bluuebunny/crossref_metadata_2025 huggingface dataset:
Destruction mechanism of III-V compound quantum well structures due to impurity diffusion
Authors: Tan T. Y. , Gösele U.
Published: July 2002

Recent experiments have shown that quantum well structures grown on a GaAs substrate can be destroyed by dopant diffusion. It is observed that existing models proposed to explain the phenomena are not in accordance with most available experimental results. We propose an alternative mechanism to explain the quantum well destruction phenomenon. The mechanism is based on the effect of the Fermi level on the concentrations of charged point defects which contribute to diffusion processes. This conceptually simple mechanism is consistent with most available experimental results on a qualitative basis. In this mechanism, the doping level and the doping type (p or n) are of primary importance, and not some other detailed atomistic nature of the dopant species. Furthermore, it is the presence of the dopant that is important, and not its motion, i.e., its diffusion.
Amorphous rare-earth–transition-metal thin films with an artificially layered structure
Authors: Sato Noboru , Habu Kazutaka
Published: July 2002

We investigated the origin of magnetic anisotropy in rare-earth–transition-metal (RE-TM) thin films with an artificially layered structure and their magnetic and crystallographic properties. The various RE-TM films such as Gd-Fe, Tb-Fe, and Dy-Fe were deposited in an alternating multilayer structure by a multisource dc-sputtering method. We made films with an anisotropic distribution of RE and TM atoms parallel to the film plane, where the monatomic layering of RE and TM was confirmed by small angle x-ray diffraction analysis. The films were thermally stable to temperature up to 400 °C. The films composed of monatomic layer of RE and several atomic layers of TM show a large perpendicular uniaxial anisotropy and a large magnetization over a wide range of RE composition. It is concluded that the anisotropic distribution of RE-TM pairs is the most important origin of the magnetic anisotropy in amorphous RE-TM films.
Method of determining capture cross section including a slow capture of carriers in the depletion edge region
Authors: Tomokage H. , Miyamoto T. , Okushi H. , Tokumaru Y.
Published: July 2002

The capture process of carriers in the pulse-filling measurements is analyzed by including the slow capture on the edge of a depletion layer. An analytical expression is derived to determine the capture cross section of majority carriers from the initial slope of the semilogarithmic plot of capacitance versus capture time in the case of low trap concentration. A method is proposed to determine the fast capture rate in the bulk region from a slow capture process in the edge region when the trap concentration is not negligible compared with the concentration of the shallow dopant. The edge effect is intentionally enhanced to observe the capacitance variation with the capture time. Pulse-filling measurements on Au-doped Si p+n and undoped liquid-encapsulated Czochralski n-GaAs Schottky diodes are made to verify the method.
Etching in a pulsed plasma
Authors: Boswell R. W. , Porteous R. K.
Published: July 2002

The etching of silicon in a pulsed plasma using SF6 gas is investigated. For short pulses the Si etch rate for a pulsed plasma is essentially the same as for the continuous plasma, in spite of the duty cycle being only 20%. An heuristic model of the etching has been developed which accurately predicts the pulsed plasma etch rates and sets limits on important parameters, such as the number of F atoms yielded by the SF6, the reaction probability of F with Si, and the overall efficiency of the etching process.
Magnetization curling in coated particles
Authors: Aharoni Amikam
Published: July 2002

Rigorous micromagnetic calculation is presented for the nucleation by the magnetization curling mode in an infinite circular cylinder, which has a uniaxial anisotropy (parallel to the cylinder axis) only in a cylindrical shell, on the surface. Numerical values used in a computed example are those of acicular γ-Fe2O3 particles, coated with CoFe2O4.
Contrasts in electron and hole trapping phenomena in pyrogenic oxides grown with different H2O partial pressures on silicon
Authors: Lakshmanna V. , Vengurlekar A. S. , Ramanathan K. V.
Published: July 2002

Trapping characteristics of both electrons and holes in pyrogenic oxides grown on silicon with different H2O partial pressures in the oxidizing ambient are studied by using the avalanche injection technique. The electron- and hole-trapping phenomena show opposite dependence on the pyrogenic oxide growth conditions. It is found that the electron-trap density increases with the H2O partial pressure, whereas the hole-trap density decreases. On the basis of the above, and from the results of further experiments on water-diffused oxides, the effect of post-metallization annealing, and infrared absorption, we examine different models of possible defects in silicon-dioxide films grown on Si for a consistent explanation. From the analysis SiH and SiOH centers appear to be the most likely hole and electron traps, respectively, in our pyrogenic oxides.
Excitonic energies and inhomogeneous line broadening effects in InAlAs/InGaAs modulator structures
Authors: Hong S. , Singh J.
Published: July 2002

The exciton problem in the In0.52Al0.48As/In0.53Ga0.47As quantum well in the presence of static transverse electric field is studied. We report results on variation of exciton size, binding energies, and emission energies as a function of electric field and well size. Inhomogeneous line broadening of exciton lines due to interface roughness and alloy disorder is also calculated. Alloy disorder in the well and barrier regions is found to be very important and its control may be critical in the performance of this system as a high efficiency modulator.
Perpendicular field ferromagnetic resonance in rectangular yttrium-iron-garnet films using a frequency sweeping spectrometer
Authors: Barak J.
Published: July 2002

