bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluorine-implanted bismuth oxide superconductors
Authors: Gupta Ram P. , Khokle W. S. , Pachauri J. P. , Tripathi C. C. , Pathak B. C. , Virdi G. S.
Published: July 2002

We report for the first time the influence of fluorine implantation in the Bi-Sr-Ca-Cu-O system. The incorporation of fluorine was found to enhance the zero resistance temperature and to sharpen the high-temperature transition. The fluorinated sample exhibited Tc (R=0)=89 K and the high Tc phase of the composition had Tc (on) as high as 124 K with an extrapolated Tc (end) of 114 K. Resistance temperature characteristics of a sample before and after fluorine implantation are presented.
Ferrotrielasticity and birefringence in cadmium chlorapatite
Authors: Amin Ahmed , Newnham Robert E.
Published: July 2002

Ferrotrielasticity is discussed in terms of the structural aspects of cadmium chlorapatite. Optical retardation in single-crystal cadmium chlorapatite Cd5 (PO4)3Cl has been measured as a function of temperature. The results will be presented and the possibility of a high-order ferrotrielastic switching will be discussed.
Properties of metal-Ba2YCu3O7 composites formed by electrodeposition from nonaqueous solutions onto the superconductor
Authors: Rubin H. D. , Rosamilia J. M. , O’Bryan H. M. , Miller B.
Published: July 2002

The electrical and magnetic properties of electrodeposits of silver, copper, and lead on Ba2YCu3O7 substrates were evaluated by two- and four-point resistivity measurements and magnetic susceptibility data on the resulting composite structure. With superconductors sufficiently dense to resist significant penetration by the nonaqueous solvents of the plating bath, no degradation of the bulk properties of the superconductor was observed in the magnetic measurements. These conclusions were supported by the resistivity results; furthermore, it was shown that the contact resistance between electrodeposited silver and the superconductor matched that for ultrasonically soldered indium.
Influence of beam coherence on measurements of roughness in film growth
Authors: Lagally M. G. , Kariotis R.
Published: July 2002

Diffracted intensity oscillations in epitaxial growth are discussed in terms of the existing roughness scale on the surface and the coherence length of the radiation used to measure them. It is shown that for systems with unbounded interface width growth, the greater the coherence length, the more rapidly the oscillations damp out. On the other hand, oscillations can occur and be persistent if the coherence length of the beam is much shorter than the characteristic horizontal length scale for roughness, even in the case where unbounded growth is present. This behavior is governed by the magnitude of the coherence length of the beam, relative to the lateral length scale that characterizes the surface structure.
Defects in molecular beam epitaxy grown GaAlAs layers
Authors: Feng S. L. , Zazoui M. , Bourgoin J. C.
Published: July 2002

Using deep level transient spectroscopy we characterized the shallow native traps in n-type doped Ga1−xAlxAs layers (with x=0.30 and 0.36) grown by molecular beam epitaxy. A trap lying at 0.18 eV below the conduction band is detected which exists in large concentration within 0.2 μm from the surface and is responsible for the freeze out of free carriers at low temperatures.
Use of luminescence for the evaluation of stoichiometry in epitaxial growth
Authors: Pistol M.-E. , Leys M. R. , Samuelson L. , Gerling M. , Gustafsson A.
Published: July 2002

Photoluminescence measurements are described through which details of the stoichiometric conditions which have prevailed on the surface of gallium phosphide (GaP) during growth have been revealed. This ability to probe the balance of the constituents on the growing surface is obtained from tracing the relative occurrences of excitonic peaks which are due to defects on the two sublattices of the binary tetrahedral material. The information on the optimization of the stoichiometry is found to correlate well with morphological evaluation of perfection of the epitaxial growth.
Interaction of Ce with Si (100)
Authors: Hillebrecht F. U.
Published: July 2002

The interaction of Ce with Si (100) surfaces has been studied qualitatively by photoemission with synchrotron radiation. For coverages of a few monolayers the reaction yields a disordered phase with a wide variation of Si-Ce coordinations which do not depend on the distance from the surface. For coverages above 5 monolayers a mixed phase of Ce and a Ce silicide is found. Segregation of a Si-like phase to the surface does not take place.
Photoluminescence spectra of shallow acceptors in GaAs-(Ga,Al)As quantum wells
Authors: Oliveira L. E. , López-Gondar J.
Published: July 2002

A theoretical study of the photoluminescence spectra associated with shallow acceptors in a GaAs-(Ga,Al)As quantum well is performed. It is shown that an analysis of the acceptor-photoluminescence line shape could allow an experimental determination of the quasi-Fermi energy level of the conduction-subband-electron gas as well as of the on-edge acceptor binding energy.
Reassessment of the rate constant for electron collision quenching of KrF(B)
Authors: Kushner Mark J. , Hanson David E. , Schneider Barry I.
Published: July 2002

The rate constant for electron collision quenching of KrF(B) has been reassessed by analyzing previous theoretical [A. Hazi, T. Rescigno, and A. Orel, Appl. Phys. Lett. 35, 477 (1979)] and experimental [D. Trainor and J. Jacob, Appl. Phys. Lett. 37, 675 (1980)] data. From this analysis we recommend that the rate constant for electron collision quenching of KrF(B), used for modeling electron beam and discharge excited lasers, should be 3–6×10−8 cm3 s−1.
Organometallic vapor phase epitaxial growth of GaAs-based pseudomorphic modulation-doped field-effect transistor structures
Authors: Thompson Alan G. , Mao Bor-Yen , Lee Gi Young
Published: July 2002

