Many-Body Enhancement of Excitonic Electron-Hole Recombination in Two-Dimensional Transition Metal Dichalcogenides

Electron-hole recombination is a fundamental process that governs energy dissipation and device efficiency in semiconductors. In two-dimensional (2D) materials, the formation of tightly bound excitons, making exciton-mediated e-h recombination the dominant decay pathway. In this work, nonradiative e-h recombination within excitons in monolayer MoS₂ is investigated using first-principles simulations that combine nonadiabatic molecular dynamics with GW and real-time Bethe-Salpeter equation propagation. A two-step process is identified: rapid intervalley redistribution induced by exchange interaction, followed by slower phonon-assisted recombination facilitated by exciton binding. By selectively removing the screened Coulomb and exchange terms from the BSE Hamiltonian, their respective contributions are disentangled - exchange interaction is found to increase the number of accessible recombination pathways, while binding reduces the excitation energy and enhances nonradiative decay. A reduction in recombination lifetime by over an order of magnitude is observed by the excitonic many-body effects. These findings provide microscopic insights for understanding and tuning exciton lifetimes in 2D TMDs.