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Hoevers HFC, Bento AC, Bruijn MP, Gottardi L, Korevaar MAN, Mels WA, et al. Thermal fluctuation noise in a voltage biased superconducting transition edge thermometer. Appl Phys Lett. 2000;77(26):4421–4.
Abstract: The current noise at the output of a microcalorimeter with a voltage biased superconducting transition edge thermometer is studied in detail. In addition to the two well-known noise sources: thermal fluctuation noise from the heat link to the bath and Johnson noise from the resistive thermometer, a third noise source strongly correlated with the steepness of the thermometer is required to fit the measured noise spectra. Thermal fluctuation noise, originating in the thermometer itself, fully explains the additional noise. A simple model provides quantitative agreement between the observed and calculated noise spectra for all bias points in the superconducting transition.
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Sprengers JP, Gaggero A, Sahin D, Jahanmirinejad S, Frucci G, Mattioli F, et al. Waveguide superconducting single-photon detectors for integrated quantum photonic circuits. Appl Phys Lett. 2011;99(18):181110(1–3).
Abstract: The monolithic integration of single-photon sources, passive optical circuits, and single-photon detectors enables complex and scalable quantum photonic integrated circuits, for application in linear-optics quantum computing and quantum communications. Here, we demonstrate a key component of such a circuit, a waveguide single-photon detector. Our detectors, based on superconducting nanowires on GaAs ridge waveguides, provide high efficiency (~0%) at telecom wavelengths, high timing accuracy (~0 ps), and response time in the ns range and are fully compatible with the integration of single-photon sources, passive networks, and modulators.
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Siddiqi I, Prober DE. Nb–Au bilayer hot-electron bolometers for low-noise THz heterodyne detection. Appl Phys Lett. 2004;84(8):1404.
Abstract: The sensitivity of present Nb diffusion-cooled hot-electron bolometer (HEB) mixers is not quantum limited, and can be improved by reducing the superconducting transition temperature TC. Lowering TC reduces thermal fluctuations, resulting in a decrease of the mixer noise temperature TM. However, lower TC mixers have reduced dynamic range and saturate more easily due to background noise. We present 30 GHz microwave measurements on a bilayer HEB system, Nb–Au, in which TC can be tuned with Au layer thickness to obtain the maximum sensitivity for a given noise background. These measurements are intended as a guide for the optimization of THz mixers. Using a Nb–Au mixer with TC = 1.6 K, we obtain TM = 50 K with 2 nW of local oscillator (LO) power. Good mixer performance is observed over a wide range of LO power and bias voltage and such a device should not exhibit saturation in a THz receiver.
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Gaggero A, Nejad SJ, Marsili F, Mattioli F, Leoni R, Bitauld D, et al. Nanowire superconducting single-photon detectors on GaAs for integrated quantum photonic applications. Appl Phys Lett. 2010;97(15):3.
Abstract: We demonstrate efficient nanowire superconducting single photon detectors (SSPDs) based on NbN thin films grown on GaAs. NbN films ranging from 3 to 5 nm in thickness have been deposited by dc magnetron sputtering on GaAs substrates at 350 °C. These films show superconducting properties comparable to similar films grown on sapphire and MgO. In order to demonstrate the potential for monolithic integration, SSPDs were fabricated and measured on GaAs/AlAs Bragg mirrors, showing a clear cavity enhancement, with a peak quantum efficiency of 18.3% at λ = 1300 nm and T = 4.2 K.
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Marsili F, Najafi F, Herder C, Berggren KK. Electrothermal simulation of superconducting nanowire avalanche photodetectors. Appl Phys Lett. 2011;98(9):3.
Abstract: We developed an electrothermal model of NbN superconducting nanowire avalanche photodetectors (SNAPs) on sapphire substrates. SNAPs are single-photon detectors consisting of the parallel connection of N superconducting nanowires. We extrapolated the physical constants of the model from experimental data and we simulated the time evolution of the device resistance, temperature and current by solving two coupled electrical and thermal differential equations describing the nanowires. The predictions of the model were in good quantitative agreement with the experimental results.
