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  • 1
    Electronic Resource
    Electronic Resource
    Iron doped bulk semi-insulating GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3319-3325 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As an acceptor dopant with a solid:liquid distribution coefficient ks〈1, iron is an example of an impurity which can be used in modest amounts to ensure that an adequate fraction of EL2 midgap defects are ionized along the length of a melt-grown GaAs crystal, as desired for semi-insulating behavior. The results of such deliberate doping with iron (when NFe is in the mid-1015 cm−3 range) are reported for crystals grown by both the liquid encapsulated Czochralski and the vertical gradient freeze methods. Except in the very tail region of such crystals (when NFe(approximately-greater-than)NEL2 and high resistivity p-type behavior results), GaAs with this modest iron modification to the compensation balance behaves with quite ordinary semi-insulating properties. The iron acceptors are then all ionized, and are optically "invisible.''
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352981
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  • 2
    Electronic Resource
    Electronic Resource
    Melt-grown p-type GaAs with iron doping (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7416-7421 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical and electrical properties are described for bulk GaAs, grown from a melt doped with iron to create FeGa deep acceptors in a sufficient amount (exceeding the EL2 defect concentration) to make high-resistivity p-type rather than semi-insulating material. Both iron photoionization and EL2+ photoneutralization contribute to the near-infrared optical absorption. This made it possible to deduce the concentrations (NAi and NAn) of ionized and lattice-neutral iron, and the ratio (NAi/NAn). Temperature dependent measurements of dc electrical transport yielded quantities such as the free hole density, and hence the Fermi energy, for the 290–420 K range. This information combined with (NAi/NAn) led to a determination of the iron acceptor's free energy εA(T): about 0.46 eV above the valence band at 300 K, and ∼40 meV closer at 420 K. The temperature dependence of εA for iron is shown to differ from εv, εc, midgap, or the free energy for CrGa acceptors in GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354006
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  • 3
    Electronic Resource
    Electronic Resource
    Assessment of the ionized EL2 fraction in semi-insulating GaAs (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2106-2108 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Both optical and electrical methods were used to provide separate evaluations of the fraction Pi of EL2 defect donors which have lost an electron. The semi-insulating GaAs which permitted these assessments had a large enough fraction of the EL2 compensated (by CAs acceptors) to make this a sensitive test. Room-temperature Hall effect data, analyzed with an ambipolar correction, indicated that Pi (approximately-equal-to)0.34 in material from a vertical-zone grown crystal, while near-infrared optical absorption could be modeled on a superposition of EL2 photoionization and photoneutralization to yield Pi (approximately-equal-to)0.35 in the same crystal. The presence of compensating CAs acceptors was verified by local mode vibrational absorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101163
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  • 4
    Electronic Resource
    Electronic Resource
    Compensation assessment in "undoped'' high-resistivity GaAs (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 256-261 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Attainment of semi-insulating status when an "undoped'' GaAs crystal is grown from the melt requires a delicate balance among concentrations of "unintentional'' donor and acceptor impurities, and defects, notably the EL2 midgap donor. In qualifying and improving material for device uses, defect identification and characterization is important. The compensation balance is analyzed in this paper for various "undoped'' crystals, relying largely on Hall data over the 290–430 K range, coupled with optical absorption measurements of carbon and EL2. The temperature-dependent data, converted into Fermi energy and into EL2 ionized fraction, provide a clearer picture than just room-temperature measurements as to whether EL2 controls the Fermi energy (giving the desired semi-insulating behavior), or whether a shallower defect species is in control.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343866
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  • 5
    Electronic Resource
    Electronic Resource
    Properties of semi-insulating GaAs grown by a vertical molten zone method (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 852-858 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical and optical measurements are reported for samples from two undoped semi-insulating GaAs crystals grown by a vertical molten zone method. The electrical data, taken over the range 290–420 K, included results for samples from both crystals that were so close to intrinsic as to require an ambipolar correction in determining the electron concentration. The compensation balance in this material is controlled by the EL2 midgap defect, of which the fraction ionized depends on trace presence of CAs shallow acceptors, and of shallow donors, probably including SiGa . An increase of the latter towards the tail (top) end of one crystal led to a reduction of the EL2 ionized fraction, and a lowered resistivity—but one still within the conventional semi-insulating range. Carbon was measured from the strength of its local vibrational mode absorption, while near-infrared measurements showed that EL2 was present in a concentration ∼1016 cm−3, with relatively small variation across a wafer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345742
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  • 6
    Electronic Resource
    Electronic Resource
