bluuebunny/crossref_metadata_2025 huggingface dataset:
High continuous wave output power InGaAs/InGaAsP/InGaP diode lasers: Effect of substrate misorientation
Authors: Mawst L. J. , Bhattacharya A. , Nesnidal M. , Lopez J. , Botez D. , Morris J. A. , Zory P.
Published: July 2002

3 W cw output power has been obtained from aluminum-free, strained-layer double-quantum well (DQW) InGaAs/InGaAsP/InGaP uncoated, 100-μm-wide stripe diode lasers (λ=0.945 μm) grown by low-pressure MOCVD on exact (100) GaAs substrates. The combination of high-band-gap (1.62 eV) InGaAsP confinement layers and the DQW structure provides relatively weak temperature dependence for both the threshold current Ith as well as the external differential quantum efficiency ηd. Furthermore, the series electrical resistance for 100 μm×600 μm stripe-contact devices is as low as 0.12 Ω. As a result, the power conversion efficiency reaches a maximum of 40% at 8×Ith, and decreases to only 33% at the maximum power (i.e., 3 W) at 28×Ith. Low-temperature (12 K) photoluminescence measurements of InGaAs/InGaAsP quantum-well structures exhibit narrow linewidths (<10 meV) for material grown on exact (100) GaAs substrates, while growths on misoriented substrates exhibit linewidth broadening, as a result of ‘‘step bunching.’’ Laser structures grown on misoriented substrates exhibit increased temperature sensitivity of both Ith and ηd, compared with structures grown on exact (100) substrates.
Design, fabrication, and characterization of a 2.3 kJ plasma focus of negative inner electrode
Authors: Mathuthu M. , Zengeni T. G. , Gholap A. V.
Published: July 2002

The design, fabrication, and characterization of a 2.3 kJ plasma focus device with negative inner electrode are discussed. The purpose of the design was to initiate research in and study of plasma dynamics, nuclear reactions, and neutron emission mechanisms at the university. Also the device will be used to teach and demonstrate plasma phenomena at the postgraduate level and to perform experiments with inverted polarity to examine different operating regimes with nonstandard gases. It is hoped that in the long run the research work will help find a solution to the polarity riddle of plasma focus devices. When the system was operated with spectrographic argon as the filling gas, the best focus was obtained at a pressure range of 0.1–1.25 Torr. With nitrogen as the filling gas, the best focus was obtained at pressures between 0.1 and 1.25 Torr. Air gave the best focus at a pressure range of 0.5–1.5 Torr. The observed good focus action is attributed to the small inner electrode length (this reduces the amount of anode material ablated into the current sheath) and tapering of the inner electrode. Positive z-directed electrons contribute to the temperature and further ionization of the plasma gas during focusing. The performance of the device compares quite well with other known devices.
Ion beam source for soft-landing deposition
Authors: Biesecker J. P. , Ellison G. B. , Wang H. , Iedema M. J. , Tsekouras A. A. , Cowin J. P.
Published: July 2002

“Soft-landing” deposition of molecular ions on various surfaces is important in making exotic radicals, modeling electrochemical double layers, and studying aqueous ion interactions. We have built a new mass-selected ion beam source for soft-landing deposition, designed to produce either positive or negative ions, including ions that depend on ion-neutral reactions (e.g., H3O+ and NH4+). The ionizer is a free jet crossed by an electron beam, producing a wide variety of positive and negative ions. The simple, short-length, planar ion deceleration minimizes defocusing and space charge effects. It currently delivers mass-selected ions with energies down to about 1 eV and currents of about 10 nA. The design allows easy maintenance. The performance of the ion beam compares favorably with previous low-energy positive ion systems.
New ion source design for ion propulsion application
Authors: Capacci M. , Noci G.
Published: July 2002

A new broad beam ion source to be used as an ion thruster for small satellites in orbit maneuvering applications has been developed at the LABEN Proel Tecnologie Division. The source uses an rf electromagnetic field with frequency in the VHF range to generate and sustain the discharge. Preliminary theoretical investigations seem to indicate that the excitation of an e-m resonant cavity mode inside the discharge chamber may be the reason for the high ionization rate found by selecting proper operating conditions of the source.
Effect of cesium on H− production in a field free region of a volume source
Authors: Nishiura M. , Sasao M. , Wada M.
Published: July 2002

The H− density and temperature in a cesium injected hydrogen discharge of the driver region of tandem H− source were investigated by use of photodetachment technique. The amount of cesium in the ion source was monitored by spectroscopic measurement. The plasma space potential, Vs, obtained from the probe I–V characteristics has increased by Cs injection. However no clear changes in ne, n−, Te, T+, and T− are observed.
Electron energy dependence of vacuum ultraviolet emission and H− production in a low-pressure hydrogen plasma
Authors: Fukumasa Osamu , Mizuki Norihisa , Niitani Eiji
Published: July 2002

