Stress Current Behavior of InAlAs/InGaAs and AlGaAs/GaAs HBT’s with Polyimide Passivation

InAJAs/InGaAs and AlGaAs/GaAs HBT’s, with heavily Be-doped base layers, have been fabricated and their reliability under excessive forward current tested. To understand the HBT material difference, a common process based on a polyimide planarization process is applied to the fabrication. While short-term degradation induced by stress current is observed for AlGaAs/GaAs HBT’s (G-HBT’s), InAlAs/InGaAs HBT’s (I-HBT’s) are stable up to a current density of 1.5 X 10^s A/cm² indicating the absence of substantial Be diffusion. An analysis of base current has shown a striking contrast between the HBT’s in terms of the stressing effect on the surface recombination along emitter junction periphery.