bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of the hydrogen plasma treatment in layer-by-layer deposition of microcrystalline silicon
Authors: Saitoh K. , Kondo M. , Fukawa M. , Nishimiya T. , Matsuda A. , Futako W. , Shimizu I.
Published: July 2002

We have investigated the role of hydrogen in hydrogenated microcrystalline silicon (μc-Si:H) formation using hydrogen plasma treatments, in particular examining the possibility of subsurface reaction due to permeating hydrogen atoms, which leads to the crystallization of hydrogenated amorphous silicon (a-Si:H). It is demonstrated that the hydrogen plasma treatment of a-Si:H film on the anode using a cathode covered by a-Si:H film, which is inevitably coated during the deposition period, gives rise to the deposition of μc-Si:H over the a-Si:H layer, i.e., chemical transport takes place. It is also found that the pure hydrogen plasma treatment using a clean cathode induces only etching of the a-Si:H layer. These results imply that the present hydrogen plasma condition does not cause crystallization of a-Si:H but only etching, and that careful experimentation is required to determine the real subsurface reaction due to atomic hydrogen.
High pressure discharges in cavities formed by microfabrication techniques
Authors: Khan Babar A. , Cammack David A. , Pinker Ronald D. , Racz Jacqueline
Published: July 2002

High pressure discharges are the basis of small high intensity light sources. In this work, we demonstrate the formation of high pressure discharges, in cavities formed by applying micromachining and integrated circuit techniques to quartz substrates. Cavities containing varying amounts of mercury and argon were fabricated to obtain high pressure discharges. A high pressure mercury discharge was formed in the electrodeless cavities by exciting them with a microwave source, operating at 2.45 GHz and in the electroded cavities by applying a dc voltage. The contraction of the discharge into a high pressure arc was observed. A broad emission spectrum due to self-absorption and collisions between excited atoms and normal atoms, typical of high pressure mercury discharges, was measured. The light output and efficacy increased with increasing pressure. The measured voltage was used to estimate the pressure within the electroded cavities, which is as high as 127 atm for one of the two cavities discussed in this work. Efficacies over 40 lumens per watt were obtained for the electrodeless cavities and over 50 ℓm/W for the electroded cavities.
Visible electroluminescence from Eu:CaF2 layers grown by molecular beam epitaxy on p-Si (100)
Authors: Chatterjee T. , McCann P. J. , Fang X. M. , Remington J. , Johnson M. B. , Michellon C.
Published: July 2002

Visible electroluminescence (EL) is observed at room temperature by current injection into Eu:CaF2 layers containing 7.5 and 8.0 at. % Eu grown by molecular beam epitaxy on lightly doped (100) p-type silicon. The EL spectra are broad with peaks near 700 and 600 nm, respectively. Room temperature photoluminescence spectra for the same samples exhibited peaks near 420 nm, with higher doped samples showing a more pronounced long wavelength tail. Although both metal and indium–tin–oxide (ITO) contacts were successfully used for current injection, the best EL intensity stability was achieved with contacts made of a 100 Å thick Al layer covered by a 2500 Å thick ITO layer.
Optical absorption of ZnS nanocrystals inside pores of silica
Authors: Tan Ming , Cai Weiping , Zhang Lide
Published: July 2002

The optical absorption of ZnS semiconductor nanocrystals inside pores of silica has been investigated. These ZnS nanoparticles were synthesized through sol–gel processing, followed by firing. X-ray diffraction and nitrogen adsorption/desorption results show that the ZnS nanocrystals are highly defective. Based on the analysis of x-ray and nitrogen adsorption–desorption results, the surface layers of ZnS nanocrystals can be regarded as being amorphous. It was found that, compared with that of the bulk ZnS, the optical absorption edge of ZnS nanoparticles shifts to a longer wavelength. We believe that the amorphous surface layers of ZnS nanocrystals can mainly be responsible for the observed redshift of the optical absorption edge.
Sub-pJ operation of broadband asymmetric Fabry–Perot all-optical gate with coupled cavity structure
Authors: Akiyama Tomoyuki , Tsuchiya Masahiro , Kamiya Takeshi
Published: July 2002

We report on all-optical gating characteristics of a novel low-temperature-grown asymmetric Fabry–Perot (AFP) device, in which improvement of performance with respect to conventional AFP all-optical switches is achieved by a short and coupled cavity configuration. Sub-pJ (∼800 fJ) operation is realized with a high contrast ratio (>10 dB) over a broad wavelength range (∼7 nm). Even for 250 fJ pump pulses, a contrast ratio of >6 dB is obtained over a 4 nm wavelength range.
Effect of gravitational acceleration on temperature wave propagation in a critical fluid
Authors: Ishii Koji , Maekawa Toru , Azuma Hisao , Yoshihara Shoichi , Onishi Mitsuru
Published: July 2002

Temperature propagation near the critical point of a classical fluid is investigated theoretically. The governing equations of thermal energy transfer near the critical point are introduced and a linear analysis is carried out. The dispersion relation between the angular frequency and the wave number is obtained and the wave characteristics are discussed. The effect of gravitational acceleration on the temperature wave propagation is made clear. Through this analysis, the following results were obtained; (1) The propagation speed of temperature waves is γ/(ρ0κT),where γ, ρ0, and κT are, respectively, the ratio of specific heats, the density, and the isothermal compressibility, with or without gravity if the wavelength is larger than 10−3.(2) The amplitude of wave increases with time in the antigravitational direction and decreases in the gravitational direction but the decay time is long if the wave number is small. (3) Waves decay quickly if the wave number is larger than 104.
Magnetization reversal in long chains of submicrometric Co dots
Authors: Martı́n J. I. , Nogués J. , Schuller Ivan K. , Van Bael M. J. , Temst K. , Van Haesendonck C. , Moshchalkov V. V. , Bruynseraede Y.
Published: July 2002

