bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of p/i interface layer on dark J-V characteristics and Voc in p-i-n a-Si solar cells
Authors: Sakai H. , Yoshida T. , Fujikake S. , Hama T. , Ichikawa Y.
Published: July 2002

Dark current-voltage (J-V) characteristics of p-i-n a-Si solar cells are studied to clarify the effect of the p/i interface layer on the open-circuit voltage (Voc). It is shown that the recombination current in the p/i interface region is predominant in the a-Si solar cells with an i-layer thickness of less than 200 nm and has a great effect on the dark-current transport in the solar cells. It is also shown that the current transport of the cells with the p/i interface layer of constant band gap of a thickness of more than 14 nm is effectively the same as that of a cell in which the band gap of the whole i layer is equal to that of the interface layer. A model in which the dark current of the cell consists of the recombination current at the p/i interface and the recombination current in the bulk region of the i layer is proposed. Using this model, the Voc degradation for the a-Si solar cells with the p/i interface layer is shown to be due to the defects generated in the i layer.
Explosive silicidation in nickel/amorphous-silicon multilayer thin films
Authors: Clevenger L. A. , Thompson C. V. , Tu K. N.
Published: July 2002

Self-propagating explosive reactions can occur in multilayer thin films. Explosive silicidation in nickel/amorphous-silicon multilayer thin films has been investigated using a combination of high-speed photography, high-speed temperature measurements, plan-view transmission electron microscopy, and thin film x-ray diffraction. The multilayer films had an atomic concentration ratio of 2 Ni atoms to 1 Si atom. The silicide phase formed by explosive silicidation was Ni2 Si. This was the same phase formed by conventional thermal annealing of the multilayer thin film. The temperature of the explosive reaction front was measured to be approximately 1565 K. The reaction-front velocity was found to vary from 22 to 27 m/s and to be at most weakly dependent on the modulation period and the total film thickness. The resulting Ni2 Si grain structure formed by explosive silicidation is less defective than Ni2 Si formed by conventional thermal annealing. This was attributed to the higher reaction temperatures and the shorter reaction times of explosively formed Ni2 Si as compared to Ni2 Si formed via conventional annealing.
Electrical activity and structural evolution correlations in laser and thermally annealed As-implanted Si specimens
Authors: Parisini A. , Bourret A. , Armigliato A. , Servidori M. , Solmi S. , Fabbri R. , Regnard J. R. , Allain J. L.
Published: July 2002

Laser-annealed and further thermally annealed arsenic implanted silicon specimens have been investigated in a range of doses from 1×1016 to 5×1016 As/cm2, with different experimental techniques: electrical measurements, transmission electron microscopy (TEM), double-crystal x-ray diffractometry (DCD), and extended x-ray absorption fine structure analysis (EXAFS). On the as laser-annealed samples, in the whole range of doses examined, a lattice contraction of the doped layer has been evidenced by DCD, whereas, on the same specimens, EXAFS measurements have shown the presence of a local expansion around substitutional As atoms. The relationship between strain and carrier concentration has been found to be approximately linear and can be described by the presence of a size and an electronic effect, as recently proposed in the literature. The former effect represents the atomic size contribution, while the latter is the strain induced by the variation of the conduction-band minima due to the doping. After a subsequent thermal annealing in a low-temperature range (350–550 °C), a strong deactivation of the dopant has been evidenced by electrical measurements. From the experimental results, a new model of the first step of the As deactivation phenomenon at low temperature is proposed. It is described by the capture of two electrons from a pair of As atoms in the second neighbor position in the Si lattice, leading to the formation of a positively charged arsenic-vacancy cluster (As2V)+, and to the emission of a negatively charged Si self-interstitial I−. This model takes into account the main phenomena that are experimentally observed simultaneously to the As deactivation, i.e., the transition from a contraction to a dilatation of the strain observed by DCD and the formation of interstitial loops. At relatively high temperatures (650–900 °C), the hypothesis of the coexistence of the clusters and of the observed precipitates has to be taken into account in order to explain the nature of the inactive As. However, whether clustering or precipitation is the dominant phenomenon still remains an open question.
Polyalkylsilyne photodefined thin-film optical waveguides
Authors: Hornak L. A. , Weidman T. W. , Kwock E. W.
Published: July 2002

Polysilynes, a new class of amorphous alkyl silicon network polymers, undergo a novel photo-oxidative crosslinking reaction associated with up to a 15% decrease in refractive index related to the loss of SiSi bonding. We describe the fabrication and initial measurements of waveguides formed with this index imaging technique in poly(cyclohexylsilyne) films on both SiO2 and poly(methyl methacrylate)-coated silicon wafers. Measurements of multimode guides show typical propagation losses of 0.68 dB/cm at 633 nm. Results indicate the polyalkylsilynes show promise as self-developing, planar optical waveguide media.
Thermal diffusivity measurements in benzophenone crystals using photoacoustic techniques
Authors: Bonno B. , Laporte J. L. , Rousset Y.
Published: July 2002

The amplitude of the photoacoustic signal is measured as a function of chopping frequency for thin benzophenone polycrystalline samples in the temperature range 100–300 K. Analysis of experimental results, obtained by rear surface illumination, allows us to determine the thermal diffusivity of benzophenone crystals in the whole temperature range.
Thermodynamic investigations of solid-state Si-metal interactions. I. Experimental and analytical studies of the Si-Ti binary system
Authors: Gong S. F. , Robertsson A. , Hentzell H. T. G. , Li X.-H.
Published: July 2002

