bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient enhanced diffusion of dopants in silicon induced by implantation damage
Authors: Angelucci R. , Negrini P. , Solmi S.
Published: July 2002

The effects of implantation damage on B, P, As, and Sb diffusion in Si during rapid thermal annealing and conventional heat treatment at low temperature (750–900 °C) have been investigated. Comparison of dopant profiles and junction depths in damaged and undamaged regions demonstrates that a Si+ implantation in the typical conditions used for preamorphization in p+/n shallow junction fabrication, produces a markedly enhanced diffusion for B and P atoms, while inducing only a negligible increase of As and Sb diffusivity. For all dopants enhanced diffusion shows a transient behavior and produces an increase in junction depth which is higher the lower the annealing temperature. This corroborates the opinion that rapid thermal annealing is a suitable technique for shallow junction fabrication.
Thermal donor formation in electron-irradiated Czochralski silicon
Authors: Svensson Johan , Svensson Bengt G. , Lindström J. Lennart
Published: July 2002

Isothermal heat treatment of Czochralski silicon samples has been performed at 450 °C. Prior to this treatment some samples were irradiated by high-energy electrons (2.0 MeV) and subsequently annealed at 311 °C. As a result, a high concentration of vacancy-dioxygen pairs was obtained. By a comparison of the thermal donor formation kinetics observed in the pretreated samples with that in as-grown samples, the vacancy-dioxygen pair can be ruled out as a ‘‘core’’ for thermal donors. A vacancy-trioxygen pair, which occurs as a result of the annealing of the vacancy-dioxygen pair, is also discussed.
Si-TaSi2 i
n s
i
t
u junction eutectic composite diodes
Authors: Ditchek Brian M. , Levinson Mark
Published: July 2002

Nearly ideal diodes have been fabricated using the in situ junctions present in Si-TaSi2 semiconductor-metal eutectic composites. The composites, prepared by directional solidification at the eutectic composition, have a high density of TaSi2 rods in a quasi-single crystalline P-doped, n-type Si matrix. Analysis of the diodes using current-voltage and capacitance-voltage techniques yields a TaSi2/Si Schottky barrier height of 0.62 eV and evidence that the voltage-dependent depletion zones can be made comparable to the interrod spacing to produce a ‘‘pinch-off’’ condition.
Improved surface nitridation of SiO2 thin films in low ammonia pressures
Authors: Ronda A. , Glachant A. , Plossu C. , Balland B.
Published: July 2002

Surface nitridation of thin SiO2 films (130 Å) has been achieved in low ammonia pressures (P≤10−1 mbar) by thermal activation (900 °C≤T≤1050 °C) or by electron-beam-enhanced reaction at room temperature. In the first case, the nitridation rate increases with P, T, and time t; in the latter, it depends on P, t, electron energy and flux, and reaches a maximum within the energy range (1–∼1.7 keV). Electrical characterization of metal-insulator-semiconductor structures shows that the SiO2/Si interfacial quality is not damaged as long as interfacial nitrogen concentration remains negligible. However, bulk and/or interfacial fixed positive charges are detected in the SiO2 films nitrided at room temperature.
Optimizing the performance of AlGaAs graded index separate confining heterostructure quantum well lasers
Authors: Shealy J. R.
Published: July 2002

High efficiency AlGaAs laser structures with graded index optical confinement regions and a single GaAs quantum well active region have been prepared using organometallic vapor phase epitaxy. The optimum quantum well thickness was determined to be near 50 Å where low internal losses are realized and the resulting threshold current densities were as low as 175 A/cm2 on single ended devices with a high reflectivity coating on the rear facet. The high injected carrier levels which are associated with thin quantum well structures lead to a severe degradation in device performance if the gain required to reach lasing threshold becomes too large. If the device length, the facet reflectivities, and the operating temperature were chosen to prevent the injected carrier concentrations in the quantum well from reaching a level coincident with the onset of nonradiative carrier loss mechanisms, single ended power efficiencies exceeded 55% for room-temperature, cw operation at 840 nm.
Ohmic contacts to n-type GaAs using high-temperature rapid thermal annealing for self-aligned processing
Authors: Chen C. L. , Mahoney L. J. , Woodhouse J. D. , Finn M. C. , Nitishin P. M.
Published: July 2002

We have formed Ge/Pd/W/Au and Ge/Mo/W/Au ohmic contacts to n-type GaAs by using a high-temperature rapid thermal annealing technique. The annealing schedule is compatible with that used for ion implantation activation, and the contact resistances (mid 10−6 Ω cm2) achieved are slightly higher than those for the commonly used Ni/Ge/Au alloyed contact. The Ge/Pd/W/Au contact maintains a good surface morphology and can be used as the implantation mask in self-aligned processes for devices such as heterojunction bipolar transistors.
Electrical effects of surface and deep states induced in n-type silicon by rapid thermal processing
Authors: Adekoya Wale-Oluseyi , Muller Jean-Claude , Siffert Paul
Published: July 2002

Induced defects in Czochralski-grown n-type 〈111〉 1–5 Ω cm silicon wafers due to high-temperature (800 °C/10 s; cooling rate≂100 °C/s) rapid thermal annealing (RTA) have been studied using deep level transient spectroscopy. The samples processed at 1000 °C and above showed a defect continuum containing at least an electron trap at E(0.58 eV) with a concentration ≂1015 cm−3. The electrical activity of the defects substantially degraded the current/voltage and capacitance/voltage characteristics of the Schottky diodes made from the processed samples with a barrier height reduction from 0.85 V at 800 °C/900 °C to 0.32 V at 1100 °C. However, a further RTA treatment at 650 °C for 60 s resulted in a complete restoration of these characteristics and no trap was recorded in the deep level transient spectroscopy spectrum. This degradation, which was not observed in oxide-encapsulated samples processed in the same temperature range, is considered to be due to impurity contamination during RTA processing which is enhanced at high temperatures (≂1000 °C) leading to a high density of surface states.
Thin silicon oxides grown by low-temperature rf plasma anodization and deposition
Authors: Nelson S. A. , Buhrman R. A.
Published: July 2002

