Fluorine-Doped N‑Type α‑Ga₂O₃ and Its Phase Stability

In this work, we investigated the impacts of fluorine (F) doping on the electrical and structural properties of metastable α-Ga₂O₃ grown on sapphire. Compared to Sn, which is a Ga-substituting dopant and one of the more common dopants for α-Ga₂O₃, doping with F resulted in more conductive α-Ga₂O₃ with Hall mobility as high as 42 cm²/V·s and the carrier concentrations of ∼1 × 10¹⁹ cm^–3 at room temperature. In contrast, Sn-doped α-Ga₂O₃ with similar carrier concentrations exhibited a Hall mobility of less than 10 cm²/V·s. Furthermore, F-doped α-Ga₂O₃ showed greater thermal stability in both electrical and structural properties compared to undoped and Sn-doped α-Ga₂O₃. The phase stability was enhanced such that single-phase F-doped α-Ga₂O₃ could be annealed or grown at temperatures as high as 700 °C. A Ti-based metal contact formed on F-doped α-Ga₂O₃ exhibited an Ohmic behavior with a specific contact resistivity of 6.5 × 10^–5 Ω·cm² after annealing. Overall, doping with F has shown promising results for high-performance α-Ga₂O₃ devices.