Transit time reduction in AlGaAs/GaAs HBTs with p-type collector

The effect of using a p-type collector structure, in which a moderate electric field maintains the velocity overshoot through almost the entire depletion region, was examined by comparison with the n-type collector structure on actual devices. Increased electron velocity in a p-type collector region was verified. Specifically, the p-type collector structure exhibited a collector transit time less than half of that in the n-collector. This advantage of velocity overshoot in the p-collector was maintained up to the bias condition, where a large potential drop in collector depletion layer induced a high electric field in the p-layer