bluuebunny/crossref_metadata_2025 huggingface dataset:
Interlayer exchange, magnetotransport, and magnetic domains in Fe-Cr layered structures (invited) (abstract)
Authors: Grünberg P.
Published: July 2002

The Fe-Cr layered structure is a model system where both the antiferromagnetic-type interlayer coupling and the magnetoresistivity (MR) effect due to antiparallel alignment occur with good strength. For a better theoretical understanding there is a need for more detailed and reliable data. Here the most recent results for the Fe-Cr system will be presented and will be compared with data obtained by other groups and on other systems. By means of light scattering from spin waves and M(H) curves obtained via the magneto-optic Kerr effect, we have examined the interlayer coupling A12 as function of the Cr thickness dCr and confirmed the oscillatory behavior first reported by another group. Our method clearly shows that the coupling becomes ferromagnetic between the ranges of antiferromagnetic coupling, which was not yet clear from available data. For large dCr the oscillations fade out and the coupling remains weakly antiferromagnetic. In the case of (100)-type growth we also find a fine structure for A12 (dCr) as expected from theory. We have also analyzed the new MR effect by using a formalism based on a modified Fuchs–Sondheimer approach. From this we conclude that the MR effect is due to a spin-dependent electron scattering at the Fe-Cr interfaces. For the diffusive scattering rate at these interfaces we obtain ∼50% for spin up and only 4% for spin down. Finally, the results of domain investigations will be presented. For samples with wedge-type interlayers, the gross features of these domains reflect the oscillatory behavior of the coupling. Further investigations suggest the existence of a quadratic term in the coupling energy favoring a perpendicular magnetization alignment of the two films with respect to each other.
Raman scattering study of InAs/GaInSb strained layer superlattices
Authors: Sela I. , Campbell I. H. , Laurich B. K. , Smith D. L. , Samoska L. A. , Bolognesi C. R. , Gossard A. C. , Kroemer H.
Published: July 2002

We present a Raman scattering study of the InAs/GaInSb superlattice. This new superlattice is promising as a long wavelength infrared detector material. The samples were grown by molecular beam epitaxy and their structural parameters were determined by Rutherford backscattering and x-ray diffraction. Samples were grown on [001] GaAs substrates with GaSb buffers, and directly on [001] GaSb substrates. Cross-sectional transmission electron micrographs show that for the samples grown on GaAs substrates, a high density of dislocations was generated at the GaAs-GaSb interface, and many of these dislocations thread through the superlattice. The samples grown directly on GaSb had a much lower dislocation density. The Raman spectra of the InAs/GaInSb superlattice shows a single peak, which is a superposition of scattering from the LO phonons in InAs and in GaInSb. For unstrained InAs and GaInSb, the LO phonon energies are sufficiently separated that they would be well resolved in Raman scattering. However, the strain introduced into these materials by the pseudomorphic boundary conditions moves the two phonons closer together energetically so that only one peak is seen in the Raman spectrum of the superlattice. A high energy Raman scattering tail is seen in some of the samples. This tail is from Ga-As local modes. Such modes may be due to As incorporation in the GaInSb, Ga incorporation in the InAs or phase mixing at the interfaces.
Interfacial reactions of Cr, Cr-Si, and Cr/Si films on GaAs
Authors: Huang T. S. , Yang M. S.
Published: July 2002

Interfacial reactions of Cr, Cr-Si, and Cr/Si films on GaAs substrate, in the temperature range 200–800 °C, have been investigated using a combination of x-ray diffraction, transmission electron microscopy, Auger electron spectroscopy, and electrical measurements. Chromium starts to react with GaAs at 500 °C by formation of CrAs and Cr3Ga compounds. At 600 °C, Cr3Ga transforms to Cr3Ga4, and the reaction products are Cr3Ga4, CrGa4, and CrAs at 700–800 °C with CrGa4 and CrAs being the final dominant phases at 800 °C. The compounds formed are consistent with the phase diagram. The surface region of the reacted Cr films is richer in Cr-Ga compounds, while the interface region is richer in CrAs compound. The Schottky barrier heights of Cr/n-GaAs diodes increase after annealing at temperatures below 400 °C, however, the diodes deteriorate severely at higher temperatures. Annealing of the codeposited Cr-Si and layer-deposited Cr/Si films results in the formation of CrSi2 at temperatures above ∼600 °C. No interfacial reaction between CrSi2 film and GaAs was observed.
Interaction of the residual hydrogen gas with the growth of Y1Ba2Cu3O7−x films under high vacuum
Authors: Kamei M. , Yoshida I. , Morishita T. , Tanaka S.
Published: July 2002

Y1Ba2Cu3O7−x films were fabricated by a reactive evaporation method using 10-mol-% O3 gas as an oxygen source. Mass spectroscopy measurement revealed that hydrogen gas was ejected from Y metal and Ba metal sources during evaporation. Y1Ba2Cu3O7−x film growth was adversely affected by the existence of this hydrogen gas, confirmed by in situ reflection high-energy electron diffraction (RHEED) observation. A streak RHEED pattern was maintained throughout evaporation only when the hydrogen partial pressure was smaller than 1×10−6 Torr. Only films grown under this condition showed superconducting behavior.
A metastable solid solution of Pd-Ni-P formed by containerless drop tube processing
Authors: Xu Yingfan , Guo Weili , Wang Zhaoxing , Wu JianGuo , Chen Hong , Wang WenKui
Published: July 2002

