Tunable optoelectronic performance of ZnO-Coated TiO2 nanowires for enhanced UV photodetection

In this study, vertically aligned TiO₂ nanowires (NWs) were fabricated on titanium (Ti) foil via thermal oxidation and subsequently coated with zinc oxide (ZnO) using zinc acetate solutions of 25, 50, and 100 mM concentrations. Structural and optoelectronic properties were systematically investigated using SEM, XRD, XPS, PL, UV–Vis, and I–V analyses. SEM results confirmed a progressive ZnO surface coverage, with complete encapsulation observed at 100 mM. EDS analysis revealed a Zn content increase from 0.81 wt.% (25 mM) to 8.43 wt.% (100 mM), accompanied by a decrease in Ti content from 70.78 wt.% to 49.02 wt.%. XRD patterns showed distinct ZnO peaks for coated samples, while XPS confirmed Zn[Formula: see text] and Ti[Formula: see text] states with minimal interdiffusion. Optical bandgap values increased slightly with ZnO concentration: 3.04 eV (pure TiO₂), 3.06 eV (25 mM), 3.05 eV (50 mM), and 3.11 eV (100 mM), attributed to enhanced crystallinity and heterojunction formation. PL spectra showed increasing green luminescence ([Formula: see text]520 nm) with ZnO content, indicating rising defect-related recombination. Electrical measurements showed a sharp rise in photocurrent from 3.67 × 10[Formula: see text] A (pure TiO₂) to 4.74 × 10[Formula: see text]A (100 mM). Correspondingly, responsivity ([Formula: see text]) increased from 0.020 to 2.168 mA/W and detectivity ([Formula: see text]*) from 8.5 × 10⁸ to 7.56 × 10⁹ Jones. These results demonstrate that ZnO coating substantially enhances light absorption, charge separation, and carrier transport properties of TiO₂ NWs. The optimized 100 mM ZnO–TiO₂ heterostructure offers high-performance UV photodetection potential for environmental sensing, wearable optoelectronics, and aerospace technologies.