JP2011077109A - Nitride semiconductor light emitting diode element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor light emitting diode element which has high light extraction efficiency and is low in operating voltage. <P>SOLUTION: The nitride semiconductor light emitting diode element includes: an n-type nitride semiconductor layer; a nitride semiconductor light emitting layer provided on the n-type nitride semiconductor layer; a p-type nitride semiconductor layer provided on the nitride semiconductor light emitting layer: an In-containing nitride semiconductor layer provided on the p-type nitride semiconductor layer; and a transparent conductive film provided on the In-containing nitride semiconductor layer. The In-containing nitride semiconductor layer contains In so as to vary in composition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor light emitting diode device.

For example, in a nitride semiconductor light emitting diode element using a group III nitride semiconductor layer represented by the formula of Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) Since the refractive index of the group III nitride semiconductor layer becomes high, for example, about 2.5, total reflection is caused at the interface between the group III nitride semiconductor layer and another material layer (for example, a substrate or a transparent conductive film). This causes a decrease in luminous efficiency.

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2008-294306), a titanium dioxide layer having a desired refractive index and a sufficiently reduced resistivity by adjusting the doping amount of metal impurities such as niobium and tantalum is p-type nitrided. A nitride semiconductor light-emitting diode element used as an electrode in contact with a semiconductor layer is described. In the nitride semiconductor light emitting diode device described in Patent Document 1, light extraction efficiency is improved by suppressing total reflection at the interface between the titanium dioxide layer doped with metal impurities and the GaN layer (for example, Patent (Refer to paragraph [0010] of Document 1).

  Also, for example, in Patent Document 2 (Japanese Patent Laid-Open No. 2007-220971), a nitride semiconductor light emitting diode in which a titanium dioxide layer doped with a metal impurity such as niobium or tantalum is provided in contact with a p-type nitride semiconductor layer An element is described (see, for example, paragraphs [0020] and [0040] of Patent Document 2).

JP 2008-294306 A JP 2007-220971 A

  However, when the titanium dioxide layer doped with a metal impurity such as niobium or tantalum is brought into contact with the p-type nitride semiconductor layer as in the nitride semiconductor light-emitting diode elements described in Patent Document 1 and Patent Document 2 However, the contact resistance between the titanium dioxide layer doped with the metal impurity and the p-type nitride semiconductor layer is high, so that the operating voltage of the nitride semiconductor light emitting diode device is high. This is presumably because the titanium dioxide layer doped with metal impurities exhibits n-type conduction.

  In view of the above circumstances, an object of the present invention is to provide a nitride semiconductor light emitting diode element having high light extraction efficiency and low operating voltage.

  The present invention relates to an n-type nitride semiconductor layer, a nitride semiconductor light-emitting layer provided on the n-type nitride semiconductor layer, a p-type nitride semiconductor layer provided on the nitride semiconductor light-emitting layer, and a p-type An In-containing nitride semiconductor layer provided on the nitride semiconductor layer and a transparent conductive film provided on the In-containing nitride semiconductor layer, and the In-containing nitride semiconductor layer has a composition fluctuation. Is a nitride semiconductor light-emitting diode element containing

  Here, in the nitride semiconductor light-emitting diode device of the present invention, the difference in In content between the region where the In content is maximum and the region where the In content is minimum in the In-containing nitride semiconductor layer. Is preferably 10 atomic% or more.

  In the nitride semiconductor light-emitting diode device of the present invention, the transparent conductive film includes a nitride semiconductor layer having an n-type conductivity, non-doped titanium dioxide not doped with metal impurities, and titanium dioxide doped with metal impurities. Alternatively, either strontium titanate is preferable.

  In the nitride semiconductor light emitting diode element of the present invention, it is preferable that the surface of the transparent conductive film on the side opposite to the In-containing nitride semiconductor layer side has irregularities.

  The nitride semiconductor light-emitting diode element of the present invention further includes a transparent insulating film provided on the transparent conductive film, the surface of the transparent conductive film opposite to the In-containing nitride semiconductor layer side, and the transparent insulating film It is preferable that at least one surface of the surface opposite to the transparent conductive film side has irregularities.

  In the nitride semiconductor light-emitting diode element of the present invention, the thickness of the In-containing nitride semiconductor layer is preferably 5 nm or more.

  In the nitride semiconductor light emitting diode device of the present invention, it is preferable that the thickness of the In-containing nitride semiconductor layer is larger than the thickness of the nitride semiconductor light emitting layer.

  According to the present invention, a nitride semiconductor light emitting diode element having high light extraction efficiency and low operating voltage can be provided.

