UV semiconductor light-emitting device and method for manufacturing a UV semiconductor light-emitting device

Abstract

The present invention provides an ultraviolet semiconductor light-emitting element and a method for manufacturing the same, which have excellent device characteristics such as a high polarization doping effect, a p-contact layer with excellent ohmic properties, a reduced turn-on voltage, and high efficiency and high output. [Solution] The material is made of an AlGaN-based semiconductor in which an n-type semiconductor layer 12, an active layer 13, an electron blocking layer 14, a p-type semiconductor layer 15, and a p-electrode 21 are sequentially stacked. The p-type semiconductor layer has a first composition gradient layer 15A formed on the electron blocking layer, in which the Al composition decreases toward the p-electrode, and a second composition gradient layer 15B formed on the first composition gradient layer, in which the Al composition decreases toward the p-electrode. The interface between the first composition gradient layer and the second composition gradient layer has a heterojunction in which the Al composition is discontinuous, and at the interface, the Al composition of the first composition gradient layer is greater than the Al composition of the second composition gradient layer.

Description

[Technical Field]

[0001] The present invention relates to an ultraviolet semiconductor light-emitting element and a method for manufacturing an ultraviolet semiconductor light-emitting element, and more particularly to a nitride semiconductor light-emitting element that emits deep ultraviolet light and a method for manufacturing the same. [Background technology]

[0002] In recent years, AlGaN-based semiconductor light-emitting devices with emission wavelengths in the deep ultraviolet region have attracted attention as light sources that have the effect of inactivating bacteria and viruses and providing sterilization. However, there is a need for even higher output power for these light-emitting devices.

[0003] For example, Patent Document 1 discloses a semiconductor light-emitting element having a single composition gradient contact layer made of an AlGaN layer or an AlInGaN layer, where the Al composition decreases towards the p electrode.

[0004] Furthermore, Patent Document 2 discloses a group III nitride semiconductor light-emitting element having a first p-type contact layer in contact with a p-type electron blocking layer and co-doped with Mg and Si, and a second p-type contact layer in contact with the p-side electrode and doped with Mg.

[0005] Furthermore, Patent Document 3 discloses a deep ultraviolet light-emitting device having a p-type contact layer with a superlattice structure in which AlGaN layers having different Al composition ratios are alternately stacked.

[0006] Non-patent document 1 describes a theoretical model of AlGaN / GaN light-emitting diodes. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-064955 [Patent Document 2] Patent No. 6908422 [Patent Document 3] Patent No. 6849641 [Non-patent literature]

[0008] [Non-Patent Document 1] Shah et al., J. Appl. Phys., Vol. 94, No. 4, 15 August 2003 [Overview of the project] [Problems that the invention aims to solve]

[0009] It has been taught that by making the p-type AlGaN contact layer a compositionally graded layer, the contact resistance can be lowered compared to the case where Al is constant (for example, Patent Document 1). However, in AlGaN-based semiconductor light-emitting devices with an emission wavelength band in the deep ultraviolet region, the conductivity, such as ohmic characteristics and resistivity, was insufficient.

[0010] The present invention has been made in view of the above-mentioned problems, and aims to provide an ultraviolet semiconductor light-emitting element and a method for manufacturing an ultraviolet semiconductor light-emitting element that have excellent ohmic characteristics of a p-contact layer, reduced turn-on voltage, and excellent element characteristics such as high efficiency and high output, while utilizing the effect of polarization doping. [Means for solving the problem]

[0011] The ultraviolet semiconductor light-emitting device according to one embodiment of the present invention is An ultraviolet semiconductor light-emitting element made of an AlGaN-based semiconductor in which an n-type semiconductor layer, an active layer, an electron blocking layer, a p-type semiconductor layer, and a p-electrode are sequentially stacked, The p-type semiconductor layer comprises a first composition gradient layer formed on the electron block layer, wherein the Al composition decreases toward the p-electrode, and a second composition gradient layer formed on the first composition gradient layer, wherein the Al composition decreases toward the p-electrode. The interface between the first composition gradient layer and the second composition gradient layer has a heterojunction in which the Al composition is discontinuous. At the interface, the Al composition of the first composition gradient layer is greater than the Al composition of the second composition gradient layer.

[0012] A method for manufacturing an ultraviolet semiconductor light-emitting element according to another embodiment of the present invention is: A method for manufacturing an ultraviolet semiconductor light-emitting element, comprising an AlGaN-based semiconductor in which an n-type semiconductor layer, an active layer, an electron blocking layer, a p-type semiconductor layer, and a p-electrode are sequentially stacked, The p-type semiconductor layer comprises a first composition gradient layer formed on the electron block layer, wherein the Al composition decreases toward the p-electrode, and a second composition gradient layer formed on the first composition gradient layer, wherein the Al composition decreases toward the p-electrode. The interface between the first composition gradient layer and the second composition gradient layer has a heterojunction in which the Al composition is discontinuous. At the interface, the Al composition of the first composition gradient layer is greater than the Al composition of the second composition gradient layer. The growth of the second composition gradient layer is carried out while gradually decreasing the growth temperature, and is terminated when the growth temperature is reduced by 20°C or more. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing the structure of an ultraviolet semiconductor light-emitting element according to one embodiment of the present invention. [Figure 2A] This is a band diagram of an ultraviolet semiconductor light-emitting device. [Figure 2B] This diagram shows the semiconductor layer structure of an ultraviolet semiconductor light-emitting device. [Figure 3A] (A) This is a band diagram schematically showing the structure of the p-type AlGaN layer in Example 1, (B) Comparative Example 1, and (C) Comparative Example 2. [Figure 3B] This figure shows the simulation results of the upper edge of the valence band near the interface with the p electrode for three cases (A) to (C) of the p-type AlGaN layer. [Figure 4] This figure shows the definition of the barrier Vb at the contact between the p-type AlGaN layer and the p-electrode. [Figure 5]This figure plots the relationship between normalized contact resistance and normalized barrier when the p-contact layer is p-GaN, a single-composition gradient layer, and a double-composition gradient layer. [Figure 6A] This is a diagram showing the equivalent circuit of a light-emitting diode. [Figure 6B] This figure schematically shows the heterobarrier between the p-AlGaN layer and the p-GaN contact in the case of (i) a p-GaN contact and (ii) a p-AlGaN contact (Example 1). [Figure 7] This figure shows the IV characteristics for a p-AlGaN contact where the p-AlGaN layer is a double-composition gradient layer (Example 1) and for a p-GaN contact. [Figure 8] This figure shows the profiles of Al composition, growth temperature TG, Mg concentration, and Si concentration during the growth of a p-type AlGaN layer. [Figure 9] This figure shows the relationship between the amount of Mg per unit layer thickness and the barrier Vb in the surface layer of the p-type AlY2Ga1-Y2N layer in contact with the p-electrode. [Figure 10A] This is the band diagram of the p-type AlGaN layer in Modification 1. [Figure 10B] This is the band diagram of the p-type AlGaN layer in Modification 2. [Figure 11A] This is the band diagram of the p-type AlGaN layer in Modification 3. [Figure 11B] This is the band diagram of the p-type AlGaN layer in Modification 4. [Figure 11C] This is the band diagram of the p-type AlGaN layer in Modification 5. [Modes for carrying out the invention]