We report the preparation of InGaAs/AlGaAs strained-layer(pseudomorphic) modulation-doped field-effect transistor (MODFET) structures by organometallic vapor phase epitaxy (OMVPE). Devices fabricated from these structures with 0.9 μm gate lengths had dc extrinsic transconductances up to 340 mS/mm. Microwave testing up to 40 GHz showed current gain cutoff frequencies ( fT ) of 22 GHz and estimated maximum frequency of oscillation ( fmax ) of 70 GHz. This is the first report to our knowledge of the use of OMVPE material in the fabrication of pseudomorphic MODFETs.
External-cavity coherent operation of InGaAsP buried-heterostructure laser array
Authors: Diadiuk V. , Liau Z. L. , Walpole J. N. , Caunt J. W. , Williamson R. C.
Published: July 2002

Coherent operation of a monolithic linear array of InGaAsP buried-heterostructure lasers operating at λ=1.3 μm has been acheived by means of a spatial filter in an external cavity. An array of mass-transported InP microlenses was used to collimate the beams of the individual laser elements and couple the laser array output to the external cavity. The coherent array output exhibited a narrow (3.2 mrad), three-lobe far-field pattern with ∼65% of the energy concentrated in the central peak.
Highly efficient separate-confinement P
p
i
n
N GaAs/AlGaAs waveguide phase modulator
Authors: Lee S. S. , Kim Y. S. , Ramaswamy R. V. , Sundaram V. S.
Published: July 2002

We report a high-efficiency PpinN GaAs/AlGaAs waveguide phase modulator for high-speed operations. By introducing p- and n-GaAs layers beside the intrinsic GaAs layer of a P-i-N double heterostructure, the absorption edge-related effect, hardly used in P-i-N phase modulators, is utilized. We demonstrate a high phase shift efficiency of 37.5°/V mm at 1.3 μm wavelength. Although this corresponds to the highest expeirmental value reported for reverse-biased GaAs/AlGaAs phase modulators, our device operates with a low junction and a very low dynamic capacitance.
Enhancement of excitonic electrorefraction by optimizing quantum well materials and structures
Authors: Nojima S.
Published: July 2002

A method to enhance excitonic electrorefraction in semiconductor quantum wells is proposed, in which the well thickness and the band gap of well materials are optimized so that the figure of merit for electrorefraction is maximized. Application of this method to crossed-waveguide optical switches using InGaAlAs/InAlAs quantum wells enhances this figure of merit by ten times compared with that of conventional InGaAs/InAlAs quantum wells.
Reflection high-energy electron diffraction intensity oscillation induced by electric current during Si epitaxial growth on Si (001) 2×1 surfaces
Authors: Nishimori K. , Tokutaka H. , Tamon T. , Kishida S. , Ishihara N.
Published: July 2002

We have observed the oscillations of specular beam intensity of reflection high-energy electron diffraction (RHEED) during Si molecular beam epitaxy on Si (001) 2×1 surfaces. The oscillation modes were measured as a function of incident beam direction, substrate temperature, or especially, dc current direction for resistive heating of the substrate. For the first time in [110] incident beam direction and at a substrate temperature above 450 °C, the phase of specular beam oscillations with the biatomic-layer growth mode can be chosen by the direction of the heating current.
Chemical vapor deposition of single-crystal films of cubic SiC on patterned Si substrates
Authors: Shigeta Mitsuhiro , Fujii Yoshihisa , Furukawa Katsuki , Suzuki Akira , Nakajima Shigeo
Published: July 2002

Stacking faults of cubic SiC films grown on Si (100) were investigated by the electrolytic etching. We find an exponential reduction of the defect density with an increase of film thickness and the anisotropy in the density for the films on off-axis Si (100) substrates. The defect reduction along the offset direction 〈011〉 is explained from the atomic step effect limiting the length of stacking faults to smaller than the equilibrium value. In addition, the defects are eliminated by controlling the film thickness and the size of the growth area using patterned substrates. Since the defects in SiC are metastable, the film thickness required for defect-free crystal is larger than √2× the lateral dimension.
Sequential Ar-O2 sputtering of Y2O3, BaF2, and CuO targets for preparation of Y-Ba-Cu-O superconducting films without wet-O2 annealing
Authors: Bhushan M. , Strauss A. J. , Finn M. C.
Published: July 2002

Superconducting Y-Ba-Cu-O (YBCO) films have been prepared by ex situ O2 annealing of multilayer films deposited on yttria-stabilized zirconia substrates by sequential rf diode sputtering of Y2O3, BaF2, and CuO targets, all of which are chemically stable. If sputtering is performed in an Ar ambient, the as-deposited films contain sufficient F to require its removal by annealing in wet O2 at about 800 °C or above before the superconducting YBCO phase can be formed by annealing in dry O2. However, sputtering in an Ar-O2 ambient greatly reduces the F content, making it possible to obtain the superconducting phase by annealing in dry O2 only. If the ambient contains about 20% O2, films with Tc (R=0)>85 K can be prepared without wet-O2 annealing. The Ar-O2 process therefore has the potential for in situ preparation of superconducting YBCO films.
Double waveguide in LiNbO3 by ion implantation
Authors: Chandler P. J. , Zhang L. , Townsend P. D.
Published: July 2002

Ion implantation has been employed to produce superposed planar waveguide structures in LiNbO3. This was achieved by constructing two optical barriers at different depths beneath the crystal surface using 1.1 and 2.2 MeV He+. The composite refractive index profile was compared with those of the two individual barriers, by means of a dark mode analysis technique based on a calculation of the reflectivity function at the coupling prism. The profiles were found to be directly additive except for a noticeable annealing effect of the first implanted barrier, and a range enhancement of the second barrier. These effects were confirmed by varying the order and temperature of the implantations. The implications of these results to possible device construction have been discussed.
Photoemission studies of the interfacial reactions between ZnS and anodic oxide film of HgCdTe
Authors: Jin S. , Lau W. M.
Published: July 2002

