Abstract:
A method for manufacturing a semiconductor light-emitting device. The semiconductor light-emitting device has a substrate, and a semiconductor layer, a n-type semiconductor layer, and a p-type semiconductor layer successively formed atop the substrate. The method forms an intermediate layer having a predetermined pattern between the substrate and the semiconductor layer, or between the semiconductor layer and the n-type semiconductor layer, or between the n-type semiconductor layer and the p-type semiconductor layer. The p-type semiconductor layer has an uneven top layer due to the intermediate layer having a predetermined pattern and the total internal reflection of the LED can be reduced. The intermediate layer is a conductive material to reduce serial resistance of the LED.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing semiconductor light-emitting device, especially to a method for manufacturing semiconductor light-emitting device with high efficiency. 
     2. Description of the Related Art 
     Semiconductor light-emitting devices such as light-emitting diodes (LEDs) have high light emission, fast response speed and longer life than other conventional light source. Therefore, the LEDs are promising in lighting application, especially after the successful development of the high-brightness blue LED. 
     To enhance light-emitting efficiency, the LED can adopt a hetero-junction structure to improve the internal quantum efficiency thereof. However, the light emitted from an active layer of the LED is subjected to total internal reflection (TIR) between the active layer and an upper cladding layer, and between the upper cladding layer and an air interface due to refractive index mismatch. In particular, when the light passes from a medium with a higher refractive index to another medium with a lower refractive index as the light is emitted out, the TIR problem is inevitable, thus degrading the external quantum efficiency of the LED. 
       FIG. 1  illustrates a schematic, cross-sectional view of a homo-junction GaN-based LED  3 . The LED  3  comprises a sapphire substrate  300 , a buffer layer  302  on the sapphire substrate  300 , an n-type GaN layer  304  and a p-type GaN layer  306 , all successively formed on the buffer layer  302 . The LED  3  further comprises p-electrode  310  and n-electrode  308  for applying electric power thereto. After applying electric power to the LED  3 , light is emitted from an active layer (not label, shown as shaded layer). Part of the light (such as ray R 2 ) suffers TIR in the interface between the p-type GaN layer  306  and air and is reflected into the LED  3 , thus degrading the external quantum efficiency of the LED. This problem is irrelevant to the structure of active layer. Therefore, an LED with a hetero-junction structure, single quantum well (SQW) structure or multiple quantum well (MQW) structure also suffers this problem. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a method for manufacturing a semiconductor light-emitting device having high efficiency. 
     To achieve the above objects, the present invention provides a method for manufacturing a semiconductor light-emitting device, which includes the steps of: 
     providing a substrate; 
     providing a semiconductor layer atop the substrate; 
     providing an intermediate layer with predetermined pattern atop the semiconductor layer; 
     providing a first-conductive type semiconductor layer atop the intermediate layer, wherein the thickness of the first-conductive type semiconductor layer atop the intermediate layer and the thickness of the first-conductive type semiconductor layer not atop the intermediate layer are different;
         providing a second-conductive type semiconductor layer, the second-conductive type semiconductor layer having uneven top face due to the intermediate layer, thus reducing total internal reflection of the semiconductor light-emitting device.       

     To achieve the above objects, the present invention provides a method for manufacturing semiconductor light-emitting device, which includes the steps of: 
     providing a substrate; 
     providing a semiconductor layer atop the substrate; 
     providing a first-conductive type semiconductor layer atop the semiconductor layer; 
     providing an intermediate layer with predetermined pattern atop the first-conductive type semiconductor layer; 
     providing a second-conductive type semiconductor layer atop the intermediate layer, wherein the thickness of the second-conductive type semiconductor layer atop the intermediate layer and the thickness of the first-conductive type semiconductor layer not atop the intermediate layer are different, the second-conductive type semiconductor layer having uneven top face due to the intermediate layer, thus reducing total internal reflection of the semiconductor light-emitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
         FIG. 1  illustrates a schematic, cross-sectional view of a prior art GaN-based LED; 
         FIGS. 2A-2C  are schematic, cross-sectional views illustrating the steps of the method for manufacturing semiconductor light-emitting device according to a first preferred embodiment of the present invention; 
         FIGS. 3A-3D  depict the preferred examples of the intermediate layer; 
         FIGS. 4A-4B  depict the effect of the intermediate layer for layers thereon; 
         FIG. 5  depicts the effect of the intermediate layer for improving TIR; and 
         FIGS. 6A-6B  are schematic, cross-sectional sectional views illustrating the steps of the method for manufacturing semiconductor light-emitting device according to a second preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 2A-2C  are schematic, cross-sectional sectional views illustrating the steps of the method for manufacturing semiconductor light-emitting device according to a first preferred embodiment of the present invention. The first preferred embodiment of the present invention is exemplified with homo-junction LED. However, the method according to the present invention can also be applied to an LED with a hetero-junction structure, single quantum well (SQW) structure, or multiple quantum well (MQW) structure. 
     As shown in  FIG. 2A , after preparing a substrate  100  such as, for example, a sapphire substrate, a semiconductor layer  102  such as, for example, a GaN buffer layer is formed along a principle axis such as, for example, the C-axis of the substrate  100 . An intermediate layer  104  with predetermined pattern is formed atop the semiconductor layer  102  by deposition or other conventional film-forming process. The predetermined pattern of the intermediate layer  104  can be a striped pattern as shown in  FIG. 3A , a dotted pattern as shown in  FIG. 3B , a rectangular pattern as shown in  FIG. 3C  or a hexagonal pattern as shown in FIG.  3 D. In the preferred embodiment shown in  FIG. 2A , the intermediate layer  104  has a striped pattern. The intermediate layer  104  can be an insulating material such as SiO 2 , Si 3 N 4 , or a conductive material such as metal or conductive oxide such as ITO. The intermediate layer  104  can be patterned by a suitable mask layer and photolithography process after a layer of insulating material or conductive material is formed. The pattern defining and etching skill is well known in related art and is not stated in detail here. 
