bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between the internal friction values of the specimen and the vibration system
Authors: Shui Jiapeng , Pei Huiyuan , Liu Yongsong
Published: July 2002

Expressions for the low frequency internal friction of a specimen and that of the vibration system of the internal friction measuring apparatus have been deduced for six linear mechanical models. It was found that in the case of forced vibration experiments, the internal friction expressions are different for different models. The relationships between the internal friction values of specimens and the vibration systems for different models have been obtained.
Measurement of the permeability of thin films
Authors: Ianno N. J. , Makovicka T. J.
Published: July 2002

A system has been developed to directly measure the flow of inert gases through an arbitrary thin film. The system employs a porous aluminum silicate ceramic as the substrate for film deposition, a flow control apparatus to hold the substrate under vacuum and allow a helium gas pressure differential to be established across the substrate, and a helium leak detector to measure the flow of helium through the substrate/film combination. This allows calculation of the permeability of the film. The permeability of plasma enhanced chemical vapor deposited diamondlike carbon films and sputter deposited silicon nitride, and nickel films were measured. A thermally grown silicon dioxide film was also tested.
A simple strain cell for the measurement of the gauge factor of a thin film
Authors: Pattabi Manjunatha , Rao K. Mohan
Published: July 2002

In this article, we present the design and fabrication of a simple strain cell using a displacement dial gauge. The strain sensitivity for this cell is of the order of 10−5 which is approximately equal to that obtained by cantilever bending. The advantage of this cell is that it can be used for the determination of the strain for the metal films deposited on any type of substrates, which do not have well defined Young’s modulus. The gauge factor for discontinuous silver film deposited on softened poly-2-vinylpyridine substrate protected by an oxide overlayer coating is determined using this strain cell and the value of the gauge factor for this film is about 45.
A low cost modulation technique for magneto-optical measurements
Authors: Isella Giovanni , Puppin Ezio
Published: July 2002

A modulation–demodulation apparatus for magneto-optical Kerr effect measurements is presented. This system is based on an intensity modulated laser and on a specially designed demodulation circuit. This approach allows us to exploit the advantages offered by modulation at a much lower cost compared to the standard design based on expensive photoelastic modulators and general purpose lock-in amplifiers.
The theory of operation of transistorized Marx bank circuits
Authors: Mallik Kanad
Published: July 2002

A theory of operation of transistorized Marx bank circuits has been formulated. It has been shown quantitatively that the current-mode second breakdown of transistors is the basic phenomenon involved. The analysis reveals that physical parameters, like the length of and the doping density in the epitaxial collector, the forward dc amplification factor, and the avalanche multiplication gain of the transistors, play important roles in the mechanism. The theory has been applied to explain a number of experimentally observed characteristics of the circuit.
Surface photovoltage measurements in liquids
Authors: Bastide S. , Gal D. , Cahen David , Kronik L.
Published: July 2002

We present a simple, compact, and robust arrangement for surface photovoltage measurements of free semiconductor surfaces immersed in liquids. It is based on the classical Kelvin probe arrangement, where the semiconductor sample is put in a liquid-containing, electrically insulating vessel, with an optically transparent window, situated between the sample and the Kelvin probe. At the price of permitting relative, rather than absolute, contact potential difference values, this modification enables easy, routine surface photovoltage measurements of semiconductors in any kind of liquid ambient. The validity and efficiency of this approach are demonstrated by surface photovoltage spectra obtained from the p-InP(100) surface in various liquid etchants.
Depth profile of the nonlinear optical susceptibility of ion-implanted KNbO3 waveguides
Authors: Fluck Daniel , Pliska Tomas , Küpfer Manfred , Günter Peter
Published: July 2002

We report on the depth profile of the nonlinear optical susceptibility in ion-implanted potassium niobate (KNbO3) waveguides using reflected second harmonic generation from wedged samples. After irradiation the waveguide layer exhibits partial loss of its optical nonlinearity that can be recovered to better than 90% of its value of the virgin crystal by subsequent annealing and repoling. We propose microscopic depolarization due to ion implantation to be responsible for the observed decrease of the nonlinear optical susceptibility.
Investigation on the origin of the blue emission in titanium doped sapphire: Is F+ color center the blue emission center?
Authors: Chen Wei , Tang Honggao , Shi Chaoshu , Deng Jie , Shi Junyan , Zhou Yinxue , Xia Shangda , Wang Yuxia , Yin Shaotang
Published: July 2002

Titanium doped sapphire (Ti:Al2O3) shows a 420 nm blue emission band whose corresponding excitation band lies at 244 nm. With the aim of ascertaining the origin of this blue emission, using synchrotron radiation we measured the vacuum ultraviolet to ultraviolet absorption spectrum of titanium doped sapphire. It is suggested that the blue emission is due to a center other than a trivalent Ti3+ ion or a tetravalent Ti4+ ion, most probably an F+-type color center formed in the crystal.
Ultrashort lifetime photocarriers in Ge thin films
Authors: Sekine N. , Hirakawa K. , Sogawa F. , Arakawa Y. , Usami N. , Shiraki Y. , Katoda T.
Published: July 2002

An ultrashort lifetime of photocarriers as short as 600 fs has been obtained in ion-implanted Ge thin films grown on sapphire substrates. The photocarrier mobility determined by photoconductivity measurements is found to be reasonably high (∼100 cm2/V s). We have observed terahertz (THz) radiation from a photoconductive dipole antenna geometry.
Microstructural dependence of penetration depth of Ag-doped YBa2Cu3O7−δ thin films probed by atomic force microscopy
Authors: Pinto R. , Kaur Davinder , Rao M. S. Ramachandra , Apte P. R. , Srinivasu V. V. , Vijayaraghavan R.
Published: July 2002

