Morphological and optical properties of vacuum evaporated ZnO thin films

ZnO thin films were deposited onto chemically and ultrasonically cleaned glass substrates by thermal evaporation in vacuum (\sim 10^{-6} mbar). The thickness of the films was measured by frequency shift of quartz crystal. The optical properties of the films have been ascertained by UV-VIS-NIR spectrophotometry in the photon wavelength range of 300--2500 nm. The effect of substrate temperature on the optical properties of the films has been investigated, where all film thickness was kept fixed at 100 \pm 10 nm. The optical transmittance spectra reveal a maximum transmittance of 88% at room temperature around photon wavelength of 2350 nm. Band gap and Urbach energy values of the films were calculated. The nature of the optical transition has been direct allowed. Surface topography studied by Atomic Force Microscopy (AFM) measurements showed a uniform film texture. The extent and nature of transmittance and optimized band gap of the material assure to utilize it for optoelectronic applications.