bluuebunny/crossref_metadata_2025 huggingface dataset:
Deep-level properties of Mn in InP
Authors: Huang K. , Wessels B. W.
Published: July 2002

Measurements of deep-level properties of Mn in InP are reported. Hall effect and deep-level transient spectroscopy were used to determine the ionization energy, thermal, and optical emission properties. A single level at Ev +0.25 eV associated with Mn was observed. The photoionization threshold of the center is 1.12 eV.
Avalanche breakdown in p-n AlGaAs/GaAs heterojunctions
Authors: Hur Jung H. , Myles Charles W. , Gundersen Martin A.
Published: July 2002

Avalanche breakdown in abrupt p-n AlGaAs/GaAs heterojunctions is invesigated, and the breakdown voltage, the maximum electric field, and the depletion layer width are calculated as functions of the doping densities, the temperature, and the AlAs mole fraction in AlGaAs. The model employed is an extension of Hauser’s model of homojunction breakdown [Appl. Phys. Lett. 33, 351 (1978)], and it includes the effects of the band offsets at the interface.
Oxide current relaxation spectroscopy in tunneling metal-oxide-semiconductor structures under high field stresses
Authors: Xu Mingzhen , Tan Changhua , Wang Yangyuan
Published: July 2002

A new technique, oxide current relaxation spectroscopy, has been presented for observing various traps and/or charges in the thin oxide. This technique is based on electron-fluence-dependent current characteristics in tunneling metal-oxide-semiconductor structures under high field stresses. It is capable of showing the spectrum of traps and/or charges in the thin-gate SiO2 as positive and negative peaks on an axis as a function of electron fluence. The height and position of each spectrum peak are related to the density, centroid, and capture cross section of the corresponding kind of the traps and/or charges. The parameters of various traps and/or charges in the thin SiO2 have been measured. The experimental results are consistent with theoretical calculations.
Gain enhancement in a free electron laser by two-stream instability
Authors: Botton Mordechai , Ron Amiram
Published: July 2002

The gain of an electromagnetic wave in a free electron laser is calculated. It is demonstrated that when the electron beam develops instabilities, this gain can be enhanced. Calculations for the case of the two-stream instability show that the growth rate is more than seven times larger and the gain per pass can be increased by more than two orders of magnitudes.
Temperature dependence of the harmonic distortion in InGaAsP distributed feedback lasers
Authors: Lin M. S. , Wang S. J. , Dutta N. K.
Published: July 2002

Measurements are reported of the second-harmonic distortion in 1.3-μm InGaAsP distributed feedback lasers operating at different temperatures. A minimum of the second-harmonic distortion exists at a particular bias current when the laser is operating at low temperature (10 °C). The minimum shifts to a higher bias current when the operating temperature is raised. At an even higher temperature, the minimum dissappears. A temperature-dependent model of the second-harmonic distortion, based on an equivalent circuit analysis, is presented to explain the experimental results.
Photoluminescence from ultrashort-period AlAs-GaAs atomic-layer superlattices
Authors: Toriyama Takeshi , Kobayashi Naoki , Horikoshi Yoshiji
Published: July 2002

Photoluminescence for (AlAs)n(GaAs)n (n=1, 2, 3, and 4) ultrashort-period superlattices grown by flow-rate modulation epitaxy is analyzed at various temperatures between 4.6 and 300 K. An excitonic intense emission line caused by an indirect transition is observed at low temperatures. Another emission band, caused by a direct transition, appears at elevated temperatures. The results of photoluminescence excitation spectroscopy reveal that the superlattices have an indirect minimum band gap. The direct and indirect band-gap energies of these superlattices, with periods of up to 1 monolayer, are presented. A simple Kronig–Penney calculation shows relatively good agreement with the experimental results for direct transitions.
Ion beam sputtering of i
n s
i
t
u superconducting Y-Ba-Cu-O films
Authors: Klein J. D. , Yen A. , Clauson S. L.
Published: July 2002

Oriented superconducting YBa2Cu3O7 thin films were deposited on yttria stabilized zirconia and SrTiO3 substrates by ion-beam sputtering of a nonstoichiometric oxide target. The films exhibited zero-resistance critical temperatures as high as 83.5 K without post-deposition anneals. Both the deposition rate and the c-lattice parameter data displayed two distinct regimes of dependence on the beam power of the ion source. Low-power sputtering yielded films with large c-dimensions and low Tc’s. Higher-power sputtering produced a continuous decrease in the c-lattice parameter and increase in critical temperature. Films having the smaller c-lattice parameters were Cu rich. The Cu content of films deposited at beam voltages of 800 V and above increased with increasing beam power.
Voltage ramp breakdown analysis of thick plasma-deposited Si3N4 metal-insulator-metal capacitors
Authors: Sterrett James E.
Published: July 2002

Thick (570 nm) plasma-enhanced chemical-vapor-deposited Si3N4 films are analyzed by voltage breakdown and I-V measurements. Exponentials of the form exp(const/E) are shown to fit the log of the reliability function of such films. An expression for dielectric lifetime that is proportional to exp[(B+H)/(3E)] and that also is a function of the cumulative fraction of failed capacitors, F, is derived. B and H are, respectively, the tunneling-current and hole-generation exponential constants. For these films, B=339 MV/cm and H=120 MV/cm. Voltage breakdown is observed to occur either while the dominant current-transport mechanism is tunneling or during a higher-current mode. In the latter case, both B and a value for H can be determined from voltage breakdown measurements.
The effect of interface roughness and island scattering on resonant tunneling time
Authors: Liu H. C.
Published: July 2002

