bluuebunny/crossref_metadata_2025 huggingface dataset:
The Einstein relation in Kane-type semiconductors
Authors: Ghatak K. P. , Chattopadhyay N. , Mondal M.
Published: July 2002

An attempt is made to investigate the Einstein relation for the diffusivity-mobility ratio of the carriers in degenerate Kane-type semiconductors, taking n-Cd3As2 as an example, on the basis of a newly derived dispersion relation of the conduction electrons allowing various types of anisotropies in the band parameters within the framework of k⋅p formalism. It is found that the above ratio increases with increasing carrier degeneracy and is in quantitative agreement with the suggested experimental method of determining the Einstein relation in degenerate semiconductors having an arbitrary dispersion relation. In addition, the corresponding results for an isotropic three-band Kane model are also obtained from the expressions derived.
Structural investigation of helium ion-beam-irradiated glassy carbon
Authors: Prawer S. , Rossouw C. J.
Published: July 2002

Raman spectroscopy, high-resolution transmission electron microscopy, energy filtered electron diffraction, and electron energy loss spectroscopy were used to investigate the microstructural changes accompanying the observed ion-beam-induced enhancement of the abrasive wear properties of glassy carbon (GC). The Raman results suggested that doses of about 1×1016 He+ cm−2 at 600 keV were sufficient to seriously disrupt the structure. However, the electron-beam-based diagnostics failed to reveal any significant differences between the as-grown and irradiated material. It is suggested that the defect concentrations created by the ion beam are sufficient to disrupt the medium to short-range order in the material but insufficient to alter the overall structure. However, ion-beam thinning glassy carbon with 5-keV Ar ions was found to partially graphitize the material.
A new type of high-resistive soft magnetic amorphous films utilized for a very high-frequency range
Authors: Karamon H.
Published: July 2002

A new type of high-resistivity soft magnetic amorphous alloy film with a very fine two-phase heterostructure was found in cosputtered Fe-B-C films. These amorphous films are found to have a number of superior properties in the high-frequency range (over∼10 MHz) over not only regular amorphous films, but also sendust film cores, which have already been applied to high-density recording media having high coercivity. They were found to exhibit unique isotropic soft magnetic B-H curves with high Bs (∼15 000 G), low Hc (∼0.3 Oe), and high ρ (∼400 μΩ cm), and the reduced magnetization versus reduced temperature curve was almost the same as the j=∞ curve of the Brillouin function. A very high permeability with less core loss, especially in the high-frequency range, was also experimentally observed in those amorphous films.
Sulfur doping behavior of gallium antimonide grown by molecular-beam epitaxy
Authors: Poole I. , Lee M. E. , Singer K. E. , Frost J. E. F. , Kerr T. M. , Wood C. E. C. , Andrews D. A. , Rothwell W. J. M. , Davies G. J.
Published: July 2002

Sulphur from an electrochemical source has been used to dope GaSb grown by molecular-beam epitaxy. The incorporation of sulphur in the epilayers has been measured by secondary ion mass spectrometry, and the effects of substrate temperature during growth and of the antimony-to-gallium flux ratio have been studied.The incorporation has been found to be a strong function of substrate temperature, varying from ∼100% below 435 °C to ∼1% at 525 °C. The incorporation also increases with antimony overpressure, varying by a factor of 3 on changing the antimony-to-gallium flux ratio from 1:1 to 4:1. The substrate temperature dependence is described by a simple kinetic model. The electrical activity of the incorporated sulphur is shown to be close to 100%.
Observation of threshold oxide electric field for trap generation in oxide films on silicon
Authors: Hsu Charles Ching-Hsiang , Nishida Toshikazu , Sah Chih-Tang
Published: July 2002

Verwey’s bipolar/metal-oxide-silicon-field-effect-transistor structure is used to inject hot electrons into thermally grown wet oxide films on crystalline silicon by forward biasing the substrate emitter-base junction. Two components are separated from the threshold voltage shift: the electron charging of existing neutral oxide traps and the generation of new oxide traps. The density of the generated new oxide traps is found to increase rapidly and exponentially with increasing oxide electric field above 1.5 MV/cm. This threshold oxide field for oxide trap generation is consistent with the bond breaking energy of the hydrogen–silicon and hydrogen–oxygen bonds in the oxide film.
Raman scattering in GaP1−xSbx
Authors: Cherng Y. T. , Jou M. J. , Jen H. R. , Stringfellow G. B.
Published: July 2002

The lattice-dynamic properties of GaP1−xSbx have been investigated for the first time by using Raman scattering measurements. This alloy, which has a large miscibility gap, has been grown by organometallic vapor phase epitaxy. The first-order Raman spectra for the ternary samples show two mode behavior over the whole composition range. The composition dependence of the intensity and energy shift of each mode is reported. The broadening and asymmetry of the GaP longitudinal-optical modes are analyzed in terms of alloy disorder effects.
Ferromagnetic antiresonance transmission through pure iron at 73 GHz
Authors: Rudd J. M. , Cochran J. F. , Urquhart K. B. , Myrtle K. , Heinrich B.
Published: July 2002

The magnetic damping in pure iron has been studied over the temperature range 140–300 K using a single-crystal slab l5 μm thick. The results at room temperature are consistent with the accepted value of the damping parameter for iron of G=0.7×108 Hz. The damping increases as the temperature is reduced and reaches a value of approximately 1.4×108 Hz at 140 K.
Improvement in optical and magnetic properties of Bi-substituted garnet sputtered films for magneto-optical recording
Authors: Gomi M. , Satoh K. , Abe M.
Published: July 2002

