The Strain Effect On The Electronic Properties Of The MoSSe/WSSe Van Der Waals Heterostructure And B₄P₄C₄/B₂P₂C₈ Monolayer:a First-principles Study

Once the two-dimensional(2D)material graphene is discovered,it has become a hot material with application potential in various fields quickly due to its excellent electrical and mechanical properties.However,the zero band gap of graphene limits its application in the semiconductor field at the same time.Therefore,modulating the band gap of graphene is of key significance for its practical application in the semiconductor field.At present,the band gap of graphene can be modulated by introducing doping,adsorbing atoms,introducing periodic defects,applying magnetic fields,electric fields,force fields and so on.Strain engineering is a regular control method of semiconductor material performance which aims to regulate the performance of 2D material flexible optoelectronic devices through tensile strain or compressive strain.Theoretical calculations and experimental studies have shown that 2D materials have far stronger deformation capabilities than their macroscopic blocks and can withstand larger elastic strains than bulk materials,maintaining the integrity of the structure.In this work,we use the first-principles calculation method based on density functional theory(DFT)to study the performance of the electronic structure characteristics of three types of graphene-like materials,Mo SSe/WSSe van der Waals heterostructure(Mo SSe/WSSe vd WHS)and B₄P₄C₄/B₂P₂C₈ monolayer,under strain.The main research contents and results are as follows:(1)The structural,mechanical and electronic properties of the Mo SSe/WSSe vd WHS under varying degrees of horizontal and vertical strain are systematically investigated based on first-principles methods.It is found that the Mo SSe/WSSe vd WHS of the most stable AB stacking is a direct band gap semiconductor and exhibits a type-?band alignment,which demonstrates an effective separation of photogenerated electron-hole pairs and increase their lifetime accordingly.The high angle-dependent Young's modulus and normal Poisson's ratios show the mechanical stability and anisotropy.It is found that the band gap of the heterostructure can be modulated effectively by applying strain,exhibiting a decreasing trend with increasing strain,and even lead to an intriguing semiconductor-metal transition under certain large tensile strain.Especially,a negative correlation between band gap and structure pressure is found when applying vertical strain,which provides a theoretical basis for experimentally regulating the electronic properties.Moreover,different strains can induce two different conditions of direct-indirect transition or keeping the characteristics of direct-band-gap.All these interesting results provide a detailed understanding of the Mo SSe/WSSe vd WHS under strain and indicate that it is a good candidate for low-dimensional electronics,nano-electronics and optoelectronic devices.(2)We predict two novel ternary graphene-like structures,B₄P₄C₄ and B₂P₂C₈monolayer.Their structural,mechanical and electronic properties are systematically investigated based on first-principles methods.The results show that the intrinsic and the strained materials possess excellent dynamic,thermal and mechanical stability.Calculation results show that the intrinsic B₄P₄C₄ monolayer has the Dirac feature.Particularly,the intrinsic B₂P₂C₈ monolayer exhibits unique double Dirac points and non-trivial topological property.It is found that the Dirac states in B₄P₄C₄ monolayer can be effectively regulated by applying horizontal strain,exhibiting the characteristics of a semiconductor with a direct or indirect band gap even an intriguing semiconductor-metal transition.In contrast,the intrinsic B₂P₂C₈ monolayer is not sensitive to biaxial strain and its stability and semi-metal state preserve well like graphene,which benefits by its non-trivial topological property.Additionally,the calculated Young's modulus and Poisson's ratio show the mechanical anisotropy and excellent resistance of deformation of both the structures.The relevant results provide a feasible method for the performance control of nanodevices developed based on B₄P₄C₄ and B₂P₂C₈ monolayer.