Defect States And Valley-dependent Transport In Monolayer Transition Metal Dichalcogenides

Two-dimensional transition metal dichalcogenides(2D TMDCs)are a new family of layered materials,which provide a good platform for researchers to study basic science and issues in the field of materials.Among them,single-layer TMDCs have attracted extensive attention due to their more excellent properties.From the band structure of single-layer TMDCs,it can be seen that it is a material with direct band gap.There is a pair of unequal valleys in the first Brillouin region,which can be used to store and process information.However,in the process of experimentally preparing materials,the lattice of TMDCS inevitabiy contain many different structural defects,which significantly change their physical and chemical properties.Therefore,after a comprehensive understanding of the structural defects,the transport properties of the device can be effectively changed by controlling the defects.In this paper,the three-band tight-binding model and recursive Green function method are used to simulate the defect states of single-layer TMDCs nanoribbons.The effects of point defects and line defects of metal atoms on the transport properties of nanoribbons are systematically studied.The valley polarization is adjusted by changing the size of the intermediate scattering region and applying gate voltage.In addition,the influence of other parameters on the transport properties of nanoribbons is discussed with the determination of the incident electron energy(Fermi energy).The simulation results show that the number of vacancy defects and random vacancy defects all affect the transport properties of single-layer TMDCs.The valley polarization of the device will be improved with the increase of the number of vacancy defects.The transport properties of the whole system will be adjusted by changing the size of the scattering region.The study also found that the valley polarization of the nanoribbon with random defects is always100% in the energy range of 1.85-1.90 e V,which indicates that edge states are robust to disordered defects.According to the number of line defects,the influence of three kinds of line defects on the transport properties of nanoribbons is analyzed.It is found that increasing the number of line defects will change the valley-dependent properties of the nanoribbons.The valley polarization of the device can be further adjusted by applying voltage,introducing random defects and changing the size of the nanoribbons,so that the valley polarizability can present the best effect.The results of this work have a certain guiding significance for the research on the properties of defective TMDCs.