We have investigated the effect on the optical and magnetic properties of adding W or Co to Bi-substituted garnet films sputtered on glass substrates. Adding a small amount (<1.2 at. %) of W makes the film optically homogeneous. It also increases coercivity more than three times, probably due to wall pinning by W atoms. Adding Co reduces coercivity. On the thin film with added W, we have successfully performed a dynamic thermomagnetic writing with a regular bit shape. This promotes development of magneto-optical memory using garnet sputtered film.
Surface magnetism of oxygen and hydrogen adsorption on Ni(111)
Authors: Elmers H. J. , Gradmann U.
Published: July 2002

The changes of surface magnetization and of surface anisotropies of Ni(111) surfaces during adsorption of oxygen and hydrogen were measured at room temperature using torsion oscillation magnetometry in situ in UHV (UTOM) of ultrathin epitaxial Ni(111) films on Re(0001). In the case of oxygen, a rapid chemisorption process is connected with an initial change in magnetic moment per O atom, Δμox=−4.5μNi (bulk Ni moment μNi), which is reduced to −3.8μNi in the saturated chemisorption state (θ= (1)/(3) ). This chemisorption is followed by a slow oxidation up to three layers of epitaxial NiO, connected with a change of the film moment Δm=−2.7mML (moment mML of bulk Ni monolayer). Surface anisotropy fields are reduced from (10±1) T (free surface) to (0±1) T both for chemisorbed and oxidized surfaces. For the case of hydrogen, saturation adsorption at room temperature (θ= (1)/(2) ) results in ΔμH=−1.6μNi and a reduction of the surface anisotropy field to (3±1) T.
Critical properties of helical magnets and triangular antiferromagnets
Authors: Kawamura Hikaru
Published: July 2002

The critical behavior of certain frustrated magnetic crystals with competing interactions has been studied. It is predicted that the layered-triangular lattice antiferromagnets VCl2, VBr2, CsMnBr3, and CsVCl3 and the helical magnets β-MnO2, MnAu2, Ho, Dy, and Tb should belong to new universality classes characterized by novel critical exponents: α≂0.34–40, β≂0.25–0.28, γ≂1.1, and υ≂0.53–0.55. The chirality κ is a new relevant operator in these systems; the corresponding exponents are found to be βκ ≂0.40 and γκ ≂0.80, which satisfy the Essam–Fisher relation with ακ ≡α. The possibility of observing the chiral order is mentioned.
Photoluminescence spectra of highly doped AlxGa1−xAs grown by molecular-beam epitaxy
Authors: Ogawa Junko , Tamamura Kohshi , Akimoto Katsuhiro , Mori Yoshifumi
Published: July 2002

Photoluminescence at various temperatures of highly doped (5×1017 cm−3) Al0.3Ga0.7As grown by molecular-beam epitaxy has been studied. A luminescence peak at about 100 meV below the edge emission was observed. The intensity of this peak decreases as the As4/(Ga+Al) flux ratio increases for p-type samples, but decreases for n-type samples. An analysis based on the configurational coordinate model suggests that the origin of the luminescence may be a vacancy-dopant complex which acts as a nonradiative center at room temperature, as the intensity of the peak is inversely proportional to the intensity of the edge emission at room temperature.
Capacitance and conduction properties of semi-insulating polycrystalline silicon films
Authors: Black R. D.
Published: July 2002

Semi-insulating polycrystalline silicon (SIPOS) is a nonlinear, resistive film which is widely used as a passivant in high-voltage planar electronic devices. We present current-voltage and capacitance-voltage data, taken from SIPOS capacitor structures, which are quite different from similar results in the literature. We propose that our data may be explained by the existence of a change in the current transport mechanism in the film at an anomalously low electric field value. We present an atomic resolution micrograph of the SIPOS/silicon interface which points to a possible morphological reason for the uniqueness of the current transport properties.
Excimer laser light induced ablation and reactions at polymer surfaces as measured with a quartz-crystal microbalance
Authors: Lazare Sylvain , Granier Vincent
Published: July 2002

We have developed a new technique to measure the etch rate of polymer films under the ablative photodecomposition condition obtained by absorption of the far-UV radiation of the excimer laser. The technique is based on the use of a quartz-crystal microbalance interfaced with a microcomputer. It has high accuracy (17 ng/cm2). Etch rates of poly(ethylene terephthalate), polycarbonate, and polystyrene were measured as a function of the laser intensity, at 193 and 248 nm. The etch rate in the region of the ablation threshold intensity is obtained precisely. A slow ablation regime between the threshold and the linear regime is evidenced. For polycarbonate and polystyrene, a reaction of the irradiated surface with molecular oxygen accelerates the ablation process at low fluence of the 248 nm radiation. The degradation reaction of poly(ethylene therephthalate) is monitored as a function of fluence by selective dissolution in acetone. A sudden increase of the degraded depth is seen at the transition between the two ablation regimes. This is attributed to the melting of the surface.
Constricted diamagnetic hysteresis loops observed for the high T
c superconductors
Authors: Atzmony U. , Shull R. D. , Chiang C. K. , Swartzendruber L. J. , Bennett L. H. , Watson R. E.
Published: July 2002

