bluuebunny/crossref_metadata_2025 huggingface dataset:
A physical model for random telegraph signal currents in semiconductor devices
Authors: Kandiah K. , Deighton M. O. , Whiting F. B.
Published: July 2002

The model proposed by McWhorter for low-frequency noise in metal-oxide-semiconductor field-effect transistors (MOSFETs) assumed that the 1/f spectrum was due to the sum of the Lorentzian spectra produced by modulation of the channel current by charge state transitions at traps in the adjacent oxide. Considerable evidence for the presence of such current modulation has been accumulated recently. From extensive studies of random telegraph signal (RTS) current waveform in many types of devices we present new results on the dependence of the amplitudes and characteristic times on device geometry, bias, and temperature. Based on these results we propose a comprehensive model for the generation of RTS waveforms in semiconductor devices. The amplitude modulation of a steady current in a device due to the trapping of a carrier at a fixed site is derived by applying an extension of Ramo’s theorem. The characteristic times of the RTS are derived from the properties of the trap, the carrier concentrations, and temperature. The model is applied to the analysis of RTS waveforms in bipolar junction transistors , junction field-effect transistors, and MOSFETs. Experimental results on the dependence of the RTS characteristics on bias and temperature provide validation of the model. It is shown that the intrinsic carrier concentration plays a dominant part in determining the characteristic times in a MOSFET in weak inversion. The problems associated with the application of standard formulas for capture when there is no spherical symmetry around the trap are discussed.
Theoretical analysis of nonlinear optical phenomena taking into account the beating vibration of the electron density in semiconductor lasers
Authors: Yamada Minoru
Published: July 2002

Nonlinear optical phenomena in semiconductor lasers are induced by two types of mechanisms. The first mechanism is beating vibration (i.e., pulsing modulation) on spectral distributions of injected carriers (i.e., electrons and holes) due to lasing frequencies, which is observed as the spectral hole burning effect and whose relaxation is characterized with the intraband relaxation time on the order of 10−13 s. This effect occurs even when the numbers of injected carriers are constant. The second mechanism is beating vibration on the number of injected carriers, whose relaxation is characterized with the electron lifetime on the order of 10−9 s due to band-to-band transition. Master equations including these two nonlinear phenomena are obtained in this paper in a general form based on the density matrix formalism. As examples of the equations, characteristics of the saturated gain profile in a laser oscillator and the four-wave mixing effect (or generation of the phase-conjugate wave) in a traveling-wave laser amplifier are analyzed. A saturated gain profile on optical frequency in a laser oscillator contains both symmetric and asymmetric properties induced by the first and the second mechanisms, respectively, where the strengths of these properties are almost the same. While in the case of the four-wave mixing effect in a traveling-wave laser amplifier, the second mechanism is more effective than the first mechanism. These results coincide well with previous analyses by other authors which treated the above-mentioned phenomena individually.
Interpretation of some experimental observations on a YBa2Cu3O7−x weak link in terms of series grain boundary junctions
Authors: Fan M. H. , Wu P. H.
Published: July 2002

To understand the behavior of a YBa2Cu3O7−x weak link (constriction), a simple model of two Josephson junctions in series with each other is proposed. Electronic simulation of this two-junction array under various conditions generates dc and ac IV curves. Some of these curves duplicate very well what has been observed on a real YBa2Cu3O7−x weak link, while others predict phenomena that have not yet been observed. These results suggest the possible applicability of this model to explain the complicated experimental features of a YBa2Cu3O7−x weak link.
The effect of annealing treatments on defect structure and diffusion lengths in bulk n-type GaAs
Authors: Wong D. , Kim H. K. , Fang Z. Q. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

Specimens from n-type GaAs wafers have been annealed at high temperature (900–1050 °C) and then characterized using deep-level transient spectroscopy (DLTS) and electron-beam-induced current techniques. Relatively short anneals result in substantial changes to the electron trap structure in this material. Diffusion lengths are, at best, marginally increased by short (16 min and below) anneals but have been found to be significantly increased by longer anneals of between 40 and 80 min. DLTS measurements of hole traps in both unannealed and annealed n-type material suggest that a hole trap we term HCX may be an important recombination center in this class of material. The results obtained demonstrate the effectiveness of wafer annealing as a technique for creating a (10 μm deep) near-surface zone in n-type bulk material in which defects are suppressed and diffusion lengths improved.
Magnetic properties of NiMnSb films
Authors: Kabani R. , Terada M. , Roshko A. , Moodera J. S.
Published: July 2002

Thin polycrystalline films of half-metallic ferromagnetic NiMnSb compound have been successfully prepared by simultaneous evaporation of Ni, Mn, and Sb elements onto heated glass and sapphire substrates. X-ray diffraction, Rutherford backscattering spectroscopy, energy-dispersive x-ray spectroscopy, and Auger studies confirmed the quality of the films and surface composition. Magnetization and Kerr rotation obtained for these films agree well with those made on a single crystal of NiMnSb. Using electron tunneling techniques, attempts have been made to measure the conduction electron spin polarization, which is theoretically predicted to be large.
Fe-Co films with an artificially layered structure
Authors: Sato Noboru
Published: July 2002

