bluuebunny/crossref_metadata_2025 huggingface dataset:
Site preference and Faraday rotation in Ce-doped DyGalG sputtered films
Authors: Alex Michael
Published: July 2002

We show here that cerium and gallium-doped dysprosium iron garnet (Ce,Ga:DylG) sputtered films may have widely varying magnetic properties that are functions of the predeposition sputtering system base pressure. A Ga site preference model that qualitatively accounts for these differences is introduced and is seen to agree with previously reported experimental results on the Ga site distribution and kinetics in liquid phase epitaxial and flux grown garnet films. Furthermore, we show strong evidence that indicates that the large Faraday rotation in highly doped Ce-substituted sputtered garnet films is not solely ascribable to Ce+3 intraorbital transitions as has been suggested for low concentration Ce:YIG. On the contrary, it is seen that the Faraday rotation in our materials increases almost exclusively in the near-infrared region as the Ce+4/Ce+3 ratio increases. It appears that this effect is largely due to an enhanced tetrahedral sublattice contribution to the Faraday rotation.
Resistometric and Mössbauer studies on structural relaxation in (Ni,Fe)75Si10B15 metallic glasses
Authors: Komatsu T. , Fujita K. , Matusita K. , Nakajima K. , Okamoto S.
Published: July 2002

The structural relaxation in (Ni,Fe)75Si10B15 metallic glasses has been studied by measuring resistivity changes and Mössbauer spectra. The sign and magnitude of resistivity changes due to the relaxation depend strongly on the Ni/Fe ratio. The isothermal resistivity changes fit well the nonlinear kinetic form, indicating that the fluctuation of local environments of Ni and Fe atoms is very large and Ni and Fe atoms in Ni-Fe-Si-B metallic glasses are mobile compared with Co and Fe atoms in Co-Fe-Si-B metallic glasses. The compositional dependence and kinetic parameters for reversible resistivity changes and Mössbauer spectra strongly support that the reversible structural relaxation corresponds to the reversible short-range ordering between Ni and Fe atoms.
A comparison by means of calorimetry of solid state interdiffusion reactions in Ni/Zr and Ni/Ti composites
Authors: White B. E. , Patt M. E. , Cotts E. J.
Published: July 2002

We have investigated solid state amorphization reactions in mechanically deformed composites in both the Ni-Ti system and the Ni-Zr system. The growth of amorphous material in our Ni/Ti composites is apparently facilitated by the relatively large degree of disorder induced in the metal layers by the mechanical deformation process. The growth of amorphous material is slower in Ni/Ti composites than in Ni/Zr composites, while we found similar kinetic constraints on the formation of equilibrium compounds in both systems. Thus the maximum thickness of amorphous Ni-Ti layers was an order of magnitude less than the 1000-Å layers grown in the Ni-Zr system.
Propagation along a dielectric-coated cylinder immersed in a magnetoplasma
Authors: Biswas S. , Basu J.
Published: July 2002

This communication presents a study of the dispersion relation for propagation in axisymmetric transverse magnetic modes along a dielectric-coated conducting cylinder embedded in a strongly magnetized plasma, the cylinder axis being placed parallel to the static magnetic field. Dispersion characteristics, covering all possible values of the plasma frequency, are plotted for typical values of εd and a/b, where εd is the dielectric constant of the coating, and a and b are the radii of the cylinder without and with the coating, respectively. A discussion of how the characteristics would change if εd or a/b is varied is also presented. In particular, the special case in which εd =1 and the coating is replaced by a vacuum sheath is investigated in detail.
Studies of low-surface 2-kT recombination current of the emitter-base heterojunction of heterojunction bipolar transistors
Authors: Wu Chung-Cheng , Ting Jing-Lung , Lee Si-Chen , Lin Hao-Hsiung
Published: July 2002

The 2-kT current at the emitter-base heterojunction of AlGaAs/GaAs heterojunction bipolar transistor grown by liquid phase epitaxy is found to be much lower than that of a GaAs homojunction diode. By measuring spectral response and current-voltage characteristics of (n)AlxGa1−xAs-(p)Al0.05Ga0.95As diodes having a similar structure to the emitter-base heterojunction, it is found that the 2-kT surface recombination current is determined by the lower doped side of the heterojunction. Therefore, a higher 1- to 2-kT current ratio and thus higher current gain can be obtained when a high-band-gap emitter with lower doping concentration is used. It is also found that by inserting an undoped AlGaAs spacer layer in between the emitter-base heterojunction and applying an edge-thinning design, a high-gain heterojunction bipolar transistor can be routinely obtained.
Electron paramagnetic resonance study of the solid solutions Ru(S1−xSex)2
Authors: Yu Jiang-Tsu , Lin Shoei-Sheng , Huang Ying-Sheng
Published: July 2002

The method of electron paramagnetic resonance (EPR) has been used to study the n-type semiconducting Ru(S1−xSex)2 single crystals grown by the method of chemical vapor transport. A chalcogen point defect model is established to account for the S=1/2 paramagnetic species detected by EPR. This model assumes that an X2−(X=S or Se)-X vacancy pair behaves like an electron donor. The g-factor anisotropy is dependent upon the degree of chalcogen deficiency which is interpreted as due to the formation of a narrow band by the magnetic electrons of the chalcogen defect below the bottom of the conduction band.
Electrical characteristics of zinc-doped indium phosphide
Authors: Benzaquen M. , Belache B. , Blaauw C. , Bruce R. A.
Published: July 2002

