Abstract:
A light-emitting diode (LED) chip including a first semiconductor layer; an active layer disposed on the first semiconductor layer; a second semiconductor layer disposed on said active layer; at least one indentation comprising a bottom part extending downward to reach the first semiconductor layer and exposing the first semiconductor layer; a first metal layer disposed on the second semiconductor layer, connecting to the first semiconductor layer at the bottom part of the indention; 
     and an first insulating layer deposited on the second semiconductor layer and between the first metal layer and the second semiconductor layer to isolate the first metal layer from the second semiconductor layer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of co-pending application Ser. No. 13/715,120, filed on 14 Dec. 2012, for which priority is claimed under 35 U.S.C. §120; and this application claims priority of Application No. 101101147 filed in Taiwan on 11 Jan. 2012 under 35 U.S.C. §119, the entire contents of all of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Fields of the Invention 
         [0003]    The present invention relates to a light-emitting diode (LED) chip, especially to an LED chip comprising indirectly overlapped metal layers which are branched and distributed over a surface of the LED chip. 
         [0004]    2. Descriptions of Related Art 
         [0005]    A light-emitting diode (LED) is a light source made from semiconductor materials such as III-V group of semiconductors including gallium phosphide, gallium arsenide, etc. When a voltage is applied to the semiconductor, electrons and holes meet and recombine under electrode voltage difference. At this moment, the electrons fall to the lower energy level and the energy is released in the form of photons. The electric power is converted to light that is emitted out. 
         [0006]    Due to exhaustion of non-renewable resources including coal, natural gas, petroleum, etc, energy saving products also need development besides developing new energy sources to slow down consumption of fossil fuels. Under the pressure of unstable oil prices, countries worldwide are dedicated to develop energy saving products. Thus technologies of light-emitting diode, a so-called green light source, become more mature over time, and the application fields thereof get broader. Right now LED&#39;s have been widely used in indicators and display of computer, communication and consumer electronics (3C) products. Along with increasing yield rate of LED&#39;s, manufacturing cost per each unit of LED is significantly reduced, prompting adoption of LED as lighting material in various fields. 
         [0007]    As mentioned above, since development of high brightness LED has been a research emphasis of manufacturers in most countries, how to further enhance the efficiency of the LED shall be the focus to be stressed for improvement. 
         [0008]    Refer to  FIG. 1 , a lateral light-emitting diode chip basically comprises a substrate  10 , a first semiconductor layer  11 , an active layer  12 , a second semiconductor layer  13 , a first electrode  40  and a second electrode  41 . As shown in the figure, the first semiconductor layer  11  which is an n-type semiconductor is disposed on the substrate  10 , and the active layer  12  is disposed on the first semiconductor layer  11 . Then the second semiconductor layer  13  which is a p-type semiconductor is disposed on the active layer  12 . The first electrode  40  and the second electrode  41  are respectively disposed on the first semiconductor layer  11  and the second semiconductor layer  13 . While in use, an external voltage is applied to the light-emitting diode chip through the electrodes to make the active layer  12  emit light. Because the current tends to traverse the shortest pathway, the current flows downward vertically from the second electrode  41  through the second semiconductor layer  13  and then arrives the active layer  12 . Such that the main emission area of the active layer  12  is restricted to a region just below the second electrode  41  and the neighborhood. As to the area farther, the emission efficiency thereof is lowered due to less current passed. 
       SUMMARY OF THE INVENTION 
       [0009]    The present application provides a light-emitting diode (LED) chip including a first semiconductor layer; an active layer disposed on the first semiconductor layer; a second semiconductor layer disposed on said active layer; at least one indentation including a bottom part extending downward to reach the first semiconductor layer and exposing the first semiconductor layer; a first metal layer disposed on the second semiconductor layer, connecting to the first semiconductor layer at the bottom part of the indention; and an first insulating layer deposited on the second semiconductor layer and between the first metal layer and the second semiconductor layer to isolate the first metal layer from the second semiconductor layer. 
