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  • 1
    Digitale Medien
    Digitale Medien
    Optimization of two dimensional gratings for very long wavelength quantum well infrared photodetectors (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4989-4994 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have performed a detailed study of two-dimensional grating coupling for quantum well infrared photodetectors in the very long wavelength spectral region λ∼16–17 μm. Using calculations based on the modal expansion method we quantitatively explain the double peaked responsivity spectrum. By optimizing the grating parameters we achieve a normal incidence responsivity and detectivity which are three times larger than the 45° angle of incidence geometry.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357209
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  • 2
    Digitale Medien
    Digitale Medien
    Dark current mechanisms and conditions of background radiation limitation of n-doped AlGaAs/GaAs quantum-well infrared detectors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6298-6304 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The most important mechanism of dark current in n-doped quantum-well infrared photodetectors (QWIPs) is due to interaction of electrons with longitudinal optical phonons. Theoretical expressions are derived for the carrier lifetime, and for generation currents originating from both photoexcitation as well as from thermal excitation in a single quantum well. Detector gain is discussed briefly. Calculated values of thermal generation currents and the ratio of photocurrent to thermal current are found to accord well with experimental data. Finally the conditions of background radiation limitation of QWIPs are investigated and the theory gives a temperature of background radiation limitation TBLIP=81 K for a 9 μm cutoff detector with a two-dimensional grating and optical cavity, for 300 K background temperature, optics f number=1 with 100% optical transmission, provided that a photocurrent to dark current ratio of 1 criterion is used. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.360510
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  • 3
    Digitale Medien
    Digitale Medien
    Factors Controlling the B-Cell Cycle (1986)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Immunology 4 (1986), S. 13-34 
    Details
    ISSN: 0732-0582
    Quelle: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Thema: Biologie , Medizin
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1146/annurev.iy.04.040186.000305
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  • 4
    Digitale Medien
    Digitale Medien
    Levonorgestrel-releasing intrauterine device in the treatment of menorrhagia (1990)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 97 (1990), S. 0 
    Details
    ISSN: 1471-0528
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Summary. In 20 women with menorrhagia (〉80 ml blood loss per menstrual period) a levonorgestrel-releasing intrauterine device (Lng-IUCD) was inserted. Menstrual blood loss (MBL) was measured in two consecutive cycles before the device was inserted and after 3, 6 and 12 months of use. MBL was significantly reduced after 3 months (86%) and after 12 months the reduction was 97%. There was a significant increase (P〈 0.001) in serum ferritin during the first year of Lng-IUCD use. The Lng-IUCD seems to be an important alternative to oral medication and to hysterectomy in the treatment of menorrhagia.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1471-0528.1990.tb16240.x
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  • 5
    Digitale Medien
    Digitale Medien
    Intersubband transitions in single AlGaAs/GaAs quantum wells studied by Fourier transform infrared spectroscopy (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4123-4127 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Infrared intersubband absorption in modulation-doped MOVPE-grown AlxGa1−xAs/GaAs single-quantum wells have been studied by Fourier transform infrared spectroscopy. High signal to noise ratio was obtained by utilizing the multiple internal reflection (MIR) technique and a quantitative model of the absorption for this geometry was developed. Overlapping from multiphonon absorption was eliminated by using radiation polarized in two orthogonal directions and taking the difference between the resulting spectra, only one of them exhibiting the intersubband peak. The absorption wavelengths and intensities were fitted to theoretical expressions and the dimensions of the quantum wells were compared with independent determinations by photoluminescence, double crystal x-ray diffraction, and Hall-effect measurements. A narrow linewidth of about 6 meV was measured, corresponding to a 0.1-ps lifetime of electrons in the excited state.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.341322
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  • 6
    Digitale Medien
    Digitale Medien
    Grating-coupled quantum-well infrared detectors: Theory and performance (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3600-3610 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A theory of the grating-coupled quantum-well infrared detector, based on the modal expansion method (MEM) is presented together with numerical simulation results. MEM is a near-exact way of determining the electromagnetic-field pattern in a reflection grating-coupled quantum-well infrared detector, and is suitable for the calculation of absorption quantum efficiencies. Both lamellar gratings and crossed (doubly periodic) gratings are dealt with. Numerical simulations show that quantum efficiencies integrated with respect to wavelength ηint equal to 1 μm may be obtained in a detector equipped with a crossed grating of square symmetry, and a waveguide. The waveguide is defined by the metal grating on one side of the infrared absorbing quantum wells, and a thick aluminum arsenide layer on the other. This implies a factor of 4 higher ηint than in a 45° polished edge detector with the corresponding quantum-well characteristics. Finally, a sensitivity analysis shows that a change in grating dimensions of the order of 0.1 μm results in relative changes of ηint of about 1%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.350916
