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1 Aug 2001

Volume 90, Issue 3, pp. 1077-1677

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Coherent all-optical polarization switching based on exciton–exciton interactions in quantum wells

Eric J. Gansen, K. Jarasiunas, Scot A. Hawkins, Martin J. Stevens, and Arthur L. Smirl

J. Appl. Phys. 90, 1077 (2001); http://dx.doi.org/10.1063/1.1383015 (5 pages) | Cited 2 times

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A coherent all-optical nonlinear polarization switch based on exciton–exciton correlations is demonstrated in a multiple-quantum-well semiconductor structure. A contrast ratio of 8:1 and a relaxation time of less than a picosecond are reported at 80 K using only ten wells. The results are compared to a simple phenomenological model to demonstrate that many-body effects are solely responsible for the switching action and that the turn-on and turn-off times are determined by the dephasing time. © 2001 American Institute of Physics.
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78.67.De Quantum wells
42.65.Pc Optical bistability, multistability, and switching, including local field effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Fd III-V semiconductors

Simplified treatment of scattering processes in quantum well structures

W. E. Hagston, T. Stirner, and F. Rasul

J. Appl. Phys. 90, 1082 (2001); http://dx.doi.org/10.1063/1.1383265 (8 pages) | Cited 1 time

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Arguments are developed which show that, to a good approximation, the essential physics and many of the quantitative details pertaining to the relative rates of carrier–carrier, carrier–longitudinal optical phonon, and carrier–photon scattering in different quantum well structures can be understood in terms of a simplified approach. The latter is based on fundamental concepts of quantum theory and involves the separation of the matrix element in the scattering rate calculation into two simpler parts: an “energy effect” term and a “wave-function effect” term. As an application of the method, the question of attaining lasing action in the far-infrared (terahertz) region of the spectrum is discussed briefly. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.67.De Quantum wells
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations
42.55.Ah General laser theory
73.21.Fg Quantum wells
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions
03.65.Nk Scattering theory
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Determination of the radial density distribution of ground and low-lying levels of mercury in a nonequilibrium plasma using emission spectroscopy

Dimitrios Karabourniotis

J. Appl. Phys. 90, 1090 (2001); http://dx.doi.org/10.1063/1.1380997 (12 pages) | Cited 9 times

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A method is described for determining the radial density distribution of the ground and the first excited states as well as the electron temperature distribution in multielement plasmas containing mercury. It is based on the spectroscopic measurement of the plasma emissivity at the maximum of self-reversed lines and the population density of a high-lying excited state. The method is independent of equilibrium assumptions and can be used in diagnostics of nonequilibrium plasmas. The proposed method was verified for the plasma of a 5 bar discharge in mercury. Plasma underionization and nonequilibrium excitation are observed spectroscopically in the bulk of the discharge. The experimental data are interpreted in terms of nonequilibrium effects. Comparison of the results obtained initially, and then assuming local thermodynamic equilibrium (LTE), shows clearly considerable departure of the plasma from LTE. © 2001 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
52.25.Kn Thermodynamics of plasmas

Dynamics of ion-ion plasmas under radio frequency bias

Vikas Midha and Demetre J. Economou

J. Appl. Phys. 90, 1102 (2001); http://dx.doi.org/10.1063/1.1383260 (13 pages) | Cited 25 times

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A time-dependent one-dimensional fluid model was developed to study the dynamics of a positive ion-negative ion (ion-ion) plasma under the influence of a rf bias voltage. The full ion momentum and continuity equations were coupled to the Poisson equation for the electrostatic field. Special emphasis was placed on the effect of applied bias frequency. Due to the lower temperature and greater mass of negative ions compared to electrons, the sheath structure in ion-ion plasmas differs significantly from that of conventional electron-ion plasmas, and shows profound structure changes as the bias frequency is varied. For low bias frequencies (100 kHz), the charge distribution in the sheath is monotonic (switching from positive to negative) during each half cycle. For intermediate frequencies (10 MHz), when the bias period approaches the ion transit time through the sheath, double layers form with both positive and negative charges coexisting in the sheath. For high frequencies (60 MHz), beyond the plasma frequency, plasma waves are launched from the sheath edge, and the sheath consists of multiple peaks of positive and negative charge (multiple double layers). For a relatively large range of bias frequencies (up to the plasma frequency), each electrode is bombarded alternately by high energy positive and negative ions during a rf bias cycle. For bias frequencies greater than the plasma frequency, however, the electrode is bombarded simultaneously by low energy positive and negative ions with ion energies approaching the thermal value. The ion energy was found to increase with the applied bias potential. Also, at relatively high pressures (20 mTorr), the ion energy at low frequencies (100 kHz) is limited by collisions. The peak ion energy may then be increased by using an intermediate bias frequency (10 MHz). At lower pressures, however, the effect of collisions is mitigated while the effect of ion transit time becomes significant as the bias frequency increases. In this case, a low bias frequency (100 s of kHz) is favorable for extracting high energy ions from the plasma. © 2001 American Institute of Physics.
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52.40.Kh Plasma sheaths
52.65.Kj Magnetohydrodynamic and fluid equation
52.30.-q Plasma dynamics and flow
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons

