bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of YBa2Cu3AgxO7−δ composite superconductors
Authors: Ganapathi L. , Kumar Ashok , Narayan J.
Published: July 2002

Superconducting properties and microstructures of the YBa2Cu3AgxO7−δ composites have been studied as a function of silver content, 0<x<6, using a variety of techniques. The superconducting transition temperature Tc of these composites was found to be the same, ∼90 K, for the above range of composites. For values of x>3, small quantities of 211 phase were detected along the grain boundaries. Alloy formation between Ag and Cu is proposed to take place which makes the residual composition poor in copper, resulting in the formation of nonsuperconducting 211 phase. The silver is observed in the form of precipitates at very low concentrations of silver, indicating that silver does not substitute for copper in YBa2Cu3O7. Lattice parameters of the composites were found to be invariant throughout the above composition range. The addition of Ag2O in the starting composition seems to stabilize the stoichiometric YBa2Cu3O7 by way of decomposition to Ag and O. As a result, the incorporation of oxygen and recovery of superconducting properties is enhanced in the silver composites.
Temperature effect on a tilted birefringent filter in a tunable laser: A limitation for Raman spectroscopy
Authors: Burneau A. , Humbert B.
Published: July 2002

The temperature effect on the wave number selected by a tilted birefringent filter inside a dye laser cavity is measured and theoretically discussed. For a quartz plate at Brewster angle, the wave-number shift is observed between 1.1 and 1.35 cm−1 K−1 according to the angle between the crystal optical axis and the incident plane. A thorough calculation is fully in agreement with these results: the main part of the shift is related to the variation of refractive indices, but both the thickness expansion and the wavelength disperson of indices moderate the temperature effect. The observed shift is still larger than the width at half height of the exciting line necessary for Raman spectroscopy. A filter with three plates whose thicknesses are in ratio 1:4:16, which transmits a band of satisfactory width, cannot be used however if a rigorous temperature stability is not achieved. A practical solution is found by combining a 1:4 filter and a Fabry–Perot étalon.
Raman studies of crystal perfection in mercury cadmium telluride wafers
Authors: Hill Ian
Published: July 2002

Resonant second-order Raman scattering of zone-center longitudinal-optical phonons [2LO(Γ)] in Hg0.8Cd0.2Te and Hg0.7Cd0.3Te is reported. Three 2LO(Γ) components are seen, which are assigned as LO1+LO1, LO1+LO2 and LO2+LO2 combinations (where 1 denotes CdTe-like and 2 denotes HgTe-like). The intensity of these bands is very sensitive to crystal damage, making this a very useful probe of near-surface crystal order. The detection of Te inclusions by Raman microscopy is reported and a variation in peak position is attributed to different inclusions being under varying tensile strain. Bromine-methanol etching of Hg1−xCdxTe is shown to lead to a buildup of Te on the surface, while an increase in intensity of the 2LO(Γ) modes of the Hg1−xCdxTe reflects removal of surface damage.
Defect clusters in zinc oxide
Authors: Simpson J. C. , Cordaro J. F.
Published: July 2002

We present new evidence that two electron traps observed in polycrystalline zinc oxide can be associated with complex intrinsic defects. One deep level, E1, can be assigned to an oxygen vacancy. The second deep level, E2, could consist of a cluster-type defect associated with oxygen vacancies. The two traps were characterized using deep-level transient spectroscopy. The energies of these traps are 0.15 and 0.24 eV, the capture cross sections are 4×10−18 and 1×10−17 cm2, and the emission rates at 300 K are 2.0×106 and 1.3×105 Hz, respectively. The relative concentrations of these traps varied uniformly as a function of the cooling rate of the zinc oxide from a sintering temperature of 1300 °C. The concentration of E1 decreased, while the concentration of E2 increased, with decreasing cooling rate.
Explanation of orientation patterns determined for sheet materials by means of microwaves
Authors: Osaki Shigeyoshi
Published: July 2002

Unstretched, biaxially stretched, and uniaxially stretched poly(ethylene terephthalate) (PET) films showed different types of three-dimensional pattern, i.e., the frequency and angular dependencies of transmitted microwave intensity. The resonance frequency and the intensity at the resonance frequency for the biaxially and uniaxially stretched PET films changed with rotation angle, while those for the unstretched PET films stayed unchanged. Thus these properties reflected the dielectric anisotropy of the polymer films. The angular dependence of transmitted microwave intensity at a fixed frequency, i.e., the orientation pattern, gave an orientation angle and a maximum-to-minimum ratio of transmitted microwave intensity. The orientation pattern can be obtained by cutting the three-dimensional pattern at the fixed frequency. This frequency should be selected above the resonance frequency, where the transmitted microwave intensity is one-half that at the resonance frequency in the resonance curve which is located at the low-frequency side. The fixed frequency so chosen is most appropriate, since the maximum-to-minimum ratio and the orientation angle are most sensitive around it. The molecules in polymer films are arrayed on an average in the direction specified by the orientation angle where the transmitted microwave intensity is the smallest because of the shift of the resonance curve to the low-frequency side. The orientation pattern reflecting the dielectric anisotropy is very convenient for determining the orientation of molecules or fibers quickly and nondestructively.
Radiation-induced charge neutralization and interface-trap buildup in metal-oxide-semiconductor devices
Authors: Fleetwood D. M.
Published: July 2002

