JP4275701B2 - Light emitting device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a light emitting device, and more particularly to a light emitting device that performs wavelength conversion using a phosphor.

  Light emitting diodes (LEDs) are one of the most widely used light sources. One of the problems that arise when using an LED as the light source is that, in principle, the LED can only generate monochromatic light and its wavelength adjustment is not easy. The wavelength of the light generated by the LED is determined by the material and structure constituting the LED, and adjustment thereof is not easy. When an LED is applied to a lighting fixture, it is required to generate light of various colors, particularly white light. However, the LED cannot meet such needs unless a special technique is used.

  As one method for obtaining light having a desired wavelength from an LED, it is known that a phosphor is mixed in a mold resin for sealing the LED. Such techniques are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 5-152609, 7-99345, and 10-242513. By converting the wavelength of the light generated by the LED using a phosphor mixed in the mold resin, light having a desired wavelength can be obtained. Japanese Patent Laid-Open No. 10-242513 discloses the use of YAG (yttrium, aluminum, garnet) doped with Ce as a phosphor. Japanese Patent Laid-Open No. 2002-363554 discloses that alpha sialon doped with at least one element of Ce, Pr, Eu, Tb, Yb, and Er is used as a phosphor.

  This technology is based on the practical application of LEDs that generate short-wavelength light, specifically blue light or ultraviolet light. Since the phosphor can basically emit only light having a wavelength longer than that of the excitation light, an LED that generates light having a short wavelength is used in order to obtain light having a desired wavelength, particularly white light. This is very important.

  One of the user's requirements for a light emitting element that performs wavelength conversion using a phosphor is to improve its light emission efficiency. High luminous efficiency leads to an improvement in luminance of the light source and a reduction in power consumption. One of the other requirements for the light emitting element is to reduce its size. The downsizing of the light emitting element facilitates mounting the light emitting element on the final product.

Accordingly, an object of the present invention is to improve the light emission efficiency of a light emitting element that performs wavelength conversion using a phosphor.
Another object of the present invention is to realize downsizing of a light emitting element that performs wavelength conversion using a phosphor.

  In one aspect of the present invention, a light emitting device includes a semiconductor active region that generates first light and a phosphor that is excited by the first light and generates second light having a wavelength different from that of the first light. And a transparent conductive layer. Such a structure of the light emitting element makes it possible to also use an electrode for supplying a driving current to the semiconductor active region as a structure supporting the phosphor. This enables a reduction in the distance between the phosphor and the semiconductor active region, and effectively improves the luminous efficiency of the phosphor. In addition, it is effective for reducing the size of the light emitting element to use the electrode that supplies the driving current to the semiconductor active region as a structure supporting the phosphor.

  When a structure in which a phosphor is dispersed in a base material is used as a transparent conductive layer, the base material is made of an oxide of a material made of at least one of indium, zinc, tin, gallium, and antimony. Is preferred.

  In one embodiment, when the light emitting device includes a semiconductor cladding layer bonded to the semiconductor active region and a semiconductor contact layer bonded to the semiconductor cladding layer, the transparent conductive layer is bonded to the semiconductor contact layer. obtain. Such a configuration makes the transparent conductive layer function as an electrode for supplying a drive current to the semiconductor active region.

  In another embodiment, when the light emitting device further includes a transparent conductive substrate that supports the semiconductor active region, the transparent conductive layer is positioned on the opposite side of the transparent conductive substrate with respect to the semiconductor active region. It is preferable that the surface to be coated is formed. Such a configuration makes it easy to adopt a face-down structure.

  The transparent conductive layer preferably includes a first transparent conductive film containing the phosphor and a second transparent conductive film that is bonded to the first transparent conductive film and does not contain the phosphor.

  The phosphor may include YAG (yttrium, aluminum, garnet) containing cerium. In another embodiment, the phosphor may include an α-sialon containing europium. In this case, in order to generate white light by the light emitting element, it is preferable that the semiconductor active region is formed of a nitride compound semiconductor.

