Nitride semiconductor light emitting element

Abstract

To provide a nitride semiconductor light emitting element that can be driven at low current and have reduced forward voltage.SOLUTION: It has a first n-type semiconductor layer, a first p-type semiconductor layer disposed on the first n-type semiconductor layer and in contact with the first n-type semiconductor layer, a first superlattice layer disposed on the first p-type semiconductor layer and containing p-type impurities, an active layer disposed on the first superlattice layer, a second n-type semiconductor layer disposed on the active layer, a first electrode electrically connected to the first n-type semiconductor layer, and a second electrode electrically connected to the second n-type semiconductor layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a nitride semiconductor light emitting device. [Background technology]

[0002] As the applications of nitride semiconductor light-emitting devices expand, there is a demand for improved light-emitting efficiency, and the light-emitting device disclosed in Patent Document 1 is said to be capable of being driven with a low current. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2020-501345 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as the applications of nitride semiconductor light emitting devices expand, there is a demand for them to be driven at a lower current and have a lower forward voltage.

[0005] In view of the above, an object of the present disclosure is to provide a nitride semiconductor light emitting device that can be driven at a low current and has a reduced forward voltage. [Means for solving the problem]

[0006] In order to achieve the above object, the nitride semiconductor light emitting device according to the present disclosure comprises: A first n-type semiconductor layer; a first p-type semiconductor layer disposed on the first n-type semiconductor layer and in contact with the first n-type semiconductor layer; a first superlattice layer that is disposed on the first p-type semiconductor layer and that contains p-type impurities; an active layer disposed on the first superlattice layer; a second n-type semiconductor layer disposed on the active layer; a first electrode electrically connected to the first n-type semiconductor layer; A second electrode electrically connected to the second n-type semiconductor layer; Includes. Effect of the Invention

[0007] According to the nitride semiconductor light emitting device configured as above according to the present disclosure, it is possible to provide a nitride semiconductor light emitting device that can be driven at a low current and that can reduce the forward voltage. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a nitride semiconductor light-emitting device according to a first embodiment. [Diagram 2] 2 is an enlarged cross-sectional view showing the first superlattice layer 40 of FIG. 1. [Diagram 3] FIG. 5 is a cross-sectional view of the nitride semiconductor light-emitting device of the second embodiment. [Figure 4] FIG. 11 is a cross-sectional view of the nitride semiconductor light-emitting device of embodiment 3. [Diagram 5] 5 is an enlarged cross-sectional view of the second superlattice layer 90 of FIG. 4. [Figure 6] FIG. 4 is a cross-sectional view of the nitride semiconductor light-emitting element of embodiment 4-1. [Figure 7] FIG. 4 is a cross-sectional view of the nitride semiconductor light-emitting element of embodiment 4-2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments and examples for carrying out the present disclosure will be described with reference to the drawings. Note that the nitride semiconductor light-emitting device and the method for manufacturing the nitride semiconductor light-emitting device described below are intended to embody the technical ideas of the present disclosure, and unless otherwise specified, the present disclosure is not limited to the following. In each drawing, components having the same function may be given the same symbol. 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, descriptions of matters common to the above will be omitted, and only the differences will be described. In particular, similar effects due to similar configurations may not be mentioned sequentially for each embodiment or example. The size and positional relationship of the components shown in each drawing may be exaggerated to clarify the explanation.

[0010] As shown in FIG. 1 etc., a nitride semiconductor light-emitting element according to an embodiment of the present disclosure includes a first n-type semiconductor layer 20, a first p-type semiconductor layer 30 disposed on the first n-type semiconductor layer 20 and in contact with the first n-type semiconductor layer 20, a first superlattice layer 40 disposed on the first p-type semiconductor layer 30 and containing p-type impurities, a first active layer 50 disposed on the first superlattice layer 40, a second n-type semiconductor layer 60 disposed on the first active layer 50, a first electrode 11 electrically connected to the first n-type semiconductor layer 20, and a second electrode 12 electrically connected to the second n-type semiconductor layer 60. The nitride semiconductor light-emitting device of the embodiment according to the present disclosure configured as described above includes the first superlattice layer 40 containing p-type impurities between the first p-type semiconductor layer 30 and the first active layer 50, thereby making it possible to reduce the forward voltage Vf and increase the light emission intensity relative to the applied voltage. In this specification, the term "nitride semiconductor" refers to a binary to quaternary semiconductor containing at least one of aluminum (Al), gallium (Ga), and indium (In) and nitrogen (N). x Al y Ga 1-x-y In the chemical formula N (0≦x≦1, 0≦y≦1, x+y≦1), the composition ratios x and y may be varied within their respective ranges. Hereinafter, the nitride semiconductor light emitting device according to the embodiment of the present disclosure will be described in detail.

[0011] [Embodiment 1] Fig. 1 is a cross-sectional view of the nitride semiconductor light-emitting device of embodiment 1. Also, Fig. 2 is a cross-sectional view of a first superlattice layer 40 in the nitride semiconductor light-emitting device of Fig. 1. 1, the semiconductor light emitting element of the first embodiment includes, for example, a substrate 10 and a first light emitting section 1 disposed on the substrate 10. The first light emitting section 1 includes a first n-type semiconductor layer 20 disposed on the substrate 10, a first p-type semiconductor layer 30 disposed on the first n-type semiconductor layer 20, a first superlattice layer 40 disposed on the first p-type semiconductor layer 30 and containing p-type impurities, a first active layer 50 disposed on the first superlattice layer 40, and a second n-type semiconductor layer 60 disposed on the first active layer 50, each of which is made of a nitride semiconductor. Furthermore, the nitride semiconductor light-emitting element of embodiment 1 includes a first electrode 11 electrically connected to the first n-type semiconductor layer 20, for example by making ohmic contact with the first n-type semiconductor layer 20, and a second electrode 12 electrically connected to the second n-type semiconductor layer 60, for example by making ohmic contact with the second n-type semiconductor layer 60. In the nitride semiconductor light-emitting device of embodiment 1 configured as above, the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30 are in contact with each other, and a current injected from the first electrode 11 is injected into the first active layer 50 via the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30, causing the first light-emitting unit 1 to emit light. That is, in the nitride semiconductor light-emitting device of embodiment 1, the first electrode 11 disposed on the first n-type semiconductor layer 20 is a positive electrode, and the second electrode 12 is a negative electrode. In the nitride semiconductor light-emitting device of embodiment 1 according to the present disclosure, the first superlattice layer 40 containing p-type impurities is disposed between the first p-type semiconductor layer 30 containing p-type impurities and the first active layer 50, thereby reducing the forward voltage Vf and increasing the light emission intensity relative to the applied voltage.

