Aluminum nitride ͑AlN͒ has been proposed as an alternative to oxide-based dielectrics for use in metal-insulator-semiconductor devices. In this study AlN deposition was performed on Si substrates using metallorganic molecular beam epitaxy at 325-425°C. The interfacial and electrical characteristics both as deposited and after rapid thermal annealing at 400 and 840°C were investigated. The lowest growth temperature, 325°C, produced partially amorphous films which did not appear to suffer from carbon or oxygen contamination. All the films deposited in this study were smooth, with root-mean-square roughnesses of typically ϳ1 Å. While the as-grown surface morphology and roughness were independent of growth temperature, annealing in forming gas at 400°C did produce slightly more surface roughening in the films grown at the higher temperatures. The lowest growth temperature produced films with significantly better capacitance-voltage ͑C-V͒ behavior than films which were completely polycrystalline. Annealing generally improved the C-V behavior but degraded the breakdown field strength values.