The interfacial reactions of zinc sulphide (ZnS) on an anodic oxide film of mercury cadmium telluride (HgCdTe) have been studied by polar angle dependent x-ray photoelectron spectroscopy (XPS). It was found that the sputter deposition of ZnS reduced the oxidized tellurium of the anodic film at the interface. In addition, the XPS results show a high Zn/S ratio when the deposition is confined to a few monolayers. The ratio, however, decreases to unity for a thick film. The results indicate that zinc atoms sputtered from the ZnS target play an important role in the interfacial reactions between the deposited overlayer and the HgCdTe anodic oxide film.
Single quantum well laser with vertically integrated passive waveguides
Authors: Chen Y. C. , Waters R. G. , Dalby R. J.
Published: July 2002

The condition for the fundamental mode operation in a single quantum well laser with vertically integrated passive waveguides has been studied. With proper choice of parameters, transverse beam divergence as low as 19° has been achieved.
Structure of (√3×√3) R 30°-B at the Si interface studied by grazing incidence x-ray diffraction
Authors: Akimoto Koichi , Hirosawa Ichiro , Tatsumi Toru , Hirayama Hiroyuki , Mizuki Jun’ichiro , Matsui Junji
Published: July 2002

The boron-induced ( 7/8 × 7/8 )R30° reconstruction at the Si interface has been investigated by grazing incidence x-ray diffraction. The in-plane projected struture is found from the structure factors near zero perpendicular momentum transfer. At the a-Si/Si (111) interface, boron atoms at 1/3 ML are substituted for silicon atoms, thus forming a ( 7/8 × 7/8 )R30° lattice and the boronsilicon bond is contracted compared with the siliconsilicon bond. Even at the interface between a solid phase epitaxial Si (111) layer and a Si (111) substrate, the boron-induced ( 7/8 × 7/8 )R30° reconstruction has also been observed and the structure is similar to that observed at the a-Si/Si (111) interface.
InGaAsP(1.3 μm)/InP vertical-cavity surface-emitting laser grown by metalorganic vapor phase epitaxy
Authors: Yang Long , Wu Ming C. , Tai Kuochou , Tanbun-Ek Tawee , Logan Ralph A.
Published: July 2002

We report InGaAsP/InP vertical-cavity surface-emitting lasers (VCSELs) with an emission wavelength near 1.3 μm grown by metalorganic vapor phase epitaxy. The VCSEL structure contains a double-heterostructure cavity, a metal mirror, and a SiO2/Si dielectric stack (three pairs) mirror with a measured reflectivity of 98%. A threshold current as low as 5 mA for 15-μm-diam devices with a 1-μm-thick active layer at 77 K was achieved, which is close to the best reported value (6 mA) within the accuracy of the pulse measurement. The highest operating temperature was 220 K.
Oxide interfacial layers in Au ohmic contacts to p-type Hg1−xCdxTe
Authors: Krishnamurthy V. , Simmons A. , Helms C. R.
Published: July 2002

Annealed Au contacts to p-type Hg1−xCdxTe with thin interfacial oxide layers exhibit ohmic behavior. These interfacial layers have been produced by plasma oxidizing the Hg1−xCdxTe surface prior to Au evaporation or as a result of electroless Au deposition from AuCl3 which also produces an interfacial layer. We believe this ohmic behavior is primarily a result of the low interface state density at the interfacial layer/Hg1−xCdxTe interface and in addition, a 100 °C anneal promotes a further reduction in the interface state density and thus lowered the contact resistance. In comparison, as-deposited and annealed Au contacts without a thin interfacial layer were rectifying with a large barrier height.
Concentration dependence and interfacial instabilities during ion beam annealing of arsenic-doped silicon
Authors: Priolo Francesco , Rimini Emanuele , Spinella Corrado , Ferla Giuseppe
Published: July 2002

Ion beam induced epitaxy of amorphous Si layers onto 〈100〉 substrates has been investigated by varying the As concentration. At As concentrations below 4×1018/cm3 no rate effect is observed. In the intermediate regime, between 4×1018/cm3 and 2×1021/cm3, the growth rate increases linearly with the logarithm of As concentration and reaches a value about a factor of 2 higher than that of intrinsic Si. At concentrations above 2×1021/cm3, the epitaxy experiences a sudden, severe retardation. Finally, at a concentration of ∼6×1021/cm3, twins are observed to form.
Theory of millimeter wave nonlinearities in semiconductor superlattices
Authors: Lam Juan F. , Guenther Bob D. , Skatrud David D.
Published: July 2002

A study of the impact of semiconductor superlattices on millimeter wave nonlinearities is reported. χ(3) as large as 10−2 esu can be achieved by using 250 GHz radiation. Self-induced transparency is also predicted, and its competition with the third-harmonic generation process is quantified.
Silicon etching with oxygen molecular beam assisted by predeposited germanium
Authors: Tatsumi Toru , Niino Taeko , Hirayama Hiroyuki
Published: July 2002

Si was etched using an O2 molecular beam according to the chemical reaction 2Si+O2→2SiO↑. The minimum etching temperature was decreased by 25 °C when a Ge layer had been deposited on a clean Si surface before etching. At 800 °C, the Ge-coated Si surface was etched while the clean Si surface was not. The O2 partial pressure during etching was 2×10−5 Torr; the etching rate was about 80 Å/min at 800 °C. Auger electron spectroscopy showed that the number of Ge atoms slightly decreased during Si etching. Ge atoms on the surface are thought to weaken Si back bonds by forming a thin Ge-Si alloy layer on the surface. Undercutting at the SiO2 mask edge was suppressed by this Ge predeposition technique at 800 °C because the sidewall without Ge was not etched at this temperature.
Formation of amorphous interlayers by a solid-state diffusion in Zr and Hf thin films on silicon
Authors: Cheng J. Y. , Chen L. J.
Published: July 2002

