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Journal of Applied Physics

Issue 10 • Date Nov 1998

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Displaying Results 1 - 25 of 80
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Crystal grain nucleation in amorphous silicon

    Page(s): 5383 - 5414
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    The solid phase crystallization of chemical vapor deposited amorphous silicon films onto oxidized silicon wafers, induced either by thermal annealing or by ion beam irradiation at high substrate temperatures, has been extensively developed and it is reviewed here. We report and discuss a large variety of processing conditions. The structural and thermodynamical properties of the starting phase are emphasized. The morphological evolution of the amorphous towards the polycrystalline phase is investigated by transmission electron microscopy and it is interpreted in terms of a physical model containing few free parameters related to the thermodynamical properties of amorphous silicon and to the kinetical mechanisms of crystal grain growth. A direct extension of this model explains also the data concerning the ion-assisted crystal grain nucleation. © 1998 American Institute of Physics. View full abstract»

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  • Effects of introduction of sodium and water on second-order nonlinearity in poled synthetic silica glass

    Page(s): 5415 - 5418
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    Second harmonic generation (SHG) from silica glasses doped with sodium or water was investigated to clarify the effects of the impurities on the second-order nonlinearity. Sodium ions were introduced into pure silica glasses from a polymer coating containing a trace amount of sodium with electrical poling. The doping of sodium drastically increased the SHG intensity from the poled silica glasses. The nonlinearity localized in the anode surface region is suggested to be ascribed to a frozen electric field formed by the drift of sodium ions. Introduction of water molecules into silica glasses was performed by hydrothermal treatment in purified water using an autoclave. The SHG intensity from the electrically poled glasses also increased with the increasing content of water molecules. In this case, the SHG was emitted from the entire region of the sample plate. The origin of the nonlinearity is tentatively assumed to be due to a frozen electric field created by charge separation with protonic conduction. © 1998 American Institute of Physics. View full abstract»

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  • Modulation response of tunneling injection laser: Analytical approach

    Page(s): 5419 - 5423
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    The modulation response of a tunneling injection laser has been studied by an analytic solution of the rate equations taking into account carrier transport effects. The formula for K factor has been derived. We have found that the modulation bandwidth increases when coupling between quantum well and separate confinement increases and that the value of K factor is underestimated in a tunneling injection laser. It indicates that the observed high modulation bandwidth in tunneling injection laser is mostly due to reduction of hot carrier effects. © 1998 American Institute of Physics.   View full abstract»

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  • Singular perturbation theory of a thin film surface-polariton polarizer for a planar optical waveguide

    Page(s): 5424 - 5435
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    An on-line polarizer of the order of a millimeter in length is designed by locating a thin metal film suitably close and parallel to a dielectric film waveguide. The polarizer transmits the transverse electric guided mode of the dielectric film with negligible insertion loss. As a consequence of the phase-matched wave interaction between the surface polariton supported by the metal film and the transverse magnetic guided mode of the dielectric film, the transverse magnetic guided mode is severely attenuated resulting in a high extinction coefficient. A singular perturbation theory using multiple space scales is developed for the analysis of this thin film surface polariton polarizer for a planar dielectric film optical waveguide and illustrative numerical results are presented. The sensitivity of the performance of the polarizer to small changes in the various physical parameters is examined. © 1998 American Institute of Physics. View full abstract»

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  • AlxGa1-xAs native-oxide-based distributed Bragg reflectors for vertical cavity surface emitting lasers

