bluuebunny/crossref_metadata_2025 huggingface dataset:
A high field Faraday magnetometer for measurements under high pressure (abstract)
Authors: Shaheen S. A. , Tucker R. , Xu X.
Published: July 2002

Commercially supplied SQUID magnetometers which provide the best sensitivity (10−8 emu) are becoming more popular for routine magnetic property measurements. However, these magnetometers generally provide a very small usable sample space (9 mm) and a maximum field limited to 5.5 T. The sensitivity of SQUID magnetometers drops with increasing magnetic fields strengths and becomes comparable to or lesser than the sensitivity of Faraday magnetometers at a field of 5.5 T (5×10−5 emu). Therefore, Faraday magnetometers are a better choice, if a high sensitivity in high magnetic fields is required and/or a large sample space is needed, for example, to accommodate a pressure clamp for high pressure measurements. We have constructed a Faraday magnetometer which facilitates the measurements under high pressure conditions (up to 20 kbars in Cu–Be clamps) and in fields up to 13 T in a 24 mm warm bore (1.3–300 K) and 45 mm cold bore. To accommodate the weight of the pressure clamp, the magnetometer is equipped with a microbalance of extended weighing capacity (100 g) with a sensitivity of 10−6 g. Its superconducting magnet was specially designed to have a gradient such that the product H dH/dz remains nearly constant over a cylindrical sample volume of 20 mm×50 mm, which is the typical size of our pressure clamps. The details of pressure clamps will also be discussed.
Exchange and lattice frustration in presence of an external magnetic field
Authors: Gallanti C. , Rastelli E. , Sedazzari S. , Tassi A.
Published: July 2002

The planar triangular antiferromagnet shows a rich phase diagram in the H–T plane, the features of which have been enlighted via analytic low temperature expansion as well as Monte Carlo simulations. Three different phases with genuine nontrivial long range order in addition to the saturated ferromagnetic phase were found. Here it is shown that an analogous scenario is found in the square planar antiferromagnet with competing exchange interactions up to third nearest neighbors for exchange competition supporting a helix characterized by a wave vector Q=(2π/3a, 0) at zero field.
Trend of f-electron localization and itinerancy in rare-earth and light-actinide systems
Authors: Sheng Q. G. , Cooper Bernard R. , Lim S. P.
Published: July 2002

An important characteristic of correlated f-electron systems is their dual nature of having both degrees of localization and itinerancy. Their magnetic behavior evolves with the amount of delocalization they have. Rare-earth monopnictides are on the localized side, with weak delocalization related to hybridization. Uranium monopnictides are on the itinerant side, but localization cannot be fully neglected. To explore the problem from both the localized and the itinerant sides, we have been developing techniques to calculate the evolving properties of f-electron systems on a first principle ab initio basis. This involves: electronic structure calculations; calculating band-f hybridization; calculating Coulomb exchange interaction; and calculating magnetic ordering. In this work, we applied these techniques to evaluate the evolution of f-electron behavior from heavy rare earths to light rare earths to actinides. We will discuss how the degree of localization of the f electrons affects their hybridization and Coulomb exchange interaction with non-f band electrons, and how this influences the two-ion exchange interaction and magnetic ordering. Our calculation is for XSb where X=Ce, Nd, Tb, Er, Yb, U and for CeTe and UTe.
Nontrivial magnetic order: Localized versus itinerant systems (invited) (abstract)
Authors: Gor’kov Lev P. , Sokol Alexander
Published: July 2002

Recently the interest in non-Neel ground states for antiferromagnetically interacting localized spin systems has been revived. We discuss to what extent the generalization of such states is possible for itinerant electrons. Multiple spin correlation functions can be used to enumerate nontrivial order parameters for localized spins. This approach can be applied to itinerant systems without any modification. However, for the transition which breaks translational symmetry, electronic states far away from the Fermi surface are important and, hence, there is no distinct energetic mechanism for the nontrivial magnetic ordering. The only exception is the Fermi surface with the nesting property. As it is shown, among all phases known for localized spins only p-type spin nematic and chiral spin states can appear as a result of a Fermi liquid breakdown with respect to the electron-hole condensation near the Fermi surface. All other phases with zero local average spin known for localized systems, either are accompanied by the charge density wave or persistent orbital currents creating orbital magnetic moments, or can not appear as a result of a phase transition driven by such mechanism. Although two aforementioned phases are equivalent to their counterparts for localized spins from the symmetry viewpoint, the driving order parameter in an itinerant case is not a multiple spin average, but a wave function of the electron-hole condensate.
Magnetic flux-drag forces for high-Tc superconductors
Authors: Chan W. C. , Chung C. J.
Published: July 2002

According to the high-Tc superconducting bearing experiments, the magnetic flux-drag torque due to the asymmetric magnetic field distribution of the magnet cannot be neglected. A homemade vertical torsion balance has been constructed to directly measure the flux-drag torque acting on a yttrium-barium-copper-oxide (YBCO) superconducting sample due to the off-axis circular motion of a small permanent magnet. It is found that these flux-drag torques, unlike the levitation forces, have no obvious hysteretic effect. Also, these flux-drag torques are larger for a melt-powder-melt-growth YBCO superconducting sample than for a ceramic YBCO sample.
Defects in electron irradiated GaInP
Authors: Zaidi M. A. , Zazoui M. , Bourgoin J. C.
Published: July 2002

