bluuebunny/crossref_metadata_2025 huggingface dataset:
Distributions of residual stress, dislocations, and EL2 in Czochralski-grown semi-insulating GaAs
Authors: Dobrilla P. , Blakemore J. S.
Published: July 2002

Distributions of stress, dislocations, and the EL2 midgap defect have been optically mapped in semi-insulating GaAs wafers, from [100]-grown crystals created by the liquid-encapsulated Czochralski method. The evolution of EL2 along the growth axis indicates that assessment of this property through the majority of the crystal volume is often poorly represented by wafers from near the two end regions. A comparison of maps for stress, dislocation and EL2 patterns as all measured with a given wafer does not support hypotheses that EL2 is a direct consequence either of stress or of dislocations. Other mechanisms, such as segregation and melt dynamics, thus appear more likely to control the formation and distribution of EL2.
Dislocation-mechanics-based constitutive relations for material dynamics calculations
Authors: Zerilli Frank J. , Armstrong Ronald W.
Published: July 2002

An improved description of copper- and iron-cylinder impact (Taylor) test results has been obtained through the use of dislocation-mechanics-based constitutive relations in the Lagrangian material dynamics computer program EPIC-2. The effects of strain hardening, strain-rate hardening, and thermal softening based on thermal activation analysis have been incorporated into a reasonably accurate constitutive relation for copper. The relation has a relatively simple expression and should be applicable to a wide range of fcc materials. The effect of grain size is included. A relation for iron is also presented. It also has a simple expression and is applicable to other bcc materials but is presently incomplete, since the important effect of deformation twinning in bcc materials is not included. A possible method of acounting for twinning is discussed and will be reported on more fully in future work. A main point made here is that each material structure type (fcc, bcc, hcp) will have its own constitutive behavior, dependent on the dislocation characteristics for that particular structure.
Modeling and control of the wafer temperatures in a diffusion furnace
Authors: Van Schravendijk B. J. , De Koning W. L. , Nuijen W. C.
Published: July 2002

In this paper the thermal behavior of a diffusion furnace is studied. The ultimate goal is to achieve control of the wafer temperatures. It is shown how some previous results from the literature on the behavior of wafer temperatures in a diffusion furnace are incomplete and partly erroneous. A control algorithm has been derived which achieves much better wafer-to-wafer uniformity than conventional control.
The UV-visible spectroscopy of laser-produced aluminum plasmas
Authors: Knudtson J. Thomas , Green William B. , Sutton David G.
Published: July 2002

The optical emission spectra (180–760 nm) of plasmas produced by a flashlamp-pumped dye laser focused on an aluminum target have been recorded and analyzed. In the incident intensity range from near plasma threshold to 5×107 W/cm2 the electron temperature was calculated from the relative emission intensity of Al(II) states (Te=8.0×103 K). The electron density was determined from Stark broadened linewidths of four Al(II) lines. Both the spatial and temporal dependence of the emission spectra were obtained providing a map of the electron density and temperature.
Void collapse and void growth in crystalline solids
Authors: Nemat-Nasser Siavouche , Hori Muneo
Published: July 2002

The problem of large deformation and eventual collapse (or growth to a final shape, depending on the microstructure and loading) of voids in a crystalline solid which undergoes plastic flow by slip on crystallographic planes is considered and solved analytically for plane problems, using certain reasonable simplifying assumptions. It is shown that because of local anisotropic plastic flow, an initially circular (in two dimensions or spherical in three dimensions) void quickly deforms into a noncircular (or nonspherical) shape, even under all-around uniform far-field pressure or tension. Using an incremental solution, the shape of the void at each loading stage is approximated by an equivalent ellipse, and this procedure is continued until either the void collapses into a crack (which occurs always under compression and in special cases even under tension) or attains a constant aspect ratio (under tension only). The residual stresses in the vicinity of the collapsing void are calculated and used to establish whether or not the crack which is formed by the void collapse will continue to grow upon the release of the overall uniform compressive loads. It is shown that this depends on the initial void size, on the ductility of the material, as well as on the rate of the loading which affects the ductility. The mechanism of possible overall failure caused by void collapse under far-field compressive loads and possible subsequent crack growth upon unloading is studied, using power-law rate-dependent plastic slip and experimental results on flow stress under shock loading. Results are compared with experimental observations, arriving at good agreement. In particular, the important effect of the loading rate on void collapse and subsequent failure mode is illustrated. Furthermore, the void growth processes under simple shear and tensile loading are investigated, and it is shown that, depending on the far-field loading condition and the microstructure, a void may grow by self-similar expansion or it may collapse into a crack. The mechanisms of void deformation under various loading conditions are illustrated.
Intrinsic magnetic properties of SmTiFe10
Authors: Yang Ying-chang , Kong Lin-shu , Sun Shu-he , Gu Dong-mei , Cheng Ben-pei
Published: July 2002

The rare-earth–iron intermetallic compounds SmTiFex, with x ranging between 8 and 10, have been synthesized by an arc-melting technique. We found that they crystallize in the ThMn12-type tetragonal structure, I4/mmm. Unusual uniaxial magnetocrystalline anisotropies have been observed. The c axis is the easy magnetization direction. Curie temperature is 610 K. After the discovery of the R2Fe14B compounds, we have other ternary rare-earth–iron intermetallic compounds with strong uniaxial anisotropy.
Experimental verification of cyclotron absorption of polarized electromagnetic waves in a plasma waveguide
Authors: Bustamante E. G. , Anabitarte E. , Calderón M. A. G. , Sentíes J. M.
Published: July 2002

