Electric/magnetic Manipulated Optoelectronic Properties In Molybdenum Disulfide And Its Nanostructures

The most typical transition-metal dichalcogenides molybdenum disulfide(MoS2)belongs to the hexagonal layered structure,monolayer MoS2 consists of one layer of Mo atoms surrounded by two layers of S atoms in a trigonal prismatic arrangement which does not have inversion symmetry.In recent years,it has received widespread attention due to its potential applications in nanoelectronic devices.monolayer MoS2 is direct band gap semiconductor with a similar geometrical structureas graphene,which owns superior physical features such as spin/valley Hall effect,it has been studied extensively for its optoelectronic properties and electronic transport,and present the significant potential application in optoelectronic and spintronic devices.In this thesis,optoelectronic properties and the electronic transport other than its external fields manipulation have been theoretically investigated based on the low-energy effective model under the tight-binding approximation,intersubband transition theorem and Kubo linear response theorem for semiconductors.This thesis is divided into four chapters.In the first chapter,we give a brief introduction about the discovery,experiment fabrication and electronic structure of monolayer MoS2,other than the intersubband transition theorem and Kubo linear response theorem for semiconductors.In chapter two,utilizing the low energy effective Hamilton model from the tightbinding approximation,we have theoretically investigated the electronic structure of the monolayer MoS2 in the presence of magnetic exchange field and off-resonant circularly polarized light.The obtained results show that,the band gap decreases with negative value of potential energy,and increases with positive value of potential energy.It has been demonstrated that,the magnetic exchange field can break and/or modulate the spin degeneracy of the conduction and/or valence bands,the band gaps around K point of the monolayer MoS2 increase with the external off-resonant circularly polarized light induced effective energy,while those for K1 increase firstly and then decrease with the light field induced effective energy,realizing the transition of semiconductor-metal-semiconductor.In chapter three,utilizing the low energy effective Hamilton model from the tightbinding approximation and Kubo linear response theorem,we have theoretically investigated optoelectronic properties and electronic transport of monolayer MOS2 and its external fields manipulation.Based on the intersubband transition theorem for the semiconductors,we have obtained the optical dielectric and function,absorption spectrum,and reflectivity of the monolayer MOS2 under the irradiation of a circulaRly and/or elliptically polarized light.The resonance frequency of the absorption spectrum and reflectivity has been observed to be same with that of the real and imaginary part of the dielectric functions,while the amplitude of the resonance peaks becomes higher with the increase of the amplitude ratio of the polarized light.The monolayer MOS2 should be more sensitive to the linearly polarized electromagnetic fields,especially to the transversally polarized light.the quantized transversal Hall conductance and spin/valley Hall conductance for monolayer MOS2 have been observed under the irradiation of the off-resonant circularly polarized light,the spin polarization is up to the largest and observed to positive to negative and/or negative to positive at the vicinity of the effective coupling energy ±0.79 eV of the off-resonant right/left circularly polarized light,while the valley polarization should increase firstly and then decrease with the off-resonant circularly polarized light,and be up to 100%at the interval of 0.79?0.87 eV of the absolute values for effective coupling energy.Furthermore,in the critical electric,The resonance peaks of the dielectric function,refractiveindex,extinction coefficient and optical conductivity from the spin-up and-down subbands should be red-shifted with the increase of negative value of potential energy,and blue-shifted with the increase of positive value of potential energy,respectively.In the four chapter,a summary of the work and a outlook of this topic are given.