Tailoring Electro-Optical Properties of ZnO/Ag/ZnO Multilayers by Low-Energy Carbon Ion Implantation

This study explores defect-mediated tuning of electro-optical properties in ZnO/Ag/ZnO (ZAZ) oxide/metal/oxide multilayer thin films via low-energy (100 keV) carbon ion implantation. The multilayers (35 nm/10 nm/35 nm) were deposited on glass substrates using RF magnetron sputtering at room temperature, followed by implantation at fluences ranging from 1×10¹³ to 1×10¹⁶ ions/cm². SRIM/TRIM simulations, incorporating the full multilayer architecture, reveal a projected ion range of ~39.4 nm with significant lateral (~88.3 nm) and radial (~119 nm) straggling, indicating that collision cascades span the entire structure. Energy loss analysis shows dominant electronic stopping (~81%) with a smaller nuclear stopping contribution (~19%) responsible for displacement damage. The simulated defect profile exhibits a broad depth distribution, with an average of ~151.7 vacancies generated per ion, leading to increased dislocation density. Structural characterization confirms retention of the wurtzite ZnO phase with strong (002) orientation, while X-ray photoelectron spectroscopy indicates modification of oxygen-related defect states. Electrical measurements demonstrate a non-monotonic response: moderate implantation improves charge transport, reducing sheet resistance from 27.48 Ω/□ (pristine) to 13.44 Ω/□ at 1×10¹⁵ ions/cm² and enhances Hall mobility to 12.28 cm²V⁻¹s⁻¹. At higher fluences, excessive defect accumulation increases carrier scattering, degrading performance and indicating a defect-density threshold. Optical analysis shows visible transmittance of ~73–77%, highlighting the trade-off between transparency and conductivity. Overall, the results establish ion implantation as an effective post-deposition strategy for controlled defect engineering in transparent conducting multilayer films.