Effect of post-growth cooling ambient on acceptor passivation in carbon-doped GaAs grown by metalorganic chemical vapor deposition

The degree of unintentional hydrogen passivation of acceptors in heavily C-doped GaAs (p≳1018 cm−3) grown by metalorganic chemical vapor deposition has been found to be a strong function of post-growth cool-down ambient. The carbon concentration in the GaAs and the amount of AsH3 in the cool-down ambient are the most important factors affecting passivation. Carbon acceptors can be reactivated by annealing in N2, then repassivated by heating and re-cooling in an AsH3/H2 or PH3/H2 ambient. Secondary ion mass spectrometry analysis shows that the hydrogen concentration is significantly higher in a C-doped GaAs surface layer which is exposed to the cool-down ambient than in a layer which is buried beneath n-type GaAs. This result is consistent with observations in n-p-n heterojunction bipolar transistor structures, where the fraction of C acceptors passivated in the base region is found to be less than in a single layer grown under identical conditions. Be-doped GaAs grown by gas-source molecular beam epitaxy has also been heated and cooled in AsH3-containing ambients, but no acceptor passivation is detectable by Hall effect measurements.