High light extraction efficiency nitride based light emitting diode by surface roughening

• US 8,835,200 B2
• Filed: 01/12/2012
• Issued: 09/16/2014
• Est. Priority Date: 11/30/2007
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Zhong, Hong, Tyagi, Anurag, Vampola, Kenneth J., Speck, James S., DenBaars, Steven P., Nakamura, Shuji
• Primary Examiner(s): Lebentritt, Michael
• Application Number:
  US13/349,342
• Publication Number:
  US 20120104412A1
• Time in Patent Office: 978 Days
• Field of Search: 438/29, 438/46, 257/98, 257/103, 257/E33.025, 257/67, 257/74
• US Class Current: 438/29
• CPC Class Codes: H01L 21/02433 Crystal orientation
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 2933/0083 Periodic patterns for optical field-shaping in or on the semiconductor body or semiconductor body package, e.g. photonic bandgap structures
• CPC Class Codes: H01L 33/0075 comprising nitride compounds
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/18 within the light emitting region
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

A III-nitride light emitting diode (LED) and method of fabricating the same, wherein at least one surface of a semipolar or nonpolar plane of a III-nitride layer of the LED is textured, thereby forming a textured surface in order to increase light extraction. The texturing may be performed by plasma assisted chemical etching, photolithography followed by etching, or nano-imprinting followed by etching.

Claims

1. A method for fabricating a III-nitride light emitting diode (LED), comprising:

texturing at least one surface of a III-nitride substrate of the LED that is oriented along a semipolar or nonpolar plane to form a textured surface for increasing light extraction efficiency through the textured surface, further comprising creating at least one feature on the textured surface with at least one sloped sidewall, which transmits the light into an external medium at an interface and reflects the light at the interface, wherein the reflected light, after undergoing subsequent reflections inside the feature, has an increased incidence angle at the interface and consequently an increased chance of being transmitted to the external medium.

2. The method of claim 1, wherein:

the III-nitride light emitting diode (LED) is comprised of the III-nitride substrate, an n-type III-nitride layer formed on or above the III-nitride substrate, an active III-nitride layer that emits light formed on or above the n-type III-nitride layer, and a p-type III-nitride layer formed on or above the active III-nitride layer; and

the textured surface is a backside surface of the III-nitride substrate opposite the n-type III-nitride layer, the active III-nitride layer, and the p-type III-nitride layer.

3. The method of claim 1, wherein the III-nitride substrate is a freestanding gallium nitride (GaN) substrate.

4. The method of claim 1, wherein the texturing is performed by etching and the etching is a plasma-assisted chemical etching.

5. The method of claim 1, wherein the textured surface is comprised of conical features.

6. The method of claim 5, wherein the conical features are truncated conical features.

7. The method of claim 6, wherein the conical features have sloped sidewalls and a concavity formed on top of each conical feature.

8. The method of claim 7, wherein the conical features have geometries that include a sidewall inclination angle, cone diameters, and a height of the cone, as well as a number density of the conical features, that are tailored for increasing the light extraction efficiency.

9. The method of claim 1, wherein the texturing is performed by etching and the etching is a photo-enhanced chemical (PEC) etching.

10. The method of claim 1, wherein the textured surface is comprised of triangular pyramid features.

11. The method of claim 10, wherein the triangular pyramid features have at least a c-polar (0001) surface and an m-face [1-100] surface.

16. The device of claim 1, wherein the textured surface is comprised of conical features.

17. The device of claim 16, wherein the conical features are truncated conical features.

18. The device of claim 17, wherein the conical features have sloped sidewalls and a concavity formed on top of each conical feature.

19. The device of claim 18, wherein the conical features have geometries that include a sidewall inclination angle, cone diameters, and a height of the cone, as well as a number density of the conical features, that are tailored for increasing the light extraction efficiency.

12. A device comprising a III-nitride light emitting diode (LED), wherein at least one surface of a III-nitride substrate of the LED oriented along a semipolar or nonpolar plane comprises a textured surface for increasing light extraction efficiency through the textured surface, further comprising at least one feature created on the textured surface with at least one sloped sidewall, which transmits the light into an external medium at an interface and reflects the light at the interface, wherein the reflected light, after undergoing subsequent reflections inside the feature, has an increased incidence angle at the interface and consequently an increased chance of being transmitted to the external medium.

13. The device of claim 12, wherein:

the III-nitride light emitting diode (LED) is comprised of the III-nitride substrate, an n-type III-nitride layer formed on or above the III-nitride substrate, an active III-nitride layer that emits light formed on or above the n-type III-nitride layer, and a p-type III-nitride layer formed on or above the active III-nitride layer; and

the textured surface is a backside surface of the III-nitride substrate opposite the n-type III-nitride layer, the active III-nitride layer, and the p-type III-nitride layer.

14. The device of claim 12, wherein the III-nitride substrate is a freestanding gallium nitride (GaN) substrate.

15. The device of claim 12, wherein the textured surface is an etched surface and the etched surface is a plasma-assisted chemical etched surface.

20. The device of claim 12, wherein the textured surface is an etched surface and the etched surface is a photo-enhanced chemical (PEC) etched surface.

21. The device of claim 12, wherein the textured surface is comprised of triangular pyramid features.

22. The device of claim 21, wherein the triangular pyramid features have at least a c-polar (0001) surface and an m-face [1-100] surface.