bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface-acoustic-wave devices with low sensitivity to mechanical and thermoelastic stresses.
Authors: Ballandras S. , Bigler E.
Published: July 2002

Surface-acoustic-wave (SAW) devices with a low sensitivity to both temperature and stresses effects are presented and experimentally tested. Devices are built on SAW quartz cuts with zero first-order temperature coefficient and zero sensitivity to planar isotropic stresses. In comparison with similar devices built on conventional (ST, X) cuts, two kinds of experiments are reported. First, devices built on circular quartz plates are submitted to in-plane diametrical compressions. The force-frequency effect is measured and results are compared to theoretical predictions either by analytical models or using finite element analysis. In a second experiment, the same devices are submitted to in-plane thermoelastic stresses in a dynamical thermal regime. It is shown that the sensitivity of the new cuts to dynamical thermal effects is one order of magnitude lower than the conventional (ST, X) cut, an attractive potentiality for fast-warm-up high-stability SAW oscillators in severe environmental conditions.
A generalized model of heat effects in surface reactions. I. Model development
Authors: Martz Joseph C. , Hess Dennis W. , Petersen Eugene E.
Published: July 2002

Many important classes of surface reactions exhibit both high heats of reaction and large, positive activation energies. In addition, many surface reactions often occur in thermally isolated environments. As a result, significant autothermic effects are possible. In part I of this article, a generalized model of these effects is presented which describes the enhancement in reaction rate as a function of activation energy, bulk temperature, and a parameter termed the characteristic temperature. Reactant concentration and reaction order effects are also considered. Part II of this work presents the application of this model to numerous experimental plasma etching data.
Photoelectron emission and avalanche electron emission from shallow Si p-n junctions
Authors: Guo Tailiang
Published: July 2002

Arrayed shallow Si p-n junctions were fabricated by using low-energy ion implantation and rapid thermal annealing technology. The p-n junctions were then activated with Cs and O2 once only at room temperature, resulting in a cathode of the structure of p+-Si/n++-Si/O/Cs. The cathode thus fabricated could be used as a photocathode or a field-assisted photocathode, as well as an avalanche cathode or a light-assisted avalanche cathode, according to the light illumination condition and the magnitude of the reverse-biased voltage applied to the p-n junctions. The quantum yields of the photocathode and the field-assisted photocathode, the emission efficiencies of the avalanche cathode and the light-assisted avalanche cathode, the work functions, and the emission stability of all the above mentioned cathodes were examined in a continuously pumped ultrahigh vacuum chamber where they were fabricated. The characters of them are analyzed and discussed.
Reactive ion etching of InP using C2H6/H2/O2
Authors: Sugimoto Hiroshi , Ohtsuka Ken-ichi , Isu Toshiro , Tada Hitoshi , Miura Takeshi , Shiba Tetsuo
Published: July 2002

Reactive ion etching of InP using a C2H6/H2/O2 mixture was investigated. The effects of oxygen gas added to a C2H6/H2 gas were systematically investigated. A very smooth etched surface was obtained by the addition of O2, even when the etching depth was 3.5 μm. Mass spectrum of the gases in the etching chamber was also investigated during etching. It was found that the O2 gas reduced the formation of hydrocarbon polymers in the etching process.
Anisotropic electrical conduction in GaAs/In0.2Ga0.8As/Al0.3Ga0.7As strained heterostructures beyond the critical layer thickness
Authors: Hiesinger P. , Schweizer T. , Köhler K. , Ganser P. , Rothemund W. , Jantz W.
Published: July 2002

The anisotropic conduction of GaAs/In0.2Ga0.8As/Al0.3Ga0.7As inverted high-electron-mobility transistor (HEMT) structures has been investigated. The heterostructures were grown by molecular-beam epitaxy on (100) GaAs substrates. The thickness of the pseudomorphic layer was increased stepwise (150–300 Å) beyond the critical layer thickness as determined by the appearance of misfit dislocations. These mixed 60° dislocations surrounded by depletion regions were observed as straight dark lines in cathodoluminescence. The measured resistance Rs was higher in the [01̄1] direction than in the perpendicular [011] direction. At T=30 K the conduction ratio of these two directions exceeded 105 in the 300-Å-thick layer. The magnitude and anisotropy of Rs was correlated with the anisotropic dislocation patterns resulting from the preferential generation of the α dislocations ∥ [011] as compared to the orthogonal β dislocations ∥ [01̄1]. In both directions Rs depended exponentially on the number of dark lines perpendicular to the probing current. Simultaneously, the functional form of the temperature-dependent Rs(T) strongly varied with layer thickness. The thin, still elastically strained layers showed the usual behavior of HEMT structures. For the thicker layers a completely different temperature dependence was gradually developing, eventually leading to an exponential increase of Rs with inverse temperature between 300 and 100 K. Below this range Rs(1/T) changed more slowly and leveled off at 30 K. All these features are convincingly explained by a model assuming that the electrons can surmount the insulating depletion barriers in the conducting channel by a thermally induced tunneling mechanism.
Water-related capacitance-voltage recovery effect in low-temperature-annealed chemical vapor deposited phosphosilicate (P glass) films
Authors: Li S. C. , Murarka S. P. , Guo X. S. , Lanford W. A.
Published: July 2002

