bluuebunny/crossref_metadata_2025 huggingface dataset:
Gray-track damage in potassium titanyl phosphate under a picosecond regime at 532 nm
Authors: Carrion Lionel , Girardeau-Montaut Jean-Pierre
Published: July 2002

We report studies of gray-track damage formation in flux-grown potassium titanyl phosphate exposed to 532 nm, picosecond pulses. We investigate the time evolution of damage formation and the evolution of gray-track susceptibility as a function of laser intensity. We demonstrate that the energy loss in the crystal is for the most part due to the formation of the centers of absorption. For 26 ps pulses, the intensity damage threshold was found to be much higher than for nanosecond pulses. Evidence is found that the mechanism of gray-track formation is nonlinear as a function of intensity and as a function of pulse duration.
Enhanced blocking temperature in NiO spin valves: Role of cubic spinel ferrite layer between pinned layer and NiO
Authors: Farrow R. F. C. , Carey M. J. , Marks R. F. , Rice P. M. , Smith David J.
Published: July 2002

We compare the blocking temperature for simple permalloy (80% Ni)/Au/permalloy/NiO spin valves with and without an interfacial, oxidized Fe layer (Fe layer 12 Å thick) inserted at the permalloy/NiO interface. We find a significantly increased blocking temperature and pinning field for spin valves with the interfacial Fe-oxide layer, as a result of moderate (230 °C/1 h) annealing of the Au/permalloy/Fe-oxide/NiO part of the spin valve. High resolution transmission electron microscopy and electron energy loss microanalysis reveal that the Fe-oxide layer is converted to a cubic spinel ferrite (Ni0.8Fe2.2O4) layer by solid state reaction with the NiO.
Frequency domain spectroscopy of free-space terahertz radiation
Authors: Takahashi Hironori , Hosoda Makoto
Published: July 2002

We demonstrate frequency domain spectroscopy of free-space terahertz (THz) radiation by using a vibrating optical delay and a rf spectrum analyzer. When the timing of the pump pulses is repeatedly varied at several Hz and an optical chopper at a frequency of several kHz simultaneously modulates the pump pulse, the spectrum analyzer directly obtains the THz spectrum as a sideband of the chopping frequency. This method can be used to measure in real time the transient change in the THz spectrum at a specific frequency corresponding to the water absorption.
Electrical properties of boron-doped p–SiGeC grown on n−–Si substrate
Authors: Ahoujja M. , Yeo Y. K. , Hengehold R. L. , Pomrenke G. S. , Look D. C. , Huffman Jim
Published: July 2002

Electrical properties of fully strained boron-doped Si0.90−yGe0.10Cy/n−–Si grown by low pressure chemical vapor deposition have been investigated as a function of carbon content (0.2%–1.5%), using the variable temperature (25–650 K) Hall-effect technique. The results of Hall-effect measurements show that the Si substrate and the SiGeC/Si interfacial layer affect significantly the electrical properties of the SiGeC epitaxial layer. Thus, a three-layer conducting model has been used to extract the carrier concentration and mobility of the SiGeC layer alone. At room temperature, the hole carrier concentration decreases from 6.8×1017 to 2.4×1017 cm−3 and the mobility decreases from 488 to 348 cm2/V s as the carbon concentration increases from 0.2% to 1.5%. The boron activation energy increases from 20 to 50 meV as C increases from 0.2% to 1.5% with an increment of 23 meV per atomic % of C.
Effect of oxidation and reoxidation on the oxide-substrate interface of 4H- and 6H-SiC
Authors: Jernigan G. G. , Stahlbush R. E. , Saks N. S.
Published: July 2002

X-ray photoelectron spectroscopy and sputter depth profiling were used to investigate SiO2 grown on 4H- and 6H-SiC with and without a reoxidation procedure. The oxides grown and oxide-substrate interfaces formed on 4H and 6H were similar in chemistry but different from Si(100). Reoxidation changes the structure of the oxide and the abruptness of the oxide-substrate interface. We propose a model for SiC oxidation where a transition layer containing Si–Si bonds is produced between the oxide and the SiC substrate.
Organic–inorganic hybrid electroluminescence device fabricated by conjugated polymer and ZnS:Mn
Authors: Yang Xiaohui , Xu Xurong
Published: July 2002

An organic–inorganic hybrid device was fabricated. The architecture of the hybrid device consisted of two layers sandwiched between two injecting electrodes, one of which was a conjugated polymer layer and the other was an inorganic material layer. Emission from both the organic and inorganic layers was observed, but the mechanisms of luminescence for the layers were different. Our primary results suggest the possibility of integrating different types of luminescence into one device structure.
Designing finite-height two-dimensional photonic crystal waveguides
Authors: So/ndergaard T. , Bjarklev A. , Kristensen M. , Erland J. , Broeng J.
Published: July 2002

Guidelines for designing planar waveguides based on introducing line-defects in two-dimensional photonic-crystal slabs are obtained by comparing calculations on two-dimensional structures with dispersion relations for the media above and below the slab.
GaNAs resonant-cavity avalanche photodiode operating at 1.064 μm
Authors: Kinsey G. S. , Gotthold D. W. , Holmes A. L. , Campbell J. C.
Published: July 2002

A resonant-cavity avalanche photodiode using a GaNAs absorption region grown on GaAs has been demonstrated. The peak quantum efficiency was 59% at 1.064 μm with a full width at half maximum of 11 nm. The absorption coefficient was determined to be α=9×103/cm at this wavelength. The devices exhibited gain up to 100 at a low breakdown voltage of 13 V.
Integration of thin-film vertical-cavity surface-emitting lasers on AlN substrates using a functional layer transfer technique
Authors: Ouchi Toshihiko , Sato Takahiro , Sakata Hajime , Handa Yuichi
Published: July 2002