A two-step process of pure H− volume production via vibrationally excited ground state molecules H2(v″⩾5) is discussed. The principal source of this vibrational excitation is through singlet excitation by fast primary electrons followed by vacuum ultraviolet (VUV) emission. The VUV emission from a low-pressure hydrogen plasma has been used to study the production mechanism of H2(v″⩾5) molecules and its electron energy dependence, in a double plasma source where both energy and density of fast electrons are well controlled. The fast electron energy and density strongly affect the VUV emission intensity at wave lengths of, for example, 123 and 124.9 nm. There exists a certain threshold in fast electron energy for singlet excitation and then for H2(v″) excitation. Fast electrons with energy in excess of 15–20 eV mainly contribute to the VUV emission intensity and are sufficient to increase H− production.
A microwave plasma cathode electron gun for ion beam neutralization
Authors: Fusellier C. , Wartski L. , Aubert J. , Schwebel C. , Coste Ph. , Chabrier A.
Published: July 2002

It is well known that there exist two distinct types of ion beam neutralization, viz., charge and current neutralization. We have designed and studied a versatile and compact microwave plasma (MP) cathode electron gun dedicated to charge as well as current neutralization. Unlike the conventional hot cathode neutralizer, this MP cathode allows operation of the electron gun in a reactive gaseous environment when it is eventually associated with an electron cyclotron resonance (ECR) ion gun. Charge neutralization can be easily carried out by extracting from the MP cathode through a 1 mm diameter hole, a 35 mA electron beam under a 20 V voltage; the MP cathode being fed with a 75 W microwave power at 2.45 GHz. Higher beam intensities could be obtained using a multiaperture thin plate. Electron beam intensities as high as 300 mA and energies of 2 keV needed for current neutralization, e.g., when an ion beam impinges onto a thick dielectric surface, are obtained via a two-stage arrangement including an anodic chamber associated with a set of three monoaperture plates for the electron beam extraction. Transport of 200–2000 eV electron beams is ensured using focusing optics composed of three aligned tubes 6 cm in diameter and unsymmetrically polarized.
Laser ion source torch for highly charged ions
Authors: Demyanov A. V. , Sidorov S. V. , Avdeev S. A. , Jatcenko B. P.
Published: July 2002

The article describes a laser ion source torch designed on the basis of a CO2 laser at Efremov Institute of Electrophysical Apparatus in collaboration with the Institute for Nuclear Research of the Ukrainian Academy of Science, Kiev. The ion extraction from the laser plasma is done by means of spherical grid electrodes. This permits to improve the efficiency several hundred times compared to the existing ion sources and to increase the ion beam correspondingly, including highly charged ions. The charge composition of the beam, the pulse frequency, and the extracted beam are determined by the operational mode of the laser.
A simple chemical etching technique for reproducible fabrication of robust scanning near-field fiber probes
Authors: Chuang Yung-Hui , Sun Kuo-Gung , Wang Chia-Jen , Huang J. Y. , Pan Ci-Ling
Published: July 2002

A two-step chemical etching procedure has been developed for fabricating probes used by scanning near-field optical microscopy. These probes have two tapered regions which can be reproducibly constructed with a wide range of cone angles. The shape of the probe allows it to be used over sample surfaces with deep and narrow regions. Furthermore, our method can be applied to silica glass fibers which are commercially available. To demonstrate, we used these tips to acquire the near-field optical image of a thin layer of polystyrene spheres. Intensity interference patterns were observed. The demonstrated in-plane resolution was estimated to be about 250 nm. This is mainly limited by the diameter of the metal-coated tip. The transmission efficiency of the tip is better than 10−4.
Differential displacement measurement using scanning x-ray beams
Authors: Canistraro Howard A. , Jordan Eric H. , Pease Douglas M.
Published: July 2002

A noncontacting method for measuring mechanical strain between two fiducial marks has been developed for use where environmental conditions would be disruptive to methods utilizing optical light. A silicon 111 Johansson crystal is used for this application where Mo Kα radiation is used to fluoresce fiducial markers made of yittria-stabilized zirconia. This substance is used for a thermal barrier coating in gas turbine engines and the technology for applying this material to withstand long term high temperature exposure is highly developed. The current system has a displacement repeatability of better than 0.1 μm which is not limited by counting statistics, but rather determined by mechanical considerations.
Broad band and absolute measurement of transient dynamic normal velocity of surface
Authors: Kim Byoung-Geuk , Enoki Manabu , Kishi Teruo
Published: July 2002

Broad band direct sensing of the transient dynamic normal velocity of an object surface and evaluating its absolute value were realized by using a sensor fabricated with a piezoelectric polyvinylidene fluoride film and a polyvinyl chloride (PVC) back load and a PVC wear plate. The transient output signal from the sensor obtained by a test employing a well-defined steplike force, at the epicenter of a steel plate, showed very good agreement with the dynamic normal velocity calculated by using a Green’s function and a simulated source function. The output was proportional to the dynamic normal velocity of the surface, and the frequency-dependent sensitivity for the velocity was flat within a deviation of ±3.8 dB for the average in the frequency range up to 2 MHz. The transient dynamic normal velocity of the surface could be absolutely determined by using a sensor calibrated by theoretical one.
An automated tracer dispersal system for snow accumulation and saltation transport investigations
Authors: Braaten David A. , Ratzlaff Kenneth L.
Published: July 2002

New automated instrumentation to assess detailed spatial and temporal dynamics of snow accumulation and saltation transport of snow in remote, harsh environments is described. The instrumentation and techniques provide important quantitative, time dependent information which current methods are incapable of providing such as precise dating of accumulated snow layers, snow grain saltation transport distance in wind-swept environments, and characteristics of wind generated surface features. This instrument consists of an ultralow power timing system, a pneumatic system, and microsphere generators to periodically disperse a tracer of colored glass microspheres onto the snow surface. Snow sampling must be conducted before melting occurs, and subsequent identification of microspheres has shown this method is capable of providing accurate dating information with detailed spatial-resolution, as well as characterizing wind blown saltation transport of snow.
Prototype negative ion sources for radioactive ion beam generation (abstract)
Authors: Alton G. D. , Welton R. F. , Williams C. , Cui B. , Murray S. N.
Published: July 2002

