bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion of Sb, Ga, Ge, and (As) in TiSi2
Authors: Gas P. , Scilla G. , Michel A. , LeGoues F. K. , Thomas O. , d’Heurle F. M.
Published: July 2002

Gallium, Sb, and Ge were implanted into thick (about 400 nm) layers of TiSi2 prepared by metal-silicon reaction. The diffusion of the implanted atoms was analyzed by means of secondary ion mass spectrometry. Gallium was introduced because a former study had shown that the usual p-type dopant B does not diffuse in TiSi2. Germanium was used in lieu of a Si tracer. Its diffusion characteristics are compared to those of P and As (as well as Si) which had been investigated previously. Germanium and Ga diffuse readily above 600 °C, but Sb does not. Its diffusion appears to be limited to grain-boundary effects. Accumulations of the diffusing atoms are observed (except for Sb) at the silicide-silicon interface. These are due to kinetic effects, namely fast diffusion at grain boundaries and interfaces, rather than to real adsorption which is an equilibrium condition. Because diffusion in intermetallic compounds has been shown to be significantly affected by variations in stoichiometry, experiments were conducted with films implanted not only with foreign atoms but with Ti as well. These did not lead to significantly different observations.
Superconducting critical current of Nb-Ti wire with anisotropic defect structure. II.
Authors: Küpfer H. , Matsushita T.
Published: July 2002

Anisotropy of the global pinning force Fp was inductively measured for Nb-49 wt. %Ti monofilamentary wire with highly anisotropic pinning structures in magnetic field parallel and transverse to the wire axis. According to the recent models of Evetts and Plummer [Proceedings of the International Symposium on Flux Pinning and Electromagnetic Properties in Superconductors (Matsukuma, Fukuoka, 1985)] and of Dew-Hughes [Philos. Mag. B 55, 459 (1987)], the morphology of pins is assumed to determine the flux pinning characteristic by the occurrence of plastic shear of the fluxoid lattice. The saturation characteristic of Fp as in Nb3 Sn is expected to be obtained if the field is parallel to the wire axis, while the nonsaturation one, as in commercial Nb-Ti, is expected in the transverse geometry. However, the results obtained show similar nonsaturation characteristics in both geometries and are contradictory to expectation. These results suggest that the pinning characteristic is mainly determined by the pinning parameters as the elementary pinning force and the pin concentration, but is not affected by the simple morphology of pinning centers.
Infrared ellipsometry study of the vibrational properties and the growth of hydrogenated amorphous silicon ultrathin films
Authors: Drevillon B. , Benferhat R.
Published: July 2002

The first experimental study of hydrogenated amorphous silicon (a-Si:H) ultrathin films (df <500 Å) deposited on glass substrates using infrared spectroscopic phase-modulated ellipsometry is presented. The high sensitivity of this new technique is emphasized. In particular, SiH and SiH2 stretching bonds are identified on 50-Å-thick samples. It is shown that the structure of a-Si:H in the early stage of the growth (df <100 Å) may differ considerably from that of bulk materials: Hydrogen–silicon bonds are not observed in the first few seconds of the growth and the imaginary part of the dielectric function of the film is found to increase with df. These behaviors are attributed to an interaction of the growing film with the substrate.
Thermal stress mechanisms in optical storage thin films
Authors: Evans K. E.
Published: July 2002

Numerical calculations are presented that show that thermal stresses induced by laser heating in optical storage media may reach the failure strength of the materials used during the early stages of a laser pulse. It is shown how these stresses arise and how the failure process may then proceed by a combination of radial compressive stresses and axial tensile stresses producing damage by elastic buckling and interface failure. The formation of a stable blister for optical storage purposes is then possible. Alternatively such effects may contribute to the initial stages of current pit formation processes. Such thermal stresses may also have long term detrimental effects, producing interface damage, in many other multilayer optical storage systems, particularly those with high thermal expansion coefficients.
Activation of boron implanted in Hg0.7Cd0.3Te by high-temperature annealing
Authors: Wu T. B. , Lam K. Y. , Chiang C. D. , Gong J. , Yang S. J.
Published: July 2002

Boron was implanted into the p-type Hg0.7Cd0.3Te epitaxial crystals. The implantation was carried out using a fluence of 1.45×1015 cm−2 and an energy of 100 keV. The implanted specimens, as well as unimplanted ones, were annealed without encapsulation by one-zone annealing in an atmosphere of mercury vapor supplied from liquid mercury at temperatures from 250–500 °C. From the annealing of unimplanted specimens, a p-n transition at 350 °C is observed. On the other hand, from the annealing of implanted specimens, it is found that the n-type conductivity induced by implantation damage is gradually reduced with the increase of annealing temperature until a minimum appears around 350 °C, and then increases again. An enhancement of n-type conductivity can be further observed from annealing under a reduced pressure of mercury. A similar result is also obtained from the annealing of implanted specimens using a HgTe compound as the mercury reservoir instead of liquid mercury. The results suggest that the implanted borons become activated dopants after annealing at high temperature. A mechanism on the activation of boron in HgCdTe is thus proposed, and the experimental results can be satisfactorily explained by the mechanism.
Forward-voltage capacitance of heterojunction space-charge regions
Authors: Liou J. J. , Lindholm F. A. , Malocha D. C.
Published: July 2002

