Ultraviolet semiconductor light-emitting element

Abstract

To provide an ultraviolet semiconductor light-emitting element having both high output characteristics and high reliability (long life).SOLUTION: The light-emitting device includes a substrate 11 made of single crystal AlN, an n-type clad layer 12 which is an n-type AlXGa1-XN layer formed on the substrate, a quantum well active layer formed on the n-type clad layer, an electron blocking layer 14 formed on the quantum well active layer, and a p-type AlGaN layer which is an Al composition gradient layer formed on the electron blocking layer and has a terminal Al composition smaller than a starting Al composition and has a terminal Al composition of more than 0.80 and 0.90 or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an ultraviolet semiconductor light-emitting device, and more particularly to a nitride semiconductor light-emitting device that emits deep ultraviolet light. [Background technology]

[0002] In recent years, research and development has been progressing on semiconductor light-emitting elements that emit light in the deep ultraviolet region as light sources that have the effect of inactivating bacteria and viruses and sterilizing them. Furthermore, semiconductor light-emitting elements that emit deep ultraviolet light have been attracting attention as light sources for resin curing and inspection.

[0003] Conventionally, deep-ultraviolet semiconductor light-emitting devices have been known that employ a composition-graded layer in which the Al composition of the p-type semiconductor layer is graded in order to improve light output. This is because the polarization doping effect increases the amount of holes generated, thereby increasing light output. For example, Patent Document 1 discloses a two-stage composition gradient structure consisting of a first composition gradient layer in which the Al composition of the p-AlGaN layer monotonically decreases from 80% to 40% toward the p-electrode, and a second composition gradient layer in which the Al composition monotonically decreases from 40% to 0%. Furthermore, Patent Document 2 discloses a two-stage composition gradient structure consisting of a first composition gradient layer in which the molar fraction of AlN in the p-AlGaN layer decreases from 90% to 60% in the direction away from the active layer, and a second composition gradient layer in which the molar fraction decreases from 60% to 0%. Patent Document 3 discloses an ultraviolet light-emitting element in which the variation in Al composition (%) in the first composition gradient layer is 20% or more and 50% or less per 1 nm of thickness, and the variation in Al composition (%) in the second composition gradient layer is 9% or more and 20% or less per 1 nm of thickness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7228176 [Patent Document 2] Japanese Patent Publication No. 2023-121445 [Patent Document 3] Patent No. 7405554 Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional technology, when a compositionally graded structure is used for the p-cladding layer, the Al composition at the end is reduced as much as possible. This is because a high Al composition reduces the amount of holes generated, and when using polarization doping, which grades the composition, the greater the gradient of the gradient, i.e., the greater the composition difference, the more holes are theoretically generated. However, in conventional technology, when the Al composition on the p-contact layer side (termination) is low, the hole concentration increases while the energy required to generate nitrogen vacancies decreases, resulting in an increase in the amount of nitrogen vacancies generated. This increases the injection efficiency, improving the initial output, but on the other hand, the amount of nitrogen vacancies increases as the amount of nitrogen vacancies increases, shortening the device's lifespan. Therefore, it has been difficult to achieve high reliability (long lifespan) while maintaining high output characteristics. The present application was made in response to the problem that an increase in the amount of nitrogen vacancies generated leads to deterioration of the element, and aims to provide an ultraviolet semiconductor light-emitting element that combines high output characteristics with high reliability (long life). [Means for solving the problem]

[0006] An ultraviolet semiconductor light emitting device according to one embodiment of the present invention comprises: a substrate made of single-crystal AlN; n-type Al formed on the substrate X Ga 1-X an n-type cladding layer, which is an N layer; a quantum well active layer formed on the n-type cladding layer; an electron blocking layer formed on the quantum well active layer; The p-type AlGaN layer is formed on the electron blocking layer and is an Al composition gradient layer in which the Al composition at the end is smaller than the Al composition at the beginning, and the Al composition at the end is greater than 0.80 and not greater than 0.90. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view schematically showing the structure of an ultraviolet semiconductor light-emitting element according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a band diagram of the ultraviolet light-emitting element of the first embodiment. [Figure 3] 1 is a table showing the configuration of each layer of the ultraviolet light-emitting device. [Figure 4] FIG. 10 is a diagram showing the forward voltage Vf, the initial output, the output maintenance ratio, and the Fermi level for the comparative example and the example. [Figure 5] FIG. 1 is a diagram in which the output maintenance ratios (%) of the comparative example and the example are plotted. [Figure 6] FIG. 1 is a plot of the optical output ratio versus the thickness of the p-type cladding layer. [Figure 7] FIG. 10 is a plot of the degradation rate after 100 hours versus the thickness of the p-type cladding layer. [Figure 8A] FIG. 2 is a diagram schematically showing band diagrams of an active layer, an electron blocking layer, and a p-type cladding layer. [Figure 8B] FIG. 10 is a diagram showing the simulation results of the quasi-Fermi energy dEf versus the layer thickness of the p-type cladding layer. [Figure 9] FIG. 10 is a diagram showing the simulation results of the quasi-Fermi energy dEf versus the layer thickness of the p-type cladding layer. [Figure 10] FIG. 4 is a diagram schematically showing a band diagram of the ultraviolet light-emitting element according to the second embodiment. [Figure 11] FIG. 10 is a diagram showing the relationship between the quantum well layer thickness and the ground levels of electrons and holes. [Figure 12] FIG. 2 is a diagram schematically showing a band diagram of an active layer. [Figure 13] 1A and 1B are diagrams schematically showing wave functions of electrons and holes when the thickness of a quantum well layer is small and large. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the following, preferred embodiments of the present invention will be described, but these may be modified and combined as appropriate. In the following description and accompanying drawings, substantially the same or equivalent parts are designated by the same reference numerals.

[0009] [First embodiment] (1) Structure of ultraviolet semiconductor light-emitting element 1 is a cross-sectional view schematically showing the structure of an ultraviolet semiconductor light-emitting element 10 according to a first embodiment of the present invention. The ultraviolet semiconductor light-emitting element (hereinafter also simply referred to as an ultraviolet light-emitting element) 10 is an ultraviolet light-emitting diode, and can be manufactured by, for example, but not limited to, metal-organic chemical vapor deposition (MOCVD).

[0010] The ultraviolet light-emitting element 10 has an n-type cladding layer 12 (n-type AlGaN layer), an active layer 13, an electron blocking layer 14 (p-type AlN layer), a p-type cladding layer 15 (p-type AlGaN layer), and a p-type contact layer 16 (p-type GaN layer) stacked in this order on a substrate 11 by epitaxial growth.

