bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes of electrical properties of implanted buried oxide in silicon by high-temperature annealing
Authors: Mogro-Campero A.
Published: July 2002

Implantation of 150-keV oxygen into silicon to a dose of 2×1018 cm−2 at 600 °C resulted in a silicon-on-insulator structure. Annealing was carried out at 1150, 1200, and 1250 °C. The top silicon layer was removed, and metal contacts were evaporated to form capacitors for C-V and C-t measurements. The values of all the electrical parameters measured changed with annealing temperature. Oxide charge and doping density in the underlying silicon decrease with increasing annealing temperature. The capacitance relaxation time after pulsing into deep depletion, and the carrier generation lifetime increase with increasing annealing temperature. Low values of doping density and high values of capacitance relaxation time are desirable for supporting high voltages across such a structure.
Modeling of the bremsstrahlung radiation produced in pure-element targets by 10–40 keV electrons
Authors: Small John A. , Leigh Stefan D. , Newbury Dale E. , Myklebust Robert L.
Published: July 2002

A new global relationship has been developed for predicting electron-excited bremsstrahlung intensities over a wide range of accelerating voltages 10–40 keV, atomic numbers 4–92, and x-ray energies 1.5–20 keV. The new relationship was determined empirically from the mathematical modeling of extensive data and is designed for calculating bremsstrahlung intensities in analytical procedures, such as those requiring peak-to-background measurements, where the direct measurement of the bremsstrahlung intensities is impracticable. The distribution of errors between the data and the model is symmetrical, centered around zero error with 63% of the values falling between ±10% relative error.
Optical reflectance measurements of Co1−xCrx
Authors: Leng Jing , Fong C. Y. , Wooten F. , Perlov C. M.
Published: July 2002

The optical reflectance of Co1−xCrx for 0.12≤x≤0.22 has been measured with photon energy between 1.5 and 4.1 eV. Light was unpolarized. For atmospheric pressure, two sets of samples have been used. Spectra were obtained under vacuum (10−3 Torr) with one set of samples. Samples are in the film form with thicknesses of the order of 1 μm. Between 1.5≤ℏω≤3.5 eV, the measured alloy spectra are similar to that for pure Co with Ē∥ĉ. The reflectance decreases monotonically as the photon energy increases. This suggests that the alloying Cr to Co at x≤0.22 has not changed appreciably the electronic properties of Co within 3.0 eV of the Fermi energy EF. At higher energy the present results show a minimum in reflectance at 4.0 eV. Therefore, the alloying of Cr seems to show its effect in higher-energy interband transitions.
Disclinations and magnetism in rare-earth–transition-metal hard magnets
Authors: Watson R. E. , Melamud M. , Bennett L. H.
Published: July 2002

An important class of magnets, involving rare-earth and 3d transition metals and sometimes metalloids, includes Nd2Fe14B and Nd2Fe17. We have noted a correlation between the local site magnetism in these two compounds and whether those sites lie on nets of so-called major ligand lines or disclinations, i.e., bond lines shared by six common nearest neighbors. We propose that a criterion for choosing candidate alloys with strong 3d moments is the occurrence of such disclination nets. We have developed a computer program for the calculation of these nets, and using this, several structures having 3d sites with this characteristic have been found.
Anisotropy in thin-film media—origins and applications (invited)
Authors: Haines William G.
Published: July 2002

The magnetic recording properties of thin-film media are sensitive to a variety of deposition variables. Detailed analyses of these variations generally indicate that the cause of this sensitivity is anisotropy of the films at the microcrystalline level. The origins of anisotropy in thin films are reviewed as are the effects of anisotropy on magnetic recording performance. Applications where anisotropy is used to create enhanced performance for magnetic recording are presented. The problems involved in controlling the microstructural properties of recording media are considered. Finally, strategies to repeatably produce high-performance recording media are presented.
Measurement of ultrasound velocity in the spin-glass C
uMn
Authors: Hsu T. C. , Marston J. B.
Published: July 2002

Ultrasound velocity measurements may be used to study the dynamics of the spin-glass phase. Near the transition temperature, the sound speed deviates slightly from that of the pure nonmagnetic host. We measured the velocity anomaly in a 1-at. % CuMn sample near the transition temperature (12 K) as a function of frequency from 5 to 100 MHz and found its size to be frequency independent. We also found changes in the anomaly when the sample was field cooled in transverse 4.7- and 14.2- kG fields. These results are discussed in light of previously published theoretical predictions.
Effect of temperature on the variance of the log-normal distribution of failure times due to electromigration damage
Authors: Schwarz J. A
Published: July 2002

To predict interconnect reliability, the mean time to failure, nature of failure time distribution, and the variance in the distribution at operating conditions must be known. The first two pieces of data can be obtained using the well-established mean time to failure technique. It is demonstrated the effect of temperature on the variance of the failure time distribution can be found from data obtained from temperature-ramp resistance analysis to characterize electromigration. The predicted variance is lowest at temperatures near where data were gathered, but the variance increases as the temperature approaches operating conditions.
An antimony-related electronic level in isovalently doped bulk GaAs
Authors: Mitchel W. C. , Yu P. W.
Published: July 2002

