bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency doubling in weakly guiding optical fibers
Authors: Chen Yijiang
Published: July 2002

The letter examines the photoinduced model for explaining efficient second-harmonic generation in glass fibers with inversion symmetry. We show that a critical pump power exists for efficient second-harmonic generation in a fiber under nonindex matching. Our study also reveals that the roles of core-cladding interface and bulk nonlinearities are comparable in achieving efficient second-harmonic generation under nonindex matching condition.
Tunnel spectroscopy of the AlGaAs-GaAs heterostructure interface
Authors: Salemink H. W. M. , Meier H. P. , Ellialtioglu R. , Gerritsen J. W. , Muralt P. R. M.
Published: July 2002

The material interface of a molecular beam epitaxy grown Al0.5Ga0.5As-GaAs heterostructure is investigated on a cross-sectional (110) cleavage plane using tunnel spectroscopy. The depleted n-type region and the electron confinement layer adjacent to the interface are identified with local current-voltage spectroscopy. The spatial width of these layers is close to 15 nm. The spectroscopy can be interpreted with the valence-band offset in the interface, and a value of 0.35 eV is found for this quantity.
Novel scalloped-mirror diffraction-coupled InGaAsP/InP buried-heterostructure laser arrays
Authors: Yap D. , Walpole J. N. , Liau Z. L.
Published: July 2002

Diffraction-coupled arrays of InGaAsP/InP buried-heterostructure lasers are reported. These arrays, fabricated by ion beam assisted etching and mass transport, have a novel scalloped mirror at the end of the coupling section that greatly increases the coupling between stripes and reduces the feedback into the same stripe. Far-field patterns show sharply defined lobes that are as narrow as 3°. An output section with cylindrical mirrors has been incorporated into the arrays to increase the power in the central far-field lobe. Threshold currents as low as 150 mA have been obtained for eight-stripe arrays.
Optoelectronic dynamic random access memory cell utilizing a three-terminal N-channel self-aligned double-heterostructure optoelectronic switch
Authors: Taylor G. W. , Crawford D. L. , Simmons J. G.
Published: July 2002

The double-heterostructure optoelectronic switch is demonstrated as a novel dynamic random access optoelectronic memory cell in an N-channel self-aligned three-terminal configuration. The cell employs a single polarity of bias and XY selectivity using the inversion channel contact and the optical input/output port. The switching powers, delays, and refresh capability offer the promise for large-scale integrated circuits.
Coherent Si growth on GaAs substrates by vapor phase deposition
Authors: Tamamura K. , Akimoto K. , Mori Y.
Published: July 2002

Epitaxial Si layers with low dislocation density were grown on GaAs substrates by pyrolysis using disilane. The dislocation density evaluated from SECCO etching (HF:H2 SO4 :K2 Cr2 O7 =100 cc:50 cc:2g) was less than 104/cm2, which is lower by two orders of magnitude than that of the GaAs layer on Si substrates. We found that the electron mobility of Si layers on GaAs substrates could be raised by decreasing the growth rate and a high mobility value the same as that of a homoepitaxial layer was obtained, although the Si layers were contaminated by an arsenic impurity of 1018 cm−3 .
Formation of a nearly pure aluminum layer in beryllium using ion implantation
Authors: Brown D. W. , Musket R. G. , Munir Z. A.
Published: July 2002

A nearly pure subsurface layer of an implanted element was created using aluminum implantation into beryllium. In particular, post-implant annealing of polycrystalline beryllium samples implanted with 200 keV aluminum caused a dramatic increase in the peak aluminum concentration as determined by Rutherford backscattering. The effect was observed for all three doses studied: 0.46, 1.1, and 4.6×1018 Al/cm2 . For the 1.1×1018 Al/cm2 case, cross-sectional transmission electron microscopy of the annealed sample revealed a distinct subsurface layer with the structure of crystalline aluminum. Auger sputter profiles of individual grains showed the layer purity to be as high as 98 at. % aluminum. However, there were indications that the layer formation and/or purity were grain dependent.
Coarsening phenomenon of Si clusters on artificial nucleation sites
Authors: Kumomi H. , Yonehara T.
Published: July 2002

A coarsening phenomenon of Si clusters is investigated in the process of nucleation and growth. In the early stage of chemical vapor deposition, multiple fine clusters of Si are nucleated on the small portion of an artifical nucleation site. A large cluster emerges among the fine clusters and grows rapidly as the deposition proceeds. As a result, the site is occupied by only one large cluster, while the fine clusters seem to disappear. Such a phenomenon is responsible for the mechanism in which a single nucleus is selected to grow on the site.
Phase front measurements of AlGaAs 830 nm phase-locked lasers with a real-refractive-index waveguide
Authors: Shinozaki K. , Furukawa R. , Fukunaga T. , Watanabe N.
Published: July 2002

A phase-locked laser array with refractive-index waveguides and emitting a low phase-aberration beam is described. A fundamental supermode operation of an evanescent-coupled three-element laser array which emits up to 200 mW in a single diffraction-limited beam is achieved. The full beam angle at the half-power point is 3.2° in the direction of parallel to the p-n junction. This phase aberration is less than λ/14 from 50 to 150 mW. The extremely low phase aberration (0.022λ) is measured at 50 mW.
Surface-emitting GaAs/AlGaAs lasers with dry-etched 45° total reflection mirrors
Authors: Hamao N. , Sugimoto M. , Takado N. , Tashiro Y. , Iwata H. , Yuasa T. , Asakawa K.
Published: July 2002

