Ultraviolet semiconductor light-emitting element and method for manufacturing the same

Abstract

To provide an ultraviolet semiconductor light-emitting element with a high efficiency, a high output, less deterioration, and an excellent element life, and a method for manufacturing the same.SOLUTION: A p-type GaN contact layer 16 has a first p-type GaN layer 16A that is grown on a p-type AlGaN layer 15, and a second p-type GaN layer 16B that is grown on the first p-type GaN layer. The first p-type GaN layer and the second p-type GaN layer are grown using magnesium (Mg) as a p-dopant. The growth of the first p-type GaN layer is performed using hydrogen ((H2) and nitrogen (N2) as a carrier gas, the N2 proportion in the carrier gas being 50% or more. The growth of the second p-type GaN layer is performed using a carrier gas in which the hydrogen (H2) proportion is 100%. The first p-type GaN layer is grown under such conditions that the ratio of Mg material / Ga material is not less than 5 times the ratio of Mg material / Ga material in the growth of the second p-type GaN layer.SELECTED DRAWING: Figure 2A

Description

Technical Field

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

Background Art

[0002] In recent years, AlGaN-based semiconductor light-emitting devices having a deep ultraviolet region as an emission wavelength band have attracted attention as light sources having an inactivating action and a bactericidal effect on bacteria and viruses. However, in AlGaN-based ultraviolet light-emitting devices, further reduction of contact resistance and driving voltage is important for increasing the output power and extending the life of the light-emitting device.

[0003] Conventionally, studies have been made on group III nitride semiconductor light-emitting devices having a reduced contact resistance of the p-electrode and a low driving voltage. For example, Patent Document 1 discloses a method of gradually increasing the Mg concentration of the p-GaN contact layer from the cladding layer side toward the surface side. This is to improve the crystallinity of the initial growth of the p-GaN layer and reduce the contact resistance with the electrode metal.

[0004] Further, Patent Document 2 discloses that a first p-type GaN layer and a second p-type GaN layer on the first p-type GaN layer are formed by supplying at least nitrogen gas as a carrier gas, and no p-type dopant gas is supplied when forming the first p-type GaN layer.

[0005] Generally, after the growth of the p-GaN contact layer, in order to enhance the activation of Mg as a dopant, activation is performed at a high temperature (for example, 600 to 800 ° C) in a nitrogen (N2) gas atmosphere (for example, Patent Document 1).

[0006] Further, in an AlN-based semiconductor light-emitting device, it is disclosed that the layer thickness of the p-type semiconductor layer cannot be increased (for example, 100 nm or less) in order to maintain a good contact state with the electrode and suppress an increase in driving voltage and electrical defects (for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] AlN and GaN that constitute an ultraviolet light-emitting element are known to have a very large bandgap and a high forward voltage. In addition, lattice relaxation occurs during the growth of GaN on an AlN-based semiconductor layer, resulting in the generation of threading dislocations. The more threading dislocations there are, the more carriers are trapped by the defects, and the proportion that does not contribute to light emission such as thermal energy increases, leading to poor conductivity and an increase in the forward voltage. Further, due to the activation for activation, alloy spikes are likely to occur during electrode formation, and there is a problem that element degradation progresses easily.

[0009] Therefore, in conventional ultraviolet semiconductor light-emitting elements, it has been difficult to realize an element with high efficiency, high output, and high reliability. In particular, the shorter the emission wavelength, the more problems there are, such as the element degradation progressing early when driven with a large current to obtain a high light output. That is, it has been difficult to achieve both high output characteristics and high reliability (long life).

[0010] The present invention has been made in view of the above problems, and an object thereof is to provide an ultraviolet semiconductor light-emitting element having high efficiency, high output, small degradation, and excellent element life, and a method for manufacturing the same.

Means for Solving the Problems

[0011] The manufacturing method according to one embodiment of the present invention is, A method for manufacturing an ultraviolet semiconductor light-emitting device by sequentially growing an n-type AlGaN layer, an active layer, a p-type AlGaN layer, and a p-type GaN contact layer on an AlN substrate by MOCVD method, The p-type GaN contact layer has a first p-type GaN layer grown on the p-type AlGaN layer and a second p-type GaN layer grown on the first p-type GaN layer, The first p-type GaN layer and the second p-type GaN layer are grown using magnesium (Mg) as a p-dopant, The growth of the first p-type GaN layer is performed using hydrogen (H2) and nitrogen (N2) as carrier gases, and the N2 ratio in the carrier gas is 50% or more, The growth of the second p-type GaN layer is performed using hydrogen (H2) 100% as the carrier gas, The first p-type GaN layer is grown under conditions such that the Mg raw material / Ga raw material ratio is 5 times or more the Mg raw material / Ga raw material ratio in the growth of the second p-type GaN layer, which is characterized.

[0012] An ultraviolet semiconductor light-emitting device according to another embodiment of the present invention is, An ultraviolet semiconductor light-emitting device in which an n-type AlGaN layer, an active layer, a p-type AlGaN layer, and a p-type GaN contact layer are sequentially grown on an AlN substrate, The p-type GaN contact layer has a layer thickness of 200 nm or more, It has a p electrode formed on the as-grown p-type GaN contact layer, which is characterized.

Brief Description of Drawings

[0013]

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Mode for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments of the present invention will be described, but these may be appropriately modified and combined. In the following description and the accompanying drawings, substantially the same or equivalent parts will be described with the same reference numerals. [Structure of Ultraviolet Semiconductor Light-Emitting Element] FIG. 1 is a cross-sectional view schematically showing the structure of an ultraviolet semiconductor light-emitting element 10 according to one embodiment of the present invention. The ultraviolet semiconductor light-emitting element 10 is an ultraviolet light-emitting diode (hereinafter, also referred to as ultraviolet LED 10), and an n-type AlGaN layer 12, an active layer 13, an AlGaN layer 14, a p-type AlGaN layer 15, and a p-type contact layer 16 which is a p-type GaN layer are sequentially epitaxially grown and laminated on a substrate 11.

[0015] Further, a p electrode 21 having an ohmic contact with the p-type contact layer 16 is formed on the p-type contact layer 16, and an n electrode 23 having an ohmic contact with the substrate 11 is formed on the substrate 11. FIGS. 2A and 2B show the band diagram and the semiconductor layer structure of the semiconductor layer of the ultraviolet LED 10, respectively. The ultraviolet LED 10 will be described in more detail with reference to FIGS. 1, 2A, and 2B.

[0016] The substrate 11 is preferably a substrate having 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 preferably reduced to 10 9 cm -2 or less, preferably 10 8 cm -2 or less. Materials that can reduce the dislocation density in the active layer are preferred, and an AlN template substrate or a single-crystalline AlN substrate in which an AlN film is laminated on a sapphire substrate can be used.

