bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of superconductivity in Y-Ba-Cu-O films by Si ion implantation
Authors: Ma Q. Y. , Dosanjh P. , Carolan J. F. , Hardy W. N.
Published: July 2002

A method of converting an oxide Y-Ba-Cu-O (YBCO) film from superconducting into insulating film is presented. With implanted Si ions, the film loses its electrical conductivity and diamagnetism while its crystalline structure is preserved. The process allows the growth of an epitaxial YBCO film on top of the inhibited area, thus providing an effective method of patterning high temperature superconducting multilayer structures.
Generation of 20 mW of blue laser radiation from a diode-pumped sum-frequency laser
Authors: Kean P. N. , Standley R. W. , Dixon G. J.
Published: July 2002

Resonant intracavity sum-frequency mixing of a diode-pumped Nd:YAG laser and a 100 mW single stripe laser diode, has been used to generate a measured output power of 20 mW of blue laser radiation at 459 nm. This represents a total conversion efficiency of approximately 68% of the single stripe laser diode power incident on the cavity. The laser was also demonstrated to operate over a tuning range of 12 nm via angle tuning of the nonlinear crystal.
Model for reflection high-energy electron diffraction intensity recovery during GaP growth in laser-triggered chemical beam epitaxy
Authors: Vaccaro Pablo , Hashimoto Tadao , Yoshimoto Masahiro , Matsunami Hiroyuki
Published: July 2002

Reflection high-energy electron diffraction (RHEED) intensity has been observed while growing GaP by laser-triggered chemical beam epitaxy simultaneously using a supply of triethylgallium (TEGa) and phosphine (PH3). The intensity decreases after each laser pulse, and then it recovers the original value. We present a semiquantitative model in order to explain the RHEED intensity changes. We assume that initially a GaP surface is saturated with chemisorbed diethylgallium (DEGa) and physisorbed TEGa. Laser irradiation decomposes a fraction of chemisorbed DEGa, and it reacts slowly with impinging P. TEGa is quickly chemisorbed on the just-reacted GaP and the initial condition is recovered. This model properly fits the experimental data and it allows a deeper understanding of chemical reactions on the surface during chemical beam epitaxial growth of GaP.
Evidence of rapid equilibration near the hot filament in diamond deposition
Authors: Ihara M. , Miyamoto K. , Yasuda T. , Komiyama H.
Published: July 2002

Chemical composition of the gas phase during the diamond growth by a hot-filament method was measured gaschromatographically for two different configurations with feed gas introduction, the conventional method from a nozzle equipped on a reactor wall and the jet feed from a hole bored in a substrate located just beneath the filament. CH4 and C2H2, diluted in H2, were used as a source gas. The results indicated that equilibration took place so rapidly near the filament that even the jet-feed mixture was converted to a thermodynamically stable composition composed mainly of C2H2, H, and H2. Insensitivity of the diamond process to the source hydrocarbon and its sensitivity to the filament-and-substrate configuration can be well interpreted.
Excimer laser ablation and activation of SiOx and SiOx-ceramic couples for electroless copper plating
Authors: Godbole Mukund J. , Lowndes Douglas H. , Pedraza A. J.
Published: July 2002

A XeCl (4.0 eV photon energy) pulsed excimer laser was used to study the ablation behavior of substoichiometric silicon oxide (SSO), SiOx with x∼1.0. The SSO ablation rate was quite high and its ablation threshold quite low (≤0.3 J/cm2), thereby making it an interesting material for pulsed laser patterning without the use of deep-UV radiation. Surface activation, as illustrated by subsequent copper deposition by the electroless process, was observed along well-defined narrow (∼10–20 μm) lines just beyond the edges of ablated trenches in SSO deposited on XeCl-transparent fused silica substrates. When a thin layer of SSO was deposited on polycrystalline Al2O3 or AlN substrates and subsequently laser treated, surface activation of these ceramics occurred on the laser-irradiated regions at much lower fluences and with fewer exposures than are required to activate the bare ceramic substrates. In both types of experiment, activation is believed to result from redeposition of elemental silicon, an ablation product.
Two-terminal bias induced dual wavelength semiconductor light emitter
Authors: Zhang D. , Reed F. E. , Zhang T. , Edwards N. V. , Kolbas R. M.
Published: July 2002

A new form of light emitting devices called BICE (bias induced color-tunable emitter) is reported. It is a voltage controlled multiwavelength semiconductor light emitter based on the bias dependent injection and collection of electrons and holes in quantum wells. In this letter, two-terminal dual wavelength BICE operation is demonstrated. It exhibits coaxial optical output, a large separation between emission wavelengths (≳500 Å) and an emission contrast ratio ranging from 4:1 to 1:33 at 77 K.
Synthesis of (BiPb)2Sr2Ca2Cu3O10 superconducting thin films on MgO using a multilayered pulsed laser deposition method
Authors: Sajjadi Amin , Boyd Ian W.
Published: July 2002

Superconducting thin films of Pb-doped BiSrCaCuO have been prepared on (001) orientation MgO substrates by a multilayer pulse laser deposition technique using both BiPbSrCaCuO and PbO targets. The PbO target was used to dope Pb into the films in sufficient quantity to facilitate the growth of the 2223 phase. The effect of post-annealing temperature and time duration on the formation of this phase is described. Using x-ray diffraction and resistivity measurements we have found that a near optimum single phase 2223 film can be grown by post-annealing the sample at 854 °C for 15 h in air. The films grown are highly c-axis oriented and exhibit Tc(zero) as high as 105.5 K.
Step-flow growth with step crossing: The effect of preferential return of adatoms on terrace width stability
Authors: Harris S.
Published: July 2002

