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

Abstract

To provide a nitride semiconductor light-emitting element which emits ultraviolet light with improved luminous efficiency.SOLUTION: The light-emitting element includes an n-side semiconductor layer, a p-side semiconductor layer, and an active layer positioned between the n-side semiconductor layer and the p-side semiconductor layer and also includes an electron blocking layer between the p-side semiconductor layer and the active layer. The active layer includes a first barrier layer containing Al, a first well layer containing Al and emitting ultraviolet light, a second barrier layer containing Al, and a second well layer being in contact with the electron blocking layer, containing Al, and emitting ultraviolet light in order from the n-side semiconductor layer side. The Al composition ratio of the second well layer is higher than the Al composition ratio of the first well layer. The film thickness of the second well layer is smaller than the film thickness of the first well layer.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] In recent years, nitride semiconductor light-emitting devices that emit ultraviolet light have been developed. For example, Patent Document 1 discloses a light-emitting device having a light-emitting layer that emits ultraviolet light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-153645 Summary of the Invention [Problem to be solved by the invention]

[0004] Nitride semiconductor light emitting elements that emit ultraviolet light have room for improvement in light emitting efficiency compared to light emitting elements that emit visible light.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a nitride semiconductor light-emitting device that emits ultraviolet light with improved luminous efficiency and a method for manufacturing the nitride semiconductor light-emitting device. [Means for solving the problem]

[0006] The nitride semiconductor light emitting device according to the present invention comprises: A light-emitting device 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, and further comprising an electron blocking layer between the p-side semiconductor layer and the active layer, the active layer includes, in order from the n-side semiconductor layer side, a first barrier layer containing Al, a first well layer containing Al and emitting ultraviolet light, a second barrier layer containing Al, and a second well layer in contact with the electron blocking layer, containing Al and emitting ultraviolet light, the Al composition ratio of the second well layer is greater than the Al composition ratio of the first well layer; The second well layer has a thickness smaller than that of the first well layer.

[0007] Further, a method for manufacturing a nitride semiconductor light-emitting device according to the present invention includes the steps 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; Including, The step of forming the active layer includes: forming a first barrier layer containing Al on the n-side semiconductor layer; forming a first well layer containing Al and emitting ultraviolet light on the first barrier layer; forming a second barrier layer containing Al on the first well layer; forming a second well layer on the second barrier layer, the second well layer having a thickness smaller than that of the first well layer, containing Al at a composition ratio higher than that of the first well layer, and emitting ultraviolet light; The method includes a step of forming an electron blocking layer in contact with the second well layer between the step of forming the active layer and the step of forming the p-side semiconductor layer. Effect of the Invention

[0008] According to an embodiment of the present invention, a nitride semiconductor light-emitting element and a method for manufacturing the nitride semiconductor light-emitting element can be provided that emits ultraviolet light with improved luminous efficiency, and a method for manufacturing the nitride semiconductor light-emitting element can be provided. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a configuration of a nitride semiconductor light-emitting device according to one embodiment of the present invention. [Diagram 2] 2 is a diagram showing the structures of an active layer and an electron blocking layer of the nitride semiconductor light-emitting element shown in FIG. [Diagram 3]3 is a cross-sectional view showing a state where a base layer is formed on the upper surface of a substrate in a manufacturing method of a light-emitting element according to an embodiment of the present invention. FIG. [Figure 4] 4 is a cross-sectional view showing a state where a superlattice layer is formed on the underlayer shown in FIG. 3 in a manufacturing method for a light-emitting device according to one embodiment of the present invention. [Diagram 5] 5 is a cross-sectional view showing a state where an n-side semiconductor layer is formed on the superlattice layer shown in FIG. 4 in a manufacturing method for a light-emitting device according to one embodiment of the present invention. [Figure 6] 6 is a cross-sectional view showing a state where an active layer is formed on the n-side semiconductor layer shown in FIG. 5 in a manufacturing method for a light-emitting device according to one embodiment of the present invention. [Figure 7] 7 is a cross-sectional view showing a state where an electron blocking layer is formed on the active layer shown in FIG. 6 in a manufacturing method for a light-emitting device according to one embodiment of the present invention. [Figure 8] 8 is a cross-sectional view showing a state where a p-side semiconductor layer is formed on the electron blocking layer shown in FIG. 7 in a manufacturing method for a light-emitting device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments and examples for carrying out the present invention will be described with reference to the drawings. Note that the light-emitting device and the method for manufacturing the light-emitting device described below are intended to embody the technical concept of the present invention, and unless otherwise specified, the present invention is not limited to the following. In each drawing, the same reference numerals may be attached to components having the same function. In consideration of the explanation or ease of understanding of the main points, the embodiments and examples may be shown separately for convenience, but partial replacement or combination of the configurations shown in different embodiments and examples is possible. In the embodiments and examples described below, the description of matters common to the above will be omitted, and only the differences will be described. In particular, similar effects due to similar configurations will not be mentioned in each embodiment or example. The size and positional relationship of the components shown in each drawing may be exaggerated to clarify the explanation. For example, the drawings attached to this specification are mainly schematic diagrams showing a laminated structure, and do not necessarily accurately reflect the film thickness of each layer.

[0011] Embodiment Fig. 1 is a schematic cross-sectional view of a nitride semiconductor light-emitting element 1 according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view showing an enlarged view of an active layer 30 and an electron blocking layer 40, which are parts of a semiconductor structure 100. 1 and 2, 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, and an active layer 30 that is located between the n-side semiconductor layer 20 and the p-side semiconductor layer 50 and emits ultraviolet light, each of which is made of a nitride semiconductor. The semiconductor structure 100 also includes an underlayer 11 and a superlattice layer 12 that are located between the substrate 10 and the n-side semiconductor layer 20, and an electron block layer 40 that is 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. Here, the active layer 30 includes, in order from the n-side semiconductor layer 20 side, a first barrier layer 31 containing Al, 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 second well layer 34 is in contact with the electron blocking layer 40. The Al composition ratio of the second well layer 34 is greater than the Al composition ratio of the first well layer 32 , and the film thickness of the second well layer 34 is smaller than the film thickness of the first well layer 32 . According to the nitride semiconductor light emitting device of the embodiment configured as described above, it is possible to provide a nitride semiconductor light emitting device that emits ultraviolet light with improved luminous efficiency. The specific configurations of the substrate 10 and each of the semiconductor layers will now be described. In the following description, the configuration excluding the active layer 30 will be described first, and then the active layer 30 will be described in detail.

