Abstract:
A light-emitting device comprises a light-emitting stack comprising a first surface, a roughened surface, and a sidewall connecting the first surface and the roughened surface; an electrode structure formed on the roughened surface of the light-emitting stack; a dielectric layer formed on the first surface of the light-emitting stack; a barrier layer covering the dielectric layer; a first reflective electrode between the barrier layer and the first surface of the light-emitting stack; and a passivation layer covering the sidewall of the light-emitting stack and the roughened surface of the light-emitting stack which is not occupied by the electrode structure, wherein the electrode structure is surrounded by the passivation layer, and the passivation layer contacts an surface of the electrode structure and terminates at the surface of the electrode structure.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 14/555,746, filed on Nov. 28, 2014, now pending, which claims the right of priority based on TW application Serial No. 102144302, filed on Nov. 29, 2013, and the contents of which are hereby incorporated by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The application relates to a light-emitting device, and more particularly, to a light-emitting device having a light-emitting stack located on a conductive substrate. 
       DESCRIPTION OF BACKGROUND ART 
       [0003]    The lighting theory of light-emitting diodes (LEDs) is that electrons and holes between an n-type semiconductor and a p-type semiconductor are combined in the active layer to release energy. Due to the difference of lighting theories between LEDs and incandescent lamps, the LED is called “cold light source”. An LED has the advantages of good environment tolerance, a long service life, portability, and low power consumption so it is regarded as another option for the lighting application. LEDs are widely adopted in different fields, for example, traffic lights, backlight modules, street lights, and medical devices and replaces conventional light sources gradually. 
         [0004]    An LED has a light-emitting stack which is epitaxially grown on a conductive substrate or an insulative substrate. The so-called “vertical LED” has a conductive substrate and includes an electrode formed on the top of a light emitting layer; the so-called “lateral LED” has an insulative substrate and includes electrodes formed on two semiconductor layers which have different polarities and exposed by an etching process. The vertical LED has the advantages of small light-shading area for electrodes, good heat dissipating efficiency, and no additional etching epitaxial process, but has a shortage that the conductive substrate served as an epitaxial substrate absorbs light easily and is adverse to the light efficiency of the LED. The lateral LED has the advantage of radiating light in all directions due to a transparent substrate used as the insulative substrate, but has shortages of poor heat dissipation, larger light-shading area for electrodes, and smaller light-emitting area caused by epitaxial etching process. 
         [0005]    The abovementioned LED can further connects to/with other components for forming a light-emitting device. For a light-emitting device, the LED can connect to a sub-carrier by the substrate side or by soldering material/adhesive material between the sub-carrier and the LED. Besides, the sub-carrier can further comprise a circuit electrically connected to electrodes of the LED via a conductive structure, for example, a metal wire. 
       SUMMARY OF THE APPLICATION 
       [0006]    A light-emitting device comprises: a light-emitting stack comprising a first surface; a patterned dielectric layer formed on the first surface, comprising a first portion and a second portion substantially surrounding the first portion and having substantially the same thickness with that of the first portion; a first reflective electrode covering the first portion of the patterned dielectric layer; and a barrier layer covering the first reflective electrode and the second portion of the patterned dielectric layer. 