This paper presents the results of an experiment dealing with the absorption of electromagnetic waves in a longitudinally magnetized plasma waveguide at electron cyclotron frequency. Our results demonstrate, under different operating conditions, the importance of the polarization of the incident waves as well as the linear behavior of the plasma density as a function of the absorbed power. The gas used in this study was argon.
Analysis of Raman spectra of ZnWO4 single crystals
Authors: Liu Y. , Wang H. , Chen G. , Zhou Y. D. , Gu B. Y. , Hu B. Q.
Published: July 2002

The first-order Raman spectra of ZnWO4 single crystals have been obtained. All the vibrational frequencies are assigned by group theory. Among them the Bg modes at 269, 166, and 147 cm−1 and Ag mode at 124 cm−1 are reported for the first time. In view of x-ray structure data of ZnWO4, we suggest that the frequencies of vibrational modes can be assigned on the basis of analysis with octahedral WO6 as a starting point, instead of tetrahedral WO4.
Hydrogen sensing with palladium-coated optical fibers
Authors: Butler M. A. , Ginley D. S.
Published: July 2002

Palladium-coated, single-mode optical fibers have been used to detect hydrogen in a concentration range 20 parts per billion to 2% in 1 atm of nitrogen. When the coated fibers are exposed to hydrogen, a hydride is formed with an expanded lattice constant, which stretches the optical fiber. This change in optical path length is measured using a Mach–Zehnder interferometer. A simple one-dimensional model is presented and shown to accurately reproduce the fiber response. Using electrodeposited palladium films, a factor of 7 enhancement in the hydrogen solubility is observed, as well as a deeply bound site which is saturated in the parts per million concentration range. The data suggest that this site may be due to hydrogen binding to a free surface of the palladium.
Voltage-assisted calorimetric ionization detector
Authors: Luke P. N.
Published: July 2002

A new approach to ionizing radiation detection is proposed. The amount of ionization produced in a detector medium is measured by the heat generated as the charged carriers are drifted across the device under an applied voltage. The amount of energy generated can be orders of magnitude larger than that deposited by the radiation itself. A dramatic increase in detector mass can be achieved compared to simple calorimetric particle detectors for equivalent energy thresholds. It is possible to obtain a sensitivity level sufficient for single-carrier detection. The principle of operation has been demonstrated with an experimental device operated at a temperature of 1.8 K, and improved performance is expected at lower temperatures.
Magnetic properties of multilayer films consisting of Fe and nonmagnetic layers
Authors: Senda Masakatsu , Nagai Yasuhiro
Published: July 2002

This paper discusses a systematic investigation on the magnetic properties of multilayer films consisting of only Fe and nonmagnetic layers (Al2O3, Cu, C, Si, and Ti). Magnetostriction increases and becomes nearly zero as the Fe layer becomes thinner, regardless of the nonmagnetic species. In Fe/Al2O3 and Fe/Cu multilayer films, the magnetostriction increase is thought to be caused by the change in crystal preferred orientation of the Fe layers. By contrast, in Fe/C, Fe/Si, and Fe/Ti multilayer films, the increase is caused by the balance in positive and negative magnetostriction. Additionally, a low hard-axis coercivity of approximately 1 Oe and a relative permeability of more than 1000 can be achieved in Fe/Cu, Fe/Al2O3, and Fe/C multilayer films. These soft-magnetic properties are thought to be caused by the weak crystalline magnetic anisotropy due to small crystal grains and the magnetostatic coupling between Fe layers.
Use of hydrogenation in the study of the properties of amorphous germanium tin alloys
Authors: Chambouleyron I. , Marques F. C.
Published: July 2002

A study of the macroscopic properties of a-Ge:Sn and a-Ge:Sn:H films is presented. The samples were prepared by the rf sputtering method on substrates held at 180 °C. Their composition and structure were characterized, and the transport and optical properties were studied. The role and influence of hydrogen on the general properties of the alloys have been established.
Laser-induced medium perturbation in a large CO2 laser
Authors: Suhre D. R. , Pechersky M. J. , Lowry J. F. , Roach J. F.
Published: July 2002

Laser-induced medium perturbation was investigated in a large ultraviolet-initiated CO2 laser using time-resolved interferometry and beam quality measurements. The beam quality was found to be severely degraded after about 3 μs, and analytical modeling was performed which predicts the onset time.
Ion-beam-induced hydrogen release from a-C:H: A bulk molecular recombination model
Authors: Adel M. E. , Amir O. , Kalish R. , Feldman L. C.
Published: July 2002

Data on the hydrogen release from a-C:H induced by ion irradiation have been analyzed using a statistical model based on bulk molecular recombination. Good fits were obtained for all available data by adjusting a single parameter which is correlated to the stopping power of the projectile in the material.
Photoluminescence of InSb, InAs, and InAsSb grown by organometallic vapor phase epitaxy
Authors: Fang Z. M. , Ma K. Y. , Jaw D. H. , Cohen R. M. , Stringfellow G. B.
Published: July 2002

