bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoluminescence properties of nitrogen-doped ZnSe layers grown by molecular beam epitaxy with low-energy ion doping
Authors: Mitsuyu T. , Ohkawa K. , Yamazaki O.
Published: July 2002

Low-energy ion doping of nitrogen has been employed in the molecular beam epitaxial (MBE) growth of ZnSe on GaAs substrates in an attempt to obtain p-type crystals. Low-temperature photoluminescence (PL) measurements of the N-doped ZnSe indicated a formation of shallow acceptors with an activation energy around 110 meV. The PL spectrum in the excitonic emission region was dominated by an acceptor bound-exciton emission I1 at 2.790 eV, suggesting a remarkable increase of an acceptor concentration in comparison with the previous work by MBE using a neutral doping source.
Observation of Bloch conduction perpendicular to interfaces in a superlattice bipolar transistor
Authors: Palmier J. F. , Minot C. , Lievin J. L. , Alexandre F. , Harmand J. C. , Dangla J. , Dubon-Chevallier C. , Ankri D.
Published: July 2002

We report the first operating bipolar transistor built with an AlGaAs/GaAs superlattice base. High current gain is measured with a suitable design of the bipolar transistor structure. Experimental results are in good agreement with a Bloch to hopping transition which is very sensitive to the AlGaAs barrier thickness. This interpretation is supported by a detailed numerical simulation reproducing the static Ic(Vce,Ib) transistor transfer data.
Trapping of oxygen at homoepitaxial Si-Si interfaces
Authors: Hull R. , Bean J. C. , Gibson J. M. , Joy D. C. , Twigg M. E.
Published: July 2002

Microstructural studies of Si-Si interfaces grown by molecular beam epitaxy reveal pockets of oxygen-rich material for certain substrate preparation conditions. For Czochralski substrates which are cleaned using an argon ion sputtering technique, a high density (about 1011/cm2) of oxygen-rich pockets about 30 Å in size is observed using cross-sectional transmission electron microscopy and x-ray microanalysis for short (less than about 15 s) sputtering times. For longer sputtering times, no significant defect density is observed. Post-deposition thermal annealing causes a dramatic increase in the density of oxygen-rich defects, and it is suggested that this is due to trapping of oxygen which has diffused from the bulk of the substrate wafer. For (100) interfaces, no significant dislocation activity is associated with the defects, even for densities up to 1012/cm2. On (111) interfaces, however, a large planar fault density is observed. Ramifications for silicon homoepitaxy are discussed.
Effect of process conditions on the quality of CdTe grown on InSb by organometallic epitaxy
Authors: Ghandhi S. K. , Taskar N. R. , Bhat I. B.
Published: July 2002

The morphology and crystal quality of CdTe grown on InSb substrates are shown to be critically dependent on the pregrowth stabilization procedure to which the substrate has been subjected. It is shown that layer growth on a dimethylcadmium stabilized InSb substrate results in CdTe layers with a large number of hillocks whereas growth on a diethyltelluride stabilized substrate results in a smooth morphology. These hillocks are initiated by the reaction of dimethylcadmium with the InSb surface; alloys of In-Cd-Sb formed at the interface result in deterioration of the layer morphology. This problem can be avoided by growth on a diethyltelluride stabilized surface, at temperatures below 400 °C. Improvement in the layer quality by use of this technique is illustrated by a study of the photoluminescence spectra (PL) of CdTe grown by these two methods. Layers have been grown with a band-edge PL peak having a full width half-maximum of 2.1 meV at 12 K. To our knowledge, this is the lowest value for epitaxial layers of CdTe on InSb grown by any technique at the present time.
Observation of a quasi-two-dimensional electron gas at an InSb/CdTe interface
Authors: Zheng Y-D. , Chang Y. H. , McCombe B. D. , Farrow R. F. C. , Temofonte T. , Shirland F. A.
Published: July 2002

Liquid-helium temperature transport and magnetotransport measurements on n-CdTe grown by molecular beam epitaxy on p-InSb substrates have demonstrated the presence of a quasi-two-dimensional electron gas in the InSb at the InSb/CdTe interface. The electron density and mobility in the channel can be varied by back gating.
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u x-ray topographic observation of dislocation behavior in In-doped GaAs crystals
Authors: Tohno S. , Shinoyama S. , Katsui A. , Takaoka H.
Published: July 2002

This letter describes the results of in situ observations of dislocation behavior in In-doped GaAs crystals at high temperatures using synchrotron radiation topography and high-temperature stressing apparatus. The generation and propagation processes of dislocations in a preyield stage have been investigated by making a comparison with undoped crystals. We find that there is a one-directional predominance in the generation and propagation of dislocations in In-doped crystals.
Very low noise, tightly coupled, dc SQUID amplifiers
Authors: Muhlfelder B. , Beall J. A. , Cromar M. W. , Ono R. H.
Published: July 2002

We have fabricated and tested thin film, niobium edge junction, double transformer, dc superconducting quantum interference devices (SQUID’s) that were stable under room-temperature storage and thermal cycling and that had very good noise performance. The input inductance, approximately 1.7 μH, was large enough to facilitate good matching to many experiments. When the SQUID was operated as a small-signal amplifier, the minimum detectable energy per unit bandwidth (Se) was 5×10−33 J/Hz at 100 kHz, referred to the SQUID loop (uncoupled). The minimum detectable energy per unit bandwidth was 1.8×10−31 J/Hz at 100 kHz, referred to the input coil. The SQUID’s had good characteristics for flux-locked operation since the small signal Se was low over a substantial range of bias current and magnetic flux. For operation in a flux-locked feedback circuit, Se was 6×10−32 J/Hz at 1 kHz.
Observation of gain compression in a GaAlAs diode laser through a picosecond transmission measurement
Authors: Johnson B. C. , Mooradian A.
Published: July 2002

