GRADED DIELECTRIC LAYER

• US 20080224157A1
• Filed: 03/13/2007
• Published: 09/18/2008
• Est. Priority Date: 03/13/2007
• Status: Active Grant

• Current Assignee: Wolfspeed, Inc.
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Slater, David B.
• Granted Patent: US 7,638,811 B2
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating

Abstract

An optoelectronic device includes a passivation layer of a dielectric material having a graded composition that varies with depth, whether continuous or stepwise, to provide a first index of refraction proximate to a semiconductor or conductor material and provide a second index of refraction adjacent to a surrounding material, such as an encapsulant. The resulting graded dielectric layer reduces Fresnel losses by reducing index of refraction mismatches between the adjacent semiconductor or conductor layer and the surrounding medium. Methods for forming graded dielectric layers include supplying a nitrogen-containing source gas at a declining flow rate or concentration, while supplying an oxygen-containing source gas an rising flow rate or concentration, to a deposition chamber.

Claims

1. An optoelectronic device comprising:

a semiconductor material;

a dielectric layer disposed over or adjacent to the semiconductor material; and

a surrounding medium disposed adjacent to the dielectric layer;

wherein the dielectric layer has a composition that varies with depth, providing an index of refraction that is graded from a first value at a depth closer to the semiconductor material to a second value at a depth closer to the surrounding medium, and the second value is different from the first value.

2. The optoelectronic device of claim 1, wherein the first value is higher than the second value.

3. The optoelectronic device of claim 1, comprising a light emitting diode.

4. The optoelectronic device of claim 1, wherein the surrounding medium comprises an encapsulant material.

5. The optoelectronic device of claim 1, wherein the surrounding medium comprises air.

6. The optoelectronic device of claim 1, wherein at least an upper portion of the semiconductor material has a first index of refraction, the surrounding medium has a second index of refraction, and the dielectric material has an index of refraction that is graded from about the first index of refraction proximate to the semiconductor material to about the second index of refraction proximate to the surrounding medium.

7. The optoelectronic device of claim 1, further comprising a conductive material layer disposed between the semiconductor material and the dielectric layer.

8. The optoelectronic device of claim 7, wherein the conductive material layer comprises a semi-transparent metal layer.

9. The optoelectronic device of claim 7, wherein the conductive material layer comprises a transparent conductive oxide layer.

10. The optoelectronic device of claim 7, wherein the conductive material has a third index of refraction, the surrounding medium has a second index of refraction, and the dielectric material has an index of refraction that is graded from about the third index of refraction proximate to the conductive material to about the second index of refraction proximate to the surrounding medium.

11. The optoelectronic device of claim 1, wherein the semiconductor material comprises any of a group III-arsenide, -phosphide, and -nitride material.

12. The optoelectronic device of claim 1, wherein the semiconductor material comprises a group III-nitride material.

13. The optoelectronic device of claim 1, wherein the dielectric layer comprises a nitride material portion, an oxide material portion, and an oxynitride material portion disposed between the nitride material portion and the oxide material portion, wherein the oxide material portion is disposed proximate to the surrounding medium.

14. The optoelectronic device of claim 13, wherein the nitride material portion is deposited on the semiconductor material.

15. The optoelectronic device of claim 13, wherein the nitride material portion is deposited on a conductive material overlying the semiconductor material.

16. The optoelectronic device of claim 13, wherein the nitride material comprises silicon nitride, the oxide material comprises silicon dioxide, and the oxynitride material comprises silicon oxynitride.

17. The optoelectronic device of claim 13, wherein the nitride material has a refractive index of about 2.5, and the surrounding medium has a refractive index in a range of about 1 to about 1.5.

18. The optoelectronic device of claim 1, wherein the dielectric layer comprises an oxynitride material having a composition that varies with depth.

19. The optoelectronic device of claim 1, wherein the dielectric layer comprises an oxide portion and an oxynitride portion.

20. The optoelectronic device of claim 1, wherein the dielectric layer comprises a nitride portion and an oxynitride portion.

21. The optoelectronic device of claim 1, wherein the dielectric layer comprises a plurality of discrete sublayers, with each sublayer of the plurality of sublayers having a substantially constant composition that is different from the composition of the other sublayers of the plurality of sublayers.

22. The optoelectronic device of claim 1, wherein the dielectric layer composition varies substantially continuously with depth.

23. The optoelectronic device of claim 1, wherein the dielectric layer composition varies stepwise with depth.

24. An optoelectronic device comprising a dielectric layer having a thickness and disposed between a semiconductor material and a surrounding medium, wherein the dielectric layer is graded in composition along its thickness to provide a first index of refraction along a first boundary and provide a second index of refraction along a second boundary, with the second index of refraction being different from the first index of refraction.

25. The optoelectronic device of claim 24, wherein the first index of refraction is greater than the second index of refraction.

26. The optoelectronic device of claim 24, wherein the first boundary is adjacent to the semiconductor material, and the second boundary is adjacent to the surrounding medium.

27. The optoelectronic device of claim 26, wherein at least a portion of the semiconductor material has an index of refraction about the same as the first index of refraction, and at least a portion of the surrounding medium has an index of refraction about the same as the second index of refraction.

