Volume 89, Issue 11, 01 June 2001
- applied physics reviews
- lasers, optics, and optoelectronics (pacs 42)
- plasmas and electrical discharges (pacs 51-52)
- structural, mechanical thermodynamic, and optical properties of condensed matter (pacs 61-68, 78)
- electronic structure and transport (pacs 71-73)
- magnetism and superconductivity (pacs 74-76)
- dielectrics and ferroelectricity (pacs 77)
- nanoscale science and design
- device physics (pacs 85)
- interdisciplinary and general physics (pacs 1-41, 43-47, 79, 81-84, 89-99)
- proceedings of the 8th joint magnetism and magnetic materials-intermag conference
- manganites i
- growth of magnetic tunnel junctions
- surface effects
- spin dynamics i
- numerical methods
- spin polarized tunneling and injection in semiconductors and oxides
- magnetic microscopy and imaging i
- spin dynamics ii
- magnetic multilayers i
- charge correlations in ferromagnetic cmr manganites
- spin transport in nanotubes and novel barriers for magnetic tunnel junctions
- electronic structure: metals, half metals, insulators
- exchange biasing
- nano-oxide layers and specular scattering in spin valves
- manganite thin films
- micromagnetics i
- magnetic semiconductors and heterostructures i
- spin glasses and frustrated systems
- magnetic multilayers ii
- high frequency probes in magnetic nanostructures
- electron transport in spin valves
- ultra thin films
- magnetic microscopy and imaging ii
- correlated electrons
- anisotropic magnetoresistance, magnetoimpedance, and hall effect
- magnetic imaging iii
- preisach models and hysteresis
- exchange biasing: domains and ae structure
- magnetic semiconductors and heterostructures ii
- granular and cpp gmr and spin-valve transistors
- electronic structure
- critical phenomena
- toward magnetic tunnel devices
- structural characterization of magnetic tunnel junctions
- thin magnetic films
- manganites ii
- symposium on spin transport
- magnetization processes
- superconductivity i
- magnetic multilayers ii
- exchange biasing, dynamics, and structural effects ii
- fundamentals of magnetic tunnel junctions
- micromagnetics ii
- magnetic aspects of spin valves
- correlated electrons and spin dynamics
- superconductivity ii
- other magnetoresistive oxides
Index of content:
- APPLIED PHYSICS REVIEWS
89(2001); http://dx.doi.org/10.1063/1.1368156View Description Hide Description
We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors:GaAs,GaSb,GaP,GaN,AlAs,AlSb,AlP,AlN,InAs,InSb,InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Analysis of the scattered light distribution of a tightly focused laser beam by a particle near a substrate89(2001); http://dx.doi.org/10.1063/1.1365941View Description Hide Description
We present a calculation method to analyze the scatteredelectromagnetic field by a particle near a substrate. The method is based on the iterative calculations of the extended Mie scatteringtheory [J. P. Barton, D. R. Alexander, and S. A. Schaub, J. Appl. Phys. 64, 1632 (1988)] and of plane-wave decompositions in order to include the multi-scattering between the particle and the substrate. The method is applicable to an arbitrary incident beam and an arbitrary distance between the particle and the substrate. It is possible to analyze the interaction between a particle and a multilayered substrate. We present the electromagnetic field distribution when the particle near the substrate is illuminated with focused laser beam.
89(2001); http://dx.doi.org/10.1063/1.1367314View Description Hide Description
Resonance of space-charge field can occur in photorefractive polymers through a moving fringe and can be described by a forced oscillation equation with damping. The resonance frequency and the magnitudes of both the amplitude and the imaginary part of the space-charge field at the resonance frequency are functions of three experimental parameters: total incident intensity, applied electric field, and grating wave vector. Thus, the diffraction efficiency of grating and the gain coefficient of two-wave mixing are dependent on the three experimental parameters. Our theory can also be applied to inorganic photorefractive crystals.
89(2001); http://dx.doi.org/10.1063/1.1370364View Description Hide Description
We fabricate semi-insulating InGaAs/GaAs multiple quantum wells and observe the excitonic enhancement of the photorefractivity in the Franz–Keldysh geometry at wavelengths of 0.92–0.94 μm. A maximum two-wave mixing gain of 138 and a maximum diffraction efficiency of are obtained. The saturation intensity and the spatial resolution are also measured by four-wave mixing. The diffraction efficiency is saturated at a high external electric field. The dominant cause of this saturation is the deviation of the excitonic electroabsorption from its quadratic law.
