Abstract:
A semiconductor light emitting diode having a textured structure and a method of manufacturing the semiconductor light emitting diode are provided. The method includes forming a first semiconductor layer on a substrate; forming a textured structured first semiconductor layer by penetrating a material of a material layer into the first semiconductor layer after the material layer is formed on the first semiconductor layer and is annealed; and forming a second semiconductor layer on the first semiconductor layer.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2004-00117960, filed on Dec. 31, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The present invention relates to a semiconductor light emitting diode, and more particularly, to a semiconductor light emitting diode having a textured structure to improve the light extraction efficiency and a method of manufacturing the same. 
     2. Description of the Related Art 
     A light emitting diode (LED) is a device used for converting electrical energy into infra red rays, visible light, or other light using the characteristics of a compound semiconductor. The light emitting diode is a kind of electro luminescent (EL) device, and at the present time the light emitting diodes that employ an III-V group compound semiconductor are being practically used. 
     The III-V group compound semiconductor is a direct transition type semiconductor, and is widely used for LEDs or laser diodes (LDs) since it provides stable operation at a higher temperature than devices that use other semiconductors. The III-V group compound semiconductor is typically formed on a substrate formed of sapphire Al 2 O 3  or SiC. To improve light emission efficiency, or light extraction efficiency, LEDs having a variety of structures have been studied. Current studies utilize a textured structure on a light extraction region of the LED to improve the light extraction efficiency. 
     At an interface between material layers having different refractive indexes, the passing of light is interrupted by different refractive indexes of the material layers. In the instance of a flat interface, when light passes from a semiconductor layer having a greater refractive index (n=2.5) into an air layer having a smaller refractive index (n=1), the light must enter the flat interface at less than a predetermined angle with respect to the normal to the flat surface. If the light enters at an angle greater than the predetermined angle, the light internally reflects in its totality at the flat interface, thereby greatly reducing the light extraction efficiency. To avoid the total internal reflection of light, a method of incorporating a textured structure at the interface has been attempted. 
       FIGS. 1A and 1B  are cross-sectional views illustrating a conventional light emitting diode having a textured structure. Referring to  FIG. 1A , a p-GaN layer  102 , an active layer  103 , an n-GaN layer  104  are sequentially formed on a p-electrode  101 , and an n-electrode  105  is formed on the n-GaN layer  104 . When light generated by the active layer  103  is extracted upward through the n-GaN layer  104 , a textured structure  106  is incorporated at an interface between the n-GaN layer  104  and the air layer to change the incidence angle of the light. 
     Referring to  FIG. 1B , an n-GaN layer  112  is formed on a sapphire substrate  111 , and an n-AlGaN layer  113 , an active layer  114 , a p-AlGaN layer  115 , a p-GaN layer  116 , and a p-electrode  117  are sequentially formed on a region of the n-GaN layer  112 . An n-electrode  118  is formed on a region of the n-GaN layer  112  where the n-AlGaN layer  113  is not formed. This is a flip-chip structure in which light generated by the active layer  114  is primarily extracted through the transparent sapphire substrate  111 . Here, the light extraction efficiency is improved by forming a textured structure  120  on the surface of the sapphire substrate  111 . 
     A conventional semiconductor light emitting diode incorporates the textured structure  120  to improve the light extraction efficiency. However, particularly as depicted in  FIG. 1B , when the textured structure  120  is incorporated by patterning the sapphire substrate  111 , the growth of a uniform semiconductor layer on the sapphire substrate  111  is difficult because the unmatched crystal structure between the sapphire substrate  111  and the semiconductor layer is likely to cause defects in the semiconductor layer, thereby reducing the light extraction efficiency. 
     SUMMARY OF THE DISCLOSURE 
     The present invention may provide a semiconductor light emitting diode having a structure that can increase light extraction efficiency and reduce inter crystal defects of the semiconductor light emitting diode and a method of manufacturing the same. 
     According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor light emitting diode, comprising: forming a first semiconductor layer on a substrate; forming a textured structure first semiconductor layer by penetrating a material of a material layer into the first semiconductor layer after the material layer is formed on the first semiconductor layer and is annealed; and forming a second semiconductor layer on the first semiconductor layer. 
