4.1 Introduction

The term "avalanche injection" was introduced by John Gunn in 1957 [90] to refer to a situation in which "the avalanche behaves as a copious source of electrons ( holes) which are injected into the material..." The term "copious" implies that the concentration of the free carriers created by avalanche breakdown exceeds the doping level in the semiconductor sample. In this case, as we have seen in Chapter 3, the space charge and electric field distribution are determined not by the fixed charge of the impurities, but by the charge of the free carriers (electrons and holes) (see Sections 3.2.3 and 3.2.4).

In reverse-biased diodes, free carriers can appear at a notable concentration only due to avalanche breakdown (Chapter 3). In this chapter we will consider the avalanche injection phenomenon in "semiconductor resistors" (i.e. slabs of the semiconductor with two ohmic contacts ( n ⁺ - n - n ⁺ or p ⁺ - p - p ⁺)) and semiconductor transistors and thyristors, i.e. in the structures in which an appreciable concentration of the free carrier can be caused by injection. It can be injection from the contacts in n ⁺ - n - n ⁺ or p ⁺ - p - p ⁺ structures, injection from the emitter in transistor structures, and injection from the gate or one of the emitters in thyristors. Free carriers (electrons or holes) injected from the outside into a...