Long chains of 400 nm diam Co dots prepared by combined electron-beam lithography exhibit interesting magnetotransport properties. The magnetoresistance of the chains of dots is markedly different from single Co films, indicating a strongly modified magnetization reversal process. Magnetic force microscopy (MFM) shows that, after magnetic saturation, in the remanent state the single-domain dots are all oriented with their magnetic moment along the chain. A comparison of the magnetoresistance and the MFM reveals that the magnetization reversal occurs by coherent rotation of the magnetic moment in the single-domain dots forming the chain.
Existence of two-dimensional absolute photonic band gaps in the visible
Authors: Barra A. , Cassagne D. , Jouanin C.
Published: July 2002

Using the plane wave method, we study two two-dimensional structures that possess absolute photonic band gaps: the triangular and the graphite photonic crystals. We compare their convenience in achieving photonic crystals which inhibit the propagation of visible electromagnetic waves. We show that this is very difficult to obtain with a triangular structure because its gap is too narrow and its dimensions are too small to be fabricated. On the contrary, wider gaps and larger dimensions that can easily be etched makes graphite a much more appropriate structure.
Atomic force microscope lithography on carbonaceous films deposited by electron-beam irradiation
Authors: Avramescu Adrian , Ueta Akio , Uesugi Katsuhiro , Suemune Ikuo
Published: July 2002

A nanometer-scale mask that can be used for selective growth or selective etching was obtained by two-stage patterning. In the first step, a microscopic patterning was performed using a scanning electron microscope (SEM). In the SEM the mask was deposited by decomposition of residual oil molecules in the vicinity of the semiconductor surface. In the second stage, patterning of the carbonaceous film was made using an atomic force microscope (AFM). Use of the AFM assures not only a precise alignment with the previous marks but also a better resolution. Applying an electric bias between the conductive tip and the substrate surface previously covered with the carbonaceous film gave the local modification of the film composition. Further etching resulted in the pattern formation on the semiconductor surface with a minimum linewidth of ∼22 nm.
Characterization of Si pn junctions fabricated by direct wafer bonding in ultra-high vacuum
Authors: Hobart K. D. , Twigg M. E. , Kub F. J. , Desmond C. A.
Published: July 2002

The electrical characteristics of pn junctions formed by direct bonding of silicon wafers in ultra-high vacuum have been quantified. The bonding process produces low reverse leakage <1 μA/cm2 and near-ideal forward current. The observation of bulk-like bonded interfaces is supported by transmission electron microscopy and infra-red transmission imaging.
Spectrum of thermal fluctuation noise in diffusion and phonon cooled hot-electron mixers
Authors: Burke P. J. , Schoelkopf R. J. , Prober D. E. , Skalare A. , Karasik B. S. , Gaidis M. C. , McGrath W. R. , Bumble B. , LeDuc H. G.
Published: July 2002

A systematic study of the intermediate frequency noise bandwidth of Nb thin-film superconducting hot-electron bolometers is presented. We have measured the spectrum of the output noise as well as the conversion efficiency over a very broad intermediate frequency range (from 0.1 to 7.5 GHz) for devices varying in length from 0.08 μm to 3 μm. Local oscillator and rf signals from 8 to 40 GHz were used. For a device of a given length, the spectrum of the output noise and the conversion efficiency behave similarly for intermediate frequencies less than the gain bandwidth, in accordance with a simple thermal model for both the mixing and thermal fluctuation noise. For higher intermediate frequencies the conversion efficiency decreases; in contrast, the noise decreases but has a second contribution which dominates at higher frequency. The noise bandwidth is larger than the gain bandwidth, and the mixer noise is low, between 120 and 530 K (double side band).
Temperature dependence of the Fermi level in low-temperature-grown GaAs
Authors: Chen Y. H. , Yang Z. , Wang Z. G. , Li R. G.
Published: July 2002

A variable-temperature reflectance difference spectroscopy study of GaAs grown by molecular beam epitaxy at low-temperature GaAs (LT-GaAs) shows that the Fermi level is mostly determined by the point defects in samples annealed at below 600 °C and can be shifted by photoquenching the defects. The Fermi level is otherwise almost temperature independent, leading to an estimated width of the defect band of 150 meV in the as-grown sample. For LT-GaAs annealed at 850 °C, the Fermi level is firmly pinned, most likely by the As precipitates.
Intensity and polarization switching behaviors of light emission induced with a scanning tunneling microscope
Authors: Wu Zhanghua , Nakayama Tomonobu , Qiao Shan , Aono Masakazu
Published: July 2002

By applying voltage pulses across the tunnel junction, switching behaviors of the intensity and the polarization of light emission induced with a scanning tunneling microscope (STM) are observed. The STM images taken subsequently indicate that these switching behaviors are caused by a cluster with asymmetric shape on the nanometer scale being transferred between the sample and the tip by the pulse applied. Possible mechanisms for the switching behaviors are discussed. These observations could find applications in photonic devices on the nanometer scale.
Energy levels of Zn in Si1−XGeX alloys
Authors: Voß S. , Bracht H. , Stolwijk N. A. , Kringho/j P. , Nylandsted Larsen A.
Published: July 2002

