Microscopic modeling of impact-ionization noise in SiGe heterojunction bipolar transistors

摘要

Terminal current noise calculations are performed for a SiGe heterojunction bipolar transistor in a wide range of collector-emitter bias conditions. The generalized hydrodynamic (HD) model with a local temperature approach for avalanche generation is used. The parameters of the local temperature model are calibrated by matching the avalanche multiplication factor to results obtained by full-band Monte Carlo simulations. The noise figure calculation results are compared with experimental values and overall good agreement is obtained. The hydrodynamic and a drift-diffusion (DD) model are used to investigate terminal current noise due to impact-ionization. The behavior of the current noise spectral intensity is found to be different for the two models. The Fano factor of the collector current fluctuations is well described by the avalanche multiplication factor in the case of the DD model, whereas the HD model evidences no correlation between the Fano factor and the avalanche multiplication factor. The collector terminal electron transfer functions are used to discuss the difference.