Composite high reflectivity layer

• US 7,915,629 B2
• Filed: 12/08/2008
• Issued: 03/29/2011
• Est. Priority Date: 12/08/2008
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Hansen, Monica, Ibbetson, James, Li, Ting
• Primary Examiner(s): Dickey; Thomas L
• Assistant Examiner(s): YUSHIN, NIKOLAY K
• Application Number:
  US12/316,097
• Publication Number:
  US 20100140635A1
• Time in Patent Office: 841 Days
• Field of Search: 257/98, 257/100, 257/79, 257/88, 257/91, 257/96, 257/E33.067, 257/E21.499, 257/E33.057, 257/E33.001, 438/29, 438/22, 438/26, 438/47, 438/478, 438/106, 438/116
• 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 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 33/10 with a light reflecting structure, e.g. semiconductor Bragg reflector
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector

Abstract

A high efficiency light emitting diode with a composite high reflectivity layer integral to said LED to improve emission efficiency. One embodiment of a light emitting diode (LED) chip comprises an LED and a composite high reflectivity layer integral to the LED to reflect light emitted from the active region. The composite layer comprises a first layer, and alternating plurality of second and third layers on the first layer, and a reflective layer on the topmost of said plurality of second and third layers. The second and third layers have a different index of refraction, and the first layer is at least three times thicker than the thickest of the second and third layers. For composite layers internal to the LED chip, conductive vias can be included through the composite layer to allow an electrical signal to pass through the composite layer to the LED.

Claims

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

an active region between two oppositely doped layers;

a composite high reflectivity layer arranged to reflect light emitted from said active region, said composite layer comprising;

a first layer;

one or more second layers and a plurality of third layers on said first layer, said second layers having an index of refraction different from said third layers, said second and third layers alternating, and each of said third layers having different thicknesses compared to the other of said third layers, said third layers comprising at least a pair of layers comprising a same material and different thicknesses; and

a reflective layer on the topmost of said second and third layers.

2. The LED chip of claim 1, wherein said first layer has a thickness at least four times greater than said second and third layers.

3. The LED chip of claim 1, wherein said first layer has a thickness at least three times greater than said second and third layers.

4. The LED chip of claim 1, wherein said first layer provides a reflectivity viewing angle cut-off above which said composite layer reflectivity is approximately 100%.

5. The LED chip of claim 4, wherein said second and third layers provide improved reflectivity below said viewing angle cut-off compared to a composite layer without said second and third layers.

6. The LED chip of claim 1, wherein said one or more second layers comprises two layers having different thicknesses.

7. The LED chip of claim 1, wherein said one or more second layers comprises one layer between said plurality of third layers.

8. The LED chip of claim 1, wherein said composite layer comprises an angle averaged reflectivity greater than a quarter wavelength distributed Bragg reflector having the same number of layers.

9. The LED chip of claim 1, further comprising conductive vias through said composite layer.

10. The LED chip of claim 1, further comprising a current spreading layer to spread current passing through said composite layer.

11. The LED chip of claim 1, wherein said one or more second layers and said plurality of third layers comprise incomplete second and third layer pairs.

12. The LED chip of claim 1, wherein said composite layer is internal to said LED chip.

13. The LED chip of claim 1, wherein said composite layer is on an external surface of said LED chip.

14. The LED chip of claim 1, wherein said active layer emits blue light and wherein said first layer has a thickness in the range of 500 to 650 nm.

15. The LED chip of claim 1, wherein said active layer emits blue light and wherein said one or more second layers comprise two layers having a thickness in the range of 100 to 120 nm and approximately 40 to 60 nm respectively.

16. The LED chip of claim 1, wherein said active layer emits blue light and wherein said third layers comprise two layers having a thickness in the range of 55 to 75 nm and 35 to 55 nm, respectively.

17. The LED chip of claim 1, wherein said first layer and said one or more second layers comprise SiO₂.

18. The LED chip of claim 1, wherein said third layers comprise TiO₂ or Ta₂O₅.

46. The LED chip of claim 1 wherein said pair of layers comprises a same index of refraction.

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

a submount with an LED mounted to said submount; and

a composite high reflectivity layer arranged between said submount and said LED to reflect LED light, said composite layer comprising a plurality of layers and a conductive path through said composite layer through which an electrical signal can pass to said LED, said plurality of layers comprising at least a pair of layers comprising a same material and different thicknesses.

