Efficient Energy Transfer in InSe-MoSe Van Der Waals Heterostructures

We show that bilayer α-phase InSe and monolayer MoSe form a type-I band alignment, with both the conduction band minimum and the valence band maximum located in MoSe. Samples were fabricated by a two-step chemical vapor deposition method. The photoluminescence yield of the heterostructure sample was found to be similar to monolayer MoSe, indicating the lack of an efficient charge transfer from MoSe to InSe. This is further confirmed by the observation that the photocarrier lifetime in the heterostructure is similar to monolayer MoSe, showing the lack of layer separation of the electrons and holes. Efficient energy transfer from InSe to MoSe was observed by the sevenfold enhancement of the differential reflection signal in the heterostructure and its ultrashort rising time. Furthermore, we observed significant photoluminescence quenching in heterostructures formed by bulk InSe and monolayer MoSe, which suggests efficient charge transfer and therefore type-II band alignment. These findings suggest that α-InSe ultrathin layers can be effectively integrated as light-absorbing layers with other transition metal dichalcogenides for novel optoelectronic applications.