Nitride semiconductor light-emitting element

Abstract

To provide a nitride semiconductor light-emitting element with improved luminous efficiency.SOLUTION: A nitride semiconductor light-emitting element includes a semiconductor structure including an n-side semiconductor layer 10, a p-side semiconductor layer 20, and an active layer 5 disposed between the n-side semiconductor layer and the p-side semiconductor layer, and a p-side electrode 21 disposed on the p-side semiconductor layer. The p-side semiconductor layer includes a first semiconductor part 8 that includes, in the order from the p-side electrode, a first layer 81 disposed in contact with the p-side electrode and containing Al and p-type impurities, a second layer 82 containing p-type impurities and having the Al composition ratio and the p-type impurity concentration smaller than those of the first layer, and a third layer 83 containing the p-type impurities and having the Al composition ratio larger than that of the second layer, the p-type impurity concentration smaller than that of the first layer, and the thickness larger than those of the first layer and the second layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Patent Document 1 describes a light emitting device made of a nitride semiconductor including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2016-178173 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for improved light emitting efficiency of nitride semiconductor light emitting devices. An object of the present disclosure is to provide a nitride semiconductor light emitting device capable of improving the light emitting efficiency. [Means for solving the problem]

[0005] In order to achieve the above object, the nitride semiconductor light emitting device according to the present disclosure comprises: a semiconductor structure having an n-side semiconductor layer, a p-side semiconductor layer, and an active layer disposed between the n-side semiconductor layer and the p-side semiconductor layer; a p-side electrode disposed on the p-side semiconductor layer, The p-side semiconductor layer has a first semiconductor portion including, in order from the p-side electrode side, a first layer in contact with the p-side electrode and containing Al and a p-type impurity, a second layer containing p-type impurities and having an Al composition ratio and a p-type impurity concentration smaller than those of the first layer, and a third layer containing p-type impurities, having an Al composition ratio larger than those of the second layer, a p-type impurity concentration smaller than those of the first layer, and a thickness larger than the thickness of the first layer and the thickness of the second layer. Effect of the Invention

[0006] According to the nitride semiconductor light emitting device according to the present disclosure configured as above, it is possible to improve the light emitting efficiency. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of a nitride semiconductor light-emitting device according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] In a nitride semiconductor light-emitting device having an n-side semiconductor layer, an active layer, and a p-side semiconductor layer, for example, by making the p-side semiconductor layer on which the p-side electrode is arranged a layer containing an AlGaN layer, the layer can be made to be a layer in which light emitted from the active layer is not easily absorbed, and the light emission efficiency can be improved. However, the AlGaN layer is a layer in which p-type impurities are less likely to be activated than the GaN layer. Also, by making the p-side semiconductor layer on which the p-side electrode is arranged a layer containing a GaN layer, the layer can be made to be a layer in which p-type impurities are easily activated, but the GaN layer is more likely to absorb light emitted from the active layer than the AlGaN layer. As a result of intensive research in consideration of the above matters, the present inventor has found that the contact resistance between the p-side electrode and the p-side semiconductor layer can be reduced and the light absorption rate of light emitted from the active layer can be reduced by making the p-side semiconductor layer on which the p-side electrode is arranged a stacked structure including an AlGaN layer containing a relatively large amount of p-type impurities and a GaN layer.

[0009] The nitride semiconductor light emitting device according to the present disclosure comprises: a semiconductor structure having an n-side semiconductor layer, a p-side semiconductor layer, and an active layer disposed between the n-side semiconductor layer and the p-side semiconductor layer; a p-side electrode disposed on the p-side semiconductor layer; The p-side semiconductor layer has a first semiconductor portion including, in order from the p-side electrode side, a first layer in contact with the p-side electrode and containing Al and a p-type impurity, a second layer containing p-type impurities and having an Al composition ratio and a p-type impurity concentration smaller than those of the first layer, and a third layer containing p-type impurities, having an Al composition ratio larger than those of the second layer and a p-type impurity concentration smaller than those of the first layer, and having a thickness larger than that of the first layer and that of the second layer.

