THEORETICAL AND EXPERIMENTAL DC CHARACTERIZATION OF INGAAS-BASED ABRUPT EMITTER HBTS

Abstract

The de characteristics of InP/InGaAs and InAlAs/InGaAs HBT's with abrupt emitter-base junctions are studied using a thermionic-field emission boundary-condition model, The model incorporates tunneling and emission into a one-dimensional drift-diffusion scheme and accounts for breakdown and bulk recombination mechanisms, The effects of abrupt heterojunction transport and electrical junction displacement on the current gain h(FE) and on the turn-on voltage are investigated, The simulations indicate that the spacer layer design has a profound effect on the de behavior of these devices, A detailed performance comparison of different emitter structures indicates that InP-emitter HBT's show a more uniform h(FE) than InAlAs-emitter HBT's especially at low current densities, Experimental data from a fabricated InAlAs/InGaAs abrupt emitter single HBT was compared to the theoretical predictions of the model, The analysis reveals that several injection and recombination mechanisms are responsible for the emitter-base forward characteristics. In the collector, the exact velocity-field profile and an anomalous multiplication factor are responsible for kinks in the output common-emitter characteristics and for soft breakdown of the collector-base junction,