An analytical treatment is presented for modeling the capacitance of heterojunction space-charge regions under forward voltages. First, the conventional depletion model is reviewed and the inadequacy of the use of such a model at forward voltages is noted. The study then turns to the development of a more accurate model for the thickness and potential barrier of the space-charge region for all voltages. Based on this model and the approximation that the intrinsic level is piecewise linear with respect to position in the space-charge region, an analytical quasistatic capacitance model applicable for forward-biased conditions is derived. The model, however, encounters difficulties at very large forward voltages, and a qualitative treatment is employed there. The comparison of the present capacitance model with measured dependencies and with existing capacitance models is included.
〈S
z〉 wall relaxation measurements of optically pumped sodium atoms at high magnetic field
Authors: Levy C. D. P. , Schmor P. W. , Law W. M.
Published: July 2002

The wall relaxation time for optically pumped 〈Sz〉 polarized sodium atoms colliding with copper, stainless-steel, and dry-film coated surfaces has been measured as a function of an applied magnetic field. Results show that the mean number of wall collisions increases from one to about four before depolarization of sodium atoms occurs on a copper wall in a high (12 kG) magnetic field, whereas the atoms relax after a single collision on a stainless-steel wall even in high fields. The relaxation time for a dry-film coated surface, for the cell geometries used in our work, is dominated by the effusion of polarized sodium atoms from the cell. Our measurements also allow an estimate of the strength of the local magnetic field causing the 〈Sz〉 depolarization and of the correlation time of the depolarization interaction on the surface. The importance of these experimental results as applied to the performance of optically pumped polarized ion sources is also discussed.
Magnetocrystalline anisotropy in Y1−xPrxCo5
Authors: Pareti L. , Moze O. , Solzi M. , Bolzoni F.
Published: July 2002

A systematic study of the magnetic properties of the system Y1−xPrxCo5 has been carried out in order to clarify the respective role of 3d and 4f anisotropy in the occurrence of first-order magnetization processes (FOMP) and spin reorientation transitions (SRT) in PrCo5. The competition between Co and Pr anisotropies is responsible for the occurrence of SRT and FOMP, which is indeed observed in Pr-rich samples. The SRT and the onset FOMP temperatures both increase with increasing Pr content. The anisotropy field, measured by the SPD technique, increases linearly with increasing Pr content. This behavior is not expected and not explainable in terms of a simple addition of Co and Pr anisotropies. A comparison is made with the anisotropy in the systems Y2Co14B and Pr2Co14B.
Magnetic clustering in LaNi5−xFex compounds
Authors: Escorne M. , Lamloumi J. , Percheron-Guegan A. , Achard J. C. , Mauger A. , Jehanno G.
Published: July 2002

The magnetic phase diagram of LaNi5−xFex (0≤x≤1.2) has recently been investigated down to 20 K. This range has been extended here down to 1.6 K. Magnetic susceptibility curves χ(T) go through a maximum and then strongly decrease upon cooling below a temperature T1 which, for all iron concentrations, is smaller than 15 K, i.e., much smaller than the Curie temperature Tc for x≥0.4 or the spin freezing temperature for x<0.3, previously determined. This anomalous behavior is correlated to a sharp decrease of the electrical resistivity at T1. Mössbauer spectra do not show any anomalous behavior of the hyperfine field upon cooling through T1. These results, associated to the continuous behavior of the magnetic susceptibility and electrical resistivity versus the iron concentration, suggest that with decreasing temperature there is a progressive freezing of small magnetic clusters which coexists with long-range ferromagnetic ordering for x≥0.4.
Local atomic structure in amorphous Fe-P alloys
Authors: McCally R. L. , Morgan J. S. , Kistenmacher T. J. , Moorjani K.
Published: July 2002

Amorphous alloys Fex P100−x have been fabricated by rf sputtering in the composition range 50≤x≤75. Only a-Fe75 P25 is ferromagnetic at 293 K, with its Mössbauer spectrum consisting of six broad lines. This simple spectrum differs markedly from that of c-Fe3 P. Similarly, thermogravimetric analysis yielded Tc=550 K for the amorphous phase, a value considerably lower than that of the crystalline phase (700 K). The Mössbauer spectra of the samples having x≤71 were all similar quadrupole-split doublets. Mean isomer shifts (IS) and P(H) and P(Q) distributions were determined using Window’s method. The isomer shift is nearly independent of concentration in the range studied here, but differs significantly from those of the crystalline compounds c-FeP, c-Fe2 P, and c-Fe3 P. The effective quadrupole interaction is also nearly constant for 50≤x≤71, indicating a similar local Fe environment. These results contrast sharply with c-Fe2 P and c-FeP, which have different crystal symmetries and whose quadrupole interactions differ substantially both from each other and from their amorphous counterparts.
Microwave solitons in magnetic garnet films (invited)
Authors: De Gasperis P. , Marcelli R. , Miccoli G.
Published: July 2002

This work concerns some recent results on the excitation of solitons at microwave frequencies in planar magnetic films. In particular, yttrium iron garnet (YIG) possesses the intrinsic properties of dispersion and nonlinearity required for a system to support such a kind of waves. In this framework, experimental results on a novel nonlinear effect, related to the propagation at about 7 GHz of magnetostatic volume waves in YIG films having thicknesses ranging between a few microns to more than 100 μm, have been interpreted in terms of a solitonic excitation process. By starting from those findings, this paper presents an analysis of the experimental aspects as a function of the various parameters involved (i.e., thickness, frequency, wave vector, and so on) together with a concise discussion with respect to the presently available theoretical approaches.
One-dimensional Dzyaloshinski–Moriya antiferromagnets in an applied field
Authors: Xia Qing , Riseborough Peter S.
Published: July 2002

