bluuebunny/crossref_metadata_2025 huggingface dataset:
A technique for projection x-ray lithography using computer-generated holograms
Authors: Jacobsen Chris , Howells Malcolm R.
Published: July 2002

X-ray projection lithography has recently been explored as a method for the manufacture of <200 nm linewidth integrated circuits. A method is described whereby projected lithographic images can be formed with x rays by means of a transmission hologram. The form of the hologram is computed by an algorithm that eliminates the unwanted signals normally present as systematic errors in in-line holographic images. Example calculations are shown in which holograms are constructed to generate images of a given test pattern. The holographic images are shown to have excellent fidelity with respect to both resolution and contrast. Such an approach to projection x-ray lithography requires an x-ray beam with very little coherence and is thus compatible with high wafer throughput schemes; in addition, image fidelity remains high even when moderately small contaminant particles block the light from small regions of the hologram. Fabrication limits for the single optic involved are compatible with current technological limits. The approach is applicable over a large range of soft-x-ray wavelengths, indicating the feasibility of a 100 nm resolution system with 6 μm depth of field using a carbon mask system operating at 5 nm, or other materials at shorter wavelengths.
Tunable photoluminescence of uniformly doped short-period GaAs doping superlattices
Authors: Choquette Kent D. , McCaughan Leon , Misemer D. K. , Potts J. E. , Vernstrom G. D.
Published: July 2002

Uniformly doped n-p GaAs doping superlattices with smaller period lengths than have been previously considered are characterized by electrochemical capacitance-voltage profiling and low-temperature photoluminescence. In spite of the short period lengths, the n-p structures exhibit obvious doping superlattice attributes. We directly observe free-carrier confinement due to the space-charge potential in superlattices with periods as short as 12 nm. The variation of the photoluminescence energy with excitation intensity decreases with reduced period lengths, while the photoluminescence intensity increases with decreasing periodicity. We observe anomalously red-shifted emission at low photoexcitation intensity in superlattices with periods of 20 nm and less. We argue that radiative recombination between spatially arranged donor and acceptor states associated to the random fluctuations in the superlattice potential occurs in superlattices with periods less than 20 nm. The occupied impurity states give rise to screening of an effective superlattice potential and the observed photoluminescence tunability.
On the excitation efficiency in ZnS:Mn thin-film electroluminescent devices
Authors: Zeinert A. , Benalloul P. , Benoit J. , Barthou C. , Dreyhsig J. , Gumlich H.-E.
Published: July 2002

In ac-coupled ZnS:Mn thin-film electroluminescent devices, the excitation efficiency ηexc depends on the insulator/ZnS interfaces and the excitation level. For optimized devices which are used in industrial production, ηexc does not depend on the transferred charge as long as the excitation level is below the saturation range. In the saturation range, ηexc decreases with increasing charge transfer. Hence the decrease of the total efficiency η at high excitation levels is partly due to the behavior of the excitation efficiency and not entirely to the decrease of the radiative efficiency ηlum. In devices with shallow insulator/ZnS interface states, however, charge injection starts at lower fields and ηexc increases strongly with the transferred charge and the applied voltage.
Effects of oxygen and pressure on diamond synthesis in a magnetoactive microwave discharge
Authors: Chang J. J. , Mantei T. D. , Vuppuladhadium Rama , Jackson Howard E.
Published: July 2002

The effects of oxygen addition and total pressure on the synthesis of diamond have been studied in a magnetically enhanced microwave discharge. Diamond films were deposited on silicon substrates at substrate temperatures from 540 to 650 °C and total pressures from 2 to 20 Torr, and were characterized by microprobe and macrochamber Raman spectroscopy and scanning electron microscopy. Without oxygen, Raman spectra of these films display only graphitic peaks. As oxygen is added, faceted crystalline diamond is observed in scanning electron microscope micrographs and a sharp diamond peak in the Raman spectrum appears. With 2% oxygen, diamond films exhibiting a pure diamond Raman peak at ∼1334 cm−1 with very small nondiamond carbon peaks were grown at relatively low temperature (∼600 °C) and low pressure (5–10 Torr).
Nonuniform strain gradients in CdS/GaAs films measured by reflection high-energy electron diffraction and Raman spectroscopy: A microscopic approach
Authors: Sinha Kislay , Menéndez José , Wright David , Niles David W. , Höchst Hartmut
Published: July 2002

Strain relaxation at the lattice mismatched CdS/GaAs (100) interface has been investigated by reflection high-energy electron diffraction (RHEED) and Raman scattering. In-situ RHEED measurements indicate a gradual relief of the mismatch strain once the critical film thickness is exceeded. After-growth Raman measurements reveal that the strain profile measured by RHEED remains ‘‘frozen’’ in the grown layer except very close to the CdS/GaAs interface, where further relaxation takes place. A microscopic calculation shows that the presence of nonuniform strain leads to phonon confinement effects, as localized modes appear in regions of similar strains.
Isolation properties and experimental ranges of high energy ions in GaAs and InP
Authors: Pearton S. J. , Jalali B. , Abernathy C. R. , Hobson W. S. , Fox J. D. , Kemper K. W. , Roa D. E.
Published: July 2002

