiconductor crystal 16 after integration indicate crystal defects (through dislocation.) fig. 5A and 6A to 6C are the same meaning).

To put it in more detail, due to the lattice mismatch between the dissimilar substrate 11 and the nitride semiconductor, relatively many crystal defects occur on the base layer 12 grown over the dissimilar substrate 11 or the portion of the nitride semiconductor crystal 15 grown early, which crystal defects can propagate to the end faces of the growth points during the growth of the nitride semiconductor 15. On the other hand, the portion of the nitride semiconductor crystal 16 formed on the selective growth mask 13 is not grown from the different-type substrate 11 or the base layer 12, but is made so that the nitride semiconductor layer crystal 15 grows in the lateral direction, and finally the adjacent nitride semiconductor crystals 15 are united with each other. Therefore, the number of crystal defects in the portion of the nitride semiconductor crystal 16 formed on the selective growth mask 13 is very small compared to the portion of the nitride semiconductor crystal that is grown directly from the different-type substrate 11 or that is initially grown in the windows 14a to 14f from the underlying layer 12. By using the nitride semiconductor crystal 16 after integration as a substrate for growing various nitride semiconductor layers constituting a device structure, a nitride semiconductor device having superior crystallinity and thus superior performance as compared with conventional devices can be realized.

Next, the principle of the nitride semiconductor growth method according to claim 2 of the present invention will be described with reference to fig. 1A to 1C. In the method for growing a nitride semiconductor according to claim 2, it is specified that the selective growth mask 13 is formed such that the total of the surface areas of the portions of the support 10 covered with the selective growth mask 13 is larger than the total of the surface areas of the portions of the support 10 exposed from the windows 14a to 14 f. By thus making the total surface area of the portion of the support 10 covered with the selective growth mask 13 larger than the total surface area of the portion of the support 10 exposed from the window 14, the nitride semiconductor crystal 16 having fewer crystal defects can be obtained. In the second aspect, the unified semiconductor crystal 16 may be grown by the same method as in the first aspect except that the selective growth mask 13 having the relationship between the covered total surface area and the exposed total surface area is used in the second aspect (see the above description of the first aspect with reference to fig. 1A to 1C).

In the 2 nd aspect of the present invention, the presence of the base layer 12 is preferable for the reasons described in the 1 st aspect, but may be omitted. That is, within the scope of the present specification and claims, the support may be constituted by the different type substrate 11 alone, or may be constituted by the different type substrate 11 and the base layer 12 formed thereon.

Of course, the selective growth mask 13 may be formed in the aspect 1, and it is preferable that the total of the surface areas of the support 10 covered with the selective growth mask 13 is larger than the total of the surface areas of the support 10 exposed from the windows 14a to 14f as in the aspect 2.

Next, ideal conditions in the growth method of a nitride semiconductor according to the present invention will be explained.

The different-type substrate 11 is not particularly limited, as described above, insofar as it is formed of a material different from that of the nitride semiconductor. For example, sapphire having a C-plane ((0001) -plane), an R-plane ((1102) -plane), or an a-plane ((1120) -plane) as a main surface, or spinel (MgAl) can be used₂O₄) An insulating substrate such as this, and a substrate formed of a material different from a nitride semiconductor such as a SiC (including 6H, 4H, 3C) substrate, a ZnS substrate, a GaAs substrate, and a silicon substrate. In addition, although there is a tendency for decomposition during the growth of the nitride semiconductor, an oxide substrate (e.g., ZnO substrate, La substrate) that can be lattice-matched with the nitride semiconductor cannot be used either_xSr_1-xAl_yTa_1-yO₃A substrate). The foreign substrate may have a major face dimension of 1 inch or 1 inch square or greater than 1 inch square in diameter, preferably having a major face dimension of 1 inch or 1 inch square in diameter to 3 inches or 3 inches square in diameter. The nitride semiconductor crystal grown by the present invention may have a surface substantially equal to the surface size of the dissimilar substrateAnd (4) size.

The different-type substrate 11 may be a substrate having a principal surface inclined from a horizontal plane, and particularly preferably a substrate having a principal surface inclined in a stepwise manner. For example, when more specifically described with reference to fig. 2 showing an enlarged cross section of a sapphire substrate 11 having a main surface which is stepped and inclined, the substrate 11 has a substantially horizontal plateau portion a and a step portion B. The surface irregularities of each land portion a can be adjusted to about 0.5 a on average and about 2a at maximum, and are formed substantially in a well-defined pattern. The step B of each step is less than 30 angstroms, more preferably less than 25 angstroms, and most preferably less than 20 angstroms. The lower limit of each step B is desirably greater than 2 angstroms. The step portion having such an inclination angle θ is desirably formed continuously over the entire range of the dissimilar substrate 11, but may be formed partially. The inclination angle θ means an angle between a straight line connecting bottoms of the plurality of steps and a flat surface of the uppermost step as shown in fig. 2, with respect to the main surface inclined in a stepwise manner. In particular, when a sapphire substrate having a C-plane as a main surface is used as the different-type substrate 11, the tilt angle θ from the C-plane is preferably not more than 1 degree, more preferably not more than 0.8 degree, and still more preferably not more than 0.6 degree. By using a different type substrate having a principal surface inclined in this manner, the atomic distance between the nitride semiconductor grown according to the present invention and the different type substrate can be made close, and thus a nitride semiconductor substrate with few crystal defects can be obtained.

The growth mask 13 is selected such that nitride growth on its surface is substantially impossible. Such selective growth mask 13 is formed of a material having a property that a nitride semiconductor is not grown or is difficult to grow on its surface. Such a material contains, for example, silicon oxide (SiO)_x) Silicon nitride (SiN)_y) Titanium oxide (TiO)_x) Zirconium oxide (ZrO)_x) And the like, or a nitride, or a multilayer film containing them, and further, a metal having a melting point higher than 1200 ℃ (e.g., W, Ir, Pt) may be used. These selective growth mask materials can also withstand the growth temperature ofthe nitride semiconductor when grown according to the present invention, about 600 ℃ to 1200 ℃, and have the property that no nitride semiconductor is grown or is difficult to grow on the surface thereof. To form a selective growth mask material on the surface of the support 10, vapor deposition techniques such as evaporation, sputtering, CVD, and the like can be used. In addition, it is desirable to form the tool from these materialsThe selective growth mask 13 with the windows 14 can be made by photolithographyA selective growth mask 13 having a predetermined shape is formed by forming a photomask having a predetermined shape and vapor-depositing the above-mentioned material through the photomask. The shape of the growth mask 13 is not particularly limited and may be formed in the shape of, for example, a dot, a stripe, or a grid, but as described later, it is desirable to form each stripe as a plurality of individual stripes in a specific plane orientation.

As described above, the selective growth mask 13 is preferably formed of a plurality of individual stripes (13a to 13e) as shown in fig. 1A. In this case, it is preferable that each of the stripe masks has a width (Ws) of 0.5 to 100 μm, more preferably 1 to 50 μm, further preferably 2 to 30 μm, further preferably 5 to 20 μm, particularly preferably 5 to 15 μm, and the ratio (Ws/Ww) of the width corresponding to the width (Ww) of each of the windows 14 is preferably 1 to 20, more preferably 1 to 10. in this case, it is particularly preferable that the width of the stripe mask is larger than the width of the window, and in this case, the ratio (Ws/Ww) is more preferably 1 to 20, more preferably 1 to 10. in this case, it is preferable that the interval (Ww) of the stripe mask is set to 8 μm or less, preferably 5 μm or less, more preferably 3 μm or less, whereby a nitride semiconductor crystal having fewer crystal defects can be grown . It is desirable that each of the strip masks has substantially the same width, substantially the same thickness, and are formed in parallel with each other at substantially the same interval on the entire surface of the support 10.

The thickness of the growth mask 13 is preferably 0.01 to 5 μm, more preferably 0.1 to 3 μm, and particularly preferably 0.1 to 2 μm.

The selective growth mask 13 does not grow a nitride semiconductor from a portion covered with it, and selectively grows a nitride semiconductor from a portion exposed from its window, and therefore, is called a 'selective growth' mask in the scope of the present specification and claims.

Fig. 3 is a unit cell diagram showing a crystal structure of a nitride semiconductor. The nitride semiconductor is exactly a rhombohedral structure, but can be approximated by such a hexagonal system. According to the method of the present invention, it is preferable to use a sapphire substrate having a C-plane as a main surface as the foreign substrate 11,the growth mask 13 is selected to extend from each of the growth masks in parallel with each other in a direction perpendicular to the a-plane of sapphire (in other words, in a direction (of the nitride semiconductor) parallel to the M-plane ((1100) plane) of the nitride semiconductor<1100>Direction) are formed by a plurality of individual strips extending parallel to each other. That is, in fig. 4 showing a plan view of the sapphire substrate on the principal surface side, the sapphire substrate 11 has a sapphire C-plane as the principal surface and an orientation plane (ORF) plane as the a-plane. It is desirable that selective growth mask 13 be constructed of a plurality of individual strips extending parallel to each other in a direction perpendicular to the a-plane of sapphire, respectively, as shown in fig. 4. Inaddition, it should be noted that in fig. 4, although only 5 individual strips are shown for ease of understanding, more individual strips are substantially formed.

When a nitride semiconductor is selectively grown on the sapphire C-plane, the nitride semiconductor tends to grow easily in a direction parallel to the a-plane in the plane and to grow hardly in a direction perpendicular to the a-plane. Therefore, if the stripe masks extending in the direction perpendicular to the a-plane are provided, the nitride semiconductor between the adjacent stripes tends to grow on the respective stripe masks as interconnected, and the crystal 16 as shown in fig. 1C tends to grow. In this case, the end faces of the growth sites of nitride semiconductor crystal 15 grown in the lateral direction are formed on the upper side of mask 13, that is, facets F (see fig. 1B) respectively form the a-faces of the nitride semiconductor.

Similarly, in the case of using a sapphire substrate having the a-plane as the main surface, assuming that the ORF plane constitutes the R-plane, for example, by forming a plurality of individual stripe masks extending parallel to each other in a direction perpendicular to the R-plane, there is a tendency that the nitride semiconductor is easily grown in the width direction of the stripe mask, and thus a nitride semiconductor crystal with few crystal defects can be grown.

In addition, for spinel (MgAl)₂O₄) The growth of the nitride semiconductor has anisotropic properties, and when the (111) plane is used as the growth plane (main surface of spinel) of the nitride semiconductor and the ORF plane constitutes the (110) plane, the nitride semiconductor tends to grow easily in a direction parallel to the (110) plane. Therefore, when a plurality of parallel individual stripe masks are formed so as to extend in a direction perpendicular to the (110) plane, adjacent nitride semiconductor crystals are integrated with each other on the selective growth mask 13, and the nitride semiconductor crystal 16 with few crystal defects can be grown.

The nitride semiconductor crystal grown by the present invention can also be grown by any known method using a gaseous group 3 element source and a gaseous nitrogen element source, MOVPE, MBE, HVPE, etc., even unsuitable for nitride semiconductors. Preferably, it is desirable to grow the nitride semiconductor crystal by MOVPE in the initial stage, followed by MOVPE or HVPE. As described later, it is particularly preferable to grow a nitride semiconductor by MOVPE in an initial stage and then grow it thick by HVPE.

In the case of growing a nitride semiconductor by MOVPE, it is desirable to adjust the molar ratio of the nitrogen source gas to the group 3 source gas (nitrogen source/group 3 source molar ratio, hereinafter often simply referred to as V/III ratio) to less than 2000. Preferably the nitrogen source/group 3 source molar ratio is less than 1800, more preferably the nitrogen source/group 3 source molar ratio is less than 1500. The lower limit of the nitrogen source/group 3 source molar ratio is not particularly limited if it is larger than the stoichiometric ratio, but it is preferably larger than 10, more preferably larger than 30, and most preferably larger than 50. If the value of the molar ratio is larger than 2000, the triangular nitride semiconductor grows from the window 14, and the crystal defects extend along with it, so that the number of crystal defects is reduced and the number of crystal defects increases. However, if the nitrogen source/group 3 source molar ratio is adjusted to 2000 or less, the crystal 15 grows in the left-right lateral direction on the selective growth mask 13 while maintaining the surface perpendicular to the upper surface of the selective growth mask after growing from the window 14, and the similarly perpendicular surface of the similarly grown adjacent crystal is brought into contact with the selective growth mask 13 to integrate the crystals, so that the crystal defect is likely to be stopped halfway on the upper surface of the selective growth mask. Further, the crystal defects extending from the window 14 are liable to stop halfway. Therefore, a nitride semiconductor crystal with less crystal defects can be grown. Particularly, MOVPE is preferably carried out under a reduced pressure of 50 to 400 Torr.

In MOVPE, a gas of a nitrogen element source is, for example, a hydride gas of ammonia, hydrazine, or the like, and a gas of a group 3 element source is, for example, an organic gallium gas of TMG (trimethyl gallium), TEG (triethyl gallium), or the like, an organic aluminum gas of TMA (trimethyl aluminum), TMI (trimethyl indium), or the like, or an organic indium gas.

In the case of growing a nitride semiconductor crystal by HVPE, for example, a gallium nitride crystal, HCl gas is flowed over molten gallium metal, while ammonia gas is flowed through another gas supply pipe, and these gases are combined to perform the following reaction on the support 10:

since the growth rate of the nitride semiconductor crystal is several times or more faster than that of MOVPE by the HVPE method, for example, a nitride semiconductor of 300 μm can be grown within several hours.

In the present invention, the nitride semiconductor crystal is grown to a thickness of 1 μm or more, preferably 5 μm or more, and most preferably 10 μm or more, although the width of the growth mask is also selected. This is the lower limit of the thickness of the nitride semiconductor crystal for covering the upper part of the selective growth mask with the nitride semiconductor crystal, and if it is smaller than 1 μm, the growing nitride semiconductor crystal tends to be difficult to grow in the lateral direction above the selective growth mask, and thus crystal defects tend to become relatively large. Under the condition that the nitride semiconductor is difficult to grow in the lateral direction, it is difficult to reduce crystal defects. Although there is no particular limitation on the upper limit of the thickness of the nitride semiconductor crystal being grown, it is desirable that the crystal is grown to 70 μm or less when the crystal is grown by MOVPE. If the growth time is longer than 70 μm, the growth time becomes long, the surface of the nitride semiconductor crystal becomes rough, and the selective growth mask tends to be easily decomposed, which is not preferable.

In the present invention, it is particularly preferable that the nitride semiconductor crystal (for example, crystal 16 or crystal 17, crystal 116, crystal 76 to be described later) grown until it becomes a substrate for supporting the nitride semiconductor device is undoped gallium nitride or n-type impurity-doped gallium nitride.

In order to grow a thicker nitride semiconductor crystal with few defects, it is desirable to first grow a nitride semiconductor crystal with MOVPE, and then switch to growing a nitride semiconductor crystal with HVPE over the MOVPE crystal.

Fig. 5A and 5B are cross-sectional views for explaining a growing method of such a thicker nitride semiconductor crystal.

According to the 1 st or 2 nd aspect described with reference to fig. 1A to 1C, on the nitride semiconductor crystal 16 that has been grown by MOVPE, a nitride semiconductor crystal 17 of the same kind as that grown by HVPE is grown until it is thicker than the nitride semiconductor crystal 16. When nitride semiconductor crystal 17 is regrown over MOVPE crystal 16 using HVPE as such, crystal defects extending in the longitudinal direction become almost nonexistent, and nitride semiconductor 17 with very few crystal defects as a whole can be grown. The crystal defects of the HVPE nitride semiconductor crystal 17 become less than those of the MOVPE nitride semiconductor crystal 16 thereunder, and for example, it is finally possible to obtain a crystal having a surface area of 1X 10⁵/cm² Nitride semiconductor crystal 17 having the following crystal defects. The crystal defect of the surface region is preferably 5X 10⁴/cm²More preferably 1X 10⁴/cm²The most preferable is 1X 10³/cm²The following. The surface region means a region extending from the surface (end face of growth end) on the opposite side to the dissimilar substrate 11 of the nitride semiconductor crystal to a depth of 5 μm, and is within 5 μmThe number of crystal defects of (2) can be measured by TEM (transmission electron microscope). In the present invention, the crystal defects of the nitride semiconductor crystal after the growth are observed visually (that is, visually on a TEM photograph) in a plane by TEM, and the average density of the defects is determined (the same applies to the following examples).

HVPE nitride semiconductor crystal 17 is thicker than MOVPE nitride semiconductor crystal 16, preferably 10 micrometers or more, more preferably 50 micrometers or more, and still more preferably 100 micrometers or more. When the number is less than 10 μm, crystal defects tend to be hardly reduced. Although the upper limit of the thickness is not particularly specified, a thickness of less than 1mm is desirable. If grown thicker than 1mm, the entire wafer will be thoroughly flexed due to the difference in thermal expansion coefficient between the nitride semiconductor and the foreign substrate 11, and as a result, it becomes very difficultto grow HVPE nitride semiconductor crystals with a uniform thickness.

In the present invention, in growing the nitride semiconductor crystal 16 and/or 17, it is desirable to dope an n-type impurity, more desirably to dope an n-type impurity into the nitride semiconductor so that the concentration of the n-type impurity has a gradient in each of the

respective crystals

16 or 17. The concentration gradient may be continuous or stepwise. It is particularly desirable that the concentration gradient of the n-type impurity in each of the

crystals

16 and 17 is given such that the concentration of the n-type impurity becomes smaller the farther from the foreign substrate. In other words, it is desirable that the doping concentration of the n-type impurity becomes higher as it approaches the different-species substrate 11 in the crystal 16, and also that the doping concentration of the n-type impurity becomes higher as it approaches the different-species substrate 11 in the crystal 17. Thus, if the n-type impurity concentration is set to be smaller as approaching the growth surface (main surface) in each crystal, and when an n-type electrode is provided after the device structure is manufactured, for example, when the different-type substrate 11, the base layer 12, the growth mask 13, and the nitride semiconductor substrate 16 are removed, or further, when the nitride semiconductor substrate 17 is also removed and the nitride semiconductor crystal substrate 16 is exposed, the surface regions of the

nitride semiconductor substrates

16 and 17 doped with the n-type impurity at a high concentration can be exposed from the back surface. Therefore, by using the exposed surface as the n-side electrode forming surface, Vf of the device can be reduced and output power can be increased. Further, even if etching is performed from the device structure side grown on the nitride semiconductor crystal substrate and an electrode is provided on the etched surface, the

nitride semiconductor crystal

16 or 17 doped with impurities at high concentration can be made into an n-electrode forming layer.

