bluuebunny/crossref_metadata_2025 huggingface dataset:
A trimodal resonator for three mutually perpendicular magnetic fields
Authors: Stievater T. H. , Lim M. J. , Colosimo P. , Michniak R. A. , Bucksbaum P. H. , Conti R. S.
Published: July 2002

We describe a trimodal resonator for the simultaneous delivery of three perpendicular magnetic fields. The resonator consists of a shielded loop single-mode radio frequency (rf) resonator placed inside of a bimodal waveguide microwave resonator. The microwave modes are nondegenerate, tunable over a range of 100 MHz, and have typical Q factors of 150 and 200. The rf mode is tunable over a range of 125 MHz, and has a typical Q of 45. Control of the relative phase between the three fields is demonstrated. The resonator will be used to drive three magnetic dipole transitions coherently between Zeeman states in the ground state of Rb87.
Substrate heater for the growth of epitaxial silicon films
Authors: Deming Matthew , Varhue Walter , Adams Edward , Lavoie Mark
Published: July 2002

The single wafer processing of epitaxial Si films requires that special attention be paid to the design of the substrate heater assembly. This document describes the evolution and testing of an in situ heater used to deposit epitaxial Si films at temperatures as high as 700 °C. One problem encountered was the production of excessive levels of ultraviolet radiation which contributed to the desorption of water vapor from the vacuum chamber walls during the in situ cleaning process. A second problem involved the formation of a molybdenum containing film that poisoned epitaxial growth. A final proven in situ heater design is presented which avoids these problems.
Single-movement fixed-exit channelcut x-ray monochromator based on profiled surfaces
Authors: Oestreich Sebastian , Kaulich Burkhard , Susini Jean
Published: July 2002

A fixed-exit channelcut monochromator, which requires only a single rotational movement, has been developed. It is based on profiled reflecting surfaces machined into a Si monocrystal. Two geometries have been evaluated theoretically: one for the energy range from 5 to 30 keV and another for the energy range from 3 to 8 keV. The latter was designed to fulfil the requirements at an x-ray microscopy beamline, where the monochromator must not introduce any change in the phase space of the x-ray beam in order to limit aberrations when microfocusing the beam with a Fresnel zone plate. A monochromator with a very simple and compact mechanical design has been built with this crystal and successfully tested under ultrahigh vacuum. The measured energy resolution (<1 eV at 5 keV) and throughput are close to the theoretical figures, and the monochromator’s suitability for spectroscopic investigations has been demonstrated. The measured beam exit stability was 150 μm over a 3.5–8 keV range. The influence of the crystal geometry on its energy acceptance, phase space degradation, throughput, and acceptable heat load is discussed.
Electronic simulation of a multiterminal quantum Hall effect device
Authors: Sosso A. , Capra P. P.
Published: July 2002

A circuit with only resistors and unity gain amplifiers can be proven to be equivalent to the Ricketts and Kemeny electrical model of multiterminal quantum Hall effect (QHE) devices. By means of the new equivalent circuit, commercial software for electronic circuit analysis can be used to study a QHE measurement system. Moreover, it can be easily implemented, and we were able to build a circuit that simulates the electrical behavior of a QHE device. Particular care was taken in the design to reduce the effect of parasitic capacitances, which act as loads connected to the device terminals. Bootstrap buffers have been adopted to significantly reduce the capacitance of input stage. The small residual loading effect can be calculated and eliminated, allowing simulation of a QHE device with good accuracy.
Investigation of the radio frequency magnetic field inside a hollow cylinder used for nuclear magnetic resonance imaging
Authors: Labiche Alexandre , Kan Siew , Leroy-Willig Anne , Wary Claire
Published: July 2002

The homogeneity of the radio frequency (rf) axial magnetic field inside a solenoid composed of a set of current-carrying coils can be improved by imposing appropriate current densities in the various loops that constitute the structure. In the case of a hollow cylinder made from a single sheet of copper foil, the rf field so generated can also attain a similar degree of homogeneity without current compensation provided the copper foil is five to six times thicker than the skin depth and the cylinder’s form factor (diameter/length) is of the order or less than 0.5. Numerical calculations based on some basic equations allow us to predict the rf field pattern of a cylinder of given dimensions. Experimental results obtained from a 32 MHz transmission line resonator show good agreement between theory and practice. The filling factor of this type of cylinder can also be evaluated from these calculations.
Two-dimensional X pendulum vibration isolation table
Authors: Barton Mark A. , Uchiyama Takeshi , Kuroda Kazuaki , Kanda Nobuyuki , Ishizuka Hideki
Published: July 2002

We have extended to two dimensions a previously developed vibration isolation table using crossed wire suspensions (X mechanisms). A load table is suspended using a combination of normal and upside-down X mechanisms so that it moves freely with a very long period in both horizontal directions but is moderately stiff in all other degrees of freedom. Periods of 5 s are easily achievable. The transfer function of the prototype reported here contains a number of elastic mode resonance peaks, but it is shown by analysis how to reduce or eliminate nearly all of these.
Nonswitching van der Pauw technique using two different modulating frequencies
Authors: Kim G. T. , Park J. G. , Park Y. W. , Müller-Schwanneke C. , Wagenhals M. , Roth S.
Published: July 2002

