bluuebunny/crossref_metadata_2025 huggingface dataset:
Artificial tunnel barriers produced by cryogenically deposited Al2O3
Authors: Moodera Jagadeesh S. , Meservey R. , Tedrow P. M.
Published: February 2003

Electron beam evaporated sapphire has been used to form tunnel barriers on substrates cooled to near 77 K. Ni/Al2O3/Al junctions show tunneling characteristics comparable with those obtained by plasma oxidation of Al and the subsequent deposition of Ni. The deposited Al2O3 barriers are stable and usually have insignificant leakage currents. The barrier heights are about 2.5 eV, and Al2O3 does not degrade the spin polarization of tunnel currents (as does oxidized amorphous Si). Au/Al2O3/Al junctions were made with good superconducting tunneling characteristics and with leakage less than 1%. Even Au/Al2O3/Au junctions apparently exhibit good tunneling characteristics.
Effect of a magnetic filter on the formation and deposition of high-Z impurities in a multicusp ion source
Authors: Ehlers K. W. , Leung K. N. , Pincosy P. A. , Vella M. C.
Published: February 2003

The presence of a magnetic filter in a multicusp ion source reduces the transport of tungsten to the extractor region by forming a uniform plasma potential region in the source chamber. Because of the reduced numbers of primary electrons in the extraction chamber, the plasma grid floats near the plasma potential and this reduces the amount of impurity ions formed from sputtered grid material.
Graphoepitaxy of germanium on gratings with square-wave and sawtooth profiles
Authors: Geis M. W. , Tsaur B-Y. , Flanders D. C.
Published: February 2003

For Ge crystallized on amorphous SiO2 by a process yielding (111) texture on smooth substrates, in-plane crystallographic orientation has been obtained by using gratings with square-wave or sawtooth profiles for orientation. Successive layers of vacuum-evaporated Cr, Au, and Ge were deposited on heated SiO2 substrates that had been patterned with the gratings. The Ge crystallized on square-wave gratings had the (111) planes parallel to the substrate surface and the (211) planes parallel to the vertical facets of the gratings. The sawtooth gratings were fabricated with facets meetings at 70.5°, the smallest angle between (111) planes. In this case the (111) planes of the Ge were parallel to the grating facets, the 〈100〉 directions were perpendicular to the substrate and the 〈110〉 directions were parallel to the grating axis.
Effects of compositional clustering on electron transport in In0.53Ga0.47As
Authors: Marsh J. H.
Published: February 2003

A new theory of alloy scattering is proposed which assumes the presence of compositional clusters in alloy semiconductors. This is used in electron transport calculations for In0.53Ga0.47As, and it is found that good agreement can be obtained with experimental velocity-field data, measured up to the threshold electric field. The theory assumes small (∼2%) fluctuations in composition over 1000 atoms.
Capped versus capless heat treatment of molecular beam epitaxial GaAs
Authors: Xin S. H. , Schaff W. J. , Wood C. E. C. , Eastman L. F.
Published: February 2003

Both capless and Si3N4 capped annealing of molecular beam epitaxial n-GaAs were investigated by photoluminescence and computerized deep level spectroscopy. It was found that the 1.507-eV emission bands (defect exciton) and the 1.4934-eV (carbon) and the 0.83-eV (EL2) electron trap are greatly enhanced after Si3N4 encapsulated annealing at 700 °C. These features were not observed in capless annealed material. It is concluded that capless annealing using an InAs ambient can avoid surface impurity, drive in, and stress effects in the MBE film. In addition, Si3N4 capping causes surface topographic degradation on annealing, whereas capless annealing does not.
New inorganic electron resist system for high resolution lithography
Authors: Singh B. , Beaumont S. P. , Bower P. G. , Wilkinson C. D. W.
Published: February 2003

A new Ag2S/As2S3 negative electron resist system is proposed for nanostructure fabrication. Linear gaps down to 30 nm wide have already been resolved. Sensitization of the Ag2S3 with a chemically deposited layer of Ag2S overcomes the limitations involved in the use of silver halides as a source of silver. Although the sensitivity of this resist is very low (4×10−3–10−2 C/cm2) its extremely high contrast (γ>5.5) is an advantage in nanostructure fabrication where it is necessary to discriminate against exposure by backscattered electrons.
Improved lasing performance of KrCl excimer laser
Authors: Armandillo E. , Luches A. , Nassisi V. , Perrone M. R.
Published: February 2003

A compact, small active volume (70 cc) discharge pumped KrCl laser with UV preionization is described. The results obtained show that KrCl compares well with the performance obtainable from the well established XeCl and KrF lasers. Considerably improved laser output energy density (≂2.5 J/1) is achieved at very high discharge power loadings (≂24 MW/cc), with a good power conversion efficiency (0.8%) and a long gas static lifetime. The output laser beam is reproducible and uniform with a cross section of 2×1 cm2.
High-speed x-ray sensitive photoconducting detector
Authors: Auston D. H. , Freeman R. R. , Smith P. R. , Mills D. M. , Siemann R. H.
Published: February 2003

A novel photoconducting detector for time-resolved measurements in the x-ray region of the spectrum has been constructed. Time resolution of better than 40 ps at energies between 3 and 10 keV has been demonstrated in bunch length measurements on the Cornell Electron Storage Ring. At high beam currents, dramatic instabilities and a breakup of the electron bunch were directly observed with this detector.
Single longitudinal mode operation of high power multiple-stripe injection lasers
Authors: Ackley D. E.
Published: February 2003