FIG. 3 is a schematic cross-sectional view of the nitride semiconductor light-emitting diode element according to the first embodiment. 6 is a schematic cross-sectional view illustrating a part of the manufacturing process of the example of the method for manufacturing the nitride semiconductor light-emitting diode element according to the first embodiment. FIG. 6 is a schematic cross-sectional view illustrating another part of the manufacturing process of the example of the method for manufacturing the nitride semiconductor light-emitting diode element according to the first embodiment. FIG. 6 is a schematic cross-sectional view illustrating another part of the manufacturing process of the example of the method for manufacturing the nitride semiconductor light-emitting diode element according to the first embodiment. FIG. 6 is a schematic cross-sectional view illustrating another part of the manufacturing process of the example of the method for manufacturing the nitride semiconductor light-emitting diode element according to the first embodiment. FIG. 6 is a schematic cross-sectional view of a nitride semiconductor light-emitting diode element according to Embodiment 2. FIG. 6 is a schematic cross-sectional view of a nitride semiconductor light-emitting diode element according to Embodiment 3. FIG. 6 is a schematic cross-sectional view of a nitride semiconductor light-emitting diode element according to Embodiment 4. FIG. It is typical sectional drawing illustrated about a part of manufacturing process of the manufacturing method of the nitride semiconductor light-emitting diode element of an Example. It is typical sectional drawing illustrated about another part of manufacturing process of the manufacturing method of the nitride semiconductor light-emitting diode element of an Example. It is typical sectional drawing illustrated about another part of manufacturing process of the manufacturing method of the nitride semiconductor light-emitting diode element of an Example. It is typical sectional drawing illustrated about another part of manufacturing process of the manufacturing method of the nitride semiconductor light-emitting diode element of an Example. It is typical sectional drawing illustrated about another part of manufacturing process of the manufacturing method of the nitride semiconductor light-emitting diode element of an Example. It is typical sectional drawing illustrated about another part of manufacturing process of the manufacturing method of the nitride semiconductor light-emitting diode element of an Example. It is typical sectional drawing illustrated about another part of manufacturing process of the manufacturing method of the nitride semiconductor light-emitting diode element of an Example. It is typical sectional drawing illustrated about another part of manufacturing process of the manufacturing method of the nitride semiconductor light-emitting diode element of an Example. It is typical sectional drawing of the nitride semiconductor light-emitting diode element of an Example.

  Embodiments of the present invention will be described below. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts.

<Embodiment 1>
FIG. 1 is a schematic cross-sectional view of a nitride semiconductor light-emitting diode element according to Embodiment 1 which is an example of the nitride semiconductor light-emitting diode element of the present invention.

  The nitride semiconductor light-emitting diode element according to the first embodiment is provided in contact with the substrate 1, the n-type nitride semiconductor layer 2 provided in contact with the surface of the substrate 1, and the surface of the n-type nitride semiconductor layer 2. The nitride semiconductor light emitting layer 3, the p-type nitride semiconductor layer 4 provided in contact with the surface of the nitride semiconductor light emitting layer 3, and the In-containing nitride provided in contact with the surface of the p-type nitride semiconductor layer 4 The semiconductor layer 5, the transparent conductive film 6 provided in contact with the In-containing nitride semiconductor layer 5, the p-side electrode 8 provided in contact with the surface of the transparent conductive film 6, and the n-type nitride semiconductor layer 2 And an n-side electrode 7 provided in contact with the exposed surface.

  Here, the In-containing nitride semiconductor layer 5 is a p-type nitride semiconductor layer containing In, and the In-containing nitride semiconductor layer 5 has an In composition fluctuation. The “In composition fluctuation” means that the In composition (In content) changes in at least part of at least one of the thickness direction, the length direction, and the lateral direction of the In-containing nitride semiconductor layer 5. Means that

  Hereinafter, an example of a method for manufacturing the nitride semiconductor light-emitting diode element according to the first embodiment will be described.

  First, as shown in the schematic cross-sectional view of FIG. 2, the n-type nitride semiconductor layer 2 and nitride are formed on the surface of the substrate 1 by, for example, MOCVD (Metal Organic Chemical Vapor Deposition). The semiconductor light emitting layer 3 and the p-type nitride semiconductor layer 4 are stacked in this order.

  Here, as the substrate 1, for example, various substrates such as a gallium nitride (GaN) substrate, a silicon carbide (SiC) substrate, a sapphire substrate, a spinel substrate, or a zinc oxide (ZnO) substrate can be used. Note that a sapphire substrate is preferably used as the substrate 1. When a sapphire substrate is used as the substrate 1, the manufacturing cost of the nitride semiconductor light-emitting diode element according to the first embodiment can be reduced, and the nitride semiconductor light-emitting diode element according to the first embodiment can be stably manufactured. Tend to be able to.

Further, as the n-type nitride semiconductor layer 2, for example, a nitride semiconductor layer made of a group III nitride semiconductor represented by the formula of Al _x1 Ga _y1 In _z1 N (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1, (0 ≦ z1 ≦ 1, x1 + y1 + z1 ≠ 0) and a layer doped with an n-type dopant can be stacked. As the n-type dopant, for example, silicon and / or germanium can be doped.

