Abstract:
Disclosed is a blue light emitting diode comprising a laminate structure formed in the center of a first conductive nitride semiconductor layer, a first electrode formed on a part of a transparent metal layer included in the laminate structure and a second electrode formed on a peripheral part of the first conductive nitride semiconductor layer, which is not covered by the laminate structure. By altering the locations of the first electrode and the second electrode and forming electrode extensions thereof, it is possible to disperse effectively the current density. Accordingly, the concentration of the current density contributing to the rapid increase of the temperature can be avoided without a significant change of the laminate structure of the conventional light emitting diode. In addition it is possible to improve resistance to electrostatic discharge and to reduce the driving voltage.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a blue light emitting diode, and more particularly a blue light emitting diode, which has such an electrode structure as to prevent the concentration of current density, causative of a rapid temperature increase in the diode, thereby increasing resistance to electrostatic discharge (ESD) and lowering a deriving voltage without significantly altering the laminate structure of the electrode.  
           [0003]    2. Description of the Related Art  
           [0004]    Recently, a light emitting diode which is able to emit light in the region of short wavelength (ultraviolet light to green), particularly blue light has gained public popularity. Such semiconductor materials include ZnSe (II-VI), nitrides such as GaN, InN, AlN (III-V) and nitride mixtures combining these nitrides in a certain ratio and particularly GaN are widely used.  
           [0005]    Growing of GaN crystal is effected by MOCVD (Metal Organic Chemical Vapor Deposition) method. The MOCVD method is carried out by supplying reactive gas of an organic compound into a reaction chamber at a temperature of 700 to 1200° C. to grow crystals in an epitaxial layer on a substrate, in which sapphire or SiC is used as the substrate. The reason that sapphire or SiC substrate is used is that there exist no substrates commercially available that can achieve lattice matching with the nitride crystal while having the same crystalline structure as the nitride crystal. Also, it can hardly be expected that the growth process of an epitaxial layer on such substrate would form a good quality of crystal, due to the stress resulting from lattice mis-matching. Therefore, a buffer layer is used as a low temperature-growing layer between the substrate and epitaxial layer.  
           [0006]    Also, the blue light emitting diode with such a limited structure differs from the general light emitting diode in terms of the driving method, as explained below with reference to FIG. 1 a  and  1   b.    
           [0007]    [0007]FIG. 1 schematically shows the difference in the driving manner between a general light emitting diode(for example, a class of LEDs using GaAs, GaP, etc) and a blue light emitting diode(III-nitride). In the general light emitting diode, as shown in FIG. 1 a,  a light emitting diode chip is operated using a total structure including a wafer which acts as a substrate for crystal growth. However, as shown in FIG. 1 b,  the blue light emitting diode is operated through a thin structure fabricated on a chip, but not through the substrate. That is, the blue light emitting diode has a planar type structure using the insulating substrate as a sapphire, unlike the general light emitting diode.  
           [0008]    Further, the blue light emitting diode is known to need a relatively high driving voltage at a constant current, compared to the general light emitting diode. FIG. 2 a  and  2   b  show the voltage-current characteristics of an infrared light emitting diode (A), a red light (wavelength 635 nm) emitting diode (B) and a blue light (wavelength 450 nm) emitting diode (C) in a driving region of a forward direction. The blue light emitting diode requires a driving voltage of about two times as high as the red light emitting diode at a rated current of 20 mA. It is thought that such a high driving voltage is attributed to properties of GaN semiconductor layer and the planar type structure.  
           [0009]    As described above, the blue light emitting diode suffers from problems in two aspects. First, the blue light emitting diode must adopt a deriving method for use in a planar type structure owing to the structural limit of growing a semiconductor layer on a sapphire substrate and a buffer layer so as to grow crystals with prevention of lattice mismatching. Another problem with the blue light emitting diode is the inherent feature of requiring a higher driving voltage as compared to general light emitting diodes. Consequently, the driving method and the high driving voltage of the blue light emitting diode may lead to reduced reliability and deteriorated quality of products.  
