Nitride semiconductor light-emitting element and method for manufacturing nitride semiconductor light-emitting element

Abstract

The purpose of the present invention is to provide a nitride semiconductor light-emitting element that emits ultraviolet light and that has improved emission output. The light-emitting element includes an n-side semiconductor layer, a p-side semiconductor layer, and an active layer between the n-side semiconductor layer and the p-side semiconductor layer. The active layer includes, in order from the n-side semiconductor layer side, a first barrier layer containing Al and an n-type impurity, a first well layer containing Al and emitting ultraviolet light, a second barrier layer containing Al, and a second well layer containing Al and emitting ultraviolet light, the peak of the highest n-type impurity concentration in the first barrier layer being located on the p-side semiconductor layer side, the peak of the highest n-type impurity concentration in the second barrier layer being located on the p-side semiconductor layer side, and the peak of the highest n-type impurity concentration in the second barrier layer being located on the p-side semiconductor layer side. The Al composition ratio of the first barrier layer is higher than the Al composition ratio of the second barrier layer.

Description

Technical Field

[0001] The present invention relates to a nitride semiconductor light-emitting element and a method for manufacturing the nitride semiconductor light-emitting element. Background Art

[0002] The development of nitride semiconductor light-emitting elements that emit ultraviolet light is progressing. For example, Patent Document 1 discloses a light-emitting element having a light-emitting layer that emits ultraviolet light.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 9-153645 Summary of the invention

[0006] Problems to be solved by the invention

[0007] Nitride semiconductor light-emitting elements that emit ultraviolet light have room for improvement in light output compared to light-emitting elements that emit visible light.

[0008] Therefore, an object of the present invention is to provide a nitride semiconductor light-emitting element that emits ultraviolet light and has improved light emission output, and a method for manufacturing the nitride semiconductor light-emitting element.

[0009] Technical solutions to solve problems

[0010] The present invention provides a nitride semiconductor light emitting element, which comprises an n-side semiconductor layer, a p-side semiconductor layer, and an active layer located between the n-side semiconductor layer and the p-side semiconductor layer, wherein:

[0011] The active layer includes, in order from the n-side semiconductor layer side: a first barrier layer containing Al and n-type impurities, a first well layer containing Al and emitting ultraviolet light, a second barrier layer containing Al, and a second well layer containing Al and emitting ultraviolet light,

[0012] The peak of the highest n-type impurity concentration in the first barrier layer is located on the p-side semiconductor layer side.

[0013] The Al composition ratio of the first barrier layer is higher than the Al composition ratio of the second barrier layer.

[0014] In addition, the present invention provides a method for manufacturing a nitride semiconductor light-emitting element, comprising:

[0015] A step of forming an n-side semiconductor layer;

[0016] forming an active layer on the n-side semiconductor layer;

[0017] forming a p-side semiconductor layer on the active layer,

[0018] The process of forming the active layer includes:

[0019] A step of forming a first barrier layer by forming a first layer containing Al and an n-type impurity on the n-side semiconductor layer, and then forming a second layer containing Al and the n-type impurity at a higher concentration than the first layer on the first layer;

[0020] forming a first well layer containing Al and emitting ultraviolet light on the first barrier layer;

[0021] forming, on the first well layer, a second barrier layer including Al and n-type impurities, wherein the Al composition ratio is lower than the Al composition ratio of the first layer and the Al composition ratio of the second layer;

[0022] A step of forming a second well layer containing Al and emitting ultraviolet light on the second barrier layer.

[0023] Effects of the Invention

[0024] According to a nitride semiconductor light emitting element and a method for manufacturing the nitride semiconductor light emitting element according to an embodiment of the present invention, it is possible to provide a nitride semiconductor light emitting element that emits ultraviolet light with high light output and a method for manufacturing the nitride semiconductor light emitting element. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a cross-sectional view showing the structure of a nitride semiconductor light emitting element according to one embodiment of the present invention.

[0026] Figure 2 Yes means Figure 1 The diagram shows the structure of the active layer and electron blocking layer of the nitride semiconductor light-emitting element.

[0027] Figure 3 This is a cross-sectional view when a base layer is formed on the upper surface of a substrate in a method for manufacturing a light emitting element according to an embodiment of the present invention.

[0028] Figure 4 In a method for manufacturing a light emitting element according to an embodiment of the present invention, Figure 3 A cross-sectional view showing a superlattice layer formed on a base layer.

[0029] Figure 5 In a method for manufacturing a light emitting element according to an embodiment of the present invention, Figure 4 A cross-sectional view showing a state where an n-side semiconductor layer is formed on the superlattice layer.

[0030] Figure 6In a method for manufacturing a light emitting element according to an embodiment of the present invention, Figure 5 A cross-sectional view showing a state where an active layer is formed on the n-side semiconductor layer.

[0031] Figure 7 In a method for manufacturing a light emitting element according to an embodiment of the present invention, Figure 6 A cross-sectional view showing a case where an electron blocking layer is formed on the active layer.

[0032] Figure 8 In a method for manufacturing a light emitting element according to an embodiment of the present invention, Figure 7 A cross-sectional view showing a case where a p-side semiconductor layer is formed on the electron blocking layer.

[0033] Fig. 9 It is a plan view showing a specific example of a nitride semiconductor light emitting element according to one embodiment of the present invention.

[0034] Fig.10 About Fig. 9 Cross-sectional view of line XX.

[0035] Description of Reference Numerals

[0036] 1 Nitride semiconductor light-emitting device

[0037] 10 substrates

[0038] 11. Basal layer

[0039] 12 superlattice layers

[0040] 20n-side semiconductor layer

[0041] 21 Undoped layer

[0042] 22n side contact layer

[0043] 201 First exposure

[0044] 202 Second exposure

[0045] 203 Third exposure

[0046] 204 Fourth exposure

[0047] 30 active layers

[0048] 31First barrier layer

[0049] 32First well layer

[0050] 33 Second barrier layer

[0051] 34 Second well layer

[0052] 40Electron blocking layer

[0053] 50p side semiconductor layer

[0054] 51 first p-side semiconductor layer

[0055] 52 second p-side semiconductor layer

[0056] 501 Base

[0057] 502 extension

[0058] 60 n electrode

[0059] 61 n-side electrode

[0060] 62 n-side pad electrode

[0061] 70 p electrode

[0062] 71 first p-side electrode

[0063] 72 second p-side electrode

[0064] 73p side pad electrode

[0065] 80 protective film

[0066] 100Semiconductor structures DETAILED DESCRIPTION

[0067] Hereinafter, embodiments or examples for implementing the present invention will be described with reference to the accompanying drawings. It should be noted that the light emitting element and the method for manufacturing the light emitting element described below are used to embody the technical concept of the present invention, and the present invention is not limited to the following contents unless otherwise specified.

[0068] In the various drawings, the same figure numbers are sometimes marked for components with the same functions. Considering the ease of description or understanding of the main points, they are sometimes divided into implementation methods or examples for convenience, but the structures shown in different implementation methods or examples may be partially replaced or combined. In the implementation methods or examples described later, the description of matters common to the above is omitted, and only the different points are described. In particular, the same effects brought about by the same structure are not mentioned one by one for each implementation method or example. In order to make the description clear, the size or positional relationship of the components shown in the various drawings is sometimes expressed in an exaggerated manner. For example, the drawings attached to this specification are schematic diagrams that mainly show the stacked structure and do not necessarily accurately reflect the film thickness of each layer.

[0069] Implementation

[0070] Figure 1 It is a schematic cross-sectional view of a nitride semiconductor light emitting element 1 according to the embodiment. Figure 2It is a cross-sectional schematic diagram showing an enlarged view of a part of the semiconductor structure 100 , namely, the active layer 30 and the electron blocking layer 40 .

[0071] like Figure 1 , 2 As shown, the nitride semiconductor light emitting element 1 has a substrate 10 and a semiconductor structure 100 disposed on the substrate 10. The semiconductor structure 100 includes an n-side semiconductor layer 20, a p-side semiconductor layer 50, each formed of a nitride semiconductor, and an active layer 30 located between the n-side semiconductor layer 20 and the p-side semiconductor layer 50 and emitting ultraviolet light. In addition, the semiconductor structure 100 includes a base layer 11 and a superlattice layer 12 located between the substrate 10 and the n-side semiconductor layer 20, and an electron blocking layer 40 located between the active layer 30 and the p-side semiconductor layer 50. The nitride semiconductor light emitting element 1 has an n-electrode 60 electrically connected to the n-side semiconductor layer 20, and a p-electrode 70 electrically connected to the p-side semiconductor layer 50.

