bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimum endoreversible power cycle with a specified operating temperature range
Authors: Ait-Ali Mohand A.
Published: July 2002

An endoreversible power cycle can be seen as one in which two heat transfer processes and one work production process in series are sharing (and competing for) the same overall temperature potential. An optimal allocation of the temperature difference available from a heat source and a heat sink between these processes therefore results in a two dimensional search. It is found that, for the Curzon–Ahlborn (C-A) endoreversible power cycle, the maximum power occurs when the available overall temperature difference is shared equally between heat transfer and work production processes, and the specified overall heat conductance equally distributed between the boiler and the condenser heat exchangers. A more flexible optimization approach consists in analyzing the C-A power cycle within a larger family of endoreversible maximum power cycles defined with a specified operating temperature range for the working fluid as a parameter. This general optimization problem is solved as a one degree of freedom search and used to fit observed efficiency and temperatures of actual cycles to separate internal from external irreversibilities.
Nickel silicide formation in silicon implanted nickel
Authors: Rao Z. , Williams J. S. , Pogany A. P. , Sood D. K. , Collins G. A.
Published: July 2002

Nickel silicide formation during the annealing of very high dose (≥4.5×1017 ions/cm2) Si implanted Ni has been investigated, using ion beam analytical techniques, electron microscopy, and x-ray diffraction analysis. An initial amorphous Si–Ni alloy, formed as a result of high dose ion implantation, first crystallized to Ni2Si upon annealing in the temperature region of 200–300 °C. This was followed by the formation of Ni5Si2 in the temperature region of 300–400 °C and then by Ni3Si at 400–600 °C. The Ni3Si layer was found to have an epitaxial relationship with the substrate Ni, which was determined as Ni3Si〈100〉∥Ni〈100〉 and Ni3Si〈110〉∥Ni〈110〉 for Ni(100) samples. The minimum channeling yield in the 2 MeV He Rutherford backscattering and channeling spectra of this epitaxial layer improved with higher annealing temperatures up to 600 °C, and reached a best value measured at about 8%. However, the epitaxial Ni3Si dissolved after long time annealing at 600 °C or annealing at higher temperatures to liberate soluble Si into the Ni substrate. The epitaxy is attributed to the excellent lattice match between the Ni3Si and the Ni. The annealing behavior follows the predictions of the Ni–Si phase diagram for this nickel-rich binary system.
Structure of AlAs/GaAs distributed Bragg reflector grown on Si substrate by metalorganic chemical vapor deposition
Authors: Egawa T. , Jimbo T. , Umeno M.
Published: July 2002

A vertical-cavity surface-emitting laser diode with 20 pairs of AlAs/GaAs distributed Bragg reflectors (DBRs) has been grown on a Si substrate using metalorganic chemical vapor deposition. Interfacial roughness and compositional profile of the AlAs/GaAs DBR structure were studied by cross-sectional scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Auger electron spectroscopy. Cross-sectional SEM and TEM observations reveal quasi-periodic zigzag roughness and nonuniformity in the AlAs and GaAs layers. Auger electron spectroscopy reveals compositional transitions at the AlAs/GaAs heterointerfaces. A lower reflectivity of the AlAs/GaAs DBR on the Si substrate is caused by the degraded heterointerfaces.
Hydrogen passivation and its effects on carrier trapping by dislocations in InP/GaAs heterostructures
Authors: Chatterjee B. , Ringel S. A.
Published: July 2002

In previous work we reported on the stable passivation of dislocations in InP/GaAs heterostructures by plasma hydrogenation (Chatterjee et al., Appl. Phys. Lett. vol. 65, p. 58, 1994). In this article we investigate and compare the trapping kinetics and general trapping properties of dislocations in strain relaxed p-InP grown on GaAs by metalorganic chemical vapor deposition prior to and after hydrogen passivation using deep level transient spectroscopy (DLTS) and current-voltage-temperature (I-V/T) measurements to determine the complete role of hydrogen passivation in these heterostructures. Three hole traps, T1A, T1B, and T2, were detected and attributed to dislocations in heteroepitaxial p-InP which displayed the logarithmic capture kinetics, extended dependence on fill pulse time, and broadened DLTS features expected for dislocation related traps. Quantitative analysis of the DLTS characteristics revealed progressive asymmetry in DLTS peak shape, an increase in characteristic peak width, and a decrease in activation energy as fill pulse time is increased until saturation values were reached.

These observations are explained on the basis of a distribution or band of energy states for each trap resulting from the interaction of electrically active sites either between closely spaced dislocations or along dislocation cores within the strain-relaxed InP. For fill pulse times increasing from 1 μs to 10 ms, activation energies for T1A decreased monotonically from 0.80 to 0.65 eV, for T1B from 0.56 to 0.45 eV, and for T2 from 0.45 to 0.35 eV, with saturation occurring at the upper and lower limits for each trap, which indicates a qualitative measure of the energy spread for each trap. Plasma hydrogenation was not only found to passivate dislocations by reducing the trap concentration from ∼6×1014 to ∼3×1012 cm−3 for a 2 h exposure, but also strikingly altered their basic trapping properties. The qualitative measure of energy spread for the T1A and T2 traps were narrowed from ∼100 to 150 meV to ∼20 to 30 meV after a 2 h hydrogen exposure, whereas T1B was not detected after passivation. In addition, a simultaneous reduction in fill pulse saturation time, DLTS peak broadening, and peak shift as a function of hydrogen exposure time were observed. These observations suggest that hydrogen passivation modifies the dislocation trapping characteristics toward a more point defectlike behavior due to an increase in the average spacing between electrically active dislocation sites. This in turn reduces the interactions between these sites and narrows the distribution of states within each defect band. Further, reverse bias I-V/T measurements revealed that the near midgap trap T1A, which was found to dominate the space charge generation current prior to passivation, is no longer dominant after hydrogen passivation. Instead a 2 h hydrogen treatment shifted the dominant center to an activation energy which more closely matches the shallow T2 level.
Analysis of Paul–Straubel trap and its variations
Authors: Yu N. , Nagourney W.
Published: July 2002

