bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular tilt direction in a slightly tilted homeotropic aligned liquid crystal cell
Authors: Hatoh Hitoshi , Shohara Kiyoshi , Kinoshita Yoshihiro , Ookoshi Noriko
Published: July 2002

The influence of hardness and topology of substrate surface on the pretilt angle were investigated for a slightly tilted homeotropic alignment achieved by the rubbing technique. On a soft surface, the grooves are produced which align in the same direction as the rubbing direction while the liquid crystal molecules tilt in the direction opposite to the rubbing direction. On a hard surface, no grooves are observed and the molecules tilt in the same direction as the rubbing direction. These results were applied to the fabrication of a two-domain vertically aligned nematic liquid crystal display.
Hardness demonstration of diamond tips by nanometer-scale controlled scratching on metallic surfaces
Authors: Chu Xing , Ma Zili , Liu Ning , Chang Zhipeng , Hu Tianmiao , Xue Zengquan , Pang Shijin
Published: July 2002

A new kind of diamond tip for the scanning tunneling microscope has been fabricated by a microwave plasma chemical vapor deposition method. The extreme hardness of the tips is demonstrated by doing nanometer-scale controlled direct scratching on various metallic surfaces using these tips. The results indicate the potential of such diamond tips for nanometer-scale mechanical polishing.
Novel fabrication technique towards quantum dots
Authors: Liu Der-Cherng , Lee Chien-Ping
Published: July 2002

A novel technique for semiconductor quantum dots fabrication is demonstrated. Using the technique of thermal etching or thermal evaporation during molecular beam epitaxial growth with a built-in evaporation mask, semiconductor quantum dots were obtained in a single growth run.
Separate-confinement heterostructure dependence of the effective carrier recombination coefficient of strained InGaAs/InGaAsP multiple quantum well lasers
Authors: Odagawa Tetsufumi , Nakajima Kaoru , Tanaka Kazuhiro , Nobuhara Hiroyuki , Inoue Tadao , Okazaki Nirou , Wakao Kiyohide
Published: July 2002

We experimentally investigated the separate-confinement heterostructure (SCH) layer thickness and SCH band-gap wavelength dependence of the effective carrier recombination coefficient of strained InGaAs/InGaAsP multiple quantum well lasers. The dependence is explained by the carrier transport between the SCH layers and the wells.
Homoepitaxial 13C diamond films studied by micro-Raman and photoluminescence spectroscopy
Authors: Behr D. , Wagner J. , Wild C. , Koidl P.
Published: July 2002

Raman microscopy has been used to study 13C and 12C/13C isotopically mixed homoepitaxial diamond films grown by chemical vapor deposition on natural diamond substrates. The measured dependencies of the frequency and the width of the first-order zone-center optic phonon line on the isotope composition agree well with those reported for diamond crystals synthesized under high pressure. To study the evolution of the epitaxial layer quality for a 13C diamond film grown on a natural type IIa diamond substrate with an isotopic composition of almost pure 12C, micro-Raman spectroscopy has been performed on a polished cross section. The width of the zone-center phonon line is found to increase in the epitaxial layer from 2.6 up to 3.0 cm−1 with increasing distance from the film/substrate interface and is thus consistently larger than the linewidth of 2.5 cm−1 measured in the substrate. Two photoluminescence bands are observed in the epitaxial film centered at 2.16 and 2.21 eV. The 2.16 eV band, which has been attributed to emission from an interstitial nitrogen-vacancy complex, shows a pronounced maximum in intensity at the film/substrate interface indicating an enhanced nitrogen incorporation at the interface.
Investigation of field, carrier, and coherent phonon dynamics in low-temperature grown GaAs
Authors: Dekorsy T. , Kurz H. , Zhou X. Q. , Ploog K.
Published: July 2002

We compare the dynamics of electric field, transport, and coherent phonons in as-grown and annealed low-temperature (LT) GaAs by an electro-optic technique on a subpicosecond time scale. The buildup and decay of space-charge fields associated with the photo-Dember effect are investigated. The recombination dynamics of trapped carriers is monitored via the ps decay of the electro-optic signal. Differences in annealed and as-grown LT GaAs are related to the different microscopic form of excess arsenic and point defect density. In the coherent phonon signal a large red shift of the LO phonon and an additional local vibration below the LO phonon provides information on structural defects in as-grown LT GaAs.
Visible InGaP/InGaAlP quantum well top surface emitting laser diodes
Authors: Tai Kuochou , Huang Kai-Feng , Wu Chang-Cherng , Wynn James D.
Published: July 2002

Vertical cavity top surface emitting lasers emitting near 0.67 μm visible spectral region were fabricated by one-step low pressure metalorganic vapor phase deposition technique. The lasers used four 80-Å-thick InGaP/InGaAlP quantum wells active region, sandwiched between two Al0.5Ga0.5As/AlAs distributed Bragg reflectors. Room temperature pulsed threshold current was 10 mA for 15 μm diam devices.
Improved solid phase epitaxial growth of lithium tantalate thin films on sapphire, using a two-step metalorganic chemical-vapor deposition process
Authors: Wernberg Alex A. , Braunstein Gabriel H. , Gysling Henry J.
Published: July 2002

Epitaxial lithium tantalate thin films were grown on sapphire substrates by metal-organic chemical-vapor deposition using a two-step growth process. After an initial thin (≊30–100 Å thick) amorphous buffer layer of LiTaO3 was deposited and annealed to induce crystallization by solid phase epitaxy (SPE), a second, thicker amorphous lithium tantalate layer was deposited and also crystallized using SPE. The use of the buffer layers substantially improved the crystalline quality of the heteroepitaxial films, with the thickest buffer layer providing the best results. The films were characterized by ion channeling, x-ray diffraction and scanning electron microscopy.
Photocurrent reversal induced by localized continuum resonances in asymmetric quantum semiconductor structures
Authors: Sirtori Carlo , Faist Jerome , Capasso Federico , Sivco Deborah L. , Cho Alfred Y.
Published: July 2002

