Group III nitride semiconductor light emitting device and method for manufacturing the same

Abstract

Provided are a III-nitride semiconductor light-emitting element having both high light output and excellent reliability and a method for manufacturing the same. The III-nitride semiconductor light-emitting element according to the present invention comprises an n-type semiconductor layer, a light-emitting layer, a p-type AlGaN electron blocking layer, a p-type contact layer and a p-side reflective electrode in sequence on a substrate, wherein the light emitted from the light-emitting layer has a central wavelength of 250 nm to 330 nm, the Al composition ratio of the p-type AlGaN electron blocking layer is 0.40 to 0.80, the film thickness of the p-type contact layer is 10 nm to 50 nm, and the p-type contact layer has a p-type AlGaN contact layer having an Al composition ratio of 0.03 to 0.25.

Description

Technical Field

[0001] The present invention relates to a Group III nitride semiconductor light emitting device and a method for manufacturing the same, and in particular to a Group III nitride semiconductor light emitting device having both high light output and excellent reliability and a method for manufacturing the same. Background Art

[0002] Group III nitride semiconductors, which are compounds of Group III elements such as Al, Ga, and In and N, are wide-bandgap semiconductors with a direct transition band structure, and are expected to be used in a wide range of fields, such as sterilization, water purification, medical treatment, lighting, and high-density optical recording. In particular, light-emitting devices using Group III nitride semiconductors in the light-emitting layer can cover the range from deep ultraviolet light to visible light by adjusting the content ratio of Group III elements, and are being promoted for practical use in various light sources.

[0003] The luminous efficiency of deep ultraviolet light emitting elements obtained using group III nitride semiconductors is usually very low, and it is said that it is difficult to achieve high output. However, in order to realize a small and high-output deep ultraviolet light emitting element, in addition to improving the internal quantum efficiency, various attempts have been made to achieve high light extraction efficiency, low resistance characteristics, etc.

[0004] A deep ultraviolet light-emitting element that emits deep ultraviolet light is usually made as follows. That is, a buffer layer is formed on a substrate such as sapphire or AlN single crystal, and an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer composed of a group III nitride semiconductor are formed in sequence. Next, an n-side electrode electrically connected to the n-type semiconductor layer and a p-side electrode electrically connected to the p-type semiconductor layer are formed respectively. Here, in order to obtain an ohmic contact, a p-type GaN contact layer that is easy to increase the hole concentration is usually formed on the p-side electrode side of the p-type semiconductor layer. However, the p-type GaN contact layer absorbs light with a wavelength of less than 360nm due to its band gap.

[0005] Patent document 1 discloses a group III nitride semiconductor device in which a GaN layer having a film thickness of 0.01 μm or more and 0.3 μm or less is provided on an AlGaInN layer having a high Al composition ratio. In Patent document 1, the growth mode of the GaN layer is set to a state close to the FM (Frank-van der Merwe) mode (quasi-FM mode) and the GaN layer is grown, so that the surface of the GaN layer is smoothed immediately after the crystal growth. As a result, even if the film thickness of the GaN layer formed on the AlGaInN layer having a high Al composition ratio is reduced, the surface can be smoothed.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2010-232364 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] According to the technique of Patent Document 1, the thickness of the p-type GaN contact layer can be reduced, so it is expected that light absorption by this layer can be suppressed and the light extraction efficiency of the Group III nitride semiconductor device can be improved.

[0011] According to the experiments of the inventors, when the thickness of the p-type GaN contact layer is extremely thinned to less than 50nm, a III-nitride semiconductor device with higher luminous output than the prior art can be obtained. However, it was confirmed that some samples of the III-nitride semiconductor light-emitting devices made in this way suddenly deteriorated in luminous output to the extent of halving the initial luminous output. In this specification, this phenomenon of sudden deterioration of luminous output is referred to as "quenching". Specifically, the luminous area is set to 0.057mm 2 The sample of the Group III nitride semiconductor light-emitting element is powered on at 20 mA to measure the initial luminous output. Then, after being powered on at 100 mA for 3 seconds, it is measured again at 20 mA. The sample that is confirmed to have an output reduction of more than half compared to the initial luminous output is considered to have quenched. Here, when the luminous output relative to the forward current is plotted for the luminous area of ​​the Group III nitride semiconductor light-emitting element, the above 20 mA is a current value in the range of maintaining linearity, and the above 100 mA is a current value in the range of losing the linearity of the output due to heat release from the light-emitting element. The reliability of the element whose luminous output suddenly deteriorates like this is insufficient, and it is unacceptable for elements with insufficient reliability to be mixed into the product in terms of product quality management.

[0012] Therefore, an object of the present invention is to provide a Group III nitride semiconductor light emitting device having both high light output and excellent reliability, and a method for manufacturing the same.

[0013] Solutions for solving problems

[0014] The present inventors have conducted in-depth research on methods for solving the above-mentioned problems. When the p-type GaN layer is formed to be extremely thin to less than 50nm, defects are introduced due to the relaxation of the large compressive strain, and the surface flatness is also deteriorated. It can be inferred that when the p-type GaN layer is grown using the FM mode, if the AlGaN layer (the AlInGaN layer when containing In) that becomes the directly underlying layer of the p-type GaN layer has bumps or dislocations, the growth will be promoted in the direction of burying the bumps or dislocations, but the relaxation of the compressive strain is easy to aggravate and defects are easily introduced. Therefore, it goes without saying that the bumps or dislocations of the directly underlying layer of the p-type GaN layer that cannot be buried, even if the p-type GaN layer appears to be flattened, new dislocations may sometimes occur. Taking into account the experimental facts, the present inventors believe that when they exist in the electrode formation area, the light-emitting element will be quenched. The present invention was completed based on the knowledge that by using an AlGaN layer having an Al composition ratio x of 0.03 or more and 0.25 or less as a p-type contact layer, quenching of the light-emitting element can be prevented while achieving both high light output and excellent reliability. That is, the main features of the present invention are as follows.

