Abstract:
A light-emitting element includes a substrate, a light-emitting module and at least two electrodes. The light-emitting module is formed on the substrate. The at least two electrodes are formed on the light-emitting module. Exterior surfaces of the light-emitting module are separated into a first part and a second part. The first part is defined between the at least two electrodes and the light-emitting module. The second part includes exterior surfaces not contacting the at least two electrodes. The first part is smooth. At least a part of the second part is rough.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure relates in general to semiconductors, and more particular to a light-emitting element and fabrication method for the light-emitting element. 
         [0003]    2. Description of the Related Art 
         [0004]    Often, luminance of a light-emitting element is limited. Therefore, there is room for improvement in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Many aspects of the embodiments can be better understood with references to the following drawings. The components in the drawings are not necessary drawn to scale, the emphasis instead being placed upon clear illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout two views. 
           [0006]      FIG. 1  is a flowchart of a fabrication method for a light-emitting element in accordance with the disclosure. 
           [0007]      FIGS. 2-4  are schematic views of the fabrication method in  FIG. 1 . 
           [0008]      FIG. 5  is a cross-section of a first embodiment of a light-emitting element in accordance with the disclosure. 
           [0009]      FIG. 6  is a cross-section of a second embodiment of a light-emitting element in accordance with the disclosure. 
           [0010]      FIG. 7  is a cross-section of a third embodiment of a light-emitting element in accordance with the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessari to the same embodiment, and such references mean at least one. 
         [0012]    Referring to  FIGS. 1-4 , a fabrication method for a light-emitting element  100  in accordance with the disclosure is as follows. 
         [0013]    A light-emitting element  100  is provided. The light-emitting element  100  includes a substrate  10  and a light-emitting module  90 . In the first embodiment, the substrate  10  is sapphire. The light-emitting module  90  includes an N-type semi-conductive layer  20 , a light-emitting layer  30 , a P-type semi-conductive layer  40  and a diffusion layer  50 . The N-type semi-conductive layer  20 , the light-emitting layer  30  and the P-type semi-conductive layer  40  are Al x In y Ga 1-x-y N, wherein 0≦x≦1, 0≦y≦1 and x+y≦1. 
         [0014]    The N-type semi-conductive layer  20  is formed on the substrate  10  by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). 
         [0015]    The light-emitting layer  30  is formed between the N-type semi-conductive layer  20  and the P-type semi-conductive layer  40 . 
         [0016]    The diffusion layer  50  is transparent and formed on the P-type semi-conductive layer  40 . The diffusion layer  50  is configured for increasing current distribution to increase the luminance of the light-emitting element  100 . The diffusion layer  50  is Ni—Au alloy, Indium Tin Oxide (ITO), Indium Zinc. Oxide (IZO), Indium Tungsten Oxide (IWO), Indium Gallium Oxide (IGO) or a combination thereof. 
         [0017]    At least two electrodes are formed on the light-emitting module  90 . In the first embodiment, a P-type electrode  60  is formed on the diffusion layer  50 . An N-type electrode  70  is formed on the N-type semi-conductive layer  20 . When the light-emitting element is fabricated as a vertical-type, the N-type electrode  70  and the P-type electrode  60  can be formed on the opposite side surfaces thereof. The N-type electrode  70  and the P-type electrode  60  are formed by vapor deposition or sputtering deposition. 
         [0018]    A photoresist layer  200  is formed on exterior surfaces of the light-emitting module  90  and the P-type electrode  60  and the N-type electrode  70 . The photoresist layer  200  is Propylene Glycol Mono-methyl Ether Acetate (PGMEA), Polymethylmethacrylate (PMMA) or a combination thereof. In the first embodiment, the photoresist layer  200  is formed on an exterior surface  52  of the current diffusion layer  50 , an exterior surface  22  of the N-type semi-conductive layer  20 , and exterior surfaces of the P-type electrode  60  and the N-type electrode  70 . Optimally, thickness of the photoresist layer  200  is from 0.1 μm to 1 μm. 
         [0019]    The photoresist layer  200  is etched, and rough surfaces of the light-emitting element  100  obtained. Light from the light-emitting module  90  can be emitted by several reflections between the rough surfaces. The photoresist layer  200  is etched by inductively coupled plasma etcher (ICP etcher). When the photoresist layer  200  is heated, non-regular patterns are formed between photoresist layer  200  and the exterior surfaces of the light-emitting element  100 . Thus, roughness of the exterior surfaces of light-emitting element  100  is increased. 
         [0020]    In the first embodiment, the photoresist layer  200  is formed on the exterior surface  52  of the diffusion layer  50  and the exterior surface  22  of the N-type semi-conductive layer  20 , the exterior surfaces of the P-type electrode  60  and the N-type electrode  70 . The rough surfaces  452 ,  462 ,  472  are respectively formed on the exterior surface  52  of the current diffusion layer  50  and the exterior surface  22  of the N-type semi-conductive layer  20 , the exterior surfaces of the P-type electrode  60  and the N-type electrode  70 . 
         [0021]    When the photoresist layer  200  is etched, the rough surfaces of light-emitting element  100  are obtained. Light from the light-emitting element  100  can be reflected several times in the rough surfaces, increasing luminance of light-emitting element  100  considerably. 
         [0022]    Because the surface between the P-type electrode  60  and the P-type semi-conductive layer  40  and the surface between the N-type electrode  70  and the N-type semi-conductive layer  20  are not rough, electrical characteristics, such as leakage current and operation voltage, are not changed. 
         [0023]    Test data of 1000 light-emitting elements is shown in Table 1 and Table 2. The operation current of each light-emitting element is 350 mA. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Light-emitting element without rough surface 
               
