bluuebunny/crossref_metadata_2025 huggingface dataset:
Calorimetric and susceptibility investigations on the MnO⋅Al2O3⋅SiO2 spin-glass system (abstract)
Authors: Hunter Gary W. , Rana Mazhar , Wenger L. E. , Wallace W. D.
Published: July 2002

A systematic heat capacity and ac magnetic susceptibility study has been performed on a magnetic ternary glass system—MnO⋅Al2O3⋅SiO2—with Mn concentrations varying from 6 to 19 at. %. At temperatures above 70 K, the susceptibilities follow a Curie–Weiss behavior with negative paramagnetic Curie temperatures and Bohr magneton numbers corresponding nearly to the free ion values of Mn++. However, below 70 K, all glass samples show strong deviations from the Curie–Weiss behavior (a decrease in 1/χ) culminating in spin-glass susceptibility maxima at liquid-helium temperatures for Mn concentrations above 9 at. %. These results suggest a formation of antiferromagnetic clusters which grow in size with decreasing temperature and become ‘‘infinitely’’ large as the spin-glass freezing temperature is approached. Since the specific heats of glasses do not follow a simple temperature dependence in the temperature range of 1–60 K, calorimetric measurements on several nonmagnetic aluminosilicate glasses were performed in order to accurately determine the magnetic specific heat contribution Cm for the Mn aluminosilicate glasses. A broad maximum in Cm/T is observed in the vicinity of the spin-glass freezing temperature and nonnegligible Cm values are still present at temperatures greater than 50 K (>10Tf). Only a small fraction of the total magnetic entropy (∼7–8% of cR ln 6) is accounted for between 0 K and Tf, in agreement with the idea that spin-glass ordering in this system is dominated by short-range interactions.
Concentration dependence of the Verwey transition in germanium- and fluorine-substituted magnetite
Authors: Barlow R. D. , Jones M. R. B. , Phillips P. J. , Pointon A. J. , Whall T. E.
Published: July 2002

The magnitude and temperature of the Verwey transition have been investigated for germanium- and fluorine-doped magnetite to assess the effectiveness of A sublattice and anion substitutions in displacing and suppressing the transition. It is found that the quantity G=d ln(σT)/d(1/T), where σ is the conductivity, is more sensitive to the existence of the transition than σ itself: the consequence is that the presence of the transition can be detected to higher degrees of substitution than heretofore. The rate of variation of the Verwey temperature Tv with level of substitution and the condition for suppression of the transition are discussed.
Analysis of long-range magnetic interactions in diluted magnetic semiconductors (abstract)
Authors: Kopinga K. , de Jonge W. J. M. , Denissen C. J. M. , Brabers V. A. M. , Nishihara H. , Twardowski A.
Published: July 2002

Specific-heat, susceptibility, and high-field magnetization of a number of diluted magnetic semiconductors will be reported. These include Zn(Mn)Se, Zn(Mn)Te, [Zn(Mn)]3As2, [Cd(Mn)]3As2, with various Mn concentrations, ranging from above to far below the percolation limit. A paramagnetic to spin-glass transition has been observed in all compounds in the whole range of concentrations. The concentration dependence of the freezing temperature was found to be compatible with a radial dependence of the antiferromagnetic exchange interaction between Mn ions of the type J(R)∼R−n, with n ranging from 7 [Zn(Mn)Se, Zn(Mn)Te] to 4 in [Cd(Mn)]3As2. Calculations of C, χ, and M have been performed by means of an extended pair-correlation approximation, including both a nearest-neighbor and a long-range (J∼R−n) interaction, as indicated by the experimental results. A satisfactory simultaneous description of all data could be obtained, whereas no adjustment of the ‘‘statistical’’ distribution of the magnetic ions was necessary. We will report a similar analysis of the available data on other diluted magnetic semiconductors, such as Cd(Mn)Te, Cd(Mn)Se, Hg(Mn)Se, and Hg(Mn)Te. Also in these cases a fair theoretical description of the thermodynamic properties can be obtained, provided the long-range character of the exchange is taken into account.
Neutron studies of ‘‘forbidden’’ magnons in Pt3Mn, a three-dimensional metallic ferromagnet (abstract)
Authors: Li W. H. , Perry C. H. , Sokoloff J. B. , Stirling W. G.
Published: July 2002

Polarized neutron measurements are presented which show clearly that ‘‘forbidden’’ and allowed magnons exist as underdamped excitations both below and above Tc in the three-dimensional metallic ferromagnet, Pt3Mn. (‘‘Forbidden’’ magnons are magnons created by neutrons polarized along the sample magnetization, which are forbidden at low temperature.) A model of magnons propagating through a crystal containing a 360° magnetization twist is studied, which indicates that ‘‘forbidden’’ magnons can exist if the range of the short-range order is at least four lattice constants long, which is consistent with our experimental results and Edward’s estimates.
Spin-resolved photoemission study of i
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u grown epitaxial Fe layers on W(110) (abstract)
Authors: Kurzawa R. , Kämper K. P. , Schmitt W. , Güntherodt G.
Published: July 2002

