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Gerecht E, Musante CF, Yngvesson KS, Waldman J, Gol'tsman GN, Yagoubov PA, et al. Optical coupling and conversion gain for NbN HEB mixer at THz frequencies. In: Proc. 4-th Int. Semicond. Device Research Symp.; 1997. p. 47–50.
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Verevkin AA, Ptitsina NG, Smirnov KV, Goltsman GN, Gershenson EM, Yngvesson KS. Direct measurements of electron energy relaxation times at an AlGaAs/GaAs heterointerface in the optical phonon scattering range. In: Proc. 4-th Int. Semicond. Device Research Symp.; 1997. p. 55–8.
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Verevkin AA, Ptitsina NG, Smirnov KV, Gol'tsman GN, Voronov BM, Gershenzon EM, et al. Hot electron bolometer detectors and mixers based on a superconducting-two-dimensional electron gas-superconductor structure. In: Proc. 4-th Int. Semicond. Device Research Symp.; 1997. p. 163–6.
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Ekström H, Kollberg E, Yagoubov P, Gol'tsman G, Gershenzon E, Yngvesson S. Phonon cooled ultra thin NbN hot electron bolometer mixers at 620 GHz. In: Proc. 8th Int. Symp. Space Terahertz Technol.; 1997. p. 29–35.
Abstract: We have measured the noise performance and gain bandwidth of 35 A thin NbN hot-electron mixers integrated with spiral antennas on silicon substrate lenses at 620 GHz. A double-sideband receiver noise temperature less than 1300 K has been obtained with a 3 dB bandwidth of GHz. The gain bandwidth is 3.2 GHz. A lower noise temperature of 1100 K has been achieved with an improved set-up. The mixer output noise dominated by thermal fluctuations is about 50-60 K, and the SSB receiver and intrinsic conversion gain is about -18 and -12 dB, respectively. Without mismatch losses and excluding the loss from the beamsplitter, we expect to achieve a receiver noise temperature of less than 700 K.
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Gerecht E, Musante CF, Wang Z, Yngvesson KS, Waldman J, Gol'tsman GN, et al. NbN hot electron bolometric mixer for 2.5 THz: the phonon cooled version. In: Proc. 8th Int. Symp. Space Terahertz Technol.; 1997. p. 258–71.
Abstract: We describe an investigation of a NbN HEB mixer for 2.5 THz. NbN HEBs are phonon-cooled de-. vices which are expected, according to theory, to achieve up to 10 GHz IF conversion gain bandwidth. We have developed an antenna coupled device using a log-periodic antenna and a silicon lens. We have demon- strated that sufficient LO power can be coupled to the device in order to bring it to the optimum mixer oper- ating point. The LO power required is less than 1 microwatts as measured directly at the device. We also describe the impedance characteristics of NbN devices and compare them with theory. The experimental results agree with theory except for the imaginary part of the impedance at very low frequencies as was demonstrated by other groups.
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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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Kawamura J, Blundell R, Tong C‐yu E, Gol’tsman G, Gershenzon E, Voronov B. Performance of NbN lattice‐cooled hot‐electron bolometric mixers. J Appl Phys. 1996;80(7):4232–4.
Abstract: The heterodyne performance of lattice‐cooled hot‐electron bolometric mixers is measured at 200 GHz. Superconducting thin‐film niobium nitride strips with ∼5 nm thickness are used as waveguide mixer elements. A double‐sideband receiver noise temperature of 750 K at 244 GHz is measured at an intermediate frequency centered at 1.5 GHz with 500 MHz bandwidth and with 4.2 K device temperature. The instantaneous bandwidth for this mixer is 1.6 GHz. The local oscillator power required by the mixer is about 0.5 μW. The mixer is linear to within 1 dB up to an input power level 6 dB below the local oscillator power. A receiver incorporating a hot‐electron bolometric mixer was used to detect molecular line emission in a laboratory gascell. This experiment unambiguously confirms that the receiver noise temperature determined from Y‐factor measurements reflects the true heterodyne sensitivity.
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Verevkin AA, Ptitsina NG, Smirnov KV, Gol’tsman GN, Gershenzon EM, Ingvesson KS. Direct measurements of energy relaxation times on an AlGaAs/GaAs heterointerface in the range 4.2–50 K. JETP Lett. 1996;64(5):404–9.
Abstract: The temperature dependence of the energy relaxation time τe (T) of a two-dimensional electron gas at an AlGaAs/GaAs heterointerface is measured under quasiequilibrium conditions in the region of the transition from scattering by acoustic phonons to scattering with the participation of optical phonons. The temperature interval of constant τe, where scattering by the deformation potential predominates, is determined. In the preceding, low-temperature region, where piezoacoustic and deformation-potential-induced scattering processes coexist, τ e decreases slowly with increasing temperature. Optical phonons start to participate in the scattering processes at T∼25 K (the characteristic phonon lifetime was equal to τLOτ4.5 ps). The energy losses calculated from the τe data in a model with an effective nonequilibrium electron temperature agree with the published data obtained under strong heating conditions.
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Verevkin AA, Ptitsina NG, Chulcova GM, Gol'tsman GN, Gershenzon EM, Yngvesson KS. Direct measurements of energy relaxation time of electrons in AlGaAs/GaAs heterostructures under quasi-equilibrium conditions. Surface Science. 1996;361-362:569–73.
Abstract: For the first time, results are presented of a direct measurement of the energy relaxation time τε of 2D electrons in an AlGaAs/GaAs heterojunction at T = 1 and 5–20 K. A weak temperature dependence of τε for the T > 4K range and a linear temperature dependence of the reciprocal of τε for T < 4K have been observed. The linear dependence τε−1 ≈ T in the Bloch-Gruneisen regime is direct evidence of the predominance of the piezo-electric mechanism of electron-phonon interaction in non-elastic electron scattering processes. The values of τε in this regime are in very good agreement with the results of the Karpus theory. At higher temperatures, where the deformation-potential scattering becomes noticeable, a substantial disagreement between the experimental data and the theoretical results is observed.
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Semenov AD, Gousev YP, Nebosis RS, Renk KF, Yagoubov P, Voronov BM, et al. Heterodyne detection of THz radiation with a superconducting hot‐electron bolometer mixer. Appl Phys Lett. 1996;69(2):260–2.
Abstract: We report on the use of a superconducting hot‐electron bolometer mixer for heterodyne detection of terahertz radiation. Radiation with a wavelength of 119 μm was coupled to the mixer, a NbN microbridge, by a hybrid quasioptical antenna consisting of an extended hyperhemispherical lens and a planar logarithmic spiral antenna. We found, at an intermediate frequency of 1.5 GHz, a system double side band noise temperature of ≊40 000 K and conversion losses of 25 dB. We also discuss the possibilities of further improvement of the mixer performance.
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