Two Dimensional Time Dependent Modeling Of Optically Switched GaAs

The advantages of high power photoconductive semiconductor switches (PCSS) such as high hold-off voltage and fast rise times have motivated significant development efforts. However, observations of lock-on, non-uniformities in the electric field, and filamentation of current flow across the device when switching at high fields have raised concerns about the scaling of PCSS to higher currents. To investigate these issues, a two dimensional time dependent computer model of GaAs PCSS has been developed with the motivation of understanding filament formation. The model solves the continuity equations for electrons and holes, conservation equations for trapping sites, the energy equation for the lattice. Poisson`s equation, and a circuit equation. Physical effects in the model include band-to-band impact ionization, trap impact ionization, photoionization, and negative differential resistance. The physical devices investigated with the model are based on the Bulk Optical Semiconductor Switch (BOSS) developed by Schoenbach. In this talk a description of the model will be presented followed by consequences of switch geometries, gain mechanisms, and non-uniform injection and illumination on the operation of the device.