InP-based heterojunction bipolar transistors with InGaAs/GaAs strained-layer-superlattice

In this paper, we report the design, fabrication, and characterization of an InP/InGaAs heterojunction bipolar transistor (HBT) employing a lattice-mismatched In0.53Ga0.47As/GaAs strained-layer-superlattice (SLS) base structure. The performance of the SLS-base device is also compared with that of an In0.53Ga0.47As uniform-base structure. The digitally graded-base devices exhibit a slightly lower gain at low bias voltage and a higher current gain at high currents. While the offset voltage remains comparable in the two structures, the graded-base InP/InGaAs HBTs, with built-in fields of ∼66 kV/cm, have typically a maximum dc current gain of 18% larger than that of transistors with uniform base.