bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlling flux pinning precipitates during MgB2 synthesis
Authors: Liao X. Z. , Serquis A. C. , Zhu Y. T. , Huang J. Y. , Peterson D. E. , Mueller F. M. , Xu H. F.
Published: July 2002

MgB 2 samples prepared by three different sets of synthesis parameters were investigated using transmission electron microscopy. Results suggest that oxygen dissolved in bulk MgB2 at high synthesis temperatures when the MgB2 samples were exposed to trace amount of oxygen from flowing ultrahigh purity Ar gas. The lower solubility of oxygen in MgB2 at a lower temperature led to the precipitation of nanometer-sized coherent Mg(B,O) in the interior of MgB2 grains during subsequent cooling. The precipitates, which act as effective flux pinning centers, are of composition-modulated structures with the same basic crystal lattice and orientation as the MgB2 matrix. This study has demonstrated the potential of tailoring the size and distribution of Mg(B,O) precipitates through optimizing synthesis parameters for optimum flux pinning.
Impurity-free disordering mechanisms in GaAs-based structures using doped spin-on silica layers
Authors: Deenapanray Prakash N. K. , Gong Bin , Lamb R. N. , Martin A. , Fu L. , Tan H. H. , Jagadish C.
Published: July 2002

We have used photoluminescence, deep level transient spectroscopy and x-ray photoelectron spectroscopy to investigate the mechanisms of impurity-free disordering in GaAs-based structures using doped spin-on silica layers. We demonstrate that VGa is efficiently converted into arsenic-antisite, AsGa, related defects (EL2-type defects) when the GaAs layer is under compressive stress. We propose that the efficient formation of EL2-type defects reduces the efficiency of impurity-free interdiffusion of GaAs/AlGaAs quantum wells.
Intersubband staircase laser
Authors: Ulbrich Nicolaus , Scarpa Giuseppe , Böhm Gerhard , Abstreiter Gerhard , Amann Markus-Christian
Published: July 2002

A quantum-cascade laser is presented in which the injection minibands are omitted. The intersubband laser operates as a four-level staircase and has potential for higher gain devices due to an increased confinement factor compared to conventional quantum-cascade lasers. A high threshold current density of 5.9 kA/cm2 with peak output powers of 230 mW at 77 K is observed. A large wavelength shift from 9.3 to 10 μm and broadband emission are observed at higher bias fields. This modification to existing quantum-cascade laser designs has potential for higher gain devices, but problems with thermal backfilling and doping limit the operating temperature currently to 200 K.
Room-temperature operation of electrically pumped quantum-cascade microcylinder lasers
Authors: Anders S. , Schrenk W. , Gornik E. , Strasser G.
Published: July 2002

We present the lasing properties of microcylinder lasers that were processed into a quantum-cascade heterostructure. At room temperature, the GaAs/Al0.45Ga0.55As superlattice structure lases at 12.55 μm. Low mirror losses, an inherent advantage of microcylinder lasers, result in a low threshold current density of 2.2 kA/cm2 at 78 K. The microcylinder lasers compare favorably to both Fabry–Pérot and distributed feedback cavities that were processed from the same material. The maximum operating temperature of the microcylinders, 54 °C, exceeds the previously reported maximum operating temperature, −3 °C, for an InP-based microlaser.
Parametric fluorescence in periodically poled LiNbO3 buried waveguides
Authors: Gallo Katia , De Micheli Marc , Baldi Pascal
Published: July 2002

We report on the periodic poling of LiNbO3 buried waveguides fabricated by reverse proton exchange. We evaluate their linear and nonlinear quadratic properties with the aid of parametric fluorescence.
Room-temperature metallic behavior in nanophase polypyrrole
Authors: Bhattacharyya S. , Saha S. K.
Published: July 2002

An ultrathin layer of polypyrrole (PPy) phase has been grown on the pore wall of a nanoporous template using oxidation polymerization technique. This thin layer of PPy phase shows metallic behavior (positive temperature coefficient of resistance) up to room temperature (300 K) and a metal-insulator transition is observed at around room temperature.
Detection of single charges and their generation-recombination dynamics in Si nanowires at room temperature
Authors: Fujiwara Akira , Yamazaki Kenji , Takahashi Yasuo
Published: July 2002

Detection of single electrons and single holes is demonstrated at room temperature in Si nanowire transistors using an electron-hole (e–h) system. Photogenerated carriers are stored in a quantum dot electrically formed in a Si wire by a front gate. The stored charges affect the current of the other type of carriers that flow along the bottom of the Si wire. The linear photoresponce of single-charge generation is observed. It is revealed that the recombination occurs by a bimolecular process, suggesting that it is due to the e–h interband transition. These results open up the possibility of developing single-photon devices with this system.
Molecular Turing structures in the biochemistry of the cell
Authors: Hasslacher B. , Kapral R. , Lawniczak A.
Published: July 2002

Reactive lattice gas automata simulations show that Turing structure can form on a mesoscopic scale and are stable to molecular fluctuations in this domain. Calculations on the Sel’kov model suggest that Turing instabilities can give rise to global spatial symmetry breaking in ATP concentration within the cell cytoplasm with a mesoscopic Turing scale well within typical cell dimensions. This leads to a new mechanism for the global breaking of energy distribution in the cell. It also leads to reappraisal of the importance of the Turing effect on extended biochemical spatial structures and energy transport available to cell morphogenesis.
The transient behaviour of models of bowed-string motion
Authors: Schumacher R. T. , Woodhouse J.
Published: July 2002

