Patent Publication Number: US-2016225956-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, and more specifically to a Group III nitride semiconductor light-emitting device exhibiting an optimized arrangement of dot electrodes. 
     2. Background Art 
     Some Group III nitride semiconductor light-emitting devices have a plurality of dot electrodes arranged. As used herein, “dot electrode” encompasses an electrode in contact with a semiconductor layer in a dotted contact region. In a device, a plurality of dot electrodes are provided. The dot electrode has, for example, a circle or polygon contact region. Needless to say, the contact region may have other shape. The dot electrode, for example, includes a circle electrode with a diameter of 50 μm or less. Needless to say, an electrode having other shape with a different diameter may be used. By arranging a plurality of dot electrodes, electric current can be diffused particularly in the p-type semiconductor layer. Therefore, a technique has been developed, in which dot electrodes are discretely arranged on the light-emitting surface. 
     Japanese Patent Application Laid-Open (kokai) No. 2011-66304 discloses a light-emitting device in which dot electrodes are discretely arranged (refer to  FIG. 1 ). 
     In a light-emitting device using a rectangular substrate, the light-emitting surface is almost rectangular. In the light-emitting device having a rectangular light-emitting surface, it is not clear which dot electrode pattern is preferable. When the number of dot electrodes is excessively increased, the emission area is decreased. That is, the light emission amount is small. 
     Particularly when the length of the short sides of the rectangle is small, it is difficult to determine the dot electrode pattern. Since the light-emitting surface has a long narrow shape, the emission area becomes narrow depending on the dot electrode pattern. Therefore, the total radiant flux is preferably ensured without sacrificing the emission area. 
     SUMMARY OF THE INVENTION 
     The present invention has been conceived to solve the foregoing problems in the prior art. It is therefore an object of the present invention to provide a Group III nitride semiconductor light-emitting device exhibiting a large light emission amount in the case of a rectangular substrate. 
     In a first aspect of the present technique, there is provided a Group III nitride semiconductor light-emitting device, the light-emitting device comprising a rectangular substrate having a first long side, a second long side, a first short side, and a second short side; an n-type semiconductor layer on the substrate; a plurality of n-dot electrodes on the n-type semiconductor layer; a first line having a part of the n-dot electrodes arranged along the first long side; and a second line having a remaining part of the n-dot electrodes arranged along the second long side. A plurality of n-dot electrodes belong to either the first line or the second line. The n-dot electrodes belonging to the first line and the n-dot electrodes belonging to the second line are alternately arranged so as not to oppose each other. 
     The Group III nitride semiconductor light-emitting device has a plurality of n-dot electrodes. The plurality of n-dot electrodes belong to either the first line or the second line. Therefore, on the light-emitting surface, even if a p-dot electrode is arranged at a position most distant from an n-dot electrode, a distance between the p-dot electrode and the n-dot electrode is comparatively small. Thus, a sufficiently bright light-emitting device is achieved while electric current is effectively diffused. 
     A second aspect of the technique is directed to a specific embodiment of the Group III nitride semiconductor light-emitting device, wherein the first short side has a length of 400 μm or less. 
     A third aspect of the technique is directed to a specific embodiment of the Group III nitride semiconductor light-emitting device, wherein a distance between the n-dot electrodes which belong to the first line and are adjacent to each other is constant, and a distance between the n-dot electrodes which belong to the second line and are adjacent to each other is constant. 
     A fourth aspect of the technique is directed to a specific embodiment of the Group III nitride semiconductor light-emitting device, wherein when a first n-dot electrode and a second n-dot electrode which belong to the first line and are adjacent to each other are projected onto the second line, a third n-dot electrode belonging to the second line is arranged at a center position between the projected first n-dot electrode and the projected second n-dot electrode. 
     A fifth aspect of the technique is directed to a specific embodiment of the Group III nitride semiconductor light-emitting device, wherein a number of the n-dot electrodes belonging to the first line is an odd number, and a number of the n-dot electrodes belonging to the second line is an even number. 
     A sixth aspect of the technique is directed to a specific embodiment of the Group III nitride semiconductor light-emitting device, wherein a plurality of p-dot electrodes are provided, and the number of the p-dot electrodes is larger than that of the n-dot electrodes. 
     A seventh aspect of the technique is directed to a specific embodiment of the Group III nitride semiconductor light-emitting device, wherein the length of the first long side is twice or more the length of the first short side. 
     An eighth aspect of the technique is directed to a flip-chip type Group III nitride semiconductor light-emitting device. 
     The present technique, disclosed in the specification, provide a Group III nitride semiconductor light-emitting device with a large light emission amount when a substrate has a rectangular shape. 
    