We examine the one-dimensional antiferromagnet, with a small Dzyaloshinski–Moriya component to the exchange, in a symmetry-breaking magnetic field. In the classical, continuum limit, this system is shown to obey a double sine-Gordon field theory which supports nonlinear, soliton excitations as well as linear, spin waves. We examine the dynamic spin-spin correlation function. We find the contributions coming from the nonlinear soliton excitations and the contributions from the quantized linear excitations. The quantized spin waves produce nonlinear contributions to the correlation functions that exhibit qualitative similarities to the soliton contributions.
Effect of pole tip alignment on magnetic fringing fields from recording heads
Authors: Koeppe P. V. , Re M. E. , Kryder M. H.
Published: July 2002

The effect of using pole tips of equal width in thin-film recording heads has been studied by examining a head having the track edges of its leading and trailing pole tips virtually aligned on one side and misaligned by 1.5 μm on the other. Magnetic fields produced by this head, as well as by a head whose edges were aligned by ion milling, have been measured. Using a magneto-optic photometer system with spatial resolution of less than 0.5 μm, the response of a thin-film medium spaced 0.25 μm from each head was dynamically monitored at a frequency of 1 MHz as the head was scanned beneath it. Results demonstrate that fringing fields emanate to a larger spatial extent in both dimensions from misaligned edges. These results are correlated with magneto-optic measurements of the dynamic response of the magnetization made directly at the pole tips of the two recording heads. Both a wider written track and broader transitions of magnetization are to be expected in a magnetic storage medium subjected to the fields in the vicinity of misaligned edges. This indicates that to achieve high track densities and to avoid interference from signals recorded on adjacent tracks as well as to minimize distortion during the read process due to a contorted field profile at misaligned edges, it is desirable to use heads with equal top and bottom pole widths.
Simulation of the magnetostrictive performance of Terfenol-D in mechanical devices
Authors: Engdahl G. , Svensson L.
Published: July 2002

A dynamic simulation model has been developed. Registered data from static measurements of the magnetostrictive strain for different magnetizations and mechanical stresses are used as numerical input. Easy examination of differences in dynamic performance between samples of different compositions and manufacturing methods is also possible due to a computer-aided input data handling system. The shape of the imposed magnetization can be a step, impulse, sinusoidal, or an arbitrary function. The mechanical load can be a prescribed force against the magnetostrictive element or an arbitrarily chosen mechanical impedance. The model has been verified against dynamic measurements in an experimental setup for sinusoidal and impulse magnetizations. Comparison between the model and the experimental data reveals that the model is a powerful tool for designing magnetomechanical devices based on giant magnetostrictive materials.
Dynamic susceptibility and damping rate of magnetic excitations in hybridizing cerium systems
Authors: Hu Gong-Jia , Cooper Bernard R.
Published: July 2002

There has been much interest in the magnetic excitation behavior of cerium and light actinide systems with partially delocalized  f  electrons. Both the dispersion and the damping show unusual characteristics. Previously we have had considerable success in dealing with the dispersion, and have now developed a theory of the dynamic susceptibility and damping rate of excitations in magnetically ordered cerium systems where the damping is due to the hybridization between the f electrons and the non-f-band electrons. We include in our calculations both the two-ion interaction, which causes anisotropic magnetic ordering, and the hybridization-dressed crystal-field effects. We have applied the theory to CeSb and CeBi and obtained very large renormalization of the single-ion spectrum. The temperature dependence of location and broadening of energy transfer peaks are in excellent agreement with experiment.
Neutron determination of the magnetic order and site preference in Er2(CoxFe1−x)17
Authors: Kumar R. , Yelon W. B. , Fuerst C. D.
Published: July 2002

Neutron powder diffraction has been used to characterize the magnetic ordering and crystallographic behavior of Er2(Co0.55Fe0.45)17 which crystallizes in the hexagonal form (Th2Ni17). The  f site, which is the dumbbell site, analogous to the c site in the rhombohedral 2-17 phase (Th2Zn17) and to the  j2 site in the 2-14-1 phase, is characterized by long TM–TM bonds (>2.55 Å) and a large number of TM near neighbors, and like its analogues, is strongly preferred by the Fe. The other three sites are slightly cobalt rich, compensating for the Co deficiency on  f. The magnetic structure at 293 and 580 K is axial with erbium moments antiparallel to the transition-metal moments as expected. At 8.7 K, basal plane components develop in addition to the axial moments on the erbium sites. Further studies will investigate the spin reorientation as a function of temperature and composition across the entire composition diagram.
Transition behavior in Gd-Co based alloys with strong anisotropy
Authors: Lee K. M. , O’Shea M. J.
Published: July 2002

We have studied the effect of random magnetic anisotropy (RMA) on transition behavior in Gd-Co glasses. The large RMA induced by alloying with anisotropic rare-earth elements produces standard speromagnetic behavior which includes nonsaturation of magnetization at large enough concentrations at 4.2 K and high fields in all the alloys except the most concentrated Tb alloys. Although these latter alloys have the largest coercivity and the strongest RMA they appear to be closer to saturation at high fields than intermediate concentration Tb alloys. We discuss a mechanism by which this saturation may be produced by short-range correlations in the anisotropy axis.
Magnetic transitions and phases in random-anisotropy magnets
Authors: Sellmyer D. J. , Nafis S. , O’Shea M. J.
Published: July 2002