A 20-m drop tube was used to study the solidification of Pd43.5Ni43.5P13 alloy in free fall. The solidified droplets were identified by x-ray diffraction, scanning electron microscopy and x-ray energy dispersive spectrum analysis. The results showed that a near single phase of Pd-Ni-P fcc solid solution was obtained.
First-order optimization of multiple magnetic lens systems for transport and focusing of annular ion beams
Authors: Olson J. C. , Kusse B. R.
Published: July 2002

A standard matrix method for tracing rays through an ion optical system is extended to include a recently discovered [W. Z. Liu and F. D. Bechetti, Rev. Sci. Instrum. 60, 1228 (1989)] defocusing solenoidal lens. The results of the matrix approach are shown to correspond with results obtained by numerical integration of particle trajectories through real coil configurations. First-order radial miss distances due to radial divergence of the beam, chromatic aberration of the lens system, and physical extent of the source are compared for one and two lens systems using the matrix formulation. It is demonstrated that a two lens system in a focusing-defocusing arrangement can simultaneously correct to first order for chromatic aberration and beam divergence, producing a better focus for thin annular beams with significant energy spread and divergence. A new calculation of the focal length for the negative solenoidal lens is also included.
Microstructural effects of emitter size on polysilicon-emitter bipolar transistors
Authors: Cunningham Brian , Ronsheim Paul A. , Yun Bob H.
Published: July 2002

As the dimensions of semiconductor devices are reduced, changes in the structure of the devices can have a pronounced effect on their electrical parameters. In some cases it may no longer be correct to assume that the electrical parameters can simply be scaled with device area. In the present study it will be shown that when polysilicon-emitter bipolar transistors are reduced to submicron dimensions, shadowing of the ion implant into the emitter sidewalls can alter the dopant concentration in the polysilicon diffusion source, thereby changing the dopant profiles in the single-crystal silicon, and hence the junction depths. This shadowing effect, although present in all devices, is only found to affect the electrical parameters of transistors when the emitter size approaches submicron dimensions.
Interference effects in x-ray double-crystal rocking curves of Ga1−xAlxAs/GaAs laser structures and superlattices
Authors: Franzosi P. , Jenichen B.
Published: July 2002

Interference effects in the x-ray double-crystal rocking curves of Ga1−xAlxAs/GaAs laser structures and superlattices have been discussed in the framework of a reliable simulation model based on the Takagi–Taupin dynamical theory. It has been found that in the laser structures the presence of the active GaAs layer between the Ga1−xAlxAs confining layers causes a splitting of the confining layer Bragg peak in subpeaks of comparable intensity; in a similar way, the presence of GaAs layers inside a superlattice is able to split each satellite peak in subpeaks. Interference effects have been experimentally revealed in an AlAs/GaAs heterostructure made of three identical superlattices separated by thin GaAs layers.
Preparation of TlCaBaCuO high-T
c superconducting thin films on LaAlO3 substrates
Authors: Yan S. L. , Cao H. L. , Yang X. M. , Zhou X. D.
Published: July 2002

Pure 2122 phase and 2223 phase superconducting TlCaBaCuO thin films have been reproducibly prepared on (100)LaAlO3 substrates by dc magnetron sputtering using a pair of superconducting Tl2Ca2B2Cu3O10 targets and post-annealing at different temperatures. X-ray diffraction analysis indicates that the films are highly c-axis oriented perpendicular to the film surface for both types of the thin films. The critical transition temperature Tc(R = 0) = 98 K and critical current Jc(77 K)=1.0×105 A/cm2 can be obtained for 2122 phase films, and for 2223 phase films Tc(R = 0) = 115 K and Jc(77 K) = 5.5 × 105 A/cm2 can be obtained.
A study of Fe-Ni-B ultrafine alloy particles produced by reduction with borohydride
Authors: Hu Zheng , Hsia Yuanfu , Zheng Jianguo , Shen Jianyi , Yan Qijie , Dai Lemei
Published: July 2002

Fe-B, Fe-Ni-B, and Ni-B ultrafine alloy particles have been prepared by reduction of metal ions in aqueous solution with borohydride. It is shown that iron and nickel contents in the particles can be easily varied by changing the Ni/(Ni+Fe) ratio in the aqueous solution; however, the boron content is constant when the concentration of the borohydride is kept constant. Several experimental results show that the alloy particles are amorphous. The scanning electron microscopic image indicates that the surface morphology of Fe35Ni15B26 alloy particles looks like cotton clusters. From the high-resolution image, the average size of the high-resolution image, the average size of the particles was determined to be about 30±5 nm and the fine structure of the particles indicates that there is an obvious boundary between the outer shell with a thickness of about 5 nm and the inner core with a diameter of about 20 nm. The particles are partially crystallized on the outer shell while the inner core is almost completely amorphous.
Fracto-emission from embedded interfaces
Authors: Ma Zhen-Yi , Dickinson J. T.
Published: July 2002

Fracto-emission is the emission of particles and photons during and after fracture of materials. The observed emissions include electrons, ±ions, neutral species in both ground states and in excited states, and visible photons. Here we examine primarily photon and electron emission during failure of axially loaded stainless-steel fixtures (e.g., rods) embedded in epoxy. The observed signals provide time resolved information on the sequence of events involving interfacial fracture preceding pullout. In addition, we examine the emissions during frictional pullout following debonding. Over a large range of strain rates this pullout exhibits stick-slip behavior. These effects model the processes of fiber/matrix debonding and fiber pullout in a brittle matrix composite.
Electron microscope studies of interdiffusion in molecular beam epitaxy grown GaInAs/AlInAs multilayers
Authors: Mallard R. E. , Long N. J. , Booker G. R. , Scott E. G. , Hockly M. , Taylor M.
Published: July 2002