Radioactive ion beams (RIBs) of F17 and F18 are of interest for investigation of astrophysical phenomena such as the “hot” CNO cycle and the rp stellar nuclear synthesis processes. In order to generate useful beam intensities of atomic F−, the species must be efficiently and expediently released from the target material, thermally dissociated from fluoride release products during transport to the ionization chamber of the ion source, and efficiently ionized in the source upon arrival. We have conceived and evaluated two prototype negative ion sources for potential use for RIB generation: a direct extraction source and a kinetic ejection source. Both sources utilize Cs vapor to enhance F− formation. The mechanical design features, operational parameters, ionization efficiencies for forming atomic F− and delay times for transport of F and fluoride compounds for the respective sources are presented. The efficiency η for formation and extraction of F− for the direct extraction negative ion source is found to be η∼1.0%, while the characteristic delay time τ for transport of F and fluorides through the source is typically, η∼120 s; the analogous efficiencies and delay times for the kinetic ejection negative ion source are, respectively: η=∼3.2% and τ=∼70 s.
Characterization of a low-energy constricted-plasma source (abstract)
Authors: Anders André , Kühn Michael
Published: July 2002

The construction and principle of operation of the constricted-plasma source are described. A supersonic plasma stream is produced by a special form of a dc-glow discharge, the constricted glow discharge. The discharge current and gas flow pass through an orifice of small diameter (constriction) which causes a space charge double layer but also serves as a nozzle to gas-dynamically accelerate the plasma flow. Plasma parameters have been measured using Langmuir probes, optical emission spectroscopy, and a plasma monitor for mass-resolved energy measurements. Experiments have been done with nitrogen as the discharge gas. It was found that the energy distribution of both atomic and molecular ions have two peaks at about 5 and 15 eV, and the energy of almost all ions is less than 20 eV. The ionization efficiency decreases with increasing gas flow. The downstream plasma density is relatively low but activated species such as excited molecules and radicals contribute to film growth when the source is used for reactive film deposition.
Dynamic behavior of periodic piezoceramic-polymer composite plates
Authors: Geng Xuecang , Zhang Q. M.
Published: July 2002

The dynamic behaviors of periodic piezoceramic-polymer composite plates, especially the effect of the finite thickness on the strain distributions and resonant modes, are studied theoretically. It is found that as long as fL1<ft1, where fL1 and ft1are the thickness and first piezoelectric active stop band-edge mode frequencies, there exists a frequency f1 near fL1at which the polymer and ceramic vibrate in phase with equal amplitude in the x3 direction. The effect of the thickness of a composite plate is to change the bandwidth in which the two vibrate in unison. It is also found that due to the finite thickness effect a series of piezoelectric active modes at frequencies near and above ft1may be excited.
Power penalty due to timing jitter for lasers modulated without prebias
Authors: Dutta N. K.
Published: July 2002

For lasers modulated with a pseudorandom bit stream without prebias, the delay between the optical pulse and the current pulse depends on the number of ‘‘0’’s preceding the current pulse (‘‘1’’). Since 1’s and 0’s occur randomly in a pseudorandom bit stream and the decision circuit is designed to start sampling at a given time, this effect results in a timing jitter. The jitter induced noise and the associated power penalty are calculated. The results suggest that the ratio of the modulation current to the threshold current of the laser should be ≳25 to keep the power penalty below 1 dB at high data rates. Low threshold lasers operating without prebias are important for laser array based transmitters.
A simple and inexpensive modulated light calorimeter using an optical fiber light guide
Authors: Garfield N. J. , Howson M. A. , Overend N.
Published: July 2002

A computer controlled ac calorimeter has been constructed which uses a simple and readily available optical fiber and an infrared light-emitting diode as the heat source. The ways in which the calorimeter differs from using halogen lamp heating are discussed.
An instrument for investigating high electric field phenomena at small electrode separations
Authors: Olson R. T. , Panitz J. A.
Published: July 2002

An instrument with the tip positioning capability of a scanning tunneling microscope and the imaging capability of a field emission electron microscope has been developed. This instrument provides the ability to investigate the current-voltage characteristics of field emitter tips in the metal-vacuum, transition, and metal-vacuum-metal tunneling regimes. It also allows a field emitter tip to be imaged before and after these “close approach” measurements are made. Nonreproducible tunneling characteristics observed in the transition region have been associated with large changes in the apex of the field emitter tip.
Thermal expansion measurements of liquid metallic samples measured under microgravity conditions
Authors: Damaschke B. , Oelgeschlaeger D. , Ehrich J. , Dietzsch E. , Samwer K.
Published: July 2002

