bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of surface topography on ion trajectories in low-pressure plasma etching
Authors: Ardehali M. , Matsumoto H.
Published: July 2002

The transport of ions through a collisionless rf glow-discharge sheath is simulated with a Monte Carlo method in order to determine the influence of surface topography on ion trajectories. The simulation results indicate that the perturbation of the local electric field by the geometric shape of the trench has very little influence on ion trajectories, and as such cannot be considered as the origin of reactive ion etching lag in low-pressure rf plasmas. These results are in sharp disagreement with the model proposed by Lee and Zhou [J. Electrochem. Soc. 138, 2439 (1991)] and with the calculations by Ingram [J. Appl. Phys. 68, 500 (1990)].
Theoretical x-ray Bragg reflection widths and reflectivities of II-VI semiconductors
Authors: Möller M. O. , Bicknell-Tassius R. N. , Landwehr G.
Published: July 2002

X-ray Bragg reflection widths and reflectivities are calculated by the dynamical scattering theory. Results on the binary II-VI semiconductors CdTe, HgTe, and the ternary alloys CdHgTe and CdZnTe are reported. For comparison, results on several III-V compounds are also reported. The dependence of the reflection widths and reflectivities on alloy composition, wavelength, layer thickness, and material properties are discussed. Especially in alloys, interesting effects, such as drastic changes of the reflectivity depending on the alloy composition, appear. The behavior of the widths and reflectivities can be understood by the examination of the competing processes of absorption and extinction. The results from calculated intrinsic reflex profiles are compared with approximation formulas.
Room-temperature stimulated emission in optically pumped narrow ZnSe/ZnSxSe1−x multiple-quantum-well structures
Authors: Dabbicco M. , Cingolani R. , Ferrara M. , Suemune I. , Kuroda Y.
Published: July 2002

Room-temperature stimulated emission in ZnSe/ZnS0.18Se0.82 multiple-quantum-well structure is reported. An optical excitation threshold around 300 kW/cm2 at 300 K and 8.4 kW/cm2 at 10 K was measured. An unsaturated optical gain coefficient of the order of 5×102 cm−1 has been measured at low temperature.
a-axis growth of YBa2Cu3O7 thin films on LaAlO3 induced by monolayer buffers of PrO2
Authors: Tröger Larc , Fork D. K. , Boyce J. B.
Published: July 2002

The deposition of an intermediate buffer of praseodymium oxide (PrO2) of only monolayer thickness (about 2 Å) in a two-temperature process results in the growth of almost exclusive epitaxial a-axis oriented YBa2Cu3O7 (YBCO) on LaAlO3 (100). Under identical experimental conditions, but without the monolayer of PrO2, epitaxial c-axis oriented YBCO films with a critical temperature Tc of 86 K and a transition width of 1 K are obtained. Critical temperatures of these a-axis oriented films are typically 10 K lower than those of the c-axis oriented films. Our findings suggest that a single layer of PrBa2Cu3O7 is formed at the interface, inducing a-axis growth throughout the whole YBCO film.
Modeling of the initiation and evolution of a laser-ionized column in the lower atmosphere: 314.5 nm wavelength resonant multiphoton ionization of naturally occurring argon
Authors: Fetzer G. J. , Stockley J. E.
Published: July 2002

A model has been developed to examine the effects of a 314.5 nm wavelength laser pulse directed vertically through the atmosphere on the local ion and electron concentrations in the beam path. The 314.5 nm wavelength was selected to exploit a three-photon excitation resonance with the 3p54s 1P10 excited state in argon. Absorption of a fourth photon of the same wavelength will ionize the excited atom. Using a rate equation formalism and a detailed collection of atmospheric chemistry reactions the model provides the concentrations of electrons and ions as functions of altitude, time, laser energy, relative humidity, focal characteristics of the pulse, and ambient atmospheric electric-field conditions. Both linear and nonlinear effects on the propagation of the laser pulse have been taken into account. The calculated charged particle concentrations are used to estimate the conductivity of the ionized column. Results presented indicate peak electron densities up to 108 cm−3 can be created using laser intensities on the order of 108 W/cm2. Electron lifetimes in the column are typically 50–200 ns, however, the lifetime of the conductive channel is long in comparison (100 μs). Long-lived ions created by charge transfer and attachment reactions between laser-produced argon ions and electrons and other atmospheric species provide a persistent enhanced conductivity in the beam path. Model results demonstrate that laser pulses having peak powers attainable with current technology can perturb the conductivity of an ionized column by as much as seven orders of magnitude in comparison to ambient conditions. A distinct tradeoff between column length and the extent of ionization is evident in the results presented. The tradeoff is a result of the competing mechanisms of multiphoton ionization and stimulated Raman scattering and is discussed.
Interstitial oxygen reduction in silicon at thermal donor temperatures
Authors: Guse M. P. , Kleinhenz R.
Published: July 2002

Silicon wafers with a range of initial oxygen and carbon concentration were annealed at 450, 475, and 500 °C for up to 500 h with the interstitial oxygen concentration being monitored every 20 h. It is found that the rate of oxygen loss scales as the fifth power of oxygen concentration for wafers annealed below 500 °C.
Deformation and thermal oxidation of GaAsP wafers locally heated by a Nd:Y3Al5O12 (yttrium aluminum garnet) laser beam
Authors: Kawamura Tsutomu , Matsumoto Takashi
Published: July 2002