Deep level transient spectroscopy measurements were performed on Zn-doped Si1−XGeX with X between 0 and 0.34. Our investigations reveal two deep hole traps which are attributed to the acceptor states Zn0/− and Zn−/2− of substitutional Zn. Taking into account band-offset data for Si1−XGeX, we have found that the energy level related to Zn0/− is horizontally aligned across the composition-dependent band gap which gives evidence for a highly localized defect state. The defect level related to the second hole trap decreases with increasing Ge content.
Repetition-rate multiplication in actively mode-locked fiber lasers by higher-order FM mode locking using a high-finesse Fabry–Perot filter
Authors: Sarwar Abedin Kazi , Onodera Noriaki , Hyodo Masaharu
Published: July 2002

We demonstrate an FM mode-locking technique for multiplying the pulse repetition rate of lasers by several times above the modulation frequency. The mode locking of the laser is based on the generation of higher-order FM sidebands by an intracavity phase modulator and the periodic selection of the sidebands by an intracavity high-finesse Fabry–Perot filter at spacings of free spectral range which is a harmonic of the modulation frequency. We show the generation of stable, uniformly spaced, equal amplitude optical pulses from a fiber ring laser with two-, three-, and fourfold enhancement in the repetition rate.
ZnSe-based blue-green lasers with a short-period superlattice waveguide
Authors: Ivanov S. , Toropov A. , Sorokin S. , Shubina T. , Lebedev A. , Kop’ev P. , Alferov Zh. , Lugauer H.-J. , Reuscher G. , Keim M. , Fischer F. , Waag A. , Landwehr G.
Published: July 2002

We report the successful application of alternatively strained short-period superlattices for the waveguide region of optically pumped and injection room-temperature ZnSe-based lasers operating within the 470–523 nm spectral range. The design of optically pumped ZnMgSSe/ZnSSe/ZnCdSe lasers provides extremely low threshold power densities due to the enhanced electronic and optical confinement. Room-temperature BeMgZnSe/ZnCdSe injection lasers with threshold current density of about 750 A/cm2 and characteristic temperature as high as 366 K are demonstrated. The peculiarities of carrier transport across the short-period superlattices are explained by a thermally activated mechanism.
Crystallographic wet chemical etching of GaN
Authors: Stocker D. A. , Schubert E. F. , Redwing J. M.
Published: July 2002

We demonstrate well-controlled crystallographic etching of wurtzite GaN grown on c-plane sapphire using H3PO4, molten KOH, KOH dissolved in ethylene glycol, and NaOH dissolved in ethylene glycol between 90 and 180 °C, with etch rates as high as 3.2 μm/min. The crystallographic GaN etch planes are {0001}, {101̄0}, {101̄ 1̄}, {101̄ 2̄}, and {101̄3}. The vertical {101̄0} planes appear perfectly smooth when viewed with a field-effect scanning electron microscope. The activation energy is 21 kcal/mol, indicative of reaction-rate limited etching.
Excitation of Er3+ ions in silicon dioxide films thermally grown on silicon
Authors: Kozanecki A. , Stepikhova M. , Lanzerstorfer S. , Jantsch W. , Palmetshofer L. , Sealy B. J. , Jeynes C.
Published: July 2002

We investigate photoluminescence (PL) and photoluminescence excitation spectroscopy of Er3+ ions implanted into SiO2 films thermally grown on silicon wafers. We show that at 10 K the Er3+ PL excited with the 514.5 nm line of an Ar laser is limited by the total number of Er ions, whereas at resonant excitation within the 960–1000 nm range the PL efficiency is rather concentration limited. Some samples were codoped with Yb3+ ions to study sensitization of the 4f–4f PL of Er3+ ions. At resonant excitation the presence of Yb leads to an enhancement of the Er3+ PL only at dilute Er concentrations.
HF-chemical etching of the oxide layer near a SiO2/Si(111) interface
Authors: Miyata Noriyuki , Watanabe Heiji , Ichikawa Masakazu
Published: July 2002

The HF-chemical etching process near the SiO2/Si(111) interface (<1 nm) is investigated by scanning reflection electron microscopy and microprobe Auger electron spectroscopy. The HF etching of the SiO2 layer thermally grown on an atomically flat Si(111)-7×7 surface progresses in a layer-by-layer manner, and then the final layer of oxide (∼0.3 nm) is removed in a two-dimensional void expansion with the H-terminated Si surface. This very uniform HF etching is thought to reflect the structural anisotropy of the SiO2 layer formed near the SiO2/Si(111) interface.
Crossed anisotropies in FeB/CoSiB bilayers induced by the bowed-substrate sputtering technique
Authors: Garcia D. , Castaño F. J. , Prados C. , Vázquez M. , Castaño F.
Published: July 2002

FeB/CoSiB bilayers were deposited onto bowed glass substrates using the radio frequency sputtering technique. On removing the bilayers from the sputtering chamber, a magnetoelastic anisotropy was induced due to the compressive stress developed when the substrates recovered their initial planar shape. The bulk magnetic behavior was investigated using magnetometry techniques over a wide temperature range (5–350 K). The surface magnetism was analyzed using room-temperature Kerr magnetometry. Due to the positive/negative magnetostrictive nature of each of the layers deposited, the induced anisotropies are found to be crossed. Evidence of crossed anisotropies is obtained from the surface hysteresis loops as well as from the low-temperature thermomagnetic behavior.
Majority- and minority-carrier traps in Te-doped AlInP
Authors: Wu Y. R. , Sung W. J. , Lee W. I.
Published: July 2002