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Baek B, Lita AE, Verma V, Nam SW. Superconducting a-WxSi1–x nanowire single-photon detector with saturated internal quantum efficiency from visible to 1850 nm. Appl Phys Lett. 2011;98(25):3.
Abstract: We have developed a single-photon detector based on superconducting amorphous tungsten–silicon alloy (a-WxSi1–x) nanowire. Our device made from a uniform a-WxSi1–x nanowire covers a practical detection area (16 μm×16 μm) and shows high sensitivity featuring a plateau of the internal quantum efficiencies, i.e., efficiencies of generating an electrical pulse per absorbed photon, over a broad wavelength and bias range. This material system for superconducting nanowire detector technology could overcome the limitations of the prevalent nanowire devices based on NbN and lead to more practical, ideal single-photon detectors having high efficiency, low noise, and high count rates.
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Zhang W, Khosropanah P, Gao JR, Kollberg EL, Yngvesson KS, Bansal T, et al. Quantum noise in a terahertz hot electron bolometer mixer. Appl Phys Lett. 2010;96(11):111113–(1.
Abstract: We have measured the noise temperature of a single, sensitive superconducting NbN hot electron bolometer (HEB) mixer in a frequency range from 1.6 to 5.3 THz, using a setup with all the key components in vacuum. By analyzing the measured receiver noise temperature using a quantum noise (QN) model for HEB mixers, we confirm the effect of QN. The QN is found to be responsible for about half of the receiver noise at the highest frequency in our measurements. The beta-factor (the quantum efficiency of the HEB) obtained experimentally agrees reasonably well with the calculated value.
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Baryshev A., Hovenier J.N., Adam A.J.L., Kašalynas I., Gao J.R., Klaassen T.O., et al. Phase locking and spectral linewidth of a two-mode terahertz quantum cascade laser. Physics Letters. 2006;89.
Abstract: We have studied the phase locking and spectral linewidth of an ~ 2.7 THz quantum cascade laser by mixing its two lateral lasing modes. The beat signal at about 8 GHz is compared with a microwave eference by applying conventional phase lock loop circuitry with feedback to the laser bias current. Phase locking has been demonstrated, resulting in a narrow beat linewidth of less than 10 Hz. Under requency stabilization we find that the terahertz line profile is essentially Lorentzian with a minimum linewidth of ~ 6.3 kHz. Power dependent measurements suggest that this linewidth does not approach the Schawlow-Townes limit.
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Mannino G, Spinella C, Ruggeri R, La Magna A, Fisicaro G, Fazio E, et al. Crystallization of implanted amorphous silicon during millisecond annealing by infrared laser irradiation. Appl Phys Lett. 2010;97(2):3.
Abstract: We investigated the homogenous nucleation of crystalline grains in amorphous Si during transient temperature pulse of few milliseconds IR laser irradiation. The crystallized volume fraction is ~80%. Significant crystallization occurs in nonsteady regime because of the rapid temperature variation (106 °C/s). Our model combines the time evolution of the crystal grain population with the consumption of the amorphous volume due to the growth of grains. Thanks to the experimental approach based on a laser source to heat α-Si and the theoretical model we extended the description of the spontaneous crystallization up to 1323 K or 250 K above the temperature investigated by conventional annealing.
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Sekine N, Hosako I. Intensity modulation of terahertz quantum cascade lasers under external light injection. Appl Phys Lett. 2009;95:201106(1–3).
Abstract: We investigated the light-current characteristics of terahertz (THz) quantum cascade lasers under external light injection, which excites interband transitions in the active materials. It was found that the amount of reduction in the THz power was constant for all injection currents above threshold, and the dependence of the reduction amount on the wavelength of the external light was observed to show a resonancelike feature. The dominant intensity modulation mechanism was found to be the loss change caused by interband transitions in the active region. Further, the effective coupling efficiency plays an important role in the intensity modulation.
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