bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of formation of the midgap donor EL2 in neutron irradiated GaAs materials
Authors: Martin G. M. , Estève E. , Langlade P. , Makram-Ebeid S.
Published: February 2003

Fast neutron irradiation of n-GaAs mainly induces two deep electron traps in the band gap. The first of these is referred to as EL6 and has an energy level at Ec −0.35 eV, where Ec is the conduction band minimum; the second one has a wide energy distribution around Ec −0.5 V and is referred to as the U band. The annealing kinetics of these two levels is studied, and it is found that EL6 vanishes by a pair-defect (short-range) type recombination while the U band anneals by a long range migration process. Both annealing processes can be observed between 400 and 500 °C. In this annealing temperature range, the concentration of deep donor level EL2 (Ec −0.75 eV) increases with temperature. It is suggested that the defect giving rise to the EL2 level is created during irradiation but that medium range (tens to hundreds of Å) interactions with other neighboring defects strongly influence the electric properties of the overall defect, which is then detected as the U band. Due to long range migration, annealing reduces medium range interaction and the U band disappears in favor of the well-defined EL2 level (Ec −0.75 eV). This allows us to reconcile the apparent contradiction between DLTS (deep level transient spectroscopy) and EPR (electron paramagnetic resonance) and to identify the EL2 level with the EPR signal attributed to the AsGa defect.
Reaction of amorphous Ni-W and Ni-N-W films with substrate silicon
Authors: Zhu M. F. , Suni I. , Nicolet M-A. , Sands T.
Published: February 2003

Amorphous films of Ni-W and Ni-N-W were deposited on single-crystal silicon with discharge gases of Ar or Ar+N2 by rf cosputtering of Ni and W. The reaction of these Ni-W and Ni-N-W films with the Si substrate were studied in the temperature range of 450–750 °C by a combination of backscattering spectrometry, x-ray diffraction, cross-sectional transmission electron microscopy, and resistivity measurements. Films with composition Ni36W64 are stable below 500 °C. NiSi and NiSi2 form at 500 °C, and WSi2 forms rapidly in the temperature range of 625–650 °C. The nickel silicide forms adjacent to and within the silicon, while the outer layer becomes a mixture of WSi2 and NiSi2. The morphologies of the reacted layers are revealed by cross-sectional transmission electron microscopy. The crystallization temperature of amorphous Ni36W64 films on SiO2 is near 650 °C also. Adding nitrogen to form amorphous Ni30N21W49 films lowers the crystallization temperature, but raises the reaction temperature with Si to 750 °C.
Deep energy levels in ZnSxSe1−x alloys
Authors: Grimmeiss H. G. , Meijer E. , Mach R. , Müller G. O.
Published: February 2003

Junction space-charge techniques were used to study the electronic properties of the self-activated center in ZnSxSe1−x alloys. Photoionization cross-section spectra of electrons and holes obtained under different experimental conditions are compared with photoluminescence data. Since the spectra did not show any refined structure it was not possible to confirm the four-center model.
Structural and chemical analysis of ion beam produced conductive regions on highly resistive organic films
Authors: Venkatesan T. , Forrest S. R. , Kaplan M. L. , Schmidt P. H. , Murray C. A. , Brown W. L. , Wilkens B. J. , Roberts R. F. , Rupp L. , Schonhorn H.
Published: February 2003

Thin films of both polymeric and nonpolymeric organic solids turn optically dense and electrically conductive on irradiation with high energy ion beams (e.g., 2 MeV Ar+). The structural and chemical properties of these films were investigated by ultraviolet (UV) visible, infrared (IR), Raman spectroscopic techniques, electron spin resonance (ESR), electron spectroscopy for chemical analysis (ESCA), and Rutherford backscattering (RBS) measurements. Specifically, in the case of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and nickel phthalocyanine (NiPc), and UV visible, IR, and Raman spectra show the loss of the initial molecular structure at low irradiation doses (1013–1014 cm−2) followed by the appearance, at high doses, of a spectrum similar to that observed for amorphous carbon. The Raman spectra indicate the absence of any long range graphitic microcrystalline structure and suggest that the films are nearly amorphous at higher doses. The RBS spectra indicate gradual loss of oxygen in PTCDA with increasing irradiation dose. There is negligible oxygen left in the film at high doses and a maximum loss of ∼35% (∼15%) of the carbon atoms in PTCDA (NiPc) is observed. The resistivity of the films decreases with increasing dose, reaching a minimum of ∼5×10−4 Ω cm at a dose of ∼1017 Ar+/cm2. Surprisingly, the resistivity of these films at high doses (∼1017 Ar+/cm2) is considerably lower than that of any amorphous phase of carbon. In the case of NiPc, such a low resistivity is obtained even though 60% of the N and 100% of the Ni originally contained in the films are retained. In situ measurements of the evolution rate of molecular fragments during the bombardment indicate a decrease with dose, suggestive of an irreversible modification of the material with ion bombardment.
Calculation of high-field diffusivity by a many-particle Monte Carlo simulation including a complete band structure for GaAs
Authors: Wang T. , Hess K.
Published: February 2003

