Structural, microchemical and superconducting properties of ultrathin NbN films on silicon

Structural, chemical and superconducting properties of thin NbN films used for development of fast and sensitive hot-electron bolometer (HEB) detectors for wide spectra range are reported. The thin NbN films with a thickness between 4 and 10 nm were deposited on the (001)Si substrates by magnetron sputtering. In order to investigate the film morphology and microchemistry, diffraction-contrast and high-resolution transmission electron microscopy (TEM) in combination with scanning TEM and electron energy loss spectroscopy (EELS) were performed. In addition, the zero-resistance critical temperature of the NbN films was measured and correlated to their thickness. The interrelations between fabrication conditions, crystalline and superconducting properties of the differently thick NbN films are discussed.