We report on the electrical properties of Zn-doped (p-type) InP epilayers grown by metalorganic vapor-phase epitaxy. A detailed Hall transport model, accounting for the various scattering mechanisms in semiconductors and including valence-band degeneracy effects and inter- and intraband transitions, has been used for the analysis of the data. It provided excellent simultaneous agreement with the free-hole concentration and the mobility for Zn concentrations in the range of 7×1016–2×1018 cm−3. Those concentrations, for which the Hall factor was found close to 1, were confirmed by secondary-ion mass spectroscopy profiles. The binding energies of the samples were in the range of 42.7–26.2 meV and decreased with increasing Zn concentration. A simple approach, based on free-hole statistics, is proposed for the determination of the impurity concentrations of the lightly doped samples. An increased residual donor concentration, observed at a higher doping level, has been discussed.
Thermal-oxidation-induced strain in 31P+-implanted Si〈100〉
Authors: Zsoldos L. , Petö G. , Schiller V. , Zsoldos E. , Brogren G.
Published: July 2002

Si〈100〉 was implanted by 31P+ and annealed in Ar and O2 at 630–1150 °C. In O2 above 1000 °C a characteristic strain developed in the near-surface layer depending on the temperature of the heat treatment, but a similar effect was not observed after annealing in Ar. The formation of strain is explained by a nonperfect near-surface regrowth.
Structure analysis of ZnTe-ZnSe strained-layer superlattices by transmission electron microscopy observation
Authors: Yang H. , Takenaka Y. , Ishida A. , Fujiyasu H.
Published: July 2002

Structural properties of ZnTe-ZnSe strained-layer superlattices grown on GaAs(001) substrates by hot wall epitaxy were investigated by transmission electron microscopy. The satellite spots observed in transmission electron diffraction patterns confirmed the superlattice periodicity and agreed very well with the results from x-ray diffraction. Smooth and abrupt interfaces are observed in (110) cross-sectional images. Strain information obtained from the transmission electron diffraction and lattice images indicates that coherent strain has not been achieved in ZnTe-ZnSe superlattices when the layer thickness of each constituent material exceeded 13 Å.
Energy-band calculation for periodic potential structure using quantum mechanical impedance
Authors: Haque A. , Haque M. , Khan M. R.
Published: July 2002

A generalized technique has been presented to calculate the energy bands of a periodic potential structure using quantum mechanical impedance. Periodic structures having a nonrectangular potential distribution can also be analyzed using this technique. Some computed results are presented for different potential distributions in the periodic structures.
A novel model of ‘‘new donors’’ in Czochralski-grown silicon
Authors: Qian J. J. , Wang Z. G. , Wan S. K. , Lin L. Y.
Published: July 2002

A new model of ‘‘new donors’’ is presented, based on electrical, infrared measurements, transmission electron microscopy, and high-resolution electron microscopy observations on Czochralski-grown silicon single crystals containing ‘‘new donors.’’ In this model, the electrical activity of ‘‘new donors’’ originates from the uncoordinated Si dangling bonds on small dislocation loops resulting from oxygen precipitation. In comparison with other models, the present model can better explain the experimental results of the heat treatment Czochralski-grown Si wafers.
Reconstruction of three-dimensional range distributions by a modified tomographic technique
Authors: Fink D. , Müller M. , Wang L.
Published: July 2002

First, an overview of the present state of art of imaging of three-dimensional particle (or damage) distributions in the field of ion implantation is given. Usually, the direct measurement of three-dimensional distributions in the field of ion implantation is restricted to cases when the impinging ion beam diameter is small against the size of the corresponding distributions, i.e., to ion energies above typically 100 MeV and to microbeams of a few μm diameter. To gain information also for lower ion energies without the restriction in the beam diameter, a modified tomographic reconstruction technique has been developed recently by us and is described here in detail. Three-dimensional distributions are reconstructed from a number of one-dimensional depth profiles, implanted under various angles. Competing algorithms for the solution are discussed. For the mathematical technique chosen, some consistency tests are presented. Good accuracy of a sufficient number of input profiles is vital for the quality of the three-dimensional reconstruction
Multibeam energy transfer in a Kerr medium
Authors: Gavrielides A. , Peterson P. R. , Sharma M. P. , Cardimona D. A.
Published: July 2002

Multibeam coupling in a Kerr medium with a finite response time is studied theoretically. Two different frequency spectra are considered. In the first case the modes are equally spaced and in the second the frequency separations are all unequal. In either case, as the beams propagate, both spectra eventually reach a saturation characterized by a cascading of energy into the lowest frequency if the Kerr constant is positive. The direction of energy transfer is reversed if the Kerr constant is negative. Representative examples are given for a multimode, equally spaced, laser source and for an unequally spaced source. For the former case, we give the optimum medium response time for conversion of a Gaussian spectra. If the frequencies are unequally spaced we present general conditions which have to be satisfied and give two examples.
Three-dimensional imaging of laser imploded targets
Authors: Chen Yen-Wei , Miyanaga Noriaki , Yamanaka Masanobu , Nakai Mitsuo , Tanaka Kazuo , Nishihara Katsunobu , Yamanaka Tatsuhiko , Nakai Sadao
Published: July 2002

An x-ray emission computed tomographic technique has been demonstrated to diagnose the laser implosion uniformity of spherical targets. Three-dimensional images of compressed core were reconstructed from five pinhole camera images obtained at different viewing directions by using an iterative algorithm. Good agreement between the experimental results and two-dimensional hydrodynamic simulations showed that the uniformity of initial target shell thickness has a significant influence on implosion symmetry.
Onset of hysteresis measured by scanning tunneling microscopy
Authors: Erber T. , McGreer K. A. , Nowak E. R. , Wan J-C. , Weinstock H.
Published: July 2002