Unconventional rf traps of the Paul–Straubel type and its variations have found increasing use in ion trapping experiments. Calculations of the properties of these traps are presented. Simple realistic trap geometries are studied for their voltage loss factor, anharmonicity, and radial symmetry breaking. Optimum geometries for these traps are indicated.
High defect density regions in neutron irradiated high-purity germanium: Characteristics and formation mechanisms
Authors: Fourches N.
Published: July 2002

A tentative model which reveals the existence of p-type regions with a significant spatial extension in either p- or n-type fast neutron irradiated high-purity germanium is presented. This model is based on transient capacitance spectroscopy data. The regions described here are present after room-temperature neutron irradiation in a material with a preirradiation free-carrier concentration at 77 K of around 1011 cm−3. They are characterized by the presence of a high concentration of point defects. Previous measurements show that these point defects act as shallow and deep acceptors. Simple calculation allows the estimation of the shallow acceptor concentration inside these regions from experimental data as well as the average size of such high defect density regions. The microscopic origin of the point defects located in these regions is also discussed. The data gives some basic insight into the properties of defects induced by displacement cascades in elemental semiconductors. Despite some limitations in the quantitative approach, this study also provides new elements for the understanding of neutron induced defects in lightly doped germanium.
Effects of annealing and α irradiation on deep levels in silver-doped n-type silicon
Authors: Ali Akbar , Iqbal M. Zafar , Baber N.
Published: July 2002

Deep-level transient spectroscopy has been used to study the deep levels introduced by silver impurity in silicon. New levels in addition to the well-known silver-related deep donor and acceptor levels have been found. Interaction of silver-related defects with radiation-induced defects has been studied using α irradiation. Data on the annealing characteristics of silver-related levels are reported. Isochronal thermal annealing before and after irradiation provides interesting insights on such interactions and on the nature of the silver-related levels. In particular, the two newly observed prominent silver-related levels exhibit a complementary annealing behavior, suggesting a mutual thermal transformation. The presence of silver is seen to produce a significant change in the annealing characteristics of the prominent radiation-induced A-center defect.
Giant magnetoresistance in f-electron systems
Authors: Kasuya Tadao
Published: July 2002

Various types of mechanisms for giant magnetoresistance, in particular for f-electron systems, are critically reviewed. First, the most typical prototype of the nesting-type magnetic ordering in the heavy-rare-earth metals is reviewed. Both negative and positive magnetoresistances are expected for the resistivities, parallel and perpendicular to the nesting wave vector, respectively. Then, the most typical negative magnetoresistance due to impurity states is studied on Eu chalcogenides with chalcogen vacancies or with trivalent rare-earth impurities substituting Eu atoms. In the former, the change from the singlet to the triplet for the trapped pair electrons is the main origin. In both cases magnetic polarons play important roles. For low-carrier-density systems in the metallic region ferromagnetic ordering is induced; the resistivity then has a peak at a temperature near above Tc due to a critical scattering resulting a negative magnetoresistance. Narrow-gap semiconductors and low-carrier semimetals are also typical materials to show exotic giant magnetoresistance. Various other cases including valence fluctuating systems are also studied.
Erbium luminescence in porous silicon doped from spin-on films
Authors: Dorofeev A. M. , Gaponenko N. V. , Bondarenko V. P. , Bachilo E. E. , Kazuchits N. M. , Leshok A. A. , Troyanova G. N. , Vorosov N. N. , Borisenko V. E. , Gnaser H. , Bock W. , Becker P. , Oechsner H.
Published: July 2002

Erbium photoluminescence at room temperature and at 77 K has been observed from porous silicon doped with erbium from a spin-on silica gel film. Erbium incorporation into silicon dioxide at the surface of porous silicon and rapid thermal processing at temperatures higher than 1223 K were found to be a necessary prerequisite for erbium-related luminescence in porous silicon. No erbium diffusion into monocrystalline silicon from the spin-on films was observed. The depth-dependent erbium concentration in the bulk of porous silicon was determined by secondary-neutral- and secondary-ion-mass spectrometry depth profiling. The laterally resolved erbium distribution in the porous silicon was derived from energy-dispersive x-ray analysis. Possible mechanisms of erbium-related luminescence in porous silicon are discussed.
Carbon impurity effects in Al-Ga interdiffused GaAs/AlAs multiple quantum wells
Authors: Oh Y. T. , Kim S. K. , Kim Y. H. , Kang T. W. , Hong C. Y. , Kim T. W.
Published: July 2002

