High efficiency group III nitride LED with lenticular surface

• US 20060060874A1
• Filed: 03/17/2005
• Published: 03/23/2006
• Est. Priority Date: 09/22/2004
• Status: Active Grant

• Current Assignee: CREE Led Incorporated (Smart Global Holdings Incorporated)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Edmond, John Adam, Donofrio, Matthew, Slater, David Beardsley Jr., Bharathan, Jayesh
• Granted Patent: US 8,174,037 B2
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating

Abstract

A high efficiency Group III nitride light emitting diode is disclosed. The diode includes a substrate selected from the group consisting of semiconducting and conducting materials, a Group III nitride-based light emitting region on or above the substrate, and, a lenticular surface containing silicon carbide on or above the light emitting region.

Claims

1. A high efficiency Group III nitride light emitting diode comprising:

a substrate selected from the group consisting of semiconducting and conducting materials;

a Group III nitride-based light emitting region on said substrate; and

a lenticular surface containing silicon carbide on said light emitting region.

2. A light emitting diode according to claim 1 wherein said lenticular surface comprises single crystal silicon carbide.

3. A light emitting diode according to claim 1 further comprising an ohmic contact to said substrate and an ohmic contact to said Group III nitride emitting region.

4. A light emitting diode according to claim 3 that is no more than 150 microns thick inclusive of said ohmic contacts for being favorably incorporated into surface mount applications.

5. A light emitting diode according to claim 3 that is no more than 150 microns thick inclusive of said lenticular surface for being favorably incorporated into surface mount applications.

6. A light emitting diode according to claim 1 further comprising a phosphor-containing structure adjacent said lenticular surface for converting emissions from said light emitting region into frequencies that will produce white light

7. A light emitting diode according to claim 1 wherein said lenticular surface comprises a plurality of cones.

8. A light emitting diode according to claim 1 wherein said lenticular surface comprises a plurality of pyramids.

9. A light emitting diode according to claim 8 wherein said pyramids are selected from the group consisting of four-sided and six-sided pyramids.

10. A light emitting diode according to claim 1 wherein said lenticular surface is separated from said light emitting region by a non-lenticular layer of silicon carbide.

11. A light emitting diode according to claim 1 wherein said lenticular surface extends to, but not beyond, said light emitting region.

12. A light emitting diode according to claim 1 wherein said lenticular surface extends into said light emitting region.

13. A high efficiency light emitting diode according to claim 1 comprising at least one p-type layer of Group III nitride and at least one n-type layer of Group III nitride for current injection and recombination of carriers in said light emitting region.

14. A light emitting diode according to claim 13 wherein said Group III nitride-based light emitting region comprises at least one of said p-type or n-type layers.

15. A light emitting diode according to claim 1 wherein said Group III nitride based light emitting region comprises a mesa structure.

16. A light emitting diode according to claim 15 comprising a passivation layer on at least portions of said mesa.

17. A light emitting diode according to claim 15 comprising a passivation layer on at least portions of said mesa and on at least portions of said lenticular surface.

18. A high efficiency Group III nitride light emitting diode comprising:

a conductive silicon carbide substrate;

an aluminum indium gallium nitride light emitting region on said substrate; and

a thin lenticular surface of silicon carbide on said light emitting region.

19. A light emitting diode according to claim 18 wherein said lenticular surface is separated from said light emitting region by a non-lenticular layer of silicon carbide.

20. A light emitting diode according to claim 18 wherein said lenticular surface extends to, but not beyond, said light emitting region.

21. A light emitting diode according to claim 18 wherein said lenticular surface extends into said light emitting region.

22. A high efficiency light emitting diode according to claim 18 comprising at least one p-type layer of Group III nitride and at least one n-type layer of Group III nitride for current injection and recombination of carriers in said diode.

23. A light emitting diode according to claim 22 wherein said aluminum indium gallium nitride light emitting region comprises at least one of said p-type or n-type layers.

24. A light emitting diode according to claim 18 wherein said aluminum gallium nitride comprises Al_xIn_yGa_1-x-yN where 0≦

x, y≦

1 and x+y≦

1.

25. A light emitting diode according to claim 22 wherein said aluminum gallium nitride comprises Al_xIn_yGa_1-x-yN where 0<

x, y<

1 and x+y<

1.

26. A light emitting diode according to claim 18 wherein said aluminum indium gallium nitride based light emitting region comprises a mesa structure.

27. A light emitting diode according to claim 26 comprising a passivation layer on at least portions of said mesa.

28. A light emitting diode according to claim 26 comprising a passivation layer on at least portions of said mesa and on at least portions of said lenticular surface.

29. A high efficiency Group III nitride light emitting diode comprising:

a substrate selected from the group consisting of conducting and semiconducting materials;

at least one metal bonding layer on one surface of said substrate;

an ohmic contact to the opposite surface of said substrate from said metal layer;

a light emitting structure based upon the Group III nitride system on said at least one metal layer on said substrate;

an ohmic contact on said light emitting structure opposite said substrate; and

a lenticular surface, at least portions of which are formed of silicon carbide, on the portions of said light emitting structure other than said ohmic contact.

