bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of arsenic incorporation and electrical properties in CdTe layers grown by metalorganic vapor phase epitaxy
Authors: Ekawa Mitsuru , Yasuda Kazuhito , Ferid Touati , Saji Manabu , Tanaka Akikazu
Published: July 2002

The As doping mechanism in (100) CdTe layers grown on (100) GaAs by atmospheric-pressure metalorganic vapor phase epitaxy was studied. Triethylarsine (TEAs) was used as a dopant source. The source materials used were dimethylcadmium (DMCd) and diethyltelluride (DETe). The As incorporation was enhanced by decreasing the DETe flow rate under a fixed DMCd flow condition, and by lowering the growth temperature. Assuming 100% activation of As, the As incorporation efficiency was estimated to be about 0.1%. The As incorporation was dominated by the sticking rate of the As species onto the Cd species. The hole concentration was controlled from 2×1015 to 3×1016 cm−3 in proportion to the TEAs flow rate below 1×10−7 mol/min. Those doped layers showed hole mobilities as high as 75 cm2/V s. Low-temperature photoluminescence (PL) studies revealed that a neutral-acceptor bound-exciton at 1.5901 eV is due to a substitutional As acceptor on the Te site. The As ionization energy was about 90 meV from the PL and electrical measurements.
Mechanism of diamond growth by chemical vapor deposition: Carbon-13 studies
Authors: D’Evelyn M. P. , Chu C. J. , Hange R. H. , Margrave J. L.
Published: July 2002

Previous 13CH4/12C2H2 isotopic competition experiments on the mechanism of diamond growth by chemical vapor deposition are reanalyzed in light of recent evidence for a nonlinear dependence of the first-order Raman shift frequency on 13C mole fraction. The new Raman data imply a 13C mole fraction for mixed-isotope diamond films several percent higher than that reported previously. The corrected carbon-13 mole fractions of polycrystalline diamond films and homoepitaxial films grown on (100), (111), and (110) natural diamond substrates were each equal, within experimental error, to that of the methane above the substrate but significantly different from that of gas-phase acetylene. As the 13C mole fractions of methyl radical and methane should be nearly identical, the methyl radical is concluded to be the predominant growth precursor regardless of the crystallographic orientation of the diamond substrate.
Estimation of the reliability of 0.98 μm InGaAs/GaAs strained quantum well lasers
Authors: Okayasu Masanobu , Fukuda Mitsuo
Published: July 2002

A reliability study has been made on 0.98 μm InGaAs/GaAs strained quantum well ridge waveguide lasers for pumping erbium-doped fiber optical amplifiers (EDFAs). Analysis of a constant power long-term aging test over 104 h shows that the degradation rate is proportional to the square root of the aging time irrespective of operating output power. A simple relationship is found between degradation rate and both operation current density and optical density. The change in light-current characteristics and emission wavelength during constant current aging are also investigated. It is found that emission wavelength exhibits a blue shift for an identical operation current accompanied by laser degradation due to an increased threshold carrier density. In constant-power mode aging, on the other hand, the shift is found to be rather complicated because of an additional factor of an increase in junction temperature causing a red shift. The influence of the wavelength shift on amplification characteristics in EDFAs is also discussed.
Diamond growth from a CO/CH4 mixture by laser excitation of CO: Laser excited chemical vapor deposition
Authors: Rebello J. H. D. , Straub D. L. , Subramaniam V. V.
Published: July 2002

We report for the first time, diamond growth from a mixture of 95% CO and 5% CH4 without gas phase hyperdilution of H2. Such a mixture has not been previously reported to yield diamond by any of the existing methods (hot-filament chemical vapor deposition, plasma-assisted chemical vapor deposition, or flame synthesis). In this paper we describe our observations of diamond growth at low pressures from vibrational excitation of CO in a CO/CH4 mixture by irradiation from a CO laser operating on its shorter wavelengths. We refer to this technique as laser excited chemical vapor deposition.
Phase formation and martensitic transformation in mechanically alloyed nanocrystalline Fe—Ni
Authors: Kuhrt C. , Schultz L.
Published: July 2002

Fe—Ni alloys were prepared by mechanical attrition of elemental powders in a planetary ball mill in argon atmosphere. A nonequilibrium phase diagram of Fe100−xNix, mechanically alloyed at various milling intensities, is presented. Disordered body-centered-cubic and/or face-centered-cubic supersaturated solid solutions with a two-phase region are found. The maximum solubilities are 30 at. % Ni in Fe and 40 at. % Fe in Ni and decrease slightly with increasing milling intensity, i.e., processing temperature. Mechanically alloyed Fe—Ni is in a nanocrystalline state with an average grain size of 25–35 nm. The grain refinement is accompanied by an increase in atomic-level strain up to about 1% root-mean-square. This high internal strain affects predominantly the coercivity which is at least 4 A/cm even for single-phase alloys. The kinetics of the martensitic γ→α′ transformation in mechanically alloyed nanocrystalline Fe—Ni are significantly modified in comparison to coarse-grained as-cast alloys. The nonequilibrium microstructure is assumed to hinder the growth of martensite which is confirmed by the investigation of the magnetic field-induced martensitic transformation.
Role of initial conductance and gas pressure on the conductance response of single-crystal SnO2 thin films to H2, O2, and CO
Authors: Vetrone J. , Chung Y.-W. , Cavicchi R. , Semancik S.
Published: July 2002

