Abstract:
Provided is a nitride semiconductor light emitting diode and a method of manufacturing the same. The method includes sequentially forming a first semiconductor layer, an active layer, and a second semiconductor layer on a substrate, in-situ depositing a mask layer on a region of the surface of the second semiconductor layer, and selectively growing a third semiconductor layer formed in a textured structure on the second semiconductor layer by depositing a semiconductor material on the second semiconductor layer and the mask layer.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
       [0001]     Priority is claimed to Korean Patent Application No. 10-2004-0114343, filed on Dec. 28, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a semiconductor light emitting device, and more particularly, to a nitride semiconductor light emitting device that improves light extraction efficiency using a textured structure formed in-situ on a semiconductor layer of a nitride semiconductor structure, and a method of manufacturing the same.  
         [0004]     2. Description of the Related Art  
         [0005]     A light emitting diode (LED) is a device used for converting electrical energy to infra red rays, visible light, or other light using the characteristics of a compound semiconductor. The transformation of the electrical energy into optical energy can be divided into heat radiation and luminescence. The luminescence includes photoluminescence according to excitation by light, cathode luminescence generated by scanning X-rays or an electron beam, and electroluminescence (EL). Here, the light emitting diode is a kind of EL device, and presently, the most widely used light emitting diodes employ an III-V group compound semiconductor.  
         [0006]     The III-V group compound semiconductor is a direct transition semiconductor, and is widely used for the LED or a laser diode (LD) since it provides stable operation at a higher temperature than 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 the light emission efficiency, or light extraction efficiency, a variety of LED structures have been studied. One of these is a textured structure on a semiconductor layer on an upper part of an active layer of the LED.  
         [0007]      FIGS. 1A and 1B  are schematic drawings illustrating light paths at an interface of material layers having different refractive indexes. In  FIG. 1A , the material layer has a flat interface, and in  FIG. 1B , the material layer has a textured structure interface.  
         [0008]     Referring to  FIG. 1A , light passing from a first material layer  11  having a greater refractive index into an air layer  12  having a smaller refractive index (n=1) must enter a flat interface  13   a  at at least a predetermined angle. If the light enters at a smaller angle, the light is totally internally reflected at the flat interface  13   a,  resulting in the reduction of the light extraction efficiency. To avoid the total internal reflection of light, a method of using a non-flat interface has been attempted.  
         [0009]     Referring to  FIG. 1B , a non-flat interface, i.e. a textured structure interface  13 b, is formed between the first material layer  11  and the air layer  12 . Accordingly, the light has an angle of incidence greater than the predetermined angle at the textured structure interface  13   b  where the light passes from the first material layer  11  into the air layer  12 . Thus, the extraction efficiency of light can be improved.  
         [0010]      FIG. 2A  is a cross-sectional view of a conventional LED having the textured structure as described above. A p-electrode  2 , a p-GaN layer  23 , an InGaN active layer  24 , an n-GaN layer  25 , and an n-electrode  26  are sequentially formed on a lower structure  21 . Here, the textured structure  27  is formed on the surface of the n-GaN layer  25 . The textured structure  27  is formed to control the incidence angle for best extraction of light generated by the active layer  24  into the air layer through the n-GaN layer  25 , since GaN has a greater refractive index (n=2.5) than the air layer (n=1).  FIG. 2B  is a SEM image of the textured structure  27 , which is formed of a material such as H 3 PO 4  by wet etching.  
         [0011]     However, in the conventional art, to form the textured structure  27 , a chemical etching process must be additionally performed after a process for forming a semiconductor LED. Therefore, the manufacturing process is complicated, and productivity is reduced.  
       SUMMARY OF THE INVENTION  
       [0012]     Exemplary embodiments of the present invention provides a method of manufacturing a semiconductor light emitting diode having a textured structure for improving light extraction efficiency, wherein a process for manufacturing the semiconductor light emitting diode and a process for forming the textured structure are performed in-situ.  
         [0013]     According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor light emitting diode, comprising: sequentially forming a first semiconductor layer, an active layer, and a second semiconductor layer on a substrate; in-situ depositing a mask layer on a region of the surface of the second semiconductor layer; and selectively growing a third semiconductor layer formed in a textured structure on the second semiconductor layer by depositing a semiconductor material on the second semiconductor layer and the mask layer.  
