bluuebunny/crossref_metadata_2025 huggingface dataset:
Band gap engineering of thin-film electroluminescent devices
Authors: Krasnov Alexey N.
Published: July 2002

We introduce an alternative concept to increase the efficiency and brightness of thin-film electroluminescent (TFEL) devices. The method utilizes band gap engineering of the active layer of the device. The initial steps of our work using a ZnSxSe1−x alloy are also presented to demonstrate the workability of the method. This letter discusses the related obstacles and future potentials of the band gap engineering for monochrome and color TFEL devices.
Low-voltage electron emission from “tipless” field emitter arrays
Authors: Busta H. , Furst D. , Rakhimov A. T. , Samorodov V. A. , Seleznev B. V. , Suetin N. V. , Silzars A.
Published: July 2002

Electron emission is obtained from “tipless” gated n-silicon arrays (6460 gate holes) by depositing about 10 nm of nanocrystalline graphite (NCG) on top of the gates and into the gate holes by a glow-discharge technique at 900 °C. The polycrystalline silicon gate diameter is 1.8 μm and the gate-to-substrate distance is 0.85 μm. The interdielectric layer is SiO2. Turn-on voltages are about 40–60 V. The gate currents are about 50% of the total emission currents. From the emission site density of the NCG films and current fluctuation measurements, it is concluded that several emission sites are generated inside the gate holes at the NCG–Si interface that exhibit gate voltage (Vg) -induced field enhancement. The field at these emission sites is expressed by E=βVg.
Giant magnetic effects and oscillations in antiferromagnetic Josephson weak links
Authors: Gor’kov L. , Kresin V.
Published: July 2002

Josephson junctions with an antiferromagnetic metal as a link are described. An especially interesting case is provided by a barrier built on a giant magnetoresistance multilayer or by using doped manganites in the metallic A-phase. Such a junction is predicted to display unusual properties. The junction can be switched off by a relatively small magnetic field. In addition, the amplitude of the Josephson current rapidly oscillates as a function of the field.
Nanometer air gaps in semiconductor wafer bonding
Authors: Liau Z. L. , Liau A. A.
Published: July 2002

Evanescent-wave tunneling of visible light is shown to be sensitive to the nanometer air gaps between dielectrics of high refractive indices. The narrow air gap in molecular-force bonded GaP/GaP was then measured to be 1.3 nm.
Epitaxy of InAs quantum dots on self-organized two-dimensional InAs islands by atmospheric pressure metalorganic chemical vapor deposition
Authors: Yeoh T. S. , Liu C. P. , Swint R. B. , Huber A. E. , Roh S. D. , Woo C. Y. , Lee K. E. , Coleman J. J.
Published: July 2002

Fully coherent InAs quantum dots and InAs quantum dots grown on self-organized two-dimensional (2D) islands by atmospheric pressure metalorganic chemical vapor deposition are investigated. The significantly lower critical thickness window of between 1 and 2.0 monolayers for fully coherent dots is attributed to the suppression of a segregated indium floating layer. An InAs quantum dot density of 4.7×1010 cm−2 was achieved on GaAs, and a highly localized InAs quantum dot density of over 5×1012 cm−2 was achieved on 2D InAs islands.
Structure and electrostatic properties of passivated CdSe nanocrystals
Authors: Rabani Eran
Published: July 2002

The electrostatic and structural properties of CdSe nanocrystals are discussed using an atomistic model that treats both the nanocrystal core and its passivation layer. The model predicts the presence of a permanent dipole moment for CdSe nanocrystals in the wurtzite crystal structure. The dipole moment is mildly screened by the nanocrystal’s passivation layer, and is significantly reduced due to surface reconstruction and relaxation. Possible explanation for preferential growth of CdSe particles along the c-axis is provided with a detailed analysis of the structural reconstruction of the different surfaces.
Nonreciprocal transmission in a direct-bonded photorefractive Fe:LiNbO3 buried waveguide
Authors: Gawith Corin B. E. , Hua Ping , Smith Peter G. R. , Cook Gary
Published: July 2002

We report the fabrication of a 20-μm-thick photorefractive Fe:LiNbO3 planar waveguide buried in MgO:LiNbO3 by direct bonding of precision polished surfaces. Nonreciprocal transmission measurements were performed in a 3-mm-long device with a continuous wave 532 nm frequency-doubled YAG laser source. A Fresnel-reflection-based counterpropagating beam arrangement was used to measure a relative change in optical density of approximately 2 within the waveguide, with a photorefractive response time of 4.9 ms.
Fabrication and optical studies of AlGaN/GaN quantum-well waveguides
Authors: Oder T. N. , Lin J. Y. , Jiang H. X.
Published: July 2002

We report the successful fabrication and optical study of submicron waveguide structures based on AlGaN/GaN multiple-quantum wells (MQWs). The MQW structures were grown by metalorganic chemical vapor deposition on sapphire substrates and the waveguides were fabricated by electron-beam lithography and inductively coupled plasma dry etching. The waveguides were patterned with a fixed width of 0.5 μm but with orientations varying from −30° to 60° relative to the a axis of GaN. Optical emission from these structures was studied by photoluminescence spectroscopy. The peak position and linewidth of the emission peak were found to vary systematically with the orientations of the waveguides and followed the sixfold symmetry of a wurtzite structure. This is most likely related to the anisotropy of the exciton/carrier diffusion coefficient along the different crystal orientations in the quasione-dimensional case. The implication from the results is that in proper designs of photonic and electronic devices where submicron structures are fabricated in III nitrides one must consider the orientations of the structures.
High-directivity planar antenna using controllable photonic bandgap material at microwave frequencies
Authors: de Lustrac A. , Gadot F. , Akmansoy E. , Brillat T.
Published: July 2002