We have demonstrated thin-film vertical-cavity surface-emitting lasers (VCSELs) on a selected substrate for the hybrid integration of optoelectronic devices. After fabricating VCSEL structures, the epitaxial side of the VCSEL wafer was bonded onto an AlN substrate using Au–Sn solder, and then the growth substrate of the wafer was removed. The devices fabricated by this technique exhibited threshold currents as low as VCSELs on the original growth substrate. The effective thermal resistance did not increase even after the growth substrate was removed.
Controlled assembly of two-dimensional colloidal crystals
Authors: Wei Q.-H. , Cupid D. M. , Wu X. L.
Published: July 2002

Under the influence of capillary forces, colloidal particles embedded in a soap film self-organize to form polycrystalline monolayers when the film is withdrawn from a concentrated suspension. Here, we show that mechanically generated capillary waves on the free surface of the bulk colloidal suspension can cause migration of grain boundaries, and under certain conditions, completely eliminate them. This dramatic effect, we call “mechanic annealing,” provides a robust means of growing two-dimensional single crystals with size that has never been achieved before. The method is expected to be applicable to a variety of self-assembling systems.
Controlled oxide removal for the preparation of damage-free InAs(110) surfaces
Authors: Veal T. D. , McConville C. F.
Published: July 2002

Controlled oxide removal from InAs(110) surfaces using atomic hydrogen (H*) has been achieved by monitoring the contaminant vibrational modes with high resolution electron energy loss spectroscopy (HREELS). The contributing oxide vibrational modes of the partially H* cleaned surface have been identified. Following hydrocarbon desorption during preliminary annealing at 360 °C, exposure to atomic hydrogen at 400 °C initially removes the arsenic oxides and indium suboxides; complete indium oxide removal requires significantly higher hydrogen doses. After a total molecular hydrogen dose of 120 kL, a clean, ordered surface, exhibiting a sharp (1×1) pattern, was confirmed by low energy electron diffraction and x-ray photoelectron spectroscopy. Energy dependent HREELS studies of the near-surface electronic structure indicate that no residual electronic damage or dopant passivation results from the cleaning process.
Very thin insulating layer formed by low-energy Ar-beam bombardment in the surface region of undoped hydrogenated amorphous silicon
Authors: Durny R. , Pincik E. , Nadazdy V. , Jergel M. , Shimizu J. , Kumeda M. , Shimizu T.
Published: July 2002

A very thin insulating layer (VTIL) is formed by low-energy Ar-beam bombardment in the surface region of undoped hydrogenated amorphous silicon (a-Si:H). Several experimental techniques have been utilized to determine the optimal argon beam bombardment conditions to prepare electrically reliable VTIL and to investigate its physical properties (thickness, structure, nature, and density of defects). VTILs prepared under such conditions make the leakage current of a-Si:H based semiconductor structures negligible and allow bias voltages of several volts (up to 5 V).
Amorphic diamond/silicon semiconductor heterojunctions exhibiting photoconductive characteristics
Authors: Davanloo F. , Collins C. B. , Koivusaari K. J. , Leppävuori S.
Published: July 2002

Amorphic diamond deposited from an intense laser plasma of C3+ and C4+ exhibits semiconductor properties. Although this material has a measured electrical breakdown strength of 3×109 V/m, it is shown to form a heterojunction with both p- and n-type Si. Regardless of the doping type and its concentration in the Si, current is rectified in the same direction with the diamond layer acting as the cathode. A photoconductive effect is observed for these junction devices and current levels from the heterojunction vary with the amount of reverse bias and the illumination. The spectral response is estimated to mostly lie in the range of 600–900 nm.
Nondestructive positron-lifetime measurements during fatigue of austenitic stainless steel using a mobile positron beam
Authors: Barbieri Andrea , Hansen-Ilzhöfer Sabine , Ilzhöfer Achim , Holzwarth Uwe
Published: July 2002

Nondestructive positron-lifetime measurements have been performed during stress-controlled symmetric fatigue of austenitic stainless steel up to failure for different applied stress amplitudes between 230 and 300 MPa. For this purpose a fatigue machine has been equipped with a mobile positron beam emitted from a 22 μCi (0.8 MBq) Se/7272As generator. A pronounced increase of the mean positron lifetime has been found within the first 10% of fatigue life. Saturation has been reached after 40% of fatigue life. The mean positron lifetime at failure depends strongly on the applied stress amplitude.
Flux pinning in ternary (Nd–Eu–Gd)Ba2Cu3O7−δ: Optimization for the highest pinning
Authors: Pradhan A. K. , Muralidhar M. , Feng Y. , Murakami M. , Nakao K. , Koshizuka N.
Published: July 2002

The optimization of high-quality melt-processed ternary (Nd–Eu–Gd)Ba2Cu3O7−δ composite samples has been carried out to achieve the largest pinning. Our results suggest that the interaction between the twin planes and the fine second-phase precipitate forms a strongly pinned entangled vortex liquid in which vortices are correlated along the c axis. This pinned vortex liquid freezes into a glassy state at low temperature rendering high critical current density, Jc. The maximum Jc can be achieved in as-grown optimally annealed twinned sample with second phase precipitate without disturbing the twin influence.
Coulomb-blockade spectroscopy on a small quantum dot in a parallel magnetic field
Authors: Duncan D. S. , Goldhaber-Gordon D. , Westervelt R. M. , Maranowski K. D. , Gossard A. C.
Published: July 2002