[0017] Further, from the viewpoint of reducing the dislocation density in the active layer, it is more preferable to use a single-crystalline AlN substrate as the substrate 11. The dislocation density of the single-crystalline AlN substrate is preferably 10 8 cm -2 or less, more preferably 10 6 cm -2 or less, and most preferably 10 4 cm-2 is as follows. Lower dislocation density, 10 6 cm -2 or less, and further 10 4 cm -2 By using an 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 element is energized and an increase in leakage current.

[0018] Also, for the same reason as the above-described AlN template substrate, 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. Naturally, also in the AlN substrate, the surface may be polished by a known polishing method such as chemical mechanical polishing.

[0019] Also, 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 decreases, leading to a decrease in light emission efficiency. Therefore, the absorption coefficients of the AlN substrate and the AlN layer of the AlN template are preferably 20 cm -1 or less, and more preferably 10 cm -1 or less. By making it 10 cm -1 or less, for example, even if the thickness of the AlN substrate 11 is 100 μm, a linear transmittance of 90% or more can be ensured.

[0020] The n-type AlGaN layer 12 is an n-type conductive layer doped with Si (silicon). The Al composition of the n-type AlGaN layer can be appropriately determined so that sufficient transmittance is obtained for the desired emission wavelength of ultraviolet light. In the ultraviolet LED 10, the ultraviolet light emitted from the active layer 13 passes through the n-type AlGaN layer 12 and the substrate 11 and is emitted to the outside. Also, as the Al composition of the n-type AlGaN layer increases, the bandgap of the n-type AlGaN layer increases, and accordingly, it becomes possible to transmit ultraviolet light with a shorter wavelength.

[0021] Further, the n-type AlGaN layer 12 may be formed of a plurality of layers having different Al compositions, and may further be a compositionally graded layer in which the Al composition is graded in the stacking direction. For example, the n-type AlGaN layer 12 may include a first n-type Al X1 Ga 1-X1 N layer 12A and a second n-type Al X2 Ga 1-X2 N layer 12B. The first n-type Al X1 Ga 1-X1 N layer 12A is a compositionally graded 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 N layer 12B can be a compositionally graded layer in which the Al composition X2 decreases from 0.75 to 0.70.

[0022] Also, the layer thickness of the n-type AlGaN layer 12 is not particularly limited and is appropriately determined. When a single-crystalline AlN substrate is used for the substrate 11, the layer thickness of the n-type AlGaN layer 12 is preferably 0.5 μm or more and 2 μm or less. From the viewpoint of reducing the resistance value of the n-type AlGaN layer, a thicker layer thickness of the n-type AlGaN layer is preferable. However, when an AlN substrate is used for the substrate 11, if the layer thickness of the n-type AlGaN layer becomes too thick, the n-type AlGaN layer is likely to undergo lattice relaxation and dislocations are likely to occur.

[0023] For example, when the n-type AlGaN layer 12 is formed in a stacked structure including the above-described first n-type Al X1 Ga 1-X1 N layer 12A and the second n-type Al X2 Ga 1-X2 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 N layer 12B can have a layer thickness of 1000 nm. Further, the layer thicknesses of the first n-type Al X1 Ga 1-X1 N layer 12A and the second n-type Al X2 Ga 1-X2 N layer 12B are not limited to the illustrated numbers, and can be appropriately determined so that the total layer thickness is 2.0 μm or less.

[0024] On the other hand, when using an AlN template substrate, the layer thickness of the n-type AlGaN layer 12 is preferably 1.5 μm or more and 10 μm or less. As the layer thickness of the n-type AlGaN layer 12 increases, in addition to reducing the resistance value, an effect of reducing dislocations can also be expected. Therefore, it is considered preferable that the layer thickness is 1.5 μm or more. Also, considering industrial aspects such as manufacturing time, the upper limit of the layer thickness of the n-type AlGaN layer 12 when using an AlN template substrate is preferably about 10.0 μm.

[0025] In addition, the Si concentration for doping the n-type AlGaN layer 12 may be appropriately determined so as to obtain a desired n-type conductivity. From the viewpoint of reducing the resistance value of the n-type AlGaN layer 12, it is preferably 1×10 18 ~1×10 20 cm -3 and more preferably 5×10 18 ~5×10 19 cm -3 The Si doping concentration may be constant in the layer thickness direction within the n-type AlGaN layer, or modulation doping with different Si concentrations in the layer thickness direction can also be performed.

[0026] Note that the Si concentration and the Mg concentration described later can be measured by known Secondary Ion Mass Spectrometry (SIMS) analysis. Also, the measured values of the Si concentration and the Mg concentration in the present application adopt the quantitative values using standard samples of AlN, Al 0.65 Ga 0.35 N, and GaN for the AlN layer, the AlGaN layer, and the GaN layer, respectively.

[0027] The active layer (ACT) 13 is composed of a barrier layer made of an Al A1 Ga 1-A1 N layer and an Al A2 Ga 1-A2It is a quantum well structure composed of a well layer consisting of N layers. The emission peak wavelength of the active layer 13 is within the range of 210 to 300 nm. Since the wavelength of the light emitted from the active layer 13 is determined by the Al composition and layer thickness of the well layer, the Al composition and layer thickness can be appropriately determined so as to obtain a desired emission wavelength within the above wavelength range. The reliability of the ultraviolet light-emitting device has a wavelength dependence, and generally, the shorter the emission wavelength, the shorter the device life. Therefore, in the present invention, it is considered that the shorter the emission wavelength, the more effective it is, and the preferable wavelength range is considered to be 210 to 270 nm, and more preferably.

[0028] For example, the layer thickness of the well layer can be set in the range of 2 to 10 nm, and the Al composition can be determined so as to obtain a desired emission wavelength. Also, regarding the Al composition and layer thickness of the barrier layer, although not particularly limited, for example, the Al composition can be set such that A2 < A1 ≤ 1.0, and the layer thickness can be set within the range of 2 to 15 nm.

[0029] Also, the well layer and the barrier layer can be n-type layers doped with Si. Both the well layer and the barrier layer may be Si-doped layers, or a structure in which only the well layer or only the barrier layer is doped with Si may be used. 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 range.

[0030] Also, the number of quantum wells is not particularly limited, and it may be a multiple quantum well (MQW: Multi Quantum Well) structure in which a plurality of well layers are formed, or a single quantum well (SQW: Single Quantum Well). The number of well layers is preferably appropriately determined within the range of 1 to 5.

[0031] Al Y1 Ga 1-Y1 The Al Y1 Ga 1-Y1 N layer 14 is a layer provided adjacent to the active layer 13. The AlY2 Ga 1-Y2 functions as an electron blocking layer (EBL) to suppress overflow into the GaN layer 15. Therefore, Al Y1 Ga 1-Y1 The GaN layer 14 has the active layer 13 and a p-type Al Y2 Ga 1-Y2 GaN layer 15 with a larger bandgap. The Al composition Y1 of the Al Y1 Ga 1-Y1 GaN layer 14 is determined in the range of 0.8 < Y1 ≤ 1.0.

