bluuebunny/crossref_metadata_2025 huggingface dataset:
Emitter grading in AlGaAs/GaAs heterojunction bipolar transistor grown by metalorganic chemical vapor deposition
Authors: Taira K. , Takano C. , Kawai H. , Arai M.
Published: July 2002

The effect of emitter grading on the injection barrier of Al0.3Ga0.7As/GaAs heterojunction bipolar transistor grown by metalorganic chemical vapor deposition was studied. The barrier height for electrons injected from the emitter was determined from the temperature dependence of collector current. It has been directly confirmed that the barriers for graded heterojunction and GaAs homojunction are comparable. However, the grading enhanced the recombination at the emitter-base depletion region, which suggests that the hole confinement was reduced.
Resonant tunneling through a HgTe/Hg1−xCdxTe double barrier, single quantum well heterostructure
Authors: Reed M. A. , Koestner R. J. , Goodwin M. W.
Published: July 2002

Resonant tunneling has been demonstrated through a double barrier, single quantum well HgTe/Hg1−xCdxTe heterostructure for the first time. Negative differential resistance is observable at room temperature, exhibiting a 1.4:1 peak to valley tunnel current ratio. The observation provides direct evidence for the existence of the proposed intrinsic interface state.
Wide-gap boron-doped microcrystalline silicon nitride
Authors: Hasegawa S. , Segawa M. , Kurata Y.
Published: July 2002

Microcrystalline SiNx:H films were prepared by rf glow discharge of SiH4-B2H6-N2-H2 mixtures with the gas volume ratio of B2H6/SiH4=4.5×10−3. The volume fraction of the crystalline phase and the crystallite size decrease with an increase in N content x, and the films were amorphous at x above 0.2. The dark conductivity σd decreases and the optical gap Eg increases with x. The gap-state density is lowest at x near 0.2, where σd∼10−2–10−3/Ω cm (the activation energy is 0.1 eV) and Eg∼1.9 eV. These electrical properties are improved as compared with those for B-doped amorphous SiNx:H.
Determination of As and Ga planes by convergent beam electron diffraction
Authors: Liliental-Weber Z. , Parechanian-Allen L.
Published: July 2002

Convergent beam electron diffraction using either the (200) systematic row and/or the (011) zone axis was successfully applied to determine the crystal polarity in (011) GaAs samples. This method makes it possible to distinguish the stacking sequence of the As and Ga planes. The information existing in the 200 disk of the diffraction pattern is different, depending on whether a particular disk refers to the As or the Ga plane. Therefore, this method can be generally applied in transmission electron microscopy for in situ samples and without any chemical etching.
Ambient dependence of metal diffusion through a less-electronegative metal layer
Authors: Chang Chin-An , Yeh Helen L.
Published: July 2002

The diffusion of metals through a less-electronegative metal layer is studied for its dependence on ambient gases. When the diffusion is essentially one directional with little interdiffusion, the observed ambient dependence is in agreement with that described by the surface potential model proposed earlier. An enhanced diffusion is expected when the ambient increases the work function of the less-electronegative metal through which the diffusion of the more-electronegative one is studied. This has been observed for the diffusion of Au and Cu across the intermediate Ni layer in the Au/Ni/Cu structure under both oxygen and hydrogen, and for the outdiffusion of Cu through Ni in the Ni/Cu structure by oxygen.
Semiconducting/semi-insulating reversibility in bulk GaAs
Authors: Look D. C. , Yu P. W. , Theis W. M. , Ford W. , Mathur G. , Sizelove J. R. , Lee D. H. , Li S. S.
Published: July 2002

Bulk, liquid-encapsulated Czochralski GaAs may be reversibly changed from semiconducting (ρ∼1 Ω cm) to semi-insulating (ρ∼107 Ω cm) by slow or fast cooling, respectively, following a 5 h, 950 °C soak in an evacuated quartz ampoule. This effect has been studied by temperature-dependent Hall-effect, photoluminescence, infrared absorption, mass spectroscopy, and deep level transient spectroscopy measurements. Except for boron, the samples are very pure, with carbon and silicon concentrations less than 3×1014 cm−3. Donor and acceptor concentrations, on the other hand, are in the mid 1015 cm−3 range, which means that the compensation is primarily determined by native defects, not impurities. A tentative model includes a donor at EC−0.13 eV, attributed to VAs−AsGa, and an acceptor at EV+0.07 eV, attributed to VGa−GaAs.
Dangling bond electron spin-lattice relaxation in rf-sputtered hydrogenated amorphous silicon and silicon carbide
Authors: Dey S. , Torgeson D. R. , Barnes R. G.
Published: July 2002

Electron spin resonance methods have been used to measure the temperature dependence of the spin-lattice relaxation time T1 of dangling bond electrons in hydrogenated amorphous silicon and silicon carbide samples prepared by radio frequency sputtering. The T1 measurements were made by a combination of continuous-wave absorption mode saturation and periodic adiabatic passage methods over the temperature range 100–400 K, yielding T−11∝T2 behavior consistent with relaxation by two-level systems.
Continuous control of coherence length in separately pumped (AlGa)As lasers
Authors: Yamamoto Saburo , Hijikata Toshiki
Published: July 2002

Continuous control of coherence length is realized in the output power region of 3–5 mW by changing the current flowing into the loss region of separately pumped (AlGa)As lasers. The controllable saturable absorption makes lasing spectra multimode and broadens the linewidth of an individual laser mode up to 2.5 Å through self-pulsation. The threshold current of the laser is 60–80 mA. The lasing wavelength is around 780 nm.
V-groove distributed feedback laser for 1.3–1.55 μm operation
Authors: Temkin H. , Dolan G. J. , Wilt D. P. , Logan R. A. , Lahtinen J. A.
Published: July 2002

