Characterization of the thin-film NbN superconductor for single-photon detection by transport measurements

• Published in: Physical review. B, Condensed matter and materials physics Vol. 87; no. 18
• Main Authors: Lin, Shi-Zeng, Ayala-Valenzuela, Oscar, McDonald, Ross D., Bulaevskii, Lev N., Holesinger, Terry G., Ronning, Filip, Weisse-Bernstein, Nina R., Williamson, Todd L., Mueller, Alexander H., Hoffbauer, Mark A., Rabin, Michael W., Graf, Matthias J.
• Format: Journal Article
• Language: English
• Published: United States American Physical Society 17-05-2013
• Subjects: Condensed matter; Fluid flow; Magnetic fields; Scanning electron microscopy; Size distribution; Superconductors; Thin films; Transport; Vortices
• ISSN: 1098-0121; 1550-235X
• DOI: 10.1103/PhysRevB.87.184507

The fabrication of high-quality thin superconducting films is essential for single-photon detectors. Their device performance is crucially affected by their material parameters, thus requiring reliable and nondestructive characterization methods after the fabrication and patterning processes. Important material parameters to know are the resistivity, superconducting transition temperature, relaxation time of quasiparticles, and uniformity of patterned wires. In this work, we characterize micropatterned thin NbN films by using transport measurements in magnetic fields. We show that from the instability of vortex motion at high currents in the flux-flow state of the IV characteristic, the inelastic lifetime of quasiparticles can be determined to be about 2 ns. Additionally, from the depinning transition of vortices at low currents, as a function of magnetic field, the size distribution of grains can be extracted. This size distribution is found to be in agreement with the film morphology obtained from scanning electron microscopy and high-resolution transmission electron microscopy images.