双轴应变和外部电场对单层MgI2电子结构的调控

Tuning the Electronic Structure of Monolayer MgI2 by Biaxial Strain and External Electric Field

摘要: 本文采用基于密度泛函理论的第一性原理方法，研究了施加双轴应变及外电场对单层MgI2电子结构的影响，并分析了能带图、态密度图等。计算结果表明：纯净体系的单层MgI2是一个间接半导体，能隙值为3.602 eV。声子谱没有虚频表明其结构可以稳定存在。随着双轴应变值从−10%到10%，单层MgI2能隙值从2.944 eV变化到3.406 eV。有趣的是，在应变值−10%到4%下，能隙值一直在增加，在4%到10%范围内，能隙值在减小，并且在4%这个应变值下获得最大能隙值3.673 eV。将外部电场设置为0 eV/Å/e至1 eV/Å/e，发现单层MgI2在0.2 eV/Å/e到0.4 eV/Å/e电场下能隙值与纯净体系能隙值相差不大，在0.6 eV/Å/e至0.7 eV/Å/e半导体类型由间接能隙半导体变为直接能隙半导体，0.9 eV/Å/e到1.0 eV/Å/e变为金属，因此判定在0.7 eV/Å/e到0.9 eV/Å/e之间发生了半导体到金属的相变。

Abstract: In this paper, the effects of biaxial strain and external electric field on the electronic structure of monolayer MgI2 are studied by using the first principle method based on density functional theory, and the energy band diagram and density of states diagram are analyzed. The results show that the monolayer MgI2 of the pure system is an indirect semiconductor with a band gap of 3.602 eV. The phonon spectrum has no virtual frequency, indicating that it can exist stably. With the biaxial strain from −10% to 10%, the band gap of monolayer MgI2 changes from 2.944 eV to 3.406 eV. In-terestingly, the strain value is −10% to 4%, the energy gap value is increasing, the energy gap value is decreasing in the range of 4% to 10%, and the maximum strain value of 3.673 eV is obtained at the strain value of 4%. When the external electric field is set to 0 eV/Å/e to 1 eV/Å/e, it is found that the band gap value of monolayer MgI2 is almost the same as that of pure system under the electric field of 0.2 eV/Å/e to 0.4 eV/Å/e, and the semiconductor type changes from indirect band gap semiconductor to direct band gap semiconductor under 0.6 eV/Å/eto 0.7 eV/Å/e, from 0.9 eV/Å/e to 1.0 eV/Å/e to metal. Therefore, it is determined that a semiconductor to metal phase transition has occurred between 0.7 eV/Å/e and 0.9 eV/Å/e.