[0032] As the emission wavelength shortens, the Al composition of the AlGaN layer epitaxially grown on the substrate 11 increases. When the emission wavelength is shorter than 270 nm, in order to fully exhibit the function as an electron blocking layer, it is preferable that 0.9 ≤ Y1 ≤ 1.0. In this embodiment, Al Y1 Ga 1-Y1 N (Y1 = 1) is used as the GaN layer 14.

[0033] Also, as long as the Al Y1 Ga 1-Y1 GaN layer 14 can exhibit the function as an electron blocking layer, it may be an undoped layer or may be doped with a p-type dopant. As the p-type dopant material in the Al Y1 Ga 1-Y1 GaN layer 14, Mg (magnesium), Zn (zinc), Be (beryllium), C (carbon), etc. can be used. In particular, it is preferable to use Mg which is generally used as the p-type dopant material for the AlGaN layer, and Mg is also used in the examples of the present invention described later.

[0034] The p-type dopant material is Al Y1 Ga 1-Y1In the stacking direction of the N layer 14, it may be uniformly doped, or the concentration of the dopant material can be changed in the stacking direction. In the present embodiment, from the side in contact with the active layer 13, it has a stacked structure composed of an undoped AlN layer 14A (layer thickness: 1 nm) and a p-type AlN layer 14B (layer thickness: 8 nm) doped with Mg (magnesium).

[0035] Al Y1 Ga 1-Y1 The p-type dopant concentration in the N layer 14 is not particularly limited, but in order to obtain the function as an electron blocking layer, it is preferably 5×10 18 ~1×10 20 cm -3 It is particularly preferably 1×10 19 ~8×10 19 cm -3 from the viewpoint of enhancing the carrier injection efficiency into the active layer.

[0036] The Al Y1 Ga 1-Y1 N layer 14 of the present invention may not contain an n-type dopant or may contain an n-type dopant at a concentration lower than that of the n-type dopant contained in the p-type Al Y2 Ga 1-Y2 N layer 15 described later. Specifically, the n-type impurity concentration in the Al Y1 Ga 1-Y1 N layer 14 is preferably 1×10 18 cm -3 or less. According to the findings of the present inventors, it is known that during the growth of the p-type Al Y2 Ga 1-Y2 N layer 15, diffusion of the dopant occurs between the adjacent Al Y1 Ga 1-Y1 N layer 14. Therefore, when the n-type dopant concentration in the Al Y1 Ga 1-Y1 N layer 14 is higher than that of the p-type Al Y2 Ga 1-Y2 N layer 15, from the Al Y1 Ga 1-Y1 N layer 14 into the p-type Al Y2 Ga 1-Y2An n-type dopant diffuses into the N layer 15, and p-type Al Y2 Ga 1-Y2 Precise control of the n-type dopant concentration in the N layer 15 may become difficult. Due to this diffusion, p-type Al Y2 Ga 1-Y2 In order to prevent the change in the concentration of the n-type dopant in the N layer 15, at least the n-type dopant in the Al Y1 Ga 1-Y1 N layer 14 should be less than the concentration of the n-type dopant contained in the p-type Al Y2 Ga 1-Y2 N layer 15.

[0037] Also, Al Y1 Ga 1-Y1 The layer thickness of the N layer 14 can be appropriately determined so that it can function as an electron blocking layer and holes can be efficiently injected from the p-type Al Y2 Ga 1-Y2 N layer 15 into the active layer. However, a range of 1 to 30 nm is preferable. If the layer thickness is less than 1 nm, electrons will tunnel, resulting in a decrease in the function as an electron blocking layer. On the other hand, if the layer thickness exceeds 30 nm, it will be difficult for holes to be injected from the p-type Al Y2 Ga 1-Y2 N layer 15 into the active layer. Considering these factors, the layer thickness of the Al Y1 Ga 1-Y1 N layer 14 is preferably 2 to 20 nm, and more preferably 5 to 15 nm.

[0038] Also, as described above, Mg doped in the Al Y1 Ga 1-Y1 N layer 14 can also have a concentration difference in the stacking direction. For example, an undoped AlN layer 14A with a layer thickness of 1 to 5 nm can be stacked on the side in contact with the active layer 13, and then a Mg-doped p-type AlN layer 14B with a thickness of 5 to 15 nm can be stacked. At this time, the Mg doping concentration is preferably 5×10 18 ~1×10 20 cm -3 as described above, and particularly preferably 1×10 19 ~8×10 19 cm -3 .

[0039] The p-type Al Y2 Ga 1-Y2 N layer 15 is formed on the Al Y1 Ga 1-Y1 N layer 14 and functions as a p-type cladding layer. In the p-type Al Y2 Ga 1-Y2 N layer 15, a p-type impurity serving as an acceptor and an n-type impurity serving as a donor are codoped.

[0040] For the p-type impurity doped into the p-type Al Y2 Ga 1-Y2 N layer 15, Mg (magnesium), Zn (zinc), Be (beryllium), C (carbon), etc. can be used. Among them, it is preferable to use Mg which is generally used as a p-type dopant material for AlGaN semiconductors. Also, for the n-type impurity, Si, Ge (germanium), Se (selenium), S (sulfur), O (oxygen), etc. can be used. Among them, it is preferable to use Si which is generally used as an n-type dopant material.

[0041] Also, the amount of the p-type impurity doped into the p-type Al Y2 Ga 1-Y2 N layer 15 is preferably 1×10 17 ~1.2×10 20 cm -3 . Also, as theoretically shown in J. Applmaru Physmaru, Volmaru 95, No. 8, 15 April (2004), it is considered that the amount of nitrogen defects considered to be a factor of degradation also increases with the amount of p-type impurities in the p-type Al Y2 Ga 1-Y2 N layer 15. Therefore, when the amount of p-type impurities exceeds 1.2×10 20 cm -3 , the amount of nitrogen defects formed initially becomes too large and it becomes difficult to obtain a high output maintenance rate.

[0042] Also, when the p-type impurity concentration decreases, especially when the Al composition Y2 is constant, due to the decrease in hole concentration and the increase in minority carrier (electron) mobility, or when the Al composition Y2 is sloped, due to the increase in minority carrier (electron) mobility, the output decreases and it becomes difficult to obtain high luminous efficiency. Therefore, the p-type impurity concentration can be appropriately determined within the above range in consideration of such a trade-off. However, in order to obtain a higher output maintenance rate and higher output, it is 1×10 19 ~5×10 19 cm -3 is preferable, and more preferably, 1×10 19 ~4×10 19 cm -3 is.

[0043] In the ultraviolet LED 10 of the present embodiment, the p-type Al Y2 Ga 1-Y2 N layer 15 is a composition gradient layer in which the Al composition Y2 decreases linearly as it moves away from the interface with the adjacent Al Y1 Ga 1-Y1 N layer 14 in the stacking direction.

