Abstract:
This disclosure discloses a light-emitting device. The light-emitting device comprises: a substrate; and a first light-emitting unit comprising a plurality of light-emitting diodes electrically connected to each other on the substrate. A first light-emitting diode in the first light-emitting unit comprises a first semiconductor layer with a first conductivity-type, a second semiconductor layer with a second conductivity-type, and a light-emitting stack formed between the first and second semiconductor layers. The first light-emitting diode in the first light-emitting unit further comprises a first connecting layer on the first semiconductor layer for electrically connecting to a second light-emitting diode in the first light-emitting unit; a second connecting layer, separated from the first connecting layer, formed on the first semiconductor layer; and a third connecting layer on the second semiconductor layer for electrically connecting to a third light-emitting diode in the first light-emitting unit.

Description:
[0001]    This application is a Continuation of co-pending application Ser. No. 13/005,075, filed Jan. 12, 2011, which is a Continuation-in-Part of application Ser. No. 12/437,908, filed May 8, 2009, which issued as U.S. Pat. No. 7,906,795 on Mar. 15, 2011, for which priority is claimed under 35 U.S.C. §120, the entire contents of all of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to a light-emitting device, and in particular to a light-emitting device comprising a plurality of recesses in a semiconductor window layer. 
         [0004]    2. Description of the Related Art 
         [0005]    The light-emitting diodes (LEDs) of the solid-state lighting elements have the characteristics of the low power consumption, low heat generation, long operational life, shockproof, small volume, quick response and good opto-electrical property like light emission with a stable wavelength, so the LEDs have been widely used in household appliances, indicator light of instruments, and opto-electrical products, etc. However, how to improve the light-emitting efficiency of light-emitting devices is still an important issue in this art. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    The present disclosure provides a light-emitting device. 
         [0007]    The light-emitting device comprises: a substrate; a transparent conductive layer disposed on the substrate; a semiconductor window layer formed on the transparent conductive layer and having a flat surface and a plurality of recesses, wherein each of the recesses has a side wall surface; and a light-emitting stack formed on the semiconductor window layer and comprising a first conductivity semiconductor layer, a second conductivity semiconductor layer, and an active layer sandwiched between the first and second conductivity layers. The side wall surface of one of the recesses is inclined with respect to the flat surface, and the contact resistance between the flat surface and the transparent conductive layer is less than that between the side wall surface in each recess and the transparent conductive layer. 
         [0008]    In another embodiment of the present disclosure, a light light-emitting device is provided. 
         [0009]    The light light-emitting device comprises: a substrate; a transparent conductive layer disposed on the substrate; a semiconductor window layer formed on the transparent conductive layer and having a flat surface and a plurality of recesses, wherein each of the recesses has a side wall surface; an ohmic contact layer formed between the semiconductor window layer and the transparent conductive layer; and a light-emitting stack formed on the semiconductor window layer and comprising a first conductivity semiconductor layer, a second conductivity semiconductor layer, and an active layer sandwiched between the first and second conductivity layers. The semiconductor window layer and the ohmic contact layer comprise the same material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawings are included to provide easy understanding of the application, and are incorporated herein and constitute a part of this specification. The drawings illustrate the embodiments of the application and, together with the description, serve to illustrate the principles of the application. 
           [0011]      FIG. 1  shows a cross-sectional view of a light-emitting device in accordance with the first embodiment of the present disclosure. 
           [0012]      FIG. 2  shows a cross-sectional view of a light-emitting device in accordance with the second embodiment of the present disclosure. 
           [0013]      FIG. 3  shows a cross-sectional view of a light-emitting device in accordance with the third embodiment of the present disclosure. 
           [0014]      FIGS. 4A  to 4C show plan views of recesses in accordance with the present disclosure. 
           [0015]      FIGS. 5A  to 5G are cross-sectional views showing a method of making the light-emitting device of the second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0016]    For to better and concisely explain the disclosure, the same name or the same reference number given or appeared in different paragraphs or figures along the specification should has the same or equivalent meanings while it is once defined anywhere of the disclosure. 
         [0017]    The following shows the description of the embodiments of the present disclosure in accordance with the drawings. 
