bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison of boron and phosphorus diffusion and dislocation loop growth from silicon implants into silicon
Authors: Xu Jingwei , Krishnamoorthy V. , Jones Kevin S. , Law Mark E.
Published: July 2002

Transient enhanced diffusion (TED) results from implantation damage creating enhanced diffusion of dopants in silicon. This phenomenon has mostly been studied using boron marker layers. We have performed an experiment using boron, phosphorus, and dislocation markers to compare TED effects. This experiment shows that phosphorus is enhanced significantly more than boron during damage annealing. Dislocation growth indicates that a number of interstitials greater than the damage dose is captured during these anneals. The time to saturate the dislocation growth agrees well with phosphorus diffusion saturation, and is greater than the boron saturation.
Quantitative assessment of the effects of carrier screening on the average electric field in a GaAs-based p–i–n nanostructure under subpicosecond laser excitation
Authors: Tsen K. T. , Joshi R. P. , Salvador A. , Botcharev A. , Morkoc H.
Published: July 2002

We have used electric-field-induced Raman scattering to quantitatively assess the effects of carrier screening on the average electric fields in a GaAs-based p–i–n nanostructure semiconductor under subpicosecond laser photoexcitation. Our experimental results demonstrated that the effects of carrier screening on the average electric field were negligible for a photoexcited electron–hole pair density of n⩽1015 cm−3. As the density of photoexcited carriers increased, we observed a significant decrease of the average electric field. In particular, for n=1018 cm−3, a decrease of electric field of about 50% was found. All of these experimental results were explained by ensemble Monte Carlo simulations and very good agreement has been obtained.
ZnS:Tm grown by metalorganic chemical vapor deposition with Cl codoping
Authors: Kato Akira , Katayama Masayuki , Mizutani Atsushi , Ito Nobuei , Hattori Tadashi
Published: July 2002

ZnS:Tm and ZnS:Tm,Cl thin films were grown by metalorganic chemical vapor deposition (MOCVD), using diethylzinc, H2S, Tm(thd)3 (thd=2,2,6,6-tetramethyl-3,5-heptanedione), and HCl. The ZnS:Tm did not contain oxygen which might be introduced through the thd-radical. It thus has only codopant-free Tm3+ luminescent centers probably associated with native defects. The electroluminescence (EL) spectrum of the ZnS:Tm,Cl showed three satellite emission lines in addition to the original emission of the ZnS:Tm, indicating the existence of Tm–Cl complex centers. In contrast, the photoluminescence (PL) spectrum of the ZnS:Tm,Cl under host excitation showed no discernible satellite emission lines. Hence, though the Tm ions in the Tm–Cl complex centers are expected to be charge compensated by Cl or a certain Cl-induced defect, they are rather inactive in the PL excitation while active in the EL excitation. The same properties were observed for the MOCVD-grown ZnS:Sm and ZnS:Sm,Cl [A. Kato, M. Katayama, A. Mizutani, N. Ito, and T. Hattori, J. Appl. Phys. 77, 4616 (1995)], and therefore they probably occur for other rare-earth luminescent centers with Cl codopant.
Deep emission band at GaInP/GaAs interface
Authors: Uchida Kazuo , Arai Takayuki , Matsumoto Koh
Published: July 2002

We have investigated the 1.46 eV deep emission band observed in the photoluminescence (PL) spectra of 100-Å-thick GaAs/Ga0.52In0.48P single quantum wells grown by metal-organic vapor-phase epitaxy. We have found that the application of GaP layers at both lower and upper GaAs/Ga0.52In0.48P interface is necessary to achieve 1.52 eV emission from the well; otherwise only the deep emission band at 1.46 eV is observed in the 77 K PL spectrum. Time-resolved PL and temperature-dependent PL measurements show that the 1.46 eV deep emission is due to recombination of electrons in the conduction band of Ga0.52In0.48P and holes bound to acceptors in GaAs at the GaAs/Ga0.52In0.48P interface, which forms type-II band alignment. We propose that the application of GaP layers modifies the band alignment from type II to type I, and makes the emission from the well observable.
Resonant micro-Raman investigations of the ZnSe–LO splitting in II–VI semiconductor quantum wires
Authors: Lermann G. , Bischof T. , Materny A. , Kiefer W. , Kümmell T. , Bacher G. , Forchel A. , Landwehr G.
Published: July 2002

Resonant micro-Raman spectroscopy was performed on ZnSe/Cd0.2Zn0.8Se quantum wires. The LO phonon frequencies observed for the wires were investigated as a function of the temperature and the wire width. ZnSe/Cd0.2Zn0.8Se quantum wells grown by molecular beam epitaxy were patterned by electron beam lithography and wet chemical etching to obtain quantum wires with widths down to the sub-100 nm region. The sample under investigation consisted of different areas each containing wires with well defined widths. Micro-Raman spectroscopy enabled us to perform measurements on a particular area of the sample. By this method Raman spectra could be obtained as a function of the wire width. The sample temperature was chosen to be between room temperature and 9 K. A splitting of the ZnSe and the ZnSe-like LO phonons of the ZnSe/ Cd0.2Zn0.8Se quantum wires was observed. The size of this splitting was found to depend only on the wire width and not on the temperature. This behavior is due to the strain relaxation, which occurs at the edge zone of each quantum wire. The increasing influence of the edge zone for decreasing wire width is the reason for the wire width dependence of the splitting between the ZnSe and the ZnSe-like LO phonon. As a result, the importance of partial strain relaxation for the discussion of the vibronic properties of the patterned semiconductor systems was confirmed.
Evolution of the transport critical current density and irreversibility field as a function of heat treatment and pressing pressure during processing of Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes
Authors: Edelman H. S. , Parrell J. A. , Larbalestier D. C.
Published: July 2002

