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

The longevity of high-gain GaAs photoconductive semiconductor switches (PCS S) has been extended to over 100 million pulses. This was achieved by impro ving the ohmic contacts through the incorporation of a doped layer that is very effective in the suppression of filament formation, alleviating curren t crowding. Damage-free operation is now possible at much higher current le vels than before. The inherent damage-free curl ent capacity of the bulk Ga As depends on the thickness of the doped layers and is at least 100 A for a dopant diffusion depth of 4 mum. This current could be increased by employ ing multiple switches connected in parallel, Thc contact metal has a differ ent damage mechanism, and the threshold for damage (similar to 40-80 A) is not further improved beyond a dopant diffusion depth of about 2 mum. In a d iffusion-doped contact sn itch, the switching performance is not degraded a t the onset of contact metal erosion, unlike a switch with conventional con tacts. For fireset applications operating at 1-kV/1-kA levels and higher, d oped contacts have not yet resulted in improved longevity, We employ multif ilament operation and InPb solder/Au ribbon wirebonding to demonstrate >100 -shot lifetime at 1-kV/1-kA.