Traveling carrier-density waves in n-type GaAs at low-temperature impurity breakdown

We present a model for traveling charge-density wave instabilities in a semiconductor revealing S-shaped negative differential conductivity. It is based on microscopic generation-recombination rates including impurity impact ionization, which are obtained from Monte Carlo simulations. By a linear stability analysis and by numerical solution of the full nonlinear system we show that traveling-wave instabilities occur in the regime of both negative and positive differential conductivity. Our simulations give detailed insight into the spatiotemporal dynamics of the instabilities, and explain self-generated small-amplitude oscillations observed at the onset of breakdown. © 1996 The American Physical Society.