Iron Pyrite Thin Films via Thermal Treatment of Chemically Deposited Precursor Films

We report on a method to deposit iron pyrite thin films via chemical bath deposition of Fe-O-S thin films followed by their thermal treatment in a sulfur-rich ambient. The deposition is made on glass substrates from an aqueous solution mixture of iron(III) nitrate, sodium thiosulfate, triethanolamine, and HCl added to adjust the pH between 7-8. After 2.5 h of deposition at 40 degrees C, a uniform specularly reflective amorphous film with thickness of 315 nm is obtained with a S:Fe ratio of 0.44 and significant oxygen content. Optical bandgap (E-g) of this material is 2.56 eV. Upon heating this film in a N-2/S ambient at 400 degrees C for 3-10 h, a dark-gray mirror-like film is obtained. The film attains a granular morphology and the S:Fe ratio approximates to 2. This thin film is polycrystalline with cubic structure, as that of FeS2-pyrite phase, with crystallite diameter of 15 nm. Orthorhombic FeS2-marcasite is present as a minor phase in the film. The film possesses optical absorption coefficient 2 x 10(5) cm(-1) in the visible region; indirect E-g of 0.85 eV; p-type electrical conductivity of 1.2-2.1 Omega(-1) cm(-1) showing photoconductivity; carrier density, 3 x 10(17) cm(-3); and Hall mobility, 14 cm(2) V-1 s(-1). (C) 2013 The Electrochemical Society. All rights reserved.