We report a detailed study on control of sputtering parameters for synthesizing NbN superconducting thick films. The NbN films are deposited on single crystalline silicon (100) by DC reactive sputtering, i.e., deposition of Nb in the presence of reactive N2 gas. After several runs, samples were prepared with Ar:N2 partial gas ratios of 90:10, 80:20 and 70:30 for a deposition time of 10 minutes. The fabricated films (400 nm thick) crystallize with a cubic structure, with a small quantity of Nb/NbOx embedded in the main NbN phase. All three samples are characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX), to examine their microstructure and elemental compositional distributions, respectively. The roughness was mesured by atomic force microscopy (AFM). The optimized film prepared with Ar:N2 gas ratio of 80:20 has a Tc(R = 0) in zero and 140 kOe fields of 14.8 K and 8.8 K, respectively. The upper critical field Hc2(0) of the studied superconducting films is calculated from magneto-transport [R(T )H] measurements using GL and WHH equations.
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