Anisotropic Electron Mobility and Contact Resistance of β-Ga₂O₃ Obtained via Radio Frequency Transmission Line...

Monoclinic semiconducting β-Ga₂O₃ has drawn attention, particularly because its thin film could be achieved via mechanical exfoliation from bulk crystals, which is analogous to van der Waals materials' behavior. For the transistor devices with exfoliated β-Ga₂O₃, the channel direction becomes [010] for in-plane electron transport, which changes to vertical [100] near the source/drain (S/D) contact. Hence, anisotropic transport behavior is certainly worth to study but rarely reported. Here we achieve the vertical [100] direction electron mobility of 4.18 cm²/(V s) from Pt/β-Ga₂O₃ Schottky diodes with various thickness via radio frequency-transmission line method (RF-TLM), which is recently developed. The specific contact resistivity (ρ_c) could also be estimated from RF-TLM, to be 4.72 × 10^-5 Ω cm², which is quite similar to the value (5.25 × 10^-5 Ω cm²) from conventional TLM proving the validity of RF-TLM. We also fabricate metal-semiconductor field-effect transistors (MESFETs) to study anisotropic transport behavior and contact resistance (R_C). R_C-free [010] in-plane mobility appears as high as maximum ∼67 cm²/(V s), extracted from total resistance in MESFETs.