Synthesis of fluorine doped zinc oxide by reactive magnetron sputtering

Abstract ZnO and fluorine doped ZnO (FZO) thin films were prepared by d.c. reactive magnetron sputtering using a zinc target in an Ar/O 2 (/F 2 ) mixture. In a first attempt ZnO films were synthesized in order to optimize the matrix properties in terms of crystalline properties and transparency. The parameters studied were the d.c. power ( P dc ), the total pressure ( P Tot ) and the O 2 content in the discharge (%O 2 ). The highest grain size of ∼25 nm is obtained for P dc = 70 W, P Tot = 30 mtorr and %O 2 = 7.5%. F 2 was then introduced in the discharge. The influence of the presence of fluorine on the crystallographic, chemical, electrical and optical properties of the deposited films were evaluated. Our X-ray photoelectron spectroscopy and X-ray diffraction (XRD) data suggest that only a certain part of the measured fluorine atoms substitute for oxygen atoms in the ZnO structure. The rest of fluorine could be adsorbed as F 2 on the grain boundaries or located in interstices of the ZnO structure. XRD data reveal a decrease in the crystallite size with an increase in the fluorine content. Above a fluorine concentration of ∼2% the FZO films become amorphous. The electrical properties have been investigated by Hall effect measurements. The optimal synthesis conditions (∼2% of fluorine in the film) were a charge carrier density of ∼10 20 cm −3 , an electrical resistivity of 10 −2 Ω cm, and a charge mobility of 4 cm 2 V s −1 . Finally, all deposited FZO films had >80% transmission in the visible range.