We demonstrate that InN quantum dots (QDs) can be spontaneously formed on AN and GaN surfaces by plasma-assisted molecular-beam epitaxy under the Stranski-Krastanow (S-K) mode. Both Si(Ill) wafers and metal-organic chemical vapor deposition grown GaN/ Al2O3(0001) templates were used as substrates in this work. Silicon is particularly interesting as a substrate for InN QD applications because of its electrical conductivity and transparency in the near-infrared. By using reflection high-energy electron diffraction (RHEED), the formation process of InN QDs can be monitored in situ. We observed the 2D - 3D transition of S-K growth mode and the lattice constant varied dramatically at the 2D - 3D transition point from AlN to InN lattice constant. Furthermore, from the ex situ atomic force microscopy and scanning electron microscopy measurements, we directly imaged InN QDs on the AN surface with an average diameter of similar to 14 nm and high areal density of similar to 1.6 x 10(11) cm(-2). (c) 2005 Elsevier B.V. All rights reserved.