In this letter, we experimentally demonstrate the capability of a controllable photonic bandgap (CPBG) material to conform the emitted radiation of a planar antenna at 12 GHz. The CPBG material is a variable conductance lattice fabricated with high-frequency PIN diodes soldered along metallic stripes on dielectric printed boards. Depending on the diode bias, the emitted radiation of the antenna can be either transmitted or totally reflected by the material. In the transmission state, the antenna radiation is spatially filtered by the CPBG material in a sharp beam perpendicular to the surface of the material.
Structural characterization of InAs/GaAs quantum-dot nanostructures
Authors: Pal D. , Towe E. , Chen S.
Published: July 2002

We have performed high-resolution x-ray diffraction measurements on vertically aligned InAs/GaAs quantum-dot nanostructures. The measurements were carried out for both the symmetric (004) and asymmetric (113) and (224) Bragg reflections. Theoretical simulations of the rocking curves indicate that the x-ray signal is primarily from the pseudomorphically strained (In,Ga)As wetting layers. The average thickness and indium composition in the wetting layers, as determined from simulations of the rocking curves, were, respectively, 0.72 nm and 88%. Transmission electron microscopy studies show the creation and annihilation of quantum dots with no observable dislocations.
Study of the thermo-optic effect in hydrogenated amorphous silicon and hydrogenated amorphous silicon carbide between 300 and 500 K at 1.55 μm
Authors: Della Corte Francesco G. , Montefusco Maurizio Esposito , Moretti Luigi , Rendina Ivo , Rubino Alfredo
Published: July 2002

The thermo-optic coefficients of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon carbide (a-SiC:H)—two of the main amorphous semiconductors in optoelectronics—have been measured and critically analyzed in the practical device operation temperature range 300–500 K, at the communication wavelength of 1.55 μm. The experimental data have been fitted using a single-oscillator model that takes into account the shape of the ε2 spectrum of the amorphous materials. In particular, for a-Si:H, the extracted parameters significantly extend, and are consistent with, the few data reported in the literature; an interesting analogy with crystalline silicon is also found and discussed. Complete results for a-SiC:H are finally reported.
Abrupt current increase due to space-charge-limited conduction in thin nitride–oxide stacked dielectric system
Authors: Chen Fen , Li Baozhen , Dufresne Roger A. , Jammy Rajarao
Published: July 2002

In this article, the conduction mechanisms in nitride–oxide stacked structures on Si are investigated experimentally and theoretically. Amorphous silicon nitride films (3–5 nm thick) were deposited by low-pressure chemical vapor deposition. The ultrathin oxide layers (1–1.5 nm thick) were formed by reoxidization of the nitride layer at about 900 °C in wet ambient. The current–voltage characteristics for negative and positive gate polarities are asymmetric. An abrupt current increase under negative gate bias prior to dielectric breakdown is reported for this structure. This current–voltage phenomenon is attributed to trap-controlled single-carrier steady-state space-charge-limited conduction—the solid state analog of space-charge-limited current in a vacuum diode. Details of space-charge-limited conduction parameters depend on the thickness of the dielectric film and temperature. The study of those parameters can yield information about the traps inside nitride–oxide films. Such information can provide considerable insight into charge transport mechanisms and carrier trapping in these materials, which are important in understanding the physical processes involved in the basic film properties.
Ballistic switching and rectification in single wall carbon nanotube Y junctions
Authors: Andriotis Antonis N. , Menon Madhu , Srivastava Deepak , Chernozatonskii Leonid
Published: July 2002

Transport properties of various semiconducting zig-zag carbon nanotube Y junctions are studied for the investigations of rectification and switching. Our results indicate that such junctions, when symmetric, can support both ballistic rectification and/or the ballistic switching operating modes. Although structural symmetry of the Y junction is found to be a necessary condition for rectification, it may not be sufficient in all cases.
Phase transition, ferroelectric, and dielectric properties of layer-structured perovskite CaBi3Ti3O12−δ thin films
Authors: Kato Kazumi , Suzuki Kazuyuki , Nishizawa Kaori , Miki Takeshi
Published: July 2002

Thin films of a bismuth-based layer-structured perovskite compound with a number of oxygen octahedron along the c axis between Bi–O layers of three, CaBi3Ti3O12−δ, were prepared using a mixture solution of complex alkoxides. The films crystallized below 550 °C. The crystal structure and surface morphology of these films changed between 600 and 650 °C. The 650 °C-annealed thin film consisted of well-developed grains and exhibited polarization–electric hysteresis loops. The remanent polarization and coercive electric field were 8.5 μC/cm2 and 124 kV/cm, respectively, at 7 V. The dielectric constant and loss factor were about 250 and 0.048, respectively, at 100 kHz.
Influence of dose rate on bubble formation by high energy He implantation in silicon
Authors: Oliviero E. , Beaufort M. F. , Barbot J. F.
Published: July 2002

