[Paper Review] High-efficiency superconducting nanowire single-photon detectors fabricated from MoSi thin-films

Varun Verma, Boris Korzh+10 more|arXiv (Cornell University)|Apr 10, 2015

Quantum Information and Cryptography33 references111 citations

TL;DR

This paper demonstrates high-efficiency superconducting nanowire single-photon detectors (SNSPDs) fabricated from MoSi thin-films and embedded in a dielectric optical stack to enhance absorption at 1542 nm. The devices achieve a maximum system detection efficiency of 87 ± 0.5% at 0.7 K with a record-low jitter of 76 ps, outperforming WSi-based SNSPDs in jitter while maintaining comparable efficiency, even at elevated temperatures up to 2.3 K.

ABSTRACT

We demonstrate high-efficiency superconducting nanowire single-photon detectors (SNSPDs) fabricated from MoSi thin-films. We measure a maximum system detection efficiency (SDE) of 87 +- 0.5 % at 1542 nm at a temperature of 0.7 K, with a jitter of 76 ps, maximum count rate approaching 10 MHz, and polarization dependence as low as 3.4 +- 0.7 % The SDE curves show saturation of the internal efficiency similar to WSi-based SNSPDs at temperatures as high as 2.3 K. We show that at similar cryogenic temperatures, MoSi SNSPDs achieve efficiencies comparable to WSi-based SNSPDs with nearly a factor of two reduction in jitter.

Motivation & Objective

• To develop high-efficiency SNSPDs using MoSi thin-films as an alternative to WSi or NbN materials.
• To reduce jitter in amorphous superconductor-based SNSPDs while maintaining high internal detection efficiency.
• To enable operation at higher cryogenic temperatures (up to 2.3 K) without sacrificing efficiency, reducing cryogenic system complexity and cost.
• To minimize polarization dependence and dark count rates through optimized optical stack design and fiber management.

Proposed method

• Deposited 6.6 nm Mo0.8Si0.2 thin-film via DC magnetron sputtering at room temperature and capped with amorphous Si to prevent oxidation.
• Fabricated SNSPDs using electron beam lithography and SF6 plasma etching to define 20 µm-wide nanowire meanders with 130 nm width and 215 nm pitch.
• Integrated the SNSPDs into a dielectric optical stack consisting of Au/Ti mirrors, SiO2 spacer, and multilayer antireflection coatings to maximize 1550 nm absorption.
• Used a 1542 nm continuous-wave laser with NIST-calibrated power meter for input power calibration and system detection efficiency (SDE) measurement.
• Employed cryogenic preamplifiers at 40 K and room-temperature amplifiers with high gain (51 dB total) to minimize electronic noise and measure system jitter.
• Coiled optical fibers near the detector to suppress background counts from blackbody radiation, reducing dark count rates.

Experimental results

Research questions

• RQ1 Can MoSi-based SNSPDs achieve system detection efficiencies comparable to state-of-the-art WSi-based SNSPDs while significantly reducing jitter?
• RQ2 Does the internal detection efficiency of MoSi SNSPDs saturate at high temperatures (e.g., 2.3 K), enabling operation with simpler cryogenic systems?
• RQ3 To what extent does the optical stack design reduce polarization dependence and enhance photon absorption in MoSi SNSPDs?
• RQ4 What is the relationship between nanowire geometry, bias current, and system jitter in MoSi SNSPDs at low temperatures?
• RQ5 How effective is fiber coiling in suppressing dark counts from blackbody radiation in high-efficiency SNSPDs?

Key findings

• The MoSi SNSPD achieved a maximum system detection efficiency (SDE) of 87 ± 0.5% at 1542 nm when operated at 0.7 K, approaching the performance of WSi-based SNSPDs.
• The system jitter was measured at 76 ps at 0.7 K, representing a nearly two-fold reduction compared to WSi-based SNSPDs (~150 ps) at much lower temperatures.
• At 2.3 K, the SNSPD maintained a saturated internal efficiency of 79 ± 2%, demonstrating high performance even at elevated cryogenic temperatures.
• The polarization dependence was measured at only 3.4 ± 0.7%, significantly lower than most reported NbN and WSi-based SNSPDs, indicating high fill factor and optical stack effectiveness.
• The maximum count rate remained linear up to input photon fluxes approaching 10^7 photons per second, indicating excellent linearity and high dynamic range.
• Background count rates were reduced to below 10 cps for bias currents below 0.9ISW by coiling the optical fiber, which suppressed long-wavelength blackbody radiation.