Relaxation of Optically Excited Carriers in Graphene

TL;DR

This paper investigates how photo-excited carriers in graphene relax through electron-phonon and electron-electron interactions, revealing conditions for population inversion and the effects of scattering on optical properties.

Contribution

It introduces a detailed simulation of carrier relaxation in graphene considering both e-ph and e-e scattering, highlighting their roles in optical phenomena.

Findings

Population inversion achievable via e-ph scattering alone

e-e scattering rapidly thermalizes carriers, eliminating negative conductivity peaks

Relaxation rates depend on photon energy and dielectric environment

Abstract

We explore the relaxation of photo-excited graphene by solving a transient Boltzmann transport equation with electron-phonon (e-ph) and electron-electron (e-e) scattering. Simulations show that when the excited carriers are relaxed by e-ph scattering only, a population inversion can be achieved at energies determined by the photon energy. However, e-e scattering quickly thermalizes the carrier energy distributions washing out the negative optical conductivity peaks. The relaxation rates and carrier multiplication effects are presented as a function of photon energy and dielectric constant.