bluuebunny/crossref_metadata_2025 huggingface dataset:
Epitaxial growth of a (100) CoSi2 layer from carbonic cobalt films deposited on (100) Si substrate using an organometallic source
Authors: Rhee Hwa Sung , Jang Tae Woong , Ahn Byung Tae
Published: July 2002

We report the epitaxial growth of a (100) CoSi2 layer on Si (100) substrate by the diffusion of Co from an amorphous carbonic cobalt film. The employment of an intermediate buffer layer, usually required between Si and pure Co, was eliminated in this experiment. The amorphous carbonic cobalt film was prepared by the organometallic chemical vapor deposition of cyclopentadienyl dicarbonyl cobalt, Co(η5–C5H5)(CO)2 at 350 °C. The carbonic cobalt film was capped by a sputtered Ti layer to avoid oxidation of Co during annealing. A CoSi2 layer was epitaxially grown on Si (100) by ex situ rapid thermal annealing at 800 °C in N2 ambient. The supply of Co by diffusion in the carbonic cobalt film seemed to be low enough to form an epitaxial CoSi2 layer.
Comparison of ultralow-energy ion implantation of boron and BF2 for ultrashallow p+/n junction formation
Authors: Park Jihwan , Huh Yun-Jun , Hwang Hyunsang
Published: July 2002

We have compared the electrical characteristics and the depth profile of ultrashallow junctions formed by boron implantation at 0.5 keV and BF2 implantation at 2.2 keV. The modeling of the boron profile was performed using the Monte Carlo method for an as-implanted profile and the computationally efficient method for transient-enhanced diffusion. A junction depth of BF2 is shallower than that of boron after annealing. For an ultrashallow junction, HF dipping prior to rapid thermal annealing causes a significant loss of dopant and high sheet resistance. Considering the 0.1 μm metal–oxide–semiconductor field-effect transistor application, the optimizations of implantation and annealing conditions are necessary to satisfy the requirement of junction depth and sheet resistance.
A four-color quantum well infrared photodetector
Authors: Tidrow M. Z. , Jiang Xudong , Li Sheng S. , Bacher K.
Published: July 2002

A four-color quantum well infrared photodetector (QWIP) has been demonstrated in this work. Four stacks of quantum well structures with four different detection wavelengths are sandwiched among three highly doped contact layers. The peak wavelengths of the four colors are centered at 4.7, 8.5, 9, and 12.3 μm. The 4.7 and 8.5 μm stacks are separated from the 9 and 12.3 μm stacks by a middle ohmic contact layer, and the change of peak detection wavelengths within the two-stack QWIPs is achieved by varying the bias voltage. Four different combinations of two-color simultaneous reading can be obtained. The detector could achieve simultaneous reading of four colors by adding two extra contact layers to the design with appropriate readout circuitry. By using a small number of quantum wells, we are able to use all four stacks for voltage-tunable detection with two terminals. In spite of using InGaAs/AlGaAs and GaAs/AlGaAs materials in the four stacks, the device shows excellent material quality and performance characteristics.
Laser action in polydialkylfluorene films: Influence of low-temperature thermal treatment
Authors: Shkunov M. N. , Österbacka R. , Fujii A. , Yoshino K. , Vardeny Z. V.
Published: July 2002

We have used a variety of optical probes to investigate the changes occurring upon low-temperature thermal treatment to the emissive properties of dialkyl substituted polyfluorene thin films. We found that the low-temperature-driven morphological changes involving aggregates formation, which are observed in the absorption and photoluminescence spectra at low excitation intensities, give rise at high excitation intensities to laser action in the blue spectral range. In some cases, switching between two stimulated emission bands was also observed.
Formation of low-index facets in Ga0.2In0.8As and InAs islands on a InP(113)B substrate
Authors: Lacombe D. , Ponchet A. , Fréchengues S. , Drouot V. , Bertru N. , Lambert B. , Le Corre A.
Published: July 2002

Strained Ga0.2In0.8As and InAs islands were grown on a InP(113)B substrate by gas source molecular beam epitaxy and examined by transmission electron microscopy and atomic force microscopy. The islands are mainly bounded by the low-index facets {001}, {111}B, and {110} [inclination with respect to the (113)B surface of 25°, 29°, and 31°, respectively]. Some of the consequences of the substrate orientation on the island shape and formation are discussed.
Technique for producing highly planar Si/SiO0.64Ge0.36/Si metal–oxide–semiconductor field effect transistor channels
Authors: Grasby T. J. , Parry C. P. , Phillips P. J. , McGregor B. M. , Morris, R. J. H. , Braithwaite G. , Whall T. E. , Parker E. H. C. , Hammond R. , Knights A. P. , Coleman P. G.
Published: July 2002

Si/Si 0.64 Ge 0.36 /Si heterostructures have been grown at low temperature (450 °C) to avoid the strain-induced roughening observed for growth temperatures of 550 °C and above. The electrical properties of these structures are poor, and thought to be associated with grown-in point defects as indicated in positron annihilation spectroscopy. However, after an in situ annealing procedure (800 °C for 30 min) the electrical properties dramatically improve, giving an optimum 4 K mobility of 2500 cm2 V−1 s−1 for a sheet density of 6.2×1011 cm−2. The low temperature growth yields highly planar interfaces, which are maintained after anneal as evidenced from transmission electron microscopy. This and secondary ion mass spectroscopy measurements demonstrate that the metastably strained alloy layer can endure the in situ anneal procedure necessary for enhanced electrical properties. Further studies have shown that the layers can also withstand a 120 min thermal oxidation at 800 °C, commensurate with metal–oxide–semiconductor device fabrication.
Modeling of the effects of dose, dose rate, and implant temperature on transient enhanced diffusion
Authors: Pelaz Lourdes , Gilmer G. H. , Venezia V. C. , Gossmann H.-J. , Jaraiz M. , Barbolla J.
Published: July 2002

