Ultrasensitive Dual-Junction-Coupled n-ZnO/n-Ga2O3/p-GaN-Based Self-Driven Broad-Band Ultraviolet Photodetector

The built-in electric field associated with a junction, e.g., p–n conjunction, can drive the separation and transport of photogenerated carriers to make self-driven photodetectors, but its strength is limited, and thus, the device performance requires further improvement. Herein, we propose to enhance the driving strength by constructive superposition of the built-in electric fields associated with two or more junctions and designed a p–n junction and n–n heterojunction-coupled photodetector involving three prevalent wide-bandgap semiconductors, namely, p-GaN, n-Ga2O3:Sn, and n-ZnO. This new n-ZnO/n-Ga2O3:Sn/p-GaN dual-junction-based photodetector turned out to be much more sensitive for ultraviolet (UV) light detection over the sole p–n junction n-Ga2O3:Sn/p-GaN-based device. It delivered the highest light-to-dark current ratio, Ilight/Idark, of ∼3.2 × 104, responsivity, R, of 178.24 mA/W, and detectivity, D*, of 1.25 × 1013 Jones toward 260 nm UV light without an external bias voltage, which are significantly higher than those of the sole p–n junction device (Ilight/Idark = 1.8 × 104, R = 142.73 mA/W, and D* = 8.45 × 1012 Jones) and are among the best figures reported so far for the self-driven Ga2O3-based photodetectors. When reversely biased at −0.5 V, the dual-junction device exhibited an even higher R value of 351.46 mA/W and D* value of 8.71 × 1011 Jones toward 255 nm UV light. This ultrasensitive dual-junction n-ZnO/n-Ga2O3:Sn/p-GaN-based photodetector, operable in both self-driven and reverse-biased modes, holds great application potential for UV detection in a broad range (240–400 nm). More interestingly, our strategy of enhancing the separation and transport of photogenerated carriers by exploiting the constructive superposition effect of the built-in electric fields in multiple junctions may be generally extended to develop high-performance optoelectronic devices where the built-in electric field plays a key role.