Magnetic hysteresis loops, ac susceptibility, and resistivity measurements have been made on a Ba2 YCu3 O7−x-type high- Tc superconductor. The shape of the hysteresis loops well below Tc are reminiscent of constricted hysteresis loops observed in certain ferromagnetic materials which are usually associated with magnetic aftereffects. Similar dynamic effects, with a time constant on the order of 10 s at 40 K, are shown to be present in the superconducting material. This dynamic magnetic viscosity effect is in addition to the flux creep observed for longer time periods.
Magnetic properties of thin-film Ag+iron-oxide granular metals
Authors: Shull R. D. , Atzmony U. , Shapiro A. J. , Swartzendruber L. J. , Bennett L. H. , Green W. J. , Moorjani K.
Published: July 2002

The magnetic properties of iron-oxide particulates dispersed in silver (prepared by rf diode sputtering silver and iron oxide over a wide composition range) have been investigated using the Mössbauer effect, electron microscopy, and vibrating sample magnetometry. The sputtered films are nanocrystalline mixtures of immiscible particles of the two constituents (even when only a very small amount of silver is present). At room temperature, the Mössbauer effect data show that for most compositions (even those with low silver content) the majority of the film is superparamagnetic, with the fraction of material in the superparamagnetic state increasing with increasing Ag content. Consistent with these results, very narrow hysteresis loops were observed. On decreasing the temperature to near 100 K, the fraction of material in the superparamagnetic state decreased and the magnetically ordered component increased. Electron diffraction patterns clearly showed the presence of polycrystalline Ag and Fe3 O4 in the films, but composition analysis (0.03 μm resolution) was unable to separate these regions.
Simple holographic method for determination of Li/Nb ratio and homogeneity of LiNbO3 crystals
Authors: Arizmendi L.
Published: July 2002

A new method for the determination of the Li/Nb ratio of LiNbO3 single crystals is described. This method, which is quick and simple, is based on the anisotropic diffraction by photorefractive gratings. The measurement of two angles formed by laser beams provides a parameter related to the refractive indices, which, as is known, markedly vary with the crystal composition. Measurements on crystals with different Li/Nb ratios are presented. The method is compared with other methods presently available.
Infrared optical absorption of thin PtSi films between 1 and 6 μm
Authors: Mooney Jonathan M.
Published: July 2002

Absorption data of thin platinum silicide films on silicon substrates are presented. The data were obtained from reflection and transmission measurements over wavelengths between 1 and 6 μm for PtSi film thicknesses between 5 and 400 Å. The measured data differ from the theoretical results calculated from the bulk values of the index of refraction of PtSi. Values for the optical constants n and k, which best describe the reflection, transmission, and absorption over both the thickness and wavelength range are also presented.
Channeling and nuclear reaction analysis of shallow B- and BF2- implanted Si
Authors: Ridgway M. C. , Whitton J. L. , Scanlon P. J.
Published: July 2002

Ion channeling and nuclear reaction analysis (NRA) have been used to study rapid thermal annealing (RTA) of 10-keV B- and 45-keV BF2-implanted, crystalline, and preamorphized Si. Samples were capped with SiO2 and annealed in a nitrogen atmosphere with an AG Associates 210T Heatpulse system. Damage depth distributions were determined with He+ ion channeling. Extensive disorder was observed near the B projected range following a 1050 °C/20-s RTA cycle of B-implanted crystalline Si. For the same annealing conditions, much less residual damage was apparent for B-implanted preamorphized Si. No disorder was observed in the near-surface region (<30 nm) following a 1050 °C/20-s RTA cycle of BF2-implanted, crystalline, and preamorphized Si. Post-anneal damage at the original amorphous/crystalline interface was greater for BF2-implanted crystalline Si compared to BF2-implanted preamorphized Si. The relative retained B and F doses were determined with NRA using the 11B(p,α)8Be* and 19F(p,α0)16O reactions, respectively. A significant loss of B was observed following RTA of BF2-implanted preamorphized Si. No loss of B was apparent for all other annealed samples. A loss of F was observed for all annealed samples. For identical annealing conditions, the relative retained F dose of BF2-implanted preamorphized Si was less than that of BF2-implanted crystalline Si.
On the normal acceleration sensitivity of ST-cut quartz surface wave resonators supported along rectangular edges
Authors: Tiersten H. F. , Shick D. V.
Published: July 2002

An analysis of the normal acceleration sensitivity of grooved ST-cut quartz surface wave resonators supported along the edges is performed. Both the simply supported and rigidly supported cases are treated. The variational principle with all natural conditions for anisotropic flexure, which is required for the new approximation procedure used in the calculation of the flexural biasing state for the case of rigid supports, is presented. The flexural biasing states are employed in an existing perturbation equation along with the proper continuous representation of the acoustic surface wave mode shape for arrays of reflecting grooves to calculate the normal acceleration sensitivity. It is shown that by appropriate selection of the planar aspect ratio of an ST-cut quartz substrate the normal acceleration sensitivity can be made to vanish.
Electrical characteristics of Ti/Si(100) interfaces
Authors: Aboelfotoh M. O.
Published: July 2002