Determination of the emission zone in a single-layer polymer light-emitting diode through optical measurements89(2001); http://dx.doi.org/10.1063/1.1350998View Description Hide Description
We study the emission zone in a single-layer polymer light-emitting diode. The emission zone is found by studying the angular distribution of the electroluminescence. The emission is modeled by accounting for optical interference. We account for birefringence of the anode layer in our model. The active polymer was, however, found to be isotropic. The anode consists of a single-layer of the conducting polymer complex poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonate) (PEDOT-PSS), with enhanced conductivity. As a cathode we use plain aluminum. By using only PEDOT-PSS we avoid having a thin metal layer or indium-tin-oxide as the anode in the path of the escaping light. The active material is a substituted polythiophene with excellent film forming properties. A comparison between the experimental and calculated angular distribution of light emission from a single-layered polymer light-emitting diode was shown to be in good agreement for the spectral region studied. By assuming a distribution of the emission zone, we deduce the position as well as the width of the zone.
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
89(2001); http://dx.doi.org/10.1063/1.1359754View Description Hide Description
Electron production rate and electron density in cold optically pumped CO–Ar and plasmas in the presence of small amounts of and NO have been measured using a Thomson discharge probe and microwaveattenuation. Nonequilibrium ionization in the plasmas is produced by an associative ionization mechanism in collisions of highly vibrationally excited CO molecules. It is shown that adding small amounts of or NO (50–100 mTorr) to the baseline gas mixtures at results in an increase of the electron density by up to a factor of 20–40 (from to This occurs while the electron production rate either decreases (as in the presence of or remains nearly constant within a factor of 2 (as in the presence of NO). It is also shown that the electron–ion recombination rates inferred from these measurements decrease by two to three orders of magnitude compared to their baseline values (with no additives in the cell), down to with 50–100 mTorr of oxygen or nitric oxide added to the baseline CO–Ar mixture, and with 75–100 mTorr of or NO added to the baseline mixture. The overall electron–ion removal rates in the presence of equal amounts of or NO additives turn out to be very close, which shows that the effect of electron attachment to oxygen at these conditions is negligible. These results suggest a novel method of electron density control in cold laser-sustained steady-state plasmas and open a possibility of sustaining stable high-pressure nonequilibrium plasmas at high electron densities and low plasma power budget.
89(2001); http://dx.doi.org/10.1063/1.1359755View Description Hide Description
This article presents an experimental demonstration of a high-pressure unconditionally stable nonequilibrium molecular plasma sustained by a combination of a continuous wave CO laser and a sub-breakdown radio frequency (rf) electric field. The plasma is sustained in a mixture containing trace amounts of NO or at pressures of The initial ionization of the gases is produced by an associative ionization mechanism in collisions of two CO molecules excited to high vibrational levels by resonance absorption of the CO laser radiation with subsequent vibration-vibration pumping. Further vibrational excitation of both CO and is produced by free electrons heated by the applied rf field, which in turn produces additional ionization of these species by the associative ionization mechanism. In the present experiments, the reduced electric field, is sufficiently low to preclude field-induced electron impact ionization. Unconditional stability of the resultant cold molecular plasma is enabled by the negative feedback between gas heating and the associative ionization rate. Trace amounts of nitric oxide or oxygen added to the baseline gas mixture considerably reduce the electron–ion dissociative recombination rate and thereby significantly increase the initial electron density. This allows triggering of the rf power coupling to the vibrational energy modes of the gas mixture. Vibrational level populations of CO and are monitored by infrared emission spectroscopy and spontaneous Raman spectroscopy. The experiments demonstrate that the use of a sub-breakdown rf field in addition to the CO laser allows an increase of the plasma volume by about an order of magnitude. Also, CO infrared emission spectra show that with the rf voltage turned on the number of vibrationally excited CO molecules along the line of sight increase by a factor of 3–7. Finally, spontaneous Raman spectra of show that with the rf voltage the vibrational temperature of nitrogen increases by up to 30%. This novel energy efficient approach allows sustaining large-volume high-pressure molecular plasmas without the use of a high-power CO laser. This opens a possibility of using the present technique for high-yield plasma chemical synthesis and plasma material processing.
