Effect of Zn Film Substrate Temperature on Optical, Structural and Vibrational Characteristics of Thermally Oxidized Zn Films

Abstract

This study presents the effect of metallic Zn film substrate temperature on the optical, morphological and structural properties of thermally oxidized Zn films. Materials and Methods: Zinc oxide (ZnO) thin films were synthesised by thermal oxidation at 400°C of metallic zinc thin films deposited by vacuum thermal evaporation onto glass substrate at different substrate temperatures of room temperature 100 and 150°C. Results: The ZnO films show significant modification in morphology with different nanostructures at different Zn film precursor substrate temperature. The stoichiometric ratio between Zn and O atoms of the ZnO films synthesised at room temperature and 100°C metallic Zn films precursor substrate temperature had a large deviation from the ideal ratio of 1:1 and was closer to ideal at a Zn film precursor substrate temperature of 150°C giving ZnO0.94. All the films exhibited preferred (011) orientation of wurtzite structure, with presence of Zn peaks that diminishes with increasing metallic Zn substrate temperature. The films had optical transmittance of 64-71% in the visible region with the transmission edge becoming sharper and the optical band gap improving from 2.35-3.30 eV with increase in substrate temperature. The characteristic wurtzite ZnO Raman peaks of E2low are observed at 106 cm–1 for 2 E the three samples showing a blue shift. The XRD and Raman analysis indicates identical crystal structures irrespective of Zn film precursor substrate temperature. Conclusion: The precursor Zn film substrate temperature show significant effect on morphology, nanostructure shape and stoichiometry of the ZnO films. The control of the growth morphology and stoichiometry of ZnO will have an impact on possible optoelectronic applications.