Emitter injection efficiency and base transport factor in InAs bipolar transistors

The factors affecting the common emitter current gain (beta) in InAs bipolar junction transistors (BJTs) have been studied by estimating the base transport factor (alpha(T)) and the emitter injection efficiency (gamma). This has been accomplished by employing a specially designed sequence of InAs npn BJTs. alpha(T), gamma, and the minority carrier (electrons) diffusion length in the base (L-B) are extracted from measured electrical characteristics by using a simple method. When the emitter doping density is large, the current gain is limited by the base transport factor alpha(T). The value of L-B in these BJTs is found to be 0.44 mum, which indicates high quality epitaxial material. The analysis developed is a general technique, also applicable to BJTs and heterojunction bipolar transistors in other material systems. (C) 2003 American Institute of Physics.