Light-emitting element and method for manufacturing the same

Abstract

To provide a light emitting element having a p-electrode with high UV reflectivity and ohmic contactable, and a method for manufacturing the same.SOLUTION: A light emitting element having group III nitride semiconductors having an emission wavelength of 200 nm to 280 nm comprises: a semiconductor layer stacked in the order of n-layer 11, light-emitting layer 12, and p-layer 14; and a p-electrode provided in contact with the p-layer 14, and the p-electrode comprises: a contact layer provided in contact with the p-layer 14, having a thickness of between 0.5 nm and 6 nm, and made of Ru or Ni / Au; and a reflective layer provided in contact with the contact layer, having a thickness of 50 nm or more, and consisting of Al or an Al-based alloy.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a light-emitting device and a method for manufacturing the same. [Background technology]

[0002] In recent years, ultraviolet LEDs (UV LEDs) made of group III nitride semiconductors with an emission wavelength of UVC (wavelength 200-280 nm) have attracted attention for their use in sterilizing and disinfecting water and air, and research and development aimed at increasing the efficiency of UV LEDs are actively underway.

[0003] Patent Document 1 describes a structure for a p-electrode in a UVC-emitting group III nitride semiconductor, in which a Rh layer with a thickness of 10 nm or less is in contact with the p-type semiconductor layer, and an Al layer with a thickness of 20 nm or more is in contact with the Rh layer. It is described that such a structure can reduce contact resistance and improve reflectivity. It is also described that by annealing the p-electrode, the Rh layer and the Al layer mix together, improving reflectivity compared to a single Rh layer. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-30948 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Currently, materials capable of ohmic contact with p-AlGaN and p-GaN have low reflectivity to ultraviolet (especially UVC) light. While Al has high reflectivity to ultraviolet light, it cannot make ohmic contact with p-AlGaN or p-GaN. Therefore, there has been a demand for a p-electrode that has high ultraviolet reflectivity and is capable of ohmic contact.

[0006] In addition, in Patent Document 1, there is a possibility that the p layer and Al may come into contact due to the diffusion of Al, and there is a possibility that the contact resistance may deteriorate.

[0007] The present invention has been made in view of such a background, and an object thereof is to provide a light-emitting device having a p electrode with high ultraviolet reflectance and capable of ohmic contact, and a method for manufacturing the same.

Means for Solving the Problems

[0008] One aspect of the present invention is In a light-emitting device composed of a group III nitride semiconductor having an emission wavelength of 200 nm or more and 280 nm or less, a semiconductor layer laminated in the order of an n layer, a light-emitting layer, and a p layer, a p electrode provided in contact with the p layer, having the p electrode is a contact layer provided in contact with the p layer, having a thickness of 0.5 nm or more and 6 nm or less, and being Ru or Ni / Au, a reflective layer provided in contact with the contact layer, having a thickness of 50 nm or more, and being Al or an alloy mainly composed of Al, death, The interface between the contact layer and the reflective layer does not have a region where the material of the contact layer and the material of the reflective layer are mixed. in the light-emitting device.

[0009] Another aspect of the present invention is In a method for manufacturing a light-emitting device composed of a group III nitride semiconductor having an emission wavelength of 200 nm or more and 280 nm or less, a semiconductor layer forming step of forming a semiconductor layer by laminating an n layer, a light-emitting layer, and a p layer in this order on the surface of a substrate, a contact layer forming step of forming a contact layer having a thickness of 0.5 nm or more and 6 nm or less and being Rh, Ru, or Ni / Au in contact with the p layer, a heat treatment step of performing heat treatment to reduce the contact resistance with respect to the p layer after the contact layer forming step, After the heat treatment step, a reflective layer having a thickness of 50 nm or more and being Al or an alloy mainly composed of Al is formed in contact with the contact layer, and a p electrode in which the contact layer and the reflective layer are laminated in order is formed. Furthermore, no heat treatment is performed after the formation of the reflective layer. It is in the manufacturing method of a light emitting element.

Effect of the Invention

[0010] In the above light emitting element, while an ohmic contact with the p layer is enabled by the contact layer, ultraviolet rays can also be reflected by the reflective layer.

[0011] As described above, according to the above aspect, it is possible to provide a light emitting element having a p electrode with high ultraviolet reflectivity and capable of ohmic contact, and a manufacturing method thereof.