High power radiation from ionization fronts in a static electric field in a waveguide

J. R. Hoffman, P. Muggli, R. Liou, M. Gundersen, J. Yampolsky, T. Katsouleas, C. Joshi, and W. B. Mori

J. Appl. Phys. 90, 1115 (2001); http://dx.doi.org/10.1063/1.1377608 (9 pages) | Cited 3 times

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The radiation produced when a relativistically moving plasma/gas boundary (i.e., an ionization front) passes between alternatively biased capacitor electrodes is studied. Results of an experiment based on a design which incorporates the capacitor electrodes into an X band waveguide are presented. The waveguided design effectively couples nearly three orders of magnitude more power into the output than the previously unguided designs. Linear theory is extended to include the depletion of the laser energy as it propagates through the ionizable gas (i.e., laser depletion), and the effect of finite output pulse duration. © 2001 American Institute of Physics.
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52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
84.40.Az Waveguides, transmission lines, striplines
52.27.Ny Relativistic plasmas

Particle fluxes in an electron cyclotron resonance plasma discharge

J. González-Damián and C. Gutiérrez-Tapia

J. Appl. Phys. 90, 1124 (2001); http://dx.doi.org/10.1063/1.1383022 (6 pages)

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In electron cyclotron resonance (ECR) plasma reactors, it is extremely important to control critical parameters such as the flux and energy distribution of ions impacting surfaces. These parameters are influenced by physical construction, magnetic field geometry, and chemical kinetics. In this article we present a model that accounts for the magnetic field geometry in the reactor region. The model is based on the drift kinetic equation approach and it is used to calculate the axial and radial ion fluxes in the materials processing zone of an ECR plasma source. Analytical expressions for the radial and axial fluxes, the mean energy, and the ion density are derived. An acceptable approximation is obtained from the described model and that reported in the literature from experimental results. © 2001 American Institute of Physics.
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52.65.-y Plasma simulation
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Dg Plasma kinetic equations
52.77.-j Plasma applications
52.80.-s Electric discharges

Diagnostics of inductively coupled chlorine plasmas: Measurement of electron and total positive ion densities

M. V. Malyshev and V. M. Donnelly

J. Appl. Phys. 90, 1130 (2001); http://dx.doi.org/10.1063/1.1381044 (8 pages) | Cited 43 times

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This work is part of a broader study that creates a set of experimentally measured chlorine plasma parameters (electron and gas temperatures, electron energy distribution function, electron density, densities of ion fractions, and total ion density). This set is obtained over a broad range of operating conditions (1–20 mTorr, 5–1000 W) of an inductively coupled plasma. In this part, we present the electron (ne) and total positive ion (ni+=nCl2++nCl+) densities. ne and ni+ were measured with a Langmuir probe across the diameter or in the middle of the reactor. Line integrated values of ne were independently obtained with microwave interferometry, and converted into the spatially resolved data using the Langmuir probe ne profiles. Finally, a method is presented for measuring relative positive ion densities, based on optical emission at 7504 Å from trace amounts of Ar. © 2001 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.25.-b Plasma properties
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Investigation of surface blistering of hydrogen implanted crystals

