bluuebunny/crossref_metadata_2025 huggingface dataset:
Three photon induced fluorescence from a conjugated organic polymer for infrared frequency upconversion
Authors: Davey A. P. , Bourdin E. , Henari F. , Blau W.
Published: July 2002

Solutions of a paraphenylene ethynylene copolymer simultaneously absorb three photons of intense near infrared radiation. When the polymer relaxes, it emits visible radiation which can be seen clearly by the naked eye. Intensity dependent transmission studies have been used to measure α3, the three photon absorption coefficient. The value obtained for a 10−3 M solution of the polymer is 10−22 cm3 W−2, which is remarkably large in view of the low concentration employed.
Molecular beam epitaxy of p-type conducting ZnSe and ZnSSe by simple nitrogen gas doping without plasma activation
Authors: Hishida Yuji , Yoshie Tomoyuki , Yagi Katsumi , Yodoshi Keiichi , Niina Tatsuhiko
Published: July 2002

Highly conducting p-type ZnSe and ZnSSe were fabricated by simple N2 gas doping during molecular beam epitaxial growth without the use of any activation method, such as discharge and cracking. p-type conduction in the N2-gas doped ZnSe is produced by a shallow N acceptor state, which is obtained only when the dopant N2 pressure is higher than 10−5 Torr. When the N2 pressure was varied from 3.2×10−5 to 1×10−4 Torr, the net acceptor concentration of N2-gas doped ZnSe and ZnS0.06Se0.94 films ranged from 3×1015 to 2×1017 cm−3 and from 1×1016 to 2.5×1017 cm−3, respectively. Light emitting diodes with a N2-gas doped p-cladding layer were fabricated and tested.
Stability of growing front of YBa2Cu3Ox superconductor in the presence of Pt and CeO2 additions
Authors: Kozlowski Gregory , Svobodny Thomas
Published: July 2002

Distinctive microstructures of textured YBa2Cu3Ox (123) superconductors were examined by scanning electron microscopy and metallurgical microscopy. The samples were synthesized under a residual thermal gradient by using a modified melt textured growth on a Y2BaCuO5 (211) substrate. Also, the unidirectional solidification by a zone-melting method was performed to fabricate 123 superconducting bars up to 12 cm long placed on the 211 substrate in the horizontal arrangement, with a growth rate R=0.5 mm/h and a temperature gradient of G=20 °C/cm (G/R=400 °C h/cm2). A ramping temperature of 1 °C/h (GR) was applied in both syntheses. Typical defects running parallel to (001) planes associated with 211 trapped particles were observed (so-called platelet structure). Besides these, unusual defects were observed running parallel to (100) and (010) planes in textured 123+Pt superconductors, and interpreted as the result of an instability of the planar front in the presence of fine 211 particles. A theoretical model of planar interface stability confirms a strong dependence of stability region on the size of 211 particles in the melt.
Trapping force by a high numerical-aperture microscope objective obeying the sine condition
Authors: Gu Min , Ke P. C. , Gan X. S.
Published: July 2002

A commercial high numerical-aperture microscope objective is designed in terms of the sine condition which is needed for two-dimensional space-invariant imaging. The axial trapping efficiency generated by an objective obeying the sine condition is found to be approximately up to 50% smaller than the prediction for an objective obeying the tangent condition which has been currently used in the ray optics theory for trapping force calculations. Our result is in good agreement with the measured value of the trapping efficiency.
Thermo-optic tuning sensitivity of phase matched second-harmonic generation in 2-amino-5-nitropyridinium-dihydrogen crystals
Authors: Khodja S. , Josse D. , Zyss J.
Published: July 2002

The thermal sensitivity of the efficient type II angular phase matching configuration for frequency doubling in 2-amino-5-nitropyridinium-dihydrogen crystals has been measured accurately. The measured thermo-optic tuning sensitivity was found to be −0.303 mrad/ °C. A wavelength shift of the noncritical phase-matching angle resulting from the thermal effect is shown to correspond to a dλ/dT coefficient of 0.176 nm/ °C.
A cryogenic fiber maker for continuous extrusion
Authors: Aliaga-Rossel R. , Bayley J.
Published: July 2002

A cryogenic fiber maker that continuously extrudes fibers is presented. The design of the fiber maker is based on the use of two cooling stages maintained at different temperatures. The fiber maker consists of two copper reservoirs that are connected in series and are kept at different temperatures. The first reservoir is used to liquefy the gas coming in from an external gas line. The second reservoir is colder than the first; here, the liquid that comes from the first reservoir is frozen and later extruded using the pressure of the external line gas supply. A two-stage closed-cycle refrigerator (a Gifford–McMahon cooler), which uses helium as a working fluid, is used as a cooling system. The frozen gas is extruded through a stainless-steel capillary nozzle with internal diameters between 50 and 250 μm and a length of 2 mm. The temperature of the two reservoirs is set independently, which permits the extrusion rate of the fibers to be controlled and to produce the fibers continuously. Using this system, hydrogen, deuterium, nitrogen, and argon fibers of various diameters were extruded.
1 pm spectrally narrowed ArF excimer laser injection locked by fourth harmonic seed source of 773.6 nm Ti:sapphire laser
Authors: Kasamatsu T. , Tsunekane M. , Sekita H. , Morishige Y. , Kishida S.
Published: July 2002

We have achieved spectrum narrowing to 1 pm in a high-power ArF excimer laser injection locked by an all solid-state fourth harmonic (193.4 nm) seed source of 773.6 nm Ti:sapphire laser radiation. Superior laser properties such as sufficient output energy (90 mJ/pulse, 50 pps), locking efficiency exceeding 90%, wavelength drift less than 0.4 pm, and spectrum bandwidth fluctuation less than 0.2 pm were obtained, which meet the requirements for 1 Gbit dynamic random access memory microlithography.
High efficiency surface emitting lasers using blazed grating outcouplers
Authors: Hagberg Mats , Eriksson Niklas , Larsson Anders
Published: July 2002

