Preparation and UV Photoelectric Properties of Aligned ZnO–TiO₂ and TiO₂–ZnO Core–Shell Structured Heterojunction Nanotubes

Large-area horizontal-aligned ZnO nanotubes (ZNTs), TiO2 nanotubes (TNTs), TiO2–ZnO core–shell nanotubes (TZNTs) and ZnO-TiO2 core–shell nanotubes (ZTNTs) were successfully synthesized by electrospinning combined with pulsed-laser deposition. The morphology, structure, and composition of the samples were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The photoluminescence (PL) spectra of these samples indicate that the addition of a TiO2 layer greatly decreases the recombination of photogenerated carriers in the heterojunction nanotubes. The photodetectors (PDs) were fabricated by assembling horizontally ordered nanotubes on the gold interdigital electrode, and their ultraviolet (UV) detection performances were compared. The test results at room temperature show that the PD with aligned ZTNTs have the best UV response and a short response recovery time. In addition, the performance of ZTNT PDs and TZNT PDs are further improved under heating. The photo/dark current ratio, responsivity (Rλ), detectivity (D*), and external quantum efficiency (EQE) of ZTNTs increased to 388, 450 uA·W–1, 1.1 × 1010 cm·Hz1/2·W–1, and 0.15%, respectively, under the 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 and structural superiority of the horizontally ordered coaxial heteronanotube were also discussed. In addition, this work provides an important method for the design of other ordered nanomaterials and structures, which have a wide range of applications in the fields of sensors, transistors, transparent flexible electrodes, and other multifunctional devices.