The feasibility of adapting scanning tunneling microscope (STM) technology to investigate the transition from reversible to irreversible behavior in mechanical systems is demonstrated. Using an STM with a graphite sample, both regimes of reversible and irreversible response to electrostrictive cycling are observed.
Dynamics of a spin glass along the hysteresis cycle
Authors: Mahdjour H.
Published: July 2002

A correlation is observed between the ESR spectra (at 1.12 GHz) and the magnetization inversions of the spin glass AgMn for a Mn concentration of 8.3 at. %. This is because of rearrangement of the spin system during the magnetization inversions. The widths of the ESR lines W↑ und W↓ which correlate, respectively, with the reversals to positive and negative magnetization are different. This is ascribed to different values of the effective anisotropy constant K during the two reversals. Thus a relationship is obtained between the ESR linewidth and the anisotropy constant.
Velocity of shear horizontal surface waves on an isotropic elastic cylinder with finite width
Authors: Kiel/czyński P. , Pajewski W. , Szalewski M.
Published: July 2002

Theoretical and experimental results describing the propagation of shear horizontal (SH) surface waves on an isotropic elastic cylinder are presented. Analytical formulas for group velocities are developed. The velocity of impulses of the SH surface waves is determined experimentally. Subsequently, the experimental results are compared to the theoretical values. The measured velocity is close to the group velocity calculated according to our theory for cylinders of finite width. As yet, the existing theories consider only the propagtion of SH surface waves over the unlimited cylinders [I. A. Viktorov, Sov. Phys. Acoust. 20, 199 (1974) and L. M. Brekhovski, Sov. Phys. Acoust. 13, 541 (1967)].
Theoretical analysis of channel-doped amorphous silicon field-effect transistors
Authors: Lin Jyh-Ling , Sah Wen-Jyh , Lee Si-Chen
Published: July 2002

The electrical characteristics of the amorphous silicon (a-Si:H) field-effect transistors have been analyzed theoretically. It is found that if no interface states exist at the SiO2 and a-Si:H interface, the transistor with undoped channel gives the best subthreshold swing and on/off current ratio. However, the existence of the interface states shifts the threshold voltage and reduces the transconductance of the transistor. It is found from numerical analysis that the problem caused by the interface states could be compensated for by doping the channel slightly with phosphorus. The physical reason for the improved performance is discussed in detail.
High-quality molecular-beam epitaxial regrowth of (Al,Ga)As on Se-modified (100) GaAs surfaces
Authors: Turco F. S. , Sandroff C. J. , Hwang D. M. , Ravi T. S. , Tamargo M. C.
Published: July 2002

It is shown that high-quality molecular-beam epitaxial (MBE) regrowth of (Al,Ga)As on GaAs can be achieved by chemically passivating the GaAs surface ex situ prior to regrowth with aqueous selenium reagents. Reflection high-energy electron diffraction intensity oscillations show the bidimensional character of the regrowth and high-resolution transmission electron microscopy reveals defect-free regrown interfaces. Photoluminescence intensity from the Se-treated GaAs surfaces on which Al0.5Ga0.5 As is regrown rivals that from an all in situ grown AlGaAs/GaAs interface. The high quality of these regrown interfaces could be attributed to the thermally and chemically stable selenium and oxygen phases that remain bound to GaAs under MBE conditions.
Damage to InP and InGaAsP surfaces resulting from CH4/H2 reactive ion etching
Authors: Hayes Todd R. , Chakrabarti U. K. , Baiocchi F. A. , Emerson A. B. , Luftman H. S. , Dautremont-Smith W. C.
Published: July 2002

Structural and electrical damage imparted to InP and In0.72Ga0.28As0.6P0.4 (λg≂1.3 μm) surfaces during CH4/H2 reactive ion etching (RIE) have been examined. X-ray photoelectron spectroscopy was used to monitor changes in the surface chemistry, Rutherford backscattering spectrometry was used to measure crystallographic damage, and current-voltage and capacitance-voltage measurements were made to examine electrically active damage and its depth. Two classes of damage are observed: crystallographic damage originating from preferential loss of P (As) and/or ion bombardment-induced collision cascade mixing and, for p-type material, hydrogen passivation of Zn acceptors. Etching at 13.6 MHz, 60–90 mTorr, 10% CH4/H2, and bias voltages of ∼300 V contains gross (≳1%) damage as measured by RBS to within 40 Å and electrically active damage to within 200 Å of the surface. This is a factor of 3–6 shallower than other RIE processes operated below 10 mT with comparable or higher bias voltages. Acceptor passivation of both InP and InGaAsP, arising from the association of hydrogen with Zn sites, occurs to a depth of 2000 Å after RIE and causes a decrease in carrier concentration in this layer. The effect is reversed, however, by rapid thermal processing at temperatures between 350 and 500 °C.
Study of perfection and evolutive mechanism of magnetic Czochralski Si
Authors: Mao Zaixian , Mai Zhenhong , Cui Shufan , Wu Lansheng
Published: July 2002