Grating coupled surface emitting lasers with rectangular as well as blazed grating outcouplers were investigated. Horizontal cavity InGaAs/AlGaAs laser oscillators, with two rectangular first order surface gratings as feedback elements, were integrated with single detuned rectangular or blazed second order gratings as surface output couplers, using electron beam lithography and chemically assisted ion beam etching. Superior differential quantum and surface emission efficiencies of 56% and 84%, respectively, were measured for lasers with optimized blazed output couplers.
Depth dependent collection functions in thin film chalcopyrite solar cells
Authors: Scheer R. , Knieper C. , Stolt L.
Published: July 2002

Electron beam induced current experiments in the planar geometry are performed on Mo/CuInX2/CdS/ZnO thin film solar cells where X is S, Se. We measure the collection efficiency of cells as a function of the beam energy and subsequently identify the depth dependent collection function. For CuInS2 devices an effective diffusion length of 1.0±0.1 μm and a depletion layer of 0.05±0.03 μm is determined. The collection function of a CuInSe2 cell points towards a low recombination rate at the back contact and a diffusion length exceeding 3 μm.
Subpicosecond optical sampling spectrometer using asynchronous tunable mode-locked lasers
Authors: Takagi Y. , Adachi S.
Published: July 2002

We have developed a subpicosecond nondegenerate pump-probe spectrometer based on the optical sampling technique using a combination of asynchronous tunable femtosecond lasers. Owing to its simple instrumentation, time evolution of subpicosecond to nanosecond excited molecular processes in solution and of exciton relaxation processes in semiconductor multiple quantum wells has been detected on an oscilloscope by an effective time base magnification of 760 000 times. Fast acquisition of the temporal profiles and ease of wavelength scanning allowed compilation of time-resolved absorption and excitation spectra. A possible extention of the spectrometer with one of the light sources being a synchrotron radiation instead of the femtosecond laser is discussed.
Table-top soft x-ray lasers
Authors: Rocca J. J.
Published: July 2002

This article reviews the progress in the development of practical table-top sources of soft x-ray laser radiation. The field is rapidly approaching the stage at which soft x-ray lasers sufficiently compact to fit onto a normal optical table will be routinely utilized in science and technology. This is the result of recent advances in the amplification of soft x-ray radiation in both compact laser-pumped and discharge-pumped devices. The use of excitation mechanisms that take full advantage of new ultrafast high power optical laser drivers and multiple pulse excitation schemes has resulted in the demonstration of saturated soft x-ray amplification at wavelengths as short as 14 nm using several Joule of laser-pump energy. Moreover, several schemes have demonstrated significant gain with only a fraction of a Joule of laser-pump energy. In addition, the demonstration of saturated table-top soft x-ray lasers pumped by very compact capillary discharges has shattered the notion that discharge-created plasmas are insufficiently uniform to allow for soft x-ray amplification, opening a route for the development of efficient, high average power soft x-ray lasers. Recently, a table-top capillary discharge laser operating at 46.9 nm has produced millijoule-level laser pulses at a repetition rate of several Hz, with a corresponding spatially coherent average power per unit bandwidth comparable to that of a beam line at a third generation synchrotron facility. This review summarizes fundamental and technical aspects of table-top soft x-ray lasers based on the generation of population inversions in plasmas, and discusses the present status of development of specific laser systems.
The dependence of ultrashallow junction depths on impact dose rates
Authors: Sultan A. , Craig M. , Reddy K. , Banerjee S. , Ishida E. , Maillot P. , Neil T. , Larson L.
Published: July 2002

Ultrashallow junctions (∼60 nm) are obtained using low energy BF2 (5 keV) implants in crystalline Si. The variation of junction depth as a function of the dose rate is studied for doses of 1×1014 and 1×1015 cm−2. Boron diffusion is retarded in the tail region for the higher dose rates and consequently the junction depth decreases as compared to the lower dose rates. The residual defect density after a 950 °C, 10 s anneal for a dose of 1×1015 cm−2 is reduced for the higher dose rate as compared to the lower dose rate.
The role of transient ion-induced defects in ion beam-assisted growth
Authors: Kellerman B. K. , Chason E. , Floro J. A. , Picraux S. T. , White J. M.
Published: July 2002

Low-energy ion bombardment, concurrent with growth, can control and improve many aspects of film growth, but confirming the atomistic mechanism responsible for these effects has been difficult. We present a simple picture of ion beam-assisted deposition as the interaction of growth-induced and ion-induced surface defects (adatoms and vacancies). We use kinetic Monte Carlo simulations to demonstrate that low-energy ion bombardment in conjunction with growth produces a smoother surface morphology than either growth or ion bombardment alone by destabilizing surface clusters and promoting step flow growth.
Room-temperature optically pumped blue-green vertical cavity surface emitting laser
Authors: Jeon H. , Kozlov V. , Kelkar P. , Nurmikko A. V. , Chu C.-C. , Grillo D. C. , Han J. , Hua G. C. , Gunshor R. L.
Published: July 2002

