Effect of Substrate on Sulfur Vacancy Defect-Mediated Photoluminescence in Two-Dimensional MoS₂

Chalcogen vacancy defects in monolayer transition metal dichalcogenides form in-gap states that can trap excitons, leading to defect-mediated photoluminescence (PL) emission. Here, we show that room-temperature (RT, 300 K) PL from sulfur vacancies in defective monolayer MoS₂ is sensitive to doping from dielectric substrates such as SiO₂ and HfO₂. The defect-mediated PL is observed for monolayer MoS₂ on untreated HfO₂ but is quenched on untreated SiO₂, which is attributed to electron doping of MoS₂ on SiO₂. Electron doping of MoS₂ is confirmed by Raman and synchrotron X-ray photoelectron spectroscopy. Annealing of the SiO₂ substrate modifies its surface states, which is reflected in the recovery of the defect-mediated PL emission. The role of substrate-induced doping on sulfur vacancy-mediated PL is further supported by gate-dependent PL measurements. Our results suggest that excess electrons fill the defect energy states from sulfur vacancies in MoS₂, reducing the probability of photoexcited carrier occupation and subsequent defect-mediated emission.