Three-dimensional Simulation of heavy-ion induced charge collection in SiGe HBTs on SOI

This work presents the three-dimensional simulation of heavy-ion induced charge collection in SiGe heterojunction bipolar transistors (HBTs) on silicon-on-insulator (SOI). Charge collection is found to be independent of the thickness of n+ buried layer, part of the SOI film, which directly relates to the collector resistance. The simulation results show that potential perturbation is confined within a thin region near the collector-base junction, due to the heavy doping of the n⁺ layer. Comparisons with bulk SiGe HBTs show that the charges collected by the collector and substrate are much smaller in SOI than in bulk HBTs, primarily because of the removal of the collector-substrate pn junction. The charges collected by the emitter and base, however, are nearly identical in SOI and bulk HBTs, because the heavily doped n+ buried layer decouples the potential perturbation and hence charge collection in the intrinsic emitter, base and collector from those in the collector-substrate junction. The load dependence of charge collection is also examined.