The thermal interdiffusion behavior of intrinsic nominally lattice-matched GaInAs/AlInAs heterostructures grown by molecular-beam epitaxy, studied using electron microscopy, is reported. At temperatures as low as 700 °C, significant degrees of interdiffusion are observed. X-ray microanalysis of the multilayers reveals that the interdiffusion takes place along a nonlinear (that is, non-lattice-matched) path. This behavior has previously been attributed to the pronounced differences in the elemental diffusivities of the constituent binary compounds. In addition, high-resolution electron microscopy (HREM) was used to determine the detailed interfacial structure of the material. Such a determination is only possible under favorable and well-defined experimental conditions. The accuracy and limitations of HREM analysis of interfacial abruptness in semiconductor interfaces are commented on.
Coupling efficiency of metallic gratings for excitation of intersubband transitions in quantum-well structures
Authors: Li W. J. , McCombe B. D.
Published: July 2002

A numerical calculation of the coupling efficiency for a perfectly conducting metallic grating for intersubband transitions in semiconductor quantum wells is presented as a function of the ratio of the grating period p to the intersubband resonance wavelength λ for various degrees of metal filling. The effect of grating parameters on the conversion efficiency is discussed. Results provide detailed guidelines for obtaining optimum coupling for infrared devices.
Effect of isothermal annealing on the magnetic behavior of amorphous ferromagnets with composition near the percolation threshold. II. In the critical region
Authors: Kaul S. N. , Mohan Ch. V.
Published: July 2002

Extensive ferromagnetic resonance (bulk magnetization) measurements have been performed on amorphous Fe90+XZr10−X alloys with X=0 and 1 (X=0, 1, and 2) in the critical region, −0.1≲(T−TC)/TC≲0.1, before and after they had been subjected to isothermal annealing treatment at 400 K for durations of time, tA, ranging from 10 to 240 min (in the ‘‘as-quenched’’ condition) with a view to study the alterations in the critical behavior as the tricritical point, Xc≂3, is approached along the ferromagnetic (FM)-paramagnetic (PM) transition line in the magnetic phase diagram and as the topological (TSRO) as well as chemical (CSRO) short-range order undergo changes on account of structural relaxation. Asymptotic values of the critical exponents β and γ and critical amplitudes m0 and (m0/h0) for spontaneous magnetization and initial susceptibility have been determined for the as-quenched as well as annealed samples. Consistent with the predictions of the infinite FM matrix plus finite spin clusters model and with the well-known Harris criterion, change in CSRO and TSRO caused by altering the alloy composition and/or by isothermal annealing leaves the values of the critical exponents β and γ, and the universal ratio m0/MS(0) unaltered from those predicted by the renormalization group theory for an ordered spin system with spatial as well as spin dimensionality of three. The presently determined values of the critical amplitudes reveal that the fraction of spins that actually participates in the FM-PM transition is as low as ≊10% and reduces drastically as X→Xc but for a given composition, it declines slowly with increasing tA.
Photoluminescence from Si1−xGex strained layers grown by atmospheric pressure chemical vapor deposition
Authors: Rowell N. L. , Noël J.-P. , Wang A. , Namavar E. , Perry C. H. , Soref R. A.
Published: July 2002

Low temperature photoluminescence due to the self-annihilation of bound excitons has been observed in Si1−xGex strained layers grown using atmospheric pressure chemical vapor deposition. Samples were grown at temperatures near 1000 °C with growth rates up to 1000 nm per minute allowing short growth times, thus preventing extensive interdiffusion at layer interfaces. Well-resolved, bulk-like photoluminescence spectra with narrow no phonon linewidths were observed from strained SiGe material indicating it to be of suitable electronic quality. For a sample consisting of 120 nm of Si0.92Ge0.08 capped with 90 nm of Si on a Si(100) substrate, the photoluminescence spectrum exhibited Si1−xGex bound exciton lines with resolved no phonon and transverse optic phonon components.
Kinetics of gettering in silicon
Authors: Chen C. S. , Schroder D. K.
Published: July 2002

Two basic functions of getters in silicon during gettering processes are investigated in detail. The sink action of getters for absorbing impurities is described by a gettering parameter g, which relates to the diffusion ratio gd, segregation coefficient S, and the activation energies Em,Si, Em,G of impurities in intrinsic Si and in the getter phase. The kickout mechanism is suggested for describing the diffusion of impurities because of the contribution of Si interstitials to kick out the impurities to be gettered. Based on the interaction of Si interstitials with impurities and the influence of the sink in absorbing impurities, a set of gettering equations is derived and used to calculate the gettering of gold in silicon with back surface getters. Theoretical results agree well with reported experimental data and five conclusions are provided to determine the optimal gettering conditions for a given gettering cycle.
Substrate bias effects on diamond synthesis in a magnetoactive microwave plasma
Authors: Chang J. J. , Mantei T. D.
Published: July 2002

