Transient absorption measurements of interlayer charge transfer in a WS₂/GeS van der Waals heterostructure

We introduce germanium sulfide (GeS) as a new layered material for the fabrication of two-dimensional van der Waals materials and heterostructures. Heterostructures of WS₂/GeS were fabricated using mechanical exfoliation and dry transfer techniques. Significant photoluminescence quenching of WS₂ in the heterostructures indicates efficient charge transfer. Transient absorption measurements were performed to study the dynamics of charge transfer. The results show that the heterostructure forms a type-II band alignment with the conduction band minimum and valence band maximum located in the WS₂ and GeS layers, respectively. The ultrafast hole transfer from WS₂ to GeS is confirmed by the faster decay of the lower peak value of the differential reflection signal in the heterostructure sample, in comparison to the WS₂ monolayer. These results introduce GeS as a promising semiconductor material for developing new novel heterostructures.