Superconducting nanowire single-photon detectors (SNSPDs) are crucial for quantum optics, quantum communication, and deep-space laser communications, offering high detection efficiency, low dark counts, and excellent timing performance. However, improving efficiency in the near- to mid-infrared, remains challenging. Ion irradiation has recently emerged as a promising post-processing method for optimizing SNSPD performance.
This work investigates the effects of helium ion irradiation on the thermal properties of NbN-based SNSPDs. We examine the evolution of thermal boundary conductance (TBC) under varying ion fluences (0–1.1×10⁷ ions/cm²), observing a nearly linear decrease with increasing fluence, followed by saturation around 9×10⁶ ions/cm². Measurements of inelastic scattering rates and hotspot relaxation times show a significant increase after irradiation. Furthermore, transmission electron microscopy (TEM) reveals irradiation-induced vacancy defects at the NbN/SiO₂ interface, leading to prolonged thermal relaxation times. Together with modifications in electrical properties, these changes contribute to enhanced internal detection efficiency in irradiated devices.
Our findings provide new insights into post-processing of SNSPDs via ion irradiation, offering a pathway to improve detection efficiency and tune thermal properties in superconducting devices. This work also advances the understanding of defect engineering in superconducting thin films and their device.