bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous shape of magnetic loops in the Rayleigh region
Authors: Seeck St. , Lambeck M.
Published: July 2002

According to its congruency property, the Preisach model demands an equivalent shape of magnetic minor loops, the so-called Rayleigh loops. We measured these loops with an inductive setup and noticed a different anomalous shape of Rayleigh loops which depends on the magnetic history. Special materials (particularly recording media) show a concave-convex shape in contrast to the normal biconvex shape. This anomalous shape can be explained by combining the Preisach model with the Stoner–Wohlfarth model. It follows from this explanation that the degree of the anomaly depends on the material, especially in how far it fulfills the conditions of the Stoner–Wohlfarth model. The experiments show the effect that is expected according to the material. In this way the measurement of the anomalous Rayleigh loops can be used as a new method to test the Stoner–Wohlfarth properties of a material. This is more effective than using the Henkel plot [G. Bertotti and V. Basso, J. Appl. Phys. 73, 5827 (1993)].
Controlled disordering of compressively strained InGaAsP multiple quantum wells under SiO:P encapsulant and application to laser-modulator integration
Authors: Hamoudi A. , Rao E. V. K. , Krauz Ph. , Ramdane A. , Ougazzaden A. , Robein D. , Thibierge H.
Published: July 2002

We investigated the potentiality of a phosphorus-doped silicon oxide (SiO:P) carrier-free disordering source for applications in photonic devices integration schemes. This is accomplished in three successive steps by employing an InGaAsP/InGaAsP structure with compressively strained wells and lattice-matched barriers designed for operation around ∼1.55 μm. First of all, we showed that the SiO:P encapsulant offers a good control over a wide range of disorder (blue shifts as high as ∼150 meV). Later on, the high optical quality of the disordered regions is demonstrated by detecting 300 K excitonic features in moderately blue-shifted (∼40 meV) samples. And, finally, a first attempt of its application in integration technology is made by realizing a monolithic composite of a distributed feedback laser and a quantum-confined stark effect electroabsorption modulator operating around 1.54 μm.
Ellipsometric studies on Cd1−xMnxTe thin films under the influence of HeNe laser and small alternating magnetic fields
Authors: Chandra Sharat , Malhotra L. K. , Rastogi A. C.
Published: July 2002

Ellipsometric studies in the energy range 1.5–5 eV have been performed on thin films of Cd1−xMnxTe deposited by sublimation from alloys prepared by melt quenching. The spectra show E0, E1, and E1+Δ1 transitions of cubic semiconductors. The changes in peak positions under influence of HeNe laser light, small alternating magnetic field, and under the influence of both applied simultaneously have been investigated. Shifts in peak positions observed for all the three transitions have been interpreted on the basis of changes in the band structure of Cd1−xMnxTe thin films at these critical points. This has been corroborated by theoretically calculating the effective number of electrons contributing to transition per atom Neff and the density-of-states data.
Effects of Al doping on deep levels in molecular-beam-epitaxy GaAs
Authors: Qurashi Umar S. , Iqbal M. Zafar , Baber N. , Andersson T. G.
Published: July 2002

The effects of Al as an isoelectronic dopant have been investigated on the deep level defects in GaAs grown by molecular-beam epitaxy (MBE), using deep level transient spectroscopy. Two different compositions containing 0.1% Al (Al0.001Ga0.999As) and 1% Al (Al0.01Ga0.99As) have been studied. At least nine different deep levels have been detected. Their detailed characteristics consisting of emission rate signatures, capture cross sections, concentrations, and junction depth profiles have been determined. The deep levels observed have been compared with the M levels normally found in MBE n-GaAs. The emission rates of deep levels have been found to shift to higher values with decrease in Al concentration. This fact has been attributed to lattice strain and random alloy effects. The relative concentrations of deep levels are seen to undergo large changes as the Al concentration is increased from 0.1% to 1%. Al doping upto 0.1% does not seem to reduce the deep level concentration, unlike the case of other isovalent dopants such as In and Sb in MBE GaAs. Further increase in the Al doping to 1% is found to lead to a pronounced increase in the overall deep level concentration. These data along with the other measured characteristics are interpreted in terms of the possible models for the various defects.
A vortex–antivortex pairs triggered Josephson shift register
Authors: Cirillo M. , Merlo V.
Published: July 2002

We study the performances of a type of single-phase shift register based on flux-quanta dynamics. The system employs as a clock signal a spatially localized sinusoidal current injection in a discrete Josephson transmission line. This drive generates fluxon–antifluxon pairs which, traveling along the transmission line, move the single flux quanta stored in attractive potential wells. These wells are obtained by inserting inductive discontinuities in the transmission line. The simulations show that the device could operate in real Josephson systems with clock frequencies in the range 10–100 GHz. Good margins are found for the most critical parameters of operation.
Mössbauer study of 57Fe ions implanted in Ti and TiN
Authors: Burda K. , Dauwe Ch. , Bakker P. De , Grave E. De , Fornal P. , Stanek J.
Published: July 2002

Ti and TiN layers implanted with 57Fe ions were studied by conversion electron Mössbauer spectroscopy at 295 and 80 K. In as-implanted Ti samples the local states of iron implants were assigned to α-Ti(Fe) and β-Ti(Fe). In TiN, about 68% of iron implants replace Ti atoms forming Fe2N and nonstoichiometric Fe–N complexes. The remaining Fe ions replace N atoms exhibiting α-Ti(Fe) and β-Ti(Fe) states. The protective properties of the TiN cover layer are discussed in terms of changes of the these states after subsequent annealing in air.
High-temperature annealing of semi-insulating GaAs and the dissociation of EL2
Authors: Morrow Richard A.
Published: July 2002

