We report on the surfactant-mediated epitaxy (SME) of Si1- xGex films with x = 0.23-1 on Si(001) using antimony as surfactant. We observe a transition in strain relaxation at a critical composition x(T) = 0.58-0.66. Above this value full relaxation is achieved by a network of full edge dislocation confined to the interface in analogy to SME of pure germanium on Si(001). 100 nm thick Si1- xGex films with surface roughness values less than 1 nm and abrupt interfaces are obtained, as the surfactant reduces strain induced roughening and hinders interdiffusion. (C) 2013 Elsevier B.V. All rights reserved.