bluuebunny/crossref_metadata_2025 huggingface dataset:
IIIIIIInteraction of Na+, K+, and Cl‐with the Binding of Amphetamine, Octopamine, and Tyramine to the Human Dopamine Transporter
Authors: Li LLLLLLLi‐Bin , Reith Maarten E. A.
Published: July 2002

Abstract:Little information is available on the role of Na+, K+, and Cl‐in the initial event of uptake of substrates by the dopamine transporter, i.e., the recognition step. In this study, substrate recognition was studied via the inhibition of binding of [3H]WIN 35,428 [2β‐carbomethoxy‐3β‐(4‐fluorophenyl)[3H]tropane], a cocaine analogue, to the human dopamine transporter in human embryonic kidney 293 cells. D‐Amphetamine was the most potent inhibitor, followed byp‐tyramine and, finally,dl‐octopamine; respective affinities at 150 mMNa+and 140 mMCl‐were 5.5, 26, and 220 μM. For each substrate, the decrease in the affinity with increasing [K+] could be fitted to a competitive model involving the same inhibitory cation site (site 1) overlapping with the substrate domain as reported by us previously for dopamine. K+binds to this site with an apparent affinity, averaged across substrates, of 9, 24, 66, 99, and 134 mMat 2, 10, 60, 150, and 300 mMNa+, respectively. In general, increasing [Na+] attenuated the inhibitory effect of K+in a manner that deviated from linearity, which could be modeled by a distal site for Na+, linked to site 1 by negative allosterism. The presence of Cl‐did not affect the binding of K+to site 1. Models assuming low binding of substrate in the absence of Na+did not provide fits as good as models in which substrate binds in the absence of Na+with appreciable affinity. The binding ofdl‐octopamine andp‐tyramine was strongly inhibited by Na+, and stimulated by Cl‐only at high [Na+] (300 mM), consonant with a stimulatory action of Cl‐occurring through Na+disinhibition.
Role of peripheral vision in terms of critical perception – its relevance to the visually impaired
Authors: Wolffe Michael
Published: July 2002

It is recognised that discrimination of fine detail is dependent on an intact macula with the peripheral retina being responsible for motion detection. There is evidence, however, to suggest that the peripheral retina does play a critical part in such discrimination. Studies of the performance of visually impaired school children have revealed levels of visual perception far exceeding anything that would be expected for individuals so severely handicapped. The art work of visually impaired youngsters was compared with the predicted results based on their visual acuity. The results showed detail that in theory could not have been resolved with such low acuity levels. All the youngsters had dense central scotomata. The peripheral retina, therefore, must have been involved in the discrimination of such detail. These results have implications not only for the visually impaired in terms of what they are capable of doing, but also for our understanding about the way the visual cortex processes information from the peripheral retina and the use that it makes of this relatively poor quality information.
660 nm In0.5Ga0.5P light-emitting diodes on Si substrates
Authors: Kondo Susumu , Matsumoto Shin-ichi , Nagai Haruo
Published: July 2002

In0.5Ga0.5P light-emitting diodes (LED’s) that operate in the 660 nm region were fabricated on Si substrates using GaAs buffer layers. InGaP layers were grown by metalorganic-chloride vapor phase epitaxy (MO-chloride VPE), and GaAs layers were grown by metalorganic vapor phase epitaxy (MOVPE) at atmospheric pressure. Red color emission was clearly seen under room light at 20 mA dc injection. The LED operation was stable at 5 kA/cm2 despite the high dislocation density of around 107 cm−2 .
Subpicosecond photoconductivity overshoot in gallium arsenide observed by electro-optic sampling
Authors: Meyer Kevin , Pessot Maurice , Mourou Gerard , Grondin Robert , Chamoun Sleiman
Published: July 2002

Electro-optic sampling of photoconductive transients on a subpicosecond time scale is used to study hot-carrier transport in GaAs. The results reported here are interpreted as direct time-domain observations of nonequilibrium transport on a subpicosecond time scale and they clearly show both an overshoot and bias-dependent delay at high excitation energy which are consistent with published Monte Carlo predictions.
Scanning tunneling microscopy of an ion-bombarded PbS(001) surface
Authors: Wilson I. H. , Zheng N. J. , Knipping U. , Tsong I. S. T.
Published: July 2002

Freshly cleaved (001) surfaces of single crystalline PbS were bombarded by 8 keV Kr+ ions at a dose of 3×1012 cm−2. Atomically resolved scanning tunneling microscopy (STM) images were taken showing damaged areas due to individual ion impacts. Analysis of a STM image shows a shallow impact crater, a stacking fault, displacement of Pb2+ and S2− ions from their regular surface sites, and migration of interstitials to the surface.
Third-order nonlinear optical properties of a soluble conjugated polythiophene derivative
Authors: Jenekhe Samson A. , Lo S. K. , Flom Steven R.
Published: July 2002

The second hyperpolarizability 〈γxxxx 〉 of a new, soluble, conjugated polythiophene derivative, containing aromatic and quinoid moieties, is measured to be 1.2×10−31 esu. The measurement was made at 532 nm in a dichloromethane solution by picosecond-resolved degenerate four wave mixing. The corresponding macroscopic third-order susceptibility χ(3 ) is estimated to be 4.6×10−9 esu, which is larger than that of the parent poly(2,5-thiophene) and many currently known nonlinear optical polymers.
Strain variations in heteroepitaxial InP-on-Si grown by low-pressure metalorganic chemical vapor deposition
Authors: Wuu D. S. , Horng R. H. , Lee M. K.
Published: July 2002