The nitride semiconductor active layer 3 is, for example, a nitride semiconductor well layer (0 ≦ x2 ≦ 1, 0 made of a group III nitride semiconductor represented by the formula Al _x2 Ga _y2 In _z2 N having different compositions. ≦ y2 ≦ 1, 0 ≦ z2 ≦ 1, x2 + y2 + z2 ≠ 0), and a nitride semiconductor composed of a group III nitride semiconductor represented by the formula Al _x3 Ga _y3 In _z3 N having a larger band gap than the nitride semiconductor well layer A stacked body in which barrier layers (0 ≦ x3 ≦ 1, 0 ≦ y3 ≦ 1, 0 ≦ z3 ≦ 1, x3 + y3 + z3 ≠ 0) are alternately stacked one by one can be stacked. The number of nitride semiconductor well layers in the nitride semiconductor active layer 3 can be six layers, for example, but is not limited thereto. The nitride semiconductor active layer 3 may have a single quantum well structure having only one nitride semiconductor well layer or a multiple quantum well structure having a plurality of nitride semiconductor well layers. May be.

In addition, as the p-type nitride semiconductor layer 4, for example, a nitride semiconductor layer made of a group III nitride semiconductor represented by the formula of Al _x4 Ga _y4 In _z4 N (0 ≦ x4 ≦ 1, 0 ≦ y4 ≦ 1, 0 ≦ z4 ≦ 1, x4 + y4 + z4 ≠ 0) and a layer doped with a p-type dopant can be stacked. As the p-type dopant, for example, magnesium and / or zinc can be doped.

  Next, as shown in the schematic cross-sectional view of FIG. 3, the In-containing nitride semiconductor layer 5 is stacked on the surface of the p-type nitride semiconductor layer 4 by, for example, MOCVD.

Here, as the In-containing nitride semiconductor layer 5, for example, a nitride semiconductor layer made of a group III nitride semiconductor represented by the formula of Al _x5 Ga _y5 In _z5 N (0 ≦ x5 ≦ 1, 0 ≦ y5 ≦ 1, A layer doped with a p-type dopant in 0 <z5 ≦ 1) can be stacked.

  The In-containing nitride semiconductor layer 5 has a portion in which the In composition is changed by the In composition fluctuation of the In-containing nitride semiconductor layer 5, but the In composition formed in a part of the In-containing nitride semiconductor layer 5. Since it is possible to reduce the contact resistance with the transparent conductive film 6 at a high part, the operating voltage of the nitride semiconductor light-emitting diode element according to the first embodiment tends to be reduced.

  The reason why the contact resistance between the In-containing nitride semiconductor layer 5 and the transparent conductive film 6 can be reduced is that (i) a piezo electric field is generated in the In-containing nitride semiconductor layer 5, and (ii) In-containing nitride The band gap of the nitride semiconductor constituting the contact surface of the semiconductor layer 5 with the transparent conductive film 6 can be reduced, and (iii) the nitride semiconductor constituting the contact surface of the In-containing nitride semiconductor layer 5 with the transparent conductive film 6 Cause misfit dislocations, and (iv) point defects occur in the nitride semiconductor constituting the contact surface of the In-containing nitride semiconductor layer 5 with the transparent conductive film 6.

  The composition fluctuation of In in the In-containing nitride semiconductor layer 5 is formed when the composition of In changes in thickness units of several nm (1 nm or more and 10 nm or less) in the thickness direction of the In-containing nitride semiconductor layer 5. It is preferable. In this case, since the region with a large In composition in the In-containing nitride semiconductor layer 5 tends to be quantized, the In composition in the region with a large In composition in the In-containing nitride semiconductor layer 5 is active in the nitride semiconductor activity. Even when the In composition of the layer 3 becomes larger, the absorption of light emitted from the nitride semiconductor active layer 3 tends to be suppressed.

  In the In-containing nitride semiconductor layer 5, the difference in In content between the region having the maximum In content and the region having the minimum In content is preferably 10 atomic% or more. In this case, the In-containing nitride semiconductor layer 5 is ensured to transmit light emitted from the nitride semiconductor active layer 3 in a region with a low In composition, and contact resistance with the transparent conductive film 6 in a region with a high In composition. There is a tendency that the layer can be combined with the reduction of. Here, in the In-containing nitride semiconductor layer 5, the region having the maximum In content is preferably a region in contact with the transparent conductive film 6. When the region where the In content of the In-containing nitride semiconductor layer 5 is maximum is a region in contact with the transparent conductive film 6, the contact resistance between the In-containing nitride semiconductor layer 5 and the transparent conductive film 6 is large. Therefore, the operating voltage of the nitride semiconductor light emitting diode element tends to be greatly reduced.

  The composition fluctuation of In in the In-containing nitride semiconductor layer 5 can be evaluated by combining, for example, TEM (Transmission Electron Microscopy) and APT (Three-dimensional atom probe tomography).

