Second-breakdown phenomena in avalanching silicon-on-sapphire diodes

A new experimental technique, based on local temperature-induced changes in optical absorption, is used to study second breakdown in avalanching reverse-biased silicon-on-sapphire diodes. The technique allows spatial resolution down to 1 µm and temperature resolution of a few degrees Celsius. Further, used stroboscopically, the technique allows time resolution on the order of nanoseconds. The technique, in conjunction with special constant-current bias circuits and light-emission studies, has been used to elucidate the physical mechanisms underlying second breakdown in avalanching diodes. It is found that second breakdown occurs when the thermally generated leakage current becomes large enough at some localized region of the junction to quench the avalanche there. Under pulse biases, the product of the average pulse power times the square root of the delay timeτDwas essentially constant forτDas short as 1½ ns. However, the junction temperature atτDincreased asτDdecreased, and for very shortτDthe heating was highly nonuniform.