Atomistic simulations are used to study the effects of implant parameters on transient enhanced diffusion (TED). We analyze 10 keV Si implants in a wide range of doses from 108 to 1014 ions/cm2, dose rates from 1010 to 1014 ions/cm2 s, and implant temperature from room temperature to 1000 °C. Different regimes with different dependence of TED on these parameters are observed. For high doses, high dose rates, and low implant temperatures, the Frenkel pairs are accumulated during ion implantation, and the resulting damage is very dense. During the postimplant annealing, the recombination of Frenkel pairs is efficient, and the extra interstitials generated by the implanted ions provide the main contribution to the enhanced diffusivity. For low doses, low dose rates, and high implant temperatures, there is little interaction between neighboring cascades during annealing. The recombination of Frenkel pairs is not complete, and many interstitials and vacancies from each cascade survive recombination and contribute significantly to TED.
An in-plane GaAs single-electron memory cell operating at 77 K
Authors: Yoo K.-H. , Park J. W. , Kim Jinhee , Park K. S. , Oh S. C. , Lee J.-O. , Kim J. J. , Choi J. B. , Lee J. J.
Published: July 2002

An in-plane single-electron memory cell operating at 77 K has been fabricated from a Si-doped thin GaAs film. This device utilizes an artificially fabricated floating node as a storage node and detects the charge stored on the floating node using a single-electron electrometer. Charging of the floating node is evidenced by a large peak in source–drain current as a function of control gate voltage, and is further confirmed by a discrete shift in the peak or threshold voltage.
Effect of threading dislocations on electron transport in In0.24Ga0.76N/GaN multiple quantum wells
Authors: Lo Ikai , Hsieh K. Y. , Hwang S. L. , Tu Li-Wei , Mitchel W. C. , Saxler A. W.
Published: July 2002

The effect of threading dislocations on electron transport in In0.24Ga0.76N/GaN multiple quantum wells has been studied by using transmission electron microscopy (TEM) and van der Pauw Hall effect measurements. From the cross-sectional TEM imaging, we observed the threading dislocations which “screw” through the multiple In0.24Ga0.76N/GaN quantum well. From the Hall effect measurement, we found that the Hall mobility decreases as the temperature decreases (μ∼T3/2) due to the threading dislocation scattering, and the Hall carrier concentration shows a transition from conduction-band transport to localized-state-hopping transport. The thermal activation energy of the residual donor level (probably Si) is about 20.2 meV.
Coulomb blockade in silicon nano-pillars
Authors: Pooley D. M. , Ahmed H. , Mizuta H. , Nakazato K.
Published: July 2002

We have investigated the current–voltage characteristics of nano-pillars of polycrystalline silicon with two 2–3 nm thick silicon nitride tunnel barriers. Pillars with diameters between 45 and 100 nm showed a Coulomb blockade region and Coulomb staircase at 4.2 K.
Mechanical relaxation in SrBi2Ta2O9 ceramics
Authors: Yan Feng , Wang Yening , Liu Jianshe , Zhang Zhigang , Chen Xiaobin
Published: July 2002

The internal friction (IF) of SrBi2Ta2O9 ceramics was measured by using the reed vibration method in the temperature range from 100 to 600 K with frequency in kilohertz. A high IF peak appeared around 500 K, which was interpreted in terms of the migration of oxygen vacancies. Another low IF peak was found with a peak temperature of 200–250 K, which varied for tens of degrees in different samples. This peak was assumed to be due to the depinning process of domain walls from oxygen vacancies. These results are helpful in the understanding of the excellent fatigue resistance property of SBT at room temperature.
Cooling of a superconductor by quasiparticle tunneling
Authors: Manninen A. J. , Suoknuuti J. K. , Leivo M. M. , Pekola J. P.
Published: July 2002

We have extended the cryogenic cooling method based on tunneling between a superconductor and another metal to the case when both metals are superconducting but when their energy gaps are different; earlier, this method was applied between a superconductor and a normal metal. The electron system of a titanium strip with the superconducting transition temperature Tc2=0.51 K has been cooled from 1.02Tc2 to below 0.7Tc2 by this method, using aluminum as the other superconductor.
All-optical focal length converter using large optical nonlinearity in guest-host liquid crystals
Authors: Ono Hiroshi , Harato Yoshiro
Published: July 2002

We present an all-optical focal length converter using both large optical nonlinearity and anisotropic complex refractive indices in guest-host nematic liquid crystals (GHLCs). The nonlinear phase modulation was generated by irradiating the GHLCs with a He–Ne laser beam (wavelength; 633 nm) having a Gaussian profile. A laser diode (LD) beam (wavelength; 788 nm) passed at the same point as the He–Ne laser beam spot. The phase of the LD beam was modulated and the LD beam was focused due to the phase modulation. The focal length of the LD beam was varied over a range of several centimeters by controlling the intensity of the He–Ne laser beam.
Radiative emission rate modulation in semiconductor heterostructures coupled to a mirror: A probe of ballistic electron mean free path
Authors: Teissier R. , Sicault D. , Goujon A. , Pelouard J. L. , Pardo F. , Mollot F.
Published: July 2002

