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

The de characteristics of InP/InGaAs and InAlAs/InGaAs HBT's with abru pt emitter-base junctions are studied using a thermionic-field emissio n boundary-condition model, The model incorporates tunneling and emiss ion into a one-dimensional drift-diffusion scheme and accounts for bre akdown and bulk recombination mechanisms, The effects of abrupt hetero junction transport and electrical junction displacement on the current gain h(FE) and on the turn-on voltage are investigated, The simulatio ns indicate that the spacer layer design has a profound effect on the de behavior of these devices, A detailed performance comparison of dif ferent emitter structures indicates that InP-emitter HBT's show a more uniform h(FE) than InAlAs-emitter HBT's especially at low current den sities, Experimental data from a fabricated InAlAs/InGaAs abrupt emitt er single HBT was compared to the theoretical predictions of the model , The analysis reveals that several injection and recombination mechan isms are responsible for the emitter-base forward characteristics. In the collector, the exact velocity-field profile and an anomalous multi plication factor are responsible for kinks in the output common-emitte r characteristics and for soft breakdown of the collector-base junctio n,