Transformation of amorphous iron oxide films pre-deposited by spray pyrolysis into FeS2-pyrite films

Amorphous iron oxide films were prepared by spray pyrolysis of FeCl3·6H2O (0.03 M)-based aqueous solution onto glass substrates heated at 350 °C. Rust red iron oxide films were obtained. Crystallized iron oxide films were achieved after heat treatments in vacuum. X-ray diffraction (XRD) patterns show two polycrystalline iron oxide phases. The dominant phase corresponds to Fe2O3 and the minor one corresponds to traces of FeOOH, which transforms immediately to Fe2O3 after further heat treatment. Scanning electron microscopy (SEM) microanalyses show that stoichiometric Fe2O3 films were obtained. Sulphuration at 450°C for 6 h under vacuum (10−4 Torr) transforms the amorphous iron oxide films into FeS2-pyrite films having good crystallinity. SEM images show that the FeS2 films are granular. The homogeneity and both dimension and distribution of the FeS2 grain sizes were found to depend on the sulphuration temperature of the pre-deposited amorphous iron oxide films. First optical analyses enabled us to deduce a direct energy band gap of about 0.72 eV. All the prepared FeS2 films show p-type conduction.