Existing data on the n–p type conversion of semi-insulating GaAs during high temperature (1100–1200 °C) anneals are fit using a previously developed model in which EL2 is identified as the native defect AsGaVGa. In this model EL2 dissociates into the acceptor VGa and the donor AsGa. The latter defect then rapidly captures a divacancy to form the electrically neutral complex AsGaVAsVGa. The decrease in EL2 concentration, the n–p type conversion of GaAs, and the subsequent increase in hole concentration as the annealing temperature is increased are correlated in the model.
Interfacial Fermi level and surface band bending in Ni/semi-insulating GaAs contact
Authors: Chen T. P. , Liu Y. C. , Fung S. , Beling C. D.
Published: July 2002

For nickel on the chemically clean surface of undoped semi-insulating GaAs at room temperature, an upward surface band bending of 0.062 eV and a barrier height of 0.690 eV have been observed by the photovoltage and the internal photoemission techniques, respectively. The observed surface band bending is in excellent agreement with its predicted value, and the observed barrier height also agrees very well with its value from the very careful analysis of reversed I-V data. It has been determined that the interfacial Fermi level lies at 0.690 eV below the GaAs conduction band minimum at the interface. The interfacial Fermi level is found to coincide with the energy level of the EL2 native defect, indicating the importance of the EL2 in the Fermi level pinning at the interface.
Calculations of hole–phonon scattering in strained-layer quantum wells
Authors: Ahn Doyeol
Published: July 2002

The scattering rate of holes in strained-layer quantum wells due to the interaction with the longitudinal optical (LO) phonon is calculated using a simple model. A many-body formalism is used to calculate the hole self-energy and the hole–LO-phonon linewidth with the static random phase approximation screening taken into account. The cases of both biaxial tensile and compressive strains are investigated. It is found that the linewidth of the hole–phonon scattering is larger for the tensile strain and smaller for the compressive strain than the lattice-matched case. The differences in the linewidth of the hole–LO-phonon scattering can be explained by the strain-induced effective mass changes at the zone center.
Laplace transform method of measuring the distribution of Si–SiO2 barrier heights: Implementation
Authors: Nicollian Edward H. , Babić Davorin
Published: July 2002

Using the Laplace transform method, the specific experimental conditions are given under which the extraction of a Gaussian distribution of barrier heights, in the Si–SiO2 heterojunction, is based. Specifically described are: (1) the maintenance of a constant oxide field despite oxide charging; (2) the determination of the substrate field produced by the backgate bias; (3) the extraction of the short-circuit source–drain photocurrent collected under the gate from the total short-circuit photocurrent which is the sum of the photocurrents collected under the gate and by the source–drain junctions; (4) the minimization of inversion layer free-carrier absorbtion to make the amount of incident light that penetrates the substrate independent of both the gate and backgate bias; and (5) the implementation of the measurement system to extract the barrier height distribution.
Current filament dynamics in n-GaAs
Authors: Kostial H. , Ploog K. , Hey R. , Boebel F. G.
Published: July 2002

Experiments on the controlled generation of up to 20 current filaments in n-type GaAs have been performed in the electric field region, where impurity impact-ionization avalanche breakdown takes place. This strongly nonlinear system is found to be very sensitive to small deviations of the technological parameters. In particular, we present the results of time-resolved current measurements on two filaments connected in parallel, which compete for the impressed total current due to nonlocal coupling via a common load resistor. The observed switching time constants down to 100 ns make this system very interesting as a ‘‘winner takes all’’ element in synergetic computer applications.
Temperature dependence of infrared photocurrent in Pb(Zr,Ti)O3 on YBa2Cu3O7−x
Authors: Zomorrodian A. R. , Wu N. J. , Lin H. , Huang T. Q. , Li X. Y. , Ignatiev A.
Published: July 2002

Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) (001) thin films, integrated to high Tc superconducting YBa2Cu3O7−x (YBCO) films used as electrodes, have been studied for their photocurrent response and permittivity as a function of temperature. A stable photocurrent was observed to increase with increasing the temperature over the range of 25–350 °C. This increase was found to be strongly polarization dependent and due to the change of the pyroelectric coefficient of PZT thin film with temperature. The pyroelectric coefficient for a PZT sample was measured as ∼30 nC/cm2 K at room temperature, and ∼80 nC/cm2 K at 320 °C. The YBCO electrode showed a stable metallic resistance behavior in this temperature range. There was no detectable photocurrent from YBCO layer. No poling is required until 350 °C for the PZT/YBCO heterostructure detector because the PZT film is oriented when grown on c-axis oriented YBCO.
Anomalous ring-shaped distribution of oxygen precipitates in a Czochralski-grown silicon crystal
Authors: Ono Haruhiko , Ikarashi Taeko , Kimura Shigeru , Tanikawa Akio
Published: July 2002