[0015] (1) A group III nitride semiconductor light emitting device, characterized in that it comprises an n-type semiconductor layer, a light emitting layer, a p-type AlGaN electron blocking layer, a p-type contact layer and a p-side reflective electrode in this order on a substrate,

[0016] The light emitted from the light emitting layer has a central wavelength of 250 nm to 330 nm.

[0017] The Al composition ratio of the p-type AlGaN electron blocking layer is 0.40 or more and 0.80 or less,

[0018] The p-type contact layer has a film thickness of 10 nm to 50 nm, and includes a p-type AlGaN contact layer having an Al composition ratio of 0.03 to 0.25.

[0019] (2) The Group III nitride semiconductor light emitting device according to (1) above, wherein the p-type contact layer consists only of the p-type AlGaN contact layer.

[0020] (3) The Group III nitride semiconductor light emitting device according to (1) above, wherein the p-type contact layer includes a p-type GaN contact layer between the p-type AlGaN contact layer and the p-side reflective electrode.

[0021] (4) The Group III nitride semiconductor light emitting device according to any one of (1) to (3) above, wherein the p-type AlGaN contact layer has a thickness of 10 nm to 25 nm.

[0022] (5) A method for manufacturing a group III nitride semiconductor light emitting device, characterized in that it comprises the following steps:

[0023] The step of forming an n-type semiconductor layer on a substrate;

[0024] forming a light emitting layer on the n-type semiconductor layer;

[0025] forming a p-type AlGaN electron blocking layer on the aforementioned light-emitting layer;

[0026] forming a p-type contact layer on the p-type AlGaN electron blocking layer; and

[0027] forming a p-side reflective electrode on the p-type contact layer,

[0028] The central wavelength of light emitted from the light-emitting layer is 250 nm to 330 nm.

[0029] The Al composition ratio of the p-type AlGaN electron blocking layer is 0.40 or more and 0.80 or less,

[0030] The p-type contact layer has a thickness of 10 nm to 50 nm.

[0031] The p-type contact layer includes a p-type AlGaN contact layer having an Al composition ratio of 0.03 to 0.25.

[0032] Effects of the Invention

[0033] According to the present invention, a Group III nitride semiconductor light emitting device having both high light emission output and excellent reliability and a method for manufacturing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic cross-sectional view illustrating one embodiment of the Group III nitride semiconductor light-emitting device of the present invention.

[0035] Figure 2 This is an enlarged schematic cross-sectional view illustrating one embodiment of the p-type contact layer of the Group III nitride semiconductor light-emitting device of the present invention.

[0036] Figure 3 This is a schematic cross-sectional view illustrating one embodiment of a method for manufacturing a Group III nitride semiconductor light-emitting device according to the present invention.

[0037] Figure 4A This is an AFM image of the surface of the p-type contact layer of Example 1.

[0038] Figure 4B This is an AFM image of the surface of the p-type contact layer of Example 2.

[0039] Figure 4C This is an AFM image of the surface of the p-type contact layer of Example 3.

[0040] Figure 4D This is an AFM image of the surface of the p-type contact layer of Comparative Example 1. DETAILED DESCRIPTION

[0041] Before describing the embodiments of the present invention, the following aspects will be described in advance. First, in this specification, when the Al composition ratio is not explicitly stated and it is abbreviated as "AlGaN", it refers to any compound in which the composition ratio of the group III element (the sum of Al and Ga) and N is 1:1, and the ratio of the group III elements Al and Ga is indefinite. In addition, even if there is no relevant description of In belonging to the group III element, "AlGaN" is regarded as optionally containing In within 5% relative to the sum of Al and Ga as group III elements, and the composition formula recorded by containing In is recorded as Al with the Al composition ratio set to x and the In composition ratio set to y (0≤y≤0.05). x In y Ga 1-x-y N. When abbreviated as "AlN" or "GaN", it means that Ga and Al are not contained, respectively, but unless otherwise specified, the abbreviated as "AlGaN" does not exclude either AlN or GaN. It should be noted that the value of the Al composition ratio can be measured by photoluminescence measurement, X-ray diffraction measurement, etc.

[0042] In addition, in this specification, a layer that functions electrically as a p-type is referred to as a p-type layer, and a layer that functions electrically as an n-type is referred to as an n-type layer. On the other hand, when a layer does not function electrically as a p-type or n-type layer without actively adding specific impurities such as Mg and Si, it is referred to as "i-type" or "undoped". Undoped layers may contain unavoidable impurities in the manufacturing process. Specifically, when the carrier density is low (e.g., less than 4×10 16 / cm 3 ), it is referred to as “undoped” in this specification. In addition, the values ​​of the impurity concentrations of Mg, Si, etc. are set to the values ​​based on SIMS analysis.

[0043] In addition, the film thickness of each layer formed by epitaxial growth can be measured as a whole using an optical interference film thickness measuring device. Furthermore, in the case where the composition of each adjacent layer is significantly different (for example, when the Al composition ratio differs by more than 0.01), the film thickness of each layer can be calculated by cross-sectional observation of the growth layer based on a transmission electron microscope. In addition, for the boundary and film thickness of the layer with the same or substantially equal Al composition ratio (for example, Al composition ratio is less than 0.01) but different impurity concentration among the adjacent layers, the boundary and film thickness of the two layers are obtained by measuring based on TEM-EDS. And the impurity concentration of the two layers can be measured by SIMS analysis. In addition, in the case where the film thickness of each layer is thin, such as a superlattice structure, TEM-EDS can be used to measure the film thickness.

[0044] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the same components are marked with the same reference numerals in principle, and the description thereof is omitted. In addition, in each figure, the aspect ratio of the substrate and each layer is exaggerated compared to the actual ratio for the convenience of description.