A simple broadband ferromagnetic resonance spectrometer was assembled for observing magnetostatic modes in yttrium-iron-garnet films while sweeping frequency. The spectrum of a rectangular sample is studied close to a ground plane and far from it in the perpendicular configuration. The modes are identified and analyzed using the theories for infinite films. It is shown that modifications of the theory are needed due to the variations of the demagnetization field in the sample and due to propagation effects.
Short-pulse high-power microwave propagation in the atmosphere
Authors: Sullivan C. A. , Destler W. W. , Rodgers J. , Segalov Z.
Published: July 2002

The propagation of high-power (10–200 kW/cm2 ) short-burst (3–30 ns) microwave pulses in the atmosphere has been studied experimentally. Microwave power from a large orbit gyrotron operating at 9.6 GHz is focused by a large-diameter parabolic reflector into a test cell. The ambient pressure in the test cell was varied over a wide range and the microwave power density necessary for atmospheric breakdown has been determined as a function of ambient pressure and pulse duration. Measurements of the microwave pulse duration before and after breakdown have been obtained to determine the extent to which microwave energy is absorbed or reflected by the breakdown plasma. Results are compared with available theory and previously reported experiments.
Mössbauer investigation of zinc ferrite particles
Authors: Tang H. , Du Y.-W. , Qiu Z.-Q. , Walker J. C.
Published: July 2002

Mössbauer spectra of Zn0.2Fe2.3O4 particles at different temperatures have been obtained. They have been analyzed with five components, one due to the A-site Fe3+ ions, and the others due to the B-site Fe3+ and Fe2+ ions. Magnetic and electronic properties have been discussed with regard to zinc substitution and temperature dependence.
Interferometric measurement of substrate heating induced by pulsed laser irradiation
Authors: Saenger K. L.
Published: July 2002

A simple interferometric technique for the study of radiation induced transient heating is demonstrated for the specific case of a glass substrate irradiated with pulsed 193-nm excimer laser radiation. The technique relies on the fact that the optical path length of (633 nm) probe laser light within the substrate is sensitive to heat-induced changes in the refractive index and thickness of the substrate. Interference between probe laser reflections from the front and back surfaces of the substrate allows these optical path length changes to be deduced from measured changes in sample reflectance. The technique offers fast response and is shown to be nearly quantitative.
Studies of effective gettering techniques using segregation annealing for complementary metal-oxide-semiconductor technologies
Authors: Gregor R. W. , Stinebaugh W. H.
Published: July 2002

Reported in this work is a series of experiments which demonstrate conditions by which metallic impurities may be gettered in a complementary metal-oxide-semiconductor (CMOS) very large scale integrated technology. Successful gettering is shown to reduce reverse biased p-n junction leakage by up to three orders of magnitude. The gettering techniques we investigated emphasized segregation annealing whereby impurities diffuse to heavily doped regions of the wafer. In addition, intrinsic gettering by oxygen precipitates and extrinsic gettering through phosphorus diffusion or wafer backside ion implantation and the addition of HCl to furnace oxidation/diffusion steps were studied. It is our conclusion that a combination of these gettering methods offers the greatest reduction in junction leakage. Application to state of the art and future fine line CMOS technologies is indicated by experiments which show that backside implantation of boron or phosphorus followed by segregation annealing allows gettering to proceed at 700–800 °C, a temperature range consistent with the trend to lower process temperatures. Junction leakage currents were measured indirectly using a hold-time tester structure. The tester allowed routine measurements of currents as low as 20 fA. The temperature dependence of the junction leakage is used to calculate activation energies which show that the dominant mechanism of the leakage current changes from generation/recombination to a diffusion component as the hold time increases.
Photoconductivity lifetime measurements on HgCdTe using a contactless microwave technique
Authors: Chen M.C.
Published: July 2002

Photoconductivity lifetime measurements on narrow band-gap HgCdTe thin films and bulk slices using a contactless microwave reflection technique have been demonstrated for the first time. A horn antenna was used to allow cooling of samples to 77 K outside the waveguide and testings of large-size samples. A good agreement was established between lifetime results from the contactless microwave reflection technique and the standard photoconductivity decay method using two ohmic contacts. The feasibility of lifetime mapping by moving the pulsed light beam to different locations on the samples was also demonstrated.
Effective shielding for low-level magnetic fields
Authors: Sasada I. , Kubo S. , Harada K.
Published: July 2002

An effective method of shielding slowly varying low-level magnetic fields is presented. The key of this method is the use of soft magnetic materials with a highly rectangular B-H loop and the application of the shaking field to them. Metglas 2705M amorphous ribbon of about 22 μm in thickness was used in the experiments since it has almost vertical flanks in the dc B-H loop in as-prepared state and small coercivity Hc∼0.5 A/m. A shielding factor of the cylindrical case with a copper pipe inside (diameter : 60 mm; length : 100 mm) and with two crossed layers of the ribbon outside was measured against low-level disturbing fields of 10 Hz applied transversely to the case. Although the shielding factor was as small as 3.5 without shaking, it became higher than 150 under the shaking field of 1 kHz, 2.9 A/m(rms). This value is far better than that with Mumetal or 4-79 Mo-Permalloy. A shaking frequency as high as 1 kHz or higher makes it easy to suppress the leakage of the shaking field into the shielded space.
Magnetism in bcc 3d transition metals
Authors: Moruzzi V. L. , Marcus P. M.
Published: July 2002

