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  • 1
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    Effects of interface and bulk properties of gate-dielectric on the performance and stability of hydrogenated amorphous silicon thin-film transistors (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-12-18
    Description: In order to investigate the effects of interface and bulk properties of gate insulator on the threshold voltage (V th ) and the gate-bias induced instability of hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs), four kinds of TFT structures were fabricated with SiNx and SiOx insulators stacked to make different combinations of the bulk and interface in the gate-dielectric layers. It was found that the V th and the stability are independently controlled by tuning stoichiometry and thickness of the SiOx insertion layer between a-Si:H and SiNx. In TFTs with SiO x insertion layer of 50 nm thickness, on increasing oxygen/silicon (O/Si = x) ratio from 1.7 to 1.9, V th increased from 0 V to 9 V. In these TFTs with a relatively thick SiOx insertion layer, positive V th shift with negative bias stress was observed, confirmed to be due to defect creation in a-Si:H with the thermalization barrier energy of 0.83 eV. On reducing the thickness of the SiOx insertion layer down to approximately 1 nm, thin enough for hole injection through SiOx by tunneling effect, stable operation was obtained while keeping the high V th value under negative stress bias. These results are consistently explained as follows: (1) the high value for V th is caused by the dipole generated at the interface between a-Si:H and SiOx; and (2) two causes for V th shift, charge injection to the gate insulator and defect creation in a-Si:H, are mutually related to each other through the “effective bias stress,” V bs eff  = V bs – ΔV fb (V bs : applied bias stress and ΔV fb : flat band voltage shift due to the charge injection). It was experimentally confirmed that there should be an optimum thickness of SiO x insertion layer of approximately 1 nm with stable high V th , where enhanced injection increases ΔV fb , reduces V bs eff to reduce defect creation, and totally minimizes V th shift.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
    Electronic Resource
    Electronic Resource
    Dependence of the x-ray photoacoustic signal intensity of copper on sample thickness and modulation frequency (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5187-5189 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hard x-ray photoacoustic signal intensities of copper have been measured at an x-ray absorption near-edge structure (XANES) region as functions of sample thickness (from 5 to 300 μm) and modulation frequency (from 5 to 50 Hz). It is shown that the photoacoustic signal intensities show maxima at the sample thickness close to 10 μm for each modulation frequency. The x-ray photoacoustic signal varies from f−1.0 ( f denotes modulation frequency) up to 20 μm sample thickness, whereas it varies from f−0.5 beyond a 20 μm sample thickness, which is not consistent with the Rosencwaig–Gersho theory for the photoacoustic effect in solids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351999
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  • 3
    Electronic Resource
    Electronic Resource
    Role of Eu2+ luminescent centers in the electro-optical characteristics of red-emitting CaS:Eu thin-film electroluminescent devices with memory (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3578-3583 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to investigate the role of the Eu2+ luminescent centers in determining the electro-optical characteristics of red-emitting CaS:Eu thin-film electroluminescent (TFEL) devices with inherent memory, light irradiation effects on these characteristics were studied. Both the threshold voltage and the response time decreased by light irradiation at wavelengths of 400–600 nm. This wavelength region coincides with that of the direct-excitation spectrum of Eu2+. Furthermore, emission peak height at the trailing edge of the pulse drive voltage increased by light irradiation in the same wavelength region. Since this emission is assumed to be caused by recombination of diffusing electrons with holes located at the ionized Eu2+ luminescent centers, increase in the emission peak height at the trailing edge of the pulse drive voltage indicated an increase in the number of the ionized Eu2+ luminescent centers. From these arguments we conclude that ionized Eu2+ luminescent center is a possible source of positive space-charge, which is known to play a decisive role in the memory and response characteristics of TFEL devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346317
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  • 4
    Electronic Resource
    Electronic Resource
    Composition dependence of lattice spacing for low dislocation density undoped liquid encapsulated Czochralski GaAs crystals (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 182-184 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Crystals with varied composition were pulled by the As-partial-pressure controlled liquid encapsulated Czochralski method. The dislocation density was found to be as low as 2×103 cm−2 at the cores of the crystals. Lattice spacing (d) was measured with a precision of Δd/d ∼ 5.9 × 10−6 using synchrotron radiation. For a variation of 7×10−5 in the As-atom fraction in the crystals, the lattice spacing varied by less than 1×10−5 A(ring).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347740
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  • 5
    Electronic Resource
    Electronic Resource
