Solar-blind AlGaN-based Schottky photodiodes with low noise and high detectivity

We report on the design, fabrication, and characterization of solar-blind Schottky photodiodes with low noise and high detectivity. The devices were fabricated on n−/n+ AlGaN/GaN heterostructures using a microwave compatible fabrication process. True solar-blind operation with a cutoff wavelength of ∼274 nm was achieved with AlxGa1−xN (x=0.38) absorption layer. The solar-blind detectors exhibited 1.8 nA/cm2 dark current density in the 0–25 V reverse bias regime, and a maximum quantum efficiency of 42% around 267 nm. The photovoltaic detectivity of the devices were in excess of 2.6×1012 cm Hz1/2/W, and the detector noise was 1/f limited with a noise power density less than 3×10−29 A2/Hz at 10 kHz.