Extended electric field-current density characteristics taken on the bare cores of monofilament (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes at 77 K have been used to measure the irreversibility field, H*, and the critical current density, Jc, at different stages of tape processing. The number of heat treatments and the uniaxial pressing pressure were the experimental variables. Both H* and Jc increased substantially with heat treatment and with deformation pressure. The data are consistent with an improvement in Jc from two factors, one being an increase in the 2223 phase fraction with increasing heat treatment, the second, independent cause being an increase in the flux pinning properties of the composite. The experiments show that improving Jc involves control of at least three factors: enhancing the volume fraction of 2223 phase; increasing flux pinning; and enhancement of the connectivity of the grain boundaries that lie within the current path.
Temperature dependence of elastic, dielectric, and piezoelectric properties of “single crystalline’’ films of vinylidene fluoride trifluoroethylene copolymer
Authors: Omote Kenji , Ohigashi Hiroji , Koga Keiko
Published: July 2002

Elastic, dielectric, and piezoelectric constant matrix elements of a “single crystalline’’ (SC) film of vinylidene fluoride trifluoroethylene copolymer, P(VDF/TrFE), in which the orthorhombic [001] and [110] axes of fully extended chain crystals are preferentially oriented parallel to the stretching axis and normal to the surface, respectively, were measured at temperatures ranging from 10 K to the Curie point (402–404 K) by using a piezoelectric resonance method. All of the electromechanical coupling factors (k31, k32, k33, k24, and k15) are larger than those of conventional lamellar crystalline films. Some of the matrix elements for a P(VDF/TrFE) single crystal are derived from the measured values of constant matrix elements for the SC film. Some features characteristic of the SC film are revealed. The SC film has a large Young’s modulus for the stretching direction (1/s11) (121 GPa at 10 K). The properties related to the molecular motions along the chain axis, such as 1/s11, shear stiffness constant c55, shear piezoelectric constant e15, etc., exhibit strong relaxations around 250 K. The origin of these relaxations in the crystalline phase is discussed.
Studies of two-photon pumped frequency-upconverted lasing properties of a new dye material
Authors: He Guang S. , Yuan Lixiang , Cui Yiping , Li Ming , Prasad Paras N.
Published: July 2002

The two-photon absorption (TPA), TPA-induced frequency upconversion emission, and two-photon-pumped (TPP) lasing properties of a new dye, trans-4[p-(N-hydroxyethylN-methylamino)stryryl]-N-methylpyridinium iodide (abbreviated as ASPI) were experimentally investigated. This new dye has a moderate TPA cross section (σ2≈3.9×20−20 cm4/GW in benzyl alcohol), but exhibits a low lasing threshold and high lasing efficiency when pumped with a 1064 nm pulsed laser beam. Furthermore, the TPA-induced fluorescence yield is strongly dependent on the polarity of the solvent, making it a promising dye for sensing applications. The spectral, temporal, and spatial structures as well as the output/input characteristics of the TPP cavity lasing and the superradiant (cavityless) lasing are systematically measured using a 1 cm path quartz cuvette filled with the ASPI solution or a doped polymer rod. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the ∼615 nm upconverted cavity lasing energy was found to be as high as ∼17%.
Micromagnetic simulation of nanoscale films with perpendicular anisotropy
Authors: Nowak U.
Published: July 2002

A model is studied for the theoretical description of nanoscale magnetic films with high perpendicular anisotropy. In the model, the magnetic film is described in terms of single domain magnetic grains with Ising-like behavior, interacting via exchange as well as via dipolar forces. Additionally, the model contains an energy barrier and a coupling to an external magnetic field. Disorder is taken into account in order to describe realistic domain and domain wall structures. The influence of a finite temperature as well as the dynamics can be modeled by a Monte Carlo simulation. Many of the experimental findings can be investigated and at least partly understood by the model introduced above. For thin films, the magnetization reversal is driven by domain wall motion. The results for the field and temperature dependence of the domain wall velocity suggest that for thin films hysteresis can be described as a depinning transition of the domain walls rounded by thermal activation for finite temperatures.
Nitrogen-doping effects on electrical, optical, and structural properties in hydrogenated amorphous silicon
Authors: Masuda Atsushi , Itoh Ken-ichi , Matsuda Kazuko , Yonezawa Yasuto , Kumeda Minoru , Shimizu Tatsuo
Published: July 2002

Electrical, optical, and structural properties of nitrogen-doped hydrogenated amorphous silicon films with the N content up to about 12 at. % are systematically studied using electrical conductivity measurements, electron-spin resonance, light-induced electron-spin resonance, constant photocurrent method, optical absorption spectrophotometry, IR absorption spectroscopy, Raman scattering spectroscopy, and x-ray photoelectron spectroscopy. Both behaviors of the dark conductivity and the charged-dangling-bond density against the N content suggest that most of charged dangling bonds originate from potential fluctuations. Only part of charged dangling bonds created by the N doping up to 2 at. % originate from positively charged fourfold-coordinated N. The decay behavior of the photoconductivity after turning off the probing light also supports that most of charged dangling bonds in N-doped hydrogenated amorphous silicon do not originate from positively charged fourfold-coordinated N. A possible origin of potential fluctuations is increased fluctuations in the net electron density at Si sites accompanying structural randomness caused by the N doping.
Magnetic tunneling applied to memory (invited)
Authors: Daughton J. M.
Published: July 2002