[0012] The material of the substrate 10 may be, for example, sapphire, silicon (Si), gallium nitride (GaN), aluminum nitride (AlN), or the like. The substrate 10 made of sapphire is preferable because it has high translucency to ultraviolet light from the active layer 30. The semiconductor structure 100 may be disposed, for example, on the c-plane of the sapphire substrate, and is preferably disposed on a plane inclined from the c-plane of the sapphire substrate toward the a-axis direction or m-axis direction of the sapphire substrate at an angle of 0.2° to 2°. The thickness of the substrate 10 may be, for example, 150 μm to 800 μm. The nitride semiconductor light-emitting element 1 does not need to have the substrate 10.

[0013] The semiconductor structure 100 is a laminated body in which a plurality of semiconductor layers made of nitride semiconductors are stacked. x Al y Ga 1-x-y This includes all semiconductors with compositions in which the composition ratios x and y in the chemical formula N (0≦x≦1, 0≦y≦1, x+y≦1) are changed within their respective ranges.

[0014] The underlayer 11 may be, for example, a layer made of AlN. The underlayer 11 has a function of reducing the lattice mismatch between the substrate 10 and the nitride semiconductor layer disposed on the underlayer 11. The underlayer 11 may have a thickness of, for example, 0.5 μm to 4 μm, and preferably 1.5 μm to 4 μm. The underlayer 11 may include a buffer layer, and the buffer layer is located near the surface of the substrate 10. In this specification, the thickness of each semiconductor layer refers to the thickness in the stacking direction of the semiconductor structure 100.

[0015] 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 relieving stress occurring in the semiconductor layers disposed above the superlattice layer 12. The superlattice layer 12 may have a multilayer structure in which, for example, 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 may be 20 pairs or more and 50 pairs or less. When the first semiconductor layer is an AlGaN layer and the second semiconductor layer is an AlN layer, for example, the thickness of the first semiconductor layer may be 5 nm or more and 30 nm or less, and the thickness of the second semiconductor layer may be 5 nm or more and 30 nm or less.

[0016] The n-side semiconductor layer 20 includes one or more n-type semiconductor layers. Examples of the n-type semiconductor layers include semiconductor layers containing n-type impurities such as silicon (Si) and germanium (Ge). The n-type semiconductor layer is, for example, an AlGaN layer containing aluminum (Al), gallium (Ga) and nitrogen (N), and may 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 More than 1×10 20 / cm 3 The n-side semiconductor layer 20 may include an undoped layer as long as it has a function of supplying electrons to the active layer 30. Here, the undoped layer is a layer that is not intentionally doped with n-type impurities or p-type impurities. When an undoped layer is adjacent to a layer intentionally doped with n-type impurities and / or p-type impurities, the undoped layer may contain n-type impurities and / or p-type impurities due to diffusion from the adjacent layer, etc.

[0017] 1 , 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.

[0018] 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, for example, not less than 25% and not more than 70%.

[0019] The n-side contact layer 22 may be, for example, a layer made of AlGaN containing n-type impurities. When the n-side contact layer is an AlGaN layer, the Al composition ratio of the AlGaN layer may be, for example, 25% or more and 70% or less. In this specification, for example, an AlGaN layer having an Al composition ratio of 50% is defined as an AlGaN layer having an Al composition ratio of 100%. X Ga 1-X In the chemical formula consisting of N, the composition ratio x of the AlGaN layer is 0.5. The n-type impurity concentration of the n-side contact layer 22 is, for example, 5×10 18 / cm 3 More than 1×10 20 / cm 3 The thickness of the n-side contact layer 22 can be set to, for example, 1.5 μm or more and 4 μm or less. 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, it is possible to reduce an increase in forward voltage. The thickness of the n-side contact layer 22 can be set to, for example, 1.5 μm or more and 4 μm or less. The n-side contact layer 22 has an upper surface on which no other semiconductor layers are arranged. An n-electrode 60 is arranged on the upper surface of the n-side contact layer 22 on which no other semiconductor layers are arranged.

[0020] The electron block layer 40 is a layer for reducing the overflow of electrons supplied from the n-side semiconductor layer 20. For the electron block layer 40, it is preferable to use a nitride semiconductor layer having a relatively large band gap. For example, as described later, when the second well layer 34 in contact with the electron block layer 40 is composed of a nitride semiconductor layer containing Al, for example, a nitride semiconductor layer having a higher Al content than the second well layer 34 can be used for the electron block layer 40. The electron block layer 40 may include multiple layers. For example, as shown in FIG. 2, the electron block layer 40 can have a multilayer structure having a first electron block layer 41, a second electron block layer 42, and a third electron block layer 43 in this order from the active layer 30 side. For example, the first electron block layer 41, the second electron block layer 42, and the third electron block layer 43 each contain Al. For example, the first electron block layer 41 can be an AlN layer, the second electron block layer 42 can be an AlGaN layer, and the third electron block layer 43 can be an AlGaN layer. In this specific example, the Al composition ratio of the second electron block layer 42 is lower than that of the third electron block layer 43. The Al composition ratio of the second electron block layer 42 is higher than that of the first well layer 32 and the second well layer 34. In the electron block layer 40 of this specific example, the Al composition ratio of the second electron block layer 42 and the Al composition ratio of the third electron block layer 43 are preferably higher than that of the second barrier layer 33, for example. This can reduce the overflow of electrons. For example, an undoped AlGaN layer or an undoped AlN layer can be used for the electron block layer 40. The total thickness of the electron block layer 40 can be, for example, 4 nm to 15 nm.

[0021] The p-side semiconductor layer 50 preferably has high light transmittance to the light from the first well layer 32 and the second well layer 34. For example, it is preferable to include an AlGaN layer having a higher Al composition ratio than the Al composition ratios of the first well layer 32 and the second well layer 34. However, an AlGaN layer having a high Al composition ratio has a larger band gap than a GaN layer or the like. Therefore, when an AlGaN layer having a high Al composition ratio is used for the p-side semiconductor layer 50, the p-side semiconductor layer 50 is likely to be insufficiently p-typed, or the contact resistance between the p-electrode 70 and the p-side semiconductor layer 50 is likely to be large. For these reasons, in a nitride semiconductor light-emitting device using an AlGaN layer having a relatively high Al composition ratio as the first well layer 32 and the second well layer 34, it is necessary to achieve both high light extraction efficiency and low forward voltage. Therefore, in this embodiment, by having the following p-side semiconductor layer 50, it is possible to obtain a nitride semiconductor light-emitting device 1 having high light extraction efficiency and low forward voltage.

[0022] For example, in this embodiment, the p-side semiconductor layer 50 includes a first p-side semiconductor layer 51 and a second p-side semiconductor layer 52, as shown in Fig. 1. Here, the first p-side semiconductor layer 51 is a layer containing p-type impurities such as magnesium (Mg) and having a large Al composition ratio, and the second p-side semiconductor layer 52 is a layer containing p-type impurities such as Mg and having a small Al composition ratio or a layer not containing Al (e.g., a GaN layer). In this way, by including the first p-side semiconductor layer 51 and the second p-side semiconductor layer 52, it is possible to provide a nitride semiconductor light-emitting element 1 having high light extraction efficiency and low forward voltage Vf.

