Impact of multipath interference in Si/SiO2 substrate on ultrafast relaxation processes in two-dimensional transition metal dichalcogenides

At present, two-dimensional transition metal dichalcogenides (2D TMDs) are of great importance due to their unique properties. These materials attracted considerable attention due to the ultrafast dynamics of excitation and relaxation processes in charge carriers. Recently, many researchers have estimated the characteristic relaxation times using standard optical pump-probe methods. The impact of multipath interference in underlying substrates on the determination of the characteristic relaxation times is generally ignored, although it can be significant due to the high transparency of 2D TMDs. In this work, we propose an approach to estimating the impact of a substrate on relaxation processes in 2D TMDs. We experimentally studied the dynamics of ultra-fast relaxation processes in monolayer, bilayer, and bulk MoS2 on Si/SiO2 substrate using time-resolved spectroscopy. It was shown that the multipath interference in substrate has a strong effect on the determination of the slow (several hundred ps) relaxation times which are associated with interband carrier recombination and can lead to the up to 20% distortion of obtained results.