Effects of switched bias on the radiation response of metal-oxide-semiconductor (MOS) devices have been investigated. Transistors with 50-nm gate oxides were irradiated at +10-V bias to create a large trapped-hole density in the oxide. Irradiation was continued under varying negative and positive biases. Very little radiation-induced charge neutralization is observed at biases <−10 V for these devices. However, significant trapped-hole neutralization is observed at biases from −10 to 0 V, with a broad maximum in neutralization rate from −6 to −1 V. The peak charge neutralization rate is approximately equal to the rate of trapped-hole buildup under positive bias. This establishes an upper bound on the rate of radiation-induced charge neutralization, and demonstrates that, under peak neutralization conditions, the effective cross section for the capture of radiation-induced electrons by a filled hole trap is similar to the effective cross section for capture of a hole by an empty trap. Interface traps are found to build up at approximately the same rate when the oxide electric field at the Si/SiO2 interface is positive, regardless of the field direction in the bulk of the oxide. This suggests that near-interfacial hydrogen may play a key role in interface-trap buildup in MOS devices.
An x-ray photoemission spectroscopy investigation of oxides grown on AuxSi1−x layers
Authors: Cros A. , Saoudi R. , Hollinger G. , Hewett C. A. , Lau S. S.
Published: July 2002

X-ray photoemission spectroscopy was used to analyze the oxide grown at low temperature on AuxSi1−x films. It was found that the oxide is stoichiometric SiO2, but is structurally distinct from oxides grown on Si at high temperatures (950 °C). Also, unoxidized Au-Si atom inclusions were observed in the oxide. The composition of the inclusions is dependent on the initial bulk AuxSi1−x composition.
Anomalous effects on the current-voltage characteristics of p-channel metal-oxide-semiconductor transistors in the temperature range 4.2–50 K
Authors: Nassiopoulos A. G. , Tsamakis D. , Rocofyllou E.
Published: July 2002

The current-voltage characteristics of p-channel MOSFETs (metal-oxide-semiconductor field-effect transistors) in the temperature range 4.2-50 K have been investigated in detail. A peak is observed at the beginning of the drain-current–drain-voltage (Id, Vd) curves for low Vg values, which is not observed in the case of n-channel MOSFETs and is found to be a very slow transient effect. This time-dependent peak is observed for temperatures below ∼25 K and for channel lengths greater than ∼3 μm. In this temperature range a strong hysteresis effect is also observed at low Vg voltages. The above behavior will be explained in terms of a very slow depletion layer formation in the drain region, introduced by the large time constant of the field-assisted thermal emission of carriers in n-type bulk semiconductors at temperatures below ∼20 K. Another effect, analogous to the ‘‘kink effect’’ observed in n-channel MOSFETs at temperatures below 16 K, is also observed for low Vg and Vd values. This effect is observed with difficulty and is less pronounced than in n-channel MOSFETs.
Microscopic theory of intervalley scattering in GaAs: k dependence of deformation potentials and scattering rates
Authors: Zollner Stefan , Gopalan Sudha , Cardona Manuel
Published: July 2002

The ‘‘rigid-pseudoion’’ model is applied to intervalley scattering processes in GaAs. The intervalley deformation potentials (IDPs) that we obtain at high-symmetry points are in good agreement with previous calculations. We find that the IDPs show a strong dependence on the wave vector of the intervalley phonon, therefore a numerical integration over the Brillouin zone (e.g., with the tetrahedron method) is necessary to obtain realistic scattering rates that can be compared with those obtained from experiments. We calculate the lifetimes of electrons at the L and X valleys as a function of temperature (L: 2.2±0.5 ps; X: 130±20 fs at room temperature) and discuss our results in comparison with recent ultrafast laser experiments and Monte Carlo simulations. Finally, the IDPs show an anisotropy that might be important when simulating electrical transport in hot-electron devices.
Grain-boundary interface electron traps in commercial zinc oxide varistors
Authors: Winston R. A. , Cordaro J. F.
Published: July 2002

A systematic study of the electronic characteristics of grain-boundary interface states was performed on a commercial zinc oxide varistor material using zero-bias deep level transient spectroscopy, current-voltage, high-frequency capacitance, and infrared reflectance techniques. Interface states, which act as deep acceptors, were found to exist at 0.97±0.12 eV below the conduction-band edge. The capture cross section is approximately 4×10−15 cm2. Characteristics of the interface states were determined as a function of the voltage of the trap filling pulse, which was varied from 0.9 to 2.0 V per grain boundary. It is shown that the trap energy is independent of the voltage of the pulse, while the apparent trap density increases with increasing voltage from 1.9 to 7.4×1011 cm−2. The results presented here indicate that this interface level is monoenergetic.
The effects of pore-scale fluid distribution on the physical properties of partially saturated tight sandstones
Authors: Endres Anthony L. , Knight Rosemary
Published: July 2002

Pore-scale fluid distribution has a significant effect on the physical properties of a partially saturated porous medium. Experimental data for the dielectric response and elastic wave velocities for a tight gas sandstone undergoing a cycle of water saturation change through imbibition and drainage are analyzed. Mathematical formulations describing the internal geometrical configuration of a porous medium in terms of a rock matrix background with embedded oblate spheroidal inclusions representing the porosity are used to theoretically predict the dielectric constant and elastic wave velocities of the partially saturated sandstone. Simple geometrical models, incorporating homogeneous and heterogeneous inclusions, are used to simulate the pore-scale fluid distribution which should result from the two saturation methods employed. It is found that these simple scenarios accurately predict the functional form and magnitude of the observed saturation-induced hysteresis in the experimental data for both the dielectric constant and the elastic wave velocities.
The electromigration failure distribution: The fine-line case
Authors: Lloyd J. R. , Kitchin J.
Published: July 2002

