bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the fabrication process of hot-worked stainless-steel and Mo sheathed PbMo6 S8 wires
Authors: Yamasaki H. , Kimura Y.
Published: July 2002

Stainless-steel and Mo sheathed PbMo6 S8 wires have been fabricated by hot working from modified PbS, Mo, and MoS2 mixed powders which were prepared by reacting Pb, Mo, and S at 530 °C. Critical current densities were investigated for different preparation conditions, and it is revealed that obtaining continuous current path between PbMo6 S8 grains is the most important factor to achieve high critical current density. The Jc value of 2.8×104 A/cm2 (8 T), 7.8×103 A/cm2 (15 T), and 1.3×103 A/cm2 (23 T) was observed for the PbMo6 S7.0 wire heat treated at 700 °C.
Soft magnetic properties of FeRuGaSi alloy films: SOFMAX
Authors: Hayashi K. , Hayakawa M. , Ishikawa W. , Ochiai Y. , Iwasaki Y. , Aso K.
Published: July 2002

To advance new soft magnetic materials of an FeGaSi alloy into the commercial world, improvements on various properties were designed by introducing additive elements without sacrificing its high saturation magnetic induction. The detailed studies on the diversified properties, such as saturation magnetic induction, film internal stress, wear resistivity, and so on, were performed. High-frequency permeability of the laminated structure film was also investigated. As a result, the Ru-added FeRuGaSi alloy films, whose typical compositions are Fe72Ru4Ga7Si17 and Fe68Ru8Ga7Si17 (at. %), prove to be excellent soft magnetic materials especially appropriate for the magnetic recording/playback head core use.
Raman scattering characterization of high-quality Cd1−xMnxTe films grown by metalorganic chemical vapor deposition
Authors: Feng Z. C. , Sudharsanan R. , Perkowitz S. , Erbil A. , Pollard K. T. , Rohatgi A.
Published: July 2002

Cd1−xMnxTe films (thickness ∼0.5 μm, x=0.10–0.37) have been grown by metalorganic chemical vapor deposition on commercial GaAs and glass substrates with and without buffer layers of CdTe and CdS. Raman scattering shows the films to be of high quality, despite the large film-substrate lattice mismatch. CdTe-like and MnTe-like phonon lines are sharp and strong in first and second order with widths ≤10 cm−1, and clearly appear in combinations up to fourth order. Raman and photoluminescence analysis also establish an optimum growth temperature and limits on the fraction of Mn.
Resolution of thermal wave imaging methods for periodic structures
Authors: Lörincz A.
Published: July 2002

A model computation was conducted in two dimensions to determine the spatial resolution of thermal wave methods for periodic structures. The model is appropriate for line heating systems used for improving speed limits of thermal wave methods. The results may be considered as approximate for problems requiring three-dimensional treatment. Numerical computations of the response of a thermal wave imaging system for periodic variations of material parameters along the surface show resonancelike behavior around the thermal diffusion length. The resolution of the system determined according to the Rayleigh criterion is about two thirds of the thermal diffusion length. Below that value the amplitude of the temperature signal decreases with increasing periodic variation wave vector with a slope of about 9.5 dB/octave. A formula is given for the determination of resolution for structures other than periodic.
Substituting low-energy (<30 eV) ion bombardment for elevated temperature in silicon epitaxy
Authors: Wehner G. K. , Warner R. M. , Wang P. D. , Kim Y. H.
Published: July 2002

Normally required high substrate temperature for achieving epitaxial film growth can be replaced by low-energy (<30 eV), high-current-density (∼1 mA/cm2) ion bombardment during film deposition. For this a Si substrate wafer was immersed like a large negative Langmuir probe in a low-pressure (5×10−4 Torr) mercury vapor plasma while receiving Si atoms sputtered from a Si wafer target. The Hg plasma was created by extracting a 4-A discharge current at 25-V discharge voltage from a Hg cathode spot on a liquid-Hg pool. Electron channeling patterns proved that uniform Si spitaxial films can be obtained over the whole substrate wafer area at temperatures not exceeding 300 °C. The best epitaxial films were obtained when the substrate is bombarded (by biasing) during deposition with 23-eV Hg ions. The electrical properties of the coatings indicated that the films were close, but not yet of device quality because of the impurities inherent in our non-ultrahigh-vacuum nonbakable Pyrex chamber pumped only with a 12-ℓ/s Hg diffusion pump.
Current-voltage characteristics of metalorganic chemical vapor deposition InP/InGaAs p-i-n photodiodes: The influence of finite dimensions and heterointerfaces
Authors: Zemel A. , Gallant M.
Published: July 2002

The electrical and optoelectronic characteristics of planar InP/InGaAs p-i-n photodiodes grown by metalorganic chemical vapor deposition were extensively investigated. A typical room-temperature dark current of 10 pA for 100-μm-diam devices was measured at −10-V bias on several wafers. A low capacitance between 0.42–0.46 pF (for 100-μm-diam devices), responsivities at 1.3 μm between 0.84–0.94 A/W (corresponding to external quantum efficiencies between 80% and 90%), and rise/fall times of less than 150 ps were measured at −5-V bias on several wafers. Excellent uniformity in dark current, junction capacitance, and optoelectronic characteristics was found over large wafer areas. The diode dark current was studied as a function of applied voltage, temperature, diode dimensions, and junction depth. The carrier transport mechanisms in different ranges of bias voltage and temperature have been identified and interpreted both in form and magnitude. At low to mid reverse bias, bulk generation-recombination currents dominate below 320 K. At higher temperatures, diffusion currents become dominant. Band-to-band tunneling current near the InP/InGaAs upper heterointerface dominates the dark current at high reverse bias. Under forward bias, the diffusion current dominates over the entire temperature range studied. Theoretical models have been developed to account for the magnitude of the reverse and forward diffusion currents and their dependence on diode dimensions. It is found that the lowest dark current measured at room temperature is very close to the theoretical limit achievable for planar InP/InGaAs/InP diodes with n doping of the InGaAs ∼1×1015 cm−3.
Antiferromagnetism in YBa2Cu3O6+x (invited)
Authors: Tranquada John M.
Published: July 2002

