Method for manufacturing reflective electrode for deep ultraviolet light-emitting element, method for manufacturing deep ultraviolet light-emitting element, and deep ultraviolet light-emitting element

Abstract

A reflective electrode for a deep ultraviolet light-emitting element that achieves both high luminous output and excellent reliability is provided. The method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element according to the present invention comprises: a first step of forming Ni as a first metal layer with a thickness of 3 to 20 nm on a p-type contact layer having a superlattice structure; a second step of forming Rh as a reflective metal with a thickness of 20 nm to 2 μm on the first metal layer; and a third step of heat-treating the first and second metal layers at a temperature of 300°C to 600°C.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element, a method for manufacturing a deep ultraviolet light-emitting element, and a deep ultraviolet light-emitting element, and in particular to a method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element that can achieve both high luminous output and excellent reliability. Background Art

[0002] Group III nitride semiconductors, composed of compounds of Al, Ga, In, and nitrogen, are wide-bandgap semiconductors with a direct transition band structure. They are expected to be used in a wide range of fields, including sterilization, water purification, medical treatment, lighting, and high-density optical recording. In particular, light-emitting devices using Group III nitride semiconductors in their light-emitting layers can cover the entire range from deep ultraviolet to visible light by adjusting the content of Group III elements, and their practical application in various light sources is progressing.

[0003] Light with a wavelength of 200 to 350 nm is called deep ultraviolet light, and deep ultraviolet light-emitting elements that emit deep ultraviolet light are usually made according to the following method. 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, on the p-side electrode side of the p-type semiconductor layer, in order to form an ohmic contact, a p-type GaN contact layer that easily increases the hole concentration is usually formed. It should be noted that the light-emitting layer widely uses a multiple quantum well (MQW) structure obtained by alternating barrier layers and well layers composed of group III nitride semiconductors.

[0004] Here, one of the properties required of deep ultraviolet light-emitting devices is high external quantum efficiency. External quantum efficiency is determined by (i) internal quantum efficiency, (ii) electron injection efficiency, and (iii) light extraction efficiency.

[0005] Patent document 1 discloses a deep ultraviolet light-emitting diode, which has a p-type contact layer of AlGaN mixed crystal and a reflective electrode on the p-side that shows reflectivity to the light emitted by the light-emitting layer, with the substrate side as the light extraction direction. With respect to short-wavelength light, the higher the Al composition ratio of the p-type contact layer composed of AlGaN, the higher the transmittance of the p-type contact layer can be. To this end, Patent document 1 proposes to use a p-type contact layer composed of AlGaN with a transmittance corresponding to the emission wavelength to replace the p-type contact layer usually composed of GaN in the prior art. In addition, as the reflective electrode at this time, a metal film with Al as the main component is preferably used. And as an inserted metal layer for forming an ohmic contact, Ni is used.

[0006] Patent document 2 discloses a Group III nitride semiconductor light-emitting element in which a positive electrode on a p-type semiconductor layer (e.g., a p-type GaN layer) uses silver (Ag), rhodium (Rh), ruthenium (Ru), platinum (Pt) or palladium (Pd), and a first thin film metal layer with a thickness of 0.2 to 20 nm composed of cobalt (Co) or nickel (Ni) is provided between the p-type semiconductor layer and the positive electrode, taking into account that metals such as nickel (Ni) and cobalt (Co) reflect little visible light with a wavelength of 380 nm to 550 nm (violet, blue, and green).

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-216352

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 2000-36619 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] According to Patent Document 1, a higher transmittance of the p-type contact layer with respect to emitted light is more preferable. Therefore, according to Patent Document 1, a higher Al composition ratio of the p-type contact layer is more preferable.

[0013] However, according to the experimental results of the inventors, when the transmittance to the central emission wavelength of the emitted deep ultraviolet light is increased only by simply increasing the Al composition ratio of the p-type contact layer in contact with the p-side electrode, it is judged to be unsuitable for practical application due to the following reasons. First, by increasing the transmittance of the p-type contact layer to deep ultraviolet light, a deep ultraviolet light-emitting element with a luminous output higher than that of the prior art can indeed be obtained. However, when an overload reliability test was conducted on samples of the deep ultraviolet light-emitting element obtained in this way (specifically, energized at 100mA for 3 seconds), it was confirmed that some samples had a sudden drop in luminous output to half the initial luminous output, or a sudden inability to light up (hereinafter also referred to as "quenching").

[0014] The inventors also investigated the relationship between the type of electrode used in deep ultraviolet light-emitting diodes and the Al composition ratio of the p-type contact layer. Using rhodium (Rh), a material inferior to aluminum (Al) but with a high reflectivity in the ultraviolet region, as a reflective electrode confirmed that while it functioned well when formed on a p-type GaN layer, the aforementioned quenching occurred when formed on a single-layer p-type AlGaN layer with an Al composition of 30% or more, indicating that it could not function reliably as an electrode.

[0015] Components with such sudden deterioration in luminous output are not reliable enough, and the inclusion of such components in products is unacceptable under product quality management. Therefore, the present invention aims to provide a method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element that achieves both high luminous output and excellent reliability. Furthermore, the present invention aims to provide a method for manufacturing a deep ultraviolet light-emitting element using such a reflective electrode, and the resulting deep ultraviolet light-emitting element.

[0016] Solutions for solving problems

[0017] The present inventors have been conducting extensive research to address the aforementioned technical issues. Furthermore, through experiments, they confirmed that using rhodium (Rh), which has a high reflectivity in the ultraviolet region, as the metal material for the reflective electrode, and providing a nickel (Ni) metal layer between the rhodium and the p-type contact layer of the superlattice structure, can address the aforementioned technical issues. This led to the completion of the present invention. Specifically, the main features of the present invention are as follows.

[0018] (1) A method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element, characterized by comprising:

[0019] In the first step, Ni is formed as a first metal layer with a thickness of 3 to 20 nm on the p-type contact layer having the superlattice structure;

[0020] a second step of forming Rh as a second metal layer on the first metal layer with a thickness of not less than 20 nm and not more than 2 μm; and

[0021] In the third step, the first metal layer and the second metal layer are subjected to a heat treatment at a temperature of 300° C. to 600° C. inclusive.

[0022] (2) The method for producing a reflective electrode for a deep ultraviolet light-emitting element according to (1) above, wherein the atmospheric gas during the heat treatment in the third step contains oxygen.

[0023] (3) The method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element according to (1) or (2) above further comprises the following steps after the second step: a step of forming a Ni layer as a third metal layer on the second metal layer; and a step of forming a Rh layer as a fourth metal layer on the third metal layer.

[0024] (4) A method for manufacturing a deep ultraviolet light-emitting element, characterized in that it comprises the following steps:

[0025] forming an n-type semiconductor layer on a substrate;

[0026] forming a light-emitting layer on the n-type semiconductor layer;

[0027] forming a p-type electron blocking layer on the light-emitting layer;

[0028] forming a p-type contact layer on the p-type electron blocking layer; and

[0029] forming a reflective electrode on the p-type contact layer;

[0030] The steps of forming the p-type contact layer are repeated alternately to form an Al having an Al composition ratio x. x Ga 1-x The first step of forming the first layer composed of N, and the first step of forming the Al layer composed of Al having an Al composition ratio y lower than the Al composition ratio x y Ga 1-y N, thereby forming the p-type contact layer having a superlattice structure, and the Al composition ratio y of the second layer is greater than 0.15,

[0031] The process of forming the reflective electrode comprises:

[0032] In a first step, Ni is formed as a first metal layer with a thickness of 3 to 20 nm on the second layer on the outermost surface of the p-type contact layer;

[0033] a second step of forming Rh as a second metal layer on the first metal layer with a thickness of not less than 20 nm and not more than 2 μm; and

[0034] In the third step, the first metal layer and the second metal layer are subjected to a heat treatment at 300 to 600°C.

[0035] (5) The method for manufacturing a deep ultraviolet light-emitting element according to (4) above, wherein in the superlattice structure of the p-type contact layer,

[0036] When the Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer is w0,

[0037] The Al composition ratio x of the first layer is higher than the Al composition ratio w0,

[0038] The Al composition ratio y of the second layer is lower than the Al composition ratio x,

[0039] The Al composition ratio w0, the Al composition ratio x, the Al composition ratio y, and the thickness-averaged Al composition ratio z of the p-type contact layer satisfy the following formulas [1] and [2]:

[0040] 0.030<z-w0<0.20 ……[1]

[0041] 0.050≤xy≤0.47……[2].

[0042] (6) A method for manufacturing a deep ultraviolet light-emitting element according to the above (5), wherein a guide layer having an Al composition ratio higher than the Al composition ratio of either the barrier layer of the light-emitting layer or the p-type electron blocking layer is further provided between the well layer closest to the p-type electron blocking layer in the light-emitting layer and the p-type electron blocking layer.

[0043] (7) The method for manufacturing a deep ultraviolet light-emitting element according to (6) above, wherein the guide layer is made of AlN.

[0044] (8) The method for producing a deep ultraviolet light-emitting element according to any one of (5) to (7) above, wherein the Al composition ratio w0 is 0.25 or more and 0.60 or less.

[0045] (9) The method for manufacturing a deep ultraviolet light-emitting element according to any one of (4) to (8) above, wherein the total thickness of the p-type electron blocking layer and the p-type contact layer is 65 to 100 nm.

[0046] (10) The method for manufacturing a deep ultraviolet light-emitting element according to any one of (4) to (9) above further includes the following steps after the second step: a step of forming a Ni layer as a third metal layer on the second metal layer; and a step of forming a Rh layer as a fourth metal layer on the third metal layer.

[0047] (11) A deep ultraviolet light-emitting element, characterized in that an n-type semiconductor layer, a light-emitting layer, a p-type electron blocking layer, and a p-type contact layer are sequentially provided on a substrate.