The formation of amorphous interlayers (a interlayers) in polycrystalline Zr and Hf thin films on single-crystal (111)Si has been observed by cross-sectional transmission electron microscopy. The growth of a interlayers in group IVa metal thin films on silicon was found to exhibit similar behavior but was fundamentally different from those of metal-metal diffusion couples. The growth of a interlayers was found to follow a linear growth law initially then slowed down until a critical thickness was reached. Si was found to be the dominant diffusing species. Good correlation was found among the maximum thickness of the a interlayer, the difference in atomic size between metal and Si, the activation energy of the linear growth, and the largest heats of formation of the respective silicides.
Electron beam induced current and cathodoluminescence imaging of the antiphase domain boundaries in GaAs grown on Si
Authors: Nauka K. , Reid G. A. , Liliental-Weber Z.
Published: July 2002

Electrical and optical properties of antiphase domain boundaries (APBs) in GaAs epitaxial layers grown on Si substrates have been investigated using cathodoluminescence, electron beam induced current, and scanning deep level transient spectroscopy. It was found that APBs reduce near-band-gap luminescence and minority-carrier lifetime. In contrast to recombination at threading dislocations in GaAs films, the nonradiative recombination processes at APBs are not due to deep traps but rather to a continuum of band-gap states introduced by APBs.
Direct overwriting capability in TM-rich side rare-earth transition metal amorphous films
Authors: Takayama Shinji , Shimizu Teruhisa , Owa Soichi , Tanaka Hiroshi
Published: July 2002

The feasibility of a new method for direct overwrite with a power-modulated laser beam under a constant external bias field Hex fixed in the same direction as an initializing field Hinit was demonstrated by means of a dynamic disk tester. TbFeCoCr amorphous films with compensation temperature (Tcomp) far below room temperature were employed, but coercivity falls below 200 Oe at 200 °C, while the saturation magnetization remains high. We found that written pits are formed by a demagnetization field Hd in the region of a weak Hex, whereas for a stronger Hex they are formed by a effective external field Heff(=Hex−Hd) fixed in the same direction as Hinit. By using a power modulation between 9 and 5 mW under a constant field of −100 Oe, we were able to demonstrate direct overwrite, although the readout carrier-to-noise ratio was low (18 dB).
Optimization of stripe width for low-threshold operation of quantum well laser diodes
Authors: Osinski J. S. , Dzurko K. M. , Hummel S. G. , Dapkus P. D.
Published: July 2002

An experimentally verified model for threshold current in GaAs/AlGaAs quantum well laser diodes has been extended to calculate for the first time the dependence of threshold current on stripe width. The lowest possible threshold is shown to occur when the lateral confinement factor is in the range of 55–60% for typical devices, a value that is not affected by mirror reflectivity or lateral index step. A simple, generalized optimization scheme for obtaining the unique width/length combination that results in lowest threshold is presented, and predicts potential as-cleaved threshold currents as low as 0.5 mA.
Integrated optic front end for polarization diversity reception
Authors: Shani Yosi , Henry Charles H. , Kistler Rodney C. , Kazarinov Rudolph F. , Orlowsky Kenneth J.
Published: July 2002

An integrated optic circuit on silicon, which can be used in balanced polarization diversity detection, is demonstrated. The device consists of a 3 dB coupler and two polarization splitters. It has excess losses of 1.8 and 3.0 dB for TM and TE polarizations, respectively, and around −22 dB rejection of the unwanted polarizations at each output.
Ion beam induced epitaxial crystallization of NiSi2
Authors: Ridgway M. C. , Elliman R. G. , Williams J. S.
Published: July 2002

Ion beam induced epitaxial crystallization of amorphous NiSi2 is reported. Epitaxial NiSi2 layers on (111) Si substrates were implanted at ∼−196 °C with low-energy Si ions to form an amorphous surface layer. The recrystallization of amorphous NiSi2 was induced at 13–58 °C by irradiating with high-energy Si or Ne ions. Recrystallization proceeded in a layer-by-layer manner from the original amorphous/crystalline interface with an activation energy of 0.26±0.07 eV.
Downstream plasma-enhanced diamond film deposition
Authors: Pickrell David J. , Zhu Wei , Badzian Andrzej R. , Messier Russell , Newnham Robert E.
Published: July 2002

Diamond films have been deposited on a variety of substrates up to 2 cm below the luminous plasma in a tubular microwave plasma-enhanced chemical vapor deposition system. Depositing downstream of the plasma appears to offer several advantages over immersion of substrates in the plasma, for coating certain oxide substrates, including a reduction in substrate etching and an improvement in film uniformity, adhesion, and transparency. Furthermore, positioning substrates downstream of the plasma and adjusting their temperature with an external heater decouples the plasma and substrate parameters, facilitating studies to determine the effect of various parameters on the chemical vapor deposition diamond process. A disadvantage of downstream deposition is the decrease in the growth rate of diamond films.
Electronic transitions in a SimGen strained monolayer superlattice measured by photoreflectance
Authors: Dafesh P. A. , Arbet V. , Wang K. L.
Published: July 2002

The first photoreflectance spectrum from a short-period strain-symmetrized SimGen superlattice has been measured at 87 K. Fifteen electronic transitions were measured between 1.1 and 2.7 eV and fit well to a third derivative functional form. Most of the transition energies were calculated using a one-band envelope-function model, adding strain and spin orbit shifts as first-order corrections. Additional transitions were observed near the expected interband energies in an unstrained Si0.2Ge0.8 random alloy. All of the calculated transition energies were found to agree to within 80 meV of the measured values.
Vapor-deposited superconducting YBa2Cu3O7−δ lines: Effect of thickness and width on morphology
Authors: Phillips J. R. , Mayer J. W. , Martin J. A. , Nastasi M.
Published: July 2002

