Nanowire single-photon detectors made of atomic layer-deposited niobium nitride

We demonstrate and characterize superconducting nanowire single-photon detectors (SNSPDs) made from atomic layer-deposited (ALD) NbN layers. To assess the suitability of these films as a detector material, transport properties of bare films and bridges of different dimensions and thicknesses are investigated. Similar ratios of the measured critical current to the depairing current are obtained for micro-bridges made from ALD and sputtered NbN films. Furthermore, we characterized the single-photon response for 5 and 10 nm-thick nanowire detectors. A 100 nm-wide straight nanowire with a length of 5 µm exhibits saturated count-rate dependencies on bias current and a cut-off wavelength in the near-infrared range. The ALD technique could open up the possibility to fabricate NbN-based detectors on the wafer scale and to conformally cover also non-planar surfaces for novel device concepts.