Growth of ZnO thin films on c-plane Al2O3 by molecular beam epitaxy using ozone as an oxygen source

The growth of c-axis oriented ZnO thin films on c-plane Al2O3 via molecular beam epitaxy (MBE) using dilute ozone (O3) as an oxygen source was investigated. Four-circle X-ray diffraction (XRD) indicates that films grown at 350 °C are epitaxial with respect to the substrate, but with a broad in-plane and out-of-plane mosaic. The films were highly conductive and n-type. Epitaxial film growth required relatively high Zn flux and O3/O2 pressure. The growth rate decreased rapidly as growth temperature was increased above 350 °C. The drop in growth rate with temperature reflects the low sticking coefficient of Zn at moderately high temperatures and limited ozone flux for the oxidation of the Zn metal. Characterization of the films included atomic force microscopy (AFM), X-ray diffraction, photoluminescence, and Hall measurements. These results show that molecular beam epitaxy of ZnO using ozone is rate limited by the ozone flux for growth temperatures above 350 °C.