bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of mixture equations for dielectric-magnetic composites
Authors: Musal H. M. , Hahn H. T. , Bush G. G.
Published: July 2002

Mixture equations relate the effective macroscopic electromagnetic properties (dielectric constant and magnetic permeability) of a composite material to the intrinsic microscopic electromagnetic properties of its constituents. The predictions of mixture equations in popular use generally agree with each other when particles are widely separated (small volume fraction), but begin to diverge when the volume fraction of particles in the composite is greater than 10%. This paper reviews the assumptions and characteristics of different representative mixture equations. The validity of these mixture equations for application to magnetic composites was tested by comparing their predictions of macroscopic electromagnetic properties to VHF and UHF measurements of these properties for a series of well-characterized dielectric-magnetic composite samples comprised of ferrite particles in an epoxy binder. The investigation emphasized the parameter regimes where large disparities between the predictions of the various equations exist, namely, large volume fraction of particles, complex dielectric constant and magnetic permeability (lossy material), and large contrast ratio between particle and binder properties. Correlation and lack of correlation between the mixture equation predictions and experimental data are shown.
Ion-pair upconversion pumped laser emission in Er3+ ions in YAG, YLF, SrF2, and CaF2 crystals
Authors: Pollack S. A. , Chang D. B.
Published: July 2002

Ion-pair upconversion pumped laser emission at 2.7–2.9 μm between the 4I11/2 and 4I13/2 excited states of triply ionized erbium ions (Er3+) has been studied at 300 and 100 K in YLF, YAG, SrF2, and CaF2 hosts. Laser action was obtained by pumping directly into the transition’s terminal laser level. In all four hosts, the lifetime of the 4I13/2 state is longer than that of the 4I11/2 state, by factors of 5 and 80 for the first two, and factors of (5)/(2) and 2 for the SrF2 and CaF2, respectively. The absorption coefficient for the 1.533-μm pump radiation is comparable in YLF, SrF2, and CaF2, but is larger by a factor of 3 in YAG. At room temperature the threshold pump energy for YAG is larger by a factor of 10 than for CaF2, SrF2, and YLF. Interpretation of the lasing delay times at threshold pumping levels in terms of a simple analytic model gives for the upconversion coefficients: αYLF =1.2×10−17 cm3 s−1, αYAG =5.4×10−17 cm3 s−1, αSrF2 =2.9×10−15 cm3 s−1, and αCaF2 =3.2×10−15 cm3 s−1. Nonoptimized upconversion pumped laser efficiency in Er:YLF was measured at 110 K to be 17%. A peculiar upconversion pumped lasing behavior was observed in Er:YAG at low temperatures.
Light-induced migration of charge in photorefractive Bi12SiO20 and Bi12GeO20 crystals
Authors: Jani M. G. , Halliburton L. E.
Published: July 2002

The photoinduced redistribution of charge has been characterized in Bi12GeO20 and Bi12SiO20 crystals using electron spin resonance, thermally stimulated luminescence, and optical absorption techniques. Excitation with 350-nm light at 77 K converts Fe3+ ions to Fe2+ ions. The source of electrons (i.e., the hole traps) is not known, but they may be other impurities or intrinsic defects such as vacancies or antisite cations. As the crystals are warmed to room temperature, recovery of the Fe3+ ions correlates with thermoluminescence peaks at 145, 165, and 245 K. We postulate that Fe2+ ions are the recombination site and that each thermoluminescence peak corresponds to the release of holes from a different trap. Our results suggest that Fe3+ ions may play an important role in the photorefractive effect in these materials.
A framework for modeling the cathode fall illustrated with a single beam model
Authors: Sommerer T. J. , Lawler J. E. , Hitchon W. N. G.
Published: July 2002

A framework for a model of the cathode fall region of a dc glow discharge is presented, and a simple model is solved as an illustration. An extremum condition independent of the model is placed on the electric field behavior to produce a unique solution that agrees with experiment. The zeroth and second moments of the Boltzmann equation are solved for the electrons with a self-consistent electric field. A single-beam model with only two parameters (number density and beam velocity) is assumed for the electron distribution function. Ion motion is modeled with a parametric fit to known ion mobilities. The model is solved for conditions corresponding to the experimental results and to Monte Carlo simulations of Doughty, Den Hartog, and Lawler [Phys. Rev. Lett. 58, 2668 (1987)]. The results are in good qualitative and ‘‘factor-of-two’’ quantitative agreement with the published results.
A study of octupoles as correctors
Authors: Shao Zhifeng , Beck Vernon , Crewe A. V.
Published: July 2002

In an electron microscope equipped with sextupole correctors the ultimate resolution is limited by the fifth-order spherical aberration of the optical system used to form the electron probe. We have examined the possibilities of using octupoles in order to correct this fifth-order spherical aberration. We find that for an electrostatic octupole, the fifth-order aberration is symmetric, while for a magnetic octupole the fifth-order aberration is asymmetric but it is possible to reduce this asymmetry by properly arranging the initial conditions. Based on these results, we propose a system which could be used to correct fifth-order aberration in a probe forming system equipped with a sextupole corrector.
Range of validity of the surface-photovoltage diffusion length measurement: A computer simulation
Authors: McElheny P. J. , Arch J. K. , Lin H.-S. , Fonash S. J.
Published: July 2002

