bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion-beam mixing of erbium into potassium titanyl phosphate by mega-electron-volt argon beams
Authors: Wang Ke-Ming , Wang Wei , Ding Pei-Jun , Lanford W. A. , Liu Yao-Gang
Published: July 2002

A 500 Å erbium (Er) film was deposited on potassium titanyl phosphate (KTiOPO4 or KTP) by electron-beam evaporation. The doping of Er into KTP was induced by mega-electron-volt Ar+ with different doses. The doping amount was investigated by Rutherford backscattering of 3.0 MeV He+. The results show that the doping concentrations of Er in KTP were 2.88 and 1.88 at. % induced by 2.0 and 3.0 MeV Ar+ with the dose of 2×1016 ions/cm2 at room temperature, respectively. Perhaps the present result can provide an important approach not only for the laser and waveguide laser fabrication, but also for the high-concentration dopants (atomic percent levels) into KTiOPO4 at room temperature.
Behavior of Bi1.7Pb0.3Sr2Ca2Cu3Ox at high temperature
Authors: Zhang H. , Ritter F. , Frieling T. , Kindler B. , Assmus W.
Published: July 2002

Carefully prepared and well-characterized Bi1.7Pb0.3 Sr2Ca2Cu3Ox samples were studied by means of differential scanning calorimetry, thermogravimetry, and room and high temperature x-ray diffraction in different atmospheres. It is found that the decomposition of Bi1.7Pb0.3Sr2Ca2Cu3Ox strongly depends on the given conditions. In argon atmosphere, the sample begins to decompose at 850 °C, and finally decomposes mainly into Bi2Sr2CuOx, Cu2O, CaO, and (Sr,Ca)2O3; in air, it decomposes at 880 °C, into Bi2Sr2CuOx, Bi2Sr2CaCu2Ox, Bi1.7Pb0.3Sr2Ca2Cu3Ox, and (Sr,Ca)O; in oxygen, it decomposes at 900 °C, into Bi2Sr2CuOx, Bi2Sr2CaCu2Ox, Bi1.7Pb0.3Sr2Ca2Cu3Ox, and (Sr,Ca)2O3. The process of the melting was in situ studied by high temperature x-ray diffraction and a quenching method. This study gives some hints for growing single crystals of Bi1.7Pb0.3Sr2Ca2Cu3Ox and how to introduce pinning centers into Bi2Sr2CaCu2Ox and Bi1.7Pb0.3Sr2Ca2Cu3Ox.
Strain measurement and estimation of photoelastic effects and strain-induced optical gain change in ridge waveguide lasers
Authors: Yang Jian , Cassidy Daniel T.
Published: July 2002

Measurement of the strain in the plane of the active region for 1.3 μm InGaAsP ridge waveguide lasers is presented. A strain model is examined and compared with experimental results. The changes in the refractive index and the optical gain owing to the measured strain are estimated. These results are important information for device simulation, modelling, and interpretation of experimental results.
Optical properties of undoped and Co-doped CuAlGeSe4 and CuAlSnSe4 single crystals
Authors: Lee Jung-Soon , Oh Seok-Kyun , Kim Wha-Tek
Published: July 2002

CuAlGeSe4, CuAlSnSe4, CuAlGeSe4:Co2+, and CuAlSnSe4:Co2+ single crystals were grown by the chemical transport reaction method. These single crystals had a defect chalcopyrite structure and a direct band structure. Optical energy gaps at 286 K were found to be 2.394, 1.874, 2.302, and 1.794 eV for CuAlGeSe4, CuAlSnSe4, CuAlGeSe4:Co2+, and CuAlSnSe4:Co2+ single crystals, respectively. Impurity optical-absorption peaks due to cobalt dopants were observed at 12 243, 7002, and 3890 cm−1 in CuAlGeSe4:Co2+ single crystal and 11 949, 7056, and 3920 cm−1 in CuAlSnSe4:Co2+ single crystal at 286 K. Each of these peaks split into four peaks due to the second-order spin-orbit coupling effect at 30 K. The peaks are assigned to the electron transition between the energy levels of a Co2+ ion sited at the cubic Td symmetry point in the host lattice. Then, for CuAlGeSe4:Co2+ and CuAlSnSe4:Co2+ single crystals, the crystal-field parameter Dq is found to be 389 and 392 cm−1, respectively, the first-order spin-orbit coupling parameter λ −194 and −202 cm−1 the second-order spin-orbit coupling parameter p 238 and 242 cm−1, and the Racah parameter B 505 and 483 cm−1.
Lattice mismatch measurement of epitaxial β-SiC on α-SiC substrates
Authors: Chien F. R. , Nutt S. R. , Yoo W. S.
Published: July 2002

The lattice mismatch in chemically vapor deposited epitaxial β-SiC (3C-SiC) films on 6H- and 15R-SiC (0001) substrates was investigated using a high-resolution x-ray diffractometer. The misfit parallel and perpendicular to the growth plane was determined to be (Δc/c)∥=−9.3×10−4 and (Δa/a)⊥=1.9×10−4 for the 3C/6H system, and (Δc/c)∥=−10.0×10−4 and (Δa/a)⊥=2.3×10−4 for the 3C/15R system. Our analysis of the lattice parameters in these three SiC polytypes revealed that the Si-C pair spacings along the c direction increased with substrate hexagonality, while the lattice spacings along the a direction decreased with hexagonality. The extent of relaxation was greater in 3C films grown on 6H substrates, a phenomenon attributed to a higher density of double position boundaries.
Lithium–gold-related defect complexes in n-type crystalline silicon
Authors: Sveinbjörnsson Einar Ö. , Kristjansson Sigurgeir , Gislason Haflidi P.
Published: July 2002

