bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and surface chemistry of oxynitride gate dielectric using nitric oxide
Authors: Hegde Rama I. , Tobin Philip J. , Reid Kimberly G. , Maiti Bikas , Ajuria Sergio A.
Published: July 2002

Oxynitride films grown on preoxidized (100) silicon surfaces in a nitric oxide (NO) ambient at 950 °C have been investigated using x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (XTEM). Compared to N2O oxynitride, NO oxynitride exhibits very different surface chemistry, interface properties, and growth mechanisms. The etch back of NO and N2O oxynitride films allows control of sample thickness for the XPS measurements. NO oxynitride has the interfacial nitrogen (Nint) sharply peaked on the Si substrate side of the interface, while it is broad and on the dielectric side of the interface for the N2O oxynitride. The N(1s) XPS results reveal a clear distinction between N2O oxynitride and NO oxynitride. Near the Si/dielectric interface the NO oxynitride shows primarily Si≡N bonds, while the N2O films showed a N(1s) binding energy peak that is in-between that of Si≡N bonds and Si2=N—O bonds. Furthermore, the NO oxynitride surface roughness as determined by AFM is lower than that of the Si/SiO2 interface.
In-plane polarized optical interconduction-subband transitions in quantum wells
Authors: Yang Rui Q.
Published: July 2002

In this work, it has been shown within the framework of a simple one-band model how the in-plane polarized optical interconduction-subband transitions could simply occur in quantum well structures. A novel approach is proposed for manipulating optical properties through the band-gap engineering based on the spatial features of wave functions. The underlying physics and consequences for device applications are discussed.
A system for systematically preparing atom-probe field-ion-microscope specimens for the study of internal interfaces
Authors: Krakauer B. W. , Hu J. G. , Kuo S.-M. , Mallick R. L. , Seki A. , Seidman D. N. , Baker J. P. , Loyd R. J.
Published: July 2002

A versatile system has been designed and fabricated to prepare atom-probe field-ion-microscope (APFIM) specimens in a systematic manner, such that internal interfaces can be positioned in the tips of these wire specimens for subsequent analysis of their chemical composition. This system incorporates both beaker electrolytic and zone electrolytic cell configurations, a specially constructed power supply, and a special transmission electron microscope holder for wires. The power supply enables ac electroetching or dc electropolishing in the automated or manual modes. The ac wave forms available are sine (0.002 Hz–200 kHz) or square (10 Hz–20 kHz). Triggering and gating are performed manually or with a pulse generator. The dc output is gated manually to produce a continuous output or with a pulse generator to produce single pulses with widths in the range 50 μs–1 s. A counter indicates the number of periods of voltage applied, and the total charge transferred in the electrolytic cell is integrated in the range 10 μA s–1 kA s. The power supply provides 0 to ±48 V peak at 1 A peak. A double-tilt stage for an Hitachi H-700H 200 kV transmission electron microscope (TEM) was radically modified to hold APFIM specimens; this stage is vibrationless at 310 000× magnification. It has a tilting range of ±30° and ±27° for the x and y tilts, respectively. Examples are given of the controlled backpolishing of W-3 at. % Re, W-25 at. % Re, Mo-5.4 at. % Re, and Fe-3 at. % Si specimens, and their observation by TEM, to selectively place grain boundaries in the tip region. The analysis of the chemical composition of a grain boundary, which is first located in a W-25 at. % Re specimen via TEM, by the APFIM technique is presented.
A new third-level charge pumping method for accurate determination of interface-trap parameters in metal-oxide-semiconductor field-effect-transistors
Authors: Autran Jean-Luc , Balland Bernard
Published: July 2002

We propose a new implementation of the third-level charge pumping technique for a precise determination of the energy distributions of electron and hole cross sections and interface state density in metal-oxide-semiconductor field-effect transistors (MOSFETs). Using an arbitrary function generator with a high clock rate and a sufficient storage memory length, it is possible to evaluate interface trap emission times and interface state densities in small geometry MOSFETs with a high-enegy resolution. The accuracy of the technique has been greatly increased owing to the high stability and the weak distortion of the signal applied to the gate of the device (numerically generating via a high-speed digital-to-analog converter) and the development of a new acquisition procedure. To illustrate the performance of this method, we present the first results concerning the characterization of 0.6 μm N-channel MOSFETs.
Conduction-type conversion in Si-doped (311)A GaAs grown by molecular beam epitaxy
Authors: Sakamoto N. , Hirakawa K. , Ikoma T.
Published: July 2002

We have systematically studied the dependence of the electrical properties of Si-doped (311)A GaAs on the growth conditions in molecular beam epitaxy and have established a phase diagram for the conduction type as functions of the growth temperature and the V4/III flux ratio. A sharp boundary is observed for the transition between the p- and n-type conduction, on both sides of which the activation efficiency of Si is close to unity. Furthermore, it is found that, in contrast to the case of the (111)A GaAs, the conduction-type conversion in Si-doped (311)A GaAs does not show a clear correlation with the macroscopic surface morphology, suggesting that the mechanism for the conduction-type conversion in Si-doped (311)A GaAs is different from that for the (111)A orientation.
Fundamental design of the high energy undulator pilot beamline for macromolecular crystallography at the SPring-8
Authors: Kamiya Nobuo , Uruga Tomoya , Kimura Hiroaki , Yamaoka Hitoshi , Yamamoto Masaki , Kawano Yoshiaki , Ishikawa Tetsuya , Kitamura Hideo , Ueki Tatsuo , Iwasaki Hitoshi , Kashihara Yasuharu , Tanaka Nobuo , Moriyama Hideaki , Hamada Kensaku , Miki Kunio , Tanaka Isao
Published: July 2002

