We examined the dependence of hydrogen passivation in carbon-doped GaAsSb grown by metal-organic chemical vapor deposition (MOCVD) under various growth conditions and found that the carbon acceptors in carbon-doped GaAssb can be passivated by hydrogen under some growth conditions, contrary to previous reports. The ratio between the hydrogen-passivated-carbon concentration, [C-H], and total carbon concentration, [C], in carbon-doped GaAsSb was smaller than that in carbon-doped GaAs and considerably smaller than that in carbon-doped InGaAs. This is apparently due to differences in the ionicity of the covalent bonds in the carbon-doped crystals and the location of the stable sites of carbon atoms. We also found that hydrogen passivation of carbon acceptors is closely related to the growth temperature. As the growth temperature is increased, the number of hydrogen-passivated carbon acceptors decreases more rapidly than the total number of carbon acceptors. As a result, carbon-doped GaAssb with almost complete suppression of hydrogen passivation can be grown at temperature above 530 degreesC. Using a high-temperature ambient apparently reduces the incorporation efficiency of hydrogen atoms, so that the hydrogen concentration passivating carbon acceptors is reduced to a negligible concentration. (C) 2003 Elsevier B.V. All rights reserved.