Avalanche degradation of hFE

Degradation of low current hFEas a result of avalanching the emitter-base junction of a silicon planar transistor is shown to be explinable by an increase in surface recombination velocity within the vicinity of the emitter-base metallurgical junction. This degradation mechanism manifests itself on a gate-controlled transistor by an additional peak in the plot of base current versus gate voltage. The magnitude as well as the "width" of this peak can be accounted for theoretically by assuming a given emitter-base impurity gradient and a localized increase in surface recombination velocity in and around the metallurgical junction. Experimental evidence is also presented for localized charge trapping within the oxide over the emitter-base junction as a result Of avalanching under an applied field.