Effects of the deposition temperature on the transport property, chemical composition and conduction band structure of CaRuO3-δ thin films directly grown on Si (100) substrates

Abstract

The transport properties, chemical composition and energy band structure of directly integrated CaRuO3−δ thin films on a Si substrate were investigated by resistance–temperature (R–T) measurement, x-ray photoelectron spectroscopy (XPS) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy of oxygen K-edge. At high deposition temperatures, the metallic characteristic of CaRuO3−δ thin film is susceptible, with a clear preference for (1 1 0) crystallite formation, which induces delocalized charge carrier migration. At low deposition temperatures, CaRuO3−δ thin film takes on semiconductor behaviour responsible for current path localization causing weakening of Ru 4d-O 2p-Ca 3d orbital overlapping due to the imperfect crystalline growth. Even though there was different crystallite formation according to deposition temperature, the relative compositional difference of each element was negligible, which was supported by XPS and wavelength dispersive x-ray spectroscopy (WDXS) analysis. Thus, the change in conductivity from semiconducting to metallic is caused by the fine crystallite nature of CaRuO3−δ at low deposition temperature which induces charge carrier localization by utilizing the incorporation of Ca–O bonding weakening, reducing the conduction energy bandwidth W and expansion of the local conduction energy band separation Δ.