The role of net positive oxide trapped charge and surface recombinatio
n velocity on excess base current in BJTs is identified. Although the
interaction of these two radiation-induced defects is physically compl
ex, simple approaches for estimating these quantities from measured BJ
T characteristics are presented. The oxide charge is estimated using a
transition voltage in the plot of excess base current vs. emitter bia
s. Two approaches for quantifying the effects of surface recombination
velocity are described; the first measures surface recombination dire
ctly using a gated diode. The second estimates its effects using an in
tercept current that is easily obtained from the BJT itself. The resul
ts are compared to two-dimensional simulations and measurements made o
n test structures. The techniques are simple to implement and provide
insight into the mechanisms and magnitudes of the radiation-induced da
mage in BJTs.