Brief Description of the Drawings

[0012] [Figure 1] It is a cross-sectional view perpendicular to the main surface of the substrate showing the configuration of the light emitting element in the embodiment. [Figure 2] It is a diagram showing the planar pattern of the electrode of the light emitting element in the embodiment. [Figure 3] It is a diagram showing the manufacturing process of the light emitting element in the embodiment. [Figure 4] It is a diagram showing the manufacturing process of the light emitting element in the embodiment. [Figure 5] It is a diagram showing the manufacturing process of the light emitting element in the embodiment. [Figure 6] It is a diagram showing the manufacturing process of the light emitting element in the embodiment. [Figure 7] It is a diagram showing the manufacturing process of the light emitting element in the embodiment. [Figure 8] It is a diagram showing the manufacturing process of the light emitting element in the embodiment. [Figure 9] It is a diagram showing the manufacturing process of the light emitting element in the embodiment. [Figure 10] It is a diagram showing the manufacturing process of the light emitting element in the embodiment. [Figure 11] Graph showing the reflectivities of samples a to e. [Figure 12] A graph showing the reflectance of samples f and g. [Figure 13] A graph showing the reflectance of samples h and i. [Modes for carrying out the invention]

[0013] The light-emitting element has an emission wavelength of 200 nm to 280 nm and is made of a group III nitride semiconductor. It also has a semiconductor layer stacked in the order of an n layer, an emission layer, and a p layer, and a p electrode provided in contact with the p layer. The p electrode is provided in contact with the p layer and has a contact layer with a thickness of 0.5 nm to 6 nm, made of Ru or Ni / Au, and a reflective layer provided in contact with the contact layer and has a thickness of 50 nm or more, made of Al or an alloy mainly composed of Al.

[0014] In the above-described light-emitting element, the contact layer is made of Ru, and the contact resistivity of the p electrode is 2 × 10⁻¹⁰ -3 Ω·cm 2 The reflectance at the emission wavelength may be 55% or higher.

[0015] In the above-described light-emitting element, the contact layer is Ni / Au, and the contact resistivity of the p electrode is 2 × 10⁻⁶. -3 Ω·cm 2 The reflectance at the emission wavelength may be 40% or higher.

[0016] In the above-described light-emitting element, the interface between the contact layer and the reflective layer does not necessarily have to have a region where the material of the contact layer and the material of the reflective layer are mixed.

[0017] The manufacturing method of a light-emitting device is a method for manufacturing a light-emitting device composed of a group III nitride semiconductor having an emission wavelength of 200 nm or more and 280 nm or less. And, a semiconductor layer forming step of forming a semiconductor layer by laminating an n-layer, a light-emitting layer, and a p-layer in this order on the surface of a substrate, a contact layer forming step of forming a contact layer, which is Rh, Ru, or Ni / Au with a thickness of 0.5 nm or more and 6 nm or less, in contact with the p-layer, a heat treatment step of performing a heat treatment for reducing the contact resistance with respect to the p-layer, and a p electrode forming step of forming a reflective layer having a thickness of 50 nm or more and being Al or an alloy mainly composed of Al in contact with the contact layer, and laminating the contact layer and the reflective layer in this order to form a p electrode.

[0018] In the manufacturing method of the above light-emitting device, the contact layer is Rh, and the contact resistivity of the p electrode may be 2×10 -2 Ω·cm 2 or less, and the reflectance at the emission wavelength may be 70% or more.

[0019] The contact layer is Ru, and the contact resistivity of the p electrode may be 2×10 -3 Ω·cm 2 or less, and the reflectance at the emission wavelength may be 55% or more.

[0020] The contact layer is Ni / Au, and the contact resistivity of the p electrode may be 2×10 -3 Ω·cm 2 or less, and the reflectance at the emission wavelength may be 40% or more.

[0021] (Embodiment) FIG. 1 is a diagram showing the configuration of a light-emitting device in an embodiment, and is a cross-sectional view perpendicular to the substrate. Further, FIG. 2 is a diagram showing the planar pattern of the electrode of the light-emitting device in the embodiment. The light-emitting device in the embodiment is a flip-chip type ultraviolet light-emitting device, and the emission wavelength is UVC, for example, 200 to 280 nm.

[0022] 1. Configuration of the light-emitting device As shown in Figure 1, the light-emitting element in this embodiment includes a substrate 10, an n-layer 11, a light-emitting layer 12, an electron blocking layer 13, a p-layer 14, a p-electrode 15, an n-electrode 16, pn-electrodes 17A and 17B, a protective film 18, a reflective film 19, a p-pad electrode 20, an n-pad electrode 21, and an anti-reflective film 22. Each of these components will be described below.

