Some new aspects of thermal stability of the current distribution in power transistors

An important characteristic of second breakdown in p-n junctions is the current constriction to a small region. This may be caused by a thermal feedback mechanism, which has been discussed by Scarlett and Shockley and by Bergmann and Gerstner. A brief review of this theory will be given and illustrated by experimental results of a simple model arrangement consisting of three thermally coupled transistors. The essential parameters influencing the thermal stability of the current distribution are device geometry, power density, and temperature dependence of current.