Microstructure and Optoelectronic Properties of WZO/Al/Cu/Al/WZO Multilayer Films

By adjusting the Cu layer thickness, this study systematically investigated the evolution of the microstructure and optoelectronic properties of WZO/Al/Cu/Al/WZO multilayer films. The results indicated that all the films exhibited a ZnO phase with hexagonal wurtzite structure and a Cu phase with face-centered cubic structure, showing preferred orientations along the (002) and (111) planes, respectively. As the Cu layer thickness increased from 5 nm to 13 nm, its crystallinity was substantially improved, with the grain size gradually increasing from 4.7 nm to 12.4 nm. In contrast, the crystalline quality of ZnO first improved and then deteriorated, reaching an optimum at a Cu layer thickness of 7 nm. With increasing the Cu layer thickness, the visible light absorption loss was enhanced and then resulted in a gradual decrease in transmittance from 79.2% to 68.0%. Benefiting from the significant improvement in the crystallinity and continuity of the Cu layer, the resistivity sharply decreased from 1.7 × 10^-3 Ω·cm to 7.1 × 10^-5 Ω·cm and tended to saturate when the thickness exceeded 9 nm. As the Cu thickness increased to 11 nm, the figure of merit (F_OM) reached a maximum value of 4.4 × 10^-3 Ω^-1, demonstrating the optimal optoelectronic performance.