bluuebunny/crossref_metadata_2025 huggingface dataset:
An energy-dependent electron backscattering coefficient
Authors: Williamson W. , Antolak A. J. , Meredith R. J.
Published: July 2002

An energy-dependent electron backscattering coefficient is derived based on the continuous slowing down approximation and the Bethe stopping power. Backscattering coefficients are given for 10–50-keV electrons incident on bulk and thin-film aluminum, silver, and gold targets. The results are compared with the Everhart theory and empirical fits to experimental data. The energy-dependent theory agrees better with experimental work.
Ferromagnetic resonance in Co-Cr multilayer films
Authors: Ramakrishna B. L. , Lee C. H. , Cheng Y. , Stearns M. B.
Published: July 2002

Magnetic properties of multilayered Co/Cr films have been investigated by ferromagnetic resonance (FMR) and compared to magnetization studies carried out on a SQUID magnetometer. The interesting feature observed in most of the spectra was that along with an intense resonance corresponding to the uniform mode, several weak but well-defined peaks were observed at higher magnetic fields. The angular and temperature variations of the line positions indicates that these are due to cobalt atoms in the interface. In conjunction with static magnetization, the FMR studies of the main resonance lead us to believe that there may be long-range magnetic effects which result in additional anisotropy fields.
Magnetic properties and structure of Pd/Co and Pd/Fe multilayers
Authors: den Broeder F. J. A. , Donkersloot H. C. , Draaisma H. J. G. , de Jonge W. J. M.
Published: July 2002

Pd/Co and Pd/Fe multilayer films containing ultrathin Co and Fe layers were prepared by vapor deposition on substrates at room temperature. Their modulated structure, even for films containing 2-Å-thin Co and Fe layers, was proved by x-ray diffraction and transmission electron microscopy. Below a Co layer thickness of about 8 Å, the Pd/Co multilayers acquire an easy magnetic axis perpendicular to the film, which is mainly caused by magnetic interface anisotropy. This leads for multilayers containing Co monolayers to almost rectangular hysteresis loops, by which these films may be very suitable as a perpendicular magnetic recording medium. Pd/Fe multilayers also have a perpendicular interface anisotropy, but the shape anisotropy dominates. Per unit Co volume the Pd/Co multilayers have a higher saturation magnetization than pure Co, which is attributed to an induced ferromagnetism on Pd interfacial atoms.
Dynamics of orientation in particulate media
Authors: Perlov C. M. , Middleman S.
Published: July 2002

The orientation of a collection of particles suspended in a Newtonian fluid is described. Magnetic interparticle interactions are included with a mean field approximation. The width of the distribution of particle orientations is used as a measure of the net orientation of the suspension. In contrast to isolated particle models, it is found that no optimum orienting field exists.
Magnetic and structural properties of Co-Ni thin films prepared by oblique incidence deposition
Authors: Zeder S. L. , Silvain J.-F. , Re M. E. , Kryder M. H. , Bauer C. L.
Published: July 2002

Thin films of cobalt, nickel, and their alloys have been produced on glass substrates by thermal evaporation at oblique angles of incidence α, measured with respect to the substrate normal, ranging from 20° to 78°. Resultant films are characterized by a columnar grain structure inclined toward the source by an angle β, also measured with respect to the substrate normal, such that 2 tan β∼tan α. For α>60°, the columnar grains assume a rodlike morphology surrounded by voids, whereas for α<60°, these grains assume a platelike morphology, also inclined toward the source and separated by voids. The void size, defined by spacing between adjacent rods or plates, increases with increasing values of α. Moreover, for α>60°, the easy axis of magnetization is oriented in the vapor plane, defined by the plane parallel to both the direction of incident flux and substrate normal, whereas, for α<60°, this axis is oriented perpendicular to the vapor plane. Accordingly, the easy axis of magnetization is oriented parallel to the rodlike morphology when α>60°, and parallel to the platelike morphology (and in the plane of the film), when α<60°. Finally, magnetic coercivity increases rapidly at the critical angle of 60°, as transition from platelike to rodlike morphology occurs.
Magnetic properties of amorphous and crystallized RT4B alloys
Authors: Aly S. H. , Hadjipanayis G. C.
Published: July 2002

The magnetic properties of RT4B amorphous and crystallized ribbons with T≡(Fe,Co) are reported. Ordering temperatures in the amorphous alloys range from 53 to 231 °C while those of crystallized alloys are between 250 and 411 °C. Room-temperature coercivities were measured to be in the range of 0.9–11.0 kOe. From all RFe4B alloys studied, with R≡Pr, Nd, Sm, Gd, Tb, Dy, and Er, only ErFe4B crystallizes in the hexagonal CeCo4B structure leading to a room-temperature coercivity of 6 kOe. In the same compound an easy axis to easy plane transition may exist in the temperature range of 4.2–300 K.
Rotation of the anisotropy direction in an X
Y spin glass
Authors: Inderhees S. E. , Salamon M. B. , Ketelsen L. J. P.
Published: July 2002

We have investigated the behavior of the frozen-in anisotropy of an XY spin glass under the influence of a reorienting field. From experiments performed using a cylindrically shaped single crystal of YTb3 at. %, we find that the anisotropy can be rotated as a whole away from its original direction by rotating the crystal in an external field HRO. The anisotropy direction lags behind HRO, suggesting behavior analogous to sliding friction.
Temperature variation of domain structure and magnetization in NdFeB magnets
Authors: Luo Yang , Zhang Nin
Published: July 2002