Theoretical models of the action of a bowed string may be able to shed light on differences of ‘‘playability’’ between different violins. Subjective judgements seem to be concerned, at least in part, with the robustness with which one particular oscillation regime of the string (the ‘‘Helmholtz motion’’) may be obtained under different bowing conditions. In this paper, after a review of bowed-string modelling, systematic simulation is used to obtain plots of the basin of attraction of the Helmholtz motion in a particular subspace of the player’s control space. Variations in the size and structure of this basin of attraction are seen when parameters of the problem are varied, and some physical interpretation of these variations is given. Some parallels and contrasts are pointed out between the particular features of the bowed string as a nonlinear system, and the range of more familiar dynamical systems.
A numerical method for the solution of the bidomain equations in cardiac tissue
Authors: Keener J. P. , Bogar K.
Published: July 2002

A numerical scheme for efficient integration of the bidomain model of action potential propagation in cardiac tissue is presented. The scheme is a mixed implicit–explicit scheme with no stability time step restrictions and requires that only linear systems of equations be solved at each time step. The method is faster than a fully explicit scheme and there is no increase in algorithmic complexity to use this method instead of a fully explicit method. The speedup factor depends on the timestep size, which can be set solely on the basis of the demands for accuracy.
Entropy balance, time reversibility, and mass transport in dynamical systems
Authors: Breymann Wolfgang , Tél Tamás , Vollmer Jürgen
Published: July 2002

We review recent results concerning entropy balance in low-dimensional dynamical systems modeling mass (or charge) transport. The key ingredient for understanding entropy balance is the coarse graining of the local phase-space density. It mimics the fact that ever refining phase-space structures caused by chaotic dynamics can only be detected up to a finite resolution. In addition, we derive a new relation for the rate of irreversible entropy production in steady states of dynamical systems: It is proportional to the average growth rate of the local phase-space density. Previous results for the entropy production in steady states of thermostated systems without density gradients and of Hamiltonian systems with density gradients are recovered. As an extension we derive the entropy balance of dissipative systems with density gradients valid at any instant of time, not only in stationary states. We also find a condition for consistency with thermodynamics. A generalized multi-Baker map is used as an illustrative example.
Numerov integration for radial wave equations in cylindrical symmetry
Authors: Onodera Y.
Published: July 2002

Numerov’s method, which is commonly used in numerical integration of a class of second-order differential equations lacking the first derivative, is generalized to cover radial wave equations in cylindrical geometry. The proposed scheme is compared with the Runge–Kutta method and the conventional Numerov method by numerically integrating Bessel’s differential equation.
FeTAC, a chainlike metamagnet
Authors: Landee C. P. , Greeney R. E. , Reiff W. M. , Zhang J. H. , Chalupa J. , Novotny M. A.
Published: July 2002

Single crystal susceptibility, magnetization and powder Mössbauer spectroscopy measurements are reported for [(CH3)3NH]FeCl3 ⋅ 2H2O, FeTAC. Powder x-ray studies show this compound to be isomorphous to previously studied one-dimensional compounds. The low-temperature susceptibilities are highly anisotropic with the greatest susceptibility along the chain (b) axis. Antiferromagnetic ordering is observed in both the susceptibility data and the Mössbauer spectra near 3.2 K. Metamagnetic transitions occur when small fields (less than 200 Oe) are applied parallel to the b axis. The data are interpreted in terms of a model of antiferromagnetic Ising-like chains aligned along the a axis while canted towards b. Results of a molecular field model for weakly coupled Ising chains are also presented.
Optical behavior of sputter-deposited platinum-oxide films
Authors: Aita Carolyn Rubin
Published: July 2002

A series of platinum-oxygen alloys were grown by sputter deposition using a platinum target and rf-excited, oxygen-bearing discharges. The films were deposited on water-cooled single-crystal silicon and glass substrates. Optical behavior in the near-ultraviolet–visible–near-infrared region was studied by spectrophotometry. Changes in reflection and transmission were correlated with changes in film chemistry and structure. The absorption coefficient and two-infrared optical transitions across the band gap were determined for a semiconducting Pt-oxide phase, identified by x-ray photoelectron spectroscopy as α-PtO2. These transitions occur at 1.30 eV (0.95 μm) and 1.47 eV (0.84 μm).
Optimum extracted negative-ion current densities from tandem high-density systems
Authors: Hiskes J. R. , Karo A. M. , Willmann P. A.
Published: July 2002

A tandem high-density hydrogen negative-ion-source system is optimized for the purpose of identifying the maximum possible extracted ion current densities. In the first chamber, vibrational excitation occurs by high-energy electron excitation (E-V process); in the second chamber negative ions are formed by dissociative attachment. The electron, atom, and molecular densities are varied together with the length of the second chamber. Electron excitation cross sections to the B1∑u and C1∏u states are calculated as a function of vibrational excitation. The vibrational excitation approaches an asymptotic value as the first-chamber electron density increases. For a system with scale length R=10 cm the optimum extracted current densities occur for gas densities near 1015 mol cm−3 for first-chamber electron densities equal to 1013 cm−3, and for second-chamber electron densities in the 4–6×1012 cm−3 range. For atomic densities equal to one-tenth the molecular density and for second-chamber scale lengths as short as Z/R=0.2, extracted current densities are approximately 30 mA cm−2. As Z/R decreases toward 0.1, the current density is doubled. If the atomic density is increased to one-fifth the molecular density, these current densities are halved; for atomic densities equal to the molecular density, these current densities are reduced by a factor of 6. Applying the system scaling law and varying R from 10 cm toward 1 cm, the extracted current densities tend toward several hundred mA cm−2.
Barrier height enhancement of triangular barrier diodes
Authors: Gupta R. S. , Chilana G. S. , Srivastava G. P.
Published: July 2002

