The influence of the emitter-base junction surface property on current gain ( h FE ) and on its degradation at moderate current levels has been investigated. Various transistors with different emitter perimeter-to-area ratios ( L E / A E ) ware fabricated on one wafer with SiO 2 or Si 3 N 4 junction passivation. The influence of the emitter-base junction surface recombination current on the h FE is analyzed by referring to the h FE -1 vs. L E / A E relation. The influence on h FE degradation is also analyzed by monitoring changes in the h FE -1 vs. L E / A E relation during accelerated life tests. It is shown that the h FE of high frequency transistors, whose f T was several GHZ, decreases to about 50% of that of surface influence independent transistors. Surface recombination current change is a major factor in inducing the h FE change during life tests.
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Noboru Shiono (1979) studied this question.