Superconducting nanowire single-photon detectors fabricated from atomic-layer-deposited NbN

Abstract

High-quality ultra-thin films of niobium nitride (NbN) are developed by plasma-enhanced atomic layer deposition (PEALD) technique. Superconducting nanowire single-photon detectors (SNSPDs) patterned from this material exhibit high switching currents and saturated internal efficiencies over a broad bias range at 1550 nm telecommunication wavelength. Statistical analyses on hundreds of fabricated devices show near-unity throughput yield due to exceptional homogeneity of the films. The ALD-NbN material represents an ideal superconducting material for fabricating large single-photon detector arrays combining high efficiency, low jitter, low dark counts.Superconducting nanowire single-photon detectors (SNSPDs) 1,2 have gained widespread attention due to their excellent performances, including high efficiency 3-6 , fast speed 7,8 , exceptional timing jitter 9-11 and ultra-low dark count rates 12,13 . In addition, their suitability for on-chip integration with various nanophotonics circuits 14-23 as well as their photon number resolving 24-26 and spectral 27-29 resolving capability render them an ideal choice for applications in quantum optics, quantum communications and quantum information processing [30][31][32] .The SNSPD is typically a narrow nanowire (20 nm -150 nm width) patterned from an ultra-thin superconducting film (3-10 nm thickness) for absorbing incident photons. So far, two main classes of superconducting materials have been utilized to fabricate high-efficiency SNSPDs: (1) poly-crystalline nitride superconductors such as NbN 4,15,33 and NbTiN 5,16,34-36 ;(2) amorphous alloy superconductors, such as WSi 3,37 , MoSi 6,11,21,38,39 and MoGe 40 . Each of these two classes of materials has their advantages and drawbacks in photon detection. The amorphous films have smaller superconducting energy gap and lower electron density, which tends to create larger photon-excited hot spots in the nanowires and thus results in better saturated internal efficiency. The structural homogeneity due to the absence of grain boundaries in these films further enables the fabrication of large-area detector arrays without suffering from serious constrictions 41,42 . The drawback is their relatively lower superconducting transition temperature T c (< 5 K for thin films) which sets their operation temperature below 2.5 K in order to achieve saturated efficiency at 1550 nm wavelength 43 . Poly-crystalline Nb(Ti)N-based detectors, on the other hand, have higher T c , higher critical current, relatively improved jitter performance and more immunity to latching at high operation speed due to their shorter hot spot relaxation time [44][45][46] . Consequently, Nb(Ti)N was exploited in the recent demonstration of GHzcounting-rate detectors 7,8 and sub-3 ps timing jitter 9 .In this Letter, we show our development of high-quality NbN thin films by plasma-enhanced atomic layer deposition (PEALD) and their applications in SNSPDs fabrication. The fabricated detectors demonstrate broad saturated plateaus in the efficiency curves that are compara...

Integrated photonics on thin-film lithium niobate

“…It is, therefore, more suitable to pattern the SNSPD after waveguide fabrication, which makes the lithography step for SNSPDs particularly challenging. Furthermore, both demonstrations employed specially tailored deposition processes for the superconducting thin film to avoid excessive heating, which is incompatible to LN thin films [423,424]. From our own experience, on bulk LN, pyroelectric effect tends to cause electrostatic discharge and damage the nanowires under rapid temperature change.…”

2022 Roadmap on integrated quantum photonics

“…To date, it appears that amorphous superconductors are favourable for the high-yield fabrication of SNSPDs with consistent properties. However, a recent report on NbN detectors realized by plasma-enhanced atomic layer deposition demonstrated excellent yield and reproducibility [211], which highlights the promising prospects for SNSPD technology upscaling via improving thin film deposition. Further advances in materials science and fabrication technology combined with developments in characterization and metrology tools for defect analysis would also allow the local identification of SNSPD failure mechanisms, which would in turn provide crucial input for the rational development of industrial detector fabrication processes to achieve superior device reliability.…”

Lithium-niobate-on-insulator waveguide-integrated superconducting nanowire single-photon detectors

“…A thin oxide layer (10 nm thickness) is deposited on top of the fabricated photonic devices in order to protect LN from the adverse effect of the subsequent NbN etching by CF 4 chemistry. Next, a thin layer of NbN (5 nm effective thickness) is deposited by the technique of plasmaenhanced atomic layer deposition (PEALD) 29 . The transition temperature and sheet resistance of the deposited NbN film are measured to be around 8 K and 410 Ω/sq, respectively.…”