We present first-principles spin-polarized total-energy-band calculations based on a fixed-spin-moment procedure to show the volume dependence of the magnetic behavior for 3d bcc transition metals. All members of the series from Sc to Ni exhibit an onset of magnetic behavior at well-defined critical volumes by way of second-order, first-order, or composite transitions. As a function of volume, calculated magnetic moments tend towards free-atom limits consistent with Hund’s rule and atomic ground-state configurations, and total energies tend towards free-atom energies. Volume-dependent l-decomposed spin configurations that provide an insight into the polarization process are presented for selected members of the series.
Origin of donor and acceptor species in undoped ZnSe grown by low-pressure metalorganic chemical vapor deposition
Authors: Morimoto Keizo
Published: July 2002

Effects of the [H2 Se]/[Dimethylzinc] source ratio on the electrical properties in the temperature range of 15–300 K and on the cathodoluminescence properties at 77 K have been investigated for undoped ZnSe films grown in one deposition run on (100)GaAs substrates at 350 °C by metalorganic chemical vapor deposition. The properties correlated with each other and depended on the degrees of deviation from stoichiometry. The dominant donor is identified with selenium vacancy from the dependence of donor concentration on the ratio and on the film thickness. Two kinds of acceptors were introduced according to the deviation from stoichiometry. They are tentatively associated with NSe and NaZn . Extended lattice defects which reduce the electron mobility are favored at the high ratios and they seem a principal factor of the high-resistive property of this material.
Electro-optic sampling of ultrashort high voltage pulses
Authors: Stearns D. G.
Published: July 2002

High voltage (∼1 kV) pulses having 12-ps rise time and a duration of 70 ps have been generated and propagated along a suspended-strip vacuum waveguide. The temporal and spatial profiles of the electric field inside the waveguide have been measured using electro-optic sampling, with resolutions of 10 ps and ∼1 mm, respectively. The field is found to be predominantly composed of the TEM00 mode, and there is no observable temporal broadening of the ultrashort pulse over a propagation distance of several centimeters. The temporal profile exhibits significant high-frequency modulation which is attributed to the LC resonance of the photoconductive switch.
Instrumentation of a resonant gravitational radiation detector with a planar thin-film dc SQUID
Authors: Folkner W. M. , Moody M. V. , Richard J.-P. , Carroll K. R. , Tesche C. D.
Published: July 2002

The instrumentation of a low-temperature three-mode gravitationa1 radiation antenna incorporating a low-noise dc SQUID provided by IBM is described. The feedback circuitry necessary to maintain the linearity and dynamic range of the SQUID was found to drive the resonant system due to high coupling between the input coil and the feedback coil of the SQUID. In order for this type of planar thin-film dc SQUID to be useful for gravitational radiation detectors and other applications requiring high Q input circuits, a solution to this feedback problem is needed. To this end, the nonlinear equations describing the dc SQUID with linear feedback are solved in terms of an isolated SQUID. The important feedback parameters for a high Q resonant system are found to be the slew rate of the electronics and the coupling constant ratio α2if/α2f, where α2if is the energy coupling efficiency between the feedback coil and input coil and α2f is the energy coupling efficiency between the feedback coil and the SQUID loop. Methods to reduce the effect of the feedback on the input circuit are also discussed.
Interface charge control of directly bonded silicon structures
Authors: Bengtsson Stefan , Engström Olof
Published: July 2002

The influence of interface states and charges on the properties of Si/Si and Si/SiO2 interfaces prepared by wafer bonding, using the direct bonding technique, has been investigated. Surface potentials of Si/Si interfaces with all combinations of doping type (n-n,p-p,p-n) are dependent on surface and heat treatments in the bonding procedure and on wafer dopant concentration. In earlier reported works, hydrophilic wafer surface properties have been reported as necessary for a good mechanical bonding. We find that wafer treatment in HF giving hydrophobic surfaces not only gives good mechanical properties, but also better electronic properties as well. For all combinations of doping type, lower magnitudes in surface potential were measured in samples prepared from wafers pretreated in HF in order to etch off the native oxide layer, normally present on silicon surfaces. If a native oxide is present when the bonded interface is prepared, the current through the interface will be influenced by an energy barrier due to the presence of charged interface states. The amount of charge trapped at the interface has been found to be dependent on the applied bias. A theoretical description is made for the Si/Si interfaces, and predictions are compared to results obtained from electrical measurements. Based on this theory, using data from the current-voltage characteristic, an interface state density in the region 5×1010–1012 cm−2 eV−1 at the bonded interface has been deduced for different samples. Bonded Si/SiO2 interfaces with interface state densities of about 1011 cm−2 eV−1 and low flat-band voltages have been achieved. No influence of different chemical pretreatments, used in this paper, on properties of bonded Si/SiO2 interfaces, as seen in flat-band voltage and interface state density, was found, although the bonding process is critical in the preparation of the Si/SiO2 interfaces.
Electrical resistivity and Hall effect of TiSi2 thin films in the temperature range of 2–300 K
Authors: Li Bing-Zong , Zhang Ai-Ming , Jiang Guo-Bao , Aitken Robert G. , Daneshvar Kasra
Published: July 2002

