The crystalline structures and morphologies of Er2O3 films epitaxially grown on both oxidized and clean Si surfaces are investigated by X-ray diffraction, in situ reflection high energy electron diffraction and atomic force microscopy. Both crystallinity and surface roughness of Er2O3 films grown on oxidized Si substrates are improved compared to those grown on the corresponding clean ones, indicating that the oxidized Si surfaces are favorable to the epitaxial growth of Er2O3 films compared with the clean ones. At the same time, the oxidized Si surface can suppress the formation of Er silicide at the interface during the film growth, which is preferable for epitaxial Er2O3 films with smooth surfaces. Good epitaxial growth of Er2O3 films, with a surface mean roughness as small as 1.51 angstrom and good crystallinity as well, has been achieved on an oxidized Si(111) surface by molecule beam epitaxy. (c) 2005 Elsevier B.V. All rights reserved.