The growth striation, resistance homogeneity, and oxygen concentration of silicon single crystal grown by both magnetic Czochralski and Czochralski methods were investigated. Theoretical analysis of the experimental results, including effect of magnetic field on the temperature fluctuation, effective segregation coefficient (keff), and oxygen concentration are discussed.
Experimental study of self-heating in undoped polycrystalline silicon thin films
Authors: Dimitriadis C. A.
Published: July 2002

The rise in temperature due to Joule-induced heating within undoped polycrystalline silicon resistors is estimated quantitatively when a moderately high electric field is applied. From the experimental results, a phenomenological expression of the rise in temperature in terms of the applied electric field, the geometrical dimensions of the resistor bar, and the resistivity of the polycrystalline silicon thin film is obtained.
The role of absorption in x-ray diffraction measurements from epitaxial layers and substrates
Authors: Stevenson Andrew W. , Pain Geoff N.
Published: July 2002

The role of normal absorption in x-ray diffraction measurements of integrated Bragg intensities from epitaxial (or other) layers and their associated substrates is discussed in terms of the transmission factor. It is shown that the technique for the determination of the polarity of an epitaxial layer by means of anomalous scattering of x rays need not be limited to the case of an effectively infinite layer thickness, in Bragg geometry. Some discussion of layer-thickness determination is also given.
Real-time monitoring of low-temperature hydrogen plasma passivation of GaAs
Authors: Gottscho Richard A. , Preppernau Bryan L. , Pearton Stephen J. , Emerson A. Bruce , Giapis Konstantinos P.
Published: July 2002

By monitoring photoluminescence (PL) in real time and in situ, hydrogen plasma operating conditions have been optimized for surface passivation of native-oxide-contaminated GaAs. PL enhancement is critically dependent on exposure time and pressure because of competition between plasma passivation and damage. Optimal exposure time and pressure are inversely related; thus, previous reports of ineffective passivation at room temperature result from overexposure at low pressure. Plasma treatment is effective in removing As to leave a Ga-rich oxide; removal of excess As increases the photoluminescence yield as the corresponding near-midgap-state density is reduced. Passivation is stable for more than a month. These results demonstrate the power of real time monitoring for optimizing plasma processing of optoelectronic materials.
Second-order nonlinear optical measurements in guest-host and side-chain polymers
Authors: Hayden L. Michael , Sauter Gerald F. , Ore F. Robert , Pasillas Peg L. , Hoover James M. , Lindsay Geoffrey A. , Henry Ronald A.
Published: July 2002

The second harmonic generation (SHG) coefficients dij of several corona-poled guest-host and side-chain polymers have been measured and studied over time using a new Maker Fringe analysis. The electro-optic coefficient r33 and scattering losses have also been measured in thin-film waveguides, on silicon and glass substrates, made from some of the polymers. Kleinman symmetry (d15=d31) was not valid for near-resonant SHG in these materials and d15/d31 was determined. Stable values of d33, for a fundamental of 1.064 μm, were as high as 40 pm/V for one of the side-chain polymers. Optical waveguide losses determined from scattering measurements were as low as 0.4 dB/cm at 1.06 μm.
Modulation effects near the GaAs absorption edge
Authors: Tober Richard L. , Bruno John D.
Published: July 2002

We show that the large features often found below the band gap in modulated spectra of GaAs samples are linked not only to impurities but also to back-surface reflection effects. Their proximity to the band edge depends on the geometry of the cavity in which the multiple reflections occur, the impurity species, and the temperature. Impurity contributions to the energy-dependent absorption coefficient become manifest in a multiple-reflection-enhanced reflectance edge. Externally applied perturbations modulate this reflectance edge, thereby producing first-derivative-like spectral features. At 5 K the extrema of the impurity-related features roughly correspond to the energies associated with donor and acceptor states. However, at room temperature they disagree significantly and therefore do not specify an impurity species with certainty.
Effect of magnetostatic field on the second-order optical susceptibility of III-V semiconductors
Authors: Sen P. , Sen P. K.
Published: July 2002

An analytical investigation of the application of a large magnetostatic field on the second-order optical susceptibility χ(2) in III-V semiconductors like GaAs and InSb is reported. The model is based upon the parity indefiniteness of the electron wave functions in crystals lacking inversion symmetry. The generalized force and the electronic dipole moment operators are accordingly taken to be 2×2 matrices with all elements being finite. We have followed perturbation technique for the density matrix. The magnetostatic field renormalizes the transition frequency and sharpens the density of states. Both the resonant as well as nonresonant three-wave parametric interactions have been discussed. Numerical estimates made for InSb crystal under resonant regime reveal considerable enhancement in the real part of χ(2) even at moderately low magnetic field while the imaginary part exhibits a near saturation behavior. Under nonresonant laser excitation, both χ(2)r and χ(2)i rise very sharply with magnetic field for effective cyclotron frequency ωc≤ω0−ωg, ω0 and ωg being the pump and crystal band-gap frequencies, respectively. Quite interestingly, χ(2)r and χ(2)i decay almost exponentially to very low values at ωc>2(ω0−ωg).
Evaluation of friction-welded aluminum-steel bonds using dispersive guided modes of a layered substrate
Authors: Adler Laszlo , de Billy Michel , Quentin Gerard , Talmant Maryline , Nagy Peter B.
Published: July 2002

In nondestructive evaluation the inspection of bond quality is a very important problem. In this paper we suggest an experimental method based on dispersion curve measurements for evaluating the quality of the bond between a layer and a substrate bonded by the inertia-friction welding process. The experimental results are in good agreement with theoretical calculations which show that the behavior of the lowest velocity modes is very sensitive to the interface conditions and to the quality of the bond.
Canonical aberration theory in electromagnetic multipoles
Authors: Ximen Jiye
Published: July 2002

