Growth mechanisms of InGaAs three-dimensional (3D) islands formed on vicinal (1 1 1)B GaAs surfaces with multi-atomic steps are studied by examining surface morphologies of InxGa1-xAs layers having various In contents x and/or nominal thickness d. When an InGaAs layer with x = 0.29 and d = 3 nm was deposited by molecular beam epitaxy (MBE), 3D islands with lateral sizes of about 40 nm, almost twice as much as the average period (similar to 20 nm) of underlying GaAs steps, were formed and densely aligned along the steps. A nearly flat surface was formed, when an InGaAs layer with x = 0.10 and d = 3 nm was deposited. In case of d = 2 nm and x = 0.30, smaller 3D islands were densely formed and their lateral size perpendicular to the steps was typically about 20 nm. Such 3D islands were hardly found when d = 2 nm and x = 0.55. These results support our hypothetical model that the 3D island formation is induced by the abrupt increase in strain energy resulting from the coherent connection of a pair of InGaAs wire-like structures on a pair of adjacent GaAs multi-atomic steps. (c) 2006 Elsevier B.V. All rights reserved.