In the present invention, as the n-type impurity to be doped into the nitride semiconductor crystal, a group 4 element such as Si, Ge, Sn, S, etc., preferably Si and/or Sn, can be used. These n-type impurities, as hydrides or gaseous organic compounds thereof, can be incorporated during the growth of the nitride semiconductor. The n-type impurity is preferably 5X 10¹⁶/cm³～5×10²¹/cm³Is incorporated within the range of (1). Ratio of 5X 10¹⁶/cm³If the concentration is too low, the carrier concentration of

nitride semiconductor crystal

16 or 17 becomes insufficient, and the resistivity tends to increase. When the n-type impurity ratio is 5X 10²¹/cm³If the concentration is too high, the crystallinity is deteriorated and crystal defects tend to increase because the impurity concentration is too high. The n-type impurity is particularly preferably 1X 10¹⁷/cm³～5×10²⁰/cm³Is incorporated within the range of (1).

In the present invention, switching from MOVPE to HVPE may be performed before nitride semiconductor crystal 15 is united by MOVPE into integrated crystal 16 (see, for example, fig. 1B). That is, although nitride semiconductor crystal 15 is laterally grown on mask 13 by MOVPE, growth of HVPE nitride semiconductor crystal 17 may be started before adjacent nitride semiconductor crystals 15 are united with each other.

After

nitride semiconductor crystals

16 and 17 are grown, as shown in fig. 5A, the structure shown in fig. 5A can be used as a device substrate as it is, as will be described later, and a desired nitride semiconductor device structure can be formed thereon. Alternatively, in the structure of fig. 5A, at least the different material is polished and removed from the back surface of the different material substrate 11 in the direction perpendicular to the main surface of the different material substrate 11The seed substrate 11, the base layer 12, and the selective growth masks 13a to 13e can provide a nitride semiconductor substrate having a double-layer structure of a nitride semiconductor crystal 16 and a nitride semiconductor crystal 17. If the nitride semiconductor crystal 16 is further removed, a free nitride semiconductor substrate composed of the HVPE nitride semiconductor crystal 17 can be obtained as shown in FIG. 5B. As can be understood from the above description, the HVPE nitride semiconductor substrate is characterized in that the crystal defects of the surface region are less than 1X 10⁵/cm². The nitride semiconductor substrate may further have: the n-type impurity has a concentration gradient in the nitride semiconductor substrate, and has one or more characteristics among three that the n-type impurity concentration becomes smaller as approaching the main surface (growth completion surface) (that is, as moving away from the different-type substrate 11). From another point of view, the substrate thus obtained also has the following features: having 1 st and 2 nd main surfaces, has been doped with an n-type impurity having a concentration gradient within the substrate.

Further, in the present invention, before a substantial portion of nitride semiconductor crystal (for example, nitride semiconductor crystal 16 or the like, crystal before lateral growth on a mask) is grown, first, a buffer layer composed of a nitride semiconductor may be grown. The buffer layer may be made of nitride semiconductor such as AlN, GaN, AlGaN, InGaN, or the like, and may be grown to a thickness of several tens of angstroms to several hundreds of angstroms at a low temperature of less than 900 ℃. It is also within the scope of the present invention to regrow a substantial portion of the nitride semiconductor crystal after such low-temperature growth of the buffer layer. This buffer layer is formed to relax lattice mismatch between the different-type substrate and the nitride semiconductor grown on the rear side, but may be omitted depending on the growth method of the nitride semiconductor, the type of substrate, and the like.

Next, a 2 nd method for producing a nitride semiconductor having fewer crystal defects will be described with reference to fig. 6A to 6C. First, as shown in fig. 6A, on the surface of nitride semiconductor crystal 16 grown following aspect 1 or 2 described in detail above, after polishing is performed as necessary to provide a flat surface, selective growth mask 2 having a plurality of windows that partially expose the surface of nitride semiconductor crystal 16 is formed on the surface of nitride semiconductor crystal 16. The description of the 1 st selective growth mask 13 (material, shape, width, thickness, shape of window, width, relationship with a different type of substrate, and the like) is similarly applied to the 2 nd selective growth mask 113 unless otherwise specified.

The 2 nd selective growth mask 113 is usually formed at a position shifted from the position where the 1 st selective growth mask 13 is formed. That is, the 2 nd selective growth mask 113 is formed so as to cover the portion of the nitride semiconductor crystal 16 on which crystal defects that occur from the interface between the support 10 and the nitride semiconductor crystal 16 and extend from the windows 14a to 14f of the 1 st selective growth mask 13 can appear, and to selectively expose the surface of the nitride semiconductor crystal 16. To put it more concretely, in fig. 6A, the selective growth mask 113 is composed of, like the 1 st selective growth mask 13, individual stripes 113a to 113f each of which is located at a position covering a surface region of the nitride semiconductor crystal 16 corresponding to the windows 14a to 14f of the selective growth mask 13, the windows 14a to 14e being located on a region corresponding to a substantially central region of the 1 st stripe mask 13a to 13 e. By forming the 2 nd selective growth mask 113 at a position corresponding to the window 14 of the 1 st selective growth mask 13 in this manner, the penetration of the crystal defect of the crystal 16 can be prevented by the 2 nd selective growth mask 113.

It is desirable to make the total area of the 2 nd selective growth mask 113 (the portion of the nitride semiconductor crystal 16 covered by it) larger than the total area of the windows 14a to 14f of the 1 st selective growth mask 13 (the portions of the nitride semiconductor crystal 16 exposed from them). Specifically, when the selective growth mask 113 is formed in a shape of a dot, a stripe, or the like, the surface area of a unit dot and the width of a unit stripe are made larger than those of a window. In this way, a nitride semiconductor with fewer defects can be grown on the crystal 16.

Next, when a nitride semiconductor crystal of the same kind as nitride semiconductor crystal 16 (preferably, undoped or n-type impurity-doped GaN) is grown by the same method as in the case of growing nitride semiconductor crystal 16, nitride semiconductor crystal 115 is grown as shown in fig. 6B in the same manner as described with reference to crystal 15 in fig. 1B, and finally adjacent nitride semiconductor crystals 115 are connected to each other on 2 nd selective growth mask 113, so that united nitride semiconductor crystal 116 can be obtained. In this case, since the 2 nd nitride semiconductor crystal 115 grown on the 1 st nitride semiconductor crystal 16 is the same kind of nitride semiconductor and is grown on the 1 st nitride semiconductor crystal 16 having few crystal defects, it is difficult for crystal defects due to lattice mismatch to occur, and transferred crystal defects are reduced, so that the 2 nd nitride semiconductor crystal 116 having excellent crystallinity can be obtained. By using this 2 nd nitride semiconductor crystal 16 as a growth substrate for a device structure, a nitride semiconductor device having very excellent crystallinity can be realized. It goes without saying that an n-type impurity may be doped in the nitride semiconductor 116 as well as in the case of the nitride semiconductor 16 or 17 (see fig. 1C, fig. 5A).

Further, the formation of the 2 nd selective growth mask and the subsequent growth of the nitride semiconductor crystal described with reference to fig. 6A to 6C may be repeated. That is, if there is a portion of the nitride semiconductor crystal where lattice defects have occurred, a new mask may be reformed at that portion, and a new nitride semiconductor may be grown on the mask.

Next, the principle of the nitride semiconductor growth method according to claim 3 of the present invention will be described. The 3 rd aspect of the present invention is a method for growing a nitride semiconductor, characterized by: after the nitride semiconductor is grown on the support of the present invention, the nitride semiconductor is used as a seed crystal to suppress the growth in the longitudinal direction thereof and to grow a new nitride semiconductor substantially only in the lateral direction, and then the semiconductor is grown in the longitudinal direction and the lateral direction. In the present invention, the suppression of the longitudinal growth of the nitride semiconductor means that at least the growth of the nitride semiconductor is not performed in the longitudinal direction but is performed in the lateral direction, and the nitride semiconductor can be grown by exposing the longitudinal surface of the nitride semiconductor grown first and growing a new nitride semiconductor only from the exposed surface. When the nitride semiconductor whose growth direction is controlledlike this is grown in the lateral direction from the longitudinal direction and is continued to be grown, the growth in the longitudinal direction is started again in addition to the lateral growth. Thus, a nitride semiconductor crystal with further reduced crystal defects can be obtained.

The method for growing a nitride semiconductor according to claim 3 of the present invention, which is performed by controlling the growth direction of the nitride semiconductor in this manner, will be described in more detail below with reference to fig. 7A to 7D.

As shown in fig. 7A, on a support 10 made of a different type substrate 11 with or without a base layer 12 formed, it is desirable to form a nitride semiconductor layer 71 over substantially the entire surface of the support 10. The support 10 includes the heterogeneous substrate 11 and the base layer 12, and is a sufficient constituent portion as already described.

The nitride semiconductor layer 71 is preferably formed of gallium nitride (GaN) doped with no impurity (undoped), or GaN doped with the above-mentioned n-type impurity.

The nitride semiconductor layer 71 can be grown on the support 10 at a high temperature, specifically at a temperature of 900 to 1100 c, desirably 950 to 1050 c. The thickness of the nitride semiconductor layer 71 is not particularly limited, and is a portion exposed from the side surface of the recess (which will be described in detail later) after the formation of the growth control mask described later. However, the nitride semiconductor layer 71 is preferably formed to have a thickness of more than 100 angstroms, preferably about 1 to about 10 micrometers, and more preferably about 1 to about 5 micrometers, which are exposed from the side surface of the recess.

Next, as shown in fig. 7B, a plurality of recesses (6 recesses 72a to 72fare visible in fig. 7B, and hereinafter, the plurality of recesses may be collectively referred to as recesses 72) are formed in the nitride semiconductor layer 71 formed on the support 10, and the nitride semiconductor layer 71 is selectively exposed on the side surfaces of the respective recesses 72. Then, a1 st growth control mask denoted by reference numerals 73a to 73g and a 2 nd mask denoted by reference numerals 74a to 74f are formed on the upper surface of the nitride semiconductor layer 71 and on the bottom surfaces of the concave portions 72a to 72f, respectively. The 1 st growth control masks 73a to 73g may be collectively referred to as only the 1 st growth control mask or mask 73, and the 2 nd growth control masks 74a to 74f may be collectively referred to as only the 2 nd growth control mask or mask 74. The 1 st and 2 nd growth control masks 73 and 74 can be formed by a similar method using the same material as the selected growth mask described above with respect to the 1 st and 2 nd aspects and the like.

The plurality of recesses 72a to 72f may be formed in any shape, for example, a single cylindrical shape, a square cylindrical shape, or a trench shape, as long as the recesses selectively expose the nitride semiconductor layer 71 on the side surfaces thereof. It is preferable that the bottom surface of each recess 72 is a surface substantially parallel to the upper surface of the support 10.

The recesses 72 formed in the nitride semiconductor layer 71 may be formed to a depth up to the middle of the nitride semiconductor layer 71, or to a depth reaching the surface of the support 10, or in some cases, to a depth reaching the inside of the support 10. The depth of the recess 72 is also controlled by the thickness of the nitride semiconductor layer 71, the thickness of the 2 nd growth control mask 74, and the like, but in general, the 2 nd growth control mask 74 may be formed sufficiently thick sothat the 2 nd growth control mask 74 formed on the bottom surface of the recess 72 does not expose the different-type substrate 11, and the growth of new nitride semiconductor grown in the lateral direction of the nitride semiconductor layer 71 exposed from the side surface of the recess 72 is not disturbed. Each recess 72 is preferably formed to a depth that does not expose the different-type substrate 11, and particularly preferably to a depth up to a halfway point in the thickness direction of the nitride semiconductor layer 71. If the recess 72 is formed to a depth at which the dissimilar substrate 11 is exposed at the bottom surface thereof, it is difficult to form the 2 nd growth control mask 74 in the vicinity of the corner of the bottom surface of the recess 72 when the 2 nd growth control mask 74 is formed, and thus, if the 2 nd growth control mask 74 does not sufficiently cover the surface of the dissimilar substrate 11, new nitride semiconductor may grow from the dissimilar substrate 11, and crystal defects may occur therefrom. The recesses 72 are generally formed to the same depth, although the depth of the recesses 72 may also vary.

To provide the recess 72, any method capable of partially removing the nitride semiconductor layer 71 may be used, including, for example, etching, dicing, and the like. When the dicing method is used, the recesses 72 formed by parallel grooves having a rectangular cross section or the recesses 72 formed by grid-shaped grooves can be easily formed.

In the case of selectively forming the concave portions 72 in the nitride semiconductor layer 71 by etching, a photomask having a stripe shape, a grid shape, or the like is formed by using mask patterns having various shapes in the photolithography technique, and a photoresist pattern is formed on the nitride semiconductor layer 71 and etched. As a method for etching the nitride semiconductor layer 71, there are methods such as wet etching and dry etching, and dry etching is preferably used to form a smooth surface. Dry etching, such as Reactive Ion Etching (RIE), Reactive Ion Beam Etching (RIBE), electron cyclotron Etching (ECR), Ion Beam Etching (IBE), etc., either of which may be performed by appropriately selecting an etching gas to etch the nitride semiconductor to form the desired recess 72. For example, a specific etching means of the nitride semiconductor described in Japanese patent laid-open No. 8-17803, which was previously filed by the present applicant, may be used.

In the case of forming the concave portion 72 by etching, the side surface of the concave portion 72 after formation may be substantially perpendicular to the different-type substrate, or may be a regular mesa surface or a reverse mesa surface, as shown in fig. 7B.

The 1 st mask 73 and the 2 nd mask 74 may be formed in a manner that is slightly different between the case where the recess 72 is formed by etching and the case where the recess is formed by dicing.

In the case of forming the concave portion 72 by etching, a mask material layer is formed on the 1 st nitride semiconductor layer 71, a photoresist film is formed thereon, a predetermined pattern is transferred, exposure and development are performed to form a1 st mask 73, and the likeThe recess 72 can be formed by etching the 1 st nitride semiconductor layer 71. Next, for the nitride semiconductor layer 71 having the 1 st mask 73 and the recess 72 formed therein, a growth control mask material layer is formed again on the bottom, side, etc. of the mask 73 and the recess 72, and then, for example, CF is used₄And O₂The dry etching by gas selectively etches the mask material layer on the side surfaces of the recess 72, forming a 2 nd mask 74. In this manner, for example, in fig. 7B, the 1 st mask 73 is illustrated as a single layer, but actually has a two-layer structure in which a mask material layer is formed on the 1 st mask 73. Of course, before the 2 nd mask 74 is formed, after the 1 st mask 73 is removed, the 1 st and 2 nd masks 73 and 74 may be formed on the portion where the 1 st mask 73 is already formed and the bottom surface of the recess 72 by the same method, respectively.

In the case of forming the recessed portion 72 by the dicing method, after the nitride semiconductor layer 71 is removed from above by the dicing blade to form the recessed portion 72, as described above, the growth control mask material layer is formed over the entire surface of the nitride semiconductor layer 71 including the inside of the recessed portion 72, and only the growth control mask material layer of the side portion of the recessed portion 72 is etched by dry etching using CF4 and O2 gas, whereby the 1 st and 2 nd growth control masks 73 and 74 can be formed simultaneously.

As for the thickness, the 1 st growth control mask 73 and the 2 nd growth control mask 74 may be formed to be different from each other as long as they have a thickness that does not impair the growth of the nitride semiconductor crystal to be described later in detail. For example, in the case where the base layer 12 is not formed on the dissimilar substrate 11 in particular, the growth control mask 74 of the 2 nd is preferably formed to have a sufficient thickness so that the dissimilar substrate 11 is not exposed on the bottom surface of the recess 72, and is preferably formed to have a sufficient thickness to a degree that pinholes are not generated therein due to the influence of heat in addition to the formation, but is not necessarily so thick as to inhibit the growth of nitride semiconductor crystal from the portion of the nitride semiconductor layer 71 exposed from the side surface of the recess. When a pinhole occurs in the 2 nd growth control mask 74, it is considered that a nitride semiconductor grows from the pinhole in the longitudinaldirection, and this is a root cause of crystal defects. Further, for example, since the height of the potential barrier over which the nitride semiconductor is to go (the thickness of the 1 st growth control mask 73) becomes low when the 1 st growth control mask 73 is formed to be relatively thin, the potential barrier may be easily crossed and grown in the lateral direction on the mask 73. The formation of such growth control masks should be known to those skilled in the art. In this case, for example, the mask formation may be performed 2 times.

However, the 1 st growth control mask 73 desirably has the same relationship with respect to the dissimilar substrate 11 as the relationship of the selective growth mask with respect to the dissimilar substrate described previously. Therefore, the matters described under the heading of<relationship between the different-type substrate and the selective growth mask>are equally applicable to the 1 st growth control mask 73. That is, it is desirable that the 1 st growth control mask 73 has a cross section substantially composed of a plurality of individual stripes having a rectangular shape. In this case, the single strip is preferably formed as: or on the sapphire C-plane, extending parallel to each other in a direction perpendicular to the sapphire a-plane, or on the sapphire a-plane, extending parallel to each other in a direction perpendicular to the sapphire R-plane, or on the spinel (111) plane, extending parallel to each other in a direction perpendicular to the spinel (110) plane. Therefore, each concave portion 72 is constituted by a plurality of individual grooves extending in the same direction as such a stripe-shaped growth control mask 73, and the top surface of each wall defined between adjacent grooves desirably has the same planar shape as that of each stripe-shaped growth control mask 73.

