JP2016001650A - Group 13 element nitride crystal layer and functional device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal layer and a function element which, in a group 13 element nitride crystal layer, obtains desired conductivity and can suppress functional heterogeneity due to heterogeneity in the conductivity of the crystal layer.SOLUTION: On the surface 3a of a crystal layer 3 made of group 13 element nitride, a first region 8, and a second region 9 having carrier concentration and defect density which are higher than those of the first region 8 are present. The ratio (second region/first region) of a product of the carrier concentration and the defect density of the second region 9 to the product of the carrier concentration and the defect density of the first region 8 is 10 or more and 1000 or less.

Description

  The present invention relates to a group 13 element nitride crystal layer and a functional element. The present invention relates to a power device used in, for example, a technical field required to have high quality, for example, a high color rendering blue LED called a post fluorescent lamp, a blue-violet laser for high-speed high-density optical memory, and an inverter for a hybrid vehicle. Can be used.

In recent years, semiconductor devices such as blue LEDs, white LEDs, and blue-violet semiconductor lasers are manufactured using group 13 element nitrides such as gallium nitride, and application of the semiconductor devices to various electronic devices has been actively studied. Yes.
As the application of white LEDs expands, LED chips are required to have higher performance. High performance means high efficiency and high brightness.

  The HVPE method is well known as a method for manufacturing a gallium nitride free-standing substrate. Among these, as a method for obtaining high-quality crystals, a DEEP method (Patent Document 1, Non-Patent Document 1) and a VAS method (Patent Documents 2 and 3) are disclosed.

In a structure generally used at present, a dislocation density of the light emitting part is 10 × 10 ⁹ to 10 × 10 ¹⁰ / cm ^{2 in} a structure in which a GaN thin film (light emitting part) is formed on a sapphire substrate by MOCVD. Therefore, non-radiative recombination of carriers occurred at the dislocation part, and it was difficult to improve luminous efficiency.

  On the other hand, the flux method is one of liquid phase methods. In the case of gallium nitride, the temperature required for crystal growth of gallium nitride is reduced to about 800 ° C. and the pressure is reduced to several MPa by using metallic sodium as the flux. Can do. Specifically, nitrogen gas is dissolved in a mixed melt of metallic sodium and metallic gallium, and gallium nitride becomes supersaturated and grows as crystals. In such a liquid phase method, dislocations are less likely to occur than in a gas phase method, so that high-quality gallium nitride having a low dislocation density can be obtained (Patent Document 4).

SEI Technical Review No. 175 in July 2009

Patent-3801125 Patent-3631724 Patent-4396816 JP2009-012986

  For example, in order to produce an LED or a laser diode having a vertical structure, the group 13 element nitride crystal layer needs to have high conductivity. However, when Si or oxygen is doped into the crystal layer to provide conductivity, the conductivity of the crystal layer becomes non-uniform, resulting in leakage current and non-uniform emission intensity distribution. .

  An object of the present invention is to obtain desired conductivity in a group 13 element nitride crystal layer and to suppress non-uniform function due to non-uniform conductivity of the crystal layer.

The present invention is a crystal layer made of a group 13 element nitride grown on a seed crystal made of a group 13 element nitride,
A first region and a second region having a higher carrier concentration and defect density than the first region exist on the surface of the crystal layer, and the product of the carrier concentration and the defect density of the first region. The ratio of the product of the carrier concentration and the defect density of the second region to the second region (second region / first region) is 10 or more and 1000 or less.

  The present invention also relates to a composite substrate comprising a seed crystal composed of a group 13 element nitride and the group 13 element nitride crystal layer provided on the seed crystal.

  In addition, the present invention relates to a functional element comprising the group 13 element nitride crystal layer and a functional layer made of a group 13 element nitride formed on a surface of the crystal layer. It is.

  As described above, doping is necessary to impart desired conductivity to the group 13 element nitride crystal layer. However, it has been difficult to dope the entire crystal layer uniformly during doping. In particular, it has been found that the crystallinity tends to deteriorate in a region where the doping amount is large in the crystal layer, and the dislocation density is increased. As a result, in a region with high conductivity, the crystallinity is deteriorated and a current easily flows. Therefore, current concentration locally occurs in that region. As a result, it has been found that local heat generation occurs and the emission intensity becomes non-uniform.

  The present inventor further examined the reason why the functional degradation of such a group 13 element nitride crystal layer occurs. That is, on the surface with good crystallinity, the dopant is not easily taken into the crystal, and the crystal growth mode is changed by the dopant element spouted around the surface, so that smooth growth cannot be performed and the crystallinity is deteriorated. An area arises. And it was thought that a large amount of dopant element was taken in the region where the crystallinity was deteriorated.

  Therefore, it is difficult to solve this problem. Even if the amount of dopant is simply increased, the overall conductivity is not improved, and a region having a high defect density and high carrier concentration, where current concentration easily occurs, is dominant. Decline is likely to occur. On the other hand, when the amount of dopant is reduced, it becomes difficult to obtain desired conductivity.