The domain structure of cast NdFeB magnets has been observed using the Kerr effect, both at room temperature and at temperatures up to the Curie point. The domain structure is typical of strongly uniaxial materials, and no substantial changes in domain size or domain structure are found up to the Curie point. The value of the Curie point has been determined from differential scanning calorimeter measurements over a range of heating and cooling rates, and also from a direct measurement of magnetization at 10 kOe versus temperature. The former method gives an extrapolated value of TC =307.5 °C, and the latter method gives TC =321 °C. The difference is attributed to the fact that one measurement is made at zero field and the other at 10 kOe.
Preparation of amorphous Tb-Fe-Co thin films by plasma-free high-rate sputtering
Authors: Naoe M. , Kitamura N. , Hirata T.
Published: July 2002

The facing targets type of sputtering (FTS) apparatus [Naoe, Yamanaka, and Hoshi, IEEE Trans. Magn. MAG-16, 646 (1986)] can prepare amorphous Tb-Fe-Co thin films on plasma-free substrates at temperatures lower than 100 °C at a deposition rate as high as 5000 Å/min. The saturation Kerr rotation at 830 nm, reflectance and coercive force of the specimen films 1000 Å thick were 0.3, 48%, and 6 kOe, respectively, comparable to those obtained in films deposited at a one-hundredth lower rate by conventional rf diode and dc magnetron sputtering. Films with good uniformity of thickness, composition, and characteristics were deposited over the whole area of 12-in. disk substrates made of PMMA or glass, without deteriorating the pregrooves. At this stage, a C/N of about 46 dB has been attained.
Temperature dependence of electron mobility for inversion-mode InP metal-insulator-semiconductor field-effect transistors
Authors: Hirota Y. , Okamura M. , Hisaki T. , Yamaguchi E.
Published: July 2002

Surface carrier transport of electrons in inversion-mode InP metal-insulator-semiconductor field-effect transistors (MISFETs) has been investigated. This was carried out as a function of induced electron density with temperature ranging between 7 and 296 K. InP MISFETs were fabricated by using a photochemically deposited phosphorous nitride (PN) film as a gate insulator. Results of these studies indicate that electron mobility depends on temperature as T−(1–1.5) and on induced electron density as N−1/3s above Ns =5×1011/cm2 from 296 to 100 K. Below 60 K and in the low Ns region, electron mobility has a different temperature dependence and dramatically decreases as temperature decreases. These temperature and induced electron density dependences of electron mobility are probably caused by acoustic surface phonon scattering in the high-temperature region and by screened Coulomb scattering and Anderson localization of electrons in the low-temperature region. In the temperature range of 70–90 K, the maximum value for effective mobility was about 9000 cm2/V s and that for field-effect mobility was about 15 000 cm2/V s.
Elimination of dislocations in bulk GaAs crystals grown by liquid-phase electroepitaxy
Authors: Boucher C. F. , Ueda O. , Bryskiewicz T. , Lagowski J. , Gatos H. C.
Published: July 2002

The dislocation density in bulk GaAs crystals (up to 4 mm thick) grown by liquid-phase electroepitaxy (LPEE) is found to be significantly reduced (by as much as a factor of 20) relative to that in the substrate. This reduction takes place when the thickness of the growing crystal exceeds a critical value of 50–70 μm. It is accompanied by a formation of misfit dislocation arrays identified by transmission electron microscopy in the interface region between the substrate and grown crystals. These findings suggest that the reduction of the dislocation density is caused by a small but finite lattice mismatch between the growing epitaxial-quality crystal and the relatively inferior quality melt-grown substrate. Dislocations which propagate from the substrate into the LPEE crystal are forced by the misfit stress to move laterally forming misfit dislocations.
Magneto-optical properties of Bi-substituted epitaxial rare-earth iron garnet thick films
Authors: Machida K. , Asahara Y. , Ishikawa H. , Nakajima K. , Fujii Y.
Published: July 2002

Films of (Yb,Tb,Bi)3Fe5O12 show excellent characteristics of the Faraday rotator at the wavelength of 1.3 μm; the rotation is −1800 deg/cm,  insertion loss 0.3 dB,  isolation 38 dB,  and the temperature dependence of the Faraday rotation is 0.060 deg/K at room temperature. The films are grown epitaxially on the (Gd,Ca)3(Ga,Mg,Zr)5O12 substrates, from the melt in the flux PbO/B2O3/Bi2O3. The melt contains rare-earth ions (R=Y,Gd,Er,Dy,Tm,Yb,Lu) as c-site components of rare-earth iron garnets, and Fe and Ga+Al as a- and d-site components. The obtained film thickness is in the range 300–400 μm without appreciable defects on the substrate, with a 2-in. diameter. This technology will lead to the efficient production of the optical isolator used in optical systems.
Conduction in illuminated GaAs/AlxGa1−xAs heterostructures. I. Experiment
Authors: Hurd C. M. , McAlister S. P. , McKinnon W. R. , Falt C. E. , Day D. J. , Miner C. J. , SpringThorpe A. J.
Published: July 2002

We have measured the Hall carrier concentration nH(T) and the Hall mobility μH(T) for some n-type, Si-doped GaAs/AlxGa1−xAs heterostructures (x=0.2 and 0.3) in the range 4.2–320 K for different levels of continuous illumination by a red light emitting diode. We interpret these data with the model of the interface carrier density described in the following paper [W. R. McKinnon and C. M. Hurd, J. Appl. Phys. 61, 2250 (1987)], which explains qualitatively the gross features in the temperature dependencies. The interpretation shows the effects of both deep and shallow donors, and of the magnetic field dependence arising from parallel conduction.
Particle size distribution from small-angle scattering data: A histogram technique
Authors: Stephens R. B.
Published: July 2002