[0011] 2 is a schematic diagram showing a band diagram of the ultraviolet light-emitting device 10. The ultraviolet light-emitting device 10 will be described in more detail below with reference to FIGS.

[0012] The substrate 11 has a dislocation density of 10 8 cm -2 The AlGaN-based semiconductor material constituting the ultraviolet light-emitting device of the present invention has a dislocation density of 10 to 100 nm, as described in OPTICS EXPRESS Vol. 25 No. 16 A639 (2017). 7 ~10 8 cm -2 It is known that the luminous efficiency drops sharply when the dislocation density exceeds 10. Therefore, the lower the dislocation density of the single crystal AlN substrate, the better. 6 cm -2 More preferably, 10 4 cm -2By using the AlN substrate 11 with such a low dislocation density, the dislocation density in the active layer 13 (described later) can be reduced to 10% without reducing the light emission efficiency. 7 cm -2 The AlN substrate 11 can be an AlN template in which AlN is grown on a substrate such as sapphire.

[0013] The growth plane (surface) of the AlN substrate 11 of the present invention is not particularly limited and can be a C-plane, M-plane, or other growth plane. However, the C-plane is preferred, as it is commonly used as a growth plane for AlGaN-based materials. Furthermore, when the C-plane is used as the crystal growth plane, the AlN substrate 11 is preferably an off-axis substrate that is slightly inclined from the C-plane, for purposes such as improving the smoothness of the AlGaN layer grown on the substrate. The inclination angle from the C-plane is not particularly limited and may be determined as appropriate to obtain a smooth AlGaN layer, but is typically selected in the range of 0.1 to 1.0°. The inclination direction from the C-plane is also not particularly limited and may be selected as appropriate, such as the A-axis or M-axis. However, the M-axis direction is preferred, as it increases the linearity of the step edges.

[0014] Furthermore, since a large surface roughness of the AlN substrate 11 can cause abnormal growth of the AlGaN layer on the substrate, the surface roughness (RSM) is preferably 1.0 nm or less, and more preferably 0.5 nm or less. In order to obtain such a smooth surface or to remove damaged layers formed on the substrate surface during the substrate manufacturing process, the substrate surface is preferably subjected to chemical mechanical polishing (CMP).

[0015] Furthermore, if the absorption coefficient of the substrate for the ultraviolet light emitted from the active layer is large, 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 light emission efficiency. Therefore, the absorption coefficient of the AlN substrate or the AlN layer of the AlN template is preferably 20 cm -1 less than 10cm, and more preferably -1 Less than 10cm -1By setting it as follows, even if the thickness of the AlN substrate 11 is 100 μm, for example, it is possible to ensure an in-line transmittance of 90% or more.

[0016] n-type cladding layer 12 (n-type Al X Ga 1-X The n-type AlGaN layer (N layer) is an n-type conductive layer doped with silicon (Si). In an ultraviolet semiconductor light-emitting device, ultraviolet light emitted from the light-emitting layer is usually emitted to the outside after passing through the n-type cladding layer 12 and the substrate 11. As the Al composition (aluminum composition) of the n-type AlGaN layer increases, the band gap of the n-type AlGaN layer increases, and accordingly, ultraviolet light of shorter wavelengths can be transmitted through the n-type AlGaN layer. Therefore, the Al composition of the n-type AlGaN layer can be appropriately determined so as to obtain sufficient transmittance for the desired ultraviolet light emission wavelength.

[0017] The n-type cladding layer 12 may be formed from a plurality of layers with different Al compositions (X), and may be a compositionally graded layer in which the Al composition is graded in the stacking direction. For example, the first n-type cladding layer 12A (n-type Al X1 Ga 1-X1 N layer) and the second n-type cladding layer 12B (n-type Al X2 Ga 1-X2 N layers).

[0018] The first n-type cladding layer 12A is, for example, a compositionally graded layer in which the Al composition X1 decreases from 1.0 to 0.75 in the stacking direction (growth direction), and the second n-type cladding layer 12B is, for example, a compositionally graded layer in which the Al composition X2 decreases from 0.75 to 0.70. Note that the Al compositions at the interfaces of the first n-type cladding layer 12A and the second n-type cladding layer 12B are preferably equal.

[0019] Furthermore, the thickness of the n-type cladding layer 12 is not particularly limited and may be determined as appropriate. However, if the thickness of the n-type cladding layer 12 is too thick, lattice relaxation occurs between the AlN substrate 11 and the n-type cladding layer 12, making dislocations more likely to occur. Therefore, it is preferable to set the total thickness of the n-type cladding layer 12 in the range of 0.5 to 2.0 μm.

[0020] For example, the n-type cladding layer 12 may be the first n-type cladding layer 12A (n-type Al X1 Ga 1-X1 N layer) and the second n-type cladding layer 12B (n-type Al X2 Ga 1-X2 In the case of a laminated structure consisting of first n-type cladding layer 12A and second n-type cladding layer 12B, a laminated structure in which first n-type cladding layer 12A has a thickness of 200 nm and second n-type cladding layer 12B has a thickness of 1000 nm may be used. Naturally, the thicknesses of first and second n-type cladding layers 12A and 12B are not limited to the exemplified values, and may be appropriately determined so that the total thickness is 2.0 μm or less.

[0021] The Si concentration to be doped into the n-type cladding layer 12 may be determined appropriately so as to obtain the desired n-type conductivity. However, from the viewpoint of reducing the resistance value of the n-type cladding layer 12, it is preferable to set the Si concentration to 1×10 18 ~1×10 20 cm -3 It is preferable that the 18 ~5×10 19 cm -3 It is preferable that:

[0022] The Si doping concentration may be constant in the layer thickness direction in the n-type cladding layer 12, or may be modulated doping in which the Si concentration varies in the layer thickness direction. The Si concentration and the Mg (magnesium) concentration, which will be described later, can be measured by known Secondary Ion Mass Spectrometry (SIMS) analysis. The Si concentration and Mg concentration in this application are measured using AlN, AlGaN, and GaN layers, respectively. 0.65 Ga 0.35 Quantitative values ​​using standard samples of N and GaN are used.

[0023] The active layer 13 (ACT) is Al W1 Ga 1-W1 A plurality of barrier layers 13B each consisting of an N layer and an Al W2 Ga 1-W2It has a multi-quantum well (MQW) structure made up of a plurality of quantum well layers 13A each made up of N layers. Note that the active layer 13 is not limited to a multi-quantum well active layer, and may be a single quantum well (SQW) active layer.

