An ionic polymer route to a stable unpinning of the Fermi level of highly doped graphene

Abstract

Epitaxial graphene on cubic silicon carbide on silicon could enable unique optical metasurface devices seamlessly integrated with CMOS technologies. However, one of the most promising methods to obtain large-scale epitaxial graphene on this challenging system typically leads to a highly p-type-doped graphene with a Fermi level pinned at ∼0.55 eV below the Dirac point. Hence, the use of conventional gate dielectric materials such as SiO2 and Si3N4 precludes the tuning of the graphene carrier concentration. We demonstrate that this limitation can be overcome with the use of polyethyleneimine (PEI) as a gate dielectric material for graphene field-effect transistors. We achieve significant tuning of the graphene's Fermi level, enabling ambipolar operation exceeding a 3 eV window. In addition, we demonstrate that excellent stability of the PEI-based devices can be achieved, thanks to the addition of a thin protective oxide film. These findings highlight the potential of ionic polymers for advancing reconfigurable graphene-based devices for photonic applications.