    
     
       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 plan view showing the structure of a light-emitting device according to Embodiment 1; 
         FIG. 2  is a cross-sectional view showing the II-II cross-section of  FIG. 1 ; 
         FIG. 3  is a plan view showing dot electrode pattern B; 
         FIG. 4  is a plan view showing dot electrode pattern C; 
         FIG. 5  is a plan view showing dot electrode pattern D; 
         FIG. 6  is a sketch for describing a distance between p-dot electrode and n-dot electrode in the dot electrode pattern A; 
         FIG. 7  is a sketch for describing a distance between p-dot electrode and n-dot electrode in the dot electrode pattern B; 
         FIG. 8  is a sketch for describing a distance between p-dot electrode and n-dot electrode in the dot electrode pattern C; and 
         FIG. 9  is a sketch for describing a distance between p-dot electrode and n-dot electrode in the dot electrode pattern D. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     A specific exemplary embodiment of the semiconductor light-emitting device will next be described with reference to the drawings. However, the present invention is not limited to the embodiment. The layered structure and electrode structure of the semiconductor light-emitting device described later are examples only. Any layered structure different from that in the embodiment may be employed. The thicknesses of layers shown in the drawings are conceptual and are not their actual thicknesses. 
     Embodiment 1 
     1. Semiconductor Light-emitting Device 
       FIG. 1  is a plan view showing the structure of a light-emitting device  100  according to Embodiment 1.  FIG. 2  is a cross-sectional view showing the II-II cross-section of  FIG. 1 . The light-emitting device  100  is a flip-chip type semiconductor light-emitting device. As shown in  FIG. 2 , the light-emitting device  100  comprises a substrate  110 , an n-type contact layer  120 , an n-side cladding layer  130 , a light-emitting layer  140 , a p-side cladding layer  150 , a p-type contact layer  160 , an n-dot electrode ND (ND 7 ), a transparent electrode TE 1 , an insulating reflective layer IR 1 , a reflective layer R 1 , insulating layers I 1  and I 2 , a p-wiring electrode PW 1 , an n-wiring electrode NW 1 , and a p-electrode P 1 . 
     The substrate  110  is a sapphire substrate. The light emitted from the light-emitting layer  140  is transmitted therethrough to a side opposite to the semiconductor layers. The substrate  110  has a rectangular shape. The substrate  110  has a first long side S 1 , a second long side S 2 , a first short side J 1 , and a second short side J 2 . Needless to say, the length of the first long side S 1  is equal to that of the second long side S 2 . The length of the first short side J 1  is equal to that of the second short side J 2 . The length of the first short side J 1  and the second short side J 2  is within a range of 100 μm to 400 μm. The length of the first long side S 1  is two times to five times that of the first short side J 1 . 
     The n-type contact layer  120  is a semiconductor layer to make contact with the n-dot electrode ND. The n-type contact layer  120  is formed on the substrate  110 . A buffer layer (not illustrated) is preferably provided between the substrate  110  and the n-type contact layer  120 . The n-side cladding layer  130  is formed on the n-type contact layer  120 . The n-type contact layer  120  and the n-side cladding layer  130  are n-type semiconductor layers. 
     The light-emitting layer  140  is a semiconductor layer to recombine holes and electrons for light emission. The light-emitting layer  140  is formed on the n-side cladding layer  130 . 
     The p-side cladding layer  150  is formed on the light-emitting layer  140 . The p-type contact layer  160  is a semiconductor layer to make contact with the transparent electrode TE 1 . The p-type contact layer  160  is formed on the p-side cladding layer  150 . The p-side cladding layer  150  and the p-type contact layer  160  are p-type semiconductor layers. 
