Beveled LED Chip with Transparent Substrate

• US 20080258130A1
• Filed: 04/23/2007
• Published: 10/23/2008
• Est. Priority Date: 04/23/2007
• Status: Abandoned Application

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Bergmann, Michael J., Emerson, David T., Haberern, Kevin W.
• Application Number:
  US11/738,665
• Publication Number:
  US 20080258130A1
• Time in Patent Office: Days
• US Class Current: 257/13
• CPC Class Codes: H01L 2224/48091 Arched
• 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 2924/10155 being other than a cuboid
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

A light emitting diode is disclosed that includes a transparent (and potentially low conductivity) silicon carbide substrate, an active structure formed from the Group III nitride material system on the silicon carbide substrate, and respective ohmic contacts on the top side of the diode. The silicon carbide substrate is beveled with respect to the interface between the silicon carbide and the Group III nitride.

Claims

1. A light emitting diode comprising:

a transparent silicon carbide substrate;

an active structure formed from the Group III nitride material system on said silicon carbide substrate;

respective ohmic contacts on the top side of said diode; and

said silicon carbide substrate being beveled with respect to the interface between said silicon carbide and said Group III nitride.

2. A diode according to claim 1 wherein said silicon carbide substrate is beveled at an angle of between about 45 and 75 degrees with respect to the interface between said silicon carbide substrate and said Group III nitride active structure.

3. A diode according to claim 1 wherein said transparent silicon carbide substrate is between about 50 and 500 microns thick and is characterized by less than 10 percent absorptive losses.

4. A diode according to claim 3 wherein said transparent silicon carbide substrate is characterized by less than 5 percent absorptive losses.

5. A diode according to claim 1 wherein said substrate is a single crystal having a polytype selected from the group consisting of the 3C, 2H, 4H, 6H, and 15R polytypes of silicon carbide.

6. A diode according to claim 1 wherein said Group III nitride material is selected from the group consisting of gallium nitride, indium gallium nitride, and aluminum indium gallium nitride.

7. A light emitting diode according to claim 1 wherein said active structure is a p-n junction between respective Group III nitride epitaxial layers.

8. A diode according to claim 1 wherein said active structure is selected from the group consisting of single quantum wells, multiple quantum wells, and superlattice structures.

9. A light emitting diode according to claim 1 wherein said active structure includes at least one light emitting layer of indium gallium nitride having the formula In_xGa_1-xN wherein the atomic fraction X of indium is no more than about 0.3.

10. A light emitting diode according to claim 1 wherein said silicon carbide substrate has a resistivity of at least about 0.1 ohm-centimeters.

11. A light emitting diode according to claim 1 wherein said silicon carbide substrate has a resistivity of at least about 0.2 ohm-centimeters.

12. A light emitting diode according to claim 1 wherein said silicon carbide substrate has a resistivity of at least about 0.3 ohm-centimeters.

13. A light emitting diode according to claim 1 wherein:

said active structure is formed from respective p-type and n-type layers of Group III nitride material; and

said ohmic contacts are selected from the group consisting of gold, gold-tin, zinc, gold-zinc, gold-nickel, platinum, nickel, aluminum, ITO, chromium, and combinations thereof.

14. A light emitting diode according to claim 1 having a radiant flux of at least 35 mw at 20 milliamps drive current in an industry standard 5 mm lamp.

15. A light emitting diode according to claim 1 characterized by the far field pattern of FIG. 5

16. A light emitting diode according to claim 1 characterized by a far field pattern in which the sidelobe emission is equal to the forward emission.

17. A light emitting diode according to claim 1 characterized by a far field pattern in which the sidelobe emission is greater than the forward emission.

18. A light emitting diode according to claim 1 that exhibits a far field pattern in which the maximum intensity is at least twice the minimum intensity, and in which the maximum and minimum intensity are between about 60°

and 90°

degrees from one another.

19. A light emitting diode according to claim 1 that exhibits an output of at least two candela at a 20 milliamp forward operating current at CIE x and y color coordinates of about 0.3 and 0.3.

20. An LED lamp comprising the light emitting diode according to claim 1 packaged with a light converting phosphor.

21. An LED lamp comprising the light emitting diode according to claim 20 packaged with a light converting phosphor in a sidelooker package.

22. An LED lamp according to claim 1 wherein said phosphor comprises YAG.

23. A display comprising a plurality of light emitting diodes according to claim 1.

24. A display according to claim 23 further comprising a plurality of red light emitting diodes and a plurality of green light emitting diodes.

