Patent Publication Number: US-2006001035-A1

Title: Light emitting element and method of making same

Description:
The present application is based on Japanese patent application Nos. 2004-184028 and 2004-252499, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a light emitting element and, particularly, to a light emitting element that has an increased emission area relative to the element&#39;s surface area and prevents unevenness in light distribution so as to increase brightness thereof. Also, this invention relates to a light emitting element that has an excellent mounting performance, a high reliability in electrical connection, and a heat radiation performance as well as having an increased emission area relative to the element&#39;s surface area. Further, this invention relates to a method of making the light emitting element thus featured while using the conventional apparatus without requiring any advance technique.  
      Herein, a light emitting element includes a light emitting device, a light emitting diode (LED) and an LED element.  
      2. Description of the Related Art  
      A light emitting element (herein also referred to as LED element) is known in which a group III nitride-based compound semiconductor is grown on a transparent underlying substrate such as sapphire. Also, it is known that the LED element is flip-chip mounted on a mounting board to extract light from the underlying substrate side since the underlying substrate is transparent (for example, see JP-A-2002-232016, paragraph 0005).  
      JP-A-2002-233016 discloses a flip-chip mounting method that an LED element is carried onto a submount board with bumps attached corresponding to a p-electrode and an n-electrode of the LED element while being in vacuum contact with a vacuum head. In process of the method, the posture of the LED element is controlled such that the n-electrode of the LED element is mounted on the p-electrode bump of the submount board and p-electrode of the LED element is mounted on the n-electrode bump of the submount board. Then, by applying ultrasonic vibration to the LED element, the LED element is pressure-bonded to the submount board while allowing the bumps to be pushed down.  
       FIG. 12  is a perspective view showing an electrode forming surface of the LED element. The LED element  30  comprises: a transparent sapphire substrate  31 ; a buffer layer  32  formed on the sapphire substrate  31 ; an n-type semiconductor layer  33  formed on the buffer layer  32 ; a light-emitting layer  34  formed on the n-type semiconductor layer  33  to emit light based on the radiative recombination of hole and electron; a p-type semiconductor layer  35  formed on the light-emitting layer  34 ; the n-electrode  36  which is formed on part of the n-type semiconductor layer  33  exposed by partially etching the p-type semiconductor layer  35  to the n-type semiconductor layer  33 ; and the p-electrode  36  which is formed on the p-type semiconductor layer  35  and whose surface area is defined except the exposed part of the n-type semiconductor layer  33 .  
      However, in the above LED element, the p-electrode and the n-electrode each needs to have a certain electrode area to facilitate the wire bonding in the flip-chip mounting. Especially, since the p-electrode area corresponding to the emission area is reduced due to the n-electrode area, the rate of the emission area relative to the element&#39;s surface area must be reduced. Therefore, a large current cannot be applied thereto since the current density of the light-emitting layer becomes too high.  
      Further, since about ¼ of the element&#39;s surface area becomes nonradiative portion due to the n-electrode area, a non-uniform light pattern is generated. When the LED element is used in combination with a convergence optical system, the non-uniform light pattern is radiated and focused. Therefore, it is difficult to enhance the brightness or to improve the light distribution.  
      To solve the above problems, an LED element is suggested in which electrodes for applying a voltage to an n-type semiconductor layer and a p-type semiconductor layer of the LED element are provided on the side face of the LED element (for example, see JP-A-B-102552, paragraphs 0024 to 0032 and FIG. 1 thereof).  
      JP-A- 8 -102552 (FIG. 1) discloses the LED element that insulation layers of SiO 2  are formed on the side faces of a semiconductor layer and a sapphire substrate. One of the insulation layers is etched at part corresponding to an end face of a p-type GaN layer at the top of semiconductor layers of the LED element, and the other of the insulation layers is etched at part corresponding to an end face of an n-type GaN layer. A p-electrode and an n-electrode each are formed on the insulation layer as a conductive film electrically connected to the p-type GaN layer and the n-type GaN layer through the etched part.  
      In the above LED element, since no electrode is formed on the surface (light extraction surface) of the semiconductor layer, light emitted from the light-emitting layer can be efficiently radiated upward without being blocked by any electrode. Further, since the area of the light-emitting layer is not reduced by etching, the light-emitting layer can have the same area as the sapphire substrate. Therefore, the mount of light radiated from the top face of the semiconductor layer increases and thereby the emission intensity can be enhanced.  
      However, the LED element of JP-A- 8 -103055 needs a process that, after a wafer is fabricated by forming the semiconductor layers on the sapphire substrate and then the wafer is diced into chips, the insulation layer is partially etched and the p- and n-electrodes are formed at the etched part through which they are electrically connected to the p-type GaN layer and the n-type GaN layer. Thus, since each chip needs to be processed by using a microscopic and advanced technique, it is difficult to produce the LED element in mass production. Further, in the LED element, although the electrical connection performance is enhanced, the heat radiation performance is insufficient for heat generated during the operation. Therefore, the emission efficiency must be reduced that much.  
     SUMMARY OF THE INVENTION  
      It is an object of the invention to provide a light emitting element that has an increased emission area relative to the element&#39;s surface area and prevents unevenness in light distribution so as to increase brightness thereof.  
      It is a further object of the invention to provide a light emitting element that has an excellent mounting performance, a high reliability in electrical connection, and a heat radiation performance as well as having an increased emission area relative to the element&#39;s surface area.  
      It is a further object of the invention to provide a method of making the light emitting element thus featured while using the conventional apparatus without requiring any advance technique.  
      (1) According to one aspect of the invention, a light emitting element comprises:  
      a semiconductor layer comprising a light-emitting layer;  
      a first electrode that is defined corresponding to the light-emitting layer to supply power to the light-emitting layer;  
      a second electrode that is defined as a counter electrode of the first electrode;  
      an insulation layer than is formed on a mounting face side of the semiconductor layer; and  
      a first terminal and a second terminal that are formed on a surface of the insulation layer corresponding to the first electrode and the second electrode, respectively,  
      wherein the first electrode and the second electrode are formed on the mounting face side of the semiconductor layer,  
      the insulation layer comprises a first opening and a second opening that are formed corresponding to the first electrode and the second electrode, respectively, and  
      the first electrode and the second electrode are electrically connected through the first hole and the second hole, respectively, to the first terminal and the second terminal.  
      (2) According to another aspect of the invention, a light emitting element comprises:  
      a semiconductor layer comprising a light-emitting layer;  
      a first electrode that is defined corresponding to the light-emitting layer to supply power to the light-emitting layer;  
      a second electrode that is defined as a counter electrode of the first electrode;  
      wherein the first electrode and the second electrode are formed on the mounting face side of the semiconductor layer, and  
      the light-emitting layer and the first electrode are surrounded by the second electrode  
      (3) According to another aspect of the invention, a light emitting element comprises:  
      a semiconductor layer comprising a light-emitting layer; and  
      an n-type electrode and a p-type electrode to supply power to the light-emitting layer,  
      wherein the n-type electrode and the p-type electrode are provided at a periphery of the semiconductor layer that has a width smaller than an entire width of the light emitting element.  
      (4) According to another aspect of the invention, a method of making a light emitting element comprises:  
      a semiconductor layer formation step of forming a semiconductor layer comprising a light-emitting layer by stacking a semiconductor material on a wafer underlying substrate;  
      a semiconductor layer removal step of partially removing the semiconductor layer in a predetermined width and a predetermined depth from a surface of the semiconductor layer to formed an exposed portion;  
      an electrode formation step of forming electrodes to supply power to an n-type layer and a p-type layer of the semiconductor layer at the exposed portion; and  
      an element formation step of cutting the underlying substrate with the semiconductor layer into a light emitting element to allow the electrodes to be exposed to a periphery of the light emitting element  
      (Advantages of the Invention)  
      In the invention, since the p-type and n-type electrodes can be varied in arbitrary form, the light emitting element can have an increased emission area relative to the element&#39;s surface area and prevent unevenness in light distribution so as to increase brightness thereof.  
      Further, the light emitting element can have an excellent mounting performance, a high reliability in electrical connection, and a heat radiation performance even in a large size type.  