The electron diffusion coefficients of GaAs in the high-field regime ranging from 10 to 500 kV/cm have been calculated by a many-particle Monte Carlo simulation. The band-structure model in the simulation, calculated using the empirical pseudopotential method, includes the lowest two conduction bands and the full many-valley structure for each band. Our calculation shows that the diffusivity decreases drastically (by a factor of ≊30) as the field increases from 10 to 250 kV/cm and extremely low diffusion coefficients, 1.1 cm2/s for D1 and 6.1 cm2/s for Dt, are obtained at ≊250 kV/cm for GaAs.
Electrical characteristics of silicon-tin oxide heterojunctions prepared by chemical vapor deposition
Authors: Varma S. , Rao K. V. , Kar S.
Published: February 2003

Silicon-tin oxide heterojunctions were prepared by chemical vapor deposition of undoped as well as antimony-doped tin oxide on n-type silicon at 300 °C. Diode current-voltage (ID-V) and reverse capacitance-voltage (C-V) characteristics were measured in the temperature range of 294–394 K. The C-V measurements were taken at a number of frequencies f. The experimental data on diode quality factor n and semilogarithmic plots of the zero-bias current density intercept J0D vs T−1, and also of J0D vs T, indicated that the dominant carrier transport mechanism could be recombination generation in the case of undoped tin oxide, and trap-assisted tunneling in the case of antimony-doped tin oxide. The reverse C−2(V, T, f) characteristics indicated high barrier heights for all devices, but the presence of a much larger density of traps in the case of antimony-doped SnO2/n-Si heterojunctions than in the case of undoped SnO2/n-Si devices.
Electronic traps and P
b centers at the Si/SiO2 interface: Band-gap energy distribution
Authors: Poindexter E. H. , Gerardi G. J. , Rueckel M.-E. , Caplan P. J. , Johnson N. M. , Biegelsen D. K.
Published: February 2003

Energy distribution of Pb centers (⋅Si≡Si3) and electronic traps (Dit) at the Si/SiO2 interface in metal-oxide-silicon (MOS) structures was examined by electric-field-controlled electron paramagnetic resonance (EPR) and capacitance-voltage (C-V) analysis on the same samples. Chips of (111)-oriented silicon were dry-oxidized for maximum Pb and trap density, and metallized with a large MOS capacitor for EPR and adjacent small dots for C-V measurements. Analysis of C-V data shows two Dit peaks of amplitude 2×1013 eV−1 cm−2 at Ev+0.26 eV and Ev+0.84 eV. The EPR spin density reflects addition or subtraction of an electron from the singly occupied paramagnetic state and shows transitions of amplitude 1.5×1013 eV−1 cm−2 at Ev+0.31 eV and Ev+0.80 eV. This correlation of electrical and EPR responses and their identical chemical and physical behavior are strong evidence that ⋅Si≡Si3 is a major source of interface electronic traps in the 0.15–0.95 eV region of the Si band gap in unpassivated material.
Direct observation of field-injected space charge in a metal-insulator-metal structure
Authors: Anderson R. A. , Kurtz S. R.
Published: February 2003

An experimental technique has been developed for measuring space charge in dielectric films, which employs a stress wave that is generated thermoelastically from the absorption of a subnanosecond laser pulse. Spatial resolution in the thickness direction approaching one micron is attainable through a deconvolution procedure, and the sensitivity to areal charge density is about 10 μC/m2. The method is sufficient to resolve the distribution of field-injected charge in films of oriented poly(ethylene terephthalate) which were electrically stressed at room temperature. Concentrations of charge are found within a few microns of either electrode but lesser amounts extend deeply into the dielectric. Enough charge is measured after stressing specimens near breakdown to have reduced the field at the negative electrode by as much as 10% during the period of stress. The gradual decay of injected charge over a period of many days is found to be consistent with a spatially uniform, ohmic conductivity which follows a simple, inverse power law of elapsed time.
External magnetic field of two-dimensional semi-infinite plates. II. Two opposite plates
Authors: Owen D. , Parris A.
Published: February 2003

A theory for examining the external magnetic field due to two symmetrically opposite electromagnetic polepieces of different end shapes is given. Five pairs of polepieces are discussed and their corresponding magnetic intensities computed along special lines. Flat-end polepieces as well as thin polepieces are also considered and two examples given.
High quality indium gallium arsenide phosphide double heterostructure material grown by the near equilibrium liquid-phase-epitaxy technique
Authors: Besomi P. , Degani J. , Dutta N. K. , Wagner W. R. , Nelson R. J.
Published: February 2003

A comparative study of the source seed and near equilibrium liquid-phase epitaxy (LPE) growth techniques is described. The results of such important characteristics as broad area laser thresholds, quaternary active layer mismatch, and photoluminescence peak wavelength for 1.3-μm InGaAsP double heterostructure material were compared. Double heterostructure material grown by the near equilibrium LPE growth technique exhibited a better overall quality. Moreover, run to run reproducibility of these same parameters, as well as their eventual intrawafer variability, were monitored over an extended period of time. Again, the near equilibrium LPE growth technique readily led to excellent quality double heterostructure material. Finally, these wafers were processed into oxide stripe gain guided lasers, having a high percentage of devices with acceptable electro-optical characteristics.
Optical absorption and luminescence in lithium fluoride TLD-100
Authors: McKeever S. W. S.
Published: February 2003