In another aspect of the present invention, a method for manufacturing a light-emitting element includes:
Forming a semiconductor active region for generating first light;
Forming a transparent conductive layer (20) including a phosphor that generates second light having a wavelength different from that of the first light from the first light. The step of forming a transparent conductive layer includes a step of applying a solution of a precursor of a transparent conductor mixed with the phosphor, and a step of sintering the applied solution. Such a manufacturing method makes it possible to introduce a large amount of phosphor into the transparent conductive layer.

ADVANTAGE OF THE INVENTION According to this invention, the luminous efficiency of the light emitting element which performs wavelength conversion using fluorescent substance can be improved.
In addition, according to the present invention, it is possible to reduce the size of a light-emitting element that performs wavelength conversion using a phosphor.

FIG. 1 is a cross-sectional view showing a configuration of a light emitting device according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing the structure of the LED chip of the first embodiment. FIG. 3 is a top view showing the structure of the LED chip of the first embodiment. FIG. 4 is a graph showing a change in resistivity of an ITO electrode containing a YAG phosphor depending on the amount of the YAG phosphor. FIG. 5A is a cross-sectional view illustrating the method for manufacturing the LED chip of the first embodiment. FIG. 5B is a cross-sectional view illustrating the method for manufacturing the LED chip of the first embodiment. FIG. 5C is a cross-sectional view illustrating the LED chip manufacturing method of the first embodiment. FIG. 6 is a cross-sectional view showing a configuration of a light emitting device according to the second embodiment of the present invention. FIG. 7 is a cross-sectional view showing the structure of the LED chip of the second embodiment. FIG. 8 is a cross-sectional view showing the structure of the LED chip of the second embodiment. FIG. 9 is a cross-sectional view showing another structure of the LED chip of the second embodiment.

(First embodiment)
FIG. 1 is a cross-sectional view showing a configuration of a light emitting device 10 according to a first embodiment of the present invention. The light emitting element 10 includes an LED chip 1 and leads 2 and 3. A cup 2a that accommodates the LED chip 1 is provided at the tip of the lead 2, and the LED chip 1 is bonded to the bottom surface of the cup 2a. The LED chip 1 and the lead 2 are electrically connected by a wire 4, and the LED chip 1 and the lead 3 are electrically connected by a wire 5. The LED chip 1, the leads 2 and 3, and the wires 4 and 5 are sealed with a mold resin 6.

  FIG. 2 is a cross-sectional view showing the structure of the LED chip 1, and FIG. 3 is a plan view showing the structure of the LED chip 1. As shown in FIG. 2, the LED chip 1 includes a sapphire substrate 11, an n-GaN layer 12, an n-AlGaN layer 13, an MQW layer 14, a p-AlGaN layer 15, and a p-GaN layer. 16, a cathode electrode 17, and an anode electrode 18. The n-GaN layer 12 is a layer that functions as an n-type contact layer, and is bonded to the cathode electrode 17. In the n-AlGaN layer 13 and the MQW layer 14, the p-AlGaN layer 15 functions as an n-type cladding layer, an active region that generates light from a driving current, and a p-type cladding layer, respectively. The MQW layer 14 is formed of a multi-quantum well in which an InGaN layer and a GaN layer are stacked. Forming the cladding layer and the MQW layer with a nitride compound semiconductor is important in order to emit light having a short wavelength, particularly blue light or ultraviolet light, from the MQW layer. The p-GaN layer 16 is a layer that functions as a p-type contact layer, and is joined to the anode electrode 18.

  The anode electrode 18 includes a metal electrode 19 joined to the wire 5 and a transparent conductive layer 20 interposed between the metal electrode 19 and the p-GaN layer 16. The transparent conductive layer 20 and the p-GaN layer 16 are ohmic-bonded. The driving current used for generating light is supplied from the lead 3 and the wire 5 to the metal electrode 19, and then the MQW layer through the transparent conductive layer 20, the p-GaN layer 16, and the p-AlGaN layer 15. 14 is injected.