Variations in the magnitude and sign of the strain in epitaxial InP directly on (001) Si are studied as a function of layer thickness using photoluminescence and x-ray diffraction techniques. The heteroepilayers were grown by low-pressure metalorganic chemical vapor deposition and showed good quality. We find that biaxial compressive strains are still present in InP layers with thickness up to 0.8 μm. The magnitudes of compressive strains are much larger than those expected from the equilibrium theory. With increasing thickness above 1 μm, the InP/Si layers suffer biaxial tensile strains as a result of differential thermal contraction during the cooling process after growth.
Γ to X transport of photoexcited electrons in type II GaAs/AlAs multiple quantum well structures
Authors: Saeta P. , Federici J. F. , Fischer R. J. , Greene B. I. , Pfeiffer L. , Spitzer R. C. , Wilson B. A.
Published: July 2002

We report novel femtosecond time-resolved measurements performed on staggered type II GaAs/AlAs multiple quantum well structures. Photoexcited electrons were determined to transfer from the Γ valley of the GaAs layers to the X valleys of the AlAs in 100 and 400 fs for 8- and 11-monolayer-thick GaAs samples, respectively.
High-power disorder-defined coupled stripe AlyGa1−yAs-GaAs-InxGa1−xAs quantum well heterostructure lasers
Authors: Major J. S. , Hall D. C. , Guido L. J. , Holonyak N. , Gavrilovic P. , Meehan K. , Williams J. E. , Stutius W.
Published: July 2002

Data are presented describing continuous (cw) room-temperature laser operation of AlyGa1−yAs-GaAs-InxGa1−xAs quantum well heterostructure (QWH) phase-locked arrays. The ten-stripe arrays have 3 μm emitters, with emitter to emitter spacing of 4 μm, and are patterned onto the QWH crystal using a self-aligned Si-O impurity-induced layer disordering (IILD) procedure. The IILD process is devised to provide limited layer intermixing to ensure optical coupling (across ∼1 μm). The coupled stripe QWH lasers exhibit narrow twin-lobed far-field patterns that show unambiguously phase locking in the highest order supermode. The cw output power of the lasers (differential quantum efficiency 52%) is shown from threshold (∼75 mA) to over 280 mW (both facets, no optical coatings).
Zn diffusion enhancement of interdiffusion in a GaInAsP-InP heterostructure
Authors: Park H.-H. , Kang B. K. , Nam E. S. , Lee Y. T. , Kim J. H. , Kwon O’D.
Published: July 2002

The influence of concurrent Zn diffusion on the interdiffusion in a Gax In1−x Asy P1−y -InP heterostructure (x=0.28, y=0.61) was investigated using Auger electron spectroscopy and secondary-ion mass spectrometry. The measured profiles showed that the Zn diffusion (600 °C, 1–4 h) predominantly enhanced the cation (In-Ga) interdiffusion. The result could not be interpreted by the Zn-vacancy complex model. Under conditions of a group V overpressure, our results suggest that cation interstitials may control both the rate of Zn diffusion and the mixing of the group III sublattices in the InP-based alloy system.
Porous silicon microstructure as studied by transmission electron microscopy
Authors: Chuang S.-F. , Collins S. D. , Smith R. L.
Published: July 2002

Cross-sectional and plan-view transmission electron micrograph analysis of the structure of porous silicon reveals that the pore walls are also porous, yielding a large distribution of pore sizes for a given porous silicon sample. This infrastructure appears to be a universal morphological feature of porous silicon, independent of formation conditions and doping. It is proposed that the observed microstructure explains the recently reported results of adsorption isotherm experiments.
Anisotropic critical currents in Ba2YCu3O7 analyzed using an extended Bean model
Authors: Gyorgy E. M. , van Dover R. B. , Jackson K. A. , Schneemeyer L. F. , Waszczak J. V.
Published: July 2002

We have extended Bean’s critical state model to explicitly include anisotropic critical currents. Measurements at 30 K of the critical currents parallel to the Cu-O planes but with vortex motion either parallel or across twin boundaries show twin boundaries are probably not an important cause of vortex pinning. In the critical state, current flow perpendicular to the Cu-O planes is about 30 times smaller than flow parallel to these planes.
Role of color center induced absorption in all-optical switching
Authors: DeLong K. W. , Mizrahi Victor , Stegeman G. I. , Saifi M. A. , Andrejco M. J.
Published: July 2002

We show that color center induced absorption can mimic two-photon absorption, and may limit all-optical switching, even for very short pulses. Two-photon and color center induced absorption are measured in a lead glass fiber.
Electroluminescence and high-field domains in GaAs/AlGaAs superlattices
Authors: Helm M. , Golub J. E. , Colas E.
Published: July 2002

Photoluminescence, electroluminescence, and current measurements are used to probe the internal field in an n+-n-n+ GaAs/AlGaAs superlattice. At low bias voltages, the photoluminescence spectrum shows several peaks arising from electric field domains in the superlattice. Their positions correlate with features in the current-voltage characteristic and are consistent with a simple calculation of the Stark shift. Above the threshold voltage for impact ionization we observe spectrally narrow electroluminescence (width 3.5 meV). The energy of this emission coincides with the zero-field photoluminescence signal, indicating that electrons and holes screen the applied electric field in the quantum wells.
In-plane-gated quantum wire transistor fabricated with directly written focused ion beams
Authors: Wieck A. D. , Ploog K.
Published: July 2002