[0023] The substrate 10 is made of sapphire with the c-plane as the main surface. In addition to sapphire, any material can be used as long as it has high transmittance to the emission wavelength and can grow a group III nitride semiconductor. The thickness of the substrate 10 is, for example, 0.4 to 1 mm. By keeping it within this range, the light extraction efficiency can be improved. On the other hand, because the substrate 10 is thicker, heat tends to accumulate inside the light-emitting element, reducing heat dissipation and causing a decrease in the element's lifespan. Therefore, in this embodiment, the heat dissipation is improved by using an electrode pattern as described later.

[0024] An anti-reflective coating 22 is provided on the back surface of the substrate 10 (the side opposite to the n-layer 11 side, which is the light extraction side). By providing the anti-reflective coating 22, the reflection of ultraviolet light from the back surface of the substrate 10 back to the element side is suppressed, thereby improving light extraction.

[0025] The anti-reflective coating 22 has a structure consisting of a single layer or alternating layers of materials with different refractive indices, with the thickness of each layer set so that reflections are weakened by light interference. The material of the anti-reflective coating 22 is an insulator that is transparent to UVC. Examples include SiO2, HfO2, and MgF2.

[0026] The n-layer 11 is located on the substrate 10 via a buffer layer (not shown). The n-layer 11 is made of n-AlGaN. The n-type impurity is Si, and the Si concentration is 5 × 10⁻⁶ 18 ~5×10 19 / cm 3 The n-layer 11 may consist of multiple layers.

[0027] The light-emitting layer 12 is located on the n layer 11. The light-emitting layer 12 has an MQW structure in which well layers and barrier layers are alternately stacked in a repeating manner. The number of repeats is, for example, 2 to 5. The well layers are made of AlGaN, and their Al composition is set according to the desired emission wavelength. The barrier layers are AlGaN with a higher Al composition than the well layers. It may also be AlGaInN, which has a higher bandgap energy than the well layers. The light-emitting layer 12 may also have an SQW structure.

[0028] The electron blocking layer 13 is located on the light-emitting layer 12. The electron blocking layer 13 is made of p-AlGaN with a higher Al composition ratio than the barrier layer of the light-emitting layer 12. The electron blocking layer 13 suppresses the diffusion of electrons injected from the n electrode 16 beyond the light-emitting layer 12 to the p layer 14 side.

[0029] The p-layer 14 is located on the electron blocking layer 13. The p-layer 14 is made of p-AlGaN. In this embodiment, all semiconductor layers from the n-layer 11 to the p-layer 14 are AlGaN, thereby suppressing ultraviolet absorption by the semiconductor layers. The Al composition of the p-layer 14 is, for example, 5-80%. The p-type impurity is Mg. The Mg concentration is 1 × 10⁻⁶ 19 / cm 3 That concludes the explanation. The p layer 14 may be composed of multiple layers with different Al compositions and Mg concentrations. In that case, the layer in contact with the p electrode 15 may be p-AlGaN with an Al composition of 5-80%. Furthermore, the p layer 14 is not limited to AlGaN, but may be any group III nitride semiconductor containing Al, such as AlGaInN.

[0030] In a portion of the surface of the p-layer 14, holes 23 are formed to a depth that reaches the n-layer 11. The holes 23 are dot-shaped, and multiple holes 23 are arranged in a grid pattern (see Figure 2). However, no holes 23 are provided in the region below the p-pad electrode 20 (one corner in the rectangular pattern of the element). The n-layer 11 is exposed at the bottom of the holes 23. By arranging the holes 23 to expose the n-layer 11 in a dot-shaped pattern, uniformity of light emission within the plane is ensured, while minimizing the reduction in the light emission area (area of ​​the p-layer 14) due to the holes 23, thereby improving the light output.

[0031] The planar pattern of each hole 23 is, for example, a circle. Alternatively, it may be a polygon such as a regular hexagon. In the case of a regular hexagon, it is preferable to make the side surface of the hole 23 the m-face. The arrangement pattern of the holes 23 can be, for example, a square grid, a regular triangular grid, or a honeycomb pattern.

[0032] The p electrode 15 (contact layer) is provided on the p layer 14. The p electrode 15 is provided on the surface of the p layer 14, excluding the vicinity of the edges of the p layer 14 (see Figure 2), thereby providing a wide light-emitting area. The p electrode 15 is a reflective electrode that reflects ultraviolet light emitted from the light-emitting layer 12 towards the substrate 10, thereby increasing the light extraction efficiency.