Random access magnetoresistive memories have been designed using anisotropic magnetoresistive (AMR) material and more recently giant magnetoresistive (GMR) material. The thin films in these memories have low sheet resistivities (about 10 Ω/sq), resulting in cell resistances of 10 to 100 Ω at competitive areal densities. High sense currents of a mA or more are required to get signals on the order of a few mV. Spin dependent tunneling (SDT) devices are intrinsically high impedance, with typical equivalent resistance values of 104–109 Ω for a square micron area. SDT cells have the potential for signals on the order of 10 mV with lower sense currents, and hence, faster access times than GMR memory. A GMR pseudospin valve memory concept is presented for comparison with SDT memory. Three different design approaches are discussed for SDT memory: (1) high-density memory arrays similar to those in AMR and GMR memories, (2) a transistor per cell approach similar to semiconductor dynamic random access memory, and (3) embedded SDT devices in a flip–flop cell similar to semiconductor static random access memory. The conclusions are: (1) SDT memory is potentially higher speed than GMR memory, (2) SDT memory has no area advantage compared with dense GMR memory, and (3) risks with SDT memory include (a) processing ultrathin dielectric layers uniformly and reliably that are compatible with integrated circuits and (b) attaining sufficiently low impedance levels to get a satisfactory signal-to-noise ratio in a small area cell.
Photothermal imaging as a tool to study phase transitions in binary mixtures of liquid crystals
Authors: Hadj Sahraoui A. , Kolinsky C. , Delenclos S. , Daoudi A. , Buisine J. M.
Published: July 2002

The photothermal beam deflection technique is used to study a binary mixture of liquid crystals in a contact preparation. The photothermal signal is generated while scanning the contact preparation. The interphase boundaries between crystal-smectic A and smectic A-nematic are detected, and their displacement is monitored as a function of temperature. The theoretical analysis of the numerically simulated signal is presented. In particular the influence of the modulation frequency on the sensitivity in the detection of interphase boundaries is investigated.
Low 1/f flux noise in sputtered YBa2Cu3O7−x bicrystal dc-superconducting quantum interference devices
Authors: Sarnelli E. , Camerlingo C. , Russo M. , Torrioli G. , Castellano M. G.
Published: July 2002

YBa 2 Cu 3 O 7−x bicrystal dc-superconducting quantum interference devices (SQUIDs) and single layer magnetometers working at 77 K have been fabricated and analyzed. Samples have been made in situ by cylindrical magnetron dc sputtering on [001] SrTiO3 bicrystal substrates. Magnetic flux noise levels and magnetic field sensitivities by standard flux-locked-loop electronics have been measured out on dc-SQUIDs and magnetometers, respectively. Flux noise levels as low as a few μΦ0Hz−1/2 in the white noise regime have been measured in SQUIDs, whereas the magnetic field sensitivity of the magnetometers was influenced by external sources. A comparison of experimental data with analytical expressions modelling the behavior of high Tc SQUIDs has been carried out, with special reference to the flux-to-voltage transfer parameter and noise characteristics. Finally, a reduction of 1/f noise of the SQUIDs has been achieved by a wide band bias reversal electronics.
Atomic configurations of Er centers in GaAs:Er,O and AlGaAs:Er,O studied by site-selective luminescence spectroscopy
Authors: Takahei K. , Taguchi A. , Hogg R. A.
Published: July 2002

Er-doped GaAs codoped with oxygen was studied by site-selective measurements of photoluminescence spectra and photoluminescence-excitation spectra directly exciting the 4f-shell electrons of one kind of Er center at a time. Within one sample, more than 10 kinds of distinctly different Er centers, showing different Er-related spectra, were observed, although its host-excited photoluminescence spectrum is dominated by the luminescence from one kind of Er center. The atomic configuration of that center has been identified as an Er atom located at the Ga sublattice with two adjacent oxygen atoms (Er-2O center). Seven kinds of Er centers in GaAs:Er, O and two kinds of Er centers in AlGaAs:Er, O were studied in detail. The numbers of lines and the magnitudes of energy separations among the lines in each spectrum indicate that the Er atoms of all nine kinds of centers are coupled with oxygen atoms and have noncubic symmetry. The nine Er centers were grouped into several classes according to similarities in their spectra which should reflect symmetries of the Er centers. The atomic configurations of two classes of Er centers are discussed in detail. The Er centers of both classes have a nearest-neighbor site atomic configuration similar to that of the Er-2O center with a symmetry close to rhombic C2v, but Er centers in the two classes have different types of deviation from C2v due to the difference in the second-nearest-neighbor atomic configurations of the Er atoms. We also discuss a large difference in the efficiency of the Er-related luminescence under host photoexcitation caused by the difference in the second-nearest-neighbor atomic configurations.
Vacuum arc deposition of Ti films with transverse current injection
Authors: Parkansky N. , Alterkop B. , Schuster W. , Boxman R. L. , Goldsmith S.
Published: July 2002

