Wire-shaped ultraviolet photodetectors based on a nanostructured NiO/ZnO coaxial p–n heterojunction via thermal oxidation and hydrothermal growth processes

Abstract

We report the facile fabrication of wire-shaped ultraviolet photodetectors (WUPDs) by employing a nanostructured zinc oxide (ZnO)/nickel oxide (NiO) coaxial p–n heterojunction. The WUPD consists of a ZnO/NiO coaxial Ni wire and a twisted gold (Au) wire where the Ni and Au are used as the anode and cathode, respectively. For the coaxial p–n heterojunction, the NiO nanostructures (NSs) and the ZnO nanorods (NRs) are subsequently formed on the surface of Ni wire via thermal oxidation and hydrothermal growth processes. With an applied bias of −3.5 V, the WUPD exhibits good photoresponsivity of 7.37 A W⁻¹ and an external quantum efficiency of 28.1% at an incident light wavelength of 325 nm. Under the UV illumination at a wavelength of 365 nm, the dark current and photocurrent are −3.97 × 10⁻⁷ and −8.47 × 10⁻⁶ A, respectively. For enhancing the photocurrent, the WUPD is threaded through a silver (Ag) coated glass tube which acts as a waveguide to concentrate the UV light of 365 nm on the WUPD. As a result, the photocurrent is significantly improved up to −1.56 × 10⁻⁵ A (i.e., 1.84 times) at the reverse bias of −3.5 V.