The Metal-Organic Chemical Vapor Deposition process assisted by reactive plasma, leads to AlN coatings with oriented (10[MATH]0) structure. The Aluminium nitride was synthesized on a wide range of substrates (Silicon (100) or (111) wafers, graphite, polycrystalline Silicon Carbide and glass plates) from trimethylaluminium and ammonia at 330°C. The a-axis orientation of AlN coatings, which does not depend on the substrate, changes with the excitation frequency. Material crystallinity and elementary composition were examined mainly by X-ray diffraction and Auger Electron Spectroscopy respectively. Crystalline AlN was obtained for low frequency fields (35-110-440 kHz) with mean crystallite sizes of 200-600 Å, whereas amorphous films were obtained using a 13.56 MHz frequency. The AES analysis has revealed compositions similar to AlN with a small percentage of Carbon (2-4 %) and no Oxygen (for all experimental conditions). To corroborate these results, Scanning Transmission Electron Microscopy and Infra-Red absorption spectroscopy are used.