On the fluctuation conductivity of NbTiN thin films in the vicinity of superconducting transition

We report studies of fluctuation conductivity (FC) near the superconducting transition temperature of NbTiN thin films prepared by varying the N2 partial pressure during DC magnetron sputtering on the MgO substrate. Transport measurements revealed that the transition temperature (Tc) of the films is dependent on the N2 partial pressure, with an optimum window of 5.8% to 8.51%. The temperature-dependent conductivities of these films were analyzed within the framework of Aslamazov and Larkin model (AL) of FC in the vicinity of Tc and away from it. In addition, the magneto-resistance of these films was also analysed. Within the framework of AL theory, the normal state conductivity just above Tc can be described by a transition from a 2D to a 1D regime. It has been concluded that the N2 partial pressure is one of the important deposition conditions to be optimized for getting the best superconducting (SC) properties. Our findings are important with respect to the optimization of the SC properties of NbTiN films, specifically for single photon detection applications, wherein fluctuation plays a dominant role in determining the efficiency and dark count rate of the detectors.