Temperature-dependent Hall-effect and photoluminescence measurements have been performed on a series of antimony-doped bulk GaAs samples that were otherwise undoped. A new donor level located 0.48 eV below the conduction-band edge has been detected by both experiments in all antimony-doped samples studied. This level reduces the resistivity of antimony-doped material below the semi-insulating limit. Comparison with known intrinsic levels in undoped material have been made and it is shown that the 0.48-eV donor is distinct from any of these. It is concluded that the defect responsible for the 0.48-eV donor involves an impurity antisite SbGa either isolated or in a complex with intrinsic defects.
Digital filtering of scanning tunneling microscope images
Authors: Park Sang-il , Quate C. F.
Published: July 2002

The images from the scanning tunneling microscope (STM) can be improved with digital filtering using the fast Fourier transform. In this communication we discuss the noise characteristics for images taken in air with the STM. The STM images are significantly enhanced if we assume the noise has an 1/f characteristic and use a Weiner optimal filter to remove this type of noise.
A simple contactless method for evaluating the low-temperature parameters of a two-dimensional electron gas
Authors: Templeton I. M.
Published: July 2002

A sample of two-dimensional electron-gas material is stuck, face upward, onto two flat, Corbino-configuration metal electrodes, thereby providing capacitive coupling (a few pF) to the gas through the high-dielectric-constant substrate material. At high magnetic fields and low temperatures, the minima in σxx produce a high resistance in series with the two coupling capacitors, and this resistance can be measured with an audio-frequency (10 kHz) capacitance bridge. The resistance peaks in high-mobility samples are very sharply defined, and their periodicity in 1/B gives directly the electron concentration. At low fields, prior to the appearance of the peaks, the resistance is proportional to μB2/n, thus relative mobilities may be determined.
Discharge currents following space-charge-limited current conditions in insulators
Authors: Wintle H. J.
Published: July 2002

We show that the decay of electric field and of charge density in a shorted dielectric, following fully saturated space-charge-limited flow, can be written very simply as a similarity transform of the original field. This is true for both planar and cylindrical geometries. A single integration is needed to find the time dependence, and both zero and finite injection fields can be readily handled. This discharge current decays monotonically to zero.
The thin-film reaction between Ti and thermally grown SiO2
Authors: Barbour J. C. , Fischer A. E. M. J. , van der Veen J. F.
Published: July 2002

Medium-energy ion scattering was used to examine the reaction between a thin Ti film (4×1015 Ti atoms/cm2) and a thermally grown SiO2 substrate. The reaction was monitored after deposition at room temperature and after annealing, up to a temperature of 800 °C. During deposition, oxygen from the SiO2 substrate dissolves into the Ti film (up to 38% oxygen) without the occurrence of Ti-Si intermixing. Heating of the sample causes a loss of oxygen but no loss of titanium. Instead, islands of titanium silicide and areas of bare Si surface are formed after an 800 °C anneal for 250 min. A comparison of the room-temperature reaction for the ternary Ti-O-Si system and the binary Ti-Si system is also given.
Determination of the dynamic response of W-2 tungsten by commercial manganin stress gauges
Authors: Rosenberg Z.
Published: July 2002

The dynamic response of a tungsten alloy (W-2, manufactured by Kennametal) was determined by using commercial manganin gauges in planar shock-wave and long-rod experiments. The gauges were used both as in-material stress transducers and as time of arrival sensors in the back surface configuration. These two techniques enabled us to determine the Hugoniot curve for W-2 in the 0–500 kbars range. The spall strength and the Hugoniot elastic limit (HEL) of this material indicates brittle behavior which is different from most other metals. The long-rod experiment yielded a value for the dynamic uniaxial stress experiment which is in excellent agreement with the static compressive strength and the dynamic one, as deduced from the measured HEL. The three values of compressive strength fall within the range of 12–14.4 kbars, indicating that the yield strength of W-2 is relatively insensitive to strain rate.
Electron states in two coupled quantum wells—A strong coupling-of-modes approach
Authors: Chuang S. L. , Do B.
Published: July 2002

In this paper, coupled-mode equations for two strongly coupled quantum wells are derived via two methods: (i) a ‘‘reciprocity’’ formulation similar to the reciprocity theorem in electromagnetics, and (ii) a variational formulation. It is shown that both formulations give the same coupled-mode equations. Numerical results for the electron energy levels and wave functions for two coupled asymmetric or symmetric quantum wells are presented, using both the strong coupling-of-modes theory and the conventional weak coupling-of-modes theory, and are compared with those of the exact calculations. The two-coupled-quantum-wells model is useful in the study of electron transport in superlattice via hopping or tunneling.
Mechanism of EL2 effects on GaAs field-effect transistor threshold voltages
Authors: Anholt R. , Sigmon T. W.
Published: July 2002

Depending on the magnitude of the out-diffusion of the deep-donor EL2 during the post-implant anneal, the substrate barrier height increases. This in turn affects the depletion of donors on the channel side of the substrate junction, so that the voltage that is needed to pinch off the channel from the Schottky barrier is reduced. Threshold-voltage shifts of the order of less than 13 mV for devices with threshold voltages of −200 mV are predicted.
Lasing operation of chemical oxygen-iodine laser without water-vapor trap
Authors: Takehisa K. , Kikuchi T. , Uchiyama T.
Published: July 2002

cw laser action from chemically pumped iodine atoms was achieved without a cold trap to freeze water vapor. An alkaline solution of H2O2 was circulated in a porous pipe generator, which made it possible to cool the solution externally. A lasing operation time of about 100 s with a constant output power of 5 W was obtained.
Frequency dependence of capacitance-voltage characteristics caused by D
X centers in Si-doped AlGaAs
Authors: Ohori Tatsuya , Takikawa Masahiko , Komeno Junji
Published: July 2002

