Multiphoton Excitation and Defect-Enhanced Fast Carrier Relaxation in Few-Layered MoS2 Crystals

Abstract

Femtosecond transient reflection spectroscopy was employed to study the carrier dynamics in few-layered MoS2 crystals prepared by either a chemical vapor deposition (CVD) technique or a mechanical exfoliation method. Three decay processes were observed in samples prepared by both methods. The faster processes were approximately 300–500 fs and could be attributed to defect-assisted scattering. The slower processes varied from 1 to 250 ps and were related to carrier–carrier and carrier–phonon scattering. Comparative studies between the CVD and exfoliated samples with different thicknesses demonstrated that faster decay processes occurred in thinner samples, in which the interface and defects had stronger effects. Wavelength-dependent transient reflection spectra demonstrated that a change in the sign of the signal occurred around the exciton absorption peaks, which could be attributed to competition of the stimulated emission and excited-state absorption processes around the exciton absorption peaks. Our re...