Abstract:
A method of treating a substrate includes forming a plurality of nicks on an upper surface of the substrate by an electromagnetic wave without using a mask, wherein sidewalls of each nick have fusion formed thereon; roughening the sidewalls by removing the fusion; and forming an epitaxial multi-layer structure on the upper surface and the nicks. The roughened sidewalls of each nick comprise an average roughness equal to or larger than  1  nm.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a substrate and, more particularly, to a substrate for increasing the light-extraction efficiency of a semiconductor light-emitting device. 
     2. Description of the Prior Art 
     The current semiconductor light-emitting devices, such as light-emitting diodes, have been used for a wide variety of applications, e.g. illumination, remote control. To ensure high functional reliability as great as possible and a low power requirement of the semiconductor light-emitting devices, the external quantum efficiency is required for the devices. 
     In principle, the external quantum efficiency of a semiconductor light-emitting device is determined both by the internal quantum efficiency and extraction efficiency. The internal quantum efficiency is determined by the material property and quality. The extraction efficiency refers to the proportion of radiation emitted from the interior of the device into surrounding air or encapsulating epoxy. The extraction efficiency is determined by the losses occurred when radiation leaves the interior of the device. If a total reflection occurred when light is to be emitted out from the semiconductor light-emitting device, light would be reflected repeatedly until being absorbed in the interior of the device, which decreases the external quantum efficiency of the semiconductor light-emitting device. 
     In the prior art, a surface of a substrate of a semiconductor light-emitting device could be designed to exhibit a particular surface morphology for scattering light emitted out from the semiconductor light-emitting device to reduce the probability of the total reflection, further enhancing the external quantum efficiency of the semiconductor light-emitting device. However, the surface morphology of the above-mentioned substrate is generally formed by a dry etching process or a wet etching process. These processes not only consume much time but cost much. 
     Therefore, the main scope of the invention is to provide a substrate for epitaxy of a semiconductor light-emitting device, and the substrate is capable of enhancing the light-extraction efficiency of the semiconductor light-emitting device. 
     SUMMARY OF THE INVENTION 
     One scope of the invention is to provide a substrate and a fabricating method thereof for epitaxy of a semiconductor light-emitting device. 
     According to an embodiment of the invention, an upper surface of the substrate has a plurality of electromagnetic-wave-scribed nicks. The epitaxy of the semiconductor light-emitting device is to be performed on the upper surface of the substrate. 
     According to another embodiment of the invention is related to a method of treating a substrate. 
     By use of an electromagnetic wave without using a mask, the method scribes an upper surface of the substrate so that the upper surface of the substrate has a plurality of electromagnetic-wave-scribed nicks. The sidewalls of each nick have fusion formed thereon and then the sidewalls are roughened by removing the fusion. The epitaxial multi-layer structure is formed on the upper surface of the substrate. The roughened sidewalls of each nick comprise an average roughness equal to or larger than 1 nm. 
     Compared to the prior art, the substrate according to the invention is scribed by the electromagnetic wave to form a surface morphology such that light emitted from the semiconductor light-emitting device is scattered to reduce total reflection. Further, the external quantum efficiency and light-extraction efficiency of the semiconductor light-emitting device are enhanced. In particular, a conventional photolithography process is not required (i.e. mask-free) in the process of forming the surface morphology. Therefore, it takes much less time and reduces cost in the process of fabricating the substrate according to the invention. 
     The advantage and spirit of the invention may be understood by the following recitations together with the appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE APPENDED DRAWINGS 
         FIG. 1A  and  FIG. 1B  are the schematic diagrams of forming a substrate according to an embodiment of the invention. 
         FIG. 2A  to  FIG. 2C  are the top views of the substrate according to an embodiment of the invention. 
         FIG. 3A  and  FIG. 3B  are the schematic diagrams of the fusion sidewalls before and after removal of the substrate according to an embodiment of the invention, respectively 
         FIG. 4  is the schematic diagram of a substrate according to another embodiment of the invention. 