He + ions were implanted into a (111) epitaxial n-type silicon wafer at different dose rates (fluxes) ranging from 2.5×1012 to 1.3×1013 cm−2 s−1 while keeping the incident energy and dose constant (1.6 MeV, 2×1016 cm−2). After implantation the samples were subjected to thermal annealing at 800 °C for 30 min. Cross section transmission electron microscopy (XTEM) was used to characterize the damage layer. Even in the as-implanted samples the TEM observations revealed the formation of a buried layer containing a dense array of small bubbles. After annealing, a large band of defects made up of bubbles and dislocations was observed in all samples. However, the characteristics of the damage layer found depended on the flux. For the lowest flux, only platelets and planar clusters of helium bubbles lying in the {001} planes were observed. Their nucleation is discussed in terms of the trap-mutation process. For higher fluxes a continuous band of bubbles with rows of prismatic punching related dislocation loops was observed. These dislocations can extend over several micrometers away from the buried layer and are emitted from clusters. For the highest flux these clusters were found to lie in the {100} or {110} planes. The plate-like structures are discussed in terms of the diluted system. The damage evolution with increasing dose rates is explained by taking into account the vacancy production.
High-repetition-rate polymeric solid-state dye lasers pumped by a copper-vapor laser
Authors: Costela A. , Garcı́a-Moreno I. , Sastre R. , Coutts D. W. , Webb C. E.
Published: July 2002

We report on the laser action of pyrromethene 567 incorporated into polymeric matrices and pumped longitudinally with the green line of a copper-vapor laser. When the dye was dissolved in a copolymer of methyl methacrylate and pentaerythritol triacrylate, 290 mW average power at 1 kHz (37% lasing efficiency) was obtained. The laser output decreased to 150 mW after 30 min irradiation time (1.8×106 shots) and to 32 mW after 70 min of operation (4.2×106 shots). Output power of up to 1 W at 6.2 kHz was obtained for short periods of time. Polymeric matrices incorporating rhodamine 6G were also studied.
Size distribution of a metallic polydispersion through capacitive measurements in a sedimentation experiment
Authors: Salazar-Neumann E. , Nahmad-Molinari Y. , Ruiz-Suárez J. C. , Ardisson P.-L. , Arancibia-Bulnes C. A. , Rechtman R.
Published: July 2002

We present a simple experimental technique to determine size distributions of metallic polydispersions. The particles are first suspended in a viscous fluid-like glycerol and then their sedimentation is followed by measuring the effective dielectric constant in a cylindrical cell at a fixed frequency. Thereafter, an inversion procedure of the data, based on the Maxwell–Garnett effective medium theory and Stokes law, is used to directly obtain the size distribution. The technique is applied to three different stainless steel dispersions and compares very well with a traditional sizing method based in microphotography.
Ultraviolet single-frequency pulses with high average power using frequency-converted passively Q-switched quasimonolithic Nd:yttrium–aluminum–garnet ring lasers
Authors: Spiekermann S. , Bode M. , Freitag I. , Laurell F.
Published: July 2002

We demonstrate a compact ultraviolet light source based on frequency-converted diode-pumped passively Q-switched miniature Nd:yttrium–aluminum–garnet (YAG) ring lasers. A unique pulse-to-pulse stability in single-frequency operation is obtained by diffusion-bonding the Nd:YAG crystal with the Cr4+:YAG saturable absorber crystal to form an all-solid-state quasimonolithic ring laser cavity. Amplified in a longitudinally pumped Nd:vanadate (YVO4) crystal and single-pass frequency quadrupled in periodically poled potassium titanyl phosphate and barium borate crystals, an average output power of 485 mW at 266 nm with 25 μJ pulse energy is achieved with an overall efficiency of 3.3% with respect to the diode pump power.
Direct signature of strained GaN quantum dots by Raman scattering
Authors: Gleize J. , Demangeot F. , Frandon J. , Renucci M. A. , Kuball M. , Damilano B. , Grandjean N. , Massies J.
Published: July 2002

We report on a Raman study of strained wurtzite GaN quantum dots embedded in AlN spacers. Various laser excitations between 2.33 and 3.81 eV were used, which allows for selective probing of the dots, through resonant enhancement of the Raman signal. A direct signature of the A1 (LO) and E2 phonons of the GaN dots has been obtained. The measured phonon frequencies show that the mean in-plane strain inside the GaN dots approaches the lattice mismatch between GaN and AlN.
On the mechanism of interface trap generation under nonuniform channel-hot-electron stress and uniform carrier-injection stress in metal–oxide–semiconductor field-effect transistors
Authors: Cheng Kangguo , Leburton Jean-Pierre , Hess Karl , Lyding Joseph W.
Published: July 2002

The interpretation of the small hydrogen/deuterium isotope effect widely observed under uniform stress has been based on an implicit assumption that interface traps in the entire channel are passivated by deuterium after the deuterium annealing process. Through a stress/anneal process, we show that this assumption is incorrect. Instead, our results clearly suggest that interface trap generation under both nonuniform channel hot-carrier stress and uniform stress, such as Fowler–Nordheim tunneling and substrate electron injection, essentially follows the same mechanism, which is the breaking of Si–H(D) bonds and the release of hydrogen/deuterium at the oxide/silicon interface.
Selective thermal desorption of ultrathin aluminum oxide layers induced by electron beams
Authors: Kundu Manisha , Miyata Noriyuki , Ichikawa Masakazu
Published: July 2002

The mechanism of electron-beam-induced selective thermal desorption of ultrathin aluminum-oxide layer (∼0.4 nm) on Si(001) surface was investigated by using scanning reflection electron microscopy, reflection high-energy electron diffraction, and Auger electron spectroscopy. We found that the change in the aluminum-oxide layer composition induced by electron-stimulated oxygen desorption accounted for the selective thermal desorption of the oxide layer. A systematic increase in the vacuum-annealing temperature to 500 °C, 600 °C and 720 °C resulted in the formation of three-dimensional metal aluminum clusters, desorption of these clusters, and creation of a nanometer-scale clean Si(001)-2×1 open window in the selected electron-beam-irradiated area.
Multiwavelength laterally complex coupled distributed feedback laser arrays with monolithically integrated combiner fabricated by focused-ion-beam lithography
Authors: Bach L. , Reithmaier I. P. , Forchel A. , Gentner J. L. , Goldstein L.
Published: July 2002