[0010] According to the nitride semiconductor light emitting device according to the present disclosure configured as above, the light emitting efficiency can be improved. Specifically, by making the p-type impurity concentration of the first layer, which contains Al and p-type impurities, higher than those of the second and third layers, holes can be moved via the level of the p-type impurity, thereby reducing the contact resistance between the first layer and the p-side electrode and lowering the forward voltage Vf. Furthermore, by including Al in the first layer, the band gap can be increased, so that absorption of light emitted from the active layer can be reduced and the light emission output can be increased. Furthermore, in order to effectively improve the luminous efficiency, the following configuration is used. First, by making the Al composition ratio of the second layer smaller than those of the first and third layers, the p-type impurities contained in the second layer can be easily activated, which makes it easier to supply holes to the active layer and reduces the forward voltage Vf. Furthermore, by making the p-type impurity concentration in the second layer lower than that in the first layer, deterioration of the crystallinity of the second layer is reduced. Furthermore, by making the third layer contain Al, the light absorption by the third layer is reduced, and by making the p-type impurity concentration in the third layer lower than that of the first layer, deterioration of the crystallinity of the third layer is reduced. Furthermore, by making the thickness of the third layer containing p-type impurities thicker than the thicknesses of the first layer and the second layer, holes can be easily supplied to the active layer.

[0011] Hereinafter, the nitride semiconductor light-emitting device of the embodiment will be described in detail. In the nitride semiconductor light-emitting device of the present embodiment, as the nitride semiconductor, a group III-V nitride semiconductor (In X Al Y Ga 1-X-Y N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1)) is exemplified, B may be used for a part of group III elements, and a mixed crystal in which a part of N of group V elements is substituted with P, As, or Sb may be used. These nitride semiconductor layers can be formed, for example, by metalorganic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), molecular beam epitaxial growth (MBE), or the like.

[0012] Embodiment Hereinafter, the nitride semiconductor light-emitting device of the embodiment according to the present disclosure will be described with reference to FIG. 1. The nitride semiconductor light-emitting device 100 according to the present embodiment includes a substrate 1, an n-side semiconductor layer 10 disposed on the substrate 1, a p-side semiconductor layer 20, an active layer 5 located between the n-side semiconductor layer 10 and the p-side semiconductor layer 20, and a p-side electrode 21 disposed on the p-side semiconductor layer 20. The n-side semiconductor layer 10 includes, for example, an underlayer 2, an n-side contact layer 3, and an n-side superlattice layer 4. The p-side semiconductor layer 20 includes a first semiconductor portion 8. The p-side semiconductor layer 20 may include a second semiconductor portion 7, and may further include a third semiconductor portion 6. Hereinafter, the p-side semiconductor layer 20 will be described first, and then the substrate 1, the n-side semiconductor layer 10, the active layer 5, the n-side electrode 11, and the p-side electrode 21 will be described in detail in this order.

[0013] <p-side semiconductor layer 20> The p-side semiconductor layer 20 has a first semiconductor portion 8. The first semiconductor portion 8 includes, in order from the p-side electrode 21 side, (i) a first layer 81 in contact with the p-side electrode 21 and containing Al and a p-type impurity, (ii) a second layer 82 containing a p-type impurity and having an Al composition ratio and a p-type impurity concentration smaller than those of the first layer 81, (iii) a third layer 83 containing p-type impurities, having an Al composition ratio greater than that of the second layer 82, a p-type impurity concentration less than that of the first layer 81, and a thickness greater than the thicknesses of the first layer 81 and the second layer 82; Includes. A nitride semiconductor light-emitting device having the first semiconductor portion 8 including the first layer 81, the second layer 82, and the third layer 83 configured as described above can improve the light-emitting efficiency by, for example, lowering the forward voltage Vf and increasing the light-emitting output. Here, the first layer 81, the second layer 82, and the third layer 83 are made of a nitride semiconductor. The p-type impurity used in the p-side semiconductor layer 20 is, for example, Mg. The first semiconductor portion 8 will be described in detail below.

[0014] (First semiconductor portion 8) The first semiconductor portion 8 includes a first layer 81 , a second layer 82 , and a third layer 83 . The first layer 81 contains Al and a p-type impurity. By containing Al in the first layer 81, the band gap can be made larger than that of the GaN layer, and the light absorption by the first layer 81 can be reduced, so that the light output can be increased. For example, a nitride semiconductor such as InGaN containing In is used for the active layer that emits light with a peak wavelength of 430 nm or more and 570 nm or less. However, since the band gap of the GaN layer is larger than that of the InGaN layer, it is considered that the light absorption by the GaN layer is relatively low. However, the present inventors have found that when the GaN layer contains p-type impurities to activate the p-type impurities, the energy gap between the energy level based on the p-type impurities and the level of the lower end of the conduction band becomes narrower than the energy gap between the valence band and conduction band of the GaN layer itself, and the light absorption increases. Therefore, in this embodiment, by containing Al in the first layer 81, the energy gap between the valence band and conduction band of the first layer 81 is made larger than that of the GaN layer, and the light absorption by the first layer 81 is reduced.