The SPring-8 project team adopted our proposal for public beamline as one of two pilot beamlines for standardizing the beamline elements. The light source of this beamline is an in-vacuum-type undulator of magnetic periodicity of 3.2 cm, which emits highly brilliant x rays in a wide energy range between 9 and 38 keV. The highest power emitted from the light source is 5 kW. The corresponding power density is 300 kW/mrad2. To handle the tremendous power density, grazing incidence diffraction with variable glancing angle will be used for the first crystal of a fixed-exit double-crystal monochromator. To focus the high energy x rays up to 38 keV, two supermirrors (Ovonic Synthetic Materials Co.) will be installed in vertical and horizontal directions independently to get a quasi-isotropic and small beam profile at a focal position. In the experimental station, the sample crystals will be mounted on the κ-type goniostat, and the Weissenberg photographs will be recorded by on-line mode on an imaging plate detector of high-speed readout. Based on the excellent performance of the beamline, the routine structure determination of macromolecules will become available by using the newly constructed software system corresponding to the multiple isomorphous replacement technique with optimized anomalous scattering. The structure analyses with smaller sample crystals than that usually used and with the specimen of the larger unit cell will also become possible.
XAFS measurements at high temperatures and pressures
Authors: Tamura K. , Inui M. , Hosokawa S.
Published: July 2002

The method of XAFS measurements at high temperatures and pressures for supercritical fluids with high critical constants have been developed. An internally heated high-pressure vessel made of super-high-tension steel and a polycrystalline sapphire cell of our own design permit XAFS measurement up to 800 bar. XAFS experiments were carried out at high temperatures up to 1600 °C, and high pressures up to 150 bar. XAFS spectra of liquid Se at 1300 °C and 150 bar, and dense Se vapor at 1600 °C and 150 bar have been obtained and clear oscillations are observed at these temperatures.
Very sharp platinum tips for scanning tunneling microscopy
Authors: Libioulle L. , Houbion Y. , Gilles J.-M.
Published: July 2002

To achieve both high stability for scanning tunneling microscopy (STM) measurements and well-defined tunnel current localization even on very rough surfaces, we have developed a new electrochemical procedure using CaCl2 etching and H2SO4 micro polishing technique to obtain a very reproducible tip geometry. The mean curvature radius is about 50 Å. The contamination-free platinum tips are usable for a long time as well in air as in ultrahigh vacuum. The tip quality has been tested by STM measurements on gold (111) surfaces and on liquid-crystal films. Tips are stable and provide good STM image in far less time than commonly used tips.
Low-temperature scanning tunneling microscope for ballistic electron emission microscopy and spectroscopy
Authors: Henderson G. N. , First P. N. , Gaylord T. K. , Glytsis E. N. , Rice B. J. , Dantzscher P. L. , Guthrie D. K. , Harrell L. E. , Cave J. S.
Published: July 2002

Design details and initial results are presented for a low-temperature scanning tunneling microscope specifically intended for measurements of ballistic-carrier transmittance through heterostructures. The basic design is of the Besocke type, modified for ballistic electron emission microscopy and spectroscopy (BEEM). This instrument is the first to acquire BEEM spectra below 77 K. Salient features are (1) operation in a liquid-helium storage Dewar to below 6 K, (2) a lateral positioning range of 5 mm at low temperature, and (3) lateral drift rate less than 0.2 nm/h at the lowest temperatures. For BEEM spectroscopy, the microscope’s high positional stability allows extended signal-averaging at a single location on the sample.
Varied line-spacing plane grating monochromator for undulator beamline
Authors: Fujisawa M. , Harasawa A. , Agui A. , Watanabe M. , Kakizaki A. , Shin S. , Ishii T. , Kita T. , Harada T. , Saitoh Y. , Suga S.
Published: July 2002

A varied line-spacing plane grating monochromator is installed at an undulator beamline BL-19B of the Photon Factory. Small contribution of aberrations to image sizes at a focal plane of the varied line-spacing plane grating is calculated with use of an optical path function. The largest resolving power obtained from a ray tracing is estimated to be 4600 at a photon energy of 1239.85 eV and 10 000 at 91.2 eV. Gas absorption spectra show the similar extent of resolution obtained by the ray tracing. A high brightness with a high resolution may be realized in this monochromator.
Observation of quantum effects and Coulomb blockade in silicon quantum-dot transistors at temperatures over 100 K
Authors: Leobandung Effendi , Guo Lingjie , Wang Yun , Chou Stephen Y.
Published: July 2002

We report the fabrication and characterization of lithographically defined nanoscale silicon quantum-dot transistors that operate at temperatures over 100 K and a bias higher than 0.07 V. In the tunneling regime, these transistors show strong current oscillations due to quantum confinement and single-electron charging effects. In the propagating regime, a different kind of current modulation has been observed, which is attributed to the interference between different modes of quantum waves in a cavity. Proper scaling of these transistors should lead to operation at room temperature and a bias of 0.3 V.
Performance of x-ray optics at the European Synchrotron Radiation Facility
Authors: Freund Andreas K.
Published: July 2002

