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  • 1
    Electronic Resource
    Electronic Resource
    Broad-band photoluminescence from ZnGeP2 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7310-7315 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The near-infrared photoluminescence from single crystals of bulk ZnGeP2 was studied as a function of excitation power, excitation wavelength, sample temperature, and polarization. The nature of this broad-band luminescence from large single crystals grown for nonlinear optical applications is established. Two distinct bands with quite different polarization, power, and temperature behaviors were resolved. At 5 K, these broad bands have peaks in intensity near 1.58 and 1.36 eV. The 1.58 eV band is partially polarized perpendicular to the crystal's c axis, has a relatively small thermal quenching activation energy (45 meV), and excitation spectra show a resonance in intensity associated with a shallow level approximately 90 meV below the minimum conduction band. The 1.36 eV band is partially polarized parallel to c, has a much larger quenching activation energy (220 meV), and its excitation spectrum includes two weak resonances corresponding to the A′ and B′ n=1 excitons. The high-energy band was enhanced in crystals containing relatively larger concentrations of phosphorus vacancies (measured by electron paramagnetic resonance). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372985
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  • 2
    Electronic Resource
    Electronic Resource
    Photoluminescence excitation study of nitrogen-doped zinc selenide epilayers (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6723-6727 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence excitation (PLE) spectroscopy at liquid-helium temperature is used to study six ZnSe:N epilayers grown by molecular beam epitaxy. These samples represent nitrogen-doping levels ranging from less than 1017 to 3×1019 cm−3. The luminescence emission bands from the heavily doped samples exhibit peak energies varying from 2.45 to 2.61 eV. The energy range over which the PLE signal intensity decays and the energy difference between the onset of this decay and the PL peak energy are essentially the same for all the heavy-doped samples. A model is proposed to explain the PL and PLE results for a semiconductor in the presence of potential fluctuations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370185
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  • 3
    Electronic Resource
    Electronic Resource
    Controlled oxygen doping of GaN using plasma assisted molecular-beam epitaxy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2740-2742 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality (0001) and (0001¯)-GaN films were grown by plasma-assisted molecular-beam epitaxy to study the dependence of oxygen incorporation on polarity and oxygen partial pressure. Oxygen incorporates at a rate ten times faster on nitrogen-polar GaN than on the Ga polarity. Oxygen doping is controllable, reproducible, and produces low compensation material up to concentrations of at least 1018 cm−3 with higher levels showing significant compensation. Layers containing oxygen at levels above 1022 cm−3 exhibit severe cracking while oxygen concentrations less than 1021 cm−3 do not introduce significant strain. The oxygen incorporation rate has a weak dependence on Ga overpressure during Ga-stable growth but dramatically increases for conditions approaching N-stable growth. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1403276
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  • 4
    Electronic Resource
    Electronic Resource
    Investigation of donor-acceptor pair luminescence from ZnSe:N epilayers (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5743-5749 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-temperature photoluminescence (PL) due to donor-acceptor pair recombination was monitored in a series of nitrogen-doped ZnSe epilayers grown by molecular beam epitaxy on GaAs substrates. Emission energies were measured for incident power densities ranging from 10−4 to 10 W/cm2 in samples having different nitrogen doping levels. An ionization energy of 50 meV for the "deep" donor in a lightly doped ZnSe:N sample is determined using power dependence data. Heavily nitrogen-doped samples (≥8×1018 cm−3) provided evidence for a second deeper donor with an ionization energy greater than 100 meV. In addition, we show the importance of accounting for interference effects when identifying the emission peaks in the PL spectra from heavily doped ZnSe:N. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368865
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  • 5
    Electronic Resource
    Electronic Resource