Stephen W. Bedell and William A. Lanford

J. Appl. Phys. 90, 1138 (2001); http://dx.doi.org/10.1063/1.1380409 (9 pages) | Cited 34 times

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The time required to observe the onset of blistering was measured for 100 keV H implanted Si, SiC, and Ge crystals as a function of dose and annealing temperature. The calculated blistering activation energy (EA) for Si was found to decrease rapidly with increasing H dose. In Ge, EA decreased only slightly, while EA did not vary with dose in SiC. Hydrogen profiling using the 1H(15N,αγ)12C technique was used to study the evolution of the H distribution in these crystals. It was observed that implanted H concentrates upon annealing in Si and SiC, but not in Ge. By measuring the H profiles on the surfaces of bonded and transfered Si layers it was concluded that fracture occurred at the H peak and 50% of the implanted H was liberated during fracture. Ion beam channeling using 2 MeV 4He was used to study the implant damage in these materials. The dechanneling levels in the channeling spectra were attributed to the presence of lattice distortions near the implant peak. It was determined that the extent of lattice distortion was greatest in Ge and least in SiC. An observed decrease in the dechanneling level in as-implanted Si above 9×1016 H/cm2 was attributed to strain relaxation during implantation. Amorphization in SiC dramatically decreased the growth rate of the microcracks, implying that amorphous materials may be difficult to use in conjunction with Smart-Cut™ technology. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.72.up Other materials
61.82.Fk Semiconductors
61.80.Jh Ion radiation effects
81.05.Hd Other semiconductors
61.72.Cc Kinetics of defect formation and annealing
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Alloy formation of Y with Pd investigated by photoemission and electron diffraction

A. Borgschulte, M. Rode, A. Jacob, and J. Schoenes

J. Appl. Phys. 90, 1147 (2001); http://dx.doi.org/10.1063/1.1381544 (8 pages) | Cited 12 times

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The structure of Pd capped Y films for an application as a switchable mirror was studied. The surface structures are investigated by reflecting high energy electron diffraction and Auger electron spectroscopy. The alloy formation between Y and Pd leads to different structural and electronic properties of the surface, which are compared to the switching behavior of the underlying Y film when exposed to hydrogen. The electronic structure of the intermetallic compound YxPd1−x(0<x<0.25) was studied by angular-resolved ultraviolet photoemission spectroscopy. The samples were prepared by Y deposition on Pd (111) surfaces of epitaxial films. The electronic structure of the alloy is discussed in the framework of a qualitative tight-binding approach. The reactivity of the Y–Pd alloy surfaces is estimated using the chemisorption model of Hammer and Norskov [Nature 376, 238 (1995)]. We show that exposure to air leads to an oxygen induced surface segregation of the Y–Pd alloy, which hinders hydrogen adsorption. © 2001 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Bx Metals, semimetals, and alloys
68.35.Dv Composition, segregation; defects and impurities
81.65.-b Surface treatments
79.60.Dp Adsorbed layers and thin films
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
79.20.Fv Electron impact: Auger emission
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Changes of the local pore space structure quantified in heterogeneous porous media by 1H magnetic resonance relaxation tomography

G. C. Borgia, V. Bortolotti, and P. Fantazzini

J. Appl. Phys. 90, 1155 (2001); http://dx.doi.org/10.1063/1.1380995 (9 pages) | Cited 11 times

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Magnetic resonance imaging and relaxation analysis are combined in a spatially resolved technique (relaxation tomography), which is able to quantify the parameters connected to the local structure in the internal regions of a porous material saturated by water, giving information on the pore space structure beyond the nominal instrumental resolution. Voxel-by-voxel longitudinal (T1) and transverse (T2) relaxation curves are acquired in order to obtain T1, T2 and S(0) maps, where S(0) is the extrapolation to zero time of the total equilibrium magnetization corrected for T2 decay. The proposed method permits evaluation of the porosity (ratio of pore space to total volume), at different length scales, from the sample to the voxel, not all achievable by traditional methods. More striking is its ability to describe how porosity is shared among different classes of surface-to-volume ratios of diffusion cells (the regions that the individual water molecules, starting at their particular positions, can experience by diffusion before relaxing). This is a consequence of the fact that relaxation times of water confined in a porous material can, under favorable circumstances, distinguish regions with the same local porosity but with different pore sizes and connections. So, parameters can be introduced, such as the microporosity fraction, defined as the fraction of the “micropore” volume with respect to the total pore volume, and several voxel average porosities, defined as the average porosities of the voxels characterized by particular classes of diffusion cells. Moreover, the imaging methods enable us to get all this information in a user-defined region of interest. The method has been applied to quantify changes in the structure of carbonate cores with wide distributions of pore sizes induced by repeated cycles of freezing and heating of the sample. With freezing, the microporosity fraction decreases significantly; the voxel average porosity of voxels with T1 shorter than for free water tend to decrease; and the distributions of porosity as functions of T1 show a trend, with much more signal with the T1 of free water, in accordance with the picture suggesting large vugs breaking, with fractures contributing to homogenizing the structure of the pore space and favoring coupling between neighboring pores. © 2001 American Institute of Physics.
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61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials
76.60.Es Relaxation effects