           [0010]    [0010]FIG. 3 a  is a plan view of the conventional blue light emitting diode and FIG. 3 b  is a sectional view of the diode, taken along line A-A in FIG. 3 a.  Referring to FIG. 3 a  and  3   b,  problems caused by the above-described restrictive problems of the blue light emitting diode will be explained in detail. As shown in FIG. 3 a,  the conventional blue light emitting diode include a sapphire substrate  1 , a buffer layer  2  formed on the substrate  1 , an n-type nitride semiconductor layer  3  comprising a central part R 1  in a predetermined region and a peripheral part R 2  surrounding the central part R 1 , and a laminated structure formed on the n-type nitride semiconductor layer  3 .  
           [0011]    The laminated structure has an active layer  4  made of intrinsic nitride semiconductor crystal in the central part R 1  on the N-type nitride semiconductor  3 , a p-type nitride semiconductor layer  5  formed on the active layer  4 , a metal layer  6  atop the semiconductor crystal layer  5 , and a first electrode  7 , corresponding to a P electrode, formed in a predetermined region on the metal layer  6 . Also, the light emitting diode includes a second electrode  8  as a N electrode formed in the peripheral part R 2  over the N-type nitride semiconductor layer  3  while keeping a predetermined distance space from the central part R 12  over the N-type nitride semiconductor layer  3 .  
           [0012]    In such conventional blue light emitting diode, current flows as injected carriers move on the surface of the diode and at the interface between the electrodes in the characteristic driving manner of the planar type structure. Also, the blue light emitting diode requires a high driving voltage across a given area for light emission, thereby forming a flow of a great quantity of injected carrier (herein electron). The current path Rp formed by the above flow of the carriers is distributed in accordance with the area of the electrode formed at an upper position. In FIG. 3 a,  therefore, the current density distribution is very high in the region Rd defined with a dotted line, and decreases gradually toward the periphery. The higher current density at the region Rd defined with the dotted line leads the temperature of the entire chip to increase, resulting in reducing the light output.  
           [0013]    In consequence, since the conventional blue light emitting diode of the planar type structure requires a high driving voltage, defects existing in the region where a high current density is generated causes the chip temperature to be increased as well as incurring quality deterioration, for example, weak resistance to electrostatic discharge (ESD), which cause fundamental problems in achieving the reliability and quality stabilization of products.  
         SUMMARY OF THE INVENTION  
         [0014]    Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a blue light emitting diode with an improved electrode structure which is capable of effectively dispersing the current density concentration causative of local temperature increase in the blue light emitting diode without requiring a significant structural change.  
           [0015]    Another object of the present invention is to provide a blue light emitting diode which is highly resistant to ESD with a resulting improvement in terms of the quality and reliability of products.  
           [0016]    Still another object of the present invention is to provide a blue light emitting diode in which the driving voltage is reduced and the rapid increasing of a temperature occurring locally in the chip is suppressed.  
           [0017]    In order to achieve the above object, the present invention provides a blue light emitting diode comprising an insulating substrate, typically in a square shape, and a first conductive nitride semiconductor layer formed on the insulating substrate to have a surface divided into a central part and a peripheral part. The peripheral part is provided over the surface adjacent to and along the edges of the nitride semiconductor layer and the central part surrounded by the peripheral part.  
           [0018]    Also, the blue light emitting diode includes a laminate structure formed over the central part of the nitride semiconductor layer, in which the laminate structure comprises a nitride active layer on the nitride semiconductor layer, a second conductive nitride semiconductor layer formed on the active layer, a transparent metal layer formed on the second conductive nitride semiconductor layer and a first electrode formed over a part of the transparent metal layer.  
           [0019]    Further, the blue light emitting diode includes a second electrode formed over the peripheral part of the first conductive nitride semiconductor layer which is not covered by the laminate structure. As the insulating substrate, sapphire substrate can be used. It is also possible to use a sapphire substrate further comprising a GaN buffer layer formed thereon.  
           [0020]    Here, the first electrode is referred to as a P electrode and the second electrode is referred to as an N electrode. The peripheral part on the first conductive nitride semiconductor layer (the layer expressed by Si-doped GaN) means the edge exposed with no active layer formed, that is, a surface part of the Si-doped GaN layer surrounding the active layer. In a predetermined region of this part, a second electrode is formed. Defined as a region in which the active layer is formed, the central part on the first conductive nitride semiconductor layer is a convex plane part surrounded by the peripheral part.  