[0048] The p-type contact layer has a superlattice structure, wherein the superlattice structure is formed by combining Al with an Al composition ratio x. x Ga 1-x The first layer is composed of N and the first layer is composed of Al with an Al composition ratio y. y Ga 1-y The second layer is formed by alternately stacking N, and the Al composition ratio y of the second layer is 0.15 or more,

[0049] A reflective electrode made of Ni and Rh is provided on the second layer on the outermost surface of the p-type contact layer.

[0050] (12) The deep ultraviolet light-emitting element according to (11) above, wherein in the superlattice structure of the p-type contact layer,

[0051] When the Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer is w0,

[0052] The Al composition ratio x of the first layer is higher than the Al composition ratio w0,

[0053] The Al composition ratio y of the second layer is lower than the Al composition ratio x,

[0054] The Al composition ratio w0, the Al composition ratio x, the Al composition ratio y, and the thickness-averaged Al composition ratio z of the p-type contact layer satisfy the following formulas [1] and [2]:

[0055] 0.030<z-w0<0.20 ……[1]

[0056] 0.050≤xy≤0.47……[2].

[0057] The deep ultraviolet light-emitting element according to (11) or (12) above, wherein the total thickness of the p-type electron blocking layer and the p-type layer of the p-type contact layer is 65 to 100 nm.

[0058] Effects of the Invention

[0059] The present invention provides a method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element that achieves both high luminous output and excellent reliability. Furthermore, the present invention provides a method for manufacturing a deep ultraviolet light-emitting element using the reflective electrode and the deep ultraviolet light-emitting element obtained thereby. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1A These are process diagrams based on schematic cross-sectional views for explaining a method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element according to one embodiment of the present invention.

[0061] Figure 1B These are process diagrams based on schematic cross-sectional views for explaining a method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element according to another embodiment of the present invention.

[0062] Figure 2 Schematic cross-sectional view illustrating a deep ultraviolet light-emitting element according to one embodiment of the present invention.

[0063] Figure 3 These are process diagrams based on schematic cross-sectional views for explaining a method for manufacturing a deep ultraviolet light-emitting element according to one embodiment of the present invention. DETAILED DESCRIPTION

[0064] Before describing the embodiments of the present invention, the following contents will be described in advance. First, in this specification, when the Al composition ratio is not clearly given and it is only marked as "AlGaN", it means that 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 element Al to Ga is not fixed. In this case, even if there is no mark about In as a group III element, "AlGaN" means that it can contain In within 5% relative to the sum of Al and Ga as group III elements. For the composition formula containing In, the Al composition ratio is marked as x0, and the In composition ratio is marked as y0 (0≤y0≤0.05), and it is recorded as Al x0 In y0 Ga 1-x0-y0 N. When simply labeled "AlN" or "GaN," it indicates that Ga and Al are not contained, respectively. However, unless otherwise specified, simply labeling "AlGaN" does not exclude either AlN or GaN. Note that the Al composition ratio can be measured by photoluminescence measurement, X-ray diffraction measurement, or the like.

[0065] 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, a layer that does not function electrically as a p-type or n-type layer without intentionally adding specific impurities such as Mg and Si is referred to as "i-type" or "undoped." Undoped layers may contain unavoidable impurities that occur during the manufacturing process. Specifically, the carrier density is low (for example, less than 4×10 16 / cm 3 ), it is referred to as "undoped" in this specification. In addition, the values of the impurity concentrations such as Mg and Si are the values obtained by SIMS analysis.

[0066] In addition, the overall thickness of each layer formed by epitaxial growth can be measured using an optical interference film thickness meter. In addition, for the thickness of each layer, when the composition of adjacent layers is significantly different (for example, when the Al composition ratio differs by more than 0.01), it can be calculated based on the cross-sectional observation of the growth layer using a transmission electron microscope. In addition, for the boundaries and thicknesses of adjacent layers with the same or substantially the same Al composition ratio (for example, less than 0.01) but different impurity concentrations, the boundaries and thicknesses of the two layers are measured using values obtained based on TEM-EDS. In addition, the impurity concentrations of the two can be measured by SIMS analysis. In addition, when the thickness of each layer is thin, such as in a superlattice structure, the thickness can be measured using TEM-EDS.

[0067] The following describes embodiments of the present invention with reference to the accompanying drawings. It should be noted that, in principle, identical components are denoted by identical reference numerals, and their descriptions are omitted. Furthermore, in each figure, for ease of explanation, the horizontal and vertical ratios of the substrate and each layer are exaggerated compared to their actual ratios.

[0068] (Reflective Electrode)

[0069] Figure 1A 8 shows a p-side reflective electrode 80 obtained by a method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element according to one embodiment of the present invention. Figure 2 FIG. 1 is a schematic cross-sectional view of a deep ultraviolet light emitting element 100 having the reflective electrode 80. Figure 1A and Figure 2 . The reflective electrode 80 can be provided directly above the p-type contact layer 70. Furthermore, the reflective electrode 80 is a reflective electrode made of a metal having a high reflectivity (for example, 60% or more) with respect to the ultraviolet light emitted from the light-emitting layer 40. In the present invention, rhodium (Rh) is used as a metal having such a reflectivity (hereinafter referred to as "reflective metal"). As rhodium (Rh), for example, commercially available metal rhodium (for example, purity 3N) can be used as an evaporation source. Furthermore, the p-type contact layer 70 has a superlattice structure, and the reflective electrode on the p-side obtained by forming the above-mentioned reflective metal on the p-type contact layer 70 with a certain thickness or more via nickel (Ni) has a high reflectivity for deep ultraviolet light. Furthermore, it was found that by performing a heat treatment at a temperature of 300°C or higher and a temperature of 600°C or lower, a relatively good ohmic contact can be formed between the p-type contact layer 70 and the reflective electrode 80 on the p-side, and the contact has the reliability to withstand high currents. It should be noted that since it is extremely difficult to directly measure the reflectivity of the reflective electrode 80 in the state of the deep ultraviolet light-emitting element 100, a method is adopted instead, in which the first metal layer 81 and the second metal layer 82 are formed on a sapphire substrate. Before and after the heat treatment process, light of various wavelengths is irradiated toward the reflective electrode 80 from the transparent sapphire substrate side. The reflectivity relative to the wavelength (for example, the reflectivity relative to a wavelength of 300 nm) is measured using an ultraviolet-visible spectrophotometer.

[0070] That is, refer to Figure 1A It can be seen that the method for manufacturing a reflective electrode for a deep ultraviolet light emitting element according to one embodiment of the present invention comprises: a first step ( Figure 1A In step 1B), the p-type contact layer 70 ( Figure 1A In step 1A), Ni is formed as the first metal layer 81 with a thickness of 3 to 20 nm; the second step ( Figure 1AIn step 1C), Rh is formed as a second metal layer 82 on the first metal layer 81 with a thickness of 20 nm or more and 2 μm or less; and a third step ( Figure 1A In step 1D), the first metal layer and the second metal layer are subjected to a heat treatment at a temperature of not less than 300° C. and not more than 600° C.

[0071] <Step 1>

[0072] In the first step, Ni is formed as the first metal layer 81 on the p-type contact layer 70 with a thickness of 3 to 20 nm. Ni can be deposited on the surface of the p-type contact layer 70 by conventional methods such as vacuum evaporation methods such as electron beam evaporation and resistance heating evaporation, and sputtering. This is because when it is less than 3 nm, it is difficult to suppress the aforementioned quenching, and when it is greater than 20 nm, the reflectivity of the reflective electrode will drop significantly. In addition, it is further preferred to set the thickness of the first metal layer 81 to 3 to 10 nm. By forming the first metal layer 81 with a thickness of less than 10 nm, the reflectivity of the reflective electrode 80 with respect to a wavelength of 300 nm after heat treatment can be made 60% or more. It should be noted that the thickness of the first metal layer 81 can be measured using a film thickness meter using a crystal oscillator.

[0073] <Step 2>

[0074] In the second step, Rh is formed as the second metal layer 82 on the first metal layer 81 with a thickness of more than 20 nm and less than 2 μm. This is because when it is less than 20 nm, there is a situation where the reflectivity of ultraviolet light relative to the second metal layer 82 cannot be made sufficiently high. In addition, when it is greater than 2 μm, cost issues related to Rh will arise. In order to improve the reflectivity of the reflective electrode after diffusion of the first metal layer 81 based on the heat treatment process described later, it is more preferable to set the thickness of the second metal layer 82 to more than 30 nm, and to control costs, it is more preferable to set it to less than 100 nm. The second step can also be formed by conventional methods such as vacuum evaporation and sputtering in the same way as the first step. The thickness of the second metal layer 82 can be measured using a film thickness meter with a crystal oscillator.

[0075] <Step 3>

[0076] In the third step, the first metal layer 81 and the second metal layer 82 are heat-treated at a temperature between 300°C and 600°C to form the reflective electrode 80. Inert gases such as nitrogen are generally used as the atmospheric gas for heat treatment to form an ohmic contact after forming the p-side electrode, as in this step. This step can also use only an inert gas as the atmospheric gas. However, it is more preferable to include oxygen in the atmospheric gas. The proportion of oxygen in the atmospheric gas is preferably greater than 0% and less than 50% in terms of flow rate.

[0077] The reflective electrode 80 thus obtained is an electrode composed of Ni and Rh. During the heat treatment in the third step, the Ni in the first metal layer 81 diffuses from the interface with the p-type contact layer 70 toward the Rh side of the second metal layer 82. Furthermore, due to the diffusion of Ni, the proportion of Rh at the interface between the p-type contact layer 70 and the reflective electrode 80 increases, resulting in a higher reflectivity at this interface compared to before the heat treatment. Since Ni in the reflective electrode 80 after the heat treatment fails to maintain its layered form and diffuses, it is difficult to accurately measure the Ni content after the heat treatment (i.e., after diffusion). Therefore, if the SEM-EDS analysis of a cross-section (vertical section) of the reflective electrode after the heat treatment shows both Ni and Rh peaks, it is determined that the reflective electrode 80 is composed of Ni and Rh. Furthermore, the Rh content in the reflective electrode 80, by volume (equivalent to the area ratio in the SEM-EDS analysis of the reflective electrode cross-section), is 50% or more, preferably 75% or more. By setting the volume ratio of Rh in the reflective electrode 80 to 75% or more, the reflectivity of the reflective electrode 80 after the heat treatment at a wavelength of 300 nm can be set to 60% or more.

