JP2007200998A - Surface-emitting light emitting element, and light emitting module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology to more uniformly inject driving current into an active layer having a wide area in a surface-emitting nitride semiconductor light emitting device employing a nitride semiconductor substrate or a ZnO substrate. <P>SOLUTION: The surface-emitting light emitting device is provided with an n-type substrate (11) made of nitride gallium or zinc oxide, a cathode electrode (18) which partly covers the rear face of the n-type substrate (11) and is bonded to the rear face thereof in ohmic manner, an active layer (14) which is made of nitride semiconductor and is formed so as to cover the main face of the n-type substrate (11) and to generate a light with longer wavelength than a wavelength equivalent to a band gap of the n-type substrate (11), p-type nitride semiconductor layers (15 and 16) covering the active layer (14), and an anode electrode (17) which is formed in a manner as to cover the entire faces of the p-type nitride semiconductor layers (15 and 16) on the opposite side of the n-type substrate (11). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface-emitting light-emitting device, and more particularly to a surface-emitting light-emitting device in which an active layer (light-emitting layer) is formed of a nitride semiconductor material.

  One of the most important achievements in recent years in the development of semiconductor light-emitting devices such as light-emitting diodes and laser diodes is the establishment of technology that emits short-wavelength light, especially blue light, by using nitride semiconductors. is there. Nitride semiconductors such as gallium nitride (GaN) and indium gallium nitride (InGaN) have a wide band gap and a direct transition type, so they are suitable for emitting short-wavelength light, especially blue light. ing. On the other hand, the difficulty of the formation process of the nitride semiconductor is being solved by the progress of technology. At present, light-emitting diodes and laser diodes employing nitride semiconductors as active layers have been put into practical use.

  One topic of recent nitride semiconductor light emitting devices is the adoption of nitride semiconductor substrates and ZnO substrates. Although it is not appropriate from the viewpoint of lattice constant, a nitride semiconductor light emitting element generally employs a sapphire substrate. This is because the production of a nitride semiconductor substrate was once difficult, and sapphire was suitable as a material that can withstand the high-temperature process of the nitride semiconductor light emitting device. However, recent advances in technology have made it possible to produce a nitride semiconductor substrate and a ZnO substrate. For this reason, light emission having an active layer formed of a nitride semiconductor layer on a nitride semiconductor substrate or a ZnO substrate. Studies on the technology for forming elements have begun. The use of a nitride semiconductor substrate or a ZnO substrate having a small lattice constant mismatch is effective in reducing lattice defects.

  For example, Japanese Patent Application Laid-Open No. 11-191537 discloses a light emitting device in which a nitride semiconductor laminate is formed on a GaN substrate. The disclosed light emitting device includes a GaN substrate, and an n-side cladding layer, an active layer, a p-side cladding layer, and a p-side contact layer sequentially formed thereon. An n-electrode is bonded to the back surface of the GaN substrate. The p-side contact layer is almost entirely covered with a p-electrode formed of Ni / Al, and a p-pad electrode that partially covers the p-electrode is formed thereon. In addition, Japanese Patent Application Laid-Open No. 2001-77423 discloses a light emitting device in which a nitride semiconductor laminate is formed on an AlGaN substrate.

  Another topic of recent nitride semiconductor light emitting devices is the adoption of a surface emitting structure. For example, a light emitting diode having a surface-emitting structure is suitable as a display light source and an illumination light source. On the other hand, a surface emitting laser diode is effective for integrating light sources with high density by forming a laser diode array.