Infrared photoluminescence (PL) from InSb, InAs, and InAs1−xSbx (x<0.3) epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy has been investigated for the first time over an extended temperature range. The values of full width at half maximum of the PL peaks show that the epitaxial layer quality is comparable to that grown by molecular-beam epitaxy. The observed small peak shift with temperature for most InAs1−xSbx epilayers may be explained by wave-vector-nonconserving transitions involved in the PL emission. For comparison, PL spectra from InSb/InSb and InAs/InAs show that the wave-vector-conserving mechanism is responsible for the PL emission. The temperature dependence of the energy band gaps, Eg, in InSb and InAs is shown to follow Varshni’s equation Eg(T)=Eg0−αT2/ (T+β). The empirical constants are calculated to be Eg0=235 meV, α=0.270 meV/K, and β=106 K for InSb and Eg0=415 meV, α=0.276 meV/K, and β=83 K for InAs.
The oligothiophene-based field-effect transistor: How it works and how to improve it
Authors: Horowitz Gilles , Peng Xuezhou , Fichou Denis , Garnier Francis
Published: July 2002

Metal-insulator-semiconductor field-effect transistors (MISFETs) based on organic semiconductors, mainly conjugated organic polymers and oligomers, have been reported recently. Unlike conventional MISFETs, these devices work through the modulation of an accumulation layer at the semiconductor-insulator interface. A model for organic MISFETs, derived by changing the classical equations according to this particular operating mode is proposed. The ohmic current, parallel to the channel current, and due to the nonrectifying character of source and drain contacts, has also been taken into account. According to this model, the characteristics of these organic devices can be improved by decreasing the doping level and the thickness of the semiconducting layer. Simple rules are deduced and applied to devices based on α-conjugated sexithienyl.
Study of resonant tunneling structures: A hybrid incremental Airy function plane-wave approach
Authors: Tan Cher Ming , Xu Jingming , Zukotynski Stefan
Published: July 2002

A numerical procedure for the calculation of the electron tunneling current through an arbitrary potential profile has been developed. It involves subdividing the profile into a number of strips for which a linear approximation of the potential is appropriate. A solution of the Schrödinger equation in the form of Airy functions is obtained. These functions are linked through boundary conditions at the interface of the strips. An expression for the transmission coefficient of the structure is obtained. The approach is found to accelerate the calculation of the electrical characteristic of resonant tunneling devices. An analysis is performed of tunneling through parabolic quantum-well and half-parabolic quantum-well structures in the presence of an electric field. The room-temperature current-voltage characteristic for the half-parabolic quantum-well structure is calculated and is found to be rectifying with multiple peaks and regions of negative differential resistance. It is also found to have a relatively high peak-to-valley ratio and high peak current density.
The general and simplified Jones matrix representations for the high pretilt twisted nematic cell
Authors: Lien A.
Published: July 2002

A general Jones matrix representation for an arbitrary pretilt twisted nematic (TN) cell at any given applied voltage is obtained. A simplified Jones matrix representation for the high pretilt TN cell at the field-off state is derived from this general Jones matrix representation. The validity of this simplified representation is examined by comparing the optical transmission of a high pretilt angle TN cell, at the field-off state, as a function of the cell gap thickness obtained from this simplified representation with that obtained by the general representation. The result shows that the simplified Jones matrix representation for a TN cell at the field-off state works very well even for the pretilt angle as high as 30°. In addition, a property of the average tilt angle of a TN cell is reported.
Frequency modulation detection using high-Q cantilevers for enhanced force microscope sensitivity
Authors: Albrecht T. R. , Grütter P. , Horne D. , Rugar D.
Published: July 2002

A new frequency modulation (FM) technique has been demonstrated which enhances the sensitivity of attractive mode force microscopy by an order of magnitude or more. Increased sensitivity is made possible by operating in a moderate vacuum (<10−3 Torr), which increases the Q of the vibrating cantilever. In the FM technique, the cantilever serves as the frequency determining element of an oscillator. Force gradients acting on the cantilever cause instantaneous frequency modulation of the oscillator output, which is demodulated with a FM detector. Unlike conventional ‘‘slope detection,’’ the FM technique offers increased sensitivity through increased Q without restricting system bandwidth. Experimental comparisons of FM detection in vacuum (Q∼50 000) versus slope detection in air (Q∼100) demonstrated an improvement of more than 10 times in sensitivity for a fixed bandwidth. This improvement is evident in images of magnetic transitions on a thin-film CoPtCr magnetic disk. In the future, the increased sensitivity offered by this technique should extend the range of problems accessible by force microscopy.
The interfacial morphology of strained epitaxial InxGa1−xAs/GaAs
Authors: Yao J. Y. , Andersson T. G. , Dunlop G. L.
Published: July 2002

The microstructure of strained layers of InxGa1−xAs/GaAs grown by molecular-beam epitaxy has been investigated by transmission electron microscopy. lt was found that the formation of irregular interfacial morphologies of the InxGa1−xAs layers was due to a transition in growth mode from two-dimensional (layer-by-layer growth) to three-dimensional nucleation via island formation. It was also found that the occurrence of irregular growth surfaces of epitaxial layers was dependent upon inhomogeneous lattice strains induced by the formation of islands. A possible role of lattice strain for the formation of irregular growth surfaces was also discussed.
Prediction of phase formation sequence and phase stability in binary metal-aluminum thin-film systems using the effective heat of formation rule
Authors: Pretorius R. , Vredenberg A. M. , Saris F. W. , de Reus R.
Published: July 2002