The carrier density and light output of a pulse modulated GaAlAs diode laser were measured with picosecond time resolution. A new technique for measuring carrier density by transmission of picosecond light pulses through a diode laser is described. The measured carrier density was compared with a density calculated from the light output data using a rate equation analysis. Gain compression of a magnitude expected from relaxation oscillation damping rates was observed. Because the experiment measures the density at the center of the waveguide, and not the average across the active layer, the compression mechanism is not spatial hole burning.
Chemical beam epitaxial growth of very low threshold Ga0.47In0.53As/InP double-heterostructure and multiquantum well lasers
Authors: Tsang W. T.
Published: July 2002

We report the successful preparation by chemical beam epitaxy and performance characteristics of Ga0.47In0.53As/InP double-heterostructure (DH) and multiquantum well (MQW) lasers emitting at 1.47–1.72 μm. The very low threshold current densities Jth of 1.3 kA/cm2 and 1.5 kA/cm2 obtained from DH and MQW laser wafers, respectively, suggest that the present materials and heterointerfaces are superior to those obtained previously by other techniques. In fact, these Jth’s are the lowest obtained thus far for such lasers. Differential quantum efficiency of ∼18% per facet was obtained for both DH and MQW lasers. Furthermore, we were able to show that there was a definite improvement in the threshold-temperature dependence characteristic coefficient T0 from ∼35–45 K for DH laser wafers to ∼65–80 K for MQW laser wafers in contrast to previous experimental results.
Optically induced far-infrared absorption from residual acceptors in as-grown GaAs
Authors: Wagner J. , Seelewind H. , Koidl P.
Published: July 2002

Far-infrared Fourier transform spectroscopy has been applied to study residual shallow acceptors in as-grown semi-insulating GaAs. Secondary optical excitation into the EL2 absorption band has been used to create a nonequilibrium hole population to neutralize the acceptors. Optically induced absorption spectra from carbon and zinc acceptors have been observed. The dependence of these spectra on the secondary illumination is studied. A comparison is made with electronic Raman spectra recorded from the same samples.
Broadband and high-reflectivity mirror using (Al,Ga)As/(Ca,Sr)F2 multilayer structures grown by molecular beam epitaxy
Authors: Tu C. W. , Ajuria S. A. , Temkin H.
Published: July 2002

By molecular beam epitaxy we have grown a quarter-wave stack of lattice-matched Al0.1Ga0.9As/Ca0.45Sr0.55F2 multilayer heterostructures which has high reflectivity (89%) over a broad spectral range. Unlike similar structures of (Al,Ga)As/GaAs which require many periods to achieve high reflectivity, the III-V/fluoride structures require only four periods due to the large difference in the refractive indices of the III-V compound and the fluoride (3.6 and 1.4 at 0.9 μm, respectively). Furthermore, for the (Al,Ga)As/GaAs structures the high-reflectivity plateau is narrower, and because of absorption in the GaAs layers the reflectivity decreases rapidly at wavelengths shorter than the band-gap wavelength of GaAs. For the III-V/fluoride structures grown the absorption is not a problem, and the high-reflectivity region extends from 0.9 μm to 0.7 μm. The ability to grow epitaxial fluoride and (Al,Ga)As with arbitrary AlAs mole fraction, and therefore different refractive indices, should stimulate interesting applications in optics.
Formation of a p
n junction on an anisotropically etched GaAs surface using metalorganic chemical vapor deposition
Authors: Leon R. P. , Bailey S. G. , Mazaris G. A. , Williams W. D.
Published: July 2002

A continuous p-type GaAs epilayer has been deposited on an n-type sawtooth GaAs surface using metalorganic chemical vapor deposition. A wet chemical etching process was used to expose the intersecting (111)Ga and (1̄1̄1)Ga planes with 6 μm periodicity. Charge collection microscopy was used to verify the presence of the pn junction thus formed and to measure its depth. The ultimate goal of this work is to fabricate a V-groove GaAs cell with improved absorptivity, high short-circuit current, and tolerance to particle radiation.
Two-dimensional electron gas in a Ga0.47In0.53As/InP heterojunction grown by chemical beam epitaxy
Authors: Tsang W. T. , Chang A. M. , Ditzenberger J. A. , Tabatabaie N.
Published: July 2002

Shubnikov–de Haas, quantum Hall effect, and cyclotron resonance measurements revealed the existence of a high mobility, two-dimensional electron gas at the Ga0.47In0.53As/InP heterointerface grown by chemical beam epitaxy. Enhanced electron mobilities were as high as ∼130×103 cm2/V s at 4.2 K. A striking feature in the data which also indicates that the sample is of high quality is the large number of Shubnikov–de Haas oscillation periods observed. Oscillations were observable up to a Landau filling factor of around 50, corresponding to a Landau level index of 25.
Effect of ion bombardment on the surface magnetism of Fe3O4
Authors: Aeschlimann M. , Bona G. L. , Meier F. , Stampanoni M. , Zampieri G. , Siegmann H. C.
Published: July 2002

We have found that ion bombardment produces dramatic changes in the surface magnetism of Fe3O4. The surface layer with irregular magnetic behavior is more than 50 Å thick. These findings are of importance for current studies of ferritelike sputtered thin films as well as magnetic alloys in general.
Enhanced injection at silicon-rich oxide interfaces
Authors: Chang K-T. , Rose K.
Published: July 2002

