Influence of the doping concentration on switching processes in psn rectifiers—I: Theory

Abstract

The theory, formerly developed for switching power rectifiers into the reverse state, which was limited to pin rectifiers, is extended to a noticeable homogeneous doping concentration of the middle region ( psn rectifier). In this case the swept-out zones originating at the boundaries of the middle region are qualitatively different. While at the side of the pn junction a Schottky space-charge zone with a quadratic voltage vs. time increase forms passing over into the stationary reverse state, at the other side of the middle region finally a zone develops that shows an approximative equilibrium concentration of the majority carriers. This zone is essentially free of space charge. its voltage drop becomes important at most in a medium period of the sweeping-out process (but only in the case of the ps p n rectifier because of the unequal mobilities of the charge carriers), but later on it is always negligible compared with the voltage across the Schottky zone at the pn junction. The temporal development of the swept-out zones is treated more accurately than in the pin case, i.e. we consider the difference between the points of time when the building up of swept-out zones begins at the respective sides. One finds that the sweeping-out at the n side proceeds not only more slowly but also later than at the p side. Some technical conclusions for the switching behaviour of rectifiers and thyristors are drawn up. p rectifiers have a shorter reverse recovery time than n rectifiers (and n thyristors).