A multiwavelength laser array with four complex coupled distributed feedback lasers was fabricated by focused-ion-beam lithography. The laser array was monolithically integrated with a combiner network to allow simultaneous operation and coupling of four wavelengths into one single-mode fiber. To reduce the fabrication complexity, focused-ion-beam technology was used to define complex coupled gratings lateral to pumped ridge waveguide sections without any further overgrowth step. A four wavelength output with 6-nm-wavelength spacing and side-mode suppression ratios of more than 35 dB were obtained with output powers up to 6 mW per channel.
Negative magnetoresistance produced by Hall fluctuations in a ferromagnetic domain structure
Authors: Barabash Sergey V. , Stroud D.
Published: July 2002

We present a model for a negative magnetoresistance (MR) that would develop in a material with many ferromagnetic domains even if the individual domains have no magnetoresistance and even if there is no boundary resistance. The negative MR is due to a classical current-distortion effect arising from spatial variations in the Hall conductivity, combined with a change in domain structure due to an applied magnetic field. The negative MR can exceed 1000% if the product of the carrier relaxation time and the internal magnetic field due to spontaneous magnetization is sufficiently large.
Improved n+-GaAs/p+-In0.49Ga0.51P/n-GaAs camel-like gate structure for high-breakdown, low-leakage, and high-temperature applications
Authors: Liu Wen-Chau , Yu Kuo-Hui , Liu Rong-Chau , Lin Kun-Wei , Cheng Chin-Chuan , Lin Kuan-Po , Yen Chih-Hung , Wu Cheng-Zu
Published: July 2002

A n+-GaAs/p+-In0.49Ga0.51P/n-GaAs camel-like gate structure has been applied to fabricate high-performance transistors. The studied heterostructure field-effect transistor exhibits a large barrier height, high breakdown voltage, low leakage current, and good temperature-dependent characteristics. Experimentally, for a 1×100 μm2 device, the gate-drain breakdown voltage and gate leakage current are 52 (31.5) V, and 37 μ A/mm (3.5 mA/mm) at the gate-drain voltage of 40 V, respectively, at the temperature of 300 (480) K. In addition, the high drain-source operation voltage over 20 V with low leakage current is obtained.
Selective area metalorganic vapor phase epitaxy of thick crack-free GaN films on trenched SiC substrates
Authors: Akasaka Tetsuya , Ando Seigo , Nishida Toshio , Saito Hisao , Kobayashi Naoki
Published: July 2002

Crack-free GaN films up to 11-μm-thick have been grown by using trenched SiC substrates and selective area metalorganic vapor phase epitaxy. These crack-free GaN films have hexagonal shapes and are surrounded by trenches. 97% of the hexagonal GaN films with side lengths of 100 μm and thickness of 11 μm was crack-free. The GaN films do not crack because the lateral propagation of cracks stops at the trenches and strain is relaxed in the small-area hexagonal GaN. This strain relaxation is confirmed by micro-Raman scattering measurements and agrees well with theoretical predictions.
Current-modulated electroluminescence spectroscopy and its application to InGaN single-quantum-well blue and green light-emitting diodes
Authors: Azuhata Takashi , Homma Takefumi , Ishikawa Yoshikazu , Chichibu Shigefusa F. , Sota Takayuki , Mukai Takashi
Published: July 2002

Current-modulated electroluminescence spectroscopy was developed to investigate the mechanism of the current-induced spectral blueshift in InGaN single-quantum-well blue and green light-emitting diodes. The evidence was obtained that tail states exist in InGaN active layers, and also the blueshift was found to be dominated by the tail-state filling effect.
Subband electron properties of highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates
Authors: Jiang C. P. , Huang Z. M. , Guo S. L. , Chu J. H. , Cui L. J. , Zeng Y. P. , Zhu Z. P. , Wang B. Q.
Published: July 2002

A Shubnikov–de Haas (SdH) oscillation measurement was performed on highly doped InAlAs/InGaAs metamorphic high-electron-mobility transistors on GaAs substrates at a temperature of 1.4 K. By analyzing the experimental data using fast Fourier transform, the electron densities and mobilities of more than one subband are obtained, and an obvious double-peak structure appears at high magnetic field in the Fourier spectrum. In comparing the results of SdH measurements, Hall measurements, and theoretical calculation, we found that this double-peak structure arises from spin splitting of the first-excited subband (i=1). Very close mobilities of 5859 and 5827 cm2/V s are deduced from this double-peak structure. The sum of the carrier concentration of all the subbands in the quantum well is only 3.95×1012 cm−2 due to incomplete transfer of the electrons from the Si δ-doped layer to the well.
Longitudinal optic phonon–plasmon coupling in δ-doped metamorphic InAlAs/InGaAs high-electron-mobility transistor structures on GaAs substrates
Authors: Jiang C. P. , Huang Z. M. , Li Z. F. , Yu J. , Guo S. L. , Lu W. , Chu J. H. , Cui L. J. , Zeng Y. P. , Zhu Z. P. , Wang B. Q.
Published: July 2002

InAlAs/InGaAs metamorphic high-electron-mobility transistor structures with different spacer layers on GaAs substrates are characterized by Raman measurements. The influence of In0.52Al0.48As spacer thickness on longitudinal optic phonon–plasmon coupling is investigated. It is found that the intensity of GaAs-like longitudinal optic phonon, which couples with collective intersubband transitions of two-dimensional electron gas, is strongly affected by the different subband energy spacings, subband electron concentrations, and wave function distributions, which are determined by different spacer thicknesses.
Self-doping near the seed/layer interface in conformal GaAs layers grown on Si
Authors: Ardila A. M. , Martı́nez O. , Avella M. , Jiménez J. , Gérard B. , Napierala J. , Gil-Lafon E.
Published: July 2002