An experimental study has been made on reactions in codeposited and multilayer films consisting of silicon and titanium deposited by electron beam evaporation. Transmission electron microscopy and Auger electron spectroscopy were used to determine structures and compositions. The experimental results from the codeposited films in the whole composition range (0%–100%) were compared with the predictions from the calculated free-energy diagram of the Si-Ti system. It is revealed that the phenomena of metal-induced crystallization of amorphous silicon and formation of amorphous alloys appear in two different composition ranges in the binary system. Metal-induced crystallization of amorphous silicon is attributed to lowering of bonding energy of SiSi bonds by titanium atoms in the Si-rich composition range and the formation of an amorphous Si-Ti alloy is attributed to the dominant SiTi bonding due to the largely negative heat of mixing between the two elements in a medium composition range.
Electronic structure of neutral and charged vacancies in Ga-related III-V compound semiconductors
Authors: Xu Hongqi
Published: July 2002

Self-consistent semiempirical tight-binding theory is used to study the neutral and charged states of the ideal vacancies in GaP and GaSb. For the neutral states, the diagonal elements of the defect potential on the first and second nearest neighbors of a vacancy are obtained by a charge-neutrality condition, while for the charged states, these matrix elements are determined self-consistently. The theory also takes the off-diagonal matrix elements corresponding to atoms adjacent to a vacancy into account. The defect energy levels and the localizations of the levels are computed using the Lanczos–Haydock recursion method. The general character of the electronic structure of vacancies in the Ga-related III-V compound semiconductors has been extracted from these calculations and from the similar calculations we performed for vacancies in GaAs. We analyze the defect states of the vacancies in terms of chemical bondings of the crystals. It is shown that, for the cation vacancies (the Ga vacancies) in the three semiconductors, both the a1 resonances at the top of the valence band and the t2 bound states in the fundamental gap consist mainly of the atomiclike p orbitals centered on the four nearest neighbors, whereas for the anion vacancies, the a1 states at the top of the valence band contain mainly the atomiclike p orbitals of the four neighboring atoms and the t2 bound states in the fundamental gap contain both the atomiclike s and the atomiclike p orbitals of the four neighboring atoms. We also find that the t2 gap levels of the charged cation (anion) vacancies in the three semiconductors are all located in the lower (upper) half of the fundamental gap. The calculated results are in agreement with available results from local density calculations and support the identifications of the vacancy defects by the positron-annihilation technique.
Deep center characterization by photo-induced transient spectroscopy
Authors: Brasil Maria J. S. P. , Motisuke P.
Published: July 2002

We show that photo-induced current transients in semi-insulating GaAs are well fitted by a unique sum of exponentials including the anomalous case, in which one of the exponentials has a negative amplitude. This fitting procedure is proposed as a more reliable method to be used in obtaining the trap emission constant. We also present an analytic solution for the kinetic equations of carriers taking into account the background current and the carrier recapture processes, which have been neglected in the previous approaches. This solution contains a very simple and physically coherent explanation for the appearance of negative peaks in the spectra of photo-induced transient current spectroscopy.
Thermally stimulated current studies of bismuth silicon oxide crystal. II. Trapping kinetics
Authors: Takamori Takeshi , Just Dieter
Published: July 2002

Thermally stimulated current (TSC) of nominally undoped bismuth silicon oxide crystals was measured as a function of the UV excitation temperature and time. It was shown that trapping into the shallowest of the three major traps observed by TSC is a precursor state for electrons to be trapped into deeper traps. When the crystal is UV excited at liquid nitrogen temperature, electrons which fill this shallow trap may ultimately fall into deeper traps. When this shallow trap is not occupied, the deeper traps are not filled, even if the UV excitation temperature is well below the TSC peaks of the deeper traps.
Redistribution and electrical activation of implanted arsenic in silicon on insulator substrates formed by oxygen ion implantation
Authors: Robinson A. K. , Reeson K. J. , Hemment P. L. F.
Published: July 2002

The redistribution and electrical activity of implanted arsenic in separation by implanted oxygen (SIMOX) and bulk silicon substrates are compared. The SIMOX substrates were prepared by high dose oxygen implantation followed by high-temperature annealing. Subsequently doses of 5×1015 As+/cm−2 at 70 keV were implanted into the substrates and, also, bulk silicon. The samples were annealed to activate the arsenic. It was observed that (i) the same percentage activation was measured in both SIMOX samples and bulk silicon, (ii) no anomalous diffusion was seen in the SIMOX samples, and (iii) during further high-temperature annealing the buried oxide acts as a diffusion barrier. This data confirms the high quality of SIMOX material currently being prepared.
Growth of epitaxial Ag/Si films by the partially ionized beam deposition technique
Authors: Nason T. C. , You L. , Yang G.-R. , Lu T.-M.
Published: July 2002

The observation of room-temperature epitaxy of vapor-deposited thin Ag films on Si(111) accomplished under conventional vacuum conditions is reported. Epitaxy was also observed at 350 °C. The films were deposited using a partially ionized beam deposition system, and were typically 1500 Å thick. Epitaxy was confirmed via pole-figure analysis. Scanning electron microscopy revealed excellent surface flatness even for the room-temperature films. Contrary to previous observations, the growth was found to proceed by the layer mode, even at the elevated temperature. This change in morphology is attributed to the enhanced density of nucleation sites due to the energetic ions.
Investigation of the thermal dissociation of PH3 and NH3 using quadrupole mass spectrometry
Authors: Baillargeon J. N. , Cheng K. Y. , Jackson S. L. , Stillman G. E.
Published: July 2002