         [0018]      FIG. 1  discloses a light-emitting device  100  according to the first embodiment of the present disclosure. The light-emitting device  100  comprises a permanent substrate  10 , a bonding layer  18 , a reflective layer  11 , a transparent conductive layer  12 , an ohmic contact layer  13 , a semiconductor window layer  14 , and a light-emitting stack  15 . The light-emitting stack  15  comprises a p-type semiconductor layer  151 , an n-type semiconductor layer  153 , and an active layer  152  sandwiched between the p-type and n-type semiconductor layers  151 ,  153 . The semiconductor window layer  14  has a flat surface  141  and a plurality of recesses  142 . Each of the recesses has a side wall surface  1421  which is inclined with respect to the flat surface  141  at an angle (Θ) greater than 90° and less than 180°. Preferably, the angle (Θ) ranges from 110° to 160°. In this embodiment, the recesses  142  have triangular shaped cross-sections. The ohmic contact layer  13  is formed between the semiconductor window layer  14  and the transparent conductive layer  12  at position corresponding to the flat surface  141  of the semiconductor window layer  14 . A surface area ratio of the surface area of the ohmic contact layer  13  to the surface area of the semiconductor window layer  14  ranges from 10% to 90%. The recesses have a depth (H) and the depth ratio of the depth of the recesses 142 to the thickness of the semiconductor window layer  14  ranges from 20% to 80%. 
         [0019]    Referring to  FIG. 1 , the light-emitting device  100  further comprises an n-side electrode  16  formed on the light-emitting stack  15  and a p-side electrode  17  formed on the permanent substrate  10 . The n-side electrode  16  comprising a bonding pad  160  and an extension  161  extending from the bonding bad  160  are formed on the light-emitting stack  15  at positions corresponding to the recesses  142 . In this embodiment, the ohmic contact layer  13  is substantially made of the same material as the semiconductor window layer  14 . In addition, the ohmic contact layer  13  further comprises doping impurities for ohmically contacting the transparent conductive layer  12 . Therefore, the contact resistance between the flat surface  141  and the transparent conductive layer  12  is less than that between the side wall surface  1421  and the transparent conductive layer  12 , which results in that, when a power source is applied on the n-side electrode  16 , most current flows through the flat surface  141  of the semiconductor window layer  14 , thereby obtaining a current-blocking effect between the side wall surface  1421  and the transparent conductive layer  12 . Furthermore, the light emitted from the light-emitting stack  15  is reflected at the side wall surface  1421  and is directed to escape from a light-emitting surface of the light-emitting stack  15  for enhancing the light extraction efficiency. The semiconductor window layer  14  is made of a material selected from the group consisting of GaP, InGaP, GaAs, AlGaAs, and combinations thereof. The doping impurities comprise a material selected from the group consisting of Mg, Be, Zn, C, and combinations thereof. 
         [0020]      FIG. 2  discloses a light-emitting device  200  according to the second embodiment of the present disclosure. The second embodiment of the light-emitting device  200  has the similar structure with the first embodiment of the light-emitting device  100  except that the recesses  142  have trapezoid shaped cross-sections and each of the recesses  142  further has a recessed surface  1422 . The recessed surface  1422  in each recess  142  is substantially parallel to the flat surface  141 . The bonding pad  160 ′ and the extension  161 ′ are formed at positions corresponding to the recessed surface  1422  and the side wall surface  1421 . Alternatively, the n-type electrode  16  can be merely formed at position corresponding to the recessed surface  1422  (not shown). The contact resistance between the recessed surface  1422  and the transparent conductive layer  12  is substantially equal to that between the side wall surface  1421  and the transparent conductive layer  12 , it is noted that the cross-section of the recesses  142  comprises at least one pattern selected from the group consisting of triangular shape, trapezoid shape, and combinations thereof. 
         [0021]      FIG. 3  shows a light-emitting device  300  according to the third embodiment of the present disclosure. The third embodiment of the light-emitting device  300  has the similar structure with the first embodiment of the light-emitting device  100  except that the side wall surface  1421  of some of the recesses  142  is not inclined to the flat surface  141 . In this embodiment, the recess  142  formed beneath the bonding pad  160 ″ has the side wall surface  1421  substantially perpendicular to the flat surface  141 , and the recess  142  formed beneath the extension  161 ″ has the side wall surface  1421  inclined to the flat surface  141 . 
         [0022]      FIG. 4A and 4B  are plan views of the n-type electrode  16  and the recesses  142 . The recesses  142  as shown in  FIG. 4B  have a first pattern which is geometrically similar to that of the n-type electrode  16  as shown in  FIG. 4A  and are formed beneath the n-type electrode  16 .  FIG. 4C  is a plan view of the recesses  142  which further have a second pattern. The second pattern is a tessellation of hexagons which are not formed beneath the n-type electrode  16 . Alternatively, in a plan view, the second pattern can be a circle, or a tessellation of triangle, rectangle, or pentagon. Depending on the actual requirements, the pattern of the n-side electrode  16  may vary and therefore the first pattern of the recesses  142  will vary with the pattern of the n-side electrode  16 . 
