Abstract:
A nitride semiconductor light-emitting device with an electron pattern that applies current uniformly to an active layer to improve light emission efficiency is provided. The nitride semiconductor light-emitting device includes multiple layers of a substrate, an n-type nitride layer, an active layer of a multi-quantum-well structure, and a p-type nitride layer. The nitride semiconductor light-emitting device further includes a p-electrode pattern and an n-electrode pattern. The p-electrode pattern includes one or more p-pads disposed on the p-type nitride layer, and one or more p-fingers extending from the p-pads. The n-electrode pattern includes one or more n-pads disposed on an exposed region of the n-type nitride layer to correspond to the p-pads, and one or more n-fingers extending from the n-pads. The n-fingers have identical resistance, and the p-fingers have identical resistance to improve current spreading to the active layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 2007-134581 filed on Dec. 20, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a nitride semiconductor light-emitting device, and more particularly, to a nitride semiconductor light-emitting device with an electron pattern that applies current uniformly to an active layer to improve light emission efficiency. 
         [0004]    2. Description of the Related Art 
         [0005]    A light-emitting diode (LED) is a nitride semiconductor light-emitting device that emits light by recombination of electrons and holes. LEDs are widely used as light sources in optical communication devices, electronic devices, and the like. 
         [0006]    In an LED, the frequency (or wavelength) of emitted light is a function of a band gap of a material of the semiconductor device. That is, an LED formed of a semiconductor material with a narrow band gap emits photons of low energy and long wavelengths. Conversely, an LED formed of a semiconductor material with a wide band gap emits photons of short wavelengths. 
         [0007]    For example, aluminum gallium indium phosphide (AlGaInP) generates light in the red wavelength range, and silicon carbide (SiC) and a group III nitride-based semiconductor, particularly gallium nitride (GaN), generate light in the blue or ultraviolet wavelength range. 
         [0008]    Among these, a gallium-based LED requires a substrate, typically a sapphire substrate, which is appropriate for crystal growth of the gallium nitride (GaN) because it is impossible to form a bulk single crystal of the gallium nitride (GaN). 
         [0009]      FIG. 1A  is a plan view of a related art flip-chip type nitride LED, and  FIG. 1B  is a cross-sectional view taken along line A-A in  FIG. 1A . An exemplary method for fabricating the related art LED  20  is as follows. A buffer layer  22 , an n-type gallium nitride (GaN) clad layer  23 A, an active layer  23 B, and a p-type gallium nitride (GaN) clad layer  23 C are sequentially formed on a sapphire substrate  21 . A dry etching is performed on the active layer  23 B and the p-type gallium nitride (GaN) clad layer  23 C to expose a portion of the n-type gallium nitride (GaN) clad layer  23 A. An n-electrode  26  is formed on the exposed portion of the n-type gallium nitride (GaN) clad layer  23 A. A transparent electrode  24  is formed on the p-type gallium nitride (GaN) clad layer  23 C, and a p-electrode  25  is formed on the transparent electrode  24 . 
         [0010]    Then, micro-bumps  27  and  28  are formed of gold (Au) or a gold alloy on the p-electrode  25  and the n-electrode  26 , respectively. 
         [0011]    The LED  20  is mounted on amount substrate, a lead frame or the like by flipping the LED  20  of  FIG. 1B  and bonding the micro-bumps  27  and  28  of the LED  20  thereto. 
         [0012]    The related art LED has been improved in terms of the light emission efficiency by forming an irregular surface of the active layer or by reducing the size of the electrode to increase the light-emitting area. However, these approaches have certain limitations that lead to processing difficulties. 
         [0013]    Particularly, the n-electrode of a vertical type nitride LED must be decreased in size because it is disposed on a surface for emitting light. However, decreasing the size of the n-electrode is accompanied by an increased driving voltage and a reduced current spreading effect, which can render the active layer for emitting light useless. 
       SUMMARY OF THE INVENTION 
       [0014]    An aspect of the present invention provides a nitride semiconductor light-emitting device with an electrode pattern that improves current spreading to an active layer. 
         [0015]    According to an aspect of the present invention, there is provided a nitride semiconductor light-emitting device with multiple layers of a substrate, an n-type nitride layer, an active layer of a multi-quantum-well structure, and a p-type nitride layer, the nitride semiconductor light-emitting device including: a p-electrode pattern including one or more p-pads disposed on the p-type nitride layer, and one or more p-fingers extending from the p-pads; and an n-electrode pattern including one or more n-pads disposed on an exposed region of the n-type nitride layer to correspond to the p-pads, and one or more n-fingers extending from the n-pads, wherein the n-fingers have identical resistance, and the p-fingers have identical resistance to improve current spreading to the active layer. 
         [0016]    Each of the p-fingers may satisfy the following relation, 
         [0000]    
       