89(2001); http://dx.doi.org/10.1063/1.1368397View Description Hide Description
Charging of micron-size particulates, often appearing in fluorocarbon plasma etching experiments, is considered. It is shown that in inductively coupled and microwave slot-excited plasmas of and Ar gas mixtures, the equilibrium particle charge and charge relaxation processes are controlled by a combination of microscopic electron, atomic and and molecular ion and currents. The impact of molecular ion currents on the particulate charging and charge relaxation processes is analyzed. It is revealed that in low-power (<0.5 kW) microwave slot-excited plasmas, the impact of the combined molecular ion current to the total positive microscopic current on the particle can be as high as 40%. The particulate charge relaxation rate in fluorocarbon plasmas appears to exceed which is almost one order of magnitude higher than that from purely argon plasmas. This can be attributed to the impact of positive currents of fluorocarbon molecular ions, as well as to the electron density fluctuations with particle charge, associated with electron capture and release by the particulates.
89(2001); http://dx.doi.org/10.1063/1.1364653View Description Hide Description
The prebreakdown phenomena and the formation process of the glow discharge in a low-pressure Ar gas were investigated under a uniform field gap. Prebreakdown phenomena were observed for (where p is pressure, d the gap distance) in Ar gas under conditions of a slowly increasing voltage. It was observed that the prebreakdown phenomena formed pulse discharges up to the transition to the glow discharge. The amplitudes of the photon and current pulses due to the pulse discharge increased with time, and then decreased as soon as the transition to a steady glow discharge occurred. When the overvoltage or external series resistance was increased, the pulse amplitudes increased with the applied voltage and decreased with the resistance. The characteristics of the prebreakdown phenomena were changed by the shape of the electrodes. The formation mechanism of the glow discharge can be qualitatively explained by that of the streamer in a high-pressuredischarge. The transient glow discharge was observed, and its duration increased with an increase in resistance. The instability of the glow discharge was controlled by three factors, namely, Kaufmann’s criterion, the Child–Langmuir law, and the density balance between the production and removal rates of electrons.
89(2001); http://dx.doi.org/10.1063/1.1365436View Description Hide Description
We propose a semianalytical ion dynamicsmodel for a collisionless radio-frequency biased sheath. The model uses bulk plasma and electrodeboundary conditions to predict the ion impact energy distribution and electrical properties of the sheath. The proposed model accounts for ion inertia and ion current modulation at bias frequencies that are of the same order of magnitude as the ion plasma frequency. A relaxation equation for ion currentoscillations is derived, which is coupled with a damped potential equation in order to model ion inertia effects. We find that inclusion of ion current modulation in the sheathmodel shows marked improvements in the predictions of the sheathelectrical properties and ion energy distribution function.
- STRUCTURAL, MECHANICAL THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER (PACS 61-68, 78)
Large-scale well aligned carbon nitride nanotube films: Low temperature growth and electron field emission89(2001); http://dx.doi.org/10.1063/1.1370114View Description Hide Description
Large-scale well aligned carbon nitride nanotubefilms (6 cm in diameter), which are easily processed and show potential for nanomanipulation, have been synthesized by microwave plasma enhanced chemical vapor deposition at a relatively low temperature of 550 °C. The characterization, using transmission electron microscopy and electron energy loss spectroscopy, shows that the nanotubes are polymerized by nanobells with nitrogen concentration of 10%. We propose a push-out growth mechanism for the formation of the special polymerized nanobell structure. A turn-on field of electron emission as low as 0.8 V/μm is obtained. Fowler–Nordheim, consisting of two straight lines with a gentle slope at low field and a steep one at relatively high field, are interpreted based on a top side emission mechanism related to the nanobell structures. No current saturation is found in the films.