A number of models for high-temperature superconductivity in the layered cuprate perovskites require strong antiferromagnetic superexchange interactions between Cu atoms. The existence of such interactions in La2CuO4−y has previously been demonstrated. In this paper a review is given of recent neutron scattering work performed at Brookhaven studying antiferromagnetism in RBaCu3O6+x with R=Y, Nd. Measurements on ceramic samples with a range of oxygen concentrations have shown that three-dimensional antiferromagnetic ordering of the Cu spins occurs throughout the nonsuperconducting tetragonal phase, corresponding to 0≤x≲0.4. Near x∼0 the Cu2+ atoms in the CuO2 layers form a simple Néel lattice, and there is no ordering of the nonmagnetic Cu1+ atoms in the ‘‘chain’’ sites. With increasing oxygen content some of the Cu1+ atoms are converted to Cu2+, which leads to frustration of the interplanar coupling and eventually to a second type of ordering. Very recently, large single crystals of YBa2Cu3O6+x have been grown, making possible inelastic scattering studies of magnetic excitations. Spin waves within the CuO2 planes are observed to have a velocity ≳0.5 eV Å.
Equimagnetization lines in the hybrid-order phase diagram of the d=3 random-field Ising model (invited)
Authors: McKay Susan R. , Berker A. Nihat
Published: July 2002

The three-dimensional random-field Ising model has been approximately solved by pursuing the global renormalization-group trajectories of the full, coupled probability distributions of local fields and bonds. This study, which in effect is the global analysis of the renormalization-group flows of 220 physical quantities (based on a generalization of the Migdal–Kadanoff approximation), yields several results that were previously unsuspected. The boundary between the ferromagnetic and paramagnetic phases is hybrid order, in the sense that the magnetization is discontinuous (as in a first-order transition) and the specific heat has a power-law singularity (as in a second-order transition). The magnetic properties of the d=3 random-field Ising model are presented in the form of equimagnetization lines. The study has been repeated for a variety of dimensions d. The lower critical dimension dl=2 is correctly obtained. Moreover, this study indicates the existence of an intermediate-critical dimension dt (between the lower- and upper-critical dimensions) where a singularity occurs in the critical properties as a function of dimension.
Model calculations of the magnetic anisotropy in 3d transition metals
Authors: Jansen H. J. F.
Published: July 2002

A simple model of the magnetic anisotropy in 3d transition metals is based on a 10×10 Hamiltonian describing all d states. We include spin-orbit interaction, a cubic crystal field, an effective Weiss exchange-correlation field which couples only to the spins, and a Breit term which couples to the orbits. Changes in the total energy are obtained from the sum of the eigenvalues after broadening the levels with an effective temperature corresponding to the bandwidth. Our calculations show that, using realistic values for the parameters in the model Hamiltonian, the experimental values of the anisotropy can only be reproduced when we include the Breit term which couples to the orbits.
The synthesis of Nd-Fe-Co-B by reduction-diffusion and its magnetic properties
Authors: Sun Guangfei , Chen Jufang , Dahl Winfried , Klaar Hans-Joachim , Burchard Wilhelm-Günther
Published: July 2002

The synthesis of Nd-Fe-Co-B by the reduction-diffusion process from neodymium trichloride and its magnetic properties and microstructure have been investigated by x-ray diffraction, scanning electron microscope, and magnetic analysis. According to the thermodynamic data, calcium is capable of reducing neodymium trichloride and then a Nd-Fe-Co-B alloy is formed by thermal diffusion in the presence of iron, cobalt, and ferro-boron powders at high temperature. The reduction reaction starts at 720 °C. Thermal diffusion commenced at 800 °C and forming some Nd2Fe14B phase, but the matrix Nd2Fe14B formed primarily at 860–950 °C. There are three types of phases with different compositions in the sintered Nd-Fe-Co-B R/D powders. The oxygen and calcium contents were 0.2 and 0.1 wt. %, respectively. The best yield of Nd-Fe-Co-B powder was up to 98%. The magnetic properties of the sintered Nd-Fe-Co-B depended on the temperature and time of the reduction-diffusion process. The best magnetic properties obtained were Br =12.6 kGs, Hc =8 kOe, and (BH)m =36.4 MGOe.
Microstructure of rapidly quenched Nd-Fe-Zr-B magnets
Authors: Yajima K. , Nakamura H. , Kohmoto O. , Yoneyama T.
Published: July 2002

An analytical microscopy characterization was carried out on rapidly quenched Nd-Fe-Zr-B magnets with 9–10 at. % Nd contents. These magnets had a high-energy product (15–17 MGOe). The microstructure of these alloys consisted of two phases where 20–40 nm size Nd2Fe14B grains were surrounded by a 2–20-nm-thick Nd-poor and Fe-rich grain-boundary phase. It is proposed that the Fe-rich boundary phase leads to higher remanence and higher energy products than those found in Nd-Fe-B ternary alloys.
Quantitative analysis of carbon concentration in MOMBE p-GaAs by low-temperature photoluminescence
Authors: Ambros S. , Kamp M. , Wolter K. , Weyers M. , Heinecke H. , Kurz H. , Balk P.
Published: July 2002