The thermal dissociation of PH3 and NH3 injected through a Ta-based high-pressure gas-injection cell were studied. Using a quadrupole mass spectrometer, the Ta was found to effectively dissociate the PH3 into primarily P2, P4, and H2 molecules with an injector temperature as low as 550 °C. The introduction of NH3 through this same injector resulted in dissociation into N2 and H2 for an injector temperature greater than 900 °C. When NH3 and PH3 were coinjected, again P2, P4, N2, and H2 were the primary molecules produced; however, an additional dimer, PN, was also detected. The PN concentration was maximum at a cell temperature of 700 °C. This dimer was found to be an effective source for introducing nitrogen as an isoelectronic trap in GaP.
Second-order nonlinear optical properties and relaxation characteristics of poled linear epoxy polymers with tolane chromophores
Authors: Jungbauer D. , Teraoka I. , Yoon D. Y. , Reck B. , Swalen J. D. , Twieg R. , Willson C. G.
Published: July 2002

A new linear epoxy polymer containing 4-amino-4′-nitrotolane chromophores attached to the chain backbone was synthesized in an attempt to enhance both the poling-induced nonlinear optical susceptibility and its long-term stability. The polymer films poled by corona discharge showed very large nonlinear optical doubling coefficients of d33 ≂ 89 pm/V and d31≂25 pm/V for incident light of 1.06 μm wavelength, and a linear electro-optic coefficient r13≂8 pm/V at 633 nm wavelength. Poling-induced alignment of the nonlinear optical moieties showed no detectable decay in two weeks at ambient temperature, as studied by the birefringence. Even at 100 °C the relaxation time estimated from the birefringence decay was ca. 450 h, consistent with roughly 16% decrease in dij coefficients in 20 h at this temperature and also the extrapolation from the dielectric α relaxation characteristics. The dielectric α relaxation temperatures of the poled polymer samples exhibited higher values than that of the unpoled counterpart. This unusual behavior may be due to a significant contribution of Maier–Saupe thermotropic interactions among the tolane moieties that favor parallel alignment.
Multiple steady states in a radio frequency chlorine glow discharge
Authors: Aydil Eray S. , Economou Demetre J.
Published: July 2002

Multiple steady states have been observed in a 13.56 MHz chlorine glow discharge in a parallel plate radial flow reactor. Measurements of the flux and energy distribution of positive ions bombarding the electrode are reported along with radial profiles of atomic chlorine (Cl) concentration and etch rate of polysilicon for different states of the plasma. At the same operating conditions the plasma may exist in one of two states. In one state the plasma appeared radially uniform, resulting in relatively uniform radial Cl concentration profiles and etch rate. In the other state the plasma appeared radially nonuniform with a higher intensity central region (‘‘plasmoid’’). The etch rate and Cl concentration profiles were nonuniform in the presence of the plasmoid. The plasmoid generally appeared under conditions of high power and pressure and could be eliminated by adding noble gases and/or decreasing the electrode spacing. The multiple states may be a result of the strongly electronegative nature of the chlorine discharge.
Size-dependent magnetic properties of manganese ferrite fine particles
Authors: Tang Z. X. , Sorensen C. M. , Klabunde K. J. , Hadjipanayis G. C.
Published: July 2002

We have developed synthetic techniques involving coprecipitation of iron(III) and manganese(II) ions from aqueous solutions using NaOH to create single-crystal, stoichiometric MnFe2O4 particles. The particle diameter could be varied between 5 and 25 nm by varying the metallic-ion to hydroxide-ion concentration ratio. Magnetic measurements revealed that the saturation magnetization decreased, the ferrimagnetic to paramagnetic transition broadened, and the apparent transition temperature increased, all with decreasing particle size.
Magneto-optical Kerr rotation on Fe-Al2O3 granular thin films
Authors: Dormann J. L. , Fiorani D. , Giammaria F. , Lucari F.
Published: July 2002

We made measurements of polar Kerr rotation (KR) on granular thin films, composed of iron particles, with different average diameter (50<Φ<100 Å), dispersed in an amorphous Al2O3 matrix. The measurements were performed at 300 and 4 K in the wavelength interval 0.5–2.5 μm. The spectra observed show a decreasing tail in the visible region and then oscillations in the near infrared due to composition of the light beams reflected by the two surfaces of the sample. Values as high as 2.8° of KR in the visible are obtained when a magnetic field of 4 KOe is applied perpendicular to the surface of the sample. The KR signal was also measured as a function of the temperature at the specific values of wavelength corresponding to some maxima and minima of the spectrum. The KR intensity increases as the temperature decreases down to a characteristic temperature T*1, below which it remains constant. T*1 increases with increasing iron concentration and particle dimensions. This behavior is in agreement with previous results of Faraday rotation and susceptibility measurements.
Antiferromagnetic order of Cu in Sm2CuO4
Authors: Skanthakumar S. , Lynn J. W. , Peng J. L. , Li Z. Y.
Published: July 2002

