bluuebunny/crossref_metadata_2025 huggingface dataset:
High-energy implantation of Hg+ ions into GaAs grown by liquid encapsulated Czochralski method: Formation of multiple shallow emissions
Authors: Harada Kentaro , Lo Bassirou , Makita Yunosuke , Beye Aboubaker C. , Halsall Matthew P. , Kimura Shinji , Kobayashi Naoto , Iida Tsutomu , Shima Takayuki , Shibata Hajime , Obara Akira , Matsumori Tokue
Published: July 2002

Optical and electrical properties of Hg acceptor in GaAs were systematically investigated as a function of Hg concentration. Samples were prepared by high-energy ion implantation of Hg+ into GaAs grown by liquid encapsulated Czochralski method. Annealing was made by rapid thermal annealing using infrared flash lamp at 950 °C during 3 s. Photoluminescence measurements at 2 K revealed that in addition to the well-defined conduction band to Hg acceptors transition, the mercury-related so-called ‘‘g’’ neutral acceptor bound exciton band is found shifted from the carbon-related ‘‘g’’ line by 0.8 meV. Moreover, two shallow emissions, are formed for net hole concentration ‖NA−ND‖ greater than 2×1017 cm−3 and 1×1019 cm−3, respectively. It is demonstrated that even a typical moderately deep acceptor Hg in GaAs, having ground-state ionization energy of 52 meV can make multiple shallow emission levels presumably attributed to acceptor–acceptor pairs.
Compositional and structural analysis of AlSb(As) tunneling barriers in InAs/AlSb(As)/GaSb resonant interband-tunneling structures
Authors: Wagner J. , Schmitz J. , Obloh H. , Koidl P.
Published: July 2002

InAs/AlSb/GaSb/AlSb/InAs interband-tunneling structures have been analyzed with respect to the composition and structural quality of the AlSb tunneling barriers. The addition of AlAs monolayers at the interfaces between the AlSb barriers and the InAs and GaSb layers was found to result in the expected reduction in the valley current density of the resonant interband-tunneling diode. Vibrational mode Raman spectroscopy showed that the introduction of AlAs monolayers led to the formation of pseudoternary Al(SbAs) barriers, which cause the observed reduction of the valley current density. Ellipsometric measurements indicate that the structural quality of both types of barrier layers, with and without AlAs monolayers added to the interfaces, is inferior to that of thick bulklike AlSb layers. The observation of Raman scattering from a coupled hole plasmon-phonon mode indicates the formation of a hole gas in the GaSb quantum well at the center of the tunneling structure.
Anisotropic high-field transverse differential mobility of holes in silicon
Authors: Hinckley J. M. , Singh J.
Published: July 2002

Anisotropy of the silicon valence band does not lead to any significant anisotropy in the longitudinal hole transport properties, but we find that the transverse mobility is quite anisotropic. The transverse mobility represents the response of charge carriers to a small transverse electric field in the presence of a strong longitudinal field. A detailed, anisotropic Monte Carlo method has been applied to the calculation of the hole transverse differential mobility in silicon. The transverse differential mobility is studied both with regard to variations in the orientation, with respect to the crystalline axes, of the high longitudinal electric field, and with regard to variations in the transverse direction of the mobility, taken in the plane perpendicular to the high electric field. The anisotropy of the valence band causes the transverse differential mobility to strongly vary with respect to the electric field orientation. Symmetry considerations show that the transverse differential mobility is isotropic in the {100} and {111} planes and has twofold rotational symmetry in the {101} planes. Our calculations bear this out. Furthermore, we show that the transverse mobility can be much different from the chordal mobility, in distinction to the case for isotropic band structures.
Distributed electron cyclotron resonance plasma immersion for large area ion implantation (invited)
Authors: Le Coeur F. , Lagarde T. , Pelletier J. , Arnal Y. , Burke R. , Brunel M.
Published: July 2002

Plasma-based ion implantation (PBII) is a recent method to implant ions into materials for modifying surface properties. Negative high voltage pulses are applied to the substrate to extract ions from the plasma and accelerate them directly onto the substrate surface. The main advantages of PBII over ion beam implantation are its simplicity for processing large surfaces or three-dimensional objects, and the possibility of preparing surfaces at low ion bombardment energy prior to the implantation process. However, in contrast to conventional ion implantation, the PBII process does not apply mass selection. Due to the wide ion sheath expansion (a few tens of cm), large volumes of plasma are mandatory around the substrate. Multipolar discharges, which produce a peripheral ionization facing the substrate and can be easily scaled up, are well adapted to the PBII process and thus widely used. However, hot filaments to sustain plasmas of reactive gases in multipolar magnetic field structures are progressively phased out in favor of distributed electron cyclotron resonance (DECR) plasma sources. The principle, the design, and the performances of DECR plasmas are presented. Then, PBII in DECR plasmas is illustrated through two selected examples.
Modulational instability oscillation and solitary waves in a nonlinear dispersive cavity with parametric gain
Authors: Longhi S. , Geraci A.
Published: July 2002

We investigate the modulational instability in a nonlinear dispersive cavity which is driven to oscillation by degenerate parametric interaction in a nonlinear χ(2) medium. Our analysis predicts the existence of stable temporal dissipative structures mediated by modulational instability when oscillation occurs through a subcritical instability. Decreasing the parametric gain below the subcritical bifurcation point, stability of these structures is broken and complicated temporal patterns in the form of weakly interacting solitary waves are predicted.
Timing discriminator for pulsed time-of-flight laser rangefinding measurements
Authors: Kilpelä Ari , Ylitalo Juha , Määttä Kari , Kostamovaara Juha
Published: July 2002

