In this paper, we present a model of the vapor-phase reaction of trimethyl-gallium (TMG), trimethyl-aluminum (TMA) and NH3 and show our attempt to control parasitic reactions. First, we present a quantum chemical study of the unimolecular and bimolecular reactions of adducts. The direct adduct reaction pathway between TMA:NH3 adducts can explain the reactivity of TMA. The calculated energy of each transition state for oligomer formation can well explain the experimental observation that TMGa:NH3 adduct formation and cracking are reversible, and that TMA:NH3 adducts react irreversibly to form higher-order oligomers. Growth results for a reactor with and without recirculation flow are compared to show the importance of flow dynamics on the interaction between nanoparticles and precursors in the gas phase. Using a laminar flow three-layer configuration to ensure stable adduct injection, AlGaN with more than 17% Al can be uniformly grown over a 6-in-diameter platen at atmospheric pressure. (C) 2004 Elsevier B.V. All rights reserved.