bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic structure of Sb in perovskite superconducting compounds
Authors: Eibschütz M. , Reiff W. M. , Cava R. J. , Krajewski J. J. , Peck W. F.
Published: July 2002

The Mössbauer effect of the 37.2 keV γ transition of 121Sb has been employed to study the electronic configuration of Sb ions in perovskite superconducting materials. The isomer shift (IS) changes with Sb content and falls in the region of the Sb(V) valence state. The IS increases from 7.00 mm/s for BaPb0.75Sb0.25O3 to 7.25 mm/s for BaPb0.75Bi0.25O3 and to 7.70 mm/s for (Ba0.6K0.4)BiO3 compounds, indicating a high degree of covalency, corresponding to changes in the 5sm5pn hybridization.
Passive transverse-mode organization in a photorefractive oscillator with saturable absorber
Authors: Fischer Baruch , Werner Ofer , Horowitz Moshe , Lewis Aaron
Published: July 2002

We present and demonstrate a self-transverse-mode organization effect (passive transverse mode locking?) in a cavity that contains a saturable absorber. It gives narrowing and filamentation of the oscillating beam in the region of the absorber. In the demonstration, we have used a resonator formed by two photorefractive phase conjugate mirrors. The saturable absorber was bacteriorhodopsin in a polymer film. Light powers of 1–100 mW were used.
Two-dimensional electron gases in delta-doped GaAs/In0.25Ga0.75As/GaAs heterostructures
Authors: Lin W. , Hsu W. C. , Wu T. S. , Chang S. Z. , Wang C. , Chang C. Y.
Published: July 2002

Delta-doped (δ-doped)GaAs/In0.25Ga0.75As/GaAs strained-layer modulation-doped field-effect transistor (δ-SMODFET) structures grown by the low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique have been studied for the first time. The δ-doped GaAs, adopted as the electron supplier, was obtained by a stop-growth process so that a very thin and heavily doped layer (1.9×1013 cm−2) can be realized. Experimental results show that a structure with an 80 Å In0.25Ga0.75As layer as the active channel and an 80 Å spacer layer demonstrated the highest two-dimensional electron gases mobility of 26 800 cm2/V s. This structure is easy to achieve by the LP-MOCVD method because the growth of AlGaAs is avoided and is promising for high performance FETs.
AlxGa1−xAs/GaAs photovoltaic cell with epitaxial isolation layer
Authors: Subramanian G. , Dodabalapur A. , Campbell J. C. , Streetman B. G.
Published: July 2002

Efficient integration of multijunction photovoltaic cells requires current matching or voltage matching. To match voltages it is necessary to achieve complete electrical isolation between the component cells. Previously, electrical isolation could only be achieved with hybrid, mechanically stacked structures. We report the growth, fabrication, and characterization of an AlxGa1−xAs/GaAs photovoltaic cell with an epitaxial isolation layer of semi-insulating GaAs grown by molecular beam epitaxy. This will facilitate the integration of subcells that absorb different portions of the solar spectrum onto a single substrate.
p-type doping of InP and Ga0.47In0.53As using diethylzinc during metalorganic molecular beam epitaxy
Authors: Hamm R. A. , Ritter D. , Temkin H. , Panish M. B. , Geva M.
Published: July 2002

Diethylzinc (DEZn) was used as a p-type dopant source during metalorganic molecular beam epitaxy of Ga0.47In0.53As and InP. The incorporation efficiency of the Zn was less than 10−3. However, doping levels from p=1×1017 to 3×1019 cm−3 were obtained at growth temperatures of 485–510 °C. Measurements with secondary-ion mass spectrometry indicated negligible diffusion of Zn in the Ga0.47In0.53As at these doping levels and growth temperatures. The DEZn was used to dope the p-type InP cladding layer of broad-area separate confinement multiquantum well (SCH-MQW) lasers. Threshold current densities as low as 600 A/cm2 were achieved in nonoptimized structures.
Native-oxide coupled-stripe AlyGa1−yAs-GaAs-InxGa1−xAs quantum well heterostructure lasers
Authors: Richard T. A. , Kish F. A. , Holonyak N. , Dallesasse J. M. , Hsieh K. C. , Ries M. J. , Gavrilovic P. , Meehan K. , Williams J. E.
Published: July 2002

Data are presented on a high-performance native-oxide coupled-stripe AlyGa1−yAs-GaAs-InxGa1−xAs quantum well heterostructure laser realized by the recently introduced simple process of ‘‘wet’’ oxidation (H2O vapor+N2,≳400 °C, 3 h) of the upper AlyGa1−yAs confining layer. If the native oxide between active stripes (ten 5 μm stripes on 10 μm centers) is brought into closer proximity with the waveguide and quantum well region (i.e., from 0.53 to 0.4 μm), the 10-stripe laser operates decoupled because of increased (coupling) absorption losses and some index guiding.
Changes in the silicon thermal donor energy level as a function of anneal time
Authors: Lamp C. D. , Jones B. D.
Published: July 2002

A deep level transient spectroscopy (DLTS) study of 450 °C annealed Czochralski silicon is presented. Particular attention is given to the relative concentrations of the two thermal donor energy levels Ec−0.15 eV and Ec−0.07 eV. Relative concentrations of the Ec−0.15 eV and Ec−0.07 eV energy levels indicate that there are fewer of the more shallow level. Also there is anomalous motion of the energy levels with anneal time indicating the gradual accretion of the thermal donor complexes. The suggested correlation with infrared absorption (IR) studies is that the nine double-donor defects found by IR form sequentially in the material and the DLTS energy level obtained merely reflects the most abundant of the nine distinct complexes. This indicates that the nine thermal donors are formed by the addition of some constituent to an earlier complex. As the thermal donor complex accretes the associated energy levels change, moving to shallower energies as anneal time increases. These findings tend to contradict the simple thermal donor models.
Aluminum oxide thin films prepared by chemical vapor deposition from aluminum 2-ethylhexanoate
Authors: Maruyama Toshiro , Nakai Tsuyoshi
Published: July 2002