The effect of interface roughness and island scattering on resonant tunneling time in double-barrier structures is investigated theoretically. The scattering process degrades the resonant tunneling peak current, broadens the resonance, and hence shortens the resonant tunneling time. For thin barrier structures, the tunneling time enhancement due to the scattering is relatively small, while the resonance width is dominated by the scattering for thick barrier samples.
Optical heterodyne investigation of the ultrasonic properties of aqueous biomolecules, dimethyl sulfoxide, and 1,4-butanediol
Authors: Bonney Rob , Davis Christopher C.
Published: July 2002

An optical heterodyne technique has been used to make new measurements of the ultrasonic properties of aqueous solutions of biomolecules, dimethyl sulfoxide, and 1,4-butanediol. A LiNbO3 transducer provided acoustic excitation from 0.2 to 1.5 GHz. Acoustic velocity and attenuation were measured using angularly resolved detection of Bragg-scattered light from the liquid sample. A thermodynamic theory based on the heat of mixing was used to explain the concentration dependence of the liquid mixture properties. This paper contributes new data at high frequencies, a calculation of measurement sensitivity for this technique, and a complete treatment of a little known thermodynamic theory that describes these results.
Electronic stopping-power calculations for heavy ions in semiconductors
Authors: Elkomoss S. G. , Pape A. , Unamuno S.
Published: July 2002

A model for ion stopping in semiconductors, which considers separate stopping contributions from valence and core electrons, and explicitly includes the effect of the gap, has been used to calculate the electronic stopping power of energetic B, P, and As in Si, Ge, GaAs, and CdTe for projectile energies 10 keV–100 MeV. Account was taken of the partially stripped incident ions by means of the effective charge. There is good agreement at low ion velocity with Lindhard and Scharff’s [J. Lindhard and M. Scharff, Phys. Rev. 124, 128 (1961)] values which for heavy ions do not depend on effective charge theory, as well as with the semiempirical curves at energies E≥0.2 MeV/nucleon where they can be compared.
Radiative recombination mechanisms in stoichiometry-controlled GaP crystals
Authors: Suto Ken , Nishizawa Jun-ichi
Published: July 2002

The near-band emission mechanism of GaP crystals with very low concentration of nonstoichiometric deep levels has been studied at high temperatures from 77 K to room temperature. Free-exciton recombination with emission and absorption of momentum conserving phonons at the site of shallow impurities are first found in the 77-K photoluminescence spectra, which has not been observed in the low-temperature luminescence. Also, excitons bound to ionized shallow acceptors Zn are identified. The free-exciton recombination increases as the temperature increases and becomes the dominant emission mechanism at room temperature, with no observable effects of nonradiative centers.
An optical frequency shifter using magnetostatic waves
Authors: Bilaniuk Nykolai , Stancil Daniel D. , Talisa Salvador H.
Published: July 2002

The optical frequency shift in the collinear magnetostatic wave–optical guided mode interaction has been observed by directly measuring the change in optical wavelength due to magnetostatic waves in the 2–12 GHz range. The experimental shift is found to be in good agreement with the theoretically predicted value of 0.058 Å/GHz at λ0=1.319 μm.
Aluminum-nitrogen isoelectronic trap in silicon
Authors: Modavis R. A. , Hall D. G.
Published: July 2002

The A, B, C luminescence system from silicon is believed to originate with the radiative decay of an exciton bound to an isoelectronic trap. It was shown previously by Sauer, Weber, and Zulehner [Appl. Phys. Lett. 44, 440 (1984)] that nitrogen is one of the trap constituents. We present experimental evidence that confirms that aluminum is also a trap constituent, suggesting that the trap is an aluminum-nitrogen pair.
Scaling in thin magnetoresistive films
Authors: Pant Bharat B.
Published: July 2002

The magnetoresistive response of long strips of thin ferromagnetic films under external field in the plane of the film is examined using analytic as well as numerical methods. This is done for a range of easy axis directions and external field angles. It is found that the dimensional as well as magnetic parameters are subsumed into two parameters—a zero-field equilibrium angle η and a field scale HS. The magnetoresistive response of the film to an external field HA appears in terms of the scaled variable (HA/ HS). As a result, the response of a large number of films for a given external field angle, and fixed η, falls on the same curve when expressed in terms of the scaled variable (HA/ HS). This also leads to a reciprocal relation between the sensitivity and range of linearity of the transfer function of a magnetoresistive transducer.
5
7Fe Mossbauer studies on Ho0.85Tb0.15Fe2Hx and Dy0.73Tb0.27Fe2Hx
Authors: Annapoorni S. , Rama Rao K. V. S.
Published: July 2002

5 7Fe Mossbauer measurements were carried out on Ho0.85Tb0.15Fe2Hx (x=0–3.1) and Dy0.73Tb0.27Fe2Hx (x=0–3.3) in the temperature range 105–360 K. The hyperfine field at the iron site was found to increase slightly with increasing hydrogen concentration in both the systems. The temperature variation studies of the hyperfine fields, the quadrupole coupling constant and the isomer shift suggest the occurance of spin reorientation. The isomer shift studied as a function of concentration indicate the charge transfer from Fe to hydrogen.
Comparison of Au/Ni/Ge, Au/Pd/Ge, and Au/Pt/Ge Ohmic contacts to n-type GaAs
Authors: Lin C. , Lee C. P.
Published: July 2002