Gas-induced conductance changes were measured on palladium-dosed single-crystal tin oxide (SnO2) thin films having well-characterized surface properties. Films were fabricated using two methods: reactive sputtering and chemical vapor deposition. Film orientation and crystal structure were determined by x-ray diffraction, while surface morphology was characterized using atomic force microscopy. Conductance changes were measured continuously on film surfaces during alternating exposure and evacuation cycles to partial pressures of H2, O2, and CO in a vacuum chamber. The conductance change was found to be proportional to the square root of the initial film conductance and was interpreted in terms of gas-induced changes in the width of a near-surface space-charge layer. The variation of conductance as a function of gas pressure during alternating exposure and evacuation cycles of H2 and O2 is consistent with a model that involves surface reactions between coadsorbates.
Enhanced surface/interface recombination and surface inversion of Ni decorated Si/Si(Ge)/Si heterostructures
Authors: Zhou T. Q. , Buczkowski A. , Radzimski Z. J. , Rozgonyi G. A.
Published: July 2002

Electron beam induced current variations in images of strain relaxed epitaxial Si/Si(Ge)/Si wafers deliberately contaminated with nickel from the backside are reported for different contamination levels. Strong recombination contrast due to NiSi2 precipitates was observed both at the top Si surface and along buried interfacial misfit dislocations. A surface conductivity inversion from n to p type was obtained for the high level Ni contaminated sample. A theoretical analysis based on the presence of a surface potential due either to a metal-silicon Schottky contact, or to the accumulation of charged traps is used to explain the observed effects.
Microstructure and magnetic properties of Zn- or Sn-bonded Sm2Fe17Nx magnets
Authors: Rodewald W. , Wall B. , Katter M. , Velicescu M. , Schrey P.
Published: July 2002

Hard magnetic Sm2Fe17Nx alloy powders with a coercivity of 5.6 kA/cm and a remanent polarization of 1 T, related to the density of 7.7 g/cm3, could be achieved by a combined heat treatment in hydrogen atmosphere and a successive nitrogenation. During nitrogenation SmFe3 and SmFe2 constituents decompose into SmN and αFe immediately. The density of die-pressed anisotropic Sm2Fe17Nx magnets containing 5 wt % Zn amounts to ∼5 g/cm3 and increases to 5.25 g/cm3 for additions of 20 wt % Zn. After annealing at 390 °C for 10 h, the remanent polarization of 0.66 T and the coercivity of 8.8 kA/cm result in a maximal energy density of 67 kJ/m3. Annealing at temperatures of ∼420 °C achieves additional αFe due to a decomposition of Sm2Fe17Nx by Zn: Sm2Fe17Nx+Zn→Sm2FeZn2+αFe+N2. Additions of 10 wt % Sn result in a density of 4.6 g/cm3 of isostatically compacted magnets. The remanent polarization amounts to ∼0.6 T, but the coercivity Hcj of ∼4 kA/cm is inferior to Zn-bonded Sm2Fe17Nx magnets.
Comment on ‘‘Current transport in Pd/n-InP diodes formed at room and low temperature’’ [J. Appl. Phys. 72, 3803 (1992)]
Authors: Tung R. T.
Published: July 2002

It is pointed out that, under most circumstances, current transport characteristics observed at Schottky barrier junctions cannot be used to unambiguously identify the mechanism responsible for electron conduction. This practice, however, is quite common and is shown to lead to an incorrect conclusion in a recent article [Z. Q. Shi and W. A. Anderson, J. Appl. Phys. 72, 3803 (1992)].
Spatial coherence measurements and x-ray holographic imaging using a laser-generated plasma x-ray source in the water window spectral region
Authors: Turcu I. C. E. , Ross I. N. , Schulz M. S. , Daido H. , Tallents G. J. , Krishnan J. , Dwivedi L. , Hening A.
Published: July 2002

The properties of a coherent x-ray point source in the water window spectral region generated using a small commercially available KrF laser system focused onto a Mylar (essentially carbon) target have been measured. By operating the source in a low-pressure (approximately 20 Torr) nitrogen environment, the degree of monochromaticity was improved due to the nitrogen acting as an x-ray filter and relatively enhancing the radiation at a wavelength of 3.37 nm (C vi 1s-2p). X-ray pinhole camera images show a minimum source size of 12 μm. A Young’s double slit coherence measurement gave fringe visibilities of approximately 62% for a slit separation of 10.5 μm at a distance of 31.7 cm from the source. To demonstrate the viability of the laser plasma as a source for coherent imaging applications a Gabor (in-line) hologram of two carbon fibers, of different sizes, was produced. The exposure time and the repetition rate was 2 min and 10 Hz, respectively.
Transmission of an obliquely incident electron wave through GaAs-AlxGa1−xAs structures: Application to an electron wave filter
Authors: Kan’an A. M. , Puri A. , Odagaki T.
Published: July 2002

Transmission of an obliquely incident electron wave through GaAs-AlxGa1−xAs structures is analyzed using a generalized transmission matrix approach. Angle dependence is investigated quantitatively. Concepts of critical angle are discussed for step barrier structures. It is verified that the transmission probability is a function of longitudinal energy. Consequences of resonant tunneling of a non-normal incident electron wave through a double barrier heterostructure (DBHS) are discussed. It is found that the angle of incidence largely affects the probability of tunneling of electrons through DBHS. Application to an electron wave filter is discussed.
Three-dimensional concentration profiles of hybrid diffusers in crystalline silicon
Authors: Coffa S. , Privitera V. , Frisina F. , Priolo F.
Published: July 2002

