Highly efficient gallium nitride based light emitting diodes via surface roughening

• US 10,446,714 B2
• Filed: 05/19/2014
• Issued: 10/15/2019
• Est. Priority Date: 12/09/2003
• 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: Fujii, Tetsuo, Gao, Yan, Hu, Evelyn L., Nakamura, Shuji
• Primary Examiner(s): Ahmadi, Mohsen
• Application Number:
  US14/281,535
• Publication Number:
  US 20140252396A1
• Time in Patent Office: 1,975 Days
• 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:

a plurality of (B, Al, Ga, In)N layers including at least an active region having an emitting layer positioned between an n-type layer and a p-type layer;

wherein light from the emitting layer is extracted through a nitrogen face (N-face) surface of the n-type layer, and the N-face surface of the n-type layer is comprised of a plurality of etched cone structures having a size not smaller than a wavelength of the light within the LED to increase extraction efficiency of the light from the emitting layer out of the N-face surface as compared to the N-face surface without the etched cone structures.

2. The LED of claim 1, wherein the etched cone structures comprise photo-enhanced chemical (PEC) etched cone structures.

3. The LED of claim 1, wherein the etched cone structures comprise 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.

4. The LED of claim 1, further comprising a p-type electrode on the p-type layer, wherein the p-type electrode has a property of high reflection to increase light reflection toward the N-face surface.

5. The LED of claim 1, further comprising an n-type electrode on the n-type layer, wherein 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, further comprising one or more solder metals deposited on the (B, Al, Ga, In)N layers, wherein the solder metals include gold (Au) and tin (Sn).

7. A method of creating a (B, Al, Ga, In)N light emitting diode (LED), comprised of:

fabricating a plurality of (B, Al, Ga, In)N layers including at least an active region having an emitting layer positioned between an n-type layer and a p-type layer;

exposing a nitrogen face (N-face) surface of the n-type layer by removing a substrate, wherein light from the emitting layer is extracted through the N-face surface of the n-type layer; and

etching the N-face surface of the n-type layer after the substrate is removed to create a plurality of etched cone structures having a size not smaller than a wavelength of the light within the LED to increase extraction efficiency of the light from the emitting layer out of the N-face surface as compared to the N-face surface without the etched cone structures.

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

at least an active region having an emitting layer positioned between an n-type layer and a p-type layer, and a p-type electrode on the p-type layer;

wherein light from the emitting layer is extracted through a nitrogen face (N-face) surface of the n-type layer and the N-face surface of the n-type layer is comprised of a plurality of etched cone structures having a size not smaller than a wavelength of the light within the LED to increase extraction efficiency of the light from the emitting layer out of the N-face surface as compared to the N-face surface without the etched cone structures; and

wherein the p-type electrode has a property of high reflection to increase light reflection towards the N-face surface.

9. The LED of claim 8, wherein the LED is further comprised of a solder metal which comprises gold (Au).

10. The LED of claim 9, wherein the solder metal is a gold-tin (Au—

Sn).

11. The LED of claim 8, 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.

12. The LED of claim 8, wherein the etched cone structures comprise 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.