         [0023]      FIGS. 5A to 5G  illustrate a method of making the light-emitting device  200  according to the second embodiment of the present disclosure. Referring to  FIG. 5A , the n-type semiconductor layer  153 , the active layer  152 , the p-type semiconductor layer  151 , and the semiconductor window layer  14  are sequentially grown on a growth substrate  20 . Referring to  FIG. 5B , the ohmic contact layer  13  is grown on the semiconductor window layer  14 . The semiconductor window layer  14  has a thickness ranging from 1 μm to 10 μm and the ohmic contact layer  13  has a thickness less than 2000 Å. Alternatively, the semiconductor window layer  14  can be subjected to a doping treatment to form the ohmic contact layer  13 . Referring to  FIG. 5C , an etching process is carried out to remove portions of the ohmic contact layer  13  and further to remove portions of the semiconductor window layer  14  such that the recesses  142  are formed within the semiconductor window layer  14 . Referring to  FIG. 5D , the transparent conductive layer  12  is formed on and conformal to the ohmic contact layer  13  and the semiconductor window layer  14  by evaporating or sputtering. Therefore, the transparent conductive layer  12  is in contact with the semiconductor window layer  14  and the ohmic contact layer  13 . It is noted that when the transparent conductive layer  12  is formed by spin coating, the recesses  142  is filled up with the transparent conductive layer  12 . Referring to FIG. SE, the reflective layer  11  is formed on the transparent conductive layer  12 . Referring to  FIG. 5F , the permanent substrate  10  is bonded to the reflective layer  11  through the bonding layer  18 . Referring to  FIG. 5G , the growth substrate  20  is separated from the n-type semiconductor layer  153  by etching. Subsequently, the n-side electrode  16  and the p-side electrode  17  are respectively formed on the n-type semiconductor layer  153  and the permanent substrate  10 . The bonding layer  18  comprises metal or glue. The metal comprises gold (Au), indium (In), tin (Sn), and combinations thereof. The glue is made of a material selected from the group consisting of indium tin oxide (ITO), benzocyclobutene (BCB), epoxy resin (Epoxy), polydimethylsiloxane (PDMS), silicone (SiOx), aluminum oxide (Al 2 O 3 ), titanium dioxide (TiO2), silicon nitride (SiNx), and combinations thereof. 
       EXAMPLES 
     Example 1 (E1) 
       [0024]    The light-emitting device has a structure as shown in  FIG. 2 . The n-type semiconductor layer  153  of AlInP, the active layer  152  of AlGaInP, and the p-type semiconductor layer  154  of AlInP are sequentially grown on the growth substrate  20  of GaAs. The semiconductor window layer  14  made of GaP and having a thickness of 10 μm is grown on the p-type semiconductor layer  154 . The ohmic contact layer  13  made of carbon-doped GaP is grown on the semiconductor window layer  14  by metal organic chemical vapor deposition (MOCVD). A wet etching is performed to etch portions of the ohmic contact layer  13  and the semiconductor window layer  14 , thereby forming the recesses  142 . The recesses  142  have a depth (H) of about 2 μm, and the depth ratio of the depth of the recesses  142  to the thickness of the semiconductor window layer  14  is about 20%. The transparent conductive layer  12  made of ITO is formed on the semiconductor window layer 14 by evaporating. The reflective layer  11  is a multi-layer structure of Ag/Ti/Pt/Au is formed on the transparent conductive layer  12 . The permanent substrate made of Si is bonded to the reflective layer  11  by metal bonding process, and then the GaAs substrate  20  is removed. Subsequently, the n-type electrode  16  is formed on the n-type semiconductor layer  153  at position corresponding to the recesses  142  and has a pattern substantially equal to the first pattern of the recesses  142  (see  FIG. 4A ). The surface area ratio of the surface area of the ohmic contact layer  13  to the surface area of the semiconductor window layer  14  is about 85%, that is, the surface area of the recesses  142  is about 15% of the total area of the semiconductor window layer  14 . 
       Example 2 (E2) 
       [0025]    The light-emitting device of Example 2 has a similar structure with that of Example 1, except that the recesses  142  further have the second pattern of hexagon on which the n-type electrode  16  are not formed (see  FIG. 4C ). Accordingly, the surface area ratio of the surface area of the ohmic contact layer  13  to the surface area of the semiconductor window layer  14  is about 80%, that is, the surface area of the recesses  142  is about 20% of the total area of the semiconductor window layer  14 . 
       Example 3 (E3) 
       [0026]    The light-emitting device of Example 3 has a similar structure with that of Example 1, except that the thickness of the semiconductor window layer  14  is 1 μm. The recesses  142  have a depth (H) of about 0.8 μm, and the depth ratio of the depth of the recesses  142  to the thickness of the semiconductor window layer  14  is about 80%. 
       Example 4 (E4) 
       [0027]    The light-emitting device of Example 4 has a similar structure with that of Example 2, except that the thickness of the semiconductor window layer  14  is 1 μm. 
       Comparative Example 1 (CE1) 
       [0028]    The light-emitting device of Comparative Example 1 has a similar structure with that of Example 1, except that the ohmic contact layer  13  and the semiconductor window layer  14  are not etched. Therefore, the recesses  142  are not formed in the semiconductor window layer  14 . 
       Comparative Example 1 (CE2) 
       [0029]    The light-emitting device of Comparative Example 2 has a similar structure with that of Example 3, except that the ohmic contact layer  13  and the semiconductor window layer  14  are not etched. Therefore, the recesses  142  are not formed in the semiconductor window layer  14 . 
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Luminous 
                 Improved 
               