[0072] Moreover, the active layer 30 includes, from the n-side semiconductor layer 20 side, a first barrier layer 31 containing Al and n-type impurities, a first well layer 32 containing Al and emitting ultraviolet light, a second barrier layer 33 containing Al, and a second well layer 34 containing Al and emitting ultraviolet light, and the peak of the highest n-type impurity concentration in the first barrier layer 31 is located on the p-side semiconductor layer 50 side.

[0073] In addition, the Al composition ratio of the first barrier layer 31 is higher than the Al composition ratio of the second barrier layer 33 .

[0074] According to the nitride semiconductor light emitting element of the embodiment described above, as described in detail later, the light emission efficiency in the first well layer 32 can be improved, and ultraviolet light can be emitted with high light emission output.

[0075] That is, the nitride semiconductor light-emitting element of the present embodiment has a multiple quantum well structure that emits ultraviolet light, wherein the light-emitting output is improved by improving the light-emitting efficiency of the well layer located on the side closer to the n-side semiconductor layer 20 than the p-side semiconductor layer 50.

[0076] Hereinafter, the specific structures of the substrate 10 and each semiconductor layer will be described.

[0077] The material of the substrate 10 can be, for example, sapphire, silicon (Si), gallium nitride (GaN), aluminum nitride (AlN), etc. The substrate 10 formed of sapphire has high light transmittance with respect to the ultraviolet light from the active layer 30, and is therefore preferred. The semiconductor structure 100 can be configured, for example, on the c-plane of the sapphire substrate, preferably on a surface inclined in the range of 0.2° to 2° from the c-plane of the sapphire substrate to the a-axis direction or the m-axis direction of the sapphire substrate. The thickness of the substrate 10 can be set, for example, to be 150 μm to 800 μm. The nitride semiconductor light-emitting element 1 may not have a substrate 10.

[0078] The semiconductor structure 100 is a stacked body formed by stacking a plurality of semiconductor layers formed of nitride semiconductors. The nitride semiconductor includes a x Al y Ga 1-x-y Semiconductors of all compositions in which the composition ratios x and y are varied within respective ranges in a chemical formula formed by N (0≤x≤1, 0≤y≤1, x+y≤1).

[0079] The base layer 11 may use a layer formed of, for example, AlN. The base layer 11 has the function of alleviating the lattice mismatch between the substrate 10 and the nitride semiconductor layer disposed on the base layer 11. The film thickness of the base layer 11 can be set, for example, to be greater than 0.5 μm and less than 4 μm, and is preferably set to be greater than 1.5 μm and less than 4 μm. The base layer 11 may include a buffer layer, which is located near the surface of the substrate 10. It should be noted that in this specification, the film thickness of each semiconductor layer refers to the thickness in the stacking direction of the semiconductor structure 100.

[0080] The superlattice layer 12 has a multilayer structure in which a first semiconductor layer and a second semiconductor layer having a lattice constant different from that of the first semiconductor layer are alternately stacked. The superlattice layer 12 has a function of alleviating stress generated in a semiconductor layer arranged above the superlattice layer 12. The superlattice layer 12 can be, for example, a multilayer structure in which an AlN layer and an aluminum gallium nitride (AlGaN) layer are alternately stacked. In the superlattice layer 12, the number of pairs of the first semiconductor layer and the second semiconductor layer can be set to be greater than 20 pairs and less than 50 pairs. When the first semiconductor layer is set to an AlGaN layer and the second semiconductor layer is set to an AlN layer, for example, the film thickness of the first semiconductor layer can be set to be greater than 5 nm and less than 30 nm, and the film thickness of the second semiconductor layer can be set to be greater than 5 nm and less than 30 nm.

[0081] The n-side semiconductor layer 20 includes one or more n-type semiconductor layers. Examples of the n-type semiconductor layer include a semiconductor layer containing n-type impurities such as silicon (Si) or germanium (Ge). The n-type semiconductor layer is, for example, an AlGaN layer containing aluminum (Al), gallium (Ga), and nitrogen (N), and may also contain indium (In). For example, the n-type impurity concentration of an n-type semiconductor layer containing Si as an n-type impurity is 5×10 18 / cm 3 Above 1×10 20 / cm 3 As follows. The n-side semiconductor layer 20 may include an undoped layer as long as it has the function of supplying electrons to the active layer 30. Here, the undoped layer refers to a layer that is not intentionally doped with n-type impurities or p-type impurities. In the case where the undoped layer is adjacent to a layer intentionally doped with n-type impurities and / or p-type impurities, n-type impurities and / or p-type impurities may be included in the undoped layer due to diffusion from the adjacent layer.

[0082] like Figure 1 As shown, the n-side semiconductor layer 20 includes, for example, an undoped layer 21 and an n-side contact layer 22. The undoped layer 21 is disposed between the superlattice layer 12 and the n-side contact layer 22. The n-side contact layer 22 is disposed between the undoped layer 21 and the active layer 30.

[0083] For example, an undoped AlGaN layer can be used as the undoped layer 21. When the undoped layer 21 is an AlGaN layer, the Al composition ratio of the AlGaN layer can be set to, for example, 25% to 70%.

[0084] The n-side contact layer 22 can be formed of, for example, AlGaN containing n-type impurities. When the n-side contact layer is an AlGaN layer, the Al composition ratio of the AlGaN layer can be set to, for example, 25% to 70%. It should be noted that, in this specification, for example, an AlGaN layer with an Al composition ratio of 50% refers to a layer formed of AlGaN. X Ga 1-X N is AlGaN with a composition ratio x of 0.5 in the chemical formula. The n-type impurity concentration of the n-side contact layer 22 can be set to 5×10 18 / cm 3 Above 1×10 20 / cm 3 The thickness of the n-side contact layer 22 is preferably thicker than the thickness of the undoped layer 21. By making the thickness of the n-side contact layer 22 thicker than the thickness of the undoped layer 21, the rise in forward voltage can be reduced. The thickness of the n-side contact layer 22 can be set to, for example, 1.5 μm to 4 μm. The n-side contact layer 22 has an upper surface on which no other semiconductor layer is configured. An n-electrode 60 is configured on the upper surface of the n-side contact layer 22 on which no other semiconductor layer is configured.

[0085] The active layer 30 is disposed between the n-side semiconductor layer 20 and the p-side semiconductor layer 50. The active layer 30 emits ultraviolet light. The emission peak wavelength of the ultraviolet light emitted by the active layer 30 is, for example, 220 nm to 350 nm.

[0086] The active layer 30 includes, in order from the n-side semiconductor layer 20 side, a first barrier layer 31 including Al and n-type impurities, a first well layer 32 including Al and emitting ultraviolet light, a second barrier layer 33 including Al, and a second well layer 34 including Al and emitting ultraviolet light. Here, both the first barrier layer 31 and the second barrier layer 33 include Al. Moreover, the peak of the highest n-type impurity concentration in the first barrier layer 31 is located on the p-side semiconductor layer 50 side. In addition, the Al composition ratio of the first barrier layer 31 is higher than the Al composition ratio of the second barrier layer 33. Thus, the light emission efficiency in the first well layer 32 can be improved. That is, in this embodiment, by making the Al composition ratio of the first barrier layer 31 higher than the Al composition ratio of the second barrier layer 33, the band gap of the second barrier layer 33 can be made smaller than the band gap of the first barrier layer 31, and the holes injected into the first well layer 32 can be increased. In addition, since the band gap of the first barrier layer 31 is larger than the band gap of the second barrier layer 33, the hole confinement effect in the first well layer 32 can be improved. For example, the Al composition ratio of the first barrier layer 31 is larger than the Al composition ratio of the second barrier layer 33 in the range of 3% to 17%. Thus, the light emission efficiency in the first well layer 32 can be improved. Moreover, in the present embodiment, in the first barrier layer 31, the difference between the band gap of the first barrier layer 31 and the band gap of the first well layer 32 in the valence band is further increased in such a manner that the peak of the n-type impurity concentration is located on the p-side semiconductor layer 50 side, and the hole confinement effect in the first well layer 32 is further improved. Thus, the light emission efficiency in the first well layer 32 can be further improved. In addition, if an n-type impurity is added to the first barrier layer 31, the crystallinity of the first barrier layer 31 may be deteriorated. However, in this embodiment, the highest n-type impurity concentration peak in the first barrier layer 31 is located on the p-side semiconductor layer 50 side, thereby increasing the barrier at the boundary between the first well layer 32 and the first barrier layer 31, and reducing the n-type impurity concentration in the first barrier layer 31 on the n-side semiconductor layer 20 side. As a result, the deterioration of the crystallinity of the entire first barrier layer 31 is reduced. Here, the value of the highest n-type impurity concentration peak in the first barrier layer 31 located on the p-side semiconductor layer 50 side is, for example, 1×10 19 / cm 3 Above 6×10 19 / cm 3 In addition, the position of the lowest n-type impurity concentration in the first barrier layer 31 is located closer to the n-side semiconductor layer 20 than the position of the peak of the highest n-type impurity concentration in the first barrier layer 31. For example, the value of the lowest n-type impurity concentration in the first barrier layer 31 is 1×1017 / cm 3 Above 9×10 17 / cm 3 the following.

