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

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 H 2 O 2 , K 2 S 2 O 8 .

2. The method of claim 1 , wherein the acid solution comprises one or more of H 2 SO 4 , HF, HCl, H 3 PO 4 , HNO 3 , and CH 3 COOH.

3. The method of claim 1 , wherein the alkaline solution comprises one or the mixture of KOH, NaOH, and NH 4 OH.

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/cm 2 .

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 H 2 SO 4 , HF, HCl, H 3 PO 4 , HNO 3 , and CH 3 COOH.

18. The method of claim 16 , wherein the alkaline solution comprises one or the mixture of KOH, NaOH, and NH 4 OH.