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 X 10^12 cmHz^1/2/ W, and the detector noise was 1/f limited with a noise power density less than 3 X 10^-29 A^2/Hz at 10 kHz.
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