Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure

TL;DR

This study demonstrates how electron thermalization pathways in a van der Waals heterostructure can be tuned by controlling interlayer carrier transport, enabling new ways to manipulate electron energy dynamics in nanoscale devices.

Contribution

We introduce a method to control electron thermalization in 2D heterostructures by tuning interlayer carrier transfer, advancing nanoscale electron energy management.

Findings

Interlayer bias voltage controls carrier transfer speed.

Photon energy variation modulates thermalization pathways.

Demonstrated direct control over electron energy transport.

Abstract

Ultrafast electron thermalization - the process leading to Auger recombination, carrier multiplication via impact ionization and hot carrier luminescence - occurs when optically excited electrons in a material undergo rapid electron-electron scattering to redistribute excess energy and reach electronic thermal equilibrium. Due to extremely short time and length scales, the measurement and manipulation of electron thermalization in nanoscale devices remains challenging even with the most advanced ultrafast laser techniques. Here, we overcome this challenge by leveraging the atomic thinness of two-dimensional van der Waals (vdW) materials in order to introduce a highly tunable electron transfer pathway that directly competes with electron thermalization. We realize this scheme in a graphene-boron nitride-graphene (G-BN-G) vdW heterostructure, through which optically excited carriers are transported from one graphene layer to the other. By applying an interlayer bias voltage or varying the excitation photon energy, interlayer carrier transport can be controlled to occur faster or slower than the intralayer scattering events, thus effectively tuning the electron thermalization pathways in graphene. Our findings, which demonstrate a novel means to probe and directly modulate electron energy transport in nanoscale materials, represent an important step toward designing and implementing novel optoelectronic and energy-harvesting devices with tailored microscopic properties.