Light emitting device with enhanced optical scattering

• US 20040113163A1
• Filed: 12/11/2002
• Published: 06/17/2004
• Est. Priority Date: 12/11/2002
• Status: Active Grant

• Current Assignee: Lumileds LLC (Apollo Global Management, Inc.)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.)
• Inventors: Steigerwald, Daniel A., Bhat, Jerome C.
• Granted Patent: US 7,071,494 B2
• Time in Patent Office: Days
• US Class Current: 257/88
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers

Abstract

A light emitting device includes a substrate, a textured layer overlying the substrate, at least one III-nitride layer overlying the textured layer, and a substantially planar light emitting region. Devices incorporating scattering layers may be formed by several different methods. In a first method, an epitaxial layer is deposited then etched to form the textured layer. In a second method, a photomask is deposited and patterned to create openings in the photomask. The textured layer is then preferentially deposited in the openings formed in the photomask. In a third method, the textured layer is deposited under conditions that favor three-dimensional growth, then optionally annealed.

Claims

1. A light emitting device comprising:

a substrate;

a textured layer overlying the substrate;

at least one III-nitride layer overlying the textured layer; and

a substantially planar light emitting region.

2. The device of claim 1 wherein the textured layer is located between the substrate and the light emitting region.

3. The device of claim 1 wherein the textured layer overlies the light emitting region.

5. The device of claim 1 wherein the substrate has an index of refraction less than about 2.4.

6. The device of claim 1 wherein the substrate is sapphire.

7. The device of claim 1 wherein the textured layer is optically transparent.

8. The device of claim 1 wherein the at least one III-nitride layer is adjacent to a textured surface of the textured layer and wherein the textured layer and the at least one III-nitride layer have different indices of refraction.

9. The device of claim 1 wherein the index of refraction of the textured layer is less than an index of refraction of the at least one III-nitride layer.

10. The device of claim 1 wherein the textured layer is AlGaN.

11. The device of claim 1 wherein the textured layer is AlGaN having an Al composition between about 50% and about 100%.

12. The device of claim 1 wherein the textured layer is AlN.

13. The device of claim 1 wherein the textured layer has a cross section comprising an island.

14. The device of claim 13 wherein the island has a height between about 0.06 micron and about 10 microns.

15. The device of claim 13 wherein the island has a height between about 0.06 micron and about 1 micron.

16. The device of claim 13 wherein the island has a width between about 0.06 micron and about 10 microns.

17. The device of claim 13 wherein the island has a width between about 0.06 micron and about 1 micron.

18. The device of claim 1 wherein the textured layer is adjacent to the substrate.

19. The device of claim 1 further comprising a conformal layer overlying the textured layer, wherein the conformal layer is substantially conformal with the underlying textured layer.

20. The device of claim 1 further comprising a III-nitride layer disposed between the substrate and the textured layer.

21. The device of claim 1 wherein the textured layer comprises three-dimensional features having a dimension greater than or equal to about λ

_n/4, where λ

_n is a wavelength of light emitted by the light emitting region in the textured layer.

22. The device of claim 1 wherein the at least one III-nitride layer overlying the textured layer comprises a non-planar surface adjacent to the textured layer and a planar surface opposite the textured layer.

23. The device of claim 1 further comprising:

an n-type region;

a p-type region, wherein the light emitting region is disposed between the n-type region and the p-type region;

an n-contact formed on the n-type region;

a p-contact formed on the p-type region;

leads electrically connected to the n-contact and the p-contact; and

a cover disposed on a side of the substrate opposite the light emitting region.

24. A method of forming a light emitting device, the method comprising:

forming a textured layer overlying a substrate;

forming a substantially planar light emitting region overlying the substrate; and

forming at least one III-nitride layer overlying the textured layer.

25. The method of claim 24, wherein the textured layer is a III-nitride material.

26. The method of claim 24 wherein forming a textured layer comprises:

depositing a layer of epitaxial material; and

etching away a portion of the epitaxial material to form a three dimensional surface.

27. The method of claim 26 wherein etching away a portion of the epitaxial material comprises etching with an etchant selected from the group consisting of H₂, N₂, NH₃, HCl, and mixtures thereof.

28. The method of claim 24 wherein forming a textured layer comprises:

depositing a layer of III-nitride material; and

annealing the layer of III-nitride material.

29. The method of claim 28 further comprising etching away portions of the III-nitride material.

30. The method of claim 24 wherein forming a textured layer comprises:

depositing a mask layer over a substrate;

creating a plurality of openings in the mask layer;

depositing at least a portion of the textured layer in the openings in the mask layer.

31. The method of claim 30, wherein the mask layer is one of silicon dioxide, silicon nitride, and silicon oxynitride.

32. The method of claim 24, wherein the substrate is sapphire.

33. The method of claim 24, wherein forming a textured layer comprises depositing a three-dimensional layer of epitaxial material.