The epitaxial growth of GaN on Si (1 1 1) substrates has been performed using plasma-assisted molecular beam epitaxy with a thin (similar to 19.3 nm) single-crystal layer of Sc2O3 as a template/buffer layer. The structural properties and in Situ epitaxial growth were studied using reflection high energy electron diffraction (RHEED), high-resolution transmission electron microscopy, and high-resolution X-ray diffraction. An orientation relationship of GaN(0 0 0 2)parallel to Sc2O3(1 1 1)parallel to Si(1 1 1) and GaN[1 0 (1) over bar 0]parallel to Sc2O3[4 (2) over bar (2) over bar] off 60 degrees with Si[4 (2) over bar (2) over bar] was determined. The excellent growth of Sc2O3 on Si and GaN on Sc2O3 Was achieved, as observed from streaky and bright RHEED patterns. The Sc2O3 template serves as an effective barrier layer preventing diffusion of Si and Ga during the GaN growth at high temperatures under nitrogen plasma. No cracking was observed in the GaN layer with thickness around 0.2 mu m when inspected with an optical microscope. (C) 2008 Elsevier B.V. All rights reserved.