Surface-emitting GaAs/AlGaAs lasers with 45° total reflection mirrors have been successfully produced using a 45° tilted reactive ion beam etching technique. The ratio of surface-emitted light output power to edge-emitted light output power was obtained at values as high as 77%. The total reflection mirror was formed within 1° of the desired precise 45° angle. This type of surface-emitting laser is promising for optoelectronic integrated circuits because of the simplicity of its structure and fabrication.
Monolayer to bilayer transition in reflection high-energy electron diffraction intensity oscillations during Si(001) molecular beam epitaxy
Authors: Clarke S. , Wilby M. R. , Vvedensky D. D. , Kawamura T. , Sakamoto T.
Published: July 2002

We report the observation of a thermally driven monolayer to bilayer transition in the period of reflection high-energy electron diffraction oscillations during molecular beam epitaxy on Si(001). This behavior is reproduced in a Monte Carlo growth simulation, from which we infer the origin of the transition results from the competition between incorporation and diffusion kinetics.
Low-power optical bistability in a thermally stable AlGaAs étalon
Authors: Masseboeuf Eric , Sahlén Olof , Olin Ulf , Nordell Nils , Rask Michael , Landgren Gunnar
Published: July 2002

Optical bistability with 10 mW input power is reported in a thermally stable, nonlinear AlGaAs étalon. A 3-μm-thick silver layer, which serves both as high-reflecting mirror and heat sink, makes it possible to operate the device at arbitrary duty cycles and pulse lengths up to 0.5 s, without any regenerative pulsations, at room temperature. The device operation depends on the plasma-induced electronic nonlinearity, and switching times are typically 10 ns. Device performance is compared with results from a numerical model which takes diffraction, diffusion, and heat conduction into account.
Fabrication and characterization of lateral InP/InGaAsP heterojunctions and bipolar transistors
Authors: Yoo H-J. , Hayes J. R. , Caneau C. , Bhat R. , Koza M.
Published: July 2002

We have investigated the fabrication of lateral InP/InGaAsP heterojunctions using both wet chemical and in situ melt-back etching and regrowth to form the device junctions. The current/voltage characteristics of the melt-back-etched and regrown heterojunctions exhibit ideality factors as low as 1.25. In addition, we have fabricated lateral heterojunction bipolar transistors with 2 μm base widths which exhibit a current gain of 6. These results indicate that regrown heterojunctions have adequate injection efficiency to form the active region of devices.
Electrical resistivity of thin epitaxial NiAl buried in (Al,Ga)As
Authors: Tabatabaie N. , Sands T. , Harbison J. P. , Gilchrist H. L. , Florez L. T. , Keramidas V. G.
Published: July 2002

We present the first measurements of electrical resistivity for NiAl layers in (Al,Ga)As/NiAl/(Al,Ga)As semiconductor/metal/semiconductor monocrystalline heterostructures. Layer thicknesses in the range 1.5–100 nm have been studied and all were found to be electrically continuous. Four separate components of resistivity are identified and discussed. The room-temperature resistivity is dominated by electron-phonon and interface-roughness scattering. For films 3 nm in thickness and above, the composition of the NiAl compound can be inferred from the phonon resistivity, while the residual resistivity yields the probability of specular reflection from the interfaces. This parameter is approximately 20% for the films studied.
Spectrally dependent photocurrent measurements in n+-n-n+ heterostructure devices
Authors: Snow E. S. , Kirchoefer S. W. , Glembocki O. J.
Published: July 2002

Photocurrent measurements are shown to be a useful tool for characterizing charge-injecting heterostructure devices under bias. The measurements rely on a large photoconductive gain mechanism which operates in single-barrier, double-barrier, and superlattice devices. Photocurrent measurements on a set of superlattice doping interface devices indicate the presence of charge domains and an interesting electric field-screening phenomenon. These phenomena are not evident in the current versus voltage data and emphasize the importance of using optical probes to characterize electronic devices.
Design considerations for diffraction coupled arrays with monolithically integrated self-imaging cavities
Authors: Wilcox J. Z. , Simmons W. W. , Botez D. , Jansen M. , Mawst L. J. , Peterson G. , Wilcox T. J. , Yang J. J.
Published: July 2002

Conditions for stabilization of in-phase or out-of-phase array eigenmodes in diffraction coupled diode laser arrays are derived and applied to several array architectures. The analysis predicts that the discrimination between these two eigenmodes is strongest in arrays with half Talbot distance long free-propagation region. In this geometry, the out-of-phase and in-phase near fields are, respectively, reproduced and channeled halfway between the original channel locations.
1.5 μm tunable wavelength filter using a phase-shift-controlled distributed feedback laser diode with a wide tuning range and a high constant gain
Authors: Numai T. , Murata S. , Mito I.
Published: July 2002

We demonstrate a 1.5 μm tunable wavelength filter which uses a newly developed phase-shift-controlled distributed feedback laser diode. A tuning range as wide as 120 GHz (9.5 Å) with 24.5 dB constant gain has been achieved. An 18-channel wavelength selection with less than −10 dB crosstalk is expected with this filter.
Synchronous and noncollinear infrared upconversion in AgGaS2
Authors: Bhar G. C. , Das S. , Chatterjee U. , Feigelson R. S. , Route R. K.
Published: July 2002

Synchronous noncollinear upconversion detection is reported for the first time with a Nd:YAG laser in AgGaS2. Q-switched pump laser pulses with a repetition rate up to 50 Hz were synchronized with intracavity chopped continuous wave CO2 laser pulses. Results were obtained both by tuning the CO2 laser and by varying the angle between the laser beams.
Microstructure of epitaxial ErBa2Cu3O7−x thin films grown on MgO (100) substrates by rf magnetron sputtering
Authors: Chang J. , Nakajima M. , Yamamoto K. , Sayama A.
Published: July 2002

