bluuebunny/crossref_metadata_2025 huggingface dataset:
Buried monocrystalline aluminum layers in beryllium using ion implantation
Authors: Brown D. W. , Musket R. G. , Munir Z. A.
Published: July 2002

A buried monocrystalline aluminum layer was formed in (101̄0) beryllium by implanting 200 keV Al+ to a dose of 1.1×1018 Al/cm2 and subsequently annealing the implanted beryllium at 500 °C for 1 h. Rutherford backscattering showed layer formation was critically dependent on aluminum dose. Electron microscopy revealed a correlation between this critical dependence and the dose dependence of the density of columnar beryllium defects extending through the aluminum layers from the beryllium overlayer to the beryllium bulk. Several common features found between the formation of this elemental layer and formation of buried compound layers strongly suggest that similar precipitate coarsening behavior is responsible for both.
Novel AlGaInAs/AlInAs lasers emitting at 1 μm
Authors: Chang-Hasnain C. J. , Bhat R. , Zah C. E. , Koza M. A. , Favire F. , Lee T. P.
Published: July 2002

We report the first AlGaInAs/AlInAs lasers emitting at 1 μm. The lasers are grown by organometallic chemical vapor deposition lattice matched to an InP substrate. We achieved 1.6 kA/cm2 threshold current density and 370 mW output power from 25-μm-wide gain-guided double heterostructure lasers. The lasers exhibit linear optical power versus current characteristics and stable near- and far-field patterns. Threshold currents as low as 50 mA were obtained with 7-μm-wide ridge-waveguide index-guided lasers. To our knowledge, this threshold current and the threshold current density are the lowest reported to date for lasers made with this material system.
Quantum well lasers in operation for four years
Authors: Waters R. G. , Yellen S. L.
Published: July 2002

AlGaAs quantum well lasers operating at 808 nm with cw lifetimes exceeding 30 000 h are reported. The devices, grown by metalorganic chemical vapor deposition, were driven at 200 mW total optical power and were not coated. A study of diode configuration shows that longevity is enhanced by using a long cavity and by junction-down mounting.
Anomalous capacitance-voltage characteristics of BF2-implanted and rapid thermal annealed p+-polycrystalline silicon gate metal-oxide-semiconductor structures
Authors: Lo G. Q. , Kwong D. L. , Lee S.
Published: July 2002

Anomalous capacitance-voltage (C-V) characteristics of BF2-implanted p+-polycrystalline silicon (polysilicon) gate metal-oxide-semiconductor (MOS) structures annealed by rapid thermal annealing (RTA) are reported for the first time. It is found that both high-frequency and quasi-static C-V curves exhibit an increased capacitance at the depletion and weak inversion regions, which increases with p+-polysilicon RTA drive-in durations. The quasi-static C-V curves show a gate bias dependence of the inversion capacitance which shows a distorted ‘‘plateau’’ (i.e., reduced inversion capacitance for a very narrow gate voltage range) in the strong inversion regions. These anomalous C-V characteristics are believed to be due to the penetrated B-F complexes which act as interface state and deep level defect centers.
Optical sensitization at the phase transition in the ferroelectric vinylidene fluoride-trifluoroethylene copolymer
Authors: Verkhovskaya K. A. , Bune A. V. , Fridkin V. M. , Legrand J. F.
Published: July 2002

At the ferroelectric phase transition in the optically sensitized ferroelectric vinylidene fluoride-trifluoroethylene copolymers P(VDF-TrFE) the sharp change of the dye energy level is revealed. In ferroelectric P(VDF-TrFE) copolymer doped by indolynospiropyran the structural chromic effect is observed, which is characterized by the reversible change of the film color at the ferroelectric phase transition.
Preparation and structure of amorphous semiconductor hydrogenated tin
Authors: Vergnat M. , Marchal G. , Mangin Ph.
Published: July 2002

Evaporation on substrates maintained at 77 K under an atomic hydrogen flow allows us to prepare amorphous semiconductor tin. The resistivity is very high, 3×103 Ω cm and the diffraction pattern is typical of the random continuous networks of amorphous germanium and silicon. This structure is stable up to 180 K.
Silver-BiSrCaCuO chemical reactions
Authors: Hwu Y. , Marsi M. , Hwang Chanyong , Seutjens J. , Larbalestier D. C. , Onellion M. , Margaritondo G.
Published: July 2002

We used synchrotron-radiation photoemission to investigate the chemical reactions that occur during the silver cladding process of BiSrCaCuO−used to increase the critical current density by over a factor of 50. We find that the Cu-O planes are not directly affected by the chemical reaction, and that such a reaction strongly affects the Bi and Sr atoms.
Through-thickness temperature gradients in double-layered magneto-optical media for direct overwrite
Authors: Ohtsuki T. , Owa S. , Yamada F.
Published: July 2002

The effect of through-thickness temperature gradients in thin films irradiated by short laser pulses is described, together with its application to direct overwrite. We found by simulation that through-thickness temperature gradients become substantial when a medium is irradiated by short laser pulses of the order of 1 ns which is the characteristic time of heat diffusivity. This effect qualitatively explains why in writing experiments on a double-layered medium short pulses expand the laser power range for a writing process.
Microwave diffraction and interference in reflection using transient radiation from optoelectronically pulsed antennas
Authors: Robertson W. M. , Arjavalingam G. , Kopcsay G. V.
Published: July 2002

Broadband (15–130 GHz) microwave interference and diffraction are demonstrated in a reflection configuration using transient radiation from optoelectronically pulsed antennas. The measured complex reflection function of Fabry–Perot interferometers and diffraction from amplitude gratings are presented. The effectiveness of the technique for quantifying the scattering from general three-dimensional objects is discussed.
InGaAs/InAlAs superlattice avalanche photodiode with a separated photoabsorption layer
Authors: Kagawa Toshiaki , Kawamura Yuichi , Asai Hiromitsu , Naganuma Mitsuru
Published: July 2002