Coulomb-blockade spectroscopy measurements are made on a small GaAs/AlGaAs quantum dot in a magnetic field oriented parallel to the plane of the sample. Coulomb-blockade peak motion is observed which can be explained by changes in the spin of successive ground states as single electrons are added. The peak movement at low field is consistent with that expected from Zeeman coupling, from which it can be inferred that electrons are not added to the dot in a strictly alternating spin up/spin down manner.
Time-gated scanning near-field optical microscopy
Authors: Sekatskii S. K. , Shubeita G. T. , Dietler G.
Published: July 2002

A time-gated scanning near-field optical microscope (SNOM) has been developed. The optical signal was recorded at the precise moment during the fiber tip oscillation period when it made contact with the sample surface. The use of such an approach substantially improves the signal-to-noise ratio for common SNOM applications such as frustrated total internal reflection, surface plasmon imaging, and fluorescence resonance energy transfer-based SNOM. The observed dependence of the frustrated total internal reflection optical signal on the gate delay time confirms that repetitive bumping is the mechanism responsible for the shear force tip–sample interaction.
Long wavelength GaInNAs/GaAs quantum-well heterostructures grown by solid-source molecular-beam epitaxy
Authors: Tournié E. , Pinault M.-A. , Vézian S. , Massies J. , Tottereau O.
Published: July 2002

We have investigated as-grown Ga1−xInxNyAs1−y/GaAs quantum-well heterostructures (QWHs) prepared by solid-source molecular-beam epitaxy (SS-MBE). We show that the QWH properties appear to depend strongly on the growth technique and that SS-MBE emerges as a technique of choice for growing these QWHs. We demonstrate photoluminescence emission at wavelength as long as 1.43 μm at 295 K, and up to 1.68 μm at 10 K. This shows that development of 1.55 μm optoelectronics based on the Ga1−xInxNyAs1−y/GaAs materials system may now be reasonably thought of.
Lattice location of implanted Cu in highly doped Si
Authors: Wahl U. , Vantomme A. , Langouche G. , Araújo J. P. , Peralta L. , Correia J. G.
Published: July 2002

We report on the lattice location of ion-implanted Cu67 in p+- and n+-Si using the emission channeling technique. Following room-temperature implantation, the majority of Cu was found on near-substitutional sites in both p+- and n+-Si. Annealing in the temperature range 200–600 °C resulted in changes of near-substitutional Cu to random sites in p+-Si, while in n+- Si all of the near-substitutional Cu was converted to ideal substitutional lattice sites. The activation energy for dissociation is estimated to be 1.7–2.0 eV for near-substitutional Cu in p+-Si and 2.9(2) eV for ideal substitutional Cu in n+-Si.
Multiple internal reflection infrared spectroscopy using two-prism coupling geometry: A convenient way for quantitative study of organic contamination on silicon wafers
Authors: Rochat Névine , Olivier Michel , Chabli Amal , Conne Francis , Lefeuvre Georges , Boll-Burdet Christophe
Published: July 2002

A multiple internal reflection infrared monitoring system based on two-prism coupling geometry has been developed for the quantitative measurement of organic contamination on 200 or 300 mm silicon wafers. The method is rapid, simple, and can be carried out nondestructively. Varying the distance between the prisms couplers allows one to perform absolute infrared absorption measurements without the need of a reference wafer. On 300 mm silicon wafers CH2 and CH3 surface concentrations as low as 4×1012 cm−2 can be measured.
Photoelectric properties of organic polysilane containing carbazolyl side groups
Authors: Mimura Shinya , Naito Hiroyoshi , Dohmaru Takaaki , Kanemitsu Yoshihiko , Aramata Mikio
Published: July 2002

The photoelectric properties of a series of N-carbazolyl-substituted silane copolymers have been studied by optical absorption, photoluminescence, and time-of-flight transient photocurrent measurements. It is found in N-carbazolyl-substituted silane copolymers that the optical absorption and the photoluminescence bands of the carbazolyl side groups, superimposed on those of the Si backbones, are observed in the blue to ultraviolet spectrum region. The hole drift mobilities of the copolymers are essentially the same as those of polymethylphenylsilane (PMePhSi) and are higher than those of poly(N-vinylcarbazole), and the photocarrier generation efficiencies of the copolymers are higher than those of PMePhSi. These results indicate that the photogenerated charge carriers on the carbazolyl side groups transfer to the Si backbones and then proceed through the Si backbones.
Resonant-cavity-enhanced p-type GaAs/AlGaAs quantum-well infrared photodetectors
Authors: Shen A. , Liu H. C. , Gao M. , Dupont E. , Buchanan M. , Ehret J. , Brown G. J. , Szmulowicz F.
Published: July 2002

Resonant cavities are used to enhance the absorption efficiency in p-type GaAs/AlGaAs quantum-well infrared photodetectors. The cavities are fabricated by applying thick gold films on the detector bottom sides after substrate removal via selective wet etching. The observed peak enhancement and spectral shape are in good agreement with model predictions. Peak absorption of about 25% is obtained for the device studied.
Chemical bonding state analysis of silicon carbide layers in Mo/SiC/Si multilayer mirrors by soft x-ray emission and absorption spectroscopy
Authors: Muramatsu Yasuji , Takenaka Hisataka , Ueno Yuko , Gullikson Eric M. , Perera Rupert C. C.
Published: July 2002

