bluuebunny/crossref_metadata_2025 huggingface dataset:
Negative transconductance in a resistive gate metal-semiconductor field-effect transistor
Authors: Yin Y. , Cooper J. A. , Neudeck P. G. , Balzan M. L. , Geissberger A. E.
Published: July 2002

Negative transconductance is reported in a resistive gate metal-semiconductor field-effect transistor (MESFET) for the first time. The negative transconductance arises as a result of the negative differential mobility of electrons in the GaAs channel, and is adequately described by a simple equivalent circuit model. The experimental device is fabricated with a planar ion-implanted MESFET process, and shows promise as a microwave signal source for use in monolithic microwave integrated circuits.
Epitaxial growth of InSb (111) on sapphire (0001)
Authors: Jamison K. D. , Bensaoula A. , Ignatiev A. , Huang C. F. , Chan W. S.
Published: July 2002

Indium antimonide has been epitaxially grown directly on sapphire. Reflection high-energy electron diffraction, transmission electron microscopy, and scanning electron microscopy data are presented to show that the indium antimonide layer is epitaxial, has an abrupt interface with the sapphire, and grows in the 〈111〉 direction. Mobility data show room-temperature mobilities as high as 1×104 cm2 /V s from some regions on the wafer.
Theory of the characteristic curves of the silver chalcogenide glass inorganic photoresists
Authors: Das Amitabha , Al-Jishi Radi
Published: July 2002

A theoretical model of the characteristic curves of the silver/chalcogenide glass inorganic photoresists, which is based explicitly on a photoinduced diffusion theory of the photodoping phenomenon, is presented. Besides the photoinduced diffusion of silver in the bulk glass, the role of the photoinduced reaction at the silver/glass interface through which silver gains entry into the glass is emphasized. It is proposed that the resists operate in the initial, interfacial reaction rate controlled regime of photodoping. Expressions for the sensitivity and the contrast parameter are derived.
Effect of back-surface polycrystalline silicon layer on oxygen precipitation in Czochralski silicon wafers
Authors: Shirai Hideki , Yamaguchi Akira , Shimura Fumio
Published: July 2002

The depth profile of oxygen precipitates in silicon wafers has been investigated for a variety of back surface conditions and thermal treatments. The results clearly show localized enhancement of oxygen precipitation in the region close to back surface polycrystalline silicon layers. The depth profile of intentionally introduced stacking faults on cleaved planes has also been shown to vary and is attributed an enhancement in the absorption of silicon self-interstitials by the back surface polysilicon layer. Consequently, the results observed in this study strongly support the enhancement effect of vacancies on oxygen precipitation in silicon crystals.
c-axis oriented YBa2Cu3O7−x superconducting films by metalorganic chemical vapor deposition
Authors: Zhang K. , Kwak B. S. , Boyd E. P. , Wright A. C. , Erbil A.
Published: July 2002

Highly textured single phase superconducting YBa2Cu3O7−x films have been successfully grown on the yttria-stabilized zirconia (100) substrates by using the metalorganic chemical vapor deposition technique. The as-deposited films grown at 650 °C were homogeneous mixtures of the related metal oxides and carbonates. Subsequent thermal annealing under oxygen flow yielded single phase superconducting films whose thickness corresponded to the deposition rates of approximately 10 μm/h. After the post-annealing the films deposited on the yttria-stabilized zirconia substrates exhibited a highly textured x-ray pattern with c axis perpendicular to the substrate surface. These films show an onset superconducting transition temperature of 93 K with the resistance becoming zero at 84 K.
New method of hot rolling for fabricating anisotropic Pr-Fe-B-based magnets
Authors: Mukai T. , Sakamoto H.
Published: July 2002

A unique method of hot rolling is described which fabricates high performance plate-shaped magnets from a cast Pr17Fe76.5B5Cu1.5 alloy. A flat ingot of the alloy with fine-scale columnar grains of a Pr2Fe14B phase is prepared by chill casting. The ingot is hot rolled in such a way that the roll pressure is applied perpendicular to the preferential growth direction of the columnar grains. A maximum energy product of 25.3 MG Oe has been obtained by this method.
Formation of palladium silicide in the presence of Al with and without a carbon barrier layer
Authors: Chang Chin-An
Published: July 2002

The formation of Pd silicides in the presence of an Al layer is studied using Al/Pd/Si structures with and without a carbon barrier layer between the Al and Pd layers. Both the reactions between Al and Pd and between Pd and Si start around 200 °C, forming Pd2Al3 and Pd2Si, respectively. At higher temperatures, the excess Al present reacts with the Pd2Si formed, converting the latter to Pd2Al3 which is completed at 400 °C. In the presence of a carbon barrier layer using an Al/C/Pd/Si structure, the Pd2Si formed stays little changed up to an anneal of 30 min at 500 °C. The Pd2Si formed reacts with the Al present at higher temperatures, about two-thirds reacted after an anneal at 550 °C, and nearly completely reacted after an anneal at 600 °C, both for 30 min. The effectiveness of the carbon barrier layer for the Al/Pd2Si reaction is compared with that for the Al/PtSi reaction, where little reaction is observed after an anneal of 30 min at 600 °C. Application of the carbon barrier layer to device contact metallurgies is also discussed.
Epitaxial growth and critical current density of thin films of YBa2Cu3O7−x on LaAlO3 substrates
Authors: Mogro-Campero A. , Turner L. G. , Hall E. L. , Garbauskas M. F. , Lewis N.
Published: July 2002