The formation of high-resistivity layers in initially highly doped n- and p-type epitaxial GaAs by the passage of 25- to 50-MeV oxygen ions was investigated. The experimentally determined projected ranges of these ions are 14.0 and 28.8 μm, respectively. The sheet resistance of thin (0.5 μm) epitaxial surface layers exposed to such ions increases rapidly with fluence in the range 1013–1015 cm−2 but, depending on the initial doping density, may decrease again at higher doses. The remnant conductivity in the epitaxial layers after implantation is dominated by hopping processes with low activation energies (43–68 meV). Secondary-ion mass spectrometry was used to measure the depth profiles of Si ions implanted into GaAs and InP at energies of 30–70 MeV. The projected ranges are slightly larger (≤10%) than those predicted by current theory, and the activation efficiency of the implanted Si ions in both GaAs and InP is higher than for low-energy (∼100 keV) ions.
Luminescence from Bi2Sr2CaCu2Ox and YBa2Cu3O7−x films in the scanning electron microscope
Authors: Domínguez-Adame F. , Fernández P. , Piqueras J. , Prieto P. , Barrero C. , Gómez M. E.
Published: July 2002

Visible and near infrared cathodoluminescence of Bi2Sr2CaCu2Ox and YBa2Cu3O7−x films is investigated in the scanning electron microscope. In particular, possible analogies in the cathodoluminescence of both systems have been analyzed. The spectra show only minor and slightly defined common features. Low-temperature observations show the capability of the cathodoluminescence technique to detect fine structural transitions. Some transformations induced by the electron beam are described.
Chemical interactions at a Ti/Bi2Sr2CaCu2O8 interface
Authors: Asoka Kumar P. S. , Mahamuni Shailaja , Nigavekar A. S. , Kulkarni S. K.
Published: July 2002

X-ray and ultraviolet photoelectron spectroscopies were used to investigate the microscopic changes at the Ti/Bi2Sr2CaCu2O8 interface. Ti extracts oxygen out of the superconductor by disrupting vital bonds such as Cu—O and Bi—O. The adatom-induced oxygen withdrawal is explained on the basis of cationic bond lengths in the superconductor and standard bond strengths. The changes associated with Cu 2p spectra are attributed to an increase in covalency of Cu—O bonds, which is the consequence of a rearrangement of oxygen anions around Cu+2 ions. In the early stages of the interface formation, bismuth and titanium are in a complex bonding configuration, which is evident from their binding energies. The line shape analysis of Ti 2p spectra reveals that Ti is in multiple oxidation states at different stages of the evolving interface. This shows that the mobility of oxygen is an important factor which controls the overlayer growth.
Temperature transients associated with pulsed heating of single particles
Authors: Monazam E. R. , Maloney D. J.
Published: July 2002

The transient thermal response of a single spherical particle in a cold quiescent gas is considered when the particle is heated by a sequence of well-characterized radiation pulses. The equations describing particle heating and cooling are formulated and a numerical solution is presented. The sensitivity of particle temperature as a function of heating pulse, particle, and gas properties is illustrated. Measured temperature histories of single particles suspended in an electrodynamic balance and pulse heated with a CO2 laser are presented in support of the analysis. The combination of unique state of the art instrumentation with the heat transfer analysis described results in a powerful new method for characterizing thermophysical properties of materials such as heat capacity and absorptivity.
Electron multiplication and electrostatic discharge wave forms
Authors: Lin D. L.
Published: July 2002

A metal block, immersed in the electric field of an electrode, has been used to study the electrostatic discharge phenomenon. Using a high-speed transient oscilloscope, current wave forms of air discharge across a small fixed gap between the metal block and a current probe have been measured. The combined bandwidth of the measurement setup, including the oscilloscope, cables, connectors, splitter, and the probe, is above 3.5 GHz. The setup is capable of measuring rise time as fast as 100 ps. Voltage change on the metal block was also measured by a low-speed transient oscilloscope. For a gap of 0.01 cm and a voltage of 1086 V, the observed current wave form of the discharge exhibits a rise time of 300 ps, a peak current of 5.8 A, and a pulse width at half-height of 770 ps, about 2.6 times the rise time. The existence of a residual voltage on the metal block after each discharge was also observed. Using the Townsend’s α coefficient for the electron multiplication in air, an analytic model and a one-dimensional numerical model have been developed to explain the wave-form characteristics and the residual voltage observed.
Limitations on the critical current density in Bi2Sr2CaCu2O8 films grown on MgO(001) by metalorganic deposition
Authors: Hung L. S. , Lee S. T. , Mir J. M. , Shin D. H. , Li Jian , Silcox J. , Mayer J. W.
Published: July 2002

A systematic study has been carried out in order to elucidate the mechanisms for low critical current densities in superconducting oxide films prepared by metalorganic deposition. Bi2Sr2CaCu2O8 films grown on MgO(001) have stoichiometric composition and exhibit limited interfacial reaction with the underlying substrates. The films have a low content of carbon and the grain boundaries are mostly clean. Rocking curve analysis shows a narrow peak, while pole figure measurements indicate a strong mosaic pattern. The films exhibit a low critical current density and the magnetic susceptibility versus temperature has a high field dependence. A substantial increase in critical current densities can be achieved when the orientations of Bi2Sr2CaCu2O8 crystallites in the a-b plane are improved.
Fourier transform infrared study of thermally grown SiO2 in the presence of 1,1,1, trichloroethane
Authors: Bhan R. K. , Ashokan R.
Published: July 2002