Lines of different widths and thicknesses of YBa2Cu3O7−δ were prepared on SrTiO3 and compared for signs of morphological dependence on line dimensions. The lines were prepared on (100) SrTiO3 by electron beam (e-beam) coevaporation, e-beam resist lift-off, and annealing in oxygen to 850 °C. Linewidths ranged from 5 to 0.8 μm, and two film thicknesses, 200 nm (‘‘thin’’) and 500 nm (‘‘thick’’), were prepared. Eddy current measurements showed all samples to be superconducting with transition onset near 95 K. The morphology was found to depend not only on film thickness but also, for finest (≤1 μm) lines, on linewidth. ‘‘Thin’’ lines of all widths showed nearly no a-type structure, while thick-film lines showed predominantly a-type structure on the surface except for the narrowest lines. Narrowest ‘‘thick’’ lines, like ‘‘thin’’ lines, contained mostly c-type structure. The results for thick fine lines suggest that reduced area growth may offer a practical advantage in achieving c-type morphology in patterned YBa2Cu3O7−δ for applications.
Calcium substitution at yttrium site in YBa2Cu3Oy
Authors: Chandrachood M. R. , Mulla I. S. , Gorwadkar S. M. , Sinha A. P. B.
Published: July 2002

We have successfully synthesized single-phase superconducting Y1−xCaxBa2Cu3Oy for 0≤x≤0.4 using a coprecipitation technique. All these compounds are orthorhombic with lattice parameters a∼3.83 and c varying from 11.69 to 11.67 Å. The Tc remains unchanged around 90 K. It may be noted that in these compounds Ca substitutes for Y. On the other hand, it is known that in the compounds where Ca substitutes for Ba, the structure changes to tetragonal and Tc decreases rapidly. [See G. J. Baldha, R. B. Jotania, H. H. Joshi, H. N. Pandya, and R. G. Kulkarni, Solid State Commun. 71, 839 (1989)]. Furthermore, these compositions sinter much better than pure 1:2:3 and one gets high-density pellets (>95% of total density) at relatively lower temperature (<950 °C).
Nature of the band gap (direct versus indirect) of short-period (GaAs)n/(AlAs)n superlattices grown along the [111] confinement direction
Authors: Cingolani R. , Tapfer L. , Ploog K.
Published: July 2002

We report on spectroscopic experimental evidence of type II band alignment in a (GaAs)6/(AlAs)6 superlattice grown by molecular beam epitaxy along the (111) direction. This result is in contrast to recent theoretical calculations predicting that the (GaAs)n/(AlAs)n superlattices grown along the (111) direction should be direct for all n’s.
Relationship between thermal stress and structural properties of SrF2 films on (100) InP
Authors: Singh R. , Thakur R. P. S. , Katz A. , Nelson A. J. , Gebhard S. C. , Swartzlander A. B.
Published: July 2002

The measurement of thermal stress of SrF2 films on InP as a function of temperature is presented. The in situ and ex situ rapid isothermal annealed films have different values of thermal stress at room temperature and show entirely different behavior of thermal stress during heating and cooling cycles. X-ray photoelectron spectroscopy measurements were used to characterize the surface of the SrF2 films as well as the SrF2/InP interface for both the ex situ and in situ annealed films. It is shown that the difference in the microstructure of in situ and ex situ rapid isothermal annealed SrF2 films on InP is indeed reflected in the significant difference in the thermal stress.
Enhanced slow positron reemission with new thin foil moderator geometry
Authors: Wu Xiao-ye , Dull Peter , Lynn K. G.
Published: July 2002

By using an inverted tungsten cone in front of a tungsten (110) thin foil moderator to backscatter the fast positrons transmitted through the foil moderator, it was found that the slow positron yield can be increased by approximately a factor of 2. The energy width of the slow positrons in the axial direction was narrowed. The highest improvement in the moderator efficiency was ∼143%.
Quantum effects and bit errors in mesoscopic logic and memory circuits
Authors: Bandara K. M. S. V. , Coon D. D.
Published: July 2002

Bistability in well known circuits employing devices with nonlinear current-voltage characteristics is shown to be a classical concept which can be modified by quantum mechanical effects. The classically stable states ‘‘0’’ and ‘‘1’’ are shown to correspond to a single stable quantum mechanical state and a metastable state. Bit error rates associated with metastable state lifetimes are estimated for circuits employing quantum well devices and found to be appreciable in the mesoscopic regime (feature sizes ≲0.2 μm).
Two-phonon laser operation (4.2–77 K) of photopumped AlxGa1−xAs-GaAs quantum well heterostructures
Authors: Nam D. W. , Holonyak N. , Vesely E. J. , Dupuis R. D.
Published: July 2002

Data are presented showing that photopumped AlxGa1−xAs-GaAs quantum well heterostructures (QWHs) are capable of stimulated emission (because of the large confined phonon population) one and two longitudinal optical (LO) phonons below the lowest confined-particle electron-to-heavy hole transition (e1→h1). The phonon-assisted laser operation two phonons below the e1→h1 transition (ΔE=2ℏωLO=2×36 meV) is identified unambiguously using (on a single sample) two types of heat sink configurations, high Q to turn on and low Q to turn off the stimulated emission on the e1→h1 (reference) transition. Because the one- and the two-phonon laser operations (4.2 K) are spectrally very narrow, narrower than that on QW confined-particle transitions, their separation affords an accurate measurement of QW phonon energy (ℏωLO=36.1 meV).
High-efficiency Al0.22Ga0.78As solar cells grown by molecular beam epitaxy
Authors: Melloch M. R. , Tobin S. P. , Bajgar C. , Keshavarzi A. , Stellwag T. B. , Lush G. B. , Lundstrom M. S. , Emery K.
Published: July 2002

