ZnO Surface Morphology and Chemistry Govern Exciton Dynamics in WS 2 /ZnO Heterostructures

Mixed-dimensional heterostructures of transition-metal dichalcogenides and metal oxides combine strong light–matter interaction with efficient charge transport, offering a versatile platform for optoelectronic devices. However, the influence of the metal oxide surface structure and chemistry on exciton behavior remains poorly understood. Here, we investigate monolayer WS 2 integrated with two ZnO model systems: single-crystalline m-plane (11 − 00) ZnO and polycrystalline ZnO grown by atmospheric-pressure spatial atomic layer deposition. Multi-modal spectroscopy, microscopy, and density functional theory reveal that single-crystalline ZnO provides a smooth, OH-rich interface that promotes type-II band alignment, efficient dielectric screening, and ultrafast exciton dissociation. In contrast, polycrystalline ZnO exhibits a rough, defect-rich surface that forms a gapped interface, inducing spatially inhomogeneous charge transfer, trap-assisted recombination, and slower, diffusion-limited exciton decay. These findings establish WS 2 /ZnO as a model system for interface-driven optoelectronic design, highlighting oxide surface engineering as a powerful tool for tailoring exciton dynamics in mixed-dimensional heterostructures.