Blue light emitting diode formed in silicon carbide

• US 5,027,168 A
• Filed: 08/28/1989
• Issued: 06/25/1991
• Est. Priority Date: 12/14/1988
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: Cree Research, Inc.
• Inventors: Edmond, John A.
• Primary Examiner(s): James, Andrew J.
• Assistant Examiner(s): Meier, S.
• Application Number:
  US07/399,301
• Time in Patent Office: 666 Days
• Field of Search: 357/17, 357/60
• US Class Current: 257/103
• 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: H01L 33/343 characterised by the doping materials

Abstract

The present invention comprises a light emitting diode formed in silicon carbide and that emits visible light having a wavelength of between about 465-470 nanometers, or between about 455-460 nanometers, or between about 424-428 nanometers. The diode comprises a substrate of alpha silicon carbide having a first conductivity type and a first epitaxial layer of alpha silicon carbide upon the substrate having the same conductivity type as the substrate. A second epitaxial layer of alpha silicon carbide is upon the first epitaxial layer, has the opposite conductivity type from the first layer, and forms a p-n junction with the first epitaxial layer. In preferred embodiments, the first and second epitaxial layers have carrier concentrations sufficiently different from one another so that the amount of hole current and electron current that flow across the junction under biased conditions are different from one another and so that the majority of recombination events take place in the desired epitaxial layer.

Claims

1. A light emitting diode formed in silicon carbide that emits light in the blue to violet portion of the visible spectrum and comprising:

an n-type substrate of alpha-type silicon carbide having a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions;

an ohmic contact to said substrate;

a substantially uncompensated n-type monocrystalline epitaxial layer of alpha-type silicon carbide upon said interface surface of said n-type substrate;

a p-type monocrystalline epitaxial layer of alpha-type silicon carbide upon said n-type epitaxial layer and forming a p-n junction with said n-type layer, said p-type epitaxial layer having a carrier concentration less than the carrier concentration of said uncompensated n-type epitaxial layer; and

an ohmic contact to said p-type epitaxial layer, said diode producing a peak emission at a wavelength of between about 455 and 460 nanometers with a spectral half width at peak wavelength of no more than about 50 nanometers.

2. A light emitting diode according to claim 1 wherein said silicon carbide substrate has a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions with said n-type epitaxial layer of alpha silicon carbide homoepitaxially deposited on said substrate interface surface.

3. A light emitting diode according to claim 1 wherein said n-type epitaxial layer has a carrier concentration greater than the carrier concentration of said n-type substrate.

4. A light emitting diode according to claim 1 that produces a peak emission at a wavelength of between about 455 and 460 nanometers with a spectral half width at peak wavelength of no more than about 25 nanometers.

5. A light emitting diode according to claim 1 wherein said n-type substrate and said n-type epitaxial layer include nitrogen as a donor carrier.

6. A light emitting diode according to claim 1 wherein said p-type epitaxial layer includes aluminum as an acceptor carrier.

7. A light emitting diode according to claim 1 wherein the alpha-type silicon carbide has a polytype selected from the group consisting of:

6H, 4H, and 15R.

8. A light emitting diode according to claim 1 wherein said ohmic contact to said n-type substrate comprises nickel and said ohmic contact to said p-type epitaxial layer comprises aluminum or an aluminum alloy.

26. A light emitting diode according to claim 2 wherein said n-type epitaxial layers include nitrogen as a donor carrier.

9. A light emitting diode formed in silicon carbide that emits light in the blue to violet portion of the visible spectrum and comprising:

a p-type substrate of alpha-type silicon carbide having a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions;

an ohmic contact to said substrate;

a substantially uncompensated p-type monocrystalline epitaxial layer of alpha-type silicon carbide upon said interface surface of said p-type substrate;

a substantially uncompensated n-type monocrystalline epitaxial layer of alpha-type silicon carbide upon said p-type epitaxial layer and forming a p-n junction with said p-type layer, said n-type epitaxial layer having a carrier concentration greater than the carrier concentration of said p-type epitaxial layer; and

an ohmic contact to said n-type epitaxial layer, said diode producing a peak emission at a wavelength of between about 455 and 460 nanometers with a spectral half width at peak wavelength of no more than about 50 nanometers.