A Ga0.6As0.4P epitaxial wafer, deposited on a GaAs substrate with a compositional graded layer placed between these two substances, was locally heated to temperatures ranging from 600 to 1300 °C (melting point) in air by a Nd:Y3Al5O12 (yttrium aluminum garnet) laser beam. The characteristics of the wafer were determined by three different x-ray diffraction methods. When the temperature gradient was very steep, large disordering took place in the irradiated region of the wafer. This resulted in the formation of explosive disordered GaAsP, fibrous β-Ga2O3 on the epitaxial-layer side, and GaPO4 polycrystals on the graded-layer side. The characteristic formation mechanisms for these by-products are discussed.
Closed-form solution for the induction heating problem with rotational symmetry
Authors: Hussein A. M. , Biringer P. P.
Published: July 2002

A closed-form solution is developed for the induction heating of an infinitely long cylindrical load by periodic circular current sheets. The wave equation is solved and various field quantities are obtained. An equivalent surface current is defined that enables studying the axial distribution of the induced current in the load. The power loss in the conducting load is derived and its dependence on different coil-load configurations and characteristics is shown. The problem of multicoil systems, where coils can be of different sizes and carry different currents and frequencies, is addressed.
Modification of interfacial carrier depletion in GaAs grown by molecular beam epitaxy
Authors: Reynolds C. L. , Geva M.
Published: July 2002

The magnitude of carrier depletion at the interface between molecular beam epitaxial GaAs and a GaAs substrate is shown to depend upon the length of exposure to ultraviolet ozone radiation. In particular, as the ozone exposure time increases, the interfacial carbon concentration and loss of carriers at the interface decrease. The data suggest a relationship between electrically measured carrier depletion and the impurity species, carbon and silicon, at the interface.
Growth and properties of a multilayer system based on Y1Ba2Cu3Ox and amorphous Y-ZrO2
Authors: Boikov Yu. , Ivanov Z. G. , Olsson E. , Alarco J. A. , Brorsson G. , Claeson T.
Published: July 2002

The growth of c-axis oriented Y1Ba2Cu3Ox thin films on an amorphous buffer layer of Y-ZrO2, deposited on sapphire substrates, was investigated. Both films were grown by a pulsed laser deposition technique. A strong correlation was observed between the properties of Y1Ba2Cu3Ox and the thickness of the buffer layer. A Tc of 89 K was obtained for an optimal buffer layer thickness of 9 nm. A model that adequately describes the film growth process was developed. A multilayer system of Y1Ba2Cu3Ox and amorphous Y-ZrO2 was grown and a Tc of 87 K for the upper c-axis oriented layer was measured.
Computer simulation of Si-implanted GaAs (001) single crystals
Authors: Lee Y. H. , Kang T. W. , Hong C. Y. , Kim T. W.
Published: July 2002

A computer simulation based on the binary collision approximation has been performed to investigate the Si implantation efficiency, the Si depth profile, and the vacancy formation for Si-implanted GaAs (001) crystals. The results reveal a strong dependence on the incident angle of the Si source. The calculated depth profile of Si agrees well with the experimental results from secondary-ion mass spectroscopy. The simulated distribution of vacancies is shallower than that of Si atoms. Also, the calculated number of Ga vacancies exceeds that of As vacancies, which suggests that the Si atoms easily occupy the Ga sites and are activated as donors.
Application of x-ray reflectometry in study of nonideal Si/Si1−x-Gex superlattices
Authors: Baribeau J.-M.
Published: July 2002

X-ray reflectometry and double-crystal diffraction have been applied to the characterization of molecular beam epitaxy-grown Si/Si1−xGex superlattices. It is shown, using specific examples, how reflectometry can help to solve difficulties encountered in double-crystal diffractometry analysis of nonideal superlattices that contain thickness fluctuations or in which partial strain relaxation has occurred.
Infrared determination of interstitial oxygen behavior during epitaxial silicon growth on Czochralski substrates
Authors: Geddo M. , Pivac B. , Sassella A. , Stella A. , Borghesi A. , Maierna A.
Published: July 2002

Interstitial oxygen profile across an epitaxial silicon and Czochralski silicon interface has been studied using high-spatial-resolution Fourier transform infrared spectroscopy. Systematic transmission measurements performed on a transversal wafer cross section evidenced oxygen contamination of the epilayer. This was due to solid-state outdiffusion from the substrate occurring during epilayer deposition. Oxygen diffusivity values resulting from the experiments suggest a mechanism scarcely influenced by the interface. Oxygen contamination is strictly related to the type of dopant present in the substrate and not to that present in the epilayer. The oxygen contamination of the epilayer (significant in n-type substrate samples) could explain the structural defects often observed in epitaxial layers by different techniques.
S-type switching characteristics from transverse transport in multiquantum well diodes
Authors: Song C. , Roenker K. P.
Published: July 2002

S-type switching characteristics have been observed at room temperature in AlAs/GaAs multiquantum well diodes at low forward bias. The multiquantum well structure consisted of a set of 10 periods of undoped 50-nm AlAs barriers with 50-nm n+ (1×1018/cm3) GaAs quantum wells inserted between a p+-GaAs anode and n+-GaAs cathode. A threshold voltage for switching from the low to high conductance state of 2.2 V was measured and a minimum holding voltage in the high conductance state of 0.9 V was observed. Switching to the high conductance state occurs due to impact ionization of electrons out of the heavily doped n+ wells forming positive space charge which enhances the cathode field and thereby electron injection giving rise to a positive feedback mechanism.
Sequential light irradiation and two-stage photoquenching in GaAs:EL2
Authors: Pandian V. , Kumar V.
Published: July 2002