The effective heat of formation (ΔH′) concept allows heats of formation to be calculated as a function of concentration. In this work the effective heat of formation rule is used to predict first phase formation in metal-aluminum thin-film systems and to predict subsequent phase sequence for thin metal films on thick aluminum or thin aluminum on thick metal substrates. The effective concentration at the growth interface is taken to be that of the lowest temperature eutectic (liquidus) for the binary system. Although the effective heat of formation rule may predict that formation of a certain phase would lead to the largest free energy change, this phase does not necessarily form at the moving reaction interface if it has difficulty to nucleate. By excluding phases with a large number of atoms per unit cell and which thus have difficulty to nucleate, the effective heat of formation rule successfully predicts first phase aluminide formation for all 15 metal-aluminum binary systems for which experimental data could be found. It is also shown how the effective heat of formation rule can be used to predict formation and decomposition of aluminide phases in contact with each other or in contact with their component metals.
Tantalum as a diffusion barrier between copper and silicon: Failure mechanism and effect of nitrogen additions
Authors: Holloway Karen , Fryer Peter M. , Cabral Cyril , Harper J. M. E. , Bailey P. J. , Kelleher K. H.
Published: July 2002

The interaction of Cu with Si separated by thin (50 nm) layers of tantalum, Ta2N, and a nitrogen alloy of Ta has been investigated to determine the factors that affect the success of these materials as diffusion barriers to copper. Intermixing in these films was followed as a function of annealing temperature by in situ resistance measurements, Rutherford backscattering spectra, scanning electron microscopy, and cross-section transmission electron microscopy. Ta prevents Cu-silicon interaction up to 550 °C for 30 min in flowing purified He. At higher temperatures, copper penetration results in the formation of η″-Cu3Si precipitates at the Ta-Si interface. Local defect sites appear on the surface of the sample in the early stages of this reaction. The Ta subsequently reacts with the substrate at 650 °C to form a planar hexagonal-TaSi2 layer. Ta silicide formation, which does not occur until 700 °C in a Ta-Si binary reaction couple, is accelerated by the presence of Cu. Nitrogen-alloyed Ta is a very similar diffusion barrier to Ta. It was found that Ta2N is a more effective barrier to copper penetration, preventing Cu reaction with the substrate for temperatures up to at least 650 °C for 30 min. In this case, local Cu-Si reaction occurs along with the formation of a uniform Ta5Si3 layer at the Ta2N-Si interface.
Thermal annealing properties of Nb-Al/AlOx-Nb tunnel junctions
Authors: Lehnert T. , Billon D. , Grassl C. , Gundlach K. H.
Published: July 2002

The increase of the normal-state resistance of Nb-Al/AlOx-Nb tunnel junctions by annealing at elevated temperatures is reported. Junctions with an area of 4 μm2 or smaller have been investigated. The resistance could be increased up to a factor of 5 with only a small influence on the quality of the quasiparticle characteristic. The effect can be used to adjust the resistance after fabrication. The increase of the AlOx barrier thickness has been estimated. Annealing experiments in nitrogen atmosphere and after nitridation have been carried out in order to find out from where the additional oxygene stems. The annealing properties of anodization curves have been investigated. A clear increase of the oxide peak could be observed. The results also show that the resistance is sensitive to temperature increases in the various fabrication steps.
Numerical simulation of field emission and tunneling: A comparison of the Wigner function and transmission coefficient approaches
Authors: Jensen K. L. , Ganguly A. K.
Published: July 2002

Quantum transport through one-dimensional potential barriers is usually analyzed using either the transmission coefficient (TC) or the Wigner distribution function (WDF) approach. Fast, accurate, and efficient numerical algorithms are developed for each and are compared for (a) calculating current-field relationships for field-emission potentials with silicon parameters (and current-voltage relationships for resonant tunneling diodes), (b) their ability to accommodate scattering, self-consistency, and time dependence, and for (c) the behavior of their ‘‘particle trajectory’’ interpretations. In making the comparisons, the concern will be on the ability of each method to be incorporated into a larger ensemble-particle Monte Carlo simulation; it is argued that, in this regard, the WDF approach has significant advantages. Since the TC calculations rely on the Airy function approach, a detailed comparison of this method is made with the widely used Wentzel–Kramers–Brillouin and Fowler–Nordheim approaches for the general problem of field emission from a material into the vacuum.
Grain boundary trap distribution in polycrystalline silicon thin-film transistors
Authors: Dimitriadis C. A.
Published: July 2002

The grain boundary trap state density is evaluated in polysilicon thin-film transistors by a method based on the dependence of the grain boundary potential barrier height on the gate voltage. Assuming a Gaussian energy distribution of the grain boundary trap states, the distribution parameters are determined by fitting the grain boundary barrier height experimental data with the theory. In low-pressure chemical vapor deposited polysilicon films, the influence of deposition pressure on the grain boundary trap distribution is examined by using this method. A large number of traps exist at the grain boundaries near the midgap of the material deposited at lower pressure due probably to an increased impurity contamination.
Temperature dependence of chromatic dispersion in dispersion-shifted fibers: Experiment and analysis
Authors: Kim Kwang S. , Lines M. E.
Published: July 2002

