A collective theory of lock-on in photoconductive semiconductor switches

Collective impact ionization has been developed to explain lock-on, an optically-triggered, electrical breakdown that occurs in GaAs photoconductive semiconductor switches (PCSS's). The basic principle of collective impact ionization is that, at high carrier density, carrier-carrier interactions increase the impact ionization probability by increasing the number of carriers with energies above the impact ionization threshold. In this paper, we describe a rate equation approach, based on collective impact ionization, that leads to new insights about electrical breakdown in insulating and semiconducting materials. In this approach, the competition between carrier generation through impact ionization and Auger recombination leads to steady state solutions for the carrier generation rate, and it is the accessibility of these steady state solutions, for a given electrical field, that governs whether breakdown does or does not occur. This approach leads to theoretical definitions for not only the lock-on field but also the intrinsic breakdown field. Results obtained for GaAs, InP, and Si using a carrier distribution function calculated by both a Maxwellian approximation and an ensemble Monte Carlo method will be discussed.