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Yngvesson, K. S., Gerecht, E., Musante, C. F., Zhuang, Y., Ji, M., Goyette, T. M., et al. (1999). Low-noise HEB heterodyne receivers and focal plane arrays for the THz regime using NbN. In R. J. Hwu, & K. Wu (Eds.), Proc. SPIE (Vol. 3795, pp. 357–368). SPIE.
Abstract: We have developed prototype HEB receivers using thin film superconducting NbN devices deposited on silicon substrates. The devices are quasi-optically coupled through a silicon lens and a self-complementary log-specific toothed antenna. We measured DSB receiver noise temperatures of 500 K (13 X hf/2k) at 1.56 THz and 1,100 K (20 X hf/2k) at 2.24 THz. Noise temperatures are expected to fall further as devices and quasi-optical coupling methods are being optimized. The measured 3 dB IF conversion gain bandwidth for one device was 3 GHz, and it is estimated that the bandwidth over which the receiver noise temperature is within 3 dB of its minimum value is 6.5 GHz which is sufficient for a number of practical applications. We will discuss our latest results and give a detailed description of our prototype setup and experiments. We will also discuss our plans for developing focal plane arrays with tens of Hot Electron Bolometric mixer elements on a single silicon substrate which will make real time imaging systems in the THz region feasible.
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Huebers, H. - W., Schubert, J., Semenov, A., Gol’tsman, G. N., Voronov, B. M., Gershenzon, E. M., et al. (1999). NbN phonon-cooled hot-electron bolometer as a mixer for THz heterodyne receivers. In J. M. Chamberlain (Ed.), Proc. SPIE (Vol. 3828, pp. 410–416). Spie.
Abstract: We have investigated a phonon-cooled NbN hot electron bolometric (HEB) mixer in the frequency range from 0.7 THz to 5.2 THz. The device was a 3.5 nm thin film with an in- plane dimension of 1.7 X 0.2 micrometers 2 integrated in a complementary logarithmic spiral antenna. The measured DSB receiver noise temperatures are 1500 K, 2200 K, 2600 K, 2900 K, 4000 K, 5600 K and 8800 K. The sensitivity fluctuation, the long term stability, and the antenna pattern were measured and the suitability of the mixer for a practical heterodyne receiver is discussed.
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Gerecht, E., Musante, C. F., Schuch, R., Lutz, C. R., Jr., Yngvesson, K. S., et al. (1995). Hot electron detection and mixing experiments in NbN at 119 micrometer wavelength. In Proc. 6th Int. Symp. Space Terahertz Technol. (pp. 284–293).
Abstract: We have performed preliminary experiments with the goal of demonstrating a Hot Electron Bolometric (HEB) mixer for a 119 micrometer wavelength (2.5 THz). We have chosen a NbN device of size 700 x 350 micrometers. This device can easily be coupled to a laser LO source, which is advantageous for performing a prototype experiment. The relatively large size of the device means that the LO power required is in the mW range; this power can be easily obtained from a THz laser source. We have measured the amount of laser power actually absorbed in the device, and from this have estimated the best optical coupling loss to be about 10 di . We are developing methods for improving the optical coupling further. Preliminary measurements of the response of the device to a chopped black-body have not yet resulted in a measured receiver noise temperature. We expect to be able to complete this measurement in the near future.
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Gousev, Y. P., Semenov, A. D., Goghidze, I. G., Pechen, E. V., Varlashkin, A. V., Gol'tsman, G. N., et al. (1997). Current dependent noise in a YBa2Cu3O7-δ hot-electron bolometer. IEEE Trans. Appl. Supercond., 7(2), 3556–3559.
Abstract: We investigated the output noise of a YBa2Cu3O7-δ (YBCO) superconducting hot-electron bolometer (HEB) in a large frequency range (10 kHz to 8 GHz); the bolometer either consisted of a structured 50 nm thick YBCO film on LaAlO/sub 3/ or a 30 nm thick film on a MgO substrate. We found that flicker noise dominated at low frequencies (below 1 MHz), while at higher frequencies Johnson noise and a current dependent noise were the main noise sources.
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Gershenzon, E. M., Gol'tsman, G. N., & Kagane, M. L. (1977). Energy spectrum of acceptors in germanium and its response to a magnetic field. Sov. Phys. JETP, 45(4), 769–776.
Abstract: We investigated the spectrum of the submillimeter photoconductivity of p-Ge at helium temperatures and the effects of a magnetic field up to 40 kOe on the spectrum. A large number of lines of transitions between the excited states of the acceptors was observed, some of the lines were identified, and the energies of a number of spectral levels B, Al, Ga, In, and TI in Ge were identified. The results are compared with calculations and with experimental data obtained from the spectra of the photoexcitation of the ground state of the impurities. Using one transition as an example, we discuss the splitting of the excited states of acceptors in the magnetic field and under uniaxial compression.