In a 2N-pole electromagnetic system, defining the electron optical Hamiltonian function, we have derived both general algebraic expressions (arbitrary N) and special numerical formulas (N=3,4,5,6,7) for different aberrations from lower to higher order (i.e., the order of N−1, N+1, 2N−3, 2N−1, 3N−5). The so-called canonical aberration theory in electromagnetic multipoles has thus been developed, which allows us to deduce angular dependencies of different aberrations and to examine the possibility for spherical correction of a round lens by using multipoles.
Electromagnetic induction (eddy currents) in a conducting half-space in the absence and presence of inhomogeneities: A new formalism
Authors: Nair Satish M. , Rose James H.
Published: July 2002

Two problems are studied. First, a new method is presented for calculating the electromagnetic field in two conjoined conducting half-spaces in the presence of current sources in either or both half-spaces. The method allows the two half-spaces to differ in the conductivity, permeability, and permittivity. The full Maxwell’s equations are used; the quasistatic results may be derived as a particular limit. The method is unique in that it depends only on the solution of two variables; the components of the magnetic field Bz, and the current 𝒥z, normal to the interface between the half-spaces. The second problem involves the determination of the fields induced by a current source in one half-space with an arbitrary 3D inhomogeneity in the other. New, coupled integral equations for the fields are written down strictly in terms of Bz, 𝒥z, and the external current source. The same formalism, used to generate the new integral equations, is also shown to yield the standard dyadic volume integral representations. Finally, it is shown that the formalism is a useful way of deriving various asymptotic results. The weak scattering limit (the Born approximation) is derived as an example.
Layer intermixing in heavily carbon-doped AlGaAs/GaAs superlattices
Authors: Szafranek I. , Szafranek M. , Cunningham B. T. , Guido L. J. , Holonyak N. , Stillman G. E.
Published: July 2002

Interdiffusion of Al and Ga in heavily C-doped Al0.3Ga0.7As/GaAs superlattice (SL) structures has been investigated quantitatively for a variety of ambient and surface encapsulation conditions. High-resolution photoluminescence (PL) at T=1.7 K was employed to evaluate the extent of layer intermixing after 24-h anneals at 825 °C. From the shifts to higher energies of the PL peaks due to n=1 electron-to-heavy hole transitions in the quantum wells of the annealed SLs relative to the position of this peak in the as-grown crystal, approximate Al-Ga interdiffusion coefficients (DAl-Ga) have been determined for different annealing conditions. For all encapsulants studied the interdiffusion in C-doped crystals is accelerated with increasing As4 pressure in the annealing ampoule. This result disagrees with previously observed trends for Group II-doped p-type structures, which have led to the charged point-defect model (Fermi-level effect) of Al-Ga interdiffusion. The Si3N4 cap has provided the most effective surface sealing against ambient-stimulated layer interdiffusion, and yielded DAl-Ga≊1.5−3.9×10−19 cm2/s. The most extensive layer intermixing has occurred for uncapped SL annealed under As-rich ambient (DAl-Ga≊3.3×10−18 cm2/s). These values are up to ∼40 times greater than those previously reported for nominally undoped AlxGa1−xAs/GaAs SLs, implying that the CAs doping slightly enhances host-atom self-diffusion on the Group III sublattice, but significantly less than predicted by the Fermi-level effect. The discrepancies between the experimental observations and the model, are discussed.
Comparative optical investigations of ZnSe/GaAs epilayers grown by molecular beam and hot-wall epitaxy
Authors: Kudlek G. , Presser N. , Gutowski J. , Hingerl K. , Sitter H. , Durbin S. M. , Menke D. R. , Kobayashi M. , Gunshor R. L.
Published: July 2002

Comparative photoluminescence and excitation spectra of ZnSe/GaAs epilayers grown by molecular beam epitaxy (MBE) and hot-wall epitaxy (HWE) show likewise features in the exciton energy regime. Two strain-split components of the free exciton are observed, as well as characteristic sets of transitions from or into ground and excited states of acceptor- and donor-bound excitons. However, all respective lines are shifted to lower energies in the HWE samples, due to the increased thermally induced strain as a consequence of the substrate temperatures being enhanced compared to the MBE growth. Whereas the dominant donors are of the same nature in both kinds of samples, specific acceptor centers are incorporated in the HWE films. Although the MBE-grown layers are of superior quality, it is shown that HWE under optimized growth conditions is a cheap and useful alternative to obtain ZnSe epilayers of reliable properties.
Comparative study of self-limiting growth of GaAs using different Ga-alkyl compounds: (CH3)3Ga, C2H5(CH3)2Ga, and (C2H5)3Ga
Authors: Sakuma Y. , Ozeki M. , Ohtsuka N. , Kodama K.
Published: July 2002

We studied the self-limiting growth of GaAs using three kinds of Ga-alkyl compounds−trimethylgallium (TMGa), ethyldimethylgallium, and triethylgallium−as atomic layer epitaxy (ALE) sources. Perfect self-limiting behavior was found only for TMGa. The self-limiting mechanism could be explained by the surface site selectivity of the metalorganic molecules in the adsorption, desorption, and decomposition processes. We found that the degree of the site selectivity declined as methyl groups attached to a Ga atom were replaced by ethyl groups. We believe that the TMGa molecule is adsorbed without decomposition in the first step, and then fully decomposed into Ga. Three methyl groups of the adsorbed TMGa play an important role in the site selectivity and make the growth self-limited. We studied the evolution of the chemical state of the TMGa-exposed (001) GaAs surface by changing the length of the interruption following a TMGa pulse. There was no change in the surface chemical conditions and in the degree of self-limiting during the H2 purge after TMGa pulse. These results provide a detailed understanding of the surface chemistry and self-limiting growth involved in ALE.
Two-dimensional analysis of microbolometer arrays
Authors: Grossman E. N. , McDonald D. G. , Sauvageau J. E.
Published: July 2002