               
                   
                 intensity (mcd) 
                 percentage 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 E1 
                 469.18 
                 118% 
               
               
                   
                 E2 
                 493.68 
                 124.1%   
               
               
                   
                 CE1 
                 397.77 
                 100% 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Luminous intensity 
                 Improved 
               
               
                   
                 (mcd) 
                 percentage 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 E3 
                 396.08 
                 112.5% 
               
               
                   
                 E4 
                 459.21 
                 130.4% 
               
               
                   
                 CE2 
                 352.19 
                   100% 
               
               
                   
                   
               
             
          
         
       
     
         [0030]    Tables 1 and 2 show experimental results. Compared to the Comparative Example 1, the light-emitting device of Example I has the luminous intensity of 469.18 mcd, which is increased by 18%, and the light-emitting device of Example 2 has the luminous intensity of 493.68 mcd, which is increased by 24.1%. Likewise, compared to the Comparative Example 2, the light-emitting device of Example 3 has the luminous intensity of 369.08 mcd, which is increased by 12.5%, and the light-emitting device of Example 4 has the luminous intensity of 459.21 mcd, which is increased by 30.4%. By forming the recesses  142  with the side wall surface  1422  that is inclined, light emitting from the light-emitting stack  15  is efficiently reflected by the side wall surface  1422  and is directed to escape from a light-emitting surface of the light-emitting stack  15 , thereby improving the light emitting intensity. In addition, since the recesses  142  further have the second pattern, which indicates that the area of the recesses  142  in Examples 2 and 4 is higher (about 5%) than that in Examples 1 and 3, there are more side wall surfaces  1422  for reflecting the light emitting from the light-emitting stack  15 . Therefore, the luminous intensity of the light-emitting device of Examples 2 and 4 is relatively higher. 
         [0031]    It will be apparent to those having ordinary skill in the art that various modifications and variations can be made to the devices in accordance with the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure covers modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.