We present a nonswitching van der Pauw technique using two independent ac current sources and two lock-in amplifiers. This technique may be useful to measure the resistance of delicate samples that might be easily damaged by electric shocks induced from switching, and can be extended to measure the anisotropy of resistance.
Over-relaxation of misfit strain in heavily carbon-doped GaAs grown by metalorganic molecular beam epitaxy after annealing
Authors: Sohn Hyunchul , Weber E. R. , Nozaki Shinji , Takahashi Kiyoshi
Published: July 2002

Using double crystal x-ray diffractometry (XRD) and transmission electron microscopy (TEM), the annealing effects on heavily carbon-doped GaAs films were studied. From isochronal annealing, the evolution of compressive strain in carbon-doped GaAs films was observed by XRD. From cross-sectional TEM, unusual misfit dislocations with extra-half planes on the GaAs side were observed in the sample annealed at 900 °C for 30 min in addition to normal misfit dislocations with extra-half planes on the film side. A possible mechanism for the formation of such misfit dislocations is proposed based on the over-relaxation of misfit strain in the film.
Measurement of thermal diffusivity of air using photopyroelectric interferometry
Authors: Wang Chinhua , Mandelis Andreas
Published: July 2002

A new photopyroelectric (PPE) method for measuring the thermal diffusivity of ambient gases with optimal precision is introduced. The technique is based on destructive PPE interferometric detection inside a thermal-wave resonant cavity with an optically transparent wall. A new PPE sensor design generating purely thermal-wave interference is used to improve the signal-to-noise ratio and the measurement dynamic range and precision by suppressing the large optically transmitted base line signal. Cavity-length scanning is employed and the thermal diffusivity of air is measured with third-significant-figure precision. Comparisons of measurement precision are made with experimental results obtained using a transparent-wall PPE thermal-wave cavity in the single-ended (noninterferometric) mode. The physical signal generation mechanisms are also discussed.
Determination of Landau level lifetimes in AlGaAs/GaAs heterostructures with a ps free electron laser
Authors: Heiss W. , Auer P. , Gornik E. , Pidgeon C. R. , Langerak C. J. G. M. , Murdin B. N. , Weimann G. , Heiblum M.
Published: July 2002

Previous determinations of Landau level lifetimes in GaAs/AlGaAs heterostructures from saturation cyclotron resonance measurements have been confused by heating effects. We have utilized a ps free electron laser to show that for samples with sheet concentration less than 3×1011 cm−2, true saturation of cyclotron resonance is observable at high magnetic fields, in the presence of polaron nonparabolicity. However, at higher concentrations, the polaron is screened and saturation is no longer possible. At low magnetic fields (i.e., long wavelengths) where the polaron nonparabolicity is negligible, saturation is not possible for any sheet density. It is confirmed that the lifetime of the first excited Landau level has an inverse dependence on carrier density.
Theoretical analysis of the geometries of the luminescent regions in porous silicon
Authors: Hill Nicola A. , Whaley K. Birgitta
Published: July 2002

The luminescence energies of a variety of crystalline silicon nanostructures are calculated using a time-dependent tight-binding technique. The calculated energies are compared with measured values for porous silicon samples to determine the geometries of the regions in which electron-hole recombination occurs. We observe a correlation between luminescence wavelength and nanostructure which is consistent with the porosity changes during the etching process. We conclude that porous silicon samples which emit visible light are composed of small crystallites, and that the active regions in longer wavelength emitters are wirelike structures.
Instantaneous measurement system of the effective photon energy for a single shot x-ray pulse radiation
Authors: Ohzu Akira , Ito Kazunori , Matoba Tohru , Kawanishi Shunichi , Arisawa Takashi
Published: July 2002

For a short pulse x-ray radiation with extremely broad spectrum such as Bremsstrahlung, the effective photon energy cannot be determined by conventional x-ray detectors with only a single x-ray pulse shot. An instantaneous measurement system capable of determining the energy with a single shot has been developed. The system is made of a metal–oxide–semiconductor linear array image sensor, a scintillation phospher, and an absorber material, and a control system of the sensor. The energy of a hard x-ray pulse with a short pulse duration of 500 ns is determined with this system. It is shown that the system can determine the energy more quickly and accurately than with the conventional method.
A novel technique for p-type doping of ZnSe
Authors: El-Emawy A. A. , Qiu Y. , Osinsky A. , Littlefield E. , Temkin H.
Published: July 2002

Thermally cracked nitric oxide (NO) has been used to grow heavily doped p-type ZnSe layers. Net acceptor densities as high as ∼4×1018 cm−3 were obtained, as determined by capacitance–voltage profiling, in molecular beam epitaxial growth at 250 °C. Cracker efficiency as a function of temperature and the nitric oxide flow rate is discussed and correlated with the doping level in the epitaxial layer.
Kinetic modeling of the atomic layer epitaxy processing window in group IV semiconductor growth
Authors: Eres Gyula
Published: July 2002

A kinetic model based on two elementary reaction steps was used for exploring the prospects of atomic layer epitaxy (ALE) on the (100) surface of group IV semiconductors using hydridic source gases. Equating the chemisorption step with depletion of active sites, and the molecular hydrogen desorption step with regeneration of active sites allowed first-principles kinetic modeling of the trends in thin film growth, unencumbered by the lack of mechanistic details of chemisorption and surface decomposition. The combination of first-order depletion and first-order regeneration steps was found to be most favorable for achieving ALE type behavior. The model shows that the ALE window is highly sensitive to the duration of the depletion (chemisorption) cycle suggesting short duration and well defined pulses as the most effective method of source gas delivery.
Visible electroluminescence from a novel β-SiC/p-Si n-p heterojunction diode prepared by rapid thermal chemical vapor deposition
Authors: Hwang J. D. , Fang Y. K. , Wu K. H. , Yaung D. N.
Published: July 2002