The magnetic penetration depth λ of laser ablated 5 wt % Ag-doped YBa2Cu3O7−δ thin films has been measured in the thickness range 1500–4000 Å and in the temperature range 18–88 K using microstrip resonator technique. A correlation of λ(T) with the film microstructure observed with atomic force microscopy has shown that λ(T) depends critically on the film microstructure.
Millimeter-wave measurements of phase transitions in thiourea using a gyrotron
Authors: Timms G. P. , Brand G. F.
Published: July 2002

In this letter the low temperature phase transitions in a compressed powder sample of thiourea, a ferroelectric, are studied at millimeter wavelengths by the reflection of a beam incident at an angle of 45°. The range of frequencies between 100 and 300 GHz was covered by an Impatt oscillator and a tunable gyrotron. The change in permittivity associated with the ferroelectric transition at 169 K was observed to decrease in magnitude and become less abrupt as the frequency was increased.
Exciton localization and temperature stability in self-organized InAs quantum dots
Authors: Lubyshev D. I. , González-Borrero P. P. , Marega E. , Petitprez E. , La Scala N. , Basmaji P.
Published: July 2002

We investigated the temperature effect on exciton localization in self-organized InAs quantum dots. Quenching energy for excitons in reference quantum well and quantum dots was found to be 2 and 7 meV, respectively. Thermoactivation energy of electron-hole emission through a GaAs barrier in the quantum dots was measured as 46 meV. We observed an unusual decrease of photoluminescence peak full width at half maximum with temperature, suggesting suppression of nonpredominant size quantum dot emissions due to carrier tunneling between nearby dots.
Growth and properties of scandium epitaxial films on GaN
Authors: Kaplan R. , Prokes S. M. , Binari S. C. , Kelner G.
Published: July 2002

Epitaxial scandium films have been grown on c-axis-oriented wurtzite GaN. The films are highly ordered, adherent, and reflective. For substrate temperatures in the range 640–780 °C an interfacial reaction yields a ScN layer whose thickness increases with temperature, consistent with Sc diffusion as the rate limiting step. Electrical contacts fabricated from the Sc/ScN/GaN films exhibit a 1.0 eV barrier height on n-type GaN. The Sc films, which represent a class of ductile materials, may constitute a compliant substrate for overgrowth of GaN.
Thin-film growth of the charge-density-wave oxide Rb0.30MoO3
Authors: van der Zant H. S. J. , Mantel O. C. , Dekker C. , Mooij J. E. , Træholt C.
Published: July 2002

We report on the thin-film fabrication of a charge-density wave (CDW) compound. Single-phase epitaxial films of the model CDW oxide Rb0.30MoO3 have been grown by pulsed-laser deposition. Detailed analyses show that the Rb0.30MoO3 films have μm-size grains with the CDW chains oriented parallel to the substrate. On SrTiO3 (510), the CDW chains align into a single direction within the film plane. The electrical resistance of the films demonstrates a CDW state below about 182 K. Structures patterned in films will permit unprecedented studies of phase-coherent CDW transport, as well as the exploration of devices based on CDWs.
Kinetic-energy measurement of a neutral stream extracted from Ar electron cyclotron resonance plasma
Authors: Tsuchizawa Tai , Jin Yoshito , Matsuo Seitaro
Published: July 2002

The kinetic energy of a neutral stream within Ar electron cyclotron resonance plasma was evaluated by means of time-of-flight mass spectroscopy. The median energy in the distribution of the neutral stream ranged between 10 and 20 eV for pressure from 1.4 to 2.9×10−4 Torr. This energy is almost equal to that of the ions. The energy of the neutral stream could be controlled by adjusting the gas pressure. A higher pressure broadened the energy distribution of the neutral stream.
Interactions and magnetic viscosity: Nonmonotonic time variation of the magnetization during relaxation at constant demagnetizing field
Authors: de Julián C. , Emura M. , Cebollada F. , González J. M.
Published: July 2002

We present magnetic relaxation data of PrNdFeB magnets. These data were obtained by measuring the time evolution of the magnetization under constant applied demagnetizing fields. The results corresponding to fields far from the range of the coercive force evidenced a nonmonotonic time variation of the magnetization. We propose that the occurrence of magnetic interactions underlies the observed anomalous behavior. This idea is checked through a micromagnetic simulation of the time evolution of the magnetization of a low field reversed nucleus which is exchange and magnetostically coupled to the main hard phase.
Optically inscribed surface relief diffraction gratings on azobenzene-containing polymers for coupling light into slab waveguides
Authors: Paterson J. , Natansohn A. , Rochon P. , Callender C. L. , Robitaille L.
Published: July 2002

Surface relief diffraction gratings inscribed on azobenzene-containing polymers are designed to act as light couplers into slab waveguides. The gratings are inscribed both directly in poly{4-[2-(methacryloyloxy)ethyl]azobenzene} (pMEA) waveguide material, and in an azopolymer cladding layer applied to polyimide, silicon nitride, and silicon oxynitride films. Input and output coupling of both 633 and 830 nm light is observed in the waveguides.
Calculations of giant magnetoimpedance and of ferromagnetic resonance response are rigorously equivalent
Authors: Yelon A. , Ménard D. , Britel M. , Ciureanu P.
Published: July 2002

It is simply demonstrated that the giant magnetoimpedance (GMI) response of a plate or ribbon is rigorously equivalent to the response of the same sample in ferromagnetic resonance (FMR) experiment. Thus, all of the solutions for FMR response behavior of metals may be applied to the description of GMI. For situations which have not been studied before, the methods which have been developed over the past 40 years for theoretical description of FMR in metals may be applied to predict the GMI behavior.
A donorlike deep level defect in Al0.12Ga0.88N characterized by capacitance transient spectroscopies
Authors: Götz W. , Johnson N. M. , Bremser M. D. , Davis R. F.
Published: July 2002

