bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of depth profile of defects in ultrathin Si film on buried SiO2 formed by implanted oxygen
Authors: Ogura Atsushi , Tatsumi Toru , Hamajima Tomohiro , Kikuchi Hiroaki
Published: July 2002

A simple technique is presented for evaluating defect profiles in ultrathin Si films on buried SiO2 formed by implanted oxygen. A combination of thinning by sacrificial oxidation and epitaxial film growth by UHV-CVD is used. By measuring the defect density of the epitaxial film with respect to the thickness prior to epitaxial growth, the profile of the initial defect density can easily be evaluated. This technique is applied to evaluate the Si on insulator structure fabricated by state-of-the-art technique, in which low dose oxygen implantation (∼4×1017 cm−2) and high temperature internal oxidation processes are used. The defect density at the surface of the film is 250 cm−2. However, as the buried interface is approached, the defect density increases. The defect density at 20 nm from the buried interface is as high as 6×105 cm−2. A defect generation mechanism is also discussed.
Dependence of threshold current density on the energy-band offsets in Zn1−uCduSe/ZnSzSe1−z/Zn1−xMgxSySe1−y separate-confinement heterostructures lasers
Authors: Shahzad Khalid , Buijs Maarten
Published: July 2002

We use a theoretical model of semiconductor lasers to calculate threshold current density (Jth), optical gain (g), and spontaneous emission rate (rsp) as a function of the two heterojunction band offsets between Zn1−uCduSe(well)/ZnSzSe1−z(guiding) layers and ZnSzSe1−z (guiding)/ Zn1−xMgxSySe1−y(cladding) layers. We find that for the conduction-band offset between the well and the guiding layers ranging from ∼0.55ΔEg to ∼0.75ΔEg (ΔEg being the energy band-gap difference), there is very little change in Jth, g, rsp. Furthermore, these three quantities are very weakly dependent on the conduction-band offset between the guiding and the cladding layers ranging from 0.2ΔEg to 0.5ΔEg. However, if the offset between the well and the guiding layers is increased from ∼0.75ΔEgto ∼0.8ΔEg, the calculations indicate a sharp drop in Jth, g, and rsp. We explain this behavior as due to the unbinding of the ground-state light-hole subband as the valence band offset is reduced.
Electrical properties of La0.7−xPrxSr0.3MnO3 perovskite
Authors: Guo Zaibing , Zhang Jianrong , Zhang Ning , Ding Weiping , Huang He , Du Youwei
Published: July 2002

We present the electrical properties of polycrystalline La0.7−xPrxSr0.3MnO3 in which the average ionic radius of the A site 〈rA〉 is systematically varied while keeping the carrier concentration fixed. Below the Curie temperature Tc, the spin-disorder scattering process has been regarded to play an important role in the resistivity. With decreasing 〈rA〉, the structure transition from rhombohedral to orthorhombic phase accompanied with the sharp increase in resistivity at Tc and the increase of the activation energies has been observed.
Excitonic luminescence up to room temperature in a ZnSe/MgS superlattice
Authors: Nashiki Hiroyuki , Suemune Ikuo , Kumano Hidekazu , Suzuki Hideki , Obinata Toshio , Uesugi Katsuhiro , Nakahara Jun’ichiro
Published: July 2002

Optical properties of a ZnSe/MgS superlattice (SL) were studied by reflection and photoluminescence (PL) spectroscopies. Excitonic structures were clearly observed in the reflection spectra up to room temperature, and the exciton absorption peak energy and linewidth were well coincident with the PL peak energy and linewidth. The origin of the lowest luminescence peak was indicated to be C1-HH1 exciton up to room temperature. The lineshape broadening due to longitudinal-optical-phonon scattering of excitons is much decreased in this SL compared to bulk ZnSe.
Contactless electroreflectance study of a vertically coupled quantum dot-based InAs/GaAs laser structure
Authors: Aigouy Lionel , Holden Todd , Pollak Fred H. , Ledentsov N. N. , Ustinov W. M. , Kop’ev P. S. , Bimberg D.
Published: July 2002

Contactless electroreflectance, at both 300 and 20 K, has been used to investigate a vertically coupled quantum dot (QD)-based InAs/GaAs laser structure. Signals have been observed from all the relevant portions of the sample including the QDs and wetting layer. The energies of the QD transitions provide evidence for both lateral as well as vertical coupling.
Optical studies of GaAs quantum wells strained to GaP
Authors: Prieto J. A. , Armelles G. , Pistol M.-E. , Castrillo P. , Silveira J. P. , Briones F.
Published: July 2002

Quantum wells of GaAs lattice matched to GaP have been studied by photoluminescence and electroreflectance. The quantum well thickness was varied between 1 and 6 monolayers in steps of 1 monolayer. Electron-hole transitions have been observed involving states both in the X band and in the Γ band, which have been modeled using a k.p. model in conjunction with the envelope function approximation. Overall agreement between theory and experiment is found using an unstrained valence band offset of 0.6 eV.
Depth-resolved micro-Raman study of porous silicon at different oxidation states
Authors: Moreno J. D. , Agulló-Rueda F. , Montoya E. , Marcos M. L. , González-Velasco J. , Guerrero-Lemus R. , Martı́nez-Duart J. M.
Published: July 2002

Photoluminescence (PL) and Raman spectra were measured along a cross section of porous silicon films at different oxidation times after application of anodic current transients. The average crystallite size was determined from the Raman spectra with the standard phonon confinement model. Before oxidation, the PL emission energy and crystallite size were found to be independent of the layer depth. Also, the integrated PL emission was larger for the middle layers. The effect of oxidation was a blueshift of the PL band and a decrease in the integrated emission for the outer layers. The crystallite size increases for all layers, particularly the outer ones.
Activation field of ferroelectric (Pb,La)(Zr,Ti)O3 thin film capacitors
Authors: Song T. K. , Aggarwal S. , Prakash A. S. , Yang B. , Ramesh R.
Published: July 2002