The microstructural properties of superconducting ErBa2Cu3O7−x films on single-crystal MgO substrates are studied by transmission electron microscopy. The as-grown films are single-crystal-like and are composed of subgrains of 0.1–0.2 μm in size. Due to annealing, the dislocations at the subgrain boundaries disappeared. The annealed films are epitaxial with either the a or the b axis of the ErBa2Cu3O7−x unit cell along 〈100〉 directions of the MgO substrate. The stress caused by lattice mismatch is relaxed by the formation of misfit dislocations at the film/substrate interface.
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u observation by ultrahigh vacuum reflection electron microscopy of terrace formation processes on (100) silicon surfaces during annealing
Authors: Inoue N. , Yagi K.
Published: July 2002

Formation processes of terraces on (100) silicon surfaces during annealing at 1000 °C were observed in situ by ultrahigh vacuum reflection electron microscopy. Terraces were formed on staircases made up of monoatomic steps, preferentially at the sites where stairs were larger than average. The sites are formed by surface undulation. It was found that the terrace grew, or extended, in both up-step and down-step directions almost at equal rates. The terrace thus grew not by sublimation, but by adhesion and removal of atoms at respective terrace edges. Thus, the interlayer migration of adatoms plays an important role in the terrace growth.
Generation of macroscopic steps on patterned (100) vicinal GaAs surfaces
Authors: Colas E. , Kapon E. , Simhony S. , Cox H. M. , Bhat R. , Kash K. , Lin P. S. D.
Published: July 2002

We show that macroscopic, as opposed to microscopic, steps can be obtained on a semiconductor vicinal surface when a perturbation has been ‘‘printed’’ on it, prior to epitaxial growth. This generic crystal growth concept has been studied here with the GaAs/AlGaAs system using organometallic chemical vapor deposition. The details of step formation, stabilization, and subsequent propagation have been investigated with scanning electron microscopy. Regular, sawtooth-like growth patterns have been obtained, with periodic growth rate differences at the step edges. This novel lateral patterning technique was employed to fabricate arrays of quantum wire-like heterostructures.
Efficient frequency doubling of a mode-locked diode-laser-pumped Nd:YAG laser
Authors: Maker G. T. , Ferguson A. I.
Published: July 2002

We report on high-efficiency frequency doubling of a mode-locked diode-laser-pumped Nd:YAG laser to 532 nm in a crystal of MgO:LiNbO3 in an external enhancement ring cavity. At a pump power of 500 mW the mode-locked Nd:YAG laser produced an average power of 66 mW incident on the enhancement cavity in pulses of 12 ps duration at a repetition rate of 366 MHz. This has been frequency doubled with a conversion efficiency of 53% to produce pulses at 532 nm of 35 mW average power in bandwidth-limited pulses of 9.5 ps duration.
Evolution of hydrogen from plasma-deposited amorphous hydrogenated silicon films prepared from a SiH4/H2 mixture
Authors: Sakka Tetsuo , Toyoda Katsuya , Iwasaki Matae
Published: July 2002

The desorption spectra of constant-rate annealing of the plasma-deposited amorphous hydrogenated silicon (a-Si:H) films prepared from the SiH4/H2 mixture gas show two peaks. The first peak is located at around 625 K and the position of the second peak varies from 765 to 903 K with the SiH4 fraction in the SiH4/H2 source gas. These experimental results seem to be strongly related to structural inhomogeneity of the plasma-deposited a-Si:H films. The change in the peak temperature of the high-temperature evolution process is explained on the basis of the difference between the activation energy of the hydrogen evolution from the SiH centers and that from the SiH2 center.
Weighted Monte Carlo for electron transport in semiconductors
Authors: Poli P. , Rota L. , Jacoboni C.
Published: July 2002

A new powerful method, the weighted Monte Carlo method, for the solution of electron transport problems in semiconductors is presented. The method is formally derived from an iterative expansion of the integral form of the Boltzmann equation and results in a simulation of electron dynamics where arbitrary probabilities for the various events which generate electron trajectories are used. It is much more flexible than the standard algorithm that can be derived by it as a very special case. The method is applied here to study the tail of the distribution function in a simple silicon model.
Spatial light modulation using surface plasmon resonance
Authors: Yeatman Eric M. , Caldwell Martin E.
Published: July 2002

A new type of spatial light modulator has been demonstrated, operating by the surface plasmon resonance effect. Devices have been constructed using nematic liquid crystal as the active material, and the operation of these devices is 50 times faster than the bulk switching of the liquid-crystal cells. We have obtained resolution of 10–20 μm and contrast ratios better than 100:1.
Formation of laterally propagating supersteps of InP/InGaAs on vicinal wafers
Authors: Cox H. M. , Lin P. S. , Yi-Yan A. , Kash K. , Seto M. , Bastos P.
Published: July 2002

We propose and demonstrate a technique for artifically bunching the atomic steps on a vicinal substrate to form supersteps of almost arbitrary height. The process involves the etching of a grating of parallel grooves on the surface of a vicinal substrate followed by epitaxial growth that fills the grooves. Steps of height proportional to the period of the grating and the substrate misorientation angle are formed. The technique is demonstrated on a macroscopic scale for the InP/InGaAs material system using chloride transport vapor levitation epitaxy, resulting in InGaAs wire-like structures confined both horizontally and vertically by InP. The growth of quantum wires and laterally periodic superlattices should be possible using this technique with proper scaling of parameters.
Synchronously pumped mode-locked dye laser pumped by a frequency-doubled mode-locked and Q-switched diode laser pumped Nd:YAG laser
Authors: Maker G. T. , Ferguson A. I.
Published: July 2002

