Electrode structures for LEDs with increased active area

Abstract

An electrode structure is disclosed for enhancing the brightness and/or efficiency of an LED. The electrode structure can have a metal electrode and an optically transmissive thick dielectric material formed intermediate the electrode and a light emitting semiconductor material. The electrode and the thick dielectric cooperate to reflect light from the semiconductor material back into the semiconductor so as to enhance the likelihood of the light ultimately being transmitted from the semiconductor material. Such LED can have enhanced utility and can be suitable for uses such as general illumination. The semiconductor material can have a cutout formed therein and a portion of the electrode can be formed outside of the cutout and a portion of the electrode can be formed inside of the cutout. The portion of the electrode outside the cutout can be electrically isolated from the semiconductor material by the dielectric material.

I claim: 
     
       1. An electrode structure for an LED, the electrode structure comprising:
 a semiconductor material having a cutout formed therein; 
 an electrically insulating porous dielectric material; 
 a metal electrode; 
 at least one pair of dielectric layers configured so as to define a DBR structure and disposed between a portion of the metal electrode and a portion of the dielectric material, wherein each pair of dielectric layers of the DBR structure is substantially optically transmissive, is comprised of layers of materials of different indices of refraction, and is a multiple of approximately ¼λ thick; and 
 wherein a portion of the electrode is formed outside of the cutout and a portion of the electrode is formed inside of the cutout, 
 wherein the portion of the electrode outside the cutout is electrically isolated from the semiconductor material by the dielectric material, and 
 wherein the portion of the electrode inside the cutout is in electrical contact with the semiconductor material. 
 
     
     
       2. The electrode structure as recited in  claim 1 , wherein the dielectric material is optically transmissive, having an index of refraction greater than or equal to one and less than that of a semiconductor upon which the dielectric material is formed, and having a thickness greater than ½λ, the dielectric material being formed to the electrode so as to enhance reflection of light. 
     
     
       3. The electrode structure as recited in  claim 1 , wherein the dielectric material has a thickness of approximately 1.75λ. 
     
     
       4. The electrode structure as recited in  claim 1 , wherein:
 the electrode is formed upon the semiconductor material; 
 the dielectric material is formed intermediate at least a portion of the electrode and the semiconductor material; and 
 the semiconductor material comprises at least one material selected from the group consisting of: 
 AlGaAs; 
 AlInGaP; 
 AlInGaN; and 
 GaAsP. 
 
     
     
       5. The electrode structure as recited in  claim 1 , wherein the dielectric material comprises at least one material selected from the group consisting of:
 silicon dioxide; 
 silicon monoxide; 
 MgF 2 ; 
 siloxane polymers; and 
 air. 
 
     
     
       6. The electrode structure as recited in  claim 1 , further comprising an ohmic contact layer formed between the electrode and a semiconductor. 
     
     
       7. The electrode structure as recited in  claim 1 , wherein the dielectric material comprises porous ITO. 
     
     
       8. The electrode structure as recited in  claim 1 , wherein the dielectric material comprises porous SiO 2 . 
     
     
       9. The electrode structure as recited in  claim 1 , wherein the dielectric material is porous enough to reduce its effective index of refraction such that total internal reflection occurs within the semiconductor material. 
     
     
       10. An electrode structure for an LED, the electrode structure comprising:
 a semiconductor material having a cutout formed therein; 
 an electrically insulating porous dielectric material layer comprising ITO; and 
 a metal electrode, wherein 
 a portion of the electrode is formed outside of the cutout and a portion of the electrode is formed inside of the cutout, 
 the portion of the electrode outside the cutout is electrically isolated from the semiconductor material by the dielectric material layer, and 
 the portion of the electrode inside the cutout is in electrical contact with the semiconductor material. 
 
     
     
       11. The electrode structure as recited in  claim 10 , wherein the dielectric material is optically transmissive, having an index of refraction greater than or equal to one and less than that of a semiconductor upon which the dielectric material is formed, and having a thickness greater than ½λ, the dielectric material being formed to the electrode so as to enhance reflection of light. 
     