Au/Ge-based Ohmic contacts to n-type GaAs with an addition of a near-noble-metal, Ni, Pd, or Pt, have been studied. It was found that both the electrical characteristics and the material properties depend very much on this added metal. The material properties of the contacts after thermal alloying were studied using transmission electron microscopy and auger electron microscopy. The contact resistances obtained with different alloying conditions and their reliability have also been studied. It was found that Au/Ni/Ge had the roughest surface while Au/Pd/Ge had the highest contact resistance. The surface morphology was attributed to the difference in the sizes of the grains formed after Ohmic contact alloying. Au/Pt/Ge was found to be the best contact in terms of its electrical characteristics as well as its surface morphology.
High repetitive plasma x-ray source produced by a zigzag slab laser
Authors: Zeng Guan-ming , Takahashi Masao , Daido Hiroyuki , Kanabe Tadashi , Aritome Hiroaki , Nakatsuka Masahiro , Nakai Sadao
Published: July 2002

Some properties of laser-generated plasma emission in the soft x-ray region (0.1 keV<hν<1.5 keV) are presented. Detailed spectral distributions are reported for several kinds of materials (carbon, aluminum, titanium, copper, zinc, molybdenum, tin, tungsten, and lead). Dependence of x-ray emission on focal size and target thickness is also studied. The experiments were carried out at a laser intensity of a few times 1012 W/cm2 using Nd-doped phosphate zigzag glass slab laser (8 J/40 ns, λ=1.054 μm). As an application of the laser-generated plasma x rays, the sensitivity of FBM-120 resist for x-ray lithography was measured and a 0.25-μm-wide space mask pattern was replicated.
Effect of humidity on chemical stability and superconductivity of YBa2Cu3O7−x
Authors: Naito N. , Kafalas J. , Jachim L. , Downey M.
Published: July 2002

The effect of relative humidity (0%, 40%, 51%, and 78%) on the stability of YBa2Cu3O7−x was investigated over a six-month period using x-ray diffraction, scanning electron microscopy, and magnetic susceptibility measurements. At 78% humidity, the fraction of superconductive phase decreased parabolically with time. After six months, the powders completely decomposed into BaCO3, Y2BaCuO5, and CuO. Most of the samples placed at humidity levels of 51% or less were in the orthorhombic YBa2Cu3O7−x phase at the end of six months and remained superconducting and stable. However, all powders kept at nonzero humidity levels were heavily agglomerated; some became hard solids with diameters equal to or greater than 0.1 mm. The microstructure of the powder indicated a surface reaction with water undetected by x-ray diffraction or magnetic susceptibility measurements.
Effect of substrate temperature on the properties of SiO2/InP structure prepared by photochemical vapor deposition
Authors: Huang C. J. , Su Y. K.
Published: July 2002

The InP metal-oxide-semiconductor structure using SiO2 film as an insulator was deposited by mercury-sensitized photoinduced chemical vapor deposition ultilizing a gaseous mixture of silane (SiH4 ) and nitrous oxide (N2 O) under 253.7-nm ultraviolet light irradiation. The structural and electrical properties of the deposited film were then evaluated with emphasis on the substrate temperature dependence. An increase of the substrate temperature (Tsub ) has effects of increasing the refractive index and decreasing the etching rate, oxide charge density, and interface state density. Postoxidation annealing in a N2 environment at 300 °C decreases the interface states as well as the oxide charge.
Stress-released layer formed by pulsed ruby laser annealing on GaAs-on-Si
Authors: Kim Yong , Kim Moo Sung , Kim Eun Kyu , Kim Hyeon-Soo , Min Suk-Ki , Lee Hyun Woo , Kim Jae Kwan , Lee Choochon
Published: July 2002

The effects of short pulsed ruby laser annealing on GaAs layers grown on Si substrates by metalorganic chemical vapor deposition have been characterized by Raman spectroscopy and double-crystal x-ray diffraction. After laser melting and regrowth, the stress-released layer is formed in the near-surface. The formation of the stress-released layer results in the microcracking of the pulsed-laser-annealed GaAs surface. However, the high crystalline quality of this stress-released layer is detected. Furthermore, when GaAs layer is overgrown on this stress-released layer, this layer plays a role of blocking the dislocation threading into the overgrown GaAs layer.
The effects of strain on morphology and structural properties of InGaAs/InP(001) grown by molecular beam epitaxy
Authors: Salokatve A. , Hovinen M.
Published: July 2002

A series of InxGa1−x As films with different compositions around x=0.53 were grown on InP(001) substrates by molecular beam epitaxy. These layers were studied by double crystal x-ray diffraction and secondary electron microscopy. It was found that the broadening of a layer Bragg peak is an indication of a large scale lattice relaxation in the highly strained heterolayer. In the less strained layers the peak widths are due to sample curvature and compositional grading. The morphologies of the strained layers suggested that the sign of strain is an important factor affecting the growth kinetics on the surface. In particular, an increasing tensile strain in the epitaxial layer tends to decrease the migration rate of the species on the growing surface.
Phase determination and spatial distribution of an ion-beam mixed internal interface: Fe/Sn
Authors: Sanders J. H. , Edwards D. L. , Williams J. R. , Tatarchuk B. J.
Published: July 2002

