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

Armakavicius, Nerijus ; Kühne, Philipp ; Eriksson, Jens ; Bouhafs, Chamseddine ; Stanishev, Vallery ; Ivanov, Ivan G. ; Yakimova, Rositsa ; Zakharov, Alexei A. LU ; Al-Temimy, Ameer and Coletti, Camilla , et al. (2021) In Carbon 172. p.248-259
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... (More)

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.

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type
Contribution to journal
publication status
published
subject
keywords
Anisotropic mobility, Anisotropic transport, Free charge carriers, Graphene, Hydrogen intercalation, Scattering mechanisms, Terahertz optical Hall effect
in
Carbon
volume
172
pages
12 pages
publisher
Elsevier
external identifiers
  • scopus:85092705887
ISSN
0008-6223
DOI
10.1016/j.carbon.2020.09.035
language
English
LU publication?
yes
id
fefca44f-9a40-40ad-8b35-1b426b3d207d
date added to LUP
2020-11-04 08:26:13
date last changed
2020-11-04 08:26:13
@article{fefca44f-9a40-40ad-8b35-1b426b3d207d,
  abstract     = {<p>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.</p>},
  author       = {Armakavicius, Nerijus and Kühne, Philipp and Eriksson, Jens and Bouhafs, Chamseddine and Stanishev, Vallery and Ivanov, Ivan G. and Yakimova, Rositsa and Zakharov, Alexei A. and Al-Temimy, Ameer and Coletti, Camilla and Schubert, Mathias and Darakchieva, Vanya},
  issn         = {0008-6223},
  language     = {eng},
  pages        = {248--259},
  publisher    = {Elsevier},
  series       = {Carbon},
  title        = {Resolving mobility anisotropy in quasi-free-standing epitaxial graphene by terahertz optical Hall effect},
  url          = {http://dx.doi.org/10.1016/j.carbon.2020.09.035},
  doi          = {10.1016/j.carbon.2020.09.035},
  volume       = {172},
  year         = {2021},
}