Si-doped, n-type heteroepitaxial layers of Al0.12Ga0.88N grown by metalorganic chemical vapor deposition on SiC substrates were characterized by capacitance transient spectroscopies. Conventional deep level transient spectroscopy (DLTS) reveals the presence of a dominant deep level with an activation energy for electron emission to the conduction band of (0.61±0.02) eV. The activation energy of this deep level displays a pronounced field dependence as determined from double-correlation DLTS (DDLTS), which is indicative of a deep donor level in n-type semiconductors. A deep level is observed by optical-DLTS (O-DLTS) with a threshold energy for electron photoemission to the conduction band of 0.77 eV, which appears to be of identical origin as the dominant deep level detected by DLTS. Two additional deep levels are detected with O-DLTS in the upper half of the band gap of our Al0.12Ga0.88N sample with threshold energies of 0.83 and 1.01 eV.
Valence band splittings and band offsets of AlN, GaN, and InN
Authors: Wei Su-Huai , Zunger Alex
Published: July 2002

First-principles electronic structure calculations on wurtzite AlN, GaN, and InN reveal crystal-field splitting parameters ΔCF of −217, 42, and 41 meV, respectively, and spin–orbit splitting parameters Δ0 of 19, 13, and 1 meV, respectively. In the zinc blende structure ΔCF≡0 and Δ0 are 19, 15, and 6 meV, respectively. The unstrained AlN/GaN, GaN/InN, and AlN/InN valence band offsets for the wurtzite (zinc blende) materials are 0.81 (0.84), 0.48 (0.26), and 1.25 (1.04) eV, respectively. The trends in these spectroscopic quantities are discussed and recent experimental findings are analyzed in light of these predictions.
Aluminum-doped n-type ZnSTe alloy grown by molecular beam epitaxy
Authors: Sou I. K. , Yang Z. , Mao J. , Ma Z. H. , Tong K. W. , Yu P. , Wong G. K. L.
Published: July 2002

Successful n-type doping of ZnSTe alloy using elemental aluminum source has been carried out by molecular beam epitaxy. Hall effect measurement (300–77 K) was performed on as-grown ZnS0.977Te0.023 epilayers with various dopant concentrations. Electron carrier concentration as high as 1.3×1019 cm−3 has been achieved. For carrier concentration higher than 5×1018 cm−3, the carrier concentration is independent of temperature, possibly indicating formation of a very shallow donor level. A group of ZnS1−xTex epilayers with different x values was doped using a constant aluminum beam flux for studying the dependence of the dopant activation on Te composition. Good activation of Al dopant was obtained for x value from 0 to a few percent, but it became poor for larger x value and finally Al became inactive for x values higher than 10%. Room temperature photoluminescence measurements on doped and undoped ZnS and ZnS1−xTex layers indicate that Al dopants form deep-level radiative centers in addition to a shallow donor level. The characteristics of these deep levels as a function of Te composition have also been studied.
Evidence for internal electric fields in two variant ordered GaInP obtained by scanning capacitance microscopy
Authors: Leong J-K. , Williams C. C. , Olson J. M. , Froyen S.
Published: July 2002

Single and two variant ordered GaInP samples are studied in cross section with the scanning capacitance microscope. Our study shows significant differences in the electronic properties of single and two variant GaInP. In unintentionally doped, ordered two variant samples, both n and p-type like domains are observed with the scanning capacitance microscope. In contrast, a spatially uniform capacitance signal is observed in unintentionally doped single variant ordered GaInP. These microscopic capacitance observations can be qualitatively explained by bend bending or internal electric fields.
Erbium luminescence from hydrogenated amorphous silicon-erbium prepared by cosputtering
Authors: Zanatta A. R. , Nunes L. A. O. , Tessler Leandro R.
Published: July 2002

Hydrogenated amorphous silicon with small amounts of erbium (Er/Si concentration ∼5 at. %) was prepared by radio frequency sputtering from a Si target partially covered by tiny metallic Er chunks. Four sets of samples were studied: nonintentionally contaminated hydrogenated and nonhydrogenated amorphous silicon-erbium (a-SiEr:H and a-SiEr); nitrogen doped a-SiEr(N):H and oxygen contaminated a-SiEr(O):H. Samples from the first two sets present only faint 1.54 μm photoluminescence characteristic from Er3+ ions even at 77 K. Samples from the other sets show this luminescence at 77 K as deposited, without any further annealing step. Thermal annealing up to 500 °C increases the photoluminescence intensity, and room temperature emissions become strong enough to be easily detected. These results indicate that in an amorphous silicon environment the chemical neighborhood of the Er3+ ions is crucial for efficient 1.54 μm emission. Raman scattering from both as-deposited and annealed samples showed that network disorder relaxation by annealing is not determinant for efficient Er3+ luminescence.
Vacuum ultraviolet absorption spectroscopy for absolute density measurements of fluorine atoms in fluorocarbon plasmas
Authors: Sasaki K. , Kawai Y. , Kadota K.
Published: July 2002

Absolute densities of fluorine (F) atoms at the ground state (2p5 2P°) were measured in helicon-wave excited high-density CF4 plasmas by vacuum ultraviolet (VUV) absorption spectroscopy. By employing an electron cyclotron resonance CF4 plasma as a light source in the VUV wavelength range, an absorption spectroscopy system with no vacuum windows was constructed. As a result, the density of F atoms was approximately 1×1013 cm−3 for an rf power of 1 kW and a CF4 gas pressure of 2.5 mTorr, which was one-order higher than the density of CFx radicals and was one-order lower than the density of the parent gas.
Exciplex emission in bilayer polymer light-emitting devices
Authors: Gebler D. D. , Wang Y. Z. , Blatchford J. W. , Jessen S. W. , Fu D.-K. , Swager T. M. , MacDiarmid A. G. , Epstein A. J.
Published: July 2002