Thin films of the high-temperature superconductor YBa2 Cu3 O7−x have been produced on (100) LaAlO3 substrates by coevaporation and furnace annealing. A 14-μm-wide and 400-μm-long constriction patterned on a 0.8-μm-thick film had a zero resistance transition temperature of 90 K, a transition width of 1.5 K, and a critical current density of 8×104 A cm−2 at 77 K. Although x-ray diffraction shows a definite c-axis alignment normal to the substrate plane, further analysis reveals that c-axis alignment in the substrate plane is also present. The detailed microstructural picture is revealed by transmission electron microscopy: a continuous layer, about 0.2 μm thick adjacent to the substrate, with c axis normal to the substrate plane, and the remaining top portion of the film, with the c axis in the film plane. In spite of the bilayer structure, the film remains epitaxial (the axes of the superconductor are parallel to the 〈100〉 directions of the substrate).
Microstructure of i
n s
i
t
u epitaxially grown superconducting Y-Ba-Cu-O thin films
Authors: Hwang D. M. , Venkatesan T. , Chang C. C. , Nazar L. , Wu X. D. , Inam A. , Hegde M. S.
Published: July 2002

The microstructure of in situ epitaxially grown Y-Ba-Cu-O thin films on (001) SrTiO3 substrates was studied using cross-sectional transmission electron microscopy. The films, prepared by pulsed laser deposition at substrate holder temperature of 650 °C without post-annealing, exhibit zero resistivity above 90 K and critical currents exceeding 106 A/cm2 at 77 K. The films are of heavily faulted single crystalline structure with the c axis approximately perpendicular to the substrate (001) surface. We suggest that, due to the fast quenching and low substrate temperature, crystalline defects and chemical fluctuations are locked into a faulted structure after each laser pulse. Despite their rather imperfect microstructure, the films are free from macroscopic grain boundaries and secondary phases and possess superb superconducting properties.
Operating characteristics of InGaAs/AlGaAs strained single quantum well lasers
Authors: Bour D. P. , Martinelli Ramon U. , Gilbert D. B. , Elbaum L. , Harvey M. G.
Published: July 2002

The performance of a series of InxGa1−xAs/AlGaAs (x=0.20 and 0.25) strained single quantum well (SSQW) lasers with lasing wavelengths in the range 930≤λ≤1000 nm is discussed. Less-strained devices, with x=0.20 and QW thickness 7 nm (λ∼930 nm), perform comparably with GaAs QW lasers. Longer wavelength (λ>950 nm), more highly strained lasers exhibit poorer performance. Our results suggest that interfacial recombination limits the performance at the longer wavelength structures.
Amorphous phase formation by solid-state reaction between polycrystalline Co thin films and single-crystal GaAs
Authors: Shiau F. Y. , Chang Y. A.
Published: July 2002

The formation of an amorphous phase between Co thin films and GaAs substrates by solid-state reaction has been investigated by transmission electron microscopy and Auger electron spectroscopy. The amorphization is ascribed to the fast diffusion of Co in GaAs. The amorphous layer, after a 300 °C, 4.5 h annealing, is measured to be ∼40 nm in thickness and has a broad composition range. Prolonged annealing at 300 °C or heat treatment at 340 °C results in the crystallization of the amorphous phase. This crystallization is found to initiate from the Co/amorphous phase interface and leads to the formation of a metastable, supersaturated phase. Finally, the equilibrium condition is reached by the decomposition of this intermediate phase into CoGa and CoAs.
(InAs)3(GaAs)1 superlattice channel field-effect transistor grown by molecular beam epitaxy
Authors: Nishiyama Naoki , Yano Hiroshi , Nakajima Shigeru , Hayashi Hideki
Published: July 2002

A metal-insulator-semiconductor field-effect transistor (MISFET) using the InAs-GaAs superlattice as a channel layer has been successfully demonstrated for the first time. Device structure was grown by molecular beam epitaxy. The MISFET with 1.0 μm gate length exhibits a maximum external dc transconductance of 212 mS/mm at Vds =3.0 V and Vg =−1.5 V. This value is high among 1.0 μm gate length devices.
Charge trapping characteristics of the interface states in an AlN/GaAs metal-insulator-semiconductor structure
Authors: Mochizuki Y. , Mizuta M. , Fujieda S. , Matsumoto Y.
Published: July 2002

Charge trapping properties of the interface states present at the AlN/n-GaAs interfaces are investigated through high-frequency capacitance transients. They change their behavior from electron to hole traps with the excursion of surface Fermi level towards the valence band. This observation indicates that it is ionization of the states near midgap, not the hole inversion, which blocks the downward excursion of surface potential in GaAs/ insulator systems. It is also found that these states are well defined in terms of having a single capture cross section within the energy range probed, and furthermore, they are spatially localized at the interface.
Band-edge discontinuities of strained-layer InxGa1−xAs/GaAs heterojunctions and quantum wells
Authors: Niki S. , Lin C. L. , Chang W. S. C. , Wieder H. H.
Published: July 2002

The conduction-band discontinuity (ΔEc ) and the band-gap offset (ΔEgh) of InxGa1−xAs/GaAs multiple quantum wells grown on GaAs substrates by molecular beam epitaxy are investigated for 0<x<0.3. The band gap of strained InxGa1−xAs , determined from the excitonic transition of room-temperature transmission spectra, is found to be linearly dependent on x and is in good agreement with the calculated values. The band-gap offset is found to be ΔEgh =1.15x eV. The conduction-band offset, compiled from published data, is ΔEc =0.75x eV, and thus (ΔEc /ΔEgh)=0.65 independent of x.
Material-dependent amorphization and epitaxial crystallization in ion-implanted AlAs/GaAs layer structures
Authors: Cullis A. G. , Chew N. G. , Whitehouse C. R. , Jacobson D. C. , Poate J. M. , Pearton S. J.
Published: July 2002