A time-pickoff circuit based on the constant fraction discriminator (CFD) timing principle has been developed for pulsed time-of-flight laser rangefinding with pulse lengths of 5–10 ns. It is based on detection of the crossing point of the trailing edge of the original timing pulse and the leading edge of its delayed replica with a fast emitter coupled logic comparator. A simplified theory is presented here for its walk error. Three types of comparator were tested in the CFD. It is shown that the dominant source of walk error is that produced by the limited gain-bandwidth product of the comparator and that walk error can be reduced to ±1 mm in a 1:10 dynamic range of input pulses by adding an external offset voltage between the input nodes of the comparator.
Selective area deposition of diamond thin films on patterns of porous silicon by hot-filament chemical vapor deposition
Authors: Mirzakuchaki S. , Hajsaid M. , Golestanian H. , Roychoudhury R. , Charlson E. J. , Charlson E. M. , Stacy T.
Published: July 2002

Diamond thin films, 5 μm in thickness, were grown selectively on patterns of porous silicon by hot-filament chemical vapor deposition (HFCVD). Monocrystalline p-type silicon substrates, with (100) orientation and resistivity 5–15 Ω cm, were patterned by conventional photolithography to provide a photoresist mask for selective anodization. The polycrystalline diamond films thus formed were studied by scanning electron microscopy, x-ray diffraction, and Raman spectroscopy which revealed high selectivity and high quality diamond films. This process proved to be simple and yet effective in developing patterns of diamond film in different shapes and sizes.
In situ observation of indium segregation by reflectance difference spectroscopy in single monolayer heterostructures grown by atomic layer epitaxy
Authors: Arès R. , Tran C. A. , Watkins S. P.
Published: July 2002

Single monolayers of InAs in GaAs and GaAs in InAs have been grown by atomic layer epitaxy (ALE) at 50 Torr. In situ reflectance difference spectroscopy monitoring of the surface during each stage of the growth showed a strong asymmetry in the surface behavior between the two systems. Following insertion of an InAs monolayer in GaAs, approximately 20 ML of GaAs are required to recover an In-free, As-stabilized GaAs surface at 390 °C. On the other hand, following the insertion of 1 ML of GaAs in InAs, the spectrum returns to a Ga-free, As-stabilized InAs surface after only 1 ML of InAs deposition. This behavior shows clear evidence of the presence of segregation caused by thermodynamic factors even at the very low growth temperatures used for ALE.
Polycrystalline GaInAs/AlInAs films for photoconductive detectors
Authors: Wood C. E. C. , Johnson W. J. , Cho P. S. , Lee C. H.
Published: July 2002

We show that thin Al0.48In0.52As layers in Ga0.47In0.53As alloy films, can be used to trap free carriers, and produce high resistivity materials suitable for 1.55 μm photoconductive detectors.
Oxygen-based deep levels in metalorganic vapor phase epitaxy indium gallium arsenide
Authors: Huang J. W. , Kuech T. F. , Anderson T. J.
Published: July 2002

We have studied the defect engineering in metalorganic vapor phase epitaxy InxGa1−x As by controlled oxygen doping. Diethylaluminum ethoxide (DEALO) was used as an oxygen precursor to provide the intentional deep level incorporation. DEALO doping in InxGa1−xAs:Si with x≤0.25 resulted in the reduction in carrier concentrations. The Al and O incorporation with a DEALO mole fraction was weakly dependent on alloy composition for x≤0.25. The degree of electrical compensation, however, decreased as the In content increased at the same oxygen content. Deep level transient spectroscopy investigations on a series of InxGa1−xAs:Si:O samples with x ranging from 0 to 0.18 reveal a set of oxygen-derived deep levels, similar to those found in DEALO-doped GaAs. These characteristic deep levels appear to remain at a relatively constant energy with respect to the valence band, as compared to the rapid decrease in the conduction band of InxGa1−xAs with x.
Be incorporation and surface morphologies in homoepitaxial InP films
Authors: Cotta M. A. , de Carvalho M. M. G. , Pudenzi M. A. A. , Landers K. M. I. , de Souza C. F. , Landers R. , Teschke O.
Published: July 2002

We have studied the mechanism of Be incorporation in InP homoepitaxial films grown by metalorganic molecular beam epitaxy. The actual Be concentration in the films reaches 1–2×1019 cm−3 while the hole concentration saturates at a lower value ■∼2×1018 cm−3 in our case). The measured lattice mismatch between film and substrate depends both on growth temperature and Be flux. The resulting changes in morphology suggest that the excess Be forms microclusters in the films grown at higher temperatures—due to the higher surface mobility, leading to the growth of oval defects. Be rejection to the surface is also observed. The surfaces of samples with no cap layer present a granulation which may be related to the formation of a new phase like Be3P2.
The influence of aluminum concentration on photoelectrochemical etching of first order gratings in GaAs/AlGaAs
Authors: Twyford Elizabeth J. , Carter Carrie A. , Kohl Paul A. , Jokerst Nan Marie
Published: July 2002

We present a set of experiments which systematically clarifies the enhancement of photoelectrochemical (PEC) etching due to the mole fraction of aluminum in AlxGa1−xAs. The spatial resolution of gratings etched in Al0.3Ga0.7As is as much as three times greater than the spatial resolution of gratings etched in GaAs, so that the smallest practical grating period is about 0.3 μm, as compared with about 0.7 μm using previous techniques. This technique enabled PEC fabrication of first order gratings for waveguide outcouplers. The lower hole mobility of AlxGa1−xAs is proposed as a possible explanation for this grating resolution improvement.
Characteristics of longitudinal optical phonon assisted quantum carrier capture process-temperature and bias dependence
Authors: Wu Ta-Chung , Kan Sidney C. , Vassilovski Dan , Lau Kam Y.
Published: July 2002