We report the first observation of single longitudinal mode operation in multiple-stripe injection lasers. The lasers are fabricated by channel etching and Zn diffusion in three-layer double heterostructures grown by organometallic vapor phase epitaxy. Linear output characteristics have been observed to cw output powers of 180 mW (uncoated facets) at room temperature with good stripe-to-stripe uniformity. Operation in a single longitudinal mode has been seen to 60-mW output and is evidence for strong stripe-to-stripe coupling.
Optically pumped 1.55-μm double heterostructure GaxAlyIn1−x−yAs/AluIn1−uAs lasers grown by molecular beam epitaxy
Authors: Alavi K. , Temkin H. , Wagner W. R. , Cho A. Y.
Published: February 2003

We report the first successful realization of room-temperature laser action at a wavelength of 1.55 μm in a new double heterostructure in which the active layer of GaxAlyIn1−x−yAs is confined between two cladding layers of AluIn1−uAs. The structure was grown on InP by molecular beam epitaxy, and was pumped optically by a Q-switched yttrium aluminum garnet laser. Peak output power of up to 5 W was obtained at an incident power corresponding to four times that required for threshold without catastrophic degradation. Temperature dependence of the threshold power can be characterized by Pth∼exp(T/T0) with T0=60 °C for 20 °C≤T≤100 °C.
Measurement of the linewidth enhancement factor α of semiconductor lasers
Authors: Harder Christoph , Vahala Kerry , Yariv Amnon
Published: February 2003

A theory of the amplitude and phase modulation characteristic of a single mode semiconductor laser is presented. In this model the amplitude modulation couples through the complex susceptibility of the gain medium to the phase. We show that this coupling constant can be obtained by a high-frequency modulation experiment. This measured coupling constant is used to infer the linewidth enhancement factor α as discussed by Henry, and Vahala and Yariv. Experiments confirmed the model and we measured a linewidth enhancement factor ‖α‖=4.6±1.0 for a GaAlAs buried optical guide laser.
Optical bistability in InSb at room temperature with two-photon excitation
Authors: Kar A. K. , Mathew J. G. H. , Smith S. D. , Davis B. , Prettl W.
Published: February 2003

We report the observation of optical bistability in an InSb resonator at room temperature. This effect and fringe shifts were caused by nonlinear refraction induced by two-photon absorption of radiation from a single longitudinal mode injection-locked pulsed CO2 laser operating at 9.6–10.6 μm. Intensities as low as 100 kW/cm2 were found to be sufficient to tune the 250-μm-thick cavity through a fringe maximum. From our results we deduce a value of χ(3) of the order of 10−4 esu over the range of intensities investigated.
Monolithic integration of a photodiode and a field-effect transistor on a GaAs substrate by molecular beam epitaxy
Authors: Wada O. , Miura S. , Ito M. , Fujii T. , Sakurai T. , Hiyamizu S.
Published: February 2003

A Schottky barrier photodiode and a field-effect transistor (FET) have been monolithically integrated on a GaAs substrate using molecular beam epitaxy. The electronic isolation between constituent elements has been achieved by the present device structure in which a semi-insulating substrate is used. The dark current at the punchthrough voltage as low as 8×10−10 A and a uniform quantum efficiency over the photosensitive area have been observed by the measurements. A linear amplification of the photocurrent by the FET over a wide range of incident light power has been confirmed. The amplification ratio of 19 has been achieved with a 10-kΩ photodiode load resistor. The present result demonstrates the usefulness of molecular beam epitaxy in realizing optoelectronic integrations.
Epitaxial relations in group-IIa fluoride/Si(111) heterostructures
Authors: Asano Tanemasa , Ishiwara Hiroshi
Published: February 2003

CaF2, SrF2, BaF2, and mixed (Ca,Sr)F2 films have been grown epitaxially on Si (111) substrates by vacuum evaporation. The epitaxial relation between these fluoride films and the substrates has been investigated by ion channeling analysis. Both the CaF2 and SrF2 films prefer to have orientations rotated 180° about the normal to the substrate surface. In contrast, the vast majority of (Ca,Sr)F2 films have orientations identical to those of the substrate, and the BaF2 film is composed of a mixture of the two. Analysis was also made on a Si/CaF2/Si(111) double heterostructure, which showed that the top Si film is again rotated 180° about the normal to the underlying CaF2 surface.
Laser-enhanced oxidation of Si
Authors: Boyd Ian W.
Published: February 2003

A scanning cw argon ion laser has been used to rapidly heat Si in a fixed oxygen atmosphere to produce thin oxide layers on the surface. Analysis of the growth rate of these films reveals an enhancement over the normal thermal equilibrium rate of oxidation for silicon dioxide layers grown by furnace in the temperature range 850–1050 °C, and is thought to be a result of the photoionizing effect of the band-gap photon flux. A simple model incorporating this characteristic is shown to qualitatively agree with the experimental results, and clearly indicates the importance of the density of broken Si–Si bonds in the oxidation reaction.
Index instabilities in proton-exchanged LiNbO3 waveguides
Authors: Yi-Yan Alfredo
Published: February 2003

Measured effective mode indices on a day to day basis reveal an oscillatory behavior which indicates that the index profile of proton-exchanged LiNbO3 waveguides evolves as a function of time. It is suggested that the profile instability might be brought about by a continuous migration of protons within the thickness of the guiding layer. Some index profile modificaiton may also be introduced during fabrication due to structural changes in the crystal as a function of exchange time.
Electrical measurements on n+-GaAs-undoped Ga0.6Al0.4 As-n-GaAs capacitors
Authors: Solomon P. M. , Hickmott T. W. , Morkoç H. , Fischer R.
Published: February 2003

