Interfacial Effect on the Transient Dielectric Function and Charge Transfer in a Monolayer WS/Si Heterojunction.

Monolayer tungsten disulfide (WS) is a highly promising material for silicon photonics. Thus, the WS/Si interface plays a very important role due to the interfacial complex effects and abundant states. Among them, the effect of charge transfer on exciton dynamics and the optoelectronic property is determined by the dielectric function, which is very crucial for the performance of optoelectronic devices. However, research on the exciton dynamics or the transient dielectric function of WS in such WS/Si junctions is still rare. In this work, both the transient dielectric function and charge transfer of WS/Si heterojunctions are analyzed based on the transient reflectance spectra measured by the pump-probe spectrometer. The dynamic processes of the A exciton, affected by charge transfer within the WS/Si heterojunction, are interpreted. Moreover, the transient dielectric function of WS is quantitatively analyzed. The dielectric function of WS exhibits a notable 19% change, persisting for more than 180 ps within the WS/Si heterojunction. These findings can pave the way for the advancement of silicon photonic devices based on WS.