      
       R=ρL/A,  
      
     
         [0000]    where R, ρ, L and A are a resistance, a resistivity, a length, and a cross-sectional area of the p-finger, respectively, so that the cross-sectional area is proportional to the length L. 
         [0017]    The p-fingers may include: a first p-finger having a first length and a first cross-sectional area; and a second p-finger having a second length greater than the first length, wherein a second cross-sectional area A 2  of the second p-finger satisfies the following relation, 
         [0000]    
       
         
           
             
               
                 
                   L 
                    
                   
                       
                   
                    
                   1 
                 
                 
                   A 
                    
                   
                       
                   
                    
                   1 
                 
               
               = 
               
                 
                   L 
                    
                   
                       
                   
                    
                   2 
                 
                 
                   A 
                    
                   
                       
                   
                    
                   2 
                 
               
             
             , 
           
         
       
     
         [0000]    where L 1 , L 2 , A 1  and A 2  are the first length, the second length, the first cross-sectional area and the second cross-sectional area, respectively. 
         [0018]    Each of the n-fingers may satisfy a relation, R=ρL/A, where R, ρ, L and A are a resistance, a resistivity, a length, and a cross-sectional area of the n-finger, respectively, so that the cross-sectional area is proportional to the length L. 
         [0019]    The n-fingers include: a first n-finger having a first length and a first cross-sectional area; a second n-finger having a second length greater than the first length; and a third n-finger having a third length greater than the second length, wherein a second cross-sectional area of the second p-finger and a third cross-sectional area of the third p-finger satisfy the following relation, 
         [0000]    
       
         
           
             
               
                 
                   L 
                    
                   
                       
                   
                    
                   11 
                 
                 
                   A 
                    
                   
                       
                   
                    
                   11 
                 
               
               = 
               
                 
                   
                     L 
                      
                     
                         
                     
                      
                     12 
                   
                   
                     A 
                      
                     
                         
                     
                      
                     12 
                   
                 
                 = 
                 
                   
                     L 
                      
                     
                         
                     
                      
                     13 
                   
                   
                     A 
                      
                     
                         
                     
                      
                     13 
                   
                 
               
             
             , 
           
         
       