The enhanced electron injection of silicon-rich oxide (SRO)/SiO2 interfaces is explained. We find an excellent fit to the current-voltage characteristics of these interfaces by calculating the field enhancement over the surface of oblate spheroids in a uniform applied field. This explains why field enhancement at SRO/SiO2 interfaces tends to be independent of island size and unaffected by annealing.
Enhancement mode InP metal-insulator-semiconductor field-effect transistors grown by chemical beam epitaxy
Authors: Antreasyan A. , Tsang W. T. , Garbinski P. A.
Published: July 2002

We have fabricated enhancement mode InP metal-insulator-semiconductor field-effect transistors having extrinsic transconductances of 64 mS/mm for a gate length of 2 μm. The epitaxial layers for the structure have been grown by chemical beam epitaxy. The field-effect transistors exhibit effective mobilities of 1235 cm2/ V s and an average drift velocity of 1.12×107 cm/s. These results are in good agreement with state of the art InP metal-insulator-semiconductor field-effect transistor technology.
Single-mode single-lobe operation of broad area AlxGa1−xAs-GaAs quantum well lasers
Authors: Deppe D. G. , Jackson G. S. , Holonyak N. , Hall D. C. , Burnham R. D. , Thornton R. L. , Epler J. E. , Paoli T. L.
Published: July 2002

A buried heterostructure broad area quantum well heterostructure AlxGa1−xAs-GaAs laser diode modified with a small multiple stripe pattern near its center is described that operates single mode and narrow lobe (<2 °) from threshold (Ith) to 2Ith or 3Ith. The broad area (wide stripe) buried heterostructure laser is made by impurity-induced layer disordering.
Characterization of epitaxial (Ca,Ba)F2 films on Si(111) substrates
Authors: Wittmer M. , Smith D. A. , Segmüller Armin , Zogg H. , Melchior H.
Published: July 2002

We have investigated epitaxial BaF2/CaF2 bilayers on Si(111) with ion channeling, grazing-incidence x-ray diffraction, and transmission electron microscopy. The BaF2 layer, which was grown on a thin intermediate CaF2 layer, showed a channeling minimum yield of 8% and a residual strain of 0.2%. Regions of BaF2 with a mosaic spread in orientation were observed but otherwise the epitaxial quality of the fluoride bilayer was found to be very good.
High-efficiency carrier collection and stimulated emission in thin (50 Å) pseudomorphic InxGa1−xAs quantum wells
Authors: Anderson N. G. , Lo Y. C. , Kolbas R. M.
Published: July 2002

Efficient collection of photoexcited electrons and holes by thin, strained quantum wells is demonstrated in an In0.16Ga0.84As-GaAs pseudomorphic quantum well heterostructure laser. The undoped laser structure, which was grown by molecular beam epitaxy, consists of five 50 Å pseudomorphic In0.16Ga0.84As quantum wells separated by thick (700 Å), unstrained GaAs confining layers. Despite the fact that the quantum wells are undoped, decoupled, and of dimensions which are known to be too small to provide efficient carrier collection in unstrained AlxGa1−xAs-GaAs structures, 77 K photopumped laser operation is achieved on quantum well transitions (λ∼870 nm) at a threshold excitation intensity of 9.3×103 W/cm2. At photoexcitation intensities even as high as five times the threshold value, spontaneous emission from the quantum well is more than 700 times as intense as the confining layer luminescence. Based upon these photoluminescence results and some simple physical arguments, we suggest that carrier collection is enhanced in pseudomorphic quantum wells.
Cross-sectional transmission electron microscope observation of step-band formation on GexSi1−x(111) vicinal surfaces
Authors: Tatsumi Toru , Aizaki Naoaki
Published: July 2002

The Ge0.1Si0.9 surface and the Ge0.1Si0.9/Si interface on the Si(111) 4° off substrate were observed by a cross-sectional transmission electron microscope. The Ge0.1Si0.9 surface grown at 750 °C was composed of alternate planes of (111) terraces and step bands, whose widths in the 〈112〉 direction were about 450 and 150 Å, respectively. A step band was formed by steps several monolayers high. On the other hand, the Ge0.1Si0.9/Si interface was very flat and the step bands were not formed in the Si on Si homoepitaxy process at 750 °C.
Integrated quantum well self-electro-optic effect device: 2×2 array of optically bistable switches
Authors: Miller D. A. B. , Henry J. E. , Gossard A. C. , English J. H.
Published: July 2002

We demonstrate 2×2 arrays of optically bistable devices with very uniform optical characteristics. They are fabricated from an integrated self-electro-optic effect device structure consisting of a quantum well p-i-n diode grown in series with a load photodiode. Operating power can be optically controlled with a separate beam between ∼40 pW and >470 μW with associated switching times of ∼10 s and <2 μs.
High resolution electron microscopy of the GaAs/Si3N4 interface produced by multipolar plasma deposition
Authors: Rutérana P. , Friedel P. , Schneider J. , Chevalier J. P.
Published: July 2002

The analysis of the Si3N4/GaAs interface produced by the multipolar plasma chemical vapor deposition has been carried out using high resolution electron microscopy. For an optimized deposition process, we are able to produce abrupt interfaces between the Si3N4 and the crystalline GaAs. These results are compared to the interfaces produced in the conventional chemical vapor deposition technique.
High-order (ν>10) eigenmodes in ten-stripe gain-guided diode laser arrays
Authors: Hadley G. R. , Hohimer J. P. , Owyoung A.
Published: July 2002

