Abstract:
An optoelectronic element comprises a semiconductor stack layer comprising a first surface and a second surface; a first transparent conductive oxide layer formed on the first surface of the semiconductor stack layer, wherein the first transparent conductive oxide layer comprises at least an opening exposing the first surface of the semiconductor stack layer; and a second transparent conductive oxide layer filled into the opening and covering the first transparent conductive oxide layer; wherein the first transparent conductive oxide layer and the second transparent conductive oxide layer are comprised of a material selected from the group consisting of indium tin oxide (ITO), indium oxide (InO), tin oxide (SnO), cadmium tin oxide (CTO), aluminum tin oxide (ATO), aluminum zinc oxide (AZO), and zinc oxide (ZnO), and the first transparent conductive oxide layer and the second transparent conductive oxide layer have the same constituent material with different refractive indexes.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/813,621 filed Jun. 11, 2010 which is incorporated by reference in its entirety. This application claims the right of priority based on TW application Serial No. 098119860 filed on Jun. 12, 2009, which is incorporated herein by reference and assigned to the assignee herein. 
    
    
     TECHNICAL FIELD 
     The application relates to an optoelectronic device, and more particularly to an optoelectronic device including a first transparent conductive oxide layer and a second transparent conductive oxide layer. 
     DESCRIPTION OF BACKGROUND ART 
     The lighting theory of light-emitting diode (LED), which is different from that of incandescent lamp, is to generate light by releasing the energy generated from the move of the electron between n type semiconductor and p type semiconductor. So the LED is called a cold lighting source. Furthermore, since LED has advantages as highly durable, long life-time, light weight, low power loss, nowadays LED is highly expected to be a new generation lighting device in the lighting market. 
       FIG. 1  is a diagram of a conventional optoelectronic element  100  including a substrate  10 , a semiconductor stacked layer  12  disposed on the substrate  10 , and at least an electrode  14  disposed on the semiconductor stacked layer  12 , wherein from top to bottom the semiconductor stacked layer  12  includes a first conductive type semiconductor layer  120 , an active layer  122 , and a second conductive type semiconductor layer  124 . 
     In the conventional optoelectronic element  100 , the surface of the semiconductor stacked layer  12  is flat, and the refractive index of the semiconductor stacked layer  12  is different from that of the external environment, so the light emitted from the active layer has total internal reflection (TIR) easily. 
     Moreover, when the conventional optoelectronic element  100  is in operation, the current flows into the semiconductor stacked layer  12  via the electrode  14 . Most of the current flows in the semiconductor stacked layer  12  by a shortest route, therefore the current distributes in the semiconductor stacked layer  12  unevenly, and the illumination efficiency of the optoelectronic element  100  is affected. 
     Besides, the optoelectronic element  100  can further connects to other elements to form an optoelectronic apparatus.  FIG. 2  is a structure diagram of a conventional optoelectronic apparatus. As shown in  FIG. 2 , an optoelectronic apparatus  200  includes: a sub-mount  20  at least having a circuit  202 ; at least a solder  22  disposed on the sub-mount  20  to attach the optoelectronic element  100  on the sub-mount  20 , and electrically connects the substrate  10  of the optoelectronic element  100  to the circuit  202 ; and an electrical connection structure  24  for electrically connecting the electrode  14  of the optoelectronic element  100  to the circuit  202  of the sub-mount  20 , wherein the sub-mount  20  can be a lead frame or a mounting structure for circuitry planning of the optoelectronic apparatus  200  and for enhancing the heat-dissipation. 
     SUMMARY OF THE DISCLOSURE 
     The present application discloses an optoelectronic element comprising a semiconductor stack layer; a first transparent conductive oxide layer located on the semiconductor stack layer, wherein the first transparent conductive oxide layer has at least an opening; and a second transparent conductive oxide layer covering the first transparent conductive oxide layer, wherein the second transparent conductive oxide layer is filled into the opening of the first transparent conductive oxide layer and contacted with the semiconductor stack layer, and any one of the first transparent conductive oxide layer and the second transparent conductive oxide layer forms an ohmic contact with the semiconductor stack layer. 