[0078] Furthermore, in the reflectivity measurement of the above-mentioned reflective electrode (after the heat treatment step), the reflectivity of Rh alone at a wavelength of 300 nm was 70-73%, while the reflectivity of the alloy of Ni and Au was less than 40%. Therefore, the reflective electrode 80 composed of Ni and Rh according to the present invention can achieve a reflectivity of 40% or more and less than 67% at a wavelength of 300 nm by setting the thickness of the first metal layer 81 to 3-20 nm and the thickness of the second metal layer 82 to 20 nm to 2 μm. Furthermore, by setting the thickness of the first metal layer 81 to 3-10 nm and the thickness of the second metal layer 82 to 30 nm to 100 nm, the reflectivity can be set to 60% or more and less than 70% at a wavelength of 300 nm. It should be noted that even when Ni alloys with Rh, the reflectivity of Rh alone does not significantly decrease. In addition, in the reflective electrode 80, as impurities other than Ni and Rh that can be contained without significantly reducing the reflectivity, ruthenium (Ru), gold (Au), platinum (Pt), palladium (Pd), and titanium (Ti) can be considered. The impurity content is 40 mass% or less, preferably 10 mass% or less.

[0079] By using the reflective electrode 80 for a deep ultraviolet light emitting element according to the present embodiment described above in a deep ultraviolet light emitting element, it is possible to achieve both high light emission output and excellent reliability.

[0080] Reference Figure 1B. As another embodiment of the above embodiment, it is also preferred to further include the following steps after the second step: a step of forming a Ni layer as the third metal layer 83 on the second metal layer; and a step of forming a Rh layer as the fourth metal layer 84 on the third metal layer 83. This step can be performed between the second and third steps, or after the third step. From the perspective of work efficiency, it is preferably performed between the second and third steps and immediately after the second step. As the third metal layer 83, the Ni layer can be formed with a thickness of 1 to 20 nm. In addition, as the fourth metal layer 84, the Rh layer can be formed with a thickness of not less than 5 nm and not more than 2 μm. Furthermore, the Ni layer and the Rh layer corresponding to the third metal layer and the fourth metal layer can be repeatedly formed on the fourth metal layer 84, and the reflective electrode can be made into a stacked body obtained by repeatedly stacking the Ni layer and the Rh layer in this order.

[0081] Although Au exists on the second metal layer 82, there is a risk of quenching when Au diffuses into the reflective electrode during heating, such as during the third step, by forming a reflective electrode composed of Ni and Rh into a stacked structure in which the Ni and Rh layers are stacked multiple times, quenching can be suppressed. Therefore, stacking Ni and Rh layers multiple times is preferred because it allows for an electrode that more reliably prevents the risk of quenching, without relying on the mounting process or external connection method (including those requiring heating, such as soldering) of contacting the stacked Rh layer with another metal (such as gold) to form an electrical connection with the outside. From this perspective, it is particularly preferred that the metal elements constituting the reflective electrode consist solely of Ni and Rh.

[0082] (Deep ultraviolet light emitting element)

[0083] Next, the deep ultraviolet light emitting element 100 having the reflective electrode 80 obtained by the present invention will be described. Figure 2 As shown, a deep ultraviolet light-emitting element 100 according to one embodiment of the present invention is a deep ultraviolet light-emitting element having an n-type semiconductor layer 30, a light-emitting layer 40, a p-type electron blocking layer 60, a p-type contact layer 70, and the p-side reflective electrode 80 on a substrate 10 in this order. In addition, the reflective electrode 80 is provided on the second layer 72 on the outermost surface of the p-type contact layer. The p-type contact layer 70 has a superlattice structure, wherein the superlattice structure is formed by combining Al with an Al composition ratio x. x Ga 1-x The first layer 71 composed of N and the Al having an Al composition ratio y y Ga 1-y The second layers 72 composed of N are alternately stacked. In addition, the Al composition ratio y of the second layer 72 is 0.15 or more (y≥0.15).

[0084] In particular, when the Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer 40 is set to w0, it is preferred that the Al composition ratio x of the first layer 71 is higher than the Al composition ratio w0, the Al composition ratio y of the second layer 72 is lower than the Al composition ratio x, and the Al composition ratio w0, the Al composition ratio x, the Al composition ratio y, and the thickness-averaged Al composition ratio z of the p-type contact layer 70 satisfy the following equations [1] and [2]:

[0085] 0.030<z-w0<0.20 ……[1]

[0086] 0.050≤xy≤0.47……[2].

[0087] It should be noted that if Figure 2 As shown, a buffer layer 20 is provided between the substrate 10 and the n-type semiconductor layer 30, a p-side reflective electrode 80 is provided directly above the p-type contact layer 70, and an n-side electrode 90 is provided on the exposed surface of the n-type semiconductor layer 30. This is a preferred embodiment of the deep ultraviolet light-emitting element 100.

[0088] In the following description, for simplicity, it is assumed that the Al composition ratio and thickness of each layer of the first layer 71 and the second layer 72 in the superlattice structure of the p-type contact layer 70 are constant. In this case, the thickness-averaged Al composition ratio z of the p-type contact layer 70 is defined as follows. First, the number of layers of the first layer 71 in the superlattice structure is represented as N, and the thickness of each layer of the first layer 71 is represented as t. a Similarly, the number of layers of the second layer 72 is represented as M, and the thickness of each layer of the second layer 72 is represented as t b At this time, the thickness-averaged Al composition ratio of the p-type contact layer 70 satisfies the following formula [3].

[0089]

[0090] It should be noted that the Al composition ratio and thickness of each layer of the first layer 71 and the second layer 72 in the superlattice structure of the p-type contact layer 70 do not necessarily need to be constant. When the Al composition ratio and thickness of each layer of the first layer 71 and the second layer 72 in the superlattice structure vary, the thickness-averaged Al composition ratio z can be a weighted average of the thicknesses and Al composition ratios of the first layer 71 and the second layer 72, respectively. The Al composition ratios x and y of the first layer 71 and the second layer 72, respectively, represent the weighted averages based on the thicknesses.

[0091] Next, refer to Figure 2 First, the details of the respective structures of the substrate 10 , the n-type semiconductor layer 30 , the light-emitting layer 40 , the p-type electron blocking layer 60 , and the p-type contact layer 70 in the deep ultraviolet light-emitting element 100 will be described.

[0092] <Substrate>

[0093] The substrate 10 is preferably a substrate that can transmit light emitted by the light emitting layer 40, such as a sapphire substrate or a single crystal AlN substrate. Alternatively, the substrate 10 may be an AlN template substrate in which an undoped AlN layer is epitaxially grown on the surface of a sapphire substrate.

[0094] <n-type semiconductor layer>

[0095] The n-type semiconductor layer 30 is provided on the substrate 10 via the buffer layer 20 as needed. The n-type semiconductor layer 30 can also be provided directly on the substrate 10. The n-type semiconductor layer 30 is doped with an n-type dopant. Specific examples of n-type dopants include silicon (Si), germanium (Ge), tin (Sn), sulfur (S), oxygen (O), titanium (Ti), zirconium (Zr), etc. The dopant concentration of the n-type dopant is not particularly limited as long as it is a dopant concentration that allows the n-type semiconductor layer 30 to function as an n-type. For example, it can be set to 1.0×10 18 atoms / cm 3 ~1.0×10 20 atoms / cm 3 . In addition, the band gap of the n-type semiconductor layer 30 is preferably wider than the band gap of the light-emitting layer 40 (well layer 41 when a quantum well structure is adopted), and has transmissivity with respect to the emitted deep ultraviolet light. In addition, in addition to being a single-layer structure or a structure composed of multiple layers, the n-type semiconductor layer 30 can also be composed of a composition-inclined layer in which the composition ratio of the group III elements is inclined toward the crystal growth direction, or a superlattice structure. The n-type semiconductor layer 30 not only forms a contact portion with the n-side electrode, but also has the function of improving the crystallinity from the substrate to the light-emitting layer.

[0096] <Luminescent layer>

[0097] Light-emitting layer 40 is provided on n-type semiconductor layer 30 and radiates deep ultraviolet light. Light-emitting layer 40 can be composed of AlGaN, and its Al composition ratio can be set so that the wavelength of radiated light is between 200 and 350 nm, which is deep ultraviolet light, or the central emission wavelength is between 265 nm and 317 nm. This Al composition ratio can be set, for example, within the range of 0.25 to 0.60.

[0098] The light-emitting layer 40 may have a single-layer structure with a constant Al composition ratio, or preferably a multiple quantum well (MQW) structure formed by repeating a well layer 41 and a barrier layer 42 composed of AlGaN with different Al composition ratios. When the light-emitting layer 40 has a single-layer structure with a constant Al composition ratio, the Al composition ratio w0 of the layer emitting deep ultraviolet light in the light-emitting layer 40 is the Al composition ratio of the light-emitting layer 40 itself. Furthermore, when the light-emitting layer 40 has a multiple quantum well structure, since the well layer 41 corresponds to the layer emitting deep ultraviolet light in the light-emitting layer 40, for convenience, the Al composition ratio w of the well layer 41 is considered to be equivalent to the aforementioned Al composition ratio w0. It should be noted that the Al composition ratio w0 of the layer emitting deep ultraviolet light (or the Al composition ratio w of the well layer) is preferably set to 0.25 to 0.60, so that the wavelength of the radiated light is 200 to 350 nm, which is the wavelength of deep ultraviolet light, or the central emission wavelength is 265 nm to 317 nm.

