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Journal of Applied Physics

Issue 6 • Date Sep 2003

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Displaying Results 1 - 25 of 86
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Band parameters for nitrogen-containing semiconductors

    Page(s): 3675 - 3696
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    We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman etal, J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature and alloy-composition dependences are also recommended wherever they are available. The “band anticrossing” model is employed to parameterize the fundamental band gap and conduction band properties of the dilute nitride materials. View full abstract»

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  • Jones matrix method for predicting and optimizing the optical modulation properties of a liquid-crystal display

    Page(s): 3697 - 3702
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    We present a simple technique for the calibration, prediction, and optimization of the optical modulation properties of a liquid-crystal display (LCD). The method is useful when there is no information about the internal fabrication parameters of the device (the orientation of liquid-crystal molecules, the twist angle, or the birefringence of the material). A complete determination of the LCD Jones matrix is accomplished by means of seven irradiance measurements for a single wavelength. This technique only requires two linear polarizers and one quarter-wave plate. Once the Jones matrix has been calibrated, the amplitude, phase, and polarization modulation response can be predicted. Therefore, it can be optimized through the control of the polarization configuration. The validity of the proposed method is experimentally probed. Finally, we present a particular application to produce phase-only modulation. © 2003 American Institute of Physics. View full abstract»

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  • Effects of classical and quantum charge fluctuations on sequential electron tunneling in multiple quantum wells

    Page(s): 3703 - 3711
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    A previous theory [M. Ershov etal, Appl. Phys. Lett. 67, 3147 (1995)] for studying the distribution of nonuniform fields in multiple-quantum-well photodetectors under an ac voltage is generalized to include nonadiabatic space-charge-field effects. From numerical results calculated by the generalized theory, it is found that field-domain effects are only important at high temperatures or high voltages, where both injection and sequential-tunneling currents are expected to be large. On the other hand, field-domain effects become negligible at low temperatures and low voltages, but nonadiabatic effects included in this extended theory are enhanced for small sequential-tunneling currents. The time duration for nonadiabatic effects is determined by the quantum capacitance. By using the generalized theory, a differential capacitance is calculated for a non-steady state, and a negative conduction current is predicted under a positive voltage in this case due to charge accumulation around the collecting contact. View full abstract»

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  • T-junction waveguide experiment to characterize left-handed properties of metamaterials

    Page(s): 3712 - 3716
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    The left-handed property of a metamaterial is demonstrated by measuring the power at the output of a T-junction waveguide loaded with a metamaterial having one edge cut at 45° with respect to the waveguide axis. Both experimental scattering data and numerical results are presented. The metamaterial sample is realized by using a periodic arrangement of wires and split-ring resonators, and the operating frequency is chosen to correspond to a refraction index of about -1. The results show that when the T junction is empty, most of the power is received at the output port directly facing the input port, whereas when it is loaded with the sample of metamaterial, most of the power is received at the output port perpendicular to the input axis. This indicates that the energy is bent by the oblique edge of the sample by an angle of -45° with respect to the normal, which suggests a negative index of refraction. © 2003 American Institute of Physics. View full abstract»

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  • Target optimization of a water-window liquid-jet laser–plasma source

    Page(s): 3717 - 3721
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    We optimize the water-window x-ray flux and debris deposition for a liquid-jet laser plasma source by varying both the target diameter and the jet material. For two target liquids, methanol and ethanol, measurements of the λ=3.37 nm C VI x-ray flux and the debris deposition rates are presented as function of the jet diameter. It is shown that the effective carbon debris deposition is more than 1 order of magnitude smaller for methanol, while the x-ray flux is reduced only ∼40%. The reduction in carbon debris deposition may be explained by reactive ion etching by oxygen from the plasma. Thus, the methanol water-window source may be operated at a 5–10× higher flux without increasing the debris deposition. The optimization potentially allows a reduction of the exposure time of compact soft x-ray microscopy or other water-window applications based on such sources without increasing damage to sensitive x-ray optics. © 2003 American Institute of Physics. View full abstract»

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  • Efficient, stable, corona discharge 172 nm xenon excimer light source

