JP7015339B2 - Ultraviolet light emitting element - Google Patents

Description

The present invention relates to an ultraviolet light emitting device.

In recent years, much interest has been focused on ultraviolet light emitting devices made of III-V nitride semiconductors. So far, various methods for relaxing the current concentration between the n-type nitride semiconductor layer and the n-type electrode in a light emitting device made of a III-V nitride semiconductor have been studied (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2008-07825

FIG. 3A is a schematic cross-sectional view showing the configuration of the ultraviolet light emitting element according to the first conventional example. FIG. 3B is a diagram visually showing the current concentration in the ultraviolet light emitting device shown in FIG. 3A. FIG. 4A is a schematic cross-sectional view showing the configuration of the ultraviolet light emitting element according to the second conventional example. FIG. 4B is a diagram visually showing the current concentration in the ultraviolet light emitting device shown in FIG. 4A. In FIGS. 3A and 3B and FIGS. 4A and 4B, 100 is a substrate, 200 is a first conductive nitride semiconductor layer, 210 is a first region, and 220 is a second region. 300 is a light emitting layer, 400 is a second conductive nitride semiconductor layer, 500 is an n-type electrode, 510 is a first electrode element, 520 is an ohmic electrode, and 600 is a p-type electrode. In addition, the arrow indicates the path of the electric current.

In the ultraviolet light emitting device having a mesa structure as shown in FIG. 3A, the sheet resistance of the n-type nitride semiconductor layer 200 is large, so that the end portion of the n-type electrode 500 (dotted circle in FIG. 3A). (Part), the current concentration is remarkable, and deterioration occurs due to the influence of uneven emission distribution and heat (semi-transparent gradation region between the n-type nitride semiconductor layer 200 and the n-type electrode 500 in FIG. 3B). However, the state of the current concentration is visually expressed).
In Patent Document 1, as shown in FIG. 4A, a contact electrode 510 having a high contact resistance with the n-type nitride semiconductor layer 200 is formed so as to surround the ohmic electrode 520, and the ohmic electrode and the n-type nitride are formed. A method of avoiding current concentration has been proposed by balancing the contact resistance with the semiconductor layer 200 and the contact resistance between the contact electrode 510 and the n-type nitride semiconductor layer 200.

However, in this structure, the current concentration points are only dispersed in two places (dotted circles in FIG. 4A), one at the end of the contact electrode 510 and the other at the end of the ohmic electrode 520. Where current concentration occurs (the translucent gradation region between the n-type nitride semiconductor layer 200 and the n-type electrode 500 in FIG. 4B visually expresses the state of current concentration at these two locations. ing).
Therefore, in the prior art, current concentration between the n-type nitride semiconductor layer 200 and the n-type electrode 500 in the ultraviolet light emitting device cannot be avoided.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultraviolet light emitting device in which current concentration is relaxed.

The present inventors have completed the present invention as a result of diligent studies to solve the above problems.
In the first aspect of the present invention, the substrate, the first region of the first conductive nitride semiconductor layer, the second region of the first conductive nitride semiconductor layer, the light emitting layer, and the second conductive nitride are used. The material semiconductor layer is provided in this order in one direction, and the second region of the first conductive type nitride semiconductor layer, the light emitting layer, and the second conductive type nitride semiconductor layer have a mesa structure. The first electrode is provided on a part of the surface of the first region of the first conductive nitride semiconductor layer, and the second electrode is provided on a part of the surface of the second conductive nitride semiconductor layer. The first electrode provides an ultraviolet light emitting element having a first electrode element including a film thickness changing portion in which the film thickness becomes continuously or stepwise, or continuously and stepwise as the film approaches the mesa structure.
The outline of the above invention does not list all the features of the present invention. A subcombination of these feature groups can also be an invention.

According to the present invention, it becomes possible to provide an ultraviolet light emitting device in which current concentration is relaxed.

