JP2004071655A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device improved in a light take-out efficiency in the light emitting device and long in the life of the same, by forming especially a p-type electrode in a specified constitution. <P>SOLUTION: The light emitting device is provided with at least an n-type nitride semiconductor and a p-type nitride semiconductor while the p-type nitride semiconductor is provided with the p-type electrode at a predetermined area. Especially, the p-type electrode is constituted of at least a first member having a contact resistance lower than that of a second member with respect to the p-type nitride semiconductor, and the second member having a reflectivity higher than that of the first member with respect to the light of the light emitting device, while one member selected from the first and the second members is provided with an opening through which the p-type nitride semiconductor is exposed, and the other member selected from the first and the second members is at least filled into the opening. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light-emitting element including a nitride semiconductor _{(In X Al Y Ga 1-} X-Y N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) a layer structure, in particular remarkably improved luminous efficiency The present invention relates to a nitride semiconductor light emitting device.
[0002]
[Prior art]
Nitride semiconductor light-emitting elements including a nitride semiconductor in a layer structure are widely used in various fields such as high-luminance pure green light-emitting LEDs and blue light-emitting LEDs, such as full-color LED displays, traffic signal lights, and backlights.
[0003]
These LEDs generally have a structure in which various n-type nitride semiconductors or p-type nitride semiconductors according to purposes are stacked on a substrate such as sapphire. Furthermore, a p-electrode is disposed on the p-type nitride semiconductor, and an n-electrode is disposed on the n-type nitride semiconductor.
[0004]
[Problems to be solved by the invention]
However, with the current demand for LEDs capable of reducing power consumption without reducing light emission output due to energy saving or the like, the above configuration is not sufficient, and further improvement is required.
[0005]
That is, in the conventional LED described above, light emitted from the light emitting region is emitted from the upper surface and side surfaces of the LED via various semiconductors or substrates. More specifically, part of the light emitted from the light emitting region is reflected at every interface, that is, the interface between the substrate and the semiconductor, the interface between the semiconductor and the semiconductor, or the interface between the semiconductor and the electrode. And even if such a process is repeated a plurality of times, the light remaining without being absorbed by each member is emitted from the LED.
[0006]
Here, in order to make an electric current flow uniformly, the LED is mainly configured to have a p-electrode on substantially the entire surface of the p-type nitride semiconductor, but part of light is absorbed by the p-electrode itself provided on the entire surface. There was a problem that. As a result, part of the light from the light emitting region is wasted, and light cannot be efficiently extracted outside the LED. In addition to this, there is a problem that it is difficult to extend the life of the LED.
[0007]
In general, Ag is a highly reflective material and can be easily taken out by using it mainly for the p-electrode. However, it is difficult to stably reduce the contact resistance, and the power consumption should be sufficiently reduced. I can't. In addition, Ag is easily converted to positive ions and causes ion migration, and it is difficult to ensure sufficient reliability.
[0008]
The present invention has been made to solve such problems, and in particular, by providing a p-electrode with a specific configuration, the light extraction efficiency of the light-emitting element is further improved, and a light-emitting element with a long lifetime is provided. The purpose is to do.
[0009]
[Means for Solving the Problems]
The light-emitting device of the present invention is a light-emitting device having at least an n-type nitride semiconductor and a p-type nitride semiconductor, and having a p-electrode on a predetermined part of the p-type nitride semiconductor. In particular, the p-electrode has a first member having a contact resistance lower than that of the second member with respect to the p-type nitride semiconductor, and a second member having a reflectance higher than that of the first member with respect to light of the light emitting element. One member selected from the first member and the second member has an opening from which the p-type nitride semiconductor is exposed, and the first member and the first member Another member selected from the two members is filled in at least the opening. Thereby, the light from the light emitting element can be reflected by the first member or the second member, and the light can be efficiently extracted from the side surface or the vertical direction of the light emitting element.