         FIG. 5  is the schematic diagram of a semiconductor light-emitting device according to an embodiment of the invention. 
         FIG. 6  is the schematic diagram of a semiconductor light-emitting device according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIG. 1A  and  FIG. 1B .  FIG. 1A  and  FIG. 1B  are the schematic diagrams of forming a substrate  1  according to an embodiment of the invention. The substrate  1  can be for epitaxy of a semiconductor light-emitting device. 
     In practical applications, the substrate  1  can be Si, GaN, AlN, sapphire, spinnel, SiC, GaAs, Al 2 O 3 , LiGaO 2 , LiAlO 2 , MgAl 2 O 4 . 
     An upper surface  10  of the substrate  1  has a plurality of electromagnetic-wave-scribed nicks  100 . The epitaxy of the semiconductor light-emitting device is to be performed on the upper surface  10  of the substrate  1 . In practical applications, the electromagnetic wave can be visible light, micro-wave, infrared, ultraviolet, laser or other energy sources capable of forming the nicks  100  on the upper surface  10  of the substrate  1 . 
     As shown in  FIG. 1A , in one embodiment, the electromagnetic wave can be a laser beam  12 . Thereby, the upper surface  10  of the substrate  1  can be scribed by the laser beam  12  to form the plurality of electromagnetic-wave-scribed nicks  100  as shown in  FIG. 1B . 
     Please refer to  FIG. 2A  to  FIG. 2C .  FIG. 2A  to  FIG. 2C  are the top views of the substrate  1  according to an embodiment of the invention. The focus and outline of the laser beam  12  can be adjusted by laser lens  14  (as shown in  FIG. 1A ) such that nicks  100  with specific patterns can be formed by the laser beam  12  on the upper surface  10  of the substrate  1 . For example, as shown in  FIG. 2A  to  FIG. 2C , the plurality of electromagnetic-wave-scribed nicks  100  can exhibit a circle, a trapezoid or a trace. 
     In practical applications, the plurality of electromagnetic-wave-scribed nicks  100  can exhibit various geometric or non-geometric patterns (i.e. not limited by the foregoing circle, trapezoid or trace) and can have particular radians or curvatures. The plurality of electromagnetic-wave-scribed nicks  100  can not only enhance the light-extraction efficiency of the semiconductor light-emitting device but also improve the epitaxy property of the semiconductor light-emitting device to enhance the opto-electronic effect thereof. 
     In one embodiment, the laser beam  12  (with a power of 25 mW and a wavelength of 248 nm or 193 nm) serving as the energy source can be focused to 5 um by the laser lens  14  to form nicks  100  with a diameter of 5 um and a pitch of 2 um on the surface of a sapphire substrate  1  with a diameter of 2 inches. 
     Please refer to  FIG. 3A . It is noted that after the upper surface  10  of the substrate  1  is scribed by the laser beam  12 , the plurality of nicks  100  can have fusion sidewalls  102 . Because the fusion sidewalls  102  are burned-black and not transparent, the fusion sidewalls  102  can be removed such that the sidewalls  102  of the plurality of nicks  100  are transparent. 
     Please refer to  FIG. 3A  and  FIG. 3B .  FIG. 3A  and  FIG. 3B  are the schematic diagrams of the fusion sidewalls  102  before and after removal of the substrate  1  according to an embodiment of the invention, respectively. In practical applications, the fusion sidewalls  102  can further be removed by a dry etching process or a wet etching process. As shown in  FIG. 3B , after the fusion sidewalls  102  are removed, the sidewalls  102  of the plurality of nicks  100  can exhibit a rough morphology. Thereby, the rough sidewalls  102  can enhance the light-extraction efficiency of the semiconductor light-emitting device. 