The electromigration failure distribution for fine-line interconnects is unknown, but expected to be strongly affected by microstructure. Results from tests on lines with controlled grain sizes and distributions of grain sizes argue for a series model of failure elements in fine lines. A new statistical model of electromigration is developed based on an extension of the failure model of Shatzkes and Lloyd [J. Appl. Phys. 59 (1986)] incorporating the statistics of microstructure and concomittant variations in the activation energy for grain-boundary diffusion. The resulting electromigration failure distribution is well-approximated by a multilognormal distribution in the fine-line case. This approach results in a failure distribution calculated from first principles which, unlike the lognormal distribution, is scalable.
Investigation of (111) strained layers: Growth, photoluminescence, and internal electric fields
Authors: Harshman P. J. , Wang S.
Published: July 2002

It has been found that AlAs, AlGaAs, and AlInAs layers grown on 2° misoriented (111)B GaAs substrates by molecular beam epitaxy are much smoother than corresponding (111)GaAs layers. The quality of Al containing (111)B layers is further demonstrated by the narrow (65 Å) photoluminescence peak from an AlAs/Al0.5In0.5As strained multiquantum well structure. The photoluminescence spectra of this structure is considered in detail, with particular attention paid to Stark effects associated with strain-generated internal electric fields. Spectral movement of the photoluminescence peak as a function of excitation intensity suggests the attainment of self-biased strained quantum wells.
Laser beam propagation through strong turbulence
Authors: Barrett J. L. , Budni P. A.
Published: July 2002

The effects of strong turbulence (C2n up to 3×10−9 m−2/3) on laser beam propagation were measured. Beam broadening of a factor of 2, and wander over several hundred microradians were observed. Long-term beam broadening agrees with values calculated from simplified analytic models.
Minority-carrier lifetime in indium-doped n-type Hg0.78Cd0.22Te liquid-phase-epitaxial films
Authors: Chen M. C. , Colombo L.
Published: July 2002

The recombination mechanisms of the minority-carrier lifetime in n-type indium-doped Hg0.78Cd0.22Te liquid-phase-epitaxial films have been studied. Its temperature dependence was measured from 78 to 200 K using standard photoconductivity decay method. The dependence on doping concentration from 1×1014 to 2×1015 cm−3 was measured using a contactless microwave reflection method at 77 K. From best fits to the experimental temperature dependence data, it was found that lifetimes at temperatures higher than 130 K were dominated by Auger recombination with a value of 0.15 for the overlap integral of Bloch functions. For most films with a doping concentration below 1×1015 cm−3, Shockley–Read–Hall recombination via an acceptor-like deep level at about 40 meV below the conduction band affected lifetimes below 120 K. It was also found that the recombination parameters determined from fitting the lifetime versus temperature curves were adequate to analyze and understand the lifetime versus doping concentration curve, which comprised data from over 100 films.
Continuum modeling of radio-frequency glow discharges. I. Theory and results for electropositive and electronegative gases
Authors: Gogolides Evangelos , Sawin Herbert H.
Published: July 2002

A self-consistent continuum (fluid) model for a radio-frequency discharge is presented. The model is one dimensional, incorporates an electron energy balance, and is valid for both electropositive and electronegative discharges. A connection of the fluid model with the underlying physics is presented: issues such as the derivation of the fluid equations from moments of the Boltzmann equation, the closure of the set of moments, and the fundamental assumptions behind the fluid equations are discussed. A detailed set of results for an electropositive and an electronegative discharge is presented, and contrasted. The sustaining mechanisms and the electrical characteristics of the two discharges are also discussed. Comparison with experimental data of spatially and temporally resolved plasma induced emission is successfully done.
The kinetics of the oxide charge trapping and breakdown in ultrathin silicon dioxide
Authors: Lee K. H. , Campbell S. A.
Published: July 2002

The kinetics of carrier trapping and breakdown in oxides of less than 5 nm was studied. It was found that electron trapping was negligible, but hole trapping was relatively high. An effective oxide trap density due to tunnel annealing was proposed. The rate equation of carrier trapping in the bulk oxide was presented in connection with the generated hole injection by anode surface plasmons. The voltage variation during a constant current test was analyzed using the hole trapping model and capacitance-voltage measured interface trap generation, and approximate values for the capture cross section and hole generation rate were extracted. The gate voltage shift rebounded after 30–100 C/cm2 electron fluence due to interface trap generation. In ultrathin oxides hole trapping causes breakdown, and that trapping is mainly developed in localized weak areas. Using the weak area breakdown model we found that the ratio of weak to robust area is about 5%.
ZnTe: A potential interlayer to form low resistance back contacts in CdS/CdTe solar cells
Authors: Rioux Dennis , Niles David W. , Höchst Hartmut
Published: July 2002

We studied the structural and electronic properties of the ZnTe/CdTe(100) interface with reflection high-energy electron diffraction and angle-resolved synchrotron radiation photoemission spectroscopy (ARPES). ZnTe overlayers grown at 300 °C on CdTe(100) were fully strained and pseudomorphic up to ≊16 Å. Beyond this coverage the ZnTe film starts to gradually relax the 6.6% in-plane lattice strain. Complete relaxation is reached at a ZnTe coverage of ∼300 Å. A valence-band offset of ΔEv=0.00±0.05 eV was measured with ARPES at the Γ point. This propitious band lineup may allow for the use of a ZnTe intermediate layer at metal/CdTe structures to induce ohmic back contacts in CdS/CdTe heterojunction solar cells.
Magnetic properties of amorphous and crystalline (Fe1−xCox)62.5Si12.5B25 alloys
Authors: Shen Bao-Gen , Cao Lei , Guo Hui-Qun
Published: July 2002

