Nitride semiconductor light-emitting element

Abstract

This invention provides a nitride semiconductor light-emitting element that can reduce the forward voltage in a light-emitting element formed by tunnel bonding of multiple semiconductor portions emitting ultraviolet light. The light-emitting element includes: a first semiconductor portion having a first n-side semiconductor layer, a first active layer disposed on the first n-side semiconductor layer and emitting ultraviolet light, and a first p-side semiconductor layer disposed on the first active layer; and a second semiconductor portion having a second n-side semiconductor layer disposed on the first semiconductor portion, a second active layer disposed on the second n-side semiconductor layer and emitting ultraviolet light, and a second p-side semiconductor layer disposed on the second active layer. The first p-side semiconductor layer includes a first layer containing Al and a second layer disposed on the first layer, the second layer containing Al and containing p-type impurities; the second p-side semiconductor layer includes a third layer containing Al and a fourth layer disposed on the third layer, the fourth layer containing Al and containing p-type impurities; the second n-side semiconductor layer is tunnel bonded to the second layer; and the thickness of the first layer is thinner than the thickness of the third layer.

Description

Technical Field

[0001] This disclosure relates to nitride semiconductor light-emitting devices. Background Technology

[0002] Patent Document 1 discloses, for example, a light-emitting element formed by connecting multiple semiconductor portions, each containing an active layer, in series via tunnel bonding. However, light-emitting elements formed by tunnel bonding multiple semiconductor portions that emit ultraviolet light have the problem of high forward voltage.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2019-517144 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] The present disclosure of the nitride semiconductor light-emitting element aims to provide a nitride semiconductor light-emitting element that can reduce the forward voltage in a light-emitting element formed by tunneling together multiple semiconductor parts that emit ultraviolet light.

[0008] Problem Solving Methods

[0009] One embodiment of the nitride semiconductor light-emitting element disclosed herein includes:

[0010] The first semiconductor section includes a first n-side semiconductor layer, a first active layer disposed on the first n-side semiconductor layer and emitting ultraviolet light, and a first p-side semiconductor layer disposed on the first active layer; and

[0011] The second semiconductor section has a second n-side semiconductor layer disposed on the first semiconductor section, a second active layer disposed on the second n-side semiconductor layer and emitting ultraviolet light, and a second p-side semiconductor layer disposed on the second active layer.

[0012] The aforementioned first p-side semiconductor layer includes a first layer containing Al and a second layer disposed on the first layer, wherein the second layer contains Al and contains p-type impurities.

[0013] The second p-side semiconductor layer includes a third layer containing Al and a fourth layer disposed on the third layer, wherein the fourth layer contains Al and contains p-type impurities.

[0014] The aforementioned second n-side semiconductor layer is tunnel-bonded to the aforementioned second layer.

[0015] The thickness of the first layer is thinner than the thickness of the third layer.

[0016] The effects of the invention

[0017] According to one embodiment of the present disclosure, a nitride semiconductor light-emitting element can be provided that can reduce the forward voltage in a light-emitting element formed by tunneling together multiple semiconductor portions that emit ultraviolet light. Attached Figure Description

[0018] Figure 1 This is a cross-sectional view illustrating an embodiment of a nitride semiconductor light-emitting element.

[0019] Symbol Explanation

[0020] 100 Nitride Semiconductor Light Emitting Device

[0021] 1 substrate

[0022] 2. Basal layer

[0023] 10 First Semiconductor Division

[0024] 11 First n-side semiconductor layer

[0025] 12 First active layer

[0026] 122 First Well Layer

[0027] 121, 123 First barrier layer

[0028] 13 First p-side semiconductor layer

[0029] 131 First Floor

[0030] 132 Second Layer

[0031] 135 Fifth Floor

[0032] 20 Second Semiconductor Division

[0033] 21 Second n-side semiconductor layer

[0034] 22 Second active layer

[0035] 222 Second Well Layer

[0036] 221, 223 Second Barrier Layer

[0037] 23 Second p-side semiconductor layer

[0038] 233 Third Floor

[0039] 234 Fourth Floor

[0040] 236 Sixth Floor Detailed Implementation

[0041] Hereinafter, embodiments for implementing the present disclosure will be described with reference to the accompanying drawings. It should be noted that the nitride semiconductor light-emitting elements described below are used to embody the technical concept of the present disclosure, and the nitride semiconductor light-emitting elements of the present disclosure are not limited to the following. For clarity, the size and positional relationships of the components shown in the drawings are sometimes exaggerated.

[0042] As described above, for example, in a light-emitting element formed by connecting multiple ultraviolet-emitting semiconductor portions via tunnel bonding, there is a problem that the forward voltage increases due to the composition of the tunnel bonding layer.

[0043] For example, GaN layers are commonly used in tunnel bonding layers. In light-emitting elements containing multiple semiconductor sections that emit blue light or light with wavelengths longer than blue, tunnel bonding of n-type GaN layers with p-type GaN layers reduces the rise in forward voltage and results in high light output. However, if a GaN layer is used as the tunnel bonding layer in a light-emitting element containing multiple semiconductor sections that emit ultraviolet light, ultraviolet light absorption and reduced light output occur in the tunnel-bonded GaN layer. As a solution to this problem, using an AlGaN layer instead of a GaN layer for tunnel bonding has been considered. However, in Al-containing nitride semiconductor layers like AlGaN layers, the activation energy of p-type impurities such as Mg is high. The higher the Al content, the higher the activation energy of p-type impurities in the Al-containing nitride semiconductor layer. That is, in Al-containing nitride semiconductor layers, the activation energy of p-type impurities is high, therefore, p-type impurities are not easily activated, the hole density is low, resulting in high resistance. Therefore, if an AlGaN layer is used as the tunneling layer, the ultraviolet absorption caused by the tunneling layer is suppressed, but the amount of holes generated by tunneling is reduced, and the forward voltage becomes higher.

