The microstructural properties at the initial growth stage of the GaSb heteroepitaxial growth on a silicon (Si) substrate were investigated using transmission electron microscopy. Well-separated and tall GaSb islands were observed when GaSb was directly grown on a Si substrate (sample A). On the other hand, GaSb was grown to the coalesced and flat islands when a low-temperature AlSb buffer (sample B) was introduced. The different morphologies of the GaSb islands were related to the microstructural properties of the interface between the GaSb and the Si substrate. The GaSb/Si interface was rough, and disordered atomic arrangements were observed at the interface in sample A. On the other hand, the GaSb/Si interface was flat, and well-ordered atomic arrangements appeared at the interface in sample B. Entirely different mechanisms for the relaxation of a misfit strain were demonstrated from a microstructural viewpoint. (C) 2009 Elsevier B.V. All rights reserved.