[0012] That is, the nitride semiconductor light-emitting device according to the first embodiment of the present disclosure has been made based on the inventor's unique findings that in a light-emitting device in which a current is injected from a positive electrode electrically connected to the first n-type semiconductor layer 20, and the current is injected into the first active layer 50 via the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30, by disposing a first superlattice layer 40 containing p-type impurities between the first p-type semiconductor layer 30, which contains p-type impurities and has p-type conductivity, and the first active layer 50, the efficiency of supplying holes to the first active layer 50 can be increased, the forward voltage Vf can be lowered, and the light emission intensity relative to the applied voltage can be increased. Specific examples and more preferred forms of the first superlattice layer 40 will be described below based on the findings of the present inventors.

[0013] <1st superlattice layer> FIG. 2 is an enlarged cross-sectional view showing the first superlattice layer 40 in the nitride semiconductor light-emitting device of the first embodiment. As shown in FIG. 2, the first superlattice layer 40 has a first layer 41 and a second layer 42. The first layer 41 and the second layer 42 are alternately stacked. The lattice constant of the second layer 42 is different from the lattice constant of the first layer 41. By disposing the first superlattice layer 40 between the first p-type semiconductor layer 30 and the first active layer 50, it is possible to reduce the crystal distortion of the first active layer 50 caused by the difference in the lattice constant between the first p-type semiconductor layer 30 and the first active layer 50. By reducing the crystal distortion of the first active layer 50, it is possible to increase the internal quantum efficiency of the first active layer 50. As a result, it is possible to improve the light emitting efficiency. The compositions of the first layer 41 and the second layer 42 are preferably set in consideration of, for example, the composition or band gap of the first active layer 50, or the composition or band gap of the well layer when the first active layer 50 has a quantum well structure. For example, when the well layer is composed of an InGaN layer, the first layer 41 and the second layer 42 are preferably layers having a smaller In composition ratio than the well layer.

[0014] The first layer 41 and the second layer 42 have different In composition ratios, for example, which causes the lattice constant of the first layer 41 and the lattice constant of the second layer 42 to differ. At least one of the first layer 41 and the second layer 42 is a layer doped with p-type impurities. By doping at least one of the first layer 41 and the second layer 42 with p-type impurities, as described above, the forward voltage Vf can be reduced. The p-type impurity concentration of at least one of the first layer 41 and the second layer 42 is 1×10 18 cm -3 More than 3×10 19 cm -3 In addition, the concentration of the p-type impurity doped into at least one of the first layer 41 and the second layer 42 is preferably lower than the p-type impurity concentration of the first p-type semiconductor layer 30.

[0015] For example, the In composition ratio of the first layer 41 can be made higher than the In composition ratio of the second layer 42. In this case, by making the p-type impurity concentration of the first layer 41 higher than the p-type impurity concentration of the second layer 42, it is easy to reduce the forward voltage Vf. This is believed to be because In is likely to be distributed near the upper surface of the first layer 41, which makes it easy to reduce the surface roughness of the upper surface of the first layer 41, and therefore even if the first layer 41 is doped with a p-type impurity, the crystallinity of the first superlattice layer 40 is unlikely to deteriorate. When the In composition ratio of the first layer 41 is made higher than the In composition ratio of the second layer 42 and the p-type impurity concentration of the first layer 41 is made higher than the p-type impurity concentration of the second layer 42, the p-type impurity concentration of the first layer 41 is set to 1×10 18 cm -3 More than 3×10 19 cm -3 It is preferable that the p-type impurity concentration of the first layer 41 is within this range. By setting the p-type impurity concentration of the first layer 41 in this range, it is possible to increase the efficiency of supplying holes to the first active layer 50 and reduce deterioration of the crystallinity of the first superlattice layer 40. In this case, it is preferable that the second layer 42 is an undoped layer. Furthermore, when the In composition ratio of the first layer 41 is made higher than the In composition ratio of the second layer 42 and the p-type impurity concentration of the first layer 41 is made higher than the p-type impurity concentration of the second layer 42, it is preferable that the thickness of the first layer 41 is thinner than the thickness of the second layer 42. By making the thickness of the first layer 41, which has a relatively high p-type impurity concentration, thin, deterioration of the crystallinity of the first superlattice layer 40 can be reduced. In particular, when the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30 are tunnel junctioned, as described below, the impurity concentration at the junction between the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30 becomes high. However, by providing the first superlattice layer 40, the diffusion of impurities into the first active layer 50 can be reduced, and the decrease in light-emitting efficiency due to the diffusion of impurities into the first active layer 50 can be effectively reduced.

[0016] The nitride semiconductor light-emitting device of embodiment 1 including the first superlattice layer 40 configured as described above can reduce the forward voltage Vf and increase the emission intensity relative to the applied voltage by disposing the first superlattice layer 40 containing p-type impurities between the first p-type semiconductor layer 30 containing p-type impurities and having p-type conductivity, and the first active layer 50. Each component of the nitride semiconductor light emitting device of the first embodiment will be described in detail below.

[0017] <Substrate> The material of the substrate 10 is, for example, sapphire, Si, SiC, GaN, etc. The substrate 10 can be a growth substrate for growing a nitride semiconductor layer. A buffer layer may be disposed between the substrate 10 and the first n-type semiconductor layer 20. The substrate 10 may be removed after the semiconductor layer such as the first n-type semiconductor layer 20 is grown.

[0018] <First n-type semiconductor layer 20> The first n-type semiconductor layer 20 can be composed of a nitride semiconductor layer containing n-type impurities such as silicon (Si) and germanium (Ge). For example, when the first active layer 50 is composed of a nitride semiconductor layer containing In, the nitride semiconductor constituting the first n-type semiconductor layer 20 may be, for example, an n-type GaN layer and may contain In and Al. Also, when the first active layer 50 is composed of a nitride semiconductor containing Al, the nitride semiconductor constituting the first n-type semiconductor layer 20 may be, for example, an n-type AlGaN layer and may further contain In. The first n-type semiconductor layer 20 may include one or more n-type nitride semiconductor layers. For example, the first n-type semiconductor layer 20 may include an n-type impurity Si of 8×10 19 cm -3 8×10 or more 20 cm -3 It is preferable that the layer forming the tunnel junction with the first p-type semiconductor layer 30 includes a nitride semiconductor layer doped at a relatively high concentration of 8×10 Si. 19 cm -3 8×10 or more 20 cm -3 The first n-type semiconductor layer 20 is preferably made of n-type GaN having a thickness of, for example, 1 nm to 10 nm, doped at a relatively high concentration of 1×10. The first n-type semiconductor layer 20 preferably includes a nitride semiconductor layer containing an n-type impurity other than the tunnel junction layer. The n-type impurity concentration of the nitride semiconductor layer containing an n-type impurity other than the tunnel junction layer is, for example, 1×10. 18 cm -3 More than 1×10 19 cm -3 For example, the n-type impurity Si is preferably 1×10 18 cm -3 More than 1×10 19 cm -3 The first n-type semiconductor layer 20 may be composed of an n-type GaN layer including the following. The first n-type semiconductor layer 20 may include an undoped semiconductor layer in part. Here, an undoped semiconductor layer refers to a layer to which n-type impurities and p-type impurities are not intentionally added. The total thickness of the first n-type semiconductor layer 20 is, for example, 5 μm or more and 15 μm or less.