We present a numerical model for a ten-stripe gain-guided diode laser array that predicts eigenmodes of order greater than the number of stripes. The existence of such high-order eigenmodes is confirmed by observing the near- and far-field emission patterns from free-running single-frequency gain-guided arrays operating near threshold. Injection seeding provides an effective tool for selectively exciting these high-order eigenmodes, including lower-gain modes which would not normally be observed in a free-running array.
Growth and properties of dilute magnetic semiconductor superlattices containing Hg1−xMnxTe
Authors: Harris K. A. , Hwang S. , Lansari Y. , Cook J. W. , Schetzina J. F.
Published: July 2002

We report details of the successful growth by molecular beam epitaxy of superlattices containing alternating layers of Hg1−xMnxTe and HgTe. These structures are the first superlattices containing layers of a mercury-based dilute magnetic semiconductor (Hg1−xMnxTe ) to be grown by any thin-film technique. The optical and electrical properties of these new magnetic multilayers are discussed.
Assessment of lattice relaxation effects in transitions from mobility gap states in hydrogenated amorphous silicon using transient photocapacitance techniques
Authors: Gelatos A. V. , Cohen J. D. , Harbison J. P.
Published: July 2002

We have employed junction photocapacitance and thermal transient capacitance measurements in n-type doped hydrogenated amorphous silicon and have identified, within each of a series of samples, the optical transitions: D−→D0+e and D0→D++e, and the thermal transitions: D−→D0+e and D+→D0+h, where D−, D0, and D+ denote the three charge states of Si dangling bond defect. We have also correlated the optical and thermal transitions associated with the valence bandtail states. Lattice relaxation energies are found to be less than 0.1 eV for the dangling bond transitions, but as large as 0.5–0.6 eV for the valence bandtail states. We also determined a value of Ueff for the D−/D0 splitting of 0.24±0.07 eV.
Low-threshold solar-pumped laser using C2F5I
Authors: De Young R. J. , Weaver W. R.
Published: July 2002

Solar-pumped lasing was achieved with pentafluoroethyl iodide, C2F5I, a new alkyl-iodide. Output power and energy of 350 mW and 45 mJ were achieved. This lasant was found to have the lowest lasing threshold of any solar-pumped gas laser to date at approximately 100 solar constants. Such low threshold enables the use in space of simple, trough solar collectors.
Noncontact detection of surface-breaking cracks using a laser acoustic source and an electromagnetic acoustic receiver
Authors: Dewhurst R. J. , Edwards C. , Palmer S. B.
Published: July 2002

An electromagnetic acoustic transducer (EMAT) is used to detect laser generated surface acoustic transients. The surface acoustic waves are broadband and can be used to detect and size surface-breaking cracks if used in conjunction with a broadband detector. We describe a broadband EMAT and demonstrate first that it can be used to locate artificial surface-breaking defects in both aluminum and steel. A second study reveals that it can also be used for the detection of real surface-breaking cracks, even on rusty steel surfaces.
Epitaxial growth of 3C-SiC on Si by low-pressure chemical vapor deposition
Authors: Fujiwara Y. , Sakuma E. , Misawa S. , Endo K. , Yoshida S.
Published: July 2002

3C-SiC was grown on Si(100) substrates by low-pressure chemical vapor deposition using a C3H8-SiH4-H2 reaction gas system in the pressure range between 1.5 and 100 Torr. The dependences of the crystal structures, growth rates, thickness distributions, and electrical properties of the SiC layers on growth conditions were investigated. At low pressure, it was found that the thickness uniformity was improved, especially at 1.5 Torr compared to atmospheric pressure. The epitaxially grown 3C-SiC layers at 100 Torr have smooth surfaces and high crystalline quality and showed almost the same electrical properties as those of the epilayers by atmospheric pressure chemical vapor deposition.
Reduction of the acceptor impurity background in GaAs grown by molecular beam epitaxy
Authors: Larkins E. C. , Hellman E. S. , Schlom D. G. , Harris J. S. , Kim M. H. , Stillman G. E.
Published: July 2002

We report very high purity, unintentionally doped n-type GaAs with the lowest acceptor background of all reported molecular beam epitaxy (MBE) GaAs layers. The residual acceptor concentration is 2.4×1013 cm−3 and the residual donor concentration is 1.5×1014 cm−3, yielding a compensation ratio of Na/Nd=0.160. The measured Hall mobility is 163 000 cm2/V s at 77 K with a peak value of 216 000 cm2/V s at 45.9 K. The limitations of the Hall mobility at 77 K as a figure of merit are discussed and more accurate figures of merit are considered. The initial preparation of the MBE system and the growth conditions leading to the reduced incorporation of acceptor impurities are also presented.
Electron beam evaporation of oriented Nb films onto GaAs crystals in ultrahigh vacuum
Authors: Eizenberg M. , Smith D. A. , Heiblum M. , Segmüller Armin
Published: July 2002

Thin layers of Nb, 100–400 Å thick, were grown by electron beam evaporation on (100)GaAs substrates in a molecular beam epitaxy system. The crystallographic relationship between deposit and substrate was monitored in situ by reflection high-energy electron diffraction, and after deposition by transmission electron microscopy and grazing-incidence x-ray diffraction. In spite of the large lattice mismatch (17%) and the low deposition temperature (40–400 °C), a quite well oriented deposit with the orientation (100)Nb∥(100)GaAs and [001]Nb∥[011]GaAs was obtained for a substrate temperature of ∼170 °C. Changing the substrate temperature from the optimum value of ∼170 °C in either direction resulted in a gradual deterioration of the epitaxy.
Diffraction-limited emission from a diode laser array in an apertured graded-index lens external cavity
Authors: Chang-Hasnain C. , Welch D. F. , Scifres D. R. , Whinnery J. R. , Dienes A. , Burnham R. D.
Published: July 2002