Undoped GaAs layers grown on Si substrates by the conformal method were studied by micro-Raman spectroscopy, cathodoluminescence, and diluted Sirtl solution with light (DSL) etching. The results show that nonintentional doping of conformal layers can take place near the seed/layer interface. The self-doped area presents a bright luminescence emission and shows longitudinal optic-plasmon coupled Raman modes. The nonintentional dopants were n type as deduced from Raman spectroscopy and DSL selective etching. The doped region extends only 2–3 μm from the seed and was tentatively associated with enhanced diffusion of Si in the presence of dislocations at the interface between the seed and the conformal layer.
Transient grating measurements of film thickness in multilayer metal films
Authors: Slayton Rebecca M. , Nelson Keith A. , Maznev A. A.
Published: July 2002

A transient grating technique has been used to measure film thicknesses in five multilayer film structures. Through-plane acoustic responses are observed through time-resolved diffraction that reveals their return to the free surface after partial reflections within the structure. Optical heterodyne detection with a controlled reference field amplitude permits optimization of the signal/noise ratio relative to detection of the signal against the far stronger incident probe field or against a dark background (homodyne detection). In-plane acoustic waves are also generated and observed.
Observation of pinching in the compact toroid injection experiment: Implications for a plasma opening switch
Authors: Baker K. L. , Hwang D. Q. , Evans R. W. , Horton R. D. , McLean H. S. , Terry S. D.
Published: July 2002

A compact toroid inductively stores the energy released by a capacitor bank as it is being accelerated. This energy can be stored for a period of more than ten microseconds and then transferred to a load on a much shorter time scale. This article presents framing camera images of the radial compression of plasma trailing behind a compact toroid as the compact toroid leaves its inner electrode. This compression illustrates the basic principles of a compact toroid plasma opening switch which could be used to drive fast z pinches.
Indium–silicon co-doping of high-aluminum-content AlGaN for solar blind photodetectors
Authors: Adivarahan V. , Simin G. , Tamulaitis G. , Srinivasan R. , Yang J. , Khan M. Asif , Shur M. S. , Gaska R.
Published: July 2002

We report on an indium–silicon co-doping approach for high-Al-content AlGaN layers. Using this approach, very smooth crack-free n-type AlGaN films as thick as 0.5 μm with Al mole fraction up to 40% were grown over sapphire substrates. The maximum electron concentration in the layers, as determined by Hall measurements, was as high as 8×1017 cm−3 and the Hall mobility was up to 40 cm2/Vs. We used this doping technique to demonstrate solar-blind transparent Schottky barrier photodetectors with the cut-off wavelength of 278 nm.
Evidence for strain-induced lateral carrier confinement in InGaAs quantum wells by low-temperature near-field spectroscopy
Authors: Zeimer U. , Bugge F. , Gramlich S. , Smirnitski V. , Weyers M. , Tränkle G. , Grenzer J. , Pietsch U. , Cassabois G. , Emiliani V. , Lienau Ch.
Published: July 2002

A strain-induced lateral variation of the band edges of a 10-nm-thick In0.16Ga0.84As quantum well embedded in GaAs is achieved by patterning of a 100-nm-thick compressively strained In0.52Ga0.48P stressor layer. The strain modulation results in a splitting of the 10 K far-field photoluminescence (PL) spectra into two emission peaks. Spectrally resolved two-dimensional near-field PL images establish a clear spatial and spectral separation of the two far-field PL peaks, indicating a lateral carrier confinement with a confinement energy of about 10 meV. Finite-element calculations of the strain distribution are used to determine the lateral band-edge shifts and are well in agreement with the experimental findings.
Hydrogen storage in carbon nitride nanobells
Authors: Bai X. D. , Zhong Dingyong , Zhang G. Y. , Ma X. C. , Liu Shuang , Wang E. G. , Chen Yan , Shaw David T.
Published: July 2002

Aligned carbon nitride (C–N) nanobells in polymer form, prepared by microwave plasma-assisted chemical vapor deposition, were used as hydrogen adsorbent. A hydrogen storage capacity up to 8 wt % was achieved reproducibly under ambient pressure and at temperature of 300 °C. The high hydrogen storage capacity under the moderate conditions was mainly derived from the short nanobell structure with openended graphitic layers, as well as the nitrogen in the nanobells, which acts as an active site for hydrogen adsorption. The high hydrogen uptake and the simple adsorption–desorption process suggest that a C–N nanobell is promising as a hydrogen storage material.
Microstructural and optical properties of SnO2 thin films grown on heavily doped n-InP(100) substrates
Authors: Kim T. W. , Lee D. U. , Choo D. C. , Yoon Y. S.
Published: July 2002

Bright-field transmission electron microscopy (TEM) and high-resolution TEM images and an electron diffraction pattern showed that the SnO2 layers grown on heavily doped n-InP(100) substrates were nanoscale thin films. X-ray photoelectron spectroscopy showed that the positions of the peaks corresponding to the Sn 3d5/2, the Sn 3d3/2, and the O 1s levels for the SnO2 thin film were slightly shifted toward the lower energy side in comparison with those for bulk SnO2. The refractive indices obtained by spectroscopic ellipsometry were above 2.2 around the SnO2 energy gap of the SnO2 thin films. The maximum intensity of the optical transmittance for the SnO2 nanoscale thin film with 3939 Å thickness was above 90%.
Effect of perimeters of induced shielding current loops on levitation force in melt grown single-domain YBa2Cu3O7−x bulk
Authors: Yang W. M. , Zhou L. , Feng Y. , Zhang P. X. , Zhang C. P. , Yu Z. M. , Tang X. D.
Published: July 2002

