The effect of base-emitter space-charge recombination on the temperature dependence of current gains in InGaP/GaAs and AlGaAs/GaAs HBTs

In this study, various N-p-n heterojunction bipolar transistors (HBT) structures with high C-doped bases, grown by metal-organic chemical vapour deposition (MOCVD), have been fabricated with identical geometry and processing steps. Measured results show that in addition to the intrinsic heterojunction emitter injection efficiency, the base bulk recombination plays an important role in maintaining the current gain at high temperature. Furthermore, it is shown that emitter/base space-charge region recombination has a significant detrimental effect on the variation of current gain with increasing temperature. A theoretical model is presented which predicts well the current gain variation with temperature for both AlGaAs/GaAs and InGaP/GaAs HBTs.