     The forming of a textured structured first semiconductor layer may comprise: forming a first material layer on the first semiconductor layer; forming a second material layer on the first material layer; and annealing to cause the materials of the first and second material layers to penetrate into the first semiconductor layer. 
     The first material layer may be formed of a material including one of Ni and Pd. 
     The second material layer may be formed of a material including one of Ag and Au. 
     The method may further comprise etching the first semiconductor layer to remove Au from the first semiconductor layer using aqua regia, after the materials of the first material layer and the second material layer have penetrated into the first semiconductor layer. 
     The forming of a textured structured first semiconductor layer may comprise annealing to cause the material layers to penetrate into defected regions of the first semiconductor layer after the material layers are formed. 
     The method may further comprise removing the material penetrated into the first semiconductor layer from the first semiconductor layer, depositing one of SiO 2  and SiN on the first semiconductor layer, and leaving SiO 2  or SiN only in the textured structure of the first semiconductor layer by treating a surface of the first semiconductor layer. 
     The annealing may be performed under a nitrogen atmosphere. 
     The method may further comprise annealing under an oxygen atmosphere after annealing under the nitrogen atmosphere. 
     The first semiconductor layer may be formed of a compound having a formula In x Al y Ga 1-x-y  N 1-x-y (0≦x≦1, 0≦y≦1, x+y≦1) undoped, doped with an n-type dopant, or doped with a p-type dopant. 
     The first semiconductor layer may have a thickness of approximately 10 nm to 5 μm. 
     According to another aspect of the present invention, there may be provided a semiconductor light emitting diode comprising: a first semiconductor layer formed in a textured structure; a material region which is formed between the textured structures of the first semiconductor layer and includes at least one metal selected from Ni, Pd, Au, and Ag; and a second semiconductor layer, an active layer, and a third semiconductor layer sequentially formed on the first semiconductor layer and the intermediate layer. 
     The first semiconductor layer may be formed of a compound having a formula In x Al y Ga 1-x-y  N 1-x-y (0≦x≦1, 0≦y≦1, x+y≦1) undoped, doped with an n-type dopant, or doped with a p-type dopant. 
     The first semiconductor layer may have a thickness of approximately 10 nm to 5 μm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention are described in detailed exemplary embodiments thereof with reference to the attached drawings in which: 
         FIGS. 1A and 1B  are cross-sectional views of conventional semiconductor light emitting diodes having a textured structure; 
         FIGS. 2 and 3  are cross-sectional views of semiconductor light emitting diodes having a textured structure according to an embodiment of the present invention; 
         FIGS. 4A through 4C  are cross-sectional views for illustrating a method of manufacturing a semiconductor light emitting diode according to an embodiment of the present invention; 
         FIGS. 5A through 5D  are cross-sectional views for illustrating a method of manufacturing a semiconductor light emitting diode according to another embodiment of the present invention; and 
         FIGS. 6A through 6E  are cross-sectional views for illustrating a method of manufacturing a semiconductor light emitting diode according to still another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present invention will now be described more fully with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. 
       FIGS. 2 and 3  are cross-sectional views of semiconductor light emitting diodes having a textured structure according to an embodiment of the present invention. In the detailed description of the present invention, a material region formed on a region between each of the textured shapes of a semiconductor layer having a textured structure is termed an intermediate layer. 
       FIG. 2  shows a textured structure applied to a flip-chip type semiconductor light emitting diode, and  FIG. 3  shows a textured structure applied to a vertical type semiconductor light emitting diode. The textured structure can be selectively formed, and the textured structure is commonly formed on a region where light generated by an active layer is emitted. 
     Referring to  FIG. 2 , a first semiconductor layer  22  and an intermediate layer  23  are formed on a transparent substrate  21  formed of sapphire Al 2 O 3 . Here, the first semiconductor layer  22  has a textured structure, and a second semiconductor layer  24  is formed on the first semiconductor layer  22 . An active layer  26 , a third semiconductor layer  27 , and a second electrode  28  are sequentially formed on a region of the second semiconductor layer  24 . A first electrode  25  is formed on another region of the second semiconductor layer  24  where the active layer  26  is not formed. 
