A Stranski-Krastanow (SK)-like growth mode is shown for GaN nanostructures on AlN template layers grown by metalorganic chemical vapor deposition on sapphire substrates. A wide temperature range from 800 to 1100 degrees C and V/III ratios ranging from 4.5 to 3500 were explored to determine the optimal growth conditions. Silicon was used as an anti-surfactant to enhance the nucleation. Further, an activation step was introduced to the GaN/AlN heterosystem to support the formation of 3D islands revealing a SK-like growth mode. Initial nucleation studies on GaMnN grown on AlN epilayers were performed to achieve multifunctional nanostructures, combining the advantages of quantum dots and diluted magnetic semiconductors. It is shown that manganese incorporation enhances the nucleation of GaN nanostructures. Further studies reveal that no additional activation step is necessary for nanostructures containing manganese. (c) 2005 Elsevier B.V. All rights reserved.