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 Zn2+ and Ti4+ 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 (∼520 nm) with ZnO content, indicating rising defect-related recombination. Electrical measurements showed a sharp rise in photocurrent from 3.67 × 10−6 A (pure TiO2) to 4.74 × 10−4 A (100 mM). Correspondingly, responsivity (R) increased from 0.020 to 2.168 mA/W and detectivity (D*) from 8.5 × 108to 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.