Low-Temperature Avalanche Multiplication In The Collector-Base Junction Of Advanced N-P-N Transistors

Abstract

This paper describes the collector-base junction avalanche in advanced n-p-n transistors in the temperature range of 293 to 83 K. The multiplication factor is shown to increase exponentially with decreasing temperature. The dependence decreases with increased collector doping concentration and, for the same device, with increased reverse bias. At a fixed collector bias, it is roughly constant at low current density, but varies with I c at high-level injection due to space-charge modulation. Measurements at low temperatures excluded self-heating in the devices, and we were able to study high-level injection effects at collector current densities higher than 10 mA/μm 2. Extensive computer simulations were performed to gain insight to the effects of the field and carrier distributions. We observed that, at very high current densities, when the injected carrier density in the collector junction exceeds 1 x 10 17 cm-3, there is an anomalous drop in the avalanche multiplication rate that conventional device simulators fail to predict. We attribute the latter to electron-electron scattering that retards impact ionization by quickly redistributing the excess energy through interparticle collisions. © 1990 IEEE