We describe a V-groove distributed feedback laser operating at λ=1.5 μm. A second-order diffraction grating has been defined by electron beam writing and transferred using ion beam milling after the crystal growth was completed. A single longitudinal mode operation with a mode rejection ratio larger than 5000:1 has been obtained under modulation rate of 1 GHz. The techniques used in this work can be applied to other types of buried heterostructure lasers.
Activated carrier density profile and scattering rate measurements of implanted and annealed silicon using infrared attenuated total reflection
Authors: Young Jeff F. , Jensen H. R. , Simard-Normandin Martine
Published: July 2002

A nondestructive infrared attenuated total reflection technique for measuring activated carrier density profiles and elastic scattering rates of ion implanted and annealed semiconductor wafers is described. The results obtained using this technique on annealed B and BF2 implanted Si wafers are presented and compared with the respective secondary ion mass spectroscopy and spreading resistance profiles.
Amorphous thin films of Zn3P2: Preparation and characterization
Authors: Deiss J. L. , Elidrissi B. , Robino M. , Weil R.
Published: July 2002

We report about the preparation and characterization of amorphous thin films of Zn3P2. The optical properties of these films are given and compared to those of polycrystalline thin films.
Function of cobalt and platinum on p-InP in the photoevolution of hydrogen from alkaline solutions
Authors: Goodman C. E. , Wessels B. W.
Published: July 2002

The role of metal deposits (e.g., Co and Pt) on p-InP photocathodes in the photoevolution of hydrogen from alkaline solutions was studied. The deposition of Co or Pt on a p-InP photocathode was found to increase the solar-to-chemical efficiency by more than an order of magnitude. Photocurrent-voltage curves before and after metal deposition have shown that the open-circuit voltage remains nearly constant at 0.65–0.77 V. Under a reverse bias of 0.1–0.6 V the presence of metal islands has a large effect on cell performance by improving the short-circuit current and fill factor. This indicates that the deposited metals act as classical catalysts on photocathodes in alkaline hydrogen generating photoelectrochemical cells.
HgTe-CdTe superlattices grown on GaAs (100) oriented substrates by molecular beam epitaxy
Authors: Ballingall J. M. , Leopold D. J. , Wroge M. L. , Peterman D. J. , Morris B. J. , Broerman J. G.
Published: July 2002

HgTe-CdTe superlattices have been grown on GaAs (100) substrates by molecular beam epitaxy. X-ray diffraction analysis shows the superlattices to be single crystalline with well defined periods. Temperature-dependent infrared absorbance measurements indicate that the superlattices have band gaps with positive temperature coefficients. The band-gap temperature dependence is in semiquantitative agreement with theoretical calculations.
Identification of Rayleigh and ‘‘breathing’’ modes for a cylindrical wire
Authors: Molinero I. , de Billy M. , Quentin G.
Published: July 2002

We describe an experimental confirmation of the existence of Rayleigh and ‘‘breathing’’ modes in the case of an infinite elastic wire immersed in water. The resonance isolation and identification method initiated by G. Maze and J. Ripoche [Rev. Phys. Appl. 18, 319 (1983)] is used. The different parameters related to the use of this method are adjusted to take into account the dimensions of the target and the attenuation of each mode. The polar diagrams of the amplitude of the resonating part of the received signal confirm the existence of (n,1) and (0,1) modes.
Effects of helium upon electron beam excitation of N+2 at 391.4 and 427.8 nm
Authors: Brake M. L. , Gilgenbach R. M. , Lucey R. F. , Pearce K. , Repetti T. , Sojka P. E.
Published: July 2002

Relativistic electron beam interactions with very small ratios of nitrogen to helium (10−1–10−4) have been found to produce extremely large N+2(B2Σ+u–X2Σ+g) intensities at 391.4 and 427.8 nm, compared to line intensities originating from helium. These results occurred in the total pressure regime of 0.1–500 Torr. The pressure scaling results presented here are inconsistent with previously proposed kinetic mechanisms for the N+2 laser pumped by helium. With a simple model of the chemical kinetics, we show that this effect is due to the collisional transfer of energy between excited states of helium atoms and the ground state of N+2.
Fluorine-enhanced photo-oxidation of silicon under ArF excimer laser irradiation in an O2+NF3 gas mixture
Authors: Morita M. , Aritome S. , Tanaka T. , Hirose M.
Published: July 2002

We have studied fluorine-enhanced oxidation of silicon in an O2+NF3 gas mixture under ArF excimer laser (193 nm) irradiation. An oxide layer of more than 60 Å can be grown even at 400 °C for 20 min at NF3 gas concentrations less than 0.5%. A considerable enhancement of the oxidation rate by laser irradiation originates in the catalytic effect of fluorine radicals produced by photodissociation of NF3 molecules not only in the gas phase, but also on the oxide surface.
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u grown-in selective contacts to n-i-p-i doping superlattice crystals using molecular beam epitaxial growth through a shadow mask
Authors: Döhler G. H. , Hasnain G. , Miller J. N.
Published: July 2002

Highly selective n- and p-type contacts to GaAs doping superlattices have been achieved by using molecular beam epitaxial growth through a silicon shadow mask to form interdigital grown-in contacts. Low contact resistance, excellent diode characteristics, and efficient lateral injection electroluminescence are obtained.
Vacancy defects in as-grown and neutron irradiated GaP studied by positrons
Authors: Dlubek G. , Brümmer O. , Polity A.
Published: July 2002