         [0010]    The present application provides a light-emitting diode (LED) chip including a first semiconductor layer; an active layer disposed on the first semiconductor layer; a second semiconductor layer disposed on the active layer; at least one indentation disposed on the second semiconductor layer, the indentation including a bottom part extending downward to reach the first semiconductor layer and exposing the first semiconductor layer; and a plurality of metal layers which disposed on the second semiconductor layer, including a first metal layer connecting to the first semiconductor layer through the bottom part, and a second metal layer indirectly deposited on the first metal layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic drawing showing structure of an LED chip; 
           [0012]      FIG. 2  is a schematic drawing showing a cross section of the embodiment according to the present invention; 
           [0013]      FIG. 3  is a schematic drawing showing a cross section of the embodiment comprising an indentation according to the present invention; 
           [0014]      FIG. 4  is a schematic drawing showing a top view of the embodiment without the transparent conductive layer according to the present invention; 
           [0015]      FIG. 5  is a schematic drawing showing a top view of the embodiment according to the present invention; 
           [0016]      FIG. 6  is a schematic drawing showing a cross section of line A-A′ of  FIG. 5  according to the present invention; 
           [0017]      FIG. 7  is a schematic drawing showing a cross section of line B-B′ of  FIG. 5  according to the present invention; and 
           [0018]      FIG. 8  is a schematic drawing showing a cross section of line C-C′ of  FIG. 5  according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    An embodiment according to the present invention, as shown in  FIG. 2  and  FIG. 3 , is an LED chip comprising a substrate  10 , a first semiconductor layer  11  deposited on the substrate  10 , an active layer  12  deposited on the portion of the semiconductor layer  11 , a second semiconductor layer  13  deposited on the active layer  12 , at least one indentation  20  (Another embodiment comprises a plurality of indentation  20 ) comprising a bottom part  201  deposited on the second semiconductor layer  13 ; a first insulating layer  30 , a first metal layer  31 , a second insulating layer  32 , a transparent conductive layer  33 , and a second metal layer  34  deposited on the second semiconductor layer  13  sequentially. Wherein the bottom part  201  of indentation  20  extends downward to reach the first semiconductor layer  11 . 
         [0020]    Further, the first insulating layer  30  is disposed on a portion of the second semiconductor layer  13  to separated the first metal layer  31  and the second semiconductor layer  13  as shown in  FIG. 2 . At the position of the indentation  20  as shown in  FIG. 3 , the first semiconductor layer  11  is exposed at the bottom part  201 , the first metal layer  31  is disposed on the first insulating layer  30  at the bottom part  201  of the indentation  20 , so that the first metal layer  31  can electrically connects to the first semiconductor layer  11 . The second insulating layer  32  covers at least a portion of the first metal layer  31 . The transparent conductive layer  33  is disposed on the second semiconductor layer  13  and the second insulating layer  32 , and the second metal layer  34  is disposed on the second transparent conductive layer  33  and the second insulating layer  32 . 
         [0021]    According to the structure of the present invention described forward, while the first metal layer  31  is disposed on the second semiconductor layer  13 , the first metal layer  31  is isolated by the first insulating layer  30  and the second insulating layer  32 . And while the first metal layer  31  proceeds to the bottom part  201  of the indentation  20 , the first metal layer  31  connects to the first semiconductor layer  11  smoothly because the first insulating layer  30  does not extend to the bottom part  201 , thereby achieving the goal of current spreading. 
         [0022]      FIG. 4  is a schematic drawing showing a top view of the embodiment of the present invention without the transparent conductive layer  33  and the second metal layer  34 . As shown in the figure, the LED chip of the present invention further comprises a first electrode  40  which connected to the first metal layer  31  deposited on the first semiconductor layer  11 , and a plurality of the indentations  20  are distributed over the surface of the LED chip wherein the bottom part  201  of each indentation exposes the first semiconductor layer  11  which originally covered by the active layer  12  and the second semiconductor layer  13 . The LED chip further comprises a branched-strip metal cover region which distributed like fingers is disposed on the second semiconductor layer  13 , where the first insulating layer  30  is disposed thereon and along edges of the indentations  20  without passing through the bottom parts  201 . So that the first metal layer  31  deposited on the insulating layer  30  will not contact the active layer  12  or the second semiconductor layer  13  resulting in short circuit. In other words, under electrical isolation from the second semiconductor layer  13  by the first insulating layer  30 , the first metal layer  31  deposited on the first insulating layer  30  can still connects to the first semiconductor layer  11  at the bottom parts  201  of the indentations  20 . 
         [0023]      FIG. 5  is a schematic drawing showing a top view of the embodiment of the present invention as illustrated in  FIG. 4  further deposited the transparent conductive layer  33 , the second metal layer  34 , and the second electrode  41 . As shown in the figure, the LED chip of the present invention further comprises a second electrode  41  which connected to the second metal layer  34  deposited on the transparent conductive layer  33  which completely covered the second semiconductor layer  13 , and the second insulating layer  32  deposited between the first metal layer  31  and the second metal layer  34 . Wherein the transparent conductive layer  33  further covered the second insulating layer  32 , the first metal layer  31 , and the first insulating layer  30 . 