When AlAs/GaAs layer samples are subjected to Ar+ ion bombardment at liquid-nitrogen temperature, it is shown that very different damage structures are produced in the two materials. While the GaAs is relatively easily amorphized, the AlAs is quite resistant to damage accumulation and remains crystalline for the ion doses employed in these investigations. Epitaxial regrowth of buried amorphous GaAs layers of thicknesses up to 150 nm can be induced by rapid thermal annealing. It is demonstrated that differences in the initial damage state have a strong influence upon the nature of lattice defects produced by annealing.
Effect of spatially variable effective mass on static and dynamic properties of resonant tunneling devices
Authors: Mains R. K. , Mehdi I. , Haddad G. I.
Published: July 2002

The effect of incorporating a spatially variable effective mass in the Schrödinger equation method of resonant tunneling device modeling is investigated. It is shown that inclusion of this effect can produce an order of magnitude difference in the calculated peak current density of the static current voltage (I-V) curve for the resonant tunneling diode. Results for a particular In0.53Ga0.47As-AlAs structure show that much better agreement between theory and experiment is obtained by including this effect. Also, comparison of transient results for an In0.53Ga0.47As-In0.52Al0.48As structure shows a significant change in the diode switching transients.
Picosecond laser sputtering of sapphire at 266 nm
Authors: Tam A. C. , Brand J. L. , Cheng D. C. , Zapka W.
Published: July 2002

We observe that 266 nm laser pulses of 30 ps duration and fluence near 10 J/cm2 causes reproducible surface sputtering and etching of crystalline sapphire in air. The etching rate for the initial ten pulses is relatively slow, 0.04 μm/pulse, producing a smooth surface of the etched area and a broad-angle plume emission. After some 20 pulses, the etching rate is dramatically faster, 0.5 μm/pulse, producing a rough etched surface and a plume composed of broad-angle emission as well as a narrow perpendicular jet emission. Micron-sized depressions can be made on the sapphire with no visible damage or cracking to the surroundings.
Grain growth and size distribution in ion-irradiated chemical vapor deposited amorphous silicon
Authors: Spinella C. , Lombardo S. , Campisano S. U.
Published: July 2002

The amorphous to polycrystal transition in chemical vapor deposited (CVD) amorphous silicon has been studied at 450 °C under Kr ion beam irradiation. The average grain size increases linearly with the ion dose, and the grain size distribution is very narrow compared to thermally grown grains. These results are consistent with the presence of crystal seeds in CVD material. All these seeds can grow simultaneously under ion beam irradiation. For layers completely preamorphized by Ge+ implantation, no ion beam induced nucleation is observed.
Monolithic integration of a thin and short metal-semiconductor-metal photodetector with a GaAlAs optical inverted rib waveguide on a GaAs semi-insulating substrate
Authors: Vinchant J. F. , Vilcot J. P. , Lorriaux J. L. , Decoster D.
Published: July 2002

The first fabrication of a thin and short GaAs metal-semiconductor-metal photodetector monolithically integrated with a GaAlAs optical inverted rib waveguide on a semi-insulating GaAs substrate is reported. An only 0.2-μm-thick and 100-μm-long GaAs absorbing layer is needed to detect 90% of the optical signal at 0.85 μm wavelength. Static, dynamic, and noise measurements have been performed and a bandwidth in excess of 15 GHz is obtained.
Charged carrier transport in Si1−xGex pseudomorphic alloys matched to Si—strain-related transport improvements
Authors: Hinckley J. M. , Sankaran V. , Singh J.
Published: July 2002

Charge carrier transport studies are reported for Si1−xGex pseudomorphic alloy layers matched to the (001) Si substrate lattice constant. The effect of biaxial compressive strain on transport is studied by first examining the band structure changes via deformation potential theory and then studying the transport via a generalized Monte Carlo approach. Marked improvements in in-plane hole transport are obtained while significant improvements also occur in the out-of-plane electron transport. These changes are ideally suited for use in n(Si)-p(Si1−xGex)-n(Si) heterojunction bipolar transistors.
Resistance of very small area ohmic contacts on GaAs
Authors: Guéret P. , Buchmann P. , Daetwyler K. , Vettiger P.
Published: July 2002

Very small area, alloyed ohmic contacts on n+-GaAs etched mesas have been fabricated and their resistance measured. The nominal contact size ranges from 10 down to 0.1 μm on a side. The data show an extremely large increase of the resistance spread as the contact size is reduced. Grain size effects in the alloyed contacts and dead zones due to ion etching are discussed as possible causes for the observations.
Strain in epitaxial CoSi2 films on Si (111) and inference for pseudomorphic growth
Authors: Bai Gang , Nicolet Marc-A. , Vreeland Thad , Ye Q. , Wang K. L.
Published: July 2002

The perpendicular x-ray strain of epitaxial CoSi2 films grown on Si(111) substrates at ∼600 °C was measured at temperatures from 24 up to 650 °C. At 600 °C, the perpendicular x-ray strain is −0.86%, which is about the x-ray strain that a stress-free CoSi2 film on Si(111) would have at that temperature. This result shows that the stress in the epitaxial CoSi2 film is fully relaxed at the growth temperature. Strains in the film below the growth temperature are induced by the difference in the thermal expansion coefficient of CoSi2 and Si, αf−αs=0.65×10−5/°C. Within experimental error margins, the strain increases linearly with decreasing temperature at a rate of (1.3±0.1)×10−5/C. The slope of the strain-temperature dependence, obtained by assuming that the density of misfit dislocations formed at the growth temperature remains unchanged, agrees with the measured slope if the unknown Poisson ratio of CoSi2 is assumed to be νf=1/3. These observations support three rules postulated for epitaxial growth.
Surface roughening associated with ∼140 °C transition of a LaGaO3 substrate for high T
c superconducting films
Authors: Miyazawa Shintaro
Published: July 2002

