  We demonstrate high-performance nanowire superconducting single photon
detectors (SSPDs) on ultrathin NbN films grown at a temperature compatible with
monolithic integration. NbN films ranging from 150nm to 3nm in thickness were
deposited by dc magnetron sputtering on MgO substrates at 400C. The
superconducting properties of NbN films were optimized studying the effects of
deposition parameters on film properties. SSPDs were fabricated on high quality
NbN films of different thickness (7 to 3nm) deposited under optimal conditions.
Electrical and optical characterizations were performed on the SSPDs. The
highest QE value measured at 4.2K is 20% at 1300nm.