A gain-guided coupled-stripe GaAs/GaAlAs diode laser array in an external cavity configuration consisting of a graded refractive index lens and a 25-μm stripe apertured mirror was studied. Output power of almost 500 mW was obtained from the cavity under pulsed operation. A centered, single-lobed far-field radiation pattern which did not steer with the drive current was observed up to 4.1Ith. At 2Ith approximately 94% of the 102-mW output power is contained in the 0.8° full width half-maximum central lobe.
Frequency response of an InGaAsP vapor phase regrown buried heterostructure laser with 18 GHz bandwidth
Authors: Olshansky R. , Lanzisera V. , Su C. B. , Powazinik W. , Lauer R. B.
Published: July 2002

The frequency response of a 1.3-μm InGaAsP vapor phase regrown buried heterostructure laser with an 18-GHz cw bandwidth is analyzed in detail. The intrinsic bandwidth of the device is shown to be 22 GHz and the 3-dB RC roll-off frequency due to electrical parasitics is found to be 10 GHz.
Dose-dependent mixing of AlAs-GaAs superlattices by Si ion implantation
Authors: Venkatesan T. , Schwarz S. A. , Hwang D. M. , Bhat R. , Koza M. , Yoon H. W. , Mei P. , Arakawa Y. , Yariv A.
Published: July 2002

The effects of Si ion implantation and annealing on AlAs-GaAs superlattices are examined with secondary ion mass spectrometry (SIMS), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy (TEM). Samples implanted with 180 keV 28Si+ of doses ranging from 3×1013 to 3×1015 cm−2 are examined before and after a 3-h 850 °C anneal. Both the TEM and RBS channeling data indicate the formation of a heavily damaged surface layer where diffusion of Al is inhibited even after thermal annealing. After annealing, however, significant mixing is observed at depths well beyond the implant range. Depth-dependent diffusion lengths of Al and Si are derived from the SIMS data. The diffusion coefficient of Si is markedly reduced in the unmixed regions with both the Si and Al concentrations exhibiting abrupt forward and rear diffusion fronts.
Multiple quantum well reflection modulator
Authors: Boyd G. D. , Miller D. A. B. , Chemla D. S. , McCall S. L. , Gossard A. C. , English J. H.
Published: July 2002

We demonstrated a quantum-confined Stark effect electroabsorption modulator consisting of quantum wells of AlGaAs and GaAs on an epitaxial multilayer dielectric mirror, all grown by molecular beam epitaxy. The resulting reflection modulator avoids problems of substrate absorption, and has relatively high contrast ratio (up to ∼8:1 with peak reflectivity of 25% at 853 nm) because the light passes twice through the quantum wells. Reflection modulators are of interest for bidirectional communication systems, in parallel arrays of optical switching and processing devices and for optical interconnects. For the latter there exists the possibility of this device grown on the same substrate alongside a GaAs integrated circuit or even on Si substrates.
Observations of β-tungsten deposited by low pressure chemical vapor deposition
Authors: Paine D. C. , Bravman J. C. , Yang C. Y.
Published: July 2002

Metastable β-tungsten was identified, using transmission electron microscopy, in arrays of low pressure chemical vapor deposited contacts on patterned silicon wafers. In contrast, only α-tungsten was found in films deposited onto bare silicon wafers under identical conditions. Thus, we have shown that contact wells etched through oxide can play a role in determining which tungsten phase is deposited by low pressure chemical vapor deposition. This effect was observed for a variety of furnace conditions (T=300–330 °C, H2/WF6=150:1–400:1). Transmission electron micrographs and selected area diffraction patterns are presented which illustrate the microstructural differences between the α- and β-tungsten phases. Possible sources of oxygen or fluorine, impurities which are believed to stabilize β-tungsten, are discussed and related to the geometry of the vias cut through oxide on patterned wafers.
Effects of 450 °C thermal annealing upon oxygen precipitation in heavily B- and Sb-doped Czochralski Si
Authors: Hahn S. , Arst M. , Rek Z. U. , Stojanoff V. , Bulla D. A. , Castro W. E. , Tiller W. A.
Published: July 2002

In this study we investigated effects of 450 °C preanneal upon oxygen precipitation during subsequent low (700 °C)-medium (950 °C) temperature two-step furnace anneals in heavily B- and Sb-doped Czochralski Si wafers. Our optical microscopy and synchrotron radiation section topographic data have shown that, for heavily B-doped materials, a 450 °C anneal up to 52 h is found to reduce oxygen precipitation in two-step furnace annealing, whereas for Sb-doped wafers, oxygen precipitation rates increase monotonically with the increase in 450 °C preanneal time.
Dielectrically isolated silicon-on-insulator islands by masked oxygen implantation
Authors: Davis J. R. , Robinson A. , Reeson K. J. , Hemment P. L. F.
Published: July 2002

A method of forming dielectrically isolated silicon-on-insulator device islands by using a thin patterned masking layer during implantation of high doses of oxygen into silicon is described. Due to energy loss in the masking layer, the oxygen ions synthesize both a surface oxide in the masked field regions and, simultaneously, a buried oxide in the unmasked windows. The field oxide is contiguous with the buried oxide under the device islands. This method of achieving total dielectric isolation has potential application in the fabrication of high-density silicon-on-insulator circuits with a very flat topography.
Synthesis of superconducting films of the Y-Ba-Cu-O system by a screen printing method
Authors: Budhani R. C. , Tzeng Sing-Mo H. , Doerr H. J. , Bunshah R. F.
Published: July 2002