Positron lifetime and Doppler-broadening measurements have been used to study vacancy defects in n-type GaP. Vacancies in the P sublattice with a concentration of some 1017 cm−3 were observed in as-grwon GaP. The vacancies disappear during annealing at 500–800 °C. In neutron-irradiated GaP positrons are trapped by Ga vacancies which anneal out in two stages situated at 300–550 °C and 550–700 °C.
Lateral solid phase epitaxy of Si over SiO2 patterns and its application to silicon-on-insulator transistors
Authors: Sasaki Masayoshi , Katoh Teruo , Onoda Hiroshi , Hirashita Norio
Published: July 2002

Lateral solid phase epitaxy (L-SPE) of vacuum deposited amorphous Si over SiO2 patterns for various substrate orientation and growth direction has been investigated and applied to fabrication of thin-film transistors on SiO2. It has been confirmed that the L-SPE growth length depends strongly on both substrate orientation and growth direction. The maximum growth length of about 7 μm has been obtained in the L-SPE toward 〈100〉 direction on a (001) substrate. n-channel and p-channel transistors on the L-SPE layer have been developed and successfully fabricated for the first time. Channel mobilities of 380 cm2/V s for n-channel transistors and 150 cm2/V s for p-channel transistors have been obtained.
Low threshold, high T0 InGaAsP/InP 1.3 μm lasers grown on p-type InP substrates
Authors: Hasenberg T. C. , Garmire E.
Published: July 2002

InGaAsP lasers have typically exhibited an undesirably sensitive temperature dependence of threshold current. In this letter we propose and demonstrate a new epitaxial layer structure, utilizing two identical active regions grown on a p-type substrate, which overcomes this problem through improved carrier confinement. By growing both active regions with the same liquid phase epitaxial melt, low threshold (2–2.5 kA/cm2) and high T0 (106–180 K) have been achieved for the first time in gain-guided 1.3 μm lasers.
Photoexcited transport in GaAs/AlAs quantum wells
Authors: Collins R. T. , Klitzing K. v. , Ploog K.
Published: July 2002

We present the results of a study of the transport of optically excited carriers perpendicular to weakly coupled GaAs/AlAs multiple quantum wells imbedded in the depletion region of a p-i-n photodiode. At temperatures above 120 K the photocurrent was thermally activated. For lower temperatures the photocurrent decreased as temperature was increased. Wavelength-dependent negative differential resistance regions were present in the reverse bias region of the photoexcited current voltage (I-V) curve as a result of the Stark shifts of the lowest energy heavy hole (h1) and light hole (l1) excitons. Additional wavelength independent structure was also visible in the photoexcited I-V curves.
Phase measurement of laser diode array radiation
Authors: Yaeli J.
Published: July 2002

The phase of either near-field or far-field distribution function of laser diode arrays can be measured by using the technique of shearing interferometry. Two generations of shearing interferometers are described and typical results using them are shown. For one gain-guided laser array the phase of the near-field distribution is shown to be a periodic function whose period is twice the distance between stripes. An example of phase measurement of the far-field distribution is shown.
Voltage-controlled optical bistability associated with two-dimensional exciton in GaAs-AlGaAs multiple quantum well lasers
Authors: Tarucha Seigo , Okamoto Hiroshi
Published: July 2002

Voltage-controlled optical bistable laser operation is demonstrated for the first time using nonlinear optical absorption of two-dimensional excitons in a GaAs-AlGaAs multiple quantum well (MQW) laser. The laser used here is the conventional MQW laser diode but with tandem electrode configuration. The L-I curve of light output as a function of current injected into one segment of electrodes can be changed by a bias voltage applied to the other segment of electrodes. At the onset of laser oscillation, a hysteresis loop appears, the shape of which depends strongly on the applied bias voltage. This bistability is ascribed to the nonlinear absorption of two-dimensional excitons.
Hydrogen-free SiN films deposited by ion beam sputtering
Authors: Kitabatake Makoto , Wasa Kiyotaka
Published: July 2002

A hydrogen-free SiN film was deposited by ion beam sputtering at low temperature. The substrate surface was almost parallel to the ion beam. The deposited SiN film exhibited high chemical endurance, high thermal endurance, and low density of memory traps.
‘‘New donors’’ in silicon: A quantum well controlled conductivity
Authors: Henry A. , Pautrat J. L. , Vendange P. , Saminadayar K.
Published: July 2002

The first stages of the formation of the so called ‘‘new donors’’ is studied by annealing initially n-type Czochralski silicon at 580 °C for 24–360 h. The analysis of electrical properties using the admittance spectroscopy technique reveals that the freezing of carriers is controlled by an activation energy of 20 meV, and a discrete level is detected at 19 meV. These effects are tentatively ascribed to levels localized within quantum wells surrounding small positively charged oxide precipitates.
Evidence of strong Auger recombination in semiconductor-doped glasses
Authors: de Rougemont F. , Frey R. , Roussignol P. , Ricard D. , Flytzanis C.
Published: July 2002

Intracavity nearly degenerate four-wave mixing has been used together with transmission measurements to evidence the important role played by Auger recombination in the relaxation rate of electron-hole pairs in semiconductor-doped glasses pumped by high laser intensities. Results show a shortening by a factor of 100 of the recombination carrier lifetime when the laser intensity is near damage threshold.
Transmission electron microscope study of the formation of Ni2Si and NiSi on amorphous silicon
Authors: Aboelfotoh M. O. , Tawancy H. M. , d’Heurle F. M.
Published: July 2002