The Schottky-barrier height of Ti/Si(100) interfaces formed by sputter deposition of Ti on both n- and p-type Si(100) has been measured in the temperature range 77–355 K with the use of current- and capacitance-voltage techniques. Auger-electron and x-ray photoemission spectroscopies were used to characterize the Si(100) surfaces prior to metal deposition, and to monitor the reaction between Ti and Si upon heat treatment. The results showed that intermixing of Ti and Si has very little or no effect on the n- and p-type barrier heights. Silicide formation was found to result in only a small change in n- and p-type barrier heights of less than 0.1 eV. Furthermore, it was found that for ‘‘only’’ the metal-Si and silicide-Si interfaces with ideal thermionic-emission behavior the n- and p-type barrier heights decreased with increasing temperature and with coefficients approximately equal to one-half the temperature coefficient of the indirect energy gap in Si. These results are consistent with the predictions of models of Schottky-barrier formation which are based on the suggestion of Fermi-level pinning in the center of the semiconductor indirect energy gap. These results thus further confirm the dependence of both n- and p-type silicon barrier heights on temperature.
Two-wave mixing with gain in liquid crystals at 10.6-μm wavelength
Authors: Sanchez F. , Kayoun P. H. , Huignard J. P.
Published: July 2002

Signal-beam amplification is achieved in degenerate two-wave mixing experiments in liquid crystals at the wavelength λ=10.6 μm of the cw CO2 laser. The origin of the dynamic grating is the large thermal index change that arises when the cell operates near the phase transition temperature. Maxwell’s equations are analytically solved for the calculation of the amplitude variations of the incident waves (Ip:pump, Is:signal) and of the self-diffracted wave (I−1). It is shown that energy transfer arises from the contribution of the π/2 component of the index modulation generated by the interference of (Ip,I−1). The resulting three-wave model yields good agreement with the experimental results.
Photoluminescence of HgTe-CdTe superlattices: Comparison of theory and experiment
Authors: Baukus J. P. , Hunter A. T. , Schulman J. N. , Faurie J. P.
Published: July 2002

Infrared photoluminescence measurements have been made of a number of HgTe-CdTe superlattice samples as a function of temperature from liquid He to room temperature. The experimental results are compared with calculations of the band gap of these materials and the effects of layer thicknesses, valence-band offset, effective mass, and Hg in the CdTe layers are investigated. The data are in reasonable agreement with the calculations for zero (or small) valence-band offset and no Hg in the CdTe layers.
Thermal stability and electrical conduction behavior of coevaporated WSi2±x thin films
Authors: Nava F. , Weiss B. Z. , Ahn K. Y. , Smith D. A. , Tu K. N.
Published: July 2002

The thermal stability of coevaporated amorphous WSi2±x(x≂±0.2) thin films from room temperature to 1000 °C has been studied by in situ resistivity measurements and hot-stage transmission-electron microscopy. During continuous heating two consecutive phase transformations were observed to occur via nucleation and growth processes. The first which occurs at ∼420 °C is the crystallization of the amorphous film to a metastable, semiconducting hexagonal phase WSi2. The second which occurs at ∼620 °C is the transformation of the hexagonal phase to the thermodynamically stable, metallic, tetragonal phase of WSi2. The hexagonal phase is characterized by an acicular morphology and its formation is associated with a drastic increase in resistivity. The crystallites (grains) of the stable tetragonal phase are equiaxed and their formation is associated with a rapid decrease in resistivity. In order to achieve a low value of resistivity, ∼70 μΩ cm at room temperature, the tetragonal phase must be annealed to the neighborhood of 1000 °C. The activation energy for the hexagonal to tetragonal transformation (∼3 eV) was found to be higher than that for the crystallization (∼2 eV). The mode parameters for both transformations were found to be almost the same, n∼2. The characteristics of both transformations were not greatly influenced by the compositional changes.
Rapid thermal annealing of shallow Sb-implanted Si
Authors: Ridgway M. C. , Whitton J. L. , Scanlon P. J. , Naem A. A.
Published: July 2002

Rapid thermal annealing (RTA) of low-energy Sb-implanted Si has been studied with Rutherford backscattering spectrometry (RBS) and sheet-resistance measurements. For comparison, some samples were also analyzed with secondary ion mass spectrometry (SIMS). Si wafers were implanted with Sb at energies of 16, 32, and 48 keV and doses of 5×1014 and 1×1015/cm2. Samples were annealed in a nitrogen atmosphere with an AG Associates 410 Heatpulse system. RTA cycles ranged from 10 to 30 s at temperatures of 1000–1150 °C. Some samples were furnace annealed at 930 °C for 30 min. RBS experimental mean projected range and range straggle values did not differ significantly from trim code calculations. However, SIMS experimental range straggle values were ∼30% greater than RBS values. With RBS, a broadening of the Sb depth distribution and Sb accumulation in the near-surface region (<5 nm) were observed for furnace-annealed samples and, to a lesser extent, for those subjected to RTA. The relative retained SB dose decreased as RTA temperature and/or time increased. No loss of Sb was observed for furnace-annealed samples. For a dose of 5×1014/cm2, lower sheet-resistance values were obtained following RTA of a 32-keV Sb implant compared to a 30-keV As implant. The opposite was true for a dose of 1×1015/cm2.
Fast photoelectrochemical etching of quarter-micrometer diffraction gratings in n-InP
Authors: Matz R. , Zirrgiebel J.
Published: July 2002

A maskless etch process for diffraction gratings in n-InP is described in detail which permits simple and reliable large-area fabrication of gratings for distributed feedback (DFB) or Bragg-reflector (DBR) lasers. With respect to processes reported earlier the exposure and etching times are reduced by an order of magnitude without sacrificing resolution, modulation depth, or surface morphology. In accordance with the recently published diffusion theory for minority-carriers generated under holographic illumination, a high etch rate is found to be advantageous with respect to high spatial resolution. In addition, however, the results demonstrate that the chemical stability of the In-rich (211) and (111) planes as against the (100) surface is of final importance for obtaining good first-order DFB gratings.
Use of the lateral photoeffect to study sample quality in GaAs/AlGaAs heterostructures
Authors: Fontein P. F. , Hendriks P. , Wolter J. , Peat R. , Williams D. E. , André J.-P.
Published: July 2002