We report results on the activation field and frequency dependence of the coercive voltage in epitaxial ferroelectric thin film capacitors. Frequency dependent hysteresis loops and pulse width dependent polarization of epitaxial La0.5Sr0.5CoO3/(Pb,La)(Zr,Ti)O3/La0.5Sr0.5CoO3 capacitor structures were measured as a function of La content. The coercive voltages and their frequency dependence vary systematically with increasing La content. We show that the activation field for polarization reversal is directly related to the c/a ratio (tetragonality ratio) of the ferroelectric layer. A larger c/a ratio leads to a larger field to activate the motion of domain walls through the lattice. An important consequence of a larger activation field is a stronger pulse width dependence of the pulse switched polarization.
Off-axis reflection zone plate for quantitative soft x-ray source characterization
Authors: Wilhein T. , Hambach D. , Niemann B. , Berglund M. , Rymell L. , Hertz H. M.
Published: July 2002

A compact system for high-resolution spectroscopy and quantitative photon flux and brilliance measurements of pulsed soft x-ray sources is described. The calibrated system combines a novel elliptical off-axis reflection zone plate with charge-coupled device detection for simultaneous spectral and spatial measurements. Experiments on a water-window droplet-target laser-plasma source demonstrate λ/Δλ⩾1000 spectral resolution and absolute flux and brilliance measurements. © 1997 American Institute of Physics.
Hydrogen complexes in epitaxial BaTiO3 thin films
Authors: Yi Gyu-Chul , Block Bruce A. , Wessels Bruce W.
Published: July 2002

Hydrogen complexes in epitaxial BaTiO3 thin films are investigated using Fourier transform infrared spectroscopy. Both undoped and Er-doped layers were grown using low-pressure metal–organic chemical vapor deposition. From the infrared spectra of the undoped and Er-doped films grown at 750–800 °C, infrared absorption was observed at 3486 cm−1. The absorption peak is attributed to a vibrational mode of O–H in BaTiO3. Moreover, the Er-doped layers showed additional absorption peaks at 2905 and 2964 cm−1. The peaks are ascribed to the vibrational modes of C–H complexes in the Er-doped layers.
Demonstration of a micro far-infrared Smith–Purcell emitter
Authors: Goldstein M. , Walsh J. E. , Kimmitt M. F. , Urata J. , Platt C. L.
Published: July 2002

A diffraction grating mounted in the focal region of a modified scanning electron microscope has been used to produce far-infrared Smith–Purcell radiation. The electron beam radius, voltage, and current ranges were 3–27 μm, 27–40 kV, and 10–140 μA, respectively. The micron scale of the electron beam was well matched to the evanescent surface waves of the grating. The measured wavelength range extended from 288 to 803 μm, and both the wavelengths and the intensities observed were in accord with expectations based on theory. The details of the experiment and a summary of the results will be discussed.
Observation of body centered cubic Cu in Cu/Nb nanolayered composites
Authors: Kung H. , Lu Y-C. , Griffin A. J. , Nastasi M. , Mitchell T. E. , Embury J. D.
Published: July 2002

The deposition of thin alternating layers of Cu and Nb on Si(100) substrates has been studied by transmission electron microscopy as a function of layer thickness. For layer thickness above 25 Å, there is a strong texture orientation relationship with the close packed planes of fcc Cu parallel to close packed planes of bcc Nb, forming the so-called “Kurdjumov-Sachs” orientation relationship. However, at thicknesses of under 12 Å, the Cu is constrained to grow as a slightly distorted bcc structure. It is thought that, when it reaches a critical thickness between 12 and 20 Å, the bcc Cu loses coherency and transforms martensitically to the fcc phase, resulting in the observed Kurdjumov–Sachs orientation relationship. Electron energy loss spectroscopy observations indicate a difference of 2 eV in the L3 edge suggesting that the Fermi energy is lower in the constrained bcc form of Cu than in the equilibrium fcc structure.
Polycrystalline silicon thin film transistor incorporating a semi-insulating field plate for high voltage circuitry on glass
Authors: Clough F. J. , Narayanan E. M. Sankara , Chen Y. , Eccleston W. , Milne W. I.
Published: July 2002

The fabrication and enhanced performance of a polycrystalline silicon high voltage thin film transistor structure, which incorporates a semi-insulating field plate, are reported. For comparison, the performance of conventional offset drain and metal field plate structures, fabricated on the same wafer using the same low temperature (⩽610 °C) polycrystalline silicon process, is described. Electrical characterization of the high voltage thin film transistor structures demonstrates that the new three terminal device offers the highest blocking capability (>200 V) without sacrificing on state performance.
Investigations of Stranski-Krastanov growth kinetics of Si-dots on 6H-SiC(0001)
Authors: Fissel Andreas , Pfennighaus Kay , Richter Wolfgang
Published: July 2002

The growth kinetics of Si dots grown on 6H-SiC(0001) by molecular beam epitaxy were studied in real time by reflection high-energy electron diffraction. The critical thickness for the Stranski–Krastanov growth mode transition was found to be kinetically delayed leading to a gradual decrease of this thickness with increasing temperature (T). At T<625 °C and coverages below the critical thickness, a post-deposition evolution of dots is clearly established. The dot growth process is, under these conditions, mainly determined by the mass transfer out of the two-dimensional layer towards the Si dots. The dots grown on top of a 1 monolayer (ML) thick wetting layer are quantum sized with typical dimensions of 5–6 nm in height and 20–30 nm in diameter after a long post-deposition evolution times at 2–3 ML coverages. Above 625 °C and coverages above the critical thickness, the dot growth is only determined by surface-diffusion kinetics resulting in the growth of larger dots.
Estimation of doping density in HgCdTe p-n junctions using scanning laser microscopy
Authors: Siliquini J. F. , Dell J. M. , Musca C. A. , Smith E. P. G. , Faraone L. , Piotrowski J.
Published: July 2002

