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  • Artikel: DFG Deutsche Nationallizenzen  (157)
  • 1
    Digitale Medien
    Digitale Medien
    The Auger recombination rate is larger in a GaSb quantum well than in bulk GaSb (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 836-840 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The band-to-band Auger recombination rate in bulk GaSb and in a GaSb quantum well is calculated. It turns out to be larger in the quantum well because the threshold of the Auger process is located at the band edge where the density of states is larger in the quantum well than in bulk. A simple picture is developed to illustrate the physics of the Auger processes in bulk and quantum-well direct-band-gap semiconductors. With this picture, we propose that the composition-disorder-induced band mixing should be considered in order to explain the unusual behavior of the Auger process in an InGaAsP quantum-well structure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.347318
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  • 2
    Digitale Medien
    Digitale Medien
    Auger recombination in HgCdTe quantum wires and quantum boxes (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3394-3398 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Quantum-wire and quantum-box structures for narrow-gap materials with small effective masses, such as HgCdTe, can readily be fabricated using current lithographic techniques. In this article, we calculate the Auger-recombination carrier lifetimes in HgCdTe quantum-wire and quantum-box structures, with band gaps in the 2–5 μm wavelength range. Quantum confinement is generally believed to increase the carrier lifetimes. However, we find the Auger recombination lifetime in a HgCdTe quantum wire is shorter than that in a quantum well, and it decreases as the wire width decreases because of the corresponding increase in the density of states. On the other hand, band-to-band Auger recombination is zero in a quantum box because the overlap functions vanish and because of the discrete nature of the energy levels. Therefore, within the confines of our model, we can expect improved temperature performance from long-wavelength quantum-box lasers but not from quantum-wire lasers. Furthermore, these conclusions are applicable for all types of band-to-band Auger processes and semiconductor materials.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350935
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  • 3
    Digitale Medien
    Digitale Medien
    Carrier lifetimes and threshold currents in HgCdTe double heterostructure and multi-quantum-well lasers (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 6869-6875 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The Auger and radiative combination carrier lifetimes in HgCdTe bulk and quantum-well structures, with band gaps in the wavelength range 2–5 μm, are calculated. The Auger recombination rate in a HgCdTe quantum well (QW) is shown to be significantly smaller than that in bulk material. Threshold current densities of HgCdTe double-heterostructure (DH) and multiquantum-well (MQW) lasers are calculated. In a HgCdTe DH laser, Auger recombination dominates the carrier loss at threshold. In a HgCdTe MQW laser, on the other hand, radiative recombination dominates the carrier loss. MQW lasers shown improved temperature performance over conventional DH lasers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.347676
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  • 4
    Digitale Medien
    Digitale Medien
    Enhanced exciton absorption and saturation limit in strained InGaAs/InP quantum wells (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 769-772 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A new approach for enhancing the exciton absorption and increasing the saturation limit in quantum wells (QWs), using tensile strain, is proposed. Because of the valence-band mixing in a strained QW, the in-plane hole mass can become very large or negative. This leads to a heavy electron-hole reduced mass (exciton mass), and therefore to a small exciton radius. Exciton absorption is substantially increased because of the increased electron-hole overlap probability in these small-radius excitons. The effects of saturation are also substantially reduced because of decreased charge-screening effects for small-radius excitons and because the rapid dispersal of the photon-generated excitons reduces the Pauli exclusion effect.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351341
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  • 5
    Digitale Medien
    Digitale Medien
    Improved performance of an optically pumped FIR laser using metallic waveguide : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4672-4674 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: In order to improve the overall output characteristics of far-infrared (FIR) lasers, recent development at UCLA has concentrated on the use of a metallic overmoded waveguide (smooth bore and corrugated) instead of a conventional smooth-bore dielectric waveguide. The metallic waveguide has substantially lower propagation losses, especially at frequencies below 500 GHz, and also supports the desired HE11 mode. Laboratory results show a substantial increase in output power using a corrugated metallic waveguide, with 37 mW being obtained at 1.22 mm using 13CH3F (isotopic methyl fluoride) while maintaining the same mode quality and polarization. This represents an improvement of 100% over a smooth-bore dielectric waveguide. Comparison of far-infrared output using the three types of waveguide will be made.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1143659
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  • 6
    Digitale Medien
    Digitale Medien