The effect of exposing low-temperature-annealed chemical vapor deposited phosphosilicate glass films directly to water on the properties of such oxides has been studied. The capacitance-voltage (C-V) curves of these as-deposited oxides have been known to shift on annealing at temperatures in the range of 150–1000 °C in gaseous or vacuum ambients. It is found that when exposed to water, with the increasing duration of water exposure, the C-V curves of these annealed oxides gradually shift back, to the original preanneal location on the voltage axis. The effect, which is similar to the reported effect of water-related traps, is directly observed without using avalanche injection. The C-V recovery is, however, limited to oxides annealed at temperatures ≤450 °C. Hydrogen concentration analysis clearly associates these C-V shifts with changes in concentration resulting from an anneal in a gaseous ambient or to the water exposure. If, however, the oxides are dry annealed at temperatures of 500 °C or higher, the C-V recovery, on water exposure, is very small. So is the increase in the hydrogen concentration, confirming the role of the hydrogenous species in the oxide. The results also suggest a structural change in the oxide occurring at temperatures above 500 °C and leading to oxides that have much lower water solubility compared to that in as-deposited oxides or oxides annealed at temperatures ≤450 °C. Possible mechanisms of oxide charge generation are discussed.
1H relaxation of H2O enhanced by suspended α-Fe2O3 particles
Authors: Jang E. K. , Yu I.
Published: July 2002

Spin-lattice and spin-spin relaxation measurements are performed on 1H in water molecules as a function of the concentration of suspended fine (1500 Å) α-Fe2O3 particles. To facilitate stability of the suspension and also to maintain a uniform distribution of the particles during the measurements, an aqueous colloidal suspension of α-alumina (Al2O3) is used for the diluting agent. The particle-concentration-dependent spin-lattice relaxation rates T1(c)−1 are analyzed with the Bloembergen–Purcell–Pound [Phys. Rev. 73, 679 (1948)] theory of spin relaxations in liquids by assuming that each particle possesses an average magnetic moment that is sitting at their centers. A departure from the Bloembergen–Purcell–Pound theory is noticed, namely a steeper concentration dependence than the usual linear one. The spin-spin relaxation measurements indicate the presence of strong diffusion effects. The magnetic-field gradient, which is deduced from the diffusion measurement, changes more strongly with the Fe2O3 particle concentrations than expected. The departures are attributed to the interactions between the magnetic moments of the Fe2O3 particles.
An improved method of using sound velocity measurements to determine the Debye temperature of cubic and noncubic materials
Authors: Wolfenden A. , Harmouche M. R.
Published: July 2002

An examination is made of the Debye theory of lattice vibrations and its applicability as an averaging scheme for computing the average phase velocity and the Debye characteristic temperature. A theoretical description of an improved averaging scheme is formulated, based on the Debye theory. The new scheme offers procedures for computation of the elastic Debye temperature with drastic reductions of computational time compared with other schemes. Numerical results are presented and compared with previous results whenever possible and with experimental data. With the new averaging scheme, there is excellent concordance between theory and observations for the elastic Debye temperature for cubic materials.
The effect of Si and Cu on the interactions between Al films and a TiW barrier layer
Authors: Chang Peng-Heng , Chen Huei-Ming , Liu Hung-Yu
Published: July 2002

The effect of doping 1 wt % Si or 0.9 wt % Cu to Al films on the interactions between Al and TiW barrier layers at 450 °C was studied. It was found that the first product is always Al12W, which forms at the Al/TiW interface, irrespective of the dopant addition. However, doping 1 wt % Si to Al film enhances the Al12W formation while doping 0.9 wt % Cu retards its formation. With excess tungsten in the system, Al12W would further react with W to form Al/W compounds with higher W content. In pure Al film, both the hexagonal Al5W phase and the monoclinic Al4W phase were detected to form after prolonged annealing at 450 °C. The addition of 1 wt % Si or 0.9 wt % Cu to Al prohibits the formation of Al5W, thus only the Al4W phase was observed at the W/Al12W interface in the doped Al films.
Stress-induced outdiffusion of Be in p+ GaAs prepared by molecular-beam epitaxy
Authors: Liu Biing-Der , Shieh Tung-Ho , Wu Meng-Yueh , Chang Tien-Chih , Lee Si-Chen , Lin Hao-Hsiung
Published: July 2002

The well-known abnormal outdiffusion problem of heavily Be-doped GaAs prepared by molecular-beam epitaxy was found to be initiated by the shrinkage of the lattice constant of the (p+) GaAs epilayer. Through detailed investigation of the double-crystal x-ray spectra, van der Pauw measurements, photoluminescence, and infrared-absorption spectra of Be-doped GaAs for various doping concentrations, it is found that there exists a critical doping concentration, i.e., 2.6×1019/cm3, beyond which the lattice constant of the epilayer starts to shrink and the Be outdiffusion into the substrate is significantly enhanced. Apparently, the tensile stress on the epilayer results in the abnormal Be outdiffusion. The absorption coefficient of Be-doped GaAs in the 8–10 μm region with carrier concentration 8.3×1019/cm3 are found to be about 104 cm−1 which is useful for the application of this layer to a p+-type AlGaAs/GaAs heterojunction infrared detector.
Method of laser-ion deposition of diamondlike carbon films
Authors: Charyshkin Yevgeny V. , Sakipov Nurlan Z.
Published: July 2002

Diamond-like films were prepared by deposition from laser plasma with simultaneous irradiation of growing film by hydrogen ions. Optical and electrophysical characteristics of these films were studied. The results obtained indicated essential improvement of diamond-like features.
Implantation of Li+ and Na+ into PbTeSe for current confinement in PbTeSe/PbSnTe ridge waveguide lasers
Authors: Harton Austin V. , Fonstad Clifton G.
Published: July 2002