Absolute electroluminescence intensities of InP/InGaAs heterostructures are monitored as a function of the position of the active layer from a mirror deposited on the semiconductor surface. The strong observed modulation is explained in terms of confinement of the electromagnetic field in the semi-infinite cavity delimited by the reflecting interface. This effect is shown to be a powerful probe of electron spatial distributions in the direction perpendicular to the layer plane, which allows minority ballistic electron mean free path, and hence femtosecond scattering times, to be precisely measured.
Organic light-emitting diodes with a bipolar transport layer
Authors: Choong Vi-En , Shi Song , Curless Jay , Shieh Chan-Long , Lee H.-C. , So Franky , Shen Jun , Yang Jie
Published: July 2002

A structure based on a bipolar transport/emitting layer is proposed and implemented for making organic light-emitting diodes. Compared to the conventional heterojunction organic light-emitting diodes, more than a factor of six improvement in device reliability (a projected operating lifetime of 70 000 h) is achieved in the structure. The significant improvement in device lifetime is attributed to the elimination of the heterointerface present in the conventional devices which greatly affects the device reliability.
Quantized conductance in up to 20 μm long shallow etched GaAs/AlGaAs quantum wires
Authors: Worschech L. , Beuscher F. , Forchel A.
Published: July 2002

Conductance quantization is observed in up to 20 μm long and 135 nm wide quantum wires fabricated by wet chemical etching of modulation-doped GaAs/AlGaAs heterostructures. With increasing wire length, the higher plateaus in the conductance vanish, whereas a fundamental step persists up to a length comparable to the transport mean free path of the two-dimensional layers. Via magnetic depopulation of the one-dimensional (1D) subbands a lateral depletion length of wdep=15 nm is estimated for a gate voltage of 1.1 V. By temperature dependent measurements the energy spacings between the 1D subbands are investigated.
Interdiffused quantum-well infrared photodetectors for color sensitive arrays
Authors: Johnston M. B. , Gal M. , Li Na , Chen Zhanghai , Liu Xingquan , Li Ning , Lu Wei , Shen S. C. , Fu L. , Tan H. H. , Jagadish C.
Published: July 2002

Proton implantation and rapid thermal annealing were used to tune the infrared spectral response of quantum-well infrared photodetectors (QWIP) by up to 1.4 μm. Multiple proton implants at energies between 200 and 420 keV were used to create homogeneous quantum-well intermixing throughout the device’s multiple-quantum-well structure. Photoluminescence and spectral response measurements were used to study the effect of proton implantation on QWIPs for a series of doses up to 3.5×1015 protons cm−2. By using a mask during implantation, a method of constructing a color sensitive array is proposed.
Kinetic Monte Carlo simulations of nucleation on a surface with periodic strain: Spatial ordering and island-size distribution
Authors: Mattsson Thomas R. , Metiu Horia
Published: July 2002

We use kinetic Monte Carlo simulations to study nucleation of adsorbate islands on a solid surface on which a periodic strain field has been imposed. We show that, in spite of its very small effect on the diffusion constant of the atoms, the field orders the ensemble of islands. Better ordering and a narrower size distribution are obtained when the ensemble of islands produced by nucleation is coarsened.
Infrared response of oxygen precipitates in silicon: Experimental and simulated spectra
Authors: Sassella A. , Borghesi A. , Geranzani P. , Borionetti G.
Published: July 2002

A suitable choice of one sample among several silicon wafers subjected to two-step thermal treatments for oxygen precipitation permits to reveal a complete series of infrared absorption peaks related to the precipitates formed in the crystal. Structured spectra are observed at 7 K and can be interpreted as due to SiO2 precipitates with different shapes and concentrations.
Optimized configuration for reflective bistable twisted nematic displays
Authors: Zhuang Zhizhong , Kim Young Jin , Patel J. S.
Published: July 2002

In this letter, we experimentally verify the operation of a single-polarizer reflective bistable twisted nematic (BTN) liquid-crystal display using an optimized geometry. Based on the polarization optimization using the Poincaré sphere representation, several optimized operating modes, which can simultaneously optimize both bistable states, are possible. One of these optimized configurations, the 67.38° and −292.62° twisted bistable states with 310.69 nm birefringence and a 24.25° incident polarization angle, is studied in detail. The evolution of the state of polarization of light passing through this reflective BTN structure is numerically studied, and the electro-optic property of the reflective BTN structure is experimentally demonstrated. Our results show that, using these optimum configurations, a high-contrast display is possible.
Micro-Raman imaging of GaN hexagonal island structures
Authors: Holtz M. , Seon M. , Prokofyeva T. , Temkin H. , Singh R. , Dabkowski F. P. , Moustakas T. D.
Published: July 2002

We use Raman scattering to obtain a stress map of lateral epitaxy overgrown GaN. Isolated hexagonal islands are grown by selective area overgrowth without a seed layer. Stress mapping is obtained from shifts in the E2 phonon. GaN in the aperture area has the greatest biaxial compressive stress, ≈0.18 GPa. The overgrowth region is under slightly smaller stress, about 0.15 GPa. We attribute marked variations in the A1(LO) phonon intensity to spatial variations in the free carrier concentration. This is found to be small in the aperture region and high in the lateral overgrowth. The position-dependent presence of the lower coupled plasmon–phonon band is consistent with this interpretation.
Temperature dependence of photoluminescence on molecular-beam-epitaxy grown Ga2O3(Gd2O3)/GaAs
Authors: Tu L. W. , Lee Y. C. , Lee K. H. , Lai C. M. , Lo I. , Hsieh K. Y. , Hong M.
Published: July 2002