     The present application further discloses an optoelectronic element comprising a semiconductor stack layer; a first transparent conductive oxide layer located on the semiconductor stack layer, wherein the first transparent conductive oxide layer has at least an opening and is in ohmic contact with the semiconductor stack layer; and a second transparent conductive oxide layer covering the first transparent conductive oxide layer, wherein the second transparent conductive oxide layer is filled into the opening. 
     The present application further discloses an optoelectronic element comprising a semiconductor stack layer; a first transparent conductive oxide layer located on the semiconductor stack layer, wherein the first transparent conductive oxide layer has at least an opening; and a second transparent conductive oxide layer covering the first transparent conductive oxide layer, wherein the second transparent conductive oxide layer is filled into the opening and in ohmic contact with the semiconductor stack layer. 
     The present application further discloses an optoelectronic element comprising a semiconductor stack layer comprising a first surface and a second surface; a first transparent conductive oxide layer formed on the first surface of the semiconductor stack layer, wherein the first transparent conductive oxide layer comprises at least an opening exposing the first surface of the semiconductor stack layer; and a second transparent conductive oxide layer filled into the opening and covering the first transparent conductive oxide layer; wherein the first transparent conductive oxide layer and the second transparent conductive oxide layer are comprised of a material selected from the group consisting of indium tin oxide (ITO), indium oxide (InO), tin oxide (SnO), cadmium tin oxide (CTO), aluminum tin oxide (ATO), aluminum zinc oxide (AZO), and zinc oxide (ZnO), and the first transparent conductive oxide layer and the second transparent conductive oxide layer have the same constituent material with different refractive indexes. 
     The present application further discloses an optoelectronic element comprising a semiconductor stack layer comprising a first surface and a second surface; a first transparent conductive oxide layer formed on the first surface and having at least one opening; and a second transparent conductive oxide layer covering on the first transparent conductive oxide layer and filled into the opening, wherein the first transparent conductive oxide layer and the second transparent conductive oxide layer are composed of the same materials but in different composition ratios. 
     The present application further discloses an optoelectronic element, comprising a semiconductor stack layer comprising a first surface and a second surface; a first transparent conductive oxide layer formed on the first surface of the semiconductor stack layer, wherein the first transparent conductive oxide layer comprises at least an opening exposing the first surface of the semiconductor stack layer; and a second transparent conductive oxide layer filled into the opening and covering the first transparent conductive oxide layer; wherein the first transparent conductive oxide layer and the second transparent conductive oxide layer are comprised of a material selected from the group consisting of indium tin oxide (ITO), indium oxide (InO), tin oxide (SnO), cadmium tin oxide (CTO), aluminum tin oxide (ATO), aluminum zinc oxide (AZO), and zinc oxide (ZnO), and the first transparent conductive oxide layer and the second transparent conductive oxide layer have the same constituent material with different grain sizes. 
     One objective of the present application is to provide an optoelectronic element comprising a first transparent conductive oxide layer having at least an opening to increase the lighting efficiency of the optoelectronic element. The first transparent conductive oxide layer can also form a structure having a plurality of openings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structure diagram of a conventional optoelectronic element. 
         FIG. 2  is a schematic structure diagram of a conventional optoelectronic device. 
         FIG. 3  is a schematic structure diagram of an embodiment of the present application. 
         FIGS. 4A to 4D  are fabrication flow diagrams of an embodiment of the present application. 