     
       12. The electrode structure as recited in  claim 10 , wherein the dielectric material has a thickness of approximately 1.75λ. 
     
     
       13. The electrode structure as recited in  claim 10 , wherein:
 the electrode is formed upon the semiconductor material; 
 the dielectric material is formed intermediate at least a portion of the electrode and the semiconductor material; and 
 the semiconductor material comprises at least one material selected from the group consisting of: 
 AlGaAs; 
 AlInGaP; 
 AlInGaN; and 
 GaAsP. 
 
     
     
       14. The electrode structure as recited in  claim 10 , wherein the dielectric material comprises at least one material selected from the group consisting of:
 silicon dioxide; 
 silicon monoxide; 
 MgF 2 ; 
 siloxane polymers; and 
 air. 
 
     
     
       15. The electrode structure as recited in  claim 10 , further comprising an ohmic contact layer formed between the electrode and a semiconductor. 
     
     
       16. The electrode structure as recited in  claim 10 , wherein the dielectric material further comprises porous SiO 2 . 
     
     
       17. The electrode structure as recited in  claim 10 , wherein the dielectric material is porous enough to reduce its effective index of refraction such that total internal reflection occurs within the semiconductor material. 
     
     
       18. The electrode structure as recited in  claim 10 , further comprising at least one pair of dielectric layers configured so as to define a DBR structure and disposed between a portion of the electrode and a portion of the dielectric, wherein each pair of dielectric layers of the DBR structure is substantially optically transmissive, is comprised of layers of materials of different indices of refraction, and is a multiple of approximately ¼λ thick. 
     
     
       19. An electrode structure for an LED emitting a light having a center wavelength of λ, the electrode structure comprising:
 an optically transmissive layer including a dielectric layer and formed on a p-type gallium nitride semiconductor layer, the optically transmissive layer further including a porous ITO layer as an ohmic contact layer for the p-type gallium nitride semiconductor layer; and 
 a metal p-electrode formed on the dielectric layer, the metal p-electrode having a wiring bond pad portion and an extension portion extending from the wiring bond pad portion, 
 wherein the dielectric layer has an index of refraction greater than or equal to one and less than that of the p-type gallium nitride semiconductor layer and has a thickness greater than ½λ, and 
 wherein the metal p-electrode partially covers the dielectric layer in a top view so that the dielectric layer is formed out of outline of the wiring bond pad portion of the metal p-electrode in the top view. 
 
     
     
       20. The electrode structure as recited in claim 19, wherein the dielectric layer is formed directly on the p-type gallium nitride semiconductor layer. 
     
     
       21. The electrode structure as recited in claim 19, wherein the dielectric layer is formed out of outline of the extension portion of the metal p-electrode in the top view. 
     
     
       22. The electrode structure as recited in claim 19, wherein the dielectric layer comprises a silicon dioxide layer. 
     
     
       23. The electrode structure as recited in claim 19, wherein the dielectric layer comprises a porous SiO 2  layer. 
     
     
       24. The electrode structure as recited in claim 19, further comprising a metal n-electrode, wherein the metal p-electrode is formed at a first corner of the top surface of the LED, and the metal n-electrode is formed at a second corner diagonal to the first corner. 
     
     
       25. The electrode structure as recited in claim 19, wherein the dielectric layer is porous enough to reduce its effective index of refraction such that total internal reflection occurs within the p-type gallium nitride semiconductor layer. 
     
     
       26. The electrode structure as recited in claim 19, wherein two lines of the dielectric layer are formed out of outline of the metal p-electrode. 
     
     
       27. The electrode structure as recited in claim 19, wherein three lines of the dielectric layer are formed out of outline of the metal p-electrode. 
     
     
       28. The electrode structure as recited in claim 19, wherein the dielectric layer is formed under the extension portion of the metal p-electrode. 
     
     
       29. The electrode structure as recited in claim 19, wherein the dielectric layer comprises a layer formed of at least one material selected from the group consisting of:
 silicon dioxide;   silicon monoxide;   MgF 2 ;   siloxane polymers; and   air.   
     