This paper gives an overview of the challenges, the strategies, and the solutions in x-ray optics research and development at the European Synchrotron Radiation Facility (ESRF), followed by an account of the practical experience gathered on the beamlines. The performances of state-of-the-art mirrors, single-crystal monochromators, and multilayer structures are given. Amongst the topics are: adaptive optics and cryogenic cooling to cope with the heat load problem, Bragg-Fresnel optics for microfocusing, x-ray phase plates for polarization production and analysis, and the use of diamond crystals. It is shown that today’s optical elements at the ESRF are capable of preserving the high quality of the present x-ray beams to a large extent.
Development of a multifunctional surface analysis system based on a nanometer scale scanning electron beam: Combination of ultrahigh vacuum-scanning electron microscopy, scanning reflection electron microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy
Authors: Watanabe Heiji , Ichikawa Masakazu
Published: July 2002

We have developed a multifunctional surface analysis system based on a scanning electron beam for nanofabrication and characterization of surface reactions for fabrication processes. The system performs scanning electron microscopy (SEM), scanning reflection electron microscopy (SREM), Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy. Nanometer scale resolution is obtained for ultrahigh vacuum (UHV)-SEM while the mechanical pumping instruments are operated. Single atomic steps on Si(111) surfaces are observed through SREM. Surface sensitive AES measurement is achieved with SREM geometry; this has a great advantage for investigating atomic step related surface reactions. High spatial resolution AES analysis is also achieved by using a nanometer scale probe beam. Auger electron signals from a hundred Ag atoms on a Si(111) surface are successfully detected with high sensitivity.
Nanocalorimeter for high resolution measurements of low temperature heat capacities of thin films and single crystals
Authors: Fominaya Fernando , Fournier Thierry , Gandit Philippe , Chaussy Jacques
Published: July 2002

An innovative nanocalorimeter has been developed for measuring specific heats of thin films, multilayers (typical thickness: 1000 Å) and single crystals (mass: 1 μg) in the temperature range of 1.5–20 K. The addenda of the device are as small as 3 nJ/K at 4 K (0.5 nJ/K at 1.5 K), thus samples with a heat capacity of the order of nJ/K at 4 K can be measured. Heat capacity differences as a function of temperature or an external magnetic field (5 T) were determined with a resolution of ΔC/C≃10−4. This way we have seen heat capacity variations of less than a pJ/K. We present as an example measurements on very small Mn12O12 acetate single crystals and a measurement of a thin superconducting Pb layer. In the latter measurement we could evidence via specific heat a finite size effect.
A facility for electrical contact resistance measurement
Authors: Maheshappa H. D. , Nagaraju J. , KrishnaMurthy M. V.
Published: July 2002

A test facility was developed for directly measuring the electrical contact resistance of switch gear contacts of real sizes under different environmental conditions and contact pressures. It can measure contact resistance to an order of one-tenth of a μΩ. It sources a constant current in the order of mA and hence avoids initial arcing across contacts. Experiments were conducted on brass–brass samples with different contact pressures and the results are in agreement with published theoretical calculations.
Methodology and instrumentation for testing the weak equivalence principle in stratospheric free fall
Authors: Iafolla V. , Nozzoli S. , Lorenzini E. C. , Milyukov V.
Published: July 2002

The use of the GiZero free-fall facility for testing the weak equivalence principle is discussed in this article. GiZero consists of a vacuum capsule, released from a balloon at an altitude of 40 km, which shields an experimental apparatus free falling inside the capsule itself. The expected residual acceleration external to the detector is 10−12 g (with g the Earth’s gravitational acceleration) for the 30 s free fall. A common-mode rejection factor of about 10−4 reduces the residual noise differential output to only 10−16 g. The gravity detector is a differential accelerometer with two test masses with coincident center of masses (i.e., zero baseline) with capacitive pick ups. Preparatory experiments have been conducted in the laboratory with a precursor detector by measuring controlled gravity signals, at low frequency, and by observing the Luni-Solar tides. The estimated accuracy in testing the weak equivalence principle, with a 95% confidence level, is 5×10−15 in a 30 s free fall. When compared to orbital free-fall experiments, the GiZero experiment can be considered as a valid compromise which is able to satisfy the requirement for improving significantly the experimental accuracy in testing the equivalence principle with a substantial lower cost, the ability to recover the detector and to repeat the experiment at relatively short time intervals.
Recent progress in high-energy, high-resolution x-ray imaging techniques for application to the National Ignition Facility (invited)
Authors: Koch J. A. , Landen O. L. , Hammel B. A. , Brown C. , Seely J. , Aglitskiy Y.
Published: July 2002

Multi-keV x-ray microscopy will be an important laser-produced plasma diagnostic at future megajoule facilities such as the National Ignition Facility (NIF). However, laser energies and plasma characteristics imply that x-ray microscopy will be more challenging at NIF than at existing facilities. In earlier work, we concluded that target-mounted pinholes and single spherical or toroidal crystals are good options for many x-ray microscopy applications at NIF. In this article, we review the experimental progress we have made investigating these systems on the Nova and Petawatt Laser Facilities. In particular, we have performed high-resolution, high-magnification target-mounted pinhole imaging of Nova implosions, and we have obtained promising preliminary spherical-crystal data from high-intensity Petawatt experiments. We are also designing a high-energy spherical-crystal imager for use on Nova experiments.
Upgrade of reflectometry profile and fluctuation measurements in Alcator C-Mod
Authors: Lin Y. , Irby J. , Stek P. , Hutchinson I. , Snipes J. , Nazikian R. , McCarthy M.
Published: July 2002