A screen printing method has been used to deposit superconducting films of Y-Ba-Cu-O materials on Al2O3 substrates. The electrical resistivity, microstructure, and adhesion of these films are highly sensitive to the post-printing heat treatment. Films heat treated at 950 °C and below are poorly adherent, whereas those annealed above 1000 °C undergo phase separation to Y2Cu2O5 and BaCuO2 and also react with the substrate. Nearly single phase, highly adherent, and smooth films showing a zero resistance state at 79 K have been synthesized by optimizing the annealing conditions.
Measurement of gaseous oxygen using diode laser spectroscopy
Authors: Kroll M. , McClintock J. A. , Ollinger O.
Published: July 2002

A commercial diode laser emitting at ∼761 nm has been used to detect the absorption of individual rotational lines of the A band of atmospheric oxygen. An output signal that is proportional to the O2 partial pressure is extracted using derivative spectroscopy. The method allows measurement of O2 pressure with an uncertainty of ±1.3% of full scale (760 Torr) using a 1-ms time constant.
Instability threshold resonances in directly modulated external-cavity semiconductor lasers
Authors: Schremer A. , Fujita T. , Lin C. F. , Tang C. L.
Published: July 2002

The relationship between the modulation frequency and maximum modulation depth for stable and low-noise oscillation in external-cavity semiconductor lasers is investigated. Sharp resonances in the threshold for the onset of instability occur when the laser is nearly synchronously modulated. A physical model is proposed to explain these observations.
Si p+-n shallow junction fabrication using on-axis Ga+ implantation
Authors: Lin C-M. , Steckl A. J. , Chow T. P.
Published: July 2002

p +-n shallow junction fabrication using on-axis Ga implantation into crystalline and preamorphized Si, in conjuction with rapid thermal annealing, is reported. The implants are performed at energies of 50 and 75 keV for doses of 1 and 3.5×1015/cm2. Taking advantage of the short Ga projection range, low critical dosage (2×1014/cm2) needed for amorphizing the implanted layer, and a low anneal temperature (550–600 °C) required to induce solid phase epitaxial regrowth and activate the Ga dopants in excess of its maximum solid solubility in Si, a shallow junction at a depth of 100 nm and with sheet resistance of 150 Ω/⧠ was obtained using 75 keV Ga implantation at a dose of 1×1015/cm2. The sheet resistance of the Ga-implanted layer can be optimized by adjusting the anneal temperature and time.
Cathodoluminescence observation of metallization-induced stress variations in GaAs/AlGaAs multiple quantum well structures
Authors: Yacobi B. G. , Elman B. , Jagannath C. , Choudhury A. N. M. Masum , Urban M.
Published: July 2002

Cathodoluminescence scanning electron microscopy is utilized to investigate the stresses present underneath 0.4 μm gold layers deposited on GaAs/AlGaAs multiple quantum well structures grown by molecular beam epitaxy on GaAs substrates. Using the known stress dependence of excitonic lines in quantum wells, the magnitude of stress is determined to be about 1 kbar. The stress-induced change in the refractive index, attributed to photoelastic effect, is about 0.01 for the structures studied in the present work.
Lateral resonant tunneling field-effect transistor
Authors: Chou S. Y. , Harris J. S. , Pease R. F. W.
Published: July 2002

A lateral resonant tunneling field-effect transistor (RTFET) is proposed. The RTFET has three closely spaced, but independent gate electrodes. The two outer gates create lateral double potential barriers in the channel, and control the barrier heights. The inner gate controls the potential of the quantum well between the barriers. These gates are capacitively coupled to the barriers and well; therefore, very small gate currents and high input impedences result. Modeling and computer simulations show that when the potential of the quantum well is scanned, the RTFET should have a better peak-to-valley ratio, narrower current peak widths, and more uniform distribution of peak and valley currents than that of a resonant tunneling diode with the same barriers and well. The independent control of the barrier heights allows us to adjust continuously the peak-to-valley ratio, amplitude, and position of current peaks. Furthermore, using an additional back gate, the peak-to-valley ratio and amplitude of peak current can also be adjusted by changing the carrier concentration next to the double barriers.
Diluted magnetic semiconductor (Cd1−xMnxTe) Schottky diodes and field-effect transistors
Authors: Dreifus D. L. , Kolbas R. M. , Harper R. L. , Tassitino J. R. , Hwang S. , Schetzina J. F.
Published: July 2002

We report the first demonstration of electronic devices, Schottky diodes, and metal-semiconductor field-effect transistors, in a diluted magnetic semiconductor Cd1−xMnxTe. These devices were fabricated using n-type, indium-doped CdMnTe films grown by photoassisted molecular beam epitaxy on (100) CdTe and CdZnTe substrates. Epitaxial layers with carrier concentrations of 1×1017 cm−3 and electron mobilities as large as 720 cm2/V s at 120 K were used. The Schottky diodes have turn-on voltages of 0.8 V, idealities in the range between 1.27 and 1.7, and reverse breakdown voltages from 5.5 to 10.5 V reverse bias. The 100 μm gate length transistors have transconductances of 1 mS/mm.
EDEN-dependent translational repression of maternal mRNAs is conserved between
Xenopus
and
Drosophila
Authors: Ezzeddine Nader , Paillard Luc , Capri Michèle , Maniey Dominique , Bassez Thérèse , Aït-Ahmed Ounissa , Osborne H. Beverley
Published: July 2002