Fe-Co films deposited in an alternating multilayer structure by a magnetron dc-sputtering method have an artificial superlattice structure with crystallographic coherence between constituent layers. The films are bcc with (110) planes parallel to the film surface. The lattice constant of films is smaller than for bulk Fe and decreases linearly to about 2.81 Å with increasing Co layer thickness. The films are ferromagnetic with an easy magnetization direction in the film plane. The magnetization of multilayer films in comparison with that of Fe-Co alloy films with similar compositions is smaller for films with a thicker Fe than Co layer, and larger for films with a thinner Fe than Co layer. The large magnetization of Fe-Co films is attributed to the large magnetization of bcc-Co in comparison with that of bulk hcp Co.
Formation of β-SiC at the interface between an epitaxial Si layer grown by rapid thermal chemical vapor deposition and a Si substrate
Authors: Kim Ki-Bum , Maillot Philippe , Morgan Alan E. , Kermani Ahmad , Ku Yen-Hui
Published: July 2002

The formation of β-SiC during rapid thermal chemical vapor deposition of an epitaxial Si layer on a (100) Si substrate has been demonstrated using high-resolution cross-sectional transmission electron microscopy and secondary ion mass spectrometry (SIMS) depth profiling. Ellipsoidal β-SiC precipitates (3×10 nm2 average size) were found with a density of (6±1)×109 cm−2 along the epilayer/substrate interface. SIMS revealed about 0.2 monolayer of carbon concentrated at the interface. The precipitates were shown to form during the hydrogen prebake as a result of improper surface cleaning. The crystalline quality of the epitaxial layer, however, was unaffected by the presence of the β-SiC.
Low-frequency characteristic of the enhanced incremental permeability by magnetic shaking
Authors: Sasada I. , Kubo S. , O’Handley R. C. , Harada K.
Published: July 2002

In order to analyze the mechanism of magnetic shaking, the permeability and the energy losses for a small amplitude, low-frequency exciting field are studied under magnetic shaking in comparison with those under the normal condition (without shaking). The permeability and the energy losses were measured for a Metglas 2705M amorphous ribbon wound core by a lock-in technique in the frequency range of 1–20 Hz under both magnetic shaking (2.7 A/m, 1 kHz) and the normal condition. The effects of the magnetic shaking on the domain wall pinning, the mean wall velocity, and the number of the active walls are described. The strong frequency dependence of the enhanced incremental permeability even at low frequency is explained as a result of these effects.
Crisis-induced intermittency in a parametrically driven, gravitationally buckled, magnetoelastic amorphous ribbon experiment (invited)
Authors: Savage H. T. , Ditto W. L. , Braza P. A. , Spano M. L. , Rauseo S. N. , Spring W. C.
Published: July 2002

Transversely annealed amorphous metallic glass ribbons exhibit extremely large magnetoelastic coupling. Consequently, the Young’s modulus of this material can be altered by a factor of 10 with the application of a small magnetic field. This effect is exploited to drive a vertically aligned ribbon, clamped at the bottom and free at the end, by buckling the ribbon gravitationally. Periodic, quasiperiodic, intermittent, and chaotic behavior are observed experimentally. A model for the system is also presented.
Strained superlattices and heterostructures: Elastic considerations
Authors: Anastassakis E.
Published: July 2002

The properties of tensor invariants are used to obtain the complete component array of the strain/stress field and the elastic energy density in strained heterostructures and superlattices of cubic materials. An arbitrary direction of growth is assumed. In-plane isotropic strains or stresses are considered independently. Normal-to-the-plane uniaxial strains are also treated, in connection with pulsed laser annealing of bulk materials. The results are expressed in terms of the elastic constants and simple geometrical functions; they are readily applicable and require no extensive computation. Specific orientations of current interest are treated explicitly.
Growth of epitaxial PrO2 thin films on hydrogen terminated Si (111) by pulsed laser deposition
Authors: Fork D. K. , Fenner D. B. , Geballe T. H.
Published: July 2002

A new epitaxial oxide, PrO2, has been grown on Si (111) by pulsed laser deposition. X-ray diffraction shows that films are oriented with the PrO2[111] direction parallel to the substrate [111]. The full width at half maximum for the omega rocking curve on the PrO2 (222) peak is as low as 0.75°, while phi scans indicate in-plane epitaxial alignment to better than one degree. In the best quality films, epitaxy is almost pure type-b epitaxy which is characteristic of epitaxial CaF2 on Si. To achieve epitaxy, it is essential to remove the native silicon oxide from the substrate prior to film growth. This is done at room temperature using a wet-chemical hydrogen-termination procedure.
Morphology of GaAs homoepitaxial layer grown on (111) A substrate planes by organometallic vapor phase deposition
Authors: Fuek Shunro , Umemura Masasi , Yamada Naoshi , Kuwahara Kazuhiro , Imai Tetsuji
Published: July 2002

Growth behavior of epitaxial layers of GaAs on(111)A plane has been studied for atmospheric pressure organometallic vapor-phase epitaxy.The arsine partial pressure and the growth temperature are the most influential factors for the surface morphology of the epitaxial layers on (111)A planes. A smooth surface morphology is obtained only under limited growth conditions and a higher AsH3 partial pressure is needed to obtain the mirror surface as the substrate temperature increases. This region is found to spread to higher values of arsine pressure by introducing the predeposition process of thin homoepitaxial layers at the most favorable deposition condition.
Birefringence images of screw dislocations viewed end-on in cubic crystals
Authors: Ge Chuan-zhen , Ming Nai-ben , Tsukamoto K. , Maiwa K. , Sunagawa I.
Published: July 2002

