Reflective ohmic contacts for silicon carbide including a layer consisting essentially of nickel, methods of fabricating same, and light emitting devices including the same

• US 6,794,684 B2
• Filed: 02/14/2003
• Issued: 09/21/2004
• Est. Priority Date: 02/01/2001
• Status: Expired due to Term

• Current Assignee: CREE Led Incorporated (Smart Global Holdings Incorporated)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Hagleitner, Helmut, Slater, David B. Jr.
• Primary Examiner(s): Brewster, William M.
• Application Number:
  US10/368,063
• Publication Number:
  US 20030168663A1
• Time in Patent Office: 585 Days
• Field of Search: 257/91, 257/99, 257/103, 257/77, 438/46, 250/370.01, 250/370.07, 338/22, 428/74
• US Class Current: 257/77
• CPC Class Codes: H01L 21/0485 Ohmic electrodes
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• 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 2924/3011 Impedance
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/34 containing only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 33/405 Reflective materials

Abstract

Reflective ohmic contacts for n-type silicon carbide include a layer consisting essentially of nickel on the silicon carbide. The layer consisting essentially of nickel is configured to provide an ohmic contact to the silicon carbide, and to allow transmission therethrough of optical radiation that emerges from the silicon carbide. A reflector layer is on the layer consisting essentially of nickel, opposite the silicon carbide. A barrier layer is on the reflector layer opposite the layer consisting essentially of nickel, and a bonding layer is on the barrier layer opposite the reflector layer. It has been found that the layer consisting essentially of nickel and the reflector layer thereon can provide a reflective ohmic contact for silicon carbide that can have low ohmic losses and/or high reflectivity.

Claims

1. A reflective ohmic contact for silicon carbide comprising:

a layer consisting essentially of nickel on the silicon carbide, which is configured to provide an ohmic contact to the silicon carbide and to allow transmission therethrough of optical radiation that emerges from the silicon carbide;

a reflector layer on the layer consisting essentially of nickel opposite the silicon carbide;

a barrier layer on the reflector layer opposite the layer consisting essentially of nickel; and

a bonding layer on the barrier layer opposite the reflector layer.

2. A reflective ohmic contact according to claim 1 wherein the layer consisting essentially of nickel is sufficiently thick to provide an ohmic contact to the silicon carbide, but is sufficiently thin to allow transmission therethrough of optical radiation that emerges from the silicon carbide.

3. A reflective ohmic contact according to claim 2 wherein the layer consisting essentially of nickel is sufficiently thin to allow transmission therethrough of substantially all optical radiation that emerges from the silicon carbide.

4. A reflective ohmic contact according to claim 2 wherein the reflector layer is sufficiently thick to reflect substantially all optical radiation that emerges from the layer consisting essentially of nickel.

5. A reflective ohmic contact according to claim 1 wherein the silicon carbide includes a surface and wherein the layer consisting essentially of nickel covers the surface.

6. A reflective ohmic contact according to claim 1 wherein the silicon carbide is n-type silicon carbide.

7. A reflective ohmic contact according to claim 1 in combination with a diode region on the silicon carbide.

8. A reflective ohmic contact according to claim 1 wherein the layer consisting essentially of nickel is a layer consisting of unannealed nickel.

9. A reflective ohmic contact according to claim 7 in further combination with a mounting assembly on the bonding layer opposite the barrier layer.

10. A reflective ohmic contact according to claim 1 wherein the layer consisting essentially of nickel is between about 15 Å

and about 100 Å

thick.

11. A reflective ohmic contact according to claim 1 wherein the layer consisting essentially of nickel is between about 15 Å

and about 25 Å

thick.

12. A reflective ohmic contact according to claim 1 wherein the reflector layer comprises silver and/or aluminum.

13. A reflective ohmic contact according to claim 1 wherein the barrier layer comprises platinum.

14. A reflective ohmic contact according to claim 1 wherein the bonding layer comprises gold.

15. A contact for silicon carbide comprising:

a first layer consisting essentially of nickel on the silicon carbide;

a second layer comprising silver and/or aluminum on the first layer opposite the silicon carbide;

a third layer comprising platinum on the second layer opposite the first layer; and

a fourth layer comprising gold on the third layer opposite the second layer.

16. A contact according to claim 15 wherein the silicon carbide includes a surface and wherein the first layer covers the surface.