Several features of low-temperature (2-K) photoluminescence (PL) spectra are used for a quantitative determination of the carbon concentration below 1018 cm−3 in GaAs samples grown by metalorganic molecular-beam epitaxy. We present a close correlation between specific PL features and hole concentration together with a calibration of the carbon content with respect to the hole concentration. This calibration was done directly on samples implanted with a known amount of carbon (1×1016 cm−3) and via local vibrational mode and secondary ion mass spectrometry analysis of samples doped to around 1018 cm−3. The method permits a fast and nondestructive determination of the carbon content from PL measurements.
Near-gap photoluminescence of GaAs grown directly on silicon
Authors: Harris T. D. , Lamont M. G. , Sauer R. , Lum R. M. , Klingert J. K.
Published: July 2002

We report a detailed study using photoluminescence and photoluminescence excitation of metalorganic chemical vapor deposition GaAs grown directly on Si substrates. Temperature variation and selective excitation allow reliable assignment of spectral features. This assignment permits measurements of strain and strain uniformity, identification of impurities, and assessment of general material quality. In 2–5-μm-thick layers similar spectra are observed with little variation from substrate character. Near 4 K, most samples show one of the two split valence-band features plus defect recombination, always including carbon. Strain uniformity varies widely and correlates with substrate thickness. The range of spectra observed from a variety of samples and guidelines for interpretation of nonresonantly excited spectra are discussed.
Microtomography observation of precipitates in semi-insulating GaAs materials
Authors: Gall P. , Fillard J. P. , Castagne M. , Weyher J. L. , Bonnafe J.
Published: July 2002

Defects introduced in GaAs materials during growth and post-growth thermal processes are known to largely influence the specifications of transistors. Various techniques have been improved to detect these defects and obtain images of their organization. Laser scanning tomography provides us with macroscale images of fault structures, the details of which up to now have not been resolved. In this paper we show that extending this technique to a microscopic scale reveals small individual scatterers which are at the origin of the tomography images: these scatterers are microprecipitates located on dislocations or condensed on point defects. Several examples of undoped, In doped, and annealed materials are reported and discussed: apart from the decoration precipitates which look rather large, smaller and abundant microprecipitates are observed, even in dislocation-free materials; their number is found to be consistent with microetched pit density responsible for the ‘‘microroughness’’ of etched surfaces. Ingot annealed materials developing a conventional cell structure are also shown to contain clouds of such microprecipitates concentrated in the central region of the cells. It is likely that the type and the arrangement of these particles are strongly related to the dislocation network and to the thermal history. There is no doubt that the chemical species involved play an important role at a microscale level in the local electronic properties of the material.
Thermomagnetic marking of rare-earth–transition-metal thin films
Authors: Bartholomeusz Brian Josef
Published: July 2002

Analytical derivation of temperature profiles in laser-irradiated thin-film structures is hindered by the nature of the heat source terms and by the geometrical complexity that often exists. This study utilizes a combined Laplace-transform–Fourier-integral method to obtain approximate solutions for a number of simple cases. The results are used to study the thermomagnetic marking process in rare-earth–transition-metal (RE-TM) thin films, and the predictions are compared with experimental observations.
Strained layer InGaAs channel negative-resistance field-effect transistor
Authors: Favaro M. E. , Fernández G. E. , Higman T. K. , York P. K. , Miller L. M. , Coleman J. J.
Published: July 2002

We report experimental results on a negative-resistance field-effect transistor (NERFET), grown by metalorganic chemical vapor deposition, which incorporates a strained In0.18Ga0.82As channel layer adjacent to the barrier. The thin InGaAs layer provides higher mobility and enhanced carrier confinement for the channel electrons. This device structure yields a significant increase in the drain current peak-to-valley ratio over comparable GaAs-AlGaAs NERFETs.
Formation of polycrystalline silicon grains in Si+-preamorphized, BF+2-implanted (111)Si
Authors: Chu C. H. , Chen L. J.
Published: July 2002

The regrowth of Si+-preamorphized and BF+2- implanted thin films on (111)Si has been studied by both plan-view and cross-sectional transmission electron microscopy. Polycrystalline Si grains were found to form in Si+-preamorphized and BF+2- implanted (111)Si with the original amorphous-crystalline (a-c) interface located deeper in the preamorphized Si substrate than in BF+2- implanted samples. Rapid thermal annealing was performed to obtain kinetic data for the formation of polycrystalline Si grains. The nucleation and growth of polycrystalline Si grains were found to occur in the amorphous phase ahead of the growing a-c interface. The incubation time for the formation of 4 nm or larger crystallites in amorphous Si at 700 °C was found to be less than 30 s. The results are discussed in terms of the competition between the propagation of the a-c interface to sweep over the potential nucleation sites and random nucleation in the amorphous phase. Ramifications of the formation of polycrystalline Si grains in instances with a relatively low ion dosage and/or moderate annealing temperature are addressed.
Study of the direct-indirect band-gap transition in GaAs/AlAs short-period superlattices using photocurrent spectroscopy
Authors: Barrau J. , Khirouni K. , Amand Th. , Brabant J. C. , Brousseau B. , Brousseau M. , Binh Phi Hoa , Mollot F. , Planel R.
Published: July 2002

We have unambiguously shown that low-energy optical transitions generate electrons that belong either to the Γ minimum of GaAs or to the X minimum of AlAs, depending on the mean aluminum concentration, for a series of 5-nm period GaAs/AlAs superlattices. We estimate the intensity of the potential responsible for the Γ-X mixing to be on the order of 1–2 meV. For this kind of study, the photocurrent technique, which gives well-structured spectra recorded on large spectral (≂0.7 eV) and temperature (4–300 K) ranges, appears more favorable than the photoluminescence excitation spectroscopy technique.
The effect of sputter cleaning on Au/GaAs contacts and the role of doping
Authors: Yeh Liu Lu-Min , Xie Yu-Jun , Holloway Paul H.
Published: July 2002

