By using a new double-buffer-layer (AlN/Si3N4) technique. wurtzite-type InN(0 0 0 1) epitaxial films have been grown on Si(1 1 1) substrates by nitrogen-plasma-assisted molecular beam epitaxy. In this technique, a single crystal Si3N4 layer (commensurately matched to the (1 1 1) face of silicon) is used as a diffusion barrier to prevent intermixing and autodoping effects. And, the AlN(0 0 0 1) layer is used to form a 9:8 commensurate heterointerface with InN(0 0 0 1) despite a large difference in lattice constants. In this paper, we focus on the effects of the AlN buffer in terms of crystalline structure, optical, and electrical properties of grown InN epitaxial films. In addition to the use of the AlN buffer layer, the two-stage growth process (the growth of low-temperature (similar to 340 degrees C) InN epilayer prior to the growth of the high-temperature (similar to 520 degrees C) InN epilayer) was also Found to be very important to obtain high-quality InN films. By using the AlN/Si3N4 double buffer, InN-on-Si epitaxial films can be grown with high structural and optical properties. This was confirmed by reflection high-energy electron diffraction, X-ray diffraction, scanning electron microscopy, atomic force microscopy, and room-temperature photoluminescence. Furthermore, room-temperature Hall effect measurements indicate that increasing AlN buffer thickness leads to higher electron mobility and lower n-type carrier concentration in the InN epilayers, very important for electronic device applications. (c) 2005 Elsevier B.V. All rights reserved.