A two-dimensional, time-dependent analysis is made of array-compatible bolometers directly deposited onto a single substrate. It applies both to antenna-coupled and surface-absorbing configurations. Unlike previous spherically symmetric treatments, it allows analysis of thermal crosstalk between closely neighboring detectors, and of the effects of finite substrate thickness. In a closely packed array of surface-absorbing detectors, thermal crosstalk generally degrades the array’s resolution more severely than optical (diffractive) crosstalk. Diffraction-limited resolution with surface-absorbing detectors is possible only by sacrificing either thermal resistance, and therefore sensitivity, or filling factor. With a minimum substrate thickness of Lmin, a closely packed, diffraction-limited array is limited to a thermal resistance of Zt≤0.08(κLmin)−1, where κ is the thermal conductivity of the substrate. An array of antenna-coupled bolometers is not subject to this limitation since the thermally and optically sensitive areas need not be equal.
Impedance and emission properties of capacitively coupled Hg-Ar discharges
Authors: Beneking C.
Published: July 2002

The impedance and emission properties of capacitively coupled Hg-Ar discharges have been studied in order to determine the limitations of efficiency and radiance of the Hg UV radiation. The background is an application in electrodeless discharge lamps. The Ar pressure was varied between 40 and 1330 Pa, the frequency range was 10–400 MHz. The radiation efficiency generally increases with frequency, in particular at low Ar pressure and high rf power. It is correlated with the variation of the resistive impedance component with rf current and frequency. The results are discussed in terms of a discharge structure consisting of a positive column-like bulk plasma and two rf sheaths. The frequency dependence is mainly caused by the power dissipation in the non-luminous sheaths. The power share between bulk plasma and sheaths is determined by a suitable impedance analysis. At high power densities, the efficiency is additionally limited by saturation phenomena. Efficiencies comparable to those known from conventional, electroded discharges can be obtained by a proper choice of parameters such as discharge current and operating frequency. The measurements of the Hg UV radiation are supplemented by a spatially resolved spectroscopy of the Ar excitation. The extension of the dark spaces corresponds to the sheath thickness ds as derived from the impedance data. ds varies with Ar pressure pAr and frequency  f approximately as (pAr)−1/3f−1/2. A recently described model for the power dissipation in the sheath of capacitively coupled rf discharges in Ar is also in good agreement with the impedance data of Hg-Ar discharges. The complex sheath impedance is represented by a semi-empirical, analytical expression over a wide range of Ar pressures and frequencies.
Dry etching of niobium using CCl2F2 and CF4: A comparison
Authors: Sasserath Jay N.
Published: July 2002

Freon 12 is compared to freon 14 as an etchant for patterning of high density superconductive circuits. Both reactive ion and plasma regimes are examined. CCl2 F2 is observed to be an excellent niobium etchant, offering significant advantages over similar CF4 processes. Improvements include a six-fold increase of Nb:photoresist selectivity, while Nb:SiO2 selectivity is increased by over 1400%. Critical dimension control was also enhanced through the reduction of photo to etch bias from between 1. 09 and 0.5 μm to 0.14 μm. Diminished photoresist loss and the elimination of photoresist undercut are the reasons for this improvement. SiO2 surface texturing is not observed with either of the two etchants. Finally, data are presented that demonstrate the importance of electrode cooling in obtaining etch rate repeatability.
Interaction of hole trapping and transit effects in the temporal response of InP/InGaAs p-type insulator n-type photodiodes
Authors: Johnson B. C. , Campbell J. C. , Dentai A. G. , Joyner C. H. , Qua G. J.
Published: July 2002

Photodiodes with thin (∼0.2 μm) InGaAs light absorbing layers placed inside much wider (∼2 μm)InP depletion regions were studied to understand the interaction of hole trapping at the InGaAs/InP heterojunction interface and carrier transit effects. In the three devices studied, the absorbing region was located (i) near the n+ side, (ii) in the center, and (iii) near the p+ side of the depletion region. The optical impulse response of these devices consists of a short pulse and a long exponential tail with a bias-dependent time constant. The relative charge in the fast and slow components could be measured and it was shown that the charge ratios correspond to the fraction of the depletion region transited before and after trapping. These studies show that electron trapping times are much shorter than hole trapping times, and that fast photodetection can occur even in the presence of a severe hole trapping problem if the distance between the trap and the p+ side of the depletion region is much smaller than the total depletion width.
Transmission electron microscopy study of the environmental degradation in Ba2YCu3O7−y
Authors: Wada O. , Odaka T. , Wakata M. , Ogama T. , Yosidome A.
Published: July 2002