The reaction of very thin (0.5–20 nm) layers of Ni with amorphous Si has been investigated by means of transmission electron microscopy and diffraction. The experiment, which is directly parallel to a previous study of similar samples prepared with Pd and Pt, has led to different observations. With Ni it is found that an amorphous Ni-Si solution is formed first, and that silicide formation, at temperatures which decrease with the amount of deposited Ni, results from the crystallization of that amorphous phase. With Pt and Pd microcrystalline silicides had been observed immediately.
Critical resolved shear stress measurements for silicon-doped GaAs single crystals
Authors: Bourret E. D. , Tabache M. G. , Elliot A. G.
Published: July 2002

The critical resolved shear stress of GaAs single crystals doped with silicon was directly measured using dynamical compression tests at high temperatures. At the melting point the critical resolved shear stress is 0.032 and 0.027 kg/mm2 for crystals doped with 1.5×1018 and 3×1018 cm−3 silicon, respectively. These values are lower than that for undoped GaAs. This reinforces our earlier conclusion that solid solution hardening and the reduction of crystallographic glide is not the only mechanism by which dopants reduce the formation of dislocations during the growth of single crystals from the melt.
Excitonic and electron-hole contributions to the spontaneous recombination rate of injected charge carriers in GaAs-GaAlAs multiple quantum well lasers at room temperature
Authors: Böttcher E. H. , Ketterer K. , Bimberg D. , Weimann G. , Schlapp W.
Published: July 2002

The spontaneous recombination rate at room temperature of GaAs-GaAlAs multiple quantum well lasers is investigated at carrier densities of 2×1017–1.7×1018 cm−3 using the small-signal electroluminescence technique. A monomolecular, partly excitonic, and a bimolecular term contribute to the recombination rate R(n)=An+Bn2, where A and B are 2.08×108 s−1 and 1.5×10−10 cm3 s−1, respectively, for a well width Lz =7.5 mm. The radiative and nonradiative contributions to the linear recombination term, A=1/τr+1/τnr, are determined as τr =8 ns and τnr =12 ns from the dependence of the spontaneously emitted light power on the injection current density. In addition the carrier density dependence of the internal quantum efficiency is reported and ηi is found to be close to unity. The results demonstrate that even at fairly high excitation levels, excitonic enhancement of radiative recombination in high quality multiple quantum well structures is an important factor.
Characterization of multiple i
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u junctions in Si-TaSi2 composites by charge-collection microscopy
Authors: Yacobi B. G. , Ditchek B. M.
Published: July 2002

The depletion zones of in situ metal-semiconductor junctions in a new class of electronic materials, Si-TaSi2 eutectic composites, which are comprised of aligned TaSi2 rods permeating a Si matrix, are characterized using charge-collection scanning electron microscopy. The increase in the depletion width of the individual Schottky junctions as a function of the reverse bias is measured. Results are in agreement with those predicted by a model of cylindrical junctions in a Si matrix. The observed overlap of the depletion zones around adjacent rods suggests possible field-effect transistor switch applications for this material.
Supplemental multilevel interconnects by laser direct writing: Application to GaAs digital integrated circuits
Authors: Black Jerry G. , Doran Scott P. , Rothschild Mordechai , Ehrlich Daniel J.
Published: July 2002

A nonperturbing sequence of laser direct-writing processes is described for applying supplemental multilevel interconnects on partially or fully fabricated circuits. The approach adds multiple levels of laser direct-written tungsten metallization and is demonstrated here for the assembly of a simple latch circuit on a standard GaAs digital test chip. Principal applications are for subsystem verification, device testing, restructuring, and fault avoidance on Si and GaAs circuits.
Hydrogen evolution in aluminum plasma deposited silicon nitride layered structures
Authors: Kikkawa T. , Watanabe H. , Murata T.
Published: July 2002

Blisters and voids in aluminum plasma enhanced chemical vapor deposited silicon nitride layered structures are studied. Results from evolved gas analysis have indicated release of hydrogen. Hydrogen evolution from silicon/nitride/aluminum/phosphosilicate glass/silicon layered structure showed a sharp peak in the temperature range between 580 and 660 °C. The results indicated that the accumulation of high pressure hydrogen gas evolved from the silicon nitride film and trapped at the aluminum silicon nitride interface could be the most dominant mechanism of the blister and void formation.
Intersubband transitions in GaAs-AlxGa1−xAs modulation-doped superlattices
Authors: Nakayama M. , Kuwahara H. , Kato H. , Kubota K.
Published: July 2002

We have investigated infrared absorptions between electron subbands in GaAs-AlxGa1−xAs modulation-doped superlattices with constant layer thicknesses (70 Å for the GaAs layer and 180 Å for the AlxGa1−xAs layer) and a wide Al concentration range from 0.3 to 0.7. Sharp resonance absorptions from the ground state to the first excited state were detected in all samples. The transition energy increases from 130 to 170 meV as the Al concentration increases. From the observed transition energies (subband spacing) we estimate that the conduction-band discontinuity is around 63% of the difference between the direct band-gap energy of GaAs and that of AlxGa1−xAs in the Al concentration range used here.
Reflection high-energy electron diffraction intensity oscillation study of InGaAs and InAlAs on InP: Application to pseudomorphic heterostructures
Authors: Lievin J.-L. , Fonstad C. G.
Published: July 2002