We report the method and first examples of thermal expansion measurements of liquid metallic samples measured under μg conditions. The experiments were performed in an electromagnetic levitation facility (TEMPUS facility) on board the space orbiter Columbia (mission MSL-1). The sample was imaged by a high-resolution CCD camera with on-board recording. After the mission the video tapes were analyzed by digital image processing. First measurements were made with a molten Pd78Cu6Si16 sample in the temperature range of about 800 to 1150 °C. The measured value of the coefficient of volume expansion is 8.9×10−5/°C in this temperature range.
Dependence of mode size and temporal response on the mirror contrast ratio in microcavity lasers
Authors: Deng H. , Deppe D. G. , Shin J.
Published: July 2002

Microcavity lasers with differing mirror designs are used to study the influence of the index contrast ratio on the mode size and temporal response. The experimental results demonstrate the advantages of high contrast Bragg reflectors for reducing the mode area while simultaneously increasing the laser temporal response. We suggest that the far-field angle is preferable to an effective cavity length as a characterization parameter, since the far-field angle is directly measurable and yields the photon lifetime.
High efficiency top surface-emitting lasers fabricated by four implantation using tungsten wire as mask
Authors: Liu Ying , Zhang Xiaobo , Jiang Xiuying , Liu Suping , Li Xuemei , Du Guotong , Gao Dingsan , Lin Shiming , Kang Xuejun , Gao Honghai , Gao Junhua , Wang Hongjie
Published: July 2002

We report the results of a high efficiency room temperature continuous wave (cw) vertical-cavity surface-emitting laser. The structure is obtained by four deep H+ implantation using tungsten wires as the mask. The fabrication process is the simplest ever reported in vertical-cavity surface-emitting laser fabrication. The largest differential quantum efficiency of 65% and maximum cw light output power over 4 mW have been achieved for the 15×15 μm2 device.
Intracavity injection lasing in a hybrid neodymium laser
Authors: Yan Li , Ding Lei
Published: July 2002

A hybrid neodymium (Nd) laser that contains Nd:YLF and Nd:phosphate glass media in a single cavity was demonstrated. In a wide range of gain conditions, the original lasing spectrum of Nd:glass can be suppressed and the hybrid laser spectrum was ‘‘locked’’ to that of Nd:YLF, even when Nd:YLF was pumped below its threshold.
Effects of degraded edges in strips of high-temperature superconducting films at microwave frequencies
Authors: Gevorgian S. , Carlsson E. , Olsson E.
Published: July 2002

A simple model is proposed to analyze microwave properties of thin superconducting strips with degraded edge regions. A high resistance edge is assumed in the superconducting strip. It is shown that with increased temperature more current will flow inside the superconducting strip away from the damaged edge resulting in a reduction of effective surface resistance.
Phase locking in a multijunction superconducting loop
Authors: Darula M. , Beuven S. , Siegel M. , Darulova A. , Seidel P.
Published: July 2002

Mutual phase locking of Josephson junctions in a multijunction superconducting loop (MSL) was investigated both theoretically and experimentally. The theoretical analysis predicts the existence of phase-locked states, where the circulating current in the loop serves for phase locking between junctions. The basic operating principles of a MSL were studied experimentally using high-TC bicrystal Josephson junctions. The enhancement of phase locking stability with respect to series arrays is reported.
Spherical field meter to measure the electric field vector—measurements in fair weather and inside a dust devil
Authors: Ravichandran M. , Kamra A. K.
Published: July 2002

A spherical field meter has been developed to measure the atmospheric electric field vector above the ground surface. Its calibrations in the radial and linear electric fields and the method to find out the distortion coefficients are described. Extensive measurements of the components of the atmospheric electric field and the resulting electric field vector in fair weather and during the passage of a small dust devil over the spherical field meter are reported. Observations made at Pune (18°32′ N, 73°51′ E, 559 m above msl), show that in fair weather the horizontal component of the electric field may be upto 5% of the vertical component. Variations in the horizontal components of the electric field when averaged over an interval of more than 4 s are small and are generally but not always identical to its vertical components. However, at a frequency of few Hertz, variations in the horizontal components may be comparatively larger and generally independent of the vertical components. Observations made during the passage of a small dust devil over the spherical field meter show the development of appreciable horizontal component of electric field above the ground surface. These observations demonstrate the capability and reliability of the spherical field meter to measure the magnitude and direction of the electric field vector. They also demonstrate that the movement of small space charge pockets close to the surface may cause the development of horizontal component of the electric field.
Reflectance and transmittance measurements of anisotropically scattering samples in focusing Coblentz spheres
Authors: Lindström T. , Roos A.
Published: July 2002

A procedure for obtaining the correct hemispherical reflectance and transmittance of anisotropically scattering samples in focusing Coblentz spheres are presented. Consideration is taken not only to the angle-dependent detector efficiency and to multiple reflections between sample and detector, but a separation of the scattered light into a low and a high angle fraction is also introduced. To validate the formalism, the correction procedure is applied to six samples with different scattering characteristics in the visible and near-infrared region. The agreement with results from a double beam spectrophotometer, equipped with an integrating sphere, was found to be good. Without making the separation into high and low angle scattering, it was not possible to reach agreement between the results from the Coblentz and integrating spheres, and errors of the order of 10% could be obtained.
Optical flow-through high pressure cell for light scattering investigations
Authors: Berger Thorleif , Steffen Werner
Published: July 2002