[0044] The Al composition Y2 is preferably a composition gradient layer in which it decreases linearly as it moves away from the interface with the Al Y1 Ga 1-Y1 N layer 14, but is not limited thereto, and may be a composition gradient layer in which the Al composition decreases curvilinearly. Alternatively, the Al composition may decrease stepwise, or these may be combined.

[0045] The amount of n-type impurity doped into the p-type Al Y2 Ga 1-Y2 N layer 15 is preferably 1.1×10 18 or more and 9.0×10 18 cm -3 or less, and more preferably, 1.8×10 18 or more and 8.0×10 18 cm -3 or less. With these amounts of n-type impurities, a light-emitting element 10 with high luminous efficiency can be obtained.

[0046] Also, for the p-type impurity and n-type impurity doped into the p-type Al Y2 Ga 1-Y2 N layer 15, their concentrations may be constant within the layer or a concentration difference may be provided in the stacking direction. However, in order to drive at a higher output and a lower voltage, the p-type Al Y2 Ga 1-Y2 It is preferable that both interface portions of the N layer 15 have no n-type impurity added or have a low concentration.

[0047] p-type Al Y2 Ga 1-Y2 By suppressing the depletion of the interface portion by partially limited n-type impurity doping into the p-type Al Y1 Ga 1-Y1 N layer 15, the increase in voltage is suppressed. And since it also contributes to the reduction of the mobility of minority carriers (electrons), a higher output can be obtained compared to the case without n-type impurity doping. Therefore, when a higher power conversion efficiency (WPE: wall plug efficiency) is desired compared to the case without n-type impurity doping, at least Al Y2 Ga 1-Y2 The n-type impurity concentration in the vicinity of the interface between the N layer 14 and the p-type Al Y2 Ga 1-Y2 N layer 15 is preferably low. Because the p-type Al Y1 Ga 1-Y1 N layer 15 is a composition gradient layer, the depletion layer width formed at the interface with the Al

[0048] p-type Al Y2 Ga 1-Y2 The Al composition Y2 of the N layer 15 is 0.5 or more and 1.0 or less, and is equal to or less than the Al composition Y1 of the Al Y1 Ga 1-Y1 N layer 14.

[0049] p-type Al Y2 Ga 1-Y2 When the Al composition Y2 of the p-type Al Y1 Ga 1-Y1 N layer 15 has a structure where Y2 is a constant value in the stacking direction, it exceeds the Al composition of the barrier layer of the active layer and is AlIt is preferable that the Al composition Y1 of the N layer 14 is 1 or less. p-type Al Y2 Ga 1-Y2 By setting the Al composition Y2 of the N layer 15 within the above range, even when the injection current amount of the ultraviolet light emitting device is large, a high carrier overflow suppression effect can be obtained. In order to obtain a higher effect, the Al composition of the well layer of the active layer and the p-type Al Y2 Ga 1-Y2 It is preferable that the difference in the Al composition Y2 of the N layer 15 is 0 or more, and more preferably the difference in the Al composition between the barrier layer and the p-type Al Y2 Ga 1-Y2 It is preferable that the difference in the Al composition Y2 of the N layer 15 is 0 or more. Also, p-type Al Y2 Ga 1-Y2 The Al composition Y2 of the N layer 15 is preferably larger than the Al composition of the n-type AlGaN layer 12, whereby the suppression effect of carrier overflow to the p-type layer is enhanced, and the light emission efficiency of the ultraviolet light emitting device can be increased. From the above, p-type Al Y2 Ga 1-Y2 When the N layer 15 has a structure in which Y2 is a constant value in the stacking direction, the Al composition Y2 is preferably 0.6 or more and 0.9 or less.

[0050] Also, p-type Al Y2 Ga 1-Y2 The N layer 15 may be a composition gradient layer in which the Al composition Y2 changes in the stacking direction. In particular, Al Y1 Ga 1-Y1 It is preferable that the structure is such that the Al composition Y2 decreases in the stacking direction from the side in contact with the N layer 14. Thereby, p-type Al Y2 Ga 1-Y2 Since a polarization doping effect can be obtained within the N layer 15, a higher hole concentration can be easily obtained, 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 Al composition on the side in contact with the N layer 14 is preferably 0.85 to 1.0, and more preferably 0.9 to 1.0. At this time, the relationship Y1≧Y2 is satisfied. On the opposite side, p-type Al Y1 Ga 1-Y1 The Al composition on the side in contact with the N layer 14 is preferably 0.85 to 1.0, and more preferably 0.9 to 1.0. At this time, the relationship Y1≧Y2 is satisfied. On the opposite side, p-type Al Y2 Ga 1-Y2The Al composition in the surface layer of the N layer 15 (i.e., the side in contact with the p-type contact layer 16 (p-type GaN layer)) is preferably 0.5 to 0.85, more preferably 0.6 to 0.85. By adopting such a structure, the above-described polarization doping effect can be enhanced and transparency can be maintained with respect to the emission wavelength, so that high luminous efficiency can be easily obtained.

[0051] Also, p-type Al Y2 Ga 1-Y2 The layer thickness of the p-type Al Y2 Ga 1-Y2 N layer 15 is not particularly limited, but may be appropriately determined within the range of 10 to 150 nm. When the layer thickness of the p-type Al Y2 Ga 1-Y2 N layer 15 is less than 10 nm, it becomes difficult to obtain the above-described carrier overflow suppression effect. On the other hand, when the layer thickness becomes thick and exceeds 150 nm, the resistance value of the p-type Al Y2 Ga 1-Y2 N layer 15 increases, resulting in an increase in the operating voltage of the ultraviolet light-emitting element. From such a viewpoint, the layer thickness of the p-type Al

[0052] p-type Al Y2 Ga 1-Y2 On the N layer 15, a p-type contact layer 16 made of a p-type GaN layer doped with a p-type dopant is formed for the purpose of reducing the contact resistance with the electrode. As the p-type dopant material, the above-described known p-type dopant materials can be used, but for the same reason, it is preferable to use Mg.

[0053] As shown in FIGS. 1 and 2, the p-type contact layer 16 (p-type GaN layer) is formed by growing a first p-type GaN layer 16A, a second p-type GaN layer 16B, and a third p-type GaN layer 16C in this order.

[0054] When using AlN as the substrate 11, except for the p-type GaN layer 16, all layers of the AlGaN layers 12, 13, 14, and 15 are crystal-grown in a state of lattice bonding with the AlN substrate 11, so they have a low dislocation density equivalent to that of the AlN substrate 11. Specifically, it has a dislocation density of 10 5 cm -2 or less.

[0055] Although the case where the ultraviolet semiconductor light-emitting element 10 is a light-emitting diode (LED) has been described above, it may be configured as a semiconductor laser element (LD: Laser Diode).

[0056] Although the semiconductor light-emitting element having the substrate 11 as the ultraviolet LED 10 has been described, the substrate 11 can be removed or optionally provided as necessary in view of the properties of the substrate to be used.