89(2001); http://dx.doi.org/10.1063/1.1367406View Description Hide Description
We report on a high-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy study of the microstructure of CdTethin films epitaxially grown on single-crystal hexagonal CdS and cubic CdTe substrates. We find that the different structures of the substrates do not make a great structural difference on the grownCdTefilms; i.e., on both substrates, the grownCdTefilms have a cubic structure and high density of planar defects near the interface regions. At the CdTe/CdS interface, interdiffusion occurs, forming and alloys. These alloys lead to significantly reduced mismatch at the interface.
89(2001); http://dx.doi.org/10.1063/1.1368176View Description Hide Description
The shape effect of anisotropic-shaped microvoid defects in Czochralski-grown silicon wafers on the intensity of laser scattering has been investigated. The size and shape of the defects were examined by means of transmission electron microscopy. Octahedral voids in conventional (nitrogen-undoped) wafers showed an almost isotropic scatteringproperty under the incident condition of a p-polarization beam. On the other hand, parallelepiped-plate-shaped voids in nitrogen-doped wafers showed an anisotropicscatteringproperty on both p- and s-polarized components of scattered light, depending strongly on the incident laser direction. The measured results were explained not by scattering calculation using Born approximation but by calculation based on Rayleigh scattering. It was found that the s component is explained by an inclination of a dipole moment induced on a defect from the scattering plane. Furthermore, using numerical electromagnetic analysis it was shown that the asymmetric behavior of the s component on the parallelepiped-plate voids is ascribed to the parallelepiped shape effect. These results suggest that correction of the scattering intensity is necessary to evaluate the size and volume of anisotropic-shaped defects from the scattered intensity.
89(2001); http://dx.doi.org/10.1063/1.1359426View Description Hide Description
We have systematically investigated the effect of C and B sequential coimplantation on B-related acceptors and deep levels in 4H–SiC using thermal admittance spectroscopy. By increasing the concentration of coimplanted C, the density of deep levels decreased and was completely suppressed for a C and B ratio of 1:1. Moreover, the density and ionization energy of B acceptors increased and decreased, respectively, with increasing C concentration. However, we found that excess C content leads to the formation of a complex defect. Capacitance–voltage results also support the expected increase in the free hole concentration with increasing concentration of the coimplanted C atoms, which is followed by a decrease in the concentration under C-rich conditions. This is in reasonable agreement with the behavior of the B acceptors and deep defect levels. Therefore, the concentration of coimplanted C atoms is considered to be very sensitive to the formation of the B acceptor levels.
Strain-induced transformation of amorphous spherical precipitates into platelets: Application to oxide particles in silicon89(2001); http://dx.doi.org/10.1063/1.1342806View Description Hide Description
The spherical shape of an amorphous precipitate becomes unstable if the combination of precipitate radius R and pressureP exceeds some critical value. This critical value was found to be about 4.44 where G is the matrix shear modulus and σ is the specific energy of the precipitate/matrix interface. Once this instability criterion is fulfilled, the initially spherical particle will reduce the total free energy (the sum of strain energy and the surface energy) by becoming a thin oblate spheroid (effectively, a platelet). The actual pressureP in the course of oxygen precipitation in silicon is controlled by a high self-interstitial supersaturation caused by emission of self-interstitials by growing precipitates. The duration of annealing necessary to reach the stage of collapse of spheres into platelets is calculated as a function of temperature and the precipitate density. Calculated results are compatible with the experimentally observed annealing conditions for platelet formation. Another important example of sphere to platelet transformation is microdefect formation in vacancy-type silicon. In this case a large negative value of P is sufficient to induce collapse.
Self-annihilation of antiphase boundaries in GaAs epilayers on Ge substrates grown by metal-organic vapor-phase epitaxy89(2001); http://dx.doi.org/10.1063/1.1368870View Description Hide Description
The self-annihilation of antiphase boundaries (APBs) in GaAsepitaxial layers grown by low-pressure metal-organic vapor-phase epitaxy on Ge substrates is studied by several characterization techniques. Cross-sectional transmission electron microscopy shows that antiphase domain free GaAsgrowth on Ge was possible due to the proper selection of the growth parameters. The antiphase boundaries annihilate with each other after a thick 3 μm layer of GaAsgrowth on a Ge substrate as observed by scanning electron microscopy studies. Double crystal x-ray diffraction data shows a slight compression of GaAs on Ge, and the full width at half maximum decreases with increasing growth temperatures. This confirms that the APBs annihilate inside the GaAsepitaxialfilms. Low temperature photoluminescence measurements confirm the self-annihilation of the APBs at low temperature growth and the generation of APBs at higher growth temperatures.