This letter reports the first reflection high-energy electron diffraction intensity oscillation study of strained, pseudomorphic In1−xGaxAs and In1−yAlyAs grown by molecular beam epitaxy on InP substrates. Strain-induced effects are studied over a broad range (up to 3%) of positive and negative mismatch. During mismatched growth, an abnormal damping of the oscillation intensity is seen which leads to the identification of a threshold thickness above which monolayer by monolayer growth no longer occurs during uninterrupted growth. This thickness is about a factor of 5 smaller than recently calculated and measured values of the critical thickness at which dislocations appear. This observation is believed to have important implications for the growth of pseudomorphic devices.
Growth of p-type ZnSe:Li by molecular beam epitaxy
Authors: Cheng H. , DePuydt J. M. , Potts J. E. , Smith T. L.
Published: July 2002

Molecular beam epitaxy has been used to grow Li-doped ZnSe on (100)GaAs substrates, resulting in material which exhibits a low-temperature photoluminescence spectrum dominated by emission from acceptor-bound excitons, with no evidence of emission from residual donors. Electrical measurements on these films indicate that, while the resistivity of the material is high, the majority carriers are holes. This is the first report of p-type conversion in ZnSe grown by molecular beam epitaxy.
Hollow cathode plasma assisted chemical vapor deposition of diamond
Authors: Singh B. , Mesker O. R. , Levine A. W. , Arie Y.
Published: July 2002

A method which combines thermal and plasma dissociation of a methane/hydrogen gas mixture for low-pressure chemical vapor deposition of diamond is described. A hot, thin-walled, refractory metal cathode is used to generate a high-current, low-voltage discharge. The substrates are located on the anode and immersed in the plasma emanating from the cathode tip. No auxiliary substrate heating is employed. Polycrystalline diamond particles and films are obtained on silicon (100) and molybdenum substrates at growth rates of 1–3 μm/h.
Very high purity InP epilayer grown by metalorganic chemical vapor deposition
Authors: Razeghi M. , Maurel Ph. , Defour M. , Omnes F. , Neu G. , Kozacki A.
Published: July 2002

Very high purity InP epilayers have been grown by low-pressure metalorganic chemical vapor deposition growth technique using trimethylindium as In source. Residual doping levels as low as 3×1013 cm−3 , with Hall mobility as high as 6000 cm2  V−1  s−1 at 300 K and 200 000 cm2  V−1  s−1 at 50 K have been measured. These results and photoluminescence at 2 K showed that it is the purest InP epilayer ever reported in the literature, with zero compensation ratio.
Polarity determination in compound semiconductors by channeling: Application to heteroepitaxy
Authors: Chami A. C. , Ligeon E. , Danielou R. , Fontenille J.
Published: July 2002

A direct method for polarity determination of the compound semiconductor (111) face is presented. Channeling shows that the (111)B CdTe face (or Te face) corresponds to the best (111) face for further II-VI epitaxy. Epitaxial relationships are also determined for (111)CdTe/(001) GaAs. It is determined that the (111)CdTe layer also ends up on a B face. The bond directions of Ga and As atoms are determined with respect to those of Te and Cd. These informations suggest a mechanism for such an epitaxial growth.
Very low threshold buried heterostructure quantum well lasers by laser-assisted disordering
Authors: Epler J. E. , Thornton R. L. , Paoli T. L.
Published: July 2002

Data are presented on high-quality buried heterostructure lasers fabricated by laser-assisted disordering of GaAs-AlGaAs quantum well heterostructures. The typical cw threshold current is 4 mA and the maximum power output is 27 mW. The devices exhibit single fundamental mode operation with 34 dB attenuation of longitudinal side modes.
Influence of Si film thickness on growth enhancement in Si lateral solid phase epitaxy
Authors: Moniwa Masahiro , Kusukawa Kikuo , Murakami Eiichi , Warabisako Terunori , Miyao Masanobu
Published: July 2002

Lateral solid phase epitaxial growth (L-SPE) of Si on SiO2 film was investigated as a function of deposited amorphous Si (a-Si) film thickness. Both the L-SPE rate and the annealing time necessary for {111} facet formation increased with film thickness. As a result, a large L-SPE length (9 μm) under {110} facet growth was obtained for a 1.6-μm-thick film sample. Above the critical film thickness (>2 μm), crack formation in a-Si films was observed during deposition. This indicates that intrinsic stresses play an important role in this growth enhancement.
Dislocation reduction by impurity diffusion in epitaxial GaAs grown on Si
Authors: Deppe D. G. , Holonyak N. , Hsieh K. C. , Nam D. W. , Plano W. E. , Matyi R. J. , Shichijo H.
Published: July 2002

Data are presented showing that low-temperature Zn diffusion (680 °C) is effective in reducing the dislocation density in epitaxial GaAs grown on Si. The GaAs-on-Si is analyzed using both cross-sectional and plan-view transmission electron microscopy. For comparison, simple thermal annealing of the GaAs-on-Si at higher temperature (850 °C) is also performed and analyzed. The reduction in the dislocation density that occurs with Zn diffusion is suggested to be due to the increased concentration of point defects generated during the Zn diffusion, resulting in enhanced dislocation climb. This mechanism is consistent with impurity-induced layer disordering, via Zn diffusion, in AlxGa1−xAs-GaAs heterostructures.
Electrical properties of Si(100) films doped with low-energy (≤150 eV) Sb ions during growth by molecular beam epitaxy
Authors: Fons P. , Hirashita N. , Markert L. C. , Kim Y.-W. , Greene J. E. , Ni W.-X. , Knall J. , Hansson G. V. , Sundgren J.-E.
Published: July 2002