The isothermal decay at 25 °C of the optical absorption bands in irradiated LiF TLD-100 single crystals has been compared with the decay, under the same conditions, of thermoluminescence (TL) and dielectric loss. The decay of the 380-nm band can be described by a third-order process suggesting that this band is directly related to free Mg-vacancy dipoles, which cluster during aging to form trimers. When compared with recent measurements which indicate that the TL peaks 2 and 3 are not related to the Mg dipoles [G. C. Taylor and E. Lilley, J. Phys. D 15, 1243, 1253 (1982)] the present results infer that the 380-nm band is not directly related to these TL peaks either, in contrast to earlier conclusions [J. H. Jackson and A. M. Harris, Phys. Lett. 29A, 423 (1969)]. This assertion receives some support from pulse annealing measurements and from x-ray-induced luminescence spectra. In particular, the latter results reveal that the spectrum consists of several overlapping bands, the relative intensities of which depend upon the aggregation state of the Mg within the LiF lattice. An emission peaking at ∼460 nm is increased if the concentration of Mg-vacancy dipoles is increased, and an emission at ∼420 nm is related to the number of dipole aggregates (Mg trimers) present. As Mg is precipitated from solid solution the main emission approaches ∼410 nm, which is that seen in Mg-free, Ti-doped LiF. A comparison of these data with recent thermoluminescence spectra measurements leads to the suggestion that TL peak 2 is caused by Mg dipole/Ti complexes, and that TL peak 5 is caused by Mg trimer/Ti complexes.
Photoionization cross sections in vanadium-doped silicon
Authors: Ohta E. , Kunio T. , Sato T. , Sakata M.
Published: February 2003

Vanadium-doped silicon has been investigated using a photocapacitance method on n+-p and p+-n junctions. The photoionization cross-section spectra showed two levels at 0.47 eV below the conduction band and 0.485 eV above the valence band, and the complementary optical transition threshold energies were 0.665 and 0.77 eV, respectively. For the Ec−0.47-eV level, the electron photoionization cross section at the threshold energy depends significantly on temperature. This would be due to the photothermal ionization process via the excited states. For the Ev+0.485-eV level, the sum of the threshold energies in electron and hole emission processes was greater than the band gap. This indicates that phonon broadening due to lattice relaxation occurs in the photoionization spectrum. According to the configuration coordinate model, the local phonon energy and the lattice relaxation energy are approximately 350 K and 0.13 eV, respectively.
Effect of powderization of irradiated LiF crystal on thermoluminescence emission
Authors: Nakajima Toshiyuki
Published: February 2003

The effect of powderization of a sample on the thermoluminescent property of irradiated LiF crystal was studied for the purpose of ensuring more accurate evaluation of the dose received by irradiated substances. The results revealed that the powderization significantly affects the height of the 220 °C glow peak, the extent of peak height modification being influenced in the case of samples irradiated to the same dose by (a) the duration of powderization, (b) by the size of crystal before powderization, and (c) by the grain size of the powdered sample, apart from being dependent on the irradiation dose. Of particular note is the finding that, with increasing irradiation dose, the detrimental effect of powderization on thermoluminescent property diminished progressively, until, at a dose of 105 R, thermoluminescence came inversely to be enhanced by powderization. Conclusive explanations remain to be offered for this and other aspects of behavior shown by the thermoluminescent property of LiF upon powderization under different conditions.
Plasmaless dry etching of silicon with fluorine-containing compounds
Authors: Ibbotson D. E. , Mucha J. A. , Flamm D. L. , Cook J. M.
Published: February 2003

Silicon is rapidly etched by the gas-phase halogen fluorides ClF3, BrF3, BrF5, and IF5, in analogy to XeF2 etching silicon. Nearly complete selectivity over SiO2 is achieved in all cases. By contrast, ClF and Groups III and V fluorides such as NF3, BF3, PF3, and PF5 do not spontaneously etch either Si or SiO2 under the same experimental conditions. These relatively inexpensive interhalogens can be applied to pattern silicon and more generally to remove silicon or polysilicon layers without a plasma. Low-temperature plasmaless gasification of substrates by these fluorine-containing interhalogens is an economically attractive alternative to fluorine-based plasma etching.
A new method to produce an annular cylindrical plasma for imploding plasma experiments
Authors: Gazaix M. , Doucet H. J. , Etlicher B. , Furtlehner J. P. , Lamain H. , Rouillé C.
Published: February 2003

We present a new method to produce a hollow cylindrical metallic plasma. A metallic foil is exploded by discharging a capacitor bank; the vapor which is produced expands through an annular diaphragm and forms a cylindrical shell of weakly ionized gas, which can be imploded to produce a hot, dense plasma, resulting in a high-power soft x-ray pulse. The density of the hollow cylindrical plasma is measured by resonant interferometry, a new and powerful diagnostic for probing the plasma mass density before the compression (neutral density ≂1016 cm−3). Our device is complementary to supersonic gas-puff or exploding wires experiments.
Electronic states and thicknesses of GaAs/GaAlAs quantum wells as measured by electroreflectance and spectroscopic ellipsometry
Authors: Erman M. , Theeten J. B. , Frijlink P. , Gaillard S. , Hia Fan Jia , Alibert C.
Published: February 2003