      In addition, the method of making the light emitting element can be conducted by using the conventional apparatus without requiring any advance technique.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The preferred embodiments according to the invention will be explained below referring to the drawings, wherein:  
       FIG. 1A  is a cross sectional view showing an LED element in a first preferred embodiment according to the invention, where the LED element is cut in a diagonal line thereof;  
       FIG. 1B  is a top view showing the form of a p-electrode and an n-electrode in the LED element in  FIG. 1A ;  
       FIG. 1C  is a top view showing an insulation layer with an opening in the LED element in  FIG. 1A ;  
       FIG. 1D  is a top view showing a p-terminal portion and an n-terminal portion in the LED element in  FIG. 1A ;  
       FIG. 2A  is a cross sectional view showing an LED element in a second preferred embodiment according to the invention, where the LED element is cut in a diagonal line thereof;  
       FIG. 2B  is a top view showing the form of a p-electrode and an n-electrode in the LED element in  FIG. 2A ;  
       FIG. 2C  is a top view showing an insulation layer with an opening in the LED element in  FIG. 2A ;  
       FIG. 2D  is a top view showing a p-terminal portion and an n-terminal portion in the LED element in  FIG. 2A ;  
       FIG. 2E  is a top view showing a modification of the n-electrode in  FIG. 2B ;  
       FIGS. 3A  to  3 E are top views showing modifications of the n-electrode and the p-electrode in the LED element of the second embodiment;  
       FIG. 4A  is a top view showing a modification of the insulation layer in the LED element of the second embodiment;  
       FIG. 4B  is a cross sectional view showing the insulation layer in  FIG. 4A ;  
       FIG. 5A  is a cross sectional view showing an LED element in a third preferred embodiment according to the invention, where the LED element is cut in a diagonal line thereof;  
       FIG. 5B  is a top view showing the form of a p-electrode and an n-electrode in the LED element in  FIG. 5A ;  
       FIG. 5C  is a top view showing an insulation layer with an opening in the LED element in  FIG. 5A ;  
       FIG. 5D  is a top view showing a p-terminal portion and an n-terminal portion in the LED element in  FIG. 5A ;  
       FIG. 6  is a cross sectional view showing an LED element in a fourth preferred embodiment according to the invention;  
       FIG. 7A  is a top view showing the form of a p-electrode is and an n-electrode in a fifth preferred embodiment according to the invention;  
       FIG. 7B  is a top view showing a p-terminal portion and an n-terminal portion in the LED element in  FIG. 7A ;  
       FIG. 9A  is a top view showing the form of a p-electrode and an n-electrode in a sixth preferred embodiment according to the invention;  
       FIG. 8B  is a top view showing a p-terminal portion and an n-terminal portion in the LED element in  FIG. 8A ;  
       FIG. 9A  is a top view showing the form of a p-electrode and an n-electrode in a seventh preferred embodiment according to the invention;  
       FIG. 9B  is a top view showing a p-terminal portion and an n-terminal portion in the LED element in  FIG. 9A ;  
       FIG. 10A  is a top view showing the form of a p-electrode and an n-electrode in an eighth preferred embodiment according to the invention;  
       FIG. 10B  is a top view showing a p-terminal portion and an n-terminal portion in the LED element in  FIG. 10A ;  
       FIG. 11A  is a top view showing the form of a p-electrode and an n-electrode in a ninth preferred embodiment according to the invention;  
       FIG. 11B  is a top view showing a p-terminal portion and an n-terminal portion in the LED element in  FIG. 11A ;  
       FIG. 12  is a perspective view showing the conventional LED element;  
       FIG. 13A  is a cross sectional view showing an LED element in a tenth preferred embodiment according to the invention, where the LED element is cut in a diagonal line thereof;  
       FIG. 13B  is a top view showing the LED element in  FIG. 13A , where the LED element is view from the light extraction side;  
       FIGS. 14A  to  14 D are cross sectional views showing a process of making the LED element of the tenth embodiment, where shown are steps until when an insulation layer  116  is formed;  
       FIGS. 15A  to  15 C are cross sectional views showing a process of making the LED element of the tenth embodiment, where shown are steps from the formation of electrodes until the completion;  
       FIG. 16A  is a cross sectional view showing a flip-chip mounting example of the LED element of the tenth embodiment onto a mounting board;  
       FIG. 16B  is a cross sectional view showing a flip-chip mounting example of the LED element of the tenth embodiment onto a mounting board with a concave portion;  
       FIG. 17A  is a top view showing an LED element in an eleventh preferred embodiment according to the invention;  
       FIG. 17B  is a cross sectional view cut along a line A-A in  FIG. 17A ;  
       FIG. 17C  is a top view showing the solder connection of the LED element of the eleventh embodiment, which is viewed from the side of a sapphire substrate thereof;  
       FIG. 18A  is a top view showing an LED element in a twelfth preferred embodiment according to the invention;  
       FIG. 18B  is a cross sectional view cut along a line B-B in  FIG. 18A ;  
       FIG. 19  is a cop view showing an LED element in a thirteenth preferred embodiment according to the invention;  
       FIG. 20  is a top view showing an LED element in a fourteenth preferred embodiment according to the invention;  
       FIG. 21  is a cross sectional view showing a mounting structure of an LED element in a fifteenth preferred embodiment according to the invention, where the LED element is connected to a copper lead;  
       FIG. 22A  is a cross sectional view showing a first mounting structure of an LED element in a sixteenth preferred embodiment according to the invention;  
       FIG. 22B  is a cross sectional view showing a second mounting structure of an LED element in the sixteenth embodiment according to the invention;  
       FIG. 23  is a cross sectional view showing a mounting structure of an LED element in a seventeenth preferred embodiment according to the invention;  
       FIG. 24  is a cross sectional view showing a mounting structure of an LED element in an eighteenth preferred embodiment according to the invention;  
       FIG. 25A  is a cross sectional view showing a large-size LED element (1 mm square) in a nineteenth preferred embodiment according to the invention; and  
       FIG. 25B  is a top view showing the LED element in  FIG. 25A , which is viewed from the side of an insulation layer formation surface thereof. 
    
    
     DETAILED DESCRIPTION OP THE PREFERRED EMBODIMENTS  
     First Embodiment  
      (Composition of LED Element  1 )  
       FIGS. 1A  to  1 D show an LED element in the first preferred embodiment according to the invention.  
      The LED element  1  is composed of: a sapphire substrate  10 ; an AlN buffer layer  11  formed on the sapphire substrate  10 ; an n-GaN layer  12  formed on the AlN buffer layer  11 ; a light-emitting layer  13  formed on the n-GaN layer  12 ; a p-GaN layer  14  formed on the light-emitting layer  13 , the n-GaN layer  12  to the p-GaN layer  14  being of group III nitride-based compound semiconductor; an n-electrode  15  as a second electrode formed on part of the n-GaN layer  12  exposed by partially etching the p-GaN layer  14  to the n-GaN layer  12 ; a p-electrode  16  as a first electrode formed on the p-GaN layer  14  to supply current to the light-emitting layer  13 ; an insulation layer  17  of a SiO 2 -based material formed to cover the electrode formation side; an n-terminal  18  electrically connected through an opening  17   n  provided in the insulation layer  17  to the n-electrode  15 ; and a p-terminal  19  electrically connected through an opening  17   p  provided in the insulation layer  17  to the p-electrode  16 . The LED element  1  has a size of 0.3 mm×0.3 mm, which is widely prevalent.  
      A method of forming a group III nitride-based compound semiconductor layer is not specifically limited, and well-known metal organic chemical vapor deposition (MOCVD) method, molecular beam epitaxy (MBE) method, hydride vapor phase epitaxy (HVPE) method, sputtering method, ion plating method, cascade shower method and the like are applicable.  
      The LED element may have a homostructure, a heterostructure, or a double heterostructure. Furthermore, a quantum well structure (a single quantum well structure or a multiquantum well structure) is also applicable.  
      The p-electrode  16  is formed such that its surface occupies 60% or more of the surface of the LED element  1 .  
      (Method of Making the LED Element  1 )  
      The method of making the LED element  1  will be explained below.  
      (Step of Providing the Substrate)  
      First, a wafer sapphire substrate  10  is provided as an underlying substrate.  
      (Step of Forming the Semiconductor Layers)  
      Then, the AlN buffer layer  11  is formed on a surface of the sapphire substrate  10 . Then, the n-GaN layer  12 , the light emitting layer  13 , and the p-GaN layer  14  are sequentially formed on the AlN buffer layer  11 . Then, a stack portion from the p-GaN layer  14  to the n-GaN layer  12  is partially removed by etching to expose the n-GaN layer  12 . The etching is conducted such that the p-GaN layer  14  has a sufficient surface area relative to the surface of the LED element  1 .  
      (Step of Forming the Electrodes)  
      Then, as shown in  FIG. 1B , the n-electrode  15  and the p-electrode  16  of Au are formed by deposition on the exposed surface of the n-GaN layer  12  and the surface of the p-GaN layer  14 , respectively. Alternatively, the n-electrode  15  and the p-electrode  16  may be formed by other film formation method suas as sputtering.  
      (Step of Forming the Insulation Layer)  
      Then, as shown in  FIG. 1C , the insulation layer  17  of the SiO 2 -based material is formed to cover the electrode formation side. Then, a mask pattern corresponding to the openings  17   n  and  17   p  is formed on the insulation layer  17  and then etched to form the openings  17   n  and  17   p  in the insulation layer  17   
      (Step of Forming the Terminals)  
      Then, as shown in  FIG. 1D  the n-terminal  18  and the p-terminal  19  of Au are formed by deposition at the corresponding openings  17   n  and  17   p  in the insulation layer  17  Although in  FIG. 1D  the n-terminal  18  is shown smaller than the p-terminal  19 , the n-terminal  18  and the p-terminal  19  can be formed in arbitrary form within a size not to be short-circuited each other since the electrode formation surface of the LED element  1  is covered with the insulation layer  17 .  
