High-Performance Dual UV-A Band Photodetector Based on Sodium-Doped Hydrothermally Synthesized ZnO Nanostructures

Abstract

We report a high-performance dual UV-A band photodetector based on sodium (Na)-doped ZnO nanostructures (NSs) synthesized via a hydrothermal method. Undoped and Na-doped ZnO samples (5-30 mM) were grown on glass substrates, where Na incorporation during growth modified the crystal quality and defect states, leading to two distinct absorption peaks at ∼330 and ∼360 nm, unlike pristine ZnO (PZO), which showed only the band-edge response at ∼360 nm. FESEM analysis revealed vertically aligned nanorods with uniform surface coverage, while XRD confirmed that both undoped and Na-doped ZnO possess a hexagonal wurtzite structure with preferential (002) orientation, however, the (002) peak intensity decreased with Na doping, indicating increased defect density and strain. EDX and XPS verified successful Na incorporation within the ZnO lattice, consistent with compositional tuning. The optimized NZO5 device exhibited a maximum responsivity of 406 A/W, sensitivity of 3.3 × 10⁶, detectivity of ∼ 6.4 × 10¹⁴ Jones, EQE of 1.53 × 10⁵ %, LDR of 130 dB, and rise/decay times of 30/45 s at excitation wavelength of 330nm and applied bias of 20V, with clear dual responsivity peaks at ∼330 and ∼360 nm. These results establish Na doping as a simple and effective route to engineer defect states in ZnO and realize selective, dual UV-A band photodetectors with superior responsivity and detectivity. © 2025 Elsevier B.V., All rights reserved.