Mobility and quasi-ballistic charge carrier transport in graphene field-effect transistors

The optimization of graphene field-effect transistors (GFETs) for high-frequency applications requires further understanding of the physical mechanisms concerning charge carrier transport at short channel lengths. Here, we study the charge carrier transport in GFETs with gate lengths ranging from 2 $μ$m down to 0.2 $μ$m by applying a quasi-ballistic transport model. It is found that the carrier mobility, evaluated via the drain–source resistance model, including the geometrical magnetoresistance effect, is more than halved with decreasing the gate length in the studied range. This decrease in mobility is explained by the impact of ballistic charge carrier transport. The analysis allows for evaluation of the characteristic length, a parameter of the order of the mean-free path, which is found to be in the range of 359–374 nm. The mobility term associated with scattering mechanisms is found to be up to 4456 cm$2$/Vs. Transmission formalism treating the electrons as purely classical particles allows for the estimation of the probability of charge carrier transport without scattering events. It is shown that at the gate length of 2 $μ$m, approximately 20% of the charge carriers are moving without scattering, while at the gate length of 0.2 $μ$m, this number increases to above 60%.