We have used the lateral photoeffect to image the variations in the conductivity of a two-dimensional electron gas (2DEG) setup in a GaAs/AlGaAs heterostructure. A description of the experimental arrangement is given and a simplified theory of the image contrast is presented. Our experiments image contrast resulting from defects such as cracks in the GaAs sublayer, and other contrast resulting from local changes in resistance of the 2DEG. Such variations have important consequences concerning both the interpretation of average parameters measured on such 2DEGs and the performance of electronic devices ( such as high electron mobility transistors ) fabricated using them. The inhomogeneities no doubt have their origin either in defects in the substrate used, or in the growth of the layers, or both.
The effect of level broadening on the tunneling of electrons through semiconductor double-barrier quantum-well structures
Authors: Gupta Rita , Ridley B. K.
Published: July 2002

Scattering and well-width nonuniformities in double-barrier structures introduce level broadening, particularly in the quantum-well region, and the effect of this level broadening on coherent and sequential transmission of electrons through these structures has been examined. First, it is shown that resonant energies are eigenenergies of the overall system, so that it is the same energy level which is involved in both tunneling mechanisms. This explains why the negative differential resistance (NDR) peak occurs at the same voltage for coherent and sequential tunneling. Expressions for the transmission coefficients and, consequently, for the current density are derived, and it is shown that the effect of broadening is to reduce the peak current and the peak-to-valley ratio for both tunneling processes, this reduction being quite remarkable for the case of coherent tunneling through the structures with thick barriers. Based on this, ways are suggested to distinguish between the two tunneling phenomena. This broadening-induced reduction in peak current and peak-to-valley ratio leads to a reduction in the NDR-related maximum operating frequency in these structures. On the other hand, the effect of broadening on coherent tunneling itself is to reduce the resonant tunneling time, thus allowing higher-frequency operation in optical devices. Above a critical amount of broadening the assumption of coherent tunneling breaks down, and sequential tunneling takes over. Critical broadenings for a number of cases are estimated. It is emphasized that the form of the NDR and hence the frequency response is dependent on whether the emitter density of states is two- or three-dimensional-like.
Growth of uniform epitaxial CoSi2 films on Si(111)
Authors: Fischer A. E. M. J. , Slijkerman W. F. J. , Nakagawa K. , Smith R. J. , van der Veen J. F. , Bulle-Lieuwma C. W. T.
Published: July 2002

Pinhole-free, pseudomorphic CoSi2 films with thicknesses from 1.3 to 16.4 nm have been grown epitaxially on Si(111) by sequentially depositing thin Co and Si films at room temperature, and subsequently annealing the resulting a-Si:Co2Si:Si(111) structure at 670 K. The film morphology is studied by high-resolution Rutherford backscattering, transmission electron microscopy, and reflection high-energy electron diffraction. The absence of pinholes in the as-grown layers is explained by a lowering of the barrier of CoSi2 nucleation owing to the presence of amorphous Si. Upon further heating the films remain uniform up to a temperature of 1000 K. Above that temperature the layers break up in islands, which corresponds with the thermodynamically most stable morphology. The lattice strain in pseudomorphic layers is found to persist even after islanding.
Thermal conversion and hydrogenation effects in AlGaAs
Authors: Adachi Sadao , Ito Hiroshi
Published: July 2002

Thermal conversion of molecular-beam epitaxially (MBE) grown AlGaAs from semi-insulating to p-type caused by annealing has been studied using Hall-effect and photoluminescence measurements. The presence of C impurities causes thermal conversion of the AlGaAs layers. A key observation is that residual C impurities can be greatly reduced by increasing growth temperature. Thermodynamic evaluation of adsorption kinetics suggests that C incorporation during AlGaAs MBE is chemisorptive. The effects of hydrogenation in MBE AlGaAs have also been studied and indicate that thermally activated C acceptors and nonradiative recombination centers can be passivated with this treatment.
Redistribution of implanted H in annealings of n-type GaAs
Authors: Räisänen J. , Keinonen J. , Karttunen V. , Koponen I.
Published: July 2002

Depth profiles of 60- and 100-keV protons implanted at room temperature to fluences of 1016 and 1017 H+ ions/cm2 in Si-doped n-type GaAs have been obtained using ion beam techniques. The profiles of H have been measured as a function of annealing temperature up to 820 K. The redistribution of implanted H is observed to depend on the migration of implantation-induced defects. The migration of H-atom-defect complexes is approximated by an Arrhenius process with an activation energy of 2.16±0.15 eV and a preexponential factor of 2×105 cm2/s.
Deep-level transient spectroscopy detection of defects created in epitaxial GaAs after electron-beam metallization
Authors: Nel M. , Auret F. D.
Published: July 2002