[0057] Although the semiconductor light-emitting element having the substrate 11 on the n-type AlGaN layer 12 side as the ultraviolet LED 10 has been described, a support substrate different from the substrate 11 used for epitaxial growth can also be provided on the p-type GaN layer 16 side. In this case, the material of the support substrate and the like are not particularly limited, and known materials such as polycrystalline AlN, Si, Al2O3Cu, and CuW that are used as support substrate members of the light-emitting element can be used without limitation.

[0058] Hereinafter, the semiconductor light-emitting element having the substrate 11 as the growth substrate of the semiconductor laminate structure as the ultraviolet LED 10 will be described. However, as described above, it can also be a semiconductor light-emitting element having a substrate 11 different from the growth substrate such as a support substrate.

[0059] [Manufacturing method of ultraviolet LED] The manufacturing method of the ultraviolet LED 10 having the structure described above will be described. The ultraviolet LED 10 of the present invention can be manufactured by the MOCVD method, which has high productivity and is widely adopted industrially. As the group III (Al, Ga) source gas and group V (N) source gas to be used, known source gases can be used without particular limitation.

[0060] For example, as the Group III source gas, gases such as trimethylaluminum (TMA), triethylaluminum (TEA), trimethylgallium (TMG), and triethylgallium (TEG) can be used. As the Group V source gas, ammonia (NH3) is usually used.

[0061] In addition, as the dopant source gas for Mg and Si, known materials can be used without limitation. For example, biscyclopentadienylmagnesium (Cp2Mg), monosilane (SiH4), tetraethylsilane, etc. can be used.

[0062] By supplying the above source gases onto the substrate 11 together with a carrier gas such as hydrogen (H2) and / or nitrogen (N2), the element layer of the ultraviolet LED 10 is grown.

[0063] The supply amount ratio of the Group III source gas to the Group V source gas (V / III ratio) may be appropriately determined so as to obtain desired characteristics, but it is preferably set within the range of 500 to 10,000.

[0064] Also, regarding the growth temperature of the element layer constituting the ultraviolet LED 10, there is no particular limitation, and it may be appropriately determined so as to obtain the desired characteristics of each layer and the characteristics of the ultraviolet LED 10. However, it is preferably grown at 1000 to 1200 °C, more preferably 1000 to 1150 °C.

[0065] [Examples] Hereinafter, the present invention will be specifically described using an example of manufacturing an ultraviolet LED having an emission wavelength of 265 nm, but the present invention is not limited to the examples. [Fabrication of the Device] For the substrate on which the ultraviolet LED element layer is grown, the dislocation density is 10 4 cm -2The following AlN substrate was used. Referring again to FIG. 2B, on this AlN substrate 11, a first n-type AlGaN layer 12A (layer thickness: 200 nm, first n-clad layer) and a second n-type AlGaN layer 12B (1000 nm, second n-clad layer) were grown by an MOCVD apparatus. Both the first n-type AlGaN layer 12A and the second n-type AlGaN layer 12B are compositionally graded layers. In the first n-type AlGaN layer 12A, the Al composition decreases from 1.0 to 0.75 from the side in contact with the AlN layer. In the second n-type AlGaN layer 12B, the Al composition decreases from 0.75 to 0.70 from the side in contact with the first n-type AlGaN layer 12A. Also, the Si concentration in the n-type AlGaN layer 12 was controlled to be 1×10 19 cm -3 .

[0066] Next, a 3-quantum well layer structure active layer 13 consisting of a barrier layer made of n-type Al 0.59 Ga 0.41 N (7 nm) and a well layer made of Al 0.5 Ga 0.5 N (4 nm) was grown. The Si concentration in the barrier layer was controlled to be 1×10 18 cm -3 .

[0067] Next, an electron blocking layer 14 made of AlN (9 nm) was grown. The electron blocking layer on the side in contact with the barrier layer of the active layer 13 was an undoped AlN layer 14A (1 nm), and the remaining electron blocking layer was a p-type AlN layer 14B with Mg doping of 4×10 19 cm -3 . Note that the undoped AlN layer 14A and the Mg-doped p-type AlN layer 14B are not doped with Si.

[0068] Next, a p-type AlGaN layer 15 (p-clad layer) was grown. The p-type AlGaN layer 15 is a compositionally graded layer in which the Al composition decreases from 0.98 to 0.6 from the side in contact with the p-type AlN layer 14B which is an electron blocking layer. Also, the layer thickness of the p-type AlGaN layer 15 was 60 nm.

[0069] Next, a p-type contact layer 16 (p-type GaN layer) was grown on the p-type AlGaN layer 15. The p-type contact layer 16 will be described in detail below.

[0070] [Growth of p-type contact layer (p-type GaN layer)] The p-type contact layer 16 (p-type GaN layer) is formed by sequentially growing a first p-type GaN layer 16A, a second p-type GaN layer 16B, and a third p-type GaN layer 16C on the p-type AlGaN layer 15. The growth mechanism and growth conditions of each of the first to third p-type GaN layers 16A to 16C will be described in detail below.

[0071] In the ultraviolet LED 10 of the present embodiment, based on the knowledge obtained regarding the growth mechanism and crystallinity of p-type GaN, the carrier gas and Mg flow rate of each of the first to third p-type GaN layers 16A to 16C were examined.

[0072] In this specification, a power of 10 may sometimes be represented using E. For example, 2.0×10 19 may be expressed as 2.0E19 or 2.0E+19.

[0073] 1. Growth conditions of the first to third p-type GaN layers 1-1 Growth conditions of the first p-type GaN layer In the growth of the first p-type GaN layer 16A, the following growth conditions (i) to (iii) were found to be suitable. (i) The Mg concentration is 2.0E+19 or more. (ii) The Mg raw material / Ga raw material ratio (hereinafter also simply referred to as the Mg / Ga ratio), that is, the ratio of the Cp2Mg flow rate / TMG flow rate, is set to 5 times or more that of the second p-type GaN layer 16B. (iii) Hydrogen (H2) and nitrogen (N2) are used as carrier gases, and the N2 ratio in the carrier gas is 50% or more. Note that the N2 ratio is preferably 60 to 80%. 1-2 Growth conditions of the second p-type GaN layer (iv) The growth of the second p-type GaN layer 16B is carried out with the carrier gas being 100% hydrogen (H2). That is, the carrier gas does not contain nitrogen (N2) or the like. 1-3 Growth conditions of the third p-type GaN layer (v) In the growth of the third p-type GaN layer 16C, hydrogen (H2) and nitrogen (N2) are used as the carrier gas, and the ratio of N2 in the carrier gas is set to 50% or more. Note that the ratio of N2 is preferably 60 - 80%.

[0074] 2. Examination of the growth mechanism of the first to third p-type GaN layers The growth mechanism of each of these first to third p-type GaN layers 16A - 16C and the growth conditions derived from the examination results will be described in detail below.