Surface emitting laser operation at room temperature at λ=496 nm by ps pulsed optical injection has been demonstrated in a II–VI separate confinement heterostructure containing three 80 Å thick (Zn,Cd)Se quantum wells (QW). The vertical cavity was formed by low loss, dielectric, distributed Bragg mirrors, yielding a quality factor for the structure of approximately Q≊2000. The room-temperature threshold excitation corresponds to an absorbed optical energy density of 1.4 μJ/cm2 or, equivalently, to an estimated electron-hole pair density of 1×1012 cm−2. At T=200 K, quasicontinuous wave operation was obtained at an average output power of up to 1 mW and an output/input conversion efficiency of 20%.
Study on self-built optical path production in Ce-doped BaTiO3 stimulated photorefractive scattering self-pumped phase conjugator
Authors: Mu Xiaodong , Shao Zongshu , Zhang Jingwen , Zhang Liangmin , Jiang Minhua , Luo Haosu , Zhong Weizhuo
Published: July 2002

The observations on the stimulated photorefractive scattering self-pumped phase conjugator (SPS-SPPC) in Ce-doped BaTiO3 demonstrate that the self-built pumped paths in the SPS-SPPC are induced by the scattering seeds. Using these results, a formation mechanism of the SPS-SPPC is presented, which is related to the scattering seeds, the contradirectional two-wave mixing, and four-wave mixing. The production conditions of the pumped paths are also given. The studies show that both too short and too long distances from the scattering seed to the region of the four-wave mixing will bring about a failure in building the optical paths, and the large backscattering coefficient is always advantageous to produce these paths.
Stability hierarchy of the pseudomorphic FeSi2 phases: α, γ, and defected CsCl
Authors: Miglio Leo , Tavazza Francesca , Malegori Giovanna
Published: July 2002

We present a total-energy stability diagram of FeSi2 phases which explains the recent experimental findings of pseudomorphic epitaxy on Si(111), depending on film thickness and growth conditions. In particular, our tight binding calculations point out that the appearance of the fluorite structure (γ) at very low coverages can only be attributed to a binding energy with the silicon substrate sizeably larger than tetragonal (α) and CsCl-defected phases.
Multimode fiber-optic sensor using photorefractive double phase conjugator
Authors: Kamshilin Alexei A. , Jaaskelainen Timo , Khomenko A. V. , Garcia-Weidner A.
Published: July 2002

An optical sensing scheme for measuring the mode phase shifts and mode amplitude modulation in a multimode fiber is proposed. The scheme uses a double phase conjugator based on photorefractive fiberlike Bi12TiO20 (BTO) crystal that allows to detect high speed changes of environmental conditions with adaptation for slow variations. An acoustic sensor based on the proposed scheme is used to demonstrate the scheme’s feasibility.
Passivation of GaAs(111)A surface by Cl termination
Authors: Lu Z. H. , Chatenoud F. , Dion M. M. , Graham M. J. , Ruda H. E. , Koutzarov I. , Liu Q. , Mitchell C. E. J. , Hill I. G. , McLean A. B.
Published: July 2002

It is found that an ordered and air-stable GaAs(111)A–(1×1)–Cl surface can be produced by chemical etching/passivation with dilute HCl solution. The synchrotron polarization-dependent Cl K-edge x-ray absorption near-edge structure and x-ray photoelectron spectroscopy studies showed that the surface is terminated with Ga–Cl bonds oriented along the surface normal. Low-energy electron diffraction studies showed a bulklike (1×1) structure on the Cl-terminated GaAs(111)A surface. The Cl termination eliminates surface band-gap states caused by surface oxides. Photoluminescence measurements showed a dramatic increase in the near-band radiative emission rate corresponding to reduction in the occupied surface band-gap states. A reduction of surface gap states by Cl termination was confirmed by surface photovoltage measurements.
New electron irradiation induced electron trap in epitaxially grown Si-doped n-GaAs
Authors: Auret F. Danie , Goodman Stewart A. , Meyer Walter E.
Published: July 2002

The defects induced by electron irradiation in epitaxially grown Si-doped n-GaAs were investigated by deep level transient spectroscopy. In addition to observing the well-known E1–E3 radiation induced defects, we detected another electron trap, Eβ3, with electronic properties, although similar to those of E3, not identical. Eβ3 is metastable and thus its energy level can be reproducibly removed by hole injection at 90–130 K and reintroduced by annealing above 160 K. We could induce Eβ3 by electron irradiation in Si-doped GaAs, but not in undoped GaAs.
Improvement in electrical properties of buried SiO2 layers by high-temperature oxidation
Authors: Mrstik B. J. , McMarr P. J. , Hughes H. L. , Anc M. J. , Krull W. A.
Published: July 2002

The density of defects in the buried oxide of implanted oxide silicon-on-insulator material which cause low resistance paths between the substrate and top silicon layer has been greatly reduced by high temperature oxidation. The mechanism for this is the diffusion of oxygen through the top silicon layer to the buried oxide, where it oxidizes chains of silicon atoms.
Measurement of the refractive index of GaInAs/InP quantum wells by a grating coupling technique
Authors: Skouri El Mostafa , Martin Patrick , Chusseau Laurent , Alibert Claude , Coriasso Claudio , Campi Domenico , Cacciatore Carmelo
Published: July 2002

Effective indices of modes propagating in multiple GaInAs wells on InP barriers (MQW) waveguides are accurately measured in the 1.4–1.75 μm wavelength range using the grating coupling technique. Quantum size effects cause a selective polarization absorption and high birefringence, strongly depending on wavelength. The temperature dependence of refractive index and absorption originating from the temperature-dependent band gap is also observed. In the transparency region the refractive indices of GaInAs wells in InP barriers are deduced for two well widths using a multilayer slab waveguide model and an exciton model based on Lorentzian oscillator.
Z-scan studies and optical limiting in a mode-locking dye
Authors: Kumar G. Ravindra , Rajgara F. A.
Published: July 2002