The distribution of interstitial oxygen and oxygen precipitates as a function of the anneal time was studied using a low-temperature infrared absorption spectroscopy. We found that the density of the precipitation nuclei formed by an anneal at 800 °C is lower in the ring area than in the other areas of the wafer. The appearance of the ring area after precipitation annealing strongly depends on the preanneal temperature. A model explaining the formation of the ring-shaped distribution of oxygen precipitates after two-step anneal is proposed. In this model, the anomalous ring-shaped distribution is explained by assuming the existence of nuclei which have been already nucleated in the ring area at an elevated temperature during crystal growth.
Crystallized amorphous deposits for relaxed epitaxy: CdTe(001) on GaAs(001)
Authors: Dhar N. K. , Wood C. E. C.
Published: July 2002

When annealed, thin amorphous deposits of highly lattice mismatched materials provide specular crystalline surfaces for epitaxy. Mismatch strain is predominantly relieved by misfit dislocations propagating in the plane of the interface, so that resulting films have low threading dislocation densities. We demonstrate the application of this concept to the growth of (001) oriented CdTe epitaxy on (001) GaAs.
Molecular structure of porous Si
Authors: Anaple G. , Burrows R. , Wu Y. , Boolchand P. , Adar F.
Published: July 2002

Nanocrystalline Si particles of 10 nm size, doped with traces (1 at. %) of Sn, are prepared by mechanical attrition in an inert ambient. After stain-etching, the particles photoluminesce at room temperature. 119Sn Mössbauer spectroscopy, Raman scattering, photoluminesce, and Fourier transform infrared spectroscopy measurements performed as a function of stain-etching time reveal systematic changes, and suggest that the molecular structure of porous Si consists of nanocrystalline Si particles with surfaces passivated by H and/or O atoms.
Si-based nanostructure waveguides
Authors: Theodorou G. , Tserbak C. , Vlachos N. D.
Published: July 2002

We investigate the possibility of constructing nanostructure waveguides using Si-based materials. For this purpose we evaluate the dielectric function of strain-symmetrized (Si)10−n/(Ge)n strained-layer superlattices (SLS’s) with n=3, 5 and 7, and (Si)6/(Ge)4 SLS coherently grown on a Si(001) surface, as well as that for bulk Si1−n/10 Gen/10 alloys with n=3, 5 and 7, and bulk Si. In particular we explore the possibility of constructing waveguides using the materials (Si)6/(Ge)4 SLS, coherently grown on a Si(001) surface, and bulk Si. We investigate the case of planar waveguide structure, giving results concerning the propagation and penetration of the transverse magnetic modes.
Measurement of linewidths of Ne-like germanium soft x-ray laser in slab targets
Authors: Yuan Gang , Kato Y. , Murai K. , Daido H. , Kodama R.
Published: July 2002

We describe our measurements of linewidths of the two J=2-1 transitions (232.24 and 236.25 Å) and the J=0-1 transition (196.20 Å) of Ne-like germanium soft x-ray laser in slab targets. The high resolution spectral measurement was performed using a grazing incidence spectrometer with an x-ray CCD camera. Time integrated linewidths, the full width at half maximum, of the two J=2-1 lasing lines are about 20(±4) mÅ when the gain-length product (GL) is ∼8. The linewidth of the J=0-1 line is measured to be 25 mÅ as the GL is ∼5. The measured linewidths of the 236.25 Å line are slightly narrower than those of 232.24 Å in the same shot, reflecting their different intrinsic linewidths. For the J=2-1 transitions, the thermal Doppler broadening (43 mÅ inhomogeneous) has been obtained by one-dimensional hydrodynamic simulation of the plasma expansion, and the collisional broadening (15 mÅ homogeneous) has been considered with all inelastic electron collisional rates among the transition levels in the plasma. The predicted 52 mÅ Voigt profile intrinsic linewidth for the 236.25 Å line has been used to calculate linewidth narrowing by the one-dimensional model of amplified spontaneous emission. The experimental data are in agreement with the model calculation in the short targets. Spectral narrowing is not evident in the long targets. We examined soft x-ray propagation in the plasma by ray-trace calculation. It is shown that refraction is an important factor affecting the spectral narrowing of soft x-ray lasers.
Photoluminescence and photoreflectance from GaAs/AlAs multiple quantum wells
Authors: Oh Y. T. , Kang T. W. , Kim T. W.
Published: July 2002

Photoluminescence (PL) and photoreflectance (PR) measurements have been performed to investigate the intermixing behavior of Al and Ga in GaAs/AlAs multiple quantum wells (MQWs) grown by molecular-beam epitaxy and treated by rapid thermal annealing. These results indicate that the magnitude of the disordering for a GaAs/AlAs MQW increases as the layer thickness increases. When the GaAs/AlAs MQWs with layer thicknesses of 34 Å are annealed at 950 °C for 10 s, the GaAs/AlAs MQWs are totally intermixed, resulting in a formation of an Al0.45Ga0.55As alloy. For the intermixed GaAs/AlAs MQWs, PL spectra show dominantly the Γ-valley direct transition, and PR signals show that the peaks originating from the interband transitions disappear. The observed increases of the full width at half-maximum (FWHM) in the PL spectra for the annealed GaAs/AlAs MQWs originate from the nonuniformity of the intermixing as a function of depth, and the decrease of FWHM in the PL spectra for the GaAs/AlAs MQWs annealed for longer times is due to the formation of Al0.45Ga0.55As alloys in the GaAs/AlAs MQWs.
Combined interface plasmon polariton and x-ray reflectivity determination of the dielectric tensor in ultrathin liquid crystal films
Authors: Pogreb R. , Cohen G. , Tarabia M. , Davidov D. , Levine M. , Sandomirsky V.
Published: July 2002