[0019] <First p-type semiconductor layer 30> The first p-type semiconductor layer 30 can be composed of a nitride semiconductor layer containing p-type impurities such as magnesium (Mg) and zinc (Zn). For example, when the first active layer 50 is composed of a nitride semiconductor layer containing In, the nitride semiconductor constituting the first p-type semiconductor layer 30 may be, for example, a p-type GaN layer and may contain In and Al. Also, when the first active layer 50 is composed of a nitride semiconductor containing Al, the nitride semiconductor constituting the first p-type semiconductor layer 30 may be, for example, a p-type AlGaN layer and may further contain In. The first p-type semiconductor layer 30 may include one or more p-type nitride semiconductor layers. For example, the first p-type semiconductor layer 30 may include a p-type impurity Mg of 8×10 19 cm -3 8×10 or more 20 cm -3 It is preferable that the first p-type semiconductor layer includes a nitride semiconductor layer doped at a relatively high concentration as described below as a layer that forms a tunnel junction with the layer included in the uppermost layer of the first n-type semiconductor layer 20. The layer that forms a tunnel junction in the first p-type semiconductor layer has a Mg content of 8×10 19 cm -3 8×10 or more 20 cm -3 The first p-type semiconductor layer 30 is preferably made of p-type GaN having a thickness of, for example, 1 nm to 30 nm, doped at a relatively high concentration of 1×10. The first p-type semiconductor layer 30 preferably includes a nitride semiconductor layer containing p-type impurities other than the tunnel junction layer. The p-type impurity concentration of the nitride semiconductor layer containing p-type impurities other than the tunnel junction layer is, for example, 1×10. 18 cm -3 More than 1×10 19 cm -3 For example, the p-type impurity Mg is preferably 1×10 18 cm -3 More than 1×10 19 cm -3 It can be composed of a p-type GaN layer including the following. The first p-type semiconductor layer 30 may include an undoped semiconductor layer in part. The total thickness of the first p-type semiconductor layer 30 can be, for example, 0.04 μm or more and 0.2 μm or less.

[0020] <1st active layer 50> The first active layer 50 is, for example, a nitride semiconductor layer that emits light with an emission peak wavelength range of 200 nm to 760 nm. The first active layer 50 may be, for example, a multiple quantum well structure having multiple well layers and multiple barrier layers, or a single quantum well structure including one well layer and barrier layers on both sides of it. When the first active layer 50 is a single or multiple quantum well, the well layer is, for example, GaN, InGaN, or AlGaN, and the barrier layer is, for example, AlGaN or GaN.

[0021] <Second n-type semiconductor layer 60> The second n-type semiconductor layer 60 includes, for example, a nitride semiconductor layer containing an n-type impurity such as silicon (Si). The second n-type semiconductor layer 60 may include one or more n-type nitride semiconductor layers, and may partially include an undoped semiconductor layer. For example, when the first active layer 50 is composed of a nitride semiconductor layer containing In, the nitride semiconductor constituting the second n-type semiconductor layer 60 may be, for example, an n-type GaN layer and may contain In and Al. Also, for example, when the first active layer 50 is composed of a nitride semiconductor containing Al, the nitride semiconductor constituting the second n-type semiconductor layer 60 may be, for example, an n-type AlGaN layer and may further contain In. The thickness of the second n-type semiconductor layer 60 can be, for example, 0.1 μm to 15 μm, preferably 0.1 μm to 5 μm, more preferably 0.1 μm to 3 μm, and particularly preferably 0.1 μm to 1 μm. When the second n-type semiconductor layer 60 contains Si as an n-type impurity, the impurity concentration is, for example, 1×10 18 cm -3 More than 1×10 19 cm -3 It can be as follows:

[0022] <First and second electrodes> The first electrode 11 and the second electrode 12 are electrodes electrically connected to the first n-type semiconductor layer 20 and the second n-type semiconductor layer 60, i.e., the n-type semiconductor layer, and can be made of, for example, a metal such as Au, Pt, Pd, Rh, Ni, W, Mo, Cr, Ti, Al, Cu, or an alloy containing these metals. The first electrode 11 and the second electrode 12 may have a single-layer structure or a laminated structure in which multiple layers are laminated. The first electrode 11 and the second electrode 12 can have a laminated structure in which, for example, a Ti layer, an Al-Si-Cu alloy layer, a Ti layer, a Pt layer, an Au layer, and a Ti layer are laminated in this order.

[0023] [Embodiment 2] FIG. 3 is a cross-sectional view of the nitride semiconductor light-emitting device of the second embodiment. As shown in FIG. 3, the nitride semiconductor light-emitting device of the second embodiment includes a second light-emitting section 2 on the first light-emitting section 1 of the nitride semiconductor light-emitting device of the first embodiment. The second light-emitting section 2 includes a second n-type semiconductor layer 60 shared with the first light-emitting section, a second active layer 70 disposed on the second n-type semiconductor layer 60, and a second p-type semiconductor layer 80 disposed on the second active layer 70. The nitride semiconductor light-emitting device of the second embodiment also includes a third electrode 13 electrically connected to the second p-type semiconductor layer 80. Here, the third electrode 13 may include a pad electrode 13a and an electrode layer 13b disposed in contact with the second p-type semiconductor layer 80. In the nitride semiconductor light-emitting device of the second embodiment, the second electrode 12 is disposed on the second n-type semiconductor layer 60 exposed by removing the second active layer 70 and the second p-type semiconductor layer 80, for example. In addition, the first electrode 11 is disposed on the first n-type semiconductor layer 20 in the same manner as the nitride semiconductor light-emitting device of the first embodiment.

