Tests On Photoconductive Semiconductor Switches For Subnanosecond Risetime, Multimegavolt pulseral-applications

Experiments were performed to determine the applicability of photoconductive semiconductor switches (PCSS) for use as output switches in subnanosecond pulse for EMP simulators. Lateral switches made of both Gallium Arsenide and Silicon with 1.5 cm long insulating regions immersed in Fluorinert were tested in a 50 ohm tri-plate transmission line geometry. Mode locked and Q- switched lasers were used to trigger both a gas switched Marx generator which pulse-charged the transmission line in 100- 150 ns and to illuminate the PCSS via an optical delay line. Illuminating beam energies and electric field strengths at switchout were varied to determine minimum risetimes and light energies required for triggering. The GaAs switches were operated in the high gain (lock- on) mode. Risetimes as fast as 600 ps were observed using a mode locked laser and 700 ps using a Q-switched laser. The minimum light energy required to trigger GaAs was 22/spl mu/J and the highest switched fields for both GaAs and Si is about 60 kV/ cm.