We have carried out interface plasmon polariton (IPP) and specular x-ray reflectivity studies of the same multilayer structure containing a thin metallic silver film and a thin (100–600 Å) smectic C* ferroelectric liquid crystal (FLC) film on a glass substrate. An additional thin nylon layer sandwiched between these two films is essential to improve the smectic FLC alignment and its stability. The specular x-ray reflectivity after each stage of layer deposition provides information on the thickness and the electron density of the individual layer. Particularly, this technique allows for the determination of the amplitude and the phase of the electronic density modulation (i.e., the smectic order parameter) of the FLC film. We demonstrate that the x-ray results are essential for the determination of the complex dielectric functions of the FLC film from the shape and the angular position of the IPP resonance. Generally, we have found that for samples with a relatively large smectic order parameter the IPP resonance can be best fitted assuming an anisotropic dielectric tensor and the presence of domains in the FLC film. For well ordered smectic C* films at room temperature, the anisotropy of the dielectric tensor is slightly higher compared to the bulk value and shows a tendency to increase with the decrease of the film thickness in ultrathin films.
Raman scattering and nuclear surface characterization of aged porous silicon
Authors: Mariotto G. , Ziglio F. , Freire F. L.
Published: July 2002

Aged porous silicon layers (∼1 μm thick) have been characterized both by optical spectroscopy (Raman scattering and photoluminescence) and by nuclear surface techniques (Rutherford backscattering, elastic recoil detection, and nuclear reaction analysis). Samples with 85% and 70% porosity were analyzed after exposure to air for 1 month. Both these aged porous silicon layers emit visible light, but their luminescence shows dissimilar spectral features while their Raman scattering suggests a dissimilar microstructure. Chemical analyses indicate the presence of carbon and hydrogen at the porous surface, besides a surprisingly different oxygen concentration. A correlation between the structural and compositional results is attempted to account for the observed light emission spectra. In particular, the relative blue shift of the luminescence peak of sample with lower porosity is attributed to the stronger consumption of silicon nanocrystals operated by the silicon oxide formation during the aging process.
The influence of ion energy, ion flux, and etch temperature on the electrical and material quality of GaAs etched with an electron cyclotron resonance source
Authors: Cole M. W. , Ko K. K. , Pang S. W.
Published: July 2002

The residual damage incurred to GaAs via etching with a Cl2/Ar plasma generated by an electron cyclotron resonance (ECR) source was investigated as a function of variations in ion energy, ion flux, and etching temperature. The residual damage and electrical properties of GaAs were strongly influenced by changes in these etching parameters. Lattice damage was incurred in all processing situations in the form of small dislocation loops. GaAs etched at high ion energies with 200 W rf power, exhibited a defect density five times higher than GaAs etched at lower ion energies with 20 W rf power. This enhanced residual damage at the higher rf powers was paralleled by a degradation in the unannealed contact resistance. Higher etch rates, which accompany the higher rf power levels, caused the width of the disordered region to contract as the rf power was elevated. Therefore, the residual etch damage is influenced by both the generation and removal of defects. Increasing the microwave power or ion flux resulted in elevating the residual defect density, surface roughness, and unannealed contact resistance. GaAs etched at high temperatures, ∼350 °C, resulted in a lower contact resistance than GaAs etched at 25 °C. The high temperature etching augmented the defect diffusion which in turn lowered the near surface defect density. This decrease in residual damage was deemed responsible for improving the electrical performance at 350 °C. The electrical measurements were found to be more sensitive to the density of defects than the vertical extent of disorder beneath the etched surface. Results of this investigation demonstrate that in order to minimize material damage and improve electrical performance, etching with an ECR source should be performed at low rf and microwave powers with a high substrate temperature.
On the doubly resonant difference frequency mixing in an asymmetric quantum well structure
Authors: Zal/użny M.
Published: July 2002

The effect of the depolarization field on the doubly resonant frequency mixing due to resonant intersubband transitions in asymmetric quantum wells, with only the ground subband occupied, is discussed. Calculations are performed in the framework of the perturbative density matrix formulation with relaxation time approximation. The results show that in the considered system the depolarization effect can be included by simple replacement (in the one-electron expression for the nonlinear susceptibility) of the intersubband energy by the depolarization shifted intersubband energy.
Photoemission investigation of the ZnSe/CdTe heterojunction band discontinuity
Authors: Nelson A. J.
Published: July 2002

Synchrotron radiation soft x-ray photoemission spectroscopy and reflection high-energy electron diffraction were used to investigate the structural and electronic properties at the ZnSe/CdTe(100) heterojunction interface. ZnSe overlayers were sequentially grown in steps on p-type CdTe(100) single crystals at 200 °C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the Cd 4d, Zn 3d, and Te 4d core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the ZnSe/CdTe heterojunction valence band discontinuity and the consequent heterojunction band diagram. Results of these measurements reveal that the valence band offset is ΔEv=0.20 eV.
A statistical model of quantum dot arrays with Coulomb coupling
Authors: Suzuki Toshi-kazu , Nomoto Kazumasa , Ugajin Ryuichi , Hase Ichiro
Published: July 2002