Neutron diffraction techniques have been used to study the magnetic order of the Cu ions in a single crystal of Sm2CuO4. The measurements revealed the development of long-range magnetic order of the Cu moments at TN = 280 ± 1 K, with a relatively simple antiferromagnetic configuration of spins as found in Nd2CuO4 and Pr2CuO4. However, the spin directions in Sm2CuO4 are rotated by 90° from the spin directions in Nd2CuO4 and Pr2CuO4. The detailed spin structure can be either collinear or noncollinear, and in these tetragonal systems it is not possible to distinguish between them with the present neutron diffraction data on multidomain samples. Our measurements demonstrate that there are no spin reorientations below the Néel temperature, in contrast to the behavior found for Nd2CuO4.
Structural and magnetic properties of UCo2Ge2
Authors: Endstra T. , Nieuwenhuys G. J. , Menovsky A. A. , Mydosh J. A.
Published: July 2002

We have studied the effect of annealing on the structural and magnetic properties of UCo2Ge2 and thereby find the existence of two different crystallographic structures. The as-cast, high-temperature (HT) phase adopts a crystal structure with symmetry lower than I4/mmm; after annealing at 750 °C for 5 days the ThCr2Si2 (I4/mmm) structure is formed. Additionally, the length of the c axis in these tetragonal structures changes dramatically: whereas the HT phase has a c parameter of ≊9.3 Å, the low-temperature (LT), annealed phase has a much larger c axis of ≊9.9 Å. This expansion of the unit cell greatly influences the magnetic properties of the material: while the LT sample orders antiferromagnetically at 174 K, the HT one does not order magnetically down to 350 mK. The antiferromagnetic transition is clearly indicated by our magnetization, resistivity and specific heat measurements.
Study of the influence of the phosphorus pressure on the preparation of nominally undoped semi-insulating InP wafers
Authors: Kipfer P. , Lindolf J. , Hofmann D. , Müller G.
Published: July 2002

The conditions for the preparation of nominally undoped semi-insulating (SI) InP wafers by annealing under controlled phosphorus pressure are described. It is demonstrated by the results of electrical profile measurements (differential Hall effect) and by photoluminescence that diffusion effects in a thin peripheral layer (≊20 μm) can be correlated to a phosphorus in- and indium out-diffusion. But diffusion of these species is correlated to a donor behavior and relatively slow. It can, therefore, not be used to explain the SI bulk property which seems not to depend on the phosphorus overpressure during annealing.
Diffusion-induced defects in GaAs by zinc and the effects of post-diffusion anneal
Authors: Ho H. P. , Harrison I. , Baba-Ali N. , Tuck B.
Published: July 2002

The crystallographic defects generated during the diffusion of zinc into GaAs have been studied using transmission electron microscopy and chemical etching techniques. By observing the effects of arsenic pressure on the defect density and the zinc penetration, the annihilation of the diffusion-induced defects in relation to the surface stoichiometry was investigated. It was found that the dissolution of the defects within the crystal is mainly caused by the out-diffusion of the diffusion-induced Ga interstitials to the surface. This is also supported by results obtained from post-diffusion annealing of the samples under different arsenic pressures. In addition, the possible inclusion of arsenic atoms in the interstitial dislocation loops found in GaAs is also discussed.
A transmission electron microscope investigation of the dose dependence of the microstructure of silicon-on-insulator structures formed by nitrogen implantation of silicon
Authors: Meekison C. D. , Booker G. R. , Reeson K. J. , Hemment P. L. F. , Peart R. F. , Chater R. J. , Kilner J. A. , Davis J. R.
Published: July 2002

Transmission electron microscope studies have been made of (100) silicon wafers implanted at 500 °C with 200-keV 14N+ ions to doses of either 0.25, 0.75, or 1.4×1018 cm−2. For all of these specimens, the as-implanted wafers contained a buried amorphous layer with a damaged upper single-crystal silicon layer. For the 1.4×1018 cm−2 specimen, the amorphous layer contained bubbles. Wafers subsequently annealed at 1200 °C in order to form silicon-on-insulator structures showed the following. For the 0.25×1018 cm−2 specimen, there was a buried discontinuous polycrystalline α-Si3N4 layer, and an upper silicon layer with no observable defects. For the 0.75×1018 cm−2 specimen, there was a buried continuous polycrystalline α-Si3N4 layer containing small silicon islands, and an upper silicon layer either without defects or with microtwins adjacent to the nitride/silicon interface. For the 1.4×1018 cm−2 specimen, there was a buried multilayer structure with the middle layer consisting of substantially single-crystal α-Si3N4 free from silicon islands but containing bubbles; and an upper silicon layer with microtwins and threading dislocations. For the 0.25 and 0.75×1018 cm−2 specimens, the α-Si3N4 had often grown epitaxially in the single-crystal silicon. For the 0.75×1018 cm−2 specimen, such epitaxy had less often occurred. For the 1.4×1018 cm−2 specimen, such epitaxy was not observed. These structural results are correlated with the implantation conditions and nitrogen depth profiles obtained by secondary ion mass spectrometry. The mechanisms responsible for producing the structures are discussed.
Optically controlled resonant tunneling in a double-barrier diode
Authors: Kan S. C. , Wu S. , Sanders S. , Griffel G. , Yariv A.
Published: July 2002