     Hereafter exemplary materials for forming the layers are provided. The transparent substrate  21  can be a sapphire substrate, which is widely used. The first and second semiconductor layers  22  and  24  can be formed of a compound having a formula In x Al y Ga 1-x-y  N 1-x-y (0≦x≦1, 0≦y≦1, x+y≦1) undoped, doped with an n-type dopant, or doped with a p-type dopant. The intermediate layer  23  can be formed of an oxide containing at least one selected from Ni, Pf, Ag, and Au. The active layer  26  can be formed of a material typically used for forming a semiconductor laser diode in a multi-layer structure of a multi-quantum barrier structure. The third semiconductor layer  27  can be formed of a compound having a formula In x Al y Ga 1-x-y  N 1-x-y (0≦x≦1, 0≦y≦1, x+y≦1) undoped, doped with an n-type dopant, or doped with a p-type dopant. Here, when the first semiconductor layer  22  is formed of an n-type or p-type conductive material, the third semiconductor layer  27  is formed of a p-type material. The first electrode  25  is formed of an n-type or p-type conductive material, and the second electrode  28  is formed of a conductive material having the opposite polarity to the first electrode  25 . 
     As shown in  FIG. 2 , in the semiconductor light emitting diode according to an embodiment of the present invention, the textured structure has the intermediate layer  23  within a region where the first semiconductor layer  22  is patterned to a textured shape. The distances between the textured patterns of the first semiconductor layer  22  are not equal, but are determined by defects in the first semiconductor layer  22 , particularly by screw dislocations. The first semiconductor layer  22  may be formed to a thickness of approximately 10 nm to 5 μm. According to the structure of the semiconductor light emitting diode of  FIG. 2 , the crystal defects in the semiconductor light emitting diode can be reduced by forming the intermediate layer  23  on the defect region of the first semiconductor layer  22  and the second semiconductor layer  24  is formed on the first semiconductor layer  22  and the intermediate layer  23 . Also, the extraction efficiency of light generated by the active layer  26  to the outside can be increased by incorporating the textured structure. 
       FIG. 3  shows a vertical type semiconductor light emitting diode having a textured structure according to an embodiment of the present invention. Referring to  FIG. 3 , a second electrode  37 , a third semiconductor layer  36 , an active layer  35 , and a second semiconductor layer  34  are sequentially formed on a lower structure  38 . A first semiconductor layer  32  and an intermediate layer  33  patterned to a texturing shape are formed on the second semiconductor layer  34 . A first electrode  31  is formed on the first semiconductor layer  32  and the intermediate layer  33 . 
     Representative materials for forming the layers of the vertical type semiconductor light emitting diode as depicted in  FIG. 3  are indicated hereafter. The first semiconductor layer  32  and the second semiconductor layer  34  can be formed of a compound having a formula In x Al y GaN 1-x-y (0≦x≦1, 0≦y≦1, x+y≦1) undoped, doped with an n-type dopant, or doped with a p-type dopant. The intermediate layer  33  can be formed of a material including at least one metal selected from Ni, Pd, Au, and Ag. The active layer  35  can be formed of a material typically used for forming a semiconductor laser diode in a multi-layer structure of a multi-quantum barrier structure. The first electrode  31  and the second electrode  37  can be formed of a conductive material. 
     As shown in  FIG. 2 , the textured structure according to an embodiment of the present invention has the intermediate layer  33  within a region of the first semiconductor layer  32  patterned to the textured shape. Here, as in the flip-chip type device shown in  FIG. 2 , the distances between the textured patterns of the first semiconductor layer  32  are not equal, but are determined by defects in the first semiconductor layer  32 , particularly by screw dislocations. According to the structure of the semiconductor light emitting diode according to the embodiment of the present invention, crystal defects in the semiconductor light emitting diode can be reduced by forming the intermediate layer  33  on the defect region of the first semiconductor layer  32  with the second semiconductor layer  24  being formed on the intermediate layer  33 , and also the extraction efficiency of light generated by the active layer  35  to the outside can be increased by incorporating the textured structure. 
     A method of manufacturing a semiconductor light emitting diode having a textured structure according to an embodiment will now be described with reference to  FIGS. 4A through 4C . Processes for forming the textured structure of the semiconductor light emitting diode, which is an aspect of the present invention, will be described in detail. The descriptions of processes for forming an active layer and electrodes are omitted, since they are well known in the art. 
