Si/Si1-yCy/Si epitaxial layers grown by reduced pressure chemical vapor deposition (RPCVD) were integrated in nMOS devices. A direct correlation between the interface state density introduced by C at the Si/SiO2 interface and the effective mobility of the electron inversion region has been demonstrated. Interface state densities can be reduced by lowering the growth and subsequent process temperatures. This way, a large amount of carbon atoms are incorporated into substitutional sites and the migration of mobile carbon atoms to the Si cap/SiO2 interface is limited. This leads to a significant improvement of the electrical performances, even for an aggressive channel stack design (ultra-thin epilayer and oxide thickness, high carbon concentrations). (C) 2003 Elsevier B.V. All rights reserved.