The resonant tunneling effect is optically enhanced in a GaAs/GaAlAs double-barrier structure that has partial lateral current confinement. The peak current increases and the valley current decreases simultaneously when the device surface is illuminated, due to the increased conductivity of the top layer of the structure. The effect of the lateral current confinement on the current-voltage characteristic of a double-barrier resonant tunneling structure was also studied. With increased lateral current confinement, the peak and valley current decrease at a different rate such that the current peak-to-valley ratio increases up to three times. The experimental results are explained by solving the electrostatic potential distribution in the structure using a simple three-layer model.
Analysis and optimization of graded-index separate-confinement heterostructure waveguides for quantum well lasers
Authors: Zou W. X. , Chuang Z. M. , Law K-K. , Dagli N. , Coldren L. A. , Merz J. L.
Published: July 2002

Waveguide structures for quantum well (QW) lasers are analyzed numerically by a straightforward 2×2 matrix approach. It is shown that this approach is capable of analyzing separate-confinement heterostructure (SCH) waveguides, having any arbitrarily graded-index (GRIN) profile in the waveguide layers and any number of QWs in the active layer, to any desired level of accuracy. Using this waveguide analysis, general GRIN-SCH waveguide structures of QW lasers can be optimized for maximum confinement factors. It is estimated that the laser threshold current density can be reduced typically by 10% as a result of this waveguide optimization.
Structure evolution in a-SiC:H films prepared from tetramethylsilane
Authors: Rynders S. W. , Scheeline A. , Bohn P. W.
Published: July 2002

The influence of deposition conditions on the molecular structure of thin films deposited from tetramethylsilane through plasma enhanced chemical vapor deposition was investigated using infrared spectroscopy, ultraviolet–visible absorption spectroscopy, and sputtered neutral atom mass spectrometry (SNAMS). The infrared spectra revealed a strong dependence of film structure on the deposition pressure, with high pressures (>50 mTorr) producing linear, polymeric films, and low pressures (<50 mTorr) producing amorphous, crosslinked films. The structure of the polymeric films was dominated by carbon atoms incorporated as intact, chain terminating methyl groups. The crosslinked films contained fewer methyl groups and proportionately more bridging methylene and branching methylidyne groups. SNAMS measurements revealed that the carbon-to-silicon ratio was inversely dependent on deposition pressure, with carbon content increasing as deposition pressures decrease. UV–visible measurements indicated that the optical properties of the films were strongly dependent on deposition pressure, particularly at pressures below 100 mTorr. Films prepared in these experiments exhibited optical gaps ranging from 2.1 to 3.9 eV. From these results, a film structure evolution model is postulated, stressing the interactions between precursor structure, fragment structure, and plasma energetics.
Induced multipole strengths for two dielectric spheres in an external electric field
Authors: Stoy Richard D.
Published: July 2002

Two nonidentical spheres are immersed in a uniform external electric field. Induced multipoles through hexadecapole are found along the mutually perpendicular axes of the system. These multipoles are expressed directly in terms of the coefficients that appear in the infinite series representation of the potential.
Harmonic generation of microwaves in semiconductors in the presence of deep repulsive traps
Authors: Pramanik T. K. , Bhattacharya D. P.
Published: July 2002

The characteristics of second-harmonic generation (SHG) of microwaves in a semiconductor at low lattice temperatures are investigated theoretically over a wide range of the dc bias field, beginning from a weakly heated carrier ensemble up to the onset of impurity breakdown giving due consideration to the effect of recombination of the nonequilibrium carriers in the presence of deep repulsive traps. The calculations are carried out for a parabolic law of dispersion and a scalar effective mass. In comparison to what can be obtained under the condition where the nonequilibrium carriers are captured by attractive traps or in the absence of recombination effects, the results of the quantum trapping of the nonequilibrium carriers by the repulsive traps bring in interestingly both qualitative and quantitative changes in the characteristics throughout the entire range of the bias field. The curves for the efficiency of SHG versus the bias field show a number of optimum fields for which the generation would be most efficient. The inadequacies of the present theory are pointed out and the scope for refinement of the same is discussed.
Preisach model with stochastic input as a model for viscosity
Authors: Mayergoyz Isaak D. , Korman Can E.
Published: July 2002

The viscosity phenomenon in hysteretic systems has been traditionally studied by using thermal activation-type models. In this paper, a new approach to viscosity modeling is explored. This approach is based upon the use of the Preisach hysteresis models driven by stochastic inputs. First, the scalar case is discussed, and the obtained results are compared with thermal activation-type models and with some known experimental facts. The paper is concluded by the discussion of the vector models for viscosity.
Kinematical x-ray diffraction model with a new boundary condition for analysis of Bragg-peak profiles of layered crystals
Authors: Wie C. R. , Kim H. M.
Published: July 2002

A new boundary condition is employed in the kinematical model analysis of Bragg-peak profiles of layered single crystals, which is the dynamical reflection amplitude of the substrate instead of the previously used dynamical intensity. It is shown that this boundary condition properly accounts for the angular shift effect in the Bragg-peak profile of very thin epitaxial layers and superlattices. A kinematical model simulates properly the interference profiles in the C-layer Bragg peak of C/A/C/sub-type samples, but not in the B-layer Bragg peak of the B/A/B-type samples. The simulated and experimental rocking curves for the thin single-layer AlGaAs/GaAs and GaInAs/InP samples and for an AlGaAs/GaAs superlattice sample are discussed. Rocking curves are simulated by using the dynamical diffraction theory and the kinematical model with the old or new boundary condition. A matrix method for the dynamical theory superlattice simulation is also presented. The superlattice simulation using this matrix method is found to be substantially faster than the conventional recursive formula approach.
High-field hole injection, conduction, and breakdown in polyethylene films fabricated by plasma polymerization
Authors: Liu D. , Kao K. C.
Published: July 2002

