High Performance Ultra-Thin Niobium Films for Superconducting Hot-Electron Devices

High-quality ultrathin film is the key element of hot-electron devices. Using a doped sputtering target, high-performance niobium (Nb) ultrathin films are grown on high-resistivity silicon (Si), magnesium oxide (MgO), and sapphire substrates, optimized by grown 1-nm-thick aluminum nitride (AlN) films on the top. Superconducting transition temperature (TC) of about 7.5 K and critical current density (JC) of about 8.2 × 106A/cm2at 4.2 K have been obtained for the Nb film of 6.5 nm thickness on MgO substrates. The results of the films' structural characterization by X-ray photo electronic spectroscopy, atomic force microscopy, transmission electron microscopy, and X-ray diffraction are also presented.