[0075] Figure 3 summarizes the evaluation results of samples (comparative example: CX1, examples: EX1 - EX3) formed by changing the Mg flow rate (cc / min) of each of the first to third p-type GaN layers 16A - 16C. Specifically, it shows the fluorescence microscope images of the growth surface, the root mean square roughness RMS, the hillock number and the coreless number, as well as the p-barrier Vb, contact resistance and resistivity of the grown layer measured using the Transmission line method (TLM method).

[0076] 2-1 The first p-type GaN layer First, in the initial stage of p-GaN growth on the p-type clad layer (p-type Al Y2 Ga 1-Y2 GaN layer 15) which is an AlGaN layer, by increasing the flow rate of the Mg source, nuclei starting from Mg in addition to normal GaN nuclei are generated on the AlGaN surface to increase the surface density of the nuclei, and by increasing N2 in the carrier gas to prevent the re-evaporation of GaN, it is effective for obtaining a uniform GaN layer to grow GaN over the entire AlGaN surface.

[0077] Figure 3 shows the cases where the Mg flow rate of the first p-type GaN layer 16A is 200 cc (CX1), 300 cc (EX1), 400 cc (EX2), and 600 cc (EX3). These Mg concentrations are 1.4E+19 cm -3 (CX1), 2.0E+19 cm -3 (EX1), 2.7E+19 cm -3 (EX2), 4.0E+19 cm -3 and are estimated to be (EX3).

[0078] When the Mg flow rate is 200 cc (CX1, Mg concentration 1.4E+19 cm -3 ), hillocks (surrounded by broken lines in the figure) were observed in the fluorescence microscope image. On the other hand, when the Mg flow rate is 300 cc or more, that is, when the Mg concentration is 2.0E+19 cm -3 or more, it was found that the number of hillocks and the number of coreless decreased.

[0079] Also, in the measurement by the TLM method, the Schottky barrier component was small as seen in the p-barrier Vb which is an index (or non-linearity) of the Schottky barrier component, and good ohmic characteristics were obtained. Also, the contact resistance and specific resistance were small, and the lateral conductivity characteristics were good.

[0080] The p-barrier Vb (V) shown in Figure 3 is defined as the voltage value at the intersection of the tangent of the I-V (current-voltage) curve and the V-axis (X-axis), as schematically shown in Figure 4. The height of the Schottky barrier is the energy difference between the Fermi level and the lower end of the valence electrons at the semiconductor surface, and the unit is eV.

[0081] Therefore, it was found that it is preferable to set the Mg concentration to 2.0E+19 or more (growth condition (i)).

[0082] Figure 5 is a diagram showing the reflectance vibration by the reflectance monitor of the crystal surface during growth by the MOCVD apparatus. The horizontal axis is the growth time, and the vertical axis is the reflectance R.

[0083] Specifically, the reflectivity was measured by irradiating light of a predetermined wavelength onto the surface of a growing crystal when only H2 was used as the carrier gas and when H2 (30%) and N2 (70%) were used as the carrier gas.

[0084] For example, when growing p-type GaN on AlGaN, due to the interference of reflected light from two surfaces, namely the AlGaN / GaN interface and the p-type GaN surface, the reflectivity R vibrates as the p-type GaN grows (layer thickness increases). When the reflectivity R does not vibrate, it indicates that the crystal is not growing. When the reflectivity R is low, it indicates that the crystal surface is rough and uneven. Also, if the maximum value Rmax of the reflectivity R is high, it indicates that crystal growth is progressing while the surface remains flat.

[0085] FIG. 6 is a graph plotted with the increase factor MF (= MR1 / MR2), which is the Mg increase ratio of the Mg / Ga ratio (MR1) during the growth of the first p-type GaN layer 16A with respect to the Mg / Ga ratio (MR2) during the growth of the second p-type GaN layer 16B, on the horizontal axis, and the maximum value Rmax of the reflectivity R measured in-situ during growth on the vertical axis.

[0086] As shown in FIG. 6, it can be seen that as the increase factor MF increases, the maximum value Rmax of the reflectivity R increases, indicating that the flatness of the first p-type GaN layer 16A increases.

[0087] This is because, as described above, in the initial stage of p-GaN growth, by increasing the flow rate of the Mg source, the surface density of nuclei starting from Mg on the AlGaN surface can be increased, and by increasing N2 in the carrier gas to prevent the re-evaporation of GaN, GaN growth can be made flat across the entire AlGaN surface.

[0088] In the case of the above-described Example EX3 (Fig. 3), the Mg flow rate of the first p-type GaN layer 16A is 600 sccm and the TMG flow rate is 9.0 sccm, and the Mg flow rate of the second p-type GaN layer 16B is 200 sccm and the TMG flow rate is 31.0 sccm. Therefore, since the Mg / Ga ratios of the first p-type GaN layer 16A and the second p-type GaN layer 16B are MR1 = 66.7 and MR2 = 6.5, respectively, the MF of the first p-type GaN layer 16A and the second p-type GaN layer 16B in EX3 is MF = MR1 / MR2 = 10.3.

[0089] Also, in the case of Example EX1, the Mg flow rate of the first p-type GaN layer 16A is 300 sccm and the TMG flow rate is 9.0 sccm, and the Mg flow rate of the second p-type GaN layer 16B is 200 sccm and the TMG flow rate is 31.0 sccm. Therefore, since the Mg / Ga ratios of the first p-type GaN layer 16A and the second p-type GaN layer 16B are MR1 = 33.3 and MR2 = 6.5, respectively, the MF of the first p-type GaN layer 16A and the second p-type GaN layer 16B in EX3 is MF = MR1 / MR2 = 5.17.

[0090] As shown in Fig. 3, in the case of Comparative Example CX1, since the Mg flow rate of the first p-type GaN layer 16A is 200 sccm and the TMG flow rate is 9.0 sccm, MF = MR1 / MR2 = 3.44. In the case of Comparative Example CX1, hillocks are observed and the number of coreless is also large. Also, from the graph of the maximum value Rmax of the reflectance R shown in Fig. 6, it is appropriate that MF ≧ 5 as the condition for the flat growth of the first p-type GaN layer 16A.

[0091] Therefore, it was found that in the growth of the first p-type GaN layer 16A, it is preferable that the Mg / Ga raw material ratio is 5 times or more that of the second p-type GaN layer 16B (growth factor MF ≧ 5) (growth condition (ii)).

[0092] FIG. 7 is a graph plotting the maximum value Rmax of the reflectance R by in-situ measurement when the ratio of N2 in the carrier gas (N2 ratio = N2 / (N2 + H2)) is changed. The maximum reflectance Rmax changes with respect to the N2 ratio, and reaches a maximum when the N2 ratio is about 70%. When the carrier gas is all H2, as shown in FIG. 5, the reflectance R is very small, and p-type GaN hardly grows.