Gate oxides for metal-oxide–semiconductor devices have been grown in presence of 1,1,1, trichloroethane (TCA) as a chlorine source for passivation. Infrared absorption was studied in these oxides and results were compared with oxides grown in presence of trichloroethylene (TCE) under identical conditions to assess the feasibility of substituting a TCA source for TCE. It is found that the stoichiometry of these oxides is not affected by the type of chlorine source, i.e., TCA or TCE. However, based on this study a different reaction mechanism for TCA or TCE oxides is proposed wherein C2H4 is also a byproduct in addition to well known HCl, Cl2, CO2, and H2O. Furthermore, Si—OH deformation observed in the infrared transmission (IR) spectra at 880 cm−1 is held responsible for passivation of interface states, i.e., tying up of dangling Si bonds at Si—SiO2 interface. A modified structural model is proposed for these oxides, which could account for all the observed IR vibrations.
Proton implantation into GaAs: Transmission electron microscopy results
Authors: Schober T. , Friedrich J. , Altmann A.
Published: July 2002

Semi-insulating liquid-encapsulated Czochralski grown GaAs wafers were implanted at room temperature with protons at energies of 2, 4, and 30 keV at doses up to 1×1018 cm−2. Without using further annealing treatments the samples were inspected, also using cross-sectional techniques, by transmission electron microscopy. Surface amorphization of the bombarded GaAs was found. Excess hydrogen precipitates in the form of large bubbles in the amorphous layer. Nearly spherical hydrogen bubbles were detected in the crystalline layer below the amorphous zone. At 30 keV, pressurized bubble rafts, where a certain number of bubbles are located in the plane of a microcrack, were detected. The recent observations of similar bubble rafts by Neethling and Snyman [J. Mater. Sci. 23, 2697 (1988)] and the present rafts are discussed in the light of the theoretical treatment by d’Olieslaeger et al. [Philos. Mag. B 63, 1321 (1991)]. The bubble rafts have presumably been produced by the collapse of pressurized hydrogen-filled microcracks.
Calculated majority- and minority-carrier mobilities in heavily doped silicon and comparisons with experiment
Authors: Bennett Herbert S. , Lowney Jeremiah R.
Published: July 2002

As silicon devices approach 0.1 μm in size, it will be essential to have accurate values of the majority and minority mobilities of electrons and holes. These mobilities have been calculated in silicon for donor and acceptor densities between 1017 and 1020 cm−3. All the important scattering mechanisms have been included. The ionized impurity scattering has been treated with a quantum-mechanical phase-shift analysis. The results are in good agreement with experiment, but predict that the change of minority electron mobility with increasing dopant density should decrease slightly at high dopant densities for a small range of densities. This effect occurs mainly because of the reduction of plasmon scattering. Some recent experiments support these findings. In addition, the ionized impurity scattering rates calculated from the quantum-mechanical phase shifts and those rates calculated from the Born approximation are shown to differ by more than factors of 3. The Born approximation is not valid for low-energy carriers near band extrema. Carrier scattering rates are key input quantities for Monte Carlo calculations of carrier-velocity versus electric-field relations and of simulations of device behavior. Our calculations do not treat the density-of-states modifications due to heavy doping, which should have only a small effect on the mobility at room temperature.
An analysis of surface acoustic wave propagation in a piezoelectric film over a GaAs/AlGaAs heterostructure
Authors: Kim Yoonkee , Hunt William D.
Published: July 2002

This paper presents a theoretical analysis of the surface acoustic wave (SAW) propagation in a GaAs/AlGaAs heterostructure covered with a piezoelectric film such as ZnO, BaTiO3, PbTiO3 or PZT. We calculate the SAW potential profile, SAW velocity, and effective piezoelectric coupling constant as functions of the film thickness using a Laguerre polynomial technique. The effective material constants such as the characteristic admittance and equivalent dielectric constant are also obtained. We concentrate on the suitable choice of the film for a heterojunction acoustic charge transport device. A ZnO film of 0.3–0.5 acoustic wavelength thickness seems to be the most suitable choice.
Resonant tunneling of holes in Ga0.51In0.49P/GaAs double-barrier heterostructures
Authors: Lippens D. , Mounaix P. , Sadaune V. , Poisson M. A. , Brylinski C.
Published: July 2002

We report the observation of resonant tunneling of holes in the GaInP/GaAs system. The tunneling structure consists of two lattice-matched 30-Å-thick Ga0.51In0.49P barriers with a 40-Å GaAs well in between, sandwiched by p-GaAs layers. Three resonances are clearly visible in the current-voltage characteristics with direct evidence of a negative differential resistance at 77 K. Analyzed in terms of tunneling probabilities for light and heavy holes, respectively, calculations show some discrepancy with experiment, suggesting band-mixing effects.
Investigation of the homogeneity of trapping centers in photorefractive crystals
Authors: Amrhein P. , Günter P.
Published: July 2002

The homogeneity of trapping centers in photorefractive crystals has been investigated with a novel method. Phase gratings written in the crystal are read out with a beam that is focused by a cylindrical lens. The diffracted intensity distribution is measured while scanning the focal line of the readout beam over the crystal plate. In an iron-doped and reduced KNbO3 crystal we find simultaneous electron and hole conduction in different crystal areas. The effects of poling and electrochemical reduction treatment are studied in doped and undoped, and reduced and unreduced KNbO3 crystals.
Negative charging in ultrathin metal-oxide-silicon tunnel diodes
Authors: Andersson M. O. , Farmer K. R. , Engström O.
Published: July 2002

