Study of Niobium Mononitride Thin Films Grown Using High Power Impulse Magnetron Sputtering

Herein, the effect of microstructure on the electronic, and superconducting properties of niobium mononitride (NbN) thin films grown using a high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (dcMS) is studied. X-ray reflectivity, cross-sectional scanning electron microscopy and atomic force microscopy measurements suggest that the film grown with dcMS has a non-uniform distribution of islands with loosely packed columns while the HiPIMS grown film has a smoother surface and a denser microstructure. Although the X-ray diffraction measurements show a single-phase rock-salt-type crystal structure in both cases, the local and electronic structure analyzed using N K-edge X-ray absorption near edge structure measurements reveals the evidence of a large amount of Nb vacancies in dcMS-NbN while HiPIMS-NbN film is closer to stoichiometry. The ordered structure of HiPIMS-NbN sample results in a relatively higher superconducting transition temperature of 15.2 K and lower normal state resistivity of 90 mu omega cm with a moderate critical field of 18 T and smaller coherence length of 4.2 nm. These results suggest HiPIMS can be utilized to grow high-quality superconducting thin films of few nanometers required in modern technological devices such as single-photon detectors, superconducting quantum interference devices.