     
         [0000]    where L 11 , L 12 , L 13 , A 11 , A 12  and A 13  are the first length, the second length, the third length, the first cross-sectional area, the second cross-sectional area and the third cross-sectional area, respectively. 
         [0020]    The nitride semiconductor light-emitting device may have a horizontal type structure, and the n-fingers and the p-fingers may be disposed alternatingly and have at least one bent section, respectively. 
         [0021]    According to another aspect of the present invention, there is provided a nitride semiconductor light-emitting device including: an active layer having a multi-quantum-well structure between an n-type nitride layer and a p-type nitride layer; a p-electrode pattern including one or more p-pads disposed on the p-type nitride layer, and one or more p-fingers extending from the p-pads; and an n-electrode pattern including one or more n-pads disposed on an exposed region of the n-type nitride layer, and one or more n-fingers extending from the n-pads, wherein the n-fingers have identical resistance, and the p-fingers have identical resistance to improve current spreading to the active layer. 
         [0022]    The p-fingers or the n-fingers may include a plurality of fingers extending alternately and radially. 
         [0023]    The n-fingers or the p-fingers each may have at least one bent section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0025]      FIG. 1A  is a plan view of a related art nitride light-emitting diode (LED); 
           [0026]      FIG. 1B  is a cross-sectional view taken along the line A-A of  FIG. 1A ; 
           [0027]      FIG. 2  is a schematic view of electrode patterns of a horizontal type nitride semiconductor light-emitting device according to an embodiment of the present invention; 
           [0028]      FIG. 3  is a schematic view of electrode patterns of a horizontal type nitride semiconductor light-emitting device according to another embodiment of the present invention; 
           [0029]      FIG. 4  is a schematic view of electrode patterns of a horizontal type nitride semiconductor light-emitting device according to still another embodiment of the present invention; 
           [0030]      FIG. 5  is a schematic view of an electrode pattern of a vertical type nitride semiconductor light-emitting device according to even another embodiment of the present invention; 
           [0031]      FIG. 6  is a schematic view of an electrode pattern of a vertical type nitride semiconductor light-emitting device according to yet another embodiment of the present invention; and 
           [0032]      FIG. 7  is a schematic view of an electrode pattern of a vertical type nitride semiconductor light-emitting device according to further another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0033]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0034]      FIG. 2  is a schematic view of electrode patterns of a horizontal type nitride semiconductor light-emitting device according to an embodiment of the present invention.  FIG. 2  illustrates a p-electrode pattern disposed on a p-type nitride layer (not shown) and an n-electrode pattern disposed on an exposed region of an n-type nitride layer in a horizontal type nitride semiconductor light-emitting device. Here, well-known configurations or functions of the nitride semiconductor light-emitting device will not be described in detail when they would obscure the subject matter of the invention. 
         [0035]    Referring to  FIG. 2 , the horizontal type nitride semiconductor light-emitting device may include the p-electrode pattern  180  and the n-electrode pattern  170 . The p-electrode pattern  180  may be disposed on the p-type nitride layer (not shown) . The n-electrode pattern  170  may include an n-pad  171  disposed on the exposed region of the n-type nitride layer (not shown) to correspond to the p-electrode pattern  180 . The n-electrode pattern  170  may further include two n-fingers  172 A and  172 B. 
         [0036]    In more detail, the n-electrode pattern  170  may include the n-pad  171  corresponding to the p-electrode pattern  180 , and a first n-finger  172 A and a second n-finger  172 B that extend from the n-pad  171  along the respective edges of the horizontal type nitride semiconductor light-emitting device. 
         [0037]    For example, the first n-finger  172 A may extend along the shorter edge of the horizontal type nitride semiconductor light-emitting device, and the second n-finger  172 B may extend along the longer edge of the horizontal type nitride semiconductor light-emitting device. 
         [0038]    The first n-finger  172 A and the second n-finger  172 B may have different lengths from each other. That is, the second n-finger  172 B may be longer than the first n-finger  172 A. In this case, the second n-finger  172 B has greater resistance than the first n-finger  172 A has because the resistance increases with the length. Therefore, in order to make the first and second n-fingers  172 A and  172 B have the same resistance R, cross-sectional areas thereof needs to be controlled properly. 
         [0039]    The resistance of the finger is expressed as 
         [0000]        R=ρL/A   (1)
 
         [0000]    where ρ, L and A are a resistivity, a length, and a cross-sectional area, respectively. 
         [0040]    Considering Equation 1, in order to make the n-fingers  172 A and  172 B have the same resistance, the lengths and the cross-sectional areas of the n-fingers  172 A and  172 B of the same material, i.e., of the same resistivity need to be controlled to satisfy the following relation 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       L 
                        
                       
                           
                       
                        
                       1 
                     
                     
                       A 
                        
                       
                           
                       
                        
                       1 
                     
                   
                   = 
                   
                     
                       L 
                        
                       
                           
                       
                        
                       2 
                     
                     
                       A 
                        
                       
                           
                       
                        
