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arXiv:2605.27179

Impact of Stoichiometry of MoSi Thin Films for Enhanced Sensitivity of Superconducting Nanowire Single-Photon Detectors

Stefanie Grotowski, Damjan Pecijareski, Hadrien Le Petit Delacour, Lucio Zugliani, Fabian Wietschorke, Christian Schmid, Stefan Strohauer, Matthias Althammer, Rudolf Gross, Kai Müller, Jonathan Finley

cond-mat.supr-conquant-phSubmitted May 26, 2026• Announced May 27, 2026• 0 citations
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Abstract

We report on the impact of the stoichiometry of superconducting MoSi thin films on the performance of superconducting nanowire single-photon detectors (SNSPDs). Specifically, we investigate the relation between the film parameters critical temperature Tc , sheet resistance Rs and superconductor thickness d and observe a universal scaling behavior. To benchmark the performance of SNSPDs fabricated from films having different stoichiometry, we measure the bias dependent count rate curves, while the detector is illuminated with wavelengths between 780 nm and 1550 nm. The detector performance as a function photon energy for different nanowire widths reveals a linear relation between the detection current and the photon energy. Furthermore, we determine the interfacial thermal boundary conductance $β$ between the superconducting thin film and the substrate, by measuring the return current of the SNSPD and find an increase of $β$ with increasing Mo concentration. The highest sensitivity amongst all compared devices is achieved for Mo$_{0.53}$Si$_{0.47}$, with low Tc (4.1 K) and high Rs (397$Ω$/sq) at a film thickness of 5.4 nm.

Related papers

Impact of stoichiometry of MoSi thin films for enhanced sensitivity of superconducting nanowire single-photon detectors

Stefanie Grotowski, Damjan Pecijareski, Hadrien Le Petit Delacour +8 more

Abstract We report on the impact of the stoichiometry of superconducting MoSi thin films on the performance of superconducting nanowire single-photon detectors (SNSPDs). Specifically, we investigate the relation between the film parameters critical temperature T c , sheet resistance R s and superconductor thickness d and observe a universal scaling behavior. To benchmark the performance of SNSPDs fabricated from films having different stoichiometry, we measure the bias dependent count rate curves, while the detector is illuminated with wavelengths between 780 nm and 1550 nm. The detector performance as a function photon energy for different nanowire widths reveals a linear relation between the detection current and the photon energy. Furthermore, we determine the interfacial thermal boundary conductance β between the superconducting thin film and the substrate, by measuring the return current of the SNSPD and find an increase of β with increasing Mo concentration. The highest sensitivity amongst all compared devices is achieved for Mo 0.53 Si 0.47 , with low T c (4.1 K) and high R s (397 Ω /sq) at a film thickness of 5.4 nm.

Materials for Quantum Technology•Aug 6, 2026•0 citations

Effect of thermal conductance on the performance of superconducting nanowire single-photon detectors (SNSPDs)

