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Highly efficient group-III nitride based light emitting diodes via fabrication of structures on an N-face surface achieved

Foreign code F110003758
File No. E06704WO
Posted date Jul 4, 2011
Country United States of America
Application number 58194003
Gazette No. 20070121690
Gazette No. 7704763
Date of filing Dec 9, 2003
Gazette Date May 31, 2007
Gazette Date Apr 27, 2010
International application number US2003039211
International publication number WO2005064666
Date of international filing Dec 9, 2003
Date of international publication Jul 14, 2005
Priority data
  • 2003WO-US39211 (Dec 9, 2003) WO
Title Highly efficient group-III nitride based light emitting diodes via fabrication of structures on an N-face surface achieved
Abstract (US7704763)
A gallium nitride (GaN) based light emitting diode (LED), wherein light is extracted through a nitrogen face (N-face) (42) of the LED and a surface of the N-face (42) is roughened into one or more hexagonal shaped cones.
The roughened surface reduces light reflections occurring repeatedly inside the LED, and thus extracts more light out of the LED.
The surface of the N-face (42) is roughened by an anisotropic etching, which may comprise a dry etching or a photo-enhanced chemical (PEC) etching.
Scope of claims [claim1]
1. A method of creating a (B, Al, Ga, In)N light emitting diode (LED), comprising: fabricating at least an n-type layer, an emitting layer and a p-type layer of the (B, Al, Ga, In)N LED on a substrate;
exposing a nitrogen face (N-face) surface of the n-type layer by removing the substrate from the layers; and
etching the N-face surface of the n-type layer after the substrate is removed to create a plurality of cones having a size not smaller than 200 nm to increase extraction efficiency of light from the emitting layer out of the N-face surface as compared to the N-face surface without the cones.
[claim2]
2. The method of claim 1, wherein the N-face surface of the n-type layer is etched using an anisotropic etching.
[claim3]
3. The method of claim 2, wherein the anisotropic etching is a dry etching.
[claim4]
4. The method of claim 2, wherein the anisotropic etching is a wet etching.
[claim5]
5. The method of claim 4, wherein the wet etching is a photo-enhanced chemical (PEC) etching.
[claim6]
6. The method of claim 1, wherein the etching of the N-face surface comprises roughening or patterning the N-face surface.
[claim7]
7. The method of claim 1, wherein the etched N-face surface reduces light reflections occurring repeatedly inside the LED, and thus extracts more light out of the LED.
[claim8]
8. The method of claim 1, wherein the substrate is removed by a laser lift off (LLO) technique.
[claim9]
9. The method of claim 1, wherein the substrate is a c-plane GaN wafer.
[claim10]
10. The method of claim 1, wherein a p-type electrode is fabricated on the p-type layer and the p-type electrode has a property of high reflection to decrease light absorption and to increase light reflection toward the N-face surface of the n-type layer.
[claim11]
11. The method of claim 1, wherein an n-type electrode is fabricated on the n-type layer and a current-blocking layer is aligned under the n-type electrode to keep current from concentrating below the n-type electrode, so that absorption of the light under the n-type electrode can be avoided and extraction efficiency of the light can be increased.
[claim12]
12. The method of claim 1, wherein the LED includes a current-confining frame made of an insulator to restrain leakage current through the sidewalls of the LED without significantly decreasing an emitting area.
[claim13]
13. The method of claim 1, wherein the cones are hexagonal shaped cones that have an angle equal to or smaller than:
2 sin-1(nair/ns)
where nair is a refractive index of air and ns is a refractive index of the n-type layer.
[claim14]
14. The method of claim 1, wherein the cones are hexagonal shaped cones that have an angle equal to or smaller than:
2 sin-1(nenc/ns),
where nenc is a refractive index of an epoxy deposited on the etched N-face surface and ns is a refractive index of the n-type layer.
  • Inventor, and Inventor/Applicant
  • FUJII TETSUO
  • GAO YAN
  • HU EVELYN L
  • NAKAMURA SHUJI
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
IPC(International Patent Classification)
Reference ( R and D project ) ERATO NAKAMURA Inhomogeneous Crystal AREA
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