Patent Publication Number: US-2010127237-A1

Title: High brightness light emitting diode structure and a method for fabricating the same

Description:
FIELD OF THE INVENTION 
     The present invention relates to an LED structure, particularly to a high-brightness LED structure and a method for fabricating the same. 
     BACKGROUND OF THE INVENTION 
     LED (Light Emitting Diode) is a luminescent element, wherein current is applied to a III-V group compound semiconductor, and energy is released in form of light in the recombination of electrons and holes. LED does not burn as an incandescent lamp. Further, LED has a small volume, long service life, low driving voltage, high response speed and superior vibration resistance. Thus, LED can satisfy the demand for lightweight and compactness and has become a very popular product in daily living. 
     LED has greatly advanced in the performance and efficiency thereof and has been extensively used in daily living. Via different compound semiconductors and structures, LED may emit red, orange, yellow, green blue, violet, infrared, or ultraviolet light. Now, LED has been widely used in outdoor signboards, brake lights, traffic signs and display devices. 
     In principle, an LED is a sandwich structure having an N-type semiconductor layer, an active layer and a P-type semiconductor layer, which are formed via depositing four elements-aluminum, gallium, indium and phosphor, or alternatively formed of another semiconductor material, such as GaP (gallium phosphide), GaAlAs (gallium aluminum arsenide), GaAs (gallium arsenide). LED has a PN structure and a unidirectional conductivity. LED is generally deposited on a GaAs substrate. However, GaAs is a light-absorptive material and absorbs a portion of light emitted by the LED epitaxial layer. Thus, the light generated by LED is not fully utilized, and the brightness thereof is decreased. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide a high-brightness LED structure and a method for fabricating the same. 
     The present invention proposes a high-brightness LED structure, which comprises a silicon substrate, a metal adhesion layer, a metal reflection layer, an N-type semiconductor layer, an active layer, and a P-type semiconductor layer, wherein the metal adhesion layer is stacked on the silicon substrate; the metal reflection layer is stacked on the metal adhesion layer; the N-type semiconductor layer is stacked on the metal reflection layer; the active layer is stacked on the N-type semiconductor layer; and the P-type semiconductor layer is stacked on the active layer. 
     The present invention also proposes a method for fabricating a high-brightness LED structure, which comprises steps: providing an N-type substrate; sequentially stacking on the N-type substrate a P-type semiconductor layer, an active layer, an N-type semiconductor layer and a metal reflection layer to form a first semi-product; preparing a silicon substrate; stacking a metal adhesion layer on the silicon substrate to form a second semi-product; bonding the metal reflection layer of the first semi-product to the metal adhesion layer of the second semi-product; and etching away the N-type substrate of the first semi-product to form the high-brightness LED structure of the present invention. 
     The present invention exempts the LED structure from using a light-absorptive GaAs substrate and uses the metal reflection layer to enhance light efficiency, whereby the generated light is fully utilized and the brightness is greatly increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of an LED structure according to the present invention; 
         FIG. 2A  is a sectional view of a first semi-product of the LED structure according to the present invention; 
         FIG. 2B  is a sectional view of a second semi-product of the LED structure according to the present invention; 
         FIG. 3  is a sectional view of the structure of the bonded first and second semi-products of the LED structure according to the present invention; 
         FIG. 4  is a sectional view of the structure of the bonded first and second semi-products shown in  FIG. 3  with the N-type substrate and the buffer layer removed according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Below, the technical contents of the present invention are described in detail with the embodiments. However, it should be understood that the embodiments are only to exemplify the present invention but not to limit the scope of the present invention. Refer to  FIG. 1 . The LED structure of the present invention comprises a silicon substrate  10 , a metal adhesion layer  20 , a metal reflection layer  21 , an N-type semiconductor layer  30 , an active layer  40 , and a P-type semiconductor layer  50 , wherein the metal adhesion layer  20  is stacked on the silicon substrate  10 ; the metal reflection layer  21  is stacked on the metal adhesion layer  20 ; and the N-type semiconductor layer  30  is stacked on the metal reflection layer  21 . The N-type semiconductor layer  30  is made of a material selected from the group consisting of GaAs (gallium arsenide), GaP (gallium phosphide), GaInAlP (gallium indium aluminum phosphide), InAlP (indium aluminum phosphide), or GaAlAs (gallium aluminum arsenide). 