Quantitative assessment of p- to n- type conversion due to reactive ion etching (RIE) of p-type Hg0.71Cd0.29Te is presented using laser-beam-induced-current (LBIC) measurements. For the RIE processing conditions used (390 mT, CH4/H2, 0.4 W/cm2), n-type conversion was observed in extrinsic arsenic-doped p-type Hg0.71Cd0.29Te which had previously undergone a Hg anneal to eliminate Hg vacancies. Effective doping density of the n-type converted region is determined by fitting a theoretically determined LBIC signature to the measured LBIC signal over a temperature range 80–300 K. Effective n-type doping density is the only fitting parameter used in the simulation, which was carried out using a commercial semiconductor device modeling package (SEMICAD™ DEVICE). This noncontact experimental technique promises to be a useful tool in the characterization of p-n junction diodes in HgCdTe, and for studying the precise nature of p to n conversion in p-type HgCdTe.
Piezoelectric effects on electrical and optical properties of wurtzite GaN/AlGaN quantum well lasers
Authors: Park Seoung-Hwan , Chuang Shun-Lien
Published: July 2002

The piezoelectric effects on the optical gain of wurtzite GaN/AlGaN QW lasers taking into account the many-body effects are presented. The self-consistent model with piezoelectric field effect shows that band structures and optical gain are significantly affected by the piezoelectric field at relatively low carrier densities. The peak gain is redshifted and smaller when compared to the flat-band model without piezoelectric field effect. Only gain peaks corresponding to C1-HH1 and C1-LH1 transitions are observed in the investigated range and transitions for C1-HH2 and C1-LH2 are negligible due to the large subband energy spacing at low carrier densities and small matrix elements at high carrier densities. At high carrier densities, the self-consistent model shows band structures and optical properties similar to the flat-band model due to the screening effects.
Growth of carbon nanotubes on cobalt disilicide precipitates by chemical vapor deposition
Authors: Mao J. M. , Sun L. F. , Qian L. X. , Pan Z. W. , Chang B. H. , Zhou W. Y. , Wang G. , Xie S. S.
Published: July 2002

We have successfully grown carbon nanotubes on cobalt-implanted silicon with various doses. The morphology of such tubes has been examined by scanning electron microscopy, transmission electron microscopy, and Raman scattering. On contrary to the commonly used transition-metal nanoparticle catalysts, nanometer-sized CoSi2 precipitates produced in the as-implanted substrates are believed to act as nucleation centers for the formation of carbon nanotubes.
Thermal stability of GaN investigated by Raman scattering
Authors: Kuball M. , Demangeot F. , Frandon J. , Renucci M. A. , Massies J. , Grandjean N. , Aulombard R. L. , Briot O.
Published: July 2002

We have investigated the thermal stability of GaN using Raman scattering. Noninvasive optical monitoring of structural damage to GaN by high-temperature anneals in nitrogen ambient has been demonstrated. Characteristic features in the Raman spectrum identify three thermal stability regimes. Thermal damage between 900 and 1000 °C results in the appearance of a broad Raman peak between the E2 and A1(LO) phonon. For anneals at temperatures higher than 1000 °C emerging macroscopic disorder gives rise to distinct Raman modes at 630, 656, and 770 cm−1. Below 900 °C no thermal damage has been observed. The evolution of the Raman spectrum of GaN with increasing annealing temperature is discussed in terms of disorder-induced Raman scattering. We find clear indications for a reaction at the GaN/sapphire interface for anneals higher than 1000 °C.
Operation of logic function in a Coulomb blockade device
Authors: Tsukagoshi K. , Alphenaar B. W. , Nakazato K.
Published: July 2002

This letter presents the experimental demonstration of a Coulomb blockade (CB) logic device. Our logic architecture consists of an array of current pathways, controlled by CB switching nodes. In this architecture, high gain is not required to transmit information, making it well suited to the CB device. Each CB node is switched between a blockaded state and a completely pinched-off state, minimizing the influence of stray potentials. Using a multi-phase clocking scheme to precisely control electron flow, the AND logic function is observed using as few as 160 electrons.
Transfer of patterned ion-cut silicon layers
Authors: Yun C. H. , Wengrow A. B. , Cheung N. W. , Zheng Y. , Welty R. J. , Guan Z. F. , Smith K. V. , Asbeck P. M. , Yu E. T. , Lau S. S.
Published: July 2002

The technique of transferring patterned ion-cut layers from one Si wafer to another was demonstrated. The starting silicon wafer was masked with checkerboard and line patterns with a 3 μm thick polymethylmethacrylate/photoresist and was implanted with 5×1016 H+ ions/cm2 at 150 keV. After stripping off the mask, the wafer was bonded to an oxide-coated receptor wafer through low-temperature direct wafer bonding. Heat treatment of this bonded pair showed that the hydrogen-induced silicon surface layer cleavage (ion cut) could propagate throughout about 16 μm×16 μm of nonimplanted material with implanted regions only 4 μm wide. Mask width, spacing, and implantation profiles through the mask shape were shown to have effects on the internal microfracturing mechanisms.
Structure and hydrogen content of stable hot-wire-deposited amorphous silicon
Authors: Brockhoff A. M. , Ullersma E. H. C. , Meiling H. , Habraken F. H. P. M. , van der Weg W. F.
Published: July 2002

