Transit-time negative resistance in bulk Si structures subjected to avalanche injection

A small-signal analytical model is developed for a bulk silicon device subjected to avalanche multiplication induced by space-charge effects. Results show that transit-time negative resistance may exist, provided the solid is biased near the onset of the dc negative resistance or above it; this ac negative resistance is into the microwave range for practical devices. The main features of this phenomenon and the differences with respect to IMPATT diodes are pointed out by using suitable approximate expressions which can help in finding the overall frequency behavior. A check of the preceding analysis by a computer solution of the small-signal impedance has also been performed.