Highly efficient gallium nitride based light emitting diodes via surface roughening

• US 20070121690A1
• Filed: 12/09/2003
• Published: 05/31/2007
• Est. Priority Date: 12/09/2003
• Status: Active Grant

• Current Assignee: Japan Science & Technology Trading Co. Limited
• Original Assignee: Japan Science & Technology Trading Co. Limited
• Inventors: Nakamura, Shuji, Fujii, Tetsuo, Gao, Yan, Hu, Evelyn
• Granted Patent: US 7,704,763 B2
• Time in Patent Office: Days
• US Class Current: 372/43.10
• 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) (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.

Claims

1. A gallium nitride (GaN) based light emitting diode (LED), wherein light is extracted through a nitrogen fare (N-face) of the LED and a surface of the N-face is roughened.

2. The GaN LED of claim 1, wherein the surface of the N-face is roughened into one or more cones.

3. The GaN LED of claim 1, wherein the roughened surface reduces light reflections occurring repeatedly inside the LED, and thus extracts more light out of the LED.

4. The GaN LED of claim 1, wherein the surface of the N-face is roughened by an anisotropic etching.

5. The GaN LED of claim 4, wherein the anisotropic etching is a dry etching.

6. The GaN LED of claim 4, wherein the anisotropic etching is a photo-enhanced chemical (PEC) etching.

7. The GaN LED of claim 1, wherein the N-face is an n-type layer of the GaN LED.

8. The GaN LED of claim 1, wherein the N-face is prepared by a laser lift off (LLO) technique.

9. The GaN LED of claim 1, wherein the LED is grown on a c-plane GaN wafer and a gallium face (Ga-face) is a p-type layer.

10. The GaN LED of claim 1, wherein the LED is comprised of an n-type electrode, n-type layer, active region, p-type layer and p-type electrode.

11. The GaN LED of claim 10, wherein the n-type layer, active region and p-type layer are each comprised of a (B, Al, Ga, In) N alloy.

12. The GaN LED of claim 10, wherein the p-type electrode has a property of high reflection to decrease light absorption and to increase light reflection toward the surface of the n-type layer.

13. The GaN LED of claim 10, wherein the LED includes a current-blocking layer aligned under the n-type electrode to keep the current from concentrating below the n-type electrode, so that absorption of light emission under the n-type electrode can be avoided and extraction efficiency can be increased.

14. The GaN LED of claim 10, 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.

15. The GaN LED of claim 2, wherein the roughened surface is comprised of a plurality of hexagonal shaped cones that have an angle equal to or smaller than:

2 sin<sup>−

1</sup>(n_air/n_s)≈

47.2°

for GaN, where n_air is a refractive index of air and n_s is a refractive index of GaN.

16. The GaN LED of claim 2, wherein the roughened surface is comprised of a plurality of hexagonal shaped cones that have an angle equal to or smaller than:

2 sin<sup>−

1</sup>(n_enc/n_s)

for epoxy, where n_enc is a refractive index of epoxy and n_s is a refractive index of GaN.

17. A method of creating a gallium nitride (GaN) based light emitting diode (LED), wherein light is extracted through a nitrogen face (N-face) of the LED, comprising:

roughening a surface of the N-face into one or more cones.

18. A light emitting diode (LED) comprised of an n-type electrode, n-type layer, active region, p-type layer and p-type electrode, wherein a surface of the n-type layer is roughened by an anisotropic etching into one or more cones and light is extracted through the roughened surface of the n-type layer.