We consider the evolution of terrace widths for the case, at step-flow conditions, where the adatom-step exchange kinetics include the possibility of step crossing as well as sticking. We find that the stability criteria are determined by the crossing probabilities, with stability resulting when crossing the lower step is favored. This result is based on a description that takes into account adatom diffusion on the terraces; the result is in direct conflict with that previously obtained which is based on computer simulations of a probabilistic model that does not include an adatom migration mechanism and fails to take into account the correlation effect due to the preferential return of adatoms to a crossed step.
Reactive cluster beam etching of fine patterns
Authors: Chung C. W. , Brock J. R. , Trachtenberg I.
Published: July 2002

A new etching technique, reactive cluster etching, has been developed, using a cluster beam of ultrafine particles formed by supersonic nozzle expansion. The method demonstrates good anisotropy and selectivity in delineation of submicrometer patterns in SiO2.
Single-frequency GaInAsSb/AlGaAsSb quantum-well ridge-waveguide lasers emitting at 2.1 μm
Authors: Choi H. K. , Eglash S. J. , Connors M. K.
Published: July 2002

Ridge-waveguide lasers emitting at ∼2.1 μm have been fabricated from a GaInAsSb/AlGaAsSb quantum-well heterostructure grown on a GaSb substrate by molecular beam epitaxy. The cw threshold current is as low as 29 mA at room temperature, and the maximum cw output power is 28 mW. The lasers operate in a single longitudinal mode which can be continuously tuned without mode hopping over 1.2 nm by changing the heatsink temperature and over 0.8 nm by changing the current.
Effects of a predeposited boron layer during the epitaxial growth of Ge on CaF2
Authors: Cho C.-C. , Liu H.-Y. , Magel L. K. , Anthony J. M.
Published: July 2002

Using a thin predeposited B layer prior to the epitaxial growth of Ge on CaF2, we have obtained significantly improved Ge crystalline quality and surface morphology for Ge/CaF2/Si(111) and Ge/CaF2/Si(100) structures. Although B acts as a surfactant in suppressing island formation, it does not migrate to the growth front during Ge growth, which was widely observed in the surfactant-assisted epitaxial growth of Ge on Si. The B predeposit also prevents Ca from migrating to the Ge surface, and promotes A-type epitaxy of Ge(111) when Si(111) substrates are used.
Stacking fault pyramid formation and energetics in silicon-on-insulator material formed by multiple cycles of oxygen implantation and annealing
Authors: Lee J. D. , Park J. C. , Venables D. , Krause S. J. , Roitman P.
Published: July 2002

The defect microstructure of silicon-on-insulator wafers produced by multiple cycles of oxygen implantation and annealing was studied with transmission electron microscopy. The dominant defects are stacking fault pyramids (SFPs), 30–100 nm wide, located at the upper buried oxide interface at a density of ∼106 cm−2. The defects are produced by the expansion and interaction of narrow stacking fault (NSF) ribbons pinned to residual precipitates in the top silicon layer. Consideration of the energetics of the transformation from a collection of four NSF ribbons to a single SFP indicates that the reaction is energetically favorable below a critical NSF length. Thus small defects are stable as SFPs while large defects are stable as NSF ribbons.
Electrical transport across oxygen-doped-silicon buried layers by substoichiometric oxygen ion implantation in silicon
Authors: Srikanth K. , Ashok S.
Published: July 2002

The electrical and physical property changes of c-Si after substoichiometric oxygen ion implantation have been investigated using I-V, spreading resistance, secondary ion mass spectroscopy, spectroscopic ellipsometry and Fourier transform infrared spectroscopy. A key observation is the presence of donors in the vicinity of the implanted region, resulting in extensive counterdoping of p-type c-Si. Redistribution of the oxygen atoms during the high-temperature anneal results in sharp interfaces aiding the formation of a heterojunction. Mesa-type diodes on the implanted sample exhibit excellent rectification with a diode ideality factor n of 1.2 and a reverse saturation current density of 1×10−8 A/cm2. The near-surface region is shown to be crucial for achieving the high rectification behavior
Structural and thermal properties of (YBa2Cu3)1−xNaxO7−δ materials
Authors: Chen Christina H. , Kumar Binod
Published: July 2002

This letter discusses experimental data on thermal expansion and thermogravimetric analysis (TGA) to elucidate the structural and thermal characteristics of (YBa2Cu3)1−xNaxO7−δ materials. The experimental data reveal that the incorporation of sodium in the (YBa2Cu3)1−xNaxO7−δ materials stabilizes its orthorhombic structure and makes it less sensitive to oxygen resorption and desorption processes. In addition, the sodium doping was found to raise the orthorhombic↔tetragonal phase transformation temperature. Furthermore, the Auger electron spectroscopy (AES) data reveal that sodium selectively replaces yttrium in the crystal lattice.
Limited spatial region for synchronous beam-wave interactions in rotating mode resonators
Authors: Velazco J. E. , Mako F. M.
Published: July 2002

An electron beam passing along an axisymmetric static magnetic field under the presence of circularly polarized electromagnetic fields, launched in a suitable rotating mode resonator, can propagate as a growing helix. This helix rotates temporally with an angular velocity equal to that of the cavity’s rotating mode. When the axial magnetic field is adjusted to obtain matching between the electrons gyrofrequency and fields rotating frequency, the electrons maintain phase coherence with the wave during the interaction. Synchronous beam-wave interactions will be shown to be limited to a spatial region near the resonator axis. This limited synchronous region results from the rotating-wave phase velocity exceeding the velocity of the particle beam.
Nonthermoluminescent dosimetry based on the afterglow response of europium-doped alkali halides
Authors: Pérez Salas R. , Meléndrez R. , Aceves R. , Barboza-Flores M.
Published: July 2002

