应力调控对单层TiOCl_(2)电子结构及光学性质的影响

Effect of stress regulation on electronic structure and optical properties of TiOCl_(2) monolayer

基于密度泛函理论的第一性原理计算,对单层TiOCl_(2)的电子结构、输运性质和光学性质进行了理论研究.对单层TiOCl_(2)材料的声子谱、分子动力学和弹性常数的计算结果表明,该材料在常温下能稳定存在,并具有较好的动力学、热力学和机械稳定性.电子结构分析表明,单层TiOCl_(2)是一种间接窄带隙半导体(能隙为1.92 eV).在应力调控下,单层TiOCl_(2)材料的能带结构、输运性质和光学性质均发生明显变化.沿a方向施加-4%的收缩应力后,单层TiOCl_(2)由间接带隙变为直接带隙,带隙减小至1.66 eV.同时TiOCl_(2)还表现出明显的各向异性特征,电子沿b方向传输(迁移率约为803 cm^(2)·V^(-1)·s^(-1)),空穴则沿a方向传输(迁移率约为2537 cm^(2)·V^(-1)·s^(-1)).此外,施加收缩应力还会使单层TiOCl_(2)材料的光吸收率、反射率和透射率的波峰(谷)发生红移,进入可见光的紫色波段,表明单层TiOCl_(2)在未来光电器件领域有着潜在应用前景.

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