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Applied Physics Letters

Issue 11 • Date Mar 1986

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Displaying Results 1 - 20 of 20
  • All‐optical power limiting of CO2 laser pulses using cascaded optical bistable elements

    Page(s): 683 - 685
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    We report the first all‐optical power limiter based on cascaded InSb étalons. The power limiting effect is due to a dispersive nonlinearity in InSb at room temperature as a result of generation of free carriers through two‐photon absorption of 10 μm radiation. The efficiency and dynamic range of this all‐optical circuit are discussed. View full abstract»

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  • Generation of soft x rays using a rare gas‐hydrogen plasma focus and its application to x‐ray lithography

    Page(s): 686 - 688
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    A conventional plasma focus device was used to produce a hot, dense plasma which emits radiation strongly in the soft x‐ray region. We showed experimentally that a plasma produced from a mixture of hydrogen and a rare gas such as neon, argon, or krypton is an effective source of a characteristic x ray of the rare gas. Resist exposures and pattern printings were made to evaluate the feasibility of this device as a source for soft x‐ray lithography. View full abstract»

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  • Significant enhancement of XeCl(B, C) and XeF(B, C) formation rate constants in reactions of Xe(5p56p) atoms with halogen donors

    Page(s): 689 - 691
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    The quenching rate constants for Xe(6p) atoms by several halogens and halogen‐containing molecules have been measured and they are substantially larger than for reactions of Xe(6s) metastable atoms. The effect is largest for molecules with small Xe(6s 3P2) quenching rate constants and the Xe(6p) rate constants for NF3 are 5–20 times larger. Moreover, the branching fractions for XeCl(B, C) and XeF(B, C) formation are also larger for Xe(6p) atoms than for Xe(6s 3P2) atoms; the branching fractions for HCl are enhanced by more than an order of magnitude. These findings may have important implications for the operation and modeling of rare gas halide lasers and other gas discharge devices. View full abstract»

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  • Fast imaging of tokamak plasmas with integrated photodiode arrays

    Page(s): 692 - 694
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    Images with high temporal and spatial resolution of the resurrector tokamak plasma were obtained. The plasma cross section was focused onto a commercially available 128 pixel photodiode array (active area: 2.5×3.2 mm2). Specially designed data acquisition electronics allowed rapid readout for the observation of the spatial profile of visible emissions with 150 μs time resolution. The breakdown and subsequent evolution of the discharge was monitored to allow improvement of the plasma parameters. View full abstract»

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  • Enhancement of the plasma density and deposition rate in rf discharges

    Page(s): 695 - 697
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    The peak and time averaged electron density in rf excited silane‐helium mixtures increased significantly above the cw value by square wave modulating the source. The deposition rate of amorphous hydrogenated silicon films is also enhanced and apparently follows the electron density. Attachment to the discharge products appears to be responsible. View full abstract»

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  • A method of poling LiNbO3 and LiTaO3 below Tc

    Page(s): 698 - 700
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    A method of poling LiNbO3 and LiTaO3 significantly below their Curie temperatures is proposed and results are presented. The technique involves excitation of the crystal lattice by an energetic beam of electrons while applying an electron field along the c axis. The lowest temperatures and fields successfully used so far are 600 °C with 10 V cm-1 for LiNbO3 and 400 °C with 900 V cm-1 for LiTaO3. These do not necessarily define lower limits for the process. View full abstract»

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  • Effects of substrate preparation conditions on GaAs oval defects grown by molecular beam epitaxy

    Page(s): 701 - 703
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    Effects of substrate preparation conditions, i.e., wet chemical and ultrahigh vacuum cleaning preparations, on GaAs oval defects grown by molecular beam epitaxy (MBE) were investigated. It is found that, with our MBE system, the presence of the smaller (≪10 μm) ovally shaped defects without macroscopic core particulates can be ascribed to surface microscopic contaminations. Most of the other remaining larger (≫10 μm) oval defects with core particulates observed on 1‐μm‐thick GaAs MBE layers are attributed to surface macroscopic contaminations. The total density is reduced to 300 cm-2 without significantly modifying the growth cell parameters. View full abstract»

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  • Dopant redistribution in silicon‐on‐sapphire films during thermal annealing