We present a study of a statistical model of arrays of quantum dots, in which electrons are confined by semiconductor heterojunctions in all three dimensions, with Coulomb coupling. Our model describes repulsively interacting localized electrons whose number can vary with changes in chemical potential. By means of a Monte Carlo simulation, it is shown that, at low temperatures, some stable electron densities hardly changing in certain ranges of chemical potential appear, which are associated with suppressed fluctuation and characteristic spatial electron distributions. Spin fluctuation, which gives magnetic susceptibility, exhibits essentially different behavior depending on temperature and Coulomb energies.
Melting dynamics in current-carrying conductors and its effect on electrodynamic characteristics
Authors: Dolinsky Yu. , Elperin T.
Published: July 2002

This work studies the dynamics of melting in current-carrying conductors. Formulae are derived which describe the dependence of temperature at the front of phase transition upon the distance from the axis of the conductor. The thermodynamic stability of a phase transition front is investigated. It is shown that due to strong variations of conductivity during melting the rate of change of conductivity is of the same order as an active resistance of a conductor. Clearly the magnitude of this effect depends upon the ratio of electric conductivities in liquid and solid phases. The effect is stronger when this ratio is lower.
Observation of quantum confined Stark effect in InxGa1−xAs/GaAs single-quantum well by photoreflectance spectroscopy
Authors: Wang D. P. , Chen C. T. , Kuan H. , Shei S. C. , Su Y. K.
Published: July 2002

The photoreflectance spectroscopy of the InxGa1−xAs/GaAs single-quantum well system has been measured at several reverse dc bias voltages. The spectrum can be divided into two parts by the photon energy; one belongs to the GaAs bulk transition and the other belongs to the InxGa1−xAs/GaAs quantum well transition. The GaAs transition has shown the Franz–Keldysh oscillations which can be used to deduce the strength of the electric field in the bulk GaAs. On the other hand, the InxGa1−xAs/GaAs quantum well transition has exhibited the quantum confined Stark effect; that is, the transition energy in the quantum well will be redshifted in the presence of an electric field. The field in the quantum well can be estimated from the amount of redshifting and it was found that the built-in field in the quantum well needs to be close to that of GaAs.
Comment on ‘‘High temperature adsorption of nitrogen on a polycrystalline nickel surface’’
Authors: Pauleau Y.
Published: July 2002

The effect of the nitrogen partial pressure on the deposition rate of nickel lines produced by laser-induced chemical vapor deposition (LCVD) from nickel tetracarbonyl, Ni(CO)4, was investigated and discussed by Boughaba and Auvert on the basis of the Langmuir–Hinshelwood model valid for heterogeneous chemical reactions with competitive adsorption of reactant gases on the surface. From these experimental results, it can be demonstrated that the adsorption energy of nitrogen molecules on the nickel surface is negligible; as a result, it can be concluded that the residence time of nitrogen molecules as adspecies on the polycrystalline nickel surface is negligible, and the adsorption of nickel molecules on the nickel surface does not occur.
Nitrogen ion implantation with energy scanning mode into Zr
Authors: Miyagawa S. , Saitoh K. , Ikeyama M. , Nakao S. , Miyagawa Y.
Published: July 2002

To study effects of ion implantation with the energy scanning mode on the surface structure and the depth profile, Zr samples were implanted with 15N2 ions, where ion energy was scanned in the range of 70–100 and 70–130 keV using a computer-controlled power supply at an interval of 2 keV while monitoring the ion current of the sample. After the implantation of a total fluence of 3.5×1017 ions/cm2, the depth profiles of 15N2 ions in Zr were measured by nuclear reaction analysis of 15N(p,αγ)12C at 429 keV and the surface was observed by scanning electron microscopy. It was found that the implanted surface structure strongly depended on the implantation mode, and blistering induced by high fluence implantation of nitrogen could be completely avoided with the implantation mode of increasing energy gradually. The depth profiles were satisfactorily in agreement with the prediction by Monte Carlo simulation.
Improved photoluminescence properties of highly strained InGaAs/GaAs quantum wells grown by molecular-beam epitaxy
Authors: Kudo Makoto , Mishima Tomoyoshi
Published: July 2002

Highly strained InxGa1−xAs/GaAs quantum well structures on GaAs substrates were grown by molecular-beam epitaxy. Even with high In composition (0.4 or higher), sharp spectra were obtained from samples grown at 400 °C due to the reduction of In surface segregation. The full width at half maximum of the photoluminescence spectrum from a 6.4-nm-thick (21 monolayers) In0.42Ga0.58As/GaAs single quantum well at 77 K and at room temperature was only 9.78 and 18.4 meV, respectively. The peak wavelength of this sample at room temperature was 1.223 μm. The theoretically calculated peak wavelengths, using a finite square-well model are in good agreement with the experimental ones over a wide In composition range (between 0.14 and 0.44), and with well widths between 6 and 53 monolayers. This study suggests that the performance of pseudomorphic devices can be improved by using high-quality InxGa1−xAs layers with high In composition pseudomorphically grown on GaAs substrates.
Effect of growth temperature on dysprosium films deposited by molecular beam epitaxy on different substrate materials
Authors: Gupta M. K. , Kothiyal G. P. , Sahni V. C. , Vyas J. C. , Gandhi D. P. , Muthe K. P. , Sabharwal S. C.
Published: July 2002

