$\Gamma$ -Gate MOS-HEMTs by Methods of Ozone Water Oxidation and Shifted Exposure

This letter reports, for the first time, a Γ-gate metal-oxide-semiconductor high-electron-mobility transistor (MOS-HEMT), which can achieve gate-length reduction, improved gate insulation, and formations of a field plate and a full surface passivation within the drain-source region at the same time by using the ozone water oxidation and shifted exposure techniques. The present Γ-gate MOS-HEMT has demonstrated significant improvements of 523% in the two-terminal gate-drain breakdown, 137% in the on -state drain-source breakdown, and 28%/39.3% in the unity-gain cutoff frequency/maximum oscillation frequency (f_T/f_max), as compared to a conventional Schottky-gate device fabricated upon the same epitaxial structure by using an identical optical mask.