JP2020120114A - Method of manufacturing reflective electrode for deep ultraviolet light-emitting element, method of manufacturing deep ultraviolet light-emitting element, and deep ultraviolet light-emitting element - Google Patents

Abstract

To provide a reflective electrode for a deep ultraviolet light-emitting element capable of achieving both high light emission output and excellent reliability.SOLUTION: The method of manufacturing a reflective electrode 80 for a deep ultraviolet light-emitting element includes: a first step of forming Ni as a first metal layer 81 with a thickness of 3 to 20 nm on a p-type contact layer 70 having a superlattice structure; a second step of forming Rh as a reflective metal with a thickness of 20 nm or more and 2 μm or less on the first metal layer; and a third step of performing heat treatment on the first metal layer and the second metal layer 82 at 300°C or higher and 600°C or lower.SELECTED DRAWING: Figure 1A

Description

The present invention relates to a method for producing a reflective electrode for a deep ultraviolet light emitting device, a method for producing a deep ultraviolet light emitting device and a deep ultraviolet light emitting device, and in particular, a reflection for a deep ultraviolet light emitting device capable of achieving both high emission output and excellent reliability. The present invention relates to a method for manufacturing an electrode.

Group III nitride semiconductors consisting of compounds of Al, Ga, In, etc. and N are wide bandgap semiconductors with a direct transition type band structure, and have a wide range of applications such as sterilization, water purification, medical treatment, lighting, and high-density optical recording. It is a material expected in the field. In particular, a light emitting device using a group III nitride semiconductor in the light emitting layer can cover from the deep ultraviolet light to the visible light region by adjusting the content ratio of the group III element, and can be applied to various light sources. Is being promoted.

Light having a wavelength of 200 to 350 nm is called deep ultraviolet light, and a deep ultraviolet light emitting device that emits deep ultraviolet light is generally manufactured as follows. That is, a buffer layer is formed on a substrate such as sapphire or AlN single crystal, and an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer made of a group III nitride semiconductor are sequentially formed. 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. Here, in order to make ohmic contact with the p-side electrode side of the p-type semiconductor layer, it has been common to form a p-type GaN contact layer that easily increases the hole concentration. A multi-quantum well (MQW) structure in which barrier layers made of a group III nitride semiconductor and well layers are alternately laminated is widely used for the light emitting layer.

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

Patent Document 1 discloses a deep ultraviolet light emitting diode having a p-type contact layer made of an AlGaN mixed crystal and a p-side reflective electrode having reflectivity for light emitted from a light emitting layer, and having a substrate side as a light extraction direction. Has been done. For light of a short wavelength, the higher the Al composition ratio of the p-type contact layer made of AlGaN, the higher the transmittance of the p-type contact layer. Therefore, Patent Document 1 proposes to use a p-type contact layer made of AlGaN having a transmittance according to an emission wavelength, instead of the p-type contact layer made of GaN which is conventionally common. Further, as the reflective electrode in that case, a metal film containing Al as a main component is preferable. And Ni is used as an insertion metal layer for ohmic contact.

In Patent Document 2, metals such as nickel (Ni) and cobalt (Co) have a small reflection amount of visible light having a wavelength of 380 nm to 550 nm (blue violet, blue, green), and are considered to be p-type semiconductor layers (for example, While using silver (Ag), rhodium (Rh), ruthenium (Ru), platinum (Pt) or palladium (Pd) for the positive electrode on the p-type GaN layer, A Group III nitride semiconductor light emitting device having a first thin film metal layer made of cobalt (Co) or nickel (Ni) and having a thickness of 0.2 to 20 nm is disclosed.

JP, 2005-216352, A JP, 2000-36619, A

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

However, according to the experiments conducted by the present inventors, when the transmittance of the emitted deep ultraviolet light with respect to the central emission wavelength is increased only by increasing the Al composition ratio of the p-type contact layer in contact with the p-side electrode. It was found that it is not suitable for practical use due to the following reasons. First, it is certainly possible to obtain a deep-ultraviolet light emitting device having a higher light emission output as compared with the prior art by enhancing the deep ultraviolet light transmissivity of the p-type contact layer. However, when an overload reliability test (specifically, energization at 100 mA for 3 seconds) is performed on the sample of the deep-ultraviolet light-emitting device manufactured in this way, the emission output of the initial sample is halved in some samples. It was confirmed that the light emission output suddenly decreased or suddenly turned off (hereinafter, also referred to as "dead death").

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

Such an element whose light emission output suddenly deteriorates has insufficient reliability, and mixing of an element with insufficient reliability into a product is unacceptable in terms of product quality control. Therefore, it is an object of the present invention to provide a method of manufacturing a reflective electrode for a deep ultraviolet light emitting device, which can achieve both high light emission output and excellent reliability. Another object of the present invention is to provide a method for manufacturing a deep ultraviolet light emitting device using the reflective electrode and a deep ultraviolet light emitting device obtained by the method.

The present inventors diligently studied how to solve the above problems. When rhodium (Rh), which has a relatively high reflectance in the ultraviolet region, is used as the metal material of the reflective electrode, a metal made of nickel (Ni) is provided between the rhodium and the p-type contact layer of the superlattice structure. It was experimentally confirmed that the above problems can be solved by providing a layer, and the present invention has been completed. That is, the gist configuration of the present invention is as follows.

(1) On a p-type contact layer having a superlattice structure,
A first step of forming Ni as a first metal layer with a thickness of 3 to 20 nm;
A second step of forming Rh as a second metal layer with a thickness of 20 nm or more and 2 μm or less on the first metal layer;
A third step of subjecting the first metal layer and the second metal layer to heat treatment at 300° C. or higher and 600° C. or lower;
A method of manufacturing a reflective electrode for a deep-ultraviolet light emitting device, comprising:

(2) The method for producing a reflective electrode for a deep ultraviolet light emitting device according to (1) above, wherein the atmospheric gas used when performing the heat treatment in the third step contains oxygen.

(3) 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. The method for manufacturing a reflective electrode for a deep ultraviolet light emitting device according to claim 1, further comprising:

(4) a step of forming an n-type semiconductor layer on the 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,
Forming a reflective electrode on the p-type contact layer;
A method of manufacturing a deep ultraviolet light emitting device comprising:
In the step of forming the p-type contact layer, a first step of forming a first layer made of Al _x Ga _{1 -x} N having an Al composition ratio x and an Al composition ratio y lower than the Al composition ratio x are performed. And a second step of forming a second layer made of Al _y Ga _1-y N is alternately repeated to form the p-type contact layer having a superlattice structure, and an Al composition ratio of the second layer. y is 0.15 or more,
The step of forming the reflective electrode includes
On the outermost surface of the p-type contact layer, the second layer,
A first step of forming Ni as a first metal layer with a thickness of 3 to 20 nm;
A second step of forming Rh as a second metal layer with a thickness of 20 nm or more and 2 μm or less on the first metal layer;
A third step of performing a heat treatment at 300 to 600° C. on the first metal layer and the second metal layer,
A method for manufacturing a deep ultraviolet light emitting device, comprising:

(5) In the superlattice structure of the p-type contact layer,
When the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer is w ₀ ,
The Al composition ratio x of the first layer is higher than the Al composition ratio w ₀ ,
The Al composition ratio y of the second layer is lower than the Al composition ratio x,
The Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer are represented by the following formulas [1] and [2]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
The method for producing a deep ultraviolet light emitting device according to (4), which satisfies the above condition (4).

(6) Between the well layer closest to the p-type electron block layer in the light-emitting layer and the p-type electron block layer, any Al composition ratio of the barrier layer of the light-emitting layer and the p-type electron block layer. The method for manufacturing a deep ultraviolet light-emitting device according to (5) above, further including a guide layer having a higher Al composition ratio than the guide layer.

(7) The method for manufacturing a deep ultraviolet light emitting device according to (6), wherein the guide layer is made of AlN.

(8) The method for producing a deep ultraviolet light emitting device according to any one of (5) to (7), wherein the Al composition ratio w ₀ is 0.25 or more and 0.60 or less.

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

(10) 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. The method for producing a deep ultraviolet light emitting device according to any one of (4) to (9) above, further including.

(11) 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 alternately includes a first layer made of Al _x Ga _1-x N having an Al composition ratio x and a second layer made of Al _y Ga _1-y N having an Al composition ratio y. Has a superlattice structure formed by stacking, and the Al composition ratio y of the second layer is 0.15 or more,
A deep ultraviolet light emitting device comprising a reflective electrode made of Ni and Rh on the outermost surface of the p-type contact layer.

(12) In the superlattice structure of the p-type contact layer,
When the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer is w ₀ ,
The Al composition ratio x of the first layer is higher than the Al composition ratio w ₀ ,
The Al composition ratio y of the second layer is lower than the Al composition ratio x,
The Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer are represented by the following formulas [1] and [2]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
The deep ultraviolet light-emitting device according to (11) above, which satisfies:

The deep ultraviolet light-emitting device according to (11) or (12), wherein the p-type electron blocking layer and the p-type contact layer have a total p-type layer thickness of 65 to 100 nm.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the reflective electrode for deep-ultraviolet light emitting elements which can make a high light emission output and the outstanding reliability compatible can be provided. Further, the present invention can provide a method for manufacturing a deep ultraviolet light emitting device using the reflective electrode and a deep ultraviolet light emitting device obtained by the method.

6A to 6D are process diagrams with schematic cross-sectional views for explaining a method of manufacturing a reflective electrode for a deep ultraviolet light emitting device according to an embodiment of the present invention. 6A to 6C are process diagrams with schematic cross-sectional views for explaining a method of manufacturing a reflective electrode for a deep ultraviolet light emitting device according to another embodiment of the present invention. 1 is a schematic cross-sectional view illustrating a deep ultraviolet light emitting device according to an embodiment of the present invention. 6A to 6C are process diagrams with schematic cross-sectional views for explaining the method for manufacturing the deep-UV light emitting device according to the embodiment of the present invention.

Prior to the description of the embodiment according to the present invention, the following points will be described in advance. First, in the present specification, when simply expressed as “AlGaN” without explicitly indicating the Al composition ratio, the composition ratio of the group III element (total of Al and Ga) and N is 1:1 and the group III element is The ratio of Al to Ga means an arbitrary arbitrary compound. Further, “AlGaN” may include In within 5% of the total of Al and Ga as the group III elements, even if there is no description about In as the group III element. The composition formula described is Al _x0 In _y0 Ga _{1 -x0-y0} N where Al composition ratio is x ₀ and In composition ratio is y ₀ (0≦y ₀ ≦0.05). When simply expressed as “AlN” or “GaN”, it means that Ga and Al are not included, respectively, but unless otherwise specified, simply expressed as “AlGaN” means either AlN or GaN. It does not preclude something. 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 p-type is referred to as a p-type layer, and a layer that electrically functions as n-type is referred to as an n-type layer. On the other hand, when a specific impurity such as Mg or Si is not intentionally added and does not electrically function as p-type or n-type, it is referred to as “i-type” or “undoped”. The undoped layer may contain unavoidable impurities in the manufacturing process. Specifically, when the carrier density is low (for example, less than 4×10 ¹⁶ /cm ³ ), it is referred to as “undoped” in the present specification. To call. Moreover, the value of the impurity concentration of Mg, Si, or the like is based on SIMS analysis.

The total thickness of each layer formed by epitaxial growth can be measured using an optical interference type film thickness measuring device. Further, the thickness of each layer can be calculated by observing the cross section of the growth layer with a transmission electron microscope when the compositions of the adjacent layers are sufficiently different (for example, the Al composition ratio is different by 0.01 or more). Regarding the boundaries and thicknesses of adjacent layers having the same or almost equal Al composition ratios (for example, less than 0.01) but different impurity concentrations, the boundaries between the two and the thickness of each layer The measurement is based on TEM-EDS. The impurity concentrations of both can be measured by SIMS analysis. When the thickness of each layer is thin like a superlattice structure, the thickness can be measured using TEM-EDS.

Embodiments of the present invention will be described below with reference to the drawings. In principle, the same constituent elements will be given the same reference numerals, and the description thereof will be omitted. Further, in each drawing, the vertical and horizontal ratios of the substrate and each layer are exaggerated from the actual ratios for convenience of description.

(Reflective electrode)
FIG. 1A shows a p-side reflective electrode 80 obtained by a method of manufacturing a reflective electrode for a deep ultraviolet light emitting device according to an embodiment of the present invention. FIG. 2 is a schematic sectional view of a deep ultraviolet light emitting device 100 having this reflective electrode 80. In the following, reference is made to the reference numerals in FIGS. 1A and 2. The reflective electrode 80 can be provided directly on the p-type contact layer 70. The reflective electrode 80 is a reflective electrode that uses a metal having a high reflectance (for example, 60% or more) with respect to the ultraviolet light emitted from the light emitting layer 40, and has such a reflectance in the present invention. Rhodium (Rh) is used as a metal (hereinafter, referred to as “reflection metal”). As for 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 nickel (Ni) having a certain thickness or more is formed on the p-type contact layer 70 to form the reflective metal on the p-side. The reflective electrode has a high reflectance for deep ultraviolet light. Further, by performing the heat treatment at 300° C. or more and 600° C. or less, relatively good ohmic contact can be made between the p-type contact layer 70 and the p-side reflective electrode 80, and the reliability that can withstand a high current is also obtained. It turned out to have sex. 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, it is extremely difficult to directly measure the reflectance of the reflective electrode 80 on the sapphire substrate. The metal layer 82 is formed, and light of each wavelength is applied from the transparent sapphire substrate side toward the reflective electrode 80 before and after the heat treatment step, and the reflectance (for example, wavelength It shall be substituted by measuring the reflectance for 300 nm).

That is, referring to FIG. 1A, a method of manufacturing a reflective electrode for a deep ultraviolet light emitting device according to an embodiment of the present invention is characterized in that a p-type contact layer 70 having a superlattice structure (step 1A in FIG. 1A) 1st step (FIG. 1A step 1B) of forming Ni as the first metal layer 81 with a thickness of 3 to 20 nm, and Rh as the second metal layer 82 on the first metal layer 81 with a thickness of 20 nm or more and 2 μm or less. A second step of forming (step 1C in FIG. 1A) and a third step (step 1D in FIG. 1A) of performing heat treatment at 300° C. or more and 600° C. or less on the first metal layer and the second metal layer. Equipped.

<First step>
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 a general method such as a vacuum deposition method such as an electron beam deposition method and a resistance heating deposition method, and a sputtering method. This is because if the thickness is less than 3 nm, it is difficult to suppress the above-mentioned death, and if the thickness exceeds 20 nm, the reflectance of the reflective electrode significantly decreases. Further, it is more preferable that the thickness of the first metal layer 81 is 3 to 10 nm. By forming the first metal layer 81 with a thickness of 10 nm or less, the reflectance of the heat-treated reflective electrode 80 for a wavelength of 300 nm can be 60% or more. The thickness of the first metal layer 81 can be measured using a film thickness meter of a crystal oscillator.

<Second step>
In the second step, Rh is formed on the first metal layer 81 as the second metal layer 82 with a thickness of 20 nm or more and 2 μm or less. This is because if the thickness is less than 20 nm, the reflectance of the second metal layer 82 with respect to ultraviolet light may not be sufficiently high. Further, if it exceeds 2 μm, there is a problem of cost for Rh. The thickness of the second metal layer 82 is more preferably 30 nm or more in order to improve the reflectance of the reflective electrode after the diffusion of the first metal layer 81 by the heat treatment process described later, and is 100 nm or less in order to reduce the cost. More preferably. Similarly to the first step, the second step can also form the second metal layer by a general method such as a vacuum deposition method and a sputtering method. The thickness of the second metal layer 82 can be measured by using a crystal oscillator film thickness meter.

<Third step>
In the third step, the first metal layer 81 and the second metal layer 82 are heat-treated at 300° C. or higher and 600° C. or lower to obtain the reflective electrode 80. As in this step, it is common to use an inert gas such as nitrogen as an atmospheric gas used when performing heat treatment for establishing ohmic contact after forming the p-side electrode. Also in this step, only the inert gas may be used as the atmospheric gas. However, in this step, it is more preferable that the atmospheric gas contains oxygen. The flow rate ratio of oxygen in the atmosphere gas is preferably more than 0% and 50% or less.

