| Two-dimensional(2D)transition metal dichalcogenides(TMDs)have been extensively studied as new generation semiconductor materials due to their elusive properties,such as large absorption coefficients,thickness-tunable bandgaps and large exciton binding energies on the order of hundreds of me V.In the research and design of2D TMDs optoelectronic devices,the insulation material is used as the gate insulator to combine with 2D TMDs to form van der Waals heterostructure.The heterostructures formed by semiconductor materials and 2D TMDs have different band alignments,which can control the photoelectric properties of 2D TMDs in optoelectronic devices.It is important to study the effect of photocarrier dynamics on the performance of 2D TMDs optoelectronic devices.In this study,WS2,as a typical representative material in 2D TMDs,is selected as the research object.Monolayer WS2 formed heterostructures with insulation material h BN and AIIIBIIIC2VI type layered semiconductor material Tl Ga S2,respectively.The effects of these heterostructures on photocarrier dynamics of monolayer WS2 was studied.The main innovations achieved are as follows:(1)Si/SiO2/WS2,Si/SiO2/h BN/WS2 and Si/SiO2/h BN/WS2/h BN samples were designed and fabricated on Si/SiO2(300 nm)substrate.The effect of h BN on time-domain photocarrier dynamics of monolayer WS2 in these van der Waals heterostructures were studied by time-resolved pump-probe technique.The experimental results show that,compared with the monolayer WS2 in Si/SiO2/WS2,the h BN layer in Si/SiO2/h BN/WS2prolongs the exciton formation time and lifetime of WS2,while the h BN layers in Si/SiO2/h BN/WS2/h BN reduce the exciton formation time,significantly prolong the exciton life of WS2and reduce the exciton–exciton annihilation rate.(2)The exciton diffusion of monolayer WS2 in Si/SiO2/WS2,Si/SiO2/h BN/WS2 and Si/SiO2/h BN/WS2/h BN samples above was studied by spatially and temporally resolved pump-probe technique and exciton diffusion coefficients of monolayer WS2 in these heterostructures was obtained.Compared with the monolayer WS2 in Si/SiO2/WS2,h BN in these heterostructures reduce the exciton diffusion coefficient of monolayer WS2,which indicates that h BN can suppress the exciton diffusion in monolayer WS2.(3)Si/SiO2/Tl Ga S2/WS2 and contrast sample Si/SiO2/WS2 was designed and fabricated on Si/SiO2(300 nm)substrate with monolayer WS2 and bulk Tl Ga S2.The photocarrier dynamics in Si/SiO2/Tl Ga S2/WS2 was studied.Photoluminescence of monolayer WS2 in Si/SiO2/Tl Ga S2/WS2 was significantly quenched,compared with the monolayer WS2 in Si/SiO2/WS2,and the carrier lifetime of monolayer WS2in the heterostructure is significantly prolonged.By comparing the difference of differential reflection signals of different materials in Si/SiO2/Tl Ga S2/WS2heterostructures under the same conditions,it is proved that WS2 and Tl Ga S2 form type II band alignment heterostructure,and Tl Ga S2 can tune the carrier lifetime of monolayer WS2. |
PDF Full Text Request