The expressions for the intensity distribution in birefringence images and computer-simulated images of a straight, pure screw dislocation with Burgers vector a[111] viewed end-on in cubic crystals have been obtained for the first time by considering the anisotropy of both elastic and photoelastic properties of the material. The effect of elastic and photoelastic anisotropy on birefringence images of screw dislocation viewed end-on has been discussed. And the computer-simulated images have been compared with the experimental images observed in Ba(NO3)2 crystals grown from aqueous solution.
On compensation and conductivity models for molecular-beam-epitaxial GaAs grown at low temperature
Authors: Look D. C.
Published: July 2002

Molecular-beam-epitaxial GaAs grown at 200 °C has an extremely high (≳1019 cm−3) concentration of AsGa defects and, after an anneal at 550–600 °C, a high concentration of As precipitates. The relative roles of the AsGa defects and As precipitates in compensation and conductivity is controversial. Here criteria are developed to distinguish between two existing models.
Laser spectroscopy of ground-state scandium ions in a high-pressure metal halide discharge I. Saturated laser-induced fluorescence
Authors: Kramer Jerry
Published: July 2002

Ground-state scandium ions in a vertically burning 60-Hz high-pressure metal halide discharge were detected by saturated laser-induced fluorescence (LIF). Scandium ions were excited with a pulsed dye laser at 363.1 nm from the a3D2 spin-orbit component of the ground state (68 cm−1 above the ground state) to the z3F03 state. The laser-induced fluorescence, observed at 440.0 nm (z3F03 → a3F3), was optically thin. The Sc+ LIF profiles along a diameter were asymmetric about the center, with a local minimum near the axis, and maxima at about ±2 mm (radius=6.5 mm). The profiles varied with axial position and lamp power. The LIF Sc+ signals are modulated during the ac phase angle. At the discharge axis the maximum signals occur just after the current zero crossings (near the voltage reignition spikes) and the minima just after the current maxima. LIF was also observed from other nearby excited electronic states of Sc+, populated by collisions. From the positional dependence of the ratio of the fluorescence at 437.5 (z3F04(z3F04→ a3F4) to 440.0 nm we suggest that neutral scandium atoms are responsible for the collisional energy transfer.
Three-dimensional theory to study photothermal phenomena of semiconductors. II. Modulated photothermal deflection
Authors: Cheng Jian-chun , Zhang Shu-yi
Published: July 2002

The investigation is further extended to the modulated photothermal deflection (PTD). The three-dimensional Navier–Stokes equation is solved analytically for a layered-structure sample, and then numerical calculations are given. The influences of the optical, thermal, and electronic parameters on the PTD signal are discussed in detail. It is shown that the thermal lens and electronic-strain effects make significant contributions to the PTD signal, but the thermoelastic effect is dominant. The potential applications of the PTD technique to microscopic imaging are discussed.
Magnetic properties of Fe/Tb multilayers
Authors: Badía F. , Badry M. A. , Zhang X. X. , Tejada J. , Brand R. A. , Scholz B. , Keune W.
Published: July 2002

Multilayered Fe/Tb samples were prepared under ultrahigh vacuum conditions (p<10−9 mbar) on kapton substrates. A total of four different samples were prepared. Three of them correspond to a series where the Tb thickness is constant at 26 Å and Fe varies from 10 to 30 Å. The fourth one is the first of a new series where Tb is 7 Å thick and Fe 40 Å. The samples were investigated by means of SQUID magnetometry and Mössbauer spectroscopy. All samples show perpendicular magnetic anisotropy at low temperature (4.2 K), but only two of them are able to show it at room temperature.
Application of CdTe epitaxial layers for passivation of p-type Hg0.77Cd0.23Te
Authors: Sarusi G. , Cinader G. , Zemel A. , Eger D. , Shapira Yoram
Published: July 2002

We have investigated the properties of CdTe/Hg0.77Cd0.23Te heterostructures in order to evaluate the use of thin CdTe cap layers for passivation of the HgCdTe surfaces. The energy band diagram across the interface of this structure was calculated using Anderson’s model. It is found that flat or near flat band conditions can be obtained by using p-type CdTe with carrier density in the range of 1014–1015 cm−3. CdTe/Hg0.77Cd0.23Te heterostructures were grown on CdTe (211)B oriented substrates using the metalorganic chemical vapor deposition technique. The interface properties of CdTe/HgCdTe were investigated by a combination of Hall and photoelectromagnetic effect measurements as a function of temperature, magnetic field, and light illumination wavelength. Interface recombination velocities of less than 5000 cm/s were obtained at 77 K for heterostructures grown under proper conditions. These values are more than two orders of magnitude lower than those obtained for freshly Br:methanol etched HgCdTe surfaces. These results demonstrate that CdTe cap layers may be used as a good passivation of HgCdTe surfaces.
Fabrication of GaAs quantum wires on epitaxially grown V grooves by metal-organic chemical-vapor deposition
Authors: Tsukamoto S. , Nagamune Y. , Nishioka M. , Arakawa Y.
Published: July 2002

