Jonas D. Buron1, Filippo Pizzocchero1, Peter U. Jepsen2, Dirch H. Petersen1, José M. Caridad1, Bjarke S. Jessen1, Timothy J. Booth1,3, and Peter Bøggild1,3 1DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark 2DTU Fotonik - Department of Photonics Engineering, Technical University of Denmark, Building 343 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark 3DTU Center for Nanostructured Graphene (CNG), DTU Nanotech - Department of Micro- and Nanotechnology, Technical University of Denmark, Building 345 Ørsteds Plads, 2800 Kgs. Lyngby, Denmark Carrier
mobility and chemical doping level are essential figures of merit for graphene,
and large-scale characterization of these properties and their uniformity is a
prerequisite for commercialization of graphene for electronics and electrodes.
However, existing mapping techniques cannot directly assess these vital
parameters in a non-destructive way. By deconvoluting carrier mobility and
density from non-contact terahertz spectroscopic measurements of conductance in
graphene samples with terahertz-transparent backgates, we are able to present
maps of the spatial variation of both quantities over large areas. The
demonstrated non-contact approach provides a drastically more efficient
alternative to measurements in contacted devices, with potential for aggressive
scaling towards wafers/minute. The observed linear relation between conductance
and carrier density in chemical vapour deposition graphene indicates dominance
by charged scatterers. Unexpectedly, significant variations in mobility rather
than doping are the cause of large conductance inhomogeneities, highlighting
the importance of statistical approaches when assessing large-area graphene
transport properties. 1. J. D. Buron et al., Nano Lett., 2012, 12, pp. 5074-5081 |