The use of electroreflectance and spectroscopic ellipsometry is demonstrated for the assessment of quantum well structures consisting of, respectively 4-, 5-, and 7-nm-thick GaAs layers deposited by organometallic chemical vapor deposition between undoped layers of Ga0.46Al0.54As. Electroreflectance provides a direct determination of all allowed optical transitions (Δn=0) in the GaAs well around the Γ point as well as their dependence versus an electric field. Spectroscopic ellipsometry gives both the thickness and the dielectric function of the GaAs well. This is a unique case where these two quantities are determined accurately at the same point under analysis. Furthermore, the two techniques have been used to analyze the optical transitions in the well around the L point (E1, E1+Δ1 type of transition), a usually unexplored region. This provides complementary information upon the electronic states in the quantum well.
Temperature dependence of the 1/f noise of carbon resistors
Authors: Fleetwood D. M. , Postel T. , Giordano N.
Published: February 2003

We have studied the temperature dependence of the 1/f noise of carbon resistors, and find it to be in good qualitative agreement with the predictions of the model developed by Dutta and Horn to describe the 1/f noise of metal films. This suggests that, as seems to be the case for metals, the noise of carbon resistors is caused by an activated process with a distribution of relaxation times. However, there are small but significant quantitative discrepancies between our experimental results and the predictions of the Dutta–Horn model, and these may yield additional insight into the origin of the noise in this system.
Field-electron emission microscopy as a probe of biomolecular adsorption from solution
Authors: Panitz J. A.
Published: February 2003

The field-electron emission microscope (FEEM) has been used as a probe of biomolecular adsorption from aqueous solution. Image contrast in vacuum has been correlated with the adsorption of tris buffer, and with ferritin/anti-rabbit goat IgG conjugate in tris buffer. If the imaging current is kept below 100 nA, tip morphology is unchanged. At higher imaging currents, in the presence of conjugate, a change in the surface morphology of the tip apex is seen by transmission electron microscopy. Control specimens exposed only to buffer and/or laboratory ambient do not change their morphology. We find that low-current FEEM imaging in vacuum can be used as a qualitative detector of biomolecule adsorption from solution. Reliable estimates of the size, the shape, and the number of adsorbates per unit area cannot be obtained with this technique.
Auger recombination rate in quantum well lasers: Modification by electron-electron interaction in quasi two dimensions
Authors: Basu P. K.
Published: February 2003

In recent calculations of the Auger recombination rate in quantum well lasers, the electron-electron interaction potential is taken either as the potential for bulk electrons or an approximate form derived from it. In the present work, the exact expression valid for quasi two-dimensional electrons is given and the expected changes in the Auger rate are pointed out. The expected variation of lifetime with width of the well is then discussed and compared with the results obtained by other workers.
Design and construction of precision heat fluxmeters
Authors: Jiménez J. , Rojas E. , Zamora M.
Published: February 2003

In this paper we discuss the design and construction of thermopiles for use as heat flux measurers. Compact structure, mechanical consistency, and a wide range of dimensions and sensitivities are possible. We can thus reach thermocouple densities up to 100 cm−2 and sensitivities of approximately 1 V W−1.
Influences of thin active layer in (GaAl)As double-heterostructure lasers grown by liquid-phase epitaxy
Authors: Hayakawa T. , Miyauchi N. , Suyama T. , Yamamoto S. , Hayashi H. , Yano S. , Hijikata T.
Published: February 2003

Studies have been carried out on the influences of thinning the active layer in (GaAl)As double-heterostructure (DH) lasers grown by liquid-phase epitaxy (LPE). The measured peak gain varies sublinearly with current in the laser with a thin active layer of d∼0.05 μm while it varies linearly for d≲0.07 μm. This sublinear gain-current relationship results from the rather wide graded-band-gap interface region formed by LPE and increases the lasing threshold. The photoluminescence (PL) peak of a DH sample with a thin active layer shifts to higher energies with the excitation due to the wide interface width, which agrees with the calculated results. High-energy bumps observed in the PL spectra are more noticeable in the sample with the thinner active layer, which demonstrates that carriers recombine at the high-energy portion of the interface region. The excitation dependence of PL intensity has shown that the nonradiative recombination rate is higher for the thinner active layer. Discussion is given concerning the causes for the rapid degradation of the lasers with the active layer thinner than a certain value.
Fast-Fourier-transform based beam-propagation model for stripe-geometry semiconductor lasers: Inclusion of axial effects
Authors: Agrawal Govind P.
Published: February 2003

The static characteristics of gain-guided double-heterostructure semiconductor lasers are modeled using a beam-propagation method that is capable of including both the axial and lateral variations of the optical-mode and carrier-density profiles. The use of the fast-Fourier-transform algorithm for the lateral mode propagation results in a relatively fast numerical procedure to obtain the self-consistent solution of the wave equation coupled to a nonlinear carrier-diffusion equation. To compare it with previous work, the model is applied to study the above-threshold behavior of an axially uniform AlGaAs laser. The inclusion of axial effects leads to minor (∼few percent) quantitative changes. As a novel application of the beam-propagation model, a tapered-stripe AlGaAs laser is analyzed in detail. In this axially nonuniform device the lateral profiles for the carrier density and the forward and backward waves exhibit considerable axial variations and affect the behavior both qualitatively and quantitatively. The calculated results are in reasonable agreement with the reported experimental observations.
Investigation of the striking characteristics of a Penning ion source
Authors: Chen Felix K.
Published: February 2003