A ferroelastic-like transition at ∼140 °C in a single-crystal LaGaO3 substrate was directly observed with an optical microscope at elevated temperatures. In addition, it was found for the first time that a polished surface morphology of a pseudocubic (001) LaGaO3 substrate degraded after a heat cycle up to only 200 °C. This surface degradation, i.e., surface roughening, is associated with the transition at ∼140 °C, and it may possibly be the major origin of relatively low critical current density reported for a superconducting YBa2Cu3Ox film grown on a LaGaO3 substrate.
Oscillations of composition near the external surface of Y-Ba-Cu-O thin films
Authors: Bakunin O. M. , Klotsman S. M. , Matveev S. A. , Stepanov K. A.
Published: July 2002

An Auger electron spectroscopy study has been made of the depth profiles of films of Y-Ba-Cu-O compounds. The films were produced by electron beam and ion plasma sputtering onto various substrate types. The specimens were annealed in air at temperatures ranging between 450 and 900 °C. The effective diffusion coefficients for the film and substrate constituents have been estimated. The depth profiles of films annealed at 600 °C reveal composition oscillations in the region adjacent to the surface. These composition oscillations are assumed to arise from the phase transformations that occur at 600 °C in films of the Y-Ba-Cu-O system.
Redistribution of Zn in GaAs-AlGaAs heterojunction bipolar transistor structures
Authors: Hobson W. S. , Pearton S. J. , Jordan A. S.
Published: July 2002

The redistribution of Zn in the base region of GaAs-AlGaAs heterojunction bipolar transistor structures during growth by organometallic vapor phase epitaxy has been examined with respect to the presence of Si doping in the emitter-contact, emitter, and collector/subcollector layers, and as a function of Zn doping concentration and Si counterdoping level in the p+ base. For a growth temperature of 675 °C the Zn shows no significant redistribution up to concentrations of 3×1019 cm−3 without Si doping. The addition of Si to the adjacent AlGaAs emitter and collector/subcollector layers causes substantial diffusion of Zn from the base, while Si doping of the GaAs emitter contact results in even greater Zn redistribution. Under these conditions, the Zn concentration in the base attains a maximum value of ∼7×1018 cm−3. Silicon counterdoping in the base region retards the Zn diffusion, while strain introduced by an InGaAs cap layer has no effect on the Zn redistribution.
Solid phase epitaxial growth of GaAs on Si substrates
Authors: Cho K. I. , Choo W. K. , Park S. C. , Nishinaga T. , Lee B.-T.
Published: July 2002

Thin films of GaAs on Si were grown by molecular beam epitaxy, which involves the solid phase epitaxial (SPE) growth of the amorphous GaAs buffer layer. A Rutherford backscattering minimum channeling yield of ∼9.4% has been obtained for a 0.8-μm-thick GaAs film. Cross-sectional transmission electron micrographs and reflection high-energy electron diffraction results have revealed that misfit dislocations are mostly confined to what used to be the buffer layer of ∼300 nm in thickness, and that the microtwins (and/or stacking faults) are mostly originated from the GaAs/Si interface and are generated during SPE growth.
High carrier concentration in InP by Si+ and P+ dual implantations
Authors: Shen Honglie , Yang Genqing , Zhou Zuyao , Zou Shichang
Published: July 2002

Dual implantations of 150 keV Si+ ions and 160 keV P+ ions with the same dose of 1×1015/ cm2 were performed at 200 °C. Si3 N4 encapsulated samples were annealed in a conventional furnace or a halogen tungsten lamp rapid thermal annealing system. The carrier concentration profiles show that the Si dopant is highly activated and its indiffusion is effectively reduced with the help of P+ implantation and rapid thermal annealing. The highest carrier concentration of 5×1019 /cm3 , corresponding to an activation of 70%, an average electron mobility of 750 cm2 /V s, and a sheet resistance of 11 Ω/⧠, has been obtained in Si+ and P+ dually implanted InP after rapid thermal annealing at 850 °C for 5 s.
Photoinduced structural defect levels in amorphous selenium films
Authors: Kamalasanan M. N. , Chand Suresh
Published: July 2002

Thermally stimulated discharge (TSD) behavior of native (dark rested) and irradiated amorphous selenium films (∼100 μm) has been studied. The TSD spectrum of nonirradiated films shows electron trapping levels at ∼0.99 eV and no detectable hole trapping levels. On the other hand, the irradiated films show both electron as well as hole trapping levels at 0.99 and 1.05 eV, respectively. These results have been explained in terms of trapping of charge carriers at intrinsic defect states and the photoinduced defect levels created during irradiation.
Improving the performance of strained InGaAs/AlGaAs single quantum well lasers
Authors: Bour D. P. , Martinelli Ramon U. , Hawrylo F. Z. , Evans G. A. , Carlson N. W. , Gilbert D. B.
Published: July 2002

By adjusting the carrier confining structure and the optical confining structure of strained InGaAs/AlGaAs single quantum well (QW) lasers, an improvement in performance has been obtained. First, the influence of optical confinement was examined by comparing two graded-index confining structures. For InxGa1−xAs QWs with either x=0.20 or x=0.25, lasers with greater optical confinement factor had improved performance, with both lower threshold (180 A/cm2 for x=0.20) and higher characteristic temperature (250 K for x=0.20), despite their reduced carrier confining potentials. Second, experiments on graded-composition quantum wells show that thin step-grading layers result in improved performance. In this structure, where the QW has x=0.35, and the step layers have x=0.15, the optimum step thickness is 30–40 Å. Thicker step layers appear to create too much strain, degrading the laser operation. These results indicate that step grading of strained QWs produces active region interfaces with lower defect density, and that step grading is especially useful in improving the performance of long-wavelength, highly strained InGaAs/AlGaAs QW lasers.
Solitary wave emission from a nonlinear slab waveguide in three dimensions
Authors: Heatley D. R. , Wright E. M. , Stegeman G. I.
Published: July 2002

