Characterization of ZnO:Al/Au/ZnO:Al trilayers for high performance transparent conducting electrodes

Symmetric ZnO:Al/Au/ZnO:Al trilayers were sputter-deposited and characterized for transparent conducting electrodes, varying the thickness of the ZnO:Al (AZO) and Au layers. The optical transmission for normal light incidence is optimum for an AZO thickness of 50 nm, due to the suppression of reflection. In this case, the transmittance is more than 0.7 for wavelengths above 400 nm and for a Au thickness of 5 nm. At the same time, the sheet resistance is approx. 30 Ω, which can be decreased to 12 Ω with the increase of the Au thickness to 9 nm. This is achieved with a moderate loss in the optical transmission. The figure of merit for transparent conducting electrodes, as introduced by G. Haacke (J. Appl. Phys. 47 (1976) 4086) yields values from 29.4 × 10− 3 to 6.9 × 10− 3 Ω− 1, depending on the Au thickness and the considered wavelength range.