20. The LED chip of claim 19, wherein said composite layer comprises a first layer, a one or more second layers and a plurality of third layers on said first layer, said second layers having an index of refraction different from said third layers, said composite layer further comprising a reflective layer on the topmost of said second and third layers.

21. The LED chip of claim 20, wherein said one or more second layers and said plurality of third layers comprise incomplete second and third layer pairs.

22. The LED chip of claim 20, wherein said plurality of third layers comprises two third layers and said one or more second layers comprises one layer sandwiched between said two third layers.

23. The LED chip of claim 20, wherein said composite layer further comprises a reflective layer on the topmost surface of the alternating second and third layers.

24. The LED chip of claim 20, wherein said second and third layers alternate on said first layer.

25. The LED chip of claim 20, wherein each of said third layers has a different thickness compared to other of said third layers.

26. The LED chip of claim 20, wherein said one or more second layers comprise two layers, each having a different thickness compared to the other of said second layers, and each of said second layers alternating with said third layers.

27. The LED chip of claim 20, wherein said first layer has a thickness at least four times greater than said second and third layers.

28. The LED chip of claim 20, wherein said first layer has a thickness at least three times greater than said second and third layers.

29. The LED chip of claim 19, wherein said composite layer provides higher reflectivity to the wavelength of light emitted from said LED compared to a distributed Bragg reflector.

30. The LED chip of claim 19, wherein said composite layer provides an angle averaged reflectivity greater than a quarter wavelength distributed Bragg reflector having the same number of layers.

31. The LED chip of claim 19 wherein said conductive path comprises conductive vias through said composite layer.

32. The LED chip of claim 19, wherein said conductive path comprises a conductive grid through said composite layer.

33. The LED chip of claim 19, wherein said first layer and said one or more second layers comprise SiO₂.

34. The LED chip of claim 19, wherein said third layers comprise TiO₂ or Ta₂O₅.

47. The LED chip of claim 19 wherein said pair of layers comprises a same index of refraction.

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

an LED comprising an active region; and

a composite high reflectivity layer integral to said LED to reflect light emitted from said active region, said composite layer comprising a first layer, and alternating second and third layers on said first layer, said second and third layers having a different index of refraction, and said first layer being at least three times thicker than the thickest of said second and third layers, said third layer comprising at least a pair of layers comprising a same material and different thicknesses.

36. The LED chip of claim 35, further comprising a reflective layer on the topmost of said second and third layers.

37. The LED chip of claim 35, wherein said first layer has the same index of refraction as said second layers.

38. The LED chip of claim 35, wherein each of said second layers has a different thickness compared to the others of said second layers.

39. The LED chip of claim 35, wherein each of said third layers has a different thickness compared to the others of said third layers.

40. The LED chip of claim 35, wherein said second and third layers comprise incomplete second and third layer pairs.

48. The LED chip of claim 35 wherein said pair of layers comprises a same index of refraction.

41. A method for fabricating a light emitting diode (LED) chip, comprising:

forming an LED;

depositing a composite high reflectivity layer on said LED, said composite layer comprising a plurality of layers, wherein said plurality of layers comprise at least a pair of layers comprising a same material and different thicknesses;

forming conductive vias through said composite layer to said LED;

mounting said LED to a submount with said composite layer between said LED and said submount; and

depositing contacts;

comprising a plurality of layers and a conductive path through said composite layer through which an electrical signal can pass to said LED, said plurality of layers comprising at least a pair of layers comprising a same material and different thicknesses.

49. The method of claim 41 wherein said composite layer comprises a plurality of layers, said plurality of layers comprising at least a pair of layers comprising a same material and different thicknesses.

50. The method of claim 49 wherein said pair of layers comprises a same index of refraction.

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

an LED; and

a composite high reflectivity layer integral to said LED to reflect light emitted from said LED, said composite layer comprising a first layer, and one or more second layers and a plurality of third layers on said first layer, said second and third layers comprising incomplete second and third layer pairs, said third layers comprising at least a pair of layers comprising a same material and different thicknesses.

43. The LED chip of claim 42, wherein said one or more second layers comprise one second layer sandwiched between said third layers.

44. The LED chip of claim 42, wherein said one or more second layers and said third layer have a different index of refraction, and said first layer is at least three times thicker than the thickest of said second and third layers.

45. The LED chip of claim 42, further comprising a reflective layer on the topmost surface of said second and third layers.

51. The LED chip of claim 42 wherein said pair of layers comprises a same index of refraction.