Structural, Electrical, and Optical Properties of Al–Mg Co-Doped ZnO Thin Films

Al–Mg co-doped ZnO thin films were fabricated by a sol–gel spin-coating process to investigate the effect of dopant ratio on their structural, electrical, and optical properties. The total dopant concentration was fixed at 3 mol%, while the Al-to-Mg ratio was systematically varied in AlₓMg₀.₀₃₋ₓZn₀.₉₇O (0 ≤ x ≤ 0.03). X-ray diffraction analysis showed that the films maintained a hexagonal wurtzite structure with a preferred (002) orientation up to an Al concentration of 1.5 mol%, whereas higher Al contents resulted in a degradation of crystallinity due to exceeding the solid solubility limit of Al in the ZnO lattice. Hall effect measurements revealed a decrease in carrier mobility with increasing Al content, attributed to enhanced ionized impurity scattering, while the carrier concentration and electrical conductivity reached optimal values at an Al–Mg co-doping ratio of 1.5 mol%–1.5 mol%. All films exhibited high optical transmittance in the visible region, with the highest average transmittance of approximately 83% observed at the same composition. These results demonstrate that controlling the Al/Mg dopant ratio is crucial for optimizing the performance of ZnO-based transparent conducting oxide thin films.