Fabrication and characterization of ultra-thin NbN hot electron bolometer for near infrared single photon detection

We describe the fabrication and characterization of thin NbN meanders to be used as fast single photon counting detectors. Photo-absorption on a thin and narrow superconducting stripe creates a short lifetime hotspot leading to a fast photo-voltage response. (1 0 0) oriented, 3.4 nm thick NbN layers are grown epitaxially smooth in a controllable way, with good superconducting properties (Tc>11 K), on 3 in. R-plane sapphire substrates. We have developed a fine patterning process based on electron beam lithography and reactive ion etching of the NbN layer. The 10 by 10 μm2 pixel area is covered by a 200–300 nm wide meander structure with a rather regular shape, leading to a filling factor of 0.5. The photon counting performance of such pixels is presently investigated for near-infrared applications in quantum optics and astronomy.