A novel structure of β-SiC/p-Si has been reported to emit visible electroluminescence (EL). The β-SiC is grown directly on a Si substrate by rapid thermal chemical vapor deposition (RTCVD) technology. The mechanism of EL emission is shown as a porous silicon (PS) layer. The PS is formed unintentionally at β-SiC/p-Si interface owing to a large lattice mismatch (20%) between β-SiC and Si substrates. In addition, the heterojunction diode exhibits excellent rectifying behavior. The ideality factor n and rectification ratio at 1.0 V are 1.8 and 340, respectively.
Electron velocity overshoot in a GaAs-based p-i-n nanostructure semiconductor observed by transient subpicosecond Raman spectroscopy
Authors: Grann E. D. , Tsen K. T. , Sankey O. F. , Ferry D. K. , Salvador A. , Botcharev A. , Morkoç H.
Published: July 2002

We report direct measurements of nonequilibrium electron distributions and electron drift velocities in a GaAs-based p-i-n nanostructure semiconductor by using transient subpicosecond Raman spectroscopy. Experimental conditions are such that the velocity overshoot phenomenon dominates the transport properties of the photoexcited carriers. These experimental results are compared with ensemble Monte Carlo calculations.
Direct modulation and optical confinement factor modulation of semiconductor lasers
Authors: Frommer A. , Luryi S. , Nichols D. T. , Lopata J. , Hobson W. S.
Published: July 2002

A method for modulation of semiconductor lasers based on the modulation of the optical confinement factor is demonstrated. Using this method, an enhanced −3 dB bandwidth is observed in agreement with the small signal rate equation analysis. A modulation response that drops at high frequencies slower than the conventional direct current modulation response is achieved.
Thermoelastic property of the torsion fiber in the gravitational experiments
Authors: Luo Jun , Hu Zhong-Kun , Hsu Houtse
Published: July 2002

The thermoelastic and the nonlinear properties of a torsion fiber were studied. A symmetric disk torsion pendulum was designed to measure the temperature coefficient of the torsion spring constant of a tungsten fiber at room temperature, and the result shows that the ambient temperature fluctuation with ±1 °C would introduce a considerable uncertainty about ∓165 ppm in the torsion spring constant of the fiber. It is suggested that the thermoelasticity of the torsion fiber should be measured in a precision torsion pendulum experiment.
Improved measurements of noise and resolution of x-ray framing cameras at 1–2 keV
Authors: Pawley Carl J. , Deniz A. V.
Published: July 2002

We describe x-ray framing cameras that were developed for experiments on the Nike laser system at the Naval Research Laboratory. These cameras have internal impedance matching to allow use of 50Ω pulsing systems from 100 ps to several nanoseconds, or for long pulse/dc operation. The cameras have been optimized for spatial resolution and low light scatter using aluminized phosphors. One of these cameras has been coupled to a charge coupled device camera and the total system was tested for resolution and image noise using both electrons and x rays. The spatial resolution was found to be well fitted to a Gaussian modulation transfer function with a value of 0.5 at 10 lp/mm. A detailed analysis of the noise in the images was performed for electrons and x rays. The noise in the images is determined by a detective quantum efficiency of approximately 10% for 1–2 keV x-ray photons.
Magnetic axial field measurements on a high resolution miniature scanning electron microscope
Authors: Khursheed Anjam
Published: July 2002

This article presents magnetic axial field measurements for a high resolution miniature scanning electron microscope (SEM). The experimental results correlate well with simulation predictions. The SEM has a total height of less than 55 mm. Based upon measured axial field distributions, the on-axis spherical and chromatic aberration coefficients for a 1 keV primary beam are predicted to be 0.36 and 0.6 mm, respectively, for a working distance of 7.5 mm. These aberrations are an order of magnitude smaller than those for conventional SEMs with comparable working distance conditions. The SEM design uses an in-specimen chamber permanent magnet objective lens that lies outside vacuum and can easily be replaced.
Multiple-reflection interferometer for high accuracy measurement of small vibration displacement
Authors: Lee Doo Hee , Kim Byoung Yoon
Published: July 2002

A novel multiple-reflection interferometer is developed for the accurate measurement of sinusoidal vibration amplitudes, and its characteristics are analyzed theoretically and experimentally. The multiple-reflection system employs a right-angle prism and a convex lens, which is located in the probe beam path of a Michelson interferometer. The performance of the multiple reflection interferometer as a function of reflection number was assessed at the vibration frequency of 1250 Hz using Bessel function null method.
Space-time resolving vacuum ultraviolet spectrometer based on a rotating polyhedral mirror
Authors: Lin Xiaodong , Xie Jikang
Published: July 2002

Using a rotating polyhedral mirror and a vacuum ultraviolet (VUV) monochromater, a space-time resolving VUV diagnostic system is developed. Measurement of the O VI (103.2 nm) radiation on the HT-6M tokamak shows that the time resolution of the system is better than 4 ms and the space resolution is better than 2 cm. Compared with traditional instruments, this system has improved measurement efficiency, and error from shot-to-shot discharge variations is avoided.
A metallic microcantilever electric contact probe array incorporated in an atomic force microscope
Authors: Ondarçuhu T. , Nicu L. , Cholet S. , Bergaud C. , Gerdes S. , Joachim C.
Published: July 2002

