Effect of stress regulation on electronic structure and optical properties of TiOCl<sub>2</sub> monolayer

Abstract

Based on first-principles calculations, the electronic structure, the transport and optical properties of TiOCl<sub>2</sub> monolayer are systematically investigated. The vibrational, thermodynamic, and mechanical properties of TiOCl<sub>2</sub> monolayer are studied by phonon spectrum, molecular dynamics and elastic constants calculations. All these results indicate that the TiOCl<sub>2</sub> monolayer possesses good structural stability at room temperature and excellent mechanical properties. The electronic structure analysis shows that the TiOCl<sub>2</sub> is an indirect band gap (1.92 eV) semiconductor. Its band structure can be significantly affected by in-plane stress. Specifically, the TiOCl<sub>2</sub> monolayer undergoes an indirect-to-direct band gap transition under –4% uniaxial stress along the <i>a</i>-axis and the gap size decreases to 1.66 eV. Moreover, the TiOCl<sub>2</sub> monolayer exhibits obvious anisotropy characteristics, and its electron mobility is 803 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup> along the <i>b</i>-axis, whereas the hole mobility reaches 2537 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup> along the <i>a</i>-axis. The wave peaks (valleys) of the absorptivity, reflectivity and transmittance shift toward the violet part of the visible band by the stress. All these appealing properties make the TiOCl<sub>2</sub> monolayer a promising candidate for applications in optoelectronic devices.