A method of reparametrizing small-angle scattered intensity spectra I(q) in terms of the q=0 contributions from populations of spheres of discrete radii I0(r) is described. The minimal assumptions are made that the scattering from a particulate system can be parameterized as a distribution of sizes of solid spheres, and that the particle positions are uncorrelated. The calculated size distribution can be used to define either the multimodal size distributions of spherical particles or the shape of monodisperse, nonspherical particles. In any case, its usefulness is limited at high concentrations where the particle–particle correlation function has significant structure. The applicability of this technique is demonstrated with calculated spectra and experimental results from water-in-oil microemulsions.
Optical properties of very fine Al particles: Quantum size effect
Authors: Truong Vo-van , Courteau Pierre , Singh Jai
Published: July 2002

The strong attenuation of the parallel-band absorption observed in very fine Al particles at 0.85 μm is interpreted in terms of a quantum mechanical size effect. Applying a quantum theoretical model, the dielectric constant for fine particles is calculated, and the effective dielectric constants for aggregated films are obtained classically from the Maxwell–Garnett theory. Calculated results of transmittance for Al blacks in the spectral range from 0.35 to 1.0 μm are found in very good agreement with experimental results.
Electric field and electrode potential drops of arcs and glow discharges in air
Authors: Novak J. P.
Published: July 2002

A simple experimental arrangement consisting of two arcs burning in series has been devised for measurement of the voltage gradient in the discharge column. The method is based on reciprocal variation of the length of the discharges so that the total length during the measurement is constant. Experiments have been performed in the current range between 20 mA and 4 A in dry air at pressures between 20 and 150 kPa. In the arc mode the current dependence of the field can be approximated by the power function E∝Iα, where the exponent α for pressures between 60 and 150 kPa is −0.54 and slightly higher at lower pressures. The pressure dependence (at constant current) can be expressed in similar form E∝pm with the exponent m equal to 0.15 and 0.24 for currents of 1 and 4 A, respectively, and for pressures above 40 kPa. Average values of the zero-length voltage were obtained in the arc and glow discharge modes, namely, 14.5 V in the case of the arc and 367, 346, 331, and 331 V for the glow discharge at pressures of 20, 60 100, and 150 kPa, respectively.
Thermal emission and capture rates of holes at the gold donor level in silicon
Authors: Lu Luke Su , Nishida Toshikazu , Sah Chih-Tang
Published: July 2002

Thermal emission rate and capture cross section of holes at the gold donor level are measured in silicon n+/p junctions with boron acceptor concentrations of 1.5×1012 cm−3 to 2.8×1015 cm−3, showing no boron concentration dependencies. The emission rate is independent of electric field in the range of 102 to 2×104 V/cm. However, the emission rate varies with the voltage applied to the insulated-gate guard ring, requiring re-evaluation of previously published data. The thermal capture cross section agrees with most of the published work. The magnitude of the capture cross section and its temperature independence support a neutral potential model for hole capture at the gold donor level.
Oxygen behavior during titanium silicide formation by rapid thermal annealing
Authors: Pantel R. , Levy D. , Nicolas D. , Ponpon J. P.
Published: July 2002

Sputtered titanium thin films on 〈100〉 Si wafers were exposed to rapid thermal annealing (RTA) in argon at temperatures of 600–900 °C. Auger depth profiling shows that when exposed to air the Ti films takes in 3×1016 oxygen atoms cm−2 independently of Ti thickness. During RTA the oxygen tends to redistribute uniformly and a snowplow effect, due to the O solubility difference between Ti and TiSi2, confines it to the unreacted titanium layer. Early on, silicon is observed at the Ti surface and a second silicide layer starts growing. All of the oxygen is finally fixed in the C54 TiSi2 where the two silicide fronts meet (at around 50 nm from the surface). This reproducible effect is associated with RTA and is not observed in classical furnace annealing.
New perturbation method for planar phase-change processes with time-dependent boundary conditions
Authors: Charach Ch. , Zarmi Y. , Zemel A.
Published: July 2002

A new perturbation method is developed for one-dimensional and conduction-controlled melting in a planar slab. The approach is suitable for boundary conditions with small amplitude but almost arbitrary time dependence. The results are uniformly valid in time. The method is applied to the case of time-dependent heat flux boundary conditions and illustrated by the example of a steplike heat pulse.
Electron spin resonance investigation of ion beam modified amorphous hydrogenated (diamondlike) carbon
Authors: Adel M. E. , Kalish R. , Prawer S.
Published: July 2002

Electron spin resonance (ESR) measurements on diamondlike carbon films show that the as-grown material possesses a very high (2.5×1020 cm−3) concentration of dangling bonds. Upon irradiation with 50-keV C+ carbon ions, the number of ESR active centers increases by a factor of 3.5 and the linewidth narrows, but no shift in the g value is observed, and the resonant peak remains Lorentzian. These effects are concomitant with the previously observed dramatic decrease in the electrical resistivity (4–5 orders of magnitude). The ESR results verify that no graphitelike islands have formed as a result of the irradiation. The likely conduction mechanism is via hopping in band tail states, the number of which increases as a result of the ion impact.
Effect of collisions on forbidden lines
Authors: Coutts J. , Peck S. K. , Stoner R. , Cooper J.
Published: July 2002

