High transparent conductive Mg, Al, and Ga co-doped ZnO multilayer thin films with Cu interlayer: fabrication, structure, and characteristics.

Overcoming the challenge of preparing high-transparency and low-resistivity thin films is of great significance for the development of indium-free transparent electrodes. In the present work, high-quality Mg, Al, and Ga co-doped ZnO (MAGZO)/Cu/MAGZO multilayer thin films are deposited on glass by magnetron sputtering. The effects of Cu layer thickness (d _Cu) on the structural, morphological, optical, and electrical characteristics of the films are investigated in detail. With increasing d _Cu from 0 to 25 nm, the growth orientation of (002) ZnO crystal weakens, while that of (111) Cu crystal strengthens, and the surface of the films exhibits uniform, low roughness, and defect-free characteristics. Additionally, both the resistivity and the optical transmittance generally decrease with increasing Cu layer thickness. Interestingly, the average visible transmittance has a reverse change as d _Cu increases from 5 to 11 nm, resulting in the optimal photoelectric performance of the multilayers at d _Cu= 11 nm: the figure of merit of 9.42 × 10^-3 Ω^-1 with the resistivity of 1.24 × 10^-4 Ω cm and the visible transmittance of 84.2%. Compared with other reported sandwich transparent conductive films, it is found that doping Mg in the oxide layer is the key to improving the overall optoelectronic properties of the multilayers.