Uniaxial locked epitaxy of ZnO on the a face of sapphire

High-quality, c-oriented ZnO epitaxial films have been grown on the a surface using molecular-beam epitaxy. The use of a-oriented sapphire eliminates rotational domains and related structural defects which have limited the use of ZnO in electronic applications. The ZnO epitaxial layers are uniquely oriented with the ZnO/sapphire orientational relationship [0001]parallel to[11 (2) over bar 0] and [11 (2) over bar 0]parallel to[0001]. This unique orientation is a consequence of the anisotropy of the a-sapphire surface in conjunction with a strong correlation along a single direction leading to the term uniaxial locked epitaxy. High-resolution x-ray diffraction measurements show an increase in x-ray lateral coherence length from several tens of nanometers to > 0.7 mu m for growth of c-oriented ZnO on the a surface as opposed to the c surface of sapphire. (C) 2000 American Institute of Physics. [S0003-6951(00)03938-3].