We have studied the low-temperature (<500 °C) growth and deposition of thin silicon oxides in an rf plasma system. Oxides were grown by plasma anodization, sputter deposition, and combinations of these two processes. The oxides were electrically characterized with high-frequency and low-frequency capacitance-voltage techniques and the quality was found to depend strongly on plasma process parameters. In particular, we found strong dependences on bias current, plasma potential, and oxygen partial pressure. Under presently optimal conditions we have fabricated oxides with oxide charge densities Qox<1×1011 charges/cm2, interface state densities Dss<2×1011 states/cm2/eV, and breakdown fields Eb>13 MV/cm. Finally, we have studied the reduction of fast surface states in the plasma oxides by rapid thermal annealing.
Effects of saturation and loss on nonlinear directional couplers
Authors: Stegeman G. I. , Seaton C. T. , Ironside C. N. , Cullen T. , Walker A. C.
Published: July 2002

We show that large changes are introduced into the operational characteristics of nonlinear directional couplers by both loss and saturation of the nonlinearity, especially the latter. Specific numerical examples are given.
Light evolution in alkaline-earth-sulfide thin-film ac electroluminescent devices
Authors: Crandall Richard S.
Published: July 2002

Results of an extensive survey of the time evolution of the light output of thin-film ac electroluminescent devices fabricated from alkaline-earth-sulfide phosphors with different activators are presented. Light output increases slowly until a steady state, which depends on voltage and drive frequency, is reached. It is shown that the slow evolution is due to tunneling of electrons from deep states and eventual trapping of these electrons in shallow states. The dynamics of the device is determined by the supply of electrons.
Electron beam pumped lasing in ZnSe grown by molecular beam epitaxy
Authors: Potts J. E. , Smith T. L. , Cheng H.
Published: July 2002

We report the first observations of lasing action in electron beam pumped ZnSe grown by molecular beam epitaxy on (100) GaAs substrates. In spite of the small thicknesses (approximately 2 μm) of the films used, lasing thresholds as low as 3.9 A/cm2 have been measured at an accelerating voltage of 20 kV when the (nominal) sample temperature was 15 K. Threshold currents increased for sample temperatures greater than 100 K, and for accelerating voltages both less than and greater than 20 kV.
Stimulated emission of photoexcited GaAs/AlxGa1−xAs single quantum wells
Authors: Borenstain S. , Fekete D. , Vofsi M. , Sarfaty R. , Cohen E. , Ron Arza
Published: July 2002

The optical gain of narrow, single quantum well GaAs/AlxGa1−xAs structures is measured by the variable illuminated stripe length method at low temperatures. Stimulated emission (SE) is observed only from the lowest states of the electron-hole plasma (EHP) excited in the well and from the cladding layers. In contrast to the case of bulk AlxGa1−xAs, the SE spectrum is independent of either excitation intensity or stripe length. The high e-h pair density in the quantum well results in higher gain values (per unit excited volume) than those observed in bulk AlxGa1−xAs under similar photoexcitation conditions.
Amorphous alloys formed by microsecond current pulses
Authors: Clemens B. M. , Gilgenbach R. M. , Bidwell S.
Published: July 2002

We report the use of microsecond current pulses to transform layered crystalline nickel-zirconium films to amorphous alloy. Starting material was electron beam deposited multilayers with a composition modulation wavelength of 34 nm, an average composition of Ni63Zr37, and a total thickness of 680 nm. Electrical pulses were approximately rectangular and about 3 μs in duration, with an intensity of several hundred amperes, directly coupling 1.6 to 3 J of energy uniformly into the film. By monitoring current and voltage, the reaction and melting of the sample were observed, and the total energy of the pulse was easily computed. A sharp threshold in pulse energy for sample transformation was observed. A simple heat flow calculation demonstrated that the chemical energy released by the reaction, and the change in diffusion kinetics as the sample temperature exceeded the glass transition temperature of the amorphous alloy, are responsible for this sudden onset. The maximum temperature estimated from this calculation is below the melting point of the constituents, and the cooling rate is 107–108 K/s which is in agreement with the formation of amorphous alloy.
Electron spin resonance studies on buried oxide silicon-on-insulator
Authors: Makino T. , Takahashi J.
Published: July 2002

Electron spin resonance is used to study defects in high-dose oxygen-ion implanted Si substrates. By this implantation, a crystalline Si/buried SiO2/crystalline Si structure is created. Two kinds of defect centers are found; one is assigned to the amorphous center, and the other, the Pb0 center, which has been observed at thermally grown SiO2/(111) Si interfaces. The observed Pb0 center appears to exist near precipitated SiO2/crystalline Si interfaces, rather than crystalline Si/buried SiO2 interfaces. When annealed at 1150 °C, spin density decreases due to oxygen outdiffusion from the crystalline Si.
Gallium arsenide field-effect transistor by close spaced vapor transport epitaxy
Authors: Mimila-Arroyo J. , Castanedo R. , Chávez F. , González R. , Navarro G. , Reynoso A.
Published: July 2002

For the first time gallium arsenide field-effect transistors have been made using epitaxial layers grown by the close spaced vapor transport technique (CSVT). The layers were unintentionally doped and their free-carrier concentration was adjusted through the growth parameters to around 1017 cm−3. For the growth of the layers, water vapor was used as transporting gas. This transistor confirms the capability of the simplest and most inexpensive epitaxial technique (CSVT) for growing device quality gallium arsenide epitaxial layers.
Selective liquid phase epitaxy and defect reduction in GaAs grown on GaAs-coated silicon by molecular beam epitaxy
Authors: Sakai Shiro , Matyi R. J. , Shichijo H.
Published: July 2002