Using deep level transient spectroscopy combined with secondary-ion-mass spectroscopy and capacitance–voltage profiling, it is demonstrated that lithium diffusion into gold-doped n-type silicon at temperatures between 200 and 300 °C results in the formation of two lithium–gold-related complexes. One of the Au–Li complexes appears to be electrically passive and is observed indirectly as gold acceptor passivation. Virtually all passivated gold acceptors are reactivated after 30 min annealing at 400 °C of samples with comparable Au and Li concentrations in the 1014 atoms/cm3 range. The process can be reversed again by additional heat treatment at lower temperatures. The passivation–reactivation cycle can be repeated as long as there is enough Li present in the crystal. This reaction can be described by a mass-action law between negatively charged gold atoms and positively charged lithium (Au−+Li+) with a free binding energy of approximately 0.87 eV. The other Au–Li complex has a deep level (labeled L1) within the silicon band gap with an activation energy of 0.41 eV. The L1 signal is strongest after annealing at temperatures between 250 and 300 °C but weaker at lower temperatures where the electrically passive Au–Li complex is favored. From the dissociation kinetics of L1 during reverse bias annealing it is deduced that the complex consists of one gold atom and one or more lithium atoms. Finally, using DLTS depth profiling it is observed that injection of hydrogen into the sample surface region by wet chemical etching results in deactivation of the L1 trap.
Switching effect and local conductivity in thin films of polydiphenylenephthalide
Authors: Scaldin O. A. , Selezneva O. A. , Lebedev Y. A. , Chuvyrov A. N.
Published: July 2002

The switching effect induced by an electric field and pressure has been investigated in thin (∼0.5 μm) films of polydiphenylenephthalide. It has been shown that the conductivity of a polymer film is affected by highly conductive filament formation. Using a liquid crystal, we were able to visualize such filaments and to determine their parameters: size, conductivity, and surface density. The low-frequency current fluctuations in thin polymer films have also been measured. The rapid growth of current fluctuations near the switching point has been found. The results of this study are evidence for the filament model.
Model for the substrate hole current based on thermionic hole emission from the anode during Fowler–Nordheim electron tunneling in n-channel metal-oxide-semiconductor field-effect transistors
Authors: Kobayashi Kiyoteru , Teramoto Akinobu , Hirayama Makoto , Fujita Yasushi
Published: July 2002

A model is proposed to explain the dependence of the substrate hole current in n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) on applied electric field and on oxide thickness. Two types of devices were prepared: n-channel MOSFETs with gate oxides of 67, 86, and 131 Å and p-channel MOSFETs in which gate oxide thicknesses were almost equal to those in the n-channel MOSFETs. The carrier-separation technique was used in the p-channel MOSFETs, and the average energy of hot electrons entering the silicon substrate was obtained. The average energy of the hot electrons is related to the energy distribution of hot holes created by hot electrons emitted from the oxide into the n+ polysilicon gate during the Fowler–Nordheim electron tunneling in the n-channel MOSFETs. The substrate hole current is numerically modeled as thermionic emission of the hot holes overcoming the energy barrier at the oxide-n+ polysilicon interface. For the gate oxides ranging from 67 to 131 Å, the dependence of the substrate hole current on the electric field and on oxide thickness is explained by using the average energy of the hot electrons and the thermionic hole emission model.
Formation dynamics of excited atoms in an ArF laser using He and Ne buffer gases
Authors: Nagai Shinji , Furuhashi Hideo , Uchida Yoshiyuki , Yamada Jun , Kono Akihiro , Goto Toshio
Published: July 2002

Time-dependent number densities of excited atoms in a discharge-pumped ArF excimer laser were measured through laser absorption probing with a cw dye laser. The He*(2p 3P) and Ne*(3s 3P2) atoms in the discharge using He/Ar/F2 and Ne/Ar/F2 gas mixtures were studied. The peak of Ne* and He* atom densities were 1.7×1012 cm−3 and 2.1×1012 cm−3, respectively. The number densities of He*, the laser output power, and the discharge voltage were also measured with varying He/Ne mixture ratio in He/Ne/Ar/F2 gas mixtures. Effects of He and Ne buffer gases on the excitation mechanisms of atoms are discussed on the basis of those measured results, and compared with the case of XeCl excimer lasers.
Transmission electron microscopy study on 2a×2b×c superstructure in bulk (Bi,Pb)2Sr2Ca2Cu3O10+δ cuprates
Authors: Wu X.-J. , Liu C.-J. , Yamauchi H.
Published: July 2002

For 7,7,8,8-tetracyanoquinodimethane (TCNQ)-treated (Bi,Pb)2Sr2Ca2Cu3Oz[(Bi,Pb)-2223] super- conductors, a superstructure which can be described as 2a0×2b0×c0 has been observed by electron diffraction. Superconductivity is virtually destroyed in the TCNQ-treated (Bi,Pb)-2223 cuprate. Superconductivity (with Tc up to 110 K) may be recovered for a TCNQ-treated sample by being annealed in flowing oxygen gas. Then the 2a0×2b0×c0 superstructure is found to disappear. This suggests that the superstructure may be caused by an ordering of oxygen vacancies. High resolution transmission electron microscopic observations reveal that the oxygen vacancies reside not only in the CuO2 sheets, but also likely in the SrO sheets. A model for the superlattice in both CuO2−x and SrO1−y sheets is proposed.
Scaling of voltage with cathode radius of a plasma opening switch
Authors: Goyer J. R. , Kortbawi D. , Sincerny P. S. , Parks D. , Waisman E.
Published: July 2002

