Strain state, microstructure and electrical transport properties of LaNiO3 films grown on Si substrates

LaNiO3 films with various thicknesses were deposited on Si substrates by sputtering. The film thickness dependent strain state, microstructure and electrical properties were investigated. X-ray diffraction analysis shows that the films are generally strained with larger lattice constants than the value for bulk LaNiO3, due to a large difference in thermal expansion coefficients between LaNiO3 and Si. However, with increasing film thickness, the internal strain is gradually relaxed with the lattice constant decreased and the crystallinity and electrical properties improved as well. The film thickness dependent resistivity can be quantitatively described by a combined Fuchs-Sondheimer and Mayadas-Shatzkes model, including both the grain boundary scattering and the surface scattering. Further low temperature resistivity measurement shows that the film of 600 nm is semiconducting. The higher activation energy acquired by the small polaron conduction fitting than by the Arrhenius fitting indicates relatively large effective masses for the polarons in the film.