The Electronic Structure And Optional Property Of Several New Two-dimensional Janus Materials And Their Heterostructures

Two-dimensional materials and their heterostructures have shown great potential application in photovoltaic power generation and nanoelectronic devices,and are new energy materials with great development prospects.The physical properties of two-dimensional materials and their heterostructures depends on their components and their interactions.It is time-consuming and laborious to screen single-layer materials and their heterostructures with excellent properties from experiments to meet the practical needs,which urgently needs theoretical guidance.The composition and geometric topological structure of two-dimensional materials determine their electronic structure and optical properties,thereby affecting their physical properties and applications.The first-principles calculation based on density functional theory can accurately predict the structure and properties of materials,which is an effective methods to explore the photoelectric properties of two-dimensional materials and their heterostructures.In this paper,several novel two-dimensional Janus materials and van der Waals heterostructures are explored based on the first principles of density functional theory,and their electronic structure,optical properties and potential applications in the field of optoelectronics are analyzed.The main research contents are as follows:（1）The electronic structure and optical properties of two-dimensional Janus-Ga₂SeTe、InS monolayers and their van der Waals heterostructures were explored.It is found that the band arrangement,band-gap type and dipole moment of heterostructures depend on the species and positions of atoms at the interface.Under the action of biaxial stress and vertical electric field,the band arrangement,band gap and electrical properties of the two type-Ⅱ heterostructures can undergo Ⅱ-Ⅰ-Ⅱ,direct-indirect-direct and semiconductor-metal transitions,respectively.The peak solar conversion efficiency of the TeGa₂Se/InS heterostructure can reach 23.2%under 4%biaxial compression stress when the intrinsic dipole moment and the interface dipole moment are in same direction.The above results indicate that the Janus heterostructure is a solar cell material with great application potential.（2）The new two-dimensional Janus-MX（M=Ge,Sn;X=Sn,As）and the geometric structure and electronic properties of van der Waals heterostructure.It is found that the species and positions of atoms will affect the properties,band gap types and dipole moments of Janus materials.Under biaxial stress and vertical electric field,the band-gap types and electrical properties of six Janus materials can undergo direct-indirect-direct and semiconductor-metal transitions,respectively.Among them,Sn₂SbAs/graphene and GeSnSb₂/graphene heterostructures exhibit p-type and n-type Schottky barriers respectively,and the Dirac point of graphene is opened,with the maximum band gap of 0.45 eV.The results provide a theoretical basis for designing new Janus heterostructure electronic devices.