Ion-beam mixing of tin on iron provides corrosion protection against high-temperature oxidation. Previous studies have been inconclusive as to the exact composition and distribution of alloys produced at the Fe/Sn interface. This study provides a detailed diagram of Fe-Sn specimens after ion-beam mixing with Ar+ at 40 keV and a dose of 5×1016 ions/cm2 . The interface was isotopically labeled with 7.5 nm of 57 Fe and 119 Sn so that dual perspective conversion electron Mössbauer spectroscopy could be performed. Analyses in this manner allowed comparison of 119 Sn conversion electron Mössbauer spectroscopy (CEMS) and 57 Fe CEMS spectra to accurately assign spectral components which could not be conclusively assigned using a single CEMS perspective. Information from Rutherford backscattering spectrometry confirmed the layered nature of specimens prior to implantation and was used for depth determination of the mixed region after implantation. X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and scanning electron microscopy also provided information after implantation. Data indicate the formation of a uniform amorphous surface during implantation resulting in a heterogeneous mixture of components consisting mainly of dilute tin in iron (approximately 8-at. % Sn) and FeSnx (x≊1). About 80% of the 37.5-nm tin overlayer was removed by sputtering. The components identified are somewhat more iron rich than previous assignments and illustrate the difference in surface structures resulting from various implantation parameters.
A non-alloyed ohmic contact formation on n-type GaAs
Authors: Dutta R. , Lahav A. , Robbins M. , Lambrecht V. G.
Published: July 2002

The ohmic contact characteristics of nickel antimonide in n-type GaAs semiconductor circuits are evaluated. Deposition techniques, structural, and electrical properties were studied. The structural analysis revealed a well-defined, sharp interface of a polycrystalline nickel antimonide phase with various solid-phase interactions at higher annealing temperatures. The sheet resistance of 1000-Å-thick films decreased to 7–10 Ω/⧠ after annealing at 400 °C. The ohmic contact formation was demonstrated using transmission line measurements. Subtractive etching of the contacts was accomplished by a wet etchant system which was found not to attack the GaAs substrate.
CO2-laser ablation of Bi-Sr-Ca-Cu oxide by millisecond pulse lengths
Authors: Meskoob M. , Honda T. , Safari A. , Wachtman J. B. , Danforth S. , Wilkens B. J.
Published: July 2002

We have achieved ablation of Bi-Sr-Ca-Cu oxide from single targets of superconducting pellets by CO2-laser pulses of l ms length to grow superconducting thin films. Upon annealing, the 6000-Å thin films have a Tc (onset) of 90 K and zero resistance at 78 K. X-ray diffraction patterns indicate the growth of single-phase thin films. This technique allows growth of uniform single-phase superconducting thin films of lateral area greater than 1 cm2.
Monte Carlo simulation of kilovolt electron transport in solids
Authors: Martínez J. D. , Mayol R. , Salvat F.
Published: July 2002

A Monte Carlo procedure to simulate the penetration and energy loss of low-energy electron beams through solids is presented. Elastic collisions are described by using the method of partial waves for the screened Coulomb field of the nucleus. The atomic charge density is approximated by an analytical expression with parameters determined from the Dirac–Hartree–Fock–Slater self-consistent density obtained under Wigner–Seitz boundary conditions in order to account for solid-state effects; exchange effects are also accounted for by an energy-dependent local correction. Elastic differential cross sections are then easily computed by combining the WKB and Born approximations to evaluate the phase shifts. Inelastic collisions are treated on the basis of a generalized oscillator strength model which gives inelastic mean free paths and stopping powers in good agreement with experimental data. This scattering model is accurate in the energy range from a few hundred eV up to about 50 keV. The reliability of the simulation method is analyzed by comparing simulation results and experimental data from backscattering and transmission measurements.
Rapid thermal annealing of Al(0.8% Si)/Ti10W90/a-Si contacts
Authors: Berger S. , Weiss B. Z. , Komem Y.
Published: July 2002

The effect of rapid thermal annealing on the composition, structure, and I-V characteristics of Al(0.8% Si)/Ti:W/a-Si contacts was studied. It was established that heat treatments in temperatures ranging between 300 and 500 °C for a time span of 10 s led to grain boundary diffusion of Si and Al through the Ti10W90 layer. Subsequently, Si diffused into the Al film while Al penetrated into the amorphous Si. No silicides or intermetallic compounds were observed to form as a result of the rapid heat treatments. The electrical measurements showed that the I-V curve in the forward bias is identical to that of the reversed bias. The electrical resistance of the contacts increased as a result of a rise in the heat treatment temperature. A model of electrical conductivity in amorphous semiconductors was applied to explain the electrical behavior of the contacts.
Improved high-field performance of Pb1−xSnxMo6S8 ribbons
Authors: Capone D. W. , Hinks D. G. , Brewe D. L.
Published: July 2002

This paper describes the effect of Sn additions to PbMo6S8 ribbons. These ribbons are produced via a vapor-transport technique. Small amounts of Sn in Sn1−xPbxMo6S8 alloy ribbons provide a significant (∼10×) increase in Jc at high fields over that obtained with PbMo6S8 alone. Critical current densities of 1×104 A/cm2 at 4.2 K near 20 T have been achieved for compositions with x near 0.5. The low Jc’s in PbMo6S8 appears to be related to the presence of a large fraction of a nonsuperconducting triclinic phase resulting from a partial phase transition at cryogenic temperatures. This phase transition is partially suppressed with Sn additions, resulting in an improved performance.
Transverse effects in optical bistability with the nonlinear Fabry–Pérot étalon: A new theoretical approach
Authors: Haelterman M. , Tolley M. D. , Vitrant G.
Published: July 2002