The diffusion of ion-implanted Au, Pt, and Zn in crystalline Si has been investigated. The implantation was performed in photolithographically defined areas of the wafer and a spreading resistance technique was used to measure the three-dimensional concentration profiles of the metal atoms after high temperature diffusion anneals. We found that the lateral spread under the mask is larger than the vertical diffusion, especially on the sample side opposite to the implanted diffusion source. All the significant features of the measured profiles can be explained as a consequence of the kick-out mechanism of diffusion for these transition metals. In fact, the peculiar shape of the concentration profiles is determined by the interplay between the influx of interstitial metal atoms and the outflux of silicon self-interstitials generated by the kick-out reaction. Despite the high lateral diffusion, it will be shown that by a suitable combination of implantation fluence and annealing temperature it is possible to limit this lateral spread inside ∼200 μm, while maintaining a high metal concentration in the region under the implanted area. This demonstrates the possibility of using transition metal diffusion to control minority carrier lifetime in a selected area of a semiconductor device.
Theory of microwave effects on bubble dosimeters
Authors: Swandic J. R.
Published: July 2002

Bubble dosimeters measure a neutron flux by its effect upon microscopic droplets of superheated liquid encased in a polymer gel. It has been observed that a microwave field can also induce bubble formation in some of the droplets. This article considers the theory of this phenomenon as an effect of a microwave-induced temperature increase. Although the droplets are superheated, their confinement by a smooth gel surface and lack of impurities such as dust particles allow only homogeneous nucleation to occur. At room temperature the thermal fluctuations that give rise to critical size bubbles are very rare; the dosimeter thus has a long shelf life and a low spontaneous noise level. In the presence of a microwave field, the gel and droplets absorb energy and can be heated by 1–2 K for moderate powers; a high-power microwave field is needed to produce an observable nucleation rate. The electromagnetic properties of the dosimeter determine the internal field and the microwave absorption. Then the microwave heating and thermal properties of the dosimeter lead to an elevated steady-state temperature for the droplets. Finally, the nucleation rate is obtained from classical homogeneous nucleation theory, while the number of bubbles formed in an ensemble of droplets is found by a simple statistical argument. Although a special case is considered and several approximations are invoked, the qualitative results show this effect could lead to spurious neutron readings only for intense microwave fields or for an ambient temperature close to the nucleation temperature. For microwave bubble dosimetry, some nonthermal mechanism would be much more useful.
An electron spin resonance study of the effects of thermal nitridation and reoxidation on P
b centers at (111) Si/SiO2 interfaces
Authors: Yount J. T. , Lenahan P. M. , Wyatt P. W.
Published: July 2002

Electron spin resonance of Pb centers is used to probe the dielectric/silicon interface in NH3-nitrided oxide (NO) and reoxidized nitrided oxide (RNO) dielectrics. The Pb spectra observed in the NO and RNO systems differ from Si/SiO2 systems only in the value of g⊥; the Δg⊥ suggests that the average value of the local strain at the defect site decreases upon nitridation, and is little changed by subsequent reoxidation. The relaxation of the Pb center structure appears to coincide with a reduction of compressive stress in the dielectric and an increase of tensile stress in the silicon substrate. These results suggest that differences in atomic scale strain due to nitrogen incorporation may be involved in the reduced radiation- and hot carrier-induced interface state generation that NO and RNO dielectrics exhibit.
Control of forward voltage in heterostructure transistors
Authors: Reynolds C. L. , Iannuzzi M. P. , Vuong H. H. , Parker S. M.
Published: July 2002

It is shown that the forward voltage of heterostructure transistors can be modified by varying the thickness of the undoped GaAs layer beneath the gate or by low energy ion implantation of a surface layer. This suggests that the effective barrier height can be controlled by either technique.
Pressure and composition effects on the gap properties of AlxGa1−xAs
Authors: Capaz R. B. , de Araújo G. C. , Koiller Belita , von der Weid J. P.
Published: July 2002

Effects of pressure and composition on the gap properties of AlxGa1−xAs randomly disordered alloys are investigated theoretically and experimentally. The analogy between pressure and alloying effects is explored. Special attention is given to the direct-to-indirect gap transition region, where the gap sensitivity to both pressure and composition variations is shown to be strongly enhanced. A 30% decrease in luminescence intensity is produced on a x=0.46 sample under applied pressure of 0.7 kbar, while a similar effect in GaAs would require pressures of several tens of kbar. Calculations are performed within the small crystal approach using 64-, 216-, and 1000-atoms basic cluster sizes, with periodic boundary conditions. Convergence of the calculated properties with the cluster size is discussed.
Study of silicon surfaces bombarded with noble gas ions in an electron cyclotron resonance plasma
Authors: Day M. E. , Delfino M. , Tsai W. , Bivas A. , Ritz K. N.
Published: July 2002