The quantum carrier capture time in a quantum well laser is calculated as a function of temperature and bias current. The calculated results show good consistency with recent measurements on the small signal frequency response of a quantum well laser at cryogenic temperatures. This calculation reveals some of the characteristics of longitudinal optical phonon assisted quantum carrier capture phenomena in quantum well structures.
A practical all-metal flange-seal for high and low temperatures
Authors: Moreh R. , Finkelstein Y.
Published: July 2002

A simple, general purpose, all-metal flange-seal is described, operable in the temperature range from liquid helium to around 600 K. The design is based on cheap commercial Al foils and can replace the more expensive rubber, indium O rings, and copper gaskets, commonly used in small cells for diffraction and scattering measurements of neutrons and γ rays. Such a seal can also be used for connecting high-vacuum tubes and also in high-pressure work.
Design, fabrication, and test of wide-angle low-loss Y-junction hybrid polymer couplers
Authors: Ni Tsang-Der , Sturzebecher Dana , Cummings Mike , Perlman Barry
Published: July 2002

Optical couplers are key components for signal distribution in optoelectronic transmitter/receiver modules. A new low-loss large-angle Y-junction hybrid polymer optical coupler incorporating an integrated microprism has been fabricated and demonstrated experimentally for use in a mixed-signal module environment. The results show that the radiation loss is small with relatively wide branching angle as compared to a conventional Y-junction coupler.
Epitaxial growth of γ - Al2O3 layers on Si(111) using Al solid source and N2O gas molecular beam epitaxy
Authors: Wado Hiroyuki , Shimizu Tadami , Ishida Makoto
Published: July 2002

High crystalline quality γ-Al2O3 films were epitaxially grown on Si(111) substrates at low growth temperatures from 750 to 900 °C by Al solid source and N2O gas molecular beam epitaxy. Very thin γ-Al2O3 films grown at 850 °C showed streaky reflection high-energy electron diffraction patterns. By in situ x-ray photoelectron spectroscopy measurements, carbon contamination, as is seen in the films grown with Al(CH3)3 source, was not detected within the sensitivity. The stoichiometry of the growth films was found to be similar to that of Al2O3. Growth rates of epitaxial γ-Al2O3 layers were found to decrease with increasing growth temperatures.
Tungsten ‘‘dye’’ induced fast blue/violet photoluminescence from nanocrystalline silicon-silica composite thin films
Authors: Vepřek S. , Rückschloss M. , Wirschem Th. , Landkammer B. , Fuss M. , Lin X.
Published: July 2002

Doping of the nanocrystalline-Si/SiO2 composite material with tungsten results in a quenching of the ‘‘red’’ photoluminescence (PL) and an appearance of an intense blue/violet one with a spectral maximum around 2.8 eV and decay time of ≤3 ns. Unlike the green/blue PL from silanol groups, this PL is stable upon annealing and does not show any polarization memory. A possible mechanism of this PL is suggested.
Production of atomic hydrogen in Al–SiO2–Si systems by vacuum ultraviolet radiation
Authors: Druijf K. G. , de Nijs J. M. M. , van der Drift E. , Granneman E. H. A. , Balk P.
Published: July 2002

A study of the generation of H-induced defects in the Al–SiO2–Si system by vacuum ultraviolet radiation (hν=10 eV) shows that small cross-section hole traps in the bulk of the oxide and donor-type states at the Si–SiO2 interface are formed by different reactions paths. In both cases the production of atomic H, required for obtaining these defects, only involves neutral species. However, the source of the hydrogen producing the bulk hole traps is located at the Al–SiO2 interface, the source for the hydrogen inducing the donor-type interface states at the Si–SiO2 interface.
Simple computer aided design formula and network interpretation for loss evaluation in microstrip superconductor–conductor bilayer structure
Authors: Ladret D. , Migliaccio C. , Cabon B. , Chilo J.
Published: July 2002

Line resistance analytical results obtained from the proposed simple surface impedance formula describing a superconductor–conductor bilayer structure were found in good agreement with numerical results. Network interpretation of this structure is performed. Important information about the loss frequency behavior (frequency cutoff, asymptotic variation) and influence of the thickness ratio of the two layers on bilayer losses, are commented on.
Fabrication of NiFe thin film elements by dry etching using CH4/H2/O2
Authors: Khamsehpour B. , Wilkinson C. D. W. , Chapman J. N.
Published: July 2002

A mixture of methane, hydrogen, and oxygen has been used to etch thin films of NiFe. The variation of etch rate with concentration of methane and oxygen has been investigated. By using a SrF2 mask, patterned by liftoff, small micrometer-sized elements have been fabricated. It is demonstrated that the use of CH4/H2/O2 as an etchant yields elements possessing similar micromagnetic properties to those produced by conventional liftoff. The process has also been successfully employed to etch other important magnetic thin films.
Observation of intercalation of excess oxygen in Bi2Sr2CaCu2O8+y single crystal
Authors: Shekhawat G. S. , Gupta Ram P. , Agarwal A. , Vyas P. D. , Srivastava P. , Saini N. L. , Venkatesh S. , Garg K. B.
Published: July 2002