A negative charging effect is studied in small, ultrathin metal-oxide-silicon diodes biased at constant voltage. The charging is seen as a gradual decrease in the magnitude of the tunnel current over time. Along with the charging, the current noise power decreases. Results are described from measurements of the temperature and voltage dependence of the current transients. A physical model is presented in which filling and emptying of electron traps in the as-grown oxide cause the noise, and the conductance decrease is caused by the transformation of these traps into fixed negative charge storage centers. From fits of the model to measured data, we obtain a thermal activation energy of 0.3 eV for the charging process. A low-temperature annealing treatment at 200 °C restores the conductance of a previously charged device to its initial value. On the other hand, the charging effect can be eliminated by a 350 °C anneal in nitrogen. Together, these experiments suggest that the traps are water- or hydrogen-related defects.
Influence of quenching speed on the superconducting transition temperature of YBa2Cu3O7−δ annealed in air at 650–1200 K
Authors: Lo Cascio D. M. R. , van Wees M. T. , Bakker H.
Published: July 2002

Both single and polycrystalline samples of YBa2Cu3O7−δ were annealed in air at different temperatures between 650 and 1200 K and subsequently quenched at two different speeds: the conventional quench in liquid nitrogen and a high-speed quench (5×104 K/s) using a special device. Both x-ray and ac-susceptibility measurements were used to investigate the influence of quenching speed on the oxygen ordering and Tc. During quenching partial reordering takes place. In the rapidly quenched samples more disorder was frozen in, which corresponds to a lower Tc.
Investigation of low-temperature I-V curves of high-quality Nb/Al-AlOx/Nb Josephson junctions
Authors: Monaco R. , Cristiano R. , Frunzio L. , Nappi C.
Published: July 2002

A detailed experimental temperature dependence of the subgap current of high-quality Nb/Al-AlOx/Nb Josephson tunnel junctions is reported. The presence of a pronounced current rise at V≂Δ/e is observed. Comparison with the theoretical model for two-particle tunneling is performed, but a substantial disagreement is found. At V<Δ/e the measured current is in remarkably good agreement with the single particle tunneling predictions down to 2 K.
Oxygen-induced Al surface segregation in AlxGa1−xAs and the effect of Y overlayers on the oxidation of the Y/AlxGa1−xAs interface
Authors: Mesarwi A. , Ignatiev A.
Published: July 2002

The oxidation of AlxGa1−xAs (x=0.15, AlGaAs) was studied by Auger electron spectroscopy and x-ray photoelectron spectroscopy at 350 °C and different oxygen exposures (up to 5×104 L). Also studied were the effects of yttrium overlayers (θ=3 ML) on the oxidation of the AlGaAs surface. Substantial oxygen-induced Al surface segregation has been observed for both yttriated and non-yttriated AlGaAs surfaces which increased with increasing oxygen exposure. Also observed is a significant Y-enhanced oxidation of the AlGaAs surface. Oxidation of the yttriated AlGaAs surface was found to be a factor of 4 greater than that of the non-yttriated surface. Also, while oxidation of the non-yttriated AlGaAs yielded mainly Al2Ox (x<3) and only little Ga2O3, the yttriated AlGaAs surface oxide layer was principally Ga2O3 and stoichiometric Al2O3. However, both the yttriated and non-yttriated surfaces were found to contain metallic As within the oxide layer.
High luminous efficiency thin-film electroluminescent devices with low resistivity insulating materials
Authors: Hsu C. T. , Li J. W. , Liu C. H. , Su Y. K. , Wu T. S. , Yokoyama M.
Published: July 2002

In order to fabricate high brightness and high efficiency thin-film electroluminescent (EL) devices, the emission characteristics of devices employing low resistivity and high dielectric constant materials, such as radio-frequency-sputtered HfO2 films, have been studied. It was found that the EL device with a glass/indium tin oxide/BaTiO3/ZnS:TbF3/HfO2/Ta2O5/HfO2/Al structure exhibited higher brightness and higher efficiency than the other devices. The highest luminous efficiency (η) and brightness of 0.9 lm/W and 1000 cd/m2, respectively, were obtained at 1-kHz sinusoidal wave voltage excitation. This was mainly due to the insulating layers adjacent to the active layer, which have low resistivity and high dielectric constant. So, it has higher density of interface states and deeper interface states at HfO2–ZnS and BaTiO3–ZnS interfaces.
On the carbon incorporation into a-SiC:H films with low carbon content
Authors: de Oliveira M. L. , Camargo S. S. , Freire F. L.
Published: July 2002

In this paper we report on carbon incorporation into a-SiC:H films with low carbon content deposited from SiH4:CH4:H2 gaseous mixtures. In the case of films deposited without H2 dilution, carbon incorporation mainly as CH3 groups, was determined. Increasing H2 dilution was found to induce a selective incorporation of radicals that affects the density of C—H bonds, thus reducing the mean number of carbon bonded hydrogen atoms per carbon atom. Our observations allowed the estimation of the oscillator strength for the C—H stretching mode of CH3 groups in undiluted a-SiC:H films, obtaining ΓC—H(CH3)=9×10−23 cm2.
Microwave demagnetization
Authors: Walton D. , Shaw J. , Share J. , Hakes J.
Published: July 2002

It has been possible to demagnetize an assembly of single-domain grains by direct excitation with microwaves.
Canonical aberration theory of multipoles: A critical reanalysis
Authors: Shao Zhifeng , Ximen Jiye
Published: July 2002

