Light-emitting diode with increased light extraction

• US 8,008,678 B2
• Filed: 07/15/2008
• Issued: 08/30/2011
• 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): Pert, Evan
• Assistant Examiner(s): AHMED, SELIM U
• Application Number:
  US12/173,662
• Publication Number:
  US 20090014743A1
• Time in Patent Office: 1,141 Days
• Field of Search: 257 94-103, 257 76- 82, 257 13- 19, 257/E33.068, 257/E33.074
• US Class Current: 257/98
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/42 Transparent materials

Abstract

Methods are disclosed for forming a vertical semiconductor light-emitting diode (VLED) device having an active layer between an n-doped layer and a p-doped layer; and securing a plurality of balls on a surface of the n-doped layer of the VLED device.

Claims

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

an n-doped layer;

an active layer for emitting light adjacent the n-doped layer;

a p-doped layer adjacent the active layer;

a metal substrate adjacent the p-doped layer;

a plurality of balls disposed above a surface of the n-doped layer; and

an optically transparent and electrically conductive contact layer disposed above the plurality of balls and configured such that a bias applied across the p-doped layer and the n-doped layer generates light that is emitted through the n-doped layer and emitted to the ambient via the contact layer.

2. The LED device of claim 1, wherein the n-doped layer is at least about four times thicker than the p-doped layer.

3. The LED device of claim 1, wherein:

the n-doped layer has a thickness in a range from about 2 microns to about 6 microns; and

the p-doped layer has a thickness in a range from about 0.05 microns to about 0.5 microns.

4. The LED device of claim 1, wherein both the n-doped layer and the p-doped layer include gallium nitride (GaN).

5. The LED device of claim 1, wherein the surface of the n-doped layer is roughened.

6. The LED device of claim 1, wherein the contact layer is greater than 80% transparent to the wavelength of the emitted light.

7. The LED device of claim 1, wherein the contact layer comprises at least one of indium tin oxide (ITO), nickel, and gold.

8. The LED device of claim 1, wherein one of the balls comprises a sub-micron sphere.

9. The LED device of claim 1, wherein one of the balls has a radius between approximately 10 nm and about 2 micron.

10. The LED device of claim 1, wherein a dimension of the balls scatters light at approximately ½

λ

.

11. The LED device of claim 1, wherein a refractive index of one of the balls is greater than approximately 2.3.

12. The LED device of claim 1, wherein a refractive index of one of the balls is approximately equal to a refractive index of the n-doped layer.

13. The LED device of claim 1, wherein one of the balls comprises at least one of TiO₂, Ta₂O₅, ZrO, ZnO, HfO₂, GaN, AlN, ZnSe, and SiO_xN_y.

21. The method of claim 1, wherein the contact layer is configured such that the bias applied across the p-doped layer and the n-doped layer generates light that is emitted through the n-doped layer, scattered by the plurality of balls, and emitted to the ambient via the contact layer.

14. A vertical light-emitting diode (VLED) device comprising:

an active layer between an n-doped layer and a p-doped layer, wherein both the n-doped layer and the p-doped layer include gallium nitride (GaN);

a metal substrate adjacent the p-doped layer;

a plurality of balls for light extraction disposed above a surface of the n-doped layer; and

an optically transparent and electrically conductive contact layer disposed above the plurality of balls and configured such that a bias applied across the p-doped layer and the n-doped layer generates light that is emitted through the n-doped layer and emitted to the ambient via the contact layer.

15. The VLED device of claim 14, wherein the n-doped layer is at least about four times thicker than the p-doped layer.

16. The VLED device of claim 14, wherein the surface of the n-doped layer is roughened.

17. The VLED device of claim 14, wherein each of the balls comprises a sub-micron sphere having a refractive index approximately equal to that of the n-doped layer.

18. The VLED device of claim 14, wherein one of the balls comprises at least one of TiO₂, Ta₂O₅, ZrO, ZnO, HfO₂, GaN, AlN, ZnSe, and SiO_xN_y.

19. The VLED device of claim 14, wherein a refractive index of one of the balls is between approximately 2.0 and 3.0.

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

an n-doped layer, wherein a surface of the n-doped layer is roughened;

an active layer for emitting light adjacent the n-doped layer;

a p-doped layer adjacent the active layer, wherein the n-doped layer is at least about four times thicker than the p-doped layer and wherein both the n-doped layer and the p-doped layer include gallium nitride (GaN);

a metal substrate adjacent the p-doped layer;

a plurality of balls disposed above the roughened surface of the n-doped layer; and

an optically transparent and electrically conductive contact layer disposed above the plurality of balls and configured such that a bias applied across the p-doped layer and the n-doped layer generates light that is emitted through the n-doped layer and emitted to the ambient via the contact layer.