bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-temperature metalorganic chemical vapor deposition of perovskite Pb(ZrxTi1−x)O3 thin films
Authors: Peng Chien H. , Desu Seshu B.
Published: July 2002

Pb(ZrxTi1−x)O3 thin films with perovskite structure were successfully prepared on sapphire disks, Pt/Ti/SiO2/Si, and RuOx/SiO2/Si substrates at temperatures as low as 550 °C by hot-wall metalorganic chemical vapor deposition. Safe and stable precursors were used, namely: lead tetramethylheptadione [Pb(thd)2], zirconium tetramethylheptadione [Zr(thd)4], and titanium ethoxide. The deposition rates were in the range of 10.0 to 20.0 nm/min. The Auger electron spectroscopy (AES) depth profile showed good uniformity across the bulk of the films. The AES spectra also showed no carbon contamination in the bulk of the films. Zr/Ti ratio were easily controlled by the precursor temperatures and the flow rate of diluent gas. Optical constants were measured by a UV-VIS-NIR spectrophotometer. As-deposited films were dense and showed uniform and fine grain size. The 600 °C annealed film (Pb/Zr/Ti=50/41/9) showed a spontaneous polarization of 23.3 μC/cm3 and a coercive field of 64.5 kV/cm.
Quantum well electroabsorption modulators at 1.55 μm using single-step selective area chemical beam epitaxial growth
Authors: Chen Y. , Zucker J. E. , Chiu T. H. , Marshall J. L. , Jones K. L.
Published: July 2002

We demonstrate a novel electroabsorption modulator operating at 1.55 μm fabricated by single-step selective area chemical beam epitaxy with no post-growth processing. The modulation depth is 14.5 dB for a voltage swing of 10 V. In addition, the modulator has a tunable absorption edge determined by the size of the growth mask opening.
Improving the performance of semiconductor ring lasers by controlled reflection feedback
Authors: Hohimer J. P. , Vawter G. A. , Craft D. C. , Hadley G. R.
Published: July 2002

We report a tenfold increase in the lasing output of single-output Y-junction semiconductor ring lasers by reducing the end-facet reflection feedback. Controlled reflection feedback is also shown to be a means for promoting unidirectional lasing in dual-output ring lasers. Finally, we show that the counterpropagating ring modes are strongly coupled by gain competition.
Lateral band-gap patterning and carrier confinement in InGaAs/GaAs quantum wells grown by molecular beam epitaxy on nonplanar dot patterns
Authors: Krahl M. , Kapon E. , Schiavone L. M. , Van der Gaag B. P. , Harbison J. P. , Florez L. T.
Published: July 2002

Two-dimensional (2D) lateral band-gap patterning and carrier confinement were observed in InGaAs/GaAs patterned quantum-well (QWL) dots grown by molecular beam epitaxy on prepatterned, nonplanar GaAs substrates. Growth of the strained QWL layers on craters of 0.2–5 μm diameters etched onto the substrate results in 2D lateral potential wells formed at the inside and outside regions of the craters due to preferential migration of Ga and In adatoms. Evidence for lateral carrier confinement and efficient radiative recombination in the resulting dot- and ring-shaped potential wells was provided by low-temperature cathodoluminescence spectroscopy and imaging. The results of this study indicate the feasibility of producing damage-free quantum dot and quantum ring heterostructures by growth of QWLs on patterned, nonplanar substrates.
Synchrotron radiation assisted deposition of aluminum oxide from condensed layers of trimethylaluminum and water at 78 K
Authors: Strongin D. R. , Moore J. F. , Ruckman M. W.
Published: July 2002

Spectroscopic evidence is presented that shows that synchrotron irradiation of trimethylaluminum (TMA) and water at 78 K on a silver substrate produces pure layers of aluminum oxide. Near-edge x-ray absorption fine structure and core level photoelectron spectroscopies are used to characterize the Al2O3 layer, which was 30 Å thick. The carbon component in the alkylaluminum precursor is completely removed during irradiation as volatile methane product. In the absence of synchrotron radiation the molecular precursors show evidence of some interactions within the solid, but upon warming to ambient temperatures (260 K) the adsorbed layers desorb from the substrate.
Accurate determination of effective quantum well thickness: Infrared absorption by transverse-optical phonons
Authors: Yang M. J. , Wagner R. J. , Shanabrook B. V. , Moore W. J. , Waterman J. R. , Twigg M. E. , Fatemi M.
Published: July 2002

We have studied far infrared transmission spectra of various AlSb/InAs/AlSb single quantum wells, where the well width ranges from 60 to 200 Å. Because the quantum well is thin, the far infrared absorption due to transverse-optical phonons is not saturated. We obtained excellent fitting to the transmission spectra by taking into account the complex dielectric functions with a transfer matrix formalism. The thickness of InAs quantum wells can be determined with monolayer resolution. High-resolution transmission electron microscopy shows clear lattice images in a region away from the AlSb/InAs interfaces. The thickness of the pure nonintermixed InAs region is in excellent agreement with our far infrared absorption results. Phonon absorption can therefore provide a nondestructive method to effectively determine the number of pure InAs monolayers, in spite of interdiffusion occurring at the interface.
Hysteretic Josephson junctions from YBa2Cu3O7−x/SrTiO3/Ba1−xKxBiO3 trilayer films
Authors: Fink R. L. , Thompson M. , Hilbert Claude , Kroger Harry
Published: July 2002

