High electron mobility transistor and fabrication method thereof

A method for forming a high electron mobility transistor, comprising:

• providing a substrate;
• forming a channel layer on the substrate;
• forming an electron supply layer on the channel layer;
• forming a dielectric passivation layer on the electron supply layer;
• forming a gate recess into the dielectric passivation layer and the electron supply layer;
• conformally depositing a surface modification layer on an interior surface of the gate recess;
• subjecting the surface modification layer to an oxidation treatment or a nitridation treatment, wherein the surface modification layer is first subjected to the oxidation treatment and is then subjected to the nitridation treatment;
• and
• forming a P-type GaN layer in the gate recess and on the surface modification layer.