An optical flow-through/stop-flow high pressure cell has been constructed for static and dynamic light scattering investigations. The cell is especially designed for investigations in supercritical fluids. Angular dependence of scattered light intensity can be measured in principle stepwise between 0° and 360°. Fused quartz as window material allows polarized as well as depolarized measurements to study relaxation functions due to translational or rotational motions. The temperature range 25–100 °C and the pressure range of up to 60 MPa make this cell well suited for studies of polymeric materials in supercritical solvents. Dynamic light scattering results of a solution of polydimethylsiloxane in sc-CO2 at a pressure of 40 MPa are presented to show the capabilities of the apparatus.
Modeling of multistage pendulums: Triple pendulum suspension for GEO 600
Authors: Husman M. E. , Torrie C. I. , Plissi M. V. , Robertson N. A. , Strain K. A. , Hough J.
Published: July 2002

Extensive dynamic six degree-of-freedom modeling of a multiple pendulum suspension has been developed for application to the design and analysis of the planned suspensions for the main mirrors in GEO 600, the German/United Kingdom gravitational wave detector. Two models were developed independently, and results from both were compared with the experiment to verify their applicability. The models have been applied to investigate the optimization of parameters for achieving the desired modal behavior. In addition, the levels of cross coupling between degrees of freedom due to mechanical misalignments have been investigated and shown to be within acceptable limits.
A selection method to improve temperature compensation of current regulator
Authors: Lin Yan-Fang
Published: July 2002

A selection method to improve temperature compensation is proposed, which is effective in forming current regulator device with low temperature coefficient. The experimental results show that the temperature coefficients are of the order of 10−5/°C. The method is simple and the device stable and reliable.
Picosecond spectroscopy of optically modulated high-speed laser diodes
Authors: Sutter D. H. , Schneider H. , Weisser S. , Ralston J. D. , Larkins E. C.
Published: July 2002

The emission transients of optically excited high-speed multiple quantum well laser diodes have been measured by up-converting the emission in a nonlinear crystal. From the gain-switched oscillation the intrinsic resonance frequency and damping factor are determined. The high temporal resolution allows us to observe additional short period oscillations with a frequency of about 170 GHz. Numerical solution of the traveling wave rate equations indicates that these high frequency oscillations arise due to inhomogeneous carrier injection.
Ultrafast intensity switching and nonthermal carrier effects in semiconductor microcavity lasers
Authors: Jahnke Frank , Koch Stephan W.
Published: July 2002

A microscopic nonequilibrium theory is applied to investigate the dynamical response of semiconductor microcavity lasers for ultrashort optical pulse excitation. It is predicted that femtosecond pulse induced carrier heating leads to picosecond switching and recovery of the laser emission.
Pseudomorphic Si1−xSnx alloy films grown by molecular beam epitaxy on Si
Authors: Shiryaev S. Yu. , Lundsgaard Hansen J. , Kringho/j P. , Nylandsted Larsen A.
Published: July 2002

Strained Si1−xSnx (0.001≤x≤0.052) alloys were synthesized on (001) Si substrates by molecular beam epitaxy at 220 and 280 °C. The as-grown alloys were found to be pseudomorphic to Si with no indication of extended defects and tin precipitates. Within the accuracy of our studies the compressive strain in the alloys corresponds to that deduced from Vegard’s linear interpolation between the lattice parameters of Si and α-Sn. The annealing experiments show that the alloys are thermally unstable at a higher temperature (1000 °C) and that the transition of the Si1−xSnx/Si system to a lower energy state occurs through two channels: (i) alloy decomposition through precipitation of tin atoms into metallic β-Sn, and (ii) introduction of 60° misfit dislocations.
Alternating-current losses in silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10 tapes II: Role of interfilamentary coupling
Authors: Fukumoto Y. , Wiesmann H. J. , Garber M. , Suenaga M. , Haldar P.
Published: July 2002

ac losses at 60 Hz have been measured for silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10 multifilamentary tapes at 27 and 77 K to investigate the role of interfilamentary coupling. The results are qualitatively well described by the use of the concept of the critical coupling length lc. Further, it is shown that to obtain effective reduction of the coupling loss, a very small twist pitch length (≪1 cm) as well as a substantial reduction in the filament thickness are required for an applied ac field of, for example, 100 rms A/cm at 77 K.
The road to Fe16N2 formation in N+ implanted 57Fe enriched films
Authors: Leroy E. , Djega-Mariadassou C. , Bernas H. , Kaitasov O. , Krishnan R. , Tessier M.
Published: July 2002

20 keV N+ ions have been implanted on 57Fe enriched Fe films and RF deposited on glass and NaCl substrates with various fluences up to 3.0×1016 N+/cm2. Conversion electron Mossbauer spectroscopy and transmission electron microscopy measurements performed at room temperature on the as-implanted samples reveal the presence of α-Fe, α′-martensite, and ε-Fe3−xN phases. α″-Fe16N2 is only detected after a subsequent annealing at 220 °C; α′-martensite with a low nitrogen content appears as the precursor of α″, The additional nitrogen content needed for this process is supplied by the ε phase.
Thickness profiles of SiO2 films deposited from tetraethoxysilane/O3 precursors in ultra-high-aspect-ratio capillaries
Authors: Soave R. J. , Ganguli S. , Gill W. N. , Shacham-Diamand Y. , Mayer J. W.
Published: July 2002