We have fabricated hysteretic Josephson junctions from YBCO/SrTiO3/BKBO trilayer films. These large area rf-sputtered junctions are reproducible, show Shapiro steps in response to microwave radiation, and their Josephson current can be modulated with a small magnetic field up to about 20 K. In addition, geometrical and magnetic field dependent resonances were observed for the first time in cuprate superconductor junctions. The devices appear to be S-N-S like without any gap structures discernable in the electrical characteristics. The decay length of critical current with SrTiO3 layer thickness indicates a normal-state coherence length in the SrTiO3 of about 5 Å.
Influence of carrier capture on the quantum efficiency of as-etched and epitaxially buried In0.53Ga0.47As/InP quantum wires
Authors: Lehr G. , Bergmann R. , Rudeloff R. , Scholz F. , Schweizer H.
Published: July 2002

Using electron beam lithography dry etching and an epitaxial regrowth step we have prepared buried In0.53Ga0.47As/InP quantum wires. Measurements of the quantum efficiency under different excitation energies reveal the strong impact of carrier loss processes in the barrier on the quantum efficiency of the wire structures. For epitaxially buried wires we find under resonant excitation nearly no decrease in the quantum efficiency down to a wire width of 65 nm. This gives evidence that the regrowth step strongly suppresses the nonradiative recombination at the boundaries of the active region of the wire. Furthermore the comparison of resonant and nonresonant excitation yields an improvement of the carrier capture due to epitaxial regrowth.
Sputter deposition of epitaxial waveguiding KNbO3 thin films
Authors: Schwyn Thöny S. , Lehmann H. W. , Günter P.
Published: July 2002

Thin, stoichiometric KNbO3 layers were sputter deposited onto (100)-spinel and (100)-MgO substrates at a substrate temperature of 610 °C. The composition of the layers was determined by Rutherford backscattering (RBS) measurements. Potassium stoichiometry was maintained by an enrichment of the target with K2CO3. Furthermore, channeling experiments indicated good crystal quality with a χmin of 40%. The x-ray diffraction spectra showed single-crystalline tetragonal films. Waveguide modes with losses of only 1.1 dB/cm at λ=632.8 nm could be excited in the sputtered films. The nonlinear optical coefficient d31=5 pm/V was determined by the Maker-fringe technique using the 1.06 μm Nd:YAG laser fundamental wavelength (compared to d31=15 pm/V measured in orthorhombic single crystals).
Scaling of critical currents in high-temperature superconducting superlattices and thin films
Authors: Fernandes A. A. R. , Chan I. N. , Guimpel J. , Nakamura O. , Lederman D. , Schuller Ivan K.
Published: July 2002

We report the measurement of transport critical current densities in a wide variety of high-temperature superconducting (high Tc) superlattices and thin films. We find that the temperature dependence of the critical current density Jc for all samples may be collapsed into a single curve through the scaling relation Jc(t)=Jc(0)(1−t)1.6, where t=T/Tc(H,Θ). This scaling relation remains valid in fields of up to 5 T and in all field directions Θ with respect to the c axis of the sample with the field kept perpendicular to the current.
Spreading resistance in proton-implanted vertical-cavity surface-emitting diode lasers
Authors: Nakwaski Wl/odzimierz , Osiński Marek , Cheng Julian
Published: July 2002

Analytical expressions are derived for calculating electrical spreading resistance in vertical-cavity surface-emitting diode lasers. Three contact configurations are considered: annular, circular, and broad area. Calculations performed for proton-implanted surface-emitting lasers demonstrate that low values of series resistance can be achieved using the broad-area contact configuration.
Comparison of light emission from stain-etch and anodic-etch silicon films
Authors: Kidder J. N. , Williams P. S. , Pearsall T. P. , Schwartz D. T. , Nosho Brett Z.
Published: July 2002

Bright visible photoluminescence (PL) has been measured in stain-etch silicon films prepared by chemical etching in a dilute hydrofluoric and nitric acid solution. The PL emission is observed to degrade exponentially when the stain-etch films are illuminated in air (intensity decreases by 1/e over 22.45 min). Anodic-etch silicon films, prepared using a novel electrochemical cell, show similar strong visible PL but a degradation rate an order of magnitude smaller. The wavelength of the PL peak for anodic-etch silicon (650–710 nm) shifts toward the blue with decreasing electrolyte HF concentration while the PL peak position of stain-etch silicon (∼650 nm) does not vary with process conditions investigated.
In situ layer-by-layer growth of YBa2Cu3O7−x thin films by multitarget sputter deposition
Authors: Yang K-Y. , Dilorio M. S. , Yoshizumi S. , Maung M. A. , Zhang J. , Tsai P. K. , Maple M. B.
Published: July 2002

We have fabricated YBa2Cu3O7−x thin films using in situ layer-by-layer sputter deposition from metal targets. Yttrium, barium, and copper metals were deposited in the atomic monolayer sequence to construct the perovskite structure in the [001] direction. X-ray diffraction indicates that these films are c-axis oriented with the [001] direction normal to the film surface. Smooth films with zero-resistance transition temperature Tc0=80 K and critical current density Jc(4.2 K)∼2×107 A/cm2, measured in zero magnetic field, have been grown on LaAlO3(100) substrates. Under the conditions studied, all films have a suppressed Tc and an expanded c-axis lattice constant, with the degree of Tc suppression inversely proportional to the lattice constant. Tc and surface morphology were shown to be sensitive to the fractional monolayer coverage φ during each layer’s deposition. The results suggest that films grow in the layer-by-layer mode as opposed to island growth.
Texturing of DyBa2Cu3O7 superconducting grains synthesized in situ in a magnetic field
Authors: Cloots R. , Rulmont A. , Hannay C. , Goldelaine P. A. , Vanderschueren H. W. , Régnier P. , Ausloos M.
Published: July 2002