    Poloidal asymmetry and gradient drive in core electron density and temperature fluctuations on the Texas Experimental Tokamak-Upgrade (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2013-2021 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Electron temperature and density fluctuations are measured in the core of the Texas Experimental Tokamak-Upgrade (TEXT-U) [P. H. Edmonds, E. R. Solano, and A. J. Wootton, in Proceedings of the 15th Symposium on Fusion Technology, Utrecht (Elsevier Science, Amsterdam, 1989), Vol. 1, p. 342] plasma across the poloidal cross section. The high spatial resolution of the heavy-ion beam probe (HIBP) and correlation radiometry of electron cyclotron emission (CRECE) reveal that both the density and temperature fluctuations are strongly poloidally asymmetric. Temperature fluctuation measurements indicate a broadband drift wave feature localized near the plasma equatorial plane on both the high- and low-field sides, which is consistent with density fluctuation measurements by far infrared (FIR) scattering. In contrast, the HIBP observes this feature localized only to the low-field side. Excellent spatial resolution allows us to investigate whether changes in the gradient affect the fluctuation amplitudes. We find that indeed, the temperature fluctuations increase with the electron temperature gradient. Results also link density fluctuations to changes in the density gradient. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871998
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  • 7
    Digitale Medien
    Digitale Medien
    Ultrafast stimulated emission spectroscopy of perylene in dilute solution: Measurement of ground state vibrational population relaxation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6075-6082 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report ultrafast stimulated emission measurements of perylene in a series of polar and nonpolar solvents. In all solvents the perylene stimulated emission spectra evolve in time. We observe individual features corresponding to distinct vibronic resonances in the stimulated emission spectra. The intensities of these features increase subsequent to excitation and persist for hundreds of picoseconds. The fast build-up seen at short delay times is related directly to the vibrational population relaxation time, T1 , of the ground vibrational state that is the lower energy state of the stimulated transition. The measured T1 times for perylene vary with both ground vibrational state and solvent. The slow decay rates for these data, the sum of the stimulated and spontaneous decay rates for the particular transition, depend critically on the particular transition that is resonant with the probe laser electric field.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.464846
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  • 8
    Digitale Medien
    Digitale Medien
    Interferometric measurement of high-frequency density fluctuations in Madison symmetric torus : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 703-706 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: As a consequence of recent improvements to the far-infrared (FIR) interferometer time response, from bandwidth of 10 kHz up to 1 MHz, high-frequency density fluctuations can now be resolved on the Madison symmetric torus (MST) reversed-field pinch. The phase measurement allows absolute calibration of the fluctuation amplitude while eleven chords generate information on the spatial distribution. Density fluctuations up to 200 kHz are observed. A unique feature of the MST interferometer is that six chords are toroidally displaced 5° from the remaining five. Hence, besides information on the poloidal structure, i.e., m=1, toroidal information is also available. By computing the cross power, coherence, and cross phase between two toroidally displaced chords, one can determine the toroidal rotation speed, dispersion, and correlation length. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1149275
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  • 9
    Digitale Medien
    Digitale Medien
    Initial operation of the two-dimensional far-infrared scattering/interferometry system on TEXT-Upgrade : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 856-858 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The UCLA far-infrared scattering/interferometry system on TEXT-Upgrade has recently been modified to include a two-dimensional capability. Along with the vertically viewing system, a horizontal view has been added. For interferometric measurements of the plasma density profile, the vertical view consists of a 45 cm array while the horizontal view array spans 15 cm. Density profiles for Text-Upgrade plasmas will be presented. For collective scattering measurements of electron density fluctuations, cross correlation of scattered signals from the two orthogonal views at the same wave vector will be examined. Finite cross coherence may be used to spatially localize the fluctuation measurements. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146252
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  • 10
    Digitale Medien
    Digitale Medien
    Multichannel far-infrared polarimeter-interferometer system on the MST reversed field pinch : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1077-1080 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: The multichannel far-infrared (FIR) heterodyne polarimeter-interferometer system on the Madison Symmetric Torus (MST) is now operational. The combined system consists of 11 channels with variable radial and toroidal spacing. Poloidal magnetic field is determined by measuring the Faraday rotation of the FIR laser beam after propagation through the plasma by use of a phase technique. The polarimeter has 3 mrad rms noise level and 1 ms temporal resolution while the interferometer resolution is nedl=1×1012 cm−2 with time response of 1 μs. Absolute calibration of the polarimeter system is achieved by use of a rotating quartz half-wave plate. The first 11-channel polarimeter measurements from MST indicate a Faraday rotation profile in good agreement with expectations from the MSTFIT equilibrium code. Future plans to reduce the polarimeter time response from 1 ms to 10 μs will allow direct measurement of magnetic fluctuations associated with global resistive tearing modes on MST. The effect of these modes on density is already clearly resolved and provides insight into the dynamics of these structures. Improving the time response will also result in lower phase noise for both the polarimeter and interferometer. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1321744
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