Aluminum oxide thin films were prepared by a low-temperature atmospheric-pressure chemical vapor deposition method. The raw material was aluminum 2-ethylhexanoate, which is nontoxic and easy to handle. At a reaction temperature above 480 °C, an amorphous film can be obtained on glass and silicon (100) substrates. The reaction temperature and the deposition rate are comparable to the corresponding values in the low-temperature chemical vapor depositions of Al2O3. In addition, the deposition can be carried out in air. Aluminum 2-ethylhexanoate appears to offer a viable alternative to alkylaluminum, aluminum β-diketonate, and alkoxide for low-temperature Al2O3 production.
Monolithic InP/InGaAsP/InP grating spectrometer for the 1.48–1.56 μm wavelength range
Authors: Soole J. B. D. , Scherer A. , LeBlanc H. P. , Andreadakis N. C. , Bhat R. , Koza M. A.
Published: July 2002

We report a two-dimensional grating spectrometer implemented in an InP/InGaAsP/InP planar waveguide for use in the low-loss 1.5 μm wavelength fiber band. The spectrometer uses a single vertical-walled focusing reflection grating to disperse 78 channels, spaced at 1 nm intervals, with diffraction-limited resolution (∼0.3 nm) and a high channel isolation (≳19 dB). The spectrometer may be used such that it is insensitive to the state of the input polarization.
Polarization bistability in semiconductor lasers with intracavity multiple quantum well saturable absorbers
Authors: Ozeki Y. , Johnson John E. , Tang C. L.
Published: July 2002

Because the confinement of carriers in a quantum well constraints the crystal momentum of the carriers near the band edge to directions close to the well normal, the selection rules for conduction to heavy-hole transitions yield a large anisotropy in the absorption cross section. We predict a new type of room-temperature polarization bistability based upon this effect in a semiconductor laser with an intracavity multiple quantum well saturable absorber. Rate equation analyses of the static device characteristics as a function of various parameters are presented, and show that two-mode bistable behavior with large hysteresis is possible over a broad range of conditions. Other modes of operation, including all-optical switching and tristable operation, have been verified by numerical calculation.
Scalable high-power optically pumped GaAs laser
Authors: Le H. Q. , Di Cecca S. , Mooradian A.
Published: July 2002

The use of disk geometry, optically pumped semiconductor gain elements for high-power scalability and good transverse mode quality has been studied. A room-temperature TEM00 transverse mode, external-cavity GaAs disk laser has been demonstrated with 500 W peak-power output and 40% slope efficiency, when pumped by a Ti:Al2O3 laser. The conditions for diode laser pumping are shown to be consistent with available power level.
Sulfur doping of GaAs and GaInP grown by metalorganic molecular beam epitaxy using a hydrogen sulfide gaseous source
Authors: Bove Ph. , Garcia J. Ch. , Maurel Ph. , Hirtz J. P.
Published: July 2002

We report in this letter the sulfur doping of GaAs and Ga0.5In0.5P layers grown by metalorganic molecular beam epitaxy using a 1000 ppm hydrogen sulfide diluted in hydrogen dopant source. No precracking of H2S molecules is necessary to achieve efficient doping. The n-type doping level of both GaAs and Ga0.5In0.5P is proportional to the input H2S flow rate. Maximum doping levels of 8×1017 and 3×1018 cm−3 are measured in GaAs and Ga0.5In0.5P, respectively, with no saturation in either material within the doping range investigated. The doping level decreases as the growth temperature increases, with activation energies of 1.5 and 1.7 eV for GaAs and Ga0.5In0.5P, respectively. The sulfur incorporation decreases on increasing the V/III ratio in GaAs. The opposite behavior occurs in Ga0.5In0.5P.
Room-temperature enhancement of electro-optical modulation by resonance-induced exciton mixing in a GaAs/AlAs superlattice
Authors: Schneider Harald , Ploog Klaus
Published: July 2002

We report on room-temperature absorption properties of a GaAs/AlAs short-period superlattice in which, at certain electric fields perpendicular to the layers, different conduction subbands centered in adjacent and nonadjacent wells show a level repulsion and an anticrossing behavior. The associated mixing between the corresponding electron wave functions reduces the oscillator strengths and influences the transition energies of certain excitons. These electric field effects can be used to improve the performance of electro-optical modulator devices. Our results also provide a method to investigate the high-field coherence properties of charge carriers in superlattices.
Effect of oxidation processing on the energy distribution and charging time of radiation-induced interface traps
Authors: Schwalke U. , Kerber M.
Published: July 2002

A simple modification of the quasi-static capacitance-voltage technique is used to obtain the charging time of interface traps in addition to their energy distribution so that fast and slow traps can be separated. Measurements on irradiated metal-oxide-semiconductor capacitors containing thin (50–150 Å) oxides reveal that a portion of the interface traps in the upper half of the band gap consist of slow trapping centers. Both the energy distribution and the charging time of radiation-induced interface traps are found to depend on the oxide growth process and gate oxide thickness. The data suggest that oxides grown at high temperatures (1200 °C) by rapid thermal oxidation possess a lower concentration of radiation-sensitive strained bonds than furnace oxides grown at 800 °C.
Low-pressure chemical vapor deposition of low in situ phosphorus doped silicon thin films
Authors: Sarret M. , Liba A. , Bonnaud O.
Published: July 2002