    Page(s): 5436 - 5440
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    The problems associated with constructing AlxGa1-xAs native-oxide-based distributed Bragg reflectors (DBRs) for vertical cavity surface emitting lasers are investigated. Reflection and stability measurements are performed on structures with central λ/2 cavities (λ∼980 nm) of GaAs surrounded by two periods of native-oxide-based DBRs on the top and 2.5 periods on the bottom. Prior to crystal oxidation (H2O vapor+N2, 430 °C) a period of the DBRs consists of a ∼λ/4 optically thick layer of GaAs and a thicker (oxidation) layer of AlxGa1-xAs (x=0.95, 0.96, 0.97, 0.98, 1.00) surrounded by thinner (∼100 Å) buffer layers that are AlyGa1-yAs (y=0, 0.25, 0.50, 0.65, 0.070, 0.75, 0.80, 0.85). The DBRs are formed after oxidation of the high Al composition AlxGa1-xAs layers, and to some extent the AlyGa1-yAs buffer layers, forming a ∼λ/4 optically thick layer of the native oxide. For comparison, more complicated DBRs are created by oxidizing superlattice layers. It is found that the AlxGa1-xAs composition, x, of the oxidation layer, choice of oxidizing or nonoxidizing AlyGa1-yAs buffer layers- (y), oxidation parameters, and post-processing parameters determine the DBR quality and stability, as well as the possibility of reoxidation. © 1998 American Institute of Physics. View full abstract»

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  • Ultrafast absorber saturation process and short pulse formation in injection lasers

    Page(s): 5441 - 5444
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    The nature of lasing threshold in passively Q-switched GaAs/AlGaAs lasers with saturable absorbers formed by heavy ion implantation is investigated in this article. After studying various laser characteristics, including threshold current density, differential quantum efficiency, spectral output, and picosecond time-resolved emission, we conclude that the origin of the Q-switching is unlikely to be caused by spontaneous emission or mode locking, and that collective coherent radiation effects may contribute to the onset of lasing. © 1998 American Institute of Physics. View full abstract»

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  • Highly directional stimulated emission from a polymer waveguide

    Page(s): 5445 - 5450
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    We report on strong amplified spontaneous emission observed both in solution and in neat films of a conjugated polymer. The emission characteristics of a three-layer polymer waveguide are presented. The intense, highly directional, completely linear polarized output emission with a small beam divergence of can be observed for pumping above a threshold of 3 kW/cm2. The properties of the output emission can be explained by leaky modes. These waveguides allow us to observe the efficient optical downconversion due to strong stimulated Raman scattering under appropriate excitation conditions. © 1998 American Institute of Physics. View full abstract»

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  • Dynamic composite elastic medium theory. Part I. One-dimensional media

    Page(s): 5451 - 5457
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    Wave propagation in stratified media may be described by scattering theory, effective medium theory or ray theory, depending upon the frequency range. We present a dynamic composite elastic medium theory which describes wave propagation at all frequencies. In the first part of the series we consider randomly layered one-dimensional media and in the second part media with three-dimensional inclusions. Non-self-consistent and self-consistent methods using the scattering functions of the individual layers are formulated which allow the calculation of phase velocity, attenuation and wave forms. In the low frequency limit only the self-consistent method agrees with the Reuss average and in the high frequency limit it yields the correct ray theory average velocity. The comparison with complete numerical solutions shows that our theory predicts the coherent wave through randomly layered media. Hence, the dynamic composite elastic medium theory can be used to compute frequency dependent elastic properties of randomly layered media without calculating the complete wave propagation solution. View full abstract»

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  • Dynamic composite elastic medium theory. Part II. Three-dimensional media

    Page(s): 5458 - 5468
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    Non-self-consistent and self-consistent methods of estimating velocity and attenuation of P waves and S waves at all frequencies for heterogeneous media with three-dimensional inclusions are formulated using the scattering functions of the individual inclusions. The methods are the generalization of methods for one-dimensional media presented in the first paper of this series. The specific case of spherical inclusions is calculated with the exact scattering function and compared with several low frequency approximations. The self-consistent estimates are consistent with Berryman’s low frequency approximation. We present spectra and wave forms of materials with solid and liquid inclusions in a solid matrix. The results show that the exact scattering functions are required to adequately describe wave propagation at all frequencies. The analysis of liquid inclusions demonstrates that viscous damping may become important only if scattering attenuation due to spherical pores is small. View full abstract»

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  • Nonlinear acoustic response from precipitate-matrix misfit in a dislocation network

