  We describe mathematically the apparently paradoxical phenomenon that an
electronic current in a semiconductor can flow because of collisions, and not
despite them. A transport model of charge transport in a one-dimensional
semiconductor crystal is considered, where each electron follows the periodic
hamiltonian trajectories, determined by the semiconductor band structure, and
undergoes non-elastic collisions with a phonon bath. Starting from the detailed
phase-space model, a closed system of ODEs is obtained for averaged quantities.
Such a simplified model is nevertheless capable of describing transient Bloch
oscillations, their damping and the consequent onset of a steady current flow,
which is in good agreement with the available experimental data.
