We describe solar-blind photodetectors based on superlattices of AlN/AlGa(In)N. The superlattices have a period of 1.4 nm, determined by x-ray diffraction, and an effective band gap of 260 nm measured by optical reflectivity. Using simple mesa diodes, without surface passivation, we obtain low dark leakage currents of 0.2-0.3 pA, corresponding to the leakage current density of ～0.3 nA/cm~(2), and high zero-bias resistance of ～1×10~(11) Ω. Excellent visible cutoff is obtained for these devices, with six orders of magnitude decrease in responsivity from 260 to 380 nm. These results demonstrate the potential of junctions formed by short-period superlattices in large-band-gap devices.
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