     A plurality of n-dot electrodes ND (ND 7 ) are electrodes to make contact with the n-type contact layer  120 . The codes of ND 1 , ND 2 , ND 3 , ND 4 , ND 5 , ND 6 , and ND 7  are assigned to the n-dot electrodes ND according to the arranged position. However, when the positions of the n-dot electrodes do not matter, the n-dot electrodes are collectively described as ND. The n-dot electrodes ND are formed on the n-type contact layer  120 . The n-dot electrode ND is made of a material such as Ti, Ni, and Cr. In order to increase the reflectance, Al, Ag, Rh, or alloy containing these may be used. Needless to say, other materials may be used. 
     The transparent electrode TE 1  is an electrode to make contact with the p-type contact layer  160 . The transparent electrode TE 1  is formed on the p-type contact layer  160 . The transparent electrode TE 1  is made of ITO. Instead of ITO, a transparent conductive oxide such as ICO, IZO, ZnO, TiO 2 , NbTiO 2 , and TaTiO 2  may be used. 
     The insulating reflective layer IR 1  is an insulating reflective layer. The insulating reflective layer IR 1  is formed on the transparent electrode TE 1 . The insulating reflective layer IR 1  has a plurality of through holes. The insulating reflective layer IR 1  is a DBR film having, for example, a multilayer of SiO 2  and TiO 2  alternately deposited. The layer IR 1  may be a single layer of SiO 2 . Needless to say, other materials may be used. 
     The reflective layer R 1  is a conductive reflective layer. The reflective layer R 1  is formed on the transparent electrode TE 1  and the insulating reflective layer IR 1 . The reflective layer R 1  is in contact with the transparent electrode TE 1  at the through holes of the insulating reflective layer IR 1 . Therefore, the through holes filled with the material of the reflective layer R 1  are the p-dot electrodes PD. The reflective layer R 1  is made of a material such as Al, Ag, and Rh, or alloy containing these. Needless to say, other materials may be used. 
     A plurality of p-dot electrodes PD are a part of the reflective layer R 1 . A plurality of p-dot electrodes PD are electrodes to be electrically conducted with the p-type contact layer  160 . A plurality of the p-dot electrodes PD are dispersively arranged on the light-emitting surface. The number of the p-dot electrodes PD is larger than that of the n-dot electrodes ND. 
     The insulating layers I 1  and I 2  are provided to insulate between the n-wiring electrode NW 1  and the p-wiring electrode PW 1 . Therefore, the insulating layer I 2  is formed so as to cover the n-wiring electrode NW 1 . The n-wiring electrode NW 1  is a wiring electrode to electrically connect the n-dot electrodes ND. The n-wiring electrode NW 1  is in contact with the n-dot electrode ND. The p-wiring electrode PW 1  is a wiring electrode to electrically connect the p-dot electrodes PD. The p-electrode P 1  is a land electrode to be actually bonded to an external circuit when mounting. The p-electrode P 1  is formed on the p-wiring electrode PW 1 . The insulating layers I 1  and I 2  are made of a material such as SiO 2 . Needless to say, other materials may be used. 
     2. Arrangement of n-dot Electrodes 
     As shown in  FIG. 1 , the light-emitting device  100  has seven n-dot electrodes ND 1 , ND 2 , ND 3 , ND 4 , ND 5 , ND 6 , and ND 7 . The light-emitting device  100  has a first line L 1  of the n-dot electrodes ND, and a second line L 2  of the n-dot electrodes ND. 
     In the first line L 1 , some of the n-dot electrodes ND are arranged along the first long side S 1 . The first line L 1  has the n-dot electrodes ND 1 , ND 2 , and ND 3 . That is, the first line L 1  has three, in other words, an odd number of n-dot electrodes. The n-dot electrodes ND 1 , ND 2 , and ND 3  belong to the first line L 1 . 
