A Study On The Electric Structure And Optical Properties Of Monolayer MoS₂ Via The First Principle Calculation

Transition metal dichalcogenides,for example MoS₂,one of the graphene-like tow-dimensional materials,has become a new hot material for research and also has drawn a lot of research attentions on the applications in electronics and optoelectronics.Monolayer MoS₂ shows a direct band gap,which improved the drawback of graphene that lack of band gap.As the same time,single-layer MoS₂ has unique properties,which let it a potential applicant in transistor manufacturing area such as field effect transistor.In the area of optical sensor,monolayer MoS₂ is still being exploration.This thesis mainly to compare with the pristine monolayer MoS₂ and its doping system in electronic structure and optical properties aspects using the first-principle calculation method.In this work,firstly,all atoms are allowed to fully relax,and then work out band structures and density of states of pristine monolayer MoS₂.We find that monolayer MoS₂ has direct band gap about 1.55eV.Then we proposed four kinds of doping systems and chose four kinds of doping atoms,namely Cl,P,O and Se,which come up with sixteen doping structures.Through the results of calculations,we find the addition of dopants atoms has transverse tensile or constringent effect on the doping surface.Secondly,based on the outcome of optimizing four kinds of doping systems,we investigate the electronic structure for these sixty cases using the first-principle calculation method.It was found that n-type doping obtained by replacing S atoms with Cl and has a magnetic ground state,but with the increasing number of dopants,4-Cl went back to nonmagnetic.However,all the different four cases of doping P atoms is p-type doping and all present magnetic compare to pristine monolayer MoS₂.The cases of replacing S atoms with O and Se atoms are neither n-type doping nor p-type doping,band gap value increased due to dopants atoms,but do not has linear relation with the number of dopants.Thirdly,we calculated the optical properties of the single-layer MoS₂,by calculating the dielectric function,thus further analyze its absorption coefficient,reflectivity index,extinction coefficient,refractive index and energy loss function.Lastly,selected four kinds of doping structures,namely 1-Cl,1-P,1-O and 1-Se,and then calculate their absorption coefficient,reflectivity index,extinction coefficient,refractive index.Compared with the pristine single-layer MoS₂,we found out that single-layer MoS₂ still presents transparent state and more sensitive to blue and purple light after doping different dopants atoms.