The quality of pn junction photodetectors made of Al0.2Ga0.8As has been investigated as a first step in the optimization of tandem solar cells. We have obtained 1 sun AM1.5 efficiencies of 16.1% for 0.25 cm2 Al0.22Ga0.78As solar cells fabricated from molecular beam epitaxy (MBE) material. This efficiency is 3.2 percentage points higher than the previously best reported efficiency of 12.9% for an Al0.2Ga0.8As solar cell fabricated from MBE material.
Realization of high coupling coefficients in 1.53 μm InGaAsP/InP first-order quarter-wave shifted distributed feedback lasers
Authors: Hillmer H. , Hansmann S. , Burkhard H.
Published: July 2002

Coupling coefficients as high as 300 cm−1 have been achieved and investigated in the performance of distributed feedback lasers. High coupling has several important advantages like lower feedback sensitivity, and lower influence on facet reflectivity, thus easy handling for coatings without any penalty in terms of mode hopping. We obtain a side-mode suppression ratio as high as 51.2 dB. 8 Gb/s ‘‘nonreturn to zero’’ modulation is demonstrated.
Intracavity frequency doubling of a Nd:YAG laser with an organic nonlinear optical crystal
Authors: Ducharme Stephen , Risk W. P. , Moerner W. E. , Lee Victor Y. , Twieg R. J. , Bjorklund G. C.
Published: July 2002

We have demonstrated intracavity second-harmonic generation of green 532 nm light in a quasi-cw 1064 nm Nd:YAG laser using organic nonlinear optical crystals of 4-(N,N-dimethylamino)-3-acetamidonitrobenzene (DAN) immersed in index matching fluid contained in an antireflection-coated cuvette. This technique permits crystals to be used directly from solution growth without polishing or antireflection coating them. Up to 0.56 mW peak power of 532 nm light was generated from 2.3 W of intracavity 1064 nm peak power in 100 μs pulses. We also report preliminary results on true cw intracavity harmonic generation with antireflection-coated DAN crystals.
Correlation between electronegativity and dopant activity in ion-implanted semi-insulating GaAs
Authors: Srinivasan G. , Sealy B. J.
Published: July 2002

The effects of rapid thermal annealing (RTA) on the electrical activity of various implanted dopants (Be, Mg, Zn, and Hg) in semi-insulating GaAs have been studied by Van der Pauw Hall measurements and Polaron profiling. The relationship between the observed variation in the electrical activation energies of these acceptors and their local electronegativity has been investigated to envisage the possible microscopic mechanism of the activation of the dopants in GaAs.
Enhanced spontaneous emission from GaAs quantum wells in monolithic microcavities
Authors: Yokoyama H. , Nishi K. , Anan T. , Yamada H. , Brorson S. D. , Ippen E. P.
Published: July 2002

Enhanced spontaneous emission has been observed with wavelength-sized monolithic Fabry–Perot cavities containing GaAs quantum wells. With an on-resonance cavity structure, the photoluminescence intensity increases in the cavity axis direction, and the spontaneous emission lifetime is experimentally found to decrease.
Early formation of chemical vapor deposition diamond films
Authors: Iijima Sumio , Aikawa Yumi , Baba Kazuhiro
Published: July 2002

Nanometer-size diamond particles formed on a silicon substrate by the hot-filament chemical vapor deposition method were examined by a high-resolution electron microscope. The particles developed well-faceted cuboctahedral habits. Examination of their morphologies and microstructures provides a wealth of information on their crystal growth mechanism. The effect of the pretreatment of the substrate by diamond powder, which has been known to enhance thin-film growth, was found to be due to seeding by ‘‘diamond dust’’ on the substrate surface.
Superconducting free-standing thin films of YBa2Cu3Ox
Authors: Kilibarda S. , Ng H. K.
Published: July 2002

We report a new technique of preparing unsupported thin films of YBa2Cu3Ox. These films are about 6×6 mm2 and less than half a micron thick. They were prepared via laser ablation on thin carbon films typically of order 50 μg/cm2 (∼2500 Å). When the film was annealed, the carbon oxidized leaving behind a free-standing film. The film has a superconducting orthorhombic phase and an onset temperature of ≂85 K.
Growth of InGaAs structures using in situ electrochemically generated arsine
Authors: Buckley D. N. , Seabury C. W. , Valdes J. L. , Cadet G. , Mitchell J. W. , DiGiuseppe M. A. , Smith R. C. , Filipe J. R. C. , Bylsma R. B. , Chakrabarti U. K. , Wang K-W.
Published: July 2002

The use, transportation, and storage of the hazardous gas, arsine, raise serious safety issues. Consequently, there is considerable interest in the generation of arsine on demand from less hazardous substances. We report the first use of in situ generated arsine for III-V epitaxy. The gas has been generated electrochemically at an arsenic cathode in an aqueous electrolyte and used to supply a hydride vapor phase epitaxy reactor. InGaAs/InP test structures were grown on InP substrates and were similar to comparison structures grown using tank arsine. Recessed-gate enhanced Schottky metal-semiconductor field-effect transistors were fabricated and exhibited well-behaved current-voltage characteristics.
Millimeter-wave harmonic mixing with high T
c superconducting materials at room temperature
Authors: Kurosawa Tomizo , Onae Atsushi , Kawate Etsuo , Miki Yukinobu , Sakuma Eiichi
Published: July 2002

Harmonic generation and mixing in the 8∼80 GHz region has been studied in point-contact junctions made with sharply tipped tungsten whisker and sintered polycrystalline YBa2Cu3O7−y or single-crystal Bi2Sr2CaCu2Ox at room temperature. The signal-to-noise ratio (SNR) of beat notes as a function of harmonic number n is observed up to the tenth order and decreases with a slope of n−5.6 for even harmonic numbers. The dependence of the SNR of the beat note on a dc bias voltage and the current-voltage characteristics have been measured simultaneously and theoretically analyzed using the current-dependent mixing characteristics. The potential barrier and the insulating thickness for YBa2Cu3O7−y are estimated.
Observation of spontaneous emission lifetime change of dye-containing Langmuir–Blodgett films in optical microcavities
Authors: Suzuki M. , Yokoyama H. , Brorson S. D. , Ippen E. P.
Published: July 2002