  In the surface light emitting element, it is important that the driving current is uniformly injected into the active layer having a large area. However, in a surface-emitting nitride semiconductor light emitting device that employs a nitride semiconductor substrate or a ZnO substrate, the high resistivity of the p-type nitride semiconductor is a problem in injecting a drive current uniformly. Specifically, since the resistivity of the p-type nitride semiconductor is high, an n-type nitride semiconductor substrate is employed in the nitride semiconductor light emitting device. In addition, with a ZnO substrate, a p-type substrate cannot be obtained in the first place. For this reason, in a light emitting device employing a nitride semiconductor substrate or a ZnO substrate, a p-type nitride semiconductor layer (for example, a cladding layer or a contact layer) is provided above the n-type substrate, and the p-type nitride semiconductor is provided. An anode electrode is formed on the layer. In the surface-emitting light emitting device, the anode electrode needs to be formed so as to partially cover the upper surface of the p-type nitride semiconductor layer in order to increase the light emission efficiency. However, in such a structure, it is necessary to flow a driving current in the lateral direction through the p-type nitride semiconductor layer having a high resistivity, and the uniformity of the driving current is deteriorated.

From such a background, a surface-emitting nitride semiconductor light emitting device employing a nitride semiconductor substrate or a ZnO substrate is required to provide a technique for uniformly injecting a drive current with an active layer having a large area. .
Japanese Patent Laid-Open No. 11-191537 JP 2001-77423 A

  An object of the present invention is to provide a technique for more uniformly injecting a drive current into an active layer having a large area in a surface-emitting nitride semiconductor light emitting device employing a nitride semiconductor substrate or a ZnO substrate. is there.

  In order to achieve the above object, the present invention employs the means described below. In the description of technical matters constituting the means, in order to clarify the correspondence between the description of [Claims] and the description of [Best Mode for Carrying Out the Invention] Number / symbol used in the best mode for doing this is added. However, the added number / symbol should not be used to limit the technical scope of the invention described in [Claims].

  A surface-emitting light-emitting device according to the present invention includes an n-type substrate (11) formed of gallium nitride, indium gallium nitride, or zinc oxide, and an n-type nitride semiconductor layer that covers the main surface of the n-type substrate (11). 12, 13) and the n-type nitride semiconductor layer (12, 13), and is configured to generate light having a wavelength longer than the wavelength corresponding to the band gap of the n-type substrate (11). An active layer (14) formed of a nitride semiconductor, a p-type nitride semiconductor layer (15, 16) that covers the active layer (14), and a cathode electrode that partially covers the back surface of the n-type substrate. (18) and an anode electrode (17) formed so as to cover the entire surface of the p-type nitride semiconductor layer (15, 16) opposite to the n-type substrate (11).

  In the surface-emitting light-emitting device having such a configuration, the anode electrode (17) covers the entire surface of the p-type nitride semiconductor layer (15, 16), and thus the p-type nitride semiconductor layer (15, 16) is covered. Potential distribution is unlikely to occur. Therefore, the uniformity of the drive current injected into the active layer (14) can be effectively improved. In addition, since the n-type substrate (11) formed of gallium nitride or zinc oxide has a sufficiently large thickness and can sufficiently reduce the resistivity, the cathode electrode (18) is an n-type substrate. The influence on the uniformity of the drive current is small when the back surface of (11) is only partially covered.

  The cathode electrode (18) is preferably configured to transmit the light generated by the active layer. For example, the cathode electrode (18) is preferably formed of a laminated electrode of gold and nickel. Instead, the cathode electrode (18) is also preferably formed of any material selected from the group consisting of indium oxide, tin oxide, ITO, and zinc oxide.

  Such a surface light emitting element (1) is preferably mounted on a light emitting module including a metal structure (3) bonded to the entire surface of the anode electrode (17).

  According to the present invention, in a surface emitting nitride semiconductor light emitting device employing a nitride semiconductor substrate or a ZnO substrate, a drive current can be more uniformly injected into an active layer having a large area.

  FIG. 1 is a cross-sectional view illustrating a configuration of a light emitting module 10 according to an embodiment of the present invention. The light emitting module 10 includes a surface emitting light emitting diode 1, a package 2, and a metal heat sink 3. A cup 2a is formed in the package 2, and a metal heat sink 3 is inserted into the bottom surface of the cup 2a. The light emitting diode 1 is bonded to the upper surface of the metal heat sink 3. Leads 4 and 5 are provided so as to penetrate the package 2. The lead 4 is electrically connected to the light emitting diode 1 by a wire 6, and the lead 5 is electrically connected to the light emitting diode 1 through a metal heat sink 3. The leads 4 and 5 are used for supplying a driving current to the light emitting diode 1. The inside of the cup 2a is sealed with a transparent sealing resin (not shown), and the light emitting diode 1 and the wire 6 are protected by the sealing resin.