This article reports on the upgrade of the reflectometry profile and fluctuation measurements in Alcator C-Mod. The reflectometer consists of five amplitude modulated O-mode millimeter-wave channels operating between 50 and 110 GHz. The system provides the electron density profile for densities up to 1.5×1020 m−3. An upgrade has been implemented to improve the reliability of the system, eliminate 2π ambiguities in the group delay measurement, and enhance the fluctuation measurements. An upgrade of the 88 GHz channel has been installed, which allows fluctuations on both the upper and lower sideband signals to be measured independently with high resolution. Some preliminary fluctuation and density profile results are discussed.
Thickness dependence of magnetoresistance in La–Ca–Mn–O epitaxial films
Authors: Jin S. , Tiefel T. H. , McCormack M. , O’Bryan H. M. , Chen L. H. , Ramesh R. , Schurig D.
Published: July 2002

Colossal magnetoresistance in excess of 106% has been obtained (at 110 K, H=6 T) in epitaxially grown La–Ca–Mn–O thin films. The as-deposited film exhibits a substantial magnetoresistance value of 39 000%, which is further improved by heat treatment. The magnetoresistance is found to be strongly dependent on film thickness, with the value reaching the maxima at ∼1000 Å thickness, and then reduced by orders of magnitude when the film is made thicker than ∼2000 Å. This behavior is interpreted in terms of lattice strain in the La–Ca–Mn–O films.
Investigation of interface intermixing and roughening in low-temperature-grown AlAs/GaAs multiple quantum wells during thermal annealing by chemical lattice imaging and x-ray diffraction
Authors: Chang J. C. P. , Woodall J. M. , Melloch M. R. , Lahiri I. , Nolte D. D. , Li N. Y. , Tu C. W.
Published: July 2002

The effect of thermal annealing on the interface quality in undoped, AlAs/GaAs multiple quantum well (MQW) structures grown at a low substrate temperature (310 °C) by molecular beam epitaxy has been investigated using chemical lattice imaging and high resolution x-ray diffraction. The low-temperature-grown MQW is of high crystalline quality comparable to the standard-temperature-grown MQW. However, significant interface roughening and intermixing occurs at the quantum well heterointerface when the structures are annealed beyond 700 °C. The effective activation energy for interdiffusion is estimated as 0.24±0.07 eV. The structural properties observed here suggest that the excess arsenic associated with the low-temperature growth substantially enhances the diffusion of column III vacancies across an interface, which leads directly to intermixing of Al and Ga.
Mid-wave infrared diode lasers based on GaInSb/InAs and InAs/AlSb superlattices
Authors: Chow D. H. , Miles R. H. , Hasenberg T. C. , Kost A. R. , Zhang Y.-H. , Dunlap H. L. , West L.
Published: July 2002

We report the characterization of a set of broad-area semiconductor diode lasers with mid-wave infrared (3–5 μm) emission wavelengths. The active region of each laser structure is a 5- or 6-period multiple quantum well (MQW) with Ga0.75In0.25As0.22Sb0.78 barriers and type-II (broken-gap) Ga0.75In0.25Sb/InAs superlattice wells. The cladding layers of each laser structure are n- and p-type InAs/AlSb (24 Å /24 Å) superlattices grown lattice-matched to a GaSb substrate. By tailoring constituent layer thicknesses in the Ga0.75In0.25Sb/InAs superlattice wells, laser emission wavelengths ranging from 3.28 μm (maximum operating temperature=170 K) to 3.90 μm (maximum operating temperature=84 K) are obtained.
Spatially resolved photoluminescence and Raman scattering experiments on the GaN/substrate interface
Authors: Siegle H. , Thurian P. , Eckey L. , Hoffmann A. , Thomsen C. , Meyer B. K. , Amano H. , Akasaki I. , Detchprohm T. , Hiramatsu K.
Published: July 2002

We present results from spatially resolved photoluminescence and Raman experiments on the substrate interface region of wurtzite GaN layers. We show that the broad photoluminescence band with an intensity maximum at 2.4 eV is not an intrinsic property of GaN. We found that this photoluminescence band is strong only near the interface. Our investigations reveal that both the substrate interface and a region of structural reorientation of the layer near the interface act as a source of the photoluminescence.
Photorefractive p-i-n diode quantum well operating at 1.55 μm
Authors: De Matos C. , Le Corre A. , L’Haridon H. , Lambert B. , Salaün S. , Pleumeekers J. , Gosselin S.
Published: July 2002

We demonstrate the performance of a semiconductor photorefractive p-i-n diode operating at 1.55 μm in the longitudinal quantum-confined Stark geometry. The device structure consists of a semi-insulating InP–GaInAs(P) multiple quantum well, sandwiched between two trapping regions, and embedded in a p-n junction. In this structure, the measured output diffraction efficiency reaches 0.6%. This value is close to the output diffraction efficiency value estimated from electroabsorption measurements.
Reduction of unintentional aluminum spikes at SiC vapor phase epitaxial layer/substrate interfaces
Authors: Burk A. A. , Rowland L. B.
Published: July 2002

Aluminum concentrations at unintentionally doped SiC vapor phase epitaxial layer/substrate interfaces were determined by secondary ion mass spectrometry to approach 1×1018 cm−3, exceeding the intentional doping of most device active layers. Capacitance–voltage measurements indicate that the aluminum is electrically active resulting in compensation of moderately doped n-type layers. The unintentional aluminum buildup was successfully reduced by two orders of magnitude by minimizing exposure of the SiC substrate to propane gas prior to epitaxial growth and by the addition of an in situ HCl etch.
Free versus localized exciton recombination in Zn1−xCdxSe/ZnSe multiple quantum wells
Authors: Lomascolo M. , Di Dio M. , Greco D. , Calcagnile L. , Cingolani R. , Vanzetti L. , Sorba L. , Franciosi A.
Published: July 2002

