Patent Publication Number: US-8987776-B2

Title: Light-emitting device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/011,502, filed on Aug. 27, 2013, which is a divisional application of U.S. application Ser. No. 13/608,750, filed on Sep. 10, 2012, now U.S. Pat. No. 8,530,927, which is a divisional application of U.S. application Ser. No. 13/009,491, filed on Jan. 19, 2011, now U.S. Pat. No. 8,263,998, which is a continuation of U.S. application Ser. No. 12/437,908, filed on May 8, 2009, now U.S. Pat. No. 7,906,795; and this application is a continuation of U.S. application Ser. No. 13/901,191, filed on May 23, 2013, which is a continuation application of U.S. application Ser. No. 13/005,075, filed on Jan. 12, 2011, now U.S. Pat. No. 8,450,767, which is a continuation-in-part (CIP) application of U.S. application Ser. No. 12/437,908, filed on May 8, 2009, now U.S. Pat. No. 7,906,795, priority to all of which is claimed under 35 U.S.C. §120, and the entire contents of all of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Technical Field 
     The present invention relates to a light-emitting device, and in particular to a semiconductor light-emitting device. 
     2. Description of the Related Art 
     The light-emitting mechanism and the structure of a light-emitting diode (LED) are different from that of the conventional light sources. The LED has advantages of small size and high reliability, and been widely used in different fields such as displays, laser diodes, traffic lights, data storage apparatus, communication apparatus, lighting apparatus, and medical apparatus. Because of the successful development of high brightness LEDs, LED can be applied to indoor or large outdoor displays. How to improve the light emitting efficiency of light emitting devices is an important issue in this art. 
     SUMMARY OF THE DISCLOSURE 
     Accordingly, the present invention provides a light-emitting device. The light-emitting device includes a semiconductor light-emitting stack having a light emitting area; an electrode formed on the semiconductor light-emitting stack, wherein the electrode comprises a current injected portion and an extension portion; a current blocking area formed between the current injected portion and the semiconductor light-emitting stack, and formed between a first part of the extension portion and the semiconductor light-emitting stack; and an electrical contact structure formed between a second part of the extension portion and the semiconductor light-emitting stack, wherein the first part of the extension portion is closer to current injected portion than the second part of the extension portion is, and wherein the ratio of the electrical contact structure and the light emitting area is between 3% to 15%. 
     Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide easy understanding of the invention, and are incorporated herein and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to illustrate the principles of the invention. 
         FIG. 1A  is a cross-sectional view of a light-emitting device in accordance with a first embodiment of the present invention. 
         FIG. 1B  is a top view of a light-emitting device in accordance with the first embodiment of the present invention. 
         FIG. 1C  is a top view of a conventional light-emitting device. 
         FIG. 2A  is a cross-sectional view of a light-emitting device in accordance with a second embodiment of the present invention. 
         FIG. 2B  is a top view of a light-emitting device in accordance with the second embodiment of the present invention. 
         FIG. 3A  is a cross-sectional view of a light-emitting device in accordance with a third embodiment of the present invention. 
         FIG. 3B  is a top view of a light-emitting device in accordance with the third embodiment of the present invention. 
         FIG. 4A  is a cross-sectional view of a light-emitting device in accordance with a fourth embodiment of the present invention. 
