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  • American Institute of Physics (AIP)  (128)
  • American Society of Hematology  (27)
  • 1995-1999  (153)
  • 1960-1964  (1)
  • 1945-1949  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Electronic properties of light-induced recombination centers in boron-doped Czochralski silicon (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3175-3180 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to study the electronic properties of the recombination centers responsible for the light-induced carrier lifetime degradation commonly observed in high-purity boron-doped Czochralski (Cz) silicon, injection-level dependent carrier lifetime measurements are performed on a large number of boron-doped p-type Cz silicon wafers of various resistivities (1–31 Ω cm) prior to and after light degradation. The measurement technique used is the contactless quasi-steady-state photoconductance method, allowing carrier lifetime measurements over a very broad injection range between 1012 and 1017 cm−3. To eliminate all recombination channels not related to the degradation effect, the difference of the inverse lifetimes measured after and before light degradation is evaluated. A detailed analysis of the injection level dependence of the carrier lifetime change using the Shockley–Read–Hall theory shows that the fundamental recombination center created during illumination has an energy level between Ev+0.35 and Ec−0.45 eV and an electron/hole capture time constant ratio between 0.1 and 0.2. This deep-level center is observed in all samples and is attributed to a new type of boron–oxygen complex. Besides this fundamental defect, in some samples an additional shallow-level recombination center at 0.15 eV below Ec or above Ev is found to be activated during light exposure. This second center dominates the light-degraded carrier lifetime only under high-injection conditions and is hence only of minor importance for low-injection operated devices. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371186
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  • 2
    Electronic Resource
    Electronic Resource
    Microwave-mixing scanning capacitance microscopy of pn junctions (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 7094-7099 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe an approach to scanning capacitance microscopy. A mixing technique is employed for imaging local capacitance variations simultaneously with the sample topography using an atomic force microscope (AFM) with a conductive tip. A SiO2/Si sample with lateral pn junctions formed by ion implantation has been investigated. Microwave signals incident on the metal–oxide–semiconductor (MOS) structure formed by the AFM tip and the sample give rise to mixing signals due to the nonlinear voltage dependence of the space charge capacitance in the Si. In our experiments two microwave input signals with frequencies f1 and f2 and a variable dc bias voltage were applied to the tip-sample MOS structure. The dependence of the generated sum frequency and third harmonic signals on the dc sample voltage shows that the f1+f2 and 3 f signals are proportional to dC/dV and d2C/dV2, respectively. Images of the sum frequency and third harmonic signals delineating the pn junctions on our model sample are presented and the dc bias voltage dependence of the images is discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371797
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  • 3
    Electronic Resource
    Electronic Resource
    2 MeV electron irradiation of silicon at elevated temperatures: Influence on platinum diffusion and creation of electrically active defects (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3556-3560 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Platinum has been diffused at 300–800 °C for 30 min into n-type epitaxial silicon samples during 2 MeV electron irradiation using a dose of 1×1017 e− cm−2. Thereafter the samples were characterized by capacitance–voltage measurements and deep level transient spectroscopy. The samples with irradiation temperatures of 500, 600, and 700 °C could be analyzed, while the compensation in the others was too high. Most of the observed deep levels were characterized using the Arrhenius method. Their possible identities are discussed. The deep level of substitutional platinum first appears in the sample irradiated at 600 °C and is the dominant defect level at even higher temperatures. We observe that at a chosen distance from the sample surface (17 μm), the concentration of electrically active platinum after an irradiation at 700 °C is a factor of 1000 higher than in an ordinarily diffused sample. Taking into account experiments where platinum was diffused into pre-irradiated samples, the observed behavior is attributed to a reduced correlated recombination of interstitials and vacancies. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369773
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  • 4
    Electronic Resource
    Electronic Resource
