Influence of Multilayer Architecture on the Structural, Optical, and Photoluminescence Properties of ZnO Thin Films

The present work systematically investigates the impact of multilayer architecture—specifically 5, 10, and 15 layers—on the structural, morphological, optical, and dielectric properties of zinc oxide (ZnO) thin films, aiming to tailor their characteristics for optoelectronic applications. The films were characterized using a comprehensive suite of techniques. X-ray diffraction (XRD) analysis of the 15-layer sample confirmed the formation of polycrystalline ZnO with a hexagonal wurtzite crystal structure, showing prominent (100), (002), and (101) diffraction peaks. Measurements indicated that the film thickness progressively increased from 43.81 nm for 5 layers to 80.68 nm for 15 layers. Concurrently, the surface roughness significantly decreased from 5.54 nm (5 layers) to 2.00 nm (15 layers) with increasing layer count, suggesting enhanced film quality and densification. Optical studies using ultraviolet–visible (UV-Vis) spectroscopy revealed an increase in absorbance and a corresponding decrease in transmittance in the UV-Vis spectrum as the film thickness increased. The calculated optical band gap showed a slight redshift, decreasing from 3.26 eV for the 5-layer film to 3.23 eV for the 15-layer film. Photoluminescence (PL) spectra exhibited characteristic near-band-edge UV emission, with the 5-layer film demonstrating the highest PL intensity. Furthermore, analysis of optical constants revealed that the refractive index, extinction coefficient, optical conductivity, and both the real and imaginary parts of the dielectric constant generally increased with an increasing number of layers, particularly in the visible region, while more nuanced and non-monotonic trends were observed in the UV range. These results underscore the significant influence of layer number on the physical properties of ZnO thin films, providing valuable insights for optimizing their performance in various optoelectronic devices.