The plurality of stripe-shaped growth control masks 73 desirably each have a width of 1 to 20 micrometers, more desirably 10 to 20 micrometers (corresponding to the width Ws of the 1 st selective growth mask), and the interval therebetween is desirably 1 to 20 micrometers, more desirably 2 to 5 micrometers.

After the recess 72 and the 1 st and 2 nd growth control masks 73 and 74 are thus formed, as shown in fig. 7C, a nitride semiconductor 75 is grown from the exposed side surfaces of the nitride semiconductor layer 71 by the vapor phase growth method described for the 1 st and 2 nd aspects.

As described with reference to fig. 7B, the nitride semiconductor layer 71 is covered with the growth control masks 73 and 74 on the upper surface thereof (that is, the top surface of the wall between the recesses) and the bottom surface of the recess 72 except the side surface of the recess 72 formed therein, and the nitride semiconductor layer 71 is exposed only on the side surface of the recess 72, so that the nitride semiconductor subjected to vapor phase growth is grown only from this selectively exposed surface of the nitride semiconductor layer 71. That is, nitride semiconductor 75 is laterally grown from the exposed side surface of nitride semiconductor layer 71. Next, while continuing the growth, nitride semiconductor 75 starts growing in the longitudinal direction in addition to the lateral growth, and when reaching the upper surface of concave portion 72, 1 st growth control mask 73 is grown in the left-right direction on both sides of the concave portion, and adjacent nitride semiconductor crystals 75 are unified with each other as described for 1 st and 2 nd aspects, as shown in fig. 7D, becoming unified nitride semiconductor crystal 76. Nitride semiconductor crystal 73 whose growth direction is controlled in the initial stage of growth as described above has very good crystallinity with extremely few crystal defects even when grown thick.

Nitride semiconductor crystal 75 tobe grown is preferably the same kind of nitride semiconductor as nitride semiconductor layer 71, and particularly preferably undoped or n-type impurity-doped GaN. In the case where n-type impurity doping is performed during the growth of nitride semiconductor crystal 76, a gradient in concentration can be made as described earlier.

However, in the 3 rd aspect, the 2 nd growth control mask 74 is ideal for forming it, but when it is not formed, a nitride semiconductor crystal excellent in crystallinity can also be grown. In this case, as for the 1 st growth control mask 73 and the recess 72, the 1 st selective growth mask 13 and the 1 st window 14 explained for the 1 st and 2 nd aspects are converted to be read as the 1 st growth control mask 73 and the recess 72, and the discussion of the 1 st selective growth mask 13 and the 1 st window 14 explained for the 1 st and 2 nd aspects can be fully applied to the 1 st growth control mask 73 and the recess 72. In this case, the recess 72 should have a depth that does not expose the surface of the support 10. In this case, it is particularly preferable that the recess 72 has a depth of 500 angstroms to 5 micrometers.

As is apparent from the above description,

nitride semiconductor crystals

16, 17, 116, and 76 (hereinafter, these crystal substrates are sometimes collectively referred to as a substrate 1000) grown by the method of the present invention are useful as substrates because they have very few defects and support a predetermined nitride semiconductor device thereon.

The nitride semiconductor substrate of the present invention, particularly the nitride semiconductor substrate grown by the method of the 1 st to 3 rd aspects, can be described as follows: having the 1 st and 2 nd main surfaces, the crystal defects are relatively small in the region near the 1 st main surface (that is, the surface supporting the device structure or the growthcompletion end surface), and the crystal defects are relatively large in the region near the 2 nd main surface. The 2 nd main surface means a main surface closer to the dissimilar substrate 11 than the 1 st main surface. When an N-type impurity is doped into the nitride semiconductor substrate, the N-type impurity tends to concentrate in a region where many crystal defects are present, so that the surface region near the 2 nd main surface can be made to be N⁺And (4) a region. Therefore, by providing the n-side electrode of the nitride semiconductor device in this region, the threshold value or forward voltage of the device can be lowered.

Further, when the nitride semiconductor substrate of the present invention is viewed from the 1 st main surface, the following can be described: the region with relatively few crystal defects (the 1 st region) and the region with relatively many crystal defects (the 2 nd region) are shifted in one direction. The 1 st region corresponds to the masks 13 and 73, and the 2 nd region corresponds to the window 14 and the recess 72.

The nitride semiconductor device of the present invention has its device structure supported by the nitride semiconductor substrate of the present invention. In this case, the nitride semiconductor substrate of the present invention may be configured to support the device structure in an independent state, except for the support 10 and the mask (13, 113, 73, 74, etc.), or may be configured to support the device structure in a state where the mask is provided. Further, the nitride semiconductor of the present invention may be formed with a device structure thereon after being previously brought into an independent state, or may be brought into an independent state by removing the support after forming a device structure thereon while keeping the state provided with the mask as it is.

The freestanding nitride semiconductor substrate of the present invention has a thickness of 70 micrometers or more, preferably 100 micrometers or more, and more preferably 300 micrometers or more. If it has a thickness of 70 μm or more, the nitride semiconductor substrate becomes difficult to crack, and handling becomes easy. The upper limit of the thickness is not particularly limited, but is preferably 1mm or less.

In addition, the nitride semiconductor substrate of the present invention having a state of a different substrate is preferably 1 to 50 μm thick. When the thickness is within this range, the phenomenon that the entire wafer is deflected due to the difference in thermal expansion coefficient between the dissimilar substrate and the substrate is reduced.

The device structure supported by the nitride semiconductor substrate of the present invention is not particularly limited as long as it exhibits a predetermined device function, and includes, but is not limited to, LED device structures, LD device structures, and the like. The device structure of the present invention may contain at least an n-type or p-type nitride semiconductor. For example, an n-type nitride semiconductor layer having a superlattice structure may be given as an n-type nitride semiconductor layer, and an n-type nitride semiconductor capable of forming an n-side electrode is already formed on the n-type nitride semiconductor layer having the superlattice structure. For example, the LED device and the LD device of the present invention basically have an active layer and 2 clad layers provided on both sides thereof.

In addition, other structures for forming the nitride semiconductor device may be used, and any suitable electrode and shape such as an electrode and a shape of the device may be used.

In the present invention, the p-side or the n-side means the side opposite to the active layer, and the p-side isthe side containing the nitride semiconductor layer into which the p-type impurity can be doped, and the n-side is the side containing the nitride semiconductor layer into which the n-type impurity can be doped.

Fig. 8A is a schematic sectional view showing a structure in which an LED device is provided over a nitride semiconductor substrate 1000 of the present invention, and fig. 8B is a plan view thereof. As can be seen from fig. 8B, the LED device is substantially rectangular parallelepiped as a whole.

As shown in fig. 8A, an n-side buffer layer 81 made of a nitride semiconductor, for example, n-type GaN, into which an n-type impurity such as Si has been doped has been formed on a nitride semiconductor substrate 1000. The buffer layer 81 is typically a nitride semiconductor crystal grown at a high temperature of 900 ℃ or higher, and unlike a low-temperature buffer layer (for example, the buffer layer 12 in fig. 1A to 1C) grown at a low temperature in order to relax lattice mismatch between the substrate and the nitride semiconductor grown thereon, the high-temperature buffer layer 81 is a buffer layer functioning as an n-type cladding layer. In the case of manufacturing an LED device, the buffer layer 81 is preferably formed to have a thickness of 20 angstroms or more. The buffer layer 81 is preferably formed as a strained superlattice structure in which 1 st and 2 nd nitride semiconductor thin layers having different compositions are alternately stacked. The buffer layer of the superlattice structure as a carrier block layer can provide an n-side clad layer excellent in crystallinity. Such a buffer layer having a superlattice structure can be formed by alternately stacking, for example, an aluminum-containing nitride semiconductor, particularly an AlGaN thin layer, into which an n-type impurity has been doped, and a GaN layer into which no impurity has been doped. In addition, the buffer layer of the superlattice structure desirably hasa thickness of 50 angstroms or more.

Over the buffer layer 81, an active layer 82 is formed. It is particularly desirable that the active layer 82 be formed as a quantum well structure including a well layer composed of InGaN. The quantum well structure includes both a Single Quantum Well (SQW) structure and a Multiple Quantum Well (MQW) structure. A multiple quantum well structure is ideal. The active layer of the multiple quantum well structure may be formed, for example, by alternately stacking 1 st and 2 nd InGaN thin layers having different compositions, or alternately stacking an InGaN thin layer and a GaN thin layer. When the active layer 82 has a quantum well structure, an n-type or p-type impurity may be doped into one or both of the well layer and the barrier layer, or no impurity may be doped. In the case where the active layers 82 do not take a quantum well structure, n-type and/or p-type impurities are doped into the respective active layers.

Over the active layer 82, a p-side cladding layer 83 made of a p-type nitride semiconductor into which a p-type impurity such as Mg has been doped is formed. The p-side cladding layer 83 is preferably formed of an aluminum-containing nitride semiconductor, particularly AlGaN.

On the p-side cladding layer 83, a p-side contact layer 84 made of a p-type nitride semiconductor into which a p-type impurity such as Mg has been doped is formed. The p-side contact layer 84 is preferably formed of p-type GaN.

The p-side contact layer is provided with a light-transmitting p-electrode 85 on almost the entire surface, and a disk-shaped bonding pad 86 is provided substantially at the center thereof.

As shown in fig. 8A, the p-side contact layer 84, the p-side cladding layer 83, the active layer 82, and the buffer layer 81 are etched so that the side surfaces are exposed,the etching is performed until reaching into the surface of the substrate 1000, and then a 'notch' is provided. By providing the grooves by etching in this manner, the impact given to the p-n junction surface is reduced when the chip is cut into individual chips, and the LED device having higher reliability can be obtained and the yield can be improved. The 'cut groove' is desirably formed at a portion corresponding to the window portion 14 of the 1 st selective growth mask 13. Further, by providing this "notch", it is possible to clearly discriminate the chip cutting position indicating the region with a large number of crystal defects and the region with a small number of crystal defects when the sapphire substrate is removed later and the growth mask is selected 1 st.

As described above, by doping the nitride semiconductor substrate 1000 with n-type impurities, the n-side electrode 87 can be provided on the entire back surface of the substrate 1000.

Fig. 9 is a cross-sectional view schematically showing an LED device of a structure similar to that shown in fig. 8A and 8B, except that the state of supporting the nitride semiconductor substrate of the present invention with the base layer 10 is maintained as it is. In the LED device of fig. 9, the p-side contact layer 84, the p-side cladding layer 83, and the active layer 85 are etched so that the side surfaces thereof are exposed, the etching also reaches the n-side cladding layer 81, and the n-side cladding layer 81 is partially left. An n-side electrode 87 is provided on the surface of the remaining n-side cladding layer 81.

Fig. 10 is a sectional view of a Laser Diode (LD) structure provided on a nitride semiconductor substrate 1000 of the present invention.

Above the nitride semiconductor substrate 1000, a buffer layer 211 made of a nitride semiconductor is formed. This buffer layer 211 is a nitride semiconductor single crystal layer grown at a high temperature of 900 ℃ or higher, and is different from a low-temperature buffer layer (for example, buffer layer 12 in fig. 1A to 1C) grown at a low temperature in order to relax lattice mismatch between the substrate and the nitride semiconductor grown thereabove. In the case of fabricating an LD device, the buffer layer 211 preferably has a thickness of 100 angstroms or less, more preferably 70 angstroms or less, and most preferably 50 angstroms or less, and is formed in a strained superlattice structure in which 1 st and 2 nd nitride semiconductor thin layers having different compositions are alternately stacked. When the strained superlattice structure is used, the crystallinity is improved, and thus a high-power LD device can be realized. In addition, the buffer layer 211 may be omitted.

An anti-cracking layer 212 made of a nitride semiconductor is formed on the buffer layer 211. If the anti-cracking layer 212 is formed of an indium-containing n-type nitride semiconductor, preferably InGaN, cracks can be effectively prevented from entering into an aluminum-containing nitride semiconductor layer to be formed later. Most preferably, In is used for the crack-preventing layer 212_xGa_1-xN (0<x<0.5). Crack prevention layer 212 is desirably formed to a thickness of 100 angstroms or more and 0.5 microns or less. If the thickness is thinner than 100. ang. it is difficult to prevent cracks, and if the thickness is 0.5. mu.m, the crystal itself tends to be blackened. The crack prevention layer 212 may be omitted.

An n-side cladding layer 213 made of an n-type nitride semiconductor is formed on the anti-cracking layer 212. The n-side cladding layer 213 functions as both a carrier confining layer and a light confining layer. The n-side cladding layer 213 is preferably a superlattice cladding layer in which 1 st and 2 nd nitride semiconductor layers having different energy band gaps are sequentially stacked. Such a superlattice structure is preferably a nitride semiconductor containing aluminum, and more preferably AlGaN. In this case, the threshold of the LD device can be lowered by doping an impurity into any of the 1 st and 2 nd layers in an excess manner and performing so-called modulation doping. The n-side cladding layer 213 of such a superlattice structure may be formed by alternately stacking an AlGaN thin layer doped with an n-type impurity such as Si and an undoped GaN thin layer. The superlattice structure can provide a crack-free carrier confinement layer with good crystallinity. The thickness of the n-side cladding layer 213 is preferably 100 angstroms to 2 micrometers, more preferably 500 angstroms to 1 micrometer.

On the n-side cladding layer 213, an n-side optical guiding layer 214 made of a nitride semiconductor is formed. The n-side optical guiding layer 214 functions as a guiding layer for light from the active layer 215 described below, and is preferably made of GaN or InGaN. The n-side optical guiding layer 214 is preferably formed to have a thickness of 100 angstroms to 5 microns, more preferably 200 angstroms to 1 micron. The n-side optical guiding layer 214 is usually doped with an n-type impurity such as Si or Ge to form an n-type conductivity, but such an impurity may not be doped. The structure of the n-side optical guiding layer 214 may be a superlattice structure. The n-side optical guiding layer 214 having such a superlattice structure can be formed by alternately stacking a1 st layer made of a1 st nitride semiconductor such as GaN and a 2 nd layer made of a 2 nd nitride semiconductor InGaN different from the 1 st layer, for example. In this case, at least one of the 1 st layer and the 2 nd layer may be doped with an n-type impurity or may be undoped.

In the present invention, the size of the energy gap is based on the layer having a large energy gap in the superlattice structure, and is based on the well layer in the active layer of the quantum well structure.

An active layer 215 made of a nitride semiconductor is formed on the n-side optical guiding layer 214. It is particularly preferable that the active layer 215 has a quantum well structure having a well layer made of an indium-containing nitride semiconductor (preferably InGaN or InAlN). Such a quantum well structure may be a Single Quantum Well (SQW) structure or a Multiple Quantum Well (MQW) structure. A multiple quantum well structure is ideal. For example, the multiple quantum well structure may be formed by alternately stacking 1 st and 2 nd InGaN thin layers having different compositions, or may be formed by alternately stacking an InGaN thin layer and a GaN thin layer. The active layer of the quantum well structure may or may not be doped with impurities into the well layer and/or the barrier layer. An undoped quantum well structure active layer is more desirable. In this case, InAlN may be used instead of InGaN as the well layer.

Above the active layer 215, a p-side cap (cap) layer 216 having an energy gap larger than that of a p-side optical guiding layer 217 to be described later and larger than that of the active layer 215 (a well layer in a quantum well structure) is formed. The thickness of the p-side cap layer 216 is preferably 0.1 μm or less, more preferably 500. ANG or less, and most preferably 300. ANG or less. When the thickness of the p-side cap layer 216 is larger than 0.1 μm, cracks easily enter the p-side cap layer 216, and the p-side cap layer 216 tends to be difficult to grow as a nitride semiconductor layer with good crystallinity. The p-side cap layer 216 is preferably made of an aluminum-containing nitride semiconductor, particularly AlGaN. In this case, when the p-side cap layer 216 is formed to be thin, the laser oscillation is more likely to occur in the LD device as AlGaNhaving a larger composition ratio of Al is used. For example, in the case of Al having a y value of more than 0.2_yGa_1-yIn the case where N forms p-side cap layer 216, it is particularly desirable to adjust the thickness of p-side cap layer 216 to 500 angstroms or less. The lower limit of the thickness of the p-side cap layer 216 is not particularly limited, but the thickness of the p-side cap layer 216 is desirably formed to be 10 angstroms or more. Although the p-side cap layer 216 may be doped with a p-type impurity to be a p-type, it may be doped with an n-type impurity to be an i-type or an undoped type in which carriers are compensated for because of its small thickness. It is most desirable to dope the p-side cap layer 216 with p-type impurities.

On the p-side cap layer 216, a p-side optical guiding layer 217 made of a nitride semiconductor having a smaller energy gap than the p-side cap layer 216 is formed. The p-side optical guiding layer 217 functions as a light guiding layer for light from the active layer 215, and is desirably formed of the same GaN or InGaN as the n-side optical guiding layer 214. The p-side optical guide layer 217 may also function as a buffer layer when the p-side cladding layer 218 described later is grown. The p-side optical guiding layer 217 is preferably formed to have a thickness of 100 angstroms to 5 micrometers, more preferably 200 angstroms to 1 micrometer, so that it can function as an ideal optical guiding layer. The p-side optical guiding layer 217 may be doped with a p-type impurity such as Mg to be p-conductive, but may not be doped with an impurity. In addition, the structure of the p-side optical guiding layer 217 may be a superlattice structure. Such a superlattice structure can be formed by stacking the 1 st and 2 nd nitride semiconductor layers having different energy gaps in this order. The p-side optical guiding layer 217 having such a superlattice structure can be formed by alternately stacking a1 st layermade of GaN and a 2 nd layer made of InGaN. In this case, the p-type impurity may be doped into at least one of the 1 st layer and the 2 nd layer, or may not be doped.

