Contactless graphene conductivity mapping on a wide range of substrates with terahertz time-domain reflection spectroscopy

• Published in: Scientific reports Vol. 7; no. 1; pp. 10625 - 9
• Main Authors: Lin, Hungyen, Braeuninger-Weimer, Philipp, Kamboj, Varun S., Jessop, David S., Degl’Innocenti, Riccardo, Beere, Harvey E., Ritchie, David A., Zeitler, J. Axel, Hofmann, Stephan
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06.09.2017; Nature Publishing Group
• Subjects: 639/624/1107/510; 639/925/918; Humanities and Social Sciences; Mapping; multidisciplinary; Science; Science (multidisciplinary); Silicon; Silicon dioxide; Spectroscopy; Spectrum analysis
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-09809-7

We demonstrate how terahertz time-domain spectroscopy (THz-TDS) operating in reflection geometry can be used for quantitative conductivity mapping of large area chemical vapour deposited graphene films on sapphire, silicon dioxide/silicon and germanium. We validate the technique against measurements performed with previously established conventional transmission based THz-TDS and are able to resolve conductivity changes in response to induced back-gate voltages. Compared to the transmission geometry, measurement in reflection mode requires careful alignment and complex analysis, but circumvents the need of a terahertz transparent substrate, potentially enabling fast, contactless, in-line characterisation of graphene films on non-insulating substrates such as germanium.