Transparent ohmic contacts on light emitting diodes with carrier substrates

• US 9,484,499 B2
• Filed: 04/20/2007
• Issued: 11/01/2016
• Est. Priority Date: 04/20/2007
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Edmond, John A., Slater, David B. Jr., Bergmann, Michael J.
• Primary Examiner(s): SAYADIAN, HRAYR
• Application Number:
  US11/738,171
• Publication Number:
  US 20080258161A1
• Time in Patent Office: 3,483 Days
• Field of Search: 257/98, 257/E33.025, 257/E33.058, 257/E33.064, 257/E33.068, 257/E33.074
• US Class Current: 1/1
• CPC Class Codes: H01L 33/0093 Wafer bonding; Removal of the growth substrate
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/22 Roughened surfaces, e.g. at the interface between epitaxial layers
• CPC Class Codes: H01L 33/42 Transparent materials

Abstract

A light emitting diode is disclosed that includes an active structure formed of at least p-type and n-type epitaxial layers of Group III nitride on a conductive carrier substrate. A conductive bonding system joins the active structure to the conductive carrier substrate. A first transparent ohmic contact is on the active structure adjacent the conductive carrier substrate, a second transparent ohmic contact is on the active structure opposite the conductive carrier substrate, and a third ohmic contact is on the conductive carrier substrate opposite from the active structure.

Claims

1. A light emitting diode comprising:

an active structure comprising p-type and n-type epitaxial layers of Group III nitride, wherein the active structure comprises a first lenticular surface;

an electrically conductive carrier substrate;

an electrically conductive bonding system joining said active structure to said electrically conductive carrier substrate;

a first transparent ohmic contact to said active structure, said first transparent ohmic contact between said active structure and said electrically conductive carrier substrate;

a second transparent ohmic contact in direct contact with said active structure, without any layer in between said active structure and said second transparent ohmic contact, said active structure between said second transparent ohmic contact and said electrically conductive carrier substrate; and

a third ohmic contact to said electrically conductive carrier substrate, said electrically conductive carrier substrate between said third ohmic contact and said active structure,

wherein said second transparent ohmic contact comprises a second lenticular surface opposite the first lenticular surface of the active structure.

2. A light emitting diode according to claim 1 wherein said Group III nitride epitaxial layers are selected from the group consisting of gallium nitride and indium gallium nitride.

3. A light emitting diode according to claim 1 wherein said first transparent ohmic contact and said second transparent ohmic contact comprise indium tin oxide.

4. A light emitting diode according to claim 1 wherein said first transparent ohmic contact and said second transparent ohmic contact are selected from the group consisting of:

indium tin oxide, nickel oxide, zinc oxide, cadmium tin oxide, titanium tungsten nickel, indium oxide, tin oxide, magnesium oxide, ZnGa₂O₄, SnO₂/Sb, Ga₂O₃/Sn, AgInO₂/Sn, In₂O₃/Zn, CuAlO₂, LaCuOS, CuGaO₂, and SrCu₂O₂.

5. A light emitting diode according to claim 1 wherein said electrically conductive bonding system comprises at least one metal layer.

6. A light emitting diode according to claim 1 further comprising at least one reflective layer selected from the group consisting of:

a bonding layer;

said electrically conductive carrier substrate;

additional layers adjacent said bonding layer; and

combinations thereof.

7. A light emitting diode according to claim 1 wherein said third ohmic contact to said electrically conductive carrier substrate is transparent.

8. A light emitting diode according to claim 7 wherein said third ohmic contact is selected from the group consisting of indium tin oxide, nickel oxide, zinc oxide, cadmium tin oxide, titanium tungsten nickel, indium oxide, tin oxide, magnesium oxide, ZnGa₂O₄, SnO₂/Sb, Ga₂O₃/Sn, AgInO₂/Sn, In₂O₃/Zn, CuAlO₂, LaCuOS, CuGaO₂, and SrCu₂O₂.

9. A light emitting diode according to claim 1 further comprising a bond pad to said second transparent ohmic contact.

10. A light emitting diode according to claim 9 further comprising a reflective layer between said bond pad and said second transparent ohmic contact for reflecting light off said bond pad.

11. A light emitting diode according to claim 1 wherein at least one of said first transparent ohmic contact and said second transparent ohmic contact comprises a plurality of layers that progress in refractive index with respect to one another to minimize Fresnel loss as light travels through said first transparent ohmic contact and said second transparent ohmic contact.

12. A light emitting diode according to claim 1 wherein at least one of said first transparent ohmic contact and said second transparent ohmic contact comprises indium tin oxide in which the amount of indium is graded through the contact to progressively change the refractive index and minimize Fresnel loss as a light travels through said first transparent ohmic contact and said second transparent ohmic contact.

13. A light emitting diode according to claim 1 further comprising a passivation layer on said second transparent ohmic contact.

14. A light emitting diode according to claim 13 wherein said passivation layer is selected from the group consisting of silicon nitride, silicon dioxide and silicon oxynitride and covers said second transparent ohmic contact and said active structure.

15. A light emitting diode according to claim 13 wherein said passivation layer comprises stoichiometric silicon nitride.

31. A light emitting diode according to claim 1, wherein said first transparent ohmic contact is adjacent to said active structure.

16. A light emitting diode comprising:

an electrically conductive carrier substrate;

a p-type epitaxial layer on said electrically conductive carrier substrate;

a first transparent ohmic contact between said p-type layer and said electrically conductive carrier substrate;

an n-type epitaxial layer on said p-type layer;

a lenticular surface on said n-type epitaxial layer;

a second transparent ohmic contact covering said n-type epitaxial layer and said lenticular surface;

said second transparent ohmic contact forming a lenticular surface opposite said n-type epitaxial layer; and

a third ohmic contact to said electrically conductive carrier substrate opposite from said epitaxial layers

wherein said first transparent ohmic contact comprises a second lenticular surface opposite the first lenticular surface of the active structure.

