Second Schottky Contact Metal Layer to Improve GaN Schottky Diode Performance

A field-effect transistor (FET) comprising:

• a substrate;
• a first nitride-based semiconductor layer disposed atop the substrate, the first nitride-based semiconductor layer being of a first conductivity type and having a first doping concentration;
• a second nitride-based semiconductor layer of the first conductivity type disposed atop a portion of the first nitride-based semiconductor layer, the second nitride-based semiconductor layer being a different nitride-based semiconductor layer than the first nitride-based semiconductor layer such that a heterojunction is formed between the first and second layers of nitride semiconductor;
• a first Schottky contact metal layer having a first metal work function disposed on a top surface of the second nitride-based semiconductor layer, a first Schottky junction with a first barrier height being formed between the first Schottky contact metal layer and the second nitride-based semiconductor layer;
• a second Schottky contact metal layer having a second metal work function disposed atop of and laterally surrounding the first Schottky contact metal layer, the second metal work function being higher than the first metal work function, a second Schottky junction with a second barrier height being formed between laterally surrounding portions of the second Schottky contact metal layer and the first nitride-based semiconductor layer;
• and
• a metal layer disposed atop a planar surface of the first nitride-based semiconductor layer, an ohmic contact being formed between the metal layer and the first nitride-based semiconductor layer.