CN113330586A

CN113330586A - 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

Info

Publication number: CN113330586A
Application number: CN202080010391.9A
Authority: CN
Inventors: 渡边康弘; 中野雅之
Original assignee: Dowa Electronics Materials Co Ltd
Current assignee: Dowa Electronics Materials Co Ltd
Priority date: 2019-01-22
Filing date: 2020-01-20
Publication date: 2021-08-31
Also published as: JP6793863B2; TW202029523A; TWI722784B; JP2020120114A; JP2020129697A

Abstract

Provided is a reflective electrode for a deep ultraviolet light-emitting element, which can achieve both high light emission output and excellent reliability. The method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element according to the present invention includes: a step 1 of forming Ni as a 1 st metal layer on a p-type contact layer having a superlattice structure at a thickness of 3 to 20 nm; a 2 nd step of forming Rh as a reflective metal with a thickness of 20nm or more and 2 μm or less on the 1 st metal layer; and a 3 rd step of subjecting the 1 st metal layer and the 2 nd metal layer to a heat treatment at 300 ℃ to 600 ℃.

Description

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

Technical Field

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 particularly relates to a method for manufacturing a reflective electrode for a deep ultraviolet light emitting element, which can achieve both high light emission output and excellent reliability.

Background

Group III nitride semiconductors composed of compounds of Al, Ga, In, and the like with N are wide band gap semiconductors having a direct transition band structure, and are expected to be applied to a wide range of fields such as sterilization, water purification, medical treatment, illumination, high-density optical recording, and the like. In particular, a light-emitting element using a group III nitride semiconductor for a light-emitting layer can cover a region from deep ultraviolet light to visible light by adjusting the content ratio of a group III element, and practical application to various light sources is being advanced.

Light having a wavelength of 200 to 350nm is called deep ultraviolet light, and a deep ultraviolet light emitting element emitting deep ultraviolet light is generally manufactured as follows. That is, a buffer layer is formed on a substrate of sapphire, AlN single crystal, or the like, and an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer, each of which is composed of a group III nitride semiconductor, are formed in this order. Next, an n-side electrode electrically connected to the n-type semiconductor layer and a p-side electrode electrically connected to the p-type semiconductor layer are formed, respectively. Here, in order to form an ohmic contact on the p-side electrode side of the p-type semiconductor layer, a p-type GaN contact layer in which the hole concentration is easily increased has been generally formed. In the light-emitting layer, a Multiple Quantum Well (MQW) structure in which barrier layers and well layers made of a group III nitride semiconductor are alternately stacked is widely used.

Here, as one of the characteristics required for the deep ultraviolet light emitting element, a high external quantum efficiency characteristic is mentioned. The external quantum efficiency is determined by (i) the internal quantum efficiency, (ii) the electron injection efficiency, and (iii) the light extraction efficiency.

Patent document 1 discloses a deep ultraviolet light emitting diode including a p-type contact layer of AlGaN mixed crystal and a p-side reflective electrode which reflects light emitted from a light emitting layer, and the substrate side is set as a light extraction direction. The transmittance of the p-type contact layer made of AlGaN can be increased as the Al composition ratio of the p-type contact layer is increased with respect to light having a short wavelength. For this reason, patent document 1 proposes to use a p-type contact layer made of AlGaN having a transmittance corresponding to the emission wavelength, instead of the p-type contact layer made of GaN which is common in the related art. In this case, the reflective electrode is preferably a metal film containing Al as a main component. And Ni is used as an insertion metal layer for forming an ohmic contact.

Patent document 2 discloses a group III nitride semiconductor light-emitting device in which silver (Ag), rhodium (Rh), ruthenium (Ru), platinum (Pt), or palladium (Pd) is used for a positive electrode on a p-type semiconductor layer (for example, a p-type GaN layer) and a 1 st thin-film metal layer having a thickness of 0.2 to 20nm and made of cobalt (Co) or nickel (Ni) is provided between the positive electrode and the p-type semiconductor layer, in consideration of the fact that the amount of reflection of visible light having a wavelength of 380nm to 550nm (blue-violet, blue, and green) by a metal such as nickel (Ni) or cobalt (Co) is small.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication (JP 2015-216352)

Patent document 2: japanese patent laid-open No. 2000-36619

Disclosure of Invention

Problems to be solved by the invention

According to patent document 1, the higher the transmittance of the p-type contact layer with respect to emitted light is, the more preferable. Therefore, according to patent document 1, the higher the Al composition ratio of the p-type contact layer is, the more preferable.

However, according to the experimental results of the present inventors, it was judged that the transmittance with respect to the central emission wavelength of the emitted deep ultraviolet light is not suitable for practical use only by simply increasing the Al composition ratio of the p-type contact layer in contact with the p-side electrode for the following reasons. First, by improving the transmittance of the p-type contact layer to deep ultraviolet light, a deep ultraviolet light emitting element having a light emission output higher than that of the prior art can be surely obtained. However, an overload reliability test (specifically, energization at 100mA for 3 seconds) was performed on the sample of the deep ultraviolet light-emitting element produced in this way, and it was confirmed that a phenomenon (hereinafter, also referred to as "quenching") in which the light emission output was suddenly reduced by half compared to the initial light emission output or suddenly turned off occurred in some samples was observed.

The present inventors also studied the relationship between the kind of the electrode used in the deep ultraviolet light emitting diode and the Al composition ratio of the p-type contact layer. When rhodium (Rh) which is inferior to aluminum (Al) but has a large reflectance in the ultraviolet region is used as the reflective electrode, it was confirmed that the reflective electrode can be used as an electrode when it is formed on a p-type GaN layer, but when it is formed on a p-type AlGaN layer having a single-layer structure and an Al composition of 30% or more, the above quenching occurs, and it was found that reliability as an electrode cannot be obtained.

Such an element whose light emission output is suddenly deteriorated is insufficient in reliability, and the mixing of the element with insufficient reliability into a product is not allowed in quality management of the product. Accordingly, an object of the present invention is to provide a method for manufacturing a reflective electrode for a deep ultraviolet light emitting element, which can achieve both high light emission output and excellent reliability. Further, an object of the present invention is to provide a method for manufacturing a deep ultraviolet light emitting element using the reflective electrode and a deep ultraviolet light emitting element obtained thereby.

Means for solving the problems

The present inventors have made extensive studies on a method for solving the above-mentioned problems. Further, it has been experimentally confirmed that when rhodium (Rh) having a large reflectance in an ultraviolet region is used as a metal material of the reflective electrode, the above-mentioned technical problem can be solved by providing a metal layer made of nickel (Ni) between the rhodium and the p-type contact layer having the superlattice structure, and the present invention has been completed. That is, the main features of the present invention are as follows.

(1) A method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element, comprising:

a step 1 of forming Ni as a 1 st metal layer on a p-type contact layer having a superlattice structure at a thickness of 3 to 20 nm;

a 2 nd step of forming Rh as a 2 nd metal layer with a thickness of 20nm or more and 2 μm or less on the 1 st metal layer; and

and a 3 rd step of subjecting the 1 st metal layer and the 2 nd metal layer to a heat treatment at 300 ℃ to 600 ℃.

(2) The method for producing a reflective electrode for a deep ultraviolet light-emitting element as described in the above (1), wherein an atmosphere gas at the time of the heat treatment in the above-described step 3 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, after the 2 nd step, the step of: forming a Ni layer as a 3 rd metal layer on the 2 nd metal layer; and forming an Rh layer as a 4 th metal layer on the 3 rd metal layer.

(4) A method for manufacturing a deep ultraviolet light emitting element, comprising the steps of:

forming an n-type semiconductor layer on a substrate;

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

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

forming a p-type contact layer on the p-type electron blocking layer; and the number of the first and second groups,

a step of forming a reflective electrode on the p-type contact layer,

the step of forming the p-type contact layer is alternately repeatedComposed of Al having an Al composition ratio x_xGa_1-xA first step of forming a 1 st layer of N, and a step of forming Al having an Al composition ratio y lower than the Al composition ratio x_yGa_1-yA second step of forming a 2 nd layer composed of N, wherein the p-type contact layer has a superlattice structure, and the 2 nd layer has an Al composition ratio y of 0.15 or more,

the step of forming the reflective electrode includes:

a 1 st step of forming Ni as a 1 st metal layer on the 2 nd layer on the outermost surface of the p-type contact layer, the Ni having a thickness of 3 to 20 nm;

and a 3 rd step of subjecting the 1 st metal layer and the 2 nd metal layer to heat treatment at 300 to 600 ℃.

(5) The method for manufacturing a deep ultraviolet light emitting element as set forth in (4) above, wherein, in the superlattice structure of the p-type contact layer,

w represents the Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer₀When the temperature of the water is higher than the set temperature,

the Al composition ratio x of the 1 st layer is higher than the Al composition ratio w₀，

The Al composition ratio y of the 2 nd layer is lower than the Al composition ratio x,

the Al composition ratio w₀The Al composition ratio x, the Al composition ratio y, and the thickness-average Al composition ratio z of the p-type contact layer satisfy the following formula [1]]、[2]：

0.030＜z-w₀＜0.20 ……[1]

0.050≤x-y≤0.47 ……[2]。

(6) The method of manufacturing a deep ultraviolet light emitting element described in (5) above, wherein a guide layer having a higher Al composition ratio than either one of the barrier layer of the light emitting layer and 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 as set forth in (6) above, wherein the guide layer is made of AlN.