A low-energy ultrahigh-vacuum compatible ion gun with single-grid optics was used to provide accelerated Sb ion doping during the growth of Si(100) by molecular beam epitaxy (MBE). The incorporation probability of accelerated Sb in MBE Si films grown at 800 °C with an ion acceleration potential of 150 eV was near unity, more than four orders of magnitude higher than for thermal Sb. The films exhibited complete dopant substitutionality and temperature-dependent electron mobilities were equal to the best reported bulk Si values for Sb concentrations up to 2×1019 cm−3, more than an order of magnitude higher than obtainable by thermal Sb doping during Si MBE. Transmission electron microscopy examination of all films showed no evidence of dislocations or other extended defects.
Growth and rapid thermal annealing of AlGaAs/InGaAs pseudomorphic modulation-doped structures
Authors: Kesan V. P. , Dodabalapur A. , Neikirk D. P. , Streetman B. G.
Published: July 2002

We have examined molecular beam epitaxial growth conditions required to obtain good surface morphology and excellent electrical properties from normal and inverted pseudomorphic Al0.15Ga0.85As/InyGa1−yAs (y=0.15–0.20) high electron mobility transistor (HEMT) structures. For the same spacer layer thickness, inverted pseudomorphic HEMT’s exhibit significantly higher sheet carrier concentrations than corresponding normal HEMT’s. In addition, we report the first study of the influence of rapid thermal annealing on the electrical properties of pseudomorphic HEMT’s, using both close-contact and arsenic overpressure annealing. An improvement in two-dimensional electron gas (2-DEG) mobility with increasing anneal temperatures that is consistent with reduction in strain in the InGaAs channel is observed. This study also shows that pseudomorphic HEMT’s exhibit excellent thermal stability with no degradation in the electrical characteristics of the device for anneal temperatures up to 800 °C.
Zn1−xCoxSe: A new diluted magnetic semiconductor grown by molecular beam epitaxy
Authors: Jonker B. T. , Krebs J. J. , Prinz G. A.
Published: July 2002

We have grown single-crystal epilayers of the new diluted magnetic semiconductor Zn1−xCox Se on GaAs(001) substrates by molecular beam epitaxy. X-ray θ-2θ and double-crystal rocking curve measurements were used to obtain the variation in lattice parameter and evaluate crystalline quality. Temperature-dependent electron paramagnetic resonance and superconducting quantum interference device magnetometry data confirm the substitutional nature of the Co2+ in the zinc site and paramagnetic behavior.
Short-period (AlAs)(GaAs) superlattice lasers grown by molecular beam epitaxy
Authors: Blood P. , Fletcher E. D. , Foxon C. T.
Published: July 2002

We have used short-period all-binary (AlAs)(GaAs) superlattices with layers as thin as three monolayers to synthesize the barrier and cladding regions of GaAs quantum well lasers grown by molecular beam epitaxy. By studying the threshold current of single- and double-well devices as a function of cavity length and temperature, we conclude that the optical scattering losses are very low, that the gain-current characteristics are similar to alloy barrier devices, and that there is evidence for current leakage by recombination in the barriers.
Siva-1 binds to and inhibits BCL-XL-mediated protection against UV radiation-induced apoptosis
Authors: Xue Li , Chu Fei , Cheng Yuan , Sun Xiangjie , Borthakur Alip , Ramarao Manjunath , Pandey Pramod , Wu Mei , Schlossman Stuart F. , Prasad Kanteti V. S.
Published: July 2002

We previously cloned Siva-1 by using the cytoplasmic tail of CD27, a member of the tumor necrosis factor receptor family, as the bait in the yeast two-hybrid system. The Siva gene is organized into four exons that code for the predominant full-length Siva-1 transcript, whereas its alternate splice form, Siva-2, lacks exon 2 coding sequence. Various groups have demonstrated a role for Siva-1 in several apoptotic pathways. Interestingly, the proapoptotic properties of Siva-1 are lacking in Siva-2. The fact that Siva-1 is partly localized to mitochondria despite the absence of any mitochondrial targeting signal, it harbors a 20-aa-long putative amphipathic helical structure that is absent in Siva-2, and that its expression is restricted to double-positive (CD3+, CD4+, CD8+) thymocytes like BCL-XL, prompted us to test for a potential interaction between Siva-1 and BCL-XL. Here, we show that Siva-1 binds to and inhibits BCL-XL-mediated protection against UV radiation-induced apoptosis. Indeed, the unique amphipathic helical region (SAH) present in Siva-1 is required for its binding to BCL-XLand sensitizing cells to UV radiation. Natural complexes of Siva-1/BCL-XLare detected in HUT78 and murine thymocyte, suggesting a potential role for Siva-1 in regulating T cell homeostasis.
The embryonic transcription factor stage specific activator protein contains a potent bipartite activation domain that interacts with several RNA polymerase II basal transcription factors.
Authors: DeFalco J , Childs G
Published: July 2002