  Based on these findings, the present inventor has devised various growth conditions to provide a first solution to the product of the carrier concentration and the defect density of the first region having a relatively low carrier concentration and defect density on the surface of the crystal layer. When the ratio of the product of the carrier concentration and the defect density in the second region (second region / first region) is 10 or more and 1000 or less, local current concentration in the second region is suppressed, and the element As a result, we succeeded in suppressing the functional decline. That is, it has been found that this allows the carrier concentration distribution to be adjusted to such an extent that the performance of functional elements such as LEDs is not affected, thereby achieving both improvement in crystal quality.

(A) is a schematic diagram which shows the group 13 element nitride crystal layer 2 formed on the seed crystal 1, (b) is a schematic diagram which shows the composite substrate 4, (c) is a composite substrate 4 is a schematic diagram showing a functional element 15 formed by forming a functional element structure 5 on 4. (A) is a schematic diagram showing a nucleus 6 generated on the seed crystal 1, and (b) is a schematic diagram showing a growth direction from the nucleus 6. It is a schematic diagram for demonstrating the surface state of the crystal layer of this invention. It is a photograph which shows the cathode minence of the surface of the crystal layer of embodiment of this invention. It is a SEM photograph about the same part as FIG. It is the photograph which wrote the crystal axis in the photograph of FIG. It is explanatory drawing of the photograph of FIG.

The present invention will be further described below with reference to the drawings as appropriate.
In a preferred embodiment, as shown in FIG. 1A, a group 13 element nitride crystal layer 2 is formed on the surface 1a of the seed crystal 1 made of a group 13 element nitride. Next, preferably, the surface 2a of the crystal layer 2 is polished to make the crystal layer 3 thinner as shown in FIG. 3a is the surface after polishing.

  A functional layer 5 is formed on the surface 3a of the composite substrate 4 obtained in this way by a vapor phase method to obtain a functional element 15 (FIG. 1C). However, 5a, 5b, 5c, 5d, and 5e are epitaxial layers designed according to the use grown on the surface 3a.

  It is not essential to polish the surface 2a of the group 13 element nitride crystal layer 2 before forming the functional layer 5, and the growth surface can be used as it is. In addition, after the composite substrate 4 of FIG. 1B is manufactured, the seed crystal 1 can be removed by grinding or the like, and then the functional layer 5 can be formed on the surface of the crystal layer 3.

(Seed crystal)
In the present invention, the seed crystal is not particularly limited as long as the group 13 element nitride crystal layer can be grown. The group 13 element referred to here is a group 13 element according to the periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like. This group 13 element nitride is particularly preferably GaN, AlN, or GaAlN.

The seed crystal may form a self-supporting substrate (support substrate) by itself, or may be a seed crystal film formed on another support substrate. This seed crystal film may be a single layer, or may include a buffer layer on the support substrate side.
The seed crystal film is preferably formed by vapor deposition, but metal organic chemical vapor deposition (MOCVD:
Examples thereof include a metal organic chemical vapor deposition (HVAP) method, a hydride vapor phase epitaxy (HVPE) method, a pulse excitation deposition (PXD) method, an MBE method, and a sublimation method. Metalorganic chemical vapor deposition is particularly preferred. The growth temperature is preferably 950 to 1200 ° C.

When the seed crystal film is formed on the support substrate, the material of the single crystal constituting the support substrate is not limited, but sapphire, AlN template, GaN template, GaN free-standing substrate, silicon single crystal, SiC single crystal, MgO single Examples thereof include crystals, spinel (MgAl ₂ O ₄ ), LiAlO ₂ , LiGaO ₂ , LaAlO ₃ , LaGaO ₃ , NdGaO _{3 and} other perovskite complex oxides, SCAM (ScAlMgO ₄ ). The composition formula _{[A 1-y (Sr 1-} x Ba x) y ] _{[(Al 1-z Ga z)} 1-u · D u ] _O 3 (A is a rare earth element; D is niobium and One or more elements selected from the group consisting of tantalum; y = 0.3-0.98; x = 0-1; z = 0-1; u = 0.15-0.49; x + z = 0 .1 to 2) cubic perovskite structure composite oxides can also be used.

  The growth direction of the group 13 element nitride crystal layer may be the normal direction of the c-plane of the wurtzite structure, or may be the normal direction of the a-plane and the m-plane.

The dislocation density on the surface of the seed crystal is desirably low from the viewpoint of reducing the dislocation density of the group 13 element nitride crystal layer provided on the seed crystal. From this viewpoint, the dislocation density of the seed crystal is preferably 7 × 10 ⁸ cm ⁻² or less, and more preferably 5 × 10 ⁸ cm ⁻² or less. Further, the lower the dislocation density of the seed crystal, the better from the viewpoint of quality, so there is no particular lower limit, but in general, it is often 5 × 10 ⁷ cm ⁻² or more.