Successful fabrication of thin GaAs quantum wires (120–200 Å)×(200–300 Å) by a novel metal-organic chemical-vapor-deposition growth technique is reported. The GaAs quantum wires were grown on a V groove formed by two GaAs triangular prisms which were selectively grown on SiO2 masked substrates. The V groove has a very sharp corner at the bottom, which results in reduction of the effective width of the quantum wire structures. The measurement of photoluminescence and photoluminescence excitation spectra with polarization dependence indicate the existence of the quantized state in the quantum wires.
Pyro-optic studies for infrared imaging
Authors: Li Jie-Fang , Viehland D. , Bhalla A. S. , Cross L. E.
Published: July 2002

The temperature dependence of the complex refractive indices of SbSI, MoS2, and BiVO4 have been investigated using spectroscopic ellipsometry. The wavelength of maximum temperature dependence was identified for an in depth study of the sensitivity of the reflectance coefficient to a small ac temperature modulation. It was found feasible to detect temperature changes of 10−3, 10−2, and 10−2 °C by monitoring the reflectance coefficient of SbSI, MoS2, and BiVO4, respectively, using null ellipsometry. It is thus possible to use the pyro-optic phenomena for long wavelength infrared imaging, analogous to pyroelectrics.
Growth rates of current-excited plasma waves in semiconductor layered systems
Authors: Xie H. , Kempa K. , Bakshi P.
Published: July 2002

We study the growth rates of current-driven plasma waves in semiconductor layered systems. We compare amplification performance of different layered systems, as well as investigate in detail the effects of various material parameters on the growth rates. This analysis provides guidelines for selecting the best systems for possible device applications.
Crystallographic and structural analyses of perpendicular magnetic Co-Pt-B-O alloy films
Authors: Murakami Yousuke , Yamamoto Tetsuya , Okabe Akihiko , Yanada Tetsunosuke , Hayashi Kazuhiko , Aso Kouichi
Published: July 2002

CoPtBO reactive sputtered film is a new type of perpendicular recording media material with high perpendicular anisotropy fields and large perpendicular coercivities. To understand the origin of the magnetic properties, several materials parameters were explored. These included the effects of the introduced oxygen on the crystal structure, as well as the orientations and the microstructure of the CoPtBO films. With increasing the oxygen partial pressure, the crystallographic structure of CoPtBO alloy films were changed from face-centered-cubic (111) texture into hexagonal-close-packed (hcp) (001) texture. Pole figure analysis is a useful method to identify the crystalline structure of the oriented films. The strong hcp (001) texture and separation of the magnetic grains are the origin of the high Hk and large Hc of the films.
Synthesis of high moment and high coercivity iron nitride particles
Authors: Bao Xiaohua , Metzger Robert M. , Doyle William D.
Published: July 2002

Fe2N particles were prepared by nitriding acicular γ-Fe2O3 particles (precoated with sodium silicate to prevent the particles from sintering) at about 450 °C for 3–6 h under a mixed stream of H2-NH3 (1:4 molar ratio). X-ray diffraction showed mostly Fe4N and small amounts of α-Fe and Fe2O3, but no Fe8N(α″-Fe16N2). The saturation magnetic moment density σS increased to 140–160 emu/g and the coercivity Hc increased to about 1000 Oe. Although the ultimate goal of preparing Fe8N particles was not attained, an impressive combination of magnetization and coercivity was achieved. To obtain Fe8N by chemical doping, the nitrogen content of Fe4N was decreased by coating with metal hydroxides of Ti, Nd, and Sm, and reducing under H2 at 300 °C: the magnetization dropped precipitously, and no Fe8N was formed.
Direct measurement of permeability up to 3 GHz of Co-based alloys under tensile stress
Authors: Acher O. , Vermeulen J. L. , Lucas A. , Baclet Ph. , Kazandjoglou J. , Peuzin J. C.
Published: July 2002

The high frequency permeability of CoNbZr and CoZrMoNi prepared by magnetron sputtering, and of CoFeSiB deposited by ion beam sputtering was investigated. The layers were deposited on thin (8–12 μm) mylar films, and it was therefore possible to induce large tensile stress with moderate force. The permeability of the layers was measured along the stress direction, in a frequency range that allowed the observation of the rotational permeability and the gyromagnetic resonance. The resonance frequency of CoNbZr shifted from 1.4 to over 3 GHz under stress. A simple model assuming that the easy axis is constant over the whole film predicts the evolution of resonance frequency and initial permeability. This model is in good agreement with measurements on CoZrMoNi, and yields a satisfactory estimation of the magnetostriction coefficient. In the case of CoNbZr, a poorer agreement is attributed to the dispersion of local magnetization direction. For very large stress, cracks in the ferromagnetic films are expected to participate to the increase in the anisotropy field. It was observed that the linewidth of the resonance is slightly affected by the stress.
Time-evolved numerical simulation of a two-dimensional electron wave packet through a quantum double slit
Authors: Endoh Akira , Sasa Shigehiko , Arimoto Hiroshi , Muto Shunichi
Published: July 2002

We performed time-evolved numerical simulation of a two-dimensional electron wave packet through a double slit by solving the time-dependent Schrödinger equation using the finite difference method to simulate the electron interference phenomenon of a single electron. The propagating directions of interference peaks show that the starting point of electron interference is the center between the two slit exits. The number of interference peaks and their angles are found to be independent of potential barrier thickness. These results are compared with the results of our previous calculation of electron diffraction through a single slit.
Electric-field-induced refractive index changes in three-step asymmetric coupled quantum wells
Authors: Susa Nobuhiko
Published: July 2002