Ion implantation of both Li+ and Na+ into n-type PbTe0.92Se0.08 has been used to convert this material to p-type. Li+-implanted samples achieved carrier-type conversion without annealing, while Na+ implanted samples required an anneal at 350 °C before carrier conversion was attained. Hall measurements at 77 K on Li+-implanted, n-type PbTe0.92Se0.08, annealed at 250 °C, indicated an estimated activation efficiency of 11%, and achievement of a hole concentration of 5×1018/cm3. The implantation of Li+ into the top layer of a PbTe0.92Se0.08(n)/PbTe0.82Se0.18Te(p) /PbTe0.92Se0.08(p) double heterostructure laser diode test structure resulted in a factor of 20 increase in series resistance at 200 mV, when compared to the series resistance of a similar unimplanted structure at the same bias voltage. The implanted structure did not exhibit breakdown until voltages exceeding 800 mV had been applied. These results suggest that ion implantation of Li+ into the top cladding layer of PbTeSe/PbSnTe laser diodes can be used to significantly reduce current spreading.
Photoreflectance study of hole-subband structures in GaAs/InxAl1−xAs strained-layer superlattices
Authors: Nakayama Masaaki , Doguchi Tomonori , Nishimura Hitoshi
Published: July 2002

We have performed photoreflectance measurements of the exciton transitions associated with the first (n=1) subbands in GaAs(dG Å)/InxAl1−xAs(dI Å) strained-layer superlattices with (dG, dI, x)=(100,100,0), (100,100,0.1), (100,100,0.2), and (40,40,0.2) grown on (001) GaAs substrates. The photoreflectance-intensity profiles of the n=1 excitons, which reflect the oscillator strength, clearly demonstrate that the order of the n=1 ‖J=3/2, mJ=±3/2≥ (heavy-hole) subband and the n=1 ‖3/2,±1/2≥ (light-hole) subband is changed by the In concentration (lattice-mismatch strain) and the layer thickness (quantum-size effect). We have analyzed the experimental results of the hole-subband order as a function of the In concentration and the layer thickness on the basis of an effective-mass approximation taking into account strain effects.
Influence of the axially varying quasi-Fermi-level separation of the active region on spatial hole burning in distributed-feedback semiconductor lasers
Authors: Champagne Yves , McCarthy Nathalie
Published: July 2002

The longitudinal-mode characteristics of distributed-feedback semiconductor lasers subjected to longitudinal spatial hole burning have been investigated using an improved numerical modeling scheme. The main new feature of the model is that it allows for the natural axial variations of the separation between the quasi-Fermi levels (Fermi voltage) in the laser’s active region. This gives rise to a current density injected into the active region that varies along the laser axis, even for uniformly biased lasers. It is found that compared to the results obtained by assuming an uniform current density, the detrimental influence of the longitudinal spatial hole burning on important static characteristics of quarter-wave-shifted distributed-feedback lasers, such as the gain margin and the lasing wavelength stability, is weakened. Therefore, the usual assumption of an uniform injected current density gives rise to an overestimated influence of the spatial hole burning, this overestimation being more important for long-cavity lasers having a grating structure with a large coupling coefficient.
Effects of temperature and bias on the microstructure of plasma-deposited amorphous silicon carbide
Authors: Lu Hsueh Yi , Petrich Mark A.
Published: July 2002

We report a new method of depositing amorphous hydrogenated silicon carbide (a-SiC:H) at low substrate temperature in a plasma-enhanced chemical vapor deposition reactor. By applying an external dc voltage to the rf-excited powered electrode, we can shift the optimal deposition temperature from 250 °C to as low as 100 °C. We find that a-SiC:H films deposited at positive powered-electrode potential and low substrate temperature exhibit less microstructure, wider optical band gaps, and faster deposition rates than films deposited at conventional conditions.
Drawing and annealing effects on thermally stimulated currents in polypropylene films
Authors: Baba Atushi , Ikezaki Kazuo
Published: July 2002

Thermally stimulated currents (TSCs) were examined in a temperature range from room temperature to 170 °C for positively corona-charged polypropylene films which were, before charging, uniaxially cold drawn to different drawing ratios D up to 3.5 or were annealed at different annealing temperatures Ta after drawn to D=3. Two main TSC bands P+1 and P+2 were observed around 60 and 140 °C, respectively. The peak temperature of P+1 strongly depended on D and Ta: It shifted toward higher temperature by drawing while it turned to shift toward lower temperature by annealing.
Selective lateral dry etching of GaAs in AlGaAs/GaAs heterostructures with CCl2F2/He
Authors: Walther M. , Tränkle G. , Röhr T. , Weimann G.
Published: July 2002

Using reactive ion etching with CCl2F2/He a selectivity in etch rates between GaAs and AlGaAs of larger than 3000 has been obtained for low dc self-bias voltages. Under isotropic etch conditions at low-bias values this selectivity is used for the lateral etching of thin GaAs layers sandwiched between AlGaAs layers. The range of lateral etching is proportional to the square roots of the etch time and the thickness of the etched GaAs layer. Lateral etch widths of 4 μm for a GaAs layer thickness of 50 nm and larger than 20 μm for a thickness of 1 μm are achieved.
Two-dimensional growth of strained Ge0.85Si0.15 on Si(111) by liquid phase epitaxy
Authors: Hansson P. O. , Ernst F. , Bauser E.
Published: July 2002

