Light emitting diode dielectric mirror

• US 9,461,201 B2
• Filed: 06/04/2013
• Issued: 10/04/2016
• Est. Priority Date: 11/14/2007
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Heikman, Sten, Ibbetson, James
• Primary Examiner(s): YUSHIN, NIKOLAY K
• Application Number:
  US13/909,927
• Publication Number:
  US 20130341634A1
• Time in Patent Office: 1,218 Days
• Field of Search: 257/76, 257/79, 257/98
• US Class Current: 1/1
• CPC Class Codes: H01L 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/38 with a particular shape
• CPC Class Codes: H01L 33/405 Reflective materials
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector

Abstract

A high efficiency LED chip is disclosed that comprises an active LED structure comprising an active layer between two oppositely doped layers. A first reflective layer can be provided adjacent to one of the oppositely doped layers, with the first layer comprising a material with a different index of refraction than the active LED structure. The difference in IR between the active LED structure and the first reflective layer increases TIR of light at the junction. In some embodiments the first reflective layer can comprise an IR lower than the semiconductor material, increasing the amount of light that can experience TIR. Some embodiments of LED chips according to the present invention can also comprise a second reflective layer or metal layer on and used in conjunction with the first reflective layer such that light passing through the first reflective layer can be reflected by the second reflective layer.

Claims

1. A light emitting diode (LED) chip, comprising:

an active LED structure comprising an active layer between two oppositely doped layers, and said active layer emitting light in response to an electrical signal applied to said oppositely doped layer;

a first reflective layer adjacent one of said oppositely doped layers, and comprising an index of refraction different than said active LED structure, said first reflective layer reflecting at least some active layer light;

a second reflective layer on said first reflective layer, said second reflective layer reflecting light not reflected by said first reflective layer;

a barrier layer on said second reflective layer; and

a passivation layer on a substantial portion of said barrier layer, wherein said passivation layer is electrically insulating.

2. The LED chip of claim 1, wherein said first reflective layer comprises a dielectric material.

3. The LED chip of claim 1, wherein said first reflective layer comprises SiO₂, SiN, Si, Ge, MgOx, MgNx, ZnO, SiNx, SiOx, AlN and alloys or combinations thereof.

4. The LED chip of claim 1, wherein said first reflective layer comprises SiO₂.

5. The LED chip of claim 1, wherein said second reflective layer comprises a metal.

6. The LED chip of claim 1, wherein said second reflective layer comprises Ag.

7. The LED chip of claim 1, further comprising a current spreading layer between said first reflective layer and said active LED structure.

8. The LED chip of claim 7, wherein said current spreading layer comprises ITO.

9. The LED chip of claim 7, wherein said current spreading layer comprises a thickness of less than 1000 Å

.

10. The LED chip of claim 7, wherein said current spreading layer comprises a thickness in the range of 50 to 300 Å

.

11. The LED chip of claim 1, further comprising an adhesion layer between said first reflective layer and said second reflective layer.

12. The LED chip of claim 1, wherein said first reflective layer comprises an index or refraction that is at least 50% different than the active LED structure'"'"'s index of refraction.

13. The LED chip of claim 1, wherein said first reflective layer comprises an index of refraction that is lower than the active LED structure'"'"'s index of refraction.

14. The LED chip of claim 1, wherein said barrier layer extends beyond said second reflective layer on at least one side.

15. The LED chip of claim 14, wherein a contact is on at least a portion of said barrier layer which extends beyond said second reflective layer.

16. The LED chip of claim 1, wherein said passivation layer is on a substantial portion of a top or bottom surface of said barrier layer.

17. The LED chip of claim 1, wherein said passivation layer is on a substantial portion of a top surface of said barrier layer.

18. A light emitting diode (LED) chip, comprising:

an active LED structure comprising an active layer between a p-type layer and an n-type layer, said active layer emitting light in response to an electrical signal applied to said p-type and n-type layers;

a current spreading layer on said p-type layer;

a dielectric first reflective layer on said current spreading layer, said dielectric first reflective layer reflecting at least some active layer light;

a metal layer on said dielectric first reflective layer, said metal layer reflecting light not reflected by said dielectric first reflective layer;

a barrier layer on said metal layer; and

a passivation layer on a substantial portion of a top or bottom surface of said barrier layer, wherein said passivation layer is electrically insulating.

19. The LED chip of claim 18, wherein said dielectric first reflective layer comprises an index of refraction different than said active LED structure.

20. The LED chip of claim 18, wherein said dielectric first reflective layer comprises an index of refraction less than said active LED structure.

21. The LED chip of claim 18, wherein said dielectric first reflective layer comprises an index of refraction up to 50% less than said active LED structure.

22. The LED chip of claim 18, wherein said dielectric first reflective layer comprises an index of refraction up to 40% less than said active LED structure.

23. The LED chip of claim 18, wherein said active LED structure comprises a Group-III nitride, and said dielectric first reflective layer comprises SiO₂.

24. The LED chip of claim 18, wherein said dielectric first reflective layer is at least 0.2 μ

m thick.

25. The LED chip of claim 18, wherein said metal layer comprises Ag.

26. The LED chip of claim 18, wherein said current spreading layer comprises ITO.

27. The LED chip of claim 18, further comprising an adhesion layer between said dielectric first reflective layer and said metal layer.

28. The LED chip of claim 18, wherein said metal layer extends beyond said reflective layer on at least one side.

29. The LED chip of claim 28, wherein a contact is on at least a portion of said barrier layer which extends beyond said metal layer.

30. The LED chip of claim 18, wherein said passivation layer is on a substantial portion of a top surface of said barrier layer.

31. A light emitting diode (LED) chip, comprising:

an active LED structure emitting light in response to an electrical signal;

a first reflective layer on said active LED structure;

a second reflective layer on said first reflective layer, both positioned to reflect LED structure light so that it contributes to use LED chip emission;

a barrier layer on said second reflective layer;

a passivation layer on a substantial portion of said barrier layer, wherein said passivation layer is electrically insulating; and

vias through said first reflective layer to conduct an electrical signal through said first reflective layer to said active LED structure.

32. The LED chip of claim 31, wherein said first reflective layer comprises an index of refraction less than said active LED structure.

33. The LED chip of claim 32, wherein said first reflective layer comprises an index of refraction that is up to 50% less than said active LED structure.

34. The LED chip of claim 31, further comprising a current spreading layer between said first reflective layer and said active LED structure.

35. The LED chip of claim 31, wherein said second reflective layer comprises a metal.

36. The LED chip of claim 31, further comprising an adhesion layer between said first reflective layer and said second reflective layer.

37. The LED chip of claim 31, wherein said barrier layer extends beyond said second reflective layer on at least one side.

38. The LED chip of claim 37, wherein a contact is on at least a portion of said barrier layer which extends beyond said second reflective layer.

39. The LED chip of claim 31, wherein said passivation layer is on a substantial portion of a top or bottom surface of said barrier layer.

40. The LED chip of claim 31, wherein said passivation layer is on a substantial portion of a top surface of said barrier layer.