AlN crystals were grown from the vapor phase in an RF heated AlN sublimation reactor. The studies were performed with the following goals: 1) to optimize the growth rate by investigating mass transfer effects, and 2) to establish a process for epitaxial growth on AlN seeds. A one-dimensional mass transfer model based on equilibrium sublimation and gas-phase diffusion was developed. Model parameters were estimated and the model was validated from growth experiments carried out in a 600 Torr nitrogen atmosphere and temperatures ranging from 2000 to 2400°C. Continuous growth on AlN seed crystals was accomplished as a result of optimizing the initial stage of growth and achieving a delicate balance between the rate of mass transfer and the rate of surface rearrangement. During this experimental study, centimeter-size single crystals of AlN were obtained within the 1.25” diameter boule that was grown at a predicted growth rate of 0.1–0.3 mm/hr, at 500 Torr of nitrogen, short source-to-seed distance, low supersaturation and growth temperatures of 2110–2140°C. Chemical analysis of impurities in the grown AlN boules confirmed a very low oxygen contamination of 100 ppm wt. Cathodoluminescence studies showed well defined near band edge emission peak located slightly above 6 eV.