Current versus voltage (I-V) and capacitance versus voltage (C-V) characteristics have been measured for n+-GaAs-undoped Ga0.6Al0.4 As-GaAs capacitors over a temperature range of 80–350 K. At low temperatures the structure behaves like a semiconductor-insulator-semiconductor diode with interface barrier heights of 0.38 and 0.40 eV for the bottom and top interfaces, respectively. The I-V curves exhibit a rectifying behavior due to the formation of a substrate depletion layer, and the C-V curves show the formation of the depletion layer under reverse bias as well as an accumulation layer containing >1012 electrons/cm2, in forward bias. The C-V curves agree closely with standard theory for SIS structures assuming Fermi–Dirac statistics for electrons in the accumulation layer, within an unaccounted-for voltage shift of 0.16 V.
Magnetically tunable stimulated emission from recombination radiation in (Cd, Mn)Se
Authors: Heiman D.
Published: February 2003

Stimulated emission of near-band-gap radiation is observed in the semimagnetic semiconductor Cd1−xMnxSe, x=0.1. Excitation was achieved by optical pumping just below the absorption edge. The photon energy of the recombination emission is a strong function of both magnetic field and temperature. With increasing field, the emission shifts to lower energy. The shift is primarily proportional to the Mn++ magnetization and at high fields saturates at approximately 60 meV. The magnitude is in reasonable agreement with that expected from the exchange energies.
Non-Maxwellian electrons in a laser produced sodium plasma
Authors: Morgan Wm. Lowell
Published: February 2003

Time-dependent Boltzmann calculations of the electron energy distribution function in a laser excited sodium plasma have been performed. Such nonequilibrium plasmas are produced in alkali metal vapor by laser irradiation of the ns–np resonance line. The electrons in these plasmas are heated by superelastic collisions with atoms in the np state giving a distribution of electrons in energy that is characterized by a series of spikes at energies separated by the ns–np transition energy, 2.1 eV for sodium.
Surface polariton reflection and radiation at end faces
Authors: Wallis R. F. , Maradudin A. A. , Stegeman G. I.
Published: February 2003

A theoretical investigation has been made of surface polariton reflection and radiation at the end face of a metal slab. Dielectric materials of dielectric constants εd and ε′d lie above and beyond the end of the metal slab, respectively. Energy transmission and reflection coefficients have been calculated for a surface polariton incident on the end face of the metal slab for various slab thicknesses when εd =εd=1 and ωp/ω=4. The energy reflection coefficient has also been investigated as a function of εd with ε′d=1. The angular distribution of the radiation pattern has also been studied for two different εd.
Effects of very low growth rates on GaAs grown by molecular beam epitaxy at low substrate temperatures
Authors: Metze G. M. , Calawa A. R.
Published: February 2003

Molecular beam epitaxy of GaAs is conventionally performed at growth rates of ∼1 μm/h. For growth rates in this range, donor-doped films grown at substrate temperatures below 500 °C have low carrier concentrations and high resistivities. We have grown Si-doped films with good electrical properties at substrate temperatures of 380 and 450 °C by reducing the growth rates to ∼0.02 and 0.2 μm/h, respectively. We believe that the improvement can be attributed to a reduction in the concentration of crystal defects, which occurs because the Ga and As atoms adsorbed on the substrate surface have sufficient time to reach appropriate lattice sites before they are incorporated into the growing film.
Monolithic high-power dual-wavelength GaAlAs laser array
Authors: Wada M. , Hamada K. , Shimizu H. , Kume M. , Tajiri F. , Itoh K. , Kano G.
Published: February 2003

Monolithic integration of high-power GaAlAs lasers is demonstrated. The new dual-wavelength laser array is implemented by integrating a twin-ridge substrate laser and a terraced substrate laser by the one-step liquid phase epitaxy technique. Both lasers integrated on a GaAs chip continuously operated at the power output as high as (30+30) mW in single longitudinal modes with a wavelength separation of 31 nm.
Preparation of ‘‘amorphous’’ Ni60Nb40 by mechanical alloying
Authors: Koch C. C. , Cavin O. B. , McKamey C. G. , Scarbrough J. O.
Published: February 2003

‘‘Amorphous’’ Ni60Nb40 has been prepared by mechanical alloying of elemental nickel and niobium powders in a laboratory ball mill in controlled environments. X-ray diffraction was used to follow the progress of the mechanical alloying which eventually produced ‘‘amorphous’’ diffraction patterns similar to those for liquid quenched amorphous Ni60Nb40. Crystallization behavior was measured by differential scanning calorimetry for the mechanically alloyed and liquid quenched material. The differences that were observed in this behavior, and in the products of crystallization, may be attributed to impurities (especially oxygen) introduced during mechanical alloying.
Collinear investigation of laser initiated reduced density channels
Authors: Horton L. D. , Gilgenbach R. M.
Published: February 2003

The characteristics of reduced density channels generated by laser initiated discharges have been investigated by means of collinear holographic interferometry and schlieren photography. We report the first direct measurements of the density profiles in the interior of such channels. Under unperturbed conditions these channels exhibit azimuthal asymmetries. Gas dynamics within the channel are also presented for the case of incident shock waves reflected from cylindrical and planar boundaries.
Oxygen vacancy creation in SiO2 through ionization energy deposition
Authors: Devine R. A. B.
Published: February 2003

Using electron paramagnetic resonance we have measured the profiles of the integrated E′1 oxygen vacancy defect densities produced in thermal SiO2 by implantation of 70-keV protons. Comparison of the experimental and theoretical profiles clearly indicates that the defects are created by energy deposited into ionization processes and not into atomic displacement. Mechanisms of oxygen vacancy creation are discussed. We estimate the maximum (saturation) defect density created by ionization energy to be ∼3.3×1019 E1 per cm3 which is the same order as found for Ar+ implantation where displacement damage dominates. This figure is also within a factor of 2 of that predicted for intrinsic E′1 defect precursors in SiO2.
New minority hole sinked photoconductive detector
Authors: Chen C. Y. , Pang Y. M. , Cho A. Y. , Garbinski P. A.
Published: February 2003

