Characterisation of amorphous molybdenum silicide (MoSi) superconducting thin films and nanowires

Abstract

We report on the optimisation of amorphous molybdenum silicide thin film growth for superconducting nanowire single-photon detector (SNSPD) applications. Molybdenum silicide was deposited via co-sputtering from Mo and Si targets in an Ar atmosphere. The superconducting transition temperature (Tc) and sheet resistance (Rs) were measured as a function of thickness and compared to several theoretical models for disordered superconducting films. Superconducting and optical properties of amorphous materials are very sensitive to short- (up to 1 nm) and medium-range order (∼1–3 nm) in the atomic structure. Fluctuation electron microscopy studies showed that the films assumed an A15-like medium-range order. Electron energy loss spectroscopy indicates that the film stoichiometry was close to Mo83Si17, which is consistent with reports that many other A15 structures with the nominal formula A3B show a significant non-stoichiometry with A:B > 3:1. Optical properties from ultraviolet (270 nm) to infrared (2200 nm) wavelengths were measured via spectroscopic ellipsometry for 5 nm thick MoSi films indicating high long wavelength absorption. We also measured the current density as a function of temperature for nanowires patterned from a 10 nm thick MoSi film. The current density at 3.6 K is 3.6 × 105 A cm−2 for the widest wire studied (2003 nm), falling to 2 × 105 A cm−2 for the narrowest (173 nm). This investigation confirms the excellent suitability of MoSi for SNSPD applications and gives fresh insight into the properties of the underlying materials.

Superconducting MoSi nanowires

“…4. The largest wire has typical characteristics of a superconductor with critical current density approximately 92 kA/cm 2 which is comparable to those observed in larger MoSi wires [13]. The second wire with diameter 54 nm has a significantly lower critical current density about 28 kA/cm 2 .…”

“…As the material, we selected thermally formed molybdenium silicide (MoSi) which is well compatible with CMOS processes for quantum circuits [23]. In general, silicides have several ideal properties: tunable superconducting critical temperature T c , possibility to tailor normal state resistivity from low to very high values, and proven high quality of the superconductor [11,13,24] when the device is fabricated on proper substrate and with diffusion barriers.…”

Quasiparticle tunnel electroresistance in superconducting junctions

“…As we will see, the superconducting properties of MoSi do not play a role in the present experiments. YBCO and MoSi have very different carrier concentration-respectively,~3 × 10 20 cm −3 and~3 × 10 22 cm −3 - 29,30 and consequently the Thomas-Fermi screening length is expectedly 29 shorter in MoSi (~Ǻ) than in YBCO (~nm). Thus, the pair of electrodes endow the junctions with the asymmetry that expectedly contributes to TER 15 of ferroelectric tunnel junctions.…”

Magic-Angle Bilayer Graphene Nanocalorimeters: Toward Broadband, Energy-Resolving Single Photon Detection

“…The inset depicts the experimentally obtained resistance of our MAG device as a function of carrier density n and base temperature T, exhibiting a variety of phases including metallic, correlated (CS) and superconducting (SC) states. Data for carrier densities is extracted from Refs(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44).…”