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where L 1  and L 2  are lengths of the first and second n-fingers  172 A and  172 B, respectively, and A 1  and A 2  are cross-sectional areas of the first and second n-fingers  172 A and  172 B, respectively. 
         [0041]    Accordingly, if the second n-finger  1723  is longer than the first n-finger  172 A as shown in  FIG. 2 , the cross-sectional area A 2  of the second n-finger  1723  is controlled to be greater than the cross-sectional area A 1  of the first n-finger  172 A so that the first and second n-fingers  172 A and  1723  have the same resistance. As such, it is possible to uniformly apply the same current uniformly across the first and second n-fingers  172 A and  172 B so that the current spreading to the active layer (not shown) can be improved. This is the same to the p-electrode pattern  180 . 
         [0042]    In summary, as the first and second n-fingers  172 A and  1723  have the same resistance, the current can be applied uniformly to the first and second n-fingers  172 A and  1723 , particularly, even to the ends of the first and second n-fingers  172 A and  172 B. As such, it is possible to improve the current spreading to the active layer and thus the light emission efficiency of the horizontal type nitride semiconductor light-emitting device. 
         [0043]    Hereinafter, electrode patterns of a horizontal type nitride semiconductor light-emitting device according to another embodiment of the present invention will be described with reference to  FIG. 3 . 
         [0044]      FIG. 3  is a schematic view of the electrode patterns of the horizontal type nitride semiconductor light-emitting device according to the embodiment.  FIG. 3  illustrates a p-electrode pattern  280  disposed on a p-type nitride layer (not shown) and an n-electrode pattern  270  disposed on an exposed region of an n-type nitride layer in the horizontal type nitride semiconductor light-emitting device. 
         [0045]    Referring to  FIG. 3 , the horizontal type nitride semiconductor light-emitting device may include the p-electrode pattern  280  disposed on the p-type nitride layer (not shown), and the n-electrode pattern  270  disposed on the exposed region of the n-type nitride layer (not shown). The p-electrode pattern  280  may include first and second p-pads  281 A and  281 B, first and second p-fingers  282 A and  282 B extending from the first p-pad  281 A, and third and fourth p-fingers  282 C and  282 D extending from the second p-pad  281 B. The n-electrode pattern  270  may include an n-pad  271  corresponding to the p-pads  281 A and  281 B, and first, second and third n-fingers  272 A,  272 B and  272 C. 
         [0046]    The n-fingers  272 A,  272 B and  272 C and the p-fingers  282 A,  282 B,  282 C and  282 D may extend alternatingly from the n-pad  271  and the p-pads  281 A and  281 B, respectively. 
         [0047]    In more detail, the first n-finger  272 A may slope up and then extend vertically between the first p-finger  282 A and the second p-finger  282 B. The second n-finger  272 B may extend vertically between the second p-finger  282 B and the third p-finger  282 C. The third n-finger  272 C may slope up and the extend vertically between the third p-finger  282 C and the fourth p-finger  282 D. 
         [0048]    Here, the first to third n-fingers  272 A,  272 B and  272 C may have different lengths L 11 , L 12  and L 13 , respectively. For example, the first n-finger  272 A and the third n-finger  272 C may be longer than the second n-finger  272 B. In such a case, the first n-finger  272 A and the third n-finger  272 C has greater resistance than the second n-finger  272 B because the resistance increases with the length. Therefore, in order to make the n-fingers  272 A,  272 B and  272 C have the same resistance R, cross-sectional areas thereof need to be controlled properly on the basis of Equation 1, as described above. That is, the lengths and the cross-sectional areas of the n-fingers  272 A,  272 B and  272 C of the same material, i.e., of the same resistivity need to be controlled to satisfy the following relation 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       L 
                        
                       
                           
                       
                        
                       11 
                     
                     
                       A 
                        
                       
                           
                       
                        
                       11 
                     
                   
                   = 
                   
                     
                       
                         L 
                          
                         
                             
                         
                          
                         12 
                       
                       
                         A 
                          
                         
                             
                         
                          
                         12 
                       
                     
                     = 
                     
                       
                         L 
                          
                         
                             
                         
                          
                         13 
                       
                       
                         A 
                          
                         
                             
                         
                          