The saturation magnetization σs and Curie temperature Tc for amorphous (Fe1−xCox)62.5Si12.5B25 alloys are found to decrease monotonically with increasing Co concentration. The variation of crystallization temperature Tcr with x shows a linear increase. These results are different from those of amorphous Fe-Co-based alloys with composition near 20 at. % (Si+B). The crystalline samples with x≤0.3 produce a single phase with Cr5B3-type structure. When the Co concentration x is richer than 0.6, the unidentified phase appears, and its Curie temperature drops with x from 910 K for x=0.6 to 426 K for x=1.0.
Catalytic oxidation of (001)Si in the presence of Cu3Si at room temperature
Authors: Liu C. S. , Chen L. J.
Published: July 2002

Room temperature oxidation of (001)Si catalyzed by Cu3Si has been investigated by transmission electron microscopy (TEM) and x-ray diffractometry (XRD). For η″-Cu3Si thin layer on (001)Si, XRD analysis showed that volume fractions η″-Cu3Si and Cu decrease and increase with the exposure time in air, respectively. TEM revealed the presence of a high density of Cu precipitates in the SiO2 layer. After prolonged exposure in air, the Cu precipitates were observed to form an irregular network. The thickness of starting Cu, hence Cu3Si, layer on silicon was found to be a critical factor in determining the oxidation behavior. Based on the microstructural evolution data, a partial reconstitution of catalytic Cu3Si mechanism is proposed to be the dominant process for the room-temperature oxidation of silicon catalyzed by Cu3Si.
Temperature dependence of the exchange coupling in the Fe(001) whisker/11 ML Cr/20 ML Fe structure
Authors: From M. , Liao L. X. , Cochran J. F. , Heinrich B.
Published: July 2002

The exchange coupling between iron layers separated by 11 monolayers (ML) of Cr(001) has been investigated using a structure in which the Cr(001) was grown on a bulk iron whisker Fe(001) surface at a temperature of approximately 300 °C. This temperature was selected to produce near optimum smoothness of the Cr layer. The Cr(001) deposition was followed by the deposition of 20 ML of Fe(001) at room temperature, and by the deposition of a 20 ML Au(001) protective layer. The frequencies corresponding to the magnetic excitations in this structure were measured by means of Brillouin light scattering (BLS). One of the observed frequencies corresponds to a surface mode in the bulk iron whisker. Another observed frequency corresponds to the lowest lying precessional mode of the magnetization in the 20 ML thick Fe(001) thin film. Typically, the thin film frequency exhibits a dependence on applied magnetic field that displays two cusps. The positions of the cusps are dependent on the exchange coupling between the 20 ML Fe film and the bulk iron substrate. The surface mode frequency increases monotonically with increasing field over most of the field range investigated. However, at the field corresponding to the low field cusp in the thin film frequency, the surface mode frequency undergoes an abrupt jump in magnitude. We have used the position of the cusps in the thin film data to deduce values for the bilinear, J1, and biquadratic, J2, coupling terms, where the coupling energy is written in the form EAB=−J1 cos(Δφ)+J2 cos2(Δφ); Δφ is the angle between the thin film and bulk iron magnetizations. Measurements of J1 and J2 have been carried out at six temperatures that span the range 100–350 K. Both J1 and J2 are found to depend strongly on temperature. The data are well described by the quadratic expression J2=−0.54+1.46 ×‖J1‖−0.52×J12, where J1 and J2 are expressed in erg/cm2. The large nonzero intercept and the linear term probably imply a significant intrinsic contribution to the biquadratic exchange.
The magnetic and magneto-optical properties of Co, Cr, Mn, and Ni substituted barium ferrite films
Authors: Carey R. , Gago-Sandoval P. A. , Newman D. M. , Thomas B. W. J.
Published: July 2002

Using rapid thermal processing (RTP) we recently demonstrated the production of high quality well ordered barium ferrite films in times much shorter than those required by a conventional annealing process. Influence over the magnetic and structural properties developed in annealed samples was also achieved by variation of the RTP heating profile (R. Carey, P. A. Gago-Sandoval, D. M. Newman, and B. W. J. Thomas, presented at Intermag-93, Stockholm, April 13–16, 1993). It is known that the magneto-optic properties of barium ferrite can be enhanced by selective substitution of some of the Fe by Co2+ and Ti4+ albeit at the expense of reducing the magnetic anisotropy. A multitarget scanning cosputtering process has been used in conjunction with rapid thermal processing to produce a series of barium ferrite films in which Co, Cr, Mn, Ni are selectively introduced to substitute for between 5 and 20 at. % of the Fe. A corresponding percentage of Ti is also added to maintain charge compensation. The magnetic and magneto-optic properties of these films are presented and discussed with reference to their composition and treatment respect to the properties of barium ferrite.
Electronic structures of Sb/Ga(Al)Sb (111) semimetal-semiconductor superlattices
Authors: Wang E. G. , Xu J. H. , Su W. P. , Ting C. S.
Published: July 2002