The temperature dependence of chromatic dispersion is reported for two different dispersion-shifted communications fibers with zero dispersion wavelengths λ0≊1.54 and 1.56 μm, respectively. Although the temperature dependence of dispersion is quite different for the two as wavelength λ→λ0, the value of dλ0/dT≊0.03 nm/K is closely equal for both. Evidence is presented to show that dλ0/dT is dominantly a property of the fiber material (germania doped silica) and is not significantly dependent on fiber design. A materials analysis is presented using a two-term Sellmeier formalism, one term each for electronic and ionic response. The relevant Sellmeier parameters and their temperature derivatives are determined and the temperature dependence of λ0 is shown to be dominantly driven by a temperature modulation ≊−0.4 meV/K of the electronic Sellmeier band gap.
Modeling of micromagnetic Barkhausen activity using a stochastic process extension to the theory of hysteresis
Authors: Jiles D. C. , Sipahi L. B. , Williams G.
Published: July 2002

Recent work by Bertotti [IEEE Trans. Magn. MAG-24, 621 (1988)] and others has shown that it is possible to model the micromagnetic Barkhausen discontinuities at the coercive point using a two-parameter stochastic model. However, the present formulation of the model is restricted to limited regions of the hysteresis curve over which dM/dH is approximately constant and when dH/dt is held at a constant rate. A natural extension of this model is to take the basic result, in which the level of Barkhausen activity in one time period is related to the activity in the previous time period, and increment it by a small amount which is dependent on the differential permeability. The extension of the model proposed here uses the theory of ferromagnetic hysteresis to determine the differential permeability at any point of the hysteresis loop. The Barkhausen activity is then assumed to vary in proportion to the differential permeability. The resulting model allows the Barkhausen sum of discontinuous changes in magnetization to be modelled around the entire hysteresis loop, leading to an important generalization of the basic model.
Modified method of electric-field induced second-harmonic generation
Authors: Uemiya Takafumi , Uenishi Naoto , Umegaki Shinsuke
Published: July 2002

Second-order hyperpolarizabilities β of organic nonlinear optical materials were measured by a modified method of the electric-field induced second-harmonic generation. Since this method avoided interference between two second-harmonic waves from a solution and cell-window glass, β of a dilute solution was easily determined and at the same time, a third-order hyperpolarizability γ of a solvent was also evaluated. The obtained β values were constant in a wide range of the concentration.
Surface orientation and stacking fault generation in strained epitaxial growth
Authors: Kvam E. P. , Hull R.
Published: July 2002

It has been observed that partial dislocation glide and stacking fault introduction occur in diamond cubic materials during tensile mismatched growth on (001) and compressive mismatched growth on (110) and (111). For reversed sense of mismatch, however, only full lattice dislocations are observed for strain relief. The general criteria are presented for when a partial misfit dislocation is possible as a function of growth surface orientation. It is shown that, for zero stacking fault energy, the slip regime (dislocation type) expected during (001) growth will hold for any growth orientation (hkl) for which 0≤h≤k≤l/2, and the opposite regime should occur for (hkl) when l≤k/2≤l. Effects of heterointerfacial line tension and stacking fault energy are also considered.
Multi-beam laser deflection measurements of reduced density channels created by electron beams propagating in near-atmospheric-pressure air
Authors: Stalder K. R. , Williams M. S. , Eckstrom D. J.
Published: July 2002

Properties of reduced density channels created by energy deposition from electron beams propagating in air are presented. A multi-beam laser deflection technique used to diagnose the channels is described, as are representative examples of density channels formed in multi-pulse propagation experiments performed at the Advanced Test Accelerator at the Lawrence Livermore National Laboratory.
Measurement of effective magnetic anisotropy of nanocrystalline Fe-Cu-Nb-Si-B soft magnetic alloys
Authors: Ho Kai-Yuan , Xiong Xiang-Yuan , Zhi Jing , Cheng Li-Zhi
Published: July 2002

The magnetic anisotropy of a nanocrystalline soft magnetic Fe73.5Cu1Nb3Si13.5B9 alloy has been determined by studying the magnetization process. The experimental results on the approach to magnetic saturation have been used to determine its effective magnetic anisotropy constant 〈K〉. This is about one tenth of the magnetocrystalline anisotropy constant K1 of individual α-Fe (Si) grains.
Electron beam charging thermography of mirrors of semiconductor laser diodes
Authors: Jakubowicz A.
Published: July 2002

Charging insulating films in a scanning electron microscope is shown to be a potentially useful thermographic technique which makes it possible to reveal hot regions in microelectronic devices, with a spatial resolution in the submicrometer range. This technique entails depositing an insulating film on the device to serve as thermographic medium. A focused, low-energy electron beam charges the insulator during the scanning process. Hot regions modify the local charge, which in turn modifies the secondary electron signal and thus generates a thermal contrast. This technique has been applied to investigate mirrors of GaAs/AlGaAs graded index separate confinement single quantum well laser diodes. Thermographic images of these mirrors have been obtained with a spatial resolution of 0.25 μm. Since the thermal images can be observed using the scanning electron microscope’s TV mode, the course of fast thermal phenomena at laser mirrors can be imaged. As an example, the thermal drift prior to the thermal runaway at laser mirrors has been investigated.
Shallow ohmic contact to both n- and p-GaAs
Authors: Han W. Y. , Lu Y. , Lee H. S. , Cole M. W. , Casas L. M. , DeAnni A. , Jones K. A. , Yang L. W.
Published: July 2002

