bluuebunny/crossref_metadata_2025 huggingface dataset:
Prolongation of a filament lifetime using SF6 plasma method
Authors: Ohkoshi Kiyonori , Saitoh Yuichi , Kamiya Tomihiro , Sakai Takuro , Tajima Satoshi
Published: July 2002

We succeeded in prolonging the lifetime of tungsten filaments in a Freeman ion source using SF6 plasma method. The plasma chamber of the source is made of molybdenum. The molybdenum fluorinated with SF6 plasma is vaporized and sticks to the filament. The stuck Mo to the filament can compensate the loss of tungsten filament. In order to prolong the lifetime of the filament, it is important that the amount of the lost W from the filament balances that of the stuck metals from the chamber wall and the filament itself. The balance can be adjusted with the arc current and the gas flow of the source. SF6(Ar) plasma method has effects of prolonging the lifetime of filaments, of stabilizing plasma, and of minimizing corrosive dirt.
Deposition of mass-selected clusters studied by thermal energy atom scattering and low-temperature scanning tunneling microscopy: An experimental setup
Authors: Jödicke Harald , Schaub Renald , Bhowmick Ashok , Monot René , Buttet Jean , Harbich Wolfgang
Published: July 2002

We present an experimental setup for the investigation of the processes occurring during the deposition of mass-selected clusters on a well-defined surface. The sample is analyzed in situ by two complementary methods: thermal energy atom scattering (TEAS) and scanning tunneling microscopy (STM). TEAS is used to study the dynamical processes during the deposition and to gather statistical information about the resulting structures on the surface. Subsequent STM measurements allow us to investigate the collision outcome on an atomic scale. The setup is highly versatile and guarantees ultra-high-vacuum conditions and cryogenic temperatures (≈30 K) of the sample at all times even during sample transfer. Clusters are produced in a CORDIS-type cluster source. A new compact multichannel effusive He source in combination with a new Wien-filter-based He detector are used for TEAS measurements. The new low-temperature STM allows measurements in a temperature range between 8 and 450 K. Atomic resolution on the Pt(111) surface is regularly observed at Tsample=8 K. The performances of the setup are illustrated by STM images obtained after the deposition of Ag7+ clusters with Ekin=95 and 1000 eV on bare Pt(111) and by measurements made of the deposition of Ag7+ clusters with Ekin=20 eV in a Xe–rare-gas matrix adsorbed on Pt(111).
Temporal response of a high-T
c superconducting field effect transistor
Authors: Schneider R. , Auer R.
Published: July 2002

YBa2Cu3O7−x/SrTiO3/Au multilayer systems have been prepared in situ by pulsed laser deposition onto (100) SrTiO3 substrates. An electric field controlled device was patterned by suitable metal masks applied successively during the deposition process. The switching time of the superconducting source-drain channel has been studied at T=4.2 K applying rectangular pulses to the gate electrode. We find that the source-drain voltage follows the gate voltage variation in accordance with the RC time constant of the device. Our result is consistent with the mechanism of direct charge transfer by the electric field, but inconsistent with a model based on electric field driven migration of the oxygen atoms in the CuO chains of YBa2Cu3O7−x which predicts characteristic times in the order of minutes.
Order domain boundaries in ion beam synthesized semiconducting FeSi2 layers
Authors: Yang Z. , Shao G. , Homewood K. P. , Reeson K. J. , Finney M. S. , Harry M.
Published: July 2002

The internal streaking contrast within ion beam synthesized β-FeSi2 (β) grains has been studied. The results show that this internal streaking contrast is caused by the interfaces between coexistent β order domains (ODs) which are 90° oriented to one another around [200]β. The interface between adjacent ODs is (200)β. The mechanism for the formation of order domain boundaries (ODBs) is attributed to the impingements of separately nucleated growing silicide nuclei during the process of ion implantation and subsequent thermal annealing.
Real-space-transfer of electrons in InGaAs/InAlAs heterostructures
Authors: Masselink W. Ted
Published: July 2002

Measurements of the electron velocity as a function of electric field in bulk InGaAs and in modulation-doped InGaAs/InAlAs (lattice-matched to InP) indicate that hot electrons transfer out of the InGaAs channel into the InAlAs. This added scattering mechanism results in a lower peak velocity for electrons in the heterosystem than in bulk InGaAs.
Measurement of the methyl radical concentration profile in a hot-filament reactor
Authors: Zalicki P. , Ma Y. , Zare R. N. , Wahl E. H. , Owano T. G. , Kruger C. H.
Published: July 2002

The spatial profile of methyl radical concentration in a hot-filament reactor has been measured using cavity ring-down spectroscopy (CRDS) at a wavelength of 213.9 nm for which the CH3 absorption cross section has been shown to be nearly independent of temperature. Methyl radicals are generated with a 25 mm long tungsten filament heated to 2400 K in a slowly flowing mixture of 0.6% CH4 in H2 (20 Torr total pressure). CRDS is employed to measure CH3 absorbance as a function of a distance perpendicular to the axis of the filament. The CH3 absorbance profiles do not change when the direction of the process gas flow through the reactor is reversed, which indicates cylindrical symmetry of the CH3 distribution about the filament. Consequently, the radial CH3concentration in the reactor is determined by Abel inversion of the CH3 absorbance profile. The CH3concentration peaks ∼4 mm from the filament (1.04×1014molecules/cm3). Methyl radicals decay rapidly as a function of a distance from the filament and disappear about 2 cm from the filament within our present detection sensitivity (3×1012molecules/cm3).
Violet light emitting SrS/SrCl:Eu thin-film electroluminescent devices
Authors: Kong W. , Ahmed S. , Ferguson J. , Solanki R.
Published: July 2002