We present a characterization of the defects created by electron irradiation at room temperature in n-type GaInP. Four electron traps, labeled E1–E4, and no hole traps have been detected using deep level transient spectroscopy in the temperature range 4–400 K. The corresponding energy levels and barriers associated with electron capture have been measured. The introduction rates, ranging from 4×10−3 to 0.4 cm−1, indicate that these defects are probably not primary defects but complexes resulting from the interaction of these primary defects between themselves or with impurities. This is not surprising, owing to the fact that defect annealing takes place below 300 K in InP.
On the identification of N dangling bonds in SiN films using x-ray absorption studies
Authors: Paloura E. C. , Knop A. , Holldack K. , Döbler U. , Logothetidis S.
Published: July 2002

Thin amorphous Si3N4 films grown on Si are studied with the near-edge x-ray absorption fine structure (NEXAFS) characterization technique. The N dangling bonds in N-rich films give rise to a strong resonance line (RL) at the onset of the N 1s absorption edge, with an intensity that increases with the N/Si ratio. Further evidence on the origin of the RL is provided by the NEXAFS spectra from nitrogen-implanted Si and Si3N4 films bombarded with Ar+ ions. The RL can be annealed out after annealing at temperatures higher than the growth temperature. We propose that the annealing of the RL is due to formation of Si—N bonds, where the Si atoms are provided by the stressed interface. The velocity of the annealing process is controlled by the diffusivity of Si interstitials in the Si3N4 and the process is characterized by an activation energy of 0.86 eV.
Deposition of high quality TiN films by excimer laser ablation in reactive gas
Authors: Mihailescu I. N. , Chitica N. , Nistor L. C. , Popescu M. , Teodorescu V. S. , Ursu I. , Andrei A. , Barborica A. , Luches A. , De Giorgi M. Luisa , Perrone A. , Dubreuil B. , Hermann J.
Published: July 2002

A new laser method is proposed for the deposition of high purity, hard fcc TiN layers of unlimited thickness. The film thickness can be very finely controlled mainly through the intermediary of the number of applied laser pulses as the deposition rate is of only 0.02–0.05 nm/pulse. The ablation is promoted from a Ti target by high intensity multipulse excimer laser irradiation in a low pressure N2 ambient gas while the forming compound is collected on a Si single-crystalline wafer. The best results have been obtained for an ambient pressure of p=10–30 mTorr and a distance between the target and support of d=10 mm. It is shown that the formation of a liquid phase within the irradiated zone, maintained even after the end of a laser pulse, is the most important requisite for TiN formation. TiN is then ablated as a stoichio- metric phase.
Charge trapping on different cuts of a single-crystalline α-SiO2
Authors: Gong H. , Le Gressus C. , Oh K. H. , Ding X. Z. , Ong C. K. , Tan B. T. G.
Published: July 2002

A scanning electron microscope is employed for the investigation of charging on different cuts of an α-SiO2. A method for the determination of trapped charges is proposed. Charging on different cuts is observed to decrease in the order of z cut, 30° cut, 45° cut, and 60° cut of the α-SiO2. This phenomenon is related to permittivity, defect density, and stress of the samples. Details of the experiments and the method of charge determination are given.
Study of CuGa(Se,Te)2 bulk materials and thin films
Authors: Massé G. , Djessas K. , Yarzhou L.
Published: July 2002

We have grown and studied CuGa(Se,Te)2 photovoltaic bulk materials and thin films. This compound can readily be grown with p-type conductivity and can have a very good lattice match with CdS for a Se:Te ratio giving an energy gap close to 1.5 eV. The lattice parameters were determined by x-ray diffraction, and the energy gap calculated for temperatures between 77 and 300 K from luminescence studies. Thin films were grown using a close-spaced vapor transport technique, with iodine as reagent. The chemical equations governing the transport were determined. Good-quality CuGaSe2 thin films were easily grown, but we could not get CuGa(SexTe1−x)2 thin films when x<0.5. This result was explained from the CuGaTe2 phase diagram. Thermal evaporation experiments gave us similar results, but flash evaporation gave us thin films with a composition close to the source composition.
Study of defects induced by high-electric-field stress into a thin gate oxide (11 nm) of metal-oxide-semiconductor capacitors
Authors: El-Hdiy Abdelillah , Salace Guy , Petit Christian , Jourdain Marc , Vuillaume Dominique
Published: July 2002

The creation of defects into a thin gate oxide (11 nm) of polycrystalline silicon-oxide-semiconductor capacitors by electron injection Fowler–Nordheim effect, their electric nature, and their behavior when stressed samples are submitted to a white-light illumination in the inversion regime are studied. It is shown that low-electron-injected fluences cause creation of positive charges and that high fluences generate negative charges in the bulk of the oxide. Current-voltage characteristics have been performed in the accumulation and the inversion regimes before and after electron injection. These characteristics show a very weak shift and a small distortion which seem to indicate that the negative charges are localized close to the injecting electrode and the positive charges near to the Si/SiO2 interface. These positive charges are annihilated by light illumination without interface-state generation when stressed samples are biased in the inversion regime. Interface states do not show any saturation and their analytical expression versus injected charge contains two different terms which correspond to two different mechanisms of interface-state creation.
Diamond growth in turbulent oxygen-acetylene flames
Authors: Snail K. A. , Vardiman R. G. , Estrera J. P. , Glesener J. W. , Merzbacher C. , Craigie C. J. , Marks C. M. , Glosser R. , Freitas J. A.
Published: July 2002