[0045] (Group III Nitride Semiconductor Light Emitting Device)

[0046] like Figure 1 As shown in the figure, the III-nitride semiconductor light-emitting device 100 according to one embodiment of the present invention includes an n-type semiconductor layer 30, a light-emitting layer 40, a p-type AlGaN electron blocking layer 60, a p-type contact layer 70, and a p-side reflective electrode 80 in this order on a substrate 10. In addition, the emission center wavelength of the light emitted from the light-emitting layer 40 is 250 nm to 330 nm, the Al composition ratio of the p-type AlGaN electron blocking layer 60 is 0.40 to 0.80, the film thickness of the p-type contact layer 70 is 10 nm to 50 nm, and the p-type contact layer 70 has a p-type AlGaN contact layer 71 having an Al composition ratio of 0.03 to 0.25.

[0047] It should be noted that if Figure 1 As shown, a buffer layer 20 is provided between the substrate 10 and the n-type semiconductor layer 30, an exposed surface is provided for the n-type semiconductor layer 30, and an n-side electrode 90 is provided for the exposed surface, which is a preferred embodiment of the III-nitride semiconductor light-emitting device 100. The details of each structure are described in order below.

[0048] <Substrate>

[0049] As the substrate 10 of the group-III nitride semiconductor light-emitting element 100, a sapphire substrate can be used. An AlN template substrate having an epitaxially grown AlN layer provided on the surface of the sapphire substrate can be used. As the sapphire substrate, any sapphire substrate can be used, with or without an off-angle. When an off-angle is provided, the crystal axis orientation of the tilt direction can be either the m-axis direction or the a-axis direction. For example, the main surface of the sapphire substrate can be a surface tilted at an off-angle θ of 0.5 degrees with respect to the C plane. When using an AlN template substrate, it is preferable that the crystallinity of the AlN layer on the surface of the sapphire substrate is excellent. In addition, it is also preferable that an undoped AlGaN layer is provided on the surface of the AlN template substrate. In addition, as the substrate 10, an AlN single crystal substrate can be used.

[0050] <n-type semiconductor layer>

[0051] The n-type semiconductor layer 30 is provided on the substrate 10 with a buffer layer 20 interposed therebetween as needed. The n-type semiconductor layer 30 can also be provided directly on the substrate 10. The n-type semiconductor layer 30 can be an AlGaN doped with an n-type dopant. As needed, group-III elements such as In can be introduced at a composition ratio of 5% or less to form AlGaInN or the like. Specific examples of the n-type dopant include silicon (Si), germanium (Ge), tin (Sn), sulfur (S), oxygen (O), titanium (Ti), zirconium (Zr), etc. The doping concentration of the n-type dopant is not particularly limited as long as the n-type semiconductor layer 30 can function as an n-type, and can be set to, for example, 1.0×10 18 atoms / cm 3 ~1.0×10 20 atoms / cm 3 . In addition, it is preferable that the bandgap of the n-type semiconductor layer 30 is wider than that of the light-emitting layer 40 (when a quantum well structure is formed, the well layer 41) and is transmissive to deep ultraviolet light for emission. In addition, it can be configured such that the n-type semiconductor layer 30 includes not only a single-layer structure and a structure composed of multiple layers, but also a composition gradient distribution layer and a superlattice structure in which the composition ratio of the group-III elements shows a composition gradient distribution along the crystal growth direction. The n-type semiconductor layer 30 not only forms a contact portion in contact with the n-side electrode 90, but can also function to improve the crystallinity from the substrate to the light-emitting layer.

[0052] <light-emitting layer>

[0053] The light-emitting layer 40 is provided on the n-type semiconductor layer 30 and emits deep ultraviolet light having a light-emitting center wavelength of 250 nm or more and 330 nm or less. The light-emitting layer 40 can be an AlGaN, and its Al composition ratio can be appropriately set in a range of, for example, 0.17 to 0.70 so as to obtain a desired light-emitting center wavelength.

[0054] The light-emitting layer 40 can be a single-layer structure with a fixed Al composition ratio, and is preferably composed of a multiple quantum well (MQW: Multiple Quantum Well) structure. The multiple quantum well structure is formed by repeatedly forming a well layer 41 and a barrier layer 42 composed of AlGaN with different Al composition ratios. In any case, group III elements such as In can be introduced at a composition ratio within 5% as needed to form an AlGaInN material, etc., and it is more preferably a ternary AlGaN material that uses only Al and Ga as group III elements.

[0055] When using the multiple quantum well structure, the Al composition ratio b of the barrier layer 42 is higher than the Al composition ratio w of the well layer 41 (i.e., b>w). Regarding the Al composition ratio b, under the condition of b>w, the Al composition ratio b of the barrier layer 42 can be set to, for example, 0.30 to 0.95. The central emission wavelength can be roughly adjusted by the Al composition ratio w of the well layer 41. For example, if the Al composition ratio w of the well layer 41 in the light-emitting layer 40 is set to 0.17 to 0.68, the central wavelength of the light emitted from the light-emitting layer 40 becomes 250 to 330 nm.

[0056] In addition, the number of repetitions of the well layer 41 and the barrier layer 42 is not particularly limited, and can be set to, for example, 1 to 10 times. It is preferable to set both ends in the film thickness direction of the light-emitting layer 40 (i.e., the first and the last) as the barrier layer. If the number of repetitions of the well layer 41 and the barrier layer 42 is set to n, it is expressed as "n.5 groups of well layers and barrier layers" at this time. In addition, the film thickness of the well layer 41 can be set to 0.5 nm to 5 nm, and the film thickness of the barrier layer 42 can be set to 3 nm to 30 nm.