25. A display according to claim 23 further comprising a plurality of white light emitting diodes.

26. A display according to claim 23 wherein said plurality of light emitting diodes backlight a plurality of liquid crystal display shutters.

27. An LED lamp comprising:

a lead frame;

a transparent beveled silicon carbide substrate on said lead frame;

an active structure formed from the Group III nitride material system on said silicon carbide substrate opposite from said lead frame;

respective ohmic contacts on the top side of said diode;

a polymer lens over said substrate and active structure; and

a phosphor distributed in said polymer lens that is responsive to the light emitted by said active structure and that produces a different color of light in response.

28. An LED lamp according to claim 27 wherein:

said active structure emits in the blue portion of the visible spectrum; and

said phosphor absorbs the blue radiation and responsively emits yellow radiation.

29. An LED lamp according to claim 27 wherein said phosphor comprises YAG.

30. A display comprising a plurality of LED lamps according to claim 29.

31. A method of designating the directional output of a light emitting diode comprising beveling a silicon carbide substrate at an acute angle with respect to an interface between the substrate and a Group III nitride epitaxial layer.

32. A method according to claim 31 comprising beveling the silicon carbide substrate to an angle at which the diode has a radiant flux of at least 35 mW at 20 milliamps drive current in an industry standard 5 mm lamp.

33. A method according to claim 31 comprising beveling the silicon carbide substrate to an angle that produces a far field pattern in which the sidelobe emission is equal to the forward emission.

34. A method according to claim 31 comprising beveling the silicon carbide substrate to an angle that produces a far field pattern in which the sidelobe emission is greater than the forward emission.

35. A method according to claim 31 comprising beveling the silicon carbide substrate to an angle that produces at least twice the intensity in directions between 60 degrees and 90 degrees from the direction of minimum intensity.

36. A method according to claim 31 comprising beveling the silicon carbide substrate to an angle that produces an output of at least two candela at a 20 milliamp forward operating current at CIE x and y color coordinates of about 0.3 and 0.3.

37. A method according to claim 31 comprising beveling the silicon carbide substrate to an angle that produces an output of at least two candela at a 20 milliamp forward operating current at CIE x and y color coordinates of about 0.3 and 0.3 in a sidelooker package.

38. A method according to claim 31 comprising beveling the silicon carbide substrate to an angle of between about 45 and 75 degrees with respect to the interface.

40. A light emitting diode according to claim 38 that exhibits an output of at least two candela at a 20 milliamp forward operating current at CIE x and y color coordinates of about 0.3 and 0.3.

39. A light emitting diode comprising:

a silicon carbide substrate that is between about 50 and 500 microns thick and is characterized by less than 10 percent absorptive losses;

an active structure reform from the Group III nitride materials system on said silicon carbide substrate;

respective ohmic contacts on the top side of said diode; and

said silicon carbide substrate having sidewalls substantially perpendicular with respect to the interface between said silicon carbide substrate and said Group III nitride active structure.

41. A light emitting diode according to claim 39 wherein said transparent silicon carbide substrate is characterized by less than 5 percent absorptive losses.

42. A diode according to claim 39 wherein said substrate is a single crystal having a polytype selected from the group consisting of the 3C, 2H, 4H, 6H, and 15R polytypes of silicon carbide.

43. A diode according to claim 39 wherein said Group III nitride material is selected from the group consisting of gallium nitride, indium gallium nitride, and aluminum indium gallium nitride.

44. A light emitting diode according to claim 39 wherein said active structure includes at least one light emitting layer of indium gallium nitride having the formula In_xGa_1-xN wherein the atomic fraction X of indium is no more than about 0.3.

45. A light emitting diode according to claim 39 wherein said silicon carbide substrate has a resistivity of at least about 0.1 ohm-centimeters.

46. A light emitting diode according to claim 39 wherein said silicon carbide substrate has a resistivity of at least about 0.2 ohm-centimeters.

47. A light emitting diode according to claim 39 wherein said silicon carbide substrate has a resistivity of at least about 0.3 ohm-centimeters.

48. A light emitting diode according to claim 39 having a radiant flux of at least 35 mw at 20 milliamps drive current in an industry standard 5 mm lamp.

49. An LED lamp comprising the light emitting diode according to claim 39 packaged with a light converting phosphor.

50. A display comprising a plurality of light emitting diodes according to claim 39.