                         13 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where L 11 , L 12  and L 13  are lengths of the first, second and third n-fingers  272 A,  272 B and  272 C, respectively, and A 11 , Al 2  and A 13  are cross-sectional areas of the first, second and third n-fingers  272 A,  272 B and  272 C, respectively. 
         [0049]    Accordingly, if the fist and third n-fingers  272 A and  272 C are longer than the second n-finger  272 B as shown in FIG.  3 , the cross-sectional areas A 11  and A 13  of the first and third n-fingers  272 A and  272 C are controlled to be greater than the cross-sectional area A 12  of the second n-finger  272 B so that the first and third n-fingers  272 A and  272 C have the same resistance as the second n-finger  272 B. As such, it is possible to apply the same current uniformly across each of the n-fingers  272 A,  272 B and  272 C so that the current spreading to the active layer (not shown) can be improved. Such a method for controlling the lengths and the cross-sectional areas of the n-fingers  272 A,  272 B and  272 C according to Equation 3 so that the n-fingers  272 A,  272 B and  272 C have the same resistance R is not limited to the n-electrode pattern  270 . But the method can also be applied to the p-fingers  282 A,  282 B,  282 C and  282 D of the p-electrode pattern  280 . 
         [0050]    In addition, the method can also be applied to a horizontal-type nitride semiconductor light-emitting device according to still another embodiment of the present invention. That is, the method can also be applied to an electrode pattern including a plurality of fingers having different lengths from one another so that all the fingers have the same resistance. 
         [0051]      FIG. 4  is a schematic view of the electrode patterns of the horizontal type nitride semiconductor light-emitting device according to the still another embodiment of the present invention.  FIG. 4  illustrates a p-electrode pattern  380  disposed on a p-type nitride layer (not shown) and an n-electrode pattern  370  disposed on an exposed region of an n-type nitride layer in the horizontal type nitride semiconductor light-emitting device. 
         [0052]    Referring to  FIG. 4 , the horizontal type nitride semiconductor light-emitting device may include the p-electrode pattern  380  disposed on the p-type nitride layer (not shown), and the n-electrode pattern  370  disposed on the exposed region of the n-type nitride layer (not shown). The p-electrode pattern  380  may include a p-pad  381  disposed on the p-type nitride layer (at a right side of a top surface of the nitride semiconductor light-emitting device), and first, second and third p-fingers  382 A,  382 B and  382 C extending from the p-pad  381  toward the left side of the top surface. The n-electrode pattern  370  may include an n-pad  371  disposed on the exposed region of the n-type nitride layer (at an upper left corner of the top surface), and first, second, third and fourth p-fingers  372 A,  372 B,  372 C and  372 D extending from the n-pad  371  toward the right side of the top surface. 
         [0053]    The n-fingers  372 A,  372 B,  372 C and  372 D and the p-fingers  382 A,  382 B and  382 C may extend alternatingly. The n-fingers  372 A,  372 B,  372 C and  372 D may extend to respective lengths L 21 , L 22 , L 23  and L 24  which are different from one another. 
         [0054]    In a specific, the first n-finger  372 A may extend horizontally along an edge of the top surface. The second n-finger  372 B may slope down and then extend horizontally between the first p-finger  382 A and the second p-finger  383 B. The third n-finger  372 C may slope down and then extend horizontally between the second p-finger  382 B and the third p-finger  382 C. The fourth n-finger  372 D may extend vertically and then horizontally along edges of the top surface. 
         [0055]    Here, the first to fourth n-fingers  372 A to  372 D may have lengths L 21 , L 22 , L 23  and L 24  different from one another. For example, the lengths of the n-fingers may increase gradually from the first n-finger  372 A to the fourth n-finger  372 D. In such a case, the resistances thereof may also increase gradually from the first n-finger  372 A to the fourth n-finger  372 D because the resistance increases with the length. Therefore, in order to make the n-fingers  372 A to  372 D have the same resistance R, cross-sectional areas thereof need to be controlled properly on the basis of Equation 1, as described above. That is, the lengths and the cross-sectional areas of the n-fingers  372 A to  372 D of the same material, i.e., of the same resistivity need to be controlled to satisfy the following relation 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       L 
                        
                       
                           
                       
                        
                       21 
                     
                     
                       A 
                        
                       
                           
                       
                        
                       21 
                     
                   
                   = 
                   
                     
                       
                         L 
                          
                         
                             
                         
                          
                         22 
                       
                       
                         A 
                          
                         
                             
                         
                          
                         22 
                       
                     
                     = 
                     
                       
                         
                           L 
                            
                           
                               
                           
                            
                           23 
                         
                         
                           A 
                            
                           
                               
                           
                            
                           23 
                         
                       
                       = 
                       
                         
                           L 
                            
                           
                               
                           
                            
                           24 
                         
                         
                           A 
                            
                           
                               
                           
                            