Translational control is a key level in regulating gene expression
in oocytes and eggs because many mRNAs are synthesized and stored
during oogenesis for latter use at various stages of oocyte maturation
and embryonic development. Understanding the molecular
mechanisms that underlie this translational control is therefore
crucial. Another important issue is the evolutionary conservation of
these mechanisms—in other words the determination of their universal
and specific aspects. We report here a comparative analysis of a
translational repression mechanism that depends on the EDEN
(
e
mbryo
d
eadenylation
e
leme
n
t) element. This small cis-acting
element, localized in the 3′ untranslated region of
c-mos
and
Eg
mRNAs, was shown to be
involved in a deadenylation process. We demonstrate here that in
Xenopus
embryos, mRNAs that contain an EDEN are
translationally repressed. Next, transgenic flies were used to study
the effect of the EDEN motif on translation in
Drosophila
oocytes. We show that this element also
causes the translational repression of a reporter gene in
Drosophila
demonstrating that the EDEN-dependent
translational repression is functionally conserved between
Xenopus
and
Drosophila
.
α-Thujone (the active component of absinthe): γ-Aminobutyric acid type A receptor modulation and metabolic detoxification
Authors: Höld Karin M. , Sirisoma Nilantha S. , Ikeda Tomoko , Narahashi Toshio , Casida John E.
Published: July 2002

α-Thujone is the toxic agent in absinthe, a liqueur popular in the 19th and early 20th centuries that has adverse health effects. It is also the active ingredient of wormwood oil and some other herbal medicines and is reported to have antinociceptive, insecticidal, and anthelmintic activity. This study elucidates the mechanism of α-thujone neurotoxicity and identifies its major metabolites and their role in the poisoning process. Four observations establish that α-thujone is a modulator of the γ-aminobutyric acid (GABA) type A receptor. First, the poisoning signs (and their alleviation by diazepam and phenobarbital) in mice are similar to those of the classical antagonist picrotoxinin. Second, a strain of
Drosophila
specifically resistant to chloride channel blockers is also tolerant to α-thujone. Third, α-thujone is a competitive inhibitor of [
3
H]ethynylbicycloorthobenzoate binding to mouse brain membranes. Most definitively, GABA-induced peak currents in rat dorsal root ganglion neurons are suppressed by α-thujone with complete reversal after washout. α-Thujone is quickly metabolized
in vitro
by mouse liver microsomes with NADPH (cytochrome P450) forming 7-hydroxy-α-thujone as the major product plus five minor ones (4-hydroxy-α-thujone, 4-hydroxy-β-thujone, two other hydroxythujones, and 7,8-dehydro-α-thujone), several of which also are detected in the brain of mice treated i.p. with α-thujone. The major 7-hydroxy metabolite attains much higher brain levels than α-thujone but is less toxic to mice and
Drosophila
and less potent in the binding assay. The other metabolites assayed are also detoxification products. Thus, α-thujone in absinthe and herbal medicines is a rapid-acting and readily detoxified modulator of the GABA-gated chloride channel.
A highly digestible sorghum mutant cultivar exhibits a unique folded structure of endosperm protein bodies
Authors: Oria Maria P. , Hamaker Bruce R. , Axtell John D. , Huang Chia-Ping
Published: July 2002

The endosperm of a sorghum mutant cultivar, with high
in vitro
uncooked and cooked protein digestibilities, was examined by transmission electron microscopy and α-, β-, and γ-kafirins (storage proteins) were localized within its protein bodies. Transmission electron microscopy micrographs revealed that these protein bodies had a unique microstructure related to high protein digestibility. They were irregular in shape and had numerous invaginations, often reaching to the central area of the protein body. Protein bodies from normal cultivars, such as P721N studied here, with much lower uncooked and cooked digestibilities are spherical and contain no invaginations. Immunocytochemistry results showed that the relative location of α- and β-kafirins within the protein bodies of the highly digestible genotype were similar to the normal cultivar, P721N. γ-Kafirin, however, was concentrated in dark-staining regions at the base of the folds instead of at the protein body periphery, as is typical of normal cultivars. The resulting easy accessibility of digestive enzymes to α-kafirin, the major storage protein, in addition to the increased surface area of the protein bodies of the highly digestible cultivar appear to account for its high
in vitro
protein digestibility.
Inorganic polyphosphate is essential for long-term survival and virulence factors in
Shigella
and
Salmonella
spp.
Authors: Kim Kwang-Seo , Rao Narayana N. , Fraley Cresson D. , Kornberg Arthur
Published: July 2002

The importance of inorganic polyphosphate (poly P) and poly P kinase (PPK), the enzyme principally responsible for its synthesis, has been established previously for stationary-phase survival of
Escherichia coli
and virulence in
Pseudomonas aeruginosa
. The gene (
ppk
) that encodes PPK is highly conserved among many bacterial pathogens, including
Shigella
and
Salmonella
spp. In view of the phylogenetic similarity of the enteropathogens and the frequency with which virulence factors are expressed in stationary phase, the
ppk
gene of pathogenic
Shigella flexneri
,
Salmonella enterica
serovar Dublin, and
Salmonella enterica
serovar typhimurium have been cloned and deleted. In some of these mutants lacking
ppk
, the phenotypes included features indicative of decreased virulence such as: (
i
) growth defects, (
ii
) defective responses to stress and starvation, (
iii
) loss of viability, (
iv
) polymyxin sensitivity, (
v
) intolerance to acid and heat, and (
vi
) diminished invasiveness in epithelial cells. Thus PPK may prove, as it has with
P. aeruginosa
, to be an attractive target for antibiotics, with low toxicity because PPK is not found in higher eukaryotes.
Identification of peptides from brain and pituitary of
Cpe
fat
/Cpe
fat
mice
Authors: Che Fa-Yun , Yan Lin , Li Hong , Mzhavia Nino , Devi Lakshmi A. , Fricker Lloyd D.
Published: July 2002

