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<p>This study presents the results of an investigation into the optical and structural properties of ZnO films with various thicknesses. Polycrystalline zinc films with thicknesses of 10, 20, 40, 50, 60, and 80&#xa0;nm were deposited onto glass substrates by magnetron sputtering. Subsequently, thermal treatment was performed in a programmable muffle furnace. During thermal oxidation, the thickness of the ZnO films increased by approximately 1.3 times, by comparision with the thickness of Zn metallic films.The morphology, structural, and optical properties of the zinc oxide films were examined using scanning electron microscopy (SEM), spectrophotometer, and X-ray diffraction (XRD).It was found that as the thickness of the ZnO films decreases, the unit cell parameters of zinc oxide change, internal mechanical stresses increase, the degree of nanocrystalline ordering decreases, and the optical band gap narrows from 3.25 to 3.19&#xa0;eV. These effects are attributed to the fact that film thickness determines the crystallite size within the film. At zinc film thicknesses of approximately 80&#xa0;nm and above, the structural parameters of the oxidized films closely approach those of bulk single-crystal ZnO. However, as the film thickness decreases, the deviation of structural parameters from those of the single crystal becomes more pronounced. The influence of the substrate increases, the crystallite size decreases, and, consequently, internal stress develops within the crystal lattice. This leads to a reduction in atomic ordering, as evidenced by the broadening of XRD peaks, i.e., an increase in full width at half maximum (FWHM), with decreasing film thickness. It can be assumed that this structural disorder is the primary reason for the observed narrowing of the band gap.</p>

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Effect of the thickness of ZnO films on their crystal structure and band gap

  • 期刊论文

  • 发表日期：

    2025年7月29日

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  • N. B. Leonov,
  • V. A. Polishchuk,
  • V. V. Tomaev,
  • V. P. Pronin

摘要

This study presents the results of an investigation into the optical and structural properties of ZnO films with various thicknesses. Polycrystalline zinc films with thicknesses of 10, 20, 40, 50, 60, and 80 nm were deposited onto glass substrates by magnetron sputtering. Subsequently, thermal treatment was performed in a programmable muffle furnace. During thermal oxidation, the thickness of the ZnO films increased by approximately 1.3 times, by comparision with the thickness of Zn metallic films.The morphology, structural, and optical properties of the zinc oxide films were examined using scanning electron microscopy (SEM), spectrophotometer, and X-ray diffraction (XRD).It was found that as the thickness of the ZnO films decreases, the unit cell parameters of zinc oxide change, internal mechanical stresses increase, the degree of nanocrystalline ordering decreases, and the optical band gap narrows from 3.25 to 3.19 eV. These effects are attributed to the fact that film thickness determines the crystallite size within the film. At zinc film thicknesses of approximately 80 nm and above, the structural parameters of the oxidized films closely approach those of bulk single-crystal ZnO. However, as the film thickness decreases, the deviation of structural parameters from those of the single crystal becomes more pronounced. The influence of the substrate increases, the crystallite size decreases, and, consequently, internal stress develops within the crystal lattice. This leads to a reduction in atomic ordering, as evidenced by the broadening of XRD peaks, i.e., an increase in full width at half maximum (FWHM), with decreasing film thickness. It can be assumed that this structural disorder is the primary reason for the observed narrowing of the band gap.