                           24 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where L 21 , L 22 , L 23  and L 24  are lengths of the first, second, third and fourth n-fingers  372 A,  372 B,  372 C and  372 D, respectively, and A 21 , A 22 , A 23  and A 24  are cross-sectional areas of the first, second, third and fourth n-fingers  372 A,  372 B,  372 C and  372 D, respectively. 
         [0056]    Accordingly, if the lengths of the n-fingers increase from the first n-finger  372 A to the fourth n-finger  372 D as shown in  FIG. 4 , the cross-sectional areas A 21 , A 22 , A 23  and A 24  of the n-fingers are controlled to increase from the first n-finger  372 A to the fourth n-finger  372 D so that the n-fingers  372 A to  372 D have the same resistance. As such, it is possible to apply the same current uniformly across the first to fourth n-fingers  372 A to  372 D so that the current spreading to the active layer (not shown) can be improved. 
         [0057]    Surely, such a method for controlling the lengths and the cross-sectional areas of the n-fingers  372 A,  372 B,  372 C and  372 D according to Equation 4 so that the n-fingers  372 A,  372 B,  372 C and  372 D have the same resistance R is not limited to the n-electrode pattern  370 . But the method can also be applied to the p-fingers  382 A,  382 B and  382 C of the p-electrode pattern  380 . 
         [0058]    In addition, the method is not limited to the horizontal type nitride semiconductor light-emitting device. But the method can also be applied to vertical type nitride semiconductor light-emitting devices as shown in  FIGS. 5 to 7 . 
         [0059]    Hereinafter, electrode patterns of a vertical type nitride semiconductor light-emitting device according to even another embodiment of the present invention will be described with reference to  FIG. 5 . 
         [0060]      FIG. 5  is a schematic view of the electrode pattern of the vertical type nitride semiconductor light-emitting device according to the even another embodiment of the present invention. The electrode pattern shown in  FIG. 5  maybe either a p-electrode pattern disposed on a p-type nitride layer (not shown) or an n-electrode pattern disposed on an exposed region of an n-type nitride layer in the vertical type nitride semiconductor light-emitting device. 
         [0061]    Surely, the vertical type nitride semiconductor light-emitting device may include the p-electrode pattern disposed on the p-type nitride layer (not shown) and the n-electrode pattern disposed on the exposed region of the n-type nitride layer. However,  FIG. 5  illustrates only one of the electrode patterns for clarity of illustration, and it will be assumed that the electrode pattern is an n-type electrode pattern. 
         [0062]    Referring to  FIG. 5 , the vertical type nitride semiconductor light-emitting device may include an n-pad  471  disposed at a center of atop surface of the n-type nitride layer. The vertical type nitride semiconductor light-emitting device further includes a plurality of first n-fingers  472 A and a plurality of second n-fingers  472 B, which extend alternatingly and radially from the n-pad  471 . 
         [0063]    The first n-fingers  472 A may extend from the n-pad  471  toward edges of the vertical type nitride semiconductor light-emitting device. The second n-fingers  472 B may extend from the n-pad  471  toward corners of the vertical type nitride semiconductor light-emitting device between the first n-fingers  472 A. The length L 31  of the first n-fingers  472 A is different from the length L 32  of the second n-fingers  472 B. 
         [0064]    In such a case, the first n-fingers  472 A have a resistance greater than that of the second n-fingers  472 B because the resistance increases with the length. Therefore, in order to make the first n-fingers  472 A and the second n-fingers  472 B have the same resistance R, cross-sectional areas thereof need to be controlled properly on the basis of Equation 1, as described above. That is, the lengths and the cross-sectional areas of the first and second n-fingers  472 A and  472 B of the same material, i.e., of the same resistivity need to be controlled to satisfy the following relation 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       L 
                        
                       
                           
                       
                        
                       31 
                     
                     
                       A 
                        
                       
                           
                       
                        
                       31 
                     
                   
                   = 
                   
                     
                       L 
                        
                       
                           
                       
                        
                       32 
                     
                     
                       A 
                        
                       
                           
                       
                        