The effect of electron cyclotron resonance plasma cleaning (100)Si surfaces with low energy Ne, Ar, and Xe ions is studied by in situ x-ray photoelectron spectroscopy, high-resolution cross-sectional transmission electron microscopy, atomic force microscopy, and measurement of both the single-surface reflectance and the modulated optical reflectance. Photoemission spectra show that complete removal of all surface contaminants with oxygen atoms knocked-in from the original native Si oxide and noble gas atoms implanted into the Si substrate are a common characteristic of this plasma cleaning process. The oxygen concentration appears to decrease with ion energy for all three ions, whereas the noble gas concentration is inversely proportional to the ion mass and essentially independent of the ion energy. This low energy ion bombardment sputters the surface causing only point defects with Ne ions, formation of a continuous thin amorphous overlayer with either Ar or Xe ions, and in addition, occasional subsurface planar defects with Xe ions alone. The original smoothness of the monocrystalline Si surface is maintained with Ne ions, while an increase in surface roughness accompanies the amorphization caused by Ar and Xe ions. The magnitude of the roughness, which depends more on the energy than on the mass of either ion is insufficiently small to account for a change in specularity at visible wavelengths. An increase in both the single-surface reflectance and the modulated optical reflectance is always observed after the plasma exposure and is shown to provide a sensitive measure of these changes in surface morphology with the latter technique being a somewhat more sensitive gauge of these effects.
Influence of the Josephson junction on the impedance and noise of a resistive superconductive quantum interference device
Authors: Soulen Robert J. , Fogle William E. , Colwell Jack H. , Cohn Joshua L. , Seppä Heikki
Published: July 2002

The impedance and noise of a resistive superconductive quantum interference device (R-SQUID) have been measured as a function of the dc and rf currents applied to it. The Josephson junction was adjustable so that data were also taken for several values of the junction critical current. The results were compared with the predictions of a resistively shunted junction (RSJ) model which takes into account the influence of the Josephson junction on the impedance and noise. The agreement was found to be quite good and demonstrates that the noise in the circuit is well understood. Use of the R-SQUID as a noise thermometer below 1 K is assessed in terms of corrections due to the RSJ model. It is demonstrated how the dc and rf currents may be adjusted so that the total noise of the R-SQUID is reduced to within 0.1% of the Johnson noise generated by the resistor alone. Under these conditions, the R-SQUID may be used as a noise thermometer to determine thermodynamic temperature to this inaccuracy from 6 to 700 mK.
Effects of thin-film thermal conductivity on the optical damage threshold of a-Si film on c-Si substrate at 1064 nm
Authors: Kuo B. S. W. , Schmid A. W.
Published: July 2002

Optical damage tests have been performed on a pair of a-Si film on c-Si substrate samples to determine their respective damage-threshold values. The thermal properties of the two samples have been determined previously in a noncontact, nondamage fashion [B. S. W. Kuo, J. C. M. Li, and A. W. Schmid, Appl. Phys. A 55, 289 (1992)], thus providing opportunity to relate the damage threshold to the thermal properties while controlling other factors. The samples have similar film thermal conductivity but much different interface thermal resistance. The damage test results show that the one with higher interface resistance is more vulnerable to high laser-pulse energy. A heat-transfer model involving both film thermal conductivity and interface thermal resistance has been developed to predict the damage-threshold dependence on film thickness. The result using predetermined thermal properties agrees with experimental data qualitatively. It also indicates that the interface property is the dominant factor here, while the impurity-dominant model cannot be applied, since no difference would be predicted for the two samples.
Investigation of indium doping in InGaAs/GaAs/AlGaAs graded-index separated confinement heterostructure lasers
Authors: Tsang J. S. , Lee C. P. , Liu D. C. , Chen H. R. , Tsai K. L. , Tsai C. M.
Published: July 2002

The effect of indium doping in the graded-index regions of the InGaAs/GaAs/AlGaAs graded-index separated confinement heterostructure quantum well laser has been studied. It was found that the threshold current density can be greatly reduced by a proper amount of In doping in the graded AlGaAs region. This result is attributed to an improvement in material quality due to a reduction in group III vacancies. The effect of thermal treatment on laser performance has also been studied. Although high temperature annealing can significantly improve non-In-doped lasers, it has little effect on In-doped lasers.
Improvement of oxide quality by rapid thermal annealing in N2
Authors: Wang L. S. , Lin M. S. , Yoo C. S. , Huang F. S.
Published: July 2002

Rapid thermal processing with a controlled cooling ramp as a postoxidation annealing in nitrogen is of considerable influence on the quality of thin (6 nm) thermal oxides. We studied how the annealing condition affected the electrical characteristics of the dielectrics, the charge-trapping properties, the gate voltage shift ΔVG, the flat band voltage shift ΔVFB, the increase of midgap interface state density ΔDitm under high field stress, the charge to breakdown, and the breakdown field. We found that controlled cooling after oxidation improved the interface between silicon and silicon dioxide. The postoxidation annealing in nitrogen reduced the fixed charge in oxides. The above measurements were correlated.
Aggregations of silicon interstitials and interstitial defect species in Czochralski silicon degenerately doped with boron during low temperature processing
Authors: Wijaranakula W.
Published: July 2002

The generation mechanism of crystallographic defects in Czochralski silicon degenerately doped with boron during low temperature processing was studied. After an extended annealing at 900 °C, the primary defects were identified as the a/2〈110〉-type elongated hexagonal- and a/6〈211〉-type rhombus-shaped dislocation loops using the transmission electron microscope. A low density of bulk stacking faults of the type a/3〈111〉 was also observed. No oxide precipitates were detected. After subsequent high temperature annealing, no significant change in the morphology or density of the interstitial-type defects was observed. Based upon the present results, it is hypothesized that aggregations of silicon interstitials and interstitial defect species during low temperature annealing could be one of the generation mechanisms of crystallographic defects in degenerately doped silicon.
Transition mechanisms of two interacting DX centers in N-type AlGaAs using reverse-bias deep level transient spectroscopy and temperature-dependent pulse-width reverse-bias deep level transient spectroscopy methods
Authors: Wang C. W. , Wu C. H.
Published: July 2002