[0015] When the peak wavelength of light emitted from the active layer is 430 nm or more and 570 nm or less, the Al composition ratio in the first layer 81 is, for example, 3% or more and 10% or less, preferably 5% or more and 9% or less. This makes it possible to reduce the occurrence of lattice relaxation between the first layer 81 and the second layer 82, maintain the crystallinity, and reduce an increase in the forward voltage Vf.

[0016] The p-type impurity concentration in the first layer 81 is higher than the p-type impurity concentration in the second layer 82 and the p-type impurity concentration in the third layer 83. This makes it possible to reduce the contact resistance between the first layer 81 and the p-side electrode 21, and to reduce the forward voltage Vf. The p-type impurity concentration in the first layer 81 is, for example, 3×10 20 / cm 3 More than 1×10 21 / cm 3 Less than or equal to 4 x 10 20 / cm 3 8×10 or more 20 / cm 3 By making the p-type impurity concentration in the first layer 81 higher than the p-type impurity concentration in the second layer 82 and the p-type impurity concentration in the third layer 83 and setting it in this range, it is possible to reduce light absorption while lowering the contact resistance between the first layer 81 and the p-side electrode 21. The thickness of the first layer 81 is, for example, 1 nm to 5 nm, or preferably 2 nm to 4 nm. By setting the thickness of the first layer 81 in this range, the contact resistance between the first layer 81 and the p-side electrode 21 can be reduced, and the absorption of light emitted by the active layer 5 can be reduced.

[0017] The second layer 82 contains p-type impurities, and has a lower Al composition ratio and a lower p-type impurity concentration than the first layer 81. For example, an AlGaN layer can be used for the second layer 82 having a smaller Al composition ratio than the first layer 81. The second layer 82 may be a nitride semiconductor that does not contain Al, for example, a GaN layer. By making the Al composition ratio of the second layer 82 smaller than that of the first layer 81, the activation rate of the p-type impurity contained in the second layer 82 can be made higher than that of the first layer 81. As a result, even if the concentration of the p-type impurity contained in the second layer 82 is lower than that of the first layer 81, the activation rate of the p-type impurity contained in the second layer 82 can be made higher and the forward voltage Vf can be made lower. Furthermore, by making the concentration of the p-type impurity in the second layer 82 lower than that of the first layer 81, deterioration of the crystallinity of the second layer 82 can be reduced.

[0018] The Al composition ratio of the second layer 82 is, for example, 0% or more and 3% or less, preferably 0% or more and 2% or less, and more preferably 0%. By setting the Al composition ratio of the second layer 82 in such a range, the activation rate of the p-type impurities contained in the second layer 82 can be increased, and the forward voltage Vf can be reduced. The p-type impurity concentration of the second layer 82 is, for example, 1×10 20 / cm 3 More than 4×10 20 / cm 3 Less than 1×10 20 / cm 3 More than 3×10 21 / cm 3 By setting the p-type impurity concentration of the second layer 82 in such a range, deterioration of the crystallinity of the second layer 82 can be reduced. The thickness of the second layer 82 is, for example, not less than 3 nm and not more than 10 nm, or preferably not less than 4 nm and not more than 8 nm.

[0019] In the above-mentioned thickness range, the thickness of the second layer 82 is preferably thicker than the thickness of the first layer 81. The second layer 82 has a lower Al composition ratio than the first layer 81 and a higher activation rate of p-type impurities than the first layer 81. Therefore, by making the second layer 82 thicker than the first layer 81, the amount of holes supplied from the second layer 82 to the active layer 5 can be increased. As a result, the forward voltage Vf can be lowered and the light emission output can be improved. Moreover, it is preferable that the thickness of the second layer 82 is thinner than that of the third layer 83. As described later, the third layer 83 is a layer having a higher Al composition ratio than the second layer 82. Therefore, by making the thickness of the second layer 82, which has a lower Al composition ratio than the third layer 83 and is relatively more likely to absorb light, thinner than the thickness of the third layer 83, it is possible to reduce light absorption by the second layer 82. It is preferable that the thickness of the second layer 82 is 20% or more and 40% or less of the total thickness of the first layer 81, the second layer 82, and the third layer 83.