Synthesis of DyBa2Cu3O7 superconducting ceramics has been made in a small magnetic field (H=0.6 T) for different sample geometries and thermal cycles. The sample is placed in a vertical furnace and in a horizontal magnetic field. Control experiments (H=0) have been performed in each case for the same conditions. We have found texturing and terrace substructures. Thus the magnetic field is relevant for texturing and growth.
InAlAs/InP modulation doped heterostructures by atmospheric pressure metalorganic chemical vapor deposition using tertiarybutylphosphine
Authors: Pan N. , Carter J. , Brierley S. , Hendriks H.
Published: July 2002

Undoped and modulation doped InAlAs/InP heterostructures with excellent optical and electrical characteristics are demonstrated using tertiarybutylphosphine (TBP). Low-temperature photoluminescence spectra showed the presence of a type II interface transition indicating the high quality of the interface. Two-dimensional electron gas transport in a modulation doped sample containing a sheet density of 1.8×1012 cm−2 was verified by observing plateaus in the quantum Hall effect. These results confirmed that TBP can be substituted for phosphine for the growth of high quality InAlAs/InP heterostructures.
InGaAs/InP hot electron transistors grown by chemical beam epitaxy
Authors: Chen W. L. , Sun J. P. , Haddad G. I. , Sherwin M. E. , Munns G. O. , East J. R. , Mains R. K.
Published: July 2002

In this letter, we report on the dc performance of chemical beam epitaxy grown InGaAs/InP hot electron transistors (HETs). The highest observed differential β (dIC/dIB) is over 100. The HETs have Pd/Ge/Ti/Al shallow ohmic base contacts with diffusion lengths less than 300 Å. Furthermore, we also demonstrated ballistic transport of electrons in an InGaAs/InP HET by obtaining an energy distribution of electrons with ∼60 meV full width at half maximum. The measured conduction band discontinuity of InGaAs/InP is 250.3 meV, which is 39.8% of the band gap difference.
Microscopic study of the surfactant-assisted Si, Ge epitaxial growth
Authors: Cao R. , Yang X. , Terry J. , Pianetta P.
Published: July 2002

The Sb-assisted Si, Ge epitaxial growth processes have been studied using high resolution photoemission. It is found that the initially ordered Sb monolayer on the Si(100) and Ge(100) surfaces occupies the epitaxial sites and fully saturates the surface dangling bonds. This results in a reduction of the surface energy. During the growth process, the Sb atoms and the deposited Si, Ge atoms change their positions. Sb atoms segregate to the growth front to form a new ordered layer while leaving the uniform epitaxial Si, Ge layer behind.
Annealing of recombination centers in the deposition and light induced high defect amorphous silicon
Authors: Yoon Jong-Hwan , Lee Yoon-Zik
Published: July 2002

We have studied the annealing behaviors of deposition and light induced recombination centers, as measured by steady-state photoconductivity, in undoped hydrogenated amorphous silicon. It was found that both annealing activation energies are identical, and of 1.1 eV. In addition, the annealing activation energies of 1.1 and 1.7 eV were found for dark conductivity recoveries in the deposition and light induced defect annealing, respectively. The results are discussed on the basis of the existing models for recombination centers.
Microfabricating bacteriorhodopsin films for imaging and computing
Authors: Haronian Dan , Lewis Aaron
Published: July 2002

An array of electrode sandwiched bacteriorhodopsin (bR) pixels was microfabricated for the wide variety of electro-optical applications that have been suggested for this unique biological molecule. The electro-optical properties of a microfabricated bR pixel was measured to prove that the production process is nondestructive. This method allows the microfabrication of biological materials that cannot be treated by conventional microelectronics technologies.
Consideration of the thermal energy in hydrodynamic transport models
Authors: Curow Matthias
Published: July 2002

The thermal energy is an important parameter in hydrodynamic transport models used for systematic studies of the behavior of hot electron devices. This contribution shows that a careful consideration is necessary in order to avoid some solution details which are not only unphysical, but which can easily lead to numerical instabilities, too. Fairly good results are obtained at least for GaAs if the thermal energy is expressed via steady-state results of Monte Carlo simulations as it is done for other transport parameters.
Formation of carbon fibers by laser ablation of graphite
Authors: Sharma A.
Published: July 2002

We describe a novel technique for the formation of carbon fibers by ablation of a graphite target with 50–150 mJ pulses of excimer laser light. Under a suitably applied electric field, carbon fibers grow on one of the electrodes as the laser ablation of graphite proceeds in a cell filled with argon gas. Optical and scanning electron micrographs of the fibers are discussed.
X-ray laser frequency near-doubling and generation of tunable coherent x rays in plasma
Authors: Shkolnikov P. L. , Kaplan A. E. , Muendel M. H. , Hagelstein P. L.
Published: July 2002

We identify and evaluate plasmas in which efficient x-ray laser frequency near-doubling is expected for a number of available x-ray lasers by means of four-wave mixing with Nd or KrF lasers. In some of these plasmas, four-wave mixing of coherent x rays and tunable optical radiation may result in tunable coherent x-ray radiation powerful enough for x-ray laser spectroscopy.
Meander-type wavelength demultiplexer with weighted coupling
Authors: Venghaus H. , Bornholdt C. , Kappe F. , Nolting H.-P. , Weinert C. M.
Published: July 2002

