Exciton luminescence efficiency and dynamics in flux-growth MoSe2 monolayers

Monolayers of transition metal dichalcogenide like MoS₂ are promising materials for optoelectronics applications due to their exceptionally strong light-matter interaction governed by very robust excitons (Coulomb bounded electron hole pairs). Nevertheless, practical usage has been hindered by their relatively low quantum efficiency (0.1-1%) due to the presence of non-radiative recombination channels (defects, exciton-exciton annihilation, relaxation to dark states …). In this work, we compare the optical properties of monolayers of MoSe2 exfoliated from different bulk crystals : commercially available crystals from 2D Semiconductors and bulk crystals synthetized with the low temperature flux-growth technique. We perform temperature dependent photoluminescence (PL) and time resolved PL measurements and observe strong differences between the materials in terms of doping level, the PL intensity evolution with temperature and the exciton dynamics at both cryogenic and room temperature. These results are interpreted evoking the lower defect density measured in our flux-growth samples.