ON THE TRANSIENT BEHAVIOR OF SEMICONDUCTOR RECTIFIERS

BEN ROGER GOSSICK, Purdue University

Abstract

Gossick, Ben Roger. Ph.D., Purdue University, May, 1954. On the Transient Behavior of Semiconductor Rectifiers. Major Professor: Karl Lark-Horovitz.If the forward current through a p-n junction suddenly ceases, an emf appears due to nonequilibrium carrier concentrations at the junction barrier. Measurements of the barrier emf have been made with a wide range of injection currents, yielding current vs. barrier voltage characteristic curves.The barrier voltage response to a delta function current pulse has been calculated for the case where the behavior may be considered in terms of a single lifetime. Taking the case where the two lifetimes are not necessarily equal, the barrier voltage response to a delta function current pulse is also calculated for (a) the time between the current pulse and a time small compared to the shorter lifetime, and (b) for time much longer than the longest lifetime. The rise time and delay time of the p-n junction are evaluated. All solutions are given first for the p-n junction alone, and then for a p-n junction in parallel with an external resistance. It was found in the calculations that all terms involving the recombination lifetimes for holes Tp and electrons In could be eliminated by the substitucion Where I. and Ins are the saturation currents for holes and electrons ps respectively, and r takes on values 1/2, 1, and 2.It is observed, as predicted by the calculations, that when a sufficiently large forward bias is applied, the character of the response changes markedly, becoming very fast.All calculations referred to above are valid only in the voltage range AV<> KT, is discussed. The voltage decay is observed to be linear with time having a slope KT/qt. It follows from an analysis based on a simple model that the excess minority carrier concentrations decrease exponentially with the time constant . The floating emitter and collector voltages, Vt) and Vet), of p-n-p transistors are observed to decay like the open circuit voltage across a p-n junction, and it is noted that V(t)V(t) in the range V>>KT/q. The relation V(t) follows from an extension of the analysis made for the p-n junction.The transient response of a semiconductor rectifier connected in parallel with a large external capacitance is analyzed. The response calculated for large negative excursions of voltage gives a simple relation by which the saturation current may be determined. Measurements are presented and discussed.Equations not included.

Degree

Ph.D.

Subject Area

Electromagnetics

COinS