Effects arising from the intercalation of excess oxygen in Bi–O layer has been observed at room temperature using atomic force microscopy. The excess oxygen is incorporated by oxygenating the pure sample. The oxygen is trapped between the alternating Bi–O layers along the b direction. This leads to a change in the local interatomic bond length along the b axis, while the periodicity remained invariant along the a axis. In addition, in-plane atomically resolved structure of single crystal has been imaged at room temperature using AFM. The lattice spacings indicate that the observed structure corresponds to the in-plane bismuth and oxygen positions. Furthermore, high-resolution scanning tunneling spectroscopy measurements show that oxygen doping increases the Bi–O layer density of states near the Fermi level giving rise to metallicity, whereas the pure sample reveals a semiconducting energy gap in the tunneling spectrum.
Transport properties of magnetic field/liquid assisted textured YBa2Cu3O7−x thick films
Authors: Lewis J. A. , Wegmann M.
Published: July 2002

Textured YBa2Cu3O7−x thick films (thickness ≊1 mm) were fabricated by vacuum filtration in an applied magnetic field (H=7 T). Platinum (1 wt %) was incorporated to induce liquid phase-assisted densification in films fired between 960 and 1030 °C in oxygen. The transport critical current densities (Jct) of films fired to 1030 °C exhibited nearly field insensitive behavior between H=0–3 T (H∥c-axis) at 77 K, with Jct≊2500 A/cm2 and corresponding critical currents (Ic) of nearly 100 A at H=1 T.
Localized heating of nickel nitride/aluminum nitride nanocomposite films for data storage
Authors: Maya L. , Thundat T. , Thompson J. R. , Stevenson R. J.
Published: July 2002

Nickel–aluminum nitride films were prepared by reactive sputtering of a nickel aluminide plate in a nitrogen plasma. The initial product is a nanocomposite containing the nickel as the nitride, Ni3N, in aluminum nitride. Heating in vacuum to 500 °C causes selective decomposition of the thermally labile nickel nitride leaving the aluminum nitride unaffected. The nickel nanocomposite is of interest for potential applications as recording media, as are other finely divided dispersions of ferromagnetic metals in insulating matrices. The nickel–aluminum nitride nanocomposite shows a moderate coercive field of 35 Oe at 300 K and, in common with ultrafine particles of ferromagnetic materials, shows superparamagnetic behavior. The Ni3N/AlN nanocomposite was subjected to localized heating with the focused beam of an argon-ion laser; this created features several microns in width that could be imaged with a magnetic force microscope, thus confirming its potential as a high density data storage medium.
Experimental apparatus for determining charge exchange between hydrogen and hydrocarbon groups in the hot filament deposition of diamond
Authors: Cherry R. I. , Whitmore T.
Published: July 2002

The charge balance in the hot filament method of depositing diamond is explored using a novel experimental arrangement. A correlation between ion activity and the growth of diamond is drawn.
High crystalline quality ZnSe films grown by pulsed laser deposition
Authors: Chern M. Y. , Lin H. M. , Fang C. C. , Fan J. C. , Chen Y. F.
Published: July 2002

We have grown epitaxial ZnSe films on (001)GaAs substrates at 300 °C by pulsed laser deposition (PLD). Before the growth, thin buffer layers of GaAs are also grown by PLD at 300 °C. While the pattern of reflection high energy electron diffraction (RHEED) of the buffer layers is spotty, the pattern of the ZnSe films subsequently grown is streaky, and shows distinct Kikuchi lines and bands. The x-ray rocking curve width of the films is as narrow as 150 arcsec. Photoluminescence (PL) at 10 K of the films shows free and bound excitons, donor-acceptor pairs (DAP), and is free of any deep level emissions, indicating good crystalline quality of the films. Scanning electron microscopy (SEM) shows that the particulate number density of the films is only about 1 particulate per 400 μm2.
Preparation of GaN films on sapphire by metalorganic chemical vapor deposition using dimethylhydrazine as nitrogen source
Authors: Sato Hitoshi , Takahashi Hirokazu , Watanabe Atsushi , Ota Hiroyuki
Published: July 2002

We report the preparation of high quality GaN films using dimethylhydrazine as a nitrogen source. GaN films were deposited on (0001) sapphire substrates by low-pressure metalorganic chemical vapor deposition. The film has excellent morphology in flat surface free from cracks. The full width at half maximum of the x-ray diffraction rocking curve measured from (0002) plane of GaN has exhibited as narrow as 147 arcsec. The optical quality of the film is concluded to be excellent from the photoluminescence property measured at room temperature, where the intensity of the band edge emission is much stronger than that of deep level emission.
Processing of highly oriented (Hg1−xRex)Ba2Ca2Cu3O8+δ tape with x
∼0.1
Authors: Meng R. L. , Hickey B. , Wang Y. Q. , Sun Y. Y. , Gao L. , Xue Y. Y. , Chu C. W.
Published: July 2002

Highly oriented HgBa2Ca2Cu3O8+δ on Ni tapes with a buffer layer of Cr/Ag have been successfully prepared with a transition temperature of 130 K and a transport critical–current density of 2.5×104 A/cm2 at 77 K in their self-field.
Simple method for examining sulphur passivation of facets in InGaAs–AlGaAs (λ=0.98 μm) laser diodes
Authors: Beister G. , Maege J. , Gutsche D. , Erbert G. , Sebastian J. , Vogel K. , Weyers M. , Würfl J. , Daga O. P.
Published: July 2002

The effect of (NH4)2Sx treatment of the facet of InGaAs/AlGaAs ridge waveguide (RW) laser diodes on the nonradiative current and catastrophic optical damage (COD) level is reported. Using the power–voltage–current (P–V–I) characteristics of the electroluminescence at low injection levels, changes in the density of surface states at the laser facets are described.
Polyquinoxaline as an excellent electron injecting material for electroluminescent device
Authors: Fukuda Takashi , Kanbara Takaki , Yamamoto Takakazu , Ishikawa Ken , Takezoe Hideo , Fukuda Atsuo
Published: July 2002

