Low-noise GaN ultraviolet p-i-n photodiodes on GaN substrates

We report low-noise GaN visible-blind homojunction p-i-n photodiodes. The devices are grown on a freestanding bulk GaN substrate and are fabricated using a ledged surface depletion technique to suppress the mesa sidewall leakage. For an 80-mu m-diameter photodetector, the dark current density is lower than 40 pA/cm(2). A room-temperature noise equivalent power of 4.27x10(-17) W Hz(-0.5) and a detectivity of 1.66x10(14) cm Hz(0.5) W-1 are achieved at a reverse bias of 20 V. The noise performance of the reverse-biased GaN p-i-n photodiodes are among the best values reported to date and demonstrate the potential of GaN photodiodes for low-noise high-speed UV detection.