The growth of an epitaxial Mg-Al spinel layer on sapphire by solid-state reactions

In this work an epitaxial Mg-Al spinel layer was successfully grown on a sapphire single crystal surface by solid-state reactions. An Mg film (15 μm) was sputtered onto the sapphire crystal using RF magnetron sputtering. An epitaxial Mg-Al spinel layer was formed on the sapphire surface; an MgO layer was formed on top of the spinel layer by solid-state reactions that occurred around 1300-1600 °C, in an air atmosphere. When the reaction time was lengthened to over 30 h at 1600 °C, these layers were almost completely transformed into an epitaxial Mg-Al spinel layer. The thickness of the epitaxial layer could be controlled by the length of the reaction time and the temperature. The results of X-ray diffraction analysis indicate that the orientation of the MgO and the spinel growth was dependent on the plane of the sapphire, that is (0 0 0 1)sapphire||(1 1 1)spinel||(1 1 1)MgO and (1 1 2¯ 0)sapphire||(1 1 1)spinel||(1 1 1)MgO. It was confirmed that the in-plane orientation of the spinel with respect to the C- and A-sapphire surface was [1 1¯ 0 0]sapphire||[1¯ 1 0]spinel, [1 1 2¯ 0]sapphire||[1¯ 1¯ 2]spinel and [1 0 1¯ 0]sapphire||[1¯ 1 0]spinel, [0 0 0 1]sapphire||[1¯ 1¯ 2]spinel, and there would be (1¯ 1 0)-oriented spinel growth on the M-plane sapphire substrate.