The reflective electrode 80 thus obtained is an electrode made of Ni and Rh. With the heat treatment in the third step, Ni as the first metal layer 81 diffuses from the interface in contact with the p-type contact layer 70 to the Rh side of the second metal layer 82. Then, since the ratio of Rh at the interface between the p-type contact layer 70 and the reflective electrode 80 increases due to the diffusion of Ni, the reflectance at the interface increases as compared to before the heat treatment. In the reflective electrode 80 after the heat treatment, Ni does not maintain a layered state and diffuses, so it is difficult to accurately measure the amount of Ni after the heat treatment (that is, after diffusion). Therefore, when both peaks of Ni and Rh are observed in the SEM-EDS analysis of the cross section (vertical cross section) of the reflection electrode after the heat treatment, it is determined that the reflection electrode 80 made of Ni and Rh is provided. In the reflective electrode 80, Rh is 50% or more, preferably 75% or more, in terms of volume ratio (corresponding to the area ratio in the SEM-EDS analysis mapping of the cross section of the reflective electrode). By setting the volume ratio of Rh in the reflecting electrode 80 to 75% or more, the reflectance of the reflecting electrode 80 after the heat treatment for the wavelength of 300 nm can be 60% or more.
Further, in the reflectance measurement of the above-mentioned reflective electrode (after the heat treatment step), the reflectance of the Rh simple substance at a wavelength of 300 nm is 70 to 73%, and the reflectance of the alloy of Ni and Au is less than 40%. The reflective electrode 80 made of Ni and Rh of the invention has a reflectance of 40 nm at a wavelength of 300 nm by setting the thickness of the first metal layer 81 to 3 to 20 nm and the thickness of the second metal layer 82 to 20 nm to 2 μm. % Or more and less than 67%, the first metal layer 81 has a thickness of 3 to 10 nm, and the second metal layer 82 has a thickness of 30 nm to 100 nm. Can be 60% or more and less than 70%. Even if Ni is alloyed with Rh, the reflectance of Rh alone does not significantly decrease. Further, in the reflective electrode 80, ruthenium (Ru), gold (Au), platinum (Pt), palladium (Pd), titanium (Ti) are included as impurities that may be contained other than Ni and Rh and do not significantly reduce the reflectance. It is considered that the impurity content is 40% by mass or less, preferably 10% by mass or less.

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

Please refer to FIG. 1B. As another embodiment of the above embodiment, a step of forming a Ni layer as the third metal layer 83 on the second metal layer after the second step, and a fourth metal layer 84 on the third metal layer 83. It is also preferable to further include the step of forming the Rh layer. This step may be performed between the second step and the third step or after the third step, but work efficiency should be performed immediately after the second step between the second step and the third step. In terms of As the third metal layer 83, a Ni layer can be formed with a thickness of 1 to 20 nm. Further, the Rh layer as the fourth metal layer 84 can be formed with a thickness of 5 nm or more and 2 μm or less. Furthermore, the Ni layer and the Rh layer corresponding to the third metal layer and the fourth metal layer are formed again on the fourth metal layer 84, and the reflective electrode is formed a plurality of times in the order of the Ni layer and the Rh layer. It may be a laminated body formed by repeatedly laminating.

In a state where Au is present on the second metal layer 82, if Au diffuses in the reflective electrode after heating in the third step or the like, death may occur. However, the reflective electrode composed of Ni and Rh may be replaced by Ni and Rh. By adopting a laminated structure in which the above-mentioned stacking order is repeated a plurality of times, death due to death can be suppressed. Therefore, if the Ni layer and the Rh layer are stacked a plurality of times, a mounting process of connecting another metal (such as gold) on the Rh layer after the stacking to form an electrical connection with the outside and a connection with the outside. It is preferable because the electrode can be more surely avoided without fear of death, regardless of the method (including the case of requiring heating such as solder). From this point of view, it is particularly preferable that the metal element forming the reflective electrode is composed of only Ni and Rh.

(Deep ultraviolet light emitting device)
Next, the deep ultraviolet light emitting device 100 having the reflective electrode 80 obtained by the present invention will be described. As shown in FIG. 2, a deep ultraviolet light emitting device 100 according to an embodiment of the present invention includes 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 on a substrate 10, and This is a deep-ultraviolet light-emitting device having the p-side reflective electrode 80 in order. The reflective electrode 80 is provided on the outermost second layer 72 of the p-type contact layer. The p-type contact layer 70 includes a first layer 71 made of Al _x Ga _1-x N having an Al composition ratio x and a second layer 72 made of Al _y Ga _1-y N having an Al composition ratio y. It has a superlattice structure formed by alternately stacking. The Al composition ratio y of the second layer 72 is 0.15 or more (y≧0.15).

Particularly, when the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer 40 is w ₀ , the Al composition ratio x of the first layer 71 is higher than the Al composition ratio w ₀ , and the Al of the second layer 72 is Al. The composition ratio y is lower than the Al composition ratio x, and the Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer 70 are represented by the following formulas [1] and [2]. ]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
Is preferably satisfied.

As shown in FIG. 2, 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-type semiconductor layer 30 is provided. Providing the n-side electrode 90 on the exposed surface is a preferred embodiment of the deep ultraviolet light emitting device 100.

In the following description, the Al composition ratio and the 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 assumed to be constant for simplification of description. In this case, 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 first layer 71 in the super lattice structure is N, representing the thickness of each layer of the first layer 71 and t _a. Similarly, the number of layers of the second layer 72 is M, and the thickness of each layer of the second layer 72 is represented by t _b . At this time, the thickness average Al composition ratio z of the p-type contact layer 70 is according to the following formula [3].

The Al composition ratios and thicknesses of the first layer 71 and the second layer 72 in the superlattice structure of the p-type contact layer 70 do not necessarily have to be constant. When the Al composition ratios and thicknesses of the first layer 71 and the second layer 72 in this superlattice structure are varied, the thickness average Al composition ratio z is equal to the thickness of each of the first layer 71 and the second layer 72. And a weighted average value (weighted average value) depending on the Al composition ratio may be used, and the Al composition ratios x and y of the first layer 71 and the second layer 72 refer to the weighted average value depending on the thickness. To do.

Next, with reference to FIG. 2, details of 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 device 100 will be described first.

<Substrate>
As the substrate 10, it is preferable to use a substrate capable of transmitting light emitted from the light emitting layer 40, and for example, a sapphire substrate or a single crystal AlN substrate can be used. Further, 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 if 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 dopant concentration allows the n-type semiconductor layer 30 to function as the n-type, and is, for example, 1.0×10 ¹⁸ atoms/cm ^{3 to} 1.0×10 ^20. It can be set to atoms/cm ³ . In addition, the band gap of the n-type semiconductor layer 30 is wider than the band gap of the light emitting layer 40 (the well layer 41 in the case of a quantum well structure), and it is preferable that the n type semiconductor layer 30 be transmissive to the emitted deep ultraviolet light. The n-type semiconductor layer 30 may have a single-layer structure or a structure having a plurality of layers, as well as a composition-graded layer in which the composition ratio of the group III elements is compositionally graded in 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 a function of enhancing crystallinity from the substrate to the light emitting layer.

<Light emitting layer>
The light emitting layer 40 is provided on the n-type semiconductor layer 30 and emits deep ultraviolet light. The light emitting layer 40 can be made of AlGaN, and the Al composition ratio thereof is set so that the wavelength of radiated light is 200 to 350 nm of deep ultraviolet light or the central emission wavelength is 265 nm or more and 317 nm or less. You can Such an Al composition ratio can be set in the range of 0.25 to 0.60, for example.

The light emitting layer 40 may have a single-layer structure with a constant Al composition ratio, or may be a multiple quantum well (MQW) formed by repeatedly forming a well layer 41 and a barrier layer 42 made of AlGaN having different Al composition ratios. It is also preferable to construct the structure. When the light emitting layer 40 has a single layer structure with a constant Al composition ratio, the Al composition ratio w ₀ of the layer that emits deep ultraviolet light in the light emitting layer 40 is the Al composition ratio itself of the light emitting layer 40. Further, when the light emitting layer 40 has a multiple quantum well structure, the well layer 41 corresponds to a layer that emits deep ultraviolet light in the light emitting layer 40. Therefore, for convenience, the Al composition ratio w of the well layer 41 is the above Al composition. It is treated as equivalent to the ratio w ₀ . The Al composition ratio w _{0 of} the layer emitting deep ultraviolet light (or the well layer so that the wavelength of emitted light is 200 to 350 nm of deep ultraviolet light or the central emission wavelength is 265 nm or more and 317 nm or less). The Al composition ratio w) is preferably 0.25 to 0.60.

The Al composition ratio b of the barrier layer 42 is set higher than the Al composition ratio w of the well layer 41 (that is, b>w). Regarding the Al composition ratio b, under the condition of b>w, the Al composition ratio b of the barrier layer 42 can be set to 0.40 to 0.95, for example. The number of repetitions of the well layer 41 and the barrier layer 42 is not particularly limited and can be set to 1 to 10 times, for example. It is preferable that both ends (that is, the first and last) in the thickness direction of the light emitting layer 40 be barrier layers, and when the number of repetitions of the well layer 41 and the barrier layer 42 is n, in this case, “n. And barrier layer". The well layer 41 can have a thickness of 0.5 nm to 5 nm, and the barrier layer 42 can have a thickness of 3 nm to 30 nm.

<Guide layer>
When the light emitting layer 40 has the above-described quantum well structure, the barrier layer 42 and the p-type layer are provided between the well layer 41 closest to the p-type electron block layer 60 in the light-emitting layer 40 and the p-type electron block layer 60 described later. It is also preferable to provide a guide layer having an Al composition ratio higher than any of the Al composition ratios of the electron block layer 60. Thereby, the light emission output of the deep ultraviolet light emitting device 100 can be increased. In this case, if the Al composition ratio of the guide layer is expressed as b _g and the Al composition ratio α of the p-type electron block layer 60 described later is used, the relationship of each Al composition ratio is as follows.
w (well layer) <b (barrier layer) <α (p-type electron block layer) <b _g (guide layer)

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

<P-type electron block layer>
The p-type electron blocking layer 60 is provided on the light emitting layer 40. The p-type electron blocking layer 60 is used as a layer for blocking electrons and injecting the electrons into the light emitting layer 40 (the well layer 41 in the case of the MQW structure) to improve the electron injection efficiency. For this purpose, although it depends on the Al composition ratio w ₀ of the layer that emits deep ultraviolet light (corresponding to the Al composition ratio w of the well layer 41 in the case of the quantum well structure), the Al composition ratio of the p-type electron block layer 60 is also dependent. The ratio α is preferably 0.35≦α≦0.95. If the Al composition ratio α is 0.35 or more, the p-type electron block layer 60 may include In in an amount of 5% or less with respect to Al and Ga as group III elements. Here, it is preferable that the Al composition ratio α be higher than the thickness average Al composition ratio z of the p-type contact layer 70 while satisfying the above conditions. That is, it is preferable that α>z. Further, it is more preferable that both of the Al composition ratio α of the p-type electron block layer 60 and the Al composition ratio b of the barrier layer 42 satisfy 0<α−b≦0.55. By doing so, the efficiency of electron injection into the well layer 41 by the p-type electron block layer 60 can be reliably increased.

The thickness of the p-type electron block layer 60 is not particularly limited, but is preferably 10 nm to 80 nm, for example. When the thickness of the p-type electron block layer 60 is in this range, a high light emission output can be reliably obtained. The thickness of the p-type electron block layer 60 is preferably larger than that of the barrier layer 42. Examples of the p-type dopant with which the p-type electron block layer 60 is doped include magnesium (Mg), zinc (Zn), calcium (Ca), beryllium (Be), manganese (Mn), and the like. Is generally used. The dopant concentration of the p-type electron block layer 60 is not particularly limited as long as it is a dopant concentration that can function as a p-type layer, and is, for example, 1.0×10 ¹⁸ atoms/cm ^{3 to} 5.0×10 ²¹ atoms/ It can be cm ³ .

<P-type contact layer>
The p-type contact layer 70 is provided on the p-type electron block layer 60. The p-type contact layer 70 is a layer for reducing the contact resistance between the p-side reflective electrode 80 provided immediately above and the p-type electron block 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 that are unavoidable in manufacturing. That is, the p-side reflective electrode 80 is in contact with the p-type contact layer 70 having the superlattice structure.

Now, as described above, the p-type contact layer 70 is formed by alternately stacking the first layers 71 made of Al _x Ga _1-x N and the second layers 72 made of Al _y Ga _1-y N. It has a superlattice structure. Here, the Al composition ratio x of the first layer 71 is set higher than the Al composition ratio w ₀ of the layer that emits deep ultraviolet light in the light emitting layer 40 (x>w ₀ ), so that the transmittance for deep ultraviolet light is increased. It is preferable to increase. If the light emitting layer 40 has a single-layer structure, the Al composition ratio x may be set 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 may be set to the well layer 41. It may be higher than the Al composition ratio w.

As described above, the Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer are represented by the following formulas [1] and [2]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
Is preferably satisfied.

In the prior art, it was general to use a p-type GaN layer that is easy to increase the hole concentration 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 360 nm or less due to its band gap. Therefore, of the deep ultraviolet light emitted from the light emitting layer, the light extraction effect from the p-type contact layer side or the light extraction effect by reflection at the p-side electrode can hardly be expected. On the other hand, if the p-type contact layer is made of AlGaN having a high Al composition ratio, the hole concentration can be reduced to some extent as compared with GaN, but since deep ultraviolet light emitted from the light emitting layer can pass through the p-type contact layer. The light extraction efficiency of the deep ultraviolet light emitting device as a whole is increased, and as a result, the light emission output of the deep ultraviolet light emitting device can be increased. However, it was found from the experiments by the present inventors that if the Al composition ratio of the p-type contact layer becomes too high, a deep ultraviolet light emitting device with insufficient reliability can be obtained. On the other hand, in the case of the p-type contact layer 70 having the superlattice structure formed by the Al composition ratio described above, the thickness average Al composition ratio z is larger than the Al composition ratio w _{0 of} the layer that emits deep ultraviolet light in the light emitting layer 40. Is high (z>w ₀ ), deep ultraviolet light can pass through the p-type contact layer 70, and as a result, a higher emission output can be obtained, which is preferable.

Here, since the deep ultraviolet light is more surely transmitted through the p-type contact layer 70, the thickness average Al composition ratio z and the Al composition ratio w of the layer emitting the deep ultraviolet light are expressed by the above formula [1]. It is preferable to make the difference of 0.030 higher than 0.030 (that is, z−w ₀ >0.030). For this purpose, 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), and higher than 0.050 (z−). w ₀ >0.050) is more preferable, and it is particularly preferable that it is higher than 0.06 (z−w ₀ >0.060).

Further, in order to obtain good ohmic contact between the p-type contact layer 70 and the p-side reflective electrode 80 to ensure sufficient reliability, it is preferable to set an upper limit of the thickness average Al composition ratio. Therefore, as in the above formula [1], it is preferable to set the upper limit of the difference between the thickness average Al composition ratio z and the Al composition ratio w of the layer that emits deep ultraviolet light to 0.20 (z−w _{0 ).} <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 0.19 (z−w ₀ <0.19), and the upper limit is 0.10. More preferably, it is 18 (zw ₀ <0.18).

Further, as 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 0.050 or more in absolute value (xy≧0.050). It is preferable. This is to ensure that the p-type contact layer 70 functions as a superlattice structure. Further, since the strain of the entire superlattice structure is reduced and the p-side reflective electrode 80 is brought into contact with a low Al composition ratio, the difference between the Al composition ratio x and the Al composition ratio y is 0.1 or more (x− y≧0.10) is preferable, and 0.15 or more (x−y≧0.15) is more preferable. On the other hand, when the difference between the Al composition ratio x and the Al composition ratio y is excessively large, the lattice constant between the first layer and the second layer changes significantly, so that strain increases and a superlattice layer having good crystallinity is obtained. Can be difficult. Therefore, in order to more reliably obtain the effect of the present invention, it is preferable that x−y≦0.47, and it is more preferable that x−y≦0.45.