We have studied the spontaneous emission properties of Langmuir–Blodgett films containing dye molecules confined in Fabry–Perot microcavity structures having wavelength thickness. The presence of the cavity causes great modifications in the emission spectrum and emission intensity in the direction of the cavity axis. A clear change in spontaneous emission lifetime occurs, which is also attributed to the microcavity effect.
Controlled growth of 3C-SiC and 6H-SiC films on low-tilt-angle vicinal (0001) 6H-SiC wafers
Authors: Powell J. A. , Petit J. B. , Edgar J. H. , Jenkins I. G. , Matus L. G. , Yang J. W. , Pirouz P. , Choyke W. J. , Clemen L. , Yoganathan M.
Published: July 2002

We have found that, with proper pregrowth surface treatment, 6H-SiC single-crystal films can be grown by chemical vapor deposition (CVD) at 1450 °C on vicinal (0001) 6H-SiC with tilt angles as small as 0.1°. Previously, tilt angles of greater than 1.5° were required to achieve 6H on 6H at this growth temperature. In addition, 3C-SiC could be induced to grow within selected regions on the 6H substrate. The 3C regions contained few (or zero) double-positioning boundaries and a low density of stacking faults. A new growth model is proposed to explain the control of SiC polytype in this epitaxial film growth process.
Image-based models of porous media: Application to Vycor glass and carbonate rocks
Authors: Crossley P. Anthony , Schwartz Lawrence M. , Banavar Jayanth R.
Published: July 2002

We develop a new class of three-dimensional geometrical models of porous media based on the smoothing of random white-noise images. With the appropriate choice of smoothing parameters, models of this kind are shown to provide reasonable representations of Vycor glass and crystalline dolomites. Transport and structural properties are found to be in accord with experimental data.
Electrical characterization of metal-insulator-semiconductor diodes fabricated from laser-ablated YBa2Cu3O7−δ /yttria-stabilized zirconia films on Si substrates
Authors: Ajimine Eric M. , Pagaduan Felino E. , Rahman M. M. , Yang Cary Y. , Inokawa Hiroshi , Fork David K. , Geballe T. H.
Published: July 2002

The purpose of this investigation is to study the electrical properties of the YBCO/YSZ/Si metal-insulator-semiconductor structure and the yttria-stabilized zirconia (YSZ)/Si interface. The YBCO and YSZ layers were epitaxially grown in situ on Si by pulsed laser deposition. Current-voltage measurements of devices fabricated on p-type Si(100) showed a small leakage current density at 292 K, which decreased further at 80 K. Comparison of capacitance-voltage measurements at 292 K for frequencies between 10 and 400 kHz showed a large variation of capacitance in the accumulation region demonstrating the presence of mobile ions in the YSZ layer. This variation is less pronounced at 80 K. A negative shift of about 5 V in threshold voltage from 292 to 80 K has been attributed to redistribution of charges in the YSZ buffer layer.
Cubic silicon cluster
Authors: Furukawa Kazuaki , Fujino Masaie , Matsumoto Nobuo
Published: July 2002

A cubic silicon cluster having eight bonds each terminated by a tert-butyl substituent, tert-butyloctasilacubane (TBOSC), is studied. TBOSC was formed and isolated by chemical procedures. The optical properties of TBOSC were measured in comparison with those of bulk silicon. TBOSC is purple and its absorption edge (λg) is observed at 650 nm (1.9 eV) at room temperature. This λg is 0.8 eV larger than that of bulk silicon. It also shows photoluminescence extending to 850 nm at 77 K although bulk silicon shows no photoluminescence.
Highly doped p+ regions by zinc diffusion utilizing metalorganic vapor-phase epitaxy
Authors: Paska Zoltán F. , Haga Dan , Willén Bo , Linnarsson Margareta K.
Published: July 2002

Zinc-diffusion doping of GaAs using metalorganic vapor-phase epitaxy and DEZn as a dopant source is evaluated. The dependence of the diffusion profile on DEZn flow and diffusion time is presented. Typical zinc concentrations and depths obtained are 1019–1021 cm−3 and 40–200 nm, respectively. The largest concentration gradient obtained in this manner was four orders of magnitude in 500 Å, and the highest zinc concentration was measured as 2×1021 cm−3 at a sample surface. A heterojunction bipolar transistor fabricated using zinc-diffusion doping of the base and a regrown emitter showed an fmax of 50 GHz.
Luminescence origins in molecular beam epitaxial Si1−xGex
Authors: Noël J.-P. , Rowell N. L. , Houghton D. C. , Wang A. , Perovic D. D.
Published: July 2002

Interstitial-type features smaller than ∼1.5 nm and in areal densities up to 7×108 cm−2 have been identified as the origin of a broad photoluminescence (PL) band from thick, fully strained layers of Si1−xGex alloys grown by molecular beam epitaxy. The strong PL band was predominant when the alloy layer thickness was greater than 4–10 nm, depending on x and the growth temperature. Thinner alloy layers exhibited phonon-resolved transitions originating from shallow dopant bound excitons, similar to bulk material but shifted in energy due to strain and hole quantum confinement.
High-temperature stable MoAl2.7/n-GaAs Schottky diodes with enhanced barrier height
Authors: Huang T. S. , Peng J. G. , Lin C. C.
Published: July 2002