The electronic structures of semimetal-semiconductor (Sb2)m/(GaSb)n (111) and (Sb2)m/(AlSb)n (111) (m,n≤10) superlattices are calculated by using a tight-binding theory including spin-orbit interaction. It is found that a narrow gap forms in these materials due to the quantum confinement effect. This may allow strong optical nonlinearity in the infrared region. With increasing the thickness of the Sb layer, a possible semiconductor-semimetal transition is suggested at a certain thickness. The influence of interface states on the formation of the band gap is investigated by adjusting the interface relaxation and band offsets. Our study shows that semimetal-semiconductor Sb/Ga(Al)Sb superlattices could potentially open a new possibility in electro-optical device manufactures.
Characterization of defects in Si and SiO2−Si using positrons
Authors: Asoka-Kumar P. , Lynn K. G. , Welch D. O.
Published: July 2002

In the past few years, there has been rapid growth in the positron annihilation spectroscopy (PAS) of overlayers, interfaces, and buried regions of semiconductors. There are few other techniques that are as sensitive as PAS to low concentrations of open-volume-type defects. The characteristics of the annihilation gamma rays depend strongly on the local environment of the annihilation sites and are used to probe defect concentrations in a range inaccessible to conventional defect probes, yet which are important in the electrical performance of device structures. We show how PAS can be used as a nondestructive probe to examine defects in technologically important Si-based structures. The discussion will focus on the quality of overlayers, formation and annealing of defects after ion implantation, identification of defect complexes, and evaluation of the distribution of internal electric fields. We describe investigations of the activation energy for the detrapping of hydrogen from SiO2−Si interface trap centers, variations of interface trap density, hole trapping at SiO2−Si interfaces, and radiation damage in SiO2−Si systems. We also briefly summarize the use of PAS in compound semiconductor systems and suggest some future directions.
Generation of electron carriers in insulating thin film of MgIn2O4 spinel by Li+ implantation
Authors: Kawazoe H. , Ueda N. , Un’no H. , Omata T. , Hosono H. , Tanoue H.
Published: July 2002

Li+ implantation at room temperature of insulating thin films of polycrystalline MgIn2O4 spinel (∼1.3 μm thick) was found to generate electron carriers efficiently. Li+ ions were implanted at 80 keV to a fluence of 1×1016 cm−2 and subsequently at 160 keV to the same fluence. Some implanted films were subjected to a post-annealing at 300 °C. Depth profiles of implanted Li+ ions measured with secondary-ion-mass spectroscopy agreed with that calculated with the trim code. Conductivity at room temperature increased from σ<10−7 to ∼101 S cm−1 upon the Li+ implantation. The generation yield of electron carriers in the as-implanted film was ∼20% and increased up to ∼40% upon post-annealing. Two optical-absorption bands were induced upon the implantation, one at about ∼500 nm and another above ∼1000 nm extending to the IR region, which was attributed to plasma oscillation of electron carriers. The former band faded and the latter absorption increased its intensity upon post-annealing. He+ implantation, which was done for comparison, induced no change in electrical conductivity and no absorption band above ∼1000 nm.
Evidence for reversal by nucleation in RE-Fe-B die-upset magnets
Authors: Henderson Lewis L. , Zhu Y. , Welch D. O.
Published: July 2002

Electron microscopy and initial magnetization studies at elevated temperatures were performed on two die-upset rare-earth magnets with bulk compositions Nd13.75Fe80.25B6 and Pr13.75Fe80.25B6. In both compositions the intergranular phase is amorphous and occurs primarily on those surfaces parallel to the tetragonal 2-14-1 phase c axis. The intergranular phase is enriched in iron relative to the bulk grain, with an average width of 8–12 Å in the Nd-based magnet and 15–20 Å in the Pr-based magnet. The initial magnetization curves and the dependence of the coercivity upon maximum magnetizing field both increase linearly with a common slope and then saturate, consistent with nucleation-dominated behavior. These results suggest that the dominant reversal mechanism in these magnets is nucleation of reversed domains in the iron-rich intergranular region of reduced anisotropy.
Al and B ion-implantations in 6H- and 3C-SiC
Authors: Rao Mulpuri V. , Griffiths Peter , Holland O. W. , Kelner G. , Freitas J. A. , Simons David S. , Chi P. H. , Ghezzo M.
Published: July 2002

Low (keV) and high (MeV) energy Al and B implants were performed into n-type 6H- and 3C-SiC at both room temperature and 850 °C. The material was annealed at 1100, 1200, or 1400 °C for 10 min and characterized by secondary ion mass spectrometry, Rutherford backscattering (RBS), photoluminescence, Hall and capacitance-voltage measurement techniques. For both Al and B implants, the implant species was gettered at 0.7 Rp (where Rp is the projected range) in samples implanted at 850 °C and annealed at 1400 °C. In the samples that were amorphized by the room temperature implantation, a distinct damage peak remained in the RBS spectrum even after 1400 °C annealing. For the samples implanted at 850 °C, which were not amorphized, the damage peak disappeared after 1400 °C annealing. P-type conduction is observed only in samples implanted by Al at 850 °C and annealed at 1400 °C in Ar, with 1% dopant electrical activation.
Laser photochemical ablation of CdWO4 studied with the time-of-flight mass spectrometric technique
Authors: Tanaka Katsumi , Miyajima Takaaki , Shirai Natsuki , Zhuang Quan , Nakata Ryohei
Published: July 2002