If the Al composition ratio y of the second layer 72, which is a layer having a low Al composition ratio in the superlattice structure, is 0.20 or more, the transmittance of deep ultraviolet light from the light emitting layer 40 can be increased more reliably. It is possible and preferable. For this purpose, the Al composition ratio y is more preferably 0.21 or more, further preferably 0.25 or more. On the other hand, when the Al composition ratio y is 0.55 or less, high reliability can be maintained more reliably, and for this purpose, the Al composition ratio y is more preferably 0.51 or less. It is particularly preferable to set it to 0.40 or less. As long as the thickness average Al composition ratio z is higher than the Al composition ratio w ₀ of the layer that emits deep ultraviolet light in the light emitting layer 40, the Al composition ratio y may be higher or lower than the Al composition ratio w _0. Good. The Al composition ratio x may be appropriately set as long as it satisfies the above formulas [1] and [2], and the upper limit and the lower limit of the Al composition ratio x are not limited. After satisfying the expressions [1] and [2], the Al composition ratio x may be set within the range of approximately 0.40 to 0.85.

Further, each of the thickness t _a of the first layer 71 and second layer 72, t _b form a superlattice structure, and the thickness of the average Al composition z, the conditions for the Al composition ratio of the light-emitting layer 40 There is no particular limitation as long as it is satisfied. For example, the thickness t _a of the first layer 71 can be 1.0 nm or more and 10.0 nm or less, and the thickness t _b of the second layer 72 can be 1.0 nm or more and 10.0 nm or less. The size relation between the thicknesses t _a and t _b is not limited, and either one may be larger, or both thicknesses may be the same. Further, the number of repetitions of the first layer 71 and the second layer 72 is set to, for example, 3 to 15 times so that the total thickness of the p-type contact layer 70 is within a range of 20 nm or more and 100 nm or less, preferably 70 nm or less. It is preferable to set it appropriately within the range.

The total thickness of the p-type layer, which is the total thickness of the p-type electron blocking layer 60 and the p-type contact layer 70, is preferably 65 nm or more and 100 nm or less, and 70 nm or more and 95 nm or less. Is more preferable. Within this range, a high light emission output can be obtained more reliably.

Here, in the thickness direction of the p-type contact layer 70, the end layer closer to the p-type electron block layer 60 is preferably the first layer 71. In other words, when there is no other layer interposed between the p-type contact layer 70 and the p-type electron block layer 60 and they are in contact with each other, the first layer is formed directly on the p-type electron block layer 60. 71 is preferably provided. 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 block layer 60. It is possible to more reliably suppress generation of defects due to strain between the layer 60 and the p-type contact layer 70.

On the other hand, in the thickness direction of the p-type contact layer 70, the end layer farther from the p-type electron block layer 60 is preferably the second layer 72. In other words, the layer in contact with 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 and the Al composition ratio y of the second layer 72 are compared, the Al composition ratio y is lower, so that ohmic contact with the p-side reflective electrode 80 is facilitated. ..

The end layer closer to the p-type electron block layer 60 in the thickness direction of the p-type contact layer 70 is the first layer 71, and the end layer farther from the p-type electron block layer 60 is the first layer 71. In the case of the second layer 72, the number of layers of the first layer 71 and the number of layers of the second layer 72 are the same. However, in this embodiment, the numbers of layers of both do not necessarily match. In the present embodiment, when both end layers in the thickness direction of the p-type contact layer 70 are the second layers 72 (in this case, the number of the second layers 72 is 1 compared to the number of the first layers 71). Including many layers).

Further, as one embodiment according to the present invention, the superlattice structure in which the two layers of the first layer 71 and the second layer 72 are repeatedly laminated has been described so far, but as another embodiment according to the present invention, the above-mentioned first A superlattice having a three-layer structure in which a third layer having an Al composition ratio between the first layer and the second layer is arranged between the first layer and the second layer while having the same relationship between the first layer and the second layer. The structure can also be applied. Also in this case, the same effects as the effects of the present invention described above can be obtained.

Here, the p-type contact layer 70 preferably has a high-concentration region having a Mg concentration of 3×10 ²⁰ atoms/cm ³ or more on the side in contact with the p-side reflective electrode 80. It is more preferably 5×10 ²⁰ atoms/cm ³ or more. By increasing the hole concentration of the p-type contact layer 70, the forward voltage Vf of the deep ultraviolet light emitting device 100 can be lowered. Although the upper limit is not intended to be limited, in view of industrial productivity, the upper limit of the Mg concentration in the high concentration region can be set to 1×10 ²¹ atoms/cm ^{3 in} the present embodiment. In this case, the Mg concentration in the region of the p-type contact layer 70 on the p-type electron block layer 60 side can be set in a general range, and is usually 5×10 ¹⁹ atoms/cm ³ or more and 3×10 ²⁰ atoms/cm ³ or more. Is less than. The Mg concentration in the p-type contact layer is the average concentration in each region measured by SIMS. In order to maintain the crystallinity of the p-type contact layer 70, the thickness of the high concentration region is usually 15 nm or less, and a few layers on the side in contact with the p-side reflective electrode 80 can be the high concentration region.

Furthermore, the p-type contact layer 70 may have a Si-doped region having a Si concentration of 5×10 ¹⁶ atoms/cm ³ or more and 1×10 ²⁰ atoms/cm ³ or less on the side in contact with the p-side reflective electrode 80. preferable. It is more preferable that the Si concentration in the region is 2×10 ¹⁹ atoms/cm ³ or more and 5×10 ¹⁹ atoms/cm ³ or less. By doing so, the emission output of the deep ultraviolet light emitting device 100 can be further increased. In addition, if the thickness of the Si-doped region is about 1 to 5 nm, this effect can be reliably obtained. It is also preferable that the Si-doped region be the last second layer in the superlattice structure of the p-type contact layer. A co-doped region may be formed by further doping Si into the high-concentration region in which the Mg concentration is 3×10 ²⁰ atoms/cm ³ or more. Further, the Si-doped region may be doped with only Si (that is, Mg may not be doped).

In addition, when a Si-doped region doped with only Si is provided on the side of the p-type contact layer 70 in contact with the reflection electrode 80 on the p-side and the region is not doped with Mg, the region is considered to be n-type as the conductivity type. You can think. However, in the case of the above thickness range (1 to 5 nm), even if Mg is not doped, it does not become a thyristor if it contacts the p-type electrode as the uppermost layer of the p-type contact layer 70. Therefore, even in such a case, the Si-doped region is regarded as a part of the p-type contact layer 70.

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

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

<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 reduce the lattice mismatch between the two. An undoped group III nitride semiconductor layer can be used as the buffer layer 20, and the buffer layer 20 preferably 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 can 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 can be appropriately selected according to the shape and size of the light emitting element. The n-side electrode 90 is not limited to being formed on 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 configurations>
Although not shown in FIG. 2, a guide layer made of AlGaN having a higher Al composition ratio than the Al composition ratio α of the p-type electron block layer 60 is provided between the light emitting layer 40 and the p-type electron block layer 60. It may be provided. By providing the guide layer, injection of holes into the light emitting layer 40 can be promoted.

<p-type clad layer>
Although not shown in FIG. 2, a p-type clad layer made of AlGaN may be provided between the p-type electron block layer 60 and the p-type contact layer 70. The p-type cladding layer is higher than the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer 40 (Al composition ratio w in the case of the quantum well structure) and the thickness average Al composition ratio z of the p-type contact layer 70. On the other hand, it is a layer having an Al composition ratio lower than the Al composition ratio α of the p-type electron block 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 that emits deep ultraviolet light, and the deep ultraviolet light emitted from the light emitting layer 40 is emitted. It is a substantially transparent layer. However, it is preferable not to provide the p-type cladding layer. The reason for this is as described in JP-A-2016-111370, and the entire disclosure content thereof is incorporated herein by reference. When the p-type cladding layer is provided, when the Al composition ratio of the p-type cladding layer is β, α>β and β>y.

In the deep ultraviolet light emitting device 100 according to the present embodiment, the substrate side or the substrate horizontal direction is the main light extraction direction by forming the p-side reflective electrode 80 with a reflective electrode material and reflecting the deep ultraviolet light. be able to. Further, the deep ultraviolet light emitting device 100 can be in a so-called flip chip type.

(Method for manufacturing deep ultraviolet light emitting device)
Next, an embodiment for obtaining the method for manufacturing the deep ultraviolet light emitting device 100 described above will be described with reference to FIG. One embodiment of the method for manufacturing the deep ultraviolet light emitting device 100 according to the present invention is a process of forming the n-type semiconductor layer 30 on the substrate 10 (see step 3A in FIG. 3), and a light emitting layer 40 on the n-type semiconductor layer 30. , A step of forming the p-type electron block layer 60 on the light emitting layer 40 (see step 3B in FIG. 3), and a step of forming a p-type contact layer on the p-type electron block layer (step in FIG. 3). 3C), and a step of forming a reflective electrode on the p-type contact layer (see step 3D in FIG. 3). The step of forming the p-type contact layer includes a first step of forming a first layer of Al _x Ga _1-x N having an Al composition ratio x, and an Al composition ratio lower than the Al composition ratio x. and a second step of forming a second layer of Al _y Ga _{1 -y} N having _y to form the p-type contact layer having a superlattice structure, and the second layer of Al The composition ratio y is 0.15 or more. Then, as described in the embodiment of the reflective electrode 80, in the step of forming the reflective electrode, Ni is used as the first metal layer 81 with a thickness of 3 to 20 nm on the p-type contact layer 70 having the superlattice structure. A first step of forming, a second step of forming Rh 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 with respect to the first metal layer and the second metal layer And a third step of performing heat treatment at 300° C. or higher and 600° C. or lower (see FIG. 1A). The step of forming the p-type contact layer 70 (see step 3C) includes the first step of forming the first layer 71 of Al _x Ga _1-x N having the Al composition ratio x and the Al composition ratio x. And a second step of forming a second layer 72 of Al _y Ga _{1 -y} N having a low Al composition ratio y, and a step of forming a p-type contact layer 70 having a superlattice structure by alternately repeating the second step. The Al composition ratio y of the second layer 72 is 0.15 or more (y≧0.15).

Further, when the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer 40 is w ₀ , the Al composition ratio x of the first layer 71 is higher than the Al composition ratio w ₀ , and the Al of the second layer 72 is Al. The composition ratio y is lower than the Al composition ratio x, and the Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer 70 are represented by the following formulas [1] and [2]. ]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
Is preferably satisfied.

The description will be continued with reference to the flowchart of FIG. However, description that overlaps with the above-described embodiment will be omitted.

First, as shown in steps 3A and 3B of FIG. 3, the n-type semiconductor layer 30, the light emitting layer 40, and the p-type electron blocking layer 60 are sequentially formed on the 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, and a sputtering method. ..

In forming each layer of the n-type semiconductor layer 30, the light emitting layer 40, the guide layer and the p-type electron block layer 60, the growth temperature, the growth pressure and the growth time for epitaxial growth depend on the Al composition ratio and the thickness of each layer. Can be general conditions. As a carrier gas for epitaxial growth, hydrogen gas, nitrogen gas, a mixed gas of the two, or the like may be used and supplied into the chamber. Furthermore, as a source gas for growing each of the above layers, TMA (trimethylaluminum), TMG (trimethylgallium), or the like can be used as a group III element source gas, and NH ₃ gas can be used as a group V element gas. Molar ratio of group V element to group III element calculated based on the growth gas flow rate of group V element gas such as NH ₃ gas and group III element gas such as TMA gas (hereinafter referred to as V/III ratio) The general conditions may also be applied to. Further, as the gas of the dopant source, cyclopentadiene magnesium gas (CP ₂ Mg) or the like as the Mg source for the p-type dopant, or monosilane gas (SiH ₄ ) or the Zn source as the Si source for the n-type dopant. Zinc chloride gas (ZnCl ₂ ) or the like may be appropriately selected and 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, the p-type contact layer 70 having a superlattice structure in which the first layer 71 and the second layer 72 described above are repeated on the p-type electron block layer 60. To form. The conditions for the thickness range and the Al composition ratio of the p-type contact layer 70 are as described above. The p-type contact layer 70 may be crystal-grown by epitaxial growth such as MOCVD.

In the p-type contact layer 70, in order to set the Mg concentration in the high-concentration region 72 on the side in contact with the p-side reflective electrode 80 to 3×10 ²⁰ atoms/cm ³ or more, The following processing may be performed. That is, in the p-type contact layer forming step, the superlattice structure is crystal-grown by supplying the group III source gas, the group V source gas, and the Mg source gas, and the flow rate of the group III source gas is changed immediately after the crystal growth is completed. The flow rate at the time of crystal growth may be reduced to 1/4 or less, and the group V source gas and the Mg source gas may be continuously supplied for 1 minute or more and 20 minutes or less.

Further, in the p-type contact layer 70, in order to dope both Mg and Si on the side in contact with the p-side reflective electrode 80, CP ₂ Mg gas as a Mg source is supplied to the chamber, and monosilane gas (as a Si source) is supplied. SiH ₄ ) or the like may be flowed. If only Si is to be doped, the CP ₂ Mg gas as the Mg source should be stopped from being supplied to the chamber, and the monosilane gas (SiH ₄ ) should be flown as the Si source. When Si is doped on the p-side contact layer 70 on the side in contact with the reflective electrode 80 as described above, the formation of the Mg high-concentration region is optional.

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

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

(Example 1)
A deep ultraviolet light emitting device according to Inventive Example 1 was produced according to the process charts shown in FIGS. 1A and 3. First, a sapphire substrate (diameter 2 inches, thickness: 430 μm, plane orientation: (0001)) was prepared. Then, an AlN layer having a central film thickness of 0.60 μm was grown on the sapphire substrate by MOCVD method to obtain an AlN template substrate. At that time, the growth temperature of the AlN layer was 1300° C., 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. Regarding the film thickness of the AlN layer, a total of 25 film thicknesses were dispersed at equal intervals including the center of the wafer by using an optical interference type film thickness measuring device (Nanospec M6100A; manufactured by Nanometrics). Was measured.

Next, the above AlN template substrate was introduced into a heat treatment furnace, and after the inside of the furnace was made a nitrogen gas atmosphere, the temperature inside the furnace was raised to subject the AlN template substrate to heat treatment. At that time, the heating temperature was 1650° C. and the heating time was 4 hours.

Then, a buffer layer of undoped Al _0.55 Ga _0.45 N having a thickness of 1 μm was formed by MOCVD. Next, a Si-doped n-type semiconductor layer having a thickness of 2 μm and made of Al _0.45 Ga _0.55 N was formed on the buffer layer. As a result of SIMS analysis, the Si concentration of the n-type semiconductor layer was 1.0×10 ¹⁹ atoms/cm ³ .

Further, on the n-type semiconductor layer, a light emitting layer was formed by alternately stacking three sets of well layers made of Al _0.29 Ga _0.71 N and having a thickness of 3 nm and barrier layers made of Al _0.51 Ga _0.49 N and having a thickness of 7 nm. .. The Al composition ratio w of the well layer is 0.29. Then, a guide layer having a thickness of 1 nm was formed from AlN on the light emitting layer. Note that Si was doped when forming the barrier layer and undoped when forming the well layer and the guide layer.

After that, a 40-nm-thick p-type electron block layer made of Al _0.58 Ga _0.42 N was formed on the guide layer using hydrogen gas as a carrier gas. Upon forming the p-type electron block layer, CP ₂ Mg gas was supplied to the chamber as a Mg source to dope Mg. As a result of SIMS analysis, the Mg concentration of the p-type electron block layer was 5.0×10 ¹⁸ atoms/cm ³ .

Then, Al _0.47 Ga _0.53 N was formed as a first layer immediately above the p-type electron blocking layer, and then Al _0.31 Ga _0.69 N was formed as a second layer, and the formation of both of them was repeated 7 _times to form a total of 14 layers. A p-type contact layer having a superlattice structure was formed. The thickness of the first layer is 5.0 nm, the thickness of the second layer is 2.5 nm, the total thickness of the p-type contact layers is 52.5 nm, and the average Al composition of the thickness is 0. 42. Further, in forming the p-type contact layer, a CP ₂ Mg gas as a Mg source is supplied to the chamber together with the group III source TMA gas, the TMG gas, and the group V source ammonia gas, and the p-type contact layer is doped with Mg. Was grown. Then, only the supply of the group III source gas was stopped, and only the Mg source gas and the group V source gas were supplied for 10.5 minutes to form a high concentration region on the surface side of the p-type contact layer.

