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

Electron-hole (e-h) 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 makes 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 (BSE) 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 due to the excitonic many-body effects. These findings provide microscopic insights for understanding and tuning exciton lifetimes in 2D transition-metal dichalcogenides.