The current-voltage (I-V) characteristics of polyethylene films fabricated by plasma polymerization have been measured at very high electric fields using linear ramp voltages. Experimental results show that at average fields higher than 1 MV/cm, electric conduction is mainly due to the Fowler–Nordheim-type tunneling injection of holes from the anode and the high hole mobility. There is no evidence of impact ionization at fields close to the breakdown strength. High-field conduction is filamentary and governed by the trapped hole space charge. Internal discharges such as electrical treeing and breakdown are initiated by thermal instability within high-current density regions of main conduction filaments (or channels), and then followed by the creation of low-density domains to provide large mean free paths for subsequent impact ionization which leads to an indefinite increase in carrier multiplication and final destruction of the material inside the filaments.
Determination of vacancy and self-interstitial contributions to gallium self-diffusion in GaAs
Authors: Tan T. Y. , Yu S. , Gösele U.
Published: July 2002

A quantitative determination of the contributions of the triply negatively charged Ga vacancies (V3−Ga) and of the doubly positively charged Ga self-interstitials (I2+Ga) to the Ga self-diffusion coefficient in GaAs has been carried out. Under thermal equilibrium and intrinsic conditions, the V3−Ga contribution is characterized by an activation enthalpy of 6 eV for As-rich crystals and of 7.52 eV for Ga-rich crystals, while the I2+Ga contribution is characterized by an activation enthalpy of 4.89 eV for As-rich crystals and of 3.37 eV for Ga-rich crystals.
Simulating electron flow in the applied-B diode
Authors: Krall Nicholas A. , Rosenthal Stephen E.
Published: July 2002

Electron flow in and into an applied-B ion diode is calculated, including the effects of turbulence produced by streaming instabilities. A technique is developed for including these effects in a numerical simulation. The results of two-dimensional simulations using this technique in the electromagnetic particle-in-cell code magic are presented.
Observation of soft x-ray emission in the corona of 0.35-μm laser-irradiated gold disks
Authors: Juraszek D. , Bayer C. , Bernard M. , Bocher J. L. , Garaude F. , Thiell G.
Published: July 2002

The Phebus laser was used to irradiate gold targets at λ=0.35 μm; the laser pulse was 0.7 or 1.3 ns and the energy on target 1 to 1.8 kJ. The incident intensity was varied from 3×1013 to 3×1015 W/cm2. The time history of x-ray emission was monitored in the range 0.2–2.5 keV with a streak camera coupled with a transmission grating. Numerical simulations cannot replicate the temporal evolution of soft x-ray emission (hν<800 eV), although the total conversion efficiency is correctly reproduced. Some observations, including time and space-resolved images, show that unexpected soft x-ray emission is produced in the corona at large distances from the target surface. A possible explanation is that cold and dense jets are generated towards the underdense plasma by an instability.
Measurement and calculation of spontaneous recombination current and optical gain in GaAs-AlGaAs quantum-well structures
Authors: Blood P. , Kucharska A. I. , Jacobs J. P. , Griffiths K.
Published: July 2002

Experimental determinations have been made of the peak optical gain as a function of spontaneous recombination current density for GaAs quantum wells of width 25 and 58 Å bounded by AlGaAs barriers. These data were obtained from measurements of spontaneous emission spectra, observed through narrow windows in the 50-μm-wide contact stripes of oxide isolated lasers, using only a single reference value of the optical absorption coefficient above the band edge to calibrate the measurements in absolute units. These results are in good agreement with gain-current curves calculated using a model which includes unintentional monolayer well width fluctuations, band-gap narrowing and intraband carrier-carrier scattering. The characteristic intraband scattering time is calculated from first principles as a function of electron energy and carrier density on the basis of a 2-dimensional Auger-type process. This lifetime gives a much better representation of our observed spontaneous spectra than a lifetime which is simply dependent upon carrier density. The comparison between experiment and model calculation involves no adjustable parameters. For the 58-Å-wide wells there is a difference between the experimental and calculated gain-current curves at low values of gain. We show that this is a consequence of applying the Einstein relations to a broadened spectrum in the process of deriving the gain from the observed spontaneous emission spectrum. A direct comparison of the shapes of experimental and calculated spontaneous emission spectra at several injection levels provides a more rigorous, yet equally valid, verification of the computer model.
The low-temperature photochromic response of bismuth germanium oxide
Authors: Martin J. J. , Foldvari I. , Hunt C. A.
Published: July 2002

Exposing the photorefractive bismuth germanium oxide (BGO) at low temperatures to 2.5–3.3 eV light produces photochromic absorption bands. In both undoped and Fe-doped material the absorption consists of overlapping bands at 1.5, 2.2, 2.7, and 3.1 eV. The 1.5- and 2.2-eV components are relatively weaker in Fe-doped BGO. In undoped BGO the photochromic bands anneal together above 200 K. Doping with iron adds an anneal stage in the 110–200 K range that matches the recovery of Fe3+. Optical bleaching with 1.5-eV light was much less efficient than with visible band light. Thus, the 1.5-eV photochromic band may be an internal transition of the center responsible for the 2.2-eV band. In BGO:Al the aluminum electronically compensates the deep donor center responsible for the yellow coloration observed in undoped crystals. Photoexcitation at 9 K produces overlapping absorption bands at 1, 1.38, and 2.45 eV. All three bands have major anneal stage in the 80–100 K range. They also bleach out together when the sample is exposed to either infrared or visible range light. The [AlO4]0 center which causes the coloration observed in smoky quartz is a plausible model for the visible range photochromic center in BGO:Al.
Temperature stability and corrosion behavior of sintered Nd-Dy-Fe-Co-TM-B magnets, TM:V,Mo (abstract)
Authors: Adler E. , Rodewald W. , Wall B.
Published: July 2002