[0024] The emission peak wavelength of active layer 13 is in the range of 200 to 360 nm. The wavelength of light emitted from active layer 13 is determined by the Al composition and thickness of quantum well layer 13A and barrier layer 13B, and therefore the Al composition and thickness of quantum well layer 13A and barrier layer 13B can be appropriately determined so as to obtain a desired emission wavelength within the above wavelength range.

[0025] It is preferable that the emission peak wavelength of the active layer 13 is in the UVC region, which is a short wavelength region of deep ultraviolet, and particularly in the range of 200-280 nm, which has an excellent bactericidal effect.

[0026] The quantum well layer 13A and the barrier layer 13B may be n-type layers doped with Si. The quantum well layer 13A and the barrier layer 13B may be Si-doped layers, or the quantum well layer 13A may be doped with Si, or the barrier layer 13B may be doped with Si. The doping concentration of Si is not particularly limited, but is preferably 1×10 17 ~5×10 18 cm -3 The range is preferred.

[0027] An electron blocking layer (EBL) 14 on the active layer 13 prevents electrons injected into the active layer 13 from passing through a p-type cladding layer (p-type Al Y Ga 1-Y Therefore, the electron blocking layer 14 (AlN layer) 15 has a function of suppressing overflow. Z Ga 1-Z The N layer preferably has a larger band gap than the active layer 13 and the p-type cladding layer 15 .

[0028] As the emission wavelength becomes shorter, the Al composition of the AlGaN layer epitaxially grown on the substrate 11 becomes higher. When the emission wavelength is shorter than 270 nm, the Al composition Z of the electron blocking layer 14 is preferably 0.95≦Z≦1.0 in order to fully exhibit the function as an electron blocking layer. Z Ga 1-Z AlN (Z=1) is used as the N layer.

[0029] 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 function as an electron blocking layer.

[0030] Examples of p-type dopant materials that can be used in the electron blocking layer 14 include magnesium (Mg), zinc (Zn), beryllium (Be), and carbon (C). 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 examples of the present invention described below.

[0031] The p-type dopant material may be doped uniformly in the stacking direction of the electron blocking layer 14, or the concentration of the dopant material may vary in the stacking direction. For example, a stacked structure consisting of an undoped AlN layer (Z=1) and an Mg (magnesium)-doped p-type AlN layer may be used from the side in contact with the active layer. The p-type dopant concentration in the electron blocking layer 14 is set to 1.0×10 from the viewpoint of obtaining the function as an electron blocking layer and increasing the efficiency of carrier injection into the light-emitting layer. 19 ~8.0×10 19 cm -3 is preferably 3.0 × 10 19 ~5.0×10 19 cm -3、 Particularly preferably, 3.0 × 10 19 ~4.0×10 19 cm -3 is.

[0032] The electron blocking layer 14 preferably has a thickness in the range of 4 to 10 nm. If the thickness is less than 4 nm, the effect as an electron blocking layer is reduced due to the tunneling effect, and if the thickness is 10 nm or more, the efficiency of hole injection decreases.

[0033] The p-type cladding layer 15 is formed on the electron blocking layer 14 and is made of p-type Al doped with Mg. Y Ga 1-Y The p-type cladding layer 15 is an N layer and functions as a cladding layer. The aluminum composition (Al composition) Y of the p-type cladding layer 15 is formed as a composition gradient layer in which the aluminum composition Y decreases with increasing distance from the electron blocking layer 14, i.e., toward the p-type contact layer 16.

[0034] Specifically, the Al composition Y of the p-type cladding layer 15 decreases from the Al composition Y1 on the side (starting end) in contact with the electron blocking layer 14 to the Al composition Y2 on the side (ending end) in contact with the p-type contact layer 16 (Y1>Y2). By making the p-type cladding layer 15 a compositionally graded layer, a polarization doping effect can be obtained within the p-type cladding layer 15, making it easier to obtain a higher hole concentration and, as a result, increasing the efficiency of hole injection into the active layer 13. The Al composition Y1 at the interface with the electron blocking layer 14 is preferably equal to or less than the Al composition Z of the electron blocking layer 14. For example, when the emission wavelength is 270 nm or less, the Al composition Y1 on the side in contact with the electron blocking layer 14 is preferably 0.95 to 1.0.

[0035] Furthermore, the Al composition Y2 on the opposite side (termination) in contact with the p-type contact layer 16 is preferably greater than 0.80, more preferably 0.83 or greater, and even more preferably 0.85 or greater. By employing such a structure, it is possible to enhance the polarization doping effect described above, maintain transparency at the emission wavelength, and obtain high luminous efficiency, as well as suppress the generation of nitrogen vacancies in the p-type cladding layer 15, thereby suppressing device degradation. The p-type dopant material can be any of the above-mentioned materials without any restrictions, but it is preferable to use Mg, as in the electron blocking layer 14 .

[0036] From the viewpoints of suppressing carrier overflow and reducing resistance, the thickness of the p-type cladding layer 15 is preferably 40 to 120 nm. In the embodiment of the present invention, a compositionally graded layer is used in which the Al composition Y decreases in the growth direction from the Al composition of the electron blocking layer 14.

[0037] The p-type cladding layer 15 (p-type Al Y Ga 1-Y The p-type cladding layer 15 is co-doped with p-type impurities that act as acceptors and n-type impurities that act as donors. It is preferable that the p-type cladding layer 15 is co-doped, but this is not limitative.

[0038] Examples of p-type impurities that can be used to dope the p-type cladding layer 15 include magnesium (Mg), zinc (Zn), beryllium (Be), and carbon (C). Of these, it is preferable to use Mg, which is commonly used as a p-type dopant material for AlGaN semiconductors. Examples of n-type impurities that can be used include germanium (Ge), selenium (Se), sulfur (S), and oxygen (O). Of these, it is preferable to use Si, which is commonly used as an n-type dopant material.