Canonical aberration theory has been applied to analyze the aberration structure of both electrostatic and magnetic multipoles. It is shown rigorously that for 2N-pole magnetic multipoles with N=even, there is no axially symmetric aberration of any order, while for all the other cases of electromagnetic multipoles, there is always an axially symmetric aberration of the order of 2N−3. The method used is general in nature and can be applied to obtain detailed formulas of higher-order aberrations of multipoles and also to study their off-axis aberrations.
Impact ionization coefficient and energy distribution function in polar and nonpolar semiconductors
Authors: Cho Sung M. , Lee Hong H.
Published: July 2002

An approximate solution of the Boltzmann transport equation is used to arrive at an expression for the electron energy distribution function. All major scattering mechanisms, including intervalley scattering, are included, and a distinction is made between nonpolar (Si, Ge) and polar (GaAs) optical phonon scattering. Numerically calculated impact ionization coefficients for electrons and holes in Ge, Si, and GaAs compare favorably with almost all experimental results reported in the literature. In polar semiconductors, in particular GaAs, intervalley scattering is found to dominate.
Properties of alloy precursors and the resulting superconducting YBa2Cu3O7−δ-Ag composites
Authors: Early E. A. , Simnad M. T. , Maple M. B.
Published: July 2002

A significant obstacle to the widespread application of high-temperature superconductors are the poor mechanical properties of these oxides. A novel processing technique was investigated that attempts to circumvent this problem using ductile alloy precursors to superconducting composites. Alloys of composition Y-2Ba-3Cu-Ag were prepared by arc- and induction melting the metals. A variety of mechanical tests show that alloys with 90 wt % Ag are ductile, and differential thermal analysis indicates a solidus temperature of 703 °C. Using thermogravimetric analysis, the oxidation rate of Y-2Ba-3Cu-90 wt % Ag alloys was studied. This rate does not follow that which is expected based upon the theory of internal oxidation, nor is there a transition to external oxidation upon lowering the partial pressure of oxygen. The superconducting properties of the oxide in the resulting composite are similar to those of polycrystalline samples, with a Tc of 90 K. Superconductivity is achieved only when the alloy is oxidized above the solidus temperature, where the presence of a liquid phase enables the oxides to be concentrated and connected.
Thermal stability of field-forced and field-assisted antiferroelectric-ferroelectric phase transformations in Pb(Zr,Sn,Ti)O3
Authors: Yang Pin , Payne David A.
Published: July 2002

Antiferroelectric (AFE)-ferroelectric phase transformations in tin-modified lead zirconate titanate, i.e., Pb(Zr,Sn,Ti)O3 are reported. A martensitic-type approach is developed to explain the observed thermal hysteresis and field-induced transformation behavior. A model is proposed with transformation fields where the forward EF and reverse EA field strengths are related to the transformation barrier to the ferroelectric state, and to the AFE sublattice coupling, respectively. The thermal stability of the AFE state can therefore be determined with respect to the field-induced transformation behavior. A distinction is made between field-forced and field-assisted transformations, which depend on temperature and thermal hysteresis, and which are related to reversible and irreversible field-induced characteristics. Data are reported for polarizations and strains, and discussed with respect to the proposed thermodynamic model and device applications.
Substituent-dependent self-assembly: Two-dimensional aggregate formation in cyanine dye-adsorbed Langmuir-Blodgett films
Authors: Saito Kazuhiro , Ikegami Keiichi , Kuroda Shin-ichi , Tabe Yuka , Sugi Michio
Published: July 2002

Interface-adsorbed complex Langmuir-Blodgett (LB) films of arachidic acid and water-soluble, mesosubstituted cyanine dyes were fabricated using the diffusion-adsorption method to examine the substituent-dependent self-assembly at the water-monolayer interface. Either a J aggregate or an H aggregate was found to be formed in the LB films depending on the substituent introduced, the ethyl or methyl group. The H aggregate is accompanied by Davydov splitting, which is characterized as the split of the band into two bands, whose transition moments are orthogonal to each other. Measurements of photoluminescence and microscopic spectroscopy were performed to identify the type of the aggregates. The molecular arrangements in the aggregates were estimated based on Davydov’s theory and the extended dipole model. Dependence of photoelectric properties of the LB films on the type of aggregates has been studied employing Schottky-type cells.
Effects of rapid thermal annealing on the formation of shallow p+n junction by implanting BF2+ ions into thin metal films on Si substrate. II. Thin cobalt films
Authors: Juang M. H. , Cheng H. C.
Published: July 2002

The effects of rapid thermal annealing (RTA) on the formation of shallow p+n junctions by the implantation of BF+2 ions into thin Co films and subsequent silicidation/drive-in have been studied. The junction formation by various implant conditions has been characterized to correlate with the dopant drive-in efficiency, defects in junctions, and junction depth under different anneal conditions. Optimum junctions were achieved by the 700 °C anneal in all the present implant conditions. Annealing at 800 °C degraded the junction formation due to the considerable formation of Co–B compounds caused by the high heating rate and high-temperature processings. Higher implant energy greatly lessened the dopant confinement due to deeper as-implanted dopant profile. Conventional furnace annealing (CFA) considerably enhanced the drive-in efficiency, while RTA is superior to CFA in annihilating damage, activating dopant, and forming shallow junctions. The benefits of RTA are particularly obvious for the implants of low-energy, low-dosage and high-energy, high-dosage. Consequently, low-temperature RTA processings can achieve silicided shallow p+n junctions with good rectifying characteristics.
A high-current-density nonclosing plasma cathode
Authors: McGeoch Malcolm W.
Published: July 2002