(Group 13 element nitride crystal layer)
The manufacturing method of the gallium nitride crystal layer is not particularly limited, but metal organic chemical vapor deposition (MOCVD) method, hydride vapor deposition (HVPE) method, pulse excitation deposition (PXD) method, MBE method, sublimation Examples thereof include gas phase methods such as the method, and liquid phase methods such as the flux method.

  In the group 13 element nitride constituting the crystal layer, the group 13 element is a group 13 element according to a periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like. This group 13 element nitride is particularly preferably GaN, AlN, or GaAlN. Examples of the additive include carbon, low melting point metals (tin, bismuth, silver, gold) and high melting point metals (transition metals such as iron, manganese, titanium, and chromium). The low melting point metal may be added for the purpose of preventing oxidation of sodium, and the high melting point metal may be mixed from a container in which a crucible is put or a heater of a growth furnace.

  In the present invention, the surfaces 2a and 3a of the crystal layers 2 and 3 have a first region 8 and a higher carrier concentration (dopant concentration) and defect density than the first region 8, as shown in FIG. There is a second region 9 having. The ratio of the product of the carrier concentration and the defect density of the second region 9 to the product of the carrier concentration and the defect density of the first region 8 (second region / first region) is 10 or more and 1000 or less. It is.

  Ratio of product of carrier concentration (dopant concentration) and defect density of second region 9 to product of carrier concentration (dopant concentration) and defect density of first region 8 (second region / first region) Is 10 or more, more preferably 20 or more. Further, if this ratio becomes too large, current concentration tends to occur. From this point of view, it is set to 1000 or less.

  Here, when the dopant is an n-type dopant and is Si, Ge, or oxygen, since the activation rate is as high as 90% or higher, it is not exactly the same, but the dopant concentration is almost equal to the carrier concentration. Can be considered. Hereinafter, although described as “carrier concentration” from the viewpoint of the present invention of leakage prevention due to current concentration, the activation rate may be regarded as almost 100%, and this may be read as “dopant concentration”.

  In a preferred embodiment, the ratio of the area of the second region 9 to the area of the first region 8 (second region / first region) is 10 or less. That is, by preventing the area ratio of the region 9 having a high carrier concentration and high defect density from increasing to a certain extent, the first region (low carrier) is present at the same time while maintaining the desired conductivity as a whole. Local concentration of current can be suppressed by concentration and low defect density.

  In a preferred embodiment, the first region 8 forms a continuous phase and the second region 9 forms a dispersed phase separated by the first region 8 on the crystal layer surface. For example, in the example of FIG. 3, the first region 8 has an elongated shape and is connected to each other to form a continuous phase. The second regions 9 are each surrounded by the first region 8 to form a dispersed phase.

  However, the continuous phase means that the first region 8 is continuous on the surface of the crystal layer, but does not necessarily require that all of the first regions 8 are completely continuous. It is allowed that a small amount of the first region 8 is separated from the other first regions 8 within a range that does not affect the entire pattern.

  The dispersed phase means that the second region 9 is roughly divided by the first region 8 and is divided into a number of regions that are not connected to each other. However, even if the second region 9 is separated by the first region 8 on the surface of the crystal layer, the second region 9 is allowed to continue inside the crystal layer.

  In a preferred embodiment, the first region 8 includes a portion 8a extending substantially parallel to the m-plane of the group 13 element nitride. This is because, in crystal growth, a dopant is not taken in so much in a direction substantially parallel to the m-plane, or in a direction extending about 60 ° or 120 ° with respect to the m-plane, and the first region 8 is formed by growing as it is. It is thought that. Further, the second region 9 is generated by discharging the dopant to the outside of the first region 8. The first regions are connected to each other during crystal growth to form a continuous phase, and the second region incorporating the dopant is partitioned by the first region.

  For example, in the example of FIG. 3, the first region 8 extends in an elongated line shape and includes many portions 8 a substantially parallel to the m-plane. At the same time, a portion 8b inclined about 60 ° and a portion 8c inclined 120 ° with respect to the m-plane are included. In other words, the second region 8 includes a portion extending in a direction parallel to the m plane and a portion extending in a direction rotationally symmetric about the c axis from the direction parallel to the m plane. Of course, the first region 8 may further include a portion that bends in another direction.

  FIG. 4 is a cathode minence photograph taken in the embodiment of the present invention, and FIG. 6 is a diagram in which each axis is entered in FIG. FIG. 7 shows a summary of the photographs in FIGS. 4 and 6. As shown in FIG. 7, the first region 8 and the second region 9 can be confirmed even in an actual photograph. In the first region 8, the presence of each portion 8a, 8b, 8c can be confirmed.

In a preferred embodiment, the crystal layer is formed by a liquid phase method, preferably a flux method, the carrier concentration of the first region is 1 × 10 ¹⁷ / cm ³ or less, and the defect density of the first region is Is 1 × 10 ⁴ / cm ² or less, the carrier concentration of the second region is 1 × 10 ¹⁸ / cm ³ or more, and the defect density of the second region is 1 × 10 ⁴ / cm ² or more, 1 × 10 ⁷ / cm ² or less.