The phenomenon of two-stage photoquenching of EL2 defect in semi-insulating GaAs [V. Pandian and V. Kumar, J. Appl. Phys. 70, 5114 (1991)] is further investigated by sequentially irradiating the sample with different energy photons in the quenching band at constant temperature. The results of the new experiments, which are similar to the sequential quenching experiments with fixed photon energy at different temperatures, support the conclusion that the two-stage quenching may be related to the possible lattice strain mediated cooperative structural distortion arising out of transition of EL2 to the metastable state.
Iron nanoparticles in copper matrix prepared by sol-gel route
Authors: Chatterjee A. , Datta A. , Giri Anit K. , Das D. , Chakravorty D.
Published: July 2002

Iron particles having diameters around 8 nm and loosely packed with nanosized copper particles have been prepared by a sol-gel route. The samples exhibit coercivities in the range 200 to 500 Oe that are typical of single-domain iron grains. The Mössbauer spectrum is consistent with the presence of α-Fe particles in the system. However, a finite value of the isomer shift is obtained that is ascribed to possible electron transfer between the iron atoms and the surrounding copper matrix.
Mapping of the localized interface and surface states of InGaAs lattice matched to Fe-doped InP by infrared spectroscopy
Authors: Peng L. H. , Broekaert T. P. E. , Choi W. Y. , Bennett B. R. , Smet J. H. , Diadiuk V. , Groves S. H. , Palmateer S. C. , Pan N. , Fonstad C. G.
Published: July 2002

Infrared absorption and photocurrent measurements have been applied to study the photoresponse below the band gap of indium gallium arsenide (In0.53Ga0.47As) grown lattice matched to Fe-doped semi-insulating indium phosphide (InP) substrates by various epitaxial growth techniques, including molecular beam epitaxy, liquid phase epitaxy, and metalorganic chemical vapor deposition. It is found that Fe at the InGaAs/InP interface is responsible for exciton-like and polarization sensitive absorption peaks. Both electron and hole emission into the conduction and valence bands, respectively, were observed, and a deep Fe level was identified 0.37 eV below the conduction band edge of bulk Fe:InGaAs. Lowering of the local crystal symmetry due to the interface electric field is proposed to be the mechanism that describes the dipole-allowed interband absorption of 3d transition metal impurities in narrow band gap III-V compounds like the Fe2+:InGaAs used in this study. The ambiguity in distinguishing InGaAs quantum well intersubband absorption signals from the Fe interband absorption signals is also addressed.
Pressure dependence of optical absorption in PbTiO3 to 35 GPa: Observation of the tetragonal-to-cubic phase transition
Authors: Zha C. S. , Kalinichev A. G. , Bass J. D. , Suchicital C. T. A. , Payne D. A.
Published: July 2002

Optical absorption of the polar material PbTiO3 has been studied up to 35 GPa (350 kbar) in the visible range of wavelengths using a single crystal samples compressed in a diamond anvil high pressure cell. The absorption edge shifts toward lower energies with increasing pressure. Pressure dependence of the absorption edge undergoes significant changes at about 11.5±0.3 GPa, close to the previously identified tetragonal-cubic phase transition. The change in pressure dependence of the spectra is consistent with second-order character of the transition.
Highly stable sputtered NiInW refractory ohmic contact to n-type GaAs
Authors: Hugon M. C. , Agius B. , Varniere F. , Froment M. , Pillier F.
Published: July 2002

Thermally stable low specific resistivity ohmic contact on n-type GaAs is required to fabricate high-speed GaAs integrated circuits. The Nix-In1−x/W (x being either 0.95 or 0.9) contact prepared by magnetron cathodic sputtering is attractive because this contact is expected to be ohmic and thermally stable after rapid thermal annealing. Moreover, the sputter deposition is well suited for refractory metals. The specific resistivity measurements and microstructural analysis were carried out to establish a simple fabrication process which forms an ohmic contact with low specific resistivity. This last parameter was found to be sensitive to the deposition sequence, and the annealing time and temperature. Low specific resistivity of 10−6 Ω cm2 was obtained for Nix-In1−x/W contact annealing at 850 °C for 10 s. This rapid thermal annealing is interesting because simultaneous annealing for contact formation and activation of implanted dopants is possible. The formation of phases during heat treatment stimulates the Schottky to ohmic contact conversion.
Permeability of highly compressible porous medium
Authors: Kataja M. , Rybin A. , Timonen J.
Published: July 2002

The dependence of the flow permeability of highly compressible porous media on the degree of compression is discussed. As examples, we study the simple capillary theory by Kozeny and its straightforward generalization to a case where the pore size is statistically distributed. Several variants of the basic models are considered by implementing constraints arising from various plausible assumptions of the deformation of the porous structure under compression.
Skin effect on the current-voltage curves of YBaCuO rings up to 100 kHz
Authors: Perea A. , Alvarez Rivas J. L.
Published: July 2002

A new contactless inductive method is used to generate currents in large YBaCuO rings at liquid-nitrogen temperature up to 100 kHz. With this method the transport current in the ring is directly measured. A study of the current-voltage curves for currents above the critical current has been made in three rings of fixed size but of different oxygen content. The experimental results indicate the occurrence of the skin effect.
Effect of substrate and antiferromagnetic film’s thickness on exchange-bias field (invited)
Authors: Allegranza Oletta , Chen Mao-Min
Published: July 2002

