Abstract:
The present invention provides a light emitting element comprising a first substrate, a light emitting unit disposed on the first substrate, at least a selective reflection layer disposed on an emitting side of the light emitting unit so that a light of a first color emitted from the light emitting unit passes through the selective reflection layer, and a fluorescent layer disposed on the emitting side of the light emitting unit and converting the light of the first color passing therethrough into a light of a second color, wherein a light of a mixed color is formed by the lights of the first and second color and only the light of the second color is reflected by the selective reflection layer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is related to a light emitting element, more particularly, to a light emitting element having a selective reflection layer. 
         [0003]    2. Description of the Prior Art 
         [0004]    LED(Light Emitting Diode) is one of the most competetive products in the optoelectronic industry of Taiwan. Taiwan has a complete supply chain for LED. Many domestic manufacturer egage in manufacturing of Gallium arsenide and die, and packaging, wherein United Epitaxy Company, LTD is one of the earliest company manufacturing high power LED. Taiwan has become the largest supply country for visible-light LED around the world and also leads in manufacturing of high-power LEDs. The scale of LED manufacturing in Taiwan only fall behind Japan and US, and ranks 3 rd  in the global LED market. Since Taiwan has a complete supply chain for LED, comprising die saw, package, application and the research and development of Gallium arsenide, Taiwan has the potential to be the largest manufacturing country of LED. 
         [0005]    LED is a semiconductor element and has been popularly used in pointers and displays of many 3C products due to its small volume, long lifetime and low power consumption. The application of LED is enhanced by the emergence of blue LED in Japan, 1994 which makes it possible to display colors by combining red, blue and green LEDs. Furthermore, the yield improvement of LED decreases the manufacturing cost, which establishes a prosperous LED market. 
         [0006]    In order to enhance the efficiency of LED, the present invention provides a light emitting element having a selective reflection layer through which light of a first color emitted by a light emitting diode passes and by which light of a second color converted by a fluorescent layer is reflected. Thus, the light of the first and second color can be mixed to enhance the efficiency of LED. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a light emitting element comprising a first substrate, a light emitting unit disposed on the first substrate, at least a selective reflection layer disposed on an emitting side of the light emitting unit so that a light of a first color emitted from the light emitting unit passes through the selective reflection layer, and a fluorescent layer disposed on the emitting side of the light emitting unit and converting the light of the first color passing therethrough into a light of a second color, wherein a light of a mixed color is formed by the lights of the first and second color and only the light of the second color is reflected by the selective reflection layer. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0008]      FIG. 1  is a diagram shown a light emitting element according to one embodiment of the invention. The light emitting element  1  includes a first substrate  10 , a light emitting unit, at least a selective reflection layer  14  and a fluorescent layer  16 . The light emitting unit includes at least a light emitting diode  12 . The selective reflection layer  14  is disposed on one side of the light emitting diode of the light emitting unit. The selective reflection layer  14  has a thickness ranging from 500 nm to 500000 nm. The fluorescent layer  16  is disposed on the first substrate  10  and covers the light emitting diode  12  of the light emitting unit. The light emitting diode  12  emits light of a first color which is blue in this embodiment. The light of the first color passes through the selective reflection layer  14  and reaches the fluorescent layer  16 . The fluorescent layer  16  converts the light of the first color into light of a second color which is yellow in this embodiment. The light of the first and second color combine to form light of a mixed color. The light of the second color may go toward the light emitting diode  12  and then may be reflected by the selective reflection layer  14 , which helps to mix the light of the first and second color. This will enhance the efficiency of the LED. 
         [0009]    The light emitting diode  12  includes a second substrate  120 , a first semiconductor layer  121 , a light emitting layer  123 , a second semiconductor layer  125 , at least a first electrode  127  and at least a second electrode  129 . The first semiconductor layer  121  is disposed on the first substrate  10 . The light emitting layer  123  is disposed on the first semiconductor layer  121 . The second semiconductor layer  129  is disposed on the light emitting layer  123 . The first electrode  127  is disposed on the first semiconductor layer  121 . The second electrode  129  is disposed on the second semiconductor layer  125 . The selective reflection layer  14  is disposed on the second semiconductor layer  125 , the first electrode  127  and the second electrode  129 . Both the first semiconductor layer  121  and the first electrode  127  are P type while the second semiconductor layer  127  and the second electrode  129  are N type. Alternatively, both the first semiconductor layer  121  and the first electrode  127  are N type while the second semiconductor layer  127  and the second electrode  129  are P type. For enhancement of the efficiency of LED, a reflection layer  128  is disposed on the first semiconductor layer  121 . In this embodiment, the reflection layer  128  is disposed between the first semiconductor layer  121  and the first substrate  10 . Alternatively, the reflection layer  128  may be disposed between the first semiconductor layer  121  and light emitting layer  123 . 
         [0010]      FIG. 2  is a diagram showing the selective reflection layer according to one embodiment of the invention. The selective reflection layer  14  includes dielectric layers  141  having at least two different thicknesses. For example, the selective reflection layer  14  may include a first, second and third dielectric layers. The first and third dielectric layers have a thickness A while the second dielectric layer has a thickness B. Furthermore, each dielectric layer is made of a different material from its adjacent dielectric layer. For example, the first and third dielectric layers are made of material C while the second dielectric layer is made of material D. The materials of the dielectric layers may be two of the following: SiO 2 , TiO 2 , TaO, ZnO, NbO, AIN, InN, TnN and MgN. 