[0039] In the p-type cladding layer 15 of this embodiment, the ratio (Nd / Na) of the n-type impurity concentration (Nd) to the p-type impurity concentration in the p-type cladding layer 15 satisfies the following formula. 0.009≦(Nd / Na)≦0.80

[0040] The amount of p-type impurities doped into the p-type cladding layer 15 is 1×10 17 ~5.0×10 19 cm -3As theoretically shown in J. Appl. Phys., Vol. 95, No. 8, 15 April (2004), the amount of nitrogen defects, which are considered to be a cause of degradation, is thought to increase with the amount of p-type impurities in the p-type cladding layer 15. Therefore, when the amount of p-type impurities is 1.2 × 10 20 cm -3 If the nitrogen vacancy amount exceeds 100%, the amount of nitrogen vacancies formed in the early stage becomes too large, making it difficult to obtain a high power retention rate.

[0041] Furthermore, when the p-type impurity concentration is low, in the case of a composition gradient layer in which the Al composition Y is gradient, the mobility of minority carriers (electrons) increases, resulting in a decrease in output and making it difficult to obtain high luminous efficiency. Therefore, the p-type impurity concentration can be appropriately determined within the above range, taking into consideration such a trade-off. However, in order to obtain a higher output maintenance rate and high output, the amount of p-type impurity doped into the p-type cladding layer 15 should be 5.0 × 10 18 cm -3 ~5.0×10 19 cm -3 It is preferable that the concentration is 1.0 × 10 19 ~4.0×10 19 cm -3 With these amounts of n-type impurities, an ultraviolet light emitting device 10 with high luminous efficiency can be obtained.

[0042] The concentrations of the p-type impurities and n-type impurities co-doped into the p-type cladding layer 15 may be constant within the layer, or may vary in concentration in the stacking direction. For example, the side in contact with the electron blocking layer 14 may be a co-doped layer, and the remaining p-type cladding layer 15 may be a layer that is not doped with n-type impurities.

[0043] For the purpose of reducing the contact resistance with the electrode, a p-type contact layer 16 (p-type GaN layer) doped with a p-type dopant may be formed on the p-type cladding layer 15. The above-mentioned known p-type dopant materials can be used as the p-type dopant material, but for the same reason, it is preferable to use Mg. The Mg doping concentration in the p-type contact layer 16 is not particularly limited, but in order to reduce the resistance value in the p-type GaN layer and the contact resistance, it is recommended to use a concentration of 1×10 18 ~2×10 20 cm -3 The thickness of the p-type contact layer 16 is not particularly limited either, and may be appropriately determined within the range of 5 to 500 nm. The p-type contact layer 16 is not limited to a p-type GaN layer. For example, a p-type Al layer having a small Al composition and a small In composition may be used. x Ga 1-x-y In y It is also possible to use N layers (0≦x≦0.3, 0≦y≦0.3) or the like.

[0044] All of the AlGaN layers 12, 13, 14, and 15, except for the p-type contact layer 16, are grown in a state of lattice matching with the AlN substrate 11, and therefore have a low dislocation density equivalent to that of the AlN substrate 11. 5 cm -2 The dislocation density is as follows:

[0045] In this specification, the ultraviolet light emitting element 10 of the present invention will be described as a light emitting diode, but it may also be configured as a semiconductor laser element (LD: Laser Diode).

[0046] Next, a method for manufacturing the ultraviolet light-emitting device 10 having the structure described above will be described. The ultraviolet light-emitting device 10 of the present invention can be manufactured by known crystal growth methods such as metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). Among these, the MOCVD method is preferred because it has high productivity and is widely used industrially. The Group III (Al, Ga) source gas and Group V (N) source gas used in the present invention can be any known source gas without any particular restrictions.

[0047] For example, the Group III source gas may be trimethylaluminum, triethylaluminum, trimethylgallium, triethylgallium, etc. The Group V source gas is usually ammonia.

[0048] Furthermore, known materials can be used without any restrictions as dopant source gases for Mg and Si, and examples that can be used include biscyclopentadienyl magnesium, monosilane, and tetraethylsilane.

[0049] The above-mentioned source gases are supplied onto the substrate 11 together with a carrier gas such as hydrogen and / or nitrogen, thereby growing the element layers of the ultraviolet light emitting element 10.

[0050] The supply ratio of the Group III source gas to the Group V source gas (V / III ratio) may be determined appropriately so as to obtain desired characteristics, but is preferably set within the range of 500 to 10,000.

[0051] Furthermore, the growth temperature of the element layers constituting the ultraviolet light-emitting element 10 is not particularly limited and may be determined appropriately so as to obtain the desired characteristics of each layer and the characteristics of the ultraviolet light-emitting element 10, but growth at 1000 to 1200°C is preferable, and 1000 to 1150°C is more preferable.

[0052] (2) Characteristics of ultraviolet semiconductor light-emitting devices (Al composition Y2 at the end of the p-type cladding layer) In the following, the present invention will be specifically explained using an example in which an ultraviolet light emitting element 10 with an emission wavelength of 265 nm was fabricated, but the present invention is not limited to the example. (a) Device structure 3 is a table showing the configuration of each layer of the fabricated ultraviolet light-emitting device 10 of the first embodiment. Samples were fabricated in which the Al composition Y2 of the end of the p-type cladding layer 15, which is a composition-graded layer, was varied. The Al composition of the p-type cladding layer 15 was graded so that it monotonically (linearly) decreased from the side in contact with the electron blocking layer 14 (starting end) to the side in contact with the p-type contact layer 16 (ending end).

[0053] More specifically, sample lots (Comparative Example (CX1), Example EX1, Example EX2, and Example EX3, respectively) were fabricated in which the Al composition Y1 of the p-type cladding layer 15 on the side in contact with the electron blocking layer 14 (starting end) was 0.98 (98%), and the Al composition Y2 on the side in contact with the p-type contact layer 16 (terminating end) was 0.80, 0.83, 0.85, and 0.90 (80%, 83%, 85%, and 90%). In addition, multiple samples were fabricated for each lot of Comparative Example (CX1) and Examples (EX1 to EX3), and the device characteristics were evaluated.

[0054] The configuration of the other semiconductor layers of the ultraviolet light emitting device 10 is as described above. X1 Ga 1-X1 N layer) and the second n-type cladding layer 12B (n-type Al X2 Ga 1-X2 N layer) is a composition gradient layer, and Si is 1.0 × 10 19 cm -3 It is doped at a concentration of

[0055] The active layer 13 is a multiple quantum well (MQW) active layer consisting of three quantum well layers 13A, and the compositions and thicknesses of the quantum well layers 13A and the barrier layers 13B are adjusted so that the emission wavelength is 265 nm. The quantum well layers 13A and the barrier layers 13B have a Si content of 1.0×10 18 cm -3 The doped layer is formed at a concentration of . The electron blocking layer 14 is formed as an AlN layer (thickness: 9 nm), and Mg is 4.0×10 19 cm -3 It is doped at a concentration of

[0056] The p-type cladding layer 15 is formed as a co-doped layer. Specifically, the p-type cladding layer 15 contains 4.0×10 Mg, which is a p-type impurity. 19 cm -3 The n-type impurity Si is doped at a concentration of 3.5 × 10 18 cm -3The p-type cladding layer 15 is doped at a concentration of 60 nm.

