bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of microcrystalline silicon by remote plasma chemical vapor deposition without hydrogen dilution
Authors: Jang Jin , Kim Sung Chul , Park Kyu Chang , Kim Sung Ki
Published: July 2002

We have grown microcrystalline silicon by a remote plasma chemical vapor deposition technique using silane and helium only, without hydrogen dilution. The optimum growth temperature and rf power are 330 °C and 100 W, respectively. These results indicate that an atomic hydrogen environment on the growing surface is not always necessary to grow microcrystalline (μc-)Si at low temperatures. It is found that the exposure of He plasma on the growing surface of μc-Si etches the Si layer, explaining the growth of μc-Si by using only silane and He and no hydrogen.
Si3N4/Si/Ge/GaAs metal-insulator-semiconductor structures grown by in situ chemical vapor deposition
Authors: Reed J. , Gao G. B. , Bochkarev A. , Morkoç H.
Published: July 2002

The in situ, heteroepitaxial growth of Ge films grown on (100) n-GaAs, followed by in situ deposition of a Si3N4/Si insulator to form a Ge metal-insulator-semiconductor structure, is reported. The growth of the Ge, Si, and Si3N4 is carried out in an ultrahigh vacuum, chemical vapor deposition system which is vacuum connected to an adjacent III-V molecular beam epitaxy machine in which the GaAs is grown. The Ge is grown at low temperature (250 °C) using GeH4 and excited He from a remote plasma. After a rapid thermal annealing step, a marked reduction in hysteresis is observed in the capacitance-voltage characteristics and the density of interface trap states at the Si3N4/Si/Ge interface, as determined from the magnitude of the conductance peak, is found to decrease by a factor of 5, to 1×1011 eV−1 cm−2.
Electrical transport properties of Cu3Ge thin films
Authors: Aboelfotoh M. O. , Tu K. N. , Nava F. , Michelini M.
Published: July 2002

Resistivity, Hall-effect, and magnetoresistance measurements have been performed in the temperature range 4.2–300 K on thin films of the ε1-Cu3Ge phase that has a long-range ordered monoclinic crystal structure. The results show that ε1-Cu3Ge is a metal with a room-temperature resistivity of ∼6 μΩ cm. The temperature dependence of resistivity follows the Block-Grüneisen model with a Debye temperature of 240±25 K. The density of charge carriers, which are predominantly holes, is ∼8×1022/cm3 and is independent of temperature and film thickness. The Hall mobility at 4.2 K is ∼ 132 cm2/V s. The elastic mean free path is found to be ∼1200 Å, which is surprisingly large for a metallic compound film. The results show that the residual resistivity is dominated by surface scattering rather than grain-boundary scattering. An increase in Ge concentration above 25 at. % (but less than 35 at. %) is found to affect the resistivity and Hall mobility, but not the density of charge carriers.
Low energy electron collision cross sections for silane
Authors: Nagpal Rajesh , Garscadden Alan
Published: July 2002

Electron collision cross sections for silane in the energy range 0–5 eV are presented. We show that the conventional two-term solution of the Boltzmann equation is not correct for unfolding the cross sections from swarm data in pure silane, silane-Ar, and silane-Kr mixtures. A Monte Carlo method is used to derive the cross sections for the these systems and the two-term solution is used in silane-He mixtures. It is shown that experimental drift velocity data for the silane-He system is a valuable adjunct for unfolding the silane cross sections from existing swarm data.
Wavelength dependence of the photoablation of carbon at low irradiance
Authors: Abhilasha  , Dwivedi R. K. , Thareja R. K.
Published: July 2002

The wavelength dependence of the photoablation of carbon at low irradiance in the presence of helium gas is reported. The vibrational temperature of the molecular species is estimated at various laser wavelengths, laser energies, and helium gas pressures using C2 Swan bands.
Proposed antiferromagnetically coupled dual-layer magnetic force microscope tips
Authors: Oti John O. , Rice Paul , Russek Stephen E.
Published: July 2002

A magnetic force microscope tip designed from dual-layer magnetic films of antiferromagnetically coupled magnetic layers is proposed. A theoretical analysis of the possible advantages of such a tip over conventional single-layer tips is given, using an extension to dual layers of a previously described micromagnetic model of single-layer tips. In contrast to single-layer tips, the magnetic domains of dual-layer tips are less sensitive to the fringing fields of the specimen, and the tips’ stray fields are greatly reduced, thus minimizing the likelihood of erasure of the sample magnetization. These properties of dual-layer tips should lead to improved resolution of magnetic force microscopy images.
Nb-based Josephson junction devices for nuclear radiation detection: Design and preliminary experimental results
Authors: Cristiano R. , Esposito E. , Frunzio L. , Pagano S. , Barone A. , Peluso G. , Pepe G. , Akoh H. , Nakagawa H. , Takada S.
Published: July 2002

In this work we apply the Electrotechnical Laboratory Josephson junction fabrication technology to realize an integrated device for nuclear radiation detection. We have integrated in a single 5×5 mm2 chip 240 Josephson tunnel junctions (JTJs) having various geometrical configurations and interconnections, in order to investigate both the effects of various detection geometrical configurations and the fabrication process uniformity and reproducibility. The junction quality was extensively tested by measurements of the current-voltage characteristics, down to T=1.2 K, showing an unexpected saturation of the Vm quality factor. Preliminary results concerning the response to α-particle radiation of these samples have been obtained. Pulse height and rise time spectra of both ‘‘island’’ type and series connected JTJs are reported. Signals generated by nuclear radiation have been observed at temperatures up to 2 K, where a reduction of the collected charge occurs because of the enhancement of the recombination rate. A strong effect of the substrate on the detector response has also been observed, providing useful indications for future improvements.
Effect of reactive-ion bombardment on the properties of silicon nitride and oxynitride films deposited by ion-beam sputtering
Authors: Ray S. K. , Das S. , Maiti C. K. , Lahiri S. K. , Chakraborti N. B.
Published: July 2002