         [0007]    A light-emitting device comprises a light-emitting stack comprising a first surface, a roughened surface, and a sidewall connecting the first surface and the roughened surface; an electrode structure formed on the roughened surface of the light-emitting stack; a dielectric layer formed on the first surface of the light-emitting stack; a barrier layer covering the dielectric layer; a first reflective electrode between the barrier layer and the first surface of the light-emitting stack; and a passivation layer covering the sidewall of the light-emitting stack and the roughened surface of the light-emitting stack which is not occupied by the electrode structure, wherein the electrode structure is surrounded by the passivation layer, and the passivation layer contacts an surface of the electrode structure and terminates at the surface of the electrode structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  illustrates a light-emitting device in accordance with a first embodiment of the present application; 
           [0009]      FIG. 2  illustrates a light-emitting device in accordance with a second embodiment of the present application; and 
           [0010]      FIGS. 3A and 3B  illustrate a light-emitting device in accordance with a third embodiment of the present application. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0011]      FIG. 1  illustrates a light-emitting device in accordance with a first embodiment of the present application. Light-emitting device  100  comprises: a permanent substrate  126 ; a lighting stack  102  formed on the permanent substrate  126  and comprising a first surface  102   a  toward the permanent substrate  126  and a second surface  102   b  opposite to the first surface  102   a;  a patterned dielectric layer  110  formed on the first surface  102   a  and comprising a first portion  110   a  and a second portion  110   b  approximately surrounding the first surface  102   a,  wherein the first portion  110   a  comprises a first thickness and the second portion  110   b  comprises a second thickness the same as the first thickness; a first reflective electrode  112  having reflectivity and covering the first portion  110   a  of the patterned dielectric layer  110 , wherein the material of the first reflective electrode  112  can comprise Ag, Al, or other metal having high reflectivity, or the sequence or alloy of aforesaid metal; and a barrier layer  122  covering the first reflective electrode  112  and the second portion  110   b  of the patterned dielectric layer  110 . The second surface  102   b  of the light-emitting stack  102  can comprise a second electrode structure  116  comprising a pattern corresponding to that of the first portion  110   a  of the patterned dielectric layer  110 . The first reflective electrode  112  ohmically contacts to the first surface  102   a  of the light-emitting surface  102 , and the second electrode structure  116  ohmically contact to the second surface  102   b  of the light-emitting stack  102 , and contact areas of the second electrode structure  116  and the first reflective electrode  112  do not overlap with each other in a vertical direction. A cross-sectional width of the barrier layer  122  can be slightly wider than the light-emitting stack  102 , and the outer edge of the second portion  110   b  of the patterned dielectric layer  110  can approximately align with a side wall of the barrier layer  122  and project from a side wall of the light-emitting stack  102 . A passivation layer  114  can cover a part of the second surface  102   b  of the light-emitting stack  102  that is not covered by the second electrode structure  116  by conforming to the shape of the light-emitting stack  102  and further cover a side wall of the light-emitting stack  102 . The bottom of the passivation layer  114  contacts with the second portion  110   b  of the patterned dielectric layer  110 . The material of the patterned dielectric layer  110  can comprise insulative oxide such as TiO 2  or SiO 2 , insulative nitride such as SiN x  or AlN, or other insulative material like MgF 2 . The material of the passivation layer  114  can comprise SiN x  or SiO 2 . The material of the patterned dielectric layer  110  can be different from that of the passivation layer  114 . In the embodiment, the material of the patterned dielectric layer  110  can comprise TiO 2 , and material of the passivation layer  114  can comprise SiO 2  or silicon nitride (SiN x  or Si 3 N 4 ). Without the second portion  110   b  of the patterned dielectric layer  110 , the barrier layer  122  would directly contact the bottom of the passivation layer  114  and a portion of the first surface  102   a.  Since the material of the barrier layer  122  is usually metal, the adhesion with the passivation layer  114  is usually poor and a gap may be formed between the bottom of the passivation  114  and the barrier layer  122 . In that case, the humidity or other outside disturbance may further affect the adhesion between the barrier layer  122  and the first surface  102   a  via the gap between the passivation  114  and the barrier layer  122 . Once the barrier layer  122  is peeled off from the first surface  102   a,  the first reflective electrode  112  may be overflowed from the side wall of the light-emitting stack  102 , and the risk of electric anomaly or function failure of the light-emitting device  100  is increased. In the embodiment, the first reflective electrode  112  further covers partial second portion  110   b  of the patterned dielectric layer  110  so the barrier layer  122  is not to be in contact with the first surface  102   a.    
         [0012]    The light-emitting stack  102  is grown from a wafer-level growth substrate (not shown) in advance, and after the patterned dielectric layer  110 , the first reflective electrode  112 , and the barrier layer  122  are formed, the first portion  110   a  and the second portion  110   b  of the patterned dielectric layer  110  are formed at the same time during fabrication process, therefore the material and thickness of the first portion  110   a  are the same with that of the second portion  110   b.  The permanent substrate  126  can attach to the light-emitting stack  102  by a connection layer  124 , the barrier layer  122  can be between the connection layer  124  and the first reflective electrode  112 , and the connection layer  124  can be between the barrier layer  122  and the permanent substrate  126 . The growth substrate can be removed after the permanent substrate  126  is attached to the light-emitting stack  102 , and the second surface  102   b  can be a rough surface by using a method like dry etching. A plurality of light-emitting device  100  can be achieved by etching the light-emitting stack  102  to form trenches to form a plurality of units insulated from each other, and cutting the wafer along the trenches. The outer part of the second portion  110   b  is thinned when the wafer is cut, and the second portion  110   b  approximately remains the second thickness on a section contacts the first surface  102   a.    
