Interlayer excitons in MoS₂/CSiH₂/WS₂ heterostructures: the role of the Janus intermediate layer

The introduction of intermediate hexagonal boron nitride (hBN) between the bilayer transition metal dichalcogenide (TMD) heterostructures has been considered an efficient approach to manipulate the interlayer excitations. However, the hBN intercalation primarily serves as a spacer to increase the interlayer distance and alter the screening, without producing a significant band offset shift. Here, we use Janus monolayer CSiH₂, possessing a prominent out-of-plane intrinsic dipole moment and large enough band gap, as an intercalation to build trilayer MoS₂/CSiH₂/WS₂heterostructures. Our calculated results by means of many-body perturbation theory reveal that the band alignment characteristics and the band gaps are dramatically altered in the presence of the CSiH₂monolayer, due to the large potential drop across the interface of bilayer TMDs. By solving the Bethe-Salpeter equation, we observe the static dipole moment of the interlayer excitons (IXs) can be reversed through tuning the stacking sequence of CSiH₂. More importantly, the radiative lifetime of IX has been substantially prolonged in MoS₂/CSiH₂/WS₂, several orders of magnitude longer than that of bilayer MoS₂/WS₂, and varies between 10^-9-10^-5s at 0 K with different stacking sequence of CSiH₂. Our explorations open the feasibility of simultaneously engineering the band alignment and the dipole moment of the dipolar IXs in TMD van der Waals heterostructures, through the introduction of Janus intercalation.