We show numerically that solitary waves, localized in two transverse dimensions, are emitted when a high-power Gaussian beam is launched into a slab waveguide in which the cladding displays a saturable self-focusing nonlinearity.
High-frequency polarization self-modulation and chaotic phenomena in external cavity semiconductor lasers
Authors: Loh W. H. , Ozeki Y. , Tang C. L.
Published: July 2002

Optical pulses with repetition rates up to several hundred MHz have been generated through a polarization self-modulation effect in an external cavity semiconductor laser modified by the insertion of a quarter-wave retardation plate. These pulses are generated without the need for any high-speed electronics. At higher bias, period doubling and chaotic phenomena are also observed.
Application of ellipsometry to crystal growth by organometallic molecular beam epitaxy
Authors: Aspnes D. E. , Quinn W. E. , Gregory S.
Published: July 2002

We report the first use of ellipsometry as a real-time monitor of III-V semiconductor crystal growth by molecular beam epitaxy, specifically growth of GaAs and AlGaAs from arsine, triethylgallium, and triethylaluminum sources. Our results provide new insight into the oxide desorption process and show a sensitivity of ±0.03 in compositions x>0.2 for 10 Å thickness increments of AlxGa1−xAs during initial deposition on GaAs.
Dynamics of reflection high-energy electron diffraction intensity oscillations during molecular beam epitaxial growth of GaAs on (111)B GaAs substrates
Authors: Yen M. Y. , Haas T. W.
Published: July 2002

We have observed intensity oscillations in reflection high-energy electron diffraction during molecular beam epitaxial growth of GaAs on (111)B GaAs substrates. These oscillations only exist over a narrow range of growth conditions and their behavior is strongly dependent on the migration kinetics of group III and the molecular dissociative reaction of group V elements.
Diffusivity of gold in amorphous silicon measured by the artificial multilayer technique
Authors: Nygren E. , Park B. , Goldman L. M. , Spaepen F.
Published: July 2002

Artificial multilayers of amorphous Si and amorphous Si containing 0.7 at. % Au, with repeat lengths between 44 and 48A, were fabricated by ion beam sputtering. The change, with annealing time in the intensity of the first-order x-ray diffraction peak resulting from the composition modulation, is used to determine the diffusivity of Au in amorphous Si. Diffusion lengths on the order of an interatomic distance have been measured. The diffusivities over the temperature range 200–260 °C have an Arrhenius-type temperature dependence with an activation enthalpy of about 1.3 eV, and are in agreement with the extrapolation of published higher temperature data.
Investigation of fluorine in SiO2 and on Si surface by the 19F(p,αγ)16O reaction, secondary-ion mass spectrometry, and x-ray photoelectron spectroscopy
Authors: Yu Byoung-gon , Arai Eiichi , Nishioka Yasushiro , Ohji Yuzuru , Iwata Seiichi , Ma T. P.
Published: July 2002

A fluorinated thermal SiO2, grown after HF surface treatment without de-ionized water rinse, was estimated to contain ∼3×1013 cm−2 of fluorine by the 19F(p,αγ)16O reaction. Secondary-ion mass spectrometry data indicate that the SiF distribution is peaked at the SiO2/Si interface in the fluorinated oxide. The time-dependent change of the absolute amount of fluorine on the HF-treated silicon surface as a function of storage time in air or in vacuum was also investigated by the 19F(p,αγ)16O reaction. The initial number of fluorine atoms on the HF-treated silicon surface was estimated to be ∼1015 cm−2 before substantial desorption took place. Fluorine atoms desorb from the silicon surface much more rapidly if the sample is stored in air than in vacuum. These results were also supported by the x-ray photoelectron spectroscopy measurement.
Synchrotron radiation-excited etching of SiO2 with SF6 at 143 and 251 Å using undulator radiation
Authors: Shobatake K. , Ohashi H. , Fukui K. , Hiraya A. , Hayasaka N. , Okano H. , Yoshida A. , Kume H.
Published: July 2002

Photoexcited etching of SiO2 surface with SF6 gas is studied using undulator radiation at 143 and 251 Å as an extreme ultraviolet light source. The SF6 pressure and the wavelength dependences of the etch rates have been measured for SiO2 in the pressure region between 0.016 and 0.50 Torr. We find that, at these wavelengths, the etch rate is proportional to the intensity of the light absorbed by the surface species, most probably SiO2 in the pressure region studied.
Dependence of thermal stability of the titanium silicide/silicon structure on impurities
Authors: Ogawa Shin-ichi , Yoshida Takehito , Kouzaki Takashi
Published: July 2002

The effect of impurity on the thermal stability of titanium silicide (TiSi2)/single-crystal silicon (Si) structures has been studied. It is found that nitrogen and oxygen in the TiSi2 film significantly influence the morphological changes of a TiSi2/Si structure during high-temperature annealing at 1100 °C for 2–20 s. Nitrogen impurity improves the thermal stability of the TiSi2/Si structure, whereas oxygen degrades it.
Optically induced femtosecond electromagnetic pulses from GaSb/AlSb strained-layer superlattices
Authors: Zhang X.-C. , Hu B. B. , Xin S. H. , Auston D. H.
Published: July 2002

The strain generated electric field in a 〈111〉 oriented misfit superlattice provides a suitable bias for generating optically induced femtosecond electromagnetic radiation. We have measured the electromagnetic radiation from GaSb/AlSb strained-layer superlattices and GaSb thin films; extremely fast electromagnetic pulses from 〈111〉 oriented superlattices have been observed. Because the quantum well structure in the superlattice samples limits the pulse duration of the transient photocurrent, it is possible to generate electromagnetic radiation having a pulse duration comparable with the photocarrier transit time across the quantum well.
Subband mobility of quasi-two-dimensional electrons in Si atomic layer doped GaAs
Authors: Yamada Syoji , Makimoto Toshiki
Published: July 2002