Soft x-ray emission and absorption spectra in the C K region of Mo/SiC/Si multilayer mirrors were measured using highly brilliant synchrotron radiation to identify the chemical bonding states of the buried silicon carbide layers. Comparison with the C 2p density of state (DOS) spectra, calculated by discrete variational-Xα molecular orbital calculations, of several SiC-based cluster models showed that the measured x-ray spectra approximately agreed with the calculated C 2p–DOS spectra of the c- and h-SiC-based SiCx models in which some silicon atoms were replaced by carbon atoms. The chemical bonding states of the silicon carbide layers in the Mo/SiC/Si multilayer mirrors were therefore estimated to be carbon-excessive silicon carbide.
Dislocation reduction in GaN films through selective island growth of InGaN
Authors: Keller S. , Parish G. , Speck J. S. , DenBaars S. P. , Mishra U. K.
Published: July 2002

Dislocation reduction in GaN films grown on sapphire and silicon substrates was achieved by inserting thin InGaN layers grown in a selective island growth mode after partial passivation of the GaN surface with a submonolayer of silicon nitride. We show that this technique is most effective at reducing the pure edge dislocation density when it is high (i.e., >1010 cm−2) and less when the density is in the 108–109 cm−2 range. Thus, the structural quality of typically highly dislocated GaN on silicon films could be significantly improved, visible in a reduction of the (0002) full width at half maximum (FWHM) from 1300 arcsec for ordinary GaN on silicon to 800 arcsec for GaN films with silicon nitride/InGaN interlayers. In the case of GaN layers grown on sapphire (dislocation density ∼109 cm−2), the method resulted mainly in a reduction of the FWHM of the (101̄2) and (202̄1) diffraction peaks.
Comparative analysis of zinc-blende and wurtzite GaN for full-band polar optical phonon scattering and negative differential conductivity
Authors: Bulutay C. , Ridley B. K. , Zakhleniuk N. A.
Published: July 2002

For high-power electronics applications, GaN is a promising semiconductor. Under high electric fields, electrons can reach very high energies where polar optical phonon (POP) emission is the dominant scattering mechanism. So, we undertake a full-band analysis of POP scattering of conduction-band electrons based on an empirical pseudopotential band structure. To uncover the directional variations, we compute POP emission rates along high-symmetry directions for the zinc-blende (ZB) crystal phase of GaN. We also compare the results with those of the wurtzite phase. In general, the POP scattering rates in the zinc-blende phase are lower than the wurtzite phase. Our analysis also reveals appreciable directional dependence, with the Γ–L direction of ZB GaN being least vulnerable to POP scattering, characterized by a scattering time of 11 fs. For both crystal phases, we consider the negative differential conductivity possibilities driven by the negative effective mass part of the band structure. According to our estimation, for the ZB phase the onset of this effect requires fields above ∼1 MV/cm.
Size effects on the luminescence spectrum in amorphous Si/SiO2 multilayer structures
Authors: Kanemitsu Yoshihiko , Kushida Takashi
Published: July 2002

We have studied size effects on the photoluminescence (PL) spectrum in amorphous silicon (a-Si)-based multilayer structures. At low temperatures, the PL spectrum and the PL lifetime are sensitive to the a-Si well thickness in a-Si/SiO2 multilayers. With a decrease of the a-Si well thickness, the PL peak energy and the mobility edge shift to higher energy. The temperature dependence of the PL spectrum shows that the size-dependent visible luminescence is ascribed to radiative recombination of carriers localized in the band-tail state, rather than the band-edge emission in quantum-confined states. The quantum confinement and localization of carriers in the band-tail states will be discussed.
X-ray and optical characterization of multilayer AlGaAs waveguides
Authors: Leo G. , Caldarella C. , Masini G. , De Rossi A. , Assanto G. , Durand O. , Calligaro M. , Marcadet X. , Berger V.
Published: July 2002

Effective-index measurements in multilayer AlGaAs waveguides are used in conjunction with x-ray reflectometry to yield refractive indices and thicknesses of the constituent layers, with the accuracy required by parametric interactions in guided-wave and photonic-band-gap structures.
Quasi-phase matched second-harmonic generation in an AlxGa1−xAs asymmetric quantum-well waveguide using ion-implantation-enhanced intermixing
Authors: Bouchard Jean-Pierre , Têtu M. , Janz S. , Xu D.-X. , Wasilewski Z. R. , Piva P. , Akano U. G. , Mitchell I. V.
Published: July 2002

Quasi-phase matched second-harmonic generation in the copropagating geometry is demonstrated in an asymmetric quantum-well waveguide. Modulation of the nonlinear susceptibility along the waveguide was achieved using a patterned quantum-well intermixing process. Photoluminescence measurements of the quantum-well bandedges indicate that a grating of alternating regions of intermixed and as-grown asymmetric quantum wells was produced for periods between 2 and 12 μm. The variation of the second-harmonic light intensity generated by guided incident light between λ=1480 and 1600 nm was measured. The resulting second-harmonic spectra show sharp quasi-phase matching resonances for grating periods near 3 μm, demonstrating that a periodic modulation of the quantum-well nonlinear susceptibility was produced.
Annealing behavior of implanted helium in indium phosphide
Authors: Simpson Todd W. , Mitchell Ian V.
Published: July 2002