On the p-side optical guiding layer 217, a p-side cladding layer 218 made of a nitride semiconductor is formed. The p-side cladding layer 218 functions as a carrier confinement layer and a light confinement layer, like the n-side cladding layer 213. The p-side cladding layer 218 is preferably a nitride semiconductor containing aluminum, more preferably AlGaN, and is formed in a superlattice structure so as to function to lower the resistivity of the p-side layer. Such a superlattice structure can be formed by sequentially stacking 1 st and 2 nd nitride semiconductor layers having different energy gaps. In this case, the threshold of the LD device can be lowered by performing so-called modulation doping in which an impurity is doped more into either of the 1 st and 2 nd layers. For example, such a p-side clad layer 218 may be formed by alternately stacking a1 st thin layer composed of AlGaN into which p-type impurities, for example, Mg, have been doped, and a 2 nd thin layer composed of undoped GaN. The thickness of the p-side cladding layer 218 is preferably 100 angstroms to 2 micrometers, more preferably 500 angstroms to 1 micrometer.

Further, the resistance of the p-side layer tends to decrease as described above, compared with the case where the n-side cladding layer 213 is made of the superlattice structure, or the p-side cladding layer 218 is made of the superlattice structure, and therefore, the LD is preferable in that the forward voltage of the device is reduced.

In a nitride semiconductor device of a double heterojunction structure having an active layer 215 of a quantum structure, particularly an LD device, a cap layer 216 comprising an aluminum-containing nitride semiconductor having an energy gap larger than that of the active layer 215 and a thickness of 0.1 μm or less is provided adjacent to the active layer 215; a p-side optical guiding layer 217 containing a nitride semiconductor having an energy gap smaller than that of the cap layer 216 is provided at a position farther from the active layer 85 than the cap layer 86; it is desirable to provide the p-side clad layer 218 of a superlattice structure containing an aluminum-containing nitride semiconductor having a larger energy gap than the p-side optical guiding layer 217 at a position farther from the active layer 215 than the p-side optical guiding layer 217. In this case, the p-side cap layer 216 has a relatively large energy gap, so electrons injected from the n-side are blocked by the cap layer 216. As a result, electrons do not overflow from the active layer 215, and thus the leakage current of the LD device is reduced.

The LD device structure is basically composed of an n-side cladding layer 213, an n-side optical guiding layer 214, an active layer 215, a p-side optical guiding layer 217, and a p-side cladding layer 218.

Further, in order to mount the p-electrode, on the p-side cladding layer 218, a p-side contact layer 219 made of a p-type nitride semiconductor is formed. The p-side contact layer 219 is preferably formed of In doped with a p-type impurity_aAl_bGa_1-a-bN (0. ltoreq. x, 0. ltoreq. y, x + y. ltoreq.1), in particular with GaN which has been doped with a p-type impurity, in particular Mg. The p-side contact layer 219 is preferably formed to have a thickness of 500 angstroms or less, more preferably 400 angstroms or less and 20 angstroms or more.

As shown in fig. 10, the p-type contact 219 and a part of the p-type clad layer 218 in the uppermost layer are etched into a stripe shape to form a ridge shape. The p-side electrode 220 is formed on the entire top surface of the ridge. If the p-side electrode 220 is desirably formed of Ni, Pt, Pd, Co, Ni/Au (stack or alloy), Pt/Au (stack or alloy), or Pd/Au (stack or alloy), a more desirable ohmic contact with the p-type contact layer 219 can be achieved.

On the exposed surfaces of the p-side cladding layer 218 and the p-side contact layer 219 excluding the top surface of the p-side electrode 220, it is desirable to form a film made of SiO₂Or ZrO₂ An insulating film 221 is formed, and a p-side pad electrode 222 electrically connected to the p-electrode 221 through the insulating film 221 is formed.

On the nitride semiconductor substrate 1000, as described above, the n-side electrode 223 is formed on substantially the entire back surface of the nitride semiconductor substrate 1000 by doping an n-type impurity. When the n-side electrode 223 is formed using a metal such as Al, Ti, W, Cu, Zn, Sn, In, a stacked body thereof, or an alloy thereof, more preferable ohmic contact with the n-type layer (In this example, the back surface of the substrate 1000) can be achieved. On the n-side electrode 223, a metal film (not shown) having a two-layer structure of Au/Sn is preferably formed as a metallization (metallization) for mounting a heat sink (not shown).

Fig. 11 is a schematic perspective view showing an LD device having a structure similar to that of fig. 10, in addition to showing that the LD device is supported in a state where the nitride semiconductor substrate 1000 of the present invention is supported by a support 10. In the LD device shown in fig. 11, the p-side cladding layer 218, the p-side optical guide layer 217, the cap layer 216, the active layer 215, the n-side optical guide layer 214, the n-side cladding layer 213, and the crack prevention layer 212 other than the ridge shape are etched so that their side surfaces are exposed, providing a rectangular parallelepiped structure, and this etching also reaches into the surface of the buffer layer 211 so that the surface of the buffer layer 211 is exposed from both sides of the rectangular parallelepiped. On both surfaces of the buffer layer 211 that have been exposed, n-side electrodes 223a and 223b are formed (in this case, the buffer layer 211 also functions as an n-side contact layer). It goes without saying that the insulating film 221 covers the exposed side surfaces of the p-side cladding layer 218, the p-side optical guide layer 217, the cap layer 216, the active layer 215, the n-side optical guide layer 214, the n-side cladding layer 213, and the crack prevention layer 212. Further, in the case where an n-type impurity has been doped into the substrate 1000, the buffer layer 211 may be completely etched by the above-described etching to expose the surface of the substrate 1000, and in this case, the n-side electrodes 223a and 223b may be formed on the exposed surface of the substrate 1000. The n-side electrode may be provided only on one side of the rectangular parallelepiped structure.

Fig. 12 shows a structure of still another LD device of the present invention. The insulating film 221 of the LD device shown in fig. 12 is formed thick so that the top surface of the p-side contact layer 219 is exposed from the exposed surface of the p-side cladding layer 218, the p-side electrode 220 is in contact with the p-side contact layer 219, and is formed widely on this insulating film 221, with the result that a structure similar to that shown in fig. 11 is provided except that the pad electrode 222 is not provided. In addition to this, in the LD device of fig. 12, only one n-side electrode stripe 223 is formed.

For growing the nitride semiconductor constituting the nitride semiconductor device structure of the present invention, any suitable method known as a method suitable for growing nitride semiconductors such as MOVPE, HVPE, MBE, and the like can be used. The ideal growth methodis MOVPE, which can grow crystals beautifully. However, since the MOVPE method takes time, it is preferable to perform the growth by a method which takes relatively little time when forming a relatively thick nitride semiconductor layer. In addition, it is desirable to grow a nitride semiconductor by appropriately selecting various methods for growing a nitride semiconductor depending on the purpose of use. In addition, when an n-type impurity or a p-type impurity is to be doped into the nitride semiconductor layer, as is well known in the art, a group 4 element as an n-type impurity is usually doped in the form of an organic compound or a hydride thereof, and a group 2 element as a p-type impurity is usually doped in the form of an organic compound thereof.

The present invention will be described below with reference to examples. In the following examples, MOVPE was carried out under a reduced pressure of 50 to 400Torr in any of the examples.

Example 1

In this embodiment, fig. 1A to 1C are referred to.

First, a photomask having a stripe shape was formed on a sapphire substrate 11 having a diameter of 2 inches and having a C-plane as a main surface and an ORF surface constituting an a-plane, and a plurality of SiO stripes each having a stripe width of 10 μm and a stripe interval (interval of windows) of 6 μm were formed by a CVD apparatus₂The selective growth mask 13 is constituted by strips, with a thickness of 0.1 micron. The respective strips are formed to extend in parallel with each other in a direction perpendicular to the ORF plane.

The sapphire substrate 11 on which the selective growth mask 13 had been formed was placed in a MOVPE reaction vessel, and a low-temperature buffer layer (not shown) composed of GaN was grown to a thickness of about 200 angstroms on the substrate 11 on whichthe selective growth mask 13 had been formed, with hydrogen as a carrier gas and ammonia and TMG as source gases, at a temperature of 510 ℃. The low temperature buffer layer is formed only within the window 14.

After the buffer layer was formed, only the flow of TMG was stopped (that is, the hydrogen carrier gas and ammonia continued to flow in), and the temperature was raised to 1050 ℃. At 1050 deg.C, using TMG and ammonia as raw material gas and silane gas as doping gas, growth is carried out by using 1X 10¹⁸/cm³Of the nitride semiconductor substrate 16 made of GaN doped with Si in a concentration of 100 μm.

Then, the wafer on which the GaN crystal substrate had grown was taken out from the reaction vessel, and the surface of GaN crystal substrate 16 was polished to form a mirror surface.

Comparative example 1

For comparison, on the sapphire substrate of example 1, without forming the selective growth mask 13, a GaN buffer layer was directly grown to a thickness of 200 angstroms by the same method, and further grown thereon to a thickness of 1 × 10¹⁸/cm³Si doped GaN, 100 microns thick.

When the number of lattice defects (crystal defects) per unit area of the GaN crystal obtained in example 1 and the GaN crystal obtained in comparative example were measured by plane TEM observation, the number of lattice defects was 1/10 or less, which was found to be the ratio to that of comparative example 1.

Example 2

In this embodiment, fig. 6A to 6C are referred to.

On the surface of the GaN crystal 16 obtained in example 1, as in example 1, a plurality of Si stripes each having a stripe width of 10 μm and a stripe interval of 6 μm were formed₃N₄The 2 nd selective growth masks 113 of strips are each formed to a thickness of 0.1 μm. The position of the 1 st selective growth mask 113 is shifted from the position of the 1 st selective growth mask 13. To put it in more detail, the mask alignment is performed such that option 2The respective strips of the growth mask 113 are located at positions corresponding to the windows 4 of the 1 st selective growth mask and are made to extend in parallel with the 1 st selective growth mask 13.

The wafer on which the 2 nd selective growth mask 113 was formed was returned again to the MOVPE reaction vessel and grown to 1X 10 by using TMG and ammonia as raw material gases and silane gas as a doping gas¹⁸/cm³Of a concentration of 150 microns thick, with Si doped GaN crystals 116.

The wafer on which the GaN crystal 116 had grown was taken out of the reaction vessel, mirror-polished on the back surface in the same manner as in example 1, and the number of lattice defects (crystal defects) per unit area was measured by plane TEM observation. The number of defects in the GaN crystal 116 of this example was 1/100 or less, which is the number of defects in the GaN crystal of comparative example 1.

Example 3

In this embodiment, reference is made to fig. 1A to 1C and fig. 6A to 6C.

On the sapphire substrate 11 of example 1, a layer of GaN having a thickness of 200 angstroms was grownThe formed low-temperature buffer layer is further grown with an undoped GaN layer having a thickness of 5 μm on the upper side to form a base layer 12 having a two-layer structure. On the plane of the base layer 12 of the thus obtained support 10, SiO with a thickness of 0.1 μm and a stripe width of 10 μm and a stripe interval of 8 μm was formed by the same method as in example 1₂The 1 st selective growth mask 13 ofstrips. The 1 st selective growth masks 13 extend parallel to each other in a direction perpendicular to the sapphire a-plane.

The wafer on which the 1 st selective growth mask 13 had been formed was transferred to an MOVPE reaction vessel, and an undoped GaN crystal 16 having a thickness of 100 μm was grown at 1050 ℃.

The wafer on which the GaN crystal 16 had grown was taken out of the reaction vessel, and the surface of the GaN crystal 16 was polished to form a mirror surface. On the surface of the GaN crystal 16, a plurality of Si pieces each having a stripe width of 12 μm and a stripe interval of 6 μm were formed by the same method as in example 1₃N₄The constituted 2 nd selective growth mask 113 is formed to a thickness of 0.1 μm. Each timeA 2 nd stripe mask is formed at a position corresponding to the window 14 of the 1 st selective growth mask.

The wafer on which the 2 nd selective growth mask 113 had been formed was returned again to the MOVPE reaction vessel, and an undoped GaN crystal 116 having a thickness of 150 μm was grown using TMG and ammonia as raw material gases. The number of crystal defects of the obtained undoped GaN crystal 116 was substantially equal to that of the GaN crystal of example 2.

Example 4

A Si-doped GaN crystal 16 having a thickness of 100 μm was grown in the same manner as in example 1, except that in example 1, a sapphire substrate having an a-plane as a main surface and an ORF surface constituting an R-plane was used as the different substrate 11, and a silicon dioxide band mask was formed to extend in a direction perpendicular to the R-plane. The number of crystal defects of this GaN crystal 16 was substantially equal to the number of crystal defects of the GaN crystal of example 1.

Example 5

In this embodiment, reference is made to fig. 1A to 1C.

First, a spinel substrate 11 having a (211) plane as a main surface and having an ORF plane constituting a (110) plane is prepared. On the surface of the spinel substrate 11, a plurality of SiO layers were formed extending in a direction perpendicular to the ORF plane by the same treatment as in example 1₂The 1 st selective growth mask 13 of strips. The individual stripes were 12 microns wide and 6 microns apart.

In the HVPE apparatus, a quartz boat for accommodating Ga metal is disposed inside a reaction vessel made of quartz. At a position apart from the quartz boat, a spinel substrate 11 on which a1 st selective growth mask 13 has been formed is obliquely disposed. A halogen gas supply line is provided at a position close to the Ga metal in the reaction vessel, and a nitrogen source supply line is provided at a position close to the substrate 11 in addition to the halogen gas supply line.

The halogen gas supply line was used to introduce the HCl gas in addition to the nitrogen carrier gas. At this point, the boat of gallium metal was heated to 900 ℃ and the spinel substrate had been heated to 1050 ℃. Then, makeReacting HCl gas with gallium metal to generate GaCl₃A nitrogen carrier gas and ammonia were supplied simultaneously from a nitrogen source supply line near the spinel substrate 11, and a hydrogen chloride gas and a silane gas were supplied from a halogen simultaneous supply line, and the substrate was grown at a growth rate of 50 μm/hr for 3 hours to grow a 150 μm-thick film doped with 1X 10¹⁸/cm³A GaN crystal of Si.

The wafer on which the HVPE gallium nitride crystal 16 had grown was taken out of the reaction vessel, the surface of the GaN crystal was polished, the irregularities on the surface were removed, and the number of lattice defects was measured. The number of crystal defects of the GaN crystal 16 obtained in this example was substantially the same as the number of crystal defects of the GaN crystal of example 1.

Example 6

In the present embodiment, fig. 8A and 8B are referred to.

First, a wafer having the Si-doped GaN crystal obtained in example 1 was placed in a reaction vessel of MOVPE apparatus, and a1 μm thick film of Si-doped GaN crystal was grown at 1050 ℃ to 1X 10¹⁸/cm³Of a GaN crystal doped with Si at a concentration ofThe high-temperature buffer layer 81.

Then, In of a single quantum well structure having a thickness of 20 angstroms is grown In this order by MOVPE on the high temperature buffer layer 81_0.4Ga_0.6An active layer 82 of N, Mg-doped A1 having a thickness of 0.3 μm_0.2Ga_0.8A p-side cladding layer 83 of N, and a p-side contact layer 84 of Mg-doped GaN with a thickness of 0.5 μm.

Then, the wafer was taken out from the reaction vessel and annealed at 600 ℃ in a nitrogen atmosphere to lower the resistance of the p-side cladding layer 83 and the p-side contact layer 84.

Thereafter, etching is performed in order from the p-side contact layer to partially expose the Si-doped GaN crystal. The etched portion provides a 'cut' for subsequent dicing.

After the etching, a light-transmitting p-side electrode 85 having a two-layer structure of Ni/Au with a thickness of 200 angstroms was formed on almost the entire surface of the p-side contact layer 84, and a bonding pad electrode 86 having a thickness of 0.5 μm was formed on the p-side electrode 85.

After the pad electrode 86 was formed, the sapphire substrate 11, the low-temperature buffer layer 12 and the 1 st selective growth mask 13 (see fig. 1C) of the wafer were removed by polishing, so that the rear surface of the Si-doped GaN crystal 16 was exposed, and an n-side electrode 87 having a thickness of 0.5 μm was formed on substantially the entire rear surface.

Then, dicing was performed along the above-described cuts from the n-electrode side, and cleavage was performed on the M-plane ((1100) plane) and the plane perpendicular to the M-plane of the Si-doped GaN crystal 16, thereby obtaining a 300 μ M square LED chip. The LED chip displays 520nm green light under 20mA, has the output power of more than 2 times and the electrostatic withstand voltage of more than 2 times compared with the LED device grown on the conventional sapphire substrate, and shows very excellent characteristics.

Example 7

In the present embodiment, reference is made to fig. 10.

The wafer on which the Si-doped GaN crystal 116 had been grown obtained in example 2 was placed in an MOVPE reaction vessel of an MOVPE apparatus, and 1 μm thick of Si-doped GaN crystal 116 doped with 1X 10 atoms was grown at 1050 deg.C¹⁸/cm³The high temperature buffer layer 211 made of a GaN crystal having Si concentration.

Next, a high temperature buffer layer 211 is grown by doping 1 × 10¹⁸/cm³In of Si_0.1Ga_0.9The anti-cracking layer 212 made of N has a thickness of 500 angstroms.

On the anti-cracking layer 212, an interactive laminated layer is formed by doping 5 x 10¹⁸/cm³N-type Al of Si_0.2Ga_0.8A1 st layer of N having a thickness of 20 a and a 2 nd layer of undoped GaN having a thickness of 20 a form an N-side clad layer 213 of a superlattice structure having a total thickness of 0.4 μm.

Next, on the n-side cladding layer 213, a seed crystal doped with 5X 10 is grown¹⁸/cm³The n-side optical guiding layer 214 of n-type GaN of Si has a thickness of 0.1 μm.

Secondly, the undoped In_0.2Ga_0.8Of N constitutionWell layer of thickness 5 angstroms and undoped In_0.01Ga_0.95The N barrier layers having a thickness of 50 a are alternately stacked to form an active layer 215 having a Multi Quantum Well (MQW) structure having a total thickness of 175 a.