Heteroepitaxy immediate to thermodynamical equilibrium is investigated for liquid phase epitaxy of Ge0.85Si0.15 on Si(111). Below and beyond the critical thickness for strain relaxation, the GeSi layer grows in a two-dimensional mode. The critical thickness agrees well with mechanical equilibrium considerations. Strain relaxation is found to take place by the confined formation of misfit dislocations directly at the Ge0.85Si0.15/Si interface. We do not observe half-loop formation at the layer surface. The misfit dislocations (b=1/6〈112〉) form regular networks, which are buried under a structurally perfect relaxed GeSi layer virtually free of threading dislocations.
Maxwell displacement-current generation due to trans-cis photoisomerization in monolayer Langmuir–Blodgett film
Authors: Majima Yutaka , Kanai Yuichiro , Iwamoto Mitsumasa
Published: July 2002

The Maxwell displacement current was generated from 4-octyl-4′-(5-carboxylpentamethyleneoxy)-azobenzene (denoted as 8A5H) monolayer Langmuir–Blodgett films prepared on SnO2-coated glass substrates due to trans-cis photoisomerization of 8A5H by application of alternate irradiation with UV light and visible light. The generation of the displacement current by the photoirradiation was examined in connection with the degree of H-aggregate of 8A5H molecules. It was concluded that the high-H-aggregate molecule of the azobenzene group is not appropriate for the application of the molecular switching based on the displacement-current measurement.
Etching polymer films with ultraviolet laser pulses of long (10–400 μs) duration
Authors: Srinivasan R.
Published: July 2002

Continuous wave ultraviolet laser radiation (300–330 nm) from an argon ion laser was chopped mechanically with a rotating disk containing an aperture to yield pulses of ∼10–400 μs duration. Such pulses when focused to give spots of radiation of 10–100 kW/cm2 of power density etched films of polymers such as polyimide (KaptonTM), polyethylene terephthalate, and polymethyl methacrylate doped with Tinuvin. This etching process shows several features that are significantly different from the etching of the same materials by 5–35 ns pulses of 308 nm radiation from an excimer laser. These differences are in the fluence threshold for etching, the evidence (or lack thereof) for ablation of the products, and the nature of the etched surface. The etched holes show that there is considerable involvement of a heating effect in this process, but lateral thermal damage outside of the irradiated area is insignificant. The characteristics of this process seem analogous to those seen in photokinetic etching, which uses a moving spot of cw ultraviolet laser light to cut polymer surfaces in transit times of the same order as the durations of the pulses used here.
Time-dependent breakdown of oxynitride gate dielectrics under unipolar ac stress
Authors: Joshi A. B. , Kwong D. L. , Lee S.
Published: July 2002

Time-dependent dielectric breakdown under unipolar ac stress is investigated for control, nitrided, and reoxidized nitrided oxides, prepared by rapid thermal processing. All these gate dielectrics show longer time-to-breakdown under ac stress compared to constant voltage stress. Nevertheless, the extent of retardation of breakdown under ac stress is observed to be minimum for nitrided oxides and maximum for reoxidized nitrided oxides. Differences in detrapping behavior in these gate dielectrics are used to explain different improvement factors for breakdown under ac stress.
Carrier concentration and compensation ratio dependence of electron drift mobility in InAs1−xSbx
Authors: Chin V. W. L. , Egan R. J. , Tansley T. L.
Published: July 2002

The electron mobility in InAs1−xSbx is calculated for an ionized impurity density between 5× 1014 cm−3 and 1 × 1017 cm−3 at 77 K. The various methods of calculating electron mobility are discussed and their respective merits and limitations summarized. In general, alloy scattering is the mobility limiting process at low carrier density (n ≤ 1015 cm−3) while ionized impurity scattering is important at higher carrier density. The effect of compensation (NA/ND) on low field drift mobility is also calculated for a range of carrier concentrations at x=0.1, 0.6, 0.9, and 1.0 compositions of particular technological significance. Compensation is found to degrade electron mobility quite significantly in all cases. The calculations at x=1.0 (InSb) are also found to be in good agreement with available experimental data.
Local nature of artificial homojunction band discontinuities
Authors: Marsi M. , De Stasio Gelsomina , Margaritondo G.
Published: July 2002

The feasibility of creating homojunction band discontinuities by dipole intralayers was recently demonstrated with photoemission studies. We explored the nature of this intriguing mechanism by studying the effects of several complex intralayers, specifically stacked sequences of dipole intralayers. Quite unexpectedly, we found that the magnitude of the corresponding discontinuities is comparable to those created by individual dipole intralayers. We discuss this result in light of the recently observed [L. Sorba, G. Bratina, G. Ceccone, A. Antonini, J. F. Walker, M. Micovic, and A. Franciosi, Phys. Rev. B 43, 2450 (1991)], similarly unpredicted saturation at low thickness of intralayer-induced heterojunction band discontinuities modifications.
a-Si:F and a-Si:F:H prepared by ion-beam-assisted reactive deposition
Authors: Zhang S. , Brodie D. E.
Published: July 2002