                       32 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where L 31  and L 32  are lengths of the first and second n-fingers  472 A and  472 B, respectively, and A 31  and A 32  are cross-sectional areas of the first and second n-fingers  472 A and  472 B, respectively. 
         [0065]    Accordingly, if the second n-finger  472 B is longer than the first n-finger  472 A as shown in  FIG. 5 , the cross-sectional area A 32  of the second n-finger  472 B is controlled to be greater than the cross-sectional area A 31  of the first n-finger  472 A so that the first n-finger  472 A and the second n-finger  472 B have the same resistance. As such, it is possible to apply the same current uniformly across each of the first and second n-fingers  472 A and  472 B so that the current spreading to the active layer (not shown) can be improved. Such a method for controlling the lengths and the cross-sectional areas of the n-fingers  472 A and  472 B according to Equation 5 so that the n-fingers  472 A and  472 B have the same resistance R is not limited to the n-electrode pattern  470 . But the method can also be applied to p-fingers of the p-electrode pattern disposed on the p-type nitride layer to correspond to the n-electrode pattern. 
         [0066]    Hereinafter, electrode patterns of a vertical type nitride semiconductor light-emitting device according to yet another embodiment of the present invention will be described with reference to  FIG. 6 . 
         [0067]      FIG. 6  is a schematic view of the electrode pattern of the vertical type nitride semiconductor light-emitting device according to the yet another embodiment of the present invention. The vertical type nitride semiconductor light-emitting device may include a p-electrode pattern disposed on a p-type nitride layer (not shown) and an n-electrode pattern disposed on an exposed region of an n-type nitride layer. However,  FIG. 6  illustrates only the n-electrode pattern disposed on the n-type nitride layer for clarity of illustration. 
         [0068]    Referring to  FIG. 6 , the vertical type nitride semiconductor light-emitting device may include an n-pad  571  disposed at an upper left corner of a top surface of the n-type nitride layer. The vertical type nitride semiconductor light-emitting device may further include four n-fingers  572 A,  572 B,  572 C and  572 D extending from the n-pad  571 . 
         [0069]    In a specific, a first n-finger  572 A, a second n-finger  572 B, a third n-finger  572 C and a fourth n-finger  572 D may extend from the n-pad  571  at the upper left corner to a right edge of the top surface of the n-type nitride layer. The first n-finger  572 A may extend horizontally along an edge of the top surface. The second n-finger  572 B may slope down and then extend horizontally below the first n-finger  572 A. The third n-finger  572 C may slope down and then extend horizontally below the second n-finger  572 B. The fourth n-finger  572 D may extend vertically and then horizontally along edges of the top surface. 
         [0070]    Here, the first to fourth n-fingers  572 A to  572 D may have lengths L 41 , L 42 , L 43  and L 44  different from one another. For example, the lengths of the n-fingers may increase gradually from the first n-finger  572 A to the fourth n-finger  572 D. In such a case, the resistances thereof may also increase gradually from the first n-finger  572 A to the fourth n-finger  572 D because the resistance increases with the length. Therefore, in order to make the n-fingers  572 A to  572 D have the same resistance R, cross-sectional areas thereof need to be controlled properly on the basis of Equation 1, as described above. That is, the lengths and the cross-sectional areas of the n-fingers  572 A to  572 D of the same material, i.e., of the same resistivity need to be controlled to satisfy the following relation 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       L 
                        
                       
                           
                       
                        
                       41 
                     
                     
                       A 
                        
                       
                           
                       
                        
                       41 
                     
                   
                   = 
                   
                     
                       
                         L 
                          
                         
                             
                         
                          
                         42 
                       
                       
                         A 
                          
                         
                             
                         
                          
                         42 
                       
                     
                     = 
                     
                       
                         
                           L 
                            
                           
                               
                           
                            
                           43 
                         
                         
                           A 
                            
                           
                               
                           
                            
                           43 
                         
                       
                       = 
                       
                         
                           L 
                            
                           
                               
                           
                            
                           44 
                         
                         
                           A 
                            
                           
                               
                           
                            
