Abstract:
A light-emitting diode device. In one embodiment, the light-emitting device includes a heat-dissipating mount and a light-emitting diode chip. The heat-dissipating mount has a cavity, wherein the cavity includes an embedded portion and an inclined surface connected with the embedded portion. The light-emitting diode chip includes a substrate partly embedded into the embedded portion. A lower region of a side surface of the substrate has a first unsmooth surface, the first unsmooth surface has an exposed portion protruding above the embedded portion, and a bottom edge of the lower region is connected to a bottom surface of the substrate.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 100113214 filed in Taiwan, R.O.C. on Apr. 15, 2011, the entire contents of which are hereby incorporated by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a light-emitting device, and more particularly to a light-emitting diode (LED) device. 
       BACKGROUND OF THE INVENTION 
       [0003]    As the LED is applied in high-luminance products like illuminators and headlights of vehicles, the operating power of the LED chip also increases accordingly. However, about 80% of the electric power input in an LED chip is transformed into heat energy and only 20% is transformed into light energy. Therefore, the high power LED chip generates more and more heat, which leads to higher and higher heat dissipation requirement of the LED chip. 
         [0004]      FIG. 1  is a sectional view of a conventional LED device. An LED device  100  is disclosed in the related art, which includes a metal heat dissipation base  102  for solving the heat dissipation requirement of the LED chip  106 . In the LED device  100 , the metal film  104  is disposed on a surface of the metal heat dissipation base  102 . The LED chip  106  is partially embedded in the metal film  104  so as to be fixed on the metal heat dissipation base  102 . Electrode pads  122  and  128  are respectively disposed on the metal films  104  on two sides of the LED chip  106  through adhesive layers  116 . 
         [0005]    The LED chip  106  includes a substrate  110 , a light emitting epitaxial structure  108  and two electrodes  112  and  114 . The light emitting epitaxial structure  108  is disposed on the substrate  110  and the electrodes  112  and  114  are disposed on the light emitting epitaxial structure  108 . On the other hand, the electrode pad  122  includes an insulating layer  118  and a conductive layer  120 , in which the conductive layer  120  is disposed on the insulating layer  118 . Likewise, the electrode pad  128  includes an insulating layer  124  and a conductive layer  126 , in which the conductive layer  126  is disposed on the insulating layer  124 . 
         [0006]    In the LED device  100 , the electrode  112  of the LED chip  106  and the conductive layer  120  of the electrode pad  122  are connected through a conductive wire  130  and the electrode  114  of the LED chip  106  and the conductive layer  126  of the electrode pad  128  are connected through a conductive wire  132  in a wire bonding manner. 
         [0007]    In the architecture of a conventional LED device  100 , as a major part of the LED chip  106  is embedded in the metal film  104  on the metal heat dissipation base  102 , the heat generated by the LED chip  106  in operation may be conducted and further dissipated through the metal film  104  and the metal heat dissipation base  102  below. Therefore, this heat dissipation design may greatly improve the heat dissipation efficacy of the LED device  100 . 
         [0008]    However, the luminous layer in the light emitting epitaxial structure  108  of the LED chip  106  is not embedded into the metal film  104 . Since a major part of the substrate  110  of the LED chip  106  is embedded into the metal film  104 , most of the light emitted by the luminous layer of the light emitting epitaxial structure  108  towards the substrate  110  below is confined within the LED chip  106  due to the opaque feature of the metal films  104  on the sides of the substrate  110 . For example, the light emitted by the luminous layer of the light emitting epitaxial structure  108  may be reflected multiple times within the substrate  110  and cannot be successfully emitted out of the LED chip  106  or severe energy loss might occur, which greatly reduces the intensity of the emitted light. As such, the light extraction efficiency of the LED chip  106  is reduced, thus resulting in the apparent decrease of the luminous efficiency. 
         [0009]    Furthermore, the design of the electrode pads  122  and  128  emitted from the metal film  104  may influence the side light of the LED chip  106 , and thus reduces the overall luminance of the LED device  100 . 
         [0010]    Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies. 
