Abstract:
An optical device is provided which includes a first electrode; a substrate disposed on the first electrode; a plurality of multi-layer film structures disposed on the substrate, and the multi-layer film structure consisted of at least two insulated layer with different reflection index formed alternately; a first semiconductor conductive layer disposed on the substrate to cover the multi-layer film structure; an active layer disposed on the first semiconductor conductive layer; a second semiconductor conductive layer disposed on the active layer; a transparent conductive layer disposed on the second semiconductor conductive layer; and a second electrode disposed on the transparent conductive layer, thereby, the multi-layer structure can increase the light reflective effect or anti-reflective effect within the optical device to improve the light emitting effective.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is an optical device, and more particularly is to form a multi-layers structure over the substrate to increase the light reflective efficiency of the optical device. 
         [0003]    2. Description of the Prior Art 
         [0004]    The conventional light emitting diode (LED) is made by a multi-layers structure and the multi-layers structure includes a illuminant layer between the N-type semiconductor layer and the P-type semiconductor layer. The illuminant layer is a single-layer structure or a multi-layer structure made by a reactive nitrogen semiconductor compound. The voltage inputted between the electrodes of the LED will generate electrons and/or holes injecting into the N-type semiconductor layer and P-type semiconductor layer and passing through the illuminant layer. The electrons and the holes will rejoin in the illuminant layer to generate light. The light generated in the illuminant layer will transmit to anywhere and release at the exposed surfaces of the LED. In order to generate the light, the light should be rejected at the predetermined direction. 
         [0005]    Generally, the illuminant efficiency of the LED is based some parameters calculated at the LED. One is the light collection efficiency, which is the ratio of the light transmitted from the LED and the light generated by the LED. Practically, because of the absorption of the different layers within the LED, the light transmitted from the LED is less than the light generated by the LED. In order to increase the light collection efficiency, a reflective layer is added within the multi-layer structure of the LED in prior art to guide the light to transmit in the desired direction. 
         [0006]    In order to improve the crystallized quality of the GaN compound layer, the problem of the lattice between the sapphire and the active layer of the GaN compound layer is needed to be solved. Therefore, in prior art, as shown in  FIG. 1A  and  FIG. 1B , a buffer layer  102  made by AiN is formed between the substrate  100  and the GaN layer  104 . The crystal structure of the buffer layer  102  is microcrystal or polycrystal and formed in the way of the amorphous Si. The crystal structure of the buffer layer  102  is able to solve the problem of the crystal mismatching between the GaN compound layers. However, the prior art described above, the reflective index generated by the light in the active layer is restrains to limit the illuminant efficiency of the optical device. 
       SUMMARY OF THE INVENTION 
       [0007]    According to the problems described above, the main object of the present invention is to use the isolated material layer forming multi-layers structure on the substrate to reduce the stacking different and generate the reflective layer and anti-reflective layer by the multi-layers structure to enhance the illuminant efficiency. 
         [0008]    According to the object described above, the present invention discloses a optical device includes a first electrode; a plurality of multi-layer film structures disposed on the substrate, and the multi-layer film structure is consisted of at least two insulated layer with different reflective index formed alternately; a first semiconductor conductive layer disposed on the substrate to cover the multi-layer film structure; an active layer disposed on the first semiconductor conductive layer; a second semiconductor conductive layer disposed on the active layer; and a transparent conductive layer disposed on the second semiconductor conductive layer. 
         [0009]    The present invention also discloses an optical device includes a substrate; a plurality of multi-layer insulated layers disposed on said substrate, and each of the multi-layer film structure includes a different reflective index and each of the different reflective indexes is increased bottom up; a first semiconductor conductive layer disposed on the substrate to cover the multi-layer insulated layers and the first semiconductor conductive layer includes a first region and a second region; an active layer disposed on the first semiconductor conductive layer; a second semiconductor conductive layer disposed on the active layer; a transparent conductive layer disposed on the second semiconductor conductive layer; and a first electrode disposed on the first region of the first semiconductor conductive layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0011]      FIG. 1A  and  FIG. 1B  are views illustrating the conventional structure of the optical device; 
           [0012]      FIG. 2A  to  FIG. 2G  are views illustrating the steps of forming the multi-layers structure in the optical device; and 
           [0013]      FIG. 3A  to  FIG. 3C  are views illustrating the steps of forming the multi-layers structure in the optical device of another embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]      FIG. 2A-FIG .  2 G are views showing an embodiment of the optical device in the present invention. Now referring to  FIG. 2A , it is a view showing that a plurality of multi-layer structures formed on the substrate. As shown in  FIG. 2A , a substrate  10 , such as a substrate made by sapphire, is provided. A conventional semiconductor process is used to form a first isolated layer  12 A on the top surface of the substrate  10  and form a second isolated layer  12 B on the first isolated layer  12 B. In this embodiment, the purpose to form the multi-layer structures  10  before a buffer layer (not shown) is formed on the substrate  10  is to have the effect of the reflector and anti-reflector by interlacedly stacking the first isolated layer  12 A and the second isolated layer  12 B and the reflective efficiency and anti-reflective efficiency of the light within the optical device will enhance. Therefore, a plurality of multi-layer structures formed on the substrate  10  are used to substitute the conventional SiO 2  single-layer film used by the lateral epitaxial silicon to increase the reflective efficiency and the anti-efficiency of the light in the optical device so as to enhance the illuminant efficiency of the optical device. 