[0033] The material of the p electrode 15 is a material with low contact with the p layer 14 and high UVC reflectivity, and is Rh, Ru, or Ni / Au. The thickness of the p electrode 15 is 0.5 to 6 nm. For Ni / Au, the thickness of the Ni layer only needs to be one atomic layer or more. By using such a thickness, the contact resistance to the p electrode 15 is reduced while allowing ultraviolet light to pass through and be reflected by the Al layer of the pn electrode 17A.

[0034] To reduce contact resistance while further increasing ultraviolet reflectivity, the thickness of the p electrode 15 is preferably 1 to 4 nm.

[0035] The ratio of the area of the p - electrode 15 to the area on the upper surface of the element (the total area of the holes 23 and the p - layer 14) shall be 70% or more. The planar patterns of the holes 23 and the p - electrode 15 are set to satisfy this. For example, the diameter, the number of arrays, and the array pitch of the holes 23 are adjusted. By making the area of the p - electrode 15 wider, the reflection of ultraviolet rays by the p - electrode 15 can be increased, and the light extraction efficiency can be improved. More preferably, it is 75% or more.

[0036] The n - electrode 16 is provided on the n - layer 11 exposed at the bottom surface of each hole 23. Therefore, the n - electrode 16 also has a dot - shaped arranged pattern (see Fig. 2). The material of the n - electrode 16 is a structure obtained by heat - treating V / Al / Ti. Other materials such as Ti / Al / Ti can also be used. The structure obtained by heat - treating V / Al / Ti is specifically a structure in which a layer made of AlN x a layer made of a metal mainly composed of Al and containing V and Ti, and a layer made of Ti are laminated in this order.

[0037] AlN x The layer made of AlN has a thickness of 1 - 3 nm. x is, for example, 0.4 - 0.7. Also, x may decrease as it moves away from the n - layer 11 in the thickness direction. In this case, the average of x in the thickness direction is 0.4 - 0.7. Also, there may be diffusion of Ga from the n - layer 11 side. In that case, Al y Ga 1-y N x (0.4 ≤ x ≤ 0.7). If the Al composition ratio of the n - layer 11 is a, then a < y ≤ 1. y is, for example, 0.7 or more. Also in this case, x may decrease as it moves away from the n - layer 11 in the thickness direction, and y may increase as it moves away from the n - layer 11 in the thickness direction.

[0038] The layer made of a metal mainly composed of Al and containing V and Ti has a thickness of 50 - 500 nm. The ratios of Al, V, and Ti are, for example, Al is 50 - 85 mol%, V is 5 - 20 mol%, and Ti is 10 - 30 mol%. <00002​In the above structure, the contact resistance of the n electrode 16 with respect to the n layer 11 is reduced. For example, the contact resistivity of the n electrode 16 with respect to the n layer 11 is 4 × 10⁻⁶. -4 Ω·cm 2 The reason is as follows. Firstly, AlN x This is thought to be because the layer consisting of these components functions as a good contact layer for the n layer 11. Secondly, it is thought that nitrogen vacancies are formed on the surface of the n layer 11, causing it to become n-type, which reduces the contact resistance.

[0040] The Ti layer is provided as a cover to suppress the evaporation of Al in the n electrode 16 during alloying. In addition to Ti, TiN, Ni, Pt, Au, etc. can also be used.

[0041] The pn electrodes 17A and 17B are provided on the p electrode 15 and the n electrode 16, respectively. The planar pattern of the pn electrode 17A is the same as that of the p electrode 15. The planar pattern of the pn electrode 17B is the same as that of the n electrode 16, and is a pattern consisting of multiple dots arranged in a grid.

[0042] The materials of the pn electrodes 17A and 17B are Al / Ti / Ni / Au / Al. The first layer of the pn electrodes 17A and 17B, the Al layer, is in contact with the p electrode 15 and the n electrode 16, respectively. The Al layer is a reflective layer that reflects ultraviolet light. Since the pn electrode 17A is formed after the heat treatment of the p electrode 15, atomic diffusion does not occur between the p electrode 15 and the Al layer, and the interface between the p electrode 15 and the Al layer does not contain a layer where the p electrode material and Al are mixed. Therefore, ultraviolet light can be reflected by the Al layer without impairing the contact resistance reduction effect of the p electrode 15. In other words, it is possible to achieve both a reduction in the forward voltage Vf and an improvement in the light extraction efficiency.