      In making an LED lamp by using the LED element  1  thus fabricated, for example, a substrate of ceramics material is provided, on the surface of which a wiring pattern of copper foil is formed. The LED element  1  is positioned on the wiring pattern of the substrate and flip-chip mounted by the reflowing of solder. Then, it is integrally sealed with a seal material such as epoxy resin and glass material to have the packaged LED lamp.  
      (Operation of the LED Element  1 )  
      When the LED lamp thus made is supplied with power by connecting the wiring pattern on the substrate to a power supply (not shown), a forward voltage is applied through the n-terminal  18  and the p-terminal  19  to the n-electrode  15  and the p-electrode  16 . Thereby, radiative recombination of hole and electron occurs in the light-emitting layer  13  and blue light is emitted according to the form of the p-electrode  16  as shown in  FIG. 1B . Blue light irradiated to the n-GaN layer  12  side is externally radiated passing through the sapphire substrate  10 . Blue light irradiated to the p-GaN layer  14  side is reflected on the p-electrode  16  back to the light-emitting layer  13  and externally radiated passing through the sapphire substrate  10  as well  
      (Effects of the First Embodiment)  
      The effects of the first embodiment are as follows. 
      (1) Since the LED element  1  is at the electrode formation surface provided with the n-terminal  18  and the p-terminal  19  of Au to have an external connection through the insulation layer  17 , the n-electrode  15  and the p-electrode  16  can be formed in arbitrary form without being limited to an electrode form needed to secure the mounting property of the LED element  1 . Thus, the p-electrode  16  can be designed considering the emission form and thereby the emission area can be increased. Therefore, even when current is supplied according to an increase in the emission area, the current density in the light-emitting layer can be kept equal. As a result, the amount of emitted light can be increased.     (2) In the conventional LED element, since there was a large nonradiative portion in area ratio, symmetry in emission must be significantly broken. However, in the first embodiment, since the nonradiative area is reduced relative to the emission area of the LED element, blue light can be uniformly radiated from the entire emission surface of the LED element  1  without unevenness in light distribution.     (3) Since the emission surface area is increased relative to the emission area of the LED element, the current density in the light-emitting layer can be reduced even in the same current supply as the conventional LED element. Therefore, the thermal localization in the LED element  1  can be prevented. Thereby, the emission efficiency can be kept even when it is used for long hours.     (4) Since the irregularity in emission form can be prevented, when it is used for an LED lamp with a converging optical system, the convergence performance can be enhanced without deforming the image of light source projected and therefore a natural emission pattern can be obtained.     (5) The n-terminal  18  and the p-terminal  19  can be formed with a size and a distance not dependent on the size of the n-electrode  15  and the p-electrode  16 , Therefore, it can be mounted by the reflowing of solder. Thus, the performance in mounting and heat radiation can be enhanced.    

      In the first embodiment, the electrical bonding to the n-terminal  18  and the p-terminal  19  can be conducted using Au bumps when the LED element  1  is mounted.  
      The composition of the LED element  1  is not limited to the blue LED element of group III nitride-based compound semiconductor. The LED element may emit light in other emission color and may be of another material.  
      Although in the first embodiment the LED element  1  is 0.3 mm×0.3 mm in size, it can be 0.2 mm×0.2 mm or smaller in size while securing an emission area. Thus, the LED element  1  can be realized in a size never before developed due to the limitation of the n-electrode area.  
      Also, the LED element  1  can have an elongated size such as 0.1 mm×0.3 mm for a practical use. The LED element  1  thus formed can increase a coupling efficiency to a thin-type light guiding plate.  
     Second Embodiment  
      (Composition of LED Element  1 )  
       FIGS. 2A  to  2 D show an LED element in the second preferred embodiment according to the invention.  
      Herein, like components are indicated by the same numerals as used in the first embodiment.  
      The flip-chip type LED element  1  is different from the first embodiment in that, as shown in  FIG. 2A , the p-GaN layer  14  is disposed like an island at the center of the LED element  1 , the p-electrode  16  is formed thereon, and the n-electrode  15  is disposed circularly around the p-electrode  16 .  
      The n-electrode  15  is about 10 μm in line width of narrowest portion and about 350 μm in line width of widest portion. The p-electrode  16  is, as shown in  FIG. 2B , shaped like a square with rounded corners, and a predetermined distance separated through an insulation portion  100  from the n-electrode  15  which circularly surrounds the p-electrode  16 . The predetermined distance is preferably such a minimum one that can prevent the light leakage from the GaN layer and the short-circuiting.  
      The insulation layer  17  is, as shown in  FIG. 2C , formed depending on the disposition of the n-electrode  15  and the p-electrode  16 . Although in  FIG. 2C , the n-electrode  15  and the p-electrode  16  are disposed diagonally at the bottom of the LED element  1 , they may be in parallel disposed a predetermined distance separated each other.  
      The n-terminal  18  and the p-terminal  19  are, as shown in  FIG. 2D , disposed to cover the openings  17   n ,  17 P. Thereby, they are electrically connected to the n-electrode  15  and the p-electrode  16  (though not shown in  FIG. 2D ) covered by the insulation layer  17 .  
     Effects of the Second Embodiment  
      The effects of the second embodiment are as follows. 
      (1) The p-GaN layer  14  is disposed like an island at the center of the LED element  1 , the p-electrode  16  is formed thereon, and the n-electrode  15  is disposed circularly around the p-electrode  16 . Thus, the emission portion can be disposed at the center of the LED element  1 . Since electros are uniformly supplied from all regions of the p-GaN layer  14 , a uniform emission can be generated in the light-emitting layer  33  under the p-electrode  16 . Therefore, uniform blue light can be externally radiated from the LED element  1  to reduce unevenness in light distribution.     (2) Since the n-electrode  15  is circularly disposed around the p-electrode  16 , heat of the n-electrode  15  can be dispersed widely to the LED element  1  to stabilize the light output characteristics. Further, due to the enhancement in thermal dispersion property, the heat radiation property can be improved to prevent the overheating of the LED element  1 .     (3) Since the light-emitting layer  13  is formed symmetrical, a natural emission pattern can be obtained even when the LED element  1  is used in combination with the convergence optical system.    

      Meanwhile, as shown in  FIG. 2E , the n-electrode  15  is not always formed perfectly around the p-electrode  16 . When it is formed substantially around the p-electrode  16 , the same effects can be obtained.  
       FIGS. 3A  to  3 E are top views showing modifications of the n-electrode and the p-electrode in the LED element of the second embodiment.  
      (Modification 1 of Electrode Form)  
      As shown in  FIG. 3A , the n-electrode  15  may have a separation portion  150  that diagonally separates the p-electrode  16 .  
      In modification 1, since the formation region of the p-electrode  16  is separated into two parts, current can be uniformly and rapidly spread and thereby good emission characteristics can be obtained under the p-electrode  16   
      (Modification 2 of Electrode Form)  
      As shown in  FIG. 3B , the n-electrode  15  may have a cross portion  151  at the center of the separation portion  150 .  
      In modification 2, since the cross portion  151  is formed while the formation region of the p-electrode  16  is separated into two parts by the separation portion  150 , current can be further uniformly and rapidly spread and thereby good emission characteristics can be obtained under the p-electrode  16 .  
      (Modification 3 of Electrode Form)  
      As shown in  FIG. 3C , a p-electrode  16 A may be formed at the center of the surface of the LED element  1  surrounded by the n-electrode  15  and a p-electrode  16 B may be formed around the n-electrode  15 .  
       FIG. 3D  shows the n-terminal  18  and the p-terminal  19  formed on the insulation layer  17 . The insulation layer  17  is formed on the surface of the n-electrode  15  and the p-electrodes  16 A,  16 B as shown in  FIG. 3C  while having the openings  17   n ,  17   p.  The n-terminal  18  and the p-terminal  19  are formed triangular in surface form while being partially embedded in the openings  17   n ,  17   p . The p-terminal  19  is embedded in the two openings  17   p ,  17   p  and thereby electrically connected to the p-electrodes  16 A,  16 B.  
      In modification 3, since the p-electrodes  16 A,  16 B are disposed inside and outside of the n-electrode  15 , a good current spreading property can be obtained to allow the good emission characteristics of the LED element  1  while reducing the area of the n-electrode  15 .  
      (Modification 4 of Electrode Form)  
      As shown in  FIG. 3E , the n-electrode  15  may have a triangle portion  153  formed at a corner of the surface of the LED element  1  while the n-electrode  15  has the cross portion  151  in the region of the p-electrode  16  to connect the triangle portion  153 .  