Thin-film transistors incorporating a hot-wire chemical-vapor-deposited silicon layer have been shown to exhibit superior electronic stability as compared to glow-discharge-deposited amorphous silicon devices. Hot-wire-deposited silicon films of various thicknesses (37–370 nm) on silicon dioxide were investigated. The films are structurally inhomogeneous. Raman measurements and transmission electron microscopy show that isolated cone-shaped crystals grow within a primarily amorphous layer. The amorphous interface region has a low hydrogen content of 2.0±0.2 at. %, while the films exhibit an enhanced hydrogen concentration in the surface region. The bond-angle distribution in the amorphous phase is comparable to that of device-quality glow-discharge-deposited amorphous silicon.
Does freezing in PbMg1/3Nb2/3O3 relaxor manifest itself in nonlinear dielectric susceptibility?
Authors: Tagantsev A. K. , Glazounov A. E.
Published: July 2002

A possible anomaly in the temperature dependence of nonlinear dielectric susceptibility χnl of relaxor ferroelectrics related with the freezing phase transition was investigated. First, based on the phenomenological approach, the anomaly in the χnl was analyzed, including its shape, sign, and crystalline anisotropy. Second, the theoretical results were applied to the analysis of experimental data on nonlinear dielectric permittivity of single crystals of PbMg1/3Nb2/3O3 (PMN) relaxor. It was concluded that in contrast to earlier publications, there is no evidence for the anomaly in χnl(T) of PMN related with the freezing transition.
Diode-pumped self-frequency doubling in a Nd3+:YCa4O(BO3)3 laser
Authors: Eichenholz J. M. , Hammons D. A. , Shah L. , Ye Q. , Peale R. E. , Richardson M. , Chai B. H. T.
Published: July 2002

We report efficient, diode-pumped, self-frequency doubling (SFD) in the newly developed laser crystal Nd3+:YCa4O(BO3)3. More than 350 mW of fundamental output power at 1060 nm was achieved with a slope efficiency of 51%. With one watt of absorbed pump power, 62 mW of green cw laser emission at 530 nm was observed with proper phase matching. This initial performance, and the good optical properties of the crystalline host, are encouraging for the development of a high power diode-pumped SFD visible light laser source.
Pendeoepitaxy of gallium nitride thin films
Authors: Linthicum Kevin , Gehrke Thomas , Thomson Darren , Carlson Eric , Rajagopal Pradeep , Smith Tim , Batchelor Dale , Davis Robert
Published: July 2002

Pendeoepitaxy, a form of selective lateral growth of GaN thin films has been developed using GaN/AlN/6H–SiC(0001) substrates and produced by organometallic vapor phase epitaxy. Selective lateral growth is forced to initiate from the (112̄0) GaN sidewalls of etched GaN seed forms by incorporating a silicon nitride seed mask and employing the SiC substrate as a pseudomask. Coalescence over and between the seed forms was achieved. Transmission electron microscopy revealed that all vertically threading defects stemming from the GaN/AlN and AlN/SiC interfaces are contained within the seed forms and a substantial reduction in the dislocation density of the laterally grown GaN. Atomic force microscopy analysis of the (112̄0) face of discrete pendeoepitaxial structures revealed a root mean square roughness of 0.98 Å. The pendeoepitaxial layer photoluminescence band edge emission peak was observed to be 3.454 eV and is blueshifted by 12 meV as compared to the GaN seed layer.
Flashlamp pumped solid-state dye laser incorporating pyrromethene 597
Authors: Finlayson A. J. , Peters N. , Kolinsky P. V. , Venner M. R. W.
Published: July 2002

Solid-state rods containing the laser dye pyrromethene 597 (Pyr 597) in a modified polymethyl methacrylate polymer host have been fabricated and shown to give significant lasing action under flashlamp excitation. The rods all displayed a favorable positive-lensing characteristic and also exhibited low bulk transmission losses. The rod with the lowest transmission loss, measured to be 0.31% cm−1 at 633 nm, gave a laser output of 880 mJ with a 0.35% energy efficiency.
Mn-doped ZnS nanoparticles as efficient low-voltage cathodoluminescent phosphors
Authors: Dinsmore A. D. , Hsu D. S. , Gray H. F. , Qadri S. B. , Tian Y. , Ratna B. R.
Published: July 2002

We have synthesized nanoparticles of ZnS doped with Mn for potential use as cathodoluminescent phosphors in field-emission displays (FEDs). We show that the cathodoluminescent efficiency of particles ⩽100 nm in diameter is within 40% of that of a commercial (micron-sized) phosphor when the electron-beam energy ranges between 500 and 3500 eV. The nanoparticles exhibit less current saturation than larger-sized phosphors, an important feature for use in FEDs. Furthermore, the nanoparticles were annealed at just 535 °C, hundreds of degrees below the processing temperatures of standard phosphors. Finally, we discuss the effect of the particle surface on low-voltage luminous efficiency.
Switching properties of self-assembled ferroelectric memory cells
Authors: Alexe M. , Gruverman A. , Harnagea C. , Zakharov N. D. , Pignolet A. , Hesse D. , Scott J. F.
Published: July 2002

In this letter, we report on the switching properties of an ordered system of Bi4Ti3O12 ferroelectric memory cells of an average lateral size of 0.18 μm formed via a self-assembling process. The ferroelectricity of these cells has been measured microscopically and it has been demonstrated that an individual cell of 0.18 μm size is switching. Switching of single nanoelectrode cells was achieved via scanning force microscopy working in piezoresponse mode.
Large coherent acoustic-phonon oscillation observed in InGaN/GaN multiple-quantum wells
Authors: Sun Chi-Kuang , Liang Jian-Chin , Stanton Christopher J. , Abare Amber , Coldren Larry , DenBaars Steven P.
Published: July 2002