(8) The method for manufacturing a deep ultraviolet light-emitting device according to any one of the above (5) to (7), wherein the Al composition ratio w₀Is 0.25 to 0.60 inclusive.

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

(10) The method for manufacturing a deep ultraviolet light emitting device according to any one of the above (4) to (9), further comprising, after the 2 nd step: forming a Ni layer as a 3 rd metal layer on the 2 nd metal layer; and forming an Rh layer as a 4 th metal layer on the 3 rd metal layer.

(11) A deep ultraviolet light emitting element comprising an n-type semiconductor layer, a light emitting layer, a p-type electron blocking layer and a p-type contact layer formed on a substrate in this order,

the p-type contact layer has a superlattice structure that is to be composed of Al having an Al composition ratio x_xGa_1-x1 st layer of N and Al having Al composition ratio y_yGa_1-yN, and the Al composition ratio y of the 2 nd layer is 0.15 or more,

a reflective electrode made of Ni and Rh is provided on the 2 nd layer on the outermost surface of the p-type contact layer.

(12) The deep ultraviolet light emitting element described in (11) above, wherein, in the superlattice structure of the p-type contact layer,

the Al composition ratio w₀The Al composition ratio x, the Al composition ratio y and the p-type contactThe thickness average Al composition ratio z of the layer satisfies the following formula [1]、[2]：

0.030＜z-w₀＜0.20 ……[1]

0.050≤x-y≤0.47 ……[2]。

The deep ultraviolet light-emitting element according to the item (11) or (12), wherein a 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.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a method for manufacturing a reflective electrode for a deep ultraviolet light emitting element can be provided that can achieve both high light emission output and excellent reliability. Further, the present invention can provide a method for manufacturing a deep ultraviolet light emitting element using the reflective electrode and a deep ultraviolet light emitting element obtained thereby.

Drawings

Fig. 1A is a process diagram based on a schematic cross-sectional view for explaining a method of manufacturing a reflective electrode for a deep ultraviolet light emitting element according to an embodiment of the present invention.

Fig. 1B is a process diagram based on a schematic cross-sectional view for explaining a method of manufacturing a reflective electrode for a deep ultraviolet light emitting element according to another embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view illustrating a deep ultraviolet light emitting element according to an embodiment of the present invention.

Fig. 3 is a process diagram based on a schematic cross-sectional view for explaining a method of manufacturing a deep ultraviolet light emitting element according to an embodiment of the present invention.

Detailed Description

Before describing embodiments according to the present invention, the following description will be made in advance. First, in the present specification, the Al composition ratio is not explicitly given, and when only "AlGaN" is given, it means that the composition ratio of the group III element (the sum of Al and Ga) to N is 1: 1, any compound having an unfixed ratio of the group III element Al to Ga. In this case, even if there is no reference to In as a group III element, "AlGaN" means that In may be contained within 5% of the total of Al and Ga as group III elements, and the packet contains InThe compositional formula expressed by In is shown with the Al composition ratio as x₀In composition ratio is denoted by y₀(0≤y₀0.05 or less), described as Al_x0In_y0Ga_1-x0-y0And N is added. When labeled only as "AlN" or "GaN," respectively, means that Ga and Al are not included, but are not excluded as either AlN or GaN by labeling only as "AlGaN" unless explicitly stated otherwise. The value of the Al composition ratio can be measured by photoluminescence measurement, X-ray diffraction measurement, or the like.

In this specification, a layer that electrically functions as a p-type layer is referred to as a p-type layer, and a layer that electrically functions as an n-type layer is referred to as an n-type layer. On the other hand, when a specific impurity such as Mg or Si is not particularly added and does not electrically function as a p-type or an n-type, it is referred to as "i-type" or "undoped". The undoped layer may be mixed with impurities inevitable in the manufacturing process, and specifically, has a small carrier density (for example, less than 4 × 10)¹⁶/cm³) In this case, the term "undoped" is used in this specification. The values of the concentrations of impurities such as Mg and Si were obtained by SIMS analysis.

The total thickness of each layer formed by epitaxial growth can be measured using an optical interference type film thickness measuring instrument. Further, for the respective thicknesses of the respective layers, when the compositions of the adjacent layers are significantly different (for example, when the Al composition ratio is different by 0.01 or more), it can be calculated based on the observation of the cross section of the grown layer by a transmission electron microscope. In addition, for the boundary and thickness of the layer having the same or substantially the same Al composition ratio (for example, less than 0.01) but different impurity concentrations in the adjacent layers, the boundary between the two layers and the thickness of each layer are measured by TEM-EDS. The impurity concentrations of both can be measured by SIMS analysis. When the thickness of each layer is small as in the superlattice structure, the thickness can be measured by TEM-EDS.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In principle, the same components are denoted by the same reference numerals, and the description thereof is omitted. In the drawings, the lateral and vertical ratios of the substrate and the layers are exaggerated compared to the actual ratio for the sake of convenience of explanation.

(reflection electrode)

A p-side reflective electrode 80 obtained by the method for manufacturing a reflective electrode for a deep ultraviolet light emitting element according to an embodiment of the present invention is shown in fig. 1A. Fig. 2 is a schematic cross-sectional view of the deep ultraviolet light emitting element 100 having the reflective electrode 80. Hereinafter, reference is made to reference numerals of fig. 1A and 2. The reflective electrode 80 may be disposed directly above the p-type contact layer 70. The reflective electrode 80 is a reflective electrode using a metal having a high reflectance (for example, 60% or more) with respect to ultraviolet light emitted from the light-emitting layer 40, and in the present invention, rhodium (Rh) is used as a metal having such a reflectance (hereinafter, referred to as "reflective metal"). As rhodium (Rh), for example, commercially available metal rhodium (for example, purity 3N) can be used as a vapor deposition source. The p-type contact layer 70 has a superlattice structure, and a p-side reflective electrode formed by forming the reflective metal on the p-type contact layer 70 with a predetermined thickness or more via nickel (Ni) has a high reflectance to deep ultraviolet light. Further, it was found that by performing the heat treatment at 300 ℃ to 600 ℃, relatively good ohmic contact can be formed between the p-type contact layer 70 and the p-side reflective electrode 80, and the reliability that can withstand high current is also obtained. Since it is extremely difficult to directly measure the reflectance of the reflective electrode 80 in the state of the deep ultraviolet light emitting device 100, the reflectance of the reflective electrode 80 is measured instead by forming the 1 st metal layer 81 and the 2 nd metal layer 82 on the sapphire substrate, irradiating light of each wavelength from the transparent sapphire substrate side toward the reflective electrode 80 before and after the heat treatment step, and measuring the reflectance with respect to the wavelength (for example, the reflectance with respect to the wavelength of 300 nm) with an ultraviolet-visible spectrophotometer.

That is, referring to fig. 1A, a method for manufacturing a reflective electrode for a deep ultraviolet light emitting element according to an embodiment of the present invention includes: a step 1 (step 1B in FIG. 1A) of forming Ni as a 1 st metal layer 81 on a p-type contact layer 70 having a superlattice structure (step 1A in FIG. 1A) to a thickness of 3 to 20 nm; a 2 nd step (step 1C in fig. 1A) of forming Rh as a 2 nd metal layer 82 with a thickness of 20nm to 2 μm on the 1 st metal layer 81; and a 3 rd step (step 1D in fig. 1A) of subjecting the 1 st metal layer and the 2 nd metal layer to heat treatment at 300 ℃ to 600 ℃.

< step 1 >

In the step 1, Ni is formed as a 1 st 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 a conventional method such as a vacuum deposition method such as an electron beam deposition method or a resistance heating deposition method, or a sputtering method. This is because when the wavelength is less than 3nm, the quenching is difficult to suppress, and when the wavelength is more than 20nm, the reflectance of the reflective electrode is significantly reduced. Further, the thickness of the 1 st metal layer 81 is preferably 3 to 10 nm. By forming the 1 st metal layer 81 to have a thickness of 10nm or less, the reflectance of the reflective electrode 80 after heat treatment with respect to a wavelength of 300nm can be set to 60% or more. The thickness of the 1 st metal layer 81 can be measured using a thickness meter for a crystal oscillator.

< 2 nd Process >

In the 2 nd step, Rh is formed as the 2 nd metal layer 82 on the 1 st metal layer 81 in a thickness of 20nm or more and 2 μm or less. This is because if the wavelength is less than 20nm, the reflectance of ultraviolet light with respect to the 2 nd metal layer 82 may not be sufficiently high. In addition, the reason is that if the thickness exceeds 2 μm, a cost problem relating to Rh is caused. In order to increase the reflectance of the reflective electrode after diffusion of the 1 st metal layer 81 by the heat treatment step described later, the thickness of the 2 nd metal layer 82 is more preferably 30nm or more, and more preferably 100nm or less for cost control. In the 2 nd step, the 2 nd metal layer may be formed by a conventional method such as vacuum evaporation or sputtering, as in the 1 st step. The thickness of the 2 nd metal layer 82 can be measured using a film thickness meter for a crystal oscillator.