A new unipolar electronic device with a quasi-one-dimensional (1D) tunable carrier channel defined by directly written focused ion beams has been fabricated and characterized. Special features of the device are simple and rapid fabrication in one single technology step, inherent self-alignment, and linear instead of planar gates with very low capacitances. High integration as well as ultrahigh speed operation in logical and linear applications are feasible. The striking new aspect of this in-plane-gate structure is that the confining electric field is parallel to the two-dimensional electron gas, and the distorted, insulating region serves as a dielectric. Ballistic 1D transport is observed at low temperatures, and field-effect transistor operation of the device is demonstrated up to room temperature.
Fabrication of channel waveguides in polydiacetylenes: Composite diffused glass/polymer structures
Authors: Schlotter N. E. , Jackel J. L. , Townsend Paul D. , Baker Gregory L.
Published: July 2002

We report the fabrication of single-mode channel waveguides in spun films of polydiacetylenes using an inverted rib design. These robust guides consist of a planar layer of the polydiacetylene spun on a glass substrate in which high-index channels have been defined by ion exchange. Models of such guides show that most of the optical field of the guided wave is confined to the polymer layer, with the high-index glass channels providing lateral confinement. End-fire coupling of 1.06, 1.15, 1.32, and 1.55 μm light into the composite guides resulted in single-mode guiding with the light confined to the polymer layer. This approach to waveguide formation should be applicable to a wide range of polymeric materials.
Rectification by resonant tunneling diodes
Authors: Wingreen Ned S.
Published: July 2002

The coefficient of rectification, arect(ω), for a resonant tunneling diode is obtained from an exact solution for the transmission probability T(ε) through an oscillating resonant level. The experimentally observed broadening and lowering of the peaks in arect(ω) with increasing frequency ω are explained by the increase in spacing between the sidebands in T(ε). Most important, arect(ω) is entirely determined by the dc current. Consequently, any mechanism which broadens the negative differential conductance region will cause a dc-like coefficient of rectification to persist to frequencies higher than the inverse charge-transport time.
Rapid measurement of static and dynamic surface forces
Authors: Ducker William A. , Cook Robert F.
Published: July 2002

We present a technique for rapid measurement of surface forces using an ac force microscope. Measurement of both the amplitude and relative phase of a cantilever probe allows simultaneous and rapid determination of static and velocity-dependent forces of order nN over nm length scales. Using this technique, we have also demonstrated the high lateral spatial resolution of the force microscope in the measurement of surface forces.
Stable and shallow PdIn ohmic contacts to n-GaAs
Authors: Wang L. C. , Wang X. Z. , Lau S. S. , Sands T. , Chan W. K. , Kuech T. F.
Published: July 2002

A thermally stable, low-resistance PdIn ohmic contact to n-GaAs has been developed based on the solid phase regrowth mechanism [T. Sands, E. D. Marshall, and L. C. Wang, J. Mater. Res. 3, 914 (1988)]. Rapid thermal annealing of a Pd-In/Pd metallization induces a two-stage reaction resulting in the formation of a uniform single-phase film of PdIn, an intermetallic with a melting point greater than 1200 °C. A thin (∼5 nm) layer of average composition In0.4Ga0.6 As uniformly covers the interface between the PdIn layer and the GaAs substrate. Specific contact resistivities and contact resistances of ∼1×10−6 Ω cm2 and 0.14 Ω mm, respectively, were obtained for samples annealed at temperatures in the 600–650 °C range. The addition of a thin layer of Ge (2 nm) to the first Pd layer extends the optimum annealing temperature window down to 500 °C. Specific contact resistivities remained in the low 10−6 Ω cm2 range after subsequent annealing at 400 °C for over two days.
Diffusion of hydrogen in low-pressure chemical vapor deposited silicon nitride films
Authors: Bik W. M. Arnold , Linssen R. N. H. , Habraken F. H. P. M. , van der Weg W. F. , Kuiper A. E. T.
Published: July 2002

Hydrogen transport in low-pressure chemical vapor deposited Si3N4 has been investigated using samples consisting of a double layer of hydrogenated and deuterated nitride films. Concentration depth profiles of hydrogen and deuterium were measured using elastic recoil detection. Diffusion coefficients for D were derived from the deuterium concentration depth profiles before and after annealing at temperatures in the range 700–1000 °C. The diffusion coefficient is characterized by an activation energy of 2.94 eV for the entire temperature range. Its value varies between 10−17 cm2/s at 700 °C and 5×10−14 cm2/s at 1000 °C.
Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers
Authors: Canham L. T.
Published: July 2002

Indirect evidence is presented that free-standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two-dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.
Effects of reactive versus unreactive metals on the surface recombination velocity at CdS and CdSe(112̄0) interfaces
Authors: Rosenwaks Y. , Burstein L. , Shapira Y. , Huppert D.
Published: July 2002

Direct measurements of the surface recombination velocity (SRV) on etched CdS(112̄0), CdSe(112̄0) and at their interfaces with various metal ions and metals (deposited by electrolyte aqueous solutions and in situ thermal evaporation, respectively) have been performed using ultrafast time-resolved photoluminescence (PL). Correlations with interface states types and energy positions have been found based on surface photovoltage spectroscopy (SPS). The results show that the original semiconductor SRV is retained, and in some cases even decreases, when these surfaces are covered with metals, which tend to react with the semiconductor’s anion, such as Al, Ti, and Zn. On the other hand, the SRV increases sharply as a function of unreactive metals coverage, such as Cu, Au, etc. The PL results are explained in terms of metal-induced recombination centers at the semiconductor interface, which are introduced or eliminated as observed by SPS.
Dielectric-assisted liftoff technique for the formation and monolithic integration of electronic and optical devices
Authors: Metze G. M. , Cornfeld A. B. , Laux P. E. , Ho T. C. , Pande K. P.
Published: July 2002

