Effect of substrate temperature on the nebulizer sprayed zinc oxide thin films

Abstract

Zinc oxide (ZnO) thin films deposited on glass substrates at various temperatures 300, 400 and 500 °C by the nebulizer spray pyrolysis technique. X-ray diffraction results indicate that the films are polycrystalline in nature having hexagonal crystal structure with preferred grain growth orientation along (002) plane. The crystallite size increases along (002) plane with temperature increase from 350 to 500 °C and attains a maximum 109 nm at 500 °C. High resolution scanning electron microscopy (HR-SEM) study shows the formation of good quality film on total substrate surface with uniformly distributed tiny spherical shaped grains at 350 °C. The UV–Vis–NIR spectroscopy confirms the possibility of good transparent ZnO thin films deposited with an average transmission of ∼85% in the visible region. Optical band gap energy increases from 3.19 to 3.27 eV with the substrate temperature 350–500 °C. The depression of NBE emission and DL emission of the films were estimated through PL measurements. As the substrate temperature increases, the peak of NBE emission is found to have a blue shift towards lower wavelength side and the same result is also found from the band gap energy determination of optical transmittance measurement. The complex impedance shows two distinguished semicircles and the diameter of the arcs got decreased in diameter as the temperature increases from 350 to 500 °C and thereafter slightly increased.