Interaction of hydrogen with gallium vacancies in wurtzite GaN

A. F. Wright

J. Appl. Phys. 90, 1164 (2001); http://dx.doi.org/10.1063/1.1383980 (6 pages) | Cited 28 times

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First-principles techniques are used to investigate the interaction of hydrogen with gallium vacancies in wurtzite GaN. The calculations reveal that hydrogen can either compensate a vacancy by donating an electron to a vacancy acceptor level, or passivate the vacancy by forming a hydrogen-vacancy complex. A gallium vacancy can bind up to four hydrogen atoms, and hydrogen removal energies are computed as a function of the number of hydrogen atoms. Removal energies are found to depend strongly on Fermi level and complexes containing more than two hydrogen atoms are predicted to be unstable in n-type GaN. Hydrogen vibration frequencies are computed and compared with previously reported infrared absorption measurements for hydrogen-implanted GaN. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
71.15.-m Methods of electronic structure calculations

Role of the impurities in production rates of radiation-induced defects in silicon materials and solar cells

Aurangzeb Khan, Masafumi Yamaguchi, Y. Ohshita, N. Dharmarasu, K. Araki, Takao Abe, Hisayoshi Itoh, T. Ohshima, M. Imaizumi, and S. Matsuda

J. Appl. Phys. 90, 1170 (2001); http://dx.doi.org/10.1063/1.1384855 (9 pages) | Cited 11 times

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The present extensive systematic study of defect introduction rates as a function of boron, gallium, oxygen, and carbon concentrations by means of deep level transient spectroscopy has drawn a quite complete picture towards the identification of the dominant radiation-induced defects in Si. The radiation-induced defect EV+0.36 eV has been identified as Ci–Oi complexes. The absence of an EC−0.18 eV complex center in gallium-doped samples and the linear dependence of its introduction rates on both the boron and oxygen content fixed its identification as the Bi–Oi complex in boron-doped Si. One of the technologically important results of present study is that the gallium appears to strongly suppress the radiation induced defects, especially hole level EV+0.36 eV (Ci–Oi), which is thought to act as a recombination center as well as the dominant compensating center at EC−0.18 eV (Bi–Oi). As a result, the effects of lifetime degradation and carrier removal could be partially offset to higher radiation fluences by using Ga as a dopant instead of boron in Si space solar cells. The anneal out of the new hole level EV+0.18 eV in gallium-doped samples at around 350 °C, together with recovery of free carrier concentration, suggests that this level may act as a donor-like center which compensates free carrier concentration in gallium-doped Si. © 2001 American Institute of Physics.
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84.60.Jt Photoelectric conversion
81.05.Cy Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
71.55.Cn Elemental semiconductors

Buried oxide and defects in oxygen implanted Si monitored by positron annihilation

A. C. Kruseman, A. van Veen, H. Schut, P. E. Mijnarends, and M. Fujinami

J. Appl. Phys. 90, 1179 (2001); http://dx.doi.org/10.1063/1.1380411 (9 pages) | Cited 6 times

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One- and two-detector Doppler broadening measurements performed on low (∼1014 to 1015 O+/cm2) and high dose (∼1017 to 1018 O+/cm2) oxygen-irradiated Si using variable-energy slow positrons are analyzed in terms of S and W parameters. After annealing the low-dose samples at 800 °C, large VxOy complexes are formed at depths around 400 nm. These complexes produce a clear-cut signature when the ratio of S to that of defect-free bulk Si is plotted. Similar behavior is found for samples irradiated with 2 and 4×1017 O+/cm2 and annealed at 1000 °C. After irradiation with 1.7×1018 O+/cm2 and anneal at 1350 °C a 170 nm thick almost-bulk-quality Si surface layer is formed on top of a 430 nm thick buried oxide layer. This method of preparation is called separation by implantation of oxygen. S−W measurements show that the surface layer contains electrically inactive VxOy complexes not seen by electron microscopy. A method is presented to decompose the Doppler broadening line shape into contributions of the bulk, surface, and defect. © 2001 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Fe Electron and positron radiation effects
78.70.Bj Positron annihilation
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
61.82.Fk Semiconductors

