LIGHT EMITTING DIODES (LEDS) WITH IMPROVED LIGHT EXTRACTION BY ROUGHENING

• US 20070099319A1
• Filed: 12/21/2006
• Published: 05/03/2007
• Est. Priority Date: 01/11/2005
• Status: Active Grant

• Current Assignee: Foshan Nationstar Semiconductor Co., Ltd. (Foshan Nationstar Optoelectronics Company Limited)
• Original Assignee: Chuong Tran, Trung Doan
• Inventors: Doan, Trung, Tran, Chuong
• Granted Patent: US 7,473,936 B2
• Time in Patent Office: Days
• 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 system for roughening a surface of a light-emitting diode (LED) wafer comprising epitaxial layers disposed on a conductive substrate via a photo-electrochemical (PEC) oxidation and etching process, the system comprising:

an electrolytic solution disposed within a container;

a support for the LED wafer positioned within the electrolytic solution;

a voltage source for applying a bias potential to the conductive substrate of the LED wafer;

a reference electrode for providing a reference voltage for the voltage source; and

a light source to trigger a reaction at the electrolytic solution and the epitaxial layers to roughen the surface of the LED wafer.

2. The system of claim 1, wherein the electrolytic solution can be a combination of an oxidizing agent and either an acid or an alkaline solution.

3. The system of claim 2, wherein the oxidizing agent comprises at least one of H₂O₂ and K₂S₂O₈.

4. The system of claim 2, wherein the acid solution comprises at least one of H₂SO₄, HF, HCI, H₃PO₄, HNO₃, and CH₃COOH.

5. The system of claim 2, wherein the alkaline solution comprises one or the mixture of KOH, NaOH, and NH₄OH.

6. The system of claim 1, wherein the voltage source is a variable voltage source.

7. The system of claim 1, wherein the bias potential is within a range from −

10 V to +10 V.

8. The system of claim 1, wherein the reference electrode comprises a platinum wire, a silver wire, or a saturated calomel electrode (SCE).

9. The system of claim 1, wherein the light source is a variable light source.

10. The system of claim 1, wherein the light source comprises an Hg or Xe arc lamp with wavelength ranging among the visible and ultraviolet (UV) spectrum.

11. The system of claim 1, wherein the composition of the electrolytic solution, the bias potential of the voltage source, and/or the intensity of the light source can be varied to roughen the surface of the LED wafer according to an oxidation-dominant or an etch-dominant PEC process.

12. A light-emitting diode (LED) device, comprising:

a conductive substrate;

a p-doped layer disposed above the conductive substrate;

an active layer for emitting light disposed above the p-doped layer; and

an n-doped layer disposed above the active layer, wherein a surface of the n-doped layer has been roughened via a photo-electrochemical (PEC) oxidation and etching method, the roughened surface having a non-ordered texture.

13. The LED device of claim 12, further comprising a conductive contact disposed above the n-doped layer, wherein the contact is used as a mask during the PEC oxidation and etching method.

14. The LED device of claim 12, wherein the dimension of the roughened surface is selected to optimally scatter light at approximately one half of the wavelength (λ

/2) of the emitted light.

15. The LED device of claim 12, wherein the root-mean-square (RMS) value of the surface roughness ranges from 0.05 μ

m to 2 μ

m.

16. The LED device of claim 12, wherein the effective refractive index of the roughened surface is approximately 2.0 to 2.5.

17. The LED device of claim 12, further comprising a reflective layer disposed between the conductive substrate and the p-doped layer.

18. The LED device of claim 17, wherein the reflective layer comprises at least one of Ni, Au, Pt, Cr, Ti, Pd, and Ag.

19. A method of fabricating a light-emitting diode (LED) device having a roughened surface for scattering light, the method comprising:

depositing an n-doped layer above a carrier substrate;

depositing an active layer for emitting light above the n-doped layer;

depositing a p-doped layer above the active layer;

forming a conductive substrate above the p-doped layer;

removing the carrier substrate to expose the n-doped layer;

immersing a surface of the n-doped layer in an electrolytic solution;

applying an electrical bias to the conductive substrate; and

illuminating the surface of the n-doped layer such that photo-electrochemical (PEC) oxidation and etching occurs to form the roughened surface of the LED device on the n-doped layer.

20. The method of claim 19, further comprising forming a conductive contact on the n-doped layer, wherein the conductive contact acts as a mask during the PEC oxidation and etching.

21. The method of claim 19, wherein the electrolytic solution can be a combination of an oxidizing agent and either an acid or an alkaline solution.

22. The method of claim 21, wherein the oxidizing agent comprises at least one of H₂O₂ and K₂S₂O₈.

23. The method of claim 21, wherein the acid solution comprises at least one of H₂SO₄, HF, HCI, H₃PO₄, HNO₃, and CH₃COOH.

24. The method of claim 21, wherein the alkaline solution comprises one or the mixture of KOH, NaOH, and NH₄OH.

25. The method of claim 19, wherein the electrical bias ranges from −

10 V to +10 V.