Surface State Mediated Interlayer Excitons in a 2D Nonlayered–Layered Semiconductor Heterojunction

Van der Waals heterojunctions of 2D layered semiconductors and nonlayered technological important II–V semiconductors provide unprecedented opportunities to engineer exciton and carrier dynamics in 2D optoelectronic devices. However, fabrication of such artificial heterojunctions with type-II band alignment structure and realization of interlayer excitons is challenging. Here, CdS–MoS₂ type-II heterojunctions vertically stacked with few layered MoS₂ and ultrathin CdS film are reported. Steady-state spectroscopy and time-resolved photoluminescence spectroscopy are used to study exciton and carrier dynamics in these heterojunctions. The surface states of the ultrathin CdS film caused by dangling bonds mediate interlayer exciton emission located at 753 nm in a CdS–bilayer MoS₂ heterojunction via charge transition between the MoS₂ indirect band and the CdS valence band. As a contrast, the surface states of CdS impede the recombination of interlayer excitons in a CdS-monolayer MoS₂ heterojunction. These results are helpful for development of high-performance ultrathin optoelectronic and energy devices including light emission diodes, solar cells, and photodetectors.