Shear strength measurements in the TiAl-based alloy Ti–48Al–2Nb–2Cr–1B during shock loading

J. C. F. Millett, N. K. Bourne, and I. P. Jones

J. Appl. Phys. 90, 1188 (2001); http://dx.doi.org/10.1063/1.1381557 (4 pages) | Cited 7 times

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The lateral stress in a titanium aluminide alloy has been investigated under different impact conditions during shock loading, using embedded manganin stress gauges. From this, the variation of the materials shear strength with longitudinal stress has been determined. Results show that shear strength increases rapidly with increasing impact stress, as would be expected in a material that displays a high degree of work hardening. The results from this alloy have also been compared to those of a similar material, which was tested in a different microstructural state. Significant differences were noted and explained in terms of the variation in phase distribution and grain size. © 2001 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
62.20.-x Mechanical properties of solids
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
46.80.+j Measurement methods and techniques in continuum mechanics of solids

Quantitative imaging of nanoscale mechanical properties using hybrid nanoindentation and force modulation

S. A. Syed Asif, K. J. Wahl, R. J. Colton, and O. L. Warren

J. Appl. Phys. 90, 1192 (2001); http://dx.doi.org/10.1063/1.1380218 (9 pages) | Cited 71 times

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In this article, we present a quantitative stiffness imaging technique and demonstrate its use to directly map the dynamic mechanical properties of materials with nanometer-scale lateral resolution. For the experiments, we use a “hybrid” nanoindenter, coupling depth-sensing nanoindentation with scanning probe imaging capabilities. Force modulation electronics have been added, enhancing instrument sensitivity and enabling measurements of time dependent materials properties (e.g., loss modulus and damping coefficient) not readily obtained with quasi-static indentation techniques. Tip–sample interaction stiffness images are acquired by superimposing a sinusoidal force (∼1 μN) onto the quasi-static imaging force (1.5–2 μN), and recording the displacement amplitude and phase as the surface is scanned. Combining a dynamic model of the indenter (having known mass, damping coefficient, spring stiffness, resonance frequency, and modulation frequency) with the response of the tip–surface interaction, creates maps of complex stiffness. We demonstrate the use of this approach to obtain quantitative storage and loss stiffness images of a fiber-epoxy composite, as well as directly determine the loss and storage moduli from the images using Hertzian contact mechanics. Moduli differences as small as 20% were resolved in the images at loads two orders of magnitude lower than with indentation, and were consistent with measurements made using conventional quasi-static depth-sensing indentation techniques. © 2001 American Institute of Physics.
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07.10.-h Mechanical instruments and equipment
07.79.-v Scanning probe microscopes and components
68.35.Gy Mechanical properties; surface strains
46.80.+j Measurement methods and techniques in continuum mechanics of solids
81.05.Qk Reinforced polymers and polymer-based composites
46.55.+d Tribology and mechanical contacts
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

On the response to shock of foil stress sensors in ceramics

N. K. Bourne

J. Appl. Phys. 90, 1201 (2001); http://dx.doi.org/10.1063/1.1383584 (7 pages) | Cited 1 time

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Measurement of the stress history at a Lagrangian position in a shocked solid has been accomplished by various means including the embedding of a thin metal piezoresistive gauge to equilibrate with the ambient conditions and register a component of the field around it. Some work has shown that such sensors may be used to show the decay of the elastic precursor amplitude recorded within a material with the distance travelled by the wave into it. Recent doubt has been placed upon the validity of such observations by pointing to an apparent increase in stress at small distances being due to an overshoot in the gauge record that results from a finite response time [J. Appl. Phys. 88, 5666 (2001)]. An analysis is presented to indicate in which regimes such effects may be important. It is compared with experiment to show the validity of the model developed. Additionally, it is used to show that some of the measured precursor decay may be a physical phenomenon in certain polycrystalline aluminas. © 2001 American Institute of Physics.
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46.80.+j Measurement methods and techniques in continuum mechanics of solids
07.10.Pz Instruments for strain, force, and torque
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
62.50.-p High-pressure effects in solids and liquids
07.07.Mp Transducers
46.40.-f Vibrations and mechanical waves

Electromigration effect upon the Sn–0.7 wt% Cu/Ni and Sn–3.5 wt% Ag/Ni interfacial reactions

