Picosecond energy transfer in a transition metal dichalcogenide-graphene heterostructure revealed by transient Raman spectroscopy

TL;DR

This study uses transient Raman spectroscopy to reveal that energy transfer, rather than charge transfer, dominates in a transition metal dichalcogenide-graphene heterostructure within a few picoseconds, impacting optoelectronic device performance.

Contribution

It provides direct experimental evidence that energy transfer is the primary interlayer interaction in TMD-graphene heterostructures on a picosecond timescale.

Findings

Energy transfer occurs within approximately 4 ps.

Charge transfer plays a lesser role in the initial dynamics.

An intermediate process influences slower electric signals.

Abstract

Intense light-matter interactions and unique structural and electrical properties make Van der Waals heterostructures composed by Graphene (Gr) and monolayer transition metal dichalcogenides (TMD) promising building blocks for tunnelling transistors, flexible electronics, as well as optoelectronic devices, including photodetectors, photovoltaics and quantum light emitting devices (QLEDs), bright and narrow-line emitters using minimal amounts of active absorber material. The performance of such devices is critically ruled by interlayer interactions which are still poorly understood in many respects. Specifically, two classes of coupling mechanisms have been proposed: charge transfer (CT) and energy transfer (ET), but their relative efficiency and the underlying physics is an open question. Here, building on a time resolved Raman scattering experiment, we determine the electronic temperature profile of Gr in response to TMD photo-excitation, tracking the picosecond dynamics of the G and 2D bands. Compelling evidence for a dominant role ET process accomplished within a characteristic time of ~ 4 ps is provided. Our results suggest the existence of an intermediate process between the observed picosecond ET and the generation of a net charge underlying the slower electric signals detected in optoelectronic applications.