In this work, we studied the effect of different substrates and the thickness dependence of the antiferromagnetic layer on the exchange-bias field, created through interfacial exchange coupling between NiFe and FeMn. The substrates considered were glass and a metallic underlayer, such as Ta, on glass. We noticed different behaviors of the two types of films when annealed in a magnetic field at 240 °C and we carefully looked at their temperature dependence, observing that the blocking temperature, at which the exchange-bias field goes to zero, decreases with increasing FeMn thickness. We also found that, when reducing the antiferromagnetic film’s thickness, the exchange-bias field of the annealed NiFe/FeMn structure improves on both types of substrate. Since a low blocking temperature is undesirable, we developed a method to take advantage of the thinner FeMn film’s properties and to compensate the decrease in blocking temperature. The FeMn was deposited in two separate layers. The first layer, at the NiFe interface, was sputtered in pure Ar, and the second in an Ar/O2 or Ar/N2 mixture. The advantage of this technique was particularly impressive for films deposited on Ta over glass, where a factor of 2 improvement in exchange bias field was obtained at both room temperature and 80 °C, when compared to the structure with the same total antiferromagnetic material’s thickness deposited in one single layer. Blocking temperatures were above 150 °C.
Thermal stability and dopant drive-out characteristics of CoSi2 polycide gates
Authors: Chen Wei-Ming , Lin Jengping , Banerjee Sanjay K. , Lee Jack C.
Published: July 2002

BF2-implanted CoSi2 polycide gates that are stable at high temperatures up to 1000 °C have been fabricated. The use of CoSi2 polycide as a boron diffusion source was evaluated using a metal-oxide-semiconductor capacitor structure on a p-type Si substrate. This structure is useful in monitoring the diffusion of the electrically activated dopants from the silicide towards the polycrystalline silicon-SiO2 interface. Our results show that using BF2-implanted CoSi2 as a diffusion source is effective in doping polycrystalline silicon gates degenerately without any degradation of the polycide resistivity.
Relation between photoluminescence wavelength and lattice mismatch in metalorganic vapor-phase epitaxy InGaAs/InP
Authors: Kuphal E. , Pöcker A. , Eisenbach A.
Published: July 2002

The photoluminescence (PL) wavelength of high-purity 0.5-μm-thick metalorganic vapor-phase epitaxy In1−xGaxAs/InP was measured at room temperature (RT) as a function of composition. The relaxed mismatch of these coherently strained layers was between −0.25% and +0.13%, corresponding to x=0.503 – 0.448. The composition was determined by x-ray diffraction (XRD) using a four-crystal monochromator. Extremely narrow XRD linewidths as a function of layer thickness are reported. The PL peak wavelength λp at RT of exactly lattice-matched InGaAs is 1668 nm, corresponding to a band gap Eg=731 meV. The bowing parameter of the strain-free Eg(x) relation is c=−0.494. The measured λp vs x relation agrees well with the strain-free Eg(x) corrected by the hydrostatic part of the strain energy. From line-shape analysis of RT and 77 K PL spectra it is found that the spectra of strained layers contain two lines in accordance with the valence band splitting under uniaxial strain. The conditions for a reliable determination of the compositional homogeneity of large InGaAs wafers by a mapping of λp are given; e.g., a variation Δx=8.7×10−3 over a 2 in. wafer is found.
The role of ion bombardment in the rf-glow-discharge preparation of intrinsic amorphous silicon
Authors: Cárabe J. , Gandía J. J. , Gutiérrez M. T.
Published: July 2002

The influence of the rf-power density and the silane mass flow rate on the properties and growth rate of glow-discharge amorphous silicon has been investigated. The silane deposition efficiency during the preparation process has been deduced using mass spectrometry. It has been found that this deposition efficiency is correlated with film quality and growth rate. Such a correlation and its dependence on the preparation parameters has allowed to find out a way to make films at increasing growth rates while keeping their properties essentially unchanged. The results are interpreted in terms of selective etching of weakly bonded radicals owing to ion bombardment. The research work undertaken has allowed to obtain intrinsic amorphous silicon of excellent photovoltaic properties with growth rates up to 10 Å s−1.
Kinetics of tungsten low-pressure chemical-vapor deposition using WF6 and SiH4 studied by in situ growth-rate measurements
Authors: Ammerlaan J. A. M. , van der Put P. J. , Schoonman J.
Published: July 2002

The kinetics of tungsten low-pressure chemical-vapor deposition (LPCVD) using WF6 and SiH4 have been studied in a vertical hot-wall reactor equipped with a microbalance. In situ growth-rate measurements were performed by monitoring the sample weight during tungsten film deposition. The kinetics of the LPCVD process appear to be determined by the ratio of the partial pressures of SiH4 and WF6. At low SiH4/WF6 ratios, i.e., p(SiH4)/p(WF6)≤0.3, the kinetics are first and zeroth order with respect to p(SiH4) and p(WF6), respectively. At higher ratios, i.e., 0.5≤p(SiH4)/p(WF6)≤1.0, the deposition rate is second and minus first order with respect to p(SiH4) and p(WF6), respectively. In both kinetic regimes a zeroth-order dependence on p(H2) was observed. The growth rate does not vary substantially in the temperature range 200–400 °C. Maximum rate values are observed near 300 °C. An attempt has been made to interpret the observed kinetic behavior in terms of a Langmuir–Hinshelwood model. The proposed surface reaction mechanism involves reaction between chemisorbed SiH species and chemisorbed WF6 molecules. Different surface reaction pathways, governed by different rate-limiting steps, have been proposed in order to explain the observed kinetics in the two regimes.
Speed response analysis of an electron-transfer multiple-quantum-well waveguide modulator
Authors: Wang Jin , Leburton J. P. , Educato J. L. , Zucker J. E.
Published: July 2002