Chih-ming Chen and Sinn-wen Chen

J. Appl. Phys. 90, 1208 (2001); http://dx.doi.org/10.1063/1.1380219 (7 pages) | Cited 46 times

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This study investigates the effect of electromigration upon the interfacial reactions between the promising lead-free solders, Sn–Cu and Sn–Ag, with Ni substrate. Sandwich-type reaction couples, Sn–0.7 wt% Cu/Ni/Sn–0.7 wt% Cu and Sn–3.5 wt% Ag/Ni/Sn–3.5 wt% Ag, were reacted at 160, 180, and 200 °C for various lengths of time with and without the passage of electric currents. Without passage of electric currents through the couples, only one intermetallic compound Ni3Sn4 with ∼7 at. % Cu solubility was found at both interfaces of the Sn–0.7 wt% Cu/Ni couples. With the passage of an electric current of 500 A/cm2 density, the Cu6Sn5 phase was formed at the solder/Ni interface besides the Ni3Sn4 phase. Similar to those without the passage of electric currents, only the Ni3Sn4 phase was found at the Ni/solder interface. Directions of movement of electrons, Sn, and Cu atoms are the same at the solder/Ni interface, and the growth rates of the intermetallic layers were enhanced. At the Ni/solder interface, the electrons flow in the opposite direction of the Sn and Cu movement, and the growth rates of the intermetallic layers were retarded. Only the Ni3Sn4 phase was formed from the Sn–3.5 wt% Ag/Ni interfacial reaction with and without the passage of electric currents. Similar to the Sn–0.7 wt% Cu/Ni system, the movement of electrons enhances or retards the growth rates of the intermetallic layers at the solder/Ni and Ni/solder interfaces, respectively. Calculation results show the apparent effective charge za∗ decreases in magnitude with raising temperatures, which indicates the electromigration effect becomes insignificant at higher temperatures. © 2001 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
66.30.Qa Electromigration
68.35.Fx Diffusion; interface formation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Growth of thin Fe/Fe2O3 films on the Cu(110) surface

Christian Pflitsch, Rudolf David, Laurens K. Verheij, and René Franchy

J. Appl. Phys. 90, 1215 (2001); http://dx.doi.org/10.1063/1.1381558 (7 pages) | Cited 2 times

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The growth of Fe/Fe-oxide double-layers on Cu(110) was studied with thermal energy atom scattering (TEAS), Auger electron spectroscopy, and low-energy electron diffraction (LEED). An iron film with a thickness of about 0.6 nm was evaporated at low temperature (130 K) on a smooth, well-ordered thin film of Fe2O3 prepared on Cu(110). This Fe film is disordered. Ordering of the film was observed at temperatures between 400 and 600 K. At 530 K, a structure corresponding to that of a well-ordered α-Fe(001) surface was observed with TEAS and LEED. Clear evidence was found for a mixing of the Fe and Fe2O3 layers at the interface, already beginning at the deposition temperature of 130 K. With increasing temperature, the mixing of the Fe and Fe2O3 layers became gradually more effective until, at around 600 K, it was essentially completed. Upon annealing the sample to 1000 K the structure of the film changes and a very thin (less than 2 ML) FeO film on top of the Cu(110) surface is obtained. © 2001 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
79.20.Fv Electron impact: Auger emission
75.50.Ee Antiferromagnetics

Modified epitaxy in Co/S/GaAs(001) and comparison with Co/GaAs(001)

Krishna G. Nath, Fumihiko Maeda, Satoru Suzuki, and Yoshio Watanabe

J. Appl. Phys. 90, 1222 (2001); http://dx.doi.org/10.1063/1.1379351 (5 pages) | Cited 7 times

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Due to the S passivation, a modified growth of Co on GaAs(001) has been found. Using reflection high-energy electron diffraction and transmission electron microscopy, we observed the formation of a hcp Co overlayer of approximately 5 nm thickness on S/GaAs(001). In contrast, a similar 5 nm Co film on GaAs(001) shows a bcc structure. The metal-semiconductor interfaces in both systems were found to be different, where Co/S/GaAs(001) showed a relatively more abrupt interface. This epitaxial modification is explained on the basis of the morphology of the initial substrate surface, chemical compositions, the nature of the chemical reaction between adatoms and substrate atoms, and the effect of atomic segregation. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
81.65.Rv Passivation
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Ct Interface structure and roughness

