Patent Publication Number: US-2015076547-A1

Title: Group III Nitride Semiconductor Light-Emitting Device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a Group III nitride semiconductor light-emitting device exhibiting improved emission performance, particularly to a light-emitting device exhibiting improved emission performance by providing a current blocking layer on a p-type layer. 
     2. Background Art 
     A technique is known in which absorption of light by a p-electrode is prevented by preventing light emission from a light-emitting layer at a position overlapping with the p-electrode in plan view, thereby improving emission performance in a Group III nitride semiconductor light-emitting device. 
     Japanese Patent Application Laid-Open (kokai) No. 2008-192710 discloses a Group III nitride semiconductor light-emitting device exhibiting improved emission performance by forming a transparent insulating film on a p-type layer directly below a pad to prevent that region from emitting light and by reflecting light at an interface between the p-type layer and the insulating film. 
     Japanese Patent Application Laid-Open (kokai) No. 2013-48199 describes that a current blocking layer is formed directly below a connecting portion of a p-side metal electrode (a portion to be wire bonded of the p-electrode). This is to suppress shielding and absorption of light by the connecting portion of the p-side metal electrode by preventing light emission from an active layer directly below the p-side metal electrode, and to thereby improve emission performance. 
     Japanese Patent Application Laid-Open (kokai) No. 2009-43934 discloses a Group III nitride semiconductor light-emitting device having a structure in which a transparent electrode, a pad electrode, and an insulating film are sequentially formed on a p-type layer, a p-electrode is provided on the insulating film, the p-electrode is connected to the pad electrode via holes provided in the insulating film, and a reflective film is provided in the insulating film. 
     In the Group III nitride semiconductor light-emitting device having a structure as disclosed in Japanese Patent Application Laid-Open (kokai) No. 2009-43934, it is arbitrary where the current blocking layer described in Japanese Patent Application Laid-Open (kokai) Nos. 2008-192710 and 2013-48199 is formed. According to the study of the present inventors, it was found that emission performance is reduced depending on the position of the current blocking layer. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, an object of the present invention is to further improve emission performance in a Group III nitride semiconductor light-emitting device having a structure in which a transparent electrode and an insulating film are sequentially formed on a p-type layer, a p-electrode is formed on the insulating film, and the transparent electrode is connected to the p-electrode via holes provided in the insulating film. 
     The present invention provides a Group III nitride semiconductor light-emitting device having a transparent electrode, an insulating film, and a p-electrode in this order on a p-type layer formed of Group III nitride semiconductor, the transparent electrode being electrically connected to the p-electrode via holes provided in the insulating film, wherein: 
     the p-electrode comprises a connecting portion being electrically connected to the outside of the device, a wiring portion extending from the connecting portion, and a contact portion connected to the wiring portion and in contact with the transparent electrode via holes; and 
     a current blocking layer made of an insulating and transparent material with a refractive index lower than that of the p-type layer is formed between the p-type layer and the transparent electrode. The current blocking layer is provided not in a region overlapping with the wiring portion but in a region including an orthogonal projection of the contact portion in plan view, the current blocking layer is larger by 0 μm to 9 μm in width than the contact portion. 
     The current blocking layer is preferably provided only in a region including the orthogonal projection of the contact portion in plan view. When the current blocking layer is provided in a region overlapping with the connecting portion in plan view, it hardly affects emission performance. Therefore, it is better and advantageous not to provide the current blocking layer in such a region in terms of production easiness. Moreover, when the current blocking layer is provided in a region overlapping with the wiring portion, the emission performance is reduced. 
     The current blocking layer is larger by 0 μm to 9 μm in width than the contact portion means that there is a distance between the outer circumference of the contact portion and the outer circumference of the current blocking layer in a direction orthogonal to the outer circumference of the contact portion in plan view. When this distance is not constant, it means an average value. More preferably, the distance is 3 μm to 9 μm, and further preferably, 6 μm to 9 μm. 
     The current blocking layer preferably has a thickness satisfying the relation of d&gt;λ/(4n) (d: thickness of current blocking layer, n: refractive index of current blocking layer, λ: emission wavelength), and less than 1,500 nm. When the thickness is λ/(4n) or less, light is not sufficiently blocked. When the thickness is 1,500 nm or more, a production problem such as disconnection of p-electrode or transparent electrode and wire occurs due to step. More preferably, the thickness satisfies a range of 100 nm to 800 nm, and further preferably, 100 nm to 500 nm. 
     The side surface of the current blocking layer may be inclined or orthogonal to the main surface of the p-type layer, but preferably inclined. That is, the current blocking layer has a trapezoid (tapered) cross section the upper base of which is smaller than the lower base. When the side surface is inclined, disconnection of p-electrode or transparent electrode and wire can be prevented. The inclination angle is preferably 5° to 60°, and more preferably 5° to 30°. 
     The current blocking layer may have any planar shape (shape in plan view) such as circle and square. It is preferably similar to the planar shape of the contact portion because the similar planar shape brings out the function of the current blocking layer evenly in a planar direction. 