[0044] In order to solve the above problems, the inventors conducted in-depth research and found that even when the tunnel bonding layer contains a nitride semiconductor layer containing Al, by adjusting the relationship between the overall layer structure and thickness of the nitride semiconductor, the reduction in the number of holes generated by the tunnel bonding can be reduced, and the rise in the forward voltage of the light-emitting element can be suppressed, thereby completing the nitride semiconductor light-emitting element of this disclosure.

[0045] The following is for reference Figure 1 The nitride semiconductor light-emitting element of this disclosure will be described in detail.

[0046] [Implementation Method]

[0047] like Figure 1As shown, the nitride semiconductor light-emitting element 100 of the embodiment includes a first semiconductor portion 10 that emits light of a given wavelength and a second semiconductor portion 20 disposed on the first semiconductor portion 10 on a substrate 1.

[0048] The first semiconductor section 10 has a first n-side semiconductor layer 11, a first active layer 12 disposed on the first n-side semiconductor layer 11 and emitting ultraviolet light, and a first p-side semiconductor layer 13 disposed on the first active layer 12.

[0049] The second semiconductor section 20 has a second n-side semiconductor layer 21 disposed on the first semiconductor section 10, a second active layer 22 disposed on the second n-side semiconductor layer 21 and emitting ultraviolet light, and a second p-side semiconductor layer 23 disposed on the second active layer 22.

[0050] The first p-side semiconductor layer 13 includes a first layer 131 containing Al and a second layer 132 disposed on the first layer 131, wherein the second layer 132 contains Al and contains p-type impurities.

[0051] The second p-side semiconductor layer 23 includes a third layer 233 containing Al and a fourth layer 234 disposed on the third layer 233, wherein the fourth layer 234 contains Al and contains p-type impurities.

[0052] Furthermore, the second n-side semiconductor layer 21 is tunnel bonded to the second layer 132, and the thickness of the first layer 131 is thinner than the thickness of the third layer 233.

[0053] It should be noted that, in this specification, the n-side semiconductor layer refers to an n-type conductivity semiconductor layer. For example, if it exhibits n-type conductivity, it is also called an n-side semiconductor layer even if it contains trace amounts of p-type impurities.

[0054] Furthermore, in this specification, a p-side semiconductor layer refers to a p-type conductivity semiconductor layer. For example, if it exhibits p-type conductivity, it is also referred to as a p-side semiconductor layer even if it contains trace amounts of n-type impurities.

[0055] In the nitride semiconductor light-emitting element 100 configured as described above, even if the second layer 132 that tunnels with the second n-side semiconductor layer 21 and the first layer 131 located below the second layer 132 are both Al-containing layers, the rise in forward voltage can be reduced by making the thickness of the first layer 131 thinner than the thickness of the third layer 233.

[0056] Therefore, according to the nitride semiconductor light-emitting element 100, a nitride semiconductor light-emitting element that emits ultraviolet light with reduced forward voltage rise can be provided.

[0057] Furthermore, by making the thickness of the third layer 233 greater than that of the first layer 131, the V-shaped pits formed during manufacturing can be properly filled when forming the third layer 233. V-shaped pits are areas where current tends to concentrate. If the V-shaped pits are not properly filled, the electrostatic discharge voltage may decrease. In other words, by filling the V-shaped pits, the decrease in electrostatic discharge voltage can be reduced.

[0058] Here, the thickness of the first layer 131 is, for example, 20nm or more and 120nm or less, and the thickness of the third layer 233 is, for example, 130nm or more and 180nm or less.

[0059] Here, the Al composition ratio of the first layer 131 is preferably lower than that of the third layer 233. This reduces the band gap of the first layer 131, thereby increasing the supply of holes to the first active layer 12.

[0060] In addition, the Al composition ratio of the first layer 131 and the Al composition ratio of the third layer 233 can be appropriately set taking into account the wavelengths of the ultraviolet rays emitted by the first active layer 12 and the second active layer 22. The difference between the Al composition ratio of the first layer 131 and the Al composition ratio of the third layer 233 is preferably 2% or less.

[0061] Alternatively, the first active layer 12 may include, for example, a first well layer 122 and first barrier layers 121 and 123 containing Al. In this case, it is preferable that the Al composition ratio of the first layer 131 is less than that of the first barrier layers 121 and 123. By making the Al composition ratio of the first layer 131 less than that of the first barrier layers 121 and 123, the reduction in the supply of holes to the first active layer 12 via tunnel bonding can be reduced. That is, the band gap of the first layer 131 can be reduced, and the reduction in the supply of holes to the first active layer 12 caused by the first layer 131 can be reduced. As will be described later, the first barrier layers 121 and 123 have different thicknesses and positions within the first active layer 12.

[0062] Additionally, the second active layer 22 may include a second well layer 222, an Al-containing second barrier layer 221, and an Al-containing second barrier layer 223. In this case, it is preferable that the Al composition ratio of the third layer 233 is less than the Al composition ratio of the second barrier layer 221 and the second barrier layer 223. As described later, the second barrier layer 221 and the second barrier layer 223 have different thicknesses and are located differently within the second active layer 22.

[0063] By making the Al composition ratio of the third layer 233 smaller than that of the second barrier layer 221 and the second barrier layer 223, the band gap of the third layer 233 will not become too large, making it easier to supply the holes generated by the fourth layer 234 to the second active layer 22.

