bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin-on and boat diffusion of Zn into InP and InGaAs grown by metalorganic vapor-phase epitaxy and liquid-phase epitaxy
Authors: König U. , Haspeklo H. , Marschall P. , Kuisl M.
Published: July 2002

The Zn diffusion into InP and In0.57Ga0.43As was studied. A comparison of three diffusion methods is presented, i.e., boat diffusion, diffusion from As- or P-doped spin-on films, and diffusion from In-doped spin-on films. The diffusion into samples made by different growth methods was investigated, i.e., bulk grown wafers, liquid-phase epitaxial films (LPE), and metalorganic vapor-phase epitaxial films (MOVPE). The in-depth profiles found are from the double diffusion front type, p+ -p−-n. The p+ -p− junction position depends on the diffusion method but not significantly on the growth method of the sample, while the p−-n junction depends on both. For example, with As or P in the spin-on film, a shallow p+ -p− junction and a deep p−-n junction appear. With In in the spin-on film, a deep p+ -p− junction with a negligibly small p− region is found. Diffusion into bulk and MOVPE samples usually yields deeper p−-n junctions than into LPE samples. Owing to the fact that in the presented experiments the amount of P, As, In, Ga, or the respective vacancies VP, VAs, VIn, VGa differ, we are able to check which of the existing diffusion models are applicable here. We propose an independent trapping of the mobile interstitially diffusing Zni by two immobile vacancy centers, i.e., Zn on VIn or VGa in the p+ region and Zn on VAsZnVAs or VPZnVP in the p− region.
Power extraction study of an e-beam-pumped atmospheric pressure, Kr-rich KrF laser amplifier
Authors: Lee Young-Woo , Kannari Fumihiko , Obara Minoru
Published: July 2002

Single-pass (50-cm) amplification characteristics of a short-pulse [65 ns full width half maximum (FWHM)] e-beam-pumped KrF laser amplifier with an atmospheric pressure Kr-rich and Kr/F2 mixture were investigated theoretically for wide excitation rate from 0.1 to 2.0 MW/cm3. We have constructed a one-dimensional propagation amplifier model which considers the gain depletion and the saturated absorption spatially and temporally in the amplifying medium. With this numerical model, good agreement was obtained between the calculated result and the experiment. As a result of this theoretical study, extraction efficiencies of over 40% and power efficiencies of over 10% are obtainable at the highest output powers for all atmospheric mixtures containing 10%–99% Kr gas for excitation rates ranging from 0.5 to 2.0 MW/cm3 using a 30-ns (FWHM) input laser pulse, indicating that high efficiency power extraction from an atmospheric pressure KrF laser amplifier is achievable.
The structure of ultrathin C/W and Si/W multilayers for high performance in soft x-ray optics
Authors: Ruterana P. , Chevalier J.-P. , Houdy P.
Published: July 2002

Ultrathin layers are now playing an important role in the field of soft x-ray optics. Their performances depend critically on their structure (thickness, interface, crystalline state, etc.). We have used electron microscopy to determine this kind of information. The usual methods of sample preparation have been optimized in order to limit irradiation damage for these highly nonhomogeneous materials. We have introduced the technique of cleavage which allows for the examination of the as-fabricated structures. We were then able to determine that the deposition technique used can produce amorphous W layers up to thicknesses of 40 Å.
Ion-induced depletion of hydrogen from a soft carbonized layer
Authors: Boutard D. , Scherzer B. M. U. , Möller W.
Published: July 2002

Soft carbonized layers prepared in a glow discharge, with a hydrogen concentration of H:C∼4/3, are exposed to helium ion bombardment at energies between 0.3 and 2.6 MeV. A strong ion-induced depletion of up to 3×103 H atoms per incident 4He+ ion is observed by means of high-energy ion beam analysis. The hydrogen release is shown to be a local process, with the electronic energy deposition as the main responsible mechanism. The results are successfully compared to a model which takes into account local bond breaking and retrapping and the local formation of hydrogen molecules.
Rapid thermal annealing of GaAs in a graphite susceptor—comparison with proximity annealing
Authors: Pearton S. J. , Caruso R.
Published: July 2002

Rapid thermal annealing of GaAs within an enclosed, SiC-coated graphite susceptor is shown to eliminate slip formation during implant activation treatments (900 °C, 10 s) and to provide much better protection against surface degradation at the edges of wafers compared to the more conventional proximity method. The peak carrier concentration obtained in Si-implanted (3×1012 cm−2, 60 keV) GaAs by both methods is comparable, but the wafers annealed in the susceptor have tighter carrier profile width distributions measured over the whole wafer area.
Compensation assessment in ‘‘undoped’’ high-resistivity GaAs
Authors: Tang R-S. , Sargent L. , Blakemore J. S.
Published: July 2002

Attainment of semi-insulating status when an ‘‘undoped’’ GaAs crystal is grown from the melt requires a delicate balance among concentrations of ‘‘unintentional’’ donor and acceptor impurities, and defects, notably the EL2 midgap donor. In qualifying and improving material for device uses, defect identification and characterization is important. The compensation balance is analyzed in this paper for various ‘‘undoped’’ crystals, relying largely on Hall data over the 290–430 K range, coupled with optical absorption measurements of carbon and EL2. The temperature-dependent data, converted into Fermi energy and into EL2 ionized fraction, provide a clearer picture than just room-temperature measurements as to whether EL2 controls the Fermi energy (giving the desired semi-insulating behavior), or whether a shallower defect species is in control.
Microwave absorption in superconducting loops formed by touching lead pieces
Authors: Trybula Zbigniew , Drumheller John E. , Stankowski Jan
Published: July 2002