[0014] Preferred embodiments of the present invention will be described below, but these may be modified and combined as appropriate. In the following description and accompanying drawings, substantially identical or equivalent parts will be denoted by the same reference numerals. [Examples]

[0015] (1) Structure of ultraviolet semiconductor light-emitting element Figure 1 is a schematic cross-sectional view showing the structure of an ultraviolet semiconductor light-emitting element 10, which is Example 1 of one embodiment of the present invention. The ultraviolet semiconductor light-emitting element 10 is an ultraviolet light-emitting diode (ultraviolet LED) and is made of an AlGaN semiconductor.

[0016] More specifically, the ultraviolet semiconductor light-emitting element 10 is formed by sequentially stacking an n-type semiconductor layer, an n-type AlGaN layer 12, an active layer 13, an electron blocking layer (EBL), and a p-type semiconductor layer, a p-type AlGaN layer 15, on a substrate 11 by epitaxial growth.

[0017] The electron blocking layer 14 includes a first electron blocking layer 14A made of an AlGaN layer and a second electron blocking layer 14B made of an AlGaN layer formed on the first electron blocking layer 14A.

[0018] The p-type AlGaN layer 15 consists of a first p-type semiconductor layer, the p-type AlGaN layer 15A, and a second p-type semiconductor layer, the p-type AlGaN layer 15B, formed on the p-type AlGaN layer 15A. The p-type AlGaN layer 15 functions as a p-type contact layer. In the following, "p-type" may be denoted as "p-".

[0019] Furthermore, a p-electrode 21 is formed on the p-type AlGaN layer 15, making ohmic contact with the p-type AlGaN layer 15. In addition, an n-electrode 23 is formed on the n-type AlGaN layer 12, making ohmic contact with the n-type AlGaN layer 12. The n-electrode 23 is formed on the n-type AlGaN layer 12, which is exposed by etching the growth layer from the p-type AlGaN layer 15 side.

[0020] In the following description, the case in which the ultraviolet semiconductor light-emitting element 10 consists of an AlN layer and an AlGaN layer will be explained, but it may also have a layer made of an AlInGaN semiconductor. Fig. 2A and Fig. 2B show the band diagram and the semiconductor layer structure of the ultraviolet semiconductor light-emitting device 10, respectively. Hereinafter, the ultraviolet semiconductor light-emitting device 10 will be described in detail with reference to Fig. 1, Fig. 2A and Fig. 2B.

[0021] The substrate 11 is preferably a substrate with a low dislocation density such that the dislocation density in the active layer is low, but is not particularly limited. The dislocation density in the active layer is 10 9 cm -2 Hereinafter, preferably 10 8 cm -2 Hereinafter, a material that can be lowered is preferable, and an AlN template substrate in which an AlN film is laminated on a sapphire substrate or a single crystal AlN substrate can be used.

[0022] Also, from the viewpoint of reducing the dislocation density in the active layer, it is preferable to use a single crystal AlN substrate as the substrate 11. The dislocation density of the single crystal AlN substrate is preferably 10 8 cm -2 Hereinafter, more preferably 10 6 cm -2 Hereinafter, most preferably 10 4 cm -2 Hereinafter. By using an AlN substrate with a lower dislocation density, 10 6 cm -2 Hereinafter, further 10 4 cm -2 of the AlN substrate, it is possible to prevent a reduction in the light emission efficiency in the active layer due to dislocations, and further, it is possible to prevent problems such as diffusion of impurities through dislocations generated when the ultraviolet light-emitting device is energized and an increase in leakage current.

[0023] In the ultraviolet semiconductor light-emitting device 10 of this embodiment, an AlN substrate having a dislocation density of 10 4 cm -2 was used.

[0024] Furthermore, the surface roughness (RMS) of the single-crystal AlN substrate 11 is preferably 1.0 nm or less, and more preferably 0.5 nm or less, for the same reasons as described above for the AlN template substrate. Naturally, the surface of the AlN substrate may also be polished using known polishing methods such as chemical mechanical polishing.

[0025] Furthermore, if the absorption coefficient of the substrate is large for ultraviolet light emitted from the active layer, there is a concern that the total amount of ultraviolet light that can be extracted to the outside will decrease, leading to a decrease in luminescence efficiency. For this reason, the absorption coefficient of the AlN layer of the AlN substrate and AlN template is preferably 20 cm². -1 The following, and more preferably 10 cm -1 The following: 10cm -1 By doing the following, for example, even if the thickness of the AlN substrate 11 is 100 μm, a linear transmittance of 90% or more can be secured.

[0026] The n-type AlGaN layer 12 is a Si (silicon) doped n-type conductive layer. The Al composition of the n-type AlGaN layer can be appropriately determined to obtain sufficient transmittance for the desired ultraviolet light emission wavelength. In the ultraviolet semiconductor light-emitting element 10, ultraviolet light emitted from the active layer 13 is transmitted through the n-type AlGaN layer 12 and the substrate 11 and emitted to the outside. Furthermore, as the Al composition of the n-type AlGaN layer increases, the band gap of the n-type AlGaN layer increases, and accordingly, it becomes possible to transmit shorter wavelength ultraviolet light.

[0027] Furthermore, the n-type AlGaN layer 12 may be formed from multiple layers with different Al compositions, and it can also be a composition gradient layer in which the Al composition is gradient in the stacking direction. In the ultraviolet semiconductor light-emitting element 10, the n-type AlGaN layer 12 is a first n-type Al X1 Ga 1-X1 N-layer 12A and second n-type Al X2 Ga 1-X2 It consists of N layers 12B. X1 Ga 1-X1The N layer 12A is a composition gradient layer in which the Al composition X1 decreases from 1.0 to 0.75 in the stacking direction, and the second n-type Al X2 Ga 1-X2 The N layer 12B can be a composition gradient layer in which the Al composition X2 decreases from 0.75 to 0.70.

[0028] The thickness of the n-type AlGaN layer 12 is not particularly limited and can be determined as appropriate. When a single-crystal AlN substrate is used for the substrate 11, the thickness of the n-type AlGaN layer 12 is preferably 0.5 μm or more and 2 μm or less. From the viewpoint of lowering the resistance of the n-type AlGaN layer 12, a thicker layer of the n-type AlGaN layer 12 is preferable. However, when an AlN substrate is used for the substrate 11, if the thickness of the n-type AlGaN layer 12 becomes too thick, the n-type AlGaN layer will undergo lattice relaxation and dislocations will be more likely to occur.

