Dielectric control of ultrafast carrier dynamics and transport in graphene

TL;DR

This study demonstrates how engineering the dielectric environment of graphene can externally control its ultrafast carrier dynamics and transport properties, impacting device performance.

Contribution

We show that dielectric screening can be used to regulate carrier interactions and dynamics in graphene without changing its Fermi energy or temperature.

Findings

Dielectric screening suppresses carrier-carrier interactions in graphene.

Slowing of carrier heating and cooling dynamics due to enhanced screening.

Increased charge mobility and Seebeck coefficient through dielectric environment engineering.

Abstract

Understanding the ultrafast dynamics of photoexcited charges in graphene is essential, as the microscopic mechanisms underlying these dynamics determine many of graphene's optical, optothermal, and optoelectronic properties. These are crucial properties for many functionalities and devices enabled by graphene, such as high-speed photodectors. Therefore, beyond scientific understanding, it is highly desirable to control ultrafast carrier dynamics for practical applications. Here, we establish this control by engineering the dielectric environment of graphene, thereby regulating both heating and cooling dynamics without altering the Fermi energy, optical power, or ambient temperature. By combining optical pump-terahertz probe experiments with theoretical calculations, we show that dielectric screening suppresses carrier-carrier interactions and slows the dynamics. In particular, reduced carrier-carrier scattering delays the formation of a quasi-equilibrium hot electron distribution, thus slowing carrier heating. It also slows carrier cooling because re-thermalization after optical-phonon emission depends on the same interactions. The enhanced screening further reduces the energy of electron-hole puddles, thereby increasing charge mobility and the Seebeck coefficient. This ability to externally control internal graphene dynamics and transport properties enables the optimization of device performance, such as the sensitivity of photodetectors for data communication and wireless communication applications.