10. A light emitting diode according to claim 9 that produces a peak emission at a wavelength of between about 455 and 460 nanometers with a spectral half width at peak wavelength of no more than about 25 nanometers.

11. A light emitting diode according to claim 9 wherein said silicon carbide substrate has a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions with said p-type epitaxial layer of alpha silicon carbide homoepitaxially deposited on said substrate interface surface.

12. A light emitting diode according to claim 9 wherein said n-type epitaxial layer includes nitrogen as a donor carrier.

13. A light emitting diode according to claim 9 wherein said p-type substrate and said p-type epitaxial layer include aluminum as an acceptor carrier.

14. A light emitting diode according to claim 9 wherein the alpha-type silicon carbide has a polytype selected from the group consisting of:

6H, 4H, and 15R.

15. A light emitting diode according to claim 9 wherein said ohmic contact to said substantially uncompensated n-type epitaxial layer comprises nickel and said ohmic contact to said p-type substrate comprises aluminum.

16. A light emitting diode formed in silicon carbide that emits light in the blue to violet portion of the visible spectrum and comprising:

an n-type substrate of alpha-type silicon carbide;

an ohmic contact to said substrate;

a substantially uncompensated n-type monocrystalline epitaxial layer of alpha-type silicon carbide upon said n-type substrate;

a substantially uncompensated p-type monocrystalline epitaxial layer of alpha-type silicon carbide upon said n-type epitaxial layer and forming a p-n junction with said n-type epitaxial layer, said p-type epitaxial layer having a carrier concentration greater than the carrier concentration of said n-type epitaxial layer; and

an ohmic contact to said uncompensated p-type epitaxial layer, said diode producing a peak emission of between about 424 and 428 nanometers with a spectral half width at peak wavelength of no greater than about 50 nanometers.

17. A light emitting diode according to claim 16 that produces a peak emission of between about 424 and 428 nanometers with a spectral half width at peak wavelength of no greater than about 25 nanometers.

18. A light emitting diode according to claim 16 wherein said n-type substrate and said n-type epitaxial layer include nitrogen as a donor carrier.

19. A light emitting diode according to claim 16 wherein said p-type epitaxial layer includes aluminum as an acceptor carrier.

20. A light emitting diode according to claim 16 wherein the alpha-type silicon carbide has a polytype selected from the group consisting of:

6H, 4H, and 15R.

21. A light emitting diode according to claim 16 wherein said ohmic contact to said substantially uncompensated p-type epitaxial layer comprises aluminum and said ohmic contact to said n-type substrate comprises nickel.

22. A light emitting diode formed in silicon carbide that emits light in the blue to violet portion of the visible spectrum and comprising:

a p-type substrate of alpha silicon carbide having a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions;

an ohmic contact to said substrate;

a substantially uncompensated p-type monocrystalline epitaxial layer of silicon carbide upon said interface surface of said p-type substrate;

a first substantially uncompensated n-type monocrystalline epitaxial layer of alpha silicon carbide upon said p-type epitaxial layer, and having a carrier concentration less than the carrier concentration of said p-type epitaxial layer;

a second substantially uncompensated n-type monocrystalline epitaxial layer of silicon carbide upon said first n-type epitaxial layer, and having a carrier concentration greater than the carrier concentration of said first n-type epitaxial layer; and

an ohmic contact to said second n-type epitaxial layer, wherein said second n-type epitaxial layer forms a conductive surface that moderates the current crowding that would otherwise occur about said contact to said second n-type epitaxial layer, said diode producing a peak emission of between about 424 and 428 nanometers with a spectral half width at peak wavelength of no greater than about 50 nanometers.

23. A light emitting diode according to claim 22 wherein said silicon carbide substrate has a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions with said p-type epitaxial layer of alpha silicon carbide homoepitaxially deposited on said substrate interface surface.

24. A light emitting diode according to claim 22 wherein said substantially uncompensated p-type epitaxial layer has a carrier concentration greater than the carrier concentration of said p-type substrate.

25. A light emitting diode according to claim 22 that produces a peak emission of between about 424 and 428 nanometers with a spectral half width at peak wavelength of no greater than about 25 nanometers.

27. A light emitting diode according to claim 22 wherein said p-type substrate and said p-type epitaxial layer include aluminum as an acceptor carrier.

