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Applied Physics Letters

Superconducting nanowire single-photon detectors with saturated quantum efficiency at 1550 nm on single-crystal diamond substrates

Zhi Qin, Mingxue Huang, Tao Tao, Xiaohan Wang, Han Bao, Tao Xu, Xuecou Tu, Labao Zhang, Qingyuan Zhao, Xiaoqing Jia, Lin Kang, Jian Chen, Peiheng Wu

Published Apr 29, 2024• 5 citations
Publisher

Abstract

Single-crystal diamond possesses exceptional physical and optical properties, rendering it an ideal platform for integrated quantum optics. The direct integration of broadband-sensitive and high-performance single-photon detectors on diamond holds significant implications for the realization of integrated diamond quantum optical circuits. In this study, we polished the diamond surface with RMS (root mean square) below 0.6 nm suitable for the deposition and patterning of NbN thin films through ion beam etching. Subsequently, we fabricated superconducting nanowire single-photon detectors directly on the polished diamond substrates and characterized for their electrical and optical properties. The NbN-SNSPD exhibited a high critical current density (2 MA cm−2), a saturated quantum efficiency (QE) below 2.5 K, and a maximum value of QE up to 88% at 4 K. These findings offer a promising solution for fully integrated quantum optical chips on single-crystal diamond substrates.

