Negative differential mobility in GaAs at ultrahigh fields: Comparison between an experiment and simulations

Abstract

Direct measurement of the electron velocity vn at an extreme electric field E is problematic due to impact ionization. The dependence vn(E) obtained by a Monte Carlo method can be verified, however, by comparing simulated and experimental data on superfast switching in a GaAs bipolar transistor structure, in which the switching transient is very sensitive to this dependence at high electric fields (up to 0.6MV∕cm). Such a comparison allows the conclusion to be made that the change from negative to positive differential mobility predicted earlier at E∼0.3MV∕cm should not happen until the electric field exceeds 0.6MV∕cm.