Characterization of InP/InGaAs double-heterojunction bipolar transistors with tunnelling barriers and composite collector structures

We study and demonstrate the dc performance of two InP/InGaAs double-heterojunction bipolar transistor (DHBTs) with the undoped tunnelling barrier and composite collector structures. Due to the mass filtering effect for holes, a thin InP tunnelling barrier can be used to replace the wide-gap emitter. By varying the thickness of the barrier, distinct collector current ideality factors can be obtained which reveal different injection mechanisms at the emitter. The 4000 Å InP collectors with InP/InGaAs abrupt junctions and InP/InGaAsP/InGaAs step-graded junctions achieve high breakdown voltages of 9.2 and 14.6 V, respectively. Furthermore, the abrupt junction and δ-doping structure eliminate carrier blocking across the base-collector heterojunction more effectively than the step-graded junction. We find that the reduction of the multiplication avalanche of the step-graded junction DHBT leads to the severe self-heating effect. For the abrupt junction DHBT, the dc current gain is almost independent of the perimeter-to-area ratio of the emitter due to the low surface recombination.