[0024] In the nitride semiconductor light emitting device of the second embodiment configured as above, the first electrode 11 functions as a positive electrode of the first light emitting section 1. The third electrode 13 functions as a positive electrode of the second light emitting section 2. The second electrode 12 functions as a negative electrode of the first light emitting section 1 and the second light emitting section 2. In the nitride semiconductor light emitting device of embodiment 2, the first light emitting section 1 can be turned on by applying a voltage between the first electrode 11 and the second electrode 12. Moreover, the second light emitting section 2 can be turned on by applying a voltage between the third electrode 13 and the second electrode 12. In this way, the first light emitting section 1 and the second light emitting section 2 can be turned on independently. Furthermore, even when the first light-emitting unit 1 and the second light-emitting unit 2 are turned on simultaneously, the light-emitting intensity of the first light-emitting unit 1 and the second light-emitting unit 2 can be individually controlled by adjusting the voltage applied between the first electrode 11 and the second electrode 12 and the voltage applied between the third electrode 13 and the second electrode 12. Furthermore, in the nitride semiconductor light emitting device of embodiment 2, the first light emitting section 1 has a configuration similar to that of the nitride semiconductor light emitting device of embodiment 1, so that the forward voltage Vf can be reduced and the light emission intensity relative to the applied voltage can be increased.

[0025] In the nitride semiconductor light emitting device of the second embodiment configured as above, the first light emitting section 1 and the second light emitting section 2 may have the same emission peak wavelength or may have different emission peak wavelengths. In other words, the emission peak wavelength of the first active layer 50 and the emission peak wavelength of the second active layer 70 may be the same or different. In the nitride semiconductor light emitting device of the second embodiment, the second active layer 70 is located above the first active layer 50. Therefore, when the emission peak wavelength of the first active layer 50 and the emission peak wavelength of the second active layer 70 are different, the color mixing can be improved. Note that the composition of the first active layer 50 is different from the composition of the second active layer 70, so that the emission peak wavelength of the first active layer 50 is different from the emission peak wavelength of the second active layer 70. For example, the In composition ratio of the first active layer 50 is different from the In composition ratio of the second active layer 70, so that the emission peak wavelength of the first active layer 50 is different from the emission peak wavelength of the second active layer 70. For example, in a nitride semiconductor light-emitting device, the light emission efficiency varies depending on the emission peak wavelength. In the nitride semiconductor light-emitting device of the second embodiment, as described above, even when the first light-emitting unit 1 and the second light-emitting unit 2 are turned on simultaneously, the emission intensities of the first light-emitting unit 1 and the second light-emitting unit 2 can be individually controlled by adjusting the voltage applied between the first electrode 11 and the second electrode 12 and the voltage applied between the third electrode 13 and the second electrode 12. Therefore, in the nitride semiconductor light-emitting device of the second embodiment, even when the emission peak wavelength of the first active layer 50 and the emission peak wavelength of the second active layer 70 are different, the light-emitting device can be made to easily obtain any emission color by adjusting the voltage applied between the first electrode 11 and the second electrode 12 and the voltage applied between the third electrode 13 and the second electrode 12.

[0026] Hereinafter, a detailed description will be given of each component of the nitride semiconductor light emitting device of embodiment 2. Note that a description of components common to embodiment 1 will be omitted.

[0027] <Second active layer 70> The second active layer 70 is, for example, a nitride semiconductor layer that emits light having an emission peak wavelength range of 200 nm to 760 nm. The second active layer 70 may be, for example, a multiple quantum well structure having multiple well layers and multiple barrier layers, or a single quantum well structure including one well layer and barrier layers on both sides of it. When the second active layer 70 is a single or multiple quantum well, the well layer is, for example, GaN, InGaN, or AlGaN, and the barrier layer is, for example, AlGaN or GaN.

[0028] <Second p-type semiconductor layer 80> The second p-type semiconductor layer 80 can be composed of, for example, a nitride semiconductor layer containing p-type impurities such as Mg, Zn, etc. For example, when the second active layer 70 is composed of a nitride semiconductor layer containing In, the nitride semiconductor constituting the second p-type semiconductor layer 80 may be, for example, a p-type GaN layer and may contain In, Al, etc. Also, when the second active layer 70 is composed of a nitride semiconductor containing Al, the nitride semiconductor constituting the second p-type semiconductor layer 80 may be, for example, a p-type AlGaN layer and may further contain In. The second p-type semiconductor layer 80 may include one or more p-type nitride semiconductor layers. The second p-type semiconductor layer 80 may include an undoped semiconductor layer in part. The entire thickness of the second p-type semiconductor layer 80 may be, for example, 0.04 μm or more and 0.2 μm or less.

[0029] <3rd electrode 13> The third electrode 13 includes, for example, a pad electrode 13a and an electrode layer 13b arranged in contact with the second p-type semiconductor layer 80. The electrode layer 13b can be made of, for example, a metal oxide having translucency, such as ITO, ZnO, IZO, or In2O3, or a light-reflective material such as silver. By using a translucent material as the electrode layer 13b, light can be emitted from the second p-type semiconductor layer 80 side. The pad electrode 13a can be made of, for example, a metal such as Au, Pt, Pd, Rh, Ni, W, Mo, Cr, Ti, Al, or Cu, or an alloy containing these metals.

[0030] [Embodiment 3] FIG. 4 is a cross-sectional view of the nitride semiconductor light-emitting device of the third embodiment. As shown in FIG. 4, the nitride semiconductor light-emitting device of embodiment 3 is configured in the same manner as the nitride semiconductor light-emitting device of embodiment 2, except that the nitride semiconductor light-emitting device of embodiment 2 includes a second superlattice layer 90 between the second n-type semiconductor layer 60 and the second active layer 70. That is, in the nitride semiconductor light emitting device of the third embodiment, the second light emitting section 2 includes a second superlattice layer 90. FIG. 5 is an enlarged cross-sectional view of second superlattice layer 90 of FIG. The second superlattice layer 90 will now be described in detail.

[0031] <Second superlattice layer 90> In this embodiment, the second superlattice layer 90 has a third layer 91 and a fourth layer 92 having a lattice constant different from that of the third layer 91. The second superlattice layer 90 is a layer in which the third layer 91 and the fourth layer 92 are alternately stacked. The third layer 91 and the fourth layer 92 have different In composition ratios, for example. By disposing the second superlattice layer 90 between the second n-type semiconductor layer 60 and the second active layer 70, it is possible to reduce the crystal distortion of the second active layer 70 caused by the difference between the lattice constant of the second n-type semiconductor layer 60 and the lattice constant of the second active layer 70. By reducing the crystal distortion of the second active layer 70, it is possible to increase the internal quantum efficiency and improve the light emission efficiency. Furthermore, as described below, various effects can be obtained by appropriately selecting the impurity concentration, composition, thickness, etc. of the third layer 91 and the fourth layer 92.

