Synthesis of pyrite (FeS₂) thin films by low pressure metal-organic chemical vapor deposition

Abstract
Thin films of iron disulfide have been prepared by Low-Pressure Chernical Vapor Deposition (LPCVD) from iron(III)acetylacetonate (Fe(acac)₃), tert-butyl disulfide (TBDS), and hydrogen. The influence of the relevant CVD parameters on the growth rate, chemical composition (stoichiometry), morphology, crystalline phases, and contaminants have been examined. Pyrite thin films with a uniformity variation of less than 5% over a length of 10 centimeters are obtained in a hot wall LPCVD reactor. We are able to deposit these films without detectable iron sulfide (FeS) phases at temperatures from 300 °C up to 340 °C on glass, titanium dioxide, and silicon. Growth rates vary between 0.2 and 12 nm/min. In all cases, the films are polycrystalline pyrite with an indirect band gap of 0.95 ± 0.05 eV, a direct band gap between 1.4 and 1.5 eV, and a dark specific resistance of 0.5 - 1.0 Ωcm. The absorption coefficient of the films is 3± 1 x 10⁵ at λ = 500 nm. The Seebeck coefficient is between 30 and 70 µVK^-1 and is always positive which indicates p- type conductivity.