[0064] The first p-side semiconductor layer 13 may have a fifth layer 135 containing Al between the first layer 131 and the first active layer 12. Furthermore, the second p-side semiconductor layer 23 may have a sixth layer 236 containing Al between the third layer 233 and the second active layer 22. The fifth layer 135 has the function of blocking the outflow of electrons supplied from the first n-side semiconductor layer 11 to the first active layer 12. On the other hand, the fifth layer 135 is a layer that controls the supply of holes generated through tunnel bonding to the first active layer 12. Furthermore, the generation of holes in tunnel bonding is, for example, less than the generation of holes in the p-side semiconductor layer. Therefore, by making the thickness of the fifth layer 135 thinner than the thickness of the sixth layer 236, even with fewer holes generated in tunnel bonding, a certain amount of holes can be easily supplied to the first active layer 12. Holes are supplied from the second p-side semiconductor layer 23 to the second active layer 22. Therefore, even if the sixth layer 236 is thicker than the fifth layer 135, it is easy to supply sufficient holes to the second active layer 22. In addition, by making the sixth layer 236 thicker than the fifth layer 135, it is possible to effectively block the outflow of electrons supplied from the tunnel bond to the second active layer 22.

[0065] In addition, as mentioned above, the fifth layer 135 containing Al is a layer that has the function of blocking electrons. In order to have the function of blocking electrons, for example, it is preferable that the Al composition ratio of the fifth layer 135 is greater than the Al composition ratio of the blocking layers of the first active layer 12 and the second active layer 22.

[0066] The first p-side semiconductor layer 13 has a fifth layer 135 containing Al between the first layer 131 and the first active layer 12. The second p-side semiconductor layer 23 has a sixth layer 236 containing Al between the third layer 233 and the second active layer 22. By making the Al composition ratio of the fifth layer 135 smaller than that of the sixth layer 236, a certain amount of electrons can be easily supplied to the second active layer 22. By making the Al composition ratio of the sixth layer 236 larger than that of the fifth layer 135, the outflow of electrons can be effectively blocked.

[0067] In addition, the thickness of the first layer 131 can be made thicker than that of the fifth layer 135, thereby effectively filling the V-shaped pits formed during the manufacturing process and improving electrostatic withstand voltage.

[0068] The fifth layer 135 and the sixth layer 236 are doped with p-type impurities, and the p-type impurity concentration of the fifth layer 135 is preferably higher than that of the sixth layer 236.

[0069] Thus, holes can be effectively supplied to the first active layer 12 through the fifth layer 135, and the sixth layer 236 can reduce the concentration of p-type impurities, thereby enabling good crystallinity.

[0070] like Figure 1 As shown, each of the layers described above is disposed on the substrate 1 with the base layer 2 in between.

[0071] In addition, the n-side electrode 3 is provided in a manner connected to the first n-side semiconductor layer 11, and the p-side electrode 4 is provided on the second p-side semiconductor layer 23.

[0072] The following describes in detail each component of the nitride semiconductor light-emitting element 100 of this disclosure.

[0073] <Substrate 1>

[0074] The substrate 1 can be, for example, an insulating substrate such as sapphire or spinel (MgAl2O4) with any one of the C-side, R-side, and A-side as the main surface. Alternatively, SiC (including 6H, 4H, and 3C), ZnS, ZnO, GaAs, Si, etc., can be used as the substrate 1. The substrate 1 can be removed after forming a semiconductor laminate including the first semiconductor portion 10 and the second semiconductor portion 20, thus ultimately eliminating the need for the substrate 1.

[0075] <Basal layer 2>

[0076] A substrate layer 2 is disposed between the substrate 1 and the first n-side semiconductor layer 11. By disposing of the substrate layer 2, a highly crystalline first n-side semiconductor layer 11 can be formed on the upper surface of the substrate layer 2. The substrate layer 2 is, for example, AlGaN or GaN. It should be noted that a buffer layer may be further included between the substrate layer 2 and the substrate 1. The buffer layer is used to reduce the lattice mismatch between the substrate 1 and the substrate layer 2, and for example, undoped AlGaN or GaN can be used.

[0077] [First Semiconductor Division 10]

[0078] The first semiconductor section 10 has a first n-side semiconductor layer 11, a first active layer 12 disposed on the first n-side semiconductor layer 11 and emitting ultraviolet light, and a first p-side semiconductor layer 13 disposed on the first active layer 12. The first semiconductor section 10 is disposed on the substrate layer 2.

[0079] <First n-side semiconductor layer 11>

[0080] The first n-side semiconductor layer 11 includes at least one n-type semiconductor layer, such as an n-side interconnect layer containing an n-type impurity. The n-type impurity can be, for example, Si, Ge, etc. The thickness of the first n-side semiconductor layer 11 is, for example, 5 μm or more and 15 μm or less. The first n-side semiconductor layer 11 may further include a superlattice layer and an undoped layer.

[0081] For example, a portion of the n-side interconnect layer of the first n-side semiconductor layer 11 is exposed, and the n-side electrode 3 (described later) is disposed on the exposed upper surface. Preferably, the n-side interconnect layer is doped with a relatively high concentration of n-type impurities. The n-type impurity concentration of the n-side interconnect layer is, for example, 1 × 10⁻⁶. 19 / cm 3 Above and 1×10 20 / cm 3 The n-side interconnect layer can be made of AlGaN, for example, with an Al content of 1% or more and 20% or less, which can be appropriately set considering the emission wavelength of the first active layer 12. The thickness of the n-side interconnect layer is, for example, 1 μm or more and 5 μm or less.

[0082] <n-side electrode 3>

[0083] For example, the n-side electrode 3 can be made of a metallic material containing Ti, Rh, Au, Pt, Al, Ag, or Ru.