Nicolò Petrini

The hotspot dynamics is one of the key process involved in the detection mechanism in superconducting nanowires single photon detectors (SNSPDs). The energy delivered by the photon absorption creates a non-equilibrium region where Cooper pairs break into quasi-particles, which undergo a thermalization process involving hot-electron–phonon interactions within the superconducting film. Eventually, phonons dissipate the excess energy into the substrate and relax to the base temperature. Hence, intrinsic reset time, count rate and possibly other parameters are conceivably affected by thermal coupling between the substrates and the superconducting film. Thus, a detailed understanding of the thermal boundary conductance is crucial for achieving the best possible performances. Even though recent studies have demonstrated that the substrate plays an important role in defining the hotspot relaxation time, no systematic study on the influence on detector performance metrics has been carried out yet. In this work, we investigated the effect of different substrates on SNSPDs performance. Meandered detectors and single nanowires with various dimensions have been successfully fabricated on ultrathin NbN film sputtered on six substrates: SiO2, Al2O3, SiC, SiN, AlN and GaN. We characterized the deposited films measuring Tc, ρ, ΔTc and RRR. Lattice mismatch is known to play an important role in determining the resulting film quality. SiO2 and SiN samples, in which the mismatch is pronounced, showed lower Tc and higher ρ compared to the other substrates. We extracted the critical and retrapping current densities (Jc, Jr respectively) for all the nanowire widths, observing a peculiar behavior in SiO2 and SiN samples which needs further investigation. Optical response was characterized in terms of reset time (τ), dark count rate (DCR) and photon count rate (PCR) with a 1550 nm wavelength laser at 3K. Single photon regime was verified in all the measured detectors. Reset time has been confirmed to be limited by kinetic inductance Lk for all the substrates. DCR behavior appeared to be correlated to the difference in film properties. Only detector fabricated on SiN and SiO2 substrates showed saturation in the photon count rate, while the highest count rate was achieved by Al2O3 sample. The different behavior of photon counts response on the substrates suggests a correlation with the measured thermal conductance β and needs further study. Nevertheless, the comparison between the extracted thermal boundary conductances and the theoretical ones highlighted relevant discrepancies between theory and experimental data. In conclusion, devices fabricated on NbN deposited on different substrates showed a peculiar detector photo-response behavior. A deeper evaluation of NbN disorder grade and a better thermal characterization of the substrate-thin film interface are needed as future work.

•Oct 25, 2019•0 citations

Emerging materials for superconducting nanowire photon counting arrays

Umberto Nasti

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.

•Jan 1, 2020•0 citations

Mo - Si superconducting nanowire single-photon detectors on Ga As

Marcel Erbe, Riad Berrazouane, Simon Geyer +8 more

We report on $\mathrm{Mo}$-$\mathrm{Si}$-based superconducting nanowire single-photon detectors on a gallium arsenide substrate. $\mathrm{Mo}$-$\mathrm{Si}$ deposited on a passivated $\mathrm{Ga}\mathrm{As}$ surface has the same critical temperature as $\mathrm{Mo}$-$\mathrm{Si}$ deposited on silicon. The critical temperature decreases slightly on depositing $\mathrm{Mo}$-$\mathrm{Si}$ directly on the native oxide of $\mathrm{Ga}\mathrm{As}$. Hence, $\mathrm{Mo}$-$\mathrm{Si}$ works well as a thin-film superconductor on $\mathrm{Ga}\mathrm{As}$. We propose that the amorphous structure of $\mathrm{Mo}$-$\mathrm{Si}$ ensures compatibility with the $\mathrm{Ga}\mathrm{As}$ matrix. Superconducting nanowire single-photon detectors (SNSPDs) are fabricated with $\mathrm{Mo}$-$\mathrm{Si}$ on $\mathrm{Ga}\mathrm{As}$ using a meander-wire design. The SNSPD metrics are very similar to those of devices fabricated with the same procedure on a silicon substrate. We observe a plateau in the response-versus-bias curve, signaling a saturated internal quantum efficiency. The plateau remains even at an elevated temperature, 2.2 K, at a wavelength of 980 nm. We achieve a timing jitter of 50 ps and a recovery time of 29 ns. These results point to the promise of integrating $\mathrm{Mo}$-$\mathrm{Si}$ SNSPDs with $\mathrm{Ga}\mathrm{As}$ photonic circuits.

Physical Review Applied•Jul 29, 2024•3 citations

MoSi Superconducting Nanowire Single-Photon Detectors on GaAs for On-Chip Integration

Erbe, M., Riad Berrazouane, Simon Geyer +8 more

We report on MoSi-based superconducting nanowire single-photon detectors on a gallium arsenide substrate. MoSi deposited on a passivated GaAs surface has the same critical temperature as MoSi deposited on silicon. The critical temperature decreases slightly on depositing MoSi directly on the native oxide of GaAs. Hence, MoSi works well as a thin-film superconductor on GaAs. We propose that the amorphous structure of MoSi ensures compatibility with the GaAs matrix. Superconducting nanowire single-photon detectors (SNSPDs) are fabricated with MoSi on GaAs using a meander-wire design. The SNSPD metrics are very similar to those of devices fabricated with the same procedure on a silicon substrate. We observe a plateau in the response-versus-bias curve signalling a saturated internal quantum efficiency. The plateau remains even at an elevated temperature, 2.2 K, at a wavelength of 980 nm. We achieve a timing jitter of 50 ps and a recovery time of 29 ns. These results point to the promise of integrating MoSi SNSPDs with GaAs photonic circuits.