The surface-photovoltage diffusion length measurement is analyzed in depth to determine its range of applicability and cause of failure when it no longer yields the diffusion length. It is shown that this technique is generally not valid for amorphous materials, but is highly useful for crystalline semiconductors. The problem of applicability of the surface-photovoltage diffusion length measurement to amorphous materials is not alleviated by using thicker samples or by using chopped light illumination through the back. It is determined that the validity of the surface-photovoltage method requires a density of midgap states <1013 cm−3 eV−1.
Lasing characteristics of Er3+-doped silica fibers from 1553 up to 1603 nm
Authors: Kimura Yasuo , Nakazawa Masataka
Published: July 2002

The laser oscillations from 1553 up to 1603 nm have been demonstrated in Er3+-doped silica fibers with a doping rate of 2500 ppm. Wide changes in laser oscillation wavelengths are due to broad splitting of the upper sublevels in the 4I15/2 manifold, caused by the random structure of the silica matrix. It has been shown that unpumped parts of the Er3+ ions in the end pumped fiber laser configuration play an important role in the wavelength changes of the laser oscillation. For an absorbed pump power of 320 mW at 514 nm, output power of 0.5 mW was obtained at 1603 nm.
A study of excess current in an Esaki junction
Authors: Chakraborty P. K. , Biswas J. C.
Published: July 2002

The objective of this paper is to provide a theoretical analysis regarding excess current in an Esaki junction. The analysis makes use of the crystal momentum representation, and takes into account, among other things, three-dimensional energy-momentum conservations. The treatment is more general than similar studies reported earlier, and is likely to explain the experimental data better than earlier studies.
Behavior of downstream plasmas generated in a microwave plasma chemical-vapor deposition reactor
Authors: Shufflebotham P. K. , Thomson D. J. , Card H. C.
Published: July 2002

The behavior of electron-cyclotron resonant (ECR) and non-ECR H2 plasmas generated in a microwave plasma chemical-vapor deposition reactor have been studied as a function of magnetic field strength and absorbed microwave power. Plasma diagnostics were performed with a planar electrostatic probe, microwave power measurements, and visual inspection. The probe measurements were concerned with the plasma impingent on a sample table placed downstream from the active core of the plasma. ECR plasmas were found to be more efficient, stable, uniform, and dense than plasmas not generated by ECR. All properties of the ECR plasmas measured by the downstream probe showed a gentle monotonic increase with the magnetic field strength. This was attributed to a reduction in the spacing between the probe and the resonant zone. In the ECR plasmas the average electron temperature was 3 eV and the average density was 1016 m−3. The degree of ionization was on the order of 5×10−4.
Photoluminescence study of the annealing behavior of transmuted impurities in neutron-transmutation-doped semi-insulating GaAs
Authors: Satoh M. , Kuriyama K. , Makita Y.
Published: July 2002

In neutron-transmutation-doped GaAs irradiated with various fast neutron fluences, the annealing behavior of band-germanium acceptor [Ge(B-A)] transitions has been evaluated using the photoluminescence technique. In the fast neutron irradiation of ≤7.0×1017 cm−2, a few percent of transmuted Ge atoms behave as acceptors in As sites and more than 98% of the transmuted Ge atoms activate as donors in Ga sites. In the fast neutron irradiation of 3.7×1018 cm−2, the shift of Ge(B-A) transitions towards lower energies originates from the band-edge distortion. Removing the band-edge distortion by annealing above 790 °C leads to the increase in the Ge acceptor, accompanied by an increase of the peak intensity of Ge(B-A) transitions. The lower electrical activation of transmuted impurities (∼75%) arises from the high-temperature annealing required to remove the radiation damage. On annealing out the radiation damage, the peak shift of Ge(B-A) transitions based on the increase in the free carrier is discussed using the Burstein–Moss model.
Diffusive processes in the cross-field flow of intense plasma beams
Authors: Newberger B. , Rostoker N.
Published: July 2002

We consider magnetic field diffusion in the presence of strongly magnetized electrons (ωceτc 0>1) as a mechanism for the rapid penetration observed in cross-field flows of high-β plasma beams. The diffusion has been investigated in several cases which are amenable to analytic solution. The flux penetration times are found to be insensitive to the particular configuration. Comparison with two experiments is made. Agreement within the limits of the experiments is found. Both require an anomalous collision rate which is consistent with observed fluctuations in one case but apparently not the other.
Passivation of bulk trapping levels in cadmium telluride by proton implantation
Authors: Biglari B. , Samimi M. , Hage-Ali M. , Koebel J. M. , Siffert P.
Published: July 2002

A passivation of deep levels in the bulk has been observed by thermally stimulated currents and photoinduced current transient spectroscopy for well-defined conditions of hydrogen implantation into high-resistivity, chlorine-compensated traveling heater method grown CdTe crystals. The influence of ion-induced damage during implantation has been evaluated and the passivation effect on deep levels in the bulk, especially in the range 0.3–0.4 eV, has been clearly identified. This passivation introduces a strong increase of the mobility carrier lifetime product, as shown by photoconductivity measurements, as well as an increase of resistivity. Finally, the stability of this compensation by hydrogen has been investigated.
Light-induced dark decays of photorefractive gratings and their observation in Bi12SiO20
Authors: Strohkendl F. P.
Published: July 2002