The electrical resistivity and Hall effect of TiSi2 thin films were measured systematically in the temperature range of 2–300 K. The results were compared with theory and other work. The TiSi2 films were formed by Ti/Si solid-state interaction on crystalline silicon or polysilicon substrates. The temperature dependence of the electrical resistivity of TiSi2 was approximated by the Bloch–Gruneisen theory. The Hall-effect data show a multicarrier conduction mechanism in TiSi2. At low temperatures the Hall coefficient is positive for both substrates, but is negative at room temperature. The temperature at which the change of sign occurs is approximately 180 K for the crystalline-Si substrate, and approximately 90 K for the polysilicon substrate. This is discussed briefly in terms of scattering mechansims for a simple model of the electronic structure.
Preparation of a-SiC:H/a-GeC:H superlattices by dual magnetron sputtering
Authors: Saito N. , Yamaguchi T.
Published: July 2002

Amorphous semiconductor superlattices composed of hydrogenated amorphous silicon carbon alloys and germanium carbon alloys have been prepared by a dual magnetron sputtering method. A small-angle x-ray diffraction measurement has indicated that the superlattices consist of well-defined smooth layers. Optical band gap has been examined for a series of samples; the thickness of the germanium carbon layer was changed from 20 to 130 Å, while the thickness of the silicon carbon layer was kept constant at 60 Å. The optical band gap increases upon decreasing the thickness of the germanium carbon layer, indicating quantum size effects due to the formation of superlattice structures.
Structural, optical, and electrical characterization of improved amorphous hydrogenated germanium
Authors: Turner W. A. , Jones S. J. , Pang D. , Bateman B. F. , Chen J. H. , Li Y.-M. , Marques F. C. , Wetsel A. E. , Wickboldt P. , Paul W. , Bodart J. , Norberg R. E. , El Zawawi I. , Theye M. L.
Published: July 2002

High-quality amorphous hydrogenated germanium has been deposited using the diode rf glow discharge method out of a gas plasma of GeH4 and H2. The optical, electrical, and structural properties of this material have been extensively characterized. The optical and electrical properties are all consistent with material containing a low density of defect related states in the energy gap. In particular, this material has an ημτ=3.2×10−7 cm2/V, ratio of photocurrent to dark current of 1.3×10−1, and flux dependence of the photocurrent with γ=0.79 at 1.25 eV measured using photoconductivity, a μτ=4×10−8 cm2/V measured using time of flight, an Urbach energy of 51 meV and α at 0.7 eV of 8.3 cm−1 measured using photothermal deflection spectroscopy, a dangling bond spin density of 5×1016 cm−3 measured using electron spin resonance, photoluminescence with a peak energy position of 0.81 eV and full width at half maximum of 0.19 eV, an activation energy of 0.52 eV and σ0 of 6.1×103 (Ω cm)−1 measured using dark conductivity, and an E04 band gap of 1.24 eV measured by optical absorption. The structural measurements indicate a homogeneous material lacking any island/tissue and columnar structure when investigated using transmission and scanning electron microscopy, respectively. Hydrogen concentrations calculated from infrared and gas evolution measurements can only by reconciled by postulating a large quantity of unbonded hydrogen whose presence is confirmed using deuteron magnetic resonance. The bonded deuterium component, as seen in this film using DMR, has a spin-lattice relaxation time of the order of 4000 s. The differential scanning calorimetry measurement shows crystallization occurring at 421 °C and the presence of large compressive stresses has been confirmed using a bending-beam method. The experimental details necessary to interpret the quantities quoted here are set out in the text which follows. It is considered that the very good optical and electrical properties of this as yet unoptimized material are directly related to the structural properties detailed above.
Interaction of a permanent magnet with a superconducting hollow cylinder
Authors: Wojtowicz Peter J.
Published: July 2002

The Meissner-effect interaction of a small permanent magnet with a superconducting hollow cylinder has been investigated by solving the Laplace equation numerically using a finite-difference method. The calculations reveal the existence of stable equilibrium configurations for a range of shapes and sizes of the cylinder. The computed magnitude of the Hooke’s law force constant is close to those measured for small magnets levitated above superconducting disks.
Measurement of instantaneous temperature in shock-loaded nonmetallic solids
Authors: Gao Juxian , Bai Rongshang , Cheng Chemin
Published: July 2002

The feasibility of direct measurement of temperature in shock-loaded, nonmetallic solids within microseconds using a foil thermocouple of 200 Å thickness has been studied over a range of pressure from 0.5 to 4 GPa. The foil thermocouple and thermopile (200 Å thickness) were designed and used to measure the temperature rise in shock-compressed polymethylmethacrylate (PMMA). The method used to manufacture the gauges is spelled out in detail in this paper. The results agree with calculated PMMA temperatures when the shock pressure is below 2.2 GPa. Above this pressure the measured temperature rise is far higher than the calculated values. This result appears to be very similar to that obtained earlier by Bloomquist and Sheffield.
Characterization of interfaces of metal/amorphized (by implantation) Si/c-Si structures
Authors: Golan A. , Fastow R. , Eizenberg M.
Published: July 2002

