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Applied Physics Letters

Superconducting nanowire single photon detector on 4H-SiC substrates with saturated quantum efficiency

Mengting Si, Liping Zhou, Wei Peng, Xingyu Zhang, Ailun Yi, Chengli Wang, Hourong Zhou, Zhen Wang, Xin Ou, Lixing You

Published Sep 25, 2023• 7 citations
Publisher

Abstract

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.

DOI
10.1063/5.0164368

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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.
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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.
Superconducting nanowire single-photon detectors (SNSPDs) provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, compatibility with an integrated optical platform is a crucial requirement for applications in emerging quantum photonic technologies. Here we present SNSPDs embedded in nanophotonic integrated circuits which achieve internal quantum efficiencies close to unity at 1550 nm wavelength. This allows for the SNSPDs to be operated at bias currents far below the critical current where unwanted dark count events reach milli-Hz levels while on-chip detection efficiencies above 70% are maintained. The measured dark count rates correspond to noise-equivalent powers in the 10(-19) W/Hz(-1/2) range and the timing jitter is as low as 35 ps. Our detectors are fully scalable and interface directly with waveguide-based optical platforms.
Superconducting nanowire single-photon detectors (SNSPDs) are the leading technology for low noise, high efficiency infrared single-photon detection. The basic SNSPD consists of a nanowire patterned in an ultrathin superconducting thin film, which is cooled below its critical temperature and biased close to its critical current. The absorption of a single-photon creates a resistive region, triggering a fast output voltage pulse which can be readily amplified and registered. The excellent performance of SNSPDs at near-infrared and telecommunications wavelengths has led to their adoption in important applications such as quantum secure communications, single-photon spectroscopy and single-photon LIDAR. A clear challenge for the SNSPD community is to extend the spectral range of SNSPDs into the mid infrared, and to improve material uniformity to enable the realization of large area arrays for multimode or free space coupling. The aim of this work is to evaluate potential materials for next generation mid-infrared SNSPD arrays. In this work, thin films of polycrystalline NbN and amorphous MoSi have been optimized to test the uniformity of a multipixel array configuration composed of 8 nanowire meander structures covering 10 um x 10 um area, 100 nm width and 50% filling factor. The 8-pixels SNSPD arrays have been patterned on 8 nm thickness NbN grown on high resistivity silicon (HR Si) substrate at room temperature and at 800 °C exhibiting respectively 4.4 K and 7.3 K as mean critical temperature across the pixels. The 8- pixels SNSPD array patterned on 8 nm thickness MoSi cooling the HR Si substrate to -180 °C has exhibited a mean critical temperature of 3.2 K across the pixels. Optical properties have been measured by an attenuated 1550 nm laser diode source delivered by single mode optical fibre at a controlled distance from the chip in order to broadly illuminate the array. The optical properties have been studied only for the 8 nm thickness NbN SNSPD array grown at room temperature has demonstrated uniform optical properties across pixels exhibiting similar saturation of the internal efficiency over a large bias, similar dark count rate and similar timing jitter (about 137 ps) across pixels. In the single photon regime at 1550 nm, pixels 4 and 6 of the 8 nm thickness NbN SNSPD array exhibit 28.4% and 4.7% pixel detection efficiency as measured at the bias current 95% of their respective critical current at 2.2 K.
Abstract The performance of superconducting nanowire single-photon detectors (SNSPDs) relies on substrate materials. Magnesium fluoride (MgF 2 ) exhibits outstanding optical properties, such as large optical transmission range and low refractive index ( n = 1.38), making it an attractive substrate. We present the fabrication and the performance of SNSPDs made of a 4.5 nm thick NbN thin film deposited on MgF 2 substrate for the wavelength of 1550 nm. The front-side illuminated SNSPDs without an optical cavity showed a maximal detection efficiency of 12.8% at a system dark count rate (DCR) of 100 Hz, while the backside illuminated SNSPDs with a SiO 2 /Au optical cavity atop displayed a maximal detection efficiency of 33% at a DCR of 100 Hz.