      In modification 4, since the n-electrode  15  has the cross portion  151  and the triangle portion  153  in the region of the p-electrode  16  without surrounding the p-electrode  16 , the p-electrode  16  can have an increased area. Thereby, the emission characteristics can be enhanced while preventing unevenness in light distribution.  
      (Modification of the Insulation Layer  17 )  
       FIGS. 4A and 4B  show a modification of the insulation layer  17 .  
      A modified insulation layer  170  is composed of a first insulation layer  171 , a second insulation layer  172 , and a reflection layer  173  formed sandwiched by the first and the second insulation layers  171  and  172 . The reflection layer  173  is made of aluminum (Al) by deposition. The insulation layer  170  is provided with openings  17   n ,  17 P to connect the underlying n-electrode  15  and p-electrode  16  with the n-terminal and the p-terminal  19  (not shown).  
      Except the openings  17   n ,  17 P, the reflection layer  173  is formed as shown in  FIG. 4B . Thereby, light can be prevented from leaking in the opposite direction of the substrate through a gap between the n-electrode  15  and the p-electrode  16 .  
      The reflection layer  173  may be made of silver (Ag) or rhodium (Rh) instead of aluminum (Al).  
      In this modification, since the leakage of light through the gap between the electrodes can be prevented, the brightness of the LED element  1  can be enhanced even when the n-electrode  15  is formed in the region of the p-electrode  16 .  
      Although a bonding pad conventionally needs to have a bonding area of about φ100 μm, it may be a pattern (in arbitrary form) narrower than this area. Especially, it is effective that it has a line width of 50 μm or less, further 25 μm or less, This is because the bonding pad needed to bond a wire or bump affects on current supplied to the LED element  1 . In general, a wire of φ25 μm or so is used and the bonding pad therefor needs an area twice the wire diameter. It is not effective that the bonding area is smaller than the wire diameter.  
      In the invention, if the n-electrode  15  is in line width narrower than the bonding pad needed conventionally as mentioned above, the effects abovementioned can be obtained. Although the n-electrode  15  is generally a narrow line of 50 μm or less, it is not limited to this size in a large current LED and may be a narrow line with a width narrower than the corresponding bonding pad.  
      Further, since the same effects can be obtained by substantially surrounding the p-electrode  16  as shown in  FIG. 2E , the n-electrode  15  is not always formed perfectly around the p-electrode  16 .  
      If the improvement of light distribution is desired primarily, the light-emitting layer  13  may be formed circular etc. In this case, there is a certain space at the diagonal position of the surface of the LED element  1 . Therefore, the n-electrode  15  is not always formed a narrow line pattern and the terminal may be formed without forming the insulation layer  17 .  
     Third Embodiment  
      (Composition of LED Element  1 )  
       FIGS. 5A  to  5 D show an LED element in the third preferred embodiment according to the invention.  
      The flip-chip type LED element  1  is different from the first embodiment in that, as shown in  FIG. 5A , the p-GaN layer  14  is disposed like an island at the center of the LED element  1 , the p-electrode  16  is formed thereon, the n-electrode  15  is disposed circularly around the p-electrode  16 , and the p-GaN layer  14  is provided with an uneven sidewall  14 A formed uneven at the side thereof.  
      The uneven sidewall  14 A is formed by partially removing the p-GaN layer  14  to the n-GaN layer  12  by etching to expose the n-GaN layer  12 . It may be formed by another process such as cutting.  
     Effects of the Third Embodiment  
      In the third embodiment, since the p-GaN layer  14  is formed like an island at the center of the LED element  1  and the uneven sidewall  14 A is formed around the p-GaN layer  14 , in addition to the effects of the second embodiment, it is easy to extract light (herein called intra-layer confined light) confined in the light-emitting layer  13 . Thus, the external radiation efficiency can be enhanced.  
      Although in  FIGS. 5B  to  5 D the uneven surface is illustrated with exaggeration, it is desirable that a fine uneven surface is made to secure a larger surface area of the p-GaN layer  14 . Thus, the fineness of the uneven surface may be in the range of an emission wavelength and an optimum design in light extraction can be made according to a refractive index of the material, the layer composition etc.  
     Fourth Embodiment  
      (Composition of LED Element  1 )  
       FIG. 6  is a cross sectional view showing an LED element in the fourth preferred embodiment according to the invention.  
      The flip-chip type LED element  1  is different from the second embodiment in that a GaN substrate  20  is used in place of the sapphire substrate  10  and is provided with cut portions  20 A being 45 degrees cut off at the corner of the light extraction surface of the LED element  1 .  
     Effects of the Fourth Embodiment  
      In the fourth embodiment, since the GaN substrate  20  is used as an underlying substrate, the group III nitride-based compound semiconductor layer has a refractive index equal to the GaN substrate  20 . Therefore, blue light emitted from the light-emitting layer  13  can reach the light extraction surface of the GaN substrate  20  instead of being totally reflected on the interface of the group III nitride-based compound semiconductor layer and the GaN substrate  20 . Further, since the GaN substrate  20  is provided with the cut portions  20 A at the corner of the light extraction surface, the light extraction efficiency can be enhanced to efficiently extract blue light.  
     Fifth Embodiment  
      (Composition of LED Element  1 )  
       FIGS. 7A and 7B  show an LED element in the fifth preferred embodiment according to the invention.  
      The flip-chip type LED element  1  is formed a large size (1 mm×1 mm), and as shown in  FIG. 7A  it is composed of the p-electrodes  16  formed rectangular and disposed in parallel and the n-electrode  15  formed to surround the p-electrodes  16  Further, as shown in  FIG. 7B , the insulation layer  17  is provided with an opening  17   n  formed linearly therein corresponding to the n-electrode  15  and multiple openings  17   p  formed circular therein corresponding to the p-electrode  16 . The n-electrode  15  and the p-electrode  16  are electrically connected through the openings  17   n ,  17   p  to the n-terminal  18  and the p-terminal  19 , respectively.  
      As shown in  FIG. 7B , the n-terminal  18  and the p-terminal  19  are formed rectangular in a predetermined width while being disposed along the opposite sides of the LED element  1 .  
     Effects of the Fifth Embodiment  
      In the fifth embodiment, since the emission area is increased relative to the surface area of the LED element  1  in the large size LED  1 , the brightness can be enhanced without reducing the heat radiation property.  
      The LED element  1  can be mounted through a solder other than Au. In using the solder, since a surface heat radiation path is formed through the solder, unevenness in temperature can be prevented in the LED element  1 .  
      Due to the large size, the design freedom of electrode formation can be enhanced.  
      Further, the productivity can be enhanced since the p-electrode  16  and the n-electrode  15  have the rectangular shape easy to form.  
      In the fifth embodiment, by using the insulation layer  170  as explained earlier instead of the insulation layer  17 , light can be prevented from leaking through a gap between the n-electrode  15  and the p-electrode  16 . Thereby, the brightness can be further enhanced.  
     Sixth Embodiment  
      (Composition of LED Element  1 )  
       FIGS. 8A and 8B  show an LED element in the sixth preferred embodiment according to the invention.  
      The flip-chip type LED element  1  is formed a large size (1 mm×1 mm), and as shown in  FIG. 8A  it has an electrode form that the formation area of the p-electrode  16  is arranged like a zigzag to the formation area of the n-electrode  15 . Further, as shown in  FIG. 8B , the insulation layer  17  is provided with openings  17   n ,  17   p , through which the n-electrode  15  and the p-electrode  16  are electrically connected to the n-terminal  18  and the p-terminal  19 , respectively.  
      The n-terminal  18  and the p-terminal  19  are diagonally disposed at the corner of the LED element  1 , and a heat radiation layer  25  of Rh—Au is formed a thin film therebetween.  
     Effects of the Sixth Embodiment  
      In the sixth embodiment, like the fifth embodiment, the emission area can be increased relative to the surface of the LED element  1 . Further, since the heat radiation layer  25  with a good heat radiation property is formed on the surface of the is insulation layer  17 , the LED element  1  can be stably operated even in large current or long operation. Since the heat radiation layer  25  can reflect light leaked through a gap between the n-electrode  15  and the p-electrode  16 , loss of emitted light can be reduced.  
      In place of the insulation layer  17 , the insulation layer  170  as explained earlier may be used. Thereby, light can be prevented from leaking through a gap between the heat radiation layer and the n-electrode  15  or the p-electrode  16 . Thereby, the brightness can be further enhanced.  
     Seventh Embodiment  
      (Composition of LED Element  1 )  
       FIGS. 9A and 9B  show an LED element in the seventh preferred embodiment according to the invention.  
      The flip-chip type LED element  1  is formed a large size (1 mm×1 mm), and as shown in  FIG. 9A  it has an electrode form that the multiple p-electrodes  16  are formed hexagonal or semi-hexagonal and arranged zigzag and the n-electrode  15  is formed around the p-electrode  16 . Further, as shown in  FIG. 9B , the insulation layer  17  is provided with openings  17   n  (in trident form),  17   p  (in circular form), through which the n-electrode  15  and the p-electrode  16  are electrically connected to the n-terminal  18  and the p-terminal  19 , respectively.  