We have observed coherent acoustic-phonon oscillation in InGaN/GaN multiple-quantum wells. With femtosecond pulse excitation, photogenerated carriers screen out the strained-induced piezoelectric field and initiate the coherent acoustic-phonon oscillation. The resulted modulation of the piezoelectric field will then cause large optical property oscillation through the quantum-confined Stark effect.
Characteristics of dielectric layers grown on Ge by low temperature vacuum ultraviolet-assisted oxidation
Authors: Craciun Valentin , Boyd Ian W. , Hutton Bernie , Williams David
Published: July 2002

The growth of thin dielectric layers on (100) Ge samples at temperatures lower than 450 °C by photoassisted oxidation with vacuum ultraviolet radiation emitted by a Xe silent discharge lamp has been investigated. The thickness of the grown layers increased with both the oxidation time and processing temperature. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy (XPS) indicated that the layers are mainly stoichiometric GeO2. XPS investigations also indicated the presence of a several-nanometer-thick substoichiometric oxide layer at the interface region for samples irradiated for short periods of time. Capacitance– and current–voltage measurement showed that layers thicker than 15 nm exhibited good electrical characteristics.
Determination of critical current density in bulk melt-processed high temperature superconductors from levitation force measurements
Authors: Kordyuk A. A. , Nemoshkalenko V. V. , Viznichenko R. V. , Gawalek W. , Habisreuther T.
Published: July 2002

A simple approach to describe levitation force measurements on bulk melt-processed high temperature superconductors was developed. A couple of methods to determine the critical current density Jc were introduced. The averaged a-b-plane Jc values for the field parallel to this plane were determined. The first and second levitation force hysteresis loops calculated with these Jc values coincide remarkably well with the experimental data.
High-temperature processing of GaN: The influence of the annealing ambient on strain in GaN
Authors: Hayes J. M. , Kuball M. , Bell A. , Harrison I. , Korakakis D. , Foxon C. T.
Published: July 2002

Using micro-Raman scattering we have investigated the influence of the annealing ambient on the high-temperature processing of GaN. Compressive strain is found in GaN layers after high-temperature processing in oxygen-containing atmospheres. This strain is significantly enhanced by the addition of water vapor to the annealing ambient, suggesting the enhanced inclusion of oxygen into GaN. Characteristic photoluminescence lines appear at 3.355 and 3.406 eV after annealing in oxygen in the presence of water vapor. No strain is introduced by high-temperature processing in nitrogen ambient, even at temperatures close to the thermal decomposition temperature and in the presence of water vapor.
Band gaps of lattice-matched (Ga,In)(As,N) alloys
Authors: Bellaiche L.
Published: July 2002

The band gaps of the GaInAsN alloys lattice-matched to GaAs and InP have been calculated as a function of the nitrogen composition and as a function of pressure, by using a pseudopotential technique. The calculations are in excellent agreement with the experimental results, which are only available for small nitrogen compositions. The band gap of both lattice-matched systems is predicted to significantly decrease when further increasing the nitrogen content. As a result, the band gap of both systems closes for large enough nitrogen compositions (around 12%–20%).
Blue polymer light-emitting diodes from poly(9,9-dihexylfluorene-alt-co-2, 5-didecyloxy-para-phenylene)
Authors: Yu Wang-Lin , Cao Yong , Pei Jian , Huang Wei , Heeger Alan J.
Published: July 2002

Deep blue photoluminescence and electroluminescence are demonstrated from a soluble conjugated polymer, poly(9,9-dihexylfluorene-alt-co-2,5-didecyloxy-para-phenylene). The PL quantum efficiency is approximately 40%. Cyclic voltammetry measurements indicate that the highest occupied molecular orbital and lowest unoccupied molecular orbital energies are 5.66 and 2.62 eV below vacuum, respectively. Single-layer and multilayer light-emitting diodes emit deep blue light (peak at ∼420 nm).
Transient enhanced diffusion after laser thermal processing of ion implanted silicon
Authors: Jones Kevin S. , Banisaukas Heather , Glassberg Josh , Andideh Ebrahim , Jasper Craig , Hoover Allen , Agarwal Aditya , Rendon Mike
Published: July 2002

The effect of laser thermal processing (LTP) on implantation-induced defect evolution and transient enhanced diffusion (TED) of boron was investigated. A 270-Å-thick amorphous layer formed by 10 keV Si+ implantation was melted and regrown using a 20 ns ultraviolet laser pulse. Transmission electron microscopy revealed that recrystallization of the amorphous layer following LTP results in a high concentration of stacking faults and microtwins in the regrown region. Also, the end-of-range loop evolution during subsequent 750 °C furnace annealing, is different in a LTP sample compared to a control sample. Secondary ion mass spectroscopy of a boron marker layer 6000 Å below the surface showed that LTP alone produced no enhanced diffusion. However, during subsequent furnace annealing, the boron layer in the LTP sample experienced just as much TED as in the control sample which was only implanted and furnace annealed. These results imply that laser melting and recrystallization of an implantation-induced amorphous layer does not measurably reduce the excess interstitials released from the end-of-range implant damage.
Schottky barrier effects in the photocurrent of sol–gel derived lead zirconate titanate thin film capacitors
Authors: Yang Y. S. , Lee S. J. , Yi S. , Chae B. G. , Lee S. H. , Joo H. J. , Jang M. S.
Published: July 2002

