2D Amorphous GaO_X Gate Dielectric for β-Ga₂O₃ Field-Effect Transistors

Appropriate gate dielectrics must be identified to fabricate metal-insulator-semiconductor field-effect transistors (MISFETs); however, this has been challenging for compound semiconductors owing to the absence of high-quality native oxides. This study uses the liquid-gallium squeezing technique to fabricate 2D amorphous gallium oxide (GaO_X) with a high dielectric constant, where its thickness is precisely controlled at the atomic scale (monolayer, ∼4.5 nm; bilayer, ∼8.5 nm). Beta-phase gallium oxide (β-Ga₂O₃) with an ultrawide energy bandgap (4.5-4.9 eV) has emerged as a next-generation power semiconductor material and is presented here as the channel material. The 2D amorphous GaO_X dielectric is combined with a β-Ga₂O₃ conducting nanolayer, and the resulting β-Ga₂O₃ MISFET is stable up to 250 °C. The 2D amorphous GaO_X is oxygen-deficient, and a high-quality interface with excellent uniformity and scalability forms between the 2D amorphous GaO_X and β-Ga₂O₃. The fabricated MISFET exhibits a wide gate-voltage swing of approximately +5 V, a high current on/off ratio, moderate field-effect carrier mobility, and a decent three-terminal breakdown voltage (∼138 V). The carrier transport of the Ni/GaO_X/β-Ga₂O₃ metal-insulator-semiconductor (MIS) structure displays a combination of Schottky emission and Fowler-Nordheim (F-N) tunneling in the high-gate-bias region at 25 °C, whereas at elevated temperatures it shows Schottky emission and F-N tunneling in the low- and high-gate-bias regions, respectively. This study demonstrates that a 2D GaO_X gate dielectric layer can be produced and incorporated into an active channel layer to form an MIS structure at room temperature (∼25 °C), which enables the facile fabrication of MISFET devices.