Superconducting nanowire single-photon detectors (SNSPDs) with high system detection efficiency (SDE) would enable remarkable experiments in quantum information processing. However, realizing a NbN SNSPD with saturated intrinsic detection efficiency (IDE) that retains high SDE at near-infrared wavelengths is challenging, due to the high critical temperature of NbN. This study uses defect engineering by helium-ion irradiation to enhance the IDE of NbN SNSPDs to saturation without sacrificing SDE. This technique also allows direct comparison of irradiation-induced changes in detector performance, making it a useful tool for studying the physics of superconducting devices.
Superconducting nanowire single-photon detectors (SNSPDs) with high system detection efficiency (SDE) would enable remarkable experiments in quantum information processing. However, realizing a NbN SNSPD with saturated intrinsic detection efficiency (IDE) that retains high SDE at near-infrared wavelengths is challenging, due to the high critical temperature of NbN. This study uses defect engineering by helium-ion irradiation to enhance the IDE of NbN SNSPDs to saturation without sacrificing SDE. This technique also allows direct comparison of irradiation-induced changes in detector performance, making it a useful tool for studying the physics of superconducting devices.
Abstract Superconducting nanowire single-photon detectors (SNSPDs) offer high system detection efficiency (SDE), low dark counts, and excellent timing resolution, making them indispensable for applications from quantum optics to deep-space optical communications. Although near-unity SDE and intrinsic detection efficiency (IDE) have been achieved at near-infrared wavelengths through advanced fabrication and optical design, further improving IDE at the material and device levels remains essential for achieving broader bandwidths, higher operating temperatures, and simplified processing. Here, we explored helium ion irradiation as a post-fabrication method to modify the thermal properties of NbN SNSPDs without altering their geometry or material stack. With increasing fluence (0–1.1 × 10 17 ions cm −2 ), the thermal boundary conductance decreases by 57% from 127 W m −2 K −4 to 54 W m −2 K −4 , and saturates near 9 × 10 16 ions cm −2 . At this fluence, the minimum hotspot relaxation time increases by 41%, rising from 17 ps to 24 ps, while the electron–phonon interaction time decreases, with the magnitude of change depending on temperature and sample batch. Transmission electron microscopy reveals interfacial disorder near the NbN/SiO₂ interface (6–8 nm) and localized defects in the SiO₂ layer (30–260 nm), correlating with thermal transport suppression. These thermal modifications have a significant impact on relaxation dynamics and contribute to IDE enhancement. Our findings establish ion irradiation as an effective strategy for thermal tuning in SNSPDs, providing new insights into defect engineering for superconducting optoelectronic devices.
Superconducting nanowire single-photon detectors (SNSPDs) have attracted considerable attention owing to their excellent detection performance; however, the underlying physics of the detection process is still unclear. In this study, we investigate the wavelength dependence of the intrinsic detection efficiency (IDE) for NbN SNSPDs. We fabricate various NbN SNSPDs with linewidths ranging from 30 nm to 140 nm. Then, for each detector, the IDE curves as a function of bias current for different incident photon wavelengths of 510–1700 nm are obtained. From the IDE curves, the relations between photon energy and bias current at a certain IDE are extracted. The results exhibit clear nonlinear energy–current relations for the NbN detectors, indicating that a detection model only considering quasiparticle diffusion is unsuitable for the meander-type NbN-based SNSPDs. Our work provides additional experimental data on SNSPD detection mechanism and may serve as an interesting reference for further investigation.
The intrinsic detection performance of superconducting nanowire single photon detectors (SNSPDs) is highly dependent on the superconducting properties of underlying thin films. This report outlines the enhancement of detection performance for single telecom wavelength photons in disordered NbTiN SNSPD at 4.2 K. By increasing the nitrogen content and deposition pressure, the NbTiN films show suppression in critical temperature and an increase in sheet resistance. Notably, the resulting SNSPDs display a broader saturation plateau at 2.2 K, leading to superior detection performance at 4.2 K. With the disordered 7-nm-thick NbTiN films, we fabricated SNSPDs with system detection efficiency up to 83% for 1550 nm photons at 4.2 K. Moreover, these devices also show saturated intrinsic detection efficiency for 2000 nm photons. With the features outlined, the devices can be integrated into the idle 4.2 K stage of the dilution refrigerator for applications in optical quantum information processing or utilize for detecting laser radar signals in airborne platforms.
