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

• US 7,186,580 B2
• Filed: 01/11/2005
• Issued: 03/06/2007
• Est. Priority Date: 01/11/2005
• Status: Active Grant

• Current Assignee: SemiLEDs Corporation (SemiLEDs Inc)
• Original Assignee: SemiLEDs Corporation (SemiLEDs Inc)
• Inventors: Tran, Chuong Anh, Doan, Trung Tri
• Primary Examiner(s): Le, Dung A.
• Application Number:
  US11/032,880
• Publication Number:
  US 20060154391A1
• Time in Patent Office: 784 Days
• Field of Search: 257 94- 95, 438/22, 438/48
• US Class Current: 438/22
• CPC Class Codes: H01L 33/0095 Post-treatment of devices, e.g. annealing, recrystallisation or short-circuit elimination
• 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-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 of fabricating a semiconductor light emitting diode (LED) device, comprising:

forming an n-gallium nitride (n-GaN) layer on the LED device; and

roughening the surface of the n-GaN layer, via a photoelectrochemical (PEC) oxidation and etching method, to form non-ordered textured surfaces to enhance light extraction from an interior of the LED device;

wherein,

the oxidation and etching is performed in a system with;

an aqueous solution, an illumination system, and an electrical biased system,

the aqueous solution comprises a combination of an oxidizing agent and either acid or alkaline solutions, and

the oxidizing agent comprises one or the combination of H₂O₂, K₂S₂O₈.

2. The method of claim 1, wherein the acid solution comprises one or more of H₂SO₄, HF, HCl, H₃PO₄, HNO₃, and CH₃COOH.

3. The method of claim 1, wherein the alkaline solution comprises one or the mixture of KOH, NaOH, and NH₄OH.

4. The method of claim 1, further comprising illuminating the LED with an Hg or Xe arc lamp system with wavelength ranging among visible and ultra-violet spectrum.

5. The method of claim 4, wherein the illumination is exposed on the n-GaN with an intensity less than 200 mW/cm².

6. The method of claim 1, wherein the n-GaN is over a conductive substrate and the method further comprises:

applying an electrical bias to the conductive substrate; and

controlling the voltage between −

5 and +5 V.

7. The method of claim 1, further comprising varying the constitution of the aqueous solution, the electrical biased, and the illumination intensity.

8. A method of roughening an exposed n-GaN of an n-side up LED wafer, the method comprising:

depositing an n-GaN portion above a carrier substrate;

depositing active layers above the n-GaN portion;

depositing a p-GaN portion above the active layers;

depositing one or more first metal layers;

applying a masking layer;

etching the first metal layers, the p-GaN portion, the active layers, and the n-GaN portion;

removing the masking layer;

depositing a passivation layer;

removing a portion of the passivation layer on top of the p-GaN portion to expose the first metal layers;

depositing one or more second metal layers;

depositing a metal substrate;

removing the carrier substrate to expose the n-GaN portion; and

roughening the n-GaN portion.

9. The method of claim 8, wherein the n-GaN up LED wafer is substantially smooth and flat before said roughening.

10. The method of claim 9, wherein the n-GaN up LED wafer has a surface roughness of less than 5000 angstrom before said roughening.

11. The method of claim 8, wherein the carrier substrate is sapphire.

12. The method of claim 8, wherein the metal substrate is deposited using one of:

electro-chemical plating, electroless chemical plating, sputtering, chemical vapor deposition, e-beam evaporation and thermal spray.

13. The LED wafer of claim 8, wherein the metal substrate is a metal or metal alloy comprising one of Copper, nickel, aluminum, Ti, Ta, Mo, W.

14. The method of claim 8, wherein the carrier substrate is removed using one of:

laser lift-off (LLO), wet etching, chemical mechanical polish.

15. The method of claim 8, wherein the roughening process is using one of wet, dry etching, patterning on the n-GaN surface.

16. The method of claim 15, wherein the wet etching is performed using either an acid or alkaline solution.

17. The method of claim 16, wherein the acid solution comprises one or more of H₂SO₄, HF, HCl, H₃PO₄, HNO₃, and CH₃COOH.

18. The method of claim 16, wherein the alkaline solution comprises one or the mixture of KOH, NaOH, and NH₄OH.