     The current blocking layer may be formed of an insulating and transparent material with a refractive index lower than that of the p-type layer. The transparency is proportional to the emission wavelength. When the p-type layer has a plurality of layers, it may have a refractive index lower than that of a layer most proximal to the current blocking layer. The p-type layer may be formed of, for example, SiO 2 , SiN, SiON, Al 2 O 3 , TiO 2 , ZrO 2 , HfO 2 , Nb 2 O 5 , and MgF 2 . 
     A reflective film may be provided in a region overlapping with the p-electrode of the insulating film in plan view. The reflective film may be a single-layer film or a multi-layer film formed of a high reflectance metal such as Al, Ag, Al alloy, and Ag alloy. Moreover, the wiring portion may be formed of a high reflectance metal. 
     The current blocking layer and the reflective film in the insulating film may be a dielectric multi-layer film. The dielectric multi-layer film has a structure in which a low refractive index material and a high refractive index material are alternately and repeatedly deposited, and each optical film thickness is designed to be ¼ of the emission wavelength. 
     The light-emitting device of the present invention may be either a face-up type or a flip-chip type. 
     In the Group III nitride semiconductor light-emitting device of the present invention, the current blocking layer prevents light emission from the light-emitting layer directly below the p-type contact portion and reduces the light directed toward the p-type contact portion by reflecting light by the current blocking layer, thereby improving the emission performance. 
     In the Group III nitride semiconductor light-emitting device of the present invention, the current blocking layer is formed in regions including the orthogonal projections of the contact portions in a plan view. Therefore, the light avoiding the current blocking layer from a diagonal direction and being directed toward the contact portions of the p-electrode is reduced, thereby suppressing the light emitted from the light-emitting layer below the contact portions. Moreover, the light being directed toward the contact portion is reduced by reflecting light at an interface between the p-type layer and the current blocking layer. As a result, the emission performance can be further improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various other objects, features, and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood with reference to the following detailed description of the preferred embodiments when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view of the structure of a Group III nitride semiconductor light-emitting device according to Embodiment 1; 
         FIG. 2  is a top plan view of the Group III nitride semiconductor light-emitting device according to Embodiment 1; 
         FIG. 3  is a graph of the emission performance when a current blocking layer is formed only under a contact portion  16   c;    
         FIG. 4  is a graph of the emission performance when a current blocking layer is formed only under a wiring portion  16   b;    
         FIG. 5  is a graph of the emission performance when a current blocking layer is formed only under a wire bonding portion  16   a;    
         FIG. 6  is a cross-sectional view of the structure of a Group III nitride semiconductor light-emitting device according to Embodiment 2; 
         FIG. 7  is a cross-sectional view of the structure of a Group III nitride semiconductor light-emitting device according to variation; 
         FIGS. 8A to 8D  are sketches showing processes for producing the Group III nitride semiconductor light-emitting device according to Embodiment 1; 
         FIG. 9  is a cross-sectional view of the structure of a Group III nitride semiconductor light-emitting device according to Embodiment 3; and 
         FIG. 10  is a top plan view of the structure of the Group III nitride semiconductor light-emitting device according to Embodiment 3. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A specific embodiment of the present invention will next be described with reference to the drawings. However, the present invention is not limited to the embodiment. 
     Embodiment 1 
       FIG. 1  is a cross-sectional view of the structure of a Group III nitride semiconductor light-emitting device according to Embodiment 1.  FIG. 2  is a top plan view of the Group III nitride semiconductor light-emitting device according to Embodiment 1.  FIG. 1  is an A-A cross-sectional view of  FIG. 2 . As shown in  FIG. 2 , the Group III nitride semiconductor light-emitting device according to Embodiment 1 is of a face-up type having a rectangular shape in plan view. 
     As shown in  FIG. 1 , the Group III nitride semiconductor light-emitting device according to Embodiment 1 includes a substrate  10 , an n-type layer  11  via a buffer layer (not illustrated) on the substrate  10 , a light-emitting layer  12  on the n-type layer  11 , and a p-type layer  13  on the light-emitting layer  12 . Each of the n-type layer  11 , the light-emitting layer  12 , and the p-type layer  13  is formed of Group III nitride semiconductor. A groove extending from the surface of the p-type layer  13  to the n-type layer  11  is formed, and the n-type layer  11  is exposed through the bottom surface of the groove. An insulating film  15  is provided so as to continuously cover the transparent electrode  14  on the p-type layer  13 , the transparent electrode  14 , and the n-type layer  11  exposed through the bottom surface of the groove. A p-electrode  16  and an n-electrode  17  are separately formed on the insulating film  15 . Moreover, current blocking layers  18  are provided in specific regions between the p-type layer  13  and the transparent electrode  14 . Each structure will be described below in detail. 
     The substrate  10  is a sapphire substrate having an a-plane main surface on which concaves and convexes (not illustrated) are formed on the n-type layer  11  side. The concaves and convexes are provided for improving emission performance. The substrate  10  may be formed of any material on which Group III nitride semiconductor crystal can grow, for example, SiC, Si, and ZnO other than sapphire. 