A novel structure superlattice avalanche photodiode is proposed. A p-InGaAs photoabsorption layer is separated from a nondoped InGaAs/InAlAs superlattice avalanche multiplication region. The electric field strength at the photoabsorption layer is controlled by a thin, highly doped p-InGaAs layer, which is sandwiched between the multiplication and photoabsorption layers. Devices with this structure were fabricated by molecular beam epitaxy. The external quantum efficiency is 73% at the multiplication factor of unity. The multiplication noise is quite small corresponding to an effective ionization rate ratio of 0.1. The maximum 3 dB bandwidth is 9.3 GHz.
Impact ionization in the base of a hot-electron AlSb/InAs bipolar transistor
Authors: Vengurlekar Arvind S. , Capasso Federico , Chiu T. Heng
Published: July 2002

The operation of a new AlSb/InAs heterojunction bipolar transistor is studied. The electrons are injected into a p-InAs base across the AlSb/InAs heterojunction. The conduction-band discontinuity at this heterojunction is sufficiently large so that energy of the electrons injected into InAs exceeds the threshold for generating electron-hole pairs by impact ionization. The observed incremental common base current at zero collector-base bias decreases and becomes negative as the emitter current is increased, thus providing direct evidence for impact ionization entirely by band-edge discontinuities.
Band offsets and exciton confinement in Zn1−yCdySe/Zn1−xMnxSe quantum wells
Authors: Wal/ecki W. J. , Nurmikko A. V. , Samarth N. , Luo H. , Furdyna J. K. , Otsuka N.
Published: July 2002

Optical characteristics of a new, weakly strained wide-gap II-VI quantum well have been studied with emphasis on the confined exciton states. Strong luminescence efficiency in the blue is observed with spectra showing only weak alloy disorder effects. Magneto-optical studies yield a measurement for the band offsets in a model which properly includes exciton effects.
Photoreflectance study of gallium arsenide grown on Si
Authors: Dutta M. , Shen H. , Vernon S. M. , Dixon T. M.
Published: July 2002

Low-temperature linear polarized photoreflectance is used to study the stress and its release in thick GaAs grown on Si. We find that the GaAs layer is mainly composed of two regions with two kinds of stress, biaxial and uniaxial. Four features, two from each region due to the split valence band, are observed. Their polarization selection rules enable us to distinguish the nature of the strain as well as the nature of the transitions.
Direct conversion of superconducting Y2Ba4Cu7O15−δ from YBa2Cu3O7−x at atmospheric pressure in an O2 ambient
Authors: Liang J. M. , Chen L. J.
Published: July 2002

Direct conversion of superconducting Y2Ba4Cu7O15−δ (Y-247) from YBa2Cu3O7−x (Y-123) was achieved at atmospheric pressure. The Y-247 samples were synthesized by the reactions of Y-123 and Cu-(NO3)2 at 860 °C in an O2 ambient. The results strongly suggest that Y-247 is a thermodynamically more stable phase than Y-123 at the atmospheric pressure. The conversion also provides a novel and simple route to synthesize the Y-247 compound.
Pyrophoric synthesis technique for multicomponent high-temperature superconductors
Authors: Bhattacharya D. , Pathak L. C. , Mishra S. K. , Sen D. , Chopra K. L.
Published: July 2002

A pyrophoric technique using an explosive exothermic reaction has been developed to yield calcined and microscopically homogeneous (0.3 μm size) powders of multicomponent cuprate systems. The technique has been used to synthesize superconducting materials of variable composition of the type M1M2⋅⋅⋅MnOx. The bulk materials prepared from these powders show sharp (1 K) superconducting transitions and nearly ideal Meissner effect.
Characterization of rapid thermally nitrided SiO2/Si interface by the conductance technique
Authors: Liu Z. H. , Lai P. T. , Cheng Y. C.
Published: July 2002

Device quality SiO2 films with a thickness of 15 nm have been thermally nitrided in NH3 by a rapid thermal processing technique. The properties of the interface between these films and a Si substrate have been investigated by a conductance technique. The results show that the nitridation increases the density and time constant of interface states and enhances the fluctuation of surface potential, but changes the hole capture cross section only slightly. Specifically, nitridation introduces a peak of interface states at 0.25 eV below midgap and the energy dependency of hole capture cross section is suppressed. Using a patchwork model, the surface potential fluctuation can be well simulated and a surface charge nonuniformity with a long-wavelength distribution may exist. These are consistent with the fact that nitridation induces a high oxide charge density. Experimental data show that all these properties depend on nitridation time and temperature.
Accelerated formation of the three Cu-O layered Tl-(Pb,Bi)-Sr-Ca-Cu-O compound
Authors: Huang Y. T. , Wu S. F. , Chiang C. K. , Lee W. H.
Published: July 2002

Bulk samples containing nearly single phase of the three Cu-O layered compound in the Tl-Pb(Bi)-Sr-Ca-Cu-O system have been readily synthesized. By partially substituting Ca for Sr, an accelerated formation of the desired three Cu-O layered phase was observed when the Ca/Sr ratio reached up to 2.4/1.6. The phase purity was clearly evidenced by x-ray diffraction and magnetization measurement. The synthesis is valuable for further application interests.
Ideal tunneling characteristics in Ba1−xKxBiO3 point-contact junctions with Au and Nb tips
Authors: Huang Qiang , Zasadzinski J. F. , Gray K. E. , Richards D. R. , Hinks D. G.
Published: July 2002

