Microstructure and optical absorption of FeS2 films formed by sulfurizing precursive iron of various crystallite scales

Precursive iron films with various crystallite scales were prepared by sputtering on substrates heated at different temperatures. The iron films were annealed in sulfur vapor at 673 K to form pyrite films. The structural and optical characters were determined. High substrate temperatures produce large crystallites in the precursive iron films. The pyrite films are composed of a surface layer with coarse columnar grains and a bottom layer with fine equiaxed grains. Sufficient formation and growth of iron grains result in improved crystallinity of the pyrite films. The optical absorption characteristics depend mainly on the crystallinity of the pyrite films or the crystallizing status of the precursive iron films. The optical absorption coefficient of the pyrite films decreases with the increase of iron grain diameter from 12 to 39 nm. The band gap of the pyrite films increases with the increase of iron grain diameter from 12 to 53 nm.