Abstract:
A light-emitting element array includes a conductive substrate; an adhesive layer disposed on the conductive substrate; a first epitaxial light-emitting stack layers disposed on the adhesive layer, the first epitaxial light-emitting stack layers including a first p-contact and an first n-contact, wherein the first p-contact and the first n-contact are disposed on the same side of the first epitaxial light-emitting stack layer; and a second epitaxial light-emitting stack layers disposed on the adhesive layer including a second p-contact and an second n-contact, wherein the second p-contact and the second n-contact are disposed on the opposite side of the epitaxial light-emitting stack layer; wherein the first epitaxial light-emitting stack layers and the second epitaxial light-emitting stack layers are electrically connected in anti-parallel.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 10/906,894, filed Mar. 11, 2005, which is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Technical Field 
     The present invention relates to a light-emitting device, and more particularly, to a light-emitting element array having an adhesive layer. 
     2. Description of the Related Art 
     Light-emitting diodes (LEDs) are employed in a wide variety of applications including optical display devices, traffic lights, data storage equipment, communications devices, illumination apparatuses, and medical treatment equipment. One of the most important goals of engineers who design LEDs is to increase the brightness of the light emitted. 
     U.S. Pat. No. 6,547,249 discloses monolithic serial/parallel LED arrays formed on highly resistive substrates. According to the patent, a Group III-V nitride light-emitting stack layer is formed on an insulating substrate. A portion of the stack layer is etched away to form a trench, and in result to form the LED array, which includes a plurality of light-emitting diodes divided by the trench. Since the insulating substrate is not conductive, both P-contacts and N-contacts for the LED array have to be formed on the same side of the LED array. In use, two LED arrays can be connected either in series or in parallel. However, the LED array disclosed by the patent cannot be applied to a quaternary AlInGaP light-emitting diode, which comprises a conductive substrate rather than an insulating substrate, P-contacts formed on one side of the conductive substrate, and N-contacts having to be formed on the other side. Therefore, two quaternary Al—In—Ga—P light-emitting diode arrays can be connected neither in series nor in parallel. Moreover, as the size of the LED array become larger, the operating voltage of the LED array becomes higher accordingly, and heat dissipation becomes an important concern for the LED array. 
     SUMMARY OF THE DISCLOSURE 
     Accordingly, this disclosure provides a light-emitting element array comprising a conductive substrate; an adhesive layer disposed on the conductive substrate; a first epitaxial light-emitting stack layers disposed on the adhesive layer, the first epitaxial light-emitting stack layers comprising a first contact and an second contact, wherein the first contact and the second contact are disposed on the same side of the first epitaxial light-emitting stack layer; and a second epitaxial light-emitting stack layers disposed on the adhesive layer, the second epitaxial light-emitting stack layers comprising a third contact and an fourth contact, wherein the third contact and the fourth contact are disposed on the opposite side of the epitaxial light-emitting stack layer; wherein the first epitaxial light-emitting stack layers and the second epitaxial light-emitting stack layers are electrically connected in anti-parallel. 
    
    
     
       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. 1  is a cross sectional schematic diagram of a light-emitting diode array having an adhesive layer of the preferred embodiment according to the present invention. 
         FIG. 2  is a top view of a schematic diagram of a plurality of serially connected LED arrays shown in  FIG. 1  according to the present invention. 
         FIG. 3  is an equivalent circuit diagram of the LED arrays shown in  FIG. 2  according to the present invention. 
         FIG. 4  is a top view of a schematic diagram of a plurality of serially and parallelly connected LED arrays shown in  FIG. 1  according to the present invention. 
         FIG. 5  is an equivalent circuit diagram of the LED arrays shown in  FIG. 4  according to the present invention. 
         FIG. 6  is a cross sectional schematic diagram of a light-emitting element array of the embodiment according to the present invention. 
         FIG. 7  is an equivalent circuit diagram of the light-emitting element array shown in  FIG. 6  according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present disclosure, 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. 
     Please refer to  FIG. 1 , which is a cross sectional schematic diagram of a light-emitting diode array  100  of the preferred embodiment according to the present invention. The LED array  100  comprises a substrate  10 , a reflective layer  11  formed on the substrate  10 , an insulating transparent adhesive layer  12  formed on the reflective layer  11 , a transparent conductive layer  13  formed on the insulating transparent adhesive layer  12 , a first conductive semiconductor stack layer  14  formed on the transparent conductive layer  13 , a light-emitting layer  15  formed on the first conductive semiconductor stack layer  14 , a second conductive semiconductor stack layer  16  formed on the light-emitting layer  15 . 