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Heusinger, M. A., Nebosis, R. S., Schatz, W., Renk, K. F., Gol’tsman, G. N., Karasik, B. S., et al. (1993). Temperature dependence of bolometric and non-bolometric photoresponse of a structured YBa2Cu3O7-δ thin film. In M. Meissner, & R. O. Pohl (Eds.), Phonon Scattering in Condensed Matter VII. Springer Series in Solid-State Sciences (Vol. 112, pp. 193–195).
Abstract: We investigated the temperature dependence of the transient voltage photoresponse of a current biased structured YBa2Cu3O7−δ thin film in its transition temperature region, around 79 K. Both, picosecond nonbolometric and nanosecond bolometric response to ultrashort far-infrared laser pulses were found for frequencies between 25 cm−1 and 215 cm−1. We will discuss optimum conditions for radiation detection and present an analysis of the dynamical behaviour of excited high T c thin films.
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Semenov, A. D., Gol’tsman, G. N., Gogidze, I. G., Sergeev, A. V., Gershenzon, E. M., Lang, P. T., et al. (1992). Subnanosecond photoresponse of a YBaCuO thin film to infrared and visible radiation by quasiparticle induced suppression of superconductivity. Appl. Phys. Lett., 60(7), 903–905.
Abstract: We observed subnanosecond photoresponse of a structured superconducting YBa2Cu3O7−δ thin film to infrared and visible radiation. We measured the voltage response of a current biased film (thickness 700 Å) in a resistive state to radiation pulses. From our results we conclude a response time of about 90 ps and a responsivity of about 4×1010 Ω/J. We attribute the response to Cooper pair breaking and suppression of the superconducting energy gap induced by nonequilibrium quasiparticles.
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Verevkin, A. A., Ptitsina, N. G., Chulcova, G. M., Gol'Tsman, G. N., Gershenzon, E. M., & Yngvesson, K. S. (1996). Determination of the limiting mobility of a two-dimensional electron gas in AlxGa1-xAs/GaAs heterostructures and direct measurement of the energy relaxation time. Phys. Rev. B Condens. Matter., 53(12), R7592–R7595.
Abstract: We present results for a method to measure directly the energy relaxation time (τe) for electrons in a single AlxGa1−xAs/GaAs heterojunction; measurements were performed from 1.6 to 15 K under quasiequilibrium conditions. We find τeαT−1 below 4 K, and τe independent of T above 4 K. We have also measured the energy-loss rate, ⟨Q⟩, by the Shubnikov-de Haas technique, and find ⟨Q⟩α(T3e−T3) for T<~4.2 K; Te is the electron temperature. The values and temperature dependence of τe and ⟨Q⟩ for T<4 K agree with calculations based on piezoelectric and deformation potential acoustic phonon scattering. At 4.2 K, we can also estimate the momentum relaxation time, τm, from our measured τe. This leads to a preliminary estimate of the phonon-limited mobility at 4.2 K of μ=3×107 cm2/Vs (ns=4.2×1011 cm−2), which agrees well with published numerical calculations, as well as with an earlier indirect estimate based on measurements on a sample with much higher mobility.
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Semenov, A. D., Hübers, H. –W., Schubert, J., Gol'tsman, G. N., Elantiev, A. I., Voronov, B. M., et al. (2000). Frequency dependent noise temperature of the lattice cooled hot-electron terahertz mixer. In Proc. 11th Int. Symp. Space Terahertz Technol. (pp. 39–48).
Abstract: We present the measurements and the theoretical model on the frequency dependent noise temperature of a lattice cooled hot electron bolometer (HEB) mixer in the terahertz frequency range. The experimentally observed increase of the noise temperature with frequency is a cumulative effect of the non-uniform distribution of the high frequency current in the bolometer and the charge imbalance, which occurs near the edges of the normal domain and contacts with normal metal. In addition, we present experimental results which show that the noise temperature of a HEB mixer can be reduced by about 30% due to a Parylene antireflection coating on the Silicon hyperhemispheric lens.
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Semenov, A. D., Hübers, H. - W., Schubert, J., Gol'tsman, G. N., Elantiev, A. I., Voronov, B. M., et al. (2000). Design and performance of the lattice-cooled hot-electron terahertz mixer. J. Appl. Phys., 88(11), 6758–6767.
Abstract: We present the measurements and the theoreticalmodel of the frequency-dependent noise temperature of a superconductor lattice-cooled hot-electron bolometer mixer in the terahertz frequency range. The increase of the noise temperature with frequency is a cumulative effect of the nonuniform distribution of the high-frequency current in the bolometer and the charge imbalance, which occurs at the edges of the normal domain and at the contacts with normal metal. We show that under optimal operation the fluctuation sensitivity of the mixer is determined by thermodynamic fluctuations of the noise power, whereas at small biases there appears additional noise, which is probably due to the flux flow. We propose the prescription of how to minimize the influence of the current distribution on the mixer performance.
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