Highly sensitive hierarchically structured Si-based UV sensor–photodetectors via optimized ZnO–Al2O3 nanocomposite architectures

Abstract The rapid and reliable detection of ultraviolet (UV) radiation is critical for applications ranging from environmental monitoring to optoelectronic security systems. This study presents an integrated theoretical and experimental investigation into highly sensitive, hierarchically structured Si-based UV sensor–photodetectors optimized via ZnO–Al 2 O 3 nanocomposite architectures. A combination of density functional theory (B3LYP/6-31G(d,p)) calculations and comprehensive materials characterization was employed to elucidate the interplay between electronic structure, surface morphology, and optical performance. Theoretical modeling provided detailed insights into band alignment, total and partial density of states, frontier molecular orbitals, and electrostatic potential distributions for pure and hybrid oxide systems, revealing that ZnO–Al 2 O 3 exhibits superior electronic coupling and enhanced carrier mobility pathways. Experimentally, ZnO and Al 2 O 3 nanoparticles were synthesized via hydrothermal routes, integrated into hybrid thin-film architectures on Si substrates, and structurally verified by XRD, FE-SEM, and EDX analyses. Surface roughness and apparent porosity measurements indicated that Al 2 O 3 incorporation increased roughness from 6.7 to 8.2 µm and porosity from 26 to 36%, fostering enhanced light scattering and active site density. Optical absorption spectroscopy (250–650 nm) revealed strong UV selectivity with calculated band gaps of 3.18 eV (ZnO), 3.11 eV (Al 2 O 3 ), and 3.26 eV (ZnO–Al 2 O 3 ), while electrochemical impedance spectroscopy confirmed reduced charge transfer resistance in the hybrid architecture. Electrical conductivity improved from 27.7 × 10 −2 S/m (ZnO) to 44.5 × 10 −2 S/m (ZnO–Al 2 O 3 ), correlating with faster response and recovery dynamics under UV illumination. These synergistic structural, optical, and electronic enhancements establish ZnO–Al 2 O 3 as a promising candidate for next-generation, high-performance UV photodetectors with superior sensitivity, stability, and spectral selectivity.