The electrical properties of metal/implanted (amorphous) Si contacts were studied, emphasizing the effects of the doping level, of the metal type, and of the heat treatments applied prior to the metal deposition. The implantation was carried out using 60-keV Ar+ ions at a dose of 1016 cm−2, and resulted in the formation of a thin (1000-Å-thick) amorphous layer on top of the crystalline substrate. The doping level of the implanted Si affected the current-voltage (I-V) characteristics of the contacts mainly in the reverse bias (low doping–low currents), while the forward bias characteristics were quite independent of this parameter. The device characteristics were very sensitive to the metal type, Al, Ti-W, or Pt. Thermal treatments applied prior to the metal deposition affected the characteristics by lowering the device resistance in correspondence with the thinning of the amorphous layer as a result of epitaxial regrowth. The I-V characteristics, as well as their dependence on the different process parameters, are explained using a model of charge injection into a thin layer of trap rich amorphous Si bounded by a metal/a-Si interface on one side and by an a-Si/c-Si heterojunction on the other side.
MnCl2⋅H2O: A quasi-one-dimensional Heisenberg antiferromagnet
Authors: DeFotis G. C. , Wiese R. S. , Scherrer C. W.
Published: July 2002

The magnetic properties of MnCl2⋅H2O, a heretofore unexamined hydrate of manganese dichloride, have been studied. The behavior is clearly distinguishable from that of the anhydrous material or either the dihydrate or the tetrahydrate. At high temperatures the susceptibility is Curie–Weiss-like, with a Weiss constant θ=−4.9±0.3 K in χM=C/(T−θ); this may be compared with the values θ=−3.3 K for the anhydrous material, −14.5±0.3 K for the dihydrate (as determined in this work), and −1.8 K for the tetrahydrate. Departures from linearity occur below 20 K, and a broad maximum in the powder susceptibility appears at T(χmax)=3.60±0.10 K with χmax=0.304±0.003 emu/mol. The susceptibility drops sharply below 2.23 K, and ∂χ/∂T is a maximum at 2.16±0.01 K, which is identified with the Néel temperature Tc. Certain features of the data suggest two-dimensional Heisenberg model behavior, for example the ratios Tc/‖θ‖=0.44 and Tc/T(χmax)=0.60. However, fits to χ(T) using a high-temperature series expansion for the S=5/2 two-dimensional square planar Heisenberg model are unconvincing, as are similar attempts based on a three-dimensional model. In contrast, the model of a classical Heisenberg antiferromagnetic spin chain scaled to S=5/2 permits an excellent fit, with J/k=−0.49±0.04 K the intrachain exchange (in Ĥex=−2J∑i> jŜi⋅Ŝ j). An interchain exchange of ‖J′/k‖=0.015±0.004 K, probably antiferromagnetic, can also be inferred, from the antiferromagnetic transition at Tc =2.16 K. The intrachain exchange is very similar to that in MnCl2⋅2H2O, while the interchain exchange is much weaker.
New Preisach-type models of hysteresis and their experimental testing
Authors: Mayergoyz I. D. , Adly A. A. , Friedman G.
Published: July 2002

New Preisach-type models of scalar hysteresis are discussed and the results concerning experimental testing of these models are given.
O2 molecules dissolved in synthetic silica glasses and their photochemical reactions induced by ArF excimer laser radiation
Authors: Awazu Koichi , Kawazoe Hiroshi
Published: July 2002

Silica glasses were prepared by three different techniques, vapor phase axial deposition method, oxidation of SiCl4 in O2-H2 flame, and O2 or O2-Ar plasma method with changing preparation conditions. This was done with the expectation that O2 molecules dissolve in the glasses with different concentrations by using a wide variety of preparation conditions. O2 molecules were found to be dissolved in the order of 1017 cm−3 and give an optical absorption above 7 eV, the so-called Schumann–Runge bands. The estimations of concentrations were done by using a molar absorption coefficient of ≡SiOH at 0.46 eV formed under a reaction of O2 with H2 diffusing from atmosphere at high temperature, 1/2 O2+H2+≡Si−O−Si≡ →2≡Si−OH. The concentration directly estimated from the absorption intensity at above 7 eV was consistent with those estimated from the IR band of ≡SiOH. On the ArF excimer laser irradiation of the glasses which possess the absorption band above 7 eV, the well-known absorption band at 4.8 eV was induced. This band was assigned to the Hartley bands of the O3 molecule. The reaction model was proposed to be O2(trapped)→2O(hν>5.1 eV) and O+O2→O3(trapped). On exciting the induced 4.8 eV band, a photoluminescence at 1.9 eV was observed. The photoluminescence excitation spectrum of the band was agreed closely with the quantum yield curve of O(1D) on the excitation of Hartley bands of ozone. This suggests that the luminescence is due to the radiative relaxation of O(1D) to O(3P). The total reaction was proposed to be O3→O(1D)+O2 and O(1D)→O(3P)+1.9 eV.
Accurate measurements of capture cross sections of semiconductor insulator interface states by a trap-filling experiment: The charge-potential feedback effect
Authors: Goguenheim Didier , Vuillaume Dominique , Vincent Gilbert , Johnson Noble M.
Published: July 2002

A measurement technique and analysis are presented for the accurate determination of the capture cross sections of the interface states in metal-oxide-semiconductor (MOS) structures. The technique utilizes the interface-trap-filling kinetics during measurements by energy-resolved deep level transient spectroscopy (DLTS). High accuracy is attained by accounting in the analysis for the charge-potential feedback effect which is a unique feature of the MOS structure and which presents a critical difficulty in the DLTS measurement of capture cross sections in MOS devices. The accurate measurement of the capture cross sections obtained in this work allows us to study several electronic properties of the Si-SiO2 interface including (i) the behavior of the capture cross sections of interface states created by high-field stress on MOS devices, and (ii) the determination of the capture cross section of dangling bonds at the 〈100〉-oriented Si-SiO2 interface. Finally, the possibility of determining the degeneracy factor of the interface states is questioned.
Performance limits for the scanning tunneling microscope
Authors: Tiedje T. , Brown A.
Published: July 2002