[0010]
In addition, the member having the opening from which the p-type nitride semiconductor is exposed has a mesh shape having a plurality of openings, and at least another member is preferably filled in the mesh-shaped opening. Thereby, since the 2nd member is filled into a plurality of openings, the 2nd member can be arranged more evenly.
[0011]
The first member preferably includes at least one element selected from Ni, Au, Rh, Ir, and Pd. Thereby, ohmic contact can be obtained easily.
[0012]
Moreover, it is preferable that the second member is mainly Ag. Thereby, efficient light reflection can be obtained, and as a result, the light emission efficiency of the light emitting element can be improved. Further, since the p-electrode has the first member having a contact resistance lower than that of Ag, when the light emitting element is actually driven, current is mainly concentrated on the first member. Thereby, the movement of Ag, that is, ion migration can be suppressed and the reliability can be improved.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In this embodiment, an example in which an LED (Light Emitting Diode) is used as a light-emitting element will be described. As each semiconductor layer constituting the LED according to the present invention, various nitride semiconductors can be used. For example, a metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE) or the like _{In X Al Y Ga 1-X} -Y N ( where, 0 ≦ X, 0 ≦ Y , X + Y ≦ 1) A semiconductor can be suitably used. As the layer structure, a known layer structure can be used. For example, a homostructure, a single heterostructure, or a double heterostructure having a MIS junction, a PIN junction, or a PN junction can be used. In addition, a specific layer may have a superlattice structure, or a single quantum well structure or a multiple quantum well structure in which an active layer is formed in a thin film that produces a quantum effect. Furthermore, various known phosphors can be disposed at predetermined positions of the light emitting element, and light from the light emitting element can be converted into desired light.
[0014]
Further, the LED is generally formed by growing each semiconductor layer on a specific substrate. At that time, when an insulating substrate is used as the substrate and the insulating substrate is not finally removed, usually, Both the p electrode and the n electrode are formed on the same surface side of the LED. In this case, it is possible to take out the emitted light from the semiconductor side with the face-up mounting, i.e. the semiconductor side placed on the viewing side, or with the face-down mounting, i.e. the board side placed on the viewing side, It is also possible to take it out from. Of course, it is also possible to adopt a configuration in which the p-electrode and the n-electrode are arranged to face each other with the semiconductor layer structure by not using the insulating substrate from the beginning or finally removing the insulating substrate.
[0015]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies an LED for embodying the technical idea of the present invention, and does not specify the LED of the present invention as follows. Further, the size and positional relationship of the members shown in each drawing may be exaggerated for clarity of explanation.
(Embodiment 1)
The LED according to the first embodiment will be described with reference to FIGS. Here, as shown in the figure, an LED in which a p-electrode and an n-electrode are arranged on the same surface side will be described. FIG. 1 is a schematic view of the LED of the present embodiment as viewed from the electrode forming surface side. FIG. 2 is a schematic cross-sectional view showing the layer structure of the LED of the present embodiment, and represents a cross section taken along the line AA of FIG.
[0016]
As shown in FIG. 2, the light emitting device of this embodiment includes, for example, a GaN buffer layer 12, a non-doped GaN layer 13, a Si-doped GaN layer 14 serving as an n-type contact layer, an n-type cladding layer, and a sapphire substrate 11. The Si-doped GaN layer 15 to be formed, the InGaN layer 16 to be the active layer, the Mg-doped AlGaN layer 17 to be the p-type cladding layer, and the Mg-doped GaN layer 18 to be the p-type contact layer have a layered structure. Further, the Mg-doped GaN layer 18, the Mg-doped AlGaN layer 17, the InGaN layer 16, the Si-doped GaN layer 15, and the Si-doped GaN layer 14 are partially removed by etching or the like, and an n electrode is formed on the exposed surface of the Si-doped GaN layer 14. 19 is formed, and a p-electrode 20 is provided on substantially the entire upper surface of the Mg-doped GaN layer 18. In the present embodiment, the n-type nitride semiconductor described in “Claims” corresponds to the Si-doped GaN layer 14 serving as the n-type contact layer, and the p-type nitride semiconductor serves as the p-type contact layer. This corresponds to the Mg-doped GaN layer 18.