  Also, (a) the In-containing nitride semiconductor layer 5 is formed thick, and (b) the In-containing nitride semiconductor layer 5 is heated to a high temperature (for example, 900 ° C. or higher) after the In-containing nitride semiconductor layer 5 is formed. It is possible to further increase the composition fluctuation of In in the In-containing nitride semiconductor layer 5 by adopting at least one of heating to (1).

  That is, (a) when the In-containing nitride semiconductor layer 5 is formed thick, in order to reduce the energy in the In-containing nitride semiconductor layer 5, the In composition separation (a region with a high In composition and a low one) (Separation from the region) is likely to occur, and the composition fluctuation of In in the In-containing nitride semiconductor layer 5 can be increased.

  Here, the thickness of the In-containing nitride semiconductor layer 5 is preferably 5 nm or more. When the thickness of the In-containing nitride semiconductor layer 5 is 5 nm or more, the In compositional fluctuation in the In-containing nitride semiconductor layer 5 tends to be further increased. The thickness of the In-containing nitride semiconductor layer 5 is preferably set to 100 nm or less from the viewpoint of reducing absorption of light emitted from the nitride semiconductor active layer 3.

  The In-containing nitride semiconductor layer 5 is preferably thicker than the nitride semiconductor active layer 3. When the thickness of the In-containing nitride semiconductor layer 5 is larger than the thickness of the nitride semiconductor active layer 3, the In-containing nitride semiconductor suffers from subsequent thermal damage due to the thin thickness of the nitride semiconductor active layer 3. Since it can be made smaller than the layer 5, there is a tendency that a decrease in the light emission efficiency of the nitride semiconductor light emitting diode element can be suppressed.

  (B) After the In-containing nitride semiconductor layer 5 is formed (may be after another layer is formed on the In-containing nitride semiconductor layer 5), the In-containing nitride semiconductor layer 5 is formed. When heated to a high temperature (for example, 900 ° C. or higher), the composition separation of In can be promoted by the heat energy in the heating.

  Here, it is preferable that the thickness of the thermal damage layer generated when the In-containing nitride semiconductor layer 5 is damaged by heat by heating the In-containing nitride semiconductor layer 5 to a high temperature is 5 nm or more. When the thickness of the thermal damage layer is 5 nm or more, energy due to distortion caused by thermal damage is accumulated, and In composition separation is likely to occur in the thermal damage layer in order to reduce the accumulated energy. Become. Therefore, also from this viewpoint, the thickness of the In-containing nitride semiconductor layer 5 is preferably 5 nm or more.

  Next, as shown in the schematic cross-sectional view of FIG. 4, a transparent conductive film 6 is laminated on the surface of the In-containing nitride semiconductor layer 5 by, for example, a sputtering method to form a laminate.

  Here, as the transparent conductive film 6, it is preferable to use a material that can transmit light emitted from the nitride semiconductor active layer 3 and has a small refractive index difference from the In-containing nitride semiconductor layer 5. In this case, the amount of light totally reflected at the interface between the In-containing nitride semiconductor layer 5 and the transparent conductive film 6 among the light emitted from the nitride semiconductor active layer 3 can be reduced. It tends to be possible to improve the light extraction efficiency of the nitride semiconductor light emitting diode element No. 1.

For example, the In-containing nitride semiconductor layer 5 is made of a group III nitride semiconductor represented by the above formula of Al _x5 Ga _y5 In _z5 N (0 ≦ x5 ≦ 1, 0 ≦ y5 ≦ 1, 0 <z5 ≦ 1). When a layer doped with a p-type dopant is used for the nitride semiconductor layer, the transparent conductive film 6 is an n-type conductivity nitride semiconductor layer, non-doped titanium dioxide that is not doped with metal impurities, metal It is preferable to use titanium dioxide or strontium titanate doped with impurities. In this case, since the difference in refractive index between the In-containing nitride semiconductor layer 5 and the transparent conductive film 6 is small (for example, the refractive index of the In-containing nitride semiconductor layer 5 is approximately 2.5, while the transparent conductive film The amount of light totally reflected at the interface between the In-containing nitride semiconductor layer 5 and the transparent conductive film 6 out of the light emitted from the nitride semiconductor active layer 3. There is a tendency that the light extraction efficiency of the nitride semiconductor light-emitting diode device of the first embodiment can be improved.

  Here, as the nitride semiconductor layer having n-type conductivity, for example, n-type GaN can be used.

  Non-doped titanium dioxide that is not doped with metal impurities includes, for example, niobium, tantalum, molybdenum, arsenic, antimony, aluminum, tungsten, titanium, cerium, copper, chromium, and platinum, which are not doped with metal impurities. Titanium or the like can be used.

  The titanium dioxide doped with metal impurities is, for example, at least one metal impurity selected from the group consisting of niobium, tantalum, molybdenum, arsenic, antimony, aluminum, tungsten, titanium, cerium, copper, chromium, and platinum. Can be used.