The thermal stability of He3 implanted into single crystal indium phosphide has been studied as a function of postimplant annealing temperature between 150 and 600 °C and annealing temperature ramp rate in the range 0.1–20 ° C/s. Retention of implanted helium (implant energy 1.0 MeV and fluence 1.0×1016 cm−2) is measured via the He3(d,p)4 nuclear reaction. Helium is shown to be a facile diffuser unless trapped by implantation induced defects. The temperature ramp rate is shown to be a dominant parameter in determining the fraction of implanted helium that becomes trapped in voids.
Directional shear force microscopy
Authors: Burns A. R. , Carpick R. W.
Published: July 2002

We describe a technique, based on shear force microscopy, that allows one to detect shear forces in a chosen direction at the nanometer scale. The lateral direction of an oscillating probe tip is determined by selecting which of the four quadrants are excited on the piezo driver. The shear forces depend directly on this lateral direction if structural anisotropies are present, as confirmed with polydiacetylene monolayers.
Photoemission study of frontier orbital alignment at a metal–organic interface as a function of conjugation length of oligothiophene derivatives
Authors: Mäkinen A. J. , Hill I. G. , Noda T. , Shirota Y. , Kafafi Z. H.
Published: July 2002

We report an ultraviolet photoemission spectroscopy (UPS) study of solid films of two molecules, 5,5′-bis(dimesitylboryl)-2,2′-bithiophene (BMB-2T) and 5,5′-bis(dimesitylboryl)-2,2′:5′2′terthiophene (BMB-3T) which have been characterized as potential electron transport materials in organic light-emitting devices. Using the frontier orbital positions at a metal-organic interface, determined from the UPS measurements, together with the optical band gaps of the molecules, the electron injection barriers for the two oligothiophene derivatives are found to be significantly different. This barrier is estimated to be ∼0.2-0.3 eV lower for BMB-2T than for BMB-3T at a metal–organic interface.
Spike annealing of boron-implanted polycrystalline-silicon on thin SiO2
Authors: Fiory A. T. , Bourdelle K. K. , Roy P. K.
Published: July 2002

Spike thermal annealing is examined for electrical activation of B implants into 100 nm Si films deposited over 1.5 to 2.4 nm thermally grown SiO2. These structures simulate gate stacks in advanced p-type metal–oxide–Si (PMOS) devices. Spike anneals, at minimized thermal budget, are shown to yield higher carrier concentrations in PMOS polycrystalline-silicon (poly-Si), as compared to conventional rapid thermal annealing. The activation energy for B diffusion through SiO2 is found to be 3.71 to 3.83 eV and near that previously reported for furnace anneals. Boron penetration appears unaffected by photoexcitation from heating lamps.
Molecular-beam epitaxy of (Al)GaAsN using ammonia as the nitrogen source
Authors: Takahashi Koji , Tomomura Yoshitaka , Ikeda Hiroaki , Kawanishi Hidenori
Published: July 2002

Molecular-beam epitaxy of an (Al)GaAsN alloy was demonstrated using uncracked ammonia as the nitrogen source. It was found that the efficiency of nitrogen incorporation into the alloy layers was dramatically enhanced when aluminum flux was supplied during growth. The nitrogen composition of an Al0.07Ga0.93As1−yNy layer grown at 580 °C was approximately 100 times larger than that of a GaAs1−yNy layer grown at the same growth condition without the aluminum supply. The nitrogen incorporation into the AlxGa1−xAs1−yNy layers was found to be proportional to the aluminum composition x. The activation energy of nitrogen incorporation was measured to be 195 kJ/mol.
Strong coupling of exciton and photon modes in photonic crystal infiltrated with organic–inorganic layered perovskite
Authors: Sumioka Kazuhiro , Nagahama Hiroyuki , Tsutsui Tetsuo
Published: July 2002

Large vacuum Rabi-splitting, the evidence of strong coupling of photon and exciton modes, was observed at room temperature in an ordered array of silica microspheres infiltrated with organic–inorganic layered perovskite. By natural sedimentation of a colloidal suspension of monodispersed silica microspheres with a diameter of 256 nm, three-dimensional ordered array of silica microspheres (silica opal) were prepared. Into an air space of the silica opal, organic–inorganic perovskite, bis-(phenethylammonium) tetraiodoplumbate (PAPI), which exhibits intense exciton absorption at 2.40 eV, was infiltrated. The silica opal infiltrated with PAPI (23% of air space was filled) exhibited a stop band at 2.13 eV, when observed at a normal direction to the sample surface. By changing the observation angle, the coupling of the stop band at around 2.1–2.4 eV and the exciton band at 2.40 eV due to PAPI was attained. From angle-tuning measurements of reflection spectra, a vacuum Rabi-splitting of 240 meV was evaluated.
Electrical characterization of TiN/a-C/Si devices grown by magnetron sputtering at room temperature
Authors: Konofaos N. , Angelis C. T. , Evangelou E. K. , Panayiotatos Y. , Dimitriadis C. A. , Logothetidis S.
Published: July 2002

Amorphous carbon (α-C) films were deposited on Si substrates by magnetron sputtering at room temperature, followed by a deposition of TiN on top of the carbon films to form heterojunction devices. The electrical properties of the TiN/α–C/Si devices were characterized by capacitance–voltage, conductance–voltage, and current–voltage measurements as a function of temperature. The results showed that the devices behaved like metal–insulator–semiconductor devices at low temperatures, while at higher temperatures, the carbon films exhibited a high internal conductivity and the overall performance was similar to that of heterojunction devices. The conductivity was adequately modeled and found to follow the thermionic field emission model. The TiN exhibited an excellent behavior as a metallic electrode of the devices.
Photoinduced insulator–metal transition in La0.81MnO3/Al2O3/Nb tunnel junctions
Authors: Gilabert A. , Plecenik A. , Fröhlich K. , Gaži Š. , Pripko M. , Mozolová Ž. , Machajdı́k D. , Beňačka Š. , Medici M. G. , Grajcar M. , Kúš P.
Published: July 2002

