Low temperature synthesis of Al doped ZnO thin films by facing target sputtering

Abstract In this work, aluminum doped zinc oxide (AZO) thin films were synthesized at room temperature on PET substrates by using two different types of magnetron sputtering sources at the same time; deposited from two facing ZnO targets in a confined magnetic field, and co-doped from an Al target located outside of this region. The purpose of this system was not only to retain the advantages of the FTS system but also to propose a new type of doping concept. With this configuration, it was expected to get more flexibility for the tuning of Al concentration by controlling the external doping source. For the first, the gas mixture effect on the film properties was studied. In order to get a high quality crystallographic structure for acquiring high mobility, we controlled Ar working pressure, O 2 partial pressure, and H 2 partial pressure in sequence. After deposition, structural, electrical, optical, and surface morphological characteristics were examined. As a result, we could optimize the gas mixture condition including 2.5 mTorr of Ar, 1.2 sccm of O 2 partial pressure, and 3 sccm of H 2 partial pressure. Secondly, Al doping concentration was controlled by changing the external Al target power density. Moderate carrier concentration could be secured by tuning the Al doping. Also, it was deduced that doping reaction might be increased by the Al particles which had moderate energy. As a result, we could deduce the optimized Al power density as 15 W/cm 2 . Under our optimized condition, AZO films could have good electrical and optical properties with a minimum resistivity of 5.344 × 10 − 4 Ωcm and a maximum transmittance of 90.2%. At the end, TCO performance was derived (13.4 mΩ − 1 ) and this value was found to be valuable compared to other authors' latest works and commercial ITO.