Modeling of high power semiconductor switches operated in the nonlinear mode

Abstract

Although optically activated high power photoconductive semiconductor switches (PCSS) are usually triggered using uniform illumination, under select conditions they can be activated and closed in <1 ns with a spot of light near the contacts. This observation requires free carriers to either travel at speeds faster than their saturation velocity or for there to be a carrier generation mechanism that propagates with similar speeds. A two-dimensional time-dependent computer model of a GaAs high power switch has been employed to investigate these observations, and activation of PCSS by spots of light in particular. Results from the model suggest that the transport of band-to-band recombination radiation plays an important role in propagating electrons across the switch when the switch is closed with a spatially nonuniform laser pulse. Reabsorption of the recombination radiation and photogeneration of carriers is a mechanism which generates free carriers in the gap between the contacts at speeds greater than saturation velocity. The results also indicate that the switch is sensitive to the location of the activating laser pulse. Less laser fluence is required to close the switch if illumination occurs near the cathode rather than near the anode.