We demonstrate a new photoconductive device called minority hole sinked photoconductive detector. This detector has a back gate electrode for removing slow minority holes, resulting in an improvement of the detector’s fall time from 1 ns to 450 ps down to 80 ps. This represents nearly an order of magnitude improvement in the gain-bandwidth product. Furthermore, the back gate bias can reduce the noise power by 1 dB at 100 MHz and 0.25 dB at 800 MHz at 1.2-MHz noise bandwidth.
Intrinsic absorptive optical bistability in CdS
Authors: Bohnert K. , Kalt H. , Klingshirn C.
Published: February 2003

An intrinsic absorptive optical bistability is observed in the transmission of high intensity, nanosecond laser pulses through thin CdS platelets at liquid helium temperature. The bistability is due to a renormalization of the band gap which is caused by the formation of an electron hole plasma and occurs in a broad spectral range below the excitonic resonances. The switching times are in the subnanosecond range. The dependence on photon energy is investigated and discussed.
Effect of chemical doping on the radiation-induced conductivity of polyethylene terephthalate
Authors: Kurtz S. R. , Arnold C. , Hughes R. C.
Published: February 2003

A large decrease in the radiation-induced conductivity of polyethylene terephthalate was produced upon doping films with an electron acceptor molecule. Transient x-ray photoconductivity data verify that this impurity acts as a deep trap. Charge transfer occurs in the doped dielectric which may be associated with this trapping process.
Optical fiber V-groove transversal filter
Authors: Newton S. A. , Jackson K. P. , Shaw H. J.
Published: February 2003

A novel single mode optical fiber tapped delay line that uses silicon V-groove substrates to align an array of directional coupler taps has been demonstrated as a transversal filter. The device was used to generate and correlate 4-bit, 400-Mb/s coded sequences. The generated codes exhibited an amplitude uniformity of ±0.04 dB. The electrical correlation output was linear over a range of 25 dB and was limited by electronic components external to the fiber filter itself. Extension of the fabrication technique to include hundreds of taps at intervals as short as several picoseconds may be possible.
Symmetrical contours of deep level EL2 in liquid encapsulated Czochralski GaAs
Authors: Holmes D. E. , Chen R. T. , Elliott K. R. , Kirkpatrick C. G.
Published: February 2003

We have determined the isoconcentration contours of the deep level EL2 across 3-in.-diam, semi-insulating GaAs crystals grown by the liquid encapsulated Czochralski technique. The contours are essentially fourfold symmetric at the seed end of the crystals. The symmetrical pattern is independent of the melt stoichiometry and the relative direction of crystal and crucible rotation. EL2 distributions in the tail of the same crystals are often of lower symmetry. The results support a native defect model for EL2 in which the formation of the defect is enhanced by stress in the crystal.
90-fs tunable optical pulses obtained by two-stage pulse compression
Authors: Nikolaus B. , Grischkowsky D.
Published: February 2003

We report a factor of 65 compression of the 5.9-ps [full width at half-maximum (FWHM)] pulses from a mode-locked dye laser by a two-stage technique. In each stage the laser pulses were frequency broadened and linearly chirped by passage through a single-mode optical fiber, and then compressed by traversal of a diffraction grating based dispersive delay line. The final compressed output pulses had pulse widths of 90 fs (FWHM), peak powers of more than five times that of the input pulses, and were continuously tunable over the 300-Å range of the laser dye.
Interface analysis by spectroscopic ellipsometry of Ga1−xAlxAs-GaAs heterojunctions grown by metal organic vapor phase epitaxy
Authors: Erman M. , Frijlink P. M.
Published: February 2003

Metal organic vapor phase epitaxy (MOVPE) grown Ga1−xAlxAs-GaAs heterostructures have been analyzed by spectroscopic ellipsometry in the 1.6–5.4-eV region. We show that this technique is capable of a nondestructive analysis of the interface region. The method can distinguish between a physical interface (roughness, alloy clustering) and a chemical one (gradual changes in Al concentration). The results show that extremely sharp interfaces (of the order of one monolayer) can be grown by MOVPE.
Large uniaxial magnetic anisotropy in amorphous Tb-Fe evaporated thin films
Authors: Kobayashi H. , Ono T. , Tsushima A. , Suzuki T.
Published: February 2003

Magnetic properties of amorphous Tb-Fe alloy films have been investigated for magneto-optic memory media applications. The perpendicular magnetic anisotropy, saturation magnetization, and Curie temperature were investigated in the samples deposited by vacuum evaporation at different substrate temperatures Ts. A very large value (2×107 erg/cc) of the uniaxial anisotropy constant Ku was found in the samples deposited at a high substrate temperature (400 °C), and it was found also that the saturation magnetization and Curie temperature exhibit a strong dependence on substrate temperature during the evaporation process.
Fermi levels in electrolytes and the absolute scale of redox potentials
Authors: Gerischer Heinz , Ekardt Walter
Published: February 2003

Based on the correlation between the work function and the Fermi level of electrons in a single phase, Fermi levels in electrolytes are defined. With the vacuum level above the electrolyte as the reference state, an absolute scale of redox potentials can be derived. It is outlined how such data can be obtained experimentally.
Improved welding penetration of a 10-kW industrial laser
Authors: Kaye A. S. , Delph A. G. , Hanley E. , Nicholson C. J.
Published: February 2003

