Fig. 4

In the interface region, O replacing N in the Ga–N bond results in a Ga-rich layer and a GaO _x layer. The Ga-rich layer acts as the GaN-to-GaO _x transition layer. The Ga–O formation eliminates the polarization of GaN and acts as positive charges. As a result, the conduction band bends gradually from upward to downward and the BE varies accordingly