Silicon nitride and oxynitride films of very low hydrogen content have been deposited on silicon at low temperatures (150–200 °C) using ion-beam sputtering. A dual-ion-beam sputtering technique, making simultaneous use of an energetic argon-ion beam to sputter silicon nitride from a target and a low-energy oxygen or nitrogen ion beam to react with the sputtered films on the substrate, has been employed to control the composition of the films. A precise control of film composition independent of deposition rate has been achieved through the control of oxygen/nitrogen ion-beam parameters and gas flow ratios. The films have been characterized by the measurement and study of refractive index, chemical etch rate, infrared absorption, and x-ray photoelectron spectra. A direct correlation between film properties with oxygen content has been obtained for silicon oxynitride films. The electrical properties have been studied by the measurement of the characteristics of metal-insulator-semiconductor capacitors fabricated using the deposited films. In situ ion-beam oxidation of silicon prior to the oxynitride deposition has resulted in a film with a low insulator charge number density (3.5×1011 cm−2) and interface trap density (4×1011 cm−2 eV−1), which is suitable for device applications.
Atomic force and scanning tunneling microscopy analysis of palladium and silver nanophase materials
Authors: Sattler K. , Raina G. , Ge M. , Venkateswaran N. , Xhie J. , Liao Y. X. , Siegel R. W.
Published: July 2002

Atomic force and scanning tunneling microscopy images of nanophase palladium and silver materials taken on various length scales are presented. The samples show a conformational packing of individual nanometer-sized clusters. In the case of silver, islands of clusters are observed on micrometer length scales. The islands are very flat and separated by deep crevices. The grains (clusters) within the islands are closely packed with shapes adjusting to the neighboring grains. The islands are compact, either equiaxed or oblong in shape. Average island diameters of 200–300 nm and average grain sizes of 20–50 nm were measured. The height variations on the islands are between 5 and 15 nm. The crevices are between 200 and 400 nm deep. In the case of palladium, the clusters are more uniformly packed and do not appear to be agglomerated in islands. Palladium grain sizes typically of 15 nm were measured along with corrugations of 10 nm in the closely packed areas.
Thermal expansion of gallium nitride
Authors: Leszczynski M. , Suski T. , Teisseyre H. , Perlin P. , Grzegory I. , Jun J. , Porowski S. , Moustakas T. D.
Published: July 2002

Lattice constants of gallium nitride (wurzite structure) have been measured at temperatures 294–753 K. The measurements were performed by using x-ray diffractometry. Two kinds of samples were used: (1) bulk monocrystal grown at pressure of 15 kbar, (2) epitaxial layer grown on a sapphire substrate. The latter had a smaller lattice constant in a direction parallel to the interface plane by about 0.03%. This difference was induced by a higher thermal expansion of the sapphire with respect to the GaN layer. However, this thermal strain was created mainly at temperatures below 500–600 K. Above these temperatures the lattice mismatch in parallel direction diminished to zero at a temperature of about 800 K.
Electric fields in high-frequency parallel-plate helium discharges
Authors: Hebner G. A. , Greenberg K. E. , Riley M. E.
Published: July 2002

Spatially and temporally resolved electric fields in the sheath region of a 13.56-MHz, parallel-plate helium discharge have been measured as a function of voltage, pressure, phase, bias, and electrode drive configuration. The electric field was determined from laser-induced fluorescence measurements of the Stark structure of the n=11 singlet Rydberg manifold. Two-dimensional maps of the electric field indicate that the field is uniform across a large fraction of the electrode diameter. Measured values of the sheath electric field are compared with the results of a hybrid Boltzmann-equation–average-equation simulation.
Impurity-mediated one-dimensional crystallization of thin amorphous Ge films on Si (111)
Authors: Hellman Olof
Published: July 2002

We have observed peculiar low temperature crystallization dynamics of thin amorphous Ge films deposited on Si (111):7×7 substrates. The one-dimensional geometry and low temperature kinetics of this crystallization indicate an impurity mediated mechanism similar to that suggested by Nygren, McCallum, Thornton, Williams, and Olson [Mater. Res. Soc. Symp. Proc. 100, 403 (1988)]. Interaction is observed between the buried surface structure and the crystallizing Ge film, in some cases resulting in Ge which grows epitaxially not on the bulk Si, but on the 7×7 reconstruction, effectively a two-dimensional substrate.
Simulations of photodeflection measurements of thermal diffusivity of solids: Wave optics approach
Authors: Glazov A. , Muratikov K.
Published: July 2002

Possible approaches to thermal wave measurement of thermal diffusivity were considered. The calculation of the transverse photodeflection signal in the framework of wave optics proves to be a more accurate approach compared to that of geometrical optics. The influence of the account of wave optics effects on the accuracy of the thermal diffusivity determination was theoretically analyzed under various conditions. It was shown that a difference between the thermal diffusivities calculated using both approaches is most apparent when the thermal diffusivity of a sample is smaller than that of the deflecting medium, at high modulation frequencies and/or at large probe beam radius.
Analysis and application of a viscoelastic model for silicon oxidation
Authors: Senez Vincent , Collard Dominique , Baccus Bruno , Brault Mathieu , Lebailly Jacques
Published: July 2002

