Ultra-thin TaN Films for Superconducting Nanowire Single-Photon Detectors

Ultra thin films of superconducting tantalum nitride are deposited by reactive magnetron sputtering on heated sapphire substrates. The critical temperature T_C = 10.5 K is reached for films thicker than 10 nm. A superconducting nanowire single photon detector in the form of a meander line with a width of 110 nm was made from 5 nm thick TaN film. The detector had a transition temperature of 8.3 K and a critical current density of 4 MA/cm^2 at 4.2 K. A photon detection efficiency of 20 has been obtained for the detector with a filling factor of 0.55 at wavelengths up to 700 nm.