Pulsed laser ablation of CdWO4 at 266 nm is studied with a quadrupole mass spectrometric (QMS) time-of-flight method. Ablation threshold, energy distribution, and angular distribution of the ablated species as well as nonlinearity of the ablated species mass intensity are elucidated as a function of laser fluence. Ablated species of O+2, Cd+, Cd2+, W+, and WO+ translate with energies strongly depending on the fragment mass, meaning that they are confined in a space with the same velocity distribution. Ablated species detected with the QMS filament off show a Gaussian distribution for their translation energy, which is interpreted by the Franck–Condon electron excitation mechanism. A simple model is proposed based on a photochemical bond breaking to explain the observed threshold and nonlinearity of the ablated species. Nonlinearity can be explained by photofragmentation of CdWO4 cluster ions and the successively occurring volume expansion. The latter will be the main cause for the desorption of ion species by ablation and supports the narrow angular spreading of the ablated species.
Modeling high-concentration boron diffusion under amorphization conditions
Authors: Baccus Bruno , Vandenbossche Eric , Lannoo Michel
Published: July 2002

A study of high-concentration boron diffusion using a precipitation model is presented in this paper. Recent experimental results on the annealing of boron implanted in preamorphized silicon give the opportunity to analyze, with the help of simulations, the precipitation kinetics and the effect of dislocation loops existing at the amorphous/crystalline interface. A nonequilibrium point-defect diffusion model is used throughout the study, including explicitly the equations describing the kinetics of precipitation. The initial conditions take into account the high level of activation observed experimentally after the solid-phase epitaxy. This influences both the sheet resistance and the doping profile shape at the end of the process. In addition, it is shown that a proper modeling of these diffused profiles includes the effect of the dislocation loops at the amorphous/crystalline interface, acting as a sink term for the interstitials. A more classical formulation of the diffusion equation does not require the modeling of such phenomena since the equilibrium concentration of the point defects is implicitly assumed. Finally, other applications to high-concentration boron diffusion are presented, demonstrating the range of validity of the involved parameters.
Effects of pressure on the formation of phosphorus-doped microcrystalline silicon films deposited by radio-frequency glow discharge
Authors: Feng M. S. , Liang C. W.
Published: July 2002

Phosphorus-doped microcrystalline silicon (P-doped μc-Si:H) has been prepared by radio- frequency glow discharge method. Effects of pressure on the formation of microcrystalline silicon film have been explored. If the hydrogen dilution ratio R is high enough, highly conductive P-doped μc-Si:H films can be obtained under the appropriate pressure. However, for lower R there is a critical pressure for the formation of microcrystalline phase. Above this pressure the film is mostly in amorphous phase and below it microcrystalline phase is formed. The structural and electrical properties studied by Raman spectroscopy, transmission electron spectroscopy, Fourier transform infrared spectroscopy, and dark conductivity measurement are reported. An ion bombardment assistance hydrogen selective etching model consistent with structural and electrical properties of μc-Si:H film is proposed and discussed.
Microscopic photoluminescence characterization of 1.3-μm InAsP/InGaAsP strained multiquantum wells and laser diodes
Authors: Nakao Masashi , Oohashi Hiromi , Hirono Takushi , Kamada Hidehiko , Sugiura Hideo
Published: July 2002

This paper presents results of a microscopic photoluminescence (μ-PL) characterization of strained InAs0.5P0.5/InGaAsP multiquantum well (MQW) crystals with a series of well numbers (n=2–14). This method is useful in detecting misfit dislocations in the crystals, especially at the initial stage of their generation. The μ-PL intensity profile measurements of a laser diode (LD) cavity shows the intensity, being mainly influenced by the [01̄1]-directed misfit dislocations, is closely correlated to the threshold current of the LD.
Analysis of the optical confinement factor in semiconductor lasers
Authors: Huang Yong-Zhen , Pan Zhong , Wu Rong-Han
Published: July 2002

We derive formulas for the optical confinement factor Γ from Maxwell’s equations for TE and TM modes in the slab waveguide. The numerical results show that the formulas yield correct mode gain for the modes propagating in the waveguide. We also compare the formulas with the standard definition of Γ as the ratio of power flow in the active region to the total power flow. The results show that the standard definition will underestimate the difference of optical confinement factors between TE and TM modes, and will underestimate the difference of material gains necessary for polarization insensitive semiconductor laser amplifiers. It is important to use correct optical confinement factors for designing polarization insensitive semiconductor laser amplifiers. For vertical cavity surface-emitting lasers, the numerical results show that Γ can be defined as the proportion of the product of the refractive index and the squared electric field in the active region.
Lattice strains in crystals under uniaxial stress field
Authors: Uchida Takeyuki , Funamori Nobumasa , Yagi Takehiko
Published: July 2002

An expression for the lattice strains in a polycrystalline specimen under uniaxial stress field has been extended for all crystal systems. Apparent Miller indices (HKL) are introduced from Miller indices (hkl) and lattice parameters. The lattice strain ε(l1l2l3) of the direction l1l2l3, normal to the plane HKL, can be uniquely expressed for all crystal systems as follows: ε(l1l2l3)={αβ(l1l2l3)+(1−α)[1/(3KV)]}σ p+α(−(t/3)(1−3 cos2 ψ){(1/2)[3/E(l1l2l3) −β(l1l2l3)]})+(1−α){−(t/3)(1−3 cos 2 ψ)[1/(2GV) ]}, where β(l1l2l3) and E(l1l2l3) denote the linear compressibility and the Young modulus, respectively. Bulk modulus KV and shear modulus GV are values for isostrain model. Variable ψ is the angle between loading axis and the normal of the plane HKL. The first term is the strain caused by the hydrostatic stress component σp. The second and third term, strains caused by the differential stress t, correspond to the isostress and the isostrain model, respectively. The parameter α takes a value between 0 (isostrain) and 1 (isostress). A method to determine the hydrostatic stress component σp, differential stress t, and the parameter α from powder x-ray-diffraction is discussed.
Theoretical modeling of long wavelength n+-on-p HgCdTe photodiodes
Authors: Rogalski A. , Ciupa R.
Published: July 2002

