Tunable Properties of Novel GaO Monolayer for Electronic and Optoelectronic Applications.

A novel two-dimensional (2D) GaO monolayer was constructed and systematically investigated by first-principles calculations. The 2D GaO has an asymmetric configuration with a quintuple-layer atomic structure, the same as the well-studied α-InSe, and is expected to be experimentally synthesized. The dynamic and thermodynamic calculations show excellent stability properties of this monolayer material. The relaxed GaO monolayer has an indirect band gap of 3.16 eV, smaller than that of β-GaO 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 GaO monolayer, which helps to separate photon-generated electrons and holes within the quintuple-layer structure. By applying compressive strain, the GaO 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 cm V s. 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 GaO monolayer sheds light on low-dimensional electronic and optoelectronic device applications.