A technique for the selective growth and patterning of device quality materials has been developed. This technology uses a dielectric-assisted liftoff (DAL) process to pattern molecular beam epitaxy (MBE) grown GaAs into isolated device regions. We have successfully demonstrated the applicability of this dielectric-assisted liftoff process by fabricating power metal-semiconductor field-effect transistor (MESFET) devices with 1, 1.5, and 3 mm gate width geometries. Material and device performance of these DAL patterned MESFETs has been found to be comparable to our standard MBE-grown and mesa isolated MESFET structures.
Observation of power gain in an inductive energy pulsed power system with an optically controlled semiconductor opening switch
Authors: Kung C. C. , Chauchard E. A. , Lee Chi H. , Rhee M. J. , Yan L.
Published: July 2002

Power gain has been observed, for the first time, in an inductive energy storage pulsed power system with an optically controlled semiconductor opening switch. A specially tailored 1.054 μm pulse from a Nd:glass laser was utilized to activate a GaAs switch of the p-i-n diode configuration, producing an output pulse with a power gain of more than 10.
Generation of blue-green 10 fs pulses using an excimer pumped dye amplifier
Authors: Schoenlein R. W. , Bigot J.-Y. , Portella M. T. , Shank C. V.
Published: July 2002

We report the generation of <25 fs pulses in the blue-green spectral region at 450 and 500 nm, using a colliding-pulse-mode-locked laser combined with a two-stage excimer pumped dye amplifier and continuum generation. The blue-green pulses are compressed to 10 fs duration using an optical fiber with pairs of gratings and prisms for phase compensation.
Scanning tunneling optical spectroscopy of semiconductor quantum well structures
Authors: Qian L. Q. , Wessels B. W.
Published: July 2002

Scanning tunneling optical spectroscopy has been used to determine the optical properties of semiconductor quantum wells. With this technique, photoenhanced tunneling currents are measured with a scanning tunneling microscope on heterostructures illuminated with monochromatic light. For the InAsxP1−x/InP strained single quantum well structures, the 295 K spectra exhibit well-resolved transitions attributable to interband transitions involving the heavy-hole valence band and the n=1 conduction subband. The observed transition energies are in good agreement with values measured using photoconductivity and photoluminescence spectroscopy on the same samples.
Longitudinal-optical-phonon assisted tunneling in tunneling bi-quantum well structures
Authors: Muto Shunichi , Inata Tsuguo , Tackeuchi Atsushi , Sugiyama Yoshihiro , Fujii Toshio
Published: July 2002

We discuss the electron tunneling time observed in a new AlGaAs/GaAs superlattice structure, the tunneling bi-quantum well (TBQ). To calculate the nonresonant tunneling time, we made experiments on resonant tunneling to confirm that the 60% rule of conduction-band discontinuity accurately evaluates the free tunneling probability of electrons. We found that the observed recovery time agrees quite well with the calculated longitudinal optical phonon emission tunneling time for thin (≤ 10 monolayers) barriers.
Correlation between the O+2 induced electron emission coefficient and the removal rate of Cu impurities segregated at the SiO2/Si interface
Authors: Wittmaack K. , Homma Y.
Published: July 2002

Sputter removal of thin overlayers of Cu on Si was studied using 10 keV O+2 primary ions at near-normal incidence. The decay length λ, which characterizes the exponential fall-off of the Cu signal, was found to depend upon the carrier type, the dopant concentration, the polarity and strength of the electric field above the (n type) samples, and the intensity of light directed at the (p type) samples, the λ values varying between 0.4 and 2.2 μm. A similar dependence on sample and bombardment parameters was observed for the ion-induced electron emission coefficient γ which ranged from 0.05 to 3 electrons/O+2 ion. The results suggest that the internal electrical field strength established in the ion-bombarded sample is largely determined by the effective rate of electron emission. The field strength across the oxide controls the transport of positively charged Cu impurities through this region and thus also determines the Cu removal rate.
Complementary optical tap fabricated in an electro-optic polymer waveguide
Authors: Van Eck T. E. , Ticknor A. J. , Lytel R. S. , Lipscomb G. F.
Published: July 2002

An active complementary optical tap made in an electro-optic polymer waveguide is reported for the first time. This device is the critical component of an optical railtap, a system capable of providing many optical interconnects with a single laser source. The device was fabricated by selective photobleaching of a uniformly poled polymer layer, and complementary switching was demonstrated.
Polarization insensitive tunable liquid-crystal etalon filter
Authors: Patel J. S.
Published: July 2002

A polarization insensitive, electrically tunable Fabry-Perot structure is demonstrated. The polarization insensitivity is realized by using two different regions of the same cell having optic axes orthogonal to each other. Using a compact geometry, the input beam of light is divided so that equal amounts pass through the two regions and thus for light of arbitrary input polarization, half of the intensity is transmitted at the resonant wavelength. We show that a wide tuning range of the order of 100 nm is possible using this geometry with a band pass of 0.7 nm, and a 70 nm free spectral range.
Calibration of the Fe2+ intracenter absorption in InP
Authors: Alt H. Ch. , Treichler R. , Völkl J.
Published: July 2002

A study is presented on the assessment of the Fe2+ concentration in Fe-doped InP by the quantitative evaluation of the Fe2+ intracenter absorption at 2800–3200 cm−1. Based on a comparison with secondary-ion mass spectrometry data from n-type samples, a calibration factor is derived for the oscillator strength of the zero-phonon lines at 10 K. The detection limit for 500 μm samples is ≊5×1013 cm−3.
Unintentional hydrogen concentration in liquid encapsulation Czochralski grown III–V compounds
Authors: Clerjaud B. , Côte D. , Naud C. , Gauneau M. , Chaplain R.
Published: July 2002

