Characterization of bias-stressed carbon-doped GaAs/AlGaAs power heterojunction bipolar transistors

We report on the performance of carbon-doped heterojunction bipolar transistors (HBTs) bias stressed at elevated temperatures. We have determined that in devices without a thin passivating layer of AlGaAs covering the extrinsic base, a tunneling-recombination current that increases in magnitude with the duration of the stress is generated. This current is seen in both the collector and the base at cryogenic temperatures. The variation of this current with temperature is primarily due to carrier freeze-out in the AlGaAs emitter. We hypothesize that this conduction mechanism is related to the generation of midgap traps in the base layer as a result of electron-hole recombination events.<>