1 (a) and 1 (b) are schematic cross-sectional views showing a configuration example of an ultraviolet light emitting device according to the first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a configuration example of an ultraviolet light emitting device according to a second embodiment of the present invention. 3A and 3B are schematic cross-sectional views showing the configuration of the ultraviolet light emitting element according to the first conventional example. 4 (a) and 4 (b) are schematic cross-sectional views showing the configuration of the ultraviolet light emitting element according to the second conventional example.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention to which the claims are made. Also, not all combinations of features described in the embodiments are essential to the means of solving the invention.
Further, in the description of the following drawings, the same or similar parts are designated by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the plane dimensions, the ratio of the thickness of each device and each member, etc. are different from the actual ones. Therefore, the specific thickness and dimensions should be determined in consideration of the following explanation. In addition, it goes without saying that parts having different dimensional relationships and ratios are included between the drawings.

(Ultraviolet light emitting element)
The ultraviolet light emitting device according to the present embodiment includes a substrate, a first region of the first conductive nitride semiconductor layer, a second region of the first conductive nitride semiconductor layer, a light emitting layer, and a second conductive type nitride. The semiconductor layer is provided in this order in one direction (for example, in the thickness direction of the ultraviolet light emitting device). The second region of the first conductive nitride semiconductor layer, the light emitting layer, and the second conductive nitride semiconductor layer have a mesa structure. A first electrode is provided on a part of the surface of the first region of the first conductive semiconductor layer. The first electrode is a first electrode element including a film thickness change portion in which the film thickness becomes continuously or stepwise, or continuously and stepwise (hereinafter, continuous and / or stepwise) as it approaches the mesa structure. Have.
The ultraviolet light emitting element according to the present embodiment has a first electrode element including a film thickness changing portion in which the film thickness continuously and / or gradually decreases as the first electrode approaches the mesa structure. It suppresses current concentration in the current path between the electrode and the second electrode, and has the effects of uniform emission distribution and extension of the life of the ultraviolet light emitting element.
Next, each component of the ultraviolet light emitting element according to this embodiment will be described.

(substrate)
The substrate in the ultraviolet light emitting device according to the present embodiment is not particularly limited as long as it can have a first conductive nitride semiconductor on the substrate.
The specific material of the substrate is not particularly limited, and examples thereof include an aluminum nitride (AlN) single crystal substrate and a sapphire substrate. In the ultraviolet light emitting device, AlN can be mentioned as a preferable material from the viewpoint of the lattice constant with the light emitting layer.

(First Conductive Nitride Semiconductor Layer)
The first conductive nitride semiconductor layer in the ultraviolet light emitting device according to the present embodiment includes a first region and a second region. The first region is a region that becomes a part of the mesa structure, and the second region is a region other than that.
Examples of the material of the first conductive type nitride semiconductor layer include AlGaN and AlInN, but the present invention is not limited to this. In the ultraviolet light emitting device, AlGaN can be mentioned as a preferable material from the viewpoint of crystallinity.
In the present embodiment, the "first conductive type" and the "second conductive type" mean the characteristics of an n-type semiconductor layer in which free electrons having a negative charge on one side move as carriers to generate an electric current, and the other side. Means the characteristics of a p-type semiconductor layer in which positively charged holes move to generate an electric current.
The first conductive type nitride semiconductor layer is preferably n-type from the viewpoint of crystallinity.
The film thickness of the first region is not particularly limited, but is preferably 0.1 μm or more and 10 μm or less, more preferably 0.3 μm or more and 5 μm or less, and even more preferably 0.5 μm or more and 3 μm or less from the viewpoint of sheet resistance.
The film thickness of the second region is not particularly limited, but is preferably 0.1 μm or more and 5 μm or less, more preferably 0.2 μm or more and 3 μm, and even more preferably 0.3 μm or more and 1 μm or less from the viewpoint of process easiness.