         [0013]    The light-emitting stack  102  can comprise a first semiconductor layer  104 , a second semiconductor layer  108 , and an active layer  106  formed between the first semiconductor layer  104  and the second semiconductor layer  108 , wherein the first semiconductor layer  104  can be p-type and comprises the first surface  102   a,  and the second semiconductor layer  108  can be n-type and comprises the second surface  102   b.  The barrier layer  122  can comprise a double layer structure comprising a first barrier layer  118  and a second barrier layer  120 , and the material thereof can comprise Ti, W, Pt, TiW or the combination thereof. The light-emitting stack  102  can comprise single heterostructure (SH), double heterostructure (DH), double-side double heterostructure (DDH) or multi-quantum well (MQW) structure. The light-emitting stack  102  can be a nitride based light-emitting stack, and the material of the light-emitting stack  102  comprises one or more elements selected from the group consisting of Al, In, Ga, P, As, and N. 
         [0014]      FIG. 2  illustrates a light-emitting device in accordance with a second embodiment of the present application. A light-emitting device  200  comprises: a permanent substrate  226 ; a lighting stack  202  formed on the permanent substrate  226  and comprising a first surface  202   a  toward the permanent substrate  226  and a second surface  202   b  opposite to the first surface  202   a;  a patterned dielectric layer  210  formed on the first surface  202   a  and comprising a first portion  210   a  and a second portion  210   b  approximately surrounding the first surface  202   a,  wherein the first portion  210   a  comprises a first thickness and the second portion  210   b  comprises a second thickness the same as the first thickness; a first reflective electrode  212  having reflectivity and covering the first portion  210   a  of the patterned dielectric layer  210 , wherein the material of the first reflective electrode  212  can comprise Ag, Al or other metal having high reflectivity, or the sequence or alloy of aforesaid metal; and a barrier layer  222  covering the first reflective electrode  212  and the second portion  210   b  of the patterned dielectric layer  210 . The second surface  202   b  of the light-emitting stack  202  can comprise a second electrode structure  216  comprising a pattern corresponding to that of the first portion  210   a  of the patterned dielectric layer  210 . The first reflective electrode  212  ohmically contacts to the first surface  202   a  of the light-emitting surface  202 , and the second electrode structure  216  ohmically contact to the second surface  202   b  of the light-emitting stack  202 , and contact areas of the second electrode structure  216  and the first reflective electrode  212  do not overlap with each other in a vertical direction. A cross-sectional width of the barrier layer  222  can be slightly wider than the light-emitting stack  202 , and the outer edge of the second portion  210   b  of the patterned dielectric layer  210  can approximately align with a side wall of the barrier layer  222  and project from a side wall of the light-emitting stack  202 . A passivation layer  214  can cover a part of the second surface  202   b  of the light-emitting stack  202  that is not covered by the second electrode structure  216  by conforming to the shape of the light-emitting stack  202  and further cover a side wall of the light-emitting stack  202 . The bottom of the passivation layer  214  contacts with the second portion  210   b  of the patterned dielectric layer  210 . The material of the patterned dielectric layer  210  can comprise insulative oxide such as TiO 2  or SiO 2 , insulative nitride such as SiN x  or AlN, or other insulative material like MgF 2 . The passivation layer  214  can comprise a first passivation layer  214   a  attaching to the second portion  210   b  of the patterned dielectric layer  210  and covering at least side wall of the light-emitting stack  202 , and a second passivation layer  214   b  covering the first passivation layer  214   a  and the second surface  202   b.  The first passivation layer  214   a  comprises Si 3 N 4  or SiN x , and the second passivation layer  214   b  comprises SiO 2 . In the embodiment, the first reflective electrode  212  and the patterned dielectric layer  210  is separated by a gap. The barrier layer  222  can comprise a first barrier layer  218  and a second barrier layer  220 . A connection layer  224  can be formed between the barrier layer  222  and the permanent substrate  226 . 