A new nonthermoluminescent dosimetric technique was developed by using the afterglow response characteristic of alkali halide single crystals doped with europium ions. The afterglow luminescence decayed very slowly and its intensity was proportional to the radiation dose. The radiation dose was measured by the time intergration of the afterglow signal in a selected region. This afterglow dosimetry was compared with the conventional thermoluminescent method, by using single crystals of different alkali halides. The results show that the technique is suitable and versatile for ultraviolet and x-ray radiation dose determination.
Palladium carbide nanoparticles by gas flow reaction synthesis
Authors: Yamamoto Takao , Adachi Motoaki , Kawabata Keisuke , Kimura Keisaku , Hahn Horst W.
Published: July 2002

Nanoparticles of palladium carbide, a metastable phase with carbon atoms on interstitial sites of metallic lattice, were synthesized by a single process, which allows palladium metallic nanoparticles formed by vapor condensation in flowing argon carrier gas to immediately come in contact with acetone vapor. The average particle size observed by transmission electron microscopy is 5 nm and the geometric standard deviation of the distribution is 1.5.
Quantum dots as a tunable microwave quantum detector
Authors: Meurer B. , Vieren J. P. , Guldner Y. , Ploog K.
Published: July 2002

In arrays of field-effect confined quantum dots, we observe a novel resonant photovoltaic response to microwave and far-infrared radiation. A maximum photosignal of 5 μV at an incoming microwave power of less than 1 mW is detected when the frequency of the radiation matches the resonance condition of the electrons confined in the quantum dots. The response frequency is tunable by means of the gate voltage or an external magnetic field. This observation leads to an efficient quantum detector working up to temperatures of about T=6 K and to a novel spectroscopic tool for the investigations of low-dimensional electronic systems.
Laser-induced fluorescence detection of polycyclic aromatic hydrocarbons in a dc arcjet used for diamond deposition
Authors: Raiche George A. , Jeffries Jay B.
Published: July 2002

Using laser-induced fluorescence techniques, we have made measurements in a dc arcjet plasma which grows chemical vapor deposition diamond. Here we present evidence for the gas-phase formation of polycyclic aromatic hydrocarbons in the diamond growth environment. We discuss their presence in the context of hydrocarbon flame chemistry, and speculate on the role of aromatics in diamond film formation.
Carrier escape mechanisms from GaAs/AlxGa1−xAs multiple quantum wells in an electric field
Authors: Fox A. M. , Ispasoiu R. G. , Foxon C. T. , Cunningham J. E. , Jan W. Y
Published: July 2002

We have studied the vertical transport mechanisms in GaAs/AlxGa1−xAs multiple quantum wells in electric fields from the temperature dependence of the photocurrent. On heating from 10 K, we observed a decrease in the photocurrent up to ∼100 K, followed by a steady increase up to room temperature. The decrease is shown to be consistent with charged-impurity-assisted nonresonant tunneling which varies as T−1/2 in two dimensions, while the increase is consistent with thermal emission. The low field activation energy measured in a sample with x=0.33 is consistent with the thermal emission of heavy holes.
Growth of superconducting Y-Ba-Cu-O films on spinel and garnet
Authors: Chan Siu-Wai , Chopra Manoj , Chi Cheng-Chung , Frey Tony , Tsuei Chang C.
Published: July 2002

Spinel and garnet single crystals of low dielectric constants and loss tangents have been investigated as possible substrate materials for the growth of the Y-Ba-Cu-O superconducting films. In addition to their desirable dielectric properties, these materials are chemically compatible with silicon and compound semiconductors and can be used as the interface materials for the integration of cuprate superconducting films with semiconducting devices. The Y-Ba-Cu-O films grown on (001) MgAl2O4 and (001) Y3Al5O12 from a co-evaporation deposition with a subsequent wet anneal exhibit superconductivity with a transition temperature Tc(R=0) of 57 and 74 K, respectively, while strongly (001) textured YBa2Cu3O7−x films from the in situ laser deposition grown on (001) MgAl2O4 and (001) Y3Al5O12 show superconducting transition temperatures Tc(R=0) of 77 and 87 K, respectively. Our work demonstrates that these two materials are viable substrates for the Y-Ba-Cu-O thin films in high frequency device applications.
Anomalous excitation density dependence of nonlinear optical responses in pseudoisocyanine J aggregates
Authors: Sasaki Fumio , Kobayashi Shunsuke
Published: July 2002

Anomalous excitation density dependence of nonlinear optical (NLO) responses in pseudoisocyanine bromide J aggregates have been observed at 77 K. The degenerate four-wave mixing signals decrease with the increase of the excitation density between 1 and 3 μJ cm−2. This anomalous excitation density dependence shows that the J aggregates in themselves have a switching property and can be used as an optical logic element with an exclusive OR function. This is the first observation of the inverted region in which the NLO properties decrease with the increase of the excitation density. The anomaly is ascribed to the coherent exciton-exciton interaction in a one-dimensional molecular aggregate.
Motion of ions in an electron cyclotron resonance plasma
Authors: Köhler W. E. , Römheld M. , Seeböck R. J. , Skaberna S.
Published: July 2002

