A theory of lock-on and electrical breakdown

In this dissertation, a collective impact ionization approach is used to develop a generalized theory of electrical breakdown in insulators, which includes both the electric field dependence and the carrier density dependence of impact ionization. This theory is applied to photoconductive semiconductor switches (PCSS's) and is used to explain the lock-on effect, an optically triggered breakdown that occurs in GaAs PCSS's. The basic principle of collective impact ionization theory is that, at high carrier densities, carrier-carrier scattering will enhance the impact ionization rate.; This generalized breakdown theory uses a rate equation approach to find the carrier densities which, at a given electric field, result in a steady state. In this approach, the competition between carrier generation (by impact ionization) and carrier recombination (by Auger and defect mechanisms) governs whether or not electrical breakdown occurs. This approach leads to a definition of the bulk breakdown field as the lowest field for which the injection of an infinitesimally small carrier density will result in a steady state with a large carrier density. It also leads to the definition of the lock-on field as the lowest field for which a stable, non-zero steady state carrier density is possible.; To implement this theory, the Ensemble Monte Carlo (EMC) method is used to calculate the carrier distribution function, including the effects of carrier-carrier scattering. Since the EMC calculations are computationally intense, this theory also uses both low and high density approximations for the distribution function. The low density limit is obtained using an EMC method without including the effects of carrier-carrier scattering. The high density limit is obtained by approximating the distribution function as a Maxwellian. Using this theory, predictions are made for both the lock-on field and the bulk breakdown field in several materials.; In this theory, the lock-on effect is a type of carrier-density dependent electrical breakdown which occurs in all insulating materials. Further, it is the difference between the predicted lock-on and the breakdown fields which determines whether or not the lock-on effect will observable as a phenomenon distinct from ordinary breakdown.