[0099] In addition, the Al composition ratio b of the barrier layer 42 is set to be higher than the Al composition ratio w of the well layer 41 (i.e., b>w). With respect to 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, 0.40 to 0.95. In addition, there is no particular restriction on the number of repetitions of the well layer 41 and the barrier layer 42, and it can be set to, for example, 1 to 10 times. It is preferred that the two end sides (i.e., the first and the last) in the thickness direction of the light-emitting layer 40 are barrier layers. If the number of repetitions of the well layer 41 and the barrier layer 42 is set to n, it is marked as "n.5 groups of well layers and barrier layers". In addition, the thickness of the well layer 41 can be set to 0.5nm to 5nm, and the thickness of the barrier layer 42 can be set to 3nm to 30nm.

[0100] <Guide layer>

[0101] When the light-emitting layer 40 has the above-mentioned quantum well structure, it is also preferable to provide a guide layer having an Al composition ratio higher than that of either the barrier layer 42 or the p-type electron blocking layer 60 between the well layer 41 closest to the p-type electron blocking layer 60 in the light-emitting layer 40 and the p-type electron blocking layer 60 described later. In this way, the light output of the deep ultraviolet light-emitting element 100 can be improved. In this case, if the Al composition ratio of the guide layer is marked as b g , using the Al composition ratio α of the p-type electron blocking layer 60 described later, the relationship between the various Al composition ratios is as follows.

[0102] w(well layer)<b(barrier layer)<α(p-type electron blocking layer)<b g (Guide layer)

[0103] Furthermore, it is also preferable to configure the light-emitting layer 40 as n sets of well layers 41 and barrier layers 42 starting from the barrier layer 42, and to configure the layer in contact with both the light-emitting layer 40 and the p-type electron blocking layer 60 as the aforementioned guide layer, with its thickness being thinner than the other barrier layers. For example, it is also preferable to configure the guide layer to be made of AlN (in this case, specifically referred to as an AlN guide layer), and to have a thickness of 0.7 to 1.7 nm.

[0104] <p-type electron blocking layer>

[0105] The p-type electron blocking layer 60 is provided on the light-emitting layer 40. The p-type electron blocking layer 60 blocks electrons and injects electrons into the light-emitting layer 40 (the well layer 41 in the case of the MQW structure), and is used as a layer for improving the injection efficiency of electrons. In order to achieve this purpose, although it may vary depending on the Al composition ratio w0 of the layer emitting deep ultraviolet light (in the case of the quantum well structure, it is equivalent to the Al composition ratio w of the well layer 41), it is preferred to set the Al composition ratio α of the p-type electron blocking layer 60 to 0.35≤α≤0.95. It should be noted that if the Al composition ratio α is greater than 0.35, the p-type electron blocking layer 60 may also contain In in an amount of 5% or less relative to Al and Ga as group III elements. Here, the Al composition ratio α is preferably higher than the thickness-averaged Al composition ratio z of the p-type contact layer 70 while satisfying the above conditions. That is, it is preferably set to α>z. Furthermore, the Al composition ratio α of the p-type electron blocking layer 60 and the Al composition ratio b of the barrier layer 42 both preferably satisfy 0<α−b≤0.55. This reliably improves the efficiency of electron injection into the well layer 41 through the p-type electron blocking layer 60.

[0106] The thickness of the p-type electron blocking layer 60 is not particularly limited, and is preferably set to, for example, 10 nm to 80 nm. If the thickness of the p-type electron blocking layer 60 is within this range, a high luminous output can be reliably obtained. It should be noted that the thickness of the p-type electron blocking layer 60 is preferably thicker than the thickness of the barrier layer 42. In addition, as p-type dopants doped into the p-type electron blocking layer 60, magnesium (Mg), zinc (Zn), calcium (Ca), beryllium (Be), manganese (Mn), etc. can be exemplified, and Mg is generally used. The dopant concentration of the p-type electron blocking layer 60 is not particularly limited as long as it is a dopant concentration that 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 .

[0107] <P-type contact layer>

[0108] The p-type contact layer 70 is provided on the p-type electron blocking layer 60. The p-type contact layer 70 is used to reduce the contact resistance between the p-side reflective electrode 80 provided directly above it and the p-type electron blocking layer 60. Therefore, there is no desired structure between the p-type contact layer 70 and the p-side reflective electrode 80, other than impurities unavoidable during manufacturing. In other words, the p-side reflective electrode 80 appears next to the p-type contact layer 70 in the superlattice structure.

[0109] As mentioned above, the p-type contact layer 70 has a x Ga 1-x The first layer 71 composed of N and the Al y Ga 1-y The superlattice structure is formed by alternating layers of second layers 72 composed of N. Here, it is preferable to make the Al composition ratio x of the first layer 71 higher than the Al composition ratio w0 of the layer emitting deep ultraviolet light in the light-emitting layer 40 (x>w0) to improve the transmittance of deep ultraviolet light. If the light-emitting layer 40 has a single-layer structure, the Al composition ratio x can be higher than the Al composition ratio of the light-emitting layer 40. If the light-emitting layer 40 has a quantum well structure, the Al composition ratio x can be higher than the Al composition ratio w of the well layer 41.

[0110] Furthermore, as described above, it is preferred that the Al composition ratio w0, the Al composition ratio x, the Al composition ratio y, and the thickness-averaged Al composition ratio z of the p-type contact layer satisfy the following formulas [1] and [2]:

[0111] 0.030<z-w0<0.20 ……[1]

[0112] 0.050≤xy≤0.47……[2].

[0113] In the prior art, a p-type GaN layer that easily increases the hole concentration is generally used as the p-type contact layer of a deep ultraviolet light-emitting element. However, due to its band gap, the p-type GaN layer absorbs light with a wavelength of less than 360nm. Therefore, in the deep ultraviolet light radiated from the light-emitting layer, it is almost impossible to expect light extraction from the p-type contact layer side or light extraction effect through reflection on the p-side electrode. On the other hand, if the p-type contact layer is made of AlGaN with an increased Al composition ratio, although the hole concentration may be slightly lower than that of GaN, since the deep ultraviolet light radiated from the light-emitting layer can pass through the p-type contact layer, the light extraction efficiency of the deep ultraviolet light-emitting element as a whole is improved, and as a result, the luminous output of the deep ultraviolet light-emitting element can be improved. However, through experiments conducted by the present inventors, it was found that when the Al composition ratio of the p-type contact layer is too high, it may become a deep ultraviolet light-emitting element with insufficient reliability. On the other hand, if the p-type contact layer 70 has a superlattice structure formed according to the above-mentioned Al composition ratio, since the thickness-averaged Al composition ratio z is higher than the Al composition ratio w0 (z>w0) of the layer emitting deep ultraviolet light in the light-emitting layer 40, the deep ultraviolet light can pass through the p-type contact layer 70. As a result, a higher light-emitting output can be obtained, which is preferred.

[0114] Here, in order to more reliably transmit deep ultraviolet light through the p-type contact layer 70, it is preferred that the difference between the thickness-average Al composition ratio z and the Al composition ratio w of the layer emitting deep ultraviolet light be greater than 0.030 (i.e., z-w0>0.030), as shown in the above formula [1]. To achieve this goal, the difference between the Al composition ratio z and the Al composition ratio w is more preferably greater than 0.040 (z-w0>0.040), further preferably greater than 0.050 (z-w0>0.050), and particularly preferably greater than 0.06 (z-w0>0.060).

[0115] Furthermore, in order to form a good ohmic contact between the p-type contact layer 70 and the p-side reflective electrode 80 and ensure sufficient reliability, it is preferable to set an upper limit for the thickness-average Al composition ratio. To this end, as shown in the above formula [1], the upper limit of the difference between the thickness-average Al composition ratio z and the Al composition ratio w of the layer emitting deep ultraviolet light is preferably set to 0.20 (z-w0 < 0.20). For this purpose, the upper limit of the difference between the Al composition ratio z and the Al composition ratio w is more preferably set to 0.19 (z-w0 < 0.19), and even more preferably set to 0.18 (z-w0 < 0.18).

[0116] Furthermore, as shown in the above formula [2], the difference between the Al composition ratio x of the first layer 71 and the Al composition ratio y of the second layer 72 is preferably set to be greater than 0.050 in absolute value (xy ≥ 0.050). This is to enable the p-type contact layer 70 to effectively function as a superlattice structure. In addition, in order to reduce the distortion of the entire superlattice structure while contacting the p-side reflective electrode 80 with a low Al composition ratio, the difference between the Al composition ratio x and the Al composition ratio y is preferably set to be greater than 0.1 in absolute value (xy ≥ 0.10), and more preferably to be greater than 0.15 (xy ≥ 0.15). On the other hand, if the difference between the Al composition ratio x and the Al composition ratio y is too large, the lattice constant between the first layer and the second layer will change significantly, thereby increasing the distortion and making it difficult to obtain a superlattice layer with good crystallinity. Therefore, in order to more effectively achieve the effect of the present invention, it is preferably set to xy ≤ 0.47, and more preferably to xy ≤ 0.45.

[0117] It should be noted that if the Al composition ratio y of the second layer 72, which is a layer with a low Al composition ratio in the superlattice structure, is set to 0.20 or more, the transmittance of the deep ultraviolet light emitted from the light-emitting layer 40 can be more reliably improved, and thus it is preferred. For this purpose, it is more preferred to set the Al composition ratio y to 0.21 or more, and further preferably to set it to 0.25 or more. On the other hand, since it is more reliably possible to maintain high reliability when the Al composition ratio y is set to 0.55 or less, it is preferred. For this purpose, it is further preferred to set the Al composition ratio y to 0.51 or less, and particularly preferably to set it to 0.40 or less. It should be noted that as long as the thickness average Al composition ratio z is higher than the Al composition ratio w0 of the layer emitting deep ultraviolet light in the light-emitting layer 40, the Al composition ratio y can be higher than the Al composition ratio w0 or lower than the Al composition ratio w0. In addition, as long as the above-mentioned formulas [1] and [2] are satisfied, the Al composition ratio x can be appropriately set, and the upper and lower limits of the Al composition ratio x are not limited. On the basis of satisfying the formulas [1] and [2], the Al composition ratio x may be roughly set within the range of 0.40 to 0.85.