We find that the temporal shape and speed of dark decays of photorefractive gratings depend on the light intensity used to write the grating. We attribute this to the fact that the population distribution of impurity levels inside the crystal under illumination is light intensity dependent and differs from the thermal equilibrium distribution. We use a simple extension of the band conduction model of Kukhtarev which considers an additional shallow trap level to analyze dark decays observed in a Bi12SiO20 crystal. We find the excitation rate for thermally excited charge carriers and their diffusion length when this crystal is under illumination and obtain estimates for the shallow trap density (∼1.5×1015 cm−3) and the shallow trap occupation lifetime (∼0.2 s). We identify the shallow trap as a shallow hole trap by comparing the results from our dark decay analysis to results obtained from beam-coupling and light-induced erasure measurements.
Effects of capping layer material and recrystallization conditions on the characteristics of silicon-on-insulator metal-oxide-semiconductor transistors in laser-recrystallized silicon films
Authors: Wouters D. J. , Maes H. E.
Published: July 2002

A study is presented of silicon-on-insulator (SOI) films obtained by laser recrystallization of polysilicon films using silicon nitride or oxynitride as a capping layer material and with either a continuous or a periodic antireflective capping structure. Different laser scan conditions are used. Electrical characterization of these recrystallized Si layers is performed on five-terminal SOI metal-oxide-semiconductor field-effect transistors by directly probing the front and back interface quality on the device level using the charge pumping technique. By this, a correlation between interface trap density and channel mobility could be determined. While the characteristics of both front and back Si-SiO2 interfaces depend on the crystalline quality (presence of grain boundaries) of the recrystallized film, the capping layer material used mainly affects the back interface properties. Both nitride and oxynitride capping layer materials introduce large amounts of nitrogen impurities in the molten silicon which can be expected to cause a deterioration of the interface quality. In case of a nitride capping layer, the (back) interface trap density is indeed found to be very dependent on the structure of the capping layer and on the actual laser recrystallization conditions, whereas in the case of an oxynitride capping layer no deterioration of the interface characteristics takes place for any scanning condition applied. The incorporation and the segregation of nitrogen impurities in the SOI structure is discussed supported by secondary ion mass spectrometry measurements of the impurity profiles and which qualitatively accounts for the observed dependencies. It is shown that even with a silicon nitride capping layer, laser-recrystallized SOI layers having good electrical properties can be obtained.
Implant-induced high-resistivity regions in InP and InGaAs
Authors: Pearton S. J. , Abernathy C. R. , Panish M. B. , Hamm R. A. , Lunardi L. M.
Published: July 2002

We have investigated the effects of ion bombardment on the electrical properties of intentionally doped InP and InGaAs grown by metalorganic molecular-beam epitaxy. The sheet resistivity and mobility of n+InP (Sn) and n+InGaAs (Sn) or p+InGaAs (Be) epilayers grown on semi-insulating InP substrates were measured as a function of ion species (O, B, H, or Fe), ion dose (1012–1015 cm−2), and post-implant annealing temperature (100–600 °C). In n+InP, the resistivity after bombardment goes through a maximum with annealing temperature, reaching a value of ∼106 Ω/⧠ for 0.5-μm-thick films after implantation with H or O and annealing at 200–300 °C. The as-grown resistivity is restored by annealing above 500 °C. Ion doses below 1012 cm−2 actually lead to a decrease in resistivity through the creation of shallow donor levels. By contrast, the implantation of Fe above a critical dose where the Fe density exceeds the dopant concentration leads to the formation of thermally stable, high-resistivity (>106 Ω/⧠) material. The temperature dependence of the resistivity shows an activation energy of 0.67 eV, which corresponds to the acceptor level of substitutional Fe in InP. Both n+InGaAs and p+InGaAs show somewhat similar behavior after implantation with maximum resistivities of ∼105 Ω/⧠ regardless of implant species. Once again for relatively low doses of O or H (below ∼1013 cm−2 in this case) there is creation of shallow defect levels that lower the resistivity of the material. The formation of these levels in InP has been investigated in more detail by measuring the depth-dependent carrier profile in implanted high-resistivity InP. The profile of the damage-induced centers is in close correlation with the nuclear energy deposition profile of the implanted ion in some cases, and with the profiles of stoichiometric excess due to unequal recoil of the lattice constituents in other cases.
Impurity dependence of film-edge-induced dislocations in silicon
Authors: Huang C. K. , Jaccodine R. J.
Published: July 2002

An experimental study is designed to reveal the generation of dislocations resulted from the interaction of discontinuous low-pressure chemical-vapor-deposited (LPCVD) nitride/thermal pad oxide window edge and atomic misfit stress. The results show that atomic misfit has a very strong effect on the dislocation generation along the film edges. Boron exhibits a misfit factor of (−)0.254, while arsenic has almost zero misfit factor in silicon. Hence the ratio of LPCVD nitride/thermal pad oxide thickness to generate film edge dislocations for boron-doped silicon is at least three times lower compared with arsenic doped silicon. The increase of boron concentration reduces the thickness ratio of LPCVD nitride/pad oxide required to the generation of dislocations. This study shows that film-edge-induced dislocation is strongly dependent on impurity species and concentration.
Preparation of dense films of crystalline ZrO2 by intense pulsed-electron-beam ablation
Authors: Jiang X. L. , Xu N.
Published: July 2002