Cpe

fat

/Cpe

fat

mice have a naturally occurring point mutation within the
carboxypeptidase E gene that inactivates this enzyme, leading to an
accumulation of many neuroendocrine peptides containing C-terminal
basic residues. These processing intermediates can be readily purified
on an anhydrotrypsin affinity resin. Using MS to obtain molecular mass
and partial sequence information, more than 100 peptides have been
identified. These peptides represent fragments of 16 known secretory
pathway proteins, including proenkephalin, proopiomelanocortin,
protachykinins A and B, chromogranin A and B, and secretogranin II.
Many of the identified peptides represent previously uncharacterized
fragments of the precursors. For example, 12 of the 13 chromogranin
B-derived peptides found in the present study have not been previously
reported. Of these 13 chromogranin B-derived peptides, only five
contain consensus cleavage sites for prohormone convertases at both the
C and N termini. Two distinct chromogranin B-derived peptides result
from cleavage at Trp-Trp bonds, a site not typically associated with
neuropeptide processing. An RIA was used to confirm that one of these
peptides, designated WE-15, exists in wild-type mouse brain, thus
validating the approach to identify peptides in
Cpe

fat

/Cpe

fat

mice. These “orphan” peptides are candidate ligands for orphan G
protein-coupled receptors. In addition, the general technique of using
affinity chromatography to isolate endogenous substrates
from a mutant organism lacking an enzyme should be applicable to a wide
range of enzyme-substrate systems.
Adaptor FYB (Fyn-binding protein) regulates integrin-mediated adhesion and mediator release: Differential involvement of the FYB SH3 domain
Authors: Geng Liping , Pfister Stefan , Kraeft Stine-Kathrein , Rudd Christopher E.
Published: July 2002

Aggregation of the high-affinity IgE receptor (FcɛRI) on mast cells activates a tyrosine phosphorylation cascade that is required for adhesion and degranulation events leading to the release of histamine and other inflammatory mediators. The full range of intracellular mediators that regulate this process is unknown. Recent studies have identified a group of immune cell-specific adaptor proteins that include linker for activation of T-cell (LAT), SH2-domain-containing leukocyte protein (SLP-76), and Fyn-T-binding protein (FYB)/SLP-76-associated protein (SLAP). In this study, we demonstrate that FYB can up-regulate integrin-mediated adhesion to fibronectin and mediator release in RBL-2H3 mast cells. The regulation of these two events could be distinguished from each other by the requirement of the FYB SH3 domain in β-hexosaminidase release, but not adhesion, and the up-regulation of mediator release by FYB in nonadherent cells. FcɛRI aggregation increased FYB tyrosine phosphorylation, whereas confocal immunofluorescence microscopy showed that FYB colocalizes with F-actin in membrane ruffles and plaques. Our findings identify FYB as a regulator of integrin-mediated adhesion and degranulation events, which, in the case of mast cells, has potential applications to inflammatory and allergic responses.
Tyrosine phosphorylation of p97 regulates transitional endoplasmic reticulum assemblyin vitro
Authors: Lavoie Christine , Chevet Eric , Roy Line , Tonks Nicholas K. , Fazel Ali , Posner Barry I. , Paiement Jacques , Bergeron John J. M.
Published: July 2002

The ATPase associated with different cellular activities family member p97, associated p47, and the t-SNARE syntaxin 5 are necessary for the cell-free reconstitution of transitional endoplasmic reticulum (tER) from starting low-density microsomes. Here, we report that membrane-associated tyrosine kinase and protein-tyrosine phosphatase (PTPase) activities regulate tER assembly by stabilizing (PTPase) or destabilizing (tyrosine kinase) p97 association with membranes. Incubation with the PTPase inhibitor bpV(phen) inhibited tER assembly coincident with the enhanced tyrosine phosphorylation of endogenous p97 and its release from membranes. By contrast, the tyrosine kinase inhibitor, genistein, promoted tER formation and prevented p97 dissociation from membranes while increasing p97 association with the t-SNARE syntaxin 5. Purification of the endogenous tyrosine kinase activity from low-density microsomes led to the identification of JAK-2, whereas PTPH1 was identified as the relevant PTPase. The p97 tyrosine phosphorylation state is proposed to coordinate the assembly of the tER as a regulatory step of the early secretory pathway.
Yeast Dam1p has a role at the kinetochore in assembly of the mitotic spindle
Authors: Jones Michele H. , He Xiangwei , Giddings Thomas H. , Winey Mark
Published: July 2002

During mitosis, replicated chromosomes are separated to daughter cells by the microtubule-based mitotic spindle. Chromosomes attach to the mitotic spindle through specialized DNA/protein structures called kinetochores, but the mechanism of attachment is not well understood. We show here that the yeast microtubule-binding protein, Dam1p, associates physically and functionally with kinetochores, suggesting a role in kinetochore attachment to the spindle. An epitope-tagged version of Dam1p colocalizes with the integral kinetochore component Ndc10p/Cbf2p in immunofluorescence analysis of chromosome spreads. In addition, Dam1p is associated preferentially with centromeric DNA as shown by chromatin immunoprecipitation experiments, and this association depends on Ndc10p/Cbf2p. We also demonstrate genetic interactions between
DAM1
and
CTF19
or
SLK19
genes encoding kinetochore proteins. Although the defect caused by the
dam1
-
1
mutation leads to activation of the spindle checkpoint surveillance system and consequent persistence of sister chromatid cohesion, the metaphase arrest spindle abnormally elongates, resulting in virtually complete chromosome missegregation. Execution point experiments indicate that Dam1p has a role in formation of a metaphase spindle and in anaphase spindle elongation. Finally, we have observed that the protein encoded by the
dam1
-
1
allele becomes delocalized at the nonpermissive temperature, correlating with the subsequent onset of the mutant phenotype. Our studies are consistent with a role for Dam1p in attachment of sister chromatids through the kinetochore to the mitotic spindle before chromosome segregation.