Study On Photoelectric Characteristics Of Monolayer WS₂

Since the monolayer of graphene has been applied extensively in the optoelectronic fields,the atomically thin materials have been received much attention.The family of semiconducting transition metal dichalcogenides?TMDCs?,involving MoS₂,WS₂,MoSe₂,and MoTe₂,have highlighted an increasingly important role,owing to their intriguing physical properties,such as their sub-nanometer thickness,large optical absorbance and sizable bandgaps around 1-2 eV.As a direct band gap semiconductor,single-layer TMDCs has a higher luminous efficiency,so in this paper,single-layer WS₂ film is selected as the research objective.Here,we made a simple and large-area photodetector based on monolayer WS₂with high light sensitivity and fast response,benefiting from the special dynamics of carrier.Also it is important to determine the time-dependent evolution of the excited monolayer WS₂,which will provide a basis for reasonable design of optoelectronic devices based on two-dimensional transition metal dichalcogenides,thus,we tested the relaxation behavior of excited monolayer WS₂ by employing transient absorption?TA?.It is found that the multi-body interaction among exciton would occur after the density of pump photon increases to 3.45×10¹⁴ photons cm^-2.The exciton dissociation accompanying with the generation of trion would appear in the photo-induced relaxation process,which would be benefit for the operation of this photodetector.The high energy exciton transition is good for the generation of carrier through comparing the relaxation behavior of WS₂ excited into A and B exciton state originated from the splitting of valence band.However,the bound exciton relaxation originated from capture process of defect state would exist and play an unfavorable role during the working of devices.In order to further study the exciton dynamics in the monolayer WS₂,we use transient absorption?TA?to detect the time-resolved optical response of the monolayer WS₂ film and identify its exciton relaxation mechanism.We find that the multi-body interaction between A exciton is further clarified through changing the intensity of pump and probe laser.Specifically,we find the trapping process of exciton and the exciton radiative recombination would be dominant in the relaxation process of A exciton,besides the exciton-exciton annihilation will also occupy the decay channel at high pump intensity.