[0020] The third layer 83 contains p-type impurities and has a higher Al composition ratio than the second layer 82. The p-type impurity concentration of the third layer 83 is lower than that of the first layer 81, and the thickness of the third layer 83 is greater than the thicknesses of the first layer 81 and the second layer 82. In this manner, by making the third layer 83 contain Al, it is possible to reduce light absorption in the third layer 83. Furthermore, by making the p-type impurity concentration in the third layer 83 lower than the p-type impurity concentration in the first layer 81, it is possible to reduce deterioration in the crystallinity of the third layer 83 more than that of the first layer 81. Furthermore, by making the thickness of the third layer 83 containing the p-type impurity thicker than the thicknesses of the first layer 81 and the second layer 82, it is possible to facilitate the supply of holes to the active layer 5.

[0021] The Al composition ratio of the third layer 83 is, for example, 3% or more and 10% or less, or preferably 5% or more and 9% or less. By setting the Al composition ratio of the third layer 83 in such a range, it is possible to reduce light absorption by the third layer 83 and to increase the activation rate of p-type impurities in the third layer 83. The p-type impurity concentration of the third layer 83 is, for example, 1×10 20 / cm 3 More than 4×10 20 / cm 3 By setting the p-type impurity concentration of the third layer 83 in this range, it is possible to easily supply holes to the active layer 5 while suppressing deterioration of the crystallinity of the third layer 83. The third layer 83 has a thickness of, for example, 5 nm or more and 12 nm or less, or preferably 6 nm or more and 10 nm or less.

[0022] Moreover, it is preferable that the p-side semiconductor layer 20 further includes one or both of the following second semiconductor section 7 and third semiconductor section 6. This makes it possible to more effectively improve the light emission efficiency.

[0023] (Second semiconductor portion 7) The p-side semiconductor layer 20 preferably includes a second semiconductor portion 7 disposed between the first semiconductor portion 8 and the active layer 5. The second semiconductor portion 7 includes a fourth layer 71 and a fifth layer 72. The fourth layer 71 is disposed closer to the first semiconductor portion 8 than the fifth layer 72, and has a larger Al composition ratio than the second layer 82 and a smaller Al composition ratio than the third layer 83. For example, the fourth layer 71 can be an AlGaN layer. The fifth layer 72 has a smaller Al composition ratio than the fourth layer 71. For example, an AlGaN layer can be used for the fifth layer 72. Note that the fifth layer 72 may be a GaN layer that does not contain Al. The p-type impurity concentration of the fourth layer 71 and the p-type impurity concentration of the fifth layer 72 are lower than the p-type impurity concentration of the third layer 83. The fourth layer 71 and the fifth layer 72 are preferably undoped layers. Here, an undoped layer means a layer that is not intentionally doped with impurities. By making the p-type impurity concentration of the fourth layer 71 and the p-type impurity concentration of the fifth layer 72 smaller than the p-type impurity concentration of the third layer 83, the electrostatic breakdown voltage characteristic of the nitride semiconductor light emitting device 100 can be improved. That is, by making the fourth layer 71 and the fifth layer 72 layers having a relatively high electrical resistance, the fourth layer 71 and the fifth layer 72 can be layers that easily diffuse current. As a result, it is possible to make it difficult for a region where current is likely to concentrate to occur in the p-side semiconductor layer 20, and therefore the electrostatic breakdown voltage characteristic of the nitride semiconductor light emitting device 100 can be improved. In addition, by making the fourth layer 71 and the fifth layer 72 undoped layers, the electrostatic breakdown voltage characteristic of the nitride semiconductor light emitting device 100 can be further improved.