The numerical modeling of the oxidation of silicon is analyzed from a nonlinear viscoelastic approach. Its mechanical and stress dependent parameters are determined for silicon dioxide and nitride. The study focuses on the rheological behavior of the materials. The two dimensional simulations of silicon cylinders oxidation and local oxidation of silicon processing reveal that at 1000 °C, a nonlinear viscous modeling is equivalent to the nonlinear viscoelastic one. But, for lower temperatures, the discrepancies between these two models, observed in the stress calculation and final oxide shape, demonstrate the necessity for a complete nonlinear viscoelastic formulation. Finally, the calibrated model is used to study the growth of a recessed isolation structure. The investigations quantify the influence of geometrical parameters of the silicon groove on the shape of the final isolation oxide (e.g., parameters such as the silicon overetch under the pad oxide, the depth of silicon etching, the slope of the silicon sidewall and the silicon concave corner rounding).
The origin of the broadband luminescence and the effect of nitrogen doping on the optical properties of diamond films
Authors: Bergman L. , McClure M. T. , Glass J. T. , Nemanich R. J.
Published: July 2002

Raman and various photoluminescence (PL) techniques were employed to investigate the role of nitrogen doping on the optical spectra of chemical-vapor-deposited (CVD) diamond films and to determine the origin of the characteristic broadband luminescence which is observed from approximately 1.5 to 2.5 eV and centered at ∼2 eV. The PL transitions attributed to the zero-phonon lines (ZPL) of nitrogen centers are observed at 1.945 and 2.154 eV. A new possible nitrogen center at 1.967 eV is also observed as well as the band A luminescence centered at ∼2.46 eV. The experimental results preclude the possibility of the broadband PL being due to electron-lattice interaction of the nitrogen ZPL centers. We establish the presence of an in-gap state distribution in CVD diamond films attributed to the sp2 disordered phase and show that its optical transitions are the likely cause of the broadband luminescence. A model of the in-gap state distribution is presented which is similar to models previously developed for amorphous materials.
Recombination centers in electron-irradiated Czochralski silicon solar cells
Authors: Zazoui M. , Bourgoin J. C. , Stievenard D. , Deresmes D. , Strobl G.
Published: July 2002

The defect responsible for the minority-carrier lifetime in p-type Czochralski silicon introduced by electron irradiation has been detected and characterized by deep-level transient spectroscopy and spin-dependent recombination. From the isotropic g value (2.0055), the defect is tentatively identified as a Si dangling bond originating from a vacancy cluster. Its energetic location in the gap is at 630 meV below the conduction band. The electron and hole cross sections and their variation with temperature have been determined, and found to account for the minority-carrier lifetime of the material.
The effects of temperature and oxygen concentration on the photoluminescence of epitaxial metalorganic vapor-phase epitaxy GaAs:O
Authors: Ryan J. M. , Huang J. W. , Kuech T. F. , Bray K. L.
Published: July 2002

Semi-insulating epitaxial GaAs:O prepared in a metalorganic vapor-phase epitaxy growth process using DEALO [(C2H5)2AlOC2H5] as the oxygen source has been characterized by temperature-dependent (12–300 K) photoluminescence. Oxygen-related deep level photoluminescence bands were detected at ∼0.8 and ∼1.1 eV. The relative intensities of the two bands were sensitive to both oxygen concentration and temperature. At a given temperature, an increase in oxygen concentration led to an increase in the intensity of the lower energy band relative to the higher energy band. A similar effect occurred at a given oxygen concentration as the temperature was raised. Band edge luminescence was also measured and was observed to quench when the oxygen concentration exceeded ∼1018 cm−3. The results indicate that oxygen is incorporated differently in epitaxial GaAs than in bulk GaAs. We propose that the difference is due to the incorporation of Al when DEALO is used in the growth of epitaxial GaAs:O. We suggest equally plausible microscopic models, based on the number of nearest-neighbor Al associated with O and multiple charge states, to explain the properties of the oxygen-related photoluminescence.
Electrical and optical properties of implanted amorphous silicon
Authors: Wei Jeng-Hua , Lee Si-Chen
Published: July 2002

The amorphous silicon hydrogen alloys (a-Si:H) prepared by plasma-enhanced chemical-vapor deposition are implanted with various impurities, i.e., phosphorus, silicon and boron, followed by 250 °C thermal annealing and hydrogen passivation. A critical phosphorus dosage of 5×1015 cm−2 is found, beyond which the doping effect becomes evident and the electrical properities of the films are comparable to the n+ a-Si:H deposited by glow-discharge decomposition of SiH4 and PH3. The silicon and boron implantation have less effect since the dosage is below 1015 cm−2. It is found that the conductivity of the implanted sample after annealing is determined by three competing mechanisms, i.e., annihilation of the implant-induced defects, defect creation due to hydrogen evolution, and the impurity activation. From the IR spectra of the high dosage phosphorus-implanted samples, a broad peak due to PHx radicals located from 2100 to 3500 cm−1 is found. In addition, most of the voids are found to be filled by extra P ions during annealing, so very few hydrogen atoms can be driven into the film after hydrogen passivation. In photoluminescence spectra, the high-energy peak at 1.4 eV drops very quickly and the low-energy shoulder at 1.25 eV becomes evident after implantation. It is found that Brodsky’s quantum-well model can be successfully applied to explain the observed results.
Electrical breakdown of polyethylene terephthalate under hydrostatic pressure
Authors: Zebouchi N. , Essolbi R. , Malec D. , Giam Hoang The , Ai Bui , Bendaoud M.
Published: July 2002

