PtSe_(2)/MoSe_(2)异质结非常规V-型能带对齐与物理场耦合下的稳定性

PtSe_(2)/MoSe_(2)heterojunction:Unconventional type-V band alignment and its stability under various physical field coupling

范德华异质结是二维材料的研究前沿及热点,特别是它的能带对齐方式,因为它决定异质结基本的电子性质.利用基于密度泛函理论的第一性原理方法,本文对过渡金属二硫化物PtSe_(2)/MoSe_(2)异质结的结构特性与电子结构进行了系统研究.计算的结合能和声子谱、分子动力学模拟以及力学性质研究表明,PtSe_(2)/MoSe_(2)异质结是高度稳定的,其实验制备是可行的.我们发现这种异质结具有与目前众多研究的异质结不同的特殊的V-型能带对齐这是因为与2D界面垂直的能量相近的MoSe_(2)层Se-pz轨道、Mo-dz2轨道与PtSe_(2)层的Se-pz轨道存在层间耦合,诱发离域的价带最大(Valance Band Maximum,VBM)杂化态.此外,我们也检验了该V-型能带对齐在各种物理场(外电场、应变)耦合下的稳定性,发现异质结的VBM和导带最小(Conduction Band Minimum,CBM)对外部物理场耦合具有完全不同的响应.在较小的负电场下以及整个正电场范围内,或在较小的垂直拉伸下和整个垂直压缩应变范围内,两单层的VBM仍保持较强的轨道耦合,不因物理场效应而消除,导致PtSe_(2)和MoSe_(2)层的VBM态同步非常规移动,从而使异质结始终保持V-型能带对齐.这一新颖的非常规的能带对齐方式呈现高稳定性,对于研发基于PtSe_(2)/MoSe_(2)异质结的特殊的高性能光电器件具有巨大的应用潜力.

The van der Waals heterojunction is a research frontier and hotspot in 2D materials,especially for its band alignment method,which determines the essential electronic behaviors.Using a first-principles approach based on density functional theory,the structural stability and electronic properties of PtSe_(2)/MoSe_(2)heterojunctions are systematically studied.The calculated binding energy and phonon spectrum,molecular dynamics simulations,and study on mechanical properties show that the PtSe_(2)/MoSe_(2)heterojunction is highly stable,thus,its experimental fabrication might be feasible.Interestingly,we find that such a heterojunction features a special type-V band alignment,which is different from the numerous heterojunctions studied so far.This is because there exists an interlayer coupling between the Se-pz and Modz2 orbits in the MoSe_(2)layer and the Se-pz orbit in the PtSe_(2)layer,perpendicularly to the 2D interface and with similar energies,which induces delocalized VBM(valance band maximum)hybrid states.In addition,we also test the stability of this type-V band alignment under the coupling of various physical fields(external electric field,strain),we find that the VBM and CBM(conduction band minimum)of heterojunctions have completely different responses to the external physical field.At smaller negative electric fields and over the entire range of positive electric fields,or under smaller vertical stretching and over the entire range of vertical compressive strain,the VBM maintains stronger orbital coupling,which is not eliminated by physical field effects,resulting in synchronous unconventional movement of the VBM states in the PtSe_(2)and MoSe_(2)layers,so that the heterojunction always maintains a type-V band alignment.This novel unconventional band alignment and high stability have great potential for the development of high-performance PtSe_(2)/MoSe_(2)heterojunction-based optoelectronic devices.