An experimental and theoretical investigation of meander-type wavelength demultiplexers with weighted coupling is reported. Numerical simulations have been performed combining a two-dimensional finite difference analysis and a suitably developed coupling mode method. Devices have been realized based on rib waveguides in GaInAsP/InP with filter center wavelengths around 1.3 μm. With weighted coupling the sinc2(λ)-type transmission characteristics of standard meander couplers change and the sidelobes of the latter devices are efficiently suppressed. We further show the determination of optimum weighted coupling for wavelength filters meeting given requirements with respect to channel separation, maximum allowable crosstalk, and total device length.
High reflectivity broadband self-pumped phase conjugator in near-infrared wavelengths
Authors: Shih Y. H. , He X. H. , Zhang H. Y.
Published: July 2002

A high reflectivity broadband BaTiO3 self-pumped phase conjugator with external ring cavity in near-infrared wavelengths (706–850 nm) is reported. Phase conjugate reflectivity as high as 77.5% was observed at 756 nm. The losses and the reflection grating are discussed in detail.
Linewidth broadening factor of a microcavity semiconductor laser
Authors: Jin R. , Boggavarapu D. , Khitrova G. , Gibbs H. M. , Hu Y. Z. , Koch S. W. , Peyghambarian N.
Published: July 2002

The emission linewidth above threshold is measured in a GaAs/AlGaAs microcavity surface-emitting laser with a single cavity mode. The measured linewidth broadening factor is in good agreement with theoretical calculations that include the most important many-body Coulomb effects of the electron-hole plasma.
Photoluminescence from submicron CaF2:Nd films grown epitaxially on Si(111) and Al(111)/Si(111)
Authors: Cho C. C. , Duncan W. M. , Lin T. H. , Fan S. K.
Published: July 2002

Nd3+ doped CaF2 films have been grown epitaxially on Si(111) and Al(111)/Si(111) using CaF2 and NdF3 evaporation. Photoluminescence spectra from these samples show high intensity and narrow emission linewidth even when the thickness of the CaF2:Nd films is reduced to 0.2 μm. The 10 457 Å emission line is not quenched until the Nd concentration exceeds 3.8 wt.%. Moreover, while similar spectra are observed, the photoluminescence intensity from the CaF2:Nd films grown on Al/Si(111) is significantly higher than from the CaF2:Nd on Si(111).
Investigating the cubic anisotropy of the confined hole subbands of an AlAs/GaAs/AlAs quantum well using resonant magnetotunneling spectroscopy
Authors: Hayden R. K. , Eaves L. , Henini M. , Takamasu T. , Miura N. , Ekenberg U.
Published: July 2002

The energy-wave-vector dispersion curves and cubic anisotropy of the confined hole subbands of a (001) AlAs/GaAs/AlAs valence-band quantum well are studied in resonant magnetotunneling experiments using pulsed magnetic fields up to 41 T. The experimental results are compared with calculations using a six-band model which includes the effect of the finite electric field in the quantum well. The comparison convincingly demonstrates that the technique is sufficiently accurate to measure fine details of the band structure of the valence-band quantum well.
Observation of nonequilibrium holes in Si-SiGe unipolar transistor structures
Authors: Liu H. C. , Buchanan M. , Baribeau J.-M.
Published: July 2002

The effect of nonequilibrium holes is investigated in double-heterojunction Si-SiGe-Si unipolar transistors with base layers of about 90 nm. We demonstrate experimentally that the carrier distribution in the base is altered when the base is used as a current drain or source. The observed effect of altered carrier distribution has important implications as it shows that the common assumption that a heavily doped region outside of the active region (e.g., a barrier) is in thermal equilibrium for quantum device modeling is only an approximation and is not, strictly speaking, valid in the presence of a current.
Synthesis and characterization of InAs multiple quantum wells in a (111)B GaAs matrix
Authors: Ilg Matthias , Ploog Klaus H.
Published: July 2002

We investigate the molecular beam epitaxy of InAs quantum wells in a [111]-oriented GaAs matrix. High-resolution x-ray diffraction measurements show the structural coherence of the samples to be maintained beyond the point where relaxation occurs in [100]-oriented structures. Low-temperature photoluminescence measurements reveal linewidths as narrow as 5 meV and show the formation of high-quality heterostructures along the [111] direction with its well-known complications for molecular beam epitaxial growth. We observe blue shifts of the luminescence lines due to the internal, piezoelectric fields. The demonstration of room-temperature emission from our samples shows these structures to be promising candidates for optoelectronic applications.
Design considerations of large aperture perpendicular gratings semiconductor ring lasers
Authors: Hardy A. , Dzurko K. M. , Welch D. F. , Scifres D. R. , Lang R. J. , Waarts R.
Published: July 2002

A new laser geometry, recently demonstrated, is analyzed. The laser cavity consists of two orthogonally oriented diffraction gratings faced by two plane boundaries, such as cleaved facets. It is shown that such lasers may operate at a single, very high mode order with excellent modal discrimination.
Study of growth temperature in gas-source molecular-beam epitaxy growth of InGaAs/GaAs quantum well lasers
Authors: Zhang G. , Ovtchinnikov A. , Pessa M.
Published: July 2002

Strained-layer InGaAs/GaAs single quantum well lasers were grown by gas-source molecular-beam epitaxy at temperatures between 430 and 610 °C. The optimum growth temperature for the quantum wells of the lasers was found to be about 520 °C, as deduced from the measurement of threshold current density of the lasers and room-temperature photoluminescence (PL) of the quantum wells. If the growth temperature is lower than 520 °C, the threshold current density dramatically increases due to the formation of nonradiative carrier recombination centers in the quantum well. These recombination centers originate from lattice mismatch defects and alloy disordering. If the growth temperature is higher than 520 °C, indium desorption and segregation become increasingly severe. Thus, at high growth temperature, the InGaAs/GaAs interfaces become rough and the threshold current density increases. In addition, rapid thermal annealing was observed to remove most of the nonradiative recombination centers from the quantum wells and to improve the threshold current density of the lasers and PL intensity of the quantum wells.
Si-acceptor passivation on n-type (AlGa)As post-growth hydrogenation
Authors: Proctor M. , Oelgart G. , Lippold G. , Reinhart F.-K.
Published: July 2002