Intense pulsed electron beams with power densities of ∼109 W/cm2 were used to evaporate solid targets of ZrO2 and pure Zr. The deposition was carried out in an environment of O2 gas of 10 Pa. The high-temperature plasma generated by intense pulsed electron beam contains energetic ions of target material and environmental gas O2. This ion flux vertical to and 2–4 mm away from the target was about 1014/cm2 per electron pulse for above power densities. The Raman spectra of ZrO2 thin films deposited on Si substrates by this technique showed their forms to consist of monoclinic, tetragonal, and cubic phases. Transmission electron microscope images showed that the ZrO2 films are even and dense, and corresponding diffraction patterns of the ZrO2 films revealed that the ZrO2 films have the microcrystalline structures in the forms of monoclinic and cubic phases.
Application of neutron diffraction to the characterization of residual thermal strains in YBa2Cu3O7−δ/Ag
Authors: Kupperman D. S. , Singh J. P. , Faber J. , Hitterman R. L.
Published: July 2002

Additions of silver (Ag) have been reported to improve the mechanical properties of high-temperature superconductor by YBa2Cu3O7−δ (abbreviated YBCO). However, during fabrication of YBCO/Ag composites, differential thermal expansion upon cooling can lead to potentially troublesome residual stresses. The Intense Pulsed Neutron Source and General Purpose Powder Diffractometer at Argonne National Laboratory were used to show that neutron diffraction techniques can be applied to YBCO/Ag composites to measure bulk residual strains in the constituent parts, and to determine the effect of Ag on stoichiometry (and thus on the critical current density). We have observed residual tensile strains in Ag as a function of crystallographic direction; three strains range from as high as 0.085% in 15% Ag samples to as low as about 0.02% in a 30% Ag sample. Compressive strains in the YBCO (111) crystallographic direction were approximated by correcting for the diffraction peak shift due to changes in stoichiometry with varying Ag content. The estimated compressive-strain values vary from 0.04% (15% Ag) to 0.09% (20% Ag) to 0.01% (30% Ag), with an uncertainty of about 0.03%. The presence of significant average tensile strain in the Ag, particularly for 15% and 20% Ag samples, indicates good interface bonding between YBCO and Ag.
Strain relief mechanisms and the nature of dislocations in GaAs/Si heterostructures
Authors: Sharan S. , Narayan J.
Published: July 2002

The nucleation and glide of misfit dislocations in the GaAs/Si system has been investigated using transmission electron microscopy. GaAs epilayers of different thicknesses were examined by electron microscopy (plan and cross section) and the elastic strain remaining in the film has been related to the average spacing of the misfit dislocations at the interface. The 1000-Å-thick GaAs epilayer contains mostly 60° misfit dislocations with an average spacing larger than the equilibrium dislocation spacing, which implies that the misfit strain is not fully relieved. The 2000-Å and thicker GaAs epilayers contain predominantly 90° misfit dislocations with an average spacing between the dislocations less than the equilibrium dislocation spacing. The formation of sessile 90° dislocations at the interface is explained on the basis of a reaction of two 60° dislocations. A model is developed based on minimum energy considerations to determine the strain-versus-thickness relationship. The theoretical predictions of strain relaxation are compared with experimental observations using high-resolution electron microscopy.
Growth of Al oxide layers on GaAs (100) by reaction with condensed molecular oxygen
Authors: Gao Y. , Lusignan C. P. , Ruckman M. W. , Strongin Myron
Published: July 2002

An Al oxide-GaAs (100) interface fabricated by the reactive deposition of Al into a molecular oxygen overlayer on a gallium terminated GaAs (100) surface at T=49 K is studied by synchrotron radiation photoemission. Al forms a stable oxide layer by reaction with O2 until all the oxygen is consumed. Limited oxidation of surface As atoms (≊20%) is observed during the initial deposition of Al, but further Al deposition reduces the AsO bond. The well-known exchange reaction between Al and Ga when Al is directly deposited on GaAs (100) is not observed.
Faraday rotation in Hg1−xMnxTe at 1.3 and 1.55 μm
Authors: Dillon J. F. , Furdyna J. K. , Debska U. , Mycielski A.
Published: July 2002

The large Faraday rotations of Mn-containing diluted magnetic semiconductors have led to their consideration for use in magneto-optical isolators. With such applications in mind, we have examined the magneto-optical properties of Hg1−xMnxTe (x=0.26, 0.31, and 0.36). The samples are polished plates cut from single-crystal boules. The compositions were chosen to have their band edges in the vicinity of wavelengths of interest for fiber optical communications, 1.3 and 1.55 μm. Faraday rotation at 295, 77, and 1.7 K, as well as the absorption coefficient at 295 K, have been measured for these alloys and the data compared with the theoretical predictions. The measured rotations at the wavelengths of interest here are about 100-fold larger than those of other high-rotation paramagnetic materials, such as Tb3Al5O10 and various rare-earth glasses. However, the specific rotations available in reasonable fields (say, 3000 Oe) are about tenfold lower than those reported for Bi-doped ferrimagnetic garnets.
Energy-level spectra of Co2+ and Fe2+ in diluted magnetic semiconductors
Authors: Villeret Murielle , Rodriguez S. , Kartheuser E.
Published: July 2002