This letter reports the first successful liquid phase epitaxial (LPE) growth of GaAs on GaAs-coated Si grown by molecular beam epitaxy (MBE). The LPE growth was found to be strongly dependent on the width of the oxide stripe window which defined the area of the sample that was accessible to the LPE melt. Uniform single-crystal layers of GaAs were obtained when the stripe was narrower than 20 μm; in contrast, meltback of the GaAs layers was observed in larger stripes. The minimum dislocation density of the LPE layer that was determined from cross-sectional transmission electron microscopy was about 2–5×106 cm−2. This value was about two orders of magnitude lower than the dislocation density that was observed in the MBE GaAs-on-Si layer which served as a substrate for the LPE growth.
Highly oriented polydiacetylene films by vacuum deposition
Authors: Kanetake Tatsuo , Ishikawa Ken , Koda Takao , Tokura Yoshinori , Takeda Kenji
Published: July 2002

Highly oriented polydiacetylene films have been fabricated by the vacuum deposition method using a new alignment technique. Details of the method are described, and optical and structural properties of typical oriented films of poly[dodecadiyne-1,12-diol- bis(n-butoxycarbonyl-methyl-urethane)][PDA-4BCMU] are reported.
Brillouin scattering from Love waves in Cu/Nb metallic superlattices
Authors: Bell J. A. , Zanoni R. J. , Seaton C. T. , Stegeman G. I. , Bennett W. R. , Falco C. M.
Published: July 2002

Love waves have been observed for the first time by Brillouin scattering. The c12 constant of the metallic superlattice Cu/Nb has been measured.
Electric field induced shifts in exciton luminescence in ZnSe/(Zn,Mn)Se superlattices
Authors: Fu Qiang , Nurmikko A. V. , Kolodziejski L. A. , Gunshor R. L. , Wu J.-W.
Published: July 2002

Application of moderate electric fields to ZnSe/(Zn,Mn)Se quantum wells yields distinct spectral shifts of the recombining exciton luminescence. This shows that confinement effects in this heterostructure are sufficient to increase the exciton ionization threshold. At high applied fields and low temperatures, injection of hot electrons from the n+GaAs/ZnSe heterojunction at our substrate/buffer layer excites yellow luminescence from internal transitions of the Mn ion in (Zn,Mn)Se layers.
Layer interdiffusion in Se-doped AlxGa1−xAs-GaAs superlattices
Authors: Deppe D. G. , Holonyak N. , Hsieh K. C. , Gavrilovic P. , Stutius W. , Williams J.
Published: July 2002

Transmission electron microscopy and carrier concentration measurements are used to characterize the layer interdiffusion (Al-Ga interdiffusion) mechanism of a Se-doped AlxGa1−xAs-GaAs superlattice (SL) under high-temperature annealing. By varying the annealing environment and comparing the results with similarly annealed undoped SL’s and Mg-doped SL’s, we find that the layer interdiffusion occurs through interaction of the Se impurity with native defects associated with As-rich conditions, the most likely of which is the column III vacancy.
Direct writing of submicron metallic features with a scanning tunneling microscope
Authors: Silver R. M. , Ehrichs E. E. , de Lozanne A. L.
Published: July 2002

We demonstrate for the first time that the scanning tunneling microscope can be used to write metallic features on a surface without further process steps. Using organometallic gases we have obtained features down to 20 nm in size.
High performance magneto-optical TbFeCo disks prepared by coevaporation
Authors: Shin Sung-Chul
Published: July 2002

We have prepared high performance TbFeCo magneto-optical recording media by coevaporation. A carrier-to-noise ratio (CNR) of about 60 dB, measured with a 30-kHz slot bandwidth, was obtained and a CNR was limited mainly by shot noise. It was found that the threshold laser power in these media linearly increased with a slope of 0.3 mW/kOe as the coercivity increased.
Molecular beam epitaxial growth of CoSi2 on porous Si
Authors: Kao Y. C. , Wang K. L. , Wu B. J. , Lin T. L. , Nieh C. W. , Jamieson D. , Bai G.
Published: July 2002

CoSi2 epitaxial layers with different thicknesses have been grown onto porous-Si substrates by molecular beam epitaxy. Good crystallinity is obtained for CoSi2 films thicker than 50 nm. The use of a thin buffer layer is found to be crucial in order to achieve abrupt interface and good crystallinity. Planar view transmission electron microscope images obtained from 30-nm-thick CoSi2 buffer-Si/porous-Si samples indicate that a large area of the epitaxial film is dislocation free, in contrast with a uniform distribution of misfit dislocations across relaxed CoSi2/single-crystal Si samples of the same thickness. This study suggests a possible pseudomorphic growth by using porous Si as a substrate.
Nonlinear spectroscopy in In0.53Ga0.47As/InP multiple quantum wells
Authors: Tai K. , Hegarty J. , Tsang W. T.
Published: July 2002

Near-band-gap optical nonlinearity in In0.53Ga0.47As/InP multiple quantum well (MQW) structures is studied by a combination of nonlinear absorption, pump-and-probe, and forward degenerate four-wave mixing experiments. Near complete saturation of the n=1 heavy-hole exciton is observed for the first time in In0.53Ga0.47As/InP MQW structures. Nonlinear susceptibility χ(3) is found to be 0.08 esu, which is about the same as that for GaAs/GaAlAs MQW structures. Saturation intensity is 200 W/cm2.
Raman scattering study of alloyed Au-Ge ohmic contacts to GaAs
Authors: Kirillov D. , Chung Y.
Published: July 2002