30. A light emitting diode according to claim 29 wherein said Group III nitride light emitting structure includes at least respective layers of p-type Group III nitride and n-type Group III nitride.

31. A light emitting diode according to claim 30 further comprising a third, light emitting Group III nitride layer between said p-type and n-type Group III nitride layers, said third Group III nitride layer having a bandgap smaller than the bandgap of either of said p-type n-type layers to thereby encourage recombination of carriers in said light emitting layer favorably with respect to said p-type layer and said n-type layer.

32. A light emitting diode according to claim 29 comprising a mirror layer between said light emitting structure and said metal bonding layer for enhancing the light extraction from the diode.

33. A light emitting diode according to claim 29 wherein said ohmic contact to said light emitting structure comprises a wire bond pad.

34. A light emitting diode according to claim 29 wherein said lenticular surface is formed entirely of silicon carbide and includes a portion of non-lenticular silicon carbide between the features that define the lenticular surface and said light emitting structure.

35. A light emitting diode according to claim 29 wherein said lenticular surface is formed entirely of silicon carbide and wherein the features that define the lenticular surface begin upon but do not include said light emitting structure.

36. A light emitting diode according to claim 29 wherein said lenticular surface is formed of portions of silicon carbide and portions of said light emitting structure.

37. A light emitting diode according to claim 29 wherein said substrate comprises silicon carbide.

38. A light emitting diode according to claim 29 wherein said substrate is selected from the group consisting of silicon, gallium arsenide and copper-tungsten.

39. A light emitting diode according to claim 37 wherein said silicon carbide is single crystal and has a polytype selected from the 3C, 4H, 6H and 15R polytypes of silicon carbide.

40. A light emitting diode according to claim 37 wherein said silicon carbide substrate is n-type.

41. A light emitting diode according to claim 29 wherein said lenticular surface is formed of a plurality of cones.

42. A light emitting diode according to claim 29 wherein said lenticular surface is formed of a plurality of pyramids selected from the group consisting of four-sided pyramids, six-sided pyramids and combinations thereof.

43. A light emitting diode according to claim 41 wherein said cones are approximately 5-10 microns high and are arranged in a geometric pattern with about 5-10 microns on a center-to-center measurement.

44. A light emitting diode according to claim 42 wherein said pyramids are approximately 5-10 microns high and are arranged in a geometric pattern with about 5-10 microns on a center-to-center measurement.

45. A light emitting diode according to claim 29 wherein said Group III nitride based light emitting structure comprises a mesa.

46. A light emitting diode according to claim 45 comprising a passivation layer on at least portions of said mesa.

47. A light emitting diode according to claim 45 comprising a passivation layer on at least portions of said mesa and on at least portions of said lenticular surface.

48. A high efficiency Group III nitride light emitting diode comprising:

a silicon carbide substrate;

a backside ohmic contact on one surface of said substrate for providing one electrical connection to said diode;

a metal bonding layer on the opposite surface of said substrate for providing a physical and electronic transition between said substrate and other portions of said diode;

a mirror layer on said metal bonding layer for enhancing light extraction from said diode;

a p-type Group III nitride layer on said mirror;

a light emitting Group III nitride layer on said p-type layer and having a bandgap smaller than the band gap of said p-type layer;

an n-type Group III nitride layer on said light emitting layer and having a bandgap larger than the bandgap of said light emitting layer;

a wire bond pad ohmic contact to said n-type layer for providing a second electrical connection to said diode; and

a lenticular surface, at least portions of which are formed of silicon carbide, on the portions of said n-type layer other than said wire bond pad.

49. A light emitting diode according to claim 48 wherein said silicon carbide substrate is single crystal and has a polytype selected from the 3C, 4H, 6H and 15R polytypes of silicon carbide.

50. A light emitting diode according to claim 48 wherein said lenticular surface is separated from said light emitting region by a non-lenticular layer of silicon carbide.

51. A light emitting diode according to claim 48 wherein said lenticular surface extends to, but not beyond, said light emitting region.

52. A light emitting diode according to claim 48 wherein said lenticular surface extends into said light emitting region.

53. A high-efficiency Group III nitride light emitting diode package comprising:

a lead frame; and

a light emitting diode on said lead frame;

said diode including,

a substrate selected from the group consisting of semiconducting and conducting materials;

a Group III nitride based light emitting region on said substrate;

a lenticular surface containing silicon carbide on said light emitting region;

an ohmic contact between said substrate and said lead frame; and

an ohmic contact to said light emitting region.

54. A package according to claim 53 wherein said lenticular surface comprises single crystal silicon carbide.

55. A package according to claim 53 wherein said diode has a total thickness no more than about 150 microns between and including said ohmic contacts.

56. A package according to claim 53 wherein said diode has a total thickness no more than about 150 microns between and including said lenticular surface.

57. A light emitting diode according to claim 53 further comprising a conductive paste between said diode and said lead frame for attaching said diode to said lead frame and wherein said substrate has sufficient thickness to prevent said paste from touching said Group III nitride based light emitting region.

58. A light emitting diode according to claim 53 wherein said substrate comprises single crystal n-type silicon carbide having a polytype selected from the 3C, 4H, 6H and 15R polytypes of silicon carbide.

