Second breakdown and damage in junction devices

Second breakdown has been studied in silicon-on-sapphire (SOS) thin-film diodes using the stroboscopic technique of Sunshine. Nucleation of current filaments, filament growth, and damage through the formation of melt channels are observed and related to the voltage waveforms, geometry, and base layer resistivity. The delay time and the minimum energy for the onset of second breakdown are related to heating of the high-resistivity side of the junction. Theoretical models are presented to describe nucleation of current channels in the junction and the melt transition. A junction channel forms when the sum of minority carrier and thermally generated current densities becomes equal to the local applied current density. The voltage across the junction then goes close to zero locally, but the internal field is not "washed out." The channel is ballasted by the spreading resistance of the high-resistance region. The melt transition is described in terms of a single heat-transfer coefficient characteristic of the device type. As the melt filament grows, the voltage across the filament (and the device) falls. The threshold current for filamentation varies as (ρ^-3/4), where ρ is the resistivity of the high-resistance region. Data on transistors are presented in support of the theoretical models.