The influence of imposing an electrical field parallel to the substrate of a growing metallic film was studied experimentally and analyzed theoretically. Ti films were deposited onto glass substrates using a filtered vacuum arc source while a voltage U of 0–300 V was applied between electrodes spaced 16 mm apart on the substrate surface. The current through the film was monitored during the deposition. Several characteristic stages of current evolution were observed after arc initiation: (1) an initial sharp jump of the current, (2) a stage of constant, relatively low current, (3) rapid current growth, (4) slower current growth, and (5) linear growth. Analyses showed that stages (1) and (2) are connected with current conduction through the plasma rather that through the sample while stages (3) and (4) are connected with tunneling and percolation during film formation. The tunneling stage could be distinguished only for U⩽6 V; in other cases, conduction through the plasma obscured the observation. The percolative exponent increased from 1.0 to 2.68 and the critical thickness decreased by a factor of 4.3 with an increased U from 1 to 60 V.
Enhanced real-space transfer in δ-doped GaAs/In0.1Ga0.9As/In0.25Ga0.75As two-step channel heterojunctions
Authors: Su Jan-Shing , Hsu Wei-Chou , Lin Wei , Lin Yu-Shyan
Published: July 2002

A two-step channel In0.1Ga0.9As/In0.25Ga0.75As heterostructure real-space transfer transistor grown by low-pressure metalorgonic chemical vapor deposition is implemented. By virtue of δ doping, shallow ohmic contacts and two-step channel, a high peak-to-valley current ratio up to 260 000 at 300 K can be obtained at low collector voltage (Vc=3 V). Moreover, from Shubnikov–de Haas (SdH) measurements, we observe a positive persistent-photoconductivity effect and variations of quantum lifetime. The SdH result is in good agreement with the critical drained-to-source onset voltage of negative differential resistance.
Defect study in amorphous silicon/crystalline silicon solar cells by thermally stimulated capacitance
Authors: Jagannathan B. , Anderson W. A.
Published: July 2002

Interface traps created by amorphous silicon (a-Si) deposition using dc magnetron sputtering or a microwave plasma-enhanced chemical vapor deposition method onto p-type crystalline silicon (c-Si) substrates in solar cell structures were studied by thermally stimulated capacitance. The trap properties (type, energy, and concentration) have been estimated as a function of various cell fabrication conditions. Plasma deposition of a-Si is seen to induce electron traps when the c-Si substrates are pretreated with hydrofluoric acid, and hole traps when a thin oxide layer is initially present on the c-Si. A strong correlation is observed between the trap activation energies when electron trapping centers are present and the corresponding photoresponse of these solar cells. Solar cells with 10% efficiency fabricated by a-Si sputtered at 64 W of power, exhibit 3×1014 cm−3 trapping centers with an activation energy of 0.44 eV.
Growth and characterizations of GaN on SiC substrates with buffer layers
Authors: Lin C. F. , Cheng H. C. , Chi G. C. , Feng M. S. , Guo J. D. , Minghuang Hong J. , Chen C. Y.
Published: July 2002

High quality GaN epitaxial layers were grown on 6H–SiC substrates by using low-pressure metalorganic chemical vapor deposition method. Samples employing a three-period GaN/Al0.08Ga0.92N (100 Å/100 Å) as a buffer layer produce a good quality GaN epitaxial layer, with mobility and carrier concentration of 612 cm2/V⋅s and 1.3×1017 cm−3 (at 300 K), respectively. The enhanced electron mobility in the Al0.08Ga0.92N/GaN heterostructures is also observed. By using the van der Pauw method of Hall measurement, the sheet carrier density and mobility at 4.2 K for the Al0.08Ga0.92N/GaN heterostructure are 5.8×1012 cm−2 and 5300 cm2/V⋅s, respectively. Strong SdH (Shubnikov–de Haas) oscillations were observed to confirm the two-dimensional electron gas (2DEG) phenomenon at the AlGaN/GaN top heterointerface. In addition, an extra SdH oscillation also resulted from the high-quality 2DEG channel of the GaN/AlGaN bottom heterointerface.
A study of interlayer exchange coupling in a Co/Cr/Co trilayer using transmission electron microscopy
Authors: Daykin A. C. , Jakubovics J. P. , Petford-Long A. K.
Published: July 2002

Magnetic induction maps from a sputter-deposited Co/Cr/Co trilayer have been obtained at different points of the hysteresis cycle, using a conventional transmission electron microscope. The sample shows hysteresis, with nearly parallel alignment of the magnetization in the two Co layers at remanence, but areas of antiparallel alignment developing in reverse fields. Such areas occur in similar positions at opposite points of the hysteresis loop. The strongly correlated domain patterns seen in opposite field directions suggest that the interlayer exchange coupling varies spatially. The parallel alignment observed at remanence suggests the presence of an energy barrier that needs to be overcome before antiparallel alignment can be formed. This conclusion is supported by observations of the film in a demagnetized state.
The breakdown and glow phases during the initiation of discharges for lamps
Authors: Pitchford L. C. , Pérès I. , Liland K. B. , Boeuf J. P. , Gielen H.
Published: July 2002

High intensity discharge (HID) lamps are often initiated by the application of one or more short, high-voltage, breakdown pulses superimposed on a 50 or 60 Hz generator voltage. A successful transition from the breakdown event to steady-state operating conditions in HID lamps requires that the lamp-circuit system be adequate to sustain the plasma created during breakdown until the electrodes are heated to thermionic temperatures. In this article, we use a one-dimensional (in the axial direction) transient discharge model to study the conditions needed to sustain the cold-cathode discharge after a breakdown event has occurred. While the application of our one-dimensional model to real lamps is approximate, we find that the model predictions are consistent with experimental results in HID lamps, a few of which are presented here. The main conclusion from this work is that, after breakdown, the voltage necessary to sustain a glow discharge is dependent on the source impedance, the gas composition, and on the plasma density created by the breakdown event.
Activation of electrical carriers in Zn-implanted InP by low-power pulsed-laser annealing
Authors: Pizzuto C. , Zollo G. , Vitali G. , Karpuzov D. , Kalitzova M.
Published: July 2002

