Growth morphologies of heteroepitaxial rutile films on sapphire substrates

Abstract

The growth morphologies of (1 0 0), (1 0 1) and (0 0 1) rutile films grown on sapphire substrates by the ion-beam sputter deposition technique have been examined as a function of film/substrate orientation, film thickness, substrate surface preparation, growth rate and growth temperature. The rutile films of each orientation appear to grow via island (Volmer-Weber) type growth. At the early stages of growth ( ⩽100 A ̊ ) on as-polished substrates, the roughnesses of the films grown at 725°C and 3 Å/min are correlated to their lattice mismatches and inversely related to the calculated surface energies of their sapphire substrates. Thicker films ( ⩾ 700 A ̊ ) have morphologies which are orientation dependent, appear to minimize their surface energies and are stable with respect to annealing. Rougher and slightly less crystallographically aligned (1 0 0) and (0 0 1) rutile films result from the more three-dimensional growth found on annealed sapphire substrates. Relatively small increases in the growth rate, at very low rates, can change the details of the surface structures present. The changes in the morphologies observed on films grown at lower temperatures indicate that the processes controlling their development have a strong temperature dependence at all stages. Comparisons were also made between (1 0 0) and (1 0 1) rutile films grown by the ion-beam sputter deposition and metalorganic chemical vapor deposition techniques under similar conditions. The chemical vapor deposited films have morphologies which are similar to the ion-beam sputtered films with comparable thicknesses, but grown at lower temperatures.