As the transparent conductive film 6, strontium titanate can also be used.
Especially, as a material of the transparent conductive film 6, it is preferable to use titanium dioxide doped with niobium at a concentration of 10 atomic% or less. When titanium dioxide doped with niobium at a concentration of 10 atomic% or less is used as the material of the transparent conductive film 6, the nitride semiconductor active layer 3 has a low resistivity of, for example, 1 × 10 ⁻³ Ωcm or less. The transparent conductive film 6 having a high transmittance of, for example, 80% with respect to visible light including light emitted from can be obtained. Therefore, the light extraction efficiency of the nitride semiconductor light-emitting diode element according to the first embodiment is further improved and the operating voltage tends to be further reduced.

  Next, as shown in the schematic cross-sectional view of FIG. 5, a part of the surface of the n-type nitride semiconductor layer 2 is exposed by removing a part of the stacked body shown in FIG. 4 by etching or the like.

  Thereafter, as shown in FIG. 1, the n-side electrode 7 is formed on the exposed surface of the n-type nitride semiconductor layer 2 by, for example, EB vapor deposition, and the p-side electrode 8 is formed on the surface of the transparent conductive film 6. As a result, the nitride semiconductor light-emitting diode element of the first embodiment can be obtained.

  In the nitride semiconductor light-emitting diode device of the first embodiment having the configuration shown in FIG. 1 manufactured as described above, the nitride semiconductor constituting the contact surface with the transparent conductive film 6 in the In-containing nitride semiconductor layer 5 In addition, the In composition fluctuation is provided so that the In composition becomes large, and the transparent conductive film 6 made of a material having a small refractive index difference from the In-containing nitride semiconductor layer 5 is brought into contact with the In-containing nitride semiconductor layer 5. Provided.

  Therefore, the In-containing nitride semiconductor layer 5 out of the light generated from the nitride semiconductor light-emitting layer 3 by flowing a current from the p-side electrode 8 to the n-side electrode 7 of the nitride semiconductor light-emitting diode element of the first embodiment. The amount of light totally reflected at the interface between the transparent conductive film 6 and the transparent conductive film 6 can be reduced, and the contact resistance between the In-containing nitride semiconductor layer 5 and the transparent conductive film 6 can be reduced.

  Thereby, the nitride semiconductor light-emitting diode element of the first embodiment can be a nitride semiconductor light-emitting diode element having high light extraction efficiency and low operating voltage.

<Embodiment 2>
FIG. 6 is a schematic cross-sectional view of a nitride semiconductor light-emitting diode element according to Embodiment 2, which is another example of the nitride semiconductor light-emitting diode element of the present invention. The nitride semiconductor light-emitting diode element according to the second embodiment is characterized in that the surface of the substrate 1 on the n-type nitride semiconductor layer 2 side has irregularities 9.

  In the nitride semiconductor light-emitting diode element according to the second embodiment, the substrate 9 of the light generated from the nitride semiconductor light-emitting layer 3 is provided by providing the unevenness 9 on the surface of the substrate 1 on the n-type nitride semiconductor layer 2 side. Due to the light scattering effect and diffraction effect due to the unevenness 9 on the surface of the substrate 1 of the light traveling to the 1 side, more light can be extracted outside than the nitride semiconductor light emitting diode element of the first embodiment.

  Therefore, the nitride semiconductor light-emitting diode element of the second embodiment can further increase the light extraction efficiency as compared with the nitride semiconductor light-emitting diode element of the first embodiment.

  The unevenness 9 on the surface of the substrate 1 can be formed, for example, by etching the surface of the substrate 1 on the n-type nitride semiconductor layer 2 side.

  Here, a plurality of recesses in the unevenness 9 on the surface of the substrate 1 are formed at intervals of, for example, 0.05 μm or more and 10 μm or less, and each recess is formed at a depth of, for example, 0.05 μm or more and 10 μm or less.

  Since the description other than the above in the second embodiment is the same as that in the first embodiment, the description thereof is omitted here.

<Embodiment 3>
FIG. 7 is a schematic cross-sectional view of a nitride semiconductor light-emitting diode element according to Embodiment 3, which is another example of the nitride semiconductor light-emitting diode element of the present invention. In the nitride semiconductor light-emitting diode element of the third embodiment, the surface of the substrate 1 on the n-type nitride semiconductor layer 2 side has irregularities 9 and the transparent conductive film 6 on the In-containing nitride semiconductor layer 5 side. It is characterized in that the surface on the opposite side of the surface has irregularities 10.

  In the nitride semiconductor light-emitting diode device of the third embodiment, the surface of substrate 1 on the n-type nitride semiconductor layer 2 side is the surface opposite to unevenness 9 and transparent conductive film 6 on the In-containing nitride semiconductor layer 5 side. By providing the projections and depressions 10 on the respective surfaces, the nitrides of the first and second embodiments can be obtained by the light scattering effect and the diffraction effect of the projections and depressions 9 on the surface of the substrate 1 and the projections and depressions 10 on the surface of the transparent conductive film 6. More light than the semiconductor light emitting diode element can be extracted to the outside.