Measurements of dc dielectric breakdown strength were made on polyethylene terephthalate films of 50 μm in thickness at temperatures of 35, 70, and 100 °C under hydrostatic pressure ranging from 50 to 500 bar. It has been found that the electrical breakdown field Eb increases with pressure and decreases with temperature. It is suggested that thermal breakdown is the dominant process.
Local structure of CuInSe2 thin film studied by extended x-ray absorption fine structure
Authors: Kuwahara Yuji , Oyanagi Hiroyuki , Yamaguchi Hirotaka , Aono Masakazu , Shirakata Sho , Isomura Shigehiro
Published: July 2002

The local structure of CuInSe2 thin films has been studied by extended x-ray absorption fine structure on the Cu K and Se K edges using synchrotron radiation. The Cu—Se and In—Se bond lengths are examined as a function of In/Cu ratio α (0.29<α<1.13). The results show that the local structure of the thin-film CuInSe2 is quite similar to that of the bulk crystal over a wide range of α; however, it is found that with decreasing α, the Cu—Se and In—Se bond lengths deviate systematically from those of the stoichiometric bulk CuInSe2 crystal, which is attributed to the chemical disorder of the cation sites and the formation of anion vacancies in the chalcopyrite lattice. The temperature dependencies of mean-square relative displacements indicate that the In—Se bond is stronger than the Cu—Se bond.
A low threshold, room temperature 1.64 μm Yb:Er:Y3Al5O12 waveguide laser
Authors: Shepherd D. P. , Hanna D. C. , Large A. C. , Tropper A. C. , Warburton T. J. , Borel C. , Ferrand B. , Pelenc D. , Rameix A. , Thony P. , Auzel F. , Meichenin D.
Published: July 2002

Room temperature 1.64 μm laser operation of Yb:Er:Y3Al5O12 has been achieved using a planar waveguide grown by liquid phase epitaxy. A comparatively low threshold of 17 mW was achieved for this transition indicating low waveguide propagation loss for this material and suggesting good prospects for low threshold 3 μm and upconversion visible lasers based on this system.
Hydrogen passivation effects in InGaAlP and InGaP
Authors: Gorbylev V. A. , Chelniy A. A. , Polyakov A. Y. , Pearton S. J. , Smirnov N. B. , Wilson R. G. , Milnes A. G. , Cnekalin A. A. , Govorkov A. V. , Leiferov B. M. , Borodina O. M. , Balmashnov A. A.
Published: July 2002

The effects of hydrogen treatment on electrical properties, luminescence spectra, and deep traps in InGaAlP and InGaP have been studied. It is shown that acceptors and donors (both shallow and deep) can be effectively passivated by hydrogen. The hydrogen is found not only to passivate the main electron and hole traps in our samples, but also to generate electron traps in n-InGaAlP and hole traps in p-InGaP. The influence of hydrogen treatment mode (direct plasma or a crossed-beams source in which the low-energy ion bombardment of the surface is effectively eliminated) on hydrogen concentration and hydrogen profiles in InGaAlP are discussed.
Surface morphology of silicon grown on CaF2/Si by electron-beam-assisted molecular-beam epitaxy
Authors: Pettersson P. O. , Miles R. J. , McGill T. C.
Published: July 2002

The surface morphology of silicon, grown on epitaxial CaF2/Si by electron-beam-assisted molecular-beam-epitaxy was studied using atomic force microscopy, x-ray photoelectron spectroscopy, and low-energy electron diffraction. It was found that the roughness of the silicon overlayer was minimized by exposing the CaF2 to an electron dose of 1.0 mC/cm2 before growing the epitaxial silicon overlayer. The observed hexagonally shaped microcrystals formed by the silicon were explained by a model based on geometrical thermodynamics. Contact angle measurements yielded a Si—Ca interface bond strength of 2.5±0.3 eV and a free energy of 520±95 erg/cm2 for the irradiated CaF2 surface.
Relaxation of magnetoresistance and magnetization in granular Cu90Co10 obtained from rapidly quenched ribbons
Authors: Allia P. , Beatrice C. , Knobel M. , Tiberto P. , Vinai F.
Published: July 2002

Bulk granular Cu90Co10 systems displaying a negative giant magnetoresistance (GMR) were produced by submitting melt-spun ribbons to conventional annealing and dc joule heating in order to induce diverse microstructures. Room-temperature GMR values up to 9% at 20 kOe were found in samples produced using both kinds of thermal treatments. An evolution from a superparamagnetic towards a ferromagnetic behavior has been observed in samples submitted to different heat treatments. A long-time, nearly logarithmic relaxation of the magnetic remanence has been measured after fast removal of a magnetic field of 10 kOe. The progressive randomization of the magnetic moments also gives rise to a corresponding increase in the zero-field electrical resistance.
Field dependence of nuclear magnetic resonance in molecular beam epitaxy grown Co(111)/Cu multilayers
Authors: Thomson T. , Kubo H. , Lord J. S. , Riedi P. C. , Walker M. J.
Published: July 2002