         FIG. 4B  is a top view of a light-emitting device in accordance with the fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     Referring to  FIGS. 1A-1B , the cross-sectional views show a light-emitting device  1  in accordance with a first embodiment of the present invention. The light-emitting device  1  such as an LED comprises a substrate  100 , a semiconductor light-emitting stack  110 , an electrical contact structure  140 , a first electrode  120 , and a second electrode  130 . The material of the substrate  100  includes semiconductor materials such as Si, SiC, GaAsP, GaAs, or GaP. The semiconductor light-emitting stack  110  formed on the upper surface of the substrate  100  includes an n-type semiconductor layer  112 , a p-type semiconductor layer  114 , and an active layer  113  interposed therebetween. In some embodiments, the arrangements of the n-type and p-type semiconductor layers  112  and  114  can be interchanged. In the embodiment, the n-type and p-type semiconductor layers  112  and  114  act as cladding layers of the LED and include MN group compound semiconductor materials such as AlGaInP, AlGaAs, AlGaInN, or other ternary or quaternary III-V group compound semiconductor materials. The active layer  113  acts as a light-emitting layer including group compound semiconductor materials such as AlGaInP, AlGaInN or other materials matched with the n-type and p-type semiconductor layers  112  and  114 . The first electrode  120  and the second electrode  130  are formed on the bottom of the substrate  100  and the top of the semiconductor light-emitting stack  110  respectively. In the embodiment, the second electrode  130  includes a current injected portion  131  and extension portion  132 . In the embodiment, the current injected portion  131  is deposited approximately on the center of the p-type semiconductor layers  114 . The extension portions  132  comprise first branches  1321  radiate from the current injected portion  131  toward the edges of the light-emitting device  1 . Second branches  1322  are diverging and extending from the first branches. The second branches are deposited along with and paralleled to the edges of the light-emitting device  1 . The electrical contact structure  140  is formed between the second branches and the semiconductor light-emitting stack  110 . A method of forming the electrical contact structure  140  includes forming a semiconductor layer on the semiconductor light-emitting stack  110 , which is ohmically contacted with the extension portions  132 . Then etching the semiconductor layer in accordance with a predetermined pattern. After that, part of the p-type semiconductor layer  114  is exposed, and the remaining region of the semiconductor layer forms the electrical contact structure  140 . Afterwards, the electrodes are formed on the p-type semiconductor layer  114  and the electrical contact structure  140 . 
     Another method for forming the electrical contact structure  140  includes a step of forming an insulated layer on the semiconductor layer to cover the area with another predetermined pattern. The exposed region of the semiconductor layer is the electrical contact structure. 
     The conductive type of the electrical contact structure  140  can be the same as the p-type semiconductor layer  114  or different from it. If the conductivity of the electrical contact structure  140  is n-type, it also forms a reverse tunneling contact with the p-type semiconductor layer  114 . Another material of the electrical contact structure  140  is metal which can be partially deposited on the p-type semiconductor layer  114  with a predetermined pattern to form the electrical contact structure  140 . 
     In one embodiment, the material of the electrical contact structure  140  is a p-type semiconductor. The second branches  1322  are electrically contacted with the electrical contact structure  140 . Because the first branches  1321  and the current injected portion  131  are current-blocked with the p-type semiconductor layer  114 , the current is injected through the current injected portion  131 , moves to the first branches  1321  and the second branches  1322 , and then is spread to the semiconductor light-emitting stack  110  through the electrical contact structure  140 . In the embodiment, the size of the light-emitting device  1  is 10 mil×10 mil, and the area of the active layer  113  is 67.24 mil 2 . The width of each of the first branches  1321  is 0.2 mil, and the width of each of the second branches  1322  is 0.4 mil. The width of each of the electrical contact structure  140  is 0.3 mil. The electrical contact structure  140  and the second branches  1322   c  have substantially the same shape. The total area of the extension portions  132  is 11.64 mil 2  and the total area of the electrical contact structure  140  is 5.8 mil 2 . The area ratio of the electrical contact structure  140  and the active layer  113  is 8.62%. The luminous efficiency of the light-emitting device  1  is 47.62 lm/W. When the width of the second branch  1322  is varied from 0.4 mil to 0.45 mil and the width of the electrical contact structure  140  is varied from 0.3 mil to 0.35 mil, the area ratio of the electrical contact structure  140  and the active layer  113  is 10.18% and the luminous efficiency of the light-emitting device  1  is 46.48 lm/W. When the width of each second branch  1322  is varied to 0.5 mil, and the width of the electrical contact structure  140  is varied to 0.4 mil, the area ratio of the electrical contact structure  140  and the active layer  113  is 11.77% and the luminous efficiency of the light-emitting device  1  is 46.13 lm/W. 
