Negative Ion Implantation Enabled Controlled Oxygen Doping in Iron Pyrite Thin Films

Iron pyrite (FeS2) is a promising material for next‐generation photovoltaic and optoelectronic applications. However, the origin of p‐type conductivity in thin films, unlike the n‐type behavior of bulk FeS2, remains unknown and is often attributed to unintentional impurity incorporation, particularly oxygen. This study explores the role of oxygen in tuning the electrical and optical properties of FeS2 thin films. Phase‐pure FeS2 thin film is deposited on glass substrates via single‐step co‐sputtering using FeS2 and S8 targets at 430°C substrate temperature. The resulting films exhibit p‐type conductivity with a carrier concentration and mobility of 4.18 × 1019 cm−3 and 5.06 cm2 V−1 s−1 respectively. Controlled oxygen incorporation is achieved through negative ion implantation at fluences ranging from 9 × 1014 to 1 × 1016 ions cm−2. X‐ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry confirm successful oxygen doping, with oxygen atoms preferentially occupying sulfur vacancies for higher doses. This incorporation enhances p‐type conductivity and induces direct bandgap widening up to 1.48 eV. The results demonstrate a pathway to fabricate FeS2 thin films with high hole concentration and offer a strategy for optimizing the optoelectronic properties for advanced semiconductor applications.