       FIGS. 4A through 4C  are cross-sectional views for illustrating a method of manufacturing a semiconductor light emitting diode according to an embodiment of the present invention. Referring to  FIG. 4A , a first semiconductor layer  42  is formed on a substrate  41 . Here, the substrate  41  is generally a sapphire substrate (refractive index n=1.78). The first semiconductor layer  42  is formed of a compound having a formula In x Al y GaN 1-x-y (0≦x≦1, 0≦y≦1, x+y≦1) undoped, doped with an n-type dopant, or doped with a p-type dopant to a thickness of approximately 10 nm to 5 μm. Next, a first material layer  44  and a second material layer  45  are formed on the first semiconductor layer  42 . The purpose of the first and second material layers  44  and  45  is to form the intermediate layer  23  or  33  of  FIGS. 2 and 3 , and the first and second material layers  44  and  45  can be formed of a material including at least one metal selected from Ni, Au, Ag, and Pd. Typically, crystal defects are generated in the first semiconductor layer  42  formed on the substrate  41 , with screw dislocations being formed perpendicular to the first semiconductor layer  42  on the substrate  41 . The screw dislocations are formed internally due to a crystal structure difference between the sapphire typically used for forming the substrate  41  and the first semiconductor layer  42  formed of GaN. 
     Next, referring to  FIG. 4B , a rapid thermal annealing (RTA) process is performed on the resultant product. The RTA process is preferably performed at a high temperature of approximately 800° C. under a nitrogen atmosphere. Low temperature annealing under an oxygen atmosphere can be selectively performed in addition to the RTA process. The annealing process causes the first and second material layers  44  and  45  to agglomerate and penetrate into the crystal defects  43  of the first semiconductor layer  42 . Thus, as depicted in  FIG. 4B , a structure in which the intermediate layer  46  is formed in the first semiconductor layer  42  can be obtained. The intermediate layer  46  becomes NiO and NiO/Ag. A Ga oxide formed by an oxidation process can also be included. The detailed technical descriptions have been disclosed in Morphology of Nickel and Nickel/Gold Contacts to Gallium Nitride by H. S. Venugopalan et. al, in J.Vac.Sci.Technol. A16(2), March/April 1998. 
     Next, as depicted in  FIG. 4C , a second semiconductor layer  47  is formed on the first semiconductor layer  42  and the intermediate layer  46 . At this time, the second semiconductor layer  47  is formed of a material having a crystal structure at least similar to that of the first semiconductor layer  42 , and is grown to coat both the first semiconductor layer  42  and the intermediate layer  46  by selectively growing from regions of the first semiconductor layer  42 . After the textured structure as described above is formed, elements of the semiconductor light emitting diode depicted in  FIG. 2 , such as an active layer and a third semiconductor layer, can be readily formed by conventional methods. 
     A process for forming a textured structure of a semiconductor light emitting diode according to another embodiment of the present invention will now be described with reference to  FIGS. 5A through 5D . 
     Referring to  FIG. 5A , a first semiconductor layer  52  is formed on a substrate  51 . The first semiconductor layer  52  is formed of In x Al y Ga 1-x-y  N 1-x-y (0≦x≦1, 0≦y≦1, x+y≦1) undoped, doped with an n-type dopant, or doped with a p-type dopant, to a thickness of approximately 10 nm to 5 μm. Next, first and second material layers  54  and  55  are formed on the first semiconductor layer  52 . The first and second material layers  54  and  55  can be formed of a material including at least one metal selected from Ni, Pd, Ag, and Au. Crystal defects such as dislocations are typically generated in the first semiconductor layer  52  formed on the substrate  51 , particularly screw dislocations, which affect the characteristics of the semiconductor light emitting diode. The crystal defects such as the screw dislocations are caused by the difference in crystal structure between the sapphire used for forming the substrate  51  and GaN used for forming the first semiconductor layer  52 . 
     Referring to  FIG. 5B , a rapid thermal annealing (RTA) process is performed on the resultant product. The RTA process is preferably performed at a high temperature of approximately 800° C. under a nitrogen atmosphere. Low temperature annealing under an oxygen atmosphere can be selectively performed in addition to the RTA process. The annealing process induces the first and second material layers  54  and  55  to agglomerate and penetrate into the crystal defects  53  of the first semiconductor layer  52 . Thus, as depicted in  FIG. 5B , a structure can be obtained in which an intermediate layer  56  is formed in the first semiconductor layer  52 . For example, when the first material layer  54  is formed of Ni and the second material layer is formed of Au, the intermediate layer  56  can be NiO (or NiO+Ga oxide)/Ag (or AuGu). 