The effects of Ar-ion sputtering on electrical properties of Au contacts on (100) GaAs and the role of doping concentration have been studied. The n-GaAs was doped with 1017 or 1018 cm−3 Si or with 1018 cm−3 Te and the p-GaAs with 1018 or 1019 cm−3 Zn. After either chemical etching or Ar-ion beam cleaning of the GaAs, Au contacts were formed by evaporation in ultrahigh vacuum (10−9 Torr). Ion bombardment with Ar+ produced clean but nonstoichiometric, damaged GaAs surfaces. Contacts on chemically cleaned GaAs were either (nearly) ohmic or Schottky, depending upon the dopant and concentration. On sputtered GaAs, all the contacts showed soft rectification but did not act as purely Schottky contacts. The type of dopants, i.e., n or p, caused differences in the I-V behavior, but the behavior for different dopants of the same type was very similar. Sputtering increased the depletion depth on all the samples, and the depletion depth became larger as the ion energy increased and/or the dopant concentration decreased. The electrical behavior of the sputtered samples is suggested to result from the creation of a compensated layer with deep defect states. The deep level states are postulated to be related to defects resulting from sputtering.
Mechanical and high-temperature (920 °C) magnetic field grain alignment of polycrystalline (Ho,Y)Ba2Cu3O7−δ
Authors: Lusnikov A. , Miller L. L. , McCallum R. W. , Mitra Sreeparna , Lee W. C. , Johnston D. C.
Published: July 2002

The effects of uniaxial compression, high-temperature (920 °C) heat treatment, and heat treatment plus magnetic field on grain alignment in bulk ceramic pellets of HoBa2Cu3O7−δ and YBa2Cu3O7−δ were studied and separated. Uniaxially cold pressing prereacted powder into pellets at room temperature is found to yield significant grain alignment on the flat end surfaces of the pellets perpendicular to the pressing axis, where the c axes of the grains are parallel to this axis, in agreement with previous reports. A simple method to quantitatively determine the degree of surface grain alignment from the powder x-ray diffraction data from these surfaces is used. These data were augmented by x-ray rocking curve measurements. The degree of alignment of the cold pressed samples was found to increase with increasing pressure up to our pressure limit of 310 MPa. However, bulk magnetization anisotropy measurements on these pellets indicate that the degree of bulk alignment is only about 1/3 to 1/2 that inferred from the above surface measurements, which in turn suggests that the degree of alignment decreases with distance from the flat end surfaces. We find that a pronounced additional surface grain alignment is produced by heat treating the cold-pressed samples at high temperature (920 °C). We also observed a significant influence during the high-temperature annealing of a small (0.7 T) applied magnetic field on the alignment of the surface grains. A model to explain these observations is presented and discussed.
A proposed model to explain impurity-induced layer disordering in AlAs-GaAs heterostructures
Authors: Tatti S. R. , Mitra S. , Stark J. P.
Published: July 2002

Impurity-induced disordering of III-V compound semiconductor quantum well heterostructures and superlattices has been extensively studied. However, the theories proposed to explain this phenomenon have dealt primarily with vacancy diffusion mechanisms and have not succeeded in explaining all the experimental observations satisfactorily. In this communication, we propose a two-atom ring mechanism of diffusion based on a simplified model of covalent bonding in III-V compound semiconductors and suggest that the phenomenon of intermixing is a consequence of a lowering in the activation energy due to coulombic interactions between the substitutional impurity atoms and the host atoms. This mechanism is consistent with experimental observations and is able to predict the behavior of other dopants. The additive effect of the simultaneous presence of different dopants can also be explained by this theory which could possibly be used to achieve controlled layer disordering for use in device technology.
Millimeter wave generation by fluxon oscillations in a Josephson junction
Authors: Cirillo M. , Modena I. , Carelli P. , Foglietti V.
Published: July 2002

A small-area Josephson tunnel junction is pumped by the radiation emitted by a long Josephson junction dc biased on a zero-field singularity. Josephson constant voltage steps are observed in the current-voltage characteristic of the small junction at voltages of ±150 μV corresponding to the fundamental frequency of emission of the oscillator. The radiation also gives rise to quasiparticle steps around the gap-sum voltage of the small junction. From the measured current amplitude of the steps we estimate that the maximum power coupled to the small junction is about 90 nW.
Effect of annealing on T
c of liquid-quenched Bi0.7Pb0.3SrCaCu1.8Ox
Authors: Nishi Yoshitake , Moriya Shuji , Manabe Toyohisa
Published: July 2002

A high Tc is found after annealing for 12 h at 1120 K, although Tc cannot be found for liquid-quenched Bi0.7Pb0.3SrCaCu1.8Ox glass. The maximum offset temperature of superconducting transition is 111.7 K at 0.01 mA/mm2. The maximum Tcoff is larger than that (the maximum Tcoff is 103.3 K) of sintered specimens.
High-speed laser chemical vapor deposition of copper: A search for optimum conditions
Authors: Markwalder B. , Widmer M. , Braichotte D. , van den Bergh H.
Published: July 2002