[0023] Furthermore, the first p-side semiconductor layer 51 and the second p-side semiconductor layer 52 may be a single layer or a layer including multiple layers. For example, the first p-side semiconductor layer 51 may include, in order from the active layer 30 side, a first layer made of an AlGaN layer, a second layer made of an AlGaN layer having an Al composition ratio lower than that of the first layer, and a third layer made of an AlGaN layer having an Al composition ratio lower than that of the second layer. In this case, the third layer may be a composition gradient layer in which the Al composition ratio is gradually decreased. The second p-side semiconductor layer 52 may include, for example, a fourth layer made of an AlGaN layer and a fifth layer made of a GaN layer from the first p-side semiconductor layer 51 side. In this way, by including the first to fifth layers, it is possible to obtain a nitride semiconductor light-emitting device 1 having higher light extraction efficiency and lower forward voltage Vf.

[0024] The n-electrode 60 is disposed on the n-side contact layer 22 and is 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 is electrically connected to the p-side semiconductor layer 50.

[0025] For example, a metal such as Ag, Al, Ni, Au, Rh, Ti, Pt, Mo, Ta, W, or Ru, or an alloy mainly composed of these metals can be used for the n-electrode 60. The n-electrode 60 can have a multilayer structure including, for example, 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.

[0026] The p-electrode 70 may be made of, for example, the same metal as the n-electrode 60 described above. In the case where the p-electrode 70 has a function of reflecting light from the active layer 30 toward the p-electrode 70 toward the n-side semiconductor layer 20, it is preferable that the metal layer of the p-electrode 70 that contacts the third layer 53 is a metal layer having a high reflectance with respect to the light from the active layer 30. For example, it is preferable to use a metal layer having a reflectance 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 may be made of, for example, a multilayer structure including an Rh layer, an Au layer, a Ni layer, and a Ti layer, or a multilayer structure including an Ru layer, an Au layer, a Ni layer, and a Ti layer.

[0027] 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, causing the active layer 30 to emit light. The active layer 30 will now be described in detail.

[0028] 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, not less than 220 nm and not more than 350 nm.

[0029] The active layer 30 includes, in order from the n-side semiconductor layer 20 side, for example, a first barrier layer 31 containing Al, 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. The first well layer 32 may have a thickness of, for example, 3 nm or more and 6 nm or less. The second well layer 34 may have a thickness of, for example, 1 nm or more and 4 nm or less. The first layer 31a of the first barrier layer 31 may have a thickness of, for example, 10 nm or more and 60 nm or less, and the second layer 31b may have a thickness of, for example, 5 nm or more and 20 nm or less. The second barrier layer 33 may have a thickness of, for example, 1 nm or more and 5 nm or less. Specific examples of the first well layer 32, the second well layer 34, the first barrier layer 31, and the second barrier layer 33 will be described below.

[0030] The first well layer 32 and the second well layer 34 may be, for example, a layer made of AlGaN. The first barrier layer 31 and the second barrier layer 33 may be, for example, a layer made of AlGaN. The Al composition ratio of the first well layer 32 and the second well layer 34 may be, for example, 10% or more, specifically 10% to 50%, and more specifically 30% to 50%. When the emission peak wavelength of the light from the first well layer 32 and the second well layer 34 is set to about 280 nm, the first well layer 32 and the second well layer 34 may be an AlGaN layer having an Al composition ratio of about 42%. The Al composition ratio of the first barrier layer 32 and the second barrier layer 33 may be, for example, 10% or more, specifically 10% to 70%, and more specifically 30% to 70%.

[0031] In the nitride semiconductor light emitting device 1, the Al composition ratio of the second well layer 34 is made larger than the Al composition ratio of the first well layer 32, and the film thickness of the second well layer 34 is made smaller than the film thickness of the first well layer 32. This makes it possible to increase the luminous efficiency of the entire active layer including the first well layer 32 and the second well layer 34. More specifically, in the second well layer 34 in contact with the electron block layer 40, a distortion occurs in the band structure, and the probability of radiative recombination tends to be low. This may cause a shift between the emission peak wavelength of the second well layer 34 and the emission peak wavelength of the first well layer 32. In the nitride semiconductor light-emitting device 1 of this embodiment, the Al composition ratio of the second well layer 34 is made larger than the Al composition ratio of the first well layer 32. By doing so, the difference between the band gap of the second well layer 34 and the band gap of the electron block layer 40 can be reduced, and the distortion occurring in the band structure of the second well layer 34 can be reduced. As a result, the shift between the emission peak wavelength of the second well layer 34 and the emission peak wavelength of the first well layer 32 can be reduced, and the luminous efficiency of the active layer as a whole can be increased. Furthermore, the light emission in the second well layer 34 is reduced by making the film thickness of the second well layer 34 smaller than the film thickness of the first well layer 32. This makes it possible to reduce the light emission from the second well layer 34 of the light having an emission peak wavelength shifted from the emission peak wavelength of the first well layer 32, thereby increasing the light emission efficiency of the active layer as a whole.

[0032] In the nitride semiconductor light-emitting device 1 of this embodiment, the difference between the Al composition ratio of the second well layer 34 and the Al composition ratio of the first well layer 32, and the ratio of the film thickness of the second well layer 34 to the film thickness of the first well layer 32 are appropriately set in consideration of the light-emitting efficiency of the active layer 30 as a whole and the shift in the light-emitting wavelength. For example, the thickness of the second well layer 34 is 30% or more and 60% or less of the thickness of the first well layer 32. Furthermore, for example, the difference between the Al composition ratio of the first well layer 32 and the Al composition ratio of the second well layer 34 is not less than 2% and not more than 10%. Furthermore, for example, the difference between the Al composition ratio of the second well layer 34 and the Al composition ratio of the electron blocking layer 40 is smaller than the difference between the Al composition ratio of the first well layer 32 and the electron blocking layer 40 . Preferred embodiments of the first barrier layer 31 and the second barrier layer 33 will be described below.