Subband mobility and conductivity of quasi-two-dimensional electrons in Si atomic layer doped GaAs are estimated for the first time. The oscillations for different subbands in low-temperature magnetoresistance are separated from each other by using the reverse Fourier transform technique. The mobility for each subband is then determined by fitting the field dependence of the amplitudes with conventional theory. A large subband mobility difference up to 20:1 is found. This is mainly due to strong screening. Furthermore, a partial conductivity for each subband is calculated and the importance of the shallower subbands in total current transport is clarified.
Influence of defect absorption on the absorption edge in Hg0.8Cd0.2Te
Authors: Wang Jue , Lu Wei , Liu Jiming , Yu Zhenzhong , Tang Dingyuan
Published: July 2002

The optical absorption edges in gettered and ungettered Hg0.8Cd0.2Te alloys have been investigated. It is found that the absorption edge was moved to the short wave direction after the sample was gettered. The change of absorption edge has also been found in Hg0.8Cd0.2Te containing different mercury concentrations. Possible explanations for the phenomena are discussed.
Broad wavelength tunability in gain-levered quantum well semiconductor lasers
Authors: Lau K. Y.
Published: July 2002

Using a gain lever effect in a single quantum well laser, it was observed that the wavelength can be electronically tuned over a range of 90 Å. Optimal device geometry that leads to a maximum tuning range was investigated.
High-energy (56 MeV) oxygen implantation in Si, GaAs, and InP
Authors: Pearton S. J. , Jalali B. , Poate J. M. , Fox J. D. , Kemper K. W. , Magee C. W. , Jones K. S.
Published: July 2002

The depth profiles measured by secondary-ion mass spectrometry of 56 MeV oxygen ions implanted into Si, GaAs, and InP are reported. Most of the oxygen is contained within a sharp (full width at half maximum ∼2 μm) non-Gaussian profile centered at ∼31 μm in GaAs, ∼36 μm in InP, and ∼46 μm in Si, with the distribution skewed towards greater depths. The experimental projected ranges appear to be 10% larger than theoretical predictions. Changes in the electrical, optical, and structural properties of the material were measured by transmission electron microscopy (TEM), photoluminescence, and spreading resistance profiling. In the as-implanted Si, the maximum perturbation in the electrical properties occurs at ∼37 μm. No defects are visible by TEM in any of the as-implanted semiconductors for oxygen ion doses of 1.35×1015 cm−2 but the photoluminescent intensity in GaAs and InP is reduced by more than an order of magnitude as a result of this type of implantation.
Direct nanometer scale patterning of SiO2 with electron beam irradiation through a sacrificial layer
Authors: Allee D. R. , Broers A. N.
Published: July 2002

Nanometer scale patterns have been fabricated in SiO2 by electron beam exposure through a sacrificial layer. Although the process of patterning SiO2 with direct electron beam irradiation was discovered over two decades ago, the smallest feature size previously achieved was 0.6 μm because finely focused electron beams form a contamination layer on the substrate blocking the subsequent development of the oxide with HF wet etches. Exposing through a sacrificial layer, the contamination is readily removed with the stripping of the sacrificial layer. Using high energy electrons (300 keV) to minimize forward scattering of the beam, arrays of lines with a period down to 21 nm have been fabricated in the SiO2.
Batch fabricated sensors for magnetic force microscopy
Authors: Grütter P. , Rugar D. , Mamin H. J. , Castillo G. , Lambert S. E. , Lin C.-J. , Valletta R. M. , Wolter O. , Bayer T. , Greschner J.
Published: July 2002

In this letter we describe force sensors suitable for magnetic force microscopy (MFM) made by coating silicon microcantilevers with various thin magnetic films. These MFM force sensors can be batch fabricated and their magnetic properties tailored by choosing appropriate coatings. This is demonstrated by analyzing the MFM response for magnetization patterns written on a longitudinal recording test sample. Selectable components of the sample stray field can be measured by coating the tips with high coercivity films. Tips coated with low coercivity films such as Permalloy respond to the total stray field. Sample perturbations due to the tip stray field are small for thin-film tips, allowing the imaging of low coercivity samples such as Permalloy.
rf plasma-generated superconducting Y1Ba2Cu3O7−x films
Authors: Shah A. , Patel S. , Narumi E. , Shaw D. T.
Published: July 2002

Using an inductively coupled rf plasma operated at atmospheric pressure, superconducting thin films of Y1Ba2Cu3O7−x have been grown in situ on single-crystal yttria-stabilized zirconia [100] from an aerosol precursor. X-ray diffraction and rocking curve results indicate that the films are highly c-axis oriented normal to the substrate with a lattice constant of 11.67–11.68 Å. The full width at half maximum of these films ranges from 0.55° to 1.0°. The films have typical Tc’s of 86 K and Jc’s in excess of 105 A/cm2 at 77 K and zero field; magnetic measurements reveal an anisotropy of 3:1 at 69 K. The dependence of the processing parameters on the transport properties of the superconducting films is discussed.
Microstructure of epitaxial YBa2Cu3O7−x thin films grown on LaAlO3 (001)
Authors: Hsieh Yong-Fen , Siegal Michael P. , Hull Robert , Phillips Julia M.
Published: July 2002