[0084] <First Active Layer 12>

[0085] The first active layer 12 can be composed of a single quantum well structure or a multi-quantum well structure, for example, a multi-quantum well structure, such as... Figure 1 As shown, after stacking multiple pairs containing a first barrier layer 121 and a first well layer 122, a first barrier layer 123 can be formed at the position closest to the first p-side semiconductor layer 13 in the first active layer 12.

[0086] The first well layer 122 is, for example, made of an Al-containing nitride semiconductor. As the first well layer 122 emitting ultraviolet light at approximately 380 nm, GaN or GaN containing trace amounts of In can also be used. Here, "trace amounts" refers to a range of 0.1% to 0.5%, for example, it can be made of a nitride semiconductor with GaN as the main component, where the In content is approximately 0.3%. Furthermore, as the first well layer 122 emitting short-wavelength ultraviolet light, it can be made of an AlGaN layer, for example; by adjusting the Al content, the desired short-wavelength ultraviolet light can be emitted.

[0087] In addition, the thickness of the first well layer 122 is, for example, 10 nm or more and 20 nm or less.

[0088] The first barrier layer 121 and the first barrier layer 123 in the first active layer 12 are made of materials such as AlGaN, which have a larger band gap than the first well layer 122. The first barrier layer 121 and the first barrier layer 123 are disposed on both sides of the first well layer 122, and the band gaps of the first barrier layer 121 and the first barrier layer 123 on one side can be the same or different. The first barrier layer 121 and the first barrier layer 123 can each be composed of two or more layers. Furthermore, the first barrier layer 121 and the first barrier layer 123 can contain n-type impurities. Alternatively, the first barrier layer 121 can be composed of a layer containing n-type impurities, and the first barrier layer 123 can be composed of an undoped layer. By including n-type impurities in the first barrier layer 121, the forward voltage of the nitride semiconductor light-emitting element 100 can be reduced.

[0089] Furthermore, the thickness of the first barrier layer 121 and the thickness of the first barrier layer 123 are, for example, 10 nm or more and 50 nm or less. The thickness of the first barrier layer 121 and the thickness of the first barrier layer 123 may be the same or different, but it is preferable that the thickness of the first barrier layer 123 is thicker than the thickness of the first barrier layer 121. By making the thickness of the first barrier layer 123 thicker than the thickness of the first barrier layer 121, the reduction in luminous efficiency can be reduced by allowing p-type impurities of the first p-side semiconductor layer 13 to diffuse into the first well layer 122. When the thickness of the first barrier layer 123 is thicker than the thickness of the first barrier layer 121, the thickness of the first barrier layer 123 is, for example, 110% or more and 200% or less of the thickness of the first barrier layer 121.

[0090] <First p-side semiconductor layer 13>

[0091] The first p-side semiconductor layer 13 includes a fifth layer 135 disposed on the first barrier layer 123, a first layer 131 disposed on the fifth layer 135, and a second layer 132 disposed on the first layer 131.

[0092] The fifth layer 135 has a larger band gap than the first barrier layer 123, the first layer 131, and the second layer 132. For example, it can be composed of an AlGaN layer with a high Al content. As described above, by including the fifth layer 135 with a large band gap in the first p-side semiconductor layer 13, it is possible to suppress the movement of electrons from the first active layer 12 to the second semiconductor portion 20, and to confine the necessary amount of electrons in the first active layer 12. For example, when the fifth layer 135 is composed of an AlGaN layer, the Al content is, for example, 1% or more and 30% or less.

[0093] The first layer 131 is an Al-containing layer. The Al composition ratio of the first layer 131 is less than at least one of the Al composition ratio of the fifth layer 135 and the Al composition ratio of the second layer 132. Preferably, the Al composition ratio of the first layer 131 is less than the Al composition ratio of the fifth layer 135 and the Al composition ratio of the second layer 132. The first layer 131 may be composed of an AlGaN layer. The Al composition ratio of the first layer 131 is 1% or more and 30% or less, preferably 4% or more and 10% or less. By reducing the Al composition ratio of the first layer 131, the rise of the forward voltage can be suppressed.

[0094] Furthermore, it is preferable that the p-type impurity concentration of the first layer 131 is lower than that of the fifth layer 135. The first layer 131 is preferably an undoped layer. Here, an undoped layer means a layer that has not been intentionally doped with impurities. By making the p-type impurity concentration of the first layer 131 lower than that of the fifth layer 135, the electrostatic discharge (ESD) withstand voltage of the nitride semiconductor light-emitting element 100 can be improved. Furthermore, by setting the first layer 131 as an undoped layer, the ESD withstand voltage of the nitride semiconductor light-emitting element 100 can be further improved. The p-type impurity concentration of the first layer 131 may also be lower than that of the second layer 132.

[0095] The first layer 131 has the function of filling V-shaped pits. Here, a V-shaped pit refers to a concave pit formed in the semiconductor layer due to dislocations formed during the epitaxial growth of the semiconductor layer, for example, formed starting from the transfer during the growth of the first active layer 12. Sometimes, V-shaped pits are formed starting from a layer lower than the first active layer 12 and extending through the first active layer 12. Here, to effectively fill the V-shaped pits and improve the electrostatic discharge withstand voltage, it is preferable that the first layer 131 be thick. Since it is an Al-containing layer, if it is too thick, there is a concern that the forward voltage will increase. Therefore, the thickness of the first layer 131 is set to be thinner than that of the third layer 233. Thus, the first layer 131 can effectively fill the V-shaped pits, improve the electrostatic discharge withstand voltage, and reduce the increase in forward voltage. A preferred thickness of the first layer 131 is, for example, 10 nm or more and 300 nm or less, and a more preferred thickness is 20 nm or more and 100 nm or less.

[0096] The second layer 132 is a p-type semiconductor layer that is tunnel bonded to the second n-side semiconductor layer 21.