       SUMMARY OF THE INVENTION 
       [0011]    Accordingly, an aspect of the present invention is directed to an LED device, in which a non-smooth surface at a side of the substrate of the LED chip is not completely embedded in the heat dissipation base below and an exposed part is emitted from the embedded surface. In this manner, the light emitted downward by the epitaxial structure may be successfully emitted to the outside from the side of the substrate. Therefore, the overall luminance of the LED device can be effectively improved. 
         [0012]    Another aspect of the present invention is directed to an LED device, in which a lower region, a middle region and/or an upper region of a side surface of the substrate of the LED chip have non-smooth surfaces, so the light emitted by the epitaxial structure may be emitted through the middle region and/or the upper region of the side surface of the substrate. Therefore, the light extraction efficiency of the LED chip may be further improved. 
         [0013]    Still another aspect of the present invention is directed to an LED device, in which a part of the substrate of the LED chip is directly embedded in the heat dissipation base, so the heat generated by the LED chip in operation is effectively conducted out by the heat dissipation base. Therefore, the LED device has an excellent heat dissipation capability. 
         [0014]    In one aspect of the present invention, an LED device is provided. The LED device includes a heat dissipation base and an LED chip. The heat dissipation base has a recessed portion. The recessed portion includes an embedded portion and an inclined side surface joined with the embedded portion. The LED chip includes a substrate partially embedded in the embedded portion. The lower region of the side surface of the substrate has a first non-smooth surface, and the first non-smooth surface has an exposed portion protruding from the embedded portion. A bottom edge of the lower region and a bottom surface of the substrate are joined. 
         [0015]    According to an embodiment of the present invention, the heat dissipation base includes a metal base, a reflective layer and a ceramic layer. The reflective layer is disposed on the metal base. The ceramic layer is disposed on the reflective layer. The substrate is partially embedded in the ceramic layer. 
         [0016]    According to another embodiment of the present invention, the first non-smooth surface has an irregular concave and convex structure or a regular concave and convex structure. 
         [0017]    According to still another embodiment of the present invention, the side surface of the substrate further includes: a middle region joined on the lower region and including an area of a half height of the substrate; and an upper region joined on the middle region, in which a top edge of the upper region and a top surface of the substrate are joined. The middle region and/or the upper region have a second non-smooth surface. For example, the second non-smooth surface has an irregular concave and convex structure or a regular concave and convex structure. 
         [0018]    According to yet another embodiment of the present invention, the LED chip further includes an epitaxial structure. The epitaxial structure includes a first conductive type semiconductor layer, an active layer and a second conductive type semiconductor layer stacked on the substrate in sequence. The first conductive type semiconductor layer has an exposed portion. A transparent conductive layer is located on the second conductive type semiconductor layer and a first electrode and a second electrode are respectively disposed on the exposed portion of the first conductive type semiconductor layer and the transparent conductive layer. 
         [0019]    According to still another embodiment of the present invention, the LED device further includes a first electrode pad, a second electrode pad and two conductive wires. The first electrode pad and the second electrode pad are respectively disposed on the heat dissipation base on two sides of the recessed portion. The two conductive wires respectively connect the first electrode pad and the first electrode and connect the second electrode pad and the second electrode. 
         [0020]    According to yet another embodiment of the present invention, the LED device further includes a third electrode pad and a fourth electrode pad disposed on a lower surface of the heat dissipation base. The heat dissipation base has two through holes and the heat dissipation base includes two conductive pins respectively filled in the through holes and two insulating layers respectively isolating the inner side surfaces of the through holes and the conductive pins. The conductive pins respectively electrically connect the first electrode pad and the third electrode pad and electrically connect the second electrode pad and the fourth electrode pad. 
         [0021]    According to yet another embodiment of the present invention, an inclined angle between the inclined side surface and the bottom surface ranges from 30° to 60°. In an exemplary embodiment, the inclined angle between the inclined side surface and the bottom surface is substantially 45°. 
         [0022]    According to yet another embodiment of the present invention, a height of the substrate protruding from the embedded portion is greater than or equal to the height of the inclined side surface, so that the epitaxial structure is higher than a top of the inclined side surface. 
         [0023]    According to yet another embodiment of the present invention, a depth of the part of the substrate embedded in the embedded portion ranges from 5 μm to 10 μm. 