On the basis of a plane-wave analysis we develop an original one-dimensional model for the nonlinear Fabry–Pérot étalon. This model facilitates numerical analysis and physical interpretations. We discuss the role of diffraction and the influence of the incident angle on bistability. A preliminary numerical study of the model is proposed.
Three-dimensional analysis of overwritable phase-change optical disks
Authors: Minemura Hiroyuki , Andoh Hisashi , Tsuboi Nobuyoshi , Maeda Yoshihito , Sato Yoshio
Published: July 2002

Three-dimensional computer calculations which analyze time-transient behavior of heat conduction and phase-change kinetics in an InSbTe overwritable disk were made. To improve the calculation accuracy, thermal conductivities of thin-film materials and critical cooling rate for crystallizing the recording film were estimated. For realization of high-performance overwrite, it was found that the cooling conditions of writing and erasing processes should be controlled to match the critical cooling rate in a given linear velocity range. This could be achieved by optimal design of the disk structure.
Mg implant activation and diffusion in GaAs during rapid thermal annealing in arsine ambient
Authors: Tews H. , Neumann R. , Hoepfner A. , Gisdakis S.
Published: July 2002

Rapid thermal annealing of GaAs in an arsine ambient has been investigated. Uncapped 2-in. GaAs wafers were annealed in an arsine-N2 gas mixture up to annealing temperatures of 1100 °C and annealing times of 10 s. No surface decomposition occurred at an arsine partial pressure of 12.5 Torr. This capless annealing technique was employed to the activation of shallow Mg implants in GaAs. The sheet resistance of the annealed layers as a function of the annealing temperature reveals a minimum at approximately 930 °C. At higher temperatures diffusion of Mg becomes significant. A part of the Mg accumulates at the GaAs surface and diffuses out. The Mg loss due to outdiffusion can be reduced using Si3 N4 cap layers. The internal diffusion of Mg at high temperatures depends on the arsenic pressure during the annealing.
Dislocation jump distances during creep of pure and doped NaCl single crystals using nuclear magnetic resonance pulse techniques
Authors: Murty K. Linga , Kanert O.
Published: July 2002

Jump distances of dislocations are determined from the spin-lattice relaxation rates in a rotating frame [1/T1ρ] using in situ nuclear magnetic resonance pulse techniques during creep of pure and doped NaCl single crystals. Effects of divalent impurity and solid solution are investigated by doping with Ca and LiCl, respectively. Compression creep tests were performed at 10–30 MPa at 473 K. Relaxation rates were evaluated from spin-echo heights following π/2, locking, and 64° pulse sequence. The amplitude of the spin echo decreased as soon as the load was applied following which it increased until the steady-state creep was reached, at which point a saturation value was observed. Mean jump distance of the mobile dislocations decreased with strain during the transient creep reaching a constant value at the onset and during the secondary creep. While the addition of 0.01 Ca has negligible influence on the jump distance, a solid solution with 0.01 LiCl resulted in about a four-fold increase. The results are compared and correlated with various microstructural parameters.
Mechanisms of silicon oxidation at low temperatures by microwave-excited O2 gas and O2-N2 mixed gas
Authors: Yasuda Y. , Zaima S. , Kaida T. , Koide Y.
Published: July 2002

Mechanisms are discussed on the enhancement of silicon oxidation at low temperatures by microwave excitation of O2 gas and on the further increase by that of O2 -N2 mixed gas. The activation energy of parabolic rate constants for the oxidation by excited pure O2 gas is 1.15 eV. This value, being almost the same as that in thermal oxidation, indicates that the oxidizing species is O2 molecules. The enhancement of oxidation is interpreted as a consequence of an increase in the O2 adsorption energy on SiO2 surfaces. For the oxidation by O2 -N2 mixed gas, on the other hand, there exist two parallel oxidation processes: one with the excited O2 gas and the other with excited N2 gas. The activation energy for the latter oxidation process is 0.49 eV, which indicates that the oxidizing species is O atoms. We also observed an abnormally high oxidation rate in the range of small O2 /N2 ratios.
Line-shape analysis of reflectance spectra from GaAs/AlAs multiple-quantum-well structures
Authors: Terzis A. F. , Liu X. C. , Petrou A. , McCombe B. D. , Dutta M. , Shen H. , Smith Doran D. , Cole M. W. , Taysing-Lara M. , Newman P. G.
Published: July 2002

The reflectance spectra from six GaAs/AlAs multiple-quantum-well structures have been analyzed with a multilayer classical dielectric function model which describes in detail the propagation of light through these microstructures. The model predicts accurately the observed line shapes. It can be used for the analysis of the reflectance or transmission spectra of any semiconductor multilayer structure.
Solid-state reactions in high-temperature superconductor-ceramic interfaces; Y-Ba-Cu-O on Al2O3 versus yttria-stabilized ZrO2, and MgO
Authors: Fartash A. , Schuller Ivan K. , Pearson J.
Published: July 2002

We have prepared, using molecular-beam epitaxial techniques, superconducting Y-Ba-Cu-O films directly on Al2O3, yttria-stabilized ZrO2 (YSZ), and MgO without buffer layers. The structure and stoichiometry of the films on Al2O3 are compared with those prepared on YSZ and MgO and found in large part determined by reactions with the substrates. The films on Al2O3 consist of textured Y2Ba4Cu8O20−x with superconducting onset at 80 K and zero resistance at 69 K, whereas on YSZ and MgO, YBa2Cu3O7−z films are formed. Auger electron depth profile spectroscopy in conjunction with structural and transport studies suggest that copper is depleted from the region near the Al2O3 substrate.
Passivation of superconducting YBa2Cu3O7−x thin films by a wet fluoride vapor method
Authors: Jia Q. X. , Anderson W. A.
Published: July 2002

