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<p>Doping Zinc Oxide (ZnO) thin films with rare earth and transition metal ions presents an effective strategy to tailor their physicochemical characteristics for advanced optoelectronic and surface-related applications. In this study, neodymium (Nd³⁺) and copper (Cu²⁺) doped ZnO thin films were synthesized via a sol–gel-derived wet chemical method. The significant ionic radius disparity between Nd³⁺ (~ 0.98 Å) and Zn²⁺ (~ 0.74 Å), as well as the close match of Cu²⁺ (~ 0.73 Å), governs the extent of lattice distortion and dopant incorporation. X-ray diffraction confirmed the retention of the hexagonal wurtzite structure in all samples, with Cu doping promoting crystallite coarsening (~ 29&#xa0;nm), while Nd doping introduced lattice strain and refined crystallite size (~ 21&#xa0;nm). SEM analysis revealed granular morphologies, with evident agglomeration in Cu-doped films, contrasting with finer and more uniformly distributed grains (~ 26&#xa0;nm) in Nd-doped films due to suppressed coalescence. FTIR spectra identified Zn–O stretching modes along with residual organics from precursor decomposition. Optical characterization via UV–Vis spectroscopy showed a bandgap narrowing from 3.14&#xa0;eV (pure ZnO) to 3.01&#xa0;eV (Nd-doped), attributed to dopant-induced defect states and tailing of the absorption edge. Correspondingly, Urbach energies increased from 0.36&#xa0;eV to 0.42&#xa0;eV (Cu-doped) and 0.47&#xa0;eV (Nd-doped), indicating enhanced structural disorder and localized energy states. Notably, Nd doping also improved surface hydrophilicity, enhancing wettability properties. These results underline the tunable optoelectronic behavior and wettability control achievable through rare earth and transition metal doping, supporting the potential application of ZnO thin films in transparent electronics, photonic devices, transparent conductive oxide layer, photoanodes, and self-cleaning surfaces.</p>

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Modulation of Urbach states and defect structures in semiconductors via Dopant ionic size for optoelectrical and wettability applications

  • 期刊论文

  • 发表日期：

    2025年8月13日

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  • Altamash Shabbir,
  • Hina Pervaiz,
  • Zuhair S. Khan,
  • Muhammad Kashif,
  • Zain Hussain

摘要

Doping Zinc Oxide (ZnO) thin films with rare earth and transition metal ions presents an effective strategy to tailor their physicochemical characteristics for advanced optoelectronic and surface-related applications. In this study, neodymium (Nd³⁺) and copper (Cu²⁺) doped ZnO thin films were synthesized via a sol–gel-derived wet chemical method. The significant ionic radius disparity between Nd³⁺ (~ 0.98 Å) and Zn²⁺ (~ 0.74 Å), as well as the close match of Cu²⁺ (~ 0.73 Å), governs the extent of lattice distortion and dopant incorporation. X-ray diffraction confirmed the retention of the hexagonal wurtzite structure in all samples, with Cu doping promoting crystallite coarsening (~ 29 nm), while Nd doping introduced lattice strain and refined crystallite size (~ 21 nm). SEM analysis revealed granular morphologies, with evident agglomeration in Cu-doped films, contrasting with finer and more uniformly distributed grains (~ 26 nm) in Nd-doped films due to suppressed coalescence. FTIR spectra identified Zn–O stretching modes along with residual organics from precursor decomposition. Optical characterization via UV–Vis spectroscopy showed a bandgap narrowing from 3.14 eV (pure ZnO) to 3.01 eV (Nd-doped), attributed to dopant-induced defect states and tailing of the absorption edge. Correspondingly, Urbach energies increased from 0.36 eV to 0.42 eV (Cu-doped) and 0.47 eV (Nd-doped), indicating enhanced structural disorder and localized energy states. Notably, Nd doping also improved surface hydrophilicity, enhancing wettability properties. These results underline the tunable optoelectronic behavior and wettability control achievable through rare earth and transition metal doping, supporting the potential application of ZnO thin films in transparent electronics, photonic devices, transparent conductive oxide layer, photoanodes, and self-cleaning surfaces.