     The n-type layer  11  has a structure in which an n-type contact layer, an n-type ESD layer, and an n-type SL layer are sequentially deposited on the substrate  10 . The n-type contact layer is in contact with the n-electrode  17 . The n-type contact layer is formed of n-GaN having a Si concentration of 1×10 18 /cm 3  or more. When the n-type contact layer comprises a plurality of layers with different carrier concentrations, contact resistance can be reduced in the n-electrode  17 . The n-type ESD layer serves as an electrostatic-breakdown-voltage-improving layer for preventing electrostatic breakdown of the device. The n-type ESD layer has a layered structure including an undoped GaN layer and a Si-doped n-GaN layer. The n-type SL layer is an n-type superlattice layer having a superlattice structure in which layer units are repeatedly deposited, each unit including an InGaN layer, a GaN layer, and an n-GaN layer. The n-type SL layer serves as a strain relaxation layer for relaxing stress applied to the light-emitting layer  12 . 
     The light-emitting layer  12  has a MQW structure in which an InGaN well layer and an AlGaN barrier layer are repeatedly deposited. A protection layer may be provided between the well layer and the barrier layer for preventing In evaporation. 
     The p-type layer  13  has a structure in which a p-type cladding layer and a p-type contact layer are sequentially deposited on the light-emitting layer  12 . The p-type cladding layer is provided for preventing diffusion of electrons to the p-type contact layer. The p-type cladding layer is formed by repeatedly depositing layer units, each layer unit including a p-InGaN layer and a p-AlGaN layer. The p-type contact layer is provided for achieving good contact between the p-electrode  16  and the p-type layer  13 . The p-type contact layer is formed of p-GaN having a Mg concentration of 1×10 19 /cm 3  to 1×10 22 /cm 3  and a thickness of 100 Å to 1,000 Å. 
     The structure of the n-type layer  11 , the light-emitting layer  12 , and the p-type layer  13  is not limited to the above, any structure which is conventionally used in the Group III nitride semiconductor light-emitting device may be employed. 
     The transparent electrode  14  may be formed of electrically conductive oxide such as ITO (indium tin oxide), IZO (indium zinc oxide), and ICO (indium cerium oxide). The transparent electrode  14  is formed so as to continuously cover the p-type layer  13  and the current blocking layers  18 . Therefore, the transparent electrode  14  is formed in a wavy film along the tops of the current blocking layers  18 . Concaves and convexes may be provided on the surface of the transparent electrode  14  to improve light extraction efficiency. 
     The insulating film  15  is formed so as to continuously cover the n-type layer  11  exposed on the bottom surface of the groove and the transparent electrode  14 . The insulating film  15  is formed of SiO 2 , and may be formed of SiN, Al 2 O 3 , TiO 2  other than SiO 2 . Holes  21  are provided in specific regions of the insulating film  15 , and pass through the insulating film  15 . The holes  21  are filled with the wiring portions  16   b  of the p-electrode  16  described later. 
     Reflective films  19  are provided in regions overlapping in plan view with the p-electrode  16  and the n-electrode  17  of the insulating film  15 . The reflective films  19  are enclosed with the insulating film  15  and thus are electrically insulated, thereby metal migration is prevented. The reflective films  19  are provided to suppress absorption of light by the p-electrode  16  and the n-electrode  17  by reflecting light directed toward the p-electrode  16  and the n-electrode  17 , and to thereby improve emission performance. 
     Each of the reflective films  19  is formed of a material with a reflectance higher than that of the p-electrode  16  or the n-electrode  17 , such as Al, Ag, an Al alloy, or an Ag alloy. The reflective film  19  may be a single-layer film or a multi-layer film. When the reflective film  19  is a multi-layer film, the film may be formed of, for example, Al alloy/Ti, Ag alloy/Al, Ag alloy/Ti, Al/Ag/Al, or Ag alloy/Ni. Hereinafter, the symbol “/” refers to a layered structure; for example, “A/B” refers to a layered structure in which layer B is formed after formation of layer A. The symbol “/” is used in a similar meaning in the description of material. In order to improve adhesion of the reflective film  19  to the insulating film  15 , a thin film formed of, for example, Ti, Cr, or Al may be provided between the reflective film  19  and the insulating film  15 . 
     The reflective film  19  may be formed of a dielectric multi-layer film. The dielectric multi-layer film is a multi-layer film formed of a plurality of alternately deposited pairs of films, each pair including a film formed of a material of low refractive index and a film formed of a material of high refractive index, wherein the thickness of each film is designed to be ¼ emission wavelength. The material of low refractive index may be, for example, SiO 2  or MgF 2 , and the material of high refractive index may be, for example, SiN, TiO 2 , ZrO 2 , Ta 2 O 5 , or Nb 2 O 5 . From the viewpoint of improvement of the reflectance of the dielectric multi-layer film, preferably, a large difference in refractive index is provided between the material of low refractive index and the material of high refractive index. The dielectric multi-layer film is preferably formed of a large number of pairs of films. The number of pairs of films is preferably 5 or more. However, the number of pairs of films is preferably 30 or less so as not to increase the overall thickness of the dielectric multi-layer film increases and cause problems in production processes. 
     The p-electrode  16  comprises a wire bonding portion  16   a  (the connecting portion of the present invention), a wiring portion  16   b , and a contact portion  16   c . The contact portion  16   c  is formed of Ni/Au/Al, the wire bonding portion  16   a  and the wiring portion  16   b  are formed of Ti/Au/Al. 