When specifying the Al composition of the p-type contact layer, the Al composition ratio of the p-type contact layer was determined from the emission wavelength (bandgap energy) of the p-type contact layer analyzed by photoluminescence measurement.

As a result of SIMS analysis, in the p-type contact layer, the Mg concentration on the p-type electron block layer side was 1×10 ²⁰ atoms/cm ³ , and the surface forming the p-side reflective electrode 80 opposite to the p-type electron block layer. The Mg concentration on the side where the concentration of Mg on the side was high (high concentration region) was 3×10 ²⁰ atoms/cm ³ .

Table 1 shows the layer structure of Example 1.

A mask was formed on the p-type contact layer and mesa etching was performed by dry etching to expose the n-type semiconductor layer. Next, on the outermost second layer (Al _0.31 Ga _0.69 N) of the p-type contact layer, a Ni layer (first metal layer) having a thickness of 7 nm and the Ni layer were formed by using an electron beam evaporation method. An Rh layer (second metal layer) having a thickness of 50 nm was sequentially formed. The thicknesses of the Ni layer and the Rh layer were measured using a crystal oscillator film thickness meter (CRTM-9000G; manufactured by ulvac). The oscillator used gold plating and a natural frequency of 4.5 MHz to 5.0 MHz. For the calibration curve (calibration) of the crystal unit, a single film of the target metal is formed with a film thickness of 100 nm or more, and the step difference between the presence and absence of film formation is determined by the stylus profilometer (Tencor P-6). It was performed by measuring using.
An n-side electrode made of Ti/Al was formed on the exposed n-type semiconductor layer. The thickness of Ti is 20 nm and the thickness of Al is 150 nm.
Finally, using the RTA device (Advance Riko; infrared lamp annealing heating device), the maximum attainable temperature was kept at 550° C. for 10 minutes, and heat treatment for ohmic contact was performed to form a reflective electrode composed of Ni and Rh. .. The heat treatment atmosphere in the RTA apparatus was a mixed gas of N ₂ and O ₂ , the N ₂ flow rate in the mixed gas was 1.0 slm, and the O ₂ flow rate was 0.5 slm. The sapphire substrate was laser-scribed into individual chips each having a chip size of 1000 μm×1000 μm, and the deep ultraviolet light emitting device according to Example 1 was produced.

A 7 nm thick Ni layer (first metal layer) and a 50 nm thick Rh layer (second metal layer) are formed on a sapphire substrate, and after the above heat treatment step, the transparent sapphire substrate side faces the reflective electrode. Then, the reflectance with respect to the wavelength was measured using an ultraviolet-visible spectrophotometer (V-650 manufactured by JASCO Corporation), and the reflectance with respect to the wavelength of 300 nm was 62%.

(Example 2)
A deep ultraviolet light-emitting device according to Example 2 in the same manner as in Example 1 except that the heat treatment atmosphere in the RTA apparatus was N ₂ gas (N ₂ flow rate 1.5 slm) instead of the mixed gas atmosphere in Example 1. Was produced and evaluated.

(Example 3)
A deep ultraviolet light emitting device according to Example 3 was prepared and evaluated in the same manner as in Example 1 except that the Al composition ratio x of the first layer was 0.43 and the Al composition y of the second layer was 0.27. did.

(Comparative Example 1)
A deep ultraviolet light emitting device according to Comparative Example 1 was prepared 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.

A 2 nm-thick Ni layer (first metal layer) and a 50 nm-thick Rh layer (second metal layer) are formed on the sapphire substrate, and after the above heat treatment process, the transparent sapphire substrate side is directed to the reflective electrode. Then, the reflectance with respect to wavelength was measured with an ultraviolet-visible spectrophotometer (V-650 manufactured by JASCO Corporation), and the reflectance with respect to wavelength 300 nm was 67%.

(Comparative example 2)
A deep ultraviolet light emitting device according to Comparative Example 2 was prepared 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)
Comparative Example 3 was the same as Example 1 except that the p-type contact layer (total thickness 52.5 nm) of the superlattice structure in Example 1 was changed to a single layer structure of Al _0.42 Ga _0.58 N layer with a thickness of 50 nm. A deep ultraviolet light emitting device according to the above was prepared and evaluated.

(Comparative Example 4)
The same procedure as in Example 1 was repeated except that the reflective electrode made of Ni and Rh in Example 1 was changed to a Ni layer having a thickness of 10 nm and an Au layer having a thickness of 20 nm formed on the Ni layer in this order. A deep ultraviolet light emitting device according to Comparative Example 4 was produced and the light emission output was evaluated.

(Comparative example 5)
The reflective electrode made of Ni and Rh in Example 1 was changed to one in which a Ni layer having a thickness of 10 nm and an Au layer having a thickness of 20 nm on the Ni layer were sequentially formed, and the Al composition ratio x of the first layer was 0. 0.43 and the Al composition y of the second layer was 0.27, and the emission output of the deep ultraviolet light emitting device according to Comparative Example 5 was evaluated in the same manner as in Example 1.

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

(Evaluation 1: Po, Vf evaluation)
The light emitting devices (chip size □1000 μm) obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were AlN submounts (size 20 mm×15 mm, thickness 0.8 mm) using spherical Au bumps in a flip chip method. Implemented in. With the AlN heatsink connected to the AlN submount, a constant current power supply was used to energize the device at 350mA, the forward voltage at that time was measured, and the photodetector was used by the light-receiving section located on the sapphire substrate side. The emission output was measured. The results are shown in Table 2. When the emission wavelength was measured with a spectrum analyzer, the emission center wavelengths were all 310 nm. The value is an average value of 10 measurements.

(Evaluation 2: Reliability evaluation 1)
After performing the measurement of the above-mentioned evaluation 1 with respect to Examples and Comparative Examples 1 to 5, 350 mA was continuously energized for 160 hours. After continuous energization, the output was measured again and compared with the initial output, and when there was no lighting or there was a sudden decrease in the output from the initial emission output to less than half, it was determined that there was death. Table 2 shows the ratio of dead chips among the 10 measured.

(Evaluation 3: Reliability evaluation 2)
In Comparative Examples 11 to 13, after the mask is formed on the p-type contact layer and the mesa etching by dry etching is performed to expose the n-type semiconductor layer, the exposed n-type semiconductor layer and the p-type contact layer are exposed. On the other hand, a small chip with a size of 560 μm × 780 μm was mounted on an AlN submount (size: 1.5 × 1.1 mm thickness: 0.2 mm) using Au bumps, and the light emission output and forward electrical thickness when 20 mA was applied. Was measured. The value is an average value of 10 measurements. Furthermore, for chips extracted from 10 locations in the wafer, the initial light emission output was confirmed by energizing at a current of 20 mA, and then the current was continuously energized at 20 mA for 250 hours, and the output was less than half the initial light emitting output after energization. Table 3 shows the ratio of chips (that is, dead). A photodetector arranged on the sapphire substrate surface side was used for measuring the light emission output.

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 [z=(2/3)x+( 1/3)y] is calculated. In Examples 1 and 2, z-w ₀ =0.42-0.29=0.13 and xy=0.47-0.31=0.16.
Therefore, the conditions of the following expressions [1] and [2] are simultaneously satisfied.
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]

(Discussion of evaluation results)
It is considered that the cause of death in Comparative Examples 1 to 3 was due to contact failure at the interface between the p-type contact layer and the p-side reflective electrode. On the other hand, in Examples 1 to 3, it is presumed that no contact failure occurred because the p-type contact layer had a superlattice structure and the Ni layer had a sufficient thickness. Further, by comparing Comparative Examples 4 and 5 with Examples 1 to 3, it can be seen that the reflective electrode made of Ni and Rh is effective in increasing the light emission output without largely changing the forward voltage.

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

(Example 4)
Whereas in Examples 1 to 3, the emission center wavelength was 310 nm, an experiment was conducted using a deep ultraviolet light emitting device having an emission center wavelength of 280 nm instead. 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 was formed by grading the Al composition ratio from 0.85 to 0.65 in the crystal growth direction.

(Comparative example 6)
The same procedure as in Example 4 except that the reflective electrode made of Ni and Rh in Example 4 was changed to a Ni layer having a thickness of 10 nm and an Au layer having a thickness of 20 nm formed on the Ni layer in this order. A deep ultraviolet light emitting device according to Comparative Example 6 was produced and the light emission output was evaluated.

(Comparative Example 7)
Comparative Example 3 was the same as Example 1 except that the p-type contact layer (total thickness 52.5 nm) of the superlattice structure in Example 4 was changed to a single layer structure of Al _0.59 Ga _0.41 N layer with a thickness of 50 nm. A deep ultraviolet light emitting device according to the above was prepared and evaluated.

(Evaluation 4)
The emission output Po and the forward voltage Vf were measured and evaluated in the same manner as in Evaluation 1 above for Example 4 and Comparative Examples 6 and 7 (all of which had a chip size of 1000 μm×1000 μm as in Example 1). The results are shown in Table 5. Then, after performing this measurement, 350 mA was continuously energized for 20 hours. After continuous energization, the output was measured again and compared with the initial output, and when there was no lighting or there was a sudden decrease in the output from the initial emission output to less than half, it was determined that there was death. Table 5 also shows the ratio of dead chips among the 10 measured.

In Example 4, z−w ₀ =0.59−0.45=0.14 and xy=0.71−0.35=0.36. Therefore, the conditions of the following expressions [1] and [2] are simultaneously satisfied.
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]

(Discussion of evaluation results)
It is considered that the reason why the death occurred in Comparative Example 7 was that a contact failure occurred at the interface between the p-type contact layer and the p-side reflective electrode, as in Comparative Example 3. On the other hand, in Example 4, it is presumed that no contact failure occurred because the p-type contact layer had a superlattice structure and the Ni layer had a sufficient thickness. In addition, comparing Example 4 with Comparative Example 6, it can be seen that the reflective electrode made of Ni and Rh is effective in increasing the light emission output without largely changing the forward voltage.

(Example 5)
Each semiconductor layer was formed in the same manner as in Example 4, and then an electron beam evaporation method was used to form a Ni layer (first metal layer) having a thickness of 7 nm and a Rh layer (first metal layer) having a thickness of 50 nm on the Ni layer. 2 metal layers) were sequentially formed. Subsequently, a Ni layer having a thickness of 3 nm was formed as a third metal layer on the Rh layer (second metal layer), and then a Rh layer having a thickness of 20 nm was sequentially formed as a fourth metal layer. Then, as in Example 4, heat treatment for ohmic contact was performed. Other manufacturing conditions are the same as in Example 4. Thus, the deep ultraviolet light emitting device according to Example 5 was manufactured. The total thickness of the p-type electron block layer and the p-type layer of the p-type contact layer is 92.5 nm.

(Comparative Example 8)
In Example 5, a Ni layer having a thickness of 3 nm was formed as a third metal layer on the Rh layer (second metal layer), and then a Rh layer having a thickness of 20 nm was sequentially formed as a fourth metal layer. A deep ultraviolet light emitting device according to Comparative Example 8 was produced in the same manner as in Example 5 except that an Au layer having a thickness of 20 nm was formed on the (second metal layer).

(Comparative Example 9)
In Example 5, a Ni layer having a thickness of 3 nm was formed as a third metal layer on the Rh layer (second metal layer), and then a Rh layer having a thickness of 20 nm was sequentially formed as a fourth metal layer. Comparative Example 9 was performed in the same manner as in Example 5 except that a Ni layer having a thickness of 3 nm was formed as a third metal layer on the (second metal layer) and an Au layer having a thickness of 20 nm was sequentially formed as a fourth metal layer. A deep-ultraviolet light emitting device according to was produced.

(Evaluation 5)
In Evaluation 4, when the continuous energization time was set to 20 hours, the presence or absence of death in the above Examples and Comparative Examples was confirmed in the same manner as in Evaluation 4 except that the continuous energization was extended to 168 hours and 1000 hours. did. The evaluation results of Evaluation 5 are shown in Table 6.

From Table 6, a state in which Au is present on the Rh layer (second metal layer) even if the occurrence of death due to death is suppressed by the combination of the p-type contact layer having the superlattice structure according to the present invention and the reflective electrodes of Ni and Rh Then, it was found that if Au diffuses in the reflective electrode after heating in the third step or the like, death may occur. It has been found that the incidence rate of death due to death can be suppressed for a long time by forming the reflective electrode of Ni and Rh into a laminated structure in which the layer order of Ni and Rh is repeated a plurality of times.

(Example 6)
A deep ultraviolet light emitting device according to Example 6 was prepared 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 block layer and the p-type layer of the p-type contact layer is 85.5 nm.

(Example 7)
Example 7 was repeated in the same manner as in Example 5 except that the thickness of the first layer of the p-type contact layer was reduced from 5 nm to 2.5 nm and the thickness average Al composition ratio z was changed to 0.53. The deep ultraviolet light emitting device was manufactured and evaluated. The total p-type thickness of the p-block layer and the p-type contact layer is 75 nm.

Regarding Examples 6 and 7, the presence or absence of death was confirmed in the same manner as in Evaluation 5 above. 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 for comparison.

From Table 7, it was found that the light emission output can be further improved by adjusting the total thickness of the p-type electron blocking layer 60 and the p-type contact layer 70 (total thickness of the p-type layers). .. What is the total thickness of the p-type layer? The thickness is preferably 65 nm or more and 100 nm or less, and more preferably 70 nm or more and 95 nm or less. Then, it was possible to obtain an electrode having higher emission output and higher reliability than the electrode using Ni and Au.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the reflective electrode for deep-ultraviolet light emitting elements which can make a high light emission output and the outstanding reliability compatible can be provided. Further, the present invention can provide a method for manufacturing a deep ultraviolet light emitting device using the reflective electrode and a deep ultraviolet light emitting device obtained by the method.

10 substrate 20 buffer layer 30 n-type semiconductor layer 40 light emitting layer 41 well layer 42 barrier layer 60 p-type electron block layer 70 p-type contact layer 71 first layer 72 second layer 80 reflective electrode 81 first metal layer 82 second metal Layer 83 Third metal layer 84 Fourth metal layer 90 n-side electrode 100 Deep ultraviolet light emitting device

The present invention relates to a method for producing a reflective electrode for a deep ultraviolet light emitting device, a method for producing a deep ultraviolet light emitting device and a deep ultraviolet light emitting device, and in particular, a reflection for a deep ultraviolet light emitting device capable of achieving both high emission output and excellent reliability. The present invention relates to a method for manufacturing an electrode.

Group III nitride semiconductors consisting of compounds of Al, Ga, In, etc. and N are wide bandgap semiconductors with a direct transition type band structure, and have a wide range of applications such as sterilization, water purification, medical treatment, lighting, and high-density optical recording. It is a material expected in the field. In particular, a light emitting device using a group III nitride semiconductor in the light emitting layer can cover from the deep ultraviolet light to the visible light region by adjusting the content ratio of the group III element, and can be applied to various light sources. Is being promoted.

Light having a wavelength of 200 to 350 nm is called deep ultraviolet light, and a deep ultraviolet light emitting device that emits deep ultraviolet light is generally manufactured as follows. That is, a buffer layer is formed on a substrate such as sapphire or AlN single crystal, and an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer made of a group III nitride semiconductor are sequentially formed. 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. Here, in order to make ohmic contact with the p-side electrode side of the p-type semiconductor layer, it has been common to form a p-type GaN contact layer that easily increases the hole concentration. A multi-quantum well (MQW) structure in which barrier layers made of a group III nitride semiconductor and well layers are alternately laminated is widely used for the light emitting layer.

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

Patent Document 1 discloses a deep ultraviolet light emitting diode having a p-type contact layer made of an AlGaN mixed crystal and a p-side reflective electrode having reflectivity for light emitted from a light emitting layer, and having a substrate side as a light extraction direction. Has been done. For light of a short wavelength, the higher the Al composition ratio of the p-type contact layer made of AlGaN, the higher the transmittance of the p-type contact layer. Therefore, Patent Document 1 proposes to use a p-type contact layer made of AlGaN having a transmittance according to an emission wavelength, instead of the p-type contact layer made of GaN which is conventionally common. Further, as the reflective electrode in that case, a metal film containing Al as a main component is preferable. And Ni is used as an insertion metal layer for ohmic contact.

