Layer-dependent photoresponse of atomically thin WSe₂/WS₂ heterojunctions

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have created new opportunities for novel electronic and optoelectronic devices due to their distinctive electrical and optical properties. Van der Waals (VdW) heterostructures based on the 2D TMD atomic layers provide a unique way to fabricate p-n junctions at the atomic scale, exhibiting completely different charge transport behaviors than bulk heterojunctions. Despite the recent progress of photoresponse in p-n junctions made of atomically thin TMDs, a systematical study of the layer-dependence of the photovoltaic effect and photodetections in these vdW heterostructures is lacking. Here, we report the fabrication of high-quality WSe₂/WS₂p-n junctions and a systematical study of their layer-dependent photoluminescence and photovoltaic effect using Scanning Electrochemical Cell Microscopy (SECCM). A strong enhancement of the photocurrent has been realized as the thickness of the compositing layer increases. We further applied the first-principle calculation to understand our observations. Our work may pave a way for making nanoscale optoelectronic devices using the TMDs heterostructures.