We present the realization and performance of a multiprobe microcontactor made of an array of metallic microcantilevers inserted in an atomic force microscope (AFM). This instrument permits simultaneous AFM imaging and electrical characterization of nanoscale devices. It is therefore well adapted for future generations of molecular devices. The probes are 2-μm-wide metallic cantilevers that are brought in contact with 3 μm×3 μm metallic pads of a nanocircuit using a nanopositioning table. The performance of the instrument, tested on mesoscopic metallic wires and carbon nanotubes, shows that the reproducibility of the electrical contact between the probes and the circuit is better than 99.2%.
Tip–sample distance feedback control in a scanning evanescent microwave probe for nonlinear dielectric imaging
Authors: Duewer Fred , Gao C. , Xiang X.-D.
Published: July 2002

We implemented tip–sample distance control in a scanning evanescent microwave probe for nonlinear dielectric microscopy. With the analytic expression of the tip–sample capacitance as a function of tip–sample distance, we can quantitatively regulate the tip–sample separation and independently measure the dielectric nonlinearity by application of an ac bias voltage. Simultaneous imaging of topography and ferroelectric domains has been demonstrated on periodically poled LiNbO3 single crystals.
Arbitrary wave-form-pulsed power source for flash-lamp-pumped solid-state lasers
Authors: Arya R. , Thomas M. Joy , Bhujle A. G. , Bhawalkar D. D.
Published: July 2002

An arbitrary wave-form-pulsed power source for driving pulsed flash lamps electrically to pump quasi-continuous-wave Nd:YAG lasers has been developed. It is based on a high-frequency switching converter as opposed to conventional pulse-forming network or linear power amplifier circuit-based pulse generators. The system can generate rectangular pulses through the flash lamp with fine adjustment in pulse parameters over a wide range. The system can also generate an arbitrary-shaped pulsed current within a bandwidth of 500 Hz. The design of the system and the results in the form of rectangular- and arbitrary-shaped pulsed-current wave forms with different pulse parameters are presented. In addition, a burst of consecutive pulses with different arbitrary shapes can also be generated as desired or as programed. The developed pulsed power source offers advantages of more flexibility in control and adjustment of output pulse parameters, arbitrary-shaped pulse generation, better efficiency, compactness, and higher reliability as compared to the pulsed power sources based on normal schemes. The electronic system developed is of immense value in studying the dependence of flash-lamp impedance, spectral output, and energy-transfer efficiency on pulse parameters as well as optimization of these parameters for use in various laser material processing applications.
PC control and data processing in relation with a standalone laser beam analyzer
Authors: Visan T. , Sporea D. G.
Published: July 2002

In this note we present a PC-based remote control and data processing setup and the associated software, developed in LabVIEW, working in conjunction with a laser beam analyzer. The setup expands the imaging processing techniques for the laser beam profile, especially in relation to the three-dimensional data representation and manipulation, by using the strong graphical processing and presentation libraries of the HIQ and IMAQ Vision software packages. One novelty of the proposed program consists in its multi-image processing ability with regard to images acquired under different conditions, and which have to be processed aligned to their centroids and their major axes.
Development of a novel fast frequency modulation scheme for the Joint European Torus multichannel reflectometer
Authors: Deliyanakis N.
Published: July 2002

A novel frequency modulation scheme has been developed for the multichannel reflectometer used to measure density profiles and density fluctuations on the Joint European Torus (JET) tokamak. This reflectometer normally uses slow frequency sweeping (6 ms), combined with fixed-frequency operation, to measure the group delay, as well as plasma fluctuations, at ten different microwave frequencies. The novel scheme uses continuous frequency modulation on a time scale much shorter (1/65 μs) than that of plasma fluctuations, the main aim being to make the group delay measurement more robust against plasma fluctuations. This article discusses the theoretical background of the scheme, gives a detailed description of the system, and presents results from plasma measurements. Although the implementation used suffered from an excessive power-dependent group delay distortion (resulting in a positional error of 10 cm), the main objectives have been achieved.
Mixed carrier conduction in modulation-doped field effect transistors
Authors: Schacham S. E. , Haugland E. J. , Mena R. A. , Alterovitz S. A.
Published: July 2002

The contribution of more than one carrier to the conductivity in modulation-doped field effect transistors (MODFET) affects the resultant mobility and complicates the characterization of these devices. Mixed conduction arises from the population of several subbands in the two-dimensional electron gas (2DEG), as well as the presence of a parallel path outside the 2DEG. We characterized GaAs/AlGaAs MODFET structures with both delta and continuous doping in the barrier. Based on simultaneous Hall and conductivity analysis we conclude that the parallel conduction is taking place in the AlGaAs barrier, as indicated by the carrier freezeout and activation energy. Thus, simple Hall analysis of these structures may lead to erroneous conclusions, particularly for real-life device structures. The distribution of the 2D electrons between the various confined subbands depends on the doping profile. While for a continuously doped barrier the Shubnikov–de Haas analysis shows superposition of two frequencies for concentrations below 1012 cm−2, for a delta doped structure the superposition is absent even at 50% larger concentrations. This result is confirmed by self-consistent analysis, which indicates that the concentration of the second subband hardly increases.
Thin dielectric degradation during silicon selective epitaxial growth process
Authors: Shih Yang-Chin , Zhang Guobiao , Hu Chenming , Oldham William G.
Published: July 2002

