Ultrafast dynamics of charge transfer in CVD grown MoS2-graphene heterostructure

We study the interlayer charge transfer dynamics across the heterojunction of graphene and chemical-vapor-deposition grown MoS2, using ultrafast optical spectroscopy. Electron-hole pairs are generated only in the graphene layer by a 100-fs pump pulse, and the presence of carriers in the MoS2 layer is observed via a probe pulse tuned to the MoS2 bandgap. Due to the band lineup, there is an initial rapid transfer of electrons from the graphene into the MoS2 layer, which cannot be well resolved within the 100-fs resolution of the experiment. This work focuses instead on the transfer of thermalized electrons back from the MoS2 to the graphene layer, as the system returns to equilibrium. The dynamics of the back transfer are found to be nonexponential and, for times after carrier cooling is complete (greater than or similar to 5 ps), can only be fit using a Porter-Thomas distribution of the charge transfer rates, indicating that the MoS2 states are localized by disorder and that the interlayer transfer process is dominated by random coupling.