Low-power pulsed-laser annealing was applied to Zn+-implanted InP samples. In order to avoid surface oxidation during the treatment, the laser irradiation was carried out in inert ambient of nitrogen at different pressures. The analytical techniques used include Rutherford backscattering spectroscopy, reflection high energy electron diffraction, and electrical measurements. The highest carrier activation, about 80%, was achieved at the same laser power density (6.5 MW/cm2) at which the best crystal recovery was obtained.
Lattice parameter and thermal expansion of monocrystalline silicon
Authors: Bergamin A. , Cavagnero G. , Mana G. , Zosi G.
Published: July 2002

We present experimental results for the lattice parameter and the thermal expansion of a silicon monocrystal at room temperature. In the precision determination of the Avogadro constant, an accurate knowledge of the value of the thermal expansion of silicon monocrystals is necessary so that their unit cell and molar volumes can both be referred to the same temperature. Recent advances in x-ray interferometry have made it possible to reduce the uncertainty of that value by one order of magnitude.
ADDENDUM: “Nonreciprocal differential detection method for scanning Kerr-effect microscopy” [J. Appl. Phys. 81, 5015 (1997)]
Authors: Silva T. J. , Kos A. B.
Published: July 2002

It has come to our attention that images of static domain patterns in Permalloy using a quadrant-detection scheme were first obtained by Clegg, Heyes, Hill, and Wright in 1991.12 Thus, our claim to have been the first group to image static domains using such a method was incorrect. The description of the instrument and its principle of operation remain correct. The quality of the image presented3 represents an improvement over previously published results using a similar detection scheme, permitting an unambiguous determination of Néel wall polarity within the imaged domain structures.
The effect of an asymmetric band of localized deep donors on the electronic transport of high-purity n-type InP
Authors: Benzaquen R. , Benzaquen M. , Leonelli R.
Published: July 2002

We have investigated the effect of the shape of a band of localized deep donors on the electronic transport of three high-purity n-type InP epilayers. A model accounting for a broad asymmetric band of localized deep donors or complexes of unknown origin, centered 167 meV below the conduction band edge with a width of about 245 meV, provided a remarkable description of both the Hall mobility and Hall electronic concentration in the temperature range of 4.2–300 K.
Hydrogen redistribution in thin silicon dioxide films under electron injection in high fields
Authors: Gadiyak G. V.
Published: July 2002

A macroscopic transport model for (i) the hydrogen redistribution in a silicon dioxide and (ii) electron-hole transport and accumulation of charge in a silicon dioxide (SiO2) layer during electrical stress are proposed in this article. The set of equations for the first model consists of two diffusion equations for the “free” atomic and molecular hydrogen and rate equations for the bound hydrogen and dangling bonds (hydrogen trap). The second model considers the kinetics of charge accumulation on the existing and new trapping centers created during electrical stress using rate equations for electrons and holes and the Poisson equation. The fitting parameters of the model have been found. Redistribution of hydrogen caused by hot-electron injection and internal photoemission for the metal-oxide-semiconductor (Al−SiO2−Si)-capacitor have been studied by a numerical simulation method. The results have been compared to experimental data.
Growth kinetics of CoSi formed by ion beam irradiation at room temperature
Authors: Baba A. , Aramaki H. , Sadoh T. , Tsurushima T.
Published: July 2002

Growth kinetics of cobalt silicide layers formed by ion beam irradiation was investigated at a temperature between room temperature and 100 °C. The CoSi phase was identified by x-ray diffraction of Co/Si samples irradiated with 25 keV argon ions to a dose of 2.0×1015 cm−2. The number of intermixed silicon atoms in the CoSi layers was evaluated as a function of dose, dose rate, and nuclear energy deposition rate at the Co/Si interface for samples irradiated with 40 keV focused silicon ion beams. The growth is shown to be diffusion-limited and attributed to radiation-enhanced diffusion with an activation energy of 0.16 eV. The number of intermixed silicon atoms is approximately proportional to the nuclear energy deposition rate at the initial Co/Si interface, while it is independent of dose rate, which shows that the CoSi phase is formed without contribution of the sample heating caused by irradiation.
The third subband population in modulation-doped InGaAs/InAlAs heterostructures
Authors: Li Hanxuan , Wang Zhanguo , Liang Jiben , Xu Bo , Wu Ju , Gong Qian , Jiang Chao , Liu Fengqi , Zhou Wei
Published: July 2002

We have observed the population of the third (n=3) two-dimensional electron subband of InGaAs/InAlAs modulation-doped structures with very dense sheet carrier density by means of Fourier transform photoluminescence (PL). Three well-resolved PL peaks centered at 0.737, 0.908, and 0.980 eV are observed, which are attributed to the recombination transitions from the lowest three electron subbands to the n=1 heavy-hole subband. The subband separations clearly exhibit the features of the stepped quantum well with triangle and square potential, consistent with numerical calculation. Thanks to the presence of the Fermi cutoff, the population ratio of these three subbands can be estimated. Temperature and excitation intensity dependence of the quantum well luminescence intensity is also analyzed.
Improvement of infrared detector performance in carrier depleted strained layer type II superlattices
Authors: Grein C. H. , Ehrenreich H.
Published: July 2002