Then, the film was grown to a thickness of 300 angstroms, and the film had a larger energy gap than the p-side optical guiding layer 217 and the active layer 215, and was doped with 1X 10²⁰/cm³P-type Al of Mg_0.3Ga_0.9N, p-side cap layer 216.

On p-type cap layer 216, a 0.1 micron thick doped 1 × 10 p-type cap layer 216 with smaller energy gap²⁰/cm³A p-side optical guiding layer 217 made of GaN of Mg.

Then, on the p-side optical guiding layer 217, a1 × 10 doped layer is alternately laminated²⁰/cm³P-type Al of Mg_0.2Ga_0.8A1 st layer of N with a thickness of 20 angstroms, and a substrate made of doped 110²⁰/cm³P-type GaN of Mg forms a 20 angstrom thick layer 2 forming a total 0.4 micron thick p-side cladding layer 218 of a superlattice structure.

Finally, the growth is carried out by doping with 1 × 10²⁰/cm³P-side contact layer 219 of p-type GaN of Mg having a thickness of 150 angstroms.

After all the nitride semiconductor layers were grown, the wafer was annealed at 700 ℃ in a nitrogen atmosphere in a reaction vessel to further lower the resistance of the p-type layer. After the annealing, the wafer was taken outfrom the reaction vessel, and the uppermost p-side contact layer 219 and the p-side cladding layer 218 were etched by an RIE apparatus to form a 4 μm wide stripe-shaped ridge, thereby forming a p-side electrode 220 having a Ni/Au double-layer structure on the entire top surface of the ridge. Next, SiO is formed on the exposed surfaces of the p-side cladding layer 218 and the contact layer 219 excluding the p-side electrode 220₂An insulating film 221 is formed, and a p-side pad electrode 222 electrically connected to the p-side electrode 220 through the insulating film 221 is formed.

After the p-side pad electrode 222 was formed, the sapphire substrate 11 of the wafer, the buffer layer 12, the 1 st selective growth mask 13, the 1 st GaN crystal 16, the 2 nd selective growth mask 113, and a part of the 2 nd GaN crystal 116 were removed by polishing to expose the back surface of the 2 nd GaN crystal, and an n-side electrode 223 having a Ti/Al double layer structure with a thickness of 0.5 μm was formed on the entire back surface thereof, and a thin film made of Au/Sn was formed thereon for metallization with a heat sink.

Thereafter, dicing is performed from the n-side electrode 223, and the 2 nd GaN crystal 116 is cleaved into a stripe shape at the surface ((1100) surface, corresponding to the side surface of the hexagonal column in FIG. 6) of the 2 nd GaN crystal 116M, thereby forming a resonance surface. Forming SiO on the resonance surface₂And TiO₂Finally, the dielectric multilayer film of (2) is cut into strips parallel to the extending direction of the p-side electrode 220 to obtain laser chips. A heat sink is provided in a state where each chip faces upward (a state where the substrate and the heat sink face each other), and wire bonding is performed on the p-side pad electrode 222. When the obtained LD device was subjected to laser oscillation at room temperature, the threshold current density was 2.0kA/cmat room temperature²And a threshold voltage of 4.0V, continuous oscillation at an oscillation wavelength of 405nm was confirmed, and the oscillation life was longer than 1000 hours.

Example 8

In this embodiment, reference is made to fig. 9.

By a method similar to that of example 6, 1X 10 doped GaN crystal was grown in this order on the undoped GaN crystal 116 obtained in example 2¹⁸/cm³High temperature buffer layer 81 of GaN of Si consisting of In_0.4Ga_0.6An active layer 82 of single quantum well structure with a thickness of 20 angstroms and composed of Mg-doped Al_0.2Ga_0.8A p-side cladding layer 83 of N having a thickness of 0.3 microns and a p-side contact layer 84 of Mg doped GaN having a thickness of 0.5 microns. Next, a translucent p-side electrode 85 was formed on almost the entire surface of the p-side contact layer 84 by the same process as in example 6, and a pad electrode 86 was formed thereon. After a predetermined etching, an n-side electrode 87 is formed on the high-temperature buffer layer 81.

The LED device of the present embodiment is different from the LED device of embodiment 6 in that: the LED device structure of this example was formed on the 2 nd GaN crystal 116 having better crystallinity than the GaN crystal 16 of example 1; the p-side electrode 85 and the p-side electrode 87 are also provided on the same side with respect to the substrate. In the nitride semiconductor device having the structure in which the nitride semiconductor layer doped with the n-type impurity (high-temperature buffer layer 81) is stacked on the undoped GaN crystal substrate, when the n-electrode is provided on the n-type layer side, the n-electrode is provided on the nitride semiconductor layer doped with the n-type impurity, and thus the LED device having low Vf and high light emission efficiency tends to be easily obtained. In fact, the LED device of example 8 has an output power increased by about 1.5 times and an electrostatic withstand voltage increased by about 1.5 times as compared with the LED device of example 6.

Example 9

In the present embodiment, fig. 1A to 1C and fig. 9 are referred to.

Similarly to example 3, a low-temperature buffer layer of 200 angstroms in thickness and an undoped GaN layer of 4 μm in thickness made of GaN were grown on a sapphire substrate 11 having an ORF plane constituting the a-plane with the C-plane as the main surface, to form a base layer 12 of a two-layer structure.On the undoped GaN layer, SiO layers of a thickness of 0.1 μm and a band width of 20 μm and a band interval of 5 μm were formed₂The 1 st selective growth mask is composed of stripes. The 1 st selective growth masks are masks respectively extending in parallel to each other in a direction perpendicular to the ORF plane.

The wafer was transferred to an MOVPE apparatus and grown with a thickness of 15 μm doped 1X 10¹⁹/cm³A GaN crystal of Si.

Thereafter, as in example 8, on the Si-doped GaN crystal, a crystal in which 1X 10 is doped was grown in order¹⁸/cm³In of single quantum well structure with thickness of 20 angstroms and high temperature buffer layer composed of GaN crystal of Si_0.4Ga_0.6N active layer of Mg-doped Al_0.2Ga_0.8A p-side cladding layer of N with a thickness of 0.3 microns and a p-side contact layer of Mg doped GaN with a thickness of 0.5 microns. Then, etching is performed from the p-side cladding layer to expose the surface of the Si-doped GaN crystal having a large impurity concentration, and an n-electrode is formed thereon, while the p-side cladding layer is formed on the p-sideA light-transmitting p-side electrode is formed on almost the entire surface of the contact layer, and a bonding pad electrode is formed on the p-side electrode. As such, in the LED device, the n-side electrode and the p-side electrode are disposed on the same side of the substrate. And finally, grinding the sapphire substrate to reduce the thickness of the sapphire substrate to about 50 microns, and scribing on one side of a grinding surface to obtain the 350-micron square LED device. Although the LED device showed substantially the same characteristics as the LED device of example 6, the yield of the device itself was 100 times or more as high as that of example 6.

Example 10

In the present embodiment, reference is made to fig. 1A to 1C, fig. 2, and fig. 9.

A sapphire substrate 11 having a 2-inch diameter and having an ORF surface constituting the a-plane and steps with an inclination angle θ from the C-plane of 0.13 °, stepwise steps of about 15 angstroms, and a mesa width W of about 56 angstroms was prepared.

On the inclined surface of this sapphire substrate, a low-temperature buffer layer of GaN was grown to a thickness of 200 angstroms and a buffer layer of 4 μm was grown thereon, as in example 9After doping a GaN layer and forming a base layer 12 of a double-layer structure, a1 st selective growth mask 13 having a thickness of 0.1 μm was formed on the undoped GaN layer by a CVD apparatus, and the selective growth mask 13 was formed of SiO having a plurality of bands with a width of 25 μm and a band interval of 5 μm₂A strip is formed. The 1 st selective growth masks are masks respectively extending in parallel to each other in a direction perpendicular to the a-plane.

The wafer was transferred to an MOVPE apparatus to grow a 10 μm thick doped 1X 10¹⁹/cm³A GaN crystal of Si.

Then, on the Si-doped GaN crystal, a crystal in which 1X 10 is doped is grown in sequence¹⁸/cm³In of single quantum well structure with thickness of 20 angstroms and high temperature buffer layer composed of GaN crystal of Si_0.4Ga_0.6N active layer of Mg-doped Al_0.2Ga_0.8A p-side cladding layer of N with a thickness of 0.3 microns and a p-side contact layer of Mg doped GaN with a thickness of 0.5 microns.

After that, the same treatment as in example 9 was performed, and a 350 μm square LED device was obtained. The LED device has an output power improved by about 5% as compared with the LED device of example 9, and the yield of the device itself is high as in example 9.

Example 11

According to the procedure of example 9, a dopant of 1X 10 is grown to a thickness of 10 μm¹⁹/cm³After the GaN crystal of Si, the wafer was taken out from the MOVPE apparatus, and 2 nd selective growth masks each composed of a silicon dioxide stripe having a stripe width of 15 μm were formed at positions corresponding to the window portions of the 1 st selective growth mask, and the thickness was 0.1 μm. The wafer on which the 2 nd selective growth mask had been formed was transferred to a MOVPE apparatus to grow a film having a thickness of 15 μm doped with 1X 10¹⁹/cm³ A GaN crystal 116 of Si.

Next, as in example 9, on the 2 nd Si-doped GaN crystal 116, a crystal in which 1X 10 Si was doped was grown in order¹⁸/cm³A high temperature buffer layer of GaN crystal of Si, In of single quantum well structure with a thickness of 20 angstroms_0.4Ga_0.6N active layer of Mg-doped Al_0.2Ga_0.8A p-side cladding layer of N0.3 μm thick and GaN Mg 0.5 thickMicron p-side contact layer. Then, the same treatment as in example 9 was performed, and a 350 μm square LED device was obtained. The LED device showed substantially the same characteristics as the LED device of example 8, and the yield of the device itself was 100 times or more as compared with example 8.

Example 12

In the present embodiment, reference is made to fig. 8A and 8B in particular.

A sapphire substrate 11 having an ORF plane constituting an A plane with a C plane as a main surface was placed in a reaction vessel of MOVPE apparatus, a low-temperature buffer layer of GaN was grown on the sapphire substrate 11 at 500 ℃ to a thickness of 200 μm, and then a GaN layer of GaN was grown at 1050 ℃ to a thickness of 5 μm to form a double-layer underlayer 12.

Taking out of the reaction vesselThe wafer was taken out, a strip-shaped photomask was formed on the top surface of the base layer 12, and a plurality of SiO films each having a thickness of 0.1 μm and a stripe width of 20 μm and a stripe interval (width of window) of 5 μm were formed by a CVD apparatus₂A selective growth mask 13 of strips. The respective strip masks are formed to extend in parallel with each other in a direction perpendicular to the ORF plane.

The wafer on which the 1 st selective growth mask 13 had been formed was placed again in an MOVPE reaction vessel and grown to incorporate 1X 10 at 1050 ℃¹⁸/cm³ A GaN crystal 16 of Si, 100 microns thick.

The wafer on which the Si-doped GaN crystal 16 had grown was taken out from the MOVPE reaction vessel, and the surface of the Si-doped GaN crystal 16 was polished to form a mirror surface. In the Si-doped GaN crystal 16, the number of crystal defects in the surface region corresponding to the 1 st selective growth mask 13 is less than 10⁶/cm²。

Then, the wafer on which the Si-doped GaN crystal 16 has grown is transferred again to the MOVPE reaction vessel, and the Si-doped GaN crystal 16 is grown with the doping amount 110¹⁸/cm³A buffer layer (n-side clad layer) 81 composed of GaN of Si and having a thickness of 1 μm.

Next, undoped In of a single quantum well structure with a thickness of 20 angstroms is sequentially grown on the n-side cladding layer 81_0.4Ga_0.6N active layer 82 made of Mg (1X 10) doped²⁰/cm³) Al of (2)_0.2Ga_0.8N p-side cladding layer 83 of 0.3 μm thickness, Mg (1X 10) doped²⁰/cm³) Is made of GaN (g) and has a p-side contact layer 84 with a thickness of 0.5 μm.

Then, the wafer was taken out from the MOVPE reaction vessel and annealed at 600 ℃ in a nitrogen atmosphere to lower the resistance of the p-side cladding layer 83 and the p-side contact layer 84. Next, etching is performed from the p-side contact layer 84 to expose the surface of the n-side cladding layer 81 or GaN crystal, thereby forming a notch.

After etching, a light-transmitting p-side electrode 85 of a Ni/Au two-layer structure was formed almost over the entire surface of the p-side contact layer 84 to a thickness of 200 angstroms, and a bonding p-side pad electrode 86 having a thickness of 0.5 μm was formed on the p-side electrode 85.

After the p-side pad electrode 86 was formed, the sapphire substrate 11, the underlying layer 12 and the 1 st selective growth mask 13 of the wafer were removed by polishing, the back surface of the GaN crystal 16 was exposed, and the n-side electrode 87 having a W/Al double-layer structure was formed on almost the entire back surface, and had a thickness of 0.5 μm.

And then, cutting the waferfrom the groove to form a strip, and cutting the strip in a direction perpendicular to the short side of the strip to obtain the LED chip. The crystal defects of the nitride semiconductor layer under the active layer of the LED chip are small at the upper part of the 1 st selective growth mask and large at the upper part of the window portion. Thus, by providing a large area of the source layer in the region with few crystal defects, a highly reliable device can be obtained. The LED obtained in this example showed 520nm green light at 20mA, an output power 2 times or more higher than that of an LED having a nitride semiconductor device structure grown on a conventional sapphire substrate, and an electrostatic withstand voltage 2 times or more, and exhibited very excellent characteristics.

In the present embodiment, although the shape of the 1 st selective growth mask is defined as a stripe shape, the selective growth mask having a shape (for example, a quadrangle) matching the shape of the chip to be cut may be formed in a dot shape with a predetermined pitch so as to cut the chip at a position corresponding to the window of the selective growth mask.

Example 13

In this embodiment, reference is made in particular to fig. 11.

By the method of example 12, the doped material with a thickness of 6 μm is grown by 1X 10¹⁸/cm³ A GaN crystal 16 of Si.

The wafer on which the GaN crystal 16 had grown was placed in an MOVPE reaction vessel, and grown by doping with 1X 10 at 1050 ℃ on the Si-doped GaN crystal 15¹⁸/cm³A high-temperature buffer layer 211 made of GaN of Si.

Secondly, on the high temperature buffer layer 211, a layer is grown to be doped1×10¹⁸/cm³In of Si_0.1Ga_0.9N, and an anti-cracking layer 212 having a thickness of 500 angstroms.

Then, on top of the crack-resistant layer 212, 100 layers are alternately laminated, which are doped with 5 × 10¹⁸/cm³In of Si of_0.2Ga_0.8A1 st layer of N having a thickness of 20 a and a 2 nd layer of undoped GaN having a thickness of 20 a form a superlattice structured N-side clad layer 213 of 0.4 μm.

Then, the growth is carried out by doping 5X 10¹⁸/cm³The n-side optical guiding layer 214 of n-type GaN of Si was 0.2 μm thick.

On the n-side optical guiding layer 214, undoped In_0.2Ga_0.8Well layer of N with thickness of 25 angstroms and undoped In_0.01Ga_0.99The barrier layers of N with a thickness of 50 a are alternately stacked to form an active layer 215 of a Multiple Quantum Well (MQW) structure with a total thickness of 175 a.

On the active layer 215, a grown energy gap is larger than the p-side optical guiding layer 217 and the active layer 215 by doping 1 × 10²⁰/cm³P-type Al of Mg_0.3Ga_0.7A p-side cap layer 216 of N, 300 angstroms thick.

1 x 10 doped on the p-side cap layer 216 with smaller growth energy gap than the p-side cap layer 216²⁰/cm³The p-side optical guiding layer 217 made of p-type GaN of Mg has a thickness of 0.1 μm.

On the p-side optical guiding layer 217, 1 × 10 of the dopant is added²⁰/cm³P-type Al of Mg_0.2Ga_0.8A1 st layer of N with a thickness of 20 angstroms, and a film formed by doping 1X 10²⁰/cm³The alternating 2 nd layer stack of p-type GaN of Mg, having a thickness of 20 angstroms, forms a p-side cladding layer 218 of superlattice structure having a total thickness of 0.4 microns.

Finally, the growth is carried out by doping with 1 × 10²⁰/cm³The p-side contact layer 219 of p-type GaN of Mg was 150 angstroms thick.

After all the nitride semiconductor layers were grown, the wafer was annealed at 700 ℃ in a nitrogen atmosphere in a reaction vessel to further lower the resistance of the p-type layer. After the annealing, the wafer was taken out from the reaction vessel, and the uppermost p-side contact layer 219 and p-side cladding layer 218 were etched by an RIE apparatus to form a ridge shape having a stripe width of 4 μm. The ridge shape is formed in a direction parallel to the stripe of the 1 st selective growth mask and is formed at a position above the 1 st selective growth mask.

After the ridge is formed, the p-side clad layer 217 exposed on both sides of the ridge stripe is etched centering on the ridge stripe to expose the surface of the n-side clad layer 211 on which the n-side electrodes 223a, 223b are to be formed.

Then, a p-side electrode 220 of a Ni/Au double-layer structure is formed on the entire top surface of the ridge. On the surface of the p-side cladding layer 218, the p-side contact layer 219 excluding the p-side electrode 220, a layer made of SiO is formed₂An insulating layer 221 is formed, and a p-side electrode 220 is formed through the insulating layer 221And an electrically connected p-side pad electrode 222. On the other hand, on the surface of the n-side cladding layer 211 which has been exposed previously, n-side electrodes 223a and 223b of a W/Au double-layer structure are formed.

After the n-side electrode was formed, the sapphire substrate of the wafer was polished to a thickness of 50 μm as in example 1, and then cleaved from the sapphire substrate 11 in a direction perpendicular to the stripe-shaped p-side electrode 220 and n-side electrodes 223a and 223b, and the cleaved surface of the active layer 215 thus cleaved was regarded as a resonance surface. In the case of an LD device, the n-side electrodes 223a and 223b are formed on the region with a large number of crystal defects so that the active layer 215 does not exist, and the active layer 215 in which heat is concentrated is not broken by the crystal defects, thereby realizing an LD device with high reliability and long lifetime.

