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 Angstrom 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 delta-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.