Current gain of SiGe HBTs under highbase doping concentrations

摘要

As high doping concentrations and high Ge contents are implemented in the base regions of SiGe heterojunction bipolar transistors (HBTs) to improve device performance, neutral base recombination (NBR) is also simultaneously enhanced. The enhanced NBR can severely degrade the current gain values of SiGe HBTs and thus needs to be carefully considered in device design. In this paper, a new analytical expression for the current gain of SiGe HBTs is derived to include the NBR component in the base current. The new current gain expression indicates that the maximum achievable current gain of SiGe HBTs is limited by the NBR and can be realized via optimization of the Ge profile. The analyses of the current gain of SiGe HBTs employing high base doping concentrations and high Ge contents are verified with MEDICI simulations.