When the LD device obtained in this example was subjected to laser oscillation at room temperature, continuous oscillation was observed at an oscillation wavelength of 405nm at a threshold current density of 2.0kA/cm2 and a threshold voltage of 4.0V, and the oscillation life was longer than 1000 hours.

Example 14

In this embodiment, reference is made to fig. 1A to 1C in particular.

First, a photomask having a stripe shape was formed on a sapphire substrate 11 having a diameter of 2 inches and an ORF surface constituting the A-plane, with the C-plane as the main surface, by the same method as in example 1, and a plurality of SiO stripes each having a stripe width of 10 μm and a stripe interval (window interval) of 6 μm were formed on each of the substrates by a CVD apparatus₂The 1 st selective growth mask 13 of strips is 1 micron thick. The respective strips 13 extend parallel to each other in a direction perpendicular to the ORF plane of the sapphire substrate 11.

The sapphire substrate 11 on which the 1 st selective growth mask 13 had been formed was placed in a MOVPE reaction vessel, and a low-temperature buffer layer (not shown) composed of GaN was grown to a thickness of about 200 angstroms on the substrate 11 on which the selective growth mask 13 had been formed, with hydrogen as a carrier gas and ammonia and TMG as raw materials, at a temperature of 510 ℃.

After the buffer layer was formed, the flow of TMG was merely stopped and the temperature was raised to 1050 ℃. At 1050 deg.C, using TMG and ammonia as raw material gas and silane gas as dopant, 1X 10 is doped in growth¹⁸/cm³ A GaN crystal 16 of Si, 100 microns thick.

Then, the wafer on which the GaN crystal 16 had grown was taken out from the reaction vessel, and the surface of the GaN crystal (substrate) 16 was polished to form a mirror surface.

The number of crystal defects of the GaN crystal obtained in example 14 and the GaN crystal obtained in comparative example 1 were measured by plane TEM observation. As a result, the number of crystal defects of the GaN crystal obtained in example 14 averaged 1.3X 10⁶/cm²The number of crystal defects in comparative example 1 was 2.4X 10⁷/cm²It was found that the number of crystal defects of the GaN crystal of example 14 was 1/10 or less, which is the number of crystal defects of comparative example 1.

Example 15

In this embodiment, fig. 1A to 1C are referred to.

On the sapphire substrate 11 used in example 14, a low-temperature buffer layer composed of GaN was grown,a thickness of 200 angstroms, and an undoped GaN layer of 5 μm thickness was grown thereon to form the base layer 12 of a double-layer structure. On the top surface of the base layer 12 of this wafer, a plurality of SiO layers each having a stripe width of 10 μm and a stripe interval of 3 μm and a thickness of 1 μm were formed by the same method as in example 14₂The 1 st selective growth mask 13 of strips. Each selective growth mask 13 extends in a direction perpendicular to the ORF plane of the sapphire substrate 11.

The wafer on which the selective growth mask 13 has been formed is transferred to an HVPE reaction vessel at 1050 ℃ with GaCl₃And ammonia as a raw material gas and a silane gas as a doping gas, to grow a Si-doped GaN crystal 16 with a thickness of 300 μm.

The wafer on which the GaN crystal 16 had grown was taken out of the reaction vessel, and after the sapphire substrate 11, the underlying layer 12 and the selective growth mask 13 were removed by polishing, the back surface of the GaN crystal 16 was mirror-finished to obtain a Si-doped GaN crystal 16.

The number of crystal defects on the polished side and the opposite side was measured in the same manner as in example 14, and it was found that the number was 1X 10³/cm²The number of GaN crystals was smaller than that of example 14, and a substrate for device fabrication having very good crystallinity was obtained.

Example 16

As the different substrate 11, a 100 μm thick Si-doped GaN crystal 16 was grown in the same manner as in example 14, except that the sapphire substrate 11 having the a-plane as the main surface and the ORF surface constituting the R-plane was used. Further, the respective strips 13 extend in a direction perpendicular to the R-plane. As a result, GaN crystal 16 with very few etch pits was obtained, which was almost equivalent to that of example 1.

Example 17

First, a spinel substrate 11 having a (111) plane as a main surface and having an ORF plane constituting a (110) plane is prepared. On the surface of the spinel substrate 11, a plurality of SiO layers having a thickness of 1 μm were formed by the same method as in example 1₂The 1 st selective growth mask 13 constituted by the strips is such that it extends in a direction perpendicular to the ORF plane. Each strip having a width of 10 μm, stripThe band spacing was 3 microns.

Using the spinel substrate 11 on which the selective growth mask 13 had been formed, a doped 1X 10 spinel substrate having a thickness of 150 μm was grown by the same HVPE method as in example 5 to a thickness of 150. mu.m¹⁸/cm³ A GaN crystal 16 of Si.

When a wafer on which a Si-doped GaN crystal had grown was taken out of the reaction vessel, the spinel substrate 11 and the selective growth mask 13 were removed by polishing, and the number of crystal defects was measured in the same manner as in example 14, it was found that the GaN crystal obtained in this example was a crystal having very few etch pits, which was substantially equal to the number of crystal defects in example 14.

Example 18

In the present embodiment, reference is made to fig. 8A and 8B in particular.

From the wafer obtained in example 14, the sapphire substrate 11, the low-temperature buffer layer and the selective growth mask 13 were removed by polishing to expose the back surface of the Si-doped GaN crystal, thereby obtaining a free-standing Si-doped GaN crystal substrate 1000.

The Si-doped GaN crystal substrate 1000 was placed in a reaction vessel of MOVPE apparatus, and grown by doping with 1X 10 at 1050 ℃ on the surface thereof¹⁸/cm³And a high-temperature buffer layer 81 made of GaN of Si.

In of a single quantum well structure having a thickness of 20 angstroms is sequentially grown on the high-temperature buffer layer 81_0.4Ga_0.6N active layer 82 made of Mg (1X 10) doped²⁰/cm³) Al of (2)_0.2Ga_0.8N p-side cladding layer 83 of 0.3 μm thickness, Mg (1X 10) doped²⁰/cm³) Is made of GaN (g) and has a p-side contact layer 84 with a thickness of 0.5 μm.

Then, the wafer on which the nitride semiconductor layers had been grown was taken out from the MOVPE reaction vessel and annealed at 600 ℃ in a nitrogen atmosphere to lower the resistance of the p-side cladding layer 83 and the p-side contact layer 84. Thereafter, etching is performed from the p-side contact layer 84 to expose the surface of the Si-doped GaN crystal substrate 1000. By this etching, 'notch' at the time of chip cutting is provided.

After the etching, a light-transmitting p-side electrode 85 having a double-layer structure of Ni/Au with a thickness of 200 angstroms was formed on almost the entire surface of the p-side contact layer 84, and a bonding pad electrode 86 having a thickness of 0.5 μm was formed on the p-side electrode 85.

After the pad electrode was formed, an n-side electrode 87 was formed on the entire back surface of the GaN crystal substrate 1000 to a thickness of 0.5 μm.

Then, the wafer was sliced along the above described cut groove, and cleaved along the plane ((1100) plane) of the GaN crystal substrate 1000M and the plane perpendicular to the M plane, to obtain a 300 μ M square LED chip. The LED chip showed 520nm green light at 20mA, the output power was 2 times or more as high as that of an LED having a conventional nitride semiconductor device structure grown on a sapphire substrate, and the electrostatic withstand voltage was 2 times or more, and the LED chip showed very excellent characteristics.

Example 19

In this embodiment, reference is made in particular to fig. 10.

The free-standing Si-doped GaN crystal substrate 1000 obtained in example 18 was placed in a reaction vessel of MOVPE apparatus, and the n-side cladding layer 213 was directly formed on the surface of the substrate 1000 without providing the buffer layer 211 and the crack prevention layer 212. More specifically, the compound is doped with 1X 10¹⁹/cm³Al of Si_0.2Ga_0.8The 1 st layer of N having a thickness of 20 a and the 2 nd layer of undoped GaN having a thickness of 20 a are alternately grown by 100 layers to form the N-side clad layer 213 of the superlattice structure having a total thickness of 0.4 μm.

Next, on the n-side cladding layer 213, a seed crystal layer doped with 1X 10 is grown¹⁷/cm³The n-side optical guiding layer 214 of n-type GaN of Si has a thickness of 0.1 μm.

Next, 1X 10 of a dopant is doped on the n-side optical guiding layer 214¹⁷/cm³Al of Si_0.2Ga_0.8N well layer with thickness of 25 angstroms and doped with 1 × 10¹⁷/cm³Al of Si_0.01Ga_0.95N, barrier layers of 50 a in thickness are alternately stacked to form an active layer 215 of a Multiple Quantum Well (MQW) structure having a total thickness of 175 a.

Next, a p-side cap layer 216 having a thickness of 300 angstroms is grown on the active layer 215, and the p-side cap layer 216 is doped with 1X 10 layers having a larger energy gap than the p-side optical guiding layer 217 and larger than the active layer 215²⁰/cm³P-type Al of Mg_0.3Ga_0.9And N is formed.

Next, a p-side optical guiding layer 217 with a thickness of 0.1 μm is grown on the p-side cap layer 216, and the p-side optical guiding layer 217 is doped with 1 × 10 of a material with a smaller energy gap than the p-side cap layer 216¹⁸/cm³P-type GaN of Mg.

Next, 1X 10 of dopant is doped on the p-side optical guiding layer 217²⁰/cm³Al of Mg_0.2Ga_0.8N of the first layer 1 with a thickness of 20 angstroms and doped with 1X 10²⁰/cm³The 2 nd layer of p-type GaN of Mg, having a thickness of 20 angstroms, is alternately stacked to form a p-side clad layer 218 of a superlattice structure having a total thickness of 0.4 μm.

Finally, on top of the p-side cladding layer 218, a seed layer of 1 × 10 is grown²⁰/cm³The p-side contact layer 219 made of p-type GaN doped with Mg was 150 angstroms thick.

In this way, the wafer on which the nitride semiconductor layers were formed was placed in a reaction vessel, and annealing treatment was performed at 700 ℃ in a nitrogen atmosphere, thereby further lowering the resistance of the p-type layer. After the annealing, the wafer was taken out from the reaction vessel, and the p-type contact layer 219 and the p-side cladding layer 218 on the uppermost layer were etched by an RIE apparatus to provide a ridge having a stripe width of 4 μm, and a p-side electrode 220 having a Ni/Au double-layer structure was formed on the entire top surface of the ridge. Then, SiO is formed on the exposed surface of the p-side electrode 220, the exposed surface of the p-side cladding layer 218 and the contact layer 19, except the top surface of the p-side electrode 220₂An insulating film 221 is formed, and a p-side pad electrode 222 electrically connected to the p-side electrode 220 through the insulating film 221 is formed.

After the p-side pad electrode 222 was formed, an n-side electrode 223 of a double-layer structure of Ti/Al with a thickness of 0.5 μm was formed on the entire back surface of the Si-doped GaN crystal substrate 1000, and a thin film of Au/Sn was formed on the top thereof for metallization with a heat sink.

Thereafter, the wafer is diced from the n-side electrode 223, and the GaN crystal substrate 1000 is cleaved at the M-plane ((1100) plane, corresponding to the side surface of the hexagonal prism in fig. 3) of the GaN crystal substrate 1000, whereby a resonance plane is provided and a bar is obtained. SiO is formed on both or either one of the two surfaces of the resonance surface₂And TiO₂Finally, the dielectric multilayer film of (2) is cut in a direction parallel to the extending direction of the p-side electrode 220 to obtain an LD device chip. The respective chips are placed face up on the heat sink, and the p-side pad electrode 222 is wire bonded. When the LD device was subjected to laser oscillation at room temperature, the threshold current density was 2.0kA/cm at room temperature²And a threshold voltage of 4.0V, continuous oscillation at an oscillation wavelength of 405nm was confirmed, and the oscillation life was longer than 1000 hours.

Example 20

In this embodiment, reference is made in particular to fig. 9.

On the undoped GaN crystal 16 (supported by the sapphire substrate 11) obtained in example 15, 1X 10 GaN was doped¹⁹/cm³Al of Si_0.2Ga_0.8The 1 st layer of N having a thickness of 20 a and the 2 nd layer of undoped GaN having a thickness of 20 a are alternately grown by 100 layers to form the N-side clad layer 81 of the superlattice structure having a total thickness of 0.4 μm.

Next, In of a single quantum well structure was grown In sequence to a thickness of 20 angstroms on the n-side cladding layer 81_0.4Ga_0.6N active layer 82 made of Mg (1X 10) doped²⁰/cm³) Al of (2)_0.2Ga_0.8N p-side cladding layer 83 of 0.3 μm thickness, Mg (1X 10) doped²⁰/cm³) Is made of GaN (g) and has a p-side contact layer 84 with a thickness of 0.5 μm. Then, etching isperformed from the p-side contact layer 84 to expose the surface of the Si-doped GaN crystal 1000 having a large impurity concentration, and an n-side electrode 87 is formed thereon. On the other hand, a light-transmitting p-side electrode 85 is formed on substantially the entire surface of the p-side contact layer 84, and a bonding pad electrode 86 is formed thereon. Finally, the sapphire substrate is ground to a thicknessAnd after the thickness is reduced to about 50 micrometers, scribing the grinding surface to obtain the 350-micrometer square LED device.

The resulting LED device showed an improvement in output power and electrostatic withstand voltage of about 5 times as compared with the device of the LED in example 18.

Example 21

According to the method of example 15, after a low-temperature buffer layer composed of GaN having a thickness of 200 angstroms is grown on the sapphire substrate 11 of example 15, and an undoped GaN layer having a thickness of 4 μm is grown thereon, the 1 st selective growth mask 13 as in example 15 is formed.

Next, the wafer was transferred to a MOVPE apparatus, and grown to incorporate 1X 10¹⁸/cm³ A GaN crystal 16 of Si, 15 microns thick.

On the GaN crystal 16, an n-side cladding layer 81, an active layer 82, a p-side cladding layer 83, and a p-side contact layer 84 were grown in this order in the same manner as in example 20, and then the same treatment as in example 20 was performed to obtain an LED device of 350 μm square. The LED device showed the same excellent characteristics as the LED device of example 20, and the life was improved as compared with the LED device of example 20.

Example 22

The same process as in example 10 was carried out except that each stripe width was 10μm and the stripe interval was 5 μm, a low-temperature buffer layer composed of GaN and an undoped GaN layer were grown on the inclined sapphire substrate 11, and a1 st selective growth mask 13 was formed thereon.

The wafer was transferred to a MOVPE apparatus and a 10 micron thickness doped 1X 10 film was grown on the wafer¹⁹/cm³ A GaN crystal 16 of Si.

Next, in the same manner as in example 20, after an n-side cladding layer 81, an active layer 82, a p-side cladding layer 83, and a p-side contact layer 84 were grown in this order, the same processing as in example 20 was performed, and a 350 μm square LED device was obtained. Compared with the LED device of the embodiment 20, the LED device has the advantages that the output power is improved by about 5 percent, and the yield of the device is the same as that of the embodiment 20.

Example 22

3 kinds of Si-doped GaN crystals 16 were grown by the same process as in example 4, except that the band gap was set to 5 μm, 3 μm and 1 μm, respectively.

As a result of measuring the number of etch pits by treating in the same manner as in example 14, the number of etch pits was reduced by about 20% in the cases of 3 μm and 1 μm, respectively, as compared with the case of 5 μm in stripe interval.

Example 23

In the present embodiment, reference is made to fig. 1A to 1C and fig. 11 in particular.

A sapphire substrate 11 having a diameter of 2 inches and having a C-plane as a main surface and an ORF-plane constituting an A-plane was placed in an MOVPE reaction vessel, a low-temperature buffer layer of GaN was grown at a thickness of 200 angstroms using hydrogen as a carrier gas and TEM and ammonia as source gases while setting a temperature at 500 ℃, and an undoped GaN layer having a thickness of 5 μm was grown thereon at 1050 ℃ to form a base layer 12 having a two-layer structure.

The wafer on which the base layer 12 was formed was taken out from the MOVPE reaction vessel, a strip-shaped photomask was formed on the surface of the base layer 12, and SiO with a strip width of 10 μm and a strip interval of 2 μm was formed by a CVD apparatus₂A1 st selective growth mask 13 of 1 micron thickness made up of strips.

The wafer on which the selective growth mask 13 was formed was placed again in an MOVPE reaction vessel, and the temperature was set to 1050 ℃, ammonia gas was flowed at a flow rate of 0.27 mol/min, and TMG was flowed at a flow rate of 225 μmol/min (V/III ratio 1200), to grow an undoped GaN crystal 16 having a thickness of 30 μm. After growth, when the GaN crystal 16 was observed by cross-sectional TEM, the number of crystal defects was large (10) in the lower region having a height of about 5 μm from the interface with the underlying layer 12⁸/cm²Above), crystal defects are reduced in the region further up than the lower region (10)⁶/cm²Hereinafter), the nitride semiconductor crystal substrate can be sufficiently used. The surface of the crystal 16 after growth is aligned with the central portion of each of the stripe masks and the central portion of each of the window portionsAlthough crystal defects appear slightly in the corresponding portions, the number of crystal defects is smaller by 2 orders or more than the case where the V/III ratio is larger than 2000.

Next, 3X 10 dopant gas was grown on the GaN crystal 16 by using ammonia gas and TMG as raw material gases and silane gas as a dopant gas¹⁸/cm³A 5 micron thick n-side buffer layer 211 of GaN of Si.

Next, In was grown on the n-side buffer layer 211 at 800 ℃using TMG, TMI and ammonia as raw material gases_0.06Ga_0.94And the thickness of the anti-cracking layer 216 made of N is 0.15 microns.

