The growth of MgO buffer layers on sapphire for the epitaxy of BaTiO3 optical thin films

BaTiO3 waveguides have been fabricated on r-cut sapphire single crystals us ing an epitaxial MgO(100) buffer layer. Both films were prepared by pulsed laser deposition (PLD). MgO was grown between 450 and 890 degreesC, and BaT iO3 was deposited at 1000-1050 degreesC. The films were investigated by mea ns of X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) , ion channeling (RBS/C), transmission electron microscopy and atomic force microscopy. These techniques revealed that the best epitaxial MgO(100) lay ers were those grown between 750 and 830 degreesC and at 2 X 10(-3) mbar of oxygen pressure. The films were characterized by a full width at half maxi mum of less than 0.5 degrees in the XRD rocking curves (Delta omega) of the MgO(200) reflection, a minimum RBS/C yield (chi (min)) of similar to5% and a root-mean-square (rms) roughness of 1.7 nm. The BaTiO3 films grown onto this buffer layers displayed similar properties: a Delta omega [BaTiO3(200) ] of approximately 0.7 degrees, a chi (min) of 4-5%, and a rms roughness of approximately 1.0 nm for a film of 440-nm thickness. The epitaxial relatio nship was found to be [BaTiO3(100)//MgO(100)] similar to //Al2O3(1102). (C) 2001 Elsevier Science B.V. All rights reserved.