Highly conducting and transparent low-E window films with high figure of merit values based on RF sputtered Al and In co-doped ZnO

In this work, we have studied the correlation between the electrical, optical and plasma properties of RF sputtered 1 at.% Al and In co-doped ZnO (AIZO) thin films with thickness 210–1590 nm in a comprehensive manner. The lattice strain of the hexagonal wurtzite ZnO structure decreases as the film thickness increases. The lowest resistivity of 8.9 × 10⁻⁴ Ω-cm is obtained for the 930 nm thick film with an electron concentration and mobility values of 3.96 × 10²⁰ cm⁻³ and 17.7 cm²/Vs respectively. Optical transmission value is ~85%–90% in the range 400–700 nm for all the films. Most notably the figure of merit value of 2.65 × 10⁻² Ω⁻¹ for the 930 nm thick film is the highest among all the reports on AIZO films till date. High transparency in the visible region as well as higher reflectivity in the NIR region (with a plasma frequency of 8.2 × 10¹⁴ Hz) indicates its promising application in the low-E window.