         [0024]    By controlling the depth of the substrate of the LED chip embedded into the heat dissipation base and making the non-smooth surface at a side surface of the substrate at least partially exposed from the heat dissipation base, the light extraction efficiency of the LED chip may be increased, thereby further improving the overall luminance of the LED device. Moreover, the design of the LED chip directly embedded in the heat dissipation base may further improve the heat dissipation efficacy of the LED device. 
         [0025]    These and other aspects of the present invention will become apparent from the following description of the preferred embodiment taken in conjunction with the following drawings, although variations and modifications therein may be effected without departing from the spirit and scope of the novel concepts of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The accompanying drawings illustrate one or more embodiments of the invention and together with the written description, serve to explain the principles of the invention. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment, and wherein: 
           [0027]      FIG. 1  is a sectional view of an LED device according to the related art; 
           [0028]      FIG. 2  is a schematic view of a light path of an LED chip according to an embodiment of the present invention; 
           [0029]      FIG. 3  is a schematic sectional view of the LED device according to an embodiment of the present invention; 
           [0030]      FIG. 4  is a schematic sectional view of the LED device according to another embodiment of the present invention; and 
           [0031]      FIG. 5  is a schematic sectional view of the LED device according to still another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The present invention is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. Various embodiments of the invention are now described in detail. Referring to the drawings, like numbers indicate like components throughout the views. As used in the description herein and throughout the claims that follow, the meaning of “a”, “an”, and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
         [0033]      FIG. 2  is a schematic view of a light path of an LED chip according to an embodiment of the present invention. In this embodiment, the LED chip  200  is a horizontal electrode LED structure. However, in other embodiments of the present invention, the LED chip may also be a vertical electrode LED structure. 
         [0034]    The LED chip  200  includes a substrate  230 , an epitaxial structure  210 , a first electrode  220  and a second electrode  222 . The substrate  230  may be for example a sapphire substrate. As shown in  FIG. 2 , the side surface  202  of the substrate  230  may be divided into a lower region  204 , a middle region  206  and an upper region  208 . The lower region  204  is located on the lower portion of the side surface  202  of the substrate  230 , and the bottom edge of the lower region  204  and the bottom surface of the substrate  230  are joined. The top edge of the lower region  204  and the middle region  206  are joined. The top edge of the middle region  206  and the upper region  208  are joined. The middle region  206  includes an area of a half height of the substrate  230 , and the top edge of the upper region  208  and the top surface of the substrate  230  are joined. The epitaxial structure  210  is located on the top surface of the substrate  230 . In an embodiment, the epitaxial structure  210  includes a first conductive type semiconductor layer  212 , an active layer  214  and a second conductive type semiconductor layer  216 . In another embodiment, as shown in  FIG. 2 , the LED chip  200  may further include a transparent conductive layer  218  located on the epitaxial structure  210 . 
         [0035]    In the fabricating of the epitaxial structure  210 , the first conductive type semiconductor layer  212 , the active layer  214  and the second conductive type semiconductor layer  216  may be grown on the substrate  230  in sequence for example in an organic metal organic chemical vapor deposition (MOCVD) manner. Hence, the epitaxial structure  210  having the first conductive type semiconductor layer  212 , the active layer  214  and the second conductive type semiconductor layer  216  stacked in sequence may be formed. In the present invention, the first conductive type and the second conductive type are opposite. For example, one of the first conductive type and the second conductive type is n-type and the other is p-type. In this exemplary embodiment, the first conductive type is n-type and the second conductive type is p-type. Then, the transparent conductive layer  218  may be formed on the second conductive type semiconductor layer  216  for example in an electron beam evaporation or sputtering manner. 
         [0036]    In this embodiment, as the LED chip  200  is a horizontal electrode structure, the transparent conductive layer  218  and the epitaxial structure  210  need mesa definition for example by a lithography and etching process, so as to expose a part of the first conductive type semiconductor layer  212 . As shown in  FIG. 2 , the first electrode  220  and the second electrode  222  are respectively disposed on the exposed portion of the first conductive type semiconductor layer  212  of the epitaxial structure  210  and a part of the transparent conductive layer  218 . 