             
          
           
               
                   
                 ITEM 
                 Min. 
                 Max. 
                 Average 
               
               
                   
                   
               
             
          
           
               
                   
                 Voltage (V) 
                 3.0 
                 4.0 
                 3.92 
               
               
                   
                 Luminance (mW) 
                 5.0 
                 300.0 
                 137.487 
               
               
                   
                 Wavelength (nm) 
                 300.0 
                 500.0 
                 398.26 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Light-emitting element of rough surface 
               
             
          
           
               
                   
                 ITEM 
                 Min. 
                 Max. 
                 Average 
               
               
                   
                   
               
             
          
           
               
                   
                 Voltage (V) 
                 3.0 
                 4.0 
                 3.94 
               
               
                   
                 Luminance (mW) 
                 5.0 
                 300.0 
                 164.551 
               
               
                   
                 Wavelength (nm) 
                 300.0 
                 500.0 
                 398.84 
               
               
                   
                   
               
             
          
         
       
     
         [0024]    Accordingly, luminance of the light-emitting element with rough surface increases effectively, electrical characteristics of the light-emitting element of rough surface, such as voltage and wavelength, are similar to those of the light-emitting element without rough surface, and mechanical structure of the light-emitting element is undamaged by forming the rough surface. 
         [0025]    Referring to  FIG. 5 , a light-emitting element  500  in accordance with a second embodiment of the disclosure differs from light-emitting element  100  only in that the photoresist layer  200  is formed on all exterior surfaces of the light-emitting element  500 , including upper surfaces and side surfaces of the light-emitting module  90 , except the substrate  10 . 
         [0026]    Referring to  FIG. 6 , a light-emitting element  600  in accordance with a third embodiment of the disclosure differs from light-emitting element  500  only in that protection layers are formed on the P-type electrode  60  and the N-type electrode  70  before the photoresist layer  200  is formed. According to the protection layers, upper surfaces  62 ,  72  of the P-type electrode  60  and the N-type electrode  70  are not rough when the photoresist layer  200  is etched. After the photoresist layer  200  is etched, the protection layers can be removed by chemical solutions. The protection layer is made of SiO 2 , Si 3 N 4  or a combination thereof. 
         [0027]    Referring to  FIG. 7 , a light-emitting element  700  in accordance with a fourth embodiment differs from light-emitting element  600  only in that a light diffusion surface  24  is formed between the N-type semiconductor layer  20  and the substrate  710 . The light diffusion surface  24  is configured for diffusing light emitted to the substrate  710 . Thus, the light from the light-emitting layer  30  can be utilized efficiently. The diffusion surface  24  is formed before forming the light emitting module on the substrate  710 . 
         [0028]    While the disclosure has been described by way of example and in terms of exemplary embodiment, it is to be understood that the disclosure is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.