         [0015]    It should be noted that, in one embodiment, the multi-layer structures  12  is made by at least two isolated layers  12 A and  12 B with different reflective index coefficients and the isolated layers  12 A and  12 B are interlacedly stacking, as shown in  FIG. 2B . In  FIG. 2B , n 1  is the reflective index coefficient of the first isolated layer  12 A and n 2  is the reflective index coefficient of the second isolated layer  12 B, and n 1  and n 2  are different. a and b are the interfaces of the isolated layers. As shown in  FIG. 2B , the reflective index coefficient in a interface is Ra and Ra=(n 2 −n 1 )/(n 1 +n 2 ) and the reflective index coefficient in b interface is Rb=(n 1 −n 2 )/(n 1 +n 2 ). As the description above, Ra=−Rb. Therefore, the phase differences of the reflective lights in an interface and b interface are 180 degree. 
         [0016]    If the thickness in each of the multi-layer structures is λ/4 (λ is the symbol of wavelength), the thickness of the film is the product of the reflective index coefficient and the wavelength. Therefore, the thickness of the first isolated layer  12 A is n 1 ×λ/4 and the thickness of the second isolated layer  12 B is n 2 ×λ/4. Therefore, as the description above, the reflective waves in the adjacent interfaces will have 180 degree phase difference. After all the phase differences are added together, the wavelengths of the reflective waves in the adjacent interface are the same and it would have the constructive interference. Because of this characteristic, the multi-layer structures are used to be the mirror. On the contrary, if the thickness in each of the multi-layer structures (such as  12 A,  12 B and so on) is ½ wavelength and the thicknesses of the thin films in each of the multi-layer structures are n 1 ×λ/2         n 2 ×λ/2, the reflective waves in the adjacent interfaces are different and the phase different is 180 degree. Because the adjacent interface will have constructive interference, the multi-layer constructors are used to be the anti-reflective layer or the reflective layer. 
         [0017]    Therefore, in the embodiment of the present invention, the reflective index coefficient of the first isolated layer  12 A is higher than the reflective index coefficient of the second isolated layer  12 B. However, in a different embodiment, the reflective index coefficient of the first isolated layer  12 A could be lower than the reflective index coefficient of the second isolated layer  12 B. 
         [0018]    Therefore, because the multi-layer structure  12  is made by the first isolated layer  12 A with low reflective index and the second isolated layer  12 B with high reflective index or the first isolated layer  12 A with high reflective index and the second isolated layer  12 B with low reflective index. The first isolated layer  12 A and the second isolated layer  12 B are interlacedly stacking, as shown in  FIG. 2B . In another embodiment, the multi-layer structures  12  are made by a plurality of isolated layers  121 ,  123 ,  125  and  127  and the isolated layers  121 ,  123 ,  125  and  127  are stacking according to their reflective index, as shown in  FIG. 2C . The reflective index of the multi-layer structures  12  made by isolated layer  121 ,  123 ,  125  and  127  is between the reflective indexes of the first semiconductor conductive layer  32  and the substrate  10 . 
         [0019]    Besides, in the embodiments of the present invention, the material of the first isolated layer  12 A and the second isolated layer  12 B are selected from the group consisting of: SiO x , Si x N y , SiO x N y , ZnSe, TiO 2  and Ta 2 O 22 . The material of the substrate  10  is selected from the group consisting of: MgAl 2 O 4 , GaN, AlN, SiC, GaAs, AlN, GaP, Si, Ge, ZnO, MgO, LAO, LGO and glasses. 
         [0020]    Now, the following steps are based on the multi-layer structures  12  with at least two isolated layers  12 A and  12 B. First of all, by the semiconductor process technology, such as photo-lithography and etching process, a patterned photoresist layer (not shown) is formed on the second isolated layer  12 B and an etching process is sequentially used on the second isolated layer  12 B and the first isolated layer  12 A so as to remove a portion of the second isolated layer  12 B and the first isolated layer  12 A to expose a portion of the top surface of the substrate  10 , as shown in  FIG. 2D . 