The photothermal laser-induced chemical vapor deposition of copper is studied as a function of the writing speed, the light intensity, and the diameter of the focal spot on the substrate, at three different pressures of the copperbishexafluoroacetylacetonate precursor. The height, the width, and the electrical conductivity of the deposited metal stripes are measured. The metalorganic vapor pressure is the key variable for attaining high writing speeds. Copper stripes have been obtained at 1 mm s−1 .
Fermi degeneracy and its effects on the open-circuit voltage of silicon solar cells
Authors: Morales-Acevedo Arturo
Published: July 2002

A theoretical explanation of the high open-circuit voltage (Voc) in n+-p silicon solar cells despite the heavy doping effects (such as Auger recombination and rigid band-gap narrowing) is given. It is shown that, contrary to recent expectations, when the surface impurity concentration is Ns ≥2×1020 cm−3 the open-circuit voltage is approximately the same as that for surface passivated cells with Ns ≤2×1019 cm−3. Furthermore, in the case of high values of Ns the open-circuit voltage becomes almost independent of the surface recombination velocity. Our model shows that these facts are due to the Fermi degeneracy and the internal electric field. Therefore, high concentrations of activated donors should be looked forward to for obtaining high-efficiency n+-p solar cells.
The barrier height of Schottky diodes with a chemical-vapor-deposited diamond base
Authors: Hicks M. C. , Wronski C. R. , Grot S. A. , Gildenblat G. Sh. , Badzian A. R. , Badzian T. , Messier R.
Published: July 2002

A barrier height of 1.13±0.03 eV was measured for Al and Au rectifying contacts to p-type chemical-vapor-deposited diamond thin films using the internal photoemission technique. The results are compared with experimental data reported for Schottky barriers on single-crystal diamond.
Organometallic vapor-phase-epitaxial growth and characterization of ZnGeAs2 on GaAs
Authors: Solomon G. S. , Timmons M. L. , Posthill J. B.
Published: July 2002

We report the epitaxial growth of single-crystal stoichiometric ZnGeAs2. The (001) ZnGeAs2 layers were deposited by organometallic vapor-phase epitaxy on (100) GaAs. The epitaxy has specular surface morphology. The stoichiometric chemical composition has been confirmed by x-ray diffraction, electron microprobe, and Auger electron spectroscopy. Selected-area electron diffraction patterns clearly indicate the chalcopyrite structure and that the [001] lattice direction is the growth direction. X-ray diffraction indicates that the c-direction lattice constant is 11.192 Å for our epitaxial material, which is an elongation of 0.35% from the bulk material value of 11.153 Å. When stiffness constants for ZnGeAs2 are approximated by those of GaAs, this c-axis elongation can be explained by a contraction in the a direction induced by the 3.4×10−3 lattice mismatch between the ZnGeAs2 epitaxy and the GaAs substrate. Absorptance and transmittance measurements indicate that this material has a direct band gap of approximately 1.15 eV and agrees well with previously reported values. Hall measurements show that the material is p type with room-temperature hole mobilities up to 56 cm2 V−1 s−1 for a corresponding carrier concentration of 9×1018 cm−3. This mobility is slightly higher than previously reported for bulk material and attests to the high quality of this material.
Phase separations of amorphous CoW films during oxidation and reactions with Si and Al
Authors: Wang S. Q. , Mayer J. W.
Published: July 2002

Reactions of thin Co55 W45 films in contact with Si(100) substrates and aluminum overlayers annealed in vacuum in the temperature ranges of 625–700 °C and 500–600 °C, respectively, and of thin Co55W45 films in air from 500 to 600 °C were investigated by Rutherford backscattering spectrometry, glancing angle x-ray diffraction, and scanning electron microscope techniques. CoW alloy films were amorphous and have a crystallization temperature of 850 °C on SiO2 substrates. The compound formed is Co7 W6. Phase separations were found in all the reactions. A layer of cobalt compounds (CoSi2 in Si/CoW, Co2 Al9 in CoW/Al, and Co3 O4 in CoW with air) was found to form at the reaction interfaces. In addition, a layer of mainly tungsten compounds (WSi2 in Si/CoW, WAl12 in CoW/Al, and WO3 in CoW with air) was found next to cobalt compound layers, but further away from the reaction interfaces. The reactions started at temperatures comparable to those required for the formation of corresponding tungsten compounds.
Resonant tunneling bipolar transistors using InAlAs/InGaAs heterostructures
Authors: Futatsugi T. , Yamaguchi Y. , Muto S. , Yokoyama N. , Shibatomi A.
Published: July 2002

Resonant tunneling bipolar transistors (RBTs) using InAlAs/InGaAs heterostructures were fabricated. These devices are bipolar transistors which use a resonant tunneling barrier as a minority-carrier injector. The RBT exhibits a collector current peak as a function of the base-emitter voltage at room temperature. The peak-to-valley ratio of the collector current is 3.5, and the peak collector current density is 5.7×104 A/cm2. The common-emitter current gain reaches a value of 24. These InAlAs/InGaAs RBTs characteristics are much better than those of AlGaAs/GaAs RBTs. We measured the microwave characteristics of the InAlAs/InGaAs RBT at room temperature, and obtained a cutoff frequency of 12.4 GHz. An equivalent circuit analysis and device simulation yielded an estimated resonant tunneling barrier response time of 1.4 ps.
Electrical properties of oxygen thermal donors in silicon films synthesized by oxygen implantation
Authors: Vettese F. , Sicart J. , Robert J. L. , Cristoloveanu S. , Bruel M.
Published: July 2002