Investigation of the cut location in hydrogen implantation induced silicon surface layer exfoliation89(2001); http://dx.doi.org/10.1063/1.1353561View Description Hide Description
The physical mechanisms of hydrogen induced silicon surface layer exfoliation were investigated using the combination of ion beamanalysis,secondary ion mass spectroscopy(SIMS),scanning electron microscopy(SEM), and cross section transmission electron microscopy (XTEM). A 〈100〉 oriented silicon wafer was implanted with 175 keV protons to a dose of The implanted wafer was bonded to a silicon oxide capped 〈100〉 silicon wafer and then heated to an elevated temperature of 600 °C to produce exfoliation. The hydrogen-implanted sample was analyzed in the as-implanted state as well as after the cleavage of the silicon wafer. The depth distribution of the implantation damage was monitored by Rutherford backscattering spectrometry (RBS) in channeling condition and XTEM imaging. Elastic recoil detection analysis and SIMS was performed to examine the hydrogen depth distribution. Cross section SEM and RBS channeling was used to measure the thickness of the exfoliated layer after cleavage. A comparison of the results deduced from the methods listed shows conclusively that the cleavage of the silicon wafer takes place above the hydrogen concentration peak near the implantation damage peak, revealing the crucial role of the implantation damage in the crystal in terms of hydrogen induced cleavage of the silicon crystal. The stress and strain field in the proton-implantation induced damage region of the silicon crystal is proposed to explain the observed results.
89(2001); http://dx.doi.org/10.1063/1.1363682View Description Hide Description
The charge states of divacancies induced by 5 MeV self-implantation of dopedsilicon were investigated by positron annihilation methods. For low doping concentrations, results were found to be in agreement with the predictions of Fermi statistics. For the case of heavily boron-doped silicon an anomalous single-negative divacancy charge state was detected. We attribute this to the introduction of new levels in the band gap, due to the capture of boron by divacancies, resulting in a boron-divacancy complex. Detailed analysis of positron annihilation spectra suggests that the boron does not reside on a nearest-neighbor site to the divacancy. Isothermal annealing experiments yield activation energy of for migration of this defect.
89(2001); http://dx.doi.org/10.1063/1.1355699View Description Hide Description
It is important to understand the distribution of recoil-implanted atoms and the impact on device performance when ion implantation is performed at a high dose through surface materials into single crystalline silicon. For example, in ultralarge scale integration impurity ions are often implanted through a thin layer of screen oxide and some of the oxygen atoms are inevitably recoil implanted into single-crystalline silicon. Theoretical and experimental studies have been performed to investigate this phenomenon. We have modified the Monte Carlo ion implant simulator, UT-Marlowe (B. Obradovic, G. Wang, Y. Chen, D. Li, C. Snell, and A. F. Tasch, UT-MARLOWE Manual, 1999), which is based on the binary collision approximation, to follow the full cascade and to dynamically modify the stoichiometry of the Si layer as oxygen atoms are knocked into it. CPU reduction techniques are used to relieve the demand on computational power when such a full cascade simulation is involved. Secondary ion mass spectrometry(SIMS) profiles of oxygen have been carefully obtained for high dose As and implants at different energies through oxide layers of various thicknesses, and the simulated oxygen profiles are found to agree very well with the SIMS data.
89(2001); http://dx.doi.org/10.1063/1.1369398View Description Hide Description
We report on the effects of photon (γ) and electron (β) irradiation in a dose range extending from 100 to in a variety of silica samples studied by electron paramagnetic resonance. The centers and a weak intensity satellite signal of their resonance line were generated both in γ- and in β-irradiated samples. We investigated the dependence of their intensity on the irradiation dose. Evidence of the existence of a common generation mechanism for the related paramagneticpoint defects is found. These defects are induced mainly through the conversion of precursors except at very high doses, where the direct activation from the unperturbed matrix is concurrent. Our data support the model attributing the satellite signal to the weak hyperfine structure of the center arising from interaction with a second nearest neighbor nuclear spin.