           [0021]    The blue light emitting diode may comprise the buffer layer made of GaN, the first conductive nitride semiconductor layer made of Si-doped GaN, the active layer made of In1-xGaxN ( 0&lt;x≦1 ) and the p-type nitride semiconductor layer made of All-xGaxN (0&lt;x≦1) and Mg-doped GaN. The above composition describes a blue light emitting diode that is currently, most commonly embodied. This is applicable to the blue light emitting diode according to another embodiment of the present invention.  
           [0022]    In such a light emitting diode, the locations of the first electrode and the second electrode are changed and extensions of these electrodes are formed, whereby the current density can be effectively dispersed. As a result, the concentration of current density, causative of a rapid temperature increase, can be avoided only by the change of the location of the electrode and the formation of extensions thereof without significant alteration of the structure of the diode. In addition, it is possible to increase the resistance to ESD and reduce the driving voltage.  
           [0023]    The reason why the present invention is interested in the improvement of the electrode structure is that the problems with conventional blue light emitting diode, including temperature increase attributable to the current density concentration, weak resistance to ESD, and high driving voltage, can be eliminated only by a metal patterning process with requiring no significant changes in other fabricating processes for the blue light emitting diode, nor employment of new equipments and materials.  
           [0024]    The most important thing to be considered in the electrode structure is which type of electrode structure, that is, which type of locations and extensions of electrodes can disperse more effectively the current density. Leading to the present invention, the extensive and thorough research and experiments were conducted by the present inventors, in which the first electrode and the second electrode were set at various locations while the distance from the central part to the peripheral part was varied. As a result, there were found preferred embodiments which have an excellent capability of dispersing the current density and high resistance to ESD, and are operable at reduced driving voltage, thereby enhancing the quality and reliability.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    The above objects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description when taken in conjunction with the drawings, in which:  
         [0026]    [0026]FIGS. 1 a  and  1   b  are schematic views showing the structural difference according to a driving method of a general light emitting diode and a blue light emitting diode.  
         [0027]    [0027]FIGS. 2 a  and  2   b  are graphs showing current-voltage characteristics and applied current-temperature change characteristics of an infrared light emitting diode, a red light emitting diode and a blue light emitting diode. FIGS. 3 a  and  3   b  are a plan view of a conventional blue light emitting diode and a sectional view taken along line A-A of FIG. 3 a,  respectively.  
         [0028]    [0028]FIG. 4 a  is a plan view of a blue light emitting diode according to the first embodiment of the present invention and FIG. 4 b  is a sectional view taken along line  2 A- 2 A of FIG. 4 a.    
         [0029]    [0029]FIGS. 5 a - 5   c  are plan views showing modifications of the first embodiment according to the present invention. FIGS. 6 a  and  6   b  is a plan view of a blue light emitting diode according to the second embodiment of the present invention and a sectional view taken along line  3 A- 3 A in FIG. 6 a,  respectively.  
         [0030]    [0030]FIG. 7 is a plan view of a blue light emitting diode according to the third embodiment of the present invention.  
         [0031]    [0031]FIG. 8 is a plan view showing a modification to the third embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    The application of the preferred embodiments of the present invention is best understood with reference to the accompanying drawings, wherein like reference numerals are used for like and corresponding parts, respectively.  
         [0033]    With reference to FIG. 4, there is shown a first preferred embodiment according to the present invention.  
         [0034]    [0034]FIG. 4 a  shows a plan view of a blue light emitting diode according to the first embodiment of the present invention and FIG. 4 b  shows a sectional view taken along line  2 A- 2 A in FIG. 4 a . As shown in FIG. 4 a,  the blue light emitting diode of the first preferred embodiment according to the present invention includes an insulating substrate  21  typically in a square shape and a first conductive nitride semiconductor layer  23  formed on an entire surface of the insulating substrate  21 . The nitride semiconductor layer  23  has a surface divided into a central part R 1  and an exposed peripheral part R 2 . The peripheral part R 2  is formed over the surfaces adjacent to edges  23   a  to  23   d  of the nitride semiconductor layer  23  and along the edges  23   a  to  23   d,  and the central part R 1  is surrounded by the peripheral part R 2 . The blue light emitting diode further comprises a buffer layer  22  disposed between the insulating substrate  21  and the first conductive nitride semiconductor layer  23 .  