We report the effect of illumination by ultraviolet and visible light on the resistance versus temperature and current versus voltage characteristics of La0.81MnO3/Al2O3/Nb tunnel junctions. Under illumination, the resistance of tunnel junctions follows the resistance in darkness at high temperatures but at temperatures lower than 95 K, the illumination induces a colossal decrease of the resistance. This is a transient effect because the changes are reversible when the light is switched on and off. Changes of the electrical properties under illumination were seen for the tunnel junctions only and not in the epitaxial La0.81MnO3 electrode which shows a classical insulator–metal transition at temperature Tc=285 K. We explain this effect by a photoinduced insulator–metal transition of the oxygen depleted manganite interface close to the tunnel barrier which changes dramatically the width of the barrier.
Optical control of charge number in single floating quantum-dot gate in field-effect transistor structure
Authors: Shima Masashi , Sakuma Yoshiki , Sugiyama Yoshihiro , Awano Yuji , Yokoyama Naoki
Published: July 2002

The optical characteristics of a single floating quantum-dot (QD) gate field-effect transistor memory cell were investigated at 77 K. The channel current, which can detect sensitively the charging of the QD, was saturated via some discrete levels after illuminations by light pulses, and the saturation value increased with the stronger illumination power. It was also found, by comparing the optical writing characteristics for different illumination powers at 77 K with retention characteristics at 120 K, that the discrete current levels observed in the optical characteristics corresponded to the hole number variation in the single QD. These results show that the number of holes stored in a single QD was controlled by changing the illumination power.
Electron energy loss near-edge structures of cubic Si3N4
Authors: Tanaka Isao , Mizoguchi T. , Sekine T. , He Hongliang , Kimoto K. , Kobayashi T. , Mo Shang-Di , Ching W. Y.
Published: July 2002

Electron energy loss near-edge structures of the newly discovered cubic-Si3N4 at the Si L2,3, edge and N K edge have been measured. The same edges were calculated using a first-principles supercell approach, including the core–hole interaction. The experimental spectra at the two edges were satisfactorily reproduced by the calculations, confirming that the present calculation has sufficient predictive power. The difference in spectral shapes between c-Si3N4 and β-Si3N4 is more clear for the Si L2,3, edge. However, the difference cannot be simply explained by the difference in coordination numbers of Si.
Observation of double peak in the substrate current versus gate voltage characteristics of n-channel metal–oxide–semiconductor field effect transistors
Authors: Anil K. G. , Eisele I. , Mahapatra S.
Published: July 2002

By employing sensitive current measurements at low drain voltages for n-channel metal–oxide–semiconductor field effect transistors with different channel dopings, substrate current versus gate voltage characteristics with two peaks were obtained for devices with low channel doping at 77 K. This differs from the single peak bell shaped curves reported in the literature. The data are analyzed and suggest that the second peak is due to the contribution of electron–electron interactions to the high energy tail of the electron energy distribution. Indirect contributions by the thermal tail of the electron energy distribution and ionized impurity scattering that make the second peak visible are also discussed.
Commensurability effects in lateral surface-doped superlattices
Authors: Deutschmann R. A. , Stocken C. , Wegscheider W. , Bichler M. , Abstreiter G.
Published: July 2002

We fabricate density-modulated two-dimensional electron systems by shallow compensation doping the donor layer of a modulation-doped heterostructure. Zinc acceptor atoms are diffused from the sample surface which is heated by a focused laser beam. Low-temperature magnetotransport experiments provide evidence that high-quality lateral surface superlattices can be fabricated. In weak periodic one-dimensional potentials, commensurability oscillations are recovered, whereas in strong periodic two-dimensional potentials the semiclassically expected antidot resistance resonances are found to dominate the low-field transport. Additionally, the homogeneity of the laser-induced doping is confirmed by magnetic focusing experiments.
Anode hole injection, defect generation, and breakdown in ultrathin silicon dioxide films
Authors: DiMaria D. J. , Stathis J. H.
Published: July 2002

Using a variety of experimental techniques, hot holes are demonstrated to produce bulk and interfacial defect sites in silicon dioxide layers of metal–oxide–semiconductor structures. Similar to defect production by hot electrons, hot holes are shown to generate these sites by the energy they deposit in contacting silicon layers near the oxide interface. This deposited energy is believed to release hydrogenic species which can move into and through the oxide layer producing defects. The buildup of these defect sites is related to the destructive breakdown of ultrathin gate oxides in p-channel field-effect transistors under inversion conditions where direct tunneling of energetic holes to the gate electrode would occur and dominate the current in the external circuit at low gate voltages. However, the results presented here are inconsistent with current reliability models which use anode hole injection to explain destructive breakdown of the oxide layer in n-channel field-effect transistors where hole currents are small relative to electron currents.
Scattering (stochastic) recoupling of a coupled ten-stripe AlGaAs–GaAs–InGaAs quantum-well heterostructure laser
Authors: Kellogg D. A. , Holonyak N.
Published: July 2002