Wet hydrofluoric acid (HF) vapor was used to treat YBa2Cu3O7−x superconducting thin films in order to realize highly controllable passivation layers on the film surface. Improved resistance to degradation by water of the films was realized by using this novel technique. In situ measurement of the resistance of the thin films, with and without wet HF vapor treatment, showed completely different behavior during deionized water immersion. Both Auger electron spectroscopy surface scanning and depth profile demonstrated the incorporation of fluorine in the surface after wet HF vapor treatment. The formation of an amorphous layer on the film surface, which was the reaction product between HF and erosion materials on the film surface, might be directly related to the improved water resistance of the superconducting YBa2Cu3O7−x thin films.
Ferromagnetic resonance of double yttrium-iron-garnet films: Perpendicular field
Authors: Barak J. , Ruppin R.
Published: July 2002

Perpendicular field ferromagnetic resonance spectra of double yttrium-iron-garnet films are presented. The evolution of the spectrum with changing interfilm spacing was traced by performing the measurements at six different spacings. The main features of the observed spectra agree well with those calculated for two films of infinite lateral dimensions by imposing quantization conditions on the in-plane wave-vector components. Some quantitative discrepancies between the observed and calculated spectra are shown to result from the deviation of the depolarization fields in the finite films from the infinite film value and from the inhomogeneity of the magnetic field inside the films.
Structure of (111) CdTe epilayers on misoriented (001) GaAs
Authors: Ligeon E. , Chami C. , Danielou R. , Feuillet G. , Fontenille J. , Saminadayar K. , Ponchet A. , Cibert J. , Gobil Y. , Tatarenko S.
Published: July 2002

Results concerning [111]CdTe growth on misoriented (001) GaAs substrates are presented and discussed. Growing CdTe on GaAs substrates with Ga steps results in twin-free layers, which is not the case for As steps. The tilt of the (111) CdTe planes with respect to the (001) GaAs planes is reported versus the GaAs substrate misorientation. We propose a model that establishes a correspondence between the measured tilt and the presence of interface dislocations as observed by high-resolution electron microscopy. This model also takes into account the effects of the surface morphology on the suppression of twins.
Surface-energy-induced mass-transport phenomenon in annealing of etched compound semiconductor structures: Theoretical modeling and experimental confirmation
Authors: Liau Z. L. , Zeiger H. J.
Published: July 2002

A comprehensive model of the mass-transport phenomenon at the surface of compound semiconductors has been developed and experimentally confirmed. In the model, the effect of surface curvature on thermal decomposition and the resulting diffusion and regrowth has been formulated, and a differential equation has been derived that describes the temporal evolution of any (spatially) slowly varying surface profile during mass transport. The model predicts an exponential decay of sinusoidal profiles with a fourth power of spatial wavelength dependence, and a grading of single mesa steps with a fourth root of time dependence. Good agreement with the model has been obtained in a systematic experimental study employing etched structures in InP. This study yields the low value of 1.5 eV for the activation energy of the mass-transport process in InP.
Interactions of intense ultraviolet laser radiation with solid aerosols
Authors: Poulain D. E. , Alexander D. R. , Barton J. P. , Schaub S. A. , Zhang J.
Published: July 2002

Characterizations of the interaction of intense ultraviolet laser radiation (λ=248 nm) with small solid aerosols are presented. Interaction dynamics, velocity measurements of expelled material, and thresholds for plasma formation are presented for aluminum, calcium fluoride, glass, silicon carbide, and tungsten particles. An excimer laser operating with a krypton fluoride gas mixture was used to irradiate small solid aerosol particles (≊5–50 μm) under atmospheric and vacuum conditions down to 10−5 Torr. Focused laser radiation intensities varied from 107 W/cm2 to a maximum of 2×1011 W/cm2. Interactions of the laser radiation with the solid aerosols were recorded in real time by an ultraviolet laser imaging system. Velocities between 250 and 2000 m/s were measured for material ejected from particles undergoing laser interaction. Laser intensity thresholds for visible plasma emission ranged from a maximum of 650 MW/cm2 for aluminum to a minimum of 59 MW/cm2 for tungsten. Thresholds for plasma formation were determined to be relatively independent of ambient pressure.
Illumination uniformity of spherical targets using kilojoule-scale lasers with optical smoothing
Authors: Colombant D. G. , Schmitt A. J.
Published: July 2002

Illumination uniformity in laser-pellet interactions is investigated for small kilojoule-range laser systems that are capable of symmetrically illuminating spherical targets. We address a variety of options that might be used to control the illumination uniformity on such targets, including the number of beams, pulse energy, laser wavelength, temporal pulse shape, and beam spatial profile shape. We consider only laser beams that are optically smoothed using methods such as induced spatial incoherence or random phase plates. The parameters that are most important for providing good uniformity are identified. We find that the most important parameters governing the uniformity are the number of beams and the shape of the beam profile. Configurations with a small number of beams (e.g., six) are much more sensitive to the beam profile; using techniques such as splitting the focal spots provides an additional degree of freedom that can significantly increase the illumination uniformity. Additionally, we show that the hydrodynamics of the plasma is important in determining the uniformity, although it is not so easily controlled. Quantitatively, we find nonuniformities (measured by peak-to-valley ablation pressure differences) can be less than 10% for six-beam kilojoule-level 1/4 -μm laser wavelength systems, and of the order of a few percent for comparable 24-beam systems.
Fluorescence characterization of ablated polymeric materials: Poly(methyl methacrylate) doped with 1-ethylpyrene
Authors: Itaya Akira , Kurahashi Akihiko , Masuhara Hiroshi , Taniguchi Yoshio , Kiguchi Masashi
Published: July 2002