A scheme for enhancing the refractive index change Δn in the wavelength region longer than that for an n=1 heavy-hole exciton peak, where the absorption coefficient α is small, is proposed and three-step GaAs/AlGaAs quantum wells (QWs) are numerically analyzed as an example. The basis of this scheme is that an electric-field-dependent oscillator strength can be controlled by designing a QW structure which yields either positive or negative absorption change, Δα at all wavelengths, resulting in an increase in the Δn in the longer wavelength region and a reduction in the operating electric field. The numerical analysis predicts that the electric field for the three-step QW that yields a Δn of ∼10−2 is as small as 5–15 kV/cm which is about one order of magnitude smaller than that for a conventional square-potential QW. In addition, the Δn and the figure-of-merit, which is defined as Δn/α, are larger than those for the conventional QW in the longer wavelength region.
Optically stabilized, constant-height mode operation of a magnetic force microscope
Authors: Proksch Roger , Dahlberg E. Dan
Published: July 2002

An optical technique for constant-height mode scanning force microscopy has been developed. This approach allows the sample-tip spacing to be held constant or varied in a quantitative manner during data acquisition. The technique uses an all-fiber interferometric system extended to include two optical cavities: one between the fiber and the cantilever and a second between the fiber and the sample surface. It is necessary that the cantilever be semitransparent or that the fiber be positioned over the edge of the cantilever. It has been experimentally verified that either case allows sufficient laser light for both the cantilever-fiber and the sample-fiber cavities. This method can be used to monitor the time dependence of surface forces, magnetic or electric phase transitions, or as a height calibration for use with scanning force microscopy. As a demonstration of the technique, spatially localized observations of the ferromagnetic phase transition in a gadolinium film are presented. During this observed phase transition, the tip-sample separation was held constant at 1000 nm with a drift of only 3 nm, nominal, for 15 min while the temperature was cycled between 285 and 295 K.
Optical properties of highly strained CdSe/ZnSe quantum wells
Authors: Shan W. , Hwang S. J. , Hays J. M. , Song J. J. , Zhu Z. Q. , Yao T.
Published: July 2002

We present a study of the optical properties of highly strained CdSe/ZnSe quantum well system. A variety of CdSe/ZnSe samples containing single quantum well or multiple quantum wells grown by molecular beam epitaxy has been studied by using low-temperature photoluminescence (PL), photoluminescence excitation, and photoreflectance measurements. The strong PL signals associated with excitonic emissions from the samples show that the CdSe/ZnSe heterostructure system is promising in the development of laser diodes and light-emitting diodes operating in the blue-green range. Linewidth narrowing of PL spectra with decreasing well width is observed and attributed to alloy formation at the interface due to lateral interdiffusion. The PL signal intensities and the pressure coefficients of interband transitions are also found to depend on the well width, which can be explained in terms of strain relaxation induced misfit dislocations and the critical thickness in the heterostructure system. Our results suggest that the critical thickness for a CdSe layer coherently grown on ZnSe is less than four monolayers.
Hybrid resonant/near-resonant photorefractive structure: InGaAs/GaAs multiple quantum wells
Authors: Wang Q. N. , Nolte D. D. , Melloch M. R.
Published: July 2002

A photorefractive structure was grown which was composed of shallow In0.1Ga0.9As/GaAs quantum wells on a photorefractive GaAs substrate. The quantum-well exciton energy is adjusted with In content to coincide with the optimum photon energy for near-resonant photorefractive effects in the substrate. The photorefractive quantum wells also operate as thin holographic gratings in four-wave mixing without the removal of the substrate, simplifying the fabrication of photorefractive quantum-well devices.
Two coupled parabolic wells under an electric field
Authors: Shen W. P. , Rustgi M. L.
Published: July 2002

The tunability of the states of two coupled parabolic quantum wells subjected to an electric field is studied by using the transfer-matrix approach. Two numerical procedures are used. Both involve subdividing the potential profile into a number of linear or step partitions. For the linear partition approach, the Airy function solution of the Schrödinger equation is employed while for the step approach, the plane-wave solution is used. Both methods give identical results if small enough partition intervals are used. It is found that the plane-wave method is easier and that it simplifies the programming without seriously sacrificing the calculational speed. The coupled well width, the barrier width, and the applied field were changed systematically to study the changes in the energy levels, wave functions, and transmission of a resonant tunneling diode based on the double parabolic structure. The anticrossing between the energy levels on changing the well width or the bias of the coupled wells is seen and discussed. It is also found that the transmission peak is sharp and deep if the resonance occurs in both of the coupled wells at the same energy, while it is smaller and broader if the resonance occurs in only one well because the wave function is blocked by the other nonresonant well.
Al–Ga interdiffusion, carbon acceptor diffusion, and hole reduction in carbon-doped Al0.4Ga0.6As/GaAs superlattices: The As4 pressure effect
Authors: You H. M. , Tan T. Y. , Gösele U. M. , Lee S.-T. , Höfler G. E. , Hsieh K. C. , Holonyak N.
Published: July 2002