Turbulent premixed oxygen-acetylene flames have been used to synthesize polycrystalline diamond films on molybdenum substrates at temperatures ranging from 500 to 1300 °C and facetted single crystals on mm-sized natural diamond substrates at temperatures of 1200–1300 °C. Turbulence was achieved by increasing the torch’s orifice diameter and/or the flow velocity; the presence of turbulence was confirmed by observations of changes in the flame shape, measurements of the flame’s noise spectrum, and calculations of the Reynolds number. The optical emission spectra of several diamond-growing turbulent flames were also compared to the spectra of laminar flames. The variation in diamond quality with temperature and oxygen acetylene flow ratio was studied with one or more of the following techniques: Raman spectroscopy, scanning and transmission electron microscopy, infrared spectroscopy, and photoluminescence spectroscopy. Crystals grown on molybdenum at temperatures of 600–1100 °C were observed to be transparent, and under the proper conditions the quality of diamond grown epitaxially in a turbulent flame equals that of natural type-IIa diamond. Although this enhanced quality has only been observed for fairly lean flames, the growth rate for type-IIa quality diamonds can still exceed 35 μm/h.
Low-energy contributions to positron implantation
Authors: Ritley K. A. , Lynn K. G. , Ghosh V. J. , Welch D. O. , McKeown M.
Published: July 2002

A detailed knowledge of low-energy positron implantation is of considerable importance for depth profiling and data analysis in slow positron experiments. Existing Monte Carlo models are capable of simulating the behavior of positrons incident at keV energies, then following the energy-loss process to final kinetic energies of from 20 to 100 eV. A Monte Carlo calculation of the final stages of positron thermalization in Al, Cu, and Au, from 25 eV to thermal energies, is described via the mechanisms of conduction-electron and longitudinal acoustic-phonon scattering. This calculation produces a wide variety of data, including implantation profiles, fraction and energy distribution of reemitted positrons, and the mean thermalization time. A way to obtain information about positron energy loss by considering the time evolution of a point concentration (delta-function distribution) of positrons is described. Diffusion coefficients are obtained that are in good agreement with experiment. The effects of a positive positron work function are examined in the context of a positron Monte Carlo calculation. It is shown that the latter stages of thermalization can have important effects on the stopping profiles and mean depth. In particular, calculated stopping profiles and mean implantation depth are not adequately described by the Makhovian distribution, in agreement with recent experimental findings. A parameterization of these profiles is provided which will be of use in the analysis of experimental data.
Spin fluctuation effect in the ordered Fe2N alloy
Authors: Chen Guan-mian , Lin Ming-xi , Ling Ji-wu
Published: July 2002

The temperature and field dependence of the magnetization of a Fe2N alloy has been measured and compared with the calculation of the Moriya–Kawabata theory and Stoner–Edwards–Wohlfarth model. It is shown that Fe2N is a very weak itinerant ferromagnet, and the Moriya–Kawabata theory and the electron gas approximation give a good description. Spin fluctuations and their interaction play a significant role in determining the thermomagnetic properties of the Fe2N alloy.
New laser ablation phenomenon of the porous Si films by focused N2 pulse laser irradiation
Authors: Hashimoto Akihiro , Iwata Kakuya , Ohkubo Mitugu , Yamamoto Akio
Published: July 2002

Porous Si films showed an anomalous photoluminescence deterioration phenomenon under focused N2 laser beam irradiation. The deterioration was due to laser ablation of the porous Si films. Photoluminescence spectra from the porous Si films under the ablation condition had multipeak structures consisting of narrow peaks with strong intensity superposed on a broad background peak. The individual peak energies of the multipeak structures correspond to the calculated energy eigenvalues of 20–30 Å quantum dot structures. This result strongly indicates that the porous Si films contain quantum dot structures.
Photoluminescence of AlxGa1−xAs alloys
Authors: Pavesi Lorenzo , Guzzi Mario
Published: July 2002

A thorough discussion of the various features of the photoluminescence spectra of undoped, p-doped and n-doped AlxGa1−xAs (0≤x≤1) alloys is given. This review covers spectral features in the energy region ranging from the energy band gap down to ≂0.8 eV, doping densities from isolated impurities to strongly interacting impurities (heavy-doping effects) and lattice temperatures from 2 to 300 K. The relevance of photoluminescence as a simple but very powerful characterization technique is stressed also in comparison with other experimental methods. The most recent determinations of the Al concentration dependence of some physical properties of the alloy (energy gaps, carrier effective masses, dielectric constants, phonon energies, donor and acceptor binding energies, etc.) are given. The main physical mechanisms of the radiative recombination process in semiconductors are summarized with particular emphasis on the experimental data available for AlxGa1−xAs. The effects of the nature of the band gap (direct or indirect) on the features of the photoluminescence spectra are discussed in detail. Particular attention is devoted to the consequences of the band structure of AlxGa1−xAs (both the multivalley conduction band or the degenerate valence band) on the impurity states by summarizing the theoretical predictions and by detailing the behavior of a number of shallow impurities. Heavy doping effects are also analyzed. A systematic presentation of the photoluminescence related to deep defects and impurities (vacancies, antisites, DX centers, Si-Si self-compensating pairs, transition metals, and rare-earth ions) is carried out after a brief introduction to the terminology used to describe the deep states in semiconductors.
Temperature-dependent lifetime distribution of the photoluminescence S-band in porous silicon
Authors: Mauckner G. , Thonke K. , Baier T. , Walter T. , Sauer R.
Published: July 2002