  As shown in FIG. 3, the transparent conductive layer 20 covers the entire top surface of the p-GaN layer 16, whereas the metal electrode 19 only partially covers the top surface of the p-GaN layer 16. Not covered. This is to improve the luminance uniformity while increasing the luminance of the light emitting element 10. Since the light transmittance of the metal electrode 19 is low, a large area of the metal electrode 19 causes a decrease in luminance of the light emitting element 10. However, if the area of the metal electrode 19 is small, the drive current injected into the MQW layer 14 may be non-uniform in the plane. The transparent conductive layer 20 diffuses the drive current in the in-plane direction and improves the in-plane uniformity of the drive current injected into the MQW layer 14.

  Returning to FIG. 2, the transparent conductive layer 20 of the anode electrode 18 includes a phosphor-containing transparent conductive film 21 containing a phosphor and a transparent conductive film 22 containing no phosphor. The use of the phosphor-containing transparent conductive film 21 is one feature of the light-emitting element 10 of the present embodiment. The phosphor-containing transparent conductive film 21 functions as a drive current path and also plays a role of performing wavelength conversion using the phosphor. When the light generated in the MQW layer 14 enters the phosphor-containing transparent conductive film 21, the phosphor contained in the phosphor-containing transparent conductive film 21 is excited, and light having a wavelength different from that of the original light is fluorescent. Emitted from the body.

  The color of light emitted from the light emitting element 10 depends on the wavelength of light generated in the MQW layer 14 and the material constituting the phosphor. When the light emitting element 10 is used to generate white light, the MQW layer 14 is formed so as to generate blue light, and YAG (yttrium aluminum garnet) containing cerium (Ce) as a phosphor is used. It is preferable to use α-sialon containing europium (Eu).

As a base material of the phosphor-containing transparent conductive film 21 (that is, a portion other than the phosphor of the phosphor-containing transparent conductive film 21), a material generally used as a transparent electrode, specifically, indium, zinc, An oxide of a material composed of at least one of tin, gallium, and antimony is used. For example, the base material of the phosphor-containing transparent conductive film 21 can be formed of ITO (Indium Tin Oxide), ZnO, or SnO ₂ .

  Similar to the base material of the phosphor-containing transparent conductive film 21, the transparent conductive film 22 is an oxidation of a material generally used as a transparent electrode, or a material made of at least one of indium, zinc, tin, gallium, and antimony. Formed of things.

  Below, the usefulness of the fluorescent substance containing transparent conductive film 21 and the transparent conductive film 22 which does not contain fluorescent substance is demonstrated in detail. The first merit of the structure in which the phosphor-containing transparent conductive film 21 is incorporated in the anode electrode 18 is that the light emission efficiency of the light emitting element 10 can be improved. The structure in which the phosphor-containing transparent conductive film 21 is incorporated in the anode electrode 18 makes it possible to reduce the distance from the MQW layer 14 to the phosphor. This effectively improves the light emission efficiency of the light emitting element 10.

  A second merit is that the light emitting device 10 can be downsized. The LED chip 1 in which the phosphor-containing transparent conductive film 21 is incorporated in the anode electrode 18 eliminates the need to provide the light emitting element 10 with a dedicated structure for performing wavelength conversion with the phosphor. This is effective for reducing the size of the light emitting element 10.

  The luminous efficiency of the light emitting element 10 increases as the amount of the phosphor contained in the phosphor-containing transparent conductive film 21 increases. However, the increase in the amount of the phosphor is a problem in that the resistivity of the phosphor-containing transparent conductive film 21 is increased. FIG. 4 is a graph showing the influence of the resistivity (IT%) of the phosphor contained in the ITO on the resistivity of the ITO electrode containing the YAG phosphor. If the amount of YAG phosphor exceeds 1.5 wt%, the resistivity of the ITO electrode increases significantly. The increase in the resistivity of the phosphor-containing transparent conductive film 21 weakens the action of diffusing the drive current of the transparent conductive layer 20 in the in-plane direction, leading to a decrease in in-plane uniformity of the drive current.