    Page(s): 704 - 706
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    Arsenic depth distributions in silicon‐on‐sapphire films, after annealing at 900 °C for a range of times, have been studied by Rutherford backscattering and spreading resistance techniques. A continuum pipe diffusion model is developed which accounts satisfactorily for the rapid diffusion and segregation effects observed. In addition, the same model predicts two‐dimensional dopant profiles with several novel features relevant to microelectronic device processing. View full abstract»

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  • Amorphous transition phase of NiSi2

    Page(s): 707 - 708
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    A glass transition phase forms at the Ni‐Si interface as a precursor to NiSi2. The crystalline to amorphous transformation occurs when a sufficient concentration of Ni atoms is present to raise the elastic energy of crystalline Si and lower the energy barrier to the reaction. NiSi2 crystals nucleate in the glass at the interface. The barrier height can depend on properties of the amorphous layer. View full abstract»

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  • Hydrogen passivation of the oxygen‐related thermal‐donor defect in silicon

    Page(s): 709 - 711
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    It is demonstrated with both spreading resistance measurements and deep level transient spectroscopy that hydrogenation neutralizes the oxygen‐related thermal‐donor defect in n‐type silicon. Hydrogen neutralization of shallow‐donor dopants (e.g., phosphorus) is also illustrated. A model which accounts for shallow‐donor passivation is applied to explain the interaction between hydrogen and thermal donors. View full abstract»

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  • First observation of the quantum Hall effect in a Ga0.47In0.53As‐InP heterostructure with three electric subbands

    Page(s): 712 - 714
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    Shubnikov–de Haas and quantum Hall effects have been studied in GaInAs‐InP heterojunctions grown by modified low pressure metalorganic chemical vapor deposition. In contrast to the results reported up till now on GaInAs‐InP heterojunctions with nearly the same channel electron density, not one but three electric subbands, E0, E1, and E2, are occupied in zero magnetic field. Two electric subbands E0 and E1 contribute to the quantum Hall effect. Magnetic depopulation of the higher (E1 and E2) subbands is observed in both perpendicular and tilted magnetic field orientations. This enables a demonstration of the importance of intersubband scattering in resistivity and cyclotron resonance. View full abstract»

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  • Homogeneity qualification of GaAs substrates for large scale integration applications

    Page(s): 715 - 717
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    A novel procedure is used to qualify the homogeneity of GaAs substrates for large scale integration (LSI) circuit applications. This procedure is particularly well adapted for assessing the electrical variations of densely packed field‐effect transistors (FET’s) used in GaAs LSI circuits. Threshold voltage nonuniformity due to crystal inhomogeneity and surface effects is measured for both conventional and In‐alloyed, dislocation‐free, slightly Cr‐doped, semi‐insulating liquid encapsulated Czochralski substrates. The average value of the threshold voltage standard deviation of about 300 dense rows over a 2‐in.‐diam wafer (30 FET’s over 300 μm for each row) is 20 mV using dislocation‐free substrates which is much smaller than in conventional substrates (50–100 mV). These data show the importance of this qualification test with the highest ever reported resolution of 10 μm suitable for the evaluation of fabrication yield of LSI circuits. View full abstract»

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  • Studies of atomic and molecular fluorine reactions on silicon surfaces

    Page(s): 718 - 720
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    X‐ray photoelectron spectroscopy (XPS) and an ultrahigh vacuum compatible microwave discharge effusive beam source have been used to study the reactions of atomic and molecular fluorine on Si(111) surfaces. Fluorine uptake and changes in binding energy and peak shape for the Si 2p and F 1s XPS peaks have been measured as functions of fluorine exposure. The results indicate that molecular fluorine is dissociatively chemisorbed to form an SiF2‐like surface species. This reaction saturates at approximately one monolayer surface coverage. In contrast, atomic fluorine uptake extends well beyond the monolayer regime to include several Si layers. Additionally, as the uptake increases, the reaction product becomes SiF4‐like. These findings are compared with previously reported results for XeF2 adsorption. View full abstract»

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  • Recombination mechanisms in Si and Si thin films determined by picosecond reflectivity measurements near Brewster’s angle

    Page(s): 721 - 723
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    A sensitive pump and probe method for measuring the transient carrier density in semiconductors is proposed and demonstrated in silicon. It relies on the magnified reflectivity changes when the picosecond probe laser is incident close to Brewster’s angle. We have measured the Auger recombination coefficient γ=2×10-31 cm6 s-1 and, in microcrystalline silicon films on insulator, the effective lifetime due to grain boundaries τ≂100 ps. Additionally, at much higher pump energies, upon melting, the reflectivity jumps by nearly one order of magnitude. View full abstract»

