Characterization of Microwave Properties of Superconducting NbTiN Films Using TDS

In this article, we perform systematic study of electrodynamic properties of superconducting NbTiN films at frequencies 0.2-2.5 terahertz (THz) and in temperature range from 4 to 15 K using time-domain spectrometer. The goal is to achieve the best parameters of the films at THz frequencies; that is to reach a tradeoff between the highest possible normal state conductivity sigma(0), the smallest London penetration depth lambda(L), and the highest energy gap and critical temperature T-c. To do this, it is necessary to determine the optimal manufacturing conditions; to this end, a set of NbTiN films of various compositions was fabricated, controlled by the nitrogen pressure in the magnetron chamber. As a result, the film with parameters sigma(0) = 11 center dot 10(3) 1/(Ohm center dot cm), lambda(L) = 280 nm, and T-c = 14.4 K were obtained. To fit the experimental data, two models with and without taking intragap states into account were used, and both of them are in good agreement with experiment.