In this study, various CuGaS2 layers were grown on GaAs (001) substrates using trietalorganic vapour phase epitaxy, for the purpose of studying the effect of sulphur-ten-nination of the substrate on layer quality. The resultant films were investigated using X-ray diffractometry, and transmission electron microscopy, with high-resolution transmission electron microscopy providing additional insights into crystallite growth on the control substrates. This paper will demonstrate that sulphur-termination limits substrate degradation. In the absence of sulphur-termination, atypical three-dimensional MOVPE growth is observed, with epitaxial crystallites varying in size from 10 run to 200 nm. Substrate degradation inhibits lateral growth at the interface resulting in amorphous regions, cavities, and epitaxial crystallites demonstrating overgrowth into mushroorn-like structures. (C) 2006 Elsevier B.V. All rights reserved.