The generality and universality of the Ising spin-glass-like phase transitions observed in several rare-earth, random-anisotropy magnets are discussed. Some uncertainties and practical problems in determining critical exponents are considered, and a comparison is made to insulating spin glasses and crystalline spin glasses where an apparent anisotropy-induced crossover from Heisenberg to Ising-like behavior is seen. The observation of a reentrant transition in a weak anisotropy system and its correlation with the theory of Chudnovsky, Saslow, and Serota [Phys. Rev. B 33, 251 (1986)] for the correlated spin glass is discussed.
Evidence for a spin-glass behavior in the diluted antiferromagnet FexZn1−xF2
Authors: Montenegro F. C. , Rezende S. M. , Coutinho-Filho M. D.
Published: July 2002

We report dc susceptibility ( χ) measurements in the diluted antiferromagnet Fex Zn1−x F2 with concentrations x=0.10, 0.25, 0.31, and 0.46. The field and temperature dependencies of χ in the x=0.10 and 0.25 samples reveal that a spin-glass (SG) phase appears at low temperatures. For x=0.31, which is slightly above the percolation limit (xp=0.24), the SG phase is also present at low temperatures, but there is a clear indication of long-range antiferromagnetic (AF) ordering at intermediate temperatures. Finally, in the sample with x=0.46, AF ordering with random-field effects determines the characteristic behavior. These studies will help in the understanding of the crossover from random field to SG behavior in dilute antiferromagnets.
Magnetic proximity effects for Fe films across a thin Ag barrier
Authors: Qiu Z. Q. , Tang H. , Du Y. W. , Stern G. P. , Walker J. C.
Published: July 2002

Multilayer (56Fe/57Fe/Ag/56Fe) films were prepared by a high vacuum evaporation technique. Magnetic proximity effects for Fe films across a thin Ag barrier were studied by Mössbauer spectroscopy using 57Fe as a probe. The hyperfine field of 57Fe increases with the increase in thickness of the Ag barrier layer. We believe the proximity effects result from the RKKY interaction, mediated by the s-p electrons of Ag.
Magnetic characterization of Er/Y superlattices
Authors: Borchers J. A. , Salamon M. B. , Du R. , Flynn C. P. , Rhyne J. J. , Erwin R. W.
Published: July 2002

Molecular-beam epitaxy techniques have been used to prepare coherent, crystalline superlattices of erbium and yttrium. Magnetometer measurements indicate that the transition temperatures for the superlattices are significantly lower than those for bulk erbium. The first-order transition to a conical ferromagnetic state observed in Er is suppressed. The c-axis modulated phase is stable in c-axis fields up to 17 kOe, while the field dependence of the basal-plane moments differs little from bulk Er. These results suggest that the magnetoelastic energy has been altered in the superlattice samples due to lattice clamping to the substrate and at the interfaces.
Magnetic and structural studies in Co-Al thin films
Authors: Tsoukatos A. , Dale B. , Strzeszewski J. , Hadjipanayis G. C.
Published: July 2002

Thin films of Co100−xAlx with 15<x<50 were prepared by evaporation. The as-deposited films had the hexagonal Co structure for x<25, a disordered bcc CoAl structure for x≂30, and a partially ordered bcc CoAl structure for x>30. After a heat treatment at 650 °C the films with x<25 changed microstructure to a fine mixture of hcp Co and an ordered fcc structure which may be interpreted as Co3Al. Films with 25≤x≤50 were transformed to ordered fcc Co3Al and bcc CoAl structures after the heat treatment. The magnetization of the films was greater than for bulk alloys with the same composition and it decreased when the films were annealed at 650 °C. The finely distributed two-phase microstructure is probably responsible for the observed coercivity (50–150 Oe).
The dependence of coercivities of ultrafine Fe particles on packing fraction and microstructure
Authors: Bridger K. , Watts J. , Chien C. L.
Published: July 2002

Isolated ultrafine ferromagnetic particles exhibit large coercivities which scale approximately as 1/d, until the diameter d becomes sufficiently small for the particles to become single domains. Many applications, e.g., magnetic recording, require high densities of particles in a film. Thus, it is of interest to study the effect of packing fraction, and ultimately particle contact, on the coercivities of the small particles. Uniform cubic iron particles having sides ∼500 Å and coercivities as high as 1000 Oe have been prepared. The effect of packing fraction on the coercivities of these particles is presented herein. The coercivities of pressed pellets of these particles is reported and correlated with the microstructures (or nanostructures), and the behavior of uncoated metal particles is compared to that of silicate-coated metal particles.
Disclinations: The magnetism and the magnetic anisotropies of the rare-earth–3d transition-metal hard magnets (invited)
Authors: Watson R. E. , Bennett L. H. , Melamud M.
Published: July 2002

An important class of hard 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 have proposed that a criterion for choosing candidate alloys with strong 3d moments is the occurrence of such disclination nets, and using this criterion, have listed several structures having 3d sites with this characteristic. We have also rationalized the crystal field anisotropies as relating to the orientation of the major ligand lines.
Nonuniform wall motion in magnetic stripe domains and its effect on vertical Bloch line propagation
Authors: Lian M. R. , Humphrey F. B.
Published: July 2002

