Velocity-field characteristics in the multivalley model of gallium arsenide

The drift-velocity response to an applied electric field is investigated in a model based on an anisotropic distribution function of electrons. The randomly oriented velocity vectors in equilibrium transform to streamlined velocity vectors in a very high electric field, thereby yielding a saturation drift velocity that is comparable to the thermal velocity in the nondegenerate approximation. A clear distinction is made between the density-of-states effective mass and the conductivity effective mass for ellipsoidal valleys in gallium arsenide (GaAs). The effective mean free path, and hence the effective mobility, degrades as the electric field is increased. It is shown that as the applied electric field increases, electrons tend to follow the velocity-field profiles of those valleys with a higher Ohmic mean free path. The results are shown to be in excellent agreement with experimental data and with empirical relations obtained from the Monte Carlo simulations. (C) 2005 American Institute of Physics.