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

Artikel i vetenskaplig tidskrift, 2022

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 μm down to 0.2 μm 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 cm2/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 μm, approximately 20% of the charge carriers are moving without scattering, while at the gate length of 0.2 μm, this
number increases to above 60%.