Adsorption configuration of AlN on sapphire surface using first-principles calculations

First-principles calculations of Al atom, N atom, and AlN molecule adsorption on sapphire surface have been carried out to explain the atomic-scale insight into the initial adsorption processes of AlN deposition on sapphire substrate. The results reveal that Al atom, N atom, and AlN molecule all form chemical bonds with substrate atoms when adsorbed on sapphire surface. Moreover, the bonding between AlN molecules and sapphire substrate are more complex than that of Al atom and N atom. Meanwhile, AlN with N atom closer to sapphire substrate has the largest charge transfer when adsorbed, which is consistent with its most complex bonding with substrate atoms. Furthermore, the bonds are formed deviating from the sapphire hexagon at an angle of about 30 degrees or 60 degrees when AlN molecule adsorbed. As a result, the lattice constant after the bonding of AlN shrinks and is closer to that of AlN, which directly reduces the crystal mismatch between AlN and sapphire. Thus, it is easier to obtain a template with a lattice closer to AlN. The results obtained provide theoretical guidance for obtaining better templates for growing AlN thin films on sapphire substrate.