Evolution of superconducting properties with disorder in epitaxial NbN films

NbN is a conventional BCS superconductor in which disorder can be tuned from moderately clean limit to dirty limit without affecting its epitaxial nature. We studied the superconducting properties of epitaxial NbN films of different disorder characterized by k_Fl ranging from 8.77 to 2.56 through the transport measurements. Using reactive magnetron sputtering NbN films of different disorder are deposited by varying the sputtering power and amount of N₂ in Ar:N₂ mixture of sputtering gas. The disorder parameter k_Fl is obtained from the carrier density (n) and the resistivity (ρ) of the films. NbN films with higher disorder have lower transition temperature (T_c) and larger resistivity which decreases with decreasing disorder. The carrier density determined from Hall measurements show that highly disordered films have lower carrier density and vice versa. Our studies show that NbN is a good system to investigate the effects of disorder on superconductivity where the superconducting properties evolve with the disorder in thin films.