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 similar to274 nm was achieved with Al(x)Ga(1-x)N (x=0.38) absorption layer. The solar-blind detectors exhibited <1.8 nA/cm(2) 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 2.6x10(12) cm Hz(1/2)/W, and the detector noise was 1/f limited with a noise power density less than 3x10(-29) A(2)/Hz at 10 kHz. (C) 2002 American Institute of Physics.