The motion of ions emerging from an electron-cyclotron-resonance plasma source has been investigated. Trajectories have been calculated by solving the ion equations of motion in a divergent magnetic field and an electrostatic longitudinal accelerating field which has to be evaluated self-consistently. The trajectory calculations have been combined with a Monte Carlo procedure for choosing the initial ion phase space variables in order to study the propagation of the ion distribution function. It is shown that outside the chamber the spatial profile of this distribution is increasingly broadened with distance from the second magnet due to the diverging magnetic field lines, while at the same time the ions gain energy from the electrostatic field. For an argon plasma a mean ion beam energy of about 16 eV with respect to the plasma source potential results at the target plane in a distance of 60 cm from the source.
Magneto-optic buried channel waveguides for a 45° nonreciprocal waveguide rotator
Authors: Sugimoto N. , Katoh Y. , Tate A.
Published: July 2002

An optical isolation ratio of −21.1 dB at λ=1.55 μm is obtained for a LPE-grown La and Ga substituted YIG single-mode buried channel waveguide. Waveguides about 3 mm long end-butted to single-mode fibers show an overall insertion loss of less than 2 dB. The Ar ion-beam etching technique using a three layered etching mask provides sufficient control of both the width (∼4 μm) and height (∼4 μm) of the core ridge. The core and cladding layers are individually grown from melts with different compositions in order to reduce stress-induced birefringence. The good reproducibility with which 45° waveguide rotators exhibiting a circular near-field intensity pattern can be fabricated will enable us to realize optical integration in future systems.
Gain-current characteristics of strained AlGaInP quantum well lasers
Authors: Summers H. D. , Blood P. , Rees P.
Published: July 2002

Single quantum well AlGaInP lasers, each having a 65 Å width well have been fabricated with GaxIn1−xP well compositions from x=0.43 to 0.54 grown on substrates orientated 10° off the (100) axis. The threshold currents have been measured from 120 K to room temperature and the samples show a systematic variation with x. At low temperature the results are in good agreement with our calculated gain-current curves and we show that at room temperature the rapid increase in threshold current density with decreasing length is due to a thermally activated leakage current rather than gain saturation.
Fluorine implantation induced tapered waveguide interconnect
Authors: Han Sang-Kook , Subramanian Muthu , Sinha Sanjai , Ramaswamy Ramu V.
Published: July 2002

We report an index tapered waveguide interconnect facilitating transfer of energy from a multi-quantum well region to a single-quantum well region. The adiabatic index tapered structure has been achieved by intermixing of Al/Ga using fluorine implantation induced disordering of GaAs/AlGaAs multi-quantum wells.
Controllable alteration of the pinning energy in Tl2Ca2BaCu2O8 films by proton irradiation
Authors: Weaver B. D. , Reeves M. E. , Summers G. P. , Soulen R. J.
Published: July 2002

Irradiation with 2 MeV protons increases the vortex pinning energy in Tl2Ca2BaCu2O8 films. The maximum pinning energy occurs at a defect density that depends on (1) the density of flux pinning centers in the unirradiated film, (2) the ratio of pinning energies of the pre- and post-irradiation defects, and (3) the effectiveness of the incident particle in creating pinning centers. An explicit formula for the pinning energy as a function of fluence is proposed.
Direct observation of oscillatory interlayer exchange coupling in sputtered wedges using circularly polarized x rays
Authors: Wu Y. , Parkin S. S. P. , Stöhr J. , Samant M. G. , Hermsmeier B. D. , Koranda S. , Dunham D. , Tonner B. P.
Published: July 2002

Oscillations in the magnetic exchange coupling between two ferromagnetic layers separated by Ru are directly observed in magnetron sputtered wedged sandwiches using x-ray magnetic circular dichroism. The magnetization of the lower magnetic layer in the sandwich is saturated in zero field by exchange biasing it to an antiferromagnetic layer of Fe60Mn40. The oscillatory exchange coupling through the Ru wedge causes the direction of the magnetic moment of the upper magnetic layer to rotate back and forth along the wedge and this is directly observed from variations in the intensity of absorption of circularly polarized x rays. Five oscillations in absorption intensity with a period corresponding to ≂11 Å were observed in a Ni81Fe19/Ru/Ni70Co30 wedge.
Study of passive mode locking of semiconductor lasers using time-domain modeling
Authors: Yang Wei , Gopinath Anand
Published: July 2002

Large signal dynamics of passive mode locking of semiconductor lasers is studied in the time domain. A two-section structure is modeled by numerical evaluation of the traveling wave rate equations. The results show simultaneous occurrence of mode locking and self-pulsation over a large parameter range. Typical transient time for mode locking is about 0.2–1.0 ns, and pulse widths of 1.5–8 ps are observed.
Observation of C60 cage opening on Si(111)-(7×7)
Authors: Balooch M. , Hamza A. V.
Published: July 2002

The ‘‘opening’’ of C60 on Si(111)-(7×7) has been directly observed by scanning tunneling microscopy and correlated with Auger electron spectroscopy (AES) and temperature-programmed desorption spectroscopy. Isolated C60 clusters are observed on Si(111)-(7×7) after annealing the surface to 620 K. Annealing the surface to 1020 K causes the C60 cages to open and thereby cover more of the surface. Also evident is that the opened clusters agglomerate on the surface. The opening of the C60 cage is correlated with an increase in the amount of silicon—carbon bonding and with the increase in the carbon-to-silicon AES peak height ratio with increasing annealing temperature. The ratio increases since the opened cages cover more of the substrate silicon atoms, reducing AES emission from the substrate.
Observation of dynamic frequency chirp in dispersive nonlinear semiconductor laser amplifiers
Authors: Pan Zeqi , Dagenais Mario
Published: July 2002