The influence of applied substrate bias on diamond film deposition has been investigated in a magnetoactive microwave discharge. The films were deposited at substrate temperatures ∼600 °C at 5 Torr on silicon (111) substrates, and were characterized by Raman spectroscopy and scanning electron microscopy (SEM). Electrons or ions are drawn from the plasma by biasing the substrate positive or negative with respect to the grounded chamber wall. Without bias, nondiamond carbon peaks are obtained in Raman spectra and ball-like features are observed in SEM micrographs. As the bias is increased, clear-cut diamond faces appear and grown diamond particles change to the (100) and (111) phase. Positively biased films are more crystalline compared to films grown with negative bias.
Saturation of the surface field with external bias for metalorganic chemical vapor deposition epilayer GaAs/GaAs as determined by electroreflection spectroscopy
Authors: Poras Henry , Goldsmith George J. , Pan Noren
Published: July 2002

The strength of the surface field on GaAs epitaxial layers of various thicknesses and doping concentrations grown by metalorganic chemical vapor deposition on a semi-insulating GaAs substrate was studied as a function of applied bias using modulation spectroscopy. While for small applied potentials the square of the field strength increases linearly with respect to reverse bias, for larger values of bias it saturates. It is shown that this saturation appears when the width of the depletion layer in the epilayer approaches the width of the epilayer itself.
Properties of NiFe-N films prepared by rf sputtering in nitrogen-argon gas mixtures
Authors: Shih K. K. , Re M. E. , Takamori T. , Dove D. B.
Published: July 2002

The structure and properties of NiFe-N films, prepared by rf reactive sputtering process using nitrogen in the range from 0 to 40% in the nitrogen-argon gas mixture during sputtering, have been studied. The concentration of nitrogen and the resistivity of the NiFe-N films were determined as a function of nitrogen partial pressure. Films with good soft magnetic properties were obtained when the nitrogen in the nitrogen-argon gas mixture during sputtering was in the range 0–10%. The resistivity of these films was low and x-ray diffraction results indicated only an fcc structure of γ-NiFe alloy. For films deposited with more than 10% of nitrogen in the gas mixture there is a transition region where resistivity and coercivity started to increase. Films deposited with 20% nitrogen mixed with argon consist of a mixture of γ-NiFe alloy and (Ni,Fe)4N phases. With further increase of nitrogen above 30% during sputtering, a (Ni,Fe)3N phase was observed. The resistivity and coercivity of these films were high.
A theoretical analysis of the thickness dependence of the localization effect on the normal-state resistivities in high-T
c Y1Ba2Cu3O7−δ thin films
Authors: Tyan J. H. , Lue J. T.
Published: July 2002

We have demonstrated that the normal-state resistivity of sufficiently thick Y1Ba2Cu3O7−δ thin films can be fitted very well by the Bloch–Gruneisen equation. As the film thickness decreases, the localization effect becomes predominant presuming the manifestation of surface defects and vacancies over the bulk region. The evaluated Debye temperatures span over a range which is consistent with experimental values. Below some critical thicknesses, the transport behavior in thin Y1Ba2Cu3O7−δ films deviates from the Boltzmann conductivity and the temperature coefficient of the electric resistivity becomes negative, which can be explained by adopting quantum corrections for localization and interaction effects. The origin of nonmetallic behavior can be understood quantitatively in terms of the competition between the quantum corrections and the conventional Boltzmann conductivity. In these ultrathin superconducting films, the elastic mean-free path arising from defect and heavy impurity scattering is very short and much smaller than the inelastic mean-free path, even at room temperature.
Magnetic properties of ternary Co-B-C melt spun alloys amorphized over an extended concentration range
Authors: Pont M. , Puzniak R. , Rao K. V. , Inoue A.
Published: July 2002

The field dependence of the magnetization at 4.2 and 294 K and the temperature dependence of the spontaneous magnetization for two series of ternary Co-based alloys, namely Co76−xB24Cx and Co88−yByC12 have been measured. The metalloid content in these series ranges from 24 to 44 at.%, and extends almost to the critical concentration for the disappearance of ferromagnetism. The composition dependence of the average magnetic moment at 4.2 K compares well, for low metalloid content, with data for other Co-based materials and also with the theoretical models that predict a linear dependence of the magnetic moment as a function of concentration. The thermal demagnetizing process at low temperatures is presented. The results have been analyzed in terms of Bloch’s law and the stiffness constant has been determined. The complete thermal demagnetization, i.e., down to Tc, is presented only for the alloys with a Curie temperature below 300 K. The results show the well known flattening of the M(T) curve as compared with crystalline materials.
Effect of optical activity on higher-order self-diffraction in absorptive photorefractive medium: Transmission geometry for two-wave mixing
Authors: Roy Amitava , Singh Kehar
Published: July 2002

Interactions between optical beams incident upon and higher-order self-diffracted beam generated within an absorptive and optically active photorefractive crystal of 23 symmetry are investigated by solving a set of coupled differential equations. It is shown that, under favorable conditions, a significant amount of power may be transferred to the newly generated wave. Investigated are the effects of optical activity, thickness and absorption of the crystal, coupling constant, and off-Bragg parameter on energy transfer to the higher-order diffracted beam. Coupled wave equations are solved numerically by a fourth-order Runge–Kutta method and results are presented in graphical form. The analysis is valid only for the near collinear interacting beams, i.e., in the limit of large grating spacing.
The formation and annealing of dislocation damage from high-dose self-ion implantation of aluminum
Authors: Vardiman R. G.
Published: July 2002