Fluorescence spectra and rise as well as decay curves of 1-ethylpyrene (EPy) in poly(methyl methacrylate) films changed using a XeCl (308-nm) excimer laser as an ablation source. This phenomenon was observed not only for the ablated area but also for the masked region of about 20 μm around the ablated area and was attributed to the change of the dispersion condition of EPy. Effects of laser ablation upon properties of polymer films were elucidated by analyzing fluorescence dynamics using a microscope and under a total internal reflection condition.
Si-TaSi2 eutectic composites as an example of a percolation system
Authors: Samalam Vijay K.
Published: July 2002

Recent measurements of the resistance of the Si-TaSi2 semiconductor-metal eutectic composite show that these systems have electronic properties different from what conventional theories predict. The conductance of these samples goes to zero at very low values of the fractional area occupied by the depletion zones surrounding the TaSi2 rods. The general functional dependence of the conductance on the fractional area of the rods is also different. We show that percolation theory can explain these results if it is assumed that the rods are distributed in cell-like structures with the density of the rods on the perimeter of the cell being given by a Poisson distribution.
Absorber versus trap model in solitary semiconductor lasers
Authors: Liu X. Y. , Bourkoff E.
Published: July 2002

The model of deep level traps is compared with that of optically saturable absorbing centers in solitary semiconductors lasers. The steady-state response is investigated both analytically and numerically. The dynamic behavior is simulated by numerically solving the rate equations. The dependence on various laser parameters of the oscillation frequencies, the onset of self-sustained pulsations (SSP), and the damping rate of relaxation oscillations (RO) is also investigated. In spite of the apparent differences between the two models, they nevertheless predict essentially similar behavior for semiconductor lasers not within an external cavity.
Electron effective-mass modulation transistor
Authors: Tokura Y. , Susa N.
Published: July 2002

A new current-controlling structure is proposed that uses a fractional layer superlattice. The gate changes the coupling between the electrons and the superlattice. Since the current changes through the quantum mechanical interference resulting from the multiple scatterings by the periodic potentials, it needs no electron redistribution time. Therefore, a very fast response time is expected.
Magnetic condensation of a photoexcited plasma during fluoropolymer sputtering
Authors: Sugimoto Iwao , Miyake Shojiro
Published: July 2002

Radio-frequency plasma can be condensed into a space with a high density of magnetic flux. Plasma condensation into a deposited substrate to which a magnetic field is applied is investigated during fluoropolymer sputtering. Space-resolved spectroscopy reveals condensation of F and CF2 species into the magnetically excited plasma space. Ultraviolet light irradiation into the plasma can also excite these plasma species. The combined effect of this magnetical condensation and photoexcitation of plasma on the deposited film structure is clarified by infrared and x-ray photoelectron spectroscopy. Films obtained from the magnetically condensed plasma contain high concentrations of C■C moieties and negligible numbers of radical sites providing oxygen contamination. The deposition rate is greatly increased by this condensed plasma. These remarkable characteristics in magnetically condensed plasma products are enhanced by ultraviolet light irradiation into the plasma.
Fitting of transmission data for determining the optical constants and thicknesses of optical films
Authors: Ying Xuantong , Feldman Albert , Farabaugh E. N.
Published: July 2002

A multiparameter, nonlinear-curve fitting method is used to determine the refractive indices, absorption coefficients, and thicknesses of mixed yttria-silica films from transmittance spectra. Both homogeneous and inhomogeneous models of refractive index in the films are used for the data analysis. Results suggest that inhomogeneity in the films should be considered when investigating the optical properties of thin films. However, care must be taken when computing a refractive index gradient in an absorbing film as both absorption and index gradients can affect the optical transmittance in a similar manner.
Be+/P+, Be+/Ar+, and Be+/N+ coimplantations into InP:Fe
Authors: Rao Mulpuri V. , Nadella Ravi K.
Published: July 2002

Single- and multiple-energy Be+/P+, Be+/Ar+, and Be+/N+ coimplantations were performed into semi-insulating InP:Fe. Significantly higher Be dopant activations were obtained for Be+/P+ and Be+/Ar+ coimplantations compared to Be+ implantation. Sharp hole-concentration depth profiles were obtained for Be+/P+ and Be+/Ar+ coimplantations in contrast to the deep diffusion fronts for Be+ implantation. A high degree of crystalline lattice damage in coimplanted material is believed to be responsible for the improved electrical characteristics of the material. A poor Be dopant electrical activation was observed for Be+/N+ coimplantation.
Saturation effect on nonlinear couplers
Authors: Chen Yijiang , Snyder A. W.
Published: July 2002

With the aid of a mode diagram, the qualitative dependence of phase space trajectory on power and saturation for saturable nonlinear couplers is revealed. The uplimit of power (due to saturation of nonlinearity) for efficient switching by a nonlinear coupler is evaluated.
Three-dimensional boundary-element method for analyzing nonrotationally symmetric perturbations in electrostatic lenses
Authors: Ximen Jiye , Li Dayue
Published: July 2002