One important potential application of high-temperature superconductors is for tunnel junctions, especially hysteretic Josephson junctions. Unfortunately, tunnel junctions of oxide superconductors with a useful Tc≳20 K have exhibited nonideal I(V) characteristics with a normalized zero-bias conductance, σs/σn(0), of 15–50%. We present data on point-contact junctions of Ba1−xKxBiO3 which clearly demonstrate that these problems are not intrinsic. Using a normal-metal counterelectrode, σs/σn(0) was <1% and σs/σn(V) agreed with the BCS theory by including only thermal smearing. Using a superconducting Nb counterelectrode, the I(V) showed very sharp features with evidence of a proximity effect, and σs/σn(0) was <0.2%. These results prove that there is no fundamental limitation for tunnel junctions using this HTS material, and one can anticipate operation of devices with two Ba1−xKxBiO3 electrodes at 15–20 K.
Electronic structure of the gold/Bi2Sr2CaCu2O8 and gold/EuBa2Cu3O7−δ interfaces as studied by photoemission spectroscopy
Authors: Dessau D. S. , Shen Z.-X. , Wells B. O. , Spicer W. E. , List R. S. , Arko A. J. , Bartlett R. J. , Fisk Z. , Cheong S-W. , Mitzi D. B. , Kapitulnik A. , Schirber J. E.
Published: July 2002

High-resolution photoemission has been used to probe the electronic structure of the gold/Bi2Sr2CaCu2O8 and gold/EuBa2Cu3O7−δ interface formed by a low-temperature (20 K) gold evaporation on cleaved high quality single crystals. We find that the metallicity of the EuBa2Cu3O7−δ substrate in the near surface region (∼5 Å) is essentially destroyed by the gold deposition, while the near surface region of Bi2Sr2CaCu2O8 remains metallic. This has potentially wide ranging consequences for the applicability of the different types of superconductors in real devices.
Atomic structure at the LaSi2−x/Si(100) interface
Authors: Qian J. J. , Wang Y. T. , Ho J. , Hsu C. C.
Published: July 2002

Interfaces between Si(100) and LaSi2−x lattices formed by rapid thermal annealing at ∼900 °C for 10 s have been studied using high-resolution transmission electron microscopy. The experimental results show that the C axis of the LaSi2−x unit cell points to the 〈332〉Si direction. A model suggesting the {100} planes of LaSi2−x grown on a {113}Si surface has been put forward to account for the observed tilting growth of LaSi2−x disilicide on the Si(100) surface.
Shock-induced superconductivity of Tl2Ba2CuO6
Authors: Kikuchi Masae , Syono Yasuhiko , Kobayashi Norio , Oku Takeo , Aoyagi Eiji , Hiraga Kenji , Kusaba Keiji , Atou Toshiyuki , Tokiwa Ayako , Fukuoka Kiyoto , Nakajima Satoru
Published: July 2002

Shock-loading experiments were done for as-prepared nonsuperconducting specimens of Tl2Ba2CuO6. The shocked specimens which were encased in the stainless-steel container with small holes exhibited a superconductivity of about Tc−75 K at 18 GPa, indicating that the overdoping state was released by oxygen loss during shock-loading. The x-ray powder diffraction pattern of the recovered specimens after shock-loading showed broadening of diffraction lines and a distortion to the orthorhombic symmetry. A transmission electron microscope image of the shocked specimen in which the orthorhombic distortion was observed in the x-ray powder diffraction patterns showed a twin structure.
Synthesis of YBa2Cu4O8 at one atmosphere oxygen pressure by the modified citrate gel process
Authors: Liu R. S. , Janes R. , Bennett M. J. , Edwards P. P.
Published: July 2002

High Tc superconducting YBa2Cu4O8 was successfully synthesized via a modified citrate gel process at one atmosphere oxygen pressure. The resulting material had a stable and reproducible superconducting transition temperature around 80 K, confirmed by both resistivity and magnetic measurements. This technique can be employed in a large-scale preparation of the YBa2Cu4O8 powders.
Diffusion coefficient of boron in tungsten silicide
Authors: Suzuki Kunihiro , Horie Hiroshi , Yamashita Yoshimi , Kataoka Yuji
Published: July 2002

We developed a method of determining the impurity diffusion coefficient in tungsten silicide. We modeled the lateral diffusion profiles in tungsten silicide wire, which enabled us to determine the diffusion coefficient of boron from the three-dimensional secondary-ion mass spectrometry impurity profiles as to be of the order of 10−8 cm2/s at 900 °C. This was the first estimate of the impurity diffusion coefficient in silicide, and revealed that it is more than one million times larger than that in silicon.
Multilayered structure and anisotropic electrical properties of (SiO2)100−x(Pb0.6Bi0.4)x alloys prepared by a combined technique of mechanical alloying and hot pressing
Authors: Kim B. G. , Kataoka N. , Matsuzaki K. , Inoue A. , Masumoto T.
Published: July 2002

Compacted (SiO2)100−x(Pb0.6Bi0.4)x (x=20–80 at. %) materials, prepared by mechanical alloying (MA) of amorphous SiO2, fcc Pb, and rhombohedral hexagonal Bi followed by hot pressing of the MA powder at 473 K for 1.8 ks under an applied stress of 250 MPa, were found to have a unique layered structure consisting of amorphous SiO2 and hexagonal close-packed (hcp) ε(Pb-Bi) phases which developed along the direction perpendicular to the uniaxial applied load. The thickness and interlayer distance of the layered ε (Pb-Bi) phase are about 1.5 and 7 μm, respectively, for (SiO2)50Pb30Bi20. Furthermore, the multilayered compacts exhibited a strong anisotropy of electrical resistivity and superconducting properties when their properties are measured along the directions parallel or perpendicular to the layer. Electrical resistivity at 300 K, superconducting critical temperature (Tc), and upper critical magnetic field (Hc2) at 4.2 K are 10.5 μΩ m, 8.5 K, and 2.29 T, respectively, for the parallel direction and 950 μΩ m, 6.9 K, and 0.24 T, respectively, for the perpendicular direction. The strong anisotropy of electrical resistivity and superconducting properties is presumably due to a significant difference in the linkage of electrical path between the parallel and perpendicular directions.
Temperature-time-transformation diagrams for crystallization process of rapidly quenched Bi-Pb-Ca-Sr-Cu-O glasses
Authors: Tatsumisago Masahiro , Tsuboi Shinzo , Tohge Noboru , Minami Tsutomu
Published: July 2002