A modified model of a triangular barrier diode has been proposed and analyzed by considering the effect of low to moderate p-type doping in the two intrinsic regions. The presence of such acceptor impurities is shown to increase the effective barrier height. The functional dependence of barrier height, saturation current, and ideality factor on various technological parameters is discussed. A method to determine the barrier height and effective Richardson constant has also been suggested. The high-speed switching behavior of this diode is shown to improve.
Thermal oxidation of heavily boron-implanted polycrystalline-silicon films
Authors: Lu C. Y. , Tsai N. S.
Published: July 2002

The thermal oxidation of heavily boron-implanted low-pressure chemical vapor deposition (LPCVD) polysilicon films in dry and wet oxygen ambients has been studied. In order to understand the roles of grain boundaries, randomly oriented crystallites, and the doping effect on oxidation behavior in polysilicon films, detailed comparisons were made among the relative oxidation behaviors for polysilicon films and single-crystal silicon. The results show no significant difference for the doping effect on oxidation rate enhancement for polysilicon films and single-crystal silicon, and are consistent with the model proposed by Saraswat and Singh.
An estimate for tolerable electron velocity spread in cyclotron resonance masers
Authors: Haldar M. K. , Tjhung T. T.
Published: July 2002

It is well known that the dispersion relation for cyclotron resonance masers (gyrotrons) is similar to the dispersion relation for traveling wave tubes (TWT’s). This dispersion relation is obtained for monoenergetic electron beams. Based on the study of the TWT dispersion relation by Pierce, an expression for the tolerable electron velocity spread in cyclotron resonance masers has been derived.
Modeling of heat flow in multilayer cw laser-annealed structures
Authors: Waechter D. , Schvan P. , Thomas R. E. , Tarr N. G.
Published: July 2002

The three-dimensional heat diffusion equation has been solved numerically for scanning cw laser-annealed multilayer structures. The computational method can be applied to laser beams with either circular or elliptical symmetry. The temperature dependence of relevant optical and thermal properties has been included and good agreement with experimental results is obtained. The dynamics of melting are examined and discussed. It is found that the presence of a thin buried oxide in a silicon wafer substantially increases the sensitivity of the maximum melt depth to laser power.
Formation of negative hydrogen ions on a coadsorbed layer of cesium and hydrogen on W(110)
Authors: van Amersfoort P. W. , Geerlings J. J. C. , Rodink R. , Granneman E. H. A. , Los J.
Published: July 2002

Negative ion formation on a W(110) surface which is covered with a coadsorbed layer of cesium and hydrogen is studied by scattering a proton beam from such a surface. The primary energy is 400 eV. The angle of incidence is 70° with respect to the surface normal. The hydrogen exposure ranges from 0 to 3000 L. The negative ion formation probability on a surface with 0.6 times the saturation cesium coverage is reduced by a factor of 4 by a hydrogen exposure of 3000 L. At small coverage the reduction is found to be proportional to the number of adsorbed hydrogen atoms. The formation probability on a surface which is covered with a thick cesium layer is hardly affected by a similar exposure. These phenomena are attributed to resonant electron transfer between a negative ion and an adsorbed hydrogen atom.
Selected-area sputter epitaxy of iron-garnet films
Authors: Krumme J.-P. , Doormann V. , Strocka B. , Willich P.
Published: July 2002

The growth of single-crystal bismuth iron-garnet films by in situ sputter epitaxy has been extended to ‘‘selected-area sputter epitaxy’’ (SASE) where epitaxial growth is locally impeded by low-energy (102 eV) ion bombardment of the substrate from an argon plasma before film deposition. Then, in a critical range of substrate temperatures, a pattern of epitaxial and amorphous patches evolves during deposition with high geometrical resolution. The optical and structural properties of both SASE phases are investigated.
Electronic transport investigations on silicon damaged by arsenic ion implantation
Authors: Jaouen H. , Ghibaudo G. , Christofidès C.
Published: July 2002

Electronic transport properties of heavily doped arsenic implanted silicon are reported. Hall mobility and sheet resistance as functions of temperature and frequency have been carried out both on annealed and as-implanted silicon films. The small values of the observed Hall mobility and strong frequency dependence of the transport coefficients emphasize the drastic alteration of nonannealed material. A semiquantitative analysis of the results is conducted using both short-range and long-range disorder considerations (hopping and percolation).
Effect of hydrogen chloride during oxidation of silicon on trap generation by avalanche electron injection
Authors: Chen Ann Joyce , Dadgar Suzanne , Hsu Charles Ching-Hsiang , Pan Samuel Cheng-Sheng , Sah Chih-Tang
Published: July 2002

The effects of HCl on trap generation in silicon dioxide layers at high electric fields are reported by comparing 700-Å, 200-Å, 9% HCl, and 0% HCl dry oxides stressed at constant avalanche electron injection currents and voltages. Experimental data indicate that HCl decreases the hydrogenation rate of boron acceptor in the silicon surface layer due to a high-density chlorine layer at the oxide/silicon interface but HCl increases the density of the peaked interface trap at 0.3 eV above the silicon midgap. A new chlorine-related positively charged electron trap in the oxide is observed and isolated from the chlorine-independent negatively charged oxide hole trap. Chlorine also reduces the density of the smaller cross-section oxide electron trap which gives the turn-around phenomena.
A model describing the electrical behavior of a-SiN:H alloys
Authors: Osenbach J. W. , Knolle W. R.
Published: July 2002