In the present embodiment, the carrier concentration in the first region is more preferably 5 × 10 ¹⁶ / cm ³ or less. The defect density in the first region is more preferably 5 × 10 ³ / cm ² or less.

In the present embodiment, the carrier concentration in the second region is more preferably 5 × 10 ¹⁸ / cm ³ or more.

In a preferred embodiment, the crystal layer is formed by a vapor phase method, the carrier concentration in the first region is 1 × 10 ¹⁸ / cm ³ or less, and the defect density in the first region is 1 ×. 10 ⁶ / cm ² or less, the carrier concentration of the second region is 1 × 10 ¹⁹ / cm ³ or more, and the defect density of the second region is 1 × 10 ⁸ / cm ² or more.

In the present embodiment, the carrier concentration in the first region is more preferably 5 × 10 ¹⁷ / cm ³ or less. In the present embodiment, the defect density in the first region is more preferably 5 × 10 ⁵ / cm ² or less. In the present embodiment, the carrier concentration in the second region is more preferably 5 × 10 ¹⁸ / cm ³ or less. In the present embodiment, the defect density in the second region is more preferably 2 × 10 ⁸ / cm ² or more.

  In a particularly preferred embodiment, the group 13 element nitride crystal layer is grown by a flux method. At this time, the type of the flux is not particularly limited as long as the group 13 element nitride can be generated. In a preferred embodiment, a flux containing at least one of an alkali metal and an alkaline earth metal is used, and a flux containing sodium metal is particularly preferred.

  For the flux, a raw material of a group 13 element is mixed and used. As the raw material, a single metal, an alloy, or a compound can be applied, but a single metal of a group 13 element is preferable from the viewpoint of handling.

In the present invention, the first region and the second region are measured and identified as follows.
Using a cathodoluminescence measuring instrument (for example, MP series manufactured by Horiba, Ltd.), the magnification is 50 to 500 times, and the image capturing area is 0.1 to 1 mm square.

(Control example of growth of group 13 element nitride crystal layer)
The suitable control method for growing the group 13 element nitride crystal layer of this invention is illustrated.

  In the case of the flux method, preferably, in the initial stage, when promoting the growth in the vertical direction, by using a supersaturation as low as possible and suppressing the convection of the melt, only the concentration gradient as much as possible is used as the driving force. Grow.

Specifically, in the initial stage, it is preferable to grow by the following method.
(1A) By increasing the average growth temperature of the melt in the crucible, the degree of supersaturation is increased to suppress the formation of nuclei 6 (FIG. 2).
(2A) By holding the upper part of the crucible at a higher temperature than the bottom part of the crucible, the convection of the melt in the crucible is suppressed.
(3A) Do not stir the melt or reduce the stirring speed.
(4A) Lower the partial pressure of the nitrogen-containing gas.

  Thereby, in the initial stage, the formation of the nucleus 6 is suppressed, and the crystal grows upward from the nucleus 6 (arrow C).

  In a preferred embodiment, after stopping the initial stage conditions, the growth conditions are changed to increase the crystal growth rate (late stage). As a result, the crystal growth 7 is mainly in the lateral direction (arrows A and B).

For example, the following conditions can be applied.
(Early stage)
(1A) The average growth temperature of the melt in the crucible is set to 870 to 885 ° C.
(2A) Keep the temperature at the top of the crucible 0.5-1 ° C. higher than the temperature at the bottom of the crucible.
(3A) The melt is not stirred or the stirring speed is 30 rpm or less. The stirring direction is one direction.
(4A) The partial pressure of the nitrogen-containing gas is set to 3.5 to 3.8 MPa.

In the later stage, the following is preferable.
(1B) The average growth temperature of the melt in the crucible is set to 850 to 860 ° C. Moreover, the difference of the average growth temperature with an initial stage shall be 10-25 degreeC.
(3B) Stir the melt and periodically change the stirring direction. In addition, stop the crucible rotation when changing the direction of rotation. In this case, the rotation stop time is preferably 100 seconds to 6000 seconds, and more preferably 600 seconds to 3600 seconds. The rotation time before and after the rotation stop time is preferably 10 seconds to 600 seconds, and the rotation speed is preferably 10 to 30 rpm.
(4B) The partial pressure of the nitrogen-containing gas is set to 4.0 to 4.2 MPa. Moreover, it is 0.2 to 0.5 MPa higher than the partial pressure of the nitrogen-containing gas in the initial stage.

  Here, preferably, in the latter stage, the low dislocation region and the carrier concentration are balanced by gradually changing the manufacturing conditions. Specifically, the stirring speed of the melt is gradually increased, or the holding time at the maximum rotation speed during stirring is gradually increased.

In the flux method, a single crystal is grown in an atmosphere containing a gas containing nitrogen atoms. This gas is preferably nitrogen gas, but may be ammonia.
The gas other than the gas containing nitrogen atoms in the atmosphere is not limited, but an inert gas is preferable, and argon, helium, and neon are particularly preferable.

  In the initial stage of the growth, it is preferably held for 1 hour or more, more preferably 2 hours or more under the conditions (1A) to (4A) described above. Further, the holding time in the initial stage is preferably 10 hours or less.

