Unveiling the Correlation between Defects and High Mobility in MoS Monolayers.

Defects in semiconductors play a crucial role in modifying their electronic structure and transport properties. In transition metal dichalcogenides, atomic chalcogen vacancies are a primary source of intrinsic defects. While the impact of these vacancies on electrical transport has been widely studied, their exact role remains not fully understood. In this work, we correlate optical spectroscopy, low-temperature electrical transport measurements, scanning tunneling microscopy (STM), and first-principles density functional theory (DFT) calculations to explore the effect of chalcogen vacancies in MoS monolayers grown by chemical vapor deposition. We specifically highlight the role of disulfur vacancies in modulating electrical properties, showing that these defects increase the density of shallow donor states near the conduction band, which facilitates electron hopping conduction, as evidenced by low-temperature transport and STM measurements. These findings are further supported by DFT calculations, which reveal that the electronic states associated with these defects are relatively delocalized, promoting hopping conduction and inducing n-type doping. This mechanism accounts for the observed high field-effect mobility (>100 cm Vs) in the samples. These findings highlight the potential for defect engineering as a universal approach to customizing the properties of 2D materials for various applications.