Abstract:
The family of two-dimensional (2D) layered materials with strong excitonic effect offers fascinating opportunities for studying excited state exciton behavior at 2D limit. While exciton dynamics in conventional 2D semiconductors (
e.g. transition metal dichalcogenides) has been extensively studied, little is known about exciton properties and dynamics in 2D layered semiconductors with strong electron/exciton-phonon coupling. Here, by combining experimental and theoretical approaches, we reveal the intrinsic highly localized exciton (
i.e. self-trapped exciton) in 2D layered As
2S
3, driven by strong exciton-phonon interaction. It is shown that photoexcited electron/hole charges in As
2S
3 localize spontaneously in ~110 fs, giving rise to large stokes-shifted and broad photoluminescence. An interlayer partial bond is formed between chalcogen atoms, triggering lattice distortion and carrier localization. Together with Urbach-Martienssen analysis, this study provides a comprehensive physical picture to understand the complex interplay between exciton and lattice dynamics in 2D semiconductors, which has strong implications to their optoelectronic properties and applications.