The electrical properties of plasma-deposited amorphous silicon nitride hydrogen alloys (a-SiN:H) deposited at different rf powers were determined. The N–H and Si–H content of these films were determined using a Fourier transform infrared spectrometer. The N–H content was relatively insensitive to the deposition conditions; however, the Si–H content was very sensitive to the deposition conditions. The conductivity of the films was found to depend upon the Si–H content [Si–H] and was given by σ=7.25×10−21 exp(2.74×10−21[Si–H]) at 70 °C and 4×106 V/cm. The high-temperature activation energy (i.e., trap height) was also strongly dependent on the Si–H content. A model is proposed which qualitatively explains the electrical behavior of the films. The material is considered to be a two-phase mixture: Phase 1 is highly structured (Si3N4-like) which has a low level of defects, and a low hydrogen content; Phase 2 is highly disordered with a high concentration of Si–H and N–H defect states and a high hydrogen content. At low temperatures the disordered structure controls the conductivity and at high temperatures the ordered phase controls the conductivity. The percentage of phase 2 decreases with decreasing hydrogen content. This decrease causes an increase in the trap height that leads to an exponential decrease in the mobility which in turn causes the conductivity to decrease exponentially.
Identification of intrinsic gettering centers in oxygen-free silicon crystals
Authors: Ueda O. , Nauka K. , Lagowski J. , Gatos H. C.
Published: July 2002

Intrinsic gettering centers in oxygen-free silicon crystals after a high–low–medium-temperature annealing cycle were successfully identified using transmission electron microscopy and energy dispersive x-ray spectroscopy. These centers have a butterfly-type shape and they consist of interstitial-type extended multiple dislocation loops in {110} planes of 0.1–0.7 μm diameter and a high density of small 3–15-nm-diam precipitates located inside the dislocation loops and/or on the dislocation line. Compositional x-ray analysis identified Cu as the predominant metal component of the precipitates. Occasionally Ni and very rarely Fe were also detected.
Diffusion of ion-implanted As in TiSi2
Authors: van Ommen A. H. , van Houtum H. J. W. , Theunissen A. M. L.
Published: July 2002

Arsenic has been implanted into TiSi2 films to study its diffusivity during subsequent annealing between 600 and 800 °C in vacuum. The diffusion coefficient turns out to be so high that the As redistributes over the entire TiSi2 film (thickness 200 nm) at temperatures as low as 600 °C. In addition to this some of the As segregates at the TiSi2/polycrystalline Si interface and part of the implanted As remains immobile in the as-implanted distribution. The mobile fraction is limited by the solubility of As in TiSi2 which has been determined from the As concentration in the bulk. This solubility turns out to be quite substantial and could be described by a Boltzmann relation with an activation energy of 1 eV and a preexponential factor of 1.06×1025 at/cm3. Evaporation of As occurs above 600 °C and can be prevented by oxidizing the TiSi2 film. The electrical resistivity and the stress of the silicide film indicate that implantation damage can only be eliminated by annealing at 800 °C, the sintering temperature of the silicide.
Behavior of hydrogen in palladium-aluminum metal-oxide-semiconductor structures
Authors: Enquist F. , Armgarth M. , Lundström I.
Published: July 2002

A new possibility to study hydrogen in composite metal films through the use of hydrogen sensitive palladium gate metal-oxide-semiconductor devices is described. Results on the behavior of hydrogen in composite layers of aluminum and palladium are presented. It is concluded that although hydrogen atoms pass through a noncatalytic Al layer, there are no adsorption sites with polarized hydrogen atoms at an Al-SiO2 interface.
Ferromagnetic resonance behavior of evaporated Gd-Fe alloy films
Authors: Lee S. R. , Miller A. E. , Blackstead H. A.
Published: July 2002

The bulk and local magnetic properties have been investigated for evaporated Gd-Fe alloy films. The origin of the multiresonance fields of amorphous Gd-Fe alloy films was speculated to be due to several compositionally different short-range-ordered structures. These results yield the locally different magnetic properties, such as the Curie temperatures, magnetizations, g values, and anisotropy field difference. The magnetization of the annealed alloy film increase mainly due to the ferromagnetically ordered α-Fe and α-Gd precipitates.
Nuclear magnetic resonance imaging of temperature profiles
Authors: Suits Bryan H. , White David
Published: July 2002

Nuclear magnetic resonance imaging using 81Br is used to obtain measurements of an inhomogeneous temperature distribution in KBr. Possible applications of the technique are presented.
Measurements of mass ablation rate and pressure in planar targets irradiated by 0.27-μm laser light
Authors: Boehly T. , Tanaka K. A. , Mochizuki T. , Yamanaka C.
Published: July 2002