Nonuniform transient motion of magnetic stripe domain walls was observed in bubble garnet material. A number of films with 2–8 μm stripe width were used for investigation. The nonuniformity of motion varies from place to place on a submicron scale in the ‘‘perfect’’ single-crystal garnet film. Observing the development through a time sequence shows that the nonuniform motion begins within the first wall width of displacement. The degree of the nonuniformity increases as the effective drive field decreases. This nonuniform wall motion is due to the existence of local fluctuations of wall coercivity within the garnet crystal film. The response of the stripe domain wall due to dc bias field variation shows behavior similar to Barkhausen jumps indicating the intrinsic nonuniformity of the garnet material. The nonuniform wall motion may seriously affect the reliability of the propagation of vertical Bloch lines (VBLs) in a VBL memory.
Magnetics of nonlaminated, bilaminated, and multilaminated permalloy stripes
Authors: Tsang C. , Kasiraj P. , Krounbi M.
Published: July 2002

Using the magnetoresistive response technique and the micro-Kerr domain imaging technique, we have studied the magnetics of 2000-Å-thick nonlaminated, bilaminated, and multilaminated permalloy stripes with a length of 2400 μm, widths varying from 100 to 2 μm, and with the uniaxial anisotropy easy axis transverse to the length of the stripes. Results show that stripes from all three types of films exhibit non-single-domain remanent states that are hysteretic in their longitudinal magnetic responses. For the nonlaminated structures, closure domains are formed for the minimization of transverse demagnetization energy. For the laminated structures, longitudinally magnetized regions along the edges are formed as a basic feature of the flux-closure configuration in the laminated films. Furthermore, for the multilaminated structures, the large number of degrees of freedom and the low wall energies have created an abundance of low-energy remanent states that might cause the small-field response of the structure to creep with time. Finally, the use of transverse biasing is found to be ineffective in eliminating hysteresis in the bilaminated structures because this hysteresis is not a consequence of transverse symmetry in the structure.
Heterogeneous formation of small aluminum clusters
Authors: Hawley J. H. , Ficalora P. J.
Published: July 2002

We have previously reported that small aluminum clusters (Aln; n≤6) were observed in a free jet expansion through a graphite nozzle. The length and the diameter of that nozzle was 1.5 mm. The results of those experiments led us to postulate that the clusters formed as the result of a heterogeneous process. Experiments, utilizing a tungsten nozzle with a 1.5 mm length and diameter showed no cluster formation. Further, experiments using a graphite nozzle with a larger surface area (1.5 mm diam, 48.0 mm length) produced clusters with n≤10. These results are presented in support of a heterogeneous formation process.
Magnetic aftereffect in CoCr films
Authors: Lottis Daniel K. , Dahlberg E. Dan , Christner J. A. , Lee J. I. , Peterson R. L. , White R. M.
Published: July 2002

We have studied the relaxation or decay of the perpendicular remanent magnetization of CoCr films after the removal of a saturating magnetic field. The films have a perpendicular anisotropy and are similar to those being studied for application as perpendicular recording media. The time dependence of the decay of the magnetization was determined by measuring the magnitude of the magnetization continuously for time periods up to a thousand minutes using a SQUID magnetometer. This time dependence was studied over a range of temperatures for each of the samples (10–300 K). The decays are found to be quasilogarithmic over at least three decades of time and have been compared to two phenomological models. A fit to one model’s decay rate indicates the temperature dependence of the decay rate is nonmonotonic, i.e., the decay rate is a maximum in an intermediate temperature region for the films we have studied.
Gain measurements of the superconducting vortex flow transistor at high frequencies
Authors: McGinnis D. P. , Beyer J. B. , Nordman J. E.
Published: July 2002

This paper presents measurements of transresistance of the vortex flow transistor (VFT). These measurements were obtained at frequencies up to 500 MHz which was one-tenth of the transit time cutoff frequency. A signal tagging scheme was developed to detect these high-frequency signals that would otherwise be obscured by high crosstalk levels. The measured frequency response of the VFT indicates that the transresistance signal is present at frequencies greater than one-tenth of the transit time cutoff frequency. Thus, the VFT is a viable active device candidate for rf superconducting electronic systems.
Microdefects in dislocation-free liquid-encapsulated Czochralski GaAs
Authors: Yamada K. , Osaka J.
Published: July 2002

The effects of different growth conditions on microdefect generation in dislocation-free liquid-encapsulated Czochralski GaAs crystals are investigated using KOH etching technique and infrared light scattering tomography. It is found that microdefects are detected as micropits by KOH etching and as scatterers by infrared light scattering tomography, but are not detected by transmission electron microscopy. It is also found that the formation of these microdefects begins at below 1000 °C during the cooling process of the growth and strongly depends on the cooling rate. Other findings—melt composition and impurities (In,B), and the existence of denuded zones around dislocations—have led the authors to conclude that the microdefects are microprecipitates of excess arsenic atoms.
Determination of grain-boundary potential barriers distribution in p-type polycrystalline Si
Authors: Alpern Y. , Shappir J.
Published: July 2002