Quantitative electron channeling and weak-beam transmission electron microscopy (TEM) measurements of dislocation density have been used to study the formation and annealing of the dislocation network in self-ion-implanted aluminum. The channeling linewidth is found to be proportional to the dislocation density. Several mathematical expressions for the dislocation network growth are examined. One by Igata et al. [in Effects of Radiation on Materials: Proceedings of the 10th International Symposium, edited by D. Kramer, H. R. Brager, and J. S. Perrin, STP 725 (ASTM, Philadelphia, 1980), p. 627] is found to describe the implantation data accurately. This model has a linear growth term and terms for dislocation loss due to surface effects and recovery. The fit is insensitive to the relative importance of the two loss terms. Annealing is found to occur in two stages; roughly one third of the dislocation density is gone by 300 °C, corresponding to typical recovery processes, while the remaining network is stable to about 500 °C.
Hydrogenated amorphous silicon/hydrogenated amorphous silicon carbide superlattice prepared continuously by pulsed plasma and photo chemical vapor deposition
Authors: Nakano Masatake , Takano Akihiro , Kawasaki Masashi , Koinuma Hideomi
Published: July 2002

Based on the study on chemical reactivity of Si2H6 and CH4 toward two different excitation modes (photo and plasma-photo hybrid), it was suggested that generating pulsed plasma under constant photo irradiation to a mixture of Si2H6 and CH4 could deposit continuously amorphous superlattices composed of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon carbide (a-SiC:H) layers. The periodical structure in the deposited film by the pulsed plasma and photo chemical vapor deposition was verified by the small angle x-ray diffraction pattern and high resolution scanning electron microscope image. The optical band gap of a-Si:H(0.5–25 nm)/a-SiC:H(5 nm) superlattices deposited by this method showed a blue shift as the well layer (a-Si:H) thickness decreased.
On the preparation and characterization of high-quality GaAs single quantum wells
Authors: Hey R. , Höricke M. , Frey A. , Egorov V. , Krispin P. , Jungk G.
Published: July 2002

A regime for growing high-quality GaAs/AlGaAs single-quantum-well structures by molecular-beam epitaxy with interruption only at the AlGaAs-on-GaAs heterointerface is reported. For 15- and 20-nm-wide wells the luminescence linewidth is found to be 0.44 and 0.29 meV, respectively. The data are among the lowest values reported to date. Photoluminescence line splitting due to the formation of extended growth islands was not observed.
Observation of a deep level in p-type Hg0.78Cd0.22Te with high dislocation density
Authors: Chen M. C. , Schiebel R. A.
Published: July 2002

To investigate the possibility that deep levels are associated with dislocations in narrow band gap HgCdTe, deep level transient spectroscopy has been used to study n+-p diodes fabricated on p-type bulk Hg0.78Cd0.22Te samples with either a ‘‘normal’’ dislocation density of about 105 cm−2 or a high dislocation density of about 106 cm−2. These samples which are gold doped with a hole concentration of 1.2×1015 cm−3, have a band gap of about 0.12 eV at 77 K. In samples with a ‘‘normal’’ dislocation density, a deep level of about 80 meV above the valence band was found. However, a midgap level of about 60 meV above the valence band with larger peak amplitude and broader line shapes was found in the sample with a high dislocation density.
Analysis of the recombination velocity and of the electron beam induced current and cathodoluminescence contrasts at a dislocation
Authors: Tarento R. J. , Marfaing Y.
Published: July 2002

A self-consistent calculation of the barrier height and of the effective recombination velocity at a dislocation has been performed. The procedure has taken account of the bending of the minority carrier quasi-Fermi level across the dislocation space-charge region and in the quasineutral region and of the nonrigid displacement of the dislocation energy levels. The dislocation energy states are considered to be uniformly distributed in a half-filled band. The continuity equation around the dislocation has been solved for the case of a low-level electron beam injection and the electron beam induced current and cathodoluminescence contrasts at the dislocation have been derived.
Current–voltage characteristics under in-plane conduction in doping-modulated amorphous silicon multilayers
Authors: Oheda Hidetoshi
Published: July 2002

For in-plane conduction in nipi multilayers, current–voltage characteristics exhibit nonlinearity and even saturating tendency is observed in some specimens under illumination. Complementary study of a distribution of relaxation times, which is evaluated with a frequency resolved spectroscopy, is made to identify a current path for in-plane conduction. Although the relaxation-time distribution consists of a single component under a low applied voltage, an additional component with a shorter relaxation time appears under an applied voltage where the nonlinearity is evident in the current–voltage characteristics. These two components in the spectrum can be identified as compositional current flows at n type and undoped sublayers, respectively, by comparing them with spectra for unlayered materials. The nonlinearity in the current–voltage characteristics in nipi multilayers comes from such a change in the current path depending on the applied voltage as well as a large difference in magnitudes of a mobility-lifetime product between undoped and n-type layers.
Dielectric relaxation in chemical vapor deposited phosphosilicate glasses
Authors: Modelli A. , Manzini S.
Published: July 2002

Dielectric properties of phosphosilicate glass (PSG) films deposited by chemical vapor deposition are studied in detail. Combined admittance measurements and flatband voltage shift measurements under bias-temperature stress on Al-PSG-Si capacitors allowed us to determine the dipolar relaxation time over more than nine decades of time. Experimental results are discussed in terms of a double-well potential model for the dipolar units with a Gaussian distribution in the logarithm of the relaxation time. Barrier height, barrier height spread, and attempt-to-escape frequency were determined to be 1.03 eV, 80 meV, and 2.6×1013 s−1, respectively. Evidence of nonlinear dielectric response was found at low temperature (room temperature) and high electric field (5 MV/cm). A value of 1.3 D units for the dipole moment was determined. The dielectric susceptibility was found to increase linearly with the phosphorus concentration in glass. The elementary dipole appears strictly associated with a single phosphorus atom (or molecular group containing a single phosphorus atom) rather than with more complex phosphorus units.
19 μm cutoff long-wavelength GaAs/AlxGa1−xAs quantum-well infrared photodetectors
Authors: Levine B. F. , Zussman A. , Kuo J. M. , de Jong J.
Published: July 2002