    On the interaction between two oppositely signed, shielded, monopolar vortices (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 3099-3110 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation two-dimensional dipolar vortices by the interaction between two shielded monopolar vortices with opposite vorticity, as shown in a numerical study by Couder and Basdevant,〈citeref RID="R1" STYLE="SUPERIOR"〉1 is investigated in detail, both experimentally, in a nonrotating stratified fluid and numerically by direct solutions of the two-dimensional Navier–Stokes equations. A comparative study between the laboratory experiments and numerical simulations is performed. The vorticity distribution measured in the early stage of the evolution in the laboratory is used as initial data for the simulations, and an additional damping term in the Navier–Stokes equations, that accounts for the vertical diffusion in the laboratory experiments, is used. The results show that, depending on the initial separation between the vortices, the shields of the monopoles are peeled off and indeed a compact dipole with a linear (ω,ψ)-relationship is formed, or when the monopoles are further apart the shields of the monopoles are perturbed and two tripoles are formed. The characteristics of the emerged dipole are analyzed and a dye visualization of the dipole formation is performed. A second, more general numerical study yields a relationship between the formation time of the dipole and the initial separation distance between the monopoles and it shows that the deshielding process can be explained by the domination of strain over vorticity. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869838
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  • 5
    Electronic Resource
    Electronic Resource
    Local transport barrier formation and relaxation in reverse-shear plasmas on the Tokamak Fusion Test Reactor : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1736-1744 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The roles of turbulence stabilization by sheared E×B flow and Shafranov shift gradients are examined for Tokamak Fusion Test Reactor [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)] enhanced reverse-shear (ERS) plasmas. Both effects in combination provide the basis of a positive-feedback model that predicts reinforced turbulence suppression with increasing pressure gradient. Local fluctuation behavior at the onset of ERS confinement is consistent with this framework. The power required for transitions into the ERS regime are lower when high power neutral beams are applied earlier in the current profile evolution, consistent with the suggestion that both effects play a role. Separation of the roles of E×B and Shafranov shift effects was performed by varying the E×B shear through changes in the toroidal velocity with nearly steady-state pressure profiles. Transport and fluctuation levels increase only when E×B shearing rates are driven below a critical value that is comparable to the fastest linear growth rates of the dominant instabilities. While a turbulence suppression criterion that involves the ratio of shearing to linear growth rates is in accord with many of these results, the existence of hidden dependencies of the criterion is suggested in experiments where the toroidal field was varied. The forward transition into the ERS regime has also been examined in strongly rotating plasmas. The power threshold is higher with unidirectional injection than with balance injection. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872275
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  • 6
    Electronic Resource
    Electronic Resource
    Band-gap renormalization and band filling in Si-doped GaN films studied by photoluminescence spectroscopy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4400-4402 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied band-gap renormalization and band filling in Si-doped GaN films with free-electron concentrations up to 1.7×1019 cm−3, using temperature-dependent photoluminescence (PL) spectroscopy. The low-temperature (2 K) PL spectra showed a line-shape characteristic for momentum nonconserving band-to-band recombination. The energy downshift of the low-energy edge of the PL line with increasing electron concentration n, which is attributed to band-gap renormalization (BGR) effects, could be fitted by a n1/3 power law with a BGR coefficient of −4.7×10−8 eV cm. The peak energy of the room-temperature band-to-band photoluminescence spectrum was found to decrease as the carrier concentration increases up to about 7×1018 cm−3, followed by a high-energy shift upon further increasing carrier concentration, due to the interplay between the BGR effects and band filling. The room-temperature PL linewidth showed a monotonic increase with carrier concentration, which could be described by a n2/3 power-law dependence. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371377
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic reversal of tapered permalloy bars with holes in the center (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4601-4603 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic reversal mechanism of tapered permalloy bars with holes in the center was studied using a Magnetic Force Microscope with in situ magnetic field capability. The samples studied were lithographically patterned from a 20-nm-thick NiFe film using a subtractive process to create tapered bars 18 wide×348 μm long. The easy axis of the permalloy is parallel to the long axis of the bar. In the center of the tapered bar was either a 10, 5, or 3 μm diameter hole. The remnant state after saturation parallel to the long axis of the bar is a large domain magnetized along the saturating field direction except near the hole. The magnetization at the edge of the hole can be explained by considering edge pinning and the last direction of a saturating magnetic field. An inplane magnetic field parallel to the long axis of the bar reverses the magnetization by domain nucleation at the edge of the hole. After the bar has reversed, the same type of wall structure is seen as in the remnant state. As the magnetic field is increased further, the magnetization rotates away from parallel to the edge of the hole, as seen by the emergence of surface poles along the hole edge. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370421
