Electronic Structures And Optical Propertie Of Two-Dimensional Transition Metal Dichalcogenides Based Heterostructures

Transition metal dichalcogenides MX₂(M=Mo,W;X=S,Se,Te)are a type of semiconductors with weak van der Waals interactions between layers,and possess excellent properties beyond graphene.MX₂monolayers have band gap values of 1.0?2.0 e V,ultra-high light absorption coefficient(10~5?10~6 cm^-1)and high carrier mobility,making them ideal materials for photovoltaic devices and photocatalytic applications.In addition,due to the breaking of inversion symmetry,they are also popular materials for valley electronics.Polar Janus TMDs have been successfully prepared experimentally by means of atom replacement.It inherits the unique electronic and optical properties of traditional TMDs,and exhibits unique characteristics,providing new ideas for the further design of electronic devices with excellent performance.In this these,we use first-principles calculation methods to study the electronic structure and optical properties of two-dimensional GeS/MX₂ and Janus MoSSe/GaN heterostructures.The main contents are as follows:(1)By stacking the transition metal chalcogenides MX₂ and GeS monolayers vertically to construct the theoretical model of GeS/MX₂ heterostructures,we found that the structural asymmetry and the orbital hybridization between the atoms of each layer caused Rashba type spin split at the?point.Moreover,due to the lack of inversion symmetry in the original MX₂monolayers,the valence band maximum of the K valley will have an obvious split with the opposite spin direction,and as the transition metal atomic number increases,the magnitude of the energy valley split will be also increases.We take the GeS/Mo Te₂heterostructure as an example for the next discussion.Due to the polar characteristic of the GeS monolayer,we have considered the two types of Ge atom side contact and S atom side contact,there are 12 alignments in total.It is shown that all configurations are stable structures.And they can realize the direct and indirect band structure characteristics respectively.Furthermore,by applying biaxial strain and external electric field to the most stable structures of AA and AF'in their respective systems,we found that the band structures of heterostructures at different atoms interfaces have different responses to strain and electric field,and show the band alignment characteristics of Type?and Type?,respectively.In addition,the biaxial strain and the applied electric field can well control the Rashba coefficient of the heterostructures.This makes it possible for the experimentally prepared GeS/Mo Te₂heterostructures to realize optoelectronic devices and spintronic devices.(2)The Janus MoSSe/GaN heterostructure formed by vertically stacking Janus MoSSe with intrinsic dipole and GaN monolayer,which have a direct band gap semiconductor characteristics and light absorption from visible to ultraviolet light,with an absorption intensity of up to 10~5 orders of magnitude.In addition,due to the inherent dipole moment caused by the broking of out-of-plane mirror symmetry,the Janus MoSSe monolayer considers the different atomic interface contacts when constructing the heterojunction,which will lead to Type-I and Type-II band alignments.The band gap value and the position of the band edge can also be adjusted by the interlayer coupling and the external electric field.These results can provide very valuable guidance for the application of 2D Janus MoSSe/GaN heterostrustures in optoelectronic devices.