38 research outputs found
Magnetic-field enhancement of performance of superconducting nanowire single-photon detector
We present SNSPDs from NbN nanowires shaped after square-spiral that allows
an increase not only in critical currents but also an extension of spectral
detection efficiencies by just applying an external magnetic field. Using
negative electron-beam lithography with the positive resist for shaping
nanowires, made it possible to reduce the inner bend radius. Consequently, the
effect of critical-current enhancement in the magnetic field becomes stronger
than it was demonstrated earlier. Here we achieved a 13% increase of the
critical current in the magnetic field. We measured spectra of the
single-photon detection efficiency in the wavelength range from 400 to 1100 nm
in the magnetic field. At zero field, the square spiral has the spectrum
similar to that of a meander. At the field providing the maximum of the
critical current, the detection efficiency and the cut-off wavelength in the
spectrum increase by 20% and by 54%, correspondingly. The magnetic-field
dependence of dark count rate is well described by proposed analytical model
Improving the Spectral Bandwidth of Superconducting Nanowire Single-Photon Detectors (SNSPDs)
This work presents a comprehensive investigation of the influence of geometry-dependent factors on performance metrics of superconducting single-photon detectors. With fundamental knowledge, main investigations are focused to extend the spectral bandwidth and to enhance the detection efficiency, especially in infrared range. The developed technology of single-spiral detectors and unconventional electron-beam lithography allows to improve the performance of superconducting detectors
Measuring thickness in thin NbN films for superconducting devices
We present the use of a commercially available fixed-angle multi-wavelength
ellipsometer for quickly measuring the thickness of NbN thin films for the
fabrication and performance improvement of superconducting nanowire single
photon detectors. The process can determine the optical constants of absorbing
thin films, removing the need for inaccurate approximations. The tool can be
used to observe oxidation growth and allows thickness measurements to be
integrated into the characterization of various fabrication processes
Enhancement of optical response in nanowires by negative-tone PMMA lithography
The method of negative-tone-PMMA electron-beam lithography is investigated to
improve the performance of nanowire-based superconducting detectors. Using this
approach, the superconducting nanowire single-photon detectors (SNSPDs) have
been fabricated from thick 5-nm NbN film sputtered at the room temperature. To
investigate the impact of this process, SNSPDs were prepared by positive-tone
and negative-tone-PMMA lithography, and their electrical and photodetection
characteristics at 4.2 K were compared. The SNSPDs made by negative-tone-PMMA
lithography show higher critical-current density and higher photon count rate
at various wavelengths. Our results suggest a higher negative-tone-PMMA
technology may be preferable to the standard positive-tone-PMMA lithography for
this application
Magnetic-field enhancement of performance of superconducting nanowire single-photon detector
We present SNSPDs from NbN nanowires shaped after square-spiral that allows
an increase not only in critical currents but also an extension of spectral
detection efficiencies by just applying an external magnetic field. Using
negative electron-beam lithography with the positive resist for shaping
nanowires, made it possible to reduce the inner bend radius. Consequently, the
effect of critical-current enhancement in the magnetic field becomes stronger
than it was demonstrated earlier. Here we achieved a 13% increase of the
critical current in the magnetic field. We measured spectra of the
single-photon detection efficiency in the wavelength range from 400 to 1100 nm
in the magnetic field. At zero field, the square spiral has the spectrum
similar to that of a meander. At the field providing the maximum of the
critical current, the detection efficiency and the cut-off wavelength in the
spectrum increase by 20% and by 54%, correspondingly. The magnetic-field
dependence of dark count rate is well described by proposed analytical model
Timing jitter in photon detection by straight superconducting nanowires: Effect of magnetic field and photon flux
We studied the effect of the external magnetic field and photon flux on
timing jitter in photon detection by straight superconducting NbN nanowires. At
two wavelengths 800 and 1560 nm, statistical distribution in the appearance
time of the photon count exhibits Gaussian shape at small times and exponential
tail at large times. The characteristic exponential time is larger for photons
with smaller energy and increases with external magnetic field while variations
in the Gaussian part of the distribution are less pronounced. Increasing photon
flux drives the nanowire from quantum detection mode to the bolometric mode
that averages out fluctuations of the total number of nonequilibrium electrons
created by the photon and drastically reduces jitter. The difference between
Gaussian parts of distributions for these two modes provides the measure for
the electron-number fluctuations. Corresponding standard deviation increases
with the photon energy. We show that the two-dimensional hot-spot detection
model explains qualitatively the effect of magnetic field
Detecting Dark Matter with Superconducting Nanowires
We propose the use of superconducting nanowires as both target and sensor for
direct detection of sub-GeV dark matter. With excellent sensitivity to small
energy deposits on electrons, and demonstrated low dark counts, such devices
could be used to probe electron recoils from dark matter scattering and
absorption processes. We demonstrate the feasibility of this idea using
measurements of an existing fabricated tungsten-silicide nanowire prototype
with 0.8 eV energy threshold and 4.3 nanograms with 10 thousand seconds of
exposure, which showed no dark counts. The results from this device already
place meaningful bounds on dark matter-electron interactions, including the
strongest terrestrial bounds on sub-eV dark photon absorption to date. Future
expected fabrication on larger scales and with lower thresholds should enable
probing new territory in the direct detection landscape, establishing the
complementarity of this approach to other existing proposals.Comment: 7 pages, 4 figure