Thin films of Dy were deposited on single crystal substrates of yttria stabilized zirconia, SrTiO3, and vitreous SiO2 by molecular beam epitaxy. The effect of the growth temperature on film composition and characteristics was investigated employing electron spectroscopy for chemical analysis, x-ray diffraction and electrical conductivity probes. For the films deposited on yttria stabilized zirconia and SrTiO3 substrates, a transformation from metallic to oxide was observed at growth temperatures of ∼200 °C. However, in the case of films deposited on SiO2 no such effect up to 500 °C was observed. The results show uptake of oxygen by the film from yttria stabilized zirconia and SrTiO3, implying poor stability of these materials with respect to oxygen at moderately high temperatures under ultrahigh vacuum.
Thermodynamic analysis of spherulitic growth in semicrystalline poly(ethylene oxide)
Authors: Marco G. Di , Lanza M. , Pieruccini M.
Published: July 2002

A thermodynamic model for the description of spherulitic growth in (semi-) crystalline polymers is presented. Its validity is restricted to the free growth stage of crystallization. The relevance of the role played by surface tension in the early stage of the process is pointed out. With the due approximations the predicted growth rate is found to be consistent with the well-known Avrami model. As an application, the melting temperatures Tm of poly(ethylene oxide) samples of different molecular weights are derived by fitting the appropriate crystallization thermograms carried out in isothermal conditions. A linear dependence of T−1m as a function of the inverse polimerization degree is found, which is consistent with a well-known result of the lattice theory.
Self-similarity in quasiperiodic Fibonacci superlattices in an in-plane magnetic field
Authors: Bruno-Alfonso A. , Reyes-Gomez E. , Oliveira L. E. , de Dios-Leyva M.
Published: July 2002

A theoretical study of the magnetic sub-bands, electron wave functions, and intraband transition strengths of GaAs–(Ga,Al)As quasiperiodic Fibonacci superlattices under in-plane magnetic fields is presented. Calculations were carried out in the effective-mass approximation and a parabolic model for the conduction band was used. Results were obtained for two magnetic fields related by integer powers of the golden mean τ=(1+√5)/2 with corresponding magnetic levels, electron wave functions, and transition strengths displaying a practically self-similar structure as appropriate for a GaAs–(Ga,Al)As Fibonacci superlattice.
Intensity threshold for holographic recording in amorphous As2S3 films
Authors: Salminen O. , Ozols A. , Riihola P. , Mönkkönen P.
Published: July 2002

The dependence of holographic recording on recording light intensity has been experimentally studied in nonannealed amorphous As2S3 films. It has been observed that the threshold of the recording intensity is about 10−5 W/cm2 for 10.5-μm-thick film and a 1 μm grating period. A phenomenological model is presented to explain the intensity dependence in the 10−5–10−1 W/cm2 intensity range. According to this model the observed intensity behavior is caused by photoinduced spatially periodic mechanical stress.
Field emission from a silicon surface-potential well based on an Airy function approach
Authors: Huang Qing-An
Published: July 2002

The properties of a silicon surface can be changed significantly when an intense electric field is applied to the surface. The difference of the field emission between metal and silicon are discussed. The quantum well arises when band bending of silicon confines the electrons to a narrow surface region. A general boundary condition for the study of field emission from silicon is presented within the framework of zero emitted current approximation. A theoretical study of the field-emission current from silicon is given based on an exact solution of the Schrödinger equation under the application of a linear potential field. The presented approach is obviously valid for treating field emission from a silicon surface-potential well.
Thermal and optical properties of PbO-KF glasses
Authors: Nachimuthu P. , Jagannathan R.
Published: July 2002

Glass formation between PbO and KF is reported. The influence of composition on thermal stability, density, molar volume, refractive index, optical band gap, Urbach energy, and Pb2+ emission spectra are presented. While KF influences thermal stability, the PbO content markedly influences the optical properties due to the formation of strong -Pb-O-Pb- covalent linkages. Increasing PbO content also results in phonon assisted nonradiative decay from 1P1 and 3P1 levels to 3P0 level leading to a marked decrease in the 1P1→1S0 emission.
Vortex dynamics in superconducting microbridges with low-vortex pinning forces and superconducting flux flow transistors
Authors: Bernstein P. , Picard C. , Becker V. , Flament S. , Beaudet N.
Published: July 2002

We present a mean-field model for the mixed state of superconducting microbridges with low pinning forces which accounts for the I–V characteristics measured on superconducting flux flow transistors (SFFTs) as well as the improvement of the performances of these devices when they include several microbridges. From the model it turns out that the vortex motion is not mostly driven by the bias current as is assumed in classical flux flow descriptions but by a diffusion process. Moreover, it is shown that due to the magnetic coupling between bridges, the critical current of a device with n bridges is larger than n times the critical current of a single bridge. Expressions for this increase in the critical current and the current gain of these devices are given. The model also accounts for the dynamic resistance modulation of SFFTs when an external magnetic field is applied.
Suppression of oxide growth on porous silicon by treatment with HF vapor
Authors: Kim Chang-Koo , Chung Chan-Hwa , Moon Sang Heup
Published: July 2002

We have observed by experiment that the oxide growth rate on porous silicon is reduced to a minimum when the surface is treated with a proper amount of HF vapor. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy observations of the treated surface suggest that the oxide growth rate is closely related to the amount of the surface fluorides.
Structure of laser deposited metallic alloys
Authors: Störmer Michael , Krebs Hans-Ulrich
Published: July 2002