28. A light emitting diode according to claim 22 wherein the alpha-type silicon carbide has a polytype elected from the group consisting of:

6H, 4H, and 15R.

29. A light emitting diode according to claim 22 wherein said ohmic contact to said second n-type epitaxial layer comprises nickel and said ohmic contact to said p-type substrate comprises aluminum.

30. A light emitting diode formed in silicon carbide that emits light in the blue to violet portion of the visible spectrum and comprising:

an n-type substrate of alpha-type silicon carbide;

an ohmic contact to said n-type substrate;

a substantially uncompensated n-type monocrystalline epitaxial layer of alpha-type silicon carbide upon said n-type substrate;

a compensated p-type monocrystalline epitaxial layer of alpha-type silicon carbide upon said uncompensated n-type epitaxial layer and forming a p-n junction with said n-type epitaxial layer; and

an ohmic contact to said compensated p-type epitaxial layer.

31. A light emitting diode according to claim 30 wherein said silicon carbide substrate has a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions with said n-type epitaxial layer of alpha silicon carbide homoepitaxially deposited on said substrate interface surface.

32. A light emitting diode according to claim 30 wherein said uncompensated n-type epitaxial layer has a carrier concentration greater than the carrier concentration of said n-type substrate.

33. A light emitting diode according to claim 30 and further comprising an uncompensated p-type epitaxial layer of alpha-type silicon carbide upon said compensated p-type epitaxial layer, said uncompensated p-type epitaxial layer having a carrier concentration greater than the carrier concentration of said compensated p-type epitaxial layer, and wherein said uncompensated p-type epitaxial layer forms a conductive surface that moderates the current crowding that would otherwise occur about said contact to said p-type epitaxial layer.

34. A light emitting diode according to claim 30 characterized by the emission of light having a peak wavelength of between about 465 and 470 nanometers with a spectral half width at peak wavelength of no greater than about 80 nanometers.

35. A light emitting diode according to claim 30 wherein said n-type substrate and said n-type epitaxial layer include nitrogen as a donor carrier.

36. A light emitting diode according to claim 30 wherein said compensated p-type epitaxial layer includes aluminum as an acceptor carrier and nitrogen as a donor carrier.

37. A light emitting diode according to claim 30 wherein the alpha-type silicon carbide has a polytype selected from the group consisting of:

6H, 4H, and 15R.

38. A light emitting diode according to claim 30 wherein said ohmic contact to said n-type substrate comprises nickel and said ohmic contact to said compensated p-type epitaxial layer comprises aluminum or an aluminum alloy.

39. A light emitting diode according to claim 30 that produces a peak emission at a wavelength of about 467 nanometers with a spectral half width of about 75 nanometers.

40. A light emitting diode formed in silicon carbide that emits light in the blue to violet portion of the visible spectrum and comprising:

a n-type substrate of alpha-type silicon carbide;

a compensated n-type monocrystalline epitaxial layer of alpha silicon carbide upon said substrate; and

a substantially uncompensated p-type monocrystalline epitaxial layer upon said n-type epitaxial layer, said p-type epitaxial layer having a carrier concentration greater than the carrier concentration of said n-type epitaxial layer, said diode producing a peak emission at a wavelength of between about 465 and 470 nanometers with a spectral half width at peak wavelength of no more than about 80 nanometers.

41. A light emitting diode according to claim 40 wherein said silicon carbide substrate has a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions with said n-type epitaxial layer of alpha silicon carbide homoepitaxially deposited on said substrate interface surface.

42. A light emitting diode according to claim 40 wherein said n-type substrate and said compensated n-type epitaxial layer include nitrogen as a donor carrier.

43. A light emitting diode according to claim 42 wherein said compensated n-type epitaxial layer further includes aluminum as an acceptor carrier.

44. A light emitting diode according to claim 40 wherein said substantially uncompensated p-type epitaxial layer includes aluminum as an acceptor carrier.

45. A light emitting diode according to claim 40 wherein the alpha-type silicon carbide has a polytype selected from the group consisting of:

6H, 4H, and 15R.

46. A light emitting diode according to claim 40 further comprising an ohmic contact to said n-type substrate and an ohmic contact to said substantially uncompensated p-type epitaxial layer.