We present results on experiments probing the effect of collisions on forbidden lines. Two contrasting lines are investigated—a spin-forbidden dipolar transition and a spin-allowed electric quadrupole transition. We explain our results in terms of straightforward physical models.
A comparison between Sb and As implantation for the formation of highly conducting shallow silicon layers
Authors: Young N. D.
Published: July 2002

Highly conducting silicon layers of less than 500 Å in thickness have been formed following the implantation of 12-keV antimony or 10-keV arsenic and subsequent annealing at 700 °C for 15 min. Minimum resistivities of 2.2×10−4 Ω cm for antimony and 6.5×10−4 Ω cm for arsenic at a dose of 1×1015 cm−2 are obtained, with corresponding peak electrical activities of ∼4.8×1020 cm−3 and ∼1.6×1020 cm−3, respectively. Both correspond to metastable states well above the equilibrium solid solubilities. Whereas the arsenic activity remains almost unchanged for anneals of up to ∼300 min, the higher antimony activity decreases, but remains above that of the arsenic.
Liquid-phase epitaxy of heavily Mg-doped GaAs: Formation of a new near-band-edge emission exclusively pertinent to acceptor impurities
Authors: Mori Masahiko , Makita Yunosuke , Okada Yoshio , Ohnishi Nobukazu , Mitsuhashi Yoshinobu , Tanaka Hideki , Matsumori Tokue
Published: July 2002

Liquid-phase epitaxy (LPE) of Mg-doped GaAs was carried out. An extremely heavy doping was accomplished with a maximum net hole concentration of 1.31×1019 cm−3. A systematic investigation of photoluminescence spectra was performed as a function of hole concentration, which revealed that a newly discovered emission characterizing acceptor impurities can be obviously recognized also in LPE-grown samples in spite of the fact that the selective optical compensation effect among doped acceptors and residual donors presumably coming from Si of the LPE quartz tube is supposed to be comparatively strong. The red shift of this emission energy with increasing hole concentration and its locking at high hole concentration were discussed theoretically by introducing a preliminary model, i.e., a pair between excited-state acceptors.
Thermally stable ohmic contacts to n-type GaAs. I. MoGeW contact metal
Authors: Murakami Masanori , Price W. H. , Shih Yih-Cheng , Childs K. D. , Furman B. K. , Tiwari S.
Published: July 2002

Thermally stable, low-resistance ohmic contacts on n-type GaAs are required to fabricate high-speed GaAs integrated circuits. MoGeW contacts prepared by annealing at high temperature around 800 °C in an InAs overpressure are attractive, because the contact is expected to be thermally stable during subsequent annealing at 400 °C, which is required by several process steps following ohmic contact formation. In the present experiment, the contact resistance measurements and microstructural analysis of MoGeW contacts were carried out to establish a fabrication process which forms ohmic contacts with low contact resistance. The contact metals were prepared by sequentially

depositing Ge, Mo, Ge, and W, with various Mo/Ge layer thickness ratios, onto (100)-oriented GaAs wafers. The conducting channels were formed by doping GaAs with about 1×1018 cm−3 Si. Contact resistances were determined by the transmission line method, and microstructural analysis was carried out by x-ray diffraction, Auger electron spectroscopy, secondary ion mass spectroscopy (SIMS), and transmission electron microscopy. Contact resistance (Rc) was found to be strongly influenced by the Mo/Ge layer thickness ratio and annealing temperature. Rc values lower than 0.5 Ω mm were obtained for samples with a Mo/Ge thickness ratio in the range 0.6–1.3 and annealed at around 800 °C. The lowest mean Rc value obtained in the present experiment was 0.3 Ω mm. The major compound formed in this contact was identified to be Mo5As4, which has a high melting point. No changes in the microstructure and the Rc values were observed after annealing the contacts at 400 °C for more than 100 h. Finally, an attempt to understand the carrier transport mechanism was carried out by correlating the electrical behavior with the film microstructure. For this purpose the samples were annealed in an InAs overpressure with or without a Si3N4 cap, by flash annealing, and in an arsine atmosphere. The ohmic behavior was observed only in the samples annealed in an InAs overpressure. The SIMS analysis indicated that a small amount of In, less than 1 at. %, was segregated at the metal/GaAs interfaces in this sample. The In could form compounds with GaAs and reduce the barrier height, resulting in reduction of the contact resistances.
Diffusion charging of ultrafine aerosol particles by positive helium, argon, and nitrogen ions
Authors: Adachi Motoaki , Okuyama Kikuo , Kousaka Yasuo , Kozuru Hiroyuki , Pui David Y. H.
Published: July 2002

The unipolar charging phenomena of ultrafine aerosol particles less than 0.1 μm in diameter by positive gas molecule ions produced by α-ray irradiation are experimentally evaluated in helium, argon, nitrogen, and helium-argon mixture gases. The dependencies of the diffusion charging process of particles on ion species of positive helium, argon, and nitrogen ions are quantitatively well explained by a numerical solution of the population balance equations with the use of Fuchs’ combination probability between particles and ions [N. A. Fuchs, Geofis. Pura Appl. 56, 185 (1963)]. The quantity of charge on particles decreases with an increase of ion mass in the order of the helium, nitrogen, and argon ions. The particle charging in a helium-argon mixture is determined by the ion concentration of both species.
Characterization of graded interface InxGa1−xAs/In0.52Al0.48As (0.53<x<0.70) structures grown by molecular-beam epitaxy
Authors: Peng C. K. , Sinha S. , Morkoç H.
Published: July 2002

