High-field transport and velocity saturation in graphene

High-field transport in graphene is studied by the Monte Carlo simulation. The results indicate velocity and current saturation in agreement with a recent experiment [I. Meric, M. Y. Han, A. F. Young, B. Oezyilmaz, P. Kim, and K. Shepard, Nat. Nanotechnol. 3, 654 (2008)]. The saturation current scales as the square root of the charge density, or equivalently, the square root of the gate overdrive voltage, which is qualitatively different from silicon field-effect transistors. By analytical fitting to the numerical simulation results, a simple expression of the field-dependent mobility is obtained at different strengths of charged impurity scattering.