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IEEE Transactions on Applied Superconductivity

NbN Superconducting Single-Photon Detectors Prepared on Single-Crystal MgO Substrates

Shigehito Miki, Mikio Fujiwara, Masahide Sasaki, Zhen Wang

Published Jun 1, 2007• 78 citations
Publisher

Abstract

We report the fabrication of NbN superconducting single photon detectors (SSPDs) and the development of a receiver system operating in a standard transport helium dewar. The NbN- SSPDs consisted of a 3.5 to 6.7-nm-thick NbN ultrathin film meander line and a 150-nm-thick NbN thin-film coplanar waveguide line. The NbN ultrathin films were deposited on single-crystal MgO substrates by reactive dc-magnetron sputtering to grow the NbN ultrathin films epitaxially, and the films were formed so that they had 80 to 200-nm-wide meander lines, which covered a 20 times 20 or 50 times 50 mum2area. All devices demonstrated good superconductivity, e.g., a device with a 3.9-nm-thick and 80-nm-wide line had a Tcof 10.8 K, an Icof 19 muA, and a Jcof 5.9 times 106A/cm2, which meant there was no serious deterioration in superconductivity compared with unprocessed films. We describe a reliable connection between an optical fiber and the detector, a setup which was used for first tests with pulsed light.

DOI
10.1109/tasc.2007.898582

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We report on the fabrication and characterization of high performance nanowire superconducting single photon detectors (SSPD) on MgO substrates. The deposition of the superconducting material (NbN) has been performed by magnetron sputtering at 400°C. This deposition temperature is low enough to be compatible with the fabrication on traditional optical materials like GaAs. First, SSPD meanders covering a surface of 5 × 5 µm2 were characterized. We measured quantum efficiencies up to 20% at 1300 nm. Then, we used a straight 250 µm-long NbN nanowire to perform a spatially resolved measurement of the efficiency. Both efficiency dips and peaks were observed. The dips were correlated to lithographic defects, as confirmed by scanning electron microscopy. Conversely, no evidence of a lithographic origin of efficiency peaks was found.