A new type of photoconductivity controlled by the wave function of the excited state is reported in suitably engineered asymmetric quantum well heterostructures grown by molecular beam epitaxy. This phenomenon manifests itself in directional charge transfer against the applied electric field as electrons in the wells are photoexcited to resonances localized above the barriers.
Phase locking of linear arrays of CO2 waveguide lasers by the waveguide-confined Talbot effect
Authors: Hornby A. M. , Baker H. J. , Colley A. D. , Hall D. R.
Published: July 2002

Phase locking of CO2 waveguide laser arrays of up to 19 channels has been attained by low-loss coupling in a slab waveguide of Talbot imaging dimensions, within a two-mirror cavity. The technique provides strong channel coupling while maintaining a low laser threshold. A seven channel array phase locked into a single mode by this technique has produced 100 W of output and 10% efficiency, demonstrating the effectiveness of Talbot imaging, when combined with confinement in a slab waveguide.
Enhancement of the vacuum ultraviolet emission from excimer laser-generated plasmas by ambient gas atoms
Authors: Mehlman G. , Chrisey D. B. , Horwitz J. S. , Burkhalter P. G. , Auyeung R. C. Y. , Newman D. A.
Published: July 2002

We have measured the axial (z) and radial (x) distribution of the vacuum ultraviolet emission from excimer laser generated aluminum plasmas in vacuum and in 300 mTorr of argon. The ratio of the radiated line intensities (emission in a gas versus vacuum) on the z axis (i.e., x=0) increased exponentially with distance from the target surface for plasmas generated in a 300 mTorr argon ambient. The absolute line intensities increased linearly with the argon pressure and approximately linearly with the ambient gas atomic cross section when other rare gases were substituted. The line intensity radial distribution was broader for plasmas in argon than in vacuum and the magnitude of the effect increased monotonically with z. The spectral data obtained from plasmas in a gas ambient are discussed in terms of the diffusion of plasma electrons in an ionized gas.
Low temperature optical response of a single grain boundary in superconducting YBa2Cu3O7−δ thin film
Authors: Bhattacharya S. , Rajeswari M. , Takeuchi I. , Xi X. X. , Mao S. N. , Kwon C. , Li Qi , Venkatesan T.
Published: July 2002

We have investigated the optical response from a single grain boundary in a thin film (∼300 nm) of superconducting YBa2Cu3O7−δ fabricated on bicrystals SrTiO3 substrate. We have studied the temperature, bias current, and magnetic field dependence of the optical response in the temperature range of 15 K≤T≤35 K. We find that the optical response from the single grain boundary in this temperature range can be satisfactorily explained in terms of the optical response of a Josephson weak link. The optical response of the grain boundary is qualitatively similar to that of granular films seen in the earlier studies, indicating that the latter may be dominated by the optical response of grain-boundary weak links.
Photocurrent nonlinearities in ultrafast optoelectronic switches
Authors: Pašiškevičius V. , Deringas A. , Krotkus A.
Published: July 2002

Nonlinearities in photoresponse of ultrafast optoelectronic switches are investigated by using a novel correlation technique. Sublinear behavior is found to be typical for low average electrical fields and superlinear for electrical fields higher than the threshold of electron negative-differential-mobility effect. The nonlinearities have been explained in terms of the electrical field redistribution.
Depth profiles of strain in In0.10Ga0.90As/GaAs multiquantum well structures obtained by variable-pump wavelength photoluminescence
Authors: Griffiths C. O. , Cooper S. L. , Klein M. V. , Forbes D. V. , Coleman J. J.
Published: July 2002

We have performed photoluminescence measurements probing the strain in a set of In0.10Ga0.90As/GaAs multiquantum well (MQW) samples. By using different continuous wave pump laser wavelengths we obtain a depth profile of strain in individual quantum wells within the MQW structure. We also present evidence for the existence of an equilibrium strain between In0.10Ga0.90As quantum well layers and GaAs barrier layers for thick strain-relaxed MQW structures.
Effects of grown-in stress on the metastable solid solubility limits in Sb implanted Ge0.1Si0.9 alloys
Authors: Hong Stella Q. , Hong Q. Z. , Mayer J. W.
Published: July 2002

Solid phase epitaxy and metastable solubility limits of implanted Sb atoms have been investigated in stressed and stress-relaxed Ge0.1Si0.9 thin films. For a 5×1015 cm−2 Sb implantation, complete recrystallization is achieved for both samples after a 60 min furnace annealing at 600 °C. In the case of stress-relaxed alloy, 91% of the Sb atoms are located at the substitutional sites of the Ge-Si matrix. For the stressed sample, however, only 60% of the Sb atoms occupy the substitutional sites of the matrix. A defect-free regrown layer is observed for the relaxed sample, while twins are formed near the location of the Sb concentration peak in the stressed Ge-Si. The maximum solid solubilities of Sb are estimated to be 1.6×1021 and 8×1020 cm−3 for the relaxed and the stressed Ge0.1Si0.9, respectively.
Influence of temperature on photocurrent of Al/chlorophyll a/Ag cells
Authors: Boussaad S. , Hotchandani S. , Leblanc R. M.
Published: July 2002