(Light emitting layer)
The light emitting layer in the ultraviolet light emitting device according to the present embodiment is a layer that emits ultraviolet rays. Examples of the material of the light emitting layer include, but are not limited to, AlGaN and AlInN. The structure of the light emitting layer is not particularly limited, and examples thereof include a multiple quantum well structure. For example, a multiple quantum well structure in which a large number of AlGaN layers having different composition ratios (different band gaps) are laminated can be adopted.

(Second Conductive Nitride Semiconductor Layer)
The second conductive nitride semiconductor layer in the ultraviolet light emitting device according to the present embodiment is formed on the light emitting layer.
Examples of the material of the second conductive type nitride semiconductor layer include GaN and AlGaN, but the present invention is not limited to this. The second conductive type nitride semiconductor layer is preferably p-type from the viewpoint of crystallinity. At this time, GaN can be mentioned as a preferable material from the viewpoint of forming an ohmic electrode with the electrode formed on the second conductive type nitride semiconductor.

(Mesa structure)
The ultraviolet light emitting device according to the present embodiment has a mesa structure including a second region of the first conductive type nitride semiconductor layer, a light emitting layer, and a second conductive type nitride semiconductor layer. The mesa structure is a top portion (in this embodiment, a second in the nitride semiconductor laminated portion) higher than a specific plane (in the present embodiment, the plane of the first region of the first conductive type nitride semiconductor layer). When the conductive nitride semiconductor layer is the top layer, it means a shape having an upper surface of the second conductive nitride semiconductor layer) and having a slope (regardless of the angle of the slope) between the top and a specific plane. ..

(1st electrode)
The ultraviolet light emitting device according to the present embodiment has a first electrode on a part of the surface of the first region of the first conductive semiconductor layer. The first electrode has a first electrode element including a film thickness change portion in which the film thickness decreases continuously and / or gradually as the mesa structure approaches a certain direction.
"The film thickness is continuously reduced" means that the thickness in the vertical direction from the bottom side of the first electrode is continuously reduced when viewed in cross section, and the shape is a slope structure. do. "The film thickness is gradually reduced" means that the thickness from the bottom of the first electrode is gradually reduced, and the shape is a staircase structure.
The inclination angle of the upper surface of the film thickness changing portion with respect to the plane of the second region of the first conductive type nitride semiconductor layer is not particularly limited, but is preferably 1 degree or more and 45 degrees or less from the viewpoint of current concentration, and is preferably 2 degrees or more. It is more preferably 30 degrees or less, and further preferably 3 degrees or more and 10 degrees or less. Further, the method of manufacturing the film thickness changing portion is not particularly limited, and examples thereof include a method of controlling the incident angle at the time of metal vapor deposition.

The first electrode element is not particularly limited as long as it includes a film thickness changing portion. Examples of the component (that is, the component) constituting the first electrode element include aluminum and nickel. From the viewpoint of crystallinity, the first conductive type nitride semiconductor layer is preferably n-type, and from the viewpoint of forming an ohmic electrode with the n-type nitride semiconductor layer, aluminum may be a preferable component.
The film thickness other than the film thickness change portion of the first electrode element is not particularly limited, but is preferably 0.05 μm or more and 3 μm or less, and more preferably 0.1 μm or more and 1 μm or less from the viewpoint of contact resistance. , 0.2 μm or more and 0.5 μm or less is more preferable.

The ultraviolet light emitting device according to the present embodiment has a first interface containing an oxide of a constituent component of the first electrode element between a part of the film thickness changing portion and the first region of the first conductive type nitride semiconductor layer. It is preferable to further provide a portion. By further providing the first interface portion, the contact resistance between the first electrode and the first conductive nitride semiconductor layer can be increased, and the current concentration can be relaxed. Although not particularly limited, the film thickness of the first interface portion is preferably 1 nm or more and 100 nm or less, more preferably 10 nm or more and 80 nm or less, and further preferably 20 nm or more and 60 nm or less. Examples of the constituent component of the first interface portion include aluminum oxide and the like.