Modulation doped InxGa1−xAs/In0.52Al0.48As/InP structures were grown by molecular-beam epitaxy with x values between 53% and 70%. For pseudomorphic cases, graded instead of abrupt interfaces were used. Hall mobility and persistent photoconductivity measurements as a function of temperature were used to characterize samples with different structural parameters. Consistent trends in the variation of mobilities and two-dimensional carrier concentration (n2D ) under light and dark conditions have been observed and discussed in terms of applicable scattering mechanisms. The Hall mobilities are comparable to the best results obtained to date but with significantly higher n2D concentration.
Theoretical study of a plasma column sustained by a guided electrostatic wave in the presence of a constant axial magnetic field
Authors: Zhelyazkov I. , Benova E. , Atanassov V.
Published: July 2002

We examine the axial structure of a surface and pseudosurface-wave-produced overdense plasma column immersed in a constant axial magnetic field. The theory allows us to derive dimensionless axial profiles of the normalized: plasma density, wave number, wave power, and wave electric field amplitude. Both cases of (i) weak magnetic field (ωc/ω<1, surface-wave excitation) and (ii) strong magnetic field (ωc/ω>1, pseudosurface-wave excitation) are considered in free fall, diffusion, and bulk recombination discharge regimes. In a weak magnetic field, only one mode (pure surface wave) can be excited, whereas in a strong magnetic field, many pseudosurface waves may occur.
Diffractive imaging in three-wave interactions
Authors: Gavrielides A. , Peterson P. , Cardimona D.
Published: July 2002

The coupled signal and idler diffractive differential equations are solved for the parametric processes of upconversion and down conversion. The complex transfer functions are found in terms of spatial frequency, propagation vectors, gain, and media length. Also, we derive the signal to the idler imaging equation by employing the transfer functions for both upconversion and down conversion.
Relation between growth conditions and deep levels in GaAs grown by molecular-beam epitaxy
Authors: Xu H.-D. , Andersson T. G. , Westin J. M.
Published: July 2002

Deep level transient spectroscopy (DLTS) has been studied in GaAs grown by molecular-beam epitaxy. Samples were grown under As- or Ga-stabilized conditions as well as in the transition region between the corresponding surface reconstructions. The layers exhibit different sets of DLTS peaks depending on the surface structure during growth. A minimum concentration, less than 1012 cm−3, was measured in samples grown in the transition region. The origin of the deep levels is related to the surface stoichiometry since the deep levels cannot be correlated either to the concentration of shallow levels or to chemical impurities detected by high-sensitivity secondary ion mass spectroscopy.
Gas evolution studies for structural characterization of hexamethyldisilazane-based a-Si:C:N:H films
Authors: Gerstenberg K. W. , Beyer W.
Published: July 2002

Gas evolution and infrared-absorption studies on a-Si:C:N:H films deposited from hexamethyldisilazane vapor and nitrogen gas by a plasma process show that hydrogen at concentrations of more than 30 at. % is incorporated in the films. The hydrogen evolution spectra are similar to the spectra of a-Si:C:H films deposited from SiH4-CH4 mixtures, suggesting the presence of a continuous void network. At low plasma power a considerable amount of methyl groups is incorporated as detected by infrared absorption, leading to a hydrocarbon effusion in the 500–700 °C region. At high power the effusion of N2 at 600–800 °C indicates the incorporation of molecular nitrogen.
Threshold voltage and field effects in semiconductor double-injection devices
Authors: Ashley K. L. , Stawski R.
Published: July 2002

An analytical formulation is presented which addresses the current-voltage characteristic of p+-π-n+ double-injection devices from square law to threshold. The model includes the assumption of charge neutrality, which limits the applicability to cases of relatively high magnitudes of thermal equilibrium carrier densities, and the assumption that the current is entirely field driven. The approach is based on a modification of the square law which accounts for the fact that the effective length becomes progressively shorter for higher currents as a low-field region moves in from the anode. The electric field dependence of carrier mobilities and capture cross sections is included in the development. Solutions are presented for the current-voltage characteristics and the threshold voltage, which include an indication for when the approximations which were used are valid and which demonstrate the conditions under which the field dependence is a factor in the results.
Structural measurements on evaporated a-Si/SiOx superlattices
Authors: Trodahl H. J. , Forbes M. , Nelson D. G. A. , Bittar A.
Published: July 2002

The structure of evaporated a-Si/SiOx superlattices has been investigated by transmission electron microscopy, Raman scattering, and optical absorption spectroscopy. The layers are smooth and regular, but all three measurements show effects of bond distortions or defects within 1–2 nm of the Si/SiOx interfaces.
Nonlinear theory of power dissipation due to the motion of heavy interstitials in a fluctuating inhomogeneous field with a strong bias: Special reference to the Snoek–Köster relaxation
Authors: Oğurtani Tarik Ö. , Seeger Alfred K.
Published: July 2002

Atomic movements of heavy interstitials (octahedral sites) in an arbitrary time-dependent and inhomogeneous field with a strong static bias have been described by a system of nonlinear autonomous first-order differential equations for a body-centered-cubic lattice. The linearized form of these equations in the vicinity of the thermodynamic equilibrium state (equilibrium with respect to the strong and inhomogeneous static bias field) has been solved exactly, using the discrete Fourier k-space transform supplemented by a Laplace transform with respect to time. The power dissipation associated with the hopping motion of interstitial species in the presence of either a simple harmonic vibration or of propagating acoustic waves in the media is also determined. The implications of the nonlinear theory for the effective activation enthalpy of the Snoek–Köster relaxation are also worked out for highly localized or delocalized static interaction fields, respectively.
Effects of dislocations on threshold voltage of GaAs field-effect transistors
Authors: Suchet P. , Duseaux M. , Maluenda J. , Martin G. M.
Published: July 2002