Effects of perimeters of induced shielding current loops (ISCL) on a levitation force have been investigated for a single-domain YBa2Cu3O7−x sample. The sample was prepared by a top-seeded melt–growth process. The levitation force of the sample decreases monotonously with the increasing perimeters of ISCL while the depth of the cutting slot increases along its diameter from one side to another. The maximum levitation force of the sample without any cutting slot is about 1.68 times higher than that of the sample bisected. A simple physical model is afforded to interpret the experimental results.
Pulsed inductively coupled chlorine plasmas in the presence of a substrate bias
Authors: Subramonium Pramod , Kushner Mark J.
Published: July 2002

Pulsed inductively coupled plasmas (ICPs) sustained in electronegative gas mixtures using a substrate bias are being investigated to achieve improved etching characteristics in microelectronics fabrication. Experiments have shown that electron temperatures in pulsed ICPs without a substrate bias monotonically decrease during the afterglow. Under select conditions with a substrate bias, electron temperatures increase in the late afterglow. These trends suggest a transition in power deposition from inductive to capacitive. To investigate these processes, a two-dimensional, computationally parallel model was developed for pulsed ICPs. Results for Cl2 plasmas indicate that with a substrate bias the sheath thickness and speed, and hence electron heating, increase during the afterglow as the electron density decays. When the sheath reaches a critical thickness, capacitive electron heating begins.
Determination of optical modes in two-dimensional finite-size photonic crystals by photonic resonance scattering
Authors: Nojima S.
Published: July 2002

The analogy of the resonance scattering of an electron by an atom is used to investigate optical modes in two-dimensional finite-size photonic-crystal resonators. This analysis enables us to determine complex resonance energies from which we can estimate optical modes and photon lifetimes in the resonators. The threshold amplitude gain of the laser exploiting this photonic-crystal resonator is inversely proportional to the photon lifetime. This linear relation is found to remain the same irrespective of the dimensionality of the photonic crystal structure, the number of unit cells, and the size of unit cell, as long as the filling factor of the gain cell is fixed. This implies that the two-dimensional finite-size photonic-crystal resonators work well despite complicated feedback mechanisms and the absence of clear-cut cavity mirrors.
High-accuracy wavemeter based on a stabilized diode laser
Authors: Banerjee Ayan , Rapol Umakant D. , Wasan Ajay , Natarajan Vasant
Published: July 2002

We have built a high-accuracy wavelength meter for tunable lasers using a scanning Michelson interferometer and a reference laser of known wavelength. The reference laser is a frequency-stabilized diode laser locked to an atomic transition in Rb. The wavemeter has a statistical error per measurement of 5 parts in 107, which can be reduced considerably by averaging. Using a second stabilized diode laser, we have verified that systematic errors are below 4 parts in 108.
Thermal activation of dislocation array formation
Authors: Janzen A. , Dumkow I. , Horn-von Hoegen M.
Published: July 2002

Surfactant-mediated epitaxy allows the growth of smooth, continuous, and relaxed Ge films on Si(111). The key process is the formation of an ordered array of misfit dislocations, which are confined to the Ge/Si interface and accommodate most of the lattice mismatch of 4.2%. Its formation crucially depends on the mobility and reactivity of the dislocations, which sets a lower limit to the possible growth temperature. Below 550 °C, the mobility of the dislocations is so low that their arrangement is disordered, causing a low film quality with a high number of threading defects.
Direct response of microstrip line coupled Nb THz hot-electron bolometer mixers
Authors: Ganzevles W. F. M. , Gao J. R. , de Korte P. A. J. , Klapwijk T. M.
Published: July 2002

We study the direct response of a superconducting Nb hot-electron bolometer mixer centered at 2.5 THz that incorporates an Au/SiO2/Al microstrip transmission line. The direct response is studied using a Fourier transform spectrometer. We find a peak response at a frequency of 2.1 THz, which is 20% lower than predicted based on a model that neglects the inductance effect in the microbridge.
Linear optical properties of Ge nanocrystals in silica
Authors: Dowd Annette , Elliman Robert G. , Luther-Davies Barry
Published: July 2002

The absorption and extinction spectra of Ge nanocrystals in silica formed by ion implantation are studied using photothermal deflection and transmission spectroscopies. It is found that scattering makes a significant contribution to the extinction spectrum, damping the spectral features and resulting in a Rayleigh scattering-like ω4 dependence. In contrast, the spectra measured by photothermal deflection clearly show features such as the E1/E1+Δ1 transitions. The Tauc gap is extracted to be ∼0.7±0.1 eV.
Nitrogen-ion-implantation synthesis of wurtzite GaN in GaP
Authors: Kuriyama K. , Kondo H. , Hayashi N. , Ogura M. , Hasegawa M. , Kobayashi N. , Takahashi Yukimi , Watanabe S.
Published: July 2002