    Compensating defects in heavily nitrogen-doped zinc selenide: A photoluminescence study (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 1724-1726 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence (PL) from a heavily nitrogen-doped ZnSe epilayer grown by molecular beam epitaxy was studied as a function of excitation wavelength, power density, and temperature. Also, the time decay of the PL emission was measured. Detailed analysis of the PL data indicates that the deep broad emission is composed of three distinct recombination processes, two are dominant at low power and a third can be detected at higher excitation power. These three bands are labeled NI, NII, and NIII with corresponding peak energies at 2.54, ∼2.58, and 2.65 eV. The NI band is accompanied by phonon replicas of energy 69±3 meV. The behaviors of the NI, NII, and NIII bands are consistent with intracenter recombination, donor–acceptor pair recombination, and electron–acceptor recombination, respectively. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118681
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  • 6
    Electronic Resource
    Electronic Resource
    Observation of singly ionized selenium vacancies in ZnSe grown by molecular beam epitaxy (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2274-2276 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron paramagnetic resonance (EPR) has been used to investigate singly ionized selenium vacancy VSe+ centers in ZnSe epilayers grown by molecular beam epitaxy (MBE). The study included undoped and nitrogen-doped films. Spectra taken at 8 K and 9.45 GHz, as the magnetic field was rotated in the plane from [100] to [010], showed an isotropic signal at g=2.0027±0.0004 with a linewidth of 5.8 G. In the two samples where this signal was observed, estimates of concentration were approximately 1.1×1017 and 6.3×1017 cm−3. The appearance of the EPR signal correlated with an increase in the Zn/Se beam equivalent pressure ratio (during growth) in undoped films and with an increase in the nitrogen concentration in doped films. We conclude that the singly ionized selenium vacancy may be a dominant point defect in many MBE-grown ZnSe layers and that these defects may play a role in the compensation mechanisms in heavily nitrogen-doped ZnSe thin films. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118836
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  • 7
    Electronic Resource
    Electronic Resource
    Plasma-target coupling in the case of TEA-CO"2 laser produced breakdown in front of a solid target
    Amsterdam : Elsevier
    Optics Communications 35 (1980), S. 96-99 
    Details
    ISSN: 0030-4018
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0030-4018(80)90367-3
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  • 8
    Electronic Resource
    Electronic Resource
    The vaporization of a metallic target by a microsecond pulsed TE-CO"2 laser radiation
    Amsterdam : Elsevier
    Optics Communications 39 (1981), S. 180-185 
    Details
    ISSN: 0030-4018
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0030-4018(81)90051-1
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  • 9
    Electronic Resource
    Electronic Resource
    Correlation between tear IgE levels and HLA-DR expression by conjunctival cells in allergic and nonallergic chronic conjunctivitis (2000)
    Springer
    Graefe's archive for clinical and experimental ophthalmology 238 (2000), S. 900-904 
    Details
    ISSN: 1435-702X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Background: Chronic conjunctival inflammatory diseases may depend upon various mechanisms. Discriminating allergy from nonspecific inflammation has become of striking importance for diagnosis and treatment. We investigated conjunctival inflammatory response by comparing two objective biological tools, tear IgE and HLA-DR expression by conjunctival epithelium, as indirect indicators of activation of the Th2 and Th1 subsets, respectiv-ely. Methods: Eighty-two patients with chronic conjunctivitis underwent tear IgE measurement by an ELISA technique and quantitation of HLA-DR expression in impression cytology specimens. Forty-two had direct or indirect clinical indications of allergic mechanisms, 26 had chronic conjunctivitis without any sign of allergy, and 14 suffered from isolated nonallergic dry eyes. Results: Patients clinically considered as allergic only showed positive IgE in 47 of 84 eyes (56%), whereas 21% and 25% of eyes with nonspecific conjunctivitis and dry eyes respectively were also positive. IgE levels were significantly higher in the allergic group than in the other two groups. HLA-DR positivity in epithelial cells was found in 28.5%, 48% and 50% of eyes, respectively. HLA-DR expression by epithelial cells was negatively correlated with tear IgE, as most specimens positive to one criterion were negative to the other one (49 eyes DR+, IgE–; 47 eyes DR–, IgE+; only 9 eyes positive to both criteria; chi-square: P=0.0001). Conclusion: As IgE synthesis and HLA-DR induction may represent indirect indicators of the activation of the Th2 and Th1 subsets, association of these two simple tests could be interesting for the routine assessment of the mechanisms of inflammatory ocular surface diseases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004170000179
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