Photoconductive Semiconductor Switch for Microwave Applications

A procedure for choosing the dimensions of a photoconductive semiconductor switch (PCSS) for operation at microwave switching frequencies, and particularly at 10.0 GHZ, is described. The critical dimension is the switch length (electrode separation), which must be small enough to force photo-induced charge removal during switch turn-off via sweep out rather than recombination. The switch depth in the direction of turn-on optical pulse absorption must be several optical absorption depths long to ensure absorption of all the incident light, which optimizes optical to electrical signal gain. The switch width is determined in conjunction with the peak intensity of the optical pulse because the switch width-optical intensity product, which represents optical power, determines both the on-state switch resistance and the turn-off delay time. Simulations show that a switch with a 0.5 mum length, 5.0 mum depth, and 20 mum width, illuminated with 1.0 W optical pulses at 10 GHz, will have a 0.23 Omega on-state resistance and a 46 ps turn-off time.