A shallow Pd/Ge/Ti/Pt/ohmic contact for both n- and p-GaAs has been investigated. The contacts were rapid thermally annealed in N2 for 15 s at temperatures from 350 to 550 °C. The lowest average specific contact resistances were 4.7×10−7 and 6.4×10−7 Ω cm2 for the n- and p-GaAs, respectively, when the n-GaAs was doped with Si to 2×1018 cm−3 and the p-GaAs was doped with carbon to 5×1019 cm−3. Electrical measurements and Auger depth profiles showed that the contacts were stable as they remained ohmic after an anneal at 300 °C for 20 h for both n- and p-GaAs. The p contact is more stable than the n contact at the higher temperatures where there is more As outdiffusion as determined by Auger depth profiles. Transmission electron microscopy showed that the interfaces between the p-GaAs and the contacts were smooth for both as-grown and annealed samples, and no oxides were detected.
Response to ‘‘Comment on ‘Surface acoustic wave studies on single crystal nickel using Brillouin scattering and scanning acoustic microscope’ ’’ [J. Appl. Phys. 75, 5459 (1994)]
Authors: Mendik M. , Sathish S.
Published: July 2002

The authors have answered all the comments and concerns raised by Kim and Weglein [J. Appl. Phys. 75, 5459 (1994)]. Figure 3 of M. Mendik, S. Sathish, A. Kulik, G. Gremaud, and P. Wachter [J. Appl. Phys. 71, 2830 (1992)] is presented in a modified form. It is once again demonstrated that the technique developed for the determination of elastic constants is reliable for the (100) plane of elastically anisotropic single crystals also.
Origin of recombination transitions at the lattice-matched GaInAsSb-GaSb n-N type-II heterojunctions
Authors: Hulicius E. , Oswald J. , Pangrác J. , Šimeček T. , Bresler N. S. , Cheban V. N. , Gusev O. B. , Titkov A. N.
Published: July 2002

Luminescence properties of GaSb-GaInAsSb isotype type-II heterojunctions with various dopings have been investigated. GaInAsSb n-type epitaxial layers were grown by liquid-phase epitaxy on Czochralski-grown N-type substrates with different tellurium concentrations. Two main luminescent peaks with mutual interchange of intensity and with wavelength shift were observed, both with temperature and excitation intensity. This effect is dependent on dopant concentration in the substrate, as well as in the layer. The explanation of this effect is based on the dominant role of double acceptor levels as final states for the luminescent transitions. A new band in the luminescence spectra was found which is interpreted as a tunneling recombination of the conduction electrons with the photoexcited holes trapped on native acceptors in the band-bending region at the GaSb side of the heterojunction.
Multiphoton ionization detection of a SiO molecule formed by O2 oxidation of a silicon surface
Authors: Nakamura K. G. , Kuroki H. , Kitajima M.
Published: July 2002

Gaseous SiO formation by silicon surface oxidation has been measured using a multiphoton ionization time-of-flight mass spectrometer. The long induction time of the SiO formation and the adsorption of the O2 beam have been observed in the time dependence of the SiO+, Si+, and O+2 signals during surface oxidation. The nonlinear dependence of the SiO and Si atom densities on O2 gas pressure has been observed in the low O2 pressure range of 10−6–10−4 Pa and suggests that the Si atoms are mainly due to the photodissociation of gaseous SiO molecules.
Interaction of iron with a grain boundary in boron-doped multicrystalline silicon
Authors: Kittler M. , Seifert W. , Stemmer M. , Palm J.
Published: July 2002

The article presents a study of the interaction of iron with a grain boundary in boron-doped multicrystalline silicon. The sample was intentionally contaminated with iron to a few 1014 cm−3 and investigated by the electron-beam-induced-current technique (measurement of minority-carrier diffusion length, quantitative imaging) in the temperature range 80–300 K. The measurements were carried out for two different states of iron in the sample: (i) iron paired with boron, i.e., as FeB, and (ii) iron as interstitial iron Fei. The differences between diffusion lengths for these two states were used to estimate the iron concentration. The analysis of the data revealed a pronounced iron profile around the grain boundary, indicating gettering of about 4×1011 iron atoms per cm2. The recombination velocity of the grain boundary is about 5×105 cm s−1 at 300 K and is not changed by the FeB destruction treatment. The temperature dependence of the iron-related diffusion length components is discussed and found to be in satisfactory agreement with what is expected from Shockley–Read–Hall theory. Further, the diffusion length analysis revealed also a strong recombination channel of unidentified origin.
Nanodispersed silicon in pregraphitic carbons
Authors: Wilson A. M. , Way B. M. , Dahn J. R. , van Buuren T.
Published: July 2002

Using chemical-vapor deposition nanodispersed silicon has been prepared in carbon at temperatures between 850 and 1050 °C. Samples with up to 11% atomic silicon in carbon show the same pregraphitic x-ray-diffraction pattern as those without silicon. X-ray-absorption spectroscopy shows that the silicon is bonded mostly to carbon neighbors and that large clusters of silicon are not found. It is believed that silicon atoms, or small clusters of a few silicon atoms, are located in regions of ‘‘unorganized carbon’’ which separate small regions of organized graphene layers. These materials may have application as electrode materials in advanced rechargeable lithium batteries.
Organic/inorganic superlattices with ordered organic layers
Authors: Tokito Shizuo , Sakata Jiro , Taga Yasunori
Published: July 2002