a-Si:F and a-Si:F:H films have been prepared by ion-beam-assisted deposition using SiF4, SiH4+Ar, or SiF4+SiH4 as the gases for the ion source. Fluorine in a-Si eliminates some dangling bonds, increases the optical gap, and decreases the dark conductivity. The results are influenced mainly by the ion-beam energy used. The a-Si:F films do not exhibit an activated conductivity even up to 150 °C, and no photoconductivity could be detected. However, film properties were significantly improved when a very small amount of H was added to the a-Si:F and much less than 1 at. % H produced films that were photoconducting and had activated conductivities. The properties of these a-Si:F:H are strongly dependent on both the fluorine concentration CF and the hydrogen concentration CH. The deposition rate decreases with increasing SiF4 content in the source gas, and neither CF nor CH vary linearly with the change in the source gas ratio SiH4/(SiF4+SiH4). Hence, CH must be known and controlled in order to evaluate the effect of fluorine on the film’s properties. By studying a series of a-Si:F:H samples containing the same CH, it is noted that incorporating some F does improve the film’s electrical properties. Annealing experiments suggest that an observed peak at 2100 cm−1 in the IR spectra of these a-Si:F:H films is not completely due to SiH2, as has been suggested by others.
Photoreflection study on the surface electric field of delta-doped GaAs grown by molecular beam epitaxy
Authors: Liu D. G. , Chang K. H. , Lee C. P. , Hsu T. M. , Tien Y. C.
Published: July 2002

Photoreflectance spectroscopy has been used to study the surface electric-field strength and the surface potential of delta-doped GaAs. Franz–Keldysh oscillations in the reflectance spectra were clearly observed and the oscillation periods were used to calculate the internal electric fields of the delta-doped samples. Based on the measured results and the self-consistent calculation, a surface potential of 0.6 eV is obtained.
SiAs related photoluminescence emissions in low-temperature AlxGa1−xAs grown by molecular beam epitaxy
Authors: Souza P. L. , Rao E. V. K. , Alexandre F.
Published: July 2002

A photoluminescence emission attributed to (SiAs-VAs) at 1.77 eV at 77 K has been previously observed in annealed Si-doped Al0.3Ga0.7As layers grown by molecular beam epitaxy at 680 °C. An emission with similar characteristics has now been observed in as-grown samples fabricated at lower temperatures. New results render the attribution of the deep PL emission to the pair (SiIII-SiAs) more likely. The possibility of a heat treatment producing the same defect as a low-temperature molecular beam epitaxy growth is also discussed.
Time-resolved optical emission and electron energy distribution function measurements in rf plasmas
Authors: Stalder K. R. , Anderson C. A. , Mullan A. A. , Graham W. G.
Published: July 2002

Comparisons between experimentally measured time-dependent electron energy distribution functions and optical emission intensities are reported for low-frequency (100 and 400 kHz) radio-frequency driven discharges in argon. The electron energy distribution functions were measured with a time-resolved Langmuir probe system. Time-resolved optical emissions of argon resonance lines at 687.1 and 750.4 nm were determined by photon-counting methods. Known ground-state and metastable-state excitation cross sections were used along with the measured electron energy distribution functions to calculate the time dependence of the optical emission intensity. It was found that a calculation using only the ground-state cross sections gave the best agreement with the time dependence of the measured optical emission. Time-dependent electron density, electron temperature, and plasma potential measurements are also reported.
Epitaxial lutetium silicide: Growth, characterization and electrical properties
Authors: Travlos A. , Aloupogiannis P. , Rokofyllou E. , Papastaïkoudis C. , Weber G. , Traverse A.
Published: July 2002

The growth of lutetium silicide layers on 〈100〉 and 〈111〉Si is studied by random and channeling Rutherford backscattering spectrometry, x-ray diffractometry, and scanning electron microscopy. The LuSi2−x layers grow epitaxially with a better crystallinity on 〈100〉Si than on 〈111〉Si by vacuum annealing at 400 °C. Silicidation of Lu layers proceeds via nonuniform spatial diffusion of silicon atoms leading to a columnar growth of the silicide layer. Resistivity measurements in the temperature range 4.6–300 K show that LuSi2−x layers are metallic.
Interband tunneling between valence-band and conduction-band quantum wells in a GaSb/AlSb/InAs/AlSb/GaSb/AlSb/InAs triple-barrier structure
Authors: Chen J. F. , Cho A. Y.
Published: July 2002

We report on the experimental studies of an interband tunneling effect between GaSb valence-band and InAs conduction-band quantum wells in a GaSb/AlSb/InAs/AlSb/GaSb/AlSb/InAs triple-barrier interband tunneling device. Multiple negative differential resistances were observed both at room temperature and 77 K. By varying the InAs well width to adjust the alignment of the conduction-band and the valence-band quasi-bound states, we observed more than one order of magnitude variation in the peak current density, indicating a significant quantization effect. Possible current conduction mechanisms were discussed based on the dependence of the peak-current density on the InAs well width.
Calculation of path-dependent shock-wave hardening
Authors: Johnson J. N.
Published: July 2002

Material hardening models can be divided broadly into two categories; those that depend on the path followed in getting to the final state and those that do not. For those that do not depend on the path, no special attention need be directed toward the case of shock fronts in numerical calculation. For those that do, however, care must be exercised in making sure that zone-size effects and artificial viscosity do not mask the real material behavior controlling the shear strength behind the shock wave. The mechanical threshold stress (MTS) model is an example of a path-dependent material constitutive description that requires such consideration. In this paper a procedure is established for treating shock waves in computations using the MTS model. It involves a means by which the presence of the shock wave and its peak amplitude is sensed and then performing a separate calculation to determine the material state immediately behind the shock.
Resonance-enhanced spontaneous emission from quantum dots
Authors: Saunders Winston A. , Vahala Kerry J. , Atwater Harry A. , Flagan Richard C.
Published: July 2002