    Slow response and Eu2+-related trapping states in CaS:Eu thin-film electroluminescent devices (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5018-5024 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to clarify causes of the slow buildup of the optical output, i.e., slow optical response, in red-emitting CaS:Eu thin-film electroluminescent devices, Eu2+ concentration and temperature dependence of the response time of transferred electrons were measured. It was found that the response time increased exponentially with the increase in Eu2+ concentration and temperature. To understand these results, trapping states in CaS:Eu phosphor layer were studied by measuring temperature dependence of the following electro-optical characteristics with Eu2+ concentration as a parameter; (i) decay profile of trapped electrons, (ii) photoluminescent intensity, and (iii) photoinduced charge density. From these measurements, it was found that there existed two kinds of shallow states in the band gap of CaS. One was electron trapping states located at approximately 0.15 eV below the conduction-band minimum. These states were considered to be generated by Eu2+ clusters. The other was located at 0.06–0.08 eV below the conduction-band minimum. These states were considered to be 5d-excited states of isolated Eu2+ activators. Based on these experimental results, an energy band model for CaS:Eu thin film was proposed and causes for the slow optical response were discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349006
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  • 6
    Electronic Resource
    Electronic Resource
    Electro- and photo-luminescent quenching effects imposed by field-induced ionization of the Eu2+ luminescent centers in CaS:Eu thin films (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7225-7230 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is found that both the high-field electroluminescent (EL) and photoluminescent intensities of CaS:Eu thin films were quenched by an applied electric field. This quenching was found to be caused by a field-induced ionization of impact-excited Eu2+ luminescent centers. This ionization was known to play an important role in the memory and slow response characteristics of CaS:Eu thin-film electroluminescent devices. Evidence for field-induced ionization of Eu2+ was obtained from the following measurements of CaS:Eu; (i) the first and second EL emission peaks, (ii) photoluminescence, and (iii) photocapacitance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347617
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  • 7
    Electronic Resource
    Electronic Resource
    Development of a fluorescent x-ray source for medical imaging : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1981-1983 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A fluorescent x-ray source for medical imaging, such as K-edge subtraction angiography and monochromatic x-ray CT, has been developed. Using a 6.5 GeV accumulation ring in Tsukuba, fluorescent x rays, which range from about 30 to 70 keV are generated by irradiating several target materials. Measurements have been made of output intensities and energy spectra for different target angles and extraction angles. The intensities of fluorescent x rays at a 30 mA beam current are on the order of 1–3×106 photons/mm2/s at 30 cm from the local spot where the incident beam is collimated to 1 mm2. A phantom which contains three different contrast media (iodine, barium, gadolinium) was used for the K-edge energy subtraction, and element selective CT images were obtained. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145776
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  • 8
    Electronic Resource
    Electronic Resource
    A scanning x-ray microscope using circularly polarized radiation at the TRISTAN accumulation ring and its application to observation of ferromagnetic domains : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1534-1536 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A scanning x-ray microscope using circularly polarized radiation has been constructed at the beamline NE1B of the 6.5-GeV TRISTAN accumulation ring (AR). It uses a Fresnel zone plate as an x-ray focusing lens. Its spatial resolution has been evaluated to be ∼1.2 μm at the energy of 933 eV. Depending on the relative orientation between the photon spin and the local magnetization direction, the magnetic domains recorded in a piece of videotape have been successfully observed visually at the L2,3 absorption edges of cobalt. The contrast of the image arises from the magnetic circular dichroism in core-level photoemission of ferromagnets. The observed contrast was certainly reversed between L2 and L3 edges. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145901
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  • 9
    Electronic Resource
    Electronic Resource
    Characterization of lattice spacing and inclination around cells in liquid-encapsulated Czochralski GaAs crystals using a 100×100 μm2 incident x-ray beam (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1352-1356 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lattice spacing and inclination around cells were investigated precisely for both undoped high etch-pit-densities (EPD) liquid-encapsulated Czochralski (LEC) GaAs crystal of the order of 104 cm−2 and undoped As-ambient LEC (As-LEC) crystal of low EPD of the order of 103 cm−2. Measurement of the lattice spacing and the inclination was carried out by the triple crystal method using a 100×100 μm2 size incident beam of high-intensity synchrotron radiation. It was revealed that the lattice spacing varied by almost Δd, on the order of 10−4 A(ring), due to the cellular structure of the high EPD crystal. In addition, the low EPD GaAs crystal grown by the As-LEC method showed considerably less variation in lattice spacing and inclination than the high EPD LEC GaAs crystal. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362934
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic domain-specific microspectroscopy with a scanning x-ray microscope using circularly polarized undulator radiation (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3124-3126 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Absorption spectra as microspectroscopy taken inside single magnetic domains of nickel have been achieved in the 2p–3d excitation region with a 1 μm spot of circularly polarized undulator radiation focused by a scanning x-ray microscope. A sample used as demonstration was a deposited nickel layer. It was confirmed that the spectra exhibited the features corresponding to the opposite magnetization of each domain using the fixed circular polarization. This technique can offer element- and domain-specific x-ray magnetic microspectroscopy in a submicrometer scale. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363125
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