The reverse-bias pulsed deep level transient spectroscopy (RDLTS) and a new temperature-dependent pulse-width RDLTS (TDP RDLTS) technique are reported to study the electric-field effect on carrier emission rates and the direct interaction between double DX centers recently detected in the Se:Al0.6Ga0.4As N confinement layer of the AlGaAs/GaAs single-quantum-well laser diodes. Traditional RDLTS measurements, with constant pulse width tp, prove that the two DX centers, Et1 and Et2, have strong direct emission interaction. Furthermore, the new TDP-RDLTS technique enables one to evaluate this direct transition time constant. Possible mechanisms for this interstate transition at different temperature ranges are provided and the new broadening effect due to this interstate transition is also reported here for the first time. Field-enhanced emission rates are calculated.
Formation of n+p shallow junction by As+ implantation through CoSi2 film
Authors: Chen Bin-Shing , Chen Mao-Chieh
Published: July 2002

Junction formation by As+ ion implantation into CoSi2 and subsequent drive-in annealing was investigated. Diodes with a leakage current density of 0.4 nA/cm2 at 5 V reverse bias can be obtained by a 700 °C/90 min furnace annealing. The performance of junction is mainly determined by the annealing temperature and time as well as the implantation dose. The implantation energy only has a minor effect on junction properties. Based on the experimental results, we define an appropriate process window for this junction formation technique.
Effect of supersaturation on the interface abruptness of AlGaAs/GaAs/AlGaAs quantum well grown by liquid phase epitaxy
Authors: Chen Mu-Kuen , Chang Tien-Chih , Lin Hao-Hsiung
Published: July 2002

The photoluminescence (PL) spectra of the AlGaAs/GaAs/AlGaAs quantum well structures grown by two different liquid phase epitaxy methods are studied. It is found that the supersaturation of the melt used to grow the top AlGaAs barrier can significantly influence the abruptness of the AlGaAs/GaAs interface. The sample of two-phase method which melt has less supersaturation shows larger PL linewidth and a special high energy shoulder. When temperature increases, the special high energy shoulder gradually shrinks. On the other hand, the sample of large supersaturation has narrower PL linewidth and does not have high energy shoulder. Local quantized states due to the serious interface fluctuaction are used to explain the PL characteristics of the sample grown by the two-phase method.
Preparation of textured diamond films on Si substrates by hot-filament chemical-vapor deposition
Authors: Ikoma Keiko , Yamanaka Mitsugu
Published: July 2002

Diamond was deposited on Si(111) substrates by a two-step hot-filament chemical-vapor deposition method consisting of the pretreatment and growth processes. In the pretreatment process, the substrate was heated at 1473 K briefly in a C3H8-CH4-H2 mixture gas. Textured 〈111〉-oriented diamond films were obtained with nucleation density of 109 cm−2. SiC grains were formed along with the nucleation sites for diamond in the present pretreatment process. Diamond was not deposited on the SiC layer, which was intentionally formed on a Si substrate, using the present growth process. SiC formation is not a sufficient condition for diamond nucleation.
Elasticity of mixed silver-halide polycrystalline optical fibers
Authors: Barkay N. , Katzir A.
Published: July 2002

The elastic strain limit of polycrystalline mixed AgClxBr1−x fibers was studied. These fibers are useful as flexible infrared optical fibers, and the elastic bending regime is preferred for applications which require many bending cycles. The experimental method was based on the spring-back upon releasing a stressed material, and used specifically calculated expressions. Elastic strain limit values are in the range of 0.15%–0.4%. They depend on composition going through a maximum at around the AgCl0.5Br0.5 composition. The dependence on composition is explained by a theoretical model, which is based on a solid-solution internal stress field, and uses material constants.
A modified Mullins–Sekerka stability analysis including surface energy effects
Authors: Zhang Lei , Garimella Suresh V.
Published: July 2002

An excess enthalpy correction is proposed to the energy balance condition at the solid-liquid interface used in the morphological stability analysis of a planar interface. The Mullins–Sekerka stability criterion is modified to account for this excess enthalpy. Numerical calculations show that the correction is especially significant at larger growth velocities; larger positive values of excess enthalpy have a stabilizing influence on the interface.
The role of phase-breaking processes in indirect-band tunneling barrier structures
Authors: Morrisey Richard A. , Khondker A. N.
Published: July 2002

A new description of the observed resonant tunneling effect in single barrier III–V structures are presented, based on inelastic or phase-breaking scattering. Near the interfaces in a GaAs/AlAs/GaAs quantum structure there is a substantial spatial overlap between Γ and X states of the GaAs and the AlAs regions, respectively. As a result, the X band in the AlAs barrier layer provides regions of enhanced current-carrying energy states into which Γ band electrons can scatter through phase-breaking scattering. In this description, scattered electrons are reinjected into states belonging either to Γ or X bands at rates determined by respective density of states.
The state of order of grain-oriented iron-silicon transformer sheets investigated by neutron scattering
Authors: Hilfrich K. , Schärpf O. , Nembach E.
Published: July 2002