Raman scattering was applied to study alloying of the Au-Ge-GaAs ohmic contact structure. The Ge layer was found to be amorphous as deposited, but transformed into polycrystalline Ge after alloying. Ge diffusion into the GaAs did not result in the formation of n+-GaAs. A broadband in the Raman spectra was found and attributed to electronic scattering by electrons in the GaAs trapped by deep levels formed by Ge and Au diffusion. These results were consistent with a model in which conduction through the contact occurred by resonant tunneling assisted by impurity levels in the graded Ge-GaAs heterojunction structure.
Quantum interference devices made from superconducting oxide thin films
Authors: Koch R. H. , Umbach C. P. , Clark G. J. , Chaudhari P. , Laibowitz R. B.
Published: July 2002

We have fabricated superconducting quantum interference devices (dc SQUID’s) from thin films of the superconducting oxide YBa2Cu3Oy. The devices were made by first lithographically patterning an ion implant mask containing a 40 by 40 μm loop and two 17-μm-wide weak links over a ∼1-μm-thick oxide film. Ion implantation was then used to destroy the superconductivity in the film surrounding the device without actually removing material, resulting in a completely planar structure for the SQUID’s. The SQUID’s were operated in the temperature range from 4.2 to 68 K. The superconducting flux quantum was measured to be h/2e in these materials.
Photoelectromagnetic effect in p-type HgCdTe layers grown by liquid phase epitaxy
Authors: Mordowicz D. , Zemel A. , Zussman A. , Eger D. , Goldstein Y.
Published: July 2002

Photo-electro-magnetic effect measurements of p-type Hg1−xCdxTe layers are made at 80 K as a function of the magnetic field. A negative (anomalous) effect is observed. The basic properties of the minority carriers, mobility, lifetime, surface and interface recombination rates, are determined from best fitting of the experimental data to the theory.
Polarization-dependent optical gain and absorption spectra of (Cd,Mn)Te and (Zn,Mn)Se multiple quantum well structures
Authors: Bonsett T. C. , Yamanishi M. , Gunshor R. L. , Datta S. , Kolodziejski L. A.
Published: July 2002

The absorption and gain spectra for TE and TM modes in (100) oriented (Cd,Mn)Te and (Zn,Mn)Se multiple quantum well (MQW) structures have been measured by observing the photoluminescence from a cleaved edge. In (Cd,Mn)Te MQW’s the TE mode absorption and gain are dominant, as observed earlier in (Ga,Al)As MQW’s; in (Zn,Mn)Se MQW’s, however, we observe a clear dominance of the TM mode near the band edge. Whereas the TE mode dominates the gain spectra of a (Cd,Mn)Te MQW, the TM mode dominates the gain spectra of a (Zn,Mn)Se MQW, providing the first report of TM-polarized stimulated emission from a MQW structure. The opposite behavior of (Cd,Mn)Te and (Zn,Mn)Se MQW’s is ascribed to the opposite sense of the uniaxial strain in these systems.
Effect of heat treatment on redistribution of hydrogen in directionally cast polycrystalline silicon
Authors: Kumar Rajesh , Kotnala R. K. , Arora N. K. , Das B. K.
Published: July 2002

The effect of heat treatment on the minority-carrier surface recombination velocity in hydrogen-passivated polycrystalline silicon samples has been studied in the temperature range 350–500 °C using the electron-beam-induced current mode of a scanning electron microscope. Minority-carrier trap center densities, calculated from the minority-carrier surface recombination velocity data, varying from 8×1012 to 1.2×1012 cm−2 have been measured. A finite decrease in the minority-carrier trap center density indicates that hydrogen atoms diffuse to the surface from the bulk of the hydrogenated samples. The activation energy of hydrogen diffusion in silicon is found to be 0.53±0.04 eV.
Comparison of low-pressure and plasma-enhanced chemical vapor deposited tungsten thin films
Authors: Greene W. M. , Oldham W. G. , Hess D. W.
Published: July 2002

Tungsten thin films deposited by low-pressure and plasma-enhanced chemical vapor deposition are characterized to detail the effect of plasma-surface interactions on nucleation and growth. Transition from α- to β-W is observed as the H2/WF6 flow ratio is decreased from 10/1 to 1/1 in plasma-enhanced deposition; transition from α-W to amorphous W is observed under the same conditions in low-pressure chemical vapor deposition. The temperature coefficient of resistivity varies from 4.9 to 2.0 ppthou/K as the plasma-deposited films switch from α to β phase; the temperature coefficient of resistivity varies from 3.2 to −0.5 ppthou/K as the low-pressure chemically vapor deposited films become amorphous. The increased crystallinity and metastable phase formation in plasma environments are attributable to higher effective surface temperature resulting in enhanced surface mobility and grain growth.
Poled electro-optic waveguide formation in thin-film organic media
Authors: Thackara J. I. , Lipscomb G. F. , Stiller M. A. , Ticknor A. J. , Lytel R.
Published: July 2002

We describe a novel technique for the fabrication of electro-optic (EO) waveguides in integrated optic device structures employing organic EO materials. The technique combines the poling and waveguide formation steps by utilizing patterned poling electrodes and the induced birefringence associated with the poling process. Several prototype waveguide devices fabricated using this procedure are reported.
Evidence of room-temperature exciton by magnetophotoreflectance in epitaxial GaAs and quantum well structures
Authors: Zheng X. L. , Heiman D. , Lax B. , Chambers F. A. , Stair K. A.
Published: July 2002

Photoreflectance experiments with magnetic fields up to 14.5 T are performed on epitaxial GaAs and GaAs/Ga1−xAlxAs quantum well samples at room temperature and 2 K. Our experiments show unique and direct evidence that photoreflectance structures are excitonic transitions in all of the above cases.
Novel high-speed transistor based on charge emission from a quantum well
Authors: Kastalsky A. , Grinberg A.
Published: July 2002