An initial study of the field dependence of 59Co nuclear magnetic resonance (NMR) has been undertaken for two Co/Cu(111) multilayer films grown by molecular beam epitaxy. The multilayer structure of the films was nominally identical, [Co(15 Å)/Cu(7 Å)]×20, however by growing the multilayers with similar structures on different buffer layers, Cu(200 Å) and Au(10 Å), saturation magnetoresistances ΔR/R of 4% and 22%, respectively, were obtained. The NMR signal in ferromagnetic materials arises due to the enhancement effect from the electronic magnetization. This enhancement effect is therefore a function of the domain structure and any external magnetic field. By applying a simple model of how the NMR enhancement factor varies with applied field, in the absence of a domain structure, the anisotropy fields at the interfaces and in the bulk were determined separately at T=4.2 K. These were then compared with the coercive field obtained from magnetization measurements. Our results show that at low temperature the anisotropy field at the interfaces is approximately equal to the coercivity obtained from magnetization measurements (260 Oe), while in the bulk the anisotropy field was found to be ∼550 Oe for the low magnetoresistance sample with ΔR/R=4%, and ∼1230 Oe for the high magnetoresistance sample with ΔR/R=22%.
Phases and phase stabilities of Fe3X alloys (X=Al, As, Ge, In, Sb, Si, Sn, Zn) prepared by mechanical alloying
Authors: Bansal C. , Gao Z. Q. , Hong L. B. , Fultz B.
Published: July 2002

Mechanical alloying with a Spex 8000 mixer/mill was used to prepare several alloys of the Fe3X composition, where the solutes X were from groups IIB, IIIB, IVB, and VB of the periodic table. Using x-ray diffractometry and Mössbauer spectrometry, we determined the steady-state phases after milling for long times. The tendencies of the alloys to form the bcc phase after milling are predicted well with the modified usage of a Darken–Gurry plot of electronegativity versus metallic radius. Thermal stabilities of some of these phases were studied. In the cases of Fe3Ge and Fe3Sn, there was the formation of transient D03 and B2 order during annealing, although this ordered structure was replaced by equilibrium phases upon further annealing.
Characterization study of strained InxGa1−xAs/GaAs superlattices
Authors: Dapkus L. , Jasutis V. , Kačiulis S. , Leščinskas D. , Mattogno G. , Stakvilevičius L. , Treideris G. , Viticoli S.
Published: July 2002

InxGa1−xAs/GaAs strained layer superlattices were studied by means of double-crystal x-ray diffractometry (DCXD), transmission electron microscopy (TEM), and selected area x-ray photoelectron spectroscopy (SAXPS) depth profiling techniques. The quality of superlattices, strain in the sublayers, and their thickness and chemical composition were evaluated. The effect of the real superlattice structure on the shape of x-ray rocking curves has been revealed. It was concluded that full identification of nonperiodic defects and the initial stage of stress relaxation can be determined by combining DCXD and TEM methods. The results of SAXPS depth profiling were found to be in good quantitative agreement with DCXD and TEM data. The linear dependence of depth resolution Δz on the sputtering depth, caused by sputtering induced development of heterointerface roughness was determined in SAXPS profiles.
Investigation of the oxidation kinetics of CoSi2 on (111)Si by transmission electron microscopy
Authors: Huang G. J. , Chen L. J.
Published: July 2002

Transmission electron microscopy has been applied to study oxidation kinetics of CoSi2 on silicon for both dry and wet oxidation. Care was taken to determine the activation energies of oxidation in the temperature and time regime where the islanding of CoSi2 does not occur. For dry oxidation, activation energies for parabolic and linear growth were found to be 1.91 and 2.01 eV (±0.1 eV), respectively. For wet oxidation, activation energies for parabolic and linear growth were found to be 1.75 and 1.68 eV (±0.1 eV), respectively. The activation energy of the parabolic rate constant is substantially different from those obtained previously. The difference is attributed to the occurrence of islanding during oxidation in the previous study. A comparison of oxidation kinetics of CoSi2, NiSi2, TiSi2 on silicon with pure silicon substrates indicated that the oxidation kinetics are practically the same for CoSi2 and NiSi2 in the parabolic growth regime, but substantially different from those of TiSi2 on silicon and pure silicon. The similarity in oxidation kinetics of cubic CaF2 structure CoSi2 and NiSi2 on silicon with small mismatches to silicon is correlated to essentially the same stress level in these two silicides during the oxidation.
Field-effect transistors based on poly(p-phenylene vinylene) doped by ion implantation
Authors: Pichler K. , Jarrett C. P. , Friend R. H. , Ratier B. , Moliton A.
Published: July 2002

We have fabricated metal-insulator-semiconductor field-effect transistors (MISFETs), with thin films of polycrystalline poly(p-phenylene vinylene) (PPV) as the semiconducting layer and report here the successful operation of a PPV MISFET based on the p-type doping of the polymer layer by ion implantation of iodine. The measured field-effect mobility of the charge carriers in this ion- implanted PPV is in the range of 10−7 to 10−8 cm2/V s. These values are in the same range as those obtained from a PPV MISFET in which the PPV was doped from the gas phase.
Defect-assisted ohmic contacts on p-InP
Authors: Park Moon-Ho , Yeh C. L. , Wang L. C. , Deng F. , Liu Q. Z. , Clawson A. R. , Lau S. S.
Published: July 2002