     The wire bonding portion  16   a  is a circular region located on the insulating film  15 , to which a bonding wire is connected. The wiring portion  16   b  is a linear portion extending from the wire bonding portion  16   a , which is located on the insulating film  15   a . By having such a linear structure, current is diffused in a direction parallel to the main surface of the device. The wiring portion  16   b  is also formed inside the holes  21  provided in the insulating film  15 . The contact portions  16   c  are a plurality of dotted circular regions provided on the transparent electrode  14 . The contact portions  16   c  are connected to the wiring portion  16   b  via holes  21  provided in the insulating film  15 . The contact portions  16   c  are provided for achieving good contact between the p-electrode  16  and the transparent electrode  14 . The holes  21  and the contact portions  16   c  do not necessarily have the same shape in plan view as long as the holes  21  have a shape to be contained in the contact portions  16   c.    
     As shown in  FIG. 2 , the wire bonding portion  16   a  is disposed in the vicinity of the center of one shorter side of the rectangle. Two linear wiring portions  16   b  extend from the wire bonding portion  16   a . The wiring portions  16   b  comprise a linear portion extending along one longer side in the vicinity of one longer side, and a linear portion extending along the other longer side in the vicinity of the other longer side. Each of the linear portions is divided in a direction perpendicular to the main surface of the device by the holes  21 , and connected to the circular contact portions  16   c  at the dividing ends. 
     The current blocking layers  18  are provided for preventing light emission from regions overlapping in plan view with the current blocking layers  18  of the light-emitting layer  12  by blocking the current in that region. Moreover, light directed toward the tops of the current blocking layers  18  is reduced by reflection or refraction at the interfaces between the p-type layer  13  and the current blocking layers  18 . Through these two effects, absorption and shielding of light by the p-electrode  16  located at the tops of the current blocking layers  18  are suppressed, thereby improving emission performance. 
     The current blocking layers  18  are located in regions including the orthogonal projections of the contact portions  16   c  in plan view as shown in  FIG. 1 . As shown in  FIG. 2 , the current blocking layers  18  are circles concentric with each of the contact portions  16   c  in plan view. In other part of the p-electrode  16 , i.e., in regions overlapping with the wire bonding portion  16   a  and the wiring portions  16   b , current blocking layers  18  are not formed. The reason for not forming a current blocking layer  18  in a region overlapping with the wire bonding portion  16   a  is that even if the current blocking layer  18  is formed in this region, the emission performance is only slightly improved. Moreover, the current blocking layer is preferably not formed in terms of production easiness and production cost. The reason for not forming current blocking layers  18  in regions overlapping with the wiring portions  16   b  is that the emission performance is, on the contrary, reduced by forming the current blocking layers  18  in these regions. 
     Each of the contact portions  16   c  and the current blocking layers  18  has a planar circle shape, and each of the contact portions  16   c  has a diameter of 16 μm. Although the contact portions  16   c  and the current blocking layers have a similar shape, the planar shapes of the current blocking layers  18  are not necessarily similar to those of the contact portions  16   c . However, when they are similar, the function of the current blocking layers  18  can be evenly performed in a planar direction. 
     The current blocking layer  18  may be formed of any insulating and transparent material with a refractive index lower than that of the p-type layer  13 , other than SiO 2 . When the p-type layer  13  comprises a plurality of layers, the refractive index of the current blocking layer  18  may be lower than that of a layer most proximal to the current blocking layer  18 . When the p-type layer  13  has a structure in which a p-type cladding layer and a p-type contact layer are sequentially deposited, the current blocking layer  18  may be formed of any material with a refractive index lower than that of the p-type contact layer. For example, metal oxide, metal nitride, metal oxynitride, specifically, SiO 2 , SiN, SiON, Al 2 O 3 , TiO 2 , ZrO 2 , HfO 2 , Nb 2 O 5 , and MgF 2  may be used. The current blocking layer  18  may be a single layer or a multilayer formed of such materials or a dielectric multi-layer film formed of a plurality of alternately deposited two types of films with different refractive indices, wherein the optical film thickness of each film is 4/1 wavelength. When such a dielectric multi-layer film is employed, the reflectance is improved, and thus light directed toward the p-electrode is reduced and absorption of light by the p-electrode is reduced, thereby improving emission performance. 
     The planar shape of the current blocking layer  18  is larger by 0 μm to 9 μm in width than that of the contact portion  16   c . Here, “width” means a distance from the outer circumference of the contact portion  16   c  to the outer circumference of the current blocking layer  18  in a direction orthogonal to the outer circumference of the contact portion  16   c  in plan view. When the width is not constant, the average width may be 0 μm to 9 μm. In Embodiment 1, the contact portion  16   c  and the current blocking layer  18  are both circles, and the width means the difference in radius. Therefore, the term “width difference” is used hereinafter to avoid confusion. When the width difference is less than 0 μm (i.e., the area of the current blocking layer  18  is smaller than that of the contact portion  16   c ), the emission performance is not sufficiently improved, which is not preferable. When the width difference is larger than 9 μm, light is not emitted from larger region by the current blocking layer  18 , and the emission performance is reduced, which is not preferable. More preferably, the width difference is 3 μm to 9 μm, and further preferably, 6 μm to 9 μm. 