New data for microwave absorption in artificial superconducting loops with Josephson junctions formed by pressing irregular lead pieces together are presented. Two simultaneous series of microwave absorption lines with periods of 0.54 and 7.0 Oe for the case formed of three irregular pieces of lead are presented. Areas of the superconducting loops with Josephson junctions are 38.3 and 2.96 μm2, respectively. The separation of the first derivative of the absorption lines indicates a band of microwave absorption which is proportional to the square root of the microwave power. Irregular, reproducible lines of microwave absorption were detected for the sample made by 500 irregular pieces of lead at low magnetic field and at high magnetic field, in mixed superconducting and normal state for very low microwave power. A simple model for the microwave absorption in the superconducting loop with Josephson junction is presented.
A new type of high efficiency with a low-cost solar cell having the structure of a μc-SiC/polycrystalline silicon heterojunction
Authors: Matsumoto Y. , Hirata G. , Takakura H. , Okamoto H. , Hamakawa Y.
Published: July 2002

A new type of high-efficiency solar cell has been developed by a simple production process only with electron cyclotron resonance plasma-assisted chemical vapor deposition of highly conductive microcrystalline silicon carbide (μ c -SiC) on polycrystalline silicon (poly-Si). The device consists of a p -type μ c -SiC/ n -type poly-Si heterojunction where the window material is a specially made wide-band gap and highly conductive μ c -SiC. At the present stage, a conversion efficiency of 15.4% with V oc=556 mV, J sc=35.7 mA/cm2, and F. F.=77.4% has been achieved. Also employing this device as a bottom cell in a four-terminal amorphous silicon ( a -Si) tandem-type solar cell, 16.8% efficiency has been obtained. A series of technical data on the fabrication technology and device performance is presented and discussed.
Theoretical and experimental study of the longitudinal uniaxial stress dependence of I-V characteristics in GaAs-AlxGa1−xAs-GaAs heterojunction barriers
Authors: Lu S. S. , Lee K. R. , Lee K. H. , Nathan M. I. , Heiblum M. , Wright S. L.
Published: July 2002

Tunneling and thermionic emission through n+-GaAs–i-AlxGa1−xAs–n-GaAs heterojunction barriers are studied as a function of temperature from 77 to 200 K and as a function of externally applied uniaxial stress up to 10 kbar. A procedure to extract parameters for theoretical calculations is also proposed. The parameters extracted from the I-V characteristics of these heterostructures grown on (100) GaAs substrates with different aluminum mole fractions from 0.3 to 0.8 and thicknesses from 300 to 400 Å agree well with those of previous reports. The dependence of the I-V characteristics on uniaxial stress in the 〈100〉 direction perpendicular to the heterojunction plane has also been measured. The experimental results show good agreement with theoretical calculations assuming there is a linear stress-dependent decrease of the energy-band edges of the longitudinal X valleys (Xl) in AlGaAs with respect to the Γ valley in GaAs. The slope of the decrease is found to be 14±2 meV/kbar. This results in an X-valley shear deformation potential of 9.6±1.8 eV, which is believed to be the most accurate measured value to date.
rf surface resistance of a magnetically aligned sintered pellet of YBa2Cu3O7
Authors: Padamsee H. , Kirchgessner J. , Moffat D. , Rubin D. , Shu Q. S. , Hart H. R. , Gaddipati A. R.
Published: July 2002

rf (radio frequency) properties of polycrystalline ceramic material are substantially inferior to those of the best microtwinned crystals. At 6 GHz and 77 K, the best surface resistance values for ceramics are ∼20 mΩ, compared to <0.5 mΩ for high-quality crystals. The microwave resistance is observed to increase at higher rf fields for ceramics, e.g., two orders of magnitude between 0.1 and 10 Oe, but remains low for crystals. A possible reason for the inferior properties in randomly oriented polycrystalline ceramics is related to the anisotropy of the superconducting properties; crystals aligned unfavorably with the sampling rf field could be responsible for the high resistance. Another possibility is related to the difficulty of carrying current across the grain boundaries due to weak links arising from second phases, impurities, cracks, etc., at the boundaries. To elucidate the contribution from these two potential problem sources, we have measured the rf properties at 6 GHz of an oriented polycrystalline ceramic pellet prepared from a suspension of high purity powder in a 4-T magnetic field. Samples were characterized by x-ray diffraction, light microscopy, transmission electron microscopy, x-ray rocking curves, and x-ray pole figure studies, indicating a high degree of alignment, although not as complete as in epitaxial thin films. At liquid He temperature, the surface resistance is 28 times lower when the c axis is perpendicular to the plane in which rf currents flow than when the c axis is in the plane. At 77 K, the surface resistance is 3 mΩ, a significant improvement over the properties of the best randomly oriented material reported. At 4 K the resistance improves to 0.3 mΩ. These resistances were all measured with rf fields below 0.1 Oe, but increased by one order of magnitude when the rf field was increased to 10 Oe, as in the polycrystalline material. Our results indicate that while the low-field rf behavior is strongly improved by orientation, the high-field behavior is dominated by the poor current carrying capacity across weak links.
On the variation of reversible permeability with intensity of remanent magnetization
Authors: Garshelis I. J. , Fiegel W. S.
Published: July 2002