     In the second line L 2 , the others of the n-dot electrodes ND are arranged along the second long side S 2 . The second line L 2  has the n-dot electrodes ND 4 , ND 5 , ND 6 , and ND 7 . That is, the second line L 2  has four, in other words, an even number of n-dot electrodes. The n-dot electrodes ND 4 , ND 5 , ND 6 , and ND 7  belong to the second line L 2 . 
     A distance between the n-dot electrodes ND which belong to the first line L 1  and are adjacent to each other is constant. A distance between the n-dot electrodes ND which belong to the second line L 2  and are adjacent to each other is constant. 
     A plurality of the n-dot electrodes ND belong to either the first line L 1  or the second line L 2 . The n-dot electrodes ND belonging to the first line L 1  and the n-dot electrodes ND belonging to the second line L 2  are alternately arranged so as not to oppose each other. 
     For example, the center position between the n-dot electrode ND 1  belonging to the first line L 1  and the n-dot electrode ND 2  belonging to the first line L 1  is a point K 1 . The n-dot electrode ND 5  is disposed at a position which a perpendicular line K 2  dropped from the point K 1  toward the second line L 2  intersects the second line L 2 . 
     That is, in the case when the first n-dot electrode ND and the second n-dot electrode ND belonging to the first line L 1  and being adjacent to each other are projected onto the second line L 2 , the third n-dot electrode ND belonging to the second line L 2  is disposed at the center position between the projected first n-dot electrode ND and the projected second n-dot electrode ND. 
     3. Effect of the Present Embodiment 
     In this way, the light-emitting device  100  has n-dot electrodes ND alternately arranged in the first line L 1  and the second line L 2  on the rectangular substrate  110 . Such arrangement makes an average of main current paths shorter in pairs of the n-dot electrode ND and the p-dot electrode PD. As a result, the drive voltage of the light-emitting device can be reduced. Moreover, the periphery of the light-emitting device is an area where the luminance is small or no light is emitted. Since the n-dot electrodes ND are disposed on the outer circumference of the light-emitting surface, the n-dot electrodes ND do not sacrifice an effective light-emitting area so much. That is, in the light-emitting device  100 , a large effective light-emitting area is ensured. And, the light-emitting device  100  can uniformly emit light from the entire light-emitting surface. 
     4. Experiment 
     Next will be described the experiment of the light-emitting device  100  according to Embodiment 1. In the experiment, with the n-dot electrodes ND arranged in different patterns, total radiant flux Po, drive voltage Vf, and emission efficiency were compared. 
     4-1. Dot Electrode Pattern 
     In the experiment, a dot electrode pattern A, a dot electrode pattern B, a dot electrode pattern C, and a dot electrode pattern D were considered. 
       FIG. 1  shows the dot electrode pattern A. The dot electrode pattern A is the electrode arrangement according to Embodiment 1. That is, the dot electrode pattern A has the first line L 1  and the second line L 2 , and the n-dot electrodes ND of the first line L 1  and the n-dot electrodes ND of the second line L 2  are alternately arranged so as not to oppose each other. 
       FIG. 3  shows the dot electrode pattern B. The dot electrode pattern B has only the first line. The first line is disposed along the center line between the first long side S 1  and the second long side S 2 . That is, the n-dot electrodes ND are arranged along the center line. 
       FIG. 4  shows the dot electrode pattern C. The dot electrode pattern C has only the first line. The first line is disposed along the first long side S 1 . That is, the n-dot electrodes ND are arranged along the first long side S 1 . There is no n-dot electrode ND on the second long side S 2 . 
