<title>Recent progress in photoconductive opening switch research at the University of Maryland</title>

Abstract

Opening switch work at the University of Maryland is primarily focused on the materials of GaAs and ZnSe. We discuss recent progress in work with both materials. Recent work in GaAs has revealed that a non-'lock on' state of sustained conductivity could be produced in GaAs photoconductive semiconductor switches (PCSS's). The sustained conductivity is produced when a PCSS is switched into a high impedance (500 (Omega) ) load by a high intensity (90 mJ - 12 ns) laser pulse. Furthermore, we have shown that the conductivity of the GaAs switch could be quenched at a time determined by circuit parameters. Thus, the switch could be used as an opening switch in an inductive energy storage pulsed power system without the need for pulse shaping or a different wavelength laser to open the switch. We have demonstrated such an inductive energy storage system with a power gain of 4.2 and a switching opening time of < 10 ns. We have also undertaken experiments with polycrystalline ZnSe which indicate that it may operate as well as a closing switch material. The ZnSe switches were found to exhibit a nonlinear effect at high applied electric fields. In this paper we report on our investigations of ZnSe opening switch using a simple lumped inductive circuit. At high fields and short wavelength, we observed in ZnSe a behavior similar to 'lock-on' as observed in GaAs. No such behavior was observed for longer wavelengths even at higher bias fields. This suggests the strong local field caused by the nonlinear effect observed in previous experiments is responsible for the onset of the observed 'lock-on' behavior.