The state of order of commercial high permeability, grain-oriented iron-silicon transformer sheets has been investigated by elastic neutron scattering. The atomic fraction of silicon was 0.061. The sheets had been subjected to the standard heat treatments. They were found to be strongly short-range ordered. The Warren–Cowley parameters αi, 1≤i≤3, were −0.063, −0.100, and +0.056, respectively. For comparison a single crystal grown from the same material was studied. From its neutron scattering data, it is concluded that the state of order of the sheets is that of the single crystal heat-treated at 723 K.
Planarized growth of AlGaAs/GaAs heterostructures on patterned substrates by molecular beam epitaxy
Authors: Ho M. C. , Chin T. P. , Tu C. W. , Asbeck P. M.
Published: July 2002

The profiles of AlGaAs/GaAs heterostructures grown by gas-source molecular beam epitaxy (GSMBE) on patterned substrates at different growth temperatures have been studied. It was found that at higher substrate temperature, the GSMBE growth results in Al clustering and the formation of high index planes. With a proper combination of low growth temperature and etched profile, a quasiplanarized surface is obtainable. A process simulation program is found to be capable of simulating the GSMBE growth profile at lower substrate temperature with reasonable accuracy.
Impedance of coils over layered metals with continuously variable conductivity and permeability: Theory and experiment
Authors: Uzal Erol , Moulder John C. , Mitra Sreeparna , Rose James H.
Published: July 2002

The frequency-dependent impedance of right-cylindrical air-core eddy-current probes over thick metal plates whose conductivity and permeability vary as a function of depth in the near-surface region have been studied both experimentally and theoretically. Measurements of probe impedance were made from 1 kHz to 1 MHz using an impedance analyzer. Precision-wound air-core coils were used for testing the theory, and commercial eddy-current probes were used to connect with industrial practice. The samples were of two types. First, to model a continuous profile, otherwise uniform plates of metal covered with many thin, discrete layers of other metals were considered. Second, as a practical example, case-hardened titanium plates, whose near-surface conductivity varies smoothly and continuously as a function of depth, were considered. Two theoretical results are presented for continuously varying profiles. First, an exact closed-form solution (within the quasistatic approximation) is reported for the impedance of a right-cylindrical air-core probe above a nonmagnetic metal whose near-surface conductivity difference varies as a hyperbolic tangent as a function of depth. Second, a new numerical technique is reported for determining the impedance of an air-core probe above a layered material whose conductivity and permeability vary arbitrarily. It is shown that the numerical technique converges and that for a hyperbolic tangent profile it agrees with the closed-form analytic solution and experiment. In general, it was found that continuous profiles can be experimentally (and theoretically) simulated by stacking many thin layers with differing conductivities, and that the probe’s impedance change is larger if the conductivity change is localized at the surface, and is smaller for more diffuse profiles.
Magnetic properties of a novel molecular-based magnetic compound containing a copper (II) monomer, a copper (II) dimer, and a ladder-like copper (II) chain
Authors: Valdes-Martinez Jesus , Cervantes-Lee Francisco , ter Haar Leonard W.
Published: July 2002

Recent results concerning synthetic, structural, and magnetic work on 3,4,9,10-perylenetetracarboxylic acid complexes of copper (II) are discussed. To date, the Cu(II)/PTCA/dien system has yielded two compositionally different crystalline products. Compound 1, [Cu3(dien)3(PTCA)(H2O)3](ClO4)22H2O represents the extremely rare case of three different molecular complexes of Cu(II), bound to the same ligands but with different stoichiometries, in the same compound. The magnetic lattice is comprised of three molecular substructures: complex 1a is a monomeric cation, [Cu(dien)(H2O)2]2+; complex 1b is a charge-neutral dimer, [Cu2(dien)2-(PTCA)(H2O)2]; and complex 1c a charge-neutral, infinite ladder-like chain structure, ∞1[Cu2(dien)2(PTCA)]n. Single crystal x-ray analysis of compound 2, [Cu2(dien)2(PTCA)(H2O)2]12H2O, reveals its structure simply consists of isolated, neutral dimers similar in structure to complex 1b. Magnetic susceptibility data in the temperature range 1.7–300 K shows the dimeric unit in 2 to be a weakly exchange-coupled antiferromagnetic dimer (−0.6 cm−1) and suggests that exchange interactions are indeed propagated through the PTCA anion over a Cu.....Cu separation of 15.7 Å. This result, in addition to the expected Curie paramagnetism of monomer 1a, affords the ladder-like chain 1c to be characterized as a chain of antiferromagnetically exchange-coupled ferromagnetic dimers (+12 cm−1). Long range ordering is not observed down to 1.7 K. Compound 1 is the first example of a molecular-based magnetic material that contains three different homonuclear magnetic molecules; a monomer, a dimer, and a ladder-like chain.
Microscopic calculations of density and field-dependent electronic trapping via attractive Coulomb centers
Authors: Joshi R. P.
Published: July 2002

We examine the dynamics of electronic transitions into the shallow states of attractive impurity centers in GaAs through numerical simulations. The molecular dynamics based formulation circumvents the difficulty of having to evaluate ‘‘sticking functions,’’ enables accurate computations of the phase-space distribution function, and allows microscopic treatment of both the carrier-phonon and carrier-carrier phenomena on an equal footing. Energy dependent trapping rates with and without the presence of external electric fields are obtained, and we consider situations involving both singly- and doubly-charged impurity centers. We show that initial trapping is reduced as a result of free-carrier screening, and hence detailed knowledge of both the trap density and the electronic concentration is necessary for a meaningful prediction of the trapping behavior. Finally, we also focus on modifications caused by electron-electron scattering, and find trapping enhancements due to the additional energy loss channel created by Auger-like phenomena.
Some wave phenomena in elastic superconductors
Authors: Zhou Shu-Ang
Published: July 2002