Photoluminescence (PL) measurements were performed in order to investigate the carbon impurity effects on the intermixing behavior of GaAs/AlAs multiple quantum wells (MQWs) grown by molecular-beam epitaxy. The GaAs/AlAs MQWs were annealed with a carbon source in a furnace annealing system. The PL spectra show that the magnitude of the intermixing of Al and Ga induced by thermal annealing in GaAs/AlAs MQWs increases with depth. This behavior is not in agreement with the intermixing mechanism considering vacancy injection of the surface. The nonuniformity of the intermixing as a function of the depth originated from the carbon impurities which were injected during thermal treatment.
Spectra of tetravalent chromium in calcium fluorophosphate
Authors: Gruber John B. , Morrison Clyde A. , Harris Daniel C. , Seltzer Michael D. , Allik Toomas H. , Hutchinson J. Andrew , Scripsick Michael P.
Published: July 2002

The spectroscopic properties of Cr-doped Ca5(PO4)3F known as Cr:FAP were examined using several different chemical and physical means. Results from analytical titration measurements indicate that chromium is tetravalent in the samples investigated. Based on electron-spin resonance measurements at temperatures as low as 11 K, no trivalent chromium and only a trace of pentavalent chromium (0.5–10 ppm) was detected in the samples used for optical studies. We postulate that Cr4+ is stabilized in the crystal as a result of the small amount of Y2O3 that was added during the crystal growth process and that charge balance is achieved when Y3+ replaces Ca2+ and Cr4+ replaces P5+. Assuming tetravalent chromium, absorption, and emission spectra were interpreted by analyzing phonon sidebands and zero-phonon transitions observed at various temperatures. The observed crystal-field splitting is compared with calculated levels based on a Tanabe–Sugano diagram for quartet and doublet states of Cr4+(3d2) in tetrahedral symmetry. The parametrized Hamiltonian includes the free-ion parameters for Cr4+(3d2) and an initial set of crystal-field parameters obtained from a point-charge lattice-sum calculation where ionic distances were obtained from x-ray crystallographic data. The parametrized Hamiltonian with crystal-field terms in C4 symmetry, when diagonalized within the complete 3d2 configuration, yields calculated Stark levels in reasonable agreement with levels established from the experiment.
Growth of epitaxial ferromagnetic MnSb layers by hot-wall epitaxy
Authors: Tatsuoka H. , Kuwabara H. , Oshita M. , Nakanishi Y. , Nakamura T. , Fujiyasu H.
Published: July 2002

Epitaxial ferromagnetic MnSb layers were grown on GaAs(100) substrates by hot-wall epitaxy. Structural and magnetic properties of the MnSb layers are examined by reflection high-energy electron diffraction and vibrating sample magnetometry, respectively. It is found that MnSb with a NiAs-type crystalline structure can be grown epitaxially on GaAs(100) with inclination of the c axis of MnSb towards GaAs[011] and [011] direction by 53°. This inclination growth causes in-plane anisotropy of the magnetic property of the layer. The simple growth technique of the ferromagnetic layers on compound semiconductor substrates indicates high potentiality of development in magnetic material—III-V semiconductor hybrid devices.
Photochromic command surface induced switching of liquid crystal optical waveguide structures
Authors: Knobloch Harald , Orendi Horst , Büchel Michael , Seki Takahiro , Ito Shinzaburo , Knoll Wolfgang
Published: July 2002

We report on optical waveguide structures containing a thin liquid crystal (LC) film held between two photochromic command surfaces. The command surfaces consist of three monomolecular layers of a polymer with azobenzene side chains deposited according to the Langmuir–Blodgett–Kuhn technique. When exposed to light of appropriate wavelength, the command surfaces undergo a trans↔cis photoisomerization process that induces a reversible change in the liquid crystalline orientation. Such an orientation change of the LC alters the optical properties of the optical waveguide. We present experiments on the dynamics of the LC orientation process. The transition is shown to be continuous, with the degree of orientation dependent on the ratio of the cis-trans chromophore concentration ratio in the command surface.
Acoustical and optical properties of Ga0.52In0.48P: A Brillouin scattering study
Authors: Hassine A. , Sapriel J. , Le Berre P. , Legay P. , Alexandre F. , Post G.
Published: July 2002

Brillouin scattering is used to determine the refractive index N=n+iκ of Ga0.52In0.48P layers, lattice matched to GaAs, in a wavelength range never investigated before (400 nm<λ<800 nm). It is shown that the variations of n are given by two different analytical expressions, depending on whether the corresponding photon energies E are lower or higher than the band gap Eg. Optical absorption measurements are deduced from the Brillouin linewidth. The whole set of elastic constant is also determined through the Brillouin shifts. For E∼Eg, i.e., in resonance conditions, n displays a small but sharp peak closely related to the abrupt increase of the optical absorption. Besides the Brillouin investigations, complementary results obtained by ellipsometry and Raman spectroscopy confirm our optical properties measurements in Ga0.52In0.48P and the electronic resonance behavior, respectively.
Ferromagnetic resonance in evaporated Co-CoO films
Authors: Kohmoto Osamu , Munakata Makoto
Published: July 2002

The magnetic properties of ∼2500-Å-thick Co films evaporated in various oxygen pressures have been studied. Our results show that as the saturation magnetization is reduced, the coercive force in the perpendicular direction (Hc⊥) increases to a maximum (1.6 kOe); this change is consistent with results of previous investigations. The sign of the effective perpendicular anisotropy field (Hk eff=2K/Ms−4πMs), as determined by ferromagnetic resonance (FMR), is always negative (<−4 kOe), indicating that the anisotropy field (2K/Ms) does not overcome the demagnetizing field (4πMs). Our FMR results also confirm that films having an Hc⊥ value larger than that in-plane coercive force (Hc∥ ) do not always demonstrate a value of Hk eff≳0.
In situ x-ray diffraction study of CoSi2 formation during annealing of a Co/Ti bilayer on Si(100)
Authors: Selinder T. I. , Roberts T. A. , Miller D. J. , Beno M. A. , Knapp G. S. , Gray K. E. , Ogawa S. , Fair J. A. , Fraser D. B.
Published: July 2002

