Quasi-type-I band alignment in WS₂/MoS₂heterostructures produced by H₂S-based CVD

In this work we report the synthesis and characterization of WS₂/MoS₂heterostructures prepared by sequential chemical vapor deposition using H₂S and thermally evaporated metal as precursors. A thin WS₂covers (1-2 monolayers) are produced on pre-formed MoS₂nanowall films, resulting in nearly complete quenching of the MoS₂photoluminescence (PL) and emergence of a dominant WS₂PL peak at higher energy. Remarkably, electrical measurements reveal that the thermally activated conduction in the both layered materials have nearly the same activation energies, suggesting comparable donor activation energies and a possible near-alignment of the CBM positions within experimental uncertainty. This particular 'quasi-type-I' alignment is in sharp contrast to the conventional staggered (type-II) alignment normally expected in WS₂/MoS₂heterostructures. Transient absorption pump-probe spectroscopy shows signatures consistent with ultrafast interlayer charge transfer and possible interlayer exciton formation. We present a comprehensive study of the optical, structural, and transport properties of prepared samples, and discuss the carrier transfer mechanisms that give rise to the observed PL redistribution.