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

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

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-7-9220

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.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz wafer-scale mobility mapping of graphene on insulating substrates without a gate

Jonas D. Buron, David M. A. Mackenzie, Dirch. H. Petersen, Amaia Pesquera, Alba Centeno, Peter Bøggild, Amaia Zurutuza, and Peter U. Jepsen
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-24-30721

We demonstrate wafer-scale, non-contact mapping of essential carrier transport parameters, carrier mobility (µdrift), carrier density (Ns), DC sheet conductance (σdc), and carrier scattering time (τsc) in CVD graphene, using spatially resolved terahertz time-domain conductance spectroscopy. σdc and τsc are directly extracted from Drude model fits to terahertz conductance spectra obtained in each pixel of 10 × 10 cm2 maps with a 400 µm step size. σdc- and τsc-maps are translated into µdrift and Ns maps through Boltzmann transport theory for graphene charge carriers and these parameters are directly compared to van der Pauw device measurements on the same wafer. The technique is compatible with all substrate materials that exhibit a reasonably low absorption coefficient for terahertz radiation. This includes many materials used for transferring CVD graphene in production facilities as well as in envisioned products, such as polymer films, glass substrates, cloth, or paper substrates.

© 2015 Optical Society of America

Full Article  |  PDF Article