X-ray diffraction was performed in situ during annealing of a Co/Ti/Si(001) multilayer, which produced an epitaxial CoSi2 layer. The results indicate that the Ti layer did not stay intact during the reaction, and thus could not act like a membrane, moderating Co/Si interdiffusion. Strongly textured phases (M) formed prior to CoSi2 nucleation, and was unobservable upon completion of the anneal. Nucleation and growth of CoSi2 on Si(001) took place in the presence of M, new Co-Ti-(O) phases that were located at the metal/Si interface, and thus M might play an important role in the perfection of the silicide.
Synthesis of diamond films using sequential chemistry: Enhanced growth rate by atomic oxygen
Authors: Kapoor Sanjiv , Kelly Michael A. , Hagström Stig B.
Published: July 2002

The growth of diamond films by sequentially exposing a heated silicon substrate to fluxes of carbon, atomic hydrogen, and atomic oxygen is reported on. High quality diamond films can be grown sequentially using only the hydrogen and carbon sources. Here the use of an additional source of atomic oxygen is reported on. Film growth for both the possible exposure sequences to the three sources has been attempted. No film is grown if the exposure sequence is carbon-oxygen-hydrogen. When the exposure sequence is carbon-hydrogen-oxygen it is found that the flux of hydrogen necessary for the growth of high quality diamond films is less than that for runs in which no oxygen is present. The growth rate of diamond is also enhanced up to 500% with atomic oxygen. The role of atomic oxygen in modifying the growth surface is discussed to explain the improvement of growth rate and quality of these films.
Process-induced strains in dry etched semiconductor nanostructures studied by photoreflectance
Authors: Tang Y. S. , Wang P. D. , Sotomayor Torres C. M. , Lunn B. , Ashenford D. E.
Published: July 2002

This article reports a photoreflectance study of the process-induced strains in both dry etched CdTe/Cd0.875Mn0.125Te and GaAs/Al0.3Ga0.7As nanostructures patterned by electron beam lithography. The results show that compressive strains can be introduced in both the dry etched nanostructures and the layers underneath the etched surfaces due to the introduction of defect complexes and/or crystographic damage inflicted in the fabrication process. The effect of post dry etch thermal annealing on the strains in the dry etched nanostructures has also been studied.
Interference oscillations in Fourier-transform infrared spectra of AlSb/GaSb superlattices
Authors: Ru Guoping , Zheng Yanlan , Li Aizhen
Published: July 2002

The interference oscillations in normal-incident Fourier-transform infrared (FTIR) spectra of AlSb/GaSb superlattices, which disturb the observation of intersub-band transitions, have been theoretically simulated and experimentally measured. Both theoretical and experimental results show that on GaSb substrates, interference oscillations are relatively weak when using GaSb rather than AlSb as the buffer layer; and by contrast, on GaAs substrates, they are weak when using AlSb rather than GaSb as the buffer layer. Using an AlSb buffer on semi-insulating GaAs substrates, normal-incident intersub-band transitions from L1 to L2 sub-bands in AlSb/GaSb superlattices have been observed by the usual FTIR technique.
Analysis of light-induced processes in bacteriorhodopsin and its application for spatial light modulation
Authors: Reddy K. P. J.
Published: July 2002

A simplified energy-level scheme is proposed for the photochemical cycle of the bacteriorhodopsin molecule. Rate equations are solved for the detailed light-induced processes based on this model and the intensity-induced population densities in various states of the molecule at steady state are computed which are used to obtain an analytic expression for the absorption coefficient of the modulation beam. Modulation of the probe laser-beam transmission by the modulation-laser-beam intensity-induced population changes is analyzed. It is predicted that for a probe beam at 412 nm up to 82% modulation can be achieved using a laser beam intensity of 3.2 W/cm2 at 570 nm. For temperatures ∼77 K, the transmission at 610 nm can be switched from zero to 81% for modulating laser intensity of 11 W/cm2. Construction of a spatial light modulator based on bacteriorhodopsin molecules is proposed and some of its features are discussed.
Mechanical stability and electronic properties of buried strained quantum wire arrays
Authors: Gosling T. J. , Willis J. R.
Published: July 2002

A closed-form solution is presented for the stresses induced in an infinite elastic body by a periodic array of misfitting inclusions. This solution is used to study the mechanical and electronic properties of buried arrays of [11̄0]-oriented strained quantum wires. A critical mismatch condition along the lines of the Matthews and Blakeslee condition for strained layers is developed and is used to show that quantum wire structures should be extremely stable in the postgrowth processing stages provided that the repeat period of the array is more than four times the dimension of a wire. If the period is more than five times the wire dimension then each member of the array behaves like an isolated wire. It is shown that stability problems for closely spaced arrays may be avoided by choosing the direction in which the wires are periodically distributed to be [001] rather than [110]. The formulas are also used to investigate the difference between the strain-induced band gap shifts of quantum wires and wells experiencing the same lattice mismatch with the growth substrate. It is found that the dilatation is identical in the two structures so that, in the InGaAs system, wells and wires of the same composition should have very similar band gaps. By contrast, conduction-band splitting in the GeSi system can give rise to differences of up to 100 meV between the band gaps of the two structures. These results are shown to compare very favorably with experiment.
Effect of hydrogenation and thermal annealing on the photoluminescence of p-InP
Authors: Balasubramanian Sathya , Koteswara Rao K. S. R. , Balasubramanian N. , Kumar Vikram
Published: July 2002