Stage specific activator protein (SSAP) is a member of a newly discovered class of transcription factors that contain motifs more commonly found in RNA-binding proteins. Previously, we have shown that SSAP specifically binds to its recognition sequence in both the double strand and the single strand form and that this DNA-binding activity is localized to the N-terminal RNA recognition motif domain. Three copies of this recognition sequence constitute an enhancer element that is directly responsible for directing the transcriptional activation of the sea urchin late histone H1 gene at the midblastula stage of embryogenesis. Here we show that the remainder of the SSAP polypeptide constitutes an extremely potent bipartite transcription activation domain that can function in a variety of mammalian cell lines. This activity is as much as 3 to 5 times stronger than VP16 at activating transcription and requires a large stretch of amino acids that contain glutamine-glycine rich and serine-threonine-basic amino acid rich regions. We present evidence that SSAP's activation domain shares targets that are also necessary for activation by E1a and VP16. Finally, SSAP's activation domain is found to participate in specific interactions in vitro with the basal transcription factors TATA-binding protein, TFIIB, TFIIF74, and dTAF(II) 110.
In vivo examination of membrane protein localization and degradation with green fluorescent protein.
Authors: Hampton R Y , Koning A , Wright R , Rine J
Published: July 2002

To test the utility of green fluorescent protein (GFP) as an in vivo reporter protein when fused to a membrane domain, we made a fusion protein between yeast hydroxymethylglutaryl-CoA reductase and GFP. Fusion proteins displayed spatial localization and regulated degradation consistent with the native hydroxymethylglutaryl-CoA reductase proteins. Thus, GFP should be useful in the study of both membrane protein localization and protein degradation in vivo.
Old World fruitbat phylogeny: Evidence for convergent evolution and an endemic African clade
Authors: Hollar Laura J. , Springer Mark S.
Published: July 2002

Knud Andersen (1912,
Catalogue of the Chiroptera in the Collections of the British Museum: I. Megachiroptera
, British Museum of Natural History, London) divided Old World fruitbats (family Pteropodidae) into the rousettine, cynopterine, epomophorine, eonycterine, and notopterine sections. The latter two sections comprise the subfamily Macroglossinae; members of this subfamily exhibit specializations for nectarivory (e.g., elongated, protrusible, brushy tongues) and cluster together in cladistic analyses based on anatomical characters. Other evidence, including single-copy DNA hybridization, suggests that macroglossines are either paraphyletic or polyphyletic; this implies that adaptations for pollen and nectar feeding evolved independently in different macroglossine lineages or were lost in nonmacroglossines after evolving in a more basal common ancestor. Hybridization data also contradict Andersen’s phylogeny in providing support for an endemic African clade that includes representatives of three of Andersen’s sections. Here, we present complete mitochondrial 12S rRNA and valine tRNA gene sequences for 20 pteropodids, including representatives of all of Andersen’s sections, and examine the aforementioned controversies. Maximum likelihood, minimum evolution, and maximum parsimony analyses all contradict macroglossine monophyly and provide support for an African clade that associates
Megaloglossus
and
Lissonycteris
and those two with
Epomophorus
. In conjunction with the DNA hybridization results, there are now independent lines of molecular evidence suggesting: (
i
) convergent evolution of specializations for nectarivory, at least in
Megaloglossus
versus other macroglossines, and (
ii
) a previously unrecognized clade of endemic Africa taxa. Estimates of divergence time based on 12S rRNA and DNA hybridization data are also in good agreement and suggest that extant fruitbats trace back to a common ancestor 25 million to 36 million years ago.
Expression of an
Arabidopsis
plasma membrane aquaporin in
Dictyostelium
results in hypoosmotic sensitivity and developmental abnormalities
Authors: Chaumont François , Loomis William F. , Chrispeels Maarten J.
Published: July 2002

The
rd28
gene of
Arabidopsis thaliana
encodes a water channel protein, or aquaporin, of the plasma membrane. A construct in which transcription of the
rd28
cDNA is controlled by the
Dictyostelium actin15
promoter was transformed into
Dictyostelium discoideum
cells. Transformants contained RD28 protein in their plasma membranes. When shifted to a low-osmotic-strength buffer, cells expressing
rd28
swelled rapidly and burst, indicating that the plant aquaporin allowed rapid water entry in the amoebae. The rate of osmotic lysis was a function of the osmotic pressure of the buffer. We also selected transformants in which the expression of the
rd28
cDNA is driven by the promoter of the prespore
cotB
gene. These transformants accumulated
rd28
mRNA uniquely in prespore cells. In low-osmotic-strength buffer, the
cotB::rd28
cells aggregated and formed normally proportioned slugs but failed to form normal fruiting bodies. The number of spores was reduced 20-fold, and the stalks of the fruiting bodies were abnormally short. The consequences of expressing RD28 in prespore cells could be partially overcome by increasing the osmolarity of the medium. Under these conditions, the
cotB::rd28
cells formed fruiting bodies of more normal appearance, and the number of viable spores increased slightly. Because prespore cells have to shrink and dehydrate to form spores, it was not unexpected that expression of an aquaporin would disrupt this process, but it was surprising to find that stalk differentiation was also affected by expression of
rd28
in prespore cells. It appears that osmotic stress on prespore cells alters their ability to signal terminal differentiation in prestalk cells. The results provide independent confirmation that plant aquaporins can function in the cells of other organisms, and that
D. discoideum
can be used to study the properties of these water channels.
Anteroposterior neural tissue specification by activin-induced mesoderm
Authors: Green Jeremy B. A. , Cook T. Les , Smith J. C. , Grainger Robert M.
Published: July 2002