A novel unipolar transistor employing properties of electrons confined in a single quantum well is proposed. The gate modulation of a charge density in the quantum well results in an exponentially strong variation of the output thermionic emission current to the collector. The device combines the attractive features of both bipolar and field-effect transistors and provides a high speed (2–3 ps intrinsic delay time) with a large current drive (∼105 A/cm2) and high transconductances (1–10 S/mm).
Room-temperature codeposition growth technique for pinhole reduction in epitaxial CoSi2 on Si (111)
Authors: Lin T. L. , Fathauer R. W. , Grunthaner P. J. , d’Anterroches C.
Published: July 2002

A solid phase epitaxy technique has been developed for the growth of CoSi2 films on Si (111) with no observable pinholes (103 cm−2 detection limit). The technique utilizes room-temperature codeposition of Co and Si in stoichiometric ratio, followed by the deposition of an amorphous Si capping layer and subsequent in situ annealing at 550–600 °C. CoSi2 films grown without the Si cap are found to have pinhole densities of 107–108 cm−2 when annealed at similar temperatures. A CF4 plasma etching technique was used to increase the visibility of the pinholes in the silicide layer. This plasma technique extends the pinhole detection resolution to 103 cm−2 and is independent of the pinhole size.
Patterned quantum well semiconductor injection laser grown by molecular beam epitaxy
Authors: Kapon E. , Harbison J. P. , Yun C. P. , Stoffel N. G.
Published: July 2002

A novel quantum well semiconductor laser structure is described. This patterned quantum well laser utilizes the thickness variations and nonplanarity exhibited by quantum wells grown on grooved substrates in order to achieve lateral carrier confinement and real index waveguiding. Index guided GaAs/AlGaAs patterned quantum well lasers with ∼1-μm-wide active layer stripes and threshold currents as low as 6 mA have been grown by molecular beam epitaxy. This patterned quantum well laser configuration is particularly attractive for fabricating quantum wire and quantum box semiconductor injection lasers.
Donor identification in bulk gallium arsenide
Authors: Harris T. D. , Skolnick M. S. , Parsey J. M. , Bhat R.
Published: July 2002

We report identification, by a spectroscopic method, of shallow donors in both epitaxial and bulk gallium arsenide. Identification is achieved using photoluminescence from resonantly excited two-electron satellites of donor bound exciton lines at 4.2 K in a magnetic field of 9.5 T. Sulfur and a previously unreported lower binding energy donor dominate in liquid-encapsulated Czochralski-grown crystals, while S and Si are dominant in the Bridgman-grown material. Central cell structure is resolved in the (D0,X) lines in a high magnetic field.
Superconducting thin films of Y-Ba-Cu-O produced by neodymium:yttrium aluminum garnet laser ablation
Authors: Lynds L. , Weinberger B. R. , Peterson G. G. , Krasinski H. A.
Published: July 2002

Superconducting thin films of Y-Ba-Cu-O produced by laser ablation of nonsuperconducting targets by 1064 nm neodymium:yttrium aluminum garnet radiation in an oxygen ambient are described. Deposition rates of 100 Å/s were achieved for 1 J pulses at 30 Hz. Scanning Auger microscopy indicates phase segregated films. Optical probing of ablated flux suggests it consists of atomic and molecular fragments.
Aluminum spiking at contact windows in Al/Ti-W/Si
Authors: Chang Peng-Heng , Hawkins R. , Bonifield T. D. , Melton L. A.
Published: July 2002

Aluminum spike formation through a Ti-W interdiffusion barrier layer at contact windows is studied by cross-sectional transmission electron microscopy for Al-1% Si and Al-2% Cu films. For Ti-W layers thinner than 1000 Å Al spikes form in both Al-Si and Al-Cu systems. The two types of Al films behave similarly in terms of the propensity for spike formation and spike morphology in the presence of a Ti-W layer. Aluminum spikes generally have an inverted pyramidal, truncated inverted pyramidal, or parallelepipedal shape. Aluminum in a spike is generally single crystal and some of the Al spikes maintain one of the following orientation relationships with the surrounding Si substrate: [011]Al∥[1̄23]Si and (200)Al∥(11̄1)Si or [001]Al∥[1̄12]Si and (200)Al is 2° off (11̄1)Si. A mechanism for Al spike formation through Ti-W is proposed.
Rapid thermal annealing of elevated-temperature silicon implants in InP
Authors: Tell B. , Brown-Goebeler K. F. , Cheng C. L.
Published: July 2002

Rapid thermal annealing of elevated-temperature Si implants in InP is shown to result in higher donor activation and electron mobility with lower-temperature–shorter-anneal cycles than for room-temperature implants. The reduced cycles (temperature below 800 °C with times of ∼10 s) also result in process simplification with negligible thermal surface degradation and insignificant Si diffusion. The results are demonstrated with a dual-energy implant scheme applicable to field-effect transistors and with a single-energy heavy-dose implant useful for achieving low-resistance ohmic contacts.
Thin films of Y-Ba-Cu-O on silicon and silicon dioxide
Authors: Mogro-Campero A. , Turner L. G.
Published: July 2002

Thin films of the high-temperature superconductor Y-Ba-Cu-O near the 1:2:3 stoichiometry were deposited on single-crystal silicon and oxidized silicon with a zirconia buffer layer. Zero-resistance transition temperatures up to 83 K have been measured on the films formed by a process of sequential evaporation and furnace annealing.
Multilayer metallization structures with titanium nitride and titanium silicide prepared by multipulse laser irradiation
Authors: Crǎciun V. , Mihǎilescu I. N. , Ursu I. , Crǎciunoiu F. , Corici A. , Leggieri G. , Luches A. , Nassisi V. , Martino M.
Published: July 2002

