Light-emitting diode with increased light extraction

• US 8,552,451 B2
• Filed: 08/01/2011
• Issued: 10/08/2013
• Est. Priority Date: 01/11/2005
• Status: Expired due to Fees

• Current Assignee: Semileds Optoelectronics Company Limited (SemiLEDs Inc)
• Original Assignee: Semileds Optoelectronics Company Limited (SemiLEDs Inc)
• Inventors: Doan, Trung Tri, Tran, Chuong Anh
• Primary Examiner(s): AHMED, SELIM U
• Application Number:
  US13/195,742
• Publication Number:
  US 20110284867A1
• Time in Patent Office: 799 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:

a p-doped layer;

an active layer on the p-doped layer configured to emit light;

an n-doped layer on the active layer; and

a light extracting element on the n-doped layer comprising a plurality of balls in an electrically conductive transparent coating and the n-doped layer is in direct contact with the coating;

the balls having a density in the coating selected to provide a plurality of empty regions and a spatially varying index of refraction, the light extracting element configured to scatter some of the light emitted by the active layer while the empty regions reflect some of the light emitted by the active layer.

2. The LED-device of claim 1 wherein the balls are configured to effectively roughen a surface of the n-doped layer.

3. The LED device of claim 2 wherein the plurality of balls comprise a plurality of polymer spheres.

4. The LED device of claim 2 wherein a refractive index of the balls is between approximately 2.0 and 3.0.

5. The LED device of claim 2 wherein the coating comprises a material selected from the group consisting of indium tin oxide (ITO) and Ni/Au.

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

a p-doped layer;

an active layer on the p-doped layer configured to emit light;

an n-doped layer disposed above on the active layer having a surface; and

a light extracting element on the surface configured to effectively roughen the n-doped layer, the light extracting element comprising a plurality of balls in an electrically conductive transparent coating and the n-doped layer is in direct contact with the coating;

the balls having a density in the coating selected to provide a plurality of empty regions, the light extracting element having a spatially varying index of refraction with the balls configured to scatter some of the light emitted by the active layer while the empty regions reflect some of the light emitted by the active layer.

7. The LED device of claim 6 wherein the density is selected to optimize a tradeoff between a brightness and electrical properties of the LED device.

8. The LED device of claim 6 wherein the n-doped layer has a thickness in a range from about 2 microns to about 6 microns and wherein the p-doped layer has a thickness in a range from about 0.05 microns to about 0.5 microns.

9. The LED device of claim 6 wherein both the n-doped layer and the p-doped layer comprises gallium nitride (GaN).

10. The LED device of claim 6 wherein the coating comprises a material selected from the group consisting of indium tin oxide (ITO) and Ni/Au.

11. The LED device of claim 6 wherein the coating comprises a material greater than 80% transparent to a wavelength of the emitted light.

12. The LED device of claim 6 wherein the coating comprises Ni/Au.

13. The LED device of claim 6 wherein the balls have a radius between approximately 10 mm and about 2 microns.

14. The LED device of claim 6 wherein a dimension of the balls scatters light at approximately λ

/2.

15. The LED device of claim 6 wherein a refractive index of the balls is approximately 2.4.

16. The LED device of claim 6 wherein a refractive index of the balls is approximately equal to a refractive index of the n-doped layer.

17. The LED device of claim 6 wherein the balls comprise a material selected from the group consisting of a polymer, TiO₂, Ta₂O, ZrO, ZnO, HfO₂, GaN, MN, ZnSe, Of and SiO_xN_y.