Tailoring of defect luminescence in CVD grown monolayer MoS 2 film

Highlights: • Optical properties of large area strictly monolayer ${\text{MoS}}_2$ films grown using a novel micro-cavity based CVD route. • Significant effect of substrate induced strain on excitonic properties, exciton-phonon coupling, etc. • Study reveals a broad luminescence (BL) that dominates photoluminescence (PL) below 200 K. • Pin down the origin of this broad luminescence. • Demonstration of controlling defect Luminescence by tuning growth parameters. Optical properties of strictly monolayer ${\text{MoS}}_2$ films, which are grown on c-sapphire substrates using microcavity based CVD route, have been investigated by temperature dependent absorption and temperature as well as excitation intensity dependent photoluminescence (PL) spectroscopy. Our study reveals a high intensity broad luminescence band appearing at $\sim$1.7 eV along with the usual free exciton/trion peak ($\sim$1.86 eV). The investigation furthermore attributes this broad transition to excitons bound to two types of defects, whose binding energies are found to be $\sim$11 and $\sim$118 meV. Integrated intensity of this feature decreases with the increase in the impinging sulfur flux during growth and by post-growth annealing in sulfur atmosphere suggesting that these defects must be related to sulfur deficiency. Interestingly, exciton-phonon coupling for these defect bound excitons is found to be much stronger than that is associated with free excitons/trions.