A Ba2YCu3O7−y high Tc superconductor degrades with time in air. In this paper we discuss the early stage of the degradation from a microscopic standpoint by using transmission electron microscopy (TEM). It has been shown by a high resolution TEM that the degradation has two modes. One is the formation of amorphous and polycrystalline phases, the latter of which are perhaps BaCO3. It has been clarified that the origin of the formation of the amorphous and polycrystalline phases is the reaction of Ba2YCu3O7−y phase with the water vapor, and the polycrystalline phase is formed sequentially after the formation of the amorphous phase. The other is the formation of planar defects which are introduced between Ba-O and Ba-O layers even in dry air. It is thought that the planar defects are formed to relax the strain energy of the dislocation caused by the migration of ions.
Oxidation of titanium, manganese, iron, and niobium silicides: Marker experiments
Authors: Stolt L. , Thomas O. , d’Heurle F. M.
Published: July 2002

The mechanism of atomic transport inside the silicide during thermal oxidation of silicide layers on Si substrates has been analyzed by means of inert gas markers implanted in TiSi2, Mn11Si19, FeSi2, and NbSi2. Oxidation was carried out in dry oxygen. The marker displacement reveals that the growth of metal-free SiO2 over the first three of these compounds occurs via the reverse motion of metal atoms, from the silicide/oxide to the silicon/silicide interface, rather than through the direct diffusion of Si atoms from the substrate to the oxide. Moreover, analysis of the marker position indicates that the total amount of Si between the marker and the free surface decreases during oxidation, as had been previously observed in the oxidation of NiSi2, CoSi2, and CrSi2. Although this could occur via the formation and evaporation of SiO, it is believed that the loss of Si is due to the motion of Si atoms, also in the ‘‘reverse’’ direction as for the metal atoms, across the silicide layer. The experiment conducted with NbSi2 shows that this silicide oxidizes via the direct motion of Si from the substrate to the oxide as anticipated. With TiSi2 the initial state of oxidation occurs as described, but the experimental observations imply that thick oxide layers grow via the direct motion of Si from the substrate to the oxide.
Gel growth of 3-methyl-4-nitropyridine-1-oxide organic crystals: X-ray and nonlinear optics characterization
Authors: Andreazza P. , Lefaucheux F. , Robert M. C. , Josse D. , Zyss J.
Published: July 2002

3-methyl-4-nitropyridine-1-oxide is an organic material presenting high optical nonlinear behavior especially for second-harmonic generation. Single crystals are obtained by spontaneous nucleation and grown by slow cooling in tetramethoxysilane gel. Coupled phase-matched second-harmonic generation and x-ray topography experiments allow one to relate nonlinear optical performance to crystalline quality.
An analysis of thickness-extensional trapped energy mode polarized ceramic transducers
Authors: Shick D. V. , Tiersten H. F.
Published: July 2002

An analysis of PZT-7A plates driven into thickness-extensional trapped energy vibrations by the application of a voltage to strip electrodes and radiating into an adjacent fluid is performed. All previous treatments of thickness-extensional trapped energy modes in piezoelectric plates have ignored the radiation into the surrounding medium and, hence, have been for resonators rather than transducers. The solution consists of a sum of a driven thickness solution and the pertinent plate eigensolutions for shorted electrodes in the electroded region and for zero surface charge in the unelectroded region, including in each instance the radiation into the adjacent fluid. Since the sum of the solutions in each region satisfies the differential equations and boundary conditions on the major surfaces including the fluid loading exactly, the substitution into the appropriate variational principle of linear piezoelectricity yields integral conditions across the thickness of the plate at the edge of the electrodes. The resulting system of inhomogeneous linear algebraic equations yields the response from very low frequency to slightly above the first thickness-extensional frequency of the unelectroded plate.
X-ray [440] diffraction of the strained-layer superlattices grown on (001) substrates
Authors: Yang H. , Ishida A. , Fujiyasu H.
Published: July 2002

X-ray diffraction from the (110) thin edges is proposed to analyze the ZnTe-ZnSe strained-layer superlattices grown on GaAs(001) substrates. Strained lattice spacings parallel to the interfaces and the critical layer thickness of coherent growth can be determined directly by this technique. In spite of the large (7%) lattice mismatch between ZnTe and ZnSe layers, the experimental results show that the ZnTe-ZnSe superlattices have been prepared coherently by hot wall epitaxy and the critical thickness is about 10 Å. The strained lattice spacings determined by x-ray [440] diffraction, together with those of Raman scattering measurement, agree very well with the theoretical results. The residual strain in ZnTe/GaAs(001) was also estimated to be about 5×10−4 (biaxial tensile) by x-ray diffraction, where the main cause is found to be the difference of thermal expansion between ZnTe films and GaAs substrates.
Preparation of hydrogenated amorphous silicon with tunable gap by homogeneous chemical vapor deposition
Authors: Qian Z. M. , Van Ammel A. , Michiel H. , Nijs J. , Mertens R.
Published: July 2002

This paper reports on the properties of doped and undoped amorphous silicon films deposited by the homogeneous chemical vapor deposition (HOMOCVD) technique. It is shown that good quality films can be grown at reasonable deposition rates of 100–150 Å/min. It is also shown that in this growth regime, the main precursor is Si2H4, shifting to SiH2 at higher H2 dilution. The real limit for the growth rate is set by the phenomena of homogeneous and local nucleation. The optical band gap of undoped films deposited at these high growth rates, changes from 2.6 eV for a substrate temperature of 20 °C down to 1.6 eV at 280 °C. Very conductive B-doped HOMOCVD amorphous silicon films with tunable band gap can be obtained. This is very important for the use of such films for window layers in photovoltaic applications as an alternative to siliconcarbide. At a substrate temperature of 40 °C films were obtained with an optical gap of 2.34 eV and a room-temperature dark conductivity of 1.6×10−5/Ω cm. Down to a thickness of 100 Å, no thickness dependence of the dark conductivity has been observed.
Al/p-CuInSe2 metal-semiconductor contacts
Authors: Chan C. L. , Shih I.
Published: July 2002