     Effects of the Seventh Embodiment  
      In the seventh embodiment, since the hexagonal emission region is formed by the electrode form with the hexagonal p-electrode  16  surrounded by the n-electrode  15 , the light-emitting layer  13  under the p-electrode  16  can have a high emission intensity. Further, due to the integration of the emission regions with a high emission intensity, the brightness can be enhanced at the entire surface of the LED element  1 .  
     Eighth Embodiment  
      (Composition of LED Element  1 )  
       FIGS. 10A and 10B  show an LED element in the eighth preferred embodiment according to the invention.  
      The flip-chip type LED element  1  is formed a large size (1 mm×1 mm), and as shown in  FIG. 10A  it has an electrode form that the cross-shaped n-electrode  15  is formed in the formation area of the p-electrode  16 . Further, as shown in  FIG. 10B , the insulation layer  17  is provided with openings  17   n ,  17   p , through which the n-electrode  15  and the p-electrode  16  are electrically connected to the n-terminal  18  and the p-terminal  19 , respectively.  
      The p-terminal  19  is formed such that its surface area is increased relative to the surface of the LED element  1  to enhance the radiation of heat generated in operating the LED element  1 . Also, it is formed to cover most of the n-electrode  15  since the n-electrode  15  generates relatively much heat.  
     Effects of the Eighth Embodiment  
      In the eighth embodiment, since the surface area of the p-electrode  16  is relatively increased by disposing the cross-shaped n-electrode  15  in the formation area of the p-electrode  16 , unevenness in temperature can be prevented in the LED element  1 . Further, unevenness in light distribution can be reduced, design freedom in electrode formation can be enhanced, and the brightness can be enhanced.  
     Ninth Embodiment  
      (Composition of LED Element  1 )  
       FIGS. 11A and 11B  show an LED element in the ninth preferred embodiment according to the invention.  
      The flip-chip type LED element  1  is formed a large size (1 mm×1 mm)), and as shown in  FIG. 11A  it has an electrode form that an inverted E-shaped n-electrode  15  is formed in the formation area of the p-electrode  16 , a linear n-electrode  15  is formed outside of the p-electrode  16 , and the inverted E-shaped n-electrode  15  is connected to the linear n-electrode  15 . Further, as shown in  FIG. 11B , the insulation layer  17  is provided with openings  17   n  (in leaner form),  17   p  (in circular form), through which the n-electrode  15  and the p-electrode  16  are electrically connected to the n-terminal  18  and the p-terminal  19 , respectively.  
      The n-terminal  18  is formed to cover the formation area of the n-electrode  15  so as to reflect light leaked through a gap between the n-electrode  15  and the p-electrode  16  back to the semiconductor layer side.  
     Effects of the Ninth Embodiment  
      In the ninth embodiment, the emission area can be increased relative to the surface of the LED element  1 . Further, a good emission property can be obtained while reducing the relative area of the n-electrode  15  to the p-electrode  16 .  
      Also in the ninth embodiment, in place of the insulation layer  17 , the insulation layer  170  as explained earlier may be used. Thereby, light can be prevented from leaking through a gap between the heat radiation layer and the n-electrode  15  or the p-electrode  16 . Thereby, the brightness can be further enhanced.  
      Since the resistivity of a p-layer is high in GaN-based semiconductors, the emission area is located substantially under or over a p-electrode. Therefore, the electrode formed as descried above is particularly effective. Alternatively, the electrode formation may be used for another semiconductor material. In this case, the electrode pattern may be reversed depending on the level of resistivity.  
     Tenth Embodiment  
      (Composition of LED Element  1 )  
       FIGS. 13A and 13B  show an LED element in the tenth preferred embodiment according to the invention.  
      As shown in  FIG. 13A , the LED element  101  is composed of: a sapphire substrate  110 ; an AlN buffer layer  111  formed on the sapphire substrate  110 ; an n-GaN layer  112  formed on the AlN buffer layer  111 ; a light-emitting layer  113  formed on the n-GaN layer  112 ; a p-GaN layer  114  formed on the light-emitting layer  113 , the n-GaN layer  112  to the p-GaN layer  114  being of group III nitride-based compound semiconductor and composing a GaN-based semiconductor layer  200 ; a p-contact electrode  115  formed on the p-GaN layer  114  to spread current into the p-GaN layer  114 ; a transparent insulation layer  116  formed on the side of the GaN-based semiconductor layer  200  and on the p-contact electrode  115 , an n-external electrode  117  formed on part of the n-GaN layer  112  exposed by partially etching the p-GaN layer  114  to the n-GaN layer  112  and on the side of the insulation layer  116 ; a p-external electrode  118  formed on the side of the insulation layer  116  in contact with the p-contact electrode  115 ; and a transparent insulation layer  119  formed to cover the element surface between the n-external electrode  117  and the p-external electrode  118 .  
      Herein, the GaN-based semiconductor layer  200  comprises a stack portion from the n-GaN layer  112  to the p-GaN layer  114 . Light emitted from the light-emitting layer  113  of the LED element  101  has an emission wavelength of 460 nm.  
      A method of forming a group III nitride-based compound semiconductor layer is not specifically limited, and well-known metal organic chemical vapor deposition (MOCVD) method, molecular beam epitaxy (MBE) method, hydride vapor phase epitaxy (HVPE) method, sputtering method, ion plating method, cascade shower method and the like are applicable.  
      The LED element may have a homostructure, a heterostructure, or a double heterostructure. Furthermore, a quantum well structure (a single quantum well structure or a multiquantum well structure) is also applicable.  
      The p-contact electrode  115  serves to spread current into the p-GaN layer  114  and to give a good electrical connection with an external member or device. It is made of rhodium (Rh) with a light reflection property. The p-contact electrode  115  may be made of transparent ITO (indium tin oxide) or ZnO or a transparent material such as Au/Co, Ni/Ti if it can be in ohmic contact with the p-GaN layer  114 .  
      The insulation layer  116  is made of SiO 2  and disposed to cover the side of the GaN-based semiconductor layer  200  to prevent the short-circuiting of the n-external electrode  117  and the p-external electrode  118  with the GaN-based semiconductor layer  200 . It may be made of another insulative material such as SiN instead of SiO 2 .  
      The n-external electrode  117  is made of V/Al, and the p-external electrode  118  is made of Ti. These external electrodes are formed such that they are exposed on an element periphery ranging from the side of the element to an edge of the surface of the insulation layer  119  so as to allow the electrical bonding at the side of the element and the surface mounting at the surface side of the p-contact electrode  115 . Herein, the element periphery comprises the side of the LED element  101  and an edge of the surface of the insulation layer  119  as shown in  FIG. 13A . As shown in  FIG. 13B , the n-external electrode  117  ranges over the entire length of two adjacent sides and the p-external electrode  118  is formed part of two sides opposed to the two sides of the n-external electrode  117 . The p-external electrode  118  has a formation region smaller than the n-external electrode  117 . The electrode surface may be solder-plated.  
      (Method of Making the LED Element  101 )  
       FIGS. 14A  to  14 D are cross sectional views showing a process of making the LED element of the tenth embodiment, where shown are steps until when the insulation layer  116  is formed at the side of the LED element  101 .  
      Hereinafter, for the sake of explanation, only part of a wafer corresponding to the LED element  101  is illustrated in the drawings although, in fact, the wafer sapphire substrate  110  is used to grow the semiconductor layer thereon and then the wafer with the semiconductor layer is diced to obtain the LED element  101 .  
      (Step of Forming the GaN-based Semiconductor Layer  200 )  
      At first, as shown in  FIG. 14A , the AlN buffer layer  111 , the GaN-based semiconductor layer  200  and the p-contact electrode  115  are formed on the wafer sapphire substrate  110  by MOCVD.  
      (First Etching Step)  
      Then, as shown in  FIG. 14B , the GaN-based semiconductor layer  200  is dry-etched to remove a stack portion from the surface of the GaN-based semiconductor layer  200  to the n-GaN layer  112 , where the stack portion corresponds to a region to form the n-external electrode  117  and the p-external electrode  118 . Thereby, an exposed portion  112 A is formed at the side of the GaN-based semiconductor layer  200 . Alternatively, the p-contact electrode  115  may be formed placing a photoresist on the semiconductor layer after the exposed portion  112 A is formed, and then the photoresist can removed  
      (Step of Forming the Insulation Layer  116 )  
      Then, as shown in  FIG. 14C , the insulation layer  116  is formed by deposition on the GaN-based semiconductor layer  200  after the dry etching.  
      (Second Etching Step)  
      Then, as shown in  FIG. 14D , a photoresist is placed on the GaN-based semiconductor layer  200  with the insulation layer  116  formed thereon, and then the insulation layer  116  is partially etched except its portion corresponding to the side of the GaN-based semiconductor layer  200 . Thereby, part of the exposed portion  112 A and the p-contact electrode  115  are exposed.  