The three-dimensional boundary-element method (3D BEM) has been discussed in some aspects involving the subdivision of boundary elements, the quadrature of surface charge density integrals, and their singularities. The 3D BEM has been applied to the analysis of nonrotationally symmetric perturbations in electrostatic lenses. The perturbations due to machining defects (including elliptical distortions, inclined end faces, misalignments, and their combinations) have been calculated and also the asymmetric aberrations have been computed. A set of computer programs has been developed. The computed perturbation potential distributions have been compared with the theoretical ones.
Cathode- and anode-spot tracks in a closed magnetic field
Authors: Swift P. D.
Published: July 2002

The velocity of cathode spots with nonretrograde motion in a closed magnetic field has been found to have a component normal to the direction of j×B, and the trajectory of the cathode spots in this field configuration is not stable, in contrast to the trajectory for retrograde motion. This component of the spot motion can be understood, as has been predicted, by consideration of the Lorentz force acting on a positive space charge, which has been proposed to be associated with cathode spots. The behavior of the motion normal to j×B of cathode spots with retrograde velocities can be explained by the same model. Further results presented are consistent with a positive space charge also being associated with anode spots.
Electric field dependence of the eigenstates of coupled quantum wells
Authors: Bloss Walter L.
Published: July 2002

We calculate the effects of the coupling between the eigenstates of two symmetric GaAs/ Alx Ga1−x As quantum wells separated by a thin barrier with an applied electric field using a very accurate numerical method that we have developed. Energy shifts with field and overlap integrals for the symmetric and antisymmetric electron and hole eigenstates are calculated. These results are compared to a single quantum well of equivalent dimensions. As suggested in the literature, the quantum-confined Stark effect is shown to be significantly increased by the use of coupled quantum wells. Comparison with the experimental results of Chen et al. [Y. J. Chen, E. S. Koteles, B. S. Elman, and C. A. Armiento, Phys. Rev. B 36, 4562 (1987)] is made with surprisingly good agreement.
Correlated transmission electron microscopy and photoluminescence studies of the Se+-ion implantation of a GaAs/(Al,Ga)As multiple quantum well
Authors: Bithell E. G. , Stobbs W. M. , Phillips C. , Eccleston R. , Gwilliam R.
Published: July 2002

We report a study of the Se+-ion implantation and subsequent annealing of a GaAs/(Al,Ga)As multiple quantum well, characterizing the process using transmission electron microscopy, photoluminescence spectroscopy, and Monte Carlo simulation techniques. We conclude that enhanced layer interdiffusion occurs at depths several times the projected range for the Se+ implant, and that there is evidence of residual stress at similar depths.
Ion bombardment effects on undoped hydrogenated amorphous silicon films deposited by the electron cyclotron resonance plasma chemical vapor deposition method
Authors: Hayama Masahiro , Murai Hiroyuki , Kobayashi Kazuhiro
Published: July 2002

Ion bombardment effects on undoped hydrogenated amorphous silicon films deposited by the electron cyclotron resonance plasma chemical vapor deposition method without substrate heating using SiH4/Ar gas have been investigated by applying a dc bias voltage to the substrate. Ion bombardment to the growing films plays an important role in decreasing the polysilane phase and dangling bonds in the films, and in the realization of a high deposition rate. As a result, ion bombardment contributes to good photoconductivity at a high deposition rate, such as 170 nm/min, without substrate heating by decreasing the polysilane phase.
Electric field in an arbitrary random pack of spherical particles
Authors: Davis I. Lee
Published: July 2002

A solution technique is presented that calculates the static electric field at any point in a concentrated random dispersion of spherical particles when a uniform external electric field is applied across the dispersion. The particles may be of arbitrary size, position, and material composition. Using a rapidly converging iterative technique, the three electric field components may be calculated at any point in the medium or inside any particle. We assume all component materials are electrically isotropic and homogeneous and that the net charge on each particle is zero. This work is a first step in gaining a more fundamental understanding of electrostatic discharge phenomena through particulate-filled systems. An important key is the use of the reduced dimension particle packing algorithms which simulate the microstructure of the particle pack.
1.4-eV photoluminescence and thermally stimulated conductivity in cadmium telluride
Authors: Cotal H. L. , Lewandowski A. C. , Markey B. G. , McKeever S. W. S. , Cantwell E. , Aldridge J.
Published: July 2002

Photoluminescence (PL) and thermally stimulated conductivity (TSC) data on high-resistivity, p-type CdTe single crystals are presented. The PL emission in these samples consists of two closely overlapping components peaking at approximately 1.47 and 1.49 eV. Thermal quenching of these signals reveals activation energies of ∼0.02 and ∼0.13 eV for the former component, and ∼0.11 eV for the latter. TSC signals at temperatures corresponding to those over which thermal quenching occurs are observed. The TSC peaks are due to hole release with activation energies which agree with those obtained from the thermal quenching studies. Etching of the samples removes surface damage caused by mechanical polishing. The surface damage produces nonradiative pathways by which electron-hole recombination can take place without luminescence. A model based on free-electron to trapped-hole recombination is presented to account for the data. It is shown, from numerical solutions of the rate equations describing the model, that by explicitly incorporating into the model more than one hole state at which radiative recombination can occur, shifts in the emission energy during time-resolved and intensity-dependence studies can be expected.