Estimation of lifetime of excitons in monolayer transition metal dichalcogenides.

In this work, we present a mathematical model for estimating the exciton lifetime in monolayer transition metal dichalcogenides (TMDs), including WS2, WSe2, MoS2, and MoSe2. The effective masses are calculated using density functional theory (DFT) within the local density approximation employing the Perdew-Zunger exchange-correlation functional. Anisotropic confinement is considered to evaluate the exciton binding energies, and the Fermi's Golden rule is applied to calculate the oscillator strength. The model is validated against an AlGaAs/GaAs double quantum well heterostructure with Coulomb interaction, and Keldysh-type screened Coulomb interaction is taken into account to evaluate the exciton ground-state properties in TMDs. The predicted binding energies (488-578 meV) and lifetimes (0.146-0.52 ns) obtained from our model for the monolayer TMDs are compared with the DFT-based models, other theoretical approaches, and reported time-resolved photoluminescence (PL) measurements. The effective lifetimes estimated by incorporating exciton thermalization effects show a good agreement with the PL decay measurements at room temperature. The present model relies solely on material parameters, and unlike the computationally intensive Green's-function-based Bethe-Salpeter equation approaches, offers an efficient method for predicting exciton energies and lifetimes in two-dimensional semiconductors.