Photoluminescent and electroluminescent studies of bilayer heterojunctions formed from a poly(pyridyl vinylene phenylene vinylene) (PPyVPV) derivative and poly(vinyl carbazole) (PVK) show an emission peak which cannot be ascribed to either the PPyVPV derivative or PVK layer. Through studies of absorption and photoluminescence excitation (PLE) spectra we demonstrate that the additional feature results from an exciplex at the bilayer interface. The photoluminescence efficiency of the exciplex is greater than 20%. The electroluminescence spectrum from the bilayer devices is entirely due to exciplex emission, with internal efficiencies initially achieved exceeding 0.1%.
Gettering of Fe impurities by bulk stacking faults in Czochralski-grown silicon
Authors: Shen B. , Zhang X. Y. , Yang K. , Chen P. , Zhang R. , Shi Y. , Zheng Y. D. , Sekiguchi T. , Sumino K.
Published: July 2002

Gettering of Fe impurities by bulk stacking faults in Czochralski-grown silicon are investigated by means of the electron-beam-induced-current technique and transmission electron microscopy. It is found that Fe impurities only precipitate on Frank partial dislocations bounding stacking faults when the specimen is cooled slowly; however, both Frank partials and fault planes are decorated by Fe impurities when the specimen is cooled rapidly. It is explained that small oxygen precipitates on fault planes serve as the gettering centers for Fe impurities in the fast cooled specimen.
Doping silver into YBa2Cu3O7−δ films by 800 keV Ag+ implantation at room temperature and elevated temperatures
Authors: Li Yupu , Liu J. R. , Cui Xingtian , Qu J. Z. , Chen Q. Y. , Chu Wei-Kan
Published: July 2002

Thin films (∼0.43 and ∼0.95 μm thick) of YBa2Cu3O7−δ on (100) LaAlO3 substrates have been implanted with 800 keV Ag+ to a dose of 5×1014/cm2, at room temperature (i.e., the total range ≈0.4 μm and the damage level ≈3.1 displacements per atom) and at elevated temperatures (450, 650, and 780 °C), followed by an in situ annealing schedule in flowing oxygen ambient. We have found that the implantation at room temperature amorphizes the implanted layer. In such a case, the implanted layer cannot regrow to the superconducting phase if there is no crystal seed remaining in the bottom of the film, whereas implantation at elevated temperatures plus an in situ annealing schedule, including a step at 870 °C in flowing oxygen ambient, can maintain the crystal structure and superconductivity of the films. For the thicker film, we have found that after the implantation at 450 or 650 °C and the in situ annealing, the total volume of the film has recovered to the superconducting 123 phase with a Tc=89 K.
Three-dimensional metallodielectric photonic crystals exhibiting resonant infrared stop bands
Authors: McIntosh K. A. , Mahoney L. J. , Molvar K. M. , McMahon O. B. , Verghese S. , Rothschild M. , Brown E. R.
Published: July 2002

Using standard microelectronic techniques, we have fabricated arrays of infrared metallodielectric photonic crystals (IR MDPCs) on silicon substrates. The metallic “atoms” are located on a three-dimensional (100)-oriented face-centered-cubic lattice. Resonant stop-band characteristics have been measured with rejection levels of up to 20 dB and widths of up to 83% of the center frequency. We demonstrate structures with stop bands across the midinfrared wavelength range from 2 to 12 μm. Angular studies of the photonic stop bands show an insensitivity to incident angle for some of the structures. The IR MDPC results are compared with measurements made on microwave-scale MDPC structures to help in understanding the infrared results.
Viscous drag effect on imaging of linearized plasmid deoxyribonucleic acid in liquid medium with the atomic force microscope
Authors: Teschke O. , Douglas R. A. , Prolla T. A.
Published: July 2002

In many attempts to image biomolecules like deoxyribonucleic acid with the atomic force microscope, the apparent width of the molecules exceeds the expected width as obtained by x-ray diffraction. This increase in size was explained by a geometrical tip convolution, but the increased width seems to persist despite improvements to the tip. Experimental evidence is shown that part of this increase is due to the liquid drag force when molecules are imaged under liquid. The liquid drag force is calculated using standard fluid dynamics where the tip motion in the liquid is modeled by the relative motion of a cylinder through a constant velocity fluid. The Reynold’s number for the experimental configuration is smaller than 1, characterizing a laminar flow and the calculated drag force is 80 pN, which is in agreement with the experimentally measured force for ethanol and relative tip velocity of 100 μm/s. Both the viscous drag force and the apparent width increase may be modeled by a vk dependence, where v is the sample velocity relative to the tip, and k is a constant independent of the liquid and the tip–sample geometry and is equal to 0.53. An apparent molecular width increase of ∼30 nm for a ∼2 nm diam molecule for a 150 μm/s scanning velocity was observed.
Anisotropy and growth-sequence dependence of atomic-scale interface structure in InAs/Ga1−xInxSb superlattices
Authors: Lew A. Y. , Zuo S. L. , Yu E. T. , Miles R. H.
Published: July 2002