This work describes a new technique which uses the time spectrum of fast neutrons produced by the extracted ions to study the switching characteristics of a small Penning ion source. It is found that the rise and delay times of the Penning discharge decrease with the pressure and the anode voltage, and are insensitive to the magnetic field provided that the electron confinement time is much longer than the mean ionization time. A proposed model successfully explains the rise-time variations with the source operating parameters.
Experimental study of laser acceleration of planar targets at the wavelength 0.26 μm
Authors: Fabbro R. , Faral B. , Cottet F. , Romain J. P.
Published: February 2003

The main characteristics of accelerated aluminum targets, which are the target velocity, the uniformity of the acceleration and the backside temperature have been studied in laser experiments performed at wavelength 0.26 μm with an absorbed flux of a few 1013 W/cm2, in 400-ps pulse duration by using the double-foil technique and an optical pyrometry diagnostic: The ablation pressure was inferred from the velocity measurements. The uniformity of the acceleration was shown to be controlled by the hot spots in the focal spot, and the importance of studying the smoothing of laser inhomogeneities for accelerated targets with large ablated fractions was emphasized. The observed dependence of the backside temperature as a function of the initial foil thickness is discussed in the light of shock wave heating and radiative heating.
A comparison of scalar multipole expansions
Authors: Wikswo John P. , Swinney Kenneth R.
Published: February 2003

Scalar multipole expansions have been widely used in many areas of physics as general solutions to Laplace’s equation. However, comparison of work by different authors is often complicated by the existence of several different forms of multipole expansions in different coordinate systems. In this paper we compare the spherical harmonic, Taylor’s series, direction cosine and traceless tensor expansions and present models of dipole configurations that in the proper limit give the individual multipoles. These pictures simplify the comparison of the series and aid in interpretation of the various multipole moments.
Impregnated-electrode-type liquid metal ion source
Authors: Ishikawa Junzo , Takagi Toshinori
Published: February 2003

An impregnated-electrode-type liquid metal ion source has been developed in which a sintered porous tungsten tip is used. The flow rate of the liquid metal can be controlled by selecting the diameters of the tungsten powders to be sintered (10 and 100 μm). Since the liquid metal can be stably supplied to the tip head, stable operation in a wide range from low (a few μA) to high ion current (a few hundred μA) is possible for various metals such as gallium and gold. Moreover, it is also a potential ion source with liquid metals such as silver with high vapor pressure at the melting point. A new method of holding and directly heating the main component of the ion source by means of knife-edged electrodes with a spring is extremely effective for high temperature operation.
Optimum beam thickness for the Raman-type free-electron laser using a two-dimensional hollow beam
Authors: Shiozawa T. , Nakashima T.
Published: February 2003

The effect of an arbitrary beam thickness is investigated for a two-dimensional Raman-type free-electron laser composed of a hollow relativistic electron beam and a parallel plate waveguide containing it. On the basis of the fluid theory for electron beams, analytical expressions are given for the dispersion relation and the spatial growth rate of a scattered wave (even TE mode) and an electron plasma wave (even TM mode) coupled under the influence of a pump wave (even TE mode). Then, from the numerical analysis for an important case where both the pump and scattered waves are the lowest-order even TE mode, the following interesting results are obtained. First, the hollow beam can propagate two distinct modes of the electron plasma wave with even symmetry characterized by different field distributions. One mode (mode 1) corresponds to the normal mode of the solid beam while the other mode is inherent to the hollow beam. In addition, the growth rate for the mode 1 is considerably larger than that for the mode 2. In particular, the optimum beam thickness is found for which the growth rate for the mode 1 becomes maximum and yet that for the mode 2 is sufficiently small.
Resolution and definition in photothermal imaging
Authors: Wetsel Grover C. , McDonald F. Alan
Published: February 2003

The influences of pump and probe beam sizes, as well as chopping frequency, on resolution and definition in photothermal laser-beam-deflection imaging of subsurface structure are investigated experimentally and theoretically. It is shown that the resolution of nearby subsurface structures is improved by decreasing pump and probe beam sizes to dimensions less than, but not necessarily much less than, the characteristic dimension of the subsurface structures. It is also shown that the photothermal image width (full width at half maximum) may be different from the structure size, and that the width may vary with frequency, for certain structure geometry. A theoretical model of thermal-wave scattering gives results consistent with the present experimental data and with previous, apparently contradictory, results in the appropriate geometric limits.
Position and pressure effects in rf magnetron reactive sputter deposition of piezoelectric zinc oxide
Authors: Krupanidhi S. B. , Sayer M.
Published: February 2003

c-axis oriented thin films of piezoelectric ZnO have been deposited on room-temperature substrates by rf magnetron sputtering of zinc in a reactive ambient of 100% oxygen over a pressure range from 5–70 mTorr. Below 10 mTorr the film structure, orientation, and physical properties depend on the position of the substrates with respect to the target. This is attributed primarily to resputtering of the film in the region of the target erosion area by high-energy neutral oxygen. At higher pressures where the mean free path inhibits such effects, the film structure and properties are uniform. At 700-W sputtering power, the optimum pressure lies between 20–30 mTorr leading to highly oriented ZnO over a large area of plasma with a dielectric constant of 11, conductivity at 300 °C=2×10−10 Ω−1 cm−1, and Rayleigh wave velocity=2600 m/s. The films are characterized using optical transmittance, electrical conductivity, dielectric constant and SAW, and acoustic microscope measurements.
Simple general analytical solution to the minority carrier transport in heavily doped semiconductors
Authors: Selvakumar C. R.
Published: February 2003

