Light Emitting Diode with a Dielectric Mirror having a Lateral Configuration

• US 20100140637A1
• Filed: 12/08/2008
• Published: 06/10/2010
• Est. Priority Date: 12/08/2008
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Donofrio, Matthew, Ibbetson, James, Li, Ting, Edmond, John
• Granted Patent: US 8,017,963 B2
• Time in Patent Office: Days
• US Class Current: 257/98
• CPC Class Codes: H01L 33/14 with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure
• CPC Class Codes: H01L 33/145 with a current-blocking structure
• CPC Class Codes: H01L 33/38 with a particular shape
• CPC Class Codes: H01L 33/42 Transparent materials
• CPC Class Codes: H01L 33/46 Reflective coating, e.g. dielectric Bragg reflector

Abstract

A light emitting diode is disclosed that includes an active structure, a first ohmic contact on the active structure, and a transparent conductive oxide layer on the active structure opposite the first ohmic contact. The transparent conductive oxide layer has a larger footprint than said active structure. A dielectric mirror is positioned on the transparent conductive oxide layer opposite said active structure and a second contact is positioned on the transparent conductive oxide layer opposite the dielectric mirror and separated from the active structure.

Claims

1. A light emitting diode comprising:

an active structure;

a first ohmic contact on said active structure;

a transparent conductive oxide layer on said active structure opposite said first ohmic contact, said transparent conductive oxide layer having a larger footprint than said active structure;

a dielectric mirror on said transparent conductive oxide layer opposite said active structure; and

a second contact, said second contact being positioned on said transparent conductive oxide layer opposite said dielectric mirror and separated from said active structure.

2. A light emitting diode according to claim 1 further comprising a reflective metal layer on said dielectric mirror opposite said transparent conductive oxide layer.

3. A light emitting diode according to claim 1 further comprising a current spreading grid located between said transparent conductive oxide layer and said dielectric mirror.

4. A light emitting diode according to claim 3 wherein:

said first ohmic contact comprises a grid; and

said current spreading grid is congruent with portions of said first ohmic contact and with portions of said second contact.

5. A light emitting diode according to claim 3 wherein said current spreading grid comprises at least one metal from the group consisting of titanium, gold, zinc, indium, nickel, and beryllium

6. A light emitting diode according to claim 1 wherein said active structure comprises a plurality of epitaxial layers formed from the Group III nitride material system.

7. A light emitting diode according to claim 1 wherein said transparent conductive oxide layer is formed from indium-tin-oxide.

8. A light emitting diode according to claim 1 wherein said dielectric mirror is formed from alternating layers of TiO₂ and SiO₂.

9. A light emitting diode according to claim 1 further comprising a lenticular surface on at least portions of said active structure.

10. A light emitting diode comprising:

a first Group III nitride epitaxial layer having a first conductivity type;

a second Group III nitride epitaxial layer adjacent said first Group III nitride layer and having the opposite conductivity type from said first layer for forming a p-n junction with said first layer;

a transparent conductive oxide layer for providing current across the p-n junction formed by said Group III nitride layers, said transparent conductive oxide layer being adjacent said second Group III nitride layer and opposite from said first Group III nitride layer;

a dielectric mirror for increasing the external quantum efficiency of said diode, said mirror being adjacent said transparent conductive oxide layer and opposite from said Group III nitride layers;

an ohmic contact to said first Group III nitride layer; and

a contact to said transparent conductive oxide layer for providing current flow between said transparent conductive oxide layer and said ohmic contact and though said Group III nitride layers to generate output.

11. A light emitting diode according to claim 10 further comprising a reflective metal layer adjacent said dielectric mirror and opposite from said transparent conductive oxide layer.

12. A light emitting diode according to claim 11 wherein said dielectric mirror is formed from alternating layers of TiO₂ and SiO₂.

13. A light emitting diode according to claim 12 wherein the layers of TiO₂ have a thickness of between about 50 and 60 nm, and wherein the layers of SiO₂ have a thickness of between about 70 and 80 nm.