[0029] For example, the n-type AlGaN layer 12 is made of the first n-type Al X1 Ga 1-X1 N-layer 12A and second n-type Al X2 Ga 1-X2 When formed as a laminated structure consisting of N layer 12B, the first n-type Al X1 Ga 1-X1 N layer 12A has a layer thickness of 200 nm, and the second n-type Al X2 Ga 1-X2 The N layer 12B can have a thickness of 1000 nm. Furthermore, these first n-type Al X1 Ga 1-X1 N-layer 12A and second n-type Al X2 Ga 1-X2 The thickness of the N layer 12B is not limited to the example figures, and can be appropriately determined so that the total layer thickness is 2.0 μm or less.

[0030] Furthermore, the Si concentration used to dope the n-type AlGaN layer 12 can be appropriately determined to obtain the desired n-type conductivity, but from the viewpoint of lowering the resistance of the n-type AlGaN layer 12, 1 × 10 18 ~1 × 10 20 cm -3 Preferably, it is 5 × 10 18 ~5×1019 cm -3 It is preferable that this is the case. Furthermore, the Si doping concentration may be constant in the thickness direction within the n-type AlGaN layer 12, or it may be modulated doping with different Si concentrations in the thickness direction.

[0031] The Si concentration and the Mg concentration, as described later, can be measured by known Secondary Ion Mass Spectrometry (SIMS) analysis. Furthermore, the Si and Mg concentrations measured in this application are for the AlN layer, AlGaN layer, and GaN layer, respectively, for AlN and AlGaN. 0.65 Ga 0.35 Quantitative values ​​using standard samples of N and GaN are employed.

[0032] The active layer 13 (ACT) is Al A1 Ga 1-A1 A barrier layer consisting of N layers and Al A2 Ga 1-A2 This quantum well structure consists of a quantum well layer made up of N layers. The emission peak wavelength of the active layer 13 is in the range of 210 to 300 nm. The wavelength of light emitted from the active layer 13 is determined by the Al composition and thickness of the well layer, so the Al composition and thickness can be appropriately determined so that a desired emission wavelength is obtained within the above wavelength range. In this embodiment, the emission wavelength of the active layer 13 is 265 nm.

[0033] The lower the Al composition of a p-type AlGaN contact layer, the lower the Schottky barrier, making it easier to achieve ohmic contact. Since this invention provides a method for achieving ohmic contact even in p-type AlGaN layers with high Al composition, it can be an effective means of increasing the power output of ultraviolet semiconductor light-emitting devices having emission wavelengths of 300 nm or less, more preferably 285 nm or less, and more preferably 270 nm or less.

[0034] For example, the layer thickness of the quantum well layer can be set within the range of 2 to 10 nm, and the Al composition (aluminum composition) can be determined such that a desired emission wavelength is obtained. Also, regarding the Al composition and layer thickness of the barrier layer, although not particularly limited, for example, the Al composition can be set within the range of A2 < A1 ≤ 1.0, and the layer thickness can be set within the range of 2 to 15 nm.

[0035] Also, the quantum well layer and the barrier layer can be n-type layers doped with Si. Both the quantum well layer and the barrier layer may be Si-doping layers, or a structure in which only the quantum well layer or only the barrier layer is doped with Si. The Si concentration to be doped is not particularly limited, but is preferably in the range of 1×10 17 ~5×10 18 cm -3 .

[0036] Also, the number of quantum wells is not particularly limited, and a multiple quantum well (MQW: Multi Quantum Well) structure in which a plurality of quantum well layers are formed may be used, or a single quantum well (SQW: Single Quantum Well) may be used. The number of quantum well layers is preferably determined appropriately within the range of 1 to 5.

[0037] The electron blocking layer 14 is an Al X3 Ga 1-X3 N layer provided adjacent to the active layer 13. The electron blocking layer 14 has a function of suppressing the overflow of electrons injected into the active layer 13 into the p-type AlGaN layer 15. Therefore, the electron blocking layer 14 has a larger bandgap than the active layer 13 and the p-type Al Y1 Ga 1-Y1 N layer 15A to be described later, and the Al composition X3 of the electron blocking layer 14 is determined within the range of 0.8 < X3 ≤ 1.0.

[0038] As the emission wavelength is shortened, the Al composition of the AlGaN layer epitaxially grown on the substrate 11 increases. When the emission wavelength is shorter than 270 nm, it is preferable that the Al composition X3 is 0.9 ≤ X3 ≤ 1.0 in order to fully exhibit its function as an electron blocking layer. In the ultraviolet semiconductor light-emitting element 10, AlN (X3=1) is used as the electron blocking layer 14.

[0039] Furthermore, the electron blocking layer 14 may be an undoped layer or may be doped with a p-type dopant, as long as it can perform its function as an electron blocking layer. As the p-type dopant material for the electron blocking layer 14, Mg (magnesium), Zn (zinc), Be (beryllium), C (carbon), etc., can be used. In particular, it is preferable to use Mg, which is commonly used as a p-type dopant material for AlGaN layers, and Mg is also used in the ultraviolet semiconductor light-emitting element 10.

[0040] The p-type dopant material may be uniformly doped in the stacking direction of the electron blocking layer 14, or the concentration of the dopant material can be varied in the stacking direction. In this embodiment, the stacked structure consists of a first electron blocking layer 14A (undoped AlN layer, thickness: 1 nm) and a second electron blocking layer 14B (Mg-doped p-type AlN layer, thickness: 8 nm) from the side in contact with the active layer 13.

[0041] The p-type dopant concentration in the electron block layer 14 is not particularly limited, but in order to obtain the function of an electron block layer, it should be 5 × 10⁻¹⁰. 18 ~1 × 10 20 cm -3 It is preferable that this is the case, and from the viewpoint of improving the efficiency of carrier injection into the active layer, 1 × 10 19 ~8×10 19 cm -3 It is particularly preferable that this be the case.