Time-resolved photoluminescence studies of Zn1−xCdxSe/ZnSe multiple quantum wells as a function of photoinjected carrier density show a typical exciton localization dynamics at all injection levels in the high-x samples (x∼0.2–0.3). On the contrary, the low-x samples (x∼0.1) exhibit a gradual saturation of the exciton localization process and band-filling behavior with increasing photoinjection. A rate-equation model provides a description of the time-dependent luminescence in all samples and allows a quantitative determination of the concentration of exciton localization centers.
The coalescence of [001] diamond grains heteroepitaxially grown on (001) silicon
Authors: Jiang X. , Jia C. L.
Published: July 2002

The coalescence of diamond grains grown by microwave plasma chemical vapor deposition was observed at an atomic level using high resolution electron microscopy in combination with scanning electron microscopy. It was shown that large diamond crystals can be grown either by a coalescence of two [001]-oriented grains which have a slight misorientation or by a switch of the grain boundary, which is usually perpendicular to the surface plane, to a parallel direction. A single crystalline film might be deposited when the growing surface is fully covered by the (001) plane, i.e., no {111} top facet appears to separate the growing (001) surface.
Dependence of generation and structures of stacking faults on growing surface stoichiometries in ZnSe/GaAs
Authors: Kuo L. H. , Kimura K. , Miwa S. , Yasuda T. , Yao T.
Published: July 2002

Thin ZnSe films were grown by molecular beam epitaxy on Zn exposed (2×4) As-stabilized surfaces of GaAs epilayers under varied beam flux ratios. A very low density of faulted defects in the range of ∼ 104/cm2 was generated in samples grown under a condition with a mixture of both (2×1) and weak c(2×2) surface reconstructions at the initial stages of growth. However, an asymmetric distribution on the densities of extrinsic cation- and anion-terminated Shockley-type stacking faults were generated, respectively, in samples grown under Zn- and Se-rich surface stoichiometries.
High resolution ion scattering study of silicon oxynitridation
Authors: Lu H. C. , Gusev E. P. , Gustafsson T. , Garfunkel E. , Green M. L. , Brasen D. , Feldman L. C.
Published: July 2002

High resolution medium energy ion scattering was used to characterize the nitrogen distribution in ultrathin silicon oxynitrides with sub-nm-accuracy. We show that nitrogen does not incorporate into the subsurface region of the substrate after oxidation of Si(100) in NO. Core-level photoemission experiments show two bonding configurations of nitrogen near the interface. Oxynitridation in N2O results in a lower concentration and a broader distribution of nitrogen than in the NO case.
Does magnetization in thin-film manganates suggest the existence of magnetic clusters?
Authors: Sun J. Z. , Krusin-Elbaum L. , Gupta A. , Xiao Gang , Parkin S. S. P.
Published: July 2002

We report results of quantitative magnetization studies on epitaxial thin films of La0.60Y0.07Ca0.33MnO3−δ and La1−x⧠xMnO3−δ, with ⧠ standing for vacancy on the La site. The magnetization in all samples shows significant field dependent broadening of the ferromagnetic transition. Classical mean-field analysis of magnetization data in applied fields above a few Tesla leads to a magnetic cluster size of the order of a few unit cells. The density of such a magnetic cluster correlates with the doping concentration x in the compound series La1−x⧠xMnO3−δ. In thin films of La0.60Y0.07Ca0.33MnO3−δ, a magnetic field dependent, non-Curie–Weiss susceptibility was found in the paramagnetic state, indicating local ferromagnetic cluster formation above macroscopic ferromagnetic ordering temperature.
Light emission from germanium nanoparticles formed by ultraviolet assisted oxidation of silicon-germanium
Authors: Craciun Valentin , Boulmer-Leborgne Chantal , Nicholls Edward J. , Boyd Ian W.
Published: July 2002

Nanocrystalline Ge particles embedded in a SiO2 layer, directly formed by an excision process from a SiGe strained layer during low temperature ultraviolet-assisted oxidation are shown to exhibit visible photoluminescence. The emission maxima of the photoluminescence spectra are situated at around 2.18 eV, a value that corresponds, according to recent data to an average particle size of 5 nm, in excellent agreement with our previous Raman and transmission electron microscopy measurements of particle size. It is proposed that stress effects associated with the oxidation of small spherical particles allow the formed nanocrystalline Ge to survive during prolonged ultraviolet oxidation of the SiGe layer.
Ultrafast excitonic room temperature nonlinearity in neutron irradiated quantum wells
Authors: Ten S. , Williams J. G. , Guerreiro P. T. , Khitrova G. , Peyghambarian N.
Published: July 2002

Sharp room temperature exciton features and complete recovery of the excitonic absorption with 21 ps time constant are demonstrated in neutron irradiated (Ga,Al)As/GaAs multiple quantum wells. Carrier lifetime reduction is consistent with the EL2 midgap defect which is efficiently generated by fast neutrons. Influence of gamma rays accompanying neutron irradiation is discussed. Neutron irradiation provides a straightforward way to control carrier lifetime in semiconductor heterostructures with minor deterioration of their excitonic properties.
Very low density two-dimensional hole gas in an inverted GaAs/AlAs interface
Authors: Hanein Y. , Shtrikman Hadas , Meirav U.
Published: July 2002