The structure of metallic alloys grown by pulsed KrF laser deposition is examined by x-ray diffraction and compared with results from literature on sputtered and evaporated films. In general, the phases and structures obtained are similar, while laser deposited films often exhibit unusually enlarged lattice parameters in direction of growth, small grain sizes, larger extensions of the single-phase regions and sometimes better alignment of the grains. These differences can be explained by the approximately 105 times higher instantaneous deposition rate of the pulsed laser ablation process and the high kinetic energy of the deposited particles of up to more than 100 eV.
Local and global ordering in rodlike polymer monolayers at the air–water interface
Authors: Zhu Yang-Ming , Wei Yu
Published: July 2002

The compressed monolayers of a rodlike polymer at the air–water interface were transferred onto solid substrates by a horizontal lifting method and studied by the liquid crystal alignment technique. It has been found that the rodlike polymer monolayers have a well ordered orientation on a local region while on a larger scale they consist of disordered domains within which the polymers are uniformly oriented.
Wave scattering by a two-dimensional band-limited fractal surface based on a perturbation of the Green’s function
Authors: McSharry P. E. , Cullen P. J. , Moroney D.
Published: July 2002

A fast approximate method is described to calculate the acoustic scattering from a one-dimensional Dirichlet band-limited fractal surface. The formulation is based on a perturbation of the Green’s function allowing an approximation of the propagator in the kernel of the Helmholtz integral equation, which reduces the integral equation to a convolution equation. This allows us to find a solution using Fourier transforms rather than the usual matrix inversion that is required. We have shown that in the limit of small kσ, where k is the incident wave number and σ is the rms height, it is possible to find accurate closed form expressions for the reflection coefficients Rn, the spectral components of the normal gradient of the field ψn, the scattered field psca, and the angular scattering coefficient Isca representing the scattering from a band-limited fractal surface. For small values of kσ≪1, we have used the generalized Rayleigh method [D. L. Jaggard and X. Sun, J. Appl. Phys. 68, 5456 (1990)] to determine the theoretical linear relationship which exists between the slope of the absolute value of the reflection coefficients in dB versus the reflection mode and the fractal dimension D. This theoretical relationship has been verified by using the Green’s function perturbation method. This relationship and an analogous relationship between the scattering coefficient and the scattering angle allows the determination of the fractal dimension D and the rms height σ from the scattering pattern when kσ≤0.2.
Radiation-induced defects in CaF2: An electron-spin resonance and dielectric constant investigation
Authors: Beuneu F. , Vajda P.
Published: July 2002

CaF2 single crystals have been irradiated at T=21 K and at 0 °C with electrons of 0.5 and 1 MeV energy. The low-temperature irradiated samples exhibit electron-spin-resonance (ESR) spectra with signals due to F-centers and an unchanged real component of the dielectric constant ε′. The room temperature irradiated crystals, on the other hand, present ESR-spectra due to VF-, U-, and, possibly, to metallic-colloid (g=2.003) centers as well as an increased (dose dependent) ε′. The introduced defects and the radiation-induced Δε′ are investigated in a thermal annealing treatment up to 900 °C. Their recovery behaviour is complex and can be interpreted as a competition between growth and annihilation processes of metallic clusters estimated to have initially a radius of ∼200 Å. Thus, the appearance of a new ESR-line near g=2.000 after an anneal at 200 °C indicates the possible transformation of colloids to larger units before vanishing. The annealing spectrum of Δε′ and the dose dependence of its substages support the ESR findings.
Formation of β-Si3N4 by nitrogen implantation into SiC
Authors: Miyagawa S. , Nakao S. , Saitoh K. , Ikeyama M. , Niwa H. , Tanemura S. , Miyagawa Y. , Baba K.
Published: July 2002

Polycrystalline β-SiC samples were implanted with 50 keV 15N ions with fluences ranging from 3×1017 to 1.5×1018 ions/cm2 at elevated temperature up to 1100 °C. Nitrogen depth profiles were measured as a function of implantation temperature and annealing temperature using nuclear reaction analysis, Rutherford backscattering spectroscopy, and Auger electron spectroscopy. It was found that the maximum concentration and the width of nitrogen depth profiles implanted at 1100 °C were reduced distinctly in comparison with the profiles implanted below 930 °C or annealed at 1100 °C. The redistribution of nitrogen implanted in SiC at 1100 °C was ascribed to the formation of β-Si3N4 crystallites in SiC, which was confirmed by x-ray diffraction at glancing incidence.
Bubble domains in garnet films studied by magnetic force microscopy
Authors: Wadas A. , Wiesendanger R. , Novotny P.
Published: July 2002

We have studied magnetic domain structure in (YSmLuCa)3(FeGe)5O12 garnet thin film by using magnetic force microscopy (MFM). Domain wall contrast of bubble domains has been revealed using Permalloy–Fe double-layer thin-film tips. We have also observed that nanometer scale deformations of the surface disturb a magnetic bubble structure by introducing stripe domains. MFM images have shown that stripe domains pin their domain walls to surface scratches. The domains can change their location with respect to a scratch by switching a domain wall pinned to a scratch.
Some optical and thermal properties of Cd0.9Mn0.1Te
Authors: Weil R. , Yampolsky O. , Furdyna J. K. , Deljouravesh R. , Steinitz M.
Published: July 2002

