Light emitting diodes (LEDs) with improved light extraction by roughening

• US 7,897,420 B2
• Filed: 12/14/2007
• Issued: 03/01/2011
• Est. Priority Date: 01/11/2005
• Status: Active Grant

• Current Assignee: Semileds Optoelectronics Company Limited (SemiLEDs Inc)
• Original Assignee: Semileds Optoelectronics Company Limited (SemiLEDs Inc)
• Inventors: Chu, Chen-Fu, Cheng, Hao-Chun, Fan, Feng-Hsu, Liu, Wen-Huang, Cheng, Chao-Chen
• Primary Examiner(s): Lee, Calvin
• Application Number:
  US11/956,962
• Publication Number:
  US 20080142814A1
• Time in Patent Office: 1,173 Days
• Field of Search: 438/22, 438/29, 438/42, 438/48, 257 88- 98, 257/E21.125, 257/E21.216
• US Class Current: 438/29
• CPC Class Codes: H01L 33/0095 Post-treatment of devices, e.g. annealing, recrystallisation or short-circuit elimination
• CPC Class Codes: H01L 33/08 with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body H01L27/15 takes precedence
• 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

Abstract

Systems and methods are disclosed for fabricating a semiconductor light-emitting diode (LED) device by forming an n-doped gallium nitride (n-GaN) layer on the LED device and roughening the surface of the n-GaN layer to extract light from an interior of the LED device.

Claims

1. A method comprising:

applying a mask to a surface of a light-emitting diode (LED) wafer;

etching the surface of the LED wafer such that protuberances remain on the etched surface, wherein lateral surfaces of the protuberances form an angle of greater than 90°

with the etched surface of the LED wafer; and

roughening or texturing the etched surface of the LED wafer including the protuberances.

2. The method of claim 1, wherein the mask comprises at least one of Ni, SiO₂, Si₃N₄, and photoresist.

3. The method of claim 1, wherein the mask comprises a plurality of hollow nubs, the nubs shaped as at least one of domes, cuboids, prisms, or cylinders.

4. The method of claim 1, wherein etching the surface of the LED wafer comprises at least one of wet etching, photoenhanced wet etching, and dry etching.

5. The method of claim 1, wherein roughening or texturing the etched surface of the LED wafer comprises at least one of wet etching, photoenhanced wet etching, dry etching, and applying objects to the etched surface including upper surfaces and the lateral surfaces of the protuberances.

6. The method of claim 5, wherein applying objects to the etched surface of the LED wafer comprises applying polystyrene spheres.

7. A method comprising:

providing a light-emitting diode (LED) wafer assembly, comprising;

a conductive substrate;

a p-doped layer disposed above the conductive substrate;

an active layer disposed above the p-doped layer;

an n-doped layer disposed above the active layer;

applying a mask to a surface of the n-doped layer;

etching the surface of the n-doped layer such that protuberances remain on the etched surface, wherein lateral surfaces of the protuberances form an angle of greater than 90°

with the etched surface of the n-doped layer; and

roughening or texturing the etched surface of the n-doped layer including the protuberances.

8. The method of claim 7, wherein the mask comprises a plurality of hollow nubs, the nubs shaped as at least one of domes, cuboids, prisms, or cylinders.

9. The method of claim 7, wherein roughening or texturing the etched surface of the n-doped layer including the protuberances comprises at least one of wet etching, photoenhanced wet etching, dry etching, and applying objects to the etched surface of the n-doped layer including upper surfaces and the lateral surfaces of the protuberances.

10. The method of claim 7, wherein the conductive substrate comprises a single layer or multiple layers of at least one of Cu, Ni, Ni—

Co, Ag, Au, Cu—

Co, Cu—

Mo, Ni/Cu, Cu/Ni—

Co/Cu, Cu/Ni—

Co/Cu/Ni—

Co, and Ni/Cu—

Mo.

11. The method of claim 7, wherein the LED wafer assembly comprises a reflective layer disposed between the conductive substrate and the p-doped layer.

12. The method of claim 7, wherein roughening the etched surface of the n-doped layer including the protuberances comprises:

immersing the etched surface of the n-doped layer including the protuberances in an electrolytic solution;

applying an electrical bias to the conductive substrate; and

illuminating the surface such that photoelectrochemical (PEC) oxidation and etching occurs to roughen the etched surface of the n-doped layer including upper surfaces and the lateral surfaces of the protuberances.

13. The method of claim 12, wherein the electrolytic solution can be a combination of an oxidizing agent and either an acid or an alkaline solution.

14. The method of claim 13, wherein the oxidizing agent comprises at least one of H₂O₂ and K₂S₂O₈.

15. The method of claim 13, wherein the acid solution comprises at least one of H₂SO₄, HF, HCl, H₃PO₄, HNO₃, and CH₃COOH.

16. The method of claim 13, wherein the alkaline solution comprises KOH, NaOH, NH₄OH, or combinations thereof.