We have developed a powerful and efficient mode-locked and Q-switched diode laser pumped Nd:YAG laser. Mode locking has been accomplished using intracavity frequency modulation (FM) to produce continuous-wave mode-locked pulses of 12 ps duration. Acousto-optic pre-lase Q switching has produced a train of pulses of about 25 ps average duration at a repetition rate of 360 MHz in an envelope of 75 ns duration. When pumped with a 500 mW diode laser array, the energy in the Q-switched envelope was 15 μJ giving a peak power in the largest pulse of 19 kW. The laser has been frequency doubled in a crystal of potassium titanyl phosphate (KTP) with an efficiency of 36%. The doubled radiation at 532 nm has been used to synchronously pump a mode-locked rhodamine 6G dye laser to produce a train of tunable pulses. The pulse duration of the dye laser was 3.2 ps and the peak power of the largest pulse in the train was 10 kW.
Lasing threshold in quantum well surface-emitting lasers: Many-body effects and temperature dependence
Authors: Gourley P. L. , Lyo S. K. , Brennan T. M. , Hammons B. E. , Schaus C. F. , Sun S.
Published: July 2002

The geometry of quantum well surface-emitting lasers has several important consequences. The ultrashort (∼1 μm) vertical cavity defines longitudinal modes with energy separation greater than the bandwidth of spectral gain. The optical confinement of these modes can approach unity. To achieve lasing, high carrier densities (∼1012 cm−2) in the quantum well are required. The confined carriers interact through enhanced many-body exchange which influences both the lasing wavelength and threshold characteristics. Indeed, the exchange interaction can facilitate the lasing process. We theoretically and experimentally study the role of the short cavity and exchange interaction on the cw lasing threshold as a function of temperature. In constrast to edge emitters, the lasing threshold in these surface emitters exhibits a well-defined minimum at a particular temperature. The temperature of the minimum can be designed by merely changing the active layer thickness.
Mode locking of a continuous wave Nd:glass laser pumped by a multistripe diode laser
Authors: Krausz F. , Brabec T. , Wintner E. , Schmidt A. J.
Published: July 2002

The performance of a continuous wave actively mode-locked Nd: phosphate glass laser longitudinally pumped by a multistripe diode laser is described. The laser operates at 1.054 μm; the pump threshold and the slope efficiency are found to be 120 mW and 11%, respectively. The shortest pulse duration is 7 ps, which appears to be approximately twice as short as predicted by the theory of amplitude modulation mode locking. We explain the improved performance by additional frequency modulation due to the nonlinear index of the active material.
Low spectral modulation high-power output from a new AlGaAs superluminescent diode/optical amplifier structure
Authors: Alphonse G. A. , Connolly J. C. , Dinkel N. A. , Palfrey S. L. , Gilbert D. B.
Published: July 2002

A double-heterojunction angled stripe AlGaAs device consisting of an index-guided ridge waveguide with gain-guided facet regions has produced cw output powers of 20 mW with less than 1% spectral modulation from a 300-μm-long diode. These properties enable these devices to have important use in high-sensitivity fiber optic gyroscopes and as broadband traveling-wave optical amplifiers.
Optical characterization of nonuniform electric fields in multiple quantum well diodes
Authors: Little J. W. , Leavitt R. P. , Ovadia Shlomo , Lee Chi H.
Published: July 2002

Low-temperature photocurrent and photoluminescence spectroscopies have been used to quantify the effects of electric field nonuniformities (on the order of 100 kV/cm) within the ∼1-μm-thick intrinsic regions of GaAs/AlGaAs multiple quantum well p-i-n photodiodes. The smearing out of excitonic spectral features due to nonuniform fields agrees well with the results of calculations performed using a single-band envelope-function approximation together with a standard depletion model for a p−/n+ junction.
Diffraction-limited operation from monolithically integrated diode laser array and self-imaging (Talbot) cavity
Authors: Jansen M. , Yang J. J. , Ou S. S. , Botez D. , Wilcox J. , Mawst L.
Published: July 2002

The monolithic integration of a linear array and a separately pumped self-imaging Talbot cavity has resulted in diffraction-limited single-lobe output beams to output powers in excess of 100 mW/facet. A study was made of the device operation as a function of the drive currents applied to the array region and the Talbot cavity.
Role of thermal fluctuations in nondegenerate two-wave mixing
Authors: Rogovin D. , McGraw R. , Gavrielides A.
Published: July 2002

The influence of thermal fluctuations on nondegenerate two-wave mixing in the nondepleted pump approximation is examined. For the specific case of an optical Kerr medium the spectrum of both amplitude and phase fluctuations as well as the signal-to-noise ratio are obtained. Detailed calculations suggest that a signal-to-noise ratio of order unity at argon-ion wavelengths and room temperatures requires a probe power of 15 μW in the strong signal regime.
Voltage-controlled Q switching of InGaAs/InP single quantum well lasers
Authors: Berthold K. , Levi A. F. J. , Tanbun-Ek T. , Logan R. A. , Chu S. N. G.
Published: July 2002

The light emission characteristics of high performance InGaAs/InP single quantum well laser diodes with a monolithically integrated intracavity loss modulator have been investigated. We demonstrate efficient voltage-controlled tuning of the lasing threshold current over more than one order of magnitude. In addition, active Q switching of 7 mW lasing light power with a change in electrical power of <30 μW is achieved.
Critical temperature enhancement of Bi2Sr2CaCu2Ox by phenolization
Authors: Ishida T.
Published: July 2002

The critical temperature (Tc ) of the sintered superconductor Bi2 Sr2 CaCu2 Ox can be raised by soaking it in a solution of phenol and ethanol. After drying at room temperature, subsequent annealing at relatively low temperature (200 °C) further increases the Tc. The transition midpoint temperature increases from 71.9 to 93.0 K. A similar effect was observed by using phenolic-based GE7031 varnish as a reagent. Phenol appears to assist in raising the Tc of Bi2 Sr2 CaCu2 Ox.
Recording of low spatial frequency gratings in photorefractive materials
Authors: Black T. D. , Hafiz A. , Larson D. A. , Magnusson R.
Published: July 2002