[0024] By making the fourth layer 71 an AlGaN layer having a higher Al composition ratio than the fifth layer 72, the V pits are easily filled, and the surface state of the fourth layer 71 can be made closer to flat. In a layer with a high Al composition ratio, the semiconductor layer tends to grow laterally, and the V pits tend to be easily filled. By forming the first semiconductor section 8 on the fourth layer 71 having high flatness, the crystallinity of the first semiconductor section 8 can be improved. In addition, the fifth layer 72 has a lower Al composition ratio than the fourth layer 71, and therefore, as described later, the V pits can be maintained at a required size, and the light emission efficiency can be improved. For example, it is preferable that the fifth layer 72 is a GaN layer. Here, the V pit is a concave pit formed in the semiconductor layer due to dislocations formed when the semiconductor layer is epitaxially grown, and is formed, for example, from dislocations when the n-side superlattice layer 4 described later is grown. The V pit is formed penetrating the active layer 5. When the p-side semiconductor layer 20 includes the third semiconductor portion 6, the V pit is formed penetrating the active layer 5 and the third semiconductor portion 6. In the top view, the V pit is, for example, a circle, an ellipse, or a hexagon. The maximum diameter of the V pit is, for example, 30 nm or more and 100 nm or less. The V pit is, for example, a cone shape, an elliptical cone shape, a polygonal cone shape, or the like, whose maximum diameter increases from the n-side semiconductor layer 10 side toward the p-side semiconductor layer 20. By filling the V pit with the p-side semiconductor layer 20, holes can be supplied to the active layer 5 through the p-side semiconductor layer 20 in the V pit, and the light emission efficiency can be increased.

[0025] The Al composition ratio of the fourth layer 71 is preferably smaller than the Al composition ratio of the first layer 81 and the Al composition ratio of the third layer 83. This allows the V pit to be effectively filled while reducing the increase in forward voltage Vf. That is, the fourth layer 71 preferably has a high Al composition ratio to fill the V pit, but if the Al composition ratio becomes high, the band gap difference with the fifth layer 72 becomes large, and there is a concern that the forward voltage Vf will increase. Therefore, by making the Al composition ratio of the fourth layer 71 smaller than the Al composition ratio of the first layer 81 and the Al composition ratio of the third layer 83, the V pit can be effectively filled while preventing the band gap difference between the fourth layer 71 and the fifth layer 72 from becoming too large. In addition, it is preferable to make the Al composition ratio of the fourth layer 71 smaller than the Al composition ratio of the first layer 81 and the Al composition ratio of the third layer 83 while setting the difference between the Al composition ratio of the first layer 81 and the Al composition ratio of the third layer 83 to be 5% or more and 10% or less. This makes it possible to reduce the occurrence of lattice relaxation between the first layer 81 and the third layer 83, maintain the crystallinity, and reduce an increase in the forward voltage Vf.

[0026] The Al composition ratio of the fourth layer 71 is, for example, not less than 0.5% and not more than 4%. The p-type impurity concentration of the fourth layer 71 is, for example, 5×10 18 / cm 3 More than 3×10 19 / cm 3 For example, the fourth layer 71 is an undoped layer. The fourth layer 71 has a thickness of, for example, not less than 15 nm and not more than 25 nm. The Al composition ratio of the fifth layer 72 is, for example, not less than 0% and not more than 3%, preferably not less than 0% and not more than 2%, and more preferably 0%. The p-type impurity concentration of the fifth layer 72 is, for example, 5×10 18 / cm 3 More than 3×10 19 / cm 3 For example, the fifth layer 72 is an undoped layer. The thickness of the fifth layer 72 is, for example, not less than 15 nm and not more than 50 nm, or preferably not less than 20 nm and not more than 40 nm.

[0027] In the second semiconductor portion 7, it is preferable that the fourth layer 71 is thicker than the third layer 83, and the fifth layer 72 is thicker than the third layer 83. This can improve the electrostatic breakdown voltage characteristics. Furthermore, it is more preferable that the thickness of the fourth layer 71 is thicker than the total thickness of the first layer 81, the second layer 82, and the third layer 83, i.e., the thickness of the first semiconductor portion 8, and it is more preferable that the thickness of the fifth layer 72 is thicker than the thickness of the fourth layer 71. This can further improve the electrostatic breakdown voltage characteristics. Here, as described above, the fifth layer 72 is an undoped semiconductor layer or has a lower p-type impurity concentration than the fourth layer 71, and therefore is less susceptible to light absorption by p-type impurities. Therefore, even if the fifth layer 72 is made of a GaN layer having a smaller band gap than an AlGaN layer, for example, it is possible to reduce light absorption by the fifth layer 72 compared to the case of using a GaN layer having a relatively high p-type impurity concentration.

