Synthesis and photo-sensing properties of Zn–ZnO core–shell nanofibers

Single-crystalline Zn–ZnO core–shell nanofibers have been prepared by thermal evaporation of metallic Zn in an oxygen atmosphere. The diameter of the Zn core is 53 ± 1.0 nm while the thickness of the outer ZnO shell is 10 ± 1.5 nm, both are single crystalline and grow along the [1 1 2¯ 0] direction. Post-growth annealing leads to sublimation and out-diffusion of the Zn core that result in the formation of polycrystalline ZnO nanotubes. Metal-semiconductor-metal photodiodes (PDs) are fabricated by depositing In and Ag interdigitated electrodes on Zn–ZnO core–shell nanofibers. PDs fabricated with In contacts exhibit a maximum responsivity of 2 A/W at 300 nm. In contrast, PDs fabricated with Ag contacts exhibit a maximum responsivity of 10 A/W at 300 nm and a much faster decay rate which has been attributed to the formation of a Schottky barrier between Ag and ZnO.