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  • Spatial location of electron trapping defects on silicon by scanning tunneling microscopy

    Page(s): 724 - 726
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    Individual electron trapping sites in thermally oxidized silicon substrates have been observed using a scanning tunneling microscope (STM). The excellent spatial resolution of the STM allows single defects to be identified and located on the surface. The tunneling current near single trapping sites was observed to switch between two well defined values as the site occupation changed. The magnitude of the change in the current and spatial extent of the current fluctuations, typically 3 nm, is consistent with the calculated change in tunneling current from a single electron being trapped in the oxide. View full abstract»

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  • Excitonic photoluminescence linewidths in AlGaAs grown by molecular beam epitaxy

    Page(s): 727 - 729
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    The linewidths of excitonic transitions were measured in AlxGa1-xAs, grown by molecular beam epitaxy as a function of alloy composition x for values of x≲0.43 using high resolution photoluminescence spectroscopy at liquid helium temperature. The values of the linewidths thus measured are compared with the results of several theoretical calculations in which the dominant broadening mechanism is assumed to be the statistical potential fluctuations caused by the components of the alloy. An increase in the linewidth as a function of x is observed which is in essential agreement with the prediction of the various theoretical calculations. The linewidths of the excitonic transitions in AlxGa1-xAs observed in the present work are the narrowest ever reported in the literature, for example σ=2.1 meV for x=0.36, thus indicating very high quality material. View full abstract»

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  • Magnetic anisotropy in dc diode getter sputtered GdCo films—How important is the argon content in the films?

    Page(s): 730 - 732
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    Amorphous magnetic GdCo films were prepared by a dc diode getter sputtering technique with no bias field applied to the substrate during the film growth. Films (type I) obtained using 1.0 kV and 60 mTorr Ar during the sputtering show perpendicular anisotropy with Keffu =1.5×105 erg/cm3. Films (type II) deposited at 2.0 kV and 28 mTorr Ar exhibit magnetic isotropy with Kinu≊0. However, the actual argon content in the type II films is three times of that in the type I films. Nevertheless, the argon impurity in both the type I and type II films is ≤1.0 at. %, which is far less than those obtained in the biased rf diode sputtered GdCo films. Also, the distribution of argon is uniform in the film as observed from the Rutherford backscattering spectrometry. View full abstract»

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  • Microstructure, domain walls, and magnetization reversal in hot‐pressed Nd‐Fe‐B magnets

    Page(s): 733 - 735
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    Transmission electron microscopy study of hot‐pressed and hot‐deformed Nd0.14(Fe0.94B0.06)0.86 magnets shows that the magnetic alignment is achieved by the formation of a microstructure consisting of platelets of Nd2Fe14B grains with the c axis normal to the platelet surface and parallel to the press direction. Magnetic domain walls, lying parallel to the c axis, run through many grains and are pinned at the intergranular phases that are produced during processing. Magnetization reversal occurs by domain wall motion. View full abstract»

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  • Laser etching of 0.4 μm structures in CdTe by dynamic light guiding

    Page(s): 736 - 738
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    CdTe single crystals have been etched by photosublimation with a cw visible laser. Structures with lateral widths comparable to the laser wavelength (∼0.5 μm) and depths exceeding 10 μm were obtained using a moderately focused beam. The formation of these structures is highly nonlinear with respect to laser power and is analyzed in terms of the dynamic interaction of the beam with the induced microstructure. Once initiated, deep structures are formed via laser‐induced tellurium enrichment of CdTe surface layers and the consequent enhanced waveguiding properties of these surfaces. The mechanism of etching has been studied by mass spectrometer and light scattering experiments. View full abstract»

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  • Generation of highly monochromatic positrons using cold moderators

    Page(s): 739 - 741
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    Slow positron beams generally employ a radioactive  β+ emitter with a crystal moderator in which the positrons thermalize. A small fraction of the thermalized positrons are desorbed at low (1–3 eV) energy, characteristic of the positron work function in the crystal. The energy width of the emitted positrons from W(110) and Ni(111) moderators can be narrowed significantly by cooling to liquid N2 temperatures. A practical configuration for a cooled moderator positron gun is presented which produces a narrow energy positron beam with good efficiency. View full abstract»

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Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics.

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Nghi Q. Lam
Argonne National Laboratory