[0042] The electron blocking layer 14 of the present invention does not contain an n-type dopant, or it contains a p-type Al as described later. Y1 Ga1-Y1 It is possible to include n-type dopants at a concentration lower than that of the n-type dopant contained in the N layer 15A. Specifically, the concentration of n-type impurities in the electron block layer 14 is 1 × 10⁻⁶. 18 cm -3 The following is preferable:

[0043] According to the inventors' findings, p-type Al Y1 Ga 1-Y1 It is known that dopant diffusion occurs between adjacent electron block layers 14 during the growth of the N layer 15A. Therefore, the n-type dopant concentration in the electron block layer 14 is p-type Al Y1 Ga 1-Y1 If it is higher than that of the N layer 15A, then p-type Al from the electron block layer 14 Y1 Ga 1-Y1 n-type dopant diffuses into layer N 15A, p-type Al Y1 Ga 1-Y1 Precise control of the n-type dopant concentration in the N layer 15A can be difficult. This diffusion of p-type Al can be a factor. Y1 Ga 1-Y1 In order to prevent changes in the concentration of the n-type dopant in the N layer 15A, at least the n-type dopant in the electron block layer 14 is p-type Al Y1 Ga 1-Y1 It is preferable that the concentration is less than the concentration of the n-type dopant contained in the N layer 15A.

[0044] Furthermore, the thickness of the electron blocking layer 14 is determined by its function as an electron blocking layer, and the p-type Al Y1 Ga 1-Y1 The thickness should be appropriately determined so that holes are efficiently injected from the N layer 15A into the active layer, but a range of 1 to 30 nm is preferable. If the layer thickness is less than 1 nm, electrons tunnel, reducing its function as an electron blocking layer, while if the layer thickness exceeds 30 nm, p-type Al... Y1 Ga 1-Y1 Holes are less likely to be injected into the active layer from the N layer 15A. Taking these factors into consideration, the thickness of the electron blocking layer 14 is preferably 2 to 20 nm, and more preferably 5 to 15 nm.

[0045] Also, as described above, Mg doped in the electron blocking layer 14 can also have a concentration difference in the stacking direction. For example, a first electron blocking layer 14A, which is an undoped AlN layer, can be stacked with a layer thickness of 1 to 5 nm on the side contacting the active layer 13, and further, a second electron blocking layer 14B, which is a Mg-doped p-type AlN layer, can be stacked with a thickness of 5 to 15 nm. The Mg doping concentration at this time is, as described above, 5×10 18 ~1×10 20 cm -3 is preferably, and 1×10 19 ~8×10 19 cm -3 is particularly preferably.

[0046] In this embodiment, the electron blocking layer 14 is made of an AlN layer, and a p-type AlGaN layer 15 composed of a p-type Al Y1 Ga 1-Y1 N layer 15A and a p-type Al Y2 Ga 1-Y2 N layer 15B is formed.

[0047] The p-type Al Y1 Ga 1-Y1 N layer 15A is a composition gradient layer (first composition gradient layer) in which the Al composition Y1 decreases in the stacking direction and has a layer thickness of 60 nm. Specifically, the Al composition Y1 of the p-type Al Y1 Ga 1-Y1 N layer 15A continuously and linearly decreases from the Al composition 1.0 (starting Al composition Y1B) of the electron blocking layer 14 (AlN layer) to the Al composition Y1E = 0.71 at the end. The composition gradient rate RY1, which is the gradient rate of the Al composition of the p-type Al Y1 Ga 1-Y1 N layer 15A in the stacking direction, is RY = (1.0 - 0.71) / 60 nm = 0.48% / nm.

[0048] Also, the p-type Al Y2 Ga 1-Y2 N layer 15B is a composition gradient layer (second composition gradient layer) in which the Al composition Y2 decreases in the stacking direction and has a layer thickness of 12 nm. Specifically, the p-type Al Y2 Ga 1-Y2The Al composition Y2 of the N layer 15B decreases continuously and linearly from the Al composition Y2B = 0.64 at the start end to the Al composition Y2E = 0.58 at the end end. p-type Al Y2 Ga 1-Y2 The composition gradient RY2 of the N layer 15B is RY2 = (0.64 - 0.58) / 12 nm = 0.50% / nm, and the relationship of the composition gradients is 0 < RY1 < RY2.

[0049] p-type Al Y1 Ga 1-Y1 The N layer 15A and p-type Al Y2 Ga 1-Y2 By using the N layer 15B as a composition gradient layer, a polarization doping effect can be obtained within the p-type AlGaN layer 15, so that a higher hole concentration is more easily obtained. As a result, the injection efficiency of holes into the active layer is increased.

[0050] In addition, p-type Al Y2 Ga 1-Y2 The composition gradient RY2 of the N layer 15B is preferably greater than the composition gradient RY1 of the N layer 15A (RY1 < RY2), but is not limited thereto. Y1 Ga<00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ By making the p-type AlGaN layer 15 a compositionally graded layer, a polarization doping effect can be obtained within the p-type AlGaN layer 15, making it easier to obtain a higher hole concentration, and as a result, the hole injection efficiency into the active layer is increased. For example, when the emission wavelength is 270 nm or less, the p-type Al on the side in contact with the electron blocking layer 14 Y1 Ga 1-Y1 The Al composition Y1 (=Y1B) of the N layer 15A is preferably 0.85 to 1.0, and more preferably 0.89 to 1.0. In this case, the relationship X3 ≥ Y1 is satisfied.

[0053] p-type Al on the opposite side of the p-type AlGaN layer 15 Y2 Ga 1-Y2 The Al composition Y2 (=Y2E) in the surface layer of the N layer 15B (i.e., the side in contact with the p electrode 21) is preferably in the range A2 to 0.85, and more preferably A1 to 0.85, which exceeds the Al composition of the well layer, from the viewpoint of maintaining transparency.

[0054] By adopting such a structure, a high polarization doping effect can be utilized, and the p-contact layer becomes transparent to the emission wavelength, resulting in a p-contact layer with excellent ohmic characteristics, a reduced turn-on voltage, and a highly efficient and high-power ultraviolet semiconductor light-emitting element.

[0055] Furthermore, the thickness of the p-type AlGaN layer 15, that is, p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 The total thickness of the N layer 15B is not particularly limited, but can be appropriately determined within the range of 1 to 150 nm. From the viewpoint of polarization doping efficiency, a thinner layer or a higher gradient is preferable. On the other hand, if the layer thickness is thick, transparency decreases (light absorption loss increases). From this viewpoint and from the viewpoint of practical productivity, the thickness of the p-type AlGaN layer 15 is preferably 2 to 120 nm, and particularly preferably 5 to 100 nm. Y2 Ga 1-Y2The thickness of the N layer 15B is preferably in the range of 1.0 to 20 nm, and more preferably in the range of 3.0 to 15 nm.

[0056] Since the p-type AlGaN layer 15 is grown in a state of pseudo-lattice matching with the AlN substrate 11, it has a low dislocation density equivalent to that of the AlN substrate 11. Specifically, 10 5 cm -2 The following dislocation densities are observed. It is preferable that the relaxation rate of the pseudo-lattice-matched semiconductor layer be within 20%.

