Dynamics of Free and Localized Excitons in Two-Dimensional Transition Metals Dichalcogenides

Exciton kinetics in transition-metal dichalcogenide materials is highly dependent to the experimental conditions and the quality of the sample. This study presents a comprehensive model comprising a complete set of rate equations, which account for charge transfer among multiexcitonic channels including bright and dark excitons, trions, localized excitons, to investigate the dynamics of excitons in monolayer WSe2. The exciton dynamics involving both intra- and intervalley scattering is discussed. In this respect, for high quality samples, it is proved that the kinetics of excitons in darkish materials is dominated by intravalley scattering in which low-lying optically dark exciton states constitute an important reservoir while in the case of molybdenides only intervalley scattering is efficient. For low quality samples, the dynamics of localized exciton states and negative trion in case of n-type doping sample is studied. It is shown that localized exciton states decay on a longer time scale than the trion and free exciton, consistent with experimental findings of Wang et al. [Phys. Rev. B 2014, 90, 075413]. Finally, the dependence of the trion and localized exciton dynamics as a function of the electron density is studied. It is found that the trion and localized exciton populations strongly depend to the doping density.