[0093] Therefore, in the growth of the first p-type GaN layer 16A, it is appropriate from this data to set the N2 ratio in the carrier gas to 50% or more, and it was found that an N2 ratio of 60 to 80% is more preferable (growth condition (iii)).

[0094] 2-2 Second p-type GaN layer FIG. 8A is a diagram showing the growth mechanism (left side) of the second p-type GaN layer 16B in this embodiment (EMB), that is, when the carrier gas is 100% hydrogen (H2) (growth condition (iv)), and a cross-sectional TEM (Transmission Electron Microscope) image of the second p-type GaN layer 16B after growth (right side).

[0095] Further, FIG. 8B is a diagram showing the growth mechanism (left side) of the p-type GaN layer when using hydrogen (H2) and nitrogen (N2) as the carrier gas and setting the ratio of N2 in the carrier gas to 50% or more in the comparative example (CMP), and a cross-sectional TEM image of the p-type GaN layer after growth when the ratio of N2 in the carrier gas is 70% (right side).

[0096] First, as shown in FIG. 8B, in the case of the prior art (N2 atmosphere) where the carrier gas is an H2 / N2 mixed gas (CMP), since it is not subjected to gas-phase etching, the deposition rate (deposition coefficient) of GaN is high, and GaN grows randomly because it grows even at places with high surface energy.

[0097] Therefore, GaN grows flat with respect to the substrate, but has many crystal defects and a high threading dislocation density. In fact, as shown in the cross-sectional TEM image (right side), a high density of threading dislocations was observed. Also, the threading dislocation density was calculated to be 5.4E+9 (cm -2 ).

[0098] On the other hand, as shown in Fig. 8A, in the case of this embodiment (EMB) where the carrier gas is H2 = 100% (H2 atmosphere), the probability that the deposited GaN re-evaporates due to gas-phase etching is high, that is, the deposition rate (adhesion coefficient) of GaN is low.

[0099] Therefore, the deposited atoms diffuse on the surface and adhere from places with low surface energy. As a result, a facet surface with slow growth with respect to the substrate appears, but the crystallinity improves. In fact, as shown in the cross-sectional TEM image (right side), it was found that the threading dislocation density was greatly improved. Also, the threading dislocation density was calculated to be 6.2E+8 (cm -2 ). That is, it was found that a p-type contact layer 16 with a threading dislocation density of less than 1.0E+9 cm -2 can be obtained. From the cross-sectional TEM image, the layer thickness of the p-type contact layer 16 was 270 nm, but according to the present invention, it was found that a p-type GaN contact layer that is very thick and has a small threading dislocation density can be realized.

[0100] Therefore, it was found that an alloy spike is less likely to occur even during electrode formation, and a p-type contact layer capable of suppressing element degradation can be provided. Note that the layer thickness of the p-type contact layer 16 is preferably 200 nm or more.

[0101] As described above, the growth method differs depending on the difference in the carrier gas. By growing in an H2 atmosphere, the adhesion coefficient becomes low and growth occurs from places with low surface energy, so it is considered that the crystallinity is improved. It is considered that due to the improved crystallinity, conductivity with low resistance can be obtained without performing activation (activation annealing).

[0102] 2-3 Third p-Type GaN Layer Figure 9A shows an AFM (Atomic Force Microscope) image of the surface of the third p-type GaN layer 16C in this embodiment (EMB), that is, when an H2 / N2 mixed gas (H2 / N2 = 30% / 70%) is used as the carrier gas (growth condition (v)). Figure 9B shows an AFM image of the surface when the second p-type GaN layer 16B is grown (growth condition (iv)) and then continuously grown under the same carrier gas condition (H2 = 100%).

[0103] Note that both Figure 9A and Figure 9B are AFM images observing the as-grown crystal surface without activation (activation annealing).

[0104] First, as shown in Figure 9B, when the third p-type GaN layer was grown using H2 (H2 = 100%) as the carrier gas, the surface roughness (RMS) was 14.3 nm.

[0105] On the other hand, as shown in Figure 9A, when the third p-type GaN layer 16C was grown using an H2 / N2 mixed gas (H2 / N2 = 30% / 70%) as the carrier gas, the surface roughness (RMS) was 6.7 nm, and it was found that the surface flatness was improved.

[0106] Note that the p-barrier V0 when using an H2 / N2 mixed gas as the carrier gas (Figure 9A) is 0.0091 (V), and the contact resistance is 1.25E-2 (Ωcm 2 ), and the p-barrier V0 when using only H2 (H2 = 100%) as the carrier gas (Figure 9B) is 0.0624 (V), and the contact resistance is 1.29E-3 (Ωcm 2 ).

[0107] When the third p-type GaN layer 16C was grown using an H2 / N2 mixed gas as the carrier gas, the p-barrier (or Schottky barrier component) became lower and the contact property was improved.

[0108] Note that, as described in the growth conditions of the first p-type GaN layer 16A (growth condition (iii)), also in the growth of the third p-type GaN layer 16C, the N2 ratio in the carrier gas is preferably 50% or more, and more preferably the N2 ratio is 60 - 80%.

[0109] [Contact Characteristics of UV LEDs] FIG. 10 shows a comparison of the growth conditions of the p-type contact layer 16 (EMB) of the example of the present invention and the p-type contact layer (CMP) of the comparative example. Further, FIG. 10 shows a comparison of various characteristics of the p-type contact layer 16 (EMB) of the example and the p-type contact layer (CMP) of the comparative example.

[0110] As shown in FIG. 10, the p-type contact layer 16 (EMB) of the example was formed in accordance with the growth conditions of the first to third p-type GaN layers 16A to 16C described above. Specifically, the growth of the second p-type GaN layer 16B was performed in an atmosphere of H2 = 100%, and the Mg / Ga ratio increase factor MF (= MR1 / MR2) was 10.3.

[0111] Also, the layer thicknesses of the first to third p-type GaN layers 16A to 16C were 5 - 10 nm, 240 - 260 nm, and 5 - 10 nm, respectively, and the total layer thickness was 270 nm. Note that since the boundaries of these layers are difficult to distinguish by analysis such as TEM, the layer thicknesses of the first and second p-type GaN layers 16A and 16B are estimated values.

[0112] On the other hand, the p-type contact layer (CMP) of the comparative example is different from the p-type contact layer 16 (EMB) of the example in that the second p-type GaN layer was grown using an H2 / N2 mixed gas (H2: 30%, N2: 70%) as the carrier gas. Also, the Mg / Ga ratio increase factor MF (= MR1 / MR2) was 4.5.

[0113] Also, in the p-type contact layer (CMP) of the comparative example, activation was performed at 700°C for 30 min in a nitrogen atmosphere, but activation was not performed in the p-type contact layer 16 (EMB) of the present invention.

[0114] FIG. 11 shows a comparison of the contact characteristics and crystallinity of the p-type contact layer 16 (EMB) of the example and the p-type contact layer (CMP) of the comparative example. In the comparative example (CMP), after activating the p-type contact layer, electrodes of the TLM pattern were formed for measurement. On the other hand, in the example (EMB), electrodes of the TLM pattern were formed on the as-grown p-type contact layer 16 for measurement.