We utilize an inverted heterostructure grown on (311)A GaAs to realize a two-dimensional hole gas (2DHG) with a built-in back gate. The density of the 2DHG is easily and reproducibly varied between 5×109 and 5×1011 cm−2. The mobility of the 2DHG is highly anisotropic in the (311)A plane.
Mid-infrared photoconductivity in InAs quantum dots
Authors: Berryman K. W. , Lyon S. A. , Segev Mordechai
Published: July 2002

Mid-infrared photoconductivity in self-assembled InAs quantum dots is reported. By embedding the InAs dots in an AlxGa1−xAs matrix, normal incidence photoconductivity has been observed at a range of wavelengths in the mid-infrared and is attributed to single carrier transitions out of the dots. The optical response of the quantum dots is investigated for several different dot structures.
The effect of impurity content on point defect evolution in ion implanted and electron irradiated Si
Authors: Libertino S. , Benton J. L. , Jacobson D. C. , Eaglesham D. J. , Poate J. M. , Coffa S. , Fuochi P. G. , Lavalle M.
Published: July 2002

We compare the defect complexes generated in crystalline Si by electron irradiation and ion implantation, using irradiation fluences which deposit the same total energy in nuclear collisions. Deep level transient spectroscopy was used to monitor both vacancy-type (e.g., divacancies) and interstitial-type (e.g., carbon–oxygen complexes) defects produced on p-type Si samples. We show that identical defect structures and annealing behavior, T⩽300 °C, are produced by both Si implantation and electron irradiation. After annealing at higher temperatures, we observe a higher residual damage in ion implanted samples, which is a direct consequence of the extra incorporated ions. We demonstrate that the substrate impurity content rather than the ion cascade dominates defect formation and evolution. In high purity Si, B-related instead of C-related (e.g., the carbon–oxygen complex) defects preferentially store the interstitials which escape direct recombination with vacancies, and the thermal stability of the CiOi complexes is decreased in Si containing low concentration of impurities.
Epitaxial Mn2Sb thin films grown by molecular-beam epitaxy on (001) GaAs and their magnetic and magneto-optical properties
Authors: Miyanishi S. , Akinaga H. , Van Roy W. , Tanaka K.
Published: July 2002

We have succeeded in growing monocrystalline ferrimagnetic Mn2Sb thin films on (001) GaAs by molecular-beam epitaxy. From the reflection high-energy electron and x-ray diffraction patterns, the orientation of Mn2Sb films grown on (001) GaAs substrates was found to be with the c axis normal to the surface. This direction is also the easy magnetization direction as determined by superconducting quantum interference device measurements at room temperature. Magneto-optical spectra of these films showed a much larger magneto-optical Kerr effect than bulk data from the infrared to the blue wavelength region.
Nanopatterning organic monolayers on Si(100) by selective chemisorption of norbornadiene
Authors: Abeln G. C. , Lee S. Y. , Lyding J. W. , Thompson D. S. , Moore J. S.
Published: July 2002

Norbornadiene (bicyclo[2.2.1]Hepta-2,5-diene) is shown to chemisorb selectivity at room temperature onto clean Si(100)-2×1 surfaces. Combining the chemoselectivity of this process with scanning tunneling microscope nanolithography allows the formation of nanometer-sized regions having a norbonadiene adlayer. This concept could serve as the basis for creating spatially resolved templates to initiate chemical reactions with other chemical species in the presence of hydrogen-passivated Si(100)-2×1 areas.
Resonant tunneling of electrons via 20 nm scale InAs quantum dot and magnetotunneling spectroscopy of its electronic states
Authors: Narihiro M. , Yusa G. , Nakamura Y. , Noda T. , Sakaki H.
Published: July 2002

The resonant tunneling of electrons through a 20 nm scale InAs quantum dot bound by a pair of very thin AlAs barriers is studied. A well-resolved composite peak resulting from the ground 1s states was observed at 4.2 K in current–voltage characteristics. By investigating the effects of inplane magnetic fields, the shape of the wave function and the spatial extent of the first two electronic states are clarified.
Thermal fixing of refractive index gratings in a photorefractive polymer
Authors: Cheng Ning , Swedek Bogdan , Prasad Paras N.
Published: July 2002

A significant increase in storage time by thermal fixing of photorefractive (PR) gratings in a polymeric composite of poly-9-vinycarbazole, tricresyl phosphate, fullerene, and 4-N,N-diethylamino-β-nitrostyrene is demonstrated. The fixing of the volume holograms is created by quasifreezing the orientation of the linearly anisotropic chromophore molecules. The fixed PR gratings can be easily erased by elevating the sample’s temperature to the glass transition temperature of the composite. The readout of the thermally fixed first-order grating does not require the presence of an external electric field.
Self-limiting growth of quantum dot heterostructures on nonplanar {111}B substrates
Authors: Hartmann A. , Loubies L. , Reinhardt F. , Kapon E.
Published: July 2002

We study the evolution of AlGaAs/GaAs growth during organometallic chemical vapor deposition on pyramidal recess patterns etched into GaAs {111}B substrates. Cross-sectional atomic force microscopy clearly demonstrates the self-organized growth behavior in the inverted pyramid structures. During AlGaAs deposition, the side corners and the tip of the pyramid sharpen up to a self-limited radius of curvature of less than 10 nm. In addition, vertical Ga-rich AlGaAs quantum wells are formed at these corners. Subsequent GaAs growth results in the formation of GaAs quantum wires along the corners of the pyramid. These wires meet at the tip of the pyramid, forming a quantum dot structure at this point.
Effect of the interface on the electrical properties of ZnSe/GaAs heterojunctions grown by molecular beam epitaxy
Authors: Seghier D. , Gislason H. P.
Published: July 2002

