Sol–Gel Spin-Coated Multilayer nc-Si Thin Films on Silicon Substrates: Controlled Growth, Composition, and Electronic Structure

Silicon multilayer thin films consisting of alternating amorphous SiOx (a-SiOx) and nanocrystalline silicon (nc-Si) layers were fabricated on p-type silicon substrates using a sol-gel spin-coating method. Boron-doped silicon powders, prepared through prolonged grinding, were mixed with a TEOS–ethanol sol-gel solution, and two nc-Si layers embedded in a-SiOx were sequentially deposited. The as-grown films were annealed at 100–400 °C and characterized using Raman spectroscopy, GXRD, FTIR, SEM, Resistivity and UV spectroscopy to analyze their structural, chemical, optical, and electronic properties. Annealing progressively enhanced crystallinity and increased the and grain sizes to ~11 nm and ~12 nm, respectively. Films annealed at higher temperatures showed a minimum mobility of ~37.5 cm²/V·s, maximum resistivity of ~7.35 Ω-cm, and a decreasing optical bandgap. Enhanced nanocrystal growth, reduced defects, and improved structural ordering intensified the 520 cm⁻¹ Raman peak. The multilayer architecture further strengthened these effects by offering additional nucleation sites, controlled nanocrystal confinement, defect-relaxing interfaces, improved phonon transport, and enhanced Si diffusion, resulting in superior crystalline quality.