Experiments have been performed to investigate voltage scaling in a plasma opening switch (POS) as the radius of the cathode is varied. Two different opening switch configurations have been used. In one of these the anode and cathode are simple coaxes with constant radii. In the other, there is an increase in anode radius immediately downstream of the switch. It is found that for all the data the peak voltage of the POS follows a simple scaling law with cathode radius for short conduction times, but that as conduction time is increased the two sets of data diverge. The configuration with the increased anode radius shows a marked improvement in operating voltage at long conduction times as compared to the simple hardware, however, the data from each set of hardware continue to follow the derived scaling law for all conduction times observed.
Formation of thin films of CoSi2 on GaAs
Authors: Hult Mikael , Persson Leif , El Bouanani Mohamed , Whitlow Harry J. , Andersson Margaretha , Östling Mikael , Lundberg Nils , Zaring Carina , Georgsson Kristina , Cohen David D. , Dytlewski Nick , Johnston Peter N. , Walker Scott R.
Published: July 2002

CoSi2 exhibits the features of low resistivity and stability at elevated temperatures which make it interesting to employ for metallization on GaAs. The interfacial reactions in GaAs samples with thin film overlayers of Si and Co [Si(220 nm)/Co(50 nm)/(〈100〉-GaAs)] were studied using x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy, and mass and energy dispersive recoil spectrometry. Samples were vacuum furnace annealed for time periods between 1 and 8 h at temperatures ranging from 300 to 700 °C. It was found that a CoSi2 layer formed without observable reaction with the substrate at 500 °C and above. The excess Si (Si/Co atomic ratio of 2.41) remained near the surface as elemental Si and as SiO2 for the 500 and 600 °C annealings. For the 700 °C annealing the excess near-surface Si was not observed.
Calculation of strain distributions in multiple-quantum-well strained-layer structures
Authors: Downes James , Faux David A
Published: July 2002

We present a simple method for calculating strain distributions in structures containing an arbitrary number and combination of strained layers of finite length buried in an infinite medium. This method is used to calculate the strain distributions for a quantum-well stack containing four compressive layers separated by barriers of different thicknesses and states of strain. It is found that the in-plane strain is relaxed along a significant length of each compressive layer if the barriers are unstrained. In contrast, if the barriers are in tension, the compressive strain is retained over most of the length of the layer. It is concluded that the judicial use of compressive and tensile layers in device structures would substantially reduce the region over which the strain is relaxed and possibly minimize the adverse effects of modified band structure or atomic diffusion arising due to the relaxation of strain. It is also confirmed that strain relaxation reduces the average strain within the square cross section of a single quantum wire to about one tenth of the misfit strain.
Tunneling assisted thermionic emission in double-barrier quantum well structures
Authors: Ehret S. , Schneider H. , Larkins E. C. , Ralston J. D.
Published: July 2002

We report on experimental and theoretical investigations of the dark current behavior in n-type GaAs/AlAs/Al0.3Ga0.7As double-barrier quantum wells (DBQW). The dark current perpendicular to the 50-period DBQW structures shows evidence of tunneling through the 2-nm-wide AlAs tunnel barriers and thermionic emission across the 25-nm-wide AlGaAs layers. The temperature dependence is in good agreement with our numerical simulations, using an effective escape rate of 2.2×1014 s−1. The dark current is further modified by internal electric fields caused by an asymmetric dopant distribution, which partially arises from a dopant segregation during epitaxial growth. We also present a theoretical simulation showing how the dark current versus voltage dependence is influenced by these space-charge fields.
Microwave response of YBa2Cu3O7−x grain boundary junction
Authors: Cho Changhyun , Shin Joongshik , Hwang Doosup , Kim Youngkeun , Lee Youngjong , Chun John S. , No Kwangsoo , Bae Sungjoon , Hong Seungbum
Published: July 2002

YBa2Cu3O7−x superconductor thin films were deposited on LaAlO3(100) single crystal substrates using a metalorganic chemical vapor deposition method. These films showed a critical temperature of about 90 K and a critical current density of over 105 A/cm2 at 77 K. These films showed granular structure with 0.5–1.5 μm grains. Bridge-type junctions, 6 μm in width and 6 μm in length, were fabricated using photolithography and Ar ion milling techniques. Current-voltage (I-V) characteristics of these junctions with microwave irradiation at 77 K were studied. The critical current densities decreased as the irradiated microwave power increased. When microwaves are irradiated on the bridge at 77 K, the I-V characteristics showed constant voltage steps (Shapiro steps) at ΔV=nhν/2e, but subharmonic steps.
Comment on ‘‘Generation phenomena of localized interface states induced by irradiation and post-irradiation annealing at the Si/SiO2 interface’’ [J. Appl. Phys. 73, 4388 (1993)]
Authors: Alexandrova S.
Published: July 2002

It is pointed out in this comment that reliable models of Si/SiO2 interface can be revealed from the energy distribution of the interface states only after careful estimation of inaccuracies in ideal interface modeling.
Vertical-cavity surface-emitting lasers with thermally stable electrical characteristics
Authors: Zhou Ping , Lu Bo , Cheng Julian , Malloy K. J. , Sun S. Z. , Hersee S. D. , Zolper J. C.
Published: July 2002