[0033] It is preferable that the highest n-type impurity concentration peak in the first barrier layer 31 is located on the p-side semiconductor layer 50 side. This can increase the luminous efficiency in the first well layer 32. That is, in the first barrier layer 31, the peak of the n-type impurity concentration is located on the p-side semiconductor layer 50 side, and 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 increased, and the hole confinement effect in the first well layer 32 is further improved. This can increase the luminous efficiency in the first well layer 32. In addition, there is a concern that the crystallinity of the first barrier layer 31 may deteriorate if an n-type impurity is added to the first barrier layer 31. However, in this example, by locating the highest n-type impurity concentration peak in the first barrier layer 31 on the p-side semiconductor layer 50 side, the barrier at the boundary between the first well layer 32 and the first barrier layer 31 is increased, while the n-type impurity concentration is decreased in the first barrier layer 31 on the n-side semiconductor layer 20 side. This reduces the deterioration of the crystallinity of the entire first barrier layer 31. Here, the highest peak value of the n-type impurity concentration in the first barrier layer 31 located on the p-side semiconductor layer 50 side is, for example, 1×10 19 / cm 3 More than 6×10 19 / cm 3 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 highest n-type impurity concentration peak in the first barrier layer 31. For example, the value of the lowest n-type impurity concentration in the first barrier layer 31 is 1×10 17 / cm 3 More than 9×10 17 / cm 3 The following is the result. Moreover, the Al composition ratio of the first barrier layer 31 is preferably higher than that of the second barrier layer 33. This can increase the luminous efficiency of the first well layer 32. That is, by making the Al composition ratio of the first barrier layer 31 higher than that of the second barrier layer 33, the band gap of the second barrier layer 33 is made smaller than that of the first barrier layer 31, and the number of holes injected into the first well layer 32 can be increased. Furthermore, since the band gap of the first barrier layer 31 is larger than that of the second barrier layer 33, the hole confinement effect in the first well layer 32 can be increased. This increases the luminous efficiency of the first well layer 32. 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 by 3% to 17%. Specific configuration examples and preferred examples of the barrier layers and well layers in this embodiment will be described below.

[0034] For example, as shown in FIG. 2, the first barrier layer 31 has a first layer 31a and a second layer 31b located closer to the p-side semiconductor layer 50 than 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 lower than the average n-type impurity concentration in the entire first barrier layer 31, and the n-type impurity concentration of the second layer 31b is higher than the average n-type impurity concentration in the entire first barrier layer 31. In this way, the first barrier layer 31 has the first layer 31a and the second layer 31b having different n-type impurity concentrations, so that 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. The position of the lowest n-type impurity concentration in the first barrier layer 31 is located within the second layer 31b. 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 higher than the average n-type impurity concentration in the entire first barrier layer 31. Therefore, by reducing the thickness of the second layer 31b having a relatively high n-type impurity concentration, it is possible to reduce the deterioration of the crystallinity of the first barrier layer 31 caused by the layer having a high n-type impurity concentration becoming thick, and improve the light emission efficiency. For example, the thickness of the second layer 31b is preferably 5% to 30% of the entire thickness of the first barrier layer 31. This makes it possible to reduce the deterioration of the crystallinity of the first barrier layer 31 while improving the hole confinement effect in the first well layer 32.

[0035] Moreover, the thickness of the second barrier layer 33 is preferably smaller than the thickness of the second layer 31b, so that the supply of holes to the first well layer 32 can be increased. The second barrier layer 33 may be undoped or may contain n-type impurities. When the second barrier layer 33 is undoped, deterioration of the crystallinity of the active layer 30 can be reduced. When the second barrier layer 33 contains n-type impurities, the electrical resistance of the second barrier layer 33 can be reduced to reduce the forward voltage. When the second barrier layer 33 contains n-type impurities, it is preferable that the n-type impurity concentration of the second barrier layer 33 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. This makes it possible to reduce the forward voltage while reducing deterioration of the crystallinity of the second barrier layer 33. In addition, it is preferable that the Al composition ratio of the first layer 31a and the Al composition ratio of the second layer 31b are substantially the same, which can reduce the band gap difference caused by the difference between the Al composition ratio of the first layer 31a and the Al composition ratio of the second layer 31b, thereby making it possible to efficiently supply electrons to the first well layer 32. Furthermore, the first barrier layer 31 is in contact with the n-side semiconductor layer 20, and it is preferable that the Al composition ratio of the first barrier layer 31 is substantially the same as that of the n-side semiconductor layer 20. This makes it possible to reduce the difference in band gap caused by the difference between the Al composition ratio of the n-side semiconductor layer 20 and the Al composition ratio of the first barrier layer 31, and therefore electrons can be efficiently supplied to the first well layer 32.

[0036] 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 preferable 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. This makes it possible to reduce the resistance of the n-side contact layer 22 while suppressing deterioration of the crystallinity of the n-side contact layer 22.

[0037] As described above, the thickness of the second well layer 34 is preferably smaller than the thickness of the first well layer 32. This makes it possible to increase the supply of holes to the first well layer 32.

[0038] As described above, the Al composition ratio of the second well layer 34 is higher than the Al composition ratio of the first well layer 32. The Al composition ratio of the second well layer 34 can be higher than the Al composition ratio of the first well layer 32 by, for example, 2% to 10%.

[0039] While specific configuration examples and preferred examples of the barrier layer and well layer have been described above, the film thickness, Al composition ratio, doping amount of n-type impurity, etc. of the first layer 31a and second layer 31b in the first barrier layer 31 and the second barrier layer 33 can be optimized in consideration of the above specific configuration examples and preferred examples based on the specifications of the target emission wavelength and emission output, driving voltage, current, etc. Similarly, the film thickness, Al composition ratio, doping amount, etc. of the first well layer 32 and second well layer 34 can also be optimized in consideration of the above specific configuration examples and preferred examples.

[0040] In this embodiment, a specific example including two barrier layers and two well layers as shown in Fig. 2 has been described, but the present invention is not limited to this example. For example, one or more barrier layers and well layers may be included between the first well layer 32 and the second well layer 34.

[0041] Hereinafter, the method for manufacturing the nitride semiconductor light emitting device according to this embodiment will be described with reference to FIGS.

[0042] The method for manufacturing a nitride semiconductor light emitting device according to the present embodiment includes the steps of: (S1) forming an n-side semiconductor layer; (S2) forming an active layer on the n-side semiconductor layer; (S3) forming a p-side semiconductor layer on the active layer; Including, (S2) The step of forming an active layer includes: (S2-1) forming a first barrier layer containing Al on an n-side semiconductor layer; (S2-2) forming a first well layer containing Al and emitting ultraviolet light on the first barrier layer; (S2-3) forming a second barrier layer containing Al on the first well layer; (S2-4) forming a second well layer on the second barrier layer, the second well layer having a thickness smaller than that of the first well layer, containing Al at a higher Al composition ratio than that of the first well layer, and emitting ultraviolet light; (S4) A step of forming an electron blocking layer in contact with the second well layer is included between the step of forming the active layer and the step of forming the p-side semiconductor layer. Here, the step of forming a first barrier layer on the n-side semiconductor layer (S2-1) includes the steps of: (S2-1-1) forming a first layer containing Al and an n-type impurity on an n-side semiconductor layer; (S2-1-2) forming a second layer on the first layer, the second layer containing Al and containing an n-type impurity at a higher concentration than the first layer; may also include In addition, when the (S2-1) step of forming a first barrier layer includes steps of forming a first layer and a second layer, the (S2-3) step of forming a second barrier layer is preferably a step of forming a second barrier layer that 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. In the following description, the above-mentioned preferred example will be included, but this preferred example is optional and is not essential to this embodiment.

