Abstract:
A fabrication method of the light emitting element and its light emitting element are disclosed herein. It utilizes the membrane forming technology to form optic films arranged in array on a substrate and then upward forming the epitaxial layer by the epitaxial lateral overgrowth (ELOG) technology so as to form light-emitting elements in array. The optic films contribute to the high reflection property and can sustain high temperature in the ELOG process.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an optical element, particularly to a fabrication method of a light-emitting element and the light-emitting element. 
         [0003]    2. Description of the Related Art 
         [0004]    Fabrication of a light-emitting diode array of prior art is shown in  FIG. 1 . Generally, an epitaxial layer of a light-emitting diode is formed on a substrate  100  by means of epitaxy, and a light-emitting element, as shown in  FIG. 1 , is formed after etching. This epitaxial layer of a light-emitting diode includes a P-type semiconductor layer  110 , a quantum well active layer  120 , and an N-type semiconductor layer  112  in order. 
         [0005]    To increase the luminous efficiency of the light-emitting element, a common approach is to form on a substrate an optical layer of high refractive property to recycle backward scattered light rays, as disclosed in U.S. patent publication US20050133796A1. However, when the optical film layer is formed external to the light-emitting element, total internal reflection of LED light rays in the epitaxial layer can happen, causing the light rays not being able to reach outside the substrate; or multiple refractions losses from transmitting light rays of LED through the epitaxial layer and the substrate can occur before the light rays reach the external optical film layer. At this time, recycled and forward directed light rays, via reflection from the optical film layer, are very limited. Consequently, if the reflective optical film layer can be embedded into the epitaxial layer, i.e. arranging the reflective mirror in a location substantially close to the active light-emitting layer, the backward directed light rays can be reflected back in the epitaxial layer to avoid multiple refraction losses and the total reflection problem and thus forward luminous efficiency of LED is improved. However, the foregoing reflective mirror must sustain high temperature during epitaxy in order to be embedded in the epitaxial layer. Currently there is no prior art disclosing the fabrication method of a high temperature sustaining reflective mirror. To sum up the aforementioned descriptions, it is an important topic how to fabricate a light-emitting element of high luminous efficiency. 
       SUMMARY OF THE INVENTION 
       [0006]    In order to solve abovementioned problems, one objective of the present invention is to provide a fabrication method of a light-emitting element and the light-emitting element, by forming patterned optical films that can increase luminous efficiency and sustain high temperature during epitaxy. 
         [0007]    One objective of the present invention is to provide a fabrication method of a light-emitting element and the light-emitting element by forming patterned optical film array directly on an epitaxial substrate and then fabricating light-emitting diode elements through epitaxy. 
         [0008]    One embodiment of the present invention is to provide a fabrication method of a light-emitting element and the light-emitting element, wherein patterned optical film array can sustain high temperature during the epitaxy process. 
         [0009]    In order to achieve aforementioned objectives, one embodiment of the present invention discloses a fabrication method of a light-emitting element including providing a substrate; forming a first optical layer on the substrate; removing a portion of the first optical layer to form a plurality of patterned first optical films, wherein the patterned first optical films are arranged in array on the substrate; forming a first semiconductor layer on the substrate and on the patterned first optical films in order via an epitaxial lateral overgrowth procedure, covering the substrate and the patterned first optical films; forming a light-emitting layer and a second semiconductor layer on the first semiconductor layer in order; and removing a portion of the first semiconductor layer, the light-emitting layer and the second semiconductor layer to form a plurality of patterned first semiconductor films, a plurality of patterned light-emitting films, and a plurality of second semiconductor films on the patterned first semiconductor films simultaneously. 
         [0010]    Another embodiment of the present invention discloses a light-emitting element including a substrate; a plurality of patterned first optical films arranged in array on the substrate; a plurality of patterned first semiconductor films, arranged on the patterned first optical films; a plurality of patterned light-emitting films, arranged on the patterned first semiconductor films; and a plurality of patterned second semiconductor films, arranged on the patterned light-emitting films. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagram schematically showing a light-emitting element of prior art. 
           [0012]      FIG. 2A-FIG .  2 G are diagrams schematically showing one embodiment of the present invention. 
           [0013]      FIG. 3  shows a schematic diagram of one embodiment of the present invention. 
           [0014]      FIG. 4  shows a schematic diagram of one embodiment of the present invention. 
           [0015]      FIG. 5A-FIG .  5 I are diagrams schematically showing one embodiment of the present invention. 
           [0016]      FIG. 6  shows a schematic diagram of one embodiment of the present invention. 
           [0017]      FIG. 7  shows a schematic diagram of one embodiment of the present invention. 
           [0018]      FIG. 8A ,  FIG. 8B  and  FIG. 8C  are schematic diagrams showing different embodiments of the present invention, respectively. 
           [0019]      FIG. 9  shows a schematic diagram of one embodiment of the present invention. 
           [0020]      FIG. 10  shows a schematic diagram of one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The objectives, technical contents and characteristics of the present invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings. 