         [0037]    The inventor finds that when the LED chip  200  is lit, the part with the highest luminance is the part of the epitaxial structure  210  and is also a primary part that contributes to the luminance. The part with the second highest luminance is the lower part of the substrate  230  of the LED chip  200  and is also a secondary part that contributes to the luminance. The light is emitted from the lower region  204  at the side surface  202  of the substrate  230 . The part with the third highest luminance is the upper part where the substrate  230  and the epitaxial structure  210  are joined and is the third part that contributes to the luminance. The light is emitted from the upper region  208  at the side surface  202  of the substrate  230 . However, it should be noted that nearly no light is emitted from the middle part of the substrate  230 . The situation of the light emission from the middle part of the substrate  230  may be observed from the middle region  206  of the side surface  202  of the substrate  230 . It can be seen from  FIG. 2  that the middle part of the substrate  230  accounts for a major part of the entire substrate  230  but contributes to the least luminance. 
         [0038]    The inventor analyzes the observation result and finds that the lower region  204  of the side surface  202  of the substrate  230  has a non-smooth surface  224 , so the non-smooth surface  224  has an irregular concave and convex structure. The inventor further analyzes the result and finds that in the fabricating of the chip scribing/breaking, the bottom of the substrate  230  is cut by a laser to form a partial slot and after the scribing/breaking procedure, an irregular laser melted surface is formed on the lower region  204  of the side surface  202  in the embodiment of the present invention. On the other hand, the upper region  208  and the middle region  206  of the side surface  202  of the substrate  230  respectively have smooth surfaces  228  and  226  generated after scribing/breaking. 
         [0039]    In an embodiment, the non-smooth surface  224  of the lower region  204  of the substrate  230  may be an irregular concave and convex structure. In another embodiment, the non-smooth surface  224  of the lower region  204  of the substrate  230  may be a regular concave and convex structure. In this embodiment, the non-smooth surface  224  having the irregular concave and convex structure may be generated by a scribing tool such as laser during the scribing/breaking process. However, the non-smooth surface  224  having the irregular concave and convex structure may also be formed by a patterning technique such as the lithography and etching process. On the other hand, the non-smooth surface  224  having regular concave and convex structure may also be formed by the patterning technique such as the lithography and etching process. 
         [0040]    Therefore, it can be seen from the light path in  FIG. 2  that when the light  236  emitted by the active layer  214  is emitted on the upper region  204  of the side surface  202  of the substrate  230 , the incident angle does not exceed the critical angle, so the light  236  may still be emitted to the outside. When the light  234  emitted by the active layer  214  is emitted on the middle region  206  of the side surface  202  of the substrate  230 , as the incident angle exceeds the critical angle, the light  234  will be totally reflected back into the substrate  230  and cannot be emitted to the outside. On the other hand, when the light  232  emitted by the active layer  214  is emitted on the lower region  204  of the side surface  202  of the substrate  230 , as the lower region  204  has the non-smooth concave and convex surface, the total reflection surface is ruined and the light  232  may still be effectively extracted from the lower region  204  of the side surface  202 . 
         [0041]    In view of the above discovery, to prevent the light  232  originally extracted from the lower region  204  of the side surface  202  of the substrate  230  from being confined in the heat dissipation base disposed on LED chip  200 , a novel LED device architecture is proposed. 
         [0042]    Referring to  FIGS. 2 and 3  together,  FIG. 3  is a schematic sectional view of the LED device according to an embodiment of the present invention. In this embodiment, the LED device  238  includes a heat dissipation base  240  and an LED chip  200 . The LED chip  200  is embedded in the heat dissipation base  240 . 
         [0043]    In an embodiment, the heat dissipation base  240  may include a metal base  242 , a reflective layer  244  and a ceramic layer  246 . The reflective layer  244  is covered on the surface of the metal base  242  and the ceramic layer  246  is covered on the reflective layer  244 . A material of the metal base  242  may be for example copper, copper alloy, ferrum/nickel alloy, nickel, tungsten, molybdenum or any alloy thereof. A material of the reflective layer  244  may be for example silver/aluminum stack structure. A material of the ceramic layer  246  preferably is the transparent material, for example, aluminum oxide. 