       FIGS. 15A  to  15 C are cross sectional views showing a process of making the LED element of the tenth embodiment, where shown are steps from the formation of electrodes until the completion.  
      (Step of Forming the External Electrodes  117 ,  118 )  
      As shown in  FIG. 15A , in the electrode formation process, the n-external electrode  117  of V/Al is formed by deposition at the exposed portion  112 A on the n-external electrode  117  side. Then, the p-external electrode  118  of Ti is formed by deposition at the exposed portion  112 A on the p-external electrode  118  side.  
      The n-external electrode  117  may be made of a material that can be in ohmic contact with the n-GaN layer  112 , for example, it may be of Ti other than V/Al. The p-external electrode  118  may be made of a material that can be electrically connected with the p-contact electrode  115 , for example, it may be of Al other than Ti.  
      Further, both of the n-external electrode  117  and the p-external electrode  118  may be of Ti. In this case, the n-external electrode  117  and the p-external electrode  116  can be formed together in the same step and thus the manufacturing step can be simplified.  
      (Step of Forming the Insulation Layer  119 )  
      Then, as shown in  FIG. 5B , the insulation layer  119  of SiO 2  is formed by deposition over the upper surface of the GaN-based semiconductor layer  200  including the electrode  115  and the formation region of the n-external electrode  117  and the p-external electrode  118 .  
      (Third Etching Step)  
      Then, as shown in  FIG. 15C , the insulation layer  119  is etched placing a photoresist on the GaN-based semiconductor layer  200  and then the photoresist is removed. Thereby, the insulation layer  119  is left except part on the n-external electrode  117  and the p-external electrode  118  at the element periphery such that it can prevent the short-circuiting of the n-external electrode  117  and the p-external electrode  118  and protect them.  
      (Dicing Step)  
      Then, the wafer composed of the GaN-based semiconductor layer  200  with the n-external electrode  117  and the p-external electrode  118  formed thereon and the sapphire substrate  110  is cut into a given element size by a dicer (not shown). As a result, the LED element  101  as shown in  FIG. 15C  can be obtained. The cutting of the wafer can be conducted by another process such as scribing instead of the dicing.  
      (Mounting of the LED Element  101 )  
       FIG. 16A  is a cross sectional view showing a flip-chip mounting example of the LED element of the tenth embodiment onto a mounting board.  
      As shown in  FIG. 16A , the LED element  101  fabricated as described above is mounted being bonded through an epoxy insulative adhesive  141  onto the surface of a ceramics board  123  with a wiring pattern  122  formed thereon. The n-external electrode  117  and the p-external electrode  118  are reflow-bonded to the wiring pattern  122  through a solder  120 A.  
      The insulative adhesive  141  may be of another material if it has a good thermal conductivity, for example, it may a paste with no adhesivity such that the LED element  101  can be in close contact with the board  123  in sheet form. It is more desirable that  141  is made of a material with high heat resistance and good adhesivity.  
      If the insulation to the wiring pattern  122  can be secured, the board  123  may be a conductive board that a metal material such as Cu and Al with a high heat conductivity is subjected to insulation treatment, instead of the abovementioned insulative board such as a flexible board of ceramics, glass epoxy, polyimide and conductive foil.  
      If no short-circuiting of the n-external electrode  117  and the p-external electrode  118  is generated, the insulative adhesive  141  may be replaced by a conductive material to bond the LED element  101  onto the board  123 . Such a material can be a conductive paste of silicone resin containing a filler such as Au, Cu and Al.  
      The solder  120 A may be replaced by a conductive adhesive such as an epoxy resin containing Ag paste or a conductive filler such as Au, Cu and Al so as to allow the electrical connection of the n-external electrode  117  and the p-external electrode  118  with the wiring pattern  122 .  
       FIG. 16B  is a cross sectional view showing a flip-chip mounting example of the LED element of the tenth embodiment onto a mounting board with a concave portion.  
      As shown in  FIG. 16B , a board  123  with the concave portion  123 A for positioning the element may be used such that part of the p-contact electrode  115  is inserted into the concave portion  123 A. The concave portion  123 A is coated with the insulative adhesive  141  to allow the bonding of the part of the p-contact electrode  115  of the LED element  101 . Like the manner as shown in  FIG. 16A , the n-external electrode  117  and the p-external electrode  118  are reflow-bonded to the wiring pattern  122  through the solder  120 A.  
      (Operation of the LED Element  101 )  
      When power is supplied connecting the wiring pattern  122  on the substrate to a power supply (not shown), a forward voltage is applied through the n-external electrode  117  and the p-external electrode  118  of the LED element  101  to the light-emitting layer  113 . Thereby, radiative recombination of hole and electron occurs in the light-emitting layer  113  and blue light is emitted. Blue light irradiated to the sapphire substrate  110  side is externally radiated passing through the sapphire substrate  110 . Heat generated during the operation of the LED element  101  is radiated through the insulative adhesive  141  to the board  123 .  
     Effects of the Tenth Embodiment  
      The effects of the tenth embodiment are as follows. 
      (1) Since the LED element  101  is fabricated with the n-external electrode  117  and the p-external electrode  118  formed around the light-emitting layer  113  based on the manufacturing process for the semiconductor LED by using the wafer sapphire substrate  110 , the LED element  101  can be easily made in a lot and in mass production by using the known apparatus and method.     (2) Since the n-external electrode  117  and the p-external electrode  118  are formed around the light-emitting layer  113 , not on the light extraction surface, while partially removing the sides of the GaN-based semiconductor layer  200 , light emitted from the light-emitting layer  113  can be prevented from being blocked by the n-external electrode  117  and the p-external electrode  118 . Further, due to the disposition of the external electrodes, the emission area of the light-emitting layer  113  can be increased in the same element size and the emission intensity can be enhanced. Thus, the LED element  101  can have a good light extraction efficiency and a high brightness.     (3) The electrical connection with the wiring pattern  122  etc. can be made in any of flip-chip mounting or face-up mounting. Namely, the type of mounting can be chosen according to use. For example, another type of mounting other than the above types can be conducted in which one side of the LED element  101  is used in electrical or mechanical bonding. Thus, various types of mounting can be offered.     (4) Since the nonradiative portion such as a wire bonding space and an n-electrode bump space can be eliminated or reduced, even the small size LED element  101  can have a sufficient ratio of emission area/LED surface area. Therefore, a further small LED element  101  can be realized which has an electrode interval near to the element width. For example, even an LED element  101  of 0.1 mm square can have a practical emission area. If n-and p-electrodes for Au stud bump mounting are disposed under the LED element  101 , an electrode with a diameter of about 0.1 mm needs to be provided correspondingly. Thus, it is difficult to make an LED element  101  of less than 0.1×0.2 mm 2 .     (5) Since the n-external electrode  117  and the p-external electrode  118  are continuously formed over the two sides of the element, the bonding area of the solder  120 A for reflow bonding can be increased, thereby offering a stable mounting and a good heat radiation property. Further, the secure mounting can be obtained without requiring a high precision in positioning like the bump bonding. Meanwhile, the n-external electrode  117  and the p-external electrode  118  are not always continuously formed over the two sides, and they may be formed not continuously.     (6) In the flip-chip bonding of the LED element  101 , the surface of the GaN-based semiconductor layer  200  is face-bonded to the board  123 , and the n-external electrode  117  and the p-external electrode  118  are electrically connected through the solder  120 A. Therefore, the bonding strength can be enhanced. The heat radiation property can be improved such that heat is radiated from the GaN-based semiconductor layer  200  to the board  123  without passing through the sapphire substrate  110 . Further, the reliability can be improved such that the seal resin does not exist at the bonding interface of the LED element  101  and, therefore, the separation of bonded portion does not occur due to thermal expansion.    

      Although in the tenth embodiment the blue LED element  101  of the group III nitride-based compound semiconductor is explained, the invention is not limited to the blue LED element  101  and may be applied to another emission color LED. Further, the LED element  101  may be made of another material instead of the group III nitride-based compound semiconductor.  
      Alternatively, a GaN substrate may be used in place of the sapphire substrate  110  as an underlying substrate to grow a group III nitride-based compound semiconductor layer thereon.  
      Even when the LED element  101  is flip-chip mounted using the p-contact electrode  115  as the mounting face as shown in  FIG. 16A , light can be extracted to a direction of the board  123  by using the p-contact electrode  118  made of transparent ITO and the board  123  made of a transparent material such as glass.  
     Eleventh Embodiment  
      (Composition of LED Element  101 )  
       FIGS. 17A  to  17 C show an LED element in the eleventh preferred embodiment according to the invention.  
      The LED element  101  is composed of five emission regions disposed in the longitudinal direction as shown in  FIG. 17A . It is further composed of plural n-external electrodes  117  and p-external electrodes  118 . The p-external electrode  118  is, as shown in  FIG. 17B , connected through an electrode connecting portion  118 A to the p-contact electrode  115  made of Rh.  