High-temperature stable and smooth gate materials are required for self-aligned GaAs metal-semiconductor field effect transistor devices processing. Furthermore, the high Schottky barrier is beneficial to the GaAs digital logic circuits based on the enhancement mode field effect transistors. We report the high-temperature (up to 900 °C) stable MoAl2.7 Schottky contacts to n-GaAs with enhanced barrier heights from 0.67 to 0.98 V and low values of ideality factors after annealing. The surface of annealed contact is lustrous and smooth. The epitaxial AlxGa1−xAs layer, which induces the enhanced barrier height, at the interface of MoAl2.7/n-GaAs contact, has been clearly identified by the high-resolution cross-sectional transmission electron microscopy.
Second harmonic generation in InGaAsP waveguides at 1.3 μm wavelength
Authors: Cada M. , Svilans M. , Janz S. , Bierman R. , Normandin R. , Glinski J.
Published: July 2002

We report the first surface emission of red light from an InGaAs waveguide, generated by the nonlinear mixing of two counterpropagating guided waves at wavelengths around 1.3 μm. A nine layer InGaAsP/InP heterostructure was grown by low pressure MOCVD on 〈100〉 InP substrate. All layers were n-doped with silicon to a level of 1.0×1017 cm−3. The structures functioned in both planar as well as ridge waveguide configurations. Measurements were performed with both a YAG laser and a semiconductor laser in the pulsed as well as the cw regime and were compared with theoretical calculations, used in the design of the structure. Red light was detected even in a single slab InGaAsP waveguide with a cw semiconductor laser diode.
Large-area YBa2Cu3O7−δ thin films on sapphire for microwave applications
Authors: Cole B. F. , Liang G.-C. , Newman N. , Char K. , Zaharchuk G. , Martens J. S.
Published: July 2002

We have deposited YBa2Cu3O7−δ(YBCO) films with low microwave surface resistance (Rs) on 5-cm-diam, oxide-buffered sapphire substrates by planar magnetron sputtering. MgO buffer layers are used on M-plane (101̄0) sapphire, and R-plane (11̄02) sapphire is buffered by CeO2. Rs values of 450–620 μΩ at 77 K and 10 GHz were measured across an entire 5-cm diam YBCO film on M-plane sapphire. For YBCO on R-plane sapphire, Rs values at 77 K and 10 GHz were 950 μΩ for a 5-cm-diam wafer and 700 μΩ for 1×1 cm2 samples.
Novel 1-to-N way integrated optical beam splitters using symmetric mode mixing in GaAs/AlGaAs multimode waveguides
Authors: Heaton J. M. , Jenkins R. M. , Wight D. R. , Parker J. T. , Birbeck J. C. H. , Hilton K. P.
Published: July 2002

We report the demonstration of novel GaAs/AlGaAs integrated optical 1-to-N way beam splitters which use symmetric mode mixing in center-fed multimode planar waveguides. Each device has one single-mode input guide, a carefully chosen length of parallel sided multimode guide, and N equally spaced single-mode output guides. The mixing of symmetric modes shares the input light equally between the output guides by a symmetric form of the self-imaging process. We demonstrate experimentally that this type of beam splitter can be used to divide power equally, with high accuracy and low loss, between the N output guides, for values of N between 2 and 20.
Flux penetration into YBa2Cu3Ox thin films covering substrate step edges
Authors: Schuster Th. , Koblischka M. R. , Kuhn H. , Kronmüller H. , Friedl G. , Roas B. , Schultz L.
Published: July 2002

Using the high-resolution Faraday effect, the flux penetration into YBa2Cu3Ox thin films grown over one or two substrate step edges is directly observed at a temperature of T=5 K. The regions at the steps are easily penetrated by the flux already present at low applied external magnetic fields due to the locally enhanced stray fields. The step edges are found to separate the sample magnetically into independent parts. It is also shown that the local observation of flux penetration allows detection of the influence of defects in the thin-film samples on the domain structures in a direct way.
Large critical currents and improved epitaxy of laser ablated Ag-doped YBa2Cu3O7−δ thin films
Authors: Kumar Dhananjay , Sharon M. , Pinto R. , Apte P. R. , Pai S. P. , Purandare S. C. , Gupta L. C. , Vijayaraghavan R.
Published: July 2002

Microstructure and critical current densities of laser ablated YBa2Cu3O7−δ thin films doped with 2–20 wt. % Ag have been studied. A critical current density as high as 1.4×107 A cm−2 at 77 K has been realized on 〈100〉 SrTiO3 substrates with YBaCuO films doped with 5 wt. % Ag which has been found to be the optimum. Evidence indicates that the improved microstructure and epitaxy which is a consequence of grain enlargement and alignment caused by Ag is responsible for the high values of critical currents observed.
Switching, fatigue, and retention in ferroelectric Bi4Ti3O12 thin films
Authors: Joshi P. C. , Krupanidhi S. B.
Published: July 2002

Thin films of bismuth titanate, Bi4Ti3O12, prepared by the metalorganic solution deposition technique and rapid thermally annealed at 700 °C for 20 s have shown good ferroelectric switching, fatigue, and retention characteristics. A switching time of 180 ns was measured for a 0.5 μm thick capacitor with an electrode area of 2.83×10−3 cm2. The switching degradation of the polarization state or fatigue was not significant, at least up to 1010 bipolar switching cycles. The films exhibited good memory retention characteristics after about 106 s.
Photoluminescent thin-film porous silicon on sapphire
Authors: Dubbelday W. B. , Szaflarski Diane M. , Shimabukuro R. L. , Russell S. D. , Sailor Michael J.
Published: July 2002

Results from the chemical stain etch fabrication and analysis of thin-film photoluminescent porous silicon on sapphire substrates are presented. The transparent sapphire substrate allows the excitation and collection of the luminescence at either the front or back of the wafer. Morphological differences found using scanning electron microscopy between porous SOS and porous bulk silicon are attributed to preferential etching of threading dislocations. This is confirmed by an observed stress relaxation in the Raman spectra. Also, it is shown for the first time that photoluminescent porous silicon (n-type) can be produced by photoinitiation of the chemical stain etch.