Current analysis of polyimide passivated InGaP/GaAs HBT

InGaP/GaAs heterojunction bipolar transistors (HBTs) were fabricated to examine the effects of polyimide deposition on the recombination current. An analytical model was developed for the base and collector currents to determine the dominant current components at low and moderate bias for abrupt InGaP/GaAs HBTs. InGaP material parameters were calculated and found to be in reasonable agreement with those obtained by other authors. It was found that recombination at the heterointerface and the emitter–base perimeter were in competition, resulting in current reduction at emitter–base bias VBE ≈ 0.8 V, and that polyimide deposition prevented current reduction and minimised the recombination at the surface, therefore reducing the leakage current.