Intrinsic high-temperature ferroelectricity, superferroelasticity, and deep-ultraviolet nonlinear optical response of GaOCl monolayer

Two-dimensional materials with coexisting multifunctional properties offer platforms for revealing multifield coupling physics in both lower dimension and symmetry, and enable the potential application demand for multifunctional devices in nanoelectronics. Preceding theoretical and experimental investigations show that layered metal oxyhalides (MOX) have diverse functional properties such as the visible-light-active photocatalyst in Bi-based system as well as the magnetic and electron-correlated properties in transition-metal-based regime. Here, applying first-principles calculations and time-dependent perturbation theory, we identify that GaOCl monolayer has intrinsically multiple functional characteristics including high-temperature ferroelectricity, superferroelasticity, and strong deep-ultraviolet nonlinear optical response. Our calculations indicate that GaOCl monolayer has a ultrawide direct band gap comparable with the third-generation semiconductors, a moderate energy barrier of ferroelectric polarization reversal but with a high Curie temperature, a superferroelasticity attributed to the largely tunable ionic radius ration of ${\mathrm{Ga}}^{3+}$ and ${\mathrm{O}}^{2\ensuremath{-}}$, and remarkable nonlinear shift and injection currents inside deep-ultraviolet frequencies. These intrinsical multifunctional properties render GaOCl monolayer possible applications on ultrathin multifunctional nanoelectronics such as integrated multiferroic devices and ultraviolet optoelectronic devices.