Planar CH targets were irradiated by 400-ps and 1-ns pulses of 0.27-μm light at intensities of 5×1012–1014 W/cm2. The mass ablation rate obtained from time integrated x-ray line emission from layered targets was found to be ṁ=1.5×105(Ia/1013 W/cm2)0.5 g/cm2 s. Using this result and the ion blowoff velocity, the ablation pressure scaled as Pa=3.9 (Ia/1013 W/cm2)0.6 Mbar. Comparisons to similar experiments at 0.53 μm indicate that the mass ablation rate and pressure scale with laser wavelength as λ−1.4 and λ−0.9, respectively. The intensity and wavelength scalings are found to agree with analytic predictions for spherical geometry rather than planar models. Comparisons are also made with previously reported measurements at other wavelengths and geometries.
Anisotropy dispersion and its influence on magneto-optical effect in rare-earth transition-metal amorphous films
Authors: Togami Y. , Saito N. , Okamoto K.
Published: July 2002

Magnetic anisotropy dispersion in sputter-deposited rare-earth transition-metal amorphous films is measured by the methods of Hall hysteresis loops and torque magnetometry. The inhomogeneity in the orientation of the easy axes of magnetization is found to be rather large; the mean inclination angle of the axes from film normal is 16.5° in a Gd–Tb–Fe film. Results show a clear correspondence between the anisotropy dispersion and Kerr rotation angle, and both depend on the bias voltage applied to the substrates during sputtering. Anisotropy dispersion is an important property for evaluating the amorphous magnetic films for magneto-optical storage application.
Structural characterization of Ti-Si thin-film superlattices
Authors: Brasen D. , Willens R. H. , Nakahara S. , Boone T.
Published: July 2002

Thin films of amorphous/polycrystalline Ti layers alternating with amorphous Si have been grown on room-temperature {001} Si substrates by electron beam evaporation. Cross-section transmission electron microscopy of these films indicates that the deposition results in the formation of ultrathin superlattice layers with no cumulative roughening and with atomically abrupt interfaces. The crystallinity of the layers containing Ti is found to depend on the layer thickness. For thicknesses ≤20 Å they appear amorphous, whereas layers thicker than ∼40 Å consist of polycrystalline hexagonal Ti grains exhibiting a (0001) preferred orientation parallel to the interfaces.
A spectrum converter dye for enhancement of blue-green laser efficiency
Authors: Han K. S. , Oh C. H. , Lee J. H.
Published: July 2002

In order to enhance the efficiency of a blue-green laser through spectrum conversion of the pumping light, a converter dye BBQ was mixed in the laser dye solutions. The laser was pumped with a plasma radiation source. The increase of laser output over the maximum obtainable from the pure dye operation was better than 80% for the dye mixture of LD490+BBQ or coumarin 503+BBQ. The estimated enhancement calculated by a simple spectrum conversion model agrees well with the experimental results. The enhancement is mainly effected by irradiance in the UV from the pumping source, the fairly good match of the fluorescence band of converter dye with the absorption band of the laser dye, and the lack of the overlap of the fluorescence band of the laser dyes with the triplet–triplet absorption band of the converter dye used.
Theory of transient temperature response of a two-layer system heated with a localized laser beam
Authors: Abtahi Abdollah , Braunlich Peter F. , Kelly Paul
Published: July 2002

A general solution of the heat diffusion equation is presented for the case of a semi-infinite two-layer system that is heated with a localized cw laser beam of Gaussian or uniform circular intensity profile. As an example, this theory is applied to thin layers of a thermoluminescent material on glass substrates. The transient thermoluminescence emission response is calculated and compared with experimental results, illustrating the validity of the solutions. Applications to transient laser heating of oxide-semiconductor sandwiches are discussed.
Influence of growth conditions on undoped and sulfur-doped InP grown by molecular-beam epitaxy
Authors: Iliadis A. , Prior K. A. , Stanley C. R. , Martin T. , Davies G. J.
Published: July 2002

Undoped and sulfur-doped InP have been grown by molecular-beam epitaxy. Undoped InP is n type and contains residual sulfur incorporated from the phosphorus source material. Increasing substrate temperatures during growth cause a decrease in the residual doping level to 2–3×1015 cm−3 but are associated with an increase in the compensation ratio and an increase in the concentration of epilayer defects, up to 105 cm−2. Doping with sulfur produced from an electrochemical sulfur cell has been studied in the range 5×1016–6×1019 cm−3. Highly doped layers show greatly improved surface morphology compared to low and undoped InP layers. Sulfur is shown not to diffuse to any measurable extent during MBE growth; however, at high growth temperatures (530 °C) there is loss of sulfur as a volatile indium sulfide. The removal of the surface oxide from the InP substrate before growth has been studied as a function of substrate temperature and phosphorus overpressure. The oxide layer can be removed at a low temperature (∼480 °C) by using a low pressure of P4 rather than P2 as is used during growth. The low-temperature oxide removal leads to improved epilayer morphology for undoped layers. The removal of the surface oxide and the loss of sulfur during growth as a volatile sulfide are discussed in terms of the free energy of formation of the various possible products.
Nonlinear optical properties of thin films of polysilane
Authors: Kajzar F. , Messier J. , Rosilio C.
Published: July 2002

Optical third harmonic generation measurements by transmission have been performed on thin films of polysilane deposited by a spinning technique with a thickness varying between 0.15 and 0.45 μm. The films have a good optical quality and support large laser power (∼200 MW/cm2 at 1.064 μm). They are transparent in visible and near infrared. The measured average value of cubic susceptibility 〈χ(3)xxxx (−3ω; ω,ω,ω)〉 is equal to (1.5±0.1)×10−12 esu at 1.064 μm. The technique used for the third harmonic generation measurements allows determination of both modulus and phase of χ(3). It is argued that the large value of χ(3) is due to a three-photon resonance at 1.064 μm.
Electron capture processes in ZnS: The role of Al related and other donors
Authors: Przybylińska H. , Godlewski M.
Published: July 2002