Capacitance of Schottky barrier diodes formed on Si-doped AlxGa1−xAs (x>0.25) decreases as the measuring frequency increases from 1 kHz to 1 MHz at room temperature. As a result of this frequency dependence, apparent donor concentrations become smaller than the true values at a measuring frequency of 1 MHz, which is widely used for derivation of donor concentrations. This frequency dependence is caused because charging and discharging at DX centers does not follow the 1-MHz measuring frequency even at room temperature. This result is important for characterizing n-AlGaAs and for its applications to electronic and optical devices.
Growth and diffusion of abrupt zinc profiles in gallium arsenide and heterojunction bipolar transistor structures grown by organometallic vapor phase epitaxy
Authors: Enquist P. , Hutchby J. A. , de Lyon T. J.
Published: July 2002

The growth and diffusion of abrupt Zn profiles in undoped gallium arsenide (GaAs), silicon-doped GaAs, and heterojunction bipolar transistor structures grown by organometallic vapor phase epitaxy have been studied using secondary ion mass spectrometry depth profiling. The depth profiles indicate that abrupt (within 100 Å) turn-on of Zn doping to levels approaching 1020 cm−3 are obtainable, while abrupt turn-off is limited to about two orders of magnitude due to dopant tailing toward the surface resulting from residual Zn in the reactor. The sharp diffusion fronts resulting from post-growth anneals indicate that the Zn diffusion coefficient has a concentration dependence. However, the diffusion of Zn at high concentrations appears to be inhibited by crystal defect kinetics resulting in a relatively concentration-independent Zn diffusion coefficient. The V/III growth ratio did not have an effect on Zn diffusion in undoped or silicon-doped GaAs. The diffusion of Zn in heterojunction bipolar transistor structures differs in that the diffusion of Zn into the GaAs collector is larger by an order of magnitude and decreases with an increase in V/III growth ratio. In addition, the diffusion of Zn into the aluminum gallium arsenide (AlGaAs) emitter is significantly lower and more effectively inhibited by an increase in V/III ratio than the diffusion of Zn into the GaAs collector.
A parameter study of streamer propagation in SF6
Authors: Morrow R.
Published: July 2002

In a recent paper a model was presented which described the main features of streamer propagation in SF6. In this communication the sensitivity of the model to changes in the input parameters is discussed. Each parameter is varied within the limited range expected from experimental determinations. It is predicted that streamers can only propagate within a limited range of streamer channel diameters, and that the charge in the streamer head varies considerably with channel diameter. Results are also presented which predict that the streamer velocity is only weakly dependent on pressure in the range 50–500 kPa.
Relationship between the transition width and the zigzag wavelength
Authors: Zhang X. Y. , Suhl H. , George P. K.
Published: July 2002

The stability of a head-to-head domain wall is analyzed and the instability is shown to have a spatial spread on the order of the zigzag wavelength. Accordingly, an idealized zigzag model is proposed and the width of a zigzag wall is related to its wavelength in the absence of an external field. For an externally applied head field the results are shown to coincide with the Williams–Comstock transition width after establishing the relationship between wavelength and head field gradient.
Hard magnetic properties of melt-spun Nd-Co-Fe-B materials
Authors: Fuerst C. D. , Herbst J. F.
Published: July 2002

The effects of cobalt substitution on the hard magnetic properties of melt-spun neodymium-iron-boron materials are reported. Samples having the starting composition Nd0.135[(CoxFe1−x)0.95B0.05 ]0.865 with x=0, 0.05, 0.10, 0.15, 0.20, 0.35, 0.50, 0.75, and 1 were prepared by melt-spinning over a range of substrate surface velocities (i.e., quench rates) and their room-temperature magnetization characteristics measured. Choosing samples having maximal energy products, it was found that in the 0≤x≤0.5 interval the coercivity and remanence show modest overall diminution with x while the energy product declines more rapidly. Above x=0.5, the remanence, energy product, and especially the coercivity, severely deteriorate. X-ray diffraction studies indicate that for x>0.5 formation of the Nd2Fe14B-type structure is suppressed, and the samples contain progressively greater amounts of Nd2(Co,Fe)17.
The influence of size and morphology of eutectoid carbides on the magnetic properties of carbon steels
Authors: Jiles D. C.
Published: July 2002

A study of the effects of adding carbon and changing its distribution within ferritic steels is reported. The magnetic properties of these steels were greatly affected by the amount of carbon and the size and morphology of the carbides. A correlation between initial permeability μin and coercivity Hc was determined from the results, which was found to be independent of the carbide morphology.
Time-resolved study of a laser-induced surface plasma by means of a beam-deflection technique
Authors: Heidecker E. , Schäfer J. H. , Uhlenbusch J. , Viöl W.
Published: July 2002

