Coherent island formation of Cu₂O films grown by chemical vapor deposition on MgO(110)

Cuprous oxide (Cu₂O) films have been grown on single-crystal MgO(110) substrates by a chemical vapor deposition process in the temperature range 690-790 °C. X-ray diffraction measurements show that phase-pure, highly oriented Cu₂O films form at these temperatures. The Cu₂O films are observed to grow by an island-formation mechanism on this substrate. Films grown at 690 °C uniformly coat the substrate except for micropores between grains. However, at a growth temperature of 790 °C, an isolated, three-dimensional island morphology develops. Using a transmission electron microscopy and atomic force microscope, both dome- and hut-shaped islands are observed and are shown to be coherent and epitaxial. The isolated, coherent islands form under high mobility growth conditions where geometric strain relaxation occurs before misfit dislocation can be introduced. This rare observation for oxides is attributed to the relatively weak bonding of Cu₂O, which also has a relatively low melting temperature.