[0043] For example, if the ratio is Rh / Al, the contact resistivity will be 2 × 10⁻⁶. -2 Ω·cm 2The ultraviolet reflectance in UVC can be set to 70% or higher. Also, for example, when using Ru / Al, the contact resistivity can be set to 3 × 10⁻⁶. -3 Ω·cm 2 The ultraviolet reflectance in UVC can be set to 55% or higher. Furthermore, for example, when using Ni / Au / Al, the contact resistivity can be set to 2 × 10⁻⁶. -3 Ω·cm 2 The following allows for a UVC ultraviolet reflectance of 40% or more.

[0044] The thickness of the Al layer in pn electrodes 17A and 17B is 10 to 500 nm. This range allows for sufficiently high UV reflectivity. UV reflectivity due to the Al layer increases with thickness up to around 50 nm, saturating above 50 nm. Therefore, considering variations in Al layer thickness, a thickness of 80 nm or more is preferable. On the other hand, considering reflectivity saturation, material cost, and deposition time, a thickness of 200 nm or less is preferable.

[0045] In this embodiment, Al / Ti / Ni / Au / Al is used for the pn electrodes 17A and 17B, but other materials may be used as long as the first layer in contact with the p electrode 15 is Al. Alternatively, an alloy mainly composed of Al may be used instead of Al.

[0046] The protective film 18 is provided so as to cover the entire upper surface of the element. Specifically, it is continuously provided on the sides and surface of the p electrode 15, n electrode 16, and pn electrodes 17A and 17B, on the surface and sides of the semiconductor layer (n layer 11, light-emitting layer 12, electron blocking layer 13, p layer 14), on the side of the element isolation groove 26, and inside the hole 23. The material of the protective film 18 is SiO2 or the like.

[0047] The protective film 18 consists of two layers, a first protective film 18A and a second protective film 18B, with a reflective film 19 made of Al provided between the first protective film 18A and the second protective film 18B. The reflective film 19 is provided over the entire surface except for the areas where the holes 24 and 25 described later are located. The reflective film 19 reflects light towards the substrate 10, thereby improving the light extraction efficiency. Furthermore, embedding the reflective film 19 in the protective film 18 improves the heat dissipation of the protective film 18 and prevents migration of the reflective film 19.

[0048] The material of the reflective film 19 is not limited to Al; any material with high reflectivity at the emission wavelength is acceptable. An alloy mainly composed of Al is also acceptable. Furthermore, the reflective film 19 may be placed within the first protective film 18A or the second protective film 18B, rather than between the first protective film 18A and the second protective film 18B. When multiple reflective films 19 are provided, the planar patterns may be varied. In addition, the first protective film 18A and the second protective film 18B may be made of the same material or different materials.

[0049] The p-pad electrode 20 and the n-pad electrode 21 are spaced apart on the protective film 18. The p-pad electrode 20 is connected to the pn electrode 17A via a hole 24 made in the protective film 18. The n-pad electrode 21 is connected to each pn electrode 17B via a hole 25 made in the protective film 18. The material of the p-pad electrode 20 and the n-pad electrode 21 is, for example, Ti / Pt / Au / AuSn.

[0050] As shown in Figure 2, the planar patterns of the p-pad electrode 20 and the n-pad electrode 21 are formed by dividing a rectangular pattern slightly inside the element's rectangular pattern into two sections at the corners of the rectangle by a linear region of width W along a straight line L that forms a 45° angle with respect to the sides of the rectangle. The section forming a right-angled isosceles triangle is designated as the p-pad electrode 20, and the other section (a pentagon with the corners of the rectangle cut off) is designated as the n-pad electrode 21. The n-electrode 16 is not located below the p-pad electrode 20, while all of the n-electrode 16 is located below the n-pad electrode 21 and is connected to the n-pad electrode 21.

[0051] The angle of the linear region is not limited to 45°, but in order to reduce the area of ​​the linear region and maximize the sum of the areas of the p-pad electrode 20 and the n-pad electrode 21, it is preferable that it be close to 45°, for example, 30 to 60° is preferable, and 40 to 50° is more preferable.

[0052] Furthermore, it is preferable to set the position and width W of the linear region such that the sum of the areas of the p-pad electrode 20 and the n-pad electrode 21 is 90% or more of the light-emitting area (area of ​​the p-electrode 15). Of course, the width W is such that a short circuit does not occur between the p-pad electrode 20 and the n-pad electrode 21. For example, the width W is 100 μm or more. Also, the p-pad electrode 20 is sized to allow good contact with the sub-mount side. This is to increase the heat dissipation area (the area of ​​the p-electrode 15 that is in contact with the sub-mount in a plan view) and improve heat dissipation.

