1. General principles

1.1 Single-pole components

The term "unipolar" indicates that only one of the two types of carriers is used to carry the current. These are the majority carriers in the large, lightly-doped region that, in all cases, constitutes the "core" of a power component. This region, which we refer to as the "base" in a generic sense (cf. article , § 1), but which can be given more specific names on a case-by-case basis, plays an essential role: it offers the space charge of the blocking junction room to develop, and thus determines the voltage withstand performance; in the on-state, it constitutes a significant part of the device's apparent resistance, especially since, in the absence of minority carrier injection, there is no moderating effect on conductivity modulation....