Abstract

The electrical, optical and structural properties of Cobalt (Co) doped SnO₂ transparent semiconducting thin films, deposited by the spray pyrolysis technique, have been studied. The SnO₂:Co films, with different Co-content, were deposited on glass substrates using an aqueous–ethanol solution consisting of tin and cobalt chlorides. X-ray diffraction studies showed that the SnO₂:Co films were polycrystalline only with tin oxide phases and preferential orientations along (1 1 0) and (2 1 1) planes and grain sizes in the range 19–82 nm. Optical transmittance spectra of the films showed high transparency ∼75–90% in the visible region, decreasing with increase in Co-doping. The optical absorption edge for undoped SnO₂ films was found to be 3.76 eV, while for higher Co-doped films shifted toward higher energies (shorter wavelengths) in the range 3.76–4.04 eV and then slowly decreased again to 4.03 eV. A change in sign of the Hall voltage and Seebeck coefficient was observed for a specific acceptor dopant level ∼11.4 at% in film and interpreted as a conversion from n-type to p-type conductivity. The thermoelectric electro-motive force (e.m.f.) of the films was measured in the temperature range 300–500 K and Seebeck coefficients were found in the range from −62 to +499 μVK⁻¹ for various Co-doped SnO₂ films.