[0053] By arranging the planar patterns of the p-pad electrode 20 and the n-pad electrode 21 as described above, the sum of the areas of the p-pad electrode 20 and the n-pad electrode 21 can be increased, thereby widening the heat dissipation area and improving the heat dissipation performance of the light-emitting element. In particular, with UVC light-emitting elements, it is necessary to increase the thickness of the substrate 10 to improve the light extraction efficiency, which reduces heat dissipation. However, as described above, heat dissipation can be improved, ensuring sufficient heat dissipation even when the substrate is thickened.

[0054] As described above, in the light-emitting element of this embodiment, a p electrode 15 made of Rh, Ru, or Ni / Au with a thickness of 0.5 to 6 nm is used, and an Al layer is used as the first layer of the pn electrode 17A. Therefore, it is possible to improve the ultraviolet reflectance while enabling ohmic contact with the p layer 14. As a result, the light-emitting element of this embodiment can achieve both a reduction in the forward voltage Vf and an improvement in the light extraction efficiency.

[0055] 2. Manufacturing process for light-emitting elements The manufacturing process for the light-emitting element in the embodiment will be described with reference to the figure.

[0056] First, a substrate 10 made of sapphire is prepared. Then, an n-layer 11, an emissive layer 12, an electron-blocking layer 13, and a p-layer 14 are sequentially formed on the substrate 10 by the MOCVD method (see Figure 3).

[0057] Next, a predetermined area of ​​the p layer 14 is dry-etched to form multiple holes 23 that reach a depth of the n layer 11 (see Figure 4).

[0058] Next, a p-electrode 15 is formed on the p-layer 14 by sputtering or vapor deposition (see Figure 5). Then, an n-electrode 16 is formed on the n-layer 11 exposed at the bottom of the hole 23 by sequentially laminating a V-layer, an Al-layer, and a Ti-layer by sputtering or vapor deposition (see Figure 6). The n-electrode 16 may be formed before the p-electrode 15, but in this embodiment, the p-electrode 15 is formed first in order to keep the surface of the p-layer 14 as clean as possible when forming the p-electrode 15.

[0059] Next, a heat treatment is performed at a temperature of 500-650°C for 1-10 minutes. The atmosphere is an inert gas atmosphere, such as nitrogen. The heat treatment is preferably carried out under reduced pressure, for example, 1 × 10⁻⁶ 2 ~1 × 10 4 The pressure is Pa. The heat treatment temperature is preferably 500-600°C. When Ni / Au is used as the p electrode 15, the heat treatment is performed in an oxygen-containing atmosphere.

[0060] This heat treatment serves both to activate the Mg in the p layer 14 and to reduce the contact resistance of the p electrode 15 and n electrode 16.

[0061] In this embodiment, the heat treatment temperature is reduced by using V / Al / Ti as the n electrode 16, and the number of heat treatments is reduced by combining and simultaneously performing the Mg activation treatment of the p layer 14 and the reduction of the contact resistance of the p electrode 15 and the n electrode 16. As a result of lowering the heat treatment temperature and reducing the number of heat treatments, the deterioration of the electrical characteristics of the light-emitting element can be suppressed.

[0062] Here, the n electrode 16 changes to the following structure due to the heat treatment described above. Of the V / Al / Ti in the n electrode 16, V diffuses into Al and does not diffuse into the n layer 11 or Ti. As a result of this diffusion, the V layer disappears. Also, the Al in V / Al / Ti reacts with N in the n layer 11, and AlN forms at the interface between the n layer 11 and the Al layer. x A structure is formed. V is thought to act as a catalyst to promote the reaction between Al and N. As a result of this heat treatment, the structure of the n electrode 16 is AlN x It transforms into a three-layer structure consisting of a layer made of [material name], a layer made of a metal mainly composed of Al and containing V and Ti, and a layer made of Ti.

[0063] The change in the structure of the n electrode 16 reduces the contact resistance of the n electrode 16 to the n layer 11. The reason for this is as already stated. Specifically, firstly, AlN x It is thought that the layer consisting of AlN functions as a good contact layer for the n layer 11, and secondly, x It is thought that the formation of nitrogen vacancies in the n layer 11 further promoted the n-type transformation of the n layer 11.

