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<p>For the study of the effects of substrate material and thin film thickness on structural and optical properties, sol–gel spin coating was utilized to successfully deposit Zn<sub>0.85</sub> Mg<sub>0.15</sub> O (MZnO) thin films onto glass, ITO, and Si substrates with 6, 8, and 10 layers. All the films maintained the hexagonal wurtzite structure (JCPDS 36-1451) with crystallite sizes ranging from 24&#xa0;nm (MZnO-6-ITO) to 38&#xa0;nm (MZnO-10-Si) with a corresponding decrease in microstrain from 48.8 × 10⁻<sup>3</sup> to 30.7 × 10⁻<sup>3</sup> and dislocation density from 1.74 × 10⁻<sup>4</sup>&#xa0;nm⁻<sup>2</sup> to 6.9 × 10⁻<sup>5</sup>&#xa0;nm⁻<sup>2</sup>, indicating improved crystallinity with thickness. AFM analysis indicated nanoscale surface roughness (<i>R</i><sub>q</sub> = 17.12–21.51&#xa0;nm; <i>R</i><sub>a</sub> = 12.40–17.01&#xa0;nm), the smoothest surface of which was achieved for MZnO-10-ITO (<i>R</i><sub>q</sub> = 17.12&#xa0;nm), beneficial for optoelectronic integration. The optical transmittance was more than 80% in the visible spectrum (400–800&#xa0;nm) for glass-based films and showed a decrease with enhanced thickness. The optical bandgap (<i>E</i><sub>g</sub>) reduced systematically from 3.524&#xa0;eV (MZnO-6-Glass) to 3.275&#xa0;eV (MZnO-10-Si), reflecting tunable optical characteristics through thickness and substrate control. PL spectra showed strong near-band-edge (NBE) UV emission at ~ 380&#xa0;nm with reduced visible bands (440–580&#xa0;nm), a maximum UV/Vis intensity ratio of 3.06 found for MZnO-10-ITO, reflecting superior optical quality and low defect density. Raman spectra indicated distinctive E₂(high) and A₁(LO) modes at 437 and 580&#xa0;cm⁻<sup>1</sup>, confirming Mg incorporation and modulation of lattice strain. Photocatalytic degradation of methylene blue under UV exposure demonstrated increased activity with Mg doping and conducting substrates—82.86% (ZnO-10-Glass), 92.66% (MZnO-10-Glass), and 94.08% (MZnO-10-ITO) degradation after 100&#xa0;min, &gt; 91% efficiency after five reuse cycles. The findings confirm Mg-doped ZnO thin films, especially MZnO-10-ITO, as multifunctional materials with excellent crystallinity, smooth morphology, tunable bandgap, and outstanding stability—strongly promising for transparent optoelectronics, UV photodetectors, and photocatalytic environmental remediation.</p>

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Mg-doped ZnO thin films with tunable optical and photocatalytic performance via substrate and thickness engineering

  • 期刊论文

  • 发表日期：

    2025年11月2日

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  • Sunena Subhash,
  • Sudheendran Kooriyattil

摘要

For the study of the effects of substrate material and thin film thickness on structural and optical properties, sol–gel spin coating was utilized to successfully deposit Zn0.85 Mg0.15 O (MZnO) thin films onto glass, ITO, and Si substrates with 6, 8, and 10 layers. All the films maintained the hexagonal wurtzite structure (JCPDS 36-1451) with crystallite sizes ranging from 24 nm (MZnO-6-ITO) to 38 nm (MZnO-10-Si) with a corresponding decrease in microstrain from 48.8 × 10⁻3 to 30.7 × 10⁻3 and dislocation density from 1.74 × 10⁻4 nm⁻2 to 6.9 × 10⁻5 nm⁻2, indicating improved crystallinity with thickness. AFM analysis indicated nanoscale surface roughness (Rq = 17.12–21.51 nm; Ra = 12.40–17.01 nm), the smoothest surface of which was achieved for MZnO-10-ITO (Rq = 17.12 nm), beneficial for optoelectronic integration. The optical transmittance was more than 80% in the visible spectrum (400–800 nm) for glass-based films and showed a decrease with enhanced thickness. The optical bandgap (Eg) reduced systematically from 3.524 eV (MZnO-6-Glass) to 3.275 eV (MZnO-10-Si), reflecting tunable optical characteristics through thickness and substrate control. PL spectra showed strong near-band-edge (NBE) UV emission at ~ 380 nm with reduced visible bands (440–580 nm), a maximum UV/Vis intensity ratio of 3.06 found for MZnO-10-ITO, reflecting superior optical quality and low defect density. Raman spectra indicated distinctive E₂(high) and A₁(LO) modes at 437 and 580 cm⁻1, confirming Mg incorporation and modulation of lattice strain. Photocatalytic degradation of methylene blue under UV exposure demonstrated increased activity with Mg doping and conducting substrates—82.86% (ZnO-10-Glass), 92.66% (MZnO-10-Glass), and 94.08% (MZnO-10-ITO) degradation after 100 min, > 91% efficiency after five reuse cycles. The findings confirm Mg-doped ZnO thin films, especially MZnO-10-ITO, as multifunctional materials with excellent crystallinity, smooth morphology, tunable bandgap, and outstanding stability—strongly promising for transparent optoelectronics, UV photodetectors, and photocatalytic environmental remediation.