Ion beam engineered band bending and photodetection in WO₃ thin films

Tailoring the functional properties of metal oxide semiconductors through controlled defect engineering is central to advancing next-generation optoelectronic and catalytic devices. In this study, the influence of 0.5 MeV Ar²⁺ ion irradiation on the structural, optical, electrical, and photocatalytic behaviour of sputter-deposited WO₃ thin films was systematically investigated. The films, annealed in air and subjected to varying ion fluences, were characterized using a suite of techniques XRD confirmed the preservation of the WO₃ phase while revealing subtle lattice modifications induced by ion bombardment. Although SEM images showed minimal morphological changes, EDAX analysis indicated significant variations in W:O atomic ratios, pointing to irradiation-driven stoichiometric shifts. Optical and electrical characterizations revealed clear fluence-dependent modulations, including bandgap narrowing and enhanced charge carrier density. Notably, photodetection measurements demonstrated a marked improvement in photoresponse and the noteworthy photocurrent polarity changes in irradiated films compared to their pristine counterpart. These observations are attributed to the introduction of oxygen vacancies and controlled surface hydroxylation, as confirmed by XPS and PL, which collectively modify band alignment and engineer the charge separation capabilities. Overall, this post-irradiation analysis establishes ion fluence as a powerful parameter to fine-tune the defect landscape and electronic structure of WO₃ thin films, paving the way for their application in high-performance optoelectronic and photocatalytic systems.