         [0014]     The in-situ depositing of a mask layer on a region of the surface of the second semiconductor layer may comprise forming the mask layer by adding a Si source and an N source to the second semiconductor layer.  
         [0015]     The Si source may comprise at least one of silicon source such as triethylsilane(TESi), tributhy silane(TBSi), ditertiarybuthysilane(DTBSI) or silicon hydride sources such as silane(SiH 4 ), disilane(Si 2 H 6 ), TESi, TBSi, SiH 4 , or Si 2 H 6 .  
         [0016]     The N source may be NH 3 .  
         [0017]     The first semiconductor layer may be formed of an n-type semiconductor material, and the second semiconductor layer may be formed of a p-type semiconductor material.  
         [0018]     According to another aspect of the present invention, there is provided a semiconductor light emitting diode having a first semiconductor layer, an active layer, and a second semiconductor layer, comprising: a mask layer formed on the second semiconductor layer; and a third semiconductor layer formed in a textured structure on a surface of the second semiconductor layer on which the mask layer is not formed.  
         [0019]     The mask layer may be formed of a material that includes Si x N y . 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0021]      FIG. 1A  is a schematic drawing illustrating the extraction of light at a flat interface of material layers having different refractive indexes;  
         [0022]      FIG. 1B  is a schematic drawing illustrating the extraction of light at a textured structure interface of material layers having different refractive indexes;  
         [0023]      FIG. 2A  is a cross-sectional view of a conventional nitride semiconductor LED having a textured structure;  
         [0024]      FIG. 2B  is a SEM image of the textured structure;  
         [0025]      FIG. 3A  is cross-sectional view of a nitride semiconductor LED according to an embodiment of the present invention;  
         [0026]      FIG. 3B  is a cross-sectional view of the structure of the nitride semiconductor LED for improving light extraction efficiency;  
         [0027]      FIGS. 4A through 4C  are cross-sectional views for explaining a method of manufacturing a nitride semiconductor LED according to an embodiment of the present invention; and  
         [0028]      FIG. 4D  is a SEM image of a textured structure manufactured by the process for forming the nitride semiconductor LED of  FIGS. 4A through 4C . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.  
         [0030]      FIG. 3A  is cross-sectional view of a nitride semiconductor LED according to an embodiment of the present invention, and  FIG. 3B  is a cross-sectional view of the structure of the nitride semiconductor LED for improving light extraction efficiency. Referring to  FIGS. 3A and 3B , a first semiconductor layer  31 , an active layer  32 , and a second semiconductor layer  33  are sequentially formed on a substrate  30 . A mask layer  34  is formed on a region of the second semiconductor layer  33 . A third semiconductor layer  35  is formed on a region of the second semiconductor layer  33  in which the mask layer  34  is not formed. Also, a transparent electrode  36  is formed on the third semiconductor layer  35 , and a first electrode is formed on the transparent electrode  36 . A second electrode  38  is formed on the first semiconductor layer  31  on which the active layer  32  is not formed.  
         [0031]     Here, if the first semiconductor layer  31  is formed of a p-type semiconductor material, the second semiconductor layer  33  and the third semiconductor layer  35  are formed of an n-type semiconductor material. Also, if the first semiconductor layer  31  is formed of an n-type semiconductor material, the second semiconductor layer  33  and the third semiconductor layer  35  are formed of a p-type semiconductor material. The first semiconductor layer  31 , the active layer  32 , the second semiconductor layer  33 , and the third semiconductor layer  35  may all be formed of a nitride semiconductor material. The mask layer  34  is formed of nitride silicon having a chemical formula Si x N y .  
         [0032]     The third semiconductor layer  35  is formed on the second semiconductor layer  33  on which the mask layer  34  is not formed, and has a textured structure. In the case of the nitride semiconductor LED according to the present embodiment, the textured structure of the third semiconductor layer  35  can be formed by incorporating the mask layer  34 , and can increase the extraction efficiency of light generated by the active layer of the semiconductor LED.  
         [0033]     Hereinafter, a method of manufacturing a nitride semiconductor LED that can increase the light extraction efficiency according to an embodiment of the present invention will now be described with reference to  FIGS. 4A through 4C .  