[0057] The p-type AlGaN layer 15 functions as a p-type contact layer. In the ultraviolet semiconductor light-emitting element 10 of this embodiment, p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 Layer N15B is co-doped with p-type impurities that act as acceptors and n-type impurities that act as donors.

[0058] Specifically, p-type Al Y1 Ga 1-Y1 In layer N 15A, magnesium (Mg) is doped as a p-type impurity, and the amount of p-type impurity is 2.0 × 10⁻⁶. 19 cm -3 Furthermore, silicon (Si) was doped as an n-type impurity, and the amount of n-type impurity was 3.0 × 10⁻⁶. 18 cm -3 That was the case.

[0059] Also, p-type Al Y2 Ga 1-Y2 In the N layer 15B, Mg is doped as a p-type impurity, and the amount of p-type impurity was 2.0 × 10⁻⁶ at the start of growth. 19 cm -3 Therefore, at the end of the process, with a layer thickness of 3-15 nm, the result is 3.0 × 10⁻⁶. 19 ~2.0×10 20 cm -3 It was increased to that extent. In addition, Si (silicon) was doped as an n-type impurity, and the amount of n-type impurity was p-type Al Y1 Ga 1-Y1 Same as N-layer 15A: 3.0 × 10⁻¹18 cm -3 That was the case.

[0060] The p-type impurities used to dope the p-type AlGaN layer 15 can include Mg, Zn (zinc), Be (beryllium), C (carbon), etc. Among these, it is preferable to use Mg, which is commonly used as a p-type dopant material for AlGaN semiconductors. The n-type impurities can include Si, Ge (germanium), Se (selenium), S (sulfur), O (oxygen), etc. Among these, it is preferable to use Si, which is commonly used as an n-type dopant material.

[0061] Furthermore, the amount of p-type impurities doped into the p-type AlGaN layer 15 is 1 × 10⁻⁶ 17 ~1.2 × 10 20 cm -3 It is preferable that this is the case. Furthermore, as theoretically shown in J.Appl.Phys., Vol.95, No.8, 15 April (2004), it is thought that the amount of nitrogen vacancies, which are considered to be a factor in degradation, increases with the amount of p-type impurities in the p-type AlGaN layer 15. Therefore, the amount of p-type impurities in the p-type AlGaN layer 15 should be 1.2 × 10⁻⁶. 20 cm -3 If this value is exceeded, the amount of nitrogen vacancies formed initially becomes too large, making it difficult to achieve a high power maintenance rate.

[0062] Furthermore, if the p-type impurity concentration in the p-type AlGaN layer 15 decreases, the mobility of minority carriers (electrons) increases, leading to a decrease in output and making it difficult to obtain high luminous efficiency. Therefore, the p-type impurity concentration in the p-type AlGaN layer 15 can be appropriately determined within the above range, taking these trade-offs into consideration. However, to obtain a higher power maintenance rate and higher output, 1 × 10 19 ~5×10 19 cm -3 Preferably, and more preferably, 1 × 10 19 ~4×10 19 cm -3 That is the case.

[0063] In the ultraviolet semiconductor light-emitting element 10 of this embodiment, p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 Each of the N layers 15B is a composition gradient layer in which the Al compositions Y1 and Y2 continuously decrease in the stacking direction, i.e., in the direction away from the interface with the adjacent electron block layer 14 (EBL) (towards the p electrode 21).

[0064] p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 The N layer 15B is preferably a composition gradient layer in which the Al compositions Y1 and Y2 decrease linearly, but is not limited to this, and may also be a composition gradient layer in which the Al composition decreases with a curvilinear profile.

[0065] Furthermore, the p-type and n-type impurities doped into the p-type AlGaN layer 15 may have a constant concentration within the layer, or a concentration difference may be provided in the stacking direction. However, in order to drive at a higher output and lower voltage, p-type Al Y1 Ga 1-Y1 It is preferable that the interface between the N layer 15A and the electron blocking layer 14 is free of or has a low concentration of n-type impurities.

[0066] Furthermore, when AlN is used as the substrate 11, all layers of the n-type AlGaN layer 12, active layer 13, electron blocking layer 14, and p-type AlGaN layer 15 are crystallized in a state of pseudo-lattice matching with the AlN substrate 11, and therefore have a low dislocation density equivalent to that of the AlN substrate 11. Specifically, 10 5 cm -2 The following dislocation densities are observed. It is preferable that the relaxation rate of the pseudo-lattice-matched semiconductor layer be within 20%.

[0067] Although a semiconductor light-emitting element 10 comprising a substrate 11 has been described, the substrate 11 can be removed as needed or optionally provided, depending on the properties of the substrate used. In this case as well, the active layer 13, electron blocking layer 14, and p-type AlGaN layer 15 are pseudo-lattice matched with the n-type AlGaN layer 12, and it is preferable that their relaxation rate is within 20%.

[0068] As an ultraviolet semiconductor light-emitting element 10, a semiconductor light-emitting element with a substrate 11 on the n-type AlGaN layer 12 side has been described, but a support substrate other than the substrate 11 used for epitaxial growth is p-type Al Y2 Ga 1-Y2 It can also be provided on the N layer 15B side. In this case, the material of the support substrate is not particularly limited, and known materials used as support substrate members for light-emitting elements, such as polycrystalline AlN, Si, Al2O3, Cu, and CuW, can be used without restriction.

[0069] Although the case where the ultraviolet semiconductor light-emitting element 10 is a light-emitting diode (LED) has been described, it may also be configured as a semiconductor laser element (LD: Laser Diode).

[0070] (2) Characteristics of the dual-composition gradient structure contact layer Figure 3A is a schematic band diagram showing the configuration of the p-type AlGaN layer 15 in (A) Example 1 (EX1), (B) Comparative Example 1 (CX1), and (C) Comparative Example 2 (CX2). Figure 3B shows the simulation results of the upper edge of the valence band near the interface with the p-electrode for the three cases (A) to (C) of the p-type AlGaN layer 15.

[0071] Figure 4 shows the definition of the barrier (or p-barrier) Vb at the contact between the p-type AlGaN layer 15 and the p-electrode 21. The barrier Vb is defined as the voltage value Vb at the intersection of the tangent to the IV (current-voltage) curve and the V-axis (X-axis). The simulation software used was SiLENSe (Simulator for Light Emitters based on Nitride Semiconductor) (registered trademark). Furthermore, since calculations with metal electrodes were not possible, the p-In value was calculated assuming a barrier Vb = 0.5eV between p-GaN and the metal electrode, as in the case of metal electrodes. 0.55 Ga 0.45 The simulation was performed assuming N was the electrode EL.