     A trench is formed by etching away a portion of the second conductive semiconductor stack layer  16 , the light-emitting layer  15 , the first conductive semiconductor stack layer  14 , the transparent conductive layer  13 , and the insulating transparent adhesive layer  12  sequentially, and therefore the LED array  100  is divided into a first LED  110  and a second LED  120 , both of which have the substrate  10  in common. Moreover, a transparent conductive layer exposed surface region is formed by etching both of the first LED  110  and the second LED  120  moderately to the transparent conductive layer  13 . The LED array  100  further comprises an insulating layer  17  formed surrounding the first LED  110  and the second LED  120  for electrically isolating the first LED  110  from the second LED  120 . First contacts  18  formed on the second conductive semiconductor stack layer  16  of the first LED  110  and the second conductive semiconductor stack layer  16  of the second LED  120  respectively. Second contacts  19  formed on the transparent conductive layer exposed surface region of the first LED  110  and the transparent conductive layer exposed surface region of the second LED  120  respectively, and a conductive line for electrically connecting a second contact of the first LED  110  to a first contact of the second LED  120 . 
       FIG. 2  is a top view of a schematic diagram of a plurality of LED arrays  100  connected in series according to the present invention.  FIG. 3  is an equivalent circuit diagram of the LED arrays shown in  FIG. 2 .  FIG. 4  is a top view of a schematic diagram of a plurality of LED arrays  100  connected in series and in parallel according to the present invention.  FIG. 5  is an equivalent circuit diagram of the LED arrays shown in  FIG. 4 . 
     The reflective layer  11  can be also formed between the transparent conductive layer  13  and the adhesive layer  12 . The reflective layer  11  is installed to increase the luminance of the LED array  100  by reflecting light projected onto the substrate  10 . However, the LED array  100  still can operate without the reflective layer  11 . 
     The insulating transparent adhesive layer  12  is installed to electrically isolate the first LED  110  and the second LED  120  from the substrate  10 . The insulating transparent adhesive layer  12  can be replaced by a conductive adhesive layer made of metal or solder. However, an insulating layer providing electrical isolation has to be installed additionally between the substrate  10  and the conductive adhesive layer  12  or between the conductive adhesive layer  12  and the transparent conductive layer  13  to electrically isolate the first LED  110  and the second LED  120  from the substrate  10 . 
     The trench together with the insulating layer  17  electrically isolates the first LED  110  from the second LED  120 . However, the LED array  100  can further comprise an ion-implanted region formed between the first LED  110  and the second LED  120  for electrically isolating the first LED  110  from the second LED  120 . 
     The substrate  10  comprises at least one material selected from a material group consisting of GaP, GaAs, Si, SiC, Al2O3, glass, quartz, GaAsP, AlN, metal, and AlGaAs. The insulating transparent adhesive layer  12  comprises at least one material selected from a material group consisting of polyimide (PI), benzocyclobutene (BCB), and perfluorocyclobutene (PFCB). The reflective layer  11  comprises at least one material selected from a material group consisting of In, Sn, Al, Au, Pt, Zn, Ge, Ag, Ti, Pb, Pd, Cu, AuBe, AuGe, Ni, PbSn, AuZn, and indium-tin oxide (ITO). The light-emitting layer  15  comprises at least one material selected from a material group consisting of AlGaInP, GaN, InGaN, AlInGaN, and ZnSe. The transparent conductive layer  13  comprises at least one material selected from a material group consisting of indium-tin oxide (ITO), cadmium-tin oxide (CTO), antimony-tin oxide (ATO), zinc oxide, and zinc-tin oxide. The insulating layer  17  comprises at least one material selected from a material group consisting of SiO2 and SiNx. The first conductive semiconductor stack layer  14  comprises at least one material selected from a material group consisting of AlInP, AlN, GaN, InGaN, AlGaN, and AlInGaN. The second conductive semiconductor stack layer  16  comprises at least one material selected from a material group consisting of AlInP, AlN, GaN, InGaN, AlGaN, and AlInGaN. 
     Since the insulating transparent adhesive layer  12  has a high resistance and is capable of electrically isolating the substrate  10  from the first LED  110  and the second LED  120  when being installed between them, the first LED  110  and the second LED  120  can comprise not only a Group III-V nitride material, but also a quaternary material. Moreover, since the substrate  10  is electrically isolated from the LEDs  110  and  120 , the substrate  10  can be an insulating substrate, a substrate having a high resistance, a conductive substrate, or a substrate having a high thermal conductivity, which has a capability to improve the heat-dissipation efficiency of the LED array  100 . 