< step 3 >

In the 3 rd step, the 1 st metal layer 81 and the 2 nd metal layer 82 are subjected to heat treatment at 300 ℃ to 600 ℃ to obtain the reflective electrode 80. As the atmosphere gas used when the heat treatment for forming the ohmic contact is performed after the p-side electrode is formed as in this step, an inert gas such as nitrogen gas is generally used. In this step, only an inert gas may be used as the atmosphere gas. However, in this step, it is more preferable that the atmosphere gas contains oxygen. The proportion of oxygen in the atmosphere gas is preferably greater than 0% and not more than 50% in terms of flow ratio.

The reflective electrode 80 thus obtained is an electrode made of Ni and Rh. With the heat treatment in step 3, Ni as the 1 st metal layer 81 diffuses from the interface in contact with the p-type contact layer 70 to the Rh side of the 2 nd metal layer 82. Further, the proportion of Rh at the interface between p-type contact layer 70 and reflective electrode 80 increases due to diffusion of Ni, and the reflectance at this interface increases as compared to before the heat treatment. Since Ni does not remain in a layer form and diffuses in the reflective electrode 80 after the heat treatment, it is difficult to accurately measure the amount of Ni after the heat treatment (i.e., after diffusion). Therefore, when peaks of Ni and Rh are simultaneously observed in SEM-EDS analysis of the cross section (vertical cross section) of the reflective electrode after the heat treatment, it is judged that the reflective electrode 80 composed of Ni and Rh is provided. In the reflective electrode 80, Rh is 50% or more, preferably 75% or more, in terms of a volume ratio (corresponding to an area ratio in an SEM-EDS analysis chart of a cross section of the reflective electrode). By setting the volume ratio of Rh in the reflective electrode 80 to 75% or more, the reflectance of the reflective electrode 80 after heat treatment with respect to a wavelength of 300nm can be set to 60% or more.

In the reflectance measurement of the reflective electrode (after the heat treatment step), since the reflectance of the Rh alone is 70 to 73% with respect to the wavelength 300nm and the reflectance of the alloy of Ni and Au is less than 40%, the reflective electrode 80 made of Ni and Rh according to the present invention can be set to a reflectance of 40% or more and less than 67% with respect to the wavelength 300nm by setting the thickness of the 1 st metal layer 81 to 3 to 20nm and the thickness of the 2 nd metal layer 82 to 20nm to 2 μm, and to a reflectance of 60% or more and less than 70% with respect to the wavelength 300nm by setting the thickness of the 1 st metal layer 81 to 3 to 10nm and the thickness of the 2 nd metal layer 82 to 30nm to 100 nm. Even if Ni is alloyed with Rh, the reflectance based on Rh alone is not significantly reduced. Further, ruthenium (Ru), gold (Au), platinum (Pt), palladium (Pd), and titanium (Ti) are conceivable as impurities that can be contained in the reflective electrode 80 in addition to Ni and Rh without greatly decreasing the reflectance, and the content of these impurities is 40 mass% or less, preferably 10 mass% or less.

By using the reflective electrode 80 for a deep ultraviolet light emitting element according to the present embodiment described above for a deep ultraviolet light emitting element, both high light emission output and excellent reliability can be achieved.

Refer to fig. 1B. As another embodiment of the above embodiment, it is also preferable that the method further includes, after the 2 nd step: forming a Ni layer as a 3 rd metal layer 83 on the 2 nd metal layer; and a step of forming an Rh layer as the 4 th metal layer 84 on the 3 rd metal layer 83. This step may be performed between the 2 nd step and the 3 rd step, or may be performed after the 3 rd step, and is preferably performed between the 2 nd step and the 3 rd step and immediately after the 2 nd step from the viewpoint of work efficiency. The Ni layer may be formed as the 3 rd metal layer 83 with a thickness of 1 to 20 nm. The Rh layer may be formed as the 4 th metal layer 84 to have a thickness of 5nm or more and 2 μm or less. Further, on the 4 th metal layer 84, an Ni layer and an Rh layer corresponding to the 3 rd metal layer and the 4 th metal layer may be repeatedly formed again, and the reflective electrode may be formed as a laminated body in which the Ni layer and the Rh layer are repeatedly laminated in this order a plurality of times.

Although there is a risk of quenching when Au diffuses in the reflective electrode by heating in the 3 rd step or the like in a state where Au is present on the 2 nd metal layer 82, quenching can be suppressed by forming the reflective electrode composed of Ni and Rh in a laminated structure in which the order of lamination of Ni and Rh is repeated a plurality of times. Therefore, it is preferable to laminate the Ni layer and the Rh layer a plurality of times because an electrode capable of more reliably preventing the risk of quenching can be obtained, regardless of the mounting step of forming an electrical connection to the outside or the connection method to the outside (including the case where heating such as soldering is necessary) by bringing another metal (such as gold) into contact with the Rh layer after lamination. From this viewpoint, the metal element constituting the reflective electrode is particularly preferably composed of only Ni and Rh.

(deep ultraviolet light emitting element)

Next, the deep ultraviolet light emitting element 100 having the reflective electrode 80 obtained by the present invention will be described. As shown in fig. 2, the deep ultraviolet light emitting device 100 according to an embodiment of the present invention is a deep ultraviolet light emitting device having an n-type semiconductor layer 30, a light emitting layer 40, a p-type electron blocking layer 60, and a p-type contact layer 70, and a reflective electrode 80 on the p-side in this order on a substrate 10. The reflective electrode 80 is provided on the 2 nd layer 72 on the outermost surface of the p-type contact layer. The p-type contact layer 70 has a superlattice structure that is to be composed of Al having an Al composition ratio x_xGa_1-x1 st layer 71 of N and Al having Al composition ratio y_yGa_1-yN-constituting 2 nd layers 72 are alternately laminated. The Al composition ratio y of the 2 nd layer 72 is 0.15 or more (y.gtoreq.0.15).

In particular, w is the Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer 40₀In this case, it is preferable that the Al composition ratio x of the 1 st layer 71 is higher than the Al composition ratio w₀The 2 nd layer 72 has an Al composition ratio y lower than the Al composition ratio x and an Al composition ratio w₀The Al composition ratio x, the Al composition ratio y and the thickness-average Al composition ratio z of the p-type contact layer 70 satisfy the following formula [1]]、[2]：

0.030＜z-w₀＜0.20 ……[1]

0.050≤x-y≤0.47 ……[2]。

As shown in fig. 2, it is a preferred embodiment of the deep ultraviolet light emitting element 100 that the buffer layer 20 is provided between the substrate 10 and the n-type semiconductor layer 30, the p-side reflective electrode 80 is provided directly above the p-type contact layer 70, and the n-side electrode 90 is provided on the exposed surface of the n-type semiconductor layer 30.

For the sake of simplicity, the description will be made on the assumption that the Al composition ratio and the thickness of each of the 1 st layer 71 and the 2 nd layer 72 in the superlattice structure of the p-type contact layer 70 are constant. At this time, the thickness-average Al composition ratio z of the p-type contact layer 70 is defined as follows. First, the number of layers of the 1 st layer 71 in the superlattice structure is represented by N, and the thickness of each layer of the 1 st layer 71 is represented by NIs t_a. Similarly, the number of layers of the 2 nd layer 72 is denoted by M, and the thickness of each layer of the 2 nd layer 72 is denoted by t_b. At this time, the thickness average Al composition ratio of the p-type contact layer 70 satisfies the following formula [3]。

Note that the Al composition ratio and the thickness of each of the 1 st layer 71 and the 2 nd 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 the thickness of each of the 1 st layer 71 and the 2 nd layer 72 in the superlattice structure are changed, the thickness average Al composition ratio z may be a weighted average (weighted average) based on the thickness and the Al composition ratio of each of the 1 st layer 71 and the 2 nd layer 72, and the Al composition ratios x and y of each of the 1 st layer 71 and the 2 nd layer 72 represent weighted averages based on the thicknesses.

Next, referring to fig. 2, the respective configurations 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 in detail.

< substrate >

As the substrate 10, a substrate that can transmit light emitted from the light-emitting layer 40 is preferably used, and for example, a sapphire substrate, a single crystal AlN substrate, or the like can be used. As the substrate 10, an AlN template substrate in which an undoped AlN layer is epitaxially grown on the surface of a sapphire substrate may be used.

< n-type semiconductor layer >

The n-type semiconductor layer 30 is provided on the substrate 10 via the buffer layer 20 as necessary. The n-type semiconductor layer 30 may be directly provided on the substrate 10. The n-type semiconductor layer 30 is doped with an n-type dopant. Specific examples of the n-type dopant include silicon (Si), germanium (Ge), tin (Sn), sulfur (S), oxygen (O), titanium (Ti), zirconium (Zr), and the like. The dopant concentration of the n-type dopant is not particularly limited as long as the n-type semiconductor layer 30 can function as an n-type, and may be, for example, 1.0 × 10¹⁸Atom/cm³～1.0×10²⁰Atom/cm³. The n-type semiconductor layer 30 preferably has a band gap wider than that of the light-emitting layer 40 (the well layer 41 in the case of a quantum well structure) and has transparency to deep ultraviolet light to be emitted. The n-type semiconductor layer 30 may have a single-layer structure or a multi-layer structure, or may have a structure including a composition-gradient layer or a superlattice structure in which the composition ratio of the group III element is gradient in the crystal growth direction. The n-type semiconductor layer 30 not only forms a contact portion with the n-side electrode but also has a function of improving crystallinity from the substrate to the light-emitting layer.