[0017]
In the present embodiment, a pad portion 21 for connecting a wire is partially formed at a position away from the n electrode 19 on the p electrode 20, and openings on the n electrode 19 and the pad portion 21 are formed. Except for this, an insulating film (not shown) is provided so as to cover each electrode and each semiconductor. The n-electrode 19 includes a pad portion for connecting a wire to the n-electrode itself.
[0018]
Here, the p-electrode 20 is composed of Rh as the first member 20a and Ag as the second member 20b. In the present embodiment, as shown in FIG. 1, the first member 20a has a mesh shape, and the second member 20b is formed in the mesh-shaped opening and on the upper surface of the first member 20a. The mesh-shaped first member 20a is formed over substantially the entire upper surface of the Mg-doped GaN layer 18 that is a p-type contact layer. Inevitably, the second member 20b filled in the opening of the first member 20a is also formed over substantially the entire upper surface of the Mg-doped GaN layer 18 that is the p-type contact layer.
[0019]
In this way, when the second member 20b is a member that easily undergoes ion migration by filling the opening of the first member 20a with the second member 20b, the ion migration of the second member 20b is performed. Can be reduced. Ion migration is a phenomenon that occurs from the + side to the-side (from the p side to the n side) of the electrode. For example, when only Ag is used as the p electrode, Ag is positively ionized when the LED is actually driven, Ag itself moves in the n-electrode direction (this phenomenon is called “ion migration”). Specifically, when viewed from the upper surface of the LED (on the electrode forming surface side), Ag, which is a p-electrode, moves on the p-type nitride semiconductor in the n-electrode direction, and in the worst case, an n-electrode is formed. There is a possibility of falling on the type nitride semiconductor or adhering to the LED side surface over the p-type nitride semiconductor and the n-type nitride semiconductor to induce leakage.
[0020]
However, as in the present invention, by making Rh, which is the first member 20a having a contact resistance lower than that of the second member 20b and easily flowing current, into a mesh shape, the current is mainly Rh and p-type. Since the contact surface of the nitride semiconductor is used as a path, Ag ion migration is effectively reduced.
[0021]
Furthermore, since Ag is a member having a very high reflectance in most of the wavelengths that can be emitted by the nitride semiconductor, the opening of the first member 20a is filled with Ag as the second member 20b. High reflection efficiency can be obtained over the entire area of the p-electrode 16. With this configuration, the light extraction efficiency of the light emitting element as a whole is improved.
[0022]
Furthermore, when a member having high reflectance such as Ag is used as the second member and ohmic annealing (heat treatment for ohmic contact) is performed on the first member having low contact resistance, as in the present embodiment, It is preferable to form the second member in the opening of the first member and on the upper surface. That is, generally, a member having a high reflectance such as Ag tends to have a reduced reflectance when heat-treated. However, after the first member having a low contact resistance is first formed on the p-type semiconductor and subjected to ohmic annealing, the second member is further disposed in the opening and on the upper surface of the first member, whereby the second member The p-electrode can be formed without affecting the heat.
[0023]
Further, as in the present embodiment, the second member 20b is disposed not only in the opening of the first member 20a but also on the upper surface of the first member 20a, so that the Mg-doped that becomes a p-type contact layer The current can be uniformly diffused by the entire GaN layer 18. That is, since the second member 20b has a contact resistance higher than that of the first member 20a and current does not flow easily, the current flowing into the p-electrode diffuses over the entire contact surface between the p-type contact layer and the p-electrode. As a result, the current flows uniformly through the entire LED, which is considered to improve the light emission efficiency.
[0024]
In the present embodiment, the mesh-shaped openings are arranged uniformly over the entire p-electrode, but the present invention is not limited to this. For example, the contact area between the member with low contact resistance and the p-type contact layer is configured to gradually increase as the distance from the n-electrode is viewed from the electrode forming surface side so that current flows uniformly through the entire LED. May be. That is, the shape, size, arrangement position, and the like of the opening can be arbitrarily set on the designer side.
