Method for fabrication of III-nitride heterojunction semiconductor device

1. A method for fabricating a III-nitride semiconductor device, comprising:

forming a III-nitride heterojunction that includes a channel layer and a barrier layer;

partially decomposing a portion of said barrier layer to obtain a reduced nitrogen region having a smaller concentration of nitrogen, compared to an adjoining region of said barrier layer;

said reduced nitrogen region being situated in said barrier layer and substantially confined under at least one of a gate, a source electrode, and a drain electrode of said III-nitride semiconductor device such that said reduced nitrogen region does not extend between said gate and either of said source electrode and said drain electrode, said reduced nitrogen region having an increased group III semiconductor concentration compared to said adjoining region of said barrier layer.

2. The method of claim 1 , wherein said channel layer is composed of GaN and said barrier layer is composed of AlGaN.

3. The method of claim 1 , further comprising:

forming a diffusion barrier over said heterojunction, said diffusion barrier including an opening;

heating said heterojunction to a temperature above a decomposition temperature of said barrier layer to allow nitrogen to escape from said opening to form said reduced nitrogen region in said barrier layer.

4. The method of claim 3 , wherein said diffusion barrier is selected from the group consisting of silicon nitride, TiN, AlN, and GaN.

5. The method of claim 1 , wherein said gate is formed over said reduced nitrogen region.

6. The method of claim 1 , wherein said gate includes a gate electrode that is Schottky coupled to said heterojunction.

7. The method of claim 1 , wherein said gate includes a gate electrode and a gate dielectric that is disposed between said gate electrode and said III-nitride heterojunction.

8. The method of claim 1 , wherein at least one of said source electrode and said drain electrode is formed over said reduced nitrogen region.

9. The method of claim 7 , wherein said gate dielectric is disposed between said gate electrode and said barrier layer.

10. The method of claim 1 , wherein said III-nitride heterojunction is disposed over a support body that includes a silicon substrate, and a III-nitride transition layer.

11. The method of claim 10 , wherein said transition layer comprises AlN.

12. The method of claim 1 , wherein said III-nitride heterojunction is disposed over a support body that includes a substrate, and a transition layer, said substrate being selected from the group consisting of SiC and sapphire.