[0097] To enable tunnel bonding, the second layer 132, which tunnels with the second n-side semiconductor layer 21, contains a high concentration of p-type impurities. The p-type impurity concentration of the second layer 132 is higher than that of the first layer 131 and the fifth layer 135. Here, the p-type impurity is, for example, Mg. The p-type impurity concentration of the second layer 132 is, for example, 1 × 10⁻⁶. 19 / cm 3 Above and 3×1021 / cm 3 The following is preferred: 1×10 20 / cm 3 Above and 1×10 21 / cm 3 the following.

[0098] <Second n-side semiconductor layer 21>

[0099] The second n-side semiconductor layer 21 is a layer that tunnels with the second layer 132 of the first semiconductor section 10. Furthermore, the second n-side semiconductor layer 21 has the function of supplying electrons to the second active layer 22. The second n-side semiconductor layer 21 can be composed of multiple n-type semiconductor layers; for example, it can include one or more n-type semiconductor layers with a high concentration of n-type impurities that tunnel with the second layer 132, and layers with a lower concentration of n-type impurities than the first layer. For example, the n-type impurity concentration of the layer with a high concentration of n-type impurities that tunnels with the second layer 132 in the second n-side semiconductor layer 21 is 1 × 10⁻⁶. 19 / cm 3 Above and 3×10 21 / cm 3 The following is preferred: 1×10 20 / cm 3 Above and 2×10 21 / cm 3 the following.

[0100] The layer tunnel bonded to the second layer 132 is, for example, an Al-containing nitride semiconductor layer, such as an AlGaN layer. The n-type impurities doped in the n-type semiconductor layer of the second n-side semiconductor layer 21 are, for example, silicon (Si) or germanium (Ge).

[0101] <Second Active Layer 22>

[0102] The second active layer 22 is similar to the first active layer 12, and can be composed of a single quantum well structure or a multi-quantum well structure containing a well layer and a barrier layer. For example, if it is a multi-quantum well structure, then... Figure 1 As shown, after stacking multiple pairs of layers including the second barrier layer 221 and the second well layer 222, the second barrier layer 223 can be formed at the position closest to the second p-side semiconductor layer 23 in the second active layer 22. The emission wavelength of the second active layer 22 can be the same as or different from the emission wavelength of the first active layer 12.

[0103] As shown below, the second active layer 22 can be constructed in the same way as the first active layer 12.

[0104] The second well layer 222 can be made of, for example, an Al-containing nitride semiconductor. As the second well layer 222 emitting ultraviolet light at approximately 380 nm, GaN or GaN containing trace amounts of In can also be used. Here, "trace amounts" refers to a range of 0.1% to 0.5%, and for example, it can be made of a nitride semiconductor with GaN as the main component, where the In content is approximately 0.3%. Furthermore, as the second well layer 222 emitting short-wavelength ultraviolet light, it can be made of, for example, an AlGaN layer, and the desired short-wavelength ultraviolet light can be emitted by adjusting the Al content.

[0105] In addition, the thickness of the second well layer 222 is, for example, 10 nm or more and 20 nm or less.

[0106] The second barrier layers 221 and 223 in the second active layer 22 are made of materials such as AlGaN, which have a larger band gap than the second well layer 222. The second barrier layers 221 and 223 are disposed on both sides of the second well layer 222, and the band gaps of the second barrier layers 221 and 223 on one side can be the same or different. The second barrier layers 221 and 223 can each be composed of two or more layers. Furthermore, the second barrier layers 221 and 223 can contain n-type impurities; alternatively, the second barrier layer 221 can be composed of a layer containing n-type impurities, and the second barrier layer 223 can be composed of an undoped layer. By including n-type impurities in the second barrier layer 221, the forward voltage of the nitride semiconductor light-emitting element 100 can be reduced.

[0107] Furthermore, the thicknesses of the second barrier layer 221 and the second barrier layer 223 are, for example, 10 nm or more and 50 nm or less. The thicknesses of the second barrier layer 221 and the second barrier layer 223 can be the same or different; preferably, the thickness of the second barrier layer 221 is greater than the thickness of the second barrier layer 223. By making the thickness of the second barrier layer 223 greater than the thickness of the second barrier layer 221, the reduction in luminous efficiency can be reduced by allowing p-type impurities in the second p-side semiconductor layer 23 to diffuse into the second well layer 222. When the thickness of the second barrier layer 223 is greater than the thickness of the second barrier layer 221, the thickness of the second barrier layer 223 is, for example, 110% or more and 200% or less of the thickness of the second barrier layer 221.

[0108] <Second p-side semiconductor layer 23>

[0109] The second p-side semiconductor layer 23 includes a sixth layer 236 disposed on the second barrier layer 223, a third layer 233 disposed on the sixth layer 236, and a fourth layer 234 disposed on the third layer 233.

[0110] The sixth layer 236 has a larger band gap than the second barrier layer 223, the third layer 233, and the fourth layer 234, and can be, for example, composed of an AlGaN layer with a high Al content. By including the sixth layer 236 with a large band gap in the second p-side semiconductor layer 23, the movement of electrons from the second active layer 22 can be suppressed, and electrons can be confined within the second active layer 22. For example, when the sixth layer 236 is composed of an AlGaN layer, the Al content is, for example, 1% or more and 30% or less, preferably 20% or more and 30% or less.

[0111] The third layer 233 is an Al-containing layer. The Al content of the third layer 233 is less than at least one of the Al content of the sixth layer 236 and the fourth layer 234. Preferably, the Al content of the third layer 233 is less than the Al content of the sixth layer 236 and the fourth layer 234. The third layer 233 may be composed of an AlGaN layer. The Al content of the third layer 233 is, for example, 1% or more and 30% or less, preferably 2% or more and 10% or less. By reducing the Al content of the third layer 233, the rise of the forward voltage can be suppressed.