Thickness profiles of silicon dioxide films deposited by ozone-augmented tetraethoxysilane have been experimentally measured in ultra-high-aspect ratio capillaries. The deposition profiles exhibit a sharp drop in film thickness near the capillary entrance followed by a gradual decrease in thickness along the capillary. A feature-scale model for this process has been developed which includes the effect of by-products on the reaction kinetics and transport inside the structure. Simulated deposition profiles agree well with the experimental data, indicating that a trapped by-product inside the capillary inhibits the film-forming reaction, thus producing the characteristic film profile.
Delayed photocurrent affected by Γ-X resonance in GaAs/AlAs type-I short-period superlattices
Authors: Mimura H. , Ohtani N. , Hosoda M. , Tominaga K. , Watanabe T. , Tanaka G. , Fujiwara K.
Published: July 2002

Delayed photocurrents were observed in GaAs/AlAs type-I short-period superlattices by measuring time-resolved photoresponses under ultrashort optical pulse excitation. According to the envelope function calculations, the X1 state in AlAs barriers resonates with the Γ2 state in the adjacent GaAs wells at a bias voltage where the delayed photocurrents were conspicuous. These results strongly suggest that the dynamic carrier transport process is significantly influenced by X1-Γ2 resonance effects in the superlattices.
Magneto-optical determination of light-heavy hole splittings in As-rich, InAsSb alloys and superlattices
Authors: Kurtz S. R. , Biefeld R. M. , Howard A. J.
Published: July 2002

Interband magnetophotoconductive spectroscopy was used to determine the reduced masses of several optical transitions in an InAs1−xSbx/In1−xGaxAs strained-layer superlattice and a superlattice constituent, InAs1−xSbx alloy (x≊0.1). In both the alloy and the superlattice, light and heavy hole transitions were identified. From the light-heavy hole splitting in the superlattice, we estimate the valence band offset and find type I behavior. Effective masses and band gap energy are measured for the CuPt ordered alloy.
Degradation behavior of amorphous silicon solar cells fabricated by mercury-sensitized photochemical vapor deposition with hydrogen dilution
Authors: Siamchai Pavan , Konagai Makoto
Published: July 2002

The effect of hydrogen dilution on the light degradation behavior of amorphous silicon (a-Si:H) p-i-n solar cells fabricated by mercury-sensitized photochemical vapor deposition has been systematically investigated. In the case of solar cells with no p/i buffer layer, the open-circuit voltage (Voc) of the cells with the i layer prepared by H2-diluted SiH4 was found to increase with the light-soaking time, while the Voc of the cell with i layer prepared from pure SiH4 decreased. Moreover, the single junction solar cell with the Voc of 1.001 V and fill factor of 0.72 has been achieved by optimizing H2 dilution ratio in i layer and employing the wide band gap p and buffer layer.
Photoluminescence spectra of C60 molecules embedded in porous Si
Authors: Yan Feng , Bao Xi-mao , Wu Xiao-wei , Chen Hui-lan
Published: July 2002

The photoluminescence (PL) spectra of C60 molecules embedded in porous Si through both physical deposition and chemical coupling were measured. In addition to the PL peak of porous Si, a peak at 730 nm caused by perfect C60 molecules and other peaks at 620 and 630 nm caused by imperfect C60 molecules were observed. The peak at 620 nm measured in the sample with physically deposited C60 is induced by C60 adsorbed on the Si atoms of the pore wall, while the peak at 630 nm measured in the sample with chemically coupled C60 molecules is caused by the coupled C60 molecules. At room temperature, the PL intensity of C60 embedded in the porous Si is obviously enhanced, and the transfer of carriers from porous Si grains into adjacent C60 is considered to be responsible for the PL enhancement.
Low-temperature oxidation of Si in a microwave electron cyclotron resonance excited O2 plasma
Authors: Martinet C. , Devine R. A. B.
Published: July 2002

The kinetics of the oxidation of Si in a microwave excited O2 plasma have been studied at temperatures in the range of 260–390 °C. The substrate was positively biased and the total electron and O− ion current maintained constant by application of an electric field ∼5 MV cm−1 across the growing oxide. This field was established for thicknesses ≥10 nm. Total current densities were 2–6 mA cm−2 while the O− current was estimated to be 0.02–0.04 mA cm−2. Oxide growth kinetics are discussed in terms of a recent physical model. Chemical etch rates and refractive indices were measured and although similar to those of thermal oxide, infrared absorption spectra suggest that the internal network structure is not the same.
High field effects in high resistivity silicon carbide in lateral configurations
Authors: Sudarshan T. S. , Gradinaru G. , Korony G. , Mitchel W. , Hopkins R. H.
Published: July 2002

Results of the high field performance of single-crystal bulk 6H–SiC of relatively high resistivity (∼500 Ω cm) are reported. Prebreakdown and breakdown phenomena of SiC at high fields are studied using lateral device geometries, particularly suitable for photoconductive power switches and other high voltage power devices. The influence of the electrode configuration, gap length, sample geometry, and contact technology on the high field responses of SiC is discussed. Ohmic response and relatively large hold-off fields (≳80 kV/cm) are reported for this material in vacuum and SF6 gas.
Discharge frequency dependence of particulate growth in high frequency silane plasmas
Authors: Kawasaki H. , Ueda Y. , Yoshioka T. , Fukuzawa T. , Shiratani M. , Watanabe Y.
Published: July 2002