We synthesized titanium nitride and titanium silicide layers on silicon by only one-step multipulse laser irradiation of titanium-coated silicon wafers in a jet of nitrogen, with characteristics appropriate for utilization in metallization schemes with very large scale integration devices.
Surface plasmon interferometry in the visible
Authors: Rothenhäusler Benno , Knoll Wolfgang
Published: July 2002

Plasmon surface polaritons that are launched at an index step from a Ag/dielectric coating/air to a Ag/air interface interfere with the evanescent waves of the driving photon field. The resulting intensity distribution on the Ag surface can be imaged by the recently developed surface plasmon microscopy. We show that it is thus possible to derive the real part as well as the imaginary part of the complex surface plasmon wave vector.
Sputter deposition of YBa2Cu3O6+x on alumina and the influence of ZrO2 buffer layers
Authors: Stamper A. , Greve D. W. , Wong D. , Schlesinger T. E.
Published: July 2002

The deposition of films of YBa2Cu3O6+x by rf diode sputtering on alumina has been investigated. Although a stoichiometric (123) target was employed, the film composition differs from that of the target and varies as a function of position on the substrate. Films displaying a broad resistive transition have been produced in a reproducible manner. It is demonstrated that the use of a ZrO2 buffer layer decreases the transition width significantly and consistently yields films which have a more metallic-like behavior above Tc.
Diagnostics of silane and germane radio frequency plasmas by coherent anti-Stokes Raman spectroscopy
Authors: Perry Joseph W. , Shing Y. H. , Allevato C. E.
Published: July 2002

I n situ plasma diagnostics using coherent anti-Stokes Raman spectroscopy have shown different dissociation characteristics for GeH4 and SiH4 in radio frequency (rf) plasma-enhanced chemical vapor deposition of amorphous silicon germanium alloy (a-SiGe:H) thin films. The GeH4 dissociation rate in rf plasmas is a factor of about 3 larger than that of SiH4. Plasma diagnostics have revealed that the hydrogen dilution of the SiH4 and GeH4 mixed plasma plays a critical role in suppressing the gas phase polymerization and enhancing the GeH4 dissociation.
Correlations between electrical properties and interfacial reactions for cobalt-germanium contacts to n-type GaAs
Authors: Genut M. , Eizenberg M.
Published: July 2002

Correlations between the electrical properties and interfacial reactions for the Co/GaAs, Co/Ge/GaAs, and Ge/Co/GaAs contact systems have been studied. Current-voltage and capacitance-voltage measurements show that for all three systems following heat treatments at temperatures not higher than 400 °C, a rectifying contact was obtained. However, annealing in the temperature range of 450–600 °C leads to an ohmic behavior; the lowest contact resistivity value (2.7×10−4 Ω cm2) was obtained for Co/Ge/GaAs following heat treatment at 500 °C. The electrical properties of the contacts are correlated with modifications in the structure and composition of the metallization interfacing the GaAs as determined by Auger electron spectroscopy, transmission electron microscopy, and x-ray diffraction.
Electrical measurements in high T
c Bi-Sr-Ca-Cu-O thin films
Authors: Setsune K. , Hirochi K. , Adachi H. , Ichikawa Y. , Wasa K.
Published: July 2002

Electrical measurements were performed on polycrystalline thin films of the high Tc Bi-Sr-Ca-Cu-O system. The resistance of the superconducting state was confirmed to be smaller than 10−8 Ω cm at 100 K. It is confirmed directly that the critical current density at 77 K was in excess of 105 A/cm2 and the dependence of critical current on temperature was able to be represented approximately by (1−T/Tc )2.
Nonplanar index-guided quantum well heterostructure periodic laser array
Authors: Zmudzinski C. A. , Givens M. E. , Bryan R. P. , Coleman J. J.
Published: July 2002

Data are presented on nonplanar index-guided quantum well heterostructure periodic laser arrays grown by metalorganic chemical vapor deposition (MOCVD). The nonplanar array structure, formed by a single MOCVD growth over a selectively etched corrugated substrate, not only provides index guiding for the individual array elements, but also suppresses lateral lasing and amplified spontaneous emission for the entire array. As a result, the entire width of the device is utilized for optical emission, and no additional processing steps are required. Devices tested exhibit uniform emission and show no signs of lateral lasing or amplified spontaneous emission for array widths up to 3.3 times the cavity length. The processing required for device fabrication is therefore minimized by taking advantage of the properties of MOCVD growth over nonplanar substrates.
Hydrogen incorporation in undoped microcrystalline silicon
Authors: Johnson N. M. , Ready S. E. , Boyce J. B. , Doland C. D. , Wolff S. H. , Walker J.
Published: July 2002

Hydrogen in undoped, unalloyed microcrystalline silicon (μc-Si:H) has been investigated with secondary-ion mass spectrometry (SIMS), Raman spectroscopy, infrared absorption spectroscopy, and nuclear magnetic resonance (NMR). The samples were grown by plasma-enhanced chemical vapor deposition with hydrogen to silane dilution ratios (H2:SiH4) ranging from 0:1 to 98:1. Microcrystallinity is obtained for dilution ratios of 20:1 and greater. The hydrogen concentration is shown to depend nonmonotonically on the degree of hydrogen dilution. The H concentration in the films decreases with dilution for ratios from 0:1 to 10:1 and then increases with greater dilution. This dependence on dilution is established with both NMR and SIMS and suggests the existence of competing processes in the incorporation of hydrogen during deposition. It is further observed that the formation of microcrystallites is accompanied by the appearance of both higher order silicon hydrides and large concentrations of unbound molecular hydrogen.
Compositional disordering of GaAs/AlGaAs multiple quantum wells using ion bombardment at elevated temperatures
Authors: Anderson K. K. , Donnelly J. P. , Wang C. A. , Woodhouse J. D. , Haus H. A.
Published: July 2002

