Improving the photoelectrical characteristics of self-powered p-GaN film/n-ZnO nanowires heterojunction ultraviolet photodetectors through gallium and indium co-doping

Abstract

ZnO, Ga-doped ZnO (GZO), In-doped ZnO (IZO), and Ga–In co-doped ZnO (GIZO) nanowire arrays were grown on a template of sapphire/p-GaN thin film by low-temperature hydrothermal method for fabricating self-powered p-GaN/n-ZnO heterojunction ultraviolet (UV) photodetectors. The authors investigated the effects of Ga or In single doping and Ga–In co-doping on the microstructural features and optical properties of hydrothermally synthesized ZnO nanowires and conducted a comparison study on the photosensing characteristics and photoelectrical response performances of four kinds of p-n heterojunction UV photodetectors. X-ray diffraction (XRD) examination showed that the as-synthesized ZnO-based nanowire arrays had a single-phase hexagonal wurtzite structure and exhibited a preferential orientation along the (002) plane. Scanning electron microscope (SEM) observation evidenced that the type of dopants modified the morphology and average diameter of the nanowires. The average diameter of ZnO-based nanowires was in the range of 61–101 nm. Room-temperature photoluminescence (PL) spectra revealed that these as-synthesized ZnO-based nanowires had high crystalline quality. The current-voltage (I–V) curves of heterojunction photodetectors based on p-GaN thin film/n-ZnO based nanowire arrays exhibited a rectification characteristic in darkness and under UV illumination. Under UV illumination, the GIZO device had the best photosensing characteristics of all the devices under 5 V bias. The light-to-dark current ratio was close to 6.0 at 5 V bias and the turn-on voltage was lower than 1.8 V. The presented p-GaN/n-GIZO heterojunction UV photodetector realized superior photoresponse performance at zero-bias voltage as compared to single-doped and un-doped ZnO devices.