Superconducting nanowire single-photon detector (SNSPD) with near-unity system efficiency is a key enabling, but still elusive, technology for numerous quantum fundamental theory verifications and quantum information applications. The key challenge is to have both a near-unity photon-response probability and absorption efficiency simultaneously for the meandered nanowire with a finite filling ratio, which is more crucial for NbN than other superconducting materials (e.g., WSi) with lower transition temperatures. Here, we overcome the above challenge and produce NbN SNSPDs with a record system efficiency by replacing a single-layer nanowire with twin-layer nanowires on a dielectric mirror. The detector at 0.8 K shows a maximal system detection efficiency (SDE) of 98% at 1590 nm and a system efficiency of over 95% in the wavelength range of 1530-1630 nm. Moreover, the detector at 2.1 K demonstrates a maximal SDE of 95% at 1550 nm using a compacted two-stage cryocooler. This type of detector also shows the robustness against various parameters, such as the geometrical size of the nanowire and the spectral bandwidth, enabling a high yield of 73% (36%) with an SDE of >80% (90%) at 2.1 K for 45 detectors fabricated in the same run. These SNSPDs made of twin-layer nanowires are of important practical significance for batch production.
Superconducting nanowire single-photon detectors (SNSPDs) play a pivotal role in infrared single-photon-detection applications owing to their free-running mode, near-unity detection efficiency, and excellent time resolution. However, conventional niobium nitride- (NbN) SNSPDs often have a trade-off between optimal detection efficiency and time resolution. We herein demonstrate NbN SNSPDs in the combination of high efficiency and time resolution by using the helium-ion-irradiated film of 10 nm and a homemade cryogenic amplifier to improve the signal-to-noise ratio. The proposed 18-μm-diameter device operated at 850 mK shows a saturated system detection efficiency of ∼90.5% at 1550 nm wavelength with a dark count rate below 50 counts per second (cps), and minimum system timing jitter of ∼14.7 ps. Meanwhile, the recovery time is 21.2 ns owing to its lower kinetic inductance. The time-of-flight light detection and ranging with this device was further carried out indoors, which demonstrates a submillimeter (<0.5 mm) depth resolution, as well as good depth and intensity reconstruction of a low-signature object even under the dwell time of 0.5 ms. It indicates that our device has a great advantage and potential in high-time-resolution and weak-signal-detection applications, such as real-time imaging, fluorescence lifetime detection, and remote laser sensing.
Superconducting nanowire single-photon detectors (SNSPDs) are indispensable in fields such as quantum science and technology, astronomy, and biomedical imaging, where high detection efficiency, low dark count rates, and high timing accuracy are required. Recently, helium (He) ion irradiation was shown to be a promising method to enhance SNSPD performance. Here, we study how changes in the underlying superconducting NbTiN film and the SiO2/Si substrate affect device performance. While irradiated and unirradiated NbTiN films show similar crystallinity, we observe He bubble formation below the SiO2/Si interface and an amorphization of the Si substrate. Both reduce the thermal conductance between the superconducting thin film and the substrate from 210 to 70 W m−2 K−4 after irradiation with 2000 ions nm−2. This effect, combined with the lateral straggle of He ions in the substrate, allows the modification of the superconductor-to-substrate thermal conductance of an SNSPD by selectively irradiating only the regions around the nanowire. With this approach, we achieved a broader bias current range (9.8 μA vs 3.7 µA) in which the detector operates at its maximum detection efficiency, which is beneficial for reducing dark counts while maintaining high sensitivity. Moreover, the photon-assisted critical current remained similar to that of the unirradiated reference device (59.0 µA vs 60.1 µA), while full irradiation reduced it to 22.4 µA. Our results suggest that the irradiation-induced reduction of the thermal conductance significantly enhances SNSPD sensitivity, offering a novel approach to locally engineer substrate properties for improved detector performance.