In Patent Document 2, metals such as nickel (Ni) and cobalt (Co) have a small reflection amount of visible light having a wavelength of 380 nm to 550 nm (blue violet, blue, green), and are considered to be p-type semiconductor layers (for example, While using silver (Ag), rhodium (Rh), ruthenium (Ru), platinum (Pt) or palladium (Pd) for the positive electrode on the p-type GaN layer, A Group III nitride semiconductor light emitting device having a first thin film metal layer made of cobalt (Co) or nickel (Ni) and having a thickness of 0.2 to 20 nm is disclosed.

JP, 2005-216352, A JP, 2000-36619, A

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

However, according to the experiments conducted by the present inventors, when the transmittance of the emitted deep ultraviolet light with respect to the central emission wavelength is increased only by increasing the Al composition ratio of the p-type contact layer in contact with the p-side electrode. It was found that it is not suitable for practical use due to the following reasons. First, it is certainly possible to obtain a deep-ultraviolet light emitting device having a higher light emission output as compared with the prior art by enhancing the deep ultraviolet light transmissivity of the p-type contact layer. However, when an overload reliability test (specifically, energization at 100 mA for 3 seconds) is performed on the sample of the deep-ultraviolet light-emitting device manufactured in this way, the emission output of the initial sample is halved in some samples. It was confirmed that the light emission output suddenly decreased or suddenly turned off (hereinafter, also referred to as "dead death").

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

Such an element whose light emission output suddenly deteriorates has insufficient reliability, and mixing of an element with insufficient reliability into a product is unacceptable in terms of product quality control. Therefore, it is an object of the present invention to provide a method of manufacturing a reflective electrode for a deep ultraviolet light emitting device, which can achieve both high light emission output and excellent reliability. Another object of the present invention is to provide a method for manufacturing a deep ultraviolet light emitting device using the reflective electrode and a deep ultraviolet light emitting device obtained by the method.

The present inventors diligently studied how to solve the above problems. When rhodium (Rh), which has a relatively high reflectance in the ultraviolet region, is used as the metal material of the reflective electrode, a metal made of nickel (Ni) is provided between the rhodium and the p-type contact layer of the superlattice structure. It was experimentally confirmed that the above problems can be solved by providing a layer, and the present invention has been completed. That is, the gist configuration of the present invention is as follows.

(1) On a p-type contact layer having a superlattice structure,
A first step of forming Ni as a first metal layer with a thickness of 3 to 20 nm;
A second step of forming Rh as a second metal layer with a thickness of 20 nm or more and 2 μm or less on the first metal layer;
A third step of subjecting the first metal layer and the second metal layer to heat treatment at 300° C. or higher and 600° C. or lower;
The equipped,
After the second step, the method further includes forming a Ni layer as a third metal layer on the second metal layer, and forming an Rh layer as a fourth metal layer on the third metal layer. A method for producing a reflective electrode for a deep ultraviolet light emitting device, comprising:

(2) The method for producing a reflective electrode for a deep ultraviolet light emitting device according to (1) above, wherein the atmospheric gas used when performing the heat treatment in the third step contains oxygen.

(3) The third step is performed after the step of forming the fourth metal layer,
The third step further includes the step of performing the heat treatment on the third metal layer and the fourth metal layer, and Production method.

(4) a step of forming an n-type semiconductor layer on the 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,
Forming a reflective electrode on the p-type contact layer;
A method of manufacturing a deep ultraviolet light emitting device comprising:
In the step of forming the p-type contact layer, a first step of forming a first layer made of Al _x Ga _{1 -x} N having an Al composition ratio x and an Al composition ratio y lower than the Al composition ratio x are performed. And a second step of forming a second layer made of Al _y Ga _1-y N is alternately repeated to form the p-type contact layer having a superlattice structure, and an Al composition ratio of the second layer. y is 0.15 or more,
The step of forming the reflective electrode includes
On the outermost surface of the p-type contact layer, the second layer,
A first step of forming Ni as a first metal layer with a thickness of 3 to 20 nm;
A second step of forming Rh as a second metal layer with a thickness of 20 nm or more and 2 μm or less on the first metal layer;
A third step of performing a heat treatment at 300 to 600° C. on the first metal layer and the second metal layer,
The equipped,
After the second step, the method further includes forming a Ni layer as a third metal layer on the second metal layer, and forming an Rh layer as a fourth metal layer on the third metal layer. A method for manufacturing a deep ultraviolet light emitting device, comprising:

(5) In the superlattice structure of the p-type contact layer,
When the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer is w ₀ ,
The Al composition ratio x of the first layer is higher than the Al composition ratio w ₀ ,
The Al composition ratio y of the second layer is lower than the Al composition ratio x,
The Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer are represented by the following formulas [1] and [2]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
The method for producing a deep ultraviolet light emitting device according to (4), which satisfies the above condition (4).

(6) Between the well layer closest to the p-type electron block layer in the light-emitting layer and the p-type electron block layer, any Al composition ratio of the barrier layer of the light-emitting layer and the p-type electron block layer. The method for manufacturing a deep ultraviolet light-emitting device according to (5) above, further including a guide layer having a higher Al composition ratio than the guide layer.

(7) The method for manufacturing a deep ultraviolet light emitting device according to (6), wherein the guide layer is made of AlN.

(8) The method for producing a deep ultraviolet light emitting device according to any one of (5) to (7), wherein the Al composition ratio w ₀ is 0.25 or more and 0.60 or less.

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

(10) The third step is performed after the step of forming the fourth metal layer,
The deep ultraviolet light emitting device according to any one of (4) to (9) above , wherein the third step further includes a step of performing the heat treatment on the third metal layer and the fourth metal layer. Method.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the reflective electrode for deep-ultraviolet light emitting elements which can make a high light emission output and the outstanding reliability compatible can be provided. Further, the present invention can provide a method for manufacturing a deep ultraviolet light emitting device using the reflective electrode and a deep ultraviolet light emitting device obtained by the method.

FIG. 6 is a process drawing by a schematic cross-sectional view for explaining the method for manufacturing the reflective electrode for the deep-ultraviolet light-emitting device that is related to the embodiment of the present invention. 6A to 6C are process diagrams with schematic cross-sectional views for explaining a method of manufacturing a reflective electrode for a deep-ultraviolet light emitting device according to an embodiment of the present invention. 1 is a schematic cross-sectional view illustrating a deep ultraviolet light emitting device according to an embodiment of the present invention. 6A to 6C are process diagrams with schematic cross-sectional views for explaining the method for manufacturing the deep-UV light emitting device according to the embodiment of the present invention.

Prior to the description of the embodiment according to the present invention, the following points will be described in advance. First, in the present specification, when simply expressed as “AlGaN” without explicitly indicating the Al composition ratio, the composition ratio of the group III element (total of Al and Ga) and N is 1:1 and the group III element is The ratio of Al to Ga means an arbitrary arbitrary compound. Further, “AlGaN” may include In within 5% of the total of Al and Ga as the group III elements, even if there is no description about In as the group III element. The composition formula described is Al _x0 In _y0 Ga _{1 -x0-y0} N where Al composition ratio is x ₀ and In composition ratio is y ₀ (0≦y ₀ ≦0.05). When simply expressed as “AlN” or “GaN”, it means that Ga and Al are not included, respectively, but unless otherwise specified, simply expressed as “AlGaN” means either AlN or GaN. It does not preclude something. 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 p-type is referred to as a p-type layer, and a layer that electrically functions as n-type is referred to as an n-type layer. On the other hand, when a specific impurity such as Mg or Si is not intentionally added and does not electrically function as p-type or n-type, it is referred to as “i-type” or “undoped”. The undoped layer may contain unavoidable impurities in the manufacturing process. Specifically, when the carrier density is low (for example, less than 4×10 ¹⁶ /cm ³ ), it is referred to as “undoped” in the present specification. To call. Moreover, the value of the impurity concentration of Mg, Si, or the like is based on SIMS analysis.

The total thickness of each layer formed by epitaxial growth can be measured using an optical interference type film thickness measuring device. Further, the thickness of each layer can be calculated by observing the cross section of the growth layer with a transmission electron microscope when the compositions of the adjacent layers are sufficiently different (for example, the Al composition ratio is different by 0.01 or more). Regarding the boundaries and thicknesses of adjacent layers having the same or almost equal Al composition ratios (for example, less than 0.01) but different impurity concentrations, the boundaries between the two and the thickness of each layer The measurement is based on TEM-EDS. The impurity concentrations of both can be measured by SIMS analysis. When the thickness of each layer is thin like a superlattice structure, the thickness can be measured using TEM-EDS.

Embodiments of the present invention will be described below with reference to the drawings. In principle, the same constituent elements will be given the same reference numerals, and the description thereof will be omitted. Further, in each drawing, the vertical and horizontal ratios of the substrate and each layer are exaggerated from the actual ratios for convenience of description.

(Reflective electrode)
FIG. 1A shows a p-side reflective electrode 80 obtained by a method of manufacturing a reflective electrode for a deep ultraviolet light emitting device according to an embodiment of the present invention. FIG. 2 is a schematic sectional view of a deep ultraviolet light emitting device 100 having this reflective electrode 80. In the following, reference is made to the reference numerals in FIGS. 1A and 2. The reflective electrode 80 can be provided directly on the p-type contact layer 70. The reflective electrode 80 is a reflective electrode that uses a metal having a high reflectance (for example, 60% or more) with respect to the ultraviolet light emitted from the light emitting layer 40, and has such a reflectance in the present invention. Rhodium (Rh) is used as a metal (hereinafter, referred to as “reflection metal”). As for 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 nickel (Ni) having a certain thickness or more is formed on the p-type contact layer 70 to form the reflective metal on the p-side. The reflective electrode has a high reflectance for deep ultraviolet light. Further, by performing the heat treatment at 300° C. or more and 600° C. or less, relatively good ohmic contact can be made between the p-type contact layer 70 and the p-side reflective electrode 80, and the reliability that can withstand a high current is also obtained. It turned out to have sex. 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, it is extremely difficult to directly measure the reflectance of the reflective electrode 80 on the sapphire substrate. The metal layer 82 is formed, and light of each wavelength is applied from the transparent sapphire substrate side toward the reflective electrode 80 before and after the heat treatment step, and the reflectance (for example, wavelength It shall be substituted by measuring the reflectance for 300 nm).

That is, referring to FIG. 1A, a method of manufacturing a reflective electrode for a deep-ultraviolet light emitting device according to an embodiment of the present invention includes a p-type contact layer 70 (FIG. 1A step 1A) having a superlattice structure. , A first step of forming Ni as a first metal layer 81 to a thickness of 3 to 20 nm (step 1B in FIG. 1A), and a second metal layer 82 on the first metal layer 81 having a Rh of 20 nm or more and 2 μm or less. And a second step (FIG. 1A step 1C), and a third step (FIG. 1A step 1D) of heat-treating the first metal layer and the second metal layer at 300° C. or higher and 600° C. or lower. ,,.

<First step>
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 a general method such as a vacuum deposition method such as an electron beam deposition method and a resistance heating deposition method, and a sputtering method. This is because if the thickness is less than 3 nm, it is difficult to suppress the above-mentioned death, and if the thickness exceeds 20 nm, the reflectance of the reflective electrode significantly decreases. Further, it is more preferable that the thickness of the first metal layer 81 is 3 to 10 nm. By forming the first metal layer 81 with a thickness of 10 nm or less, the reflectance of the heat-treated reflective electrode 80 for a wavelength of 300 nm can be 60% or more. The thickness of the first metal layer 81 can be measured using a film thickness meter of a crystal oscillator.

<Second step>
In the second step, Rh is formed on the first metal layer 81 as the second metal layer 82 with a thickness of 20 nm or more and 2 μm or less. This is because if the thickness is less than 20 nm, the reflectance of the second metal layer 82 with respect to ultraviolet light may not be sufficiently high. Further, if it exceeds 2 μm, there is a problem of cost for Rh. The thickness of the second metal layer 82 is more preferably 30 nm or more in order to improve the reflectance of the reflective electrode after the diffusion of the first metal layer 81 by the heat treatment process described later, and is 100 nm or less in order to reduce the cost. More preferably. Similarly to the first step, the second step can also form the second metal layer by a general method such as a vacuum deposition method and a sputtering method. The thickness of the second metal layer 82 can be measured by using a crystal oscillator film thickness meter.

<Third step>
In the third step, the first metal layer 81 and the second metal layer 82 are heat-treated at 300° C. or higher and 600° C. or lower to obtain the reflective electrode 80. As in this step, it is common to use an inert gas such as nitrogen as an atmospheric gas used when performing heat treatment for establishing ohmic contact after forming the p-side electrode. Also in this step, only the inert gas may be used as the atmospheric gas. However, in this step, it is more preferable that the atmospheric gas contains oxygen. The flow rate ratio of oxygen in the atmosphere gas is preferably more than 0% and 50% or less.

The reflective electrode 80 thus obtained is an electrode made of Ni and Rh. With the heat treatment in the third step, Ni as the first metal layer 81 diffuses from the interface in contact with the p-type contact layer 70 to the Rh side of the second metal layer 82. Then, since the ratio of Rh at the interface between the p-type contact layer 70 and the reflective electrode 80 increases due to the diffusion of Ni, the reflectance at the interface increases as compared to before the heat treatment. In the reflective electrode 80 after the heat treatment, Ni does not maintain a layered state and diffuses, so it is difficult to accurately measure the amount of Ni after the heat treatment (that is, after diffusion). Therefore, when both peaks of Ni and Rh are observed in the SEM-EDS analysis of the cross section (vertical cross section) of the reflection electrode after the heat treatment, it is determined that the reflection electrode 80 made of Ni and Rh is provided. In the reflective electrode 80, Rh is 50% or more, preferably 75% or more, in terms of volume ratio (corresponding to the area ratio in the SEM-EDS analysis mapping of the cross section of the reflective electrode). By setting the volume ratio of Rh in the reflecting electrode 80 to 75% or more, the reflectance of the reflecting electrode 80 after the heat treatment for the wavelength of 300 nm can be 60% or more.
Further, in the reflectance measurement of the above-mentioned reflective electrode (after the heat treatment step), the reflectance of the Rh simple substance at a wavelength of 300 nm is 70 to 73%, and the reflectance of the alloy of Ni and Au is less than 40%. The reflective electrode 80 made of Ni and Rh of the invention has a reflectance of 40 nm at a wavelength of 300 nm by setting the thickness of the first metal layer 81 to 3 to 20 nm and the thickness of the second metal layer 82 to 20 nm to 2 μm. % Or more and less than 67%, the first metal layer 81 has a thickness of 3 to 10 nm, and the second metal layer 82 has a thickness of 30 nm to 100 nm. Can be 60% or more and less than 70%. Even if Ni is alloyed with Rh, the reflectance of Rh alone does not significantly decrease. Further, in the reflective electrode 80, ruthenium (Ru), gold (Au), platinum (Pt), palladium (Pd), titanium (Ti) are included as impurities that may be contained other than Ni and Rh and do not significantly reduce the reflectance. It is considered that the impurity content is 40% by mass or less, preferably 10% by mass or less.

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

Please refer to FIG. 1B. As an embodiment of the present invention, a step of forming a Ni layer as a third metal layer 83 on the second metal layer after the second step, and a Rh layer as a fourth metal layer 84 on the third metal layer 83. further including the step of forming a. This step may be performed between the second step and the third step or after the third step, but it is necessary to perform this step immediately after the second step between the second step and the third step. In terms of As the third metal layer 83, a Ni layer can be formed with a thickness of 1 to 20 nm. Further, the Rh layer as the fourth metal layer 84 can be formed with a thickness of 5 nm or more and 2 μm or less. Further, the Ni layer and the Rh layer corresponding to the third metal layer and the fourth metal layer are repeatedly formed on the fourth metal layer 84, and the reflection electrode is formed a plurality of times in the order of the Ni layer and the Rh layer. It may be a laminated body formed by repeatedly laminating.