Emission of bright (over 9 cd/m2) violet light centered at 404 nm has been achieved from SrS:Eu thin-film electroluminescent (EL) devices. The brightness has remained stable after several hours of operation. The source of this light is believed to be the 5d–4f transition of Eu2+ in the SrCl2 host, which is formed near the ZnS/SrS interfaces within the sandwich structure of the EL devices. Similar device structures were also utilized to produce ultraviolet EL emission at 367 nm from SrCl2:Ce3+ layers. These devices were grown via atomic layer epitaxy.
Towards perfect Ge δ layers on Si(001)
Authors: Falta J. , Bahr D. , Materlik G. , Müller B. H. , Horn-von Hoegen M.
Published: July 2002

The effect of different methods of growth on the interface quality of extremely thin buried GexSi1−x films (δ layers) was studied by means of in situ spot profile analysis low-energy electron diffraction and extensive postgrowth x-ray characterization by measurements of crystal truncation rods and x-ray standing waves. In comparison to molecular beam epitaxy, solid phase epitaxy and surfactant mediated growth result in a significant reduction of Ge–Si intermixing and interface roughness.
Supercooled melting in multicomponent Zr–Al–Cu–Ni diffusion couples
Authors: Busch R. , Bakke E. , Johnson W. L.
Published: July 2002

Diffusion couples combining a hcp Zr90Al10 supersaturated solid solution with a fcc Cu64Ni36 solid solution were annealed at 410 °C for different times. The reaction at the interface was investigated by transmission electron microscopy and energy dispersive x-ray spectroscopy. The investigations show the formation of a noncrystalline layer at the interface between the two solid solutions that grows to a maximum thickness of more than 0.3 μm. Concentration profiles reveal that two noncrystalline phases coexist in the diffusion couple. One is Ni-rich and was in the amorphous state during the reaction at 410 °C. The other phase is Zr-rich and grew in its supercooled liquid state. This novel supercooled melting process has not been previously observed in a solid state reaction. Kinetic and thermodynamic aspects that contribute to the high thermal stability of the Zr–Al–Ni–Cu in the supercooled liquid are discussed.
Long-wavelength SiGe/Si resonant cavity infrared detector using a bonded silicon-on-oxide reflector
Authors: Carline R. T. , Robbins D. J. , Stanaway M. B. , Leong W. Y.
Published: July 2002

Resonant-enhanced detection of long wavelength infrared radiation using a SiGe/Si multiquantum well device grown on a bonded silicon-on-insulator substrate reflector is reported. A low refractive index in the wavelength region below the 9.2 μm absorption peak in SiO2 gives high Si/SiO2 reflectivities between 7 and 9 μm. Comparison with a control device grown on a p+-Si substrate shows a fivefold enhancement in the peak responsivity at 7.2 μm, which is the resonant wavelength of the cavity formed between the buried Si/SiO2 and the Si/air interfaces.
Effect of nitrogen–oxygen complex on electrical properties of Czochralski silicon
Authors: Yang Deren , Fan Ruixing , Li Liben , Que Duanlin , Sumino Koji
Published: July 2002

Effect of nitrogen–oxygen (N–O) complexes on electrical properties of nitrogen-rich Czochralski (CZ) silicon grown in a nitrogen atmosphere has been investigated during annealing in the temperature range from 650 to 1000 °C. Electrical and low temperature (8 K) Fourier transmission infrared spectrometer (FTIR) measurements point out that the carrier concentration of the nitrogen-rich silicon varies with the annealing time and temperature, which is due to the formation and elimination of the N–O complexes acting as shallow thermal donors. After the N–O complexes are eliminated by annealing above 900 °C the carrier concentration of the nitrogen-rich silicon is stabilized. It is suggested that the N–O complexes attract more oxygen atoms to form new electrically inactive N–O clusters, and lose their electrical activity.
Accurate in situ lattice matching from the dynamics of high energy electron diffraction
Authors: Cunningham J. E. , Pathak R. N. , Jan W. Y.
Published: July 2002

We report an in situ electron diffraction measurement which allows In0.53Ga0.47As to be lattice matched to InP during growth. This method uses analysis of the dynamics of intensity oscillations during electron diffraction to determine when lattice matched growth occurs. With this method we demonstrate closely lattice matched ternary alloys; InGaAs on InP, GaInP on GaAs, and quarternary alloys of InAlGaAs on InP.
Room-temperature normal-mode coupling in a semiconductor microcavity utilizing native-oxide AlAl/GaAs mirrors
Authors: Nelson T. R. , Prineas J. P. , Khitrova G. , Gibbs H. M. , Berger J. D. , Lindmark E. K. , Shin J.-H. , Shin H.-E. , Lee Y.-H. , Tayebati P. , Javniskis L.
Published: July 2002

A GaAs/AlAs microcavity containing six InGaAs quantum wells was grown, and the sample was then etched via chemically-assisted ion-beam etching to form 50-μm-diam cylindrical mesas. The formation of native oxides, accomplished by baking the samples at 400 °C in the presence of a pressurized N2/H2O vapor line, lowered the refractive index of the AlAs layers to 1.5. The higher refractive index contrast more effectively confined the intracavity field, leading to well-resolved reflectivity dips with an exciton-polariton splitting of 6.72 nm=9.44 meV at room temperature.
Photoassisted poling induced second harmonic generation with in-plane anisotropy in azobenzene containing polymer films
Authors: Jiang X. L. , Li L. , Kumar J. , Tripathy S. K.
Published: July 2002