The weld penetration of a multikilowatt CO2 laser has been increased by reducing the laser beam divergence. This near diffraction limited laser has now demonstrated that CO2 lasers are capable of full-penetration welding of 1-in. steel with typically 11 kW on the work. Bead-on-plate tests combined with previous data indicate that the penetration scales with laser power as P0.8.
Spatially resolved Kα spectra of two-structure plasmas in a vacuum spark
Authors: Morita Shigeru , Fujita Junji
Published: February 2003

Spatially resolved Fe Kα spectra in the wavelength range of 1.7–2.0 Å (FeII-XXVI) and 1.91–1.95 Å (FeII-XIX) are first observed in a single shot with low-resolution Johansson and high-resolution Johann type crystal spectrometers, respectively. The spectra show the evident proof that the vacuum spark plasma has two different structures. One is a thermalized point plasma (≲10 μm) with high temperature (Te ∼2 keV) and high density (ne ∼1021 cm−3). The spectrum contains x-ray lines from FeXXIII-XXVI. The other is an extended plasma (∼3 mm) associated with nonthermal electrons, where the region of intense emission of Kα lines from FeIII-XX shifts toward the cathode with the increase of the ionic charge.
Absorption of carbon from residual gases during Ti implantation of alloys
Authors: Singer I. L. , Barlak T. M.
Published: February 2003

Secondary ion mass spectrometry (SIMS) has been used to analyze the surface composition of several steel and Ni-plated substrates implanted with Ti ions (5×1017 Ti/cm2 at 190 keV). SIMS showed clearly the carbonaceous subsurface layer previously reported in Auger and nuclear backscattering analyses of Ti-implanted Fe-based alloys. Moreover, substrates implanted in a vacuum which was backfilled with isotopic 13CO gas showed 20 to 50× higher mass 13/ mass 12 ratios for surface concentrations and integrated subsurface doses than substrates implanted in normal vacuum atmospheres at pressures near 10−6 Torr. Auger analysis confirmed the subsurface C profile and found no O (〈1 at %) below the oxide layer. The experiments provide direct evidence that C atoms can be absorbed from residual gas molecules in a vacuum chamber near room temperatures during implantation of carbide-forming ions. A second possible source of C atoms is also discussed.
Efficient femtosecond optical Kerr shutter
Authors: Etchepare J. , Grillon G. , Migus A. , Martin J. L. , Hamoniaux G.
Published: February 2003

Conjugated molecules, with large optical nonlinearities, are tested as materials usable for femtosecond optical Kerr shutter technique. With β-carotene, in acetone solution, we have achieved responses limited by the 100-fs width of the optical pulses and characterized by a resolution better than 1 ps with a dynamic range of 100.
Growth of Ga0.47In0.53As-InP quantum wells by low pressure metalorganic chemical vapor deposition
Authors: Razeghi M. , Hirtz J. P. , Ziemelis U. O. , Delalande C. , Etienne B. , Voos M.
Published: February 2003

We describe the growth of multiquantum well and single quantum well Ga0.47In0.53As-InP structures by low pressure metalorganic chemical vapor deposition. The multiwell structure consists of 25-, 50-, 100-, and 200-Å quantum wells (Ga0.47In0.53As layers) separated by 500-Å barriers (InP layers). Auger measurements indicate the presence of four distinct wells with abrupt boundaries. Photoluminescence measurements are consistent with the existence of four wells; however, deviations are noted between experimentally determined and theoretically predicted recombination energies. An analogous situation exists for the single (50 and 100 Å) quantum well structures. Possible explanations, including variation of well composition, variation of well thickness, and participation of impurities in the recombination process are suggested.
Analysis of epitaxial fluoride-semiconductor interfaces
Authors: Gibson J. M. , Phillips Julia M.
Published: February 2003

It is known that the epitaxial quality of alkaline-earth fluorides on semiconductors is not simply related to the degree of lattice mismatch. The interfacial structure in two such systems has been examined by high-resolution electron microscopy. For the high-mismatch system (9%), BaF2 on (111) Ge, an ‘‘incommensurate’’ interface is observed. In contrast, the lower mismatch BaF2 on (100) InP system (5%), displays a locally ‘‘commensurate’’ interface with closely spaced misfit dislocations. These observations demonstrate that epitaxy can occur with or without strong bonding across the substrate overlayer interface, depending on the lattice mismatch. The discovery of a truly incommensurate, epitaxial interface [in the BaF2 on (111) Ge system] is furthermore quite unique.
Probing the transition layer at the SiO2-Si interface using core level photoemission
Authors: Hollinger G. , Himpsel F. J.
Published: February 2003

High resolution Si 2p photoelectron spectra obtained with synchrotron radiation are used to determine the distribution of oxidation states in the intermediary layer at the SiO2-Si interface. A ratio of 0.4:0.3:0.3 is found for the Si3+:Si2+:Si1+ intensities independent of Si surface orientation and oxide thickness. The interface is not completely abrupt (5±1 Å width).
Phase noise characteristics of single mode semiconductor lasers with optical feedback
Authors: Chen Y. C.
Published: February 2003

The phase noise characteristics of single mode semiconductor lasers with optical feedback have been studied. A correlation is found between the suppression of the low-frequency noise and the enhancement of the high-frequency noise near the relaxation oscillation frequency. Contrary to previous analyses, the low-frequency noise is minimized when the reflected light is 70°–90° out of phase with respect to that inside the diode laser cavity. A calculation of the laser frequency fluctuation spectrum, taking into account the amplitude-phase coupling of the laser field, agrees with the observation. A new explanation is proposed for the feedback-induced phase noise reduction effect.
Improved AlxGa1−xAs bulk lasers with superlattice interfaces
Authors: Fischer R. , Klem J. , Drummond T. J. , Kopp W. , Morkoç H. , Anderson E. , Pion M.
Published: February 2003