A rigorous analytical evaluation of minority carrier current in a heavily doped region (such as emitter) of a semiconductor device is presented that includes position-dependent band-gap narrowing, position-dependent mobility, and position-dependent lifetime. In addition, the analysis takes into account the possible finite surface recombination velocity.
Amorphicity, heterogeneity, and the Arrott plots
Authors: Aharoni Amikam
Published: February 2003

It is shown that experimental data on amorphous alloys are consistent with a heterogeneous system of ferromagnets, which implies an ill-defined region of transition from ferromagnetism to paramagnetism. For a rather low degree of disorder, the transition may be almost as sharp as in a crystal. But in many cases a seemingly sharp transition at a well-defined Curie point might originate from an inappropriate extrapolation of the Arrott plots. Properties and features of these plots are reviewed, with ways suggested for their interpretation.
Mössbauer study of plastic deformation in some magnetic metallic glasses
Authors: Gupta Ajay , Lal S. , Verma R. P.
Published: February 2003

Plastic deformation of some magnetic transition metal–metalloid metallic glasses has been studied through Mössbauer spectroscopy and other magnetic measurements. Present studies clearly indicate generation of structural defects throughout the volume of the specimen. The elastic stress field associated with these defects results, through magnetoelastic coupling, in deterioration of soft magnetic properties and a change in the alignment of atomic spins in the sample. Cold rolling results in a decrease in the average interatomic distance. Possible origin of the roll-induced magnetic anisotropy has been discussed. The apparent contradiction with earlier studies is interpreted in terms of the defect structure in amorphous alloys.
Defect trapping of ion-implanted deuterium in copper
Authors: Besenbacher F. , Nielsen B. Bech , Myers S. M.
Published: February 2003

Trapping of ion-implanted deuterium (D) by lattice defects in copper has been studied by ion-beam-analysis techniques. The evolving depth distribution of D was monitored by using the nuclear reaction D (3He, p) 4He, and the D lattice location was obtained by means of ion channeling. Linear-ramp annealing following a 15-keV D+ implantation revealed two annealing stages at 250 and 300 K, respectively, corresponding to trap-binding enthalpies of 0.22 and 0.42 eV, referenced to an untrapped solution site. From a comparison of these results with theoretical calculations based on the effective-medium theory, the 0.42-eV trap has been associated with monovacancies and perhaps small vacancy clusters, an assignment supported by previous positron-annihilation experiments, whereas the 0.22-eV trap tentatively is associated with self-interstitials. The channeling data have been analyzed, utilizing an extended multirow continuum model, and it is found that the data for D trapped to vacancies cannot be interpreted in terms of a single lattice site. This is consistent with the theoretical effective-medium results, which show that D trapped at a vacancy is delocalized with maximum probability between the vacancy and the octahedral interstitial site, consistent with the experimental findings.
Electrothermomigration and filament growth in p-InP with Au contacts
Authors: Brasen D. , Vaidya S. , Kammlott G. W. , Chin B. H.
Published: February 2003

Metal migration induced by electric field and temperature gradients has been studied in Zn-doped InP with Au contacts. A new failure mode has been observed which involves a temperature-induced decomposition of InP, followed by the formation of a liquid filament nucleating at the negative Au contact. The filament subsequently grows to short out the two contacts. Two forms of filaments are observed; type I is straight and narrow and contains no Au, whereas type II is broader, propagates more slowly, and contains Au. An explanation is presented to rationalize the results.
Cosputtered cobalt silicides on silicon, polycrystalline silicon, and silicon dioxide
Authors: Murarka S. P. , Vaidya S.
Published: February 2003

Silicide formation in cosputtered (Co+Si) films on silicon, polycrystalline silicon, and silicon dioxide (SiO2) has been studied by using the techniques of x-ray diffraction, Rutherford backscattering, and scanning electron microscopy and by measuring the sheet resistance and stress as a function of the composition and sintering temperature. Films with nominal Si/Co atomic ratios of 1 to 3 were investigated. The resistivity and the stress were found to be the lowest for the films with actual Si/Co ratio closest to a value of 2 (i. e., CoSi2). For silicon-rich or silicon-deficient films, sintering led to a Si/Co ratio variation across the thickness of the film. The magnitude of the Si/Co ratio variation was found to depend on the as-deposited Si/Co ratio and the substrate type. The differences in Si/Co ratios at the inner and outer silicide surfaces, the resistivity, and the stress were found to increase with increasing deviations from the CoSi2 stoichiometry (Si/Co=2). At temperatures above 950 °C, an intermixing of CoSi2 and silicon occurred leading to deleterious effects on the properties of the silicide. Also in the absence of silicon (i. e., for CoSi2 films on oxide), sintering in an inert ambient at temperatures ≥ 1000 °C led to decomposition of CoSi2 into CoSi and silicon which was lost in the furnace. The decomposition, however, could be suppressed by capping the silicide with a SiO2 film or by introducing small amounts of oxygen in the annealing ambient. It has been suggested that the observed high temperature instability of cobalt silicides could be associated with (a) very narrow concentration range of stability of the cosputtered cobalt disilicide, (b) tendency of CoSi2 and Si to grow epitaxially on substrate silicon, and (c) permeability of CoSi2 to silicon diffusion at temperatures above 950° C.
Effects of phosphorus diffusion on growth and shrinkage of oxidation-induced stacking faults
Authors: Nishi Kenji , Antoniadis Dimitri A.
Published: February 2003