We report a microstructural investigation of the epitaxial growth of YBa2Cu3O7−x (YBCO) thin films on LaAlO3 (001) substrates using transmission electron microscopy (TEM). Epitaxial films grow with two distinct modes: c epitaxy (YBCO) single crystal with the c axis normal to the surface) and a epitaxy (YBCO) single crystal with the c axis in the interfacial plane), where c epitaxy is the dominant mode grown in all samples 35–200 nm thick. In 35 nm YBCO films annealed at 850 °C, 97±1% of the surface area is covered by c epitaxy with embedded anisotropic a-epitaxial grains. Quantitative analysis reveals the effect of film thickness and annealing temperature on the density, grain sizes, areal coverages, and anisotropic growth of a epitaxy.
Microwave plasma generation of arsine from hydrogen and solid arsenic
Authors: Omstead Thomas R. , Annapragada Ananth V. , Jensen Klavs F.
Published: July 2002

The generation of arsine from the reactions of hydrogen and elemental arsenic in a microwave plasma reactor is described. The arsenic is evaporated from a solid source upstream and carried into the microwave plasma region by a mixture of hydrogen and argon. Stable reaction products, arsine and diarsine are observed by molecular beam sampled mass spectroscopy along with partially hydrogenated species (e.g., AsH and AsH2). The effect of composition and flow rate of the argon/hydrogen carrier gas mixture on the amount of arsine generated is investigated. The arsine production reaches a maximum for an argon-to-hydrogen ratio of unity indicating that metastable argon species act as energy transfer intermediates in the overall reaction. The generation of arsine and diarsine from easily handled solid arsenic by this technique makes it attractive as a possible arsenic source for the growth of compound semiconductors by low-pressure metalorganic chemical vapor deposition.    
Growth and properties of YBa2Cu3O7 thin films on vicinal and polycrystalline MgO substrates
Authors: Moeckly B. H. , Russek S. E. , Lathrop D. K. , Buhrman R. A. , Norton M. G. , Carter C. B.
Published: July 2002

We discuss the results of a study on the growth by laser ablation of YBa2Cu3O7 thin films on polycrystalline and annealed vicinal (001) MgO substrates. In both instances the films were found to grow predominantly with the c axis normal to the plane of the substrate, regardless of the orientation of the MgO surface. In the case of the vicinal substrates the films were found to have superconducting properties comparable to those obtained with films grown on (001) oriented, annealed single-crystal substrates.
Sputter deposition of YBa2Cu3O7−x films on Si at 500 °C with conducting metallic oxide as a buffer layer
Authors: Jia Q. X. , Anderson W. A.
Published: July 2002

Superconducting YBa2Cu3O7−x thin films were deposited on Si substrates at 500 °C by rf magnetron sputtering from a stoichiometric oxide target. Metallic oxide RuO2, sputtered by reactive dc magnetron, was used as a buffer layer to nucleate the superconducting film and minimize the reactions between Si and superconductor. The as-deposited thin films, without further post high-temperature annealing, were completely superconductive at 79 K. Very smooth surface morphology was demonstrated by scanning electron microscopy. X-ray diffraction data indicated that the films had a randomly oriented polycrystalline structure. Auger electron spectroscopy did not reveal interdiffusion of elements in the three layers.
Up to the 51st harmonic mixing in YBa2Cu3O7−y weak link operated in liquid nitrogen
Authors: Wu P. H. , Xu Yunhui , Heiden C.
Published: July 2002

When a signal at the nominal frequency of 76 GHz and a local oscillation (LO) at the frequency of a few gigahertz were both applied to a YBa2Cu3O7−y weak link immersed in liquid nitrogen, the former mixed with the harmonics of the latter giving rise to output at the intermediate frequency (IF) of about 150 MHz. The highest observed harmonic number was 51. Without exhaustive effort to optimize, the typical IF output power referred to the mixer output ranged between −103 and −112 dbm while the IF signal-to-noise ratio ranged between 16 and 4 db, depending strongly on the local oscillation power, the dc bias current, and the signal power. Reported in this letter are the experimental details as well as the requirements for a superconducting weak link to be a harmonic mixer.
Influence of oxygen pressure on laser ablation of YBa2Cu3O7−x
Authors: Scott K. , Huntley J. M. , Phillips W. A. , Clarke John , Field J. E.
Published: July 2002

The luminous ablation plume formed by laser irradiation of the superconductor YBa2Cu3O7−x has been investigated by high-speed framing photography. The pressure of the background oxygen gas was found to influence significantly the velocity distribution of ejected products. Pressures above 0.25 mbar resulted in the formation of shock waves and instabilities on the shock front.
Lead zirconate titanate films by rapid thermal processing
Authors: Kumar C. V. R. Vasant , Sayer M. , Pascual R. , Amm D. T. , Wu Z. , Swanston D. M.
Published: July 2002

Lead zirconate titanate films have been fabricated by a dc sputtering technique with a post deposition rapid thermal annealing treatment at 650 °C for 10 s. The films exhibited good structural, dielectric, and ferroelectric properties compared to conventional furnace-annealed films. The measured dielectric constant and loss tangent at 1 kHz were 900 and 0.04 and the remanent polarization and coercive field values were 10 μC/cm2 and 23 kV/cm, respectively. No significant fatigue in polarization was observed in the films up to 1010 cycles of bipolar stress. The films were optically transparent and showed a linear electro-optic (EO) effect after poling with an EO coefficient of 1.5×10 −11 m/V.
Combined local and carrier transport optical nonlinearities in a hetero n-i-p-i structure
Authors: Kost Alan , Jupina Michael , Garmire Elsa , Hasenberg T. C.
Published: July 2002

