The strain-relief and structural properties of GaSb films with thin AlSb islands and thick AlSb buffer layers grown on GaAs (0 0 1) substrate at low temperature (LT) by molecular beam epitaxy are investigated by atomic force microscopy and transmission electron microscopy. The strain arising from depositing the buffer layer onto the GaAs substrate was relieved by a periodic array of the 90 degrees misfit dislocations with the Burgers vector of 1/2a [1 1 0] for the thin AlSb islands buffer, but by both 60 degrees and 90 degrees misfit dislocations for the thick rough-and-flat AlSb buffer. The 90 degrees-misfit dislocation array of AlSb/GaAs interface had an average spacing of 4.80 nm. The mean roughness of the GaSb film on the thin AlSb islands buffer layer was found to be less than 1 nm. These results clearly demonstrate that the presence of a thin, LT AlSb islands initiation layer is very useful for improving the quality of GaSb crystals grown on GaAs substrates. (c) 2007 Elsevier B.V. All rights reserved.