Over the p-GaN layer or the donor-supply layer, one or more gate material layers including metals or other conductive materials are deposited to complete gate film layer 209. In various examples, the gate film stack metal layers may include a refractory metal or its compounds, e.g., tungsten (W), titanium nitride (TiN) and tantalum (Ta). Other commonly used gate metals include nickel (Ni) and gold (Au). Other gate film layers may be polysilicon. This part of the gate film layer may be about 300 angstroms to about 3000 angstroms thick. In addition to p-GaN and gate conductors, other material layers may be included in the gate stack. Examples include a thin dielectric film layer.

The refractory metals and its compounds in the gate film layer 209 may be deposited using a sputtering process at a process temperature of between about 200 degrees Celsius to about 450 degrees Celsius. Polysilicon may be deposited using chemical vapor deposition (CVD), for example, low pressure CVD, at about 600 degrees Celsius to about 800 degrees Celsius.

After the gate film layer 209 is deposited, a photoresist layer is patterned over the gate film layer 209. A photoresist material is deposited, usually by a spin coating process, and is cured. A portion of the photoresist material is exposed to radiation that changes material properties in the portion exposed. Then the photoresist material is developed to remove a portion of the photoresist, either the exposed portion or unexposed portion depending on the type of photoresist used. The photoresist pattern is thereby formed. In some embodiments, a hardmask layer is deposited first under the photoresist to better protect a portion of the gate film layer 209.