     As shown in  FIG. 2B , an n-type semiconductor layer  106  is formed atop the intermediate layer  104  by epitaxial technology such as MOCVD or VPE. The n-type semiconductor layer  106  can be, for example, a GaN layer doped with Si. The patterned intermediate layer  104  provides an uneven top surface on the semiconductor layer  102 . The n-type semiconductor layer  106  is grown not only along the principle C-axis of the substrate  100  but also along other axes of GaN crystal such as an S-axis, and the growth rates along different direction are different for the n-type semiconductor layer  106 . The n-type semiconductor layer  106  has a higher growth rate on the surface of the semiconductor layer  102  exposed by the patterned intermediate layer  104 . Therefore, the n-type semiconductor layer  106  has a ridged cross section as shown in FIG.  4 A. The top face of the n-type semiconductor layer  106  has a plurality of ridges  1060 , each of the ridges  1060  has two inclined faces  1062 .  FIG. 4B  shows the perspective view of the n-type semiconductor layer  106  when the intermediate layer  104  has dot shaped pattern. As shown in this figure, the n-type semiconductor layer  106  has sphere-like projections  1064  on top face thereof. In a word, the n-type semiconductor layer  106  has an uneven top face due to the roughness provided by the patterned intermediate layer  104 . 
     As shown in  FIG. 2C , a p-type semiconductor layer  108  is formed atop the n-type semiconductor layer  106 . The p-type semiconductor layer  108  can be, for example, a GaN layer doped with Mg. The p-type semiconductor layer  108  is formed atop the uneven n-type semiconductor layer  106  and still has uneven top face  1080  with inclined faces  1082 . Finally, a p-electrode (not shown) and an n-electrode (not shown) are formed on resulting structure to complete the LED. 
     As shown in  FIG. 5 , if the p-type semiconductor layer  108  has uneven top face such as a spherical top face, most light emitted from the p/n junction of the LED has incident angles less than the critical angle for LED-air interface. The external quantum efficiency of the LED can be enhanced. The efficiency and life of the LED can be further enhanced if the intermediate layer  104  adopts a conductive material to reduce series resistance of the LED. 
       FIGS. 6A-6B  are schematic, cross-sectional views showing the steps of the method for manufacturing a semiconductor light-emitting device according to a second preferred embodiment of the present invention. The second preferred embodiment of the present invention is exemplified with an MQW LED. However, the method according to the present invention can also be applied to an LED with a hetero-junction structure or a single quantum well (SQW) structure. 
     As shown in  FIG. 6A , after preparing a substrate  200  (such as a sapphire substrate), a semiconductor layer  202  such as a GaN buffer layer is formed along a principle axis such as a C-axis of the substrate  200 . An n-type semiconductor layer  206  is formed atop the semiconductor layer  202  by epitaxial technology such as MOCVD or VPE. The n-type semiconductor layer  206  can be, for example, a GaN layer doped with Si. A MQW layer  205 , such as an InGaN MQW layer, is formed atop the n-type semiconductor layer  206 . An intermediate layer  204  with predetermined pattern is formed atop the MQW layer  205  by deposition or another conventional film-forming process. The predetermined pattern of the intermediate layer  204  can be striped, dotted, rectangular, or hexagonal in shape. In the example shown in  FIG. 6A , the predetermined pattern of the intermediate layer  204  is a striped pattern. The intermediate layer  204  can adopt insulating material such as SiO 2 , Si 3 N 4 , or conductive material such as metal or conductive oxide such as ITO. The intermediate layer  204  can be patterned by a suitable mask layer and photolithography process after a layer of insulating material or conductive material is formed. The pattern defining and etching skill is well known in related art and is not stated in detail here. 
     As shown in  FIG. 6B , a p-type semiconductor layer  208  is formed atop the patterned intermediate layer  204 . The p-type semiconductor layer  208  can be, for example, a GaN layer doped with Mg. The p-type semiconductor layer  208  is formed atop the uneven intermediate layer  204 . The p-type semiconductor layer  208  is grown not only along the principle C-axis of the substrate  200  but also along another axis of GaN crystal such as the S-axis, and the growth rates in different directions are different for the p-type semiconductor layer  208 . The p-type semiconductor layer  208  has a higher growth rate on the surface of the MQW layer  205  uncovered by the patterned intermediate layer  204 . Therefore, the p-type semiconductor layer  208  has a ridge shaped cross-section as shown in FIG.  6 B. The top face of the p-type semiconductor layer  208  has a plurality of ridges  2080  and each of the ridges  2080  has two inclined faces  2082 . Finally, a p-electrode (not shown) and an n-electrode (not shown) are formed on resulting structure to complete the LED. 
     Similarly, if the p-type semiconductor layer  208  has an uneven top face such as a spherical top face, most light emitted from MQW layer  205  of the LED has incident angles less than the critical angle for LED-air interface. The external quantum efficiency of the LED can be enhanced. The efficiency and life of the LED can be further enhanced if the intermediate layer  204  adopts a conductive material to reduce series resistance of the LED. 
     Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have suggested in the foregoing description, and others will occur to those of ordinary skill in the art. For example, the intermediate layer can also be provided between the substrate and the semiconductor layer and can be adopted other material. The substrate can be other substrate such as GaAs. The semiconductor layer is a GaN layer or an AIN layer. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.