[0043] 3, for example, an underlayer 11 made of AlN is formed on the c-plane of a substrate 10 made of sapphire. The underlayer 11 is formed by, for example, a metalorganic chemical vapor deposition (MOCVD) method or a sputtering method. Here, the step of forming the underlayer 11 may include a step of forming the underlayer 11 including a buffer layer. For example, a buffer layer made of AlN is formed by a sputtering method, and then an AlN layer is formed on the buffer layer by, for example, a metalorganic chemical vapor deposition (MOCVD) method, thereby forming the underlayer 11 including a buffer layer. Each semiconductor layer described below can be formed by epitaxial growth using, for example, the MOCVD method.

[0044] Next, as shown in FIG. 4, a superlattice layer 12 is formed on the underlayer 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 by growing an AlN layer using, for example, trimethylaluminum (TMA) gas and ammonia gas as raw material gases and mainly hydrogen (H2) gas as a carrier gas. The second semiconductor layer is formed by growing an AlGaN layer using, for example, TMA gas, trimethylgallium (TMG) gas and ammonia gas as raw material gases and mainly hydrogen gas as a carrier gas. Each layer of the superlattice layer 12 can be formed at a temperature of, for example, 1000° C. or more and 1250° C. or less.

[0045] Next, as shown in FIG. 5, 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 by growing an AlGaN layer using, for example, TMA gas, TMG gas, and ammonia gas as raw material gases and mainly hydrogen gas as a carrier gas. The n-side contact layer 22 is formed by growing an AlGaN layer including n-type impurities using, for example, TMA gas, TMG gas, and ammonia gas as raw material gases, monosilane (SiH4) gas as n-type impurity gas, and mainly hydrogen gas as a carrier gas. Each layer of the n-side semiconductor layer 20 can be formed at a temperature of, for example, 1000° C. or more and 1250° C. or less.

[0046] Next, as shown in FIG. 6, the active layer 30 is formed on the n-side contact layer 22. Specifically, first, a first barrier layer 31 containing Al is formed on the n-side contact layer 22. The first barrier layer 31 is formed by growing an AlGaN layer containing Si as an n-type impurity or an undoped AlGaN layer using, for example, TMA gas, TEG gas, or ammonia gas as a source gas, monosilane (SiH4) gas as an n-type impurity gas as necessary, and mainly nitrogen gas as a carrier gas. Next, a first well layer 32 containing Al and emitting ultraviolet light is formed on the first barrier layer 31. The first well layer 32 is formed by growing an AlGaN layer using, for example, TMA gas, TEG gas, and ammonia gas as source gases and mainly nitrogen gas as a carrier gas. Next, a second barrier layer 33 containing Al is formed on the first well layer 32. The second barrier layer 33 is formed in the same manner as the first barrier layer 31 by growing an AlGaN layer containing Si as an n-type impurity or an undoped AlGaN layer using, for example, TMA gas, TEG gas, or ammonia gas as a source gas, monosilane (SiH4) gas as necessary as an n-type impurity gas, and mainly nitrogen gas as a carrier gas.

[0047] Next, a second well layer 34 is formed on the second barrier layer 33. The second well layer 34 has a thickness smaller than that of the first well layer 32, contains Al in a higher composition ratio than the Al composition ratio of the first well layer 32, and emits ultraviolet light. The second well layer 34 can be formed using the same source gas and carrier gas as those for the first well layer 32, for example, by increasing the ratio of TMA gas in the source gas and growing the second well layer 34 for a shorter time than the first well layer 32. In this way, the second well layer 34 can be formed to a thickness smaller than that of the first well layer 32 and containing Al at a higher composition ratio than the Al composition ratio of the first well layer 32.

[0048] When the first barrier layer 31 is formed so as to include the first layer 31a and the second layer 31b containing the n-type impurity at a higher concentration than the first layer 31a, it is formed, for example, as follows. First, for example, TMA gas, TEG gas, and ammonia gas are used as raw material gases, monosilane (SiH4) gas is used as an n-type impurity gas, and nitrogen gas is mainly used as a carrier gas to form a first layer containing Al and n-type impurities on the n-side semiconductor layer. Next, the flow rate of monosilane (SiH4) gas is increased to form a second layer on the first layer, the second layer containing Al and containing n-type impurities at a higher concentration than the first layer.

[0049] Next, as shown in FIG. 7, an electron block layer 40 is formed on the active layer 30 in contact with the second well layer 34 and having a band gap larger than that of the first well layer 32 and the second well layer 34. The electron block layer 40 is formed to include a first electron block layer 41 which is an AlN layer, a second electron block layer 42 which is a first AlGaN layer, and a third electron block layer 43 which is a second AlGaN layer. The first electron block layer 41 is formed, for example, by using TMA gas and ammonia gas as raw material gases and mainly using nitrogen gas as a carrier gas. The second electron block layer 42 is formed, for example, by using TMA gas, TEG gas, and ammonia gas as raw material gases and mainly using nitrogen gas as a carrier gas. The third electron block layer 43 is formed, for example, by using TMA gas, TEG gas, and ammonia gas as raw material gases and mainly using nitrogen gas as a carrier gas. For example, in the step of forming the third electron block layer 43, the flow rate ratio of TMA gas, which is a source gas for Al, is set to be higher than the flow rate ratio of TMA gas in the step of forming the second electron block layer 42. This allows the third electron block layer 43 to be formed so that its Al composition ratio is higher than that of the second electron block layer 42. Each layer of the electron block layer 40 can be formed at a temperature of, for example, 750° C. or higher and 950° C. or lower.

[0050] 8, 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 this order from the active layer 30 side. The first p-side semiconductor layer 51 is formed by growing an AlGaN layer containing Mg as a p-type impurity using, for example, TMA gas, TEG gas, and ammonia gas as source gases and cyclopentadienyl magnesium (Cp2Mg) gas as a p-type impurity gas. The second p-side semiconductor layer 52 is formed, for example, by using TMA gas, TMG gas, and ammonia gas as raw material gases and cyclopentadienyl magnesium (CpMg) gas as a p-type impurity gas to grow an AlGaN layer containing Mg as a p-type impurity, or by using TMG gas and ammonia gas without using TMA gas as a raw material gas and cyclopentadienyl magnesium (CpMg) gas as a p-type impurity gas to grow a GaN layer containing Mg as a p-type impurity. 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.