< light emitting layer >

The light emitting layer 40 is disposed on the n-type semiconductor layer 30 and radiates deep ultraviolet light. The light-emitting layer 40 may be made of AlGaN, and the Al composition ratio thereof may be set so that the wavelength of the emitted light is 200 to 350nm of deep ultraviolet light or the central emission wavelength is 265nm to 317 nm. The Al composition ratio may be, for example, in the range of 0.25 to 0.60.

The light-emitting layer 40 may have a single-layer structure with a constant Al composition ratio, and preferably has a multi-Quantum Well (MQW) structure in which a Well layer 41 and a barrier layer 42 made of AlGaN with different Al composition ratios are stacked. In the case where the light-emitting layer 40 has a single-layer structure with a constant Al composition ratio, the Al composition ratio w of the layer emitting deep ultraviolet light in the light-emitting layer 40₀The Al composition ratio itself of the light emitting layer 40. In addition, in the case where the light emitting layer 40 has a multiple quantum well structure, since the well layer 41 corresponds to a layer which emits deep ultraviolet light in the light emitting layer 40, for convenience, the Al composition ratio w of the well layer 41 is regarded as corresponding to the Al composition ratio w described above₀. It is preferable that the Al composition ratio w of the deep ultraviolet light-emitting layer is set to be lower than that of the deep ultraviolet light-emitting layer₀(or the Al composition ratio w of the well layer) is set to 0.25-0.60, so that the wavelength of the radiation light is 200-350 nm of the deep ultraviolet light, or the central light emitting wavelength is 265nm to 317 nm.

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). The Al composition ratio b of the barrier layer 42 may be, for example, 0.40 to 0.95 under the condition that b > w. The number of repetitions of the well layer 41 and the barrier layer 42 is not particularly limited, and may be, for example, 1 to 10 times. It is preferable that the barrier layers be disposed at both ends (i.e., the first and last ends) in the thickness direction of the light-emitting layer 40, and if the number of repetitions of the well layer 41 and the barrier layer 42 is n, the well layer and the barrier layer in "n.5 group" are marked. The thickness of the well layer 41 may be 0.5nm to 5nm, and the thickness of the barrier layer 42 may be 3nm to 30 nm.

< guide layer >

In the case where the light-emitting layer 40 has the quantum well structure, it is also preferable to provide a guiding 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. This can improve the light emission output of the deep ultraviolet light emitting element 100. In this case, the Al composition ratio of the guide layer is denoted by b_gWhen the Al composition ratio α of the p-type electron blocking layer 60 described later is used, the relationship between the respective Al composition ratios is as follows.

w (well layer) < b (barrier layer) < alpha (p-type electron blocking layer) < b_g(guide layer)

It is also preferable that the light-emitting layer 40 be formed of n sets of the well layer 41 and the barrier layer 42 from the barrier layer 42, and that the layer in contact with both the light-emitting layer 40 and the p-type electron blocking layer 60 be formed as the guide layer, and that the thickness be thinner than the other barrier layers. For example, the guide layer is made of AlN (in this case, it is particularly called AlN guide layer), and it is also preferable that the thickness thereof is 0.7 to 1.7 nm.

< p-type electron blocking layer >

The p-type electron blocking layer 60 is disposed on the light emitting layer 40. The p-type electron blocking layer 60 blocks electrons, injects the 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 the electrons. To achieve this, although according to the Al composition ratio w of the layer emitting deep ultraviolet light₀(in the case of the quantum well structure, the Al composition ratio w corresponding to the well layer 41 may vary, but it is preferable that the Al composition ratio α of the p-type electron blocking layer 60 is 0.35. ltoreq. α.ltoreq.0.95. When the Al composition ratio α is 0.35 or more, the p-type electron blocking layer 60 may be contained as IIIThe group elements Al and Ga are In an amount of 5% or less. Here, the Al composition ratio α is preferably higher than the thickness-average Al composition ratio z of the p-type contact layer 70 while satisfying the above-described conditions. That is, α > z is preferable. Further, it is more preferable that both the Al composition ratio α of the p-type electron blocking layer 60 and the Al composition ratio b of the barrier layer 42 satisfy 0 < α -b.ltoreq.0.55. This can reliably improve the efficiency of injecting electrons into the well layer 41 through the p-type electron blocking layer 60.

The thickness of the p-type electron blocking layer 60 is not particularly limited, and is preferably 10nm to 80nm, for example. When the thickness of the p-type electron blocking layer 60 is within this range, high light emission output can be obtained reliably. The thickness of p-type electron blocking layer 60 is preferably greater than the thickness of barrier layer 42. Examples of the p-type dopant doped in the p-type electron blocking layer 60 include magnesium (Mg), zinc (Zn), calcium (Ca), beryllium (Be), manganese (Mn), and the like, and Mg is generally used. The dopant concentration of the p-type electron blocking layer 60 is not particularly limited as long as it can function as a p-type layer, and may be, for example, 1.0 × 10¹⁸Atom/cm³～5.0×10²¹Atom/cm³。

< p-type contact layer >

The p-type contact layer 70 is disposed on the p-type electron blocking layer 60. The p-type contact layer 70 is a layer for reducing the contact resistance between the reflective electrode 80 provided on the p-side directly above it and the p-type electron blocking layer 60. Therefore, there is no desired configuration other than the impurities inevitable in manufacturing between the p-type contact layer 70 and the p-side reflective electrode 80. That is, the p-side reflective electrode 80 is next present on the p-type contact layer 70 of the superlattice structure.

As mentioned above, the p-type contact layer 70 is made of Al_xGa_1-x1 st layer 71 of N and Al_yGa_1-yN-constituting 2 nd layers 72 are alternately stacked. Here, it is preferable that the Al composition ratio x of the 1 st layer 71 is higher than the Al composition ratio w of the layer emitting deep ultraviolet light in the light emitting layer 40₀(x＞w₀) The transmittance with respect to deep ultraviolet light is improved. If the light-emitting layer 40 has a single-layer structure, the Al composition ratio x is higher than that of the light-emitting layer 40In other words, if the light-emitting layer 40 has a quantum well structure, the Al composition ratio x may be higher than the Al composition ratio w of the well layer 41.

Further, as described above, the Al composition ratio w is preferable₀The Al composition ratio x, the Al composition ratio y and the thickness average Al composition ratio z of the p-type contact layer satisfy the following formula [1]]、[2]：

0.030＜z-w₀＜0.20 ……[1]

0.050≤x-y≤0.47 ……[2]。

Conventionally, a p-type GaN layer, which is likely to increase the hole concentration, has been used as a p-type contact layer of a deep ultraviolet light emitting device. However, the p-type GaN layer absorbs light having a wavelength of 360nm or less due to its band gap. Therefore, in deep ultraviolet light radiated from the light emitting layer, light extraction from the p-type contact layer side or light extraction effect by reflection on the p-side electrode is hardly expected. On the other hand, if the p-type contact layer is AlGaN having an increased Al composition ratio, the deep ultraviolet light emitted from the light-emitting layer can pass through the p-type contact layer, although the hole concentration may be slightly reduced compared to GaN. However, experiments by the present inventors have found that when the Al composition ratio of the p-type contact layer is too high, a deep ultraviolet light emitting element with insufficient reliability may be obtained. On the other hand, in the p-type contact layer 70 having a superlattice structure formed according to the above-described Al composition ratio, the average Al composition ratio z is higher than the Al composition ratio w of the layer emitting deep ultraviolet light in the light-emitting layer 40 due to the thickness thereof₀(z＞w₀) Therefore, deep ultraviolet light is preferably transmitted through the p-type contact layer 70, and as a result, higher light emission output can be obtained.

Here, in order to more reliably transmit deep ultraviolet light through the p-type contact layer 70, the above formula [1] is preferable]It is shown that the difference between the thickness average Al composition ratio z and the Al composition ratio w of the deep ultraviolet light-emitting layer is made higher than 0.030 (i.e., z-w)₀> 0.030). To achieve this object, it is more preferable that the difference between the Al composition ratio z and the Al composition ratio w is higher than 0.040 (z-w)₀> 0.040), further preferably higher than 0.050 (z-w)₀> 0.050), particularly preferably above 0.06 (z-w)₀＞0.060)。

In order to form a good ohmic contact between the p-type contact layer 70 and the p-side reflective electrode 80 and to ensure sufficient reliability, the upper limit of the thickness-average Al composition ratio is preferably set. For this purpose, the above formula [1] is preferred]As shown, the upper limit of the difference between the thickness-average Al composition ratio z and the Al composition ratio w of the deep ultraviolet light-emitting layer was set to 0.20 (z-w)₀< 0.20), for this purpose, it is more preferable to set the upper limit of the difference between the Al composition ratio z and the Al composition ratio w to 0.19 (z-w)₀< 0.19), and it is further preferable to set the upper limit to 0.18 (z-w)₀＜0.18)。

Further, as shown in the above formula [2], the difference between the Al composition ratio x of the 1 st layer 71 and the Al composition ratio y of the 2 nd layer 72 is preferably 0.050 or more in absolute terms (x-y ≧ 0.050). This is to cause the p-type contact layer 70 to function reliably as a superlattice structure. In order to reduce distortion of the entire superlattice structure and contact the p-side reflective electrode 80 at a low Al composition ratio, the difference between the Al composition ratio x and the Al composition ratio y is preferably 0.1 or more (x-y ≧ 0.10), more preferably 0.15 or more (x-y ≧ 0.15) in absolute terms. 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 1 st layer and the 2 nd layer is greatly changed, which increases the distortion, and it becomes difficult to obtain a superlattice layer having good crystallinity. Therefore, in order to more reliably obtain the effects of the present invention, it is preferable to set x-y.ltoreq.0.47, and more preferably set x-y.ltoreq.0.45.