The formation process of the superconducting phases from the rapidly quenched Bi2−xPbxCa2Sr2Cu3Ow (0≤x≤0.4) glasses has been studied as a function of both heat treatment temperature and time. The temperature-time-transformation (T-T-T) diagrams constructed for the glasses greatly depend on the Pb content. The formation region of Ca2PbO4, which may play an important role in producing the 110 K phase, is very wide in the T-T-T diagrams of Pb-rich samples.
Optical scatter in epitaxial semiconductor multilayers
Authors: Gourley P. L. , Dawson L. R. , Brennan T. M. , Hammons B. E. , Stover J. C. , Schaus C. F. , Sun S.
Published: July 2002

We report measurements of optical scatter in epitaxial semiconductor multilayer structures. The structures comprise quarter-wave layers of Al0.2Ga0.8As/AlAs and GaAs/AlAs grown by molecular beam epitaxy and Al0.2Ga0.8As/AlAs grown by metalorganic chemical vapor deposition to assess differences due to growth technique and layer composition. The bidirectional reflective distribution function (BRDF) is measured at a wavelength of 835 nm corresponding closely to the Bragg reflection condition of the multilayer. The BRDF measurement yields calculated values for the total integrated scatter and effective surface roughness. The former is in the range 7×10−4–5×10−3 while the latter is typically 3–16 Å over the spatial frequency range 3×10 −2–1 μm−1. Both growth techniques yield comparable scatter loss on average, but there are significant differences in microscopic surface morphology, uniformity of scatter across the wafer, and lower limits of scatter. The measurements have significant implications for applications such as surface-emitting laser technology.
Improved characteristics of GaAs metal-semiconductor field-effect transistors on Si substrates back-coated with SiO2 by metalorganic chemical vapor deposition
Authors: Egawa T. , Nozaki S. , Soga T. , Jimbo T. , Umeno M.
Published: July 2002

GaAs metal-semiconductor field-effect transistors (MESFETs) on Si substrates back-coated with SiO2 grown at high temperature by metalorganic chemical vapor deposition have shown good pinch-off and suppressed sidegating. The SiO2 back-coating suppresses Si incorporation into an undoped GaAs layer during growth, and use of such an undoped layer with a low electron concentration beneath the channel layer improves a pinch-off characteristic. Higher growth temperature also improves crystallinity of GaAs layers grown on Si and helps to suppress the sidegating effect of GaAs MESFETs. The maximum transconductance of 160 mS/mm and the K value of 46.8 mA/V2 mm have been obtained for a MESFET with 2.5 μm gate length.
Global planarization of spun-on thin films by reflow
Authors: Bornside David E. , Brown Robert A. , Mittal Sanjiv , Geyling Franz T.
Published: July 2002

The leveling of a thin-liquid film on a substrate having a mesa-like feature is analyzed by finite element analysis and lubrication theory applied to the free-surface viscous flow problem. The height of the mesa is on the order of 1 μm and has a width on the order of 100 μm; the thin-liquid film is initially conformal to the substrate and has a thickness on the order of 1 μm. Capillarity is found to be the primary driving force for flow. The predicted leveling times from the numerical simulations compare favorably with an analytical solution developed from lubrication theory for the leveling of a thin film on a smooth substrate.
Uniform junction temperature AlGaAs/GaAs power heterojunction bipolar transistors on silicon substrates
Authors: Gao Guang-bo , Fan Zhi-fang , Blackburn D. L. , Ünlü M. S. , Chen J. , Adomi K. , Morkoç H.
Published: July 2002

AlGaAs/GaAs power heterojunction bipolar transistors on Si substrates exhibiting uniform junction temperature distribution are reported. Owing to a unique device design, the temperature spread across the entire device area is about 1 °C. The device exhibits a common emitter current gain of 20, a maximum collector current of 0.6 A, and a collector base junction breakdown voltage of 25 V.
Epitaxial growth study of Bi2(Sr,Ca)3Cu2Ox films on cleaved MgO substrates
Authors: Fujita J. , Yoshitake T. , Satoh T. , Igarashi H.
Published: July 2002

In situ epitaxial growth of Bi2(Sr0.6Ca0.4)3Cu2Ox films by ion beam sputtering on cleaved MgO substrates was studied. The crystallographic structures were analyzed by in situ reflection high-energy electron diffraction, a four-circle x-ray diffractometer, and a scanning electron microscope. While the epitaxial films on polished MgO substrates commonly showed the fourfold symmetry, epitaxial films having twofold symmetry were grown on cleaved MgO substrates and the films contained two types of equivalently misoriented domains. The epitaxial relationship between these domains and cleaved MgO substrates was such that the b axis of each domain deviated approximately ±13° from [010]MgO where the cleavage steps ran along [100]MgO. The step edges seemed to play an important role in the occurrence of the twofold epitaxial relationship, where the incommensurate modulation tended to align its direction so as to avoid the step edges.
Microstrip resonators using two-sided metalorganic chemical vapor deposited Er-Ba-Cu-O thin films
Authors: Takemoto J. H. , Jackson C. M. , Manasevit H. M. , St. John D. C. , Burch J. F. , Daly K. P. , Simon R. W.
Published: July 2002