59. A light emitting diode according to claim 53 comprising at least one p-type Group III nitride epitaxial layer and at least one n-type Group III nitride epitaxial layer for current injection and carrier recombination in said diode.

60. A light emitting diode according to claim 53 wherein said lenticular surface is separated from said light emitting region by a non-lenticular layer of silicon carbide.

61. A light emitting diode according to claim 53 wherein said lenticular surface extends to, but not beyond, said light emitting region.

62. A light emitting diode according to claim 59 wherein said lenticular surface extends into said light emitting region.

63. A light emitting diode according to claim 53 wherein said Group III nitride based light emitting region comprises a mesa structure.

64. A light emitting diode according to claim 63 comprising a passivation layer on at least portions of said mesa.

65. A light emitting diode according to claim 63 comprising a passivation layer on at least portions of said mesa and on at least portions of said lenticular surface.

66. A wafer structure for high efficiency Group III nitride light emitting diode precursors, said wafer structure comprising:

a conductive silicon carbide substrate wafer;

a Group III nitride epitaxial layer on said substrate;

a plurality of discrete ohmic contacts on the surface of said Group III nitride epitaxial layer, said ohmic contacts defining a plurality of discrete light emitting diode precursors; and

a lenticular surface containing silicon carbide on said Group III nitride epitaxial layer.

67. A wafer structure according to claim 66 wherein said lenticular surface comprises single crystal silicon carbide.

68. A wafer structure according to claim 66 having a total dimension between and including said ohmic contacts of no more than 150 microns.

69. A wafer structure according to claim 66 wherein said substrate comprises single crystal n-type silicon carbide having a polytype selected from the 3C, 4H, 6H and 15R polytypes of silicon carbide.

70. A wafer structure according to claim 66 wherein said substrate is selected from the group consisting of silicon, gallium arsenide and copper-tungsten.

71. A wafer structure according to claim 66 comprising at least one p-type Group III nitride epitaxial layer and at least one n-type Group III nitride epitaxial layer for current injection and carrier recombination in said diode.

72. A wafer structure according to claim 66 wherein said lenticular surface is separated from said light emitting region by a non-lenticular layer of silicon carbide.

73. A wafer structure according to claim 66 wherein said lenticular surface extends to, but not beyond, said light emitting region.

74. A wafer structure according to claim 66 wherein said lenticular surface extends into said light emitting region.

75. In a light emitting diode having a vertical orientation with an ohmic contact on portions of a top surface of said diode and a mirror layer adjacent the light emitting region of said diode;

the improvement comprising;

an opening in said mirror layer beneath the geometric projection of said top ohmic contact through the diode that defines a non-contact area between said mirror layer and said light emitting region of said diode to encourage current flow to take place other than at said non-contact area to in turn decrease the number of light emitting recombinations beneath said ohmic contact and increase the number of light emitting recombinations in the more transparent portions of said diode.

76. A light emitting diode according to claim 75 wherein said top ohmic contact comprises a wire bond pad having an area less than half of the area of said top surface of said diode.

77. A light emitting diode according to claim 75 formed on a substrate and having an ohmic contact to said substrate that is larger in area than said top ohmic contact.

78. A light emitting diode according to claim 77 wherein said mirror layer is positioned between said substrate and said light emitting region.

79. A light emitting diode according to claim 75 wherein the size of said non-contact area is substantially the same area as the size of said top ohmic contact.

80. A light emitting diode according to claim 75 wherein said mirror layer comprises a plurality of metal layers.

81. A light emitting diode according to claim 75 wherein said light emitting region comprises a plurality of Group III nitride layers, including at least one p-type layer and at least one n-type layer.

82. A light emitting diode according to claim 75 wherein said opening is filled with a metal that is not ohmic with respect to said light emitting region to thereby provide additional reflection from said mirror layer.

83. In a light emitting diode having a vertical orientation with an ohmic contact on portions of a top surface of said diode and a mirror layer adjacent the light emitting region of said diode;

the improvement comprising;

a passivated portion of said light emitting region beneath the geometric projection of said top ohmic contact the diode that defines a less conductive area between said mirror layer and said light emitting region of said diode to encourage current flow to take place other than at said passivated portion to in turn decrease the number of light emitting recombinations beneath said ohmic contact and increase the number of light emitting recombinations in the more transparent portions of said diode.

84. A light emitting diode according to claim 83 wherein said top ohmic contact comprises a wire bond pad having an area less than half of the area of said top surface of said diode.

85. A light emitting diode according to claim 83 formed on a substrate and having an ohmic contact to said substrate that is larger in area than said top ohmic contact.

86. A light emitting diode according to claim 85 wherein said mirror layer is positioned between said substrate and said light emitting region.

87. A light emitting diode according to claim 83 wherein the size of said passivated portion is substantially the same area as the size of said top ohmic contact.

88. A light emitting diode according to claim 83 wherein said mirror layer comprises a plurality of metal layers.

89. A light emitting diode according to claim 83 wherein said light emitting region comprises a plurality of Group III nitride layers, including at least one p-type layer and at least one n-type layer.