     The side surface  18   a  of the current blocking layer  18  is inclined by 5° to 60° to the main surface of the p-type layer  13 . That is, the current blocking layer  18  has a trapezoid (tapered) shape in a cross section of the device. Such a shape prevents disconnection of the transparent electrode  14 , the p-electrode  16 , and the wire. More preferably, the inclination angle is 5° to 30°. 
     The thickness of the current blocking layer  18  is preferably larger than λ/(4n) (λ: emission wavelength, n: refractive index of current blocking layer  18 ). Sufficient insulation and reflecting function can be obtained by having a thickness larger than λ/(4n). More preferably, the thickness is 100 nm or more. The thickness of the current blocking layer  18  is preferably less than 1,500 nm. This is because when the thickness is larger than this, it may lead to a problem such as disconnection of the wire or the transparent electrode  14  and the p-electrode  15  due to step caused by the thickness. More preferably, the thickness is 500 nm or less. 
     The n-electrode  17  comprises a wire bonding portion  17   a , a wiring portion  17   b , and a contact portion  17   c  in the same as the p-electrode  16 , and each of them serves in the same as the p-electrode  16 . As shown in  FIG. 2 , the wire bonding portion  17   a  is located in the vicinity of the center of the end side opposite to the wire bonding portion  16   a . One linear wiring portion  17   b  extends along the longer side from the wire bonding portion  17   a , and is disposed between two linear wiring portions  16   b . The wire bonding portion  17   a  and the wiring portion  17   b  of the n-electrode  17  are formed of the same materials as those of the wire bonding portion  16   a  and the wiring portion  16   b  of the p-electrode  16 . The contact portion  17   c  is formed of the same materials as those of the contact portion  16   c.    
     In a region except for the wire bonding portion  16   a  of the p-electrode  16  and a region except for the wire bonding portion  17   a  of the n-electrode  17 , a protective film  20  is formed to prevent current short circuit. 
     As described above, in the Group III nitride semiconductor light-emitting device according to Embodiment 1, the current blocking layers  18  are provided in regions including the orthogonal projections of the contact portions  16   c  in plan view, and each of them is larger by 0 μm to 9 μm in width than each of the contact portion  16   c . Thus, there are the following three advantages. 
     The first advantage is that since each of the current blocking layer  18  is larger by 0 μm to 9 μm in width than each of the contact portion  16   c , light avoiding the current blocking layer  18  and being directed toward the contact portion  16   c  from an oblique direction is reduced, thereby improving emission performance. 
     The second advantage is that since the current blocking layers  18  are not provided in regions overlapping with the wire bonding portion  16   a  and the wiring portions  16   b , the emission performance is not impaired. 
     The third advantage is that even in a region where the reflective film  19  cannot be provided, absorption of light by the p-electrode  16  can be suppressed by the current blocking layer  18 . The contact portions  16   c  are provided to be connected to the wiring portions  16   b  via the holes  21  in a direction perpendicular to the main surface of the substrate. Therefore, the insulating film  15  cannot be provided between the transparent electrode  14  and the contact portion  16   c , and absorption of light by the p-electrode  16  cannot be suppressed by the reflective film  19  in the insulating film  15 . However, even in a region where the reflective film  19  cannot be provided, the current blocking layer  18  can be provided. Thus, absorption of light by the contact portion  16   c  can be suppressed by forming the current blocking layer  18  in such a region (i.e., region overlapping with the contact portion  16   c ), thereby improving emission performance. 
     Next will be described processes for producing the Group II nitride semiconductor light-emitting device according to Embodiment 1 with reference to  FIG. 8 . 
     Firstly, a sapphire substrate  10  having concaves and convexes thereon was prepared. Thermal cleaning was performed in a hydrogen atmosphere to remove impurities from the surface of the sapphire substrate  10 . 
     Subsequently, an n-type layer  11 , a light-emitting layer  12 , and a p-type layer  13  were sequentially deposited on the substrate  10  through MOCVD. The gases employed were as follows: TMG (trimethylgallium) as a Ga source; TMA (trimethylaluminum) as an Al source; TMI (trimethylindium) as an In source; ammonia as a nitrogen source; bis-cyclopentadienyl magnesium as a p-type dopant gas; and silane as an n-type dopant gas. Hydrogen or nitrogen was employed as a carrier gas. 
     Then, current blocking layers  18  were formed on the p-type layer  13 . The current blocking layers  18  were patterned by photolithography and wet etching after SiO 2  film was formed by vapor deposition or CVD. They may be patterned by photolithography, sputtering or vapor deposition, and the lift-off process. The current blocking layers  18  were formed only in regions including contact portions  16   c  of a p-electrode  16  being formed later, on the p-type layer  13 . Each of them was formed larger by 0 μm to 9 μm in width than the contact portion  16   c  (refer to  FIG. 8A ). 