Spin- and angle-resolved photoemission spectroscopy of in situ grown epitaxial Fe layers on W(110) shows bulklike behavior for more than two atomic Fe layers.1 For about 10 and more atomic layers of Fe we find a spin polarization of about −100% near the Fermi energy and +80% between 1 and 3 eV binding energy. For the bilayer of Fe drastic changes in the spin-resolved spectra and a 20% enhancement of the spin polarization compared to the bulk value are observed. The monolayer of Fe is ferromagnetically ordered with a spin polarization reduced by about 50%. A switching of the easy magnetization axis from [001] to [11̄0] is observed in the spin polarization with decreasing Fe layer thickness near d=(65±5) Å.
Magnetic proximity effect at a superconductor–rare-earth oxide interface
Authors: Tkaczyk J. E. , Tedrow P. M.
Published: July 2002

Using spin-polarized electron tunneling, we have observed an enhancement of an applied magnetic field in a thin superconducting Al film in contact with an oxide of a rare-earth metal. The Zeeman splitting of the superconducting density of states of this Al film is 2μ(B+B*), where B is the applied field and B* is of the order of the magnetization of the rare-earth oxide. The field is applied parallel to the plane of the film. Oxides of Eu, Gd, Tb, Dy, and Er have produced this effect. The enhancement can be quite large: an Al film in contact with Gd2O3 in an applied field of 1.5 T behaves as though it were in a field of over 4 T. Both S-I-S tunneling and critical field measurements provide quantitative confirmation of the enhancement. A proximity model by de Gennes accounts qualitatively for some but not all of the observations, and quantitative aspects of the experiment are not understood. This proximity effect may provide a method of studying the surface magnetism of insulating magnetic materials in an applied magnetic field.
Superconductivity and antiferromagnetic order in the U(Pt,Pd)3 system
Authors: Franse J. J. M. , Kadowaki K. , Menovsky A. , van Sprang M. , de Visser A.
Published: July 2002

A phase diagram is presented for the superconducting and antiferromagnetic states in the heavy-fermion compounds U(Pt1−xPdx)3, x≤0.10. Superconductivity is depressed for x values larger than 0.005, whereas antiferromagnetism is observed in the composition range 0.01<x<0.1. Specific heat experiments show a sharp transition at the Néel temperature of 6.1 K for x=0.05, in contrast to the alloys with x=0.02 and 0.07 in which rather broad anomalies are observed around 3.6 and 5.5 K, respectively. Experimental observations indicate an optimal condition for antiferromagnetism around x=0.05. The effect of pressure on the phase diagram is discussed.
Resonant band-f scattering and the magnetic properties of highly correlated actinide systems
Authors: Hu G.-J. , Kioussis N. , Cooper B. R. , Banerjea A.
Published: July 2002

To understand the magnetic properties of moderately delocalized light actinide (uranium, neptunium, plutonium) systems, it is necessary to treat correctly the way in which the highly correlated behavior of the f electrons within the actinide ion is linked to the non-f band behavior via the hybridization process. We do this by transforming the hybridization into band-f resonant scattering. We have successfully applied the theory to PuSb by considering both dominant and next-to-dominant scattering channels.
Periodic permanent magnet field-transported relativistic electron beams
Authors: Matsuzawa Hidenori , Akitsu Tetsuya , Suzuki Yoshihiko , Fuki Satoshi
Published: July 2002

The utility of periodic permanent magnet (PPM) focusing for transporting relativistic electron beams (REB) was demonstrated experimentally and these results were supported by REB trajectory simulations. The PPM field was made by a series of permanent toroidal Sm-Co magnets and pure iron-made spacers of alternate magnetic orientation along the axis of the REB. When a foilless beam diode was operated at a pressure of approximately 0.2 Torr of nitrogen gas with an applied voltage of 420 kV, the PPM focused and transported the REB (200 keV, 1.2 kA, 10-ns pulse width). About 12% of the energy charged at the high-voltage generator was converted to the REB. Optimization of the beam diode and PPM configuration was not attempted.
Spike-mode oscillations in flashlamp pumped Nd lasers
Authors: Lindgren Lars , Lundgren Lennart
Published: July 2002

Regular spiking-mode oscillations have been investigated theoretically and experimentally. Stable and regular spiking oscillations can be obtained if the modulation signal is phase locked to the output pulse. Experimental investigation of intracavity loss modulation of a flashlamp pumped Nd-YAG (yttrium aluminum garnet) laser is reported.
Demonstration of optical bistability with a nonlinear prism coupler
Authors: Vitrant G. , Arlot P.
Published: July 2002

A guided wave is launched through a nonlinear prism coupler whose prism-waveguide gap is filled with a liquid crystal. We observed that the intensity of the excited guided wave exhibits optical bistability when the incident intensity is modulated. This result, which is rather surprising when compared to recent theoretical predictions, is shown to arise from a thermal averaging process in the liquid crystal.
Swirling flow through variable area ducts: Effects of entrance-flow velocity nonuniformity
Authors: Hokenson Gustave J.
Published: July 2002

The effect of nonuniformities in the streamwise-velocity distribution of a flow which is swirling in rigid-body motion at the entrance to a (rapid) change in area is analyzed. Experimental data obtained on the flow through a contraction with a rigid-body swirl are compared to the solution of the inviscid flow equations in which streamwise-flow nonuniformity is accommodated. At the higher of two imposed swirl rates, comparison between experiment and theory is acceptable, considering the fact that the actual distortion in the entrance streamwise-velocity profile is unknown. At the lower of the two swirl rates, the analytical solution is used to suggest that a localized boundary layer separation existed near the exit plane of the contraction which resulted in a weak expansion of the core streamtubes. Even the slightest pressure rise is shown to enhance the effect of streamwise-flow nonuniformities on the classical uniform swirling flow results.
Rare-earth substitution in (BiYCa)3(FeSiGe)5O12 bubble films
Authors: Luther L. C. , Slusky S. E. G. , Brandle C. D. , Norelli M. P.
Published: July 2002