A fundamental issue in silicon selective epitaxial growth (SEG) processes is the impact of the pre-epitaxy silicon surface treatments and the SEG ambient on the properties of thin insulating materials exposed to the preclean environment. In this study, we compare pinhole formation in 10–50 nm thermal oxides with more robust oxide/nitride composites of similar thickness. The degradation of thin thermal oxide is attributed to pinhole formation and expansion in the ultrathin oxide layers during ex situ pre-epi surface treatments, in situ H2 prebake, and selective epitaxial deposition process. The superior resistance of oxide/nitride/oxide (ONO) structures to dielectric degradation may be attributed to the existence of the sandwiched silicon nitride layer which suppresses the mechanism of oxide decomposition during the pre-epitaxy wet cleaning, and the selective epitaxial growth processes.
Core-level shifts of silicon–hydrogen species on chemically treated Si surfaces studied by high-resolution x-ray photoelectron spectroscopy
Authors: Bjorkman C. H. , Alay J. L. , Nishimura H. , Fukuda M. , Yamazaki T. , Hirose M.
Published: July 2002

Chemical shifts of Si–Hx (x=1,2) species on Si surfaces obtained by ex situ chemical treatment have been evaluated by high-resolution x-ray photoelectron spectroscopy at a take-off angle of 5°. Optimizing the water rinse and sample loading conditions enables identification of the Si–Hx components of the Si 2p core-level spectra, whose intensities display strong dependence on crystallographic orientation and surface treatment. NH4F-treated Si(111) exhibits almost exclusive monohydride termination which induces a chemical shift of 250 meV relative to the bulk component. On the other hand, 4.5% HF-treated Si(111) and 1% HF-treated Si(100) surfaces show increased dihydride termination with an associated shift of 480 meV.
Phosphorus diffusion effect on defect structure of silicon with oxygen precipitates revealed by gold diffusion study
Authors: Yakimov E. , Périchaud I.
Published: July 2002

Gold diffusion was used to understand the influence of phosphorus diffusion on defect structure of two step annealed Czochralski silicon wafers which contain oxygen related precipitates. Thanks to deep level transient spectroscopy measurements and use of relations already published, it was found that substitutional gold concentration is independent of oxygen precipitation, while phosphorus diffusion, by means of the injection of self-interstitials in the bulk, shrinks the oxygen precipitates and increases substitutional gold concentration approximately to the solubility limit.
Photoluminescence studies of hydrogenated GaAlAs grown by metalorganic vapor phase epitaxy
Authors: Muralidharan R. , Srinivasan T. , Tyagi Renu , Padmavati M. V. G. , Bal Mahesh , Purohit R. K. , Agarwal S. K.
Published: July 2002

Photoluminescence studies on ‘‘as-grown’’ as well as hydrogenated undoped AlGaAs epitaxial layers grown by metalorganic vapor phase epitaxy has been carried out to study the effective passivation of defect centers. We report the observation of defect bound excitons which are effectively passivated by hydrogenation and the preferential enhancement of excitonic features after hydrogenation.
Integrated high T
c superconducting magnetometer with multiturn input coil and grain boundary junctions
Authors: Shen Y. Q. , Sun Z. J. , Kromann R. , Holst T. , Vase P. , Freloft T.
Published: July 2002

We have fabricated and tested integrated magnetometers based on the superconducting quantum interference device (SQUID). The magnetometer consists of two patterned films of YBa2Cu3O7, separated by an insulating layer of SrTiO3. A multiturn input coil was integrated on top of the SQUID, where the misorientation angle in a SrTiO3 bicrystal substrate was used to form the grain boundary junctions. The noise spectrum was characterized at 77 K and showed that above 10 Hz the magnetometer sensitivity is limited by a white noise level of around 4×10−5 Φ0/Hz1/2. In the 4 mm × 4 mm detection area of the input coil, this translates into a magnetic field sensitivity of 320 fT/ Hz1/2 at 100 Hz. Compared to the theoretical value of an optimized SQUID the white noise level of the magnetometer is two times higher. Below 10 Hz the noise is dominated by 1/f noise mainly due to the critical current fluctuations.
Cyclotron mass of two-dimensional holes in strained-layer GaAs/In0.20Ga0.80As/GaAs quantum well structures
Authors: Lin Shawn-Yu , Wei H. P. , Tsui D. C. , Klem J. F.
Published: July 2002

We report a systematic study of the effective mass of two-dimensional (2D) holes in a series of ten p-type GaAs/In0.20Ga0.80As/GaAs quantum well structure samples. The 2D hole density and its effective mass (m*)are independently determined from Shubnikov–de Haas and cyclotron resonance measurements at 4.2 K. We find the m* increases from (0.123±0.005) me to (0.191±0.015) me as the 2D hole density is varied from 0.54×1011/cm2to 8.5×1011/cm2. The experimental data are described quantitatively in terms of a two-band tight binding model using the valence band edge mass and strain-induced valence band splitting as parameters.
Nanoparticle precursor route to low-temperature spray deposition of CdTe thin films
Authors: Pehnt Martin , Schulz Douglas L. , Curtis Calvin J. , Jones Kim M. , Ginley David S.
Published: July 2002

