(20-23) ZnO thin films grown by pulsed laser deposition on CeO2-buffered r-sapphire substrate

Composite ZnO/CeO2 thin films were grown epitaxially on r-sapphire substrates using the pulsed laser deposition technique. Their crystalline properties were established using x-ray diffraction and showed the ZnO (wurtzite structure) and CeO2 (fluorite structure) layers to be highly textured with the (20-23) and (100) orientations, respectively. phi-scan measurements were also carried out and the (20-23)ZnO parallel to(100CeO(2)), [1-210]ZnO parallel to < 011 > CeO2 epitaxial relations established. The rocking curve profiles indicated that the ZnO films grew as four crystallographically equivalent domains. Series of rocking curve and chi-scan measurements at varying phi angles, respectively, were used to investigate the domain structure. These showed that the normal to the (20-23) plane in each domain is tilted away from the substrate normal towards one of the four equivalent CeO2 < 111 > directions by similar to 1.6(0). Atomic force microscopy measurements showed that the ZnO/CeO2 composite film has a granular microstructure with a rough surface (typical root mean square roughness of 7.9 nm). Low temperature photoluminescence spectra showed an intense near-band-edge emission at a photon energy of 3.361 eV, with a full width at half maximum of 1.8 meV, testifying to the good optical quality of the ZnO material. The optical transmission of the ZnO/CeO2 composite film was measured in the 200-1000 nm spectral domain; it was completely opaque to UV radiation and became transparent with a sharp transition above 380 nm. Secondary ion mass spectrometry measurements were used for depth profiling of the ZnO/CeO2 composite structure. The corresponding data suggest that the CeO2 buffer layer acts as an efficient barrier against the diffusion of aluminum from the sapphire substrate into the ZnO layer. (c) 2007 American Institute of Physics.