Vertical-cavity surface-emitting lasers (VCSELs) with thermally stable electrical characteristics, including slowly changing operating voltages and series resistance, have been achieved over a wide temperature range between 100 and 380 K. A stable and low threshold voltage (1.9 V at 300 K to 3.0 V at 100 K) results from the temperature insensitive carrier transport across the continuously graded heterojunction interfaces of a distributed Bragg mirror, and from the very low series resistance that has been achieved by reducing the spreading resistance of the VCSEL.
Thin InSb films—A candidate for multiple recording
Authors: Chou L. H. , Kuo M. C.
Published: July 2002

Thin In46Sb54 films were prepared on glass substrates via flash evaporation. Films of 1000 Å were deposited at room temperature. After 7 min of thermal annealing at 450 °C, an average grain size increased from 20 to 200 nm. Under exposure to Fraunhofer diffracted pulsed Nd-YAG laser beam, the films exhibited different microstructures for different applied laser powers. Five regions were basically identified, i.e., ablation region, regions with grain sizes less than 20 nm, grain sizes ranging from 400 to 1000 nm, grain sizes ranging from 200 to 400 nm, and an unchanged region. The previous five regions were counted from the center of the exposed area outward. The pulse duration was 16 ns. Also, an atomic migration mechanism was proposed which accounts for the power dependent microstructural changes. Transmission electron microscopy was primarily used in characterizing the films. This type of phase transformation could find potential application in the phase change multiple recording.
Structure and magnetoresistance of granular Ag-FexCo1−x alloys: Influence of a phase change from fcc to bcc
Authors: Kubinski D. J. , Holloway H.
Published: July 2002

The structure and magnetoresistance of granular Ag-FexCo1−x films with 23.5 vol % of the ferromagnetic phase that were grown epitaxially on MgO{100} are reported. When x is increased from 0.2 to 0.3 the structure of the FexCo1−x precipitates changes from fcc to bcc. An epitaxial relationship is maintained, but the bcc precipitates are oriented at 45° to the Ag matrix, rather than parallel to it, as is found with the fcc precipitates. With the change from fcc to bcc the size of the precipitates increases nearly twofold. This is accompanied by decreases in the magnetoresistance ratio and the magnetic-field-dependent resistivity that are of similar magnitude. After allowance for the influence of particle size, it is found that there is no discontinuity in magnetoresistive properties that might be attributed to the phase change. At low temperatures and with constant precipitate size and concentration there are broad peaks in the magnetic-field-dependent resistivity and the magnetoresistance ratio at x≊0.3–0.4. Unlike previous results with fcc precipitates, in the region with bcc precipitates the magnetic-field-dependent resistivity is not proportional to the saturation magnetization.
Reduction of saturation magnetic field in superlattices by addition of subsidiary ferromagnetic layers
Authors: Takahashi Y. , Inomata K.
Published: July 2002

The saturation magnetic field along the hard axis, Hsh for the giant magnetoresistance is studied theoretically within the continuum approximation in a composite magnetic film consisting of a conventional magnetic sandwich film and subsidiary soft ferromagnetic layers epitaxially grown on both sides of it. The Hsh is given as a solution of an equation, which describes the interplay between dimensions and the magnetic properties of the subsidiary layers and the conventional magnetic sandwich film. By analyzing the effect due to the subsidiary layers, a drastic reduction of the Hsh is shown. Since the subsidiary layer is coupled ferromagnetically to the ferromagnetic layer of the sandwich structure, the rotation of the magnetization in a subsidiary layer in an external magnetic field can easily induce the rotation of the magnetization in an adjacent magnetic layer. The calculated results for the Hsh are in good agreement with the experimental results.
Cation distribution of indium-substituted garnet, Y2.4In0.6Fe5O12
Authors: Chae Kwang Pyo , Lee Young Bae , Paik Seo Wook , Lee Sung Ho
Published: July 2002

The cation distribution of the Y2.4In0.6Fe5O12 system has been studied by means of Mössbauer spectroscopy and x-ray diffractometry. The structure of the system is yttrium-iron-garnet structure with a lattice constant of 12.387 Å. Four Zeeman lines from Fe3+ ions at the a,a′ and d,d′ sites have been observed at room temperature. Using the temperature dependence of the absorption area of Mössbauer line and the results of x-ray diffractometry, the cation distribution of the system can be written as {Y2.4In0.6Feα−β}(Fe2−α) [Fe3+β]O12.
Nonlinear properties of partially resonant composites
Authors: Levy Ohad
Published: July 2002

The dielectric response of a random mixture of coated cylinders, of nonlinear cores and linear shells, is studied. It is shown that under conditions of partial resonance the system behaves as a mixture of nonlinear solid cylinders of radii equal to, or larger than, these of the original coated cylinders. The electric field in those effective cylinders is larger than that obtained in a mixture of the equivalent solid cylinders. These two effects facilitate the emergence of an enhanced nonlinear response in a composite containing very small quantities of nonlinear material. Also examined is the phenomenon of intrinsic optical bistability when the core component has quadratic or cubic nonlinearity. It is shown that bistability can, in principle, be achieved even when not in the close vicinity of a sharp plasmon resonance, as is the case for nonpartially resonant systems; however, the threshold intensities required for bistable behavior are much higher than in some three-component microgeometries previously discussed.
Index of refraction of GaAs/AlxGa1−xAs multiple quantum wells with an applied electric field using the grating coupling technique
Authors: Kaufman R. G. , Hulse G. R. , Stair K. A. , Bird T. E. , Devane G. P. , Moretti A. L.
Published: July 2002