    Page(s): 5469 - 5472
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    An analytical model is presented for the effects on the acoustic nonlinearity of the interaction of matrix dislocations with precipitate coherency strains in metallic alloys. The acoustic nonlinearity parameters are shown to depend linearly on the dislocation density, volume fraction of precipitates and precipitate-matrix misfit parameters, and on the fourth power of the dislocation loop length. The model predicts changes in the acoustic nonlinearity parameter associated with the growth of precipitates during the artificial aging of aluminum alloy 2024 that are in good agreement with experimental measurements reported in the literature.   View full abstract»

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  • Quantitative interpretation of electron-beam-induced current grain boundary contrast profiles with application to silicon

    Page(s): 5473 - 5481
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    An improved method is described for extracting material parameters from an experimental electron-beam-induced current (EBIC) contrast profile across a vertical grain boundary by directly fitting an analytical expression. This allows the least-squares values of the grain boundary recombination velocity and the diffusion length in each grain to be determined without the need for the reduction of the experimental profile to a few integral parameters, as is required in a previously reported method. Greater accuracy of the extracted values is expected since none of the information contained in the experimental contrast data is discarded and a less extensive spatial range of measured data is required than in the commonly used method. Different models of the carrier generation volume are used in the fitting and the effect of the choice of generation model on extracted values is investigated. In common with other EBIC approaches, this method is insensitive to changes in the diffusion length when the collection efficiency is high and diffusion lengths may not be reliably established in those cases. © 1998 American Institute of Physics. View full abstract»

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  • X-ray crystal truncation rod scattering analysis of reactive ion etched silicon

    Page(s): 5482 - 5486
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    We have investigated lattice damage in reactive ion etched silicon by using x-ray crystal truncation rod (CTR) scattering. The x-ray intensity associated with the rod in the reciprocal space depends on the etching-induced lattice distortion. To estimate the magnitude of the lattice distortion, we analyzed the obtained data with a kinematic x-ray diffraction model on the assumption that the lattice distortion decays exponentially with the depth. We found that the lattice distortion extends to a depth of about 9 nm. In addition, we propose a method for quantitatively evaluating lattice damage based on our analysis. This method allows us to compare lattice damage among samples etched under different conditions. This study indicates that x-ray CTR experiments provide a useful means of characterizing lattice distortions near processed surfaces. © 1998 American Institute of Physics. View full abstract»

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  • Beyond the solid on solid model: An atomic dislocation formation mechanism

    Page(s): 5487 - 5494
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    We investigate the growth of mismatched thin films by a kinetic Monte Carlo computer simulation. The strain is introduced through an elastic energy term based on a valence force field approximation and stress is relaxed along “atomic chains” at each step of the simulation. The calculations use a set of elementary atomic processes including, besides well-known standard processes, the collective incorporation of atoms. This leads us to introduce a new “hanging” position with only one bond created toward the substrate contrary to solid on solid models. This position plays a role of defects initiation, and thus an atomic dislocation nucleation mechanism is described. Finally, we present the influence of a step in the dislocations creation. © 1998 American Institute of Physics. View full abstract»

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  • X-ray irradiation induced bulk space charge in stabilized a-Se x-ray photoconductors

    Page(s): 5495 - 5501
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    The time-of-flight (TOF) transient photoconductivity technique is used with an appropriate method and algorithm, based on the time dependence of the transient photocurrent i(t), to probe the spatial distribution of x-ray induced net bulk space charge in stabilized a-Se (a-Se:0.3%As doped with 10 to 20 ppm Cl) x-ray photoconductors with long carrier lifetimes (hole lifetime of ∼500 μs and electron lifetime of ∼750 μs from interrupted TOF). It is observed that x-ray irradiation of biased a-Se photoconductors results in a net negative space charge distribution. The spatial variation of the space charge density ρ(x) was found to decay exponentially from the irradiation surface. The spatial dependence of ρ(x) did not follow the photon absorption profile as closely as observed previously when only unbiased a-Se layers were irradiated. However, the changes in the spatial distribution of ρ(x) with the x-ray mean photon energy exhibited the same tendency as the photon absorption profile. The distribution of the trapped charge and rate of detrapping was examined as a function of temperature, photon energy, and with infrared illumination. The total negative space charge was found to decrease with time following a power law dependence of the form N∼t-n, where n≈0.3 and was independent of the irradiation intensity, which indicates that electron detrapping occurs from an energy distribution of deep localized states. Using an infrared (IR) filter that allows photon energies smaller than 1.1 eV to pass, it is shown that IR illumination increases the rate of detrapping and confirms that electrons are trapped in deep electron trapping states between 0.6 and 1.1 - eV in the density of states diagram of a-Se [M. Abkowitz Philos. Mag. Lett. 58, 53 (1988)]. The mean detrapping current was found to be ∼10 pA, orders of magnitude smaller than the expected dark current. However, the trapped charge modifies the electric field at the top metal electrode causing it to become more injecting and leading to an increase in the dark current. The increase in the dark current is a possible origin for the persistent x-ray photocurrents recently reported for a-Se x-ray photoconductors. © 1998 American Institute of Physics. View full abstract»

