Longevity improvement of 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 itself 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 connecting and triggering parallel switches. The contact metal has a different damage mechanism and the threshold for damage (/spl sim/40 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 a 1 kV/1 kA levels and higher, doped contacts have not yet resulted in improved longevity. The authors employ multi-filament operation and InPb solder/Au ribbon wirebonding to demonstrate >100 shot lifetime at 1 kV/1 kA.