A self-consistent, two-dimensional, time-dependent, drift-diffusion model is developed to simulate the response of high power photoconductive switches. Effects of spatial inhomogeneities associated with the contact barrier potential are incorporated and shown to foster filamentation. Results of the dark current match the available experiment data. Persistent photoconductivity is shown to arise at a high bias even under the conditions of spatial uniformity. Filamentary currents require an inherent spatial inhomogeneity, and are more likely to occur for low optical excitation. Under strong uniform illumination, the spatial nonuniformities were quenched as a result of a polarization-induced collapse in the internal fields. However, strong electric fields resulting at the contacts create a bipolar plasma, and hence, a virtual “double injection.”

Simulations have been performed to determine the internal temperature profiles of high-power GaAs photoconductive switches in the presence of a current filament. No thermal instability is predicted below a power generation density level of about 1.3×1014 W/m3. This prediction is in keeping with recent experimental data on photoconductive semiconductor switch devices. It is shown that this power dissipation density threshold for stability exists under both dc and transient conditions. A simple model provides qualitative support for the power density threshold, and an explanation of the filamentary current radii that have been observed experimentally.

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