[0072] (A) Example 1 (EX1) is a p-type Al layer in which the Al composition Y decreases from 1.0 to 0.80 in the direction of electrode EL. Y1 Ga 1-Y1 N layer 15A and p-type Al, which is a composition gradient layer where the Al composition Y decreases from 0.70 to 0.60. Y2 Ga 1-Y2 It consists of an N layer 15B and p-type Al. Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 The Al composition at the interface of layer N 15B is discontinuous.

[0073] (B) Comparative Example 1 (CX1) is a p-type Al composition gradient layer in which the Al composition Y decreases from 1.0 to 0.80. Y1 Ga 1-Y1 N layer 15A and p-type Al with Al composition Y constant at 0.60 Y2 Ga 1-Y2 It consists of an N layer 15B and p-type Al. Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 The Al composition at the interface of layer N 15B is discontinuous.

[0074] (C) Comparative Example 2 (CX2) is a single composition gradient layer in which the p-type AlGaN layer 15 decreases from 1.0 to 0.60.

[0075] As described above, in (A) Example 1, (B) Comparative Example 1 and (C) Comparative Example 2, the electrode EL(p-In) of the p-type AlGaN layer 15 0.55 Ga0.45 The simulation was performed with the Al composition Y on the side in contact with N fixed at 0.60.

[0076] In Figure 3B, the depletion layer width WD is the thickness at which the energy from the interface with the electrode EL becomes nearly constant. A narrower depletion layer width WD is preferable because it facilitates the tunneling effect and lowers resistance.

[0077] In Example (A) 1 and Comparative Example (B), the p-type AlGaN layer 15 consists of two layers with a compositional gradient, and the depletion layer width WD is narrower than in Comparative Example (C) 2. Furthermore, p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 In Example (A), where both N layers 15B are compositionally graded layers, the depletion layer width WD (=WD(A)) is narrower and more effective than in Comparative Example (B) 1. Furthermore, in Example (A), the depletion layer width WD(A) is much closer to the depletion layer width of GaN than in Comparative Example (B) 1 and Comparative Example (C) 2.

[0078] Figure 5 plots the relationship between normalized contact resistance and normalized barrier when the p-contact layer is p-type GaN, a single-composition gradient layer, and a double-composition gradient layer.

[0079] By using a p-type AlGaN layer with a double-composition gradient as the p-contact layer, we obtained results that closely approximated the electrode characteristics of a p-type GaN contact layer.

[0080] Figure 6A shows the equivalent circuit of a light-emitting diode. As described in the paper by Sher et al. (Non-Patent Literature 1), the heterojunction Jup (unipolar junction) between the p-GaN contact layer and the p-AlGaN layer acts as a parasitic diode and parasitic resistance, increasing the ideal factor of the diode, which is a factor that increases the turn-on voltage of the light-emitting diode.

[0081] Figure 6B schematically shows the heterobarrier (valence band) HB between the p-AlGaN layer and the p-AlGaN contact in the case of (i) p-GaN contact and (ii) p-AlGaN contact (Example 1, EX1). Specifically, in the case of a (i) p-GaN contact where the p-GaN layer is in contact with the p-electrode, the heterobarrier HB between the second p-AlGaN layer and the p-GaN layer is larger than the heterobarrier HB between the first p-AlGaN layer and the second p-AlGaN layer in the case of a (ii) p-AlGaN contact where the p-AlGaN layer is in contact with the p-electrode.

[0082] Figure 7 shows the IV (current-voltage) characteristics for a p-AlGaN contact where the p-type AlGaN layer 15 is a double-composition gradient layer (Example 1, EX1) and for a p-GaN contact. Specifically, it shows the normalized forward current IF for the normalized operating voltage Vop.

[0083] Therefore, in the case of (ii) p-AlGaN contact (Example 1), the ideal factor becomes smaller, and the forward voltage (Vf) can be reduced by the amount of the reduction in turn-on voltage.

[0084] As explained above, by using a p-type AlGaN contact layer which is a double-composition gradient layer, it is possible to provide an ultraviolet semiconductor light-emitting element that has a p-contact layer with excellent ohmic characteristics, a reduced turn-on voltage, and excellent device characteristics such as high efficiency and high output.

[0085] (3) Method for manufacturing ultraviolet semiconductor light-emitting devices The method for manufacturing the ultraviolet semiconductor light-emitting element 10 made of the AlGaN semiconductor layer of this embodiment is described below. The ultraviolet semiconductor light-emitting element 10 of the present invention can be manufactured by the MOCVD method, which has high productivity and is widely used in industry. There are no particular restrictions on the use of known source gases for the Group III (Al, Ga) source gas and Group V (N) source gas.

[0086] Furthermore, known materials can be used without restriction as Mg and Si dopant feedstock gases, such as biscyclopentadienylmagnesium (Cp2Mg), monosilane (SiH4), and tetraethylsilane.

[0087] The above-mentioned raw material gases are supplied onto the substrate 11 together with a carrier gas such as hydrogen (H2) and / or nitrogen (N2) to grow the element layer of the ultraviolet semiconductor light-emitting element 10.

[0088] Furthermore, the growth temperature of the element layers constituting the ultraviolet semiconductor light-emitting element 10 is not limited except as specifically specified, and can be appropriately determined to obtain the desired characteristics of each layer and the characteristics of the ultraviolet semiconductor light-emitting element 10. However, it is preferable to grow them at 1000 to 1200°C, and more preferably at 1000 to 1150°C.

[0089] (3.1) Growth of each semiconductor layer The substrate on which the semiconductor layer of the ultraviolet semiconductor light-emitting element 10 is grown has a dislocation density of 10 4 cm -2 The following AlN substrate was used as substrate 11. Referring again to Figure 2B, the first n-type Al was processed on this substrate 11 using an MOCVD apparatus. X1 Ga 1-X1 N-layer 12A (layer thickness: 200 nm), second n-type Al X2 Ga 1-X2 An N-layer 12B (1000 nm) was grown on the substrate 11 and the first n-type Al X1 Ga 1-X1 An AlGaN buffer layer may be present between the N layers 12A (the Al composition is the first n-type Al X1 Ga 1-X1 Al composition of N-layer 12A or higher, up to 100%.

[0090] First n-type Al X1 Ga 1-X1 N-layer 12A and second n-type Al X2 Ga 1-X2 The N layer 12B is a compositionally graded layer, and the first n-type Al X1 Ga 1-X1In the N layer 12A, the Al composition (X1) decreases from 1.0 to 0.75 from the side in contact with the AlN layer, forming a second n-type Al X2 Ga 1-X2 In layer N12B, the first n-type Al X1 Ga 1-X1 From the side in contact with the N-type AlGaN layer 12A, the Al composition (X2) decreases from 0.75 to 0.70. Also, the Si concentration in the n-type AlGaN layer 12 is 1 × 10⁻⁶. 19 cm -3 It was controlled to achieve that.