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  • Effect of iron on oxygen precipitation in nitrogen-doped Czochralski silicon

    Page(s): 5502 - 5505
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    The effect of iron on oxygen precipitation in nitrogen-doped Czochralski (NCZ) silicon was investigated by Fourier transform infrared spectroscopy at room temperature or at liquid helium temperature. The experiments revealed that the oxygen precipitation could be enhanced by the contamination of iron in common Czochralski (CZ) silicon, or by the doping of nitrogen in NCZ silicon. In NCZ silicon, iron did not affect the precipitation of oxygen during annealing at high temperatures. After preannealing at 750 °C, the oxygen precipitation in NCZ silicon was suppressed due to the addition of iron. It is concluded that the generated iron nitride, which is related to an optical absorption line at 669 cm-1, emits self-interstitial silicon atoms to impede the nucleation of oxygen precipitates at low temperatures. © 1998 American Institute of Physics. View full abstract»

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  • Role of the A-site size and oxygen stoichiometry in charge ordering commensurability of Ln0.50Ca0.50MnO3 manganites

    Page(s): 5506 - 5514
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    The commensurability of the charge ordering process of the Ln0.50Ca0.50MnO3 manganites (Ln=Pr, Nd, Sm, Eu, and Gd) has been studied by electron diffraction and lattice imaging versus temperature. For the as-synthesized phases, it is shown that an incommensurate state at low temperature (92 K) is favored as the size of the lanthanide increases. A large transition width (ΔT ranging from 40 to 110 K) is observed which is closely related to the size of Ln3+, and also to the size mismatch between Ln3+ and Ca2+ cations. The most important result concerns the effects of oxygen stoichiometry, varied via different annealings carried out at low temperature (T≤600 °C) under Ar/H2 flow, air or O2 at PO2=100b. It is shown that very tiny deviations in the oxygen stoichiometry, which are not measurable using conventional techniques, affect significantly the transition width and commensurability, keeping the magnetic properties nearly unchanged. It is demonstrated that oxidized samples are systematically incommensurate whereas stoichiometric or the less oxidized ones are commensurate. A structural model is proposed to account for the modulated distribution of the additional [Mn4+] layers, with respect to the 1:1 ordering that should be obtained for the perfectly stoichiom- etric Ln0.50Ca0.50MnO3 phase. The concomitant influence of oxygen stoichiometry, cationic size, and mismatch effect upon the charge ordering phenomena in these oxides is discussed. © 1998 American Institute of Physics. View full abstract»

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  • X-ray diffraction, extended x-ray absorption fine structure and Raman spectroscopy studies of WO3 powders and (1-x)WO3-y∙xReO2 mixtures