    Page(s): 3722 - 3731
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    We demonstrate that corona discharges in xenon gas can be an efficient source of 172 nmXe2* excimer vacuum ultraviolet (VUV) radiation. Conversion efficiencies of electrical power into VUV light greater than 50% have been observed. A model describing the light production mechanism in the discharge region including the influence of water vapor content in the 10 ppm region is presented. A prototype large area lamp consisting of 21 corona discharges operating in parallel has been built with 38 mW/cm2 VUV output power per area at the lamps surface. Based on the model and experimental results achieved, a continuous wave large area Xe2* 172 nm excimer light source with 130 mW/cm2 output and a possible wall plug efficiency close to 48% is proposed. © 2003 American Institute of Physics. View full abstract»

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  • Electron plasma ion trap/source

    Page(s): 3732 - 3739
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    A theoretical study is presented on a type of Penning trap configuration referred to as an electron plasma ion trap/source. Ions in the configuration are confined within a three-dimensional electric potential well, which is produced by a combination of the electric field generated by the trap electrodes and the electric field generated by a trapped electron plasma. The ion density is not limited by the Brillouin ion density limit. Instead, the ion charge density must be smaller than the electron charge density. Various mechanisms that may limit the electron charge density are identified. Example calculations are used to find that the most restrictive limit on the electron charge density is likely to be the voltage difference that must be applied to trap the electron plasma parallel to a magnetic field. For confinement of low-charge-state ions, the ion temperature must be smaller than the electron temperature. Relatively long ion confinement times are found to be possible, however, because the equilibration of the ion temperature and the electron temperature is a slow collisional process due to the disparate masses involved. The ions can be easily extracted before the ion temperature reaches a value such that ion loss to the electrode walls becomes a significant source of impurities. Thus, since ion–wall interactions can be minimal, high purity ion plasmas may be generated. A self-consistent finite-differences computation is used to predict a possible plasma equilibrium. © 2003 American Institute of Physics. View full abstract»

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  • Simulation of plasma molding over a ring on a flat surface

    Page(s): 3740 - 3747
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    A fluid/Monte Carlo simulation model was developed to study plasma molding over an axisymmetric feature (a ring) resting on an otherwise planar surface in contact with a high-density rf plasma. The two-dimensional (r,z) time-dependent sheath potential, and ion density and flux profiles were predicted with a self-consistent fluid simulation. The trajectories of ions and energetic neutrals (resulting mainly by ion neutralization on the cylindrical sidewalls of the ring) were then followed with a Monte Carlo simulation, in an effort to obtain their energy and angular distributions on the substrate surface. When the sheath thickness was comparable to the size of the ring, strong radial electric fields deflected oncoming ions toward the sidewalls of the ring. The ion density was lower in the cylindrical well formed by the ring, compared to outside, resulting in a locally thicker sheath and a smaller spread in the double-peaked ion energy distributions at the bottom of the well. The ion impact angle increased progressively as the sidewalls were approached. The angular distribution of energetic (fast) neutrals at the bottom of the well was bimodal. The energy distribution of fast neutrals at the bottom of the well was broader compared to the parent ion energy distributions. © 2003 American Institute of Physics. View full abstract»

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  • Numerical study of Ar/CF4/N2 discharges in single- and dual-frequency capacitively coupled plasma reactors

    Page(s): 3748 - 3756
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    A one-dimensional particle-in-cell/Monte Carlo model is developed to study capacitively coupled (cc) radio-frequency discharges in a gas mixture of Ar, CF4, and N2. The charged species, which are followed in the model, are: Electrons and Ar+, CF3+, N2+, F-, and CF3- ions. The simulation considers electron – neutral (Ar, CF4, and N2) collisions, various kinds of collisions of ions with neutrals, positive–negative ion recombination, and electron–ion recombination. The model yields results for electron and ion densities, fluxes and energy distributions, collision rates and electric field, and potential distributions. The simulations are performed for a 0.8/0.1/0.1 ratio of Ar/CF4/N2 mixture at a pressure of 30 mTorr in single (13.56 MHz) and dual frequency (2+27 MHz) cc reactors and a comparison between the two frequency regimes is made. Results show that the structure of the discharges is electronegative in both cases. F- and CF3- ions are the main negative charge carriers in the single and dual frequency regime, respectively. In the presence of low-frequency (2 MHz) and a strong electric field, the light F- ions are no longer confined in the bulk plasma and they partially respond to the instantaneous electric field. The calcul- ated electron energy probability function profiles can be approximated to a Druyvesteyn and bi-Maxwellian distribution with high-energy tails in the single- and dual-frequency regime, respectively. The ion energy distribution is narrow with one outstanding peak in the single-frequency scheme, whereas it is wide and bimodal in the dual-frequency scheme. © 2003 American Institute of Physics. View full abstract»