The grating coupling technique is used to determine the index of refraction under an applied electric field. Light is coupled into a GaAs/AlxGa1−xAs multiple quantum well slab waveguide using a conducting grating which has been etched onto the waveguide. The coupling angle is measured with high precision and the effective index of the mode is calculated with the mode coupling equation. The technique is very sensitive, allowing the index to be determined to within ±2×10−5. The strong absorption of the quantum wells prevents measurements at photon energies near the quantum well absorption peaks. This is not a serious limitation as the measurable range is the most technologically important region for electro-optic devices which utilize refractive index changes. The linear and quadratic electro-optic coefficients, evaluated from the change in index with electric field, agree well with previous measurements by other methods.
Surface passivation and microroughness of (100) silicon etched in aqueous hydrogen halide (HF, HCl, HBr, HI) solutions
Authors: Li L. , Bender H. , Trenkler T. , Mertens P. W. , Meuris M. , Vandervorst W. , Heyns M. M.
Published: July 2002

The surface reactivity of hydrogen-passivated, HF-last-cleaned Si(100) toward aqueous HX and HF/HX (X=Cl, Br, I) is examined. The HCl and HBr solutions are found to leave the HF-cleaned bare Si surface unaltered, while the HI solution reoxidizes the hydrogen-passivated surface. Treatments in aqueous HF/HCl or HF/HBr solutions lead to the same surface passivation and surface microroughness as for HF-cleaned surfaces. In the HF/HI solution, a simultaneous oxidation and etching process takes place, resulting in an increased (111) microfaceting of the Si(100) surface.
Continuous wave spectral width of surface-emitting lasers
Authors: Dutta N. K. , Vakhshoori D. , Wynn J. D. , Leibenguth R. E.
Published: July 2002

Measurements of the continuous wave spectral width of GaAs gain-guided surface-emitting lasers are reported. The linewidth is found to vary inversely as the output power with a linewidth-power product of 92 MHz. This value agrees well with the calculated result.
Static electric fields due to seeding inside and outside of a planar waveguide
Authors: Brauer M. L. , Dajani I.
Published: July 2002

The semipermanent charge distribution at saturation in a germanium-doped silica planar waveguide is modeled for the case of seeding by a low-intensity fundamental wave and its second harmonic both propagating in the lowest order transverse magnetic mode. Based on the asymmetric photoionization model, the total current in the waveguide is taken to be the sum of the photoinduced current and the current due to the resulting static electric field caused by the charge separation. This current is used in the charge conservation equation to determine the charge distribution at saturation which is then used to compute the resulting static electric field inside and outside the waveguide. To compare with other models, the spatial profile of the resulting static electric field is compared to the direct current (dc) optical field due to a four-wave mixing process.
Layering of inertial confinement fusion targets in microgravity environments
Authors: Parks P. B. , Fagaly R. L.
Published: July 2002

A critical concern in the fabrication of targets for inertial confinement fusion is ensuring that the hydrogenic (D2 or DT) fuel layer maintains spherical symmetry. Because of gravitationally induced sagging of the liquid prior to freezing, only relatively thin (<10 μm) layers of solid fuel can be produced by fast refreeze methods. One method to reduce the effective gravitational field environment is free-fall insertion into the target chamber. Another method to counterbalance the gravitational force is to use an applied magnetic field combined with a gradient field to induce a magnetic dipole force (Fm) on the liquid fuel layer. For liquid deuterium, the required B⋅∇B product to counterbalance the gravitational force (Fg) is ∼10 T2/cm. In this paper, we examine the time-dependent dynamics of the liquid fuel layer in a reduced gravitational field environment. We employ an energy method which takes into account the sum of the free energy associated with the surface tension forces, net vertical force [F=Fm−Fg (in the case of magnetic field-assisted microgravity) or FD (the drag force in the case of free fall)], London–van der Waals forces, the kinetic energy of motion and viscous dissipation. By assuming that the motions are incompressible and irrotational, the volume integrals of the free energies over the deformed liquid fuel layer may be converted to surface integrals. With the surface expressed as the sum of Legendre polynomials, rsurface=a+∑al(t)Pl(μ), the perturbed amplitude of the individual modes, al(t) can be obtained. We show that the l=1 vertical shift mode takes the longest to damp out, and may be problematic for free-fall insertion even for thin ∼1 μm overfilled foam targets. For a given liquid fuel layer thickness Δ, the equilibrium value of a1/a (the concentricity of the inner fuel layer) is shown to be dependent on the net vertical force F and layer thickness, i.e., a1∼FΔ5, but independent of the surface tension.
Photosensitivity of proton implanted germania-doped planar silica structures
Authors: Kyle D. J. , Weiss B. L. , Maxwell G. D.
Published: July 2002

Results are presented which demonstrate that an absorption peak at a wavelength of 240 nm is produced in germania-doped planar silica structures by the implantation of a dose of 1×1017 cm−2 300 keV protons into a sample heated to 800 °C. This proton implantation induced absorption was found to saturate for a total implanted dose of 1×1017 protons cm−2 and the effect did not increase when multiple energy implants with a dose of 1×1017 protons cm−2 were used. The 240 nm absorption peak was partially removed by exposure to 0.5 J, 10 ns, 249 nm laser pulses for 7 min using a pulse repetition frequency of 50 Hz.
Monte Carlo investigation of the intrinsic mechanism of subpicosecond pulse generation by nonuniform illumination
Authors: Zhou Xing , Alexandrou Sotiris , Hsiang Thomas Y.
Published: July 2002