     Subsequently, a transparent electrode  14  was formed on specific regions of the p-type layer  13  and the current blocking layers  18 . The transparent electrode  14  was patterned by photolithography and wet etching after the formation of an ITO film by sputtering. Thereafter, thermal cleaning was performed at 700° C. for 5 minutes in a nitrogen atmosphere at a reduced-pressure not higher than 10 Pa. The p-type layer  13  was converted, i.e., activated, to the p-type conduction, and the transparent electrode  14  was crystallized, thereby lowering the resistance. Thermal cleaning may be performed at a normal pressure. 
     Next, a specific portion of the p-type layer  13  was subjected to dry etching, to thereby form a groove so that the n-type layer  11  was exposed through the bottom of the groove. The contact portions  16   c  of the p-electrode  16  were formed in specific regions on the transparent electrode  14 , and the contact portions  17   c  of the n-electrode  17  were formed in specific regions on the n-type layer  11  exposed through the bottom of the groove (refer to  FIG. 8B ). The contact portions  16   c  and  17   c  were patterned by photolithography, vapor deposition and the lift-off process. The contact portions  16   c  and  17   c  may be separately formed. However, when the contact portions  16   c  and  17   c  are formed of the same material, the contact portions  16   c  and  17   c  may be formed simultaneously. Therefore, production processes can be simplified, and production cost can be reduced. Thereafter, thermal cleaning was performed at 550° C. for five minutes in a reduced-pressure oxygen atmosphere of 25 Pa, and the contact portions  16   c  and  17   c  were alloyed. 
     Subsequently, an insulating film  15  including the reflective film  19  therein was formed so as to cover the entire top surface ( FIG. 8C ). The insulating film  15  was formed as follows. Firstly, a first insulating film  15   a  was formed on the entire top surface by CVD. Then, reflective films  19  were formed on specific regions on the first insulating film  15   a  (corresponding to regions overlapping with the p-electrode  16  and the n-electrode  17  in plan view) by vapor deposition, photolithography, and etching. The reflective films  19  may be formed by the lift-off process. Next, second insulating film  15   b  was formed on the first insulating film  15   a  and on the reflective films  19 . The first insulating film  15   a  and the second insulating film  15   b  together formed an insulating film  15 , to thereby form the insulating film  15  including reflective films  19  in specific regions therein. 
     Subsequently, specific regions of the insulating film  15  (corresponding to the tops of the contact portions  16   c  and  17   c ) were subjected to dry etching, to thereby form holes  21  passing through the insulating film  15 . The contact portions  16   c  and  17   c  were exposed through the bottoms of the holes  21 . Then, a wire bonding portion  16   a  and wiring portions  16   b  of the p-electrode  16 , and a wire bonding portion  17   a  and wiring portions  17   b  of the n-electrode  17  were formed on regions of the insulating film  15  corresponding to the tops of the reflective films  19  by photolithography, vapor deposition and the lift-off process. Here, the wiring portions  16   b  and  17   b  were formed so as to fill the inside of the holes  21  so that the wiring portions  16   b  were connected to the contact portions  16   c  and the wiring portions  17   b  were connected to the contact portions  17   c  inside the holes  21  (refer to  FIG. 8D ). 
     Thereafter, a protective film  20  was formed on the entire top surface except for the wire bonding portions  16   a  and  17   a  by CVD, photolithography, and dry etching. Thus, the Group III nitride semiconductor light-emitting device according to Embodiment 1 was produced. 
     Next will be described the Experimental Examples.  FIGS. 3 to 5  show the result of how the emission performance varies depending on positions and width differences of the current blocking layers  18 . The difference in emission performance shown on the vertical axes of  FIGS. 3 to 5  was obtained from the comparison with the device having no current blocking layer  18 . Here, “the difference in emission performance” is defined as the emission performance of the light-emitting device having current blocking layers  18  minus the emission performance of the light-emitting device having no current blocking layer  18 .  FIG. 3  shows the case when the current blocking layers  18  are provided only in regions overlapping with the contact portions  16   c  in plan view,  FIG. 4  shows the case when the current blocking layers  18  are provided only in regions overlapping with the wiring portions  16   b  in plan view, and  FIG. 5  shows the case when the current blocking layer  18  is provided only in a region overlapping with the wire bonding portion  16   a  in plan view. The vertical axes of  FIGS. 3 to 5  indicate the difference in the emission performance when compared to the case when the current blocking layer  18  is not provided. The horizontal axes indicate the width differences, i.e., the width of the current blocking layer  18  minus the width of the contact portion  16   c.    
     As shown in  FIG. 3 , when the contact portion  16   c  and the current blocking layer  18  coincide in shape in plan view (i.e., when the width difference is 0 μm), the emission performance is improved by 0.15% compared with when the current blocking layer  18  is not provided. The larger the current blocking layer  18  than the contact portion  16   c , the more the emission performance is improved. When the width difference between the current blocking layer  18  and the contact portion  16   c  is 6 μm to 9 μm, the emission performance is increased by 0.30%, and almost saturated. When the width difference is 9 μm, the emission performance is slightly reduced than when the width difference is 6 μm. From this, it is considered that even if the current blocking layer  18  is larger by 9 μm in width than the contact portion  16   c , the emission performance is not improved, and non-emitting region of the light-emitting layer  12  is enlarged and conversely the emission performance is reduced. It is also considered that contact between the p-type layer  13  and the transparent electrode  14  is impaired. Therefore, it was found that the current blocking layer  18  is preferably larger by 0 μm to 9 μm in width than the contact portion  16   c , particularly preferably 3 μm to 9 μm, and further preferably 6 μm to 9 μm. 