     Besides, after the fusion sidewalls  102  are removed, the substrate  1  can be placed in MOCVD equipment for epitaxy of a light-emitting diode. In one embodiment, with precursors of TMGa and NH 3 , an epitaxial layer of GaN which is about 1 um thick can be grown on the upper surface  10  of the substrate  1 . Subsequently, an n-type dopant SiH 4  can be added to grow a layer of n-type GaN which is about 2 um thick. Then, a multiple quantum well based light-emitting layer made of InGaN/GaN can be formed on the n-type GaN. Finally, a layer of p-type GaN with a p-type dopant Cp 2 Mg can be formed on the light-emitting layer to finish the light-emitting diode. 
     The light-emitting diode fabricated on the substrate  1  according to the invention can have a light output power of 19 mW, which is increased by 26.7%, compared to the light-emitting diode fabricated on a conventional substrate and having a light output power of 15 mW. 
     Please refer to  FIG. 4 .  FIG. 4  is the schematic diagram of a substrate  2  according to another embodiment of the invention. An upper surface  20  of the substrate  2  has a plurality of nicks  200 , and the sidewalls  202  of each nick  200  have an average roughness equal to or larger than 1 nm. Thereby, the nicks  200  and the rough sidewalls  202  thereof can enhance the light-extraction efficiency of the semiconductor light-emitting device. 
     In one embodiment, the nicks  200  can be formed by an electromagnetic wave. The electromagnetic wave can be visible light, micro-wave, infrared, ultraviolet, laser or other energy sources capable of forming the nicks  200  on the upper surface  20  of the substrate  2 . 
     Please refer to  FIG. 5 .  FIG. 5  is the schematic diagram of a semiconductor light-emitting device  3  according to an embodiment of the invention. As shown in  FIG. 5 , the semiconductor light-emitting device  3  includes a substrate  30 , a multi-layer structure  32 , and an ohmic electrode structure  34 . 
     An upper surface  300  of the substrate  30  has a plurality of electromagnetic-wave-scribed nicks  3000 . The multi-layer structure  32  is formed on the substrate  30  and includes a light-emitting region  320 . The ohmic electrode structure  34  is formed on the multi-layer structure  32 . 
     In practical applications, the electromagnetic wave can be visible light, micro-wave, infrared, ultraviolet, laser or other energy sources capable of forming the nicks  3000  on the upper surface  300  of the substrate  30 . 
     Please refer to  FIG. 6 .  FIG. 6  is the schematic diagram of a semiconductor light-emitting device  4  according to another embodiment of the invention. As shown in  FIG. 6 , the semiconductor light-emitting device  4  includes a substrate  40 , a multi-layer structure  42 , and an ohmic electrode structure  44 . 
     An upper surface  400  of the substrate  40  has a plurality of nicks  4000 , and the sidewalls  4002  of each nick  4000  have an average roughness equal to or larger than 1 nm. The multi-layer structure  42  is formed on the substrate  40  and includes a light-emitting region  420 . The ohmic electrode structure  44  is formed on the multi-layer structure  42 . 
     In one embodiment, the nicks  4000  can be formed by an electromagnetic wave. 
     Please refer to  FIG. 1A  and  FIG. 1B  again. According to another embodiment of the invention is related to a method of treating a substrate  1 . By use of an electromagnetic wave, the method scribes an upper surface  10  of the substrate  1  so that the upper surface  10  of the substrate  1  has a plurality of electromagnetic-wave-scribed nicks  100 . Afterwards, the epitaxy of a semiconductor light-emitting device is to be performed on the upper surface  10  of the substrate  1 . 
     Compared to the prior art, the substrate according to the invention is scribed by the electromagnetic wave to form a surface morphology such that light emitted from the semiconductor light-emitting device is scattered to reduce total reflection. Further, the external quantum efficiency and light-extraction efficiency of the semiconductor light-emitting device are enhanced. In particular, a conventional photolithography process is not required (i.e. mask-free) in the process of forming the surface morphology. Therefore, it takes much less time and reduces cost in the process of fabricating the substrate according to the invention. 
     With the example and explanations above, the features and spirits of the invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.