Radiation photoconductivity in ovonic switches

Abstract

The radiation-induced switching behavior and ionization conductivity of some ovonic threshold switches have been investigated using 30-MeV electrons to simulated high gamma dose rates. Irradiation of devices biased near the threshold voltage for switching did not induce switching that could be attributed to charge transfer through the device. The maximum radiation photocurrent in the amorphous material was about two orders of magnitude lower than the minimum holding current for the device. The dependence of the photoconductivity on the intensity and on the total energy deposition was investigated. The appearance of delayed components of the conductivity as well as the non-linear dependence of the conductivity on dose rate indicate a distribution of trapping states for the carriers. As a result of the charge transfer through the device, a persistent internal polarization is observed. The polarization effect saturates at quite low doses, and, at least for the devices tested, it is not symmetric in the voltage polarity. Some evidence for saturable fast trapping states is reported.