INFLUENCE OF Al MONOLAYERS ON THE PROPERTIES OF AlN LAYERS ON Si (111)

High-quality aluminum nitride (AlN) layers with full width at half maximum (FWHM) values of 11 arcmin were grown by plasma-assisted molecular-beam epitaxy on Si (111) substrates. AlN nucleation layers are being investigated for the growth of GaN on Si. Growth using AlN buffer layers leads to Al-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Al-rich as possible, although Al droplets tend to form. Before starting the AlN growth, a few monolayers of Al are deposited on the substrate to avoid the formation of Si3N4. X-ray diffraction (XRD) techniques were employed to determine the surface and structural quality of the layers. XRD revealed that monocrystalline AlN was obtained. Best AlN films were obtained at high substrate temperatures (875°C) and III/V ratios close to stoichiometry.