Photoassisted poling of azobenzene containing polymer films at room temperature using polarized Ar+ laser beam as pump light was studied. Irradiating the films with p-polarized pump light at an incident angle to the normal during the poling process, second harmonic generation with in-plane anisotropy could be induced. Second order nonlinear optical coefficient, d33, of the poled sample was measured to be 20 pm/V. The second harmonic generation properties induced by photoassisted poling and thermal assisted poling were compared.
Tailoring the birefringence in a vertical-cavity semiconductor laser
Authors: Jansen van Doorn A. K. , van Exter M. P. , Woerdman J. P.
Published: July 2002

We demonstrate a technique to modify the strain in a planar vertical-cavity semiconductor laser. The technique consists of locally melting a hole in the wafer next to the device by means of a focused laser beam. This allows manipulating both the magnitude and the orientation of the native birefringence in a permanent way.
Single-mode and single-beam emission from surface emitting laser diodes based on surface-mode emission
Authors: Köck A. , Golshani A. , Hainberger R. , Gornik E. , Korte L.
Published: July 2002

Single-mode and single-beam emission have been achieved from surface emitting laser diodes based on the surface-mode-emission technique. By employing an optimized device design and a first-order grating coupler, the laser diodes show under pulsed operation condition a single-mode emission with a linewidth of 0.11 nm. A power up to 3.6 mW is emitted into a single, surface-emitted beam, which has a beam divergence of 0.20°.
Cathodoluminescence study of the influence of misfit dislocations on hole accumulation in an n-AlGaAs/p-GaAs/n-InGaAs heterojunction phototransistor
Authors: Lin H. T. , Rich D. H. , Sjölund O. , Ghisoni M. , Larsson A.
Published: July 2002

We have studied the influence of misfit dislocations on hole accumulation in the base layer of an n-AlGaAs/p-GaAs/n-InGaAs heterojunction phototransistor (HPT). Spatially and temporally resolved cathodoluminescence (CL) measurements reveal that variations in the hole accumulation is caused primarily by strain-induced defects which impede the transport of holes in the collector. The lifetime of holes in the InGaAs/GaAs collector is found to be negligibly affected by the underlying misfit dislocations in the InGaAs/GaAs collector. The reduction in the local electron-beam-induced current signal by the dislocations is less than ∼20%, indicating that these defects have a minor impact on the overall device performance.
Preparation of wide band gap microcrystalline silicon film by using SiH2Cl2
Authors: Ki Kim Sung , Yeon Moon Byeong , Seong Byun Jae , Bin Jeon Hong , Jang Jin
Published: July 2002

We have studied the growth of Cl incorporated microcrystalline silicon [μc-Si(:Cl)]. The flow rates of H2 and SiH2Cl2 were varied to deposit wide band gap n+ μc-Si(:Cl) films by using SiH4/SiH2Cl2/H2/PH3 mixtures. The n+ μc-Si(:Cl) film deposited with SiH2Cl2/SiH4 = 1 exhibited a room temperature conductivity of 2 S/cm and an optical band gap of ∼2.0 eV that is at least 0.2 eV higher than that of conventional n+ μc-Si. The surface morphology of the μc-Si(:Cl) film is much rougher than that of conventional μc-Si prepared by using SiH4/H2 plasma.
Direct evidence for a piezoelectriclike effect in coherently strained SiGe/Si heterostructures
Authors: Khizhny V. I. , Mironov O. A. , Parker E. H. C. , Phillips P. J. , Whall T. E. , Kearney M. J.
Published: July 2002

A hybrid acoustic spectroscopy technique has been used to demonstrate the (reversible) conversion of high frequency electric fields into longitudinal acoustic waves within a modulation-doped pseudomorphic Si/Si0.88Ge0.12/Si heterostructure. This provides compelling evidence for the existence of a piezoelectriclike coupling within such structures.
Identification of first and second layer aluminum atoms in dilute AlGaAs using cross-sectional scanning tunneling microscopy
Authors: Smith Arthur R. , Chao Kuo-Jen , Shih C. K. , Anselm K. A. , Srinivasan A. , Streetman B. G.
Published: July 2002

Cross-sectional scanning tunneling microscopy is used to study dilute AlxGa1−xAs with x=0.05 to investigate the bonding configurations within this ternary alloy. Atomically resolved scanning tunneling microscopy images combined with symmetry considerations provide the assignment of first and second layer aluminum atoms. The Al–Al pair distribution function based on the experimental data is compared with the theoretical pair distribution function of a random alloy. While there exists a qualitative agreement, small deviations from the ideal random distribution are also found.
Optical transitions in cubic GaN investigated by spatially resolved cathodoluminescence
Authors: Menniger J. , Jahn U. , Brandt O. , Yang H. , Ploog K.
Published: July 2002

Spatially resolved cathodoluminescence (CL) spectroscopy in connection with scanning electron microscopy performed on cubic (c) GaN between 5 and 300 K reveals that at low temperatures the CL spectra of c-GaN single crystals consist of four well-separated lines. The two lines highest in energy were previously identified as excitonic and donor-acceptor transitions, respectively. Here, we show that the lines lowest in energy are due to an additional free-to-bound transition, involving an impurity different from those related to the donor-acceptor transition, and its phonon replica. The CL spectra of c-GaN layers, while being rather broad, are composed of these four lines. Moreover, at 300 K the spectra of the layers and of the crystals are both dominated by the excitonic transition and closely resemble each other.
Atom transport in nickel by displacement cascades for spatially dependent displacement rate and sink strength
Authors: Fielitz P. , Macht M.-P. , Naundorf V. , Wollenberger H.
Published: July 2002

