α-In2O3 monolayer: A promising material as field-effect phototransistor and out-of-plane piezoelectric device

Two-dimensional (2D) semiconductors have opened promising avenues for designing advanced functional devices due to their novel electronic features. In this work, the 2D α-In2O3 monolayer is systematically studied using first-principles calculations. Our calculations show that the α-In2O3 monolayer exhibits a stable configuration with good oxidation resistance. The electronic structure calculations identify that α-In2O3 monolayer is a semiconductor with a direct bandgap of 1.41 eV, which makes the α-In2O3 monolayer to be as a promising candidate in modern bottom/top gate technologies. Interestingly, the partial charge density shows that the valence band maximum and conduction band minimum locate at the different atomic region, and the electron carrier mobility of the α-In2O3 monolayer is much larger than hole carrier mobility, indicating that the electrons and holes can be effectively separated. Additionally, the α-In2O3 monolayer has excellent optical absorption coefficient among the infrared and visible range. Hence, the α-In2O3 monolayer can be used as field-effect phototransistor. Moreover, the asymmetric atomic-layer configuration and strong inner covalent bond of the α-In2O3 monolayer induce a superior out-of-plane piezoelectric response (e31 = 1.81 × 10-10C·m−1, d31 = -0.89 pm·V−1), make α-In2O3 monolayer as a promising material as out-of-plane piezoelectric device.