Forward Metal-Assisted Chemical Etching for Self-Aligned Gate-Recess Enhancement-Mode β-Ga2O3 Metal−Semiconductor Field-Effect Transistors

Achieving fail-safe normally-off operation without plasma-induced damage remains a significant challenge in β-Ga2O3-based high-power electronics. We demonstrate a forward metal-assisted chemical (f-MAC) etching that functions as a damage-free and self-aligned process for recessed-gate β-Ga2O3 metal–semiconductor field-effect transistors. The asymmetric work functions of a Ti Ohmic electrode and buried Pt gate electrode establish a built-in electric field that separates photogenerated electron−hole pairs and drives the localized etching of β-Ga2O3, generating a recessed gate structure. A vertical etching rate of 7.9 nm/min enables a channel thickness reduction from 402 to 230 nm, shifting the threshold voltage from −9.14 to +1.55 V to achieve enhancement-mode operation. The device demonstrates a 33.7% reduction in subthreshold swing and a 5.26-fold enhancement in the on/off current ratio owing to the strengthened channel modulation and defect-preferential nature of f-MAC etching, establishing f-MAC etching as a promising damage-free fabrication process for high-performance β-Ga2O3 high-power electronics.