Diffusion coefficients D were measured in nickel under 600 keV Kr++ ion irradiation at 77 K and at 800 K using multilayer specimens. At 77 K the diffusion coefficient closely follows the calculated depth dependence of the displacement rate K indicating that athermal atomic mixing with an efficiency of Dmix/K=0.6 nm 2/dpa is responsible for the observed transport at this temperature. At 800 K considerable diffusion is observed far from the irradiated surface in a region where the displacement rate is zero. The exponential slope of the diffusion coefficient measured here indicates annihilation of mobile defects in a microstructure with a sink strength of 7×1013 m−2. An upper limit of the fraction of freely migrating defects of 0.05 is estimated.
Exciton spectral splitting near room temperature from high contrast semiconductor microcavities
Authors: Graham L. A. , Deng Q. , Deppe D. G. , Huffaker D. L.
Published: July 2002

Spectral splitting due to the exciton response of a three InGaAs quantum well active region placed in various high contrast semiconductor microcavities is observed near room temperature. The planar microcavities consist of one-wavelength thick cavity spacers surrounded by AlGaAs/GaAs along with high contrast distributed Bragg reflectors formed from AlxOy/GaAs and MgF/ZnSe. Microcavities having different loss rates are characterized over a range of temperatures using reflectance, transmission, and photoluminescence.
Investigation of the inversion layer electron mobility in α-SiC
Authors: Ueno Katsunori , Seki Yasukazu
Published: July 2002

The inversion layer mobility of 6H- or 4H-SiC is one of the very important parameters for metal oxide semiconductor field effect transistor applications. In this contribution, we have calculated the theoretical value of the inversion layer mobility of α-SiC at the low-temperature limit. The calculations include the Coulomb scattering by the ionized acceptors and by the surface charges, the roughness scattering at the interface between SiO2 and semiconductor, and the screening effect by free electrons. The results show that the mobility calculated for SiC is higher than that of silicon (001) surface. We conclude that the higher mobility than silicon (001) surface is mainly due to the larger number of conduction band minima in SiC than in silicon in this calculation. In addition, the simple model for the phonon scattering predicts the higher mobility in SiC than in silicon.
Metal complex polymer for second harmonic generation and electroluminescence applications
Authors: Tao X. T. , Suzuki H. , Watanabe T. , Lee S. H. , Miyata S. , Sasabe H.
Published: July 2002

We report the second harmonic generation and electroluminescent (EL) properties of a soluble metal complex polyurethane (PU). The PU was prepared by the reaction of a zinc Schiff base with 4,4′-diphenylmethane-diisocyanate. The polymer film has been effectively poled under a corona field and its linear and nonlinear optical (NLO) properties were characterized. The results indicated that the NLO effects of the polymer are mainly originated in the distorted coordination tetragonals formed by the central zinc atoms and coordination atoms. The polymer shows strong photoluminescence under a ultraviolet-lamp illumination and can be used as a luminescent material for EL devices.
Mid-infrared In1−xAlxSb/InSb heterostructure diode lasers
Authors: Ashley T. , Elliott C. T. , Jefferies R. , Johnson A. D. , Pryce G. J. , White A. M. , Carroll M.
Published: July 2002

Stimulated emission at 5.1 μm was demonstrated from a broad area In1−xAlxSb/InSb heterostructure diode laser grown by molecular beam epitaxy. For a 5 μs pulse and a 500 Hz repetition rate the threshold current density was 1480 A cm−2 at 77 K and the maximum operating temperature was 90 K at a current density of 2680 A cm−2. Maximum peak power output was estimated to be 28 mW per facet at 77 K and 4500 A cm−2.
Surface emission of InxGa1−xN epilayers under strong optical excitation
Authors: Jiang H. X. , Lin J. Y. , Khan M. Asif , Chen Q. , Yang J. W.
Published: July 2002

Effects of strong optical excitation on the properties of surface emission from an InGaN/GaN heterostructure grown by metal-organic chemical-vapor deposition have been investigated. An intriguing feature observed was that as the excitation intensity increased the surface emission spectrum evolved abruptly from a single dominating band to two dominating bands at a critical intensity. This phenomenon has a sharp phase transition or a switching character and can be accounted for by (i) the formation of an electron–hole plasma state in the InGaN vertical cavity under strong optical excitation, (ii) the photoreflectance effect (variation of index of refraction with excitation intensity), and (c) the Fabry–Pérot interference effect in the InGaN vertical cavity. These findings are expected to have impact on the design of the laser structures, in particular on the design of the vertical-cavity surface-emitting laser diodes based on III-nitride wide-band-gap semiconductors.
Formation of a stable decagonal quasicrystal in cobalt ion implanted aluminum
Authors: Chen L. F. , Wang L. M.
Published: July 2002

A binary Al–Co decagonal quasicrystal has formed after 100 keV Co+-ion implantation into pure Al with a dose of 1.5×1017 ion/cm2, and the quasicrystal has shown a high thermal stability. The composition of stable decagonal quasicrystal is believed to be Al11Co4. Co+ ion implantation into Al first produced a multiple layer surface structure. The first layer was an amorphous layer. The second layer consisted of a decagonal quasicrystal and a coexisting amorphous phase. The amorphous phase in the implanted region where composition is close to Al11Co4 was transformed into the decagonal quasicrystal during annealing in a temperature range between 550 and 600 °C. Possible transformation mechanisms for the experimental results are discussed.
Electron paramagnetic resonance of nitrogen pairs and triads in 6H-SiC: Analysis and identification
Authors: Young C. F. , Xie K. , Poindexter E. H. , Gerardi G. J. , Keeble D. J.
Published: July 2002