The variation of reversible permeability (μ) with the intensity of remanent magnetization (Mr) is studied in three magnetically semihard materials having comparable values of Hc (20–30 Oe) and Ms (≂16 kG), but widely different M-H loop shapes. Mr was altered by the transient exposure of wire specimens to mechanical vibrations, excursions of temperature, and a wide range of field conditions. At low-to-moderate values of Mr, μ showed greater dependence on the magnetization path than on the magnitude of Mr. Both the value of μ and its path sensitivity were found to decrease at high values of Mr. Modest transient heating of a two-phase high carbon steel strongly influenced both μ and Mr. No such effects were observed in the other materials.
A self-consistent solution of Schrödinger–Poisson equations using a nonuniform mesh
Authors: Tan I-H. , Snider G. L. , Chang L. D. , Hu E. L.
Published: July 2002

A self-consistent, one-dimensional solution of the Schrödinger and Poisson equations is obtained using the finite-difference method with a nonuniform mesh size. The use of the proper matrix transformation allows preservation of the symmetry of the discretized Schrödinger equation, even with the use of a nonuniform mesh size, therefore reducing the computation time. This method is very efficient in finding eigenstates extending over relatively large spatial areas without loss of accuracy. For confirmation of the accuracy of this method, a comparison is made with the exactly calculated eigenstates of GaAs/AlGaAs rectangular wells. An example of the solution of the conduction band and the electron density distribution of a single-heterostructure GaAs/AlGaAs is also presented.
Computerized tomographic imaging for space plasma physics
Authors: Zhang Yuhong , Coplan Michael A. , Moore John H. , Berenstein Carlos A.
Published: July 2002

We have considered the measurement of plasma electron velocity distribution functions as a problem in imaging and image reconstruction. We present a model instrument that measures the integral of the distribution function along lines in velocity space. This allows us to use the powerful mathematical and numerical methods that have recently been so successful in other areas of imaging. We find that this approach leads to classes of instruments that are qualitatively different from contemporary designs. An investigation of different methods of reconstruction of the distribution function from integral measurements reveals that the mathematical tools appropriate to one particular imaging problem may be very different from those required to deal with another.
Dielectric properties of polypyrrole doped with tosylate anion in the far infrared and microwave
Authors: Phillips G. , Suresh R. , Waldman J. , Kumar J. , I-Chen J. , Tripathy S. , Huang J. C.
Published: July 2002

We report measurements of the dielectric behavior in the far infrared (10–200 cm−1) and in the microwave (8.5–12.5 GHz) regime for the conducting polypyrrole (PP) doped with tosylate anion. The dielectric constants have been determined from reflection and transmission data using the Fresnel equations. The magnitude and dispersive nature of the complex index of refraction is described for a number of samples with different levels of conductivity. The ability to tailor the dielectric behavior of these materials has been demonstrated by suitably reducing the oxidized PP films. The high reflectivity in the far infrared and microwave region cannot be accounted for in terms of the Drude model defining metallic behavior. An application exploiting the large real part of the index of refraction and relatively low loss observed in the microwave region is discussed.
Atomic scale structure of microtwins in single crystal Si grown by lateral solid phase epitaxy
Authors: Ueno Tomo , Showya Tomoyuki , Ohdomari Iwao
Published: July 2002

Structural study of microtwins in single-crystal Si grown by lateral solid phase epitaxy has been done using high-resolution cross-sectional transmission electron microscopy. Microtwins with a few {111} atomic planes grow from the Si/SiO2 interface and extend to 20–30 nm in length. Using multibeam interference technique near the Scherzer focus, a structure image of a microtwin with a thickness of four {111} atomic planes was obtained. Lattice fringes of the matrix on both sides of the microtwin are shifted each other by one third of the {111} planar distance. From the analysis of a structural model of the microtwins, the growth mechanism of microtwins and the appearance of moire fringes are discussed. Consequently, the fact that the microtwins which originate from the Si/SiO2 interface are localized near the interface is shown clearly.
A high-gain, high-bandwidth In0.53Ga0.47As/InP heterojunction phototransistor for optical communications
Authors: Leu L. Y. , Gardner J. T. , Forrest S. R.
Published: July 2002

We describe investigations of the effects of inserting a thin, low-doped layer into the emitter of an InP/In0.53Ga0.47As heterojunction phototransistor (HPT). This high-low emitter structure has improved sensitivity and bandwidth over conventional structures at low input optical power by decreasing the bulk recombination current at the heterointerface. Experimental data show that the photocurrent gain is independent of the incident optical power at high input powers, corresponding to a heterojunction ideality factor of 1. At low input power, the gain is found to have a small power dependence, with an ideality factor of 1.25. A current gain as high as 260 is obtained at an input power of only 40 nW. These results, which are consistent with numerical simulations of the HPTs, give direct evidence that bulk recombination in the space- charge region at the emitter/base junction is the major source of recombination current for an InP/In0.53Ga0.47As HPT. A second structure is also proposed to improve the sensitivity by inserting a heavily doped layer into the base.
Uniaxial stress dependence of the current-voltage characteristics of n-type AlAs/GaAs/AlAs tunnel diodes at 77 K
Authors: Lu S. S. , Nathan M. I. , Meng C. C.
Published: July 2002