[0087] Hereinafter, specific structural examples and preferred examples of the barrier layer and the well layer according to the present embodiment will be described.

[0088] For example, Figure 2 As shown, the first barrier layer 31 includes a first layer 31a and a second layer 31b located on the p-side semiconductor layer 50 side relative to the first layer 31a. The n-type impurity concentration of the first layer 31a is different from the n-type impurity concentration of the second layer 31b. Specifically, the n-type impurity concentration of the first layer 31a is a concentration lower than the average value of the n-type impurity concentration in the entire first barrier layer 31, and the n-type impurity concentration of the second layer 31b is a concentration higher than the average value of the n-type impurity concentration in the entire first barrier layer 31. In this way, by having the first layer 31a and the second layer 31b having different n-type impurity concentrations, the highest peak of the n-type impurity concentration in the first barrier layer 31 can be located on the p-side semiconductor layer 50 side. The highest peak of the n-type impurity concentration in the first barrier layer 31 is located in the first layer 31a. In addition, the position of the lowest n-type impurity concentration in the first barrier layer 31 is located in the second layer 31b.

[0089] Here, the thickness of the second layer 31b is preferably smaller than the thickness of the first layer 31a. The n-type impurity concentration of the second layer 31b is a concentration higher than the average value of the n-type impurity concentration in the first barrier layer 31 as a whole. Therefore, by reducing the thickness of the second layer 31b having a higher n-type impurity concentration, the deterioration of the crystallinity of the first barrier layer 31 caused by the thickening of the layer having a high n-type impurity concentration can be reduced, and the luminous efficiency can be improved. For example, the thickness of the second layer 31b is preferably not less than 5% and not more than 30% of the thickness of the entire first barrier layer 31. As a result, the confinement effect of holes in the first well layer 32 can be improved, and the deterioration of the crystallinity of the first barrier layer 31 can be reduced.

[0090] In addition, the film thickness of the second barrier layer 33 is preferably smaller than the film thickness of the second layer 31 b . This can increase the supply of holes to the first well layer 32 .

[0091] The second barrier layer 33 may be undoped or may contain n-type impurities. When the second barrier layer 33 is undoped, the deterioration of the crystallinity of the active layer 30 can be reduced. In addition, when the second barrier layer 33 contains n-type impurities, the resistance of the second barrier layer 33 can be reduced and the forward voltage can be reduced. When the second barrier layer 33 contains n-type impurities, it is preferred that the n-type impurity concentration of the second barrier layer 33 is less than the n-type impurity concentration of the second layer 31b and greater than the n-type impurity concentration of the first layer 31a. Thus, the deterioration of the crystallinity of the second barrier layer 33 can be reduced and the forward voltage can be reduced.

[0092] In addition, the Al composition ratio of the first layer 31a and the Al composition ratio of the second layer 31b are preferably substantially the same. Thus, the difference in band gap caused by the difference in Al composition ratio of the first layer 31a and the Al composition ratio of the second layer 31b can be reduced, so that electrons can be efficiently supplied to the first well layer 32.

[0093] Furthermore, the first barrier layer 31 is in contact with the n-side semiconductor layer 20, and the Al composition ratio of the first barrier layer 31 is preferably substantially the same as the Al composition ratio of the n-side semiconductor layer 20. Thus, the difference in band gap caused by the difference in Al composition ratio of the n-side semiconductor layer 20 and the Al composition ratio of the first barrier layer 31 can be reduced, and thus, electrons can be efficiently supplied to the first well layer 32.

[0094] When the n-side semiconductor layer 20 includes the n-side contact layer 22 and the first barrier layer 31 is in contact with the n-side contact layer 22, it is preferred that the n-type impurity concentration of the n-side contact layer 22 is lower than the n-type impurity concentration of the second layer 31b and higher than the n-type impurity concentration of the first layer 31a. Thus, the deterioration of the crystallinity of the n-side contact layer 22 can be reduced, and the resistance of the n-side contact layer 22 can be reduced.

[0095] The film thickness of the second well layer 34 is preferably smaller than the film thickness of the first well layer 32. This can increase the supply of holes to the first well layer 32.

[0096] The Al composition ratio of the second well layer 34 may also be greater than the Al composition ratio of the first well layer 32. As described later, in order to reduce electron overflow, the Al composition ratio of the electron blocking layer 40 is preferably higher than the Al composition ratio of the barrier layer. However, for example, in the case where the Al composition ratio of the layer in contact with the second well layer 34 in the electron blocking layer 40 is large, deformation sometimes occurs in the second well layer 34, and the emission wavelength of the second well layer 34 becomes longer. By making the Al composition ratio of the second well layer 34 greater than the Al composition ratio of the first well layer 32 and increasing the band gap of the second well layer 34, the emission wavelength of the second well layer 34 can be reduced. The Al composition ratio of the second well layer 34 can be greater than the Al composition ratio of the first well layer 32, for example, in the range of 2% to 10%.

[0097] The first well layer 32 and the second well layer 34 can use a layer formed of AlGaN, for example. The first barrier layer 31 and the second barrier layer 33 can use a layer formed of AlGaN, for example. The Al composition ratio of the first well layer 32 and the second well layer 34 can be set to, for example, 10% or more, specifically, 10% or more and 50% or less, and more specifically, 30% or more and 50% or less. When the emission peak wavelength of the light from the first well layer 32 and the second well layer 34 is set to about 280nm, an AlGaN layer with an Al composition ratio of about 42% can be used as the first well layer 32 and the second well layer 34. The Al composition ratio of the first barrier layer 31 and the second barrier layer 33 can be set to, for example, 10% or more, specifically, 10% or more and 70% or less, and more specifically, 30% or more and 70% or less.

[0098] The thickness of the first well layer 32 can be set to, for example, 3 nm to 6 nm. The thickness of the second well layer 34 can be set to, for example, 1 nm to 4 nm, and is preferably thinner than the first well layer 32 as described above. The thickness of the first layer 31a of the first barrier layer 31 is, for example, 10 nm to 60 nm, and the thickness of the second layer 31b is, for example, 5 nm to 20 nm. The thickness of the second barrier layer 33 is, for example, 1 nm to 5 nm.

[0099] In the above, the specific structural examples and preferred examples of the barrier layer and the well layer are described, but the film thickness, Al composition ratio, and doping amount of n-type impurities of the first layer 31a and the second layer 31b in the first barrier layer 31 and the second barrier layer 33 can be optimized based on the target emission wavelength and emission output, driving voltage and current, etc., taking into account the above specific structural examples and preferred examples. Similarly, the film thickness, Al composition ratio, and doping amount of the first well layer 32 and the second well layer 34 can also be optimized taking into account the above specific structural examples and preferred examples.

[0100] The electron blocking layer 40 is provided to reduce the overflow of electrons supplied from the n-side semiconductor layer 20. The electron blocking layer 40 can be provided with a multilayer structure having a plurality of semiconductor layers including Al. Figure 2As shown, the electron blocking layer 40 can be set to a multilayer structure having, for example, an AlN layer 41, a first AlGaN layer 42, and a second AlGaN layer 43 in order from the active layer 30 side. For example, the Al composition ratio of the first AlGaN layer 42 can be lower than the Al composition ratio of the second AlGaN layer 43. In addition, for example, the Al composition ratio of the first AlGaN layer 42 can be lower than the Al composition ratio of the second AlGaN layer 43, and higher than the Al composition ratio of the first well layer 32 and the second well layer 34. The electron blocking layer 40 preferably includes an AlGaN layer having an Al composition ratio higher than the Al composition ratio of the first barrier layer 31 and the second barrier layer 33. Thereby, the overflow of electrons can be reduced. In the electron blocking layer 40, for example, an undoped first AlGaN layer 42, an undoped second AlGaN layer 43, and an undoped AlN layer 41 can be used. The total film thickness of the electron blocking layer 40 can be set to, for example, 4 nm or more and 15 nm or less.