We present a first direct experimental observation of dynamic frequency chirp associated with the turn-on spike in the output of a Fabry–Perot semiconductor laser amplifier. Such a frequency chirp exists because of the change in the refractive index at the onset of light injection due to carrier saturation. The experimental observation is made by using a novel technique to optically isolate the turn-on spike from the steady-state response level. Using this technique, we have also successfully demonstrated conversion of a high duty-cycle data stream to a low duty-cycle data stream of the same frequency, which could have potential applications in optical time division multiplexing.
Diamond growth using remote methane injection in a direct current arcjet chemical vapor deposition reactor
Authors: Reeve S. W. , Weimer W. A. , Dandy D. S.
Published: July 2002

A significant enhancement in the quality of diamond films grown using a remote CH4 carbon source was observed in a direct current arcjet chemical vapor deposition reactor. The linewidths of the diamond peak at 1332 cm−1 in the Raman spectra from these films were reduced from 9.0 to 6.5 cm−1 with no reduction in mass deposition rate as compared to films grown using premixed reactor gas feeds. For diamond growth conditions, the percentage of the reactor feed carbon reaching the substrate was measured to be ∼35%. The enhanced quality of the films is attributed to reduced residence times of the carbon source in the plasma, which would limit the gas phase chemistry from proceeding beyond CH3 formation before the gas reaches the substrate.
New low pressure chemical vapor deposition technique for Ge crystalline thin films
Authors: Yamamoto Masaji , Hanna Jun-ichi , Miyauchi Masato
Published: July 2002

A new type of low pressure chemical vapor deposition for Ge thin films was investigated by using a gaseous mixture of GeF4 and Si2H6. At relatively low gas flow ratios of Si2H6/GeF4, etching of Si substrates was observed and the film growth replaced the etching with an increase in the gas flow ratio. The epitaxial growth was achieved at the low temperature of 350–400 °C on a Si(100) substrate, and at a higher temperature region polycrystalline growth took place. The experimental results suggested a major contribution of reductive surface reaction of GeF4 activated by Si2H6 to the Ge film growth.
Compositional control of PbTiO3 thin films by plasma enhanced metalorganic chemical vapor deposition
Authors: Lee Won Gyu , Woo Seong Ihl , Kim Jong Choul , Choi Soo Han , Oh Kye Hwan
Published: July 2002

PbTiO3 thin films on the Si substrates were prepared by plasma enhanced chemical vapor deposition (PECVD) using Ti(O-i-C3H7)4, Pb(C2H5)4, and oxygen. The composition of PECVD PbTiO3 thin films was intensively influenced by the input flow rate ratio of precursors while it was independent of the deposition temperatures. As-deposited PECVD PbTiO3 thin film showed a uniform distribution of the Pb, Ti, and C component throughout the bulk of film. When an annealing process was performed at 750 °C under the O2 ambient for 1 h, the Pb/(Pb+Ti) ratio of thin films was reduced from 0.567 to 0.509.
Resonant nonlinear optical response of electronic excited state of a cyanine dye crystal with large oscillator strength
Authors: Kawabe Y. , Sakai T. , Ikeda H. , Hasegawa R. , Kawasaki K.
Published: July 2002

Resonant nonlinear optical response was measured in a crystalline cyanine dye MPER, 5-(5-morpholino-2,4-pentadienilydene)-3-ethylrhodanine, which had a broad reflection band due to large oscillator strength of an electronic excited state in the visible wavelength region. Nonlinear optical response measured by the change of reflectivity under optical pumping at the wavelength of the peak of the excited state was composed of fast and slow components. Response time of the fast component was less than 4 ps and its nonlinear optical coefficient χ(3) was evaluated to be (5±2)×10−15 m2/V2 [(4±2)×10−7 esu], which was one of the largest among organic materials.
Escape tunneling out of shallow multiple quantum wells studied by transient four-wave mixing
Authors: von Plessen G. , Feldmann J. , Göbel E. O. , Goossen K. W. , Miller D. A. B. , Cunningham J. E.
Published: July 2002

We demonstrate that transient optical dephasing experiments on electrically biased, shallow multiple quantum wells offer the unique possibility of studying the first step in carrier sweep-out, namely, the tunneling escape out of the individual quantum wells. We find that the electron tunneling times out of the quasibound n=1 quantum well states into the continuum states lie in the subpicosecond regime at high electric fields. In addition, the experimentally determined escape rate is resonantly enhanced when the quasibound n=1 quantum well state couples with the resonant n=2 continuum state originating from the second-nearest neighbor well.
Optical investigation of interwell coupling in strained Si1−xGex/Si quantum wells
Authors: Fukatsu S. , Shiraki Y.
Published: July 2002

Photoluminescence is reported in strained Si1−xGex/Si(100) coupled double quantum well (CDQW) systems. Systematic red shift of luminescence energy was found in symmetric CDQWs with decreasing width of the Si barrier centered at the DQW, the characteristics of which were used to determine the band offsets. The total and valence-band discontinuities, ΔEc+ΔEv=156 meV and ΔEv=149±1 meV, were obtained, suggesting that the band alignment is of type I for x=0.177. Variation of the inserted Si barrier width in asymmetric CDWs revealed well-resolved spectral evolution due to the reduction in tunneling-controlled carrier escape competing with the radiative recombination.
Impurity levels in heterostructures for optical absorption and emission
Authors: Parihar S. R. , Lyon S. A.
Published: July 2002

We present calculations showing the effect of placing impurities in quantum wells and heterostructure barriers. With a suitable configuration of the band edge, both the spacing of energy levels and their ordering can be controlled. The results should be of use in designing more flexible impurity infrared detectors and enhancing the radiative efficiency of transitions between impurity levels.
On the determination of the fully critical field and critical current density from the Bean model
Authors: Paulius L. M. , Almasan C. C. , Maple M. B.
Published: July 2002

