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

ABSTRACT Iron pyrite (FeS 2 ) 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 FeS 2 , 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 FeS 2 thin films. Phase‐pure FeS 2 thin film is deposited on glass substrates via single‐step co‐sputtering using FeS 2 and S 8 targets at 430°C substrate temperature. The resulting films exhibit p ‐type conductivity with a carrier concentration and mobility of 4.18 × 10 19 cm −3 and 5.06 cm 2 V −1 s −1 respectively. Controlled oxygen incorporation is achieved through negative ion implantation at fluences ranging from 9 × 10 14 to 1 × 10 16 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 FeS 2 thin films with high hole concentration and offer a strategy for optimizing the optoelectronic properties for advanced semiconductor applications.