In this letter we report a nanoparticle-derived route to CdTe thin films. CdTe nanoparticles 39±8 Å in diameter, prepared by an organometallic route, were characterized by x-ray diffraction, UV-Vis spectroscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopy. CdTe thin-film deposition was realized by spraying a nanoparticle/butanol colloid onto SnO2-coated glass substrates at variable susceptor temperatures. The resultant CdTe films were characterized by atomic force microscopy, x-ray diffraction, and UV-Vis spectroscopy. Smooth and dense CdTe thin films were obtained using growth temperatures ∼200 °C less than conventional spray pyrolysis. A growth temperature dependence upon CdTe grain size formation and crystallinity was observed by atomic force microscopy and x-ray diffraction. UV-Vis characterization revealed a transformation in the optical properties of the CdTe thin films as a function of growth temperature.
Dopant interactions during the diffusion of arsenic and boron in opposite directions in polycrystalline/monocrystalline silicon structures
Authors: Burghartz Joachim N. , Stanis Carol L. , Ronsheim Paul A.
Published: July 2002

Experimental results of the effects of the arsenic doping concentration on the boron outdiffusion in n-polycrystalline/p-monocrystalline silicon structures are presented. The boron diffusivity is only 30 times larger in polycrystalline silicon than in monocrystalline silicon if the arsenic doping is high enough to cause enhanced grain growth. The diffusivity increase is about 130 if the polycrystalline silicon has small grains due to low arsenic doping. The boron loss from the base region of an advanced bipolar transistor doping profile by outdiffusion into the emitter polycrystalline silicon is of the order of 20% and needs to be considered for accurate device modeling.
Plasmons in a superlattice in a parabolic quantum well
Authors: Sundaram M. , Allen S. J. , Geller M. R. , Campman K. L. , Gossard A. C.
Published: July 2002

Well-defined plasma oscillations are observed in a superlattice miniband even though the Fermi energy lies in the minigap. Despite the complex band structure, the resonance shows a remarkable insensitivity to changes in the number of electrons in the parabolic well in which the superlattice is placed, a feature of the generalized Kohn theorem that is expected only in the limit that the Fermi energy is near the bottom of the lowest miniband.
Field emission switch
Authors: McClelland Gary M. , Watanabe Fumiya
Published: July 2002

Large positive and negative voltage pulses applied to field emission tips can rearrange atomic or molecular adsorbates on the tip. If this rearrangement persists when field emission is measured at a lower negative voltage, the rearrangement will alter the field emission rate, and the device will function as a switch with memory. This effect has been observed for single sodium atoms adsorbed on a tungsten tip and is applicable to adsorbed films or ferroelectric layers.
Binary coding and correlations in the noise frequencies of an oscillator
Authors: Planat M. , Marianneau G. , Ratier N. , Lardet-Vieudrin F.
Published: July 2002

We report on a multifractal type approach to the study of low frequency noise in oscillators. The time sequence is interrogated by means of a multiscale local stability exponent which acts as a sliding filtering window. Its discontinuities are reflected into a binary coding of which the correlations are analyzed. The mapping of binary data into a devil’s staircase is used to emphasize the correlated origin of frequency fluctuations.
Interface state buildup by high-field stressing in various metal-oxide-semiconductor insulators using deep level transient spectroscopy
Authors: Belkouch S. , Jean C. , Aktik C. , Ameziane E. L.
Published: July 2002

The buildup of interface states with high field (HF) stressing have been observed in thermally grown oxide, N2O nitrided oxide (NO), and reoxided nitrided oxide (RNO). The DLTS technique was used to analyze the electronic properties of the Si/SiO2 interface. We show that N2O nitridation of SiO2 changes the electronic distribution of states at the Si/SiO2 interface after HF electrical stress. Our results indicate that this nitrogen plays an important role in preventing the creation of a center at Et1=0.34 eV below the bottom of the conduction band. However, the nitrogen is responsible for a new level at Et2=0.22 eV below the bottom of the conduction band after the NO device is stressed. Also, reoxidation and increasing time of the reoxidation shift the maximum of the peak level away from the Et2 toward Et1.
Anomalous temperature effect in electric field orientation of poly(cyclohexylmethylsilane)
Authors: Nakayama Yoshikazu , Hirooka Keiichi , West Robert
Published: July 2002

We observed an anomalous temperature effect for poly(cyclohexylmethylsilane) (PHMS) in a systematic study on formation of electrically oriented polysilane films by casting on interdigital electrodes to which a dc voltage is applied. The orientation of PHMS is quite sensitive to the process temperature: polysilanes align well along the electric field at 14 °C but do not at temperatures higher than 15 °C or lower than 11 °C. It is also shown that the degree of orientation of polysilanes in the films reflects to the electric conduction.
Influence of spatial correlations on the analysis of diffusion noise in submicron semiconductor structures
Authors: Mateos Javier , González Tomás , Pardo Daniel
Published: July 2002

We present a microscopic analysis of the influence of the spatial correlations between local diffusion noise sources on the noise calculation in a submicron GaAs n+ nn+ diode under different applied voltages. The simulation is carried out using an ensemble Monte Carlo simulation. We demonstrate that in the case of submicron nonhomogeneous structures the use of the diffusion coefficient to characterize the local noise sources is not correct, specially under far-from-equilibrium conditions. The nonuniformity of the electric field and the nonstationary behavior of the electrons lead to significant changes in the spatial correlations with respect to the case of an homogeneous semiconductor. Therefore, the diffusion noise at the terminals must be calculated in terms of the correlations between the local noise sources.
Modeling and design of InAs/AlSb-resonant tunneling diodes
Authors: Sigurdardottir A. , Krozer V. , Hartnagel H. L.
Published: July 2002