It is preferable that the Al composition ratio y of the 2 nd layer 72, which is a layer having a low Al composition ratio in the superlattice structure, is 0.20 or more because the transmittance of deep ultraviolet light emitted from the light-emitting layer 40 can be more reliably improved. For this purpose, the Al composition ratio y is more preferably 0.21 or more, and still more preferably 0.25 or more. On the other hand, it is preferable to set the Al composition ratio y to 0.55 or less because high reliability can be more reliably maintained. For this purpose, the Al composition ratio y is more preferably 0.51 or less, and particularly preferably 0.40 or less. It should be noted that as long as the thickness average Al composition ratio z is higher than that of the layer emitting deep ultraviolet light in the light emitting layer 40Al composition ratio w of₀Then the Al composition ratio y may be higher than the Al composition ratio w₀Or may be lower than the composition ratio w of Al₀. In addition, as long as the above formula [1] is satisfied]、[2]The Al composition ratio x may be set as appropriate, and the upper limit and the lower limit of the Al composition ratio x are not limited. In the following formula [1]、[2]In addition, the Al composition ratio x may be set approximately within a range of 0.40 to 0.85.

Further, the thickness t of each of the 1 st layer 71 and the 2 nd layer 72_a、t_bThe conditions are not particularly limited as long as the superlattice structure is formed and the condition that the thickness average Al composition z with respect to the Al composition ratio of the light-emitting layer 40 is satisfied. For example, the thickness t of the 1 st layer 71 may be set_aThe thickness t of the 2 nd layer 72 is set to be 1.0nm to 10.0nm_bIs set to be 1.0nm to 10.0 nm. Thickness t_a、t_bThe size of (d) is not limited, and either may be large or both may have the same thickness. The number of times of repetition of the 1 st layer 71 and the 2 nd layer 72 is preferably set appropriately within a range of, for example, 3 to 15 times so that the thickness of the entire p-type contact layer 70 is within a range of 20nm or more and 100nm or less, preferably 70nm or less.

The total thickness of the p-type layer, which is 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 65nm to 100nm, and more preferably 70nm to 95 nm. By setting the light emission amount within this range, a high light emission output can be more reliably obtained.

Here, a layer close to the end of the p-type electron blocking layer 60 side in the thickness direction of the p-type contact layer 70 is preferably the 1 st layer 71. In other words, it is preferable that the 1 st layer 71 be provided directly above the p-type electron blocking layer 60 in the case where there is no other layer interposed between the p-type contact layer 70 and the p-type electron blocking layer 60 and the both are in contact with each other. Since the Al composition ratio x of the 1 st layer 71 is higher than the Al composition ratio y of the 2 nd 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 due to distortion between the p-type electron blocking layer 60 and the p-type contact layer 70 can be more reliably suppressed.

On the other hand, the layer at the end of the p-type contact layer 70 on the side away from the p-type electron blocking layer 60 in the thickness direction is preferably the 2 nd layer 72. In other words, the layer in contact with the p-side reflective electrode 80 is preferably the 2 nd layer 72. This is because the Al composition ratio x of the 1 st layer 71 is lower than the Al composition ratio y of the 2 nd layer 72, and therefore, it is easier to form ohmic contact with the reflective electrode 80 on the p side.

When the end of the p-type contact layer 70 closer to the p-type electron blocking layer 60 in the thickness direction is the 1 st layer 71 and the end farther from the p-type electron blocking layer 60 is the 2 nd layer 72, the number of layers of the 1 st layer 71 is equal to the number of layers of the 2 nd layer 72. However, in the present embodiment, the number of layers of both is not necessarily the same. This embodiment includes a case where two layers at the end of the p-type contact layer 70 in the thickness direction are the 2 nd layer 72 (in this case, the number of layers of the 2 nd layer 72 is 1 layer more than the number of layers of the 1 st layer 71).

In addition, although a superlattice structure in which 2 layers of the 1 st layer 71 and the 2 nd layer 72 are repeatedly stacked has been described as one embodiment of the present invention, a superlattice structure in which a 3 rd layer having the same relationship with the 1 st layer and the 2 nd layer and having an Al composition ratio between the 1 st layer and the 2 nd layer is disposed between the 1 st layer and the 2 nd layer may be employed as another embodiment of the present invention. In this case, the same effects as those of the present invention can be obtained.

Here, the p-type contact layer 70 preferably has a Mg concentration of 3 × 10 on the side in contact with the p-side reflective electrode 80²⁰Atom/cm³In the high concentration region, the Mg concentration in the high concentration region is more preferably 5X 10²⁰Atom/cm³The above. The hole concentration of the p-type contact layer 70 can be increased and the forward voltage Vf of the deep ultraviolet light emitting device 100 can be decreased. Although the upper limit is not limited, in the present embodiment, the upper limit of the Mg concentration in the high concentration region may be set to 1 × 10 in consideration of industrial productivity²¹Atom/cm³. At this time, the Mg concentration of the region on the p-type electron blocking layer 60 side in the p-type contact layer 70 may be set to a normal range, typically 5 × 10¹⁹Atom/cm³Above and less than 3 × 10²⁰Atom/cm³. In addition, p-typeThe Mg concentration in the contact layer is an average concentration in each region obtained by SIMS measurement. In order to ensure the crystallinity of the p-type contact layer 70, the thickness of the high concentration region is usually 15nm or less, and several layers on the side in contact with the p-side reflective electrode 80 may be set as the high concentration region.

The p-type contact layer 70 has an Si concentration of 5 × 10 on the side in contact with the p-side reflective electrode 80¹⁶Atom/cm³Above and 1 × 10²⁰Atom/cm³The following Si doped regions are also preferred. More preferably, the Si concentration in this region is set to 2X 10¹⁹Atom/cm³Above and 5 × 10¹⁹Atom/cm³The following. This can further improve the light emission output of the deep ultraviolet light emitting element 100. The thickness of the Si-doped region is about 1 to 5nm, and this effect can be obtained reliably. The last 2 nd layer in the superlattice structure with the Si doped region as a p-type contact layer is also preferred. The Mg concentration may be 3X 10²⁰Atom/cm³The above high concentration region is further doped with a co-doped region of Si. In addition, only Si may be doped in the Si-doped region (i.e., Mg may not be doped).

In the case where a Si-doped region doped with only Si and not doped with Mg is provided on the p-type contact layer 70 on the side in contact with the p-side reflective electrode 80, the region can be considered to be n-type in terms of conductivity type. However, if the thickness is within the above range (1 to 5nm), the thyristor will not be formed unless Mg is doped, as long as the uppermost layer of the p-type contact layer 70 is in contact with the p-type electrode. For this reason, even in this case, the Si-doped region is considered as a part of the p-type contact layer 70.

The deep ultraviolet light emitting element 100 according to the present embodiment described above can achieve both high light emission output and excellent reliability.

Hereinafter, a specific form of the deep ultraviolet light emitting element 100 applicable to the present embodiment will be described, but the present embodiment is not limited to the following form.

< buffer layer >

As shown in fig. 2, it is also preferable to provide a buffer layer 20 between the substrate 10 and the n-type semiconductor layer 30 to mitigate lattice mismatch therebetween. As the buffer layer 20, an undoped group III nitride semiconductor layer can be used, and it is also preferable that the buffer layer 20 has a superlattice structure.

< n-side electrode >

The n-side electrode 90 that can be provided on the exposed surface of the n-type semiconductor layer 30 may be, for example, 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 may be appropriately selected according to the shape and size of the light emitting element. The n-side electrode 90 is not limited to the one formed on the exposed surface of the n-type semiconductor layer 30 as shown in fig. 2, and may be electrically connected to the n-type semiconductor layer.

< other constitutions >

Although not shown in fig. 2, an orientation layer made 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. By providing the guide layer, injection of holes into the light-emitting layer 40 can be promoted.

< p-type cladding layer >

Although not shown in fig. 2, a p-type cladding layer made 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 the following Al composition ratio: higher than the Al composition ratio of the layer emitting deep ultraviolet light in the light emitting layer 40 (Al composition ratio w in the case of a quantum well structure) and the thickness average 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, the p-type electron blocking layer 60 and the p-type cladding layer are both layers having an Al composition ratio higher than that of the layer emitting deep ultraviolet light, and are layers that substantially transmit deep ultraviolet light emitted from the light emitting layer 40. However, it is preferable not to provide the p-type cladding layer. The reason for this is described in Japanese patent laid-open publication No. 2016-111370, the entire disclosure of which is incorporated herein by reference. When the p-type cladding layer is provided, α > β and β > y are obtained when the Al composition ratio of the p-type cladding layer is β.