The properties of deep levels found in Te-doped AlInP grown by metal–organic chemical vapor deposition have been studied. By using pn-junction structure, both minority- and majority-carrier traps can be observed. Two deep levels are found in Te-doped AlInP: one majority-carrier trap and one minority-carrier trap. The activation energies of majority- and minority-carrier traps are 0.24±0.05 and 0.25±0.03 eV, respectively. The majority-carrier trap is uniformly distributed, indicating that this level belongs to some kind of bulk defect.
Microstructural study of optically degraded ZnCdSe quantum wells
Authors: Tomiya S. , Noguchi H. , Sanaka Y. , Hino T. , Taniguchi S. , Ishibashi A.
Published: July 2002

The defect structure of optically degraded ZnCdSe quantum wells was investigated using transmission electron microscopy. The defects were composed of the dislocation dipoles with a Burgers vector of b=−(a/2)[101] inclined at 45° to the (001) plane. The dislocation dipoles consist of two segments aligned along the [11̄0] direction and the [120] direction. The [11̄0] dipole segments lying in the (111̄) plane were developed by the recombination-enhanced dislocation glide process, while the [1̄2̄0] dipole segments lying in the (2̄11) plane were developed by the recombination-enhanced dislocation climb process. Both processes operate simultaneously.
Capacitance–voltage characteristics of liquid crystal displays with periodic interdigital electrodes
Authors: Chen C.-J. , Sarma K. R. , Kolosovskaya A.
Published: July 2002

Capacitance–voltage properties of the liquid crystal displays (LCD) with periodic interdigital electrodes (PIE) are characterized. The extreme capacitances at high and low driving voltages are derived analytically, based on the technique of conformal mapping. Its validity is verified by carrying out the two-dimensional simulations numerically. The results of theoretical modeling agree reasonably well with the capacitance measurement of an LCD with PIEs.
1.5 μm infrared photoluminescence phenomena in Er-doped porous silicon
Authors: Stepikhova M. , Palmetshofer L. , Jantsch W. , von Bardeleben H. J. , Gaponenko N. V.
Published: July 2002

We analyze the photoluminescence (PL) in nanoporous Si (po-Si) doped with Er by electrochemical deposition and by spin-on doping. Two kinds of optically active Er centers appear in electrochemically doped po-Si with the main sharp and intense lines at 1.548 and 1.539 μm, respectively. The features characteristic for the spin-on doping method are: intense dislocation-related PL at 1.53 μm and strong luminescent activity of the silica gel used for Er doping. High-temperature PL observed up to 360 K is attributed to Er centers incorporated in the silica-like matrix at the oxidized surface of electrochemically doped po-Si and in erbium-containing silica gel.
65 GHz InGaAs/InAlGaAs/InP waveguide-integrated photodetectors for the 1.3–1.55 μm wavelength regime
Authors: Kollakowski St. , Strittmatter A. , Dröge E. , Böttcher E. H. , Bimberg D. , Reimann O. , Janiak K.
Published: July 2002

We report on ultrafast waveguide-integrated metal-semiconductor-metal photodetectors based on low pressure metal organic chemical vapor deposition grown semiinsulating InP/InGaAs/InAlGaAs/InP layers. The vertically coupled detectors have an internal coupling efficiency of >90% at 1.3 and 1.55 μm wavelength for detector lengths of 30 μm. A 3 dB bandwidth of 65 GHz at 1.55 μm wavelength is achieved by employing 0.3 μm feature-size finger electrodes and an active layer thickness of 150 nm. Furthermore, we present results on high-performance devices with a buried waveguide structure fabricated by regrowth of InP:Fe.
Ballistic transport of electrons in T-shaped quantum waveguides
Authors: Debray P. , Raichev O. E. , Rahman M. , Akis R. , Mitchel W. C.
Published: July 2002

Ballistic transport of electrons through T-shaped quantum waveguides with stubs of small lithographic area (0.075 μm2) has been studied. Measurements of the conductance G at 90 mK as a function of the top gate voltage, which changes the stub height, show well-defined, almost periodic oscillations in G. A theoretical analysis, involving estimation of the shape and size of the device under gate biases and computation of the transmission probabilities from numerical analysis of the Schrödinger equation, successfully explains the main features of the experimental observations. The observed minima in G can be attributed to reflection resonances of electron waves from the resonant states of the stub cavity. This work establishes the potential of electron stub tuners in microelectronics applications.
Effects of a low-energy ion beam on the growth of titanium nitride layers near the interface of a polyimide
Authors: Abramowitz Peter , Kiene Michael , Ho Paul S.
Published: July 2002

In this letter two different growth methods, reactive evaporation and ion-assisted reactive evaporation, were used to grow titanium nitride films on the polyimide biphenyl tetracarboxylic acid dianhydride-para phenylene diamine. The films were examined with x-ray photoemission spectroscopy and it was found that the chemical properties of the film depend on the distance from the polyimide/titanium nitride interface. While both techniques produced very similar films at distances greater than 5 nm from the interface, only the ion-assisted grown film had a significant amount of nitride near the interface. This is due to the ability of low-energy (100 eV) nitrogen ions to break the initial titanium/polyimide bonds which would otherwise prevent the growth of titanium nitride at the interface.
Direct transition at the fundamental gap in light-emitting nanocrystalline Si thin films
Authors: Toyama Toshihiko , Kotani Yoshihiro , Shimode Akihito , Okamoto Hiroaki
Published: July 2002

