Resolving mobility anisotropy in quasi-free-standing epitaxial graphene by terahertz optical Hall effect

Nerijus Armakavicius, Philipp Kühne, Jens Eriksson, Chamseddine Bouhafs, Vallery Stanishev, Ivan G. Ivanov, Rositsa Yakimova, Alexei A. Zakharov, Ameer Al-Temimy, Camilla Coletti, Mathias Schubert, Vanya Darakchieva

Research output: Contribution to journalArticlepeer-review

Abstract

In this work, we demonstrate the application of terahertz-optical Hall effect (THz-OHE) to determine directionally dependent free charge carrier properties of ambient-doped monolayer and quasi-free-standing-bilayer epitaxial graphene on 4H–SiC(0001). Directionally independent free hole mobility parameters are found for the monolayer graphene. In contrast, anisotropic hole mobility parameters with a lower mobility in direction perpendicular to the SiC surface steps and higher along the steps in quasi-free-standing-bilayer graphene are determined for the first time. A combination of THz-OHE, nanoscale microscopy and optical spectroscopy techniques are used to investigate the origin of the anisotropy. Different defect densities and different number of graphene layers on the step edges and terraces are ruled out as possible causes. Scattering mechanisms related to doping variations at the step edges and terraces as a result of different interaction with the substrate and environment are discussed and also excluded. It is suggested that the step edges introduce intrinsic scattering in quasi-free-standing-bilayer graphene, that is manifested as a result of the higher ratio between mean free path and average terrace width parameters. The suggested scenario allows to reconcile existing differences in the literature regarding the anisotropic electrical transport in epitaxial graphene.

Original languageEnglish (US)
Pages (from-to)248-259
Number of pages12
JournalCarbon
Volume172
DOIs
StatePublished - Feb 2021

Keywords

  • Anisotropic mobility
  • Anisotropic transport
  • Free charge carriers
  • Graphene
  • Hydrogen intercalation
  • Scattering mechanisms
  • Terahertz optical Hall effect

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

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