Electron injecting properties have been studied for one of polyquinoxaline (PQx) derivatives. PQx was clarified to be an excellent electron injecting material for electroluminescent (EL) device because it has many advantageous properties such as high electron affinity, good thermal stability, good processability, and sufficiently low refractive index. On the other hand, since poly(p-phenylenevinylene) (PPV) was known as a good hole injecting material, an EL device with ITO/PPV/PQx/metal type structure was suggested. It was shown that the quantum efficiency of the cell was higher than that of ITO/PPV/metal cell. Related physical and optical properties of PQx derivatives are also investigated.
Point defects in Si after formation of a TiSi2 film: Evidence for vacancy supersaturation and interstitial depletion
Authors: Herner S. B. , Jones K. S. , Gossmann H.-J. , Poate J. M. , Luftman H. S.
Published: July 2002

The influence of TiSi2 formation on native Si point defects has been studied at temperatures between 800 and 890 °C. Sb and B in doping superlattices were employed to trace point defect behavior. Formation of TiSi2 at 890 °C gives rise to an interface root-mean-square (rms) roughness of 22 nm. Ambiguities in the interpretation of the data arising from possible secondary ion mass spectroscopy artifacts due to sputtering through such a rough interface were avoided by etching the TiSi2 film and replanarizing the Si surface. A rms roughness of 0.05 nm was obtained, as checked by atomic force microscopy and cross-sectional transmission electron microscopy. We observed an enhancement in Sb diffusion and retardation of B diffusion over control samples without TiSi2. This indicates a vacancy supersaturation and an interstitial depletion in the Si due to the presence of the silicide. Possible mechanisms of vacancy creation and interstitial depletion are discussed.
Intense second harmonic generation and long-range structural ordering in thin films of an organic salt grown by organic vapor phase deposition
Authors: Forrest S. R. , Burrows P. E. , Stroustrup A. , Strickland D. , Ban V. S.
Published: July 2002

We discuss the growth of thin films of the organic salt, 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) by the novel process of organic vapor phase deposition (OVPD). These films show long-range structural ordering and very intense second harmonic generation efficiencies (SHG) significantly greater (when normalized for thickness) than that of randomly oriented pure DAST powders. This is the first demonstration of such intense SHG radiation and long-range ordering for a thin film sample of a nonlinear organic salt. Furthermore, this work suggests that OVPD represents a general technique for growing thin films of highly polar, nonlinear optical materials such as DAST.
Ultrathin oxides using N2O on strained Si1−xGex layers
Authors: Mukhopadhyay M. , Ray S. K. , Nayak D. K. , Maiti C. K.
Published: July 2002

Microwave N2O plasma oxidation of strained Si1−xGex layers at low temperature (<200 °C) is reported. The hole confinement in accumulation in a metal oxide semiconductor (MOS)-gated SiGe/Si heterostructure has been confirmed by both simulation and experiments. Electrical properties are also discussed.
Fluorescence emission from high purity synthetic diamond anvil to 370 GPa
Authors: Liu Jun , Vohra Yogesh K.
Published: July 2002

We report laser excited fluorescence in high purity synthetic diamond anvil to pressures of 370 GPa in a diamond anvil cell device. The nitrogen impurity level in this diamond is extremely low, and it allows us to study the stress effects on the optical transitions in diamond without interference from impurities. Pressure in the diamond anvil cell was measured by x-ray diffraction using the platinum standard. Pressure dependence of the fluorescence peak was measured between 270 and 370 GPa in the visible spectral range. The variation of excitation laser wavelength shows clear cutoff in the excitation threshold in the 514–633 nm range at 370 GPa.
Enhanced hydrogenation in polycrystalline silicon thin films using low-temperature ultrasound treatment
Authors: Ostapenko S. , Jastrzebski L. , Lagowski J. , Smeltzer R. K.
Published: July 2002

Ultrasound treatment (UST) was applied to improve electronic properties of polycrystalline silicon films on silica-based substrates. A strong decrease of sheet resistance by a factor of two orders of magnitude was observed in hydrogenated films at UST temperatures lower than 100 °C. This is accompanied by improvement of a film homogeneity as confirmed by spatially resolved photoluminescence study. The UST effect on sheet resistance demonstrates both stable and metastable behavior. A stable UST effect can be accomplished using consecutive cycles of UST and relaxation. An enhanced passivation of grain boundary defects after UST is directly measured by nanoscale contact potential difference with atomic force microscope. Two specific UST processes based on interaction between the ultrasound and atomic hydrogen are suggested: enhanced passivation of grain boundary defects and UST induced metastability of hydrogen related defects.
Femtosecond dynamics of the nonlinear anisotropy in polarization insensitive semiconductor optical amplifiers
Authors: Lenz G. , Ippen E. P. , Wiesenfeld J. M. , Newkirk M. A. , Koren U.
Published: July 2002

The nonlinear response of polarization insensitive semiconductor optical amplifiers shows that anisotropy may be induced as a function of intensity. With a hetrodyne pump-probe technique, the nonlinear gain and index components may be polarization resolved as well as time resolved. By extending this measurement technique we measure the dynamic anisotropy directly.
Stripe patterns formed by the thermal desorption of Ga atoms on Ga-terminated Si(111) surfaces
Authors: Fujita K. , Kusumi Y. , Ichikawa M.
Published: July 2002