[0025]
On the other hand, the second member 20b can be disposed only in the opening of the first member 20a without being disposed on the upper surface of the first member 20a. That is, since the first member 20a can surround the second member 20b in each mesh-shaped opening existing over the entire p-electrode, ion migration of the second member 20b is more effective. Can be reduced. In this case, it is considered that the first member 20a becomes a wall that prevents ion migration of the second member 20b. Further, when viewed from the p-electrode forming surface side, Rh located at the periphery of the p-electrode is formed higher than the inside, and the inside is filled with Ag, thereby effectively preventing ion migration of Ag. You can also.
(Embodiment 2)
The LED according to the second embodiment will be described with reference to FIGS. Here, an LED in which a p-electrode and an n-electrode are arranged to face each other as shown in the drawing will be described. FIG. 3 is a schematic view of the LED of the present embodiment as viewed from the p-electrode formation surface side. FIG. 4 is a schematic cross-sectional view showing the layer structure of the LED of the present embodiment, and shows a cross section taken along the line AA of FIG.
[0026]
As shown in FIG. 4, the light emitting device of the present embodiment includes, for example, a Si-doped GaN layer 34 serving as an n-type contact layer, a Si-doped GaN layer 35 serving as an n-type cladding layer, InGaN 36 serving as an active layer, and p-type. The Mg-doped AlGaN layer 37 serving as a cladding layer and the Mg-doped GaN layer 38 serving as a p-type contact layer have a layered structure. Further, an n-electrode 39 is formed on the Si-doped GaN layer 34, and a p-electrode 40 is provided on substantially the entire surface of the Mg-doped GaN layer 38. In the present embodiment, the n-type nitride semiconductor described in “Claims” corresponds to the Si-doped GaN layer 34 serving as the n-type contact layer, and the p-type nitride semiconductor serves as the p-type contact layer. This corresponds to the Mg-doped GaN layer 38.
[0027]
In the present embodiment, as viewed from the p-electrode forming surface side, a pad portion 41 for connecting a wire is partially formed at a substantially center on the p-electrode 40, and is formed on the n-electrode 39 and the pad portion 41. An insulating film (not shown) is provided so as to cover each electrode and each semiconductor except for the opening. In the present embodiment, the n-electrode 39 includes a pad portion (not shown) for connecting wires.
[0028]
Further, the p-electrode 40 is composed of Rh, which is the first member 40a, and Ag, which is the second member 40b, as in the first embodiment, and the configuration is as shown in FIG. The member 40a has a mesh shape, and the second member 40b is formed in the mesh-shaped opening and on the upper surface of the first member 40a. The mesh-shaped first member 40a is formed over substantially the entire upper surface of the Mg-doped GaN layer 38 that is a p-type contact layer. Inevitably, the second member 40b filled in the opening of the first member 40a is also formed over substantially the entire upper surface of the Mg-doped GaN layer 38 which is a p-type contact layer.
[0029]
By configuring in this way, the same effect as in the first embodiment can be obtained. In particular, when the electrodes are arranged to face each other as in the present embodiment, it is preferable that the p electrode side is mounted on the mounting substrate and the n electrode side is the viewing side. Thereby, compared with the case where the n electrode side is mounted on the mounting substrate and the p electrode side is the viewing side, the light extraction efficiency can be further improved.
[0030]
Further, when the electrodes are arranged to face each other as in the present embodiment, the contact area between the member having low contact resistance and the p-type nitride semiconductor can be made non-uniform for the entire p electrode. For example, it is preferable to reduce the contact area with the p-type nitride semiconductor in the vicinity of the portion located immediately above the n electrode (corresponding to the vicinity of the portion immediately below the p electrode in FIG. 3) compared to other portions. By configuring in this way, the current flowing through the light emitting element can be more uniformly diffused without concentrating the current only in the vicinity of the portion where the p electrode and the n electrode are connected by a straight line.
