Measurement of Ultrafast Carrier Dynamics in Epitaxial Graphene

TL;DR

This study uses ultrafast optical spectroscopy to measure carrier relaxation times in epitaxial graphene, revealing two distinct relaxation processes linked to carrier interactions and disorder levels.

Contribution

First measurement of ultrafast carrier dynamics in epitaxial graphene, correlating relaxation times with crystalline disorder and scattering mechanisms.

Findings

Fast relaxation in 70-120 fs range

Slow relaxation in 0.4-1.7 ps range

Slow relaxation inversely related to disorder level

Abstract

Using ultrafast optical pump-probe spectroscopy, we have measured carrier relaxation times in epitaxial graphene layers grown on SiC wafers. We find two distinct time scales associated with the relaxation of nonequilibrium photogenerated carriers. An initial fast relaxation transient in the 70-120 fs range is followed by a slower relaxation process in the 0.4-1.7 ps range. The slower relaxation time is found to be inversely proportional to the degree of crystalline disorder in the graphene layers as measured by Raman spectroscopy. We relate the measured fast and slow time constants to carrier-carrier and carrier-phonon intraband and interband scattering processes in graphene.