A fast-beam deflection technique is used to investigate the transient behavior of a laser-induced surface plasma generated by CO2-laser pulses of 2-kW average power near an aluminum surface in various protective gas atmospheres, with a typical pulse energy of 3.3×10−2 J, a pulse repetition rate of 60 kHz, and an average peak power per pulse of 30 kW, corresponding to an intensiy of 6×1012 W/m2. As a laterally probing beam, a cw 10-W CO2 laser is used, whose beam is focused into a small volume in front of the surface. The electrons of the laser-induced plasma passing this volume diffract the cw CO2 laser beam, and the resulting beam deflection is determined by means of a partially absorbing CaF2 wedge in connection with a fast infrared detector. The evaluation of beam deflection 0.15 cm above the surface renders a maximum electro density of 2×1023 m−3 for a surrounding argon atmosphere and 0.7×1023 m−3 for pure helium. Additives of O2 reduce the attainable electron density even more. No plasma can be detected below a threshold of, say, 10 mJ energy per laser pulse. It is verified that high electron density as in the case of argon shields the surface against the incoming CO2 laser pulses so that material processing, such as welding, is rather poor. Better welding results are achieved in helium-oxygen mixtures.
Annealing of damage and stability of implanted ions in ZnO crystals
Authors: Sonder E. , Zuhr R. A. , Valiga R. E.
Published: July 2002

The annealing of Bi, Cr, and Mn, implanted in ZnO, has been studied by Rutherford backscattering, ion channeling, and secondary ion mass spectroscopy. Implantation of ∼1016 ions/cm2 of any of these elements produces large concentrations of Zn interstitials, but no completely amorphous region. The temperature at which these interstitials anneal is a function of the implant species. Other defects produced by the implantation, which give rise to dechanneling and a consequent increased scattering probability in the tails of backscattering spectra, anneal at significantly higher temperature. This annealing is also a function of the implant species. Motion of the implant ions themselves does not occur when the interstitials anneal; it takes place above 700 °C for Bi and Mn, and above 1000 °C for Cr.
A study of heating rate and texture influences on annealing hillocks by a statistical characterization of Al thin-film topography
Authors: Bacconnier B. , Lormand G. , Papapietro M. , Achard M. , Papon A.-M.
Published: July 2002

In order to study the quantitative influence of thin-film elaboration conditions on annealing hillock characteristics, an original statistical analysis of profilometer recording was performed. It allows, with suitable hypothesis on hillock shape, a determination of the true hillock volume per unit area. On various annealed Al-Si-Ti films this volume decreases when the degree of preferred orientation increases. On both Al and Al-Si-Ti films an increase of heating rate induces a decrease of hillock volume. We developed a stress relaxation model where relative relaxing mechanism contributions are computed versus grain size and heating rate. Our experimental results interpreted through this model confirm the preponderance of grain boundary diffusion mechanisms in mass transport during hillock growth. The correlation between preferred orientation and hillock volume in Al-Si-Ti films is found to be related to both grain boundary diffusivity and grain size. The absence of small hillocks on high-temperature-deposited Al-Si-Ti films is discussed.
Catalytic chemical vapor deposition method to prepare high quality hydro-fluorinated amorphous silicon
Authors: Matsumura Hideki , Ihara Hisanori
Published: July 2002

A new type of chemical vapor deposition method, named ‘‘Catalytic-CVD’’ method, is presented. In the method, deposition gases are decomposed by catalytic or pyrolytic reaction between deposition gases and a heated catalyzer, and films are thermally grown on a substrate at temperatures lower than 300 °C without any help from glow discharge plasma. Hydro-fluorinated amorphous silicon (a-Si:F:H) films are deposited by this method using both a SiF2 and H2 gas mixture and a SiH2F2 and H2 mixture. It is found that a very high quality a-Si:F:H film can be obtained, and for instance, that the photosensitivity for AM-1 of 100 mW/cm2 exceeds 106 and the spin density is as low as 6×1015 cm−3.
Magnetic x-ray dichroism of rare-earth materials
Authors: Goedkoop J. B. , Fuggle J. C. , Thole B. T. , van der Laan G. , Sawatzky G. A.
Published: July 2002

We discuss recent developments in the magnetic x-ray dichroism of rare-earth materials. The application of this technique to the study of magnetic materials is discussed. Also, other work on magneto-optical effects in the x-ray range is reviewed.
Anomalous low-frequency dispersion in phospholipid-water multilayers
Authors: Hawton M. H. , Keeler W. J.
Published: July 2002

We have studied the dielectric properties of hydrated phospholipids as a function of water content and temperature for frequencies between 5 Hz and 13 MHz. At low frequencies, plots of the log of the imaginary part of the dielectric constant versus the log of frequency were found to be linear with a slope of −0.87 for up to six decades. At higher frequencies a loss peak with a slope of −0.35 above the peak was observed. The slopes were found to be insensitive to variations in temperature and water content, although the separation between the loss peak and the low-frequency process increased with temperature. These results are discussed in the context of infrared divergence theories and models invoking fractal time processes and fractal structure.
Determination of interfacial stress during thermal oxidation of silicon
Authors: Murray Paul , Carey G. F.
Published: July 2002

We develop a theoretical model to obtain the stress in oxide films occurring during thermal oxidation of silicon. The model results in a prediction of 4.5×109 dyn/cm2 for the interfacial stress, in excellent agreement with laboratory measurements. Moreover, we establish generally that the interfacial stress is proportional to 1−γ, where γ is the molar volume ratio of reactant to product. For silicon oxidation, γ=4/9, and the resulting stress is compressive.
Doping of InP and GaInAs with S during metalorganic vapor-phase epitaxy
Authors: Logan R. A. , Tanbun-Ek T. , Sergent A. M.
Published: July 2002

