MODELING OF HIGH-POWER SEMICONDUCTOR SWITCHES OPERATED IN THE NONLINEAR MODE

Although optically activated high power photoconductive semiconductor switches (PCSS) are usually triggered using uniform illumination, unde r select conditions they can be activated and closed in <1 ns with a s pot of light near the contacts, This observation requires free carrier s to either travel at speeds faster than their saturation velocity or for there to be a carrier generation mechanism that propagates with si milar speeds. A two-dimensional time-dependent computer model of a GaA s high power switch has been employed to investigate these observation s, and activation of PCSS by spots of light in particular. Results fro m the model suggest that the transport of band-to-band recombination r adiation plays an important role in propagating electrons across the s witch when the switch is closed with a spatially nonuniform laser puls e. Reabsorption of the recombination radiation and photogeneration of carriers is a mechanism which generates free carriers in the gap betwe en the contacts at speeds greater than saturation velocity. The result s also indicate that the switch is sensitive to the location of the ac tivating laser pulse. Less laser fluence is required to close the swit ch if illumination occurs near the cathode rather than near the anode. (C) 1996 American Institute of Physics.