The optical nonlinearity of a mode-locking dye (Kodak 9740) under picosecond excitation at 532 nm, is studied using the Z-scan technique. Theoretical fits to the data give a value of 3.2 cm/GW for the two-photon absorption coefficient (β) and −2.1×10−5 cm2/GW for the real part (γ) of the nonlinearity. In addition, we demonstrate optical limiting using two-photon absorption as well as self-defocusing.
Luminescence properties of submicron features fabricated by using magnetron reactive ion etching with different sample biases
Authors: Freiler M. , McLane G. F. , Kim S. , Levy M. , Scarmozzino R. , Herman I. P. , Osgood R. M.
Published: July 2002

Deep-etch-defined GaAs/Al0.3Ga0.7As square features of multiquantum well material, with dimensions as small as 160 nm, have been fabricated using magnetron reactive ion etching (MIE). Luminescence spectroscopy shows confinement of charge carriers to the features’ center. The effects of rf power and etching time on the luminescence efficiency of these features and its concomitant etch-induced damage are examined.
Diamond nucleation by seeding from the gas phase
Authors: Ajji Z. , Buck M. , Wöll Ch.
Published: July 2002

In a hot-filament reactor diamond films were deposited on various substrates without pretreatment. A nickel wire placed at a short distance above the substrate yields an increase of the nucleation density by five orders of magnitude. Closed diamond films were obtained for different substrate materials. The deposits were characterized by scanning electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. The presence of Ni in the diamond films indicates that Ni containing species are transported through the gas phase during the reaction to the substrate surface thus forming nucleation centers. Replacing the Ni wire by a diamond membrane nucleation enhancement is reduced by about three orders of magnitude. The pronounced distance dependence observed suggests that volatile unstable species are produced which form nucleation centers upon impact on the substrate surface.
Growth and interfacial evolution of oriented C60 overlayers on Au(111)
Authors: Fartash A.
Published: July 2002

High-quality C60(111) overlayers are grown on Au(111)/Ag(111)/mica substrates and their structures studied by x-ray diffraction. The structural evolution of these overlayers is investigated for growth temperatures from 120 to 290 °C. C60(111) overlayers undergo an in-plane orientational reordering at To∼150 °C. Above this temperature, the rotated and commensurate in-plane structures coexist with each other. The rotated structures evolve from the in-plane structures, which predominate at temperatures below To.
Origins of interfacial disorder in GaSb/InAs superlattices
Authors: Thibado P. M. , Bennett B. R. , Twigg M. E. , Shanabrook B. V. , Whitman L. J.
Published: July 2002

The interface surfaces of short-period GaSb/InAs superlattices grown by molecular beam epitaxy have been studied in situ with scanning tunneling microscopy. Migration enhanced epitaxy was used at the interfaces in order to control bond type. Interfaces on GaSb(001) are found to be smoother than those on strained InAs(001), and the InSb-like interfaces are smoother than GaAs-like ones. The primary source of disorder at these interfaces appears to be the kinetically determined topography of the growth surfaces, with intermixing playing a secondary role.
Influence of the position of deep levels on generation-recombination noise
Authors: Godoy A. , Palma A. , Jiménez-Tejada J. A. , Carceller J. E.
Published: July 2002

Power spectral density due to deep traps has been calculated in a junction field effect transistor (JFET) by a numerical procedure. Distribution of potential, density of carriers, and occupation factors were evaluated for any point of the structure. Different effects were found depending on the depth of the trap considered, such as spectra different from the pure Lorentzian shape or anomalous behavior of the noise amplitude with reverse voltage applied. The explanation of these effects may be useful for the characterization of midgap levels produced in JFETs under irradiation stress. Good agreement is achieved with the experiment.
Novel current–voltage characteristics in an InP-based resonant-tunneling high electron mobility transistor
Authors: Chen K. J. , Maezawa K. , Yamamoto M.
Published: July 2002

We report novel current–voltage characteristics in an InP-based resonant-tunneling high electron mobility transistor (RTHEMT). This device incorporates a pseudomorphic InGaAs/AlAs/InAs resonant-tunneling diode into the source of a nonalloyed ohmic contact InAlAs/InGaAs high electron mobility transistor. Both pronounced negative differential resistance and negative transconductance are observed at room temperature. Most significantly, a near-flat valley current is obtained in the output current–voltage characteristics. This feature is achieved by the nonalloyed ohmic contact cap layer structure employed in the HEMT, which significantly reduces the parasitic resistance. The novel characteristics of RTHEMTs should lead to many attractive circuit applications.
Femtosecond carrier dynamics in low-temperature grown Ga0.51In0.49P
Authors: Kostoulas Y. , Ucer K. B. , Wicks G. W. , Fauchet P. M.
Published: July 2002

Pump-probe spectroscopy is used to determine the dynamics of carriers in thin films of Ga0.51In0.49P grown at temperatures of 500, 300, and 200 °C. The carrier trapping time τtr, is found to be ∼0.2 ps for the 200 °C sample and ∼0.9 ps for the 300 °C sample. Annealing of the 200 °C sample at 450 °C for 10 min causes the optical response to slow appreciably (τtr∼0.7 ps), indicating that the point defects are directly responsible for the ultrashort optical response observed in this material.
Real and reciprocal space mapping of the mosaic dispersion in self-nucleated AlxGa1−xN thin films on (00.1) sapphire
Authors: Kistenmacher T. J. , Wickenden D. K. , Hawley M. E. , Leavitt R. P.
Published: July 2002

