High resolution X-ray diffraction mapping studies on the domain structure of LaAlO 3 single crystal substrates and its influence on SrTiO 3 film growth

Abstract

High resolution X-ray diffraction mapping studies have been done on 001-oriented LaAlO 3 substrates and epitaxial 001-oriented SrTiO 3 thin films grown on the LaAlO 3. Using high resolution ω-ω 2θ reciprocal space mapping over the 002 peak, the lattice constant of LaAlO 3 could be accurately determined; however, it was not possible to determine the small splitting of the 002 peak due to the different twin domains. This is due to the poor resolution, inherent from the diffractometer design, for planes perpendicular to the diffraction plane. The pole plot method also makes use of the resolution perpendicular to the diffraction plane and will therefore not resolve the domain either. However, ω-ø mapping has been successfully used to resolve the domain distribution and angles between the domains since it scans the diffraction space in a plane parallel to the sample surface and it has high resolution along the ω direction. It was found that the LaAlO 3 usually contains four domains with four-fold twinning symmetry. The angular separations of the domains were 0.177°, 0.177° and 0.253°. Annealing the sample showed to have a detwinning effect sometimes resulting in a single domain sample. To investigate the influence of the domain structure on the growth of SrTiO 3 films, two kinds of films were studied. For stoichiometric SrTiO 3 film the domain structure of the substrate was exactly copied into the film as revealed by the ω-ω 2θ map and ω-ø maps. On the other hand Sr-deficient film exhibited a large degree of mosaicity and the resulting peak broadening overwhelmed the splitting due to domains.