Previously, defects formed during the electron-beam metallization process have been observed both in Si and GaAs. In the present study the defects caused during EB metallization of different metals on undoped (ND−NA =1015/cm3) epitaxial GaAs layers were characterized using deep-level transient spectroscopy. Although the maximum energy of the electrons causing the defects was only 3.6 keV, the results indicated that the properties of these defects closely correspond with those of high-energy (1 MeV) electron irradiation-induced defects.
Monolithic integrated photoreceiver for 1.3–1.55-μm wavelengths: Association of a Schottky photodiode and a field-effect transistor on GaInP-GaInAs heteroepitaxy
Authors: Therani A. Hosseini , Decoster D. , Vilcot J. P. , Razeghi M.
Published: July 2002

We present a monolithic integrated circuit associating a Schottky photodiode and a field-effect transistor which has been fabricated, for the first time, on Ga0.49In0.51P/Ga0.47In0.53As strained heteroepitaxial material. Static, dynamic, and noise properties of the Schottky photodiode, the field-effect transistor, and the integrated circuit have been investigated and are reported. As an example, dynamic responsivity up to 50 A/W can be achieved at 1.3-μm wavelength for the integrated photoreceiver. The performance of the device is discussed, taking into account the integrated circuit design and the main characteristics of the material.
Dependence of photoelectric behavior of TiO2 electrodes on processing variables
Authors: Yoon Ki Hyun , Park Kyung Bong
Published: July 2002

The photoelectrochemical conversion behavior of TiO2 ceramic electrodes has been investigated as a function of electrode processing variables such as Al2O3 dopant, surface roughness, and grain size. The photocurrent increased with Al2O3 dopant up to 0.1 and 0.05 wt. % in the specimens reduced at 700 and 800 °C, respectively, and then decreased. However, the photoresponse appeared around 415 nm, which very closely corresponded to the energy band gap of TiO2(∼3.0 eV), regardless of reduction temperature and the amount of Al2O3. These results suggest a bulk excitation process involving dopant and a defect-related state in the gap of the TiO2 semiconductor. The photocurrent increased with increasing surface roughness and grain size in the undoped TiO2 ceramic electrode behavior due to adsorption and/or reflection of light and the grain-boundary effect.
Electrical activation of silicon coimplanted with nitrogen, phosphorus, or arsenic in semi-insulating GaAs substrates grown by the liquid encapsulated Czochralski method
Authors: Morrow Richard A.
Published: July 2002

We fit some existing data on the electrical activation of Si ions coimplanted with either N, P, or As ions in semi-insulating GaAs substrates grown by the liquid encapsulated Czochralski method. For one data set the activation anneal was done with proximity capped samples in a flowing H2 ambient, and for the other data sets anneals were done with dielectric capped samples. We are able to obtain good fits to all data with simple choices for the depth profiles of implanted ions if we adopt the following assumptions: (1) With no group V coimplants, the Si donors formed during a dielectric cap anneal, possibly SiGaVAs, are 100% ionized, while some of those formed during a proximity cap anneal in H2, possibly SiGaHAs, are less than 100% ionized and also serve to eliminate some arsenic vacancies. (2) All Si-related acceptors appear as BGaSiAs defects. (3) The observed enhancement of Si activation with coimplanted P is due to a decreased concentration of BGaSiAs acceptors whose formation is inhibited by P. (4) Coimplanted N or As does not inhibit the formation of BGaSiAs acceptors but, like coimplanted P at high doses, forms deep acceptors.
Thermal-wave imaging of epoxy/aluminum interfaces
Authors: No Kwangsoo , McClelland John F.
Published: July 2002

Laser-excited thermal-wave image magnitude and phase were acquired by photoacoustic detection in the 10–1000-Hz modulation frequency range on epoxy/aluminum interface systems with surface (black) and bulk (white) laser-absorbing epoxy, different planar interface distances, surface and subsurface flaws, and different surface angle boundaries. The following conclusions were reached from the thermal-wave results: (1) thermally thin epoxy on aluminum layer thicknesses can be estimated from variable modulation frequency data; (2) planar and subsurface defect interface structures of epoxy/aluminum systems are best studied by examining both magnitude and phase images; (3) thermal-wave images are more straightforward to interpret for the systems that absorb light at the irradiated surface rather than in the bulk. These conclusions are consistent with thermal diffusion length and thermal-wave reflection effects predicted by theory for surface light-absorption conditions.
Intersubband absorption of silicon-based quantum wells for infrared imaging
Authors: Yang Chan-lon , Pan Dee-Son
Published: July 2002

We have calculated the 10-μm intersubband absorptoin in quantum wells made of the silicon-based system, Si/Si1−xGex. The necessary details of the effective-mass anisotropy are included in our analysis. We find that it is readily possible to achieve an absorption constant of order of 104 cm−1 in Si quantum wells with current doping technology. For [110] and [111] growth directions, a further advantage of Si quantum wells is pointed out, namely, an allowed absorption at normal incidence due to the anisotropic effective mass in Si.
High-symmetry transition-metal sites in Ti56Ni28−xFexSi16 quasicrystals
Authors: Dunlap R. A. , McHenry M. E. , O’Handley R. C. , Bahadur D. , Srinivas V.
Published: July 2002

Rapidly solidified Ti-Ni-Fe-Si alloys are found to form a metastable phase with x-ray diffraction patterns which can be indexed to a structure with icosahedral symmetry. 57 Fe Mössbauer effect spectra show a negligible quadrupole splitting for the icosahedral phase. This observation, along with a comparison of the measured x-ray diffraction line intensities with calculated values, suggests a structure based on a decoration of a three-dimensional Penrose tiling, with transition-metal atoms in sites with local icosahedral symmetry. Magnetic susceptibility measurements show that a local moment of ∼0.2 μB forms on the Fe atom. These results are discussed in terms of possible local Fe environments.
Magnetic and structural characterization of copper/cobalt multilayers
Authors: England Craig D. , Bennett Wayne R. , Falco Charles M.
Published: July 2002