In situ low phosphorus doped silicon films are deposited onto glass substrates by low-pressure chemical vapor deposition method. The deposition parameters, temperature, total pressure, and pure silane gas flow are, respectively, fixed at 550 °C, 0.08 Torr, and 50 sccm. The varying deposition parameter is phosphine/silane mole ratio; when this ratio varies from 2×10−6 to 4×10−4, the phosphorus concentration and the resistivity after annealing, respectively, vary from 2×1018 to 3×1020 atoms cm−3 and from 1.5 Ω cm to 2.5×10−3 Ω cm.
Buried heterostructure laser fabricated using three-step gas source molecular beam epitaxy
Authors: Liévin J.-L. , Bonnevie D. , Poingt F. , Starck C. , Sigogne D. , Le Gouezigou O. , Goldstein L.
Published: July 2002

Buried heterostructure lasers fabricated using a three-step gas source molecular beam epitaxy (GSMBE) process are presented for the first time. We propose a new structure design compatible with nonselective regrowth for the blocking layers, therefore avoiding the use of a dielectric mask. The structure is terminated by a second overgrowth after a material lift-off. Preliminary results show cw operation with threshold currents of 60 mA for 800-μm-long devices and maximum output power up to 27 mW per facet.
Differential photoreflectance from δ-doped structures and GaAs/n-GaAs interfaces
Authors: Sydor Michael , Badakhshan Ali , Engholm James R.
Published: July 2002

Using a differential modulation technique we suppress the perturbation of the surface electric field of the sample and extract photoreflectance from buried interfaces. The resulting signals show combinations of a low-field GaAs signature and a high-field oscillatory signal which suggest existence of an ∼30 meV potential offset at the highly doped GaAs/n-GaAs interfaces. The offset is present at both, δ-doped interfaces and simple doped interfaces. For low differential modulation intensities, we observe a signal which could be attributed to two-dimensional electron gas in δ-doped samples, however, the signal cannot be easily differentiated from low-field Franz–Keldysh oscillations.
Grating spectrograph in InGaAsP/InP for dense wavelength division multiplexing
Authors: Cremer C. , Ebbinghaus G. , Heise G. , Müller-Nawrath R. , Schienle M. , Stoll L.
Published: July 2002

A grating spectrograph in InGaAsP/InP suitable for use in the wavelength region from 1.2 to 1.6 μm is presented. Experiments for devices with a channel spacing of 3.7 nm and more than 30 channels between 1.48 and 1.59 μm are described. The measured cross talk level is below −25 dB. The devices have only very low polarization sensitivity. This spectrograph is suited for monolithic integration with photodiodes, laser diodes, or optical amplifiers on a single chip.
Evidence of the wavelength switching caused by a blocked carrier transport in an asymmetric dual quantum well laser
Authors: Ikeda Sotomitsu , Shimizu Akira
Published: July 2002

The mechanism of wavelength switching in an asymmetric dual quantum well laser was investigated. Switching between 830 and 780 nm was achieved, with increasing injection current under cw as well as under pulsed operation. This is the widest switching range of monolithic LDs under cw operation ever reported. Time-resolved spectra for the dual-wavelength simultaneous lasing under short-pulse operation show that emissions at the two wavelengths have a time difference. This provides evidence that holes are inhomogeneously injected into the two wells with a time difference and that their dynamics govern the lasing for each wavelength and the switching.
Continuous B→X excimer fluorescence using direct current discharge excitation
Authors: Taylor R. S. , Leopold K. E. , Tan K. O.
Published: July 2002

Continuous cw (B→X) excimer fluorescence has been obtained at the KrCl, KrF, XeCl, and XeF wavelengths, using longitudinal direct current (dc) electrical excitation at current levels up to l A and gas pressures as high as 400 Torr. Electrical power deposition to (B→X) fluorescence conversion efficiencies of up to ∼1% have been measured.
Generation of an extremely short single mode pulse (∼2 ps) by fiber compression of a gain-switched pulse from a 1.3 μm distributed-feedback laser diode
Authors: Liu Hai-Feng , Ogawa Yoh , Oshiba Saeko
Published: July 2002

A train of 2 ps pulses, which is believed to be the shortest single mode pulses ever reported from semiconductor lasers, is produced by compressing the chirped pulses generated from a gain switched 1.3 μm distributed feedback laser diode with a dispersive fiber. An analytic model for the pulse compression in fiber is presented, which shows fairly good agreement with the experiment. The analytical results derived from the model can be advantageously used in the design of the fiber compressor for semiconductor lasers.
In situ determination of flux nonuniformities during molecular beam epitaxial growth
Authors: Shanabrook B. V. , Katzer D. S. , Wagner R. J.
Published: July 2002

We have observed an amplitude modulation superimposed on growth induced reflection high energy electron diffraction (RHEED) oscillations in molecular beam epitaxial growth of GaAs, AlSb, and GaSb. An analysis of spatially resolved luminescence measurements from a single GaAs/Al0.3Ga0.7As quantum well and RHEED oscillation data verifies an earlier suggestion of Van Hove and co-workers that this modulation is related to nonuniform group III fluxes at the substrate. This phenomenon is very useful because it allows a quantitative in situ determination of group III flux nonuniformity. Furthermore, this study indicates that theories relating the decay of the RHEED oscillations to growth induced roughening of the surface should account for modifications that arise in the apparent decay rate because of flux nonuniformities.
In situ technique for measurement and control of transistor characteristics during remote plasma etching
Authors: Lishan David , Hu Evelyn
Published: July 2002

In situ electrical monitoring has been carried out in a remote plasma etching system allowing accurate control of device electrical parameters. We have used this technique to gate recess-etch two different high electron mobility transistor structures while recording device source-drain I-V characteristics throughout the etching. Current versus etching time data and time elapsed I-V curves are presented.
New buffer layer for high-temperature superconducting ceramics on sapphire: LaBa2Cu3Oy/Ag bilayers
Authors: Nakamura O. , Chan I. N. , Guimpel J. , Schuller Ivan K.
Published: July 2002