[0112] Furthermore, the p-type impurity concentration of the third layer 233 is lower than that of the sixth layer 236 and the fourth layer 234, and it is preferably an undoped layer. Here, an undoped layer means a layer that has not been intentionally doped with impurities. By making the p-type impurity concentration of the third layer 233 lower than that of the sixth layer 236 and the fourth layer 234, the electrostatic discharge (ESD) withstand voltage of the nitride semiconductor light-emitting element 100 can be improved. In addition, by making the third layer 233 an undoped layer, the ESD withstand voltage of the nitride semiconductor light-emitting element 100 can be further improved.

[0113] The third layer 233 has the function of filling V-shaped pits. Here, as described above, a V-shaped pit refers to a concave pit formed in the semiconductor layer due to dislocations formed during the epitaxial growth of the semiconductor layer. As described above, V-shaped pits formed by transfer during the growth of the first active layer 12, or V-shaped pits formed through the first active layer 12 by a layer lower than the first active layer 12, are partially filled by the first layer 131. However, when layers higher than the first active layer 12, such as the first p-side semiconductor layer 13, the second n-side semiconductor layer 21, and the second active layer 22, are grown, new V-shaped pits are generated starting from residual V-shaped pits formed in layers lower than the first active layer 12. By forming a third layer 233 that is thicker than the first layer 131, residual V-shaped pits can also be well filled.

[0114] If the good filling of the remaining V-shaped pits is taken into account, the preferred thickness of the third layer 233 is, for example, 50 nm or more and 400 nm or less. Thus, the V-shaped pits can be well filled by the third layer 233, thereby improving the electrostatic withstand voltage.

[0115] The fourth layer 234 is a p-type semiconductor layer with a p-side electrode 4 formed thereon. To reduce the contact resistance between the fourth layer 234 and the p-side electrode 4, it contains p-type impurities at a relatively high concentration, at least higher than that of the third layer 233. Here, the p-type impurity is, for example, Mg. The p-type impurity concentration of the fourth layer 234 is, for example, 1 × 10⁻⁶. 19 / cm 3 Above and 1×10 21 / cm 3 Below. Additionally, the thickness of the fourth layer 234 is, for example, 1 nm or more and 30 nm or less.

[0116] <p-side electrode 4>

[0117] The p-side electrode 4 is disposed on the second p-side semiconductor layer 23 and grounded to the fourth layer 234, which contains Al and p-type impurities. The p-side electrode 4 may, for example, comprise a transparent conductive layer 41 formed of ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), ZnO, In2O3, etc., and a pad electrode 42. The transparent conductive layer 41 is grounded to the fourth layer 234, and the pad electrode 42 is disposed on the transparent conductive layer 41. The pad electrode 42 may, for example, be a metallic material containing Ti, Rh, Au, Pt, Al, Ag, or Ru.

[0118] The nitride semiconductor light-emitting element 100 according to the above embodiments can provide a nitride semiconductor light-emitting element that emits ultraviolet light with a low forward voltage.

[0119] Examples and Comparative Examples

[0120] The following describes the embodiments and comparative examples.

[0121] Nitride semiconductor light-emitting elements of Examples 1-4 and Comparative Examples 1-3 shown below were fabricated, and their forward voltages were measured.

[0122] Here, the nitride semiconductor light-emitting elements of Examples 1-4 and Comparative Examples 1-3 have Figure 1 The layer structures shown are identical except for the film thickness of the first layer 131 and the third layer 233.

[0123] Therefore, the common layers in the nitride semiconductor light-emitting elements of Examples 1-4 and Comparative Examples 1-3, except for the film thickness of the first layer 131 and the third layer 233, will be specifically described first. Then, the film thickness of the first layer 131 and the third layer 233 and the measurement results of the forward voltage in the nitride semiconductor light-emitting elements of Examples 1-4 and Comparative Examples 1-3 will be described.

[0124] 1. Substrate 1

[0125] Substrate 1 is a sapphire substrate with its upper surface as C-plane obtained by growing a nitride semiconductor layer.

[0126] 2. Basal layer 2

[0127] An undoped GaN layer with a thickness of 6500 nm was grown on the C-surface of a sapphire substrate 1 to form a base layer 2.

[0128] 3. First n-side semiconductor layer 11

[0129] Al with Si doped composition of 5% 0.05 Ga 0.95 The N layer is grown on the substrate 2 with a thickness of 3000 nm. 0.05 Ga 0.95 On the N-layer, a superlattice layer containing AlGaN layers with different Al composition ratios is grown to form the first n-side semiconductor layer 11.

[0130] Here, by making the Al composition of Si-doped Al 9.5% 0.095 Ga 0.905 After growing an N-layer of 29 nm, the undoped Al with an Al composition of 4% was obtained. 0.04 Ga 0.96 The N-layer is grown to 5nm, and the resulting superlattice layer is formed by growing the N-layer for 3 cycles.

[0131] 4. First active layer 12

[0132] Al with Si doped Al content of 9.5% 0.095 Ga 0.905 After the N-layer is grown to 29 nm on the superlattice layer of the first n-side semiconductor layer 11 to form the first barrier layer 121, the In composition ratio is 0.3% undoped In. 0.003 Ga 0.997 An N-layer is grown 15 nm on the first barrier layer 121 to form a first well layer 122, forming two cycles of pairs formed by the first barrier layer 121 and the first well layer 122. Then, an undoped Al composition of 9.5% is formed. 0.095 Ga 0.905The N-layer grows to 40 nm to form the first barrier layer 123, thereby forming the first active layer 12.