The longest-wavelength quantum-well infrared photodetector ever achieved, with a cutoff wavelength λc=19 μm, is demonstrated. Detailed measurements and an in-depth analysis of the noise, optical gain, detectivity, quantum efficiency, and quantum-well escape probability, are also discussed.
Diffraction of light by a focused ultrasonic wave
Authors: Huang J. , Nissen J. A. , Bodegom Erik
Published: July 2002

The measurement of the acoustic pressure of a planar ultrasonic wave by light diffraction is well established. The ability to do similar measurements in the case of spherical waves has been doubted. However, we show that the range of validity can be extended to the focal region of a spherical concave piezoelectric transducer. Light is passed through the focal plane of a spherical concave transducer and is diffracted as a result of the variation in the index of refraction. The peak pressure can be calculated from the diffraction intensity by making the following simplification. We assume that in the focal plane the ultrasound can be approximated by a profiled planar wave, which in turn can be modeled by a wave of constant amplitude and effective width. The experimental results for moderate-pressure amplitudes in water compare favorably with the calculations using the Khokhlov–Zabolotskaya–Kuznetsov equation, which incorporates both nonlinearity and diffraction effects of the acoustic field.
Analysis of photon scanning tunneling microscope images
Authors: Cites J. , Sanghadasa M. F. M. , Sung C. C. , Reddick R. C. , Warmack R. J. , Ferrell T. L.
Published: July 2002

Photon scanning tunneling microscope (PSTM) images are made by scanning an optically conducting probe tip in an evanescent field above a sample surface. These images contain a mixture of topographical information, scattering effects, and variations in optical properties across the sample. Proper interpretation of PSTM images is therefore dependent upon knowledge of the field-surface interactions giving rise to these features. The subject of this work is the calculation of PSTM image features arising from the topography of the sample surface. Image features of a model sinusoidal grating structure are calculated using small perturbation theory. Image amplitudes are shown to depend on the sample orientation and the shape and position of the probe tip. The calculated results are compared with actual PSTM images of a holographically produced sinusoidal grating surface.
Vacuum arc cathode spot parameters from high-resolution luminosity measurements
Authors: Anders A. , Anders S. , Jüttner B. , Pursch H. , Bötticher W. , Lück H.
Published: July 2002

Cathode spots on arc-cleaned copper and molybdenum electrodes in vacuum were studied by fast image converter framing and streak camera photography with high temporal and spatial resolution. The frame exposure time was 20 ns and the interframe period was 200 ns; the streak sweep time was between 200 ns and 1 μs. Spatial structures with a resolution of 5 μm could be determined by observing the spot movement with a small slit at the streak camera and a high sweep speed. Strong fluctuations of the light emission of the spot were found with characteristic times of 50–100 ns. When the spot moved out of the slit field of view a stepwise decrease occurred in the measured light, indicating an internal substructure of the spot with distances between fragments less than 10 μm and even smaller fragment diameters. The current per fragment was estimated to be 20–40 A. The frames confirm the short time constants of the spot. From frame to frame a spot motion was observed in most cases, yielding spot residence times <200 ns.
Electronic structure of some I–III–VI2 chalcopyrite semiconductors studied by synchrotron radiation
Authors: Takarabe K. , Kawai K. , Minomura S. , Irie T. , Taniguchi M.
Published: July 2002

Photoemission spectra were measured for the I–III–IV2 chalcopyrite semiconductors CuInSe2, CuInS2, CuInTe2, and CuGaS2 with various photon energies (32 to 140, and 1253 eV). The partial density-of-states (DOS) of Cu 3d orbital is selectively observed at the photon energies beyond 100 eV. The DOS of Cu 3d spreads from the top of valence band (VB) to 5 or 6 eV below. Three dominant peaks are labeled as A, B, and C, the structures of which are interpreted as antibonding, nonbonding, and bonding states. Reflection spectra were also measured for CuInSe2 from 2 to 100 eV at room temperature and 98.5 K. The In 4d core reflection is observed at 17.5, 18.9, 19.8, and 21.2 eV at 98.5 K; very similar characteristics are also observed at 5.28, 6.21, 7.35, and 8.67 eV. These contributions are due to the Cu 3d nonbonding electrons. Photoemission and reflection experiments thus confirm conclusively the existence of nonbonding Cu 3d states in I–III–VI2 chalcopyrites. This result proves the theoretical model that attributes the upper VB to the antibonding state, in contrast with the bonding state of sp3-hybridized semiconductors.
High-efficiency second-Stokes-order Raman conversion of KrF laser radiation in hydrogen
Authors: Huo Yunsheng , Shimizu Kouki , Yagi Takashi
Published: July 2002

