  This letter reports the impact of surface morphology on the carrier transport
and RF performance of graphene FETs formed on epitaxial graphene films
synthesized on SiC substrates. Such graphene exhibits long terrace structures
with widths between 3-5 {\mu}m and steps of 10\pm2 nm in height. While a
carrier mobility above 3000 cm2/Vs at a carrier density of 1e12 cm-2 is
obtained in a single graphene terrace domain at room temperature, the step
edges can result in a vicinal step resistance of ~21 k{\Omega}.{\mu}m. By
orienting the transistor layout so that the entire channel lies within a single
graphene terrace, and reducing the access resistance associated with the
ungated part of the channel, a cut-off frequency above 200 GHz is achieved for
graphene FETs with channel lengths of 210 nm, which is the highest value
reported on epitaxial graphene thus far.
