HIGH REFLECTIVITY MIRRORS AND METHOD FOR MAKING SAME

• US 20110049546A1
• Filed: 09/02/2009
• Published: 03/03/2011
• Est. Priority Date: 09/02/2009
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Li, Ting, HEIKMAN, STEN, Ibbetson, James, Jacob-Mitos, Matthew
• Granted Patent: US 9,362,459 B2
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: H01L 33/00 Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof H10K50/00 takes precedence; devices consisting of a plurality of semiconductor components formed in or on a common substrate and including semiconductor components having potential barriers, specially adapted for light emission H01L27/15; semiconductor lasers H01S5/00
• CPC Class Codes: H01L 33/0062 for devices with an active region comprising only III-V compounds
• CPC Class Codes: H01L 33/387 with a plurality of electrode regions in direct contact with the semiconductor body and being electrically interconnected by another electrode layer
• CPC Class Codes: H01L 33/405 Reflective materials
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector
• CPC Class Codes: H01L 33/60 Reflective elements

Abstract

A composite high reflectivity mirror (CHRM) with at least one relatively smooth interior surface interface. The CHRM includes a composite portion, for example dielectric and metal layers, on a base element. At least one of the internal surfaces is polished to achieve a smooth interface. The polish can be performed on the surface of the base element, on various layers of the composite portion, or both. The resulting smooth interface(s) reflect more of the incident light in an intended direction. The CHRMs may be integrated into light emitting diode (LED) devices to increase optical output efficiency.

Claims

1. A method for fabricating a highly reflective element, comprising:

providing a base element;

depositing at least one transparent dielectric layer on said base element, said at least one dielectric layer having a first index of refraction that is smaller than said base index of refraction;

depositing a reflective cap layer on said at least one transparent dielectric layer opposite said base element; and

polishing at least one internal surface of said highly reflective element.

2. The method of claim 1, wherein said polishing comprises polishing a surface of said base element such that said at least one transparent dielectric layer is on said base element polished surface.

3. The method of claim 1, wherein said at least one transparent dielectric layer comprises at least first and second materials.

4. The method of claim 3, said first material having said first index of refraction, said second material having a second index of refraction.

5. The method of claim 3, wherein depositing said at least one transparent dielectric layer further comprises depositing said first and second materials in alternating layers.

6. The method of claim 5, further comprising decreasing the thickness of said respective alternating layers with distance away from said base element such that a layer of said first material closer to said base element is thicker than a layer of said first material farther from said base element, and a layer of said second material closer to said base element is thicker than a layer of said second material farther from said base element.

7. The method of claim 5, further comprising polishing a surface of said first or second material between at least one pair of said alternating layers.

8. The method of claim 5, further comprising polishing multiple internal surfaces of said highly reflective element.

9. The method of claim 3, said first material comprising silicon dioxide (SiO₂).

10. The method of claim 9, said second material comprising tantalum pentoxide (Ta₂O₅) or titanium dioxide (TiO₂).

11. The method of claim 1, wherein said base element comprises a transparent current spreading layer.

12. The method of claim 1, wherein said base element comprises a layer of indium tin oxide (ITO).

13. The method of claim 1, where said polishing comprises exposing a surface of said base element to an etch process.

14. The method of claim 13, wherein said etch process comprises a plasma etch.

15. The method of claim 13, wherein said etch process comprises a reactive ion etch.

16. The method of claim 1, wherein said polishing is done ex-situ.

17. The method of claim 1, wherein said polishing is done in-situ.

18. A composite high reflectivity mirror (CHRM), comprising:

a base element;

at least one transparent dielectric layer on said base element; and

a reflective cap layer on said at least one transparent dielectric layer opposite said base element,

wherein at least one interior surface of said CHRM is polished.

19. The CHRM of claim 18, wherein said base element comprises a polished surface such that said at least one dielectric layer is on said polished surface.

20. The CHRM of claim 18, said base element comprising a transparent current spreading layer.

21. The CHRM of claim 18, said base element comprising a layer of indium tin oxide (ITO).

22. The CHRM of claim 18, said at least one transparent dielectric layer comprising a plurality of layers, at least one of said layers having a polished surface.

23. The CHRM of claim 18, wherein said at least one interior polished surface has a root mean square (RMS) roughness that is not more than approximately 2 nm.

24. The CHRM of claim 18, wherein said at least one interior polished surface has a root mean square (RMS) roughness that is not more than approximately 1 nm.

25. The CHRM of claim 18, said at least one transparent dielectric layer comprising first and second materials arranged in alternating layers on said base element.

26. The CHRM of claim 25, wherein a layer of said first material closer to said base element is thicker than a layer of said first material farther from said base element and a layer of said second material closer to said base element is thicker than a layer of said second material farther from said base element.

27. The CHRM of claim 25, said first material comprising silicon dioxide (SiO₂).

28. The CHRM of claim 27, said second material comprising tantalum pentoxide (Ta₂O₅) or titanium dioxide (TiO₂).

29. The CHRM of claim 18, said reflective cap layer comprising a metal.

30. A light emitting diode (LED), comprising:

a light emitting structure;

a current spreading layer on said light emitting structure comprising a polished surface;

at least one dielectric layer on said polished surface of said current spreading layer opposite said light emitting structure; and

a reflective cap layer on said at least one dielectric layer opposite said current spreading layer.

31. The LED of claim 30, said light emitting structure comprising an active region interposed between a p-type semiconductor layer and an n-type semiconductor layer.

32. The LED of claim 31, wherein said current spreading layer is on said p-type semiconductor layer opposite said active region.

33. The LED of claim 30, said light emitting structure comprising Group-III nitride materials.

34. The LED of claim 30, said current spreading layer polished surface having a root mean square (RMS) roughness of not more than 2 nm.

35. The LED of claim 30, said current spreading layer polished surface having an RMS roughness of not more than 1 nm.

36. The LED of claim 30, wherein said current spreading layer provides a reflectivity viewing angle cut-off above which said composite layer reflectivity is approximately 100%.

37. The LED of claim 36, wherein said at least one dielectric layer provides improved reflectivity below said viewing angle cut-off compared to a composite layer without said at least one dielectric layer.

38. The LED of claim 30, said at least one transparent dielectric layer comprising first and second materials arranged in alternating layers on said base element.

39. The LED of claim 38, wherein a layer of said first material closer to said base element is thicker than a layer of said first material farther from said base element and a layer of said second material closer to said base element is thicker than a layer of said second material farther from said base element.

40. The LED of claim 38, said first material comprising silicon dioxide (SiO₂).

41. The LED of claim 40, said second material comprising tantalum pentoxide (Ta₂O₅).

42. The LED of claim 40, said second material comprising titanium dioxide (TiO₂).

43. The LED of claim 30, further comprising conductive vias through said at least one dielectric layer.

44. The LED of claim 30, said light emitting structure comprising:

at least two oppositely doped semiconductor layers;

an active region interposed between said at least two oppositely doped semiconductor layers; and

a substrate disposed such that said current spreading layer is on said substrate.

45. The LED of claim 30, said reflective cap layer comprising a metal.

46. The LED of claim 30, said reflective cap layer comprising a conductive material and electrically contacting said current spreading layer.

47. The LED of claim 30, said reflective cap layer comprising at least one conductive via through said at least one dielectric layer to said current spreading layer.