By simultaneous additions of Co and V or of Co and Mo the temperature stability of sintered Nd-Fe-Al-B magnets can be improved.1–3 A partial substitution of Nd by Dy increases the coercivity by 1.4 kA/cm per wt. % Dy in the alloy, which results in strong coercivities at high temperatures. At 150 °C, for instance, coercivities of about 9 kA/cm can be achieved. The magnetizing behavior is determined by nucleation of reversed domains. A complete magnetization requires a magnetizing field strength of about 25 kA/cm and does not depend on the coercive field strength. Although in Nd-Dy-Fe-Co-Mo-B magnets the Nd-rich Fe eutectic and the Nd1.1Fe4B4 boride are replaced by the Nd3Co compound and the Mo2FeB2 boride, respectively, the corrosion is similar to sintered Nd-Dy-Fe-B magnets. The corrosion rate at the 85 °C–85% relative humidity test is much more determined by the surface treatment of the magnets.
Magnetism and structural stability in CoMn alloys
Authors: Acet M. , John C. , Wassermann E. F.
Published: July 2002

The magnetic and structural properties of Co100−xMnx alloys have been studied in the range 0≤x≤50 at. %. The structural phase diagram, which was revised with the aid of resistivity and thermal-expansion measurements for 4<T<1200 K, shows that the fcc↔hcp (γ↔ε) martensitic transformation temperature in Co-rich ferromagnetic CoMn alloys decreases progressively with increasing Mn content and vanishes at x≂32 at. %, rather than abruptly decreasing at a lower concentration as previously suggested. It is found that antiferromagnetic order, which occurs at x≳32 at. %, causes a large increase in the atomic volume, thereby preventing the structure from collapsing into the smaller volume hcp phase. The atomic volumes at 0 K of fcc Co and fcc Mn, which were determined by extrapolation, were found to be in good agreement with those obtained from band calculations.
Effect of oxide layer on the hysteresis behavior of fine Fe particles
Authors: Gangopadhyay S. , Hadjipanayis G. C. , Shah S. I. , Sorensen C. M. , Klabunde K. J. , Papaefthymiou V. , Kostikas A.
Published: July 2002

The effects of surface oxidation on the structural and magnetic properties of fine Fe particles prepared by the evaporation technique have been studied using transmission electron microscopy, x-ray photoelectron spectroscopy, superconducting quantum interference device magnetometry, and Mössbauer spectroscopy. By varying the argon pressure, particles were obtained with sizes in the range of 60–350 Å. The hysteresis behavior was found to be strongly dependent on the variation in the amount of surface oxidation. The differences in the magnetic behavior due to variation in size and oxidation have been explained by considering a shell/core model for the particle morphology with the shell consisting of Fe oxides surrounding the α-Fe core.
Reflectance modulator utilizing an electro-optic polymer film
Authors: Rider C. B. , Schildkraut J. S. , Scozzafava M.
Published: July 2002

Device fabrication and experimental results are reported for a reflectance modulator in which coupling between a 632.8 nm laser beam reflected from the base of a prism and a guided mode in an electro-optic polymer is electrically varied. The beam intensity was varied ±31% by application of 46 V rms across the polymer. The response is independent of frequency up to at least 5 MHz.
Reaction kinetics of CH radical during etching of polymers in argon and oxygen rf plasmas
Authors: Baggerman J. A. G. , Collart E. J. H. , Visser R. J.
Published: July 2002

During sputtering of polymethylmethacrylate in a low-pressure argon rf plasma, the density and the reaction kinetics of ground-state methylidyne (CH radical) were determined by laser induced fluorescence spectroscopy (LIF). For a plasma in a steady-state condition at 10 Pa and 100 W, the density of CH in the bulk of the plasma was 6.8×1010 cm−3. By pulsing the rf power, the production rate of CH was determined to be 5.1×1013 cm−3 s−1. This production rate was found to be independent of CH density and time after the plasma had been switched on, indicating that CH is not formed in the gas phase, but is sputtered from the substrate. A model, taking diffusion of CH from the substrate into the plasma and chemical reactions in the gas phase into account, has been set up to calculate the CH flux from the substrate surface. The calculated rise curve of CH could be fitted to the measured data with a diffusion coefficient D=1800 cm2 s−1 and an overall reaction rate coefficient k=55 s−1. These data have been used to calculate the total CH flux from the substrate. From this CH flux and the ion current density on the powered electrode, the CH yield was determined to be 0.02 CH radicals per ion, indicating that CH is not the main sputtered species since the overall carbon yield is 4.8 per ion. In an oxygen plasma the CH density is below the detection limit of LIF due to a high overall reaction rate coefficient with O and O2.
Alloy scattering in p-type AlxGa1−xAs
Authors: Look D. C. , Lorance D. K. , Sizelove J. R. , Stutz C. E. , Evans K. R. , Whitson D. W.
Published: July 2002