  FIG. 2 is a cross-sectional view showing the structure of the light-emitting diode 1, and FIG. 3 is a plan view showing the structure of the light-emitting diode 1. As shown in FIG. 2, the light emitting diode 1 includes an n-type GaN substrate 11. The n-type GaN substrate 11 has a high impurity concentration, so that sufficient conductivity is given.

On the main surface of the n-type GaN substrate 11, an n-type contact layer 12, an n-type cladding layer 13, an MQW (multi-quantum well) layer 14, a p-type cladding layer 15, and a p-type contact layer 16 are provided. It is formed sequentially. In the present embodiment, the light-emitting diode 1 employs a surface-emitting structure, and the area of the main surface of the n-type GaN substrate 11 is 0.5 × 0.5 mm ² .

  The n-type contact layer 12, the n-type cladding layer 13, the MQW layer 14, the p-type cladding layer 15, and the p-type contact layer 16 are all formed of a nitride semiconductor. In one embodiment, the n-type contact layer 12 is formed of n-type GaN, and the n-type cladding layer 13 is formed of n-type AlGaN. The MQW layer 14 is a layer that functions as an active layer that generates light. In one embodiment, the MQW layer 14 is formed of a multilayer quantum well in which an InGaN layer and a GaN layer are stacked. In addition, the p-type cladding layer 15 is formed of p-type AlGaN, and the p-type contact layer 16 is formed of p-type GaN.

  Furthermore, an anode electrode 17 made of metal is ohmic-bonded to the p-type contact layer 16. The metal heat sink 3 of the light emitting module 10 is joined to the anode electrode 17.

  In addition, the cathode electrode 18 is ohmically joined to the back surface of the n-type GaN substrate 11. The wire 6 of the light emitting module 10 is joined to the cathode electrode 18.

  One of the structural features of the light-emitting diode 1 of the present embodiment is that the light generated in the MQW layer 14 is configured to be emitted from the back surface of the n-type GaN substrate 11. In order to emit light from the back surface of the light emitting diode 1, as shown in FIG. 3, the cathode electrode 18 covers not only the entire back surface of the n-type GaN substrate 11 but only a part of the back surface. Is formed. In the present embodiment, the cathode electrode 18 includes a circular dot portion formed in the center of the light emitting diode 1 and a protruding portion extending from the dot portion toward the corner of the light emitting diode 1. ing.

  In addition, the MQW layer 14 is configured to generate light having a wavelength longer than the wavelength corresponding to the band gap of the n-type GaN substrate 11. This is important for making it difficult for the n-type GaN substrate 11 to absorb the light generated by the MQW layer 14. If the wavelength of the light generated by the MQW layer 14 is too short, the generated light is significantly absorbed by the n-type GaN substrate 11 and the intensity of the light emitted from the back surface of the light emitting diode 1 becomes weak.

  On the other hand, the anode electrode 17 is formed so as to cover the entire surface of the p-type contact layer 16 opposite to the n-type GaN substrate 11. It should be noted that the anode electrode 17 is not required to transmit light because light is emitted from the back surface of the n-type GaN substrate 11. Therefore, the anode electrode 17 can be formed of a thick metal electrode. In order to reduce the resistance in the in-plane direction and improve the light reflectivity, the anode electrode 17 is rather thick metal. It is preferable that the electrode is formed of electrodes.

  The advantage of the structure described above is that the drive current can be uniformly injected into the MQW layer 14 even if the resistivity of the p-type nitride semiconductor layer (that is, the p-type cladding layer 15 and the p-type contact layer 16) is large. In the point. Since the entire surface of the p-type contact layer 16 is covered with the anode electrode 17 formed of metal and thus having a low resistivity, and the metal heat sink 3 is bonded to the anode electrode 17, the p-type cladding layer 15 and the p-type The in-plane distribution of the potential of the contact layer 16 is small. This effectively improves the in-plane uniformity of the drive current.

