Performance enhancement of a self-biased n-ZnO microwire/p-GaN heterojunction ultraviolet photodetector incorporating Ag nanowires

Abstract

Low-dimensional self-powered ultraviolet photodetectors have attracted considerable attention on account of their wide potential applications. However, the photodetector performances severely suffer from various surface states and structural defects induced by a large volume-to-surface ratio of low-dimensional semiconductors, as well as conventional metal and ITO electrodes. Herein, a high-performance ultraviolet photodetector containing a single Ga-doped ZnO microwire covered by Ag nanowires (AgNWs@ZnO:Ga MW) and a p-type GaN wafer was proposed and constructed. Using an AgNW film as a highly transparent electrode, the fabricated photodetector can operate in a self-biasing manner, which exhibits a peak responsivity of 137 mA W⁻¹ and a detectivity of 2.15 × 10¹² Jones under 370 nm light illumination. Further, an ultrafast photoresponse (rising/falling times ∼22/339 μs) is achieved. Compared with a pristine ZnO:Ga MW/GaN heterojunction photodetector using ITO as a top electrode, the photosensitivity is significantly improved. In particular, the responsivity and detectivity are enhanced over 1100% and 700%, respectively. The enhanced mechanism was researched systematically. In the photodetector structure, the AgNW electrode serving as a transmission window has a higher optical transparency in the ultraviolet band, a more outstanding electrical property than that of the conventional ITO film electrode. Meanwhile, the plasmonic effect of the covered AgNWs on ZnO:Ga can facilitate the increase of light absorption, and then enhance the photocurrent at corresponding plasmon resonant wavelengths, directly resulting in an excellent photosensitivity. This work sheds light on the development of designing and fabricating high-performance self-powered ultraviolet photodetectors with ultrafast response speed and high photoresponsivity.