Surface Recombination Limited Lifetimes of Photoexcited Carriers in Few-Layer Transition Metal Dichalcogenide MoS2

TL;DR

This study investigates how the lifetimes of photoexcited carriers in few-layer MoS2 increase with layer number, revealing surface recombination as the limiting factor and highlighting defect-assisted Auger processes.

Contribution

It demonstrates that carrier lifetimes in few-layer MoS2 are governed by surface defect densities and provides a quantitative analysis of how lifetimes scale with layer number and defect presence.

Findings

Carrier lifetimes increase from tens of picoseconds to over a nanosecond with more layers.

Inverse lifetime scales linearly with photoexcited carrier density.

Carrier lifetimes are largely independent of temperature.

Abstract

We present results on photoexcited carrier lifetimes in few-layer transition metal dichalcogenide MoS2 using nondegenerate ultrafast optical pump-probe technique. Our results show a sharp increase of the carrier lifetimes with the number of layers in the sample. Carrier lifetimes increase from few tens of picoseconds in monolayer samples to more than a nanosecond in 10-layer samples. The inverse carrier lifetime was found to scale according to the probability of the carriers being present at the surface layers, as given by the carrier wavefunction in few layer samples, which can be treated as quantum wells. The carrier lifetimes were found to be largely independent of the temperature and the inverse carrier lifetimes scaled linearly with the photoexcited carrier density. These observations are consistent with defect-assisted carrier recombination, in which the capture of electrons and holes by defects occurs via Auger scatterings. Our results suggest that carrier lifetimes in few-layer samples are surface recombination limited due to the much larger defect densities at the surface layers compared to the inner layers.