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  • 7
    Digitale Medien
    Digitale Medien
    Quantum efficiency enhancement of AlGaAs/GaAs quantum well infrared detectors using a waveguide with a grating coupler (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2264-2266 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Long wavelength quantum well detectors with very high quantum efficiency, based on the coupling of radiation into an optical resonant cavity or waveguide defined by a reflection grating coupler on one side of the infrared absorbing multiquantum well stack, and an aluminum arsenide cladding layer on the other, have been fabricated and the results compared with theory. Theory shows that quantum efficiencies up to 90% may be obtained (for polarized radiation). However, experimental results indicate that the response peak becomes broadened due to spread in the grating period and therefore the maximum quantum efficiency is in practice limited to 60%, corresponding to a current responsivity of 2.1 A/W. This is 2.7 times larger than for a 45° polished edge detector with the same quantum well characteristics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.104917
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  • 8
    Digitale Medien
    Digitale Medien
    Efficiency of grating coupled AlGaAs/GaAs quantum well infrared detectors (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3361-3363 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The efficiency of grating coupling of radiation into the quantum well infrared detector is studied experimentally, with special emphasis on the influence of detector mesa size. It is found that compared to a 45° polished edge detector, the integrated quantum efficiency for crossed grating detectors of mesa size as small as 45 μm is about four times larger with a waveguide included, and two times larger without a waveguide. Furthermore, the importance of a high conductivity grating metal, the use of crossed gratings instead of lamellar gratings, as well as of a dielectric reflector is demonstrated. To show the superior coupling efficiency, the detectivity is measured for a detector with a crossed grating and a waveguide, and of mesa size 500 μm, resulting in D*=1.4×1011 cm Hz1/2 W−1 at 77 K operating temperature with the detector shielded from background radiation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.110145
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  • 9
    Digitale Medien
    Digitale Medien
    Near-unity quantum efficiency of AlGaAs/GaAs quantum well infrared detectors using a waveguide with a doubly periodic grating coupler (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 857-859 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Quantum well infrared detectors based on a waveguide with a doubly periodic grating coupler are shown to provide quantum efficiencies of nearly unity with respect to unpolarized polarization. This is a factor of six larger than for a conventional 45° polished edge detector with the same quantum well characteristics. As a further advantage the detector response becomes nearly insensitive to the polarization direction of the incident radiation. Detectors have been fabricated and tested. Measurements lead to a maximum quantum efficiency of 92% with respect to unpolarized radiation, with a response linewidth =0.8 μm, thus confirming theory.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.105259
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  • 10
    Digitale Medien
    Digitale Medien
    Haematological responses in the European eel, Anguilla anguilla L., to sublethal infestation by Anguillicola crassus in a thermal effluent of the Swedish Baltic (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish diseases 15 (1992), S. 0 
    Details
    ISSN: 1365-2761
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: Abstract. Haematological variations were studied in a European eel population, Anguilla anguilla L., naturally infested by the sanguivorous nematode Anguillicola crassus. This occurred off the Swedish Baltic coast in an area receiving heated cooling water from a nuclear power station. The erythrocyte count, haematocrit, leucocrit, haemoglobin concentration, mean corpuscular volume, mean corpuscular haemoglobin and mean corpuscular haemoglobin concentrations, the various cell types in peripheral blood, serum iron concentration, the amount of total serum protein, and scrum protein fractions α1, β1, α2, β2 and γ were all measured. Each variable was correlated to: (1) the intensity of infestation, i.e. number of parasites per host; and (2) a parasitization index, i.e. the weight of parasites per somatic weight of the host. Most variables showed no or only minor reactions to the infestation. However, a marked increase in the γ-fraction of scrum proteins, reduced lymphocyte numbers and increased granulocyte numbers are indicative of a humoral and cellular immune response.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2761.1992.tb00682.x
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