We study the recombination mechanism of the visible photoluminescence (PL) S-band in p-doped porous Si layers by time-resolved photoluminescence. From the observed ‘‘stretched-exponential’’ PL decays we present a simple yet accurate evaluation method for lifetime distributions G(τ) and average recombination lifetimes 〈τ〉. The average lifetimes feature a strong temperature dependence and a characteristic thermal activation energy of 10–20 meV for low temperatures. Our results are discussed within the models of quantum-confined exciton recombination and surface state recombination.
Evidence of bistable shallow-deep silicon donors in GaAs-AlAs superlattices
Authors: Sellitto P. , Sicart J. , Robert J. L.
Published: July 2002

We have investigated the electrical properties of silicon-doped superlattices under hydrostatic pressure. Hall data are interpreted with a conduction model involving a nonmetastable shallow donor besides the metastable DX states lying in GaAs and AlAs layers. A change from a Γ miniband conduction into a X miniband conduction is induced by increasing pressure, showing that the shallow donor is linked with the X minimum of the superlattice miniband.
Te doping of GaAs using diethyl-tellurium
Authors: Kamp M. , Mörsch G. , Gräber J. , Lüth H.
Published: July 2002

The performance of the gaseous precursor diethyl-tellurium (DETe) for n-type doping of GaAs is studied. We report on both the properties of the molecular source DETe as well as on the suitability of the dopant element tellurium. Te is found to be an excellent dopant, comparable to Si in the lower-doping regime and superior at highest-doping levels. DETe reveals itself to be a convenient and reproducible doping source. At substrate temperatures above 540 °C, dopant desorption (most probably Te) is observed which limits its applications. Memory effects after doping up to the mid 1018 cm−3 range can be eliminated. At still higher-doping levels an optimized technique limits unintentional background carrier concentrations in subsequent layers to the 1014 cm−3 range.
Electron-density and energy distributions in a planar inductively coupled discharge
Authors: Mahoney Leonard J. , Wendt Amy E. , Barrios Ernesto , Richards Carolyn J. , Shohet J. Leon
Published: July 2002

Electron-density and electron energy distribution functions (EEDFs) are measured in a 20-cm-diam by 14-cm-long cylindrical, inductively coupled plasma source driven by fields from a planar, spiral coil at 13.6 MHz. Radio-frequency (rf) -filtered Langmuir probes are used to obtain spatial profiles of electron population characteristics in argon at powers and pressures of interest for etching and plasma-assisted deposition (1–100 mT). Electron densities range from 1010 to 1012 cm3 with 100–500 W of rf power and peak on axis in the center of the cylindrical volume. The EEDFs show that the observed average electron energy varies by 1–2 eV spatially, with the highest values of average energy occurring at those regions of strongest rf electric field. The EEDF measurements also reveal a significant population of cold electrons trapped in a potential well at the location of peak electron density. From these spatial measurements, spatial estimates of conductivity and ionization rate are deduced.
Suppression of thermocapillary waves in laser melting of metals and semiconductors
Authors: Tokarev V. N. , Konov V. I.
Published: July 2002

A theoretical study of surface relief stability in the laser melting of materials with relatively high thermal diffusivity and/or relatively high absorption coefficient (mainly metals and semiconductors) is given. Irradiation regimes are found where it is possible to avoid the development of surface wavy relief of the nonresonant type (with periodicities much greater then the radiation wavelength) both for cw and pulsed irradiation. The results obtained can have important consequences for the improvement of the quality of laser materials processing, e.g., in laser applications for microelectronics, or in laser modification of a surface.
Elimination of hydrogen-related instabilities in Si/SiO2 structures by fluorine implantation
Authors: Afanas’ev V. V. , de Nijs J. M. M. , Balk P.
Published: July 2002

In this study we have investigated the effect of fluorination on the electrical properties of the Si/SiO2/Al system, including their degradation. Fluorine was introduced by ion implantation into the gate oxide with doses ranging from 109–1015 cm−2. Study of the electron and hole trapping properties of the as-fabricated system showed that water-related electron traps and hole traps with small cross section are removed after introduction of fluorine. Hole traps with large cross section related to oxygen vacancies are not affected. Fluorination also suppresses generation of donor-type interface states and of oxide electron traps generated by vacuum ultraviolet irradiation. The data indicate that the involvement of fluorine is mostly of a catalytic nature. It is proposed that the post-metallization anneal in the presence of fluorine promotes the elimination of hydrogen available for radiolysis.
Raman image study of flash-lamp annealing of ion-implanted silicon
Authors: Mizoguchi Kohji , Harima Hiroshi , Nakashima Shin-ichi , Hara Tohru
Published: July 2002