The substitution of Y by Sm, Tb, Gd, and Ho in (BiYCa)3 (FeSiGe)5O12 bubble garnet is shown to have large effects on the growth-induced anisotropy Kgu. The presently accepted film composition intended for 6- or 8-μm period bubble memory devices demands partial substitution of Y by Gd and Ho. However, comparing films grown under the same growth conditions it is observed that YGdHoBiIG films possess less Kgu than their Gd, Ho-free counterparts. Thus, to satisfy Kgu requirements, the supercooling during growth must be increased by 20 K to 80 or 85 K with undesirable effects on defect densities. A new film composition containing Sm, Tb, and Gd has been formulated to satisfy all known material property specifications for 6- or 8-μm period memory devices. It can be grown with only 45–50 K supercooling.
Influence of electrical resonance on the interpretation of optogalvanic data
Authors: Lee Seong-Poong , Rothe Erhard W. , Reck Gene P.
Published: July 2002

Resonant laser light and electrical pulses are used to induce time-dependent optogalvanic signals from commercial hollow-cathode lamps. Previous workers observed such signals induced by a laser and interpreted them in terms of specific molecular processes. It is argued that electrical resonance in the lamp and its associated circuit, when combined with the negative resistance characteristic in the lamp, create a circuit which is capable of oscillation. This circuit, under certain conditions, has been found to oscillate spontaneously or it may be stimulated to yield damped oscillations through the action of an electrical pulse, or by a resonant-laser pulse. Such effects must be considered in the interpretation of time-dependent optogalvanic data in addition to specific molecular processes which may be taking place.
Electron paramagnetic resonance of Er3+, Dy3+, and Gd3+ in Y(CF3SO3)3⋅9H2O
Authors: Bellesis G. H. , Simizu Satoru , Friedberg S. A.
Published: July 2002

The paramagnetic resonance spectra of 1% Er3+ and 1% Dy3+ substituted in hexagonal Y(CF3SO3)3⋅9H2O (YTFMS) single crystals have been measured at 4.2 K and 9.215 GHz. Resonances due to Gd3+ impurities were identified and studied at 77 K. In each case, the results strongly resemble those for the given ion in an Y(C2H5SO4)3⋅9H2O (YES) or La(C2H5SO4)3⋅9H2O (LaES) host suggesting that R3+ site symmetry in YTFMS is also C3h. For Er3+, the spin Hamiltonian parameters are found to be g∥ =1.62, g⊥ =8.67, A=0.006 cm−1, B=0.030 cm−1, and P=0.001 cm−1. For Gd3+ we find g=1.988, b02 =0.010 88 cm−1, b04 =−0.000 418 cm−1, and b06 =0.000 058 cm−1. In the case of Dy3+, resonance is observed for ions whose major g-tensor axis coincides with the YTFMS c axis and have g∥ =10.90 and g⊥ ≊0. Another resonance, which splits into a six line pattern when the field is rotated away from the c axis, is attributed to ions whose g tensors are tipped by 20° from that axis by the perturbing effect of lattice imperfections. These have gx =3.79, gy =2.41, and gz =10.84 and are believed to be relatively few in number. Similar tipping is seen for Dy3+ in YES.
Magnetic and magneto-optical properties of perpendicular magnetic 3d transition-metal fluoride films
Authors: Sugawara E. , Shirakawa K. , Masumoto T. , Nakayama T.
Published: July 2002

Optically transparent, ferromagnetic films of Fe-F, Co-F, and Ni-F have been prepared by rf sputtering from powder-compacted targets of FeF3, CoF3, and NiF2. The films are amorphous, containing a small amount of crystalline fluoride. Some films showed perpendicular magnetic anisotropy, high coercivity (700–1500 Oe), and fairly high remanence ratio (0.23–0.7). Faraday rotation coefficients of 104 deg/cm at a wavelength of 633 nm were found.
A fundamental parameters XRF approach for the determination of the composition and thickness of multilayer metal films (abstract)
Authors: Linder R. , Kladnik G. , Augenstine J. , Ungemach S.
Published: July 2002

Analysis of the composition and thickness of magnetic thin films is important in controlling the properties of these materials. For instance, of all factors which determine the overall behavior of Permalloy films used in magnetic recording, composition is perhaps the most critical. For a film near the magnetomechanical zero point, a change in the composition of as little as 0.3% can alter the nature of the magnetization rotation process to the point where errors in readback occur. For this reason it is a necessity to perform accurate and precise analyses of the film composition. One means of performing rapid and precise analysis of these films is x-ray fluorescence (XRF). General algorithms have been developed to provide fundamental parameter corrections for XRF data from single and multilayer metal films. The corrections yield precise values for both thickness and composition. For example, the precision for a replicate analysis on a Permalloy sample was measured to be 80.34 ± 0.07% (weight) Ni (1σ). The fundamental parameter algorithms are quite general and are capable of dealing with variable compositions in each of the films in a multilayer stack. Previously, the restrictions were such that: (1) each element analyzed must appear only once in the films or substrate, and (2) the signal from each element is not obscured by that of another element. We have developed a procedure for the case where the substrate contains an element which is repeated once in the films, for example, nickel over alloy 42. In either case, the accuracy and precision of the measurement is improved if a substrate signal is observed.
New model for magnetism in disordered materials
Authors: O’Handley R. C.
Published: July 2002

