Crystal chemistry of epitaxial ZnO on (111) MgAl2O4 produced by hydrothermal synthesis

ZnO powders and epitaxial thin films were synthesized hydrothermally in aqueous solutions of zinc nitrate and ammonia at 150degreesC. Powder yield and particle size varied with changes in pH from 7 to 10.5. The films grew with a c-axis orientation on (1 1 1) MgAl2O4 substrates, with an out-of-plane orientation given by (1 1 1)(s)parallel to(0 0 0 1)(Zn), and an in-plane orientation given by (1 1 2)(s)parallel to(1 1 2 0)(Zn). Based on etching studies, the polarity of the films was determined to be zinc faced (0 0 0 1). The in-plane orientation relation corresponds to a 30degrees rotation of the close packed oxygen directions of the two respective structures. This rotation produces periodic, tetrahedrally coordinated Zn sites at the spinel/ZnO interface and facilitates the epitaxy of ZnO with only a small lattice strain. The crystal chemistry of the interfacial atomic layer that lies between the spinel and wurtzite is discussed in relation to cation coordination and charge balance. (C) 2003 Elsevier B.V. All rights reserved.