         [0034]     Referring to  FIG. 4A , a first semiconductor layer  31 , an active layer  32 , and a second semiconductor layer  33  are sequentially formed on a substrate  30 . This structure can be formed using a conventional semiconductor manufacturing process, such as metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). In the MOCVD apparatus, on a substrate formed of GaSa, sapphire (Al 2 O 3 ), SiC, or Si, n-GaN is deposited as the first semiconductor layer  31 , InGaN is deposited as the active layer  32 , and p-GaN is epitaxy deposited as the second semiconductor layer  33 .  
         [0035]     Referring to  FIG. 4B , a mask layer  34  is formed on the second semiconductor layer  33 . At this time, the mask layer  34  is not formed on the entire surface of the second semiconductor layer  33 , but is formed in a region of the second semiconductor layer  33  in an island structure. The mask layer  34  is used as a device for forming the semiconductor LED of  FIG. 4A , and is preferably formed of Si x N y . The mask layer  34  will now be described in detail.  
         [0036]     After the second semiconductor layer  33  is formed in a reaction chamber of the MOCVD apparatus, raw materials of Si and N are added. For example, the raw material of Si can be silicon source such as triethylsilane(TESi), tributhy silane(TBSi), ditertiarybuthysilane(DTBSI) or silicon hydride sources such as silane(SiH 4 ), disilane(Si 2 H 6 ). The raw material of N can be NH 3  (ammonia). When Si and N are added to the reaction chamber of the MOCVD apparatus, SiN x  is produced. Here, the Si x N y  mask layer  34  is controlled to be formed in an island structure on regions of the second semiconductor layer  33  by controlling the amount of Si and N added to the reaction chamber of the MOCVD apparatus. The mask layer  34  is formed to a thickness in the range of from a few monolayers to 100 nm, which is very thin compared to the second semiconductor layer  33 . Consequently, the mask layer  34  is formed in an island structure on the second semiconductor layer  33 , and the second semiconductor layer  33  is exposed in the regions where the mask layer  34  is not formed.  
         [0037]     Referring to  FIG. 4C , a third semiconductor layer  35  is deposited on the second semiconductor layer  33 . Here, the third semiconductor layer  35  can be formed of the same material as the second semiconductor layer  33 . For example, both the second semiconductor layer  33  and the third semiconductor layer  35  can be formed of p-GaN.  
         [0038]     The third semiconductor layer  35  is only grown epitaxially on the second semiconductor layer  33 , not on the mask layer  34 . That is, the third semiconductor layer  35  grows in a preferential growth surface direction. As a result, as depicted in  FIG. 4C , the third semiconductor layer  35  grows only on the second semiconductor layer  33 , and not on the mask layer  34 . Consequently, the third semiconductor layer  35  can be grown with a textured structure. The epitaxial growth preferentially progresses upward from the surface of the second semiconductor layer  33 , and then progresses laterally above the mask layer  34 . The manufacturing of a semiconductor LED can be completed when a transparent electrode (not shown) is formed on the third semiconductor layer  35 .  
         [0039]     The textured structure shown in  FIG. 4C  corresponds to the conventional textured structure shown in  FIG. 2 , and improves the extraction efficiency of light generated by the active layer. In the method of manufacturing the semiconductor LED with improved light extraction efficiency according to the present invention, the textured structure can be readily formed in one process apparatus without an additional etching process, by forming the Si x N y  mask layer  34  on a region of the second semiconductor layer  33 .  
         [0040]      FIG. 4D  is a SEM image of a textured structure manufactured by the process for forming the nitride semiconductor LED of  FIGS. 4A through 4C . Referring to  FIG. 4D , the third semiconductor layer  35  is formed on the second semiconductor layer  33 , and the mask layer  34  is formed on the second semiconductor layer  33 .  
         [0041]     According to the present invention, a semiconductor LED having a textured structure can be manufactured in one manufacturing apparatus by combining a process for manufacturing a semiconductor device epitaxial growth and a process for manufacturing the textured structure on a semiconductor layer, instead of a conventional method in which the process for manufacturing the semiconductor device epitaxial growth and the process for manufacturing the textured structure are separately performed.  
         [0042]     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.