Al–Ga interdiffusion, carbon acceptor diffusion, and hole reduction were studied in carbon doped Al0.4Ga0.6As/GaAs superlattices (SL) annealed under different ambient As4 pressure conditions in the temperature range of 825 °C–960 °C. The SL were doped with carbon to an initial acceptor concentration of ∼2.9×1019 cm−3. Al–Ga interdiffusion was found to be most prominent under Ga-rich annealing ambient conditions, with interdiffusivity values, DAl–Ga, turned out to be about two orders of magnitude smaller than those predicted by the Fermi-level effect model. Under As-rich ambient conditions, the DAl–Ga values are in approximate agreement with those predicted by the Fermi-level effect model. The hole concentrations in the SL decreased significantly after annealing under As-rich and As-poor ambient conditions, while those after annealing in the Ga-rich ambient were almost totally intact. By analyzing the measured hole concentration profiles, it has been found that both carbon acceptor diffusion and reduction have occurred during annealing. Both the carbon acceptor diffusivity data and the carbon acceptor reduction coefficient data are characterized approximately by a dependence on As4 pressure values to the one-quarter power. These As4 pressure dependencies indicate that carbon diffuses via the interstitialcy or interstitial–substitutional mechanism, while hole reduction is governed by a carbon acceptor precipitation mechanism.
Dy3Fe5O12 garnet thin films grown from sputtering of metallic targets
Authors: Ostoréro J. , Escorne M. , Pecheron-Guegan A. , Soulette F. , Le Gall H.
Published: July 2002

Dysprosium iron garnet Dy3Fe5O12 (DyIG) thin films have been synthesized by postoxidizing at a temperature Tox (400 °C<Tox<1100 °C) of rf sputtered amorphous Dy-Fe metallic films. The sputtering conditions strongly influence the growth, the composition and magnetic and magneto-optic properties of the oxidized films. Pure DyIG films, free of DyFeO3, are synthesized at Tox∼1000 °C. Magnetic and Faraday rotation (FR) experiments at three wavelengths (543.5, 632.8, and 1152 nm) were performed on DyIG films in the 4–300 K temperature range, as a function of magnetic field up to 20 kOe perpendicular to the film plane. Magnetization and FR data are in good agreement with results obtained on bulk DyIG materials. Temperature dependent coercivity is observed with a discontinuity in the vicinity of the compensation temperature (Tcomp∼225 K). The temperature variations of the spontaneous FR values for the three wavelengths are interpreted on the basis of contributions proportional to the magnetization of each sublattice.
Analysis of write and read spacing loss for perpendicular recording (abstract)
Authors: Tanaka Yoichiro , Komai Tomoko , Hikosaka Takashi
Published: July 2002

Spacing loss phenomena for perpendicular recording have been experimentally investigated but are yet analytically unclear. This paper provides an analytical model of the write and read processes for perpendicular recording to study spacing loss. In the write process, the magnetic transition length is determined mainly by the head field gradient and demagnetizing field gradient at transition assuming perfectly square M-H loops of the perpendicular media. An arctangent transition is a reasonable approximation just in the process of creating transitions under a single-pole-type write head field. Decreased magnetization, however, between transitions due to a strong demagnetizing field has to be involved to simulate the write process more accurately. A double arctangent transition model is newly proposed to represent both a sharp transition and magnetization decay away from transition which is supposed to change the transition length after writing. Magnetization decay is characterized by a maximum demagnetization limit (Hd<Hc) near the transition. Write spacing loss (=Kw d/λ [dB]) is derived from the derivative of double arctangent transition length in terms of spacing. Read spacing loss (=Kr d/λ [dB]) is characterized by both exp(−2πd/λ) and the head-to-media magnetic interaction parameter η as a function of spacing. Experimental proof is shown with double-layer perpendicular media and single-pole-type flying heads. Write and read spacing is independently controlled by the air pressure of the vacuum chamber enclosing the spinstand. It has been found that the write spacing loss factor Kw depends on the head field distribution and wavelength. Measured Kw values showed a maximum value of −110 [dB] at short wavelength where magnetization decay is considered to give little effect. Kw decreased with wavelength as the calculated loss factor behaved. The wavelength dependence of the read spacing loss factor Kr has been found to quantify the strength of the head-to-media magnetic interaction.
Reptation and viscosity in particulate recording media in the time-limited switching regime
Authors: Doyle W. D. , Varga L. , He L. , Flanders P. J.
Published: July 2002

Measurement of P, the percentage reduction in remanence after the application of 1≤n≤104 reverse field pulses of width 0.6 ns ≤ τ ≤9 ns, are reported for five particulate tape samples including γ-Fe2O3, Co-γFe2O3, Fe, and two different barium ferrites. For τ≳τc, P depended only on nτ. It increases quite rapidly at small values of nτ depending on the media and then at higher values of nτ approximately linearly with log(nτ). In the linear regime, the decrements δ (% change/decade) agree within experimental error with the quasistatic values obtained from viscosity measurements between 10 and 100 s. Considering the arbitrariness of the logarithmic assumption, it is remarkable that the decrement is the same over eleven orders of magnitude. The reduction in P at τ<τc is evidence for time-limited switching as reported previously. However, the dependence of P on nτ for small nτ cannot be explained by the usual viscosity model but is consistent with reptation, a phenomenon suggested by Néel.
The effect of thermal annealing on GaN nucleation layers deposited on (0001) sapphire by metalorganic chemical vapor deposition
Authors: Wickenden A. Estes , Wickenden D. K. , Kistenmacher T. J.
Published: July 2002