From a combined secondary ion mass spectroscopic and optical absorption investigation, the unintentional hydrogen concentration in III–V compounds grown by the liquid encapsulation Czochralski technique is shown to be about 1016 cm−3. In GaAs materials annealed for few hours at high temperature, this concentration is only in the 1013 cm−3 range.
Optical study of microvoids, voids, and local inhomogeneities in amorphous silicon
Authors: Vanecek M. , Holoubek J. , Shah A.
Published: July 2002

Elastic light scattering has been used for a study of microstructure in amorphous hydrogenated silicon. A simple theory to get quantitative informations on the microstructure has been presented for the first time, both for Rayleigh and Mie scattering. For optimal very high frequency glow discharge amorphous silicon layers, the presence of voids with diameter between 1 and 20 nm is typical.
Kinetics of particle generation in sputtering and reactive ion etching plasmas
Authors: Yoo W. J. , Steinbrüchel Ch.
Published: July 2002

Particle formation from a Si substrate in an Ar sputtering plasma and a reactive ion etching plasma of 10% CCl2F2 in Ar has been investigated by laser light scattering. The kinetics of particle growth are studied as a function of rf power and chamber pressure. Threshold behavior for particle generation has been observed with respect to rf power and pressure. In both reactive ion etching and sputtering, the smallest particles detected on the wafer are ∼0.2 μm in size. In reactive ion etching, most particles seem to have grown on the substrate itself. However, in sputtering most particles are spherical and must have been deposited from the plasma. Particle formation is correlated with redeposition in sputtering and with deposition of a surface film in reactive ion etching.
Investigations of behavior of particles generated from laser-ablated YBa2Cu3O7−x target using laser-induced fluorescence
Authors: Okada Tatsuo , Shibamaru Noboru , Nakayama Yasushi , Maeda Mitsuo
Published: July 2002

YBa2Cu3O7−x target was laser ablated by an ArF excimer laser, and the time of flight (TOF) distributions of Ba atoms were investigated by laser induced fluorescence (LIF) as a function of the irradiation laser fluence (0.2–3 J/cm2) and the surrounding oxygen gas pressure (0–5.32 Pa). At higher irradiation fluence (≳2 J/cm2) without oxygen gas, the TOF distribution showed a twin-peak distribution with fast and slow velocities, while only the slow velocity component was observed at lower fluence. When oxygen gas was introduced, the low velocity component was quenched at lower oxygen pressure than the high one, indicating that the TOF distribution can be controlled by the oxygen pressure.
Resonant cavity light-emitting diode
Authors: Schubert E. F. , Wang Y.-H. , Cho A. Y. , Tu L.-W. , Zydzik G. J.
Published: July 2002

A novel concept of a light-emitting diode (LED) is proposed and demonstrated in which the active region of the device is placed in a resonant optical cavity. As a consequence, the optical emission from the active region is restricted to the modes of the cavity. Resonant cavity light-emitting diodes (RCLED) have higher spectral purity and higher emission intensity as compared to conventional light emitting diodes. Results on a top-emitting RCLED structure with AlAs/AlxGa1−xAs quarter wave mirrors grown by molecular beam epitaxy are presented. The experimental emission linewidth is 17 meV (0.65 kT) at room temperature. The top-emission intensity is a factor of 1.7 higher as compared to conventional LEDs.
Whispering-gallery mode microdisk lasers
Authors: McCall S. L. , Levi A. F. J. , Slusher R. E. , Pearton S. J. , Logan R. A.
Published: July 2002

A new microlaser design based on the high-reflectivity whispering-gallery modes around the edge of a thin semiconductor microdisk is described and initial experimental results are presented. Optical confinement within the thin disk plane results in a microresonator with potential for single-mode, ultralow threshold lasers. Initial experiments use selective etching techniques in the InP/InGaAsP system to achieve 3–10 μm diameter disks as thin as 500 Å suspended in air or SiO2 on an InP pedestal. Optically pumped InGaAs quantum wells provide sufficient gain when cooled with liquid nitrogen to obtain single-mode lasing at 1.3 and 1.5 μm wavelengths with threshold pump powers below 100 μW.
Microstructure of visibly luminescent porous silicon
Authors: Cole M. W. , Harvey J. F. , Lux R. A. , Eckart D. W. , Tsu R.
Published: July 2002

The microstructure of luminescent porous silicon, formed by electrochemical etching of silicon wafers has been characterized by cross-sectional high-resolution transmission electron microscopy. Results of this study reveal the structure to consist of Si crystallites. The crystallites are ∼3.5 nm in size and are randomly distributed throughout the porous Si region.
Synthesis of metastable epitaxial zinc-blende-structure AlN by solid-state reaction
Authors: Petrov I. , Mojab E. , Powell R. C. , Greene J. E. , Hultman L. , Sundgren J.-E.
Published: July 2002

Epitaxial metastable zinc-blende-structure β-AlN was synthesized by the solid-state reaction between single-crystal Al(001) and TiN(001) layers grown on MgO(001) by ultrahigh vacuum magnetron sputter deposition. At an annealing temperature Ta=600 °C, the interaction proceeded according to the following overall reaction: 4Al+TiN→Al3Ti+AlN, in which β-AlN was formed pseudomorphically between cubic TiN and tetragonal Al3Ti layers. The lattice constant of β-AlN was found to be 0.438 nm, which corresponds to a 3.3% lattice mismatch with the underlying TiN layer.
Graded InGaP Schottky diodes on Si-doped InP
Authors: Pan N. , Carter J. , Jackson G. S. , Lee D. , Hein S. , Haase M. A. , Wu C. H. , Hsieh K. C.
Published: July 2002

