Electronic And Optical Properties Of Type-? VdW Heterojunctions Base On ?-? Group Janus

Two-dimensional layered materials,such as graphene,transition metal sulfides and black phosphorus are widely used in nanoelectronic and optoelectronic due to extraordinary electronic and optical properties.It is show that van der Waals(vdW)heterojunctions,forming by stacking different two-dimensional(2D)materials,can integrate the properties of the single layer and create particularly superior performance.Constructing vdW heterojunctions has been considered to be an effective strategy to obtain the desired properties.MX and their Janus-XM2X'(M=Al,Ga,In;X/X'=S,Se,Te,X'?X)possess high-performance electronic and optical properties,such as high mobility(103cm-2v-1s-1),excellent light absorption(104cm-1)in the visible light wavelength range and suitable band gap.In recent years,the first-principles calculation based on density functional theory(DFT)has become an indispensable tool to interpretation of physical phenomena and predict the properties of materials.In this work,we use the first-principles calculation method based on density functional theory to systematically investigate the electronic properties and optical properties of 2D XM2X'/MX heterostrutures.And we make some significant results which are expected to provide theory instruction for designing XM2X'/MX vdW heterojunctions in experiment.The main studies and results of this paper are as follows:(1)The Janus-XM2X' and MX within no more than 3%of the lattice mismatch are selected to constructing XM2X'/MX heterojunctions.Four possible stacking configurations are considered for all possible XM2X'/MX heterostructures to check the effects of stacking on photoelectric properties of the heterostructure.The results show that AB2 is the most stable stacking pattern.Five XM2X'/MX heterostructures(SeAl2Te/InS,SeGa2Te/InS,SeGa2Te/InSe,SGa2Te/InS and SIn2Te/InSe)are found to be direct-band-gap type-II band structures with large band offset,which is beneficial to the separation and transmission of photo-generated electron-hole pairs,thus facilitates effective utilization of the solar visible light.We find that the band gaps under HSE06 functional ranging from 1.17 to 1.73eV,which is comparable to the silicon(?1.16eV)and show potential applications in solar cells.Moreover,heterostructures show a higher optical absorption coefficient(?105cm-1)compares with isolated layers from the visible to the ultraviolet region.Above results indicates that the heterostructure is more suitable for application in high-performance photoelectric devices than its isolated monolayers.(2)We investigate the stability of the excellent electronic and optical properties of heterostructures under in-plane biaxial strain which induced by lattice mismatching.These results indicate that,except SeGa2Te/InSe,other four heterojunctions maintain excellent optoelectronic properties within 3%in-plane strain.(3)The optoelectronic properties of layered materials can be modulated by changing the interlayer coupling.Both external electric field(E-field)and vertical strain are effective approaches to tune the interlayer coupling.It is shown that both the band gap and the band offset can be turn into an optimal range(0.3eV<Eg<3eV,?EC<1eV)to obtain high power conversion efficiency under the effect of external electric field and vertical strain.At the same time the heterojunctions can keep a high optical absorption and direct-band-gap type-? band structures.These results indicate the potential applications of 2D XM2X'/MX heterostructures in solar energy conversion.