We have grown highly oriented LaBa2Cu3Oy (110)/Ag (111) bilayers on sapphire (112̄0). This structure constitutes a potentially excellent buffer layer for the growth of 1-2-3 ceramic oxides on sapphire substrates. This bilayer does not show superconductivity in resistive measurements. A DyBa2Cu3Oy film grown on this bilayer also exhibited (110) orientation.
Stark ladders in strongly coupled GaAs-AlAs superlattices
Authors: Degani Marcos H.
Published: July 2002

The energy spectrum of a superlattice in the presence of an electric field is calculated using the split time scheme. It is shown that even for a low field two interpenetrating Stark ladders exist in a GaAs-AlAs superlattice and the spacing between the energy levels in each of the ladders is eEd. When the external field is increased the number of ladders with the same period eEd is also increased.
1.5 μm InGaAsP/InP vertically coupled semiconductor optical pre-amplifier
Authors: Lee Henry P. , Scherer A. , Hong W. P. , Zah C. E. , Orenstein M. , Bhat R. , Beebe E. D. , Andreadakis N. , Koza M. A.
Published: July 2002

Vertical coupling of light output from a stripe InGaAsP/InP laser amplifier to the bottom of the substrate for detection by means of a 45° mirror has been demonstrated. The composite-cavity amplifier structure is shown to have an inherent low facet reflectivity and unidirectional amplification property. With a fiber-to-detector gain of 15.4 dB and a nearly diffraction-limited output spot size, the device is suitable for compact integration with a photodetector as an optical pre-amplifier in a high bit-rate direct detection system.
InyGa1−yAs/InyAl1−yAs resonant tunneling diodes on GaAs
Authors: Wolak Edmund , Harmand Jean Christophe , Matsuno Toshinobu , Inoue Kaoru , Narusawa Tadashi
Published: July 2002

Resonant tunneling diodes are fabricated using InyGa1−yAs/InyAl1−yAs on GaAs substrates for the first time. The devices showed increasing peak current density as the In content was raised from 0 to 0.3, which is shown to be consistent with the Γ valley being the predominant transport mechanism at the tunneling resonance. Devices with y=0.2 showed an average peak to valley current ratio of 4.2 at room temperature, versus 3.3 for y=0. The decrease in the peak to valley current ratio is attributed to a decreased tunneling component in the X valleys of the In0.2Al0.8As barrier layers. Devices with y=0.3 show room-temperature peak to valley current ratios of approximately 2.5; the increased valley current is attributed to interface roughness scattering and other effects.
Initial stages of Ga and As growth on EuBa2Cu3O7−y(001)
Authors: Maeda F. , Sugahara H. , Oshima M. , Michikami O.
Published: July 2002

The first photoelectron spectroscopy results are presented for Ga and As growth on EuBa2Cu3O7−y(001) (EBCO) surfaces. Growth models are shown that explain these results. In Ga growth, the oxide state Ga initially covers the EBCO surface and then metallic state Ga grows on this surface as islands. On the other hand, As grows only one monolayer as the As oxide form without breaking CuO bonds at the As-EBCO interface, implying that it may be possible to grow GaAs films on EBCO with the As-oxide interlayer.
Bi-Sr-Ca-Cu-O superconductor with improved zero resistance temperature of 122 K
Authors: Padam G. K. , Dhingra Indu , Tripathi R. B. , Das B. K.
Published: July 2002

An improvement in zero resistance temperature (T0c) of the 2223 phase in the Bi-Sr-Ca-Cu-O system by using a nominal composition Bi0.8Pb0.2SrCa2Cu2Ox has been achieved. The bulk Bi0.8Pb0.2SrCaCu2Ox samples synthesized from a matrix reaction method exhibited a superconducting transition with T0c of 110 K. Addition of one Ca-atom per molecule of the above composition, that is, Bi0.8Pb0.2SrCa2Cu2Ox resulted in enhanced T0c of 122 K with onset temperature (Tonsetc) of 140 K. Interestingly, T0c of 122 K was also observed in the Pb-free BiSrCa2Cu2Ox samples, but it decreases to 115.5 K after 3–4 thermal cycles. However, no such decrease in T0c was observed in the Pb-doped samples, indicating the formation of stable 2223 phase. On the basis of x-ray diffraction, energy dispersive spectra and scanning electron microscopy data, it is concluded that excess of Ca facilitate the nucleation of 2223 phase.
High-speed InP/GaInAs heterojunction phototransistor on InP-on-Si grown by organometallic vapor phase epitaxy
Authors: Aina O. , Serio M. , Mattingly M. , O’Connor J. , Shastry S. K. , Hill D. S. , Salerno J. P. , Ferm P.
Published: July 2002

We have fabricated the first heterojunction phototransistor (HPT) on InP-on-Si. These phototransistors, based on the InP/GaInAs heterojunction, have optical gains as high as 125 A/W at 1300 nm and dark currents as low as 300 pA, for a 48×64 μm HPT. The bandwidth was determined from impulse photoresponse measurements to be 4.4 GHz. The intrinsic bandwidth was estimated from the zero bias capacitance (0.2 pf) to be as high as 16 GHz.
Fabrication of GaAs fine stripe structures by selective metalorganic chemical vapor deposition using diethylgalliumchloride
Authors: Yamaguchi Ko-ichi , Okamoto Kotaro
Published: July 2002