Metal-oxide-semiconductor structures employing lightly boron doped polycrystalline Si electrode are studied. The frequency dispersion of their admittance is explained by the existence of a broad distribution of intergrain potential barriers. A simple one-dimensional model is presented which yields the form of the potential barrier distribution. The observed results for the temperature and doping concentration dependence of the distribution are described and shown to be consistent with the resistivity activation energies.
Range measurements and thermal stability study of AZ111 photoresist implanted with Bi ions
Authors: Guimarães R. B. , Amaral L. , Behar M. , Zawislak F. C. , Fink D.
Published: July 2002

The Rutherford backscattering technique has been used to determine the range parameters of Bi ions implanted into AZ111 photoresist film at energies from 10 to 400 keV. An overall good agreement is found between the experimental results and the theoretical predictions by Biersack, Ziegler, and Littmark. It is also observed that a variation in the implantation dose does not affect the projected range and range straggling results, despite the fact that chemical modification of the implanted polymer layer is detected. In addition, we find that a shallow implantation of the polymer film with Bi ions increases the temperature at which the photoresist starts to decompose. Finally, at 300 °C the implanted Bi atoms diffuse preferentially toward the bulk. For this temperature, two different diffusion coefficients are estimated, one for the damaged region Dd=1.2×10−5 cm2/s and another for the bulk Db=1.2×10−14 cm2/s.
Trapping time in processed polycrystalline silicon measured by picosecond time-resolved reflectivity
Authors: Bambha N. K. , Nighan W. L. , Campbell I. H. , Fauchet P. M. , Johnson N. M.
Published: July 2002

We have used the methods of picosecond time-resolved reflectivity to measure the carrier lifetime in fine grain polycrystalline silicon films grown by low pressure chemical vapor deposition at 625 °C. After monatomic hydrogen diffusion or implantation with phosphorus ions followed by high temperature annealing (1150 °C), the trapping time τ increased from 40 to 150 ps, consistent with passivation of the grain boundaries or an increase in grain size, respectively. If implantation was not followed by annealing, τ decreased to less than 10 ps, while if it was followed by low temperature annealing (900 °C), which approximately restored the original grain size, τ recovered to 50 ps, very close to the trapping time measured in the as-grown samples. In all cases, we found indications that trapping of carriers was much faster than their subsequent recombination.
Characterization of a-Si1−xCx:H/a-Si:H and a-SiN:H/a-Si:H heterojunctions by photothermal deflection spectroscopy
Authors: Asano A. , Ichimura T. , Uchida Y. , Sakai H.
Published: July 2002

The subgap absorption spectra for hydrogenated amorphous silicon carbide/silicon (a-Si1−x Cx :H/a-Si:H) and silicon nitride/silicon (a-SiN:H/a-Si:H) alternatively multilayered films were measured by photothermal deflection spectroscopy and the defect density at the heterojunction was evaluated from the increase in absorption shoulder with the number of layering periods. The defect density at the a-Si0.66 C0.34 :H/a-Si:H heterojunction increased with increasing a-SiC:H layer thickness, while that at the a-Si0.50N0.50:H/a-Si:H heterojunction showed no dependence on the a-SiN:H layer thickness and was 1.4×1011 cm−2 . The defect density at the a-Si1−x Cx :H/a-Si:H heterojunction increased to 1×1011 cm−2 with increasing carbon content in the 0.1–0.5 range. Hydrogen dilution of the starting gases of the a-SiC:H layer was effective to decrease the interface defect density to less than 2×1010 cm−2 . A graded composition layer at the a-SiC:H/a-Si:H interface did not decrease the defect density.
Raman spectra of the pentanary alloy semiconductor (AlxGa1−x)1−zInzPyAs1−y
Authors: Emura Shuichi , Gonda Shun-ichi , Mukai Seiji
Published: July 2002

The Raman scattering of (AlxGa1−x)1−zInzPyAs1−y (x<0.33, y<0.18) pentanary alloy semiconductor lattice matched to GaAs is investigated for the first time. Five Raman peaks are found in the composition range studied here, indicating that these materials display the multimode nature in the lattice mode character. The four peaks except the lowest one in frequency are assigned to InAs-, GaAs-, GaP-, and AlAs-like longitudinal optical modes, and the lowest one to disorder activated longitudinal acoustic modes. The other possible two modes, the InP- and AlP-like modes, could not be distinguished.
Effects of deep levels on the optoelectronic properties of InGaAs/InAlAs multiquantum-well structures
Authors: Nojima S. , Nakashima K. , Kawamura Y. , Asahi H.
Published: July 2002

Deep electron-trapping centers present in InAlAs (barrier layers) are found to have significant effects on the optoelectronic properties of InGaAs/InAlAs multiquantum-well structures grown by molecular-beam epitaxy. When the energy depths of these centers are less than the discontinuity of the conduction band for this heterojunction, they come to be ionized to produce two-dimensional electron gas in the quantum well (InGaAs). The excess electrons thus accumulated dissociate the excitons by screening the attractive potential between electrons and holes. Hence, the deep levels in barrier layers must be reduced in order to improve the optoelectronic quality of this class of multiquantum-well structures.
Diffusion in InP using evaporated Zn3P2 film with transient annealing
Authors: Wang Kou-Wei , Parker Sandra M. , Cheng Chu-Liang , Long Judith
Published: July 2002

