Tuning microstructural and optical properties of ZnO thin films on p-type Si(100)

Very thin ZnO films were fabricated on p-type Si (100) substrates using two different solvents, methanol (M) and 2-methoxyethanol (2M), via a simple spin-coating method. Five-layer ZnO films were characterized structurally using X-ray diffraction (XRD), with detailed analysis performed using the Williamson–Hall (W-H) method. Surface morphology was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM), while ultraviolet–visible (UV–Vis) spectroscopy provided optical properties, including the optical band gap determined via the Kubelka–Munk theory. The crystallite sizes calculated from W-H models were larger than those estimated by the Debye–Scherrer method, indicating that peak broadening is influenced by both crystallite size and lattice strain. Strain, stress, and deformation energy density values, derived from the Uniform Deformation Model (UDM), Uniform Stress Deformation Model (USDM), and Uniform Deformation Energy Density Model (UDEDM), respectively, were higher in films prepared with 2-methoxyethanol than methanol. ZnO films from 2-methoxyethanol exhibited greater homogeneity and lower surface roughness, while their optical band gap (~3.3 eV) was slightly higher than that of methanol-derived films (~3.02 eV) but still below bulk ZnO (3.37 eV). These results show that ZnO thin films prepared with 2-methoxyethanol exhibit superior microstructural, mechanical, and optical properties, producing smoother and more uniform films with enhanced optical characteristics, and are therefore more commonly preferred for optoelectronic and photovoltaic applications due to their improved crystallinity, low surface roughness, and suitable band gap.