Conductivity and Hall measurements have been carried out on thin silicon films formed by oxygen implantation (SIMOX) and high-temperature annealing. These layers have then been annealed between 450 and 850 °C for 1 h in order to study the electrical behavior of oxygen thermal donors (TD). The maximum donor concentration occurs at 550 °C for TD-I and 750 °C for TD-II. The concentration of TD-II is higher than that of TD-I and the distribution of TD-II can be nonuniform. Thermal ionization energies of these donor states are also derived. A TD level (220 meV) deeper than the typical one (150 meV) is responsible for the electrical properties of the SIMOX layers. Subsequent annealing activates shallow TD states and compensation centers. Thus the ionization energy of the deep TD level decreases greatly, when TDs are generated. High carrier mobilities have been measured which have been limited only at low temperatures by interface scattering.
Structure and electrical properties of interfaces between silicon films and n+ silicon crystals
Authors: Ogawa Shin-ichi , Okuda Seiji , Yoshida Takehito , Kouzaki Takashi , Tsukamoto Kazuyoshi , Sinclair Robert
Published: July 2002

We have studied the morphology and electrical characteristics of the interfaces between silicon-implanted, low-pressure chemical-vapor-deposited (LPCVD) silicon films with an n+ single-crystal silicon substrate. Using high-resolution transmission electron microscopy, it is shown that the silicon implant causes a ‘‘balling up’’ of the native oxide layer at the interface and epitaxial growth occurs in the LPCVD silicon film even after rapid thermal annealing at only 940  °C for 30 s. This morphological change results in a realization of a low-ohmic-resistivity LPCVD silicon/ n+ single-crystal silicon contact even at a sub-half-μm size, although the unimplanted contact becomes nonohmic. The leakage current for the implanted contact is as low as that for the unimplanted one in shallow junctions.
Elastic and vibrational properties of nickel films measured by surface Brillouin scattering
Authors: Jorna R. , Visser D. , Bortolani V. , Nizzoli F.
Published: July 2002

Surface Brillouin scattering has been used to measure the dispersion relations of surface, interface, and guided modes in nickel films supported on quartz glass with thicknesses of 100, 200, 500, 1000, and 2000 nm. The elastic constants of nickel have been estimated near the glass interface and near the free surface of the film. Thin films (up to 500 nm) turn out to be homogeneous, while thicker films show increasingly higher values of the elastic constant c44. This behavior could be related to a change from the (111) preferentially oriented nickel crystallites on the glass, typical of thin FCC films, to a more isotropic growth for thicknesses greater than about 500 nm.
Optical characterization of two-dimensional charge density in GaAs-(Al0.3Ga0.7As) multiple quantum wells
Authors: Liu D. W. , Brody E. M. , Chi J.
Published: July 2002

Utilizing the photoluminescence emission and excitation techniques, we can determine the concentration of two-dimensional (2D) plasma in GaAs-(Al0.3 Ga0.7As) multiple quantum wells (MQW) at lattice temperature ∼5 K; the results are consistent with the Hall densities. The optical processes investigated also provide the information on the uniformity of 2D electron gas concentration between the wells, which is not available by Hall measurements. The resonant Raman scattering method was taken as an auxiliary tool to confirm the intersubband transition in MQW and substantiates a two-band model. The absorption edge of the photoluminescence excitation spectrum, especially the low-energy tail, was fitted with a Fermi distribution function. The results indicate that the temperature of the 2D plasma, Tc, was around 20 K during the measurements.
Photoemission study of nitrogen-implanted GaAs surfaces
Authors: Carin R. , Le Moël A. , Duraud J. P.
Published: July 2002

Monocrystalline p- and n-type GaAs (100) substrates were bombarded with 3-keV Ar+ and 10-keV N+ ions. Chemical states and composition of the surface were analyzed from x-ray and uv photoemission spectroscopy with photoelectron escape depths of 5–20 Å. Ion sputter etching eliminates chemisorbed impurities and produces an As deficit near the surface involving a high reactivity. For nitrogen-ion implantation, N atoms partially substitute to As atoms, which gives an unsaturated GaAs1−x Ny compound in our experimental conditions. The analysis with the He ii line (ℏω=40.8 eV) shows predominance to GaN close to the surface.
Electron-beam-induced current and photoetching investigations of dislocations and impurity atmospheres in n-type liquid-encapsulated Czochralski GaAs
Authors: Frigeri C. , Weyher J. L.
Published: July 2002

Typical defects in n-type liquid-encapsulated Czochralski GaAs, i.e., grown-in dislocations and grown-in and then stress-induced glide (GS) dislocations have been studied by electron-beam-induced current (EBIC) and diluted Sirtl-like etching with light (DSL photoetching). The study of GS dislocations was possible because both EBIC and DSL can reveal the recombinative traces left behind the moving dislocations. Grown-in dislocations and the ending points of GS dislocations exhibit a central feature more recombinative than the external atmosphere. No such central feature has been detected at the starting points of the GS dislocations. A model for the formation of the impurity atmospheres in the GS defects has been put forward. By quantitative EBIC measurements performed right in the impurity atmospheres (∼5–20 μm in size) around dislocations, the local space-charge region width of the EBIC Schottky diode was determined. Information on the net ionized impurity concentration in the atmospheres could thus be obtained. It has been established that silicon (dopant) autocompensation along with the gettering of other unknown impurities and point defect reactions probably involving arsenic interstitials are important features of the atmospheres.
Room-temperature acoustic loss peaks in quartz
Authors: Martin J. J. , Hwang Ho B. , Bahadur H. , Berman G. A.
Published: July 2002