A study of electron paramagnetic resonance (EPR) of nitrogen-doped 6H-SiC is reported here. By use of both first- and second-harmonic EPR detection, the predicted spectral fingerprints for nitrogen pairs and triads were found at low temperatures. The pair spectrum was present in the second harmonic, while the spectral feature for both nitrogen pairs and triads was evidenced in the first harmonic. At least one nitrogen donor of the identified pairs and triads is located at one of the two available quasicubic carbon sites, and the other(s) could be at any one of the two quasicubic sites and the hexagonal carbon site.
Error-free 2.5 Gbit/s operation of a semi-insulating buried heterostructure side-injection light-controlled bistable laser diode
Authors: Tadokoro T. , Kobayashi F. , Kishi K. , Nonaka K. , Amano C. , Itoh Y. , Kurokawa T.
Published: July 2002

We demonstrate optical response from a side-injection light-controlled bistable laser diode buried with semi-insulating InP using hydride vapor phase epitaxy. The buried surface around both the 〈110〉 and 〈−110〉 oriented mesas is flat. The bistable operation is obtained by applying control voltage to the saturable absorption region. After optimization of the device parameters, we obtained error-free operation at a bit rate as high as 2.5 Gbit/s.
Widely tunable efficient intracavity quasiphase-matched midinfrared generation
Authors: Wang Gary Y. , Zhao Jing , Chen Qiushui , Conin-Golomb Mark
Published: July 2002

We describe in this letter a novel approach to obtain a tunable midinfrared (mid-IR) laser output. By applying quasiphase-matched difference frequency generation in a periodically domain inverted LiNbO3 crystal placed inside a Cr3+:LiSAF laser cavity, more than 50 mW of mid-IR output was generated using only 1.8 watts of red diode or dye laser pumping. Wavelength tuning of the mid-IR signals from 3.3 to 4.2 μm was demonstrated by tuning only the wavelength of the Cr3+:LiSAF emission, without the need to reorient the LiNbO3 crystal for domain period adjustment.
Improvement in quality of epitaxial Zn0.5Cd0.5Se layers grown on (001) InP substrates by using an InP buffer layer
Authors: Snoeks E. , Herko S. , Zhao L. , Yang B. , Cavus A. , Zeng L. , Tamargo M. C.
Published: July 2002

Zn 1−x Cd x Se  (x≈0.5) , a II–VI wide band gap semiconductor, is grown lattice matched by molecular beam epitaxy on (001) InP substrates. The effect of incorporating an InP buffer layer on structural and optical properties of the ZnCdSe films is studied. Transmission electron microscopy shows that a reduction in the density of stacking faults by two orders of magnitude (from 5×109 down to 5×107/cm2) is realized by use of the buffer layer. Grown-in Shockley-type stacking faults are the only defects observed in the ZnCdSe. The (004) x-ray diffraction rocking curve becomes as narrow as 73 arcsec, and the photoluminescence emission peak becomes narrower and more intense. The lower defect density is attributed to the overall improved InP surface allowing for better two-dimensional nucleation of II–VI growth.
Photoluminescence in Si1−x−yGexCy alloys
Authors: Lorentzen J. D. , Loechelt G. H. , Meléndez-Lira M. , Menéndez J. , Sego S. , Culbertson R. J. , Windl W. , Sankey O. F. , Bair A. E. , Alford T. L.
Published: July 2002

We report photoluminescence from Si1−x−yGexCy films grown epitaxially on Si (100) by chemical vapor deposition. We observe significant energy shifts but no dramatic changes in the photoluminescence line shape caused by the presence of carbon. Using standard deformation potential theory to correct the epitaxial strain shifts, we conclude that the band gap of relaxed Si1−x−yGexCy alloys has a lower energy than the band gap of relaxed Si1−xGex with the same Si/Ge ratio. We propose an explanation of these results based on the assumption that carbon forms a resonant level within the conduction band of Si1−xGex.
Microscopic chemical state identification of a silicon-carbide fiber by soft x-ray photoabsorption spectroscopy
Authors: Ma Qing , Rosenberg Richard A. , Kim Changyoung , Grepstad Jostein , Pianetta Piero
Published: July 2002

Chemical states of a 140 μm silicon carbide fiber are determined by soft x-ray photo-absorption spectroscopy, using a magnetic projection photoelectron microscope, performed on the surface obtained by fracturing. The spectrum of the carbon core of the fiber has prominent π* and σ* resonance peaks and is very similar to that measured on highly oriented pyrolitic graphite, indicating a graphitic nature of the carbon core. The spectrum of the silicon carbide coating of the fiber reveals similar features to those of single-crystal silicon carbide, indicating that this coating is in the crystalline or polycrystalline phase.
Second harmonic generation in LaBGeO5:Nd3+
Authors: Capmany J. , Garcı́a Solé J.
Published: July 2002

The nonlinear properties relevant to second harmonic generation in LaBGeO5:Nd3+ are reported. This work focuses on the infrared region of the spectrum leading to blue-green laser radiation by self-frequency doubling, but covers a wide spectral range useful for other lanthanide Ln3+ rare-earth doping ions. Phase matching conditions, walk-off angle, and thermo-optic tuning sensitivity for second harmonic generation are reported.
C60 induced photoluminescence of a silica molecular sieve
Authors: Gu Gang , Ding Weiping , Du Youwei , Huang Houjin , Yang Shihe
Published: July 2002

The optical properties of the regular, 3-nm-wide hexagonal channels of the mesoporous silica molecular sieve (MCM–41) containing C60 are reported. Besides an intensive photoluminescence response at 642 nm from confined C60, a more intensive photoluminescence at 484 nm has been observed, which is considered to result from the passivation of silica zeolite with C60. Our studies indicate that both the properties of guest and host can be modified due to the interaction at the interface of them.
Synthesis of fullerenes via the thermal plasma dissociation of hydrocarbons
Authors: Alexakis Theodora , Tsantrizos Peter G. , Tsantrizos Youla S. , Meunier Jean-Luc
Published: July 2002

