Although we recently found that a high-quality GaSb film can be grown on Si substrate by using an AlSb initiation layer, the growth mechanism, especially the effects of AlSb initiation layer, was not clear. Therefore, we investigated the initial growth stage of GaSb on Si(0 0 1) substrates with AlSb initiation layers by atomic force microscopy. When small AlSb islands were formed on the Si substrate before the growth of GaSb, two-dimensional GaSb growth occurred. In contrast, without the growth of AlSb small islands, large GaSb islands were formed on the Si substrate. Therefore, the AlSb islands played an important role in preventing excessive surface diffusion of Ga atoms on the Si surface and promoting two-dimensional growth of GaSb. (c) 2005 Elsevier B.V. All rights reserved.