A graded superlattice composed of AlxGa1−xAs and GaAs having a total thickness of 150 Å was incorporated on each side of the active layer of an otherwise standard double heterojunction laser. In spite of no optimization, current threshold densities as low as 600 A/cm2 at 880 nm were obtained in broad area devices with 300-μm cavity lengths. Otherwise identical structures with abrupt heterointerfaces in place of a graded superlattice exhibited current threshold densities in the range 1.2–1.4 kA/cm2. Silicon and beryllium were used for n- and p-type dopants. These results represent the best values for bulk laser and are attributed to improved interfaces primarily that between the bottom confining layer (substrate side) and the active layer.
GaAs light-emitting diodes fabricated on Ge-coated Si substrates
Authors: Fletcher Robert M. , Wagner D. Ken , Ballantyne Joseph M.
Published: February 2003

Light-emitting diodes have been fabricated in GaAs grown by metalorganic chemical vapor deposition on vapor-deposited epitaxial Ge films on Si substrates. The light-emitting junction was formed by zinc diffusion into the n-type GaAs layer. Room-temperature light emission centered at 872 nm has been observed.
Determination of the capture cross section and degeneracy factor of Si-SiO2 interface states
Authors: Eades Wendell D. , Swanson Richard M.
Published: February 2003

A modified form of deep level transient spectroscopy (DLTS) has been employed to perform energy-resolved measurements of Si-SiO2 interface states. Decreasing the height of the trap filling pulse from the order of volts, as in the usual DLTS procedure, to tens of millivolts allows trap filling measurements to be made, rendering possible the use of Shockley–Read–Hall theory to show that the degeneracy factor of interface states is around unity. The energy dependence of the capture cross section in the upper band gap is also calculated from Shockley–Read–Hall theory and is contrasted for oxidation ambients with and without added HCl.
Spin polarized photoemission from GaAs and Ge: Temperature dependence of the threshold polarization
Authors: Allenspach R. , Meier F. , Pescia D.
Published: February 2003

The temperature dependence of the photoelectron polarization is identical for GaAs with positive and negative electron affinity, as well as for Ge. It is concluded that the depolarization is due to a surface effect.
Improved high field performance of Nb-Al powder metallurgy processed superconducting wires
Authors: Thieme C. L. H. , Pourrahimi S. , Schwartz B. B. , Foner S.
Published: February 2003

Improved overall critical current densities Jc’s were achieved with powder metallurgy processed Nb-A1 which combined reduced powder sizes and increased nominal areal reductions R. Increased Jc values were obtained for a variety of different heat treatments. For a Nb-8 wt. % A1 wire with R=3.4×105 a very short treatment at 1100 °C followed by a 750 °C treatment gave (at 4.2 K)Jc>104 A/cm2 at 19 T; a 900 °C treatment followed by a 750 °C treatment gave Jc=104 A/cm2 at 18 T and, at 2 K, Jc was greater than 104 A/cm2 at 20 T; and a treatment of 800 °C for 8 h gave (at 4.2 K)Jc=104 A/cm2 at 17.5 T.
Hot electrons in modulation-doped GaAs-AlGaAs heterostructures
Authors: Shah Jagdeep , Pinczuk A. , Störmer H. L. , Gossard A. C. , Wiegmann W.
Published: February 2003

We have investigated electric field heating of high mobility electrons in modulation-doped GaAs-AlGaAs heterostructures by simultaneous measurement of luminescence and mobility. We find that hot electrons have a Fermi-Dirac distribution function for fields up to 750 V/cm and that the high field mobility of electrons can be understood in terms of field-induced electron heating and the temperature dependence of low field mobility.
Improved GaAs/AlGaAs single quantum wells through the use of thin superlattice buffers
Authors: Masselink W. T. , Klein M. V. , Sun Y. L. , Chang Y. C. , Fischer R. , Drummond T. J. , Morkoç H.
Published: February 2003

In general, single GaAs quantum wells surrounded by AlxGa1−xAs cladding layers show only weak photoluminescence corresponding to exciton recombination. This is attributed to the poor quality of the AlGaAs in the lower cladding layer resulting in a degraded interface and poor GaAs in the quantum well. The situation gets worse when the thickness of the bottom AlGaAs layer is increased, the GaAs thickness is reduced, or the Al mole fraction is increased. Using a graded three-period superlattice ahead of the quantum well causes the intensity of the photoluminescence associated with exciton recombination to increase to more than 160 times that associated with the conventional structure. This exciton recombination peak is due to either very shallow bound or free-electron recombination and has a full width at half-maximum of only 2 meV.
Nitrogen in silicon: Towards the identification of the 1.1223-eV (A,B,C) photoluminescence lines
Authors: Sauer R. , Weber J. , Zulehner W.
Published: February 2003

We show that the ‘‘new’’ photoluminescence line in silicon at 1.1223 eV which was recently reported and ascribed to a nitrogen complex is identical with the A line of the isoelectronic A, B, C exciton system as previously studied. New data are presented which confirm that nitrogen is incorporated in the optical center. Further defect constituents cannot be identified on the basis of the present data.
Mode-locked picosecond pulse generation from high power phase-locked GaAs laser arrays
Authors: van der Ziel J. P. , Temkin H. , Dupuis R. D. , Mikulyak R. M.
Published: February 2003