         [0044]    To improve the luminance of the LED device  238 , the heat dissipation base  240  has a recessed portion  248 . The recessed portion  248  includes an embedded portion  249  and an inclined side surface  252  joined with the embedded portion  249 . The embedded portion  249  includes a bottom surface  250  and an embedded side surface  251 . Therefore, the surface where the recessed portion  248  of the heat dissipation base  240  is located may have a cup structure. 
         [0045]    The LED chip  200  is disposed in the recessed portion  248  of the heat dissipation base  240 , and the substrate  230  of the LED chip  200  is partially embedded in the embedded portion  249  of the recessed portion  248 . That is to say, a part of the substrate  230  is embedded in the embedded side surface  251  and the bottom surface  250  of the ceramic layer  246 . By embedding a part of the substrate  230  of the LED chip  200  in the ceramic layer  246 , the ceramic layer  246  may be used to deliver the heat generated by the LED chip  200  in operation and the heat is further downwardly conducted to the metal base  242  and then dissipated to the outside. 
         [0046]    Furthermore, as shown in  FIG. 2 , to prevent the light  232  that can be extracted from the lower region  204  of the side surface  202  of the substrate  230  from being confined in the heat dissipation base  240 , the depth of the substrate  230  embedded in the heat dissipation base  240  is controlled in this embodiment, so that the non-smooth surface  224  of the lower region  204  of the side surface  202  is not completely embedded in heat dissipation base  240  and has an exposed portion protruding from the embedded portion  249  of the recessed portion  248 . In other words, the height of the embedded side surface  251  of the embedded portion  249  is smaller than that of the lower region  204 . 
         [0047]    For example, referring to  FIGS. 2 and 3  together, if the height  284  of the overall LED chip  200  is about 150 μm, in which the height  286  of the substrate  230  is about 140 μm to about 145 μm and the height of the lower region  204  of the substrate  230  is about 20 μm to about 35 μm. The height  288  of the heat dissipation base  240  is about 200 μm. At this time, the depth of the substrate  230  of the LED chip  200  embedded in the ceramic layer  246  of the heat dissipation base  240  is about 5 μm to about 10 μm, that is, the height of the embedded side surface  251  is about 5 μm to about 10 μm. In this manner, the major part of the lower region  204  of the side surface  202  of the substrate  230  is still protruded from the embedded portion  249  of the recessed portion  248  of the heat dissipation base  240 . Therefore, the light emitted by the active layer  214  may still be emitted to the outside by the epitaxial structure  210 , the transparent conductive layer  218 , and the upper region  208  and the major part of the lower region  204  of the side surface  202  of the substrate  230 . Although the light emitted by the active layer  214  is emitted to the bottom surface of the substrate  230  embedded in the ceramic layer  246 , the light may still be easily reflected by the ceramic layer  246  and/or the reflective layer  244  and leave the embedded part of the substrate  230 , and then is emitted through the upper side of the LED chip  200  or the non-embedded region of the side surface  202 . The light emitted on the bottom of the substrate  230  of the LED chip  200  passing through the transparent ceramic layer  246  may also be reflected by the reflective layer  244  below to be emitted to the outside. Therefore, the overall luminance of the LED device  238  may be improved. 
         [0048]    In an exemplary embodiment, the depth  278  of the part of the substrate  230  of the LED chip  200  embedded in the embedded portion  249  of the recessed portion  248  may for example ranges from about 5 μm to about 10 μm. Furthermore, to prevent the heat dissipation base  240  from blocking the side light of the active layer  214 , the height  280  obtained by subtracting the depth  278  of the substrate  230  embedded in the embedded portion  249  of the recessed portion  248  from the height  286  of the substrate  230  is the height of the substrate  230  protruding from the embedded portion  249 , and preferably is greater than or equal to the height  282  of the inclined side surface  252  of the recessed portion  248 . In this manner, the epitaxial structure  210  is higher than the top of the inclined side surface  252 , thereby increasing the light extraction efficiency of the LED device  238 . In an embodiment, the inclined angle θ between the inclined side surface  252  and the bottom surface  250  may for example range from 30° to 60°, and preferably 45° for reflecting the side light of the LED chip  200  upwards. 
