Blue light-emitting diode with degenerate junction structure

• US 5,338,944 A
• Filed: 09/22/1993
• Issued: 08/16/1994
• Est. Priority Date: 09/22/1993
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: Cree Research, Inc. (Wolfspeed, Inc.)
• Inventors: Dmitriev, Vladimir, Kong, Hua-Shuang, Edmond, John A., Bulman, Gary E.
• Primary Examiner(s): MINTEL, WILLIAM A
• Application Number:
  US08/125,284
• Time in Patent Office: 328 Days
• Field of Search: 257/76, 257/77, 257/101, 257/102, 257/103
• US Class Current: 257/76
• CPC Class Codes: H01L 33/0008 having p-n or hi-lo junctions
• CPC Class Codes: H01L 33/34 containing only elements of Group IV of the Periodic Table
• CPC Class Codes: H01S 5/3095 Tunnel junction

Abstract

A light emitting diode is disclosed that emits light in the blue region of the visible spectrum with increased brightness and efficiency. The light emitting diode comprises an n-type silicon carbide substrate; an n-type silicon carbide top layer; and a light emitting p-n junction structure between the n-type substrate and the n-type top layer. The p-n junction structure is formed of respective portions of n-type silicon carbide and p-type silicon carbide. The diode further includes means between the n-type top layer and the n-type substrate for coupling the n-type top layer to the light-emitting p-n junction structure while preventing n-p-n behavior between the n-type top layer, the p-type layer in the junction structure, and the n-type substrate.

Claims

1. A light emitting diode that emits light in the blue region of the visible spectrum with increased brightness and efficiency, said light emitting diode comprising:

an n-type silicon carbide substrate;

an n-type silicon carbide top layer;

a light emitting p-n junction structure between said n-type substrate and said n-type top layer, said p-n junction being formed of respective portions of n-type silicon carbide and p-type silicon carbide; and

means between said n-type top layer and said n-type substrate for coupling said n-type top layer to said light-emitting p-n junction structure while preventing n-p-n behavior between said n-type top layer, said p-type portion in said junction structure, and said n-type substrate.

2. A light emitting diode according to claim 1 wherein said coupling means comprises a degenerate junction structure, said degenerate junction structure being formed of a p-type portion and an n-type portion of silicon carbide, with said p-type portion of said degenerate junction structure being adjacent said p-type layer of silicon carbide in said junction structure.

3. A light emitting diode according to claim 2 wherein said doping in said p-type portion and said n-type portion in said degenerate junction structure is sufficiently heavy to substantially eliminate the barrier between the p-type portion and the n-type portion of the silicon carbide from which the portions are formed.

4. A light emitting diode according to claim 2 wherein said degenerate junction structure is on said substrate and said light emitting junction structure is on said degenerate junction structure.

5. A light emitting diode according to claim 2 wherein said light emitting junction structure is on said substrate and said degenerate junction structure is on said light emitting junction structure.

6. A light emitting diode according to claim 1 and further comprising an ohmic contact to said n-type substrate and an ohmic contact to said n-type top layer.

7. A light emitting diode according to claim 2 wherein said n-type portion of silicon carbide and said p-type portion of silicon carbide in said junction structure are each an epitaxial layer.

8. A light emitting diode according to claim 2 wherein said degenerate junction structure comprises an epitaxial layer of p-type silicon carbide and an epitaxial layer of n-type silicon carbide.

9. A light emitting diode according to claim 8 wherein said p-type layer and said n-type layer in said degenerate junction structure are thin enough to substantially avoid absorption of light emitted from said light emitting junction.

10. A light emitting diode according to claim 1 wherein said substrate is a single crystal.

11. A light emitting diode according to claim 10 wherein said substrate has a polytype of silicon carbide selected from the group consisting of 3C, 4H, 6H, and 15R.

12. A light emitting diode according to claim 1 wherein said n-type top layer comprises an epitaxial layer.

13. A light emitting diode that emits light in the blue region of the visible spectrum with increased brightness and efficiency, said light emitting diode comprising:

an n-type silicon carbide substrate;

an n-type epitaxial layer of silicon carbide on said n-type substrate;

a compensated p-type epitaxial layer of silicon carbide on said n-type layer and defining a light emitting p-n junction between said p-type layer and said n-type layer;

a degenerate junction on said p-type layer, said degenerate junction being formed of a p-type epitaxial layer and an n-type epitaxial layer of silicon carbide, with said p-type portion of said degenerate junction being adjacent said p-type layer of silicon carbide; and

a second epitaxial layer of n-type silicon carbide on said n-type layer of said degenerate junction.

14. A light emitting diode according to claim 13 wherein said n-type epitaxial layer on said substrate is a compensated n-type layer.

15. A light emitting diode according to claim 14 wherein said compensated n-type epitaxial layer has a carrier concentration greater than said compensated p-type layer so that electron injection predominates across said junction.

16. A light emitting diode according to claim 13 and further comprising an ohmic contact to said second epitaxial layer of n-type silicon carbide.

17. A light emitting diode according to claim 16 wherein said ohmic contact comprises nickel.

18. A light emitting diode according to claim 13 and further comprising a third epitaxial layer of n-type silicon carbide on said second epitaxial layer, said third layer being more heavily doped than said second layer.