The doping characteristics of S in the metalorganic vapor-phase epitaxial growth of InP and GaInAs are studied using three different but consistent methods of determining the doping level in the crystal, Hall effect, electrochemical C-V profiling and by C-V bias over distances of ∼0.5 μm. It is shown that under the same growth conditions the doping level in InP is 3.5 times larger than in GaInAs and increases 100-fold when the growth temperature is decreased from 625 to 525 °C. S is shown to be a useful donor, essentially completely ionized at room temperature, easily incorporated at levels ≲1018 cm−3 into metalorganic vapor-phase epitaxy growth at 625 °C where crystal morphology is optimized and at high levels ∼1020 cm−3 to form low-impedance n-contact layers with growth at 525 °C.
Optical bistability in small metallic particle composites
Authors: Haus J. W. , Kalyaniwalla N. , Inguva Ramarao , Bowden C. M.
Published: July 2002

We predict that a composite dielectric material composed of silver particles can have an optical bistable transmission without cavity feedback. Our model includes propagation and exhibits an inhomogeneous absorption characteristic that can be useful for device applications. Results are presented for quantum-size silver particles embedded in silica glass.
Observation of interface defects in strained InGaAs-GaAs by photoluminescence spectroscopy
Authors: Joyce M. J. , Gal M. , Tann J.
Published: July 2002

We have described a number of new, broad-linewidth emission bands in the photoluminescence spectrum of strained InGaAs-GaAs single-quantum wells. The variation of the luminescence intensity as a function of layer thickness and excitation intensity suggests that these bands are caused by interface defects, most likely misfit dislocations at the InGaAs/GaAs interface.
Photoionization cross section of InP:Fe
Authors: Takanohashi T. , Nakajima K.
Published: July 2002

The spectral dependence of the photoionization cross section of Fe doped in InP is determined by photocapacitance spectroscopy. The optical process of the carrier emission from the deep acceptor level of Fe is discussed from the results. For the crystal-field-split level of Fe2+:5E, the photoionization cross sections for the fundamental transitions of 5E→Γ1 and Γ15→5E are adequately described by the Lucovsky model. Those optical thresholds are 0.63 and 0.78 eV, respectively, at 77 K. In comparison with the deep-level transient spectroscopy measurements, the following conclusions are obtained. The energy separation between the Fe acceptor level and the conduction-band edge is constant, but that between the Fe level and the valence-band edge varies correspondingly to the temperature variation of the InP band-gap energy. The fact that there is no difference between the optical and thermal activation energies for the 5E→Γ1 transition indicates that the Fe acceptor level is not perturbed by the InP lattice vibration.
Steady-state temperature profiles in thermally thin substrates induced by arbitrarily shaped laser beams
Authors: Imen K. , Lin J. Y. , Allen S. D.
Published: July 2002

The steady-state temperature profiles in flat, thermally thin slabs in a low thermal conductivity medium such as air or gas are calculated. For sufficiently thin samples, conduction to the ambient dominates. Solutions applicable to laser processing of technologically interesting samples such as thin semiconductor wafers heated with Gaussian beams are derived. Included are simple expresssions that allow estimation of the front and back surface temperatures and deviation from the assumption of semi-infinity in both depth and radius.
Characterization of thin AlGaAs/InGaAs/GaAs quantum-well structures bonded directly to SiO2/Si and glass substrates
Authors: Klem J. F. , Jones E. D. , Myers D. R. , Lott J. A.
Published: July 2002

Strained GaAs/InGaAs/AlGaAs quantum-well structures grown on GaAs have been removed from their original substrates by a lift-off process and bonded directly to glass or SiO2-coated Si substrates. Both undoped and modulation-doped structures have been characterized before and after transfer by Hall measurements, variable temperature x-ray diffraction, and photoluminescence. The bonded structures retain the high quality of the as-grown layers.
Defect-property correlations in garnet crystals. V. Energy transfer in luminescent yttrium aluminum–yttrium iron garnet solid solutions
Authors: Rotman S. R. , Warde C. , Tuller H. L. , Haggerty J.
Published: July 2002

The absorption and luminescence spectra of yttrium aluminum garnet single crystals doped with iron have been studied. At low levels of iron doping, the intensity of the defect photoluminesence at 320 nm decreases with increasing iron concentration, as a result of energy transfer to Fe+3 ions which luminesce at 800 nm. Further increases in iron concentrations eliminate luminescence at all wavelengths. Differences between the absorption bands of iron in octahedral and tetrahedral sites, and inter-ion charge transfer processes are discussed.
Optical dispersion relations for Si and Ge
Authors: Adachi Sadao
Published: July 2002

A method is described for calculation of the optical constants (the refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity) of Si and Ge in the entire range of photon energies (0–0.6 eV). The imaginary part of the dielectric function [ε2(ω)] is derived first from the joint-density-of-states functions at energies of various critical points (CPs) in the Brillouin zone; then its real part [ε1(ω)] is obtained analytically using the Kramers–Kronig relation. The indirect-band-gap transitions are also assumed to provide a gradually increasing absorption spectrum expressed by a power law of (ℏω−EIDg)2, where ℏω is the photon energy and EIDg is the indirect-band-gap energy. The optical dispersion relations are expressed in terms of these model dielectric functions. The present model reveals distinct structures in the optical data at energies of the E0, E0+Δ0 [three-dimensional (3D) M0 critical point (CP)], E1, E1+Δ1 [3D M1 or two-dimensional (2D) M0 CP], E2 [a mixture of damped harmonic oscillator (DHO) and 2D M2 CP], E′0 triplet (DHO), and E1 (DHO). Calculated optical spectra are in satisfactory agreement with the experimental data over a wide range of the photon energies.
Hall-effect depletion corrections in ion-implanted samples: Si29 in GaAs
Authors: Look D. C.
Published: July 2002