A new method has been developed for compositional mixing of heterostructures by ion bombardment at elevated temperatures. Complete mixing of a 1-μm-thick GaAs/AlGaAs 40-period multiple quantum well layer has been achieved by bombardment with 380 keV Ne+ ions for 1 h with the sample at 700 °C. This temperature is much lower than the annealing temperatures used in other vacancy-enhanced disordering techniques, and even lower temperatures and shorter durations should be possible. Compositional disordering is verified by sputter-profile Auger electron spectroscopy and transmission electron microscopy. Complete mixing is also demonstrated by optical transmission spectra of the disordered material, which exhibit the same band edge as a uniform alloy with the average aluminum mole fraction of the multiple quantum well layer.
Complex pattern of
Mycobacterium marinum
gene expression during long-term granulomatous infection
Authors: Chan Kaman , Knaak Timothy , Satkamp Laura , Humbert Olivier , Falkow Stanley , Ramakrishnan Lalita
Published: July 2002

During latent infection of humans with
Mycobacterium tuberculosis
, bacteria persist in the asymptomatic host within granulomas, organized collections of differentiated macrophages, and other immune cells. The mechanisms for persistence remain poorly understood, as is the metabolic and replicative state of the microbes within granulomas. We analyzed the gene expression profile of
Mycobacterium
marinum
, the cause of fish and amphibian tuberculosis, during its persistence in granulomas. We identified genes expressed specifically when
M. marinum
persists within granulomas. These granuloma-activated genes were not activated
in vitro
in response to various conditions postulated to be operant in tuberculous granulomas, suggesting that their granuloma-specific activation was caused by complex conditions that could not be mimicked
in vitro
. In addition to the granuloma-activated genes, the bacteria resident in granulomas expressed a wide range of metabolic and synthetic genes that are expressed during logarithmic growth in laboratory medium. Our results suggest a dynamic host-pathogen interaction in the granuloma, where metabolically active bacteria are kept in check by the host immune system and where the products of granuloma-specific bacterial genes may thwart the host's attempt to completely eradicate the bacteria.
Element-specific localization of
Drosophila
retrotransposon Gag proteins occurs in both nucleus and cytoplasm
Authors: Rashkova S. , Karam S. E. , Pardue M.-L.
Published: July 2002

Many
Drosophila
non-long terminal repeat (LTR) retrotransposons actively transpose into internal, gene-rich regions of chromosomes but do not transpose onto chromosome ends.
HeT-A
and
TART
are remarkable exceptions; they form telomeres of
Drosophila
by repeated transpositions onto the ends of chromosomes and never transpose to internal regions of chromosomes. Both telomeric and nontelomeric, non-LTR elements transpose by target-primed reverse transcription, and their targets are not determined simply by DNA sequence, so it is not clear why these two kinds of elements have nonoverlapping transposition patterns. To explore roles of retrotransposon-encoded proteins in transposition, we analyzed intracellular targeting of Gag proteins from five non-LTR retrotransposons,
HeT-A
,
TART
,
jockey
,
Doc
, and
I
factor. All were expressed as green fluorescent protein-tagged proteins in cultured
Drosophila
cells. These Gag proteins have high levels of sequence similarity, but they have dramatic differences in intracellular targeting. As expected,
HeT-A
and
TART
Gags are transported efficiently to nuclei, where they show specific patterns of localization. These patterns are cell cycle-dependent, disappearing during mitosis. In contrast, only a fraction of
jockey
Gag moves into nuclei, whereas neither
Doc
nor
I
factor Gag is detected in the nucleus. Gags of the nontelomeric retrotransposons form characteristic clusters in the cytoplasm. These experiments demonstrate that closely related retrotransposon Gag proteins can have different intracellular localizations, presumably because they interact differently with cellular components. We suggest that these interactions reflect mechanisms by which the cell influences the level of transposition of an element.
Identification in mice of two isoforms of the cysteinyl leukotriene 1 receptor that result from alternative splicing
Authors: Maekawa Akiko , Kanaoka Yoshihide , Lam Bing K. , Austen K. Frank
Published: July 2002

Two classes of human G protein-coupled receptors, cysteinyl leukotriene 1 (CysLT1) and CysLT2receptors, recently have been characterized and cloned. Because the CysLT1receptor blockers are effective in treating human bronchial asthma and the mouse is often used to model human diseases, we isolated the mouse CysLT1receptor from a mouse lung cDNA library and found two isoforms. A short isoform cDNA containing two exons encodes a polypeptide of 339 aa with 87.3% amino acid identity to the human CysLT1receptor. A long isoform has two additional exons and an in-frame upstream start codon resulting in a 13-aa extension at the N terminus. Northern blot analysis revealed that the mouse CysLT1receptor mRNA is expressed in lung and skin; and reverse transcription–PCR showed wide expression of the long isoform with the strongest presence in lung and skin. The gene for the mouse CysLT1receptor was mapped to band XD. Leukotriene (LT) D4induced intracellular calcium mobilization in Chinese hamster ovary cells stably expressing either isoform of the mouse CysLT1receptor cDNA. This agonist effect of LTD4was fully inhibited by the CysLT1receptor antagonist, MK-571. Microsomal membranes from each transformant showed a single class of binding sites for [3H]LTD4; and the binding was blocked by unlabeled LTs, with the rank order of affinities being LTD4>> LTE4= LTC4>> LTB4. Thus, the dominant mouse isoform with the N-terminal amino acid extension encoded by an additional exon has the same ligand response profile as the spliced form and the human receptor.
Nanoindentation: Toward the sensing of atomic interactions
Authors: Fraxedas J. , Garcia-Manyes S. , Gorostiza P. , Sanz F.
Published: July 2002

