High-performance self-powered ultraviolet photodetector in SnO2 microwire/p-GaN heterojunction using graphene as charge collection medium

Abstract

• Using a facile vapor transport deposition method, the samples of SnO 2 microwires were synthesized individually self-catalyzed by a fast and simple CVD method. By combining p-type GaN substrate, a single SnO 2 microwire heterojunction photodetector working in the ultraviolet wavelengths was constructed. • By replacing the top electrodes from ITO to monolayer graphene, enhanced ultraviolet photoresponses were obtained, which exhibiting a peak responsivity 223.7 mA/W, detectivity ∼ 6.9 × 10 12 Jones, high EQE of 77%, and a fast response speed (rising/decaying times ∼ 18/580 μs) at 360 nm light illumination when the device is operated in self-driven mode. Our results suggest that the graphene transparent electrodes can not only allow the majority of the incident light to reach the contact area but also offer an easy carrier transport channel when the electron-holes were separated. • In particular, the microscopic photoresponse mechanism of the fabricated n-SnO 2 microwire/p-GaN heterojunction photodetector that using monolayer graphene as charge collection medium was studied. The Schottky-potential is formed by the built-in electric-field from graphene to the SnO 2 wire. The built-in field is in the same direction as the original SnO 2 /GaN built-in electric field, which was similar to the reverse voltage applied to the heterojunction. Therefore, the net built-in field toward the SnO 2 /GaN heterointerface can be increased, resulting in the increment of the carrier collection efficiency through graphene as a charge collection medium. Graphene monolayer has been extensively applied as a transparency electrode material in photoelectronic devices due to its high transmittance, high carrier mobility, and ultrafast carrier dynamics. In this study, a high-performance self-powered photodetector, which is made of a SnO 2 microwire, p-type GaN film, and monolayer graphene transparent electrode, was proposed and fabricated. The detector is sensitive to ultraviolet light signals and illustrates pronounced detection performances, including a peak responsivity ∼ 223.7 mA W –1 , a detectivity ∼ 6.9 × 10 12 Jones, fast response speed (rising/decaying times ∼ 18/580 μs), and excellent external quantum efficiency ∼ 77% at 360 nm light illumination without external power supply. Compared with the pristine SnO 2 /GaN photodetector using ITO electrode, the device performances of responsivity and detectivity are significantly increased over 6 × 10 3 % and 3 × 10 3 %, respectively. The performance-enhanced characteristics are mainly attributed to the high-quality heterointerface of n-SnO 2 /p-GaN, the highly conductive capacity, and the unique transparency of graphene electrodes. Particularly, the built-in potential formed at the SnO 2 /GaN heterojunction interface could be strengthened by the Schottky potential barrier derived from the graphene electrode and SnO 2 wire, enhancing the carrier collection efficiency through graphene as a charge collection medium. This work is of great importance and significance to developing excellent-performance ultraviolet photodetectors for photovoltaic and optoelectronic applications in a self-powered operation manner.