[0115] The forward voltage Vf of the p-type contact layer 16 (EMB) of the example was 7.1 V, and it was confirmed that it was improved compared to the forward voltage Vf = 8.2 V of the p-type contact layer (CMP) of the comparative example.

[0116] Also, in the p-type contact layer 16 (EMB) of the example, the p-barrier V0 is small, and high ohmic characteristics can be obtained. It can also be seen that the contact resistance and specific resistance were greatly improved. That is, good contact characteristics and conductivity were obtained without performing activation (activation annealing).

[0117] Furthermore, the through dislocation density is also about one order of magnitude lower, alloy spikes are less likely to occur, and an ultraviolet semiconductor light-emitting device that is less likely to deteriorate the element can be obtained. [Ultraviolet LED element] As shown in FIG. 1, the ultraviolet LED 10 of the present embodiment is formed by sequentially growing an n-type AlGaN layer 12, an active layer 13, a p-type AlGaN layer 15, and a p-type contact layer 16 on an AlN substrate 11. As described above, an AlGaN layer 14 (including an AlN layer), which is an electron blocking layer, may be provided between the active layer 13 and the p-type AlGaN layer 15.

[0118] Note that the n-type AlGaN layer 12 may be composed of a plurality of layers instead of a single layer. In that case, not all layers need to be n-layers (n-doped layers), and undoped layers (i-layers) may be included. The same applies to the p-type AlGaN layer 15.

[0119] The p - electrode 21 is formed on the as - grown p - type contact layer 16 that has not undergone activation (activation annealing).

[0120] More specifically, after forming a metal layer in which, for example, a Ni layer and an Au layer are laminated on the p - type contact layer 16, heat treatment is performed under conditions of, for example, 500 °C so that an ohmic contact is made with the p - type contact layer 16.

[0121] Note that although a metal layer in which a Ni layer and an Au layer are laminated is exemplified for the p - electrode 21, it is not limited to this.

[0122] In this specification, the "as - grown" p - type contact layer 16 includes cases where a process that does not affect the crystallinity (for example, dislocation density) of the p - type contact layer 16 is performed. Examples of such a process include cleaning of the wafer on which the semiconductor layer of the ultraviolet LED 10 has grown, and etching of a part of the surface layer.

[0123] Therefore, it is possible to provide an ultraviolet semiconductor light - emitting device that does not require activation, has high efficiency and high output, and has a small deterioration and an excellent element life.

[0124] (Codoping impurity) In the above - described embodiment, the case where Mg is used as the p - type impurity of the p - type clad layer p - type Al Y2 Ga 1-Y2 N layer 15 and Si is used as the codoping impurity has been described, but it is not limited to this.

[0125] p - type Al Y2 Ga 1-Y2 By being codoped into the p - type Al Y2 Ga 1-Y2It is considered that the effect of reducing nitrogen defects is manifested by the interaction between Mg, which is an acceptor impurity doped into the N layer 15, and Si, which is a donor impurity. Therefore, p-type Al Y2 Ga 1-Y2 Any material that functions as an acceptor and a donor can be used without limitation for the N layer 15.

[0126] Specifically, in addition to Mg, p-type impurities that act as acceptors such as Zn (zinc), Be (beryllium), and C (carbon) can be used. Also, in addition to Si, n-type impurities (codoping impurities) that act as donors such as Ge (germanium), Se (selenium), S (sulfur), and O (oxygen) can be used.

[0127] As described in detail above, according to the present invention, it is possible to thicken the p-type GaN contact layer, activation is not required, and there can be provided an ultraviolet semiconductor light-emitting device having high efficiency, high output, and excellent element life with little deterioration, and a method for manufacturing the same.

Explanation of symbols

[0128] 10: Ultraviolet semiconductor light-emitting device, 11: Substrate, 12: n-type AlGaN layer, 12A: First n-type Al X1 Ga 1-X1 N layer, 12B: Second n-type Al X2 Ga 1-X2 N layer, 13: Active layer, 14: Al Y1 Ga 1-Y1 N layer, 14A: AlN layer, 14B: p-type AlN layer, 15: p-type AlGaN layer, 16: p-type contact layer, 16A: First p-type GaN layer, 16B: Second p-type GaN layer, Third p-type GaN layer, 21: p electrode

Claims

1. A method for manufacturing an ultraviolet semiconductor light-emitting device by sequentially growing an n-type AlGaN layer, an active layer, a p-type AlGaN layer, and a p-type GaN contact layer on an AlN substrate by MOCVD method, wherein the p-type GaN contact layer has a first p-type GaN layer grown on the p-type AlGaN layer and a second p-type GaN layer grown on the first p-type GaN layer, the first p-type GaN layer and the second p-type GaN layer are grown using magnesium (Mg) as a p-dopant, The growth of the first p-type GaN layer is carried out using hydrogen (H ２ ), and nitrogen (N ２ ) as carrier gases, and the ratio of N in the carrier gases is 50% or more, ２ ​ The growth of the second p-type GaN layer is carried out using a carrier gas of hydrogen (H ２ ) at 100%, the first p-type GaN layer is grown under conditions such that the Mg raw material / Ga raw material ratio is 5 times or more the Mg raw material / Ga raw material ratio in the growth of the second p-type GaN layer, A method for manufacturing an ultraviolet semiconductor light-emitting device.

2. The method for manufacturing an ultraviolet semiconductor light-emitting device according to claim 1, wherein the Mg concentration of the first p-type GaN is 2.0E+19 or more.

3. A third p-type GaN layer is grown on the second p-type GaN layer, The growth of the third p-type GaN layer is carried out using hydrogen (H ２ ), and nitrogen (N ２ ) as carrier gases, and the ratio of N ２ in the carrier gases is 50% or more. The method for manufacturing an ultraviolet semiconductor light-emitting device according to claim 1 or 2.

4. The method for manufacturing an ultraviolet semiconductor light-emitting device according to claim 1, wherein the p-type GaN contact layer is grown to have a layer thickness of 200 nm or more.

5. The method for manufacturing an ultraviolet semiconductor light-emitting device according to claim 3, further comprising a step of forming a p-electrode on the as-grown third p-type GaN layer.

6. An ultraviolet semiconductor light-emitting device in which an n-type AlGaN layer, an active layer, a p-type AlGaN layer, and a p-type GaN contact layer are sequentially grown on an AlN substrate, wherein the p-type GaN contact layer has a layer thickness of 200 nm or more, An ultraviolet semiconductor light-emitting device having a p-electrode formed on the as-grown p-type GaN contact layer.

7. The threading dislocation density of the p-type GaN contact layer is less than 1.0E+9 cm －２ The ultraviolet semiconductor light-emitting device according to claim 6, wherein the density is less than 1.0E+9 cm

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