We have studied AlGaAs:Si grown by molecular beam epitaxy before and after post-growth hydrogen plasma treatment by low temperature photoluminescence (PL) capacitance-voltage, and Hall effect. The PL strength increases after hydrogen plasma treatment. We observe, for the first time, that in n-type AlGaAs:Si not only the shallow donors but also the Si acceptor can be passivated by a long time (3 h) hydrogen diffusion, at 570 K. The change of the relative PL intensities associated with the Si and C acceptors demonstrates the dependence of the passivation effect on the chemical species.
Time-dependent formalism for interband tunneling application to the InxGa1−xAs system
Authors: Sankaran V. , Singh J.
Published: July 2002

A formalism is presented to study interband tunneling which involves a direct, numerical solution of the time-dependent Schrödinger equation, employing the tight-binding representation for electronic states with an eight-element (sp3) basis. Using this explicitly time-dependent formalism, one can study the dynamics of interband tunneling in the presence of complicated space- and time-dependent electric field profiles encountered in many devices. This technique is well suited to study interband tunneling in heterostructures since the tight-binding method describes their band structure adequately. In conjunction with deformation potential theory, it can be applied to strained systems as well. The technique is applied to the important semiconductor system of InxGa1−xAs.
Source of sidelobe asymmetry in integrated acousto-optic filters
Authors: Smith D. A. , d’Alessandro A. , Baran J. E. , Herrmann H.
Published: July 2002

The often-observed extreme asymmetry in the sidelobe spectra of integrated acousto-optic filters exacerbates cross talk between wavelength-multiplexed optical channels. We explain the source of this asymmetry in terms of a systematic even-order variation of the effective waveguide birefringence as a function of distance from the device center. Calculations show what degree of nonuniformity in Ti-stripe thickness, width, or diffusion temperature are required to account for typical asymmetries. We describe two experiments in which temperature gradients were applied to low-power acousto-optic filters in order to induce sidelobe suppression on either side of the optical transmission function, while greatly enhancing sidelobes on the opposite side.
Stimulated Raman scattering from a laser-produced Pb vapor
Authors: Akiyama Yasuhiro , Matsunawa Yuuki , Midorikawa Katsumi , Obara Minoru , Tashiro Hideo
Published: July 2002

We have demonstrated that the Pb metal vapor produced by moderate laser irradiation is an effective medium for stimulated electronic Raman scattering. The maximum density of 1016 cm−3 of Pb atoms in the ground state was produced by focusing a Nd:YAG laser pulse onto a solid Pb target at the focused intensity of 40 MW/cm2. A 277-nm pump pulse of 50-mJ energy and of 5-ns width (FWHM) was converted to the Stokes pulse (393 nm) of 0.1 mJ.
Fabrication of a novel electro-optical intensity modulator from the conjugated polymer, poly(2,5-dimethoxy-p-phenylene vinylene)
Authors: Parker I. D. , Gymer R. W. , Harrison M. G. , Friend R. H. , Ahmed H.
Published: July 2002

We report an electro-optic absorption modulator based around a metal-insulator-semiconductor field-effect transistor structure in which the active semiconductor is the polymer poly(2,5-dimethoxy-p-phenylene vinylene). It incorporates a single optical waveguide formed by the polymer, insulator, and a polyimide top layer which is ribbed to define the guide laterally. Charge injection creates polaron and bipolaron states which change the subgap absorption between 2 and 1.4 μm and between 800 nm and the band edge at 600 nm.
Structure and location of misfit dislocations in InGaAs epilayers grown on vicinal GaAs(001) substrates
Authors: Chen Y. , Zakharov N. D. , Werner P. , Liliental-Weber Z. , Washburn J. , Klem J. F. , Tsao J. Y.
Published: July 2002

The atomic structure of misfit dislocations at In0.2Ga0.8As/GaAs interfaces misoriented 2°–10° from (001) has been investigated by high-resolution electron microscopy. The misfit dislocations are predominantly dissociated 60° dislocations consisting of 90° and 30° Shockley partial dislocations and enclosed stacking faults. These dissociated 60° dislocations form increasingly asymmetrically on the different {111} glide planes as the misorientation increases. The 90° partial dislocations are not confined to the interface, but lie 0–100 Å beneath it. The 30° partial dislocations, in turn, are pushed even further into the substrate.
Thermal expansion of gallium arsenide layers grown by molecular beam epitaxy at low temperatures
Authors: Leszczynski M. , Walker J. F.
Published: July 2002

The thermal expansion of low-temperature (190–220 °C) MBE grown gallium arsenide (LT GaAs) was measured using x-ray diffraction methods. The experiment was performed in order to observe the influence of high nonstoichiometric excess (about 1%) of arsenic on the thermal expansion of gallium arsenide. The diffraction measurements enabled the simultaneous monitoring of the lattice constants of the LT GaAs layers and their semi-insulating GaAs substrates. Their lattice mismatch was only slightly temperature dependent and decreased by about 5% with a temperature rise from 77 K (in dark) up to 550 K. This means that the value of the thermal expansion coefficient of as-grown LT GaAs was lower only by about 0.05×10−6 K−1 than that of the semi-insulating GaAs substrate. Reduction of arsenic excess by air annealing at 420 °C resulted in the decrease of lattice mismatch and the difference in the thermal expansion. This means that both are related to such point defects as arsenic antisites and interstitials. The experimental results are compared with the previously published data for variously doped gallium arsenide samples.
Short-pulse scattering measurements from dielectric spheres using photoconductively switched antennas
Authors: Kralj David , Carin Lawrence
Published: July 2002