The Si(111)-7×7 area surrounded by the Si(111)-√3×√3R30°-Ga region has been observed by scanning tunneling microscopy during the thermal desorption of Ga atoms at ∼600 °C and after the desorption. The 7×7 area exhibits triangular and strip patterns on the nanometer scale for the Si(111) substrates tilting toward the [112̄] and [1̄1̄2] directions, respectively. This is because faulted halves of the 7×7 reconstruction are adjacent to the √3×√3-Ga area on the boundary between the 7×7 and √3×√3-Ga areas during Ga desorption. It has been found that strip patterns with nanometer-scale precision are formed on the Si(111) substrates tilting toward the [1̄1̄2] direction.
Pb(Zr,Ti)O3 thin films on zirconium membranes for micromechanical applications
Authors: Maeder T. , Muralt P. , Sagalowicz L. , Reaney I. , Kohli M. , Kholkin A. , Setter N.
Published: July 2002

An efficient, electrically conductive, chemical barrier for the integration of piezoelectric Pb(Zr,Ti)O3 (PZT) films on reactive metal substrates has been developed, opening new possibilities for PZT integration on micromechanical and semiconductor devices. Very reactive zirconium films have been taken in order to test the quality of the specially designed RuO2/Cr buffer under the condition of in situ sputter deposition of PZT at 600 °C. The PZT/RuO2 interface was found to be free of intermediate phases. A PZT activated metallic micromechanical element was demonstrated with a thin film Zr membrane.
A multilayer YBa2Cu3Ox Josephson junction process for digital circuit applications
Authors: Mallison W. H. , Berkowitz S. J. , Hirahara A. S. , Neal M. J. , Char K.
Published: July 2002

We have demonstrated a multilayer high-Tc junction process capable of fabricating small-scale digital circuits. The process uses superconductor/normal–metal/superconductor YBa2Cu3Ox (YBCO) edge junctions with a cobalt-doped YBCO barrier and an integrated YBCO ground plane. We have measured spreads in the junctions’ critical currents as low as 12% (1σ) both on and off the ground plane. The proper functioning of the ground plane was verified by measuring the reduced inductance of superconducting quantum interference devices (SQUIDs) on the ground plane compared to identical SQUIDs off the ground plane. At a temperature of 70 K, the inductance on the ground plane is as low as 1.2 pH/⧠. The inferred YBCO penetration depth is 250 nm at 70 K and 280 nm at 77 K.
Structural and carrier density dependence of carrier lifetime in InGaAs/GaAs multiple-quantum-well lasers
Authors: Czotscher K. , Weisser S. , Larkins E. C. , Fleissner J. , Ralston J. D. , Schönfelder A. , Rosenzweig J. , Esquivias I.
Published: July 2002

The carrier lifetime in undoped and p-doped mesa and ridge waveguide In0.35Ga0.65As/GaAs multiple-quantum-well lasers is extracted from the frequency response of the spontaneous emission. The radiative recombination coefficient is found to be the same for mesa and ridge waveguide lasers, and is nearly independent of the doping level. For ridge waveguide lasers, a simple method is proposed to obtain the lateral broadening of the active region due to carrier diffusion. When the corrected active region width is considered, the threshold carrier densities for both undoped and p-doped lasers are independent of the lateral structure and cavity width. Further, the surface recombination velocity in mesa lasers is determined.
A desensitized displacement interferometer applied to impact recovery experiments
Authors: Espinosa H. D. , Mello M. , Xu Y.
Published: July 2002

A variable sensitivity displacement interferometer (VSDI) used to monitor both normal and in-plane particle displacements in stress wave propagation experiments is introduced. The general system consists of two interferometers working in tandem. Normally reflected light is interfered with each of two symmetrically diffracted light beams generated by the specimen rear surface. In cases where the surface motion simultaneously exhibits both in-plane and normal displacements, the fringes represent a linear combination of the longitudinal and transverse components of motion. Decoupling of the normal and in-plane displacement histories can be achieved through a linear combination of the two VSDI records. The variable sensitivity feature of the VSDI greatly desensitizes normal displacement measurements and is particularly well suited for wave propagation studies. Experimental results are presented which demonstrate the application of this technique to monitoring particle motion histories in pressure-shear recovery experiments.
Radio frequency-SQUID effect in YNi2B2C due to natural grain boundary weak links
Authors: Khare Neeraj , Gupta A. K. , Khare Sangeeta , Gupta L. C. , Nagarajan R. , Hossain Z. , Vijayaraghavan R.
Published: July 2002

We report the observation of radio frequency-superconducting quantum interference device (rf-SQUID) effect due to natural grain boundary weak links in a bulk sample of a YNi2B2C superconductor at 4.2 K, confirming that the superconducting grains are coupled at the grain boundaries through Josephson effect. Periodic oscillations in voltage-flux characteristic due to rf-SQUID effect have been clearly observed at 4.2 K when the driving rf frequency was kept slightly away from the resonance frequency of the tank circuit. Phase reversal in the voltage-flux characteristics on changing the rf frequency has been observed. Noise spectrum of the YNi2B2C bulk rf-SQUID is also reported.
Mach–Zehnder interferometer measurement of the Pockels effect in a poled polymer film with a coplanar electrode structure
Authors: Cho H. R. , Shin M. J. , Han S. H. , Wu J. W.
Published: July 2002

Mach–Zehnder interferometry was used to measure the Pockels effect in a poled electro-optic polymer thin film with a coplanar electrode structure. The beam at the sample arm of the Mach–Zehnder interferometer passed through a polymer thin film which had been spin-coated on top of a clear gap between two electrodes patterned on an optical substrate. This unique optical geometry enabled the Pockels coefficients of the poled electro-optic polymer film in the directions of the ordinary and the extraordinary optic axes to be determined independently. As an example, the tensor ratio r33/r13 for a stilbene-dye-doped polyimide guest/host polymer film was determined experimentally; the ratio turned out to be 4.6, which was higher than the value of 3 predicted by the thermodynamic model.
Enhancement of beam coupling in the near infrared for tin hypothiodiphosphate
Authors: Odoulov Serguey G. , Shumelyuk Alexander N. , Brost George A. , Magde Kevin M.
Published: July 2002

