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Burke, P. J., Schoelkopf, R. J., Prober, D. E., Skalare, A., Karasik, B. S., Gaidis, M. C., et al. (1998). Spectrum of thermal fluctuation noise in diffusion and phonon cooled hot-electron mixers. Appl. Phys. Lett., 72(12), 1516–1518.
Abstract: A systematic study of the intermediate frequency noise bandwidth of Nb thin-film superconducting hot-electron bolometers is presented. We have measured the spectrum of the output noise as well as the conversion efficiency over a very broad intermediate frequency range (from 0.1 to 7.5 GHz) for devices varying in length from 0.08 μm to 3 μm. Local oscillator and rf signals from 8 to 40 GHz were used. For a device of a given length, the spectrum of the output noise and the conversion efficiency behave similarly for intermediate frequencies less than the gain bandwidth, in accordance with a simple thermal model for both the mixing and thermal fluctuation noise. For higher intermediate frequencies the conversion efficiency decreases; in contrast, the noise decreases but has a second contribution which dominates at higher frequency. The noise bandwidth is larger than the gain bandwidth, and the mixer noise is low, between 120 and 530 K (double side band).
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Kawamura, J., Blundell, R., Tong, C. -yu E., Gol’tsman, G., Gershenzon, E., Voronov, B., et al. (1997). Low noise NbN lattice-cooled superconducting hot-electron bolometric mixers at submillimeter wavelengths. Appl. Phys. Lett., 70(12), 1619–1621.
Abstract: Lattice-cooled superconducting hot-electron bolometric mixers are used in a submillimeter-wave waveguide heterodyne receiver. The mixer elements are niobium nitride film with 3.5 nm thickness and ∼10 μm2 area. The local oscillator power for optimal performance is estimated to be 0.5 μW, and the instantaneous bandwidth is 2.2 GHz. At an intermediate frequency centered at 1.4 GHz with 200 MHz bandwidth, the double sideband receiver noise temperature is 410 K at 430 GHz. The receiver has been used to detect molecular line emission in a laboratory gas cell.
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Baselmans, J. J. A., Hajenius, M., Gao, J. R., Klapwijk, T. M., de Korte, P. A. J., Voronov, B., et al. (2004). Doubling of sensitivity and bandwidth in phonon cooled hot electron bolometer mixers. Appl. Phys. Lett., 84(11), 1958–1960.
Abstract: We demonstrate that the performance of NbN lattice cooled hot electron bolometer mixers depends strongly on the interface quality between the bolometer and the contact structure. We show experimentally that both the receiver noise temperature and the gain bandwidth can be improved by more than a factor of 2 by cleaning the interface and adding an additional superconducting interlayer to the contact pad. Using this we obtain a double sideband receiver noise temperature TN,DSB=950 K
at 2.5 THz and 4.3 K, uncorrected for losses in the optics. At the same bias point, we obtain an IF gain bandwidth of 6 GHz.
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Mason, W., & Waterman, J. R. (1999). Electrical and optical characteristics of two color mid wave HgCdTe infrared detectors. Appl. Phys. Lett., 74(11), 1633–1635.
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Zhang, W., Khosropanah, P., Gao, J. R., Kollberg, E. L., Yngvesson, K. S., Bansal, T., et al. (2010). Quantum noise in a terahertz hot electron bolometer mixer. Appl. Phys. Lett., 96(11), 111113–(1–3).
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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