THIN-BASE INGAAS HETEROJUNCTION BIPOLAR-TRANSISTOR WITH PARABOLICALLY GRADED INGAALAS EMITTER

We describe an InGaAs heterojunction bipolar transistor lattice-matched to InP with a parabolically graded quaternary In(Ga1-xAlx)As emitter and a thin base. We obtain a room-temperature common-emitter DC current gain of more than 100, indicating the successful operation of the parabolic grading. High-frequency properties are equally promising, with current gain cutoff frequencies up to 125 GHz. These studies provide evidence for a significant reduction of base and collector transit times at high current densities, due to the velocity overshoot effect.