  From the viewpoint of the present invention, the ratio (mol ratio) of Group 13 element nitride / flux (for example, sodium) in the melt is preferably increased, preferably 18 mol% or more, and more preferably 25 mol% or more. However, if this ratio becomes too large, the crystal quality tends to deteriorate, so 40 mol% or less is preferable.

(Processing and morphology of crystal layer)
In the preferred embodiment, the group 13 element nitride crystal layer is disk-shaped, but other forms such as a square plate may be used. In a preferred embodiment, the crystal layer has a diameter of 25 mm or more. Thereby, an easy-to-handle crystal layer suitable for mass production of functional elements can be provided.

The case where the surface of the group 13 element nitride crystal layer is ground and polished will be described.
Grinding refers to scraping off the surface of an object by bringing fixed abrasive grains, which are fixed by abrasive bonds, into contact with the object while rotating at high speed. A rough surface is formed by this grinding. When grinding the bottom surface of a gallium nitride substrate, it is formed of high hardness SiC, Al ₂ O ₃ , diamond, CBN (cubic boron nitride, the same shall apply hereinafter), etc., and contains abrasive grains having a particle size of about 10 μm to 100 μm Fixed abrasives are preferably used.

In addition, polishing (lapping) means that a surface plate and an object are brought into contact with each other through loose abrasive grains (referred to as non-fixed abrasive grains hereinafter), or fixed abrasive grains and an object. The surface of the object is polished by rotating and rotating each other. By this polishing, a surface having a surface roughness smaller than that in the case of grinding and a surface rougher than that in the case of fine polishing (polishing) is formed. Abrasive grains formed of SiC, Al ₂ O ₃ , diamond, CBN, or the like having high hardness and having a particle size of about 0.5 μm to 15 μm are preferably used.

  Fine polishing (polishing) means that the polishing pad and the object are brought into contact with each other through rotating abrasive grains, or the fixed abrasive grains and the object are brought into contact with each other while being rotated, and the surface of the object is brought into contact. This means smoothing by smoothing. By such fine polishing, a crystal growth surface having a smaller surface roughness than that in the case of polishing is formed.

(Functional layer and functional element)
The functional layer described above may be a single layer or a plurality of layers. As functions, it can be used for white LEDs with high luminance and high color rendering, blue-violet laser disks for high-speed and high-density optical memory, power devices for inverters for hybrid vehicles, and the like.

  When a semiconductor light emitting diode (LED) is fabricated on a group 13 element nitride crystal layer by a vapor phase method, preferably by a metal organic chemical vapor deposition (MOCVD) method, the dislocation density inside the LED becomes equal to that of the crystal layer.

  The film forming temperature of the functional layer is preferably 950 ° C. or higher, more preferably 1000 ° C. or higher, from the viewpoint of the film forming speed. Further, from the viewpoint of suppressing defects, the film formation temperature of the functional layer is preferably 1200 ° C. or lower, and more preferably 1150 ° C. or lower.

  The material of the functional layer is preferably a group 13 element nitride. Group 13 elements are Group 13 elements according to the periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like.

  The light-emitting element structure includes, for example, an n-type semiconductor layer, a light-emitting region provided on the n-type semiconductor layer, and a p-type semiconductor layer provided on the light-emitting region. In the light emitting element 15 of FIG. 1C, an n-type contact layer 5a, an n-type cladding layer 5b, an active layer 5c, a p-type cladding layer 5d, and a p-type contact layer 5e are formed on the composite substrate 4. A light emitting element structure 5 is formed.

  The light emitting structure may further include an n-type semiconductor layer electrode, a p-type semiconductor layer electrode, a conductive adhesive layer, a buffer layer, a conductive support, and the like (not shown).

  In this light emitting structure, when light is generated in the light emitting region due to recombination of holes and electrons injected from the semiconductor layer, the light is transmitted to the translucent electrode or the group 13 element nitride single crystal film side on the p-type semiconductor layer. Take out from. The translucent electrode is a translucent electrode made of a metal thin film or a transparent conductive film formed on almost the entire surface of the p-type semiconductor layer.

The material of the semiconductor constituting the n-type semiconductor layer and the p-type semiconductor layer is made of a III-V group compound semiconductor, and the following can be exemplified.
Al _y In _x Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1)
Examples of the doping material for imparting n-type conductivity include silicon, germanium, and oxygen. Moreover, magnesium and zinc can be illustrated as a dope material for providing p-type conductivity.

  Examples of the growth method of each semiconductor layer constituting the light emitting structure include various vapor phase growth methods. For example, an organic metal compound vapor phase growth method (MOCVD (MOVPE) method), a molecular beam epitaxy method (MBE method), a hydride vapor phase growth method (HVPE method), or the like can be used. Among them, the MOCVD method can obtain a semiconductor layer with good crystallinity and flatness. In the MOCVD method, alkyl metal compounds such as TMG (trimethyl gallium) and TEG (triethyl gallium) are often used as the Ga source, and gases such as ammonia and hydrazine are used as the nitrogen source.