         [0035]    Also, the blue light emitting diode includes a laminate structure formed over the central part of the nitride semiconductor layer  23 . The laminate structure comprises a nitride active layer  24  formed on the nitride semiconductor layer, a second conductive nitride semiconductor layer  25  formed on the active layer  24 , a transparent metal layer  26  formed on the second conductive nitride semiconductor layer  25  and a first electrode  27  formed on a part of the transparent metal layer  26 .  
         [0036]    Further, according to the first preferred embodiment of the present invention, the blue light emitting diode comprises a second electrode formed on the peripheral part R 2  of the first conductive nitride semiconductor layer  23  which is not covered by the laminate structure. The second electrode is formed with a main portion  28  and extensions  28   a,    28   b  extended from the main portion  28 , in a band shape. The main portion  28  is formed near a corner where adjacent edges  23   c,    23   d  intersect each other in the surface of the first nitride semiconductor layer  23 . The extensions  28   a,    28   b  are formed adjacent to edges  23   c,    23   d  of the surface of the first conductive nitride semiconductor layer  23  so that they are extended along at least one edge ( 23   c  or  23   d ) of the surface of the first conductive nitride semiconductor layer  23 .  
         [0037]    Preferably, the first electrode  27  is formed diagonally to the main portion  28  of the second electrode and the extensions  28   a,    28   b  of the second electrode is extended along each of the edges  23   c,    23   d  to which the main portion  28  of the second electrode is adjacent. By the extensions  28   a,    28   b  of the second electrode formed on the peripheral part R 2  over the first conductive nitride semiconductor  23 , that is, a region N 1  extended in a lateral direction and a region N 2  extended in a longitudinal direction, the concentration of the current density as in the region d of FIG. 3 is prevented, thereby avoiding a current crowding phenomenon due to the concentrated current density.  
         [0038]    [0038]FIGS. 5 a  to  5   c  show plan views of a blue light emitting diode according to modifications of the first preferred embodiment of the present invention. Referring to FIG. 5 a,  the first electrode  27  is formed near a corner including any one of two edges of the transparent metal layer  26  to which the main portion  28  of a second electrode is adjacent. The extension  28   a  of the second electrode is extended along the two edges  23   a,    23   d  intersecting each other at the corner in the first conductive nitride semiconductor layer  23 , which is located on a diagonal line to the first electrode  27 .  
         [0039]    Referring to FIG. 5 b,  the first electrode  27  is formed on the middle of one of two edges of the transparent metal layer  26  which are not adjacent to the main portion  28  of the second electrode. As shown in FIG. 5 b,  when the first electrode  27  is formed on the middle of the edge  23   b,  the extension  28   a  of the second electrode is extended along the two edges  23   a,    23   d  and the extension  28   b  is extended along the edge  23   c.  That is, the two extensions are extended from the main portion  28  of the second electrode along all the edges over the peripheral part  2  except for the edge on which the first electrode  27  is formed.  
         [0040]    Next, referring to FIG. 5 c , the first electrode  27  is formed in the center of the transparent metal layer  26 . The extension  28   a  of the second electrode is extended over the peripheral part R 2  of the first conductive nitride semiconductor layer  26  while surrounding the central part R 1 . That is, the extension  28   a  is formed on four edges  23   a  to d of the first conductive nitride semiconductor  26  and thus forms a closed square pattern surrounding the central part R 1 .  
         [0041]    By the above described electrode structure, that is, the location of electrodes and their extensions according to the modification of the first preferred embodiment of the present invention, the concentration region of the current density can be dispersed in all directions. Further, the current crowding phenomenon due to the concentrated current density can be further decreased.  
