Polarization properties of nonpolar ZnO films grown on R-sapphire substrates using high-temperature H2O generated by a catalytic reaction

Nonpolar ZnO films were grown on r-plane sapphire substrates through the reaction between dimethylzinc (DMZn) and high-temperature H2O, the latter produced by the Pt-catalyzed reaction between H2 and O2. The resulting ZnO films were characterized using atomic force microscopy, X-ray diffraction, and photoluminescence (PL) measurements. They were found to have an anisotropic surface morphology with stripe arrays, and exhibited a diffraction peak associated with ZnO (11-20) index planes. The PL spectra indicated anisotropy in polarization between the directions parallel and perpendicular to the c-axis. The band-edge luminescence at 3.3 eV exhibited a maximum when the electric field vector E was perpendicular to the c-axis (parallel to the [1-100] direction) and another minimum when E was parallel to the c-axis. The angular dependence of the linear polarization of the band-edge luminescence was large for ZnO films grown at low temperatures. The large degree of polarization observed for low-temperature growth is thought to be due to the film geometry.