[0091] Next, n-type Al 0.59 Ga 0.41 A barrier layer made of N (thickness: 7 nm) and Al 0.5 Ga 0.5 An active layer 13 with a triple quantum well layer structure, consisting of a quantum well layer made of N (4 nm), was grown. The Si concentration of the barrier layer was 1 × 10⁻⁶. 18 cm -3 It was controlled to achieve that.

[0092] Next, an electron blocking layer 14 made of AlN (9 nm) was grown. The first electron blocking layer 14A on the side in contact with the barrier layer of the active layer 13 was made of an undoped AlN layer (1 nm), and the remaining second electron blocking layer 14B was made of 4 × 10⁻¹⁶ 19 cm -3 The p-type AlN layer was made Mg-doped. Note that Si was not doped into the first electron blocking layer 14A and the Mg-doped second electron blocking layer 14B.

[0093] Next, a p-type AlGaN layer 15 was grown. The p-type AlGaN layer 15 is made of p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y1 Ga 1-Y1 p-type Al grown on N layer 15A Y2 Ga 1-Y2 It consists of N layers 15B.

[0094] (3.2) Growth of p-type AlGaN layer Figure 8 shows the profiles of Al composition, growth temperature TG, Mg concentration, and Si concentration during the growth of the p-type AlGaN layer 15. Specifically, p-type AlGaN is co-doped with Mg and Si from the interface with the substrate 11 (AlN). Y1 Ga 1-Y1 N-layer 15A was grown. Next, p-type Al Y2 Ga 1-Y2 Layer N, 15B was grown.

[0095] Growth temperature TG is 1030°C, Mg concentration is 2 × 10 19 cm -3 Growth was carried out at a constant concentration, and in the final growth temperature reduction region Rg of the p-type AlGaN layer 15, the growth temperature TG was gradually reduced from the previous 1030°C to 990°C (reduced growth temperature = 990°C), and the Mg flow rate was increased to increase the Mg concentration. Y2 Ga 1-Y2 The Mg concentration on the surface of layer N15B is 4 × 10 19 cm -3 That was the case.

[0096] Furthermore, the Si concentration remained consistently 3 × 10⁻⁶ from the start to the end of growth. 18 cm -3 That is, p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 N layer 15B was grown as a layer co-doped with Mg and Si.

[0097] Furthermore, the Mg concentration in the layer in which the Mg concentration was increased was 3 × 10⁻⁶. 19 ~2×10 20 cm -3 It is preferable that this is the case. Furthermore, the thickness of the growth temperature reduction region Rg is preferably in the range of 1.0 to 20 nm, and more preferably in the range of 3 to 15 nm.

[0098] Figure 9 shows p-type Al in contact with p-electrode 21. Y2 Ga 1-Y2 The amount of Mg per unit layer thickness (1 nm) in the surface layer of N-layer 15B (cm -3This shows the relationship between the increased amount of Mg (cm³) in the surface layer. -3 This is the value (or average value) obtained by dividing the amount of Mg by the thickness (nm) of the region where the Mg content has been increased.

[0099] In Figure 9, "No Si co-doping" indicates that Si co-doping was not performed only in the surface layer portion (layer thickness 12 nm).

[0100] In the following explanation, the surface layer portion in which the Mg content is increased or which is Si co-doped will be defined as the "surface contact layer SC".

[0101] As shown in Figure 8, in the growth temperature reduction region Rg, the growth temperature TG was gradually reduced to 40°C to complete the growth, and p-type Al Y2 Ga 1-Y2 As shown in Figure 9, by performing Si co-doping in the N layer 15B, good ohmic contact can be achieved even with a relatively low amount of Mg. Y2 Ga 1-Y2 It is effective if n-type impurities are co-doped in at least the surface contact layer SC of the N layer 15B.

[0102] More specifically, the amount of Mg (acceptor amount) in the surface contact layer SC is 8 × 10 18 cm -3 If the density is greater than or equal to / nm, the barrier Vb (V) will be 0.1(V) or less, resulting in good contact performance. Here, the acceptor amount is defined as the amount of Mg per unit layer thickness. The barrier Vb is defined as the voltage value Vb at the intersection of the tangent to the IV curve and the V axis (X axis) (Figure 4).

[0103] This is thought to be because lowering the growth temperature TG suppresses the generation of point defects, reduces the Schottky barrier, and improves the ohmic properties. The preferred temperature range for reducing the growth temperature TG is 20-60°C.

[0104] Also, p-type Al Y2 Ga1-Y2 On the interface side of the p - electrode 21 of the N - layer 15B, p - type Al Y2 Ga 1-Y2 The donor concentration (Si concentration) in the surface layer of 1 nm or more of the N - layer 15B is 1×10 17 ~2×10 20 cm -3 is preferable. In this case, for the p - type Al Y2 Ga 1-Y2 Mg - Si codoping is performed only on the surface contact layer SC (for example, layer thickness 8 nm) of the N - layer 15B, and in other regions, only Mg which is a p - dopant may be doped. The p - type Al Y2 Ga 1-Y2 N - layer 15B having such a Mg - Si codoping profile has the advantages of low contact resistance, realizing good ohmic contact, and low specific resistance (series resistance).

[0105] (4) Modified Example FIG. 10A is a band diagram of the p - type AlGaN layer 15 of Modified Example 1. In the p - type AlGaN layer 15, for the p - type Al Y2 Ga 1-Y2 The composition gradient rate RY2 of the N - layer 15B is larger than the composition gradient rate RY1 of the p - type Al Y1 Ga 1-Y1 N - layer 15A (RY1 < RY2), which is the same as in Example 1 described above.

[0106] Also, the point that the Al composition is discontinuous at the interface between the p - type Al Y1 Ga 1-Y1 N - layer 15A and the p - type Al Y2 Ga 1-Y2 N - layer 15B is the same as in Example 1 described above.

[0107] On the other hand, in the p - type AlGaN layer 15 of Example 1, the case where the p - type Al Y1 Ga 1-Y1 N - layer 15A and the p - type Al<000029​​​​​​​Y2 Ga 1-Y2 Layer N15B is an uncodoped layer. That is, p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 The N-layer 15B is doped with p-type impurities, but not with n-type impurities.

[0108] Figure 10B is the band diagram of the p-type AlGaN layer 15 of Modification 2. In the p-type AlGaN layer 15 of Modification 2, p-type Al Y2 Ga 1-Y2 The compositional gradient RY2 of layer N15B is p-type Al Y1 Ga 1-Y1 This differs from Example 1 described above in that the compositional gradient of layer N 15A is smaller than RY1 (RY1 > RY2 > 0).

[0109] p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga 1-Y2 The other configurations are the same as in Example 1 described above, including the fact that the Al composition is discontinuous at the interface of the N layer 15B.

