First Principles Study Of MoSe₂ And Its Heterojunction

With the rapid development of industries such as information technology and new energy,the demand for high computational power and low energy consumption in chips has been increasing.However,traditional semiconductor materials have approached their performance limits.Therefore,the search for new semiconductor materials has significant strategic importance.Transition-metal dichalcogenides（TMDs）exhibit excellent properties such as optical,electrical,and mechanical properties,which have attracted increasing attention to these new two-dimensional materials.As a member of TMDCs,Mo Se₂exhibits high specific surface area,good thermal conductivity,and high mechanical strength,among other properties.In order to achieve practical application and wider range of applications of Mo Se₂in the field of electronic devices,doping and constructing van der Waals heterostructures（vd WHs）can be used to further regulate its optical,electrical,and magnetic properties,so as to compensate for the shortcomings of monolayer Mo Se₂due to its own characteristics.The main research content of this paper is as follows:（1）The electronic and optical properties of intrinsic Mo Se₂were first calculated.And we doped the monolayer Mo Se₂,we doped it with three alkaline earth elements（Mg,Ca,Sr）and four transition metals（Mn,Fe,Co,Ni）.Calculate the energy band structure,density of states,dielectric function,absorption coefficient,reflection coefficient,etc.Analysis of the effect of different impurity atom doping on electronic structure and optical properties.By comparison,the band gap of doped Mo Se₂decreases significantly,resulting in the generation of impurity energy levels,and the emergence of new spin states in the conduction band minimum and valence band maximum,spin polarization effect is generated in doping system.All atoms except Sr atoms doped with Mo Se₂exhibit large magnetic moments,these results indicate that doping may cause magnetism in Mo Se₂.In terms of optical properties,it can be observed that doping increases the absorption coefficient of Mo Se₂in the ultraviolet region,with the Co-doped system showing the highest enhancement.It is worth noting that doping can significantly improve the static dielectric constant of the system,indicating that doping will increase the polarization degree of Mo Se₂,strengthen the binding ability of charges,and greatly improve the utilization efficiency of light.The above results provide a theoretical basis for the application of monolayer Mo Se₂in optoelectronic devices,spin electronic devices,transistors,and other fields.（2）Mo Se₂/Pt SSe heterostructure are constructed using two contact methods,one is a heterostructure that contacts Mo Se₂with the S surface of Pt SSe（later called Mo Se₂/SPt Se heterostructure）,and the other is a heterostructure that contacts Mo Se₂with the Se surface of Pt SSe（later called Mo Se₂/Se Pt S heterostructure）.The electronic structure and optical properties of the monolayer Mo Se₂,Pt SSe,and Two heterostructures were compared and analyzed.At the same time,the effect of stress on the electronic and optical properties of the Mo Se₂/Pt SSe heterostructures was studied.The calculation results show that both Mo Se₂/Se Pt S and Mo Se₂/SPt Se heterostructures are indirect bandgap semiconductors with a type-II band alignment.The bandgap of Mo Se₂/SPt Se heterostructure is 0.65 e V,which has a higher carrier mobility.The bandgap of Mo Se₂/Se Pt S heterostructure is 1.12 e V.Regarding the optical properties,both heterostructures exhibit higher optical absorption coefficients in the visible and ultraviolet regions,and the absorption edge in the infrared region is red-shifted,which enhances the light absorption range.Moreover,it can be observed from the photoconductivity that both heterostructures exhibit superior conductivity.Furthermore,through stress modulation,we found that applying stress can adjust the bandgap of both Mo Se₂/Pt SSe heterostructures.At the same time,stress can also achieve a transition in band alignment type,transforming the Mo Se₂/Pt SSe heterojunction from a type-II to a type-I band alignment.In terms of optical properties,tensile stress can increase the absorption and reflection coefficients of both Mo Se₂/Pt SSe heterostructures in the infrared and visible regions.Conversely,compressive stress can enhance the absorption and reflection coefficients in the ultraviolet region for both Mo Se₂/Pt SSe heterostructures.The above conclusions indicate that the construction of heterostructures can broaden the light absorption range,increase the light absorption coefficient,and enhance the electrical conductivity of Mo Se₂,making it a candidate material for optoelectronic devices,solar cells,photodetectors etc.Meanwhile,the performance of van der Waals heterostructures can be further adjusted by applying different stresses,providing a theoretical basis for the research and application of heterostructures based on Mo Se₂.