A direct method for determining the magnetic field Hfcs at which a superconductor enters the fully critical state (i.e., the field at which flux first penetrates throughout the entire sample) is described, and a formula for calculating the critical current density JcH from the value of Hfcs is presented. The behavior of JcH(x) is compared to the variation of the fluxoid pinning energy U, inferred from magnetic relaxation measurements in the Y1−xPrxBa2Cu3O7−δ system.
Backscattered deposition in Ar sputter etch of silicon dioxide
Authors: Chang C. Y. , McVittie J. P. , Saraswat K. C. , Lin K. K.
Published: July 2002

Detailed mechanisms of sputter etch of silicon dioxide in argon plasma are studied using a novel test structure. We have found that a significant amount of the sputtered material (up to 50% of the sputter flux) returns, as an isotropic backscattered flux to the wafer. This backscattered flux results in significant deposition that cannot be accounted for by redeposition, i.e., line-of-sight deposition of the sputtered material, alone. A profile simulator is used to demonstrate a new physical model for the Ar sputter-etch process, based on the interaction of three simultaneous processes: (1) sputtering, (2) direct (i.e., line-of-sight) redeposition of sputtered material, and (3) isotropic deposition of sputtered material backscattered from the gas phase. Simulated profiles show good agreement with experimental results on the test structure and a common device structure.
Role of excitation frequency in a low-pressure, inductively coupled radio-frequency, magnetized plasma
Authors: Cui Chunshi , Boswell R. W.
Published: July 2002

We have experimentally studied the role of the excitation frequency frf in a low-pressure, inductively coupled radio-frequency (rf), magnetized plasma. Planar Langmuir probe measurements of the electron energy distribution function and the plasma density ne clearly demonstrate a sudden change in the nature of plasma-rf coupling as frf approaches the electron cyclotron frequency fce from below or above. The observed mode change is qualitatively explained by different wave coupling mechanism for frf<fce and frf≳fce. These observations could have important applications for plasma processing.
Low-temperature in situ preparation of ferroelectric Pb(Zr0.55Ti0.45)O3 thin films by reactive sputtering
Authors: Li Xingjiao , Liu Jianshe , Zeng Yike , Liang Junwen
Published: July 2002

Ferroelectric thin films with a composition Pb(Zr0.55Ti0.45)O3 have been prepared on Pt-coated Si substrates by a reactive sputtering technique at substrate temperatures as low as 250 °C. By means of x-ray diffraction, titanium zirconium oxide was identified as one of the reaction products. Based on this fact, a possible Pb(Zr,Ti)O3 formation mechanism has been proposed. X-ray diffraction patterns of these films show nearly no pyrochlore phase. Ferroelectric hysteresis loops show a remanent polarization of 25.6 μC/cm2 and a coercive field of 17.1 kV/cm.
Equilibrium dissociation configuration of misfit dislocations in low strained In0.1Ga0.9As/GaAs single heterostructures
Authors: Zou J. , Cockayne D. J. H.
Published: July 2002

Equilibrium dissociation configurations of 60° misfit dislocations in low strained [001] In0.1Ga0.9As/GaAs single heterostructures are investigated by high resolution electron microscopy. The dissociation configuration of misfit dislocations is with the 90° partial being located near the strained interface and the 30° partial lying in the substrate. The equilibrium dissociation width of misfit dislocations has the same value as that in the bulk GaAs material. This equilibrium geometry is explained using the elasticity theory.
Nonconservative formation of 〈100〉 misfit dislocation arrays at In0.2Ga0.8As/GaAs(001) interfaces during post-growth annealing
Authors: Chen Y. , Liliental-Weber Z. , Washburn J. , Klem J. F. , Tsao J. Y.
Published: July 2002

Transmission electron microscopy is applied to investigate the effect of annealing on misfit dislocations in an In0.2Ga0.8As/GaAs(001) heterostructure. In as-grown samples, an orthogonal array of 60° dislocations along 〈110〉 directions is observed in the interface. During annealing, the 60° dislocations along 〈110〉 directions are bent from 〈110〉 directions toward 〈100〉 directions. The process represents a new strain relaxation mechanism in semiconductor heterostructures. As the dislocation segments along 〈100〉 can relieve the strain more effectively than 60° dislocations, we propose that the dislocations move nonconservatively in or near the interface by diffusion along the dislocation cores or in the heterointerface.
10 GHz bandwidth monolithic p-i-n modulation-doped field effect transistor photoreceiver
Authors: Dutta N. K. , Lopata J. , Berger P. R. , Wang S. J. , Smith P. R. , Sivco D. L. , Cho A. Y.
Published: July 2002

A photoreceiver circuit using an InGaAs p-i-n photodiode and InGaAs/InAlAs pseudomorphic modulation-doped field effect transistor (MODFET) based preamplifier has been fabricated. The 18 μm diam photodiode has a bandwidth of 29 GHz and the ft and fmax of the MODFET are 26 and 30 GHz, respectively. The photoreceiver circuits have bandwidths of 10 GHz and 17 dB gain. The sensitivity at 2.5 Gb/s is −26.4 dBm.
Evidence of a shallow junction formation from plasma enhanced chemical vapor deposition of boron nitride and silicon boron nitride
Authors: Nguyen Tue , Van Nguyen Son , Dobuzinsky David M.
Published: July 2002