Planar antennas are switched photoconductively using optical pulses generated by a picosecond laser system. The freely propagating radiation, of picosecond duration and with bandwidth extending from 5 to 75 GHz, is used to perform short-pulse scattering measurements on three-dimensional targets. Results are shown for scattering from dielectric spheres, with the time-domain results clearly showing the early and late-time scattered signal. All measurements are compared with theory, directly in the time domain.
State filling effect on spectral linewidth of quantum well lasers
Authors: Zhao B. , Chen T. R. , Iannelli J. , Zhuang Y. H. , Yamada Y. , Yariv A.
Published: July 2002

The effect of state filling (undesired, but inevitable, carrier population in the optical confining layers) on quantum well laser characteristics such as modulation dynamics and threshold current has been well documented. Here we present experimental and theoretical evidence showing that the state filling also influences in a major way the amplitude-phase coupling factor (α) of quantum well lasers and thus their spectral linewidth.
Spatial evolution of filaments in broad area diode laser amplifiers
Authors: Lang Robert J. , Mehuys David , Hardy Amos , Dzurko Ken M. , Welch David F.
Published: July 2002

We report a numerical model that demonstrates the evolution of a uniform array of filaments from random fluctuations in the input of a single-pass semiconductor laser amplifier. We also report the first direct experimental observation of the spatial evolution of filaments in a broad area active grating semiconductor laser amplifier. The observed filamentation shows good agreement with the numerical model. This agreement suggests that such filaments may result from the unstable growth of microscopic fluctuations in the input and/or nonuniformities within the amplifier.
Field-assisted ion exchange in glass: The effect of masking films
Authors: Pantchev B. , Danesh P. , Nikolov Z.
Published: July 2002

The two-step ion exchange process for the fabrication of optical waveguide structures in glass is studied. The first step is field-assisted ion exchange through the structure forming ‘‘windows’’ in the masking films. It is established that, in the case of metal masking films, the exchange ability of glass in the region under the mask decreases significantly. The second ion exchange in these regions is even totally blocked when soda-lime glass is used. The mechanism and the application of this effect are briefly considered.
Role of Si-H and Si-H2 in the photoluminescence of porous Si
Authors: Lavine J. M. , Sawan S. P. , Shieh Y. T. , Bellezza A. J.
Published: July 2002

FTIR spectra reported by Brandt et al. [Solid State Commun. 81, 307 (1992)], Tischler et al. [Appl. Phys. Lett. 60, 639 (1992)], and Tsai et al. [Appl. Phys. Lett. 59, 2814 (1991), and 60, 1700 (1992)] have shown the presence of Si-H and Si-H2 lines in porous Si which Canham [Appl. Phys. Lett. 57, 1046 (1990)], Tischler and Tsai have considered essential to the observation of visible photoluminescence (PL). Hydrogen has been ascribed as a surface passivating agent which eliminates nonradiative transitions thus enabling PL to occur. Photo-oxidation has been described as replacing some of the surface passivants with oxygen, generating nonradiative transitions which quench the PL. We have markedly reduced the Si-H and Si-H2 content of anodized samples by treatment with CCl4 vapor. Comparison of the photoluminescent emission and excitation spectra for CCl4 treated and untreated samples show very similar results. Comparison of the FTIR spectra of photo-oxidized samples which exhibit no PL and as-anodized samples show the similar presence of Si-H and Si-H2. These observations suggest that neither Si-H nor Si-H2 is essential for the observation of PL in anodized Si. This result and the similarity in the behavior of porous Si with the polysilynes lead us to concur with Brandt et al. that visible PL in anodized Si is generated by the backbone of a 2D Si polymer.
Bound-to-bound intersubband transitions in a δ-doped p-type Si/SixGe1−x/Si quantum well
Authors: Chun S. K. , Pan D. S. , Wang K. L.
Published: July 2002

The absorption spectrum in p-type Si/Si0.6Ge0.4/Si structure with a δ-doped quantum well grown on Si(001) substrate is calculated using a multiband model. We have generalized the previous treatment of the depolarization effect in n-type Si to include subband multiplicity, nonparabolicity, and valence band anisotropy. An implicit formula for the effective plasma frequency was used to conveniently include these effects in the calculation. We found that it is necessary to treat the depolarization effect in the complicated couplings among valence bands in order to explain the observed spectrum.
Excitation and quenching of Yb intra-4f-shell luminescence in InP0.93As0.07
Authors: Kozanecki A. , Karpinska K. , Kalinski Z.
Published: July 2002

Photoluminescence excitation (PLE) experiments on Yb3+ in InP0.93As0.07 has been performed for the first time. The PLE spectra were measured at 4.2, 42, and 70 K. At each temperature the most efficient luminescence of Yb was achieved with the excitation wavelength tuned to an energy level located at a depth of 28±2 meV in the band gap, which we assign to an axial Yb-P3As center. It has been shown that the 4f-shell emission is thermally deactivated with a characteristic energy of 115±10 meV (190±10 meV in a reference InP:Yb sample), equal to the difference between the band gap and the 2F5/2-2F7/2 transition energy, thereby confirming dissociation of the excited state of Yb3+ by phonon absorption.
Scanning tunneling microscopy studies of vapor deposited films of tetrathiafulvalene with iodine
Authors: Breen J. J. , Tolman J. S. , Flynn G. W.
Published: July 2002

