Analysis of collector-emitter offset voltage of InGaP/GaAs composite collector double heterojunction bipolar transistor

The Ebers-Moll-like terminal current expressions of a composite collector double heterojunction bipolar transistor (DHBT), which takes the recombination effect into account, have been formulated and an expression for collector-emitter offset voltage [V-CE(offset)] has been derived. Factors affecting the V-CE(offset) of a composite collector DHBT are investigated and good agreement between the calculated and reported experimental results is shown. Analytical results showed that the transmission coefficient of the base-collector (B-C) junction does not have a considerable effect on the V-CE(offset), provided that the B-C junction is of good quality. Thus, despite its asymmetric structure, the V-CE(offset) of an optimally designed composite collector DHBT could be as low as that of a conventional DHBT. Hence a composite collector DHBT with low saturation voltage and negligible V-CE(offset) is possible if the two conditions: (i) good quality B-C junction, (ii) base transport factor, alphaapproximate to1, are fulfilled. (C) 2002 American Institute of Physics.