A novel two-dimensional (2D) Ga2O3 monolayer was constructed and systematically investigated by first-principles calculations. The 2D Ga2O3 has an asymmetric configuration with a quintuple-layer atomic structure, the same as the well-studied α-In2Se3, and is expected to be experimentally synthesized. The dynamic and thermodynamic calculations show excellent stability properties of this monolayer material. The relaxed Ga2O3 monolayer has an indirect band gap of 3.16 eV, smaller than that of β-Ga2O3 bulk, and shows tunable electronic and optoelectronic properties with biaxial strain engineering. An attractive feature is that the asymmetric configuration spontaneously introduces an intrinsic dipole and thus the electrostatic potential difference between the top and bottom surfaces of the Ga2O3 monolayer, which helps to separate photon-generated electrons and holes within the quintuple-layer structure. By applying compressive strain, the Ga2O3 monolayer can be converted to a direct band gap semiconductor with a wider gap reaching 3.5 eV. Also, enhancement of hybridization between orbitals leads to an increase of electron mobility, from the initial 5000 to 7000 cm2 V-1 s-1. Excellent optical absorption ability is confirmed, which can be effectively tuned by strain engineering. With superior stability, as well as strain-tunable electronic properties, carrier mobility, and optical absorption, the studied novel Ga2O3 monolayer sheds light on low-dimensional electronic and optoelectronic device applications.
Keywords: Ga2O3 monolayer; first-principles calculations; intrinsic dipole, carrier mobility; strain engineering.