Enhanced and inhibited spontaneous emission from a pointlike quantum dot embedded in a finite dielectric sphere are treated classically. Numerical results given for a GaAs quantum dot embedded in an Al0.4Ga0.6As sphere show the spontaneous emission rate is decreased by a factor of 80 when the radius of the sphere is small compared to the wavelength of emitted light. When the radius of the sphere is comparable to the wavelength, the spontaneous emission rate depends strongly on the radius. Sharp resonances, related to Mie resonances, with enhancements up to a factor of 100, are found in some cases.
Flux motion dependence of resistive properties in superconducting YBa2Cu3O7−x thin films
Authors: Haung C. J. , Chen Y. C. , Tseng T. Y.
Published: July 2002

Two models of flux motion are employed to study the resistive properties of superconducting YBa2Cu3 O7−x thin films. The thermally activated flux creep model is employed to explain the dissipative behavior in the low resistivity region. However, when the resistivity is raised and approaches the normal state resistivity, the dissipative mechanism is gradually transferred from flux creep to flux flow. Based on the flux flow model, the upper critical field is estimated and shown as a function of temperature. In addition, a parallel resistivity circuit model is proposed to describe the transition behavior of the magnetic field dependence of resistivity versus current density characteristics.
Magnetic thin film domain wall motion under dynamic fields
Authors: Yuan Samuel W. , Bertram H. Neal
Published: July 2002

Previous computer simulation models are utilized to study two-dimensional domain wall motion in submicron thin permalloy films driven by in-plane sinusoidal fields. Under suitable ac fields applied in the easy direction, the wall motion is periodic and regular, yielding a phase lag in magnetization response giving the same effective wall mass as obtained previously from pulse fields. With a hard axis ac field, rich patterns of wall motions are observed, in contrast to a dc hard axis field. Unlike wall creep, a small dynamic hard axis field alone is sufficient to drive the wall in the film thickness direction or along the hard axis (wall streaming or worm motion). Accompanying this motion, wall structure transitions between Bloch and Néel may also take place, depending on both the amplitude and the frequency of the applied field. Such transitions are more favorable for larger amplitude and lower frequency fields. The frequency dependence of the magnetization response of a domain wall to a transverse field may also be characterized by approximate scalings of the hysteresis loops. At frequencies up to 500 MHz, the domain magnetization is conducted by wall motion, wall structure transition or a combination of both; whereas at higher frequencies, these effects are largely suppressed.
Current density dependence of the activation energy in type II superconductors
Authors: Sengupta S. , Shi Donglu , Salem-Sugui S. , Wang Zuning , McGinn P. J. , DeMoranville K.
Published: July 2002

We have conducted magnetic relaxation experiments to calculate the effective activation energy, U, as a function of critical current density. We have shown that, from the nonlinearity of U, one can explain the nonlogarithmic decay of magnetization in type II superconductors. The nonlinearity of U was considered by expanding U about a current density, J0. The coefficients of expansion were determined experimentally and were used to develop the relationship between U and J for both conventional type II superconductors (Nb3Sn filamentary) and high-Tc superconductors (YBa2Cu3O7−δ and Bi2Sr2CaCu2Oy single crystals). Both types of superconductor were observed to behave in similar fashion. We have also calculated U0 using the standard formulas and the intercepts of the tangent of the U vs M curve and have found the results to be comparable.
Optical study of high density two-dimensional electron gas in GaAs/Al0.3Ga0.7As modulation-doped quantum wells
Authors: Chen Y. F. , Lin L. Y. , Shen J. L. , Liu D. W.
Published: July 2002

We have investigated the optical properties of high density electron gas in GaAs/Al0.3Ga0.7As modulation doped quantum wells by using the photoluminescence measurements with the pumping photon energies above and below the band gap of the barrier and the resonant Raman scattering. We point out that the previous assignment of the transition between the second conduction subband and the ground-state heavy-hole subband in the photoluminescence spectra may be flawed. Thus, there is no large breakdown of the parity selection rule of the optical matrix element in quantum wells even if the carrier concentration is as high as 1012 cm−2. Our results are consistent with the theoretical investigation. We have also estimated the band gap shrinkages due to many-body interactions, which are comparable with the previous calculations.
Modeling of the role of atomic hydrogen in heat transfer during hot filament assisted deposition of diamond
Authors: Tankala K. , DebRoy T.
Published: July 2002

The temperature and atomic hydrogen concentration profiles in a hot filament type diamond deposition reactor were determined experimentally and theoretically to demonstrate that the reaction of atomic hydrogen on the substrate surface plays an important role in the heating of the substrate. For a given filament temperature, the substrate temperature in helium was significantly lower than that in either pure hydrogen or 1% methane-hydrogen atmospheres. The presence of small amounts of methane in hydrogen did not have any significant effect in influencing the shape of the atomic hydrogen concentration profile. In the space between the filament and the substrate, the concentration field is established mainly due to the diffusive mixing of the atomic hydrogen with the molecular hydrogen and other species in the gas phase. Homogeneous chemical reactions in the gas phase do not significantly affect the atomic hydrogen concentration distribution in this region.
Investigation of Si1−xGex films and SimGen superlattices by x-ray diffraction
Authors: Koschinski W. , Dettmer K. , Kessler F. R.
Published: July 2002