       FIG. 1C  shows the top view of a conventional light-emitting device without implementing the present invention. The electrical contact structure  140  is formed under the first branches  1321  and the second branches  1322 . The luminous efficiency of the light-emitting device  1  is 46.01 lm/W which is lower than that of the light-emitting device  1  in accordance of the first embodiment of the present invention. 
     In some embodiments, the surface of the semiconductor light-emitting stack  110  and/or the interface between the semiconductor light-emitting stack  110  and the substrate  100  can be optionally roughened to improve the light extraction efficiency. The roughened surface can be formed during the epitaxial process, by a randomly etching method or a lithographical etching to form a regular or an irregular patterned surface. 
       FIGS. 2A-2B  show the cross-sectional views of a light-emitting device  2  in accordance with a second embodiment of the present invention. The light-emitting device  2  includes a substrate  200 , a conductive adhesive layer  201 , a reflective layer  202 , a first transparent conductive oxide layer  220 , a semiconductor light-emitting stack  210 , an electrical contact structure  250 , a first electrode  230 , and a second electrode  240 . 
     The material of the substrate  200  includes but is not limited to Si, GaAs, metal or other similar materials which can mechanically support the other structure of the light-emitting device  2 . The conductive adhesive layer  201  is formed on the substrate  200 , and a first bonding interface is formed therebetween. The material of the conductive adhesive layer  201  includes but is not limited to Ag, Au, Al, In, spontaneous conductive polymer, or polymer doped with conductive materials like Al, Au, Pt, Zn, Ag, Ni, Ge, In, Sn, Ti, Pb, Cu, Pd, or other metals. The reflective layer  202  is formed on the conductive adhesive layer  201 , and a second bonding interface is formed therebetween. The material of the reflective layer  202  includes but is not limited to metal, insulated material, or the combination thereof. The metal material for the reflective layer  202  includes Al, Au, Pt, Zn, Ag, Ni, Ge, In, Sn or alloys of the abovementioned metals. The insulated material for the reflective layer  202  includes but is not limited to AlO x , SiO x , or SiN x . The first transparent conductive oxide layer  220  formed on the reflective layer  202  includes materials such as indium tin oxide, cadmium tin oxide, zinc oxide, or zinc tin oxide. 
     The semiconductor light-emitting stack  210  formed on the first transparent conductive oxide layer  220  includes a thick semiconductor layer  211 , a p-type semiconductor layer  214 , an n-type semiconductor layer  212 , and an active layer  213  interposed therebetween. In the embodiment, the semiconductor light-emitting stack  210  is etched partially from the n-type semiconductor layer  212 , the active layer  213 , and the p-type semiconductor layer  214  to the thick semiconductor layer  211  to expose part of the thick semiconductor layer  211 . The materials of the n-type and p-type semiconductor layers  212  and  214  include III-V group compound semiconductor materials such as AlGaInP, AlGaAs, AlGaInN or other ternary or quaternary III-V group compound semiconductor materials. The active layer  213  includes III-V group compound semiconductor materials such as AlGaInP, AlGaInN or other materials matched with the n-type and p-type semiconductor layers  212  and  214 . The thick semiconductor layers  211  acts as a light extraction layer for improving the light extraction efficiency and includes materials such as GaP or GaN. 
     The method of forming the light-emitting device  2  includes forming a semiconductor layer on a growth substrate (not illustrated), and next forming the semiconductor light-emitting stack  210  on the semiconductor layer. After the semiconductor light-emitting stack  210  is grown, the first transparent conductive oxide layer  220  is formed on the semiconductor light-emitting stack  210 , which can spread the current injected from the electrode. Next, the reflective layer  202  is formed on the first transparent conductive oxide layer  220 . Then, the semiconductor light-emitting stack  210  with the first transparent conductive oxide layer  220  and the reflective layer  202 , and the substrate  200  are adhered together by the adhesive layer  201 . 
     After the adhering step, the growth substrate is removed, and the semiconductor layer is etched with a predetermined pattern. Part of the n-type semiconductor layer  212  is exposed, and the remaining semiconductor layer forms the electrical contact structure  250 . 