A new diffusion technique in InP using a Zn3P2 layer as the diffusion source with rapid thermal annealing is evaluated, and a number of interesting features are discussed. A p+ layer can only be achieved at temperatures ranging between 500 and 550 °C with a 15-s minimum diffusion time. Diffusivity is calculated and it is comparable with that of furnace diffusion. However, in order to form a shallow layer, there should not be any high temperature treatment or any other cause for the redistribution of Fe or dopant. Annealing at 850 °C for 15 s prior to diffusion moves the carrier profile from 3000 to 6000 Å deep, and the second diffusion front extends to 2.4 μm for the semi-insulating InP substrate. Similar results are obtained on MOCVD grown semi-insulating Fe:InP epiwafer. Diffusion performed on samples without preannealing resulted in two diffusion fronts and a 2.8-μm deep second diffusion front is observed for a diffusion performed on a preannealed epiwafer.
Magnetic resonance experiments on ion beam sputtered {100} Fe films
Authors: Oliver S. A. , Vittoria C. , Schloemann E. , Van Hook H. J. , Tustison R. W.
Published: July 2002

Ferromagnetic resonance (FMR) measurements have been performed on single-crystal Fe films, produced by ion beam sputtering techniques on GaAs substrates. In-plane FMR results over the frequency range 0.1–20.0 GHz were obtained by a slot line technique. The magnetic parameters deduced from these measurements are comparable to bulk Fe. In-plane angular variation reveals a negligible uniaxial anisotropy contribution to the magnetic anisotropy energy. Spin-wave excitations were observed in 9.5-GHz cavity measurements, and are found to obey the n2 law. The exchange stiffness constant is found to be somewhat larger than seen in other epitaxial Fe films. These results show that epitaxial Fe/GaAs films possessing good magnetic properties may be produced by ion beam sputtering techniques.
Characterization of AlAs/GaAs superlattice barriers using electrical barrier height analysis
Authors: Paulus M. J. , Huang C. I. , Bozada C. A. , Cheney M. E. , Dudley S. C. , Stutz C. E. , Evans K. R. , Jones R. L.
Published: July 2002

Electrical barrier height measurements on n+-GaAs–insulator–n-GaAs structures with short-period AlAs/GaAs superlattices forming the insulator show the effective conduction-band discontinuity (ΔEC) of a superlattice barrier (SLB) to be defined by the lowest superlattice energy state. Five structures with different AlAs and GaAs SLB layer thicknesses are investigated. A SLB with GaAs layers greater than 10 monolayers is found to have a ΔEC defined by Γ-valley states in the GaAs layers, while a SLB with GaAs and AlAs layers less than 10 monolayers and with thicker AlAs layers than GaAs layers is found to have a ΔEC defined by X-valley states in the AlAs layers. The SLB with GaAs and AlAs layers less than 10 monolayers and thicker GaAs layers than AlAs layers behaves as a random alloy. Negative differential resistance is observed in the current-voltage characteristic of the sample whose barrier height is defined by Γ-valley states in the GaAs layers.
Shallow diffusion of zinc into InAs and InAsSb
Authors: Khald H. , Mani H. , Joullie A.
Published: July 2002

Elemental zinc was diffused using the close-tube method into InAs and InAs1−xSbx solid solution (x=0.10–0.12). All the samples were (100) oriented. The diffusion temperatures were 500, 400, and 350 °C. Shallow junction depths (∼1 μm) were obtained. The temperature dependence of the effective diffusion coefficient of zinc is described by the formula: D=1.6×10−4 exp(−1.07/kT). The mean concentration of zinc for diffused layers at 500 °C is 3×1019 atoms cm−3. Diffused p+n diodes showing good electrical characteristics at 77 K were prepared at 350 °C from the n-InAsSb/n+GaSb system.
Improved measurements of the stimulated Raman scattering spectrum generated in a single mode fiber at λ=1.064 μm in continuous-wave regime
Authors: Irrera Fernanda , Pozza Davide
Published: July 2002

Continuous-wave stimulated Raman-scattering phenomenon has been generated in single mode fibers, pumping with a 10 W power cw radiation of a Nd:YAG at λ=1.064 μm. Critical power, line shape, and polarization angular shift has been determined for the first Stokes order. Comparison with previous works is reported.
Optimization of the photorefractive properties of KNbO3 crystals
Authors: Medrano C. , Voit E. , Amrhein P. , Günter P.
Published: July 2002

Photorefractive effects of nominally pure and iron-doped KNbO3 crystals with concentrations between 150 and 300 ppm have been investigated. In order to optimize the photorefractive recording times and the amplitude of the refractive changes, the crystals were thermally treated with simultaneous photorefractive testing. The photoconductivity data and the photorefractive experiments (grating spacing dependence of the beam coupling gain) show that the relative influence of electron and hole contribution is altered depending on the reduction treatment. The experimental results are discussed with a two-carrier model.
Spin-orbit band effects on silicon hot-hole transport
Authors: Ohno Yasuo
Published: July 2002

High-field transport of silicon holes has been analyzed considering carrier excitation to the spin-orbit band, which is separated by 44 meV from the heavy-hole and light-hole bands. Velocity-field relationships from 6 to 300 K, were interpreted by transport characteristics for holes excited to that band. According to a thermodynamic theory of irreversible processes in hot-carrier transports, the hole temperature at high electric fields was estimated to be lower than the electron temperature at the same electric fields, due to the short momentum and energy relaxation times for holes in the spin-orbit band.
Dopant redistribution during the solid-phase growth of CrSi2 on Si(100)
Authors: Rockett A. , Greene J. E. , Jiang H. , Östling M. , Petersson C. S.
Published: July 2002