Then, at 1050 ℃, the mixture is doped with 1 × 10¹⁹/cm³In of Si_0.2Ga_0.8A1 st layer composed of N and 25 a thick (with TMA, TMG, ammonia and silane gases), and a 2 nd layer composed of undoped GaN and 25 a thick (with TMG and ammonia) were grown alternately, and a superlattice structure N-side cladding layer 213 with a total thickness of 0.8 μm was grown.

Next, an n-side optical guiding layer 214 composed of undoped GaN and having a thickness of 0.1 μm was grown at 1050 ℃.

Next, undoped In was reacted at 800 ℃ with TMA, TMI and ammonia_0.2Ga_0.8A well layer of N and 40 angstroms In thickness, and undoped In_0.01Ga_0.95The barrier layers of N with a thickness of 100 angstroms are alternately stacked, and the active layer 215 of each quantum well structure with a total thickness of 440 angstroms, which ends at the barrier layer, is finally grown.

Secondly, the temperature was raised to 1050 ℃ with TMA, TMG, Ammonia and Cp₂Mg has a larger growth energy gap than the p-side optical guiding layer 217 and is doped with 1 × 10²⁰/cm³P-type In of Mg_0.3Ga_0.7N constitutes a p-side cap layer 216 with a thickness of 300 angstroms.

Next, a p-side optical guiding layer 217 made of undoped GaN having an energy gap smaller than that of the p-side cap layer 216 was grown at 1050 ℃.

Then, at 1050 ℃, the mixture is doped with 1 × 10²⁰/cm³P-type In of Mg_0.2Ga_0.8A1 st layer of N having a thickness of 25 a and a 2 nd layer of undoped GaN having a thickness of 25 a are grown alternately to grow a p-side clad layer 218 of a superlattice structure having a total thickness of 0.8 μm.

Finally, a 2X 10 doped seed crystal was grown on the p-side cladding layer 218 at 1050 deg.C²⁰/cm³The p-side contact layer 219 of p-type GaN of Mg was 150 angstroms thick.

The wafer on which the nitride semiconductor layer was grown by the above-described treatment was placed in a reaction vessel, and annealing treatment was performed at 700 ℃ in a nitrogen atmosphere to further lower the resistance of the layer doped with the p-type impurity.

After annealing, the wafer was taken out of the reaction vessel, and the uppermost p-type contact layer 219 and p-side cladding layer 218 were etched by an RIE apparatus to provide a ridge shape having a stripe width of 4 μm. At this time, a ridge stripe is formed on a surface region other than a position corresponding to the central portion of the stripe mask 13 and the central portion of the window where the crystal defect occurs. Thus, if a ridge stripe is formed at a position where there is almost no crystal defect, the crystal defect tends to be hard to transfer from the substrate to the active region during laser oscillation, so that the lifetime of the device becomes longer and the reliability is improved.

Next, a protective mask was formed on the ridge top surface, and RIE was performed to expose the surface of the n-side buffer layer 211. The exposed n-side buffer layer 211 also functions as a contact layer for forming the n-side electrodes 223a, 223 b. The exposed surface may be provided as a contact layer by etching to a region of the GaN crystal 16 where many crystal defects are present.

Next, on the top surface of the ridge-shaped p-side contact layer 219, a p-side electrode 220 made of Ni and Au is formed ina stripe shape. On the other hand, on the surface of the n-side buffer layer 211 exposed by the above etching, n-side electrodes 223a and 223b made of Ti and Al are formed in a stripe shape.

Then, SiO is formed on the side surface of the nitride semiconductor layer exposed by the etching₂An insulating film 221 is formed, and a p-pad electrode 222 electrically connected to the p-electrode 220 through the insulating film is formed.

Subsequently, the obtained wafer was transferred to a polishing apparatus, the back surface of the sapphire substrate 11 was polished with a diamond abrasive until the thickness became 70 μm, and then 1 μm polishing was performed with a fine abrasive to mirror the back surface of the sapphire substrate 11, and the entire back surface was metallized with Au/Sn.

And then, scribing the wafer on one side of the Au/Sn, and splitting the wafer into strips in the direction vertical to the strip-shaped electrodes to form split surfaces. A dielectric multilayer film of SiO2 and TiO2 was formed on the resonance surface, and finally the bar was cut in a direction parallel to the p-electrode to obtain an LED device chip. The chip is placed face up on a heat sink and wire bonding is performed to each electrode. When the LD device was subjected to laser oscillation at room temperature, the threshold current density was 2.0kA/cm²And a threshold voltage of 4.0V, and a continuous oscillation at an oscillation wavelength of 405nm was confirmed, and the oscillation life was longer than ten thousand hours. Further, when the lifetime of an LD device was measured by arbitrarily extracting 500 LD devices from the LD devices obtained from the wafer, the lifetime was 70% or more of ten thousand hours or more.

An LD device was fabricated in the same manner as in example 23, except that when the GaN crystal 16 was grown, the flow rate of ammonia was 0.36 mol/min and the flow rate of TMG was 162 μmol/min (V/III ratio 2222), an undoped GaN crystal 16 having a thickness of 30 μm was grown, and ridge stripes were formed at arbitrary positions. The life of the obtained LD devices was arbitrarily extracted to less than 5% of ten thousand hours from the obtained LD devices.

Example 24

An LD device was fabricated by the same method as in example 23, except that GaN crystal 16 having a thickness of 10 μm was grown. In this case, the number of crystal defects appearing on the surface of the GaN crystal 16 tended to be one order of magnitude larger than that of the LD device of example 23, and the lifetime of ten thousand hours was 50% or more of that of the LD device obtained by arbitrarily extracting 500 LD devices.

Example 25

This embodiment is mainly described with reference to fig. 11.

In example 23, a GaN crystal 16 was grown to a thickness of 30 μm by treating the material gas in the same manner as in example 23 except that ammonia was flowed at 0.27 mol/min and TMG was flowed at a flow rate of 150 μmol/min (V/III ratio 1800), and a silane gas was added to the material gas. The GaN crystal 16 is about 5 μm away from the interface with the base layer 12The lower region of about a meter has a large number of crystal defects and the region above the lower region has a small number of crystal defects (10)⁶/cm²Hereinafter), the nitride semiconductor substrate can be sufficiently used.

Thereafter, nitride semiconductor layers 211 to 219 similar to those of example 23 were formed. Next, by etching, the GaN crystal 16 was exposed in a region having a relatively large number of crystal defects until about 6 μm was removed from the surface of the GaN crystal 16, and processing was performed in the same manner as in example 23 except that the n-side electrodes 223a and 223b were formed on the exposed surface to obtain an LD device. The LD device also continuously oscillates at a low threshold value as in the LD device of example 3, and the lifetime of 500 devices is 50% or more of ten thousand hours or more.

Example 26

An LD device was produced in the same manner as in example 23, except that ammonia was flowed at a flow rate of 0.27 mol/min and TMG was flowed at a flow rate of 180 μmol/min (V/III ratio: 1500) during growth of the GaN crystal 16. As a result, the LD devices were obtained in the number almost equal to that of example 23 while oscillating continuously at the same low threshold.

Example 27

An LD device was fabricated by the same method as in example 23, except that the flow rate of TMG was increased and the V/III ratio was set to 800 when a GaN crystal was grown. As a result, the LD devices were obtained in the number almost equal to that of example 23 while oscillating continuously at the same low threshold.

Example 28

An LD device was produced in the same manner as in example 23, except that ammonia was flowed at a flow rate of 0.15 mol/min and TMG was flowed at a flow rate of 5 mmol/min (V/III ratio: 30) during growth of the GaN crystal 16. As a result, the lifetime of 500 LD devices randomly extracted from the obtained LD devices was 30% or more of ten thousand hours, regardless of whether the devices were continuously oscillated at the same low threshold.

Example 29

In growing the GaN crystal 16, nitride semiconductor layers 211 to 219 were grown as in example 23 except that a Si-doped GaN crystal doped with Si with a Si thickness of 90 μm was grown. Then, after the wafer was taken out from the reaction vessel, the wafer had been flexed due to the difference in thermal expansion coefficient between the sapphire substrate 11 and the Si-doped GaN crystal. Then, the wafer is polished from the sapphire substrate 11, and the sapphire substrate 11, the base layer 12, and the selective growth mask 13 are removed. The resulting freestanding GaN crystal became unflexed and was substantially flat.

Next, as in example 23, the p-side contact layer 219 and the p-side cladding layer 218 are processed into a ridge shape by etching to form a p-side electrode 220, and after an insulating film 221 is formed, a p-pad electrode 222 is formed. In this case, since the position of the ridge stripe has been removed from the selective growth mask 13, it is difficult to make it coincide with the window portion by means of microscopic observation. On the other hand, n-side electrodes 223a and 223b made of Ti/Au are provided on substantially the entire rear surface of the exposed GaN crystal 16 having a large number of crystal defects. Then, this structure was processed in the same manner as in example 23 to obtain an LD device. These LD devices were also allowed to oscillate continuously at room temperature at a low threshold, and the lifetime was 70% or more of ten thousand hours or more among 500 devices which were randomly extracted.

Example 30

In the present embodiment, reference is made to fig. 1A to 1C and fig. 5A to 5B in particular.

A sapphire substrate 11 having a diameter of 2 inches and having a C-plane as a main surface and an ORF-plane constituting an A-plane was placed in an MOVPE reaction vessel, a low-temperature buffer layer of GaN was grown at a thickness of 200 angstroms using hydrogen as a carrier gas and TEM and ammonia as source gases with a temperature of 500 ℃, and an undoped GaN layer having a thickness of 4 μm was grown thereon at 1050 ℃ toform a base layer 12 having a two-layer structure.

The wafer on which the base layer 12 was formed was taken out from the MOVPE reaction vessel, a strip-shaped photomask was formed on the surface of the base layer 12, and a plurality of SiO films having a thickness of 0.5 μm and a width of each strip of 10 μm and an interval of 2 μm were formed on the surface by a CVD apparatus₂The 1 st selective growth mask 13 of strips.

The wafer on which the selective growth mask 13 was formed was placed again in an MOVPE reaction vessel, and the temperature was set to 1050 ℃, ammonia gas was flowed at a flow rate of 0.27 mol/min, and TMG was flowed at a flow rate of 225 μmol/min (V/III ratio 1200), to grow an undoped GaN crystal 16 having a thickness of 30 μm. When a GaN crystal is grown with the V/III ratio set to 2000 or less in this way, the GaN crystal 15 grows in the lateral direction on the mask 13 while the growth end face constitutes a facet substantially perpendicular to the plane of the mask 13, and therefore a crystal 16 with very few crystal defects can be obtained. A GaN crystal (MOVPE GaN crystal) 16 has been grown to have a uniform surface, and when the surface region thereof is observed by TEM, it is found that almost all of the crystal defects extending from the window 14 have stopped in the middle of the inside of the GaN crystal 16 and do not appear on the surface.

Subsequently, the wafer on which the GaN crystal 16 had grown was transferred to an HVPE apparatus, and an undoped GaN crystal 17(HVPE GaN crystal) having a thickness of 200 μm was grown using gallium metal, HCl gas, and ammonia as raw materials. The number of crystal defects in the surface region of the obtained HVPEGaN crystal 17 was measured by plane TEM observation at 1X 10⁴/cm²Hereinafter, it is known that a GaN crystal having very good crystallinity is obtained. The very few crystal defects which are present are also only those which extend substantially horizontally for a plane.

The wafer on which the HVPE GaN crystal 17 had grown was sent to a polishing apparatus, and the sapphire substrate 11, the foundation layer 12, the selective growth mask 13, and the MOVPE GaN crystal 16 were removed with a diamond abrasive to expose the back surface of the HVPE GaN crystal 17, thereby obtaining a free-standing GaN crystal substrate having a total thickness of 195 μm.In addition, the crystal defects on the back surface of the crystal substrate are reduced to 1 × 10⁵/cm²The following.

Example 31

In growing HVPE GaN crystal 17, the initial doping was carried out by 1X 10 in addition to the addition of silane gas to the source gas¹⁹/cm³Growing GaN on the Si side, reducing the flow of silane gas along with the growth, and finally growing and doping 5 × 10¹⁶/cm³A free-standing GaN crystal substrate was obtained in the same manner as in example 30, except that GaN having a Si concentration gradient was grown to a thickness of 200 μm. In this GaN crystal substrate, the surface with a small amount of Si had the number of crystal defects substantially equal to that of the crystal substrate of example 30.

Example 32

In growing MOVPE GaN crystal 16, except for adding silane gas to the raw gas, 1X 10 was initially edge-doped¹⁹/cm³Growing GaN on the Si side, reducing the flow of silane gas along with the growth, and finally growing and doping 1 × 10¹⁷/cm³A MOVPE GaN crystal substrate was obtained in the same manner as in example 30, except that GaN with Si concentration gradient was grown to a thickness of 200 μm. Next, when HVPE GaN crystal was grown, except that 1X 10 wasdoped¹⁷/cm³Except for Si in (b), a Si-doped hvpean crystal 17 was grown to a thickness of 200 μm by the same method as in example 30. Thereafter, while removing all of the sapphire substrate 11, the underlying layer 12 and the selective growth mask 13, the MOVPE GaN crystal 16, which is only 15 μm thick, is also removed.

In the thus obtained GaN crystal substrate having a double-layer structure of MOVPE GaN crystal and HVPE GaN crystal, the number of crystal defects on the main surface of the HVPE GaN crystal was substantially equal to that of the GaN crystal substrate of example 30, but the number of crystal defects on the back surface of the MOVPE GaN crystal was about one order of magnitude larger than that of the crystal defects on the main surface of the HVPE GaN crystal.

Example 33

In this embodiment, reference is made to fig. 12.

On the surface (the surface opposite to the back surface from which the sapphire substrate 11 and the like were removed by polishing) of the HVPE GaN crystal substrate (1000) obtained in example 30, ammonia and TMG were used as raw material gases, and a silane gas was used as an impurity gas, and the substrate was grown at 1050 ℃¹⁸/cm³An n-side contact layer 211 of GaN of Si was 4 μm thick.

In is grown on the n-side contact layer 211 by using TMG, TMI and ammonia as raw material gases and setting the temperature at 800 DEG C_0.06Ga_0.94And the thickness of the anti-cracking layer 212 consisting of N is 0.15 microns.

Then, on the anti-cracking layer 212, a thickness of 25 deg.C is alternately grown at 1050 deg.CA of Al not doped_0.16Ga_0.84A1 st layer of N (using TMA, TMG and ammonia), and a thickness of 25 angstroms of 1X 10 doped¹⁹/cm³And 2 nd layer of n-type GaN of Si, and n-side cladding layer 213 of a superlattice structure having a total thickness of 1.2 μm is grown.

Next, an n-side optical guiding layer 214 composed of undoped GaN was grown on the n-side cladding layer 213 at 1050 ℃ with a thickness of 0.1 μm using TMG and ammonia.

Next, undoped In was grown alternately 3 times at a temperature of 800 ℃ to a thickness of 100 angstroms_0.01Ga_0.95Barrier layer 212 composed of N and undoped In_0.2Ga_0.8The well layer composed of N was grown to form the active layer 215 of MQW structure having a total thickness of 520 angstroms, which was finally terminated by the barrier layer.

Subsequently, the temperature was raised to 1050 ℃ using TMA, TMG, Ammonia and Cp₂Mg growth is carried out by doping with 1 × 10²⁰/cm³P-type Al of Mg_0.3Ga_0.7N constitutes a p-side cap layer 216 with a thickness of 300 angstroms.

Next, 1 × 10 dopant is doped on the p-side cap layer 216²⁰/cm³The p-side optical guiding layer 217 made of GaN as Mg has a thickness of 0.1 μm.

Next, undoped Al is grown alternately to a thickness of 25 angstroms_0.16Ga_0.84A1 st layer of N and a layer of 25 angstroms thick doped with1×10¹⁹/cm³A 2 nd layer of n-type GaN of Mg was grown with a total thickness of 0.6 microns of a p-side cladding layer 218 of superlattice structure.

Finally, a seed layer of 1X 10 is grown to a thickness of 150 angstroms²⁰/cm³P-side contact layer 219 of p-type GaN of Mg.

The wafer on which the nitride semiconductor layer has grown in the above manner is taken out from the reaction vessel, and SiO is formed on the surface of the uppermost p-side contact layer 219₂Protective film by RIE, by SiCl₄The wafer is etched with the gas to expose the surface of the n-side contact layer 211 on which the n-side electrode is to be formed.

Next, after a ridge stripe having a width of 1 μm is formed by etching the n-side contact layer 219 and the p-side cladding layer 218 by applying a mask having a predetermined shape to the n-side contact layer 219 of the uppermost layer, ZrO is formed on the side surface of the ridge and the exposed surface of the p-side cladding layer 218₂The insulating film 221 exposes the top of the p-side contact layer 219, and forms a wide p-side electrode 220 electrically connected to the p-side contact layer 219 through the insulating film 211. On the other hand, an n-side electrode 223 is formed on the surface of the n-side contact layer 211 exposed by etching.

After the wafer GaN crystal substrate 1000 obtained as described above is polished to be thin, the GaN crystal substrate 1000 is cleaved, and the resonance surface of the LD device is formed on the cleaved surface. After cleaving, the respective LD devices are separated into chips, and the back surface of the GaN crystal substrate 1000 is set on a heat sink. Showing that the LD device has a threshold current density of 1.5kA/cm²Continuous laser oscillation occurs at room temperature, and the service life reaches more than 1000 hours under the output power of 20 mW.

In this example, although the LD device was fabricated using the substrate obtained in example 30, even when the structure in which both the n and p electrodes were taken out from the same side was employed, the nitride semiconductor substrate obtained in example 31 and example 32 and provided with a concentration gradient in the n-type impurity could be used. In this case, the n-side contact layer 211 may be omitted, and the n-side electrode 223 may be formed on the exposed surface by exposing the MOVPE crystal or HVPE crystal provided with the concentration gradient by etching.