       FIG. 5  shows the dot electrode pattern D. The dot electrode pattern D has the first line and the second line. When the first line is projected onto the second line, the positions of the n-dot electrodes ND in the first line are overlapped with the positions of the n-dot electrodes ND in the second line. 
     4-2. Distance Between Dot Electrodes 
     Table 1 shows the patterns of n-dot electrodes ND and the characteristics. As shown in  FIG. 6 , in the dot electrode pattern A, the n-dot electrodes ND are arranged on the low-luminance outer circumference of the light-emitting surface. Therefore, one n-dot electrodes ND do not occupy a large effective light-emitting area. Thus, a large light-emitting area is ensured in the light-emitting device having the dot electrode pattern A. The n-dot electrodes closest to each of the p-dot electrodes PD are determined, and pairs of the p-dot electrode and the n-dot electrode are made. The maximum value of the distance between the p-dot electrode and the n-dot electrode in each pair is defined as a distance between the p-dot electrode and the n-dot electrode. More specifically, it will be described with reference to  FIGS. 6 to 9 . In  FIGS. 6 to 9 , the short side a of the light-emitting device and the half widths b of the distance between the dot electrodes are indicated. 
     As shown in  FIG. 7 , in the dot electrode pattern B, the n-dot electrodes ND are arranged along the high-luminance center line of the light-emitting surface. Therefore, the effective light-emitting area occupied by one n-dot electrode ND is larger than that in the dot electrode patterns A and C. The effective light-emitting area of the light-emitting device having the dot electrode pattern B is smaller than those of the light-emitting devices having the dot electrode patterns A and C. The distance between the p-dot electrode and the n-dot electrode in the dot electrode pattern B tends to be smaller than that in the dot electrode pattern A. 
     As shown in  FIG. 8 , in the dot electrode pattern C, similarly to the dot electrode pattern A, the n-dot electrodes ND are arranged at the end of the light-emitting surface. Therefore, one n-dot electrode ND does not occupy a large effective light-emitting area. Thus, a large effective light-emitting area is ensured in the light-emitting device having the dot electrode pattern C. However, the distance between the p-dot electrode and the n-dot electrode in the dot electrode pattern C is larger than that in the dot electrode pattern A. Therefore, the drive voltage Vf of the light-emitting device having the dot electrode pattern C is higher than that of the light-emitting device having the electrode pattern A, which is not preferable. In addition, the n-dot electrodes ND are not uniformly arranged on the entire light-emitting surface. Therefore, the light-emitting device having the dot electrode pattern C emits light a little nonuniformly. 
     As shown in  FIG. 9 , the dot electrode pattern D is similar to the dot electrode pattern A. Since the n-dot electrodes ND are arranged at the end of the light-emitting surface, one n-dot electrode ND does not occupy a large effective light-emitting area in the dot electrode pattern D. Therefore, a large effective light-emitting area is ensured in the light-emitting device having the dot electrode pattern D. However, since the distance between the p-doe electrode and the n-dot electrode in the dot electrode pattern D is larger than that in the dot electrode pattern A, the drive voltage Vf in the dot electrode pattern D is higher than that in the dot electrode pattern A. Thus, the dot electrode pattern A is more preferably than the dot electrode pattern D. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 A 
                 B 
                 C 
                 D 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Electrode 
                 Seven n-dot 
                 Seven n-dot 
                 Seven dot 
                 Six dot 
               