[0133] 5. First p-side semiconductor layer 13

[0134] On the first barrier layer 123 of the first active layer 12,

[0135] (a) Al with a Mg-doped Al composition of 25% 0.25 Ga 0.75 The N layer is grown to a thickness of 22.5 nm, thus forming the fifth layer, 135.

[0136] (b) On this fifth layer 135, undoped Al with an Al composition of 6.5% 0.065 Ga 0.935 Layer N grows with a thickness of t1nm, thus forming the first layer 131.

[0137] (c) On the first layer 131,

[0138] Al with Mg doping content of 8.5% 0.085 Ga 0.915 The N-layer grows to 18.5 nm, forming the second layer at 132 nm.

[0139] This forms the first p-side semiconductor layer 13.

[0140] In addition, in order to tunnel bond with the second n-side semiconductor layer 21, the doping amount of Mg in the second layer 132 is set to 1×10⁻⁶. 20 / cm 3 .

[0141] 6. Second n-side semiconductor layer 21

[0142] On the first p-side semiconductor layer 13,

[0143] (a) Al with a Si-doped Al composition of 9.5% 0.095 Ga 0.905 The N layer was grown with a thickness of 47.5 nm.

[0144] (b) In the Al 0.095 Ga 0.905 On the N-layer, the Al composition with Si doped in it is 6.5%. 0.065 Ga 0.935 The N layer is grown with a thickness of 80 nm.

[0145] (c) In the Al 0.065 Ga 0.935 On the N-layer, superlattice layers containing alternating AlGaN layers with different Al composition ratios are grown.

[0146] This forms the second n-side semiconductor layer 21.

[0147] Here, by making the Al composition of Si-doped Al 9.5% 0.095 Ga 0.905 After growing an N-layer of 29 nm, the undoped Al with an Al composition of 4% was obtained. 0.04 Ga 0.96 The N-layer is grown to 5nm, and the resulting superlattice layer is formed by growing the N-layer for 3 cycles.

[0148] In addition, in order to tunnel bond with the first p-side semiconductor layer 13, Al with an Al composition ratio of 9.5% is used. 0.095 Ga 0.905 The Si doping concentration of the N-layer is set to 1×10⁻⁶. 21 / cm 3 .

[0149] 7. Second active layer 22

[0150] Al with Si doped Al content of 9.5% 0.095 Ga 0.905 After the N-layer is grown at 29 nm on the superlattice layer of the second n-side semiconductor layer 21 to form the second barrier layer 221, the In composition ratio is 0.3% undoped In. 0.003 Ga 0.997 An N-layer is grown 15 nm on the second barrier layer 221 to form a second well layer 222. After two cycles are formed by the pair formed by the second barrier layer 221 and the second well layer 222, the undoped Al composition is made to be 9.5% Al. 0.095 Ga 0.905 The N layer grows to 40 nm to form the second barrier layer 223, thereby forming the second active layer 22.

[0151] 8. Second p-side semiconductor layer 23

[0152] On the second barrier layer 223 of the second active layer 22,

[0153] (a) Al with a Mg-doped Al composition of 25% 0.25 Ga 0.75 The N layer was grown to a thickness of 22.5 nm, thus forming the sixth layer, 236.

[0154] (b) On the sixth layer 236, undoped Al with an Al composition of 6.5% 0.065 Ga 0.935 Layer N grows with a thickness of t2nm, thereby forming the third layer 233.

[0155] (c) On this third layer 233, an Al composition with Mg doped in it is 8.5%. 0.085 Ga 0.915 Layer N is grown to 12nm, forming the fourth layer 234.

[0156] This forms the second p-side semiconductor layer 23.

[0157] After each layer is formed as described above, the Al layer located below the superlattice layer 11 on the first n-side semiconductor layer 11, with an Al composition ratio of 5% doped with Si, is formed. 0.05 Ga 0.95 A portion of the N layer is exposed to form the n-side electrode 3, and the p-side electrode 4 is formed on the fourth layer 234 of the second p-side semiconductor layer 23.

[0158] Here, the n-side electrode 3 is configured as a Ti / Pt / Au / Pt / Ti stacked structure starting from the first n-side semiconductor layer 11. For the p-side electrode 4, the pad electrode 42 is configured as a Ti / Pt / Au stacked structure starting from the second p-side semiconductor layer 23. It should be noted that the transparent conductive layer 41 is not used in any of the embodiments and comparative examples.

[0159] In the nitride semiconductor light-emitting elements of Examples 1-4 and Comparative Examples 1-3, the film thicknesses of the first layer 131 and the third layer 233 are formed as shown in Table 1.

[0160]

[0161] The results of the forward voltage measurement in the nitride semiconductor light-emitting elements of Examples 1-4 and Comparative Examples 1-3 are shown in Table 2.

[0162]

[0163] As shown in Tables 1 and 2, it was confirmed that in Examples 1 to 4 where the film thickness t1 of the first layer 131 is thinner than the film thickness t2 of the third layer 233, the forward voltage can be reduced compared to Comparative Examples 1 to 3 where the film thickness t1 of the first layer 131 is the same as the film thickness t2 of the third layer 233, or where the film thickness t1 of the first layer 131 is thicker than the film thickness t2 of the third layer 233.

[0164] The nitride semiconductor light-emitting elements of the embodiments of this disclosure include, for example, the following methods.

[0165] [Item 1]

[0166] A nitride semiconductor light-emitting element comprising:

[0167] The first semiconductor section includes a first n-side semiconductor layer, a first active layer disposed on the first n-side semiconductor layer and emitting ultraviolet light, and a first p-side semiconductor layer disposed on the first active layer; and

[0168] The second semiconductor section has a second n-side semiconductor layer disposed on the first semiconductor section, a second active layer disposed on the second n-side semiconductor layer and emitting ultraviolet light, and a second p-side semiconductor layer disposed on the second active layer.