Scanning tunneling microscopy studies are reported for vacuum deposited conducting films of tetrathiafulvalene (TTF) with iodine (I) codeposited on mica substrates. Molecular resolution images reveal a crystal structure consistent with that of single crystals of a material with chemical composition (TTF)7I5 with the crystal c axis parallel to the plane of the mica substrate. The imaged surface is terminated with TTF molecules, and the submicron dimension crystal planes which are observed reveal surface steps consistent with the layered and stacked nature characteristic of charge transfer salt materials.
Real time electron microscopy inspection of high temperature processes in W free standing wires
Authors: Gómez-Herrero J. , Pascual J. I. , Méndez J. , Baró A. M.
Published: July 2002

High temperature structural changes in a W wire are studied in situ by scanning electron microscopy. This is made possible by the microscopic size of the wire. Grain-boundary grooving and faceting are observed in real time. The constriction exhibits a strong thermal gradient (∼100 K μm−1) which is the driving force for the migration mechanisms responsible for the observed phenomena.
Electric-field-induced phase changes in polyvinylidene fluoride: Effects from corona polarity and moisture
Authors: Costa Mauro M. , Giacometti José A.
Published: July 2002

The constant-current corona triode has been used to charge and monitor the surface potential buildup of polyvinylidene fluoride samples in α form. Under dry air and positive polarity it is possible to pole the samples to sufficiently high electric fields so as to cause a phase change from the nonpolar to the polar δ form. This phase transition is confirmed by x-ray diffractograms. Surface potential measurements on δ samples display a ferroelectric behavior in which a plateau appears in the surface potential buildup curve due to the dipole reorientation. The values of the remanent polarization and the coercive field were estimated to be ∼50 mC/m2 and ∼65 MV/m, respectively.
Transport properties of indium tin oxide/p-InP structures
Authors: Luo J. K. , Thomas H.
Published: July 2002

I-V properties of indium tin oxide (ITO)/p-InP solar cell structures measured at various temperatures show that the conduction mechanism is dominated by tunneling at low forward bias, and by thermionic emission at high forward bias. An increase of barrier height of 200–300 meV was found for all ITO/InP diodes compared with Au/InP Schottky diodes. Donorlike defects were found to be responsible for the increase of barrier height, and to cause the defect-assisted tunneling conduction. The experimental results support the model of a buried n+/p junction with the n+ layer induced by the sputter deposition of ITO.
1.3 μm decoupled confinement heterostructure lasers grown by chemical beam epitaxy
Authors: Hausser Stefan , Harder Christoph S. , Meier Heinz P. , Walter Willi
Published: July 2002

A novel 1.3 μm quantum well laser structure, the decoupled confinement heterostructure (DCH) laser is presented. This laser has, at the same time, deep quantum wells and low band-gap confinement layers, which leads to high optical confinement. Internal barriers prevent carriers from leaking into the confinement layers. We compare results obtained on DCH and conventional 1.3 μm quantum well lasers grown by chemical beam epitaxy (CBE). The DCH lasers have a transparency current density as low as 140 A/cm2, internal optical losses of only 5 cm−1 and their temperature performance has been improved over that of conventional quantum well lasers. Measurements of the spontaneous emission of these lasers clearly show the reduction of carrier leakage at higher temperatures.
Directed beam emission from film edge in organic electroluminescent diode
Authors: Hiramoto Masahiro , Tani Jun-ichi , Yokoyama Masaaki
Published: July 2002

Narrow beamed light emission was successfully obtained in a new type of organic electroluminescent (EL) diode whose organic layer was sandwiched between two metal layers acting as charge injecting electrodes and mirrors. EL from the organic film edge showed much sharper spectrum with a peak depending on the thickness of the organic layer and about 100 times larger emission density compared with that from the film surface of a conventional EL diode.
X-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy studies of titanium nitride/titanium/silicon structures after thermal annealing
Authors: Ryu S. R. , Shin D. S. , Oh J. E. , Choi J. S. , Paek S. H. , Lee S. I. , Lee J. K. , Sim T. U. , Lee J. G. , Sheng G. T.
Published: July 2002

Oxygen diffusion/incorporation behaviors of TiN/Ti/Si structures after thermal annealing in nitrogen ambients have been studied by x-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy measurements. At the interface between Ti and TiN, titanium dioxides, thermodynamically most stable, are formed as a consequence of grain boundary diffusion, while inside TiN layer the contents of TiO and Ti2O3 compounds increases as the annealing temperature increases. At the interface between Ti and Si, titanium silicide formation is observed in the samples annealed above 450 °C consuming a part of pure Ti layer. One thing to note is that a severe blistering is observed in a sample annealed at 600 °C, probably caused by the difference of thermal expansion coefficients between TiSi2 and TiO2.
Study of tellurium precipitates in CdTe crystals
Authors: Jayatirtha H. N. , Henderson D. O. , Burger A. , Volz M. P.
Published: July 2002

