Exciton Radiative Lifetimes in Two-Dimensional Transition Metal Dichalcogenides

TLDR

Light emission in 2D transition metal dichalcogenides varies strongly with layer number and stacking, yet exciton dynamics and radiative recombination remain poorly understood. The study aims to compute intrinsic exciton radiative lifetimes at 4 K and 300 K for monolayer, bilayer, bulk MoS₂, and MX₂ heterobilayers using first‑principles methods. Using density‑functional theory and many‑body perturbation theory, the authors calculate radiative lifetimes from exciton wavefunctions and transition dipole moments across different TMD structures. The calculations reveal that monolayer TMDs have picosecond lifetimes at 4 K and nanosecond lifetimes at 300 K, while bulk and bilayer MoS₂ exhibit slower recombination; heterobilayers host interlayer excitons with 20–30 ns lifetimes at room temperature, demonstrating wide tunability and promising applications in optoelectronics and solar energy conversion.

Abstract

Light emission in two-dimensional (2D) transition metal dichalcogenides (TMDs) changes significantly with the number of layers and stacking sequence. While the electronic structure and optical absorption are well understood in 2D-TMDs, much less is known about exciton dynamics and radiative recombination. Here, we show first-principles calculations of intrinsic exciton radiative lifetimes at low temperature (4 K) and room temperature (300 K) in TMD monolayers with the chemical formula MX2 (X = Mo, W, and X = S, Se), as well as in bilayer and bulk MoS2 and in two MX2 heterobilayers. Our results elucidate the time scale and microscopic origin of light emission in TMDs. We find radiative lifetimes of a few picoseconds at low temperature and a few nanoseconds at room temperature in the monolayers and slower radiative recombination in bulk and bilayer than in monolayer MoS2. The MoS2/WS2 and MoSe2/WSe2 heterobilayers exhibit very long-lived (∼20–30 ns at room temperature) interlayer excitons constituted by electrons localized on the Mo-based and holes on the W-based monolayer. The wide radiative lifetime tunability, together with the ability shown here to predict radiative lifetimes from computations, hold unique potential to manipulate excitons in TMDs and their heterostructures for application in optoelectronics and solar energy conversion.