Evaluation of the single-photon detector characteristics depending on the parameters of a W$_x$S$_{(i-x)}$ superconducting film

The absorption efficiency, cut-off wavelength, and recovery time of a superconducting nanowire single-photon detector were calculated as functions of the surface resistance Rs and the critical temperature $T_c$ of the W$_x$S$_{(i-x)}$ film. The calculated dependences for the SNSPD on W$_x$S$_{(i-x)}$ films show that films with $T_c$ > 3.5 K and 300 < $R_c$ < 420 $\Omega$/sq will provide $\eta_{\mathrm{abs}}\approx15\dots$ 20%, $\eta_{\mathrm{IDE}}$=100% at a wavelength of 1550 nm and the recovery time $\tau$ < 40 ns, which corresponds to the possible SNSPD count rate $CR_{\mathrm{max}}$ = 25 MHz.