         [0049]    In this embodiment, by embedding the LED chip  200  in the heat dissipation base  240  and exposing a part of the non-smooth surface  224  of the lower region  204  of the side surface  202  of the substrate  230  from the embedded portion  249  of the recessed portion  248 , it is verified by the experiment that the luminous efficiency of the LED chip  210  increases by about more than 10%, thus effectively improving the overall luminance of the LED device  238 . Furthermore, the heat dissipation base  240  may effectively remove the heat generated by the LED chip  200  in operation, thus greatly improving the heat dissipation efficacy of the LED device  238 . 
         [0050]    In an embodiment, as shown in  FIG. 3 , the LED device  238  further includes two electrode pads  266  and  268 . The two electrode pads  266  and  268  are respectively disposed on the heat dissipation bases on two sides of the recessed portion  248  of the heat dissipation base  240 . In an exemplary embodiment, the electrode pads  266  and  268  are respectively disposed on two opposite sides of the recessed portion  248 . Furthermore, in the LED device  238 , the conductive wires  274  and  276  respectively connect the electrode  220  and the electrode pad  266  and connect the electrode  222  and the electrode pad  268  of the LED chip  200 , thereby electrically connecting the electrode  220  and the electrode pad  266  and connecting the electrode  222  and the electrode pad  268  in the wire bonding process. 
         [0051]    In an embodiment, two more conductive wires are used to connect the above two electrode pads  266  and  268  respectively to the two electrodes of an external power source. However, in this exemplary embodiment, the LED device  238  and the external power source are electrically connected by using a surface mount technology (SMT) process. As shown in  FIG. 3 , the heat dissipation base  240  of this embodiment further includes two through holes  254  and  256 . The two through holes  254  and  256  respectively extend downwardly from the bottom surfaces of the electrode pads  266  and  268  to the lower surface of the heat dissipation base  240  and thus penetrating the entire heat dissipation bases  240 . 
         [0052]    The inner side surfaces of the through holes  254  and  256  are respectively covered by the insulating layers  258  and  260 . A material of the insulating layers  258  and  260  may be for example metal oxide, silicon dioxide or silicon nitride. The heat dissipation base  240  may also include two conductive pins  262  and  264 . The two conductive pins  262  and  264  are respectively filled in the through holes  254  and  256  and the side surfaces of the conductive pins  262  and  264  are respectively encapsulated by the insulating layers  258  and  260 . Therefore, the insulating layers  258  and  260  may respectively isolate the inner side surface of the through hole  254  and the conductive pin  262 , and isolate the inner side surface of the through hole  256  and the conductive pin  264 . The conductive pins  262  and  264  may be formed by a conductive material, for example a metal material such as copper or gold and any alloy thereof. 
         [0053]    The LED device  238  includes two electrode pads  270  and  272 . The two electrode pads  270  and  272  are disposed on the lower surface of the heat dissipation base  240 , and respectively shield the opening on one end of the through hole  254  and the opening on one end of the through holes  256 , and are respectively electrically connected to one end of the conductive pin  262  and one end of the conductive pin  264 . In this manner, the conductive pins  262  and  264  may respectively electrically connect the electrode pads  266  and  270  and the electrode pads  268  and  272  on two opposite surfaces of the heat dissipation base  240 . Therefore, the LED device  238  may be fixed on the package base or circuit board (not shown) by for example the SMT process through the electrode pads  270  and  272 , and is then electrically connected to the external power source by the package base or circuit board. 
         [0054]    Therefore, in the LED device  238 , the LED chip  200  may be electrically connected to the two electrodes of the external power source respectively through the two electrodes  220  and  222  thereon via the conductive wires  274  and  276 , the electrode pads  266  and  268 , the conductive pins  262  and  264  and the electrode pads  270  and  272 . In this manner, the external power source may successfully input the power to the LED chip  200 , so that the LED chip  200  emits the light. 
         [0055]    The non-smooth surface of the side surface of the LED chip of the present invention may be not limited to be disposed on the lower region.  FIG. 4  is a schematic sectional view of the LED device according to another embodiment of the present invention. The architecture of the LED chip  290  of this embodiment is substantially identical to the LED chip  200  of the above embodiment, and the difference lies in that in the LED chip  290 , the lower region  204  of the side surface  202  has a non-smooth surface  224 , and the middle region  206  joined with the lower region  204  also has a non-smooth surface  292 . 