We studied the photoresponse of Pb(Zr0.53Ti0.47)O3 (PZT) thin films by measuring the current–voltage (I–V) curve at several ferroelectric polarization states illuminated by a monochromatic 3.5 eV UV light. The photocurrent in Pt/PZT/Pt capacitors was sensitive to the polarization state, and the poling voltage-dependent photocurrent showed very asymmetric hysteresis behavior. The capacitance that is dependent upon the thickness of the samples was first measured. Then, the capacitance of the interfacial layer at a state with no interdiffusion between Pt and PZT film was extrapolated by using an equivalent circuit model. The result of the extrapolation was 28.1 μF/cm2.
Mode Grüneisen parameters and negative thermal expansion of cubic ZrW2O8 and ZrMo2O8
Authors: Wang Kai , Reeber Robert R.
Published: July 2002

Thermal expansion for ZrW2O8 and ZrMo2O8 is analyzed by a multifrequency Einstein model. Vibrational modes that contribute significantly to the thermal expansion are empirically identified. For ZrW2O8, a negative Grüneisen parameter mode is consistent with the observed Raman spectral peak of 40 cm−1. Experimental confirmation of the results is proposed.
Growth of AlGaN on Si(111) by gas source molecular beam epitaxy
Authors: Nikishin S. A. , Faleev N. N. , Zubrilov A. S. , Antipov V. G. , Temkin H.
Published: July 2002

Gas source molecular beam epitaxy with ammonia was used to grow AlxGa1−xN on Si(111). Three types of buffer layers, containing AlN, AlGaN/AlN, and AlGaN/GaN short period superlattices, were used and their effectiveness evaluated by x-ray diffraction. We determined that a combination of AlN buffer layer, prepared under the two-dimensional growth mode, with a short period superlattice of AlGaN/GaN results in the highest quality AlGaN. Under optimized growth conditions, x-ray diffraction coherence length almost equal to the layer thickness was obtained for low Al content layers. The normalized coherence length was reduced to ∼0.4 for x=0.66 and it increased again to ∼0.75 in AlN. From room temperature band edge cathodoluminescence of AlGaN grown on Si(111) we determined the alloy bowing coefficient of b=1.5 eV, in good agreement with previous results obtained by absorption measurements.
Electrical characteristics of an ultrathin (1.6 nm) TaOxNy gate dielectric
Authors: Jung Hyungsuk , Im Kiju , Hwang Hyunsang , Yang Dooyoung
Published: July 2002

This letter describes a process for the preparation of high-quality tantalum oxynitride (TaOxNy) via NH3 annealing of Ta2O5, for use in gate dielectric applications. Compared with tantalum oxide (Ta2O5), a significant improvement in the dielectric constant was obtained by the NH3 treatment. In addition, light reoxidation in a wet ambient at 450 °C resulted in a significantly reduced leakage current. We confirmed nitrogen incorporation in the tantalum oxynitride (TaOxNy) by Auger electron spectroscopy. By optimizing the nitridation and reoxidation processes, we obtained an equivalent oxide thickness as thin as 1.6 nm and a leakage current of less than 10 mA/cm2 at −1.5 V.
Low-loss one-dimensional metallodielectric photonic crystals fabricated by metallic insertions in a multilayer dielectric structure
Authors: Ye Yong-Hong , Bader Georges , Truong Vo-Van
Published: July 2002

Low-loss one-dimensional metallodielectric photonic crystals were obtained by inserting Ag layers into ZnS/MgF2 quarter-wave multilayers. They were fabricated by thermal evaporation of ZnS, MgF2, Ag, and MgF2 layers alternately onto a glass substrate. For a sample of 3.5 periods of ZnS (61.7 nm)/MgF2 (52.5 nm)–Ag (19 nm)–MgF2 (52.5 nm), the transmittance spectrum shows a wide and deep band gap between 420 and 790 nm with rejection level of 10 dB per lattice. Above 790 nm, there is a 210 nm wide high passband. The transmittance at the bandedge is about 60%. Its reflectance spectra over an incident angle range of 10°–70° show a 240 nm wide low-loss omnidirectional high reflection band for both p and s polarizations. All the experimental measurements match well with the theoretical results calculated by the transfer matrix method.
Upconversion luminescence of Er3+ in alkali bismuth gallate glasses
Authors: Man S. Q. , Pun E. Y. B. , Chung P. S.
Published: July 2002

Frequency upconversion of Er3+ in alkali bismuth gallate glasses have been investigated. The upconversion mechanisms are discussed, and the dominant mechanisms are excited state absorption for the H11/22→I15/24 and S3/24→I15/24 transitions, and energy transfer upconversion for the F9/24→I15/24 transition. Intense green (around 525–550 nm) and red (around 660 nm) emission bands were observed under 800 nm excitation. At a pump intensity of 15.6 W/cm2, frequency upconversion efficiencies of 2.1×10−2 and 4.8×10−3 were obtained for the green and red emissions, respectively. The results are the highest among doped oxide glasses, and are comparable to those reported for Er3+/Yb3+ codoped fluoride glasses.
Atomic-scale analysis of CoFe/Cu and CoFe/NiFe interfaces
Authors: Larson D. J. , Clifton P. H. , Tabat N. , Cerezo A. , Petford-Long A. K. , Martens R. L. , Kelly T. F.
Published: July 2002

Internal interfaces in metallic multilayers grown on planar silicon substrates have been chemically analyzed with atomic resolution using three-dimensional atom probe microscopy. The structure studied was a NiFe/CoFe/Cu/CoFe multilayer grown with (111) texture. Atom probe measurements across the NiFe/CoFe interfaces yield widths of 1.1±0.2 nm for NiFe grown on CoFe and 1.7±0.2 nm for CoFe grown on NiFe. The widths of interfaces between CoFe and Cu layers vary as well, with values of 0.82±0.10 nm for CoFe grown on Cu, but only 0.47±0.15 nm for Cu grown on CoFe. In addition, the Fe concentration is enriched at the interface where Cu is grown on CoFe, and depleted where CoFe is grown on Cu. These results indicate that the Fe segregates to the surface during the deposition of CoFe so that the composition at the top of this layer is Fe rich.
Coulomb blockade and cotunneling in single electron circuits with on-chip resistors: Towards the implementation of the R pump
Authors: Zorin A. B. , Lotkhov S. V. , Zangerle H. , Niemeyer J.
Published: July 2002