         [0024]    Regarding to material of the structure of the embodiment described forward, when the first semiconductor layer  11  is an n-type semiconductor layer, the second semiconductor layer  13  is a p-type semiconductor layer. And accordingly, the first electrode  40  is an n-type electrode and the second electrode  41  is a p-type electrode. On the other hand, when the first semiconductor layer  11  is a p-type semiconductor layer, the second semiconductor layer  13  is an n-type semiconductor layer; and the first electrode  40  is a p-type electrode, the second electrode  41  is an n-type electrode. And the transparent conductive layer  33  comprises indium tin oxide that is a mixture of indium oxide (In 2 O 3 ) and tin oxide (SnO 2 ). Generally, the mass ratio of the mixture is 90% In 2 O 3  and 10% SnO 2 . When indium tin oxide is in a film form, it is transparent and conductive. Thus, light emitted from the active layer  12  can pass the transparent conductive layer  33  smoothly. Moreover, due to conductivity of the transparent conductive layer  33 , current generated by the voltage applied to the second metal layer  34  can flow to the second semiconductor layer  13  through conduction of the transparent conductive layer  33 . 
         [0025]    In order to disclose the structure of the LED chip of the present invention in more detail, the cross sections at line A-A′, B-B′, and C-C′ of  FIG. 5  are illustrated as backward. 
         [0026]    As shown in  FIG. 6 , the cross section at the line A-A′ of  FIG. 5  illustrated the structure of indentation  20  of the LED chip of the present invention, the first metal layer  31  connects to the first semiconductor layer  11  at the bottom part  201 . The first insulating layer  30  effectively isolates the first metal layer  31  from the second semiconductor layer  13  or the active layer  12 , so that the LED chip can operate normally under the structure comprising indentations. 
         [0027]    As shown in  FIG. 4  to  FIG. 6 , the LED chip of the present invention comprises the first metal layer  31  and the second metal layer  34  which are arranged into an indirect overlapping structure and electrically isolated with each other by the second insulating layer  32 . And the metal layers with the indirect overlapping structure are branched into several strips like fingers and distributed on the surface of the LED chip, then the electric current can be distributed and flows more evenly, which increasing not only the emission area of the active layer  12  but also the emission efficiency. In order to achieve the indirect overlapping, the shape and volume of the overlapped portions of the first metal layer  31  and the second metal layer  34  are the same, and the first metal layer  31  and the second metal layer  34  comprise metal compound. In order to decrease and avoid any possible shielding on the active layer  12  caused by stacking of the metal layers there above, the first metal layer  31  and the second metal layer  34  are overlapped mostly and precisely from the top view of the LED chip of the present invention to ensure the light extraction efficiency. 
         [0028]    As shown in  FIG. 7 , the cross section at the line B-B′ of  FIG. 5  illustrated the structure at the position of the first electrode  40  of the LED chip of the present invention, the first electrode  40  disposed on the first semiconductor layer  11  is located on one side of the LED chip, and connects to the first metal layer  31  along the first insulating layer  30  which separated/isolated the electrode  40  and the first metal layer  31  from the second semiconductor layer  13  and the active layer  12  to prevent short circuit. 
         [0029]    As shown in  FIG. 8 , the cross section at the line C-C′ of  FIG. 5  illustrated the structure at the position of the second electrode  41  of the LED chip of the present invention, the second electrode  41  disposed on the transparent conductive layer  33  is located on the other side of the LED chip, and connects to the second metal layer  34 . The first electrode  40  and the second electrode  41  are positioning for wire bonding of the LED chip with adjacent LED chips or a power source. By bonding wires made of gold, a voltage can be applied to the LED chip of the present invention to emit light. 
         [0030]    According to the present invention as illustrated forward, the first metal layer  31  electrically connects to the first semiconductor layer  11  at the bottom part  201  of each indentation  20 . Then the current can flow along a path formed by the second metal layer  34 , the transparent conductive layer  33 , the second semiconductor layer  13 , the active layer  12 , the first semiconductor layer  11 , and the first metal layer  31 , so as to make the active layer  12  emit light evenly and enhancing the light emission efficiency. Because the voltage applied is distributed evenly by the branched-strip design, the region far away from the center of the LED can still get the same voltage supply through the branched-strip distribution of the overlapped metal layers. And there is needless to reduce the area of the active layer and the second semiconductor layer  13  greatly for exposing the electrode on the first semiconductor layer  11 . Therefore the present invention increases a ratio of the area of the active layer  12  to that of the overall chip, the light extraction area the light extraction efficiency. 
         [0031]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.