Physical properties of amorphous molybdenum silicide films for single-photon detectors

We systematically investigated the physical properties of amorphous MoXSi1-X films deposited by magnetron co-sputtering. The critical temperature Tc of MoXSi1-X films increases gradually with the Mo stoichiometry x, and the highest Tc = 7.9 K was found in Mo0.83Si0.17, where homogeneous films with the maximum Mo content can be obtained. The thick films of Mo0.83Si0.17 show surprising degradation in which the onset of zero-resistivity is suppressed below 2 K. The thin Mo0.83Si0.17films, however, reveal robust superconductivity even with thickness d ≈ 2 nm. We also characterized wide microwires based on the 2 nm thin Mo0.8Si0.2 films with wire widths 40 and 60 μm, which show single-photon sensitivity at 780 nm and 1550 nm wavelength.