In this paper we study the low-lying energy levels of Co2+ and Fe2+ in diluted magnetic semiconductors, such as Cd1−xCoxTe and Cd1−xCoxSe, and their iron-based counterparts. In the first of these compounds, the magnetic ion sits on a site of symmetry Td, while in the second the symmetry is trigonal (C3v). We develop a formulation that permits a continuous variation from Td to C3v symmetry. Comparison with experimental data in Cd1−xCoxSe shows that the C3v distortion amounts to about 10% of the crystal potential at the Co2+ site. Our study of the energy spectra of Fe2+ in Td and C3v crystal potentials reveals that, even in the cubic field, the levels exhibit an anisotropy which manifests itself in an anisotropy of the magnetization M in the regime in which M is not a linear function of the magnetic field B. The study includes all the levels in the lowest terms of the (3d)7 and (3d)6 configurations of Co2+ and Fe2+, thus considerably extending work by previous authors. The calculations are carried out to second order in the spin-orbit interaction and in B for the lowest orbital states, and to first order in B for the excited states. The g factors of all the levels are obtained including their anisotropy for the Co2+ Γ8 states.
Crystal structure and magnetic softness of Fe-Si polycrystalline films
Authors: Hosono Akihiko , Shimada Yutaka
Published: July 2002

Magnetic softness of polycrystalline Fe-based alloy films is investigated. From calculation of magnetocrystalline anisotropy and magnetostriction assuming the magnetization is confined in a certain crystal plane of bcc Fe or Fe-Si alloy, Fe alloy films with (111) orientation parallel to the film plane are expected to have good magnetic softness. Fe-6.9 wt. % Si polycrystalline films with various crystallographic orientations such as (100), (110), or (111) oriented parallel to the film plane plane are deposited on underlayers such as MgO, ZnO, and ZnSe by a high-rate sputtering system. Fe-Si films on ZnSe underlayers with (111) orientation exhibit smaller Hc and better thermal stability than those of films with other orientations. Magnetic softness and thermal stability are improved for the double-layered films with those orientations. For multilayered Fe-6.9 wt. % Si films on ZnSe underlayers, the Hc of deposited films is about 0.5 Oe, and is stable against annealing up to 500 °C.
The thermal conductivity of rare-earth–transition-metal films as determined by the Wiedemann–Franz law
Authors: Anderson Roger J.
Published: July 2002

Measurements have been made of the electrical conductivity of sputtered rare-earth–transition-metal films. The Wiedemann–Franz law has been used to relate these values to the electronic component of the thermal conductivity of the films. A small lattice contribution to the thermal conductivity was estimated and added to the electronic component to obtain the total thermal conductivity of the materials. This total thermal conductivity is about one order of magnitude smaller than that of the pure bulk materials composing the films. Knowledge of the thermal conductivity of such rare-earth–transition-metal films has proved to be useful in the modeling of the thermomagnetic recording processes. These processes are used to record information on magneto-optic data storage disks.
Texture analysis of polycrystalline silicon films
Authors: Wenk H. R. , Sintubin M. , Huang J. , Johnson G. C. , Howe R. T.
Published: July 2002

A method for the quantitative characterization of texture in thin films using x-ray diffraction is presented. The traditional technique, which makes use of a powder diffractometer, relies on peak intensity measurements at normal incidence. By using pole figure measurements and subsequent orientation distribution analysis we obtain the substantially improved coverage necessary to accurately characterize textures of thin silicon films which exhibit great variation and complexity.
Plasticity of undoped GaAs deformed under liquid encapsulation
Authors: Siethoff Hans , Behrensmeier Ralf
Published: July 2002

Undoped GaAs single crystals with 〈123〉 orientation are compressed at different strain rates in the temperature range between 730 and 900 °C, using the liquid encapsulation technique to prevent As loss. The resulting stress-strain curves are characterized by five deformation stages, as is known for other semiconductors. From the lower yield point, at high strain rates, an activation energy of 1.37 eV and a stress exponent of 3.6 are deduced; these parameters nearly agree with those obtained earlier at lower temperatures and under a protective atmosphere of argon. At low strain rates deviations occur, whose origin is discussed. The analysis of the first stage of dynamical recovery (stage III), which shows a uniform behavior over the whole temperature and strain-rate range, yields an activation energy of 2.3 eV and a stress exponent of 4.2. These values are discussed in terms of a diffusion-controlled recovery mechanism. The second recovery stage (stage V) probably is governed by cross slip; the cross over of both recovery regimes takes place near 550 °C. The deformation behavior of GaAs is compared to that observed in other semiconductors.
Atomic scale study of local TiSi2/Si epitaxies
Authors: Catana A. , Schmid P. E. , Heintze M. , Lévy F. , Stadelmann P. , Bonnet R.
Published: July 2002

The TiSi2/Si system is investigated using high-resolution transmission electron microscopy (HRTEM) and electron diffraction in both cross-section and flat-on modes. The results show that the large crystallographic differences between both crystals and the complexity of the reaction path are not obstacles to the formation of flat and well-defined interfaces. (1̄01) TiSi2 proves to be a preferential plane for epitaxial growth on Si (111). In this case, the terminal TiSi2 plane at the interface is composed of single atomic species. It is proposed that the reasons leading to such an epitaxy are related to the small discrepancy of atomic densities and interplanar spacings characteristic of these planes. Observation of local epitaxial relationships are reported and investigated using a lattice matching model. It turns out that they minimize the two-dimensional misfit at the interface.
The growth of GaAs, AlGaAs, and selectively doped AlGaAs/GaAs heterostructures by metalorganic vapor phase epitaxy using tertiarybutylarsine
Authors: Kikkawa T. , Tanaka H. , Komeno J.
Published: July 2002