The sheet free-carrier concentration in a thin, conducting layer on an insulating substrate is lower than the net, sheet-dopant concentration because of free-carrier depletion in the surface and interface regions. Here we develop an algorithm to give the true, net sheet-donor concentration from the measured sheet-Hall concentration under the assumption of a Gaussian donor profile, which is usually sufficiently accurate for ion-implanted samples. Correction curves are generated for Si29 ions implanted into GaAs at energies of 60, 100, 130, 150, and 200 keV, and at doses of 1×1011–2×1014 ions/cm2. Also, the Hall mobilities and r factors are calculated at various carrier concentrations for NA/ND=0 and NA/ND=0.5.
Basic circuits for inductive-energy pulsed power systems
Authors: Rhee M. J. , Fine T. A. , Kung C. C.
Published: July 2002

A comprehensive analysis of pulse formation in inductive-energy pulsed power circuits is presented. The output waveforms, with relevant circuit parameters, are derived for four basic systems, including two new circuit configurations useful for practical applications.
The effect of interstital Frank partial dislocations on the gradual degradation of 1.3-μm double-channel planar buried heterostructure laser diodes
Authors: de Cooman B. C. , Bulle-Lieuwma C. W. T. , de Poorter J. A. , Nijman W.
Published: July 2002

The structure of defects occurring in degraded 1.3-μm double-channel planar buried heterostructure type laser diodes was studied in detail by conventional diffraction contrast, weak-beam dark-field microscopy and high-resolution lattice imaging in a transmission electron microscope. The electrical activity of the defects was analyzed by means of the electron-beam-induced current. Device degradation is associated with the presence of interstitial Frank partial dislocation loops with a Burgers vector of (a/3) {111} at the interfaces between the InGaAsP active layer exposed after the channel etching and the first p+-InP layer of the liquid-phase-epitaxy-grown current-blocking layers. No other types of defects were observed in the course of the present study. The implications of the latter finding are far-reaching and lead to a new degradation model for the microstrctural changes associated with the gradual degradation of long-wavelength lasers. A new degradation model is proposed, and laser diode design considerations for degradation-free operation are given. These consdierations are twofold: the device structure should (a) not favor Frank partial dislocation loop nucleation and (b) suppress the dissociation of the Frank partial dislocations.
Investigation of different Si-related photoluminescence emissions involved in a deep broadband in Al0.3Ga0.7As
Authors: Souza P. L. , Rao E. V. K.
Published: July 2002

A detailed photoluminescence study of a deep broadband emission as a function of the dopant concentration is conducted in molecular-beam epitaxy-grown silicon-doped Al0.3Ga0.7As single layers. The deep broadband which is correlated to the Si concentration consists of several emissions among which three are suggested to be due to different Si complexes. The effects of annealing the samples contributed immensely to this investigation. A model to explain the direct and indirect participations of SiAs in the formation of Si complexes during heat treatment is proposed. The photoluminescence is complemented by the Hall-effect, capacitance, and secondary-ion-mass spectroscopy measurements.
Magnetism and anisotropy of Tb/Fe multilayers
Authors: Shan Z. S. , Sellmyer D. J.
Published: July 2002

Studies of the layer-thickness dependence of hysteresis loops for Tb/Fe compositionally modulated films (CMF) are reported. The characteristics of magnetic properties, such as magnetization and uniaxial anisotropy, which depend on the FE layer thickness, can be interpreted in terms of the compositional dependence of magnetic properties of the constituent subnetworks and the spatial distribution of the constituent atoms. The magnetic properties of Tb/Fe CMF are analyzed with a micromagnetic model, and the behavior of the anisotropy and constituent magnetization near the compensation point is discussed.
Localized stimulation of the human brain and spinal cord by a pair of opposing pulsed magnetic fields
Authors: Ueno S. , Matsuda T. , Hiwaki O.
Published: July 2002

A method of localized stimulation of the human brain and spinal cord is proposed. The basic idea is to concentrate induced eddy currents locally in the vicinity of a target by a pair of opposing pulsed magnetic fields. A pair of coils are positioned outside the head in the opposite directions around a target. The eddy currents induced at the target are expected to flow together, which results in an increased current flow at the target. A figure-eight coil is designed, and the magnetic brain stimulation is carried out using ourselves as volunteers. The results show that the selective stimulation of the brain is realized with a 5-mm resolution. The functional mapping of the human motor cortex related to the hand, arm, and foot areas is obtained. It is also obtained that an optimum direction of stimulating currents for neural excitation exists in each functional area in the cortex. Magnetic stimulation of the spinal cord is carried out by the same method as used in the brain stimulation. Rabbits are used in the experiments. A figure-eight coil is positioned on the surface of the spine. Shifting the stimulating points on the spine, electromyographic (EMG) signals are recorded from limb muscles. The EMG signals are clearly responding to the stimulation at a segment which innervates limb muscles, whereas no EMG signals are obtained by stimulation of segments higher than the critical segment. It is also obtained that the amplitude of the EMG signals varies with the direction of stimulating currents.
Probe determination of the electron energy distribution in a Hg-Ar low-pressure positive column
Authors: Wani Koichi
Published: July 2002