This article formulates some wave phenomena in elastic superconductors, in which the effect of interaction of elastic waves with electromagnetic fields are taken into account. The effect of normal conduction current is also taken into consideration. It is shown that, due to the effect of dynamic motion, transverse magnetic waves may be induced by a transverse elastic wave in an elastic superconductor. Magnetic surface waves may also be induced by the Rayleigh elastic surface wave in the superconductor. The magnitude of the magnetic induction field associated with the induced magnetic wave can be significant at a certain excitation frequency. Furthermore, by considering the coupling effect between the elastic wave and the electromagnetic field, a study is given to investigate electromagnetoelastic surface waves in a semi-infinite elastic superconductor with the aid of the theoretical formulation given in the article. It is shown that the characteristics of the coupled wave in a superconductor can be quite different from that in a perfect conductor due to the presence of the Meissner effect in the superconductor.
Radiation damage behavior of LiNbO3 crystal by MeV F ion implantation
Authors: Shi Bo-Rong , Wang Ke-Ming , Wang Zhong-Lie , Liu Xiang-Dong , Xu Tian-Bing , Zhu Pei-Ran
Published: July 2002

X, Y, and Z crystalline cut LiNbO3 crystals were implanted by 1.0 MeV F ions with a dose of 1×1015 ions/cm.2 The virgin and implanted LiNbO3 crystals were investigated using the Rutherford backscattering/channeling technique. The obtained minimum yields of virgin crystals were 4%, 8%, and 6% for X-, Y-, and Z-cut LiNbO3 crystals, respectively, because of their different arrangements of lattice sites in channeling direction. The measured damage profiles are also influenced by the arrangement of lattice sites in channeling measurements. The damage profiles of X-cut LiNbO3 crystal induced by 1.0 MeV F+ at a fluence range of 1×1014–3×1015 ions/cm2 have been studied and compared with the Transport of Ions in Matter, version 1990 calculation. It has been found that not only the nuclear energy deposition but also the electronic energy deposition influences the defect production.
Semiconductor laser damage due to human-body-model electrostatic discharge
Authors: Twu Y. , Cheng L. S. , Chu S. N. G. , Nash F. R. , Wang K. W. , Parayanthal P.
Published: July 2002

Various types of InP-based semiconductor lasers, Fabry–Perot (FP), and distributed feedback (DFB), in different wavelength regions of 1.3, 1.48, and 1.55 μm have been subjected to human-body-model electrostatic discharge (ESD) testing. The reverse V-I characteristics of these diode lasers were found to be generally most sensitive in detecting ESD damage than the forward characteristics (e.g., threshold current) of the laser. The laser ESD failure voltages were much lower for the reverse than the forward polarity and DFB lasers were found to be more vulnerable to ESD than FP lasers. The failure mechanism was found to be due to localized melting—a thermal effect—in both polarities of ESD testing. We also report the study of the latent ESD effects on the long-term aging rates of semiconductor lasers.
Hydrogen effects on oxygen precipitation in Czochralski silicon crystals
Authors: Hara Akito , Aoki Masaki , Fukuda Tetsuo , Ohsawa Akira
Published: July 2002

We reported enhanced oxygen precipitation in quenched Czochralski silicon crystals after solution annealing at 1270 °C in nitrogen or in dry oxygen [J. Appl. Phys. 66, 3958 (1989)]. We attributed this phenomena to intrinsic point defects. However, hydrogen was introduced into samples during solution annealing at 1270 °C and aggregates of hydrogen were formed during quenching. This article examines hydrogen aggregates by Secco etching and transmission electron microscope. Hydrogen-related aggregates are found to be related to enhanced oxygen precipitation.
Determination of zinc cluster size in ionized cluster beam film deposition
Authors: Urban Frank K. , Feng Susan W. , Nainaparampil Josekutty J.
Published: July 2002

Ionized cluster beam deposition uses a beam of ionized, accelerated atom clusters to grow thin films. Earlier unsuccessful attempts at forming such cluster beams by homogeneous nucleation used 1 mm×1 mm nozzles at crucible pressures around 2 Torr. Recently, Gspann [Proc. German Phys. Soc. 3, 387 (1992)] and the authors [Appl. Phys. Lett. 61, 1180 (1992)] produced significant numbers of large zinc clusters by increasing the crucible pressure to the 1000 Torr range and using a converging-diverging nozzle 18 mm long and 0.4 mm in diameter at the throat. The cluster distribution for a crucible temperature of 1180 °C peaked around an average of 2200 atoms per cluster. This distribution was measured by extending the previous deflected deposition method for average size to apply for the entire ionized fraction of the beam. Cluster velocity was nearly constant over the entire distribution in agreement with what would be expected for a homogeneous nucleation process. Over 99% of the ionized beam was in the form of clusters.
Directionality in photoluminescence from λ/2 periodic quantum wells
Authors: Raja M. Y. A. , Aktas Y.
Published: July 2002

