ABSTRACT
The basic concept of the bipolar junction transistor (BJT) was patented by W. Shockley in 1947, but the BJT was not experimentally realized until 1951. In a real sense, the silicon (Si) BJT was the device that launched the microelectronics revolution and hence spawned the “information age.” In contrast to the depictions commonly found in many standard electronics textbooks, Si BJT technology evolved radically over time, from double- or triple-diffused, large geometry, nonself-aligned structures to very compact, self-aligned, doublepolysilicon structures, to at present self-aligned, epitaxially grown silicon-germanium (SiGe) structures. In the present analysis, the SiGe heterojunction bipolar transistor (HBT) and the Si BJT are taken to be of identical geometry, and it is assumed that the emitter, base, and collector doping profiles of the two devices are identical, apart from the Ge in the base of the SiGe HBT. Typical metallurgical emitter–base junction depths range from 25 to 50 nm in modern SiGe HBTs.
