ErF3 layers were grown on Si(111) substrates at 400, 550, and 700 degrees C by molecular beam epitaxy. Reflection high-energy electron diffraction in situ and x-ray rocking curve analysis ex situ showed that at the high growth temperature of 700 degrees C, an ErF3 layer of the native orthorhombic structure could be,orown conformably on the hexagonal atomic arrangement of the Si(111) substrate. The surface morphology and flatness of the resulting layers were studied by atomic force microscopy as a function of growth temperature and layer thickness. At higher temperatures, layers consist of highly perfect crystallites aligned with b axes normal to the substrate, and c axes along one of six symmetrically related [01 (1) over bar] directions of the Si substrate. (C) 2060 American Vacuum Society. [S0734-2101(00)04003-3].