  The transparent conductive film 22 containing no phosphor plays a role of suppressing a decrease in in-plane uniformity of the drive current due to an increase in resistivity of the phosphor-containing transparent conductive film 21. The transparent conductive film 22 which does not contain a phosphor and can reduce its resistance is effective for sufficiently diffusing the drive current in the in-plane direction and improving the in-plane uniformity of the drive current. . In FIG. 2, the transparent conductive film 22 is provided between the phosphor-containing transparent conductive film 21 and the p-GaN layer 16, but the positions of the phosphor-containing transparent conductive film 21 and the transparent conductive film 22 are interchangeable. Note that there are. In addition, it should be noted that the transparent conductive film 22 may not be provided if the resistivity is sufficiently low.

  FIG. 5A to FIG. 5C are cross-sectional views showing suitable manufacturing steps for the LED chip 1 of the first embodiment. First, as shown in FIG. 5A, an n-GaN layer 12, an n-AlGaN layer 13, an MQW layer 14, a p-AlGaN layer 15, and a p-GaN layer 16 are sequentially formed on a sapphire substrate 11. Is done.

  Subsequently, as shown in FIG. 5B, a transparent conductive film 22 and a phosphor-containing transparent conductive film 21 are sequentially formed. The transparent conductive film 22 and the phosphor-containing transparent conductive film 21 are most simply formed by sputtering.

  However, according to the inventors' investigation, the sputtering method is not suitable for adding a large amount of phosphor to the phosphor-containing transparent conductive film 21. In order to increase the amount of the phosphor contained in the phosphor-containing transparent conductive film 21, it is preferable to use a sol-gel method. Specifically, a phosphor-containing transparent conductive film 21 may be formed by applying a precursor solution of a base material mixed with a phosphor onto the transparent conductive film 22 and firing the solution. Is preferred.

  For example, the phosphor-containing transparent conductive film 21 whose base material is ITO can be formed by the following steps. First, a solution containing ITO (ITO sol) is prepared. As the ITO sol, for example, acetate ester containing 5% ITO is used. Subsequently, the phosphor powder is mixed with the ITO sol. The ITO sol mixed with the phosphor is subjected to ultrasonic stirring, and the phosphor is uniformly dispersed in the ITO sol. Subsequently, ITO sol is applied on the transparent conductive film 22 by spin coating. Subsequently, after the ITO sol applied by heating at 120 ° C. for 30 minutes is dried, the phosphor-containing transparent conductive film 21 is formed by baking at 550 ° C. for 1 hour. According to such a method, it is possible to include a sufficiently large number of phosphors in the phosphor-containing transparent conductive film 21.

  After the formation of the phosphor-containing transparent conductive film 21, as shown in FIG. 5C, the n-AlGaN layer 13, the MQW layer 14, the p-AlGaN layer 15, the p-GaN layer 16, the transparent conductive film 22, and The phosphor-containing transparent conductive film 21 is patterned, and a part of the n-GaN layer 12 is exposed. Further, the cathode electrode 17 is formed on the exposed portion of the n-GaN layer 12, and the metal electrode 19 is formed on the upper surface of the phosphor-containing transparent conductive film 21, thereby completing the LED chip 1 of FIG.

  As described above, in the light-emitting element 10 of the present embodiment, the phosphor-containing transparent conductive film 21 is incorporated in an electrode (the anode electrode 18 in the present embodiment) for supplying a drive current. As a result, the improvement of the light emission efficiency of the light emitting element 10 and the miniaturization of the light emitting element 10 are realized.

  In addition, in the light-emitting element 10 of the present embodiment, the transparent conductive film 22 that does not contain a phosphor is bonded to the phosphor-containing transparent conductive film 21, thereby improving the in-plane uniformity of the drive current.

(Second embodiment)
The structure of the LED chip 1 shown in FIG. 2 is a so-called face-up structure. However, in order to increase the light extraction efficiency of the light emitting element, it is known that a face-down structure in which light is extracted from the substrate side is suitable. In the second embodiment, the face-down structure is provided with a light-emitting element on which an LED chip that employs the face-down structure is mounted.

