Correlation of Electron-Induced Changes in Transistor Gain with Components of Recombination Current

After low-exposure dosage of electron and/or gamma radiation, anomalous permanent changes in transistor gain have been observed which cannot be attributed to changes in base minority-carrier lifetime or to temporary surface effects. A study of these permanent effects has been performed using base current component analysis similar to that applied to neutron damage by Goben. By this method it was possible to observe the buildup with dose of individual components of base recombination current. These components can be related to damage in the base-emitter space-charge region and in the base regions of the devices. It was possible to correlate the buildup and/ or saturation of the components with structure observed in the curves of anomalous gain degradation. Furthermore, analysis of damage in the base region revealed two components which appear to be related to changes in the surface recombination velocity and to changes in the minority-carrier lifetime, respectively.