Doped contacts for high-longevity optically activated, high-gain GaAs photoconductive semiconductor switches

The longevity of high-gain GaAs photoconductive semiconductor switches (PCSS) has been extended to over 100 million pulses. This was achieved by improving the ohmic contacts through the incorporation of a doped layer that is very effective in the suppression of filament formation, alleviating current crowding. Damage-free operation is now possible at much higher current levels than before. The inherent damage-free current capacity of the bulk GaAs depends on the thickness of the doped layers and is at least 100 A for a dopant diffusion depth of 4 /spl mu/m. This current could be increased by employing multiple switches connected in parallel. The contact metal has a different damage mechanism, and the threshold for damage (/spl sim/40-80 A) is not further improved beyond a dopant diffusion depth of about 2 /spl mu/m. In a diffusion-doped contact switch, the switching performance is not degraded at the onset of contact metal erosion, unlike a switch with conventional contacts. For fireset applications operating at 1-kV/1-kA levels and higher, doped contacts have not yet resulted in improved longevity. We employ multifilament operation and InPb solder/Au ribbon wirebonding to demonstrate >100-shot lifetime at 1-kV/1-kA.