Wigner transport in the presence of phonons: Particle models of electron kinetics

摘要

Carrier transport in conventional microelectronic devices is governed by the Boltz-mann equation (BE). The equation provides a physical picture where carriers are point-like particles (with well-defined position and momentum which compose the phase space) subject to drift and scattering events. During the drift process carriers are accelerated by the device electric field over classical Newton's trajectories. The interaction with the lattice imperfections, such as phonons, gives rise to scattering events which are local in time and space. This means that the interaction is instantaneous and causes a change of the carrier momentum but not of the carrier position. Averaged physical quantities such as mean free path or time between the collisions characterize the transport conditions. The channel of a conventional MOSFET is many mean free paths long. As the field is moderate and changes smoothly, the scattering with phonons maintains the carriers in a local balance with the lattice. The channel of a modern submicron device is only few mean free paths long. The field is strong and exhibits strong changes with the distance. Carriers are no more in a local balance with the lattice. Single carriers may cross the channel without any interaction with phonons. This transport regime is nearly ballistic.