Method for manufacturing a gate terminal of a hemt device, and hemt device

A HEMT device, comprising:

• a heterostructure;
• a dielectric layer on the heterostructure;
• a gate electrode extending through the dielectric layer and contacting the heterostructure, the gate electrode including:
• a first gate metal layer overlying heterostructure;
• and
• a protection layer between the heterostructure and the first gate metal layer, the protection layer configured to impede diffusion of metal atoms from the first metal layer towards the heterostructure;
• and
• a source or drain electrode extending into the heterostructure to a greater depth than the gate electrode.

A high electron mobility transistor (HEMT) device, comprising:

• a semiconductor body including a semiconductor heterostructure;
• a dielectric layer on the semiconductor heterostructure and including an opening exposing a superficial region of the semiconductor heterostructure;
• a gate electrode on the dielectric layer and in the opening and including:
• a first gate metal layer configured to form a Schottky contact with the heterostructure;
• a second gate metal layer on and in direct contact with the first metal layer and with the dielectric layer;
• and
• a third gate metal layer on the second gate metal layer, the third gate metal layer including aluminum, the second gate metal layer forming a barrier against diffusion of aluminum atoms from the third metal layer towards the heterostructure.