Large parasitic series resistances of the heterostructure bipolar tran
sistors are shown to cause a sharp rise in the base current of the Gum
mel plot at high current levels. This effect is analysed and attribute
d to a forward-biased base-collector junction due to the large voltage
drop across the collector series resistance of the device. The occurr
ence or this effect results in a severe reduction in current gain of t
he device at high current levels. A DC Ebers-Moll model is presented w
ith ail the parameters extracted from DC characterisation of the HBT,
and an excellent fit between the model and experimental data is obtain
ed. The method can be used to determine the base, collector and emitte
r series resistances of the bipolar transistors for DC applications. F
inally. the effect of temperature on the onset of this effect is demon
strated. (C) 1998 Elsevier Science Ltd. All rights reserved.