A thermal plasma process is described for the synthesis of fullerenes via the dissociation of hydrocarbons. The plasma reactor is equipped with a nontransferred dc plasma torch which was used to dissociate hydrocarbons. The hydrocarbons investigated include CH4, C2H2, CBrF3, CCl2F2, and C2Cl4. The best results are obtained with C2Cl4. The collection temperature of the fullerene soot in the process was found to play a critical role in the collection rate of fullerenes.
Experimental evidence of single round-trip oscillation in polarization self-modulated vertical-cavity surface emitting lasers
Authors: Ropars G. , Langot P. , Brunel M. , Vallet M. , Bretenaker F. , Le Floch A. , Choquette K. D.
Published: July 2002

The polarizations and frequencies of the two eigenstates of a vertical cavity surface emitting laser with an external cavity containing a quarter-wave plate are theoretically and experimentally analyzed. It is shown that the polarizations of these eigenstates are fixed by the neutral axes of the quarter-wave plate. The optical pulses at a frequency equal to a half of the free spectral range of the external cavity, observed through a linear polarizer, are due to beats between the two eigenstates. All these features show that such polarization self-modulated lasers oscillate in a single round trip.
White light from InGaN/conjugated polymer hybrid light-emitting diodes
Authors: Hide Fumitomo , Kozodoy Peter , DenBaars Steven P. , Heeger Alan J.
Published: July 2002

We report white light emission from InGaN/conjugated polymer hybrid light-emitting diodes (LEDs). White light sources (or sources with various colors) are achieved by combining the photoluminescence (PL) from semiconducting (conjugated) polymers with the emission from high efficiency InGaN based LEDs; the InGaN based LED provides the blue component and, simultaneously, serves as the short wavelength pump source for exciting the PL of the polymer film(s).
Improved mobility of amorphous silicon thin-film transistors deposited by hot-wire chemical vapor deposition on glass substrates
Authors: Chu V. , Jarego J. , Silva H. , Silva T. , Reissner M. , Brogueira P. , Conde J. P.
Published: July 2002

High quality thin-film transistors (TFTs) with hydrogenated amorphous silicon, a-Si:H, deposited by hot-wire chemical vapor deposition as the active layer at growth rates above 20 Å/s, have been prepared using a standard, low-temperature process on glass substrates. These TFTs show a switching ratio above 3×106, a threshold voltage of 6 V, a subthreshold slope of 1.7 V/decade, and a field effect mobility of 0.1 cm2 V−1 s1.
Enhanced electroabsorption in tensile-strained GayIn1−yAs/AlxIn1−xAs/InP quantum well structures, due to field-induced merging of light-hole and heavy-hole transitions
Authors: Schwander T. , Anhegger M. , Bürger N. , Feifel T. , Hirche K. , Korn M. , Panzlaff K. , Schröter S. , Warth M. , König P. , Hangleiter A.
Published: July 2002

Enhanced electroabsorption, due to field-induced degeneration of light-hole and heavy-hole states, is found in tensile-strained Ga0.53In0.47As quantum wells with Al0.48In0.52As barriers. This behavior seems to be specific for the AlGaInAs material system, where the Stark shift is dominated by heavy holes rather than by electrons. The effect, predicted theoretically by band structure calculations, is verified by differential electrotransmission experiments at 300 and 77 K.
Relation between the cooling time in the film-growth process of YBa2Cu3O7−δ and the electrical properties of bicrystal Josephson junctions
Authors: Ogawa T. , Koyanagi M.
Published: July 2002

We have studied the film deposition condition for bicrystal Josephson junctions to obtain reliable device parameters Ic and Rn at 77 K. In addition, it was found that the cooling time in the film-growth process of YBa2Cu3O7−δ was a very important factor to determine the electrical properties of bicrystal Josephson junctions with the misorientation angle θ=36.8°. In the three regions of the cooling time as 5–6, 10–20, and more than 30 min, the junctions’ Tc were above 87, 50–86, and above 86 K, and the average values of the IcRn products at 77 K were 0.12 mV, 50 μV, and 80 μV, respectively. The junction parameters and the shapes of the I–V curves were changed due to the change of the cooling time.
Semiconducting epitaxial films of metastable SrRu0.5Sn0.5O3 grown by pulsed laser deposition
Authors: Christen H.-M. , Boatner L. A. , Budai J. D. , Chisholm M. F. , Gea L. A. , Norton D. P. , Gerber Christoph , Urbanik Michael
Published: July 2002

Synthesis of the perovskite solid solution that forms between metallic SrRuO3 and insulating SrSnO3 is reported. This material is proposed as a conducting thin-film electrode/epitaxial-substrate material. While the bulk solid solution could not be formed, thin films of single-phase SrRu0.5Sn0.5O3 were grown on (001) KTaO3 single-crystal substrates by pulsed laser deposition. These films exhibit a commensurate in-plane lattice match with KTaO3 (a=3.989 Å); accordingly, the lattice constant of SrRu0.5Sn0.5O3 is larger than that of commonly used conducting-oxide thin-film electrodes (e.g., SrRuO3, LaNiO3, and YBa2Cu3O7−δ). The SrRu0.5Sn0.5O3 films were analyzed using x-ray diffraction, Rutherford backscattering, atomic force microscopy, Z-contrast transmission electron microscopy, and Hall effect measurements. The results revealed excellent atomic-scale structural properties, flat surfaces (13 Å rms roughness), and p-type conduction with a room-temperature resistivity of 16 mΩ cm.
Effect of magnetic field on breakdown voltage characteristics of a multigap pseudospark
Authors: Sriram D. , Jain K. K.
Published: July 2002

