Self limiting deposition of pyrite absorbers by pulsed PECVD

Self-limiting growth of pyrite thin films was accomplished by pulsed plasma-enhanced chemical vapor deposition (PECVD) with continuous delivery of iron pentacarbonyl diluted in a mixture of H₂S and argon. The growth rate per cycle was controlled between 0.1 and 1 Å/pulse by adjusting the duty cycle and/or plasma power. The onset of thermal chemical vapor deposition was identified at ∼300  °C, and this process resulted in films containing substoichiometric pyrrhotite. In contrast, pulsed PECVD produced stoichiometric FeS₂ films without the need for postdeposition sulfurization. Films contained a mixture of pyrite and marcasite, though the latter could be attenuated using a combination of high duty cycle, low temperature, and low plasma power. Pulsed PECVD films displayed similar optical properties with a band gap of ∼1 eV and an absorption coefficient of ∼10⁵ cm⁻¹, regardless of the pyrite:marcasite ratio.