  Therefore, the nitride semiconductor light-emitting diode element of the third embodiment can further increase the light extraction efficiency as compared with the nitride semiconductor light-emitting diode elements of the first and second embodiments.

  Here, a plurality of recesses in the unevenness 10 on the surface of the transparent conductive film 6 are formed at intervals of, for example, 0.05 μm or more and 10 μm or less, and each recess is formed at a depth of, for example, 0.05 μm or more and 10 μm or less. .

  Further, in the nitride semiconductor light-emitting diode element of the third embodiment, the unevenness 9 is not formed on the surface of the substrate 1 and only on the surface opposite to the In-containing nitride semiconductor layer 5 side of the transparent conductive film 6. The unevenness 10 may be formed.

  Further, the unevenness 10 on the surface of the transparent conductive film 6 can be formed, for example, by etching the surface of the transparent conductive film 6 after the formation of the transparent conductive film 6.

  Since the description other than the above in the third embodiment is the same as that in the first and second embodiments, the description thereof is omitted here.

<Embodiment 4>
FIG. 8 is a schematic cross-sectional view of a nitride semiconductor light-emitting diode element according to Embodiment 4, which is another example of the nitride semiconductor light-emitting diode element of the present invention. In the nitride semiconductor light emitting diode element of the fourth embodiment, a transparent insulating film 20 is provided so as to be in contact with the surface of the transparent conductive film 6, and the surface of the transparent insulating film 20 opposite to the transparent conductive film 6 side is provided. It has a feature that it has irregularities 21.

  In the nitride semiconductor light emitting diode element according to the fourth embodiment, the unevenness 21 on the surface of the transparent insulating film 20 is provided by providing the unevenness 21 on the surface of the transparent insulating film 20 opposite to the transparent conductive film 6 side. Due to the light scattering effect and diffraction effect, the light extraction efficiency tends to be increased.

Here, as the transparent insulating film 20, a film that can transmit light emitted from the nitride semiconductor active layer 3 and has a resistivity of 1 × 10 ⁴ Ωcm or more can be used.

  Further, the unevenness 21 on the surface of the transparent insulating film 20 can be formed, for example, by etching the surface of the transparent insulating film 20 after the transparent insulating film 20 is formed.

  Further, a plurality of recesses in the unevenness 21 on the surface of the transparent insulating film 20 are formed at intervals of, for example, 0.05 μm or more and 10 μm or less, and each recess is formed at a depth of, for example, 0.05 μm or more and 10 μm or less.

  In the nitride semiconductor light emitting diode element of the fourth embodiment, in addition to forming the irregularities 21 on the surface of the transparent insulating film 20, for example, as in the third embodiment, the In-containing nitride of the transparent conductive film 6 is used. Concavities and convexities may be formed on at least part of the surface opposite to the physical semiconductor layer 5 side.

  Since the description other than the above in the fourth embodiment is the same as that in the first to third embodiments, the description thereof is omitted here.

(Example)
First, a sapphire substrate 11 shown in the schematic cross-sectional view of FIG. 9 is prepared, and the sapphire substrate 11 is set in a reaction furnace of an MOCVD apparatus. Then, the surface of the sapphire substrate 11 is cleaned by raising the temperature of the sapphire substrate 11 to 1050 ° C. while flowing hydrogen gas into the reactor. Here, in the unevenness on the surface of the sapphire substrate 11, a plurality of recesses are formed at intervals of 2 μm, and each recess is formed to a depth of 1 μm.

  Next, the temperature of the sapphire substrate 11 is lowered to 510 ° C., hydrogen gas as a carrier gas, ammonia gas and TMG (trimethylgallium) gas as a source gas are flown into the reactor, and the uneven surface (C A non-doped GaN buffer layer (not shown) having a thickness of about 20 nm is stacked on the surface) by MOCVD.

Next, the temperature of the sapphire substrate 11 is raised to 1050 ° C., and hydrogen gas as a carrier gas, ammonia gas and TMG gas as source gases, and silane as impurity gases are flowed into the reactor to a thickness of 6 μm on the GaN buffer layer. The Si-doped n-type GaN underlayer (carrier concentration: 1 × 10 ¹⁸ / cm ³ ) is laminated by MOCVD.

Next, a thickness of 0.5 μm is formed on the Si-doped n-type GaN foundation layer in the same manner as the Si-doped n-type GaN foundation layer except that Si is doped so that the carrier concentration becomes 5 × 10 ¹⁸ / cm ^3. The Si-doped n-type GaN contact layer is laminated by MOCVD.

  As described above, as shown in FIG. 9, the Si-doped n-type GaN base layer and the Si-doped n-type GaN contact layer are formed on the uneven surface (C-plane) of the sapphire substrate 11 via the non-doped GaN buffer layer (not shown). N-type nitride semiconductor layers 12 are stacked in this order.