Selective GaAs fine stripe structures, aligned along 〈011〉 direction, were grown by atmospheric-pressure metalorganic chemical vapor deposition using diethylgalliumchloride. The width of the (100) top surface of the triangle-shaped selective epilayers could be changed from 0 to 25 nm by controlling the growth temperature, and was independent of the growth time. This phenomena can be explained by reevaporation enhancement effect of reactant species containing chloride and two-dimensional nucleation.
Simulations of layer-by-layer sputtering during epitaxy
Authors: Chason E. , Bedrossian P. , Houston J. E. , Tsao J. Y. , Dodson B. W. , Picraux S. T.
Published: July 2002

We have performed computer simulations of simultaneous and sequential ion bombardment and epitaxial growth. In agreement with recent reflection high-energy electron diffraction (RHEED) measurements on Si, we observe ion-induced RHEED oscillations, a cancellation of RHEED oscillations during simultaneous equal-rate ion bombardment and growth, and a reversal of growth-induced roughening by subsequent ion bombardment. Comparison between simulations and measurements indicate that a model of the ion/surface interaction characterized by the creation of mobile vacancies with minimal preferential sputtering is sufficient to simulate all the RHEED measurements.
Study of the submillimeter absorptivity of high T
c superconductors by photothermal interference spectroscopy
Authors: Müller M. , Basun S. , Glaser S. , Renk K. F.
Published: July 2002

We report on the study of the submillimeter absorptivity of high-Tc superconductors by a new method, the photothermal interference spectroscopy. Absorption in a sample leads to a temperature change of the sample and, by heat transfer, also of a gas volume adjacent to the sample and to a change of refractive index in the gas volume that we detect by an interferometric method. We demonstrate the feasibility of the method by determination of the absorptivity of high-Tc superconducting YBa2Cu3O7−δ samples for submillimeter radiation at a frequency near 1 THz. The absorptivity shows a peak at Tc, that is most likely due to fluctuation effects, a strong drop below Tc and a finite value at low temperatures, with a peak near 15 K.
Copper exchange plating on palladium and its relation to circuit repair
Authors: von Gutfeld R. J. , Vigliotti D. R. , Acosta R. E.
Published: July 2002

We describe a series of experiments using local heating to deposit copper from solution onto a palladium pattern. We show that palladium, the more noble metal, does not dissolve during thermally induced exchange plating when sacrificial copper is appropriately placed with respect to the palladium. Rather, the palladium becomes cathodic locally without dissolution, consistent with its position in the electronegativity series. However, without sacrificial copper, no deposition occurs. These results help to explain the mechanisms for a recently described electrochemical ‘‘open’’ microcircuit repair method.
Diffuse phase transition in a new perovskite Pb(In1/2Ta1/2)O3
Authors: Yasuda Naohiko , Imamura Susumu
Published: July 2002

A new perovskite Pb(In1/2Ta1/2)O3 compound was successfully prepared through the wolframite phase oxide, utilizing fast firing for the enhancement of formation of the perovskite phase and densification. Dielectric properties of Pb(In1/2Ta1/2)O3 are found to be typical of a ferroelectric relaxor exhibiting a broad maximum of the permittivity at 5 °C at 1 kHz, strong dielectric dispersion around room temperature, and rounded polarization-electric field hysteresis loops.
Transient absorption and fluorescence spectroscopy in fused silica induced by pulsed KrF excimer laser irradiation
Authors: Leclerc N. , Pfleiderer C. , Wolfrum J. , Greulich K. , Leung W. P. , Kulkarni M. , Tam A. C.
Published: July 2002

We have carried out in situ transient absorption and fluorescence spectroscopy measurements in two ‘‘wet’’(OH content ∼0.1%) fused silica samples (Suprasil II from Heraeus Amersil and P-30 from Shin-Etsu Quartz Product) during KrF laser irradiation. Both samples exhibit an absorption peak at 210 nm corresponding to the E′ center. For Suprasil II, there is also a 265 nm absorption peak, and both peaks increase with the number of irradiated pulses showing little relaxation after the laser was turned off. The region irradiated with three million pulses at 400 mJ/cm2 fluence ten months ago has a residual absorption of about 10%/cm at 210 nm. On the other hand, the P-30 shows a rapid increase in the 210 nm absorption in both the unirradiated and previously irradiated regions during the initial irradiation and levels off after a few thousand pulses. There is no residual absorption at the spot irradiated for 63 million pulses ten months ago. However, the initial rate of increase in the previously irradiated spot is twice as high as compared to the unirradiated spot. This suggests the density of the precursor state for the E′ center is higher in the previously irradiated region. The fluorescence intensity at 650 nm increases with the induced absorption for Suprasil II, but is almost independent of the number of irradiation pulses in P-30. The quasilinear repetition-rate dependence suggests the fluorescence is transient in nature and relaxes partially between successive laser pulses.
Optically detected Auger recombinations in erbium- and ytterbium- doped InP
Authors: Heijmink Liesert B. J. , Godlewski M. , Gregorkiewicz T. , Ammerlaan C. A. J.
Published: July 2002

Microwave-induced impact ionization of excitons and shallow donors is studied in Er- and Yb-doped InP. The experimental results indicate a high efficiency of free-electron-related Auger recombination. Yb and Er intrashell emissions are deactivated due to an energy transfer to either free or bound carriers. A new Auger-type nonradiative process is suggested in which the rare-earth-related photoluminescence decays via an energy transfer to a free carrier which has become localized via a short-range potential.
Highly conductive ultrathin crystalline Si layers by thermal crystallization of amorphous Si
Authors: Kakkad R. , Fonash S. J. , Weideman S.
Published: July 2002