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  • Early stage of plastic deformation in thin films undergoing electromigration

    Page(s): 3757 - 3761
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    Electromigration occurs when a high current density drives atomic motion from the cathode to the anode end of a conductor, such as a metal interconnect line in an integrated circuit. While electromigration eventually causes macroscopic damage, in the form of voids and hillocks, the earliest stage of the process when the stress in individual micron-sized grains is still building up is largely unexplored. Using synchrotron-based x-ray microdiffraction during an in-situ electromigration experiment, we have discovered an early prefailure mode of plastic deformation involving preferential dislocation generation and motion and the formation of a subgrain structure within individual grains of a passivated Al (Cu) interconnect. This behavior occurs long before macroscopic damage (hillocks and voids) is observed. © 2003 American Institute of Physics. View full abstract»

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  • Random field models for two-phase microstructures

    Page(s): 3762 - 3770
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    Level-cut filtered Poisson fields are defined by cuts of filtered Poisson fields above prescribed levels and used to model two-phase microstructures. The filtered Poisson fields are sums of deterministic functions h scaled by random variables and centered at random points generated by a Poisson field N. The structure of the level-cut filtered Poisson fields depends on the functional form of h, the properties of the random variables scaling h, and the intensity of N. Level-cut Gaussian fields used extensively to represent two-phase microstructures are special cases of level-cut filtered Poisson fields. A Monte Carlo algorithm was developed for generating two-phase composites based on level-cut filtered Poisson fields. It is shown by examples that level-cut filtered Poisson fields can produce a broad range of two-phase microstructures. © 2003 American Institute of Physics. View full abstract»

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  • Ultrasonic absorption in ultra-low carbon steel

    Page(s): 3771 - 3780
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    The laser-based reverberant technique is used to measure ultrasonic absorption spectra in the 2 to 45 MHz frequency range. This technique, being contactless, allows measurements at high temperature. The absorption spectra of ultra-low carbon steel samples are studied at room temperature in a magnetic field (in order to suppress the magnetoelastic contribution) and in a high temperature furnace (20–1200 °C) without magnetic field. Small steel samples (about 10×10×1 mm3) are used. At room temperature, two main contributions to the ultrasonic absorption are identified: microeddy currents (magnetoelastic contribution) and absorption caused by dislocations (deformation contribution). A typical microeddy current peak is observed and yields a reasonable estimate of the magnetic domain size. Above 10 MHz, the nonmagnetic contribution to the total absorption follows the classical vibrating string model. However, other phenomena also contribute to the absorption spectra. Below 10 MHz, an amplitude-independent damping background is observed. In addition, a small frequency-independent contribution to the absorption is observed at room temperature and is attributed to a thin surface layer. The absorption at high temperature is dominated below the Curie point by the magnetoelastic contribution. Two internal friction peaks are also detected. The first one, at 100 °C, is related to the dislocation kink motion. The second one, measured at 330 °C and 10 MHz, is attributed to the Snoek relaxation of carbon and/or nitrogen in α-iron. The Curie transition as well as the ferrite-austenite transition strongly affect the internal friction spectra. View full abstract»

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  • Brillouin scattering in RbNbWO6