The performance of long wavelength infrared high quality n+-on-p HgCdTe photodiodes is reexamined theoretically. It is shown that the performance can be explained taking into account only thermal generation governed by the Auger mechanism. The investigations are carried out for photodiodes operated in a temperature range between 300 and 50 K. The effect of doping profiles on the photodiode parameters (R0A product, I–V characteristic, photoelectrical gain and noise) is solved by forward-condition steady-state analysis. The theoretical predictions of photodiode parameters are compared with experimental data obtained at the Laboratoire d’Electronique de Technologie et d’Instrumentation (Grenoble, France). Excellent agreement between both types of results has been achieved.
Valence hole subbands and optical gain spectra of GaN/Ga1−xAlxN strained quantum wells
Authors: Fan W. J. , Li M. F. , Chong T. C. , Xia J. B.
Published: July 2002

The valence hole subbands, TE and TM mode optical gains, transparency carrier density, and radiative current density of the zinc-blende GaN/Ga0.85Al0.15N strained quantum well (100 Å well width) have been investigated using a 6×6 Hamiltonian model including the heavy hole, light hole, and spin-orbit split-off bands. At the k=0 point, it is found that the light hole strongly couples with the spin-orbit split-off hole, resulting in the so+lh hybrid states. The heavy hole does not couple with the light hole and the spin-orbit split-off hole. Optical transitions between the valence subbands and the conduction subbands obey the Δn=0 selection rule. At the k≠0 points, there is strong band mixing among the heavy hole, light hole, and spin-orbit split-off hole. The optical transitions do not obey the Δn=0 selection rule. The compressive strain in the GaN well region increases the energy separation between the so1+lh1 energy level and the hh1 energy level. Consequently, the compressive strain enhances the TE mode optical gain, and strongly depresses the TM mode optical gain. Even when the carrier density is as large as 1019 cm−3, there is no positive TM mode optical gain. The TE mode optical gain spectrum has a peak at around 3.26 eV. The transparency carrier density is 6.5×1018 cm−3, which is larger than that of GaAs quantum well. The compressive strain overall reduces the transparency carrier density. The Jrad is 0.53 kA/cm2 for the zero optical gain. The results obtained in this work will be useful in designing quantum well GaN laser diodes and detectors.
Annealing of irradiated epitaxial InP solar cells
Authors: Walters R. J. , Messenger S. R. , Cotal H. L. , Summers G. P.
Published: July 2002

The annealing behavior of electron, proton, and alpha particle irradiated, epitaxial n+p InP solar cells has been characterized using several techniques. Current–voltage measurements were made under simulated 1 sun, AM0 solar illumination and in the dark. The radiation-induced defect spectra were monitored using deep level transient spectroscopy and the base carrier concentration profiles were determined through capacitance–voltage measurements. The irradiated cells were annealed at temperatures ranging from 300 up to 500 K. Some cells were annealed while under illumination at short circuit while others were annealed in the dark. These experiments produced essentially the same results independent of illumination and independent of the irradiating particle. An annealing stage was observed between 400 and 500 K, in which the radiation-induced defects labeled H3 and H4 were removed and the carrier concentration recovered slightly. Concurrently there was a small reduction in the junction recombination current and a slight increase in the photovoltaic (PV) output of the cell; however, most of the radiation-induced defects did not anneal, and the overall PV recovery was very small. A full analysis of the annealing data is given, and a model for the radiation response and annealing behavior of the cells is presented. The results are compared to those reported previously for irradiated, diffused junction InP solar cells. Although the radiation-induced degradation mechanisms appear to be essentially the same in the two cell types, the recovery of the PV output is found to be quite different. This difference in cell recovery is explained in terms of the defect annealing characteristics in the individual cell types.
Electrical properties of layer semiconductor p-GaSe doped with Cu
Authors: Shigetomi S. , Ikari T. , Nakashima H.
Published: July 2002

Measurements of Hall effect and deep-level transient spectroscopy have been made on Cu-doped p-GaSe. The moderately deep acceptor and shallow acceptor levels located at 0.13 and 0.04 eV above the valence band are obtained from the temperature dependence of the hole concentration. The hole-trapping level at 0.14 eV above the valence band is detected by deep-level transient spectroscopy and shows almost the same position as the moderately deep acceptor level. We find that the shallow acceptor level of 0.04 eV is attributed to Cu atoms, whereas the moderately deep acceptor level of 0.13 eV is governed by the defects or defect complexes.
Mechanism and performance of forward and reverse bias electroluminescence at 1.54 μm from Er-doped Si diodes
Authors: Franzò Giorgia , Coffa Salvatore , Priolo Francesco , Spinella Corrado
Published: July 2002