Existing models of disordered magnetism fail to explain adequately both the higher Curie temperature of amorphous cobalt–rare-earth alloys and the suppressed Curie temperature of iron–rare-earth amorphous alloys relative to their crystalline counterparts. A new model is proposed in which the chemical short-range order is altered by nonequilibrium processing so as to favor greater T-T (T=transition metal) coordination and smaller T-T distances in the noncrystalline material. This model correctly accounts for moment and Curie temperature differences between crystalline and noncrystalline alloys based on cobalt or iron.
Effects and behavior of arsenic during titanium silicidation by halogen lamp annealing
Authors: Okamoto Tatsuo , Tsukamoto Katsuhiro , Shimizu Masahiro , Matsukawa Takayuki
Published: July 2002

Effects and behavior of arsenic atoms existing in a titanium layer formed on silicon during silicidation by halogen lamp annealing were investigated. Using Rutherford backscattering spectroscopy and sheet resistance measurements, it was found that arsenic atoms in the titanium layer had the effect of retarding silicidation. At the initial stage of silicidation, arsenic atoms implanted into the titanium surface rapidly diffused into the titanium layer, and with the progress of silicidation, they were redistributed again toward the surface. Also, in the case of the lateral silicidation of titanium, a retardation effect by arsenic atoms was observed, and it became more conspicuous as the lateral silicidation proceeded. By scanning Auger electron spectroscopy measurements, the following was made clear: The arsenic accumulation layer was formed at the unreacted titanium side of the interface between the laterally grown silicide layer and the unreacted titanium layer. With the progress of the lateral silicidation, the width of the arsenic-accumulated layer increased and the layer acted as a more effective barrier against the progress of the lateral silicidation.
Ferromagnetic resonance spectra in reduced Ca-rich CaGe:YIG film
Authors: Han Z. Q. , Pardavi-Horvath M. , Wigen P. E. , DeGasperis P.
Published: July 2002

Ferromagnetic resonance (FMR) spectra have been obtained in an 11-μm-thick charge uncompensated garnet film having the composition of Y2.0Ca1.0Ge0.9Fe4.1O12 as a function of the reducing time up to 80 h in a solution of FeCl2 and in a N2 atmosphere at 1100 °C for up to 16 h. The temperature dependence of the cubic anisotropy field, the effective uniaxial anisotropy field, the g factor, and the linewidth were determined between 80 K and room temperature. The results show that, contrary to previous data based on the measurements of averaged properties, surface reduction is the dominant process and a surface layer having magnetic properties that differ significantly from the bulk region of the film is developed during reduction. The internal field parameters of the bulk layer of the film in the case of FeCl2 reduction are observed to be only slightly changed from those of the as-grown material, while for the nitrogen reduction process the growth-induced uniaxial anisotropy of the film is annealed out. The results are interpreted in the frame of the reduction of the charge compensating non-S-state Fe4+ ions to Fe3+ with the introduction of oxygen vacancies.
Photoluminescent properties of p-GaAs electrodes related to the ‘‘photocurrent anomaly’’: Determination of surface electron-capture velocities and depletion widths in photoelectrochemical cells
Authors: Johnson Phelps B. , McMillan Christopher S. , Ellis Arthur B. , Hobson William S.
Published: July 2002

Steady-state photoluminescence (PL) measurements have been used to determine depletion widths W and surface electron-capture velocities S for p-GaAs electrodes in aqueous acidic electrolytes. Electrodes subjected to slow cycling of applied potential (10 mV/s) exhibit a hysteresis in PL intensity in the ‘‘photocurrent anomaly’’ (PA) potential regime, characterized by negligible photocurrent at voltages up to ∼0.5 V negative of the flat-band potential (∼0.1 V versus a saturated calomel reference electrode, SCE). A marked hysteresis in S values is observed in the PA potential regime of ∼−0.1 to −0.4 V vs SCE. Estimated S values are high, approaching 107 cm/s, but decrease significantly during anodic-going scans. Variations in W between −0.1 and −0.8 V vs SCE indicate that strong Fermi-level pinning does not obtain. Electrode operation under a pulsed potential program (−0.05 to −1.00 V vs SCE) caused a transient reduction in S of approximately an order of magnitude.
Néel-line motion along Bloch walls
Authors: Hartmann U.
Published: July 2002

The motion of Néel lines along subdivided 180° Bloch walls has been investigated on iron whisker single crystals by indirect optical observation through the influence on Bitter patterns. The field-induced displacement of the lines is dominated by microscopic Barkhausen jumps, where the lines exhibit a striking flexibility along their longitudinal extent. Phenomena such as line fusion, line nucleation, and interactions with crystal defects have been investigated more closely.
InP electroluminescence as a tool to directly monitor carrier leakage in InGaAsP/InP buried heterostructure lasers
Authors: Stern M. B. , Brody E. , Sowell B.
Published: July 2002

Direct measurements of homojunction and heterojunction carrier leakage currents in InGaAsP/InP buried heterostructure lasers have been made by monitoring the electroluminescence (EL) at 0.96 μm in the InP confinement layers. These EL measurements show directly, for the first time, a correlation between homojunction leakage currents and the sublinearity in the 1.3-μm light output-current characteristic. The observed decrease in the 0.96-μm intensity with increasing p-dopant concentration is a direct confirmation that heterojunction leakage is reduced when the doping level in the p-InP confinement layer is increased.
Digital optical processing with photorefractive materials: Applications of a parallel half-adder circuit to algorithmic state machines
Authors: Rajbenbach H.
Published: July 2002