[0101] The p-side semiconductor layer 50 preferably has high light transmittance with respect to the light from the first well layer 32 and the second well layer 34. For example, it is preferred to include an AlGaN layer having an Al composition ratio higher than the Al composition ratio of the first well layer 32 and the second well layer 34. However, the AlGaN layer having a high Al composition ratio has a larger band gap than the GaN layer and the like. Therefore, if the AlGaN layer having a high Al composition ratio is used for the p-side semiconductor layer 50, it is easy to produce insufficient p-type conversion of the p-side semiconductor layer 50, or the contact resistance caused by the p-electrode 70 and the p-side semiconductor layer 50 becomes larger. Therefore, in a nitride semiconductor light-emitting element in which an AlGaN layer formed with a higher Al composition ratio is used as the first well layer 32 and the second well layer 34, it is necessary to take into account both high light extraction efficiency and low forward voltage. Therefore, in the present embodiment, by having the following p-side semiconductor layer 50, a nitride semiconductor light-emitting element 1 having high light extraction efficiency and low forward voltage can be made.

[0102] For example, in this embodiment, Figure 1 As shown, the p-side semiconductor layer 50 includes a first p-side semiconductor layer 51 and a second p-side semiconductor layer 52. Here, the first p-side semiconductor layer 51 is a layer with a large Al composition ratio containing p-type impurities such as magnesium (Mg), and the second p-side semiconductor layer 52 is a layer with a small Al composition ratio containing p-type impurities such as magnesium (Mg) or a layer without Al (for example, a GaN layer). In this way, by including the first p-side semiconductor layer 51 and the second p-side semiconductor layer 52, a nitride semiconductor light-emitting element 1 with high light extraction efficiency and low forward voltage can be manufactured.

[0103] Moreover, the first p-side semiconductor layer 51 and the second p-side semiconductor layer 52 may be a single layer or a layer including a plurality of layers. For example, the first p-side semiconductor layer 51 may include, in order from the active layer 30 side, a first layer formed of an AlGaN layer, a second layer formed of an AlGaN layer having a lower Al composition ratio than the first layer, and a third layer formed of an AlGaN layer having a lower Al composition ratio than the second layer. In this case, the third layer may also be a composition gradient layer that gradually reduces the Al composition ratio. The second p-side semiconductor layer 52 may also include, for example, a fourth layer formed of an AlGaN layer and a fifth layer formed of a GaN layer from the first p-side semiconductor layer 51 side. In this way, by including the first to fifth layers, a nitride semiconductor light-emitting element 1 having higher light extraction efficiency and lower forward voltage can be made.

[0104] The n-electrode 60 is disposed on the n-side contact layer 22 and electrically connected to the n-side semiconductor layer 20 . The p-electrode 70 is disposed on the second p-side semiconductor layer 52 of the p-side semiconductor layer 50 and electrically connected to the p-side semiconductor layer 50 .

[0105] For example, metals such as Ag, Al, Ni, Au, Rh, Ti, Pt, Mo, Ta, W, and Ru, or alloys containing these metals as main components can be used for the n-electrode 60. For example, the n-electrode 60 can be a multilayer structure including a Ti layer, an Al alloy layer, a Ta layer, and a Ru layer in this order from the n-side contact layer 22 side.

[0106] In the p-electrode 70, for example, the same metal as the above-mentioned n-electrode 60 can be used. In the case of the p-electrode 70 having the function of reflecting the light from the active layer 30 toward the p-electrode 70 side toward the n-side semiconductor layer 20 side, it is preferable to set the metal layer in contact with the third layer 53 in the p-electrode 70 as a metal layer having a high reflectivity with respect to the light from the active layer 30. For example, it is preferable to use a metal layer having a reflectivity of 70% or more, preferably 80% or more with respect to the light from the active layer 30. As such a metal layer, for example, an Rh layer or a Ru layer is preferably used. The p-electrode 70 can be set as a multilayer structure including an Rh layer, an Au layer, a Ni layer, and a Ti layer, or a multilayer structure including a Ru layer, an Au layer, a Ni layer, and a Ti layer.

[0107] When a forward voltage is applied between the n-electrode 60 and the p-electrode 70 , a forward voltage is applied between the p-side semiconductor layer 50 and the n-side semiconductor layer 20 , and holes and electrons are supplied to the active layer 30 , whereby the active layer 30 emits light.

[0108] It should be noted that, in this embodiment, Figure 2Although the specific example of including two barrier layers and two well layers is described, the present invention is not limited thereto. For example, one or more barrier layers and two or more well layers may be included between the first well layer 32 and the second well layer 34 .

[0109] Below, refer to Figure 3 to Figure 8 , a method for manufacturing the nitride semiconductor light-emitting element of this embodiment is described.

[0110] The method for manufacturing a nitride semiconductor light emitting device of this embodiment includes:

[0111] (S1) a step of forming an n-side semiconductor layer;

[0112] (S2) a step of forming an active layer on the n-side semiconductor layer;

[0113] (S3) a step of forming a p-side semiconductor layer on the active layer,

[0114] (S2) The step of forming an active layer includes:

[0115] (S2-1) a step of forming a first barrier layer by forming a first layer containing Al and an n-type impurity on the n-side semiconductor layer, and then forming a second layer containing Al and the n-type impurity at a higher concentration than the first layer on the first layer;

[0116] (S2-2) forming a first well layer containing Al and emitting ultraviolet light on the first barrier layer;

[0117] (S2-3) forming a second barrier layer on the first well layer, which contains Al and an n-type impurity and has an Al composition ratio lower than the Al composition ratio of the first layer and the Al composition ratio of the second layer;

[0118] ( S2 - 4 ) A step of forming a second well layer containing Al and emitting ultraviolet light on the second barrier layer.

[0119] First, if Figure 3 As shown, for example, a base layer 11 formed of AlN is formed on the c-plane of a substrate 10 formed of sapphire. The base layer 11 is formed, for example, by a metal organic vapor deposition (MOCVD) method or a sputtering method. Here, the process of forming the base layer 11 may also include a process of forming a buffer layer. For example, after a buffer layer formed of AlN is formed by a sputtering method, an AlN layer is formed on the buffer layer by, for example, a MOCVD method, thereby forming the base layer 11 including the buffer layer.

[0120] It should be noted that each semiconductor layer described below can be formed by epitaxial growth using, for example, the MOCVD method.

[0121] Then, if Figure 4As shown, a superlattice layer 12 is formed on the base layer 11. The superlattice layer 12 is formed by alternately growing a first semiconductor layer and a second semiconductor layer having a lattice constant different from that of the first semiconductor layer. The first semiconductor layer is formed, for example, by growing an AlN layer using trimethylaluminum (TMA) gas and ammonia gas in the raw material gas, and mainly using hydrogen (H2) gas as a carrier gas. The second semiconductor layer is formed, for example, by growing an AlGaN layer using TMA gas, trimethylgallium (TMG) gas, and ammonia gas in the raw material gas, and mainly using hydrogen as a carrier gas. Each layer of the superlattice layer 12 can be formed, for example, by setting the temperature to be above 1000°C and below 1250°C.

[0122] Then, if Figure 5 As shown, an n-side semiconductor layer 20 including an undoped layer 21 and an n-side contact layer 22 is formed on the superlattice layer 12. The undoped layer 21 is formed, for example, by growing an AlGaN layer using TMA gas, TMG gas, and ammonia gas as the raw material gas, and mainly using hydrogen as a carrier gas. The n-side contact layer 22 is formed, for example, by growing an AlGaN layer containing n-type impurities using TMA gas, TMG gas, and ammonia gas as the raw material gas, using monosilane (SiH4) gas as the n-type impurity gas, and mainly using hydrogen as a carrier gas. Each layer of the n-side semiconductor layer 20 can be formed, for example, by setting the temperature to be above 1000°C and below 1250°C.

[0123] Then, if Figure 6 As shown, an active layer 30 is formed on the n-side semiconductor layer 20, and the active layer 30 includes: a first barrier layer 31 including a first layer 31a and a second layer 31b, a first well layer 32, a second barrier layer 33 and a second well layer 34. The first barrier layer 31 is formed by, for example, using TMA gas, TEG gas, and ammonia gas as raw material gases, using monosilane (SiH4) gas as an n-type impurity gas, and mainly using nitrogen gas as a carrier gas to grow an AlGaN layer containing Si as an n-type impurity.