The electromechanical performance limits of a tube scanner type, scanning tunneling microscope are analyzed with respect to the three figures of merit: noise level, scan speed, and scan range. A simple tradeoff between the tube resonant frequency and scan range is defined. For a critically damped scanner tube, a good balance between scan speed and scan range is achieved with a preamplifier bandwidth equal to the resonant frequency of the scanner tube, in which case the closed loop control system bandwidth (90° phase margin) is 2/π times the resonant frequency of the tube, for a proportional-integral controller. This control loop bandwidth is shown to be compatible with a noise performance that is limited by shot noise in the tunnel junction.
Polarization-dependent gain, gain nonlinearities, and emission characteristics of internally strained InGaAsP/InP semiconductor lasers
Authors: Yu B. M. , Liu J. M.
Published: July 2002

A polarization-dependent rate-equation model on polarization-dependent emission characteristics of internally strained 1.3-μm InGaAsP/InP semiconductor lasers is presented. Among the rate-equation parameters, the polarization-dependent gain and gain-saturation coefficients are calculated using the density-matrix approach and the confinement factors and loss coefficients are related to the waveguide structure. Numerical simulations show that anomalous polarization-dependent emission characteristics can occur when the internal stress is in the 108-dyn/cm2 order of magnitude. Various types of emission characteristics from measurements and simulations are shown and the conditions for these emission characteristics are discussed. Single-polarization emission and two-polarization switching, including polarization bistability, are found in the low-stress regime and two-polarization coexisting characteristics are found in the high-stress regime.
Electro- and photo-luminescent quenching effects imposed by field-induced ionization of the Eu2+ luminescent centers in CaS:Eu thin films
Authors: Ando M. , Ono Y. A.
Published: July 2002

It is found that both the high-field electroluminescent (EL) and photoluminescent intensities of CaS:Eu thin films were quenched by an applied electric field. This quenching was found to be caused by a field-induced ionization of impact-excited Eu2+ luminescent centers. This ionization was known to play an important role in the memory and slow response characteristics of CaS:Eu thin-film electroluminescent devices. Evidence for field-induced ionization of Eu2+ was obtained from the following measurements of CaS:Eu; (i) the first and second EL emission peaks, (ii) photoluminescence, and (iii) photocapacitance.
Role of surface morphology in wafer bonding
Authors: Maszara W. P. , Jiang B-L. , Yamada A. , Rozgonyi G. A. , Baumgart H. , de Kock A. J. R.
Published: July 2002

The strain patterns detected by x-ray topography in wafers bonded for silicon-on-insulator (SOI) technology were found related to the flatness nonuniformity of the original wafers. Local stresses due to the bonding process are estimated to be about 1×108 dynes/cm2. The stress is reduced about 100 times for the thin (0.5 μm) SOI films. Most of the wafer deformation occurs during room temperature mating of the wafers. The deformation is purely elastic even at 1200 °C. The magnitude of the stress appears insignificant for complimentary metal-oxide-semiconductor devices performance.
Micromagnetic analysis of thin-film elements (invited)
Authors: Hubert Alex , Rührig Manfred
Published: July 2002

The magnetization behavior of soft magnetic thin-film elements is investigated in detail, based on a nanocrystalline iron-Permalloy multilayer system. Advantages of this material for domain analysis are a smooth surface and a good magneto-optical contrast due to a high saturation. Deviations from the mathematical model of an ideally soft magnetic two-dimensional film are due to the presence of anisotropy, to the actual structure of domain walls, and to edge anisotropies due to stress relaxation. These phenomena are observed for elements of various shapes. The effects of different anisotropies are studied by applying an external stress onto the thick ceramic substrate. Particular features connected with hysteresis, such as regular and anomalous corner configurations and the transitions between asymmetric Bloch and Néel walls are investigated.
Magnetic-field distributions in zinc-nickel ferrite
Authors: Dooling T. A. , Cook D. C.
Published: July 2002

The Mössbauer effect has been used to study the microscopic magnetic properties of the cubic microwave ferrite (Zn0.41Ni0.59)Fe2O4 at 300 K. The magnetically split spectrum is broad and unresolved due to the overlap of the hyperfine magnetic fields at the tetrahedral and octahedral sites. This is caused by a distribution of magnetic fields at each site. The distribution is especially large and asymmetric at the octahedral site and is due to the fact that the iron atoms at this site are influenced by the presence of both iron and zinc at the tetrahedral site. The octahedral site is more sensitive to changes in the number of zinc neighbors than is the tetrahedral site. Assuming a random distribution of the zinc at the tetrahedral site, and knowing the fraction of zinc in the ferrite, the binomial distribution has been used to calculate the expected magnetic-field distribution at the octahedral site as a function of the number of zinc neighbors. These figures have been compared with the magnetic-field distribution profile determined from the fit to the Mössbauer spectrum. Sufficiently good agreement has been found to allow us to isolate the magnetic-field contribution due to most of the different numbers, between zero and six, of neighboring zinc atoms.
Micromagnetics of ultrathin films and surfaces
Authors: Arrott Anthony S.
Published: July 2002

