Avalanche degradation of hFE

When the emitter base junction of a silicon planar transistor is reverse biased beyond avalanche, the low current hFEof that device, under normal operating conditions, can be degraded by as much as 90%. It will be shown that this avalanche stress causes a localized increase in the surface recombination velocity. If during normal operation the emitter base junction intersects the surface in the region of increased recombination velocity, hFEis decreased. No relationship was found to exist between this localized increase in surface recombination and oxide contamination. The effect can be completely annealed in five minutes at 300°C.