[0118] In addition, the thickness t of each of the first layer 71 and the second layer 72 is a , t b There is no particular limitation as long as a superlattice structure is formed and the thickness average Al composition z relative to the Al composition ratio of the light emitting layer 40 is satisfied. For example, the thickness of the first layer 71 can be t a The thickness of the second layer 72 is set to be 1.0 nm or more and 10.0 nm or less. b The thickness t is set to be 1.0 nm or more and 10.0 nm or less. a , t bThe size relationship of the first layer 71 and the second layer 72 is not limited, and either one may be larger, or the thickness of the two layers may be the same. In addition, it is preferable to appropriately set the number of repetitions of the first layer 71 and the second layer 72, for example, within a range of 3 to 15 times, so that the overall thickness of the p-type contact layer 70 is greater than or equal to 20 nm and less than or equal to 100 nm, preferably less than or equal to 70 nm.

[0119] Furthermore, the total thickness of the p-type layer (the sum of the thickness of the p-type electron blocking layer 60 and the thickness of the p-type contact layer 70) is preferably 65 nm to 100 nm, more preferably 70 nm to 95 nm. By setting the thickness within this range, high luminous output can be more reliably achieved.

[0120] Here, the first layer 71 is preferably the layer at the end of the p-type contact layer 70 closer to the p-type electron blocking layer 60 in the thickness direction. In other words, it is preferable to provide the first layer 71 directly above the p-type electron blocking layer 60, with no other layers interposed between the p-type contact layer 70 and the p-type electron blocking layer 60, and with the two in contact. Because the Al composition ratio x of the first layer 71 is higher than the Al composition ratio y of the second layer 72, and the Al composition ratio x is closer to the Al composition ratio α of the p-type electron blocking layer 60, the occurrence of defects caused by distortion between the p-type electron blocking layer 60 and the p-type contact layer 70 can be more reliably suppressed.

[0121] On the other hand, the layer at the end of the p-type contact layer 70, which is farther from the p-type electron blocking layer 60 in the thickness direction, is preferably the second layer 72. In other words, the layer that contacts the p-side reflective electrode 80 is preferably the second layer 72. This is because, when the Al composition ratio x of the first layer 71 is compared with the Al composition ratio y of the second layer 72, the Al composition ratio y is lower, making it easier to form an ohmic contact with the p-side reflective electrode 80.

[0122] It should be noted that when the layer at the end of the p-type contact layer 70 in the thickness direction close to the p-type electron blocking layer 60 is the first layer 71, and the layer at the end away from the p-type electron blocking layer 60 is the second layer 72, the number of layers of the first layer 71 is the same as the number of layers of the second layer 72. However, in this embodiment, the number of layers of the two layers does not necessarily need to be the same. This embodiment includes the case where the two layers at the ends in the thickness direction of the p-type contact layer 70 are the second layer 72 (in this case, the number of layers of the second layer 72 is one more than the number of layers of the first layer 71).

[0123] Furthermore, although a superlattice structure in which the first layer 71 and the second layer 72 are repeatedly stacked has been described as one embodiment of the present invention, another embodiment of the present invention may employ a three-layer superlattice structure in which a third layer having the same Al composition ratio as the first and second layers is disposed between the first and second layers. In this case, the same effects as those of the present invention described above can also be achieved.

[0124] Here, it is preferable that the p-type contact layer 70 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 deep ultraviolet light-emitting element 100 can be reduced. It should be noted that, although the upper limit is not limited, considering industrial productivity, in this embodiment, the upper limit of the Mg concentration in the high concentration region can be set to 1×10 21 atoms / cm 3 At this time, the Mg concentration in the region of the p-type contact layer 70 on the p-type electron blocking layer 60 side can be set to a normal range, usually 5×10 19 atoms / cm 3 More than 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. To ensure the crystallinity of the p-type contact layer 70, the thickness of the high-concentration region is generally 15 nm or less. The high-concentration region can be formed on the side contacting the p-side reflective electrode 80.

[0125] Furthermore, the p-type contact layer 70 has a Si concentration of 5×10 16 atoms / cm 3 Above and 1×10 20 atoms / cm 3 The following Si doping region is also preferred. More preferably, the Si concentration in this region is set to 2×10 19 atoms / cm 3 Above and 5×10 19 atoms / cm 3As a result, the luminous output of the deep ultraviolet light emitting element 100 can be further improved. It should be noted that the effect can be effectively achieved when the thickness of the Si doped region is about 1 to 5 nm. It is also preferred to use the Si doped region as the last second layer in the superlattice structure of the p-type contact layer. It can also be used as the above-mentioned Mg concentration of 3×10 20 atoms / cm 3 The high-concentration region is further doped with Si to form a co-doped region. Alternatively, only Si may be doped in the Si-doped region (ie, Mg may not be doped).

[0126] It should be noted that if the side of the p-type contact layer 70 that contacts the p-side reflective electrode 80 includes a Si-doped region doped only with Si and not doped with Mg, this region can be considered n-type from a conductivity perspective. However, within the aforementioned thickness range (1-5 nm), even without Mg doping, as long as it is the topmost layer of the p-type contact layer 70 and in contact with the p-type electrode, it will not form a thyristor. Therefore, even in this case, the Si-doped region is considered part of the p-type contact layer 70.

[0127] The deep ultraviolet light-emitting element 100 of this embodiment as described above can achieve both high light output and excellent reliability.

[0128] Hereinafter, specific forms of the deep ultraviolet light-emitting element 100 applicable to this embodiment will be described, but this embodiment is not limited to the following forms.

[0129] <Buffer layer>

[0130] like Figure 2 As shown, it is also preferable to provide a buffer layer 20 between the substrate 10 and the n-type semiconductor layer 30 to alleviate the lattice mismatch therebetween. The buffer layer 20 can be an undoped Group III nitride semiconductor layer, and it is also preferable to have a superlattice structure.

[0131] <n-side electrode>

[0132] In addition, the n-side electrode 90 that can be provided on the exposed surface of the n-type semiconductor layer 30 can be formed of a metal composite film having a Ti-containing film and an Al-containing film formed on the Ti-containing film. The 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 the following. Figure 2 It is formed on the exposed surface of the n-type semiconductor layer 30 as shown, and only needs to be electrically connected to the n-type semiconductor layer.

[0133] <Other components>

[0134] It should be noted that although Figure 2 Although not shown, a guide layer composed of AlGaN having an Al composition ratio higher than the Al composition ratio α of the p-type electron blocking layer 60 may be provided between the light-emitting layer 40 and the p-type electron blocking layer 60. Providing the guide layer can promote the injection of holes into the light-emitting layer 40.

[0135] <p-type cladding>

[0136] In addition, although Figure 2 Although not shown, a p-type cladding layer composed of AlGaN may be provided between the p-type electron blocking layer 60 and the p-type contact layer 70. The p-type cladding layer is a layer having an Al composition ratio that is higher than the Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer 40 (the Al composition ratio w in the case of a quantum well structure) and the thickness-averaged Al composition ratio z of the p-type contact layer 70, but lower than the Al composition ratio α of the p-type electron blocking layer 60. That is, both the p-type electron blocking layer 60 and the p-type cladding layer are layers having an Al composition ratio higher than the Al composition ratio of the layer emitting deep ultraviolet light, and are layers that basically transmit the deep ultraviolet light emitted from the light-emitting layer 40. However, it is preferred not to provide a p-type cladding layer. The reason for this is described in Japanese Patent Application Laid-Open No. 2016-111370, the entire disclosure of which is incorporated into this specification by reference. It should be noted that when a p-type cladding layer is provided, if the Al composition ratio of the p-type cladding layer is set to β, then α>β, and β>y.

[0137] It should be noted that the deep ultraviolet light-emitting element 100 of this embodiment reflects deep ultraviolet light by forming the p-side reflective electrode 80 with a reflective electrode material, thereby making the substrate side or the substrate horizontal direction the primary light extraction direction. Furthermore, the deep ultraviolet light-emitting element 100 can be configured as a so-called flip-chip type.

[0138] (Method for manufacturing deep ultraviolet light-emitting element)

[0139] Next, use Figure 3 An embodiment of a manufacturing method for obtaining the deep ultraviolet light emitting element 100 will be described. An embodiment of a manufacturing method of the deep ultraviolet light emitting element 100 according to the present invention comprises: Figure 3 Step 3A) forming an n-type semiconductor layer 30; forming a light-emitting layer 40 on the n-type semiconductor layer 30; forming a p-type electron blocking layer 60 on the light-emitting layer 40 (refer to Figure 3 Step 3B); forming a p-type contact layer on the p-type electron blocking layer (refer to Figure 3 Step 3C); forming a reflective electrode on the p-type contact layer (refer to Figure 3 Step 3D). Furthermore, the process of forming the p-type contact layer is repeated alternately to form an Al having an Al composition ratio x.x Ga 1-x The first step of forming the first layer composed of N and the first step of forming the Al layer composed of Al having an Al composition ratio y lower than the Al composition ratio x y Ga 1-y The second step of forming the second layer composed of N, thereby forming the p-type contact layer having a superlattice structure, and the Al composition ratio y of the second layer is greater than 0.15. In addition, as described in the embodiment of the reflective electrode 80, the step of forming the reflective electrode includes: a first step of forming Ni as a first metal layer 81 with a thickness of 3 to 20 nm on the p-type contact layer 70 having a superlattice structure; a second step of forming Rh as a second metal layer 82 with a thickness of greater than 20 nm and less than 2 μm on the first metal layer 81; and a third step of heating the first metal layer and the second metal layer at a temperature of greater than 300°C and less than 600°C (see Figure 1A ). In addition, the process of forming the p-type contact layer 70 (refer to step 3C) is to alternately and repeatedly form Al with an Al composition ratio x. x Ga 1-x The first step of forming the first layer 71 composed of N and the first step of forming the Al layer 71 composed of Al having an Al composition ratio y lower than the Al composition ratio x y Ga 1-y The second step of forming the second layer 72 composed of N is a step of forming the p-type contact layer 70 having a superlattice structure, and the Al composition ratio y of the second layer 72 is 0.15 or more (y≥0.15).