We have measured very low microwave losses in microstrip resonators produced in a newly developed process which deposits high-temperature Er-Ba-Cu-O superconducting films by metalorganic chemical vapor deposition on both sides of a LaAlO3 substrate. These in situ films have critical temperatures of 92 K. High Tc superconductor (HTS) linear microstrip resonators demonstrated Q’s of 3500 at 10 GHz and 4.2 K, corresponding to surface resistances less than 330 μΩ, which is 45 times better than measured silver resoantors. HTS meanderline resonators with a fundamental frequency of 1.3 GHz have Q’s of 9600 at 4.2 K. Identical silver meanderline circuits have 300 times more surface resistance than HTS circuits.
Third-harmonic generation measurement of nonlinearities in SiO2-TiO2 sol-gel films
Authors: Torruellas W. E. , Weller-Brophy L. A. , Zanoni R. , Stegeman G. I. , Osborne Z. , Zelinski B. J. J.
Published: July 2002

Third-harmonic generation has been used to measure the magnitude and phase of the nonlinear susceptibility χ(3)(3ω) of SiO2-TiO2 sol-gel thin films as a function of TiO2 concentration. Nonlinearities 20 times larger than those of fused silica were found, making such films useful for nonlinear optics in glass waveguides.
Centroid shift of γ rays from positron annihilation in the depletion region of metal-oxide-semiconductor structures
Authors: Leung T. C. , Kong Y. , Lynn K. G. , Nielsen B. , Weinberg Z. A. , Rubloff G. W.
Published: July 2002

Using metal-oxide-semiconductor (MOS) structures, the shift of centroid (peak) of γ-ray energy distributions emitted from positron annihilation has been measured as a function of incident positron energy. The Doppler centroid shift was found to be consistent with the positron motion in the MOS depletion region. The results are described by a one-dimensional positron diffusion model, and provide information on ‘‘effective’’ positron diffusion length under applied field.
Nanometer-size surface modifications with preserved atomic order generated by voltage pulsing
Authors: Schimmel Th. , Fuchs H. , Akari S. , Dransfeld K.
Published: July 2002

We report on the generation of atomically resolved nanometer-size surface modifications by applying voltage pulses at predefined locations on the surface of the layered semiconductor tungsten diselenide (WSe2). Time-stable structures with diameters between 8 nm and less than 1 nm have been reproducibly written both in air and under vacuum. For small diameters, the resulting structures have the shape of mounds, whereas for diameters in excess of about 4 nm, a ring-like appearance is observed. In both cases, the atomic order of the formerly undisturbed surface is preserved and no defects in the lateral atomic order of the surface layer are found.
Thermal stability of PtSi contact to GexSi1−x
Authors: Hong Q. Z. , Zhu J. G. , Carter C. B. , Mayer J. W.
Published: July 2002

Thermal stability of PtSi contact to epitaxial Ge0.5Si0.5/(100)Si has been investigated. The PtSi layer remained structurally and morphologically intact on the epitaxial Ge-Si alloy at temperatures around 650 °C. When annealed at higher temperatures, PtSi penetrated locally into the alloy, although no chemical reaction was observed. The observed stability of PtSi is explained on the basis of a ternary Pt-Ge-Si equilibrium phase diagram. Other choices of contact compounds on Ge-Si alloys are also discussed.
Interferometric determination of the linewidth enhancement factor of a 1.55 μm GaInAsP optical amplifier
Authors: Ehrhart J. F. , Villeneuve A. , Assanto G. , Stegeman G. I. , Mersali B. , Accard A. , Gelly G. , Fernier B.
Published: July 2002

We report on the measurement of the small signal gain and index variation of a GaInAsP semiconductor optical amplifier as a function of the injected current in the wavelength range 1.53–1.58 μm. Employing interferometry to evaluate the index changes, we have determined that the linewidth enhancement factor varies from 9 to 4 for photon energies ranging from below to above the band gap, respectively.
Improvement of GaAs crystal quality grown on Si by metalorganic chemical vapor deposition through two-dimensional-like nucleation with an in situ H2/AsH3 plasma cleaning at 450 °C
Authors: Yoon Euijoon , Reif Rafael
Published: July 2002

We demonstrate that in situ Si cleaning techniques prior to low-temperature GaAs buffer layer growth affect the morphology of the GaAs buffer layer in the early stages of growth and the crystal quality of 3-μm-thick GaAs grown epitaxially afterward on the buffer layer at 650 °C. Both thermal cleaning and hydrogen/arsine plasma cleaning at 650 °C result in a bimodal distribution of GaAs nuclei on Si, although the number of larger nuclei with {111} facets decreases with the plasma cleaning. No such larger islands are observed with hydrogen/arsine plasma cleaning at 450 °C, and this makes possible a two-dimensional-like nucleation of the buffer layer. This two-dimensional-like nucleation of the buffer layer, in contrast to the bimodal nucleation behavior observed in other cleaning conditions, leads to a significant improvement in GaAs crystal quality with a reduction of full width at half maximum from 755 to 306 arcsec as measured by double-crystal diffractometry.
Chemical beam epitaxial selective growth of InP for laser fabrication
Authors: Gailhanou M. , Labourie C. , Liévin J. L. , Perales A. , Lambert M. , Poingt F. , Sigogne D.
Published: July 2002

Chemical beam epitaxy (CBE) is demonstrated here to be a suitable technique for the planarization of etched structures by selective overgrowth of InP layers. We present the fabrication of planar buried heterostructure laser diodes (PBH-LDs) with a separate confinement multiquantum well active layer grown by gas source molecular beam epitaxy and p-n InP current blocking layers grown by CBE. These lasers have been operated cw showing threshold current as low as 17 mA and maximum power up to 25 mW. We also achieved for the first time the fabrication of PBH-LD using molecular beam epitaxy techniques only.
In situ growth of PbSrYCaCuO films by laser ablation
Authors: Hughes R. A. , Lu Y. , Timusk T. , Preston J. S.
Published: July 2002