[0028] (Third Semiconductor Part 6) The p-side semiconductor layer 20 preferably includes a third semiconductor portion 6 disposed between the second semiconductor portion 7 and the active layer 5. The third semiconductor portion 6 includes a sixth layer 61 disposed on the second semiconductor portion 7 side and a seventh layer 62 disposed on the active layer 5 side. The Al composition ratio of the sixth layer 61 is greater than the Al composition ratio of the first layer 81 and the Al composition ratio of the third layer 83. The seventh layer 62 has a higher p-type impurity concentration than the sixth layer 61.

[0029] By providing the sixth layer 61 having an Al composition ratio greater than the Al composition ratios of the first layer 81 and the third layer 83, it is possible to easily confine electrons in the active layer 5. The Al composition ratio of the sixth layer 61 is, for example, not less than 25% and not more than 45%, and preferably not less than 30% and not more than 40%. Setting the Al composition ratio of the sixth layer 61 in this range makes it possible to easily confine electrons. The sixth layer 61 has a thickness of, for example, 3 nm or more and 7 nm or less. By setting the thickness of the sixth layer 61 in this range, electrons can be easily confined.

[0030] By providing a seventh layer 62 having a p-type impurity concentration greater than the p-type impurity concentration of the sixth layer 61, the supply of holes to the active layer 5 can be increased. The p-type impurity concentration of the seventh layer 62 is, for example, 5×10 19 / cm 3 or more and 3×10 20 / cm 3 or less. It is preferable to lower the Al composition ratio of the seventh layer 62 so that the p-type impurities in the seventh layer 62 can be efficiently activated. The Al composition ratio of the seventh layer 62 is 0% or more and 3% or less, preferably 0% or more and 2% or less, and more preferably 0%. Also, the p-type impurity concentration of the seventh layer 62 is preferably smaller than the p-type impurity concentration of the first layer 81, whereby the crystallinity of the seventh layer 62 can be improved. The thickness of the seventh layer 62 is, for example, 2 nm or more and 6 nm or less.

[0031] As described above, by forming the p-side semiconductor layer 20 with a plurality of layers having various functions and setting parameters such as the composition and thickness of each layer so as to effectively exhibit the functions of each layer, the luminous efficiency can be improved. Hereinafter, the configuration other than the p-side semiconductor layer 20 in the nitride semiconductor light-emitting device 100 of the present disclosure will be described.

[0032] <Substrate 1> As the substrate 1 (see FIG. 1), for example, an insulating substrate such as sapphire or spinel (MgAl2O4) having any one of a C plane, an R plane, and an A plane as a main surface can be used. Also, as the substrate 1, SiC (including 6H, 4H, 3C), ZnS, ZnO, GaAs, Si, etc. may be used. For example, a semiconductor laminate is disposed on a substrate 1 made of sapphire having a C plane as a main surface. The substrate 1 may not be finally provided.

[0033] <n-side semiconductor layer 10> 1, the n-side semiconductor layer 10 includes, in order from the substrate 1 side, an underlayer 2, an n-side contact layer 3, and an n-side superlattice layer 4. The n-side semiconductor layer 10 includes at least one n-type semiconductor layer containing an n-type impurity. For example, Si or Ge can be used as the n-type impurity.

[0034] The underlayer 2 is disposed between the substrate 1 and the n-side contact layer 3. By disposing the underlayer 2, the n-side contact layer 3 having high crystallinity can be formed on the upper surface of the underlayer 2. The underlayer 2 is, for example, AlGaN or GaN. A buffer layer may be further included between the underlayer 2 and the substrate 1. The buffer layer is a layer for reducing lattice mismatch between the substrate 1 and the underlayer 2, and may be, for example, undoped AlGaN or GaN.

[0035] The n-side contact layer 3 is disposed on the upper surface of the underlayer 2, and at least a portion of it contains an n-type impurity. As shown in FIG. 1, an n-side electrode 11, which will be described later, is disposed on the upper surface of the n-side contact layer 3. The n-side contact layer 3 is preferably doped with a relatively high concentration of n-type impurity in order to supply electrons from the n-side electrode 11 to the active layer 5. The n-type impurity concentration of the n-side contact layer 3 is, for example, 6×10 19 / cm 3 More than 1×10 19 / cm 3 The n-side contact layer 3 may be formed of, for example, GaN, AlGaN, AlN, or InGaN. The n-side contact layer 3 may have a laminated structure, for example, by alternately laminating undoped GaN and GaN doped with n-type impurities. The thickness of the n-side contact layer 3 is, for example, 5 μm or more and 20 μm or less.