[0140] Furthermore, when the Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer 40 is set to w0, it is preferred that the Al composition ratio x of the first layer 71 is higher than the Al composition ratio w0, the Al composition ratio y of the second layer 72 is lower than the Al composition ratio x, and the Al composition ratio w0, the Al composition ratio x, the Al composition ratio y, and the thickness-averaged Al composition ratio z of the p-type contact layer 70 satisfy the following equations [1] and [2]:

[0141] 0.030<z-w0<0.20 ……[1]

[0142] 0.050≤xy≤0.47……[2].

[0143] Next, refer to Figure 3 However, descriptions that overlap with those in the aforementioned embodiment will be omitted.

[0144] First, if Figure 3As shown in steps 3A and 3B, an n-type semiconductor layer 30, a light-emitting layer 40, and a p-type electron blocking layer 60 are sequentially formed on a substrate 10. In each of these steps, each layer can be formed by a well-known epitaxial growth technique such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or sputtering.

[0145] When forming each of the n-type semiconductor layer 30, the light-emitting layer 40, the guide layer, and the p-type electron blocking layer 60, the growth temperature, growth pressure, and growth time for epitaxial growth can be set to conventional conditions corresponding to the Al composition ratio and thickness of each layer. As a carrier gas for epitaxial growth, hydrogen or nitrogen, or a mixture of the two, can be supplied into the chamber. Furthermore, as raw material gases for growing the above-mentioned layers, TMA (trimethylaluminum), TMG (trimethylgallium), etc., which are raw material gases of group III elements, can be used, and NH3 gas can be used as a group V element gas. Conventional conditions can also be used for the molar ratio of group V elements to group III elements (hereinafter referred to as V / III ratio) calculated based on the growth gas flow rate of group V element gases such as NH3 gas and group III element gases such as TMA gas. Furthermore, as the dopant source gas, for p-type dopants, cyclopentadienyl magnesium gas (CP2Mg) as a Mg source can be appropriately selected, and for n-type dopants, for example, monosilane gas (SiH4) as a Si source, zinc chloride gas (ZnCl2) as a Zn source can be appropriately selected, and they can be supplied into the chamber at a specified flow rate.

[0146] Then, in Figure 3 In the p-type contact layer formation step shown in step 3C, a p-type contact layer 70 having a superlattice structure formed by repeating the first layer 71 and the second layer 72 described above is formed on the p-type electron blocking layer 60. The thickness range and Al composition ratio conditions of the p-type contact layer 70 are as described above. The p-type contact layer 70 can also be grown by epitaxial growth using methods such as MOCVD.

[0147] It should be noted that in order to make the Mg concentration of the high-concentration region 72 on the side in contact with the p-side reflective electrode 80 in the p-type contact layer 70 to be 3×10 20 atoms / cm 3In the p-type contact layer formation step, the following process is performed. Specifically, in the p-type contact layer formation step, the superlattice structure crystal is grown by supplying a Group III source gas, a Group V source gas, and a Mg source gas. Immediately after crystal growth is complete, the flow rate of the Group III source gas is reduced to less than one-quarter of the flow rate during crystal growth, while the Group V source gas and the Mg source gas are continued to be supplied for a period of at least one minute and no more than 20 minutes.

[0148] Furthermore, in order to dope the p-type contact layer 70 with both Mg and Si on the side in contact with the p-side reflective electrode 80, CP2Mg gas, serving as a Mg source, can be supplied to the chamber while monosilane gas (SiH4) serving as a Si source is introduced. To dope only Si, the supply of CP2Mg gas, serving as a Mg source, to the chamber can be stopped while monosilane gas (SiH4) serving as a Si source is introduced. It should be noted that, as described above, when doping the p-type contact layer 70 with Si on the side in contact with the p-side reflective electrode 80, the formation of the high-Mg concentration region is optional.

[0149] In addition, if Figure 3 As shown in step 3D, the light-emitting layer 40, the p-type electron blocking layer 60, and a portion of the p-type contact layer 70 can be removed by etching or the like, thereby forming an n-side electrode 90 on the exposed n-type semiconductor layer 30. It should be noted that the n-side electrode 90 can be formed by sputtering, vacuum deposition, or the like. Alternatively, the buffer layer 20 can be formed on the surface 10A of the substrate 10.

[0150] Example

[0151] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to the following examples.

[0152] (Example 1)

[0153] according to Figure 1A and Figure 3The deep ultraviolet light-emitting element involved in Example 1 is produced according to the process diagram shown in . First, a sapphire substrate (diameter 2 inches; thickness: 430 μm; surface orientation: (0001)) is prepared. Then, an AlN layer with a central film thickness of 0.60 μm is grown on the above-mentioned sapphire substrate by the MOCVD method to form an AlN template substrate. At this time, the growth temperature of the AlN layer is 1300°C, the growth pressure in the chamber is 10 Torr, and the growth gas flow rates of ammonia gas and TMA gas are set so that the V / III ratio is 163. It should be noted that for the film thickness of the AlN layer, an optical interference film thickness meter (NanoSpec M6100A; manufactured by Nanometrics Incorporated) is used to measure the film thickness of 25 equally spaced locations including the center of the wafer.

[0154] Next, the AlN template substrate was placed in a heat treatment furnace, and after the furnace was filled with nitrogen, the temperature in the furnace was raised to heat the AlN template substrate at 1650° C. for 4 hours.

[0155] Then, an undoped Al 0.55 Ga 0.45 A buffer layer of 1 μm thick made of N was then formed on the buffer layer. 0.45 Ga 0.55 N-type semiconductor layer with a thickness of 2 μm and doped with Si. It should be noted that according to the results of SIMS analysis, the Si concentration of the n-type semiconductor layer is 1.0×10 19 atoms / cm 3 .

[0156] Furthermore, an Al 0.29 Ga 0.71 The well layer with a thickness of 3 nm is composed of N and Al 0.51 Ga 0.49 The light-emitting layer is composed of three sets of 7nm thick barrier layers composed of AlN, stacked alternately. The Al composition ratio w in the well layer is 0.29. Next, a 1nm thick guide layer composed of AlN is formed on the light-emitting layer. It should be noted that the barrier layers are Si-doped, while the well and guide layers are undoped.

[0157] Then, on the guide layer, hydrogen is used as a carrier gas to form a 0.58 Ga 0.42 A p-type electron blocking layer with a thickness of 40 nm was formed by N. When forming the p-type electron blocking layer, CP2Mg gas was supplied into the chamber as a Mg source to dope Mg. It should be noted that according to the results of SIMS analysis, the Mg concentration of the p-type electron blocking layer was 5.0×1018 atoms / cm 3 .

[0158] Next, an Al layer is formed as the first layer directly above the p-type electron blocking layer. 0.47 Ga 0.53 N, then Al is formed as the second layer 0.31 Ga 0.69 N, repeating the formation of these two sets for 7 times, forming a total of 14 layers of p-type contact layer of superlattice structure. It should be noted that the thickness of the first layer is set to 5.0nm, the thickness of the second layer is set to 2.5nm, the total thickness of the p-type contact layer is set to 52.5nm, and the thickness-averaged Al composition ratio is set to 0.42. In addition, when forming the p-type contact layer, while supplying TMA gas and TMG gas as group III sources and ammonia gas as group V source into the chamber, CP2Mg gas as a Mg source is supplied to grow Mg-doped p-type contact layer crystals. Then, only the supply of group III source gas is stopped, and only Mg source gas and group V source gas are supplied for 10.5 minutes, forming a high concentration region on the surface side of the p-type contact layer.

[0159] Note that, when determining the Al composition of the p-type contact layer, the Al composition ratio of the p-type contact layer is determined based on the emission wavelength (bandgap energy) of the p-type contact layer obtained by photoluminescence measurement analysis.

[0160] According to the results of SIMS analysis, the Mg concentration on the p-type electron blocking layer side in the p-type contact layer is 1×10 20 atoms / cm 3 The Mg concentration on the side (high concentration region) where the Mg concentration is high is set to 3×10 20 atoms / cm 3 .

[0161] The layer structure of Example 1 is shown in Table 1.

[0162] [Table 1]

[0163]

[0164] A mask is formed on the p-type contact layer, and mesa etching is performed by dry etching to expose the n-type semiconductor layer. Next, the second layer (Al 0.31 Ga 0.69N), an electron beam evaporation method is used to form a Ni layer (first metal layer) with a thickness of 7nm and an Rh layer (second metal layer) with a thickness of 50nm on the Ni layer. The thickness of the Ni layer and the Rh layer is measured using a film thickness meter with a crystal vibrator (CRTM-9000G; manufactured by ulvac). The vibrator is gold-plated and has a natural frequency of 4.5MHz to 5.0MHz. The calibration curve (correction) of the crystal vibrator is performed by forming a target metal single-layer film with a film thickness of more than 100nm and measuring the height difference between the formed films using a stylus step profiler (P-6 manufactured by Tencor).

[0165] Furthermore, an n-side electrode composed of Ti / Al was formed on the exposed n-type semiconductor layer, with the thickness of Ti being 20 nm and the thickness of Al being 150 nm.