(2nd electrode element, 3rd electrode element)
The first electrode may further include a second electrode element and a third electrode element on the first electrode element. When the second electrode element and the third electrode element are further provided, it is preferable to have a second interface portion at the interface between a part of the film thickness changing portion of the first electrode element and the second electrode element. The constituent component of the second interface portion is not particularly limited, but titanium is preferable from the viewpoint of adhesion. Although not particularly limited, the film thickness of the second interface portion is preferably 1 nm or more and 100 nm or less, more preferably 10 nm or more and 80 nm or less, and further preferably 20 nm or more and 60 nm or less. Further, from the viewpoint of adhesion, it is also preferable that the second interface portion contains at least one of the constituent components of the third electrode element.
The constituent components of the second electrode element are not particularly limited, and examples thereof include aluminum and the like. Nickel is preferred from the standpoint of adhesion and manufacturing cost.
The constituent components of the third electrode element are not particularly limited, and examples thereof include aluminum and the like. An alloy of gold and titanium is preferable from the viewpoint of adhesion and antioxidant.

(Insulation layer)
From the viewpoint of reliability, at least a part of the surface of the ultraviolet light emitting device according to the present embodiment may be covered with an insulating layer. The material of the insulating layer is not particularly limited, and examples thereof include silicon oxide and silicon nitride.

(First Embodiment)
FIG. 1A is a schematic cross-sectional view showing a configuration example of an ultraviolet light emitting device according to the first embodiment of the present invention. FIG. 1B is a diagram visually showing the current concentration in the ultraviolet light emitting device shown in FIG. 1A. In FIG. 1A, 10 is a substrate, 20 is a first conductive nitride semiconductor layer, 21 is a first region, 22 is a second region, 30 is a light emitting layer, and 40 is a second conductive nitride semiconductor layer. 50 is the first electrode, 51 is the first electrode element, 51a is the film thickness changing portion, 52b is other than the film thickness changing portion, 52 is the second electrode element, 53 is the third electrode element, 60 is the second electrode, and 71 is. The first insulating layer and 72 are the second insulating layer. In addition, the arrow indicates the path of the current, and the thickness indicates the density of the current (hereinafter, the description of the same reference numeral is omitted). Further, in FIG. 1 (b), the translucent gradation between the first conductive type nitride semiconductor layer 20 and the first electrode 50 visually indicates the current density.
Since the ultraviolet light emitting element according to the first embodiment has the film thickness changing portion 51a, the first electrode 50 and the first electrode 50 are compared with the prior art shown in FIGS. 3A and 4A. The current concentration at the interface of the first conductive type nitride semiconductor layer 20 is relaxed.

In the prior art, as shown in FIG. 3B, when the contact resistance between the n-type electrode 500 and the n-type nitride semiconductor layer 200 is uniform, the n-type electrode 500 and the n-type nitride semiconductor layer 200 are used. Current concentration occurred in the region near the mesa structure in the interface of. Or, as shown in FIG. 4 (b), when the contact resistance in a specific region is specifically uniform, current concentration occurs in that region.
However, the ultraviolet light emitting element according to the first embodiment has a film thickness changing portion 51a whose film thickness gradually and / or gradually decreases as the first electrode element 51 of the first electrode 50 approaches the mesa structure. .. As the structure approaches the mesa structure, the electrical resistance in the film thickness changing portion 51a increases. As a result, a current flows through the first conductive type nitride semiconductor layer 20 in a well-balanced manner as compared with the prior art, and the current concentration is alleviated.

