Investigation of AlF3 doped ZnO thin films prepared by RF magnetron sputtering

Transparent conducting ZnO thin films co-doped with aluminium and fluorine (AZO:F) were produced on glass substrates by RF magnetron sputtering at room temperature. The chemical AlF3 was selected as a dopant, which allowed Al and F elements to be simultaneously substituted into sub-lattices sites of Zn and O, respectively. The microstructure, electrical and optical properties of ZnO thin films as a function of AlF3 concentration were evaluated and compared to the films doped with Al2O3. From XRD analysis, it was revealed that the favoured orientation of ZnO films shifted from (0 0 2) to (1 0 3) as the amount of AlF3 increased from 1 to 7 wt%. The film doped with 2 wt% AlF3 showed improved crystallinity and a microstructure with larger, pyramid-like grains that were 120 nm long and 50 nm wide. As a result, the electrical resistivity of the AZO:F films had a minimum of 5.2 x 10(-4) Omega, cm. The improvement in the electrical resistivity of AZO:F films was due to the increase in carrier concentration from 7.0 x 10(20) to 1.25 x 10(21) cm(-3) and the mobility from 4.7 to 9.3 cm(2) V-1 s(-1). Meanwhile, the electrical resistivity of the ZnO film doped with AlF3 was found to be lower than that of the Al2O3-doped film. This was mainly attributed to the increase in carrier concentration by substituting Al and F atoms into the Zn and O sub-lattice sites, respectively, despite the slight decrease in the mobility. This increase in carrier concentration was also found to affect the optical property of the films due to the Moss-Burstein shift. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.