Optical transitions at the fundamental gaps of 1.20–1.37 eV are observed at 293 K directly by electroreflectance (ER) spectroscopy in nanocrystalline Si (nc-Si) thin films, from which photoluminescence (PL) with dominant peak energies of 1.65–1.75 eV is observed. Also observed by ER are optical transitions at 2.2 and at 3.1–3.4 eV. With a decrease in the mean crystal size from ∼3 nm to below 2 nm, the transition energy of the fundamental gap is increased and the ER signal is intensified. The band-gap widening would be due to quantum confinement in Si nanocrystals, and the increased signal indicates the appearance of direct transitions. In conjunction with the ER results, the PL mechanisms have been discussed.
Donor–acceptor-pair spectroscopy of GaAs grown in space ultravacuum
Authors: Neu G. , Teisseire M. , Freundlich A. , Horton C. , Ignatiev A.
Published: July 2002

Selective pair luminescence has been used to identify shallow acceptor levels in undoped GaAs epilayers grown by molecular beam epitaxy (MBE) in the ultrahigh vacuum of space generated in the wake of the free-flying Wake Shield Facility satellite (Space Shuttle Endeavor mission STS69). The low-temperature photoluminescence spectra are typical of high-purity GaAs. Unlike for conventional MBE-grown undoped GaAs where the near-band-edge excitonic luminescence is dominated by acceptor-bound excitons, the space-grown GaAs near-band-edge luminescence was found to be dominated by donor-bound excitons. The comparison of measured ground (1S3/2) and excited acceptor states to published acceptor spectra leads to the identification of CAs as the main residual acceptor impurity in the layer. Furthermore, the existence of a donor–acceptor-pair emission band demonstrates that a second acceptor is electronically active. Excited-state spectroscopy clearly identifies the second residual acceptor as ZnGa, which is scarcely observed for GaAs samples grown in terrestrial MBE systems. In addition, the absence of a Be impurity, introduced in large quantities to the growth environment prior to the epilayer growth, suggests a minimized memory effect on the free flyer as opposed to terrestrial chambers.
A robust and powerful green light photoemission source: The ferroelectric ceramics
Authors: Doria A. , Gallerano G. P. , Giannessi L. , Giovenale E. , Boscolo I. , Parafioriti R. , Porcari A. , Scurati A. , Castellano M. , Catani L. , Ferrario M. , Patteri P. , Tazzioli F. , Handerek J.
Published: July 2002

The photoemission characteristics of ceramic disks of lead zirconate titanate lanthanum doped (PLZT), have been investigated. We observe 1 nC of extracted charge under an accelerating field of 20 kV/cm in poor vacuum conditions. The emission is clearly limited by space charge effects. The extrapolated quantum efficiency results in ≈10−6. The yield of a PLZT ceramic in the ferroelectric state and its slope versus light intensity have turned out higher than those of antiferroelectric ceramic. Samples in different experimental configurations have shown different nonlinear yields.
A potential method to correlate electrical properties and microstructure of a unique high-Tc superconducting Josephson junction
Authors: Verbist K. , Lebedev O. I. , Van Tendeloo G. , Tafuri F. , Granozio F. Miletto , Di Chiara A. , Bender H.
Published: July 2002

A method to correlate microstructure from cross-section transmission electron microscopy (TEM) investigations and transport properties of a single well characterized high-Tc artificial grain boundary junction is reported. A YBa2Cu3O7−δ 45° twist junction exhibiting the typical phenomenology of high-Tc Josephson weak links was employed. The TEM sample preparation is based on focused ion beam etching and allows to easily localize the electron transparent area on a microbridge. The reported technique opens clear perspectives in the determination of the microstructural origin of variations in Josephson junction properties, such as the spread in Ic and IcRN values and the presence of different transport regimes in nominally identical junctions.
The effects of misfit dislocation distribution and capping layer on excess stress
Authors: Jin Zhi , Yang Shuren , Wang Benzhong , An Haiyan , Ma Chunsheng , Liu Shiyong
Published: July 2002

It is generally accepted that in the buried strained-layer structure, the strain is relaxed by paired misfit dislocations: one at the upper interface and the other at the lower interface. But, experimentally it is not so. In this letter, the effect of a mixture of single and paired misfit dislocations is incorporated in the formula of excess force. In this formula, the effects of the capping layer with arbitrary thickness and the interaction of misfit dislocations at different interfaces are also included. Based on the formula, the excess stresses are derived. These formulas can be used to predict the excess stress of strained layers with arbitrary heterostructure structures. They also can describe the transition process from the single-kink to the double-kink mechanism.
Threshold reduction of stimulated Brillouin scattering by the enhanced Stokes noise initiation
Authors: Kim Hyun Su , Kim Sung-Ho , Ko Do-Kyeong , Lim Gwon , Cha Byung Heon , Lee Jongmin
Published: July 2002

A method of threshold reduction for stimulated Brillouin scattering (SBS) has been demonstrated in a SBS medium combined with a laser dye. It is based on the enhanced Stokes noise initiated by additional field with a Brillouin-shifted frequency component emitted from the laser dye in the SBS medium. Rhodamine 6G dye dissolved in SBS medium (ethanol), which was pumped by a 570 nm wavelength laser, was used to prove the SBS threshold reduction by the additional Stokes fields. The SBS threshold of this solution was reduced to a level about four times lower than that of the pure SBS medium. Also, the experimental results were investigated using the modified formula for the SBS threshold.
Degenerate four-wave mixing experiments on GaN in the quasistationary regime
Authors: Haag H. , Gilliot P. , Lévy R. , Hönerlage B. , Briot O. , Ruffenach-Clur S. , Aulombard R. L.
Published: July 2002