α-GaN phase (wurtzite) was synthesized in GaP(100) by 140-keV N2+ ion implantation with a dose of 3.0×1017 cm−2 at 400 °C and subsequent furnace annealing at 950 °C for 20 min or rapid thermal annealing at 1000 °C for 15 s. The traces of α-GaN were recognized by glancing-angle x-ray diffraction, supporting by the observation of the planes belonging to the [0100]-zone axis in α-GaN by a selected-area electron diffraction analysis. The formation of microcrystalline GaN of <1000 Å in size was confirmed by using Auger electron spectroscopy and cross sectional transmission electron microscopy. A1 transverse optical phonon mode in α-GaN was observed at around 525 cm−1, indicating a nearly orientation relationship with GaN〈112̄0〉//GaP〈100〉.
Degradation of ultrathin oxides by iron contamination
Authors: Choi B. D. , Schroder D. K.
Published: July 2002

Iron-contaminated oxides of metal-oxide-semiconductor devices were investigated to study gate oxide integrity (GOI) degradation dependence on oxide thickness for oxide thicknesses from 3 to 5 nm and iron densities from 4×1010 to 1.4×1012 cm−3. In contrast to other publications, we show that oxides as thin as 3 nm show gate oxide integrity degradation, especially for the higher iron densities. But even for the low iron density we observe GOI degradation for all oxides.
Mass-density-modulated structures of crystalline hydrogenated carbon films
Authors: Zhang Z. J. , Narumi K. , Naramoto H.
Published: July 2002

Hydrogenated carbon films with a crystalline structure have been synthesized by radio-frequency plasma-enhanced chemical vapor deposition. The mass density of the films is dependent on the plasma power applied. By switching alternatively two different plasma powers during deposition, mass-density-modulated structures of the crystalline hydrogenated carbon films can be produced. The structure and properties of these mass-density-modulated structures have also been investigated.
Morphological, optical, and photoluminescent characteristics of GaAs1−xNx nanowhiskered thin films
Authors: Canales-Pozos S. A. , Rı́os-Jara D. , Alvarez-Fregoso O. , Alvarez-Pérez M. A. , Garcı́a-Hipólito M. , Martı́nez-Sánchez E. , Juárez-Islas J. A. , Zelaya-Angel O. , Mendoza-Alvarez J. G.
Published: July 2002

GaAs 1−x N x solid-solution thin films of nanometric size were prepared on glass substrates by the radio-frequency sputtering technique. Atomic-force microscopy images show that the films are composed of grains with a whisker shape, whose size is practically independent of the substrate temperature. Their typical diameters range between 40 and 45 Å. The surface morphology exhibits a high density of whisker-like features that are almost normal to the substrate plane. This density increases as the substrate temperature increases, but, in essence, the nanowhisker diameter does not. Optical absorption spectra of the samples show a band-gap energy blueshift as large as 1.5 eV with respect to that of the GaAs bulk value, which was associated with strong quantum-confinement effects. Photoluminescence emission spectra in the blue range of 428–438 nm confirm the quantum-size effects in the GaAs1−xNx nanowhiskered thin films.
Distinguishing surface and bulk contributions to third-harmonic generation in silicon
Authors: Saeta P. N. , Miller N. A.
Published: July 2002

We report measurements of third-harmonic generation from ultrathin crystalline silicon layers of gradually varying thickness. Both the angular and thickness dependence of the third-harmonic light generated in transmission at normal incidence are consistent with negligible surface contribution to third-harmonic generation in silicon, even under tight focusing. This work illustrates a method for distinguishing surface and bulk contributions to harmonic generation.
Charge-transfer nature in luminescence of YNbO4:Bi blue phosphor
Authors: Shin Sang Hoon , Jeon Duk Young , Suh Kyung Soo
Published: July 2002

Bismuth doped yttrium niobate (YNbO4:Bi) is a potential blue phosphor for field emission displays application. It is observed after introducing Bi ions that cathodoluminescence efficiency of YNbO4:Bi becomes lower than that of YNbO4. From the calculations of critical distance (RC) of energy transfer and Huang–Rhys parameter (SHR) of YNbO4:Bi, it is found that the energy transfer by a dipolar-type interaction is unlikely compared with that of a short-range interaction possible in the luminescence of YNbO4:Bi. Thus, it is believed that the luminescence property of YNbO4:Bi is mainly affected by the host lattice YNbO4 having self-luminescent NbO43− complex. By time-resolved spectroscopy, it is found that luminescence characteristics of activator Bi3+ in YNbO4:Bi shows a charge-transfer behavior.
Two-phase (ferroelectric and antiferroelectric) nuclei and diffuse phase transition in the vicinity of the ferroelectric–antiferroelectric–paraelectric triple point
Authors: Ishchuk V. M. , Matveev S. V. , Sobolev V. L.
Published: July 2002

X-ray studies of the crystal structure in Pb1−x(Li1/2La1/2)xZr1−yTiyO3 solid solutions at the phase transition from a paraelectric state into ordered states near the triple ferroelectric–antiferroelectric–paraelectric point of the “Ti-content–temperature” phase diagram are carried out. Analysis of the shape of characteristic x-ray lines indicates the presence of two-phase nuclei with ferroelectric and antiferroelectric types of dipole ordering in the crystal lattice of the solid solutions above the point of the paraelectric phase transition (the Curie temperature).
Electric field-induced junctions in epitaxial layers of CuInSe2
Authors: Gartsman Konstantin , Cahen David , Scheer Roland
Published: July 2002

Epitaxial films of CuInSe2 on Si(111) were modified by the application of an electric field through a movable tip. The electric field induces stable junction regions which are identified by efficient separation and collection of electron beam-induced charge carriers. The movable tip allows for scribing of these junction regions. The junctions can be explained by symmetrical p/p+/n/p+/p regions formed within the CuInSe2 epilayers. The reported method presents an alternate way for junction patterning in two dimensions.
Complete basis set extrapolation limit for electronic structure calculations: Energetic and nonenergetic properties of HeBr and HeBr2 van der Waals dimers
Authors: de Lara-Castells M. P. , Krems R. V. , Buchachenko A. A. , Delgado-Barrio G. , Villarreal P.
Published: July 2002