19. A light emitting diode according to claim 18 and further comprising an ohmic contact to said third epitaxial layer of n-type silicon carbide.

20. A light emitting diode according to claim 19 wherein said ohmic contact comprises nickel.

21. A light emitting diode according to claim 13 and further comprising an ohmic contact to said n-type substrate.

22. A light emitting diode according to claim 21 wherein said ohmic contact comprises nickel.

23. A light emitting diode according to claim 13 and further comprising a fourth epitaxial buffer layer of n-type silicon carbide between said substrate and said light emitting junction structure.

24. A light emitting diode according to claim 13 wherein said doping in said p-type layer and said n-type layer in said degenerate junction is sufficiently heavy to substantially eliminate the barrier between the p-type layer and the n-type layer to be greater than the bandgap of the silicon carbide from which said layers are formed.

25. A light emitting diode according to claim 13 wherein said p-type layer and said n-type layer in said degenerate junction are thin enough to substantially avoid absorption of light emitted from said light emitting junction.

26. A light emitting diode according to claim 13 wherein said substrate is a single crystal.

27. A light emitting diode according to claim 26 wherein said substrate has a polytype of silicon carbide selected from the group consisting of 3C, 4H, 6H, and 15R.

28. A light emitting diode that emits light in the blue region of the visible spectrum with increased brightness and efficiency, said light emitting diode comprising:

an n-type silicon carbide substrate;

a degenerate junction on said n-type substrate, said degenerate junction diode being formed of a p-type epitaxial layer and an n-type epitaxial layer of silicon carbide, with said n-type layer of said degenerate junction being adjacent said n-type substrate;

a compensated p-type epitaxial layer of silicon carbide on said p-type layer of said degenerate junction;

an n-type epitaxial layer of silicon carbide on said compensated p-type epitaxial layer, and defining a light emitting p-n junction between said p-type layer and said n-type layer; and

a second epitaxial layer of n-type silicon carbide on said compensated n-type layer.

29. A light emitting diode according to claim 28 wherein said n-type epitaxial layer on said substrate is a compensated n-type layer.

30. A light emitting diode according to claim 29 wherein said compensated n-type epitaxial layer has a carrier concentration greater than said compensated p-type layer so that electron injection predominates across said junction.

31. A light emitting diode according to claim 28 and further comprising an ohmic contact to said second epitaxial layer of n-type silicon carbide.

32. A light emitting diode according to claim 31 wherein said ohmic contact comprises nickel.

33. A light emitting diode according to claim 28 and further comprising a third epitaxial layer of n-type silicon carbide on said second epitaxial layer, said third layer being more heavily doped than said second layer.

34. A light emitting diode according to claim 33 and further comprising an ohmic contact to said third epitaxial layer of n-type silicon carbide.

35. A light emitting diode according to claim 34 wherein said ohmic contact comprises nickel.

36. A light emitting diode according to claim 28 and further comprising an ohmic contact to said n-type substrate.

37. A light emitting diode according to claim 36 wherein said ohmic contact comprises nickel.

38. A light emitting diode according to claim 28 wherein said doping in said p-type layer and said n-type layer in said degenerate junction is sufficiently heavy to substantially eliminate the barrier between the p-type layer and the n-type layer to be greater than the bandgap of the silicon carbide from which said layers are formed.

39. A light emitting diode according to claim 28 wherein said p-type layer and said n-type layer in said degenerate junction are thin enough to substantially avoid absorption of light emitted from said light emitting junction.

40. A light emitting diode according to claim 28 wherein said substrate is a single crystal.

41. A light emitting diode according to claim 40 wherein said substrate has a polytype of silicon carbide selected from the group consisting of 3C, 4H, 6H, and 15R.

42. A light emitting diode that emits light in the blue region of the visible spectrum with increased brightness and efficiency, said light emitting diode comprising:

an n-type silicon carbide substrate;

an n-type layer of silicon carbide on said n-type substrate;

a p-type layer of silicon carbide on said n-type layer and defining a light emitting p-n junction between said p-type layer and said n-type layer; and

a degenerate junction on said p-type layer, said degenerate junction being formed of a p-type portion and an n-type portion of silicon carbide, with said p-type portion of said degenerate junction being adjacent said p-type layer of silicon carbide.

43. A light emitting diode according to claim 42 wherein said doping in said p-type portion and said n-type portion in said degenerate junction is sufficiently heavy to substantially eliminate the barrier between the p-type portion and the n-type portion of the silicon carbide from which the portions are formed.

44. A light emitting diode according to claim 42 and further comprising an ohmic contact to said n-type substrate and an ohmic contact to said n-type portion in said degenerate junction.

45. A light emitting diode according to claim 42 wherein said p-type layer and said n-type layer in said degenerate junction are thin enough to substantially avoid absorption of light emitted from said light emitting junction.

46. A light emitting diode according to claim 42 wherein said substrate is a single crystal.

47. A light emitting diode according to claim 46 wherein said substrate has a polytype of silicon carbide selected from the group consisting of 3C, 4H, 6H, and 15R.