[0057] On the p-type cladding layer 15, Mg is 3.0 to 5.0 × 10 19 cm -3 On the other hand, a p-type contact layer 16 (p-type GaN layer, layer thickness: 270 nm) doped at a concentration of 0.1 to 0.5 nm is formed.

[0058] (b) Device characteristics FIG. 4 is a diagram showing the forward voltage Vf (V), initial output (mW), output maintenance rate after 250 hours (%, @50mW equivalent), and Fermi level (calculated value) for the above-mentioned comparative example (CX1) and examples (EX1 to EX3). The output maintenance rate (%) was calculated by performing a life test at a drive current of 440 mA (at room temperature) and measuring the output of the ultraviolet light-emitting element 10 in one lot at the initial stage and after 250 hours. Therefore, the variation in the plot corresponds to the output variation within each lot.

[0059] FIG. 5 is a diagram plotting the output maintenance rate (%) after 250 hours relative to the initial output (mW) for each of the comparative example (CX1) and examples (EX1 to EX3). In the comparative example (CX1) in which the Al composition Y2 at the end of the p-type cladding layer 15 was 0.80, the output maintenance ratio (%) was 85%, but compared to the comparative example (CX1), in the examples (EX1 to EX3) in which the Al composition Y2 exceeded 0.80, the output maintenance ratio (%) was significantly improved to 90% or more. Furthermore, when the Al composition Y2 was 0.85 (EX2), the output maintenance ratio (%) improved to 97%. That is, at 50 mW, an improvement of 15% in the output maintenance ratio was observed. On the other hand, when the Al composition Y2 was 0.90 (EX3), a decrease in the initial output was observed.

[0060] These results demonstrate that the device lifetime can be improved by setting the Al composition Y2 at the termination of the p-type cladding layer 15 to a value exceeding 0.80. The Al composition Y2 at the termination of the p-type cladding layer 15 is preferably greater than 0.80 and equal to or less than 0.90, and more preferably equal to or greater than 0.83 and less than 0.90 (0.83≦Y2<0.90).

[0061] (3) Characteristics of ultraviolet semiconductor light-emitting devices (thickness of p-type cladding layer) Fig. 6 is a plot of the optical output ratio versus the layer thickness (nm) of the p-type cladding layer 15. Fig. 7 is a plot of the degradation rate after 100 hours versus the layer thickness of the p-type cladding layer 15. The graph shows the measurement results for an ultraviolet light-emitting device 10 having a p-type cladding layer 15 with an Al composition Y1 of 0.98 at the starting end and an Al composition Y2 of 0.80 at the end.

[0062] 6, the thinner the p-type cladding layer 15 (composition gradient layer), the more improved the optical output. This is thought to indicate that the hole injection efficiency is increased by the polarization doping effect.

[0063] 7, it was found that reliability (device life) was improved by increasing the thickness of the p-type cladding layer 15. The thickness of the p-type cladding layer 15 is preferably 45 nm or more and 80 nm or less, and more preferably 50 nm or more and 70 nm or less.

[0064] (4) Consideration of p-type cladding layer and device degradation (a) Mechanism of element degradation The external quantum efficiency (EQE) ηext of a semiconductor light emitting device is expressed by the following formula (1) using the internal quantum efficiency ηint, the injection efficiency ηinj, and the light extraction efficiency ηextract. ηext=ηint+ηinj+ηextract (1) Since the light extraction efficiency ηextract can be ignored as a factor in reducing reliability, it is thought that the rate of increase in the non-radiative recombination probability in the internal quantum efficiency ηint and the rate of deterioration in the injection efficiency ηinj determine the trend in reliability due to current flow.

[0065] In other words, the main factors that reduce reliability are thought to be a decrease in the recombination probability due to the diffusion of nitrogen defects in the p-type cladding layer into the active layer (i.e., deterioration of the active layer), and a decrease in the efficiency of hole injection from the p-type cladding layer (i.e., an increase in the amount of nitrogen defects in the p-type cladding layer (a decrease in injection efficiency)). Therefore, it is clear that the p-type cladding layer, which is related to these two factors, has a significant impact on reliability, and in particular, controlling the amount of nitrogen vacancies in the p-type cladding layer is extremely important for improving reliability.

[0066] Nitrogen vacancies, which act as donors, are generated in the p-type cladding layer to maintain electrical neutrality within the crystal. These nitrogen vacancies diffuse into the active layer while current is flowing, resulting in a decrease in the output maintenance rate. Furthermore, ultraviolet semiconductor light-emitting devices have a significantly lower light extraction efficiency than, for example, blue LEDs, so they increase their light output by passing a large current through them. A large current value also means that the semiconductor light-emitting device generates a large amount of heat. Therefore, thermal damage to the light-emitting layer due to heat generation is likely to increase non-radiative recombination centers, i.e., nitrogen defects, which is thought to be the reason for the significant decrease in lifespan.

[0067] (b) Compositional gradient of the p-type cladding layer FIG. 8A is a diagram schematically showing a band diagram of the active layer 13 (ACT in the figure), the electron blocking layer 14 (EB), and the p-type cladding layer 15 (p-CLAD). It has been shown that when the Al composition Y2 at the end of the p-type cladding layer 15 is increased, for example from 0.80 to 0.85, the hole concentration decreases, and the difference (dEf) between the valence band edge of the p-type cladding layer 15 and the quasi-Fermi level Fv increases.

[0068] 8B is a diagram showing the simulation results, with the horizontal axis representing the thickness (nm) of the p-type cladding layer 15 and the vertical axis representing the quasi-Fermi energy dEf (eV) measured from the band edge. Note that the figures show calculated values ​​using the Al composition Y2 of the termination of the p-type cladding layer 15 as a parameter.

[0069] As explained with reference to Figure 5, increasing the Al composition Y2 at the termination of the p-type cladding layer 15 improved the power retention ratio. The generation energy of point defects (nitrogen vacancies) in AlGaN depends on the quasi-Fermi level, and the nitrogen vacancy concentration decreases as the quasi-Fermi energy dEf measured from the band edge increases. That is, increasing the Al composition Y2 increases the generation energy, thereby reducing the amount of nitrogen vacancies generated and, ultimately, the amount of nitrogen vacancies diffusing into the active layer 13.