      Also in the elongated LED element  101 , the n-external electrode  117  and the p-external electrode  118  are provided at the side of the element and have a bonding width to give a sufficient bonding property. The n-external electrode  117  and the p-external electrode  118  are disposed opposed to, each other at the longer sides of the LED element  101 . The n-external electrode  117  is exposed at the shorter sides of the LED element  101 .  
      The n-external electrode  117  and the p-external electrode  118  are flip-chip bonded on a wiring pattern of a board (not shown) through a solder  120 A as shown in  FIG. 17C .  
     Effects of the Eleventh Embodiment  
      In the eleventh embodiment, in addition to the effects of the tenth embodiment, the LED element  101  is suitable for a use in need of a large amount of light since it is easy to form the wiring on the LED element  101  though having the elongated structure. Also, since the n-external electrode  117  and the p-external electrode  118  are provided with a given bonding with at the side of the LED element  101 , a uniform and good electrical bonding property can be obtained.  
      Even when the plural emission regions are provided as shown in  FIG. 17A , heat can be rapidly radiated from the GaN-based semiconductor layer  200  to the mounting face (not shown) as described in the tenth embodiment. Thus, a sufficient heat radiation property can be offered even in a high-output LED element  101 .  
      Although in the eleventh embodiment is explained the elongated LED element  101  with the five emission regions, the number, size and form of emission regions may be arbitrarily varied according to use.  
      The LED element  101  is not limited to a use for the flip-chip mounting, and it may be face-up mounted while making modifications that the p-contact electrode  115  is made of a transparent material such as ITO, ZnO, Au/Co and Ni/Ti and that the sapphire substrate  110  is used as the mounting face.  
     Twelfth Embodiment  
      (Composition of LED Element  101 )  
       FIGS. 18A and 18B  show an LED element in the twelfth preferred embodiment according to the invention.  
      The LED element  101  is a large size (1 mm square) LED element. It is provided with an n-external electrode  117  that extends like a comb from the side of the element into the emission region and plural electrode connecting portions  118 A to connect the p-contact electrode  115  and the p-external electrode  118 .  
      Also in the twelfth embodiment, the n-external electrode  117  and the p-external electrode  118  are exposed opposite to each other at the side of the element and formed over the entire width of one side of the element.  
      The p-contact electrode  115  may be made of a transparent material when the LED element  101  is used to extract light from the surface of the GaN-based semiconductor layer  200 . In contrast, it may be made of a reflective conductive material such as Rh other than the transparent material when the LED element  101  is used to extract light from the surface of the sapphire substrate  110 .  
     Effects of the Twelfth Embodiment  
      In the twelfth embodiment, since the n-external electrode  117  and the p-external electrode  118  are disposed at the side of the element not on the light extraction surface, the large size LED element  101  can have an increased area to extract light from the inside of the element so as to enhance the light extraction efficiency.  
      Since the n-external electrode  117  and the p-external electrode  118  are formed opposite to each other at the side of the element, the bonding area to the external member or device can be increased, thereby enhancing the bonding strength, the heat radiation property and the uniformity in Current spreading. Further, the LED element  101  can be securely mounted without requiring a troublesome adjustment such as positioning in the mounting as compared to an Au bump mounting.  
      Although in the large size LED element  101  the amount of heat generation is increased as compared to a standard size LED element, a sufficient heat radiation property can be secured since the n-external electrode  117  and the p-external electrode lie are disposed at the side of the element to be in close contact with the mounting board.  
      Although in the twelfth embodiment the n-external electrode  117  and the p-external electrode  118  are disposed opposite to each other at the side of the LED element  101  and formed over the entire width of the side, these electrodes may be formed in arbitrary position and size if the n-external electrode  117  and the p-external electrode  118  are exposed at the side of the LED element  101  without being short-circuited each other.  
      Although in the twelfth embodiment the LED element  101  is provided with the nine electrode connecting portions  118 A, the number, size and form of the electrode connecting portions  118 A may be arbitrarily varied according to use.  
     Thirteenth Embodiment  
       FIG. 19  shows an LED element in the thirteenth preferred embodiment according to the invention.  
      The LED element  101  is formed such that the n-external electrode  117  and the p-external electrode  118  are disposed along the side of the large size LED element  101 .  
      This structure can also enhance the bonding strength, the heat radiation property and the uniformity in current spreading as described in the twelfth embodiment.  
     Fourteenth Embodiment  
       FIG. 20  shows an LED element in the fourteenth preferred embodiment according to the invention.  
      The LED element  101  is formed such that the n-external electrode  117  and the p-external electrode  118  are disposed opposite to each other at the side of the large size LED element  101  and formed extending like a comb toward the center of the LED element  101  from the side.  
      This structure can also enhance the bonding strength and the heat radiation property as described in the twelfth embodiment.  
      Further, since the n-external electrode  117  and the p-external electrode  118  are formed extending like a comb, the uniformity in current spreading can be further enhanced.  
     Fifteenth Embodiment  
      (Mounting Structure of LED Element  101 )  
       FIG. 21  is a cross sectional view showing a mounting structure of an LED element in the fifteenth preferred embodiment according to the invention, where the LED element  101  is connected to a copper lead  121 .  
      The copper lead  121  is made by forming a copper alloy material into a lead form by pressing etc. It is connected to the n-external electrode  117  and the p-external electrode  118  at the side of the LED element  101  by the solder bonding with solder plating  120 .  
      The LED element  101  is provided with the p-contact electrode  115  made of Rh so as to extract light from the surface of the sapphire substrate  110 .  
      Although the n-GaN layer  112  is at a side thereof in face contact with the copper leads  121 ,  121  to supply current to the anode side and the cathode side, short-circuiting does not occur since it is not in ohmic contact with them at the contact face.  
      As shown in  FIG. 21 , one pair of the copper leads  121 ,  121  serve as an electrical connection and a mechanical support, and the LED element  101  is suspended supported by the copper leads  121 ,  121 .  
      In order to protect the LED element  101  and the copper lead  121  and to enhance the light extraction efficiency, it is desirable that the LED element  101  and the copper lead  121  are integrally sealed with a seal resin such as epoxy resin.  
      The solder plating  120  may be replaced by a conductive bonding material to electrically connect the copper lead  1201  and the LED element  101 . Such a conductive bonding material includes, e.g., epoxy adhesive containing Ag paste or a conductive filler.  
      (Operation of the LED Element  101 )  
      When power is supplied connecting the copper lead  121  on to a power supply (not shown), a forward voltage is applied through the n-external electrode  117  and the p-external electrode  118  of the LED element  101  to the light-emitting layer  113 . Thereby, radiative recombination of hole and electron occurs in the light-emitting layer  113  and blue light is emitted. Blue light irradiated to the sapphire substrate  110  side is externally radiated passing through the sapphire substrate  110 . In contrast, blue light irradiated to the p-contact electrode  115  side is reflected on the p-contact electrode  115  and then externally radiated passing through the sapphire substrate  110   
     Effects of the Fifteenth Embodiment  
      The effects of the fifteenth embodiment are as follows. 
      (1) Since the n-external electrode  117  and the p-external electrode  118  are disposed at the side of the LED element  101  not on the light extraction surface, another type of mounting other than face-up and flip-chip can be realized as shown in  FIG. 21 . Thus, the mounting structure can be low-profile and compact and the package with a seal material can be enhanced in sealability and downsized. It is more desirable that the copper lead  121  is in height lower than the LED element  101  to enhance the light extraction efficiency from the side face.     (2) Since the copper lead  121  with a good thermal conductivity is disposed at the side of the element, heat generated during the operation can be rapidly radiated through the GaN-based semiconductor layer  200  and the solder plating  120  without blocking the external radiation of emitted light of the LED element  101 .    

      In the fifteenth embodiment the LED element  101  is provided with the p-contact electrode  115  made of Rh. However, when the p-contact electrode  115  is made of a transparent material such as ITO, light can be extracted from any of the surface of the sapphire substrate  110  and the surface of the GaN-based semiconductor layer  200 .  
     Sixteenth Embodiment  
      (Mounting Structure of LED Element  101 )  
       FIG. 22A  is a cross sectional view showing a first mounting structure of an LED element  101  in the sixteenth preferred embodiment according to the invention.  
      As shown in  FIG. 22A , the LED element  101  is provided with the p-contact electrode  115  made of a transparent material such as ITO. The sapphire substrate  110  is at the bottom face bonded to the insulative board  123  made of Al 2 O 3  through an adhesive (not shown). The n-external electrode  117  and the p-external electrode  118  are electrically connected through the solder  120 A to the wiring pattern  122  formed on the surface of the board  123 .  
      The solder  120 A may be replaced by a conductive adhesive such as Ag paste and epoxy adhesive containing a conductive filler. The conductive adhesive may be transparent. For example, if a transparent epoxy resin containing a conductive filler is used, light can be extracted from the side of the LED element  101 .  
