Recombination in the Ge-spiked monoemitter of the SiGe:C HBTs

A SiGe spike in the monoemitter of a SiGe:C HBT locally increases the recombination rate. The narrower energy bandgap of SiGe compared to Si increases the minority charge storage, resulting in higher recombination rate. The SiGe spike acts as a virtual contact and increases the base current. This results in lower current gain, and hence higher BVCEO. This paper studies the physical mechanism for this higher recombination rate in the SiGe spike, and it calculates the minority carrier lifetime in the SiGe spike.

Research highlights
► A SiGe spike in the monoemitter is used to increase Ib, hence improve BVCEO.
► We modeled the Auger and SRH recombination rate accounting for the increased Ib.
► In a sharp spike, from low to medium bias condition, SRH recombination dominates.
► In a sharp spike at high bias and in a diffused spike, Auger recombination dominates.
► A sharp spike results in the reduced effective minority carrier lifetime in the spike.