In the deep ultraviolet light emitting element 100 according to the present embodiment, the substrate side or the substrate horizontal direction can be set as the main light extraction direction by forming the reflective electrode 80 on the p side with a reflective electrode material to reflect deep ultraviolet light. The deep ultraviolet light emitting element 100 may be in a so-called flip-chip type.

(method for manufacturing deep ultraviolet light-emitting device)

Next, an embodiment of a manufacturing method for obtaining the deep ultraviolet light emitting element 100 will be described with reference to fig. 3. One embodiment of the method for manufacturing the deep ultraviolet light emitting element 100 according to the present invention includes: a step of forming an n-type semiconductor layer 30 on the substrate 10 (see step 3A in fig. 3); a step of forming a light-emitting layer 40 on the n-type semiconductor layer 30; a step of forming a p-type electron blocking layer 60 on the light-emitting layer 40 (see step 3B in fig. 3); a step of forming a p-type contact layer on the p-type electron blocking layer (see step 3C in fig. 3); and a step of forming a reflective electrode on the p-type contact layer (see step 3D in fig. 3). And the step of forming the p-type contact layer is alternately repeated to form a p-type contact layer composed of Al having an Al composition ratio x_xGa_1-xA first step of forming a 1 st layer of N, and a step of forming Al having an Al composition ratio y lower than the Al composition ratio x_yGa_1-yAnd a second step of forming the 2 nd layer composed of N, thereby forming the p-type contact layer having a superlattice structure, and the 2 nd layer has an Al composition ratio y of 0.15 or more. As described in the embodiment of the reflective electrode 80, the step of forming the reflective electrode includes: a step 1 of forming Ni as a 1 st metal layer 81 on a p-type contact layer 70 having a superlattice structure at a thickness of 3 to 20 nm; a 2 nd step of forming Rh as a 2 nd metal layer 82 with a thickness of 20nm or more and 2 μm or less on the 1 st metal layer 81; and a 3 rd step of subjecting the 1 st metal layer and the 2 nd metal layer to heat treatment at 300 ℃ to 600 ℃ (see fig. 1A). In addition, the step of forming the p-type contact layer 70 (refer to step 3C) is to alternately and repeatedly form Al having the Al composition ratio x_xGa_1-xA first step of forming a 1 st layer 71 composed of N, and forming Al having an Al composition ratio y lower than the Al composition ratio x_yGa_1-yN is formed ofAnd a second step of forming 2 a layer 72, thereby forming a p-type contact layer 70 having a superlattice structure, wherein the Al composition ratio y of the 2 nd layer 72 is 0.15 or more (y.gtoreq.0.15).

Further, w represents an Al composition ratio of the layer emitting deep ultraviolet light in the light-emitting layer 40₀In this case, it is preferable that the Al composition ratio x of the 1 st layer 71 is higher than the Al composition ratio w₀The 2 nd layer 72 has an Al composition ratio y lower than the Al composition ratio x and an Al composition ratio w₀The Al composition ratio x, the Al composition ratio y and the thickness-average Al composition ratio z of the p-type contact layer 70 satisfy the following formula [1]]、[2]：

0.030＜z-w₀＜0.20 ……[1]

0.050≤x-y≤0.47 ……[2]。

Next, description is made with reference to the flowchart of fig. 3. However, the description overlapping with the above-described embodiment will be omitted.

First, as shown in steps 3A and 3B of fig. 3, 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 known epitaxial growth technique such as a Metal Organic Chemical Vapor Deposition (MOCVD) method, a Molecular Beam Epitaxy (MBE) method, or a sputtering method.

In the formation of each of the n-type semiconductor layer 30, the light-emitting layer 40, the guiding layer, and the p-type electron blocking layer 60, as for the growth temperature, the growth pressure, and the growth time for epitaxial growth, conventional conditions corresponding to the Al composition ratio and the thickness of each layer can be set. As the carrier gas for epitaxial growth, hydrogen, nitrogen, or a mixed gas of both may be used. Further, TMA (trimethylaluminum), TMG (trimethylgallium), or the like, which is a source gas of a group III element, may be used as a source gas for growing the above-described layers, and NH (NH) may be used as a group V element gas₃A gas. For with NH₃The flow rates of the growth gas of the group V element gas such as a gas and the group III element gas such as a TMA gas may be set to the calculated molar ratio of the group V element to the group III element (hereinafter referred to as V/III ratio) under the conventional conditions. Further, the gas as a dopant source forp-type dopant, cyclopentadienyl magnesium gas (CP) as Mg source₂Mg), and the n-type dopant may be appropriately selected from, for example, monosilane gas (SiH) as a Si source₄) And zinc chloride gas (ZnCl) as a Zn source₂) And the like, and may be supplied into the chamber at a predetermined flow rate.

Next, in the p-type contact layer forming step shown in step C of fig. 3, a p-type contact layer 70 having a superlattice structure is formed on the p-type electron blocking layer 60 by repeating the above-described 1 st layer 71 and 2 nd layer 72. The thickness range and the Al composition ratio of the p-type contact layer 70 are referred to above. The p-type contact layer 70 may be grown by epitaxial growth by MOCVD or the like.

In the p-type contact layer 70, the Mg concentration of the high concentration region 72 on the side in contact with the p-side reflective electrode 80 is 3 × 10²⁰Atom/cm³In the p-type contact layer forming step, the following treatment may be performed. That is, in the p-type contact layer forming step, the group III source gas, the group V source gas, and the Mg source gas are supplied to grow the superlattice crystal, and immediately after the crystal growth is completed, the flow rate of the group III source gas is reduced to 1/4 or less of the flow rate at the time of crystal growth, and the supply of the group V source gas and the Mg source gas is continued for 1 minute or more and 20 minutes or less.

In the p-type contact layer 70, a CP serving as a Mg source is doped to dope both Mg and Si on the side in contact with the p-side reflective electrode 80₂While the Mg gas was supplied to the chamber, monosilane gas (SiH) as a Si source was introduced₄) And the like. If only Si is doped, the supply of CP as a Mg source to the chamber is stopped₂While Mg gas was introduced, monosilane gas (SiH) as a Si source was introduced₄) And (4) finishing. As described above, when Si is doped into the p-type contact layer 70 on the side in contact with the p-side reflective electrode 80, the Mg high concentration region may be formed arbitrarily.

As shown in step D of fig. 3, the light-emitting layer 40, the p-type electron blocking layer 60, and a part of the p-type contact layer 70 may be removed by etching or the like, and the n-side electrode 90 may be formed on the exposed n-type semiconductor layer 30. The n-side electrode 90 may be formed by a sputtering method, a vacuum deposition method, or the like. It is also preferable that the buffer layer 20 is formed on the surface 10A of the substrate 10.

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

(example 1)

The deep ultraviolet light-emitting device according to example 1 of the present invention was produced according to the process diagrams shown in fig. 1A and 3. First, a sapphire substrate (diameter: 2 inches; thickness: 430 μm; plane orientation: 0001)) was prepared. Subsequently, an AlN layer having a center film thickness of 0.60 μm was grown on the sapphire substrate by the MOCVD method to prepare an AlN template substrate. At this time, the growth temperature of the AlN layer was 1300 ℃, the growth pressure in the chamber was 10 Torr, and the growth gas flow rates of the ammonia gas and the TMA gas were set so that the V/III ratio was 163. The AlN layer was measured for its thickness at a total of 25 points at which the AlN layer was dispersed at equal intervals, including the center of the wafer, by an optical interference type film thickness measuring instrument (NanoSpec M6100A; manufactured by Nanometrics Incorporated).

Next, the AlN template substrate was introduced into a heat treatment furnace, and after the furnace was made into a nitrogen atmosphere, the temperature in the furnace was raised to perform heat treatment on the AlN template substrate. At this time, the heating temperature was 1650 ℃ and the heating time was 4 hours.

Then, undoped Al is formed by MOCVD_0.55Ga_0.45N, and a buffer layer having a thickness of 1 μm. Then, Al is formed on the buffer layer_0.45Ga_0.55An N-type semiconductor layer of 2 μm thickness formed of N and doped with Si. As a result of SIMS analysis, the Si concentration of the n-type semiconductor layer was 1.0 × 10¹⁹Atom/cm³。

Further, Al is formed on the n-type semiconductor layer_0.29Ga_0.71Well layer of N and 3nm in thickness and made of Al_0.51Ga_0.49N barrier layers having a thickness of 7nm are alternately stacked in 3 groups to form a light-emitting layer. Of well layersThe Al composition ratio w was 0.29. Next, a guide layer of AlN with a thickness of 1nm was formed on the light-emitting layer. The barrier layer was doped with Si, and the well layer and the guide layer were formed without doping.