Raman image measurements have been carried out to characterize the spatial variation in the crystallinity of silicon crystals which are ion-implanted and subsequently flash-lamp annealed. The spatial distributions of the peak frequency, band width, and normalized intensity (Raman parameters) have been examined for samples lamp annealed at different temperatures from 600 to 1100 °C. For specimens annealed at temperatures higher than 800 °C, the Raman parameters are constant and the same as those of silicon crystals in almost all areas. However, in sparse regions with a few micron in size, a broad band shifted to the lower frequency side of the crystalline band is observed. The Raman parameters of the broad band change with location within the small region. These results of the Raman imaging, together with the result of transmission electron microscopy, show that these small areas correspond to high defect density clusters located in the outer surface of the annealed layer. It is concluded that the high density of defects within the clusters introduces the shift and broadening of the band relevant to the clusters.
Obliquely evaporated Cr films with large angular selectivity
Authors: Mbise G. W. , Niklasson G. A. , Granqvist C. G.
Published: July 2002

Obliquely evaporated Cr films had inclined columnar microstructure and showed angular selectivity in the optical properties. Specifically, the p-polarized transmittance was much larger for light incident along the columns than across the columns. Optimization of the deposition parameters yielded higher angular selectivity than reported in earlier work.
InP optical constants between 0.75 and 5.0 eV determined by variable-angle spectroscopic ellipsometry
Authors: Herzinger C. M. , Snyder P. G. , Johs B. , Woollam J. A.
Published: July 2002

Using variable-angle spectroscopic ellipsometry (VASE) InP optical constants for photon energies have been determined in the range from 0.75 to 5.0 eV, which includes the fundamental gap at 1.35 eV. Above 1.5 eV the results are consistent with previously measured pseudovalues from an oxide-stripped sample when a very thin residual overlayer is accounted for. They are also shown to be compatible with previously published prism measurements of refractive index below the band gap. Real and imaginary parts of the dielectric function are shown to be Kramers–Kronig (KK) self-consistent above the gap, and the KK analysis was used to extend the dielectric function below the measurement range to 0.5 eV. The assumptions underlying biased fitting of VASE data and the importance of variable-angle measurements were investigated. The detection and significance of systematic errors for general VASE data analysis were also investigated, especially with regard to fit parameter confidence limits.
Interface-trap generation at ultrathin SiO2 (4–6 nm)-Si interfaces during negative-bias temperature aging
Authors: Ogawa Shigeo , Shimaya Masakazu , Shiono Noboru
Published: July 2002

This article reports an investigation of the negative-bias temperature instability in metal-oxide-silicon (MOS) systems with gate oxide thickness (Tox) in the range of 4.2–30 nm. The bias temperature aging was performed on p-type samples with applied negative oxide fields (1.6–5.0 MV/cm) over a temperature range of 150–290 °C. The maximum aging time was 5000 h. The interface-trap distribution was evaluated by the conductance technique. This time-consuming method yields reliable results even in ultrathin oxides, if appropriate corrections are made. The interface-trap generation and the concurrent fixed oxide charge can be expressed by simple empirical expressions. Their characteristic features are the inverse proportionality to oxide thickness (Tox) for the generated interface-trap density (Nit) and no thickness dependence for the fixed charge generation. A general phenomenological model is proposed to explain these empirical expressions in terms of the diffusion-reaction chemistry between hydrogenated trivalent silicon and the diffusing species. It is developed for the uncharged (neutral) and positively charged cases of diffusing species. Experimental results support the neutral-species (molecular hydrogen) model and the observed T−1ox dependence of Nit generation implies that the negative-bias temperature instability becomes more severe for ultrathin gate oxide MOS devices.
Al-Si crystallographic-orientation transition in Al-Si/TiN layered structures and electromigration performance as interconnects
Authors: Onoda Hiroshi , Kageyama Makiko , Hashimoto Keiichi
Published: July 2002

Formation of aluminum-silicon (Al-Si) alloy/titanium nitride (TiN) layered structures and their electromigration (EM) performance have been investigated. The crystallographic structure of the TiN film changes with the sputter-deposition conditions. A large negative substrate bias in reactive sputtering induces a structural transition in the TiN film. The crystal orientation normal to the film surface is easily controlled from the 〈111〉 to the 〈200〉 direction. The crystallographic orientation of the Al-Si alloy film has been successfully controlled by the film deposition on an orientation controlled barrier TiN film. The Al-Si alloy film grows epitaxially on TiN at the initial stage of deposition and this causes the Al-Si alloy’s preferred orientation to the underlying TiN film. These layered structures with different levels of Al-Si alloy preferred orientation have been subjected to EM tests, and the Al-Si alloy film with stronger 〈111〉 orientation was found to have a longer EM lifetime. The best EM resistance has been obtained on Al-Si alloy film with the strongest 〈111〉 orientation, which is achieved on a TiN film formed by the nitridation of a titanium (Ti) film. Thus, highly reliable interconnects can be obtained by improving the preferred orientation of Al-Si alloy film using texture improved TiN film.
Role of the chamber wall in low-pressure high-density etching plasmas
Authors: O’Neill James A. , Singh Jyothi
Published: July 2002

Ultraviolet-adsorption spectroscopy has been used to examine how the chamber wall affects the concentration of gas-phase reactants in high-density etching plasmas. This technique was employed to detect CF2 in an inductively coupled discharge used for the selective etching of silicon dioxide relative to silicon nitride and polycrystalline silicon (polysilicon) films. In plasmas containing C2F6 and CF4, the concentration of CF2 depends strongly on the applied power and operating pressure as well as the amount of polymer on the walls of the chamber. Changes in the conditioning of the chamber during the etch process cause significant variations in the concentration of CF2 in the discharge. The selectivity of etching SiO2 relative to Si3N4 films closely follows the concentration of CF2 under a variety of plasma operating conditions. The ability to measure a fundamental plasma characteristic that reflects the level of conditioning of the chamber is an important step in the real-time monitoring of a reactor parameter that currently can only be determined from postprocess measurements.
Investigation of carrier transport effects in multiple-quantum-well lasers
Authors: Chen Y. , Wartak M. S. , Lu H. , Makino T.
Published: July 2002