[0031]
Here, the pad portion is partially provided on the p electrode, but the pad portion on the p electrode is not necessarily required. That is, for example, when various semiconductors are grown on a sapphire substrate and then the sapphire substrate is removed, the sapphire substrate is removed after bonding the metal substrate to the p-electrode using solder or the like as a conductive connecting member. . This is to secure a certain thickness by sticking the metal substrate to the p-electrode side and to facilitate removal of the sapphire substrate. For this reason, in the light emitting element having the bonded metal substrate, the metal substrate itself corresponds to the pad portion. In addition, although the member which comprises a metal substrate is not specifically limited, For example, the alloy of Cu and W, the alloy of Al and Cu, etc. can be used.
(Embodiment 3)
Although not shown in the drawing, it is manufactured in the same manner as in Embodiment 1 except that the positional relationship between the first member and the second member is reversed. In the present embodiment, it is more preferable that Ag as the second member is completely covered with Rh as the first member. Thereby, the migration of Ag as the second member can be further reduced.
(Embodiment 4)
Although not shown in the drawing, it is manufactured in the same manner as in Embodiment 2 except that the positional relationship between the first member and the second member is reversed. Even in this case, similarly to the second embodiment, the light extraction efficiency can be effectively improved. In the present embodiment, it is more preferable that Ag as the second member is completely covered with Rh as the first member. Thereby, the migration of Ag as the second member can be further reduced.
[0032]
In Embodiment 1-4, although the shape of the 1st member or the 2nd member was demonstrated as a mesh shape, it cannot be overemphasized that this invention should just have an opening part and is not limited to a mesh shape. As other shapes, for example, one member can be simply arranged in a dot shape, and the other member can be filled at least between the dots. Further, the p-electrode only needs to include at least a first member and a second member. That is, as long as the effects of the present invention are not hindered, the third member, the fourth member, and the like can be further provided in the configuration of the p-electrode.
[0033]
【The invention's effect】
As described above, according to the light emitting device of the present invention, light absorption at the p-electrode can be minimized. Thereby, the light extraction efficiency can be significantly improved. Further, even when a member such as Ag that easily causes migration is used as the p-electrode, the migration can be effectively reduced.
[Brief description of the drawings]
FIG. 1 is a plan view of an LED according to a first embodiment when viewed from a p-electrode formation surface side.
FIG. 2 is a cross-sectional view taken along a line AA in FIG.
FIG. 3 is a plan view of the LED according to the second embodiment as viewed from the p-electrode formation surface side.
4 is a cross-sectional view taken along a line AA in FIG.
[Explanation of symbols]
11 ... sapphire substrate 12 ... GaN buffer layer 13 ... non-doped GaN layer 14, 34 ... Si-doped GaN layer 15, 35 ... Si-doped GaN layer 16, 36 ... InGaN layer 17, 37 ... Mg-doped AlGaN layers 18, 38 ... Mg-doped GaN layers 19, 39 ... n electrodes 20, 40 ... p electrodes 20a, 40a ... first members 20b, 40b ... Second member 21, 41 ... pad

Claims (4)

In a light emitting device having at least an n-type nitride semiconductor and a p-type nitride semiconductor, and having a p-electrode on a predetermined part of the p-type nitride semiconductor,
The p-electrode includes a first member having a lower contact resistance than the second member with respect to the p-type nitride semiconductor, and a second member having a higher reflectance than the first member with respect to the light of the light emitting element. Consisting of at least members of
One member selected from the first member and the second member has an opening from which the p-type nitride semiconductor is exposed,
The other member selected from the first member and the second member is filled in at least the opening. The member having an opening from which the p-type nitride semiconductor is exposed has a mesh shape having a plurality of openings, and at least another member is filled in the mesh-shaped opening. 2. The light emitting device according to 1. The light emitting device according to claim 1, wherein the first member includes at least one element selected from Ni, Au, Rh, Ir, and Pd. The light emitting element according to claim 1, wherein the second member is mainly Ag.

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