Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Progress in Crystal Growth and Characterization of Materials 25 (1992), S. 241-256 
    ISSN: 0960-8974
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physica B: Physics of Condensed Matter 170 (1991), S. 235-239 
    ISSN: 0921-4526
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3253-3255 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have applied positron spectroscopy to study the formation of vacancy defects in undoped n-type metal organic chemical vapor deposition grown GaN, where the stoichiometry was varied. Ga vacancies are found in all samples. Their concentration increases from 1016 to 1019 cm−3 when the V/III molar ratio increases from 1000 to 10 000. In nitrogen rich conditions Ga lattice sites are thus left empty and Ga vacancies are abundantly formed. The creation of Ga vacancies is accompanied by the decrease of free electron concentration from 1020 to 1016 cm−3, demonstrating their role as compensating centers. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 3512-3521 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this work undoped semi-insulating (SI) GaAs grown by vertical gradient freeze and liquid encapsulated Czochralski methods was studied by near-infrared absorption (NIRA), thermally stimulated current (TSC) and positron annihilation techniques. The positron experiments reveal both gallium and arsenic vacancies, as well as gallium and arsenic antisites, in the samples. By comparing the results from the TSC and positron measurements, the following relations are found in the defect concentrations: trap T2 correlates with the arsenic antisite and trap T5 with the arsenic vacancy. The ionized fraction of the arsenic-antisite-related EL2 defect is obtained from NIRA measurements. The positive charge of these ionized EL2 defects correlates with the net negative charge, 3[VGa3−]+2[GaAs2−]−[VAs+], related to the gallium vacancies and antisites and arsenic vacancies detected in positron measurements. The intrinsic defects may thus contribute significantly to the electrical compensation in SI GaAs. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science, Ltd
    Clinical & experimental allergy 31 (2001), S. 0 
    ISSN: 1365-2222
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The diagnosis of cow's milk allergy is based on a clinical response to an elimination-challenge test with cow's milk.We studied the usefulness of the skin-prick and patch tests and measurement of cow's milk-specific IgE and eosinophil cationic protein in serum as diagnostic tools for cow's milk allergy in a cohort of 6209 unselected infants followed from birth for the development of cow's milk allergy.Of the 239 infants challenged with cow's milk, 118 showed a positive and 121 a negative response at a mean age of 6.9 months. A positive reaction to a skin-prick test with cow's milk (〈inlineGraphic alt="geqslant R: gt-or-equal, slanted" extraInfo="nonStandardEntity" href="urn:x-wiley:09547894:CEA1015:ges" location="ges.gif"/〉 3 mm) was seen in 72 (61%) and 29 (24%) infants with positive and negative challenges, elevated serum cow's milk-specific IgE (〈inlineGraphic alt="geqslant R: gt-or-equal, slanted" extraInfo="nonStandardEntity" href="urn:x-wiley:09547894:CEA1015:ges" location="ges.gif"/〉 0.7 kU/L) in 52 (45%) and 15 (13%) infants, a positive reaction to patch test with cow's milk protein fractions in 26 (26%) and eight (8%) infants, and elevated serum eosinophil cationic protein (〈inlineGraphic alt="geqslant R: gt-or-equal, slanted" extraInfo="nonStandardEntity" href="urn:x-wiley:09547894:CEA1015:ges" location="ges.gif"/〉 20 μg/L) in 22 (21%) and seven (13%) infants, respectively. Parallel use of the four tests with the above-mentioned cut-off values correctly classified 73% of the infants with a sensitivity of 0.76 and a specificity of 0.67. An immediate reaction to cow's milk challenge correlated with skin prick test positivity and elevated serum milk-specific IgE, and tended to correlate with patch test positivity.No single test or parallel use of the four tests could predict the challenge outcome acceptably in this prospectively followed, unselected cohort of 6209 infants. A positive reaction to one or more tests needs to be confirmed by a challenge test and a negative response to all four tests does not rule out the possibility of cow's milk allergy.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1325-1332 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defect characterization of as-grown Zn1−xMgxSe mixed crystals (0≤x〈0.6) and the effect of Zn vapor annealing has been studied by positron lifetime and photoluminescence measurements. We obtain both experimental and theoretical evidence that the bulk lifetime of free positrons increases linearly with Mg alloying. The average positron lifetime increases with temperature indicating that both vacancies and negative ions trap positrons. The decompositions of the lifetime spectra show that the vacancy has the characteristic positron lifetime of 325 ps. The comparison with theoretical calculations indicate that the lifetime 325 ps corresponds either to divacancies relaxed inwards or to monovacancies strongly relaxed outwards. We consider the latter identification more likely and attribute the positron lifetime 325 ps to Zn vacancy or a complex involving VZn. The vacancy concentration is almost independent of Mg content above x=0.2 but decreases strongly at x=0.56. The Zn vapor annealing decreases the concentration of Zn vacancies. The intensity of the green photoluminescence correlates with the concentration of VZn both as a function of Mg alloying and Zn vapor annealing. We thus conclude that the electron levels of the Zn vacancy are involved in the optical transition leading to the green photoluminescence. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1888-1897 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use a low-energy positron beam to study the influence of doping and stoichiometry on the native defects in GaAs grown by molecular-beam epitaxy at 250 °C. Ga vacancies are identified in all samples by measuring the momentum distribution of annihilating core electrons. The charge of VGa is negative in Si-doped samples but neutral in undoped and Be-doped material. We propose that the Ga vacancies are complexed with As antisites in undoped and Be-doped samples and with Si impurities in n-type material. The concentration of Ga vacancies depends on the doping and stoichiometry of growth conditions. It follows generally the trends in the VGa formation energy as a function of the Fermi level position and stoichiometry. The strong loss of free carriers in the As-rich Si-doped samples is attributed to the formation of Ga vacancy complexes, negative ion defects and inactive clusters of Si atoms. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2441-2443 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Gallium vacancies and negative ions are observed in GaN bulk crystals by applying positron lifetime spectroscopy. The concentration of Ga vacancies decreases with increasing Mg doping, as expected from the behavior of the VGa formation energy as a function of the Fermi level. The concentration of negative ions correlates with that of Mg impurities determined by secondary ion mass spectrometry. We thus attribute the negative ions to MgGa〈sup ARRANGE="STAGGER"〉−. The negative charge of Mg suggests that Mg doping converts n-type GaN to semi-insulating mainly due to the electrical compensation of ON〈sup ARRANGE="STAGGER"〉+ donors by MgGa〈sup ARRANGE="STAGGER"〉− acceptors. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show that positron trapping at negative As vacancies revealed under illumination in bulk semi-insulating GaAs correlates with a form of near-band-edge absorption known as reverse contrast (RC). We conclude that it is the ionization of As vacancies to their negative charge state that gives rise to RC absorption. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1843-1845 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positron annihilation experiments have been performed to investigate the compensating defects in silicon δ-doping superlattices in (001) GaAs. The results reveal vacancies and ion-type defects, which are located between the delta planes in undoped GaAs. The vacancy defect is identified as the Ga vacancy and the negative ion is attributed to the Ga antisite. The concentrations of these defects increase strongly, when the areal concentrations of free carriers are reduced at the delta planes. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...