Device-quality Ga2O3(Gd2O3) thin films have been grown on GaAs using molecular-beam epitaxy. Photoluminescence measurements have been performed within a temperature range of 4.2–300 K. Detailed analysis on the peak position, peak width, and peak intensity has been compared with those of a conventional Al0.45Ga0.55As/GaAs sample, which is known to be the state-of-the-art structure of dielectrics/GaAs. Both the peak intensity and the peak width are very similar between the two. The results show an almost indistinguishable excellent quality between the Ga2O3(Gd2O3)/GaAs and the Al0.45Ga0.55As/GaAs samples. This demonstrates the superiority of the Ga2O3(Gd2O3)/GaAs structure and supports further the reported successfully manufactured GaAs metal-oxide-semiconductor field-effect transistors using this Ga2O3(Gd2O3) as the gate oxide.
Light emission spectra of individual GaAs quantum wells induced by scanning tunneling microscope
Authors: Tsuruoka T. , Ohizumi Y. , Tanimoto R. , Ushioda S.
Published: July 2002

We have investigated the light emission from individual single GaAs quantum wells of cleaved (110) AlGaAs/GaAs heterostructures, using the scanning tunneling microscope tip as a local injection source of minority carriers. Single emission peaks were observed to shift to the high-energy side with decreasing well width. The emission peaks are assigned to the transition between n=1 single-quantum-well electron and heavy-hole states of the respective wells.
The effect of an electric-field gradient on avalanche noise
Authors: Plimmer S. A. , Tan C. H. , David J. P. R. , Grey R. , Li K. F. , Rees G. J.
Published: July 2002

The effect of an electric-field gradient on the excess avalanche noise is examined using both a Monte Carlo model and experiment. Nonlocal effects cause the noise to be significantly reduced as the electric-field gradient increases in a p+–n junction. For equal electron and hole ionization coefficients, lower noise is always achieved when carriers are injected into the high field end of these structures. Furthermore, for a constant noise figure and depletion thickness, a higher gain is always achieved in a p+–n junction compared a p+–i–n+. The results are explained in terms of coherence in ionization events.
Bistable twisted nematic liquid-crystal optical switch
Authors: Zhuang Zhizhong , Kim Young Jin , Patel J. S.
Published: July 2002

In this letter, we describe a bistable twisted nematic (BTN) liquid-crystal device optimized for use in a fiber optical system. The device configuration is optimized so that the states of polarization for the two bistable states are linear and orthogonal to each other for a linearly polarized input light. This optimization is accomplished by the use of the Poincaré sphere method. Using this method, we obtained the analytical forms of the optimization conditions. Several different optimized conditions are obtained. In order to experimentally explore the use of the BTN structure in optical latching switches, one optimized structure (11.25° and −348.75° twists, dΔn/λ=0.496) is studied in the infrared region by the measurement of the output state of polarization. The experimental results agree well with our theoretical predictions. This study also suggests that transmissive BTN displays with high contrast are possible by the use of these optimized conditions with nonparallel and noncross polarizer configurations.
Room temperature La0.7Sr0.3MnO3 magnetoresistive prototype memory element
Authors: Cadieu F. J. , Chen Li , Li Biao , Theodoropoulos T.
Published: July 2002

Highly (110) textured La0.7Sr0.3MnO3 polycrystalline film strips in conjunction with a small interacting bias magnet have been used to construct a prototype room temperature memory element. The film strips were made by high laser pulse energy pulsed laser deposition such that the temperature of the resistance maximum was elevated to room temperature. Consequently room temperature operation did not require any temperature compensation. The magnetoresistance of such film strips exhibited highly anisotropic low field magnetoresistance with the largest response for applied fields in plane and parallel to the current direction. Perpendicular to the plane applied fields produced no response in the low field region. A simple bridge was configured in which the sensing element was a 100-μm-wide manganite strip made to exhibit a broad resistance maximum at room temperature. The memory element magnetoresistive response for field excursions approaching the intrinsic coercivity of the bias magnet exhibited two distinct zero applied field resistance values. Parallel versus antiparallel field excursions to 60 mT produced zero applied magnetic field voltage states separated by 18 mV at room temperature in a geometry investigated.
Large interband second-order susceptibilities in InxGa1−xN/GaN quantum wells
Authors: Schmidt H. , Abare A. C. , Bowers J. E. , Denbaars S. P. , Imamoǧlu A.
Published: July 2002

We present measurements of second-harmonic generation in interband transitions of InxGa1−xN/GaN multiple quantum well samples. The second-order susceptibility χ(2) is studied as a function of pump wavelength and quantum well width. For the narrowest wells, we obtain χ(2)=1.3±0.4×10−10 m/V, which is an order of magnitude larger than the intrinsic value for bulk GaN. The corresponding power conversion efficiency was 6.3×10−7. An enhancement of the nonlinearity due to strong internal piezoelectric fields could not be observed.
Coulomb blockade in quasimetallic silicon-on-insulator nanowires
Authors: Tilke A. , Blick R. H. , Lorenz H. , Kotthaus J. P. , Wharam D. A.
Published: July 2002

Using highly doped silicon-on-insulator (SOI) films, we demonstrate metallic Coulomb blockade in silicon nanowires at temperatures up to almost 100 K. We propose a process that leads to island formation inside the wire due to a combination of structural roughness and segregation effects during thermal oxidation. Hence, no narrowing of the SOI wire is necessary to form tunneling contacts to the single-electron transistors.
Near-field photoconductivity of stretch-oriented poly(para-phenylene vinylene)
Authors: DeAro J. A. , Moses D. , Buratto S. K.
Published: July 2002

