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

• US 9,040,326 B2
• Filed: 08/11/2014
• Issued: 05/26/2015
• 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:
  US14/456,768
• Publication Number:
  US 20140346542A1
• Time in Patent Office: 288 Days
• Field of Search: 438/29, 438/52, 438/80, 438/96, 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 light emitting device, comprising:

a III-nitride light emitting diode (LED) comprised of an active III-nitride layer that emits light formed between n-type and p-type III-nitride layers, wherein;

the III-nitride layers are semi-polar or non-polar III-nitride layers;

at least one surface of the LED is a textured surface;

the textured surface is comprised of at least one conical feature having at least one sloped sidewall that reflects or transmits at least one light ray incident thereon from inside the conical feature; and

the sidewall is inclined, such that each time the light ray is reflected, there is an increased chance of the light ray being transmitted through the sidewall.

2. The device of claim 1, wherein:

the textured surface forms an interface with an external medium;

the conical feature with the sloped sidewall transmits the light ray into the external medium at the interface and reflects the light ray at the interface; and

the reflected light ray, after undergoing subsequent reflections inside the conical feature, has an increased incidence angle at the interface and consequently an increased chance of being transmitted to the external medium.

3. The device of claim 2, wherein the external medium has a refractive index less than the III-nitride layers.

4. The device of claim 1, wherein:

the sidewall is inclined, such that each time the light ray is reflected, an angle of incidence of the light ray relative to a surface normal of the sidewall decreases;

when the angle of incidence of the light ray is smaller than a critical angle, the light ray'"'"'s transmission through the sidewall is increased; and

when the angle of incidence of the light ray is at least equal to the critical angle, the light ray is reflected by the sidewall.

5. The device of claim 4, wherein the sidewall is inclined such that the light ray escapes the conical feature when the angle of incidence is near normal.

6. The device of claim 1, wherein the conical features tile up most of the textured surface.

7. The device of claim 1, wherein the LED includes a substrate, and the textured surface is a surface of the substrate opposite the LED'"'"'s growth front.

8. The device of claim 1, wherein the light is extracted from both sides of the LED.

9. A method for fabricating a light emitting device, comprising:

creating a III-nitride light emitting diode (LED) comprised of a III-nitride active layer that emits light formed between n-type and p-type III-nitride layers, wherein;

the III-nitride layers are semi-polar or non-polar III-nitride layers;

at least one surface of the LED is a textured surface;

the textured surface is comprised of at least one conical feature having at least one sloped sidewall that reflects or transmits at least one light ray incident thereon from inside the conical feature; and

the sidewall is inclined, such that each time the light ray is reflected, there is an increased chance of the light ray being transmitted through the sidewall.

10. The method of claim 9, wherein:

the textured surface forms an interface with an external medium;

the conical feature with the sloped sidewall transmits the light ray into the external medium at the interface and reflects the light ray at the interface; and

the reflected light ray, after undergoing subsequent reflections inside the conical feature, has an increased incidence angle at the interface and consequently an increased chance of being transmitted to the external medium.

11. The method of claim 10, wherein the external medium has a refractive index less than the III-nitride layers.

12. The method of claim 9, wherein:

the sidewall is inclined, such that each time the light ray is reflected, an angle of incidence of the light ray relative to a surface normal of the sidewall decreases;

when the angle of incidence of the light ray is smaller than a critical angle, the light ray'"'"'s transmission through the sidewall is increased; and

when the angle of incidence of the light ray is at least equal to the critical angle, the light ray is reflected by the sidewall.

13. The method of claim 12, wherein the sidewall is inclined such that the light ray escapes the conical feature when the angle of incidence is near normal.

14. The method of claim 9, wherein the conical features tile up most of the textured surface.

15. The method of claim 9, wherein the LED includes a substrate, and the textured surface is a surface of the substrate opposite the LED'"'"'s growth front.

16. The method of claim 9, wherein the light is extracted from both sides of the LED.

17. The method of claim 9, wherein the textured surface is formed by photolithography or nano-imprinting followed by etching.

18. The method of claim 9, wherein the textured surface is formed using a plasma assisted chemical etching.

19. The method of claim 9, wherein the textured surface is formed using a photo-enhanced chemical (PEC) etching.

20. A method for emitting light, comprising:

emitting light from a III-nitride light emitting diode (LED) comprised of a III-nitride active layer formed between n-type and p-type III-nitride layers, wherein;

the III-nitride layers are semi-polar or non-polar III-nitride layers;

at least one surface of the LED is a textured surface;

the textured surface is comprised of at least one conical feature having at least one sloped sidewall that reflects or transmits at least one light ray incident thereon from inside the conical feature; and

the sidewall is inclined, such that each time the light ray is reflected, there is an increased chance of the light ray being transmitted through the sidewall.