We investigate Al single electron structures equipped with miniature (8 μm long) on-chip Cr resistors of R>Rk=h/e2≈26 kΩ. From the measurement of the Coulomb blockade in single-junction structures we evaluate the self-capacitance of our resistors per unit length, c≈62 aF/μm. We demonstrate that the cotunneling current in the transistor samples in the Coulomb blockade regime obeys the power law, I∝V3+2(R/Rk), predicted by Odintsov, Bubanja, and Schön for a transistor with pure ohmic-resistance leads. The concept of the three-junction single electron pump with on-chip resistors (R pump) is developed. We demonstrate that the technology available allows the R pump with a relative accuracy of the electron transfer of 10−8 to be implemented.
Complete eigenfunctions of linearized integrable equations expanded around a soliton solution
Authors: Yang Jianke
Published: July 2002

Complete eigenfunctions for an integrable equation linearized around a soliton solution are the key to the development of a direct soliton perturbation theory. In this article, we explicitly construct such eigenfunctions for a large class of integrable equations including the KdV, NLS and mKdV hierarchies. We establish the striking result that the linearization operators of all equations in the same integrable hierarchy share the same complete set of eigenfunctions. Furthermore, these eigenfunctions are precisely the squared eigenfunctions of the associated eigenvalue problem. The key step in our derivation is to show that the linearization operator of an integrable equation can be factored into a function of the integro-differential operator which generates the integrable equation, and the linearization operator of the lowest-order integrable equation in the same hierarchy. We also obtain similar results for the adjoint linearization operator of an integrable equation. Even though our analysis is conducted only for the KdV, NLS and mKdV hierarchies, similar results are expected for other integrable hierarchies as well. We further explicitly present the complete eigenfunctions for the KdV, NLS and mKdV hierarchy equations and give their inner products, thus they can be readily used to develop a direct soliton perturbation theory for any of those hierarchy equations.
Candlestick rubidium beam source
Authors: Walkiewicz M. R. , Fox P. J. , Scholten R. E.
Published: July 2002

We describe a long-lived, bright and intense rubidium atomic beam source based on a previously published recirculating candlestick design for sodium, with several modifications and enhancements. The device operates for thousands of hours without maintenance, with brightness of 1.9×1022 m−2 s−1 sr−1.
Finite size effects and rotational relaxation in superfluid helium nanodroplets: Microwave-infrared double-resonance spectroscopy of cyanoacetylene
Authors: Callegari C. , Reinhard I. , Lehmann K. K. , Scoles G. , Nauta K. , Miller R. E.
Published: July 2002

Microwave-infrared double-resonance spectroscopy has been used to probe the solvation environment and its influence on the rotational relaxation of a cyanoacetylene molecule embedded in a superfluid He4 nanodroplet. The results support a model in which (within any given rotational state) the guest molecules are distributed over a set of spectroscopically inequivalent states which are most likely “particle-in-a-box” states originating from the confinement of the guest molecule within the droplet. Revisitation of previously collected microwave–microwave double-resonance data suggests that transitions between these states occur at a rate which is comparable to the rotational relaxation rate, but not fast enough as to produce motionally narrowed, homogeneous absorption lines. The relative intensities of the rotational lines in the microwave-infrared double-resonance spectra are observed to depend strongly on the average droplet size. In the large droplet limit we can explain the observed pattern by invoking a “strong collision” regime, i.e., one in which the branching ratios of the rotational relaxation do not depend on the initial rotational state. For small droplets we speculate that, because of finite size effects, the density of (surface) states may become discontinuous, producing deviations from the “thermal” behavior of the larger systems.
Self-aligned coupled cavity GaAs/AlGaAs midinfrared quantum-cascade laser
Authors: Hvozdara L. , Lugstein A. , Gianordoli S. , Schrenk W. , Strasser G. , Unterrainer K. , Bertagnolli E. , Gornik E.
Published: July 2002

A monolithic GaAs/AlGaAs quantum-cascade laser with self-aligned focused ion beam-cut coupled cavities, emitting in the range of λ=9.4 μm is demonstrated. Separate pulsing of two optically coupled laser sections enables control of the lasing in single-mode and in multimode regimes. Side mode suppression ratios better than 25 dB are shown. Mode control over two single modes spaced by 3.6 cm−1 is presented. An optical output intensity modulation in a range of 20 dB is achieved. The laser exhibits a peak output power in the range of 180 mW at cryogenic temperatures. The observed mode spacing is in a good agreement with the calculation.
Subcycle high electron acceleration by crossed laser beams
Authors: Salamin Yousef I. , Keitel Christoph H.
Published: July 2002

We present an exact plane-wave-based analysis of the vacuum acceleration, to energy gradients in the TeV/m range, of a single electron, using two laser beams crossing at an arbitrary angle. Our analysis of the dynamics evolves from analytic solutions to the relativistic equations of motion and predicts that, for a given laser intensity, a unique crossing angle maximizes the energy gain due to constructive interference.
Accurately solving the electronic Schrödinger equation of atoms and molecules by extrapolating to the basis set limit. I. The helium dimer (He2)
Authors: Gdanitz Robert J.
Published: July 2002

