Recent developments in opening photoconductive semiconductor switches

Abstract

While developing high power photoconductive semiconductor switches (PCSS) for opening and closing (toggling) applications, we have recorded extremely fast opening times and what appears to be the onset of non-destructive electron avalanching. Using 1- and 2-inch diameter wafers of GaAs, Cr:GaAs, and Au:Si, we have switched a 50-ohm, 80-ns transmission line at voltages up to 65 kV. In the dark, the GaAs switches will stand-off dc fields up to 30 kV/cm in SF/sub 6/. Upon optical triggering, the behavior depends on the average electric field. Below 4 kV/cm (8 kV/cm doped) they open with a 20-ns (< 3 ns doped) exponential recovery time. When the light is removed above these fields, the switches lock on, conducting whatever current the circuit will supply and stabilizing to 4 kV/cm (8 kV/cm doped) across the switch. Additionally, reliable triggering of a 2-inch GaAs switch (3.4-cm gap) in this ''locking on'' mode was achieved with a 70-..mu..J, 532-nm, 10-ns light pulse (less than 1/100th the light required to trigger the switch at low voltages). The Au:Si samples did not lock-on. They opened with an exponential recovery time of 20 to 40 ns at fields up to 35 kV/cm. Undoped silicon samples show recovery timesmore » of several hundred microseconds.« less