The effect of hydrogenation and thermal annealing on the photoluminescence (PL) of InP:Mg and InP:Zn is presented. On hydrogenation, a rise in near-band-edge PL intensity by a factor of 16 for the InP:Mg sample and a factor of 50 for the InP:Zn sample is observed and this is attributed to the passivation of nonradiative centers. A donor–acceptor pair transition before hydrogenation in the InP:Mg sample and after hydrogenation in the InP:Zn sample was observed. In both cases, the magnitude of the shift in peak position with excitation intensity shows the involvement of a donor deeper than the normally present shallow donors. The ionization energy of the donor in InP:Mg is estimated to be 48 meV and that in InP:Zn is estimated to be <40 meV. No hydrogenation induced radiative transitions were observed. In the InP:Mg samples, the acceptor passivation effects are lost after annealing at a temperature of 350 °C for 2 min, whereas the nonradiative center passivation after hydrogenation is not completely lost. In InP:Zn, the acceptor passivation along with nonradiative and deep center passivation are lost after an annealing treatment of 300 °C for 2 min. A thermally induced D–A pair emission in InP:Zn which moves to lower energies with increasing annealing temperature is observed. Such a transition is not observed for InP:Mg. This can be either due to a preferential pairing of the donor and acceptor which becomes randomized after the heat treatment or due to the removal of hydrogenation effects by annealing.
A matrix formalism for the simulation of pyroelectric sensors
Authors: Lienhard D. , Ploss B.
Published: July 2002

A pyroelectric sensor generates an electrical output signal as the response to incident radiation. Aside from the pyroelectric effect, the absorption of radiation and the heat propagation are essential for the signal generation. Therefore, the simulation of the sensor signal must cover the optical, thermal, and electrical processes. For the optical and thermal modelling of pyroelectric multilayer structures, a matrix formalism is given, which handles the propagation of electromagnetic and thermal waves in a similar way. Starting with the dielectric properties of the materials involved, the local absorption density is determined. With the thermal properties and the polarization distribution the temperature profile and the pyroelectric current are obtained. Implemented in a computer program, sensor signals of arbitrary multilayer sensors can be calculated. The method is applied to the modelling of integrated pyroelectric sensors.
Epitaxial thin films and heterostructures of a copper-oxide-based isotropic metallic oxide (La8−xSrxCu8O20)
Authors: Eom C. B. , Cava R. J. , Phillips Julia M. , Werder D. J.
Published: July 2002

Epitaxial thin films of a copper-oxide-based isotropic metallic oxide (La8−xSrxCu8O20) and superconducting heterostructures (YBa2Cu3O7/La8−xSrxCu8O20/YBa2Cu3O7) have been fabricated by 90° off-axis sputtering. La8−xSrxCu8O20 is an oxygen-deficient pseudocubic perovskite that exhibits Pauli paramagnetism. X-ray diffraction and cross-sectional transmission electron microscopy reveal the heterostructures to have high crystalline quality and clean interfaces. This material will facilitate fabrication of ideal superconductor–normal-metal–superconductor Josephson junctions with low boundary resistance due to its excellent chemical compatibility and lattice match with cuprate superconductors and will be useful for determining the source of interface resistance in such heterostructures.
Laser induced pyrolytic deposition of copper from (hexafluoroacetylacetonate)(trimethylvinylsilane) copper
Authors: Widmer M. , van den Bergh H.
Published: July 2002

The photothermal laser induced chemical vapor deposition of copper from its hexafluoroacetylacetonate trimethylvinylsilane derivative is studied as a function of added water vapor pressure. The height, width, electrical conductivity, and chemical composition of the deposited copper lines are measured. Under anhydrous conditions, the lines are characterized by a low growth rate, high carbon contamination, and poor electrical resistivity. In the presence of water vapor, a high growth rate (1800 μm/min) and high purity copper lines are obtained with a resistivity ratio of 1.1.
Effect of stress on grain boundary motion in thin films
Authors: Génin F. Y.
Published: July 2002

For thin films on a substrate, strains due to thermal expansion mismatch can produce very large stresses. While capillary forces create a grain boundary (GB) thermal groove, compressive and tensile stresses can form, respectively, a ridge or a canal at the grain boundary and can strongly influence the GB mobility. Following Mullins’ analysis of the effect of thermal grooving on GB motion [Acta Metall. 6, 414 (1958)], this treatment shows that GB pinning is enhanced by the formation of the canal, whereas the formation of the ridge tends to repel grain boundaries. Analytical and numerical solutions for surface profiles of traveling grain boundaries under stress are presented. The results are discussed in the context of stress-induced grain growth and stress relaxation in thin films. The model also explains the formation of hillocks in thin films and offers the prospect of measuring GB self-diffusion coefficients and GB velocities.
Schottky barrier enhancement using reacted Ni2Al3/Ni/n-GaAs, Ni/Al/Ni/n-GaAs, and NiAl/Al/Ni/n-GaAs contacts
Authors: Chen C.-P. , Chang Y. A. , Kuech T. F.
Published: July 2002