     The active layer  40  is stacked on the N-type semiconductor layer  30 . The active layer  40  is a quantum well containing a period structure of GaInAlN (gallium indium aluminum nitride). The N-type semiconductor layer  30  includes an N-type cladding layer  31  and an N-type window layer  32 . The N-type window layer  32  contacts the metal reflection layer  21 , and the N-type cladding layer  31  contacts the active layer  40 . 
     The P-type semiconductor layer  50  is stacked on the active layer  40 . The P-type semiconductor layer  50  is made of a material selected from the group consisting of GaAs (gallium arsenide), GaP (gallium phosphide), GaInAlP (gallium indium aluminum phosphide), InAlP (indium aluminum phosphide), or GaAlAs (gallium aluminum arsenide). The P-type semiconductor layer  50  includes a P-type ohmic contact layer  51  and a P-type cladding layer  52 , and the P-type cladding layer  52  contacts the active layer  40 . A protection layer  60  is stacked on the P-type semiconductor layer  50 . The protection layer  60  is made of silicon dioxide or silicon nitride. A contact pad  70  penetrates the protection layer  60  to contact the P-type semiconductor layer  50 . 
     Refer to  FIG. 2A  and  FIG. 2B . The method for fabricating a high-brightness LED structure of the present invention comprises steps: providing an N-type substrate  90  with a buffer layer  91  stacked on the N-type substrate  90 , wherein the buffer layer  91  is of the P-type or N-type conductivity; and sequentially stacking on the buffer layer  91  of the N-type substrate  90  a P-type semiconductor layer  50 , an active layer  40 , an N-type semiconductor layer  30  and a metal reflection layer  21  to form a first semi-product A (shown in  FIG. 2A ), wherein the active layer  40  may be a quantum well containing a period structure of GaInAlN (gallium indium aluminum nitride), and wherein the P-type semiconductor layer  50  and N-type semiconductor layer  30  are made of a material selected from the group consisting of GaAs (gallium arsenide), GaP (gallium phosphide), GaInAlP (gallium indium aluminum phosphide), InAlP (indium aluminum phosphide), or GaAlAs (gallium aluminum arsenide). 
     In stacking the P-type semiconductor layer  50 , a P-type ohmic contact layer  51  is stacked firstly, and then a P-type cladding layer  52  is stacked. In stacking the N-type semiconductor layer  30 , an N-type cladding layer  31  is stacked firstly, and then an N-type window layer  32  is stacked. The method of the present invention also comprises steps: preparing a silicon substrate  10 ; and stacking a metal adhesion layer  20  on the silicon substrate  10  to form a second semi-product B (shown in  FIG. 2B ). 
     Refer to  FIG. 3  and  FIG. 4 . The method of the present invention also comprises steps: bonding the metal reflection layer  21  of the first semi-product A to the metal adhesion layer  20  of the second semi-product B; and etching away the N-type substrate  90  and the buffer layer  91  of the first semi-product A. 
     Refer to  FIG. 1  again. The method of the present invention may further comprise steps: stacking a protection layer  60  on the P-type semiconductor layer  50  of the first semi-product A, wherein the protection layer  60  is made of silicon dioxide or silicon nitride; and forming a contact pad  70  penetrating the protection layer  60  and contacting the P-type semiconductor layer  50 . 
     In conclusion, the present invention proposes a high-brightness LED structure and a method for fabricating the same, which needn&#39;t use a GaAs substrate, and which uses a metal reflection layer to reflect light. Therefore, the present invention can increase light efficiency and provide a high-brightness LED for users.