Near-field scanning optical microscopy (NSOM) with photoconductivity contrast is used to map the transport properties of stretch-oriented poly(p-phenylene vinylene) thin films on a 150 nm length scale. Near-field photoconductivity is highly sensitive to film morphology and contrast is observed even in films with uniform photoluminescence. Regions of relatively higher photocurrent signals are correlated to regions with higher molecular order which have contrast approaching 15%. In addition, the photocurrent signal decreases sharply as the near-field tip approaches the surface of the film while at the same time the photoluminescence signal increases. The sharp decrease is attributed to the perturbation of the applied electric field within the polymer film by the metal on the NSOM tip.
Structure and magnetic properties of Pr2Co17−xMnx compounds
Authors: Sun Zhi-gang , Zhang Hong-wei , Wang Jing-yun , Shen Bao-gen
Published: July 2002

The structure and magnetic properties of Pr2Co17−xMnx (x=0–14) compounds were studied. A single phase with the rhombohedral Th2Zn17-type structure was obtained from x-ray diffraction patterns for x=0–11. The unit-cell volumes were found to increase linearly at a rate of about 5.7 Å3 per Mn atom. Both the Curie temperature and saturation magnetic moment at 5 K decrease monotonously with increasing Mn concentration. The spin reorientation was found in Pr2Co17−xMnx compounds for x=1–5. The magnetic phase diagram of the compounds was given. A transition from ferromagnetic to antiferromagnetic for x=8–9 was observed due to the Mn substitution. At high Mn concentration (x=12,13,14), a rare-earth intermetallic 3:29 phase was found. This kind of 3:29 phase shows a paramagnetic character when the temperature is above 5 K.
A transmission electron microscopy quantitative study of the growth kinetics of H platelets in Si
Authors: Grisolia J. , Ben Assayag G. , Claverie A. , Aspar B. , Lagahe C. , Laanab L.
Published: July 2002

Proton implantation and thermal annealing of silicon result in the formation of a specific type of extended defects involving hydrogen, named “platelets” or “cavities.” These defects have been related to the exfoliation mechanism on which a newly developed process to transfer thin films of silicon onto various substrates is based. The density and the size of these platelets depend on the implantation and annealing conditions. In this letter, rigorous statistical methods based on transmission electron microscopy have been used to quantitatively study the thermal behavior of these defects. Upon annealing, it is shown that the cavities grow in size, reduce their density, while the overall volume they occupy remains constant. This phenomenon is due to a conservative ripening of the cavities. The transfer of hydrogen atoms from small to large cavities leads to a decrease of the elastic energy within the implanted layer while the strain locally increases around the projected range of the protons.
Thermal lensing effects in small oxide confined vertical-cavity surface-emitting lasers
Authors: Brunner M. , Gulden K. , Hövel R. , Moser M. , Ilegems M.
Published: July 2002

The thickness and position of an oxide layer inside a vertical-cavity surface-emitting laser structure have been optimized for minimum optical scattering loss. In the resulting structure, the index guiding provided by the oxide aperture is very small. Consequently, for an oxide aperture radius <2 μm, the optical mode is only weakly confined. In devices using such small apertures, the formation of a thermal lens has a strong influence on optical guiding. The thermal lens leads to lower threshold currents and increased differential efficiency with continuous wave as compared to pulsed injection operation in devices with small apertures.
A diagnostic method for both plasma ion and electron temperatures under simultaneous incidence of charge-exchange particles and x rays into a semiconductor detector array
Authors: Numakura T. , Cho T. , Kohagura J. , Hirata M. , Minami R. , Nishizawa Y. , Sasuga T. , Yoshida M. , Sakamoto Y. , Nakashima Y. , Tamano T. , Yatsu K. , Miyoshi S.
Published: July 2002

An idea for using semiconductor detectors to simultaneously observe both plasma ion Ti and electron Te temperatures is proposed. The idea is also experimentally verified in tandem-mirror plasma shots. This method is developed on the basis of an alternative “positive” use of a semiconductor “dead layer” as an energy-analysis filter. Filtering dependence of charge-exchange neutral particles from plasmas on the thickness of a thin (on the order of nm thick) SiO2 layer is employed for analyzing Ti in the range from hundreds to thousands of eV. Even under the conditions of simultaneous incidence of such particles and x rays into semiconductor detectors, the different dependence on their penetration lengths and deposition depths in semiconductor materials makes it possible to distinguish particles (for Ti) from x rays (for Te). In this letter, proof-of-principle plasma experiments for the proposed idea are carried out to verify the availability of this concept of distinguishing and identifying each value of Ti and Te by the use of various thin filtering materials prior to the use of thinner dead layers.
Evolution of the electron energy distribution function in a planar inductive argon discharge
Authors: Seo Sang-Hun , Kim S. S. , Hong Jung-In , Chang C. S. , Chang Hong-Young
Published: July 2002

The evolution of the electron energy distribution function (EEDF) over a pressure range of 5–100 mTorr is investigated in a planar inductive argon discharge. It is found that the EEDF, which appears to be a bi-Maxwellian distribution with a two-temperature structure at low pressures, evolves into a Druyvesteyn-like distribution as the pressure increases. The electron energy diffusion coefficient, which describes electron heating, is calculated under the same discharge conditions using discharge parameters and numerical results show that the heating of low-energy electrons is enhanced as the pressure increases resulting in a transition of the EEDF to a Druyvesteyn distribution.
Electroluminescence thermal quenching in SrS:Cu thin-film electroluminescent devices
Authors: Baukol B. A. , Hitt J. C. , Keir P. D. , Wager J. F.
Published: July 2002