Single-element contacts, Pd or Ni, on various p-InP substrates grown by liquid-encapsulation Czochralski (LEC) and by metal-organic chemical vapor deposition were investigated. Pd or Ni contacts on the substrates supplied by one certain manufacturer were found to be ohmic with a minimum contact resistivity of ∼5×10−5 Ω cm2 after annealing between 420 and 500 °C. However, ohmic behavior was not observed for these contacts on other substrates. Hall measurement, double-crystal x-ray diffractometry, and photoluminescence technique were used to evaluate the substrates. It was speculated that existence of intrinsic defects, such as P vacancies and other possible defects, in p-InP grown by LEC method may be responsible for the observed difference in ohmic behavior. A defect-assisted tunneling mechanism is proposed to account for the observed ohmic behavior of single-element contacts on certain p-InP substrates. This approach is potentially useful for making ohmic contacts to other compound semiconductors.
Transient phases of a-Si by rapid heating
Authors: Masaki Y. , Suzuki M. , Kitagawa A.
Published: July 2002

A structural model of a-Si and a model for its transient phases have been proposed. In these models, it is assumed that a-Si is composed of many small regions (or clusters with a radius of about 50 Å) having different free energies. When a-Si is rapidly heated to a temperature slightly less than 1450 K so as to avoid crystallization, it transforms to a new phase in which both a-Si clusters and super-cooled l-Si coexist. By using these models, anomalous phenomena observed in explosive crystallization and enhanced diffusion phenomena in rapid thermal annealing (RTA) process can be explained. Furthermore, the viscosity of super-cooled Si fluid at 1000 °C induced by the RTA process is estimated to be 107–108 mPa s, which leads to the determination of T0 value of about 1300 K in Vogel–Fulcher–Tammann (VFT) relation. However, this T0 value differs from that previously reported. This discrepancy has been discussed and it is concluded that T0 in the VFT relation is not a constant but a function of (dT/dt).
Dynamic characteristics of a high-T
c superconducting bearing with a set of alternating-polarity magnets
Authors: Komori Mochimitsu , Matsushita Teruo , Fukata Satoru , Tsuruta Akira , Ide Takahiko
Published: July 2002

Dynamics of a superconducting bearing with a high-Tc superconductor and a set of alternating-polarity magnets are discussed. The superconductor used is prepared by the quench and melt growth process. The set of magnets levitates over the superconductor which is field cooled in liquid nitrogen. To construct a dynamic model of the superconducting bearing, responses for impulse forces given to the levitating magnets in vertical direction are investigated. Damped free-vibration curves of the levitating magnets are observed. Dynamic stiffness and viscous damping coefficient can be defined by using the periodical vibration curves. It is also found that the stiffness and the damping coefficient depend on the width of a bar magnet. The resultant energy loss of the superconducting bearing is evaluated by using the force-displacement relationship and Bean’s critical state model [Phys. Rev. Lett. 8, 250 (1962)].
Liquid-phase epitaxial growth and characterization of InGaAsP layers grown on GaAsP substrates for application to orange light-emitting diodes
Authors: Chen Chyuan-Wei , Wu Meng-Chyi
Published: July 2002

The growth conditions of undoped InGaAsP layers grown on GaAs0.61P0.39 substrates and effects of Te and Zn-doping on electrical and optical properties have been examined in detail. The narrowest full widths at half-maximum (FWHM) of photoluminescence (PL) spectra were measured to be 40 meV at 300 K and 12 meV at 8 K for an undoped InGaAsP sample with a background electron concentration of 2×1016 cm−3. Room-temperature carrier concentrations in the range of 1.8×1017–3.4×1018 cm−3 for n-type dopant and 1.6×1017–2.8×1018 cm−3 for p-type dopant are obtained reproducibly. The 50 K PL spectra of Zn-doped layers show three distinctive peaks and their relative intensities change with various hole concentrations. Visible light-emitting diodes (LEDs) emitting at 619 nm and employing the InGaP/InGaAsP/InGaP double-heterostructure (DH) grown on a lattice-matched GaAs0.61P0.39 substrate have been fabricated. The DH LEDs are characterized by current-voltage (I-V) measurement, electroluminescence (EL), light output power, and external quantum efficiency. A forward-bias turn-on voltage of 1.8 V with an ideality factor of 1.3 and a breakdown voltage of 16 V are obtained from the I-V measurements. The emission peak wavelength and FWHM of room-temperature EL spectra are around 619 nm and 48 meV (15 nm) at 20 mA, respectively. The light output power of the bare diodes is as high as 0.32 mW at a dc current of 100 mA and an external quantum efficiency of 0.22% is observed.
Electron-beam-pumped lasing in ZnSe epitaxial layers grown by metal-organic vapor-phase epitaxy
Authors: Gurskii A. L. , Gruzinskii V. V. , Gavrilenko A. N. , Kulak I. I. , Mitskovets A. I. , Yablonskii G. P. , Scholl M. , Söllner J. , Heuken M.
Published: July 2002

Stimulated emission and laser action under N2 laser radiation and electron-beam excitation at room temperature was studied in ZnSe epitaxial layers grown by metal-organic vapor-phase epitaxy. The laser threshold was about Ithr=1 MW/cm2, the pulse energy was Eem=0.3 μJ at the excitation intensity of Iexc=26 MW/cm2. The duration was tem=2 ns and the wavelength was λem=473.2–475.2 nm. Stimulated emission and laser action are due to the recombinations in a high-density electron-hole plasma at Iexc≳Ithr. The light amplification takes place in both the Fabry–Pérot cavity and in the scheme of the zig-zag ray propagation inside the crystal without feedback.
The growth behavior of Pb0.95La0.05(Zr0.7Ti0.3)0.9875O3 films on silicon substrates synthesized by pulsed laser deposition
Authors: Yeh M. H. , Liu K. S. , Ling Y. C. , Wang J. P. , Lin I. N.
Published: July 2002

