Carbon Ion Implantation Effects on Morphology, Bandgap, and Urbach Tailing in ZnO Thin Films

Zinc oxide (ZnO) is a wide-bandgap semiconductor with diverse applications in optoelectronics and sensing. In this study, we examine how 20 keV C+ ion implantation affects the morphology and optical properties of ZnO thin films. Using atomic force microscopy and ultraviolet-visible spectroscopy, we observe that ion implantation leads to a reduction in grain size, increased morphological disorder, and a fluence-dependent increase in both the optical bandgap and Urbach energy. Simulations using the Transport of Ions in Matter code indicate that implanted ions penetrate the ZnO layer to an average depth of around 41 nm, generating near-surface structural damage. Post-implantation annealing at 500°C partially restores the optical properties, indicating some level of defect recovery. These findings demonstrate that low-energy carbon ion implantation enables controlled tuning of the properties of ZnO thin film without structural degradation.