Micromagnetics in ultrathin films can be carried out in the manner of calculating liquid-crystal patterns. Magnetostatic interactions are neglected except for the restriction of the magnetization to the plane of the film. For magnetization patterns described by large wave vectors, rapid changes on the scale of nanometers, the micromagnetics is a competition between inhomogeneous anisotropy fields, exchange fields, and applied fields. The method of calculation is illustrated by showing the role of pinning sites in reducing the coercivity in ultrathin films. The method can also be applied to thicker films and surfaces when the pinning sites are at the surface.
Magnetic properties of CoPtCr thin films with 〈112̄0〉 crystal orientation
Authors: Mirzamaani M. , Jahnes C. V. , Russak M. A.
Published: July 2002

The microstructure and magnetic properties of CoPtCr thin films with 〈112̄0〉 restricted fiber texture grown on (100) planes of Cr single-crystal films were characterized and subsequently correlated with the domain configuration during the magnetization reversal process. These films exhibited a bicrystal mode associated with two orthogonal easy axes of magnetization in the plane of the film. The domain configuration of these films during the magnetization-reversal process consisted of two sets of domains extending in two orthogonal directions. These properties were compared with those of CoPtCr films with random crystallographic orientation.
A magnetization model for computational magnetodynamics
Authors: Hayano S. , Namiki M. , Saito Y.
Published: July 2002

In order to calculate the magnetodynamic fields exactly, it is essential to work out a magnetization model. We have previously proposed a Chua-type magnetization model based on magnetic domain theory. This Chua-type model is now applied to typical ferromagnetic materials, such as iron, ferrite, and amorphous magnetic material. As a result, it is revealed that the typical magnetization characteristics of representative ferromagnetic materials can be satisfactory reproduced by our Chua-type model.
Positive charge generation in metal-oxide-semiconductor capacitors
Authors: Trombetta L. P. , Feigl F. J. , Zeto R. J.
Published: July 2002

This work examines the electrical behavior of metal-oxide-semiconductor capacitors in which positive charge has been generated in the silicon dioxide layer using either avalanche hole injection, avalanche electron injection, or Fowler-Nordheim Tunneling injection. It is concluded on the basis of flatband voltage measurements made as a function of time following charge injection that two distinct species of positive charge are generated in the oxide layer, depending on the nature of charge generation. In particular, avalanche hole injection results in the generation of trapped holes, while avalanche electron injection and Fowler-Nordheim Tunneling result in so-called ‘‘slow-states’’ or anomalous positive charge centers. The electrical behavior of these two species is discussed. In addition, interface trap density measurements following avalanche hole injection show that both a background level of interface traps and a peak at approximately 0.8 eV above the valence band edge build with time following injection. Further, the dependence of the interface trap density on injection fluence and time supports a model in which a neutral species is released from the bulk of the oxide during hole injection and subsequently generates an interface defect.
Temporal behavior of the electron and negative ion densities in a pulsed radio-frequency CF4 plasma
Authors: Kono A. , Haverlag M. , Kroesen G. M. W. , de Hoog F. J.
Published: July 2002

Electron and negative ion densities in the afterglow and in the plasma initiation phase of a 13.56-MHz rf discharge in CF4 were measured by using a microwave cavity method and a laser photodetachment technique. Measurements were carried out at low rf powers (≲10 W) and in the pressure range from 100 to 300 mTorr. The electron density in the afterglow showed an enhanced decay rate due to the presence of negative ions. Electrons originating from negative ions through associative collisional detachment with neutral radicals were also detected in the afterglow. Decay curve analysis of the negative ion density gave an ion–ion (presumably CF+3−F−) recombination rate constant of (5±2)×10−13 m3 s−1, and showed that, in the active plasma, the negative ion loss rates by associative detachment and ion–ion recombination are of the same order of magnitude. The behavior of the electron and negative ion densities in the plasma initiation phase indicates that molecules and radicals that slowly accumulate in the plasma do not play a significant role in the production of negative ions.
Identification of point defects in hydrothermally grown KTiOPO4
Authors: Scripsick M. P. , Edwards G. J. , Halliburton L. E. , Belt R. F.
Published: July 2002

Electron paramagnetic resonance has been used to investigate radiation-induced point defects in hydrothermally grown single crystals of potassium titanyl phosphate ( KTiOPO4 or KTP). The crystals were irradiated at 77 K with 60–kV x rays. A trapped-hole center, a Ti3+ center, and a Pt3+ center were observed between 10 and 30 K after the initial 77-K irradiation. These defects become thermally unstable near 160 K. The trapped hole is localized on an oxygen ion adjacent to a potassium vacancy and has resolved hyperfine interactions with three phosphorus nuclei. The Ti3+ ion is the intrinsic self-trapped electron center in KTP and has weak hyperfine interactions with four phosphorus nuclei.
Annealing behavior of photoconductance relating to electron-irradiation-induced defects in semi-insulating GaAs
Authors: Kuriyama K. , Takahashi Hirokazu , Irie Y. , Kawakubo T.
Published: July 2002