Discharge frequency dependence of growth of particulates is studied in high frequency silane plasmas. Particulates appear earlier after discharge initiation and the increasing rate of their amount in the subsequent phase decreases with increasing the discharge frequency from 3.5 to 28 MHz. Even in the early phase of their formation for all 3.5–28 MHz discharges, particulates grow principally around the plasma/sheath boundary near the powered electrode, where short lifetime radicals are actively generated. For 28 MHz, the density of particulates in the early discharge phase is extremely high (≥1011 cm3). The latter two features suggest that many short lifetime neutral radicals (such as SiH2), being produced at a high rate, significantly contribute to the nucleation and initial growth of one particulate, at least, for a relatively high power density of the order of 0.5 W/cm2.
Electrical properties of Schottky barrier formed on as-grown and oxidized surface of homoepitaxially grown diamond (001) film
Authors: Kiyota Hideo , Matsushima Eiichi , Sato Keisuke , Okushi Hideyo , Ando Toshihiro , Kamo Mutsukazu , Sato Yoichiro , Iida Masamori
Published: July 2002

Characteristics of Schottky barriers formed on homoepitaxial diamond film have been studied. Current–voltage characteristics of Al contacts on both the as-grown film and the oxidized film show rectification. On the other hand, ohmic property is observed on Au/as-grown film while Au/oxidized film shows rectification. These results imply that the mechanism of the barrier formation on the as-grown diamond is drastically changed by oxidation. The difference of electrical properties between the as-grown film and the oxidized film is also observed from capacitance–voltage characteristics. This result suggests that additional acceptors which are not related to boron, exist in the as-grown film and disappear after oxidation.
Effect of step structure on ordering in GaInP
Authors: Su L. C. , Stringfellow G. B.
Published: July 2002

Ga0.5ln0.5P layers grown by organometallic vapor phase epitaxy at rates of between 0.1 and 4.0 μm/h on exactly (001)-oriented GaAs substrates have been studied using atomic force microscopy. The surface is found to be covered by islands several monolayers in height that are elongated in the [110] direction. The edges of the islands are formed of clearly resolved bilayer (5.9 Å) steps. Monolayer steps are rare and no steps larger than 6 Å were observed. These observations explain the nature of the order twin boundaries in ordered GaInP grown on exactly (001)-oriented substrates. The (001) domain laminae are always found to consist of an even number of monolayers. For bilayer steps, the domain thickness will be twice the number of steps moving across the surface before the direction of step motion switches due to the undulating nature of the surface. This switch in the direction of step motion at a particular location on the surface produces the order twin boundaries observed.
Pulsed excimer laser etching of La0.75Ca0.25MnOx thin films
Authors: Dhote A. M. , Shreekala R. , Patil S. I. , Ogale S. B. , Venkatesan T. , Williams C. M.
Published: July 2002

Pulsed (λ=248 nm, pulse width=20 ns) KrF-excimer-laser-induced etching of La0.75Ca0.25MnOx (LCMO) thin films exhibiting giant magnetoresistance (GMR) has been studied. The variation of etch depth as a function of the number of laser pulses shows a linear dependence in the fluence range between 0.15 and 4 J cm−2. The threshold fluence for ablation is found to be 0.07 J cm−2. The photoetching process is seen to follow the Beer–Lambert’s relation based on a linear absorption model with an absorption length of 28.3 nm. The nanomorphology of the laser etched surface as revealed by atomic force microscopy shows significant improvement in the surface smoothness of the deposited films for etching at low energy densities (typically 0.17 J cm−2) and enhanced roughness at higher energy densities (typically 0.86 J cm−2). Changes in the resistivity and GMR effect due to laser treatment are also examined.
Calibrated intensity noise measurements in microcavity laser diodes
Authors: Goobar E. , Scott J. W. , Thibeault B. , Robinson G. , Akulova Y. , Coldren L. A.
Published: July 2002

Calibrated intensity noise measurements of microcavity lasers diodes are presented. Partition noise due to polarization degeneracy is found to render excess noise that destroys squeezing. The measurements indicate that it may be necessary to introduce polarization control to realize sub-shot-noise levels in microcavity laser diodes.
Effect of phosphorus composition on the structural quality of GaInP/GaAsP short-period superlattices
Authors: Whittingham K. L. , Emerson D. T. , Shealy J. R. , Matragrano M. J. , Ast D. G.
Published: July 2002

Short-period Ga0.51In0.49P/GaAsyP1−y strained superlattices were grown, by organometallic vapor phase epitaxy, with periods around 70 Å and phosphorus compositions from 0.04 to 0.31. Ground state emission as high as 1.73 eV was observed. Model solid theory predictions fit this data well, particularly at lower P compositions. Type II structures were obtained for phosphorus compositions above 0.04. The introduction of phosphorus in the low bandgap regions of these superlattices was found to significantly improve their structural and optical quality. These superlattices provide, in many applications, a viable alternative to the quaternary alloy GaInAsP, which is required for obtaining these bandgaps in Al-free systems lattice-matched to GaAs. To our knowledge this is the first report on the growth and modeling of short-period superlattices using this material system.
Addition of N2 as a polymer deposition inhibitor in CH4/H2 electrocyclotron resonance plasma etching of Hg1−xCdxTe
Authors: Keller Robert C. , Seelmann-Eggebert M. , Richter H. J.
Published: July 2002