  FIG. 6 is a diagram illustrating a configuration of a light emitting element 10A according to the second embodiment. In the second embodiment, instead of the LED chip 1 adopting the face-up structure, the LED chip 1A adopting the face-down structure is used. Accordingly, the LED chip 1A is flip-chip connected to the lead 2, and no wire is used for electrical connection between the LED chip 1A and the lead 2.

  FIG. 7 is a cross-sectional view showing the structure of the LED chip 1A of the second embodiment. The LED chip 1A includes an n-SiC substrate 11A, an n-GaN layer 12, an n-AlGaN layer 13, an MQW layer 14, a p-AlGaN layer 15, a p-GaN layer 16, and an anode electrode 17A. I have. The anode electrode 17A is formed of a metal film. When the LED chip 1A is mounted on the light emitting element 10A, the anode electrode 17A is flip-chip connected to the lead 2.

  It should be noted that the n-SiC substrate 11A is conductive and transparent. Since the n-SiC substrate 11A has conductivity, the n-SiC substrate 11A can be used as a path for supplying a drive current to the MQW layer 14. Further, since the n-SiC substrate 11A is transparent, the light generated by the MQW layer 14 can pass through the inside, and the LED chip 1A does not prevent light from being emitted. As is clear from this discussion, a substrate that is conductive and transparent can be used instead of the n-SiC substrate 11A. For example, when the MQW layer 14 is configured to generate blue light, a GaN substrate doped with an n-type impurity at a high concentration can be used. The GaN substrate is transparent to blue light.

  In order to realize the face-down structure, in the present embodiment, the cathode electrode 18A is formed on the back surface of the n-SiC substrate 11A (that is, the surface opposite to the side on which the MQW layer 14 is provided). Accordingly, in this embodiment, the cathode electrode in which the transparent conductive layer 20 composed of the phosphor-containing transparent conductive film 21 and the transparent conductive film 22 containing no phosphor is provided on the back surface of the n-SiC substrate 11A. 18A. On the transparent conductive layer 20, a metal electrode 19A is formed. As shown in FIG. 8, the transparent conductive layer 20 covers the entire back surface of the n-SiC substrate 11A, whereas the metal electrode 19 only partially covers the back surface of the n-SiC substrate 11A. Not covered. The effectiveness of this is as discussed in the first embodiment. A drive current for generating light is injected from the anode electrode 17A to the MQW layer 14 and further flows to the metal electrode 19 through the n-SiC substrate 11A and the transparent conductive layer 20.

  Such a structure enjoys the same advantages as the light-emitting element 10 of the first embodiment (that is, improvement in light-emitting efficiency and size reduction of the light-emitting element 10 by using the phosphor-containing transparent conductive film 21). This makes it possible to realize a face-down structure.

  As described above, the structure of FIG. 6 utilizes the fact that the n-SiC substrate 11A is conductive and transparent. However, for practical reasons, it may be desirable to use a transparent and insulating substrate, such as a sapphire substrate.

  FIG. 9 shows a structure of the LED chip 1B for satisfying such a requirement. The LED chip 1B illustrated in FIG. 9 uses a sapphire substrate 11B instead of the n-SiC substrate 11A. It should be noted that the sapphire substrate 11B is transparent and insulating. The transparent conductive layer 20 is formed so as to cover the back surface of the sapphire substrate 11B, and the metal electrode 19 is joined to the transparent conductive layer 20.

  In the LED chip 1B of FIG. 9, the electrical connection between the cathode electrode 18A and the n-GaN layer 12 is achieved by bonding the transparent conductive layer 20 directly to the n-GaN layer 12. A drive current for generating light is injected from the anode electrode 17 </ b> A into the MQW layer 14, and further flows to the metal electrode 19 through the n-GaN layer 12 and the transparent conductive layer 20. That is, the sapphire substrate 11B is excluded from the path through which the drive current flows. Such a structure makes it possible to adopt a face-down structure even if the sapphire substrate 11B is insulative.