[0057] It should be noted that it is preferable to set the conductivity type of the barrier layer 42 to n-type. This is because the electron concentration increases and it has the effect of compensating for lattice defects in the well layer 41. It should be noted that the light-emitting layer 40 can be a general multiple quantum well (MQW: Multiple Quantum Well) structure formed by repeatedly forming the barrier layer 42 and the well layer 41 and clamped by the barrier layer 42, or a structure obtained by removing the last barrier layer 42 on the p-type AlGaN electron blocking layer 60 side as needed.

[0058] <p-type AlGaN electron blocking layer>

[0059] The p-type AlGaN electron blocking layer 60 is provided on the light-emitting layer 40. The p-type AlGaN electron blocking layer 60 is used as a layer for blocking electrons and injecting electrons into the light-emitting layer 40 (the well layer 41 in the case of the MQW structure) to improve the electron injection efficiency. In the present invention, as the p-type AlGaN electron blocking layer, a p-type AlGaN with an Al composition ratio of 0.40 or more and 0.80 or less can be used. z Ga 1-z N (0.40 ≤ z ≤ 0.80). As needed, a quaternary AlGaInN material into which a group III element such as In is introduced at a composition ratio within 5% or the like can be formed, and it is more preferably a ternary AlGaN material using only Al and Ga as group III elements. If the Al composition ratio is within this range, a large number of dislocations will be formed in the p-type AlGaN electron blocking layer 60. Therefore, it is effective to use the p-type contact layer 70 of the present invention at this time. When the Al composition ratio is 0.60 or more and 0.70 or less, dislocations are particularly likely to be formed.

[0060] The film thickness of the p-type AlGaN electron blocking layer 60 is not particularly limited, and is preferably set to, for example, 10 nm to 80 nm. If the film thickness of the p-type AlGaN electron blocking layer 60 is within this range, a high light emission output can be reliably obtained. It should be noted that it is preferable that the film thickness of the p-type AlGaN electron blocking layer 60 is thicker than the film thickness of the barrier layer 42. In addition, examples of the p-type dopant doped into the p-type AlGaN electron blocking layer 60 include magnesium (Mg), zinc (Zn), calcium (Ca), beryllium (Be), manganese (Mn), etc., and Mg is usually used. The doping concentration of the p-type AlGaN electron blocking layer 60 is not particularly limited as long as it can function as a p-type layer, and can be set to, for example, 1.0×10 18 atoms / cm 3 ~5.0×10 21 atoms / cm 3 。

[0061] <p-type contact layer>

[0062] The p-type contact layer 70 is directly provided on the p-type AlGaN electron blocking layer 60. The p-type contact layer 70 is a layer for reducing the contact resistance between the p-side reflective electrode 80 provided on its outermost surface and the p-type AlGaN electron blocking layer 60. In the present invention, the film thickness of the p-type contact layer 70 is set to 10 nm or more and 50 nm or less. And, the p-type contact layer 70 has a p-type AlGaN layer 71 with an Al composition ratio x of 0.03 or more and 0.25 or less. And, the p-type AlGaN contact layer 71 is formed so as to be in contact directly above the p-type AlGaN electron blocking layer 60, and the composition formula is Al x Ga 1-xThe Al composition ratio x of N can be 0.03≤x≤0.25. The inventors have confirmed through experiments that by providing the p-type contact layer 70 with the p-type AlGaN layer 71 directly above the p-type AlGaN electron blocking layer 60, quenching of the Group III nitride semiconductor light emitting device 100 can be prevented. This is believed to be because the p-type AlGaN contact layer 71 (AlGaN) is formed instead of the p-type GaN layer being formed directly above the p-type AlGaN electron blocking layer 60. x Ga 1-x N, 0.03≤x≤0.25), the adverse effect of deterioration of surface flatness is suppressed, and the occurrence of dislocations formed in the early stage of growth is suppressed.

[0063] In order to obtain the effect of the present invention, it is sufficient that the p-type contact layer 70 has the p-type AlGaN contact layer 71 just above the p-type AlGaN electron blocking layer 60. The p-type contact layer 70 may be composed of only the p-type AlGaN contact layer 71 (see Figure 1 ), on the other hand, the p-type contact layer 70 may have a p-type GaN contact layer between the p-type AlGaN contact layer 71 and the p-side reflective electrode 80 (see Figure 2 ). In any case, the film thickness of the p-type AlGaN contact layer 71 can be set to be greater than 10nm and less than 50nm, as long as the overall film thickness of the p-type contact layer 70 is greater than 10nm and less than 50nm. It should be noted that in order to obtain the effect of the present invention and increase the light output of the III-nitride semiconductor light-emitting element 100, it is more preferred to set the film thickness of the p-type AlGaN contact layer 71 to be greater than 10nm and less than 25nm. In addition, in order to more reliably suppress quenching to zero, it is further preferred to set the thickness of the p-type contact layer 70 to be greater than 15nm.

[0064] It should be noted that, although not shown in the figure, the p-type contact layer 70 preferably has a Mg concentration of 3×10 20 atoms / cm 3 More preferably, the Mg concentration in the high concentration region is 5×10 20 atoms / cm 3 The hole concentration of the p-type contact layer 70 can be increased, and the forward voltage Vf of the III-nitride semiconductor light-emitting device 100 can be reduced. It should be noted that, although the upper limit is not deliberately limited, if industrial productivity is taken into consideration, the upper limit of the Mg concentration in the high concentration region in this embodiment can be set to 1×10 21 atoms / cm 3At this time, the Mg concentration in the region of the p-type contact layer 70 on the side of the p-type AlGaN electron blocking layer 60 can be set within a general range, usually 5×10 19 atoms / cm 3 or more and less than 3×10 20 atoms / cm 3 . It should be noted that the Mg concentration in the p-type contact layer is the average concentration in each region measured by SIMS. In order to maintain the crystallinity of the p-type contact layer 70, the film thickness of the high-concentration region is usually 15 nm or less.

