Epitaxial growth of aluminium-doped zinc oxide films by magnetron sputtering on (001), (110), and (012) oriented sapphire substrates

Highly aluminium-doped zinc oxide (ZnO) films have been grown on differently oriented sapphire substrates by magnetron sputtering from an oxidic target. Rocking curve measurements, Rutherford backscattering analysis and transmission electron microscopy show that the films exhibit a disturbed film growth. However, despite the large nominal lattice mismatch between ZnO and sapphire (-31%), the films grow epitaxially on every sapphire orientation, even at room temperature. This was proven by pole figure analysis. The reason that epitaxial growth can be observed is an incommensurate lattice fitting between ZnO and sapphire by a mutual rotational alignment of their lattices. Films of the best crystallographic quality have been grown on (110)-oriented sapphire, which is also reflected by the highest Hall mobility in these layers.