The index of refraction of Cd0.9Mn0.1Te was measured at a wavelength of 10.25 μm at room temperature on twinned unoriented monocrystal samples. The result was n=2.57±0.01. Furthermore, the temperature dependence of the index of refraction was measured to be (1/n)dn/dt=5.0±0.1×10−5 K−1. The optical absorption coefficient was α=0.13 cm−1. Finally, the linear expansion coefficient in the range of 293–373 K was found to be γ=−1±1×10−6 K−1.
The strain relaxation of In0.1Ga0.9As on GaAs (110) grown by molecular beam epitaxy
Authors: Zhang X. , Pashley D. W. , Neave J. H. , Hart L. , Joyce B. A.
Published: July 2002

The strain relaxation of In0.1Ga0.9As layers on GaAs (110) was studied by transmission electron microscopy (TEM) and x-ray diffraction. TEM observation showed that strain relief in the (110) interface is initially dominated in the [001] direction by the formation of 60° type dislocations and stacking faults via {111}〈011〉 slip systems for layer thicknesses up to approximately 200 nm. As the layer thickness increases, {113}〈011〉 slip systems became active and the resultant misfit dislocations contribute strain relief in both [001] and [11̄0] directions. The efficiency of strain relief by the different misfit dislocations is discussed.
A non-invasive technique for the assessment of the onset of optical damage in molecular crystals
Authors: Bailey R. T. , Cruickshank F. R. , Kerkoc P. , Pugh D. , Sherwood J. N.
Published: July 2002

The extent of the mechanical distortion of the (001) crystal plane of (-)2-(α-methylbenzylamino)-5-nitropyridine consequent upon the absorption of a 25 ns full width at half maximum, 10 J/cm2 pulse from a Nd:YAG laser operating at the wavelength 1064 nm has been measured by a nondestructive and noninvasive technique. The anisotropy of the distortion has been quantified.
Annealing-induced effects on the stability of hydrogenated amorphous silicon
Authors: Schmidt J. A. , Koropecki R. R. , Arce R. , Buitrago R. H.
Published: July 2002

We performed isothermal annealing on a hydrogenated amorphous silicon (a-Si:H) sample deposited at low temperature in a glow discharge reactor. In order to change the hydrogen bonding configuration without affecting the silicon structure we choose a relatively low annealing temperature. We studied the dependence on the annealing time of the dark conductivity, photoconductivity, light-induced degradation of the photoconductivity, optical gap, vibrational spectra, and subgap defect density. As the annealing time increased we found an increase in the dark conductivity activation energy. This shift of the dark Fermi level toward the valence band was correlated with the growth of a peak in the density of states below midgap. From the vibrational spectra we obtained the microstructure parameter, which is indicative of the amount of hydrogen bonded as polihydrides and/or to some sort of internal surface. We used the bond-breaking model to fit photoconductivity decay as a function of illumination time, and we found a correlation between the Staebler–Wronski susceptibility and the microstructure parameter. This would mean that the stability of the material concerning light-induced degradation is related to the way hydrogen is attached in the amorphous network.
Cluster emission during sputtering of liquid gallium-aluminum eutectic alloy
Authors: Lill Th. , Calaway W. F. , Pellin M. J.
Published: July 2002

Abundance distributions of ionic and neutral clusters sputtered by 4 keV argon ion impacts on a liquid gallium-aluminum eutectic alloy have been measured by time-of-flight mass spectrometry. To photoionize the neutral species, a 193 nm (6.4 eV) ArF laser has been used. Neutral and ionic clusters as large as Ga14 and mixed clusters of the form GanAl with n≤13 were detected. The abundance of the monoaluminum mixed clusters is found to increase with nuclearity and is discussed as the consequence of an increasing clusters depth of origin as the nuclearity increases. A comparison of the results with those obtained from the gallium-indium eutectic alloy reveals a similar cluster nuclearity dependence of the depth of origin.
Effect of water vapor on the nucleation and growth of chemical vapor deposited copper films on spin-coated polyimide
Authors: Kim Jung-Yeul , Marzouk H. A. , Reucroft P. J. , Eloi C. C. , Robertson J. D.
Published: July 2002

The effect of water vapor on the mechanisms of nucleation and growth of metallo-organic chemical vapor deposited copper films from copper (II) hexafluoroacetylacetonate [Cu(hfa)2] on a polyimide substrate has been investigated. Minimal copper deposition was observed on the polyimide substrate in the absence of water vapor. When water vapor was introduced into the system, blanket copper deposition was observed on the whole polyimide surface. The initial nucleation and growth of copper film on polyimide is initiated by the reaction between the vapor phase precursor and water vapor not the surface chemistry reaction between the vapor phase precursor and the substrate. Copper film growth on the polyimide substrate can thus be attributed to an initial oxidation of the organic ligand by water vapor followed by reduction of the resulting copper oxide by hydrogen.
Numerical modeling of the dependence of the steady-state photoconductivity in hydrogenated amorphous silicon on the rate of carrier generation
Authors: Shen D. S. , Wagner S.
Published: July 2002

The photoconductivity σph of hydrogenated amorphous silicon measured in experiments has a power law dependence on the carrier generation rate G: σph∝Gγ. The exponent γ is often interpreted as a measurement of the density of states distribution in the upper half of the band gap. This paper reports the numerical modeling of the dependence of the photoconductivity on the carrier generation rate. Examination of the traditional closed form solution shows that for the important case of γ close to unity, numerical modeling is required. The results of such numerical modeling show that γ is more sensitive to the total number of gap states rather than the distribution of states. A γ close to unity is better interpreted as a supplementary indication of low total defect density in the upper half of the band gap, instead of a certain distribution of these states.