A compositionally graded InGaP alloy layer grown on a Si-doped InP layer was used to enhance the Schottky barrier height of InP. The fabricated diodes were characterized by Auger depth profiling, variable temperature I-V, capacitance-voltage (C-V), and internal photoemission. Rectification behavior with a low leakage current was achieved (J=8.3×10−7 A/cm2 at −1V). An enhanced Schottky barrier height of 1.18 eV was measured. The large barrier height permitted a reliable C-V profile of a moderately doped InP layer (7×1017 cm−3).
Small signal and continuous wave operation of the lateral current injection heterostructure field-effect laser
Authors: Evaldsson P. A. , Taylor G. W. , Cooke P. , Claisse P. R. , Burrus C. A. , Tell B.
Published: July 2002

The lateral current injection heterostructure field-effect laser structure is operated both as a three-terminal laser and a field-effect transistor. The structure was grown by low-temperature molecular-beam epitaxy (580 °C) and excellent performance characteristics were obtained for both devices. The laser is shown to have both source/emitter and source/collector modes of operation. Both modes exhibited a continuous wave operation and the source/emitter mode has a −3 dB bandwidth of 4 GHz limited by heating caused by a high source resistance. The transistor had a peak transconductance of 95 mS/mm and a peak drain to source current density of 120 mA/mm for a 2μm×50 μm device.
Photoionization energy variation among three types of As-stabilized GaAs (001) 2×4 surfaces
Authors: Tsuda Hiroshi , Mizutani Takashi
Published: July 2002

Variation in ionization energy is studied for 2×4-α,β,γ phases of As-stabilized GaAs (001) 2×4 surfaces. Photoemission due to energy scanned monochromatic light is measured in a molecular beam epitaxy (MBE) chamber. The results show that ionization energy does not change monotonically with the surface As coverage but exhibits a maximum in the region of the 2×4-β phase. This is explained in terms of surface dipole variation among the three phases. These findings confirm that these three surfaces have different electrical properties.
Spatial coherence of a repetitive laser-plasma point x-ray source in the water window spectral region
Authors: Daido H. , Turcu I. C. E. , Ross I. N. , Watson J. G. , Steyer M. , Kaur R. , Schulz M. S. , Amit M.
Published: July 2002

We propose and demonstrate a coherent laser-plasma point x-ray source in the water window spectral region operating at a repetition rate of up to 100 Hz. The emission from the 10-μm-diameter source is filtered to generate monochromatic radiation at a 3.37 nm wavelength. Soft x-ray fringes of the Young’s interference experiment were obtained with a visibility of 0.62±0.1 with a slit pair of 10.5 μm separation at a distance of 31.7 cm from the source. The source can be used to take either a hologram or transmission scanning x-ray micrograph within a reasonable exposure time of several minutes.
Arsenic dimers and multilayers on (001)GaAs surfaces in atmospheric pressure organometallic chemical vapor deposition
Authors: Kamiya Itaru , Tanaka H. , Aspnes D. E. , Florez L. T. , Colas E. , Harbison J. P. , Bhat R.
Published: July 2002

Arsenic dimers and multilayers are shown to exist on (001)GaAs surfaces under atmospheric pressure (AP) organometallic chemical vapor deposition (OMCVD) conditions. We obtained reflectance-difference spectra from surfaces in AP H2 that are equivalent to those obtained from the (2×4) and disordered-c(4×4) reconstructions prepared in ultrahigh vacuum by molecular beam epitaxy. Implications for models of OMCVD growth.
Experimental verification of the theory on the inverse Smith–Purcell effect at a submillimeter wavelength
Authors: Bae J. , Shirai H. , Nishida T. , Nozokido T. , Furuya K. , Mizuno K.
Published: July 2002

The inverse Smith–Purcell effect is a candidate for laser-driven linacs utilizing the interaction between laser light and an electron beam traveling just in front of a metallic grating. We have performed experiments to study electron energy spread as a function of electron beam position above the grating. A submillimeter wave laser (CH3F, 496 μm) is used as a driving source. It is found that the energy spread characteristics show exponential decay of the interaction strength (field intensity) in the direction perpendicular to the grating surface, as a classical theory on the effect predicts.
Observation of stripe-direction dependence of threshold current density for AlGaInP laser diodes with CuPt-type natural superlattice in Ga0.5In0.5P active layer
Authors: Fujii H. , Ueno Y. , Gomyo A. , Endo K. , Suzuki T.
Published: July 2002

An anisotropy for threshold current densities for AlGaInP laser diodes with CuPt-type natural superlattice (NSL) in a Ga0.5In0.5P active layer, grown on a (001) GaAs substrate, was observed, for the first time. Threshold current densities (Jth) for laser diodes with stripes in the [1̄10] and [110] direction were 1.35 and 2.10 kA/cm2, respectively. The lasers with a weak NSL formation in the active layer showed a very small anisotropy in Jth. Stripe direction dependence of electroluminescence (EL) polarization properties were also observed for lasers with well-developed NSL. The anisotropies in Jth and EL polarization properties are attributed to the existence of the NSL in the active layer and the appearance asymmetry previously observed in the NSL.
Sample depolarization effects from thin films of ZnS on GaAs as measured by spectroscopic ellipsometry
Authors: Jellison G. E. , McCamy J. W.
Published: July 2002