In this letter we present a simple but effective single band model for the calculation of the current-voltage characteristics in InAs/AlSb double barrier resonant tunneling diodes. We have obtained a very good agreement for the overall characteristics and especially for both peak and valley current densities as compared with previously published data. The influence of the doping concentration in the injection layer on the current density is studied, as well as the influence of the quantum well width. We discuss a diode design with a view to tunneling diode oscillators suitable for submillmeter wave mixing.
Determination of the band offsets of the 4H–SiC/6H–SiC heterojunction using the vanadium donor (0/+) level as a reference
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C.
Published: July 2002

Optical admittance spectroscopy has been used to study defects in 4H–SiC; the vanadium donor level at EC-1.73 eV has been identified. The optical admittance spectrum of 4H–SiC is similar to that of 6H–SiC, where the vanadium donor level is at EC-1.59 eV. The band gaps of 6H–SiC and 4H–SiC were measured. The values of 3.10±0.03 eV for 6H–SiC and 3.41±0.03 eV for 4H–SiC are in reasonable agreement with reported values. Using the vanadium donor level in both 4H–SiC and 6H–SiC as a common reference, the band offsets for 6H–SiC/4H–SiC heterojunction are estimated to be ΔEC=0.14 eV and ΔEV=0.17 eV.
Theoretical study of chlorine adsorption on GaAs(111)A surfaces
Authors: Guo-Ping Jiang , Ruda Harry E.
Published: July 2002

The mechanism for Cl atom adsorption on GaAs(111)A surfaces is investigated using ab initio Hartree–Fock molecular orbital calculations on specially designed cluster models. The energy-minimized geometry and binding energies are obtained for Cl adsorbed on the (111)A surfaces. Cl is shown to bond to surface Ga atoms and result in (a) a lowering of the occupied surface electronic state energy, (b) a strongly enhanced surface dipole moment, and (c) a profound effect on the surface Ga–As bonding. The different bonding characteristics of Cl and H adsorbed on such surfaces are shown to manifest themselves in the local density of states. Model results are used to explain the observed enhanced photoluminescence response of chlorinated GaAs(111)A surfaces.
Influence of a NbN overlayer on Nb/Al–AlOx/Nb high quality Josephson tunnel junctions for x-ray detection
Authors: Cristiano R. , Esposito E. , Frunzio L. , Pagano S. , Parlato L. , Peluso G. , Pepe G. , Scotti di Uccio U. , Nakagawa H. , Aoyagi M. , Akoh H. , Takada S.
Published: July 2002

Nb/Al–AlOx/Nb–NbN Josephson junctions for use as x-ray detectors have been fabricated. The NbN overlayer has been used to realize the trapping of quasiparticles in the Nb top layer with an increase of the charge collection efficiency. The temperature dependence of quasiparticle and Josephson critical current have been investigated and compared with that without a NbN overlayer, showing low leakage currents, about 200 pA (V=0.5 mV, T=0.67 K, A=20×20 μm2), and high dynamical resistances in the subgap region. Preliminary measurements under 6 keV x-ray irradiation have shown an increased value of the maximum collected charge.
Micro-Raman study of polydioxolane/LiClO4 and NaClO4 electrolytes
Authors: Silva R. A. , Silva G. Goulart , Pimenta M. A.
Published: July 2002

A micro-Raman study of polydioxolane (PDXL)/NaClO4 and PDXL/LiClO4 polymeric electrolytes has been carried out in a wide range of salt concentration, at room temperature. The ion–ion interactions and the precipitation of salt microcrystals in the host polymer have been evidenced by means of a line shape analysis of the band associated to the totally symmetric stretching mode (ν1) of the ClO4− anion. The Raman spectra results reveal changes of the crystallinity of the PDXL/MCLO4 systems which are directly related to the salt concentration.
Terahertz response of zero-dimensional states in resonant tunneling diodes
Authors: Langerak C. J. G. M. , Murdin B. N. , Cole B. E. , Chamberlain J. M. , Henini M. , Pate M. , Hill G.
Published: July 2002

The photoresponse of zero-dimensional states in double barrier resonant tunneling diodes has been observed using high intensity THz radiation (photon frequencies ranging from 4 to 10 THz) from a free-electron laser. The double barrier resonant tunneling diodes have silicon donors in the quantum well which act as individual localized tunneling channels. The high frequency response of these diodes shows additional features due to the presence of these extra channels. The temperature dependence allows us to identify the contribution of the zero-dimensional states. The absence of wavelength dependence in the observed photoresponse indicates that photoassisted tunneling does not occur under these measurement conditions.
The sticking coefficient of barium on a MgO substrate measured by laser induced fluorescence
Authors: Gabbanini C. , Gozzini S. , Lucchesini A.
Published: July 2002

We present the measurement of the sticking coefficient of Ba atoms on a MgO substrate by resonant laser induced fluorescence. The substrate is used as a target for a thermal atomic beam of barium while a laser crosses the substrate and counterpropagates to the atomic beam monitoring its velocity profile. A signal corresponding to negative velocity atoms with respect to the beam direction allows to determine the sticking coefficient. It resulted equal to 0.76 ±0.05.
Addendum: ‘‘Influence of misfit dislocations on the surface morphology of Si1−xGex films’’ [Appl. Phys. Lett. 66, 724 (1995)]
Authors: Lutz M. A. , Feenstra R. M. , LeGoues F. K. , Mooney P. M. , Chu J. O.
Published: July 2002