Data are presented on coupled ten-stripe AlGaAs–GaAs–InGaAs quantum well heterostructure (QWH) lasers recoupled stochastically at the cleaved end mirrors. Recoupling of neighboring elements of a ten-stripe laser is accomplished by the scattering (random feedback) afforded by applying ∼10-μm-diam Al powder or 0.3 μm α-Al2O3 polishing compound in microscopy immersion oil or in epoxy at the cleaved ends (mirrors). Data on QWH samples with the end mirrors coated with the scatterer (Al or Al2O3 powder in “liquid”) exhibit spectral and far-field broadening, as well as increased laser threshold because of the reduced cavity Q. Single mode operation is possible with the conventional evanescent wave coupling of the ten-stripe QWH and is destroyed, even the laser operation itself, with the scattering recoupling (dephasing) at the end mirrors, which is reversible (removable). The narrow ten-stripe QWH laser with strong end-mirror scattering, a long amplifier with random feedback, indicates that a photopumped III–V or II–VI powder (a random “wall” cavity) has little or no merit.
Characteristics of radio frequency wave propagation in bounded plasma under the various magnetic field configurations
Authors: Shinohara Shunjiro , Fujii Akira
Published: July 2002

Detailed characteristics of radio frequency (rf) waves with pulsed modes in the whistler wave range were studied in a cylindrical rf-produced plasma, where the plasma boundary lay in the intermediate regime between infinite whistler wave propagation and bounded geometry helicon wave propagation. Excited magnetic field amplitudes and phases with three components in two-dimensional space were measured for different experimental conditions. Three magnetic field configurations were used and the diameter of the excitation loop antenna was also varied. Numerical calculation by the finite element method, which has been demonstrated to be a powerful means for this analysis, showed good agreement with the observed results, satisfying the dispersion relation and wave structures of helicons in the semisteady state and also satisfying the dispersion of whistlers with a short pulsed mode. The excited waves propagated nearly along the magnetic field lines within a small angle of less than 10°. Furthermore, in the low (high) collisionality regime, domination of standing (propagating) waves was found from the wave analysis.
Depth profiling of ZnO thin films by cathodoluminescence
Authors: Ong H. C. , Li A. S. K. , Du G. T.
Published: July 2002

The depth-resolved luminescence of the ZnO epilayer has been studied by using cathodoluminescence (CL) at room temperature. Other than the usual excitonic and deep level emissions, two peaks at 3.13 and 2.57 eV have been observed and are attributed to the defects. The variation of all the emission peaks has been examined as a function of accelerating voltage. The decrease of near-band edge emissions with depth is due to the internal absorption caused by the pronounced band tail. The deep level emission, however, is shown to increase with increasing depth. We have modeled the CL spectra with the consideration of internal absorption and determine the profile of the Urbach parameter, EUrbach, to study the structural imperfection at different depths. A strong dependence between the intensity ratios of the defect emissions to the excitonic emission and the imperfection of material has been found.
Electron spectroscopy from solid-state field-controlled emission cathodes
Authors: Binh Vu Thien
Published: July 2002

Measured energy distributions of the electrons emitted from solid-state field-controlled emission (SSE) cathodes showed one-peak spectra having a specific profile and also a peak shift towards lower energies for increasing applied voltages. The peak shifts are related to an effective resistive behavior during the electron transport through the ultrathin wide-gap semiconductor (UTSC) layer prior to the emission. The analysis of the experimental energy distribution confirmed the main characteristics of the emission model for SSE cathodes, in particular the formation of injected space charges in the UTSC conduction band leading to a strong lowering of the surface barrier.
Structure and formation mechanism of the Eα′ center in amorphous SiO2
Authors: Uchino T. , Takahashi M. , Yoko T.
Published: July 2002

We provide a possible formation mechanism for one of the Si-related paramagnetic centers in amorphous silica, Eα′, which is stable only below 200 K, on the basis of the quantum-chemical calculations. We show that the divalent Si defect can trap a hole, resulting in two different types of paramagnetic centers that are consistent with the experimental spectral features for Eα′. The highly anisotropic symmetry and the isotropic hyperfine coupling constants observed for one of the Eα′- center variants are reproduced by the present model.
Etching of crystalline Si in Cl2 atmosphere by means of an optical fiber tip
Authors: Wysocki G. , Dai S. T. , Brandstetter T. , Heitz J. , Bäuerle D.
Published: July 2002

We report experiments on laser-induced chemical etching of silicon in chlorine atmosphere using a near-field optical configuration. Crystalline (100) Si surfaces were locally illuminated in 300 mbar Cl2 through a tapered fiber tip. In most of the experiments, we used UV argon ion laser lines around 350 nm for illumination. The etched samples were analyzed by means of atomic force microscopy. Patterns with a width of 140 nm at full width half maximum and a vertical etch rate of the order of 15 nm/s have been achieved. Comparison of etching with a visible wavelength at intensities that cannot cause surface melting shows that the etching is primarily a photophysical process.
Temperature influence on optical charging of self-assembled InAs/GaAs semiconductor quantum dots
Authors: Karlsson K. F. , Moskalenko E. S. , Holtz P. O. , Monemar B. , Schoenfeld W. V. , Garcia J. M. , Petroff P. M.
Published: July 2002

It is demonstrated that the photoluminescence spectra of single self-assembled InAs/GaAs quantum dots are very sensitive to excitation energy and crystal temperature. This is qualitatively explained in terms of the effective diffusivity of photogenerated particles, which affects the capture probability of the quantum dot. As a consequence, this opens the possibility of controlling the average number of excess electrons in the quantum dot by optical means. This technique may be used as a simple tool to create and study charged exciton complexes without any specially fabricated samples.
Linear growth of thin films under the influence of stress
Authors: Palasantzas G. , De Hosson J. Th. M.
Published: July 2002

