Tailoring of defect luminescence in CVD grown monolayer [formula omitted] film

Abstract

Optical properties of strictly monolayer MoS2 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 ∼1.7 eV along with the usual free exciton/trion peak (∼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 ∼11 and ∼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.