Al/p-CuInSe2 Schottky contacts have been fabricated by vacuum-depositing Al onto Bridgman-grown p-CuInSe2 single crystals. The barrier heights from the temperature-dependent forward I-V characteristics are significantly less than the C−2-V intercepts. This is evidence of the presence of an interfacial layer and surface states in equilibrium with p-CuInSe2. The barrier height, electron affinity, effective acceptor density, and relative Fermi potential as well as diffusion potential were estimated. The surface-state density of the minimum order of 1012 cm−2 eV−1 was obtained for the etched CuInSe2 surface. The transverse doping profile was qualitatively determined.
Maximum entropy calculation of the island-size distribution for a simple diffraction profile
Authors: Kariotis R. , Lagally M. G.
Published: July 2002

In this article we derive several results concerning diffraction from random surface configurations. First, we describe a practical method for inverting diffraction data in order to obtain an explicit expression for the size distribution of diffracting islands on a substrate. The principle of maximum entropy is used to fix the distribution in the form P=exp[−F(A)], where F(A) is a polynomial in the island area A. Then we show that the most general use of the maximum entropy principle requires that F for the exact size distribution be a simple, linear function of the geometry of the scatterers. While this result is of considerable practical use, of greater importance is the fact that it puts distinct and well-defined limits on the possible functional form that P(A) may exhibit. An example calculation is made using our diffraction data for indium on gallium arsenide.
The double-shear theory and the amorphous-to-crystal transition
Authors: Shneck R. , Brokman A. , Dariel M. P.
Published: July 2002

Crystals formed upon crystallization of amorphous solids are often plate shaped and contain a high density of twins. The objective of the present work was to further the understanding of the microstructure of such crystals. It is suggested that the elastic energy associated with the crystallization-induced dilatational strains can be reduced significantly by the formation of a macroscopically invariant plane, lying parallel to the basal plane of plate-shaped crystals. The invariant plane is obtained by means of a double-twinning mechanism. The model accounts for continuity being maintained across the crystal-amorphous matrix interface in spite of the volume change involved in the crystallization. The situation bears close resemblance to that dealt with by the crystallographic theory of the martensitic transformation.
Characteristics of step-graded separate confinement quantum well lasers with direct and indirect barriers
Authors: Miller L. M. , Beernink K. J. , Cockerill T. M. , Bryan R. P. , Favaro M. E. , Kim J. , Coleman J. J. , Wayman C. M.
Published: July 2002

Data are presented on step-graded separate confinement quantum well lasers with Al0.85Ga0.15As outer confining layers, AlxGa1−xAs barriers and a 50-Å GaAs quantum well grown by metalorganic chemical vapor deposition. By varying xb from 0.15 to 0.60, we show that, given an adequate optical waveguide confinement factor and sufficient cavity length, the collection of electrons in thin quantum wells with either direct or indirect barriers can be highly efficient, transfer of electrons from indirect barriers to thin direct wells does not degrade laser performance, and electron confinement in the separate confinement region plays no role in the operation of the laser.
Optical step frequency reflectometer
Authors: Iizuka K. , Imai Y. , Freundorfer A. P. , James R. , Wong R. , Fujii S.
Published: July 2002

The carrier generated by a solid-state laser can be frequency shifted by a significant amount. This fact was exploited to implement a high-resolution optical-fiber fault locator. A resolution of 4 mm was achieved. Compared to the resolution of a frequency-domain reflectometer that shifts the frequency of the AM modulation of the light, the proposed fault locator has a resolution about 1000 times better. The potential of developing the proposed reflectometer into an ultrahigh-resolution integrated optics fault locator is also discussed. UFaipxr
Weak electromagnetic missiles
Authors: Wang Xueming , Ruan Chengli , Huang Yafei
Published: July 2002

It is known that the energy flux of a transient electromagnetic wave can decrease with distance more slowly than the usual inverse-square law. Such cases are referred to as electromagnetic missiles. The rate of decrease depends on the frequency spectrum of the exciting current. For a class of excitations where the frequency spectrum behaves as ‖ω‖−1/2−ε , the rate of decrease has been stated to be z−2ε for 0≤ε≤1, implying that ε must be less than 1 in order for the decrease to be slower than z−2. It is shown that, in fact, the case ε=1 results in a dependence of z−2 ln z, i.e., an electromagnetic missile—albeit a weaker one than those previously discussed.
Two-dimensional paraconductivity in superconducting Bi1.6Pb0.4Sr2Ca2Cu3OY
Authors: Gridin Vladimir V. , Krause Thomas W. , Datars W. R.
Published: July 2002

Measurements of the electrical resistance R of polycrystalline samples of Bi1.6Pb0.4Sr2Ca2Cu3OY with the 108-K superconducting phase show that the Aslamazov–Larkin (AL) two-dimensional paraconductivity corrections are observable in the vicinity of the mean-field theory transition temperatureT0C. The effective thickness, d≊23 Å, of the superconducting electronic sheet as found from the zero field data is comparable to the a,b-plane separation. This result agrees well with the recent single-crystal data. The data for magnetic fields up to 1.5 T also show paraconductivity effects. T0C (H) is found to decrease as a function of increasing magnetic field H; this result agrees with the prediction of the AL model.