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Verevkin AI, Ptitsina NG, Chulkova GM, Gol'tsman GN, Gershenzon EM, Yngvesson KS. Electron energy relaxation in a 2D channel in AlGaAs-GaAs heterostructures under quasiequilibrium conditions at low temperatures. JETP Lett. 1995;61(7):591–5.
Abstract: The energy relaxation time of 2D electrons, Te, has been measured under quasiequilibrium conditions in AlGaAs—GaAs heterojunctions over the temperature range T= 1.5—20 K. At T> 4 K, Te depends only weakly on the temperature, while at T< 4 K 7;'(T) there is a dependence fr; lNT. A linear dependence 7: 1 (T) in the Bloch—-Grfineisen temperature region (T< 5 K) is unambiguous evidence that a piezoacoustic mechanism of an electron—phonon interaction is predominant in the inelastic scattering of electrons. The values of T6 in this temperature range agree very accurately with theoretical results reported by Karpus [Sov. Phys. Semicond. 22 (1988)]. At higher temperatures, where scat—tering by deformation acoustic phonons becomes substantial, there is a significant discrepancy between the experimental and theoretical re-sults.
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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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Gerecht E, Musante CF, Zhuang Y, Yngvesson KS, Gol’tsman GN, Voronov BM, et al. NbN hot electron bolometric mixerss—a new technology for low-noise THz receivers. IEEE Trans Appl Supercond. 1999;47(12):2519–27.
Abstract: New advances in hot electron bolometer (HEB) mixers have recently resulted in record-low receiver noise temperatures at terahertz frequencies. We have developed quasi-optically coupled NbN HEB mixers and measured noise temperatures up to 2.24 THz, as described in this paper. We project the anticipated future performance of such receivers to have even lower noise temperature and local-oscillator power requirement as well as wider gain and noise bandwidths. We introduce a proposal for integrated focal plane arrays of HEB mixers that will further increase the detection speed of terahertz systems.
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Verevkin AA, Ptitsina NG, Smirnov KV, Voronov BM, Gol’tsman GN, Gershenson EM, et al. Multiple Andreev reflection in hybrid AlGaAs/GaAs structures with superconducting NbN contacts. Semicond. 1999;33(5):551–4.
Abstract: The conductivity of hybrid microstructures with superconducting contacts made of niobium nitride to a semiconductor with a two-dimensional electron gas in a AlGaAs/GaAs heterostructure has been investigated. Distinctive features of the behavior of the conductivity indicate the presence of multiple Andreev reflection at scattering centers in the normal region near the superconductor-semiconductor boundary.
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Gerecht E, Musante CF, Jian H, Yngvesson KS, Dickinson J, Waldman J, et al. New results for NbN phonon-cooled hot electron bolometric mixers above 1 THz. IEEE Trans Appl Supercond. 1999;9(2):4217–20.
Abstract: NbN Hot Electron Bolometric (HEB) mixers have produced promising results in terms of DSB receiver noise temperature (2800 K at 1.56 THz). The LO source for these mixers is a gas laser pumped by a CO/sub 2/ laser and the device is quasi-optically coupled through an extended hemispherical lens and a self-complementary log-periodic toothed antenna. NbN HEBs do not require submicron dimensions, can be operated comfortably at 4.2 K or higher, and require LO power of about 100-500 nW. IF noise bandwidths of 5 GHz or greater have been demonstrated. The DC bias point is also not affected by thermal radiation at 300 K. Receiver noise temperatures below 1 THz are typically 450-600 K and are expected to gradually approach these levels above 1 THz as well. NbN HEB mixers thus are rapidly approaching the type of performance required of a rugged practical receiver for astronomy and remote sensing in the THz region.
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