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 50 million pulses. This was achieved by improving the ohmic contacts through the incorporation of a doped layer beneath the PCSS contacts which is very effective in the suppression of filament formation and alleviating current crowding to improve the longevity of PCSS. Damage-free operation is now possible with virtually infinite expected lifetime at much higher current levels than before. The inherent damage-free current capacity of the switch depends on the thickness of the doped layers and is at least 100 A for a dopant diffusion depth of 4 /spl mu/m. 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 when contact metal erosion occurs. This paper compares thermal diffusion and epitaxial growth as approaches to doping the contacts. These techniques are contrasted in terms of the fabrication issues and device characteristics.