  A real-space quantum transport simulator for carbon nanoribbon (CNR) MOSFETs
has been developed. Using this simulator, the performance of carbon nanoribbon
(CNR) MOSFETs is examined in the ballistic limit. The impact of quantum effects
on device performance of CNR MOSFETs is also studied. We found that 2D
semi-infinite graphene contacts provide metal-induced-gap-states (MIGS) in the
CNR channel. These states would provide quantum tunneling in the short channel
device and cause Fermi level pining. These effects cause device performance
degradation both on the ON-state and the OFF-state. Pure 1D devices (infinite
contacts), however, show no MIGS. Quantum tunneling effects are still playing
an important role in the device characteristics. Conduction due to band-to-band
tunneling is accurately captured in our simulations. It is important in these
devices, and found to dominate the off-state current. Based on our simulations,
both a 1.4nm wide and a 1.8nm wide CNR with channel length of 12.5nm can
outperform ultra scaled Si devices in terms of drive current capabilities and
electrostatic control. Although subthreshold slopes in the forward-bias
conduction are better than in Si transistors, tunneling currents are important
and prevent the achievement of the theoretical limit of 60mV/dec.