Next, in a state where the temperature of the sapphire substrate 11 is set to 700 ° C., nitrogen gas as a carrier gas, ammonia gas, TMG gas, and TMI gas as a source gas are flowed into the reaction furnace, and the n-type nitride semiconductor layer 12 is formed. As shown in the schematic cross-sectional view of FIG. 10, a non-doped In _0.2 Ga _0.8 N well layer having a thickness of 2.5 nm and a non-doped GaN barrier layer having a thickness of 10 nm are alternately stacked in this order for six periods. Then, an MQW light emitting layer 13 having a multiple quantum well structure is stacked on the n-type nitride semiconductor layer 12 by MOCVD. Needless to say, when the non-doped GaN barrier layer is stacked, no TMI gas is allowed to flow into the reactor.

  Next, the temperature of the sapphire substrate 11 is maintained at 700 ° C., nitrogen gas as the carrier gas, ammonia gas and TMG gas as the source gas are flowed into the reactor, and as shown in the schematic cross-sectional view of FIG. A non-doped GaN evaporation prevention layer 14 having a thickness of 15 nm is laminated on the MQW light emitting layer 13 by MOCVD.

Next, the temperature of the sapphire substrate 11 is raised to 950 ° C., hydrogen gas as the carrier gas, ammonia gas, TMG gas and TMA (trimethylaluminum) gas as the source gas, and CP ₂ Mg (biscyclopentadienylmagnesium as the impurity gas) ) Gas was allowed to flow into the reactor to form an Mg-doped p-type Al _0.2 Ga _0.8 N layer having a thickness of about 20 nm doped with Mg at a concentration of 1 × 10 ²⁰ / cm ³ on the non-doped GaN evaporation prevention layer 14. Lamination is performed by MOCVD.

Next, while maintaining the temperature of the sapphire substrate 11 at 950 ° C., hydrogen gas as the carrier gas, ammonia gas and TMG gas as the source gas, and CP ₂ Mg gas as the impurity gas are allowed to flow into the reactor, and Mg doping p An Mg-doped p-type GaN layer having a thickness of 80 nm doped with Mg at a concentration of 1 × 10 ²⁰ / cm ³ is laminated on the type Al _0.2 Ga _0.8 N layer by MOCVD.

As described above, as shown in the schematic cross-sectional view of FIG. 12, the p-type in which the Mg-doped p-type Al _0.2 Ga _0.8 N layer and the Mg-doped p-type GaN layer are stacked in this order on the non-doped GaN evaporation prevention layer 14. A nitride semiconductor layer 15 is stacked.

Next, the temperature of the sapphire substrate 11 is lowered to 700 ° C., hydrogen gas as the carrier gas, ammonia gas, TMG gas and TMI gas as the source gas, and CP ₂ Mg gas as the impurity gas are allowed to flow into the reaction furnace. As shown in the schematic cross-sectional view, a 10 nm thick Mg-doped p-type InGaN layer 16 doped with Mg at a concentration of 1 × 10 ²⁰ / cm ³ is formed on the p-type nitride semiconductor layer 15 by MOCVD. Laminate.

  Here, the Mg-doped p-type InGaN layer 16 is formed while changing the flow rate of the TMI gas introduced into the reactor of the MOCVD apparatus, and the Mg-doped p-type InGaN layer 16 includes the Mg-doped p-type InGaN layer. In In compositional fluctuations, the In composition ratio is changed in the thickness direction of 16 in the range of 0.15 to 0.3.

The outermost surface of the Mg-doped p-type InGaN layer 16 is a nitride semiconductor region having the largest In composition, and the composition of only the nitride semiconductor excluding Mg in that region is In _0.3 Ga _0.7 N. It was confirmed by a method combining TEM and APT.

Further, the composition of only the nitride semiconductor excluding Mg in the region of the nitride semiconductor having the smallest In composition in the Mg-doped p-type InGaN layer 16 is In _0.15 Ga _0.85 N by a method combining TEM and APT. confirmed.

  Therefore, in the Mg-doped p-type InGaN layer 16, the difference in In content between the region where the In content is maximum and the region where the In content is minimum is 15 atomic%, which is 10 atomic% or more. It has become.

  Further, the refractive index of the nitride semiconductor constituting the outermost surface of the Mg-doped p-type InGaN layer 16 is 2.5.

  Next, in a state where the temperature of the sapphire substrate 11 is maintained at 700 ° C., hydrogen gas is flowed as a carrier gas into the reaction furnace to anneal the wafer after the Mg-doped p-type InGaN layer 16 is stacked.

  Next, the wafer after the lamination of the Mg-doped p-type InGaN layer 16 is taken out of the reactor, and as shown in the schematic cross-sectional view of FIG. 14, niobium is 6 atomic% on the outermost surface of the Mg-doped p-type InGaN layer 16. A titanium dioxide layer 17 having a thickness of 400 nm doped at a concentration of 1 nm was formed by sputtering. Here, the refractive index of the titanium dioxide layer 17 is 2.5.