A numerical model is presented for the electronic properties of a novel InxGa1−xAs/In1−yAlyAs multiple-quantum-well waveguide modulator and a theoretical analysis of electron and hole escape mechanisms from the quantum well is developed. The influence of carriers and dopant ion charges on the band structure is simulated with a self-consistent Poisson–Schrödinger solver. The different escape mechanisms for both electrons and holes are: direct tunneling, phonon-assisted sequential tunneling, and thermionic emission. At high forward biases, the electron escape time limits the device speed, while at high reverse biases, heavy holes take a longer time than electrons for escaping the quantum well. For both particles, phonon-assisted sequential tunneling is a key mechanism in determining the device speed operation. The calculated escape times are in good agreement with the experimental data.
Self-consistent analysis of electric field-dependent intersubband transitions for a thin layer inserted quantum well
Authors: Chen W. Q. , Andersson T. G.
Published: July 2002

A self-consistent theoretical analysis, using both the Schrödinger and Poisson equations, is made to calculate the electric field-dependent intersubband electron transition for a thin layer inserted in a quantum well. In a 100-Å-wide square quantum well a layer is embedded giving a deeper wall (or a barrier). This layer is carefully adjusted in its position and composition to optimize the dependence of intersubband transition on the external electric field. The analysis shows that the structure with a narrow well thickness between 30 and 45 Å, located at the side of the wide well, has optimal properties in terms of large near-linear Stark shifts associated with high oscillator strengths and a wide range of voltage tunability in the transition wavelength.
Electronic stopping powers for energetic protons in solids in the low- and intermediate-energy regions
Authors: Wang You-Nian , Ma Teng-Cai , Cui Tao
Published: July 2002

With linear-response dielectric theory and the method of local density approximation, electronic stopping powers for protons in solids are calculated in the low- and intermediate-energy regions. Comparison of theoretical predictions with experimental data is made for several targets.
Fine speckle contrast in InGaAs/InP systems: Influence of layer thickness, mismatch, and growth temperature
Authors: Peiró F. , Cornet A. , Herms A. , Morante J. R. , Clark S. A. , Williams R. H.
Published: July 2002

This work is focused on the study of the fine speckle contrast present in planar view observations of matched and mismatched InGaAs layers grown by molecular beam epitaxy on InP substrates. Our results provide experimental evidence of the evolution of this fine structure with the mismatch, layer thickness, and growth temperature. The correlation of the influence of all these parameters on the appearance of the contrast modulation points to the development of the fine structure during the growth. Moreover, as growth proceeds, this structure shows a dynamic behavior which depends on the intrinsic layer substrate stress.
Suppression of interface reaction and modification of band offset by Sb interlayers in CdS/InP (110) heterojunctions
Authors: Maierhofer Ch. , Zahn D. R. T. , Evans D. A. , Horn K.
Published: July 2002

Core and valence level photoelectron spectra demonstrate that the deposition of monatomic interlayers at the interface between CdS and InP(110) efficiently suppresses the interface reaction characteristic for this system, and has a marked influence on the valence-band offset ΔEv.
Local oxidation of GaP wafers heated by a Nd:YAG laser beam
Authors: Kawamura Tsutomu , Shimizu Toshihiro
Published: July 2002

Two types of GaP wafers, a low-resisting and a semi-insulating, were locally heated by a Nd:YAG laser beam having a wavelength of 1.06 μm. Remarkable differences in their thermal properties were observed, such as temperature elevation and exothermic reactions. The differences may be related to how the function of the free carrier densities differ and the existence of a midgap energy level in the GaP wafers. The different thermal phenomena were quantitatively well explained by a proposed physical model.
An efficient formulation to find the scattering field of a conducting cylinder coated with lossy magnetic material
Authors: Lin Chi-Sen , Yaqoob M. Tahir
Published: July 2002

A new formulation for the scattered field from a two dimensional conducting cylinder coated with a lossy magnetic material is presented for transverse electric polarization of the incident field. A conduction current on the conducting surface and a magnetic polarization current in the coating material is supposed to be induced when an electromagnetic field is incident over the cylinder. The scattered field is supposed to be originated in these induced currents. Two H-field integral equations are developed, which are then solved by the Method of Moments to find these currents. Scattering cross section for circular configuration is calculated and compared with exact solution. Good agreement of results is achieved. The advantage of the formulation is that it solves the scattered field without the computation of complex argument Hankel functions. Second, by considering the polarization of the magnetic coating, the effects of surface wave excitation are automatically included in the solution.
Shallow boron junctions and preamorphization for deep submicron silicon technology
Authors: Walker A. J. , Woerlee P. H. , Pomp H. G. , Cowern N. E. B.
Published: July 2002