         [0011]      FIG. 3  is a diagram showing a light emitting element according to another embodiment of the invention. The difference between the light emitting elements showing in  FIGS. 1 and 3  is that, in  FIG. 3 , the light emitting diode  12  is disposed upside down on the first substrate  10  so that it becomes a Flip-Chip LED. The first semiconductor layer  121  is disposed on the second substrate  120 . The light emitting layer  123  is disposed on the first semiconductor layer  121 . The second semiconductor layer  125  is disposed on the light emitting layer  123 . The first electrode  127  is disposed on the first semiconductor layer  121 . The second electrode  129  is disposed on the second semiconductor layer  125 . The first and second electrodes  127  and  129  are coupled to the first substrate  10  through metal contacts  124  and  126 . The selective reflection layer  14  is disposed on the second substrate  120 . Alternatively, the second substrate may be removed to prevent stress problem so that the selective reflection layer  14  is disposed on the first semiconductor layer  121 . Both the first semiconductor layer  121  and the first electrode  127  are P type while the second semiconductor layer  127  and the second electrode  129  are N type. Alternatively, both the first semiconductor layer  121  and the first electrode  127  are N type while the second semiconductor layer  127  and the second electrode  129  are P type. For enhancement of the efficiency of LED, a reflection layer  128  is disposed on the second semiconductor layer  125 . In this embodiment, the reflection layer  128  is disposed between the second semiconductor layer  125  and the second substrate  129 . 
         [0012]      FIG. 4  is a diagram showing a light emitting element according to another embodiment of the invention. The difference between the light emitting element  1  shown in  FIGS. 3 and 4  is that the substrate  10  in the  FIG. 4  is in a shape of a bowl. This focuses the light from the light emitting diode  12  and enhance the efficiency of LED. The first substrate  10  shown in  FIG. 1  could be also in the shape of a bowl. 
         [0013]      FIG. 5  is a diagram showing a light emitting element according to another embodiment of the invention. The difference between the light emitting element  1  shown in  FIGS. 1 and 5  is that the light emitting diode  12  in  FIG. 5  is an AC LED. 
         [0014]    The AC LED includes light emitting diodes  12  coupled to each other. Each light emitting diode  12  includes a first semiconductor layer  121 , a light emitting layer  123 , a second semiconductor layer  125 , a first electrode  127  and a second electrode  129 . The first semiconductor layer  121  is disposed on the first substrate  10 . The light emitting layer  123  is disposed on the first semiconductor layer  121 . The second semiconductor layer  129  is disposed on the light emitting layer  123 . The first electrode  127  is disposed on the first semiconductor layer  121 . The second electrode  129  is disposed on the second semiconductor layer  125 . Dielectric layers  122  are disposed between the light emitting diodes  12  and the second electrode  129  of each light emitting diode  12  is coupled to the first electrode  127  of its adjacent light emitting diode  12 . For enhancement of the efficiency of LED, a reflection layer  128  is disposed between the first semiconductor layer  121  and the first substrate  10 . Alternatively, the reflection layer  128  may be disposed between the first semiconductor layer  121  and the light emitting layer  123 . 
         [0015]    Alternatively, the substrate  10  may be in a shape of a bowl, as shown in  FIG. 4 . 
         [0016]      FIG. 6  is a diagram showing a light emitting element according to another embodiment of the invention. The difference between the light emitting element  1  shown in  FIGS. 1 and 6  is that, in  FIG. 6 , the first semiconductor layers  121  are disposed on the second substrate  120 . The first and second electrodes  127  and  129  are coupled to the first substrate  10  through metal contacts  124  and  126 . The selective reflection layer  14  is disposed on the second substrate  120 . For enhancement of the efficiency of LED, a reflection layer  128  is disposed between the second semiconductor layer  125  and the second electrode  129 . Alternatively, the substrate  10  may be in a shape of a bowl, as shown in  FIG. 4 . 
         [0017]    In conclusion, the present invention provides a light emitting element having a selective reflection layer through which light of a first color emitted by a light emitting diode passes and by which light of a second color converted by a fluorescent layer is reflected. Thus, the light of the first and second color can be mixed to enhance the efficiency of LED. Further, the first substrate may be in a shape of a bowl, which help to focus the light from the light emitting diode. 
       BRIEF DESCRIPTION OF DRAWINGS 
       [0018]      FIG. 1  is a diagram shown a light emitting element according to one embodiment of the invention. 
         [0019]      FIG. 2  is a diagram showing the selective reflection layer according to one embodiment of the invention. 
         [0020]      FIG. 3  is a diagram showing a light emitting element according to another embodiment of the invention. 
         [0021]      FIG. 4  is a diagram showing a light emitting element according to another embodiment of the invention. 
         [0022]      FIG. 5  is a diagram showing a light emitting element according to another embodiment of the invention. 
         [0023]      FIG. 6  is a diagram showing a light emitting element according to another embodiment of the invention.