Electron and optical phonon temperatures in electrically biased graphene

TL;DR

This study investigates energy dissipation in biased graphene by combining optical emission and Raman spectroscopy, revealing high electron and phonon temperatures and partial thermal equilibrium under current saturation.

Contribution

It provides new insights into the energy distribution and thermal behavior of electrons and optical phonons in electrically biased graphene.

Findings

Electrons and holes obey a thermal distribution with temperatures over 1500 K.

Optical phonons are highly excited and in equilibrium with electrons.

The Raman G-mode shift indicates incomplete equilibrium among phonon modes.

Abstract

We examine the intrinsic energy dissipation steps in electrically biased graphene channels. By combining in-situ measurements of the spontaneous optical emission with a Raman spectroscopy study of the graphene sample under conditions of current flow, we obtain independent information on the energy distribution of the electrons and phonons. The electrons and holes contributing to light emission are found to obey a thermal distribution, with temperatures in excess of 1500 K in the regime of current saturation. The zone-center optical phonons are also highly excited and are found to be in equilibrium with the electrons. For a given optical phonon temperature, the anharmonic downshift of the Raman G-mode is smaller than expected under equilibrium conditions, suggesting that the electrons and high-energy optical phonons are not fully equilibrated with all of the phonon modes.