On the wide-range bias dependence of transistor d.c. and small-signal current gain factors

Abstract

A critical reappraisal is made of the bias dependence of the d.c. and small-signal a.c. current gain factors of planar bipolar transistors over a wide range of currents. This is based on a straightforward consideration of the three basic components of the d.c. base current arising due to emitter-to-base injected minority carrier transport, base-to-emitter carrier injection, and emitter-base surface depletion layer recombination effects. Among other important results it is shown that over a useful bias range the d.c. and small-signal current gain factors, respectively, obey the simple relationships: H FE∞ I c 1 3 and h fe≈ 1.5h FE Experimental results on representative n- p- n and p- n- p silicon devices are given which support most of the analytical findings.