By using the moving grating technique, without an applied electric field, it is possible to significantly increase the steady-state two-beam coupling gain in photorefractive Sn2P2S6. Another technique of gain enhancement consists of cooling of the sample to −30 °C. The measured data confirm the existence of two out-of-phase gratings in Sn2P2S6 generated by charge carriers of different sign, with relaxation times of 70 ms and 500 s.
Textured diamond growth by low pressure flat flame chemical vapor deposition
Authors: Wolden C. A. , Sitar Z. , Davis R. F. , Prater J. T.
Published: July 2002

A laminar, flat-flame burner has been constructed for the deposition of diamond films using an acetylene/oxygen flame at reduced pressures. The stagnation flow results in uniform deposition conditions across the diameter of the burner. Under certain operating conditions the growth rate and morphology are primarily controlled by the substrate temperature. Conditions for the deposition of <100≳ textured films are reported for a flat-flame system. From growth rate measurements an apparent activation energy of 22 kcal/mol was observed. The maximum growth rate of 5.5 μm/h is the highest reported to date for a low pressure combustion system.
Exciton dynamics in a novel high-yield GaInP quantum-wire array
Authors: Dua P. , Cooper S. L. , Chen A. C. , Cheng K. Y.
Published: July 2002

We report the carrier dynamics in a spontaneously organized array of quantum wires grown by a novel technique that involves strain induced lateral ordering (SILO). Our cw–photoluminescence (PL) measurements reveal a very strong optical anisotropy associated with these wires, while the time-resolved PL measurements demonstrate a very interesting carrier dynamics due to localization of excitons and slow interwire scattering. The high quality and freedom from defects of the SILO multiple quantum wire array are nicely borne out by the long decay photoluminescence times (∼4 ns).
Evidence for the role of the surface potential and native oxide on thermal properties of crystalline Si
Authors: Kumar Shailendra
Published: July 2002

Thermal properties of crystalline Si have been studied using the photopyroelectric (PPE) technique in the temperature range 100–300 K. It has been observed that the generation and propagation of the thermal waves in Si depends upon the thermal history of the sample. The native amorphous silicon dioxide layer on Si and the surface potential affect the propagation of the thermal waves and this effect is not reversible in the temperature range 150 K<T<260 K. It is observed that the contactless PPE technique can also be used to study recombination processes of excess carriers in semiconductors.
Elastic guided waves in plates with rough surfaces
Authors: Lobkis O. I. , Chimenti D. E.
Published: July 2002

In this letter we report experimental measurements and calculations of elastic wave propagation and dispersion in a waveguide with randomly rough surfaces, as a model of incipient corrosion. Experiments are performed in fluid immersion on a smooth aluminum plate and on one with 26-μm rms roughness, determined by independent acoustic profilometry. The calculation exploits the phase-screen approximation as the basis for a transverse-resonance derivation of the frequency/velocity dispersion relation in an elastic waveguide with rough surfaces. Comparisons of frequency spectra for two propagation lengths show good agreement between model and experiment.
Electron-electron scattering in a high purity mesoscopic conductor
Authors: Cumming David R. S. , Davies John H.
Published: July 2002

We have carried out measurements on the nonlinear behavior of the current–voltage characteristics of a mesoscopic cross, fabricated in a high mobility GaAs/AlGaAs two-dimensional electron gas. Our measurement show two distinct peaks, one at an electron excess energy of 3.3 meV, and a second at an excess energy of 50 meV. The first peak arises when electron-electron scattering reduces the mean free path below the dimensions of the cross. The second peak is due to electron cooling by LO phonon emission.
Three-dimensional atom probe analysis of Co–Cr–Ta thin film
Authors: Nishimaki J. , Hono K. , Hasegawa N. , Sakurai T.
Published: July 2002

Three-dimensional elemental mappings of Co–Cr–Ta thin film sputter-deposited at 200 °C were obtained using a three-dimensional atom probe. We have confirmed that Ta atoms are dissolved in the film homogeneously, and no segregation of Ta was found at the grain boundaries. On the other hand, Cr atoms are inhomogenously dissolved within grains, and it is strongly enriched at the grain boundaries forming a Cr-enriched grain boundary phase with a thickness of approximately 4 nm.
Atomic configurations of group V acceptors in ZnSe, ZnTe, and CdTe
Authors: Ostheimer V. , Jost A. , Filz T. , Lauer St. , Wolf H. , Wichert Th.
Published: July 2002

The formation of donor–acceptor pairs was detected by perturbed γγ angular correlation spectroscopy. In ZnSe, ZnTe, and CdTe crystals doped with the donor 111In and one of the acceptors N, P, As, or Sb the strength of the electric field gradient shows a systematic correlation of the bond length between the respective acceptor and the neighboring cation. For N acceptors, an inward relaxation of the neighboring cations is concluded to occur.
Transverse modes and lasing characteristics of selectively grown vertical cavity semiconductor lasers
Authors: Orenstein M. , Satuby Y. , Ben-Ami U. , Harbison J. P.
Published: July 2002

Vertical-cavity surface emitting lasers (VCSELs) were grown by molecular beam epitaxy over openings in a SiN4 mask, deposited on a GaAs wafer. We obtained ready to use lasers and laser arrays, laterally defined by the polycrystalline, highly resistive material grown over the SiN4 laser. The performance of the lasers (e.g., 20×20 μm2 by size) were similar to that of VCSELs defined by post growth processing methods. Special transverse modes characteristics and a well defined polarization were observed in square shaped lasers and it was attributed to selective growth induced anisotropy.
Planar anchoring of nematic 4-n-pentyl-4′-cyanobiphenyl on self-assembled monolayers formed from alkanethiols on gold
Authors: Miller William J. , Abbott Nicholas L. , Paul Jonathan D. , Prentiss Mara G.
Published: July 2002

