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.

1. Introduction 
2. Experimental Section 
    2.1 Materials and Precursor Solution Preparation 
    2.2 Thin Film Deposition and Heat Treatment 
    2.3. Film Characterization 
3. Results and Discussion 
    3.1 Structural Characteristics of Al-Mg Co-Doped ZnO Thin Films 
    3.2 Electrical Transport Properties of Al-Mg Co-Doped ZnO Thin Films 
    3.3 Optical Transmittance Characteristics of Al-Mg Co-Doped ZnO Thin Films 
    3.4 Film Morphology and Thickness Optimization 
4. Conclusion 
Funding
Conflict of Interest 
Data Availability Statement 
Author Information and Contribution 
Acknowledgments
References

• Jong-Mu Kim(Department of Materials Science and Engineering, Hongik University, Sejong 30016, Republic of Korea)
• Jun-Seo Park(Department of Materials Science and Engineering, Hongik University, Sejong 30016, Republic of Korea)
• Jun-Ha Lee(Department of Materials Science and Engineering, Hongik University, Sejong 30016, Republic of Korea)
• Min-Woo Kim(Department of Materials Science and Engineering, Hongik University, Sejong 30016, Republic of Korea)
• Jung-Woo Lee(Department of Materials Science and Engineering, Hongik University, Sejong 30016, Republic of Korea) Corresponding author