Site-Selective Enhancement of Superconducting Nanowire Single-Photon Detectors via Local Helium Ion Irradiation

Achieving homogeneous performance metrics between nominally identical pixels is challenging for the operation of arrays of superconducting nanowire single-photon detectors (SNSPDs). Here, local helium ion irradiation is utilized to post-process and tune single-photon detection efficiency, switching current, and critical temperature of individual devices on the same chip. For 12 nm thick highly absorptive SNSPDs, which are barely sensitive to single photons with a wavelength of 780 nm prior to He ion irradiation, an increase of the system detection efficiency from <0.05% to (55.3 +/- 1.1)% is observed following irradiation. Moreover, the internal detection efficiency saturates at a temperature of 4.5 K after irradiation with 1800 ions nm(-2). Compared to 8 nm SNSPDs of similar detection efficiency, a doubling of the switching current (to 20 A) is observed for irradiated 10 nm thick detectors, increasing the amplitude of detection voltage pulses. Investigations of the scaling of superconducting thin film properties with irradiation up to a fluence of 2600 ions nm(-2) revealed an increase of sheet resistance and a decrease of critical temperature towards high fluences. A physical model accounting for defect generation and sputtering during helium ion irradiation is presented and shows good qualitative agreement with experiments.