                           44 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where L 41 , L 42 , L 43  and L 44  are lengths of the first, second, third and fourth n-fingers  572 A,  572 B,  572 C and  572 D, respectively, and A 41 , A 42 , A 43  and A 44  are cross-sectional areas of the first, second, third and fourth n-fingers  572 A,  572 B,  572 C and  572 D, respectively. 
         [0071]    Accordingly, if the lengths of the n-fingers increase from the first n-finger  572 A to the fourth n-finger  572 D as shown in  FIG. 6 , the cross-sectional areas A 41 , A 42 , A 43  and A 44  of the n-fingers are controlled to increase from the first n-finger  572 A to the fourth n-finger  572 D so that the n-fingers  572 A to  572 D have the same resistance. As such, it is possible to apply the same current uniformly across the first to fourth n-fingers  572 A to  572 D so that the current spreading to the active layer (not shown) can be improved. 
         [0072]    Surely, such a method for controlling the lengths and the cross-sectional areas of the n-fingers  572 A,  572 B,  572 C and  572 D according to Equation 6 so that the n-fingers  572 A,  572 B,  572 C and  572 D have the same resistance R is not limited to the n-electrode pattern  570 . But the method can also be applied to p-fingers of the p-electrode pattern disposed on a p-type nitride layer. 
         [0073]    Hereinafter, electrode patterns of a vertical type nitride semiconductor light-emitting device according to further another embodiment of the present invention will be described with reference to  FIG. 7 . 
         [0074]      FIG. 7  is a schematic view of the electrode pattern of the vertical type nitride semiconductor light-emitting device according to the further another embodiment of the present invention. The vertical type nitride semiconductor light-emitting device may include a p-electrode pattern disposed on a p-type nitride layer (not shown) and an n-electrode pattern disposed on an exposed region of an n-type nitride layer. However,  FIG. 7  illustrates only two n-electrode patterns disposed on the n-type nitride layer for clarity of illustration. 
         [0075]    Referring to  FIG. 7 , the vertical type nitride semiconductor light-emitting device may include a first n-pad  671  disposed at an upper left corner and a second n-pad  672  disposed at a lower right corner on a top surface of the nitride layer. The vertical type nitride semiconductor light-emitting device may further include n-fingers  671 A and  671 B extending from the first n-pad  671  to the second n-pad  672 , and n-fingers  672 A and  672 B extending from the second n-pad  672  to the first n-pad  671 . 
         [0076]    In a specific, the first and second n-fingers  671 A and  671 B and the third and fourth n-fingers  672 A and  672 B may extend alternately from the respective n-pads  671  and  672 . That is, the first n-finger  671 A may extend horizontally and then vertically along edges of the top surface. The second n-finger  671 B may slope down and then extend horizontally between the fourth n-finger  6728  and the third n-finger  672 A. The third n-finger  672 A may extend horizontally and then vertically along edges of the top surface. The fourth n-finger  672 B may slope up and then extend horizontally between the first n-finger  671 A and the second n-finger  671 B. 
         [0077]    Here, the first and third n-fingers  671 A and  672 A may have a length L 51  different from the length L 52  of the second and fourth n-fingers  671 B and  672 B. For example, the length L 51  of the first and third n-fingers  671 A and  672 A may be greater than the length L 52  of the second and fourth n-fingers  671 B and  672 B. In such a case, the first and third n-fingers  671 A and  672 A have a resistance greater than that of the second and fourth n-fingers  671 B and  672 B. Therefore, in order to make the n-fingers  671 A,  671 B,  672 A and  672 B have the same resistance R, cross-sectional areas thereof need to be controlled properly on the basis of Equation 1, as described above. That is, the lengths and the cross-sectional areas of the n-fingers  671 A,  671 B,  672 A and  672 B of the same material, i.e., of the same resistivity need to be controlled to satisfy the following relation 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       L 
                        
                       
                           
                       
                        
                       51 
                     
                     
                       A 
                        
                       
                           
                       
                        
                       51 
                     
                   
                   = 
                   
                     
                       L 
                        
                       
                           
                       
                        
                       52 
                     
                     
                       A 
                        
                       
                           
                       
                        
                       52 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where L 51  is a length of the first and third n-fingers  671 A and  672 A, L 52  is a length of the second and fourth n-fingers  671 B and  672 B, A 51  is a cross-sectional area the first and third n-fingers  671 A and  672 A, and A 52  is a cross-sectional area of the second and fourth n-fingers  671 B and  672 B. 
         [0078]    Accordingly, if the length L 51  of the first and third n-fingers  671 A and  672 A is greater than the length L 52  of the second and fourth n-fingers  671 B and  672 B as shown in  FIG. 7 , the cross-sectional area A 51  of the first and third n-fingers  671 A and  672 A are controlled to be greater than the cross-sectional area A 52  of the second and fourth n-fingers  671 B and  672 B so that the n-fingers  671 A,  671 B,  672 A and  672 B have the same resistance. As such, it is possible to apply the same current uniformly across the first to fourth n-fingers  671 A,  671 B,  672 A and  672 B so that the current spreading to the active layer (not shown) can be improved. 
         [0079]    Surely, such a method for controlling the lengths and the cross-sectional areas of the n-fingers  671 A,  671 B,  672 A and  672 B so that the n-fingers  671 A,  671 B,  672 A and  672 B have the same resistance R may also be applied to the case where all of the four n-fingers  671 A,  671 B,  672 A and  672 B have respective lengths different from one another. 
         [0080]    In addition, the method for controlling the lengths and the cross-sectional areas of the n-fingers  671 A,  671 B,  672 A and  672 B so that the n-fingers  671 A,  671 B,  672 A and  672 B have the same resistance R is not limited to the n-electrode pattern  670 . But the method can also be applied to the p-fingers of the p-electrode pattern disposed on a p-type nitride layer. 
         [0081]    As described above, the n-fingers and the p-fingers can have the same resistance so that the same current is applied uniformly across each of the n-fingers and the p-fingers. As a result, it is possible to improve the current spreading to the active layer, and thus to improve the light emission efficiency of the nitride semiconductor light-emitting device. 
         [0082]    While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.