In a state where Au is present on the second metal layer 82, if Au diffuses in the reflective electrode after heating in the third step or the like, death may occur. However, the reflective electrode composed of Ni and Rh may be replaced by Ni and Rh. By adopting a laminated structure in which the above-mentioned stacking order is repeated a plurality of times, death due to death can be suppressed. Therefore, if the Ni layer and the Rh layer are stacked a plurality of times, a mounting process of connecting another metal (such as gold) on the Rh layer after the stacking to form an electrical connection with the outside and a connection with the outside. It is preferable because the electrode can be more surely avoided without fear of death, regardless of the method (including the case of requiring heating such as solder). From this point of view, it is particularly preferable that the metal element forming the reflective electrode is composed of only Ni and Rh.

(Deep ultraviolet light emitting device)
Next, the deep ultraviolet light emitting device 100 having the reflective electrode 80 obtained by the present invention will be described. As shown in FIG. 2, a deep ultraviolet light emitting device 100 according to an embodiment of the present invention includes 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 on a substrate 10, and This is a deep-ultraviolet light-emitting device having the p-side reflective electrode 80 in order. The reflective electrode 80 is provided on the outermost second layer 72 of the p-type contact layer. The p-type contact layer 70 includes a first layer 71 made of Al _x Ga _1-x N having an Al composition ratio x and a second layer 72 made of Al _y Ga _1-y N having an Al composition ratio y. It has a superlattice structure formed by alternately stacking. The Al composition ratio y of the second layer 72 is 0.15 or more (y≧0.15).

Particularly, when the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer 40 is w ₀ , the Al composition ratio x of the first layer 71 is higher than the Al composition ratio w ₀ , and the Al of the second layer 72 is Al. The composition ratio y is lower than the Al composition ratio x, and the Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer 70 are represented by the following formulas [1] and [2]. ]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
Is preferably satisfied.

As shown in FIG. 2, 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-type semiconductor layer 30 is provided. Providing the n-side electrode 90 on the exposed surface is a preferred embodiment of the deep ultraviolet light emitting device 100.

In the following description, the Al composition ratio and the 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 assumed to be constant for simplification of description. In this case, 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 first layer 71 in the super lattice structure is N, representing the thickness of each layer of the first layer 71 and t _a. Similarly, the number of layers of the second layer 72 is M, and the thickness of each layer of the second layer 72 is represented by t _b . At this time, the thickness average Al composition ratio z of the p-type contact layer 70 is according to the following formula [3].

The Al composition ratios and thicknesses of the first layer 71 and the second layer 72 in the superlattice structure of the p-type contact layer 70 do not necessarily have to be constant. When the Al composition ratios and thicknesses of the first layer 71 and the second layer 72 in this superlattice structure are varied, the thickness average Al composition ratio z is equal to the thickness of each of the first layer 71 and the second layer 72. And a weighted average value (weighted average value) depending on the Al composition ratio may be used, and the Al composition ratios x and y of the first layer 71 and the second layer 72 refer to the weighted average value depending on the thickness. To do.

Next, with reference to FIG. 2, details of 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 device 100 will be described first.

<Substrate>
As the substrate 10, it is preferable to use a substrate capable of transmitting light emitted from the light emitting layer 40, and for example, a sapphire substrate or a single crystal AlN substrate can be used. Further, 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 if 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 dopant concentration allows the n-type semiconductor layer 30 to function as the n-type, and is, for example, 1.0×10 ¹⁸ atoms/cm ^{3 to} 1.0×10 ^20. It can be set to atoms/cm ³ . In addition, the band gap of the n-type semiconductor layer 30 is wider than the band gap of the light emitting layer 40 (the well layer 41 in the case of a quantum well structure), and it is preferable that the n type semiconductor layer 30 be transmissive to the emitted deep ultraviolet light. The n-type semiconductor layer 30 may have a single-layer structure or a structure having a plurality of layers, as well as a composition-graded layer in which the composition ratio of the group III elements is compositionally graded in 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 a function of enhancing crystallinity from the substrate to the light emitting layer.

<Light emitting layer>
The light emitting layer 40 is provided on the n-type semiconductor layer 30 and emits deep ultraviolet light. The light emitting layer 40 can be made of AlGaN, and the Al composition ratio thereof is set so that the wavelength of radiated light is 200 to 350 nm of deep ultraviolet light or the central emission wavelength is 265 nm or more and 317 nm or less. You can Such an Al composition ratio can be set in the range of 0.25 to 0.60, for example.

The light emitting layer 40 may have a single-layer structure with a constant Al composition ratio, or may be a multiple quantum well (MQW) formed by repeatedly forming a well layer 41 and a barrier layer 42 made of AlGaN having different Al composition ratios. It is also preferable to construct the structure. When the light emitting layer 40 has a single layer structure with a constant Al composition ratio, the Al composition ratio w ₀ of the layer that emits deep ultraviolet light in the light emitting layer 40 is the Al composition ratio itself of the light emitting layer 40. Further, when the light emitting layer 40 has a multiple quantum well structure, the well layer 41 corresponds to a layer that emits deep ultraviolet light in the light emitting layer 40. Therefore, for convenience, the Al composition ratio w of the well layer 41 is the above Al composition. It is treated as equivalent to the ratio w ₀ . The Al composition ratio w _{0 of} the layer emitting deep ultraviolet light (or the well layer so that the wavelength of emitted light is 200 to 350 nm of deep ultraviolet light or the central emission wavelength is 265 nm or more and 317 nm or less). The Al composition ratio w) is preferably 0.25 to 0.60.

The Al composition ratio b of the barrier layer 42 is set higher than the Al composition ratio w of the well layer 41 (that is, b>w). Regarding the Al composition ratio b, under the condition of b>w, the Al composition ratio b of the barrier layer 42 can be set to 0.40 to 0.95, for example. The number of repetitions of the well layer 41 and the barrier layer 42 is not particularly limited and can be set to 1 to 10 times, for example. It is preferable that both ends (that is, the first and last) in the thickness direction of the light emitting layer 40 be barrier layers, and when the number of repetitions of the well layer 41 and the barrier layer 42 is n, in this case, “n. And barrier layer". The well layer 41 can have a thickness of 0.5 nm to 5 nm, and the barrier layer 42 can have a thickness of 3 nm to 30 nm.

<Guide layer>
When the light emitting layer 40 has the above-described quantum well structure, the barrier layer 42 and the p-type layer are provided between the well layer 41 closest to the p-type electron block layer 60 in the light-emitting layer 40 and the p-type electron block layer 60 described later. It is also preferable to provide a guide layer having an Al composition ratio higher than any of the Al composition ratios of the electron block layer 60. Thereby, the light emission output of the deep ultraviolet light emitting device 100 can be increased. In this case, if the Al composition ratio of the guide layer is expressed as b _g and the Al composition ratio α of the p-type electron block layer 60 described later is used, the relationship of each Al composition ratio is as follows.
w (well layer) <b (barrier layer) <α (p-type electron block layer) <b _g (guide layer)

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

<P-type electron block layer>
The p-type electron blocking layer 60 is provided on the light emitting layer 40. The p-type electron blocking layer 60 is used as a layer for blocking electrons and injecting the electrons into the light emitting layer 40 (the well layer 41 in the case of the MQW structure) to improve the electron injection efficiency. For this purpose, although it depends on the Al composition ratio w ₀ of the layer that emits deep ultraviolet light (corresponding to the Al composition ratio w of the well layer 41 in the case of the quantum well structure), the Al composition ratio of the p-type electron block layer 60 is also dependent. The ratio α is preferably 0.35≦α≦0.95. If the Al composition ratio α is 0.35 or more, the p-type electron block layer 60 may include In in an amount of 5% or less with respect to Al and Ga as group III elements. Here, it is preferable that the Al composition ratio α be higher than the thickness average Al composition ratio z of the p-type contact layer 70 while satisfying the above conditions. That is, it is preferable that α>z. Further, it is more preferable that both of the Al composition ratio α of the p-type electron block layer 60 and the Al composition ratio b of the barrier layer 42 satisfy 0<α−b≦0.55. By doing so, the efficiency of electron injection into the well layer 41 by the p-type electron block layer 60 can be reliably increased.

The thickness of the p-type electron block layer 60 is not particularly limited, but is preferably 10 nm to 80 nm, for example. When the thickness of the p-type electron block layer 60 is in this range, a high light emission output can be reliably obtained. The thickness of the p-type electron block layer 60 is preferably larger than that of the barrier layer 42. Examples of the p-type dopant with which the p-type electron block layer 60 is doped include magnesium (Mg), zinc (Zn), calcium (Ca), beryllium (Be), manganese (Mn), and the like. Is generally used. The dopant concentration of the p-type electron block layer 60 is not particularly limited as long as it is a dopant concentration that can function as a p-type layer, and is, for example, 1.0×10 ¹⁸ atoms/cm ^{3 to} 5.0×10 ²¹ atoms/ It can be cm ³ .

<P-type contact layer>
The p-type contact layer 70 is provided on the p-type electron block layer 60. The p-type contact layer 70 is a layer for reducing the contact resistance between the p-side reflective electrode 80 provided immediately above and the p-type electron block 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 that are unavoidable in manufacturing. That is, the p-side reflective electrode 80 is in contact with the p-type contact layer 70 having the superlattice structure.

Now, as described above, the p-type contact layer 70 is formed by alternately stacking the first layers 71 made of Al _x Ga _1-x N and the second layers 72 made of Al _y Ga _1-y N. It has a superlattice structure. Here, the Al composition ratio x of the first layer 71 is set higher than the Al composition ratio w ₀ of the layer that emits deep ultraviolet light in the light emitting layer 40 (x>w ₀ ), so that the transmittance for deep ultraviolet light is increased. It is preferable to increase. If the light emitting layer 40 has a single-layer structure, the Al composition ratio x may be set 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 may be set to the well layer 41. It may be higher than the Al composition ratio w.

As described above, the Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer are represented by the following formulas [1] and [2]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
Is preferably satisfied.

In the prior art, it was general to use a p-type GaN layer that is easy to increase the hole concentration 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 360 nm or less due to its band gap. Therefore, of the deep ultraviolet light emitted from the light emitting layer, the light extraction effect from the p-type contact layer side or the light extraction effect by reflection at the p-side electrode can hardly be expected. On the other hand, if the p-type contact layer is made of AlGaN having a high Al composition ratio, the hole concentration can be reduced to some extent as compared with GaN, but since deep ultraviolet light emitted from the light emitting layer can pass through the p-type contact layer. The light extraction efficiency of the deep ultraviolet light emitting device as a whole is increased, and as a result, the light emission output of the deep ultraviolet light emitting device can be increased. However, it was found from the experiments by the present inventors that if the Al composition ratio of the p-type contact layer becomes too high, a deep ultraviolet light emitting device with insufficient reliability can be obtained. On the other hand, in the case of the p-type contact layer 70 having the superlattice structure formed by the Al composition ratio described above, the thickness average Al composition ratio z is larger than the Al composition ratio w _{0 of} the layer that emits deep ultraviolet light in the light emitting layer 40. Is high (z>w ₀ ), deep ultraviolet light can pass through the p-type contact layer 70, and as a result, a higher emission output can be obtained, which is preferable.

Here, since the deep ultraviolet light is more surely transmitted through the p-type contact layer 70, the thickness average Al composition ratio z and the Al composition ratio w of the layer emitting the deep ultraviolet light are expressed by the above formula [1]. It is preferable to make the difference of 0.030 higher than 0.030 (that is, z−w ₀ >0.030). For this purpose, 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), and higher than 0.050 (z−). w ₀ >0.050) is more preferable, and it is particularly preferable that it is higher than 0.06 (z−w ₀ >0.060).

Further, in order to obtain good ohmic contact between the p-type contact layer 70 and the p-side reflective electrode 80 to ensure sufficient reliability, it is preferable to set an upper limit of the thickness average Al composition ratio. Therefore, as in the above formula [1], it is preferable to set the upper limit of the difference between the thickness average Al composition ratio z and the Al composition ratio w of the layer that emits deep ultraviolet light to 0.20 (z−w _{0 ).} <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 0.19 (z−w ₀ <0.19), and the upper limit is 0.10. More preferably, it is 18 (zw ₀ <0.18).

Further, as 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 0.050 or more in absolute value (xy≧0.050). It is preferable. This is to ensure that the p-type contact layer 70 functions as a superlattice structure. Further, since the strain of the entire superlattice structure is reduced and the p-side reflective electrode 80 is brought into contact with a low Al composition ratio, the absolute value of the difference between the Al composition ratio x and the Al composition ratio y is 0.1 or more (x− y≧0.10) is preferable, and 0.15 or more (x−y≧0.15) is more preferable. On the other hand, when the difference between the Al composition ratio x and the Al composition ratio y is excessively large, the lattice constant between the first layer and the second layer changes significantly, so that strain increases and a superlattice layer having good crystallinity is obtained. Can be difficult. Therefore, in order to more reliably obtain the effect of the present invention, it is preferable that x−y≦0.47, and it is more preferable that x−y≦0.45.

If the Al composition ratio y of the second layer 72, which is a layer having a low Al composition ratio in the superlattice structure, is 0.20 or more, the transmittance of deep ultraviolet light from the light emitting layer 40 can be increased more reliably. It is possible and preferable. For this purpose, the Al composition ratio y is more preferably 0.21 or more, further preferably 0.25 or more. On the other hand, when the Al composition ratio y is 0.55 or less, high reliability can be maintained more reliably, and for this purpose, the Al composition ratio y is more preferably 0.51 or less. It is particularly preferable to set it to 0.40 or less. As long as the thickness average Al composition ratio z is higher than the Al composition ratio w ₀ of the layer that emits deep ultraviolet light in the light emitting layer 40, the Al composition ratio y may be higher or lower than the Al composition ratio w _0. Good. The Al composition ratio x may be appropriately set as long as it satisfies the above formulas [1] and [2], and the upper limit and the lower limit of the Al composition ratio x are not limited. After satisfying the expressions [1] and [2], the Al composition ratio x may be set within the range of approximately 0.40 to 0.85.

Further, each of the thickness t _a of the first layer 71 and second layer 72, t _b form a superlattice structure, and the thickness of the average Al composition z, the conditions for the Al composition ratio of the light-emitting layer 40 There is no particular limitation as long as it is satisfied. For example, the thickness t _a of the first layer 71 can be 1.0 nm or more and 10.0 nm or less, and the thickness t _b of the second layer 72 can be 1.0 nm or more and 10.0 nm or less. The size relation between the thicknesses t _a and t _b is not limited, and either one may be larger, or both thicknesses may be the same. Further, the number of repetitions of the first layer 71 and the second layer 72 is set to, for example, 3 to 15 times so that the total thickness of the p-type contact layer 70 is within a range of 20 nm or more and 100 nm or less, preferably 70 nm or less. It is preferable to set it appropriately within the range.

The total thickness of the p-type layer, which is the total thickness of the p-type electron blocking layer 60 and the p-type contact layer 70, is preferably 65 nm or more and 100 nm or less, and 70 nm or more and 95 nm or less. Is more preferable. Within this range, a high light emission output can be obtained more reliably.

Here, in the thickness direction of the p-type contact layer 70, the end layer closer to the p-type electron block layer 60 is preferably the first layer 71. In other words, when there is no other layer interposed between the p-type contact layer 70 and the p-type electron block layer 60 and they are in contact with each other, the first layer is formed directly on the p-type electron block layer 60. 71 is preferably provided. 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 block layer 60. It is possible to more reliably suppress generation of defects due to strain between the layer 60 and the p-type contact layer 70.

On the other hand, in the thickness direction of the p-type contact layer 70, the end layer farther from the p-type electron block layer 60 is preferably the second layer 72. In other words, the layer in contact with 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 and the Al composition ratio y of the second layer 72 are compared, the Al composition ratio y is lower, so that ohmic contact with the p-side reflective electrode 80 is facilitated. ..

The end layer closer to the p-type electron block layer 60 in the thickness direction of the p-type contact layer 70 is the first layer 71, and the end layer farther from the p-type electron block layer 60 is the first layer 71. In the case of the second layer 72, the number of layers of the first layer 71 and the number of layers of the second layer 72 are the same. However, in this embodiment, the numbers of layers of both do not necessarily match. In the present embodiment, when both end layers in the thickness direction of the p-type contact layer 70 are the second layers 72 (in this case, the number of the second layers 72 is 1 compared to the number of the first layers 71). Including many layers).