47. A light emitting diode according to claim 40 that produces a peak emission at a wavelength of about 467 nanometers with a spectral half width of about 75 nanometers.

48. A light emitting diode formed in silicon carbide that emits light in the blue to violet portion of the visible spectrum and comprising:

a p-type substrate of alpha silicon carbide;

a compensated p-type monocrystalline epitaxial layer of alpha silicon carbide upon said substrate; and

a substantially uncompensated n-type monocrystalline epitaxial layer upon said compensated p-type epitaxial layer and forming a p-n junction with said compensated p-type layer.

49. A light emitting diode according to claim 48 that produces a peak emission at a wavelength of between about 465 and 470 nanometers with a spectral half width of no more than about 80 nanometers.

50. A light emitting diode according to claim 48 wherein said silicon carbide substrate has a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions with said p-type epitaxial layer of alpha silicon carbide homoepitaxially deposited on said substrate interface surface.

51. A light emitting diode according to claim 48 wherein said n-type epitaxial layer includes nitrogen as a donor carrier.

52. A light emitting diode according to claim 48 wherein said p-type substrate and said compensated p-type epitaxial layer include aluminum as an acceptor carrier.

53. A light emitting diode according to claim 52 wherein said compensated p-type epitaxial layer further includes nitrogen as a donor carrier.

54. A light emitting diode according to claim 48 wherein the alpha-type silicon carbide has a polytype selected from the group consisting of:

6H, 4H, and 15R.

55. A light emitting diode according to claim 48 further comprising an ohmic contact to said p-type substrate and an ohmic contact to said substantially uncompensated n-type epitaxial layer.

56. A light emitting diode according to claim 48 wherein said n-type epitaxial layer has a carrier concentration greater than the carrier concentration of said compensated p-type epitaxial layer.

57. A light emitting diode according to claim 48 that produces a peak emission at a wavelength of about 467 nanometers with a spectral half width of about 75 nanometers.

58. A light emitting diode formed in silicon carbide that emits light in the blue to violet portion of the visible spectrum and comprising:

a p-type substrate of alpha silicon carbide;

an ohmic contact to said substrate;

a substantially uncompensated p-type monocrystalline epitaxial layer of silicon carbide upon said substrate;

a compensated n-type monocrystalline epitaxial layer upon said p-type epitaxial layer, said n-type epitaxial layer having a carrier concentration less than the carrier concentration of said p-type epitaxial layer; and

a substantially uncompensated n-type monocrystalline epitaxial layer upon said compensated n-type epitaxial layer and having a carrier concentration greater than the carrier concentration of said compensated n-type epitaxial layer; and

an ohmic contact to said uncompensated n-type epitaxial layer, and wherein said n-type epitaxial layer forms a conductive surface that moderates the current crowding that would otherwise occur about said contact to said n-type epitaxial layer, and in which said diode produces a peak emission at a wavelength of between about 465 and 470 nanometers with a spectral half width at peak wavelength of no more than about 80 nanometers.

59. A light emitting diode according to claim 58 wherein said silicon carbide substrate has a flat interface surface that is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions with said p-type epitaxial layer of alpha silicon carbide homoepitaxially deposited on said substrate interface surface.

60. A light emitting diode according to claim 58 that produces a peak emission at a wavelength of between about 475 and 480 nanometers with a spectral half width at peak wavelength of no greater than about 25 nanometers.

61. A light emitting diode according to claim 58 wherein said compensated n-type epitaxial layers and said substantially uncompensated n-type epitaxial layer include nitrogen as a donor carrier.

62. A light emitting diode according to claim 61 wherein said compensated n-type epitaxial layer further includes aluminum as an acceptor carrier.

63. A light emitting diode according to claim 58 wherein the alpha-type silicon carbide has a polytype elected from the group consisting of:

6H, 4H, and 15R.

64. A light emitting diode according to claim 58 wherein said ohmic contact to said substantially uncompensated n-type epitaxial layer comprises nickel and said ohmic contact to said p-type substrate comprises aluminum or aluminum alloy.

65. A light emitting diode according to claim 58 that produces a peak emission at a wavelength of about 467 nanometers with a spectral half width of about 75 nanometers.