[0166] Finally, an RTA device (manufactured by ADVANCE RIKO; infrared lamp annealing heating device) was used to maintain a maximum temperature of 550°C for 10 minutes to perform a heat treatment for forming an ohmic contact, thereby forming a reflective electrode composed of Ni and Rh. It should be noted that the heat treatment atmosphere in the RTA device was a mixed gas of N2 and O2, with the N2 flow rate in the mixed gas set to 1.0 slm and the O2 flow rate set to 0.5 slm. The sapphire substrate was laser diced into a single chip with a chip size of 1000 μm × 1000 μm to produce the deep ultraviolet light-emitting element involved in Example 1.

[0167] A Ni layer (first metal layer) with a thickness of 7 nm and a Rh layer (second metal layer) with a thickness of 50 nm were formed on a sapphire substrate. After the above-mentioned heat treatment step, the reflectivity relative to wavelength was measured from the transparent sapphire substrate side toward the reflective electrode using a UV-visible spectrophotometer (manufactured by JASCO Corporation; V-650). The result was that the reflectivity relative to a wavelength of 300 nm was 62%.

[0168] (Example 2)

[0169] The deep ultraviolet light emitting element of Example 2 was produced and evaluated in the same manner as in Example 1, except that the heat treatment atmosphere in the RTA apparatus was set to N 2 gas (N 2 flow rate 1.5 slm) instead of the mixed gas atmosphere in Example 1.

[0170] (Example 3)

[0171] A deep ultraviolet light-emitting element according to Example 3 was produced and evaluated in the same manner as in Example 1, except that the Al composition ratio x of the first layer was set to 0.43 and the Al composition y of the second layer was set to 0.27.

[0172] (Comparative Example 1)

[0173] A deep ultraviolet light-emitting element according to Comparative Example 1 was produced and evaluated in the same manner as in Example 1, except that the thickness of Ni in the reflective electrode in Example 1 was changed to 2 nm.

[0174] A 2nm-thick Ni layer (first metal layer) and a 50nm-thick Rh layer (second metal layer) were formed on a sapphire substrate. After the heat treatment step, the reflectivity relative to wavelength was measured from the transparent sapphire substrate side toward the reflective electrode using a UV-visible spectrophotometer (V-650, manufactured by JASCO Corporation). The result was a reflectivity of 67% relative to a wavelength of 300nm.

[0175] (Comparative Example 2)

[0176] A deep ultraviolet light-emitting element according to Comparative Example 2 was produced and evaluated in the same manner as in Example 1 except that the Ni reflective electrode in Example 1 was not provided.

[0177] (Comparative Example 3)

[0178] In addition to changing the p-type contact layer (total thickness 52.5 nm) of the superlattice structure in Example 1 to Al 0.42 Ga 0.58 A deep ultraviolet light-emitting element according to Comparative Example 3 was produced and evaluated in the same manner as in Example 1, except that the N layer had a single-layer structure with a thickness of 50 nm.

[0179] (Comparative Example 4)

[0180] A deep ultraviolet light-emitting element according to Comparative Example 4 was prepared in the same manner as in Example 1, except that the reflective electrode composed of Ni and Rh in Example 1 was changed to a 10 nm thick Ni layer and a 20 nm thick Au layer formed in this order. The light-emitting output was evaluated.

[0181] (Comparative Example 5)

[0182] The luminous output of the deep ultraviolet light-emitting element of Comparative Example 5 was evaluated in the same manner as in Example 1, except that the reflective electrode composed of Ni and Rh in Example 1 was changed to a Ni layer with a thickness of 10 nm and an Au layer with a thickness of 20 nm formed on the Ni layer in sequence, and the Al composition ratio x of the first layer was set to 0.43 and the Al composition ratio y of the second layer was set to 0.27.

[0183] (Comparative Examples 11 to 13)

[0184] The p-type contact layer of the superlattice structure in Example 1 was replaced with a single-layer AlGaN layer with the Al composition ratio and thickness shown in Table 3. Ni was not used for the reflective electrode. Deep ultraviolet light-emitting devices according to Comparative Examples 11 to 13 were fabricated and evaluated in the same manner as in Example 1, except that the chip size was changed to 560 μm × 780 μm.

[0185] (Evaluation 1: Po, Vf evaluation)

[0186] The light-emitting elements (chip size □1000μm) obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were mounted on an AlN substrate (size: 20mm×15mm; thickness: 0.8mm) using spherical gold bumps in a flip-chip manner. Furthermore, while the Al heat sink was connected to the AlN substrate, a constant current power supply was used to apply 350mA of power, and while measuring the forward voltage at this time, the luminous output based on the photodetector was measured by the light receiving portion arranged on the sapphire substrate side. The results are shown in Table 2. It should be noted that, based on the measurement results of the luminous wavelength by the spectrum analyzer, the luminous center wavelength was 310nm. The value is the average value of 10 measurements.

[0187] (Evaluation 2: Reliability Evaluation 1)

[0188] For Examples and Comparative Examples 1-5, after performing the measurements in Evaluation 1 above, the current was continuously applied at 350 mA for 160 hours. After the continuous power application, the output was measured again. If the chip failed to illuminate or the output dropped sharply to less than half of the initial luminous output, quenching was considered to have occurred. The percentage of chips experiencing quenching in the 10 measurements is shown in Table 2.

[0189] (Evaluation 3: Reliability Evaluation 2)

[0190] For Comparative Examples 11 to 13, a mask was formed on the p-type contact layer and mesa etching based on dry etching was performed to expose the n-type semiconductor layer. Then, for the exposed n-type semiconductor layer and p-type contact layer, a small chip of 560 μm × 780 μm was mounted on an AlN substrate (size: 1.5 × 1.1 mm thickness: 0.2 mm) using gold bumps, and the luminous output and forward electrical thickness were measured when 20 mA was applied. The value is the average of 10 measurements. Furthermore, for the chips extracted from 10 positions in the wafer, the initial luminous output was confirmed by applying a current of 20 mA. Then, the current was continuously applied at 20 mA for 250 hours, and the ratio of the chips whose output after application was changed from the initial luminous output to less than half (i.e., quenched) is shown in Table 3. It should be noted that when measuring the luminous output, a photodetector arranged on the side of the sapphire substrate surface was used.

[0191] [Table 2]

[0192]

[0193] [Table 3]

[0194]

[0195] Note that since the thickness of the first layer is 5.0 nm and the thickness of the second layer is 2.5 nm, the thickness-average Al composition ratio z of the p-type contact layer is calculated according to [z = (2 / 3)x + (1 / 3)y]. In Examples 1 and 2, z - w0 = 0.42 - 0.29 = 0.13, and xy = 0.47 - 0.31 = 0.16.

[0196] Therefore, the following conditions of formula [1] and formula [2] are satisfied at the same time.

[0197] 0.030<z-w0<0.20 ……[1]

[0198] 0.050≤xy≤0.47 ……[2]

[0199] (Review of evaluation results)

[0200] It is believed that quenching in Comparative Examples 1-3 occurred due to poor contact at the interface between the p-type contact layer and the p-side reflective electrode. On the other hand, in Examples 1-3, since the p-type contact layer has a superlattice structure and the Ni layer is sufficiently thick, poor contact is presumed to have occurred. Furthermore, a comparison of Comparative Examples 4 and 5 with Examples 1-3 shows that the reflective electrode composed of Ni and Rh is effective in increasing luminous output without significantly changing the forward voltage.

[0201] The above results confirmed that high light output can be obtained while maintaining reliability by forming a p-side reflective electrode that meets the conditions of the present invention on the p-type contact layer of the superlattice structure.

[0202] (Example 4)

[0203] In Examples 1 to 3, the central wavelength of emission was 310 nm. Instead, a deep ultraviolet light-emitting element with a central wavelength of emission of 280 nm was used for the experiment. The deep ultraviolet light-emitting element of Example 4 was fabricated in the same manner as in Example 1, except that the Al composition ratio of each semiconductor layer in Example 1 was changed to that shown in Table 4 below. It should be noted that the undoped AlGaN layer was formed on the AlN template substrate by tilting the Al composition ratio from 0.85 to 0.65 in the crystal growth direction.

[0204] [Table 4]

[0205]

[0206] (Comparative Example 6)

[0207] A deep ultraviolet light-emitting element according to Comparative Example 6 was prepared in the same manner as in Example 4 except that the reflective electrode composed of Ni and Rh in Example 4 was changed to a 10 nm thick Ni layer and a 20 nm thick Au layer formed in sequence on the Ni layer, and the light emission output was evaluated.

[0208] (Comparative Example 7)

[0209] In addition to changing the p-type contact layer (total thickness 52.5 nm) of the superlattice structure in Example 4 to Al 0.59 Ga 0.41 A deep ultraviolet light-emitting element according to Comparative Example 7 was produced and evaluated in the same manner as in Example 4, except that the N layer had a single-layer structure with a thickness of 50 nm.

[0210] (Rating 4)

[0211] For Example 4 and Comparative Examples 6 and 7 (the chip size is 1000μm×1000μm as in Example 1), the luminous output Po and forward voltage Vf were measured and evaluated in the same manner as in Evaluation 1 above. The results are shown in Table 5. Then, after the measurement, the power was continuously applied at 350mA for 20 hours. After continuous power application, the output was measured again and compared with the initial output. If the light cannot be lit or the output drops sharply from the initial luminous output to less than half, it was determined that quenching had occurred. The ratio of chips that quenched in the 10 measurements is shown in Table 5.

[0212] [Table 5]

[0213]

[0214] In Example 4, z-w0=0.59-0.45=0.14, xy=0.71-0.35=0.36. Therefore, the following conditions of formula [1] and formula [2] are satisfied simultaneously.

[0215] 0.030<z-w0<0.20 ……[1]

[0216] 0.050≤xy≤0.47 ……[2]

[0217] (Review of evaluation results)

[0218] It is believed that quenching occurred in Comparative Example 7 due to poor contact at the interface between the p-type contact layer and the p-side reflective electrode, similar to Comparative Example 3. On the other hand, in Example 4, since the p-type contact layer has a superlattice structure and the Ni layer has a sufficient thickness, poor contact is presumed to have not occurred. Furthermore, a comparison of Example 4 and Comparative Example 6 shows that the reflective electrode composed of Ni and Rh is effective in increasing luminous output without significantly changing the forward voltage.