A systematic study of the enhancement of Schottky barriers to n-GaAs has been carried out using the following diodes, Ni2Al3/n-GaAs, Ni2Al3/Ni/n-GaAs, Ni/Al/Ni/n-GaAs and NiAl/Al/Ni/ n-GaAs, prepared by sputter deposition at a base pressure ∼2×10−7 Torr. A high Schottky barrier height ranging from 0.95 to 0.98 eV (deduced from current-voltage measurements) was observed for all the annealed contacts except for Ni2Al3/n-GaAs. Enhancement of the Schottky barrier height in all the contacts was attributed to the formation of a high Al content (Al,Ga)As layer at the metal/semiconductor interface. A regrowth mechanism was used to rationalize the Schottky barrier enhancement. In this mechanism, Ni reacts with GaAs initially at low temperatures, forming NixGaAs. The NixGaAs layer then reacts with the Ni-Al layer on top to form the (Al, Ga)As layer under subsequent high temperature annealing. A (200) dark-field XTEM image of the annealed contact was used to demonstrate the existence of this (Al,Ga)As phase.
Photo-induced variation of optical and dielectric properties of ferrites at room temperature
Authors: Katsnelson E.
Published: July 2002

Photo-induced phenomena have been observed at low temperatures in ferrites doped with a small concentration of certain ions. These effects disappear when the material is heated above some critical temperature Tk. We have observed photo-induced effects which appear and persist for a long time at room temperature in undoped single crystal ferrites (Mn0.91Zn0.09Fe2O4, bulk, and MeFe2O4, films, with Me=Mn, Mg, Ni, and Co) which are irradiated with a low intensity laser beam in a dc magnetic field. At room temperature a photo-induced variation was found in both the infrared reflectivity (in the range 2%–16%) and the optical transmission spectra (in the range 2%–22%) depending on the spectral wavelength and pumping laser beam polarization (linear or circular). This variation exceeds the low-temperature photo-induced change in transmission for semiconductors by 1–3 orders of magnitude. At room temperature we observed a photo-induced shift toward lower wavelengths of both the peak of the infrared reflectivity band (ω2, by 8 cm−1) and optical transmission bands (in the range 2–217 nm). The ω2 band shift and the reflectivity change are mainly reversible for right- and left-handed polarization. The refractive indices n, the absorption factors k, the dielectric constants ε, and the ionic charges were determined from the experimental infrared spectra (250–800 cm−1) of bulk ferrite by the technique of ‘‘successive analysis’’ (dispersion analysis followed by Kramers–Krönig analysis), both before and after the irradiation. The photo-induced changes in the optical and dielectric properties of ferrites are connected with the photo-induced change in the magnetization, which was directly measured with a torque magnetometer. The observed effects might find an application in optical recording.
Photosensitivity and switching of ZnSe/GaAs heterostructures
Authors: Markov E. A. , Zlenko A. A. , Zhukov I. A.
Published: July 2002

High photosensitivity increasing with decreasing incident light intensity and switching are observed in ZnSe/GaAs heterostructures. A model based on the possibility of conduction induced by carriers hopping between deep defect centers located in the bulk of ZnSe is presented.
Effects of iron on the infrared photoresponse of carbon/n-Si junctions prepared by plasma decomposition of propylene and ferrocene
Authors: Ozaki Jun-ichi , Nishiyama Yoshiyuki
Published: July 2002

Iron containing carbon films were deposited on n-Si substrate at 300 °C by dc plasma decomposition of propylene gas and ferrocene vapor. The films were investigated for the effect of iron on the photoresponse of a light emitting diode at 940 nm wavelength. The photocurrent was shown to vary with iron content and the variation in the photovoltage with iron content showed the same trend as that of photocurrent against iron content. The dependence of photocurrent on the light chopping frequency revealed that the attenuation of photocurrent with the frequency was small compared with the junction without iron. The states of iron in the carbon matrix were studied by x-ray photoelectron spectroscopy. The peak position shifted to higher binding energies with higher iron content. Peak analysis revealed two separate elemental peaks at 709 and 711 eV. The intensity of the 709 eV peak due to the iron in the low valence state showed a correlation with the magnitude of the photocurrent. From those observations the action of the iron in the low valence state was inferred to change the electronic state at the carbon film/n-Si junction to promote the photocarrier generation and ultimately enhance the photoresponse.
Thermomagnetic analysis of NdFeB melt-spun alloys with low Nd content
Authors: Kim Y. B. , Park W. S. , Kim H. T. , Cho Y. S. , Kim C. S. , Park M. J. , Kim T. K.
Published: July 2002

The phase transformation of NdFeB melt-spun alloys with low Nd content of 4–8 at. % was investigated by thermomagnetic analysis and x-ray diffractometry. Experimental results have shown that the metastable Nd2Fe23B3 compound formed in the alloys is considered to be transformed to Nd2Fe23B3+α-Fe+Fe3B in the temperature range of 550–690 °C, α-Fe+Fe3B+Nd1+eFe4B4 in the temperature range of 690–730 °C and finally α-Fe+Nd1+eFe4B4 above 840 °C. From the results, it has been concluded that Nd2Fe14B is not formed from metastable Nd2Fe23B3. On the other hand, the melt-spun alloy of Nd2Fe23B3 (∼Nd7.1Fe82.1B10.7) annealed under optimum conditions has been found to be composed of α-Fe, Fe3B, and Nd2Fe14B phases. The alloy has a coercivity comparable to Fe3B-based Nd4Fe77B19 and relatively high-energy product of about 71.6 kJ/m3 (∼9 MG Oe).
Control of the in-plane epitaxy for bi-epitaxial grain boundary junctions using a new multilayer structure
Authors: Li M. Y. , Kao H. L. , Chang W. J. , Lin C. L. , Chi C. C. , Guan Weiyan , Wu M. K.
Published: July 2002

