Input power induced thermal effects related to transition time between avalanche and second breakdown in p-n silicon junctions

The dependence of the transition time between avalanche breakdown and second breakdown on the input power to a p-n junction was studied. Second breakdown was observed both in transistor configurations and in single junction structures. Fine structure inthe breakdown was also observed. Specimens at temperatures of 77°K and 300°K were pulsed with a fast-rising rectangular voltage obtained by standard coaxial line techniques. The voltage across the sample and the current through it are monitored, and clearly show the effects of second breakdown. The transition time between avalanche and second breakdown was easily measured. The transition time is observed to decrease with increased input power. For operation at 77°K, a longer transition time was observed than that for similar input at 300°K. The dependence of the transition time on the input power indicates a constant input energy for which second breakdown occurs. It is deduced that second breakdown is caused by a thermal breakdown of the depletion region. The constant energy required and related occurrence of melt channels in the junction region supports this deduction.