Nonlinear optical effects have been measured in a novel hetero n-i-p-i structure with strained InAs/GaAs superlattices as the quantum wells. For intensities below 6 W/cm2, changes in transmission are observed due to the screening of built-in fields in conjunction with the quantum-confined Stark effect. For intensities greater than 30 W/cm2, a further increase in transmission is observed due to state filling and exciton screening in the wells. It is demonstrated that a n-i-p-i structure, because of its lengthened carrier lifetime, can be used to reduce the intensity necessary for exciton saturation and state filling in quantum wells when the wells are placed in the i regions. Total changes in transmission greater than 25% have been seen, with no sign that the nonlinearity is saturating at 1 kW/cm2 (the highest excitation used here).
Clear energy level shift in ultranarrow InGaAs/InP quantum well wires fabricated by reverse mesa chemical etching
Authors: Notomi M. , Naganuma M. , Nishida T. , Tamamura T. , Iwamura H. , Nojima S. , Okamoto M.
Published: July 2002

We have fabricated ultranarrow InGaAs/InP buried quantum well wires by means of electron beam lithography and reverse mesa wet etching. Owing to the reverse mesa etching profile, the lateral dimension of the wires has been reduced to 10 nm. Furthermore, we investigated the optical characteristics of these wires by photoluminescence and observed, for the first time, clear dependence of luminescence wavelength upon the wire width even for wires down to 10 nm, which is well explained by the theoretical calculation. The blue-shifted shoulder structures were also observed and they were assigned theoretically to be the second quantized level.
Photoluminescence of GaAs quantum wells grown by molecular beam epitaxy with growth interruptions
Authors: Kopf R. F. , Schubert E. F. , Harris T. D. , Becker R. S.
Published: July 2002

Single GaAs/AlxGa1−xAs quantum wells, grown by molecular beam epitaxy with growth interruptions at each interface, are investigated using low-temperature photoluminescence. The three clearly resolved photoluminescence peaks are attributed to discrete monolayer thicknesses of the well. The splitting of the peaks is investigated for several hundred points across a 2 in. wafer. The negligible variation of the peak splitting is consistent with abrupt interfaces in the growth direction, atomically smooth interfaces, and discrete thicknesses of the quantum well with changes of only integer multiples of monolayers.
Spectral dependence of external reflection switching from indium antimonide
Authors: Feng S. , Irene E. A.
Published: July 2002

We demonstrate a novel InSb optical switch that relies on an increasing absorption mechanism and uses only the surface reflection. Observations of external switching of the reflectivity of the InSb surface have been made. In this study the switching or pump beam was from a pulsed CO2 laser. The polarity of the switched out signal, the probe beam, was found to depend on the wavelength of the probe beam. This novel spectral dependence was used to demonstrate several optical logic elements.
Growth of YBa2Cu3O7−x thin films on Si with a CoSi2 buffer layer
Authors: Luo Li , Muenchausen R. E. , Maggiore C. J. , Jimenez J. R. , Schowalter L. J.
Published: July 2002

By using the pulsed laser deposition technique, high-temperature superconducting YBa2Cu3O7−x (YBCO) films were grown on Si(001) with a 36 nm single-crystal 〈001〉 oriented CoSi2 buffer layer. The films, grown at a substrate temperature of ∼700 °C, have a metallic resistive temperature dependence with zero resistance at 85 K. X-ray diffraction, scanning electron microscopy, and ion channeling studies show that the YBCO films are polycrystalline but are strongly c-axis oriented normal to the Si substrate. Diffusion at the interface between the YBCO film and silicide buffer layer was minimized. This is essential to the growth of high-temperature superconducting films on Si substrates.
Preparation of PrBa2Cu3Oy and PrBa2Cu3Oy/YBa2Cu3Oy epitaxial films using molecular beam epitaxy
Authors: Obara H. , Kosaka S. , Kimura Y.
Published: July 2002

Using molecular beam epitaxy, we have successfully prepared PrBa2Cu3Oy (PBCO) films and PBCO/YBa2Cu3Oy (YBCO) layered structures. Epitaxial growth of these films was confirmed by in situ reflection high-energy electron diffraction. The temperature dependence of resistivity in the PBCO film showed semiconducting behavior. The lattice parameters of Pr1+xBa2−xCu3Oy films decreased when x increased and almost coincided with that of well-oxidized YBa2Cu3Oy films (y∼7) when x∼0.3. These experimental results indicate that YBCO/PBCO/YBCO multilayers are suitable for artificial layered structures of oxide superconductors, i.e., electronic devices.
Pulsed laser deposition of stoichiometric potassium-tantalate-niobate films from segmented evaporation targets
Authors: Yilmaz S. , Venkatesan T. , Gerhard-Multhaupt R.
Published: July 2002

The preparation of epitaxial potassium-tantalate-niobate (KTa0.7Nb0.3O3, KTN) films on strontium-titanate substrates by means of pulsed excimer laser evaporation in vacuum is reported. In the most successful deposition experiments, a segmented evaporation target consisting of a semicircular KTN single crystal and a semicircular potassium nitrate pellet was utilized−to our knowledge for the first time; it was thus possible to overcome the otherwise observed partial loss of the volatile potassium and to avoid potassium deficiency in the KTN films. Rutherford backscattering spectrometry and x ray diffraction results indicate that the samples have the desired stoichiometric composition as well as the orientation prescribed by the substrate crystal.
High-temperature operation (to 180  °C) of 0.98 μm strained single quantum well In0.2Ga0.8As/GaAs lasers
Authors: van der Ziel J. P. , Chand Naresh
Published: July 2002

Graded refractive index In0.2Ga0.8As/GaAs strained single quantum well ridge lasers, emitting at 0.98 μm, have been grown by molecular beam epitaxy. For pulsed excitation, laser operation has been obtained up to 180 °C for 1016-μm-long lasers. This record high operating temperature results from a high T0=160 °C characteristic of these long lasers. Anomalous threshold current dependences on temperature are found for shorter lasers and are attributed to band filling at high current densities and a shift of the emission from the n=1 quantum level to the n=2 level.