Si1−xGex alloy films and SimGen superlattices (SLs) were prepared by molecular beam epitaxy on 〈001〉 silicon wafers. The crystalline quality of the films is characterized by analyzing the x-ray diffraction pattern. The intensity measured at constant diffraction angle provide (by rocking the sample) the distribution of the angles made by the diffraction planes in the film with the substrate. The lattice constants indicate the strain conditions in the films. A relationship between the strain and the width of the diffraction peaks is shown. Si1−xGex alloy films on 〈001〉 Si are used as a buffer layer, i.e., as a virtual substrate for SimGen SL. The SimGen SL parameters are obtained from the satellite position around the (004) Bragg reflection. Fitting the satellite intensities yields the average lattice parameter of the single Si and Ge layers. A comparison of different SLs reveals a significant dependence of the lattice parameters on the thickness of the Si1−xGex alloy buffer layers.
Growth kinetics and inhibition of growth of chemical vapor deposited thin tungsten films on silicon from tungsten hexafluoride
Authors: Leusink G. J. , Kleijn C. R. , Oosterlaken T. G. M. , Janssen G. C. A. M. , Radelaar S.
Published: July 2002

The growth kinetics and inhibition of growth of chemical vapor deposited thin W films on Si(100) from WF6 was studied with in situ growth stress and reflectivity measurements and ex situ weight gain measurements. A systematic series of experiments at varying WF6 flow, total pressure, and temperature show that the thickening kinetics and inhibition of the growth are controlled by two processes: WF6 diffusion through the gas phase and Si diffusion through the thickening columnar film. The steady state growth kinetics are controlled by WF6 diffusion in the gas phase whereas inhibition of the growth occurs at the transition from WF6 gas diffusion limited to Si solid state diffusion limited growth. A simple model based on WF6 gas phase diffusion and Si solid state diffusion is presented which gives a quantitative description of the experimental results.
Thickness uniformity and electrical properties of ultrathin gate oxides grown in N2O ambient by rapid thermal processing
Authors: Yoon G. W. , Joshi A. B. , Ahn J. , Kwong D. L.
Published: July 2002

Thickness uniformity of ultrathin (30–100 Å) dielectric films grown on 4 in. silicon wafers in pure N2O ambient using a specially designed rapid thermal process reactor is studied. Excellent thickness uniformity in terms of percentage standard deviation (≤5%) is observed. Metal-oxide-semiconductor capacitors with these thin (∼100 Å) dielectrics have been fabricated. Results show that N2O oxides exhibit comparable interface state density and slightly larger breakdown field, but significantly reduced interface state generation and charge trapping under constant current stressing compared to oxides grown in pure O2.
Base-emitter leakage and recombination current in an implant isolated region of a GaAs/AlGaAs heterojunction bipolar transistor
Authors: Henderson T. , Bayraktaroglu B.
Published: July 2002

The effects of regions made semi-insulating by ion implantation on the base current of a GaAs/AlGaAs heterojunction bipolar transistor (HBT) have been investigated. The implanted region, which overlaps both ends of the emitter and base fingers in the device structures studied, is intended to reduce parasitic capacitances. It is shown that the current between the base and emitter fingers at these implant isolation edges can be divided into two distinct components: a leakage current which is linear with bias and a recombination current which has an ideality of 2.0. Both of these parasitic current components reduce the HBT current gain, particularly at low current densities. A measurement technique was developed to separate these two currents using dc current-voltage characteristics of the device.
Bistability and switching in a native-oxide-defined AlxGa1−xAs-GaAs quantum-well-heterostructure laser coupled to a linear array
Authors: El-Zein N. , Holonyak N. , Kish F. A. , Maranowski S. A.
Published: July 2002

Bistability and switching are observed in the light versus current (L-I) characteristic of a native-oxide-defined AlxGa1−xAs-GaAs quantum-well-heterostructure stripe laser side-coupled to a linear array of end-coupled rectangular minilasers. These diodes, with internally coupled elements and the current partitioned among the elements, exhibit a large hysteresis in the L-I curve, with switching from the stimulated to the spontaneous regime occurring over substantial power (light) and current ranges. The linear array of minilasers and their resonances modulates and switches the stripe laser operation. The overall planar twin-stripe laser structure is defined by H2O vapor oxidation (425 °C), in patterned form, of a significant thickness of the high-gap AlxGa1−xAs upper confining layer of an AlxGa1−xAs-GaAs quantum-well heterostructure.
Low-temperature solid-state reaction of in situ growth of YBa2Cu3O7−δ thin films by resistive evaporation
Authors: Azoulay Jacob
Published: July 2002

Thin films of Y-Ba-Cu-O were in situ prepared with the use of a simple conventional inexpensive vacuum system. No thickness monitor or control system is required. A pulverized mixture of Y, BaF2, and Cu constituents weighed in the atomic proportion was evaporated from resistively heated source onto a MgO substrate. The substrates temperature was then raised to 700 °C after evaporation. Oxygen was injected through a nozzle placed near the substrate surface, thus raising the pressure to about 8 Pa (60 mTorr). The film was kept at this stage for about 15 min, after which it was gradually cooled to room temperature and the pressure raised to atmospheric pressure. The obtained films with no further heat treatment were found to be superconductors with zero resistance at 85 K detected by four-probe dc measurements.
Fine structure of oxygen absorption bands in Si at low temperature
Authors: Ryoo K. , Kim H. R. , Koh J. S. , Seo G. , Lee J. H.
Published: July 2002

