Ultrafast carrier dynamics in a monolayer MoS₂ at carrier densities well above Mott density

Abstract

Due to the growing interest in monolayer Molybdenum Disulfide (MoS2) in several optoelectronic applications like lasers, detectors, sensors, it is important to understand the ultrafast behavior of the excited carriers in this material. In this article, a comprehensive study of the charge carrier dynamics of a monolayer MoS2 flake has been studied using transient transmission technique near A-exciton under high excitation densities well above the Mott density. Fluence dependent studies has been carried out to understand the origin of the processes which modifies its optical response under excitation. The dissociation of excitons leads to an observed fast bandgap renormalization. At later times when large number of carriers relax the remaining carriers forms excitons leading to a bleaching effect.

Electron–phonon interaction and ultrafast photoemission from doped monolayer MoS2

“…There are also interesting observations on 1L MoS 2 on the effect of the time-dependent electronic temperature on the emission 42,43 and fluence. 43–47 For example, femtosecond pump–probe spectroscopy found that electron–phonon scattering is responsible for an ultrafast redshift of the exciton resonance energy observed after photoexcitation.…”

“…There are also interesting observations on 1L MoS 2 on the effect of the time-dependent electronic temperature on the emission 42,43 and fluence. 43–47 For example, femtosecond pump–probe spectroscopy found that electron–phonon scattering is responsible for an ultrafast redshift of the exciton resonance energy observed after photoexcitation. 42 The energy from the cooling of hot carriers and from the formation of bound states is transferred to the phonon subsystem within 2 ps, though some sub-ps emission dynamics was also observed.…”

“…Indeed, PL spectra and nonequilibrium response of the latter are topics of active experimental studies. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] Note that the PL spectrum is dominated by exciton peaks. 34,35 For instance, the spectrum includes one sharp PL peak at 640 nm and one broad peak at 684 nm corresponding to the excitonic A (1.94 eV) and B (1.81 eV) direct-gap optical transitions, respectively.…”

“…42 The energy from the cooling of hot carriers and from the formation of bound states is transferred to the phonon subsystem within 2 ps, though some sub-ps emission dynamics was also observed. Electron temperature-change and fluence dependent studies 43 imply that the dissociation of excitons leads to an observed ultrafast bandgap renormalization. Analysis of exciton generation and dynamics at different pump fluences found that both ultrafast phenomena strongly depend on fluence.…”

Ultrafast dynamics under high-pressure

“…The mechanism of above dynamics processes is possible to be observed through the analysis of in situ high-pressure dynamics spectra. Therefore, it is possible to use high-pressure dynamic spectra to analyze the high-pressure affected mechanism of physical and chemical properties of various materials [68][69][70][71].…”