Ultrafast charge dynamics and photoluminescence in bilayer MoS2

TL;DR

This study investigates ultrafast charge dynamics and electron-phonon interactions in bilayer MoS2, revealing how these processes influence its photoluminescence features and emission pathways.

Contribution

It provides a microscopic understanding of charge recombination pathways and phonon-assisted relaxation in bilayer MoS2 using time-dependent density functional theory.

Findings

Charge accumulates near the Q point after excitation.

Emission occurs via direct K point recombination and phonon-assisted pathways.

Higher energy peak linked to phonon-assisted electron relaxation from Q to K.

Abstract

Our examination of the interplay of ultrafast charge dynamics and electron-phonon interaction in bilayer MoS2 provides a microscopic basis for understanding the features (two peaks) in the emission spectrum. We demonstrate that while the initial accumulation of excited charge occurs at and near the Q point of the two-dimensional Brillioun zone, emission takes place predominantly through two pathways: direct charge recombination at the K point and indirect phonon-assisted recombination of electrons at the K valley and holes at {\Gamma} hill of the Brillouin zone. Analysis of the wave vector dependencies of the electron-phonon interaction traces the higher energy peak to phonon-assisted relaxation of the excited electrons from the Q to the K valley in the conduction band. Our results thus reveal the importance of ultrafast charge dynamics in understanding photoemissive properties of a few-layer transition-metal dichalcogenide. These calculations are based on time dependent density functional theory in the density matrix formulation.