Measures of the mosaic dispersion of a series of self-nucleated AlxGa1−xN thin films, grown by low-pressure metalorganic chemical vapor deposition in a nitrogen carrier gas, have been accumulated by a combination of reciprocal space x-ray scattering patterns and real space images from scanning tunneling and atomic force microscopies. The films are shown to be dense mosaics of highly oriented islands whose in-plane and out-of-plane orientational coherence and in-plane island size decrease with increasing x. The highly correlated reductions in island size and orientational coherence are believed to be attributable to a decrease in surface mobility of reactants, which is independent of nucleation layer or carrier gas.
Calculation of gain-current characteristics in ZnCdSe-ZnSe quantum well structures including many body effects
Authors: Rees P. , Logue F. P. , Donegan J. F. , Heffernan J. F. , Jordan C. , Hegarty J.
Published: July 2002

The gain-spontaneous recombination characteristics have been calculated for a 40 Å Zn0.8Cd0.2Se-ZnSe quantum well including many body effects. We examine the effect of the inclusion of the Coulomb enhancement on the gain spectra and the gain-current relationship. We show that, in the absence of the Coulomb enhancement, the threshold current density of a 340 μm 40 Å Zn0.8Cd0.2Se-ZnSe quantum well laser is underestimated by approximately 40% and the lasing wavelength overestimated by 4 nm. Our calculation of the scattering lifetime for the first electron-heavy hole transition gives a lifetime varying between 29 and 37 fs, and shows that the carrier-phonon scattering mechanism in II-VI quantum wells is more dominant than in III-V materials. We also comment on the effect the neglect of Coulomb enhancement has on the calculation of leakage currents in a laser at threshold.
Very intensive red light emission from C60 trapped in 13X molecular sieve
Authors: Gu Gang , Ding Weiping , Cheng Guangxu , Zang Wengceng , Zen Hao , Du Youwei
Published: July 2002

Very intensive red light emission from C60 trapped in 13X molecular sieve has been observed, and it is attributed to the active forbidden transition of C60 anion due to the interaction of C60 with the sketch structure of 13X molecular sieve.
Picosecond laser dynamics of gain-coupled and index-coupled InGaAs/InGaAlAs quantum well distributed feedback lasers
Authors: Kovač J. , Schmidt H. , Kaden C. , Hofsäss V. , Gauggel H. P. , Schweizer H. , Hase A. , Künzel H.
Published: July 2002

High frequency modulation of gain-coupled (GC) and index-coupled (IC) InGaAs/InGaAlAs distributed feedback (DFB) lasers is investigated. Laser dynamics of conventionally fabricated IC DFB lasers are compared with GC DFB lasers realized by the new technology of masked implantation enhanced intermixing. Band structure dependence of the modulation response at low temperature (T=2K) is analyzed by detuning the emission energy of the DFB lasers with respect to the gain maximum using different grating periods. Pulse widths decreasing from 53 ps down to 4.5 ps with increasing emission energy demonstrate the capability of both coupling types. The experimental results are in excellent agreement with a theory without any fit parameter based on laser rate equations.
Preparation and characterization of Cu(In1−xGax)3Se5 thin films
Authors: Negami Takayuki , Kohara Naoki , Nishitani Mikihiko , Wada Takahiro , Hirao Takashi
Published: July 2002

Polycrystalline Cu(In1−xGax)3Se5 thin films were prepared by four source evaporation with controlling and shielding of the molecular beams from elemental sources. Ga content x, can be controlled by deposition times of CuIn3Se5 and CuGa3Se5 layers, which form Cu(In1−xGax)3Se5 films through the interdiffusion. X-ray diffraction analyses showed that the films with x≲0.5 have an ordered vacancy chalcopyrite and the films with x≳0.5 have a zinc blende structure. The optical band gap of the films linearly increased from 1.23 eV (x=0) to 1.85 eV (x=1) with increasing Ga content. The conductivity of the films was about 10−6/Ω cm and about 10−7/Ω cm under and above x=0.3, respectively.
Optical properties of Ca3Mn2Ge3O12
Authors: Sugg B. , Gnatchenko S. L. , Faust B. , Rupp R. A.
Published: July 2002

Tetragonal calcium manganese germanium garnet (Ca3Mn2Ge3O12) is determined to be optically negative. An analysis of the angular dependence of the transmission for a-cut crystals reveals the presence of dichroism. Absorption is largest for extraordinarily polarized light. Both properties allow to determine and orient the crystallographic axes of Ca3Mn2Ge3O12 samples.
Low-damage processing of CdTe(110) surfaces using atomic hydrogen
Authors: Luo Y. , Slater D. A. , Osgood R. M.
Published: July 2002

We present the results of an AES, XPS, and LEED study of the reaction of oxide and contaminant overlayers on the CdTe(110) surface with atomic hydrogen. Exposure of an oxidized surface to a flux of atomic hydrogen produced by ‘‘cracking’’ ambient molecular hydrogen on a hot tungsten filament results in a rapid, quantitative removal of the oxide overlayer with substrate temperatures as low as 300 K to produce a stoichiometric surface free of contaminants which has sufficient surface order to produce a sharp (1×1) LEED pattern.
Pyroelectric PbSc0.5Ta0.5O3/Y1Ba2Cu3O7−x thin-film heterostructures
Authors: Björmander C. , Sreenivas K. , Grishin A. M. , Rao K. V.
Published: July 2002

A highly c-axis oriented PbSc0.5Ta0.5O3/Y1Ba2Cu3O7−x (0.5 μm/0.2 μm) thin-film heterostructure has been grown in situ on LaAlO3 substrates using a Nd:YAG pulsed laser deposition system. The ferroelectric phase transition in the PbSc0.5Ta0.5O3 thin film is broadened, and suppressed to 195 K with a maximum dielectirc permittivity of εmax′ (1 kHz)=950. The observed low loss tangent tan δ=0.063 and high pyroelectric coefficient dP/dT=4.8×10−4 Cm−2 K−1 at 195 K renders PbSc0.5Ta0.5O3 films promising for pyroelectric sensor applications. Furthermore, the dielectric properties are easily controlled by the dc bias electric field E. The field dependence of the reduced polarizability αE2/3 is found to be a universal function of (T/Tc−1)E−2/3 over the wide temperature range 77–300 K. This universal behavior is quantitatively explained in the framework of the Landau mean field theory.
Investigation of minority carrier trapping in n-type doped ZnSe using photoluminescence decay measurements
Authors: Massa J. S. , Buller G. S. , Walker A. C. , Simpson J. , Prior K. A. , Cavenett B. C.
Published: July 2002