Further, as one embodiment according to the present invention, the superlattice structure in which the two layers of the first layer 71 and the second layer 72 are repeatedly laminated has been described so far, but as another embodiment according to the present invention, the above-mentioned first A superlattice having a three-layer structure in which a third layer having an Al composition ratio between the first layer and the second layer is arranged between the first layer and the second layer while having the same relationship between the first layer and the second layer. The structure can also be applied. Also in this case, the same effects as the effects of the present invention described above can be obtained.

Here, the p-type contact layer 70 preferably has a high-concentration region having a Mg concentration of 3×10 ²⁰ atoms/cm ³ or more on the side in contact with the p-side reflective electrode 80. It is more preferably 5×10 ²⁰ atoms/cm ³ or more. By increasing the hole concentration of the p-type contact layer 70, the forward voltage Vf of the deep ultraviolet light emitting device 100 can be lowered. Although the upper limit is not intended to be limited, in view of industrial productivity, the upper limit of the Mg concentration in the high concentration region can be set to 1×10 ²¹ atoms/cm ^{3 in} the present embodiment. In this case, the Mg concentration in the region of the p-type contact layer 70 on the p-type electron block layer 60 side can be set in a general range, and is usually 5×10 ¹⁹ atoms/cm ³ or more and 3×10 ²⁰ atoms/cm ³ or more. Is less than. The Mg concentration in the p-type contact layer is the average concentration in each region measured by SIMS. In order to maintain the crystallinity of the p-type contact layer 70, the thickness of the high concentration region is usually 15 nm or less, and a few layers on the side in contact with the p-side reflective electrode 80 can be the high concentration region.

Furthermore, the p-type contact layer 70 may have a Si-doped region having a Si concentration of 5×10 ¹⁶ atoms/cm ³ or more and 1×10 ²⁰ atoms/cm ³ or less on the side in contact with the p-side reflective electrode 80. preferable. It is more preferable that the Si concentration in the region is 2×10 ¹⁹ atoms/cm ³ or more and 5×10 ¹⁹ atoms/cm ³ or less. By doing so, the emission output of the deep ultraviolet light emitting device 100 can be further increased. In addition, if the thickness of the Si-doped region is about 1 to 5 nm, this effect can be reliably obtained. It is also preferable that the Si-doped region be the last second layer in the superlattice structure of the p-type contact layer. A co-doped region may be formed by further doping Si into the high-concentration region in which the Mg concentration is 3×10 ²⁰ atoms/cm ³ or more. Further, the Si-doped region may be doped with only Si (that is, Mg may not be doped).

In addition, when a Si-doped region doped with only Si is provided on the side of the p-type contact layer 70 in contact with the reflection electrode 80 on the p-side and the region is not doped with Mg, the region is considered to be n-type as the conductivity type. You can think. However, in the case of the above thickness range (1 to 5 nm), even if Mg is not doped, it does not become a thyristor if it contacts the p-type electrode as the uppermost layer of the p-type contact layer 70. Therefore, even in such a case, the Si-doped region is regarded as a part of the p-type contact layer 70.

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

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

<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 reduce the lattice mismatch between the two. An undoped group III nitride semiconductor layer can be used as the buffer layer 20, and the buffer layer 20 preferably 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 can 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 can be appropriately selected according to the shape and size of the light emitting element. The n-side electrode 90 is not limited to being formed on 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 configurations>
Although not shown in FIG. 2, a guide layer made of AlGaN having a higher Al composition ratio than the Al composition ratio α of the p-type electron block layer 60 is provided between the light emitting layer 40 and the p-type electron block layer 60. It may be provided. By providing the guide layer, injection of holes into the light emitting layer 40 can be promoted.

<p-type clad layer>
Although not shown in FIG. 2, a p-type clad layer made of AlGaN may be provided between the p-type electron block layer 60 and the p-type contact layer 70. The p-type cladding layer is higher than the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer 40 (Al composition ratio w in the case of the quantum well structure) and the thickness average Al composition ratio z of the p-type contact layer 70. On the other hand, it is a layer having an Al composition ratio lower than the Al composition ratio α of the p-type electron block 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 that emits deep ultraviolet light, and the deep ultraviolet light emitted from the light emitting layer 40 is emitted. It is a substantially transparent layer. However, it is preferable not to provide the p-type cladding layer. The reason for this is as described in JP-A-2016-111370, and the entire disclosure content thereof is incorporated herein by reference. When the p-type cladding layer is provided, when the Al composition ratio of the p-type cladding layer is β, α>β and β>y.

In the deep ultraviolet light emitting device 100 according to the present embodiment, the substrate side or the substrate horizontal direction is the main light extraction direction by forming the p-side reflective electrode 80 with a reflective electrode material and reflecting the deep ultraviolet light. be able to. Further, the deep ultraviolet light emitting device 100 can be in a so-called flip chip type.

(Method for manufacturing deep ultraviolet light emitting device)
Next, an embodiment for obtaining the method for manufacturing the deep ultraviolet light emitting device 100 described above will be described with reference to FIG. One embodiment of the method for manufacturing the deep ultraviolet light emitting device 100 according to the present invention is a process of forming the n-type semiconductor layer 30 on the substrate 10 (see step 3A in FIG. 3), and a light emitting layer 40 on the n-type semiconductor layer 30. , A step of forming the p-type electron block layer 60 on the light emitting layer 40 (see step 3B in FIG. 3), and a step of forming a p-type contact layer on the p-type electron block layer (step in FIG. 3). 3C), and a step of forming a reflective electrode on the p-type contact layer (see step 3D in FIG. 3). The step of forming the p-type contact layer includes a first step of forming a first layer of Al _x Ga _1-x N having an Al composition ratio x, and an Al composition ratio lower than the Al composition ratio x. and a second step of forming a second layer of Al _y Ga _{1 -y} N having _y to form the p-type contact layer having a superlattice structure, and the second layer of Al The composition ratio y is 0.15 or more. Then, as described in the embodiment of the reflective electrode 80, in the step of forming the reflective electrode, Ni is used as the first metal layer 81 with a thickness of 3 to 20 nm on the p-type contact layer 70 having the superlattice structure. A first step of forming, a second step of forming Rh 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 with respect to the first metal layer and the second metal layer And a third step of performing heat treatment at 300° C. or higher and 600° C. or lower (see FIG. 1A). The step of forming the p-type contact layer 70 (see step 3C) includes the first step of forming the first layer 71 of Al _x Ga _1-x N having the Al composition ratio x and the Al composition ratio x. And a second step of forming a second layer 72 of Al _y Ga _{1 -y} N having a low Al composition ratio y, and a step of forming a p-type contact layer 70 having a superlattice structure by alternately repeating the second step. The Al composition ratio y of the second layer 72 is 0.15 or more (y≧0.15).

Further, when the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer 40 is w ₀ , the Al composition ratio x of the first layer 71 is higher than the Al composition ratio w ₀ , and the Al of the second layer 72 is Al. The composition ratio y is lower than the Al composition ratio x, and the Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer 70 are represented by the following formulas [1] and [2]. ]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
Is preferably satisfied.

The description will be continued with reference to the flowchart of FIG. However, description that overlaps with the above-described embodiment will be omitted.

First, as shown in steps 3A and 3B of FIG. 3, the n-type semiconductor layer 30, the light emitting layer 40, and the p-type electron blocking layer 60 are sequentially formed on the 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, and a sputtering method. ..

In forming each layer of the n-type semiconductor layer 30, the light emitting layer 40, the guide layer and the p-type electron block layer 60, the growth temperature, the growth pressure and the growth time for epitaxial growth depend on the Al composition ratio and the thickness of each layer. Can be general conditions. As a carrier gas for epitaxial growth, hydrogen gas, nitrogen gas, a mixed gas of the two, or the like may be used and supplied into the chamber. Furthermore, as a source gas for growing each of the above layers, TMA (trimethylaluminum), TMG (trimethylgallium), or the like can be used as a group III element source gas, and NH ₃ gas can be used as a group V element gas. Molar ratio of group V element to group III element calculated based on the growth gas flow rate of group V element gas such as NH ₃ gas and group III element gas such as TMA gas (hereinafter referred to as V/III ratio) The general conditions may also be applied to. Further, as the gas of the dopant source, cyclopentadiene magnesium gas (CP ₂ Mg) or the like as the Mg source for the p-type dopant, or monosilane gas (SiH ₄ ) or the Zn source as the Si source for the n-type dopant. Zinc chloride gas (ZnCl ₂ ) or the like may be appropriately selected and 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, the p-type contact layer 70 having a superlattice structure in which the first layer 71 and the second layer 72 described above are repeated on the p-type electron block layer 60. To form. The conditions for the thickness range and the Al composition ratio of the p-type contact layer 70 are as described above. The p-type contact layer 70 may be crystal-grown by epitaxial growth such as MOCVD.

In the p-type contact layer 70, in order to set the Mg concentration in the high-concentration region 72 on the side in contact with the p-side reflective electrode 80 to 3×10 ²⁰ atoms/cm ³ or more, The following processing may be performed. That is, in the p-type contact layer forming step, the superlattice structure is crystal-grown by supplying the group III source gas, the group V source gas, and the Mg source gas, and the flow rate of the group III source gas is changed immediately after the crystal growth is completed. The flow rate at the time of crystal growth may be reduced to 1/4 or less, and the group V source gas and the Mg source gas may be continuously supplied for 1 minute or more and 20 minutes or less.

Further, in the p-type contact layer 70, in order to dope both Mg and Si on the side in contact with the p-side reflective electrode 80, CP ₂ Mg gas as a Mg source is supplied to the chamber, and monosilane gas (as a Si source) is supplied. SiH ₄ ) or the like may be flowed. If only Si is to be doped, the CP ₂ Mg gas as the Mg source should be stopped from being supplied to the chamber, and the monosilane gas (SiH ₄ ) should be flown as the Si source. When Si is doped on the p-side contact layer 70 on the side in contact with the reflective electrode 80 as described above, the formation of the Mg high-concentration region is optional.

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

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

( Reference example 1 )
A deep ultraviolet light emitting device according to Inventive Example 1 was produced according to the process charts shown in FIGS. 1A and 3. First, a sapphire substrate (diameter 2 inches, thickness: 430 μm, plane orientation: (0001)) was prepared. Then, an AlN layer having a central film thickness of 0.60 μm was grown on the sapphire substrate by MOCVD method to obtain an AlN template substrate. At that time, the growth temperature of the AlN layer was 1300° C., 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. Regarding the film thickness of the AlN layer, a total of 25 film thicknesses were dispersed at equal intervals including the center of the wafer by using an optical interference type film thickness measuring device (Nanospec M6100A; manufactured by Nanometrics). Was measured.

Next, the above AlN template substrate was introduced into a heat treatment furnace, and after the inside of the furnace was made a nitrogen gas atmosphere, the temperature inside the furnace was raised to subject the AlN template substrate to heat treatment. At that time, the heating temperature was 1650° C. and the heating time was 4 hours.

Then, a buffer layer of undoped Al _0.55 Ga _0.45 N having a thickness of 1 μm was formed by MOCVD. Next, a Si-doped n-type semiconductor layer having a thickness of 2 μm and made of Al _0.45 Ga _0.55 N was formed on the buffer layer. As a result of SIMS analysis, the Si concentration of the n-type semiconductor layer was 1.0×10 ¹⁹ atoms/cm ³ .

Further, on the n-type semiconductor layer, a light emitting layer was formed by alternately stacking three sets of well layers made of Al _0.29 Ga _0.71 N and having a thickness of 3 nm and barrier layers made of Al _0.51 Ga _0.49 N and having a thickness of 7 nm. .. The Al composition ratio w of the well layer is 0.29. Then, a guide layer having a thickness of 1 nm was formed from AlN on the light emitting layer. Note that Si was doped when forming the barrier layer and undoped when forming the well layer and the guide layer.

After that, a 40-nm-thick p-type electron block layer made of Al _0.58 Ga _0.42 N was formed on the guide layer using hydrogen gas as a carrier gas. Upon forming the p-type electron block layer, CP ₂ Mg gas was supplied to the chamber as a Mg source to dope Mg. As a result of SIMS analysis, the Mg concentration of the p-type electron block layer was 5.0×10 ¹⁸ atoms/cm ³ .

Then, Al _0.47 Ga _0.53 N was formed as a first layer immediately above the p-type electron blocking layer, and then Al _0.31 Ga _0.69 N was formed as a second layer, and the formation of both of them was repeated 7 _times to form a total of 14 layers. A p-type contact layer having a superlattice structure was formed. The thickness of the first layer is 5.0 nm, the thickness of the second layer is 2.5 nm, the total thickness of the p-type contact layers is 52.5 nm, and the average Al composition of the thickness is 0. 42. Further, in forming the p-type contact layer, a CP ₂ Mg gas as a Mg source is supplied to the chamber together with the group III source TMA gas, the TMG gas, and the group V source ammonia gas, and the p-type contact layer is doped with Mg. Was grown. Then, only the supply of the group III source gas was stopped, and only the Mg source gas and the group V source gas were supplied for 10.5 minutes to form a high concentration region on the surface side of the p-type contact layer.

When specifying the Al composition of the p-type contact layer, the Al composition ratio of the p-type contact layer was determined from the emission wavelength (bandgap energy) of the p-type contact layer analyzed by photoluminescence measurement.

As a result of SIMS analysis, in the p-type contact layer, the Mg concentration on the p-type electron block layer side was 1×10 ²⁰ atoms/cm ³ , and the surface forming the p-side reflective electrode 80 opposite to the p-type electron block layer. The Mg concentration on the side where the concentration of Mg on the side was high (high concentration region) was 3×10 ²⁰ atoms/cm ³ .

Table 1 shows the layer structure of Reference Example 1 .

A mask was formed on the p-type contact layer and mesa etching was performed by dry etching to expose the n-type semiconductor layer. Next, on the outermost second layer (Al _0.31 Ga _0.69 N) of the p-type contact layer, a Ni layer (first metal layer) having a thickness of 7 nm and the Ni layer were formed by using an electron beam evaporation method. An Rh layer (second metal layer) having a thickness of 50 nm was sequentially formed. The thicknesses of the Ni layer and the Rh layer were measured using a crystal oscillator film thickness meter (CRTM-9000G; manufactured by ulvac). The oscillator used gold plating and a natural frequency of 4.5 MHz to 5.0 MHz. For the calibration curve (calibration) of the crystal unit, a single film of the target metal is formed with a film thickness of 100 nm or more, and the step difference between the presence and absence of film formation is determined by the stylus profilometer (Tencor P-6). It was performed by measuring using.
An n-side electrode made of Ti/Al was formed on the exposed n-type semiconductor layer. The thickness of Ti is 20 nm and the thickness of Al is 150 nm.
Finally, using the RTA device (Advance Riko; infrared lamp annealing heating device), the maximum attainable temperature was kept at 550° C. for 10 minutes, and heat treatment for ohmic contact was performed to form a reflective electrode composed of Ni and Rh. .. The heat treatment atmosphere in the RTA apparatus was a mixed gas of N ₂ and O ₂ , the N ₂ flow rate in the mixed gas was 1.0 slm, and the O ₂ flow rate was 0.5 slm. A sapphire substrate was laser scribed into individual chips each having a chip size of 1000 μm×1000 μm to fabricate a deep ultraviolet light emitting device according to Reference Example 1 .

A 7 nm thick Ni layer (first metal layer) and a 50 nm thick Rh layer (second metal layer) are formed on a sapphire substrate, and after the above heat treatment step, the transparent sapphire substrate side faces the reflective electrode. Then, the reflectance with respect to the wavelength was measured using an ultraviolet-visible spectrophotometer (V-650 manufactured by JASCO Corporation), and the reflectance with respect to the wavelength of 300 nm was 62%.

( Reference example 2 )
A deep ultraviolet light emitting device according to Reference Example 2 in the same manner as in Reference Example 1 except that the heat treatment atmosphere in the RTA apparatus was N ₂ gas (N ₂ flow rate 1.5 slm) instead of the mixed gas atmosphere in Reference Example 1. Was prepared and evaluated.