[0065] <p-side electrode>

[0066] The p-side reflective electrode 80 can be provided directly above (on the outermost surface) the p-type contact layer 70. The p-side reflective electrode 80 is preferably made of a metal having a high reflectivity (e.g., 60% or more) with respect to the ultraviolet light emitted from the light-emitting layer 40. As the metal having such a reflectivity, for example, rhodium (Rh), platinum (Pt), iridium (Ir), ruthenium (Ru), molybdenum (Mo), tungsten (W), tantalum (Ta), and an alloy containing at least any one of them can be cited. These metals or alloys are preferred because they have a high reflectivity to deep ultraviolet light and can also exhibit a good ohmic contact between the p-type contact layer 70 and the p-side reflective electrode 80. It should be noted that from the viewpoint of reflectivity, among these, the p-side reflective electrode 80 preferably contains rhodium (Rh) in the form of a single substance or an alloy. In addition, the film thickness, shape, and size of the p-side reflective electrode 80 can be appropriately selected according to the shape and size of the group-III nitride semiconductor light-emitting element 100. For example, the film thickness of the p-side reflective electrode 80 can be set to 30 to 45 nm.

[0067] The group-III nitride semiconductor light-emitting element 100 based on the present embodiment described above can achieve both high light emission output and excellent reliability.

[0068] Hereinafter, specific modes applicable to the present embodiment will be described, but the present embodiment is not limited to the following modes.

[0069] <Buffer layer>

[0070] As Figure 1 shown, it is also preferable to provide a buffer layer 20 for alleviating the lattice mismatch between the substrate 10 and the n-type semiconductor layer 30. As the buffer layer 20, an undoped group-III nitride semiconductor layer can be used, and for example, undoped AlN can be used. The buffer layer 20 can be formed into a superlattice structure. One or more buffer layers selected from an AlGaN layer, a composition gradient distribution layer, and a superlattice layer can be further provided between the buffer layer 20 and the n-type semiconductor layer 30.

[0071] <n-side electrode>

[0072] The n-side electrode 90 that can be provided on the exposed surface of the n-type semiconductor layer 30 can be formed of, for example, a metal composite film having a Ti-containing film and an Al-containing film formed on the Ti-containing film. The film thickness, shape, and size of the n-side electrode 90 can be appropriately selected according to the shape and size of the light-emitting element. The n-side electrode 90 is not limited to being formed on Figure 1 the exposed surface of the n-type semiconductor layer 30 as shown, as long as it is electrically connected to the n-type semiconductor layer.

[0073] <p-type guiding layer>

[0074] It should be noted that although not shown in Figure 1 , a p-type guiding layer made of AlGaN or AlN with an Al composition ratio higher than that of the p-type AlGaN electron blocking layer 60 can be provided between the light-emitting layer 40 and the p-type AlGaN electron blocking layer 60. By providing the guiding layer, the injection of holes into the light-emitting layer 40 can be promoted.

[0075] <n-type guiding layer>

[0076] Furthermore, although not shown in Figure 1 , an n-type guiding layer can be provided between the light-emitting layer 40 and the n-type semiconductor layer 30. The n-type guiding layer is preferably made of AlGaN, and its Al composition ratio is preferably set to be equal to or higher than that of the aforementioned n-type semiconductor layer 30 and lower than the Al composition ratio b of the barrier layer 42. Its film thickness can be set to 3 nm to 30 nm. In addition, the n-type guiding layer is preferably doped with an n-type dopant (impurity) in the same manner as the n-type semiconductor layer 30, but the doping amount is preferably lower than that of the n-type layer.

[0077] It should be noted that the group-III nitride semiconductor light-emitting element 100 according to the present embodiment reflects deep ultraviolet light by forming the p-side reflective electrode 80 from a reflective electrode material, so that the substrate side or the substrate horizontal direction can be set as the main light extraction direction. In addition, the group-III nitride semiconductor light-emitting element 100 can be formed in a so-called flip-chip type form.

[0078] (Manufacturing method of group-III nitride semiconductor light-emitting element)

[0079] Next, referring to Figure 3One embodiment of the method for manufacturing the above-mentioned III-nitride semiconductor light-emitting device 100 is described. One embodiment of the method for manufacturing the III-nitride semiconductor light-emitting device 100 according to the present invention includes the following steps: forming an n-type semiconductor layer 30 on a substrate 10 (see step A), forming a light-emitting layer 40 on the n-type semiconductor layer 30, forming a p-type AlGaN electron blocking layer 60 on the light-emitting layer 40 (see step B), forming a p-type contact layer 70 on the p-type AlGaN electron blocking layer 60 (see step C), and forming a p-side reflective electrode 80 on the p-type contact layer 70 (see step D). Here, in one embodiment of the present manufacturing method, the emission center wavelength of light emitted from the light-emitting layer 40 is greater than 250 nm and less than 330 nm, the Al composition ratio of the p-type AlGaN electron blocking layer 60 is greater than 0.40 and less than 0.80, and the film thickness of the p-type contact layer 70 is greater than 10 nm and less than 50 nm. Furthermore, the p-type contact layer 70 includes a p-type AlGaN contact layer 71 having an Al composition ratio of 0.03 to 0.25.

[0080] Hereinafter, reference will be made to a flowchart showing a preferred embodiment of the present embodiment. Figure 3 , the details of each process are described in sequence together with the specific method, but repeated descriptions related to the various structures of the group III nitride semiconductor light-emitting element 100 are omitted.

[0081] First, if Figure 3 As shown in steps A and B, an n-type semiconductor layer 30, a light-emitting layer 40, and a p-type AlGaN electron blocking layer 60 are sequentially formed on a substrate 10. In each of these steps, each layer can be formed using a known epitaxial growth technique such as an organic metal vapor deposition (MOCVD: Metal Organic Chemical Vapor Deposition) method, a molecular beam epitaxy (MBE: Molecular Beam Epitaxy) method, or a sputtering method.

