Substrate Surface Structure Effects on Microstructure of Epitaxial Films

Abstract

ABSTRACTThe microstructure of epitaxial thin films grown on sapphire substrates using the metal organic chemical vapor deposition (MOCVD) technique were found to depend on the substrates surface structure. The epitaxial Ti02 films grown on the sapphire (0001) substrates were highly-oriented poly-crystal and the films on the (1120) substrates were single crystal. First-principles total energy calculations were carried out to gain atomistic understandings of sapphire surface structures and their effects on microstructure of epitaxial films. The surface terminating atom planes were found to be Al atoms for the (0001) surface and O atoms for the (1120). The minimum step heights were found to be one sixth of the lattice constant c for the (0001) and one half of the lattice constant α for the (1120). The steps of the minimum height or its odd multiples on sapphire (0001) surface were shown to double the number of variants in the deposited films. The symmetry and step of the substrate surface and the symmetry of the epitaxial growth plane were found to control the microstructure of the epitaxial films.