An experimental investigation of the effect of magnetic field on the breakdown voltage characteristics of a multigap pseudospark device, with hydrogen gas, in a hollow anode–cathode, as well as a hollow cathode–anode configuration, is presented. The breakdown pressure at a particular discharge voltage increases with the increase in the applied axial magnetic field, and the magnitude of the increase is more pronounced at lower discharge voltages causing a right shift to the characteristic discharge curve in both the configurations. Application of a transverse magnetic field also resulted in a shift of the characteristic discharge curve towards the right. The observed results are compared and discussed with that found for parallel electrode geometry.
High characteristic voltages in Nb/p-type InAs/Nb Josephson junctions
Authors: Chrestin A. , Merkt U.
Published: July 2002

An investigation of superconductor/semiconductor/superconductor Josephson junctions with separations between the Nb superconducting electrodes down to 20 nm is presented. To achieve such short distances, a preparation technique employing an anodic Nb oxide film as a spacer has been developed. The Nb electrodes are coupled through the quasi two-dimensional electron gas in the native inversion layer at the surface of p-type InAs. High characteristic voltages up to 1.35 mV at T=2 K are observed. A sensitive dependence of the magnitude of the characteristic voltage on interface quality is demonstrated. Good agreement is found between the experimental temperature dependence of the critical current and a theoretical model valid for short weak links.
High
-T
c
edge junctions with Y0.8Pr0.2Ba2Cu2.7Co0.3O7−δ barrier layers near the metal–insulator transition
Authors: Antognazza L. , Char K. , Geballe T. H.
Published: July 2002

We report the use of an epitaxial barrier of Y0.8Pr0.2Ba2Cu2.7Co0.3O7−δ in order to study the effect of Pr in the barrier layer. The bulk behavior of this Pr and Co-doped YBa2Cu3O7−δ (YBCO) material shows it is just on the insulating side of the metal–insulator transition. We present the temperature dependence of the critical current Ic and the resistance Rn for junctions with 150-, 300-, and 450-Å-thick barriers of Y0.8Pr0.2Ba2Cu2.7Co0.3O7−δ. The temperature dependence of the critical currents was analyzed within the framework of the proximity effect of de Gennes. The fittings show that the junctions are in the dirty limit with a diffusion constant of D=2.3 cm2/s and a pair-breaking scattering time of 8.6×10−14 s. The value of the diffusion constant is three times lower than the value we have found in the pure 14% Co-doped YBCO barrier, showing that the Pr doping decreases the mean free path in the junction barrier. The presence of the inelastic pair-breaking process was identified as a key issue in the barrier near the metal–insulator transition.
Gain and noise bandwidth of NbN hot-electron bolometric mixers
Authors: Ekström H. , Kollberg E. , Yagoubov P. , Gol’tsman G. , Gershenzon E. , Yngvesson S.
Published: July 2002

We have measured the noise performance and gain bandwidth of 35 Å thin NbN hot-electron mixers integrated with spiral antennas on silicon substrate lenses at 620 GHz. The best double-sideband receiver noise temperature is less than 1300 K with a 3 dB bandwidth of ≈5 GHz. The gain bandwidth is 3.2 GHz. The mixer output noise dominated by thermal fluctuations is 50 K, and the intrinsic conversion gain is about −12 dB. Without mismatch losses and excluding the loss from the beamsplitter, we expect to achieve a receiver noise temperature of less than 700 K.
Multi-wavelength lasing oscillation of a Vernier-type unidirectional Er3+-doped fiber compound ring
Authors: Zhao Y. , Shu C.
Published: July 2002

A Vernier-type unidirectional Er3+-doped fiber compound ring is constructed. Simultaneous lasing oscillations at multiple wavelengths are obtained by adopting a number of fiber gratings as the wavelength selective elements. The output exhibits reduced linewidths and nearly identical powers at the emission wavelengths, and the spectrum is free from parasitic oscillations.
The impact of using AlGaAs as a carrier supplying layer in an InAlAs/InGaAs high electron mobility transistor structure on thermal stability
Authors: Tanabe Mitsuru , Kashiwagi Noboru , Matsuno Toshinobu , Tamura Akiyoshi
Published: July 2002

The impact of using a thin AlGaAs layer as a carrier supplying layer in an InAlAs/InGaAs high electron mobility transistor structure (HEMT) on thermal stability has been investigated. The new structure exhibited no deterioration in its sheet carrier concentration after annealing for 15 min at 450 °C in nitrogen atmosphere, while in the conventional HEMT structure 20% deterioration was observed. The secondary ion mass spectroscopy analysis indicated that this excellent thermal stability originated from the absence of reaction between dopant and fluorine. By exposing the new and conventional HEMT structure in a fluorine atmosphere, it was obvious that the new structure had at least a five times higher tolerance to fluorine.
GaAs based anti-resonant Fabry–Perot saturable absorber fabricated by metal organic vapor phase epitaxy and ion implantation
Authors: Lederer M. J. , Luther-Davies B. , Tan H. H. , Jagadish C.
Published: July 2002

We have fabricated an antiresonant Fabry–Perot saturable absorber (A-FPSA), for potential use in laser passive mode locking, using metalorganic vapor phase epitaxy followed by ion implantation and thermal annealing. We show that the implantation/annealing cycle shortens the free-carrier dwell time without degrading the other optical properties of the A-FPSA.
A lower bound on implant density to induce wafer splitting in forming compliant substrate structures
Authors: Freund L. B.
Published: July 2002

