Epitaxial growth of AlN on sapphire (0 0 0 1) by sputtering: a structural, morphological and optical study

We report on the growth conditions dependence of the morphology and structural quality of epitaxial AlN thin films deposited by normal incidence reactive sputtering. The crystallographic quality is increased for higher concentrations of nitrogen in the plasma during the deposition process. Also the presence of an intermediate AlN buffer is found to reduce the stress induced by the substrate and to enhance the quality of the subsequent AlN deposit; the morphology and roughness of the surface of the deposit depend on the deposition temperature of the buffer layer. From spectroscopic ellipsometry measurements we deduce and present the evolution of the refractive index and extinction coefficient with the wavelength for AlN deposits obtained under different growth conditions.