Improvement of channel mobility and reliability in GaN-MOSFETs

The channel mobility and positive bias temperature instability is improved by the additional two processes of the gate structures in recessed normally-off GaN-MOSFETs. The one is the surface treatment for removal of the damage by the recess etching. The other is annealing process of gate insulator to reduce the impurity density drastically. These additional processes realize the channel mobility and reliability improvement by the suppression of coulomb scattering and the trap reduction at the gate insulators.