[0032] (Embodiment 3-1) In embodiment 3-1, the third layer 91 and the fourth layer 92 are both undoped layers. In general, the more layers with different compositions are stacked on a growth substrate, the more likely the crystallinity of a nitride semiconductor is to deteriorate in the upper layers. Therefore, in the second superlattice layer 90 stacked on the first light emitting section 1, the third layer 91 and the fourth layer 92 are both undoped layers, thereby reducing the deterioration of the crystallinity of the second superlattice layer 90.

[0033] (Embodiment 3-2) In the embodiment 3-2, at least one of the third layer 91 and the fourth layer 92 is a layer containing an n-type impurity. For example, an example of the n-type impurity is Si. The n-type impurity concentration of at least one of the third layer 91 and the fourth layer 92 is 1×10 18 cm -3 More than 1×10 19 cm -3 It is preferable that the following is satisfied: By doing so, it is possible to improve the efficiency of supplying electrons to the second active layer 70, and therefore the light emitting efficiency.

[0034] In the embodiment 3-2, the third layer 91 is preferably a layer containing n-type impurities, and further, the third layer 91 is preferably a layer containing In, such as an InGaN layer. This can improve the efficiency of supplying electrons to the second active layer 70 by the n-type impurities while reducing the deterioration of the crystallinity of the second superlattice layer 90 by the n-type impurities. The reason why the deterioration of the crystallinity of the second superlattice layer 90 by the n-type impurities can be reduced is that In is likely to be distributed near the upper surface of the third layer 91, which tends to reduce the surface roughness of the upper surface of the third layer 91, and as a result, even if the third layer 91 is doped with n-type impurities, the crystallinity of the second superlattice layer 90 is unlikely to deteriorate.

[0035] In the embodiment 3-2, it is more preferable that the third layer 91 is a layer containing n-type impurities and containing In, and the fourth layer 92 is a layer having a lower n-type impurity concentration and a lower In composition ratio than the third layer 91. In this way, the n-type impurity concentration of the second superlattice layer 90 is increased, and the crystallinity of the second superlattice layer 90 is less likely to deteriorate. In this case, the fourth layer 92 may be a layer not containing In. Also, the fourth layer 92 may be an undoped layer.

[0036] Furthermore, in embodiment 3-2, when third layer 91 is a layer containing n-type impurities and containing In, and fourth layer 92 is a layer having a lower n-type impurity concentration than third layer 91 and a lower In composition ratio than third layer 91, it is preferable that third layer 91 be thinner than fourth layer 92. By reducing the thickness of third layer 91, which has a higher n-type impurity concentration than fourth layer 92, deterioration of the crystallinity of second superlattice layer 90 can be reduced.

[0037] [Embodiment 4] 6 and 7 are cross-sectional views of the nitride semiconductor light-emitting device of the fourth embodiment. Here, Fig. 6 is a cross-sectional view of the nitride semiconductor light-emitting device of embodiment 4-1, and Fig. 7 is a cross-sectional view of the nitride semiconductor light-emitting device of embodiment 4-2. As shown in Fig. 6 and Fig. 7, in the nitride semiconductor light-emitting device of embodiment 4-1 and the nitride semiconductor light-emitting device of embodiment 4-2, the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30 are configured in the same manner. Specifically, in the nitride semiconductor light-emitting device of embodiment 4-1 and the nitride semiconductor light-emitting device of embodiment 4-2, (a) the first n-type semiconductor layer 20 includes a third superlattice layer 22 and a first bonding layer 21 disposed on the third superlattice layer 22 and in contact with the first p-type semiconductor layer 30; (b) The first p-type semiconductor layer 30 includes a second junction layer 31 that forms a tunnel junction with the first junction layer 21 . 6, the nitride semiconductor light-emitting device of embodiment 4-1 is configured similarly to the nitride semiconductor light-emitting device of embodiment 2, except for the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30. Moreover, the nitride semiconductor light-emitting device of embodiment 4-2 is configured similarly to the nitride semiconductor light-emitting device of embodiment 3, except for the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30, as shown in FIG. The nitride semiconductor light emitting device of the fourth embodiment will be described in detail below. In the following description, when a common configuration between the nitride semiconductor light-emitting device of Embodiment 4-1 and the nitride semiconductor light-emitting device of Embodiment 4-2 is comprehensively described, the device will simply be referred to as the nitride semiconductor light-emitting device of Embodiment 4.

[0038] As described above in the first embodiment and the like, it is preferable that the first n-type semiconductor layer 20 includes a layer that forms a tunnel junction with the first p-type semiconductor layer 30, the first p-type semiconductor layer 30 includes a layer that forms a tunnel junction with the first n-type semiconductor layer 20, and the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30 form a tunnel junction. Here, when the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30 are tunnel junctioned, it is preferable to lower the forward voltage Vf without deteriorating it. Therefore, the nitride semiconductor light emitting device of the fourth embodiment includes layers that form a tunnel junction with the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30, respectively, and further, a superlattice layer is disposed on the substrate 10 side of the layer in the first n-type semiconductor layer 20 that forms a tunnel junction with the second p-type semiconductor layer. That is, as described above with reference to Figures 6 and 7, the nitride semiconductor light-emitting device of embodiment 4 has: (a) a first n-type semiconductor layer 20 that includes a third superlattice layer 22 and a first junction layer 21 that is disposed on the third superlattice layer 22 and in contact with the first p-type semiconductor layer 30; and (b) the first p-type semiconductor layer 30 that includes a second junction layer 31 that forms a tunnel junction with the first junction layer 21.

[0039] 6 and 7, in the nitride semiconductor light-emitting device of the fourth embodiment, the first n-type semiconductor layer 20 includes, in order from the substrate 10 side, an n-type contact layer 23, a third superlattice layer 22, and a first bonding layer 21. Here, the first bonding layer 21 is located in the uppermost layer of the first n-type semiconductor layer 20 on the first p-type semiconductor layer 30 side. Also, in the nitride semiconductor light-emitting device of the fourth embodiment, the first p-type semiconductor layer 30 includes, in order from the substrate 10 side, a second bonding layer 31 and a third p-type semiconductor layer 32. Here, the second bonding layer 31 is located in the first p-type semiconductor layer 30 on the first n-type semiconductor layer 20 side, and is a layer that forms a tunnel junction with the first bonding layer 21.

