Chapter 5 Hetero-Bipolar Transistor and Its LSI Application

Abstract

Publisher Summary This chapter presents a study on hetero-bipolar transistor (HBT) and its large-scale integrated (LSI) application. The basic idea of HBT is the use of a wide-gap emitter in the emitter/base junction to provide higher emitter efficiency—that is, a higher current gain in HBTs than in homojunction bipolar transistors. This emitter efficiency enhancement is generated by the suppression of base current, which results from a confinement effect on hole flow from the base into the emitter (in the case of n-p-n type). The wide-bandgap emitter removes the restriction for doping in the emitter and base that is necessary to maintain the current gain for homojunction transistors. HBTs offer the following general advantages: first, the base resistance can be reduced by higher base doping and second, the emitter capacitance can be minimized by the lower emitter doping. The development of new epitaxial growth techniques, molecular-beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD), has enabled fabrication of HBT epilayers suitable for high-frequency and high-speed devices. HBTs are very promising devices for ultrahigh-speed integrated circuits because of their high cutoff frequency, large driving capability, and freedom of various transistor structures.