17. A contact according to claim 15 wherein the silicon carbide is n-type silicon carbide.

18. A contact according to claim 15 in combination with a diode region on the silicon carbide.

19. A contact according to claim 15 wherein the first layer consists of unannealed nickel.

20. A contact according to claim 18 in further combination with a mounting assembly on the fourth layer opposite the third layer.

21. A contact according to claim 15 wherein the first layer is between about 15 Å

and about 100 Å

thick.

22. A contact according to claim 15 wherein the second layer is at least about 700 Å

thick.

23. A contact according to claim 15 wherein the third layer is at least about 250 Å

thick.

24. A contact according to claim 15 wherein the fourth layer is at least about 250 Å

thick.

25. A light emitting device comprising:

a silicon carbide substrate having first and second opposing faces;

a light emitting region on the second face;

an ohmic contact on the diode region opposite the second face;

a layer consisting essentially of nickel on the first face, which is configured to provide an ohmic contact to the first face and to allow transmission therethrough of optical radiation that emerges from the first face;

a reflector layer on the layer consisting essentially of nickel opposite the first face;

a barrier layer on the reflector layer opposite the layer consisting essentially of nickel; and

a bonding layer on the barrier layer opposite the reflector layer.

26. A device according to claim 25 wherein the layer consisting essentially of nickel is sufficiently thick to provide an ohmic contact to the silicon carbide, but is sufficiently thin to allow transmission therethrough of optical radiation that emerges from the silicon carbide.

27. A device according to claim 26 wherein the layer consisting essentially of nickel is sufficiently thin to allow transmission therethrough of substantially all optical radiation that emerges from the first face.

28. A device according to claim 26 wherein the reflector layer is sufficiently thick to reflect substantially all optical radiation that emerges from the layer consisting essentially of nickel.

29. A device according to claim 25 wherein the layer consisting essentially of nickel covers the first face.

30. A device according to claim 25 wherein the layer consisting essentially of nickel is a layer consisting of unannealed nickel.

31. A device according to claim 25 in further combination with a mounting assembly on the bonding layer opposite the barrier layer.

32. A device according to claim 25 wherein the layer consisting essentially of nickel is between about 15 Å

and about 100 Å

thick.

33. A device according to claim 25 wherein the reflector layer comprises silver and/or aluminum.

34. A device according to claim 25 wherein the barrier layer comprises platinum.

35. A device according to claim 25 wherein the bonding layer comprises gold.

36. A light emitting device comprising:

a silicon carbide substrate having first and second opposing faces;

a light emitting region on the second face;

an ohmic contact on the light emitting region opposite the second face;

a first layer consisting essentially of nickel on the first face;

a second layer comprising silver and/or aluminum on the first layer opposite the first face;

a third layer comprising platinum on the second layer opposite the first layer; and

a fourth layer comprising gold on the third layer opposite the second layer.

37. A device according to claim 36 wherein the first layer covers the first face.

38. A device according to claim 36 wherein the first layer consists of unannealed nickel.

39. A device according to claim 36 in further combination with a mounting assembly on the fourth layer opposite the third layer.

40. A device according to claim 36 wherein the first layer is between about 15 Å

and about 100 Å

thick.

41. A device according to claim 36 wherein the second layer is at least about 700 Å

thick.

42. A device according to claim 36 wherein the third layer is at least about 250 Å

thick.

43. A device according to claim 36 wherein the fourth layer is at least about 250 Å

thick.

44. A method of fabricating a light emitting device comprising:

depositing a first layer consisting essentially of nickel on a first face of a silicon carbide substrate that includes a light emitting region on a second face thereof;

depositing a second layer comprising silver and/or aluminum on the first layer opposite the first face;

depositing a third layer comprising platinum on the second layer opposite the first layer;

depositing a fourth layer comprising gold on the third layer opposite the second layer; and

bonding the fourth layer to an external element, wherein annealing is not performed during the depositing a first layer, between the depositing a first layer and the depositing a second layer, between the depositing a second layer and the depositing a third layer, between the depositing a third layer and the depositing a fourth layer, between the depositing a fourth layer and the bonding the fourth layer, and during the bonding the fourth layer.

45. A method according to claim 44 wherein patterning also is not performed during the depositing a first layer, between the depositing a first layer and the depositing a second layer, between the depositing a second layer and the depositing a third layer, between the depositing a third layer and the depositing a fourth layer and between the depositing a fourth layer and the bonding the fourth layer.

46. A method according to claim 44 wherein the depositing a first layer, the depositing a second layer, the depositing a third layer and the depositing a fourth layer all are performed at room temperature.