Coupled excitonic quasiparticle-electron–phonon and interlayer coupling in vertically and horizontally aligned MoS2
Abstract
Excitonic quasi-particles, excitons/trions/bi-excitons, and their coupling with phonons and charge carriers play a crucial role in controlling the optical properties of atomically thin semiconducting 2D materials. In this study, we revealed the dynamics of excitons/trions and their coupling with phonons and charge carriers in few-layer vertically and horizontally aligned MoS2. We observed the trion signature up to the highest recorded temperature (330 K) in both systems and have shown that the dynamics of excitons/trions and their coupling with phonons and electrons are more affected in vertically aligned MoS2. Homogeneous linewidth broadening was observed with an increase in temperature, which is attributed mainly to acoustic phonons in the low-temperature regime (<100 K). In contrast, acoustic and longitudinal optical phonon contributions to linewidth broadening were observed at high temperature. We also observed the significant effects of interlayer coupling in both systems by understanding their temperature-dependent valence band splitting and trion binding energy. A decrease of ∼22% and 12% in valence band splitting with an increase in temperature was observed for the vertically and horizontally aligned MoS2, respectively, suggesting that the valence band splitting is affected more in the case of vertically than horizontally aligned MoS2. Furthermore, we also observed significant thermal quenching in the intensity of the trion band compared to that of exciton bands, which is attributed to the small binding energy of the trions.