During elevated-temperature bias stress, InGaP/GaAs HBT's grown by MOC
VD show a medium term degradation in current gain of about 20%, with a
n activation energy of 0.64 eV. They also show a corresponding decreas
e in base resistance and an increase in turn-on voltage. InGaP/GaAs HB
T's grown by GSMBE, however, do not show this degradation. SIMS measur
ements show a five times greater than GSMBE-epi hydrogen concentration
of about 10(19) cm(-3) in the base layer of the MOCVD-grown epi. The
degradation can be explained by acceptor depassivation due to hydrogen
out-diffusion from the epi during stress.