The prevention of disastrous leakage of AsH3 is a requirement for metalorganic vapor phase epitaxy systems. Less hazardous organoarsine has been investigated as an alternative to AsH3 , and recently, tertiarybutylarsine (tBAs) has been used as an arsenic source. So far the use of tBAs has been restricted to fundamental experiments. The growth of GaAs, AlGaAs, and selectively doped AlGaAs/GaAs heterostructures has been studied using tBAs and AsH3, and the properties of the epilayers grown using both sources have been compared. From the PL spectra at 4.2 K, it was determined that GaAs films using tBAs were of high purity and equivalent to those using AsH3. The properties of AlGaAs grown using tBAs are as good as those using AsH3. A higher V/III ratio results in high-quality AlGaAs layers. The epitaxial uniformity of growth rate and AlAs mole fraction along a wafer using tBAs was poorer than those using AsH3 due to vapor phase reactions in the trimethylgallium-tBAs mixture. However, the increase of total gas flow rate in the reactor has the effect of improving uniformity. The activation efficiency of Si in AlGaAs is the same for both sources. The properties of heterostructures grown using tBAs are similar to those using AsH3. The sheet carrier concentration and electron mobility at 77 K with a spacer layer thickness of 35 Å were 9.5×1011 cm−2 and 48 000 cm2  V−1 s−1, respectively. This suggests that tBAs can be used as an alternative to AsH3, for growing device-quality GaAs and AlGaAs.
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u optimization of coupling between semiconductor claddings and dielectric waveguides
Authors: Veasey David L. , Larson Donald R. , Batchman Theodore E.
Published: July 2002

Coupling interactions between the low loss-modes of dielectric waveguides and the high-loss modes supported by semiconductor waveguide claddings are of prime importance in the design and fabrication of integrated optical photodetectors and polarizers. It is desirable to maximize energy transfer from dielectric waveguides to semiconductor claddings in order to achieve optimal operation of detectors and polarizers. We have experimentally verified that the intermodal coupling of light from a low-loss dielectric guiding region to a highly absorbing semiconductor cladding region is periodic as a function of cladding thickness. Results were obtained by the in situ monitoring of output intensity during the growth and etching of hydrogenated amorphous silicon on polarization-preserving, D-shaped, optical fiber. Strong correlation exists between theoretical and experimental results for both TE and TM polarizations. The in situ, intensity monitoring technique allows for precise control of attenuation characteristics in clad-waveguide devices allowing for optimum performance of clad-waveguide polarizers and detectors.
Atomspheric pressure organometallic vapor-phase epitaxial growth and characterization of Ga0.4In0.6P/(Al0.4Ga0.6)0.5In0.5P strained quantum wells
Authors: Wang T. Y. , Kimball A. W. , Chen G. S. , Birkedal D. , Stringfellow G. B.
Published: July 2002

Single and multiple Ga0.4In0.6P/(Al0.4Ga0.6)0.5In0.5P quantum wells have been grown using atmospheric pressure organometallic vapor phase epitaxy. The Ga0.4In0.6P well layers are coherently strained to match the lattice parameter of the GaAs substrate. Transmission electron microscopic results showed that the quantum-well layers are very uniform in thickness and the interface is abrupt and free of misfit dislocations. The photoluminescence peak energy increases as the well width decreases, due to carrier confinement in the quantum well. Growth interruptions do not change the photoluminescence peak energy of the quantum well. However, the photoluminescence intensity is drastically reduced for longer growth interruption times. Higher-order x-ray diffraction satellite peaks and a narrow photoluminescence halfwidth are observed in a 20-layer multiple-quantum-well sample, indicative of high structural uniformity and precise control of the composition and thickness during the growth process. Considering the effect of strain on the heterojunction band offsets, the photoluminescence peak energy of the strained quantum well can be described by a simple theory as a function of the well width.
The effect of frictional stress on the calculation of critical thickness in epitaxy
Authors: Fox Bradley A. , Jesser William A.
Published: July 2002

A critical-thickness model is proposed for lattice-mismatched epitaxial layers which incorporates for the first time both the equilibrium and kinetic components of misfit accommodation. The model is an attempt to provide a physical basis for the discrepancy between the observed and calculated critical thickness in zinc-blende semiconductors. The equilibrium components of the model use a force balance and a Volterra description of the dislocation line tension with frictional forces includiing Peierls barriers and dislocation atmospheres. The effect of the frictional forces is to shift the critical thickness to a larger value and to produce a residual elastic strain which persists for large thicknesses. The frictional barriers are low in face-centered-cubic metals and produce minor changes from the previous theories; however, for semiconductors the frictional forces may be high and produce a substantial increase in the predicted critical thickness. The kinetic component of misfit accommodation has been addressed through a dynamic frictional force. The explicit form of the kinetic component of misfit accommodation depends on the operative mechanism of misfit-dislocation generation. A simple criterion is proposed to estimate whether the generation of misfit dislocations will be controlled by equilibrium or kinetic factors.
Solid-phase reactions and crystallographic structures in Zr/Si systems
Authors: Yamauchi T. , Zaima S. , Mizuno K. , Kitamura H. , Koide Y. , Yasuda Y.
Published: July 2002