  The light emitting region includes a quantum well active layer. The material of the quantum well active layer is designed so that the band gap is smaller than the materials of the n-type semiconductor layer and the p-type semiconductor layer. The quantum well active layer may have a single quantum well (SQW) structure or a multiple quantum well (MQW) structure. The material of a quantum well active layer can illustrate the following.

  As a preferred example of the quantum well active layer, an AlxGa1-xN / AlyGa1-yN-based quantum well active layer (x = 0.15, y = 0.20) having a thickness of 3 nm / 8 nm, respectively, 3 An MQW structure formed for 10 to 10 periods is mentioned.

(Example 1)
(Preparation of seed crystal substrate)
A 50-nm low-temperature GaN buffer layer was deposited on a c-plane sapphire substrate having a diameter of 52 mm and a thickness of 500 μm at 530 ° C. using a HVPE method, and then a GaN seed crystal having a thickness of 150 μm at 1100 ° C. The membrane was laminated. The defect density by TEM observation was 1 × 10 ⁸ / cm ² . The seed crystal substrate 1 was obtained by ultrasonically washing with an organic solvent and ultrapure water for 10 minutes and then drying.

(Liquid phase GaN crystal growth)
In a glove box filled with an inert gas, metal Ga and metal Na were weighed at a molar ratio of 20:80, and placed together with the seed crystal substrate at the bottom of an alumina crucible. Further, germanium was added as a dopant in an amount of 0.8 mol% with respect to gallium. The crucibles are stacked in a plurality of stages and stored in a stainless steel holding container (inside container), and the crucibles are stored in a plurality of stages and stored in a stainless steel holding container (inner container). . This was placed on a turntable provided in a pressure vessel that had been vacuum-baked in advance, and then the pressure vessel was covered and sealed. Next, the inside of the pressure vessel was evacuated to 0.1 Pa or less with a vacuum pump. The inner container and the inner container used in this experiment are those described in Patent Document 4.

  Subsequently, by heating the heater installed inside the pressure vessel, the raw material in the crucible was melted to produce a Ga—Na mixed melt. Crystal growth was started by introducing nitrogen gas from a nitrogen gas cylinder until the temperature of the crucible became 880 ° C. until the temperature became 3.8 MPa. This temperature-pressure condition is a condition in which the degree of supersaturation is low and hardly grows. Under the main growth conditions in which no agitation is actively performed, nuclei are generated while local growth and meltback occur, and a GaN crystal of about 2 microns grows after 5 hours (initial stage).

  Thereafter, the temperature of the crucible was lowered to 850 ° C. over 20 minutes, and the pressure was changed to 4.0 MPa. At the same time, stirring by continuous inversion of the turntable was started to change the crystal growth mode. The rotation conditions were a clockwise rotation and a counterclockwise rotation at a constant cycle at a speed of 20 rpm around the central axis. Acceleration time = 6 seconds, holding time = 200 seconds, deceleration time = 6 seconds, stop time = 1 second. This state was maintained for 1 hour. At this stage, grain growth occurs, and the nuclei grow as they are gathered. Thereafter, the inversion frequency was changed (the holding time was slowly increased to 1000 seconds over 20 hours), and the acceleration, deceleration time, and stop time were not changed. Under these conditions, the grains grew larger with further association, during which the GaN crystal thickness increased by approximately 100 microns (late stage).

  Subsequently, it was naturally cooled to room temperature, and the grown gallium nitride crystal plate was recovered. When the thickness of the gallium nitride grown on the seed crystal substrate was measured using a 12-stage crucible, the minimum thickness was about 90 microns, the maximum thickness was about 130 microns, the average was 110 microns, and the standard deviation The variation was as small as 10 microns.

  Next, laser lift-off processing is performed, the gallium nitride crystal layer is separated from the sapphire substrate, the both sides of the obtained gallium nitride crystal layer are polished, the total thickness is 200 microns, and the outer peripheral portion is beveled Thus, a gallium nitride wafer having a diameter of 2 inches was produced. No cracks were observed.

When the polished surface was observed by the cathodoluminescence method, it was confirmed that the surface was divided into a second region 9 where light emission was observed brightly and a dark first region 8 (see FIGS. 4 and 6). ). FIG. 5 is an SEM photograph of the same portion as FIG. Moreover, the dark spot density was calculated by counting the number of dark spots in a 100 μm × 100 μm square region, and was defined as the defect density. The defect density in the second region 9 was 1 × 10 ⁴ / cm ² to 1 × 10 ⁷ / cm ² . On the other hand, the defect density in the first region 9 was 2 × 10 ³ / cm ² to 1 × 10 ⁴ / cm ² smaller than the entrance density in the second region.