We have used cross-sectional scanning tunneling microscopy to study the atomic-scale interface structure of InAs/Ga1−xInxSb superlattices grown by molecular beam epitaxy. Detailed, quantitative analysis of interface profiles obtained from constant-current images of both (110) and (11̄0) cross-sectional planes of the superlattice indicate that interfaces in the (11̄0) plane exhibit a higher degree of interface roughness than those in the (110) plane, and that the Ga1−xInxSb-on-InAs interfaces are rougher than the InAs-on-Ga1−xInxSb interfaces. The roughness data are consistent with anisotropy in interface structure arising from anisotropic island formation during growth, and in addition a growth-sequence-dependent interface asymmetry resulting from differences in interfacial bond structure between the superlattice layers.
GaN hexagonal microprisms with smooth vertical facets fabricated by selective metalorganic vapor phase epitaxy
Authors: Akasaka T. , Kobayashi Y. , Ando S. , Kobayashi N.
Published: July 2002

Selective growth of GaN was performed by low-pressure metalorganic vapor phase epitaxy using a mask-patterned GaN epitaxial layer on a (0001) sapphire substrate. GaN hexagonal microprisms of 5–16 μm in diameter, with smooth vertical facets and no ridge growth, were fabricated on a (0001) sapphire substrate. This vertical {11̄00} facet of GaN was parallel to a {112̄0} face of the sapphire substrate. Both the use of an epitaxial GaN layer on the sapphire substrate and low working pressure contributed to obtaining smooth top and vertical facet surfaces. Also, the stripe structures of GaN were obtained that had a rectangular cross section. Moreover, the selection of the mask-patterning direction was found to be important because of the 30° rotation of the crystallographic orientation between the GaN layer and the sapphire substrate.
Effects of high hydrogen dilution at low temperature on the film properties of hydrogenated amorphous silicon germanium
Authors: Shima Masaki , Terakawa Akira , Isomura Masao , Tanaka Makoto , Kiyama Seiichi , Tsuda Shinya
Published: July 2002

The effects of hydrogen dilution of up to 54:1 (=H2:SiH4) on hydrogenated amorphous silicon germanium (a-SiGe:H) was investigated at a low substrate temperature, while keeping the optical gap (Eopt) constant. It was found that deterioration of the film properties, when substrate temperature decreases, can be compensated by the high hydrogen dilution method. As the substrate temperature decreases from 230 to 180 °C, the high photoconductivity, high photosensitivity, and low silicon dihydride content of a-SiGe:H can be maintained with a high hydrogen dilution ratio of 54:1, although these properties becomes worse with conventional low hydrogen dilution ratios. Probably, hydrogen radicals substitute for the surface reaction energy lost by decreasing the temperature. Besides, a-SiGe:H films deposited under higher hydrogen dilution have more germanium and less hydrogen content than those of the conventional films, despite having the same Eopt. One possible explanation for why Eopt can be kept constant is the suppression of the formation of Ge–Ge bonds at the growing surface by the energy supplied by the hydrogen radicals.
An electrically controlled Bragg reflector integrated in a rib silicon on insulator waveguide
Authors: Cutolo A. , Iodice M. , Irace A. , Spirito P. , Zeni L.
Published: July 2002

In this letter, we present a novel structure for light amplitude modulation based on a lateral p-i-n diode combined with a Bragg reflector which transforms the phase shift induced by the plasma dispersion effect in the intrinsic region of the diode into a voltage controlled variation of the reflectivity of the Bragg mirror. Numerical simulations show a modulation depth of 50% achieved in about 12 ns with a power dissipation of 4.0 mW and an insertion loss of 1.0 dB. The device is demonstrated to be very attractive in terms of power dissipation as compared to a Mach–Zehnder interferometer occupying the same area on chip.
Strain determination in heteroepitaxial GaN
Authors: Skromme B. J. , Zhao H. , Wang D. , Kong H. S. , Leonard M. T. , Bulman G. E. , Molnar R. J.
Published: July 2002

Residual strains have been evaluated in a variety of GaN layers grown on sapphire or 6H-SiC from wafer curvature at 293 K, which avoids needing to know the unstrained lattice parameters or energy gap of GaN in advance. Estimated strains at 1.7 K are correlated with the energy of the A free exciton to determine its strain dependence. We find that strain-free GaN has an A exciton energy of 3.468±0.002 eV at 1.7 K, and 293 K lattice parameters a=3.1912 Å and c=5.1836 Å. These values imply that GaN on SiC is frequently under net biaxial compressive stress due to residual lattice mismatch stress, and that several hundred μm thick GaN layers on sapphire and homoepitaxial layers grown on bulk platelets grown at high pressure are both under about 1×10−3 in-plane compressive strain. These conclusions conflict with most previous assumptions.
Diffusion of zinc acceptors in InAsP by the metal-organic vapor-phase diffusion technique
Authors: Wada Morio , Izumi Kyoko , Sakakibara Katsutoshi
Published: July 2002

Diffusion of zinc acceptors in InAsP by a metal-organic vapor-phase diffusion technique, whereby a low-pressure metal-organic vapor-phase epitaxy with dimethylzinc and phosphine is utilized as an open tube diffusion system, is demonstrated to accurately control the diffusion depth in the submicrometer range. The annealing effect on the zinc diffusion profiles in InAsP was found to be the activation of zinc acceptors similar to that in InP, but the maximum hole concentration of 1×1019 cm−3 for the zinc diffusion in InAsP was achieved.
Nonlinear optical waveguide fabrication by direct electron-beam irradiation and thermal development using a high Tg polymer
Authors: Nakayama Hideki , Sugihara Okihiro , Okamoto Naomichi
Published: July 2002

