Preparation\nand UV Photoelectric Properties of Aligned ZnO–TiO₂ and TiO₂–ZnO Core–Shell Structured Heterojunction\nNanotubes

Abstract

Large-area\nhorizontal-aligned ZnO nanotubes (ZNTs), TiO₂ nanotubes\n(TNTs), TiO₂–ZnO core–shell nanotubes (TZNTs)\nand ZnO-TiO₂ core–shell nanotubes (ZTNTs) were successfully\nsynthesized by electrospinning combined with pulsed-laser deposition.\nThe morphology, structure, and composition of the samples were characterized\nby scanning electron microscopy, high-resolution transmission electron\nmicroscopy, and Raman spectroscopy. The photoluminescence (PL) spectra\nof these samples indicate that the addition of a TiO₂ layer\ngreatly decreases the recombination of photogenerated carriers in\nthe heterojunction nanotubes. The photodetectors (PDs) were fabricated\nby assembling horizontally ordered nanotubes on the gold interdigital\nelectrode, and their ultraviolet (UV) detection performances were\ncompared. The test results at room temperature show that the PD with\naligned ZTNTs have the best UV response and a short response recovery\ntime. In addition, the performance of ZTNT PDs and TZNT PDs are further\nimproved under heating. The photo/dark current ratio, responsivity\n(<i>R</i>_λ), detectivity (<i>D</i>*), and external quantum efficiency (EQE) of ZTNTs increased to 388,\n450 uA·W^–1, 1.1 × 10¹⁰ cm·Hz^1/2·W^–1, and 0.15%, respectively, under\nthe condition of 365 nm UV radiation with a power density of 4.9 mW·cm^–2 and a 1 V bias at 90 °C. The UV response mechanism\nand structural superiority of the horizontally ordered coaxial heteronanotube\nwere also discussed. In addition, this work provides an important\nmethod for the design of other ordered nanomaterials and structures,\nwhich have a wide range of applications in the fields of sensors,\ntransistors, transparent flexible electrodes, and other multifunctional\ndevices.