28. The optoelectronic device of claim 24, comprising a light emitting diode.

29. The optoelectronic device of claim 24, wherein the surrounding medium comprises an encapsulant material.

30. The optoelectronic device of claim 24, wherein the surrounding medium comprises air.

31. The optoelectronic device of claim 24, further comprising a conductive material layer disposed between the semiconductor material and the dielectric layer.

32. The optoelectronic device of claim 31, wherein the conductive material layer comprises a semi-transparent metal layer.

33. The optoelectronic device of claim 31, wherein the conductive material layer comprises a transparent conductive oxide layer.

34. The optoelectronic device of claim 31, wherein the first boundary is adjacent to the conductive material, and the second boundary is adjacent to the surrounding medium.

35. The optoelectronic device of claim 34, wherein at least a portion of the conductive material has an index of refraction about the same as the first index of refraction, and at least a portion of the surrounding medium has an index of refraction about the same as the second index of refraction.

36. The optoelectronic device of claim 24, wherein the semiconductor material comprises any of a group-III arsenide, phosphide, and nitride material.

37. The optoelectronic device of claim 24, wherein the semiconductor material comprises a III-nitride material.

38. The optoelectronic device of claim 24, wherein the dielectric layer comprises a nitride material portion, an oxide material portion, and an oxynitride material portion disposed between the nitride material portion and the oxide material portion, wherein the oxide material portion is disposed proximate to the surrounding medium.

39. The optoelectronic device of claim 38, wherein the nitride material portion is deposited on the semiconductor material.

40. The optoelectronic device of claim 38, wherein the nitride material portion is deposited on a conductive material overlying the semiconductor material.

41. The optoelectronic device of claim 38, wherein the nitride material comprises silicon nitride, the oxide material comprises silicon dioxide, and the oxynitride material comprises silicon oxynitride.

42. The optoelectronic device of claim 38, wherein the nitride material has a refractive index of about 2.5, and the surrounding medium has a refractive index in a range of about 1 to about 1.5.

43. The optoelectronic device of claim 24, wherein the dielectric layer comprises an oxynitride material having a composition that varies with depth.

44. The optoelectronic device of claim 24, wherein the dielectric layer comprises an oxide portion and an oxynitride portion.

45. The optoelectronic device of claim 24, wherein the dielectric layer comprises a nitride portion and an oxynitride portion.

46. The optoelectronic device of claim 24, wherein the dielectric layer comprises a plurality of discrete sublayers, with each sublayer of the plurality of sublayers having a substantially constant composition that is different from the composition of the other sublayers of the plurality of sublayers.

47. The optoelectronic device of claim 24, wherein the dielectric layer composition varies substantially continuously with depth.

48. The optoelectronic device of claim 24, wherein the dielectric layer composition varies stepwise with depth.

49. A method for forming an optoelectronic device, the method comprising the steps of:

ramping from high to low any of the flow rate and concentration of a first nitrogen-containing source gas supplied to a deposition chamber in production of a dielectric material; and

ramping from low to high any of the flow rate and composition of a second oxygen-containing source gas supplied to the deposition chamber in production of said dielectric material.

50. The method of claim 49, wherein the nitrogen-containing source gas ramping step is performed substantially simultaneously with the oxygen-containing source gas ramping step.

51. The method of claim 49, further comprising depositing Si₃N₄ material over a semiconductor material.

52. The method of claim 51 wherein the semiconductor substrate comprises any of a group-III arsenide, phosphide, and nitride emitter.

53. The method of claim 51, further comprising depositing a conductor between the semiconductor material and the Si₃N₄ material.

54. The method of claim 51, further comprising depositing SiO₂ material above said Si₃N₄ material.

55. The method of claim 54, further comprising depositing Si_XO_YN material between said Si₃N₄ material and said SiO₂ material.

56. The method of claim 49, wherein the nitrogen-containing source gas is ramped from high to low flow rate, and the oxygen-containing source gas is ramped from low to high flow rate.

57. The method of claim 49, wherein nitrogen atoms from the nitrogen-containing source gas and oxygen atoms from the oxygen-containing source gas are deposited on or over a semiconductor substrate in a plasma-enhanced chemical vapor deposition process.

58. The method of claim 49, wherein nitrogen atoms from the nitrogen-containing source gas and oxygen atoms from the oxygen-containing source gas are deposited on or over a semiconductor substrate in a reactive sputtering process.

59. The method of claim 49, wherein any of the nitrogen-containing source gas and the oxygen-containing source gas comprises a noble gas.

60. The method of claim 49, wherein the nitrogen-containing source gas comprises ammonia.

61. The method of claim 49, wherein the oxygen-containing source gas comprises any of diatomic oxygen and nitrous oxide.

62. The method of claim 49, further comprising forming a dielectric passivation layer having a composition that varies substantially continuously with depth.

63. The method of claim 49, further comprising forming a dielectric passivation layer having a composition that varies stepwise with depth.

64. The method of claim 49, further comprising forming a dielectric layer comprising an oxynitride material having a composition that various with depth.

65. The method of claim 49, further comprising forming a dielectric layer comprising an oxide portion and an oxynitride portion.

66. The method of claim 49, further comprising forming a dielectric layer comprising a nitride portion and an oxynitride portion.