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Chulcova GM, Ptitsina NG, Gershenzon EM, Gershenzon ME, Sergeev AV. Effect of the interference between electron-phonon and electron-impurity (boundary) scattering on resistivity Nb, Al, Be films. In: Czech J. Phys. Vol 46.; 1996. p. 2489–90.
Abstract: The temperature dependence of the resistivity of thin Nb, Al, Be films has been studied over a wide temperature range 4-300 K. We have found that the temperature-dependent correction to the residual resistivity is well described by the sum of the Bloch-Grüneisen term and the term originating from the interference between electron-phonon and electron-impurity scattering. Study of the transport interference phenomena allows to determine electron-phonon coupling in disordered metals. The interference term is proportional to T2 and also to the residual resistivity and dominates over the Bloch-Grüneisen term at low temperatures (T<40 K).
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Kawamura J, Blundell R, Tong C-YE, Golts'man G, Gershenzon E, Voronov B. Superconductive NbN hot-electron bolometric mixer performance at 250 GHz. In: Proc. 7th Int. Symp. Space Terahertz Technol.; 1996. p. 331–6.
Abstract: Thin film NbN (<40 A) strips are used as waveguide mixer elements. The electron cooling mechanism for the geometry is the electron-phonon interaction. We report a receiver noise temperature of 750 K at 244 GHz, with / IF = 1.5 GHz, Af= 500 MHz, and Tphysical = 4 K. The instantaneous bandwidth for this mixer is 1.6 GHz. The local oscillator (LO) power is 0.5 1.tW with 3 dB-uncertainty. The mixer is linear to 1 dB up to an input power level 6 dB below the LO power. We report the first detection of a molecular line emission using this class of mixer, and that the receiver noise temperature determined from Y-factor measurements reflects the true heterodyne sensitivity.
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Gerecht E, Musante CF, Wang Z, Yngvesson KS, Mueller ER, Waldman J, et al. Optimization of hot eleciron bolometer mixing efficiency in NbN at 119 micrometer wavelength. In: Proc. 7th Int. Symp. Space Terahertz Technol.; 1996. p. 584–600.
Abstract: We describe an investigation of a NbN HEB mixer for 2.5 THz. An intrinsic conversion loss of 23 dB has been measured with a two-laser measurement technique. The conversion loss was limited by the LO power available and is expected to decrease to 10 dB or less when sufficient LO power is available. For this initial experiment we used a prototype device which is directly coupled to the laser beams. We present results for a back-short technique that improves the optical coupling to the device and describe our progress for an antenna-coupled device with a smaller dimension. Based on our measured data for conversion loss and device output noise level, we predict that NbN HEB mixers will be capable of achieving DSB receiver noise temperatures of ten times the quantum noise limit in the THz range.
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Ekström H, Kroug M, Belitsky V, Kollberg E, Olsson H, Goltsman G, et al. Hot electron mixers for THz applications. In: Rolfe EJ, Pilbratt G, editors. Proc. 30th ESLAB.; 1996. p. 207–10.
Abstract: We have measured the noise performance of 35 A thin NbN HEB devices integrated with spiral antennas on antireflection coated silicon substrate lenses at 620 GHz. From the noise measurements we have determined a total conversion gain of the receiver of—16 dB, and an intrinsic conversion of about-10 dB. The IF bandwidth of the 35 A thick NbN devices is at least 3 GHz. The DSB receiver noise temperature is less than 1450 K. Without mismatch losses, which is possible to obtain with a shorter device, and with reduced loss from the beamsplitter, we expect to achieve a DSB receiver noise temperature of less ‘than 700 K.
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Verevkin AA, Ptitsina NG, Chulcova GM, Gol'Tsman GN, Gershenzon EM, Yngvesson KS. 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. 1996;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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