The highly (110) textured Pb0.95La0.05(Zr0.7Ti0.3)0.9875O3 (PLZT) films have been successfully grown on SrTiO3(STO)-buffered silicon substrates. The films, deposited by pulsed laser deposition process, are assumed to form via a two-step process, i.e., cluster adherence and phase transformation. The beneficial effect of using STO as buffer layers involves enhancing the kinetics of phase transformation from amorphous phase to perovskite. The loss of Pb species from the films is thereby suppressed. The optimum dielectric constants obtained are around εr=490 for PLZT/STO/Si films deposited at 550 °C (1 mbar oxygen pressure, PO2) and post-annealed at 550 °C (1 atm PO2). The corresponding charge storage density is around Qc≂1.5 μC/cm2 at 50 kV/cm applied field strength.
Experimental study on stacked Josephson tunnel junction arrays under microwave irradiation
Authors: Klushin A. M. , Kohlstedt H.
Published: July 2002

We investigated the behavior of vertically stacked tunnel junctions in a circuit suitable for voltage standards. Such three-dimensional (3D) circuits might offer a considerable reduction of chip size when compared with conventional, two-dimensional circuits. Up to 84 series connected stacks with four junctions in a stack were incorporated into a microstripline. In the current-voltage characteristic, we measured quantized current steps until 100 mV upon applying microwave irradiation in the W band. We observed both chaotic and nonchaotic behavior. Whether chaos or nonchaotic behavior is observed under microwave radiation depends on the coupling strength which is defined by the intermediate niobium layer thickness between the junctions of a stack. Large thickness corresponds to weak coupling and absence of chaos. We showed that 3D circuits are promising for voltage standard application.
Kinetic smoothening: Growth thickness dependence of the interface width of the Si(001)/SiO2 interface
Authors: Dawson J. L. , Krisch K. , Evans-Lutterodt K. W. , Tang Mau-Tsu , Manchanda L. , Green M. L. , Brasen D. , Higashi G. S. , Boone T.
Published: July 2002

Using x-ray diffraction techniques, we measure the root-mean-square width of the buried crystalline/amorphous Si(001)/SiO2 interface, as a function of oxide thickness. We find that the interface width decreases with increasing oxide thickness; the oxide growth process kinetically smoothens the buried interface. We also find a difference between the rate of smoothing for wet and dry oxides.
Spectroscopic studies of the effects of two-dimensional electron gas on interband transitions
Authors: Liu Wei , Jiang Desheng , Zhang Yaohui , Jin Shan , Wang Ruozhen
Published: July 2002

By using photoreflectance and photovoltaic spectra we have studied the behavior of two-dimensional electron gas in pseudomorphic high electronic mobility transistor structures. We find that the screening effect of two-dimensional electron gas on higher index subbands is much weaker than that on lower index subbands, and excitonic resonance is found to persist at the onset of the high-energy interband transition in both spectra despite the very large carrier concentration within the quantum well. In the meantime, band filling effects have different influences on the transition energy and strength at critical points for high and low temperature spectra, respectively.
Generation of electric fields by ice and snow friction
Authors: Petrenko Victor F. , Colbeck Samuel C.
Published: July 2002

Strong electric fields up to 2×106 V/m having potentials up to 1.6 kV were generated in the gap between ice (or snow) and metallic and dielectric sliders, including alpine skis. Experimental data on the ice frictional electrification over wide ranges of sliding velocity and temperature are presented both for metal and dielectric sliders. Several possible physical mechanisms are discussed. The observed high magnitude of the potential difference V generated by friction between ice and sliders and the dependencies of V upon the slider velocity, ice conductivity, and temperature can be best explained in terms of high density electric charges picked up by a slider from the ice surface. The observed surface charge density corresponds to strong polarization of water molecules in the surface layer of ice. The phenomenon can play a significant role in forming a frictional force.
Combined electron spin resonance and capacitance-voltage analysis of hydrogen-annealing induced positive charge in buried SiO2
Authors: Vanheusden K. , Stesmans A. , Afanas’ev V. V.
Published: July 2002

A novel charge sensing technique, based on monitoring donor defects in near-interfacial Si by electron spin resonance (ESR), has been applied to measure positive charge in buried oxide (BOX) layers of separation by implantation of oxygen material. This positive charge is introduced into the BOX layer by annealing in hydrogen in the temperature range 450–700 °C. Standard capacitance-voltage (C-V) analysis of the areal BOX-charge densities was used as a crucial test for this ESR-based method, yielding good agreement between the two techniques. Photoinjection of charges, optical excitation, and C-V and ESR etchback experiments have been performed on BOX layers subsequent to the hydrogen charging treatment leading to additional information on location, nature, and stability of the hydrogen-induced positive centers. The results show that these centers are very stable (not even affected by electron injection) and that they are located near the two Si/BOX interfaces (within a layer of ≤20 nm).
Room-temperature midwavelength two-color infrared detectors with HgCdTe/CdTe multilayer structures by metal-organic chemical-vapor deposition
Authors: Chen M. C. , Bevan M. J.
Published: July 2002

