Early voltage of SiGe heterojunction bipolar transistors

Abstract

An analytical equation of the Early voltage, including the neutral-base recombination effect, is evaluated. The general analytical equation is valid for SiGe bipolar transistors with a flat, trapezoid, linear, or stepped Ge profile in the base. The present model predictions are compared with other published results and experimental data. The agreement between this work and experimental data is excellent. The analytical predictions without taking into account neutral-base recombination are overestimated. The model predictions, taking into account 100% neutral-base recombination, however, gives a fixed normalized Early voltage of 0.5, independent of Ge grading.