Electrical determination of bandgap narrowing and parasitic energy barriers in SiGe and SiGeC heterojunction bipolar transistors

A novel electrical method is described which allows the extraction of bandgap narrowing within the base of SiGe heterojunction bipolar transistors due to heavy doping effects and the presence of germanium. In addition it is shown that the method's sensitivity to doping tails makes it ideal for determining the presence of parasitic energy barriers due to B outdiffusion from the base, a cause of major concern for HBT technology. The analysis is applied to SiGe and SiGeC HBTs showing that background carbon incorporation (/spl ap/10/sup 20/ m/sup -3/) completely suppresses TED.