[0082] When forming each layer of the n-type semiconductor layer 30, the light-emitting layer 40, and the p-type AlGaN electron blocking layer 60, the growth temperature, growth pressure, and growth time for epitaxial growth can be set to general conditions that are consistent with the Al composition ratio and film thickness of each layer. As a carrier gas for epitaxial growth, hydrogen or nitrogen or a mixed gas of the two can be used and supplied into the chamber. Furthermore, as a raw material gas for growing the above-mentioned layers, TMA (trimethylaluminum), TMG (trimethylgallium), etc. can be used as a raw material gas of the III group element, and NH 3 Gas is a Group V element gas. 3The molar ratio of the group V element to the group III element (hereinafter referred to as V / III ratio) calculated by the growth gas flow rate of the group V element gas such as Mg gas and the group III element gas such as TMA gas can also be set as a general condition. Furthermore, as the gas of the dopant source, cyclopentadienyl magnesium gas (CP) as a Mg source is appropriately selected for the p-type dopant. 2 Mg) etc., and as for the n-type dopant, for example, monosilane gas (SiH 4 ), zinc chloride gas (ZnCl 2 ) etc., and supply it into the chamber at a prescribed flow rate.

[0083] Then, in Figure 3 In the p-type contact layer forming step shown in step C of the present invention, a p-type AlGaN contact layer 71 is formed on the p-type AlGaN electron blocking layer 60. The conditions regarding the film thickness range of the p-type contact layer 70 and the Al composition ratio of the p-type AlGaN contact layer 71, and the conditions regarding the optional formation of the p-type GaN contact layer 72 ( Figure 3 Not shown. Figure 2 ) as described above. In addition, the p-type contact layer 70 can also be crystal-grown by epitaxial growth based on the MOCVD method, etc., similarly to the p-type AlGaN electron blocking layer 60. Moreover, the growth conditions are not particularly limited, but it is preferred to adjust the gas flow rate, V / III ratio, and growth temperature so that the growth rate in the thickness direction is set to 0.03 to 0.50 μm / h, more preferably 0.03 to 0.19 μm / h, and most preferably 0.10 to 0.15 μm / h. It should be noted that the carrier gas preferably uses H 2 .

[0084] It should be noted that in order to increase the Mg concentration of the p-type contact layer 70 , it is only necessary to appropriately adjust the Mg / Group III element gas ratio.

[0085] In addition, if Figure 2 As shown in step D of the embodiment, the light emitting layer 40, the p-type AlGaN electron blocking layer 60, and a portion of the p-type contact layer 70 can be removed by etching or the like, and an n-side electrode 90 can be formed on the exposed n-type semiconductor layer 30. It should be noted that the p-side reflective electrode 80 and the n-side electrode 90 can be formed by sputtering, vacuum evaporation, etc. In addition, it is also preferred to form a buffer layer 20 on the surface 10A of the substrate 10.

[0086] Example

[0087] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to the following examples at all.

[0088] (Example 1: Wavelength is 280nm)

[0089] Prepare a sapphire substrate (diameter: 2 inches, film thickness: 430μm, surface orientation: (0001), m-axis deviation angle θ: 0.5 degrees). Then, grow an AlN layer with a central film thickness of 0.60μm (average film thickness of 0.61μm) on the above sapphire substrate by MOCVD to make an AlN template substrate. At this time, the growth temperature of the AlN layer is 1300°C, the growth pressure in the chamber is 10Torr, and the growth gas flow rates of ammonia and TMA gas are set so that the V / III ratio becomes 163. Group V element gas (NH 3 ) was 200 sccm, and the flow rate of the group III element gas (TMA) was 53 sccm. It should be noted that the film thickness of the AlN layer was measured using an optical interference film thickness measuring machine (Nanospec M6100A; manufactured by NANOMETRICS) to measure the film thickness of a total of 25 locations at equal intervals, including the center of the wafer surface.

[0090] Next, the AlN template substrate was introduced into a heat treatment furnace, and after the pressure was reduced to 10 Pa, it was purged with nitrogen gas to normal pressure, thereby forming a nitrogen atmosphere in the furnace, and then the temperature in the furnace was increased to perform heat treatment on the AlN template substrate. At this time, the heating temperature was set to 1650° C. and the heating time was set to 4 hours.

[0091] Next, an undoped AlGaN layer with an Al composition ratio of 0.85 to 0.65 and a film thickness of 200 nm and a composition gradient distribution along the crystal growth direction was formed by MOCVD as an undoped AlGaN layer. 0.65 Ga 0.35 N and doped with Si to form an n-type layer with a thickness of 2 μm. It should be noted that the Si concentration of the n-type layer was 1.0×10 19 atoms / cm 3 .

[0092] Next, Al is formed on the n-type layer. 0.65 Ga 0.35 A 20 nm thick n-type guide layer composed of N and doped with Si was formed, and a 4 nm thick Al 0.65 Ga 0.35 N. Then, two layers of Al 0.45 Ga 0.55 The well layer is composed of N with a thickness of 3 nm and the Al layer is composed of N with a thickness of 4 nm. 0.65 Ga 0.35 N barrier layer, and then form a barrier layer composed of Al 0.45 Ga 0.55N has a thickness of 3 nm. That is, the number of well layers and the number of barrier layers N are both 3, the Al composition ratio b of the barrier layer is 0.65, and the Al composition ratio w of the well layer is 0.45. It should be noted that Si is doped in the formation of the barrier layer.

[0093] Thereafter, an undoped AlN guide layer was formed on the third well layer using nitrogen as a carrier gas. The thickness of the AlN guide layer was set to 1 nm. Next, the supply of TMA gas was stopped and the supply of ammonia gas was continued. In this state, the nitrogen gas as a carrier gas was stopped and hydrogen gas was supplied. After the carrier gas was changed to hydrogen gas, TMA gas and TMG gas as the raw gas of the group III element were supplied again to form an AlN guide layer. 0.68 Ga 0.32 An electron blocking layer with a layer thickness of 40 nm and composed of N and doped with Mg.