Theoretical and experimental results are presented for a real-time parallel half-adder circuit with the use of nonlinear interactions in photorefractive media. The two-valued intensity input bit planes contain 256 bits in a 16×16 format. They are processed in parallel by three photorefractive BaTiO3 crystals operating in a two-wave mixing configuration. Sequential algorithms for binary arithmetic can be implemented by providing the processor with a feedback loop. A prototype photorefractive algorithmic state machine that performs multibit operations between two arrays of numbers is proposed. The addition of two sequences of 5-bit numbers is experimentally demonstrated, and improved performances are expected with the use of phase conjugation techniques.
A study of silicon interstitial kinetics using silicon membranes: Applications to 2D dopant diffusion
Authors: Ahn S. T. , Griffin P. B. , Shott J. D. , Plummer J. D. , Tiller W. A.
Published: July 2002

The kinetics of silicon interstitial generation, recombination, and diffusion in floatzone (FZ) and Czochralski (CZ) silicon were studied during oxidation at 1100 °C using thin silicon membranes as test structures. One side of the membrane was oxidized to inject interstitials and the other side was covered with films of pad-oxide and silicon nitride. The interstitial concentration was monitored at both sides of the membrane simultaneously to determine the interface and transport kinetics of interstitials. The interstitial supersaturation at the oxidizing side was found to be insensitive to both the thickness variation and to the interface condition of the other side of the membrane. A model for this effect is proposed. At the interface opposite the oxidizing side, a delayed buildup of interstitials was observed. Using these results for FZ Si and assuming that there was no bulk recombination, an effective interstitial diffusivity of 9×10−10 cm2/s and an effective interface recombination rate of 3×10−7 cm/s for a silicon/pad-oxide interface were obtained. Interstitial transport across the CZ Si membranes during oxidation was slower than that across FZ membranes. The parameters extracted from these studies have been used to successfully model 2D dopant diffusion.
Excitonic interference phenomena in electrolyte electroreflectance: Application to n-CuInSe2
Authors: Bicelli L. Peraldo
Published: July 2002

Excitonic interference effects which may be observed on the low-field electroreflectance response of a semiconductor/electrolyte junction by varying the dc bias voltage at a constant wavelength are discussed in an attempt to generalize current results. Such effects are evaluated in a manner similar to that employed in analyzing conventional interference phenomena, but introducing some simplifying approximations which are also examined. The theoretical response turns out to be periodic in, and damped by, the square root of the band bending at the semiconductor surface in agreement with experimental results. Moreover, the first extremum is a minimum or a maximum according to whether the refractive index of the dead layer is smaller or greater than that of the region containing the excitons. These conclusions are applied to the analysis of the experimental data due to Shen, Siripala, Tomkiewicz, and Cahen [J. Electrochem. Soc. 133, 107 (1986)] concerning n-CuInSe2, a very promising direct-gap material for photoelectrochemical devices. Excitons are shown to exist at room termperature in this compound, in spite of the very small value of the exciton ionization energy. Furthermore, useful information is obtained on basic semiconductor parameters such as the donor concentration, the flatband potential, and the refractive index.
Redistribution of phosphorus in high-energy ion-implanted silicon
Authors: Kato Juri , Yonenaga Tomihiro
Published: July 2002

Phosphorus ions were implanted into silicon at an energy range between 0.4–1.5 MeV with a dose of 5×1013 ions/cm2. High concentration of phosphorus was accumulated below the interface between the SiO2 and Si substrate during the implantation, and enhanced diffusion of phosphorus occurred during the subsequent annealing in N2. The broadening of dopant profile after annealing at 1000 °C was smaller than that after annealing at 800 °C.
Electron-paramagnetic-resonance study of heat-treatment centers in n-type silicon
Authors: Bekman H. H. P. Th. , Gregorkiewicz T. , van Wezep D. A. , Ammerlaan C. A. J.
Published: July 2002

Donor formation in heat-treated phosphorus-doped Czochralski-grown silicon has been studied by electron paramagnetic resonance and resistivity measurements. Both ‘‘thermal-donor-’’ and ‘‘new-donor’’-formation temperature regions (470 and 650 °C, respectively) have been investigated. The results allow one to identify the spectra in both regions as arising from the Si-NL10 defect.
Organized and semiorganized doping for ZnS:Mn electroluminescent devices
Authors: Hunter Adolph , Kitai Adrian H.
Published: July 2002

The potential to achieve nonrandom Mn doping in ZnS:Mn material is discussed. By making diffusion measurements, we determine the required conditions during growth and operation of ZnS:Mn devices that are compatible with nonrandom doping. The probability of forming nearest neighbors and nearby neighbors of Mn in ZnS is calculated for various doping schemes, and the impact of these arrangements on the brightness of electroluminescence and photoluminescence in ZnS:Mn is discussed.
Radiation damage of gallium arsenide induced by reactive ion etching
Authors: Hara Tohru , Suzuki Hidenori , Suga Akio , Terada Toshiyuki , Toyoda Nobuyuki
Published: July 2002

