Direct correlation of defects with photoluminescence and electrical conductivity in monolayer transition metal dichalcogenides*

Transition metal dichalcogenides (TMDs) are promising candidates for emerging applications such as transparent and flexible optoelectronics and electronics. Understanding the impact of defects on TMD properties is essential for the advancement of these materials. Here, we demonstrate the ability to observe electronically active defects in monolayer TMDs using conductive atomic force microscopy in ambient conditions, and we correlate defect density with local optoelectronic and electronic properties. We find that CVD-grown WS₂ samples have up to an order of magnitude variation in defect density within a single triangular grain. We also find that photoluminescence (PL) intensity is inversely proportional to defect density. To investigate electronic properties, we use kelvin probe force microscopy to obtain spatial maps of electrostatic potential in operating TMD transistors. We find that regions with low PL intensities exhibit large potential gradients, corresponding to high resistivity. This suggests that the defects responsible for decreased PL intensity are also responsible for decreased electrical conductivity.