Then, Al is formed on the guide layer by using hydrogen as a carrier gas_0.58Ga_0.42N, and a p-type electron blocking layer with a thickness of 40 nm. When forming the p-type electron blocking layer, CP as a Mg source is supplied into the chamber₂The Mg gas thereby dopes Mg. The Mg concentration of the p-type electron-blocking layer was 5.0X 10 as a result of SIMS analysis¹⁸Atom/cm³。

Then, Al as a 1 st layer was formed directly above the p-type electron blocking layer_0.47Ga_0.53N, then, Al as the 2 nd layer is formed_0.31Ga_0.69N, the formation of 7 groups of both was repeated to form a total of 14 layers of the p-type contact layer of the superlattice structure. The thickness of the 1 st layer was set to 5.0nm, the thickness of the 2 nd layer was set to 2.5nm, the total thickness of the p-type contact layer was set to 52.5nm, and the Al composition of the average thickness was set to 0.42. In the formation of the p-type contact layer, a group III source TMA gas, a group V source TMG gas and a group V source ammonia gas are supplied into the chamber, and CP as a Mg source is supplied₂And Mg gas is used for growing the p-type contact layer crystal doped with Mg. Then, the supply of only the group III source gas was stopped, and the supply of only the Mg source gas and the group V source gas was stopped for 10.5 minutes, thereby forming a high concentration region on the surface side of the p-type contact layer.

When the Al composition of the p-type contact layer is determined, the Al composition ratio of the p-type contact layer is determined based on the emission wavelength (band gap energy) of the p-type contact layer obtained by photoluminescence measurement analysis.

According to the results of SIMS analysis, the Mg concentration on the p-type electron blocking layer side in the p-type contact layer was 1X 10²⁰Atom/cm³The Mg concentration on the side (high concentration region) where the Mg concentration is high on the surface side of the p-side reflective electrode 80 opposite to the p-type electron blocking layer is set to 3X 10²⁰Atom/cm³。

The layer structure of example 1 is shown in table 1.

[ Table 1]

A mask is formed on the p-type contact layer, and mesa etching by dry etching is performed to expose the n-type semiconductor layer. Next, the 2 nd layer (Al) on the outermost surface of the p-type contact layer_0.31Ga_0.69N), an Ni layer (1 st metal layer) having a thickness of 7nm and an Rh layer (2 nd metal layer) having a thickness of 50nm on the Ni layer were sequentially formed by an electron beam evaporation method. The Ni layer and the Rh layer were measured for thickness using a thickness meter for a crystal oscillator (CRTM-9000G; manufactured by ULVAc). The vibrator is gold-plated and has a natural frequency of 4.5MHz to 5.0 MHz. The calibration curve (calibration) of the crystal oscillator was carried out by forming a target metal single-layer film with a film thickness of 100nm or more and measuring the difference in height between the formed films by using a stylus type step meter (P-6 manufactured by Tencor).

An n-side electrode made of Ti/Al was formed on the exposed n-type semiconductor layer. The thickness of Ti is 20nm and the thickness of Al is 150 nm.

Finally, the substrate was kept at a maximum reaching temperature of 550 ℃ for 10 minutes by using an RTA apparatus (manufactured by ADVANCE RIKO Co.; infrared lamp annealing heating apparatus), and heat treatment for ohmic contact formation was performed to form a reflective electrode composed of Ni and Rh. In addition, N was used as the heat treatment atmosphere in the RTA apparatus₂And O₂The mixed gas of (2), N in the mixed gas₂The flow rate was set to 1.0slm, O₂The flow rate was set to 0.5 slm. The sapphire substrate was laser-diced into individual pieces having a chip size of 1000 μm × 1000 μm, and the deep ultraviolet light-emitting device according to example 1 was fabricated.

After the heat treatment step, a Ni layer (1 st metal layer) having a thickness of 7nm and an Rh layer (2 nd metal layer) having a thickness of 50nm were formed on the sapphire substrate, and the reflectance with respect to the wavelength was measured from the transparent sapphire substrate side toward the reflective electrode using an ultraviolet-visible spectrophotometer (manufactured by Nippon Kagaku Co., Ltd.; V-650), and the reflectance with respect to the wavelength of 300nm was 62%.

(example 2)

Except that the heat treatment atmosphere in the RTA apparatus was set to N₂Gas (N)₂Flow rate 1.5slm) was prepared and evaluated in the same manner as in example 1 except for replacing the mixed gas atmosphere in example 1, thereby obtaining a deep ultraviolet light-emitting device according to example 2.

(example 3)

The 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 1 st layer was 0.43 and the Al composition y of the 2 nd layer was 0.27.

Comparative example 1

The 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 of the reflective electrode in example 1 was changed to 2 nm.

After the heat treatment step, a Ni layer (1 st metal layer) having a thickness of 2nm and an Rh layer (2 nd metal layer) having a thickness of 50nm were formed on the sapphire substrate, and the reflectance with respect to the wavelength was measured from the transparent sapphire substrate side toward the reflective electrode using an ultraviolet-visible spectrophotometer (manufactured by Nippon Kagaku Co., Ltd.; V-650), and the reflectance with respect to the wavelength of 300nm was 67%.

Comparative example 2

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 Ni of the reflective electrode in example 1 was not provided.

Comparative example 3

Except that the p-type contact layer (total thickness 52.5nm) of the superlattice structure in example 1 was changed to Al_0.42Ga_0.58The deep ultraviolet light-emitting device 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.

Comparative example 4

The deep ultraviolet light-emitting element according to comparative example 4 was produced and the light emission output 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 having a thickness of 10nm and an Au layer having a thickness of 20nm on the Ni layer, which were formed in this order.

Comparative example 5

The light emission output of the deep ultraviolet light emitting element according to 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 having a thickness of 10nm and an Au layer having a thickness of 20nm formed on the Ni layer in this order, the Al composition ratio x of the 1 st layer was 0.43, and the Al composition y of the 2 nd layer was 0.27.

Comparative examples 11 to 13

The p-type contact layer of the superlattice structure in example 1 was replaced with a single-layer structure of an AlGaN layer whose Al composition ratio and thickness are as shown in table 3, and Ni was not used for the reflective electrode. The deep ultraviolet light-emitting devices according to comparative examples 11 to 13 were produced and evaluated in the same manner as in example 1, except that the chip size was set to 560. mu. m.times.780. mu.m.

(evaluation 1: evaluation of Po and Vf)

The light-emitting elements (chip size □ 1000 μm) obtained in examples 1 to 3 and comparative examples 1 to 5 were flip-chip mounted on an AlN substrate (size: 20 mm. times.15 mm; thickness: 0.8mm) using spherical gold bumps. Further, in a state where the Al heat sink was connected to the AlN substrate, the current was supplied at 350mA using a constant current power supply device, and the forward voltage at that time was measured, and the light emission output by the photodetector was measured by a light receiving unit disposed on the sapphire substrate side. The results are shown in table 2. The emission center wavelength was 310nm in all of the results of measurement of the emission wavelength by the spectrum analyzer. The value is the average of 10 measurements.

(evaluation 2: reliability evaluation 1)

In the examples and comparative examples 1 to 5, the measurement of evaluation 1 was performed, and then the current was continuously applied at 350mA for 160 hours. After the continuous energization, the output is measured again, and when the output is not lit or the output is sharply reduced from the initial light emission output to less than half as compared with the initial output, it is determined that quenching has occurred. The ratio of the chips quenched in 10 measurement numbers is shown in table 2.

(evaluation 3: evaluation of reliability 2)

In comparative examples 11 to 13, after forming a mask on the p-type contact layer and performing mesa etching by dry etching to expose the n-type semiconductor layer, small chips having a size of 560 μm × 780 μm were mounted on an AlN substrate (having a size of 1.5 × 1.1mm and a thickness of 0.2mm) using gold bumps with respect to the exposed n-type semiconductor layer and p-type contact layer, and the light emission output and the forward electrical thickness were measured when 20mA was applied. The value is the average of 10 measurements. Further, table 3 shows the ratio of chips in which the initial light emission output was confirmed by applying current of 20mA to chips extracted from 10 positions in the wafer, and then the output after applying current was halved from the initial light emission output (i.e., quenched) for 250 hours by continuously applying current of 20 mA. In the measurement of the emission output, a photodetector disposed on the sapphire substrate surface side is used.

[ Table 2]

[ Table 3]

Since the thickness of the 1 st layer was 5.0nm and the thickness of the 2 nd layer was 2.5nm, [ z ═ x + (1/3) y]The thickness average Al composition ratio z of the p-type contact layer was calculated. In examples 1 and 2, z-w₀＝0.42-0.29＝0.13，x-y＝0.47-0.31＝0.16。

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

0.030＜z-w₀＜0.20 ……[1]

0.050≤x-y≤0.47 ……[2]

(examination of evaluation results)

It is considered that quenching occurred in comparative examples 1 to 3 because contact failure occurred at the interface between the p-type contact layer and the p-side reflective electrode. On the other hand, in examples 1 to 3, since the p-type contact layer had a superlattice structure and the Ni layer had a sufficient thickness, it is estimated that no contact failure occurred. Further, it is understood from comparison of comparative examples 4 and 5 with examples 1 to 3 that the reflective electrode made of Ni and Rh is effective in increasing the light emission output without greatly changing the forward voltage.