Superlattices consisting of alternating layers of organic and inorganic materials have been fabricated from 3,4,9,10-perylenetetracarboxylic diimide (PTCDI), copper phthalocyanine (CuPc), and MgF2 by molecular-beam deposition. From the small-angle x-ray diffraction patterns of PTCDI/MgF2 and CuPc/MgF2 superlattices, a periodically layered structure is confirmed through the entire stack. The PTCDI layers in the PTCDI/MgF2 superlattices have a high degree of structural ordering, in which molecular planes are nearly parallel to the substrate surface. On the other hand, the CuPc/MgF2 superlattices have a poorly ordered structure in the CuPc layers. It is found that the optical absorption spectra of these superlattices are different from those of organic single films and significantly change with varying organic layer thickness. Such spectral changes can be interpreted by the effect of the aggregate size and the coexistence of two different crystal forms.
Model of partitioning of point defect species during precipitation of a misfitting compound in Czochralski silicon
Authors: Huh J.-Y. , Tan T. Y. , Gösele U.
Published: July 2002

The partitioning of point defect species during diffusion controlled precipitation of a misfitting compound in Czochralski silicon is studied using the principle of maximum degradation rate of the total system free energy. The degradation rate of the system free energy is obtained from the entropy production due to mass diffusion in the matrix. The results are then compared with those obtained using the principle of maximum growth rate. It is shown that, for a precipitation process involving more than one chemical or structural component species with their concentrations deviating from the appropriate thermal equilibrium values, the maximum growth rate description does not generally correspond to that of the maximum degradation rate of the system free energy. The results are then applied to oxygen precipitation in silicon, showing some equilibrium characteristics pertinent to a multicomponent system with intrinsic point defects acting as pseudocomponents. It is also shown that, depending on the intrinsic point defect concentrations at the far field of diffusion, the oxide precipitate can grow either by emitting or by absorbing both vacancies and Si self-interstitials.
Electrical and photoluminescent properties of high-quality GaSb and AlGaSb layers grown from Sb-rich solutions by liquid-phase epitaxy
Authors: Jiang Wen-Jang , Sun Yuh-Maoh , Wu Meng-Chyi
Published: July 2002

The growth-temperature dependence of electrical and photoluminescent (PL) properties of GaSb and Al0.065Ga0.935Sb layers grown from Sb-rich solutions by liquid-phase epitaxy has been studied. The GaSb and AlGaSb epitaxial layers grown at 606 °C exhibit a low hole concentration of 4×1015 and 2×1016 cm−3, respectively. The low-temperature PL spectra of GaSb and AlGaSb is dominated by free-exciton transition and excitons bound to neutral acceptors. As the growth temperature is increased, both the residual hole concentration and the intensity of band A related to native lattice defects in GaSb and AlGaSb increase. The high-quality GaSb and AlGaSb epitaxial layers can be grown at low temperatures from Sb-rich solutions.
Derivation of the Weibull distribution based on physical principles and its connection to the Rosin–Rammler and lognormal distributions
Authors: Brown Wilbur K. , Wohletz Kenneth H.
Published: July 2002

We describe a physically based derivation of the Weibull distribution with respect to fragmentation processes. In this approach we consider the result of a single-event fragmentation leading to a branching tree of cracks that show geometric scale invariance (fractal behavior). With this approach, because the Rosin–Rammler type distribution is just the integral form of the Weibull distribution, it, too, has a physical basis. In further consideration of mass distributions developed by fragmentation processes, we show that one particular mass distribution closely resembles the empirical lognormal distribution. This result suggests that the successful use of the lognormal distribution to describe fragmentation distributions may have been simply fortuitous.
Atomistic models of vacancy-mediated diffusion in silicon
Authors: Dunham Scott T. , Wu Can Dong
Published: July 2002

Vacancy-mediated diffusion of dopants in silicon is investigated using Monte Carlo simulations of hopping diffusion, as well as analytic approximations based on atomistic considerations. Dopant/vacancy interaction potentials are assumed to extend out to third-nearest neighbor distances, as required for pair diffusion theories. Analysis focusing on the third-nearest neighbor sites as bridging configurations for uncorrelated hops leads to an improved analytic model for vacancy-mediated dopant diffusion. The Monte Carlo simulations of vacancy motion on a doped silicon lattice verify the analytic results for moderate doping levels. For very high doping (≳2×1020 cm−3) the simulations show a very rapid increase in pair diffusivity due to interactions of vacancies with more than one dopant atom. This behavior has previously been observed experimentally for group IV and V atoms in silicon [Nylandsted Larsen et al., J. Appl. Phys. 73, 691 (1993)], and the simulations predict both the point of onset and doping dependence of the experimentally observed diffusivity enhancement.
Long wavelength InAs/InGaSb infrared detectors: Optimization of carrier lifetimes
Authors: Grein C. H. , Young P. M. , Flatté M. E. , Ehrenreich H.
Published: July 2002