    Page(s): 3781 - 3784
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    Micro-Brillouin scattering measurements of RbNbWO6, a defect pyrochlore, that exhibits superionic conductivity and ferroelectric properties, have been performed in the 213–573 K temperature range. In this work the presence of quasielastic scattering (central peak) has been documented. The obtained results suggest that the main contribution to the observed central peak comes from Rb+ ion hopping. The temperature dependences of the central peak intensity and bandwidth exhibit broad anomalies around 360 K. This result clearly shows that ion hopping is related to the phase transitions at 361.6 and 356.5 K. © 2003 American Institute of Physics. View full abstract»

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  • Optical spectroscopy of localized electronic states in SrS:Cu

    Page(s): 3785 - 3790
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    A combination of optical spectroscopy and thermoluminescence measurements were used to determine the mechanisms that can influence the emission in SrS:Cu+ thin film structures and increase the electroluminescence brightness by a factor of 2. In particular, the interaction of the emitting center with the trap states and the conduction band is considered. Thermal quenching, thermoluminescence, and temperature-dependent fluorescence transient results are compared to appropriate population dynamics models in order to determine the position of the Cu excited state and the trap states with respect to the conduction band. © 2003 American Institute of Physics. View full abstract»

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  • Optical properties of CdxZn1-xTe epilayers grown by molecular-beam epitaxy

    Page(s): 3791 - 3795
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    CdxZn1-xTe epilayers were grown on GaAs(001) substrates by molecular-beam epitaxy. The optical properties of the epilayers were studied by taking reflectance (R) and photoluminescence (PL) measurements. From the R and PL spectra, the energy gaps of the epilayers were determined and shown to decrease as the Cd concentration increased. A quadratic equation that related the energy gap to Cd concentration was also derived. The dependence of the PL spectra on temperature was studied as well. A redshift of the PL peaks was observed as the temperature increased. The exciton activation energy of the epilayers was determined from the plots of integrated PL intensity versus temperature. It tends to decrease as the Cd content increased. The temperature dependence of the energy gaps, determined from the PL spectra, was fitted according to both Varshni’s and O’Donnell and Chen’s relations [Y. P. Varshni, Physica 34, 149 (1967); K. P. O’Donnell and X. Chen, Appl. Phys. Lett. 58, 2924 (1991)]. Good fits were obtained using both relations for the samples with small Cd concentration. However, the fitted O’Donnell’s curve for the Cd0.582Zn0.418Te epilayer shows a more reasonable trend as temperature increases. © 2003 American Institute of Physics. View full abstract»

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  • Electron paramagnetic resonance characterization of impurity Gd3+ ions in a PbWO4 single crystal

    Page(s): 3796 - 3799
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    Lead tungstate single crystals doped with Gd2O3 were grown by the Czochralski method in Ar atmosphere. The electron paramagnetic resonance of the Gd3+ ion in a PbWO4 single crystal has been investigated at 9.4 GHz. The spectroscopic splitting tensor g and zero-field splitting parameters Bkq were determined using the effective spin Hamiltonian. The rotation patterns in the crystallographic planes together with spin Hamiltonian parameters of Gd3+ ion show that the local site symmetry of the Gd3+ ion in PbWO4 crystal is tetragonal and that the Gd3+ ion substitutes for the Pb2+ ion without local charge compensation at the nearby surroundings. © 2003 American Institute of Physics. View full abstract»

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  • Effects of dry etching processes on effective refractive index of ZnTe surface layers in terahertz region

    Page(s): 3800 - 3804
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    We report on the far-infrared (FIR) reflection spectra of high-quality ZnTe crystals exposed to CH4/H2 gases under different rf plasma powers. The effects of reactive ion etching on the effective refractive index of perturbed ZnTe surface layers have been investigated in the terahertz (THz) frequency range of 1.5–10.0 THz. The FIR refractive index has been found to decrease with the increase of plasma power, which has been well described by Sellmeier formulas. Furthermore, the obtained experimental data have been employed for THz electro-optic applications by predicting the effects of RIE on the second-order nonlinear susceptibility and the THz pulse intensity after dispersive propagation/absorption in the ZnTe surface layers. © 2003 American Institute of Physics. View full abstract»

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  • Properties of Cu/Au Schottky contacts on InGaP layer