[0064] Next, pn electrodes 17A and 17B are formed on the p electrode 15 and n electrode 16, respectively, by sputtering and deposition (see Figure 7). The pn electrodes 17A and 17B are made of Al / Ni / Au / Al, and the first layer, the Al layer, is in contact with the p electrode 15.

[0065] Here, the pn electrode 17A is formed after heat treatment of the p electrode 15, but no heat treatment is performed after the formation of the pn electrode 17A. Therefore, atomic diffusion does not occur between the p electrode 15 and the first layer Al layer of the pn electrode 17A, and no region is formed at the interface between the p electrode 15 and the Al layer where atoms of the p electrode 15 and Al are mixed. As a result, it is possible to improve the ultraviolet reflectivity of the Al layer without impairing good contact between the p electrode 15 and the p layer 14.

[0066] Next, an element isolation groove 26 is formed. The element isolation groove 26 is to a depth that exposes the substrate 10. Next, a first protective film 18A is formed to cover the entire upper surface of the element (see Figure 8). The first protective film 18A can be formed by CVD, sputtering, vapor deposition, ALD, etc. Sputtering, CVD, and ALD are preferred due to the density of the film.

[0067] Next, a reflective film 19 made of Al is formed on the first protective film 18A, excluding the areas where pores 24 and 25 will later be formed (see Figure 9). The reflective film 19 is formed by vapor deposition or sputtering, and the patterning is done by wet etching.

[0068] Next, a second protective film 18B is formed on the first protective film 18A and the reflective film 19. The second protective film 18B can be formed by CVD, sputtering, vapor deposition, ALD, etc. Sputtering is preferred due to the density of the film. This forms a protective film 18 with a structure in which the first protective film 18A and the second protective film 18B are stacked in order, with the reflective film 19 formed in between (see Figure 10).

[0069] Furthermore, it is preferable that the protective film 18 is not formed on the bottom surface of the element separation groove 26, and that the protective film 18 is separated for each element. This is to prevent force from being applied to the protective film 18 or fluctuations in the stress of the protective film 18 from occurring when separating the elements.

[0070] Next, a predetermined area of ​​the protective film 18 is dry-etched to form holes 24 and 25 that reach the pn electrodes 17A and 17B. Then, a p-pad electrode 20 and an n-pad electrode 21 are formed on the protective film 18, with the p-pad electrode 20 connected to the pn electrode 17A via hole 24 and the n-pad electrode 21 connected to the pn electrode 17B via hole 25. The patterns of the p-pad electrode 20 and n-pad electrode 21 are shown in Figure 2. The film deposition of the p-pad electrode 20 and n-pad electrode 21 is done by evaporation or sputtering, and the patterning is done by lift-off.

[0071] Next, the back surface of the substrate 10 is polished to a predetermined thickness, and then an anti-reflective film 22 is formed on the back surface of the substrate 10. Then, the substrate 10 is divided into individual elements. Through these steps, the light-emitting element in the embodiment shown in Figure 1 is manufactured.

[0072] 3. Experimental Results Various experimental results according to the embodiment will be described.

[0073] Experimental Example 1 Ni / Au was formed on a sapphire substrate, heat-treated, and then an Al layer was formed on top of the Au layer. The reflectance was measured by irradiating the sapphire substrate with ultraviolet light at a wavelength of 275 nm. For comparison, the reflectance of a Ni / Au-only layer was also measured in the same manner.

[0074] Figure 11 is a graph showing the reflectance of samples a to e. Samples a to e differ in the thickness of the Ni / Au layer and the presence or absence of an Al layer. The thicknesses of the Ni / Au layer and the Al layer in each sample a to e are shown in Table 1 below. In Table 1, the Ni / Au column includes the total thickness, as well as the thicknesses of the Ni and Au layers in parentheses.

[0075] [Table 1]

[0076] As shown in Figure 11, it was found that in the Ni / Au / Al structure, the reflectivity improves as the Ni / Au layer thins. In particular, it was found that if the thickness of the Ni / Au layer is 6 nm or less, the reflectivity can be improved compared to the Ni / Au-only structure, and the reflectivity can be increased to 35% or more. Therefore, it was found that by setting the thickness of the Ni / Au layer to 6 nm or less in the Ni / Au / Al structure, it is possible to improve the ultraviolet reflectivity while enabling ohmic contact with the p-layer 14.

[0077] Experimental Example 2 An Rh layer was formed on a sapphire substrate, heat-treated, and then an Al layer was formed. The reflectance was measured in the same manner as in Experimental Example 1. For comparison, the reflectance was also measured in the case where only Rh was used.