     As shown in  FIG. 4 , when the wiring portion  16   b  and the current blocking layer  18  coincide in shape in plan view (when the width difference is 0 μm), and when the current blocking layer  18  is smaller than the wiring portion  16   b  (when the width difference is −3 μm), the difference in emission performance is almost 0. When the current blocking layer  18  is larger than the wiring portion  16   b , the emission performance is reduced. Therefore, it is better not to provide the current blocking layer  18  in a region overlapping with the wiring portion  16   b  in plan view. 
     The reason why the emission performance is reduced when the current blocking layer  18  is provided in a region overlapping with the wiring portion  16   b  in plan view, is as follows. Firstly, since the reflective films  19  and the insulating films  15  are formed directly below the wiring portion  16   b , less light from the light-emitting layer  12  is shielded by the wiring portion  16   b . Secondly, the non-emitting region is enlarged by the current blocking layer  18 . As a result, the deterioration of the emission performance is larger than the effect of reducing light, which is shielded by the wiring portion  16   b , by the current blocking layer  18 . 
     As shown in  FIG. 5 , when the current blocking layer  18  is provided only in the wire bonding portion  16   a , even if the width difference between the current blocking layer  18  and the wire bonding portion  16   a  varies, the difference in emission performance is not significantly changed, and only improved by 0.10% to 0.15%. This is considered as follows: Since the area of the wire bonding portion  16   a  is large, more light from the light-emitting layer  12  is shielded. The emission performance is improved due to reduction of light shielding by the current blocking layer  18 . However, when the width of the current blocking layer  18  is increased, the non-emitting region is enlarged, and thus the effect of improving emission performance is cancelled. Consequently, the emission performance is kept almost constant. Even if the current blocking layer  18  is provided in a region overlapping with the wire bonding portion  16   a , the effect of improving emission performance is small. Therefore, the current blocking layer  18  may not be provided in a region overlapping with the wire bonding portion  16   a , considering time or production cost. Needless to say, when time or cost is not a problem, the current blocking layer  18  may be provided in the wire bonding portion  16   a.    
     As is clear from the above results in  FIGS. 3 to 5 , the current blocking layers  18  are formed in regions including the contact portions  16   c  in plan view so that each of the current blocking layers  18  is larger by 0 μm to 9 in width μm than each of the contact portion  16   c . Preferably, the current blocking layers  18  are not formed in regions overlapping with the wire bonding portion  16   a  and the wiring portions  16   b.    
     Embodiment 2 
       FIG. 6  is a cross-sectional view of the structure of a Group III nitride semiconductor light-emitting device according to Embodiment 2. The Group III nitride semiconductor light-emitting device according to Embodiment 2 has the same structure as the Group III nitride semiconductor light-emitting device according to Embodiment 1, except that the reflective films are omitted in the insulating films  15 , the wiring portions  16   b  and  17   b  are respectively replaced with the wiring portions  216   b  and  217   b , each of which is formed of a high reflectance metal. A high reflectance metal may be formed of a metal material exhibiting a high reflectance (e.g., 80% or more) for light of emission wavelength of the Group III nitride semiconductor light-emitting device, such as Ag, Al, or Rh. Such use of high reflectance metal as wiring portions  216   b  and  217   b  suppresses absorption of light by the wiring portions  216   b  and  217   b  and improves light extraction performance of the device. 
     Similar to the case of Embodiment 1, the Group III nitride semiconductor light-emitting device according to Embodiment 2 also exhibits improved emission performance because the current blocking layers  18  are provided in regions including the contact portions  16   c  in plan view. 
     Embodiment 3 
       FIG. 9  is a cross-sectional view of the structure of the Group III nitride semiconductor light-emitting device according to Embodiment 3.  FIG. 10  is a top plan view of the structure of the Group III nitride semiconductor light-emitting device according to Embodiment 3.  FIG. 9  is a I-I cross-sectional view of  FIG. 10 . As shown in  FIGS. 9 and 10 , the Group III nitride semiconductor light-emitting device according to Embodiment 3 is a rectangular flip-chip-type device in plan view. 
     As shown in  FIG. 9 , the Group III nitride semiconductor light-emitting device according to Embodiment 3 includes a substrate  310 ; an n-type layer  311 , a light-emitting layer  312 , and a p-type layer  313  which are sequentially deposited on the sapphire substrate  310  via a buffer layer (not illustrated), and each of which is formed of a Group III nitride semiconductor. On the surface of the p-type layer  313 , there are provided holes  324  having a depth extending from the top surface of the p-type layer  313  to the n-type layer  311 . ITO transparent electrodes  314  are provided on almost entire surface other than regions having holes  324  of the p-type layer  313 . Current blocking layers  318  are provided in specific regions between the p-type layers  313  and the transparent electrodes  314 . Moreover, an insulating film  315  is provided so as to continuously cover the surface of the transparent electrodes  314 , the side surfaces and bottom surfaces of holes  324 . A p-electrode  316  and an n-electrode  317  are separately formed on the insulating film  315 . 