[0040] In the nitride semiconductor light emitting device of the fourth embodiment configured as described above, the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30 are tunnel junctioned, and the first n-type semiconductor layer 20 further includes the third superlattice layer 22. This allows carriers generated in the layer forming the tunnel junction to effectively contribute to light emission, thereby lowering the forward voltage Vf. Specifically, it is believed that the forward voltage Vf can be reduced for the following reasons. Usually, the first bonding layer 21 and the second bonding layer 31, which are layers for forming a tunnel junction, are set to have a higher impurity concentration than the other layers, as described later. Therefore, by using the first bonding layer 21 and the second bonding layer 31 that have a higher impurity concentration than the other layers, more carriers are generated than in the other layers, and the forward voltage Vf can be reduced. However, by using the first bonding layer 21 and the second bonding layer 31, which have a higher impurity concentration than the other layers, the generated carriers cannot be effectively contributed to light emission, and the forward voltage Vf may become higher. The inventors speculated that the reason why the large amount of generated carriers cannot be effectively contributed to light emission may be due to defects present in the first bonding layer 21 and the second bonding layer 31. Specifically, it is believed that the generated carriers are trapped by defects present in the first bonding layer 21 and the second bonding layer 31, and therefore the carriers are not able to effectively contribute to light emission. Therefore, when a third superlattice layer 22 was placed in the first n-type semiconductor layer 20 in order to reduce defects occurring in the first bonding layer 21 and the second bonding layer 31, the forward voltage Vf could be lowered, leading to the invention of the nitride semiconductor light-emitting element of embodiment 4. The configurations of the first n-type semiconductor layer 20 and the first p-type semiconductor layer 30 in the nitride semiconductor light emitting device of the fourth embodiment will be described in more detail below.

[0041] <First n-type semiconductor layer 20> In the nitride semiconductor light emitting device of the fourth embodiment, as described above, the first n-type semiconductor layer 20 includes the n-type contact layer 23, the third superlattice layer 22, and the first bonding layer 21 in this order from the substrate 10 side.

[0042] (n-type contact layer 23) The n-type contact layer 23 is a layer on which the first electrode 11 is formed, and may be composed of, for example, a nitride semiconductor layer containing n-type impurities such as silicon (Si) or germanium (Ge). For example, when the first active layer 50 is composed of a nitride semiconductor layer containing In, the nitride semiconductor constituting the n-type contact layer 23 may be, for example, an n-type GaN layer and may contain In and Al. Also, for example, when the first active layer 50 is composed of a nitride semiconductor containing Al, the nitride semiconductor constituting the n-type contact layer 23 may be, for example, an n-type AlGaN layer and may further contain In. The n-type impurity concentration of the n-type contact layer 23 is, for example, 1×10 18 cm -3 More than 1×10 19 cm -3 For example, the n-type impurity Si is preferably 1×10 18 cm -3 More than 1×10 19 cm -3 It can be composed of an n-type GaN layer including:

[0043] (Third superlattice layer 22) The third superlattice layer 22 is a layer for reducing defects in the first junction layer 21 and the second junction layer 31 that form a tunnel junction, and is disposed between the n-type contact layer 23 and the first junction layer 21 . The third superlattice layer 22 has a fifth layer and a sixth layer. The fifth layer and the sixth layer are alternately stacked, and the lattice constant of the fifth layer is different from the lattice constant of the sixth layer. By disposing the third superlattice layer 22 between the n-type contact layer 23 and the first bonding layer 21, it is possible to reduce lattice defects in the first bonding layer 21 compared to the case where the first bonding layer 21 is disposed in contact with the n-type contact layer 23. The compositions of the fifth layer and the sixth layer can be set, for example, in consideration of the compositions or band gaps of the n-type contact layer 23, the first bonding layer 21, and the second bonding layer 31. For example, when the n-type contact layer 23, the first bonding layer 21, and the second bonding layer 31 are composed of GaN layers, the fifth layer can be composed of a GaN layer, and the sixth layer can be composed of an InGaN layer. In addition, when the n-type contact layer 23, the first bonding layer 21, and the second bonding layer 31 are composed of GaN layers, the fifth layer and the sixth layer may all be composed of InGaN layers, and the In composition ratios of the fifth layer and the sixth layer may be different.

[0044] The third superlattice layer 22 may contain an n-type impurity. When the third superlattice layer 22 contains an n-type impurity, electrons can be efficiently supplied from the n-type contact layer 23 to the first junction layer 21. When the third superlattice layer 22 contains an n-type impurity, either one or both of the fifth layer and the sixth layer may contain an n-type impurity. When the third superlattice layer 22 contains an n-type impurity, the n-type impurity concentration of the third superlattice layer 22 is 1×10 19 cm -3 or less. For example, in the nitride semiconductor device of embodiment 4-2, the n-type impurity concentration of third superlattice layer 22 is preferably lower than the n-type impurity concentration of the second superlattice layer. Here, the n-type impurity concentration of third superlattice layer 22 refers to the average value of the n-type impurity concentration of the entire third superlattice layer 22.

[0045] The thickness of the third superlattice layer 22 is preferably as thin as possible while obtaining the desired defect reduction effect for the first bonding layer 21 and the second bonding layer 31, and for example, the thickness of the third superlattice layer 22 is preferably thinner than the thickness of the first superlattice layer 40. By making the thickness of the third superlattice layer 22 thin, carrier injection into the first p-type semiconductor layer 30 via the tunnel junction can be performed satisfactorily without degradation. That is, when the third superlattice layer 22 is disposed, there is a risk that a V pit will be formed starting from the superlattice layer. Even if a V pit is formed, the reduction in carrier injection into the first p-type semiconductor layer 30 due to the formation of the V pit can be suppressed by making the third superlattice layer 22 thin. Specifically, when the third superlattice layer 22 is disposed thick and a V pit is formed starting from the third superlattice layer 22, the effect of the V pit formed in the third superlattice layer 22 becomes large, the flatness of the tunnel junction interface decreases, and it becomes difficult to efficiently obtain the tunnel effect. That is, in order to efficiently obtain the tunnel effect, the tunnel junction interface needs to be flat at a certain level, and if the tunnel junction interface does not have the flatness at a certain level, the tunnel effect decreases. Therefore, in order to efficiently obtain the tunnel effect, even if a V pit is formed starting from the third superlattice layer 22, it is necessary to suppress the effect of the V pit so that the tunnel junction interface can have a flatness at a certain level. For this purpose, it is preferable to make the thickness of the third superlattice layer 22 thin.

