Ohmic contacts to nitrogen polarity GaN

• US 20080185608A1
• Filed: 01/31/2008
• Published: 08/07/2008
• Est. Priority Date: 02/01/2007
• Status: Active Grant

• Current Assignee: Creeled Incorporated
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Chitnis, Ashay
• Granted Patent: US 8,021,904 B2
• Time in Patent Office: Days
• US Class Current: 257/99
• CPC Class Codes: H01L 33/0093 Wafer bonding; Removal of the growth substrate
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/40 Materials therefor

Abstract

Contacting materials and methods for forming ohmic contact to the N-face polarity surfaces of Group-III nitride based semiconductor materials, and devices fabricated using the methods. One embodiment of a light emitting diode (LED) a Group-III nitride active epitaxial region between two Group-III nitride oppositely doped epitaxial layers. The oppositely doped layers have alternating face polarities from the Group III and nitrogen (N) materials, and at least one of the oppositely doped layers has an exposed surface with an N-face polarity. A first contact layer is included on and forms an ohmic contact with the exposed N-face polarity surface. In one embodiment, the first contact layer comprises indium nitride.

Claims

1. A method for fabricating a light emitting diode (LED), comprising:

forming an epitaxial active region between first and second oppositely doped epitaxial layers on a growth substrate with said first oppositely doped layer adjacent said growth substrate, wherein said epitaxial layers are formed on said growth substrate with alternating face polarities;

removing said growth substrate exposing a surface of said first oppositely doped layer; and

forming a first contact layer on said exposed surface of said first oppositely doped layer, said first contact layer cooperating with the polarization effects of said face polarity of said exposed surface to form an ohmic contact.

2. The method of claim 1, wherein said epitaxial active region and said oppositely doped epitaxial layers are formed from a Group-III nitride material system.

3. The method of claim 1, wherein said epitaxial active region and said oppositely doped epitaxial layers are formed from a gallium nitride (GaN) material system.

5. The method of claim 1, wherein said epitaxial layers are formed from a GaN material system and wherein said first contact layer comprises indium nitride (InN).

6. The method of claim 1, further comprising forming a second contact layer in contact with said second oppositely doped layer.

7. The method of claim 1, wherein said first contact layer reduces the barrier height at the interface between said first contact layer and said first oppositely doped layer to allow electron tunneling though the interface.

8. The method of claim 7, wherein said electron tunneling provides low contact resistivity ohmic contact.

4. The method of claim 4, wherein said epitaxial layers are formed of alternating N-face and Ga-face polarities, said exposed surface having an N-face polarity.

9. A light emitting diode (LED), comprising:

a Group-III nitride active epitaxial region between two Group-III nitride oppositely doped epitaxial layers, said oppositely doped layers having alternating face polarities from the Group III and nitrogen (N) materials, at least one of said oppositely doped layers having an exposed surface with an N-face polarity;

a first contact layer on and forming an ohmic contact with said exposed N-face polarity surface.

10. The LED of claim 9, wherein said first contact layer cooperates with the polarization of said N-face polarity surface to form said ohmic contact.

11. The LED of claim 9, wherein said first contact layer reduces the barrier height at the interface between said first contact layer and said N-face polarity surface to promote electron tunneling though the interface.

12. The LED of claim 11, wherein said electron tunneling provides a low resistivity between said first contact layer and said N-face polarity surface.

13. The LED of claim 9, wherein said epitaxial layers are formed of gallium nitride (GaN).

14. The LED of claim 9, wherein said first contact layer is formed of indium nitride (InN).

15. The LED of claim 9, further comprising a second contact layer in contact with one of said oppositely doped layers.

20. The LED of claim 9, wherein said first contact layer reduces the barrier height at the interface between said first contact layer and said N-face polarity surface to promote electron tunneling though the interface.

21. The LED of claim 11, wherein said electron tunneling provides a low resistivity between said first contact layer and said N-face polarity surface.

16. A light emitting diode (LED), comprising:

a gallium nitride (GaN) based active region between a GaN based p-type layer and a GaN based n-type layer, said n-type layer having an exposed surface with an N-face polarity;

a first contact layer on and forming an ohmic contact with said exposed N-face polarity surface.

17. The LED of claim 16, wherein said n-type layer has alternating Ga-face and N-face polarity surfaces.

18. The LED of claim 16, wherein said first contact layer comprises indium nitride (InN).

19. The LED of claim 16, wherein said first contact layer cooperates with the polarization of said N-face polarity surface to form said ohmic contact.

22. A method for fabricating a light emitting diode (LED), comprising:

forming an first doped semiconductor layer made of a material having alternating face polarities surfaces, with one of said face polarities being an nitrogen (N)-face polarity;

forming a first contact layer integral to said first doped layer, said first contact layer cooperating with one of said N-face polarity surfaces to provide an ohmic contact to said first doped layer;

forming an active semiconductor region on said first doped layer; and

forming a second doped semiconductor layer on said active region.

23. The method of claim 22, wherein said doped semiconductor layers and active region are formed successively on a growth substrate with said first doped semiconductor layer adjacent said growth substrate, further comprising removing said growth substrate from said first doped semiconductor layer.

24. The method of claim 22, wherein said first contact layer is embedded in said first doped semiconductor layer.

25. The method of claim 23, wherein said first contact layer is on the surface of said first doped semiconductor layer exposed following said removal of said growth substrate.

26. The method of claim 22, wherein said active region and said doped semiconductor layers are formed from a gallium nitride (GaN) material system.

27. The method of claim 22, wherein said doped semiconductor layers are formed from a GaN material system and wherein said first contact layer comprises indium nitride (InN).

28. The method of claim 22, wherein said first contact layer reduces the barrier height at the interface between said first contact layer and said first oppositely doped layer to promote electron tunneling though the interface.