[0070] As shown in FIG. 8B, compared to the Al composition Y2=0.80 (Comparative Example CX1) indicated by the dashed circle, the theoretical differences (Δ) in quasi-Fermi energy dEf for Y2=0.85 (Example EX2) and Y2=0.90 (Example EX3) are 0.020 eV and 0.078 eV, respectively. It is believed that increasing the Al composition Y2 at the termination reduces the amount of nitrogen vacancies. Therefore, it is believed that the diffusion of nitrogen vacancies into the active layer 13 is suppressed, which suppresses degradation of the ultraviolet light-emitting device 10 and improves reliability. However, if the Al composition Y2 at the termination is too large, the hole concentration decreases, resulting in a decrease in light output.

[0071] (c) Co-doping concentration 9 shows the simulation results of the quasi-Fermi energy dEf (eV) versus the thickness (nm) of the p-type cladding layer 15, and shows calculated values ​​using the co-doped Si concentration as a parameter. Note that the calculated values ​​are fixed at an Al composition Y2 of 0.85 at the end of the p-type cladding layer 15. The dashed line (wo CoSi) indicates the case where no co-doping is performed.

[0072] It can be seen that the quasi-Fermi energy dEf increases by increasing the co-doping concentration Nd. For example, when the co-doping concentration Nd is 3.0 × 10 18 cm-3 to 4.0 x 10 18 cm -3 By increasing the quasi-Fermi energy dEf to Δ=0.048 eV, From the simulation results, the co-doping concentration Nd is 2.0×10 18 cm -3 Over 4.0 x 10 18 cm -3 Preferably, it is 3.0 x 10 or less. 18 cm -3 Over 4.0 x 10 18 cm -3 It is even more preferable that:

[0073] [Second embodiment] (1) Structure of ultraviolet semiconductor light-emitting element The ultraviolet light-emitting device 30 of the second embodiment differs from the ultraviolet light-emitting device 10 of the first embodiment in that the active layer 13 has one main quantum well layer and multiple sub-quantum well layers. The other configurations are the same as those of the ultraviolet light-emitting device 10 of the first embodiment. That is, the configuration of the p-type cladding layer 15, which is a composition-graded layer, is also the same as that of the ultraviolet light-emitting device 10 of the first embodiment.

[0074] 10 is a schematic diagram showing a band diagram of the ultraviolet light emitting device 30 of the second embodiment. The active layer 13 of the ultraviolet light emitting device 30 is Al W1 Ga 1-W1 A plurality of barrier layers 13B each consisting of an N layer and an Al W2 Ga 1-W2 It has a multiple quantum well (MQW) structure consisting of three quantum well layers QS1, QS2, and QM, each consisting of N layers.

[0075] The active layer 13 has one main quantum well layer QM and two sub-quantum well layers QS1 and QS2, with the sub-quantum well layers QS1 and QS2 and the main quantum well layer QM being provided in this order from the substrate 11 side.

[0076] Further, the active layer 13 includes a first barrier layer 13B1 (layer thickness: TB1) provided on the n-type cladding layer 12, a second barrier layer 13B2 (layer thickness: TB2) provided between the first sub quantum well layer QS1 and the second sub quantum well layer QS2, a third barrier layer 13B3 (layer thickness: TB3) provided between the second sub quantum well layer QS2 and the main quantum well layer QM, and a final barrier layer 13L (layer thickness: TL) provided between the main quantum well layer QM and the electron blocking layer 14.

[0077] The first sub quantum well layer QS1 and the second sub quantum well layer QS2 have the same crystal composition and layer thickness TS. Also, the first sub quantum well layer QS1, the second sub quantum well layer QS2, and the main quantum well layer QM have the same crystal composition (Al composition: W2). Here, in this specification, "the same" in terms of crystal composition and layer thickness includes substantial identity and refers to the degree of identity obtained in the crystal growth of the semiconductor layer.

[0078] Further, the barrier layers 13B, that is, the first barrier layer 13B1, the second barrier layer 13B2, the third barrier layer 13B3, and the final barrier layer 13L have the same crystal composition (Al composition: W1). When not particularly distinguishing each of these multiple barrier layers, they will be collectively referred to as the barrier layer 13B for description.

[0079] It is preferable that the layer thickness of the barrier layer between the sub quantum well layers (in the above case, TB2) is the same as the layer thickness of the barrier layer between the sub quantum well layer closest to the main quantum well layer QM (in the above case, TB3).

[0080] The main quantum well layer QM is the quantum well layer closest to the electron blocking layer 14. Also, the two sub quantum well layers QS1 and QS2 have the same layer thickness TS, and the main quantum well layer QM has a larger layer thickness TM (TS < TM) than the sub quantum well layers QS1 and QS2.

[0081] Although the example shows the case where two sub-quantum well layers are provided, it is sufficient to provide at least one sub-quantum well layer QS1, QS2, ..., QSn (n is an integer of 1 or more). When multiple sub-quantum well layers are provided, the multiple sub-quantum well layers have the same crystal composition and layer thickness. When multiple sub-quantum well layers are not particularly distinguished from one another, they will be collectively referred to as sub-quantum well layer QS.

[0082] The emission peak wavelength of the active layer 13 is in the range of 200 to 360 nm. The wavelength of the light emitted from the active layer 13 is determined by the Al composition and layer thickness of the main quantum well layer QM, and therefore the Al composition and layer thickness can be appropriately determined so as to obtain a desired emission wavelength within the above wavelength range.

[0083] It is preferable that the emission peak wavelength of the active layer 13 is in the UVC region, which is a short wavelength region of deep ultraviolet, and particularly in the range of 200-280 nm, which has an excellent bactericidal effect.

[0084] The main quantum well layer QM, the sub-quantum well layers QS1 and QS2, and the barrier layer 13B may be n-type layers doped with Si. The main quantum well layer QM, the sub-quantum well layers QS1 and QS2, and the barrier layer 13B may be Si-doped layers, or either the main quantum well layer QM or the sub-quantum well layers QS1 and QS2 may be doped with Si, or only the barrier layer 13B may be doped with Si. The doping Si concentration is not particularly limited, but may be 1×10 17 ~5×10 18 cm -3 The range is preferred.