In order to determine the third order of the nonlinear susceptibility χ(3) of GaN, we perform degenerate four-wave mixing measurements in a two-beam configuration at low temperature on a GaN epilayer on sapphire substrate. We measure the excitation spectrum of χ(3) close to the exciton resonances. Besides the χ(3) contribution, higher orders of the nonlinear susceptibility show already up around 10 kW cm−2, leading to a saturation of the signal. Results are complemented by a study of the influence of a band-to-band excitation (ℏωP=4.02 eV) on the nonlinear susceptibility.
Laser-induced capillary wave at air/liquid interfaces in time domain
Authors: Yasumoto Kaori , Hirota Noboru , Terazima Masahide
Published: July 2002

The capillary wave at air/liquid interfaces is detected by the forced Brillouin and Rayleigh light scattering in the time domain. The forced Brillouin scattering signal from the air/water surface shows clear oscillation. The wave is not pure sine or cosine wave but it shows dual features. A strongly overdamped signal is observed from the air/hexanol surface in 1.4–2.0×106 m−1, while the signal shows a trace of oscillation in a lower wave number region. The oscillation also indicates the existence of two waves. The mechanism to create the capillary wave by the photothermal effect is discussed.
All-optical inverter operating at 1.53 μm laser in erbium yttrium aluminum garnets
Authors: Maeda Yoshinobu
Published: July 2002

An all-optical inverter derived from the negative nonlinear absorption effect was demonstrated in erbium–yttrium aluminum garnet crystals using 1.53 μm laser diode. The effect was obtained at wavelengths of 1532 to 1534 nm in absorption spectra corresponding to the transition from the I15/24 to the I13/24 levels in Er3+ for sample lengths greater than 1.0 mm. The reversed-phase transmitted wave forms were observed at modulation frequencies from 1 kHz to 1 GHz. The negative nonlinear absorption effect can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion.
Experimental time-domain study of THz signals from impulse excitation of a horizontal surface dipole
Authors: McGowan R. W. , Grischkowsky D.
Published: July 2002

Using optoelectronic techniques with sub-ps resolution, we have characterized the electric-field time-domain response from an impulsively excited, micron-sized dipole antenna on a dielectric surface. When detected by an adjacent dipole antenna 400 μm distant, two primary signals are observed, a far-field pulse reflected from the back surface of the substrate and a surface-wave pulse. The surface-wave pulse appears as two distinct surface-propagating pulses despite originating from the dipole simultaneously.
Piezoelectrically induced electronic confinement obtained by three-dimensional elastic relaxation in III–V semiconducting overhanging beams
Authors: Fierling G. , Letartre X. , Viktorovitch P. , Lainé J. P. , Priester C.
Published: July 2002

In this work, we demonstrate theoretically that the piezoelectric effect can be used to achieve confinement over quantum distances in systems grown on [001] GaAs substrates. Such an effect can be achieved by making use of elastic relaxation of micromachined strained structures. At the free corners of the overhanging beams, shear deformations appear which induce a three-dimensional V-shape potential. Calculations show the creation of quantum dots near the corners of the overhanging beams.
A model of radiative recombination in n-type porous silicon–aluminum Schottky junction
Authors: Balucani M. , Bondarenko V. , Franchina L. , Lamedica G. , Yakovtseva V. A. , Ferrari A.
Published: July 2002

It is common knowledge that silicon emits visible light in its breakdown condition, but it is also known to have low efficiency. In this letter, we report an in-depth analysis of data for light emitting devices based on porous silicon. A theoretical model of luminescence from reverse biased p-n junction has been developed for this n-type porous silicon–aluminium Schottky junction to explain the higher efficiency of these electroluminescence devices in comparison with that from a reverse biased p-n junction structure. Through this model, it is possible to understand the steps that are necessary to improve the efficiency of porous-aluminum Schottky junction.
Low-field magnetostriction in an annealed Co–30% Fe alloy
Authors: Chen L. H. , Klemmer T. J. , Mavoori H. , Jin S.
Published: July 2002

Magnetostriction properties of a deformed and annealed Co–Fe alloy have been investigated. A significant magnetostriction value greater than ∼110×10−6 was obtained in a cold-rolled and recrystallized sample at a practical, low field of ∼100 Oe, while the as-cold-rolled sample gave a small magnetostriction of only ∼15×10−6 for the same applied field. Cold rolling and recrystallization produces much smaller magnetostriction in the longitudinal direction than the transverse direction in the low-field regime. The saturation magnetostriction of the recrystallized Co–Fe alloy was ∼140×10−6. The drastic dependence of the magnetostriction behavior on the alloy processing is tentatively attributed to the microstructure and texture changes brought about by the heat-treatment processing. The availability of such a high magnetostriction in low applied fields using a ductile and low-cost alloy material can be useful for various technical applications.
Characterization of femtosecond self-pumped phase conjugation in BaTiO3
Authors: Yang Changxi , Minoshima K. , Seta K. , Matsumoto H.
Published: July 2002

We report the generation and characterization of the self-pumped phase conjugation of 450 nm femtosecond pulses in BaTiO3. The pump beam is incident on the crystal from the −c face of the crystal. We suggest that the transmission grating exclusively contribute to the self-pumped phase conjugation and that the femtosecond self-pumped phase conjugator operate with a mechanism of holographic grating sharing. The self-pumped phase conjugate pulses are narrower than the transmitted pulses. The pulse width of the self-pumped phase conjugation increases as the incident angle. The angular dispersion caused by the air crystal interface and the dynamic gratings compensates for the material dispersion of the crystal, leading to narrower reflected pulses from the phase conjugator.
In situ photoexpansion measurements of amorphous As2S3 films: Role of photocarriers
Authors: Ganjoo Ashtosh , Ikeda Y. , Shimakawa K.
Published: July 2002