Thin films of ZnS grown on GaAs by laser ablation are examined using spectroscopic two-channel polarization modulation ellipsometry (2-C PME). It is found that variations in the film thickness over the illumination spot result in the quasidepolarization of the incident light, which can be measured directly using 2-C PME. Quantitative fits of the ellipsometry data using a distribution-of-thicknesses model agree with independent reflectivity measurements of the thickness gradient, and allow for the accurate determination of the optical functions of the ZnS film.
Point defects in Si thin films grown by molecular beam epitaxy
Authors: Gossmann H.-J. , Asoka-Kumar P. , Leung T. C. , Nielsen B. , Lynn K. G. , Unterwald F. C. , Feldman L. C.
Published: July 2002

Depth profiles of vacancylike defects have been determined by positron annihilation spectroscopy in 200-nm-thick Si films grown by molecular beam epitaxy on Si(100) substrates at growth temperatures Tgrowth=200–560 °C. The line shape of the radiation emitted from implanted positrons annihilating in the near-surface region of a solid gives quantitative, depth-resolved information on defect concentrations in a nondestructive way. In particular, the method is sensitive to vacancylike defects in a concentration range inaccessible to electron microscopy or ion scattering, but important for electrical device characteristics. The sensitivity limit for these defects in the present experiments is estimated as 5×1015 cm−3. Films grown at Tgrowth≥475±20 °C are indistinguishable from virgin wafers. So are samples with Tgrowth=220±20 °C, subjected to a 2 min, TRTA≳500 °C rapid thermal anneal (RTA) after every ≊30 nm of Si growth. If TRTA=450±20 °C, part of the film contains a concentration of vacancylike defects on the order of 1018 cm−3. Our results indicate the importance of the growth parameters, such as temperature and substrate preparation, for the production of high quality films.
InAs/Ga0.47In0.53As quantum wells: A new III-V materials system for light emission in the mid-infrared wavelength range
Authors: Tournié Eric , Ploog Klaus H. , Alibert Claude
Published: July 2002

We propose the use of strained InAs/Ga0.47In0.53As quantum wells (QWs) for light emission in the technologically important mid-IR wavelength range. Temperature dependent photoluminescence measurements on single QWs demonstrate that light emission at room temperature is obtained from all samples having InAs QW widths between 2 and 23 monolayers. Luminescence up to 2.4 μm is obtained at 300 K, which is the longest wavelength achieved so far for QWs grown on InP. These results demonstrate the potential of the InAs/Ga0.47In0.53As QW materials system for the fabrication of optoelectronic devices operating in the mid-IR.
Organic solar cell based on multistep charge separation system
Authors: Hiramoto Masahiro , Fukusumi Hiroyuki , Yokoyama Masaaki
Published: July 2002

The p-n heterojunction organic solar cell composed of n-type multilayer of two different perylene pigments and p-type metal-free phthalocyanine pigment was investigated. A downward potential step of the conduction band in the n-type multilayer enhanced the photocurrent quantum efficiency by a factor of about 3, owing to the suppression of the charge recombination of photogenerated carriers in the vicinity of the p-n junction. The multistep charge separation system consisting of energetically well-arranged organic thin layers was shown to offer an effective system to obtain highly efficient organic solar cells.
Time resolved photoluminescence studies in a reverse biased quantum well laser structure
Authors: Halliday D. P. , Moss D. , Charbonneau S. , Aers G. , Chatenoud F. , Landheer D.
Published: July 2002

We report measurements of photoluminescence decay time in a reverse biased GaAs/AlGaAs graded index separate confined heterostructure single quantum well (GRINSCH-SQW) laser, as a function of bias voltage at temperatures of 20, 70, and 150 K. For certain bias voltages and temperatures, we observe extremely fast escape times of optically generated carriers. We propose a simple model based on photogenerated electron recombination in the quantum well, and escape via direct tunneling out of the lower bound electronic level, thermally assisted tunneling out of the upper weakly bound state, or thermionic emission over the barrier. We have performed a theoretical calculation of each of these processes and show that the data agrees well with the direct and thermally assisted tunneling times and that the thermionic emission term underestimates the times.
Formation of two-dimensional arsenic-precipitate arrays in GaAs
Authors: Melloch M. R. , Otsuka N. , Mahalingam K. , Chang C. L. , Kirchner P. D. , Woodall J. M. , Warren A. C.
Published: July 2002

GaAs epilayers were grown by molecular beam epitaxy under normal conditions, except a substrate temperature of 250 °C was used instead of the normal 600 °C. This results in an excess of arsenic of about 1.5% in the epilayer. The epilayers also contained regions that were delta doped with silicon, beryllium, and indium. Samples were annealed for 30 s at 600, 700, and 800 °C to investigate the effects of the Si, Be, and In impurities on the precipitation of the excess As. It was found that the As precipitates form preferentially on planes of Si while forming preferentially between planes of Be. The isoelectronic impurity In appeared to have no effect on the precipitation process.
Effects of ordering on the operation of AlGaInP lasers grown by metalorganic chemical vapor deposition
Authors: Nakano K. , Toda A. , Yamamoto T. , Ishibashi A.
Published: July 2002

We have observed large differences in the lasing wavelength and threshold current for [11̄0]- and [110]-striped AlGaInP lasers that are fabricated from a single wafer grown by metalorganic chemical vapor deposition. With the laser stripe aligned parallel to the [110] direction, the lasing wavelength is about 6 nm shorter than that with the [11̄0] stripe. The threshold current (Ith) of the [110]-striped laser is 10 mA higher than that of the [11̄0]-striped laser. The differences are found to be well explained by the splitting of the valence band due to the (111) ordering in the AlGaInP lasers.
Effect of post-growth cooling ambient on acceptor passivation in carbon-doped GaAs grown by metalorganic chemical vapor deposition
Authors: Stockman S. A. , Hanson A. W. , Jackson S. L. , Baker J. E. , Stillman G. E.
Published: July 2002