The annealing behavior of photoconductance in electron-irradiated semi-insulating GaAs grown by the magnetic-applied liquid-encapsulated Czochralski technique is studied in terms of the electron-irradiation-induced defects. A decrease in photoconductance for samples annealed at 350 °C is attributed to the interband transition of the photoexcited electrons within the electron-irradiation-induced defect observed at around 0.98 eV using infrared absorption spectroscopy. The recovery of the photoconductance for samples annealed above 400 °C is enhanced by the annihilation of the 0.98-eV defect, accompanied by the photoquenching of the photoconductance below 140 K. An unquenchable component in photoconductance appeared by an annealing above 600 °C is proposed to be a VAs-CAs complex by photoluminescence measurements.
Formation of interface traps in metal-oxide-semiconductor devices during isochronal annealing after irradiation at 78 K
Authors: Saks N. S. , Klein R. B. , Yoon S. , Griscom D. L.
Published: July 2002

We have studied the mechanisms of interface trap (Nit) formation in metal-oxide-semiconductor devices during isochronal annealing after irradiation at 78 K. Two distinct Nit formation processes are observed at 120 and 250 K. After irradiation but before annealing, some samples were injected with electrons to remove all the radiation-induced positive oxide charges. In these samples, the Nit formation process at 250 K is nearly eliminated, in agreement with previous reports, but the lower-temperature 120 K process increases substantially. Results are explained using a hydrogen model. We also discuss the use of substrate hot-electron injection, which is used to annihilate the radiation-induced positive charge, in some detail.
Characterization of annealed high-dose oxygen-implanted silicon by spectroscopic ellipsometry and reflectometry
Authors: Jans J. C. , Hollering R. W. J. , Lifka H.
Published: July 2002

Experimental results are presented on the optical characterization of high-dose oxygen-implanted (∼2×1018 cm−2, 200 keV) and annealed (6 h, 1300 °C) silicon-on-insulator structures by spectroscopic ellipsometry. The ellipsometric sensitivity to variations in the multilayer geometry, induced by small variations in implantation dose, is demonstrated. In the analysis a five-layer model is used. For the given conditions of sample preparation the results show a linear relation between the thicknesses of the buried oxide layer and the silicon top layer. Additional spectroscopic reflectometry measurements, interpreted by using a simplified two-layer model, are correlated to the ellipsometric results.
The impact of the directional solidification on the magnetic properties of NdFeB magnets
Authors: Ma B. M. , Bounds C. O.
Published: July 2002

Microstructures of cast Nd15Fe78B7 ingots with thicknesses of 8.7 and 4.4 mm have been investigated. Usually, a flat cast ingot consists of three different types of grains: fine, coarse, and columnar grains. Fine grains appear near the cast interface, columnar grains usually show in regions which undergo directional solidification and coarse grains exist in regions of a lower solidification rate. Low solidification rate results in a segregation of dendritic Fe, which is undesirable in magnet processing. Magnets made from a 8.7-mm-thick ingot yield a Br of 11.7 kG and a BHmax of 34.0 MGOe while magnets made from a 4.4 mm ingot give rise to a Br of 12.3 kG and a BHmax of 37.5 MGOe. The magnetic properties of final magnets have been correlated to the microstructures in flat cast ingots. Columnar grains have been shown to be desirable for achieving higher Br and BHmax in final magnets.
Electromigration in multilayer metallization: Drift-controlled degradation and the electromigration threshold of Al-Si-Cu/TiNxOy/TiSi2 contacts
Authors: Oates A. S.
Published: July 2002

Metallizations that incorporate a conductive layer beneath an Al alloy (multilayers) are necessary for the improvement in electromigration performance required by the continued feature size reduction and increased integration of microelectronic devices. Degradation of contact structures that utilize multilayer metallization will result from electromigration-induced voiding of the Al layer. A detailed understanding of the mechanisms of voiding is required for the accurate prediction of contact reliability. We have examined electromigration voiding in Al-Si-Cu/TiNxOy/TiSi2 multilayer contacts. Accelerated testing reveals that a TiNxOy/TiSi2 layer formed by rapid thermal anneal of Ti is an effective Si diffusion barrier at operating temperatures (<125 °C) and eliminates electromigration-induced leakage failures. Contact degradation occurs by increased resistance due to voiding of the Al-Si-Cu layer. Voiding involves drift-controlled edge displacement where the Al-Si-Cu layer migrates out of positively biased contacts, leaving the TiNxOy/TiSi2 layer intact. For 1-μm-diam contacts, the drift velocity has a significant lattice diffusion component and failure times are expected to far exceed operation lifetimes of devices. Additionally, evidence is presented for an electromigation threshold that eliminates voiding degradation for contacts connected by stripes.
Morphology of hydrofluoric acid and ammonium fluoride-treated silicon surfaces studied by surface infrared spectroscopy
Authors: Niwano M. , Takeda Y. , Ishibashi Y. , Kurita K. , Miyamoto N.
Published: July 2002

Morphologies of Si surfaces treated with aqueous solutions of hydrofluoric acid (HF) and ammonium fluoride (NH4F) have been investigated using surface infrared spectroscopy. We confirm that HF-treated Si(111) surfaces are terminated with a monohydride (Si—H), dihydride (Si—H2), and trihydride (Si–H3), whereas NH4F-treated Si(111) surfaces are dominantly terminated with Si—H. For Si(100), treatment in NH4F produces a surface for which the dihydride mode is enhanced compared to HF treatment, suggesting that surface Si—Si bonds on Si(100) are readily cleaved in a NH4F solution to generate a dihydride Si. The effect of varying the HF concentration on the morphology of HF-treated Si(100) surfaces is investigated. It is demonstrated that 5% HF treatment produces Si(100) surfaces which have a larger density of surface Si—Si bonds than 50% HF or 0.5% HF treatment.