Enhanced Performance in Epitaxial Graphene FETs With Optimized Channel Morphology

This letter reports the impact of surface morphology on the carrier transport and radio-frequency performance of graphene FETs formed on epitaxial graphene synthesized on SiC substrates. Such graphene exhibits long terrace structures with widths between 3-5 μm and steps of 10 ± 2 nm in height. While a carrier mobility value above 3000 cm²/V·s at a carrier density of 10¹² cmx² is obtained in a single graphene terrace, the step edges can result in a step resistance of ~21 kΩ·μm. By orienting the transistor layout so that the entire channel lies within a single graphene terrace and by reducing the access resistance associated with the ungated part of the channel, a cutoff frequency above 200 GHz is achieved for graphene FETs with channel lengths of 210 nm, i.e., the highest value reported on epitaxial graphene thus far.