Characterisation of amorphous molybdenum silicide (MoSi) superconducting thin films and nanowires. (12th July 2017)

• Record Type: Journal Article
• Authors: Banerjee, Archan; Baker, Luke J; Doye, Alastair; Nord, Magnus; Heath, Robert M; Erotokritou, Kleanthis; Bosworth, David; Barber, Zoe H; MacLaren, Ian; Hadfield, Robert H
• Is Part Of: Superconductor science & technology. Volume 30:Number 8(2017:Aug.)
• Publication Date: 2017-07-12
• Subjects: superconducting thin films -- superconducting nanowire single-photon detector -- amorphous superconductor -- molybdenum silicide; Superconductivity -- Periodicals; Superconductors -- Periodicals; 537.623
• DOI: 10.1088/1361-6668/aa76d8
• Languages: English
• ISSNs: 0953-2048

Abstract

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 ( T c ) and sheet resistance ( R s ) 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 Mo83 Si17, which is consistent with reports that many other A15 structures with the nominal formula A 3 B 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 × 10 5 A cm −2 for the widest wire studied (2003 nm), falling to 2 × 10 5 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.