We studied the effect of Sb-4 irradiation on the growth of GaAs thin films on Si (1 1 1) substrates. GaAs thin films were grown by molecular beam epitaxy (MBE) system with As-2 as a source. Sb-4 was also supplied during the GaAs growth. We evaluated surface roughness with an atomic force microscope and crystallinity with an X-ray diffraction system. When GaAs is grown without Sb-4 irradiation, crystallinity can be improved by subjecting it to high temperatures, although the surface becomes very rough. In contrast, GaAs grown with Sb-4 irradiation showed both good crystallinity and a very flat surface. As the growth temperature increased, both crystallinity and surface flatness were improved, probably due to the enhanced migration with two-dimensional growth modes. Furthermore, plan-view observation with a transmission electron microscope (TEM) showed that Sb-4 irradiation was very effective for reducing stacking faults. (c) 2013 Elsevier B.V. All rights reserved.