Copper/cobalt multilayers were deposited by magnetically enhanced dc triode sputtering onto single-crystal sapphire substrates. According to the binary-phase diagram, no stable alloys of copper and cobalt exist. Because the multilayers are not exposed to high temperatures, we expect no alloy formation at the interfaces. X-ray diffraction techniques demonstrate crystalline layering existing down to monolayer thicknesses of copper and cobalt. The saturation magnetization behavior of the multilayers was modeled using the perpendicular and in-plane hysteresis curves obtained using a vibrating sample magnetometer. A torque magnetometer was used to determine the net magnetic anisotropy. Here we discuss the correlation between the magnetic behavior and the structural properties.
Anomalously soft magnetic properties of boron-rich CoB thin films
Authors: Kim D. Y. , Walser R. M. , Herring J. H.
Published: July 2002

Sequentially cosputtered, amorphous thin films with an average composition of 〈Co61B39〉 were found to have an anomalously high Curie temperature (>575 K) compared to those reported for their bulk counterparts. Melt-spun Co-B ribbons, for example, with only 30-at. % B(max) have a measured Tc ≊500 K. Tc of ≤300 K would be expected for ribbons with 39-at. % B. The sputtered films crystallized at ≊675 K, but became extremely soft when annealed in a rotating field at 500 K≤Tc. The coercivity of the as-deposited films was reduced from 1 to 2 Oe to approximately 0.01 Oe and the large uniaxial anisotropies of 5–10 Oe vanished; the annealed films were isotropic. Extremely large initial permeabilities of 8000–10 000 were measured to over 10 MHz. The observed anomalies indicate that the center regions of the columnar structure of the sputtered films were enriched by ≊10% Co compared to the boundaries.
Trends of hybridization in correlated electron magnetism (invited)
Authors: Cooper B. R. , Wills J. M. , Kioussis N. , Sheng Q.-G.
Published: July 2002

Over the past decade, we have: (1) developed phenomenological theory for the behavior of ‘‘well-ordered’’ magnetic states of moderately delocalized light rare-earth and actinide systems (characteristically obtaining unusual anisotropic magnetism in agreement with experiment); (2) developed theory and computational technique to synthesize first principles electronic structure information into that phenomenological theory to make it materially predictive. As discussed in this paper, the resulting theory allows us to predict the triggering of an instability from unusual anisotropic, but well-ordered, magnetism to an unstable state. The unstable state can be either of a valence fluctuation type or of what probably is a heavy fermion type, and the detailed way in which these two types of instability is triggered differs.
Correlation of process parameters with morphology and magnetic properties of Co-based amorphous, soft, thin films
Authors: Valanju A. P. , Jeong I. S. , Kim D. Y. , Walser R. M. , Herring J. H.
Published: July 2002

The in-plane, dipolar anisotropy of a soft magnetic thin film with columnar growth features is thought to result from the alignment and eccentricity of the column cross sections. This anisotropy can be reduced either by randomizing the alignment of the elliptic axes or by reducing the eccentricity. To determine the origin of the reductions produced by processing variations, we image processed micrographs from transmission electron microscope (TEM) of sequentially sputtered, amorphous CoB alloy thin films, and correlated their in-plane magnetic anisotropies with the statistics of the nanoscale features in their morphologies. The results confirmed that the in-plane anisotropies were dominated by correlations in the alignment of the major axes of the anisotropic growth features. Reduced anisotropies were observed in obliquely deposited films grown under the influence of a substrate bias, even though the eccentricity in their growth features was significantly increased. The effect of the increased eccentricity was apparently overcompensated by a randomization in the orientation of the features of the relaxed film structures.
On the temperature dependence of the magnetoresistance of ferromagnetic alloys
Authors: Berger L. , Freitas P. P. , Warner J. D. , Schmidt J. E.
Published: July 2002

The ferromagnetic anisotropy of resistivity Δρ/ρ0=(ρ∥−ρ⊥)/ρ0 depends strongly on the nature of the dominant electron scattering centers, and is usually larger for impurity scattering than for phonon scattering. This explains why Δρ/ρ0 decreases with increasing temperature T in crystalline transition-metal alloys. Parker has proposed an expression for Δρ/ρ0 as a function of T, based on Matthiessen’s rule. It contains the parameters (Δρ/ρ0)im and (Δρ/ρ0)ph, representing the Δρ/ρ0 values for impurity scattering and phonon scattering, respectively. In an alloy series with weak electron scattering, such as Fe-Co, (Δρ/ρ0)ph is found experimentally to be positive and equal to a fixed fraction ≂ (1)/(4) of (Δρ/ρ0)im. On the other hand, in crystalline alloy series with strong, resonant electron scattering, such as Ni-Fe, Fe-Cr, Fe-V, (Δρ/ρ0)ph is found to be negative and has a minimum at the composition where (Δρ/ρ0)im is maximum.
Chaos and strange attractors of magnons observed by parallel pumping (invited)
Authors: Yamazaki Hitoshi
Published: July 2002

