p-NiO Gate-Engineered AlGaN/GaN UV Phototransistor With Enhanced Photogating for Visible-Blind Detection

We report a p-NiO gate-engineered AlGaN/GaN ultraviolet phototransistor (UVPT) that achieves high-sensitivity, visible-blind UV detection with ultralow dark current and strong photogating. The device employs an ultrathin in-situ SiNx interlayer beneath the p-NiO gate, which preserves an intact 2DEG transport interface while enabling gate-side charge storage. The large vertical band bending under reverse gate bias creates a strong electric field across the gate stack, which efficiently separates photogenerated carriers and drives holes toward the gate dielectric. Under 365 nm illumination (VGS/VDS= −8/10 V), the UVPT achieves a photo-to-dark current ratio (PDCR) exceeding 4 × 109, responsivity (R) up to 1 × 106A/W, and UV-to-visible rejection ratio (UVRR) surpassing 1 × 1010. A significant negative threshold-voltage shift is observed and intensifies with photon injection, indicating a photogating mechanism associated with gate-side hole retention at the p-NiO/SiNxinterface. The accumulatedQphotopartially offsets the reverse gate bias, shiftsVthnegatively, and thereby gives rise to the large current contrast. The device further exhibits fast dynamics (200-ns-rise/34.2-μs-decay) and a flicker-noise-limited specific detectivity (D*) of 5.52 × 1016cm∙Hz1/2∙W−1. These results highlight p-NiO/SiNxgate engineering as an effective design paradigm for high-sensitivity and visible-blind UV photodetection in wide-bandgap semiconductor platforms.