Current dependence of the hot-spot response spectrum of superconducting single-photon detectors with different layouts

Abstract

We show that avoiding bends in a current-carrying superconducting nanowire enhances the probability for low energy photons to be detected and that this enhancement is entirely due to the increase in the experimentally achievable critical current. We studied nanowires shaped as either meander or spiral. The spirals had different layouts, a double-spiral layout with an S-turn in the middle and a single-spiral layout without such turn. Nanowires were prepared from films of niobium nitride with a thickness of 5 nm. For specimens with each layout we measured the spectra of the single-photon response in the wavelength range from 400 nm to 1600 nm and defined the cut-off wavelength (λc) beyond which the response rolls off. The largest and the smallest λc were found for the single-spiral layout and for the meander, respectively. For all three layouts the relationship between λc and the relative bias current falls onto a universal curve which has been predicted earlier in the framework of the modified hot-spot model. For the single-spiral layout, the efficiency of photon detection at wavelengths smaller than λc reaches the expected absorbance of the spiral structure and the timing jitter per unit length of the nanowire has the smallest value.

Design of NbN superconducting nanowire single photon detectors with enhanced infrared photon detection efficiency

“…These data show that the internal detection efficiency for a telecommunication wavelengths of 1550 nm is less than 100% in devices and depends on polarization. Good quantitative agreement between these data and the empirical model can be achieved if one assumes that these meandering wire devices cannot be biased beyond a current density that is ∼ 90% of the material limited critical current density measured on the nanodetector [3,15,20] In this article we are interested in the implications of the local detection efficiency for future detector design and we need a stable and reliable implementation of the function γ(x). The original empirical model shows small, non-monotonic, variations in detection efficiency closer to the edges of the wire that are currently not understood.…”

“…significantly wider than the nanowires in NbN based SSPDs [1,2]. In this simple geometry the device critical current is closer to the critical current density of the material [15]. For (meandering) wires the device critical current is limited by other factors such as current crowding in bends [17], fabrication defects along the wire [14,18], thickness variations of the wire, or inhomogeneities intrinsic to the superconducting material [19].…”

“…In general, thin and narrow wires are more difficult to fabricate but are expected to be better for detecting low energy photons because the absorption of a single photon in these devices affects a larger fraction of the total available Cooper pairs compared to a thicker and wider wire. However, thicker and wider wire are easier to fabricate with fewer defects [14,15] and, more importantly, imply a lower kinetic inductance of the wire which yields detectors with a desirable faster response time [3]. As a numerical example we estimate the kinetic inductance of a standard, 100 nm wide meandering wire covering a 10×10 µm 2 area to be L k = λ k L/A = 450 nH.…”

Design of NbN Superconducting Nanowire Single-Photon Detectors with Enhanced Infrared Detection Efficiency

“…In general, thin and narrow wires are more difficult to fabricate but are expected to be better for detecting low-energy photons because the absorption of a single photon in these devices affects a larger fraction of the total available Cooper pairs compared to a thicker and wider wire. Thicker and wider wires are easier to fabricate with fewer defects [14,15] and, more importantly, imply a lower kinetic inductance of the wire which yields detectors with a desirable faster response time [3]. As a numerical example, we estimate the kinetic inductance of a standard, 100-nmwide meandering wire covering a 10 × 10 μm 2 area to be L k ¼ λ k L=A ¼ 450 nH.…”

“…We have reported a linear relation between a threshold current and photon energies for 150-nm-wide NbN nanodetectors [16], i.e., significantly wider than the nanowires in NbN-based SSPDs [1,2]. In this simple geometry, the device critical current is closer to the critical current density of the material [15]. For (meandering) wires, the device critical current is limited by other factors, such as current crowding in bends [17], fabrication defects along the wire [14,18], thickness variations of the wire, and inhomogeneities intrinsic to the superconducting material [19].…”