Electrical, optical and structural properties of transparent and conducting ZnO thin films doped with Al and F by rf magnetron sputter

Al and F-doped ZnO films of 200 nm thicknesses were prepared on glass substrates by co-sputtering ZnO targets composed of 2 wt.% Al₂ O₃, 1.3 wt.% ZnF and pure ZnO targets, respectively. After annealing in vacuum pressure of 10^-6 Torr at 300 °C for 2 h, the resistivity of ZnO films decreased down to 4.75 × 10^-4 Ω cm and ZnO film which composed of Al-doped ZnO 25% and F-doped ZnO 75% by volume fraction showed the highest mobility of 42.2 cm²/V s. From XRD measurements it was found that F dopants improved crystallization of ZnO films. Form XPS spectra of oxygen 1 s binding energy and Hall measurements it was confirmed that by vacuum annealing chemisorbed oxygens at the grain boundary desorbed and reduced grain boundary scattering. Also figure of merit (FOM) defined as ratio of electrical conductivity to optical absorption coefficient increased up to 2.67 Ω^-1 after post annealing.