The electron energy distribution function in a mercury-argon low-pressure positive column was determined from the second derivative of voltage-current characteristics of a single probe. The probe signals were analyzed with a digital signal processing technique. The high-energy tail of the distribution functions ( f∼10−5) was obtained at mercury coldest spot temperature of 20, 42, and 60 °C (mercury density ratio of 4.8×10−4, 2.8×10−3, and 1.0×10−2 ), and discharge current of 0.2, 0.4, and 0.6 A for a 24-mm-diam tube. The electron density and electric field strength were measured at the same time, and used as input to a Boltzmann equation analysis code. General agreement was found between the experimental and theoretical results for the distribution function.
Fourier transform infrared study of ion irradiated nitrocellulose
Authors: Merhari L. , Moliton J. P. , Belorgeot C.
Published: July 2002

The self-developing mechanism of nitrocellulose is studied by means of low-temperature infrared spectroscopy. It is found that 150-keV A+ beams with fluences ranging from 1013 ions cm−2 to 6×1013 ions cm−2 induce atomic bond breaks leading to absorption bands at 2344, 2138, 1868, 1750, and 1590 cm−1, corresponding, respectively, to CO2, CNH, CO, CHO, and NO vibrations. At low temperature and under vacuum, intensity measurements of the CO2 absorption band versus ion fluences are performed. Carbylamine formation, cyclic anhydride of five carbon atom formation, and denitration are observed. A theoretical model, based upon those three mechanisms is presented which partially explains the self-development of the ion irradiated nitrocellulose.
Upper bound to a single-domain behavior of a ferromagnetic cylinder
Authors: Aharoni Amikam
Published: July 2002

For a right circular, finite ferromagnetic cylinder with a radius R, a parameter, Rc1, is calculated so that for R>Rc1 there is always a nonuniform magnetization state whose free energy is smaller than that of the uniform magnetization state. Numerical computations for the cases of permalloy and of magnetite give Rc1, which is quite close to the recently calculated Rc0 in a cylinder of these materials. The latter is defined, as in the fundamental theorem of Brown on spherical particles, so that the lowest free-energy state is that of a uniform magnetization, if R<Rc0. The closeness of Rc0 and Rc1 makes them a sufficiently good estimate for the critical size at which the particle changes from uniform to nonuniform magnetization state, without going through the complicated numerical computation of the exact value.
High concentration Zn doping in InP grown by low-pressure metalorganic chemical vapor deposition
Authors: Chichibu S. , Kushibe M. , Eguchi K. , Funemizu M. , Ohba Y.
Published: July 2002

High concentration Zn doping in InP grown by low-pressure metalorganic chemical vapor deposition (MOCVD) was investigated in terms of saturated Zn and hole concentrations. A hole concentration of 4.5×1018 cm−3 was obtained using the conventional doping source (dimethylzinc). The saturated Zn and hole concentrations were almost independent of growth temperature and PH3 flow rate. However, the saturated concentrations increased with increasing growth rate. Zn in the epilayer was essentially electrically active. The Zn incorporation saturation and the accompanying rapid diffusion were thought to have originated from the increase of Zn in interstitial sites. A possibility of achieving a heavily Zn-doped layer was demonstrated in terms of the nonequilibrium nature of the MOCVD growth.
Thermal oxidation of reactively sputtered amorphous W80N20 films
Authors: Vu Q. T. , Pokela P. J. , Garden C. L. , Kolawa E. , Raud S. , Nicolet M-A.
Published: July 2002

The oxidation behavior of reactively sputtered amorphous tungsten nitride of composition W80N20 was investigated in dry and wet oxidizing ambient in the temperature range of 450 °C–575 °C. A single WO3 oxide phase is observed. The growth of the oxide follows a parabolic time dependence which is attributed to a process controlled by the diffusivity of the oxidant in the oxide. The oxidation process is thermally activated with an activation energy of 2.5±0.05 eV for dry ambient and 2.35±0.05 eV for wet ambient. The pre-exponential factor of the reaction constant for dry ambient is 1.1×1021 Å2/min; that for wet ambient is only about 10 times less and is equal to 1.3×1020 Å2/min.
Analytical calculation of the capacitance associated with a single quantum well located in a junction
Authors: Letartre X. , Stiévenard D. , Barbier E.
Published: July 2002

We perform an analytical calculation of the capacitance of a single quantum well located in a junction versus the applied bias (the so-called capacitance-voltage characteristic), using mainly the Poisson equation and the Fermi statistics of the electrons in the well. This model reproduces the experimental behavior of such a structure and is validated by a comparison with a complete numerical simulation. Finally, we use our model to study a GaAs-GaInAs-GaAs single quantum well.
Stability of the ferroelectric phase in polycrystalline KNO3 investigated by photoacoustic and calorimetric techniques
Authors: Isaac Johney , Philip J.
Published: July 2002

