Interlayer Charge Transfer And Exciton Resonance Absorption Of Tungsten Disulfide And Its Heterostructures

With the size of semiconductor devices reaching nanometer scale,the failure of Moore's law makes the development of semiconductor technology represented by wafer foundry encounter a bottleneck.The microscopic study of charge transfer and exciton resonance in twodimensional transition metal dichalcogenides and their heterostructures will have an important impact on the breakthrough of semiconductor technology in the future.However,using the electronic charge detection technology,people can't capture the transferring information of micro particle in time.Therefore,based on the theory of screening effect and nonlinear optics,the exciton resonance absorption of single-layer tungsten disulfide is studied and a new method for detecting the charge transfer between layers is presented.The van der Waals heterostructures composed of single-layer tungsten disulfide and single-layer graphene,double-layer graphene and six-layer graphene are fabricated by exfoliation and transfer process.Under condition that graphene and tungsten disulfide are excited at the same time and condition that only graphene is excited,the influence of the external charge on the exciton resonance absorption intensity of the single-layer tungsten disulfide is studied on time-resolved way by using the ultrafast pump-probe technique.At the same time,the reason that screening effect plays an important role in the modulation of the exciton binding energy of single-layer tungsten disulfide by changing the number of graphene layers is explained.These results are of great significance to the integrated optoelectronic devices with gate layered structure.A new method based on second harmonic generation is presented,which combines the steady-state photoluminescence system and ultrafast pump-probe system.To detect the charge transfer between layers,only the macroscopic physical quantities with finite time resolution can be obtained by using electrical detection method;On the other hand,the ultrafast pumpprobe technique can improve the time resolution,but still needs people to figure out if the charge transfer happens between layers in two-dimensional heterostructures by comparing the transient absorption signals of heterostructures and single layer in them.In view of these limitations,a nonlinear optical way to detecting the charge transfer between two layers in twodimensional heterostructures is presented.The feasibility of this detection method is demonstrated in heterostructure composed of single-layer tungsten disulfide and single-layer molybdenum disulfide.The van der Waals heterostructure composed of single-layer tungsten disulfide and singlelayer molybdenum disulfide is prepared,and the dynamic process of field induced second harmonic in heterostructure is studied by the new method based on second harmonic generation.The intensity and lifetime of the field induced second harmonic signal in heterostructure composed of tungsten disulfide and molybdenum disulfide were measured experimentally.At the same time,By comparing the lifetime of field induced second harmonic signal with the carrier lifetime in single-layer tungsten disulfide after charge transfer,the relationship between the field induced second harmonic signal and the charge transfer between layers is studied.