Effects of phosphorus diffusion on growth and shrinkage of oxidation-induced stacking faults (OSF) in silicon have been investigated using the Wright etch and transmission electron microscopy (TEM). Within the phosphorus-doped layer, the Wright etch fails to delineate OSF whose existence TEM observations have confirmed. Faster growth or slower shrinkage of OSF has been observed not only during phosphorus deposition but also during subsequent annealing with increasing phosphorus dose, indicating interstitial supersaturation. A model for interstitial generation has been proposed.
Sequential silicide formation between vanadium and amorphous silicon thin-film bilayers
Authors: Psaras P. A. , Eizenberg M. , Tu K. N.
Published: February 2003

Solid-state reactions between bilayer thin films of vanadium and amorphous silicon with an excess amount of vanadium have been studied by Rutherford backscattering spectroscopy and Seemann–Bohlin x-ray diffraction. In prior studies of the interaction between vanadium thin films and single-crystal silicon, VSi2 has been the only compound observed. In the present study a sequence of compounds was observed. The first silicide, VSi2, was observed to form at 475 °C. At higher temperatures the compounds V5Si3 and V3Si formed in sequence. The growth of VSi2 is linear in time with an activation energy of 2.3±0.4 eV. The growth of V5Si3 is also linear with an activation energy of 2.5±0.1 eV.
Electronic profile of a GaAs solar cell through photoluminescence
Authors: Hollingsworth R. E. , Sites J. R.
Published: February 2003

A p-n junction diode is modeled as three spatial regions: n type, depletion, and p type, each of which is distinguished by its own photoluminescence signature. Variation in bias alters the spatial boundaries of these three regions; variation in excitation wavelength changes the depth which is probed. A direct electronic profile of a shallow junction GaAs photovoltaic diode as a function of bias is made using these two variations. Special care is taken in forward bias to distinguish between junction and terminal voltages and to separate out electroluminescence effects.
Electrical properties of MnxCd1−xSe
Authors: Stankiewicz J. , David L.
Published: February 2003

Electrical conductivity and Hall effect of Mnx Cd1−xSe have been measured from 40 to 300 K for the composition range 0<x≤0.30. The compositional dependence of the density-of-state mass of conduction band was obtained by fitting to the Hall-coefficient data, a model based upon a parabolic conduction band and a single ionized donor level. A variational calculation of the electron mobility for Mnx Cd1−xSe was performed, taking as the limiting scattering mechanisms longitudinal-optical-phonon scattering, acoustic-phonon scattering, piezoelectric scattering, and scattering by charged defects. The results of this calculation are in good agreement with the experiment.
Bulk and surface spin waves in thin-film antiferromagnets
Authors: Stamps R. L. , Camley R. E.
Published: February 2003

We discuss antiferromagnetic bulk and surface spin waves, in the long wavelength region, on a finite thickness slab geometry. Implicit dispersion relations for both surface and bulk modes are derived, along with numerical calculations for MnF2 and GdAlO3. We find that the application of a magnetic field strongly localizes the surface spin wave to either the top or bottom surface of the film.
Reply to ‘‘Comment on ‘Threshold switching in chalcogenide-glass thin films’ ’’
Authors: Adler D. , Shur M. S. , Silver M. , Ovshinsky S. R.
Published: February 2003

We analyze a simple model of a semiconductor containing only deep hole traps with a free-carrier generation rate proportional to the carrier concentrations. We show conclusively that trap filling can lead to an S-type negative differential conductance and current filamentation.
Field-induced uniaxial magnetic anisotropy of electrodeposited Fe-Co films
Authors: Tanahashi K. , Maeda M.
Published: February 2003

An investigation is reported of the field-induced uniaxial magnetic anisotropy of the electrodeposited Fe-Co alloy films with the composition 15–52 at. % Co. The observed value of the uniaxial anisotropy constant Ku attained the maximum value of 9×104 erg/cm3 which is considerably larger than that obtained for the vacuum evaporated Fe-Co films. Measurement of an average internal stress was made on these films, and the notable increase in the stress was observed at 52 at. % Co where the partial formation of super lattice FeCo was also observed. The characteristics of the magnetic and the structural properties obtained here are fairly different from those obtained for the vacuum evaporated Fe-Co films. The observed anisotropy seems to depend mainly on the atomic ordering.
Time dependence of optical absorption in n
p-layered superlattice structures
Authors: Madarasz Frank L. , Woody William R.
Published: February 2003

Recent experimental data measuring channel conductance in np-layered superlattice structures during optical excitation have been used in a phenomenological calculation to determine the optical absorption coefficient as a function of time. Additionally, internal fields and depletion widths as functions of time are calculated. With the appropriate data one may also determine these quantities as a function of irradiation intensity and energy. This type of information should prove valuable in electro-optical device applications.
Photoluminescence of AlGaAs/GaAs quantum wells grown by metalorganic chemical vapor deposition
Authors: Kawai H. , Kaneko K. , Watanabe N.
Published: February 2003