[0078] Figure 12 is a graph showing the reflectance of samples f and g. Sample f is a single layer of Rh with a thickness of 150 nm, while sample g is Rh / Al with a 4 nm Rh layer and a 150 nm Al layer.

[0079] As shown in Figure 12, the reflectivity of Rh / Al was found to be higher than that of a single Rh layer, and it was possible to achieve a reflectivity of over 70%. As a result, it was found that by using an Rh / Al structure, ohmic contact is possible while improving ultraviolet reflectivity.

[0080] Experimental Example 3 A Ru layer was formed on a sapphire substrate, heat-treated, and then an Al layer was formed. The reflectance was measured in the same manner as in Experimental Example 1. For comparison, the reflectance was also measured in the case where only Ru was used.

[0081] Figure 13 is a graph showing the reflectance of samples h and i. Sample h is a single layer of Ru with a thickness of 150 nm, while sample i is Ru / Al with a Ru layer of 4 nm and an Al layer of 150 nm.

[0082] As shown in Figure 13, the reflectivity of Ru / Al is higher than that of a single Ru layer, and it was found that the reflectivity can be increased to over 55%. As a result, it was found that the Ru / Al structure can improve ultraviolet reflectivity while enabling ohmic contact. [Explanation of Symbols]

[0083] 10: Circuit board 11:n layer 12: Emitting layer 13: Electron Block Layer 14:p layer 15:p electrode 16:n electrode 17A, 17B: pn electrode 18:Protective film 18A: 1st protective film 18B:Second protective film 19: Reflective film 20: p-pad electrode 21: n-pad electrode

Claims

1. In a light-emitting element made of a group III nitride semiconductor having an emission wavelength of 200 nm or more and 280 nm or less, A semiconductor layer stacked in the order of n layer, light-emitting layer, and p layer, A p-electrode provided in contact with the p-layer, It has, The p electrode is, A contact layer is provided in contact with the aforementioned p-layer, has a thickness of 0.5 nm to 6 nm, and is made of Ru or Ni / Au. The system includes a reflective layer provided in contact with the aforementioned contact layer, having a thickness of 50 nm or more, and made of Al or an alloy mainly composed of Al. A light-emitting element that does not have a region at the interface between the contact layer and the reflective layer in which the materials of the contact layer and the reflective layer are mixed.

2. The contact layer is made of Ru, and the contact resistivity of the p electrode is 3 × 10⁻¹⁰. －３ Ω・cm ２ The light-emitting element according to claim 1, wherein the reflectance at the emission wavelength is 55% or more.

3. The contact layer is Ni / Au, and the contact resistivity of the p electrode is 2 × 10⁻⁶. －３ Ω・cm ２ The light-emitting element according to claim 1, wherein the reflectance at the emission wavelength is 40% or more.

4. In a method for manufacturing a light-emitting element made of a group III nitride semiconductor having an emission wavelength of 200 nm or more and 280 nm or less, A semiconductor layer formation process involves stacking an n-layer, an emissive layer, and a p-layer on the surface of a substrate in that order to form a semiconductor layer, A contact layer formation step is to form a contact layer in contact with the aforementioned p layer, the contact layer being made of Rh, Ru, or Ni / Au with a thickness of 0.5 nm or more and 6 nm or less, After the contact layer formation step, a heat treatment step is performed to reduce the contact resistance to the p layer, The process includes a step of forming a p-electrode after the heat treatment step, by forming a reflective layer in contact with the contact layer, having a thickness of 50 nm or more and made of Al or an alloy mainly composed of Al, and sequentially stacking the contact layer and the reflective layer to form a p-electrode. A method for manufacturing a light-emitting element, wherein no heat treatment is performed after the formation of the reflective layer.

5. The contact layer is Rh, and the contact resistivity of the p electrode is 2 × 10 －２ Ω・cm ２ The method for manufacturing a light-emitting element according to claim 4, wherein the reflectance at the emission wavelength is 70% or more.

6. The contact layer is made of Ru, and the contact resistivity of the p electrode is 3 × 10 －３ Ω・cm ２ The method for manufacturing a light-emitting element according to claim 4, wherein the reflectance at the emission wavelength is 55% or more.

7. The contact layer is Ni / Au, and the contact resistivity of the p electrode is 2×10 －３ Ω·cm ２ The method for manufacturing a light-emitting device according to claim 4, wherein the reflectance at the light emission wavelength is 40% or more.

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