Radiation damage induced in the surface of gallium arsenide (GaAs) by reactive ion etching (RIE)is studied using physical and electrical analyses. The number of displaced Ga and As atoms observed by Rutherford backscattering spectrometry aligned spectra is 7.8×1015 cm−2 and 1.3×1016 cm−2 at rf power of 300 W (0.47 W/cm2) and 500 W (0.78 W/cm2), respectively. The barrier height of the Schottky electrode formed on the undamaged layer is 0.745 V. The height decreases with increasing rf power and reaches 0.47 V at 0.78 W/cm2. Carrier concentration at the surface of the GaAs channel layer decreases with increasing rf power. The damage can be reduced by annealing at 400 °C for 30 min. For instance, the barrier height at 300 W increases from 0.47 to 0.70 V, and the carrier concentration increases from 7.0×1016 to 1.3×1017 cm−3. However, the carrier concentration cannot recover to the same level as that of an undamaged layer with annealing at 400 °C. The temperature conventionally employed in GaAs electrode annealing process.
A correlation between the enthalpy of mixing and the internal strain energy in the III-V alloy semiconductor system
Authors: Sonomura H. , Uda H. , Sugimura A. , Ashida A. , Horinaka H. , Miyauchi T.
Published: July 2002

The enthalpy of mixing calculated using the delta lattice parameter model has been compared with the internal strain energy estimated by the elastic sphere approximation. The composition dependencies of both energies are very similar for the quaternary III-V alloy semiconductors. Substantial origin of increase of the enthalpy in the alloy is concluded to be the internal strain caused by the difference in the bond length of constituent compounds.
Thermal diffusivity of GE-7031 varnish
Authors: Tsatis Demetre E.
Published: July 2002

The thermal diffusivity of an air dried sample of GE-7031 varnish has been measured by the temperature wave method at 85 and 300 K. The thermal conductivity under steady-state conditions was also measured and the results are compared with those of literature.
Stray-light correction in photoacoustic measurements of solid samples
Authors: Krueger S. , Kordecki R. , Pelzl J. , Bein B. K.
Published: July 2002

An experimental correction procedure is presented which allows one to measure separately and to eliminate signal contributions produced at the walls of photoacoustic cells by the directly incident light or by the light (diffusively) reflected from the solid sample. This stray-light correction procedure is tested for an opaque and a transparent photoacoustic cell. It helps to reduce the systematic error of photoacoustic measurements considerably when the solid to be analyzed and the reference material have different reflection properties and when in quantitative thermal depth profiling a larger interval for the modulation frequency of heating is needed.
Kinetic studies of the annealing behavior of a-Si:H p-i-n solar cells
Authors: Bennett M. S. , Newton J. L. , Rajan K. , Rothwarf A.
Published: July 2002

Results of measurements of the annealing of photodegraded amorphous silicon p-i-n solar cells are presented. The annealing process can be characterized by a relatively fast initial stage followed by a much slower second stage. Although the annealing behavior cannot be described by simple exponential kinetics, it can be characterized by a single activation energy of 1.2 eV. The degradation temperature and the duration of the light soaking do not affect this activation energy, although the ratio of the ‘‘fast’’ to the ‘‘slow’’ portions of the recovery change as these experimental parameters are varied. We have explained these phenomena in terms of hydrogen motion in the material.
Photoreflectance of reduced poly 3-methyl thiophene
Authors: Yuan Ren-Kuan , Shen S. C. , Tomkiewicz Micha , Ginley David S.
Published: July 2002

We present photoreflectance studies of poly 3-methyl thiophene as a function of doping level, temperature, and light intensity. The as-grown polymer does not show any photoreflectance signal. As the doping level is reduced by electrochemical reduction of the polymer, two peaks are observed in the spectra. One peak, at ∼2 eV, corresponds to the band-to-band transition. The second peak, at ∼1.7 eV, corresponds to the transition between the top of the valence band and the upper bipolaron level. These results are almost identical to those reported for the electrolyte electroreflectance of the polymer when it was in contact with an aqueous electrolyte. The major difference in the results using these two techniques is in the observation, in photoreflectance, of the bipolaron transition in the neutral, fully reduced polymer. This was interpreted in terms of bipolaron formation through photodoping. The similar spectral characteristics between the photodoped and electrodoped bipolaron are further support to the findings that the bipolarons are intrinsic excitations which are independent of the way in which they are generated.
Ballistic transport in hot-electron transistors
Authors: Xu Jingming , Shur Michael
Published: July 2002

We demonstrate that the performance of hot-electron transistors and other ballistic devices can be greatly improved if a focused beam of energetic electrons is injected into the active region of a high-speed device. The results of the Monte Carlo simulations of 72 000 electrons show that the angular distribution of electrons arriving at the collector of a hot-electron transistor is sharper since those electrons injected into the base under large angles primarily contribute to the base current. Our calculations also confirm that ballistic motion may be considerably enhanced by the built-in electric field in the base region. Based on these results, we propose a new device—the double base hot-electron transistor—where the first base acts as an ‘‘electron gun’’ focusing and accelerating the electron beam, which is then injected into the second (active) base where an input signal is applied. Our calculations show that the mean transit time of electrons traversing the active base can be considerably reduced and that the fraction of energetic electrons reaching the collector can be significantly increased in the proposed double-base hot-electron transistor in comparison with a conventional hot-electron transistor.
X-ray study of reactive ion etch damage to 〈100〉 silicon
Authors: Nemiroff M. , Stuber M. , Troutt R. , Gerber D. , Mittal S.
Published: July 2002