    Page(s): 3805 - 3809
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    We use Auger electron spectroscopy (AES) measurements to obtain elemental distributions for Cu/Au Schottky contacts to an InGaP layer in as-deposited and thermally annealed samples. The AES depth profile shows an obvious Cu layer with no apparent interdiffusion between the Cu and the InGaP layers in either the as-deposited samples or in the samples annealed at 450 °C. However, when the annealing temperature reached 500 °C, the metallic Cu layer was released, and a distinct interdiffusion between the Cu and the InGaP layers is observed. Metallic Cu and Au intermixed to form a stable intermetallic region. Below this intermetallic region, an interaction region, composed mainly of Cu and P, is observed. The formation of this region is attributable to the diffusion of Cu into the InGaP layer, and is responsible for the thermal degradation of Cu/Au Schottky contacts to the InGaP layer. In the deep-level transient spectroscopy spectra, we find an obvious trap at 150 K. This was determined to be a native trap that exists in the InGaP materials with activation energies of 0.35–0.42eV. After annealing at 500 °C, another trap appeared. According to a thermal degradation investigation, this trap at Ec-0.70 eV can be attributed to the diffusion of Cu into the InGaP layer. © 2003 American Institute of Physics. View full abstract»

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  • Structure of electroless deposited Co0.9W0.02P0.08 thin films and their evolution with thermal annealing

    Page(s): 3810 - 3822
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    Electroless deposited Co0.9W0.02P0.08 thin films have been proposed as diffusion barriers and encapsulation layers for Cu metallization in ultralarge-scale integrated microelectronic devices. In this article, we present a study of the structure of these films and their evolution with thermal anneal up to 700 °C. The as-deposited microstructure is comprised of an amorphous CoWP component and nanocrystallites of hexagonal-close-packed (hcp) Co, approximately 5 nm in size. The amorphous CoWP component crystallizes to hcp Co at approximately 290 °C with an apparent activation energy of 1.6±0.1 eV, according to the Kissinger analysis. Isothermal anneals show that the rate of nucleation with time of the hcp Co grains is constant, and grain growth is controlled by diffusion. This diffusion is most probably of the P and W elements, which enrich the grain boundaries. At approximately 420 °C, the orthorhombic (o-) Co2P phase nucleates. The apparent activation energy of this phase transformation is 4.6±0.1 eV, according to the Kissinger analysis. We suggest that the nucleation of the o-Co2P phase occurs when the grain boundaries are saturated with P. At higher temperatures, the main structural changes observed in the films are the grain growth of the predominately hcp Co grains and a delayed transformation to face-centered-cubic Co compared to bulk Co. The chemical binding state of P after high temperature anneals is covalent as in the o-Co2P phase. I- n the as-deposited film, the chemical binding state of P is significantly different, attributed to the amorphous CoWP component and the P in a solid solution in the hcp Co grains. © 2003 American Institute of Physics. View full abstract»

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  • Study on atomic coordination around Er doped into anatase– and rutile– TiO2: Er–O clustering dependent on the host crystal phase

    Page(s): 3823 - 3827
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    Alternative Er doping into anatase (A–) or rutile (R-)TiO2 can be achieved by O2 pressure control during Er-doped TiO2 deposition using laser ablation. An x-ray absorption fine structure analysis of the atomic coordination around Er revealed the dynamics of Er–O clustering in A– and R-TiO2. The Er local structure in A-TiO2 can be determined by a Ti–O arrangement of the host crystal surrounding Er, while that in R-TiO2 can be decided by the Er–O chemical properties rather than the Ti–O arrangement. Moreover, a substitution of Er for Ti induced O deficit in A-TiO2 and induced Ti removal in R-TiO2. These differences can be explained by the ErO6 stabilization mechanism based on the spontaneous symmetry reduction (SSR) theory. The Ti–O arrangement in A-TiO2 prevents the SSR, resulting in ErO6 instability. However, ErO6 is stabilized in the host crystal because the SSR is smoothly induced in R-TiO2. © 2003 American Institute of Physics. View full abstract»

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  • X-ray reciprocal space mapping of strain relaxation in GaAs1-xNx on GaAs [100] by molecular-beam epitaxy

