The effects of Si doping on the structural properties of a high-quality AlN layer grown on a trench-patterned AlN/sapphire by metalorganic vapor phase epitaxy (MOVPE) were systematically studied. With a high Si doping concentration, void formation became much slower than that in undoped AlN film. This phenomenon was attributed to the anti-surfactant effect of Si in the growth process. Moreover, as the Si doping concentration increased, compressive stress was significantly relaxed in Sidoped AlN films. A high Si doping concentration of 1 x 10(18) cm(-3) was successfully achieved for AlN grown at 1500 degrees C. (C) 2012 Elsevier B.V. All rights reserved.