It has been shown by optical and x-ray measurements that GaN nucleation layers deposited at 540 °C on (0001)-oriented sapphire substrates have a measurable crystalline component, although the x-ray data and the lack of absorbance features near the direct band gap of GaN suggest that the crystallite size is very small. Upon annealing to higher temperatures, the crystallite size increases and the crystal perfection improves markedly, until at temperatures near those empirically determined to be optimum for growth of an epitaxial overlayer, it approaches that of good quality single-crystal material. Most of the recrystallization of the nucleation layer occurs during the ramp from its deposition temperature to the growth temperature of the GaN overlayer, and there appears to be no advantage to prolonged annealing at high temperatures prior to epitaxial growth. In fact, x-ray diffractometer results suggest that the nucleation layer deteriorates after 20 min at temperatures above 1015 °C, under the conditions used in this study.
Optical study of strained ZnSe/GaAs and ZnMnSe/GaAs epilayers
Authors: Chou W. C. , Twardowski A. , Chern-Yu K. , Chen F. R. , Hua C. R. , Jonker B. T. , Yu W. Y. , Lee S. T. , Petrou A. , Warnock J.
Published: July 2002

We studied strain-induced band splittings of ZnSe/GaAs and Zn1−xMnxSe/GaAs epilayers of 0.064–3 μm thickness by reflectance and polarized photoluminescence. Polarized photolumi- nescence was found particularly useful in optical transition identification. The spectacular difference in magnetic field sensitivity of heavy hole and light hole exciton in ZnMnSe is also very helpful in transition identification. The evaluated heavy-light hole band splitting is in general accordance with previous data. An exceptionally strong variation of the strain with epilayer thickness is observed in the thickness range 0.5–2 μm.
The origin of quantum efficiencies greater than unity in a-Si:H Schottky barriers
Authors: Rubinelli F. A.
Published: July 2002

A photogating effect, recently predicted with computer simulations and subsequently observed in a-Si:H p-i-n structures, is shown to be also present in a-Si:H Schottky barrier devices. it is experimentally demonstrated that this photogating effect can be so significant that it can lead to quantum efficiency values greater than unity in Schottky barrier a-Si:H devices even in the annealed state. This photogating effect is found to be present under blue bias light and, for the annealed state, at low forward biasing conditions. Using our computer simulations, we show that, as in p-i-n devices, this photogating effect is caused by modulation of the field with blue bias light present near the front contact. We show also that this photogating effect is dependent on material and device parameters.
Study of the effect of defect sizes and their distribution on the coercivity of magnetic media
Authors: Jatau James A. , Della Torre Edward
Published: July 2002

The nature of domain-wall motion coercivity in magnetic media is studied using a two-dimensional numerical micromagnetic model. It is necessarily assumed that the source of the coercivity is cylindrical anomalies in the material that have anisotropy or exchange parameters which are either larger or smaller than that of the surrounding media. Varying these parameters from those required to obtain the observed coercivity shows that a larger decrease in either parameter is required to obtain the same change in coercivity as a given increase. Thus, the dependence of coercivity on these parameters is nonlinear. It was also found that the computed coercivity decreases with an increase in the separation of the defects, and increases with an increase in defect size. It is shown that a correction for the calculated coercivity is required to account for the statistical distribution in defect sizes and locations. Finally, a suitable variation in the defect parameters can accurately characterize the temperature behavior of the coercivity.
Creep-induced magnetic anisotropy in a Co-rich amorphous wire
Authors: Kraus L. , Vázquez M. , Hernando A.
Published: July 2002

Magnetic anisotropy of amorphous (Fe0.06Co0.94)72.5Si12.5B15 wire induced by current annealing under applied stress is investigated. The anisotropy constant is determined either from the axial or circular ac hysteresis loop, depending on the sign of the anisotropy constant. At low annealing temperatures and short annealing times weak easy-wire-axis anisotropy is observed. With increasing time and temperature of annealing hard-wire-axis anisotropy develops. Relaxation annealing without stress causes change of the sign of anisotropy constant. The induced anisotropy, however, is fully reversible indicating that plastic strain does not contribute to creep-induced magnetic anisotropy. A simple bond-orientational-anisotropy model, proposed to explain the observed behavior, assumes that competition between opposite contributions of two different kinds of excess atomic bonds is responsible for creep-induced anisotropy of this alloy.
Effect of microstructure of YBa2Cu3Ox films on power handling capability studied with microstrip resonators
Authors: Yoshitake T. , Tsuge H. , Inui T.
Published: July 2002

Microwave properties of two types of YBa2Cu3 Ox (YBCO) films with different microstructure have been studied at 4.2 K and 6 GHz. One type of film was grown at a constant substrate temperature of 705 °C during the film growth (constant-growth films). The other type of film ws prepared with two-stage process: initial growth at a lower temperature of 630 °C and subsequent higher-temperature deposition at 705 °C (two-stage-growth films). Although both types of film have very similar intrinsic YBCO material properties such as c-axis lattice constant, Tc, and unloaded quality factor Qu at low power levels, quite different microwave properties are observed at high power levels. The two-stage-growth films with small grains less than 100 nm show fairly small power dependence of Qu and resonance frequency on input power up to +10 dBm. On the other hand, the constant-growth films with large grains (∼200 nm) show significant changes in these properties, accompanied by an appearance of asymmetric resonance curves. These results show that the power handling capability of granular YBCO films is mainly affected by the extrinsic film microstructure and that the quality of the grain boundaries causes the difference in power dependence.
Effects of temperature and filament poisoning on diamond growth in hot-filament reactors
Authors: Dandy David S. , Coltrin Michael E.
Published: July 2002

