Hot carrier and hot phonon coupling during ultrafast relaxation of photoexcited electrons in graphene

TL;DR

This study uses a Monte Carlo simulator to analyze hot phonon effects on ultrafast electron relaxation in graphene, revealing significant impacts on relaxation times and the importance of considering non-equilibrium phonon distributions.

Contribution

It provides a detailed multi-particle simulation showing the critical role of hot phonons in electron relaxation dynamics in graphene, especially at higher excitation energies and specific carrier densities.

Findings

Neglecting hot phonons underestimates relaxation times.

Hot phonon effects are more significant at higher excitation energies.

Acoustic intervalley phonons influence carrier cooling rates.

Abstract

We study, by means of a Monte Carlo simulator, the hot phonon effect on the relaxation dynamics in photoexcited graphene and its quantitative impact as compared to considering an equilibrium phonon distribution. Our multi-particle approach indicates that neglecting the hot phonon effect significantly underestimates the relaxation times in photoexcited graphene. The hot phonon effect is more important for a higher energy of the excitation pulse and photocarrier densities between $1$ and $3\times 10^{12} \mathrm{~cm}^{-2}$. Acoustic intervalley phonons play a non-negligible role, and emitted phonons with wavelengths limited up by a maximum (determined by the carrier concentration) induce a slower carrier cooling rate. Intrinsic phonon heating is damped in graphene on a substrate due to additional cooling pathways, with the hot phonon effect showing a strong inverse dependence with the carrier density.