Temperature dependent photoluminescence decay measurements have been used to study the minority carrier dynamics in iodine-doped ZnSe grown by molecular beam epitaxy. The existence of three deep acceptor levels with energies at 80, 120, and 350 meV above the valence band has been established. The 80 and 120 meV levels have a density dependence directly related to the iodine doping density whilst the level at 350 meV does not. Significant broadband donor–acceptor emission is observed from this material and appears to be associated with the acceptor level at 350 meV.
A simple velocity model for low-pressure metalorganic chemical vapor deposition
Authors: Aktik Cetin , Belkouch Said
Published: July 2002

A new simple transport model is used to describe the dependence of the electrical characteristics of the epitaxial layer on the growth parameters in low-pressure metalorganic chemical vapor deposition. The important parameters of this model are the mean velocity of the gases and the [V]/[III] ratio. Undoped GaAs epitaxial layers are prepared at various operating pressures. A semi-empirical correlation relating the reactor pressure and flow rate is established that dictates the operating conditions for a single set of film properties. This enables growth of a material with constant characteristics while pressure can be varied.
Influence of thermal cycling on the levitation force of melt-textured YBaCuO
Authors: Ullrich M. , Leenders A. , Freyhardt H. C.
Published: July 2002

The influence of thermal cycling on the levitation force of VGF melt-textured YBaCuO is investigated. With an increasing number of thermal cycles from room temperature down to the boiling point of liquid nitrogen the levitation force is decreasing. This decrease could be explained by the generation and propagation of cracks inside the melt-textured domains which decrease the radii of the screening currents. Furthermore, water condensed at the surface of the superconductor leads to a decomposition of the superconducting Y1Ba2Cu3O7−δ phase and the formation of large nonsuperconducting areas.
Photoelectron spectra enhanced by x-ray total reflection and diffraction from periodic multilayer
Authors: Hayashi Kouichi , Kawato Shin’ichi , Horiuchi Toshihisa , Matsushige Kazumi , Kitajima Yoshinori , Takenaka Hisataka , Kawai Jun
Published: July 2002

Photoelectron spectra from a periodic multilayer of (Mo/B4C)30/Si were measured by changing the x-ray glancing angle. The angular dependencies of the photoelectron intensities of O 1s and Mo 3d revealed the atomic depth profiles of the Mo oxide overlayer, and the compositions of the MoO3 upper layer and MoO2 lower layer. Furthermore, we observed enhancement of photoelectron emission by means of x-ray standing waves generated near the multilayer surface during x-ray diffraction from the superlattice.
Magnetic coupling in amorphous Co–Dy–B and Fe–Dy–B alloys
Authors: Krishnan R. , Driouch L. , Kayzel F. E. , Franse J. J. J. M.
Published: July 2002

We have studied the magnetization of amorphous Co–Dy–B and Fe–Dy–B alloys at 1.5 K under very high fields up to 35 T. Above a critical field the antiferromagnetic coupling breaks as indicated by the strong increase in the magnetization. This is explained by a model. The analysis of this behavior enables us to obtain some important parameters of fundamental interest, such as, the molecular field coefficient, the exchange integral, etc.
Resonant Raman scattering from phonons in GaAs/(GaAs)m(AlAs)n quantum wire structures
Authors: Maciel A. C. , Freyland J. M. , Rota L. , Kiener C. , Ryan J. F. , Marti U. , Martin D. , Morier-Gemoud F. , Reinhart F. K.
Published: July 2002

Raman spectroscopy has been used to measure phonons in GaAs v-groove quantum wire structures containing (001) and (111) GaAs/AlAs superlattice barrier regions. Resonance enhancement permits the identification of modes in different regions of the structure, and the measured phonon frequencies provide structural information which shows clear evidence of GaAs migration during growth from (001) surfaces into the grooves. Confined and interface phonons with large in-(111) plane wavevectors are observed.
Degenerate-four-wave-mixing of fullerene doped inorganic glass
Authors: Liu Huimin , Taheri Bahmam , Jia Weiyi , Lin Fucheng , Mao Sen
Published: July 2002

A very recently developed high Tm (melting temperature) optical glass doped with C60/C70 molecules has been studied. Using a picosecond laser operating at 532 nm, the observed time-resolved degenerate-four-wave-mixing (DFWM) spectra show remarkable changes with addition of fullerene into the glass host.
Carrier profile for In0.35Ga0.65As/GaAs multiquantum well lasers from capacitance–voltage measurements
Authors: Arias J. , Esquivias I. , Ralston J. D. , Larkins E. C. , Weisser S. , Rosenzweig J. , Schönfelder A. , Maier M.
Published: July 2002

The carrier profile for MBE grown In0.35Ga0.65As/GaAs multiquantum well laser structures with nominally undoped and beryllium-doped active regions was determined by using the capacitance–voltage (C–V) technique at room temperature. A simple theoretical model was used to extract the impurity concentration and the quantum-well carrier density from the experimental profiles. We obtained a high carrier concentration in nominally undoped devices caused by a strong growth temperature dependent Be diffusion from the p-cladding layer, and no difference between doped samples with different nominal dopant location.
Magnetic field behavior of small sputtered step-edge junctions
Authors: Vaupel M. , Ockenfuss G. , Wördenweber R.
Published: July 2002