Ultrathin, highly conductive polycrystalline Si films have been produced on glass by crystallization of 200 Å a-Si films. The films, which result from our relatively low-temperature process (e.g., 700 °C/4 min), are completely crystallized with grain sizes of the order of 1 μm for doped films. Both n- and p-type Si films of high conductivity (∼102 S/cm) can be obtained by this process. These 200 Å crystallized films, produced from doped a-Si:H precursors, are over 10 orders of magnitude more conductive than deposited microcrystalline Si films of the same thickness. The high conductivities in these ultrathin films on glass make them very attractive for applications in photodetector and solar cell structures.
Time-division multiplexing by a photoconducting antenna array
Authors: Froberg N. M. , Hu B. B. , Zhang X.-C. , Auston D. H.
Published: July 2002

When a photoconducting antenna array is illuminated by a subpicosecond laser pulse, the spatial profile of the applied bias field is mapped onto the temporal waveform of the radiated electric field. This property allows the array to function as a multiplexer, in which parallel electronic data are converted to a sequence of radiated pulses.
New modulator for far-infrared light: Integrated mirror optical switch
Authors: Stiens J. , Kuijk M. , Vounckx R. , Borghs G.
Published: July 2002

We report on the first prototype IMOS (integrated mirror optical switch), FIR (far-infrared: 8–12 μm) light modulator. The operation of this type of modulator is based on the reflection properties of a high density, thin electron sheet in semiconductors. The present prototype was built to give experimental backing for earlier theoretical predictions. Low electric power (4 W) and low voltage (12 V) operation have been achieved. A modulation depth of about 30% and a 3 dB frequency of 400 kHz were obtained.
Hot hole effects in single barrier p-type GaAs/(AlGa)As/GaAs tunnel structures
Authors: Alikacem M. , Maude D. K. , Eaves L. , Henini M. , Hill G. , Pate M. A.
Published: July 2002

Oscillatory structure in the low-temperature current-voltage characteristics of Be-doped p-type GaAs/(AlGa)As/GaAs single barrier tunneling devices is observed. The oscillations have period ΔV=39 mV, close to ℏωL/e, where ℏωL is the longitudinal optic (LO) phonon energy in GaAs. They result from energy relaxation of hot holes injected through the tunnel barrier. The oscillatory amplitude varies as exp(Ea/2kT), where Ea is the ionization energy of the Be acceptors.
Critical currents in silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10−y superconducting tapes
Authors: Shi Donglu , Salem-Sugui S. , Wang Zuning , Goodrich L. F. , Dou S. X. , Liu H. K. , Guo Y. C. , Sorrell C. C.
Published: July 2002

Nearly 95 vol % of the 110 K superconducting phase was formed by lead doping in a Bi–Sr–Ca–Cu–O system. The processed 110 K superconducting powders were used to produce long silver-sheathed tapes with a highly textured microstructure by rolling and prolonged sintering. The transport critical current density was measured at 4.0 K to be 0.7×105 A/cm2 (the corresponding critical current is 74 A) at zero field and 1.6×104 A/cm2 at 12 T for H∥ab. At 76 K, the critical current density reached a value of ∼1×104 A/cm2 at zero field for H∥ab and gradually decreased to 419 A/cm2 at 1 T. Excellent grain alignment in the a–b plane led to greatly improved critical current densities under a magnetic field. The relationship between the transport properties and the microstructure of the tapes is discussed.
Wavelength tuning in a grating-assisted vertical coupler filter using quantum well electrorefraction
Authors: Sakata Hajime , Takeuchi Shinsuke
Published: July 2002

We present a demonstration of the electro-optic tuning in a GaAs/AlGaAs quantum well vertical codirectional coupler filter. Tunable range over 2 nm was realized through the quantum-confined Stark effect with a tuning rate of 0.28 nm/V2 for transverse magnetic polarization. A filter bandwidth as narrow as 1.7 nm (full width at half-maximum) at 830 nm with a coupling region length of 490 μm was obtained.
Study of the changes in the infrared transmission of SiO2 spin-on-glass due to ion implantation
Authors: Shacham-Diamand Y. , Finkman E. , Pinkas Y. , Moriya N.
Published: July 2002

The ion implantation of phosphorus into spin-on-glass (SOG) SiO2 thin-film films modified the infrared transmission spectrum of the films. Two SOG types, polysiloxane and silicate, were ion implanted with doses in the 1×1014–1×1015 cm−2 range and an energy of 40 keV. The Fourier-transform infrared spectrum of such films on silicon substrates was measured and the results are presented as a function of the implanted dose. The effect of the ion implantation on the silicate SOG was minute while significant changes were observed in the polysiloxane SOG. The major absorption peaks in the transmission spectrum were numerically analyzed and fitted to a set of Lorentzian functions. The peak heights, width, and area were measured. The ion implantation reduces the number of CH3 groups while the location of the Si-O absorption peak is shifted towards a shorter wavelength, i.e., a denser material. A physical interpretation of the absorption peak dependence on the ion-implanted dose is presented.
Initial growth mechanism of AlAs on Si(111) by molecular beam epitaxy
Authors: Kawai T. , Yonezu H. , Yamauchi Y. , Takano Y. , Pak K.
Published: July 2002

The initial growth mechanism of AlAs-on-Si(111) substrate was investigated. The suppression of three-dimensional growth was successfully realized at the initial growth stage, which is difficult in the growth of GaAs on Si. The initial growth process was clarified, in which the lattice relaxation proceeded gradually. It took about 30 ML to relax the lattice completely at the growth temperature of 400 °C. GaAs was grown in the two-dimensional mode on the completely relaxed AlAs on the Si(111) substrate.
Iso-electronic impurity-induced disordering: AlxGa1−xAs-GaAs/In
Authors: Tang T. K. , Alwan J. J. , Herzinger C. M. , Cockerill T. M. , Crook A. , DeTemple T. A. , Coleman J. J. , Baker J. E.
Published: July 2002