     The Group III nitride semiconductor light-emitting device according to Embodiment 3 is of a flip-chip type, in which reflective films  319  are enclosed with the insulating film  315 , and light is extracted by reflecting light to the substrate  310  by the reflective films  319 . Conductive films  323  are formed in regions directly above the reflective films  319  in the insulating film  315 . The conductive films  323  may be formed of an electrically conductive material, preferably a material with good adhesion to the insulating film  315 , for example, Al, Ti, Cr, or ITO. A part of the conductive films  323  is in contact with the transparent electrode  314  via holes  330  provided in the insulating film  315 . Although the conductive films  323  may be in contact with the transparent electrode  314  in any position, the area of the contact range is preferably as small as possible to prevent deterioration of light extraction performance due to the decrease of the areas of the reflective films  319 . The conductive films  323  may be partially in contact with the reflective films  319 . By providing such conductive films  323 , the transparent electrode  314  and the conductive films  323  have almost the same potentials. Therefore, since the reflective films  319  are located in the same potential regions between the n-electrode  317  and the transparent electrode  314  via the insulating film  315 , no electric filed is generated in the reflective films  319 , thereby preventing migration. 
     The p-electrode  316  comprises a connecting portion  316   a , a wiring portion  316   b , and a contact portion  316   c . The connecting portion  316   a  is a region which is connected to a solder layer  327 . The wiring portions  316   b  are regions formed in a wiring pattern continuous with the connecting portion  316   a . The insulating film  315  has holes  321  for passing through the insulating film  315  and exposing the transparent electrode  314 , and the wiring portions  316   b  are also formed inside the holes  321 . The contact portions  316   c  are circular regions provided on the transparent electrode  314 . The contact portions  316   c  are connected to the wiring portions  316   b  via the holes  321 . 
     Similar to the case of p-electrode  316 , the n-electrode  317  comprises a connecting portion  317   a , a wiring portion  317   b , and a contact portion  317   c . The contact portions  317   c  are circular regions provided on the n-type layer  311  exposed through the bottoms of the holes  324 . The insulating film  315  has holes  320  passing through regions for filling in the holes  324 , and the wiring portions  317   b  and the contact portions  317   c  are connected via the holes  320 . 
     As shown in  FIG. 10 , the wiring portions  316   b  and  317   b  are respectively formed in a comb pattern, and arranged so that the teeth are engaged with each other. 
     The tops of the p-electrode  316  and the n-electrode  317  are covered with a protective film  322 . The protective films  322  directly above the connecting portion  316   a  and the connecting portion  317   a  have respectively holes  329  and  328 . The solder layer  327  directly above the protective film  322  is connected to the connecting portion  316   a  via the holes  329 , and the solder layer  326  directly above the protective film  322  is connected to the connecting portion  317   a  via the holes  328 . 
     The current blocking layers  318  are located in regions including the orthogonal projections of the contact portions  316   c  in plan view. The current blocking layers  318  are circles concentric with the contact portions  316   c . The current blocking layers  318  are not provided in other part of the p-electrode  316  overlapping with the connecting portions  316   a  and the wiring portions  316   b . The planar shape of the current blocking layers  318  is larger by 0 μm to 9 μm in width than that of the contact portions  316   c . That is, the radius of the current blocking layer  318  is larger by 0 μm to 9 μm than that of the contact portion  316   c . The side surface  318   a  of the current blocking layer  18  is inclined to the p-type layer  313  at an angle of 5° to 60°, thereby preventing disconnection of the p-electrode  316  or the transparent electrode  314 . 
     Similar to the cases of the Group III nitride semiconductor light-emitting device according to Embodiments 1 and 2, the Group III nitride semiconductor light-emitting device according to Embodiment 3 also exhibits improved emission performance because the current blocking layers  318  are provided in regions including the orthogonal projections of the contact portions  316   c  in plan view. 
     Variation 
     In Embodiments 1 to 3, the current blocking layer may be formed on the p-type layer so that a part of or the entire current blocking layer is enclosed with the p-type layer, and particularly so that the surface of the current blocking layer and the surface of the transparent electrode are on the same level. A difference in level (step) is not caused by provision of the current blocking layer, thereby preventing disconnection of wire or electrode.  FIG. 7  shows the case when such a structure is employed in Embodiment 1. As shown in  FIG. 7 , the p-type layer  13  and the current blocking layers  18  are replaced with a p-type layer  413  having concave portions thereon and current blocking layers  418  for filling in the concave portions. With such a structure, the surface of the p-type layer  413  and the surfaces of the current blocking layers  418  are on the same level, and a transparent electrode  414  being formed thereon is a flat layer. In Embodiments 1 to 3, a part of or the entire current blocking layer may be enclosed with the transparent electrode. 
     In the Group III nitride semiconductor light-emitting devices according to Embodiments 1 to 3, the reflective films are formed in the insulating film. The reflective films may be omitted. 
     The Group III nitride semiconductor light-emitting device of the present invention can be employed as a light source of an illumination apparatus, or a display apparatus.