A nonlinear optical waveguide fabrication process for use with dye doped polymer is described. The ridge-type channel waveguide containing the chromophores was fabricated by direct electron-beam irradiation. The electron beam with an energy of 25 kV and dose of 1000 μC/cm2 was exposed directly onto the dye doped polymer film, and then thermal development and corona-poling were performed simultaneously. We could also demonstrate the periodically poled nonlinear optical polymer waveguide on the basis of this new process.
High power switching behavior in electrically conductive polymer composite materials
Authors: Duggal Anil R. , Levinson Lionel M.
Published: July 2002

The electrical switching properties of electrically conductive polymer composites are studied at high current densities. It is shown that the switching properties at high current densities are substantially different from those at low current densities which depend on a positive temperature coefficient of resistance effect. This type of switching appears to be a general feature of conductor-filled polymer composite materials and should lead to a new class of fast, current-limiting devices for power circuits.
Molecular dynamics studies of interacting hydrogenated Si(001) surfaces
Authors: Conrad D. , Scheerschmidt K. , Gösele U.
Published: July 2002

The interaction of hdyrogenated Si(001) surfaces is studied by means of molecular dynamics using an empirical potential. Above a certain critical external force covalent bonds may be formed between the surfaces even at room temperature, leaving a hydrogenated interface. The critical force is related to the assumptions of the molecular dynamics, thus scaling with the potential, heat transfer, boundary conditions, and the weak long-range interaction omitted. Below this critical force, the hydrogen–hydrogen interactions prevent covalent bonding.
Effect of total deposition pressure on the structure of polycrystalline-silicon films
Authors: Kamins T. I. , Fischer-Colbrie A.
Published: July 2002

The effect of total deposition pressure on the structure of chemically vapor deposited polycrystalline-silicon films was examined over the pressure range from 10–600 Torr using thermal decomposition of SiH4 in a hydrogen carrier gas in the 625–675 °C temperature range in a cold-wall, lamp-heated reactor. The temperature and deposition rate were kept constant for each set of experiments to isolate the effect of hydrogen on the surface diffusion of the silicon species. Both the amorphous-to-polycrystalline transition and the dominant crystal orientation depend on the total deposition pressure; however, the dependence is only moderate. Differences in gas purity and system integrity between different reactors also play a strong role in controlling the structure.
An iodine-doped polymer light-emitting diode
Authors: Huang F. , MacDiarmid A. G. , Hsieh B. R.
Published: July 2002

The performance of polymer light-emitting diodes (LEDs) having the configuration Al/MEH–PPV/ITO, where MEH–PPV=poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) has been improved by light iodine doping of the emissive MEH–PPV polymer layer whereby the turn-on voltage is reduced and the external quantum efficiency is increased by an order of magnitude. It differs from nondoped MEH–PPV LEDs in that light emission is observed in both forward and reverse bias modes. It is believed that the mobility of the I3− anions in the (MEH–PPV)x+y(I3)xy− species formed on doping the MEH–PPV compensate for injected charges at the electrodes, thus reducing the electron and hole injection barriers.
Direct excitation spectroscopy of Er centers in porous silicon
Authors: Stepikhova M. , Jantsch W. , Kocher G. , Palmetshofer L. , Schoisswohl M. , von Bardeleben H. J.
Published: July 2002

We report direct excitation of optically active Er centers in porous Si. Excitation spectroscopy performed close to the intracenter I415/2→I411/2 and I415/2→I49/2 transitions of Er3+ (4f11) ions allows us to identify two kinds of Er centers in porous Si: (i) Er diffused into porous nanograins with lower than cubic symmetry and (ii) Er centers incorporated in an amorphous silicalike matrix. The latter show much weaker thermal quenching of the Er3+ emission which decreases only by a factor of eight when the temperature is increased from 4.2 K up to 360 K.
Burning of high Tc bridges
Authors: Gaevski M. E. , Johansen T. H. , Galperin Yu. , Bratsberg H. , Bobyl A. V. , Shantsev D. V. , Karmanenko S. F.
Published: July 2002

Burning of superconducting thin film bridges by large transport currents (up to densities of 2×107 A/cm2) is investigated by magneto-optical imaging of flux distribution and low-temperature scanning electron microscopy providing Tc maps. It is shown that the destruction is preceded by significant penetration of magnetic field inside a weak-pinning region. In bridges containing extended defects magneto-optic investigation is sufficient to locate the incipient burning region. In high-quality bridges free from such defects only a combination of the two techniques will allow prediction of the place of fatal destruction.
D–Si(111)(1×1) surface for the study of silicon etching in aqueous solutions
Authors: Luo Huihong , Chidsey Christopher E. D.
Published: July 2002

Deuterium-terminated Si(111) surfaces are formed in a solution of KF and DCl in D2O. Infrared spectroscopy shows the surface to be flat with a D–Si bond normal to the surface. H–Si is formed preferentially to D–Si in a mixture of protonated and deuterated etchants. From the D-to-H exchange rate and the terrace width, we estimate the rate of the stepflow etching process to be 4.2 nm/s in Ar-sparged 40% NH4F solution. Dissolved O2 in the solutions substantially increases the D-to-H exchange rate by the formation of pits and the consequent increase in the step density.
Real time control of InxGa1−xN molecular beam epitaxy growth
Authors: Grandjean N. , Massies J.
Published: July 2002

The growth of GaN and InxGa1−xN on c-plane sapphire substrates was carried out by molecular beam epitaxy using NH3. In situ reflection high-energy electron diffraction (RHEED) was used to monitor the growth process. Oscillations of the specular beam intensity were observed during both GaN and InxGa1−xN deposition. This allows determining in real time the composition of InxGa1−xN alloys. The effects of the growth temperature and the Ga flux on the In incorporation rate were investigated. The critical thickness for InGaN islanding as a function of In mole fraction is also easily deduced from RHEED experiments.
Modulation doping of InAs/AlSb quantum wells using remote InAs donor layers
Authors: Bennett Brian R. , Yang M. J. , Shanabrook B. V. , Boos J. B. , Park D.
Published: July 2002

