不同浓度Mg掺杂单层Janus WSSe的第一性原理研究

二维Janus WSSe作为一种新型过渡金属硫族化合物(TMDs)材料由于其独特的面外非对称结构及众多新颖的物理特性，在自旋电子器件中具有巨大的应用潜力.本文基于密度泛函理论的第一性原理平面波赝势方法，通过构建四种掺杂模型W_9-xMg_xS₉Se₉(x=0、1、2、3),分别计算了不同浓度Mg掺杂单层WSSe的电子结构和光学性质.结果表明：掺杂使得WSSe由直接带隙半导体变为间接带隙半导体，并且随着掺杂浓度的增加，带隙逐渐减小，费米能级穿过价带，使得掺杂体系变成P型半导体，当x=3时，掺杂体系呈现金属性.此外，掺杂体系的静态介电常数随着掺杂浓度的增加而变大，极化程度显著增强，介电函数虚部和光吸收峰都发生了红移，说明掺杂有利于可见光的吸收.并且，静态折射率随着掺杂浓度的增加而呈现上升趋势，同时消光系数的峰值也与Mg原子的掺杂浓度呈现正相关.

First-principles study of different levels of Mg-doped Janus WSSe monolayer

Two-dimensional Janus WSSe, as a novel transition metal dichalcogenide (TMDs) material, has great potential for application in spintronic devices due to its unique out-of-plane asymmetric structure and novel physical properties. In this paper, by using the first-principles plane wave pseudopotential method of the density functional theory, the electronic structures and optical properties of four Mg-doped models of W9-xMgxS9Se9 (x=0,1,2,3) were calculated separately, and their energy band structures, densities of states and optical properties were analyzed. The results show that doping makes WSSe change from a direct band gap semiconductor to an indirect band gap semiconductor. Furthermore, with the increasing of doping concentration, the band gap gradually decreases, the Fermi level passes through the valence band, and the doping system becomes a P type semiconductor. When x=3, the doping system presents a metallic property. In addition, the static dielectric constant of the doping system increases and the polarization degree is significantly enhanced with the increasing doping concentration. Both the imaginary part of the dielectric function and the light absorption peak are red-shifted, indicating that the doping is beneficial to the absorption of visible light. The static refractive index increases with the increasing doping concentration, and the peak value of extinction coefficient is positively correlated with the doping concentration of Mg atoms.