Physical device modelling of emitter–base junction of In _0.52 Al _0.48 As/In _0.53 Ga _0.47 As-based SHBTs

This paper aims to evaluate the base–emitter forward characteristics of In _0.52 Al _0.48 As/In _0.53 Ga _0.47 As heterojunction bipolar transistors using numerical simulations in Silvaco while comparing results with fabricated devices. Analysis drawn from simulations reveals that in addition to doping, thickness of emitter and spacer region also plays an important role in determining the operational behaviour of device. The thickness of spacer region strongly influences the nature of heterojunction barrier formed that in turn controls the injection efficiency and dictates various recombination mechanisms. Even a few angstroms added to a spacer layer can cause considerable shift in DC characteristics. Methodology of device modelling is first validated by matching simulated results with the experimental measurements of two different structures. Spacer thickness and emitter doping is then varied in each of the structures to comprehensively study the effect of these variations onto important DC figures of merit.