High-quality quaternary ZnSSeTe epitaxial layers were successively grown on GaAs substrates by molecular beam epitaxy. It was found that a ZnSSe layer was automatically formed between a ZnSe buffer layer and ZnSSeTe epitaxial layer when we increased the ZnS cell temperature. It was also found that the photoluminescence (PL) activation energy of the sample was 263 meV, which was much larger than those observed from ZnSe and/or ZnSSe epitaxial layers. The much larger PL activation energy was attributed to the fact that excitons in ZnSSeTe were still bounded at the localized Te or Te-n cluster states. (C) 2004 Elsevier B.V. All rights reserved.