The very first stages of AIN and GaN epitaxial growth by molecular beam epitaxy on the Si(1 1 1) surface using NH3 as nitrogen source are studied mainly using reflection high-energy electron diffraction and scanning tunnelling microscopy. This study is performed in order to find a way to selectively nucleate AIN and GaN on Si(1 1 1). Exposing the Si surface to NH3 is sufficient even at very low pressure to provoke the formation of beta-Si3N4-like zones at the surface. Such zones are stable under Ga deposition but are converted into AIN by Al deposition. Therefore, combining partial surface nitridation and Al deposition gives rise to the selective epitaxy of AIN clusters in the nitrided zones. Moreover, the subsequent exposure to NH3 and Ga leads to the growth of GaN only in places where AIN has previously nucleated. (C) 2007 Elsevier B.V. All rights reserved.