    Page(s): 3828 - 3833
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    The effect of strain on GaAs1-xNx grown on GaAs is observed using two-dimensional [115] high-resolution x-ray diffraction rocking curves. The instance when the epilayer changes from a highly strained to a relaxed state, is captured and a change in peak profile is observed. The increase of growth rate is found to have an effect of maintaining the crystal quality and surface reconstruction. Interstitial N complex lowers the tensile strain due to its compressive nature, thereby increasing the critical thickness at high N%. We demonstrated that GaAs0.952N0.048 can be coherently grown to 100 nm on GaAs, exceeding the critical thickness by 4.7 times after an optimization of III–V–N growth by means of higher rf power compensation under an increased growth rate. © 2003 American Institute of Physics. View full abstract»

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  • Cu gettering in ion implanted and annealed silicon in regions before and beyond the mean projected ion range

    Page(s): 3834 - 3839
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    The strong gettering of Cu atoms in single-crystal Si implanted with 3.5 MeV P+ ions is studied after thermal treatment and Cu contamination. Cu decorates the remaining implantation damage. Three separate Cu gettering layers are detected by secondary ion mass spectrometry: at the main projected ion range RP below RP (RP/2 effect) and beyond RP (trans-RP effect). The defects acting as gettering centers at RP/2 and RP are implantation induced excess vacancies and excess interstitials, respectively. Cu profiles fit very well with depth distributions of excess vacancies and excess interstitials determined by binary collision simulations for random and channeled ion incidence. The RP/2 effect for P+ implantation is found to be significantly reduced in comparison with Si+ implantation. It disappears completely for higher P+ ion fluences. The trans-RP gettering layer is formed by thermal treatment. The Cu accumulation in the trans-RP region increases with increasing temperature and/or with increasing annealing time. These results are in qualitative agreement with the assumption that interstitials carried by P diffusion are the origin of Cu gettering in the trans-RP region. The P diffusion may inject interstitials into the bulk and also into the RP/2 region thus decreasing the RP/2 effect. © 2003 American Institute of Physics. View full abstract»

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  • Molecular dynamics study of structural, mechanical, and vibrational properties of crystalline and amorphous Ga1-xInxAs alloys

    Page(s): 3840 - 3848
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    Using an interaction potential scheme, molecular dynamics (MD) simulations are performed to investigate structural, mechanical, and vibrational properties of Ga1-xInxAs alloys in the crystalline and amorphous phases. For the crystalline phase we find that: (i) Ga–As and In–As bond lengths vary only slightly for different compositions; (ii) the nearest-neighbor cation–cation distribution has a broad peak; and (iii) there are two nearest-neighbor As–As distances in the As (anion) sublattice. These MD results are in excellent agreement with extended x-ray absorption fine structure and high-energy x-ray diffraction data and also with ab initio MD simulation results. The calculated lattice constant deviates less than 0.18% from Vegard’s law. The calculated phonon density of states exhibits a two-mode behavior for high-frequency optical phonons with peaks close to those in binary alloys (GaAs and InAs), which agrees well with a recent Raman study. Calculated elastic constants show a significant nonlinear dependence on the composition. For the amorphous phase, MD results show that: (i) the nearest-neighbor cation–anion distribution splits into well-defined As–Ga and As–In peaks as in the crystal phase; (ii) the cation–cation distribution is similar to that in the crystal phase; and (iii) the As–As distribution is quite different from that in the crystal, having only one nearest-neighbor distance. © 2003 American Institute of Physics. View full abstract»

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  • Control parameters for the tunable refractive index of magnetic fluid films

    Page(s): 3849 - 3852
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    In this work, we systematically investigate the influence of control parameters, including the concentration of magnetic particles, film thickness, external field direction, and field sweep rate, on the magnetically tunable refractive index of magnetic fluid films. We find that the variation in the refractive index of the magnetic fluid film with rising field strength is enhanced by increasing either the concentration or the film thickness, or by applying the field along the film surface, whereas it is independent of the sweep rate of the field. The results clearly reveal how to control the tunable refractive index of magnetic fluid films. Furthermore, they provide valuable information that may assist in the development of magnetic-fluid-based index-tunable devices. © 2003 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