[0051] After the p-side semiconductor layer 50 is formed, a part of the p-side semiconductor layer 50, a part of the electron blocking layer 40, and a part of the active layer 30 are removed to expose a part of the n-side contact layer 22.

[0052] Then, as shown in FIG. 1, 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.

[0053] By carrying out the steps described above, the nitride semiconductor light emitting device of this embodiment can be manufactured.

[0054] Hereinafter, nitride semiconductor light emitting devices according to examples will be described.

[0055] <Example> A substrate made of sapphire with a C-plane as the main surface was used as the substrate 10. On the substrate 10, an underlayer 11 made of AlN including a buffer layer was formed to a thickness of 2.1 μm.

[0056] Next, the temperature was raised to 1175° C., and Al was deposited on the underlayer 11 using TMA gas, TMG gas, and ammonia gas as source gases. 0.60 Ga 0.40 The N layer was formed to a thickness of about 21 nm. Then, the temperature was raised to 1175° C., and an AlN layer was formed to a thickness of about 10 nm using TMA gas and ammonia gas as the raw material gas. The superlattice layer 12 was formed by forming 30 pairs of stacked bodies of the AlGaN layer and the AlN layer thus formed.

[0057] Next, the temperature was raised to 1175° C., and Al was deposited on the superlattice layer 12 using TMA gas, TMG gas, and ammonia gas as source gases. 0.60 Ga 0.40 An N layer was formed to a thickness of about 0.5 μm to form an undoped layer 21. Next, the temperature was set to 1175° C., and TMA gas, TMG gas, ammonia gas, and SiH4 gas were used as raw material gases to form an Al layer containing n-type impurities. 0.60 Ga 0.40 The N layer was formed to a thickness of about 2.2 μm to form the n-side contact layer 22. The n-side semiconductor layer 20 was formed including the undoped layer 21 and the n-side contact layer 22. The n-type impurity concentration of the n-side contact layer 22 was about 9.5×10 18 / cm 3 It was decided.

[0058] Next, the temperature was raised to 950° C., and TMA gas, TMG gas, ammonia gas, and SiH4 gas were used as raw material gases to form Al containing n-type impurities on the n-side semiconductor layer 20. 0.60 Ga 0.40 The first layer 31a was formed by forming an N layer with a thickness of about 40 nm. Then, the temperature was raised to 950° C., and TMA gas, TMG gas, ammonia gas, and SiH4 gas were used as raw material gases to form an Al layer containing n-type impurities. 0.60 Ga 0.40The second layer 31b was formed by forming an N layer with a thickness of about 10 nm. The flow rates of the source gases used to form the first layer 31a were TMA gas 16 sccm, TEG gas 45 sccm, ammonia gas 10 slm, and SiH4 gas 0.5 sccm, and the flow rates of the source gases used to form the second layer 31b were TMA gas 16 sccm, TEG gas 45 sccm, ammonia gas 10 slm, and SiH4 gas 16 sccm. In this manner, the first barrier layer 31 was formed, which included the first layer 31a containing n-type impurities and the second layer 31b containing more n-type impurities than the first layer 31a. In addition, the thicknesses of the first layer 31a and the second layer 31b referred to here are thicknesses during the manufacturing process, and the thicknesses of the first layer 31a having an n-type impurity concentration lower than the average value in the entire first barrier layer 31, and the thicknesses of the second layer 31b having an n-type impurity concentration higher than the average value in the entire first barrier layer 31, specified in the manufactured product, do not necessarily match. Next, the temperature was raised to 950°C, and Al was grown using TMA gas, TEG gas, and ammonia gas as the raw material gas. 0.43 Ga 0.57 The first well layer 32 was formed by forming an N layer to a thickness of about 4.4 nm.

[0059] Next, the temperature was raised to 950°C, and Al was grown using TMA gas, TEG gas, and ammonia gas as the raw material gas. 0.53 Ga 0.47 The N layer was formed to a thickness of about 2.5 nm to form the second barrier layer 33. Then, the temperature was raised to 950° C., and Al was grown using TMA gas, TEG gas, and ammonia gas as source gases. 0.47 Ga 0.53 The N layer was formed to a thickness of about 2.2 nm to form the second well layer 34. In this manner, the active layer 30 including two well layers and two barrier layers was formed.

[0060] Next, the temperature was raised to 870° C., and TMA gas and ammonia gas were used as the source gas to form the first electron blocking layer 41, which is an AlN layer, on the active layer 30 to a thickness of about 1.3 nm. Next, the temperature was raised to 870° C., and TMA gas, TEG gas, and ammonia gas were used as the source gas to form the AlN layer. 0.55 Ga 0.45 The N layer was formed to a thickness of about 1.2 nm to form the second electron blocking layer 42, which is the first AlGaN layer. Then, the temperature was raised to 870° C., and TMA gas, TEG gas, and ammonia gas were used as the source gases to form the Al 0.78 Ga 0.22 By forming an AlGaN layer with a thickness of about 4 nm, the third electron blocking layer 43, which is the second AlGaN layer, was formed. In this manner, the electron blocking layer 40 including the AlN layer and the two AlGaN layers was formed.

[0061] Next, the temperature was raised to 870° C., and TMA gas, TEG gas, ammonia gas, and Cp2Mg gas were used as source gases to form Al containing p-type impurities on the electron block layer 40. 0.63 Ga 0.37 The N layer was then formed to a thickness of about 75 nm. The temperature was then raised to 870° C., and TMA gas, TEG gas, ammonia gas, and Cp2Mg gas were used as the source gases to form an Al layer containing p-type impurities. 0.53 Ga 0.47 The N layer was formed to a thickness of about 27 nm. Then, the temperature was raised to 870° C., and TMA gas, TEG gas, ammonia gas, and Cp2Mg gas were used as the source gas. The TMA gas was gradually reduced to form a p-type impurity-containing AlN layer. 0.53 Ga 0.47 A composition gradient layer was formed to a thickness of 3 nm, which was made up of a layer in which the Al composition ratio was gradually reduced from N until it reached 0. In this manner, the first p-side semiconductor layer 51 was formed.

[0062] Next, the temperature was raised to 900°C, and Al containing p-type impurities was grown using TMA gas, TMG gas, ammonia gas, and Cp2Mg gas as the source gas. 0.40 Ga 0.60The N layer was formed to a thickness of about 10 nm. Then, the temperature was raised to 900° C., and a GaN layer containing p-type impurities was formed to a thickness of about 10 nm using TMA gas, TMG gas, and ammonia gas as the source gas. 0.40 Ga 0.60 A second p-side semiconductor layer 52 was formed, which included an N layer and a GaN layer containing p-type impurities.