The temperature-dependent study of photocurrent of Al/chloropyll a/Ag cells has been carried out. The results show that the photocurrent (Iph), unlike dark current, shows an unusual behavior in that it increases as the temperature decreases. The striking feature is that Iph passes through a maximum and then decreases as the temperature is further decreased or increased. This is interpreted in terms of different efficiency of exciton dissociation into free charges at negatively charged traps associated with changes in microcrystalline structure of chlorophyll a with temperature.
High-T
c multilayer step-edge Josephson junctions and SQUIDs
Authors: Missert N. , Harvey T. E. , Ono R. H. , Reintsema C. D.
Published: July 2002

We have developed a reliable process to fabricate high-quality YBa2Cu3O7−x (YBCO) superconductor-normal metal-superconductor (SNS) step-edge junctions and SQUIDs over YBCO ground planes. These multilevel circuits employ thin films of SrTiO3 and NdGaO3 as the insulating layer between the active device and the ground plane and use Ag as the normal metal in the Josephson junction. The reproducibility and uniformity of the junctions are better than our single-level devices grown directly on step edges cut into single-crystal substrates. Here the critical current variation among junctions on a single wafer is less than a factor of 2. Junctions grown on thin-film step edges of SrTiO3 have critical currents near 2 mA at 4 K, while those grown on NdGaO3 step edges have critical currents near 0.5 mA at 4 K.
Far-infrared photon-induced current in a quantum point contact
Authors: Wyss Rolf A. , Eugster C. C. , del Alamo J. A. , Hu Qing
Published: July 2002

Motivated by the recently developed theory of photon-assisted quantum transport, we have studied transport properties of an antenna-coupled quantum point contract under coherent far-infrared (285 GHz) radiation. A pronounced photon-induced drain/source current is observed. The amplitude of the photon-induced current is about 10% of that corresponding to a quantized conductance step, and it oscillates with the gate voltage. Our analysis suggests that the observed photon-induced current is mainly due to heating of the electron gas in the source and drain (a bolometric effect) rather than photon-assisted quantum transport. Future improvement of the device parameters to enhance the effect of photon-assisted transport will be discussed.
Monolithic optoelectronic transistor: A new smart-pixel device
Authors: Aull B. F. , Nichols K. B. , Maki P. A. , Palmateer S. C. , Brown E. R. , Lind T. A.
Published: July 2002

A new optical switching and logic device, the monolithic optoelectronic transistor (MOET), is demonstrated. The MOET is an integrated circuit consisting of a p-i-n photodiode, a resonant tunneling diode, a multiple-quantum-well modulator, and a field-effect transistor. The device can function as an optical inverter or NOR gate. Present devices switch at an input optical power of 12.5 μW and have a large-signal optical gain exceeding ten. The advantages of the MOET include abrupt switching thresholds, saturated ‘‘on’’ and ‘‘off’’ states, and nonlatching operation.
Interface structure and chemical bondings in Al/S-passivated GaAs(111)
Authors: Sugiyama M. , Maeyama S. , Scimeca T. , Oshima M. , Oigawa H. , Nannichi Y. , Hashizume H.
Published: July 2002

The position and chemical state of S atoms have been investigated for the Al/S-passivated GaAs(111)A and (111)B samples using the soft x-ray standing wave technique and synchrotron radiation photoemission spectroscopy. The x-ray standing wave results indicate that the S atoms at the Al/S/GaAs(111) interface are significantly more disordered than the S atoms at the S/GaAs(111) surface. The position of the S atoms does not change upon the Al deposition. The synchrotron radiation photoemission spectra suggest that the Ga atoms bonded to S atoms before the Al deposition exchange with Al atoms upon deposition.
Bistable switching in a nonlinear Bragg reflector
Authors: Acklin B. , Cada M. , He J. , Dupertuis M.-A.
Published: July 2002

Numerical simulations and experimental results are reported on bistable switching in a semiconductor nonlinear vertical Bragg reflector. An improved structure with an additional linear rear mirror and a phase-adjusting layer was predicted to have lower threshold for bistability than a Fabry–Perot type device. The experimental observation of bistable switching in a nonlinear Bragg reflector is reported. Achieved threshold was comparable with a nonlinear Fabry–Perot device; the simpler structure of a nonlinear Bragg device may represent an advantage with respect to growth tolerances.
Temporal development of electric field structures in photoconductive GaAs switches
Authors: Schoenbach K. H. , Kenney J. S. , Peterkin F. E. , Allen R. J.
Published: July 2002

The temporal development of the electric field distribution in semi-insulating GaAs photoconductive switches operated in the linear and lock-on mode has been studied. The field structure was obtained by recording a change in the absorption pattern of the switch due to the Franz–Keldysh effect at a wavelength near the band edge of GaAs. In the linear mode, a high field layer develops at the cathode contact after laser activation. With increasing applied voltage, domainlike structures become visible in the anode region and the switch transits into the lock-on state, a permanent filamentary electrical discharge. Calibration measurements show the field intensity in these domains to exceed 40 kV/cm, which is greater than three times the value of the average applied field.
Mechanical wafer engineering for semitransparent polycrystalline silicon solar cells
Authors: Willeke G. , Fath P.
Published: July 2002