A new formula, EL−E∝(L+3/4)−3, to extrapolate energies, EL (that arise when the basis set is truncated at a finite angular momentum quantum number, L) to the limit, E, is derived and applied to the computation of the pair potential of He. Large basis sets up to d-aug-cc-pV5Z and -6Z are used, and in addition, a new cc-pV7Z set is presented. The full-CI is approximated using the “multireference averaged coupled-pair functional” (MR-ACPF) with 121 references. The calculated molecular constants of He2 are in excellent agreement with those recently obtained with r12-MR-ACPF [R. J. Gdanitz, Mol. Phys. 96, 1423 (1999)], but they agree only fairly with the complete-CI estimate of van Mourik and Dunning [J. Chem. Phys. 111, 9248 (1999)]. The potential of Komasa [J. Chem. Phys. 110, 7909 (1999)] which has been calculated with the “exponentially correlated Gaussians” method does not give a bound state. The sensitivity of the molecular constants 〈R〉 and D0 to errors of the interaction potential at different distances is estimated by perturbing the potential by Gaussian functions. The region of 5≲R/a0≲9 is found to be most sensitive. From this analysis, doubts arise that recent calculations (including the present one) are accurate enough to allow the molecular constants to be determined to better than ≈10%.
Relative intensity noise characteristics of injection-locked semiconductor lasers
Authors: Jin X. , Chuang S. L.
Published: July 2002

An experimental and theoretical study of relative intensity noise (RIN) spectra of side-mode injection-locked Fabry–Pérot semiconductor lasers is reported. It is shown that the injection-locking technique effectively increases the relaxation oscillation frequency from 4.5 GHz (free-running mode) to 12 GHz (injection-locked mode) and enhances relaxation peaks of the slave laser RIN spectra. Results from our theoretical model, which include the key parameters for semiconductor quantum-well lasers, such as the linewidth enhancement factor, the nonlinear gain saturation coefficients, and optical confinement factor, show good agreement with our experimental results.
Shear Alfvén wave radiation from a source with small transverse scale length
Authors: Leneman D. , Gekelman W. , Maggs J.
Published: July 2002

Shear Alfvén waves are studied in the kinetic and inertial regimes. The waves are launched from an antenna which is on the order of the electron collisionless skin-depth, δ=c/ωpe, in size. The experiment is performed in the LArge Plasma Device, LAPD [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles, using a new antenna design that modulates parallel plasma electron current. The plasma is 100 skin-depths in diameter and 3.6 Alfvén wavelengths long. The results include the calculation of the wave currents based on measurements of the wave magnetic field. Differences in the perpendicular phase velocity of the wave in the kinetic regime as compared to the inertial regime are also reported. Results generally compare favorably with predictions of a theory which includes collisional damping and kinetic electron dynamics with fluid ions.
Retrieving interaction potentials from the topology of the electron density distribution: The case of hydrogen bonds
Authors: Espinosa E. , Molins E.
Published: July 2002

The dependence of the total electron energy density at the (3,−1) critical point (CP) of the H…O interaction against the interatomic distance (ECP) has been obtained by the addition of the local electron kinetic (GCP) and potential (VCP) energy densities dependences (ECP=GCP+VCP) for a set of 83 X-H…O hydrogen bonds (X=C, N, O). The ECP function has been related to the interaction potential by means of a proportionality relationship U=−υ⋅ECP, υ being a positive constant in volume units. Based on the GCP and VCP functionalities, the proposed H…O interaction potential has been successfully checked against several physical and chemical properties. The behavior of the U function has been compared to Morse and Buckingham-type potentials, leading to an almost perfect matching between all of them when they were constrained to have the same three parameters: the potential well depth U0, its position r0, and the curvature of the potential function at r0. The resulting U(r) function is simply described by the addition of two exponential terms: U(r)=49 100 exp(−3.6r)−11 800 exp(−2.73r), where U is in kJ/mol and r is the H…O distance in Å.
Nonlinear electron beam interaction with a whistler wave packet
Authors: Krafft C. , Volokitin A. S. , Flé M.
Published: July 2002

The nonlinear evolution of a thin monoenergetic electron beam injected in a magnetized plasma and interacting with a whistler wave packet through Cherenkov resonance is considered. It is shown that effective dissipation due to whistlers’ wave field leakage out of the bounded beam volume to infinity (effective radiation outside the beam) strongly influences the evolution of the beam electrons’ distribution. Self-organization of beam structure leads to the formation of electron bunches continuously decelerated by waves. In the presence of effective energy losses, the phases of all waves in the packet can become strongly correlated and thus can prevent the stochastic phase mixing required for validity of quasilinear theory. In the asymptotic stage of the beam–waves interaction, dynamically stable electron bunches are present together with a diffusion plateau in the velocity distribution; these nonlinear structures allow the beam to radiate wave energy on a significative distance from its injection point.
Multicolor infrared detection using two stacks of superlattice structures in a back-to-back configuration
Authors: Hsu M. C. , Kuan C. H. , Wang S. Y.
Published: July 2002

Voltage-controlled multicolor detection with a two-stack GaAs/AlGaAs superlattice structure is reported. Each stack contains a superlattice and current blocking layers. The responsivity of each stack has a voltage-tunable spectral range and can be turned on or off by controlling the bias polarity. In a back-to-back configuration of the two stacks, a variable detection range with peak wavelength at 5.5, 6.8, 8.5, and 10.8 μm is achieved by changing the applied voltage at 45 K.
Families of metrics geodesically equivalent to the analogs of the Poisson sphere
Authors: Topalov Petar
Published: July 2002

The metric of the Poisson sphere can be obtained as a result of reduction from the kinetic energy of the free motion of a rigid body. It is proved that the metric of the Poisson sphere admits nontrivial one-parameter family of metrics that have the same geodesic lines. In the present paper we prove that the Clebsch case of motion of the rigid body and the case of the free motion of a rigid body in Minkowski space lead (after reduction) to Riemannian metrics that also admit nontrivial geodesical equivalence. A new integrability criterion of geodesical equivalence is proved.