Recording of low spatial frequency gratings in iron-doped LiNbO3 crystals using a single write beam by both direct contact and optical projection methods is reported. Gratings with periods in the range 50–200 μm have been produced generating up to 40 visible diffraction orders when probed with a low-power HeNe laser. Diffraction efficiencies over 20% are achieved for the first diffraction order.
Resistive, magnetic, and structural studies of Tl0.5Pb0.5(Ca1−x
M
x)Sr2Cu2Oy compounds with M equal to the natural mixture of rare-earth elements
Authors: Liu R. S. , Wang W. N. , Liang J. M. , Wu P. T.
Published: July 2002

We report the resistivity, structural, and magnetic susceptibility measurements for Tl0.5Pb0.5(Ca1−xMx)Sr2Cu2Oy superconductors with M equal to the natural mixture of rare-earth elements and x=0, 0.05, 0.1, 0.2, and 0.3, respectively. The powder x-ray diffraction profile indicates a single-phase, P4/mmm tetragonal crystal structure with a=0.380±0.002 nm and c=1.205±0.002 nm for a Tl0.5Pb0.5(Ca0.9M0.1)Sr2Cu2Oy superconductor. Tc (zero)’s were found to be 79, 91, 101, 97, and 87 K for x=0, 0.05, 0.1, 0.2, and 0.3, respectively. Hc1 of Tl0.5Pb0.5(Ca0.9M0.1)Sr2Cu2Oy was estimated to be around 1.8 kG at 5 K, and Jc about 1.35×103 A/cm2 with a 20 kG applied field at 5 K. The Meissner signal of this sample indicates the Tc onset ∼100 K, and the mass diamagnetic susceptibility −χg at 5 K is 2.52×10−3 cm3/g (field cooled at 100 G).
Mutually coherent beam induced self-pumped phase conjugate reflection in BaTiO3
Authors: Ye Peixian , Wang Dadi , Zhang Zhiguo , Wu Xing
Published: July 2002

A self-pumped phase conjugate reflection induced by another mutually coherent incident beam has been observed and explained successfully for the first time in a photorefractive crystal BaTiO3. Other relevant phenomena, such as the destruction of the coupling channel when two incident beams are mutually coherent, have also been studied. Possible applications are pointed out.
Active mode locking of lasers by piezoelectrically induced diffraction modulation
Authors: Krausz F. , Turi L. , Kuti Cs. , Schmidt A. J.
Published: July 2002

A new amplitude-modulation mode-locking technique is presented. Acoustic waves are generated directly on the faces of a resonant photoelastic medium. The created standing waves cause a highly efficient diffraction modulation of light. The modulation depth of standing-wave mode lockers is related to material and drive parameters and a figure of merit is introduced. With a lithium niobate crystal modulation depths over 10 are achieved at 1.054 μm and 1 W of radio frequency power. Using this device for the active mode locking of a continuous-wave Nd:glass laser pulses as short as 3.8 ps are produced at a repetition rate of 66 MHz. Limitations of amplitude-modulation mode locking by standing acoustic waves are discussed.
Multielectrode quantum well laser for digital switching
Authors: Levi A. F. J. , Nottenburg R. N. , Nordin R. A. , Tanbun-Ek T. , Logan R. A.
Published: July 2002

A multielectrode laser can be used to perform digital logic functions and threshold detection. In addition, the intrinsic gain in these devices allows control of lasing light output without using conventional high-current electrical switches. Device potential is illustrated by demonstrating logical and operation (demultiplexing) at 1.5 Gbit s−1 with a bit error rate of <10−11 s−1.
Variable resonator (variable Q) photopumped phonon-assisted quantum well laser operation
Authors: Holonyak N. , Nam D. W. , Vesely E. J. , Guido L. J. , Gavrilovic P. , Meehan K. , Stutius W. , Williams J. E.
Published: July 2002

Data are presented on a photopumped rectangular (w=40 μm, l=250 μm) quantum well heterostructure (QWH), with variable resonator Q along the sample, showing that phonon-assisted laser operation predominates. To achieve variable resonator Q, the QWH sample is heat sunk embedded in In over half of its length (reflecting edges, high Q), as opposed to simple contact with a Au shim over the remaining half and no reflecting metal on the sample edges (low Q). Photopumping at the low Q, high Q boundary near the sample center turns on and off the n=1 confined-particle recombination transition (E11 ) and sets a higher energy experimental (as well as calculated) reference, ℏω2 =E11, for the lower energy phonon-assisted laser operation, ℏω1 =E11 −ℏωLO .
Integrated-optical Q-switch/mode locker for a Nd3+ fiber laser
Authors: Geister G. , Ulrich R.
Published: July 2002

An electro-optic phase modulator and a switched directional coupler are integrated on a common LiNbO3 substrate and inserted into the cavity of a 3-m-long Nd3+ single-mode fiber laser (λ≊1088 nm). Their simultaneous operation yields groups of ≊10 pulses at rates up to 2 kHz, with 50 ps pulse duration, 30 ns separation, and 200 W peak power.
Tracer impurity diffusion in amorphous NixZr1−x alloys
Authors: Wu H.-M. , Averback R. S.
Published: July 2002