A transient electron spin resonance experiment shows that the Al-related donor in ZnS plays an insignificant role in electron-capture processes, which are dominated by a 35-meV native donor of unknown nature. The methods of determining effective capture cross sections of these donors are discussed.
Characterization of transport parameters of hole traps in phosphorus-doped hydrogenated amorphous silicon
Authors: Oheda Hidetoshi
Published: July 2002

The presence of two kinds of hole traps in phosphorus-doped hydrogenated amorphous silicon has been previously clarified from the analysis of the excitation-energy dependence of the steady-state lifetimes; namely, X and Y states are located at about 1.1 eV and at an eneergy shallower than 0.7 eV below the conduction-band edge, respectively. In order to characterize the role of these hole traps in transport processes, transient photocurrent decays induced by a single pulse of light were measured at several excitation energies in a frequency domain as well as in a time domain. Almost the same photoresponses have been observed under the excitation with an energy is greater than 1.1 eV irrespective of whether the excitation energy is above or below the band-gap energy. It has been concluded that the relative magnitude of hole-capture coefficients of these hole traps is equivalent to that of optical-transition coefficients of respective hole traps. The recombination coefficients of electrons of these hole traps have been also discussed on the basis of the excitation-energy dependence of the steady-state lifetimes. It has een inferred that the Y state has a recombination coefficient higher by at least one order of magnitude than the X state.
High-energy photon spectra from a coaxial gas-puff experiment
Authors: Warren S. W. R. , Degnan J. H. , Beason C. W. , Price D. W. , Snell M. P.
Published: July 2002

An array of plastic scintillator photomultiplier detectors was used to determine the high-energy (hν>35 keV) photon spectra of a 130-kJ, 60-kV gas-injected coaxial gun experiment. The detector array used six different filter material/thickness combinations. High-energy photon signals were readily observed. The spectra were determined by deconvolution. The spectra have three characteristic components—radiative emission from high Z impurities in the plasma, beam-target excited line emission, and thick-target bremsstrahlung from an electron beam generated in the plasma column. The electron beam consistent with the thick-target bremsstrahlung assumption was of the order of 100 A above 10 keV.
Deep-level photoluminescence spectroscopy of CdTe grown by molecular-beam epitaxy
Authors: Han He-Xiang , Feldman Bernard J. , Wroge M. L. , Leopold D. J. , Ballingall J. M.
Published: July 2002

We report the observation of a broad photoluminescence line at 0.75 eV in CdTe grown by molecular-beam epitaxy at both high- and low-substrate temperatures. This line is in excellent agreement with the E2 line observed by deep-level transient spectroscopy by previous workers. The origin of both of these lines is probably a deep defect or impurity level native to CdTe.
Detection of minority-carrier defects by deep level transient spectroscopy using Schottky barrier diodes
Authors: Auret F. D. , Nel M.
Published: July 2002

The injection of minority carriers into Schottky barrier diodes (SBDs) is controlled by the barrier height φb, the substrate doping density, the forward current density, and the geometry of the SBD, among others. Previously it was shown that the detection of minority-carrier defects by deep-level transient spectroscopy (DLTS) using SBDs without optical injection is possible if SBDs with ultrahigh barrier heights (e.g., φb>0.90 eV for n-Si) are used. In the present paper it is shown that minority-carrier defects may also be detected by DLTS using SBDs with moderately high barrier heights (φb=0.83 eV) on low doped n-Si, provided the SBD is forward biased during the DLTS filling pulse.
The effect of scan velocity on the measurement of semiconductor parameters by optical-beam excitation
Authors: Wilson T. , Pester P. D.
Published: July 2002

We analyze the effect of the speed of scanning a monochromatic light source across a p-n junction which is perpendicular to the sample surface. It is found that the collected junction current is sensitive to both the magnitude of scan speed and also its direction. This provides a simple method of determining both the minority-carrier-diffusion coefficient and lifetime independently. Scan speeds as small as 10% of the diffusion velocity can significantly modify the form of the junction current versus scan-position curve. The conclusions apply qualitatively to analogous techniques in the scanning electron microscope.
Electron mobility and compensation ratios in high-purity n-type InP
Authors: Taguchi Akihito , Yamada Syoji
Published: July 2002

Theoretical and experimental studies of electron mobility and compensation ratio in n-type InP are reported. From far-infrared magnetoabsorption measurements, compensation ratios of nine epitaxial samples are determined experimentally. Electron mobility is calculated by considering all essential scattering processes and by taking into account the compensation effect. By comparing the theoretical results with the experiments, it is found that the appropriate deformation potential and piezoelectric constant values for InP are 6.5 eV and 0.01, respectively. A new electron mobility and carrier concentration relationship, which can be used to determine the compensation ratio of high-purity n-type InP, is proposed.
Phase equilibria in metal-gallium-arsenic systems: Thermodynamic considerations for metallization materials
Authors: Beyers Robert , Kim Ki Bum , Sinclair Robert
Published: July 2002

We propose a classification scheme for phase equilibria in elemental metal-gallium-arsenic systems. Using available data we assign as many metals as possible to seven generic types of ternary phase diagrams. We describe how the phase diagrams can provide a framework for interpreting previous studies of metal reactions with GaAs substrates and for identifying stable materials for GaAs metallizations.
Multiple hydrogen occupancy of vacancies in Fe
Authors: Besenbacher F. , Myers S. M. , Nordlander P. , No/rskov J. K.
Published: July 2002

