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  • 11
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 8039-8045 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The measurement of quantum-size behavior in semiconductor crystals has been examined through an analysis of the size dependence of the semiconductor's absorption edge. In past studies, there appeared to be little agreement between theory and experiment for very small crystals. In this paper, the effects of crystal-size distribution and tunneling of the carrier wave functions into the quantum well barrier are considered. An analysis of the microstructure size and absorption edge of CdTe clusters in a glass matrix is conducted with samples ranging from 0.16 to 0.8 times the exciton Bohr diameter at the Γ point and from 1 to 5 times the exciton Bohr diameter at the L point. Results show fully coupled exciton behavior at the L point and a more complex process at the Γ point. In the latter, the band-gap energy increase with decreasing cluster size is significantly smaller than that calculated using a model in which the photoexcited carriers are assumed to be confined to a monosize set of clusters bounded by an infinite potential well. Analysis presented here shows that this discrepancy can be explained in part by inhomogeneous broadening of the absorptive transition and by carrier penetration into the insulator. The quantum-size behavior of CdTe crystals at the Γ point is subsequently found to follow fully decoupled carrier behavior modeled by Efros and Efros [Sov. Phys. Semicond. 16, 772 (1982)] when the inhomogeneous broadening and tunneling effects are taken into account.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4935-4982 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the past few years, there has been rapid growth in the positron annihilation spectroscopy (PAS) of overlayers, interfaces, and buried regions of semiconductors. There are few other techniques that are as sensitive as PAS to low concentrations of open-volume-type defects. The characteristics of the annihilation gamma rays depend strongly on the local environment of the annihilation sites and are used to probe defect concentrations in a range inaccessible to conventional defect probes, yet which are important in the electrical performance of device structures. We show how PAS can be used as a nondestructive probe to examine defects in technologically important Si-based structures. The discussion will focus on the quality of overlayers, formation and annealing of defects after ion implantation, identification of defect complexes, and evaluation of the distribution of internal electric fields. We describe investigations of the activation energy for the detrapping of hydrogen from SiO2−Si interface trap centers, variations of interface trap density, hole trapping at SiO2−Si interfaces, and radiation damage in SiO2−Si systems. We also briefly summarize the use of PAS in compound semiconductor systems and suggest some future directions.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1634-1636 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple form for an implantation profile of monoenergetic, low-energy (1–10 keV) positrons in solids is presented. Materials studied include aluminum, copper, molybdenum, palladium, and gold with atomic number ranging from 13 to 79. A simple set of parameters can describe the currently used Makhov profile in slow positron studies of solids. We provide curves and tables for the parameters that can be used to describe the implantation profiles of positrons in any material with atomic number in between 13 and 79.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 385-387 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using Doppler broadening annihilation spectroscopy, we investigated the properties of irradiated samples of SiO2/Si(100) with 117 nm thick oxide layer, grown in dry O2 on p- and n-type substrates. These samples were irradiated with γ rays and x rays at doses in the range of 7×104–9×106 rad and 50–2000 mJ/cm2, respectively. The changes observed in the Doppler broadening line shape parameter after irradiation and its recovery during isochronal annealing were used to obtain an activation energy of 1.48–1.61 eV required for annealing the defects.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 540-542 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Depth profiles of vacancylike defects have been determined by positron annihilation spectroscopy in 200-nm-thick Si films grown by molecular beam epitaxy on Si(100) substrates at growth temperatures Tgrowth=200–560 °C. The line shape of the radiation emitted from implanted positrons annihilating in the near-surface region of a solid gives quantitative, depth-resolved information on defect concentrations in a nondestructive way. In particular, the method is sensitive to vacancylike defects in a concentration range inaccessible to electron microscopy or ion scattering, but important for electrical device characteristics. The sensitivity limit for these defects in the present experiments is estimated as 5×1015 cm−3. Films grown at Tgrowth≥475±20 °C are indistinguishable from virgin wafers. So are samples with Tgrowth=220±20 °C, subjected to a 2 min, TRTA(approximately-greater-than)500 °C rapid thermal anneal (RTA) after every ≈30 nm of Si growth. If TRTA=450±20 °C, part of the film contains a concentration of vacancylike defects on the order of 1018 cm−3. Our results indicate the importance of the growth parameters, such as temperature and substrate preparation, for the production of high quality films.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 330-332 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of low temperature (≤700 °C ) annealing on the thermal dissociation of hydrogen-passivated interface trap centers of a SiO2-Si(100) system is studied using positron annihilation spectroscopy. The Si—H bonds dissociate with an activation energy of 2.60±0.06 eV. Assuming that the anneal generates trap centers with a single charge, positron measurements indicate that ∼4.5×108 trap centers/cm2 are created by a 600 °C anneal.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1684-1686 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a positron annihilation study of defects created in Si by rf hydrogen-plasma exposure at 275 °C. Analysis of positron annihilation spectroscopy data indicates voidlike structures in a defective layer extending to ≈14 nm from the surface at a concentration of 1.9±0.5×1020 cm−3. The Doppler broadening parameter for the annihilation gamma rays is strongly correlated to the hydrogen coverage of the void surfaces, voids remain in the Si to at least 800 °C while the hydrogen is desorbed from their surfaces between 600 and 800 °C.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 765-767 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe a new technique for the synthesis of ultrahomogeneous nanoparticles of precursor oxalate powder by coprecipitation in the aqueous core of a water-in-oil microemulsion for the preparation of Bi-Pb-Sr-Ca-Cu-O (2223) oxide superconductor. This process ensures a uniform mixing of metal cations down to a scale of at least 10 nm. This finely dispersed precursor powder results in phase pure (2223) oxide superconductor after proper heat treatment.
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 87-89 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The annihilation characteristics of monoenergetic positrons implanted in a molecular beam epitaxy layer of low-temperature (LT) GaAs annealed at temperatures from 300 to 600 °C were measured. A gallium vacancy concentration of approximately 3×1017 cm−3 is inferred for the as-grown material. The S parameter increased significantly upon anneal to 500 °C. The dominant positron traps in samples annealed at and below 400 °C are distinct from those acting for samples annealed to 500 or 600 °C. The change in S parameter for the 600 °C annealed sample compared to the GaAs substrate, SLT,600=1.047Ssub, is consistent with divacancies or larger open volume defects.
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2320-2322 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Damping rates and natural frequencies of the fundamental axisymmetric mode in circular cylinders were measured when the contact angle between the water and the side walls was acute, obtuse, and about π/2. Damping rates decreased with increasing contact angle; natural frequencies increased with increasing contact angle.
    Type of Medium: Electronic Resource
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