         [0021]    Now, please referring to  FIG. 2E , is a view showing that a buffer layer formed on the substrate and the multi-layer structure. The substrate  10  with the multi-layer structure  12  is installed into a MOVPE reactive container, and a buffer layer  20  is formed on the substrate  10 . The buffer layer  20  is a multi-strain releasing layer structure and used to get a high quality GaN layer. In the present embodiment, the buffer layer  20  is made by a compound layer (not shown) and an II-V group compound layer. The compound layer is made by GaN, such as AlGaN. 
         [0022]    Please referring to  FIG. 2F , it is a view showing that a semiconductor epi-stacked structure is formed on the buffer layer. As shown in  FIG. 2F , a semiconductor epi-stacked structure  30  is formed on the buffer layer  20  and includes a first semiconductor conductive layer  32  formed on the buffer layer  20 , an active layer formed on the first semiconductor conductive layer  34  and the second semiconductor conductive layer  36 . The first semiconductor conductive layer  32  and the second semiconductor conductive layer  34  is compound semiconductor conductive layer made by III-V group material, such as Nitrogen semiconductor layer. Besides, the electrode of the first semiconductor conductive layer  32  is different the electrode of the second semiconductor conductive layer  34 . For example, when the first semiconductor conductive layer  32  is an N-type semiconductor conductive layer, the second semiconductor conductive layer  34  must be P-type semiconductor conductive layer. It is very clear to know that the active layer  40  is formed between the N-type semiconductor conductive layer and the P-type semiconductor conductive layer. The electrons and holes between the N-type semiconductor conductive layer and the P-type semiconductor conductive layer will be driven to the active layer  34  by adding some voltage and the recombination is generated to emit the light. 
         [0023]    Therefore, as the description above, first semiconductor conductive layer  32  and the second semiconductor conductive layer  34  can be N-type semiconductor conductive layer or P-type semiconductor conductive layer in the lateral epitaxial silicon structure of the optical device of the present invention. In the embodiment of the present invention, when the second semiconductor conductive layer  34  is P-type semiconductor conductive layer, the first semiconductor conductive layer  32  must be a N-type semiconductor conductive layer and vice versa. The lateral epitaxial silicon structure  30  of the optical device disclosed in the present invention can be a conventional lateral epitaxial silicon structure such as, light emitting diode (LED), laser, photo-detector or VCSEL. 
         [0024]    Now, please referring to  FIG. 2F , there is a transparent conductive layer  40  formed on the lateral epitaxial silicon structure  30 . After the lateral epitaxial silicon structure  30  is formed on the buffer layer  20 , the temperature of the reactive container is reduced to the room temperature and the lateral epitaxial silicon die is took out from the reactive container. Therefore, the transparent layer  40  is formed on the surface of the second semiconductor conductive layer  36  of the lateral epitaxial silicon structure  30 . The thickness of the transparent layer  40  is about 2500 A and the material is made by Ni/Au, Nio/Au, TA/Au, TiWN, TiN, Indium Tin Oxide (ITO), Antimony Doped Tin Oxide (ATO), AZO or Zn 2 SnO 4 . 
         [0025]    Please referring to  FIG. 2G , it is a view showing that the first electrode and the second electrode are formed on the structure shown in  FIG. 2F . The second electrode  60  is formed on the transparent layer  40  and the thickness of the second electrode  60  is about 2000 um. In the present invention, the second semiconductor conductive layer  36  is a P-type nitrogen semiconductor conductive layer, so the material of the second electrode  60  is Au/Ge/Ni, Ti/Al, Ti/Au, Ti/Al/Ti/Au, Cr/Au or the compound thereof. 
         [0026]    Therefore, according to the description above, the optical device is formed. It should be noted that manufacture process of the first electrode  50  and the second electrode  60  are well know in the conventional art, therefore the detail description of the manufacture process is omitted herein. 
         [0027]    In another embodiment, there is a photoresist layer (not shown) formed on the transparent layer by using a semiconductor process. A lithography process, such as etching step, is used to remove a portion of the transparent layer  40  to expose a portion of the surface of the second semiconductor conductive layer  36  to remove the photoresist layer. The material of the second electrode  60  is Au/Ge/Ni, Ti/Al, Ti/Au, Ti/Al/Ti/Au, Cr/Au or the ally thereof. The first electrode  50  is formed on the bottom surface of the substrate  10 . The material of the first electrode  50  is Au/Ge/Ni, Ti/Al, Ti/Au, Ti/Al/Ti/Au, Cr/Au ally or W/Al alloy. Therefore, according to the description above, the optical device is formed. It should be noted that manufacture process of the first electrode  50  and the second electrode  60  are well know in the conventional art, therefore the detail description of the manufacture process is omitted herein. 
         [0028]    Therefore, as the description above, no matter the optical device is made by the isolated materials  121 ,  123 ,  125  and  127  respectively stacking from bottom to top in accordance with the reflective index or at least two multi-layers structures  12  with different reflective index, because of the multi-layers with high reflective index, a flip-chip method is used in the semiconductor process to turn over the optical device and the optical device is electrically connected to another circuit board (not shown) to complete the packing process of the optical device. 