arXiv:2312.00528•Dec 1, 2023•0 citations

Superconducting single-photon detector made of MoSi film

Yu. P. Korneeva, M. Yu. Mikhaı̆lov, Yuriy P. Pershyn +8 more

We fabricated and characterized nanowire superconducting single-photon detectors made of 4 nm thick amorphous Mo x Si 1− x films. At 1.7 K the best devices exhibit a detection efficiency (DE) up to 18% at 1.2 wavelength of unpolarized light, a characteristic response time of about 6 ns and timing jitter of 120 ps. The DE was studied in wavelength range from 650 nm to 2500 nm. At wavelengths below 1200 nm these detectors reach their maximum DE limited by photon absorption in the thin MoSi film.

arXiv:1309.7074•Superconductor Science and Technology•Aug 12, 2014•97 citations
We report on the impact of the stoichiometry of superconducting MoSi thin films on the performance of superconducting nanowire single-photon detectors (SNSPDs). Specifically, we investigate the relation between the film parameters critical temperature Tc , sheet resistance Rs and superconductor thickness d and observe a universal scaling behavior. To benchmark the performance of SNSPDs fabricated from films having different stoichiometry, we measure the bias dependent count rate curves, while the detector is illuminated with wavelengths between 780 nm and 1550 nm. The detector performance as a function photon energy for different nanowire widths reveals a linear relation between the detection current and the photon energy. Furthermore, we determine the interfacial thermal boundary conductance βββ between the superconducting thin film and the substrate, by measuring the return current of the SNSPD and find an increase of βββ with increasing Mo concentration. The highest sensitivity amongst all compared devices is achieved for Mo0.53_{0.53}0.53​Si0.47_{0.47}0.47​, with low Tc (4.1 K) and high Rs (397ΩΩΩ/sq) at a film thickness of 5.4 nm.
Abstract We report on the impact of the stoichiometry of superconducting MoSi thin films on the performance of superconducting nanowire single-photon detectors (SNSPDs). Specifically, we investigate the relation between the film parameters critical temperature T c , sheet resistance R s and superconductor thickness d and observe a universal scaling behavior. To benchmark the performance of SNSPDs fabricated from films having different stoichiometry, we measure the bias dependent count rate curves, while the detector is illuminated with wavelengths between 780 nm and 1550 nm. The detector performance as a function photon energy for different nanowire widths reveals a linear relation between the detection current and the photon energy. Furthermore, we determine the interfacial thermal boundary conductance β between the superconducting thin film and the substrate, by measuring the return current of the SNSPD and find an increase of β with increasing Mo concentration. The highest sensitivity amongst all compared devices is achieved for Mo 0.53 Si 0.47 , with low T c (4.1 K) and high R s (397 Ω /sq) at a film thickness of 5.4 nm.
The hotspot dynamics is one of the key process involved in the detection mechanism in superconducting nanowires single photon detectors (SNSPDs). The energy delivered by the photon absorption creates a non-equilibrium region where Cooper pairs break into quasi-particles, which undergo a thermalization process involving hot-electron–phonon interactions within the superconducting film. Eventually, phonons dissipate the excess energy into the substrate and relax to the base temperature. Hence, intrinsic reset time, count rate and possibly other parameters are conceivably affected by thermal coupling between the substrates and the superconducting film. Thus, a detailed understanding of the thermal boundary conductance is crucial for achieving the best possible performances. Even though recent studies have demonstrated that the substrate plays an important role in defining the hotspot relaxation time, no systematic study on the influence on detector performance metrics has been carried out yet. In this work, we investigated the effect of different substrates on SNSPDs performance. Meandered detectors and single nanowires with various dimensions have been successfully fabricated on ultrathin