[0085] The final barrier layer 13L may contain a p-type dopant such as Mg. The Mg contained in the final barrier layer 13L may be obtained by diffusion doping from the electron blocking layer 14, which will be described later, or may be obtained by intentionally doping with Mg.

[0086] (2) Consideration of device characteristics (a) Improved external differential efficiency (EQE) and light output First, in ultraviolet semiconductor light-emitting devices, the hole concentration in the p-type semiconductor layer is generally low, and the mobility of holes is lower than that of electrons, resulting in low external quantum efficiency and light output.

[0087] In the ultraviolet light-emitting device 30 of this embodiment, the efficiency of hole injection from the p-type cladding layer 15 to the active layer 13 via the electron blocking layer 14 is increased. That is, because the thickness of the main quantum well layer QM closest to the electron blocking layer 14 is increased, the efficiency of hole carrier capture by the main quantum well layer QM from the electron blocking layer 14 increases, and the number of carriers contributing to light emission increases, resulting in an increased recombination probability and an increased external differential efficiency (EQE) and optical output.

[0088] 11 shows a schematic diagram of the relationship between the quantum well layer thickness Lz and the ground levels of electrons and holes. As shown in the figure, increasing the quantum well layer thickness Lz brings the ground levels of electrons and holes (quantum levels En1 and Eh1) closer to the band edges of the quantum well, i.e., the conduction band Ec and the valence band Ev, respectively, making radiative recombination easier and increasing the light output.

[0089] (b) The light emission from the main quantum well layer QM is dominant. 12 is a schematic diagram of the band diagram of the active layer 13. The reason why light emission from the main quantum well layer QM is dominant in the ultraviolet light emitting device 30 of this embodiment will be described below.

[0090] 12, since the mobility of holes is lower than that of electrons, it is thought that the main quantum well layer QM closest to the electron blocking layer 14 captures most of the holes and confines them within the main quantum well layer QM. Therefore, it is thought that light emission from the main quantum well layer QM becomes dominant.

[0091] In fact, when the EL (electroluminescence) spectrum of a device in which the thickness TM of the main quantum well layer QM is twice the thickness TS of the sub-quantum well layers QS1 and QS2 was examined, the wavelength shift amount compared to a comparative device having the same structure except for the fact that it consists of three quantum well layers with the same thickness as the sub-quantum well layer QS matched the wavelength shift amount obtained as a result of simulation for the increase in the thickness of the main quantum well layer QM relative to the sub-quantum well layer QS.

[0092] Furthermore, the EL spectrum showed no increase in the full width at half maximum (FWHM), and in fact the FWHM was reduced compared to the comparative device. Therefore, it is presumed that the light emission from the sub-quantum well layers QS1 and QS2 is very small. The reason for the reduced full width at half maximum compared to the comparative device is thought to be that the thicker main quantum well layer QM has a lower rate of change in the ground state relative to thickness fluctuations.

[0093] (c) Function of the sub-quantum well layer The following describes the function of the sub-quantum well layer QS provided in the active layer 13. Referring again to Fig. 12, when the thickness TB3 of the third barrier layer 13B3 between the main quantum well layer QM and the sub-quantum well layer QS2 adjacent to the main quantum well layer QM is small (for example, several nm), electrons confined in the sub-quantum well layer QS2 tunnel due to the tunnel effect and are injected into the main quantum well layer QM, which has a low ground level.

[0094] It is believed that electron tunneling can confine and inject carriers into the thick main quantum well layer QM, and that electron tunneling can reduce electron overflow, further increasing the probability of radiative recombination and increasing output power.

[0095] On the other hand, in the valence band, the hole concentration is low and the hole mobility is small, so most of the holes are captured in the main quantum well layer QM. Therefore, the sub-quantum well layer QS has the function of enhancing the carrier confinement in the main quantum well layer QM.

[0096] The thickness TB3 of the third barrier layer 13B3 is preferably 10 nm or less, more preferably 7 nm or less, and even more preferably 6 nm or less, from the viewpoint of electron tunneling.

[0097] (d) Thickness of the main quantum well layer FIG. 13 is a diagram schematically showing the wave functions of electrons and holes when the quantum well layer thickness Lz is small (left side of the diagram) and large (right side of the diagram).

[0098] The difference in crystal composition between the quantum well layer and the barrier layer causes lattice distortion between the quantum well layer and the barrier layer, generating a piezoelectric field. As a result, the wave functions of electrons and holes in the quantum well layer are misaligned, reducing their overlap, which reduces the probability of radiative transitions and reduces the luminous efficiency. Increasing the quantum well layer thickness Lz reduces the overlap of the wave functions, resulting in a decrease in luminous efficiency.

[0099] Furthermore, when an AlGaN layer is stacked on an AlN substrate, the difference in lattice constant causes it to be pulled by the underlying layer, resulting in compressive strain. As the AlGaN layer is made thicker, lattice relaxation occurs when it reaches a critical thickness, causing threading dislocations in the AlGaN layer, reducing the internal quantum efficiency and light-emitting efficiency.

[0100] Using band gap modeling software for semiconductor devices ("SiLENSe"), simulations were performed by varying the thickness of the sub-quantum well layers QS1, QS2 and the main quantum well layer QM based on the composition and layer thickness of the AlGaN stack.

[0101] According to this simulation, it was found that the internal quantum efficiency increases with increasing quantum well layer thickness, and that a thickness of 1.2 times or more the thickness of the sub-quantum well layer QS2 is effective. Furthermore, in order to fully and effectively exert the above-mentioned electron tunneling effect from the sub-quantum well layer QS2 to the main quantum well layer QM and the electron confinement effect, the thickness TM of the main quantum well layer QM is more preferably 1.5 times or more the thickness TS of the sub-quantum well layer QS (sub-quantum well layer QS2) adjacent to the main quantum well layer QM, and even more preferably 2 times or more.

[0102] On the other hand, the thickness TM of the main quantum well layer QM is preferably 16 nm or less, which is the critical thickness when an AlGaN layer is stacked on an AlN substrate, and more preferably 10 nm or less, which is the range in which the electron-hole overlap integral is significant based on a simulation.

[0103] (e) Thickness of the final barrier layer The inventors of the present application have conducted research and experiments on the diffusion of p-type impurities (Mg) from the p-type cladding layer 15 into the active layer 13. 18 cm -3 If the concentration is greater than this, that is, if a large number of nitrogen defects are present in the main quantum well layer QM, the device life will be reduced.