  Thereafter, a photomask formed in a predetermined shape is formed on the surface of the titanium dioxide layer 17, and then the wafer after the formation of the titanium dioxide layer 17 is etched by RIE (Reactive Ion Etching). As shown in the schematic cross-sectional view, the surface of the n-type nitride semiconductor layer 12 is exposed.

  Further, after a photomask formed in a predetermined shape is formed on the surface of the titanium dioxide layer 17, the titanium dioxide layer 17 is etched by RIE, and as shown in the schematic sectional view of FIG. Asperities are formed on the surface.

  Next, as shown in the schematic cross-sectional view of FIG. 17, a Ti layer and an Al layer are formed on the exposed surface of the n-type nitride semiconductor layer 12 and the surface of the titanium dioxide layer 17 by the EB vapor deposition method, respectively. An n-side pad electrode 19 and a p-side pad electrode 18 each formed of a laminate with layers are formed.

  Thereafter, each wafer after the formation of the p-side pad electrode 18 and the n-side pad electrode 19 is divided into a plurality of chips to obtain an LED (Light Emitting Diode) chip.

  In the nitride semiconductor light-emitting diode device of the example manufactured as described above, the Mg-doped p-type InGaN layer 16 is provided with In composition fluctuation, and a region with a large In composition is in contact with the titanium dioxide layer 17. Therefore, the contact resistance between the Mg-doped p-type InGaN layer 16 and the titanium dioxide layer 17 can be lowered, and the operating voltage of the nitride semiconductor light-emitting diode element is lowered.

  In addition, in the nitride semiconductor light emitting diode element of the example manufactured as described above, the Mg dioxide doped p-type InGaN layer 16 and the titanium dioxide layer 17 made of a material having a small refractive index difference are used. Since the total reflection of light at the sea surface between the p-type InGaN layer 16 and the titanium dioxide layer 17 can be suppressed, the light extraction efficiency of the nitride semiconductor light-emitting diode element is increased.

  Further, in the nitride semiconductor light-emitting diode device of the example manufactured as described above, since the surface of the titanium dioxide layer 17 opposite to the Mg-doped p-type InGaN layer 16 is provided with unevenness, nitriding is performed. The light extraction efficiency of the semiconductor light emitting diode device is further increased.

  Furthermore, in the nitride semiconductor light-emitting diode device of the example manufactured as described above, the Mg composition p-type InGaN layer 16 has a thickness of 5 nm or more, so that the composition fluctuation of In increases.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be suitably used for a nitride semiconductor light emitting diode element.

  1 substrate, 2,12 n-type nitride semiconductor layer, 3 nitride semiconductor light emitting layer, 4,15 p-type nitride semiconductor layer, 5 In-containing nitride semiconductor layer, 6 transparent conductive film, 7 n-side electrode, 8 p Side electrode, 9, 10, 21 Concavity and convexity, 20 Transparent insulating film, 11 Sapphire substrate, 13 MQW light emitting layer, 14 Non-doped GaN evaporation prevention layer, 16 Mg-doped p-type InGaN layer, 17 Titanium dioxide layer, 18 p-side pad electrode, 19 n-side pad electrode.

Claims (7)

an n-type nitride semiconductor layer;
A nitride semiconductor light emitting layer provided on the n-type nitride semiconductor layer;
A p-type nitride semiconductor layer provided on the nitride semiconductor light emitting layer;
An In-containing nitride semiconductor layer provided on the p-type nitride semiconductor layer;
A transparent conductive film provided on the In-containing nitride semiconductor layer,
The nitride semiconductor light-emitting diode element, wherein the In-containing nitride semiconductor layer contains In so as to have a composition fluctuation.   In the In-containing nitride semiconductor layer, a difference in In content between a region where the In content is maximum and a region where the In content is minimum is 10 atomic% or more, Item 14. The nitride semiconductor light-emitting diode device according to Item 1.   The transparent conductive film is any one of a nitride semiconductor layer having n-type conductivity, non-doped titanium dioxide not doped with metal impurities, titanium dioxide doped with metal impurities, or strontium titanate. The nitride semiconductor light-emitting diode element according to claim 1 or 2.   4. The nitride semiconductor light-emitting diode element according to claim 1, wherein a surface of the transparent conductive film opposite to the In-containing nitride semiconductor layer side has irregularities. 5. A transparent insulating film provided on the transparent conductive film;
The surface of the transparent conductive film opposite to the In-containing nitride semiconductor layer side and the surface of the transparent insulating film opposite to the transparent conductive film side have at least one surface having irregularities. The nitride semiconductor light-emitting diode device according to any one of claims 1 to 3, wherein   6. The nitride semiconductor light-emitting diode element according to claim 1, wherein the In-containing nitride semiconductor layer has a thickness of 5 nm or more.   The nitride semiconductor light-emitting diode element according to claim 1, wherein a thickness of the In-containing nitride semiconductor layer is thicker than a thickness of the nitride semiconductor light-emitting layer.

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