Speaker
Description
Transition metal dichalcogenides (TMDs), such as $\text{WSe}_2$ and $\text{MoS}_2$, have attracted considerable attention due to their distinctive excitonic properties and promising applications in optoelectronic devices. In this work, we investigate the optical transitions and defect-related excitonic states in chemical vapor deposition (CVD)-grown $\text{WSe}_2$ and $\text{MoS}_2$, where the defect density is controlled by the gas flow rate during growth. Low-temperature photoluminescence (PL) and differential reflectance (DR) spectroscopy are employed to accurately identify various band-to-band optical transitions, including neutral excitons, trions, and defect-bound excitons. Moreover, PL mapping combined with dielectric engineering is used to elucidate the microscopic mechanisms and charge states of defect-bound excitons. The energy separations between defect-related emissions and free excitons exhibit similar trends in both materials, indicating analogous defect origins. These findings offer critical insights into defect engineering, bandgap modulation, and essential parameters for optimizing crystal growth in two-dimensional semiconductors.