In order to obtain 100% bi-epitaxial 45° grain boundary junctions of YBa2Cu3Ox (YBCO), we have systematically examined the in-plane epitaxy of CeO2 films grown on MgO substrates. The inevitable presence of CeO2[110]∥MgO[100] causes mixtures of in-plane rotation of 0° and 45° between YBCO/CeO2/MgO and YBCO/MgO. We have further developed a new structure, namely YBCO/CeO2/Yttria-stabilized ZrO2/MgO and YBCO/MgO boundary, so that 100% in-plane rotation of 45° can be routinely obtained. The model of the in-plane epitaxial relationship between the multilayers using near coincident site lattices was proposed. The critical current density of the junctions made on the boundary is 3×103 A/cm2 at 77 K, while the order of the Jc of YBCO films on both sides of the grain boundary is 106 A/cm2. The current-voltage characteristics of the junctions show resistively shunted junction behavior. The better epitaxy of our new structure can lead to a better control of grain boundary critical current density.
A numerical study of the ζ2 and η2 structural parameters for a class of fiber-reinforced composites
Authors: Christiansson Henrik , Helsing Johan
Published: July 2002

Linear elasticity for a fiber reinforced two-component periodic composite is treated numerically. Given volume fractions and elastic moduli of the two components, which are the realizable combinations of the effective moduli? A reduced problem is solved for a system of concentric cylindrical shells arranged in a hexagonal unit cell. The effective moduli are estimated via third-order bounds, which in turn are determined by the structural parameters ζ2 and η2, trivially bounded by the inequality 0≤ζ2,η2≤1. Using an interface integral technique, we compute these parameters for hundreds of millions of different configurations. Realizable regions in the ζ2-η2 plane, are presented together with cross-sections of the composites that correspond to points on the boundary of the realizable region. This will highlight the geometric significance of ζ2 and η2. For composites with roughly the same amount of the two components we realize over 60% of the area 0≤ζ2,η2≤1.
The effect of ultrasonic pre-treatment on nucleation density of chemical vapor deposition diamond
Authors: Tang Chi , Ingram David C.
Published: July 2002

Using statistical design of experiments, the effect of ultrasonic pre-treatment on the nucleation density of diamond was studied. The parameters investigated included ultrasonic excitation power, concentration of diamond powder in water, duration of ultrasonic excitation, and duration of cleaning with water after ultrasonic excitation. Diamond films were deposited on silicon (100) substrates using microwave assisted plasma chemical vapor deposition. The nucleation density varied from 106 nuclei/cm2 to 109 nuclei/cm2. The results illustrated that the dominant effect in ultrasonic pre-treatment was seeding. Moreover, scratches caused by the seeds during the treatment enabled more seeds to be retained on the surface. Based on these results, an optimized ultrasonic pretreatment has been developed. The new procedure yields a uniform nucleation density of 109 nuclei/cm2 on silicon (100) substrates.
Efficient electroluminescence of distyrylarylene with hole transporting ability
Authors: Hosokawa Chishio , Tokailin Hiroshi , Higashi Hisahiro , Kusumoto Tadashi
Published: July 2002

We report that organic electroluminescence devices with a hole transporting emitting layer composed of distyrylarylene derivatives realized highly efficient and bright emission in the blue-green region. Luminous efficiency was obtained to be 2.1 lm/W in the low-luminance region (135 cd/m2) using an indium tin oxide/emitting layer/electron transporting layer/Mg:Ag structure. The external quantum efficiency was estimated to be about 1.5%. The highest luminance was obtained to be 4000 cd/m2 for the device.
Dissipative electron tunneling from the phosphorus ground level to the conduction band of silicon
Authors: Dargys A. , Žurauskienė N.
Published: July 2002

The influence of thermal acoustic vibrations on impurity field ionization is investigated. At lattice temperatures T<15 K, when tunneling from the ground level predominates, thermal acoustic phonons in silicon are found to enhance phosphorus field ionization. The experiments are compared with recent theoretical calculations, which take into account the deformation potential interaction of thermal acoustic phonons with a localized center.
Energy straggling of protons in solids
Authors: Wang Neng-ping , Ho Yu-kun
Published: July 2002

By use of the linear-response dielectric theory and local electron density approximation, we calculate the energy straggling of protons in solids. The correlation and exchange interaction of electron gas in solids is taken into consideration by introducing a static local-field-correction function in the dielectric function. The theoretical results are compared with experimental and empirical data, as well as with other previous theoretical results.
Laplace transform method of measuring the distribution of Si–SiO2 barrier heights: Basic principles
Authors: Babić Davorin , Nicollian Edward H.
Published: July 2002

The electronegativity difference between silicon and SiO2 produces a dipole layer at the Si–SiO2 interface which determines the barrier height between the silicon and SiO2 conduction bands. Because thermally grown SiO2 is amorphous, the alignment of these dipoles with respect to each other fluctuates resulting in a barrier height distribution. Photon-assisted injection of electrons into the thermally grown gate oxide of a metal-oxide-semiconductor field-effect transistor is used to extract this distribution by experiment. The ratio of the injected gate current to the short-circuit source–drain photocurrent collected under the gate is shown to be the Laplace transform of the barrier height distribution. By inverting the Laplace transform, measured under the specific experimental conditions described, the barrier height distribution is found to be Gaussian. The average zero-field barrier height is found to be 3.5 eV with a standard deviation of 0.64 eV measured in the oxide over a plane parallel to the Si–SiO2 interface. The relation is given between the average barrier height and the high-field extrapolated barrier height of 3.1 eV, and it is argued that the standard deviation is a measure of the degree of disorder in the SiO2.
Luminescence of Cr3+ and energy transfer between Cr3+ and Nd3+ ions in yttrium aluminum garnet
Authors: Hong P. , Zhang X. X. , Struck C. W. , Di Bartolo B.
Published: July 2002