         FIG. 5  is a schematic structure diagram of another embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 3  is a schematic structure diagram of an embodiment of the present application. As shown in  FIG. 3 , an optoelectronic element  300  includes a semiconductor stack layer  30  having a first principal surface  302  and a second principal surface  304 ; a first transparent conductive oxide layer  32  located on the first principal surface  302  or second principal surface  304 ; in the present embodiment, the first transparent conductive oxide layer  32  is located on the first principal surface  302 ; and a second transparent conductive oxide layer  34  covering the first transparent conductive oxide layer  32  to form a surface substantially parallel to the first principal surface  302  or the second principal surface  304 , wherein the first transparent conductive oxide layer  32  further includes a plurality of openings  320  thereon, and the second transparent conductive oxide layer  34  is filled into the openings  320  of the first transparent conductive oxide layer  32  and in contact with the semiconductor layer  30 , wherein the first transparent conductive oxide layer  32  or the second transparent conductive oxide layer  34  can form an ohmic contact with the semiconductor stack layer  30 . In the present embodiment, the first transparent conductive oxide layer  32  forms an ohmic contact with the semiconductor stack layer  30  for an electrical connection, and where the second transparent conductive oxide layer  34  in contact with the semiconductor layer  30  dose not form an ohmic contact but a schottky contact. 
     Additionally, the optoelectronic element  300  further includes a substrate  36  located under the second principal surface  304 , and an electrode  38  located on the second transparent conductive oxide layer  34 , wherein the electrode  38  is located directly above the opening  320  of the first transparent conductive oxide layer  32 . 
     The semiconductor stack layer  30  from top to bottom can include a first conductive type semiconductor layer  306 , an active layer  308 , and a second conductive type semiconductor layer  310 . The material of the semiconductor stack layer  30  is selected from the III-V group materials, for example, the semiconductor materials contain Al, Ga, In, N, P or As, such as GaN series, AlGaInP series or GaAs series; and the materials of the first transparent conductive oxide layer  32  and the second transparent conductive oxide layer  34  can be ITO, InO, SnO, CTO, ATO, AZO, or ZnO, wherein the grain size or the reflective index of the first transparent conductive oxide layer  32  differs from that of the second transparent conductive oxide layer  34 . The first transparent conductive oxide layer  32  and the second transparent conductive oxide layer  34  are composed of different materials, or are composed of the same materials but in different composition ratios. The first transparent conductive oxide layer  32  and the second transparent conductive oxide layer  34  can form an ohmic contact therebetween to promote current spreading effect. 
     Additionally, the first transparent conductive oxide layer  32  has a plurality of openings  320 , and the top surface of the second transparent conductive oxide layer  34  that fills into the opening  320  and covers the first transparent conductive oxide layer  32  can be a flat surface substantially parallel to the first principal surface  302  or the second principal surface  304 , or a roughing surface (not shown) to reduce the probability of total reflection for the light emitted from the optoelectronic element  300 , therefore raising the light extraction efficiency of the optoelectronic element  300 . 
     Moreover, in the present embodiment, the first transparent conductive oxide layer  32  forms an ohmic contact with the semiconductor stack layer  30  for forming an electrical connection, and the contact between the second transparent conductive oxide layer  34  and the semiconductor layer  30  is not ohmic but such as a schottky contact. When flowing into the optoelectronic element  300 , the current is conducted into the second transparent conductive oxide layer  34  via the electrode  38 . However, the contact between the second transparent conductive oxide layer  34  and the semiconductor stack layer  30  is not ohmic, and the contact between the first transparent conductive oxide layer  32  and the semiconductor stack layer  30  is ohmic, so the current flowing through the second transparent conductive oxide layer  34  can be conducted into the semiconductor stack layer  30  via the first transparent conductive oxide layer  32 . If the electrode  38  of the optoelectronic element  300  is located directly above the opening  320  of the first transparent conductive oxide layer  32 , the current spreading effect can be much improved, therefore the light-emitting efficiency of the optoelectronic element  300  in enhanced. 