Longitudinal uniaxial stress along 〈100〉 has been applied in AlAs-GaAs-AlAs resonant tunneling heterostructures grown on (100) substrates to study the current-voltage characteristics as a function of stress. We find that the nonresonant current is due to Fowler–Nordheim tunneling currents by both longitudinal and transverse X valleys (X1 and Xt). This current decreases with low stress (<1 kbar), increases with intermediate stress and decreases with high stress (>9 kbar) again. This is due to the increase of the Xt barrier at low stress, the decrease of the X1 barrier at intermediate stress, and the formation and the increase of X1 potential well depth at high stress. We also find a large unexplained monotonic decrease of the resonant current through the Γ valley.
Preparation of bismuth-substituted yttrium iron garnet powders by the citrate gel process
Authors: Matsumoto Koji , Yamaguchi Kazuhiro , Fujii Toshitaka , Ueno Akifumi
Published: July 2002

The synthesis temperature and the bismuth content in bismuth-substituted yttrium iron garnet (Y3−xBixFe5O12, Bi:YIG) powders prepared by sol-gel processing were investigated, where a gel reaction of nitrates of constituent metal ions and citrate was used. Crystallographic single-phase garnet powders were obtained after the dried gel was subjected to calcination above 700 °C in air. The synthesis temperature of garnets tends to decrease with increasing Bi content. The maximum Bi substitution x is about 1.7.
Thermodynamic analysis of thermoelectric generator
Authors: Lampinen Markku J.
Published: July 2002

The aim of this research has been to investigate the role of the second law in thermoelectric phenomena. Considering the thermoelectric generator as a heat engine cycle process, the Kelvin relations for the thermoelectric circuit are derived from the energy balance and from the second law without using reversibility or equilibrium assumptions. A new formula has been derived for the thermal efficiency of the thermoelectric generator, also taking into account Thomson heat. An equation for maximum efficiency is derived and a representative numerical example of this equation is presented.
An improved impact-ionization model for high-energy electron transport in Si with Monte Carlo simulation
Authors: Thoma R. , Peifer H. J. , Engl W. L. , Quade W. , Brunetti R. , Jacoboni C.
Published: July 2002

A new model for impact ionization in Si is presented, which goes beyond the limitations of the Keldysh formula and is based on a more realistic scheme developed starting from a first-order perturbation theory. This scattering mechanism is modeled by an extended band structure which includes many bands for electrons and one band for holes in a finite Brillouin zone. Some processes have been identified to bring the dominant contribution to the scattering probability, in the present approach, for electron energies ranging up to 3 eV. Expressions for the differential and integrated scattering probabilities have been obtained which are consistent with the band model and can be included in a Monte Carlo simulation of the electron gas. Results for transport quantities are shown for a bulk material in presence of homogeneous and static electric fields under physical conditions where impact ionization influences the carrier dynamics. A comparison with theoretical and experimental data from the literature is also given.
Intrinsic magnetic properties of R2Fe17CyNx compounds: (R=Y, Sm, Er, and Tm)
Authors: Kou X. C. , Grössinger R. , Katter M. , Wecker J. , Schultz L. , Jacobs T. H. , Buschow K. H. J.
Published: July 2002

Samples of R2Fe17CyNx (R=Y, Sm, Er, Tm) were prepared by arc melting appropriate amount of R, Fe, and C, vacuum annealing at 1373 K and finally annealing at 740 K in nitrogen for 10 h. The magnetic properties of these compounds were investigated by means of ac initial susceptibility, magnetization measurements, and x-ray diffraction. The thermal stability of the nitride phase was studied by differential scanning calorimetry. It was found that, when heated above 600 K, R2Fe17CyNx irreversibly decomposes N which is irrespective of the carbon concentration and rare-earth element. The Curie temperatures of R2Fe17CyNx are independent of the carbon concentration and are approximately 400 K higher than those of the corresponding pure R2Fe17 compounds. However, the Curie temperatures cannot be correlated to the composition x of the initial R2Fe17CyNx compounds at room temperature because some N was lost during the heating to Tc. In the Er and Tm compounds spin reorientation transitions were found, marking the change of the easy magnetization direction from the c axis to the basal plane with increasing temperature. The Tm compounds show an additional magnetic transition at low temperatures (below 40 K). A coexistence of the hexagonal and the rhombohedral structural modifications was found in Er2Fe17CyNx when y<1.5, characterized by two different spin reorientation temperatures. The anisotropy fields of Sm2Fe17CyNx are higher than that of Sm2Fe17Nx. Indications of a magnetic phase transition were found also in Sm2Fe17C0.7Nx and Sm2Fe17C0.9Nx.
Growth and characterization of radio-frequency plasma deposited gold-carbon composites
Authors: Flouttard J. L. , Akinnifesi J. , Cambril E. , Despax B.
Published: July 2002

Gold-hydrocarbon composite thin films with various metal volume fractions have been deposited by a combination of sputtering and plasma deposition in argon-propane plasma. Partial pressure control and optical spectroscopy of the gas phase have shown the growth processes to be partially dependent on the chemical reactions occurring on the substrate. The polymer matrix structure was analyzed by several techniques and found to consist of dense hydrocarbon with a density of 1.7. For low metal volume fractions, optical spectra of films show that the dielectric nature of the polymer predominates while the metallic phase governs the absorption phenomenon for gold-rich films. Electrical conductivity measurements have revealed the influence of graphitic structures in the film just above a metal volume fraction p=0.03, below which carbon-carbon sp2 bonds are more predominant. Similarly the percolation threshold has been found to occur at about p=0.3 and the conductivity exponent is evaluated at 1.55.
Second- and third-harmonic generations in ultrathin phthalocyanine films prepared by the molecular-beam epitaxy technique
Authors: Hoshi Hajime , Nakamura Naoki , Maruyama Yusei
Published: July 2002

