Khosropanah, P., Gao, J. R., Laauwen, W. M., Hajenius, M., & Klapwijk, T. M. (2007). Low noise NbN hot electron bolometer mixer at 4.3 THz. Appl. Phys. Lett., 91, 221111 (1 to 3).
Abstract: We have studied the sensitivity of a superconducting NbN hot electron bolometer mixer integrated with a spiral antenna at 4.3 THz. Using hot/cold blackbody loads and a beam splitter all in vacuum, we measured a double sideband receiver noise temperature of 1300 K at the optimum local oscillator (LO) power of 330 nW, which is about 12 times the quantum noise (hnu/2kB). Our result indicates that there is no sign of degradation of the mixing process at the superterahertz frequencies. Moreover, a measurement method is introduced which allows us for an accurate determination of the sensitivity despite LO power fluctuations.
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An, Z., Chen, J. - C., Ueda, T., Komiyama, S., & Hirakawa, K. (2005). Infrared phototransistor using capacitively coupled two-dimensional electron gas layers. Appl. Phys. Lett., 86, 172106-3.
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Barends, R., Hajenius, M., Gao, J. R., & Klapwijk, T. M. (2005). Current-induced vortex unbinding in bolometer mixers. Appl. Phys. Lett., 87, 263506 (1 to 3).
Abstract: We present a description of the current-voltage characteristics of hot electron bolometers in terms of the current-dependent intrinsic resistive transition of NbN films. We find that, by including this current dependence, we can correctly predict the complete current-voltage characteristics, showing excellent agreement with measurements for both low and high bias and for small as well as large devices. It is assumed that the current dependence is due to vortex-antivortex unbinding as described in the Berezinskii–Kosterlitz–Thouless theory. The presented approach will be useful in guiding device optimization for noise and bandwidth.
Keywords: HEB mixer numerical model, HEB model, IV-curves, vortex-antivortex, Berezinskii–Kosterlitz–Thouless theory, diffusion cooling channel, diffusion channel, distributed HEB model, distributed model, self-heating effect, temperature profile
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Stevens, M., Hadfield, R., Schwall, R., Nam, S. W., Mirin, R., & Gupta, J. (2006). Fast lifetime measurements of infrared emitters using a low-jitter superconduct- ing single-photon detector. Appl. Phys. Lett., 89, 031109.
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Li, T. F., Pashkin, Y. A., Astafiev, O., Nakamura, Y., Tsai, J. S., & Im, H. (2008). High-frequency metallic nanomechanical resonators. Appl. Phys. Lett., 92, 043112(1)-043112(3).
Abstract: We developed a technology to fabricate fully metallic doubly clamped beams working as nanomechanical resonators. Measured with a magnetomotive detection scheme, the beams, made of polycrystalline metal films, show as good quality as previously reported ones made of single crystal materials, such as Si, GaAs, AlN, and SiC. Our method is compatible with the conventional fabrication process for nanoscale electronic circuits and thus offers a possibility of easily integrating the beams into superconducting charge and flux qubits and single-electron transistors as well as coupling them to coplanar waveguide resonators.
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Walther, C., Scalari, G., Faist, J., Beere, H., & Ritchie, D. (2006). Low frequency terahertz quantum cascade laser operating from 1.6 to 1.8 THz. Appl. Phys. Lett., 89, 231121(1–3).
Abstract: The authors report a GaAs/Al0.1Ga0.9As quantum cascade laser based on a bound-to-continuum transition optimized for low frequency operation. High tunability of the gain curve is achieved by the Stark effect and laser emission is measured between 1.6 and 1.8 THz. Pulsed mode operation up to 95 K and continuous wave operation up to 80 K are reported. The dynamical range in current is as high as 43%.
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Sekine, N., & Hosako, I. (2009). Intensity modulation of terahertz quantum cascade lasers under external light injection. Appl. Phys. Lett., 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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Tretyakov, I., Ryabchun, S., Finkel, M., Maslennikova, A., Kaurova, N., Lobastova, A., et al. (2011). Low noise and wide bandwidth of NbN hot-electron bolometer mixers. Appl. Phys. Lett., 98, 033507 (1 to 3).
Abstract: We report a record double sideband noise temperature of 600 K (5hν/kB) offered by a NbN hot-electron bolometer receiver at 2.5 THz. Allowing for standing wave effects, this value was found to be constant in the intermediate frequency range 1–7 GHz, which indicates that the mixer has an unprecedentedly large noise bandwidth in excess of 7 GHz. The insight into this is provided by gain bandwidth measurements performed at the superconducting transition. They show that the dependence of the bandwidth on the mixer length follows the model for an HEB mixer with diffusion and phonon cooling of the hot electrons.
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Inderbitzin, K., Engel, A., Schilling, A., Il'in, K., & Siegel, M. (2012). An ultra-fast superconducting Nb nanowire single-photon detector for soft x-rays. Appl. Phys. Lett., 101.