Impurity tracer diffusion coefficients for Co and Hf were measured in a series of amorphous NixZr1−x alloys at various temperatures for 0.3<x<0.7. The diffusion coefficients for Co, an impurity with small atomic radius were, depending on alloy composition and temperature, two to four orders of magnitude larger than those for Hf, an impurity with large atomic radius. Whereas the Hf tracer diffusion coefficients are independent of alloy composition, those of Co decrease strongly with increasing Ni concentration. These results suggest that the diffusion mechanisms for atoms with small or large atomic radii are different in amorphous Ni-Zr alloys.
Repeatability dependence of phase-change optical disks on morphology of protective layers
Authors: Chiba R. , Yamazaki H. , Yagi S. , Fujimori S.
Published: July 2002

The surface or the Si3N4-sputtered protective layer of phase change optical recording media was observed with a scanning tunneling microscope. We found the morphology of the protective layer can be controlled by changing the sputtering gas conditions and that overwrite cycle repeatability strongly depends on it. As the Ar gas pressure in the sputtering chamber is decreased, the protective layers become denser and have a flatter surface, and the repeatability is improved from 3×103 to 5×105. The media sensitivity also depends on the morphology of the protective layers. The causes of media deterioration after a large number of overwrite cycles are discussed
In situ reflectivity monitoring of antireflection coatings on semiconductor laser facets through facet loss induced forward voltage changes
Authors: Landreau Jean , Nakajima Hisao
Published: July 2002

In situ fully electrical monitoring of the reflectivity of antireflection coatings on semiconductor laser facets is experimentally demonstrated. The operating principle consists of detecting changes in the forward voltage drop induced by the modification of facet reflectivity of a constant current-driven semiconductor laser. This technique allows one to detect the optimum thickness giving the lowest reflectivity without optical measurement. A reflectivity as low as 1×10−4 was currently obtained with electron beam deposited SiOx films on 1.5 μm buried ridge stripe lasers.
Dependence of GaAs etch rate on the angle of incidence of a hydrogen plasma beam excited by electron cyclotron resonance
Authors: Suemune I. , Kishimoto A. , Hamaoka K. , Honda Y. , Kan Y. , Yamanishi M.
Published: July 2002

Hydrogen (H) plasma irradiation effect on (100)  GaAs surfaces was studied. The etching of GaAs surfaces was found to be effectively ceased after some etch at the initial stage when the plasma beam was incident on the surface at a shallow glancing angle. The etched surface was an atomically flat (100)  GaAs surface as previously observed by clear Laue spots in the reflection high-energy electron diffraction measurement reported by I. Suemune, Y. Kunitsugu, Y. Kan, and M. Yamanishi [Appl. Phys. Lett. 55, 760 (1989)]. A physical model for the newly found relation between the etch rate and the surface structure is discussed.
Direct overwrite without initialization in a bilayer magneto-optical disk
Authors: Watson Mathew D. , Meystre Pierre
Published: July 2002

We propose and analyze a bilayer direct overwrite scheme that does not require an initialization bias field. This is achieved by using permanent domains in a reference layer to help stabilize bits in a memory layer on writing, and to destabilize the memory layer bits on erasure.
Phase accurate optical probing of surface acoustic wave devices
Authors: Ginter A. , Sölkner G.
Published: July 2002

In this letter, we present a method which detects the angle deflection of a laser beam due to the mechanical undulation of the substrate surface. This method allows us to measure amplitude and phase of a surface acoustic wave with high spatial resolution. Because of the use of a picosecond laser source the method has a bandwidth of 10 GHz limited only by the jitter of the driving electronics and the spot size of the laser beam. In addition we report first measurements at frequencies up to 1 GHz.
Saturation of phase coherence length in GaAs/AlGaAs on-facet quantum wires
Authors: Fukai Yoshino K. , Yamada Syoji , Nakano Hayato
Published: July 2002

Phase coherence length Lφ of on-facet quantum wires is determined at temperatures down to 50 mK by three methods: magnetoresistance, conductance fluctuation amplitude, and the conductance fluctuation correlation field. It is found that Lφ saturates below about 0.4 K. This saturation is identified as due to spin-orbit interaction, which has no temperature dependence. This result is supported by positive magnetoresistance under a weak magnetic field.
Conformal vapor phase growth of submicron thick (100) GaAs films
Authors: Pribat D. , Collet C. , Legagneux P. , Karapiperis L.
Published: July 2002

Using a newly developed technique of shaped crystal growth from the vapor, we have obtained a lateral conformal GaAs single-crystal growth between two Si3N4 films. 0.6-μm-thick GaAs films of (100) surface orientation were grown over extensions of 15 μm in a standard arsenic trichloride vapor phase epitaxy reactor. The surface aspect of the films after removal of the top Si3N4 layer is specular and these films are virtually dislocation-free.
Low threshold current implanted-planar buried-heterostructure graded-index separate confinement heterostructure laser in GaAs/AlGaAs
Authors: Vawter G. Allen , Myers D. R. , Brennan Tom M. , Hammons B. E.
Published: July 2002

We report dramatic improvements to the implanted-planar buried-heterostructure graded-index separate confinement heterostructure (IPBH-GRINSCH) laser in (AlGa)As/GaAs which produces low threshold current, continuous-wave operation. Our process features significantly reduced fabrication complexity of high quality, index-guided laser diodes compared to regrowth techniques and, in contrast to diffusion-induced disordering, allows creation of self-aligned, buried, blocking junctions by ion implantation. The improved single-stripe IPBH-GRINSCH lasers exhibit 39 mA threshold current, cw operation.
Current confinement in a GaAs/AlGaAs heterostructure by i
n s
i
t
u laser-patterned desorption of a current-blocking quantum well
Authors: Epler J. E. , Treat D. W. , Paoli T. L.
Published: July 2002