A novel plasma cathode has been demonstrated. Its operation depends on the presence of a magnetic field and requires a low-pressure burst of gas to form a crossed-field discharge. The electron current that can be extracted is controlled by the discharge current. When the extracted current is less than the space-charge limit there is no diode closure. The fundamental characteristics of intense crossed-field discharges are measured, and cathode tests up to 6 A cm−2 at 100 kV are reported, in a 100-cm2 cathode with 5-μs pulses.
Relationship between interfacial native oxide thickness and bonding temperature in directly bonded silicon wafer pairs
Authors: Ling L. , Shimura F.
Published: July 2002

High-resolution transmission electron microscopy was employed to observe the morphology of the interfacial native oxide layers in the bonding interfaces of Czochralski (CZ) and float-zone (FZ) silicon pairs that were bonded at different temperatures. It is shown that the thickness of the interfacial native oxide layers decreases with increasing bonding temperature in the temperature range of 200 °C to 600 °C, and remains fairly constant in the range of 600 °C to 1200 °C in both CZ and FZ silicon wafer pairs. Three factors are proposed to interpret this phenomenon: bonding interface phase transition, variation of native oxide chemical structure, and relaxation of stress in native oxide. A different factor dominates the change in thickness of the interfacial oxide layers in a different temperature range.
Metalorganic vapor phase epitaxy and characterization of boron-doped (Al,Ga)As
Authors: Tischler M. A. , Mooney P. M. , Parker B. D. , Cardone F. , Goorsky M. S.
Published: July 2002

The epitaxial growth of GaAs and (Al,Ga)As doped with boron (from diborane) and silicon was investigated to examine the effect of boron on (DX) centers in silicon-doped material. The addition of diborane to the growth of GaAs and (Al,Ga)As results in the superlinear incorporation of boron into the solid with a concurrent reduction in the growth rate. Boron incorporation also decreases as the growth temperature is increased. Additionally, the AlAs mole fraction increases with increasing diborane during (Al,Ga)As growth. The DX center was not eliminated in (Al,Ga)As by the addition of boron. The thermal stability of these materials was also investigated.
Surface CoSi2 layers by moderate dose cobalt implantation for self-aligned contacts
Authors: Maszara W. P.
Published: July 2002

CoSi2 layers produced by implantation of cobalt into silicon at 20 keV with doses 3–6×1016 cm−2 were investigated. Room temperature and 355 °C implants produced continuous layers of silicides with similar electrical properties. The minimum sheet resistivity of annealed samples was 9.2 Ω/sq. and the films were thermally stable up to about 900 °C. Low leakage currents (estimated <1×10−14 Å per μm of a typical side-wall spacer length) in a SiO2 film which was similarly implanted with Co demonstrate the usefulness of this method for the formation of thin (≂20 nm) cobalt silicides for self-aligned source-drain contacts in shallow junction complimentary metal-oxide-semiconductor technology.
The role of the voltage criterion in the interpretation of flux pinning in epitaxial films of YBa2Cu3O7
Authors: Wördenweber R. , Abd-El-Hamed M. O.
Published: July 2002

The determination of the critical current is usually based upon a voltage criterion that is used as an indication that the critical state has been reached in the superconducting regime. Resistive measurements of the I-V characteristics are carried out on patterned thin films of epitaxially grown and c-axis-oriented YBa2Cu3O7. Bridges with widths ranging between 1 and 100 μm and lengths between a few μm and 7 mm are characterized. The sensitivity of the measurement is better than 10−9 V. The volume pinning force is evaluated for different voltage criteria. Although the absolute values of the volume pinning force change with the value of the criteria, the field and temperature scaling is not affected. They agree with the expectations of the flux-line sheer model. The value obtained for the width of the weakly pinning channels is independent of the chosen criterion. Finally, model calculations on the basis of a modified flux-line shear mechanism are carried out that are in good agreement with the experimentally measured I-V characteristics.
Measurement of anisotropy energy for magneto-optical media
Authors: Hajjar R. A. , Wu T. H. , Mansuripur M.
Published: July 2002

A technique is proposed for measuring the anisotropy energy of magneto-optical media. the technique consists of rotating a sample in a fixed external magnetic field and monitoring the extraordinary Hall effect signal of the sample. From the Hall effect signal, the angle of rotation of the sample, and the saturation magnetization of the sample (which is measured separately by a vibrating sample magnetometer), we obtain the anisotropy energy as a function of the deviation of magnetization from the easy axis. The technique is applied to multilayered Co/Pd and Co/Pt films as well as to amorphous rare-earth transition metal TbFeCo alloy films. The anisotropy constants thus obtained are compared with those obtained using other techniques such as torque magnetometry and Hall effect (or Kerr effect) measurements with applied field in the plane of the sample.
Focusing of the ion beam from a scanning tunneling microscope tip
Authors: Bar’yudin L. E. , Bulatov V. L. , Telnov D. A.
Published: July 2002

The effect of polarization of ions in an electric field on their trajectories is considered with respect to the mass transfer from the tip. The effect is in focusing of the ion beam due to the dipole momenta of the ions induced by the electric field between the tip and the surface. The dependence of the focusing effect on the tip shape, distance and potential difference between the tip and the surface as well as on material the tip is made of and the kind of the ions, is investigated. The results show the possibility of utilizing the focusing effect in installations for producing a molecule-size structure on the surface, e.g., in nanoelectronics.
The electrical properties of metal-sandwiched Langmuir–Blodgett multilayers and monolayers of a redox-active organic molecular compound
Authors: Geddes N. J. , Sambles J. R. , Jarvis D. J. , Parker W. G. , Sandman D. J.
Published: July 2002