The combined effects of suppressing Auger recombination in strained layer superlattices (SL), photon recycling, and the suppression of both Auger and radiative recombination with carrier depletion are calculated quantitatively for a 11 μm 35.9 Å InAs/15.7 Å In0.225Ga0.775Sb and a 3.5 μm 16.7 Å InAs/35 Å In0.25Ga0.75Sb SL operating at temperatures between 200 and 300 K. The results are compared to their HgCdTe counterparts. The SL performance is better in all cases. However, the carrier concentrations required for background limited performance (300 K, 2π field of view), ranging between about 1×1013 and 4×1013 cm−3 at 300 K in both SLs, are seen to be impractically low. The carrier concentration in a 11 μm photon detector yielding equivalent performance to a 300 K thermal detector is about 1014 cm−3. Large performance enhancement using carrier depletion therefore appears impractical even in optimized SLs.
Differential type giant magnetoresistive memory using spin-valve film with a NiO pinning layer
Authors: Yamane Haruki , Kobayashi Masanobu
Published: July 2002

The giant magnetoresistive (GMR) memory device of differential type is able to perform data readout without a magnetic field, and has many highly efficient properties, such as a nonvolatile, nondestructive readout, high-speed access, large output signal, and low electric power consumption. We have demonstrated data read/write of this memory by means of a spin-valve film with a NiO pinning layer. The spin-valve film was constructed of a multilayered structure [NiO/NiFeCo/Cu/NiFeCo], and exhibited the appropriate properties of a storage element, such as a MR ratio of 5%, a squareness ratio of unity, a writing field of 20 Oe, and a high corrosion resistance. The differential type memory device is constructed of a memory cell including two storage elements, in which the word currents of each element are in opposite directions. The information storage is performed by storing different resistance values in each element. The data readout of this memory is accomplished by sensing the differentiation of each element output, therefore magnetic field is not necessary for the readout process. The data read/write was established by observing a step-shape output signal: [plus or minus] against a three-step input signal: [zero/plus/zero/minus].
A deep level transient spectroscopy characterization of defects induced in epitaxially grown n-Si by low-energy He-ion bombardment
Authors: Auret F. D. , Deenapanray P. N. K. , Goodman S. A. , Meyer W. E. , Myburg G.
Published: July 2002

Epitaxially grown n-Si was bombarded with low-energy (1 keV) He ions. Deep level transient spectroscopy revealed that this introduced four prominent defects with energy levels at 0.14, 0.20, 0.30, and 0.55 eV, respectively, below the conduction band. The electronic properties and annealing behavior of these defects are different to those of the main defects, namely, divacancies (V2) and vacancy-phosphorous centers, observed after 5.4 MeV He-ion bombardment of the same material. We propose that, except for the defect with an energy level at Ec−0.14 eV, the defects introduced by 1 keV He-ion bombardment of n-Si may be related to: (1) vacancy clusters larger than divacancies, or (2) incorporation of He and H into V2 or higher-order vacancy clusters.
Extension of the primary solidification region of Nd2Fe14B by levitation of undercooled melts
Authors: Hermann R. , Löser W.
Published: July 2002

Undercooled Nd–Fe–B melts with compositions near the Nd2Fe14B phase (Φ phase) were studied by the electromagnetic levitation technique. In situ measurements of the solidification kinetics were accomplished and melt drops with controlled undercooling were quenched onto chill substrates in order to reveal the solidification sequence and microstructure formation processes. Crystal growth velocities of the Φ phase of the order of 1 mm s−1 were estimated from in situ measurements. Consistent with the nucleation theory, which predicts primary γ-Fe phase crystallization up to 650 K undercooling for the stoichiometric alloy, γ-Fe nucleation could not be avoided during undercooling but the quenching of the melt drops led to dissolution of the γ-Fe nuclei during Φ-phase formation. The γ-Fe phase growth was suppressed in a seam adjacent to the chill surface, whereas Fe dendrites occurred in the remaining parts of the quenched samples. Reduced solute rejection on growth is believed to be responsible for the preferred metastable Φ-phase formation from the undercooled melt on chill substrates. The investigation gives some clues to understand different microstructures and magnetic properties of powder precursors for permanent magnets obtained from different rapid solidification routes.
Soft x-ray resonant magnetic reflectivity study of thin films and multilayers
Authors: Tonnerre J. M. , Sève L. , Barbara-Dechelette A. , Bartolomé F. , Raoux D. , Chakarian V. , Kao C. C. , Fischer H. , Andrieu S. , Fruchart O.
Published: July 2002

Soft x-ray resonant magnetic reflectivity measurements on thin films and multilayers in a transverse geometry using linear polarized photons are presented. Magneto-optic calculations taking into account the layer roughness allows us to reproduce all the experimental features of the angular and energy reflectivity curves as well as the asymmetry ratio in both cases. Application to FexMn1−x alloy films epitaxially grown on Ir(001) brings more insights on the magnetic transition occurring at x=0.75.
Switching phenomena in chromium-doped vanadium sesquioxide
Authors: Chudnovskii F. A. , Pergament A. L. , Stefanovich G. B. , Metcalf P. A. , Honig J. M.
Published: July 2002

( V 1−x Cr x ) 2 O 3 with x=0.012 exhibits both S- and Z-type switching characteristics in studies of current–voltage curves at temperatures 170–230 K. The effects are linked to electrothermal instabilities and to filamentary conduction. The samples are stable under voltage cycling in appropriate temperature ranges.
Photoelectron spectroscopy of chalcopyrites and Zn based II–VI semiconductor heterostructures
Authors: Wörz M. , Pschorr-Schoberer E. , Flierl R. , Preis H. , Gebhardt W.
Published: July 2002

