EPITAXIAL-GROWTH OF (1 1 (2)OVER-BAR 0) ZNO ON (0 1 (1)OVER-BAR 2) AL2O3 BY METALORGANIC CHEMICAL-VAPOR-DEPOSITION

There has been increased interest in high quality ZnO films for use in a diverse range of applications such as in high frequency surface aco ustic wave filters, buffer layers for GaN growth, transparent and cond uctive electrodes, and solid state lasers. In the present paper, ZnO f ilms were epitaxially grown on R-plane sapphire substrates by metalorg anic chemical vapor deposition at temperatures in the range 350-450 de grees C. X-ray diffraction and electron microscopy results indicate th at the ZnO films are epitaxially grown on (0 1 (1) over bar 2) Al2O3 s urface with the (1 1 (2) over bar 0) plane parallel to the surface. Cr oss-sectional resolution-transmission electron microscopy imaging of t he as-grown film shows that the interface is semi-coherent and atomica lly sharp, with misfit dislocations relieving the misfit strain betwee n ZnO and sapphire. In order to check the thermal stability of the as- grown ZnO films, annealing in an O-2 + N-2 ambience at 850 degrees C f or 30 min was performed. The annealed films showed improved crystallin ity. At the same time, limited reaction between ZnO and sapphire occur red, resulting in the formation of a 15-20 nm thick spinel layer at th e interface.