( Reference example 3 )
A deep ultraviolet light emitting device according to Reference Example 3 was prepared and evaluated in the same manner as in Reference Example 1 except that the Al composition ratio x of the first layer was 0.43 and the Al composition y of the second layer was 0.27. did.

(Comparative Example 1)
A deep ultraviolet light emitting device according to Comparative Example 1 was prepared and evaluated in the same manner as in Reference Example 1 except that the thickness of Ni of the reflective electrode in Reference Example 1 was changed to 2 nm.

A 2 nm-thick Ni layer (first metal layer) and a 50 nm-thick Rh layer (second metal layer) are formed on the sapphire substrate, and after the above heat treatment process, the transparent sapphire substrate side is directed to the reflective electrode. Then, the reflectance with respect to wavelength was measured with an ultraviolet-visible spectrophotometer (V-650 manufactured by JASCO Corporation), and the reflectance with respect to wavelength 300 nm was 67%.

(Comparative example 2)
A deep ultraviolet light emitting device according to Comparative Example 2 was prepared and evaluated in the same manner as in Reference Example 1 except that Ni of the reflective electrode in Reference Example 1 was not provided.

(Comparative example 3)
P-type contact layer of a superlattice structure in Example 1 (total thickness 52.5 nm), was replaced with a single-layer structure having a thickness of 50nm of Al _0.42 Ga _0.58 N layer as the same manner as in Reference Example 1, Comparative Example 3 A deep ultraviolet light emitting device according to the above was prepared and evaluated.

(Comparative Example 4)
The same procedure as in Reference Example 1 except that the reflective electrode made of Ni and Rh in Reference Example 1 was changed to a Ni layer having a thickness of 10 nm and an Au layer having a thickness of 20 nm formed on the Ni layer in this order. A deep ultraviolet light emitting device according to Comparative Example 4 was produced and the light emission output was evaluated.

(Comparative example 5)
The reflective electrode made of Ni and Rh in Reference Example 1 was changed to one in which a Ni layer having a thickness of 10 nm and an Au layer having a thickness of 20 nm on the Ni layer were sequentially formed, and the Al composition ratio x of the first layer was 0. 0.43 and the Al composition y of the second layer was 0.27, the light emission output of the deep ultraviolet light emitting device according to Comparative Example 5 was evaluated in the same manner as in Reference Example 1 .

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

(Evaluation 1: Po, Vf evaluation)
The light-emitting devices (chip size □1000 μm) obtained in Reference Examples 1 to 3 and Comparative Examples 1 to 5 were AlN submounts (size 20 mm × 15 mm, thickness 0.8 mm) using spherical Au bumps in a flip chip method. Implemented in. With the AlN heatsink connected to the AlN submount, a constant current power supply was used to energize the device at 350mA, the forward voltage at that time was measured, and the photodetector was used by the light-receiving section located on the sapphire substrate side. The emission output was measured. The results are shown in Table 2. When the emission wavelength was measured with a spectrum analyzer, the emission center wavelengths were all 310 nm. The value is an average value of 10 measurements.

(Evaluation 2: Reliability evaluation 1)
After performing the measurement of the above-mentioned evaluation 1 with respect to Examples and Comparative Examples 1 to 5, 350 mA was continuously energized for 160 hours. After continuous energization, the output was measured again and compared with the initial output, and when there was no lighting or there was a sudden decrease in the output from the initial emission output to less than half, it was determined that there was death. Table 2 shows the ratio of dead chips among the 10 measured.

(Evaluation 3: Reliability evaluation 2)
In Comparative Examples 11 to 13, after the mask is formed on the p-type contact layer and the mesa etching by dry etching is performed to expose the n-type semiconductor layer, the exposed n-type semiconductor layer and the p-type contact layer are exposed. On the other hand, a small chip with a size of 560 μm × 780 μm was mounted on an AlN submount (size: 1.5 × 1.1 mm thickness: 0.2 mm) using Au bumps, and the light emission output and forward electrical thickness when 20 mA was applied. Was measured. The value is an average value of 10 measurements. Furthermore, for chips extracted from 10 locations in the wafer, the initial light emission output was confirmed by energizing at a current of 20 mA, and then the current was continuously energized at 20 mA for 250 hours, and the output was less than half the initial light emitting output after energization. Table 3 shows the ratio of chips (that is, dead). A photodetector arranged on the sapphire substrate surface side was used for measuring the light emission output.

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 [z=(2/3)x+( 1/3)y] is calculated. In Reference Examples 1 and 2, z−w ₀ =0.42-0.29=0.13, and xy=0.47−0.31=0.16.
Therefore, the conditions of the following expressions [1] and [2] are simultaneously satisfied.
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]

(Discussion of evaluation results)
It is considered that the cause of death in Comparative Examples 1 to 3 was due to contact failure at the interface between the p-type contact layer and the p-side reflective electrode. On the other hand, in Reference Examples 1 to 3, since the p-type contact layer has a superlattice structure and the Ni layer has a sufficient thickness, it is presumed that no contact failure occurred. Further, by comparing Comparative Examples 4 and 5 with Reference Examples 1 to 3, it is found that the reflective electrode made of Ni and Rh is effective in increasing the light emission output without largely changing the forward voltage.

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

( Reference example 4 )
In Reference Examples 1 to 3, the emission center wavelength was 310 nm, but instead of this, an experiment was conducted using a deep ultraviolet light emitting device having an emission center wavelength of 280 nm. A deep ultraviolet light emitting device according to Reference Example 4 was produced in the same manner as in Reference Example 1 except that the Al composition ratio of each semiconductor layer in Reference Example 1 was changed as shown in Table 4 below. The undoped AlGaN layer on the AlN template substrate was formed by grading the Al composition ratio from 0.85 to 0.65 in the crystal growth direction.

(Comparative example 6)
The same procedure as in Reference Example 4 except that the reflective electrode made of Ni and Rh in Reference Example 4 was replaced with a Ni layer having a thickness of 10 nm and an Au layer having a thickness of 20 nm formed on the Ni layer in this order. A deep ultraviolet light emitting device according to Comparative Example 6 was produced and the light emission output was evaluated.

(Comparative Example 7)
Comparative Example 3 was the same as Reference Example 1 except that the p-type contact layer of superlattice structure (total thickness 52.5 nm) in Reference Example 4 was changed to a single layer structure of Al _0.59 Ga _0.41 N layer with a thickness of 50 nm. A deep ultraviolet light emitting device according to the above was prepared and evaluated.

(Evaluation 4)
With respect to Reference Example 4 and Comparative Examples 6 and 7 (all having a chip size of 1000 μm×1000 μm as in Reference Example 1 ), the light emission output Po and the 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 performing this measurement, 350 mA was continuously energized for 20 hours. After continuous energization, the output was measured again and compared with the initial output, and when there was no lighting or there was a sudden decrease in the output from the initial emission output to less than half, it was determined that there was death. Table 5 also shows the ratio of dead chips among the 10 measured.

In Reference Example 4 , z−w ₀ =0.59−0.45=0.14 and xy=0.71−0.35=0.36. Therefore, the conditions of the following expressions [1] and [2] are simultaneously satisfied.
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]

(Discussion of evaluation results)
It is considered that the reason why the death occurred in Comparative Example 7 was that a contact failure occurred at the interface between the p-type contact layer and the p-side reflective electrode, as in Comparative Example 3. On the other hand, in Reference Example 4 , it is presumed that no contact failure occurred because the p-type contact layer had a superlattice structure and the Ni layer had a sufficient thickness. In addition, comparing Reference Example 4 and Comparative Example 6, it can be seen that the reflective electrode made of Ni and Rh is effective in increasing the light emission output without largely changing the forward voltage.

(Example 5)
Each semiconductor layer was formed in the same manner as in Reference Example 4, and then a Ni layer (first metal layer) having a thickness of 7 nm and a Rh layer (first layer) having a thickness of 50 nm on the Ni layer were formed using an electron beam evaporation method. 2 metal layers) were sequentially formed. Subsequently, a Ni layer having a thickness of 3 nm was formed as a third metal layer on the Rh layer (second metal layer), and then a Rh layer having a thickness of 20 nm was sequentially formed as a fourth metal layer. Then, as in Reference Example 4 , heat treatment for ohmic contact was performed. Other manufacturing conditions are the same as in Reference Example 4 . Thus, the deep ultraviolet light emitting device according to Example 5 was manufactured. The total thickness of the p-type electron block layer and the p-type layer of the p-type contact layer is 92.5 nm.

(Comparative Example 8)
In Example 5, a Ni layer having a thickness of 3 nm was formed as a third metal layer on the Rh layer (second metal layer), and then a Rh layer having a thickness of 20 nm was sequentially formed as a fourth metal layer. A deep ultraviolet light emitting device according to Comparative Example 8 was produced in the same manner as in Example 5 except that an Au layer having a thickness of 20 nm was formed on the (second metal layer).

(Comparative Example 9)
In Example 5, a Ni layer having a thickness of 3 nm was formed as a third metal layer on the Rh layer (second metal layer), and then a Rh layer having a thickness of 20 nm was sequentially formed as a fourth metal layer. Comparative Example 9 was performed in the same manner as in Example 5 except that a Ni layer having a thickness of 3 nm was formed as a third metal layer on the (second metal layer) and an Au layer having a thickness of 20 nm was sequentially formed as a fourth metal layer. A deep-ultraviolet light emitting device according to was produced.

(Evaluation 5)
In Evaluation 4, when the continuous energization time was set to 20 hours, the presence or absence of death in the above Examples and Comparative Examples was confirmed in the same manner as in Evaluation 4 except that the continuous energization was extended to 168 hours and 1000 hours. did. The evaluation results of Evaluation 5 are shown in Table 6.

Table 6 shows that Au was present on the Rh layer (second metal layer) even if the occurrence of death due to death was suppressed by the combination of the p-type contact layer having the superlattice structure according to the present invention and the reflective electrodes of Ni and Rh. Then, it was found that if Au diffuses in the reflective electrode after heating in the third step or the like, death may occur. It has been found that the incidence rate of death due to death can be suppressed for a long time by forming the reflective electrode of Ni and Rh into a laminated structure in which the layer order of Ni and Rh is repeated a plurality of times.

(Example 6)
A deep ultraviolet light emitting device according to Example 6 was prepared 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 block layer and the p-type layer of the p-type contact layer is 85.5 nm.

(Example 7)
Example 7 was repeated in the same manner as in Example 5 except that the thickness of the first layer of the p-type contact layer was reduced from 5 nm to 2.5 nm and the thickness average Al composition ratio z was changed to 0.53. The deep ultraviolet light emitting device was manufactured and evaluated. The total p-type thickness of the p-block layer and the p-type contact layer is 75 nm.

Regarding Examples 6 and 7, the presence or absence of death was confirmed in the same manner as in Evaluation 5 above. 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 for comparison.

From Table 7, it was found that the light emission output can be further improved by adjusting the total thickness of the p-type electron blocking layer 60 and the p-type contact layer 70 (total thickness of the p-type layers). .. What is the total thickness of the p-type layer? The thickness is preferably 65 nm or more and 100 nm or less, and more preferably 70 nm or more and 95 nm or less. Then, it was possible to obtain an electrode having higher emission output and higher reliability than the electrode using Ni and Au.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the reflective electrode for deep-ultraviolet light emitting elements which can make a high light emission output and the outstanding reliability compatible can be provided. Further, the present invention can provide a method for manufacturing a deep ultraviolet light emitting device using the reflective electrode and a deep ultraviolet light emitting device obtained by the method.

10 substrate 20 buffer layer 30 n-type semiconductor layer 40 light emitting layer 41 well layer 42 barrier layer 60 p-type electron block layer 70 p-type contact layer 71 first layer 72 second layer 80 reflective electrode 81 first metal layer 82 second metal Layer 83 Third metal layer 84 Fourth metal layer 90 n-side electrode 100 Deep ultraviolet light emitting device

Claims (13)

On a p-type contact layer having a superlattice structure,
A first step of forming Ni as a first metal layer with a thickness of 3 to 20 nm;
A second step of forming Rh as a second metal layer with a thickness of 20 nm or more and 2 μm or less on the first metal layer;
A third step of subjecting the first metal layer and the second metal layer to heat treatment at 300° C. or higher and 600° C. or lower;
A method of manufacturing a reflective electrode for a deep-ultraviolet light emitting device, comprising: The method for producing a reflective electrode for a deep ultraviolet light emitting device according to claim 1, wherein the atmospheric gas used when performing the heat treatment in the third step contains oxygen. After the second step, the method further includes forming a Ni layer as a third metal layer on the second metal layer, and forming an Rh layer as a fourth metal layer on the third metal layer. The method for producing a reflective electrode for a deep ultraviolet light emitting device according to claim 1. Forming an n-type semiconductor layer on the 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,
Forming a reflective electrode on the p-type contact layer;
A method of manufacturing a deep ultraviolet light emitting device comprising:
In the step of forming the p-type contact layer, a first step of forming a first layer made of Al _x Ga _{1 -x} N having an Al composition ratio x and an Al composition ratio y lower than the Al composition ratio x are performed. And a second step of forming a second layer made of Al _y Ga _1-y N is alternately repeated to form the p-type contact layer having a superlattice structure, and an Al composition ratio of the second layer. y is 0.15 or more,
The step of forming the reflective electrode includes
On the outermost surface of the p-type contact layer, the second layer,
A first step of forming Ni as a first metal layer with a thickness of 3 to 20 nm;
A second step of forming Rh as a second metal layer with a thickness of 20 nm or more and 2 μm or less on the first metal layer;
A third step of performing a heat treatment at 300 to 600° C. on the first metal layer and the second metal layer,
A method for manufacturing a deep ultraviolet light emitting device, comprising: In the superlattice structure of the p-type contact layer,
When the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer is w ₀ ,
The Al composition ratio x of the first layer is higher than the Al composition ratio w ₀ ,
The Al composition ratio y of the second layer is lower than the Al composition ratio x,
The Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer are represented by the following formulas [1] and [2]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
The method for manufacturing a deep ultraviolet light emitting device according to claim 4, which satisfies the above condition. Between the well layer closest to the p-type electron block layer in the light-emitting layer and the p-type electron block layer, Al having a higher Al composition ratio than either the barrier layer of the light-emitting layer or the p-type electron block layer is formed. The method for manufacturing a deep ultraviolet light emitting device according to claim 5, further comprising a guide layer having a high composition ratio. The method for manufacturing a deep ultraviolet light emitting device according to claim 6, wherein the guide layer is made of AlN. The method for manufacturing a deep ultraviolet light emitting device according to claim 5, wherein the Al composition ratio w ₀ is 0.25 or more and 0.60 or less. The method for manufacturing a deep ultraviolet light emitting device according to claim 4, wherein a total thickness of the p-type layers of the p-type electron block layer and the p-type contact layer is 65 to 100 nm. After the second step, the method further includes forming a Ni layer as a third metal layer on the second metal layer, and forming an Rh layer as a fourth metal layer on the third metal layer. The method for manufacturing a deep ultraviolet light emitting device according to claim 4. An n-type semiconductor layer, a light-emitting layer, a p-type electron block layer and a p-type contact layer are sequentially formed on the substrate,
The p-type contact layer alternately includes a first layer made of Al _x Ga _1-x N having an Al composition ratio x and a second layer made of Al _y Ga _1-y N having an Al composition ratio y. Has a superlattice structure formed by stacking, and the Al composition ratio y of the second layer is 0.15 or more,
A deep ultraviolet light emitting device comprising a reflective electrode made of Ni and Rh on the outermost surface of the p-type contact layer. In the superlattice structure of the p-type contact layer,
When the Al composition ratio of the layer that emits deep ultraviolet light in the light emitting layer is w ₀ ,
The Al composition ratio x of the first layer is higher than the Al composition ratio w ₀ ,
The Al composition ratio y of the second layer is lower than the Al composition ratio x,
The Al composition ratio w ₀ , the Al composition ratio x, the Al composition ratio y, and the thickness average Al composition ratio z of the p-type contact layer are represented by the following formulas [1] and [2]:
_{0.030 <z-w 0 <0.20} ··· [1]
0.050≦x−y≦0.47... [2]
The deep ultraviolet light emitting device according to claim 11, which satisfies: The deep ultraviolet light emitting device according to claim 11 or 12, 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.

Images