Electroluminesence (EL) thermal quenching refers a reduction in luminance, concomitant with a reduction in transferred charge, when an alternating-current thin-film electroluminescent (ACTFEL) device is operated at an elevated temperature. EL thermal quenching is found to be significant in SrS:Cu ACTFEL devices operated above ∼60-80 °C. Maximum transferred charge-maximum applied voltage (Qmax-Vmax) and transferred charge capacitance (i.e., dQmax/dVmax vs Vmax) measurements as a function of temperature in conjunction with ACTFEL device simulation are employed in order to establish that EL thermal quenching arises from a thermally activated annihilation of positive space charge and a corresponding increase in the threshold voltage.
Initial growth of Ga2O3(Gd2O3) on GaAs: Key to the attainment of a low interfacial density of states
Authors: Hong M. , Lu Z. H. , Kwo J. , Kortan A. R. , Mannaerts J. P. , Krajewski J. J. , Hsieh K. C. , Chou L. J. , Cheng K. Y.
Published: July 2002

Growth of the first few layers of an oxide mixture Ga2O3(Gd2O3) on GaAs (100) substrate, electron-beam evaporated from a Ga5Go3O12 source, was found to be a single crystal. Reflection high-energy electron diffraction and x-ray diffraction studies show that the thin oxide film is epitaxially grown on GaAs with the surface normal (110) and in-plane axis [001] parallel to (100) and [011] of GaAs, respectively, and has a structure isomorphic to Mn2O3. Studies using high-resolution transmission electron microscopy on the oxide–GaAs interface indicate some atomic registry between the oxide and GaAs during the initial growth. The chemical composition of the oxide film was determined by x-ray photoelectron spectroscopy to be unequivocally pure Gd2O3.
X-ray microdiffraction study of Cu interconnects
Authors: Zhang X. , Solak H. , Cerrina F. , Lai B. , Cai Z. , Ilinski P. , Legnini D. , Rodrigues W.
Published: July 2002

We have used x-ray microdiffraction to study the local structure and strain variation of copper interconnects. Different types of local microstructures have been found in different samples. Our data show that the Ti adhesion layer has a very dramatic effect on Cu microstructure. Strain measurement was conducted before and after electromigration test, Cu fluorescence was used to find the mass variations around voids and hillocks, and x-ray microdiffraction was used to measure the strain change around that interested region.
Stimulated emission study of InGaN/GaN multiple quantum well structures
Authors: Liao Chi-Chih , Feng Shih-Wei , Yang C. C. , Lin Yen-Sheng , Ma Kung-Jen , Chuo Chang-Cheng , Lee Chia-Ming , Chyi Jen-Inn
Published: July 2002

We report the study results of an InGaN/GaN multiple quantum well structure with a nominal indium content of 25%. The high-resolution transmission electron microscopy and x-ray diffraction show clear indium aggregation and phase separation. Stimulated emission data always show two major peaks in spectrum. The long- (short-) wavelength peak is assigned to the recombination of localized state carriers (free carriers). At low temperatures or optical pump levels, the localized-state recombination dominates the stimulated emission; however, at high temperatures or pump levels, the free-carrier recombination becomes dominant. The peak position corresponding to localized states changes little in spectrum as temperature or pump level varies. This result is attributed to carrier overflow, strain relaxation, and carrier shielding in increasing temperature or carrier supply.
Delayed release of Li atoms from laser ablated lithium niobate
Authors: Chaos J. A. , Dreyfus R. W. , Perea A. , Serna R. , Gonzalo J. , Afonso C. N.
Published: July 2002

The present vapor-phase optical (atomic) absorption measurements study the escape dynamics of Li atoms from a LiNbO3 target surface upon laser ablation in vacuum. The objective is to understand the low-Li content of LiNbO3 films prepared by pulsed laser deposition. A primary result is a delayed release of Li atoms, 2–20 μs after the laser pulse; they eject with a velocity of 6×105 cm s−1, which is consistent with an electronic ejection mechanism. The long emission period means there are almost no intraplume Li collisions in the gas phase and no forward focusing of the delayed released atoms. This appears to explain the low-Li content usually found in films grown in the normal direction.
Cross-sectional electron-beam-induced current analysis of the passivation of extended defects in cast multicrystalline silicon by remote hydrogen plasma treatment
Authors: Vyvenko O. F. , Krüger O. , Kittler M.
Published: July 2002

Cross-sectional and temperature-dependent measurements of the electron-beam-induced current reveal the depth profile of the recombination activity of grain boundaries and intragrain dislocations in cast multicrystalline Si. After remote hydrogen plasma treatment for 1 h at 310 °C, defects are passivated down to a depth of 100 μm. Even the activity of crystal defects exhibiting small or not detectable room temperature contrast is further reduced by hydrogenation. We interpret the experimental data in terms of a recently developed model, which relates the temperature behavior of the recombination activity to the density of (contaminant-induced) deep levels at the defects.
Atomic force microscope tip-surface behavior under continuous bias or pulsed voltages in noncontact mode
Authors: Legrand B. , Stiévenard D.
Published: July 2002

The atomic force microscope is now widely used to oxidize a silicon surface with a continuous bias or pulsed voltages applied between the tip and the silicon surface. The aim of this letter is to study the induced electrostatic effect on the cantilever oscillation in noncontact mode when pulsed voltages are used for nanooxidation. Depending on the relative amplitudes between electrostatic and mechanical excitations, and also on the phase between the pulsed voltages and the mechanical excitation, the cantilever response can dramatically vary. We focus on the details of controlling the feedback loop and exposure conditions in noncontact mode.
Oxygen-deficiency-activated charge ordering in La2/3Sr1/3MnO3−δ thin films
Authors: Li J. , Ong C. K. , Liu J.-M. , Huang Q. , Wang S. J.
Published: July 2002

