Quasi-two-dimensional β-gallium oxide solar-blind photodetectors with ultrahigh responsivity

Solar-blind photodetectors have received a great deal of interest owing to their high selectivity for deep ultra-violet light in the presence of visible light. The development of alternative materials and innovative device designs are necessary for such solar-blind photodetectors, as the currently available commercial devices have issues pertaining to chemical and thermal instability, cost, and material handling due to their rigidity. Here, we fabricated solar-blind photodetectors based on exfoliated quasi-two-dimensional β-Ga₂O₃ flakes with optimal opto-electrical properties (direct bandgap of ∼4.9 eV), chemical and thermal stability, and then systematically characterized their photoresponsive properties. The fabricated device structures were based on back-gated field-effect transistors, allowing us to control the dark currents. These photodetectors exhibit extraordinary photoresponsive properties including the highest responsivity (1.8 × 10⁵ A W^-1) among reported semiconductor thin-film solar-blind photodetectors.