The hole mobility of Be-doped ( ∼ 2 × 1017 cm−3) AlxGa1−xAs, for x=0–1, is analyzed both theoretically and experimentally. Alloy scattering is very important, and in fact reduces the hole mobility from 150 to less than 90 cm2/V s at x=0.5. The main parameter in the alloy scattering formulation, the alloy potential Eal, is found to be about 0.5 eV for p-type AlxGa1−xAs.
Effect of multilayer structure and laser pulse width on the reversible cycling of phase change optical storage media
Authors: Rubin Kurt A. , Birnie Dunbar P. , Chen Martin
Published: July 2002

The static cycling behavior of chalcogenide phase change optical recording media was investigated. Thin-film multilayer structure and laser pulse conditions were both varied to determine optimum conditions for good cycling behavior. For all structures, cyclability was always best for short pulses. An aluminum overcoat layer was found to substantially increase the performance. The effect of the temperature excursion experienced during writing on cycling was determined. At the shortest pulses it was demonstrated that the thermal excursions did not depend upon the presence of an aluminum overcoat, suggesting that mechanical strength was important for enhancing cyclability. For longer pulses the aluminum changed the thermal characteristics of the stack. These differences between various samples are compared to try to elucidate modes of failure in optical data storage structures.
A multipoint correlation method with binomial weighting coefficients for deep-level measurements in metal-oxide-semiconductor devices
Authors: Dmowski K.
Published: July 2002

A multipoint correlation method is proposed for an improvement in the selectivity of bulk trap and interface-state measurements in metal-oxide-semiconductor devices from capacitance, voltage, and current transients. It relies on using a multipoint weighting function with binomial weighting coefficients instead of a two-point weighting function originally proposed by Lang [J. Appl. Phys. 45, 3023 (1979)].
Mössbauer spectroscopy study on double rare-earth orthoferrites Eu0.2R0.8FeO3 (R=rare earth)
Authors: Liu Xuewu , Jin Mingzhi , Zhang Cailing
Published: July 2002

Double rare-earth ferrites Eu0.2R0.8FeO3 (R=rare earth) are synthesized by a high-temperature method. X-ray-diffraction determinations show that all the compounds possess orthorhombic structure. Both 151Eu and 57Fe Mössbauer spectra are measured. The results indicate that the isomer shift of the 151Eu nucleus depends on the unit-cell volume of Eu0.2R0.8FeO3, and the quadrupole interaction of 151Eu Mössbauer spectra is relative to the inverse of the unit-cell volume. The hyperfine field parameter of 57Fe Mössbauer spectra increases linearly with increasing unit-cell volume.
Characterization of a-SiC:H films produced in a standard plasma enhanced chemical vapor deposition system for x-ray mask application
Authors: Jean A. , Chaker M. , Diawara Y. , Leung P. K. , Gat E. , Mercier P. P. , Pépin H. , Gujrathi S. , Ross G. G. , Kieffer J. C.
Published: July 2002

Hydrogenated amorphous a-SixC1−x:H films with various compositions (0.2≤x≤0.8) were prepared by a radio frequency (rf 100 kHz) glow discharge decomposition of a silane and methane mixture diluted in argon. The deposition system used was a commercially available plasma enhanced chemical vapor deposition reactor allowing a high throughput (22 wafers of 4 in. diameter each run). The properties of the films such as thickness, density, and stress were investigated. The composition, including hydrogen content and Si/C ratio, and the structure of the films were systematically examined by means of several diagnostics including electron recoil detection, x-ray photoelectron spectroscopy, and infrared (IR) absorption analysis. Thickness and density of the films were dependent on the film composition, while the stress of the films was highly compressive (3×109–1×1010 dynes/cm2). Density was about 2.4 g/cm3 for nearly stoichiometric SiC films. The hydrogen content of the films was practically constant at 27 at. % over the whole investigated composition range. The IR analyses suggested that the structure of the silicon carbide films is inorganic-like over the whole range of compositions. From stoichiometric to carbon-rich films, the structure mainly consists of a tetrahedral network where silicon atoms are randomly replaced by carbon atoms and one hydrogen atom is bonded to silicon (SiH group). However, the presence of SiH2 groups and microvoids was observed in the structure of Si-rich silicon carbide films. Finally, the development of SiC membranes for x-ray lithography was presented including the control of film stress by means of rapid thermal annealing. Silicon carbide membranes of relatively high surface area (32×32 mm2) and showing high optical transparency (80%) were successfully fabricated.
Photocurrent multiplication in a hydrogenated amorphous silicon-based p-i-n junction with an a-SiN:H layer
Authors: Yoshimi M. , Ishiko T. , Hattori K. , Okamoto H. , Hamakawa Y.
Published: July 2002

Photocurrent multiplication has been observed in a hydrogenated amorphous silicon-based p-i/a-SiN:H/i-n structure junction under a reverse biased condition. A systematic investigation on the photocurrent characteristics in this junction system has been carried out. It has been shown from the analysis of the results that multiplication arises from the interband tunneling injection of valence band ‘‘electron’’ through the a-SiN:H barrier layer. A device modeling on the basis of the experimental data permits us to design the device structure for achieving better performances. As a preliminary optimization of device structure, an external quantum efficiency exceeding 70 has been obtained under the operation voltage 30 V in the heterojunction photodiode having an a-SiN:H (thickness of 40 nm with optical energy gap 2.1 eV) at the p a-SiC:H/i a-Si:H interface. The proposed highly sensitive photomultiplier device might have a wide variety of application fields such as a solid-state imager for high-definition televisions, etc.