[0104] As a result of extensive research, it has been found that the Mg concentration entering the main quantum well layer QM from the p-type cladding layer 15 through the electron blocking layer 14 is 1×10 18 cm -3 It was also found that when the layer thickness TL of the final barrier layer 13L is 12 nm or more, the Mg concentration in the main quantum well layer QM can be suppressed to 1×10 17 cm -3 It was found that this could be reduced to the following:

[0105] On the other hand, increasing the layer thickness TL of the final barrier layer 13L may result in a decrease in light output. This is because the hole injection efficiency decreases as the layer thickness TL of the final barrier layer 13L increases. However, no significant decrease in light output was observed when the layer thickness TL was 30 nm or less. Note that a layer thickness TL of 27 nm or less is more preferable, and a layer thickness of 21 nm or less is even more preferable.

[0106] (3) Consideration of device life As described above, nitrogen vacancies diffuse from the p-type cladding layer to the active layer, reducing the probability of non-radiative recombination in the quantum well layer and thereby impairing reliability. However, in the ultraviolet light-emitting device 30 of this embodiment, the thickness of the main quantum well layer, which is primarily responsible for light emission, is thick, reducing the injected carrier density per volume, thereby suppressing the proliferation of nitrogen vacancies in the quantum well. This makes it possible to provide an ultraviolet light-emitting device that is less susceptible to device degradation and has an excellent device life.

[0107] Furthermore, an increase in non-radiative recombination centers due to heat generation in the active layer, that is, an increase in nitrogen vacancies, can be suppressed. Therefore, it is possible to provide an ultraviolet light emitting device that is capable of suppressing deterioration of the element and has an excellent element life.

[0108] As described above in detail, according to the present invention, it is possible to provide an ultraviolet semiconductor light-emitting element that can suppress element degradation and achieves both high output characteristics and high reliability (long life).

[0109] The present invention is not limited to the contents of the above-described embodiments, and can be modified and applied within the scope of the present disclosure. For example, in the above embodiment, the Al composition gradient of the p-type cladding layer (AlGaN layer) has been described, but the present disclosure can be applied to a p-type semiconductor layer that increases the hole generation concentration by the polarization doping effect. Although the p-type cladding layer has been described as a compositionally graded layer in which the Al composition monotonically decreases from the beginning to the end, the p-type cladding layer may include a layer in which the Al composition is constant or increases in part. For example, a compositionally graded layer in which the Al composition decreases stepwise may be employed. [Explanation of symbols]

[0110] 10: Ultraviolet light emitting element 11: Circuit board 12: n-type cladding layer 13:Active layer 13A: Quantum well layer 13B: Barrier layer 13L: Final barrier layer 14: Electron blocking layer 15: p-type cladding layer 16: p-type contact layer QM: Primary quantum well layer QS1, QS2: Sub-quantum well layers

Claims

1. a substrate made of single crystal AlN; n-type Al formed on the substrate Ｘ Ga １－Ｘ an n-type cladding layer, which is an N layer; a quantum well active layer formed on the n-type cladding layer; an electron blocking layer formed on the quantum well active layer; a p-type AlGaN layer formed on the electron blocking layer, the p-type AlGaN layer having an Al composition gradient layer in which the Al composition at the end is smaller than the Al composition at the beginning, the Al composition at the end being greater than 0.80 and not greater than 0.90; An ultraviolet semiconductor light-emitting element comprising:

2. 2. The ultraviolet semiconductor light-emitting element according to claim 1, wherein the thickness of the p-type AlGaN layer formed on the electron blocking layer is 45 nm or more and 80 nm or less.

3. 2. The ultraviolet semiconductor light-emitting element according to claim 1, wherein the thickness of the p-type AlGaN layer formed on the electron blocking layer is 50 nm or more and 70 nm or less.

4. The p-type AlGaN layer formed on the electron blocking layer is co-doped with n-type impurities, and the concentration of the n-type impurities is 2.0×10 １８ cm －３ Above 4.0 x 10 １８ cm －３ 2. The ultraviolet semiconductor light-emitting device according to claim 1, wherein:

5. The p-type impurity concentration of the p-type AlGaN layer is 5.0×10 １８ cm －３ ~5.0 x 10 １９ cm －３ 5. The ultraviolet semiconductor light-emitting element according to claim 4, wherein the wavelength of said ultraviolet semiconductor light-emitting element is within the range of 1000 nm to 1500 nm.

6. 6. The ultraviolet semiconductor light-emitting element according to claim 5, wherein a ratio (Nd / Na) of the concentration of the n-type impurity (Nd) to the concentration of the p-type impurity (Na) in the p-type AlGaN layer satisfies 0.009≦(Nd / Na)≦0.

80.

7. 2. The ultraviolet semiconductor light emitting device according to claim 1, wherein the Al composition of the termination of the p-type AlGaN layer formed on the electron blocking layer is 0.83 or more and less than 0.

90.

8. 2. The ultraviolet semiconductor light-emitting element according to claim 1, wherein the p-type AlGaN layer formed on the electron blocking layer has an Al composition that monotonically decreases with increasing distance from the electron blocking layer.

9. 2. The ultraviolet semiconductor light emitting device according to claim 1, further comprising a p-type contact layer formed on the p-type AlGaN layer formed on the electron blocking layer.

10. the quantum well active layer includes barrier layers having the same crystal composition as each other, at least one sub-quantum well layer separated from each other by the barrier layers, and a main quantum well layer which is the quantum well layer closest to the electron blocking layer; the at least one sub-quantum well layer has the same crystal composition and layer thickness; the at least one sub-quantum well layer and the main quantum well layer have the same crystal composition, and the main quantum well layer has a thickness that is 1.2 times or more that of the at least one sub-quantum well layer. The ultraviolet semiconductor light-emitting element according to claim 1 .

11. 11. The ultraviolet semiconductor light emitting device according to claim 10, wherein the thickness of the main quantum well layer is 16 nm or less.

12. 11. The ultraviolet semiconductor light emitting device according to claim 10, wherein the main quantum well layer has a thickness at least 1.5 times that of the sub-quantum well layer.

13. 11. The ultraviolet semiconductor light emitting device according to claim 10, wherein the thickness of the barrier layer between the main quantum well layer and the sub-quantum well layer adjacent to the main quantum well layer is 7 nm or less.

14. 11. The ultraviolet semiconductor light-emitting device according to claim 10, wherein the final barrier layer between the main quantum well layer and the electron blocking layer has a thickness in the range of 9 to 27 nm.

Images