[0036] The n-side superlattice layer 4 is disposed on the upper surface of the n-side contact layer 3. By disposing the n-side superlattice layer 4, lattice relaxation between the n-side contact layer 3 and the active layer 5 can be reduced, and the crystallinity of the active layer 5 can be improved. The n-side superlattice layer 4 has a structure in which semiconductor layers having different lattice constants are alternately stacked. The n-side superlattice layer 4 includes, for example, n pairs of a single pair including one undoped InGaN layer and one undoped GaN layer. The number of pairs n of the n-side superlattice layer 4 is set, for example, in the range of 10 or more and 40 or less layers, preferably in the range of 15 or more and 35 or less layers, and more preferably in the range of 25 or more and 35 or less layers.

[0037] <active layer 5> The active layer 5 can be configured, for example, by a single quantum well structure or a multiple quantum well structure including a well layer and a barrier layer.

[0038] The well layer is composed of, for example, a nitride semiconductor containing In. For example, In X Al Y Ga 1-X-Y When N (0≦X, 0≦Y, X+Y≦1) is used, by setting the In composition ratio x to a desired amount, the peak wavelength of the nitride semiconductor light-emitting device can be in the range of 430 nm or more and 570 nm or less.

[0039] The barrier layer in the active layer 5 is composed of a material that confines carriers in the well layer. The barrier layer is composed of, for example, GaN, InGaN, or AlGaN having a larger bandgap than the well layer. The barrier layer is located on both sides of the well layer, and one or both of the barrier layers on both sides may be composed of two or more layers having different bandgaps. Further, the barrier layer may contain an n-type impurity. For example, when the barrier layer contains an n-type impurity, the forward voltage Vf of the nitride semiconductor light-emitting device 100 can be reduced.

[0040] <n-side electrode 11> The n-side electrode 11 is disposed in contact with the n-side contact layer 3. As the n-side electrode 11, for example, a metal material containing Ti, Rh, Au, Pt, Al, Ag, or Ru can be used.

[0041] <p-side electrode 21> The p-side electrode 21 is disposed on the p-side semiconductor layer 20 and in contact with the first layer 81. As the p-side electrode 21, for example, a metal material containing Ti, Rh, Au, Pt, Al, Ag, or Ru can be used. Further, the p-side electrode 21 may include a translucent conductive layer made of ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), ZnO, In2O3, etc. in addition to the layer made of these metal materials. When the p-side electrode 21 includes a translucent conductive layer, the translucent conductive layer is preferably disposed in contact with the first layer 81.

[0042] According to the nitride semiconductor light-emitting device according to the present disclosure configured as described above, the luminous efficiency can be improved.

[0043] This embodiment includes the following forms. [Item 1] A semiconductor structure having an n-side semiconductor layer, a p-side semiconductor layer, and an active layer disposed between the n-side semiconductor layer and the p-side semiconductor layer, A p-side electrode disposed on the p-side semiconductor layer, The p-side semiconductor layer includes, in order from the p-side electrode side, a first layer containing Al and a p-type impurity in contact with the p-side electrode, a second layer containing a p-type impurity and having an Al composition ratio and a p-type impurity concentration smaller than those of the first layer, and a third layer containing a p-type impurity, having an Al composition ratio larger than that of the second layer, a p-type impurity concentration smaller than that of the first layer, and a thickness thicker than the thicknesses of the first layer and the second layer. A nitride semiconductor light-emitting device having a first semiconductor portion. [Item 2] The nitride semiconductor light-emitting device according to Item 1, wherein the thickness of the second layer is thicker than the thickness of the first layer. [Item 3] the p-side semiconductor layer further includes a second semiconductor portion disposed between the first semiconductor portion and the active layer, the second semiconductor portion includes, in order from the first semiconductor portion side, a fourth layer having an Al composition ratio larger than that of the second layer and smaller than that of the third layer, and a fifth layer having an Al composition ratio smaller than that of the fourth layer; 3. The nitride semiconductor light emitting device according to item 1 or 2, wherein a p-type impurity concentration of the fourth layer and a p-type impurity concentration of the fifth layer are lower than a p-type impurity concentration of the third layer. [Section 4] The fourth layer has a thickness greater than a thickness of the third layer, Item 4. The nitride semiconductor light emitting device according to item 3, wherein the fifth layer is thicker than the third layer. [Section 5] the p-side semiconductor layer further includes a third semiconductor portion disposed between the second semiconductor portion and the active layer, 5. The nitride semiconductor light-emitting device according to item 3 or 4, wherein the third semiconductor section includes a sixth layer having an Al composition ratio larger than an Al composition ratio of the first layer and an Al composition ratio of the third layer, and a seventh layer that is located closer to the active layer than the sixth layer and has a p-type impurity concentration larger than a p-type impurity concentration of the sixth layer. [Section 6] 6. The nitride semiconductor light emitting device according to item 5, wherein the seventh layer has a p-type impurity concentration lower than the p-type impurity concentration of the first layer. [Section 7] 7. The nitride semiconductor light emitting device according to any one of items 1 to 6, wherein a thickness of the second layer is 20% to 40% of a total thickness of the first layer, the second layer, and the third layer. [Section 8] an Al composition ratio of the fourth layer is smaller than an Al composition ratio of the first layer and an Al composition ratio of the third layer; The nitride semiconductor light emitting device according to any one of items 3 to 6 and item 8, or item 7 quoting any one of items 3 to 6, wherein a difference between an Al composition ratio of the first layer and an Al composition ratio of the third layer is 5% or more and 10% or less. [Explanation of symbols]

