Plastically relaxed GeSi films with a fraction of Ge ranging from 0.19 to 0.29 are grown on Si(001) substrates with the use of a low-temperature (350 degrees C) buffer layer of Si. Their root mean square (RMS) surface roughness is in the 1.7-2.7 nm range. Addition of Sb as a surfactant smoothing the surface of the stressed film during its growth is shown to reduce the surface roughness of the plastically relaxed heterostructure. The RMS roughness lower than 1 nm is reached for a film with a 0.29 fraction of Ge and a threading dislocation density Close to 10(6)cm(-2). (c) 2006 Elsevier B.V. All rights reserved.