Pulsed laser deposited zinc oxide thin films for optical gas sensor applications

Zinc oxide thin films were grown by pulsed laser deposition technique. The ZnO targets were irradiated by an UV KrF* (λ=248 nm, τFWHM≈20 ns, v=2 Hz) excimer laser, at 2 J/cm2 incident fluence value. We used (001) SiO2 wafers as substrates, heated during the thin films grown process at temperature values within the range (150-500) °C. The experiments were performed in oxygen pressure at fixed values between 1 and 12 Pa. We investigated the effect of substrate temperature and oxygen presssure on the thin films morphology, crystalline status and optical properties. The thin films surface morphology was investigated by scanning electron microscopy and atomic force microscopy. The crystalline state and chemical composition of the films were investigated by X-ray diffractometry. The optical transmittance measurements were performed with a double beam spectrometer in the 300-1500 nm range. Our results show that the films deposited at oxygen pressure values higher than 10 Pa and substrate temperatures above 300 °C are c-axis oriented. Their average transmission in the visible-infrared spectral region is about 85%, and the corresponding refractive indexes and extinction coefficients are very close to those of the tabulated reference values.