Using current–voltage and ac conductance measurements, nitrogen-doped ZnSe grown by molecular beam epitaxy on p-GaAs substrates heterostructures was studied. The reverse current–voltage characteristics of the heterojunction show a soft saturation and a hysteresis. A slow current increase takes place following the application of a constant reverse bias until a steady-state value is reached. This behavior is explained in a model involving slow interface states at the heterointerface that result in a voltage-induced barrier lowering. The observation of a broad peak in the ac conductance vs temperature spectra confirms the model. The presence of such states may seriously affect the performance of ZnSe/GaAs-based devices.
Microscopic theory of gain for an InGaN/AlGaN quantum well laser
Authors: Chow W. W. , Wright A. F. , Girndt A. , Jahnke F. , Koch S. W.
Published: July 2002

This letter describes a microscopic gain theory for an InGaN/AlGaN quantum well laser. The approach, which is based on the semiconductor Bloch equations, with carrier correlations treated at the level of quantum kinetic theory in the Markovian limit, gives a consistent treatment of plasma and excitonic effects, both of which are important under lasing conditions. Inhomogeneous broadening due to spatial variations in quantum well thickness or composition is taken into account by a statistical average of the homogeneously broadened spectra.
An analysis technique for extraction of thin film stresses from x-ray data
Authors: Cornella Guido , Lee Seok-Hee , Nix William D. , Bravman John C.
Published: July 2002

We demonstrate a technique for experimentally determining stresses in crystalline thin films without any knowledge of the elastic properties of the thin film material. The results are obtained from interplanar spacing versus sin2 Ψ plots for different stress states. The interplanar spacings are measured by non-symmetric x-ray diffraction. The different stress states are produced by annealing the thin film/substrate samples at elevated temperatures in air and by cooling them in liquid nitrogen. Poisson’s ratio for isotropic films or a similar quantity for anisotropic films can be found through the use of this technique. An extension of this technique also permits the measurement of the coefficient of thermal expansion without removing the film from the substrate.
Charging of substrates irradiated by particle beams
Authors: Guzdar P. N. , Sharma A. S. , Guharay S. K.
Published: July 2002

A simple dynamical model for studying the charging of substrates irradiated by particle beams is developed. The charging potential for positive ion beams can be as large as the beam voltage. For negative ion beams, the charging potential is significantly lower and is governed by the secondary electrons. A closed form expression derived for the charging voltage in the case of negative ion beams agrees well with our numerical work. The results are consistent with observations on charging of isolated substrates during ion implantation with positive and negative ion beams.
Characterization of AlGaInN diode lasers with mirrors from chemically assisted ion beam etching
Authors: Kneissl M. , Bour D. P. , Johnson N. M. , Romano L. T. , Krusor B. S. , Donaldson R. , Walker J. , Dunnrowicz C.
Published: July 2002

Current-injection InGaAlN heterostructure laser diodes grown by metalorganic chemical vapor deposition on sapphire substrates are demonstrated with mirrors fabricated by chemically assisted ion beam etching. Due to the independent control of physical and chemical etching, smooth vertical sidewalls with a root-mean-squared roughness of 4–6 nm have been achieved. The diodes lased under pulsed current-injection conditions at wavelengths in the range from 419 to 423 nm. The lowest threshold current density was 25 kA/cm2. Lasing was observed in both gain-guided and ridge-waveguide test diodes, with cavity lengths from 300 to 1000 μm; and output powers of 10–20 mW were achieved. Laser performance is illustrated with light output-current and current–voltage characteristics and with a high-resolution optical spectrum.
Direct and inverse equivalent InAlAs–InP interfaces grown by gas-source molecular beam epitaxy
Authors: Vignaud D. , Wallart X. , Mollot F.
Published: July 2002

InAlAs–InP type II heterostructures grown by gas-source molecular beam epitaxy have been studied by photoluminescence. The interface recombination energy is found around 1.27–1.28 eV in the low injection limit and shifts towards higher energy when increasing the incident power. Similar results are obtained for direct (InAlAs grown on InP) and inverse (InP on InAlAs) structures.
Growth of epitaxial AlxGa1−xN films by pulsed laser deposition
Authors: Huang Tzu-fang , Harris James S.
Published: July 2002

Epitaxial AlxGa1−xN films have been grown on c-cut sapphire substrates at 800 °C and 10−2 Torr N2 by pulsed laser deposition (PLD) using a KrF laser. Throughout the composition range from x=0 to 0.6, the films show epitaxial patterns in reflection high-energy electron diffraction, in agreement with the results from x-ray diffraction. The lattice constants of the films vary linearly with x. The composition dependence of the band gaps of the films deviates from linearity and bows downward. This letter reports the application of PLD to controlling the lattice constant and band gap by varying the proportion of AlN and GaN in the target mixture.
Observation and creation of current leakage sites in ultrathin silicon dioxide films using scanning tunneling microscopy
Authors: Watanabe Heiji , Fujita Ken , Ichikawa Masakazu
Published: July 2002

We used scanning tunneling microscopy (STM) to investigate the local leakage current through ultrathin silicon dioxide (SiO2) films grown on Si substrates. Individual leakage sites, which were created by hot-electron injection from the STM tip under a high sample bias of +10 V, were identified from the local change in surface conductivity due to defect creation in the oxide films. When we reversed the stressing polarity (using a negative sample bias) no leakage sites were created in the oxide film.
Mid-infrared interband cascade lasers with quantum efficiencies >200%
Authors: Yang B. H. , Zhang D. , Yang Rui Q. , Lin C.-H. , Murry S. J. , Pei S. S.
Published: July 2002