In this study, shallow p+-n junction diodes were formed by implanting BF+2 ions into single-crystal silicon or silicon preamorphized by either Si or Ge implantation. BF+2 implantation at energies of 20 or 25 keV and a dose of 1×1015 cm−2 was followed by furnace annealing at 600 °C in nitrogen ambient. Most samples received a further nitrogen-ambient anneal at 850 °C, with various periods of time. Secondary ion mass spectroscopy was used to measure the B profiles. Cross-sectional transmission electron microscopy was used to study the amorphous layers and the defects remaining after annealing. Electrical characterization of the diodes is described. In preamorphized samples, the residual defect density decreases, and the defect band located at the original amorphous-crystalline interface becomes sharper, as the mass of the amorphizing ion species is increased. Ideal low-leakage shallow junctions can be made following either Si or Ge preamorphization and furnace annealing, without removing all the defects induced by preamorphization. This is achieved by containing the implanted B profile completely within the amorphous layer, and by containing the defect band completely within the final biased junction. However, even without a preamorphization step, ideal low-leakage shallow junctions were obtained after BF+2 implantation and 600 °C furnace annealing. This suggests that preamorphization may not ultimately be needed for practical engineering of shallow junctions.
Conductivity in insulators due to implantation of conducting species
Authors: Prawer S. , Hoffman A. , Petravic M. , Kalish R.
Published: July 2002

Control of the surface conductivity of insulators can be accomplished by high dose ion implantation of conductive species. The use of C+ as the implant species is particularly interesting because C can either form electrically insulating sp3 bonds or electrically conducting sp2 bonds. In the present work, fused quartz plates have been irradiated with 100 keV C+ ions to doses up to 1×1017 ions/cm2 at room temperature and at 200 °C. The ion beam induced conductivity was monitored in situ and was found to increase by up to 8 orders of magnitude for the ion dose range studied. Xe implantations over a similar range did not induce any changes in the conductivity showing that the increase in conductivity is caused by the presence of the C in the fused quartz matrix and not by damage. The conductivity, σ, is found to vary with dose D as log σ∝D−1/3 over a wide dose range, strongly supporting a hopping model for the conduction mechanism. The dependence of the conductivity on implantation temperature and on post-implantation annealing sheds light on the clustering of the C implants. The temperature dependence of the conductivity for the highest doses employed (1×1017 C+/cm2) can be described very well by ln σ∝T. This is a peculiar dependence which does not comply with any of the standard models for conduction.
Ion irradiation induced atomic transport and phase formation in the system nickel–aluminum
Authors: Weber Thomas , Lieb Klaus-Peter
Published: July 2002

Nickel–aluminum bi-, multi-, and marker layers were irradiated with 80–900 keV Ar, Kr, and Xe ions at 80 and 300 K. The ion induced mass transport through the interface(s) was measured via Rutherford backscattering spectrometry. A bilayer mixing efficiency of 157 Å5/eV was obtained, independent on the irradiation temperature, and the ion species. In the mixing of 0.5–5 nm Ni marker layers embedded in Al, the influence of thermodynamic driving forces was verified by varying the Ni marker thickness. The results as discussed in the light of current ion beam mixing models, are neither consistent with the ballistic nor the global thermal spike model. The phases formed after multilayer mixing were studied by means of x-ray diffraction and perturbed angular correlation spectroscopy. The latter is a novel method to investigate early stages of ion beam induced phase transformations and changes produced by single implanted (111In) tracer ions. For the RT mixing of equiatomic multilayers, the formation of crystalline NiAl was followed. By changing the multilayer composition different crystalline and amorphous Ni–Al phases were identified.
End reflections and triple transit contribution to the band shape of magnetostatic volume wave delay lines
Authors: Marcelli R. , Rossi M. , De Gasperis P.
Published: July 2002

An analysis of the signal reflections originating at the garnet film ends and of the triple transit between the microstrip transducers in magnetostatic volume wave delay lines has been performed. The influence of those effects on the band shape and on the insertion loss of magnetostatic wave devices has been inferred and compared with experimental results. In this framework, the possible utilization of the reflections for filterbank applications is also proposed.
The influence of hydrogen plasma treatment and proton implantation on the electrical properties of InAs
Authors: Polyakov A. Y. , Ye M. , Pearton S. J. , Wilson R. G. , Milnes A. G. , Stam M. , Erickson J.
Published: July 2002

The effects produced in InAs by hydrogen plasma treatment and proton implantation are discussed. It is shown that both treatments can produce an n-type layer at the surface of p-InAs. For the hydrogen plasma treatment the effect is explained by hydrogen donors complexing with the Be and Zn acceptors and rendering them electrically inactive, thus leaving the residual donors uncompensated. In proton implanted samples the p-n conversion is due to a creation of donor-type lattice defects.
Electronic properties of n-i-n-i doping superlattices
Authors: Tan C. M. , Xu J. M. , Zukotynski S.
Published: July 2002

Band structures of n-i-n-i doping superlattices are found using a self-consistent calculation based on the envelope function formalism. The modulation potentials, the charge density distributions, the dispersion relationships, and the occupation of the subbands in the n-i-n-i superlattices are computed and their dependence on temperature and the structural parameters of the superlattices are studied. It is found that the modulation potentials of n-i-n-i doping superlattices are weak, and quantum effects are, therefore, also weak. The density of states in n-i-n-i superlattices can be adjusted by varying the structural parameters of the superlattices. As a result, the n-i-n-i doping superlattices behave like uniformly doped semiconductors with an adjustable density of states. The density of states is found to be temperature dependent. Electron mobilities of the n-i-n-i doping superlattices are also computed. It is found that both impurity scattering processes that are observed in uniform lightly doped semiconductor and heavily doped semiconductor can coexist in the n-i-n-i doping superlattices.
Ellipsometric determination of thickness and refractive index at 1.3, 1.55, and 1.7 μm for In(1−x)GaxAsyP(1−y) films on InP
Authors: Amiotti M. , Landgren G.
Published: July 2002