Radiation from Ar+ and Nd:YAG lasers is used within a metalorganic chemical vapor deposition reactor to thermally desorb selected areas of GaAs quantum well (QW) layers during a pause in the epitaxial growth. The process, called laser-patterned desorption, is used to laterally pattern current confinement in an AlGaAs/GaAs diode laser structure. Current channels are produced by completely removing selected areas (∼3 mm wide) of an n+ GaAs QW blocking layer embedded in the AlGaAs p cladding of a separate confinement heterostructure laser. Scanning electron microscopy cross sections indicate the blocking layer is completely removed in regions illuminated with the focused laser beam. Current confinement is confirmed by observing the localized optical emission from a 1-cm-long bar containing a 1-mm-wide desorbed region. Broad-area diode lasers fabricated from the sample exhibit a forward voltage varying from a minimum (∼2 V) within the lase-desorbed region to a maximum (∼4 V) in the surrounding field. This work is the first demonstration of current confinement produced by epitaxial patterning in an optical device during growth.
Superconductor film growth on LaGaO3 substrates by liquid phase epitaxy
Authors: Belt R. F. , Ings J. , Diercks G.
Published: July 2002

Growth conditions and solubility relations were investigated for controlled crystallization of YBa2Cu3O7−x and Bi2Sr2CaCu2O8+x films from KCl solutions. Applications were made to film growth by liquid phase epitaxy using the dipping process. Epipolished substrates of LaGaO3 with (001) orientations were employed. The micrometer thick films were identified by x ray to be of the correct phases. Furthermore, the polycrystalline films showed a highly preferred orientation with (001) of the films parallel to (001) of LaGaO3. The Bi2Sr2CaCu2O8 film composition was superconducting as-grown with a zero resistance Tc of 78 K and a ΔTc of 7 K, while the YBa2Cu3O7−x films required an oxidation for optimum properties.
Effect of sputtering current on the growth of Y-Ba-Cu-O films
Authors: Lin R. J.
Published: July 2002

Y-Ba-Cu-O (YBCO) films were grown on (100)MgO and (100)Si substrates by the high-pressure dc diode sputtering process. The target was a Y1Ba2Cu3Ox compound, made by a solid-state reaction. The sputtering gas was Ar-50% O2 and the total pressure was 1.5 Torr. As-deposited superconducting YBCO films can be prepared at low substrate temperatures (420 °C) with a high discharge current. The phases of the as-deposited films strongly relate to the discharge current and substrate temperature. The high concentration of active species (excited atoms and ions) in the plasma during deposition is the main factor that permits superconducting YBCO films to be formed at such low substrate temperatures.
Electronic structure and dynamics of thin Ge/GaAs(110) heterostructures
Authors: Haight R. , Silberman J. A.
Published: July 2002

Using angle-resolved picosecond laser photoemission we have investigated both occupied and transiently excited empty states at the surface of Ge grown epitaxially on GaAs(110). We observe a normally unoccupied, Ge layer derived state whose separation from the valence-band maximum of the system is 700±50 meV at six monolayers Ge coverage. The evolution of the electronic structure is followed as a function of coverage and correlated with low-energy electron diffraction. The time dependence of the transiently occupied Ge signal is compared with that of the clean GaAs(110) surface and shows that electrons are prevented from diffusing into the GaAs bulk by the conduction-band offset of 330±40 meV.
In situ observations of optical emission spectra in the diamond deposition environment of arc discharge plasma chemical vapor deposition
Authors: Zhang Fangqing , Zhang Yafei , Yang Yinghu , Chen Guanghua , Jiang Xiangliu
Published: July 2002

In order to investigate the growth mechanism of diamond thin films, the in situ optical emission spectra of direct current (dc) arc discharge plasma, including the spatial distributions and different CH4/H2 ratios, have been measured during the growth processes of diamond thin films prepared by the dc arc discharge plasma chemical vapor deposition method. The results show that there are a great number of atomic hydrogens in the arc discharge plasma. This is the key factor for the growth of diamond films with a high rate and high quality. In addition, the effects of the CH4/H2 ratio on the quality of diamond films are discussed in detail in this letter.
Ultrafast optical nonlinearities of type II AlxGa1−xAs/AlAs multiple quantum wells
Authors: Feldmann J. , Göbel E. , Ploog K.
Published: July 2002

We present experimental studies of the transient optical nonlinearities near the direct band gap of type II AlxGa1−xAs/AlAs multiple quantum wells. The response of the optical nonlinearity at the band-gap excitonic transition is critically dependent on laser photon energy. A complete recovery of the bleached absorption in the lower part of the excitonic resonance with a picosecond time constant at room temperature occurs due to an enhanced collision broadening of the excitonic resonance after the fast spatial Γ–X transfer. Our results demonstrate that the intrinsic response of optical devices based on exciton nonlinearities can be much faster in type II structures as compared to type I structures.
Deep energy levels of substitutional impurity pairs in the wurtzite semiconductor ZnS
Authors: Wu Xiaojiang , Huang Mingzhu , Ren Shang Yuan
Published: July 2002

Employing the on-site tight-binding Koster–Slater Green’s function method, the deep energy levels of two series of paired substitutional sp3-bonded impurities in the II-VI wurtzite semiconductor ZnS are presented. The chemical trends in the deep levels, as the spectator impurity varies, are predicted.
Behavior of high dose O+-implanted Si/Ge/Si structures
Authors: Zhang J. P. , Tang Y. S. , Robinson A. K. , Bussmann U. , Hemment P. L. F. , Sealy B. J. , Newstead S. M. , Powell A. R. , Whall T. E. , Parker E. H. C.
Published: July 2002

The synthesis of a buried oxide layer in multilayer Si/Ge/Si structures by the implantation of high doses of 200 keV O+ ions is studied by Rutherford backscattering analysis. The presence of Ge is found to have a minimal effect upon the mass transport of excess oxygen and interstitial silicon. Infrared transmission spectroscopy and x-ray photoelectron spectroscopy confirm that the oxygen atoms bond preferentially to silicon forming silicon dioxide and SiOx, where x<2, with no evidence for Ge—O bonding.
Is the cation sticking coefficient unity in molecular beam epitaxy at low temperature?
Authors: Chiu T. H. , Chu S. N. G.
Published: July 2002