[0219] (Example 5)

[0220] Each semiconductor layer is formed in the same manner as in Example 4, and then, an electron beam evaporation method is used to sequentially form a Ni layer (first metal layer) with a thickness of 7 nm and a Rh layer (second metal layer) with a thickness of 50 nm on the Ni layer. Next, a Ni layer with a thickness of 3 nm is formed on the Rh layer (second metal layer) as the third metal layer, followed by a Rh layer with a thickness of 20 nm as the fourth metal layer. Then, as in Example 4, a heat treatment is performed to form an ohmic contact. The other manufacturing conditions are the same as in Example 4. Thus, the deep ultraviolet light-emitting element involved in Example 5 is manufactured. It should be noted that the total thickness of the p-type layer of the p-type electron blocking layer and the p-type contact layer is 92.5 nm.

[0221] (Comparative Example 8)

[0222] A 20 nm thick Au layer is formed on the Rh layer (the second metal layer), instead of forming a 3 nm thick Ni layer as the third metal layer and then a 20 nm thick Rh layer as the fourth metal layer on the Rh layer (the second metal layer) as in Example 5, the deep ultraviolet light-emitting element involved in Comparative Example 8 is manufactured in the same manner as in Example 5, except that the Au layer is formed on the Rh layer (the second metal layer).

[0223] (Comparative Example 9)

[0224] A Ni layer with a thickness of 3 nm is formed on the Rh layer (the second metal layer) as the third metal layer, followed by an Au layer with a thickness of 20 nm as the fourth metal layer, instead of forming a Ni layer with a thickness of 3 nm as the third metal layer, followed by an Rh layer with a thickness of 20 nm as the fourth metal layer as in Example 5. Except for this, the deep ultraviolet light-emitting element involved in Comparative Example 9 is manufactured in the same manner as Example 5.

[0225] (Rating 5)

[0226] In Evaluation 4, the presence or absence of quenching in the Examples and Comparative Examples was confirmed in the same manner as in Evaluation 4, except that the continuous power supply time was extended to 168 hours and 1000 hours, while the continuous power supply time was 20 hours.

[0227] [Table 6]

[0228]

[0229] Table 6 shows that even though quenching is suppressed by combining the p-type contact layer of the superlattice structure according to the present invention with the Ni and Rh reflective electrode, the presence of Au on the Rh layer (second metal layer) poses a risk of quenching if the Au diffuses into the reflective electrode during heating, such as during the third step. Furthermore, it is shown that by constructing the Ni and Rh reflective electrode into a stacked structure with multiple Ni and Rh layers, the occurrence of quenching can be suppressed for a long period of time.

[0230] (Example 6)

[0231] A deep ultraviolet light-emitting device according to Example 6 was produced and evaluated in the same manner as in Example 5, except that the thickness of the p-type electron blocking layer was changed from 40 nm to 33 nm. The total thickness of the p-type electron blocking layer and the p-type contact layer was 85.5 nm.

[0232] (Example 7)

[0233] A deep ultraviolet light-emitting device according to Example 7 was produced and evaluated in the same manner as in Example 5, except that the thickness of the first p-type contact layer was reduced from 5 nm to 2.5 nm and the thickness-averaged Al composition ratio z was set to 0.53. The total thickness of the p-type barrier layer and the p-type contact layer was 75 nm.

[0234] The presence or absence of quenching was confirmed in the same manner as in Evaluation 5 for Examples 6 and 7. For comparison, the production conditions and evaluation results of Examples 6 and 7 are shown in Table 7 below together with Example 5 and Comparative Example 6 described above.

[0235] [Table 7]

[0236]

[0237] As shown in Table 7, by adjusting the combined thickness of the p-type electron blocking layer 60 and the p-type contact layer 70 (the total thickness of the p-type layer), the luminous output can be further increased. The total thickness of the p-type layer is preferably 65 nm to 100 nm, and more preferably 70 nm to 95 nm. Furthermore, compared to electrodes using Ni and Au, an electrode with improved luminous output and higher reliability can be obtained.

[0238] Industrial applicability

[0239] The present invention provides a method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element that achieves both high luminous output and excellent reliability. Furthermore, the present invention provides a method for manufacturing a deep ultraviolet light-emitting element using the reflective electrode and the deep ultraviolet light-emitting element obtained thereby.

[0240] Description of Reference Numerals

[0241] 10 substrate

[0242] 20 buffer layer

[0243] 30 n-type semiconductor layer

[0244] 40 Luminescent Layer

[0245] 41 well layer

[0246] 42 Barrier layer

[0247] 60 p-type electron blocking layer

[0248] 70 p-type contact layer

[0249] 71 1st floor

[0250] 72 2nd floor

[0251] 80 reflective electrode

[0252] 81 1st metal layer

[0253] 82 2nd Metal Layer

[0254] 83 3rd Metal Layer

[0255] 84 Metal Layer 4

[0256] 90 n-side electrode

[0257] 100 Deep UV light emitting elements

Claims

1. A method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element, characterized in that: have: In the first step, Ni is formed as a first metal layer with a thickness of 3 to 20 nm on the p-type contact layer having the superlattice structure; a second step of forming Rh as a second metal layer on the first metal layer with a thickness of not less than 20 nm and not more than 2 μm; as well as In the third step, the first metal layer and the second metal layer are subjected to a heat treatment at a temperature of 300° C. to 600° C. inclusive.

2. The method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element according to claim 1, wherein: The atmosphere gas during the heat treatment in the third step contains oxygen.

3. The method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element according to claim 1 or 2, further comprising the following steps after the second step: forming a Ni layer as a third metal layer on the second metal layer; and forming a Rh layer as a fourth metal layer on the third metal layer.

4. A method for manufacturing a deep ultraviolet light-emitting element, characterized in that: It has the following processes: forming an n-type semiconductor layer on a substrate; forming a light-emitting layer on the n-type semiconductor layer; forming a p-type electron blocking layer on the light-emitting layer; forming a p-type contact layer on the p-type electron blocking layer; and forming a reflective electrode on the p-type contact layer; The steps of forming the p-type contact layer are repeated alternately to form an Al having an Al composition ratio x. x Ga 1-x The first step of forming the first layer composed of N, and the first step of forming the Al layer composed of Al having an Al composition ratio y lower than the Al composition ratio x y Ga 1-y N, thereby forming the p-type contact layer having a superlattice structure, and the Al composition ratio y of the second layer is greater than 0.15, The process of forming the reflective electrode comprises: In a first step, Ni is formed as a first metal layer with a thickness of 3 to 20 nm on the second layer on the outermost surface of the p-type contact layer; a second step of forming Rh as a second metal layer on the first metal layer with a thickness of not less than 20 nm and not more than 2 μm; as well as In the third step, the first metal layer and the second metal layer are subjected to a heat treatment at 300 to 600°C.

5. The method for manufacturing a deep ultraviolet light-emitting element according to claim 4, wherein: In the superlattice structure of the p-type contact layer, When the Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer is w0, The Al composition ratio x of the first layer is higher than the Al composition ratio w0, The Al composition ratio y of the second layer is lower than the Al composition ratio x, The Al composition ratio w0, the Al composition ratio x, the Al composition ratio y, and the thickness-averaged Al composition ratio z of the p-type contact layer satisfy the following formulas [1] and [2]: 0.030<z-w0<0.20……[1] 0.050≤xy≤0.47……[2].

6. The method for manufacturing a deep ultraviolet light-emitting element according to claim 5, wherein: A guide layer having an Al composition ratio higher than that of either the barrier layer of the light-emitting layer or the p-type electron blocking layer is further provided between the well layer closest to the p-type electron blocking layer in the light-emitting layer and the p-type electron blocking layer.

7. The method for manufacturing a deep ultraviolet light-emitting element according to claim 6, wherein: The guide layer is composed of AlN.

8. The method for manufacturing a deep ultraviolet light-emitting element according to any one of claims 5 to 7, wherein: The Al composition ratio w0 is 0.25 or more and 0.60 or less.

9. The method for manufacturing a deep ultraviolet light-emitting element according to any one of claims 4 to 7, wherein: The total thickness of the p-type electron blocking layer and the p-type contact layer is 65-100 nm.

10. The method for manufacturing a deep ultraviolet light-emitting element according to any one of claims 4 to 7, further comprising the following steps after the second step: forming a Ni layer as a third metal layer on the second metal layer; and forming a Rh layer as a fourth metal layer on the third metal layer.

11. A deep ultraviolet light emitting element obtained according to the method for manufacturing a deep ultraviolet light emitting element according to claim 4, characterized in that: An n-type semiconductor layer, a light-emitting layer, a p-type electron blocking layer and a p-type contact layer are sequentially provided on the substrate. The p-type contact layer has a superlattice structure, wherein the superlattice structure is formed by combining Al with an Al composition ratio x. x Ga 1-x The first layer is composed of N and the first layer is composed of Al with an Al composition ratio y. y Ga 1-y The second layer is formed by alternately stacking N, and the Al composition ratio y of the second layer is 0.15 or more, A reflective electrode made of Ni and Rh is provided on the second layer on the outermost surface of the p-type contact layer.

12. The deep ultraviolet light emitting element according to claim 11, wherein: In the superlattice structure of the p-type contact layer, When the Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer is w0, The Al composition ratio x of the first layer is higher than the Al composition ratio w0, The Al composition ratio y of the second layer is lower than the Al composition ratio x, The Al composition ratio w0, the Al composition ratio x, the Al composition ratio y, and the thickness-averaged Al composition ratio z of the p-type contact layer satisfy the following formulas [1] and [2]: 0.030<z-w0<0.20……[1] 0.050≤xy≤0.47……[2].

13. The deep ultraviolet light-emitting element according to claim 11 or 12, wherein: The total thickness of the p-type electron blocking layer and the p-type contact layer is 65-100 nm.

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