The effect of carrier transport on the small-signal dynamics of multiple-quantum-well lasers is investigated both theoretically and experimentally. The dependence of modulation bandwidth on quantum-well number is examined. Based on the phenomenological model, it is shown that there is an optimum value of the ratio between carrier quantum capture time and escape time, at which the modulation bandwidth of multiple-quantum-well lasers achieves maximum. The theoretical results agree well with experimental data.
Film thickness effects in the Ti–Si1−xGex solid phase reaction
Authors: Aldrich D. B. , Heck Holly L. , Chen Y. L. , Sayers D. E. , Nemanich R. J.
Published: July 2002

The effects of film thickness on the Ti–Si1−xGex solid phase reaction were investigated. Thin C49 TiM2 (M=Si1−yGey) films were formed from the solid phase reaction of 400 Å Ti or 100 Å Ti with Si1−xGex alloys. It was determined that for films formed from 400 Å Ti, the nucleation barrier of the C49-to-C54 transformation decreases with increasing germanium content, for alloy compositions with up to ≊40 at. % germanium (i.e., x≤0.40). It was also observed that germanium segregates out of the TiM2 lattice, for both the C49 and C54 phases, and is replaced on the TiM2 lattice with Si from the substrate. The germanium segregation changes the Ge index y of the Ti(Si1−yGey)2. For films formed from a 100 Å Ti layer it was observed that the C54 TiSi2 nucleation temperature was increased by ≥125 °C. The addition of germanium to the silicon increased the agglomeration of the C49 phase and caused the C54 TiM2 nucleation barrier to increase further. The results also indicate that the increased temperature required for the transition to the C54 phase, for the 100 Å films, leads to an increased rate of germanium segregation.
Growth of diamond films using an enclosed combustion flame
Authors: Morrison Philip W. , Somashekhar Ambika , Glass Jeffrey T. , Prater John T.
Published: July 2002

This paper discusses the growth of diamond thin films using an enclosed oxyacetylene torch operating at 700 Torr. Using response surface methodologies, we have systematically explored the parameter space to construct maps of nucleation density, film quality, growth rate, and orientational texture as functions of conditions. The deposition process has been broken down into a nucleation enhancement step and a growth step, and each step is optimized separately. In the study of the nucleation enhancement, we vary the flow ratio=O2/C2H2 (R), substrate-flame distance (z), and pretreatment time (t) while holding substrate temperature (Tsub) ≤ 550 °C and flow rate (F)=4 slm. Scanning electron microscopy determines the nucleation density and nucleation uniformity. The best nucleation enhancement occurs at R=0.91, z=50% of the feather length, and t=5 minutes. For the growth study, the variables are R, z, and Tsub (F=4 slm), and we employ two different Raman scattering measurements to assess film quality. In one case, we determine quality using the quality fraction=diamond peak/(diamond peak + nondiamond peak); the second indicator is the luminescence (L) determined from the baseline of the spectrum and is related to defects in the film. The highest quality films appear at high R (0.95-0.97), z=1 mm, and high Tsub (900–1000  °C). We have also determined the growth rate as a function of conditions using infrared spectroscopy and find that the growth rate is a factor of 10 less than in the unenclosed flame (i.e., open to the atmosphere). Films grown for one hour show orientational texturing predominantly in the 〈111〉 direction.
On the criterion of perfect regeneration for a magnetic Ericsson cycle
Authors: Yan Zijun
Published: July 2002

It is pointed out that the condition ΔQout=0 cannot be taken as the criterion of perfect regeneration for a magnetic Ericsson cycle, but ΔCH=0 can. By using the criterion, the regenerative performance of the magnetic Ericsson refrigeration cycle is discussed. Some new characteristics of the cycle are expounded.
Influence of misfit dislocations on thermal quenching of luminescence in InxGa1−xAs/GaAs multiple quantum wells
Authors: Rammohan K. , Lin H. T. , Rich D. H. , Larsson A.
Published: July 2002

The temperature dependence of the cathodoluminescence (CL) originating from In0.21Ga0.79As/GaAs multiple quantum wells has been studied between 86 and 250 K. The CL intensity exhibits an Arrenhius-type dependence on temperature (T), characterized by two different activation energies. The influence of misfit dislocations and point defects associated with strain relaxation on the thermal quenching of luminescence has been investigated, and the spatial variation in the activation energies has been examined. The CL intensity dependence on temperature for T≲150 K is controlled by thermally activated nonradiative recombination. For T≳150 K the decrease in CL intensity is largely influenced by thermal re-emission of carriers out of the quantum wells.
Electronic structure of the ridge quantum wire based on an analytic confinement model
Authors: Inoshita T. , Sakaki H.
Published: July 2002