    Page(s): 5515 - 5524
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    Pure ground tungsten trioxide WO3 and (1-x)WO3-y∙xReO2 mixtures were studied by x-ray absorption spectroscopy, x-ray powder diffraction and Raman spectroscopy in comparison with hydrogen bronzes HxWO3 and hydrogenated calcium tungstate CaWO4:H. It was found that a grinding of pure WO3 leads to a decrease of the crystallites size and a development of the bluish coloration. The color change was found to be reversible under moderate heat treatment or after storage in oxidizing atmosphere and is attributed to the reduced W5+ ions, located at the surface of freshly ground powder. The (1-x)WO3-y∙xReO2 mixtures were found to be composed of monoclinic/orthorhombic WO3 and orthorhombic ReO2 phases with a grain boundary containing reduced W5.7+ ions which are mainly responsible for the compound color at low rhenium ion concentrations. In both cases, the W(6-z)+ (0≪z≤1) color centers are responsible for strong optical absorption resulting in the dramatic decrease of the total Raman intensity. The structural models of free surface in pure ground WO3 and bulk WO3/ReO2 intragrain boundary in (1-x)WO3-y∙xReO2 mixtures are proposed and discussed. © 1998 American Institute of Physics. View full abstract»

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  • Stresses, deformation, and void nucleation in locally debonded metal interconnects

    Page(s): 5525 - 5530
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    Three-dimensional analyses of stresses and deformation in metal interconnects were carried out using the finite element method within the continuum framework. Particular attention is devoted to the preexisting local debond between the metal line and dielectric, which serves as the void nucleation site. Thermal mismatch induced stresses in the aluminum line near the interface defect are considered. The local reduction of stresses as well as the stress gradient along the line are quantified for various debond sizes. It is found that, for aluminum lines with an aspect ratio of unity, the influence of local debond on the stress profile along the line direction becomes negligible in regions greater than about one line height away from the debond edge. A unique stress pattern due to the preexisting debond is identified, which forms the basis of constructing a void nucleation model in terms of crystallographic slip. This three-dimensional modeling provides quantitative information on the initial stress field useful for modeling stress and electromigration induced voiding; it also confirms the qualitative features of stress evolution obtained from a previous two-dimensional analysis. © 1998 American Institute of Physics. View full abstract»

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  • Slow interfacial reamorphization of Ge films melted by ps laser pulses

    Page(s): 5531 - 5537
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    Melting and rapid solidification is induced in 50-nm-thick amorphous Ge films on glass substrates by single laser pulses at 583 nm with a duration of 10 ps. The solidification process is followed by means of reflectivity measurements with ns time resolution both at the air/film (front) and the substrate/film (back) interfaces. Due to interference effects between the light reflected at the film–substrate and film–liquid interfaces, the back side reflectivity measurements turn out to be very sensitive to the melt depth induced by the laser pulse and their comparison to optical simulations enables the determination of the solidification dynamics. For low fluences, only a thin layer of the film is melted and solidification occurs interfacially leading to reamorphization of the molten material. The results provide a critical interface velocity for amorphization of ∼4 m/s, much slower than the one that has widely been reported for elementary semiconductors. For high fluences, the molten layer depth approaches the film thickness and the results are consistent with a bulk solidification process. In this case, recalescence effects upon solid phase nucleation become important and lead to the formation of crystallites distributed throughout the whole resolidified volume. © 1998 American Institute of Physics. View full abstract»

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  • Deposition of hydrogenated diamond-like carbon films under the impact of energetic hydrocarbon ions

    Page(s): 5538 - 5542
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    In this article we studied the influence of bombardment energy of hydrocarbon ions on the properties of hydrogenated diamond-like carbon (DLC) films using x-ray reflectivity, Raman spectroscopy, and Fourier-transform infrared. The DLC films were prepared with an electron cyclotron resonance system using H2 and CH4 gases and the ion energy was tunable through a rf-induced dc bias voltage. It was observed that the surface roughness is increased and C–H bonded hydrogen concentration is decreased with increased ion energy, whereas the mass density, hardness, and sp3/sp2 ratio exhibited optimum values. A thin SiC layer was found to form between the DLC films and silicon substrates. Two proposed carbon deposition mechanisms, i.e., the shallow implantation (subplantation) model and the adsorbed layer model, are examined based on the results obtained in this study. Our results indicate that ion bombardment energy is a critical factor in determining the film properties and the ion subplantation could be an important deposition process even for hydrogenated DLC films. © 1998 American Institute of Physics. View full abstract»

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  • Laser-induced structural relaxation and crystallization phenomena in the picosecond time scale in GeSbO thin films

