Dynamics of nascent current filaments in low-temperature impurity breakdown

We present two-dimensional simulations showing the spatiotemporal dynamics of the formation of current filaments in n-type GaAs films in the regime of impurity impact ionization breakdown. From the spatial distribution of carrier densities, electron temperature, current density, and electric field for nascent and for fully developed filaments, we find a three-stage scenario for breakdown: (i) front creation and propagation from the cathode, (ii) stagnation in the phase of a rudimentary filament, (iii) filament growth. Our model combines semiclassical rate equations with microscopic transport parameters, which are obtained from Monte Carlo simulations.