The physical system under study is a bonded semiconductor wafer into which hydrogen ions have been implanted within a planar zone, typical of a configuration used in forming semiconductor-on-insulator compliant substrates by wafer splitting. Under the assumption that splitting is a consequence of crack growth driven by hydrogen gas pressure, a lower bound estimate of the implant density required for large area crack growth is obtained which, for an ideal gas, depends only on the cohesive strength of the material and on temperature.
Porous silicon lateral superlattices
Authors: Lérondel G. , Romestain R. , Vial J. C. , Thönissen M.
Published: July 2002

Lateral superlattices in porous silicon layers have been generated. Using the photosensitivity of the etching process, periodic stripes are formed not only on the surface but also in the depth of the layer. The modulation depth depends on the illumination wavelength. The periodicity is obtained from the interference pattern of two laser beams, and can be easily modified by changing the wavelength or the incidence angles of the beams. The samples formed by this procedure were characterized by light diffraction. Two-dimensional structures can also be obtained by rotating the sample or by interference of four laser beams. This kind of in-depth lithography and the resulting low-cost fabrication of gratings out of porous silicon offer a wide range of potential applications in integrated optics and photonics.
Photophysical and photochemical investigations of fullerene presence in amorphous hydrogenated carbon films
Authors: Chen J. Q. , Meeker D. L. , Barashkov N. N.
Published: July 2002

The plasma-enhanced chemical vapor deposition system was used to grow amorphous hydrogenated carbon films deposited on silicon substrates. Extracts of the films were obtained by treatment with boiling cyclohexane solvent. The absorption spectra of these extracts showed the existence of small quantities of fullerenes. Using the molar extinction coefficient of C60 in cyclohexane, the mass of fullerenes in the films was estimated to be about 0.019 mg. C60 induced fluorescence quenching of anthracene was also observed. Additional evidence for the presence of fullerenes was based on their capability to accelerate the photo-oxidation of anthracene through the generation of singlet oxygen with a high quantum yield under ultraviolet irradiation.
Dielectric fluid motors
Authors: Otsubo Yasufumi , Edamura Kazuya
Published: July 2002

On the application of high electric fields to a dielectric fluid, a convective motion of the fluid is induced. By controlling the fluid motion in nonuniform dc fields, a new type of fluid motor is developed. An angular velocity of more than 15 s−1 (150 rpm) can be achieved at a dc voltage of 5 kV for a motor with a rotor radius of 10 mm. The efficiency of energy transformation from electric to kinetic energy is about 4%. Since magnetic fields and switching circuits are not required, the advantage of the fluid motor will be enhanced by size reduction. The dielectric fluid motor is attractive as a source of mechanical energy in a micromachine.
Reflection high-energy electron diffraction oscillations during growth of GaAs at low temperatures under high As overpressure
Authors: Shen A. , Horikoshi Y. , Ohno H. , Guo S. P.
Published: July 2002

Reflection high-energy electron diffraction oscillations were observed during molecular beam epitaxy of GaAs at temperatures as low as 150 °C under various V/III beam equivalent pressure ratios using As4 as an arsenic source. At the As/Ga beam equivalent pressure ratio of 40, the amplitude of the oscillations was shown to first decrease with the decrease of substrate temperature and then increase when the temperature was further lowered to below 300 °C. The oscillation characteristics at 200 °C were comparable to those recorded at around 600 °C. At fixed temperatures in the low temperature region (<350 °C), the oscillations were shown to be greatly affected by the V/III ratio, with the maximum amplitude at a certain V/III ratio which depends on the substrate temperature used. The strong oscillations at low temperatures and at high V/III ratios were tentatively explained by assuming that the migration of Ga atoms is enhanced on the surface passivated by excess As.
Nanostructure array fabrication with a size-controllable natural lithography
Authors: Haginoya Chiseki , Ishibashi Masayoshi , Koike Kazuyuki
Published: July 2002

A simple technique for size-controllable nanostructure array formation has been developed, using self-assembled polystyrene beads whose diameters can be arbitrarily reduced by reactive ion etching. We have produced a hole array of 83 and 157 nm diameter with 200 nm pitch on Si substrate. This technique can find potential applications in many areas of science and technology.
Resistless patterning for selective growth
Authors: Shiralagi Kumar , Tsui Raymond , Goronkin Herbert
Published: July 2002

We present a simple and novel method of resistlessly patterning GaAs substrates with an oxide mask. The GaAs surface native oxide is optically modified into a stable gallium oxide mask, which then allows InAs to be grown with excellent selectivity by chemical beam epitaxy. The conventional approach to pattern wafers for selective growth is to use photoresist to pattern the silicon nitride or oxide first deposited on the wafers. Photoresist residue can remain even after elaborate cleaning and the molecular scale features can impede selectivity during growth. This method is a one-step resistless process that eliminates such photoresist related problems. Our understanding of the patterning process and results on the selective growth of InAs are presented.
On the spectral strength of the noise source entering the transfer impedance method
Authors: Shiktorov P. , Gružinskis V. , Starikov E. , González T. , Mateos J. , Pardo D. , Reggiani L. , Varani L.
Published: July 2002

We show that within the transfer impedance method, the spectral strength of the local noise source originally defined by Van Vliet et al. [J. Appl. Phys. 46, 1804 (1975)] should be more generally replaced by the two-point spectral density of current fluctuations. The theoretical arguments are further supported by numerical results for the voltage noise spectrum associated with conduction–current fluctuations in submicron n+nn+ structures. The above two-point spectral strength is, in general, a complex quantity related to fluctuations induced by velocity fluctuations only.