A diffraction-coupled laser array has been actively mode locked in an external cavity to yield Gaussian pulses as short a 61-ps full width at half-maximum with a peak power of 1.1 W and an average power of 0.07 W. The array consists of 10 lasers, each 3 μm wide with 9-μm center to center spacing. It emits with a stable double-lobed far-field pattern characteristic of the out-of-phase coupling between neighboring lasers. These arrays may be useful where high peak as well as high average optical powers are required.
Hot-electron energy deposition profiles in CO2 laser target interaction: A comparison between Kα and continuum measurements
Authors: Kieffer J. C. , Pépin H. , Amiranoff F.
Published: February 2003

In CO2 laser target interaction, the axial and lateral hot-electron energy deposition profiles are determined from Kα emission and compared with those inferred from hard x-ray continuum spectra, in the same experimental conditions. The two approaches are complementary and give the same results provided that the continuum and the Kα are produced by a similar electron distribution.
Reactively sputtered a-SixGe1−x:H alloys with compositional gradient in plane of film
Authors: Weisz S. Z. , Gomez M. , Muir J. A. , Resto O. , Perez R. , Goldstein Y. , Abeles B.
Published: February 2003

A reactive sputtering technique has been utilized which enables one to deposit in a single run the alloy system a-SixGe1−x :H over the range x=0.05–0.7 and survey IR, optical, and electrical transport properties. The technique can readily be generalized to other binary and ternary semiconductor systems.
Tunable far-infrared spectroscopy
Authors: Evenson K. M. , Jennings D. A. , Petersen F. R.
Published: February 2003

Tunable, cw, far-infrared radiation has been generated by nonlinear mixing of radiation from two CO2 lasers in a metal-insulator-metal (MIM) diode. The FIR difference-frequency power radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two-tenths of a microwatt of FIR power was generated by 250 mW from each of the CO2 lasers. The combination of lines from a waveguide CO2 laser, with its larger tuning range, with lines from CO2, N2O, and CO2 isotope lasers promises complete coverage of the entire far-infrared band from 100 to 5000 GHz (3–200 cm−1) with stepwise-tunable cw radiation. To demonstrate the usefulness of the technique, we observed the J=4–5 line of CO at 567 GHz.
Growth kinetics of thin silicon dioxide in a controlled ambient oxidation system
Authors: Ng K. K. , Polito W. J. , Ligenza J. R.
Published: February 2003

The growth kinetics of thin silicon oxide films less than 300 Å are studied by using a stainless steel controlled ambient oxidation system. The oxidation system features resistive heating of silicon and high vacuum capability of 10−8 Torr. It is shown that the data, obtained in the oxygen pressure range of 0.01–0.5 atmosphere and in the temperature range of 930–1030 °C, can be approximated by parabolic growth law, with an activation energy of 1.34 eV. Electrical characteristics pertinent to metal-oxide-semiconductor devices are also described.
Effects of the internally produced nonthermal electrons on the temperature diagnostics of a hollow gas shell Z pinch
Authors: Hammel Bruce A. , Jones Larry A.
Published: February 2003

Experimental evidence is presented indicating that a nonthermal electron energy distribution occurs in a collapsing gas shell Z pinch at the time of pinch. It is estimated that these results can be explained if less than 10% of the current is associated with an energetic (∼4 keV) electron beam. Interpreting the spectroscopic diagnostics consistently with the nonthermal electron energy distribution indicates that the temperature of the plasma ‘‘hot spots’’ could be as low as ∼400 eV instead of the 1 keV obtained by assuming a thermal distribution.
Diffusion of silicon in gallium arsenide using rapid thermal processing: Experiment and model
Authors: Greiner Mark E. , Gibbons James F.
Published: February 2003

Rapid thermal processing was used to diffuse Si into GaAs from a thin elemental source. Several encapsulants were applied. The diffusion was found to be dependent on the type of encapsulant. A model is developed based on the formation and rapid diffusion of Si nearest neighbor donor-acceptor pairs. Results from the codiffusion of Si and Ge support this model.
Mechanism for dynamic annealing during high flux ion irradiation in Si
Authors: Holland O. W. , Narayan J.
Published: February 2003

The results of high current density implantation of Si and As ions are presented. Significant lattice recovery during implantation is shown to occur as a result of ‘‘dynamic’’ or self-annealing processes. The mechanism for these processes will be discussed. Also, the morphology of the residual damage is shown to depend critically upon the mass of the implanted ion and the current density.
Neutralization of acceptors in silicon by atomic hydrogen
Authors: Pankove J. I. , Wance R. O. , Berkeyheiser J. E.
Published: February 2003

Atomic hydrogen can neutralize the following acceptors in silicon: boron, aluminum, gallium, and indium. Up to 1019 B cm−3 have been neutralized. Hydrogen penetration seems to follow a diffusive transport that is impeded by the concentration of binding sites.
Highly photosensitive transistors in single-crystal silicon thin films on fused silica
Authors: Johnson N. M. , Chiang A.
Published: February 2003

Exceptionally high photosensitivity has been obtained in metal-oxide-semiconductor field-effect transistors fabricated in single-crystal silicon thin films on fused silica. The silicon films were laser crystallized and used to fabricate depletion mode transistors. Operating in pinch-off these buried-channel devices display an optical responsivity of ≳ 300 A/W of incident visible radiation. This is some four orders of magnitude greater than that achieved in enhancement mode devices of comparable design and processing. The basic mechanism for the high sensitivity is the spatial separation of photogenerated electrons and holes which results in long carrier lifetimes, as indicated by optical gains >103 and photocurrent decay times of the order of 10 μs.
Metal-semiconductor field-effect transistors fabricated in GaAs layers grown directly on Si substrates by molecular beam epitaxy
Authors: Metze G. M. , Choi H. K. , Tsaur B-Y.
Published: February 2003