[0169] The aforementioned first p-side semiconductor layer includes a first layer containing Al and a second layer disposed on the first layer, wherein the second layer contains Al and contains p-type impurities.

[0170] The second p-side semiconductor layer includes a third layer containing Al and a fourth layer disposed on the third layer, wherein the fourth layer contains Al and contains p-type impurities.

[0171] The aforementioned second n-side semiconductor layer is tunnel-bonded to the aforementioned second layer.

[0172] The thickness of the first layer is thinner than the thickness of the third layer.

[0173] [Item 2]

[0174] According to the nitride semiconductor light-emitting element of item 1, wherein,

[0175] The Al composition ratio of the first layer is less than that of the third layer.

[0176] [Item 3]

[0177] According to the nitride semiconductor light-emitting element of claim 1 or claim 2, wherein,

[0178] The thickness of the first layer is 20nm or more and 120nm or less, and the thickness of the third layer is 130nm or more and 180nm or less.

[0179] [Item 4]

[0180] The nitride semiconductor light-emitting element according to any one of items 1 to 3, wherein,

[0181] The aforementioned first active layer comprises a first well layer and a first barrier layer containing Al.

[0182] The Al composition ratio of the first layer is less than that of the first barrier layer.

[0183] [Item 5]

[0184] The nitride semiconductor light-emitting element according to any one of items 1 to 4, wherein,

[0185] The aforementioned second active layer comprises a second well layer and a second barrier layer containing Al.

[0186] The Al composition ratio of the third layer is less than that of the second barrier layer.

[0187] [Item 6]

[0188] The nitride semiconductor light-emitting element according to any one of items 1 to 5, wherein,

[0189] The aforementioned first p-side semiconductor layer has a fifth layer containing Al between the aforementioned first layer and the aforementioned first active layer.

[0190] The second p-side semiconductor layer has a sixth layer containing Al between the third layer and the second active layer.

[0191] The thickness of the fifth layer is thinner than that of the sixth layer.

[0192] [Item 7]

[0193] The nitride semiconductor light-emitting element according to any one of items 1 to 6, wherein,

[0194] The aforementioned first p-side semiconductor layer has a fifth layer containing Al between the aforementioned first layer and the aforementioned first active layer.

[0195] The second p-side semiconductor layer has a sixth layer containing Al between the third layer and the second active layer.

[0196] The Al composition ratio of the fifth layer is less than that of the sixth layer.

[0197] [Item 8]

[0198] The nitride semiconductor light-emitting element according to item 6 or item 7 of reference 6, wherein,

[0199] The thickness of the first layer mentioned above is greater than the thickness of the fifth layer mentioned above.

[0200] [Item 9]

[0201] The nitride semiconductor light-emitting element according to item 6 or item 7 of reference 6, wherein,

[0202] The fifth and sixth layers mentioned above are doped with p-type impurities, and the concentration of p-type impurities in the fifth layer is higher than that in the sixth layer.

Claims

1. A nitride semiconductor light-emitting element, comprising: A first semiconductor section has a first n-side semiconductor layer, a first active layer disposed on the first n-side semiconductor layer and emitting ultraviolet light, and a first p-side semiconductor layer disposed on the first active layer; and The second semiconductor portion has a second n-side semiconductor layer disposed on the first semiconductor portion, a second active layer disposed on the second n-side semiconductor layer and emitting ultraviolet light, and a second p-side semiconductor layer disposed on the second active layer. The first p-side semiconductor layer includes a first layer containing Al and a second layer disposed on the first layer, the second layer containing Al and containing p-type impurities. The second p-side semiconductor layer includes a third layer containing Al and a fourth layer disposed on the third layer, the fourth layer containing Al and containing p-type impurities. The second n-side semiconductor layer is tunnel bonded to the second layer. The thickness of the first layer is thinner than the thickness of the third layer.

2. The nitride semiconductor light-emitting element according to claim 1, wherein, The Al composition ratio of the first layer is less than that of the third layer.

3. The nitride semiconductor light-emitting element according to claim 1 or 2, wherein, The thickness of the first layer is greater than 20 nm and less than 120 nm, and the thickness of the third layer is greater than 130 nm and less than 180 nm.

4. The nitride semiconductor light-emitting element according to claim 1 or 2, wherein, The first active layer comprises a first well layer and a first barrier layer containing Al. The Al composition ratio of the first layer is less than that of the first barrier layer.

5. The nitride semiconductor light-emitting element according to claim 1 or 2, wherein, The second active layer comprises a second well layer and a second barrier layer containing Al. The Al composition ratio of the third layer is less than that of the second barrier layer.

6. The nitride semiconductor light-emitting element according to claim 1, wherein, The first p-side semiconductor layer has a fifth layer containing Al between the first layer and the first active layer. The second p-side semiconductor layer has a sixth layer containing Al between the third layer and the second active layer. The fifth layer is thinner than the sixth layer.

7. The nitride semiconductor light-emitting element according to claim 1 or 6, wherein, The first p-side semiconductor layer has a fifth layer containing Al between the first layer and the first active layer. The second p-side semiconductor layer has a sixth layer containing Al between the third layer and the second active layer. The Al composition ratio of the fifth layer is less than that of the sixth layer.

8. The nitride semiconductor light-emitting element according to claim 6 or claim 7, wherein, The thickness of the first layer is greater than the thickness of the fifth layer.

9. The nitride semiconductor light-emitting element according to claim 6 or claim 7, wherein, The fifth and sixth layers are doped with p-type impurities, and the concentration of p-type impurities in the fifth layer is higher than that in the sixth layer.

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