The transforming growth factor β superfamily member, activin, is able to induce mesodermal tissues in animal cap explants from
Xenopus laevis
blastula stage embryos. Activin can act like a morphogen of the dorsoventral axis in that lower doses induce more ventral, and higher doses more dorsal, tissue types. Activin has also previously been reported to induce neural tissues in animal caps. From cell mixing experiments it was inferred that this might be an indirect effect of induced mesoderm signaling to uninduced ectoderm. Here we demonstrate directly that neural tissues do indeed arise by the action of induced mesoderm on uninduced ectoderm. Dorsal mesoderm is itself subdivided into posterior and anterior domains
in vivo
, but this had not been demonstrated for induced mesoderm. We therefore tested whether different concentrations of activin recreate these different anteroposterior properties as well. We show that the anteroposterior positional value of induced mesoderm, including its neuroinductive properties, depends on the dose of activin applied to the mesoderm, with lower doses inducing more posterior and higher doses giving more anterior markers. We discuss the implications of these results for patterning signals and the relationship between anteroposterior and dorsoventral axes.
Neuronal nicotinic threonine-for-leucine 247 α
7
mutant receptors show different gating kinetics when activated by acetylcholine or by the noncompetitive agonist 5-hydroxytryptamine
Authors: Palma E. , Maggi L. , Eusebi F. , Miledi R.
Published: July 2002

Mutation of the highly conserved leucine residue (Leu-247) converts 5-hydroxytryptamine (5HT) from an antagonist into an agonist of neuronal homomeric α
7
nicotinic acetylcholine receptor expressed in
Xenopus
oocytes. We show here that acetylcholine (AcCho) activates two classes of single channels with conductances of 44 pS and 58 pS, similar to those activated by 5HT. However, the mean open time of AcCho-gated ion channels (11 ms) is briefer than that of 5HT-gated ion channels (18 ms). Furthermore, whereas the open time of AcCho channels lengthens with hyperpolarization, that of 5HT channels is decreased. In voltage-clamped oocytes, the apparent affinity of the α
7
mutant receptor for 5HT is not modified by the presence of dihydro-β-erythroidine, which acts on the AcCho binding site in a competitive manner. This indicates a noncompetitive action of 5HT on nicotinic acetylcholine receptors. Considered together, our findings show that AcCho gates α
7
mutant channels with similar conductance but with different kinetic profile than the channels gated by 5HT, suggesting that the two agonists act on different docking sites. These results will help to understand the crosstalk between cholinergic and serotonergic systems in the central nervous system.
Segregation of steroid receptor coactivator-1 from steroid receptors in mammary epithelium
Authors: Shim Woo-Shin , DiRenzo James , DeCaprio James A. , Santen Richard J. , Brown Myles , Jeng Meei-Huey
Published: July 2002

Steroid receptor coactivator-1 (SRC-1) family members interact with steroid receptors, including estrogen receptor α (ERα) and progesterone receptor (PR), to enhance ligand-dependent transcription. However, the expression of ERα and SRC-1 was found to be segregated in distinct subsets of cells within the epithelium of the estrogen-responsive rat mammary gland. This finding was in contrast to the finding for the stroma, where significant numbers of cells coexpressed ERα and SRC-1. Treatment of animals with estrogen induced PR expression in the ERα-expressing mammary epithelial cells in the absence of detectable SRC-1 and did not affect the segregated pattern of SRC-1 and ERα expression. PR was neither expressed nor induced by estrogen treatment in stroma, despite the coexpression of ERα and SRC-1. These results suggest that SRC-1 is not necessary for ERα-mediated induction of PR in mammary epithelial cells and is also not sufficient for PR induction in stromal cells expressing both ERα and SRC-1. Furthermore, the expression of SRC-1 in a subpopulation of mammary epithelial cells distinct from those expressing ERα or PR raises the possibility that SRC-1 has cell type-specific functions other than simply to act as coactivator for ERα or PR in the mammary epithelium.
The Role of Lymphocyte Subsets in Accelerated Diabetes in Nonobese Diabetic–Rat Insulin Promoter–B7-1 (NOD-RIP-B7-1) Mice
Authors: Susan Wong F. , Visintin Irene , Wen Li , Granata Jennifer , Flavell Richard , Janeway Charles A.
Published: July 2002

B7-1 transgene expression on the pancreatic islets in nonobese diabetic (NOD) mice leads to accelerated diabetes, with >50% of animals developing diabetes before 12 wk of age. The expression of B7-1 directly on the pancreatic β cells, which do not normally express costimulator molecules, converts the cells into effective antigen-presenting cells leading to an intensified autoimmune attack. The pancreatic islet infiltrate in diabetic mice consists of CD8 T cells, CD4 T cells, and B cells, similar to diabetic nontransgenic NOD mice. To elucidate the relative importance of each of the subsets of cells, the NOD–rat insulin promoter (RIP)-B7-1 animals were crossed with NOD.β2microglobulin −/− mice which lack major histocompatibility complex class I molecules and are deficient in peripheral CD8 T cells, NOD.CD4 −/− mice which lack T cells expressing CD4, and NOD.μMT −/− mice which lack B220-positive B cells. These experiments showed that both CD4 and CD8 T cells were necessary for the accelerated onset of diabetes, but that B cells, which are needed for diabetes to occur in normal NOD mice, are not required. It is possible that B lymphocytes play an important role in the provision of costimulation in NOD mice which is unnecessary in the NOD-RIP-B7-1 transgenic mice.
Continuous collocation approximations to solutions of first kind Volterra equations
Authors: Kauthen J.-P. , Brunner H.
Published: July 2002

In this paper we give necessary and sufficient conditions for convergence of continuous collocation approximations of solutions of first kind Volterra integral equations. The results close some longstanding gaps in the theory of polynomial spline collocation methods for such equations. The convergence analysis is based on a Runge-Kutta or ODE approach.