Photoluminescence of AlxGa1−xAs/GaAs(x=0.54) single quantum wells grown by metal organic chemical vapor deposition has been investigated at both 75 and 4.2 K. AlGaAs/GaAs heterojunction abruptness was estimated to be within a few atomic layers by comparing the peak energy of the quantum well photoluminescence with the values calculated on the assumption that the radiative transition takes place between the n=1 electron subband and the n=1 heavy-hole subband in the finite square potential well at 75 K. At 4.2 K, however, the peak energy shifts by several meV below the calculated energy, the cause of which may be formation of a two-dimensional free exciton. The sharp photoluminescence line of the narrower well indicates that the fluctuation in thickness is less than one half the lattice constant. The emission peak shift to lower energy with the increase of excitation intensity may be the result of exchange interaction among carriers.
Grain-driven zone melting
Authors: Anthony Thomas R.
Published: February 2003

Grain-driven zone melting is a new method of recrystallizing polycrystalline silicon films. A liquid alloy zone driven by the free-energy difference between polycrystalline and single-crystal silicon migrates and converts a polycrystalline film of deposited silicon into a single crystal. Processing is carried out under isothermal conditions so that batch processing of silicon wafers in conventional diffusion furnaces is practicable. The liquid-zone velocity is determined from theory for various alloys, grain sizes, and temperatures. At a typical processing temperature of 800 °C, a polycrystalline Si film on a wafer 4 in. in diameter can be recrystallized in 1 h utilizing multiple zones. The stability of the liquid zone is related to its shape and orientation. Zone orientations for 〈111〉 and 〈100〉 wafers are derived which prevent the interfaces of the zone from breaking up. The morphology of the liquid zone is shown to be static, in practice, because of the extremely long times required for any shape change.
Static and nonequilibrium transient conductance at strong carrier freeze-out in a buried channel, metal-oxide-semiconductor transistor
Authors: Tewksbury S. K. , Biazzo M. R. , Harrison T. R. , Lindstrom T. L. , Tennant D. M. , Storz F. G.
Published: February 2003

A simple model of the low temperature (T<30 °K), static and nonequilibrium transient conductance of the potential minimum region in a silicon, buried channel, metal-oxide-semiconductor field effect transistor is developed and experimental measurements of these conductances under carrier freeze-out conditions are presented. The transient, nonequilibrium conductance is considered as a potential mechanism for low voltage (∼25 mV), low switching energy (∼10 aJ), high density dynamic logic.
A novel structure, high conversion efficiency p-SiC/graded p-SiC/i-Si/n-Si/metal substrate-type amorphous silicon solar cell
Authors: Lim Koeng Su , Konagai Makoto , Takahashi Kiyoshi
Published: February 2003

A novel structure, high conversion efficiency amorphous silicon (a-Si)/metal substrate-type solar cell has been developed. The new structure, deduced from the conventional pin junction by the use of a gradual compositional grading p-type a-SiC:H layer between an ultrathin (∼20 Å) wide optical band gap (∼2.4 eV) p-type a-SiC:H layer and the i layer, exhibits markedly enhanced open-circuit voltage (Voc) and short-circuit current density (Isc) over the conventional a-Si pin/substrate-type solar cell. Especially, the collection efficiency in the newly developed structure was found to be remarkably increased at short wavelengths. The experimentally observed improvement in the blue response is due to the reduction in effective interface recombination combined with the enhanced window effect. An energy conversion efficiency of 8.40% under air mass (AM) 1 (100 mW/cm2) illumination has been obtained in the first trial of a cell fabricated by the rf glow discharge decomposition of pure silane (SiH4).
Electron-beam irradiation enhanced dislocation glide in GaAs observed by transmission electron microscopy
Authors: Maeda K. , Suzuki K. , Ichihara M. , Takeuchi S.
Published: February 2003

I n-situ transmission electron microscopic straining tests on electron beam irradiated n-GaAs were carried out. The quantitative results are consistent with previous results on bulk specimens, and with the operation of the Peierls mechanism.
fcc needle crystals of molybdenum grown from Mo(CO)6
Authors: Okuyama F. , Fujimoto Y.
Published: February 2003

It is shown that fcc needle crystals vapor-grown from Mo(CO)6 through a cathodic growth process are fcc polymorphs of Mo. Electron diffraction studies coupled with Auger spectroscopy revealed that the needles consist of randomly oriented single microcrystals, whose lattice constant, determined by electron diffraction, is 4.14 – 4.21 Å. This is greater than the theoretically expected value. It is believed that this expanded fcc lattice is attributable primarily to the growth of the needles in a high electric field.
The importance of the anode field in controlling the generation rate of the donor states at the Si–SiO2 interface
Authors: Fischetti Massimo V.
Published: February 2003

The generation of positive charge at the Si–SiO2 interface during constant current electron injection has been investigated at low (Avalanche) and high (Fowler–Nordheim) fields at 295 and 77 K on several differently processed metal-oxide–semiconductor capacitors. It was found that the rate at which the charge is generated increases exponentially with the field at the anode for both polarities and independently of processing variables. It follows that water-related and other electron traps have the sole effect of enhancing the generation rate by increasing this field. The role of hot-electron energy losses at the SiO2-anode interface is also discussed.