General principles
Unipolar and mixed power semiconductors (part 1)

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. The N type is therefore the preferred...