Second- and third-harmonic generations in ultrathin (200-Å)films of fluoro-bridged aluminum phthalocyanine polymer have been observed in the geometry of Maker fringe experiment using Nd:YAG laser fundamental light. Two types of films, single-crystalline and polycrystalline films, with different orientations grown by the molecular-beam epitaxy technique have been used. Observed dependence of the generated second- and third-harmonic intensities on the polarization of light and the angle of incidence is discussed based on the symmetry of the film structures. Enhancement of the harmonic intensities is realized in the single-crystalline film.
Studies of domain dynamics in amorphous Dy/Fe multilayers
Authors: Kirby Roger D. , Shen J. X. , Shan Z. S. , Sellmyer D. J.
Published: July 2002

Compositionally-modulated Dy/Fe films were prepared by dc magnetron sputtering onto glass substrates. For this series of samples, the Dy thickness was fixed at 5 Å, while the Fe thickness was varied from 4 to 6 Å. To study the magnetization reversal, the samples were first saturated. The magnetic field was then reversed to a value near the coercive field, and the Kerr rotation was measured as a function of time after reversal. We interpret our results in terms of the model of domain reversal first described by Fatuzzo for ferroelectrics. For some Fe thicknesses, we found that the reversal process was dominated by domain nucleation, while for other thicknesses it was dominated by domain wall motion. The observed behavior is discussed in terms of the magnetic and structural properties of the films.
Experimental studies on primary and secondary pyroelectric effects in Pb(ZrxTi1−x)O3, PbTiO3, and ZnO thin films
Authors: Ye Chian-ping , Tamagawa Takashi , Polla D. L.
Published: July 2002

The pyroelectric coefficients and pyroelectric response in lead zirconate titanate (Pb(ZrxTi1−x)O3), lead titanate (PbTiO3), and zinc oxide (ZnO) thin films (0.1–2.0-μm thick) have been studied for possible integrated thermosensor applications. Pyroelectric properties of these films deposited on thick (500-μm) silicon substrates and thin (1.0-μm) polysilicon membranes have been investigated. The measured pyroelectric coefficients for these materials are 70, 95, and 1.0 nC/cm2 K for Pb(Zr0.54Ti0.46)O3, PbTiO3, and ZnO, respectively. Coupling effects between the pyroelectric film and substrate were studied. It was observed that the primary pyroelectric effect dominates the pyroelectric response in Pb(Zr0.54Ti0.46)O3 and PbTiO3 thin films while the secondary effect is dominant in ZnO thin films.
New symmetrical pi-conjugated molecules having large third-order optical nonlinearities
Authors: Kurihara Takashi , Oba Naoki , Mori Yuhei , Tomaru Satoru , Kaino Toshikuni
Published: July 2002

New symmetrical pi-conjugated molecules having large third-order nonlinear susceptibilities, χ(3), are reported. The χ(3) spectra of these molecules have been measured by a THG Maker-fringe method. The magnitudes of the three-photon resonant χ(3) reach 10−10 esu. The positions of the three-photon resonance lie at the lowest-energy peaks in the vibrational structure of each absorption spectra for these molecules.
Experimental studies of a microsecond plasma opening switch in the positive polarity regime with inductive load/extraction ion diode
Authors: Bystritskii V. M. , Lisitsyn I. V. , Sinebryukhov V. A. , Volkov S. N. , Krasik Ya. E.
Published: July 2002

Systematic studies of the microsecond plasma opening switch (MPOS) operation in the positive polarity of its inner electrode with an inductive load/B-applied ion diode of the extraction type at a level of 0.3 TW of dissipated power were performed at the DOUBLE generator (300 kA, 480 kV, 1 μs). The detailed measurements of ion flow parameters in the conductive phase of the MPOS showed the considerable enhancement of the ion current amplitude over the thermal flow limit (3–10 times) which is coupled with a significant decrease of electron conductivity in the MPOS across its self-magnetic field. The positive polarity MPOS operation proved to be more critical to the stored current amplitudes and geometry of the electrodes in comparison with the negative polarity case. This fact resulted in limitations of satisfactory performance of the MPOS involving short high-voltage pulse duration, low stored current amplitudes, and a narrow region of acceptable electrode diameters. The variation of the diode anode-cathode (AC) gap provided a sensitive control of the MPOS + magnetically insulated diode (MID) system, which displayed very strong coupling, resulting in clamping of the output voltage in a wide region of diode impedances. The early long-duration (<300 ns) high-voltage (50–200 kV) prepulse improves plasma production at the anode of the MID prior to the application of the main pulse. The optimal performance of the MPOS+MID system was realized at the level of ZMPOS/ZMID = 2.5. The energy of the extracted high-power ion beam made up 3.5 kJ, its power being 120 GW with 40% efficiency of energy transfer from MPOS to the MID.
Reduction of crystalline disorder in molecular beam epitaxy GaAs on Si by MeV ion implantation and subsequent annealing
Authors: Xiao Guangming , Yin Shiduan , Zhang Jingping , Dong Aihua , Zhu Peiran , Liu Jiarui
Published: July 2002