Two-color photoconductive detectors in the 3–5 μm wavelength range using multilayer undoped n-type Hg1−xCdxTe heterostructures have been demonstrated at room temperature. These heterostructures, consisting of three or four Hg1−xCdxTe layers separated with CdTe layers, were grown by the metal-organic chemical-vapor-deposition (MOCVD) technique. The quality of MOCVD films was verified by near-theoretical values of the minority-carrier lifetime at 300 K, ranging from 0.8 to 4.7 μs depending on the x value. The Hg1−xCdxTe layers are either detectors or filters, and the CdTe layers serve as insulating separators. The concept of using the exponential absorption tails of two Hg1−xCdxTe layers with different band gaps to form an absorption band was verified by the difference in the photoconductive spectral responses between backside and frontside illumination. Two different multilayer heterostructures with two-color peaks at 3.2/3.8 μm and 3.7/4.6 μm, respectively, were studied.
Time-of-flight analysis of the plume dynamics of laser-ablated 6H-silicon carbide
Authors: Capano Michael A.
Published: July 2002

The mass and velocity distributions of neutral species, ejected from a laser-ablated 6H-SiC target, are measured by time-of-flight mass spectroscopy. The laser-generated plume is shown to consist of atomic silicon and carbon and small neutral clusters. Measured values of the mean kinetic energies of neutral Si and SiC2 species are 1.1 and 1.5 eV, respectively, when a 6H-SiC target is irradiated with 248 nm radiation at a power density of 1×108 W/cm2. The kinetic energy distribution of Si+ ions is also measured for comparison with the neutral species, and shows a peak in the distribution at 38 eV. These data illustrate that an electronic, and not a thermal, mechanism for particle emission is active during the ablation of a 6H-SiC target. The relationship between the dynamics of the photoablation process and the properties of pulsed-laser-deposited films is also briefly discussed.
Stability of ammonium fluoride-treated Si(100)
Authors: Houston Michael R. , Maboudian Roya
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and contact angle analyses have been employed to investigate the chemical stability of silicon surfaces treated by an ammonium fluoride (NH4F) solution. Consistent with earlier results [Dumas and Chabal, Chem. Phys. Lett. 181, 537 (1991)], it is found that an NH4F final etch produces surfaces exhibiting lower oxygen and carbon contamination levels in comparison to the surfaces obtained with the traditional HF or buffered HF (BHF) etch. In conjunction with lower contamination levels, surfaces treated in ammonium fluoride show higher contact angles with water, indicating lower surface free energies. The Si-H surfaces produced by the ammonium fluoride etch were found to remain hydrophobic for weeks in air and showed no signs of oxidation for several days. After an induction period of about one week in air, oxidation began to occur in a more rapid fashion. The stability of the Si-H surfaces in water was also investigated, and it was found that the oxygen contamination levels measured by x-ray photoelectron spectroscopy were extremely sensitive to the final rinse time. An induction period of approximately one hour in water existed before any signs of oxidation were evident. Despite the fact that the NH4F-treated samples were initially cleaner than the HF-treated samples, both of these surfaces showed similar temporal behavior in air and water. We attribute this finding to the surface topographies produced by these treatments, as well as to the extreme sensitivity of the results to such factors as water rinse time.
Strain-induced shift in photoluminescence energy in In0.2Ga0.8As/GaAs quantum wires
Authors: Tentarelli E. S. , Reed J. D. , Chen Y.-P. , Schaff W. J. , Eastman L. F.
Published: July 2002

Quantum, wires, ranging in width from 900 to 42 nm, were patterned onto a 10-nm-thick In0.2Ga0.8As quantum well in GaAs cladding then regrown by migration-enhanced epitaxy. Atomic-resolution transmission electron microscopy images of two of the quantum wires, one 400 nm wide and the other 42 nm wide, show lattice deformation of the quantum wires due to compression by the cladding. The lattice constant in the growth direction varies with horizontal position inside each wire, from largest in the wire center to smallest at the sidewalls. In the 400 nm wire, the lattice constant in the growth direction fully reaches the pseudomorphically strained value of 5.83 Å at a distance of 165 Å from the sidewall, while the lattice constant in the 42 nm wire reaches only 5.79 Å, at 75 Å from the sidewall. From the value of the compressed lattice constant in the center of the 42 nm wire, the amount of strain in the center of the wire is inferred and, from this strain, the expected strain-induced band-gap energy shift is calculated. Photoluminescence measurements are made on the wires, showing a strain-induced increase in peak emission energy with decreasing wire size. That this energy shift is strain induced is verified by comparing it to the far smaller energy shift of an unregrown but, otherwise, identical sample, which has no regrowth-induced compressive strain. For the 42 nm quantum wire, after the calculated contribution due to increased quantum confinement is accounted for, the energy shift measured by photoluminescence is consistent with the calculated value to within the experimental error.
Investigation on the properties and the applications of vertically stacked Josephson tunnel junctions
Authors: Monaco R. , Polcari A. , Capogna L.
Published: July 2002

High quality vertically stacked Josephson tunnel junctions have been experimentally studied in the light of their potential applications. They have been realized using a simple fabrication process based on Nb technology. A number of aspects of such new devices were investigated. Among other things, we report on the dc characteristics (and their temperature and magnetic field dependence) of vertical stacks with particular attention to the case in which the intermediate layers are very thin. Furthermore, the Swihart velocities of the electromagnetic waves propagating in double-barrier junctions were measured from the voltages of zero field steps, Fiske steps, and flux flow steps in the current-voltage curve of electrically long devices. Each section is discussed in the light of the potential applications of vertically stacked junctions. We interpret the main features of the phenomena observed experimentally in terms of basic mechanisms. Strong evidence has been found of the proximity effect in thin intermediate layers. Vertically stacked Josephson tunnel junctions seem to be good candidates for applications as particle and photon detectors and high frequency oscillators.