NbN film sputtered on six substrates: SiO2, Al2O3, SiC, SiN, AlN and GaN. We characterized the deposited films measuring Tc, ρ, ΔTc and RRR. Lattice mismatch is known to play an important role in determining the resulting film quality. SiO2 and SiN samples, in which the mismatch is pronounced, showed lower Tc and higher ρ compared to the other substrates. We extracted the critical and retrapping current densities (Jc, Jr respectively) for all the nanowire widths, observing a peculiar behavior in SiO2 and SiN samples which needs further investigation. Optical response was characterized in terms of reset time (τ), dark count rate (DCR) and photon count rate (PCR) with a 1550 nm wavelength laser at 3K. Single photon regime was verified in all the measured detectors. Reset time has been confirmed to be limited by kinetic inductance Lk for all the substrates. DCR behavior appeared to be correlated to the difference in film properties. Only detector fabricated on SiN and SiO2 substrates showed saturation in the photon count rate, while the highest count rate was achieved by Al2O3 sample. The different behavior of photon counts response on the substrates suggests a correlation with the measured thermal conductance β and needs further study. Nevertheless, the comparison between the extracted thermal boundary conductances and the theoretical ones highlighted relevant discrepancies between theory and experimental data. In conclusion, devices fabricated on NbN deposited on different substrates showed a peculiar detector photo-response behavior. A deeper evaluation of NbN disorder grade and a better thermal characterization of the substrate-thin film interface are needed as future work.
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.
We report on Mo\mathrm{Mo}Mo-Si\mathrm{Si}Si-based superconducting nanowire single-photon detectors on a gallium arsenide substrate. Mo\mathrm{Mo}Mo-Si\mathrm{Si}Si deposited on a passivated GaAs\mathrm{Ga}\mathrm{As}GaAs surface has the same critical temperature as Mo\mathrm{Mo}Mo-Si\mathrm{Si}Si deposited on silicon. The critical temperature decreases slightly on depositing Mo\mathrm{Mo}Mo-Si\mathrm{Si}Si directly on the native oxide of GaAs\mathrm{Ga}\mathrm{As}GaAs. Hence, Mo\mathrm{Mo}Mo-Si\mathrm{Si}Si works well as a thin-film superconductor on GaAs\mathrm{Ga}\mathrm{As}GaAs. We propose that the amorphous structure of Mo\mathrm{Mo}Mo-Si\mathrm{Si}Si ensures compatibility with the GaAs\mathrm{Ga}\mathrm{As}GaAs matrix. Superconducting nanowire single-photon detectors (SNSPDs) are fabricated with Mo\mathrm{Mo}Mo-Si\mathrm{Si}Si on GaAs\mathrm{Ga}\mathrm{As}GaAs using a meander-wire design. The SNSPD metrics are very similar to those of devices fabricated with the same procedure on a silicon substrate. We observe a plateau in the response-versus-bias curve, signaling a saturated internal quantum efficiency. The plateau remains even at an elevated temperature, 2.2 K, at a wavelength of 980 nm. We achieve a timing jitter of 50 ps and a recovery time of 29 ns. These results point to the promise of integrating Mo\mathrm{Mo}Mo-Si\mathrm{Si}Si SNSPDs with GaAs\mathrm{Ga}\mathrm{As}GaAs photonic circuits.
We report on MoSi-based superconducting nanowire single-photon detectors on a gallium arsenide substrate. MoSi deposited on a passivated GaAs surface has the same critical temperature as MoSi deposited on silicon. The critical temperature decreases slightly on depositing MoSi directly on the native oxide of GaAs. Hence, MoSi works well as a thin-film superconductor on GaAs. We propose that the amorphous structure of MoSi ensures compatibility with the GaAs matrix. Superconducting nanowire single-photon detectors (SNSPDs) are fabricated with MoSi on GaAs using a meander-wire design. The SNSPD metrics are very similar to those of devices fabricated with the same procedure on a silicon substrate. We observe a plateau in the response-versus-bias curve signalling a saturated internal quantum efficiency. The plateau remains even at an elevated temperature, 2.2 K, at a wavelength of 980 nm. We achieve a timing jitter of 50 ps and a recovery time of 29 ns. These results point to the promise of integrating MoSi SNSPDs with GaAs photonic circuits.