     The first and second electrodes  230  and  240  are formed on the top surface of the semiconductor light-emitting stack  210  and the bottom of the substrate  200  respectively. In the embodiment, the second electrode  240  includes a current injected portion  241  and extension portions  242 . In the embodiment, the current injected portion  241  is deposited approximately on the center of the semiconductor light-emitting stack  210 . The extension portions  242  comprise first branches  2421  radiating from the current injected portion  241  toward the edges of the light-emitting device  2 . Second branches  2422 , third branches  2423 , and fourth branches  2424  are diverging and extending from the first branches respectively. The second branches  2422  are deposited along with and parallel to the edges of the light-emitting device  2 . The second, third and fourth branches  2422 ,  2423 ,  2424  are parallel to each other. The electrical contact structure  250  is formed between the second, third and fourth branches  2422 ,  2423 ,  2424  and the semiconductor light-emitting stack  210  respectively. In this embodiment, the material of the electrical contact structure  250  is an n-type semiconductor including III-V group compound semiconductor materials such as GaP, GaAs, GaN or other ternary or quaternary III-V group compound semiconductor materials. The second, third and fourth branches  2422 ,  2423 ,  2424  are electrical contact with the electrical contact structure  250 . The first branches  2421  and the current injected portion  241  are current-blocked with the semiconductor light-emitting stack  210 . The current is injected through the current injected portion  241  and moves to the first, second, third and fourth branches  2421 ,  2422 ,  2423 ,  2424 , and then is spread to the semiconductor light-emitting stack  210  through the electrical contact structure  250 . In the embodiment, the size of the light-emitting device  2  is 28 mil×28 mil, and the area of the active layer  213  is 645.16 mil 2 . The width of each of the first branches  2421  is 0.15 mil. The width of each of the second, third and fourth branches  2422 ,  2423 ,  2424  is 0.4 mil. The width of each of the electrical contact structure  250  is 0.3 mil. The electrical contact structure  250  and the second branches have substantially the same shape. The total area of the extension portions  242  is 34.39 mil 2 , and the total area of the contact structure  250  is 41.16 mil 2 . The area ratio of the electrical contact structure  250  and the active layer  213  is 6.38%. The luminous efficiency of the light-emitting device  2  is 55 m/W. 
     In another embodiment, a structure of a light-emitting device without the conductive adhesive layer  201  and the first transparent conductive oxide layer  220  can be formed by direct bonding method with high pressure to join the semiconductor light-emitting stack  210  and the substrate  200 , or join the reflective layer  202  and the substrate  200  together. 
     In another embodiment, a second transparent conductive oxide layer can be formed on the semiconductor light-emitting stack  210 , and includes materials such as indium tin oxide, cadmium tin oxide, zinc oxide, or zinc tin oxide. 
       FIGS. 3A-3B  show the cross-sectional views of a light-emitting device  3  in accordance with a third embodiment of the present invention. The structure of the light-emitting device  3  is similar to the light emitting device  1 , and the difference is the n-type semiconductor  212  of the light emitting device  3  includes a roughened top surface. The roughened top surface can be formed during the epitaxial process or by a randomly etching method to form a multi-cavity surface. It also can be formed by a lithographical etching to form a regular or an irregular patterned surface. The n-type semiconductor  212  also includes an even top surface. A second electrode  340  is formed on the even top surface. The second electrode  340  includes a current injected portion  341  and windmill-like extension portions  342 . In the embodiment, the current injected portion  341  is deposited approximately on the center of the even top surface of the n-type semiconductor layer  212 . The windmill-like extension portions  342  comprise branches  3421  radiating from the current injected portion  341  and form a windmill like shape. The branches  3421  comprise first regions and second regions, wherein the first regions are closer to the current injected portion  341  than the second regions are. There is an electrical contact structure  350  formed between second regions of branches  3421  and the semiconductor light-emitting stack  210 , and the electrical contact structure  350  are ohmically contacted with the second regions of branches  3421 . In this embodiment, the material of the electrical contact structure  350  is an n-type semiconductor including III-V group compound semiconductor materials such as GaP, GaAs, GaN or other ternary or quaternary III-V group compound semiconductor materials. The first regions of branches  3421  and the current injected portion  341  are current-blocked with the semiconductor light-emitting stack  210 . The current is injected through the current injected portion  341  and moves to the branches  3421 , and then is spread to the semiconductor light-emitting stack  210  through the electrical contact structure  350 . In the embodiment, the size of the light-emitting device  3  is 14 mil×14 mil, and the area of the active layer  213  is 135 mil 2 . The width of each of the branches  3421  is 0.25 mil. The width of each of the electrical contact structure  350  is 0.15 mil. The electrical contact structure  350  and the second regions of branches have substantially the same shape. The total area of the extension portions  342  is 8.13 mil 2 , and the total area of the electrical contact structure  350  is 3.37 mil 2 . The area ratio of the electrical contact structure  350  and the active layer  213  is 2.51%. The luminous efficiency of the light-emitting device  3  is 67 lm/W. 