Device-quality GaAs layers have been grown directly on Si(100) substrates by molecular beam epitaxy. Metal-semiconductor field-effect transistors have been fabricated in these layers with transconductance as high as 85 mS/mm and leakage current as low as 1 μA at Vgs =−3 V for gate dimensions of 2.0 μm×200 μm.
Origin of high offset voltage in an AlGaAs/GaAs heterojunction bipolar transistor
Authors: Lee Si-Chen , Kau Jau-Nan , Lin Hao-Hsiung
Published: February 2003

The high offset voltage of an Npn AlGaAs/GaAs heterojunction bipolar transistor prepared by liquid phase epitaxy is proved to be equal to the turn-on voltage difference between emitter-base heterojunction and base-collector homojunction. The potential spike at the emitter-base heterointerface is experimentally confirmed by observing an activated transport process and a reachthrough effect under reverse operation. It is believed that the electron thermionic emission process plays an important role in determining the p-n junction I-V characteristics.
Demonstration of nonlinear prism coupling
Authors: Valera J. D. , Seaton C. T. , Stegeman G. I. , Shoemaker R. L. , Mai Xu , Liao C.
Published: February 2003

The coupling of light into a waveguide characterized by an intensity dependent propagation constant has been demonstrated experimentally. Limiting action was observed at milliwatt waveguide powers with a liquid crystal medium filling the gap between a prism and a glass waveguide.
Anomalous nonlinear guided wave cut-off phenomena
Authors: Seaton Colin T. , Valera Jesus D. , Shoemaker Richard L. , Stegeman George I. , Chilwell John , Smith S. Desmond
Published: February 2003

We show that mode cutoff can occur at finite powers for waves guided by a thin-film waveguide bounded by one or two media characterized by a defocusing nonlinearity. This phenomenon produced optical limiting action.
Heteroepitaxial ridge-overgrown distributed feedback laser at 1.5 μm
Authors: Tsang W. T. , Logan R. A. , Olsson N. A. , Johnson L. F. , Henry C. H.
Published: February 2003

A new distributed feedback laser, the heteroepitaxial ridge-overgrown distributed feedback (HRO DFB) laser, is proposed and demonstrated. The HRO DFB lasers operated in stable single longitudinal mode with no observable mode partition events under 2-Gb/s pseudo-random pulse modulation with dynamic spectral widths typically 0.5–2 Å even with both facets cleaved. Other characteristics of these 1.5-μm GaInAsP HRO DFB lasers include ∼10 mW/facet (no antireflection coating) of stable beam, single longitudinal mode output power, and narrow lateral beam divergence of ∼12° (half-power full width). Actual transmission experiments with dispersive fibers (17 ps/km nm) at ∼1.55 μm confirmed that the HRO DFB laser is an excellent ‘‘single-frequency’’ optical source.
Inverted-V chirped phased arrays of gain-guided GaAs/GaAlAs diode lasers
Authors: Kapon E. , Lindsey C. P. , Smith J. S. , Margalit S. , Yariv A.
Published: February 2003

Inverted-V chirped arrays of multiple quantum well GaAs/GaAlAs lasers were grown by molecular beam epitaxy. These arrays consisted of seven gain-guided lasers whose stripe widths decreased, from the central laser to the outermost ones, symmetrically. This structure makes it possible to discriminate against the higher order array supermodes, which results in diffraction limited beams with a single lobe directed perpendicular to the laser facet. Single lobed far-field patterns, 3°–4° wide, were obtained from inverted-V chirped arrays operated up to 1.5Ith. The supermode structure of these arrays was identified by studying their spectrally resolved near fields.
Enhancement of thin metallic film adhesion following vacuum ultraviolet irradiation
Authors: Mitchell I. V. , Nyberg G. , Elliman R. G.
Published: February 2003

The adhesion of thin metallic films to silicon substrates is shown to improve following irradiation with a flux of either 21.2-eV (He I) 10.2-eV (H Lyman α) photons. The improved adhesion is similar to that found following MeV energy ion irradiation and keV energy electron irradiation, adding support to the view that electronic excitation and/or ionization and precursors to the stronger bonding configuration.
Q switching of low-threshold buried-heterostructure diode lasers at 10 GHz
Authors: Tsang D. Z. , Walpole J. N. , Liau Z. L. , Groves S. H. , Diadiuk V.
Published: February 2003

Buried-heterostructure actively Q-switched diode lasers have been made with threshold currents as low as 14 mA. The lasers operate continuously at room temperature. Modulation has been observed at rates up to 10.5 GHz. Evidence of several modes of Q switching has been obtained.
Optical absorption in ion-implanted lead lanthanum zirconate titanate ceramics
Authors: Seager C. H. , Land C. E.
Published: February 2003

Optical absorption measurements have been performed on unmodified and on ion-implanted lead lanthanum zirconate titanate ceramics using the photothermal deflection spectroscopy technique. Bulk absorption coefficients depend on the average grain size of the material while the absorption associated with the ion-damaged layers does not. The damage-induced surface absorptance correlates well with the photosensitivity observed in implanted PLZT devices, supporting earlier models for the enhanced imaging efficiency of the materials.
Effect of argon ion implantation dose on silicon Schottky barrier characteristics
Authors: Ashok S. , Kräutle H. , Beneking H.
Published: February 2003

The electrical characteristics of Schottky diodes fabricated on silicon surfaces subject to low-energy (10 keV) argon ion implantation have been studied as a function of Ar+ ion dose. Significant changes in electrical characteristics are seen for ion doses as low as 5×1011 cm−2, well below the amorphization threshold dose for Si. In conjunction with the ion energy threshold established earlier for Si surface damage effects (∼25 eV), these results outline fundamental limits on the effect of ion-assisted dry etching processes on Si surface barriers.