Fabrication of a Nb-Doped β-Ga₂O₃ Nanobelt Field-Effect Transistor and Its Low-Temperature Behavior

For the first time, we report the successful fabrication of well-behaved field-effect transistors based on Nb-doped β-Ga₂O₃ nanobelts mechanically exfoliated from bulk single crystals. The exfoliated β-Ga₂O₃ nanobelts were transferred onto a purified surface of the 110 nm SiO₂/Si substrate. These Nb-doped devices showed excellent electrical performance such as an ultrasmall cutoff current of ∼10 fA, a high current on/off ratio of >10⁸, and a quite steep subthreshold swing (SS, ∼120 mV/decade). Furthermore, we investigated the temperature dependence down to 200 K, providing insightful information for its operation in a harsh environment. This work lays a foundation for wider application of Nb-doped β-Ga₂O₃ in nano-electronics.