Plasma-driven growth mechanisms of ZnO:Cu sputtered Films: Emission spectroscopy insights

Abstract

This study provides significant insights into the growth mechanisms and optical properties of copper-doped ZnO films sputtered in an oxygen-argon plasma environment. Using optical emission spectroscopy, we demonstrated the critical influence of gas composition on the emission characteristics, particularly the variations in the intensity of transition lines associated with Ar, O, Zn, and Cu species. Our findings indicate that increasing the concentration of active oxygen species enhances reaction rates and promotes more effective oxidation, which are crucial for improving film quality. However, this improvement is counteracted by a diminishing concentration of argon, which reduces the density of metal species available for deposition. The analysis reveals that there exists an optimal flux ratio that maximizes film growth and crystallinity; beyond this point, excessive Cu incorporation disrupts the ZnO lattice, leading to a decline in crystalline quality. Additionally, the films exhibit high transmittance (>85 %) at low Cu concentrations, whereas higher Cu content decreases transparency and narrows the optical band gap. The findings suggest that minimal Cu doping has negligible impact on transparency, while higher doping levels significantly alter the optical properties, reflecting the complex interplay between Cu and ZnO within the crystal structure. Finally, this research enhances the understanding of the deposition process and offers pathways for optimizing the optical and structural properties of ZnO:Cu films for advanced technological applications.