On the InP/InGaAS double heterojunction bipolar transistor (DHBT) with emitter tunneling barrier and composite collector structure

An InP/InGaAs double heterojunction bipolar transistor (DHBT) with an undoped emitter tunneling barrier and composite collector structure is fabricated and studied. Due to the. mass filtering effect for holes, a thin InP tunneling barrier can be used to replace the wide-gap emitter. Experimentally, an appropriate tunneling barrier thickness of 150Angstrom is employed to achieve good IV characteristics. In addition. InGaAsP compositionally step-graded layers are introduced between the p(+)-InGaAs base and n(-)-InP collector. By modulating the bandgap energy of InGaAsP, the large base-collector (B-C) potential spike can be divided into several small spikes with lower barrier height. The 4000Angstrom InP collectors with InP/InGaAsP/InGaAs step-graded junction achieve high breakdown voltages of 14.6V. A small offset voltage of 80mV and a small saturation voltage of 1.8V at the collector Current level of 5mA are obtained. Prior to the current gain fall-off caused by the self-heating effect, the step-graded DHBT has the current gain as high as 118 at I-C = 30mA and V-CE = 3V.