[0063] After each semiconductor layer was formed, a heat treatment was performed on each semiconductor layer in a reaction vessel. The heat treatment was carried out in a nitrogen atmosphere at a temperature of about 475°C.

[0064] After the heat treatment, a part of the p-side semiconductor layer 50 and a part of the active layer 30 were removed, and a part of the n-side contact layer 22 was exposed from the p-side semiconductor layer 50 and the active layer 30.

[0065] Next, an n-electrode 60 was formed on the n-side contact layer 22, and a p-electrode 70 was formed on the p-side semiconductor layer 50. The n-electrode 60 was a multilayered electrode having a Ti layer, an AlSi layer, a Ta layer, a Ru layer, and a Ti layer stacked in this order from the n-side contact layer 22 side. The p-electrode 70 was a multilayered electrode having a Ti layer, a Ru layer, and a Ti layer stacked in this order from the third layer 53 side.

[0066] The nitride semiconductor light emitting device of this example fabricated as described above had a forward voltage of 5.16 V and a light output power Po of 172 mW. Note that the forward voltage and light output power Po shown here are values ​​when a current of 350 mA was applied. The position of the highest peak of the n-type impurity concentration in the first barrier layer 31 was in the second layer 31b. The value of the highest peak of the n-type impurity concentration in the first barrier layer 31 was about 3×10 19 / cm 3 It was.

[0067] The nitride semiconductor light emitting device according to the embodiment of the present disclosure includes, for example, the following aspects. [Section 1] A light-emitting device 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, and further comprising an electron blocking layer between the p-side semiconductor layer and the active layer, the active layer includes, in order from the n-side semiconductor layer side, a first barrier layer containing Al, a first well layer containing Al and emitting ultraviolet light, a second barrier layer containing Al, and a second well layer in contact with the electron blocking layer, containing Al and emitting ultraviolet light, the Al composition ratio of the second well layer is greater than the Al composition ratio of the first well layer; The second well layer has a thickness smaller than that of the first well layer. Nitride semiconductor light emitting device. [Section 2] 2. The nitride semiconductor light emitting device according to item 1, wherein the thickness of the second well layer is 30% to 60% of the thickness of the first well layer. [Section 3] 3. The nitride semiconductor light emitting device according to item 1 or 2, wherein the difference between the Al composition ratio of the first well layer and the Al composition ratio of the second well layer is 2% or more and 10% or less. [Section 4] the first barrier layer contains an n-type impurity; 4. The nitride semiconductor light emitting device according to any one of items 1 to 3, wherein the highest peak of the n-type impurity concentration in the first barrier layer is located on the p-side semiconductor layer side. [Section 5] 5. The nitride semiconductor light-emitting device according to any one of items 1 to 4, wherein the first barrier layer includes a first layer containing an n-type impurity at a concentration lower than an average value of an n-type impurity concentration in the entire first barrier layer, and a second layer located closer to the p-side semiconductor layer than the first layer and containing an n-type impurity at a concentration higher than the average value. [Section 6] 6. The nitride semiconductor light emitting device according to any one of items 1 to 5, wherein the Al composition ratio of the first barrier layer is larger than the Al composition ratio of the second barrier layer. [Section 7] The nitride semiconductor light emitting device according to item 5 or item 6 citing item 5, wherein the first layer has a thickness larger than that of the second layer. [Section 8] Item 5. The nitride semiconductor light emitting device according to item 5 or item 6 citing item 5, wherein the second layer has a thickness of 5% to 30% of the thickness of the first barrier layer. [Section 9] The nitride semiconductor light emitting device according to item 5 or any one of items 6 to 8 which cite item 5, wherein the second barrier layer has a smaller thickness than the second layer. [Section 10] The nitride semiconductor light-emitting device according to item 5 or any one of items 6 to 9 which quotes item 5, wherein the second barrier layer contains an n-type impurity, and 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. [Section 11] 11. The nitride semiconductor light emitting device according to any one of items 1 to 10, wherein an Al composition ratio of the first barrier layer and an Al composition ratio of the n-side semiconductor layer are substantially the same. [Section 12] The nitride semiconductor light-emitting device according to item 5 or any one of items 6 to 11 which cites item 5, wherein an n-type impurity concentration of the n-side semiconductor 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. [Section 13] 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; Including, The step of forming the active layer includes: forming a first barrier layer containing Al on the n-side semiconductor layer; forming a first well layer containing Al and emitting ultraviolet light on the first barrier layer; forming a second barrier layer containing Al on the first well layer; forming a second well layer on the second barrier layer, the second well layer having a thickness smaller than that of the first well layer, containing Al at a composition ratio higher than that of the first well layer, and emitting ultraviolet light; a step of forming an electron blocking layer, the electron blocking layer being in contact with the second well layer and having an Al composition ratio larger than those of the first well layer and the second well layer, between the step of forming the active layer and the step of forming the p-side semiconductor layer. [Section 14] Item 14. The method for producing a nitride semiconductor light-emitting device according to item 13, wherein in the step of forming the second well layer, the second well layer is formed to a thickness that is 30% to 60% of a thickness of the first well layer. [Section 15] Item 15. The method for manufacturing a nitride semiconductor light-emitting device according to item 13 or 14, wherein in the step of forming the second well layer, the second well layer is formed to have an Al composition ratio that differs from the Al composition ratio of the first well layer by 2% to 10%. [Section 16] the first barrier layer contains an n-type impurity; Item 16. The method for manufacturing a nitride semiconductor light-emitting device according to any one of items 13 to 15, wherein the first barrier layer is formed so that a highest peak of an n-type impurity concentration in the first barrier layer is positioned on the p-side semiconductor layer side. [Section 17] The step of forming the first barrier layer includes: forming a first layer containing an n-type impurity; forming a second layer located closer to the p-side semiconductor layer than the first layer and containing an n-type impurity at a higher concentration than the first layer. [Section 18] In the step of forming the first barrier layer, the first barrier layer is formed containing Al; Item 18. The method for manufacturing a nitride semiconductor light-emitting device according to any one of items 13 to 17, wherein in the step of forming the second barrier layer, a second barrier layer containing Al at a composition ratio lower than an Al composition ratio of the first barrier layer is formed. [Section 19] Item 19. The method for producing a nitride semiconductor light-emitting device according to item 17 or item 18 citing item 17, wherein in the step of forming the second layer, the second layer is formed to a thickness smaller than a thickness of the first layer. [Section 20] 20. The method for manufacturing a nitride semiconductor light-emitting element according to item 17, or item 18 or 19 citing item 17, wherein in the step of forming the second layer, the second layer is formed to a thickness that is 5% to 30% of a thickness of the first barrier layer. [Section 21] The method for manufacturing a nitride semiconductor light-emitting element according to item 17 or any one of items 18 to 20 citing item 17, wherein in the step of forming the second layer, the second barrier layer is formed to a thickness smaller than a thickness of the second layer. [Section 22] 22. The method for manufacturing a nitride semiconductor light-emitting element according to any one of items 13 to 21, wherein in the step of forming the first barrier layer, the first barrier layer is formed so that an Al composition ratio therein is substantially the same as an Al composition ratio of the n-side semiconductor layer. [Section 23] The method for manufacturing a nitride semiconductor light-emitting element according to item 17 or any one of items 18 to 22 citing item 17, wherein in the step of forming the first barrier layer, the first layer is formed so as to have an n-type impurity concentration smaller than that of the n-side semiconductor layer, and the second layer is formed so as to have an n-type impurity concentration larger than that of the n-side semiconductor layer. [Explanation of symbols]

