Longevity of optically activated, high gain GaAs photoconductive semiconductor switches

The longevity of high gain GaAs photoconductive semiconductor switches (PCSS) for pulsed power applications has been extended to well over 10 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 first was achieved by varying the spatial distribution of the trigger light, thereby widening the current filaments that are characteristic of the high gain switches. The authors 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 /spl sim/2 kV. At currents of /spl sim/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, the authors measured a carrier density of 6/spl times/10/sup 18/ electrons (or holes)/cm/sup 3/ in filaments that carry a current of 5 A.