An electronic structure calculation for the novel quantum wire structure recently fabricated and named the ‘‘ridge quantum wire’’ [Koshiba et al., Appl. Phys. Lett. 64, 363 (1994)] is reported. In the calculation, the actual confinement potential was approximated by an analytic model, which considerably facilitates the solution of the Schrödinger equation by the finite element method. The result clearly indicates the strong confinement of both electrons and holes. Also the quantization energy obtained, with exciton effects included, is in good agreement with the photoluminescence peak energy.
Neutron diffraction study of the magnetic structures of CeMn2Ge2 and CeMn2Si2
Authors: Fernandez-Baca J. A. , Hill Peggy , Chakoumakos B. C. , Ali Naushad
Published: July 2002

We have performed high-resolution neutron powder diffraction measurements on CeMn2Si2 and CeMn2Ge2 at temperatures between 12 and 550 K. Our measurements indicate that at high temperatures both compounds are paramagnetic. Below TN=380 K CeMn2Si2 becomes a collinear AF, with a structure similar to that reported by Siek et al. in which the magnetic propagation vector is τ=(0 0 1). CeMn2Ge2, on the other hand, exhibits two different magnetic transitions. At TN≊415 K there is a transition to a collinear AF phase characterized by the commensurate propagation wave vector τ=(1 0 1). At TC≊318 K there is a transition to a conical structure with a ferromagnetic component along the c axis and a helical component in the ab plane. The helical component is characterized by the incommensurate propagation vector τ=(1 0 1−qz), where qz is temperature dependent.
Depth profile of trapped charges in oxide layer of 6H-SiC metal–oxide–semiconductor structures
Authors: Yoshikawa M. , Saitoh K. , Ohshima T. , Itoh H. , Nashiyama I. , Yoshida S. , Okumura H. , Takahashi Y. , Ohnishi K.
Published: July 2002

Oxide layers etched at an angle were fabricated on a 6H-SiC substrate by varying etching time in diluted hydrofluoric acid, and 6H-SiC metal–oxide–semiconductor structures with various oxide thicknesses were formed. High-frequency capacitance–voltage measurements were carried out for determining the change in gate voltages corresponding to the midgap condition as a function of the thickness of the oxide layer, and the depth profile of trapped charge density in the oxide was estimated from the result. It is found that negative charges build up near the 6H-SiC/SiO2 interface, and that positive charges accumulate in the region at 40 nm from the interface. No significant difference is observed in the depth profiles of the trapped charge density between the oxide layers on the carbon and silicon faces. The origin of these trapped charges is discussed in conjunction with the carbon-related compounds in the oxide layers.
Cascade emission and four-wave mixing parametric processes in potassium
Authors: Efthimiopoulos T. , Movsessian M. E. , Katharakis M. , Merlemis N.
Published: July 2002

Strong stimulated cascade emission and coherent four-wave parametric radiations are observed. By proper observation of the excitation spectra, the cascade emission and the coherent four-wave mixing parametric processes can be identified. The effect of the buffer gas pressure on the intensity and the pulse compression of the emitted radiation were investigated. Cascade inversionless coherent radiation emission with absorption reduction and third order nonlinear susceptibility enhancement due to the presence of a strong internally generated field are discussed for the 4p–4s strong emission observed.
Electrical properties of epitaxial tungsten films grown by laser ablation deposition
Authors: Mikhailov G. M. , Chernykh A. V. , Petrashov V. T.
Published: July 2002

An investigation was made of electrical properties of tungsten films of thickness in the range of 30–140 nm, grown by laser ablation deposition in ultrahigh vacuum on [1̄012] sapphire substrate. From the data on the size effect and the temperature dependence of the resistivity r, supported with reflection high energy electron diffraction measurements, we find that the films, deposited onto clean substrates kept at temperatures higher than 500 °C, grow epitaxially with high quality crystalline structure. The effective electron mean free path changes from 300 to 1400 nm while the residual resistance ratio RRR=r (295 K)/r (4.2 K) changes from 7 to 35. At low temperatures we find the temperature dependent part ρ(T)≊ATn, with A=1.56 mΩ cm K−n, n=3–3.4 for the temperatures T<20 K. From the fit of the data to the equations of the classical size effect theory it was found that the main source of electron scattering at helium temperatures is interface scattering with a specular coefficient q≊0.3 and the bulk electron mean free path l∞ (4.2 K)∼200 μm, which is up to 103 times larger than the film thickness.
Stresses, curvatures, and shape changes arising from patterned lines on silicon wafers
Authors: Shen Y.-L. , Suresh S. , Blech I. A.
Published: July 2002

Experimental and numerical results are presented on the evolution of stresses and the accompanying changes in the overall curvatures due to the patterning of silicon oxide lines on silicon wafers and subsequent thermal loading. The finite element analysis involves a generalized plane strain formulation, which is capable of predicting the wafer curvatures in directions parallel and perpendicular to the lines, for both the patterning and thermal cycling operations. The predictions compare reasonably well with systematic curvature measurements for several different geometrical combinations of the thickness, width and spacing of the patterned lines. The non-uniform stress fields within the fine lines and the substrate are also analyzed. It is shown both experimentally and theoretically that certain geometries of patterned lines on the substrate induce dramatic shape changes and reversals of curvature in the direction perpendicular to the lines. The mechanistic origin of this effect is identified to be the Poisson effect arising from the anisotropic strain coupling in the patterned structure.
Transport in extrinsic photoconductors: A comprehensive model for transient response
Authors: Haegel N. M. , Brennan C. R. , White A. Michael
Published: July 2002