To understand the dynamics of photoinduced volume expansion (PVE) in amorphous chalcogenides, in situ PVE (time evolution of thickness changes during illumination) measurements have been performed. Two distinct behaviors, transient and metastable PVE, have been observed. A strong correlation between the changes in thickness and photocurrent is reported.
Application of selective removal of mesa sidewalls for high-breakdown and high-linearity Ga0.51In0.49P/In0.15Ga0.85As pseudomorphic transistors
Authors: Lour Wen-Shiung , Chang Wen-Lung , Liu Wen-Chau , Shie Yung-Hsin , Pan Hsi-Jen , Chen Jing-Yuh , Wang Wei-Chou
Published: July 2002

High-linearity Ga0.51In0.49P/In0.15Ga0.85As pseudomorphic high electron-mobility transistors have been successfully fabricated and demonstrated in both direct-current and alternating-current performance. Together with a wide-gap Ga0.51In0.49P gate insulator, a gate-to-drain breakdown voltage of 33 V is further improved to over 40 V by selectively removing mesa sidewalls. The transconductance and current density of a 1×100 μm2 device at room temperature (77 K) are 90 (120) mS/mm and 646 (780) mA/mm, respectively. The measured fT and fmax are 12 and 28.4 GHz, respectively. These are consistent with 1 μm gate devices when the parasitic capacitance is reduced by selectively removing mesa sidewalls.
Investigations on the performance of multiquantum barriers in short wavelength (630 nm) AlGaInP laser diodes
Authors: Raisch P. , Winterhoff R. , Wagner W. , Kessler M. , Schweizer H. , Riedl T. , Wirth R. , Hangleiter A. , Scholz F.
Published: July 2002

Al 0.5 In 0.5 P/Ga 0.5 In 0.5 P superlattice structures have been investigated as multiquantum barriers (MQB) in 630 nm band laser diodes in order to reduce thermal current losses. By inserting an optimized MQB, we have succeeded in improving both threshold currents and characteristic temperatures of such devices. However, the optimized dimensions of the MQB found experimentally deviated strongly from those predicted theoretically, indicating that the commonly used theoretical description assuming effective mass approximation, electron wave interference, and using transfer matrix calculation is not adequate.
Influence of single-ion anisotropy fluctuations on temperature-driven reorientation transition in two-dimensional ferromagnets
Authors: Hu Liangbin , Li Haijin , Tao Ruibao
Published: July 2002

The influence of single-ion anisotropy fluctuations on the temperature-driven reorientation transition in two-dimensional ferromagnets is studied. We show that in the presence of the spatial fluctuations of the single-ion anisotropy constants, the temperature-driven perpendicular to in-plane reorientation transition should be a continuous transition, and there are temperature regions in which both the perpendicular and in-plane magnetization are nonzero, in agreement with experimental observations.
Patterning of hydrogen-passivated Si(100) using Ar(3P0,2) metastable atoms
Authors: Hill S. B. , Haich C. A. , Dunning F. B. , Walters G. K. , McClelland J. J. , Celotta R. J. , Craighead H. G.
Published: July 2002

We describe the patterning of silicon by exposing a hydrogen-passivated Si(100) surface to Ar(3P0,2) metastable atoms through a fine Ni grid in the presence of a small background pressure of oxygen. Metastable atom impact leads to the formation of a uniform oxide layer that is sufficiently resistant to chemical etching to allow feature depths ≳20 nm to be realized. With optical manipulation of the incident metastable atoms, this technique could provide the basis for massively parallel nanoscale fabrication on silicon without the use of organic resists.
Analytic expressions for impact ionization rates and secondary particle energy distributions in semiconductors
Authors: Childs P. A. , Dyke D. W.
Published: July 2002

Analytic expressions are obtained for the energy dependent impact ionization rate and secondary particle energy distribution functions in semiconductors based on the random-k technique. By approximating the conduction and valence band structure by a simple parabolic energy dispersion the impact ionization rate in semiconductors is found to have the form ∝(E−ET)7/2. The analytic expressions obtained for the secondary particle energy distribution functions are found to give excellent agreement with results obtained from a rigorous full band structure analysis for the case of silicon. By extending the model to multiple parabolic bands which emulate the true density of states a good agreement with results obtained on the basis of the full band structure is obtained for a range of semiconductor materials.
Actively mode-locked erbium fiber ring laser using a Fabry–Perot semiconductor modulator as mode locker and tunable filter
Authors: Li Shenping , Chan K. T.
Published: July 2002

A wavelength-tunable actively mode-locked erbium fiber ring laser was demonstrated using a Fabry–Perot semiconductor modulator. The modulator played the simultaneous roles of an intensity mode locker and a tunable optical filter. Stable single- or dual-wavelength nearly transform-limited picosecond pulses at gigabit repetition rates were generated. Continuous wavelength tuning was achieved by simply controlling the temperature of the modulator. Pulse train with a repetition rate up to 19.93 GHz (eight times the driving frequency) was obtained by using rational harmonic mode-locking technique.
The role of macroscopic transport phenomena in film microstructure during epitaxial growth
Authors: Vlachos D. G.
Published: July 2002

A multiscale integration hybrid algorithm is introduced to describe film microstructure in epitaxial growth under conditions where fluid mechanics and transport phenomena in the adjacent fluid phase are important, such as in chemical vapor deposition at relatively high pressures. This algorithm is demonstrated in a stagnation point flow reactor. It is shown that mass transfer limitations delay the transition from the step flow to the two-dimensional nucleation growth mode, as the substrate temperature decreases, and could possibly eliminate kinetic microroughening. Furthermore, the temporal development of morphological features upon changes in operating conditions is determined by the bulk convective flow.
Combined laser and atomic force microscope lithography on aluminum: Mask fabrication for nanoelectromechanical systems
Authors: Abadal G. , Boisen A. , Davis Z. J. , Hansen O. , Grey F.
Published: July 2002