The mechanical properties of surfaces of layered materials (highly oriented pyrolytic graphite, InSe, and GaSe) and single-crystal ionic materials (NaCl, KBr, and KCl) have been investigated at the nanometer scale by using nanoindentations produced with an atomic force microscope with ultrasharp tips. Special attention has been devoted to the elastic response of the materials before the onset of plastic yield. A new model based on an equivalent spring constant that takes into account the changes in in-plane interactions on nanoindentation is proposed. The results of this model are well correlated with those obtained by using the Debye model of solid vibrations.
Mmh
/
Ogg1
gene inactivation results in accumulation of 8-hydroxyguanine in mice
Authors: Minowa Osamu , Arai Tsuyoshi , Hirano Masanori , Monden Yoshiaki , Nakai Shigeyasu , Fukuda Mayuko , Itoh Masaki , Takano Hiroshi , Hippou Yoshitaka , Aburatani Hiroyuki , Masumura Ken-ichi , Nohmi Takehiko , Nishimura Susumu , Noda Tetsuo
Published: July 2002

The major mutagenic base lesion in DNA caused by exposure to reactive oxygen species is 8-hydroxyguanine or 7,8-dihydro-8-oxoguanine (8-OH-G). Products of the human
MMH
/
OGG1
gene are known to catalyze
in vitro
the reactions repairing this DNA lesion. To analyze the function of
Mmh
in vivo
, we generated a mouse line carrying a mutant
Mmh
allele by targeted gene disruption.
Mmh
homozygous mutant mice were found to have a physically normal appearance, but to have lost nicking activity in liver extracts for substrate DNA containing 8-OH-G, exhibiting a 3-fold increased accumulation of this adduct at 9 weeks of age compared with wild-type or heterozygous mice. Further elevation to 7-fold was observed in 14-week-old animals. Substantial increase of spontaneous mutation frequencies was clearly identified in
Mmh
mutant mice bearing transgenic
gpt
genes. These results indicate that exposure of DNA to endogenous oxidative species continuously produces the mutagenic adduct 8-OH-G in mice, and
Mmh
plays an essential role in repair of this DNA damage.
Microglia at brain stab wounds express connexin 43 andin vitroform functional gap junctions after treatment with interferon-γ and tumor necrosis factor-α
Authors: Eugenín Eliseo A. , Eckardt Dominik , Theis Martin , Willecke Klaus , Bennett Michael V. L. , Sáez Juan C.
Published: July 2002

Gap junctional communication between microglia was investigated at rat brain stab wounds and in primary cultures of rat and mouse cells. Under resting conditions, rat microglia (FITC-isolectin-B4-reactive cells) were sparsely distributed in the neocortex, and most (95%) were not immunoreactive for Cx43, a gap junction protein subunit. At brain stab wounds, microglia progressively accumulated over several days and formed aggregates that frequently showed Cx43 immunoreactivity at interfaces between cells. In primary culture, microglia showed low levels of Cx43 determined by Western blotting, diffuse intracellular Cx43 immunoreactivity, and a low incidence of dye coupling. Treatment with the immunostimulant bacterial lipopolysaccharide (LPS) or the cytokines interferon-γ (INF-γ) or tumor necrosis factor-α (TNF-α) one at a time did not increase the incidence of dye coupling. However, microglia treated with INF-γ plus LPS showed a dramatic increase in dye coupling that was prevented by coapplication of an anti-TNF-α antibody, suggesting the release and autocrine action of TNF-α. Treatment with INF-γ plus TNF-α also greatly increased the incidence of dye coupling and the Cx43 levels with translocation of Cx43 to cell–cell contacts. The cytokine-induced dye coupling was reversibly inhibited by 18α-glycyrrhetinic acid, a gap junction blocker. Cultured mouse microglia also expressed Cx43 and developed dye coupling upon treatment with cytokines, but microglia from homozygous Cx43-deficient mice did not develop significant dye coupling after treatment with either INF-γ plus LPS or INF-γ plus TNF-α. This report demonstrates that microglia can communicate with each other through gap junctions that are induced by inflammatory cytokines, a process that may be important in the elaboration of the inflammatory response.
The contribution of trait-mediated indirect effects to the net effects of a predator
Authors: Peacor Scott D. , Werner Earl E.
Published: July 2002

Many prey modify traits in response to predation risk and this modification of traits can influence the prey's resource acquisition rate. A predator thus can have a “nonlethal” impact on prey that can lead to indirect effects on other community members. Such indirect interactions are termed trait-mediated indirect interactions because they arise from a predator's influence on prey traits, rather than prey density. Because such nonlethal predator effects are immediate, can influence the entire prey population, and can occur over the entire prey lifetime, we argue that nonlethal predator effects are likely to contribute strongly to the net indirect effects of predators (i.e., nonlethal effects may be comparable in magnitude to those resulting from killing prey). This prediction was supported by an experiment in which the indirect effects of a larval dragonfly (Anaxsp.) predator on large bullfrog tadpoles (Rana catesbeiana), through nonlethal effects on competing small bullfrog tadpoles, were large relative to indirect effects caused by density reduction of the small tadpoles (the lethal effect). Treatments in which lethal and nonlethal effects ofAnaxwere manipulated independently indicated that this result was robust for a large range of different combinations of lethal and nonlethal effects. Because many, if not most, prey modify traits in response to predators, our results suggest that the magnitude of interaction coefficients between two species may often be dynamically related to changes in other community members, and that many indirect effects previously attributed to the lethal effects of predators may instead be due to shifts in traits of surviving prey.