The results of an investigation into the redistribution of dopants—As, B, and P—during the solid-phase reaction of Cr with Si substrates to form CrSi2 are presented. Cr layers, 47 nm thick, were evaporated onto B-doped Si substrates which had previously been implanted with one of the three dopants. Two implant doses were investigated for each dopant. Following heat treatment at 500 °C, doping profiles were determined by secondary-ion mass spectrometery (SIMS) and, for arsenic-doped samples, by Rutherford backscattering spectroscopy (RBS). Both SIMS and RBS were also used to measure the extent of silicide formation. The results demonstrate that B and P are transported from the Si substrate to the surface of the growing CrSi2 layer while As accumulates at the CrSi2/Si interface. The silicide formation reaction is shown to be inhibited by large As concentrations. No other dopant-concentration-related effects were observed. A model, based on dopant segregation driven by the relative free energies of CrSi2 and Cr-dopant compounds, is proposed to explain the results.
Molecular-beam epitaxial growth and microstructural characterization of GaAs on Si with a buried implanted oxide
Authors: Das K. , Humphreys T. P. , Posthill J. B. , Tarn J. C. L. , Wortman J. J. , Parikh N. R.
Published: July 2002

The direct growth of GaAs by molecular-beam epitaxy on nominally (100)-oriented silicon with a buried implanted oxide is demonstrated. Nomarski interference contrast optical microscopy, transmission electron microscopy, and Rutherford backscattering techniques have been employed to characterize these layers. The formation of hillocks and a uniform layer of GaAs in the intervening regions between hillocks have been observed. Microtwins and threading dislocations are the predominant defects in these layers. Furthermore, we report the absence of antiphase domain boundaries within the GaAs hillocks.
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u doping by As ion implantation of silicon grown by molecular-beam epitaxy
Authors: Denhoff M. W. , Houghton D. C. , Jackman T. E. , Swanson M. L. , Parikh N. R.
Published: July 2002

The incorporation and electrical activation of As, implanted in situ during molecular-beam epitaxial growth of epilayers on Si(100), is reported. Parameters varied included growth temperature (460–700 °C), implantation energy (500–1000 eV), and concentration (1017→>1020/cm3 ). In general, the material was excellent with 100% activation and bulk mobilities for concentrations up to the equilibrium solid solubility limit and carrier densities in excess of five times this limit in highly doped samples.
Properties of plasma-deposited Si-rich silicon nitride films in current enhancement injectors
Authors: Kaya Çetin , Ma Tso-Ping , Barker Richard C.
Published: July 2002

Si-rich silicon nitride (SiNx:H) film deposited on top of thermal SiO2 has been found to give rise to current enhancement through the double-layer sandwich structure similar to the injector device based on Si-rich SiO2 [DiMaria et al., J. Appl. Phys. 51, 2722 (1980)]. In this paper, the properties of the SiNx:H film, deposited by the plasma-enhanced chemical vapor deposition technique and its injector structure, are reported. It has been found that the as-deposited film is amorphous, but subsequent annealing done at 900–1100 °C leads to the crystallization of the excess Si in the material. For injector structures made of moderately Si-rich films, the current enhancement effect does not depend strongly on the film composition and the subsequent heat treatment. For samples made of very Si-rich films, however, the post-metallization anneal step (at 400 °C) causes the as-deposited SiNx:H film to react strongly with the gate Al. This lowers the crystallization temperature of the excess Si very significantly, and also supresses the current enhancement in the corresponding injector structure. Possible mechanisms are discussed. The cyclability of the injector structure, in particular, charge trapping and degradation of the underlying SiO2 layer as a result of current injection, is also discussed.
Effects of dopants on the deep bulk levels in the ZnO-Bi2O3-MnO2 system
Authors: Shim Youngjae , Cordaro James F.
Published: July 2002

Small amounts of In2O3 and Li2O were added to the ZnO-Bi2O3-MnO2 ternary primitive varistor system. Considering Schottky disorder and Frenkel disorder, oxygen vacancy or zinc interstitial density was expected to decrease with In2O3 doping and to increase with Li2O doping. Using admittance spectroscopy, a 0.32-eV electron trap, which is suggested to be an ionized oxygen vacancy, was observed regardless of the doping conditions. Changes in the peak height, for the 0.32-eV trap, in the admittance spectra are correlated with In2O3 and Li2O doping. Doping with In2O3 reduces the conductance contribution due to the trap, while doping with Li2O enhances it. However, calculations show that small amounts of dopants, less than 100 ppm, do not greatly influence the trap density. The trap density remains within experimental error approximately 1.0×1017 cm−3.
Simultaneous operation of gain- and index-guided lateral modes in twin-stripe laser diode arrays
Authors: Heflinger D. G. , Fenner W. R.
Published: July 2002

Twin-stripe laser diodes have been fabricated which exhibit two distinct sets of lateral modes. One is associated with a single-lobe near-field intensity profile corresponding to an effective index-guide centered between the stripes. The other has a double-lobe near-field distribution, each lobe centered under a stripe, corresponding to one of the twin-stripe gain-guided supermodes. A large spectral separation between these two modes, believed to be due to band filling, was also observed.