[0124] Here, in the process (S2-1) of forming the first barrier layer 31, after a first layer 31a containing Al and n-type impurities is formed on the n-side semiconductor layer using the above-mentioned raw material gas, the flow rate of monosilane (SiH4) gas is increased to form a second layer 31b containing Al and n-type impurities at a higher concentration than the first layer 31a on the first layer.

[0125] The first well layer 32 is formed by growing an AlGaN layer using, for example, TMA gas, TEG gas, and ammonia gas as raw material gases and mainly nitrogen gas as a carrier gas.

[0126] The second barrier layer 33 is formed by growing an AlGaN layer using, for example, TMA gas, TEG gas, and ammonia gas as raw material gases, and mainly using nitrogen gas as a carrier gas. In addition, in the process of forming the second barrier layer 33, no n-type impurity gas is used, or the flow rate of the n-type impurity gas is made smaller than the flow rate of the n-type impurity gas in the process of forming the first barrier layer 31.

[0127] For example, the second well layer 34 is grown in the same manner as the first well layer 32. The second well layer 34 is preferably formed with a thinner film thickness than the first well layer 32. In addition, in the process of forming the second well layer 34 so that the Al composition ratio of the second well layer 34 is smaller than the Al composition ratio of the first well layer 32, it is preferable to reduce the flow rate of the TMA gas compared to the process of forming the first well layer 32.

[0128] Then, if Figure 7 As shown, an electron blocking layer 40 is formed on the active layer 30. The electron blocking layer 40 is formed in a manner including an AlN layer 41, a first AlGaN layer 42, and a second AlGaN layer 43. The AlN layer 41 of the electron blocking layer 40 is formed, for example, by using TMA gas and ammonia gas in the raw material gas, and mainly using nitrogen as a carrier gas. The first AlGaN layer 42 of the electron blocking layer 40 is formed, for example, by using TMA gas, TEG gas, and ammonia gas in the raw material gas, and using nitrogen as a carrier gas. The second AlGaN layer 43 of the electron blocking layer 40 is formed, for example, by using TMA gas, TEG gas, and ammonia gas in the raw material gas, and mainly using nitrogen as a carrier gas. For example, in the process of forming the second AlGaN layer 43, the flow ratio of the TMA gas as the raw material gas of Al is made larger than the flow ratio of the TMA gas in the process of forming the first AlGaN layer 42. Thus, the Al composition ratio of the second AlGaN layer 43 is formed to be higher than the Al composition ratio of the first AlGaN layer 42. Each layer of the electron blocking layer 40 can be formed at a temperature of, for example, 750° C. or higher and 950° C. or lower.

[0129] Then, if Figure 8As shown, a p-side semiconductor layer 50 is formed on the electron blocking layer 40. The p-side semiconductor layer 50 is formed by growing a first p-side semiconductor layer 51 and a second p-side semiconductor layer 52 in sequence from the active layer 30 side. The first p-side semiconductor layer 51 is formed, for example, by growing an AlGaN layer containing Mg as a p-type impurity using TMA gas, TEG gas, and ammonia gas as raw material gases and cyclopentadienyl magnesium (Cp2Mg) gas as a p-type impurity gas. The second p-side semiconductor layer 52 is formed, for example, by growing an AlGaN layer containing Mg as a p-type impurity using TMA gas, TMG gas, and ammonia gas as raw material gases and cyclopentadienyl magnesium (Cp2Mg) gas as a p-type impurity gas, or by growing a GaN layer containing Mg as a p-type impurity using TMG gas and ammonia gas as raw material gases and cyclopentadienyl magnesium (Cp2Mg) gas as a p-type impurity gas instead of TMA gas.

[0130] Each layer of the p-side semiconductor layer 50 can be formed at a temperature of, for example, 750° C. or higher and 950° C. or lower.

[0131] After the p-side semiconductor layer 50 is formed, a portion of the p-side semiconductor layer 50 , a portion of the electron blocking layer 40 , and a portion of the active layer 30 are removed to expose a portion of the n-side contact layer 22 .

[0132] Moreover, if Figure 1 As shown, an n-electrode 60 is formed on the exposed n-side contact layer 22 , and a p-electrode 70 is formed on the third layer 53 of the p-side semiconductor layer 50 .

[0133] By performing the above steps, the nitride semiconductor light emitting element of this embodiment can be manufactured.

[0134] Hereinafter, a specific embodiment of the nitride semiconductor light emitting element of this embodiment will be described.

[0135] Fig. 9 1 is a top view of the nitride semiconductor light emitting element 1, showing the positional relationship between the n-side semiconductor layer 20 and the p-side semiconductor layer 50 when viewed from above, and the electrodes respectively arranged on the n-side semiconductor layer 20 and the p-side semiconductor layer 50. Fig. 9 As shown, the shape of the nitride semiconductor light emitting element 1 in a plan view is a rectangle.

[0136] Hereinafter, a preferred positional relationship between the n-side semiconductor layer 20 and the p-side semiconductor layer 50 in a plan view of the nitride semiconductor light emitting element 1 and an example of an electrode structure respectively arranged on the n-side semiconductor layer 20 and the p-side semiconductor layer 50 in this positional relationship will be described.

[0137] like Fig. 9As shown, in a plan view, the p-side semiconductor layer 50 has a base portion 501 extending in a first direction X, and a plurality of extension portions 502 extending from the base portion 501 in a second direction Y orthogonal to the first direction X. In addition, the exposed portion of the n-side semiconductor layer 20 exposed from the p-side semiconductor layer 50 has a first exposed portion 201 extending in the first direction X, four second exposed portions 202 extending from the first exposed portion 201 in the second direction Y, two third exposed portions 203 extending from the first exposed portion 201 in the second direction Y, and a fourth exposed portion 204 extending in the first direction X. The second exposed portion 202 is located between the plurality of extension portions 502 of the p-side semiconductor layer 50. In the first direction X, the four second exposed portions 202 are located between the third exposed portions 203. The third exposed portion 203 connects the first exposed portion 201 and the fourth exposed portion 204. The fourth exposed portion connects the two third exposed portions 203. Here, the first exposed portion 201 is arranged along one side of the nitride semiconductor light emitting element 1 extending along the first direction X. In addition, the fourth exposed portion 204 is arranged along one side opposite to the one side of the nitride semiconductor light emitting element 1 along the first exposed portion 201 and extending along the first direction X. The two third exposed portions 203 exist respectively along two sides of the nitride semiconductor light emitting element 1 extending along the second direction Y. It should be noted that the width of the fourth exposed portion 204 in the second direction Y can be smaller than the width of the first exposed portion 201 in the second direction Y.

[0138] As described above, by making the positional relationship between the n-side semiconductor layer 20 and the p-side semiconductor layer 50 in a plan view as shown in FIG. Fig. 9 As shown, a nitride semiconductor light-emitting element that emits ultraviolet light with high reliability can be provided.

[0139] The reason is described below.

[0140] Generally, in a nitride semiconductor light-emitting element having a rectangular shape when viewed from above, the active layer and the p-side semiconductor layer thereon are preferably arranged near the periphery of the nitride semiconductor light-emitting element in order to arrange them in a larger area. However, the present inventors have obtained the following knowledge: in a nitride semiconductor light-emitting element emitting ultraviolet light, if the active layer and the p-type semiconductor layer are arranged near the corners of the nitride semiconductor light-emitting element, the heat generated during light emission is concentrated at the corners, and reliability may be reduced.

[0141] Fig. 9 The positional relationship between the n-side semiconductor layer 20 and the p-side semiconductor layer 50 in the plan view shown is a positional relationship based on the findings independently obtained by the above-mentioned inventors, and can provide a nitride semiconductor light emitting element that emits ultraviolet light with high reliability.

[0142] That is, the exposed portion of the n-side semiconductor layer 20 is arranged along each side of the nitride semiconductor light-emitting element, and the active layer 30 and the p-side semiconductor layer 50 are arranged on the inner side of the exposed portion of the n-side semiconductor layer 20 when viewed from above. Thus, the active layer and the p-side semiconductor layer are not arranged near the four corners of the nitride semiconductor light-emitting element, and the concentration of heat generated during light emission on the corners can be reduced, thereby improving reliability.

[0143] The following, Fig. 9 An example of an electrode structure in the positional relationship between the n-side semiconductor layer 20 and the p-side semiconductor layer 50 shown in FIG.