Intrinsic stress in chemical vapor deposited diamond films: An analytical model for the plastic deformation of the Si substrate

J.-h. Jeong, D. Kwon, W.-S. Lee, and Y.-J. Baik

J. Appl. Phys. 90, 1227 (2001); http://dx.doi.org/10.1063/1.1383263 (10 pages) | Cited 11 times

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The intrinsic stress in diamond film deposited on a Si substrate is difficult to measure because high-temperature deposition induces plastic deformation in the Si and so renders useless an elastic solution. In this study, an analytical model is proposed to estimate intrinsic stress using a substrate-curvature technique and considering the plastic deformation of substrate. The stress distribution of the as-deposited film is affected not only by the intrinsic stress of the film but also by the bending and plastic deformation of the substrate. In this model, the distribution is formulated, based on elastic/plastic plate-bending theory, in terms of substrate curvatures, intrinsic stress in the film, and yield stress of the substrate. The intrinsic stress of the film together with the yield stress of the substrate can be obtained from experimentally measured substrate curvatures by solving two equilibrium equations and a moment-relaxation equation describing the film removal. Diamond films were deposited by microwave plasma chemical vapor deposition at varying film thicknesses and deposition temperatures. For the application of the model, the curvature of the film-removed substrate was measured as well as that of as-deposited substrate. The results show that overestimated intrinsic stress can be corrected successfully through this new model. The validity of the results was confirmed by stress measurement using a Raman-peak-shift method. In addition, the generation mechanism of intrinsic stress is analyzed as reflecting a competition between a grain-size effect and nondiamond carbon effect. © 2001 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Grazing incidence x-ray scattering study of the structure of epitaxial Cr/Sn multilayers

Ajay Gupta, Amitesh Paul, Sanghamitra Mukhopadhyay, and Ko Mibu

J. Appl. Phys. 90, 1237 (2001); http://dx.doi.org/10.1063/1.1379776 (5 pages) | Cited 6 times

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The structure of epitaxial Cr/Sn multilayers has been studied experimentally using x-ray reflectivity and x-ray diffuse scattering measurements, as well as theoretically using linear muffin-tin orbital (LMTO) calculations. Measurements show a distinct variation in the structure of the multilayers as the Sn layer thickness increases from 0.4 to 0.6 nm. A decrease in the electron density of the Sn layer and an increase in the jaggedness of the interfaces accompany a partial transformation of the Sn layer from an epitaxial bcc structure to a β-Sn structure, as observed using in situ reflection high energy electron diffraction measurements [K. Mibu, S. Tanaka, and T. Shinjo, J. Phys. Soc. Jpn. 67, 2633 (1998)]. Present measurements along with the LMTO calculations support a structure for the multilayer in which Sn layers grow epitaxially with Cr in a bcc structure with a finite density of steps at the interfaces which causes the average electron density of a Sn layer to decrease. Diffuse scattering measurements give the average distance between steps to be about 50–100 nm. Taking the structure of the epitaxial Sn layer to be bcc, the calculated variation in the lattice strain and Sn layer energy with the thickness of Cr and Sn layers explains qualitatively the range of Cr layer thicknesses for which epitaxial growth is observed. © 2001 American Institute of Physics.
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68.65.Cd Superlattices

Electrical characterization and metallurgical analysis of Pd-containing multilayer contacts on GaN

E. F. Chor, D. Zhang, H. Gong, G. L. Chen, and T. Y. F. Liew

J. Appl. Phys. 90, 1242 (2001); http://dx.doi.org/10.1063/1.1383977 (8 pages) | Cited 18 times

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Ti(250 Å)/Al(2200 Å)/Pd(600 Å)/Au(1600 Å) contact on aqua-regia surface treated n-GaN (Si∼1.0×1019 cm−3) has yielded a minimum specific contact resistance (ρc) of 4.21×10−8 Ω cm2, achieved after thermal annealing at 500 °C for 8 min. This is superior to the most common n-GaN contact, Ti/Al, which has also been studied in the current work and produced a lowest ρc of 4.63×10−6 Ω cm2, obtained after annealing at 700 °C for 2 min. The long-term thermal stability analysis has also revealed that the Ti/Al/Pd/Au contact is more stable than Ti/Al on n-GaN. The projected mean time to 50% increase in ρc(μ50) at 150 °C for the former is 1.22×1012 h, which is higher by about three orders of magnitude than that of the latter at 3.54×109 h. Pd(200 Å)/Ni(300 Å)/Au(2000 Å) contact on boiling aqua-regia surface treated p-GaN (Mg∼1.0×1018 cm−3) has also been investigated and demonstrated a reasonable ohmic behavior with a ρc of 5.03×10−4 Ω cm2 after thermal annealing at 450 °C for 2 min. However, its thermal stability is mediocre with μ50 at 150 °C of only 1.49×103 h. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing

