High-gain AlGaN/GaN visible-blind avalanche heterojunction phototransistors

We report the fabrication and characterization of the visible-blind AlGaN/GaN-based avalanche heterojunction phototransistors (AHPT) with a collector-up configuration. The fabricated devices with 150-μm-diameter active area exhibit low dark currents of less than 20 pA at collector-emitter voltage ( V CE ) below 5.0 V. Optical gain as high as 3.6 × 10 4 was obtained due to the combination of photon-induced current amplification and carrier multiplication at an operating voltage of V CE = 53.5 V, which is much lower than the avalanche breakdown voltage required for GaN-based visible-blind avalanche photodiodes. An ultraviolet–visible rejection ratio of more than 100 was measured at zero bias. Under V CE = 5 V, a peak responsivity of 0.91 A/W was obtained at 335 nm.