[0144] The n-electrode 60 includes an n-side electrode 61 and an n-side pad electrode 62. The p-electrode 70 includes a first p-side electrode 71, a second p-side electrode 72 disposed on the first p-side electrode 71, and a p-side pad electrode 73 disposed on the second p-side electrode 72. The n-side electrode 61 is disposed at a position overlapping the first exposed portion 201, the second exposed portion 202, and the third exposed portion 203 in a plan view. The n-side electrode 61 is disposed on the n-side contact layer 22 of the n-side semiconductor layer 20 and is electrically connected to the n-side semiconductor layer 20. The first p-side electrode 71 is disposed at a position overlapping the base portion 501 of the p-side semiconductor layer 50 and the plurality of extension portions 502 of the p-side semiconductor layer 50 in a plan view. The first p-side electrode 71 is disposed on the second p-side semiconductor layer 52 of the p-side semiconductor layer 50 and is electrically connected to the p-side semiconductor layer 50. The first p-side electrode 71 is disposed on the upper surface of the second p-side semiconductor layer 52. The second p-side electrode 72 is disposed on the upper surface of the first p-side electrode 71. The p-side pad electrode 73 is disposed on a portion of the upper surface of the second p-side electrode 72. Fig. 9 As shown, the p-side pad electrode 73 includes, for example, a base portion arranged on substantially the entire surface of the second p-side electrode 72 located on the base portion 501 of the p-side semiconductor layer 50, and an extension portion extending from the base portion along the plurality of extension portions 502 of the p-side semiconductor layer 50. The n-side electrode 61 is arranged in contact with the exposed portion of the n-side semiconductor layer 20. The n-side pad electrode 62 is arranged on a portion of the upper surface of the n-side electrode 61. The n-side pad electrode 62 includes a base portion arranged at a position overlapping with the first exposed portion 201 when viewed from above, and an extension portion extending from the base portion along the second exposed portion 202.

[0145] like Fig.10As shown, a protective film 80 is arranged to cover the semiconductor structure 100, the n-side electrode 61, the first p-side electrode 71, and the second p-side electrode 72 provided on the substrate 10. The protective film 80 has an opening 81 located above the n-side electrode 61 and an opening 82 located above the second p-side electrode 72. The n-side pad electrode 62 is connected to the n-side electrode 61 via the opening 81 of the protective film 80, and the p-side pad electrode 73 is connected to the second p-side electrode 72 via the opening 82 of the protective film 80. For example, SiO2, SiON, etc. can be used for the protective film 80. The thickness of the protective film 80 can be set to, for example, 1 μm or more and 2 μm or less.

[0146] In the n-side electrode 61, for example, metals such as silver (Ag), Al, nickel (Ni), gold (Au), rhodium (Rh), titanium (Ti), platinum (Pt), molybdenum (Mo), tantalum (Ta), tungsten (W), ruthenium (Ru), or alloys containing these metals as main components can be used. The n-side electrode 61 can be, for example, a multilayer structure including a plurality of metal layers. The n-side electrode 61 can be, for example, a multilayer structure including a Ti layer, an Al alloy layer, a Ta layer, and a Ru layer in order from the n-side semiconductor layer 20 side.

[0147] The n-side pad electrode 62 can be made of a metal such as Ni, Au, Ti, Pt, or W, or an alloy containing these metals as a main component. The n-side pad electrode 62 can be a multilayer structure including a Ti layer, a Pt layer, and an Au layer in order from the n-side electrode 61. The thickness of the n-side pad electrode 62 can be set to, for example, 500 nm or more and 1500 nm or less.

[0148] For example, the same metal as the above-mentioned n-electrode 60 can be used for the p-electrode 70. The p-electrode 70 preferably reflects light from the active layer 30 toward the p-electrode 70 side toward the n-side semiconductor layer 20 side. For example, it is preferred that at least one of the first p-side electrode 71 and the second p-side electrode 72 use a metal having a high reflectivity with respect to the light from the active layer 30. The metal having a high reflectivity is, for example, a metal having a reflectivity of 60% or more with respect to the light from the active layer 30. It is preferred that at least one of the first p-side electrode 71 and the second p-side electrode 72 use, for example, Rh or Ru.

[0149] In the case where the first p-side electrode 71 uses a layer containing Rh or Ru, the first p-side electrode 71 preferably also contains an Au layer. As a result, compared with the case where the first p-side electrode 71 is formed of, for example, only a Rh layer or a Ru layer, a high reflectivity can be maintained, and the adhesion between the first p-side electrode 71 and the p-side semiconductor layer 50 can be improved. The first p-side electrode 71 can be, for example, a multilayer structure including an Rh layer, an Au layer, and a Ni layer in order from the p-side semiconductor layer 50 side, or a multilayer structure including a Ru layer, an Au layer, and a Ni layer. In addition, the first p-side electrode 71 can be a layer containing an alloy layer, the alloy layer containing: Rh or Ru; and Au and / or Ni.

[0150] The p-side pad electrode 73 can be made of, for example, the same metal as that of the n-side pad electrode 62 described above.

[0151] The p-side pad electrode 73 can be, for example, a multilayer structure including a Ti layer, a Pt layer, and an Au layer in order from the p-side semiconductor layer 50. The thickness of the p-side pad electrode 73 can be, for example, 500 nm to 1500 nm.

[0152] Hereinafter, the nitride semiconductor light emitting element of the example will be described.

[0153] <Example>

[0154] A substrate made of sapphire having a C-plane as a major surface was used as the substrate 10. On the substrate 10, a base layer 11 made of AlN including a buffer layer was formed with a film thickness of about 2.1 μm.

[0155] Next, the temperature was set to 1175° C., TMA gas, TMG gas, and ammonia gas were used as raw material gases, and Al was formed on the base layer 11 with a film thickness of about 21 nm. 0.60 Ga 0.40 Next, the temperature was set to 1175° C., and TMA gas and ammonia gas were used as raw material gases to form an AlN layer with a film thickness of about 10 nm. By forming 30 pairs of stacked bodies of the AlGaN layer and the AlN layer formed in this way, the superlattice layer 12 was formed.

[0156] Next, the temperature was set to 1175° C., TMA gas, TMG gas, and ammonia gas were used as raw material gases, and Al was formed on the superlattice layer 12 with a film thickness of about 0.5 μm. 0.60 Ga 0.40 N layer, thereby forming an undoped layer 21. Next, the temperature was set to 1175°C, TMA gas, TMG gas, ammonia gas, and SiH4 gas were used as raw material gases, and Al containing n-type impurities was added. 0.60 Ga 0.40The N layer is formed to a thickness of about 2.2 μm, thereby forming an n-side contact layer 22. The n-side semiconductor layer 20 including the undoped layer 21 and the n-side contact layer 22 is formed. The n-type impurity concentration of the n-side contact layer 22 is set to about 9.5×10 18 / cm 3 .

[0157] Next, the temperature was set to 950° C., and TMA gas, TMG gas, ammonia gas, and SiH 4 gas were used as raw material gases to form an Al 2 O layer containing n-type impurities with a film thickness of about 40 nm on the n-side semiconductor layer 20. 0.60 Ga 0.40 Next, the temperature was set to 950° C., TMA gas, TMG gas, ammonia gas, and SiH 4 gas were used as raw material gases, and Al containing n-type impurities was added. 0.60 Ga 0.40 The N layer is formed to a film thickness of about 10 nm, thereby forming the second layer 31b. Here, the flow rate of the raw material gas when forming the first layer 31a is set to 16 sccm of TMA gas, 45 sccm of TEG gas, 10 slm of ammonia gas, and 0.5 sccm of SiH4 gas, and the flow rate of the raw material gas when forming the second layer 31b is set to 16 sccm of TMA gas, 45 sccm of TEG gas, 10 slm of ammonia gas, and 16 sccm of SiH4 gas.

[0158] As described above, the first barrier layer 31 including the first layer 31 a including the n-type impurity and the second layer 31 b including a larger amount of the n-type impurity than the first layer 31 a is formed.

[0159] In addition, the film thickness of the first layer 31a and the film thickness of the second layer 31b mentioned here are the thicknesses during the manufacturing process, and the film thickness of the first layer 31a having a specific concentration lower than the average value of the n-type impurity concentration in the first barrier layer 31 as a whole and the film thickness of the second layer 31b having an n-type impurity concentration higher than the average value of the n-type impurity concentration in the first barrier layer 31 as a whole in the manufactured product may not be the same.

[0160] Next, the temperature was set to 950° C., TMA gas, TEG gas, and ammonia gas were used as raw material gases, and Al 0.43 Ga 0.57 The N layer is formed to a thickness of about 4.4 nm, thereby forming the first well layer 32 .