               
                 pattern 
                 electrodes 
                 electrodes 
                 electrodes 
                 electrodes 
               
               
                   
                 alternately 
                 arranged 
                 arranged at 
                 symmetrically 
               
               
                   
                 arranged at 
                 along the 
                 one end 
                 arranged at 
               
               
                   
                 both ends 
                 center line 
                   
                 both ends 
               
               
                 Light- 
                 Large 
                 Small 
                 Large 
                 Large 
               
               
                 emitting 
               
               
                 area (→ Po) 
               
               
                 Distance 
                 Small 
                 Very small 
                 Large 
                 Large 
               
               
                 between 
               
               
                 p-dot 
               
               
                 electrode 
               
               
                 and n-dot 
               
               
                 electrode 
               
               
                 (→ Vf) 
               
               
                   
               
            
           
         
       
     
     4-3. Measurement Results 
     Table 2 shows the measurement results. In the dot electrode pattern A, the total radiant flux Po was 29.53 (mW), and the drive voltage Vf was 2.80 (V). The emission efficiency was 52.7%. As used herein, the efficiency (%) refers to an ratio of output power (mW) to electric power (mW) applied to the light-emitting device  100 . 
     In the dot electrode pattern B, the total radiant flux Po was 28.96 (mW), and the drive voltage Vf was 2.80(V). The emission efficiency was 51.7%. 
     In the dot electrode pattern C, the total radiant flux Po was 29.56 (mW), and the drive voltage Vf was 2.81(V). The emission efficiency was 52.6%. 
     For the dot electrode pattern D, measurement was not performed. 
     As described above, in the dot electrode patterns A and C, the total radiant flux and the emission efficiency were higher than those in the dot electrode pattern B. In the light-emitting device having the dot electrode pattern A, light is more uniformly emitted from the entire light-emitting surface than in the light-emitting device having the dot electrode pattern C. Therefore, the dot electrode pattern A is most preferable. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 A 
                 B 
                 C 
                 D 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Tester results 
                 Po_medium 
                 29.53 
                 28.96 
                 29.56 
                 Not 
               
               
                 after separation 
                 Vf_medium 
                 2.80 
                 2.80 
                 2.81 
                 performed 
               
               
                   
                 Efficiency 
                 52.7% 
                 51.7% 
                 52.6% 
               
               
                   
               
            
           
         
       
     
     5. Variations 
     5-1. Definition of Line 
     In the present embodiment, the first line L 1  has three n-dot electrodes, and the second line L 2  has four n-dot electrodes. However, the first line L 1  and the second line L 2  are just a matter of definition, and may be exchanged. That is, the first line L 1  may have four n-dot electrodes and the second line L 2  may have three n-dot electrodes. Each of the first line L 1  and the second line L 2  may have a different number of n-dot electrodes from the number of the n-dot electrodes shown in  FIG. 1 . 
     5-2. Face-up Type 
     The light-emitting device  100  according to the present embodiment is a flip-chip type semiconductor light-emitting device. However, the technique of the present embodiment may be applied to a face-up type light-emitting device. 
     6. Summary of the Present Embodiment 
     As described above, the light-emitting device  100  according to the present embodiment is a semiconductor light-emitting device having a plurality of n-dot electrodes ND. In the light-emitting device  100 , a substrate  110  has a rectangular shape. The rectangular substrate  110  has a short side with a length of 400 μm or less. The light-emitting device  100  has a first line L 1  along the first long side S 1  and a second line L 2  along the second long side S 2 . The n-dot electrodes ND belonging to the first line L 1  and the n-dot electrodes ND belonging to the second line L 2  are alternately arranged so as not to oppose each other. Therefore, a bright light-emitting device  100  is achieved while the light emitting area is ensured. 
     The aforementioned embodiment is merely an example. It is therefore understood that those skilled in the art can provide various modifications and variations of the technique, so long as those fall within the scope of the present technique. The stacking structure of semiconductor layer or wiring should not be limited to those as illustrated, and the stacking structure, the thickness, and other factors may be arbitrarily chosen. The method for producing a light-emitting device  100  is not limited to metalorganic chemical vapor deposition (MOCVD), and other vapor phase epitaxy techniques and other liquid-phase epitaxy techniques may also be employed.