Interaction of degradation mechanisms in Be-doped GaAs HBTs

Be-doped GaAs HBTs subjected to various life tests were found to degrade more rapidly than predicted by the current lifetime model. All failed devices which were examined exhibited the failure mode which is dominant for C-doped HBTs: increased base current at low voltages, accompanied by an increase in the base current ideality factor. Failed devices also showed an increase in the emitter-base turn-on voltage, indicating Be diffusion into the AlGaAs emitter. In addition to exhibiting two distinct degradation mechanisms, failure analysis data indicate interactions between these two mechanisms which support identification of the dominant failure mode under extended operation as recombination-enhanced defect reaction.