Data are presented on the disordering of an AlxGa1−xAs-GaAs laser structure using indium solid sources. Using separate and co-diffusion of silicon and indium from thin-film sources, indium was inferred to have a higher diffusion coefficient than silicon, and to result in a similar degree of impurity-induced disordering. The degree of index guiding was tested by excess-loss measurements in single-mode raised-cosine s-bends. In particular, structures patterned by SiO2/In disordering had excess losses similar to those patterned with SiO2. A 260 μm transition length for 3 dB loss was measured for 1-μm-wide guides with 100 μm guide offsets, which corresponds to a lateral index of refraction difference of ≊0.8–1.0%. There was no evidence for increased linear loss due to the presence of a dilute InGaAs alloy at the measurement wavelength of 870 nm.
Response to ‘‘Comment on ‘E′ centers and nitrogen-related defects in silicon dioxide films’ ’’
Authors: Stathis J. H. , Chapple-Sokol J. , Tierney E. , Batey J.
Published: July 2002

The anomalous properties of defect centers observed by Warren and Lenahan (ref. 1), in certain plasma enhanced chemical vapor deposited silica films must be examined in a broader light. The presence of a compensating impurity is indicated.(AIP)
Polarization-independent optical waveguide intensity switch with parabolic quantum well
Authors: Tada Kunio , Nishimura Shinji , Ishikawa Takuya
Published: July 2002

In a parabolic quantum well, the shift in optical transition energy due to the quantum confined Stark effect is independent of the carrier effective mass. This fact enables us to realize polarization-independent optical waveguide intensity switches with high on/off ratio. An absorption-type switch with GaAs/Al0.3Ga0.7As equivalent parabolic quantum wells is fabricated with molecular beam epitaxy. Both transverse-electric and transverse-magnetic mode lights exhibit an on/off ratio of 27.6 dB at an applied voltage of 6.84 V at 850 nm wavelength. To our knowledge, this is the first polarization-independent optical waveguide intensity switch based on the electric-field-induced effect in the semiconductor quantum well.
Properties of p-GaAs/sawtooth doping superlattice/n+-GaAs structure prepared by molecular beam epitaxy
Authors: Sun Chung-Yih , Liu Wen-Chau
Published: July 2002

The transport properties of a p-GaAs/sawtooth doping superlattice (SDS)/n+-GaAs structure has been studied. It is known that the transport properties vary with temperature. Experimentally, a diode-like performance is obtained, due to the thermionic emission, at room temperature. However, a quite different S-shaped negative-differential-resistance (NDR) phenomenon, resulting primarily from the avalanche multiplication in the SDS region, is observed at 77 K. The existence of different performance modes, i.e., diode and switch, on the same wafer chip provides more flexibility for device and circuit applications.
Metallic tungsten phosphide films formed by spin coating peroxopolytungstic acid on InP
Authors: Karlicek R. F. , Williams K. , Baiocchi F. A. , Thomas P. M. , Nakahara S.
Published: July 2002

Metallic β-WP2 films have been formed on InP by reacting amorphous peroxopolytungstic acid (APA) films on InP in a PH3/H2 ambient at 600 °C. The resulting metallic film exhibits a low sheet resistance (310 μΩ cm) and preliminary measurements suggest the contact on n-InP is ohmic. By using the unreacted peroxopolytungstic acid films as a negative inorganic photoresist, patterned β-WP2 metallic films on InP have been made without the use of a separate metal film etching step. The reacted metallic films show a smooth, abrupt metal/semiconductor interface. The high temperature stability of β-WP2 on InP suggests that this material may be useful as a refractory contact to InP.
Controlling the sulphur content of ZnSe1−ySy epitaxial layers grown by metalorganic chemical vapor deposition using diethyl selenide, hydrogen sulphide, and dimethylzinc
Authors: Yates H. M. , Williams J. O. , Cole-Hamilton D. J.
Published: July 2002

Epitaxial layers of ZnSe1−ySy on (100) GaAs substrates have been grown by metalorganic chemical vapor deposition. The reactants used are dimethylzinc (DMZn), hydrogen sulphide (H2S) and diethylselenide (DESe). The DESe has been used rather than the more usual selenium precursor, hydrogen selenide (H2Se). Results on the relationship between the sulphur incorporated into the epilayer and the group VI gas phase reactant molar ratio show a more linear relationship than previously found for the atmospheric pressure growth of this material using the hydrides. Despite the higher growth temperature (450 °C) and nonoptimized conditions the epilayers are shown to be comparable with those grown with hydrides and at lower growth temperatures (280 °C). Low-temperature (10 K) photoluminescence gave near-band-edge emission linewidths of 6.8 meV for the ZnSe0.87S0.13 ternary.
Depressed index cladding graded barrier separate confinement single quantum well heterostructure laser
Authors: Cockerill T. M. , Honig J. , DeTemple T. A. , Coleman J. J.
Published: July 2002

In this letter, we present data for a novel depressed index cladding laser structure which provides reduced perpendicular far-field divergence angle with acceptable low-threshold current densities. Narrow perpendicular divergence angles of 27° full width at half maximum for a nearly perfect Gaussian beam shape have been measured, with a corresponding near-field spot size of 1.30 μm. Threshold current densities of 309 A/cm2 are observed for 150 μm stripewidth, 780 μm long devices with 0.80 μm transverse spot sizes. Pulsed output powers for unmounted devices are greater than 0.9 W/uncoated facet.
Optical gain of CdZnSe/ZnSe quantum well lasers
Authors: Ahn D. , Yoo T.-K. , Lee H. Y.
Published: July 2002