The lowest Σ+2 and Π2 electronic states of the HeBr molecule have been calculated by the ab initio coupled cluster approach in conjunction with a series of increasing size augmented correlation-consistent basis sets of double through quintuple zeta quality. Different extrapolation formulas to the complete basis set limit have been tested by comparing estimated and actual quintuple zeta quality counterpoise corrected interaction energies. Frozen-core approach is checked by performing calculations in which all electrons are correlated. The potential energy surfaces of the HeBr2 van der Waals complex have been obtained from the HeBr potentials by means of the diatomic-in-molecule approach. Finally, transport, scattering, and spectroscopic properties of HeBr and HeBr2(B) systems derived from ab initio data for different basis sets are examined. It is shown that their convergence closely follows the convergence of corresponding potential energy surfaces.
Photoluminescence of multilayer GaSb/GaAs self-assembled quantum dots grown by metalorganic chemical vapor deposition at atmospheric pressure
Authors: Motlan  , Goldys E. M.
Published: July 2002

We investigate photoluminescence from multilayer GaSb self-assembled quantum dots embedded in GaAs grown by metalorganic chemical vapor deposition. The spectra show the emission from quantum dots at about 1.09 eV and from the wetting layer at 1.39 eV. With increasing temperature the wetting layer emission quenches faster than the quantum dot emission. We also observe a decrease of the quantum dot peak energy at temperatures between 50 and 70 K and a peak shift with increasing excitation powers typical of type II structures. A large separation (300 meV) between the photoluminescence peaks from quantum dots and the wetting layer suggests differences in the intermixing at the GaSb/GaAs interface in the structures grown by metalorganic chemical vapor deposition and by molecular-beam epitaxy.
Cluster glass structure in nanohybrids of nonstoichiometric zinc ferrite in silica matrix
Authors: Zhou Z. H. , Wang J. , Xue J. M. , Chan H. S. O.
Published: July 2002

A cluster glass structure has been observed to occur in nanohybrids consisting of zinc ferrite in an amorphous silica matrix. Such a unique cluster glass structure has been supported by studies of x-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and magnetic characterization. By increasing the Fe/Zn ratio in silica gel to 10, crystallites of zinc ferrite of partially inverted structure were nucleated and grown in amorphous iron oxide pockets dispersed in the silica network. The zinc ferrite crystallites, together with the confinement of silica matrix, suppress nucleation and crystallization of α-Fe2O3 to a temperature above 900 °C, preserving the cluster glass structure. The resulting cluster glass structure consists of amorphous iron oxide pockets of ∼10 nm in dimensions together with zinc ferrite crystallites of ∼3 nm in sizes, which are uniformly dispersed in the amorphous silica glass matrix.
Use of TiN(O)/Ti as an effective intermediate stress buffer and diffusion barrier for Cu/parylene-n interconnects
Authors: Gadre Kaustubh S. , Alford T. L. , Mayer J. W.
Published: July 2002

Copper and parylene-n (Pa-n) are studied for ultralarge scale integration circuits because of their low electrical resistivity, resistance to electromigration and low dielectric constant, chemical inertness, and compatibility with current integrated circuit manufacturing, respectively. Copper diffusion observed at and above 300 °C in Pa-n correlates to an increase in the crystallinity of the α phase and subsequent transformation to the more open structure of β parylene. Titanium nitride (oxygen) [TiN(O)]/titanium (Ti) bilayers are successfully implemented as a diffusion barrier. TiN is proven to be a very good diffusion barrier up to 500 °C for copper due to its large negative heat of formation and hence its thermal stability. Incorporation of an intermediate titanium layer reduced the residual stress and thermal mismatch between Pa-n and TiN. Without the Ti layer thermal cracking of TiN occurred. The presence of the buffer layer had no detrimental effects on the overall resistivity. The effectiveness of the barrier is attributed to stuffing of the grain boundaries with oxygen and nitrogen. This results in the elimination of rapid diffusion paths. This work provides the foundation for future implementation of Cu/Pa-n for higher temperature microelectronics.
Hybrid optical fiber-apertured cantilever near-field probe
Authors: Minh Phan Ngoc , Ono Takahito , Watanabe Hisashi , Lee Seung Soup , Haga Yoichi , Esashi Masayoshi
Published: July 2002

In this letter, we propose a hybrid optical fiber-apertured cantilever probe for optical near-field applications. A thermal SiO2 cantilever beam with a SiO2 pyramidal tip was formed by Si micromachining technique and bonded with an optical fiber using a polyimide adhesive layer. A subwavelength aperture at the apex of the SiO2 tip was formed by etching the SiO2 in a buffered-HF solution. Optical near-field imaging in contact mode was observed with the fabricated probe. The probe could work in contact mode because the cantilever at the end of the fiber can flexibly move on the sample surface. By detecting the far-field light which is reflected-back by the tip of the cantilever, the vibration of the cantilever was observed using the probe itself. With the proposed structure, a hybrid fiber bundle-apertured cantilever array is feasible for application in parallel near-field processing or data storage.
Multidimensional phase space and sunset diagrams
Authors: Bashir A. , Delbourgo R. , Roberts M. L.
Published: July 2002

We derive expressions for the phase space of a particle of momentum p decaying into N particles, that are valid for any number of dimensions. These are the imaginary parts of so-called “sunset” diagrams, which we also obtain. The results are given as a series of hypergeometric functions, which terminate for odd dimensions and are also well suited for deriving the threshold behavior.