         [0029]      FIG. 3A-FIG .  3 C are views showing that the steps to enhance the illuminant efficiency of the optical device with multi-layers structure. As shown in  FIG. 3A , a multi-layers structure  12 , a buffer layer  30 , and lateral epitaxial silicon  30  are formed on the substrate  10 . The steps of forming the multi-layers structure  12 , the buffer layer  30 , and lateral epitaxial silicon  30  are the same as the description above, so the detail descriptions are omitted therein. 
         [0030]    It should be noted that the multi-layers  12  is made by a plurality of isolated layers  121 ,  123 ,  125  and  127  in an embodiment and they are respectively stacking from bottom to top in accordance with the reflective index, as shown in  FIG. 2C . Therefore, the reflective index of the multi-layers structure  12  is between the reflective indexes of the first semiconductor conductive layer  32  and the substrate  10 . 
         [0031]      FIG. 3B  is a view showing that a first region and a second region of the lateral epitaxial silicon on the buffer layer. As shown in  FIG. 3B , a lithography process or an etching process is used to form a patterned photoresist layer (not shown) on the second semiconductor conductive layer  36  of the lateral epitaxial silicon  30 . Then, the etching process is used to remove a portion of the semiconductor conductive layer  36 , the active layer  34  and the first semiconductor conductive layer  32  to expose a portion of the surface of the first semiconductor conductive layer  32  to form a lateral epitaxial silicon  30  with a first region  30 A (the exposed portion of the first semiconductor conductive layer  32 ) and the second region  30 B (the region covered by the active layer  34  and the second semiconductor conductive layer  36 ). 
         [0032]      FIG. 3C  is a view showing that a first electrode and a second electrode of the transparent conductive layer are formed on the lateral epitaxial structure. Similarly, a transparent conductive layer  40  is formed on the second semiconductor conductive layer  36  of the second region  30 B of the lateral epitaxial structure  30 . After the lateral epitaxial silicon structure  30  is formed on the buffer layer  20 , the temperature of the reactive container is reduced to the room temperature and the lateral epitaxial silicon die is took out from the reactive container. Therefore, the transparent layer  40  is formed on the surface of the second semiconductor conductive layer  36  of the lateral epitaxial silicon structure  30 . The thickness of the transparent layer  40  is about 2500 A and the material is made by Ni/Au, Nio/Au, TA/Au, TiWN, TiN, Indium Tin Oxide (ITO), Antimony Doped Tin Oxide (ATO), AZO or Zn2SnO4. 
         [0033]    Please refer to  FIG. 3C  it is a view showing that the first electrode  50  is formed on the first region  30 A of the first semiconductor conductive layer  32  and the second electrode  60  are formed on the transparent conductive layer  40  to complete the optical device structure. In a different embodiment, there is a photoresist layer (not shown) formed on the transparent layer  40  by using a semiconductor process. A lithography process, such as etching step, is used to remove a portion of the transparent layer  40  to expose a portion of the surface of the second semiconductor conductive layer  36  to remove the photoresist layer. The material of the second electrode  60  is Au/Ge/Ni, Ti/Al, Ti/Au, Ti/Al/Ti/Au, Cr/Au or the ally thereof. The first electrode  50  is formed on the first region  30 A of the first semiconductor conductive layer  32 . The material of the first electrode  50  is Au/Ge/Ni, Ti/Al, Ti/Au, Ti/Al/Ti/Au, Cr/Au ally or W/Al ally. Therefore, according to the description above, the optical device is formed. It should be noted that manufacture process of the first electrode  50  and the second electrode  60  are well know in the conventional art, therefore the detail description of the manufacture process is omitted herein. 
         [0034]    The purpose of forming the multi-layers structure  12  on the substrate  10  is to let the isolated layer  12 A and  12 B be a reflective mirror or anti-reflective layer because the isolated material layers  12 A and  12 B are interlacedly stacking with reflective or anti-reflective ability. 
         [0035]    Therefore, the reflective or anti-reflective efficiency of the optical device (as shown in  FIG. 2E  and  FIG. 3C ) is enhanced. Therefore, a plurality of patterned multi-layers structure is to replace the conventional single layer SiO to increase the reflective or anti-reflective efficiency of the light in the device and enhance the illuminant efficiency of the optical device. 
         [0036]    Therefore, no matter the optical device is made by the isolated materials  121 ,  123 ,  125  and  127  respectively stacking from bottom to top in accordance with the reflective index or at least two multi-layers structures  12  with different reflective index, Because of the multi-layers with high reflective index, a flip-chip method is used in the semiconductor process to turn over the optical device and the optical device is electrically connected to another circuit board (not shown) to complete the packing process of the optical device.