The effect of tellurium precipitates was studied in medium resistivity (103–106 Ω cm) undoped and Cl-doped CdTe using differential scanning calorimetry (DSC) and mid-infrared spectroscopy and the results were correlated with near-infrared microscopy photographs. When present in a significant quantity (∼0.25 wt %), we show that Te precipitates are detectable using DSC measurements. In the mid-infrared, the contribution of the absorption by free-carriers is negligible, and therefore, the effect of the Te precipitates in these crystals can be considered uncoupled from the effects of Cd vacancies.
Kinetics of solid phase epitaxial regrowth in amorphized Si0.88Ge0.12 measured by time-resolved reflectivity
Authors: Lee C. , Haynes T. E. , Jones K. S.
Published: July 2002

Time-resolved reflectivity has been used to measure the rate of solid phase epitaxial regrowth (SPER) in situ during annealing of strained Si0.88Ge0.12 epilayers on Si preamorphized by the implantation of Si. The SPER velocities were measured over more than two orders of magnitude at temperatures from 503 to 603 °C. The results confirm that the average SPER velocity in thin, strained Si0.88Ge0.12 layers is less than that in pure Si. Furthermore, these real-time measurements demonstrate that the SPER rate for strained Si0.88Ge0.12 alloys is not a constant during regrowth at a fixed temperature but varies systematically as a function of the position of the amorphous-crystalline interface. The activation energy barrier of SPER in strained Si0.88Ge0.12 is higher than that in pure Si and is also a function of interface position, ranging from 2.94 to 3.11 eV. Cross-section transmission electron microscopy shows that strain-relieving defects are introduced coincidentally with the minimum regrowth rate.
Focused-ion-beam defined and overgrown collector-up AlGaAs/GaAs heterojunction bipolar transistors
Authors: Ishibashi T. , Fischer A. , Wieck A. D. , Ploog K.
Published: July 2002

The focused-ion-beam technique combined with overgrowth of AlGaAs/GaAs heterostructures by molecular beam epitaxy has been successfully applied to injection current confinement in collector-up heterojunction bipolar transistors. A potential barrier to block electron injection is produced by Ga focused-ion-beam implantation into n+-GaAs subemitter layer and is embedded beneath the extrinsic emitter. The fabricated collector-up transistors with intrinsic emitter dimensions of 20×20 μm and extrinsic emitter dimensions of 85×110 μm yield current gains of 30, demonstrating the effective current confinement in the proposed device structure.
Ultrafast, large angle, noncollinear, and nonlinear, broadband multilayer deflectors
Authors: Cada M. , Normandin R. , Chatenoud F.
Published: July 2002

We demonstrate the use of a multilayer waveguide to enhance harmonic mixing over a large noncollinear angle and present first results for three-dimensional nonlinear waveguide wave mixing. The resulting surface emission can be used to select any target coordinate within an output plane or half-space with subpicosecond addressing speeds and large deflection angles. The electro-optic version is limited only by device capacitance.
Continuous electronic tuning of a narrow-band Nd3+-fiber laser
Authors: Sabert Hendrik
Published: July 2002

Continuous electronic tuning of a linear Nd3+-fiber laser near 1088 nm wavelength is demonstrated by controlling the relative phase of two cascaded intracavity frequency shifters. A servoloop tracks the mode selecting elements of the laser with respect to the oscillation frequency and permits complete suppression of mode jumps.
Influence of silicon wafer surface orientation on very thin oxide quality
Authors: Ohmi T. , Matsumoto K. , Nakamura K. , Makihara K. , Takano J. , Yamamoto K.
Published: July 2002

We studied effects of silicon wafer surface orientation on very thin oxide quality, testing Si(100) and (111) wafers. It has been found that the very thin oxide structure is dominating by the silicon wafer surface orientation, and that when Si(111) is oxidized, SiO2/Si(111) interface microroughness increases as oxide gets thicker than 10 nm, resulting in a degradation of oxide films quality on Si(111). When oxide thickness is decreased to less than 10 nm, SiO2/Si interface smoothness is maintained similar to Si(100) and (111) but the SiO2/Si interface exhibits larger interface charges and larger flatband voltage shift for Si(111) than for Si(100).
Acoustic shear wave imaging using an annular lens
Authors: Zhang D. , Crean G. M.
Published: July 2002

Annular lenses for acoustic shear wave imaging are investigated in this letter. Both theoretical analysis of the distribution of the focused acoustic field in Al2O3 and experimental results show that the longitudinal wave field in a solid will be seriously suppressed by a small absorbing disk at the center of the lens which does not significantly effect the shear wave field in the material. Internal material images are also presented showing that an annular lens is very suitable for obtaining a high quality shear wave image.
Concentration and collimation of diffuse linear light sources
Authors: Davidson N. , Friesem A. A.
Published: July 2002

We present an approach for concentration and collimation of a diffuse linear light source to achieve extremely high concentration in the long direction at the expense of the short direction. The approach is based on free-space optics and involves either arrays of prisms or holographic optical elements that couple between the two spatial directions. The results for a specific arrangement that concentrates a 40 mm by 0.4 mm source, with diffusive angle of about 0.1 rad, into a 1 mm by 1 mm isotropic spot are presented.
Morphology of flattened diamond crystals synthesized by the oxy-acetylene flame method
Authors: Hirabayashi Keiji , Kimura Takeshi , Hirose Yoichi
Published: July 2002

Flattened diamond crystals were synthesized by the oxy-acetyle flame method under high O2/C2H2 gas ratio conditions (≥0.95). The morphology of the flattened diamond crystals is characterized as follows: the ratio of the size of the top face and the height is 5:1 or more and all the faces are {111} faces. The twin boundaries are formed many times parallel to the top face. Scanning electron microscopy observations indicate that the flattened diamond crystals exhibit a good crystalline morphology. The motive force of lateral growth is caused by a re-entrant corner effect which results from the formation of twin boundaries.