[0161] Next, the temperature was set to 950° C., TMA gas, TEG gas, and ammonia gas were used as raw material gases, and Al 0.53 Ga 0.47The N layer was formed to a thickness of about 2.5 nm, thereby forming the second barrier layer 33. Next, the temperature was set to 950° C., TMA gas, TEG gas, and ammonia gas were used as raw material gases, and Al 0.47 Ga 0.53 The N layer is formed to a film thickness of about 2.2 nm to form the second well layer 34. In this way, the active layer 30 including two well layers and two barrier layers is formed.

[0162] Next, the temperature was set to 870°C, TMA gas and ammonia gas were used as raw material gases, and an AlN layer 41 with a film thickness of about 1.3 nm was formed on the active layer 30. Next, the temperature was set to 870°C, TMA gas, TEG gas, and ammonia gas were used as raw material gases, and an AlN layer 41 with a film thickness of about 1.3 nm was formed on the active layer 30. 0.55 Ga 0.45 The N layer was formed to a thickness of about 1.2 nm, thereby forming the first AlGaN layer 42. Next, the temperature was set to 870° C., and TMA gas, TEG gas, and ammonia gas were used as raw material gases to form the AlGaN layer 42. 0.78 Ga 0.22 N is formed to a film thickness of about 4 nm, thereby forming the second AlGaN layer 43. In this way, the electron blocking layer 40 including the AlN layer and the two AlGaN layers is formed.

[0163] Next, the temperature was set to 870° C., TMA gas, TEG gas, ammonia gas, and Cp2Mg gas were used as raw material gases, and Al containing p-type impurities was formed on the electron blocking layer 40 with a film thickness of about 75 nm. 0.63 Ga 0.37 Next, the temperature was set to 870°C, TMA gas, TMG gas, ammonia gas, and Cp2Mg gas were used as raw material gases, and Al containing p-type impurities was added. 0.53 Ga 0.47 The N layer is formed to a thickness of about 27 nm. Next, the temperature is set to 870°C, TMA gas, TEG gas, ammonia gas, and Cp2Mg gas are used as raw material gases, and the TMA gas is gradually reduced, thereby forming a layer containing p-type impurities and starting from Al 0.53 Ga 0.47 The composition gradient layer formed by gradually reducing N and Al and finally making the Al composition ratio 0 was formed to a film thickness of 3 nm. As described above, the first p-side semiconductor layer 51 was formed.

[0164] Next, the temperature was set to 900°C, TMA gas, TMG gas, ammonia gas, and Cp2Mg gas were used as raw material gases, and Al containing p-type impurities was added. 0.40 Ga 0.60The N layer is formed to a thickness of about 10 nm. Next, the temperature is set to 900°C, and TMA gas, TMG gas, and ammonia gas are used as raw material gases to form a GaN layer containing p-type impurities to a thickness of about 10 nm. 0.40 Ga 0.60 N layer and a second p-side semiconductor layer 52 of a GaN layer containing p-type impurities.

[0165] After forming each semiconductor layer, each semiconductor layer is heat-treated in the reaction container.

[0166] The heat treatment is performed in a nitrogen atmosphere at a temperature of about 475°C.

[0167] After the heat treatment, a portion of the p-side semiconductor layer 50 and a portion of the active layer 30 are removed, so that a portion of the n-side contact layer 22 is exposed from the p-side semiconductor layer 50 and the active layer 30 .

[0168] Next, an n-electrode 60 is formed on the n-side contact layer 22, and a p-electrode 70 is formed on the p-side semiconductor layer 50. The n-electrode 60 has a multilayer structure in which a Ti layer, an AlSi layer, a Ta layer, a Ru layer, and a Ti layer are stacked in this order from the n-side contact layer 22 side. The p-electrode 70 has a multilayer structure in which a Ti layer, a Ru layer, and a Ti layer are stacked in this order from the third layer 53 side.

[0169] The nitride semiconductor light emitting device of the example fabricated as described above had a forward voltage of 5.16 V and a light output Po of 172 mW. It should be noted that the forward voltage and light output Po shown here are values ​​when a current of 350 mA is applied.

[0170] The peak with the highest n-type impurity concentration in the first barrier layer 31 is located in the second layer 31 b. The peak with the highest n-type impurity concentration in the first barrier layer 31 has a value of about 3×10 19 / cm 3 .

[0171] The nitride semiconductor light emitting element according to the embodiment of the present disclosure includes the following aspects, for example.

[0172] [Item 1]

[0173] A nitride semiconductor light emitting element comprises an n-side semiconductor layer, a p-side semiconductor layer, and an active layer located between the n-side semiconductor layer and the p-side semiconductor layer, wherein:

[0174] The active layer includes, in order from the n-side semiconductor layer side: a first barrier layer containing Al and n-type impurities, a first well layer containing Al and emitting ultraviolet light, a second barrier layer containing Al, and a second well layer containing Al and emitting ultraviolet light,

[0175] The peak of the highest n-type impurity concentration in the first barrier layer is located on the p-side semiconductor layer side.

[0176] The Al composition ratio of the first barrier layer is higher than the Al composition ratio of the second barrier layer.

[0177] [Item 2]

[0178] The nitride semiconductor light emitting element according to item 1, wherein

[0179] The first barrier layer has:

[0180] a first layer containing an n-type impurity at a concentration lower than an average value of the n-type impurity concentration in the entire first barrier layer;

[0181] The second layer is located closer to the p-side semiconductor layer than the first layer, contains n-type impurities at a concentration higher than the average value, and has a smaller film thickness than the first layer.

[0182] [Item 3]

[0183] The nitride semiconductor light emitting element according to item 2, wherein:

[0184] The film thickness of the second layer is not less than 5% and not more than 30% of the film thickness of the entire first barrier layer.

[0185] [Item 4]

[0186] The nitride semiconductor light emitting device according to item 2 or 3, wherein

[0187] The second barrier layer has a film thickness smaller than that of the second layer.

[0188] [Item 5]

[0189] The nitride semiconductor light emitting device according to any one of items 2 to 4, wherein

[0190] The second barrier layer includes n-type impurities, and a concentration of the n-type impurities in the second barrier layer is lower than a concentration of the n-type impurities in the second layer and higher than a concentration of the n-type impurities in the first layer.

[0191] [Item 6]

[0192] The nitride semiconductor light emitting device according to any one of items 2 to 5, wherein

[0193] The Al composition ratio of the first layer and the Al composition ratio of the second layer are substantially the same.

[0194] [Item 7]

[0195] The nitride semiconductor light emitting device according to any one of claims 1 to 6, wherein

[0196] The first barrier layer is in contact with the n-side semiconductor layer.

[0197] The Al composition ratio of the first barrier layer is substantially the same as the Al composition ratio of the n-side semiconductor layer.

[0198] [Item 8]

[0199] The nitride semiconductor light emitting device according to any one of claims 2 to 6 and claim 7 as cited in claims 2 to 6, wherein:

[0200] The n-side semiconductor layer includes an n-side contact layer in contact with the first barrier layer, wherein the n-type impurity concentration of the n-side contact layer is lower than the n-type impurity concentration of the second layer and higher than the n-type impurity concentration of the first layer.

[0201] [Item 9]

[0202] The nitride semiconductor light emitting device according to any one of items 1 to 8, wherein

[0203] The film thickness of the second well layer is smaller than the film thickness of the first well layer.

[0204] [Item 10]

[0205] The nitride semiconductor light emitting device according to any one of items 1 to 9, wherein

[0206] The Al composition ratio of the second well layer is greater than the Al composition ratio of the first well layer.

[0207] [Item 11]

[0208] A method for manufacturing a nitride semiconductor light-emitting element, the method comprising:

[0209] A step of forming an n-side semiconductor layer;

[0210] forming an active layer on the n-side semiconductor layer;

[0211] forming a p-side semiconductor layer on the active layer,

[0212] The process of forming the active layer includes:

[0213] A step of forming a first barrier layer by forming a first layer containing Al and an n-type impurity on the n-side semiconductor layer, and then forming a second layer containing Al and the n-type impurity at a higher concentration than that of the first layer on the first layer;

[0214] forming a first well layer containing Al and emitting ultraviolet light on the first barrier layer;

[0215] forming a second barrier layer on the first well layer, which contains Al and n-type impurities and has an Al composition ratio lower than the Al composition ratio of the first layer and the Al composition ratio of the second layer;

[0216] A step of forming a second well layer containing Al and emitting ultraviolet light on the second barrier layer.

[0217] [Item 12]

[0218] The method for manufacturing a nitride semiconductor light emitting element according to item 11, wherein:

[0219] In the step of forming the first barrier layer, the second layer is formed to have a film thickness thinner than that of the first layer.