Solid-phase reactions and crystallographic structures in the interfacial region of Zr/(100)Si systems, which is closely related to the specific contact resistivity, have been investigated by x-ray diffraction, Auger electron spectroscopy and cross-sectional high-resolution transmission electron microscopy. As-grown Zr films are in an amorphous phase including crystallites. The Zr film on silicon annealed at a temperature of 420 °C for 30 min has a bilayer structure. The upper layer is a crystalline α-Zr layer with a (0001) fibrous structure and the lower layer is an amorphous zirconium silicide layer. The formation of the amorphous silicide layer is considered to result from the diffusion of Si atoms from the substrate into the Zr film and to play a major role in a low contact resistivity of 4×10−8 Ω cm2 achieved in this system. By annealing above 560 °C, which brings about an increase in contact resistivity, the crystalline Zr layer with the fibrous structure is changed to an amorphous silicide throughout the film and, subsequently, ZrSi2 regions with a (010) preferred orientation is formed at the interface between the amorphous interlayer and the single-crystal Si.
Effect of signal discreteness on correlation functions
Authors: Uebing C. , Gomer R.
Published: July 2002

Number or density autocorrelation functions can sometimes be obtained in terms of electron emission current autocorrelation functions if the current fluctuations are related to the number fluctuations. This is the case in field emission where the fluctuations in adsorbate number in a small probed region, caused by surface diffusion, are essentially proportional to the field emission current fluctuations. The autocorrelation function of the current fluctuations then mirrors that of the adsorbate number fluctuations. When correlation intervals are very short they may contain an average number of electrons so small that the rms electron fluctuation resulting from adsorbate number fluctuations is less than 1 e− and thus shows up only infrequently. The electron fluctuation can then ‘‘miss’’ most adsorbate fluctuations. We have examined this problem by Monte Carlo modeling and confirm the existence of this effect when the electron fluctuation number is truncated to integer values. Even in this case the electron fluctuation correlation images the adsorbate number correlation function quite well to values of rms electron fluctuations as low as 0.4 e− per correlation interval. When shot noise is included imaging is good to the lowest value tested, 0.18 e−, but the number of summations required to overcome noise goes up very steeply. The reason for the improvement in imaging is that shot noise circumvents the problem of electron fluctuation inadequacy, since very small changes in mean electron emission probability, corresponding to much less than 1 e− per correlation interval, are reflected in the Poisson distribution. Thus shot noise in a way ‘‘amplifies’’ the fluctuations but at the price of vastly increased noise. This conclusion is probably not confined to the specific case examined here but seems generally valid.
Defect states in ZnSe single crystals irradiated with gamma rays
Authors: Karai M. , Kido K. , Naito H. , Kurosawa K. , Okuda M. , Fujino T. , Kitagawa M.
Published: July 2002

Defect states in ZnSe single crystals induced by 60Co γ-ray irradiation have been investigated with deep-level transient spectroscopy (DLTS) and optical deep-level transient spectroscopy (ODLTS). 5-MeV-electron-irradiated crystals have also been examined for comparison. With DLTS measurements it is found that two electron traps at Ec − 0.27 eV and Ec − 0.49 eV are newly introduced, and the concentration of an electron trap at Ec − 0.30 eV, which exists in unirradiated ZnSe, is increased by γ-ray or electron irradiation. Two additional electron traps located at Ec − 0.15 eV and Ec − 0.79 eV are also observed, and are unique to the γ-ray and the 5-MeV-electron-irradiated material, respectively. In ODLTS spectra a newly introduced hole trap at Ev+0.71 eV and the increase in the concentration of a trap at Ev+0.19 eV are observed in the ZnSe irradiated with γ ray or 5 MeV electron. It is concluded that the electron trap at Ec−0.30 eV and the hole trap at Ev+0.71 eV are attributed to a Se and Zn vacancy-associated defect in the ZnSe single crystal, respectively. The hole trap at Ev +0.19 eV is tentatively identified as arising from an impurity Se vacancy complex.
Defect formation in the solid phase epitaxial growth of GaAs films on Si (001) substrate
Authors: Cho K. I. , Choo W. K. , Lee J. Y. , Park S. C. , Nishinaga T.
Published: July 2002

The defect structures of GaAs film on (001) Si substrate tilted ∼3° towards the [110] direction were investigated by the high-resolution transmission electron microscopy. GaAs films were grown by the molecular beam epitaxy (MBE) on the Si (001) substrate by a modified two-step process, in which amorphous GaAs buffer layers were grown first. High-resolution electron micrographs show that stacking faults (and/or microtwins) are preferentially formed on the tilted step-rich surface, whereas misfit dislocations are preferentially formed on the flat surface. However, the difference in the defect density on the two cross sections is small. Between the observed 90° edge and 60° misfit dislocations the density of the latter is higher irrespective of the substrate tilt. This occurrence is explained by the difference in distribution of initial nucleating islands between the present and the conventional two-step MBE techniques.
Magnetic force microscopy with batch-fabricated force sensors
Authors: Grütter P. , Rugar D. , Mamin H. J. , Castillo G. , Lin C.-J. , McFadyen I. R. , Valletta R. M. , Wolter O. , Bayer T. , Greschner J.
Published: July 2002