A concept for the realization of semitransparent bifacially active highly efficient and light weight crystalline silicon solar cells is presented. The concept is based on the preparation of perpendicular V-grooves in silicon blanks by mechanical abrasion using a dicing saw and beveled blades. Holes of variable diameter are formed automatically in the processing step, which provide a connection between the passivated phosphorus doped front and back side emitters. A maximum bulk-emitter distance of ∼30 μm has been realized in 200 μm thick structures which should result in highly efficient solar cell devices even in small grain low quality polycrystalline material. The partial transparency of the presented solar cell structure opens the way for new applications (crystalline Si photovoltaic windows, etc.). The feasibility of the mechanical grooving process has been demonstrated on Wacker SILSO cast silicon. Double-side V-grooved structures (distance between grooves 90 and 140 μm, bevel angle 35°) with hole diameters in the range 10–70 μm, corresponding to a transmittance of up to 30% in the visible, have been prepared with excellent uniformity and mechanical stability over a large area (5×5 cm2). An average total reflectance in the range 500–1000 nm of Rav=0.9% has been measured on a structure with a geometrical hole fraction of 1.7% after growth of a 1170 Å thick layer of thermal oxide. This SILSO structure had an effective silicon thickness of 120 μm, whereas the absorptance spectrum near the band edge was similar to a 5.5 mm thick nongrooved silicon wafer, indicating the excellent light trapping obtained.
Local texture and percolative paths for long-range conduction in high critical current density TlBa2Ca2Cu3O8+x deposits
Authors: Kroeger D. M. , Goyal A. , Specht E. D. , Wang Z. L. , Tkaczyk J. E. , Sutliff J. A. , DeLuca J. A.
Published: July 2002

A possible microstructural origin of the high critical current densities which have been obtained in c-axis-aligned, polycrystalline TlBa2Ca2Cu3O8+x deposits has been identified. The results of x-ray diffraction determinations of basal plane texture of Tl-1223 deposits prepared by spray pyrolysis are observed to depend on the size of the x-ray beam. Furthermore, most grain boundaries were found from transmission electron microscopy to have small misorientation angles. It is concluded that although overall the basal plane orientations are nearly random, there is a high degree of local texture indicative of colonies of similarly oriented grains. The spread in a-axis orientation within a colony is ∼10°–15°. Intercolony conduction, it is suggested, may be enhanced by a percolative network of small-angle grain boundaries at colony interfaces.
Excitonic luminescence from locally grown SiGe wires and dots
Authors: Brunner J. , Rupp T. S. , Gossner H. , Ritter R. , Eisele I. , Abstreiter G.
Published: July 2002

SiGe quantum wells with finite lateral size have been fabricated using local molecular beam epitaxy through shadowing masks. Scanning electron microscope and transmission electron microscope micrographs show good quality of the mesas and an effective in situ passivation by overgrowth of the buried SiGe quantum wells at the sidewalls of the mesa due to the applied growth technique. Photoluminescence measurements show clear excitonic emission from the SiGe wires and dots with lateral widths down to 2 μm. Intensities per area from the mesas are comparable to intensities from reference areas, suggesting very effective protection of the carriers against possible nonradiative recombination at the sidewalls of the mesa.
Electrochromism of gold-vanadium pentoxide composite thin films prepared by alternating thermal deposition
Authors: Nagase Katsumi , Shimizu Youichi , Miura Norio , Yamazoe Noboru
Published: July 2002

The composite thin films of Au-V2O5 were prepared by means of an alternating thermal deposition technique. The electrochromic properties of the films were dependent on Au contents and calcination temperature. The composite film containing 26 at. % Au calcined at 400 °C gave clear electrochromism of reddish-violet (cathodic polarization) ↔ green (anodic). The film had a strong optical absorption peak ascribable to the dispersed Au particles at 615 nm (cathodic) or 555 nm (anodic). The shift of this absorption peak, coupled with that of the absorption edge of the V2O5 matrix, was responsible for the new electrochromism.
High T
c superconductor bolometer with record performance
Authors: Brasunas J. C. , Lakew B.
Published: July 2002

We have used prethinned sapphire substrates to make a YBa2Cu3O7−x thin-film, transition-edge bolometer with peak detectivity of 6×109 cm Hz1/2/W near 4 Hz and 90 K. This is a new record for high Tc superconductor bolometers, and is comparable to the best detectivity yet achieved for a thermal-type infrared detector with no more than moderate cooling (liquid-nitrogen temperature and above). We discuss some simple improvements which may push the detectivity above 1010.
Volume holographic storage in hydrogen treated germano-silicate glass
Authors: Partovi A. , Erdogan T. , Mizrahi V. , Lemaire P. J. , Glass A. M. , Fleming J. W.
Published: July 2002

Strong permanent gratings (index change Δn∼3×10−3) have been formed in bulk hydrogen treated germano-silicate glass with 242 nm exposure. Diffraction efficiencies of 6% and initial sensitivity (Δn/incident energy density) of 2×10−5 cm2/J have been obtained. The observed sensitivity is comparable to the values achieved in other holographic storage materials such as LiNbO3. It is estimated that by more uniform hydrogen loading of the sample, diffraction efficiencies of 100% can be obtained in 3 mol % GeO2 samples of only 175 μm thickness. These materials are potentially useful as fast access time (sub-μs), high capacity (∼0.8 Tbits), robust, inexpensive write-one-read-many storage media, narrow (subangstrom) linewidth optical filters, and other optical components.
High reflectivity 1.55 μm (Al)GaSb/AlSb Bragg mirror grown by molecular beam epitaxy
Authors: Lambert B. , Toudic Y. , Rouillard Y. , Baudet M. , Guenais B. , Deveaud B. , Valiente I. , Simon J. C.
Published: July 2002

We report the molecular beam epitaxy growth of (Al)GaSb/AlSb Bragg mirrors around the 1.55 μm wavelength region. Mirrors with 97% reflectivity have been achieved by using 10 pairs of (Al)GaSb (1048 Å) and AlSb (1207 Å) quarter wavelength layers. This demonstrates the capability of the antimonide system to obtain efficient Bragg mirrors grown on GaAs substrates.
InAlAs/InGaAs metal-semiconductor-metal photodiodes heteroepitaxially grown on Si substrates
Authors: Sasaki T. , Enoki T. , Tachikawa M. , Sugo M. , Mori H.
Published: July 2002