Sheet carrier concentrations in quantum wells of InAs clad by AlSb were enhanced by modulation doping with very thin (9–12 Å) remote InAs(Si) donor layers. The growth temperature of the donor layers was a key parameter, with relatively low temperatures required to minimize Si segregation into the AlSb. Sheet carrier concentrations as high as 3.2×1012/cm2 and 5.6×1012/cm2 were achieved by single- and double-sided modulation doping, respectively. High electron mobility transistors fabricated using the modulation doped structure exhibited a unity current gain cut-off frequency of 60 GHz for a 0.5 μm gate length at a source-drain voltage of 0.5 V.
Relaxed InxGa1−xAs graded buffers grown with organometallic vapor phase epitaxy on GaAs
Authors: Bulsara Mayank T. , Leitz Chris , Fitzgerald Eugene A.
Published: July 2002

In x Ga 1−x As structures with compositionally graded buffers were grown with organometallic vapor phase epitaxy on GaAs substrates and characterized with plan-view and cross-sectional transmission electron microscopy, atomic force microscopy, and x-ray diffraction. The results show that surface roughness experiences a maximum at growth temperatures where phase separation occurs in InxGa1−xAs. The strain fields from misfit dislocations induce this phase separation in the 〈110〉 directions. At growth temperatures above and below this temperature, the surface roughness is decreased significantly; however, only growth temperatures above this regime ensure nearly complete relaxed graded buffers with the most uniform composition caps. With the optimum growth temperature for grading InxGa1−xAs determined to be 700 °C, it was possible to produce In0.33Ga0.67As diode structures on GaAs with threading dislocation densities <8.5×106/cm2.
Intermittent-contact scanning capacitance microscope for lithographic overlay measurement
Authors: Kopanski J. J. , Mayo S.
Published: July 2002

A scanning-capacitance-microscope (SCM) mode was implemented by using an atomic force microscope (AFM) operated in intermittent contact and by measuring the tip-to-sample capacitance change at the tip vibration frequency. The intermittent-contact-mode SCM was able to image and determine the overlay separation of metal lines buried under a 1-μm-thick, planarized dielectric layer. Modeling of the intermittent-contact SCM signal across buried metal lines was consistent with the experimental results. This hybrid intermittent-contact AFM and SCM has the potential to measure the lithographic overlay between metal lines located at consecutive levels beneath dielectric layers in an integrated circuit.
Measurement of the magnetic induction vector in superconductors using a double-layer Hall sensor array
Authors: Abulafia Y. , McElfresh M. , Shaulov A. , Yeshurun Y. , Paltiel Y. , Majer D. , Shtrikman H. , Zeldov E.
Published: July 2002

We describe an experimental technique for simultaneous measurement of both the normal (Bz) and the in-plane (Bx) components of the magnetic induction field near the surface of a superconducting sample. This technique utilizes a novel design of a double-layered Hall sensor array fabricated from a GaAs/AlGaAs heterostructure containing two parallel layers of a two-dimensional electron gas. The effectiveness of this technique is demonstrated in measurements of Bx and Bz and the current distribution at the surface of a thin YBa2Cu3O7 crystal.
Role of surface and of dopant-impurity interactions on the electrical activation of B implants in crystalline Si
Authors: Priolo Francesco , Mannino Giovanni , Miccichè Monica , Privitera Vittorio , Napolitani Enrico , Carnera Alberto
Published: July 2002

The electrical activation of B in Si after ion implantation in the energy range between 5 and 160 keV and rapid thermal annealing processes is investigated. It is found that it critically depends on the purity of the substrate as well as the distance from the surface. In particular, while in very pure epitaxial Si layers (where O and C contents are below ∼1×1015/cm3) typically the total B content is electrically active, in Czochralski Si (containing ∼1×1018 O/cm3 and ∼1×1017 C/cm3) the active fraction is very small at doses of 1×1012/cm2 and increases with increasing dose. For very shallow B implants (∼5 keV), the electrical activation in Czochralski Si further decreases to a few percent of the total amount. These results are interpreted in terms of the formation of boron-impurity complexes deactivating the dopant, the dose effect being a result of trap saturation. Vacancies can eventually dissolve some of the inactive complexes. However, close to the surface an enhanced vacancy annihilation process reduces the dissolution probability producing the observed dramatic effects on the electrically active profiles. Finally, at very low energies (∼5 keV), also in epitaxial Si layers, part of the dopant can be electrically inactive due to B–B interactions, the process being negligible at low doses and increasing with dose. The implications of these results on the formation of ultrashallow junctions are discussed.
The use of a biomolecular target for crystalline carbon nitride film deposition by Ar ion-beam sputtering without any other source of nitrogen
Authors: Chen L. C. , Lu T. R. , Kuo C. T. , Bhusari D. M. , Wu J. J. , Chen K. H. , Chen T. M.
Published: July 2002

Carbon nitride films have been synthesized by argon ion-beam sputtering from a biomolecular compound target, 8-aza-6-aminopurine (C4N6H4). The compound has a six-membered ring structure similar to that existing in the hypothetical β-C3N4. Except for the target material, no other source of nitrogen was used during sputtering deposition. It was found that crystalline carbon nitride with high N/C atomic composition ratios of 0.43–0.56 can be formed even at room temperature. The infrared spectra of the film exhibit two peaks at 1383 and 1643 cm−1, corresponding to C–N and C=N stretching modes, respectively. No detectable peak at 2200 cm−1 (C≡N stretching mode) is observed. Both x-ray diffraction and transmission electron microscopy show a very strong broad peak at 3.2 Å, comparable to the d spacing of the (110) orientation in the β-C3N4 structure. However, it is suggested that the film contains a nanocrystalline phase with a crystal structure yet to be determined.
Ion implantation enhanced intermixing of Al-free 980 nm laser structures
Authors: Piva P. G. , Charbonneau S. , Goldberg R. D. , Mitchell I. V. , Hillier G. , Miner C.
Published: July 2002