Defect-related acoustic loss peaks with maximum temperatures near 300 K have been observed in AT-cut cultured quartz crystals. For as-grown quartz in which lithium is the dominant alkali impurity, a small loss peak is observed at 305 K. In sodium-swept material, the 305-K peak is replaced with a much stronger peak centered near 335 K. Both peaks grow rapidly with irradiation and then show some decay at higher radiation doses. For samples with small OH growth defect to aluminun ratios the decay of the loss peaks is nearly complete, while for samples with relatively large OH growth defect to aluminum ratios the peaks show only a small decay. The peaks may be caused by lithium or sodium trapped at the growth-defect sites rather than hydrogen. Air or hydrogen electrodiffusion which replaces the alkalis with hydrogen removes both the 305- and 335-K peaks. Neither the 305-K Li-related peak nor the 335-K Na-related peak were observed in the two natural quartz resonators that were tested. Instead, radiation produced a peak at 249 K that is probably due to a germanium center. This peak matches the one recently found in germanium-doped cultured quartz. Conventionally grown cultured quartz does not show this Ge-related loss peak.
High-resolution multiphoton laser-induced fluorescence spectroscopy of zinc atoms ejected from laser-irradiated ZnS crystals
Authors: Arlinghaus H. F. , Calaway W. F. , Young C. E. , Pellin M. J. , Gruen D. M. , Chase L. L.
Published: July 2002

Time-of-flight (TOF) measurements employing high-resolution multiphoton laser-induced fluorescence spectroscopy (LFS) have been used as a probe to determine the yield and velocity distributions of Zn atoms ejected from a ZnS single crystal under irradiation by 308-nm photons. For fluences between 20 and 80 mJ/cm2 (irradiated area 2 mm2), the velocity distributions could be fitted by Maxwell–Boltzmann distributions where the characteristic temperature increased from 2000 to 9000 K, respectively. The absolute neutral Zn yield also increased from 108 to 1012 atoms per pulse over this same fluence range. Plots of temperature (T) as a function of fluence (F) and yield as a function of 1/T and 1/F suggest thermal evaporation as the mechanism for the Zn emission.The results indicate that with increasing fluence a critical combination of particle density and laser intensity is reached for formation of a plasma which interacts with the surface to cause catastrophic failure. For consecutive laser shots at constant ablation laser fluences, a nearly exponential increase of the Zn particle density was observed, although the measured kinetic temperature remains approximately constant even beyond the onset of visible damage to the ZnS surface. Doppler-shift techniques have been combined with TOF measurements for the first time in order to separate prompt from delayed emission of ablated atoms as well as to probe possible molecular or cluster ejection and fragmentation. Evidence for the latter phenomena was obtained.
Electronic structure and deep impurity levels in [111] GaAs/AlxGa1−xAs semiconductor superlattices
Authors: Ren Shang Yuan , Dow John D.
Published: July 2002

A theory of the electronic structures of periodic N1×N2 GaAs/AlxGa1−xAs superlattices grown along the [111] direction is presented. Deep levels associated with s- and p-bonded substitutional impurities in these superlattices are also predicted. It is found that: (i) in contrast with [001] superlattices, [111] superlattices are almost always direct band-gap superlattices. (ii) The [111] superlattices exhibit weaker quantum-well confinement than the corresponding [001] superlattices. (iii) As the thickness, t(GaAs), of each GaAs layer is reduced below a critical value (tc ≂13 Å or N1≂4 for x=0.7iii), common shallow donor impurities such as Si cease donating electrons to the conduction band and instead become deep traps. For [111] superlattices tc is smaller than the corresponding tc for [001] superlattices. The fundamental band gap and the band edges of the superlattice, and hence the ionization energies of deep levels, depend strongly on the layer thickness t(GaAs) but only weakly on t(AlxGa1−xAs). The T2- and A1-derived deep levels (of the bulk point group Td) are split and shifted, respectively, near a GaAs/AlxGa1−xAs interface: the p-like T2 level splits into an a1 ( pσ-like) level and a doubly degenerate e ( pπ -like) level of the point group for any general superlattice site (C3v), whereas the s-like A1 bulk level becomes an a1 (s-like) level of C3v. The order of magnitude of the shifts and splittings of deep levels at a GaAs/AlxGa1−xAs interface is less than 0.1 eV, depends on x, and becomes very small for impurities more than ≂3 atomic planes away from an interface. These predictions are based on a periodic

superslab calculation for unit superslabs with total thickness t(GaAs)+t(AlxGa1−xAs) as large as 65.3 Å or N1+N2=20 two-atom-thick layers. The Hamiltonian is a tight-binding model in a hybrid basis that is a generalization of the Vogl model and properly accounts for the nature of interfacial bonds. The deep levels are computed using

the Hjalmarson et al. theory [Phys. Rev. Lett. 44, 810 (1980)] and the special points method.
Low-pressure metalorganic chemical vapor deposition growth and characterization of δ-doped InP
Authors: di Forte-Poisson M. A. , Brylinski C. , Blondeau E. , Lavielle D. , Portal J. C.
Published: July 2002

This work describes the low-pressure metalorganic chemical vapor deposition growth of planar-doped InP epilayers using Si donors. Capacitance-voltage measurements and analysis by secondary ion mass spectroscopy show that the width of such δ-doped layers is of only a few lattice planes. Transport measurements give evidence for quantum confinement of the electronic gas in the layer and thus confirm the narrow width.
Impurity-induced layer disordering in In0.5(Alx Ga1−x)0.5P-InGaP quantum-well heterostructures: Visible-spectrum-buried heterostructure lasers
Authors: Dallesasse J. M. , Plano W. E. , Nam D. W. , Hsieh K. C. , Baker J. E. , Holonyak N. , Kuo C. P. , Fletcher R. M. , Osentowski T. D. , Craford M. G.
Published: July 2002