Polarization-dependent optical gain of recently demonstrated CdZnSe/ZnSe quantum well lasers is calculated for the first time. Our analysis is based on the multiband effective mass theory (k⋅p theory) and the density matrix formalism with intraband relaxation taken into account. It is shown theoretically that the TE mode gain is significantly larger than the TM mode gain for a wide range of carrier density. Comparison of the room-temperature TE mode gain of CdZnSe/ZnSe quantum well with that of GaAs/AlGaAs quantum well gives disappointing results for the II-VI semiconductor lasers. It is expected that the optical gain of the ZnSe-based semiconductor lasers would be substantially smaller than the optical gain of the GaAs-based semiconductor lasers for a same quantum well width and carrier density.
Characteristics of all YBa2Cu3O7 edge junctions operating above 80 K
Authors: Koren G. , Polturak E. , Aharoni E. , Cohen D.
Published: July 2002

a-b plane YBa2Cu3O7-YBa2Cu3O7 (YBCO) edge junctions with improved properties were prepared by the use of SrTiO3 instead of BaF2 as an insulating layer in the c-axis direction. The junctions were fabricated in an all in situ laser ablation deposition process, with the barriers formed by a plasma discharge in CF4 gas. Photolithographic rather than laser ablation patterning of the junctions was used, to avoid possible laser induced damage to the films. The normal resistance of the junction decreased with T for T≳40 K, and increased at lower temperatures, indicating that carrier localization takes place in the barrier. At 80 K, a pronounced diffraction pattern of the voltage across the junction versus magnetic field was observed. Critical currents persisted up to 84 K, and under microwave radiation many Shapiro steps were observed.
Effect of cable and strand twist-pitch coincidence on the critical current of flat, coreless superconductor cablesa)
Authors: Ekin J. W.
Published: July 2002

Data are presented which indicate that a very simple technique for enhancing the critical current in flat, coreless superconductor cables is to match the cable twist pitch with the strand twist pitch in such a way that the same group of filaments within each strand is degraded at each successive bend at the cable edges. This coincidence condition minimizes current transfer among filaments, enhances the slope of the voltage-current characteristic, consistently improves the critical current by about 10% in these tests, and is easy to apply.
Formation of defect clusters in electron-irradiated diamond at 16 and 87 K
Authors: Koike J. , Mitchell T. E. , Parkin D. M.
Published: July 2002

A type IIa natural diamond was irradiated with 300 kV electrons at 16 and 87 K. Transmission electron microscopy and electron energy-loss spectroscopy were employed to investigate the phase stability of diamond under electron irradiation. At both temperatures, the diamond structure was found to be stable, and the formation of defect clusters was observed. The present results in comparison to previous work on ion implantation indicate that displacement cascade damage is a prerequisite for irradiation-induced phase transformation from diamond to amorphous carbon or graphite. The temperature dependence of the cluster size suggests that interstitials are thermally mobile above 50 K.
Tuning of the Schottky barrier height using bi-metallic layered structures
Authors: Narayan Chandrika , Karakashian A. S. , Kegel G. H. R. , Rivera Z.
Published: July 2002

Bi-metallic Schottky contacts of Cr-Al on p-type Si using a layered structure have been investigated. In these contacts, the thickness of the inner layer in contact with Si was varied, while that of the outer metal layer was kept constant. Our studies indicate that the barrier height changes with the thickness of the inner metal layer. Furthermore, the morphology of our samples was examined with a transmission electron microscope (TEM) which indicates the presence of inhomogeneous mixing of Cr and Al.
Effect of surface recombination on the spectral dependence of photocurrent in intrinsic hydrogenated amorphous silicon films
Authors: Li Y. M. , Dawson R. M. , Collins R. W. , Wronski C. R. , Wiedeman S.
Published: July 2002

The spectral dependence of the photocurrent in intrinsic hydrogenated amorphous silicon (a-Si:H) films was measured in the annealed and light-soaked states. The photocurrents were modeled using numerical analysis which quantified the recombination in both the bulk as well as at the film surface and glass substrate interface. The results on films, having thicknesses between 1 and 3 μm, are consistent with thickness independent bulk transport properties and surface and substrate interface recombination velocities of (3–6)×104 and (1–2)×106 cm/s, respectively.
Modification of nonlinear optical response in Langmuir–Blodgett films by ultraviolet laser-induced bleaching
Authors: Hsiung H.
Published: July 2002

Permanent modifications of the second-order nonlinear susceptibility χ(2)(−2ω;ω,ω) of certain Langmuir–Blodgett (LB) films can be induced photochemically by local irradiation with UV laser light, with the spatial resolution limited only by the laser spot size. In a LB film consisting of alternating monolayers of poly[N-(p-perfluorodecylsulfonylphenyl)-L-prolinol acrylate] and a ‘‘buffer’’ polymer, the kinetics of the laser bleaching process, as studied by optical second-harmonic generation, is found to be first order. The generation of a ‘‘χ(2)-grating’’ in the LB film is also demonstrated.
Cathodoluminescence from diamond films grown by plasma-enhanced chemical vapor deposition in dilute CO/H2, CF4/H2, and CH4/H2 mixtures
Authors: Graham R. J. , Posthill J. B. , Rudder R. A. , Markunas R. J.
Published: July 2002

Diamond films grown by rf plasma-enhanced chemical vapor deposition in dilute CO, CF4, and CH4 (diluent H2) mixtures have been examined by cathodoluminescence (CL) in a transmission electron microscope to assess the incorporation of optically active impurities and defects. The details of the CL spectra are found to be dependent on the different gas mixtures and are correlated with the different film microstructures. Dislocation-related band A CL due to closely spaced donor-acceptor (D-A) pairs was observed from both the CO and CH4-grown films, but was absent in the CF4-grown material. Band A CL due to widely separated (D-A) pairs was seen in all samples but was especially dominant in the CF4-grown film. Emission due to a di-Si interstitial impurity was observed in CO- and CF4-grown films but was absent in the CH4-grown material.