# US 9,040,326 B2 · High light extraction efficiency nitride based light emitting diode by surface roughening

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- Number: US 9,040,326 B2
- Document ID: US9040326B2
- Status: Granted
- Kind: B2
- Application number: 14/456,768
- Filed: 2014-08-11
- Published: 2014-11-27
- Granted: 2015-05-26
- Earliest claimed: 2007-11-30
- Assignees: The Regents of the University of California
- Applicants: The Regents of the University of California
- Inventors: Hong Zhong; Anurag Tyagi; Kenneth J. Vampola; James S. Speck; Steven P. DenBaars; Shuji Nakamura
- Web page: https://patentgrep.com/patent/US9040326B2

## CPC

- H10H 20/82: Roughened surfaces, e.g. at the interface between epitaxial layers
- H10H 20/0137: {the light-emitting regions comprising nitride materials}
- H10H 20/814: having reflecting means, e.g. semiconductor Bragg reflectors
- H10H 20/825: containing nitrogen, e.g. GaN
- H10P 14/2926: {Crystal orientations}
- H10P 14/3216: {Nitrides}
- H10H 20/818: within the light-emitting regions
- H10H 20/819: characterised by their shape, e.g. curved or truncated substrates
- H10H 20/872: {Periodic patterns for optical field-shaping, e.g. photonic bandgap structures}
- H10H: INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## 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

### Claim 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.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 2)

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

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 4)

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.

### Claim 6 (depends on 1)

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

### Claim 7 (depends on 1)

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.

### Claim 8 (depends on 1)

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

### Claim 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.

### Claim 10 (depends on 9)

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.

### Claim 11 (depends on 10)

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

### Claim 12 (depends on 9)

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.

### Claim 13 (depends on 12)

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.

### Claim 14 (depends on 9)

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

### Claim 15 (depends on 9)

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.

### Claim 16 (depends on 9)

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

### Claim 17 (depends on 9)

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

### Claim 18 (depends on 9)

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

### Claim 19 (depends on 9)

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

### Claim 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.