Research on the Correlation of Physical Properties Between NbN Superconducting Thin Films and Substrates

This paper investigates the relationship between the physical properties of NbN thin films and a series of different substrates/buffer layers used for the thin film growth. Substrates, including 4H-SiC, AlN/Si, AlN/sapphire, and annealed AlN/sapphire, were selected for NbN film deposition via DC magnetron sputtering. Post-deposition annealing was also employed to study its impact on the films’ quality. Comprehensive characterizations were performed on NbN films, focusing on superconducting critical temperature (TC), transition width (ΔTC), crystalline quality, and surface roughness. The results demonstrate that the annealed NbN films grown on 4H-SiC substrates with the highest crystalline quality exhibit optimal crystalline quality, achieving a TC of 16.3 K. Experimental results reveal intrinsic correlations between the critical properties of NbN superconducting thin films and substrate structural characteristics; the impact of post-growth annealing on the TC is also studied.