Abstract
We demonstrate high-performance MOSFETs on β-Ga(2)O(3) films grown by plasma-assisted molecular beam epitaxy (PA-MBE). The high crystalline quality of the β-Ga(2)O(3) epilayer was confirmed by X-ray diffraction and atomic force microscopy. An optimized CF(4)-plasma treatment was employed to introduce fluorine (F) into the near-surface region, effectively suppressing donor-like states. The resulting devices exhibit an ultralow off-state current of 1 × 10(-9) mA/mm and a stable on/off ratio of 10(5). A controllable positive threshold voltage shift up to +12.4 V was achieved by adjusting the plasma duration. X-ray photoelectron spectroscopy indicates that incorporated F atoms form F-Ga-related bonds and compensate oxygen-related donor defects. Sentaurus TCAD simulations reveal reduced near-surface charge and a widened depletion region, providing a physical explanation for the experimentally observed increase in breakdown voltage from 453 V to 859 V. These results clarify the role of fluorine in modulating surface defect states in PA-MBE β-Ga(2)O(3) and demonstrate an effective route for threshold-voltage engineering and leakage suppression in Ga(2)O(3) power devices.