The omission of a key reference (Ref. 2) in the authors’ earlier publication (Ref. 1) is noted. The major conclusion of (Ref. 2) was the same as that of the authors’ in (Ref. 1), namely, that surface steps generated by dislocation glide play an important role in the morphology in Si1−xGex films. (AIP)
Spatial and spectral characteristics of spontaneous emission from semiconductor quantum wells in microscopic cylindrical cavities
Authors: Vurgaftman Igor , Singh Jasprit
Published: July 2002

The spontaneous emission rate from an In0.2Ga0.8As quantum well in a cylindrical dielectric cavity with submicron radii and without mirrors in the emission plane is calculated based on a rigorous description of the cavity modes and their interaction with the 2D electronic system. The rate is suppressed for radii much less than the peak optical wavelength (rcav≪λ/n), enhanced by up to a factor of ≊8 for rcav≊λ/n, and remains similar to its value in the absence of a cavity for rcav≫λ/n. The emitted light produces a highly collimated vertical beam in the intermediate region with the majority of photons emitted into the guided cavity modes, and its spatial distribution broadens dramatically in the smallest structures. The global spectral width of spontaneous emission in cavities that can presently be fabricated is largely unaffected by the introduction of lateral dielectric boundaries.
Pulse-shaping mechanism in colliding-pulse mode-locked laser diodes
Authors: Bischoff S. , So/rensen M. P. , Mo/rk J. , Brorson S. D. , Franck T. , Nielsen J. M. , Mo/ller-Larsen A.
Published: July 2002

The large signal dynamics of passively colliding pulse mode-locked laser diodes is studied. We derive a model which explains modelocking via the interplay of gain and loss dynamics; no bandwidth limiting element is necessary for pulse formation. It is found necessary to have both fast and slow absorber dynamics to achieve mode-locking. Significant chirp is predicted for pulses emitted from long lasers, in agreement with experiment. The pulse width shows a strong dependence on both cavity and saturable absorber length.
Influence of low energy Ar-sputtering on the electronic properties of InAs-based quantum well structures
Authors: Magnée P. H. C. , den Hartog S. G. , Wees B. J. van , Klapwijk T. M. , van de Graaf W. , Borghs G.
Published: July 2002

The influence of low energy (80–500 eV) Ar-ion milling cleaning techniques on InAs based quantum well structures is investigated. It is found that both etching with a Kaufmann source and sputter-etching with a rf-plasma enhances the electron density and reduces the mobility. An anneal at 180 °C has little effect, and only recovers damage caused by low energy (80 eV) Kaufmann etching.
Spontaneously formed long-range Al-rich and Ga-rich AlxGa1−xAs/AlyGa1−yAs superlattice and optical properties enhancement in (111)A AlGaAs
Authors: Chin Albert , Lin B. C. , Gu G. L. , Hsieh K. Y.
Published: July 2002

Spontaneously formed long-range Al-rich and Ga-rich AlxGa1−xAs/AlyGa1−yAs superlattice in (111)A was demonstrated. This was observed by cross-sectional transmission electron microscopy (TEM) in 0.75 μm Al0.30Ga0.70As grown on (111)A GaAs substrates at 640 °C. In contrast, none of the above superstructure was observed by TEM on a side-by-side grown (100) oriented substrate. 15 K photoluminescence (PL) showed a 31 meV redshift and six times peak intensity enhancement in layers grown on (111)A substrates to that on (100). A reduced long-range compositional modulation can be achieved by growth at higher temperatures and is shown in the finer and moderately modulating (111)A Al0.40Ga0.60As grown at 700 °C. A 15 K PL linewidth of 17 meV was achieved in 700 °C grown (111)A A0.40Ga0.60As that is the narrowest reported linewidth for (111)A AlGaAs.
Growth of polycrystalline silicon at 470 °C by magnetron sputtering onto a sputtered μc-hydrogenated silicon seed layer
Authors: Yang Y. H. , Abelson J. R.
Published: July 2002

We deposit polycrystalline silicon (px-Si) with mean grain diameter ∼400 Å using dc magnetron sputtering of a Si target in an Ar plasma. We analyze the nucleation process and crystallite size as a function of film thickness using in situ, real time spectroscopic ellipsometry. For direct deposition on glass substrates at 470 °C, the initial ∼0.3 μm is amorphous silicon, then crystalline nuclei appear, and the growth becomes fully polycrystalline by ∼0.6 μm. To promote nucleation, we deposit a 100 Å layer of μc-Si:H (hydrogenated polycrystalline silicon with a mean grain diameter of ∼60 Å) by sputtering in an Ar plus H2 atmosphere at 210 °C. Returning to an Ar-only plasma at 470 °C, px-Si grows on this seeded substrate with no detectable amorphous interfacial layer. Since magnetron sputtering is a large-area, high throughput technique, this two-step process appears technologically attractive.
Effects of nonuniform photon distribution on high speed response in semiconductor distributed feedback lasers
Authors: Feng J. , Chen T. R. , Yariv A.
Published: July 2002

The high speed performance of distributed feedback (DFB) lasers, with nonuniform longitudinal photon density distributions, has been analyzed. It was found that the relaxation resonance frequency and damping rate of the lasers depended on the distribution of traveling electric fields in the lasers. A two section DFB laser was used to demonstrate the effects of spatial hole burning on the high speed response of the DFB laser. By adjusting the photon density distribution in the laser through nonuniform current injection, the resonance frequency and damping rate of the two section DFB laser can be changed even if the output optical power is kept constant.