         [0042]    As described above, the location for the first electrode to be formed can be altered variously. The locations described above are applicable to the blue light emitting diode according to another embodiment of the present invention.  
         [0043]    Meanwhile, the main portion  28  and its extension  28   a  of the second electrode keep a prescribed spacing from the central part R 1 . The spacing is preferably set to be any value within the range between 5 μm and 20 μm, which is applicable to the blue light emitting diode according to another embodiment of the present invention. The value is derived from the ones generally used in the blue light emitting diode, however, the present invention is not limited to it. The value may be varied depending on the standard for the products. Following the trend toward optimization and hence, miniaturization of products the value may be made smaller.  
         [0044]    Therefore, according to the blue light emitting diode according to the first preferred embodiment of the present invention, through the extensions  28   a  of the second electrode formed over the peripheral part of the first conductive nitride semiconductor  23 , that is, the region N 1  extended in the lateral direction and the region N 2  extended in the longitudinal direction in FIG. 4 a,  the concentration region D of the current density in FIG. 3 can be dispersed, thereby the current crowding phenomenon due to the concentrated current density can be decreased.  
         [0045]    Next, a blue light emitting diode according to the second preferred embodiment of the present invention will be described.  
         [0046]    [0046]FIG. 6 a  shows a plan view of a blue light emitting diode according to the second embodiment of the present invention and FIG. 6 b  shows a sectional view taken along line  3 A- 3 A in FIG. 6 a.  As shown in FIG. 6 a,  the blue light emitting diode of the second preferred embodiment according to the present invention includes an insulating substrate  31  typically in a square shape and a first conductive nitride semiconductor layer  33  formed on an entire surface of the insulating substrate  31 . The nitride semiconductor layer  33  has a surface divided into a central part R 1  and an exposed peripheral part R 2 . The peripheral part R 2  is formed over the surfaces adjacent to edges  33   a  to  33   d  of the nitride semiconductor layer  33  and along the edges  33   a  to  33   d  of the nitride semiconductor layer  33  and the central part R 1  is surrounded by the peripheral part R 2 . The blue light emitting diode further comprises a buffer layer  32  disposed between the insulating substrate  31  and the first conductive nitride semiconductor layer  33 .  
         [0047]    Also, the blue light emitting diode includes a laminate structure formed over the central part of the nitride semiconductor layer  33 . The laminate structure comprises a nitride active layer  34  formed on the nitride semiconductor layer, a second conductive nitride semiconductor layer  35  formed on the active layer  34 , a transparent metal layer  36  formed on the second conductive nitride semiconductor layer  35  and a first electrode  37  formed on a part of the transparent metal layer  36 .  
         [0048]    Further, according to the second preferred embodiment of the present invention, the blue light emitting diode comprises a second electrode formed on the peripheral part R 2  of the first conductive nitride semiconductor layer  33  which is not covered by the laminate structure. The second electrode is formed with a main portion  38  and extensions  38   a,    38   b  extended from the main portion  38 , in a band shape. The main portion  38  is formed on the middle of an edge  33   c  over the surface of the first nitride semiconductor layer  33 . The extensions  38   a,    38   b  are formed adjacent to and along edges  33   b,    33   c,    33   d  over the surface of the first conductive nitride semiconductor layer  33  so that they are extended along at least one edge over the surface of the first conductive nitride semiconductor layer  33 .  
         [0049]    Preferably, the first electrode  37  is formed near the middle of an edge of the transparent metal layer  36 , opposite to the main portion  38  of the second electrode and the extensions  38   a,    38   b  of the second electrode are extended along the edges  33   b,    33   c,    33   d  of the first conductive nitride semiconductor  33  to which the first electrode is not adjacent. By the above described electrode structure, that is, the main portion and the extensions of electrodes according to the second preferred embodiment of the present invention, the concentration region of the current density can be dispersed in all directions. Further, the current crowding phenomenon due to the concentrated current density can be further decreased.  