The degree of unintentional hydrogen passivation of acceptors in heavily C-doped GaAs (p≳1018 cm−3) grown by metalorganic chemical vapor deposition has been found to be a strong function of post-growth cool-down ambient. The carbon concentration in the GaAs and the amount of AsH3 in the cool-down ambient are the most important factors affecting passivation. Carbon acceptors can be reactivated by annealing in N2, then repassivated by heating and re-cooling in an AsH3/H2 or PH3/H2 ambient. Secondary ion mass spectrometry analysis shows that the hydrogen concentration is significantly higher in a C-doped GaAs surface layer which is exposed to the cool-down ambient than in a layer which is buried beneath n-type GaAs. This result is consistent with observations in n-p-n heterojunction bipolar transistor structures, where the fraction of C acceptors passivated in the base region is found to be less than in a single layer grown under identical conditions. Be-doped GaAs grown by gas-source molecular beam epitaxy has also been heated and cooled in AsH3-containing ambients, but no acceptor passivation is detectable by Hall effect measurements.
Near-field optical microscope using a silicon-nitride probe
Authors: van Hulst N. F. , Moers M. H. P. , Noordman O. F. J. , Tack R. G. , Segerink F. B. , Bölger B.
Published: July 2002

Operation of an alternative near-field optical microscope is presented. The microscope uses a microfabricated silicon-nitride probe with integrated cantilever, as originally developed for force microscopy. The cantilever allows routine close contact near-field imaging on arbitrary surfaces without tip destruction. The effect of adhesion forces on the coupling to the evanescent wave has been observed. Images with a lateral resolution of about 50 nm are presented and compared with atomic force images. A specific sample area can be selected using an integrated conventional light microscope.
Very low temperature (<400 °C) silicon molecular beam epitaxy: The role of low energy ion irradiation
Authors: Murty M. V. Ramana , Atwater Harry A. , Kellock A. J. , Baglin J. E. E.
Published: July 2002

Concurrent low energy (50–70 eV) ion irradiation during silicon molecular beam epitaxy results in an increased epitaxial thickness at very low temperatures relative to conventional molecular beam epitaxy. Ion irradiation of a (1×1) dihydride-terminated Si(001) results in a (2×1) reconstruction, indicating irradiation-induced hydrogen desorption. Conventional molecular beam epitaxial growth is possible on a dihydride-terminated Si(001) surface following (2×1) reconstruction such that the substrate temperature never exceeds 150 °C; which is not possible without irradiation.
Study on thermal stability of carbon-doped GaAs using novel metalorganic molecular beam epitaxial structures
Authors: Nozaki Shinji , Takahashi Kiyoshi , Shirahama Masanori , Nagao Keisuke , Shirakashi Junichi , Tokumitsu Eisuke , Konagai Makoto
Published: July 2002

Two novel carbon-doped structures grown by metalorganic molecular beam epitaxy were used to study thermal stability over the temperature range from 650 to 800 °C. Each structure consists of several GaAs layers with different carbon concentrations to characterize thermal stability of GaAs layers with various carbon concentrations simultaneously. The structure shows no significant carbon diffusion even after an 800 °C-240 min anneal. However, the hole concentration of each carbon-doped GaAs layer in both structures has decreased, and a decrease of the hole concentration is more significant for a higher carbon concentration. With increasing the annealing time or temperature, the hole concentrations of all carbon-doped GaAs layers approach to the same value, low 1019 cm−3.
Apparent and true feature heights in force microscopy
Authors: Burnham N. A.
Published: July 2002

In a force microscope, the stiffness of the cantilever beam convolutes with the tip-sample interaction stiffness to influence the data in a systematic way. The analysis presented here relates the measured feature height to the true feature height in the variable force, constant force, and constant force gradient modes of operation. In this way, one can understand previously published data: the enhanced measured atomic corrugation observed in high resolution force microscopy images, its increase with load, and the improved resolution of lateral force images. The correct interaction stiffness can be obtained for use in surface force and mechanical properties studies. The need for complementary stiffness and topological data is emphasized.
Low resistivity indium tin oxide films by pulsed laser deposition
Authors: Zheng J. P. , Kwok H. S.
Published: July 2002

Indium tin oxide films were grown by pulsed laser deposition on glass substrates. The electrical and optical properties of these films were studied. At optimized oxygen pressures, films with resistivity values of 1.4×10−4 and 5.6×10−4 Ω cm were deposited at substrate temperatures of 310 and 20 °C, respectively. Films with a thickness of 180 nm had a transmission of nearly 100% for the wavelength range of 600–800 nm.
4H-SiC/6H-SiC interface structures studied by high-resolution transmission electron microscopy
Authors: Iwasaki Hiroshi , Inoue Shinji , Yoshinobu Tatsuo , Tarutani Masayoshi , Takai Yoshizo , Shimizu Ryuichi , Ito Akira , Kimoto Tsunenobu , Matsunami Hiroyuki
Published: July 2002

The interface structures of 4H-SiC/6H-SiC heterostructures formed in monocrystalline bulk silicon carbide were studied by high-resolution electron microscopy of cross-sectional specimens. The samples were grown on the (0001̄) C face of a 6H-SiC seed with in situ Ce doping. The observed transition region is atomically flat over regions of several hundreds nm. The transition from the initial 6H-SiC growth to the 4H-SiC growth happens all at once at certain thicknesses with the occurrence of only a few layers of 4H-SiC (6H-SiC) before (after) the transition. The atomic stacking sequence at the interface of the two polytype crystals can be resolved.