We report the successful preparation of 1212 PbSrYCaCuO thin films by laser ablation. The films are grown in situ on (100)LaAlO3 at the relatively low substrate temperature of 610 °C. The starting composition of the target is not that of the superconductor produced. Its composition was choosen to yield the 2213 PbSrYCaCuO phase, but the structural analysis shows a predominantly 1212 film with a small impurity phase. The films are highly oriented and show superconducting transitions with onsets at 90 K and zero resistance by 75 K.
Characteristics of interfaces for sputter deposited Bi2Sr2Ca1Cu2Ox/Bi2Sr2Cu1Oy/Bi2Sr2Ca1Cu2Oz structure
Authors: Mizuno K. , Higashino H. , Setsune K. , Wasa K.
Published: July 2002

A depth profile of an Auger electron spectroscopy (AES) for a Bi2Sr2Ca1Cu2Ox/Bi2Sr2Cu1Oy/Bi2Sr2Ca1Cu2Oz structure was investigated. This multilayered structure was fabricated by an in situ sputtering process and used for sandwich-type Josephson junctions. A little diffusion of Ca atoms from a top layer into the Bi2Sr2Cu1Oy layer was observed. It was confirmed that selective sputter etching during the AES measurement did not occur so seriously. The transition width at the two interfaces was estimated as about 10 nm, which was close to the depth resolution of our AES measurement. In addition, the interdiffusion between a Bi-based oxide film and a MgO substrate was hardly observed.
Critical heat transfer analysis of pulsed laser melting of pure metals
Authors: Basu Biswajit
Published: July 2002

Laser surface melting allows selective and rapid melting and solidification which leads to various improved properties. In this letter heat transfer during pulsed laser melting is critically analyzed for aluminum and iron using a numerical model. Using a pulse of few milliseconds and 0.5 mm spot radius, we show that there is a critical range of peak powers for which complete solidification occurs even before the end of the pulse. This is due to the rate of heat diffusion through the substrate being higher than the decaying laser heat flux. In this range, a directional growth of the solidification front can be expected.
Switching power dependence on detuning and current in bistable diode laser amplifiers
Authors: Pan Zeqi , Lin Hongchin , Dagenais M.
Published: July 2002

Measurements of the optical power required to switch on-and-off an optical bistable diode laser amplifier as a function of detuning and current from threshold are presented. Good quantitative agreement between the theory for a nonlinear Fabry–Perot and the experimental results are obtained. A linewidth enhancement factor of 3.1 and a value for the change of the refractive index versus carrier density of −1.8×10−20 cm3 are extracted from the measurements.
Effect of high-temperature anneal on interface states generation in stressed metal-oxide-semiconductor devices
Authors: Berger M. , Avni E. , Shappir J.
Published: July 2002

Polycrystalline silicon gate metal-oxide-semiconductor transistors, fabricated with polycrystalline silicon leads, were repeatedly electrically stressed by constant-current Fowler–Nordheim tunneling cycles. After every stress cycle the devices were annealed for various time intervals at 950 °C. Capacitance-voltage measurements were used to detect stress-related interface-state generation rates and saturation values. It was found that although the stress-generated interface states are totally annealed by the thermal treatment, their generation rates and saturation values after anneal are a strong function of the anneal time, significantly exceeding the values of the fresh devices and inversely dependent on the anneal time. From the results it is concluded that a new type of latent interface-state sites is generated by the combination of tunneling stress and high-temperature annealing.
Characteristics of 4×4 photonic switch array with gain and high contrast
Authors: Mori Yoshihiro
Published: July 2002

A two-dimensional semiconductor photonic switch array with a new operating principle based on the change of the gain coefficient in the GaAs crystal is reported. This switch realizes direct amplification and absorption of the optical signal and features optical gain of 4 dB, contrast of 9.6 dB, applied voltage of 2.2 V, and a simple planar structure. This array is applicable to photonic parallel data transmission systems.
Reactions in Pd/GaAs(001) contacts at 7×108 Pa pressure
Authors: Zhao Y. C. , Wu Z. Q.
Published: July 2002

In this letter, we present the transmission electron microscopy and x-ray diffraction studies of Pd/GaAs (001) contacts that were annealed in an argon ambient with a pressure of 7×108 Pa. Our observations show that this ambient inhibits not only the decomposition of As-rich phases but the reactions accompanying the As sublimation for the Pd/GaAs (001) contacts and that the reactions are described as 4Pd+GaAs→Pd4GaAs (between 25 and 200 °C) and 3Pd+2GaAs→2PdGa+PdAs2 (between 350 and 800 °C).
Effect of arsenic dimer species to silicon doping of GaAs layers prepared by molecular beam epitaxy
Authors: Wu B. J. , Mii Y. J. , Chen M. , Wang K. L.
Published: July 2002

A strong dependence of Si doping on dimer arsenic (As2) flux and substrate temperature is observed for GaAs films grown by molecular beam epitaxy. Using an arsenic effusion cell with a cracker, Si doping levels are shown to depend on the cracking efficiency and substrate temperature. With the same Si cell temperature and GaAs growth conditions, the measured carrier concentration of the grown films decreases as the cracker temperature (cracker current) is increased and this dependence becomes stronger as the substrate temperature is increased. For samples grown at 660 °C, more than a factor of four decrease of the doping concentration is observed for the cracker current changing from 5 to 6.5 A. For those grown at 560 °C, there is only a weak dependence. Evidence is given to show that carbon contamination and Si self-compensation are not the causes of this effect. The formation of volatile SixAsy compound at the substrate surface is proposed to account for this phenomenon.
Electron diffraction study of defects at a semiconductor heterostructure interface
Authors: Rajan Krishna
Published: July 2002