DOI
10.1063/5.0205809

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•Jan 1, 2017•1 citation
Single-crystal diamond possesses exceptional physical and optical properties, rendering it an ideal platform for integrated quantum optics. The direct integration of broadband-sensitive and high-performance single-photon detectors on diamond holds significant implications for the realization of integrated diamond quantum optical circuits. In this study, we polished the diamond surface with RMS (root mean square) below 0.6 nm suitable for the deposition and patterning of NbN thin films through ion beam etching. Subsequently, we fabricated superconducting nanowire single-photon detectors directly on the polished diamond substrates and characterized for their electrical and optical properties. The NbN-SNSPD exhibited a high critical current density (2 MA cm−2), a saturated quantum efficiency (QE) below 2.5 K, and a maximum value of QE up to 88% at 4 K. These findings offer a promising solution for fully integrated quantum optical chips on single-crystal diamond substrates.
On-chip single photon detection is crucial for implementing on-chip quantum communication, quantum simulation, and calculation. Superconducting nanowire single-photon detectors (SNSPDs) have become one of the essential techniques to achieve high-efficiency, on-chip, single-photon detection at scale due to their high detection efficiency, low dark count rate, and low jitter. Silicon carbide (SiC) has emerged as a promising integrated photonics platform due to its nonlinear optical processing capabilities, compatibility with CMOS technology, and outstanding quantum properties as a device for single photon sources. However, achieving high-efficiency superconducting nanowire single-photon detection on SiC substrates has yet to be demonstrated. In this study, we deposited polycrystalline NbN thin films onto 4H-SiC substrates. We also ensured that the deposited NbN thin film had a flat surface with a roughness less than 1 nm on the C-side 4H-SiC substrate through optimized chemical mechanical polishing. The NbN-SNSPD achieved a saturated quantum efficiency covering the color center emission bandwidth wavelength range (from 861 to 1550 nm) of the 4H-SiC material. These results offer a promising solution for high-efficiency single-photon detection on fully integrated quantum optical chips on 4H-SiC substrates.
Superconducting nanowire single photon detectors are fabricated directly on diamond substrates and their optical and electrical properties are characterized. Dark count performance and photon count rates are measured at varying temperatures for 1310 nm and 632 nm photons. A multi-step diamond surface polishing procedure is reported, involving iterative reactive ion etching and mechanical polishing to create a suitable diamond surface for the deposition and patterning of thin film superconducting layers. Using this approach, diamond substrates with less than 300 pm Root Mean Square surface roughness are obtained.
We demonstrate high-performance nanowire superconducting single photon detectors (SSPDs) on bN thin films grown at a temperature compatible with monolithic integration. NbN films ranging from 150 nm to 3 nm in thickness were deposited by dc magnetron sputtering on MgO substrates at 400 degrees C SSPDs were fabricated on high quality NbN films of different thickness (7 to 3 nm) deposited under optimal conditions. Electrical and optical characterizations were performed on the SSPDs. The highest QE value measured at 4.2K is 20% at 1300 nm.
Superconducting nanowires used in single-photon detectors have been realized on amorphous or poly-crystalline films. Here, we report the first use of single-crystalline NbN thin films for superconducting nanowire single-photon detectors (SNSPDs). Grown by molecular beam epitaxy (MBE) at high temperature on nearly lattice-matched AlN-on-sapphire substrates, the NbN films exhibit a high degree of uniformity and homogeneity. Even with relatively thick films, the fabricated nanowire detectors show saturated internal efficiency at near-IR wavelengths, demonstrating the potential of MBE-grown NbN for realizing large arrays of on-chip SNSPDs and their integration with AlN-based χ(2) quantum photonic circuits.
We report on superconducting single-photon detectors (SSPDs) based on NbN nanowires and their application to single-photon measurements at telecom wavelengths. The detectors are realized by patterning ultra thin (3 - 5 nm-thick) NbN films into meanders of 100 nm-wide wires. The films are deposited by DC magnetron sputtering at relatively low temperatures (≈500 °C) on MgO and GaAs substrates (as compared to the approach of high-temperature deposition on sapphire). In 5 nm-thick films, TCsas high as 10 K and 11 K have been obtained on GaAs and MgO, respectively (Fig. 1). SSPDs have been fabricated by a two-mask process using electron beam lithography and reactive ion etching on 3.5nm thick NbN films deposited under optimal conditions on MgO. The detectors are 5 × 5 μm2in size, and composed of a 100 μm long, 100 nm wide nanowire folded in a meander pattern with filling factor of 40%. Typical room temperature resistivity ρ is of 190 μΩ·cm, and I-V curves at 4.2 K show a critical current density JCof about 6 MA·cm-2, which are state of the art values. Quantum efficiency (QE) was measured illuminating the detectors mounted in a liquid He bath through an optical fiber. Quantum efficiencies >10% are measured at 4.2 K, comparable to best results on sapphire substrates. In particular, SSPDs show a large increase in sensitivity, temporal resolution and maximum counting frequencies as compared to InGaAs avalanche photodiodes.
Single photon detectors are a vital part of many emerging technologies which harness the quantum properties of light to benefit the fields of communication, computation and sensing. Superconducting nanowire single photon detectors (SNSPDs) offer high detection efficiency, low dark count rates, low timing jitter, and infrared sensitivity that are required by the most demanding single photon counting applications. This thesis presents SNSPDs fabricated and tested at the University of Glasgow that are integrated with optical structures which enable enhanced detection efficiency and integration with waveguide circuit technology. The monolithic integration of waveguide circuit components presents a route towards realisation of an optical quantum information processor that has the stability and scalability to perform the demanding tasks of quantum computation. A novel process is introduced for incorporating superconducting detectors with single mode gallium arsenide waveguides and quantum dot single photon sources. Together these elements would enable the generation of quantum states of light which could be manipulated and detected on a single chip. Detectors are patterned in NbTiN thin superconducting films on to suspended nanobeam waveguides with better than 50 nm alignment accuracy. Low temperature electrical and optical testing confirms the detectors’ single photon sensitivity under direct illumination as well as to waveguide coupled light. Measured detectors were found to have internal registering efficiencies of 6.8 ± 2.4%. Enhancing absorption of photons into thin superconducting films is vital to the creation of high efficiency superconducting single photon detectors. Fabricating an SNSPD on a dielectric mirror creates a partial cavity that can be tailored to enhance detection of light at specific wavelengths. Devices have been fabricated and tested in this thesis with enhanced detection efficiency at infrared and visible wavelengths for quantum cryptography, remote sensing and life science applications. Detectors fabricated in NbTiN on GaAs/AlGaAs Bragg mirrors exhibited a system detection efficiency of 1.5% at 1500 nm wavelength for the best device measured. SNSPDs were also fabricated in NbN on aperiodic dielectric mirrors with a range of different bandwidths. A peak system detection efficiency of 82.7% at 808 nm wavelength was recorded.