From the above results, it was confirmed that a high light emission output can be obtained and reliability can be achieved at the same time by forming a p-side reflective electrode satisfying the conditions of the present invention on a p-type contact layer having a superlattice structure.

(example 4)

In examples 1 to 3, experiments were conducted using a deep ultraviolet light-emitting device having an emission center wavelength of 280nm in place of 310 nm. A deep ultraviolet light emitting device according to example 4 was produced in the same manner as in example 1, except that the Al composition ratio of each semiconductor layer in example 1 was changed as shown in table 4 below. The undoped AlGaN layer on the AlN template substrate is formed by inclining the Al composition ratio from 0.85 to 0.65 in the crystal growth direction.

[ Table 4]

Comparative example 6

The deep ultraviolet light-emitting element according to comparative example 6 was produced and the light emission output was evaluated 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 Ni layer having a thickness of 10nm and an Au layer having a thickness of 20nm on the Ni layer, which were formed in this order.

Comparative example 7

Except that the p-type contact layer (total thickness 52.5nm) of the superlattice structure in example 4 was changed to Al_0.59Ga_0.41The deep ultraviolet light-emitting device 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.

(evaluation 4)

With respect to example 4 and comparative examples 6 and 7 (chip sizes were 1000 μm × 1000 μm in the same manner as in example 1), the evaluation light emission output Po and forward voltage Vf were measured in the same manner as in the above evaluation 1. The results are shown in table 5. Then, after the measurement, the current was continuously applied at 350mA for 20 hours. After the continuous energization, the output was measured again, and when the output was not lit or decreased sharply from the initial light emission output to half or less as compared with the initial output, it was determined that quenching occurred. The ratio of the chips quenched in 10 measurement numbers is shown in table 5.

[ Table 5]

In example 4, z-w₀0.59-0.45-0.14, and 0.71-0.35-0.36. Therefore, the following [1] is satisfied at the same time]Formula (II) and (2)]The condition of formula (II) is shown.

0.030＜z-w₀＜0.20 ……[1]

0.050≤x-y≤0.47 ……[2]

(examination of evaluation results)

It is considered that quenching occurred in comparative example 7 because contact failure occurred at the p-type contact layer and the reflective electrode interface on the p-side, as in comparative example 3. On the other hand, in example 4, since the p-type contact layer had a superlattice structure and the Ni layer had a sufficient thickness, it is estimated that no contact failure occurred. Further, it is understood from comparative examples 4 and 6 that the reflective electrode composed of Ni and Rh has an effect of increasing the light emission output without greatly changing the forward voltage.

(example 5)

Each semiconductor layer was formed in the same manner as in example 4, and then an Ni layer (1 st metal layer) having a thickness of 7nm and an Rh layer (2 nd metal layer) having a thickness of 50nm on the Ni layer were sequentially formed by an electron beam evaporation method. Next, an Ni layer with a thickness of 3nm was formed as a 3 rd metal layer, and an Rh layer with a thickness of 20nm was formed as a 4 th metal layer in this order on the Rh layer (2 nd metal layer). Then, heat treatment for forming an ohmic contact was performed in the same manner as in example 4. Other production conditions were the same as in example 4. Thus, the deep ultraviolet light emitting element according to example 5 was produced. The total thickness of the p-type layers of the p-type electron blocking layer and the p-type contact layer was 92.5 nm.

Comparative example 8

A deep ultraviolet light-emitting element according to comparative example 8 was fabricated in the same manner as in example 5, except that an Au layer having a thickness of 20nm was formed on the Rh layer (the 2 nd metal layer), and instead of forming an Ni layer having a thickness of 3nm as the 3 rd metal layer and then an Rh layer having a thickness of 20nm as the 4 th metal layer in this order on the Rh layer (the 2 nd metal layer) in example 5.

Comparative example 9

A deep ultraviolet light-emitting element according to comparative example 9 was produced in the same manner as in example 5 except that a Ni layer having a thickness of 3nm was formed as a 3 rd metal layer, followed by an Au layer having a thickness of 20nm as a 4 th metal layer in this order on the Rh layer (2 nd metal layer), and a Ni layer having a thickness of 3nm was formed as a 3 rd metal layer, followed by an Rh layer having a thickness of 20nm as a 4 th metal layer in example 5.

(evaluation 5)

In evaluation 4, the continuous energization time was 20 hours, and 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 energization was carried out after being extended to 168 hours and 1000 hours. The evaluation results based on evaluation 5 are shown in table 6.

[ Table 6]

As can be seen from table 6, even if the occurrence of quenching is suppressed by the combination of the p-type contact layer of the superlattice structure according to the present invention and the reflective electrodes of Ni and Rh, there is a risk of quenching occurring when Au diffuses into the reflective electrodes through heating in the 3 rd step or the like in a state where Au is present on the Rh layer (2 nd metal layer). Further, it was found that the occurrence of quenching can be suppressed for a long time by forming the reflective electrode of Ni and Rh into a laminated structure in which the order of the layers of Ni and Rh is repeated a plurality of times.

(example 6)

The 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 40nm to 33 nm. The total thickness of the p-type layers of the p-type electron blocking layer and the p-type contact layer was 85.5 nm.

(example 7)

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 1 st layer of the p-type contact layer was reduced from 5nm to 2.5nm, and the thickness-average Al composition ratio z was set to 0.53. The total thickness of the p-type of the p-barrier layer and the p-type contact layer is 75 nm.

In examples 6 and 7, the presence or absence of quenching was confirmed in the same manner as in the above evaluation 5. For comparison, the production conditions and evaluation results of examples 6 and 7 are shown in table 7 below together with those of examples 5 and comparative example 6 described above.

[ Table 7]

As is clear from table 7, the light emission output can be further improved by adjusting the sum of the thickness of the p-type electron blocking layer 60 and the thickness of the p-type contact layer 70 (the total thickness of the p-type layer). The total thickness of the p-type layer is preferably 65nm or more and 100nm or less, and more preferably 70nm or more and 95nm or less. Further, an electrode having improved light emission output and high reliability can be obtained as compared with an electrode using Ni and Au.

Industrial applicability

Description of the reference numerals

10 base plate

20 buffer layer

30n type semiconductor layer

40 light emitting layer

41 well layer

42 barrier layer

60 p-type electron blocking layer

70 p type contact layer

71 layer 1

72 layer 2

80 reflective electrode

81 st metal layer

82 nd metal layer 2

83 metal layer 3

84 th metal layer

90 n side electrode

100 deep ultraviolet light emitting element.

Claims

1. A method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element, comprising:

2. The method for manufacturing a reflective electrode for a deep ultraviolet light-emitting element according to claim 1, wherein an atmosphere gas at the time of the heat treatment in the 3 rd 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, after the 2 nd step, the step of: forming a Ni layer as a 3 rd metal layer on the 2 nd metal layer; and forming an Rh layer as a 4 th metal layer on the 3 rd metal layer.

4. A method for manufacturing a deep ultraviolet light emitting element, comprising the steps of:

forming an n-type semiconductor layer on a substrate;

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

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

a step of forming a reflective electrode on the p-type contact layer,

the step of forming the p-type contact layer is alternately repeated to form a p-type contact layer composed of Al having an Al composition ratio x_xGa_1-xA first step of forming a 1 st layer of N, and a step of forming Al having an Al composition ratio y lower than the Al composition ratio x_yGa_1-yA second step of forming a 2 nd layer composed of N, wherein the p-type contact layer has a superlattice structure, and the 2 nd layer has an Al composition ratio y of 0.15 or more,

the step of forming the reflective electrode includes:

5. The method according to claim 4, wherein in the superlattice structure of the p-type contact layer,

the Al composition ratio w₀The Al composition ratio x, the Al composition ratio y and the thickness average Al composition ratio z of the p-type contact layer are satisfiedThe following formula [1]、[2]：

0.030＜z-w₀＜0.20……[1]

0.050≤x-y≤0.47……[2]。

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

7. The method according to claim 6, wherein the guide layer is made of AlN.

8. The method for manufacturing a deep ultraviolet light-emitting device according to any one of claims 5 to 7, wherein the Al composition ratio w₀Is 0.25 to 0.60 inclusive.

9. The method for manufacturing a deep ultraviolet light-emitting element according to any one of claims 4 to 8, wherein a 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.

10. The method for manufacturing a deep ultraviolet light-emitting device according to any one of claims 4 to 9, further comprising, after the 2 nd step, the step of: forming a Ni layer as a 3 rd metal layer on the 2 nd metal layer; and forming an Rh layer as a 4 th metal layer on the 3 rd metal layer.

11. A deep ultraviolet light emitting element comprising an n-type semiconductor layer, a light emitting layer, a p-type electron blocking layer and a p-type contact layer formed on a substrate in this order,

the p-type contact layer has a superlattice structure that is to be composed of Al having an Al composition ratio x_xGa_1-xLayer 1 of N and consisting of AlY to Al_yGa_1-yN, and the Al composition ratio y of the 2 nd layer is 0.15 or more,

12. The deep ultraviolet light emitting element according to claim 11, wherein in the superlattice structure of the p-type contact layer,

0.030＜z-w₀＜0.20……[1]

0.050≤x-y≤0.47……[2]。

13. The deep ultraviolet light emitting element according to claim 11 or 12, wherein a 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.