Abstract
One of the aspirations of quantum metrology is to deliver primary standards directly to end-users thereby significantly shortening the traceability chains and enabling more accurate products. Epitaxial graphene grown on silicon carbide (epigraphene) is known to be a viable candidate for a primary realisation of a quantum Hall resistance standard, surpassing conventional semiconductor two-dimensional electron gases, such as those based on GaAs, in terms of performance at higher temperatures and lower magnetic fields. The bottleneck in the realisation of a turn-key quantum resistance standard requiring minimum user intervention has so far been the need to fine-tune the carrier density in this material to fit the constraints imposed by a simple cryo-magnetic system. Previously demonstrated methods, such as via photo-chemistry or corona discharge, require application prior to every cool-down as well as specialist knowledge and equipment. To this end we perform metrological evaluation of epigraphene with carrier density tuned by a recently reported permanent molecular doping technique. Measurements at two National Metrology Institutes confirm accurate resistance quantisation below 5 nΩ Ω−1. Furthermore, samples show no significant drift in carrier concentration and performance on multiple thermal cycles over three years. This development paves the way for dissemination of primary resistance standards based on epigraphene.
Highlights
Epitaxial graphene on silicon carbide can be grown as a high quality monocrystalline film on a waferscale, allowing for scalable production of electronic devices
Epitaxial graphene grown on silicon carbide is known to be a viable candidate for a primary realisation of a quantum Hall resistance standard, surpassing conventional semiconductor two-dimensional electron gases, such as those based on GaAs, in terms of performance at higher temperatures and lower magnetic fields
Epigraphene has since proven itself superior to the conventional two-dimensional electron gas (2DEG) systems based on GaAs/AlGaAs ( GaAs) due to its unique electronic properties, which result in a robust quantum Hall effect (QHE) measurable at higher probing currents, higher temperatures and lower magnetic fields [2, 3]
Summary
Epitaxial graphene on silicon carbide (epigraphene) can be grown as a high quality monocrystalline film on a waferscale, allowing for scalable production of electronic devices. The metrological viability of epigraphene as a quantum Hall resistance (QHR) standard was first shown experimentally in 2010 [1]. Due to the presence of an insulating interface layer (buffer layer) between the SiC substrate and graphene, epigraphene shows both high n-doping on the order of 1013 electrons per cm and Fermi level pinning. These two factors in combination make tuning the carrier density to the useful range a challenge [6]. In this paper we demonstrate that this approach affords stable and controllable tuning of the charge carrier density in epigraphene while maintaining all of its major advantages for the realisation of a quantum resistance standard. We have demonstrated stability upon repeated thermal cycles and operation of the standard in a dry table-top cryo-magnetic system
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