The performance characteristics of type-II InAs/InxGa1−xSb superlattices for long and very long-wave infrared detection are discussed. This system promises benefits in this wavelength range over conventional technology based on Hg1−xCdxTe, in part because of suppressed band-to-band Auger recombination rates which lead to improved values of detectivity. The formalism for calculating Auger rates in superlattices is developed and the physical origin of Auger suppression in these systems is discussed. Accurate K⋅p band structures are used to obtain radiative, electron–electron, hole–hole, and band-to-band Auger rules, as well as shallow trap level assisted Auger recombination rates for photodiodes. Theoretical limits for high temperature operation of ideal photovoltaic detectors are presented and compared with HgCdTe.
Thermal conductivity of dc-plasma assisted chemical vapor deposited diamond films
Authors: Chae Hee-Baik , Han Yong-Jin , Seong Dae-Jin , Kim Jong-Chul , Baik Young-Joon
Published: July 2002

The dc-plasma assisted chemical vapor deposition method has been used to synthesize diamond films. Thermal diffusivity of these films has been measured in 120–800 K with a modified Angstrom method. Phonon scattering processes are considered to analyze thermal conductivity with the full Callaway model. In analysis, microstructure of grain boundaries and extended defect concentration give significant effects to the mean free path of phonons in low temperatures. At high temperatures, the thermal conductivity is governed by the intrinsic thermal resistive process, the umkalpp process. Thermal conductivity of the films above 500 K is shown to close to a recent measurement of natural diamond. This supports that the crystal structure of the films is not different with the bulk diamond.
Brewster angle technique to study metal nanoparticle distributions in dielectric matrices
Authors: Tognini P. , Geddo M. , Stella A. , Cheyssac P. , Kofman R.
Published: July 2002

We report experimental results obtained by means of the Brewster angle technique on samples constituted by Pb and Sn nanoparticles embedded in an amorphous SiO matrix. The extended comparison with different effective medium models gives clear indications on (i) the structural composition of the samples and (ii) the spatial distribution of the metallic particles in these systems, pointing to a quasi-two-dimensional arrangement.
The growth and properties of Al and AlN films on GaN(0001)–(1×1)
Authors: Bermudez V. M. , Jung T. M. , Doverspike K. , Wickenden A. E.
Published: July 2002

The growth, structure, and annealing behavior of Al films, formed by in situ vapor deposition on GaN(0001)–(1×1) near 25 °C, have been studied using Auger, electron energy loss, x ray and ultraviolet photoemission spectroscopies and low-energy electron diffraction. Film growth occurs by a Stranski–Krastanov process with reaction at the immediate interface leading to metallic Ga. Annealing at ≳800 °C leads to release of N, which reacts with Al to form a (1×1)-ordered layer of AlN, possibly alloyed with a small amount of Ga. The AlN layer has been characterized using the various spectroscopies, and the work function, band bending, and electron affinity of GaN and of the AlN overlayer have been obtained. The Al/GaN Schottky barrier height has been measured and compared with previous results for Ni/GaN.
Improved piezoelectricity in thick lamellar β-form crystals of poly(vinylidene fluoride) crystallized under high pressure
Authors: Hattori Takeshi , Kanaoka Masashi , Ohigashi Hiroji
Published: July 2002

Poly(vinylidene fluoride) (PVDF) was crystallized under high pressures on the basis of the pressure-temperature (P-T) phase diagram obtained recently, and piezoelectric and ferroelectric properties of the resulting films were evaluated. Crystallization in the metastable hexagonal phase appearing at high pressure and temperature below the triple point yielded a film comprising extended chain lamellar crystals of a mixture of β and γ forms, the latter of which is transformed into β form by poling at an elevated temperature (120 °C). The poled film exhibits strong piezoelectric effect persistent up to the melting temperature (205 °C). The electromechanical coupling factor kt for the thickness extensional piezoelectric effect is 0.27 at 25 °C, the largest value ever found in PVDF. The results of studies on morphology, structure, and thermal properties are also described.
Spatially resolved, excited state densities and neutral and ion temperatures in inductively coupled argon plasmas
Authors: Hebner G. A.
Published: July 2002

Spatially resolved, line integrated, excited state densities, and neutral and ion temperatures have been measured in inductively coupled argon plasmas. Absorption spectroscopy was used to measure the line integrated density and temperature of the argon 1s5, 1s4, 1s3, and 1s2 energy levels. Laser-induced fluorescence was used to confirm the neutral temperatures and to measure argon metastable ion temperatures. For rf powers between 50 and 300 W and pressures of 4–50 mTorr, the line integrated density of the 1s5 energy level varied between 1×1016 and 2×1016 m−2. The densities of the 1s4, 1s3, and 1s2 levels were approximately 4–10 times smaller. In the center of the plasma, the ion and neutral temperatures were identical, between 550 and 1000 K for plasma powers between 30 and 240 W and pressures between 4 and 50 mTorr. The neutral temperature had a maximum in the center of the discharge and decreased towards the edge of the discharge. However, the ion temperature increased to between 3000 and 4000 K at the edge of the discharge. Ion drift velocity in the radial direction was between 1×105 and 2×105 cm/s at the edge of the plasma. No significant changes in the spatial density distribution or temperature were observed when either a rf bias was applied to the lower electrode or when the stainless-steel lower electrode was covered with a bare silicon wafer. The addition of nitrogen to the argon discharge resulted in the density of the 1s5 state decreasing by a factor of 2 and the density of the 1s4 state decreasing by a factor of 10. Implications of these measurements on the radial electric fields, radiation trapping, and the energy transport in the plasma are discussed.