Dielectric constant characterization of plasma-enhanced chemical vapor deposition (PECVD) of boron nitride (BN) and silicon boron nitride (SiBN) films is studied using metal-insulator-semiconductor (MIS) and metal-insulator-metal (MIM) structures. Using the measurement technique of calculating the dielectric constant value from the capacitance, the average dielectric constant value for the BN and SiBN films deposited under similar conditions can vary as much as 40% (from 2.8 to 4.4). Low dielectric constant values are normally observed on MIS structures where the silicon substrate is n-type. Detailed C-V analysis at various test frequencies (100 Hz–1 MHz) shows that the flatband and the threshold voltages shift more than 30 V in n-type and p-type substrate wafers, respectively. These C-V characteristics suggest the formation of a junction at the insulator-substrate interface. This interface junction is probably formed by the boron-rich nitride deposition during the transient period and subsequent boron diffusion to the silicon substrate. Accounting for this p-n junction on n-type substrate wafers, the adjusted dielectric constant for MIS structures on n-type substrate is between 4 and 5, which is the same for MIS structures on p-type substrate and MIM structures.
Photoelastic AlGaAs/GaAs waveguide polarizer
Authors: Yu L. S. , Guan Z. F. , Liu Q. Z. , Deng F. , Pappert S. A. , Yu P. K. L. , Lau S. S. , Florez L. T. , Harbison J. P.
Published: July 2002

AlGaAs/GaAs double heterostructure transverse-electric (TE) waveguide polarizers, 5 mm long, with extinction ratios exceeding 20 dB and excess losses of <1 dB have been fabricated using simple thin film technology. The single-mode photoelastic waveguides were made by depositing either a thin Ni film (∼1000 Å) with a 5-μm-wide window stripe pattern followed by thermal annealing or a thin W film (∼900 Å) with a 5-μm stripe pattern using rf sputtering with the substrate under negative dc bias. The polarization mode selection is caused by the stress-induced birefrigence of the photoelastic waveguides. The change in dielectric constant due to stresses in the thin film structure was obtained from the experimental intensity output profile using an iterative calculation method. The tensile stress is 3×109 dyn/cm2 in the fully reacted Ni3GaAs stressor layer. The stress in the as-sputtered W films was compressive and decreased from 1×1010 dyn/cm2 to 4×109 dyn/cm2 after annealing between 300 and 500 °C for 30 min.
Suppression of threading dislocation generation in highly lattice mismatched heteroepitaxies by strained short-period superlattices
Authors: Kawai T. , Yonezu H. , Ogasawara Y. , Saito D. , Pak K.
Published: July 2002

The threading dislocation density was remarkably reduced in highly lattice mismatched heteroepitaxies of the In0.5Ga0.5As/GaAs(001) and GaAs/GaP(001) systems. The two-dimensional growth mode was obtained even after the lattice relaxation by applying the strained short-period superlattices. The misfit dislocations aligned along the 〈110〉 direction were mainly generated at heterointerfaces. The misfit strain was relieved by the generation of the misfit dislocations in the absence of three-dimensional island growth. It was found that the generation of threading dislocations is effectively suppressed by introducing strained short-period superlattices at the initial growth stage of highly lattice mismatched heteroepitaxies.
Schottky characteristics of GaAs surface cleaned by ultrasonic running deionized water treatment
Authors: Hirota Y.
Published: July 2002

Schottky characteristics for n-type (001)-GaAs surfaces prepared by ultrasonic running deionized water treatment (URDIW) are investigated by measuring Schottky diodes. Schottky barrier height for the URDIW treated surfaces is more sensitive to the metal work function, and is smaller compared to those of the chemically etched surfaces. We discuss Schottky characteristics for the URDIW treated surfaces based on the hydrogen-terminated model.
Ultrahigh mobility two-dimensional electron gas in AlxGa1−xAs/GaAs heterostructures by organometallic vapor phase epitaxy
Authors: Basco Ricardo , Agahi Farid , Lau Kei May
Published: July 2002

Ultrahigh mobility AlxGa1−xAs/GaAs two-dimensional electron gas (2DEG) structures were grown by conventional low-pressure organometallic vapor phase epitaxy (LP-OMVPE). We achieved maximum mobilities of 766 000 cm2/V s at 2.2 K and 171 000 cm2/V s at 77 K after exposure to light (to our knowledge, the highest ever by OMVPE growth), with a sheet carrier density of 4.9×1011/cm2. The high-mobility structures were obtained by either growing an AlGaAs-related buffer underneath the 2DEG structure or preconditioning of the reactor with an undoped AlGaAs run. The dark mobilities of samples grown with the preconditioning procedures and without the AlGaAs-related buffer are much higher than those with the buffer.
Observation of spin structure related positive magnetoresistance in antiferromagnetically coupled magnetic multilayers
Authors: Parkin S. S. P.
Published: July 2002

We report the observation of a previously unobserved positive magnetoresistance effect in several antiferromagnetically coupled magnetic multilayers. The effect is typically very small with the largest magnetoresistance values observed of less than 0.1% at 4.2 K. We find that the effect is common in magnetic multilayers comprised of magnetic layers of Fe and Co and spacer layers composed of elements from the left hand portions of the 4d and 5d transition metal periods. We propose the magnetoresistance is a consequence of Lorentz magnetoresistance and is unrelated to the giant magnetoresistance effect observed in related structures.
Pulse buildup in passively mode-locked monolithic quantum-well semiconductor lasers
Authors: Solgaard Olav , Kiang Meng-Hsiung , Lau Kam Y.
Published: July 2002

The buildup of pulses in a passively mode-locked monolithic semiconductor laser is investigated experimentally and theoretically. A simple model, based on competition between the fundamental and higher order mode-locking ‘‘supermodes,’’ gives a time constant for the buildup in good agreement with the experimental values, which are on the order of 3.5 ns. The theory shows that to minimize the pulse buildup time, the photon life time and the width of the gain spectrum should be minimized, and the gain and the gain modulation, should be maximized.
Elimination of light scattering from grating irregularities by using a quantum well grating in index or gain-coupled distributed feedback lasers
Authors: Chu S. N. G. , Tsang W. T. , Choa F. S. , Logan R. A. , Flynn E. J. , Coblentz D. L.
Published: July 2002