Example 34

With the concentration gradient obtained in example 31, on the surface of the Si-doped HVPE GaN crystal (the surface opposite to the back surface from which the sapphire substrate 11 and the like were polished off), the crack preventing layer 212, the n-side cladding layer 213, the n-side optical guiding layer 214, the active layer 215, the p-side cap layer 216, the p-side optical guiding layer 217, the p-side cladding layer 218, and the p-side contact layer 219 were sequentially grown in the same manner as in example 33 without forming the n-side contact layer 211.

Next, the p-side contact layer 219 and the p-side cladding layer 218 were etched in the same manner as in example 33 to form a ridge stripe 1 μm wide, an insulating film 221 was formed, and a p-side electrode 220 was formed on the p-side contact layer, while an n-side electrode 223 was formed on the back surface of the GaN crystal substrate. Then, the GaN crystal substrate was polished from the back surface to a thickness at which cleavage was possible, and cleaved in the same manner as in example 33 to obtain an LD device. In this embodiment, even if the GaN crystal substrate is polished, since a concentration gradient is provided, the exposed surface is often a surface doped with an n-type impurity at a high concentration in the nitride semiconductor substrate. The resulting LD device had substantially the same characteristics as in example 33.

Example 35

In this embodiment, fig. 7A to 7D are referred to.

A sapphire substrate 11 having a diameter of 2 inches and having a C-plane as a main surface and an ORF-plane constituting an A-plane was placed in an MOVPE reaction vessel. A low-temperature buffer layer 12 made of GaN was grown to a thickness of about 200 angstroms on a sapphire substrate 11 with hydrogen as a carrier gas and TEM and ammonia as source gases, with the temperature set at 500 ℃. On the substrate layer 12, a 2 μm doped layer was grown at 1050 ℃ using TEM and ammonia as raw material gases and silane as a dopant gas to a thickness of 1X 10¹⁸/cm³A GaN layer 71 of Si.

Then, a strip-shaped photomask was formed on the GaN layer 71, and 1 st silicon dioxide strips having a strip width of 15 μm and a strip interval of 3 μm and a thickness of 1 μm were formed by a sputtering apparatus. Subsequently, the trench 72 is formed by etching with the RIE apparatus to a position halfway in the GaN layer 71. The GaN layer 71 is exposed only at the side and bottom surfaces of the trench 72. In addition, each silicon dioxide strip extends in a direction perpendicular to the ORF plane of the sapphire substrate 11.

After forming the trench 72 in this way, after forming the 2 nd silicon oxide on the entire surface including the 1 st silicon oxide mask, the side surface and the bottom surface of the trench 71 of the obtained structure by a sputtering apparatus, CF is used except for the portion on the bottom surface of the trench 72 and the portion on the 1 st silicon oxide strip of the 2 nd silicon oxide layer₄And O₂The gas mixture is used as an etching gas to etch only a portion on the side surface of the trench 72. Thus, a1 st growth control mask 73 made of 1 st and 2 nd silicon oxides is formed on the straight wall between the adjacent trenches 72,a 2 nd growth control mask 74 composed of a 2 nd silicon oxide is formed at the bottom of the trench 72.

A wafer having a GaN layer 71 with a groove 72 and 1 st and 2 nd growth control masks 73 and 74 formed thereon was placed in an MOVPE reaction vessel, andgrown to a thickness of 30 μm and doped with 1X 10 at 1050 ℃ using TMG and ammonia as raw material gases and silane as a dopant gas¹⁸/cm³A GaN crystal 76 of Si.

The wafer on which the Si-doped GaN crystal 76 had thus grown was taken out of the reaction vessel.

On the other hand, for comparison, on the sapphire substrate 11, after the buffer layer 12 was grown, a GaN layer 71 having a thickness of 30 μm was formed thereon, resulting in a GaN substrate for comparison.

When the number of crystal defects of the two GaN substrates was measured by plane TEM observation, it was found that the number of crystal defects was 6X 10 for the GaN substrate of example 35⁶/cm²In contrast, the GaN substrate for comparison was 6X 10¹⁰/cm²。

Example 36

The foundation layer 12 and the Si-doped GaN layer 71 were grown on the sapphire substrate 11 by the method of example 35. On the GaN layer 71, a groove 72 similar to that of example 35 was formed by a dicing method. A silicon dioxide layer is formed on the entire surface of the resulting structure, and only the silicon dioxide on the side surfaces of the trench 72 is removed by etching, thereby forming a1 st growth control mask 73 covering the top surfaces of the partition walls of the trench 72 and a 2 nd growth control mask 74 covering the bottom of the trench 72, and exposing the GaN layer 71 only on the side surfaces of the trench 72. Using this wafer, a Si-doped GaN crystal 76 was grown by the same method as in example 35. The number of crystal defects in the obtained GaN crystal substrate 76 was measured, and the same good results as in example 35 were obtained.

Example 37

Si-doped GaN crystal 76 was grown in the same manner as in example 35, except that the etching of GaN layer 71 was performed until reaching sapphire substrate 11. The GaN crystal had as few crystal defects as the crystal of example 35.

Example 38

In the present embodiment, fig. 8A and 8C are referred to.

By the same method as in example 35, a 200 μm thick Si-doped GaN crystal 76 was grown. The sapphire substrate 11, the foundation layer 12, the GaN layer 71, and the growth control masks 73 and 74 were removed from the wafer by polishing, to obtain a free-standing Si-doped GaN crystal substrate.

The Si-doped GaN crystal substrate (substrate 1000) was placed in an MOVPE reaction vessel of an MOVPE apparatus, and grown on the surface of the substrate at 1050 ℃ by doping with 1X 10¹⁸/cm³And a high-temperature buffer layer 81 made of GaN of Si.

Then, In of a single quantum well structure with a thickness of 20 angstroms is sequentially grown on the high temperature buffer layer 81_0.4Ga_0.6N active layer 82 made of Mg (1X 10) doped with Mg with a thickness of 0.3 μm²⁰/cm³) Al of (2)_0.2Ga_0.8A p-side cladding layer 83 of N, formed of Mg (1X 10) doped to a thickness of 0.5 μm²⁰/cm³) P-side contact layer 84 of GaN.

The wafer having the nitride semiconductor layer formed in this way was taken out from the reaction vessel, and annealing was performed at 600 ℃ in a nitrogen atmosphere to lower the resistance of the p-side cladding layer 83 and the p-side contact layer 84. Thereafter, etching is performed from the p-side contact layer to expose the surface of the GaN crystal substrate 1000.

After etching, a light-transmitting p-side electrode 85 made of Ni/Au and having a thickness of 200 angstroms is formed on almost the entire surface of thep-side contact layer 84, and a bonding pad electrode 86 having a thickness of 0.5 μm is formed on the p-electrode 85.

Then, an n-electrode 87 having a thickness of 0.5 μm was formed on the entire back surface of the GaN crystal substrate 1000.

The obtained wafer was diced from the n-electrode 87 side, and cleaved on the M-plane ((1100) plane) and the plane perpendicular to the M-plane of the GaN substrate 1000, to obtain a 300- μ M square LED chip. The LED emits 520nm green light at 20mA, and has output power and electrostatic withstand voltage 2 times or more higher than those of an LED having a nitride semiconductor device structure grown on a conventional substrate, and very excellent characteristics.

Example 39

In the present embodiment, reference is made to fig. 10.

The Si-doped GaN crystal substrate (substrate 1000) was placed in an MOVPE reaction vessel of an MOVPE apparatus, and the buffer layer 211 and the crack prevention layer 212 were formed on the surface of the Si-doped GaN crystal substrate 1000 without the need to dope the substrate with 1X 10 atoms¹⁹/cm³Al of Si_0.2Ga_0.8A1 st layer of N having a thickness of 20 a and a 2 nd layer of undoped GaN having a thickness of 20 a are alternately grown by 100 layers to form an N-side clad layer 213 of a superlattice structure having a total thickness of 0.4 μm.

Next, on the n-side cladding layer 213, a seed crystal having a thickness of 0.1 μmand doped with 1X 10 atoms was grown¹⁷/cm³And an n-side optical guiding layer 214 made of n-type GaN of Si.

Then, the mixture is doped with 1 × 10¹⁷/cm³In of Si_0.2Ga_0.8N well layer with thickness of 25 angstroms and doped with 1 × 10¹⁷/cm³In of Si_0.01Ga_0.95The barrier layers of N with a thickness of 50 a are alternately grown to form an active layer 215 of a Multiple Quantum Well (MQW) structure with a total thickness of 175 a.

Secondly, the p-side optical guiding layer 217 is grown to have a larger energy gap than the active layer 215Also large, incorporating 1X 10²⁰/cm³P-type Al of Mg_0.3Ga_0.9N constitutes a p-side cap layer 216 with a thickness of 300 angstroms.

Next, a doped 1X 10 layer with a smaller energy gap than p-type cap layer 216 is grown¹⁸/cm³A p-side optical guiding layer 217 composed of GaN as Mg and having a thickness of 0.1 μm.

Then, the catalyst is doped with 1 × 10²⁰/cm³P-type Al of Mg_0.2Ga_0.8N of the first layer 1 with a thickness of 20 angstroms and doped with 1X 10²⁰/cm³A 2 nd layer of p-type GaN of Mg, having a thickness of 20 angstroms, is grown alternately to form a p-side cladding layer 218 of superlattice structure with a total thickness of 0.4 microns.

Finally, the growth is carried out by doping with 1 × 10²⁰/cm³P-side contact layer 219 of p-type GaN of Mg and 150 angstroms in thickness.

The wafer having the nitride semiconductor layer formed in this way was placed in a reaction vessel and annealed at 700 ℃ in a nitrogen atmosphere, thereby further lowering the resistance of the p-type layer. After the annealing, the wafer was taken out of the reaction vessel, and the uppermost p-type contact layer 219 and p-type clad layer 218 were etched by an RIE apparatus to obtain a ridge having a stripe width of 4 μm, and a p-side electrode 220 made of Ni/Au was formed on the entire surface of the ridge. Next, SiO is formed on the exposed surfaces of the p-side cladding layer 48 and the contact layer 49 except the p-side electrode 220₂An insulating film 221, and a pad electrode 222 electrically connected to the p-electrode 220 through the insulating film 221 are formed.

Then, on the entire back surface of the GaN crystal substrate 1000, an n-side electrode 223 made of Ti/Al with a thickness of 0.5 μm was formed, and thereon a thin film made of Au/Sn was formed for metallization with a heat sink.

Thereafter, the wafer is diced from the n-electrode 223 side, and the GaN substrate 1000 is cleaved into strips on the M-plane ((1100) plane; corresponding to the hexagonal-prism side surface in fig. 3) of the GaN substrate 1000, thereby forming resonance surfaces. Forming SiO on both or either one of the resonance surfaces₂And TiO₂Finally cutting the strips in a direction parallel to the p-electrode to obtain a laserAnd (4) a chip. Then, the chip is placed on the heat sink with its surface facing upward (with the substrate and the heat sink facing each other), and the pad electrode 222 is wire-bonded. When the LD device was subjected to laser oscillation at room temperature, the threshold current density was 2.0kA/cm²And a threshold voltage of 4.0V, and a continuous oscillation at an oscillation wavelength of 405nm, and an oscillation life of more than 1000 hours.

Example 40

In the present embodiment, reference is made to fig. 8.

In the case of growing a GaN crystal, undoped GaN crystal 76 was grown in the same manner as in example 35, except that Si was not doped. This GaN crystal 76 (substrate 1000) is supported by a sapphire substrate 11 and used for the following device structure.

On the substrate 1000, the substrate is doped with 1 × 10²⁰/cm³Al of Si_0.2Ga_0.8The 1 st layer of N having a thickness of 20 a and the 2 nd layer of undoped GaN having a thickness of 20 a are alternately grown by 100 layers to form the N-side clad layer 81 of the superlattice structure having a total thickness of 0.4 μm.

Next, In of a single quantum well structure was grown In sequence to a thickness of 20 angstroms on the n-side cladding layer 81_0.4Ga_0.6N active layer 82 made of Mg (1X 10) doped with Mg with a thickness of 0.3 μm²⁰/cm³) Al of (2)_0.2Ga_0.8A p-side cladding layer 83 of N, formed of Mg (1X 10) doped to a thickness of 0.5 μm²⁰/cm³) P-side contact layer 84 of GaN. Next, etching is performed from the p-side contact layer 84 to expose the surface of the n-side cladding layer 81, and the n-side electrode 87 is formed on the surface thereof, while the translucent p-side electrode 85 is formed on almost the entire surface of the p-side contact layer 84, and the translucent p-side electrode 85 is formed on the surface thereofOn the top, a bonding pad electrode 86 is formed. And finally, grinding the sapphire substrate from the back until the thickness of the sapphire substrate becomes about 50 microns, and then scribing on one side of the grinding surface to obtain a 350-micron square device.

The obtained LED device showed about 1.5 times improvement in both output power and electrostatic withstand voltage as compared with the LED device of example 38.

Claims

1. A nitride semiconductor substrate containing a nitride semiconductor crystal and having first and second main faces, wherein a region near the first main face has a relatively small number of crystal defects, and a region near the second main face has a relatively large number of crystal defects.

2. The substrate according to claim 1, wherein first regions each having a relatively small number of crystal defects and second regions each having a relatively large number of crystal defects are unevenly distributed in the first main face.

3. A nitride semiconductor device comprising a nitride semiconductor device structure supported on the nitride semiconductor substrate as defined in claim 1.

4. The device of claim 3, wherein the nitride semiconductor substrate is supported on a foreign substrate made of a material different from the nitride semiconductor.

5. A nitride semiconductor substrate comprising a nitride semiconductor crystal and having first and second main faces, characterized in that the number of crystal defects in a surface region in the first main face is not more than 1 x 10⁵/cm²。

6. The nitride semiconductor substrate according to claim 5, wherein the substrate is doped with n-type impurities.

7. The nitride semiconductor substrate according to claim 6, wherein the n-type impurity has a concentration gradient in the substrate.

8. The nitride semiconductor substrate according toclaim 7, wherein the substrate is grown by a halide vapor phase epitaxial growth method.

9. A nitride semiconductor laser diode device comprising: a nitride semiconductor substrate; and a laser diode element provided over the nitride semiconductor substrate, wherein the nitride semiconductor substrate has been prepared by: (a) forming a first selective growth mask on a support, the support comprising: (i) a hetero substrate made of a material different from the nitride semiconductor and having a main surface; and (ii) a base layer made of a nitride semiconductor formed over the main surface of the dissimilar substrate, the first selective growth mask having a plurality of first windows that selectively expose an upper surface of the base layer of the support; and (b) growing nitride semiconductor portions from the upper surface portion of the base layer exposed by the window by using a gaseous group 3 element source and a gaseous nitrogen element source until the nitride semiconductor portions grown in the adjacent windows are united on the upper surface of the selective growth mask to provide the nitride semiconductor substrate.

10. The device according to claim 9, wherein the laser diode element includes an active layer made of a nitride semiconductor material provided between a p-type cladding layer made of a p-type nitride semiconductor material and an n-type cladding layer made of an n-type nitride semiconductor material.

11. A nitride semiconductor device comprising: a dissimilar substrate having a first main surface which is inclined stepwise from a second main surface of the dissimilar substrate; a nitride semiconductor layer selectively grown on the main surface of the hetero-substrate substantially in a lateral direction; and an active layer including a nitride semiconductor containing indium on the nitride semiconductor layer, wherein an inclination angle θ of the inclined first main surface with respect to a C-plane of the dissimilar substrate is 1 ° or less.

12. The nitride semiconductor device according to claim 11, wherein said stepwise inclined main surface includes a plateau portion a and a plateau portion B, wherein a surface of each plateau portion a is substantially parallel to said second main surface of said dissimilar substrate.

13. A nitride semiconductor device comprising: a nitride semiconductor substrate having a first surface and a second surface; a nitride semiconductor structure having an indium-containing active layer, the nitride semiconductor structure having been grown on the first surface of the nitride semiconductor substrate; and an n-side electrode formed on the second surface of the nitride semiconductor substrate.

14. The nitride semiconductor device according to claim 13, further comprising a buffer layer in contact with the nitride semiconductor substrate, the buffer layer being a strained superlattice structure formed by alternately stacking first and second nitride semiconductor layers having different compositions.

15. The nitride semiconductor device according to claim 14 wherein the buffer layer is operable as an n-side cladding layer that acts as a carrier confining layer.

16. The nitride semiconductor device according to claim 15, wherein the n-side cladding layer is formed by alternately stacking an aluminum-containing nitride semiconductor doped with an n-type impurity and an undoped GaN layer.

17. The nitride semiconductor device according to claim 13 wherein the nitride semiconductor substrate is doped with an n-type impurity.

18. The nitride semiconductor device according to claim 13, wherein the n-side electrode is made of a metal selected from the group consisting of Al, Ti, W, Cu, Zn, Sn, In, multilayers thereof, and alloys thereof.

19. The nitride semiconductor device according to claim 13, wherein the n-side electrode is formed on substantially the entire second surface of the nitride semiconductor substrate.

20. The nitride semiconductor device according to claim 13, wherein the nitride semiconductor device is a light emitting diode or a laser diode device having the n-side electrode provided on the back surface of the nitride semiconductor substrate.

21. The nitride semiconductor device according to claim 13, wherein an n-side electrode having a double-layer structure made of Ti/Al is formed on the nitride semiconductor substrate.

22. The nitride semiconductor device according to claim 13, wherein the number of crystal defects in the nitride semiconductor substrate is less than 1 x 10⁵/cm²。

23. The nitride semiconductor device according to claim 13 wherein the nitride semiconductor substrate is grown by a halide vapor phase epitaxial growth method.

24. The nitride semiconductor device according to claim 13 wherein said nitride semiconductor substrate is doped with an n-type impurity such that said n-type impurity concentration has a gradient, wherein said gradient from said first surface to said surface is from a smaller concentration to a larger concentration.

25. The nitride semiconductor device according to claim 24 wherein the concentration gradient is continuous or stepped.

26. The nitride semiconductor device according to claim 24, wherein the n-type impurity is one element selected from the group consisting of Si, Ge, Sn, and S.