    Undoped semi-insulating GaAs grown by a vertical Bridgman method: Electrical property analysis using a simple ambipolar correction (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5428-5434 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple procedure is described for numerical correction of conductivity and Hall-effect data in a (GaAs) sample which is near intrinsic or slightly on the n side of intrinsic, such that hole conduction affects the conductivity and Hall coefficient to a modest extent. The numerical procedure is based on the ratio of the measured Hall coefficient to that expected for intrinsic GaAs at the same temperature. One can thereby deduce the electron concentration n0 and the electron mobility, simply, but with reasonable accuracy. The method can be used for any temperature at which transport measurement are normally made with semi-insulating GaAs, and its use is demonstrated with data for three high-resistivity "undoped'' samples from crystals grown by a vertical Bridgman method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343691
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization and mapping of semi-insulating GaAs crystals grown by vertical zone melting and by vertical zone refining
    Amsterdam : Elsevier
    Journal of Crystal Growth 103 (1990), S. 323-329 
    Details
    ISSN: 0022-0248
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0022-0248(90)90206-Z
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  • 8
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    A single amino acid in the F2 subunit of respiratory syncytial virus fusion protein alters growth and fusogenicity [ANIMAL: RNA VIRUSES] (2013)
    Society for General Microbiology (SGM)
    Details
    Publication Date: 2013-11-16
    Description: Respiratory syncytial virus (RSV) causes severe lower respiratory tract infection in children, especially in infants less than 1 year of age. There are currently no licensed vaccines against RSV. rA2M2-2 is a promising live-attenuated vaccine candidate that is currently being evaluated in the clinic. Attenuation of rA2M2-2 is achieved by a single deletion of the M2-2 gene, which disrupts the balance between viral transcription and replication. Whilst performing a manufacturing feasibility study in a serum-free adapted Vero cell line, differences in growth kinetics and cytopathic effect (CPE) were identified between two rA2M2-2 vaccine candidates. Comparative sequence analysis identified four amino acid differences between the two vaccine viruses. Recombinant rA2M2-2 viruses carrying each of the four amino acid differences identified a K66E mutation in the F 2 fragment of the fusion (F) protein as the cause of the growth and CPE differences. Syncytium-formation experiments with RSV F protein carrying mutations at aa 66 suggested that a change in charge at this residue within the F 2 fragment can have a significant impact on fusion.
    Print ISSN: 0022-1317
    Electronic ISSN: 1465-2099
    Topics: Medicine
    Published by Society for General Microbiology (SGM)
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  • 9
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    Consensus guidelines on the optimal management in interventional EUS procedures: results from the Asian EUS group RAND/UCLA expert panel (2018)
    BMJ Publishing Group
    In: Gut
    Details
    Publication Date: 2018-06-08
    Description: Objectives Interventional endoscopic ultrasonography (EUS) procedures are gaining popularity and the most commonly performed procedures include EUS-guided drainage of pancreatic pseudocyst, EUS-guided biliary drainage, EUS-guided pancreatic duct drainage and EUS-guided celiac plexus ablation. The aim of this paper is to formulate a set of practice guidelines addressing various aspects of the above procedures. Methods Formulation of the guidelines was based on the best scientific evidence available. The RAND/UCLA appropriateness methodology (RAM) was used. Panellists recruited comprised experts in surgery, interventional EUS, interventional radiology and oncology from 11 countries. Between June 2014 and October 2016, the panellists met in meetings to discuss and vote on the clinical scenarios for each of the interventional EUS procedures in question. Results A total of 15 statements on EUS-guided drainage of pancreatic pseudocyst, 15 statements on EUS-guided biliary drainage, 12 statements on EUS-guided pancreatic duct drainage and 14 statements on EUS-guided celiac plexus ablation were formulated. The statements addressed the indications for the procedures, technical aspects, pre- and post-procedural management, management of complications, and competency and training in the procedures. All statements except one were found to be appropriate. Randomised studies to address clinical questions in a number of aspects of the procedures are urgently required. Conclusions The current guidelines on interventional EUS procedures are the first published by an endoscopic society. These guidelines provide an in-depth review of the current evidence and standardise the management of the procedures.
    Keywords: Gut
    Print ISSN: 0017-5749
    Electronic ISSN: 1468-3288
    Topics: Medicine
    Published by BMJ Publishing Group
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  • 10
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    Origins of enhanced thermoelectric power factor in topologically insulating Bi0.64Sb1.36Te3 thin films (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-01-28
    Description: In this research, we report the enhanced thermoelectric power factor in topologically insulating thin films of Bi 0.64 Sb 1.36 Te 3 with a thickness of 6–200 nm. Measurements of scanning tunneling spectroscopy and electronic transport show that the Fermi level lies close to the valence band edge, and that the topological surface state (TSS) is electron dominated. We find that the Seebeck coefficient of the 6 nm and 15 nm thick films is dominated by the valence band, while the TSS chiefly contributes to the electrical conductivity. In contrast, the electronic transport of the reference 200 nm thick film behaves similar to bulk thermoelectric materials with low carrier concentration, implying the effect of the TSS on the electronic transport is merely prominent in the thin region. The conductivity of the 6 nm and 15 nm thick film is obviously higher than that in the 200 nm thick film owing to the highly mobile TSS conduction channel. As a consequence of the enhanced electrical conductivity and the suppressed bipolar effect in transport properties for the 6 nm thick film, an impressive power factor of about 2.0 mW m −1  K −2 is achieved at room temperature for this film. Further investigations of the electronic transport properties of TSS and interactions between TSS and the bulk band might result in a further improved thermoelectric power factor in topologically insulating Bi 0.64 Sb 1.36 Te 3 thin films.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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