     In a conventional light-emitting device, the electrical contact structure  350  is varied to be formed between the first and second regions of the extension portions  342  and the semiconductor light-emitting stack  210 , the total area of the electrical contact structure  350  is 4.89 mil 2 . The area ratio of the electrical contact structure  350  and the active layer  213  is 3.64%. The luminous efficiency of the conventional light-emitting device is 65 lm/W which is lower than that of the light-emitting device  3  in accordance with the third embodiment of the present invention. 
       FIGS. 4A-4B  show the cross-sectional view of a light-emitting device  4  in accordance with a fourth embodiment of the present invention. The light-emitting device  4  includes a substrate  400 , a conductive adhesive layer  401 , a reflective layer  402 , a first transparent conductive oxide layer  420 , a semiconductor light-emitting stack  410 , a current blocking structure  403  formed between the first transparent conductive oxide layer  420  and the semiconductor light-emitting stack  410 , an electrical contact structure  450 , a first electrode  430 , and a second electrode  440 . The material of the substrate  400  includes but is not limited to Si, GaAs, metal or other similar materials which can mechanically support the other structure of the light-emitting device  4 . The conductive adhesive layer  401  is formed on the substrate  400 , and a first bonding interface is formed therebetween. The material of the conductive adhesive layer  401  includes but is not limited to Ag, Au, Al, In, spontaneous conductive polymer, or polymer doped with conductive materials like Al, Au, Pt, Zn, Ag, Ni, Ge, In, Sn, Ti, Pb, Cu, Pd, or other metals. The reflective layer  402  is formed on the conductive adhesive layer  401 , and a second bonding interface is formed therebetween. The material of the reflective layer  402  includes but is not limited to metal, oxide, or the combination thereof. The metal material for the reflective layer  402  includes Al, Au, Pt, Zn, Ag, Ni, Ge, In, Sn or alloys of the abovementioned metals. The first transparent conductive oxide layer  420  is formed on the reflective layer  402 , and includes but is not limited to indium tin oxide, cadmium tin oxide, zinc oxide, or zinc tin oxide. The material of current blocking structure  403  includes but is not limited to AlO x , SiO x , SiN x , or metal. The metal of the current blocking structure  403  is selected from material capable of forming a Schottky contact with the first transparent conductive oxide layer  420 . The semiconductor light-emitting stack  410  is formed on the first transparent conductive oxide layer  420 , including a thick semiconductor layer  411 , a p-type semiconductor layer  414 , an n-type semiconductor layer  412 , and an active layer  413  interposed therebetween. In the embodiment, the semiconductor light-emitting stack  410  is etched partially from the n-type semiconductor layer  412 , the active layer  413 , and the p-type semiconductor layer  414  to the thick semiconductor layer  411  to expose part of the thick semiconductor layer  411 . The n-type semiconductor  412  of the light emitting device  4  includes a roughened top surface. The materials of the n-type and p-type semiconductor layers  412  and  414  include III-V group compound semiconductor materials such as AlGaInP, AlGaAs, AlGaInN or other ternary or quaternary III-V group compound semiconductor materials. The active layer  413  includes III-V group compound semiconductor materials such as AlGaInP, AlGaInN or other materials matched with the n-type and p-type semiconductor layers  412  and  414 . The thick semiconductor layers  411  acts as a light extraction layer for improving the light extraction efficiency and includes materials such as GaP or GaN. 