Claims (8)

A substrate,
A first semiconductor clad layer formed to cover the substrate;
A semiconductor active region bonded to a surface of the first semiconductor clad layer opposite to the substrate and generating a first light;
A second semiconductor cladding layer bonded to a surface of the semiconductor active region opposite to the substrate;
A semiconductor contact layer bonded to a surface of the second semiconductor cladding layer opposite to the substrate;
A light-emitting element comprising a transparent conductive layer used as an electrode for supplying a drive current before Symbol semiconductor active region,
The transparent conductive layer is composed of laminated first and second transparent conductive films ,
The first and second transparent conductive films are formed so as to cover the entire surface of the semiconductor contact layer opposite to the substrate,
The first transparent conductive film includes a phosphor that is excited by the first light, has a wavelength different from that of the first light, and generates second light emitted to the outside of the light emitting element. ,
The second transparent conductive film does not include a phosphor. A transparent conductive substrate;
A first semiconductor clad layer formed to cover the transparent conductive substrate;
A semiconductor active region bonded to a surface of the first semiconductor cladding layer opposite to the transparent conductivity and generating a first light;
A second semiconductor cladding layer bonded to a surface of the semiconductor active region opposite to the transparent conductivity;
Transparent conductive layer used as an electrode for supplying a driving current to the semiconductor active region
A light emitting device comprising:
The transparent conductive layer is composed of laminated first and second transparent conductive films ,
The first and second transparent conductive films are formed to cover the entire surface of the transparent conductive substrate opposite to the first semiconductor clad layer, the semiconductor active region, and the second semiconductor clad layer,
The first transparent conductive film includes a phosphor that is excited by the first light, has a wavelength different from that of the first light, and generates second light emitted to the outside of the light emitting element. ,
The second transparent conductive film does not contain a phosphor.
Light emitting element. A transparent and insulating substrate;
A semiconductor contact layer formed to cover the substrate;
A first semiconductor clad layer bonded to a surface of the semiconductor contact layer opposite to the substrate;
A semiconductor active region bonded to a surface of the first semiconductor cladding layer opposite to the transparent conductivity and generating a first light;
A second semiconductor cladding layer bonded to a surface of the semiconductor active region opposite to the transparent conductivity;
Transparent conductive layer used as an electrode for supplying a driving current to the semiconductor active region
A light emitting device comprising:
The transparent conductive layer is composed of laminated first and second transparent conductive films ,
The first and second transparent conductive films cover the entire surface of the substrate opposite to the first semiconductor cladding layer, the semiconductor active region, and the second semiconductor cladding layer, and the first and second transparent conductive films. A conductive film located on the semiconductor contact layer side of the transparent conductive film is formed so as to be directly bonded to the semiconductor contact layer,
The first transparent conductive film includes a phosphor that is excited by the first light, has a wavelength different from that of the first light, and generates second light emitted to the outside of the light emitting element. ,
The second transparent conductive film does not contain a phosphor.
Light emitting element. A light-emitting device according to any one of claims 1 to 3,
It said first magnetic Akirashirubedenmaku includes a base material in which the phosphor is dispersed,
The base material and the second transparent conductive film are made of an oxide of a material made of at least one of indium, zinc, tin, gallium, and antimony. A light-emitting device according to any one of claims 1 to 3,
The phosphor includes YAG (yttrium, aluminum, garnet) containing cerium. A light-emitting device according to any one of claims 1 to 3,
The phosphor includes an α-sialon containing europium. The light-emitting device according to claim 5 or 6,
The semiconductor active region is formed of a nitride compound semiconductor. The method for manufacturing a light emitting device according to any one of claims 1 to 7,
Forming the first semiconductor cladding layer, the semiconductor active region, and the second semiconductor cladding layer ;
Forming the first transparent conductive film;
Forming the second transparent conductive film,
The step of forming the first transparent conductive film includes:
Applying a solution of a precursor of a transparent conductor mixed with the phosphor;
And a step of sintering the applied solution.

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