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  • 8
    Electronic Resource
    Electronic Resource
    Carrier recombination at silicon–silicon nitride interfaces fabricated by plasma-enhanced chemical vapor deposition (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3626-3633 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the light-biased microwave-detected photoconductance decay method, injection level dependent measurements of the effective surface recombination velocity Seff at silicon surfaces passivated by plasma-enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx) films are performed on monocrystalline silicon wafers of different resistivities and doping types. In order to theoretically simulate the measured dependences of Seff on the bulk injection level Δn, the extended Shockley-Read-Hall formalism is used. Simulation input parameters are the energy dependent interface state densities and capture cross sections of the involved interface defects as well as the positive insulator charge density Qf. The energy dependent properties of the interface defects are experimentally determined by means of small-pulse deep-level transient spectroscopy. These measurements reveal the existence of three "deep" silicon dangling bond defects at the Si-SiNx interface with similar interface state densities but very different capture cross sections and hence recombination rates. Another defect is found very close (≤0.1 eV) to the edge of the silicon conduction band. This defect is identified with the K+ center which is responsible for the large positive Qf values (∼1012 cm−2) at Si-SiNx interfaces obtained from standard dark capacitance-voltage measurements. In order to get a good agreement between measured and calculated Seff(Δn) dependences, a reduction of Qf by one order of magnitude is found to be necessary. The explanation for this reduction is the capture of electrons from the silicon conduction band into the K+ centers. The comparison of Si-SiNx interfaces fabricated by different PECVD techniques shows that the dominant interface defect is produced by the ion bombardment during the SiNx deposition. Thus, avoidance of the ion bombardment leads to a strongly reduced interface recombination and hence a better surface passivation quality. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369725
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  • 9
    Electronic Resource
    Electronic Resource
    Size distribution of coherently strained InAs quantum dots (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 4268-4272 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of the InAs coverage on the size and density of coherently strained InAs islands was investigated. At moderate InAs coverages the photoluminescence signal reflects the Gaussian size distribution of small coherently strained islands. However, before the coherently strained islands transform into dislocated ones the Gaussian line shape of their photoluminescence signal changes and a narrow peak appears on the low-energy tail. We attribute this change to an accumulation of coherently strained islands at a maximum size before dislocated island transformation occurs. Effects of luminescence from dislocated islands, size-dependent relaxation processes, capture efficiencies, and dot-dot coupling are also discussed. However, our calculations and the magnetophotoluminescence, as well as the photovoltage experiments, confirm our interpretation of a size accumulation process of coherently strained islands. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368644
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  • 10
    Electronic Resource
    Electronic Resource
    Microwave-frequency alternating current scanning tunneling microscopy by difference frequency detection: Atomic resolution imaging on graphite (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3377-3380 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a detailed description of an experimental setup for alternating current scanning tunneling microscopy, in which two slightly detuned high frequency signals are mixed at the tunneling junction and the resulting difference frequency signal is amplified using conventional scanning tunneling microscope electronics. This signal is used to control the distance between the microscope tip and the sample. With graphite as a model surface atomic resolution images have been obtained. It is demonstrated that the origin of the generated signal on graphite is the nonlinearity of the static current–voltage characteristics. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149922
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