We have investigated CuInSe2 surfaces as well as the interfaces of the systems ZnSe/CuInSe2 and ZnS/CuInSe2 by vacuum ultraviolet photoelectron spectroscopy with synchrotron radiation. The CuInSe2 substrates are prepared with a hydrogen plasma and show high quality surfaces suitable for further growth of ZnSe in order to determine the valence-band offset of ZnSe/CuInSe2. At the surface of CuInSe2 Se atoms have been replaced by Te or S atoms, so that CuInTe2 or CuInS2 surfaces were formed. We determined the valence-band offsets of CuInTe2/CuInSe2 and CuInS2/CuInSe2 to be ΔEvb(CuInTe2/CuInSe2)=(0.85±0.05)eV and ΔEvb(CuInS2/CuInSe2)=(0.87±0.05)eV. ΔEvb(ZnSe/CuInSe2)=−(0.5±0.1)eV is in good agreement with values from literature. Furthermore we have examined the interface ZnS/CuInS2 and obtained the valence-band offset ΔEvb(ZnS/CuInS2)=−(2.3±0.1)eV.
Perpendicular magnetic anisotropy and magnetic domain structure in sputtered epitaxial FePt (001) L1 films
Authors: Thiele J.-U. , Folks L. , Toney M. F. , Weller D. K.
Published: July 2002

The magnetic domain structure and magnetization curves of chemically ordered epitaxial FePt (001) films with perpendicular magnetic anisotropy are discussed. Films were dc magnetron sputtered from a Fe50Pt50 alloy target onto Pt seeded MgO (001) at substrate temperatures of 550 °C. The thickness of the FePt layers was varied between 18 and 170 nm. Specular and grazing incidence x-ray diffraction measurements confirm the presence of the anisotropic, face centered tetragonal (L10) crystal structure. Long range chemical order parameters of up to 0.95 and small mosaic spread, similar to results reported for FePt (001) films grown by molecular beam epitaxy. For film thicknesses ⩾50 nm in-plane and out-of-plane hysteresis measurements indicate large perpendicular magnetic anisotropies and at the same time low (about 10%) perpendicular remanence. Magnetic force microscopy reveals highly interconnected perpendicular stripe domain patterns. From their characteristic widths, which are strongly dependent on the film thickness, a value of the dipolar length D0∼50±5 nm is derived. Assuming an exchange constant of 10−6 erg/cm, this value is consistent with an anisotropy constant K1∼1×108 erg/cc.
Luminescence properties of poly(p-phenylenevinylene): Role of the conversion temperature on the photoluminescence and electroluminescence efficiencies
Authors: Morgado J. , Cacialli F. , Grüner J. , Greenham N. C. , Friend R. H.
Published: July 2002

We have investigated the luminescence properties of poly(p-phenylenevinylene) (PPV) prepared via the standard precursor route as a function of the conversion temperature in the range 170–270 °C. In particular, we have determined the absolute photoluminescence (PL) efficiencies of PPV thin films prepared on quartz or indium–tin oxide (ITO) coated glass substrates and found that the dependence on conversion temperature is different, depending on the type of substrate. The optical data show that heating at 170 °C for 10 h is sufficient to achieve full conversion. For PPV on quartz, a further increase of the temperature induces a decrease of the PL efficiency, whereas for PPV on ITO the PL efficiency shows a nonmonotonic dependence on the conversion temperature, with a maximum for conversion at about 205 °C. We discuss this behavior with reference to the interplay between the decrease in concentration of PL-quenching impurities (formed by reaction of the conversion byproducts and ITO) and an increase of exciton quenching efficiency due to polymer oxidation and/or crystallization, with increasing conversion temperature. We have also investigated the dependence on conversion temperature of the electroluminescence (EL) efficiency of single-layer ITO/PPV/Ca light-emitting diodes (LEDs) and of two-layer LEDs where an electron-transport/hole-blocking layer [namely 2-(4-biphenylyl)-5-butylphenyl-1,3,4-oxadiazole blended with polystyrene] is inserted between the PPV and the calcium cathode. The EL efficiency for the single-layer devices increases monotonically with increasing conversion temperature, whereas it decreases for the two-layer diodes. This complex behavior is due to the combined effects of the conversion temperature on the luminescence and injection/transport processes in PPV and is consistent with an interpretation based on a hole mobility which decreases with increasing conversion temperature.
Quantum-dot cellular automata: Review and recent experiments (invited)
Authors: Snider G. L. , Orlov A. O. , Amlani I. , Zuo X. , Bernstein G. H. , Lent C. S. , Merz J. L. , Porod W.
Published: July 2002

An introduction to the operation of quantum-dot cellular automata is presented, along with recent experimental results. Quantum-dot cellular automata (QCA) is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental device is a four-dot QCA cell with two electrometers. The dots are metal islands, which are coupled by capacitors and tunnel junctions. An improved design of the cell is presented in which all four dots of the cell are coupled by tunnel junctions. The operation of this basic cell is confirmed by the externally controlled polarization change of the cell.
Measuring interactions between tunnel-coupled quantum dots in the quantum Hall regime
Authors: Livermore C. , Duncan D. S. , Westervelt R. M. , Maranowski K. D. , Gossard A. C.
Published: July 2002