There is a definite need for accurate, but simple techniques for evaluation of refractive index and thickness of epitaxial In(1−x)GaxAsyP(1−y) films on InP. By ellipsometry, one can obtain these quantities for a transparent film on a substrate by a single measurement. We have calculated the ellipsometric angles Ψ and Δ for an In(1−x)GaxAsyP(1−y) film on InP at λ=1.3, 1.55, and 1.7 μm to determine the best experimental conditions. A 1 nm thick oxide layer on the top of the quaternary was found not to affect the Ψ and Δ at these wavelengths in a significant way. Futhermore, by studying the relative error in the refractive index and the thickness versus the error in the angle of incidence, we could deduce that at the optimum experimental conditions one can obtain the refractive index and the thickness with a 5% precision or better using ellipsometry. We have also measured the refractive index and the thickness by null ellipsometry for several In(1−x)GaxAsyP(1−y) films with different composition grown by metal organic vapor phase epitaxy on InP substrates. The refractive index data agree well with those obtained by other techniques as reported in literature and the thicknesses agree within the experimental precision with the nominal thickness obtained by the growth conditions.
The possibility of x-ray pulse shortening through laser induced ac Stark shift in atoms
Authors: Chen Li
Published: July 2002

It is suggested that an originally long x-ray pulse may be shortened substantially, or, alternatively, a short sharp dip may be introduced into an originally long x-ray pulse, by passing the x rays through a resonant absorbing medium that is illuminated by an intense ultrashort laser pulse at certain chosen times. The various conditions for this scheme are stated. Neon and xenon gas media are discussed as examples.
Depth profiling and secondary ion mass spectrometry relative sensitivity factors and systematics for polymers/organics
Authors: Wilson R. G. , Lux G. E. , Kirschbaum C. L.
Published: July 2002

Depth profiles and secondary ion mass spectrometry (SIMS) relative sensitivity factors (RSF) for quantification (inverse relative ion yields) are reported for oxygen ion bombardment and positive secondary ion mass spectrometry and for cesium bombardment and negative secondary ion mass spectrometry measured for implants of more than 40 elements in PMMA/polymethyl methacrylate/Lucite/AZ111, polypyromellitimide/polyimide/Kapton, and epoxy, using magnetic sector SIMS instruments (CAMECA IMS 3f or 4f). The RSFs are plotted versus ionization potential (positive secondary ions) and versus electron affinity (negative secondary ions), and the resulting patterns are compared among themselves and with those for semiconductors reported previously. Charge compensation using electron flooding was employed in most cases for both oxygen (oblique incidence flooding) and cesium (normal incidence flooding) primary beams. Profiles in these low atomic number materials are relatively deep. Crater depths are sometimes difficult to measure; some are distorted and some are not. More work in this area of SIMS quantification and depth profiling in organic polymers appears to be needed, but these results are promising.
Levitation pressure and stiffness of a high T
c superconducting bearing in field-cooling process
Authors: Komori Mochimitsu , Iwakuma Masataka , Kitamura Tadashi , Matsushita Teruo , Takeo Masakatsu
Published: July 2002

Properties of a high Tc superconducting bearing consisting of a set of alternating-polarity magnets and a superconductor are investigated. The superconducting bearing is field-cooled in liquid nitrogen, because it is expected that field-cooling process will be used for superconducting bearings in the future. To analyze the levitation pressures of the superconducting bearing Bean’s critical state model was applied. The results of the analyses show that it is possible to estimate the levitation pressures to some extent by using the model.
Investigation of GaAs/AlAs multilayer systems for optical Bragg reflectors using x-ray double crystal techniques
Authors: Jenichen B. , Hey R. , Höricke M. , Köhler R.
Published: July 2002

Layer systems for optical Bragg reflectors (grown by molecular beam epitaxy) were studied using double crystal topography and diffractometry. The initiation of stress relaxation was detected topographically in the substrate reflection and in different satellite reflections for undoped and slightly silicon doped layers (up to a doping level of 3×1017 cm−3). Higher silicon doping (1018 cm−3) prevented misfit dislocations. When using Czochralsky substrates it was observed that half-loops were formed by misfit dislocations between pairs of threading dislocations. Misfit dislocations were shown to be situated on different levels of the layer stack. Satellite reflection topography is suggested as a new tool for directly observing strains in multilayer systems since the signal originates in the layer stack. Even for very small layer thicknesses good defect contrasts can be expected for high-quality layers, as shown by simulations.
Theoretical modeling of chemical generators producing O2(1Δ) at high pressure for chemically pumped iodine lasers
Authors: Barmashenko B. D. , Rosenwaks S.
Published: July 2002