Interface dislocation periodicity at a Ge/Si interface is studied using electron diffraction. Relaxation effects due to these defects, normal to the interface, are measured. 
Interface compound formation and dependence on In-layer thickness in Ni/In thin-film systems
Authors: Platzer R. , Wöhrmann U. , Ding X. L. , Fink R. , Krausch G. , Luckscheiter B. , Voigt J. , Schatz G.
Published: July 2002

Interdiffusion and interface compound formation has been observed at the system Ni/In by using thin-film couples as well as thin In films on low index Ni single-crystal substrates. The method applied was the perturbed γγ-angular correlation technique, which is very sensitive to local structures and their changes around probe atoms. The successive occurrence of different Ni/In compounds could be observed on isochronal annealing above 230 K. A correlation between the appearance of compounds and In film thickness has been found.
Minority electron lifetimes in heavily doped p-type GaAs grown by molecular beam epitaxy
Authors: Ito Hiroshi , Furuta Tomofumi , Ishibashi Tadao
Published: July 2002

Minority electron lifetimes in molecular beam epitaxy grown Be-doped p-type GaAs are characterized systematically. Samples grown at temperatures from 550 to 700 °C have hole concentrations from 1017 to 1020 cm−3. Although electron lifetime in samples grown at temperatures higher than 650 °C remains nearly constant for each free-carrier concentration, it decreases significantly at lower growth temperatures. These tendencies are observed in common for various hole concentrations. These results can be explained in terms of an increase in nonradiative recombination centers incorporated during growth.
Electrostatic and bubble nature of ball lightning
Authors: Mesenyashin A. I.
Published: July 2002

Ball lightnings are considered to be electrostatically bipolar charged shells of orderly oriented water molecules. The time of life of this model for ball lightnings of typical sizes is shown to exceed tens of seconds, the energy being caused by orientation of dipolar water molecules. Issues pertaining to ball lightning formation, stability, and specialties of motion are discussed.
Compression of nonamplified femtosecond pulses using nonlinear organic fibers
Authors: Yamashita Mikio , Torizuka Kenji , Uemiya Takafumi , Shimada Junichi
Published: July 2002

It is shown that a 39 fs output pulse from a colliding-pulse mode-locked cw dye laser is directly compressed to 22 fs, without amplification, using a highly nonlinear 4-(N, N-dimethylamino)-3-acetamidonitrobenzene single-crystal cored fiber followed by a dispersive delay line of a grating pair.
Efficient vertical coupling of photodiodes to InGaAsP rib waveguides
Authors: Deri R. J. , Doldissen W. , Hawkins R. J. , Bhat R. , Soole J. B. D. , Schiavone L. M. , Seto M. , Andreadakis N. , Silberberg Y. , Koza M. A.
Published: July 2002

We demonstrate vertical integration of InGaAs mesa photodiodes with InGaAsP rib waveguides employing an intermediate optical impedance matching layer. The diode length necessary for 90% light absorption at 1.52 μm wavelength was 42 μm, a threefold reduction in diode length with respect to previous work employing similar waveguides without a matching layer. The quantum efficiency was observed to be almost independent of the optical wavelength and polarization. The influence of spatial transient intensity redistribution effects on these devices is investigated in detail.
Large Schottky barrier heights on n-InP−A novel approach
Authors: Yamada Masao , Wahi Anita K. , Kendelewicz Tom , Spicer William E.
Published: July 2002

An unusually high Schottky barrier height (SBH) of 0.82 eV has been observed at Au/n-InP(110) interfaces with one monolayer of Sb as an interlayer using photoemission techniques. For Au deposited on clean cleaved InP(110), Au-In alloying that occurs with increasing Au coverage destroys interfacial perfection. The resulting Fermi level position lies ∼ 0.5 eV below the conduction band minimum, as is common for metal interfaces with clean cleaved InP. However, for InP surfaces first passivated with one monolayer of Sb, this Au–In alloying is completely inhibited. An abrupt interface results in an increased possibility of a low interface defect density. This represents a possible way to control of SBH and produces high SBH for n-InP.
Explosive anisotropic grain growth of delta-NiMo by solid-state diffusion
Authors: Chou T. C. , Nieh T. G.
Published: July 2002

Anomalous, anisotropic grain growth has been observed in delta(δ)-NiMo intermetallic compound during the annealings of Mo/Ni thin-film diffusion couples at 700 and 800 °C. Two layered microstructures showing median-sized, equiaxed grains and large columnar single crystalline grains were generated. The growth direction of the columnar grains was parallel to the direction of Ni diffusion flux. Electron diffraction indicated that both the median-sized and the columnar grains were δ-NiMo. The composition of δ-NiMo was determined to be Ni48-Mo52 (at.%). According to the thickness of reaction-formed δ-NiMo, the apparent interdiffusion coefficient was measured to be about 10−10 cm2/s which is 4 to 5 orders of magnitude greater than literature data. The enhanced diffusion rate in Ni-Mo, and the anomalous anisotropic grain growth of δ-NiMo compound are discussed on the basis of exothermic reactions between Ni and Mo during diffusional intermixing. The enthalpy of the formation of δ-NiMo is calculated and demonstrated to be sufficient to cause melting/solidification of the compound.
Characterization of ion-implanted InxGa1−xAs/GaAs 0.25 μm gate metal semiconductor field-effect transistors with F
t≳100 GHz
Authors: Feng M. , Laskar J. , Miller W. , Kolodzey J. , Stillman G. E. , Lau C. L.
Published: July 2002

This work presents millimeter wave performance achieved by ion-implanted InGaAs/GaAs metal semiconductor field-effect transistor devices. A current gain cutoff frequency ft of 126 GHz and maximum frequency of oscillation fmax of 232 GHz have been measured for 0.20 μm gate length devices. The ft and low-field Hall mobility data, measured at 300 and 112 K, lead us to conclude that the average electron velocity under the gate is mainly due to the high-field velocity rather than low-field electron mobility.
Influence of memory propagation on phase-resolved stochastic behavior of ac-generated partial discharges
Authors: Van Brunt R. J. , Cernyar E. W.
Published: July 2002