17. A light emitting diode according to claim 16 wherein said third ohmic contact to said electrically conductive carrier substrate is transparent.

18. A light emitting diode according to claim 17 wherein said third ohmic contact is selected from the group consisting of:

indium tin oxide, nickel oxide, zinc oxide, cadmium tin oxide, titanium tungsten nickel, indium oxide, tin oxide, magnesium oxide, ZnGa₂O₄, SnO₂/Sb, Ga₂O₃/Sn, AgInO₂/Sn, In₂O₃/Zn, CuAlO₂, LaCuOS, CuGaO₂, and SrCu₂O₂.

19. A light emitting diode according to claim 16 wherein at least one of said first transparent ohmic contact and said second transparent ohmic contact are selected from the group consisting of:

indium tin oxide, nickel oxide, zinc oxide, cadmium tin oxide, titanium tungsten nickel, indium oxide, tin oxide, magnesium oxide, ZnGa₂O₄, SnO₂/Sb, Ga₂O₃/Sn, AgInO₂/Sn, In₂O₃/Zn, CuAlO₂, LaCuOS, CuGaO₂, and SrCu₂O₂.

20. A light emitting diode according to claim 16 further comprising a bond pad to said second transparent ohmic contact.

21. A light emitting diode according to claim 16 further comprising bonding layers between said first transparent ohmic contact and said electrically conductive carrier substrate.

22. A light emitting diode according to claim 21 wherein said bonding layers comprise at least one metal layer.

23. A light emitting diode according to claim 22 further comprising a reflective layer selected from the group consisting of one of said bonding metal layers and said electrically conductive carrier substrate.

24. A light emitting diode according to claim 16 wherein said electrically conductive carrier substrate is selected from the group consisting of silicon, silicon carbide, gallium arsenide and metals.

25. A light emitting diode according to claim 16 further comprising a passivation layer covering said second transparent ohmic contact.

26. A light emitting diode according to claim 25 wherein said passivation layer comprises silicon nitride.

27. A light emitting diode according to claim 16 wherein at least one of said first transparent ohmic contact and said second transparent ohmic contact comprises a plurality of layers of transparent material with progressing indexes of refraction for minimizing Fresnel loss as light passes through said first transparent ohmic contact and said second transparent ohmic contact.

28. A light emitting diode according to claim 16 wherein at least one of said first transparent ohmic contact and said second transparent ohmic contact comprises a layer of indium tin oxide in which the content of indium is progressively graded across the contact to minimize Fresnel loss as light passes through said first transparent ohmic contact and said second transparent ohmic contact.

32. A light emitting diode according to claim 16, wherein said second transparent ohmic contact is adjacent to said n-type epitaxial layer.

29. A light emitting diode comprising:

an active structure comprising p-type and n-type epitaxial layers of Group III nitride, the active structure comprising a lenticular surface;

an electrically conductive carrier substrate;

an electrically conductive bonding system joining said active structure to said electrically conductive carrier substrate;

a first transparent ohmic contact to said active structure;

a second transparent ohmic contact in direct contact with said lenticular surface of said active structure, without any layer in between said active structure and said second transparent ohmic contact, said active structure between said second transparent ohmic contact and said electrically conductive carrier substrate, wherein said second transparent ohmic contact comprises a progressive refractive index; and

a third ohmic contact to said electrically conductive carrier substrate, said electrically conductive carrier substrate between said third ohmic contact and said active structure.

33. A light emitting diode according to claim 29, wherein said first transparent ohmic contact is adjacent to said active structure.

34. A light emitting diode according to claim 29, wherein said electrically conductive bonding system comprises at least one metal layer.

35. A light emitting diode according to claim 29, wherein said electrically conductive bonding system comprises a first metal layer and second metal layer.

36. A light emitting diode according to claim 29, wherein said second transparent ohmic contact includes a lenticular surface.

37. A light emitting diode according to claim 29, wherein said n-type epitaxial layer includes a lenticular surface.

38. A light emitting diode according to claim 29, further comprising:

a bond pad to said second transparent ohmic contact.

39. A light emitting diode according to claim 38, wherein said bonding pad includes a reflective layer.

40. A light emitting diode according to claim 29, further comprising:

a passivation layer on said second transparent ohmic contact.

30. In a light emitting diode that includes an electrically conductive carrier substrate and a Group III nitride active portion, the improvement comprising:

an n-type layer of Group III nitride including a lenticular surface;

a transparent metal ohmic contact in direct contact with said lenticular surface, without any layer in between said lenticular surface and said transparent metal ohmic contact, in which the transparent metal ohmic contact comprises a progressive refractive index; and

an electrically conductive bonding system between the electrically conductive carrier substrate and the Group III nitride active portion.

41. A light emitting diode according to claim 30, further comprising:

a bond pad to said transparent metal ohmic contact.

42. A light emitting diode according to claim 30, further comprising:

a passivation layer on said transparent metal ohmic contact.

43. A light emitting diode according to claim 30, further comprising:

a p-type layer of Group III nitride; and

a second metal ohmic contact in direct contact with said p-type layer, without any layer in between said p-type layer and said second metal ohmic contact.

44. A light emitting diode according to claim 30, wherein said electrically conductive bonding system comprises a conductive bonding metal.

45. A light emitting diode according to claim 30, further comprising:

a third metal ohmic contact in direct contact with said electrically conductive carrier substrate, without any layer in between said electrically conductive carrier substrate and said third metal ohmic contact.

46. A light emitting diode according to claim 30, further comprising:

a reflective layer on said transparent metal ohmic contact; and

a bond pad on said reflective layer.