Next, in-plane carrier concentration distribution was measured in 5 mm steps using terahertz waves. Next, the defect density in the 0.1 mm × 0.1 mm square region was measured by the cathodoluminescence method at the center of the measurement location. The defect density in the second region 9 having a carrier concentration of 1 × 10 ¹⁸ / cm ³ or more was 2 × 10 ⁴ / cm ² , whereas the defect in the region having a carrier concentration of 1 × 10 ¹⁷ / cm ³ or less. The density was 5 × 10 ³ / cm ² and a significant difference was observed.

  The ratio of the product of the carrier concentration and the defect density in the second region to the product of the carrier concentration and the defect density in the first region (second region / first region) was 10 to 200. .

  A blue LED structure was formed by MOCVD using this gallium nitride substrate. A comb-shaped p-type electrode pattern (1 mm × 1 mm square) was formed thereon, and then the sapphire substrate was separated using a laser lift-off technique, and the n-type electrode was formed after the separation surface was polished smoothly. . The LED chip having a vertical structure was prepared by cutting into 1 mm × 1 mm square chips by laser dicing. When the internal quantum efficiency at 350 mA drive was measured, a high value of about 80% was obtained. The emission intensity was uniform in the plane.

  When the internal quantum efficiency was further increased to 1000 mA, the high value of 70% was maintained. The rate of decrease in internal quantum efficiency relative to the case of 300 mA was 10%.

(Example 2)
An experiment was conducted in the same manner as in Example 1 except that GaN was regrown using the HVPE method instead of regrowth by GaN using the liquid phase method.
A hydride VPE method using gallium chloride (GaCl), which is a reaction product of gallium (Ga) and hydrogen chloride (HCl), as a group III source and ammonia (NH ₃ ) gas as a group V source was used. A sapphire substrate on which a MOCVD GaN film (thickness: 2 microns) was formed was set in a hydride VPE growth apparatus and heated to a growth temperature of 1000 ° C. in an ammonia atmosphere. After the growth temperature was stabilized, an HCl flow rate was supplied at 40 cc / min, and an n-type GaN crystal was grown at an NH ₃ flow rate of 1000 cc / min and a silane (SiH ₄ ) flow rate of 0.01 cc / min. . After maintaining for 2 hours to grow about 100 microns, the NH3 flow rate was gradually increased to 2000 cc / min over 3 hours and further grown to 150 microns. After cooling to room temperature in the NH ₃ gas atmosphere, taken out of the growth apparatus.

  Next, laser lift-off processing was performed to separate the gallium nitride crystal layer from sapphire. By polishing both surfaces of the obtained gallium nitride crystal layer, the total thickness was 200 microns, and the outer peripheral portion was beveled to prepare a gallium nitride wafer having a diameter of 2 inches. No cracks were observed.

The defect density was measured by the cathodoluminescence method. In the polished surface, it was confirmed that it was divided into a second region where light emission was observed brightly and a dark first region. The defect density was calculated by counting the number of dark spots in a 100 μm × 100 μm square area. The defect density of the bright second region was 1 × 10 ⁸ / cm ^{2 to} 5 × 10 ⁸ / cm ² . On the other hand, the defect density of the dark first region was smaller than that of the relatively bright first region, and was 2 × 10 ⁵ / cm ² to 1 × 10 ⁶ / cm ² .

Next, in-plane carrier concentration distribution was measured in 5 mm steps using terahertz waves. Next, the defect density in the 0.1 mm × 0.1 mm square region was measured by the cathodoluminescence method at the center of the measurement location. The defect density in the region where the carrier concentration is 1 × 10 ¹⁸ / cm ³ or more was 2 × 10 ⁸ / cm ² , whereas the defect density in the region where the carrier concentration was 1 × 10 ¹⁷ / cm ³ or less was 7 ×. It was 10 ⁵ / cm ² , and a significant difference was observed.

The ratio of the product of the carrier concentration and the defect density in the second region to the product of the carrier concentration and the defect density in the first region (second region / first region) was 500 to 1000. .

  A blue LED structure was formed by MOCVD using this gallium nitride substrate. A comb-shaped p-type electrode pattern (1 mm × 1 mm square) was formed thereon, and then the sapphire substrate was separated using a laser lift-off technique, and the n-type electrode was formed after the separation surface was polished smoothly. . An LED chip having a vertical structure was formed by cutting into 1 mm × 1 mm square chips by laser dicing.

  When the internal quantum efficiency at 350 mA drive was measured, a high value of about 65% was obtained. The emission intensity was uniform in the plane. Furthermore, when the driving current was increased to 1000 mA and the internal quantum efficiency was measured, it was maintained at a relatively high value of 50%. The decrease in internal quantum efficiency was about 15% compared to when driving at 350 mA.

(Comparative Example 1)
In Example 1, in the latter stage of crystal growth, the reversal frequency during stirring was changed (the holding time increased slowly over 20 hours up to 1000 seconds). In this comparative example, an experiment was performed in the same manner as in Example 1 except that the reversal frequency was not changed and crystal growth was consistently performed under the same rotation conditions. That is, under the conditions of this comparative example, the rotation was performed at a speed of 20 rpm around the central axis in a clockwise direction and a counterclockwise direction. Acceleration time = 6 seconds, holding time = 200 seconds, deceleration time = 6 seconds, stop time = 1 second.