         [0056]    In an embodiment, the non-smooth surface  292  of the middle region  206  of the substrate  230  may be the irregular concave and convex structure. In another embodiment, the non-smooth surface  292  may also be the regular concave and convex structure. In this embodiment, the non-smooth surface  292  having the irregular concave and convex structure may also be the melted surface formed by a scribing tool such as laser. However, the non-smooth surface  292  having the irregular concave and convex structure may be formed by the patterning technique such as the lithography and etching process. On the other hand, the non-smooth surface  292  having the regular concave and convex structure may be formed by the patterning technique such as the lithography and etching process. 
         [0057]    In the LED chip  290 , as the middle region  206  of the side surface  202  of the substrate  230  has the non-smooth surface  292 , the light  234  emitted by the active layer  214  is emitted to the outside through the middle region  206  of the side surface  202  of the substrate  230 . In this manner, the light extraction efficiency of the LED chip  290  may be further increased. 
         [0058]      FIG. 5  is a schematic sectional view of the LED device according to still another embodiment of the present invention. The architecture of the LED chip  294  of this embodiment is substantially identical to the architecture of the LED chip  290  of the above embodiment, and the difference lies in that in the LED chip  294 , the lower region  204  and the middle region  206  of the side surface  202  respectively have the non-smooth surfaces  224  and  292 , and the upper region  208  joined with the middle region  206  also has the non-smooth surface  296 . 
         [0059]    In an embodiment, the non-smooth surface  296  of the upper region  208  of the substrate  230  may also be the irregular concave and convex structure. In another embodiment, the non-smooth surface  296  may also be the regular concave and convex structure. In this embodiment, the non-smooth surface  296  having the irregular concave and convex structure may be the melted surface formed by a scribing tool such as laser. However, the non-smooth surface  296  having the irregular concave and convex structure may be formed by the patterning technique such as the lithography and etching process. On the other hand, the non-smooth surface  296  having the regular concave and convex structure may be formed by the patterning technique such as the lithography and etching process. 
         [0060]    In the LED chip  294 , as the middle region  206  and the upper region  208  of the side surface  202  of the substrate  230  respectively have the non-smooth surfaces  292  and  296 , the light  234  and  236  emitted by the active layer  214  are respectively emitted to the outside by the middle region  206  and the upper region  208  of the side surface  202  of the substrate  230 . In this manner, the light extraction efficiency of the LED chip  294  may be further increased. 
         [0061]    It should be noted that the non-smooth surface area of the side surface of the substrate of the LED chip of the present invention may be located on the lower region, the middle region and/or the upper region of the side surface of the substrate. For example, in an embodiment, the non-smooth surface area of the side surface of the substrate may be located on the lower region and the upper region of the side surface of the substrate at the same time. Therefore, in the present invention, the configuration of the non-smooth surface is not limited to the above embodiment. 
         [0062]    It may be known from the above embodiment that the present invention has the following advantage. As the non-smooth surface of the side surface of the substrate of the LED chip of the LED device is not completely embedded in the heat dissipation base below, the exposed portion of the embedded portion protrudes from the embedded heat dissipation base. Therefore, the light emitted downwardly by the epitaxial structure may be successfully emitted to the outsides by the side surface of the substrate. Therefore, the overall luminance of the LED device can be effectively improved. 
         [0063]    It may be known from the above embodiment that the present invention has another advantage. The lower region, the middle region and/or the upper region of the side surface of the substrate of the LED chip of the LED device have the non-smooth surface, so the light emitted by the epitaxial structure may be emitted through the middle region and/or the upper region of the side surface of the substrate. Therefore, the light extraction efficiency of the LED chip may be further improved. 
         [0064]    It may be known from the above embodiment that the present invention has still another advantage that a part of the substrate of the LED chip of the LED device is directly embedded in the heat dissipation base, so the heat generated by the LED chip in operation is effectively conducted out by the heat dissipation base. Therefore, the LED device has an excellent heat dissipation capability. 
         [0065]    The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. 
         [0066]    The embodiments are chosen and described in order to explain the principles of the invention and their practical application so as to activate others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.