A direct-write laser system and an atomic force microscope (AFM) are combined to modify thin layers of aluminum on an oxidized silicon substrate, in order to fabricate conducting and robust etch masks with submicron features. These masks are very well suited for the production of nanoelectromechanical systems (NEMS) by reactive ion etching. In particular, the laser-modified areas can be subsequently locally oxidized by AFM and the oxidized regions can be selectively removed by chemical etching. This provides a straightforward means to define the overall conducting structure of a device by laser writing, and to perform submicron modifications by AFM oxidation. The mask fabrication for a nanoscale suspended resonator bridge is used to illustrate the advantages of this combined technique for NEMS.
Study of ground-state titanium ion velocity distributions in laser-produced plasma plumes
Authors: Martin G. W. , Weaver I. , Williamson T. P. , El-Astal A. H. , Riley D. , Lamb M. J. , Morrow T. , Lewis C. L. S.
Published: July 2002

The velocity distribution of ground-state titanium ions within a low-temperature plasma resulting from the laser ablation of a titanium target has been investigated. A KrF excimer laser was focused onto the target at moderate fluences (<10 J cm−2) in vacuum (∼2×10−5 Torr). Time-of-flight distributions were determined as functions of distance from target and laser fluence using absorption spectroscopy. The results were found to be described consistently by a Maxwell–Boltzmann distribution with zero flow velocity. The most probable velocity was found to scale with the square root of the incident laser fluence.
Influence of illumination on the properties of Bi2Sr2CaCu2O8+y bicrystal grain boundary junction
Authors: Gilabert A. , Plecenik A. , Medici M. G. , Grajcar M. , Karlovsky K. , Dittman R.
Published: July 2002

We observed a significant persistent change in the transport properties [current–voltage characteristics I(V) and resistance versus temperature R(T) curves] of bicrystal Bi2Sr2CaCu2O8+y grain boundary tunnel junctions by illumination with visible light. After illumination, the I(V) curves show a decrease of the energy gap while the R(T) curves show an increase of the critical temperature of the junction. We have also observed a characteristic temperature T*≃260 K above which the photoinduced conductivity is suddenly removed. These experiments can be understood as an increase of the doping by light in the oxygen depleted Bi2Sr2CaCu2O8+y grain boundary which is thought to be underdoped.
Vertical integration of a spin dependent tunnel junction with an amorphous Si diode
Authors: Sousa R. C. , Freitas P. P. , Chu V. , Conde J. P.
Published: July 2002

This work demonstrates integration of magnetic tunneling junctions with hydrogenated amorphous silicon (a-Si:H) diodes. In the finished device 11.4% current change is measured when the junction free layer is switched in an external magnetic field, for 0.86 V applied to the junction-diode series. In the integrated device, the measured individual tunneling magnetoresistance signal is 25.3% at 7 mV bias, demonstrating junction robustness and process compatibility. The junction-diode series is necessary for bit selectivity in magnetic random access memories. Vertical growth of these devices may allow higher density architectures.
Demonstration of high-brightness-mode propagation in a compound waveguide structure
Authors: Patchell J. A. , Logue F. P. , O’Gorman J. , Hegarty J. , Usievich B. A. , Sychugov V. A.
Published: July 2002

We demonstrate the existence of an unusual and useful high-brightness guided mode of a multimode AlGaAs/GaAs heterostructure compound slab waveguide. This mode has a narrow near-field single lobe confined to the low-index regions of the waveguide. This mode was selectively probed by optically exciting quantum wells optimally placed in the waveguide. By pumping in a stripe geometry, lasing is observed above a threshold of 80 kW/cm2 indicating efficient lasing in the highest-order waveguide mode. The near-field emission pattern of the waveguide was imaged to provide a direct measurement of the intensity profile of the higher-order mode.
Measurement of fluid properties with a near-field acoustic sensor
Authors: Patois R. , Vairac P. , Cretin B.
Published: July 2002

The proposed microsensor is derived from the electromechanical resonator of our ac force microscope: the scanning microdeformation microscope (SMM). A submillimetric spherical probe immersed in the fluid sample replaces the tip usually used in SMM. This sphere is connected to a cantilever, which is excited at the resonance frequency. The measurement of the resonance frequency and of the damping enables the quantitative characterization of the investigated fluid. A theoretical approach allows to model the system behavior. The model takes into account two aspects: the mechanical vibration of the cantilever and the fluid mechanics. The values predicted by the model are in good agreement with the experimental measurements performed for various viscous media.
Wavelength-tunable actively mode-locked erbium-doped fiber ring laser using a distributed feedback semiconductor laser as mode locker and tunable filter
Authors: Li Shenping , Chan K. T.
Published: July 2002

A wavelength-tunable actively mode-locked erbium fiber ring laser was demonstrated using a distributed feedback semiconductor laser as an intensity mode locker and a tunable optical filter. Very stable optical pulse trains at gigabit repetition rates were generated using harmonica mode locking. The supermode noise was suppressed to 60 dB below the signal level and the root-mean-square timing jitter (0.45 kHz–1 MHz) was found to be about 1% of the pulse duration. A continuous wavelength tuning range of 1.8 nm was achieved by changing the semiconductor laser temperature from 11.4 to 30 °C.