14. A light emitting diode according to claim 10 further comprising a current spreading grid positioned between said epitaxial layers and said dielectric mirror.

15. A light emitting diode according to claim 14 wherein:

said ohmic contact to said first Group III nitride layer comprises a grid; and

said current spreading grid is congruent with portions of said ohmic to said first Group III nitride layer and with portions of said contact to said transparent conductive oxide layer.

16. A light emitting diode according to claim 14 wherein said current spreading grid is formed from one or more metals.

17. A light emitting diode according to claim 16 wherein said current spreading grid comprises at least one metal from the group consisting of titanium, gold, zinc, indium, nickel, and beryllium.

18. A light emitting diode according to claim 14 wherein said current spreading grid is positioned between said transparent conductive oxide layer and said dielectric mirror.

19. A light emitting diode according to claim 14 wherein said current spreading grid is positioned on said second Group III nitride epitaxial layer.

20. A light emitting diode according to claim 10 wherein said transparent conductive oxide layer is formed from indium-tin-oxide.

21. A light emitting diode according to claim 10 wherein said transparent conductive oxide layer is formed from fluorine doped tin oxide.

22. A light emitting diode according to claim 10 wherein said transparent conductive oxide layer is formed from aluminum doped zinc oxide.

23. A light emitting diode according to claim 10 wherein said transparent conductive oxide layer is formed from zinc-tin-oxide.

24. A light emitting diode according to claim 10 further comprising a carrier substrate bonded to said dielectric mirror opposite said transparent conductive oxide layer with a bonding material.

25. A light emitting diode according to claim 24 wherein said bonding material comprises one or more metals.

26. A light emitting diode according to claim 24 wherein said bonding material comprises glue.

27. A light emitting diode according to claim 24 wherein said carrier substrate is selected from the group consisting of SiC, sapphire, silicon, and metals.

28. A light emitting diode according to claim 24 wherein said carrier substrate is formed from an electrically insulating material.

29. A light emitting diode according to claim 11 further comprising a carrier substrate bonded to said reflective metal layer with a bonding material.

30. A light emitting diode according to claim 29 wherein said bonding material comprises one or more metals.

31. A light emitting diode according to claim 29 wherein said bonding material comprises glue.

32. A light emitting diode according to claim 29 wherein said carrier substrate is selected from the group consisting of SiC, sapphire, silicon, and metals.

33. A light emitting diode according to claim 29 wherein said carrier substrate is electrically insulating.

34. A method of forming a light emitting diode with increased light extraction, the method comprising:

forming a transparent conductive oxide layer on a p-type epitaxial layer of a light emitting diode structure that also includes at least an n-type layer adjacent the p-type layer;

adding a dielectric reflector to the transparent conductive oxide opposite from the p-type layer;

etching the n-type and p-type layers into a mesa using an etch that will remove the n-type and p-type layer materials, but that does not etch the transparent conductive oxide material;

adding an n-type ohmic contacts to the n-type layer; and

adding an ohmic contact to the transparent conductive oxide layer for connecting to the p-type layer.

35. A method according to claim 34 comprising forming a current spreading grid after the step of forming the TCO layer and before the step of adding the dielectric reflective layer.

36. A method according to claim 34 comprising:

creating a reduced conductivity region in the p-type layer; and

adding an ohmic contact to the n-type layer with geometry that is congruent with the geometry of the reduced conductivity region.

37. A method according to claim 36 comprising forming the reduced conductivity region before adding the transparent conductive oxide to the p-type layer.

38. A method according to claim 34 further comprising the steps of:

growing the n-type and p-type layers on a growth substrate;

bonding the dielectric reflector layer to a carrier substrate; and

removing the growth substrate to expose the n-type epitaxial layer;

prior to the step of etching the n-type and p-type layers into a mesa

39. A method according to claim 38 comprising growing n-type and p-type layers of Group III nitride on a silicon carbide growth substrate.

40. A method according to claim 39 further comprising growing at least one undoped Group III nitride layer between the n-type and p-type Group III nitride layers.