Generation of the second Stokes order with a photon efficiency of 68% has been obtained from a single-pass hydrogen Raman oscillator. The third-order Stokes generated by four-wave mixing is effectively suppressed by phase mismatching. The 1.6 times diffraction-limited pump-beam quality used in the present experiment was found to be essential to the high-efficiency second-Stokes-order generation.
Electrical characteristics at 4.2 K and high magnetic fields in metal-oxide-semiconductor field-effect transistors utilizing sputter-deposited gate-oxide films
Authors: Suyama S. , Okamoto A. , Shirai S. , Serikawa T. , Takaoka S. , Murase K.
Published: July 2002

Characteristics of metal-oxide-semiconductor field-effect transistors (MOSFETs) with sputter-deposited gate-oxide films at 4.2 K under high magnetic fields of up to 10 T are presented. The gate-oxide films are deposited by oxygen-argon sputtering of an SiO2 target at 200 °C, much lower than a conventional thermal oxidation temperature of 1000 °C. The MOSFET using a sputter-deposited film has a Hall mobility of 7000 cm2/V s at 4.2 K. The quantum Hall effect and Shubnikov–de Haas oscillations are successfully observed. The magnetic angle dependence of the magnetoresistance and the Shubnikov–de Haas oscillation indicate that this MOSFET has a two-dimensional electron gas. Analysis of the perpendicular magnetoresistance and the quantum Hall effect indicates that this MOSFET has a weakly localized state similar to that of thermal oxide film.
Understanding quantum wires with circular bends
Authors: Sprung D. W. L. , Wu Hua , Martorell J.
Published: July 2002

It is shown that propagation around a circular bend in a quantum wire is well approximated by a one-dimensional problem with a square-well potential replacing the bend. Simple analytic expressions are obtained for the transmission and bound states.
Enhancement of gold solubility in silicon wafers
Authors: Li Jianxing , Yang Woun-Suck , Tan Teh Y.
Published: July 2002

Edge-defined film-fed grown silicon wafers with a thin Au film deposited on one side were annealed at 950 °C for various times. Spreading resistance probe measurements showed that at the wafer free surface the Au concentration was higher than the Au solubility in silicon found at the Au source side. Scanning electron microscopy, transmission electron microscopy, and energy-dispersive spectroscopy investigations revealed Au particles of nanometer size at the wafer free surface. The enhancement of the Au solubility at the wafer free surface is attributed to the existence of these small Au particles.
Room-temperature photoluminescence in strained quantum wells of InGaAs/GaAs grown by molecular-beam epitaxy
Authors: Martelli Faustino , Proietti Maria Grazia , Simeone Maria Gabriella , Bruni Maria Rita , Zugarini Marco
Published: July 2002

In this work first room-temperature photoluminescence in strained single and multiple quantum wells of InxGa1−xAs/GaAs grown by molecular-beam epitaxy is presented. The In mole fraction x varies from 0.06 to 0.23 and the well width from 5 to 20 nm. The data suggest that carrier generation in the well is caused by trapping carriers photoexcited in GaAs. The thermal behavior of this mechanism must be taken into account when the temperature dependence of the luminescence is analyzed.
Minority electron transport across p+ doped submicron layers of GaAs
Authors: Osman M. A.
Published: July 2002

The dynamics of transient transport of minority electrons injected into p+ doped submicron layers of GaAs have been investigated using ensemble Monte Carlo method. It is found that the transit times of electrons across these layers are longer or shorter depending on the electric field strength, injection energy, and the width of the layers. The transit time across a 0.4 μm p+ doped GaAs layer increased from 1.0 to 2.0 ps at 10 kV/cm, while it decreased from about 3.0 to 2.0 ps at 50 kV/cm when the inelastic scattering of the minority electrons by the hole plasma is taken into account. Also, the calculated transit times across a 0.4 μm wide layer do not show any significant dependence on the injection energy when electron–hole (e–h) interaction is accounted for. The average drift velocity across the 0.4 μm layer doped p = 2 × 1018 cm−3 is 2 × 107 cm/s which is more than twice the saturation velocity in GaAs. This is attributed to the role of the e–h interaction which leads to reducing both the mobility of electrons and their transfer rates to the upper valleys in GaAs, and the rapid thermalization of the energy and momentum distributions of the electrons.
Abnormal T
c change of Bi1.6Pb0.4Sr2Ca2(Cu1−zTiz)3Ox (0.01<z<0.1)
Authors: Nishi Yoshitake , Nozaki Kazuo , Kurotaki Takuya , Kita Yuichiro , Oguri Kazuya
Published: July 2002

Influence of Ti addition (substitution for Cu) on Tc is studied for high Tc Bi1.6Pb0.4Sr2Ca2(Cu1−zTiz)3Ox. An abnormal Tc change is found between z=0.01 and 0.1. Based on results of the electrical resistivity and x-ray diffraction, the abnormal Tc change is discussed.
Photointercalation characteristics of thin WO3 films
Authors: Nagasu Masahiro , Koshida Nobuyoshi
Published: July 2002

Photoinduced proton injection properties of amorphous thin WO3 films have been studied for a cell of the form quartz glass/semitransparent Au/ethanol/WO3/indium-tin-oxide- coated glass. When the cell was illuminated with near-uv light through a quartz window under open circuit conditions, a definite reversible change was induced in the optical and electrical properties of WO3 films. On the basis of some experimental analyses, this effect is attributed to photointercalation (PI) of protons into WO3 films. It is also demonstrated that WO3-based PI cells efficiently operate as an erasable device for storage and modulation of optical information.
Effects of annealing on infrared and thermal-effusion spectra of sputtered a-Si:H alloys
Authors: Talukder G. , Cornish J. C. L. , Jennings P. , Hefter G. T. , Clare B. W. , Livingstone J.
Published: July 2002