The intrinsic mechanism of the generation of subpicosecond electrical pulses by nonuniform illumination of GaAs transmission-line gaps is investigated using a self-consistent Monte Carlo approach. It is attributed to the photocarrier-induced field redistribution, which results in a displacement current pulse that is independent of the carrier lifetime. Partial-gap illumination and high dark resistivity are the prerequisites for this pulse generation technique. The pulse dependence on light intensity, excitation wavelength, bias voltage, and the asymmetric response to bias polarity are discussed and clarified. It is predicted that this mechanism should also be observable in other semiconductors such as silicon.
Xerographic effects of small chlorine additions to amorphous selenium
Authors: Wang Y. , Champness C. H.
Published: July 2002

A study has been made of the xerographic properties of amorphous selenium doped with chlorine at concentrations below 100 parts per million (ppm) by weight. The sample consisted, in each case, of an aluminum plate with a thin deposited rf sputtered aluminum oxide film, on which a 50 μm layer of amorphous selenium was deposited by evaporation, at a substrate temperature of 50 °C. It was found that the chlorine decreased the acceptance voltage following corona charging, increased the dark decay rate, and decreased the residual voltage after illumination discharge. The changes were such as to be beneficial xerographically for small additions of chlorine to the selenium in the ppm range. Analysis of the time derivative of the dark decay voltage indicated that depletion discharge was the dominant process in the decrease of dark decay voltage with time and a modified relation was introduced to describe the increase of bulk space-charge density with time, arising from thermal excitation of holes from deep discrete centers in the photoreceptor. This analysis indicated a decrease of the release time of the holes with increase of chlorine content, whereas an observed decrease of single cycle and cycled-up residual voltages with increased chlorine indicated an increase of hole capture time from their relevant trapping centers.
Comparison of the radiation resistance of electron irradiated indium phosphide grown by metal-organic chemical-vapor deposition and liquid encapsulated Czochralski
Authors: Thomas H. , Luo J. K.
Published: July 2002

Electrical characterization has been carried out on electron irradiated InP grown by metal-organic chemical-vapor deposition (MOCVD) and liquid encapsulated Czochralski (LEC), through I–V (–T), C–V, deep level transient spectroscopy (DLTS) and admittance spectroscopy measurements and the resistance to electron radiation for these two materials has been compared. It was found that MOCVD-InP was more resistant to electron radiation than LEC-InP, as demonstrated by the lower carrier removal rate and change of series resistance in the MOCVD-InP diodes as a result of electron radiation. The introduction rates for the dominant hole defects H3 and H4 and for additional electron defect states were found to be similar for both materials, but were insufficient to explain the degree of degradation of solar cell efficiency incurred by these known defects. A new defect, HD1, has been found to be responsible for the high carrier removal rate and the introduction of a large series resistance which accounts for the difference of radiation hardness between these two materials. The results again show that the dominant irradiation defects in InP are not the defects H3 and H4 as is usually accepted, but the new found defect HD1, which was undetected by the DLTS technique.
Influence of annealing on Fermi-level pinning and current transport at Au-Si and Au-GaAs Interfaces
Authors: Chen T. P. , Liu Y. C. , Fung S. , Beling C. D.
Published: July 2002

The measurements of internal photoemission and photovoltage within the temperature range of 7–300 K have been performed for unannealed and annealed Au/n-Si and Au/n-GaAs samples. From the internal photoemission measurements, it was observed that annealing at different temperatures does not affect the relativity of interfacial Fermi-level pinning to either the conduction band (for Au/GaAs) or the valence band (for Au/Si) but leads to a significant change of the Schottky barrier height. On the other hand, the photovoltage measurements show that the current transport at the metal/semiconductor interfaces is seriously affected by annealing.
Extraction of morphological quantities from a digitized medium
Authors: Coker David A. , Torquato Salvatore
Published: July 2002

We present an analysis of the effect of digitization at a moderate resolution on the determination of various morphological quantities for a model three-dimensional digitized medium. Specifically, we study systems of digitized overlapping spheres which have many of the features found in man-made and geologic materials. The goal of this paper is to demonstrate which quantities are most sensitive to the process of digitization and resolution. In addition, the question of whether three-dimensional data sets are necessary to obtain reliable results concerning material structure is answered in the affirmative.
Luminescent Sr1−xErxF2+x thin films grown on InP(100) substrates. I. Growth and physico-chemical characterizations
Authors: Barrière A. S. , Kim B. Y. , Mombelli B. , Porté B. , Raoux S.
Published: July 2002

Sr1−xErxF2+x solid solution thin films were grown on InP (100) substrates by sublimation under ultrahigh vacuum of high purity powders. The composition of the layers was mainly deduced from Rutherford backscattering and secondary ion mass spectrometry studies. For an erbium substitution rate, x, lower than 0.2, it is shown that the film compositions are analogous with those of the solid solution initial powders, quite homogeneous, and insensitive to an air exposure. X-ray diffraction and Rutherford backscattering in channeling conditions were performed to study the texture and the structure of the layers. It is shown that heteroepitaxial Sr1−xErxF2+x/InP (100) structures can be grown for a substrate temperature of 300 °C.
Ultrasound stimulated dissociation of Fe-B pairs in silicon
Authors: Ostapenko S. S. , Bell R. E.
Published: July 2002

We found that application of ultrasound vibrations to p-type silicon promotes a dissociation of iron-boron pairs. This effect is manifested by a decrease of the minority carrier diffusion length, L, after ultrasound treatment (UST) of the silicon wafer. Post-UST recovery of the diffusion length is identical after thermal and optical pair dissociation. This provides an unambiguous proof for dissociation of Fe-B pairs stimulated by ultrasound vibrations. The UST process creates interstitial iron donors which acts as efficient recombination centers and lower the L value. A relevant physical mechanism of the ultrasound effect is discussed.
Investigation of titanium silicide formation in Ti+Si reactions using infrared spectroscopy and x-ray diffraction
Authors: Saenger K. L. , Cabral C. , Clevenger L. A. , Roy R. A.
Published: July 2002