       FIG. 4A  to  FIG. 4D  are the fabrication flow diagram of the optoelectronic element  300 . As shown in  FIG. 4A , a substrate  36  is firstly provided, and a semiconductor stack layer  30  is formed on the substrate  36  by Metal Organic Chemical Vapor Deposition (MOCVD) or Liquid Phase Epitaxy (LPE), wherein the semiconductor stack layer  30  includes a first conductive type semiconductor layer  306 , an active layer  308 , and a second conductive type semiconductor layer  310 . Then, as shown in  FIG. 4B , a first transparent conductive oxide layer  32  formed on the semiconductor stack layer  30  by e-beam vapor deposition or sputtering deposition, and a plurality of openings  320  exposing the semiconductor stack layer  30  are formed on the first transparent conductive oxide layer  32  by photo-lithography etching technology, wherein the an ohmic contact is formed at the interface between the first transparent conductive oxide layer  32  and the semiconductor stack layer  30 . Then, as shown in  FIG. 4C , a second transparent conductive oxide layer  34  is formed on the first transparent conductive oxide layer  32  by applying e-beam vapor deposition or sputtering deposition, wherein the second transparent conductive oxide layer  34  covers the first transparent conductive oxide layer  32  and fills into the pluralities openings  320  thereof and is in contact with the semiconductor stack layer  30 . Besides, by adjusting the forming method or fabrication process condition, such as controlling gas species or flow rate, reactor temperature or pressure, and/or annealing temperature or time, the second transparent conductive oxide layer  34  does not form an ohmic contact with the semiconductor stack layer  30 . In the present embodiment, the second transparent conductive oxide layer  34  is positioned in an environment having sufficient nitrogen and is partially processed by laser annealing, so the second transparent conductive oxide layer  34  does not form an ohmic contact with the semiconductor stack layer  30 . Finally, as shown in  FIG. 4D , a roughing structure is formed on the top surface of the second transparent conductive oxide layer  34  by etching, and an electrode  38  is formed on the second transparent conductive oxide layer  34 , wherein the electrode  38  is located opposite to the opening  320  of the first transparent conductive oxide layer  32 , and the optoelectronic element  300  is formed accordingly. 
       FIG. 5  is a schematic structure diagram of another embodiment of the present application. As shown in  FIG. 5 , an optoelectronic element  500  at least includes a semiconductor stack layer  50 , a first transparent conductive oxide layer  52  located on the bottom surface of the semiconductor stack layer  50 , and a second transparent conductive oxide layer  54  located under the first transparent conductive oxide layer  52 , wherein the semiconductor stack layer  50  at least includes a first conductive type semiconductor layer  502 , an active layer  504 , and a second conductive type semiconductor layer  506 . The first transparent conductive oxide layer  52  has a plurality of openings  520 , the second transparent conductive oxide layer  54  is filled into the openings  520  and is in contact with the semiconductor stack layer  50 , so there is no ohmic contact formed between the first transparent conductive oxide layer  52  and the semiconductor stack layer  50  but non-ohmic contact like schottky contact, and there is ohmic contact formed between the second transparent conductive oxide layer  54  and the semiconductor stack layer  50 . 
     The material of the semiconductor stack layer  50  can be III-V group semiconductor materials, containing Al, Ga, In, N, P or As, such as GaN series, AlGaInP series or GaAs series, and the materials of the first transparent conductive oxide layer  52  and the second transparent conductive oxide layer  54  can be ITO, InO, SnO, CTO, ATO, AZO, or ZnO, wherein the grain size or the reflective index of the first transparent conductive oxide layer  52  differs from that of the second transparent conductive oxide layer  54 . The first transparent conductive oxide layer  52  and the second transparent conductive oxide layer  54  have different composing materials, or have the same composing materials but different composing ratio. The first transparent conductive oxide layer  52  and the second transparent conductive oxide layer  54  can form an ohmic contact therebetween to promote current spreading effect. 
     Additionally, the optoelectronic element  500  further includes a conductive adhesion layer  56  located under the second transparent conductive oxide layer  54 , a substrate  58  located under the conductive adhesion layer  56 , and an electrode  60  located on the semiconductor stack layer  50 , wherein the electrode  60  is located directly above the first transparent conductive oxide layer  52 . The interface of the first transparent conductive oxide layer  52  and the semiconductor stack layer  50  dose not form an ohmic contact, so when the current flows into the semiconductor stack layer  50  from the electrode  60 , it flows to the conductive adhesion layer  56  and the substrate  58  via the second transparent conductive oxide layer  54  filled into the openings  520 . Because the electrode  60  is located directly above the first transparent conductive oxide layer  52 , most current does not directly flow through the active layer  504  under the electrode  60 , therefore the current spreads effectively.