YBa2Cu3O7 step-edge junctions with widths down to 0.5 μm are fabricated on SrTiO3 substrates by Ar ion-beam milling of the steps, high-pressure on-axis magnetron sputtering, electron beam patterning and ion-beam etching of the microbridge. For ratios of film thickness to step height of ∼1/2 the current-voltage characteristics show Shapiro steps under microwave irradiation and resistively shunted junction like behavior. The periodic dependence of the critical current upon the magnetic field resembles a Fraunhofer pattern. The period of the current variation ΔB0 depends upon the width w of the junction according to the theoretical prediction for planar thin Josephson junctions: ΔB0=1.84φ0/w2. Junctions with widths of 0.7 μm possess a large magnetic field stability with ΔB0≊100 G. Small junctions (w<1 μm) exhibit voltage jumps in the Fraunhofer pattern, which are explained by flux penetration of single vortices into the electrodes.
Initial stage of layer-by-layer sputtering of Si(111) surfaces studied by scanning reflection electron microscopy
Authors: Watanabe Heiji , Ichikawa Masakazu
Published: July 2002

The initial stage of layer-by-layer sputtering of Si(111) surfaces with 500 eV Ar ions has been studied by using scanning reflection electron microscopy. At a moderate temperature of 900 K, vacancy islands are formed in the middle of wide terraces. At higher temperatures over 990 K, the atomic steps retreat as the ion dose is increased. The results show that layer-by-layer sputtering is characterized by vacancy creation caused by ion impact, and by thermally activated surface migration of vacancies. Moreover, the step area decorated by electron-beam-assisted carbon deposition acts as a step pinning site during the layer-by-layer sputtering.
New method for in situ control of Bragg reflector fabrication
Authors: Callard S. , Gagnaire A. , Joseph J.
Published: July 2002

A simple, robust method for real time monitoring of Bragg reflector layer thickness is described. The method is based on the choice of the appropriate ellipsometric measurement wavelength to control the deposition of the top layer. This method requires no information on the underlying structure. To evaluate the method, Bragg reflectors were developed with SiO2 and SiNx stacks grown by electron cyclotron resonance plasma chemical vapor deposition. Reflectivity measurements performed on these reflectors confirm the reproducibility and accuracy of the method.
Direct observation of second neighbor interactions for Cr4+ doped forsterite by resonance Raman scattering
Authors: Calistru Dana M. , Demos S. G. , Alfano R. R.
Published: July 2002

Fifteen Cr4+ local modes are observed using resonance Raman scattering in a Cr:Mg2SiO4 crystal, instead of a maximum of nine internal vibrations predicted by first neighbor interactions. The larger-than-predicted number of modes is explained in terms of second neighbor interactions for the Cr4+ ion. The frequency dependence of the two tetrahedral stretching modes measured at 361 and 765 cm−1 on second neighbor parameters shows a different degree of localization at the Cr4+ site for these modes.
Effect of implantation dose on photoluminescence decay times in intermixed GaAs/AlGaAs quantum wells
Authors: Piva P. G. , Charbonneau S. , Mitchell I. V. , Goldberg R. D.
Published: July 2002

The effect of ion implantation induced intermixing on the effective radiative lifetimes in GaAs/AlGaAs quantum wells is investigated using the technique of time-resolved photoluminescence (TRPL). Below the critical dose, the carrier lifetimes appear enhanced by the processing although no changes are discernible in the continuous wave photoluminescence (CWPL) spectra. Above the critical dose, carrier lifetimes are reduced by residual defects created in the intermixed wells by the implantation procedure. These observations demonstrate the greater sensitivity of TRPL over CWPL in detecting residual damage produced by processing quantum well material.
Magnetic behavior and transport properties of Hg-1201 prepared by vapor-solid reaction
Authors: Masini R. , Eggenhöffner R. , Bellingeri E. , Giannini E. , Vaccarone R.
Published: July 2002

A vapor-solid reaction performed in a two-temperature zones reactor operated at low pressure is demonstrated successfully to prepare Hg-1201 material of good superconducting properties as shown by the temperature dependence of resistivity and ZFC susceptibility. To investigate further the connectivity of the material, we performed high sensitivity magnetization measurements at very low magnetic fields and temperature. A hysteretic behavior is observed due to an intergranular critical state regime.
Effect of ion sputtering on Ge epitaxy on GaAs(110)
Authors: Wang X.-S. , Brake J. , Pechman R. J. , Weaver J. H.
Published: July 2002

The possibility that ion sputtering could be used to modify the growth mode of Ge on GaAs(110) was investigated by scanning tunneling microscopy. Analysis shows that the nucleation density was significantly increased following vacancy island creation by ion sputtering. The Ge/GaAs(110) structures were thermodynamically stable because of energy gained by saturating dangling bonds at steps. Accordingly, a uniform film could be obtained at a smaller thickness compared to conventional growth.
Modulation bandwidth of high-power single quantum well buried heterostructure InGaAsP/InP (λ=1.3 μm) and InGaAsP/GaAs (λ=0.8 μm) laser diodes
Authors: Berishev I. E. , Gorbachev A. Yu. , Mishournyi V. A. , Ilyinskaya N. D. , Stankevich A. L. , Tarasov I. S.
Published: July 2002