The successive phase transitions in a polycrystalline KNO3 sample have been studied using photacoustic and calorimetric techniques. The measured temperature dependence of the photoacoustic amplitude carries signatures of the transitions undergone by the sample. The results indicate that the intermediate ferroelectric phase in KNO3 is only a metastable one. This raises doubts regarding its applicability in fabricating ferroelectric memory devices.
Quantum balance equations for electronic transport in AlxGa1−xAs/GaAs heterojunctions
Authors: Sala C. , Magnus W. , De Meyer K.
Published: July 2002

We have derived a set of quantum balance equations suitable for the analysis of steady-state electronic transport in AlGaAs/GaAs heterojunctions. Initially, approximate semianalytical expressions for the subband wavefunctions, energy levels, and populations of the two-dimensional electron gas (2DEG) confined at the heterojunction interface are obtained, which are subsequently used in the calculation of the intra- and intervalley correlation functions of the 2DEG. The resulting force and energy balance equations are solved to yield drift velocities and electron temperatures of the electrons as a function of the applied electric field. Remote impurity, longitudinal optical phonon and intervalley phonon scattering are taken into account, as well as the nonparabolicity of the GaAs bandstructure.
A study of the mechanism of consolidating metal powder under explosive-implosive shock waves
Authors: Gao Juxian , Shao Binghuang , Zhang Ke
Published: July 2002

A study of the two-dimensional flow pattern of particles in consolidation process under explosive-implosive shock waves has been performed to further understand the mechanism of shock-wave consolidation of metal powder, in which bunched low-carbon steel wires were used instead of powder. Pressure in the compact ranges from 6 to 30 GPa. Some wires were electroplated with brass, some pickled. By this means, the flow pattern at particle surfaces was observed. The interparticle bonding and microstructure have been investigated systematically for the consolidated specimens by means of optical and electron microscopy, as well as by microhardness. The experimental results presented here are qualitatively consistent with Williamson’s numerical simulation result when particle arrangement is close packed, but yield more extensive information. The effect of surface condition of particle on consolidation quality was also studied in order to explore ways of increasing the strength of the compacts. Based on these experiments, a physical model for metal powder shock consolidation has been established.
Diffusion-alloyed additives in die-upset Nd-Fe-B magnets
Authors: Fuerst C. D. , Brewer E. G.
Published: July 2002

In general, the stoichiometry of melt-spun ribbons and subsequent hot-worked Nd-Fe-B magnets derives from the composition of the starting ingot. We have shown, however, that it is possible to introduce small amounts of powdered metals into the ribbons after the ingot has been melt spun. Many elements, when mixed with the ribbons as a fine powder and then hot pressed, have been observed to diffuse into nearby ribbons, and in some cases (Cd, Cu, Au, Ir, Mg, Ni, Pd, Pt, Ru, Ag, and Zn) the elements diffused fairly evenly throughout the Nd-Fe-B ribbon matrix. These eleven elements significantly enhanced the coercivity of die-upset magnets, with the highest coercivity observed with the addition of zinc (∼16 kOe).
Correlations of modulation noise with magnetic microstructure and intergranular interactions for CoCrTa and CoNi thin-film media
Authors: Khan Mahbub R. , Lee S. Y. , Duan S. L. , Pressesky J. L. , Heiman Neil , Speliotis Dennis E. , Scheinfein M. R.
Published: July 2002

This paper reports on two thin-film media alloys Co86Cr12Ta2 and Co75Ni25 which have very different noise characteristics. The magnetic microstructure of these films was observed with scanning electron microscopy with polarization analysis (SEMPA). The variance (σ 2t) of the magnetization across the transition region was calculated. The origin of anisotropy was determined by measuring the temperature coefficients of Hc and Ms. The interaction strengths between grains, δM(H), were obtained from the measurements of the reverse demagnetization remanence Md(H) and the forward magnetization remanence Mr(H). We found that the CoNi film showed a greater degree of interparticle interaction, which may explain the observed cross-bit linkages in SEMPA image, larger rms transition variation (σt), and higher modulation noise.
Simulation of current-voltage characteristics of Ti-W/nSi Schottky diodes using defects parameters extracted from deep level transient spectroscopy
Authors: Bauza D. , Pananakakis G.
Published: July 2002

The parameters of electrically active defects created during the technological fabrication process of Ti-W/nSi Schottky diodes are studied by deep level transient spectroscopy (DLTS). Using a self-consistent simulation model and trap parameters extracted from DLTS measurements, current-voltage characteristics of these diodes are simulated. It is found that a very satisfactory fitting can thus be obtained.
Analysis of recombination centers in (AlxGa1−x)0.5In0.5P quaternary alloys
Authors: Sugiura K. , Domen K. , Sugawara M. , Anayama C. , Kondo M. , Tanahashi T. , Nakajima K.
Published: July 2002

We studied nonradiative recombination centers in undoped (AlxGa1−x)0.5In0.5Pgrown by metalorganic vapor phase epitaxy using transient capacitance spectroscopy. We found three deep energy levels, including a mid-gap level. We drew an equation to get a capture cross section for minority carriers, and obtained it using isothermal capacitance transient spectroscopy measurement. The mid-gap level had an electron capture cross section of 2 × 10−10 cm2 and a hole capture cross section of 1 × 10−15 cm2. The time constant of nonradiative recombination through the mid-gap level was found to be comparable to that of radiative recombination. We concluded that the mid-gap level is an effective nonradiative recombination center that reduces photoluminescence intensity.