[0220] [Item 13]

[0221] The method for manufacturing a nitride semiconductor light-emitting element according to item 11 or 12, wherein:

[0222] In the step of forming the first barrier layer, the second layer is formed to have a thickness not less than 5% and not more than 30% of the entire thickness of the first barrier layer.

[0223] [Item 14]

[0224] The method for manufacturing a nitride semiconductor light-emitting device according to any one of items 11 to 13, wherein:

[0225] In the step of forming the second barrier layer, the second barrier layer is formed to have a film thickness thinner than a film thickness of the second layer.

[0226] [Item 15]

[0227] The method for manufacturing a nitride semiconductor light-emitting device according to any one of items 11 to 14, wherein:

[0228] In the step of forming the second barrier layer, the second barrier layer is formed such that an n-type impurity concentration of the second barrier layer is lower than an n-type impurity concentration of the second layer and higher than an n-type impurity concentration of the first layer.

[0229] [Item 16]

[0230] The method for manufacturing a nitride semiconductor light-emitting element according to any one of items 11 to 15, wherein:

[0231] In the step of forming the first barrier layer, the first barrier layer is formed so that an Al composition ratio of the first layer and an Al composition ratio of the second layer are substantially the same.

[0232] [Item 17]

[0233] The method for manufacturing a nitride semiconductor light-emitting element according to item 16, wherein:

[0234] In the step of forming the first barrier layer, the first barrier layer is formed so that an Al composition ratio of the first barrier layer and an Al composition ratio of the n-side semiconductor layer are substantially the same.

[0235] [Item 18]

[0236] The method for manufacturing a nitride semiconductor light-emitting element according to any one of items 11 to 17, wherein:

[0237] The step of forming the n-side semiconductor layer includes the step of forming the n-side contact layer.

[0238] In the step of forming the active layer, the first barrier layer is formed in contact with the n-side contact layer.

[0239] In the above-mentioned process of forming the first barrier layer, the first layer is formed in a manner such that the n-type impurity concentration of the first layer is lower than the n-type impurity concentration of the n-side contact layer, and the second layer is formed in a manner such that the n-type impurity concentration of the second layer is higher than the n-type impurity concentration of the n-side contact layer, thereby forming the first barrier layer.

[0240] [Item 19]

[0241] The method for manufacturing a nitride semiconductor light-emitting element according to any one of items 11 to 18, wherein:

[0242] In the step of forming the second well layer, the second well layer is formed so that the film thickness of the second well layer is smaller than the film thickness of the first well layer.

[0243] [Item 20]

[0244] The method for manufacturing a nitride semiconductor light-emitting device according to any one of items 11 to 19, wherein:

[0245] In the step of forming the second well layer, the second well layer is formed so that an Al composition ratio of the second well layer is greater than an Al composition ratio of the first well layer.

Claims

1. A nitride semiconductor light emitting element comprising an n-side semiconductor layer, a p-side semiconductor layer, and an active layer located between the n-side semiconductor layer and the p-side semiconductor layer, wherein: The active layer includes, in order from the n-side semiconductor layer side: a first barrier layer containing Al and n-type impurities, a first well layer containing Al and emitting ultraviolet light, a second barrier layer containing Al, and a second well layer containing Al and emitting ultraviolet light, The peak of the highest n-type impurity concentration in the first barrier layer is located on the p-side semiconductor layer side. The Al composition ratio of the first barrier layer is higher than the Al composition ratio of the second barrier layer.

2. The nitride semiconductor light emitting element according to claim 1, wherein: The first barrier layer has: a first layer containing an n-type impurity at a concentration lower than an average value of the n-type impurity concentration in the entire first barrier layer; The second layer is located closer to the p-side semiconductor layer than the first layer, contains n-type impurities at a concentration higher than the average value, and has a smaller film thickness than the first layer.

3. The nitride semiconductor light emitting element according to claim 2, wherein: The thickness of the second layer is not less than 5% and not more than 30% of the thickness of the entire first barrier layer.

4. The nitride semiconductor light emitting element according to claim 2 or 3, wherein: The film thickness of the second barrier layer is smaller than the film thickness of the second layer.

5. The nitride semiconductor light emitting element according to claim 2 or 3, wherein: The second barrier layer includes n-type impurities, and a concentration of n-type impurities in the second barrier layer is less than a concentration of n-type impurities in the second layer, and greater than a concentration of n-type impurities in the first layer.

6. The nitride semiconductor light emitting element according to claim 2 or 3, wherein: The Al composition ratio of the first layer and the Al composition ratio of the second layer are substantially the same.

7. The nitride semiconductor light emitting element according to claim 1 or 2, wherein: The first barrier layer is in contact with the n-side semiconductor layer, An Al composition ratio of the first barrier layer and an Al composition ratio of the n-side semiconductor layer are substantially the same.

8. The nitride semiconductor light emitting element according to claim 2 or 3, wherein: The n-side semiconductor layer includes an n-side contact layer connected to the first barrier layer, wherein the n-type impurity concentration of the n-side contact layer is lower than the n-type impurity concentration of the second layer and higher than the n-type impurity concentration of the first layer.

9. The nitride semiconductor light emitting device according to claim 1 or 2, wherein: The second well layer has a smaller thickness than the first well layer.

10. The nitride semiconductor light emitting element according to claim 1 or 2, wherein: The Al composition ratio of the second well layer is greater than the Al composition ratio of the first well layer.

11. A method for manufacturing a nitride semiconductor light-emitting element, the method comprising: A step of forming an n-side semiconductor layer; forming an active layer on the n-side semiconductor layer; forming a p-side semiconductor layer on the active layer, The process of forming the active layer includes: A step of forming a first barrier layer by forming a first layer containing Al and an n-type impurity on the n-side semiconductor layer, and then forming a second layer containing Al and the n-type impurity at a higher concentration than the first layer on the first layer; forming a first well layer containing Al and emitting ultraviolet light on the first barrier layer; forming, on the first well layer, a second barrier layer including Al and n-type impurities and having an Al composition ratio lower than the Al composition ratios of the first layer and the second layer; A step of forming a second well layer containing Al and emitting ultraviolet light on the second barrier layer.

12. The method for manufacturing a nitride semiconductor light emitting element according to claim 11, wherein: In the step of forming the first barrier layer, the second layer is formed to have a film thickness thinner than that of the first layer.

13. The method for manufacturing a nitride semiconductor light emitting element according to claim 11 or 12, wherein: In the step of forming the first barrier layer, the second layer is formed to have a thickness not less than 5% and not more than 30% of the entire thickness of the first barrier layer.

14. The method for manufacturing a nitride semiconductor light emitting element according to claim 11 or 12, wherein: In the step of forming the second barrier layer, the second barrier layer is formed to have a film thickness thinner than a film thickness of the second layer.

15. The method for manufacturing a nitride semiconductor light emitting element according to claim 11 or 12, wherein: In the step of forming the second barrier layer, the second barrier layer is formed so that an n-type impurity concentration of the second barrier layer is lower than an n-type impurity concentration of the second layer and higher than an n-type impurity concentration of the first layer.

16. The method for manufacturing a nitride semiconductor light emitting element according to claim 11 or 12, wherein: In the step of forming the first barrier layer, the first barrier layer is formed so that an Al composition ratio of the first layer and an Al composition ratio of the second layer are substantially the same.

17. The method for manufacturing a nitride semiconductor light emitting element according to claim 16, wherein: In the step of forming the first barrier layer, the first barrier layer is formed so that an Al composition ratio of the first barrier layer and an Al composition ratio of the n-side semiconductor layer are substantially the same.

18. The method for manufacturing a nitride semiconductor light emitting element according to claim 11 or 12, wherein: The step of forming the n-side semiconductor layer includes the step of forming an n-side contact layer. In the step of forming the active layer, the first barrier layer is formed in contact with the n-side contact layer. In the process of forming the first barrier layer, the first layer is formed in a manner such that the n-type impurity concentration of the first layer is lower than the n-type impurity concentration of the n-side contact layer, and the second layer is formed in a manner such that the n-type impurity concentration of the second layer is higher than the n-type impurity concentration of the n-side contact layer, thereby forming the first barrier layer.

19. The method for manufacturing a nitride semiconductor light emitting element according to claim 11 or 12, wherein: In the step of forming the second well layer, the second well layer is formed so that the film thickness of the second well layer is smaller than the film thickness of the first well layer.

20. The method for manufacturing a nitride semiconductor light emitting element according to claim 11 or 12, wherein: In the step of forming the second well layer, the second well layer is formed so that the Al composition ratio of the second well layer is greater than the Al composition ratio of the first well layer.

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