Contact resistance measurements, x-ray double-crystal diffraction, and Auger electron spectroscopy were used to evaluate reactive ion etch (RIE) damage to silicon wafers. Wafers were exposed to plasmas at different powers with gas mixtures of CHF3/O2 and O2 only. The CHF3/O2 mixture was typical of a gas mixture used for etching contacts to silicon. The O2 alone was used as a damaging, bombarding gas. Some oxidation of silicon occurs during the O2 bombardment. However, O2 was used to determine the effects of ion bombardment at conditions similar to those that occur during RIE etching of contacts. It has been found that the depth of damage to the underlying silicon increases with cathode bias and that at −550 V the damage is 200–250 Å deep. The damage at −550 V consists of two layers: one is an amorphous and/or polycrystalline silicon layer at the surface 100–125 Å thick. The surface layer contains impurities as a result of the reactive ion etch process. The second single-crystal dilated layer, 100–125 Å thick, lies beneath the amorphous/poly Si layer. The thickness of these layers is the same when either CHF3/O2 or O2 alone are used as the etchant gases.
High locking efficiency XeCl ring amplifier injection locked by backward stimulated Brillouin scattering
Authors: Sugii Masakatsu , Sugihara Okihiro , Ando Masaaki , Sasaki Keisuke
Published: July 2002

Performance of a XeCl ring amplifier injection locked by backward stimulated Brillouin scattering is described. High locking efficiency of ∼100% and a high-quality beam have been successfully obtained by using a Brillouin mirror.
Radiative leakage of space-charge waves by a modulated thin-sheet electron beam propagating parallel to a reflection grating
Authors: Yasumoto K. , Tanaka T.
Published: July 2002

A two-dimensional radiation by a modulated thin-sheet electron beam, which propagates parallel to a reflection grating composed of a slightly corrugated conducting surface, is investigated. The radiation can be interpreted as a radiative leakage of space-charge waves supported by the electron beam, when the effect of radiated fields back on the motion of electrons is taken into account. A self-consistent analysis of the leaky space-charge waves is presented using a perturbation approach based on the multiple-space scales. The coupled-wave equations governing the radiative leakage of space-charge waves are systematically derived. The analytical expressions for physical quantities characterizing the radiation are obtained in closed form. Numerical results of the leakage coefficient, the phase change due to the leakage, and the radiation efficiency are given for both of the fast and slow space-charge waves.
Achromatic storage ring for free-electron lasers
Authors: Cutolo Antonello , Madey John M. J.
Published: July 2002

We discuss the possibility of taking advantage on achromatic magnetic mirrors (α magnets) to construct a storage ring for free-electron lasers, where the electron trajectories are energy independent in the straight sections. This property might be efficiently used to noticeably reduce the momentum compaction.
Spectroscopy of 3-μm laser transitions in YAlO3:Er
Authors: Stalder M. , Lüthy W.
Published: July 2002

YAlO3:Er laser crystals with medium dopant concentration can emit on different transitions of the 4I11/2→4I13/2 manifolds within a laser pulse. In a 20-at. % doped a rod the three most prominent laser lines oscillate at wavelengths of λ1=2.73 μm, λ2=2.79 μm, and λ3=2.92 μm. The temporal sequence of λ1, λ2, and λ3 within a train of relaxation oscillations has been measured and is analyzed on the basis of inversion, linewidth of transitions, and ion-ion interaction in the 4I13/2 state.
Surface-wave-induced total absorption of radiation in an inhomogeneous warm plasma
Authors: Dragila R. , Vukovic S.
Published: July 2002

We have found conditions in which a structure consisting of an optically thin underdense warm plasma layer adjacent to a half-space of homogeneous overdense warm plasma acts as a 100% absorber for an obliquely incident p-polarized electromagnetic wave. Two mechanisms are involved in this phenomenon: conversion of the electromagnetic wave into a plasma wave and resonant excitation of a surface wave by the plasma wave.
Use of the R-matrix propagation technique to calculate the electronic energy levels of aperiodic structures: Application to an AlAs/GaAs quasiperiodic superlattice
Authors: Vasquez R. P.
Published: July 2002

The R-matrix propagation technique is shown to be a practical technique for estimating the electronic energy levels in aperiodic semiconductor structures within a simple one-dimensional potential model. As an example, the energy levels of an AlAs/GaAs quasiperiodic Fibonacci superlattice are calculated for electrons, light holes, and heavy holes. Those features which are unique to the quasiperiodic nature of the structure, rather than due to the choice of basis, are identified. These features are shown to be of a magnitude which makes detection using optical techniques possible.
Refinements in the determination of minority-carrier diffusion length measurements of polycrystalline silicon materials by the surface photovoltage method
Authors: Yan Ruyue , Wang Franklin F. Y. , Corderman Reed R. , Khattak Chandra P. , Leipold Martin H.
Published: July 2002

The microstructures of polycrystalline silicon samples show significant differences in their absorption coefficients within the range of wavelength of interest for the surface photovoltage (SPV) method. The accuracy in the determination of the minority-carrier diffusion length of polycrystalline materials by the SPV method was demonstrably improved with the use of the determined absorption coefficients for each individual sample.
Barrier formation in graded Hg1−xCdxTe heterojunctions
Authors: Madarasz Frank L. , Szmulowicz Frank
Published: July 2002