     Next, as depicted in  FIG. 5C , Au can be selectively removed from the intermediate layer  56  by using aqua regia for example. This is because Au has a high light absorption rate and may adversely affect the characteristics of the semiconductor light emitting diode when used to form the second material layer  55 . 
     Also, as depicted in  FIG. 5D , a second semiconductor layer  57  is formed on the first semiconductor layer  52  and the intermediate layer  56 . At this time, the second semiconductor layer  57  is formed of a material having a crystal structure at least similar to that of the first semiconductor layer  52 , and is grown to coat both the first semiconductor layer  52  and the intermediate layer  56  by selectively growing from regions of the first semiconductor layer  52 . After the textured structure as described above is formed, elements of the semiconductor light emitting diode depicted in  FIG. 2 , such as an active layer and a third semiconductor layer, can be readily formed by conventional methods. 
     A process for forming a textured structure of a semiconductor light emitting diode according to still another embodiment of the present invention will now be described with reference to  FIGS. 6A through 6E . 
     Referring to  FIG. 6A , a first semiconductor layer  62  is formed on a substrate  61 . Here, the first semiconductor layer  62  is formed of a compound having a formula In x Al y Ga 1-x-y  N 1-x-y (0≦x≦1, 0≦y≦1, x+y≦1) undoped, doped with an n-type dopant, or doped with a p-type dopant to a thickness of approximately 10 nm to 5 μm. Next, first and second material layers  64  and  65  are formed on the first semiconductor layer  62 . The first and second material layers  64  and  65  can be formed of a material including at least one metal selected from Ni, Pd, Ag, and Au. Crystal defects such as dislocations are typically generated in the first semiconductor layer  62  formed on the substrate  61 , particularly, screw dislocations affect to the characteristics of the semiconductor light emitting diode. As described above, the crystal defects such as screw dislocations are caused by the difference in crystal structure between the sapphire used for forming the substrate  61  and the GaN used for forming the first semiconductor layer  62 . 
     Referring to  FIG. 6B , a rapid thermal annealing (RTA) process is performed on the resultant product. The RTA process is preferably performed at a high temperature of approximately 800° C. under a nitrogen atmosphere. Low temperature annealing under an oxygen atmosphere can be selectively performed in addition to the RTA process. The annealing process induces the first and second material layers  64  and  65  to agglomerate and penetrate into the crystal defects  63  of the first semiconductor layer  62 . Thus, as depicted in  FIG. 6B , a structure can be obtained in which an intermediate layer  66  is formed in the first semiconductor layer  62 . 
     Next, referring to  FIG. 6C , the intermediate layer  66  is removed by wet etching. By removing the entire intermediate layer  66 , only the first semiconductor layer  62  remains on the substrate  61 . 
     Referring to  FIG. 6D , a second intermediate layer  67  is formed by performing a planarizing process after SiO 2  or SiN is coated on the first semiconductor layer  62 . 
     Referring to  FIG. 6E , a second semiconductor layer  68  is formed on the first semiconductor layer  6  and the second intermediate layer  67 . At this time, the second semiconductor layer  68  is formed of a material having a crystal structure at least similar to that of the first semiconductor layer  62 , and is grown to coat both the first semiconductor layer  62  and the second intermediate layer  67  by selectively growing from regions of the first semiconductor layer  62 . After the textured structure as described above is formed, elements of the semiconductor light emitting diode depicted in  FIG. 2 , such as an active layer and a third semiconductor layer, can be readily formed by conventional methods. 
     Through the methods of manufacturing a semiconductor light emitting diode according to the embodiments of the present invention, a first semiconductor layer having a textured structure is formed on a light emitting region of the semiconductor light emitting diode. 
     According to the present invention, the extraction efficiency of light generated by an active layer can be greatly improved by forming a textured structure pattern in a semiconductor layer of the semiconductor light emitting diode, and stable operation can be achieved by reducing internal defects of the semiconductor device, thereby improving the lifespan of the semiconductor light emitting diode. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.