We present measurements of the relaxation of frustrated charge configurations via tunneling in a double quantum dot in the quantum Hall regime. We studied transport through two quantum dots in series at each of three Landau level filling factors: ν=2, 3, and 4. The double dot conductance was measured as a function of the induced charge on each dot and of the interdot tunnel conductance to demonstrate the evolution of the charging diagram with increasing interdot electron tunneling. At all three filling factors, we find that the evolution from well separated to joined dots is complete at an interdot tunnel conductance Gint≅e2/h, in contrast with the zero magnetic field case. We also observe that the residual interaction energy relative to the charging energy increases above the zero field value.
Matteucci effect as exhibited by cylindrical CoP amorphous multilayers
Authors: Favieres C. , Aroca C. , Sánchez M. C. , Madurga V.
Published: July 2002

CoP amorphous samples, electrodeposited on copper wires and exhibiting a longitudinal magnetic anisotropy, show a spontaneous Matteucci effect once the substrate has been subjected to torque. This induces an easy axis to allow for magnetization to occur, breaking away from its original longitudinal direction. The magnetic domain structures, as observed by the Bitter technique, revealed that the anisotropy changes direction, rotating gradually from its initial longitudinal position to a 45° helix, as the torque was increased. The reversible part of the circular magnetization switching curves, set against the longitudinal magnetic field, was fitted by assuming a magnetization rotation model in which constant anisotropic magnitude values were hardly modified, while allowing changes in direction.
Homopolar band gap and thermal activation parameters of plasticity of diamond and zinc-blende semiconductors
Authors: Siethoff Hans
Published: July 2002

It is known from earlier work that the activation energies of dislocation glide and diffusion-controlled climb of semiconductors with diamond and zinc-blende structures are correlated. It is shown in the present work in a semiempirical approach that both energies are proportional to Phillips’ homopolar band gap. A single relationship for all these materials is deduced, which is in agreement with the experimental data. Equivalently, both activation energies are related to the product of shear modulus and lattice constant which is a measure of the force constant.
Ab initio effective core potentials for molecular calculations. Potentials for K to Au including the outermost core orbitals
Authors: Hay P. Jeffrey , Wadt Willard R.
Published: July 2002

Ab initio effective core potentials (ECP’s) have been generated to replace the innermost core electron for third-row (K–Au), fourth-row (Rb–Ag), and fifth-row (Cs–Au) atoms. The outermost core orbitals—corresponding to the ns2np6 configuration for the three rows here—are not replaced by the ECP but are treated on an equal footing with the nd, (n+1)s and (n+1)p valence orbitals. These ECP’s have been derived for use in molecular calculations where these outer core orbitals need to be treated explicitly rather than to be replaced by an ECP. The ECP’s for the forth and fifth rows also incorporate the mass–velocity and Darwin relativistic effects into the potentials. Analytic fits to the potentials are presented for use in multicenter integral evaluation. Gaussian orbital valence basis sets are developed for the (3s, 3p, 3d, 4s, 4p), (4s, 4p, 4d, 5s, 5p), and (5s, 5p, 5d, 6s, 6p) ortibals of the three respective rows.
The Nose–Hoover thermostat
Authors: Evans D. J. , Holian B. L.
Published: July 2002

We derive equilibrium fluctuation expressions for the linear response of many body systems thermostated by the Nose–Hoover thermostat. We show that in the thermodynamic limit this response is the same as that of the corresponding Gaussian isothermal system. Numerical comparisons for shear flow show however that the Gaussian methods provide a significantly more efficient means of calculating the shear viscosity coefficient.
A Mo/ller–Plesset study of the electron affinities of the diatomic hydrides XH (X=Li, B, Be, C, N, O)
Authors: Frenking Gernot , Koch Wolfram
Published: July 2002

Electron affinities for LiH, BeH, BH, CH, NH, and OH are computed at the MP2, MP3, and full MP4(SDTQ) order of perturbation theory employing the basis sets 6-31G(d,p), 6-311G(d,p), 6-311++G(d,p), and 6-311++G(3df,3pd), using geometries optimized at MP2/6-31G(d,p). At the MP4(SDTQ)/6-311++G(3df,3pd)//MP2/6-31G(d,p) level including zero-point corrections, electron affinities are predicted with a maximum deviation of 0.2 eV from experiment. At the same level of theory, dissociation energies of the anions are computed to an accuracy of 0.11 eV. The energy results reported here are in most cases in better agreement with experiments than previous theoretical results. Vibrational frequencies and atomic distances are determined at the MP2/6-31G(d,p) level indicating longer bonds and lower frequencies as a consequence of electron attachment to the neutral hydrides.
A new density functional for fractionally occupied orbital systems with application to ionization and transition energies
Authors: Heaton Richard A. , Pederson Mark R. , Lin Chun C.
Published: July 2002

The use of fractional occupation of energy levels in the self-interaction-corrected local spin density (SIC-LSD) theory of electronic energy structure is studied with reference to calculation of ionization and excitation energies. With the original form of the SIC-LSD energy functional for fractional occupation, the one-electron eigenvalues exhibit nonlinear dependence on the occupation number. A new SIC-LSD density functional for fractional occupation based on the general behavior of the universal functional is proposed. The one-electron eigenvalues derived from this new functional vary quite linearly with the occupation number. This makes it possible to obtain ionization and excitation energies by a simple numerical integration over the occupation number. A one-point integration gives ionization energies that agree on the average with the results on taking the difference in self-consistent-field total energy between the atom and the ion to within 0.4% for the atoms He, Li, Be,...,Ar. Improvement can be made by using a three-point integration over the occupation number. This method is also applied to calculate excitation energies of selected transitions for He through Ar and the results are in good agreement with the corresponding total-energy differences.