Quality assessment of terahertz time-domain spectroscopy transmission and reflection modes for graphene conductivity mapping

David M.A. Mackenzie*, Patrick Rebsdorf Whelan, Peter Bøggild, Peter Uhd Jepsen, Albert Redo-Sanchez, David Etayo, Norbert Fabricius, Dirch Hjorth Petersen

*Corresponding author for this work

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Abstract

We present a comparative study of electrical measurements of graphene using terahertz time-domain spectroscopy in transmission and reflection mode, and compare the measured sheet conductivity values to electrical van der Pauw measurements made independently in three different laboratories. Overall median conductivity variations of up to 15% were observed between laboratories, which are attributed mainly to the well-known temperature and humidity dependence of non-encapsulated graphene devices. We conclude that terahertz time-domain spectroscopy performed in either reflection mode or transmission modes are indeed very accurate methods for mapping electrical conductivity of graphene, and that both methods are interchangeable within measurement uncertainties. The conductivity obtained via terahertz time-domain spectroscopy were consistently in agreement with electrical van der Pauw measurements, while offering the additional advantages associated with contactless mapping, such as high throughput, no lithography requirement, and with the spatial mapping directly revealing the presence of any inhomogeneities or isolating defects. The confirmation of the accuracy of reflection-mode removes the requirement of a specialized THz-transparent substrate to accurately measure the conductivity.
Original languageEnglish
JournalOptics Express
Volume26
Issue number7
Pages (from-to)9220-9229
ISSN1094-4087
DOIs
Publication statusPublished - 2018

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