Longevity of optically activated, high gain GaAs photoconductivesemiconductor switches

The longevity of high gain GaAs photoconductive semiconductor switches (PCSSs) has been extended to well over ten million pulses by reducing the density of carriers at the semiconductor to metal interface. This was achieved by reducing the density in the vertical and lateral directions. The latter was achieved by varying the spatial distribution of the trigger light thereby widening the current filaments that are characteristic of the high gain switches. We reduced the carrier density in the vertical direction by using ion implantation. These results were obtained for currents of about 10 A, current duration of 3.5 ns, and switched voltage of ~2 kV. At currents of ~70 A, the switches last for 0.6 million pulses. In order to improve the performance at high currents, new processes such as deep diffusion and epitaxial growth of contacts are being pursued. To guide this effort we recorded open shutter, infra-red images, and time-resolved Schlieren images of the current filaments, which form during high gain switching. We measured, under varying conditions, a carrier (electrons or holes) density that ranges from 3×10¹⁷ cm^-3 to 6×10¹⁸ cm^-3