         [0022]      FIG. 2A ,  FIG. 2B ,  FIG. 2C ,  FIG. 2D ,  FIG. 2E ,  FIG. 2F  and  FIG. 2G  constitute a flowchart of the fabrication method of a light-emitting element of one embodiment of the present invention. In this embodiment, the fabrication method of a light-emitting element comprises the following steps: first, a substrate  10  is provided, as shown in  FIG. 2A . Next, please referring to  FIG. 2B ,  FIG. 2C  and  FIG. 2D , a first optical layer  20  is formed on the substrate  10 , and a portion of the first optical layer  20  is removed by patterning photoresist layer  30  via photomasking to form a plurality of patterned first optical films  20 ′ arranged in array on the substrate  10 . 
         [0023]    In continuation to the abovementioned description, as shown in  FIG. 2E , a first semiconductor layer  40  is formed on the substrate  10  and on the patterned first optical films  20 ′ by an epitaxial lateral overgrowth procedure. The epitaxial lateral overgrowth procedure is conducted in a high temperature environment of a temperature above 900° C. Afterwards, a light-emitting layer  50  and a second semiconductor layer  42  are formed on the first semiconductor layer  40  in order, as shown in  FIG. 2F . Then, please referring to  FIG. 2G , a portion of the first semiconductor layer  40 , light-emitting layer  50 , and the second semiconductor layer  42  are removed to form a plurality of patterned first semiconductor films  40 ′, a plurality of patterned light-emitting films  50 ′, and a plurality of patterned second semiconductor films  42  simultaneously on patterned first optical films  20 ′. 
         [0024]    In the abovementioned embodiment, the material of the substrate can be selected from the group consisting of sapphire, SiC, Si, GaAs, LiAlO 2 , LiGaO 2 , AlN or organic materials, etc. The first optical layer is a mutli-layer structure fabricated by sputtering, evaporation, chemical vapor deposition, chemical liquid deposition, chemical vapor epitaxy, or chemical liquid epitaxy. Epitaxial lateral overgrowth procedure can employ techniques such as molecular bean epitaxy (MBV), metal-organic chemical vapor deposition (MOCVD) or liquid phase epitaxy (LPE) and so on. 
         [0025]    In one embodiment, the steps for removing a portion of the first optical layer  20  and removing a portion of the first semiconductor layer  40 , light-emitting layer  50  and the second semiconductor layer  42  can be realized by lithography etching or laser drilling, etc. 
         [0026]    Please referring to  FIG. 3 , in one embodiment, the fabrication method of a light-emitting element further comprises forming a plurality of second optical films  22 ′ each of which on a portion of the surface of each patterned second semiconductor film  42 ′. Patterned second optical films  22 ′ can be fabricated by sputtering, evaporation, chemical vapor deposition, chemical liquid deposition, chemical vapor epitaxy, or chemical vapor epitaxy and so on. Besides, in one embodiment, fabrication method of a light-emitting element further comprises forming an electrode ( 60 ,  62 ) on the patterned first semiconductor films  40 ′ and the patterned second semiconductor films  42 ′. 
         [0027]      FIG. 5A ,  FIG. 5B ,  FIG. 5C ,  FIG. 5D ,  FIG. 5E ,  FIG. 5F ,  FIG. 5G ,  FIG. 5H  and  FIG. 5I  constitute a flowchart of the fabrication method of a light-emitting element of another embodiment of the present invention. In the present embodiment, a substrate  10  contains a seed layer thereon, as shown in  FIG. 5A . The seed layer  12  can be made of GaN. Then, as shown in  FIG. 5B ,  FIG. 5C  and  FIG. 5D , a first optical layer  20  is formed on the substrate  10  and a patterned photoresist layer  30  is deposited for removing a portion of the first optical layer  20  via photomasking to form a plurality of first optical films  20 ′ arranged in array on the substrate  10 . As shown in  FIG. 5E , a first semiconductor layer  40 , covering the substrate  10  and the patterned first optical films  20 ′, is formed by a procedure which applies epitaxial lateral overgrowth on the substrate  10  and the patterned first optical films  20 ′. Thereafter, a light-emitting layer  50  and a second semiconductor layer  42  are formed in order on the first semiconductor layer  40 , as shown in  FIG. 5F . 
         [0028]    In continuation, please referring to  FIG. 5G , the substrate  10  is removed with the seed layer  12  in contact with the patterned first optical films  20 ′ preserved, and a sub-substrate  10 ′ is set up under the seed layer  12 . The substrate  10  can be recycled for reuse to effectively lower the cost. Low cost and better heat dissipating material can be selected for the sub-substrate  10 ′ according to needs. 
         [0029]    Following the aforementioned description, a portion of the first semiconductor layer  40 , light-emitting layer  50  and the second semiconductor layer  42  are removed to form a plurality of patterned first semiconductor films  40 ′, a plurality of patterned light-emitting films  50 ′ and a plurality of patterned second semiconductor films  42 ′ on the patterned first optical films  20 ′ simultaneously. 