[0094] Next, the growth of the electron blocking layer was stopped, the carrier gas was switched to nitrogen, and the gas flow rate was changed to p-type Al 0.08 Ga 0.92 After setting the conditions for the N contact layer, the carrier gas was switched to hydrogen to form a 20nm thick p-type Al doped with Mg. 0.08 Ga 0.92 The N-type contact layer (hereinafter referred to as “p-type contact layer” in the examples) was analyzed by SIMS. The average Mg concentration of the p-type contact layer was 1.2×10 20 atom / cm 3 It should be noted that the growth rate in the thickness direction when forming the p-type contact layer was set to 0.12 μm / h.

[0095] After that, a mask is formed on the p-type contact layer, and mesa etching is performed by dry etching to expose a portion of the n-type semiconductor layer, and a p-side electrode composed of Ni / Au is formed on the p-type contact layer, and an n-side electrode composed of Ti / Al is formed on the exposed n-type layer. It should be noted that the thickness of Ni in the p-side electrode is The film thickness of Au is In addition, the thickness of Ti in the n-side electrode is The Al film thickness is Finally, contact annealing (RTA) was performed at 550° C. to form each electrode.

[0096] Table 1 shows the structure of each layer of the Group III nitride semiconductor light-emitting device of Example 1 produced as described above.

[0097] [Table 1]

[0098]

[0099] (Examples 2 to 5, Examples 8 to 11, Comparative Example 1, Conventional Example 1, Comparative Examples 4 to 7: wavelength is 280 nm)

[0100] The same operation as in Example 1 was performed except that the film thickness and Al composition ratio of the p-type contact layer in Example 1 were changed as shown in Table 2 to prepare Group III nitride semiconductor light-emitting devices of Examples 2 to 5, Comparative Example 1, and Conventional Example 1. It should be noted that in Example 3, the p-type Al 0.68 Ga 0.32 A 20nm thick p-type Al layer is formed on the N electron blocking layer. 0.08 Ga 0.92 N contact layer, and then, a p-type GaN contact layer with a thickness of 20 nm was formed. Furthermore, except that the film thickness and Al composition ratio of the p-type contact layer in Example 1 were changed as described in Table 2, the same operation as in Example 1 was performed to produce Group III nitride semiconductor light-emitting devices of Examples 8 to 11 and Comparative Examples 4 to 7.

[0101] (Example 6, Examples 12 to 13, Comparative Example 2, Conventional Example 2: wavelength is 310 nm)

[0102] The Group III nitride semiconductor light emitting devices described in Example 6, Comparative Example 2, and Conventional Example 2 were fabricated in the same manner as in Example 1, except that the Al composition ratio w:0.45 of the well layer in Example 1 was changed to 0.30, and further, the Al composition ratio of the undoped layer was changed to 0.55, the Al composition ratio of the n-type semiconductor layer was changed to 0.45, the Al composition ratio of the n-guide layer and the barrier layer was changed to 0.55, and the Al composition ratio of the p-type electron blocking layer was changed to 0.58, and the film thickness and Al composition ratio x of the p-type contact layer were changed as described in Table 2. Group III nitride semiconductor light emitting devices of Examples 12 and 13 were fabricated in the same manner as in Example 6, except that the film thickness and Al composition ratio of the p-type contact layer in Example 6 were changed as described in Table 2.

[0103] (Example 7, Example 14, Comparative Example 3, Conventional Example 3: wavelength is 265 nm)

[0104] The Group III nitride semiconductor light emitting devices of Example 7, Comparative Example 3, and Conventional Example 3 were fabricated in the same manner as in Example 1, except that the Al composition ratio w:0.45 of the well layer in Example 1 was changed to 0.58, and further, the Al composition ratio of the barrier layer was changed to 0.76, and the film thickness and Al composition ratio x of the p-type contact layer were changed as described in Table 2. Furthermore, the Group III nitride semiconductor light emitting device of Example 14 was fabricated in the same manner as in Example 7, except that the film thickness and Al composition ratio of the p-type contact layer in Example 7 were changed as described in Table 2.

[0105] [Table 2]

[0106]

[0107] Note 1: Unable to measure

[0108] (Evaluation 1: Measurement of Film Thickness and Al Composition of Each Layer)

[0109] For each of Examples 1 to 7, 8 to 14, Comparative Examples 1 to 3, 4 to 7, and Conventional Examples 1 to 3, the film thickness of each layer formed by epitaxial growth was measured using an optical interference film thickness measuring device. In addition, for layers with a film thickness as thin as several nm to several tens of nm, including barrier layers and electron blocking layers, the film thickness and Al composition ratio of each layer were measured using TEM-EDS in cross-sectional observation of each layer using a transmission electron microscope. It should be noted that the film thickness of each layer was measured at the center of the wafer.

[0110] (Evaluation 2: Reliability evaluation)

[0111] For the light-emitting elements obtained from Examples 1 to 7, 8 to 14, Comparative Examples 1 to 3, 4 to 7, and Existing Examples 1 to 3 (the number of measurements was 24), a constant current voltage power supply was used to conduct electricity at a current of 20 mA, and the light-emitting output was measured. Then, after conducting electricity at 100 mA for 3 seconds, electricity was conducted again at 20 mA, and the light-emitting output was measured. The change in light-emitting output relative to the initial light-emitting output was measured. At this time, the area of ​​light emitted by conducting electricity was 0.057 mm 2 . Confirm the number of light-emitting elements whose luminous output drops to less than half of the initial luminous output after being energized with 100mA for 3 seconds, that is, quenching occurs. In Examples 1 to 7 and Existing Examples 1 to 3, there is no obvious change even after energizing with a current of 100mA, but in Comparative Examples 1 to 3, after energizing with a current of 100mA, it is confirmed that there are light-emitting elements in the chip that are not lit or whose output is less than half of the initial luminous output (that is, quenching is confirmed). The ratio of light-emitting elements that fail to light up and whose luminous output drops sharply to less than half of the initial luminous output is shown in Table 2 as the quenching incidence rate. It should be noted that an integrating sphere was used when measuring the luminous output Po. The average value of the initial luminous output and the results of the quenching incidence rate are shown in Table 2. It should be noted that the luminescent center wavelength of each sample was measured using a fiber optic spectrometer. The luminescent center wavelength is also shown in Table 2.