The oxygen-deficiency-activated charge ordering (CO) transition has been observed in C-oriented La2/3Sr1/3MnO3−δ thin films prepared by pulsed laser deposition on LaAlO3 substrates. A rapid growth of the sample resistivity at temperatures below TC is observed, while significant thermal hysteresis and electrical field induced transition from the insulator CO state to metallic-like state are recorded. Such a CO state can also be partially melted under a magnetic field of 0.4 T, resulting in enhanced magnetoresistance at low temperatures. Magnetic properties of the films can be well understood as the coexistence of the ferromagnetic state and the CO state. The CO state in oxygen deficient thin films is explained in terms of the Mn–O octahedral distortion or the narrowness of the conduction bandwidth of the eg carriers.
Conduction-band offset of single InAs monolayers on GaAs
Authors: Colombelli Raffaele , Piazza Vincenzo , Badolato Antonio , Lazzarino Marco , Beltram Fabio , Schoenfeld Winston , Petroff Pierre
Published: July 2002

A determination of the InAs/GaAs band-offset energy is presented. Electronic-transport analysis, based on capacitance-voltage and deep-level transient spectroscopy techniques, demonstrates high crystalline quality of our sample and yields a band-offset estimate of 0.69 eV, corresponding to a band-offset ratio of 70÷30. The present results agree well with reported theoretical values and allow the accurate modeling of electronic states in GaAs/AlGaAs heterostructures containing InAs ultrathin layers.
Direct measurement of internal potential distribution in organic electroluminescent diodes during operation
Authors: Hiramoto Masahiro , Koyama Keiji , Nakayama Ken-ichi , Yokoyama Masaaki
Published: July 2002

Direct measurement of the internal potential distribution in an organic electroluminescent (EL) diode under operating conditions was carried out by inserting a third gold electrode in the bulk of the organic thin film to monitor the potential. This electrode was sandwiched between two driving metal electrodes. During the operation of the organic EL diode, consisting of hole transporting and emitter layers, the applied voltage was distributed mainly across the emitter layer. The present technique provides a useful method for elucidating the operating mechanism of various types of organic thin-film devices.
Spin-exchange optical pumping using a frequency-narrowed high power diode laser
Authors: Nelson I. A. , Chann B. , Walker T. G.
Published: July 2002

We describe a method for frequency narrowing commercial high power diode lasers from 2 to 0.1 nm bandwidth with modest loss of power (<2 dB). The resulting laser light is well suited for spin-exchange optical pumping, and we demonstrate that the polarization produced by a 2.5 W narrowband laser exceeds that of a 15 W array by 40% in our optical pumping system.
Colossal magnetoresistance magnetic tunnel junctions grown by molecular-beam epitaxy
Authors: O’Donnell J. , Andrus A. E. , Oh S. , Colla E. V. , Eckstein J. N.
Published: July 2002

Using molecular-beam-epitaxy growth techniques, we have synthesized ferromagnet/insulator/ferromagnet trilayer heterostructures with the “colossal” magnetoresistance material La1−xSrxMnO3 as the ferromagnet. These trilayer films were fabricated into magnetic tunnel junctions which exhibit magnetoresistance ΔR/R(H) of as much as 450% in 200 Oe applied field at 14 K, and which persists up to ∼250 K. In situ reflection high-energy electron diffraction (RHEED) allows us to correlate the quality of the epitaxial growth with the magnetoresistive properties. Samples which showed signs of disorder in RHEED also exhibit disorder effects in low-temperature transport and have smaller magnetoresistance which vanishes at lower temperatures.
Photoluminescence and recombination mechanisms in GaN/Al0.2Ga0.8N superlattice
Authors: Bergman Leah , Dutta Mitra , Stroscio M. A. , Komirenko S. M. , Nemanich Robert J. , Eiting C. J. , Lambert D. J. H. , Kwon H. K. , Dupuis R. D.
Published: July 2002

A detailed study of photoluminescence (PL) of GaN(1 nm)/Al0.2Ga0.8N(3.3 nm) twenty periods superlattice grown via metal-organic chemical vapor deposition is presented. The dependence of the PL emission energy, linewidth, and intensity on temperature, in the low temperature regime, is consistent with recombination mechanisms involving bandtail states attributed to a small degree of interfacial disorder. The activation energy of the nonradiative centers in our superlattice agrees well with the value we derive for the width of the tail-state distribution. Moreover, we find that the average phonon energy of the phonons that control the interband PL energy at high temperatures is larger for the superlattice than for a high-quality GaN film. This observation is consistent with model calculations predicting the phonon mode properties of GaN–AlN-based wurtzite heterostructures.
Duplexer using microwave photonic band gap structure
Authors: Oh Sang Soon , Kee Chul-Sik , Kim Jae-Eun , Park Hae Yong , Kim Tae Il , Park Ikmo , Lim H.
Published: July 2002

We propose a frequency selective duplexer using microwave photonic band gap (PBG) structures. It uses two different PBGs to control the propagation of electromagnetic waves in the microwave region. In this structure, an additional narrow reflection band appears in the transmission spectrum when the PBG structure is not properly located relative to the T junction. By considering multiple reflections, it is proved that this additional reflection band in each PBG structure results from the interference between the input wave and the reflected wave from the other PBG structure. An effective way to prevent this interference effect is also discussed.
Enhanced damage due to light in low-damage reactive-ion etching processes
Authors: Deng L. G. , Rahman M. , Wilkinson C. D. W.
Published: July 2002

Enhanced dry-etch damage in GaAs/GaAlAs and InGaAs/InAlAs quantum well structures due to additional illumination in low-power reactive-ion etching environments has been studied. We observed that damage in shallow quantum wells is increased significantly when above band-gap laser illumination is present during etching, although there is no measurable effect for illumination subsequent to etching. Contributing factors include the influence on ion channeling and also to a form of radiation-enhanced diffusion. The study shows that the effective defect diffusion coefficient is constrained to lie within the range 10−15 to 10−14 cm2/s.
Large and stable field-emission current from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy
Authors: Kasu Makoto , Kobayashi Naoki
Published: July 2002