Diffusion of Si into quantum-well heterostructures and superlattices employing the high gap III-V quaternary system Iny (AlxGa1−x )1−yP is shown to result in impurity-induced layer disordering. Secondary ion mass spectroscopy, transmission electron microscopy, and photoluminescence data indicate that the diffusion of Si into an InAlP-InGaP superlattice grown lattice matched on GaAs (y≊0.5) results in the intermixing of the layers, thus forming an alloy of average composition. Buried-heterostructure lasers are fabricated using Si layer disordering of In0.5 (Alx Ga1−x )0.5 P p-n quantum-well heterostructures. The disorder-defined stripe-geometry diode lasers operate pulsed at 300 K near 6400 Å. Continuous wave operation at λ∼6255 Å is achieved at −47 °C.
The interaction between thin films of cobalt and GaAs (001) substrates
Authors: Genut M. , Eizenberg M.
Published: July 2002

The interfacial reactions between thin films of cobalt and (001)-oriented GaAs substrates have been studied. The interaction starts at 325 °C by Co atoms in-diffusion, resulting in the formation of a ternary phase, Co2GaAs, which grows epitaxially on the substrate in two coexisting alignments. The growth of Co2GaAs in the temperature range of 325–400 °C is diffusion limited with an activation energy of 0.6–0.7 eV. Contacts produced in this annealing regime are rectifying with nearly ideal thermionic emission behavior. The ternary phase decomposes and loses stoichiometry at higher temperatures by the formation of the stable binary compounds, CoGa and CoAs. At 500 °C vertical phase separation of the binary components occurs, resulting in a CoGa layer on top of the CoAs phase. Heat treatment at 600 °C in an open system (vacuum anneal) results in decomposition of CoAs by arsenic out-diffusion. Contacts produced at the higher temperature regime (>400 °C) have very low effective barriers; this is attributed mainly to modifications in the stoichiometry of the GaAs subsurface region and to the formation of a diffused interfacial layer due to Ga and As out-diffusion.
Diamondlike carbon film deposition using a reactive pulsed electromagnetic inductive plasma process
Authors: Ebihara Kenji , Ikegami Tomoaki , Matsumoto Toshiyuki , Nishimoto Hirofumi , Maeda Sadao , Harada Kazuhiko
Published: July 2002

A reactive pulsed electromagnetic inductive plasma process has been developed and used to deposit amorphous carbon films in methane discharges. The plasma state was investigated by analyzing spectral intensity emitted from H atoms and molecular fragments CH, which were produced by methane dissociation. The films deposited with this technique have outstanding characteristics due to the magnetohydrodynamic effect, good adhesion to room-temperature substrates, wide optical gap, highly insulating, and diamondlike structure. The film properties are correlated with excitation temperature and intensity ratio between specified spectral lines. Furthermore, it is shown that a pulsed plasma process combined with an rf glow discharge deposits amorphous carbon films that contain crystalline particles.
Simple predictive models for the thermal response of optical data storage media
Authors: Bartholomeusz B. , Bowers P. , Genova D.
Published: July 2002

Simple expressions are derived that describe the laser marking of loss-free optical recording media in terms of measurable and known quantities. In particular, the mark-length error was found to be proportional to the ratio of the second-harmonic minimum power (PSHM) to the write power. Predictions made with the derived expressions are in reasonably good agreement with data obtained for both poorly and highly conducting thin-film media, validating their usefulness as first-order investigative tools.
Brillouin scattering from spin waves in sputtered Co-Zr films
Authors: Yoshihara Akira , Haneda Yoichi , Shimada Yutaka , Fujimura Tadao
Published: July 2002

Thermally excited spin waves in thin Co91-Zr9 sputtered films have been studied at room temperature by Brillouin scattering in external magnetic fields of up to 3.5 kOe. In order to precisely determine the g factor and the surface exchange constant, we extensively studied the Damon–Eshbach mode in a 1-μm-thick film. From the slope of the surface magnon frequency in an external magnetic field, the g factor of 2.17±0.04 is determined. The surface exchange stiffness constant Ds has been determined by examining the surface wave-vector dependence on the surface magnon frequency. We obtained a value of Ds =6.9±2.0×10−9 Oe cm2. The best way to determine the bulk stiffness constant is to observe the standing spin waves excited in a thin film whose thickness is less than 200 nm. We could observe scattering from the standing spin waves of up to a third order in a film of 85±5 nm thick. The bulk exchange stiffness constant Db of 2.2±0.4×10−9 Oe cm2 is obtained from the external field dependence of the standing spin-wave frequencies.
Crystalline to amorphous transformation in GaAs during Kr ion bombardment: A study of elastic behavior
Authors: Sharma R. P. , Bhadra R. , Rehn L. E. , Baldo P. M. , Grimsditch M.
Published: July 2002

A marked softening in the shear elastic properties of GaAs following 1.5-MeV Kr ion irradiation is observed. Ion channeling and Raman scattering are used to monitor the accumulation of damage, which for 1.5-MeV incident energy extends to a depth of ∼8000 Å. Both techniques show that the sample is amorphized by a dose of 2×1014 ions/cm2. Brillouin scattering reveals that a shear elastic modulus of this near-surface irradiated region decreases by 43% as the material transforms from crystalline to amorphous. The observed results are discussed and compared with similar measurements on Si and intermetallic compounds.
New field emission gun with energy filtering effect
Authors: Troyon M.
Published: July 2002

We have developed and tested a new kind of field emission gun. This electron gun is an energy filtering field emission gun that is able to reduce the energy spread of the beam. An energy spread as small as ΔE=0.16 eV full width at half maximum has been measured, at an accelerating voltage V=10 kV, for a probe current Ip=2.1 nA and an illuminating half-angle α=1.2 mrad.