Parallel-pumping experiments in two ferromagnets, YIG and (CH3NH3)2CuCl4 (abbreviated as MACC) have been performed at a pumping frequency of 9 GHz band at liquid-helium temperatures. Above the spin-wave instability threshold, auto-oscillations of magnon number which include period-doubling and period-halving bifurcations, chaos, and periodic windows are observed. From experimental time-series data, return maps, fractal dimensions, positive Lyapunov exponents, phase space portraits of strange attractors, and two-dimensional Poincare sections are obtained. A Lyapunov exponent is one of the quantitative measures of a strange attractor. Lyapunov exponents are obtained by analyzing experimental return maps as 0.34 for YIG and 0.21 for MACC. Phase space trajectories, i.e., strange attractors, are constructed by the conventional time-delay method. The successive Poincare sections of the strange attractors exhibit the stretching and folding effects of sheets of trajectories which confirms the fractal characteristics of the strange attractors. The fractal dimensions of the attractors are obtained by the correlation integral method to be 2.0 for YIG and 2.3 for MACC.
Kinetics of titanium silicide formation on single-crystal Si: Experiment and modeling
Authors: Pico C. A. , Lagally M. G.
Published: July 2002

The growth kinetics of titanium silicide grown from thin-film Ti-on-Si(100) and Si(111) reaction couples are investigated using primarily Auger electron spectroscopy. A Ti/precursor-phase/TiSi2/Si layered structure is found. The growth law of TiSi2 depends on substrate orientation. An activation enthalpy of ΔH=2.5–2.6±0.25 eV/atom, substantially higher than previously reported values, is determined. The total silicide growth (TiSi2+precursor) has nearly a parabolic time dependence implying that the precursor phase forms as ‘‘At1/2−Bt’’ using Si(111) as a substrate. A model based on mass diffusion from a moving interface is presented and is shown to be in good agreement with the experimental results. This model, which is used to determine the diffusion coefficient of Si in the precursor phase, can be applied to other similar binary compound systems containing line compounds.
New scaling relation for sputtered NbN films
Authors: Capone II D. W. , Gray K. E. , Kampwirth R. T.
Published: July 2002

A scaling relationship has been discovered between the sputtering rate and the partial pressure of argon PAr, which leaves the superconducting properties of NbN films invariant. As PAr increases for a given sputtering rate, there is a linear reduction of Tc together with a rapid increase, followed eventually by saturation, in Hc2 at 4.2 K. These produce a maximum in Jc (measured at 19 T and 4.2 K) at a particular value of PAr. Films exhibiting nearly the same set of superconducting properties and microstructures can be made at a higher fixed sputtering rate if the values of PAr are multiplied by a constant scale factor. This scaling relation is found to hold for two separate sputtering systems, one of which uses a standard diffusion pump while the other uses an oilless turbo pump. Additional comparisons with the results of others reinforces the conclusion that the scaling relationship is universal and thus may provide some insight into those factors in the sputtering process which are important for determining the superconducting properties and microstructure of sputtered NbN films.
Shallow melting of thin heavily doped silicon layers by pulsed CO2 laser irradiation
Authors: James R. B. , Christie W. H.
Published: July 2002

We show that an extremely shallow (≲800 Å) melt depth can be easily obtained by irradiating a thin (∼200 Å) heavily doped silicon layer with a CO2 laser pulse. Since the absorption of the CO2 laser pulse is dominated by free-carrier transitions, the beam heating occurs primarily in the thin degenerately doped film at the sample surface, and there is little energy deposited in the underlying lightly doped substrate. For CO2 pulse-energy densities exceeding a threshold value of about 5 J/cm2, surface melting occurs and the reflectivity of the incident laser pulse increases abruptly to about 90%. This large increase in the reflectivity acts like a switch to reflect almost all of the energy in the remainder of the CO2 laser pulse, thereby greatly reducing the amount of energy available to drive the melt front to deeper depths in the material. This is in contrast to the energy deposition of a laser pulse that has a photon energy exceeding the band gap, in which case the penetration depth of the incident radiation is only weakly affected by the free-carrier density. Transmission electron microscopy shows no extended defects in the near-surface region after CO2 laser irradiation, and van der Pauw electrical measurements verify that 100% of the implanted arsenic dopant is electrically active. Calculated values for the melt depth versus incident pulse-energy density (EL) indicate that there exists a window where the maximum melt-front penetration increases slowly with increasing EL and has a value of less than a few hundred angstroms. For silicon specimens having a thin degenerately doped film at the surface and a lightly doped substrate, the two primary reasons for using a CO2 laser pulse to achieve very shallow melt depths are (1) the pulse energy is deposited only in the thin surface layer and (2) the melting of this layer causes the reflectivity to jump abruptly to a value of almost unity.
Stability of a ferroelectric copolymer-induced inversion layer in silicon
Authors: Noirhomme B. , Filion A. Y. , Caron L. G. , Rambo A. , Lebel J.
Published: July 2002

A copolymer of vinylidene fluoride and tetrafluoroethylene is solution cast on a p-type silicon wafer. A strong inversion is produced at the silicon surface when the copolymer film is corona charged or when a subsequently evaporated aluminum gate is biased. Although the dipole alignment in the copolymer is stable, the inversion decays. The decay of the inversion layer is monitored by measuring the decay of the surface channel currents between a source and a drain. For the case of corona charging, an initial rapid decay not observed in the gated device is explained by the motion of excess positive charges (dielectric relaxation). The slow decay subsequently observed is explained in terms of the thermionic injection of inversion electrons across an interface barrier and also using a space-charge-limited injection model. Both models fit the results and their validity is discussed.