Influence of sheet resistance and strip width on the detection efficiency saturation in micron-wide superconducting strips and large-area meanders
Yu. P. Korneeva, N. N. Manova, Mikhail Dryazgov, N O Simonov, Philipp Zolotov, A. Korneev
Abstract
Abstract We report our study of detection efficiency (DE) saturation in wavelength range 400–1550 nm for the NbN superconducting microstrip single-photon detectors (SMSPDs) featuring the strip width up to 3 µ m. We observe an expected decrease of the DE saturation plateau with the increase of photon wavelength and decrease of film sheet resistance. At 1.7 K temperature DE saturation can be clearly observed at 1550 nm wavelength in strip with the width up to 2 µ m when sheet resistance of the film is above 630 Ω sq −1 . In such strips the length of the saturation plateau almost does not depend on the strip width. We used these films to make meander-shaped detectors with the light sensitive area from 20 × 20 µ m 2 to a circle 50 µ m in diameter. In the latter case, the detector with the strip width of 0.49 µ m demonstrates saturation of DE up to 1064 nm wavelength. Although DE at 1310 and 1550 nm is not saturated, it is as high as 60%. The response time is limited by the kinetic inductance and equals to 20 ns (by 1/ e decay), timing jitter is 44 ps. When coupled to multi-mode fibre large-area meanders demonstrate significantly higher dark count rate which we attribute to thermal background photons, thus advanced filtering technique would be required for practical applications.