Collector offset voltage of heterojunction bipolar transistors grown by molecular beam epitaxy

The collector-emitter offset voltages of InAlAs/InGaAs heterojunction bipolar transistors grown by molecular-beam epitaxy are discussed. Both the difference between emitter and collector areas and electrical asymmetry between emitter and collector junctions in these mesa-isolated transistors account for the offset voltages observed. Devices exhibited offset voltages in the range of 50-300 mV, depending on the structures and device sizes. Several electrical and geometrical factors affecting the offset voltage are discussed in detail.>