We report measurements of planar anchoring of nematic 4-n-pentyl-4′-cyanobiphenyl (5CB) on self-assembled monolayers (SAMs) formed from CH3(CH2)mSH (7⩽m⩽17) on films of gold (prepared without oblique deposition) by using reflection interferometry. The anchoring observed contrasts with past reports of homeotropic anchoring of 5CB by surfaces, such as monolayers formed from octadecyltrichlorosilane on silica, with energies as low as alkanethiols on gold (19 mN/m). The anisotropic dispersion force acting between 5CB and gold was calculated to favor planar anchoring of 5CB on SAMs formed from CH3(CH2)15SH by ∼0.1 mN/m, and can, therefore, override self-interactions of 5CB that lead to homeotropic anchoring. Electric field-induced Freederiksz transitions of 5CB supported on bare gold, and on SAMs formed from CH3(CH2)15SH on gold, confirm weaker (planar) anchoring of 5CB on SAMs on gold as compared to bare gold.
Reverse bias voltage dependent pulse shape and transmission change through a semiconductor saturable absorber
Authors: Kim Dug K.
Published: July 2002

The effect of reverse bias voltage on optical transmission through a waveguide semiconductor saturable absorber is measured for various optical input pulse energies. Reverse bias voltage dependent pulse shape narrowing after a single pass through the device is also observed. Experimental results show that the transmission through the device can be controlled very effectively by modulating the reverse bias voltage on the device when the input pulse energy is low so that the absorption of the saturable absorber is unsaturated. We believe that this kind of controllable semiconductor saturable absorber can be used for many laser systems or modulator and limiter applications in optical communication systems.
Lattice effects on the magnetic and transport properties of La2/3−xNdxCa1/3MnO3
Authors: Sun J. R. , Rao G. H. , Liang J. K. , Zhou W. Y.
Published: July 2002

The magnetic and transport properties of La2/3−xNdxCa1/3MnO3 (x=0–0.67) are studied. Two magnetic transitions occur in compounds with composition x=0.1–0.4, leading to a low moment state at high temperature and a high moment state at low temperature. A metal–insulator transition was observed for x≤0.4 between the two magnetic transitions. An electronic and magnetic phase diagram is depicted on a temperature–tolerance factor plane. The interesting feature of this diagram is the appearance of a new metamagnetic phase. Present investigation suggests that the tolerance factor is not the only parameter determining the lattice effects.
Far-infrared study of a quasi-one-dimensional electron gas formed on (100)GaAs facets with hole gas sidegates on a (311)A GaAs substrate
Authors: Arnone D. D. , Burroughes J. H. , Pepper M. , Norman C. , Evans R. J. , Burke T. , Ritchie D. A. , Grimshaw M. P.
Published: July 2002

A new type of quasi-one-dimensional electron gas has been realized by using molecular beam epitaxy to grow a high mobility heterostructure on a (311)A GaAs substrate selectively etched to expose (100) facets. The electron gas formed on the (100) facets is confined in one lateral dimension by the p–n junctions formed with the adjacent two-dimensional hole gases on (311)A, thereby forming a p–n–p structure. Far-infrared cyclotron resonance spectra demonstrate the dimensionality of such structures and yield typical lateral confinement energies of 22.3 cm−1 and electronic widths of ∼900 nm. These estimates are supported by cathodoluminescence data.
Influence of AsH3 cracking temperature on the H passivation of C acceptors in In0.53Ga0.47As grown by beam epitaxy techniques
Authors: Jackson Steven L. , Baker Judith E. , Stillman Gregory E.
Published: July 2002

The influence of subhydride species generated in a low-pressure Ta-based AsH3 cracker on the degree of H passivation of C acceptors in heavily doped (p⩾3×1019 cm−3) In0.53Ga0.47As grown by gas source and metalorganic molecular beam epitaxy has been studied. A strong correlation has been observed between the relative abundance of AsH3, AsH, and H in quadrupole mass spectra and the degree of passivation. Enhanced effects were observed at reduced growth temperatures. Design of experiments techniques have been used to study the influence of hydride cracker temperature, substrate temperature, H2 pumping speed, group III sources, AsH3 flow rate and the second order interactions on the H passivation of C acceptors. The substrate temperature, hydride cracking temperature, and H2 pumping speed, were determined to have the dominant effects, while second order interactions were dominated by substrate temperature, H2 pumping speed, and AsH3 flow rate interactions with the hydride cracking temperature. Optimized parameters were determined that permit the growth of essentially unpassivated (⩽10%) C-doped In0.53Ga0.47As with net hole concentrations as high as p=8×1019 cm−3 by both gas source and metalorganic molecular beam epitaxy techniques.
Mutual phase-locking of ten YBa2Cu3O7 step-edge Josephson junctions up to 45 K
Authors: Kunkel G. , Ono R. H.
Published: July 2002

We have developed a microwave circuit using ten parallel-biased high-temperature superconductor Josephson junctions to demonstrate phase-locking for applications such as oscillators, mixers, and detectors. The basic cell consists of two Josephson junctions enclosed in a microstrip resonator, which provides voltage-locking and low dynamic resistance in the current–voltage characteristic. Partial synchronization of the ten junctions was observed up to 45 K and up to 1 THz. The implications of this design for power and radiation linewidth will be discussed.