    Page(s): 5543 - 5546
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    Structural relaxation phenomena in the ps time scale have been observed upon pulsed laser irradiation of (GeSb)O amorphous films. The transformation of the irradiated surfaces has been temporally resolved by means of in situ optical techniques with ns and ps resolution. The results show the occurrence of structural relaxation phenomena in a time shorter than 600 ps in the as-deposited material or about 200 ps in thermally relaxed samples. In the latter case, a substantial amount of crystalline material is nucleated at the initial stage of the transformation. © 1998 American Institute of Physics. View full abstract»

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  • Recrystallization kinetics of electroplated Cu in damascene trenches at room temperature

    Page(s): 5547 - 5553
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    Cu metallization for sub-0.25 μm interconnects marks not only a change in metallurgy from Al and a change in architecture from subtractive to damascene but also a major shift in deposition technology from sputtering to electroplating. A remarkable feature of electroplated Cu films is the recrystallization or grain growth process that takes place at room temperature over a period of hours to weeks after plating. While this phenomenon has been described for blanket films, the influence of substrate topography on the kinetics of recrystallization has not previously been reported. Using focused ion beam imaging we demonstrate that recrystallization of the small grained as-plated Cu is initiated at the upper corners of damascene trenches and grains continue to grow laterally, eventually transforming the entire film. Removal of overlying Cu by chemical mechanical polishing before the transformation leads to incomplete recrystallization of the Cu left in the trenches. The kinetics of the recrystallization process for trench widths of 0.3, 0.5, 0.8, 2, and 5 μm reveal a minimum time for recrystallization for the 0.8 μm trenches. An acceleration of the room temperature recrystallization rates for all trench widths is observed if the films are first cycled to -78 °C immediately after plating, and a more pronounced minimum time for recrystallization is observed for the 0.8 μm trenches. These observations lead us to propose that the initiation of this process at the upper corners of the trenches and the trench width dependence of the recrystallization rate are related to higher stress or dislocation densities. © 1998 American Institute of Physics. View full abstract»

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  • Properties of the titanium related level in Cd0.96Zn0.04Te crystals

    Page(s): 5554 - 5559
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    Semi-insulating and n-type conductor titanium (Ti) doped CdZnTe has been investigated by deep level transient spectroscopy, deep level optical spectroscopy and photoinduced current transient spectroscopy. A main electron trap at 0.82 eV is detected and its electrical and optical characteristics are given. The σno optical cross section spectrum of this level exhibits a resonance band attributed to the internal transition of the Ti2+ ion in CdZnTe. Starting from this identification, this deep trap is formally proposed to be the Ti2+/Ti3+ single donor level. The semi-insulating properties of the CdZnTe:Ti are interpreted in relation to this deep donor. Finally, the impact of the optical cross sections σno and σpo of this level on the photorefractive behavior of CdZnTe crystal is also discussed. © 1998 American Institute of Physics. View full abstract»

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  • Effect of oxygen stoichiometry on the electrical property of thin film La0.5Sr0.5CoO3 prepared by pulsed laser deposition

    Page(s): 5560 - 5565
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    A measurement of electrical conductivity and Hall effect has been made for thin film La0.5Sr0.5CoO3-δ (LSCO) prepared on (001) SrTiO3 substrates by pulsed laser deposition under reduced oxygen pressures. A considerable effect of oxygen stoichiometry on electrical resistivity of LSCO thin films has been observed. The semiconducting behavior was observed as long as the sample was slightly oxygen deficient. The Hall effect measurements revealed a change ranging from four to six orders of magnitude in the carrier density, from 1019 to 1015 cm-3 at room temperature, and 1020–1012 cm-3 at ∼80 K for the films prepared inbetween 1 bar and 1 μbar O2. A chemical equilibrium approach of the interaction between oxygen vacancies and hole carriers was used to explain the measured data. The results were compared with the microstructural measurements, yielding an empirical relation between the lattice expansion along c-axis and oxygen vacancies for LSCO films. © 1998 American Institute of Physics. View full abstract»

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Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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P. James Viccaro
Argonne National Laboratory