We report on the growth of high-quality GaN epitaxial layers on Si(1 1 1) substrates using high-temperature-grown AIN as buffer layer by metalorganic chemical vapor deposition. It is found that the nitride compounds on the reactor wall have great influence on the initial surface condition of the Si substrates because they are dissociated from the wall and modifies the Si surface during the initial heat-up procedure. When the reactor wall is coated with the GaN after the growth of GaN/AIN/Si, the harmful Ga-containing droplets are formed on the AIN buffer layer, leading to deteriorated films. To prevent the droplets, coating AIN on the reactor wall (pre-treatment) is followed by the growth GaN/ALN/Si. This pre-treatment insures AIN environment and suppresses the formation of the droplets during initial heat-up, leading to reproducible and favorable surface condition for the growth of AIN buffer layer and subsequent GaN epitaxial films. In order to illustrate the optical properties of the GaN layer, photoluminescence is measured between 14 K and room temperature. Intense band edge emission and well-resolved excitonic transitions indicate an excellent optical quality of the epitaxial GaN films. (C) 2002 Elsevier Science B.V. All rights reserved.