We report on the electron field emission (FE) from heavily Si-doped AlN grown by metalorganic vapor phase epitaxy. We found that, as the Si-dopant density increases, the threshold electric field decreases and, consequently, the FE current from AlN increases drastically. We show that heavily Si-doped (2.5×1020 cm−3) AlN has a threshold electric field of 34 V/μm, a maximum FE current density of 4.8 mA/cm2, and stable FE current (fluctuation: 3%).
Effect of uniaxial stress on the polarization of SrBi2Ta2O9 thin films
Authors: Lü Xiaomei , Zhu Jinsong , Li Xuelian , Zhang Zhigang , Zhang Xuesong , Wu Di , Yan Fen , Ding Yong , Wang Yening
Published: July 2002

The effect of uniaxial stress on the ferroelectric properties of SrBi2Ta2O9 films with different thicknesses (330, 440, and 660 nm) has been investigated. It is found that both the remnant polarization (Pr) and the spontaneous polarization (Ps) decrease with the application of compressive stress, but increase with the application of tensile stress. And the changes of Pr and Ps become larger for thicker films. For the 660 nm film, as the stress changed from −100 MPa (compressive) to +100 MPa (tensile), the Pr increases from −1.8% to +1.8%. Testing voltages in the range of 3–6 V showed no impact on the amplitude of change on the polarization under mechanical stress. Mechanical stress also did not show significant impact on the coercive field.
Photovoltaic quantum-dot infrared detectors
Authors: Pan Dong , Towe Elias , Kennerly Steve
Published: July 2002

We demonstrate the operation of photovoltaic quantum-dot infrared detectors fabricated from (In, Ga)As/GaAs heterostructures. These detectors are sensitive to normal incidence light. At zero bias, we obtain a low-temperature (78 K) peak detectivity of 2×108 cm Hz1/2/W, with a responsivity of 1 mA/W at a wavelength of 13 μm for one of the devices. The photovoltaic effect in our detectors is a result of the intrinsic inversion asymmetry of the band structure of self-formed quantum dots. A compensation voltage of 18 mV is measured.
Reorientational magnetic transition in high-density arrays of single-domain dots
Authors: Guslienko K. Yu. , Choe Sug-Bong , Shin Sung-Chul
Published: July 2002

A theoretical study on the reorientational transition from in-plane to out-of-plane magnetized state is performed for two-dimensional magnetic dot arrays coupled by magnetostatic interaction. The square lattice of nanoscale cylindrical dots is considered with the assumptions that the dots are magnetically soft and they have uniform magnetization. The present study predicts that the interdot magnetostatic coupling determines the reorientation transition for close-packed arrays of such magnetic dots. Recent experimental results on the nanometer-scale single-domain dot arrays are discussed in light of the present calculation.
High coercivity of Nd–Dy–Fe–(C, B) ribbons prepared by melt spinning
Authors: Yang J. B. , Gutfleisch O. , Handstein A. , Eckert D. , Müller K.-H.
Published: July 2002

High coercivities μ0iHC of 1.8 and 2.0 T, twice as high as previously reported, remanences Br of 0.63 and 0.69 T, and maximum energy products (BH)max of 70 and 89 kJ/m3 at 293 K are achieved for Nd13Dy2Fe77C8−xBx ribbons with x=0 and 2 after optimum heat treatment, respectively. The samples prepared by rapid quenching and short-time vacuum annealing are of tetragonal Nd2Fe14B (2:14:1)-type structure. It was confirmed that boron addition accelerates the formation of the 2:14:1-type structure, which is formed directly from melt spinning. A very high coercivity of 2.5 T was observed for as-quenched Nd13Dy2Fe77C6B2 ribbons, however with poorer B–H-loop shape.
Noise mechanisms in superconducting tunnel-junction detectors
Authors: Segall K. , Wilson C. , Frunzio L. , Li L. , Friedrich S. , Gaidis M. C. , Prober D. E. , Szymkowiak A. E. , Moseley S. H.
Published: July 2002

We present a theory and measurements of noise mechanisms in superconducting tunnel-junction detectors used as single-photon spectrometers. These mechanisms result from incomplete cooling of the excited quasiparticles in the tunnel-junction electrode. Due to the incomplete cooling, only a fraction of the initially created charge is collected by tunneling. Additional effects include reduced dynamic resistance, voltage dependence of the integrated charge, and increased statistical broadening of the signal. We demonstrate these noise mechanisms in our device, and show that they explain the measured energy resolution of 25 eV at 5.9 keV. We also suggest ways to reduce their contribution in future devices.
Reoxidation effects on the chemical bonding states of nitrogen accumulated at the oxynitride/silicon interface
Authors: Miura Yoshinao , Ono Haruhiko , Ando Koichi
Published: July 2002

Nitrogen bonding states near oxynitride/Si interfaces in NO-nitrided oxide films were investigated by x-ray photoelectron spectroscopy (XPS). A reoxidation process was used to change the nitrogen location in the depth profile. Charge-up effects on the XPS spectra were removed by considering a highly nonuniform nitrogen distribution. We found that the N 1s core-level shifts to a higher energy by 0.4 eV as the interfacial nitrogen is incorporated into the oxide during the reoxidation. It was also shown that the chemical environment of the interfacial nitrogen differs from that in Si3N4. We attribute this gradual chemical shift to the difference in the second nearest neighbor atoms surrounding the nitrogen.