     The method of forming the light-emitting device  4  includes forming a semiconductor layer on a growth substrate (not illustrated), forming the semiconductor light-emitting stack  410  on the semiconductor layer, forming current blocking structure  403  on the semiconductor light-emitting stack  410 , forming the first transparent conductive oxide layer  420  on the semiconductor light-emitting stack  410  and current blocking structure  403  with a first predetermined pattern, and forming the reflective layer  402  on the first transparent conductive oxide layer  420  to form a first stack. Next the first stack and the substrate  400  are adhered together by the adhesive layer  401 . 
     After the adhering step, the growth substrate is removed, and the semiconductor layer is etched in accordance with a second predetermined pattern to expose part of the n-type semiconductor layer  412 , and the remaining semiconductor layer forms the electrical contact structure  450 . In this embodiment, the material of the electrical contact structure  450  is an n-type semiconductor including III-V group compound semiconductor materials such as GaP, GaAs, GaN or other ternary or quaternary III-V group compound semiconductor materials. 
     The first and second electrodes  430  and  440  are formed on the top surface of the semiconductor light-emitting stack  410  and the electrical contact structure  450 , and the bottom of the substrate  400  respectively. In the embodiment, the second electrode  440  includes a current injected portion  441  and extension portions  442 . In the embodiment, the current injected portion  441  is deposited approximately on the center of semiconductor light-emitting stack  410 . The extension portions  442  comprise first branches  4421  radiating from the current injected portion  441  toward the edges of the light-emitting device  4 . Second branches  4422  are diverging and extending from the first branches  4421 . The second branches  4422  are deposited along with and parallel to the edges of the light-emitting device  4 . The electrical contact structure  450  is formed between the second branches  4422  and the semiconductor light-emitting stack  410 . The second predetermined pattern of the electrical contact structure  450  is similar to that of the second branches  4422 . The second branches  4422  are electrically contacted with the electrical contact structure  450 . The first branches  4421  and the current injected portion  441  are current-blocked with the semiconductor light-emitting stack  410 . 
     The current blocking structure  403  is deposited under the second branches  4422  and between the p-type semiconductor layer  414  and the first transparent conductive oxide layer  420 . The first predetermined pattern of the current blocking structure  403  is similar to that of the electrical contact structure  450 , and the width of the current blocking structure  403  is larger than that of the electrical contact structure  450  so the area of the current blocking structure  403  is larger than that of the electrical contact structure  450 . The current is injected through the current injected portion  441  and moves to the first and second branches  4421 ,  4422  and then is spread to the semiconductor light-emitting stack  410  through the electrical contact structure  450 . The current is blocked by the current blocking structure  403  so there is less light generated by the active layer under the second branches  4422  and less light is absorbed by the second branches  4422 . 
     In the embodiment, the size of the light-emitting device  4  is 14 mil×14 mil, and the area of the active layer  413  is 135 mil 2 . The width of each of the first branches  4421  is 0.14 mil, and the width of each of the second branches  4422  is 0.24 mil. The width of each of the electrical contact structure  450  is 0.14 mil, and the width of each of the current blocking structure  403  is 0.12 mil. 
     The electrical contact structure  450  and the second branches have substantially the same shape. The total area of the extension portions  442  is 8.83 mil 2 , and the total area of the contact structure  450  is 4.26 mil 2 . The area ratio of the electrical contact structure  450  and the active layer  413  is 3.16%. The luminous efficiency of the light-emitting device  4  is 80 lm/W. 
     It will be apparent to a person having ordinary skill in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of this, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.