The role of hydrogen in current-induced degradation of carbon-doped [formula omitted] heterojunction bipolar transistors

Abstract

At current densities ≥ 5 × 10 4 A cm −2 carbon-doped base GaAs AlGaAs HBTs can display decreases in d.c. current gain which are correlated with the amount of hydrogen incorporated in the base layer during growth by Metalorganic Molecular Beam Epitaxy (MOMBE). During device operation, minority carrier injection-induced debonding of hydrogen from neutral CH complexes leads to an increase in effective base doping level and therefore to a decrease in current gain. In structures grown under conditions where large concentrations of hydrogen are incorporated in the base region, post-growth in situ or ex situ annealing eliminates this effect by breaking up the CH complexes. Properly designed HBTs are stable for >90 h even for very high collector current densities (10 5 A cm −2).