Measurements of threshold voltage of GaAs FET’s (field-effect transistors) show a larger heterogeneity when dislocated rather than free dislocated substrates are used. Therefore, the aim of this study is to find an accurate model for the influence of dislocations on such devices. The model proposed takes into account a cumulative effect of each dislocation located on or around the FET on the value of VT. This effect is merely a function of the distance between the dislocation and the FET. With the use of a computer, the best influence curve has been determined for one wafer. Nevertheless, due to differences in thermal histories, this curve can vary from wafer to wafer. Therefore, it is suggested that, in addition to the average standard deviation of the threshold voltage, it could be accurate to give the influence curve to characterize the substrates.
Atomic chlorine concentration measurements in a plasma etching reactor. II. A simple predictive model
Authors: Richards Albert D. , Sawin Herbert H.
Published: July 2002

Atomic chlorine concentrations in Cl2 plasmas have been measured using the technique of infrared absorption spectroscopy. A wide range of plasma conditions were examined, including power input densities of 0.05–0.5 W/cm−3, pressures of 200–800 mTorr, and excitation frequencies of 0.1–13.5 MHz. A simple kinetic model accurately predicts atomic chlorine concentrations as a function of discharge parameters. The primary source of atomic chlorine was assumed to be an electron-impact dissociation of Cl2, and the reaction rate coefficient was assumed to be independent of plasma conditions. The electron density was estimated from a plasma impedance analysis. The depletion of atomic chlorine was successfully modeled assuming second-order recombination on the electrode surfaces; depletion by gas-gas recombination and by flow from the reactor were insignificant over the range of plasma conditions studied. Because the diffusion of atomic chlorine is fast relative to the formation and depletion rates, the atomic chlorine concentration is fairly independent of interelectrode position. Atomic chlorine concentrations were accurately represented by the equation [Cl]=3.5×108 [e−]0.5P0.5, where [Cl] and [e−] are in cm−3 and P is in mTorr.
Preparation of silicon nitride films at room temperature using double-tubed coaxial line-type microwave plasma chemical vapor deposition system
Authors: Kato Isamu , Noguchi Kazuto , Numada Kouji
Published: July 2002

Silicon nitride films were prepared at room temperature using the double-tubed coaxial line-type microwave plasma chemical vapor deposition system. The dependence of film composition and properties on the flow rate of SiH4 gas and on the partial pressure of N2 gas in the deposition chamber has been investigated. A new simple method was suggested and employed to determine the film composition from the refractive index and nitrogen concentration. The flow rate of SiH4 gas was varied between 1 and 10 ml/min. The flow rate of N2 gas was at 50 ml/min and the partial pressures of N2 gas in the deposition chamber were set at 0.015 and 0.0036 Torr by changing the size of the substrate table. With an increasing flow rate of SiH4 gas, the following effects upon the films were obtained: proportional increases in the deposition rate, shifts to lower energy of the absorption edge, decreases in the film density, and decreases in the concentration of N and the N–H bond. Increases in the refractive index, the Si/N ratio, and the concentrations of Si and the Si–H bond were also observed. In the case of low partial pressure of N2 gas, the deposition rate decreases, the absorption edge shifts to higher energy, the N concentration increases, and the films become denser. The optical properties of the film vary slowly with the flow rate of SiH4, and these properties can be determined more precisely by varying the flow rate of SiH4.
Analysis of two-step thermal oxidation of silicon
Authors: Ghibaudo Gérard
Published: July 2002

It is shown that two-step oxidation experiments give evidence of the stress dependence of the oxidation diffusivity during dry thermal oxidation of silicon. It is demonstrated that the stress state model of oxidation is also adequate for the analysis of two-step oxidations. In particular, it gives a reasonably good description of the second oxidation kinetics and of the behavior of the activation energy of the oxygen diffusivity with the temperature of the second oxidation and the relaxation state.
Study of defects in GaAs by differential thermal analysis
Authors: Lim H.-J. , von Bardeleben H. J. , Bourgoin J. C.
Published: July 2002

Differential thermal analysis is applied to the measurement of defect total energies in GaAs. First, the technique is used to determine the energy liberated in the recombination of an As vacancy-interstitial pair; the result, in agreement with the theoretical estimate of the energy stored in such defect, allows the demonstration of the validity of the technique as well as its limitations. Then, the technique is used to evaluate the introduction rate of such defects by electron irradiation in a semi-insulating material in which electrical techniques cannot be applied. Finally, a characterization of native defects is attempted; it shows that recombination of native vacancies, with interstitials liberated when the movement of α dislocations takes place, occurs around 450 °C.
Oxygen diffusion and phase transformation in Y1Ba2Cu3Ox
Authors: Krebs H. U. , Wördenweber R.
Published: July 2002