Infrared spectroscopy and thermal effusion have been used to study the nature of the silicon-hydrogen bond in sputtered a-Si:H alloys. The samples were prepared by reactive sputtering under different deposition conditions to produce varying hydrogen contents. The Fourier transform infrared spectra have been analyzed using the simplex algorithm to deconvolute the component peaks. This technique has been applied separately to both the stretching- and bending-mode regions of the infrared absorption spectra. Studies have been made of the effects of annealing on both the infrared and the thermal evolution spectra of hydrogen. The results indicate a redistribution and transformation of different bonding configurations due to annealing. A comparative study is presented of the thermal-effusion spectra for partial and total degassing with the infrared spectra taken before and after each phase of degassing.
Rayleigh scattering in Sr0.61Ba0.39Nb2O6
Authors: Wilde Jeffrey P. , Wilde Richard E.
Published: July 2002

Rayleigh scattering (λ=488 nm) is observed in single-crystal Sr0.61Ba0.39Nb2O6 (SBN:61). In particular, the scattered intensity is measured as a function of temperature across the ferroelectric–paraelectric phase transition. The results show that the scattered intensity can vary by as much as two orders of magnitude in passing through the transition. The particular form of the intensity-vs-temperature curve is found to depend on the poling history of the crystal. The unpoled crystal exhibits a rapid change from strong scattering below the transition (ferroelectric state) to weak scattering above the transition (paraelectric state). The measured inflection point is near 63 °C upon heating and near 58 °C upon cooling. In this case the scattering is predominantly attributed to the presence of high-density ferroelectric domains, which vanish above the transition. If the crystal is thermally poled (by cooling through the transition with an electric field applied), it shows no measurable domain scattering but does exhibit strong central-peak behavior at 65 °C upon heating and 59 °C upon cooling. Despite repeated cycling through the transition, the previously thermally poled crystal consistently displays central-peak behavior. The results suggest that thermal poling in SBN followed by thermal depoling produces a significant increase in the average ferroelectric domain size when compared to the unpoled crystal.
Studies of coherent and diffuse x-ray scattering by porous silicon
Authors: Bellet Daniel , Dolino Gérard , Ligeon Mireille , Blanc Pierre , Krisch Michäel
Published: July 2002

The microstructure of porous silicon layers has been studied by means of x-ray diffraction. Using a double-crystal diffractometer, the observed diffraction patterns give directly the mismatch between the lattice parameters of the porous layers and of the substrate, and the curvature of various porous silicon samples obtained in different conditions. From measurements with the same experimental set-up, but with a larger scan range, broad diffuse bumps produced by the pore structure have been observed. This new feature allows us to obtain structural informations on the porous silicon in a nondestructive way. In particular, we have observed the anisotropic pattern showing a preferential elongation of the pores perpendicular to the (100) surface.
Theoretical and experimental study of a high-current vacuum arc in a uniform axial magnetic field
Authors: Morimiya Osami
Published: July 2002

Measurements of the electron temperature, floating potential, plasma density, and average plasma pressure in a magnetically confined high-current vacuum arc are described. A 40-mm-diam, 30-mm-long arc was initiated between OFCu copper electrodes in a uniform axial magnetic field by triggering the gap. The crest values of the arc current ranged from 3 to 20 kA. The electron temperature by Langmuir probe measurement was Te= 2.5–3.0 eV with a uniform space distribution and was independent of the arc current. The space distribution of the ion density was parabolic in the radial direction and with a zero derivative in the axial direction. The average plasma pressure by paramagnetic measurement increased with the square of the arc current. The experiment showed that the arc column could be considered as an infinitely long column in which the plasma parameters have zero axial derivatives. Theoretical analysis has been carried out under the following assumptions. An infinitely long cylindrical and fully ionized steady-state plasma in which all quantities varied in the r direction only was considered. The anisotropy factor σ∥/σ⊥ for electrical conductivities was taken into account in the theoretical analysis, where σ∥ and σ⊥ were electrical conductivities parallel to the magnetic field and perpendicular to it, respectively. The plasma parameters determined from the experiments and theoretical analysis agreed closely with each other when the factor σ∥/σ⊥ was equal to ∼2, which is the theoretical upper limit in a high magnetic field. Constant temperature characteristics independent of the arc current have been found to be clearly seen by using line radiation as the dominant power loss in the power balance equation.
Deep levels in undoped horizontal Bridgman GaAs by Fourier transform photoconductivity and Hall effect
Authors: Mitchel W. C. , Brown Gail J. , Rea Laura S. , Smith S. R.
Published: July 2002

Deep levels between 0.1 and 1.0 eV in semi-insulating and high resistivity undoped horizontal Bridgman GaAs have been studied by temperature-dependent Hall effect (TDH) and Fourier transform photoconductivity (FTPC). Activation energies at 0.77, 0.426, and 0.15 eV have been observed by TDH. Photoionization thresholds at 1.0, 0.8, 0.56, 0.44, and 0.25 are reported. The photoconductivity thresholds at 0.56 and 0.25 eV are reported for the first time. New features in the 0.44 eV threshold suggest that the defect responsible for this level has a small lattice relaxation and Frank–Condon shift. Possible associations of the FTPC and TDH energies with the deep-level transient spectroscopy levels EL2, EL3, and EL6 are presented.