Temperature dependence of charge transfer processes in WS2/MoSe2 heterobilayers probed by ultrafast spectroscopy*

We report transient reflection experiments to probe electron transfer processes from MoSe2 to WS2 in WS2/MoSe2 heterobilayers. The measurements were performed for temperatures from 15 - 300K. Complementing temperature dependent static reflection contrast measurements, we investigate charge transfer by pump-probe measurements and discuss its relation to the temperature-dependent band alignment for the WS2/MoSe2 system. Our motivation stems from the theoretical prediction that the conduction band minima of the two materials are separated only by a few tens of meV [i.e. B. Amin et al. Phys. Rev. B 92, 075439 (2015)]. Hence, their alignment and the corresponding electron transfer process from one material to its neighbor are potentially tunable using external knobs such as temperature. The present study seeks to clarify this important issue for future applications that require understanding and controlling the electronic band structure and dynamic processes in this heterostack.