      The board  123  may be transparent. In this case, light is can be extracted from the surface of the GaN-based semiconductor layer  200  and from the surface of the sapphire substrate  110  toward the board  123 .  
      The board  123  may be made of a conductive material such as Cu and Al. In this case, although an insulation layer needs to be formed on the surface to prevent the short-circuiting through the board  123 , it is effective to choose the conductive material to secure a heat radiation property.  
       FIG. 22B  is a cross sectional view showing a second mounting structure of an LED element in the sixteenth embodiment according to the invention.  
      The second mounting structure is different from the first structure in that the LED element  101  is placed in a concave portion  123 A formed in the board  123 .  
      The concave portion  123 A is provided with a slope  123 B so as to have a space around the LED element  101 . Since the LED element  101  is placed in the concave portion  123 A, the amount of protrusion from the surface of the board  123  can be reduced. The LED element  101  is electrically connected through the solder  120 A embedded in the space formed between the slope  123 B and the LED element  101  to a pair of wiring patterns  122 .  
      The board  123  in  FIG. 22B  may be made of a metal material with a light reflection property. In this case, although an insulation layer is formed on the surface, light irradiated to the side direction of the LED element  101  can be reflected on the reflective slope  123 B so as to be extracted upward. Further, the solder  120 A may be a transparent and conductive adhesive to enable the light extraction even in the electrical connection portion  
     Effects of the Sixteenth Embodiment  
     
         
          (1) In the first mounting structure, since the electrical connection is made through the solder  120 A to the n-external electrode  117  and the p-external electrode  118  formed at the side of the LED element  101 , the light extraction area from the GaN-based semiconductor layer  200  can be increased. The electrical connection at the side of the element may be made through the conductive adhesive etc. instead of the solder  120 A Thus, a suitable way of bonding can be chosen according to use. Further, when the board  123  is made of a transparent material, light can be extracted from the surface of the board  123 .  
          (2) In the second mounting structure, in addition to the effects of the first mounting structure, since the LED element  101  is place in the concave portion  123 A of he board  123 , the LED element  101  can be easily positioned and made low-profile by reducing the amount of protrusion from the surface of the board  123 . Further, since the concave portion  123 A is provided with the slope  123 B, light irradiated to the side direction of the LED element  101  can be reflected on the slope  123   b  to be extracted upward.  
       
    
     Seventeenth Embodiment  
      (Mounting Structure of LED Element  101 )  
       FIG. 23  is a cross sectional view showing a mounting structure of an LED element in the seventeenth preferred embodiment according to the invention.  
      The LED element  101  of the seventeenth embodiment is different from the LED element  101  in  FIG. 16A  in that the sapphire substrate  110  is lifted off.  
      The LED element  101  is prepared by lifting off the sapphire is substrate  110  and the AlN buffer layer  111  by irradiating laser light toward the surface of the sapphire substrate  110 . Meanwhile, after the lift-off, the AlN buffer layer  111  may be left on the surface of the n-GaN layer  112 . In such a case, it is desirable that the remaining AlN buffer layer  111  is removed by acid cleaning.  
      In operation, when power is supplied connecting the wiring pattern  122  to a power supply (not shown), a forward voltage is applied through the n-external electrode  117  and the p-external electrode  118  of the LED element  101  to the light-emitting layer  113 . Thereby, radiative recombination of hole and electron occurs in the light-emitting layer  113  and blue light is emitted. Blue light irradiated to the n-GaN layer  112  is externally radiated passing through the n-GaN layer  112 . In contrast, blue light irradiated to the p-contact electrode  115  is reflected on the p-contact electrode  115  made of Rh and then externally radiated passing through the n-GaN layer  112 .  
      The p-contact electrode  115  may be made of a transparent material such as ITO if the board  123  is made of a transparent material. Thereby, light can be extracted from the bottom side of the GaN-based semiconductor layer  200 .  
     Effects of the Seventeenth Embodiment  
      In the seventeenth embodiment, light can be extracted from the n-GaN layer  112  of the flip-chip mounted LED element  101 . Therefore, the intra-layer confined light being not externally radiated from the GaN-based semiconductor layer  200  can be reduced so as to enhance the external radiation efficiency.  
      Further, since the n-external electrode  117  and the p-external electrode  118  are disposed at the side of the LED element  101 , the LED element  101  can be low profiled to meet the downsizing of a mounted object or to avoid a restriction caused by the form of a mounted object. Further, the heat radiation property through the insulation layer  119  to the board  123  can be enhanced.  
      In view of the protection of the LED element  101 , it is desirable that the n-GaN layer  112  is covered with a transparent material or sealed with a seal material such as epoxy resin as well as the wiring pattern  122  and the board  123 .  
      The n-GaN layer  112  may be provided with an uneven surface to reduce the intra-layer confined light to enhance the external radiation efficiency.  
     Eighteenth Embodiment  
      (Mounting Structure of LED Element  101 )  
       FIG. 24  is a cross sectional view showing a mounting structure of an LED element in the eighteenth preferred embodiment according to the invention.  
      The LED element  101  is composed such that a glass member  130  with a high refractive index and a wiring pattern  122  is bonded through a transparent adhesive  142  onto the surface of the n-GaN layer  112  of the LED element  101  as shown in  FIG. 23 .  
      The p-contact electrode  115  of the LED element  101  is made of Rh.  
      The transparent adhesive  142  is an epoxy adhesive which does not block the transmission of light emitted from the LED element  101 .  
      The n-external electrode  117  and the p-external electrode  118  are electrically connected through the transparent and conductive adhesive  142  to the wiring pattern  122 . The adhesive  142  can be, as described earlier, epoxy resin containing a conductive filler.  
      In operation, when power is supplied connecting the wiring pattern  122  to a power supply (not shown), a forward voltage is applied through the n-external electrode  117  and the p-external electrode  118  of the LED element  101  to the light-emitting layer  113 . Thereby, radiative recombination of hole and electron occurs in the light-emitting layer  113  and blue light is emitted. Blue light irradiated to the n-GaN layer  112  is externally radiated passing through the n-GaN layer  112 , the transparent adhesive  142  and then the glass member  130 . In contrast, blue light irradiated to the p-contact electrode  115  is reflected on the p-contact electrode  115  made of Rh and then externally radiated passing through the n-GaN layer  112 , the transparent adhesive  142  and then the glass member  130 .  
      On the other hand, a light component reflected on the interface of the glass member  130  and then laterally propagated through the GaN-based semiconductor layer  200  can be externally radiated after it is entered into an adhesive  120 B from the side of the LED element  101 .  
     Effects of the Eighteenth Embodiment  
      In the eighteenth embodiment, since the LED element  101  is bonded through the transparent adhesive  142  onto the glass member  130 , a light source suitable for a transmitting illumination such as a backlight can be offered.  
      Although in the eighteenth embodiment the p-contact electrode  115  is made of Rh with a light reflecting property, it may be made of a transparent material such as ITO so as to also extract light from the bottom of the GaN-based semiconductor layer  200 .  
     Nineteenth Embodiment  
      (Composition of LED Element  101 )  
       FIG. 25A  is a cross sectional view showing a large-size LED element (1 mm square) in the nineteenth preferred embodiment according to the invention.  FIG. 25B  is a top view showing the LED element in  FIG. 25A , which is viewed from the side of an insulation layer formation surface thereof.  
      The LED element  101  is, as shown in  FIG. 25B , composed of: a hole  101 A which is formed at the center of the element and in the depth direction from the p-GaN layer  114  to the n-GaN layer  112 ; an n-external electrode  117  formed covering the n-GaN layer  112  exposed by etching inside the hole  10 A; and a p-external electrode  118  formed covering the periphery of the GaN-based semiconductor layer  200  and electrically connected to the p-contact electrode  115 . The p-contact electrode  115  of the LED element  101  is made of Rh.  
      The LED element  101  can be flip-chip bonded onto a board (not shown) which is provided with a wiring pattern corresponding to a pattern of solder plating that corresponds to the n-external electrode  117  and the p-external electrode  118 .  
     Effects of the Nineteenth Embodiment  
      In the nineteenth embodiment, since the n-external electrode  117  is disposed at the center of the element and the p-external electrode  118  are formed on the periphery of the element, even the large size LED element  101  can render the entire surface of the light-emitting layer  113  uniformly emit light.  
      By flip-chip mounting the LED element  101 , a good emission property can be obtained while securing a good heat radiation property to the mounting board etc.  
      In the nineteenth embodiment, when the LED element  101  is mounted in face-up disposition, the p-contact electrode  115  may be made of a transparent material such as ITO. Thereby, a good wire bonding property can be obtained while preventing a reduction in light extraction efficiency as much as possible in the case of the face-up mounting.  
      Although the abovementioned embodiments relate to the light emitting element (=LED element), the invention is not limited to the light emitting element and may be applied to another optical element (or device) such as a solar cell and a light-receiving element and a method of making the same.  
      Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.