Gallium nitride normally off mosfet using dual-metal-gate structure for the improvement in current drivability

A gallium nitride (GaN)-based normally off metal–oxide–semiconductor field-effect transistor (MOSFET) using a dual-metal-gate (DMG) structure was proposed and fabricated to improve current drivability. Normally off operation with a high V_th of 2.3 V was obtained using a Cl₂ /BCl₃-based recess etching process. The DMG structure was employed to improve current characteristics, which can be degraded by recess etching. The I_D and g_m of a DMG-based device with nickel (Ni)-aluminum (Al) were improved by 42.1% and 30.9%, respectively, in comparison to the performances of a single-metal-gate-based device with Ni because the DMG structure increased electron velocity in the channel region. This demonstrates that the DMG structure with a large work-function difference significantly improves the carrier transport efficiency. GaN-based recessed-gate MOSFETs based on the DMG structure hold promising potentials for high-efficiency power devices.