Optical properties of transparent ZnO-SnO2 thin films deposited by filtered vacuum arc

ZnO-SnO2 films were deposited onto glass substrates by filtered vacuum arc deposition. The source was equipped with a 70 at% Zn and 30 at% Sn cathode that was the source of Zn and Sri ion beam. Arc current was 200-300 A. The oxygen background pressure was 4-8 mTorr. The deposition time was 60 or 120 s, resulting in film thickness in the range 100-900 nm. The maximum deposition rate was 7.6 nm s(-1). All films were found to be amorphous. The transmission of the film in the VIS was 80%-90%, affected by interference. The refractive index and the extinction coefficient were determined from the measured optical transmission in the range 300-1100 nm by fitting a theoretically calculated film transmission to the measured one, using a single oscillator model. The values of n and k were determined from spectroscopic ellipsometry data and were in the ranges 2.38-1.97 and 0.24-0.013, respectively, depending on wavelengths and deposition parameters. The optical band gap (E-g) was determined by the dependence of the absorption coefficient on the photon energy at short wavelengths. Its values were in the range 3.5-3.62 eV, depending on the deposition conditions.