         [0050]    In order to verify a resistance to Electro-Static Discharging (ESD), the conventional blue light emitting diode shown in FIG. 3 and the blue light emitting diode according to the second preferred embodiment of the present invention shown in FIG. 6 are subjected to an ESD test under identical conditions. The conditions include charging a capacitor of 200 pF at an applied voltage of 200 V for each of the lamps having a diameter of 3 mm, and discharging at an interval of  1  second in the forward direction through a resistance of 0Ω. The results with a conventional blue light emitting diode and the blue light emitting diode of the present invention are given in Tables 1 and 2, below. In the tables, Vf (V) means a driving voltage in the forward direction, Po means a power of output light and Iv means brightness of light.  
                                                           TABLE 1                           Conventional Blue Light Emitting Diode of FIG. 3                Before the ESD test   After the ESD test            Test   Vf   Po   Iv   Vf   Po   Iv       Round No.   (V)   (MW/sr)   (cd)   (V)   (MW/sr)   (cd)               1   3.50   2.3004   0.1485   *   *   *       2   3.32   2.9898   0.1873   3.36   3.0591   0.1923       3   3.37   3.5225   0.1968   3.35   3.1015   0.1760       4   3.46   3.3217   0.1999   3.38   1.8834   0.1222       5   3.34   3.5914   0.2248   3.32   3.6457   0.2302       6   3.37   3.3670   0.1959   3.36   3.1262   0.1870       7   3.50   3.0425   0.1715   *   *   *       8   3.41   3.2869   0.2039   *   *   *       9   3.36   3.1178   0.1797   *   *   *       10    3.46   1.9343   0.1135   3.45   2.1165   0.1230       Average   3.41   3.0474   0.1822   3.37   2.8221   0.1718       Deviation   0.07   0.5335   0.0316   0.04   0.6759   0.0422                          
 
         [0051]    [0051]                                                           TABLE 2                           Blue Light Emitting Diode of FIG. 6                Before the ESD test   After the ESD test            Test   Vf   Po   Iv   Vf   Po   Iv       Round No.   (V)   (MW/sr)   (cd)   (V)   (MW/sr)   (cd)               1   3.24   1.9128   0.1590   3.22   1.8385   0.1544       2   3.25   3.5098   0.2838   3.22   2.9615   0.2446       3   3.24   2.2783   0.1931   3.43   1.9416   0.1654       4   3.28   3.1015   0.2488   3.22   2.8606   0.2338       5   3.23   2.1798   0.1799   3.06   0.7413   0.0721       6   3.23   2.4579   0.2040   3.22   2.4245   0.2060       7   3.25   2.4246   0.2004   3.25   2.2248   0.1866       8   3.23   2.3103   0.1954   3.22   2.0674   0.1750       9   3.30   2.8122   0.2215   3.28   2.3888   0.1903       10    3.23   2.6388   0.2187   3.21   2.0611   0.1740       Average   3.25   2.5626   0.2105   3.23   2.1510   0.1802       Deviation   0.02   0.4713   0.0354   0.09   0.6183   0.0477                    
         [0052]    From the results shown in Table 1, it is noted that 40% of the conventional blue light emitting diodes illustrated in FIG. 3 were broken down in the ESD test. As apparent from the data of Table 2, the blue light emitting diodes of the present invention were not broken down in the same test. Therefore, it is proved that the blue light emitting diode of the present invention has an increased resistance to ESD than the conventional blue light emitting diode.  
         [0053]    Next, a blud light emitting diode according to the third preferred embodiment of the present invention will be described.  
         [0054]    [0054]FIG. 7 shows a plan view of a blue light emitting diode according to the third preferred embodiment of the present invention and FIG. 8 shows a plan view of a blue light emitting diode according to a modification of the third preferred embodiment of the present invention. The blue light emitting diodes shown in FIGS. 7 and 8 are the same in their organization and structure with the blue light emitting diode illustrated in the above first and second preferred embodiments of the present invention, except for the first electrode, the second electrode and extensions thereof. Therefore, descriptions with regard to the same organization and structure will be omitted.  
