Functionalized two-dimensional vdW multijunction MoS2−MoS2/WS2−WS2/WS2−WS2 platform for defect-related carrier dynamics studies

Defect engineering plays a critical role in two-dimensional (2D) semiconductor devices, especially for 2D transition-metal dichalcogenides (2D-TMDs) due to their extraordinary optoelectronic properties. However, directly comparing defect-related effects on various devices presents challenges, as it requires multiple growth processes and device fabrication procedures including stacking. Here, we have designed and produced one platform for 2D-TMD multijunction MoS2−MoS2/WS2−WS2/WS2−WS2 on a single flake via chemical vapor deposition (CVD) growth to investigate its photoexcited carrier dynamics. Ultrafast pump-probe transient transmittance measurements at four junctions reveal the defect-related effects on fast and slow relaxation processes and further uncover passivation occurring at the MoS2/WS2 junction, with a longer relaxation time of 25 ps. This work paves the way to establish a paradigm for examining charge-carrier dynamics in functionalized 2D van der Waals multijunctions via CVD growth and a unique microscopic method.