Using measurements of phase-restricted conditional partial-discharge pulse-amplitude and phase distributions, it is shown for the first time that the stochastic properties of a dielectric-barrier type of partial discharge generated by an ac voltage are significantly influenced by memory associated with charge deposited on the dielectric surface by preceding discharge events. This memory effect must be considered in any attempt to interpret results of phase-resolved partial-discharge measurements.
Enhancement of optical reflectivity of high T
c superconducting films by ion milling
Authors: Kim J. H. , Char K. , Bozovic I. , Lee W. Y. , Kapitulnik A. , Harris J. S.
Published: July 2002

We report optical reflectivity data of several representative high Tc superconducting films before and after ion milling. A significant enhancement of optical reflectivity after ion milling of a few thousand Å is observed. We observed that features associated with a-axis texture vanished after ion milling, resulting in pure c-axis films. This suggests that a-axis grains reside mostly near the surface in post-annealed high Tc superconducting films. The fact that highly oriented c-axis films can be retained even after post-annealing (for raising Tc) may be important for practical applications.
Low-pressure growth of ZnTe by Ar laser-assisted metalorganic vapor phase epitaxy
Authors: Ogawa Hiroshi , Nishio Mitsuhiro , Ikejiri Makoto , Tuboi Hideyuki
Published: July 2002

The effect of Ar laser irradiation upon ZnTe homoepitaxial growth has been investigated in low-pressure metalorganic vapor phase epitaxy. Dimethylzinc and diethyltelluride were used as source materials. The growth rate of the ZnTe layer was greatly enhanced by irradiating vertically onto the (100) substrate. Photoluminescence measurements revealed that the quality of the layer is improved by the irradiation. Diethyltelluride is effectively decomposed on the surface by the irradiation.
Low dark current, planar In0.4Ga0.6As p-i-n photodiode prepared by molecular beam epitaxy growth on GaAs
Authors: Tzeng Y. C. , Li S. S. , Lin Y. W. , Ribas P. , Park R. M.
Published: July 2002

We report here the successful fabrication of a planar, low dark current, and high sensitivity In0.4Ga0.6As p-i-n photodiode fabricated on a semi-insulating GaAs substrate with the aid of a multistage strain-relief buffer system. Without using surface passivation and anti-reflection coatings, the detector has a quantum efficiency of 42% and a peak responsivity of 0.45 A/W at 1.3 μm wavelength. The reverse leakage current for the mesa-etched photodiode with an active area of 2×10−4 cm2 is 5×10−9 A at −5 V, and the breakdown voltage exceeds 25 V.
Electronic properties of semiconductor nanostructures probed by scanning tunneling microscopy
Authors: Weiner J. S. , Hess H. F. , Robinson R. B. , Hayes T. R. , Sivco D. L. , Cho A. Y. , Ranade M.
Published: July 2002

We demonstrate the novel application of the scanning tunneling microscope to find and probe the electronic transport properties of single semiconductor nanostructures at temperatures from room temperature to as low as 1.5 K. The current-voltage characteristics of InGaAs/InAlAs resonant tunneling nanostructures clearly show negative differential resistance. From the dependence of the current on cross-sectional area the lateral depletion is estimated to be 300 Å.
Oxygen incorporation in highly c-axis oriented YBa2Cu3O7−x thin films deposited by plasma-enhanced metalorganic chemical vapor deposition
Authors: Li Y. Q. , Zhao J. , Chern C. S. , Lemoine E. E. , Gallois B. , Norris P. , Kear B.
Published: July 2002

YBa2Cu3O7−x superconducting thin films prepared by chemical vapor deposition which exhibit high transition temperatures (Tc∼90 K) and high critical current densities (Jc≳106 A/cm2 at 77.7 K and 0 T) generally have copper-rich precipitates on the surface. We have studied both near-stoichiometric and nonstoichiometric highly c-axis oriented thin films formed by plasma-enhanced metalorganic chemical vapor deposition. We show that the reduction in transport properties (Tc and Jc) observed in stoichiometric films with smooth morphologies may result from a dramatic reduction of the oxygen diffusion rate in these thin films as compared to nonstoichiometric films. The significant enhancement of the transport properties of these films was achieved by further oxygen anneals at 480 °C.
Second-harmonic generation transition in NaNb3O8 solid solutions
Authors: Zhang Wei Jia , Liu Wen , Shen Hong Yuan
Published: July 2002

An apparent transition between active and nonactive second-harmonic generation (SHG) has been discovered in the NaNb3O8 solid solutions with the tetragonal tungsten bronze structure. No SHG was detected in 0.35Na2O:Nb2O5 solid solution crystal or its powder. Nevertheless, powder SHG with a magnitude comparable to KH2PO4 was observed when a small amount of Nb2O5 was added to the powder ground from the crystal and sintered again. Microcracks and ferroelectric domain boundaries have been observed in the crystal using transmission electron microscopy. The only difference between the lattice images of SHG active powder and non-SHG active powder is the absence of microcracks and ferroelectric domain boundaries in the SHG active powder. Dielectric constant of the 0.35Na2O:Nb2O5 crystal is about 300 and δ is 0.003 for frequency from 120 kHz to 12 MHz.
Resonant self-pumped phase conjugation in cesium vapor at 0.85 μm
Authors: Gaeta Celestino J. , Lam Juan F.
Published: July 2002

We report the first observation of resonant self-pumped phase conjugation at diode laser wavelengths. A phase conjugate reflectivity of 0.01%, and a cw threshold intensity of 75 W/cm2 were measured.