[0046] As described above, for example, the thickness of the third superlattice layer 22 is preferably thinner than the thickness of the first superlattice layer 40. The thickness of the third superlattice layer 22 can be changed, for example, by adjusting the thickness of each of the fifth layer and the sixth layer and by adjusting the number of pairs including the fifth layer and the sixth layer. For example, the first superlattice layer 40 includes n pairs including a first layer 41 and a second layer 42, and the third superlattice layer 22 includes m pairs including a fifth layer and a sixth layer. Here, n and m are integers of 1 or more. For example, the thickness of the first layer 41 of the first superlattice layer 40 and the thickness of the fifth layer of the third superlattice layer 22 can be 1 nm or more and 3 nm or less. The thickness of the second layer 42 of the first superlattice layer 40 and the thickness of the sixth layer of the third superlattice layer 22 can be 0.5 nm or more and 1.5 nm or less. For example, the number of pairs n in the first superlattice layer 40 can be 16 or more and 60 or less, and the number of pairs m in the third superlattice layer 22 can be 3 or more and 15 or less. The thicknesses of the first superlattice layer 40 and the third superlattice layer 22 can be adjusted within the above-mentioned thickness ranges and number of pairs ranges, respectively, so that the thickness of the third superlattice layer 22 can be thinner than the thickness of the first superlattice layer 40. For example, the first layer 41 and the fifth layer are made to have the same thickness, the second layer 42 and the sixth layer are made to have the same thickness, and the number of pairs m of the third superlattice layer 22 is made smaller than the number of pairs n of the first superlattice layer 40. This allows the thickness of the third superlattice layer 22 to be thinner than the thickness of the first superlattice layer 40. In addition, when the first layer 41 of the first superlattice layer 40 and the fifth layer of the third superlattice layer 22 are GaN layers, and the second layer 42 of the first superlattice layer 40 and the sixth layer of the third superlattice layer 22 are InGaN layers, for example, the thicknesses of the first layer 41 and the fifth layer, which are GaN layers, are made thicker than the thicknesses of the second layer 42 and the sixth layer.

[0047] (1st bonding layer 21) The first bonding layer 21 has an n-type impurity concentration of, for example, 8×10 19 cm -3 8×10 or more 20 cm -3 The first bonding layer 21 is a nitride semiconductor layer doped at a relatively high concentration and forms a tunnel junction with the second bonding layer 31. The n-type impurity concentration of the first bonding layer 21 is higher than the n-type impurity concentration of the n-type contact layer . The thickness of the first bonding layer 21 is, for example, not less than 1 nm and not more than 10 nm. The first bonding layer 21 may contain In. When the first bonding layer 21 contains In, the band gap of the first bonding layer 21 can be made small, making it easier to obtain the tunnel effect. The first bonding layer 21 may include two or more layers, for example, a GaN layer and an InGaN layer. For example, the first bonding layer 21 may include a GaN layer having a thickness of 1 nm or more and 10 nm or less, and an InGaN layer having a thickness of, for example, 0.5 nm or more and 5 nm or less, disposed on the n-type contact layer 23 side. The In composition ratio of the InGaN layer is, for example, 1% or more and 6% or less.

[0048] <First p-type semiconductor layer 30> In the nitride semiconductor light emitting device of embodiment 4, the first p-type semiconductor layer 30 includes a second bonding layer 31 and a third p-type semiconductor layer 32 in this order from the substrate 10 side.

[0049] (Second bonding layer 31) The second bonding layer 31 has a p-type impurity concentration of, for example, 8×10 19 cm -3 8×10 or more 20 cm -3 The second bonding layer 31 is a nitride semiconductor layer doped at a relatively high concentration and forms a tunnel junction with the first bonding layer 21. The p-type impurity concentration of the second bonding layer 31 is higher than the p-type impurity concentration of a third p-type semiconductor layer 32 described below. The thickness of the second bonding layer 31 is, for example, 1 nm or more and 30 nm or less. The second bonding layer 31 may include two or more layers each containing a p-type impurity at a higher concentration than the third p-type semiconductor layer 32. The second bonding layer 31 may include, for example, Mg of 8×10 19 cm -3 8×10 or more 20 cm -3 A p-type GaN layer having a thickness of 1 nm to 10 nm and doped with a concentration of 1000 u / s or less and a p-type GaN layer having a lower concentration (but not exceeding 8×10 19 cm -3 More than 3×10 20 cm -3 The p-type GaN layer may include a p-type GaN layer doped with Mg at a concentration in the range of 10 nm to 20 nm in thickness.

[0050] (Third p-type semiconductor layer 32) The third p-type semiconductor layer 32 is a nitride semiconductor layer containing p-type impurities and disposed on the second bonding layer 31. The third p-type semiconductor layer 32 has a p-type impurity concentration of, for example, 1×10 18 cm -3 More than 1×10 19 cm -3 For example, the p-type impurity Mg is preferably 1×10 18 cm -3 More than 1×10 19 The layer may be made of a p-type GaN layer having a GaN concentration of 0.1 to 1.0 nm.