     
       30. An electrode structure for a light emitting device, the electrode structure comprising:
 a semiconductor layer having a cutout formed therein;   an electrically insulating dielectric layer disposed on the semiconductor layer;   a metal electrode disposed on a first portion of the electrically insulating dielectric layer;   at least one pair of dielectric layers configured so as to define a DBR structure and disposed between the metal electrode and the first portion of the electrically insulating dielectric layer, wherein each pair of dielectric layers of the DBR structure is substantially optically transmissive, and is comprised of layers of materials of different indices of refraction; and   wherein a portion of the metal electrode is disposed outside of the cutout and a portion of the metal electrode is disposed inside of the cutout,   wherein the portion of the metal electrode outside the cutout is electrically isolated from the semiconductor layer by the first portion of the electrically insulating dielectric layer, and   wherein the portion of the metal electrode inside the cutout is in electrical contact with the semiconductor layer.   
     
     
       31. The electrode structure as recited in claim 30, wherein each pair of the dielectric layers of the DBR structure comprises a niobium oxide layer and a silicon oxide layer. 
     
     
       32. The electrode structure as recited in claim 30, wherein the first portion of the electrically insulating dielectric layer is thicker than each pair of dielectric layers of the DBR structure. 
     
     
       33. The electrode structure as recited in claim 30, further comprising an ITO layer disposed between the first portion of electrically insulating dielectric layer and the semiconductor layer. 
     
     
       34. The electrode structure as recited in claim 30, wherein each pair of the dielectric layers of the DBR structure is a multiple of approximately ¼λ thick, where λ is a wavelength of light incident on the DBR structure. 
     
     
       35. The electrode structure as recited in claim 30, wherein the electrically insulating dielectric layer is optically transmissive, having an index of refraction greater than or equal to one and less than that of the semiconductor layer upon which the electrically insulating dielectric layer is formed, and having a thickness greater than ½λ, where λ is a wavelength of light incident on the DBR structure, the electrically insulating dielectric layer being formed to the metal electrode so as to enhance reflection of light. 
     
     
       36. The electrode structure as recited in claim 30, wherein the electrically insulating dielectric layer has a thickness of approximately 1.75λ, where λ is a wavelength of light incident on the DBR structure. 
     
     
       37. The electrode structure as recited in claim 30, wherein:
 the metal electrode is formed upon the semiconductor layer;   the electrically insulating dielectric layer is formed intermediate at least a portion of the metal electrode and the semiconductor layer; and   the semiconductor layer comprises at least one material selected from the group consisting of:   AlGaAs;   AlInGaP;   AlInGaN; and   GaAsP.   
     
     
       38. The electrode structure as recited in claim 30, wherein the electrically insulating dielectric layer comprises at least one material selected from the group consisting of:
 silicon dioxide;   silicon monoxide;   MgF 2 ;   siloxane polymers; and   air.   
     
     
       39. The electrode structure as recited in claim 30, further comprising an ohmic contact layer formed between the metal electrode and the semiconductor layer. 
     
     
       40. The electrode structure as recited in claim 30, wherein the electrically insulating dielectric layer comprises porous SiO 2 . 
     
     
       41. The electrode structure as recited in claim 30, wherein the electrically insulating dielectric layer is porous enough to reduce its effective index of refraction such that total internal reflection occurs within the semiconductor layer. 
     
     
       42. The electrode structure as recited in claim 30, wherein a portion of the metal electrode constitutes an n-side electrode of the light emitting device. 
     
     
       43. The electrode structure as recited in claim 42, further comprising a p-side metal electrode disposed on a second portion of an electrically insulating dielectric layer. 
     
     
       44. The electrode structure as recited in claim 43, further comprising at least one pair of dielectric layers configured so as to define a DBR structure and disposed between the p-side metal electrode and the second portion of the electrically insulating dielectric layer, wherein each pair of dielectric layers of the DBR structure is substantially optically transmissive, and is comprised of layers of materials of different indices of refraction.