[0044] 1 Board 2 Base layer 3. N-side contact layer 4 n-side superlattice layer 5 Active layer 6. Third Semiconductor Department 61 6th layer 62 7th layer 7 Second Semiconductor Department 71 4th layer 72 5th layer 8 First Semiconductor Department 81 1st layer 82 2nd layer 83 3rd layer 10 n-side semiconductor layer 11 n-side electrode 20 p-side semiconductor layer 21 p side electrode 100 Nitride semiconductor light emitting device

Claims

1. A semiconductor structure having an n-side semiconductor layer, a p-side semiconductor layer, and an active layer disposed between the n-side semiconductor layer and the p-side semiconductor layer; a p-side electrode disposed on the p-side semiconductor layer, the p-side semiconductor layer includes, in order from the p-side electrode side, a first layer in contact with the p-side electrode and containing Al and a p-type impurity, a second layer containing p-type impurities and having an Al composition ratio and a p-type impurity concentration smaller than those of the first layer, and a third layer containing p-type impurities, having an Al composition ratio larger than those of the second layer, a p-type impurity concentration smaller than those of the first layer, and a thickness larger than the thickness of the first layer and the thickness of the second layer.

2. The nitride semiconductor light emitting device according to claim 1 , wherein the second layer is thicker than the first layer.

3. the p-side semiconductor layer further includes a second semiconductor portion disposed between the first semiconductor portion and the active layer, the second semiconductor portion includes, in order from the first semiconductor portion side, a fourth layer having an Al composition ratio larger than that of the second layer and smaller than that of the third layer, and a fifth layer having an Al composition ratio smaller than that of the fourth layer, 3 . The nitride semiconductor light emitting device according to claim 1 , wherein a p-type impurity concentration of the fourth layer and a p-type impurity concentration of the fifth layer are lower than a p-type impurity concentration of the third layer.

4. The fourth layer has a thickness greater than a thickness of the third layer, The nitride semiconductor light emitting device according to claim 3 , wherein the fifth layer is thicker than the third layer.

5. the p-side semiconductor layer further includes a third semiconductor portion disposed between the second semiconductor portion and the active layer, 4. The nitride semiconductor light-emitting element according to claim 3, wherein the third semiconductor portion includes a sixth layer having an Al composition ratio greater than an Al composition ratio of the first layer and an Al composition ratio of the third layer, and a seventh layer, which is located closer to the active layer than the sixth layer and has a p-type impurity concentration greater than a p-type impurity concentration of the sixth layer.

6. The nitride semiconductor light emitting device according to claim 5 , wherein a p-type impurity concentration of the seventh layer is lower than a p-type impurity concentration of the first layer.

7. 3 . The nitride semiconductor light emitting device according to claim 1 , wherein a thickness of the second layer is 20% or more and 40% or less of a total thickness of the first layer, the second layer, and the third layer.

8. an Al composition ratio of the fourth layer is smaller than an Al composition ratio of the first layer and an Al composition ratio of the third layer; 4. The nitride semiconductor light emitting device according to claim 3, wherein a difference between an Al composition ratio of the first layer and an Al composition ratio of the third layer is not less than 5% and not more than 10%.

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