The semiquantitative analysis of optical absorption for interstitial oxygen in silicon was carried out using the molecular orbital theory and compared with results from Fourier transform-infrared equipment having a high resolution of 0.05 cm−1. Six finely split peaks were observed with the wave numbers of 1120.2, 1123.6, 1128.3, 1132.8, 1133.5, and 1136.4 cm−1 at 30 K, among which 1120.2, 1132.8, and 1133.5 cm−1 were newly observed. It is concluded that there seems to be a reliable correlation between the observed band splitting and the likely energy transitions from an S6 symmetry model. Fine splitting of the absorption peaks at low temperature indicates the close relationship between the local Si—O—Si bond and six nearest neighbor silicon atoms forming S6 symmetry. Absorption peaks also were narrower and higher as the measurement temperature was lowered. Hence, it can be said that low-temperature measurement improves the oxygen detectability by a factor of 10 compared with measurement at room temperature.
Activation mechanism of implanted boron in a Si substrate
Authors: Juang M. H. , Cheng H. C.
Published: July 2002

The recrystallization and dopant activation in the BF2+ implanted samples with a 110 keV/5×1015 cm−2 condition into a Si substrate and annealed with different heating rates to various preset temperatures for zero holding time have been studied. A higher heating rate yielded a higher carrier mobility and a better crystallinity. A statistical model was proposed to characterize the dopant activation. The activated dopant concentration n was expressed as γ exp(−Ea/kT). The pre-exponential term γ is a function of critical temperature Tc, due to a finite melting point of Si, and heating rate. Both the effective activation energy Ea and Tc values decreased with increasing heating rate. With increasing heating rate, the γ term rapidly decreased at low rates due to the shortened effective annealing time, but showed slight increase at high rates due to the decreased Tc value. Low heating rates facilitated the dopant activation via the γ term, while high heating rates enhanced the activation efficiency via the Ea term.
Analysis of the optical spectra of trivalent holmium in yttrium scandium gallium garnet
Authors: Gruber John B. , Hills Marian E. , Seltzer Michael D. , Stevens Sally B. , Morrison Clyde A.
Published: July 2002

The absorption spectrum of Ho3+ ions in yttrium scandium gallium garnet (Ho3+:YSGG) is reported at 4 K between 1.93 and 0.28 μm. Laser excitation spectra and laser-excited fluorescence spectra from Ho3+(4f10)2S+1LJ multiplet manifolds 5F4, 5S2, and 5F3 to the ground-state manifold 5I8 were obtained at 4, 8, and 70 K. Unresolved emission is observed from Ho3+ ions in slightly disturbed cation (Y3+) sites along with emission coming from Ho3+ ions occupying the regular cation (Y3+) sites having D2 symmetry. Temperature-dependent transitions (hot bands) observed in absorption at 8 and 70 K establish experimental crystal-field split (Stark) levels in 24 excited manifolds and the seven lowest energy Stark levels in 5I8 (Z1=0, Z2=6, Z3=17, Z4=29, Z5=87, Z6=95, and Z7=102, all in cm−1). An algorithm is used to establish D2 symmetry labels Γ1, Γ2, Γ3, or Γ4 of individual experimental Stark levels. These levels are compared with results obtained from a calculation in which a parameterized Hamiltonian was diagonalized within the 50 lowest multiplet manifolds of Ho3+(4f10). Comparison between 157 experimental Stark levels and the corresponding predicted levels out of a total of 486 calculated levels yields a root-mean-square deviation of 5 cm−1.
Improved n contact and series resistance in InP/InGaAs heterostructures by Si ion implantation demonstrated on junction field-effect transistors
Authors: Römer D. , Bauer J. G. , Lauterbach Ch. , Müller J. , Walter J. W.
Published: July 2002

The reduction of contact and series resistances in an n-type InP/InGaAs heterostructure by a multiple-energy Si implantation is described. AuGe/Au was used as an n contact metallization on the InP top layer. The contacts and the implanted layers were electrically characterized. With an electron concentration of 3×1018 cm−3 corresponding to a sheet resistance of 15.6 Ω/⧠ a contact resistance of 0.026 Ω mm was obtained. The application to a junction field-effect transistor leads to a significant improvement of the device characteristics with the transconductance increasing from 64 to 140 mS/mm due to reduced series resistances.
Schottky diodes on n-type InP with CdOx interfacial layers grown by the adsorption and oxidation method
Authors: Sawatari H. , Oda O.
Published: July 2002

A novel method to fabricate stable Schottky diodes on n-type InP was reported. The method is based on the chemical adsorption of metals and their successive oxidation for growing very thin metal oxide layers on top of n-type InP substrates. Schottky diodes were formed by using Au electrodes and the current-voltage characteristics were evaluated. It was found that nearly ideal Schottky diodes with barrier heights as high as 0.73 V, ideality factor of 1.16, and the reverse current of 5.5×10−7 A/cm2 at −1 V could be reproducibly obtained. CdOx interfacial layers were analyzed by Auger electron spectroscopy.
Analysis and optimization of quantum-well thickness for GaAs/AlGaAs and InGaAs/GaAs/AlGaAs quantum-well lasers
Authors: Zou W. X. , Merz J. L. , Coldren L. A.
Published: July 2002

The gain-current coefficient and current density at transparency of GaAs/AlGaAs and InGaAs/GaAs/AlGaAs quantum-well (QW) laser structures have been calculated as a function of the QW thickness by a straightforward numerical calculation. The optimum QW thicknesses are determined to be 100 and 105 Å for typical GaAs/AlGaAs and InGaAs/GaAs/AlGaAs QW laser structures, respectively, using the widely accepted semilogarithmic expression for threshold current density of QW lasers. These calculated optimum QW thicknesses agree with the reported experimental data very well. The reduction of the laser threshold current density as a result of using the optimum QW thickness is estimated to be 15% typically.