Our investigations on the photoluminescence from InGaAs/AlGaAs half-wave periodic quantum wells show an enhanced directivity, and suppression of transverse amplified spontaneous emission. These properties are explained by a model that treats the quantum wells as periodic arrays of radiating dipoles, like ‘‘directional antennas’’ for the micro- and radio frequency regimes. Such quantum optic structures have potential for efficient optical amplifiers and external cavity broad area semiconductor lasers.
Photoluminescence study of undoped-like GaAs/AlGaAs quantum wells in high electric fields
Authors: Shigekawa Naoteru , Furuta Tomofumi , Arai Kunihiro , Tomizawa Masaaki
Published: July 2002

We perform photoluminescence (PL) measurements of undoped-like GaAs/AlGaAs quantum well channels as a function of electric field parallel to their interfaces. The obtained spectra for high fields include subsidiary peaks due to the Γ-L intervalley scattering. We also extract the energy distribution of carriers and discuss its non-Maxwellian features and the dominant energy-loss mechanism of electrons. Furthermore, the energy distributions calculated by the Monte Carlo method are found to reveal the measured features.
Photoconductive properties of a dye dispersed (oligo phenylene sulfide)-polyimide
Authors: Takimoto Akio , Wakemoto Hirofumi , Ogawa Hisahito
Published: July 2002

A dye dispersed photoconductor has been developed using (oligo phenylene sulfide)-polyimide (OPS-PI) as a matrix polymer. The OPS-PI was comprised of a series of thiophenylene moieties, –C6H4S–, and imide rings, having a novel carrier transport ability. The dispersed photoconductor showed a panchromatic photosensitivity in the wide wavelength 400–900 nm region, which resulted from the carrier generation of the OPS-PI in the wavelength 400–600 nm region and from that of the dyes, metal-free phthalocyanines, in the wavelength 600–900 nm region. A model of sensitizing the OPS-PI by means of dye dispersion is presented based both on the electronic structural study of the crystalline OPS-PI and on the optical and photoconductive studies of the copolymers derived from the OPS-PI and its modified polyimide. According to our proposed model, the optimum of the dye content in the OPS-PI for enhancing photosensitivity has been determined in the range not to destroy the carrier transport paths.
Evolution of the photoconductance decay versus wavelength in silicon doped GaInAs
Authors: Le Cleac’h X.
Published: July 2002

Photoconductance investigations with square light pulses have been made on semiconducting thin films of GaInAs doped with silicon. Two wavelengths are used: 870 and 1300 nm. One unexpected evolution of the photoconductance transients resulting from traps is observed when the wavelength is varied. A model based on the representation of each trap by a well located between two disymmetrical potential barriers is consistent with the experimental results.
Tunneling of quasiparticles in the normal-insulator-superconductor-insulator-normal geometry
Authors: Hidaka Mutsuo , Ishizaka Satoshi , Sone Jun’ichi
Published: July 2002

The probability of quasiparticle transmission going through a normal-insulator- superconductor-insulator-normal (NISIN) geometry is theoretically calculated using Bogoliubov–de Gennes equations to investigate the feasibility of electron devices utilizing this geometry. This new calculation is able to include a current carried by Cooper pairs by employing hole injections from the outlet which destroy Cooper pairs at the outlet super- conductor-insulator boundary. Resonant tunneling phenomena occur even if the electron kinetic energy is less than the superconducting energy gap and electron tunneling probabilities are greatly modified by the resonance. When the unevenness of the superconductor (S) width thickness is large compared with the electron wavelength in the S layer, the resonance is smeared out in averaged tunneling probabilities. Then the tunneling probabilities can be controlled by the electron kinetic energy. Applications of the NISIN geometry for superconducting transistors are also discussed.
Zero chirp quantum well asymmetric Fabry–Perot reflection modulators operating beyond the matching condition
Authors: Trezza J. A. , Larson M. C. , Harris J. S.
Published: July 2002

We demonstrate asymmetric Fabry–Perot reflection modulators using both InGaAs and GaAs quantum wells which operate beyond the matching condition and exhibit zero phase change (zero chirp) when switched. These devices are structurally similar to devices which can operate before the matching condition, and with incorporation of only a small etch step enable planar realization of zero phase change modulators operating before and beyond the matching condition which reflect 180° out of phase. We also show how observation of the reflectivity spectrum can provide quick information about the voltage necessary to obtain this zero chirp behavior. These structures provide a basis for low chirp optical switching, beam steering, and spatial light modulation.
In-plane acceleration sensitivity of contoured quartz resonators stiffened by quartz cover plates supported by clips
Authors: Zhou Y. S. , Tiersten H. F.
Published: July 2002

It has been shown that the resultant acceleration sensitivity of contoured quartz resonators vanishes for perfect symmetry of the resonator with respect to the support system. It has further been shown that any loss of symmetry in the combined resonator plus support configuration results in a linear increase in the acceleration sensitivity. Since it is impossible to construct a perfectly symmetric resonator plus support configuration in practice, a stiffened structure is investigated. The structure consists of the active biconvex quartz resonator attached to identical top and bottom quartz cover plates by means of small sidewalls around the periphery. The mounting clips are attached to the top and bottom cover plates without touching the active plate. An analysis of the linear increase in the in-plane acceleration sensitivity of the stiffened configuration is performed. Results are presented which show the influence on the in-plane and resultant acceleration sensitivities of differences in the properties of the clips and a mispositioning of either a clip or the mode shape for a range of thickness of the cover plates relative to the active plate.