About the obtained crystal layer, the defect density was measured by the cathodoluminescence method. The cathode minence image was divided into a bright light emitting region and a weak light emitting region. The defect density in the brightly emitting region was 2 to 5 × 10 ⁷ / cm ² , and the defect density in the region with low emission intensity was almost uniform and 3 × 10 ⁶ / cm ² .

  As a precaution, the ratio of the product of the carrier concentration and the defect density of the second region to the product of the carrier concentration and the defect density of the first region (second region / first region) is When measured in the same manner, it was almost 2000.

  The LED was made in the same manner as in Example 1, and the light emission characteristics were examined. As a result, the leakage current when 2V was applied was as large as 100 microamperes, and many LEDs had poor light emission characteristics. There were only half.

(Comparative Example 2)
The experiment was performed in the same manner as in Example 2 except that the growth conditions of the HVPE method were set so that the NH3 flow rate was constant at 1000 cc / min.

The defect density of the polished surface of the crystal layer was measured by the cathodoluminescence method. The cathode minence image was divided into a bright light emitting region and a weak light emitting region. The defect density in the brightly emitting region was 2 to 5 × 10 ⁸ / cm ² , and the defect density in the region with low emission intensity was almost uniform and 3 × 10 ⁷ / cm ² .

  As a precaution, the ratio of the product of the carrier concentration and the defect density of the second region to the product of the carrier concentration and the defect density of the first region (second region / first region) is When measured in the same manner, it was 10,000, and the defect density was large in the region where the carrier concentration was high.

  When LEDs were prepared in the same manner as in Example 1 and the light emission characteristics thereof were examined, the leakage current when 2 V was applied was as large as 150 microamperes, and many LEDs had poor light emission characteristics. Only less than half were able to produce good LEDs.

Claims (12)

A crystal layer made of a group 13 element nitride,
A first region and a second region having a higher carrier concentration and defect density than the first region are present on the surface of the crystal layer, and the carrier concentration and defect density of the first region are present. The ratio of the product of the carrier concentration of the second region and the defect density to the product of the second region (second region / first region) is 10 or more and 1000 or less, the group 13 element nitride A crystal layer consisting of   The said surface WHEREIN: Said 1st area | region forms the continuous phase, Said 2nd area | region forms the dispersed phase divided by said 1st area | region. Crystal layer.   3. The crystal layer according to claim 1, wherein the first region includes a portion extending substantially parallel to the m-plane of the group 13 element nitride. The crystal layer is formed by a flux method, the carrier concentration of the first region is 1 × 10 ¹⁷ / cm ³ or less, and the defect density of the first region is 1 × 10 ⁴ / cm ² or less. Yes, the carrier concentration of the second region is 1 × 10 ¹⁸ / cm ³ or more, and the defect density of the second region is 1 × 10 ⁴ / cm ² or more and 1 × 10 ⁷ / cm ² or less. The crystal layer according to any one of claims 1 to 3, wherein the crystal layer is characterized in that The crystal layer is formed by a vapor phase method, the carrier concentration of the first region is 1 × 10 ¹⁸ / cm ³ or less, and the defect density of the first region is 1 × 10 ⁶ / cm ² or less. The carrier concentration of the second region is 1 × 10 ¹⁹ / cm ³ or more, and the defect density of the second region is 1 × 10 ⁸ / cm ² or more. The crystal layer according to any one of claims 1 to 3. The crystal layer is formed by a flux method, the dopant concentration of the first region is 1 × 10 ¹⁷ / cm ³ or less, and the defect density of the first region is 1 × 10 ⁴ / cm ² or less. Yes, the dopant concentration of the second region is 1 × 10 ¹⁸ / cm ³ or more, and the defect density of the second region is 1 × 10 ⁴ / cm ² or more and 1 × 10 ⁷ / cm ² or less. The crystal layer according to any one of claims 1 to 3, wherein the crystal layer is characterized in that The crystal layer is formed by a vapor phase method, the dopant concentration of the first region is 1 × 10 ¹⁸ / cm ³ or less, and the defect density of the first region is 1 × 10 ⁶ / cm ² or less. The dopant concentration of the second region is 1 × 10 ¹⁹ / cm ³ or more, and the defect density of the second region is 1 × 10 ⁸ / cm ² or more. The crystal layer according to any one of claims 1 to 3.   The crystal layer according to claim 1, wherein the surface of the crystal layer is a polished surface.   A composite comprising a seed crystal composed of a group 13 element nitride, and a group 13 element nitride crystal layer according to any one of claims 1 to 8 provided on the seed crystal. substrate.   A group 13 element nitride crystal layer according to any one of claims 1 to 8, and a functional layer made of a group 13 element nitride formed on the surface of the crystal layer. A functional element.   The functional element according to claim 10, wherein the functional layer has a light emitting function.   The functional element according to claim 10 or 11, further comprising a seed crystal made of a group 13 element nitride, wherein the group 13 element nitride crystal layer is provided on the seed crystal.

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