Tantalum nitride superconducting single-photon detectors with low cut-off energy

Abstract

Materials with a small superconducting energy gap are expected to favor a high detection efficiency of low-energy photons in superconducting nanowire single-photon detectors. We developed a TaN detector with smaller gap and lower density of states at the Fermi energy than in comparable NbN devices, while other relevant parameters remain essentially unchanged. The observed reduction of the minimum photon energy required for direct detection is in line with model predictions of ≈ 1/3 as compared to NbN.

Numerical analysis of detection-mechanism models of superconducting nanowire single-photon detector

“…However, more plausible values 9,12,41 for the conversion efficiency are on the order of 0.1, in which case correspondingly higher photon energies are required.…”

“…In Table I, we summarize typical values of material parameters for high-quality films of TaN 9 and NbN 25 as we used them in the calculations. The parameters D; n; k GL , and D qp are assumed to be temperature dependent (see Appendix B for details).…”

“…The effective diffusion coefficient becomes t-dependent and approaches D qp once the generation of additional QPs has stopped for t ) s qp . (5) and (9). Arrows indicate the times of maximum total number of QPs, s th , maximum number of QPs in the n-slab, t max , and QP multiplication time scale, s qp .…”

“…5,6 The active element of these detectors consists of a typically square meander of a superconducting NbN film of a few nanometer thickness. 7 Recently, alternative superconducting materials have been suggested, such as NbTiN, 8 TaN, 9 or WSi, 10 which may be better suited than NbN for certain applications. The detectors are biased with a constant direct current I bias which usually equals about 90% to 95% of the experimental critical current I c .…”

Optically probing the detection mechanism in a molybdenum silicide superconducting nanowire single-photon detector

“…15 SNSPDs based on these materials currently have the highest reported detection efficiencies (93% for WSi 12 ), as well as a higher fabrication yield 16 than devices made of polycrystalline materials such as niobium nitride (NbN), 1 niobium titanium nitride (NbTiN) 17 and tantalum nitride (TaN). 18 MoSi SNSPDs tailored to specific advanced photon counting applications have recently been reported, including integration on an optical waveguide, 19 UV single-photon detection 20 and integrated ion trapping. 21 One striking difference with polycrystalline materials is that amorphous SNSPDs have a detection efficiency that saturates at bias currents well below the critical current.…”