         [0015]      FIG. 3  illustrates a light-emitting device in accordance with a third embodiment of the present application. A light-emitting device  300  comprises: a permanent substrate  326 ; a lighting stack  302  formed on the permanent substrate  326  and comprising a first surface  302   a  toward the permanent substrate  326  and a second surface  302   b  opposite to the first surface  302   a;  a patterned dielectric layer  310  formed on the first surface  302   a  and comprising a first portion  310   a  and a second portion  310   b  approximately surrounding the first surface  302   a,  wherein the first portion  310   a  comprises a first thickness and the second portion  310   b  comprises a second thickness the same as the first thickness; a first reflective electrode  312  having reflectivity and covering the first portion  310   a  of the patterned dielectric layer  310 , wherein the material of the first reflective electrode  312  can comprise Ag, Al or other metal having high reflectivity, or the sequence or alloy of aforesaid metal; and a barrier layer  322  covering the first reflective electrode  312  and the second portion  310   b  of the patterned dielectric layer  310 . The second surface  302   b  of the light-emitting stack  302  can comprise a second electrode structure  316  comprising a pattern corresponding to that of the first portion  310   a  of the patterned dielectric layer  310 . The first reflective electrode  312  ohmically contacts to the first surface  302   a  of the light-emitting surface  302 , and the second electrode structure  316  ohmically contact to the second surface  302   b  of the light-emitting stack  302 , and contact areas of the second electrode structure  316  and the first reflective electrode  312  do not overlap with each other in a vertical direction. A cross-sectional width of the barrier layer  322  can be slightly wider than the light-emitting stack  302 , and the outer edge of the second portion  310   b  of the patterned dielectric layer  310  can approximately align with a side wall of the barrier layer  322  and project from a side wall of the light-emitting stack  302 . A passivation layer  314  can cover a part of the second electrode structure  316  of the second surface  302   b  of the light-emitting stack  302  that is not covered by the second electrode structure  316  by conforming to the shape of the light-emitting stack  302  and further cover a side wall of the light-emitting stack  302 . The bottom of the passivation layer  314  contacts with the second portion  310   b  of the patterned dielectric layer  310 . The material of the patterned dielectric layer  310  can comprise insulative oxide such as TiO 2  or SiO 2 , insulative nitride such as SiN x  or AlN, or other insulative material like MgF 2 . The passivation layer  314  can comprise a first passivation layer  314   a  attaching to the second portion  310   b  of the patterned dielectric layer  310  and covering at least side wall of the light-emitting stack  302 , and a second passivation layer  314   b  covering the first passivation layer  314   a  and the second surface  302   b.  The first passivation layer  314   a  comprises Si 3 N 4  or SiN x , and the second passivation layer  314   b  comprises SiO 2 . In the embodiment, the first reflective electrode  312  and the patterned dielectric layer  310  is separated by a gap. The barrier layer  322  can comprise a first barrier layer  318  and a second barrier layer  320 . A connection layer  324  can be formed the barrier layer  322  and the permanent substrate  326 . 
         [0016]    As shown in  FIG. 3B , the second electrode structure  316  can comprise at least an electrode pad  316   a  and an extensive-branch like electrode  316   b,  the second portion  310   b  of the patterned dielectric layer  310  overlaps the electrode pad  316   a  and the extension-branch like electrode  316   b  from a top view. The second portion  310   b  of the patterned dielectric layer  310  can comprise a boundary surrounding the light-emitting stack  302 , and the second portion  310   b  comprises a width wider than that of the extensive-branch like electrode  316   b,  and the section overlapping the electrode pad  316   a  of the second portion  310   b  corresponds to the pattern of the electrode pad  316   a.    
         [0017]    The principle and the efficiency of the present application illustrated by the embodiments above are not the limitation of the application. Any person having ordinary skill in the art can modify or change the aforementioned embodiments. Therefore, the protection range of the rights in the application will be listed as the following claims.