Using identical Ga flux density, we have measured the growth rate difference between GaAs and GaSb. The large discrepancy of 15% seems to suggest a change in the sticking coefficient of Ga when different group V species are involved. However, when lattice parameters are taken into account correctly, the discrepancy appears to be a natural consequence because fewer Ga atoms are needed to complete a monolayer on the GaSb surface. Similar results are also observed for the growth of Al(Sb,As) and In(Sb,As). This points to the possible systematic error in the estimation of ternary composition, such as InGaAs, by adding the growth rates of binary constituents InAs and GaAs without correction for change in lattice constants.
Reducing slip in a far-infrared free-electron laser using a parallel-plane waveguide
Authors: Ride S. K. , Pantell R. H. , Feinstein J.
Published: July 2002

There are several interesting applications for a picosecond, far-infrared (100–1000 μ) free-electron laser. One obstacle to its development is the slip that occurs between the electron beam and the radiation. This can be reduced by operating the laser in a parallel-plane waveguide, and choosing the laser parameters and transverse guide dimension such that the group velocity of the wave nearly matches the axial velocity of the electrons. The laser wavelength depends on both the electron energy and the waveguide dimension, and the laser can be tuned by varying either. Both the tuning characteristics and the slip as a function of wavelength are different from those of a conventional free-electron laser.
Hydrogen annealing of PtSi-Si Schottky barrier contacts
Authors: Tsaur B-Y. , Mattia J. P. , Chen C. K.
Published: July 2002

Schottky barrier PtSi-Si diodes formed by ultrahigh vacuum deposition and annealing of 1-nm-thick Pt films on n- and p-type (100) Si substrates were characterized by current-voltage measurements at liquid-nitrogen temperature. The diodes exhibited nearly ideal characteristics, with barrier heights of 0.914 and 0.197 eV, respectively, for typical n- and p-type devices. Subsequent annealing in hydrogen increased the barrier height by 0.013 eV for the n-type devices and decreased it by the same amount for the p-type devices. Vacuum annealing of H2-annealed devices restored the barrier heights to approximately their initial values. These results can be attributed to the presence of Si interface defects that are passivated by hydrogen incorporation and subsequently reactivated by vacuum annealing to remove the hydrogen.
Optical measurement of electron bunching in vacuum
Authors: Smith Richard S. , Woodard Nathan G.
Published: July 2002

We report the homodyne detection of phase modulation sidebands induced on a laser beam by a coherently bunched electron beam. This provides a sensitive and nonperturbing measurement of complex Fourier time series components of the electron density. A proof-of-principle measurement of the microwave frequency component of electron density in a crossed-field device, which agrees well with a calculation of the same quantity, is reported.
Flux motion in a two-dimensional single-crystal Nb film
Authors: Hsu J. W. P. , Kapitulnik A.
Published: July 2002

We have studied thermally activated flux motion (flux creep) in the resistive transition of a single-crystal ultrathin (20 Å) Nb film in perpendicular magnetic fields. This thermally activated resistance extends over four decades from 0.5 Rn to 10−5 Rn. Possible pinning mechanisms and the field dependence of the activation energy are discussed. Comparisons between this system and the high Tc cuprate superconductors, which are quasi-two-dimensional in nature, are made.
Reflection high-energy electron diffraction studies of the growth of strained InxGa1−xAs on GaAs substrate by migration-enhanced epitaxy
Authors: Chen Y. C. , Bhattacharya P. K. , Singh J.
Published: July 2002

Reflection high-energy electron diffraction oscillations have been studied during the growth of strained InxGa1−xAs on GaAs by molecular beam epitaxy and migration-enhanced epitaxy. The oscillations decay rapidly for x≳0.2 during molecular beam epitaxy, while they persist for a long while during migration-enhanced epitaxy. We believe that the altered surface reconstruction pattern in the latter case changes the growth mode from three-dimensional to a near perfect two-dimensional mode for high strain values. Using migration-enhanced epitaxy, we demonstrate improved channel mobility and performance of GaAs-based modulation-doped field-effect transistors and narrower linewidths in the low-temperature excitonic photoluminescence of In0.1Ga0.9As/Al0.3Ga0.7As quantum wells.
Efficient generation of ultrafast broadband radiation in a submillimeter liquid-core waveguide
Authors: Zhou J. Y. , Wang H. Z. , Yu Z. X.
Published: July 2002

An experimental investigation of picosecond laser propagation in a submillimeter liquid-core waveguide is presented. It is observed that the pump is spectrally broadened towards its Stokes frequency upon passing through the waveguide and the spectral bandwidth is further extended by stimulated raman scattering. This stable ultrafast broadband radiation is shown to be enhanced due to the use of the waveguide.
Metalorganic vapor phase epitaxial growth of high quality InGaAs on InP using tertiarybutylarsine
Authors: Abdalla M. I. , Kenneson D. G. , Powazinik W. , Koteles E. S.
Published: July 2002

We report the growth by low-pressure metalorganic vapor phase epitaxy of lattice-matched InGaAs on InP substrates using tertiarybutylarsine as the arsenic source. The grown layers are uniform in composition and are consistently n type with low background carrier concentrations (2–3×1015/cm3). Room-temperature mobility as high as 11 200 cm2/V s with a corresponding 77 °K mobility of 57 000 cm2/V s are measured. Photoluminescence gave a strong narrow peak with a full width half maximum=3.1 meV, with no evidence of carbon incorporation.