         [0030]    Please referring to  FIG. 3  and  FIG. 4 , in this embodiment, a light emitting element is disclosed, which includes a substrate  10 ; a plurality of patterned first optical films  20 ′ arranged in array on the substrate  10 ; a plurality of patterned first semiconductor films  40 ′ arranged on the patterned first optical films  20 ′; a plurality of patterned light-emitting films  50 ′ arranged on the patterned first semiconductor films  40 ′; and a plurality of second semiconductor films  42 ′ arranged on the patterned light-emitting films  50 ′. In one embodiment, a plurality of patterned second optical films  22 ′ each of which is formed on a portion of the surface of each patterned second semiconductor film  42 ′. In one embodiment, an optical resonant cavity is formed between the patterned first optical films  20 ′ and the patterned second optical films  22 ′. 
         [0031]    In one embodiment, the material of the first semiconductor films and the second semiconductor films can be semiconductor materials from group III-V or organic materials. In one embodiment, the first semiconductor films and the second semiconductor films are made of GaN or organic materials. In one embodiment, the patterned light-emitting films are PN junctions or quantum well structures. 
         [0032]    In continuation to the aforementioned description, in one embodiment, each of the patterned first optical films is a multi-layer structure which is composed of at least two materials of different refractive rate overlaying one another. The material of the multi-layer structure can be selected from the group consisting of TiO 2 , Ta 2 O 5 , Nb 2 O 5 , CeO 2 , ZnS, ZnO, SiO 2 , MgF 2  and organic materials. In one embodiment, the multi-layer structure is a photonic crystal structure. In one embodiment, the multi-layer structure can be planar, saw-toothed, wavy, square-shaped or periodic as shown in  FIG. 8A ,  FIG. 8B  and  FIG. 8C . 
         [0033]    In one embodiment, the structure of the patterned second optical films  22 ′ is multi-layered, similar to that of the patterned first optical films  20 ′. Nevertheless, the patterned second optical films  22  can also be a non multi-layer structure. In one embodiment, the patterned second optical films can be a photonic crystal structure. 
         [0034]    Please referring to  FIG. 9 , in different embodiments of the present invention, the shape of the patterned first optical films can be triangular, circular, square or polygonal. The patterned first optical films can be arranged in an array of a square shape, a triangular shape, or a polygonal shape. 
         [0035]    According to the above descriptions, one characteristic of the present invention is to introduce an optical structure between each substrate and light-emitting structure. The optical structure makes each of the light-emitting unit of the semiconductor light-emitting element array to have a high reflective property. For a light-emitting diode array, the luminous efficiency is improved and for a semiconductor laser array, high reflective mirrors can be provided. In addition, the optical structures can sustain the high temperature during epitaxy, without deformation and peeling off. 
         [0036]    Please referring to  FIG. 6A ,  FIG. 6B ,  FIG. 7A  and  FIG. 7B , the optical films of the present invention is placed in a quartz furnace tube to conduct a heating test which increases the temperature from room temperature to 1200□ in 30 minutes. Then the optical films are quickly cooled by fans and cycling water to room temperature in 60 minutes. From the experimental results shown in  FIG. 6C ,  FIG. 6D ,  FIG. 7C  and  FIG. 7D , the optical films do not have any deformation, peel-off, fracture, or bulge and so on, a result which can prove the optical structure being able to sustain the high temperature during epitaxy of the semiconductor fabrication process. Moreover, please referring to  FIG. 10 , it shows the pictures of the optical films enduring the epitaxy process of the high temperature experiment.  FIG. 10A  and  FIG. 10B  show the vertical view and the cross-sectional view of the unfinished epitaxy process, respectively. As shown in  FIG. 10A  and  FIG. 10B , in the epitaxy process, a semiconductor layer grows laterally until covering the optical films, and the optical films of the present invention do not show any deformation. Please continuingly referring to  FIG. 10C  and  FIG. 10D , after the expitaxy process is completed, the semiconductor layer covers the optical films completely, and thus one can obviously know that there is no deformation, peel-off, fracture or bulge and so on during the high temperature epitaxy process. 
         [0037]    In conclusion, the present invention discloses a fabrication method of patterned optical films which can increase luminous efficiency and sustain high temperature during epitaxy. The patterned optical film array is directly formed on the epitaxial substrate, and then the light-emitting diodes are formed by epitaxy. The patterned optical film array can sustain the high temperature during the epitaxy process. Each optical film and epitaxial layer of the present invention is not separately fabricated and then combined together, so the procedures can be reduced and the cost is effectively lowered. The technique of the present invention is not limited to the foregoing applications, and it also can be applied to organic light-emitting elements such as organic light-emitting diodes (OLED). 
         [0038]    The embodiments described above are to demonstrate the technical contents and characteristics of the preset invention to enable the persons skilled in the art to understand, make, and use the present invention. However, it is not intended to limit the scope of the present invention. Therefore, any equivalent modification or variation according to the spirit of the present invention is to be also included within the scope of the present invention.