Molecular beam epitaxy GaAs films on Si, with thicknesses ranging from 0.9–2.0 μm, were implanted with Si ions at 1.2–2.6 MeV to doses in the range 1015–1016 cm−2. Subsequent rapid infrared thermal annealing was carried out at 850 °C for 15 s in a flowing N2 atmosphere. Crystalline quality was analyzed by using Rutherfold backscattering/channeling technique and Raman scattering spectrometry. The experimental results show that the recrystallization process greatly depends on the dose and energy of implanted ions. Complete recrystallization with better crystalline quality can be obtained under proper implantation and subsequent annealing. In the improved layer the defect density was much lower than in the as-grown layer, especially near the interface.
Zinc diffusion in InP using diethylzinc and phosphine
Authors: Wisser J. , Glade M. , Schmidt H. J. , Heime K.
Published: July 2002

A low pressure open tube system with diethylzinc (DEZn) and phosphine (PH3) as precursors was used to study the Zn-diffusion in InP. This system offers a flexible and precise control of the diffusion parameters. We investigated the effect of the DEZn and PH3 partial pressures and of the diffusion temperature and time on the hole and Zn concentration profiles. Annealing the samples leads to an increased hole concentration due to out-diffusion of interstitial Zn donors. The Zn and hole concentration profiles were obtained by secondary-ion mass spectroscopy and C–V etch profiling showing maximum hole concentrations between 1017 cm−3 and 4×1018 cm−3 for diffusion depths from 0.3 to 2 μm.
Marker and radioactive silicon tracer studies of PtSi formation
Authors: McLeod J. E. , Wandt M. A. E. , Pretorius R. , Comrie C. M.
Published: July 2002

Marker and radioactive 31Si experiments have been performed to investigate atomic diffusion during PtSi formation. The marker work used a thin metallic layer (Ti, Co, Ni) as a marker. Analysis of the marker displacement indicated growth dominated by silicon diffusion (∼90%). The interpretation of data from the radioactive tracer experiments is less clear cut. However, when examined in conjunction with the marker results, it would appear that either PtSi growth took place by silicon substitutional diffusion or by a mixed interstitial mechanism (i.e., a mixture of interstitial and interstitialcy diffusion). Arguments are presented to suggest that silicon vacancy diffusion during silicide growth is the most likely mechanism. This interpretation is found to be generally consistent with other recently published work on PtSi formation.
Electrical characteristics of excimer laser ablated bismuth titanate films on silicon
Authors: Maffei N. , Krupanidhi S. B.
Published: July 2002

Bismuth titanate thin films were deposited by the excimer laser ablation technique directly onto bare silicon substrates. Current-voltage studies suggested the formation of a heterojunction at the Bi4Ti3O12/Si interface. The current characteristics at voltages ≥1 V were ascribed to trap-limited space-charge conduction. Hysteretic capacitance-voltage data indicated that charge injection was dominant, masking any polarization mode necessary for nonvolatile memory operation. Ferroelectric hysteretic studies, however, indicated that the films were ferroelectric with Pr≂10 μC/cm2 and Ec≂150 kV/cm.
Rotational versus alternating hysteresis losses in nonoriented soft magnetic laminations
Authors: Fiorillo F. , Rietto A. M.
Published: July 2002

Rotational and alternating hysteresis losses have been investigated in theory and experiment in nonoriented soft magnetic laminations. Attention has been focused on the dependence of energy loss on peak magnetization Ip. The experiments, performed in a wide induction range (∼2×10−4 T≤Ip≤∼1.6 T), show that the ratio between rotational and alternating energy losses Whr/Wha is a monotonically decreasing function of Ip. A quantitative theoretical investigation is carried out through modeling of the magnetization process under rotating field and its relation to processes under alternating field. Three basic mechanisms of magnetization rotation are considered: linear combination of unidirectional hysteresis loops at low inductions (Rayleigh region), cyclic rearrangement of magnetic domains between different easy directions at intermediate inductions, and coherent spin rotation toward the approach to magnetic saturation. The ensuing predicted behavior of Whr/Wha is found to be in good agreement with the experiments performed in nonoriented low carbon steel and 3% FeSi laminations.
Study of magnetic recording transitions at very low flying heights
Authors: Che Xiaodong , Bertram H. N.
Published: July 2002

In this article, a micromagnetic model is utilized to study dibits recorded under an almost contact condition. Transitions, which are sharply written at contact, suffer irreversible demagnetization while they leave the recording head. Dibit stability under a small perturbing field is examined. A small dc field and a thin-film edge field are utilized for the perturbing field. It is found that, in contact recording, Mrδ/Hc should be sufficiently small for magnetic pattern stability.
Observation of surface charge screening and Fermi level pinning on a synthetic, boron-doped diamond
Authors: Baker Shenda M. , Rossman George R. , Baldeschwieler John D.
Published: July 2002

Spectroscopic current-voltage (I-V) curves taken with a scanning tunneling microscope on a synthetic, boron-doped diamond single crystal indicate that the diamond, boiled in acid and baked to 500 °C in vacuum, does not exhibit ideal Schottky characteristics. These I-V curves taken in ultrahigh vacuum do not fit the traditional theory of thermionic emission; however, the deviation from ideal can be accounted for by charge screening at the diamond surface. At ambient pressure, the I-V curves have a sharp threshold voltage at 1.7 eV above the valence band edge indicating pinning of the Fermi energy. This measurement is in excellent agreement with the 1/3 band gap rule of Mead and Spitzer [Phys. Rev. 134, A713 (1964)].
The 900 °C upper yield stress of Czochralski silicon single crystals with carbon concentrations of 4.0×1014 and 3.5×1015 cm−3
Authors: Fukuda Tetsuo , Koizuka Masaaki
Published: July 2002

