The Electrical Characteristics of Silicon P-N-P-N Triodes

An investigation is made of the electrical characteristics of three-terminal silicon p-n-p-n structures, where electrical contact is made to both outer (emitter) regions and to one of the inner (base) regions. When the base current Ib is zero, the V-I characteristic naturally is identical to the two-terminal case, i.e., ranges of high and low impedance separated by a region of differential negative resistance. Base current supplied from an independent, external circuit is found to decrease the breakover (peak) voltage and to decrease the turn-off current, i.e., the current at which the device enters the low impedance state. In fact, the p-n-p-n triode is found to exhibit switching properties closely analogous to the conventional thyratron. As an extension of earlier work, a general analysis of four-region structures is presented and is applied specifically to the p-n-p-n triode. Much of the detailed behavior of the device can be explained in terms of this analysis, and theoretical curves are given which are in good agreement with the experimental results.