Photoluminescence inhomogeneity and excitons in CVD-grown monolayer WS₂

Transition metal dichalcogenides two-dimensional materials are of great importance for future electronic and optoelectronic applications. In this work, triangular WS₂ monolayers with size up to 130 μm were prepared via chemical vapor deposition method. WS₂ monolayers presented uniform Raman intensity, while quenched photoluminescence (PL) was observed in the center. The PL quenching in the central part of WS₂ monolayer flakes was attributed to the gradually increasing sulfur vacancies toward the center. The proportion of negative trion (X⁻) in PL spectrum increases with increasing sulfur vacancies in WS₂. The enhanced binding energy of X⁻ suggests higher Fermi level and n-doping level with larger sulfur vacancy concentration. Our findings may be beneficial to the development of integrated devices, and also explore the defect-induced optical and electrical properties for nanophotonics.