To study performance and reproducibility of photodiodes (PDs) on Si in the long-wavelength region, InAlAs/InGaAs metal-semiconductor-metal PDs were fabricated on high-quality heteroepitaxial InP layers on Si substrates. A dark current of 0.5–2×10−8 A and a responsivity of 0.05–0.15 A/W were reproducibly obtained, at least at one of the ±5 V bias voltages. These dark currents and responsivity are similar to those of PDs with the same structure fabricated on InP substrates. The PDs on Si have pulse responses with full widths at half-maximum of 150–600 ps.
Strain effects on the spectra of spontaneously ordered GaxIn1−xP
Authors: Wei Su-Huai , Zunger Alex
Published: July 2002

Spontaneous (111) CuPt-like ordering has been widely observed in GaxIn1−xP lattice matched (x=x0) to a GaAs(001) substrate. This leads to a band-gap reduction ΔEg and to a valence-band splitting ΔE12. We explore here the consequence of the coexistence of (001) epitaxial strain (produced by selecting x≠x0) and (111) chemical ordering. This leads to distinct changes in ΔEg and ΔE12 which could serve as new fingerprints of ordering.
Laser-induced sub-half-micrometer periodic structure on polymer surfaces
Authors: Hiraoka Hiroyuki , Sendova Mariana
Published: July 2002

Periodic structures of sub-half-micrometer size are produced on the surface of different polymers [poly(ethylene terephthalate)], polyimide-type Kapton (DuPont), and polyimide-type XU 293 (Ciba-Geigy)] by Nd:YAG laser irradiation at 266 nm wavelength. The obtained relief is observed by scanning electron microscopy characterized by x-ray photoelectron spectroscopy, and an atomic force microscopy. A phenomenological explanation for the ripple formation in terms of generating waveguide modes on the polymer surface is proposed.
Mechanism of the growth of native oxide on hydrogen passivated silicon surfaces
Authors: van der Zwan M. L. W. , Bardwell J. A. , Sproule G. I. , Graham M. J.
Published: July 2002

The native oxide growth in water on HF etched, hydrogen passivated silicon surfaces has been studied by 18O labeling techniques, with analysis by secondary ion mass spectrometry, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy. It is shown that ≳85% of the oxygen in the native oxide originates from H2O and not from dissolved O2. The role of the dissolved O2/H2O couple is to anodically polarize the electrode, thus driving the H2O/Si-oxide reaction.
Efficient polarization insensitive electroabsorption modulator using strained InGaAsP-based quantum wells
Authors: Chelles S. , Ferreira R. , Voisin P. , Ougazzaden A. , Allovon M. , Carenco A.
Published: July 2002

Polarization insensitivity is presently an important challenge for electro-optical components for optical-fiber telecommunications. We report on a polarization insensitive electroabsorption modulator based on strained InGaAsP/InGaAsP multiple quantum wells and having remarkably high static performances, as illustrated by a record figure of merit of 4.3 (dB/100 μm)/(V/μm). We also discuss in detail the theoretical aspects of electroabsorption polarization independence for quantum well modulators.
Effects of the interface bonding type on the optical and structural properties of InAs-AlSb quantum wells
Authors: Brar Berinder , Ibbetson James , Kroemer Herbert , English John H.
Published: July 2002

InAs-AlSb short period superlattices were grown with both InSb-like or AlAs-like interfaces and their properties were studied using photoluminescence, x-ray diffraction, and transmission electron microscopy. A shift of 96 meV in the photoluminescence peak position is observed, with the peak from the sample with InSb-like interfaces being at a lower energy. The shift is interpreted as an interface band structure effect. X-ray diffraction patterns indicate that the sample with InSb-like interfaces grows pseudomorphically to the AlSb buffer layer, while the sample with AlAs-like interfaces is heavily dislocated. Transmission electron micrographs confirm the x-ray data.
Copper patterning on dielectrics by laser writing in liquid solution
Authors: Minì L. , Giaconia C. , Arnone C.
Published: July 2002

A technique suitable for laser induced deposition of copper on LiNbO3 and glass is presented. Deposition is achieved from Cu salt solution mixed with glycerol, after coating the surface with a very thin metal film. High resolution and low electrical resistivity can be achieved, using laser power levels in the 20-mW range. The technique can be used for electrode and interconnect fabrication in integrated optical devices, as well as mask repair or microelectronics applications.
Cyclotron resonance studies of GaInP and AlGaInP
Authors: Emanuelsson P. , Drechsler M. , Hofmann D. M. , Meyer B. K. , Moser M. , Scholz F.
Published: July 2002

The electron effective masses for Al0.15Ga0.35In0.5P and Ga0.5In0.5P have been investigated using conventional and optically detected cyclotron resonance. For AlGaInP (partly ordered) it is determined to be m*=(0.14±0.01) m0. For disordered GaInP the mass is found to be m*=(0.092±0.003) m0 and for ordered material (band gap reduction ∼50 meV) m*=(0.088±0.003) m0. The experimentally deduced values are compared with those obtained from five-band k⋅p calculation.
Blue electroluminescent devices with high quantum efficiency from alkoxy-substituted poly(para-phenylene vinylene)-trimers in a polystyrene matrix
Authors: Tachelet W. , Jacobs S. , Ndayikengurukiye H. , Geise H. J. , Grüner J.
Published: July 2002

We report electroluminescence of electroluminescent devices fabricated from cis,trans- 2,5-dimethoxy-1,4 -bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene blended in a polystyrene matrix as emission layer. This choice of materials avoids the inherently poor miscibility of polymers with other compounds and minimizes interactions between the host polymer and the electro-optically active guest, which can produce quenching sites. A blue light-emitting device with high internal quantum efficiency (∼1%) results.
Ultraviolet photosulfidation of III-V compound semiconductors: A new approach to surface passivation
Authors: Ashby Carol I. H. , Zavadil Kevin R. , Howard Arnold J. , Hammons B. E. (Gene)
Published: July 2002