It is well established experimentally that the transient response of extrinsic photoconductors often consists of multiple components, with a slow component whose characteristic time can far exceed either the free carrier lifetime or dielectric relaxation time. However, various models that developed over a period of 30 years have failed to adequately explain the experimental results. We present a comprehensive model for the transient response to changes in photoexcitation of a low temperature extrinsic semiconductor of finite length. The model includes both drift and diffusion effects and, in contrast to earlier work, can be applied through a range of low to high fields, where both carrier diffusion and/or field-dependent sweep-out may occur. Changes in carrier concentration and electric field are calculated for a common operating regime where sweep-out is dominant and displayed in three-dimensional plots illustrating spatial and temporal variations. The slow transient response depends on generation rate, electric field and intercontact length but is independent of mobility and lifetime. Analytical models are presented for the limits where either carrier diffusion or carrier sweep-out is clearly dominant. The results offer insight into the role of contacts and space charge for transport in insulators and low temperature semiconductors.
Magnetic phase transition of gadolinium studied by acoustically detected magnetocaloric effect
Authors: Glorieux C. , Caerels J. , Thoen J.
Published: July 2002

This article reports on an investigation of the ferromagnetic to paramagnetic phase transition of gadolinium by means of a novel acoustic detection technique of magnetically induced temperature oscillations. Equations are derived for the magnetocaloric signal at the fundamental frequency of the magnetic field oscillation as well as for the second harmonic of the signal in terms of the temperature derivatives of the magnetization and of the susceptibility and specific heat capacity at constant magnetic field. Experimental data for three samples of different quality are analyzed with the theoretically derived equations and qualitatively compared with the linear model for critical behavior.
Grain size effect on ferro-antiferromagnetic coupling of NiFe/FeMn systems
Authors: Nishioka Koichi , Hou Chunghong , Fujiwara Hideo , Metzger Robert D.
Published: July 2002

In order to investigate grain size effects on ferro–antiferromagnetic coupling in NiFe/FeMn systems, samples of glass/Cu zÅ/NiFe 75 Å/FeMn 150 Å/Ta 30 Å were made and the grain size of FeMn was changed by changing the Cu thickness z. Increasing z from 0 to 315 Å, the mean grain size increases from 18 to 50 Å. The blocking temperature, at which the coupling field NiFe/FeMn disappears, increases from 330 to 430 K with the increase of the mean grain size. The curve shape of the temperature dependence of the coupling field changes from a concave type to a convex type with the increase of the mean grain size. Temperature dependence of the coupling field were calculated using a thermal fluctuation model of antiferromagnet. The calculated curve of the temperature dependence of the coupling field agrees with the experiment qualitatively. However, the calculated curves of the temperature dependence of coercivity does not agree with the experiment.
Highly oriented layers of the three-dimensional semiconductor CdTe on the two-dimensional layered semiconductors MoTe2 and WSe2
Authors: Löher T. , Tomm Y. , Klein A. , Su D. , Pettenkofer C. , Jaegermann W.
Published: July 2002

The II–VI semiconductor CdTe was sequentially deposited onto the (0001) van der Waals surfaces of the layered compound semiconductors MoTe2 and WSe2 by molecular beam epitaxy. Growth could only be achieved after deposition of a nucleation layer of CdTe at room temperature. After nucleation subsequent deposition steps followed at increased substrate temperatures (T=170–370 °C) in order to increase the crystalline quality of the films. The deposited films were investigated after each growth step by low energy electron diffraction and photoelectron spectroscopy. The diffraction pattern indicates a facetting of the (111) oriented film surfaces. From photoemission data we exclude interface reactions between substrate and film material. Transmission electron microscopy was used to examine the film morphology after the UHV experiments. The mean diameter of the film crystallites is 200–400 Å.
Interface-phonon-assisted transitions in quantum-well lasers
Authors: Stroscio Michael A.
Published: July 2002

Interface-phonon-assisted transitions are shown to be important in determining the rates for bound–bound transitions as well as the optimum quantum-well parameters for recently proposed quantum-well lasers including the tunneling injection laser and the quantum cascade laser. In particular, it is demonstrated through the use of the dielectric continuum model for interface and confined phonons that the exploitation of interface-phonon-assisted transitions offers a means of maximizing key transition rates and thus of optimizing the performance of both the tunnel injection laser and the quantum cascade laser.
Type-II photoluminescence from GaP/AlP/GaP quantum wells
Authors: Nagao S. , Fujimori T. , Gotoh H. , Fukushima H. , Takano T. , Ito H. , Koshihara S. , Minami F.
Published: July 2002

We have studied both continuous-wave and time-resolved photoluminescence from type-II GaP/AlP/GaP quantum wells with thickness of 1, 2, 3, 5, and 8 monolayers. Highly efficient no-phonon luminescence was observed at low temperatures, indicating long-lived temporal behavior. Photoluminescence results indicated that the lowest confined electron states in the AlP wells were the Xz states. Nonexponential time decay of the no-phonon line suggested that the high efficiency of luminescence was due to the localization of indirect excitons by fluctuations in the potential at the interfaces. The effective interface roughness, which gave rise to the in-plane localization of the excitons, was much less than 1 atomic layer. A fit to the observed type-II transition energies gave a value for the conduction band offset of 0.38 eV for the GaP/AlP heterointerface.