The effect of post-deposition annealing on the optical properties of filtered vacuum arc deposited ZnO-SnO2

Cetinorgu E., Goldsmith S., Boxman R. L.

JOURNAL OF PHYSICS-CONDENSED MATTER, vol.19, no.25, 2007 (SCI-Expanded) identifier identifier


Zinc stannate (ZnO-SnO2) thin films were deposited on ultraviolet fused silica (UVFS) substrates using filtered vacuum arc deposition (FVAD). During deposition, the substrates were at 200 and 400 degrees C. As-deposited films were annealed at 500 and 600 degrees C in Ar for 50 min. The structure was determined before and after annealing using x-ray diffraction (XRD). The XRD patterns of all ZnO-SnO2 thin films had an amorphous structure. The average optical transmission of the film in the visible spectrum was > 80% and was affected by annealing. The films' optical constants in the 250-989 nm wavelength range were determined by variable angle spectroscopic ellipsometry (VASE). The refractive indexes of as-deposited and annealed films were in the ranges 1.95-2.35 and 2.0-2.32, respectively. The extinction coefficients of as-deposited annealed films were in the same range, approximately 0-0.5. However, in the UV range (< 450 nm) the extinction coefficient values decreased significantly for annealed films. The optical energy band gap (Eg) was determined by the dependence of the absorption coefficient on the photon energy at short wavelengths. It varied between 3.65 and 3.72 eV for annealed films as a function of deposition pressure. Although the lowest electrical resistivity of zinc stannate films obtained for as-deposited films on 400 degrees C heated substrates, using 0.93 Pa oxygen pressure, was 1.08 x 10(-2) Omega cm, highly resistive films (> 10(5) Omega cm) were obtained by annealing.