A new passivation technique for III-V compound semiconductors based on ultraviolet photolysis of elemental sulfur vapor has been developed. Photosulfidation produces a greater increase in the photoluminescence intensity from GaAs samples than that produced by conventional (NH4)2S dip treatments and is more photostable than the conventional wet process. X-ray photoelectron spectroscopy of the photosulfided GaAs surfaces indicate formation of a surface sulfide rather than the disulfide characteristic of the (NH4)2S process.
Observation of a large capacitive current in a double barrier resonant tunneling diode at resonance
Authors: Jo J. , Li H. S. , Chen Y. W. , Wang K. L.
Published: July 2002

Capacitance-voltage measurements of double barrier In0.53Ga0.47As/AlAs resonant tunneling diodes show a large capacitance peak at a bias near resonance. The measured peak capacitance is about five times larger than the calculated depletion capacitance. This large capacitance is interpreted as the capacitance between the emitter and the quantum well, which is activated near resonance only when the quantum well has a sufficient number of electrons to screen the ac electric field. An equivalent circuit with the new added series RC component is proposed and the effect on the high frequency operation of a resonant tunneling diode is discussed.
Photoresponse characteristics of n-type tetrahedral amorphous carbon/p-type Si heterojunction diodes
Authors: Veerasamy V. S. , Amaratunga G. A. J. , Park J. S. , Milne W. I. , MacKenzie H. S. , McKenzie D. R.
Published: July 2002

The photovoltaic behavior and spectral response of n-type (nitrogen-doped) tetrahedral amorphous carbon (ta-C)/p-type crystalline silicon heterojunction photodiodes are reported. Abrupt step junction type characteristics are observed with ta-C films ranging in thickness from 40 to 160 nm. The photovoltage increases and the prominent peak in responsivity shifts from 800 nm to longer wavelengths of 1000 nm as the doping in the ta-C films is increased, indicative of a widening of the depletion region in the Si. Use of the responsivity vs wavelength data with the Donnelly and Milnes model for an abrupt heterojunction is successful in predicting the depletion width in the Si and the doping level in the higher doped ta-C. The latter value coupled with the x-ray photoemission spectroscopy derived N concentration in the ta-C films enables an estimation of the doping efficiency. Secondary ion mass spectroscopy studies also confirm the abrupt nature of the junctions.
AlxGa1−xAs-GaAs-InyGa1−yAs quantum well heterostructure lasers with native oxide current-blocking windows formed on metallized devices
Authors: Maranowski S. A. , Chen E. I. , Holonyak N. , Richard T. A.
Published: July 2002

Data are presented demonstrating improved laser operation of AlxGa1−xAs-GaAs-InyGa1−yAs quantum well heterostructures modified with buried native oxide current-blocking windows. The windows are formed by low temperature (425 °C) anisotropic ‘‘wet’’ oxidation of an Al0.9Ga0.1As layer exposed at the facets of metallized laser bars. These window devices operate continuously to powers as high as 248 mW/facet (uncoated, ∼10.5 μm aperture), a ∼25% improvement over nonwindow devices.
Carrier dynamics in staggered-band lineup n-InAlAs/n-InP heterostructures
Authors: Böhrer J. , Krost A. , Bimberg D.
Published: July 2002

The temperature and time dependence of the spatially indirect recombination of two-dimensional (2D) electrons and holes localized at adjacent sides of an isotype n-InAlAs/n-InP heterojunction having a staggered band lineup is investigated. With increasing temperature, a much weaker drop of the photoluminescence intensity than in quantum wells and 3D layers is observed. Still more surprising is the observed decrease of the decay time with increasing temperature from 3.8 ns at 6 K to 1.2 ns at 300 K. Both observations are consistently explained by an increasing occupation of higher subband levels of the interface potential well and an activation of new radiative and nonradiative recombination channels including Δn≠0 ones with increasing temperature.
Negative differential resistance at room temperature in δ -doped diodes grown by Si-molecular beam epitaxy
Authors: Sardela M. R. , Radamson H. H. , Hansson G. V.
Published: July 2002

Negative differential resistance effects at room temperature in delta-doped diodes grown by silicon-molecular beam epitaxy are reported. High tunneling current densities (≊4 kA/cm2) and peak-to-value ratios close to 1.1 were achieved.
Cyclotron effective mass of holes in Si1−xGex/Si quantum wells: Strain and nonparabolicity effects
Authors: Cheng J.-P. , Kesan V. P. , Grutzmacher D. A. , Sedgwick T. O.
Published: July 2002

The Ge-composition dependence of cyclotron effective mass of quasi-two-dimensional holes in strained Si1−xGex/Si quantum well structures has been investigated by far-infrared magneto-optical spectroscopy at low temperatures and high magnetic fields up to 23 T. The in-plane effective mass determined from cyclotron resonance energies is much less than that of unstrained Si1−xGex alloys and decreases systematically from 0.40me to 0.29me as the Ge composition increases from x=0.13 to x=0.37, indicating the importance of the strain effect on the valence-band structure. The nonparabolicity correction is significant in explaining the discrepancy between the measured values and the calculated band-edge masses.
Jitter improvement in mark edge recording for phase change optical disks with optical phase encoding
Authors: Ide Tatsunori , Okada Mitsuya
Published: July 2002

