Highly efficient gallium nitride based light emitting diodes via surface roughening

• US 8,766,296 B2
• Filed: 10/08/2009
• Issued: 07/01/2014
• Est. Priority Date: 12/09/2003
• Status: Expired due to Term

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Japan Science And Technology Agency, Regents of the University of California (University of California)
• Inventors: Fujii, Tetsuo, Gao, Yan, Hu, Evelyn L., Nakamura, Shuji
• Primary Examiner(s): Jackson, Jr., Jerome
• Application Number:
  US12/576,122
• Publication Number:
  US 20100025717A1
• Time in Patent Office: 1,727 Days
• Field of Search: 257/95
• US Class Current: 257/95
• CPC Class Codes: H01L 2224/16225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 33/00 Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof H10K50/00 takes precedence; devices consisting of a plurality of semiconductor components formed in or on a common substrate and including semiconductor components having potential barriers, specially adapted for light emission H01L27/15; semiconductor lasers H01S5/00
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/0093 Wafer bonding; Removal of the growth substrate
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/50 Wavelength conversion elements
• CPC Class Codes: H01L 33/54 having a particular shape
• CPC Class Codes: H01L 33/60 Reflective elements

Abstract

A gallium nitride (GaN) based light emitting diode (LED), wherein light is extracted through a nitrogen face (N-face) of the LED and a surface of the N-face 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 is roughened by an anisotropic etching, which may comprise a dry etching or a photo-enhanced chemical (PEC) etching.

Claims

1. A (B, Al, Ga, In)N light emitting diode (LED), comprised of:

at least an n-type layer, an emitting layer, and a p-type layer;

wherein light from the emitting layer is extracted through a nitrogen face (N-face) surface of the LED and the N-face surface of the LED is comprised of structures that increase extraction efficiency of the light out of the N-face surface of the LED;

wherein the structures comprise a plurality of etched cones; and

wherein the etched cones have a size not smaller than a wavelength of the light extracted from the N-face surface.

2. The LED of claim 1, wherein the light from the emitting layer is extracted through the N-face surface of a layer other than the emitting layer of the LED.

3. The LED of claim 2, wherein the light from the emitting layer is extracted through the N-face surface of the n-type layer of the LED.

4. The LED of claim 3, wherein the LED is further comprised of a p-type electrode on the p-type layer, and the p-type electrode has a property of high reflection to increase light reflection toward the N-face surface of the n-type layer.

5. The LED of claim 3, wherein the LED is further comprised of an n-type electrode 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 is avoided and the extraction efficiency of the light is increased.

6. The LED of claim 1, wherein the etched cones are hexagonal shaped cones that have an angle equal to or smaller than:

2 sin<sup>−

1</sup>(n_air/n_s)

where n_air is a refractive index of air and n_s is a refractive index of the N-face surface.

7. The LED of claim 1, wherein the etched cones are hexagonal shaped cones that have an angle equal to or smaller than:

2 sin <sup>−

1</sup>(n_enc/n_s) ,

where n_enc is a refractive index of an epoxy deposited on the N-face surface and n_s is a refractive index of the N-face surface.

8. The LED of claim 1, wherein the n-type layer, the emitting layer and the p-type layer are each comprised of a (B, Al, Ga, In)N alloy.

9. The LED of claim 1, wherein the extraction efficiency of the light out of the N-face surface of the LED is increased by more than 100% as compared to the N-face surface without the structures.

10. The LED of claim 1, wherein the light does not show any cavity mode, interference effects, or longitudinal modes caused by a cavity formed along a growth direction of the LED.

11. The LED of claim 1, wherein the LED includes a current-confining frame made of an insulator to restrain leakage current through sidewalls of the LED without significantly decreasing an emitting area.

12. The LED of claim 1, wherein the LED is mounted on a high thermal conductivity material.

30. The LED of claim 1, wherein the LED includes a substrate, and the N-face surface is structured after being exposed by removing the substrate from the LED.

32. The LED of claim 1, wherein the LED includes a GaN substrate, and the N-face surface is the N-face surface of the GaN substrate.

13. 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; and

structuring a nitrogen face (N-face) surface of the LED, in order to increase extraction efficiency of the light out of the N-face surface of the LED;

wherein the structures comprised a plurality of etched cones; and

wherein the etched cones have a size not smaller than a wavelength of the light extracted from the N-face surface.

14. The method of claim 13, wherein the N-face surface of the LED is structured using an anisotropic etching.

15. The method of claim 14, wherein the anisotropic etching is a dry etching.

16. The method of claim 14, wherein the anisotropic etching is a wet etching.

17. The method of claim 16, wherein the wet etching is a photo-enhanced chemical (PEC) etching.

18. The method of claim 13, wherein the structuring of the N-face surface of the LED comprises roughening or patterning the N-face surface of the LED.

19. The method of claim 13, wherein the light from the emitting layer is extracted through the N-face surface of a layer other than the emitting layer of the LED.

20. The method of claim 19, wherein the light from the emitting layer is extracted through the N-face surface of the n-type layer of the LED.

21. The method of claim 20, wherein the LED is further comprised of a p-type electrode on the p-type layer, and the p-type electrode has a property of high reflection to increase light reflection toward the N-face surface of the n-type layer.

22. The method of claim 20, wherein the LED is further comprised of an n-type electrode 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 is avoided and the extraction efficiency of the light is increased.

23. The method of claim 13, wherein the etched cones are hexagonal shaped cones that have an angle equal to or smaller than:

2 sin<sup>−

1</sup>(n_air/n_s )

where n_air is a refractive index of air and n_s is a refractive index of the N-face surface.

24. The method of claim 13, wherein the etched cones are hexagonal shaped cones that have an angle equal to or smaller than:

2 sin<sup>−

1</sup>(n_enc/n_s)

where n_enc is a refractive index of an epoxy deposited on the N-face surface and n_s is a refractive index of the N-face surface.

25. The method of claim 13, wherein the n-type layer, the emitting layer and the p-type layer are each comprised of a (B, Al, Ga, In)N alloy.

26. The method of claim 13, wherein the extraction efficiency of the light out of the N-face surface of the LED is increased by more than 100% as compared to the N-face surface without the structures.

27. The method of claim 13, wherein the light does not show any cavity mode, interference effects, or longitudinal modes caused by a cavity formed along a growth direction of the LED.

28. The method of claim 13, wherein the LED includes a current-confining frame made of an insulator to restrain leakage current through sidewalls of the LED without significantly decreasing an emitting area.

29. The method of claim 13, wherein the LED is mounted on a high thermal conductivity material.

31. The method of claim 13, wherein the LED includes a substrate, and the N-face surface is exposed before structuring by removing the substrate from the LED.

33. The method of claim 13, wherein the LED includes a GaN substrate, and the N-face surface is the N-face surface of the GaN substrate.