In this paper the properties of force sensors suitable for magnetic force microscopy (MFM) made by coating silicon microcantilevers with various thin magnetic films are analyzed. These MFM force sensors are batch fabricated and their magnetic properties controlled by choosing appropriate coatings. Theoretical calculations show that thin-film MFM tips have a significantly reduced stray field, a good signal-to-noise ratio, and yield improved resolution when compared to etched wire tips. The sample perturbation due to the tip stray field is small, allowing the imaging of low-coercivity samples such as Permalloy.
Magnetic properties of the icosahedral phase of Ti transition metal alloys
Authors: Ali Naushad , Willis Frank , Holzer J. C. , Zhang X. , Kelton K. F.
Published: July 2002

We report the magnetic properties of the icosahedral phase (i phase) in rapidly quenched Ti-Mn based alloys. Ribbons of i-phase samples of composition Ti61Mn37Si2, Ti61Mn22Cr15Si2, Ti61Mn22Fe15Si2, and Ti61Mn22Co15Si2 were prepared by melt spinning onto a copper disk in an argon atmosphere. Low-field magnetization data reveal a ferromagnetic ordering at Tc ≂ 40 K for Ti61Mn37Si2 samples. A partial substitution of Mn by Cr enhances Tc to 58 K with large thermal hysteresis, whereas samples of composition Ti61Mn22Fe15Si2 show no long-range magnetic ordering down to 4 K. We have found that the sample Ti61Mn22Co15Si2 shows evidence of spin-glass behavior below 15 K.
Microstructure and composition of composite SiO2/TiO2 thin films
Authors: Gluck N. S. , Sankur H. , Heuer J. , DeNatale J. , Gunning W. J.
Published: July 2002

The microstructure and composition of the SiO2/TiO2 analog (codeposited) and digital (thin layer pairs) gradient-index films were examined by transmission electron microscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, scatterometry, and in situ ellipsometry. Both analog and digital structures were amorphous as-grown. The SiO2 was incompletely oxidized at some of the interfaces in the layered structures and in the codeposited films, indicated competition from the TiO2 for available oxygen during growth. Digital structures with thin (65 Å) layers remained well defined after annealing at 900 °C, but their order was completely destroyed by 1100 °C. Structures with thick (500 Å) layers remained intact up to 1100 °C, with the TiO2 crystallizing throughout the layer width. Both anatase and rutile TiO2 crystallites were present in the layered and codeposited films after a high-temperature anneal (T≳650 °C), while only the anatase phase was observed for 300 °C<T<650 °C. The optical scatter of the digital films increased with increasing annealing temperature and layer thickness. TiO2 precipitated out of the codeposited films after a high-temperature anneal; however, the scatter of these films at 0.633 μm was several orders of magnitude lower than that of the annealed layered films. Codeposited films consisting of greater than ∼60% TiO2 displayed form birefringence in the as-grown state.
Micromagnetic model of an exchange coupled NiFe-TbCo bilayer
Authors: Smith Neil , Cain William C.
Published: July 2002

We present a micromagnetic model for NiFe-TbCo exchange coupled bilayers that can quantitatively predict and explain the major macroscopic features observed in measured M-H characteristics. Comparison of theoretical and experimental results shows conclusively that the strong interfacial exchange coupling in NiFe-TbCo is essentially indistinguishable from that of a perfect, homogeneous interface. Commonly invoked assumptions concerning the existence or origin of a grossly weakened exchange coupling at a highly imperfect interface are neither necessary nor consistent with experimental measurements. The mechanism of the unidirectional exchange anisotropy is the formation of Bloch-type domain walls in a ≂0.08-μm-thick TbCo sublayer of uniaxial, in-plane anisotropy adjacent to the NiFe interface. The manner in which the observable magnetic behavior of NiFe-TbCo bilayers depends on film thicknesses, TbCo anisotropy, interfacial exchange coupling strength, as well as the previously unconsidered large hysteretic effects due to the small net magnetization in ferrimagnetic TbCo, are discussed in detail. It is demonstrated, for a strongly coupled system such as NiFe-TbCo, that the often used single parameter ‘‘exchange field’’ description of a shifted NiFe M-H loop is inadequate. A quantitatively accurate description requires that one take into account the spatial variations in the micromagnetic magnetization distributions of both layers.
Plasticity path effects in metals under shock compression
Authors: Tonks D. L.
Published: July 2002

When plasticity data from weak shocks are plotted in the form of plastic strain rate versus deviatoric stress, the resulting curve exhibits a loop for several metals. Using the single-state- variable theory of E. W. Hart [Acta Metall. 18, 599 (1970)], this loop is interpreted to mean more than one state variable is necessary to explain the shock-wave plasticity for these metals. This circumstance could be due to a change in the mechanism of plastic flow to dislocation drag. Other explanations are possible, however.
Small-hole coupling of radiation into a near-field probe
Authors: Roberts A.
Published: July 2002

The coupling of electromagnetic energy into a conical waveguide through an electrically small hole near the cone tip is considered. This problem is relevant to near-field microscopy, where tapered metallic probes are used to either illuminate, or collect light from, the structure under investigation. The situation considered in detail here is simplified by assuming that the aperture is surrounded by a planar baffle, which approximates the flat ends of fabricated probes. An established formulation for small-hole coupling into waveguides is used and the waveguide itself taken to be a truncated, perfectly conducting cone. As expected, the values obtained for the energy transmitted through an aperture with a diameter significantly less than that of the radiation being used are small. However, it is also found that the size of the waveguide at the hole position strongly affects the percentage of the incident energy transmitted.