A theoretical model is developed for chemical generators producing O2(1Δ) at high pressure. Such generators are especially important for supersonic chemical oxygen-iodine lasers. The model treats different types of generators, e.g., bubble-column, film, aerosol, and jet generators. The main factor affecting the O2(1Δ) yield under high pressure is liquid-phase quenching enhanced by depletion of HO2− ions near the gas/liquid interface. Simple analytical expressions are derived for the O2(1Δ) yield at the exit of the generator. Output characteristics of different specific generators are calculated and compared with available experimental results. O2(1Δ) yield ≥0.5 can be achieved for oxygen pressure up to 50 Torr and flow rates of 3 mmol/cm2 s. For equal velocities of the gas and the liquid the maximum flux of the energy carried by O2(1Δ) for jet or aerosol generators reaches 200 W/cm2. It can be increased by increasing the liquid velocity in the generator.
Theory of ferroelectric-paraelectric transitions in VF2/F4E random copolymers
Authors: Zhang Renshi , Taylor P. L.
Published: July 2002

The problem of calculating the free energy of a ferroelectric random copolymer is discussed in terms of a mean field model. The intrachain interactions are treated in detail, but the interchain interactions are approximated as a function only of the torsional angle at a chain segment and of an order parameter determined by averaging over the conformations of all chains. This formalism is applied to a simple model of the random copolymer of vinylidene fluoride and tetrafluoroethylene. The results of this calculation are combined with the known Curie temperatures of these copolymers to determine the magnitude of the effective interchain interaction over a range of copolymer compositions.
A Monte Carlo method for study of Auger recombination effects in semiconductors
Authors: Lui Wayne W. , Yoshikuni Yuzo , Yamanaka Takayuki , Yokoyama Kiyoyuki
Published: July 2002

A Monte Carlo method is proposed to study Auger recombination effects in semiconductors, which is general enough to study these effects in one (1D), two, or three dimensions, to accommodate arbitrary band structures, and to use either Boltzmann or Fermi–Dirac statistics. Auger recombination coefficients can readily be extracted from Monte Carlo calculation results, and distributions of each species of carriers that are involved in the recombination process are also obtained. Calculation results using this Monte Carlo method are compared against results obtained from previous work. In 1D cases, the Monte Carlo results agree very well with those previously obtained. It is also shown that results previously derived are applicable only to 1D cases. This is because in higher dimensions, considerations of the higher degree of freedom, which are not incorporated in previous work, are necessary. All in all, the Monte Carlo method proposed in this article is expected to provide useful insight into Auger recombination effects, and directions for bandgap engineering towards design of material less prone to such effects.
Resonant level lifetime in the double-barrier structure for both quasi-bound and extended states
Authors: Peng Jian-Ping , Mu Yao-Ming , Shen Xue-Chu
Published: July 2002

The lifetime of resonant levels of the double-barrier structure is studied within a simple effective mass picture. Analytical results of the lifetime is presented for both quasi-bound and extended resonant states, taking into account the mass variation in well and barrier regions. Relevance of these results to carrier lifetime in multiquantum well infrared detectors is discussed. It is shown that the resonant level lifetime determines the up-limit of the lifetime of an electron injected into the excited state.
New optical absorption lines in heat-treated gallium arsenide
Authors: Suezawa Masashi , Sumino Koji
Published: July 2002

New optical absorption lines were found in GaAs doped with B or Al subjected to some thermal treatment. They were grouped into three bands termed L, M, and H on the basis of the energy ranges in which they are observed; 70.8 and 72.7 meV for the L band, 172.3, 181.0, and 186.3 meV for the M band, and 208.7, 217.4, and 222.5 meV for the H band at 6 K. All of these lines originate in electronic transitions. The L band is related to complexes containing the Al impurity while the M and H bands to complexes containing the B impurity.
Diffusion of P in a novel three-dimensional device based on Si–TaSi2 eutectic
Authors: Pelleg Joshua , Ditchek Brian M.
Published: July 2002

The diffusion of P in Si–TaSi2 eutectic and silicon single crystal specimens was investigated at a concentration of about 1019 atoms cm−3 in the temperature range of 767–1227 °C. No definite distinction can be made between diffusion of P in the eutectic structure and in silicon. A nonlinear Arrhenius plot was obtained, indicating a P diffusion enhancement at the lower temperature range. From the linear portion of the Arrhenius line drawn through all the experimental points, an activation energy and pre-exponential factor of 3.75 eV and 5.7 cm2 s−1 were derived, respectively.
Amorphization of TbFe3 by nitrogen absorption
Authors: Cheng S. F. , Segnan R. , Cullen J. R. , Clark A. E. , Huang M. Q.
Published: July 2002

The nitrogenation process of the TbFe3 intermetallic compound was studied by heat treating the alloy between 573 and 873 K in a nitrogen atmosphere. The structural and magnetic properties of the nitrogenated samples were characterized by x-ray diffraction (XRD), Mössbauer spectroscopy, and magnetic measurements. The magnetic moments of the nitrogenated samples were found to be a function of the annealing temperature and showed a minimum for the sample heat treated at 673 K. The XRD pattern of this sample (673 K) showed that the Bragg peaks of the 1-3 phase had completely disappeared and were replaced by a broad maximum indicating a breakdown of the TbFe3 structure into an amorphous phase. The room-temperature Mössbauer spectrum of the same sample consisted almost entirely of a quadrupole-split doublet plus a small amount of α-Fe and TbFe3. This doublet split into a broad spectrum upon cooling which is typical of amorphous rare-earth–transition-metal compounds. For samples heat treated at higher temperatures, the amount of α-Fe and TbN phases gradually increased. This nitrogenation process is unlike that of R2Fe17. In this study, nitrogen atoms do not go into the interstitial sites. Instead, they create a ferromagnetic (TC≊215 K) amorphous phase of Tb, Fe, and N which is stable over a wide temperature range.