  The cathode electrode 18 only partially covers the back surface of the n-type GaN substrate 11, but this hardly affects the uniformity of the drive current. This is because the resistance in the in-plane direction of the n-type GaN substrate 11 is small. Since the n-type GaN substrate 11 is sufficiently thick and the resistivity of the n-type GaN can be sufficiently reduced, the in-plane resistance of the n-type GaN substrate 11 is easily reduced. be able to.

  The above-described structure with excellent drive current uniformity is particularly effective for fabricating an LED having a large area such that one side of the n-type GaN substrate 11 is 0.5 mm or more.

In the present embodiment, an n-type In _x Ga _1-x N substrate may be used instead of the n-type GaN substrate 11. In this case, the MQW layer 14 is configured to generate light having a wavelength longer than the wavelength corresponding to the band gap of the n-type In _x Ga _1-x N substrate. The In composition x of the n-type In _x Ga _1-x N substrate used is preferably greater than 0 and 0.5 or less.

  In addition, the above structure is effective even when an n-type ZnO substrate is used instead of the n-type GaN substrate 11. Since ZnO has a large band gap, the ZnO substrate hardly absorbs light emitted from the MQW layer 14 formed of a nitride semiconductor. Therefore, even if a structure for emitting light from the back surface of the substrate as shown in FIG. 2 is adopted, the reduction in light emission efficiency is small.

  In the present embodiment, the cathode electrode 18 is preferably configured to transmit at least part of the light generated by the MQW layer 14. For example, the cathode electrode 18 is preferably formed of a laminated electrode of a gold thin film and a nickel thin film. Since gold and nickel have high transmittance with respect to blue light, by appropriately determining the thickness of the gold thin film and the nickel thin film, the laminated electrode formed of the gold thin film and the nickel thin film functions as a transparent electrode. The cathode electrode 18 is also preferably formed of a transparent electrode such as indium oxide, tin oxide, ITO, and zinc oxide.

FIG. 1 is a cross-sectional view illustrating a configuration of a light emitting module according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating a configuration of a light emitting diode according to an embodiment of the present invention. FIG. 3 is a plan view showing a configuration of a light emitting diode according to an embodiment of the present invention.

Explanation of symbols

1: Light-emitting diode 2: Package 3: Metal heat sink 4, 5: Lead 6: Wire 10: Light-emitting module 11: n-type GaN substrate 12: n-type contact layer 13: n-type cladding layer 14: MQW layer 15: p-type cladding Layer 16: p-type contact layer 17: anode electrode 18: cathode electrode

Claims (5)

An n-type substrate formed of gallium nitride, indium gallium nitride or zinc oxide;
An n-type nitride semiconductor layer covering the main surface of the n-type substrate;
An active layer formed of a nitride semiconductor that covers the n-type nitride semiconductor layer and is configured to generate light having a wavelength longer than a wavelength corresponding to a band gap of the n-type substrate;
A p-type nitride semiconductor layer covering the active layer;
A cathode electrode partially covering the back surface of the n-type substrate;
A surface-emitting light emitting device comprising: an anode electrode formed so as to cover the entire surface of the p-type nitride semiconductor layer opposite to the n-type substrate. The surface-emitting light-emitting device according to claim 1,
The surface emitting light emitting device, wherein the cathode electrode is configured to transmit the light generated by the active layer. The surface-emitting light emitting device according to claim 2,
The cathode electrode is a surface-emitting light emitting device formed of a laminated electrode of gold and nickel. The surface-emitting light emitting device according to claim 2,
The surface-emitting light-emitting device, wherein the cathode electrode is formed of any material selected from the group consisting of indium oxide, tin oxide, ITO, and zinc oxide. The surface-emitting light-emitting device according to any one of claims 1 to 4,
A metal structure bonded to the entire surface of the anode electrode;
And a wire bonded to the cathode electrode.

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