Characterization of the effectiveness of carbon incorporation inSiGe for the elimination of parasitic energy barriers in SiGe HBTs

An electrical method is applied to SiGe and SiGe:C heterojunction bipolar transistors (HBTs) to extract the bandgap narrowing in the base layer and to characterize the presence of parasitic energy barriers in the conduction band, arising from boron transient enhanced out-diffusion from the SiGe layer. It is shown that a background carbon concentration within the base (≈10²⁰ cm^-3) eliminates parasitic energy barriers at the collector/base junction, and hence shows that transient enhanced diffusion of boron from the base has been completely suppressed