Transient analysis in Al-doped barium strontium titanate thin films grown by pulsed laser deposition

S. Saha and S. B. Krupanidhi

J. Appl. Phys. 90, 1250 (2001); http://dx.doi.org/10.1063/1.1384493 (5 pages) | Cited 9 times

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Thin films of (Ba0.5Sr0.5)TiO3 (BST) with different concentrations of Al doping were grown using a pulsed laser deposition technique. dc leakage properties were studied as a function of Al doping level and compared to that of undoped BST films. With an initial Al doping level of 0.1 at. % which substitutes Ti in the lattice site, the films showed a decrease in the leakage current, however, for 1 at. % Al doping level the leakage current was found to be relatively higher. Current time measurements at elevated temperatures on 1 at. % Al doped BST films revealed space-charge transient type characteristics. A complete analysis of the transient characteristics was carried out to identify the charge transport process through variation of applied electric field and ambient temperature. The result revealed a very low mobility process comparable to ionic motion, and was found responsible for the observed feature. Calculation from ionic diffusivity and charge transport revealed a conduction process associated with an activation energy of around 1 eV. The low mobility charge carriers were identified as oxygen vacancies in motion under the application of electric field. Thus a comprehensive understanding of the charge transport process in highly acceptor doped BST was developed and it was conclusive that the excess of oxygen vacancies created by intentional Al doping give rise to space-charge transient type characteristics. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.J- Point defects and defect clusters
77.22.Jp Dielectric breakdown and space-charge effects
73.50.Dn Low-field transport and mobility; piezoresistance
66.30.H- Self-diffusion and ionic conduction in nonmetals

Methods for surface roughness elimination from thermal-wave frequency scans in thermally inhomogeneous solids

Lena Nicolaides and Andreas Mandelis

J. Appl. Phys. 90, 1255 (2001); http://dx.doi.org/10.1063/1.1383579 (11 pages) | Cited 10 times

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Two approaches for eliminating surface roughness in the thermal-wave frequency response of inhomogeneous solids are developed. The first approach is based on the theoretical formulation of roughness as an effective homogeneous overlayer and is adequate for eliminating low roughness levels from experimental data. The second approach models roughness as random spatial white noise resulting in a linear superposition of logarithmic-Gaussian distributions representing roughness scales in the spatial frequency spectrum and in the modulation frequency domain. Two scales of roughness on the surface of hardened AISI 8620 steel with the same hardness depth profiles are found and the experimental data are reconstructed to retrieve similar inhomogeneous thermal diffusivity depth profiles. © 2001 American Institute of Physics.
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07.20.-n Thermal instruments and apparatus
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains

In-plane optical anisotropy of symmetric and asymmetric (001) GaAs/Al(Ga)As superlattices and quantum wells

Xiaoling Ye, Y. H. Chen, J. Z. Wang, B. Xu, Z. G. Wang, and Z. Yang

J. Appl. Phys. 90, 1266 (2001); http://dx.doi.org/10.1063/1.1383018 (5 pages) | Cited 4 times

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Two sensitive polarized spectroscopies, reflectance difference spectroscopy and photocurrent difference spectroscopy, are used to study the characteristic of the in-plane optical anisotropy in the symmetric and the asymmetric (001) GaAs/Al(Ga)As superlattices (SLs). The anisotropy spectra of the symmetric and the asymmetric SLs show significant difference: for symmetric ones, the anisotropies of the 1HH→1E transition (1H1E) and 1L1E are dominant, and they are always approximately equal and opposite; while for asymmetric ones, the anisotropy of 1H1E is much less than that of 1L1E and 2H1E, and the anisotropy of 3H2E is very strong. The calculated anisotropy spectra within the envelope function model agree with the experimental results, and a perturbation approach is used to understand the role of the electric field and the interface potential in the anisotropy. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
78.67.De Quantum wells
78.20.Jq Electro-optical effects
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
73.63.Hs Quantum wells
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