[0051] The nitride semiconductor light emitting device according to the embodiment of the present disclosure includes, for example, the following aspects. [Section 1] A first n-type semiconductor layer; a first p-type semiconductor layer disposed on the first n-type semiconductor layer and in contact with the first n-type semiconductor layer; a first superlattice layer that is disposed on the first p-type semiconductor layer and that contains p-type impurities; an active layer disposed on the first superlattice layer; a second n-type semiconductor layer disposed on the active layer; a first electrode electrically connected to the first n-type semiconductor layer; A second electrode electrically connected to the second n-type semiconductor layer; A nitride semiconductor light emitting device comprising: [Section 2] the first superlattice layer is formed by alternately stacking a first layer and a second layer having a lattice constant different from that of the first layer; 2. The nitride semiconductor light emitting device according to item 1, wherein the first layer contains In and a p-type impurity. [Section 3] the second layer contains In and a p-type impurity; a p-type impurity concentration of the second layer is lower than a p-type impurity concentration of the first layer; 3. The nitride semiconductor light emitting device according to item 2, wherein the second layer has an In composition ratio smaller than the In composition ratio of the first layer. [Section 4] 4. The nitride semiconductor light emitting device according to item 3, wherein a p-type impurity concentration of the first layer is lower than a p-type impurity concentration of the first p-type semiconductor layer. [Section 5] The p-type impurity concentration of the first layer is 1×10 18 cm -3 More than 3×10 19 cm -3 5. The nitride semiconductor light emitting device according to any one of items 2 to 4, wherein: [Section 6] 6. The nitride semiconductor light emitting device according to any one of items 2 to 5, wherein the first layer has a thickness smaller than a thickness of the second layer. [Section 7] a second active layer disposed on the second n-type semiconductor layer; a second p-type semiconductor layer disposed on the second active layer; 7. The nitride semiconductor light emitting device according to any one of items 1 to 6, further comprising a third electrode electrically connected to the second p-type semiconductor layer. [Section 8] 8. The nitride semiconductor light emitting device according to item 7, further comprising a second superlattice layer disposed between the second n-type semiconductor layer and the second active layer. [Section 9] the second superlattice layer is formed by alternately stacking a third layer and a fourth layer having a lattice constant different from that of the third layer; 9. The nitride semiconductor light emitting device according to item 8, wherein the third layer and the fourth layer are undoped layers. [Section 10] the second superlattice layer is formed by alternately stacking a third layer and a fourth layer having a lattice constant different from that of the third layer; Item 10. The nitride semiconductor light emitting device according to item 8 or 9, wherein the third layer contains an n-type impurity. [Section 11] 11. The nitride semiconductor light emitting device according to any one of items 8 to 10, wherein the third layer contains In. [Section 12] the fourth layer has an n-type impurity concentration lower than an n-type impurity concentration of the third layer; Item 12. The nitride semiconductor light emitting device according to item 11, wherein the fourth layer has an In composition ratio smaller than the In composition ratio of the third layer. [Section 13] 13. The nitride semiconductor light emitting device according to any one of items 9 to 12, wherein the third layer has a thickness smaller than a thickness of the fourth layer. [Section 14] the first n-type semiconductor layer includes a third superlattice layer and a first junction layer disposed on the third superlattice layer and in contact with the first p-type semiconductor layer; 5. The nitride semiconductor light emitting device according to any one of items 1 to 4, wherein the first p-type semiconductor layer includes a second junction layer forming a tunnel junction with the first junction layer. [Section 15] Item 15. The nitride semiconductor light emitting device according to item 14, wherein the third superlattice layer is thinner than the first superlattice layer. [Section 16] Item 16. The nitride semiconductor light emitting device according to item 14 or 15, wherein the third superlattice layer contains an n-type impurity. [Section 17] a second superlattice layer disposed on the second n-type semiconductor layer and containing n-type impurities; a second active layer disposed on the second superlattice layer; a second p-type semiconductor layer disposed on the second active layer; a third electrode electrically connected to the second p-type semiconductor layer, 17. The nitride semiconductor light emitting device according to any one of items 14 to 16, wherein the third superlattice layer has an n-type impurity concentration lower than an n-type impurity concentration of the second superlattice layer. [Explanation of symbols]

[0052] 1 First light emitting part 2 Second light emitting part 10 Substrate 11 1st electrode 12 2nd electrode 13 Third electrode 13a Pad electrode 13b Electrode layer 20 First n-type semiconductor layer 21 1st bonding layer 22 Third superlattice layer 23 n-type contact layer 30 First p-type semiconductor layer 31 Second bonding layer 32 Third p-type semiconductor layer 40 1st superlattice layer 50 1st active layer 60 2nd n-type semiconductor layer 70 2nd active layer 80 2nd p-type semiconductor layer 90 Second Super Grid Layer

Claims

1. A first n-type semiconductor layer; a first p-type semiconductor layer disposed on the first n-type semiconductor layer and in contact with the first n-type semiconductor layer; a first superlattice layer disposed on the first p-type semiconductor layer and containing p-type impurities; an active layer disposed on the first superlattice layer; a second n-type semiconductor layer disposed on the active layer; a first electrode electrically connected to the first n-type semiconductor layer; A second electrode electrically connected to the second n-type semiconductor layer; A nitride semiconductor light emitting device comprising:

2. the first superlattice layer is formed by alternately stacking a first layer and a second layer having a lattice constant different from that of the first layer; The nitride semiconductor light emitting device according to claim 1 , wherein the first layer contains In and a p-type impurity.

3. the second layer includes In and a p-type impurity; a p-type impurity concentration of the second layer is lower than a p-type impurity concentration of the first layer; The nitride semiconductor light emitting device according to claim 2 , wherein an In composition ratio of said second layer is smaller than an In composition ratio of said first layer.

4. The nitride semiconductor light emitting device according to claim 3 , wherein a p-type impurity concentration of the first layer is lower than a p-type impurity concentration of the first p-type semiconductor layer.

5. The p-type impurity concentration of the first layer is 1×10 １8 cm －3 Above 3 x 10 １９ cm －3 The nitride semiconductor light emitting device according to any one of claims 2 to 4, wherein:

6. 5. The nitride semiconductor light emitting device according to claim 2, wherein the first layer is thinner than the second layer.

7. a second active layer disposed on the second n-type semiconductor layer; a second p-type semiconductor layer disposed on the second active layer; 5. The nitride semiconductor light emitting device according to claim 1, further comprising: a third electrode electrically connected to the second p-type semiconductor layer.

8. The nitride semiconductor light emitting device according to claim 7 , further comprising a second superlattice layer disposed between the second n-type semiconductor layer and the second active layer.

9. the second superlattice layer is formed by alternately stacking a third layer and a fourth layer having a lattice constant different from that of the third layer; The nitride semiconductor light emitting device according to claim 8 , wherein the third layer and the fourth layer are undoped layers.

10. the second superlattice layer is formed by alternately stacking a third layer and a fourth layer having a lattice constant different from that of the third layer; The nitride semiconductor light emitting device according to claim 8 , wherein the third layer contains an n-type impurity.

11. The nitride semiconductor light emitting device according to claim 10 , wherein the third layer contains In.

12. an n-type impurity concentration of the fourth layer is lower than an n-type impurity concentration of the third layer; The nitride semiconductor light emitting device according to claim 11 , wherein an In composition ratio of the fourth layer is smaller than an In composition ratio of the third layer.

13. The nitride semiconductor light emitting device according to claim 10 , wherein the third layer has a thickness smaller than a thickness of the fourth layer.

14. the first n-type semiconductor layer includes a third superlattice layer and a first junction layer disposed on the third superlattice layer and in contact with the first p-type semiconductor layer; 5. The nitride semiconductor light-emitting device according to claim 1, wherein the first p-type semiconductor layer includes a second junction layer forming a tunnel junction with the first junction layer.

15. The nitride semiconductor light-emitting device according to claim 14 , wherein the third superlattice layer has a thickness smaller than a thickness of the first superlattice layer.

16. The nitride semiconductor light emitting device according to claim 14 , wherein the third superlattice layer contains an n-type impurity.

17. a second superlattice layer disposed on the second n-type semiconductor layer and containing n-type impurities; a second active layer disposed on the second superlattice layer; a second p-type semiconductor layer disposed on the second active layer; a third electrode electrically connected to the second p-type semiconductor layer, The nitride semiconductor light emitting device according to claim 16 , wherein the n-type impurity concentration of the third superlattice layer is lower than the n-type impurity concentration of the second superlattice layer.

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