The luminescence properties of Cr3+ ions and the energy transfer between Cr3+ and Nd3+ ions have been studied quantitatively in yttrium aluminum garnet (YAG). The energy level diagram and the emission spectrum of 4T2→4A2 transition of Cr3+ ions were calculated in this crystal using the single-configurational-coordination model and the absorption data. Our calculated Δ value (the energy difference between the 2E zero-vibrational level and the crossover point of 2E and 4T2 states), ∼730 cm−1 at room temperature, in contrast to the previously estimated value of ∼1000 cm−1, accounts for a variety of experimental results more satisfactorily. Both the 4T2 and 2E states of Cr3+ ions were found to contribute to the energy transfer to Nd3+ ions. The contribution of the former dominates at high temperatures and the latter at low temperatures. The thermal population distribution between the 4T2 and 2E states of Cr3+ ions was shown to be responsible for the temperature dependences of the Cr3+ luminescence properties and the Cr3+ to Nd3+ energy transfer processes. An electric dipole–dipole interaction mechanism was found to be adequate to describe the energy transfer process for temperatures up to about 400 K.
A Raman spectroscopic study of the Si, Be, and C incorporation in InxGa1−xAs relaxed layers
Authors: Alvarez A.-L. , Calle F. , Sacedón A. , Calleja E. , Muñoz E. , Wagner J. , Maier M. , Mazuelas A. , Ploog K. H.
Published: July 2002

The incorporation of high concentrations (≳1019 cm−3) of Si, Be, and C in InxGa1−xAs relaxed layers has been studied as a function of In content (x≤0.16) by Raman spectroscopy of local vibrational modes (LVM). The frequencies of the Raman peaks resulting from the convolution of several split modes shift to lower values as the In content is increased, the carbon acceptor (CAs) local mode frequency showing the strongest dependency on x. Features attributed exclusively to the influence of In on second-neighbor sites are identified only in the Si-doped samples. The transverse and longitudinal modes expected from the splitting of a LVM of CAs with one In first neighbor are not observed in layers with x up to 0.085. A new calibration for the BeGa, CAs, and Si-related LVM leads to the conclusion that In increases the total electrical activation of Si and favors its incorporation on group-III sublattice sites. In contrast, no influence of In on the Be or C doping activation has been detected. The analysis of the CAs LVM spectra supports the view that in InxGa1−xAs CAs is preferably surrounded by Ga instead of In atoms for x≤0.085.
Structure and resistivity of vacancy-ordered Sr2Ti2O5 films in high-T
c superconducting heterostructures
Authors: Diao Chien Chen , Oya Gin-ichiro
Published: July 2002

Vacancy-ordered Sr2Ti2O5 (110) epitaxial films in situ deposited on YBa2CU3O7−δ (YBCO) (103) epitaxial films are studied for insulating layers in high-Tc superconducting heterostructures. The ordered structure is interpreted by a 2×2×2 superstructure with a long-range ordered arrangement of oxygen vacancies in the film and a 2×1 surface superstructure with an ordered arrangement of surface oxygen vacancies on it. The resistivity of the Sr2Ti2O5 film sandwiched between Au and YBCO films is measured as a function of the thickness and temperature, and discussed with respect to electron scattering induced by a deficiency of oxygen in the film and at the film boundary.
Lateral mode behavior of reactive-ion-etched stable-resonator semiconductor lasers
Authors: Biellak Stephen A. , Sun Yan , Wong S. Simon , Siegman Anthony E.
Published: July 2002

We report experimental results on monolithic stable-resonator semiconductor lasers. Curved end mirrors defining a near-concentric stable resonator were fabricated on wide-stripe GaAs/AlGaAs GRINSCH-SQW lasers using reactive-ion-etching. These lasers oscillate in close to the expected lowest-order Gaussian stable-resonator modes at threshold, evolving into a coherent superposition of higher-order modes as the pump current is increased up to two to three times threshold. At higher pump currents nonlinear defocusing effects cause the resonators to become geometrically unstable so that the lateral modes are determined by both the resonator geometry and the saturated gain and index profile.
Effects of annealing, using a plasma-excited chemical vapor deposition SiN film as a cap, on the carrier density of AlGaAs/GaAs heterostructures and Si-doped GaAs
Authors: Nakata S. , Yamamoto M. , Mizutani T.
Published: July 2002

We investigate how the mobility and carrier density of AlGaAs/GaAs two-dimensional electron gas are influenced by the fabrication process with plasma-excited chemical vapor deposition (plasma-CVD) SiN film. These properties are greatly reduced by annealing with plasma-CVD SiN film as a cap but are restored by reannealing after removing the SiN film. We further use capacitance-voltage measurements to investigate the influence of this same process on a more simplified structure, Si-doped GaAs layer. Annealing with a plasma-CVD SiN film changes the defect density of Si-doped GaAs in two, temperature dependent ways: annealing below 380 °C reduces deposition damage, and annealing above 300 °C produces new defects, which might be caused by the film stress. These new defects can be reduced by reannealing after removing the SiN film.