Yttria-stabilized zirconia buffered silicon to optimize in-plane electrical conductivity of [Ca2CoO3]0.62[CoO2] thin films

The monolithic integration of thermoelectric generators and magnetoresistive functionality on the basis of misfit cobaltate [Ca2CoO3](0.62)[CoO2] thin films into silicon technology is a prerequisite for their application in miniaturized electric circuits. Here, we report on [Ca2CoO3](0.62)[CoO2] thin films grown by pulsed laser deposition on (001)-silicon with a thin epitaxial yttria-stabilized zirconia (YSZ) buffer layer. X-ray diffraction and cross-sectional high resolution transmission electron microscopy analysis reveal that high quality c-axis oriented heteroepitaxial [Ca2CoO3](0.62)[CoO2] films with a 12-fold in-plane rotational symmetry can be grown, which exhibit remarkable lower electrical resistivity compared to those with random in-plane orientation. This result is explained by energetically preferred epitaxial growth directions of the pseudo hexagonal [CoO2] sublayer in monoclinic [Ca2CoO3](0.62)[CoO2] onto the cubic (001)-YSZ surface leading to a highly symmetric in-plane mutual orientation of the charge transporting CoO2 sublayer domains. (C) 2014 AIP Publishing LLC.