In order to investigate the influence of carbon on the high-temperature strength of Czochralski silicon single crystals, we measured the 900 °C upper yield stress of crystals containing carbon at concentrations of 4.0×1014 cm−3 (‘‘low C’’) and 3.5×1015 cm−3 (‘‘standard C’’). Prior to testing, all crystals were heat treated for 20 h at 700 °C. They were then annealed at 1000 °C for periods between 1.5–7 h. During the longest anneal, the interstitial oxygen content fell from 2.0×1018 to 1.0×1018 cm−3 in low C crystals and from 1.9×1018 to 7×1017 cm−3 in ‘‘standard C’’ crystals. The 900 °C upper yield stress of 7 h annealed low C crystals is 13 MPa, which is 30–40% higher than that measured in standard C crystals. The precipitate density, measured optically, is 4×105 cm−2 in low C samples and 9×105 cm−2 in standard C crystals. In all cases, the precipitates punched out dislocations. A model that assumes that the higher interstitial oxygen content retained by the low C crystals results in higher locking stresses for glide dislocations can quantitatively account for these observations.
Elimination of an artifact in the photoluminescence spectra of heavily doped C-GaAs epitaxial layers on undoped GaAs substrates
Authors: Lu Z. H. , Majerfeld A.
Published: July 2002

Selective absorption of light in the undoped GaAs substrate is shown to be responsible for a spurious but prominent feature observed in the photoluminescence spectra of C-doped epitaxial GaAs layers that have smaller band gaps than the substrate. It is shown that the feature is an optical artifact and, indeed, an intrinsic characteristic of luminescence spectroscopy techniques when they are used for analysis of epitaxial layers on semiconductor substrates. The artifact may lead to false interpretation of data and hinder quantitative photoluminescence analysis of the electronic structure of heavily doped GaAs epilayers. We show experimental and analytical methods that can be easily implemented to remove the artifact and, thereby, restore the true emission spectrum.
Strain mapping of ultrathin epitaxial ZnTe and MnTe layers embedded in CdTe
Authors: Jouneau P. H. , Tardot A. , Feuillet G. , Mariette H. , Cibert J.
Published: July 2002

High-resolution electron microscopy is used to investigate the morphology of ultrathin pseudomorphic (001) ZnTe and MnTe strained layers grown in CdTe. Local distortions of the crystal lattice are measured directly on high-resolution images by use of image processing software. In the case of ZnTe/CdTe superlattices, the method yields the location of Zn within each place in the heterostructure and the total amount of Zn per period. For MnTe layers embedded in CdTe, one can deduce the atomic morphology of the interfaces which are shown to present a clear asymmetry.
Piezoelectric constant for binary piezoelectric 0-3 connectivity composites and the effect of mixed connectivity
Authors: Jayasundere N. , Smith B. V. , Dunn J. R.
Published: July 2002

An analytic expression is presented for the piezoelectric d constant of a binary piezoelectric 0-3 connectivity composite. The expression is developed under the limiting assumption that the dielectric constant of the ceramic is much greater than the matrix. Predictions made using the theory compare very favorably with available experimental data. A 0-3/1-3 mixed connectivity model is also described for composites in which the average piezoceramic particle size is a significant fraction of the thickness of the composite.
The effect of interactions on GMR in granular solids
Authors: El-Hilo M. , O’Grady K. , Chantrell R. W.
Published: July 2002

In this article the effects of dipolar and exchange interactions on the magnetoresistance curves in granular solids has been calculated using a generalized 3-d Monte Carlo model. This model allows the final configuration of magnetic moments to be calculated as a function of concentration, temperature, and magnetic field. The results show that interaction effects give rise to a finite resistivity in small magnetic fields. The magnitude of this finite magnetoresistance is found to increase with increasing concentration. Thus the maximum change in MR with field is found to be lowered by the interaction effects.
Design and performance of very long-wavelength GaAs/AlxGa1−xAs quantum-well infrared photodetectors
Authors: Sarusi G. , Gunapala S. D. , Park J. S. , Levine B. F.
Published: July 2002

We present an extensive and detailed study of very long wavelength quantum well infrared photodetectors covering the spectral region between 14 and 20 μm. Measurements were made on seven different molecular beam epitaxy grown samples having different well widths and barrier heights. In this study we combine experimental results with theoretical analysis and focus on the relationship between the quantum well structure and detector performance, i.e., responsivity, dark current, dynamic resistance, noise current, optical-gain, and detectivity. These results provide the basis for further optimization, and the detector parameters needed for the design of the readout circuit for focal plane arrays.
The heat capacity of titanium disilicide
Authors: Sylla W. K. , Stillman S. E. , Sabella M. S. , Cotts E. J.
Published: July 2002