The construction of a high power single quantum well buried heterostructure InGaAsP/InP (λ=1.3 μm) and InGaAsP/GaAs (λ=0.8 μm) laser diode with reduced values of parasitic capacitance has been proposed and investigated. This design uses a 3.5 μm thick polyimide layer in the current confinement regions of the buried laser. The active area of the laser is surrounded by semiconductor material and the entire structure was grown by liquid phase epitaxy. Lasers with λ=1.3 μm and resonator lengths of 310, 450, and 560 μm exhibited modulation bandwidths of 8.7, 9.2, and 6.6 GHz at operating powers of 41, 72, and 91 mW, respectively. Lasers with λ=0.8 μm and a 600 μm resonator showed a 5.6 GHz modulation bandwidth at an output power of 98 mW.
Second harmonic generation in LiTaO3 thin films by modal dispersion and quasi phase matching
Authors: Armani-Leplingard Florence , Kingston John J. , Fork David K.
Published: July 2002

Green light was generated by second harmonic generation in LiTaO3 thin films grown on sapphire. We describe the optical properties of the thin films grown by rf magnetron sputtering. We report on the experimental conditions for second harmonic generation by modal dispersion and quasi phase matching. For quasi phase matching, proton exchange was used to periodically deaden the nonlinearity of the crystal.
Synchrotron radiation excited etching of diamond
Authors: Ohashi Haruhiko , Ishiguro Eiji , Sasano Tomohiko , Shobatake Kosuke
Published: July 2002

We have succeeded in synchrotron radiation (SR) excited etching of crystalline diamond. It proceeds even at low temperatures at which diamond is thermally not oxidized in the gaseous environment. It has been demonstrated that any of the three types of crystalline diamond, i.e., industrial diamond made at high pressures, thin films grown by chemical vapor deposition, and natural diamond, can be etched by irradiating SR in the O2 atmosphere. From the etched pattern obtained by placing a Ni mesh made of 40 μm wires above the sample, it has been concluded that only the irradiated area is etched and thus surface excitation by SR is essential along with the supply of reactive radical species formed by photodissociation.
A combined in situ optical reflectance–electron diffraction study of Co/Cu and Co/Au multilayers grown by molecular beam epitaxy
Authors: Emmerson C. M. , Shen T-H. , Evans S. D. , Allinson H.
Published: July 2002

The variation in optical reflectance during growth was investigated in situ for Co/Cu and Co/Au multilayers prepared in a molecular beam epitaxy (MBE) chamber, while the specular RHEED (reflection high energy electron diffraction) intensity was simultaneously monitored. The experimental reflectance data were found to agree well with the prediction of a numerical simulation. The final reflectance and the effective optical constants of the films are affected by the modulation of the multilayer structures. The RHEED data indicated different growth behaviors for Cu and Au and an unexpected drop in reflectance for the initial deposition of Cu on Co layers was confirmed. A similar effect was observed for the growth of Au on Co.
Reduction of fanning influence in two-wave mixing coefficient measurements in thick crystals
Authors: Zhang Jiasen , Gao Hong , Zhu Yong , Ye Peixian
Published: July 2002

We propose and demonstrate a new method to measure the two-wave mixing coefficient with slight influence of beam fanning in thick crystals with high coupling constants. The strong beam fanning was suppressed by introducing an additional erase beam. By measuring the effective two-wave mixing coefficient with the additional erase beam, the coupling coefficient without the additional erase beam can be calculated.
Anomalous above-threshold spontaneous emission in gain-guided vertical-cavity surface-emitting lasers
Authors: Shin J. H. , Hwang J. K. , Ha K. H. , Lee Y. H.
Published: July 2002

Anomalously large decrease in spontaneous emission is observed in gain-guided vertical-cavity surface-emitting lasers after the onset of lasing. By analyzing two-dimensional profiles of the lasing mode and carrier density, we found that this unexpected phenomenon originates from the contraction of transverse lasing mode size. Under the condition of the constant modal gain, it is explained that the above-threshold average carrier density could decrease in contradiction to the general understanding. Unless this anomalous effect is taken into account properly, nontrivial errors could occur in determination of the external quantum efficiency.
Theoretical study on intervalence band absorption in InP-based quantum-well laser structures
Authors: Cho Taehee , Kim Hyungsuk , Kwon Youngse , Hong Songcheol
Published: July 2002

Intervalence band absorptions of 1.5 μm light in various InGaAs/InGaAsP quantum well laser structures are investigated theoretically. The intervalence band absorption formalism based on 6×6 Luttinger-Kohn Hamiltonian is developed. The absorption tends to decrease with the barrier height of quantum wells. The tensile strain in the well causes the absorption to reduce, while the compressive strain causes it to increase. Also is found that the absorption decreases with increase in temperature.
Photocurrent multiplication in hydrogenated amorphous silicon staircase photodiode films
Authors: Sawada Kazuaki , Akata Shinya , Takeuchi Toshinori , Ando Takao
Published: July 2002

The available multiplication of photocurrent was observed in the a-Si:H/a-Si1−xCx:H staircase photodiode film which was fabricated by a high-vacuum plasma enhanced chemical vapor deposition on a heavily doped n-type silicon substrate. It was found that the saturated maximum gain is about 6 for the staircase photodiode having three conduction band steps. The fabrication process and device characteristics are reported in this letter.
Dynamical switching behavior of n-i-p-i modulator structures
Authors: Pfeiffer U. , Kneissl M. , Knüpfer B. , Müller N. , Kiesel P. , Döhler G. H. , Smith J. S.
Published: July 2002

We report on the ac switching behavior of surface-normal electro-optical modulators based on hetero-n-i-p-i structures. We have investigated systematically the way the transition times scale with device dimensions and present a straightforward theoretical model including sheet resistivities of n and p layers as well as contact resistances. The model is in excellent agreement with experimental data. With a voltage swing as low as 3.7 V, we achieved a single path contrast ratio in excess of 2:1 and maximum 3 dB frequencies larger than 250 MHz.