The problem of equilibrium barrier formation in graded Hg1−xCdxTe heterojunctions is solved with the use of a highly accurate computer model. The present calculation incorporates several features designed to improve on past efforts. The Poisson equation is solved as a nonlinear integro-differential equation. Fermi–Dirac statistics are used to allow for the degeneracy associated with inversion for narrowly graded junctions and the degeneracy of the native defect donors. The band structure is obtained from the numerical solution of the secular equation. Fermi–Dirac statistics are taken to govern the degree of ionization of the acceptors and acceptorlike traps. Acceptors are treated as divalent flaws and their ionization energies as linear functions of the cadmium composition. The results are compared to the recent work of Bratt and Casselman [J. Vac. Sci. Technol. A 3, 238 (1985)], and the earlier work of Migliorato and White [Solid-State Electron. 26, 65 (1983)]. Significant differences are found. The results and differences are analyzed. Further computations are made in order to investigate the impact of elevated temperatures and the interdiffusion of doping concentrations along with compensation effects. It is shown that even a smeared p-n junction can have an advantageous effect.
Aerosol clearing model for a high-energy laser beam propagating through vaporizing media
Authors: Chitanvis Shirish M. , Gerstl S. A. W.
Published: July 2002

We describe the clearing phenomenon that occurs when a continuous wave (cw) high-energy laser beam, incident upon a cloud of hygroscopic droplets, vaporizes these droplets. We consider the case when the incident wavelength is greater than the average droplet radius. The model of F. A. Williams [Int. J. Heat Mass Transfer 8, 575 (1965)] is used to describe the vaporization of a single droplet. The propagation of the laser beam is described by the radiative transfer equation in one dimension. We establish the existence of an ‘‘inertial’’ characteristic time ti that it takes for evaporation to be established in an aerosol cloud. Agreement of our model with a set of experimental data on vaporizing fog is demonstrated.
Analysis of a field-effect transistor with a channel made of ultrafine metal particles
Authors: Tamura Hirotaka , Hasuo Shinya
Published: July 2002

We calculate the characteristics of a type of field-effect transistor whose channel consists of ultrafine metal particles between the source and drain electrodes. The particles are capacitively coupled to a gate electrode through an insulating film. Electrons move between the source and the drain via the particles by tunneling. If the electrostatic energy required to add or to subtract an electron from a particle is much larger than the thermal energy, transistorlike behavior can be observed. The characteristics of the transistor are periodic with respect to the gate voltage. In principle, the proposed transistor has a subpicosecond carrier transit time and a transconductance of more than several Siemens per millimeter of channel width.
Laser-induced chemical vapor deposition of hydrogenated amorphous silicon. II. Film properties
Authors: Meunier M. , Flint J. H. , Haggerty J. S. , Adler D.
Published: July 2002

Properties of hydrogenated amorphous silicon thin films prepared by the laser-induced chemical vapor deposition (LICVD) of silane gas are described. We report the results of measurements of hydrogen concentration, infrared absorption, unpaired-spin density, optical and mechanical properties, electrical conductivity, and photoconductivity experiments. We conclude that the film properties are controlled primarily by the substrate temperature Ts. LICVD films are superior to those produced by conventional CVD because of the permissibly low values of Ts. This results in an increased hydrogen content (up to 30 at. %) and a reduced defect density (∼1016 spins/cm3). The hydrogen concentration is determined by the surface chemistry for Ts<300 °C ([H]>20 at. %) and by H2 evolution for Ts>300 °C([H]<20 at. %). The hydrogen is incorporated primarily in the SiH2 configuration and for Ts<300 °C, the films contain some polysilane (SiH2)n regions. All the physical properties of the films are discussed in conjunction with the LICVD process characteristics and are also compared with the properties of films prepared by the plasma-decomposition and homogeneous chemical vapor deposition (HOMOCVD) techniques. In all cases, the differences can be attributed to variations in the processing conditions.
Positron-annihilation study of vacancy defects in GaAs liquid-phase epitaxial layers
Authors: Tu Xiang-Zheng
Published: July 2002

Positron-lifetime measurements were used to study vacancy defects in as-grown GaAs liquid-phase epitaxial layers. The second lifetime τ2 was identified to be related to arsenic vacancies. The effect of growth temperature on positron annihilation was observed. The defect concentration as a function of growth temperature was estimated.
Excimer and dye laser annealing of silicon-nitride-capped, Si-implanted GaAs
Authors: Compaan A. , Abbi S. C. , Yao H. D. , Bhat A. , Langer D. W.
Published: July 2002

Carrier concentrations exceeding 1019/cm3 in GaAs implanted with Si (2×1014/cm2 at 140 keV) have been obtained by pulsed laser annealing with either a dye laser (λ=728 nm) or a XeCl excimer laser (λ=308 nm). Dye-laser annealing through a ∼55-nm-thick Si3N4 cap consistently produced higher activations than excimer-laser annealing with or without the cap. Carrier densities were measured by phonon-Raman and plasmon-Raman scattering.
High-temperature behavior of tungsten and TiN films on polycrystalline silicon
Authors: Quateman J. H. , Sisak S.
Published: July 2002

The electrical and materials properties of low-temperature oxide (LTO) covered tungsten and TiN films on polysilicon after a 1000 °C furnace anneal have been studied. The TiN was unaffected by the anneal. Its resistivity was a stable 42.5 μΩ cm, there was no reaction with the silicon or LTO, and adhesion was good. The tungsten films had 20% oxygen dissolved in the metal due to the LTO process. Upon annealing, oxygen diffused to the W-Si interface and produced a 120-Å SiO2 film which lead to poor adhesion and electrical contact. Deposition of a 200-Å tantalum film between the W and the LTO helped to solve this problem.