Detailed in situ x-ray diffraction experiments, differential scanning calorimetry, and thermogravimetrical analyses are performed during annealing of superconducting Y1Ba2Cu3Ox samples in order to study the influence of the oxygen diffusion on the structure and structural changes of these alloys. The superconducting properties before and after annealing are checked via resistivity measurements. Annealing in vacuum leads to an irreversible and diffusion controlled phase transformation from the superconducting orthorhombic to the semiconducting tetragonal perovskite structure. For small heating rates, the transition starts at about 550 °C. With increasing heating rates the diffusion mechanism causes a delayed onset and a broadening of the temperature regime of the transition. The interdiffusion constant D(700 °C) for oxygen in Y1Ba2Cu3Ox is about 10−12 cm2/s. Annealing at 550 °C in oxygen atmosphere regains the orthorhombic superconducting phase with its properties.
Interfacial nucleation of compounds for thin-film Co-Hg1−xCdxTe contacts
Authors: Ehsani H. , Bené R. W.
Published: July 2002

We have determined the phases formed at the interfacial contact between deposited Co thin films prepared with both e-beam evaporation and sputtering of Co onto CdTe (111) and Hg0.8Cd0.2Te substrates using transmission electron microscopy and diffraction. Sputter profiling with Auger electron spectroscopy has been used to determine the depth profiles of Co, Cd, Te, and Hg at the interface and throughout the Co overlayer on Hg0.8Cd0.2Te and CdTe. For the Co-Hg0.8Cd0.2Te system, the γ phase is formed upon sputter deposition of Co films of 80 Å or thicker at room temperature. This Co-Te phase is also seen for thinner films upon annealing (e.g., 100 °C for a 40-Å Co film) after sputter deposition. However, after the deposition of 80-Å Co by e-beam evaporation onto an Hg0.8Cd0.2Te substrate, the γ phase forms only after annealing at 150 °C in vacuum. Texturing of the γ phase was observed in the transmission electron diffraction patterns with the Hg0.8Cd0.2Te substrates, indicating at least a partial ordering of this phase with respect to the substrate. On the CdTe substrates, Te was observed after Co deposition in either deposition system. The Te generated by either sputter deposition or e-beam evaporation with a high deposition rate (8–10 Å/s) of Co onto CdTe (111) was polycrystalline, whereas the slow deposition rate (0.3–0.5 Å/s) e-beam evaporation resulted in amorphous Te. Auger electron spectroscopy results indicated that the Te generated is distributed throughout the Co film. The Co-Te γ phase was formed upon annealing at 300 °C after sputter deposition and at 350 °C after e-beam evaporation, but the crystallites did not have the relationship to the substrate (texturing) which was displayed by those on the Hg0.8Cd0.2Te substrates. Annealing of the Co overlayer on Hg0.8Cd0.2Te causes the growth of the crystals and an increase in ordering of the γ phase.
Bulk thermal conductivity of composites with spherical inclusions
Authors: Sangani A. S. , Yao C.
Published: July 2002

The problem of determining the bulk or effective thermal conductivity of a two-phase composite material whose unit cells contain N(N>1) spherical particles of thermal conductivity αk suspended in a medium of thermal conductivity k has been treated by extending an earlier analysis of McPhedran and Milton [Appl. Phys. A 26, 207 (1981)] who considered the case N=1. The technique is applied to computer-generated two-phase composites with N=16 whose radial distribution functions approximately satisfy the Percus–Yevick equation. The results, which are presented for a wide range of α and φ (the volume fraction of the spheres), are shown to be in good agreement with the experimental values of conductivity of fluidized beds reported by Turner [Chem. Eng. Sci. 31, 487 (1976)].
Localized epitaxial growth of IrSi3 on (111) and (001) silicon
Authors: Chu J. J. , Chen L. J. , Tu K. N.
Published: July 2002

Transmission electron microscopy has been applied to the study of interfacial reactions of iridium thin films on silicon with particular emphasis on the epitaxial growth of IrSi3 on (111) and (001)Si. The formation of precursor phases, IrSi and IrSi1.75, were found to occur mainly in the temperature ranges of 300–500 and 600–900 °C, respectively. The stable IrSi3 was found to grow epitaxially on (111) and (001)Si annealed at 1000–1100 °C. There are three dominant modes of epitaxial IrSi3 on (111)Si and one dominant mode of epitaxial IrSi3 on (001)Si. Interface structures of these different epitaxial modes were determined by diffraction contrast analysis. The quality of IrSi3 epitaxy in terms of the fraction of the silicon surface coverage, size, and the regularity of the interfacial dislocations was found to be the best in (111) samples annealed at 1000 °C. Epitaxial regions of IrSi3, as large as 40 μm in size, were observed on (111)Si. No direct correlation between lattice match and quality of epitaxy could be found. The Burgers vectors of edge-type dislocations for several modes of silicide epitaxy were found to be along the directions with larger lattice mismatches in agreement with a theory by Markov and Milchev [Surf. Sci. 136, 519 (1984)]. A superlattice structure of IrSi3 was found from diffraction pattern analysis. The superlattice structure was determined to be of hexagonal structure and has a unit cell with dimensions three times larger than that reported for IrSi3.
Aging and field-effect studies of Cu island films at near liquid-nitrogen temperatures
Authors: Pattabi Manjunatha , Murali Sastry M. S. , Sivaramakrishnan V.
Published: July 2002

We report the results of the investigation carried out on the aging and field effect of discontinuous copper films deposited on glass substrates held at around 125 K. Using the scheme adopted in our earlier investigations, it was found that even at this temperature there is considerable increase in resistance. However, the agglomeration rate is much less than for films deposited at room temperature. The I-V characteristics of the films revealed an irreversible change in resistance following removal of the field. On stabilization, heating of the films revealed a decrease in resistance with temperature followed by an irreversible resistance increase beyond a transition temperature which was less than room temperature.
The nonexistence of α′ high-temperature phase of HgI2
Authors: Burger A. , Morgan S. , Jiang H. , Silberman E. , Schieber M. , van den Berg L. , Keller L. , Wagner C. N. J.
Published: July 2002