[0068] 1. Nitride semiconductor light emitting device 10 Substrate 11 Base layer 12 superlattice layer 20 n-side semiconductor layer 21 Undoped layer 22 n-side contact layer 30 Active layer 31 First barrier layer 31a 1st layer 31b 2nd layer 32 First Well Layer 33 Second Barrier Layer 34 Second Well Layer 40 Electron Block Layer 50 p-side semiconductor layer 51 First p-side semiconductor layer 52 Second p-side semiconductor layer 60n electrode 70p electrode 100 Semiconductor structure

Claims

1. A light-emitting device including 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, and further including an electron blocking layer between the p-side semiconductor layer and the active layer, the active layer includes, in order from the n-side semiconductor layer side, a first barrier layer containing Al, a first well layer containing Al and emitting ultraviolet light, a second barrier layer containing Al, and a second well layer in contact with the electron blocking layer, containing Al and emitting ultraviolet light, the Al composition ratio of the second well layer is greater than the Al composition ratio of the first well layer; The second well layer has a thickness smaller than that of the first well layer. Nitride semiconductor light emitting element.

2. 2 . The nitride semiconductor light emitting device according to claim 1 , wherein the thickness of the second well layer is 30% to 60% of the thickness of the first well layer.

3. 3 . The nitride semiconductor light emitting device according to claim 1 , wherein a difference between an Al composition ratio of the first well layer and an Al composition ratio of the second well layer is 2% or more and 10% or less.

4. the first barrier layer contains an n-type impurity; 3 . The nitride semiconductor light emitting device according to claim 1 , wherein the highest peak of the n-type impurity concentration in the first barrier layer is located on the p-side semiconductor layer side.

5. 3. The nitride semiconductor light-emitting element according to claim 1, wherein the first barrier layer includes a first layer containing an n-type impurity at a concentration lower than an average value of an n-type impurity concentration in the entire first barrier layer, and a second layer located closer to the p-side semiconductor layer than the first layer and containing an n-type impurity at a concentration higher than the average value.

6. The nitride semiconductor light emitting device according to claim 1 , wherein the Al composition ratio of the first barrier layer is larger than the Al composition ratio of the second barrier layer.

7. The nitride semiconductor light emitting device according to claim 5 , wherein the first layer has a thickness greater than a thickness of the second layer.

8. 6. The nitride semiconductor light emitting device according to claim 5, wherein the thickness of the second layer is 5% to 30% of the thickness of the first barrier layer.

9. The nitride semiconductor light emitting device according to claim 5 , wherein the second barrier layer has a thickness smaller than a thickness of the second layer.

10. The nitride semiconductor light-emitting device according to claim 5 , wherein the second barrier layer contains an n-type impurity, and the n-type impurity concentration of the second barrier 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.

11. The nitride semiconductor light-emitting device according to claim 1 , wherein an Al composition ratio of the first barrier layer and an Al composition ratio of the n-side semiconductor layer are substantially the same.

12. The nitride semiconductor light emitting device according to claim 5 , wherein the n-type impurity concentration of the n-side semiconductor 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.

13. 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; Including, The step of forming the active layer includes: forming a first barrier layer containing Al on the n-side semiconductor layer; forming a first well layer containing Al and emitting ultraviolet light on the first barrier layer; forming a second barrier layer containing Al on the first well layer; forming a second well layer on the second barrier layer, the second well layer having a thickness smaller than that of the first well layer, containing Al at a higher Al composition ratio than that of the first well layer, and emitting ultraviolet light; A method for manufacturing a nitride semiconductor light-emitting device, comprising the step of forming an electron blocking layer in contact with the second well layer between the step of forming the active layer and the step of forming the p-side semiconductor layer.

14. The method for manufacturing a nitride semiconductor light-emitting device according to claim 13, wherein in the step of forming the second well layer, the second well layer is formed to a thickness that is 30% or more and 60% or less of a thickness of the first well layer.

15. 15. The method for manufacturing a nitride semiconductor light-emitting device according to claim 13, wherein in the step of forming the second well layer, the second well layer is formed to have an Al composition ratio that differs from the Al composition ratio of the first well layer by 2% or more and 10% or less.

16. the first barrier layer contains an n-type impurity; 15. The method for manufacturing a nitride semiconductor light-emitting device according to claim 13, wherein the first barrier layer is formed so that the highest peak of the n-type impurity concentration in the first barrier layer is located on the p-side semiconductor layer side.

17. The step of forming the first barrier layer includes: forming a first layer containing an n-type impurity; forming a second layer located closer to the p-side semiconductor layer than the first layer and containing an n-type impurity at a higher concentration than the first layer.

18. In the step of forming the first barrier layer, the first barrier layer containing Al is formed; 15. The method for manufacturing a nitride semiconductor light-emitting device according to claim 13, wherein in the step of forming the second barrier layer, a second barrier layer containing Al at a composition ratio lower than an Al composition ratio of the first barrier layer is formed.

19. The method for manufacturing a nitride semiconductor light-emitting device according to claim 17 , wherein in the step of forming the second layer, the second layer is formed to a thickness smaller than a thickness of the first layer.

20. The method for manufacturing a nitride semiconductor light-emitting device according to claim 17 , wherein in the step of forming the second layer, the second layer is formed to a thickness that is 5% to 30% of a thickness of the first barrier layer.

21. The method for manufacturing a nitride semiconductor light-emitting device according to claim 17 , wherein in the step of forming the second layer, the second barrier layer is formed to a thickness smaller than a thickness of the second layer.

22. 15. The method for manufacturing a nitride semiconductor light-emitting element according to claim 13, 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 is substantially the same as an Al composition ratio of the n-side semiconductor layer.

23. 18. The method for manufacturing a nitride semiconductor light-emitting element according to claim 17, wherein, in the step of forming the first barrier layer, the first layer is formed so as to have an n-type impurity concentration smaller than that of the n-side semiconductor layer, and the second layer is formed so as to have an n-type impurity concentration larger than that of the n-side semiconductor layer.

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