An investigation of the intermixing enhancement in an InGaAs/InGaAsP/InGaP partial laser structure following phosphorous implantation at 30, 80, and 7000 keV was carried out. We find that for the 30 and 80 keV implant energies, band gap shifts in excess of 80 meV could be imparted to a single embedded 8.5 nm InGaAs quantum well (QW) lying several thousand angstroms beyond the maximum ion range. As both the 30 and 80 keV implants kept the end of range damage spatially separate from optical mode region, the optical quality (inferred from photoluminescence intensity measurements) of the QW material was preserved to a greater extent than that resulting from the 7000 keV implants (where implant damage was directly created in the QW during ion bombardment). This result suggests that device structures containing InGaP cladding layers are well suited for monolithic integration as the masking of low energy ions with high lateral resolution can be achieved using routinely available masking techniques.
Photoinduced superconducting nanowires in GdBa2Cu3O6.5 films
Authors: Decca R. S. , Drew H. D. , Maiorov B. , Guimpel J. , Osquiguil E.
Published: July 2002

We report the fabrication of high-Tc superconducting wires by photodoping a GdBa2Cu3O6.5 thin film. An optical near-field probe was used to locally excite carriers in the system at room temperature. Trapping of the photogenerated electrons define a confining potential for the conducting holes in the CuO planes. Spatially resolved reflectance measurements show the photogenerated nanowires to be ∼250 nm wide. Electron diffusion, before electron capture, is believed to be responsible for the observed width of the wires.
Charge transport, optical transparency, microstructure, and processing relationships in transparent conductive indium–zinc oxide films grown by low-pressure metal-organic chemical vapor deposition
Authors: Wang Anchuan , Dai Jiyan , Cheng Jizhi , Chudzik Michael P. , Marks Tobin J. , Chang Robert P. H. , Kannewurf Carl R.
Published: July 2002

Indium–zinc oxide films (ZnxInyOx+1.5y), with x/y=0.08–12.0, are grown by low-pressure metal-organic chemical vapor deposition using the volatile metal–organic precursors In(TMHD)3 and Zn(TMHD)2 (TMHD=2,2,6,6–tetramethyl–3,5–heptanedionato). Films are smooth (rms roughness=40–50 Å) with complex microstructures which vary with composition. The highest conductivity is found at x/y=0.33, with σ=1000 S/cm (n-type; carrier density=3.7×1020 cm3; mobility=18.6 cm2/V s; dσ/dT<0). The optical transmission window of such films is broader than Sn-doped In2O3, and the absolute transparency rivals or exceeds that of the most transparent conductive oxides. X-ray diffraction, high resolution transmission electron microscopy, microdiffraction, and high resolution energy dispersive X-ray analysis show that such films are composed of a layered ZnkIn2O3+k phase precipitated in a cubic In2O3:Zn matrix.
Transverse surface acoustic wave detection by scanning acoustic force microscopy
Authors: Behme G. , Hesjedal T. , Chilla E. , Fröhlich H.-J.
Published: July 2002

We present a scanning acoustic force microscope (SAFM) for the study of surface acoustic wave (SAW) phenomena on the submicron lateral scale. Until now, SAWs with in-plane oscillation components could only be studied effectively via nonvanishing out-of-plane oscillation contributions. By operating the microscope in lateral force mode, where both bending and torsion of the cantilever are detected, additional amplitude-dependent signals are found, which are due to the interaction with purely in-plane polarized surface oscillations. To demonstrate the capabilities of this type of SAFM, Love waves were studied on the surface of layers deposited on ST-cut quartz with SAW propagation perpendicular to the crystal X-axis. The phase velocity of the wave as well as the amplitude of a standing wave field was measured and compared to calculated values.
High-power (>10 W) continuous-wave operation from 100-μm-aperture 0.97-μm-emitting Al-free diode lasers
Authors: Al-Muhanna A. , Mawst L. J. , Botez D. , Garbuzov D. Z. , Martinelli R. U. , Connolly J. C.
Published: July 2002

By incorporating a broad transverse waveguide (1.3 μm) in 0.97-μm-emitting InGaAs(P)/InGaP/GaAs separate-confinement-heterostructure quantum-well diode-laser structures we obtain record-high continuous-wave (cw) output powers for any type of InGaAs-active diode lasers: 10.6–11.0 W from 100-μm-wide-aperture devices at 10 °C heatsink temperature, mounted on either diamond or Cu heatsinks. Built-in discrimination against the second-order transverse mode allows pure fundamental-transverse-mode operation (θ⊥=36°) to at least 20-W-peak pulsed power, at 68×threshold. The internal optical power density at catastrophic optical mirror damage (COMD) P̄COMD is found to be 18–18.5 MW/cm2 for these conventionally facet-passivated diodes. The lasers are 2-mm-long with 5%/95% reflectivity for front/back facet coating. A low internal loss coefficient (αi=1 cm−1) allows for high external differential quantum efficiency ηd (85%). The characteristic temperatures for the threshold current T0 and the differential quantum efficiency T1 are 210 and 1800 K, respectively. Low differential series resistance Rs: 26 mΩ; leads to electrical-to-optical power conversion efficiency values in excess of 40% from 1 W up to 10.6 W cw output power, and as much as 50% higher than those of 0.97-μm-emitting Al-containing devices.