Type-II WS 2 –ReSe 2 heterostructure and its charge-transfer properties

We fabricated a van der Waals heterostructure of WS 2 –ReSe 2 and studied its charge-transfer properties. Monolayers of WS 2 and ReSe 2 were obtained by mechanical exfoliation and chemical vapor deposition, respectively. The heterostructure sample was fabricated by transferring the WS 2 monolayer on top of ReSe 2 by a dry transfer process. Photoluminescence quenching was observed in the heterostructure, indicating efficient interlayer charge transfer. Transient absorption measurements show that holes can efficiently transfer from WS 2 to ReSe 2 on an ultrafast timescale. Meanwhile, electron transfer from ReSe 2 to WS 2 was also observed. The charge-transfer properties show that monolayers of ReSe 2 and WS 2 form a type-II band alignment, instead of type-I as predicted by theory. The type-II alignment is further confirmed by the observation of extended photocarrier lifetimes in the heterostructure. These results provide useful information for developing van der Waals heterostructure involving ReSe 2 for novel electronic and optoelectronic applications and introduce ReSe 2 to the family of two-dimensional materials to construct van der Waals heterostructures.