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 а tradeoff between the highest possible normal state conductivity
σ₀
, the smallest London penetration depth
λ_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
σ
₀
= 11·10
³
1/(Ohm·сm),
λ_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.