We have analyzed the mechanisms and the efficiency of the 1.54 μm electroluminescence from Er-doped crystalline Si. Optical doping of a 0.25 μm deep p+−n+ junction was achieved by multiple Er and O implants which realize a uniform concentration of 1019 Er/cm3 and 1020 O/cm3 from 0.2 to 0.9 μm from the surface. It has been found that, for the same current density passing through the device, the room temperature electroluminescence signal is 2–10 times higher under reverse bias at the diode breakdown than under forward bias. Detailed analyses of the spectrum line shape, temperature, and current density dependencies and modulation performances under both forward and reverse bias allowed us to elucidate the reasons for this difference. In forward bias, in spite of the large effective excitation cross section (>6×10−17 cm2 at 300 K), the efficiency of room temperature electroluminescence is limited by the small number of excitable sites (∼1% of the total Er concentration) and by the efficiency of nonradiative de-excitation processes of the Er ions. Furthermore, since in forward bias Er ions are excited by electron–hole recombination at an Er related level in the Si band gap, the electroluminescence yield is also reduced by competitive carrier recombinations at the residual defects left over after diode processing. On the other hand, under reverse bias, Er ions are excited by hot carrier impact excitation in the thin (∼70 nm) depletion layer. In this case all of the Er atoms in the depletion region are excitable and nonradiative de-excitation processes, such as Auger de-excitation to free electrons, are inhibited. This allows one to achieve an internal quantum efficiency of 1.5×10−4 at 300 K. Moreover, fast modulation of the diode can be achieved. At the diode turn-off, the excited Er ions are embedded in the heavily doped (∼1019/cm3) neutral regions of the diode where Auger-type de-excitation processes produce fast decay of the Er ions thus allowing to achieve modulation frequencies higher than 80 kHz. The major limitations to the achievement of a higher efficiency under reverse bias are the thin excitable region and the limited fraction of hot carriers having enough energy to impact excite the Er ions.
Growth of AlBN solid solutions by organometallic vapor-phase epitaxy
Authors: Polyakov A. Y. , Shin M. , Qian W. , Skowronski M. , Greve D. W. , Wilson R. G.
Published: July 2002

Layers of AlBN were grown on sapphire by organometallic vapor-phase epitaxy at 1050 °C using triethylboron, trimethylaluminum, and ammonia as precursors. It is shown that boron is readily incorporated into the layers and its concentration in the solid phase can be as high as 40%. However, single phase Al1−xBxN films can only be grown for compositions not exceeding x=0.01. For higher boron concentrations in the solid the second B-rich phase is formed. This phase was identified as wurtzite BN based on the results of transmission electron microscopy and x-ray diffraction. The growth of this thermodynamically unfavorable phase becomes possible, most probably, because it occurs within the framework provided by wurtzite AlN islands first formed on the surface and setting up the sites for lateral growth of wurtzite BN. That leads to formation of columnar structure of AlN and BN crystallites oriented in the basal plane and existing side by side.
Reactively sputtered Ti-Si-N films. II. Diffusion barriers for Al and Cu metallizations on Si
Authors: Sun X. , Reid J. S. , Kolawa E. , Nicolet M.-A. , Ruiz R. P.
Published: July 2002

Ti-Si-N films synthesized by reactively sputtering a TiSi2, a Ti5Si3, or a Ti3Si target in Ar/N2 gas mixture were tested as diffusion barriers between planar (100) Si substrates and shallow n+p Si diodes, and Al or Cu overlayers. The stability of the Ti-Si-N barriers generally improves with increasing nitrogen concentration in the films, with the drawback of an increase in the film’s resistivity. Ti34Si23N43 sputtered from the Ti5Si3 target is the most effective diffusion barrier among all the Ti-Si-N films studied. It works as an excellent barrier between Si and Cu. A film about 100 nm thick, with a resistivity of around 700 μΩ cm, maintains the stability of Si n+p shallow junction diodes with a 400 nm Cu overlayer up to 850 °C for 30 min vacuum annealing. When it is used between Al and Si, the highest temperature of stability achievable with a 100-nm-thick film is 550 °C. A thermal treatment at 600 °C causes a severe intermixing of the layers. The microstructure, atomic density, and electrical resistivity of these films are described in an accompanying Part I.
Epitaxial La0.67Sr0.33MnO3 magnetic tunnel junctions
Authors: Li X. W. , Lu Yu , Gong G. Q. , Xiao Gang , Gupta A. , Lecoeur P. , Sun J. Z. , Wang Y. Y. , Dravid V. P.
Published: July 2002

We report the observation of a large magnetoresistance (83%) at low magnetic fields of tens of Oe at 4.2 K in the epitaxial trilayer junction structure, La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3. The spin-polarization parameter of the manganite has been determined from the magnetoresistance value. The switching fields of the two magnetic layers were designed by using the magnetic shape anisotropy. By limiting the sweeping field in a low field range (∼100 Oe), we have achieved bistable resistive states at zero field, which is of potential interest for magnetoelectronic applications.
Comment on “Phase equilibria of the Ga–Ni–As ternary system” [J. Appl. Phys. 80, 543 (1996)]
Authors: Guérin Roland , Guivarc’h André
Published: July 2002

The phase equilibria of the Ga–Ni–As ternary system, especially in its upper part, has given rise to much controversy. An attempt to clarify this situation is given in this comment. We show that the re-examined diagram proposed by Ingerly et al. [J. Appl. Phys. 80, 543 (1996)] is not right owing to a much too limited number of synthesized samples, and that this diagram cannot rationalize the complex solid-state interdiffusion which occurs in the Ni/GaAs contacts. We confirm the occurrence of ordered ternary phases which crystallize in hexagonal superlattices a√3,3c and 2a,4c derivative from the NiAs-type structure. Finally, we point out that these superlattices index successfully all the extra lines of the x-ray diffraction pattern that Ingerly et al. were unable to explain.