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

## TL;DR

This paper develops a highly sensitive UV sensor using a ZnO–Al2O3 nanocomposite on a silicon base, combining theory and experiments to improve performance.

## Contribution

The novel ZnO–Al2O3 nanocomposite architecture is shown to enhance UV sensor performance through optimized electronic and optical properties.

## Key findings

- ZnO–Al2O3 hybrid structures exhibit improved carrier mobility and electronic coupling compared to pure ZnO or Al2O3.
- Al2O3 incorporation increases surface roughness and porosity, enhancing light scattering and active site density.
- The hybrid architecture shows faster response and recovery dynamics under UV illumination with higher electrical conductivity.

## 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–Al2O3 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–Al2O3 exhibits superior electronic coupling and enhanced carrier mobility pathways. Experimentally, ZnO and Al2O3 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 Al2O3 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 (Al2O3), and 3.26 eV (ZnO–Al2O3), 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–Al2O3), correlating with faster response and recovery dynamics under UV illumination. These synergistic structural, optical, and electronic enhancements establish ZnO–Al2O3 as a promising candidate for next-generation, high-performance UV photodetectors with superior sensitivity, stability, and spectral selectivity.