[0110] Figure 11A is the band diagram of the p-type AlGaN layer 15 of the modified example 3.

[0111] In the p-type AlGaN layer 15 of the modified example 3, p-type Al Y1 Ga 1-Y1 This example differs from Example 1 described above in that the N layer 15A has a superlattice structure (SL).

[0112] In the modified example 3, the Al composition of multiple ultrathin films constituting the superlattice structure is modulated in the stacking direction, the Al composition decreases continuously in the stacking direction, and a composition gradient layer is formed in which the effective Al composition (Y1eff, shown by the dashed line) is sloped.

[0113] Note that p-type Al Y1 Ga 1-Y1 N-layer 15A and p-type Al Y2 Ga1-Y2 It is sufficient that at least one of the N-layer 15B has a superlattice structure.

[0114] Figure 11B is the band diagram of the p-type AlGaN layer 15 of the modified example 4.

[0115] The p-type AlGaN layer 15 in modified example 4 is made of p-type Al Y1 Ga 1-Y1 This differs from Example 1 described above in that the N layer 15A has a constant Al composition Y1. Y2 Ga 1-Y2 The N layer 15B is configured as a composition gradient layer, the same as in Example 1.

[0116] Figure 11C is the band diagram of the p-type AlGaN layer 15 of Modification 5.

[0117] In the p-type AlGaN layer 15 of modified example 5, p-type Al Y1 Ga 1-Y1 N layer 15A is configured as a composition gradient layer, the same as in Example 1, but p-type Al Y2 Ga 1-Y2 This example differs from Example 1 in that the N layer 15B has a constant Al composition Y2.

[0118] The same effects as in Example 1 can be obtained in the above-described modifications 1 to 5.

[0119] As described in detail above, it is possible to provide an ultraviolet semiconductor light-emitting element that has a high polarization doping effect, a p-contact layer with excellent ohmic characteristics, a reduced turn-on voltage, and excellent device characteristics such as high efficiency and high output. [Explanation of symbols]

[0120] 10: Ultraviolet semiconductor light-emitting element 11: Circuit board 12:n-type AlGaN layer 12A: First n-type AlGaN layer 12B: Second n-type AlGaN layer 13:Active layer 14: Electron Block Layer 14A: First electron block layer 14B: Second electron block layer 15:p-type AlGaN layer 15A: p-type AlY1Ga1-Y1N layer 15A:p-type Al Y1 Ga 1-Y1 N layer 15B:p-type Al Y2 Ga 1-Y2 N layer 21:p electrode 23:n electrode RY1,RY2: Composition gradient rate SC: Surface Contact Layer Vb: Barrier WD: Depletion layer width X1,X2,X3:Al composition Y1,Y2:Al composition ΔY: Al composition difference

Claims

1. An ultraviolet semiconductor light-emitting element made of an AlGaN-based semiconductor in which an n-type semiconductor layer, an active layer, an electron blocking layer, a p-type semiconductor layer, and a p-electrode are sequentially stacked, The p-type semiconductor layer comprises a first composition gradient layer formed on the electron block layer, wherein the Al composition decreases toward the p-electrode, and a second composition gradient layer formed on the first composition gradient layer, wherein the Al composition decreases toward the p-electrode. The interface between the first composition gradient layer and the second composition gradient layer has a heterojunction in which the Al composition is discontinuous. At the interface, the Al composition of the first composition gradient layer is greater than the Al composition of the second composition gradient layer. Ultraviolet semiconductor light-emitting device.

2. The ultraviolet semiconductor light-emitting element according to claim 1, wherein the composition gradient ratio RY2 of the second composition gradient layer is greater than the composition gradient ratio RY1 of the first composition gradient layer.

3. The ultraviolet semiconductor light-emitting element according to claim 1, characterized in that the Al composition of the first composition gradient layer and the second composition gradient layer decreases continuously toward the p electrode.

4. The Al composition of the first composition gradient layer in contact with the electron block layer is in the range of 0.8 to 1.0, and the Al composition of the second composition gradient layer in contact with the p electrode is in the range of ~0.85 of the Al composition of the well layer in the active layer. The difference in Al composition at the interface between the first composition gradient layer and the second composition gradient layer is 0.01 or greater. The ultraviolet semiconductor light-emitting element according to claim 1.

5. The ultraviolet semiconductor light-emitting element according to claim 1, wherein the second composition gradient layer has a layer thickness of 1 nm or more and 20 nm or less.

6. The acceptor quantity at the surface layer of the interface where the second composition gradient layer contacts the p electrode is 8 × 10 １８ cm －３ The ultraviolet semiconductor light-emitting element according to claim 1, wherein the element is ≥ / nm.

7. The ultraviolet semiconductor light-emitting element according to claim 1, wherein the first composition gradient layer and the second composition gradient layer are co-doped with p-type impurities and n-type impurities.

8. The donor concentration in the surface layer of 1 nm or more at the interface where the second composition gradient layer contacts the p electrode is 1 × 10 １７ ~2 x 10 ２０ cm －３ The ultraviolet semiconductor light-emitting element according to claim 7.

9. The ultraviolet semiconductor light-emitting element according to claim 1, wherein the active layer, the electron blocking layer, and the p-type semiconductor layer are pseudo-lattice-matched with respect to the n-type semiconductor layer with a relaxation rate of 20% or less.

10. The n-type semiconductor layer, the active layer, the electron blocking layer, and the p-type semiconductor layer are stacked on an AlN substrate. The ultraviolet semiconductor light-emitting element according to claim 1, wherein the n-type semiconductor layer, the active layer, the electron blocking layer, and the p-type semiconductor layer are pseudo-lattice-matched with respect to the AlN substrate with a relaxation rate of 20% or less.

11. The ultraviolet semiconductor light-emitting element according to any one of claims 1 to 10, wherein the emission wavelength of the active layer is in the range of 210 to 300 nm.

12. A method for manufacturing an ultraviolet semiconductor light-emitting element, comprising an AlGaN-based semiconductor in which an n-type semiconductor layer, an active layer, an electron blocking layer, a p-type semiconductor layer, and a p-electrode are sequentially stacked, The p-type semiconductor layer comprises a first composition gradient layer formed on the electron block layer, wherein the Al composition decreases toward the p-electrode, and a second composition gradient layer formed on the first composition gradient layer, wherein the Al composition decreases toward the p-electrode. The interface between the first composition gradient layer and the second composition gradient layer has a heterojunction in which the Al composition is discontinuous. At the interface, the Al composition of the first composition gradient layer is greater than the Al composition of the second composition gradient layer. The growth of the second composition gradient layer is carried out while gradually decreasing the growth temperature, and is terminated when the growth temperature drops by 20°C or more. A method for manufacturing ultraviolet semiconductor light-emitting devices.

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