The growth of diamond in a hot-filament reactor has been modeled, and compared with existing experimental data. Studies have been carried out on non-growth systems containing only hydrogen, as well as on systems where the methane concentration at the inlet was varied between 0.4% and 7.2%. The one-dimensional stagnation flow model used here includes detailed gas-phase and surface kinetics. A simple model of filament poisoning has been implemented. The effect of the gas/filament temperature discontinuity on species distributions has also been examined. Gross errors between theory and experiment are obtained when filament poisoning is neglected, but good agreement is found using a simple linear poisoning model. A nonzero temperature discontinuity at the filament produces good overall agreement with experiment.
Precise evaluation of deep-level concentrations in capacitance transient analyses
Authors: Shiraki H. , Tokuda Y. , Sassa K. , Toyama N.
Published: July 2002

A detailed treatment of space-charge and free-carrier densities is proposed to precisely analyze deep-level concentrations by using capacitance transient measurements. This treatment is very effective for analysis of midgap levels, if thermally activated carriers from other defect levels play an important role in the free-carrier density. The application of this analysis to evaluation of the midgap defect in bulk GaAs materials is demonstrated.
Magnetic hardening by crystallization of amorphous precursors using very high heating rates
Authors: de Julián C. , González J. M. , Morón C.
Published: July 2002

The dependence of the treatment parameters of the coercivity of PrNdFeB samples prepared by crystallization of melt spun amorphous precursors is investigated. The crystallization treatments were carried out at high temperatures and using very high heating rates (‘‘flash crystallization’’). From the analysis of the temperature dependence of the critical field of the samples, it is concluded that this kind of crystallization treatment leads to very fine and homogeneous microstructures which result in a significant enhancement of the hard magnetic properties.
Oxide trap relaxation spectroscopy: A new difference method to determine trap in oxidized silicon
Authors: Tan Changhua , Xu Mingzhen , Liu Xiaowei , He Yandong , Wang Yangyuan
Published: July 2002

A difference analysis method has been presented to separate and characterize interface and oxide traps generated in the metal–oxide–semiconductor structure under Fowler–Nordheim stress. The oxide trap relaxation measurement has been performed in dynamic voltage mode. For a high constant voltage stress condition, the effective oxide traps can be obtained by the difference Fowler–Nordheim current relaxation characteristics. For a low-voltage condition, the interface and effective oxide traps can be separated and determined by the difference subthreshold voltage relaxation characteristics. Using combined difference Fowler–Nordheim current and subthreshold voltage measurements, the density, centroid, and generation/capture cross section of the oxide traps can be obtained without the double current–voltage technique, thus permitting more accurate and quick measurement of the generated oxide traps. All difference Fowler–Nordheim current and subthreshold voltage versus the electron-fluence characteristics exhibit spectrum features. Analytical expressions for computing the interface and oxide traps have been derived and experimental results have been presented for a Fowler–Nordheim tunnel metal–oxide–semiconductor structure. Two interface and two oxide traps generated at Fowler–Nordheim stress have been obtained by the new technique.
Angular distributions of 12C, 14N, and 16O ion elastic scattering by sulfur near the Coulomb barrier and the high-energy limits of heavy-ion Rutherford scattering
Authors: Räisänen J. , Rauhala E.
Published: July 2002

Elastic scattering of 12C, 14N, and 16O ions by sulfur has been investigated near the non-Rutherford energy threshold below 31 MeV. Angular distributions in the range 72°–170° have been measured. Decreasing elastic scattering cross sections with increasing angle above a threshold energy and smooth oscillations were observed. As a function of energy, the cross sections fall off rapidly above the threshold energy, rendering heavy-ion backscattering spectrometry practically useless. A classical semiempirical model is introduced for predicting the angular and target dependence of the high-energy limit for 12C, 14N, and 16O ion Rutherford backscattering spectrometry. The present energy thresholds are reproduced by the model within experimental accuracy.
Chemical aspects in copper-implanted fused silica and soda-lime glasses
Authors: Bertoncello R. , Trivillin F. , Cattaruzza E. , Mazzoldi P. , Arnold G. W. , Battaglin G. , Catalano M.
Published: July 2002

Fused silica and soda-lime glasses were implanted with copper, copper+nitrogen and copper+argon. Samples were characterized primarily by x-ray photoelectron spectroscopy and x-ray-excited Auger electron spectroscopy. Measurements of optical absorption, transmission electron microscopy, secondary-ion mass spectrometry, and Rutherford backscattering spectrometry were also carried out. Copper nanocluster formation and their size have been found to depend on the reactivity of the host vitreous matrix as well as on the implanted metal concentration. In the copper+nitrogen-implanted fused silica a chemical interaction between copper and nitrogen together with the dissolution of the metallic nanoclusters has been observed. In the copper+nitrogen-implanted soda-lime glass interactions between substrate and nitrogen occur without the dissolution of copper precipitates. The dissolution of copper clusters is induced in the soda-lime glass when implantation with argon (which does not chemically react with the host glass substrate) is made.