An approach is presented which eliminates the problems caused by hydrocarbon polymer deposition in etching compound semiconductor with CH4/H2 based plasmas. We find that atomic nitrogen, created by the addition of N2 to the plasma, inhibits polymer deposition in the chamber and on the sample. Atomic nitrogen has several beneficial effects; the elimination of polymer precursors, the reduction of the atomic hydrogen concentration, and a potential increase of methyl radical concentration. It is also demonstrated that the addition of N2 to CH4/H2 based electrocyclotron resonance plasmas used to etch HgCdTe eliminates the roughness normally formed during etching.
Broadly tunable resonant-cavity light emission
Authors: Larson M. C. , Harris J. S.
Published: July 2002

Wavelength-tunable light emission is demonstrated from a planar microcavity employing a deformable-membrane top mirror. A gold/silicon nitride membrane is suspended by an air gap above a GaAs cavity, containing In0.2Ga0.8As multiple quantum wells, and a GaAs/AlAs distributed Bragg reflector. Micromechanical displacement of the membrane allows for broad and continuous wavelength tuning of the cavity resonance formed by the combination of the semiconductor cavity and the air gap. Optically excited luminescence from the quantum wells is restricted to the resonant cavity modes and exhibits a 31 nm (42 meV) tuning range and 2.2 nm (3 meV) linewidth near 960 nm for 0–15 V applied bias.
Demonstration of ultrafast, all-optical, low control energy, single wavelength, polarization independent, cascadable, and integratable switch
Authors: Kang K. I. , Chang T. G. , Glesk I. , Prucnal P. R. , Boncek R. K.
Published: July 2002

A new type of ultrafast all optical switch based on a Mach–Zehnder interferometer is demonstrated with a 10 ps switching window which requires only 0.65 pJ of control pulse energy. The optical nonlinearity which is utilized is associated with the gain compression of semiconductor optical amplifiers, and the switching turnoff transition does not depend on the slow amplifier recovery time. Both data and control pulses are at the same wavelength of 1.313 μm, and are not polarized orthogonal to each other. The device configuration and the semiconductor amplifiers allow for small scale integration and data output cascadability.
Evidence of interstitial location of Er atoms implanted into silicon
Authors: Kozanecki A. , Wilson R. J. , Sealy B. J. , Kaczanowski J. , Nowicki L.
Published: July 2002

Silicon implanted with 2 MeV Er ions at 350 °C is studied by Rutherford backscattering and channeling spectroscopy. Angular scans through the 〈100〉, 〈111〉, and 〈110〉 axial channels were measured. The angular scan profiles of erbium, in particular flux peak in the 〈110〉 scan profile suggest that the implanted Er atoms are predominantly located in the middle of the 〈110〉 channel (the hexagonal interstitial site). Monte Carlo simulations have been performed for the assumed hexagonal interstitial location of Er atoms. They well reproduce the experimental data, giving additional evidence for the location of Er atoms in the middle of the 〈110〉 channel.
Preparation of crystalline beta barium borate (β-BaB2O4) thin films by pulsed laser deposition
Authors: Xiao R.-F. , Ng L. C. , Yu P. , Wong G. K. L.
Published: July 2002

Crystalline beta barium borate (β-BaB2O4) thin films have been prepared on silicon (001) and sapphire (001) substrates by the pulsed laser deposition technique. The crystallinity of these films was found to depend sensitively on the deposition temperature. At a deposition temperature around 800 °C and in the presence of 75 mTorr of O2 gas, films grown on Si(100) substrates are typically polycrystalline with x-ray diffraction peaks along (104) and (001) orientations while the film grown on a sapphire (001) substrate is highly textured with (001) orientation (c axis) normal to the film surface. The film grown on sapphire (001) substrate exhibits a maximum effective second harmonic generation coefficient deff of 2.2 pm/V, which is comparable to that of bulk β-BaB2O4 single crystals.
Determination of nonradiative recombination coefficients of vertical-cavity surface-emitting lasers from lateral spontaneous emission
Authors: Shin Jae-Heon , Lee Y. H.
Published: July 2002

A simple method to determine nonradiative recombination coefficients of vertical-cavity surface-emitting lasers is proposed and demonstrated. The dependence of the lateral spontaneous emission on the current density is used to determine the nonradiative recombination coefficients and the threshold carrier densities. In this scheme, the lateral spontaneous emission obtained from the nearest neighbor devices is analyzed. For 10-μm diameter proton-implanted vertical-cavity surface-emitting lasers, the obtained nonradiative recombination coefficient is about 1.8×108 s−1, responsible for 25% of threshold current density.
Experimental investigation of the relative importance of carrier heating and spectral-hole-burning on nonlinear gain in bulk and strained multi-quantum-well 1.55 μm lasers
Authors: Girardin François , Duan Guang-Hua , Gallion Philippe , Talneau Anne , Ougazzaden Abdallah
Published: July 2002

The transverse spontaneous emission is used to characterize the gain suppression in semiconductor lasers during their operation for the first time. The carrier heating and the spectral-hole-burning are distinguished by using their different spectral behavior. The measurements show a very strong carrier heating in strained multi-quantum-well lasers which do not appear in bulk devices. Moreover, the total nonlinear gain coefficient is measured by using a modulation method; the results show a high value of ε=16.10−17 cm3 for the strained multi quantum-well laser and an usual value of ε=2.10−17 cm3 for the bulk, consistent with the measurement of gain suppression spectrum.