Grating irregularities in distributed feedback (DFB) laser structures form strong light scattering centers during lasing operation. The existence of such scattering centers may possibly affect the laser reliability. We report an elimination of the light scattering centers in index or gain-coupled DFB lasers using a quantum well (QW) grating under the active laser stripe. The improved grating quality is a result of an inherent uniformity of the QW grating amplitude determined by a precharacterized QW structure as well as an improved crystalline perfection of the overgrown InP instead of a quaternary waveguide layer in a regular substrate grating structure.
Novel short-gas-residence-time electron cyclotron resonance plasma etching
Authors: Tsujimoto Kazunori , Kumihashi Takao , Tachi Shinichi
Published: July 2002

Novel short-gas-residence-time electron cyclotron resonance (ECR) plasma etching is described. Using a newly equipped high-pumping-rate etching system (5000 ℓ/s), we obtained a high etch rate and high anisotropic etching of silicon at low pressure and high gas flow rate. The residence time obtained was 30 ms. The silicon etch rate with Cl2 dramatically increased up to 1 μm/min as the gas flow rate increased to 90 sccm at 0.5 mTorr. It was proven by plasma emission measurement that the reaction products were minimized by the present method. These results indicate that the short-gas residence time produces a small amount of reaction products and a large amount of etching species.
Surface topography and ordering-variant segregation in GaInP2
Authors: Friedman D. J. , Zhu Jane G. , Kibbler A. E. , Olson J. M. , Moreland J.
Published: July 2002

Using transmission electron diffraction dark-field imaging, atomic force microscopy (AFM), and Nomarski microscopy, we demonstrate a direct connection between surface topography and cation site ordering in GaInP2. We study epilayers grown by organometallic vapor-phase epitaxy on GaAs substrates oriented 2° off (100) towards (110). Nomarski microscopy shows that, as growth proceeds, the surface of ordered material forms faceted structures aligned roughly along [011]. A comparison with the dark-field demonstrates that the [11̄1] and [111̄] ordering variants are segregated into complementary regions corresponding to opposite-facing facets of the surface structures. This observation cannot be rationalized with the obvious but naive model of the surface topography as being due to faceting into low-index planes. However, AFM reveals that the facets are in fact not low-index planes, but rather are tilted 4° from (100) towards (111)B. This observation explains the segregation of the variants: the surface facets act as local (111)B-misoriented growth surfaces which select only one of the two variants.
Formation of four new shallow emissions in Mn+ ion-implanted GaAs grown by molecular beam epitaxy having extremely low concentration of background impurities
Authors: Shen Honglie , Makita Yunosuke , Niki Shigeru , Yamada Akimasa , Iida Tsutomu , Shibata Hajime , Obara Akira , Uekusa Shin-ichiro
Published: July 2002

Mn+ ions were implanted into ultrapure GaAs layers grown by molecular beam epitaxy. 2 K photoluminescence revealed that in addition to the well-established Mn-related deep acceptor emission at ∼1.41 eV, four new shallow emissions denoted by (Mn°, X), ‘‘G’’, ‘‘H’’, and (D, A)2 are formed in the near band edge when the Mn concentration [Mn] exceeds 3×1016 cm−3. Both ‘‘G’’ and ‘‘H’’ exhibit no energy shift with growing [Mn] up to 1×1019 cm−3. In contrast, for shallow acceptor- (such as C) doped GaAs with extremely low background concentrations of donor impurities, a series of [g-g]-like energy levels, which present strong energy shifting with increasing acceptor concentration, are universally formed. These results show that pairs between deep Mn acceptors do not produce such [g-g] like energy levels.
Novel method for rejuvenating and fabricating stable Se/GaAs surfaces
Authors: Scimeca T. , Prabhakaran K. , Watanabe Y. , Maeda F. , Oshima M.
Published: July 2002

Rejuvenation of the oxidized Se/GaAs surface has been realized by deposition of a thin Al layer. The results provided by synchrotron radiation photoelectron spectroscopy show that upon Al deposition, oxygen originally bound to Ga segregates to the surface and forms a more thermodynamically stable Al oxide species. In addition, a reduction in band bending is realized suggesting that this method may be useful as a means of fabricating a wide range of passivated overlayer/Se/GaAs interfaces.
Critical current versus normal-state resistivity in granular Y1Ba2Cu3O7−δ
Authors: Díaz A. , Pomar A. , Domarco G. , Maza J. , Vidal Félix
Published: July 2002

Precision measurements of critical current densities at zero applied magnetic field Jc for six granular Y1Ba2Cu3O7−δ samples have been performed by using a low frequency induction method. Also, the intergrain resistivity ρct for each sample has been extracted from the normal-state resistivity. It is found experimentally that at any temperature distance from the transition, Jc is inversely proportional to ρct. A way to estimate Jc from the resistivity of the granular samples in the normal state is thus open.
Ion-ripple wiggler for short wavelength lasers
Authors: Kupershmidt H. , Ron Amiram
Published: July 2002

We propose a new scheme for creating a dynamic wiggler of ion density grating. This can be incorporated into an ion-ripple laser to generate pulses of tunable coherent radiation of very short wavelengths. Two optical waves interfere in a plasma, and produce a density grating of wavelength ∼1–10 μm. An electron beam, obliquely injected into the plasma, expels the plasma electrons along its path, and generates radiation by interacting with the ion-ripple wiggler left behind.