         [0055]    The blue light emitting diode according to the third preferred embodiment of the present invention includes a first electrode formed over a part of a transparent metal layer  46  included in the laminate structure as described above and a second electrode formed over a peripheral part R 2  of the first conductive nitride semiconductor layer which is not covered by the laminate structure. The first electrode is formed with a main portion  47  and extensions  47   a,    47   b  extended from the main portion  47 , in a band shape. The main portion  48  is formed near a corner where adjacent edges intersect each other on a surface of the metal layer  46 . The extensions  47   a,    47   b  are formed along at least one edge on the surface of the metal layer  46 .  
         [0056]    The second electrode is formed with a main portion  48  and extension  48   a  extended from the main portion  48 , in a band shape. The main portion  48  of the second electrode is formed near a corner where adjacent edges  43   c,    43   d  intersect each other in the surface of the first nitride semiconductor layer  43 . The extensions  48   a  are formed adjacent an edge  43   d  of the surface of the first conductive nitride semiconductor layer  43  along at least one edge of the surface of the first conductive nitride semiconductor layer  43 .  
         [0057]    Preferably, as shown in FIG. 7, the main portion  47  of the first electrode is formed on the middle of any one of two edges of the transparent metal layer  46  which are not adjacent to the main portion  48  of the second electrode. The extensions  47   a,    47   b  of the first electrode are extended along the one edge to which the main portion  47  of the first electrode is adjacent, from the main portion  47  in the both lateral direction. The extension  48  of the second electrode is formed on the edge  43   d  of the first conductive nitride semiconductor layer  43  opposite to the main portion  47  of the first electrode.  
         [0058]    Referring to FIG. 8, the main portion  47  of the first electrode is formed near a corner including any one of two edges of the transparent metal layer  46  to which the main portion  48  of the second electrode is adjacent. The extension  47   a,    47   b  of the first electrode is extended along the edges of the transparent metal layer  46  to which the main portion  47  of the first electrode is adjacent. The extension  48   a  of the second electrode is extended along the two edges  43   a,    43   d  intersecting each other at the corner of the surface of the first conductive nitride semiconductor layer  23 , which is located on a diagonal line to the main portion  47  of the first electrode  47 .  
         [0059]    By the above described main portion and the extensions of the electrodes according to the third preferred embodiment of the present invention and the modification thereof, the concentration region of the current density as shown in FIG. 3 can be dispersed evenly. Further, the current crowding phenomenon due to the concentrated current density can be further decreased.  
         [0060]    As described above, the embodiments of the present invention are given for the purpose of illustration. For example, the spacing between the second electrode formed on the peripheral part and the central part over the N-type semiconductor layer having the active layer formed thereon means a certain distance capable of dispersing the concentrated current density through the extension of the electrode. Thus, one skilled in the art can make modifications in connection with the extension of the first electrode or the extension of the second electrode according to the present invention. However, the extension of the first electrode or the extension of the second electrode for the efficient dispersion of the current density will be involved in the spirit and scope of the present invention. This is because by such extensions of the electrode, the present invention disperses the concentrated current path to the extensions to prevent the rapid temperature increase. Accordingly, the present invention can be applied in various forms to planar type semiconductor devices requiring the efficient dispersion of the current density in the chip.  
         [0061]    As described above, the blue light emitting diode according to the present invention disperses the current path locally concentrated through the extensions of the electrode, thereby reducing the temperature deviation in the chip and preventing the rapid temperature increase. Also, the blue light emitting diode according to the present invention is resistant to ESD in contrast to the general blue light emitting diode.  
         [0062]    Further, the blue light emitting diode of the present invention is operated at a reduced driving voltage, circumventing the problem the conventional blue light emitting diode suffers from owing to a high driving voltage. Therefore, the present invention overcomes the problems associated with the rapid temperature increase due to the high current density resulting from the concentration of the current path and the low resistance to the ESD, thereby leading to improvement in the reliability of the blue light emitting diode and improvement of the quality.  
         [0063]    Moreover, the structure of the electrode with the extensions according to the present invention can be applied to other planar type semiconductor devices in which the pyrogenetic phenomenon caused by the concentration of the current path is problematic.  
         [0064]    In addition, the present invention can be applied to a modified manufacturing process, for example, in which after growing an epitaxial layer as a basic structure, the N-type semiconductor layer is etched.  
         [0065]    Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.