The binding of multiple deuterium (D) atoms to vacancies in iron (Fe) is investigated both experimentally, by use of ion-beam techniques, and theoretically, by use of the effective-medium scheme. The experimental D-release stages are accounted for by trapping at vacancies with a binding enthalpy that depends on occupancy. It is found that for 1–2 D in a vacancy, the trap strength is 0.63 eV, whereas the binding enthalpy for 3–6 D in a vacancy is 0.43 eV. These results are in good agreement with predictions from the effective-medium theory.
Investigation of zinc incorporation in GaAs epilayers grown by low-pressure metalorganic chemical-vapor deposition
Authors: Chang C. Y. , Chen L. P. , Wu C. H.
Published: July 2002

Low-pressure metalorganic chemical-vapor deposition was adopted to grow p-type GaAs epilayers. Triethylgallium and arsine (AsH3) are used as Ga and As sources, respectively. Diethylzinc (DEZn) is used as a p-type dopant. The hole-carrier concentration and zinc incorporation efficiency are studied by Hall measurements and 16-K photoluminescence spectral. The influence of growth parameters, such as the DEZn mole fraction, growth temperature, and AsH3 mole fraction, on the zinc incorporation and the epilayer growth rate are discussed. The hole-carrier concentration increases with increasing DEZn and AsH3 mole fractions and decreases with increasing growth temperature. A vacancy control model can be adopted to explain the above results consistently. The growth rate of the epilayer is enhanced by zinc incorporation and decreases with increasing growth temperature. The decrease in growth rate is presumably due to the decrease in diethylzinc incorporation at higher growth temperatures.
Conductance of silicon grain boundaries in as-grown and annealed bicrystals
Authors: Poullain G. , Mercey B. , Nouet G.
Published: July 2002

The conductivity across the grain boundary plane was investigated on p-type silicon bicrystals. A correlation was found between the electrical properties and the crystallographic structure for boundaries with the coincidence structures Σ9, 13, 25, 27, and for noncoincidence orientations with Σ>100. The boundaries were analyzed using electron beam induced current (EBIC) (minority carriers) and conductance measurements (majority carriers). The influence of a vacuum heat treatment (850 °C, 30 min) was studied for the different grain boundary structures. This was compared with an annealing at 850 °C in a POCl3 atmosphere as used in the solar cell diffusion step. A narrow band centered respectively at 0.14 and 0.10 eV above the valence band is proposed to explain the experimental behavior of the Σ25 and 27 boundaries.
Studies of microwave radiation from a low-energy rotating electron beam in a multiresonator magnetron cavity
Authors: Chojnacki E. , Destler W. W. , Lawson W. , Namkung W.
Published: July 2002

The generation of microwave radiation at high harmonics of the cyclotron frequency by a low-energy annular rotating electron beam (27 kV, 1 A, 3 μs) via interaction with the modes of a magnetron-type conducting boundary has been studied experimentally. Details of producing the axis-encircling E layer by magnetic cusp injection are presented. Narrow-band microwave radiation has been obtained from the device at power levels of 9.1 kW at 6.78 GHz (eighth cyclotron harmonic) and 2.2 kW at 8.85 GHz (tenth cyclotron harmonic). Measurements of the radiated power spectra and confining magnetic field have allowed identification of operating waveguide modes and instability mechanisms. An experimental comparison with respect to threshold beam power is presented between waveguide structures operating in the π mode and the 2π mode.
Identification of acceptors and donors in high-purity InP grown by metalorganic chemical vapor deposition
Authors: Uwai Kunihiko , Yamada Syoji , Takahei Kenichiro
Published: July 2002

Photoluminescence at 1.9 K and far-infrared photoconductivity at 4.2 K reveal that Si and S are the predominant residual donors and Zn is the predominant acceptor in high-purity epitaxial InP grown by metalorganic chemical vapor deposition using triethylindium at temperatures from 575 to 700 °C. The epitaxial layers show 77 K electron Hall mobilities exceeding 100 000 cm2/V⋅s. Si accumulation near the epitaxial layer/substrate interface is revealed by far-infrared photoconductivity measurements. Although no residual C acceptor is observed in any samples, an unidentified acceptor called A1 is observed in samples grown at 700 °C.
Current noise in silver β″ alumina ceramics and single crystals
Authors: Brophy James J.
Published: July 2002

Conductivity fluctuations and contact noise observed in ceramic and single-crystal silver β″ alumina are very similar to those in sodium β″ alumina. The current-noise spectral density varies as f−3/2, indicative of diffusion noise, is thermally activated with an activation energy of 0.5 eV, significantly smaller than for sodium β″ alumina. In both materials, single-crystal specimens are noisier than the ceramics, and the granular nature of the ceramics does not seem important in the diffusion noise process. The standard expression for diffusion noise is unable to account for either the observed noise magnitude or the temperature dependence.
Laser-stimulated thermoluminescence. II
Authors: Kelly Paul , Abtahi Abdollah , Braunlich Peter F.
Published: July 2002