Differential scanning calorimetry measurements of mercuric iodide (HgI2 ) do not suggest the existence of the α′-HgI2 phase, as previously reported, when the necessary precautions are taken to avoid any chemical reaction with the sample holder. This conclusion is supported by variable temperature Raman spectroscopic measurements performed in the vicinity of the melting point, where the α′ was supposed to exist.
Compensating impurities as the limiting factor in atmospheric pressure chemical vapor deposition of a-Si:H from Mg2Si generated higher silanes
Authors: McCurdy Richard J. , Gordon Roy G.
Published: July 2002

The limiting factor for the lack of reproducibility in previous studies of atmospheric pressure chemical vapor deposition of a-Si:H from Mg2Si generated higher silanes is contamination by gas phase dopant impurities, both n and p type originating from the higher silanes production system. An n-type impurity is shown to originate from the drying column. After elimination of this impurity, the a-Si:H films produced showed evidence of p-type doping. Secondary ion mass spectroscopy analyses of the resulting films identify boron as the p-type dopant. The incorporation of boron into the films was varied by preheating the reactant gas immediately prior to deposition. The ideal preheat temperature is shown to be between 350 and 400 °C. Films deposited with a preheat of 375 °C showed no flow dependence of the hole diffusion length and the best electron transport properties. Attempts at removing the boron impurity from the gas stream were also made. A Porapak Q■ column installed at the end of the drying column was found to be reasonably effective. Depositions of a-Si:H were also made utilizing a commercially purified tank of Si2H6. The lack of evidence of compensating or p-type doping in this system firmly establishes the impurities as originating from the Mg2Si based silanes production system.
A theoretical analysis of Auger recombination induced energetic carrier leakage in GaInAsP/InP double heterojunction lasers and light emitting diodes
Authors: Chik K. D.
Published: July 2002

An Auger recombination induced energetic carrier leakage model is presented, which takes into consideration the rate of generation of energetic carriers through Auger recombination processes, the rate of energy relaxation of the energetic carriers through carrier-phonon interactions, and the leakage of energetic carriers over the heterojunction barriers limited by diffusion and drift mechanisms. By including this energetic carrier leakage in the rate equations of injected carriers, the leakage behavior of GaInAsP/InP double heterojunction lasers and light emitting diodes can be calculated. Analytic results are found to be in excellent agreement with experimental measurements.
Modeling parallel conduction in GaAs/AlxGa1−xAs heterostructures
Authors: Hurd C. M. , McAlister S. P. , McKinnon W. R. , Stewart B. R. , Day D. J. , Mandeville P. , SpringThorpe A. J.
Published: July 2002

We consider several features of the dc properties of illuminated, n-type GaAs/AlxGa1−x As heterostructures that normally are neglected when modeling the parallel conduction. These are: (1) multivalley conduction in the undepleted AlxGa1−x As layer, (2) internal resistances in the heterostructure, (3) illumination-dependent properties of the undepleted layer or of the internal resistances, and (4) the photoexcitation from the shallow donor component of the DX center. We show the importance of these refinements by comparing the calculated carrier densities with those from experimental results obtained in the range 4.2–320 K. The comparison shows that (1)–(3) are important effects that should be considered when modeling the dc conduction, but (4) can safely be neglected in the samples we have studied.
Degradation of bipolar transistors under high current stress at 300 K
Authors: Wachnik R. A. , Bucelot T. J. , Li G. P.
Published: July 2002

We have observed the onset of degradation of bipolar transistor characteristics under high current forward stress at room temperature. The observed degradation may be attributed to interface states generated next to the sidewall oxide at the emitter base junction in a self-aligned bipolar transistor. Individual steps in the generation and annealing kinetics may be resolved. The sensitivity of the device to the extrinsic base doping profile is demonstrated and a model based on the generation of hot carriers by Auger recombination and bond breaking by these hot carriers is proposed.
Energy gap in concentrated spin glasses
Authors: Liao S. B. , Bhagat S. M. , Manheimer M. A. , Moorjani K.
Published: July 2002

Using magnetic resonance data at several frequencies, we have obtained the temperature dependence of the field-induced magnetization (M) in three concentrated spin glasses. At every frequency, M is independent of T for T≲TSG and drops linearly with T at higher temperatures. [M(0)−M(T)]/M(0) is closely represented by the function [exp(Δ/T)−1]−1, where Δ is a characteristic gap energy with values close to the corresponding Curie–Weiss temperatures θp but much larger than the respective spin-glass transition temperatures TSG.
Aging effects in bulk and fiber TlBr-TlI
Authors: Wysocki Joseph A. , Wilson Robert G. , Standlee Arlie G. , Pastor Antonio C. , Schwartz Robert N. , Williams Arthur R. , Lei Guan-Dao , Kevan Larry
Published: July 2002

A study of optical aging in bulk and extruded fibers of thallium bromo-iodide (TlBr-TlI) is presented. A variety of techniques including secondary ion mass spectrometry (SIMS), powder neutron and x-ray diffraction, infrared spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy are used to probe the chemical and structural properties of both pristine and aged material. High concentration levels of a hydrogen bearing impurity have been detected by SIMS and neutron scattering in aged TlBr-TlI, and have been shown to be localized in the surface layers of fibers as well as bulk samples. We present EPR evidence which indicates that the hydrogen bearing impurity is water.