     Referring to  FIGS. 6-7 , the cross-sectional views show a light-emitting element array  6  in accordance with a second embodiment of the present invention. The light-emitting element array  6  such as an LED array comprises a conductive substrate  61 , an adhesive layer  62  formed on the conductive substrate  61 , a reflective layer  63  formed on the adhesive layer  62 , a transparent conductive layer  64  formed on the reflective layer  63 , a first conductive semiconductor stack layer  661  formed on the transparent conductive layer  64 , a light-emitting layer  662  formed on the first conductive semiconductor stack layer  661 , a second conductive semiconductor stack layer  663  formed on the light-emitting layer  662 . In this embodiment, the first conductive semiconductor stack layer  661  is a p-type semiconductor layer, and the second conductive semiconductor stack layer  663  is an n-type semiconductor layer. The conductive substrate  61  comprises at least one material selected from a group consisting of GaP, GaAs, Si, SiC, GaAsP, AlN, metal, and AlGaAs. 
     Next, a trench is formed by etching away a portion of the second conductive semiconductor stack layer  663 , the light-emitting layer  662 , and the first conductive semiconductor stack layer  661  sequentially, and therefore the light-emitting element array  6  is divided into a first light-emitting element  6   a  and a second light-emitting element  6   b,  both of which have the conductive substrate  61  in common. Before forming the first conductive semiconductor stack layer  661 , an insulating layer  65  is formed below the first light-emitting element  6   a  and on part of the transparent conductive layer  64  to isolate the first light-emitting element  6   a  and the transparent conductive layer  64 . Moreover, a first conductive semiconductor stack layer exposed surface region is formed by partially etching from the second conductive semiconductor stack layer  663  and the light-emitting layer  662  to the first conductive semiconductor stack layer  661 . The light-emitting element array  6  further comprises an insulating layer  68  formed between the first light-emitting element  6   a  and the second light-emitting element  6   b  for electrically isolating the first light-emitting element  6   a  from the second light-emitting element  6   b.  Next, first contacts  671   a  and  671   b  are formed on the first conductive semiconductor stack layer  661  of the first light-emitting element  6   a  and the lower surface of the conductive substrate respectively. Second contacts  672   a  and  672   b  are formed on the second conductive semiconductor stack layer  663  of the first light-emitting element  6   a  and the second conductive semiconductor stack layer  663  of the second light-emitting element  6   b  respectively. 
     The transparent conductive layer  64  ohmically contacts with the first conductive semiconductor stack layer  661  of the second light-emitting element  6   b.  A first conductive line  69  is formed on the insulating layer  68  and connects the first contact  671   a  of the first light-emitting element  6   a  and the second contact  672   b  of the second light-emitting element  6   b.  A second conductive line  69  is formed on the insulating layer  68  and connects the second contact  672   a  of the first light-emitting element  6   a  and the transparent conductive layer  64 .  FIG. 7  is an equivalent circuit diagram of the light-emitting element array shown in  FIG. 6 . The first light-emitting element  6   a  and the second light-emitting element  6   b  are electrically connected in anti-parallel. The light-emitting element array  6  can be driven by alternating current. 
     The adhesive layer  62  can be a conductive adhesive layer made of metal in the embodiment. The reflective layer  63  comprises at least one material selected from a material group consisting of In, Sn, Al, Au, Pt, Zn, Ge, Ag, Ti, Pb, Pd, Cu, AuBe, AuGe, Ni, PbSn, AuZn, and multi-layer structure of indium-tin oxide/metal. The light-emitting layer  662  comprises at least one material selected from a material group consisting of AlGaInP, AlInP, GaP, GaN, InGaN, AlInGaN, and ZnSe. The transparent conductive layer  64  comprises at least one material selected from a material group consisting of indium-tin oxide (ITO), cadmium-tin oxide (CTO), antimony-tin oxide (ATO), zinc oxide, and zinc-tin oxide. The insulating layers  65  and  68  comprise at least one material selected from a material group consisting of SiO2 and SiNx. The first conductive semiconductor stack layer  661  comprises at least one material selected from a material group consisting of AlGaInP, GaP, AlInP, AlN, GaN, InGaN, AlGaN, and AlInGaN. The second conductive semiconductor stack layer  663  comprises at least one material selected from a material group consisting of AlGaInP, GaP, AlInP, AlN, GaN, InGaN, AlGaN, and AlInGaN. The first and second contacts  671   a,    671   b,    672   a,    672   b  are metal contacts. 
     Those having ordinary skill in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.