Infrared (IR)-absorbance spectroscopy was investigated as a technique for monitoring titanium silicide formation during the reaction of Ti films on (100) Si substrates. Films annealed to various stages of reaction were monitored by x-ray diffraction, film resistivity, and optical reflectance in order to relate the changes in the IR-absorbance spectra to reaction progress. Films at different stages of reaction showed distinctly different extinction coefficients α, and absorbance versus wave-number curves. IR absorbance was determined to be a useful indicator of reaction progress, especially in those cases where samples at different stages of the silicidation reaction have the same resistance but different absorbance behaviors.
Photoconductivity of gallium arsenide epitaxial layers
Authors: Parenteau Martin , Fengmei Wu , Jorio Anouar , Carlone Cosmo
Published: July 2002

We have adapted a model first proposed by DeVore, to fit photoconductivity (PC) spectra of lightly doped GaAs epilayers of different thicknesses, taken at T=20 K. The model involves only the excitonic and interband transitions and the carrier lifetime is assumed to be shortened by recombinations at the surface of the sample. The modeling and the comparison with photoluminescence spectra have shown that the free exciton transition appears as a dip in our PC spectra. The position of the main peak does not correspond to a resonance; it is caused by an enhancement of the carrier recombinations, due to an increase of the absorption coefficient. By calculating PC line shapes with the model, we found that there are two thickness ranges for the signature of the free exciton transition: it should appear as a peak in GaAs layers thinner than about 2 μm and as a dip in thicker ones. The data published in previous papers can also be modeled with the expression used in the present article. We infer that the signature of free exciton transitions is also a dip in most of them.
Experimental investigation of the kinetic inductance in YBa2Cu3O7 square washer superconducting quantum interference devices
Authors: Grundler Dirk , David Bernd , Doessel Olaf
Published: July 2002

The inductance Ls of YBa2Cu3O7 thin-film square washer dc superconducting quantum interference devices was measured directly from 4.2 K up to the critical temperature Tc of the film. Ls(T) diverges close to Tc. Examining the temperature dependence of Ls two contributions are distinguished: the magnetic inductance, defined by the outer device geometry, and the temperature-dependent kinetic inductance Lk associated with the thin-film slit structure. Lk is found to scale with the square of the magnetic penetration depth λ(T) in a broad temperature range. The specific magnetic inductance per unit length of a long slit within the washer is measured to be ∼0.3 pH/μm. The impact of Ls(T) on device performance at elevated temperature is discussed.
Method of solution of forward problems in eddy-current testing
Authors: Kolyshkin A. A. , Vaillancourt Rémi
Published: July 2002

An analytical formula for the change in the eddy-current probe impedance is obtained for the forward problem in the case the conductivities, σ2 and σ1, of the flaw and surrounding medium, respectively, are almost the same. The small parameter ε=1−σ2/σ1 is introduced and the vector-valued solution is expanded in power series in ε. Then, a first-order approximation to the solution is obtained by a perturbation method. The general procedure is illustrated in detail by two examples where the flaw is not in a symmetric position with respect to the coil axis, namely, a double conductor line above an infinitely long conducting cylinder with a flaw, and a single-turn coil above a conducting ball with a flaw. It is shown that, in some cases, only one component of the vector potential (or even a part of this component) needs to be known in order to compute the impedance change.
Laser oscillation mechanisms of KrF-laser-pumped iron vapor plasma
Authors: Yoshida H.
Published: July 2002

In order to study laser oscillation mechanisms of a KrF-laser-pumped iron vapor plasma, the population densities of iron atoms, the temperature, and the electron density in iron vapor plasma have been measured. The iron vapor plasma was produced from an iron plate by irradiation with a pulsed YAG laser (2 J/pulse). The population density of the ground-state iron atoms is about 1014–1015 cm−3, the temperature is about 5000–20 000 K, and the electron density is about 1013–1016 cm−3. When a KrF laser of 34 mJ/pulse irradiates the iron vapor plasma, the absorption cross section of the KrF laser by the iron atom is about 10−16–10−15 cm2. An optical gain has been calculated on the basis of the experimental results, and it is compared with the gain measured experimentally.
Study of C2F6 overetch induced damage and the effects of overetch on subsequent SiCl4 etch of GaAs/AlGaAs
Authors: Ooi B. S. , Hicks S. E. , Bryce A. C. , Wilkinson C. D. W. , Marsh J. H.
Published: July 2002

A quantum well intermixing probe system has been used to study the damage in GaAs/AlGaAs due to exposure to C2F6 plasmas as a function of rf power. At an etching power of ≤80 W, the photoluminescence energy shift after rapid thermal processing is rf power dependent. The etch rate selectivities between SiO2 and GaAs, and between GaAs and AlGaAs were found to increase with decreasing power, while the etching of AlGaAs was inhibited at an rf power of 10 W and below. In situ reflectometry measurements during subsequent SiCl4 etching suggest that fluorocarbon contaminants are deposited on the GaAs surface during the C2F6 etch, that these contaminants protect the surface from oxidation in the air, and therefore the GaAs induction time in SiCl4 is reduced. However, during a SiCl4 etch of a GaAs/AlGaAs layered structure, these contaminants are redeposited on the AlGaAs surface resulting in an increased AlGaAs induction time, a nonconstant etch rate and surface roughening.
Gettering effects in BF2-implanted Si(100) by ion-beam defect engineering
Authors: Zhao Qing-Tai , Wang Zhong-Lie , Cao Yongming , Xu Tian-Bing , Zhu Pei-Ran
Published: July 2002