Abstract: Although superconducting nanowire single-photon detectors (SNSPDs) are well studied regarding the
detection of infrared/optical photons and keV-molecules, no studies on continuous x-ray photon
counting by thick-film detectors have been reported so far. We fabricated a 100 nm thick niobium
x-ray SNSPD (an X-SNSPD) and studied its detection capability of photons with keV-energies in
continuous mode. The detector is capable to detect photons even at reduced bias currents of 0.4%,
which is in sharp contrast to optical thin-film SNSPDs. No dark counts were recorded in extended
measurement periods. Strikingly, the signal amplitude distribution depends significantly on the photon
energy spectrum.VC
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Kataoka, T., Kajikawa, K., Kitagawa, J., Kadoya, Y., & Takemura, Y. (2010). Improved sensitivity of terahertz detection by GaAs photoconductive antennas excited at 1560 nm. Appl. Phys. Lett., 97, 201110 (1–3).
Abstract: The terahertz detection by photoconductive antennas (PCAs) based on low-temperature grown (LTG) GaAs with 1.5 μm pulse excitation was revisited. We found that the detection efficiency can be improved by a factor of 10 (20 dB) by reducing the excitation spot size and the gap length of the PCA, maintaining the low noise feature of the PCA on LTG GaAs. As a result, the signal-to-noise ratio higher than 50 dB was obtained at a reasonable incident power of 9.5 mW, suggesting that the scheme is promising for the detection of terahertz waves in practical time domain systems.
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Gao, J. R., Hovenier, J. N., Yang, Z. Q., Baselmans, J. J. A., Baryshev, A., Hajenius, M., et al. (2005). Terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer. Appl. Phys. Lett., 86, 244104 (1 to 3).
Abstract: We report the first demonstration of an all solid-stateheterodyne receiver that can be used for high-resolution spectroscopy above 2THz suitable for space-based observatories. The receiver uses a NbN superconducting hot-electron bolometer as mixer and a quantum cascade laser operating at 2.8THz as local oscillator. We measure a double sideband receiver noise temperature of 1400K at 2.8THz and 4.2K, and find that the free-running QCL has sufficient power stability for a practical receiver, demonstrating an unprecedented combination of sensitivity and stability.
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Bennett, D. A., Schmidt, D. R., Swetz, D. S., & Ullom, J. N. (2014). Phase-slip lines as a resistance mechanism in transition-edge sensors. Appl. Phys. Lett., 104, 042602.
Abstract: The fundamental mechanism of resistance in voltage-biased superconducting films is poorly understood despite its importance as the basis of transition-edge sensors (TESs). TESs are utilized in state-of-the-art microbolometers and microcalorimeters covering a wide range of energies and applications. We present a model for the resistance of a TES based on phase-slip lines (PSLs) and compare the model to data. One of the model's predictions, discrete changes in the number of PSLs, is a possible explanation for the observed switching between discrete current states in localized regions of bias.
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Swetz, D. S., Bennett, D. A., Irwin, K. D., Schmidt, D. R., & Ullom, J. N. (2012). Current distribution and transition width in superconducting transition-edge sensors. Appl. Phys. Lett., 101, 242603.
Abstract: Present models of the superconducting-to-normal transition in transition-edge sensors (TESs) do not describe the current distribution within a biased TES. This distribution is complicated by normal-metal features that are integral to TES design. We present a model with one free parameter that describes the evolution of the current distribution with bias. To probe the current distribution experimentally, we fabricated TES devices with different current return geometries. Devices where the current return geometry mirrors current flow within the device have sharper transitions, thus allowing for a direct test of the current-flow model.Measurements from these devices show that current meanders through a TES low in the resistivetransition but flows across the normal-metal features by 40% of the normal-state resistance. Comparison of transition sharpness between device designs reveals that self-induced magnetic fields play an important role in determining the width of the superconducting transition.
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Miao, W., Zhang, W., Zhong, J. Q., Shi, S. C., Delorme, Y., Lefevre, R., et al. (2014). Non-uniform absorption of terahertz radiation on superconducting hot electron bolometer microbridges. <ef><bf><bc>Appl. Phys. Lett., 104, 052605(1–4).
Abstract: We interpret the experimental observation of a frequency-dependence of superconducting hot electron bolometer (HEB) mixers by taking into account the non-uniform absorption of the terahertz radiation on the superconducting HEB microbridge. The radiation absorption is assumed to be proportional to the local surface resistance of the HEB microbridge, which is computed using the Mattis-Bardeen theory. With this assumption the dc and mixing characteristics of a superconducting niobium-nitride (NbN) HEB device have been modeled at frequencies below and above the equilibrium gap frequency of the NbN film.
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Gousev, Y. P., Semenov, A. D., Pechen, E. V., Varlashkin, A. V., Nebosis, R. S., & Renk K. F. (1996). Coupling of terahertz radiation to a high-Т(с) superconducting hot electron bolometer mixer. Appl. Phys. Lett.,, 69, 691–693.
Abstract: We report on efficient coupling of THz radiation to a high-T(c) superconducting hot electron bolometer that is suitable for heterodyne detection. Our quasioptical system consisted of a planar self-complementary spiral antenna on a dielectric substrate clamped to an extended hyperhemispherical lens. The antenna was integrated into a co-planar line for broadband intermediate frequency matching. Measurements in the homodyne regime at a frequency of 2.5 THz showed a radiation pattern with a beam width of 1° and a coupling efficiency of 0.1. We measured, at an intermediate frequency of 1.5 GHz, an output noise temperature of'160 K and estimated for the device, operated in the heterodyne regime, a system noise temperature of 30 000 K. We also discuss possibilities of significant improvement of the sensitivity.
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