We have developed a novel absorptivity control method for phase change optical disks for improving overwriting jitter in mark edge recording. In order to control absorptivity more easily, we have designed a disk with a small difference in reflectivity between the amorphous and the crystalline states, and with a large optical phase difference between the reflected light from those two states, which produces a high carrier to noise ratio. We have obtained remarkably reduced overwriting jitter, down to 2.47 ns from 5.69 ns for the leading edge, and this has meant greatly increased applicability of mark edge recording to phase change optical disks.
Microstructure and epitaxy of c-axis oriented single crystal cobalt films grown on rigid underlayers
Authors: Krishnan Kannan M. , Honda Y. , Hirayama Y. , Futamoto M.
Published: July 2002

We have established the conditions to grow c-axis oriented Co films on mica substrates and characterized their crystallography and microstructure in detail. In particular, these films are single crystal, c-axis oriented, Cohcp and are grown epitaxially by e-beam evaporation on either Ti or Ru underlayers. The orientation relationship is basically (00.1)mica∥(00.1)underlayer∥(00.1)Co, and [11.0]mica∥[10.0]underlayer∥[10.0]Co. Films grown on Ru underlayers have an average grain size of 50–80 nm with negligible fcc content. For Ti underlayers, the 15–20 nm size grains contain a small fraction of fcc cobalt. The growth of such films makes it possible to measure fundamental magnetic properties of the individual microstructural components/grains of a thin film recording media.
Characteristics of strengthened Ag substrates for Bi2Sr2CaCu2Ox doctor-bladed tapes
Authors: Nomura K. , Sato J. , Kuma S. , Kumakura H. , Togano K. , Tomita N.
Published: July 2002

The characteristics of Ag-(Mg,Ni) and Ag-Mn alloys as substrate materials for Bi2Sr2CaCu2Ox (Bi-2212) tapes and their influence on the superconducting properties were studied. Alloying with Mg+Ni or Mn drastically decreased the grain size of Ag after heat treatment. The additives in Ag-(Mg,Ni) and Ag-Mn alloys were oxidized during heat treatment in air. Both the fine grain structure and the internal oxidation of the additives increased the mechanical strength of the Ag alloys. Both alloys were 3–6 times stronger than pure Ag. The superconducting properties of Bi-2212 prepared on these Ag alloys were slightly degraded; however the critical current densities at 4.2 K in 8 T were still well over 104 A/cm2.
Strain tolerance of multifilament Bi-Pb-Sr-Ca-Cu-O/silver composite superconducting tapes
Authors: Yau John , Savvides Nick
Published: July 2002

The bend strain characteristics of Bi-Pb-Sr-Ca-Cu-O/silver composite tapes were determined from measurements of the critical current, Ic(77 K), as a function of bend strain (0%–2%) or radius of curvature (∞−10 mm). The powder-in-tube method was used to prepare monofilament and multifilament (up to 49 filaments) tapes, 0.2–0.4 mm overall thickness, with 5–20 vol % superconductor. The irreversible strain limit, εirr, for the onset of bend strain damage, increases with the number of filaments from εirr=0.2%–0.3% for monofilament tapes to values up to 1.5% for 49-filament tapes. Although strains beyond this limit cause irreversible damage in the form of microcracks and fracture of the superconductor filaments, multifilament tapes are exceptionally strain tolerant, with 49-filament tapes retaining 85%–90% of the initial critical current at strains of 2%.
Field-induced broadening of optical absorption in InP-based quantum wells with strong and weak quantum confinement
Authors: Yamanaka Takayuki , Wakita Koichi , Yokoyama Kiyoyuki
Published: July 2002

We have studied in detail the field-induced broadening of optical absorption in InP-based quantum well (QW) structures with both strong and weak quantum confinement. Electroabsorption process in the QW structures with the weak confinement is modeled taking both excitonic absorption and subband-to-subband absorption into account. It is theoretically shown that the spectral broadening associated with the applied electric fields is largely due to the quantum confinement of the barrier structures. In the InP-based QW structures absorption spectra, calculated assuming their broadening is due solely to carrier tunneling, successfully explain the measured photocurrent spectra.
Novel approach for detecting distributed surface-breaking cracks
Authors: Burke S. K. , Rose L. R. F. , Scala C. M.
Published: July 2002

A novel approach to the problem of detecting finely distributed surface cracks in a structure is proposed. The approach relies on the detection of anisotropy introduced into the surface by an oriented array of cracks and can be used for crack detection even when individual cracks in the array are below the practical threshold of detectability by conventional inspection techniques. The feasibility of detecting anisotropy associated with distributed cracking was established experimentally using: (i) a directional eddy-current probe to detect anisotropy in the effective electrical conductivity and (ii) a line-focused laser-ultrasonic source to detect anisotropy in the attenuation of ultrasonic Rayleigh waves.
Optical spectra of Si/Ge-network copolymers: [Si(C6H13)]1−x[Ge(C6H13)]x
Authors: Kishida H. , Tachibana H. , Matsumoto M. , Tokura Y.
Published: July 2002

Optical properties of silicon- and germanium-based network copolymers, [Si(C6H13)]1−x- [Ge(C6H13) ]x, have been investigated for various Si/Ge compositions (x). The backbone Si/Ge atoms are coordinated by the three other Si/Ge backbone atoms in the polymers. These Si/Ge copolymers show the absorption spectra which are typical of amorphous semiconductors. Their color continuously traverses the visible range with x, which is due to the change of the band gap (Tauc gap) energy as well as to the presence of localized subgap states. The Si/Ge copolymer shows a broad band of luminescence in the visible region. The luminescence band maximum was observed to shift by ∼0.5 eV with change of the Si/Ge ratio.
Effects of extra low-frequency noise injection on microwave signals generated by a gain-switched semiconductor laser
Authors: Lima C. R. , Davies P. A.
Published: July 2002