The heat capacity of TiSi2 has been measured in the temperature range 105–500 K. The heat capacity of TiSi2 varies monotonically between temperatures of 100 and 500 K with a reference value of 22.0±0.2 J/g atom K at 298.15 K. Based upon our heat capacity data, the standard molar entropy of TiSi2 at 298.15 K is estimated to be 22.2±0.8 J/g atom K. Our data support estimates of the higher temperature heat capacity of TiSi2 based upon previously measured heat capacities of different, but similar, substances. A number of TiSi2 samples were prepared by rapidly quenching (≳105 K/s) from the melt. The structure and the measured heat capacity of these samples were similar to those of well annealed samples, underscoring the thermal stability of this material.
Effect of power on interface and electrical properties of SiO2 films produced by plasma-enhanced chemical-vapor deposition
Authors: Landheer D. , Xu D.-X. , Tao Y. , Sproule G. I.
Published: July 2002

The effect of power on the electrical and interface properties of silicon dioxide films produced by direct plasma-enhanced chemical-vapor deposition, using nitrous oxide and silane with high helium dilution, has been investigated. Auger depth profiling measurements indicate that while the bulk of the films have no measurable impurities, the interface region contains about 1.6×1015 atoms/cm2 of nitrogen. In contrast to thermal oxides, there is no thick interface layer with a large intrinsic compressive stress. The interface-state densities of the films obtained from capacitance-voltage measurements on metal-oxide-semiconductor diodes increase with increasing plasma power, but these can be removed to some extent by high-temperature annealing at temperatures in the range 800–950 °C. The flatband voltage is relatively insensitive to plasma power. Thermal oxide samples have been subjected to the plasma processes and these also show evidence of plasma damage. A thin layer produced at the interface by a separate plasma oxynitridation process is shown to be incapable of protecting the Si/SiO2 interface from the plasma damage produced by subsequent high-power plasma deposition processes. The nature of the interface states is discussed.
Two-dimensional growth model for laser-ablated Ag-doped YBa2Cu3O7−x thin films
Authors: Kumar Dhananjay , Apte P. R. , Pinto R.
Published: July 2002

Ag-doped YBa2Cu3O7−x (YBCO) thin films using 2–20 wt % Ag-doped YBCO targets have been grown in situ by the laser ablation technique. The improvement in properties in normal and superconducting states of Ag-doped YBCO films has been interpreted using a two-dimensional growth model. The model is simple and is based on widely accepted characteristics of Ag such as its flux action at high temperatures and its nonreactivity with YBCO phase. Experimental evidence in support of the growth model is presented by carrying out microstructural studies and measurements of room-temperature resistivity, critical current density, and microwave surface resistance in superconducting state.
Photon-assisted oxidation of the GaAs(100) surface using water at 90 K
Authors: Ettedgui E. , Park Ken T. , Cao Jianming , Gao Y. , Ruckman M. W.
Published: July 2002

Photoelectron spectroscopy is used to study the interaction of H2O with GaAs(100) at 90 K and to assess its use as a photon-assisted oxidizing agent. The condensation of H2O at 90 K produces a thin physisorbed layer on GaAs(100). We found that intense synchrotron radiation causes most of the water to desorb in a sequential manner, without reacting with the substrate. The fraction of water that does not desorb reacts with Ga, giving rise to a Ga oxide. The As present in the substrate does not react with H2O during the process, thereby avoiding the formation of volatile As compounds.
Atomic force microscopy and Raman spectroscopy studies on the oxidation of Cu thin films
Authors: Gong Y. S. , Lee Chiapyng , Yang C. K.
Published: July 2002

The oxidation of sputtering deposited copper thin films has been investigated. Phase identification and surface morphology characterization were performed by x-ray diffraction, Raman spectroscopy, and atomic force microscopy (AFM). The copper film is first oxidized to Cu2O below 300 °C and then to CuO at higher temperatures (≥300 °C) near the surface of the copper. AFM results show that the as-deposited Cu film contains grains of similar sizes. After heat treatment at 200 °C, small grains are observed due to nucleation of the Cu2O phase. Further annealing in air leads to aggregation and growth of the grains whereas the grain boundary of the grains before coalescence is still evident. The Cu2O and CuO phases form alternating layers when the annealing temperature is 400 °C.
Quasi-static electrical resonances and optical bistability in periodic composite materials
Authors: Levy-Nathansohn R. , Bergman David J.
Published: July 2002

A variational approach is used to examine the possibility of bistable behavior in a two-component metal-dielectric composite medium with a periodic microstructure where one component has a Kerr- type field dependent part in the dielectric constant ε while the field independent part of ε in both materials is in general complex. It is shown that under certain conditions bistable behavior can occur even though the field dependent nonlinearity is weak everywhere. This is achieved by operating the material sufficiently close to one of its sharp quasi-static, microgeometric electrical resonances. The physical characteristics of the threshold intensity are worked out and considerations made on how to optimize the chances for observing optical bistability in such a material.
Transmission electron microscopy analysis of heavily As-doped, laser, and thermally annealed layers in silicon
Authors: Dokumaci O. , Rousseau P. , Luning S. , Krishnamoorthy V. , Jones K. S. , Law M. E.
Published: July 2002

The extended defects in laser activated and subsequently thermally annealed high concentration arsenic layers have been investigated in a range of surface concentrations from 2.3×1020 to 1.9×1021 As/cm3 with transmission electron microscopy. We observe a rapid change in the density of dislocation loops with dose which is indicative of a homogeneous nucleation mechanism. The number of atoms bound by the defects is insufficient to account directly for all of the inactive arsenic. The defects lie uniformly inside the As layer up to the junction depth, which suggests that As inactive complexes are aiding the loop formation. Our results support the proposition that arsenic deactivation injects silicon interstitials.