SiCl4-based reactive ion etching for controlled low-damage mesa and gate recess formation in β-Ga2O3 MOSFETs

β-Ga 2 O 3 is a promising ultra-wide-bandgap semiconductor for next-generation power electronics. However, its chemical inertness makes controlled etching a critical challenge during device fabrication. In this work, dry etching processes for β-Ga 2 O 3 were systematically investigated with emphasis on mesa isolation and gate recess formation for processing of normally-off metal-oxide-semiconductor field-effect transistor (MOSFET) fabrication. Multiple plasma chemistries, including those based on Ar, Cl 2 , SF 6 , and SiCl 4 were evaluated using reactive ion etching (RIE) and inductively coupled plasma (ICP) conditions. Although chlorine and fluorine-based chemistries achieved higher etch rates, they also introduced increased surface roughness, residue formation, unwanted trenching, and degraded etch profiles attributable to ion-induced damage and low-volatility reaction by-products.In contrast, SiCl 4 -based process provided a moderate and highly controllable etch rate of 11.6 ± 0.08 nm/min while significantly improving surface morphology, with reduced RMS roughness. The optimized process was successfully applied to mesa isolation and gate recess formation, providing smooth surfaces, well-defined sidewalls, and accurate recess-depth control. β-Ga 2 O 3 MOSFETs fabricated using the optimized process exhibited normally-off operation with a maximum current of approximately 2.8 mA/mm, threshold voltage of ∼8.3 ± 1.2 V, an ON/OFF current ratio of (2.3 ± 1.7) ×10 6 , a subthreshold swing of 0.74 ± 0.16 V/dec, and a maximum transconductance of 4.1 ± 0.8 mS/mm. These results demonstrate that SiCl 4 -RIE enables controlled, reduced plasma-induced damage etching of β-Ga 2 O 3 , promising for MOSFET fabrication.