(Second embodiment)
FIG. 2A is a schematic cross-sectional view showing a configuration example of an ultraviolet light emitting device according to a second embodiment of the present embodiment. FIG. 2B is a diagram visually showing the current concentration in the ultraviolet light emitting device shown in FIG. 2A. The ultraviolet light emitting device according to the second embodiment is different from the first embodiment in that it has a first interface portion 54 and a second interface portion 55.
The ultraviolet light emitting element according to the second embodiment has the first interface portion 54 and the second interface portion 55, so that the electric resistance and the first electrode element 51 in the film thickness changing portion 51a as the film approaches the mesa structure. And the contact resistance between the first conductive type nitride semiconductor layer 20 and the first conductive type nitride semiconductor layer 20 increases. As a result, in the ultraviolet light emitting device according to the second embodiment, a current flows through the first conductive type nitride semiconductor layer 20 in a more balanced manner than in the first embodiment, and the current concentration is relaxed.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that the form with such changes or improvements may be included in the technical scope of the present invention.

10 Substrate 20 1st conductive type nitride semiconductor layer 21 1st region 22 2nd region 30 light emitting layer 40 2nd conductive type nitride semiconductor layer 50 1st electrode 51 1st electrode element 51a film thickness change part 52b film thickness change part Other than 52 Second electrode element 53 Third electrode element 54 First interface portion 55 Second interface portion 60 Second electrode 71 First insulating layer 72 Second insulating layer 100 Substrate 200 n-type nitride semiconductor layer 210 First region 220 Second region 300 Light emitting layer 400 p-type nitride semiconductor layer 500 n-type electrode 510 Contact electrode 520 Ohmic electrode 600 p-type electrode

Claims (13)

The substrate, the first region of the first conductive nitride semiconductor layer, the second region of the first conductive nitride semiconductor layer, the light emitting layer, and the second conductive nitride semiconductor layer are oriented in one direction. Prepare in the order of the conductor,
The second region of the first conductive nitride semiconductor layer, the light emitting layer, and the second conductive nitride semiconductor layer have a mesa structure.
A first electrode is provided on a part of the surface of the first region of the first conductive nitride semiconductor layer.
A second electrode is provided on a part of the surface of the second conductive nitride semiconductor layer.
The first electrode has a first electrode element including a film thickness change portion in which the film thickness becomes continuously or stepwise, or continuously and stepwise as the film thickness approaches the mesa structure.
A first interface portion containing an oxide of a constituent component of the first electrode element is further provided between a part of the film thickness changing portion and the first region of the first conductive type nitride semiconductor layer. , Ultraviolet light emitting element. The first electrode further has a second electrode element and a third electrode element on the first electrode element in this order .
The ultraviolet light emitting device according to claim 1 , further comprising a second interface portion made of titanium at an interface between a part of the film thickness changing portion of the first electrode element and the second electrode element. The ultraviolet light emitting device according to claim 1 or 2 , wherein the inclination angle of the upper surface of the film thickness changing portion with respect to the plane of the second region of the first conductive type nitride semiconductor layer is 1 degree or more and 45 degrees or less. The ultraviolet light emitting device according to claim 1 , wherein the film thickness of the first interface portion is 1 nm or more and 100 nm or less. The ultraviolet light emitting device according to claim 2 , wherein the film thickness of the second interface portion is 1 nm or more and 100 nm or less. The ultraviolet light emitting device according to any one of claims 1 to 5 , wherein the component of the first electrode element is aluminum. The ultraviolet light emitting device according to claim 1 , wherein the constituent component of the first interface portion is aluminum oxide. The ultraviolet light emitting element according to claim 2 , wherein the constituent component of the third electrode element is an alloy of gold and titanium. The ultraviolet light emitting device according to claim 2 or 8 , wherein the component of the second electrode element is nickel. The ultraviolet light emitting device according to any one of claims 2, 8 and 9 , wherein the second interface portion contains at least one of the constituent components of the third electrode element. The ultraviolet light emitting device according to any one of claims 1 to 10 , wherein the substrate is aluminum nitride. The ultraviolet light emitting device according to any one of claims 1 to 11 , wherein the first conductive nitride semiconductor layer is AlGaN. The ultraviolet light emitting device according to any one of claims 1 to 12 , wherein the second conductive nitride semiconductor layer is GaN.

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