The gettering effects of ion-beam defect engineering (IBDE) in BF2-implanted silicon have been studied. It has been shown that the IBDE technique may be useful in the improvement of the properties of BF2-implanted silicon. The gettering layer introduced by MeV Si ion irradiation and formed during the process of thermal annealing collects not only impurities but also simple defects. Thus, it effected (1) reductions of secondary defects and F impurity accumulation in the BF2-doped region; (2) reduction of the anomalous diffusion of B atoms; and (3) enhancement of the electrical activation of B atoms.
Radiation of acoustic phonons from quantum wires
Authors: Mickevičius R. , Mitin V. , Kochelap V. , Stroscio Michael A. , Iafrate Gerald J.
Published: July 2002

We have investigated by the Monte Carlo technique the radiation of ballistic acoustic phonons from quasi-one-dimensional electron gas in quantum wires. At low temperatures and over a wide range of electric fields, all excess heat in quantum wires is dissipated by means of acoustic phonons. Due to the uncertainty of momentum conservation during electron–acoustic-phonon scattering, electrons emit acoustic phonons with large transverse momentum components. Consequently, in this transport regime quantum wires radiate fluxes of nonequilibrium acoustic phonons into surrounding material. Nonequilibrium acoustic phonons can propagate ballistically over macroscopic distances. Ballistic fluxes of nonequilibrium acoustic phonons have been previously detected experimentally in quantum well structures. We have calculated the angular and energy spectrum of nonequilibrium acoustic phonons radiated from quantum wires.
Characterizing, modeling, and optimizing high-T
c superconducting quantum interference devices
Authors: Foglietti V. , Koch R. H. , Sun J. Z. , Laibowitz R. B. , Gallagher W. J.
Published: July 2002

We have measured the current-voltage, flux-voltage, and noise characteristics of 77 K superconducting quantum interference devices made with step edge junctions and multilevel edge junctions on SrTiO3 substrates and with step edge junctions on LaAlO3. We find in each case that the I-V curves can have excess currents of up to 50%–80%, that the responsivity, ∂V/∂Φ, can be substantially smaller than expected from the resistively shunted junction (RSJ) model, but that the white noise voltage spectral density is about as expected. We discuss the extent to which the reduction of the responsivity is correlated with the excess current. We note that the observed unchanged magnitude of the voltage noise and the reduced responsivity would both be expected if we based the RSJ predictions on a model in which the excess current is not considered part of the Josephson current. Finally and perhaps fundamentally, we find that simulations made assuming a nonsinusoidal current-phase relationship give rise to an excess current, a reduction of the responsivity, and little change in the voltage noise spectral density, at least qualitatively as is observed.
Lattice relaxation of AlGaAs layers grown on GaAs(100) substrate plane by organometallic vapor phase epitaxy
Authors: Fuke Shunro , Sano Kazutoshi , Kuwahara Kazuhiro , Takano Yasushi , Sato Masahiro , Imai Tetsuji
Published: July 2002

In order to investigate the behavior of AlxGa1−xAs lattice relaxation caused by opposite directions of biaxial stress, i.e., tensile or compressive stress, AlxGa1−xAs (X=0–0.45) layers were grown on undoped and heavily In-doped GaAs substrates by organometallic vapor phase epitaxy. Al0.45Ga0.55As layers on undoped GaAs substrates are subject to biaxial compressive stress and have a large coherent length. Al0.3Ga0.7As layers grown on heavily In-doped GaAs substrates with a lattice constant larger by about 0.1% than that of undoped GaAs are subject to biaxial tensile stress and have much smaller coherent length. Furthermore, it is found that the coherent length depends on the growth temperature and that an increase in coherent length is brought in by the introduction of even a small amount of Al in the layers.
Modeling of optical and electrical behavior of semiconducting thin films: Application to sprayed CdS on transparent substrates
Authors: Ebothe Jean
Published: July 2002

Both the optical absorption coefficient α, and the carrier density N, of semiconducting thin films are analytically investigated in relation with their deposition substrate influence. It is shown that these two properties are sensitive to the film thickness d, particularly when incident monochromatic light is very close to the film transmission cutoff wavelength. α behaves according to the α≊f(d−1) type of function while N obeys the law N≊f(d−m) whose precise form varies with m value and depends on the substrate influence. Experimental results report on sprayed CdS films respectively deposited on glass, SnO2, and ITO substrates which illustrate the suitability of the model proposed. The film absorption coefficient is affected by the migration phenomenon at the film-substrate interface, the rate of the migration depending upon the substrate involved. m≊1 obtained with SnO2 and m≊2 with ITO indicate different CdS film interface properties, typical of the substrate used.
Temperature and doping dependence of the photon recycling effect in GaAs/AlGaAs heterostructures
Authors: Bergman J. P. , Hallin C. , Janzén E.
Published: July 2002

We have calculated the effect of photon recycling, as a function of energy, temperature, and doping level in GaAs/AlGaAs double heterostructures. The calculations have been performed numerically using energy-dependent expressions for the absorption, emission, and refractive indices. Our calculations are compared to experiments, and we demonstrate the influence of the photon recycling on the photoluminescence line shape, both peak position and the high energy slope, total intensity, and decay time. The calculations show that the total emitted photoluminescence intensity should weakly increase with increasing temperature, if the internal quantum efficiency is 1. The experimentally observed intensity loss at high temperatures (700 K) is explained as due to a reduction of the internal quantum efficiency.