[0112] (Evaluation 3: Measurement of surface roughness Ra)

[0113] As a representative example, an AFM image was obtained using an atomic force microscope (AFM) for the outermost surface of the p-type contact layer of Examples 1 to 5 and Comparative Example 1, and Ra (average roughness; based on JIS B 0601:2001) was measured as an indicator of surface roughness. It should be noted that the measurement site was the center of the wafer. The measured values ​​of Ra are shown in Table 2. It should be noted that for Examples 1 to 5 and Comparative Example 1, the presence or absence of pits based on substrate observation is also shown. Furthermore, the AFM images based on Examples 1 to 3 and Comparative Example 1 are shown in Table 2, respectively. Figure 4A to Figure 4D .

[0114] (Review of evaluation results)

[0115] In Examples 1 to 7 based on the conditions of the present invention, when compared at the same wavelength, reliability was ensured and the luminous output was increased compared to each of the prior art examples 1 to 3. In Comparative Examples 1 and 2, the light absorption from the luminescent layer was suppressed by thinning the p-type contact layer, and as a result, the luminous output was increased, but the occurrence of quenching was confirmed. In Comparative Example 3, quenching occurred frequently from the initial power-on, and even the luminous output could not be measured.

[0116] Depend on Figure 4A to Figure 4D The AFM images shown and the values ​​of the surface roughness Ra of Examples 1 to 5 and Comparative Example 1 confirm that quenching occurs even when the surface roughness is sufficiently small. From the observation of pits in Examples 1, 2, 4 and Comparative Example 1, it can be judged that it is important to prevent quenching while filling the unevenness or dislocations of the electron blocking layer and suppressing the increase of crystal defects associated with the relaxation of the compressive strain.

[0117] In addition, when comparing Examples 1 to 5, 8 to 11 with a wavelength of 280 nm with Comparative Examples 1, 4 to 7, and Conventional Example 1, it can be seen that by setting the Al composition ratio of the p-type contact layer in the range of 0.03 to 0.25 and the film thickness in the range of 10 to 50 nm, a light-emitting element with no quenching and a larger light output than the conventional one can be obtained. It can also be seen that the same results can be observed in Examples 6, 12, and 13 with a wavelength of 310 nm and Examples 7 and 14 with a wavelength of 265 nm.

[0118] From the above results, it was confirmed that by forming a p-type contact layer that satisfies the conditions of the present invention, high light emission output can be obtained while achieving reliability.

[0119] Industrial Applicability

[0120] According to the present invention, a Group III nitride semiconductor light emitting device having both high light emission output and excellent reliability and a method for manufacturing the same can be provided.

[0121] Description of Reference Numerals

[0122] 10 substrate

[0123] 20 Buffer layer

[0124] 30 n-type semiconductor layer

[0125] 40 Luminous Layer

[0126] 41 Well layer

[0127] 42 Barrier layer

[0128] 60 p-type AlGaN electron blocking layer

[0129] 70 p-type contact layer

[0130] 71 p-type AlGaN contact layer

[0131] 72 p-type GaN layer

[0132] 80 p side reflective electrode

[0133] 90 n side electrode

[0134] 100 Group III nitride semiconductor light emitting device

Claims

1. A group III nitride semiconductor light emitting device, characterized in that: It has an n-type semiconductor layer, a light-emitting layer, a p-type AlGaN electron blocking layer, a p-type contact layer and a p-side reflective electrode on a substrate in sequence. The light emitted from the light emitting layer has a central wavelength of 250 nm to 280 nm. The Al composition ratio of the p-type AlGaN electron blocking layer is greater than or equal to 0.40 and less than or equal to 0.

80. The p-type contact layer has a film thickness of 10 nm to 50 nm, and includes a p-type AlGaN contact layer having an Al composition ratio of 0.03 to 0.

25.

2. The Group III nitride semiconductor light emitting device according to claim 1, wherein: The p-type contact layer is composed only of the p-type AlGaN contact layer.

3. The Group III nitride semiconductor light emitting device according to claim 1, wherein: The p-type contact layer includes a p-type GaN contact layer between the p-type AlGaN contact layer and the p-side reflective electrode.

4. The Group III nitride semiconductor light emitting device according to any one of claims 1 to 3, wherein The p-type AlGaN contact layer has a thickness of not less than 10 nm and not more than 25 nm.

5. A method for manufacturing a group III nitride semiconductor light emitting device, characterized in that: It includes the following steps: The step of forming an n-type semiconductor layer on a substrate; forming a light-emitting layer on the n-type semiconductor layer; forming a p-type AlGaN electron blocking layer on the light-emitting layer; forming a p-type contact layer on the p-type AlGaN electron blocking layer; and forming a p-side reflective electrode on the p-type contact layer, The central wavelength of light emitted from the light-emitting layer is 250 nm or more and 280 nm or less. The Al composition ratio of the p-type AlGaN electron blocking layer is greater than or equal to 0.40 and less than or equal to 0.

80. The thickness of the p-type contact layer is not less than 10 nm and not more than 50 nm. The p-type contact layer includes a p-type AlGaN contact layer having an Al composition ratio of 0.03 to 0.25.

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