Carrier Lifetime vs. Ion-Implantation Dose in Silicon on Sapphire

The generation of subpicosecond electrical pulses has recently been demonstrated using fast photoconductive switches driven by short laser pulses [1]. In these measurements electrical pulses on the order of 0.6 ps were obtained by shorting a charged transmission line fabricated on an ion-implanted silicon-on-sapphire (SOS) wafer. The major factors determining the shape and duration of these electrical pulses were the laser pulsewidths, the circuit characteristics of the photoconductive gaps and the transmission line, and the carrier lifetime of the semiconductor [2]. Since laser pulses shorter than 100 fs are routinely obtained from colliding-pulse-modelocked dye lasers, the laser pulsewidth can be made negligible compared to the generated electrical pulse. In addition, the limiting factors on the time response due to the circuit reactance may be eliminated if the capacitance of the generation site is reduced to negligible amounts. Under these conditions the duration of the electrical pulse would be mainly determined by the carrier lifetime in the ion-implanted SOS. However, no systematic measurements of this lifetime are available.