Both ac and dc conduction processes through thin Langmuir–Blodgett (LB) films of the dodecyloxyphenylurethane of 2-bromo-5 (2′-hydroxyethoxy) tetracyanoquinodimethan (DDOP-C-TCNQ, a redox-active molecule) sandwiched between dissimilar metal (Pt and Mg) electrodes have been studied. The dc conduction changed from a linear I/V characteristic for the lowest applied voltages (±20 mV) to a symmetric nonlinear characteristic obeying a ln I∝V1/4 dependence for voltages up to ±1.5 V, in as-prepared samples. For larger positive voltages, a large increase in current was observed with the dependence changing to a ln I∝V3 law, a dependence not reported previously for metal/LB film/metal systems. For increased negative voltages, the ln I∝V1/4 was again observed. For low applied ac fields, the conductance was found to follow a ωn law with a value of n close to 0.8. The effect of heat annealing the samples was also studied with significant differences in the observed changes in conductance between bilayer and monolayer structures. Emphasis was placed on understanding the conduction process through the single DDOP-C-BHTCNQ layer film. For the monolayer device, hysteresis is observed in the positive bias, and both as-prepared and annealed samples exhibit ln I∝V3 behavior. Such behavior was not observed for the corresponding negative voltages, indicating rectification across a distance approximated by the length of an individual molecule. Possible models of the three-dimensional arrays for both monolayer and multilayer metal/LB film/Mg structures are presented. The weight of existing experimental results does not support the Aviram–Ratner ‘‘molecular rectifier’’ concept for presently known Pt/LB monolayer/Mg devices.
Dislocations and precipitates in gallium arsenide
Authors: Schlossmacher P. , Urban K. , Rüfer H.
Published: July 2002

A complete dislocation analysis on a large number of grown-in dislocations was performed on wafers taken from three different semi-insulating liquid encapsulation Czochralski GaAs single crystals. By determining the Burgers vector, line direction, and habit plane of nearly 800 dislocations a decision could be made on dislocation type, dislocation generation, and multiplication mechanisms. Taking into account possible dislocation reactions between stress-induced glide systems all detected glide systems could be explained. The influence of post-growth annealing on both dislocations and arsenic precipitates was also investigated. Little effect was found on dislocations. Arsenic precipitates, however, showed a different distribution in size and significant effects on fine structure giving information on their nucleation and growth mechanisms.
The effect of multiple laser pulses on damage to thin metallic films
Authors: Cohen S. S. , Bernstein J. B. , Wyatt P. W.
Published: July 2002

The mechanical effects due to the application of multiple laser pulses to thin metallic films are studied. Particular attention is paid to systems involving thin aluminum films deposited on an insulating substrate such as silica. This film/substrate combination is widely employed in silicon semiconductor technology. In building such devices laser energy is sometimes used for the purpose of cutting conducting lines, while in other applications it is used to effect linking between two levels of metallization. Both processes have been greatly facilitated by employing a multiple-pulse scheme. The mechanism responsible for this effect is discussed and it is shown how the present model leads to a good agreement between the measured and calculated quantities.
Bending loss in optical waveguides for nonplanar laser array applications
Authors: Lee S. M. , Chew W. C. , Chuang S. L. , Coleman J. J.
Published: July 2002

The optical transmission loss in dielectric waveguide bends is investigated using the finite-difference time-domain approach. An absorbing boundary condition, applied to reduce the size of the mesh, is proven to work very well for the waveguide structure. The desired modes are excited using the solution of a one-dimensional waveguide structure. The bending loss is then obtained using the methods of overlap integral and least-square fit. The structures of multiple-bend waveguides are analyzed. It is shown that the coupling between neighboring bends leads to direct transmission to the waveguide section on the aligned plane in addition to the transmission through the zigzag path. The bending loss in nonplanar laser arrays is investigated in detail. The possibility of having a shallow groove depth laser array is then discussed. Lateral lasing is prohibited by the radiation loss due to the bend. It is observed that the optical coupling between neighboring emitters is enhanced by the shallow groove depth, implying that phase-locked array modes can be obtained.
Transport critical currents in field-oriented Y1Ba2Cu3Oy polycrystals
Authors: Nakagawa Y. , Yamasaki H. , Umeda M. , Kosaka S.
Published: July 2002

Field-orientedY1Ba2Cu3Oy samples with various values of the transport critical current density, Jc, have been prepared with various heat treatments. The Jc increased rapidly with an increase in relative sintered density of the oriented samples. The field-oriented samples with higher Jc had grains of larger sizes and better connections between the neighboring grains than the low Jc samples. The maximum values of Jc at a magnetic field of 7 T were 370 A/cm2 at 4.2 K and 24 A/cm2 at 77 K. The hysteresis in the Jc-H curves at 4.2 K decreased with an increase in Jc both for an applied field H∥ab plane and for H∥c axis. The critical currents of the samples with higher Jc were less degraded by aging in the air for 1 year than those of the low Jc samples. The relation between the field-cooled Jc-H curves and the zero-field-cooled ones for an oriented sample with low Jc is qualitatively interpreted by the effect of the intragrain currents on the intergrain fields.
The origin of the ∼0.75 eV photoluminescence emission band in ion-implanted InP
Authors: Thompson T. D. , Barbara J. , Ridgway M. C.
Published: July 2002

