Growth of epitaxial pyrite (FeS₂) thin films using sequential evaporation

Pyrite (FeS₂), a semiconductor composed of inexpensive, non-toxic elements, has a band gap of ∼0.95 eV and an absorption coefficient higher than conventional direct band gap semiconductors, including GaAs. These facts have inspired the use of pyrite as a potential candidate for terawatt-scale photovoltaic systems. However, there has been limited progress synthesizing thin films of sufficient quality to produce efficient solar cells. Here we describe the layer-by-layer growth of stoichiometric, single-phase pyrite thin films on heated substrates using sequential evaporation of Fe under high vacuum followed by sulfidation at pressures ranging from 1 mTorr to 1 Torr. High-resolution transmission electron microscopy reveals high-quality, defect-free pyrite grains. We demonstrate that epitaxial pyrite layers can be deposited with this method on natural pyrite substrates.