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Monolayer and bilayer graphenes have generated tremendous excitement as the potentially useful electronic materials due to their unique features. We report on monolayer and bilayer epitaxial graphene field-effect transistors (GFETs) fabricated on SiC substrates. Compared with monolayer GFETs, the bilayer GFETs exhibit a significant improvement in dc characteristics, including increasing current density IDS, improved transconductance gm, reduced sheet resistance Ron, and current saturation. The improved electrical properties and tunable bandgap in the bilayer graphene lead to the excellent dc performance of the bilayer GFETs. Furthermore, the improved dc characteristics enhance a better rf performance for bilayer graphene devices, demonstrating that the quasi-free-standing bilayer graphene on SiC substrates has a great application potential for the future graphene-based electronics. [ABSTRACT FROM AUTHOR]

In this paper, high temperature direct current (DC) performance of bilayer epitaxial graphene device on SiC substrate is studied in a temperature range from 25 °C to 200 °C. At a gate voltage of −8 V (far from Dirac point), the drain-source current decreases obviously with increasing temperature, but it has little change at a gate bias of +8 V (near Dirac point). The competing interactions between scattering and thermal activation are responsible for the different reduction tendencies. Four different kinds of scatterings are taken into account to qualitatively analyze the carrier mobility under different temperatures. The devices exhibit almost unchanged DC performances after high temperature measurements at 200 °C for 5 hours in air ambience, demonstrating the high thermal stabilities of the bilayer epitaxial graphene devices. [ABSTRACT FROM AUTHOR]

We report dc and the first-ever measured small signal rf performance of epitaxial graphene field-effect transistors (GFETs), where the epitaxial graphene is grown by chemical vapor deposition (CVD) on a 2-inch c-plane sapphire substrate. Our epitaxial graphene material has a good flatness and uniformity due to the low carbon concentration during the graphene growth. With a gate length Lg = 100 nm, the maximum drain source current Ids and peak transconductance gm reach 0.92 A/mm and 0.143 S/mm, respectively, which are the highest results reported for GFETs directly grown on sapphire. The extrinsic cutoff frequency (fT) and maximum oscillation frequency (fmax) of the device are 12 GHz and 9.5 GHz, and up to 32 GHz and 21.5 GHz after de-embedding, respectively. Our work proves that epitaxial graphene on sapphire substrates is a promising candidate for rf electronics. [ABSTRACT FROM AUTHOR]