We have performed a photoluminescence study of InP:Fe (100) substrates after implantation with carbon, silicon, germanium, tin, indium, and phosphorous ions with a projected range of 1 μm. The main part of our study concentrated on the ∼0.75 eV emission band previously reported for silicon-implanted InP. We conclude that this emission is due to a donor-acceptor pair center comprised of a group IV element and a defect. The center can be formed by silicon implantation, but other group IV elements such as germanium or tin produce an essentially identical emission. Thus this band cannot be treated as a silicon ‘‘signature’’. The defect related to this center is formed during annealing of implantation damage and is enhanced by deviations in stoichiometry toward excess indium. We have also shown that a band at ∼1.19 eV can be produced by a variety of methods some of which directly involve phosphorous depletion.
Low-frequency ac conduction and dielectric relaxation in vinyl chloride:vinyl acetate copolymers
Authors: Singh Ramadhar , Panwar V. S. , Tandon R. P. , Gupta N. P. , Chandra Subhas
Published: July 2002

ac conductivity σ(ω), dielectric constant ε′, and loss ε″ of vinyl chloride:vinyl acetate (VC:VAc) copolymers having 3%, 10%, and 17% VAc content (by weight) have been measured in the temperature range 77–410 K and in the frequency range 50 Hz–100 kHz. At low temperatures up to 250 K, the ac conductivity can be expressed by σ(ω)=Aωs, where the slope s is close to unity and its value decreases with the increase in temperature. The dielectric constant in this temperature region shows a very weak frequency and temperature dependence. At temperatures above 300 K, the ac conductivity shows a strong temperature dependence; however, in this temperature region the dielectric constant shows a strong frequency dispersion. The measured dielectric loss as a function of temperature reveals the β1, the β2, and the α relaxations. The β1 relaxation is associated with the movement of the more flexible side group dipoles and the β2 relaxation is due to the movement of rigidly attached side group dipoles, whereas the α relaxation is attributed to the segmental motion of the main chain of the copolymer. Both the latter relaxations seem to be long range in nature with distribution of relaxation times associated with the cooperative motion. The mechanism of conduction in the low- and high-temperature regions have been discussed in light of existing theoretical models.
Tight-binding calculations on the electronic structure of neutral divacancies in the Ga-related III-V compound semiconductors
Authors: Xu Hongqi
Published: July 2002

We present a tight-binding theory for the calculations of the electronic structure of divacancies in compound semiconductors. The theory has taken both intra- and interatomic electron–electron interactions into account. The effect of charge transfer between the components of the complex defects on the electronic structure can thus be included in the calculations. We apply the theory to the electronic-structure calculations for the neutral divacancies in the Ga-related III-V compound semiconductors, GaP, GaAs, and GaSb. The calculations are done with the use of the recursion method and the supercell approximation. The energy positions and localizations of the deep levels for the defects are predicted. It is shown that each divacancy introduces seven defect levels, three at the edges of the lower gap and four in or around the fundamental band gap. A model for the description of the physical origin of these four fundamental gap-related defect levels is presented. It is also shown that for the neutral divacancy in the three Ga-related III-V compound semiconductors the last occupied a1 and e fundamental gap levels stay at very close energies and have very different localization characters.
Defect characterization in GaAlInAs alloys
Authors: Nubile P. , Zazoui M. , Bourgoin J. C. , Grey R. , Powell A. L. , Claxton P. A. , Rockett P. I.
Published: July 2002

Deep level transient spectroscopy (DLTS) and capacitance-voltage measurements at various temperatures have been used to characterize defects in Si-doped (Ga1−xAlx)1−yInyAs materials for x=0.3 and different values of y (0, 0.005, and 0.07). We only detect DX centers, those associated with the doping impurity (Si), but also others associated with Te and, eventually, Sn not introduced intentionally. When the experimental conditions are chosen to obtain exponential transients, the shape of the DLTS spectrum and its variation with the filling pulse duration can be accounted for by this contamination; i.e., no sign of the so-called alloying effect is detected.
Application of photothermal ionization spectroscopy to the study of epitaxially grown germanium on silicon
Authors: Navarro H. , Timusk T. , Datars W. R. , Houghton D. C.
Published: July 2002

We have applied the technique of photothermal ionization spectroscopy to the study of a 1-μm-thick p-Ge epilayer, grown by molecular beam epitaxy on a n-Si substrate, 500 μm in thickness. The spectra indicate that in the Ge layer there exists a series of charged acceptor defects with an ionization energy continuum starting at 15 meV, an ionization energy somewhat larger than those of the elemental substitutional acceptors. Our results show that photothermal ionization spectroscopy can be applied very advantageously to epitaxial layers of the Si1−xGex alloys that are Ge-like, i.e., for x≥0.85. For these layers, charged impurity centers and defects have their spectral features well separated from those of the Si substrate.
Analysis of a nonlinear Schrödinger equation with numerical techniques
Authors: Eguchi Masashi , Hayata Kazuya , Koshiba Masanori
Published: July 2002

We investigate the reliability of numerical analysis techniques for the perturbed nonlinear Schrödinger equation that predicts soliton propagation in optical fibers. We use the propagating-beam method and the split-step finite-element method for this purpose, and offer useful data on the parameters, such as the number of descretizing points and the step size along the propagating direction.