Low-frequency upconverted noise (1/f laser intensity noise and the low-frequency noise of the driver source) has been identified as the dominant noise generation mechanism in microwave signals generated by a Fabry–Perot gain-switched semiconductor laser. An experimental investigation is carried out using extra low-frequency noise injection added to the drive signal. Results show the dependence of the broadband intensity noise level, formed by the overlapping of the upconverted noise sidebands present at each harmonic, on gain-switching input parameters.
Indium migration control on patterned substrates for optoelectronic device applications
Authors: Pratt A. R. , Williams R. L. , Norman C. E. , Fahy M. R. , Marinopoulou A. , Chatenoud F.
Published: July 2002

Strained layer InGaAs/GaAs quantum wells have been grown by molecular-beam epitaxy on patterned (100) GaAs substrates. Indium migration away from the facets of patterned mesas is shown to be strongly dependent upon the arsenic flux during growth. Based upon this effect we have grown structures in which the number of active quantum wells in adjacent areas of a segmented contact device can be varied.
Simultaneous generation of sum, difference, and harmonics of two laser frequencies by spread spectrum phase matching
Authors: Horowitz Moshe , Bekker Alexander , Fischer Baruch
Published: July 2002

We demonstrate the simultaneous generation of sum, difference, and harmonics of two laser frequencies (which can be tunable) by spread spectrum phase matching in a nonlinear Sr0.61Ba0.39Nb2O6 crystal. The phase matching is obtained by inducing in the crystal domain gratings with broadband periodicity. Conversion efficiencies up to ∼1% were observed. We also give a calculation that shows the effect of the spread spectrum domains on the mixing.
Two-dimensional electron gas in modulation-doped, ordered-disordered GaInP2 homojunctions
Authors: Driessen F. A. J. M. , Bauhuis G. J. , Hageman P. R. , Giling L. J.
Published: July 2002

Capacitance-voltage (C-V) profiling techniques and temperature-dependent Hall and resistivity measurements have been used to characterize modulation-doped ordered-GaInP2/disordered-GaInP2 homojunctions grown by metalorganic vapor phase epitaxy. The C-V measurements showed a narrow profile at the homointerface with an order of magnitude reduction in carrier density within 3 nm. Typical two-dimensional behavior was observed from Hall data showing sheet carrier densities as high as 3.6×1013 cm−2 without carrier freeze out and constant mobilities around 900 cm2 V−1 s−1 below T=100 K. The 300 K channel conductivity of this new junction is 3.2×10−3 Ω−1, which is higher than reported in other two-dimensional electron gases.
Oriented diamond on graphite flakes
Authors: Suzuki T. , Yagi M. , Shibuki K. , Hasemi M.
Published: July 2002

Diamond was deposited by the microwave plasma chemical vapor deposition method on a Si(100) substrate on which graphite flakes had been spread with their basal planes parallel to the substrate before deposition. Before diamond deposition, the substrate was preheated at 1200 °C under hydrogen at 60 Torr to clean the surface of graphite flakes. Scanning electron micrographs showed that most of diamond particles were cubo-octahedral in morphology. The {111} planes of some diamond particles, which were judged by their triangular shape, were often parallel to the (0001) plane of graphite. Furthermore, some 〈111〉-oriented diamond particles were clearly nucleated at the edge of graphite. The possibility of heteroepitaxy of diamond on graphite was discussed based on crystallographic considerations.
Transport properties in Tl-Ba-Ca-Cu-O grain boundary junctions on SrTiO3 bicrystal substrates
Authors: Sarnelli E. , Chaudhari P. , Lee W. Y. , Esposito E.
Published: July 2002

We have investigated the electrical properties of Tl-Ba-Ca-Cu-O high-Tc superconductor bicrystal grain boundary junctions. The behavior of the transport parameters is very similar to those obtained in YBaCuO7−δ junctions. In particular, the temperature dependence of the critical current and the scaling behavior of the critical current density as a function of the misorientation angle were analyzed. Relatively good control of the transport parameters as a function of the misorientation angle has been achieved. The current-voltage characteristics showed a resistively shunted junction model-like behavior at large angles (θ≥20°); at lower angles, the characteristics were more flux-flow like. Preliminary results on noise characteristics are also presented.
Characterization of heteroepitaxial CuIn3Se5 and CuInSe2 layers on Si substrates
Authors: Tiwari A. N. , Blunier S. , Filzmoser M. , Zogg H. , Schmid D. , Schock H. W.
Published: July 2002

Epitaxial CuIn3Se5 layers were grown on CuInSe2/Si(111) substrates by molecular beam epitaxy. Photoemission spectra of (112)-oriented CuIn3Se5 and CuInSe2 epitaxial layers were studied and the structures in the upper valence band are correlated with the Cu 3d and Se 4p density of states. The main valence band of CuInSe2 exhibits the three peak structure (consistent with theory) while a broadband with a shoulder is observed for the CuIn3Se5 phase. Electron channeling and x-ray diffraction confirmed the epitaxial growth of (112)-oriented layer. Surface and bulk composition analyses, position of valence band maxima, and a Se related vibrational mode at 153 cm−1 in Raman scattering measurements established the growth of the CuIn3Se5 phase.
Nanosecond time-resolved interferometric study on morphological dynamics of doped poly(methyl methacrylate) film upon laser ablation
Authors: Furutani Hiroshi , Fukumura Hiroshi , Masuhara Hiroshi
Published: July 2002

A highly sensitive nanosecond time-resolved interferometry was developed and applied to study dynamics of morphological changes of a thin poly(methyl methacrylate) film doped with biphenyl upon laser ablation. It was confirmed that morphological changes started during a nanosecond excitation laser pulse and then followed by an ejection of ablated polymer fragments. Even below the ablation threshold, a transient expansion of the polymer film, followed by slow contraction, was observed. New features of laser ablation dynamics were clarified.