An external differential quantum efficiency exceeding 200% has been observed from 4 μm InAs/InGaSb/AlSb interband cascade lasers under 1 μs pulses and 0.1% duty cycle at 80 K. By increasing the pulse lengths and the repetition rates, average powers >16 mW have been measured with 5 μs pulses at 10% duty cycle, the internal quantum efficiency and the internal loss are determined to be 220% and 14 cm−1, respectively.
Vertical polarization of quantum magnets in high density arrays of nickel dots with small height-to-diameter ratio
Authors: Meier G. , Kleiber M. , Grundler D. , Heitmann D. , Wiesendanger R.
Published: July 2002

Using interferometric lithography and postexposure processing we have fabricated high density (1.3×1010/in.2) magnetic nickel dot arrays on silicon substrates. The dots have the shape of truncated cones and are 75 nm in height and about 120 nm in diameter. The arrays are characterized using magnetic force microscopy (MFM). We demonstrate that such shallow dots with a small height-to-diameter ratio of only 0.63, show single-domain behavior with vertical, out-of-plane magnetization, i.e., along their short axis. The coercive field of these dots is drastically enlarged due to shape anisotropy and is exceeding the dot interaction strength by about one order of magnitude. Local manipulation of the magnetization state using an additional external field and the stray field of the MFM tip is demonstrated.
Influence of Si doping on characteristics of InGaN/GaN multiple quantum wells
Authors: Cho Yong-Hoon , Song J. J. , Keller S. , Minsky M. S. , Hu E. , Mishra U. K. , DenBaars S. P.
Published: July 2002

We have systematically studied the influence of Si doping on the characteristics of InGaN/GaN multiple quantum wells (MQWs) by means of high-resolution x-ray diffraction (HRXRD), photoluminescence (PL), PL excitation (PLE), and time-resolved PL spectroscopy. The twelve- period MQWs were grown by metalorganic chemical vapor deposition. Si doping in the GaN barriers was varied from 1×1017 to 3×1019 cm−3. Information on the structural quality of the MQWs as a function of Si doping was extracted from the linewidth broadening of the higher-order superlattice satellite peaks measured in HRXRD. The HRXRD measurements indicate that increased Si doping results in better interface properties of the MQWs. PL and PLE measurements show a decrease in the Stokes shift with increasing Si doping concentration. The 10 K radiative recombination lifetime was observed to decrease from ∼30 ns (for n<1×1017 cm−3) to ∼4 ns (for n=3×1019 cm−3) with increasing Si doping concentration. The reduced Stokes shift, the decrease in radiative recombination lifetime, and the increase in the interface quality indicate that Si doping results in a decrease in carrier localization at potential fluctuations in the InGaN active layers.
Experimental evidence for a dual vacancy–interstitial mechanism of self-diffusion in silicon
Authors: Ural A. , Griffin P. B. , Plummer J. D.
Published: July 2002

Epitaxially grown isotopically enriched Si layers have been used to study self-diffusion in Si directly at the temperatures of 1000 and 1100 °C. We obtain equilibrium diffusion coefficients in accordance with previous experiments and theoretical calculations. Comparison of diffusion data of self-, antimony, and phosphorus diffusion in Si under identical conditions of perturbed self-interstitial and vacancy concentrations created by surface reactions enables us to determine the microscopic mechanisms of Si self-diffusion. We find that, in this temperature range, self-interstitials contribute roughly 2/3 to Si self-diffusion, and vacancies 1/3, with the concerted exchange component being less than 14%. This constitutes direct experimental evidence that, on the atomic scale, self-diffusion in Si is mediated both by self-interstitials and vacancies.
High performance interminiband quantum cascade lasers with graded superlattices
Authors: Tredicucci Alessandro , Capasso Federico , Gmachl Claire , Sivco Deborah L. , Hutchinson Albert L. , Cho Alfred Y.
Published: July 2002

A new class of quantum cascade lasers is presented. They are based on interminiband transitions in chirped superlattices (SL), where the applied electric field is compensated by the quasielectric field resulting from a gradually varying SL period length and average composition. In this way “flat” minibands can be obtained without the need for dopants. At room temperature record high peak (0.5 W) and average (14 mW) powers are obtained for a laser of 7.6 μm wavelength, with the lowest threshold current densities (5 kA/cm2) reported so far for quantum cascade lasers. The maximum temperature for continuous wave operation is an unprecedented 160 K.
Electron field emission from phase pure nanotube films grown in a methane/hydrogen plasma
Authors: Küttel Olivier M. , Groening Oliver , Emmenegger Christoph , Schlapbach Louis
Published: July 2002

Phase pure nanotube films were grown on silicon substrates by a microwave plasma under conditions which normally are used for the growth of chemical vapor deposited diamond films. However, instead of using any pretreatment leading to diamond nucleation we deposited metal clusters on the silicon substrate. The resulting films contain only nanotubes and also onion-like structures. However, no other carbon allotropes like graphite or amorphous clustered material could be found. The nanotubes adhere very well to the substrates and do not need any further purification step. Electron field emission was observed at fields above 1.5 V/μm and we observed an emission site density up to 104/cm2 at 3 V/μm. Alternatively, we have grown nanotube films by the hot filament technique, which allows to uniformly cover a two inch wafer.