The theory of heating a semi-infinite two-layer system with a localized CO2 laser beam of uniform circular intensity profile is applied to configurations consisting of thin thermoluminescent LiF:Mg,Ti phosphor layers on borosilicate glass substrates. We study thermoluminescence because it serves as a convenient monitor for the temperature distribution and because of its importance in developing the laser-heating technique for solid-state dosimetry. Experimental and calculated results are compared in an attempt to completely characterize the thermoluminescence response curves. The two-layer system is heated in two different modes: the laser beam impinges onto (a) the phosphor layer, and (b) the glass substrate. We investigate in detail changes in the thermoluminescence response due to different laser powers and variations in the optical and thermal properties of the samples.
The design of a small-orbit/large-orbit gyroklystron experiment
Authors: Lawson W. , Latham P. E.
Published: July 2002

Detailed here are the characteristics of the designs of a 500-kV, 45-A electron gun and two 10-GHz gyroklystron circuits. The electron gun produces a rotating beam by passing an annular, linearly streaming beam through a nonadiabatic magnetic transition followed by an adiabatic-compression region. It is demonstrated that the same gun can produce either a small-orbit beam suitable for interaction with a TEo01 cavity mode or a large-orbit beam suitable for interaction with a TEo31 cavity mode. A detailed comparison of the relevant circuit characteristics, including peak gain and efficiency, performance degradation with increasing velocity spread, and AM and PM sensitivities to voltage and current fluctuations, is made.
Two-dimensional defects in InSe
Authors: Houdy Ph. , Maurice J. L. , Besson J. M. , Laval J. Y. , Chevy A , Gorochov O.
Published: July 2002

Two-dimensional precipitates associated with stacking faults in layer semiconductors have previously been put forward to explain transport properties of these crystals, especially their remarkable electrical anisotropy. High-field cyclotron resonance behavior, among others, can be accounted for by two-dimensional accumulation layers in the vicinity of these defects. Direct evidence for the existence of these defects has been obtained by electron microscopy and x-ray microprobe analysis in indium selenide. Planar faults act like sinks for impurity atoms. This accounts for the unique behavior of layer compounds which exhibit intrinsic behavior (low apparent carrier concentration—high mobilities) even with high (100 ppm) initial doping levels. Optical, transport, and magnetotransport properties at low temperature can be explained along this model. As regards the applications of indium selenide to the photovoltaic conversion of solar energy, the existence of these defects explains most features of this semiconductor in this respect: (i) Its comparatively low effective diffusion length parallel to the c axis. (ii) p- to n-type switching under thermal annealing which allows fabrication of p-n junctions. (iii) Low apparent carrier density which precludes abrupt profiles for p-n structures.
Surface-depletion effect correction to nonuniform carrier distributions by Hall measurements
Authors: Yeo Y. K. , Hengehold R. L. , Elsaesser D. W.
Published: July 2002

Significant errors in the determination of carrier profiles obtained by the Hall-effect method result if the depletion effect at a semiconductor surface is not taken into account. A practical procedure for correcting the apparent measured carrier profiles for this surface-depletion effect is described for nonuniformly doped semiconductors. This correction method is then applied to Si-implanted GaAs and the results are compared with those of capacitance-voltage measurements. The number of total trapped charges in free-surface states are estimated to be about 1×1012 cm−2.
High-energy ion irradiation effects on the surfaces of silicon carbide and silicon nitride
Authors: Bhattacharya R. S. , Rai A. K. , Pronko P. P.
Published: July 2002

High-energy ion irradiation effects on the surfaces of α-silicon carbide (SiC) and hot-pressed silicon nitride (Si3N4) were studied by optical microscopy, surface profilometry, Auger electron spectroscopy, and transmission electron microscopy (TEM) techniques. Optical microscopy and surface profilometry revealed that 1-MeV Ni+ ion irradiation at a dose of 1×1016 cm−2 produces swelling and roughness on both SiC and Si3N4. Auger electron spectroscopy in combination with sputtering revealed that the SiC surface becomes C rich, whereas the Si3N4 surface becomes Si rich due to ion irradiation. Cross-section TEM analysis of the surface layer of irradiated SiC showed that about 1 μm of material at the surface has become amorphous due to irradiation with 1-MeV Ni+ at a dose of 1×1016 cm−2. Amorphization has also been observed in Si3N4. These results are discussed with reference to the information available in the literature.
Defect-induced compensation in the bulk of implanted indium phosphide
Authors: Rao E. V. K. , Djamei M. , Krauz P.
Published: July 2002

By studying the properties of nondopant impurities (P and In matrix elements, and Fe deep impurity) implanted Zn-doped p+-InP (p∼7×1017 holes cm−3) before and after varied annealing treatments (conventional furnace and rapid thermal anneals), we show the following; (i) the implantation-induced defects lead to electrical compensation in the bulk of InP far beyond the implanted regions; (ii) the compensating centers result from a direct interaction between fast diffusing defects (both during implantation and annealing processes) and Zn atoms.
The heteroepitaxial growth of ZnSe on GaP and GaAs substrates
Authors: Fuke S. , Ogawa K. , Kuwahara K. , Imai T.
Published: July 2002

Single-crystal layers of ZnSe have been grown on GaP and GaAs substrates in a hydrogen transport system. By the use of the H2 bypass flow, the growth rate versus substrate temperature characteristics are found to be modified. The growth on GaP (111)B substrates is limited by thermodynamic mass transport and that on GaP (100) substrates by the kinetics of the surface chemical reaction. ZnSe layers grown on the GaAs (100) face have larger growth rates and smoother surface morphologies than those on GaP (100). This result may originate from the lattice parameter mismatch between the epitaxial layers and the substrates.