We have studied the growth of thin films in the presence of stress instability that enhances the roughness and roughening induced by conservative as well as nonconservative noise. It is clearly illustrated that nonconservative noise effects may enhance stress induced roughness. Nevertheless, the incorporation of conservative noise appears to also be substantial in growth processes driven by diffusion. For growth on a rough substrate the dependence of the amplitude of the surface roughness on the film thickness differs from that of a film growing on a flat substrate. The amplitude shows a minimum at a particular substrate thickness, which indicates that the growth up to this thickness is enforced by undulations of the substrate.
Conductance peak splitting in hole transport through a SiGe double quantum dot
Authors: Cain Paul A. , Ahmed Haroon , Williams David A.
Published: July 2002

We have observed the splitting of Coulomb oscillation peaks in coupled Si0.9Ge0.1 double quantum dots at 4.2 K. The quantum dots are formed by trench isolation, which means that the dots can be made much smaller than possible with the surface-gated approach. A dot diameter of 50 nm or less increases the charging energy and, therefore, the operating temperature of the device compared to previous approaches. A simulation of the results using parameters calculated from the lithographic dimensions of the device shows that a good fit to the experimental data can be achieved with a realistic interdot capacitance value.
Effective enhancement of C54 TiSi2 phase formation with multi-thermal-shock processing at 600 °C
Authors: Li S. , Lee Y. K. , Zhang L. , Gao W. , Lee K. S.
Published: July 2002

Enhancing C54 TiSi2 phase formation and reducing its formation temperature are two key issues in ultralarge-scale integration semiconductor industry. This work demonstrated that the formation of C54 TiSi2 phase can be effectively enhanced and the processing temperature can be reduced by 150–200 °C through multi-thermal-shock processing. The result shows that the resistivity of the TiSi2 compound decreased with increasing thermal shock frequency and consequently reached 15.90 μΩ cm at 600 °C. It is believed that the enhancement of C54 phase formation is due to the increase of internal energy of C49 crystals, which is caused by multi-thermal-shock processing.
Effect of sintering temperature under high pressure on the superconductivity of MgB2
Authors: Jung C. U. , Park Min-Seok , Kang W. N. , Kim Mun-Seog , Kim Kijoon H. P. , Lee S. Y. , Lee Sung-Ik
Published: July 2002

We report on the effect of sintering temperature on the superconductivity of MgB2 pellets prepared under a high pressure of 3 GPa. The superconducting properties of the nonheated MgB2 were poor. However, as the sintering temperature increased, the superconducting properties were vastly enhanced, which was demonstrated by the narrow transition width for the resistivity and the low-field magnetization. The observed surface morphology using scanning electron microscopy showed that these changes were closely related to changes in the microscopic level such as the connectivity of the grains.
Optical control of an integrated interferometer using a photochromic polymer
Authors: Rodrı́guez A. , Vitrant G. , Chollet P. A. , Kajzar F.
Published: July 2002

An integrated optical interferometer has been fabricated using ion exchange technology in glass. Using a photochromic polymer, we show that it is possible to reversibly modulate the phase of the guided wave with an optical control beam. This constitutes a demonstrator of an optically controlled integrated optical device.
Enhancement of dislocation velocities by stress-assisted kink nucleation at the native oxide/SiGe interface
Authors: Stach E. A. , Hull R.
Published: July 2002

Experiments have shown that a native oxide layer on the surface of a strained SiGe epilayer causes an order of magnitude increase in dislocation velocities during annealing over those observed in atomically clean samples and during crystal growth [E. A. Stach, R. Hull, R. M. Tromp, M. C. Reuter, M. Copel, F. K. LeGoues, and J. C. Bean, J. Appl. Phys. 83, 1931 (1998)]. This behavior is explained herein by stress-assisted dislocation kink nucleation at the oxide/epilayer interface. Finite element models are used to estimate the stress local to steps at this interface due to both intrinsic and thermal expansion stresses, and dislocation theory is used to determine the resulting increase in single kink nucleation.
Anisotropic domain structure of KTiOPO4 crystals
Authors: Urenski P. , Lesnykh M. , Rosenwaks Y. , Rosenman G. , Molotskii M.
Published: July 2002

Highly anisotropic ferroelectric domain structure is observed in KTiOPO4 (KTP) crystals reversed by low electric field. The applied Miller–Weinreich model for sidewise motion of domain walls indicates that this anisotropy results from the peculiarities of KTP crystal lattice. The domain nuclei of dozen nanometer size, imaged by atomic force microscopy method, demonstrate regular hexagonal forms. The orientation of domain walls of the elementary nuclei coincides with the orientation of the facets of macroscopic KTP crystals. The observed strong domain elongation along one principal crystal axis allows us to improve tailoring of ferroelectric domain engineered structures for nonlinear optical converters.
Increased thermal budget for selectively doped heterostructures by employing AlAs/GaAs superlattices
Authors: Reuter D. , Meier C. , Álvarez M. A. Serrano , Wieck A. D.
Published: July 2002

The degradation of selectivity doped Al0.35Ga0.65As/GaAs heterostructures caused by rapid thermal annealing (RTA) was studied. The samples were annealed for 30 s at temperatures between 600 °C and 850 °C. Thereafter, the samples were characterized by Hall measurements at room temperature. Conventional heterostructures with a random alloy Al0.35Ga0.65As spacer and donor layer show a strong degradation for annealing temperatures of 650 °C or higher. For heterostructures employing a stoichiometric equivalent short period superlattice (SPS) in spacer and donor region only a slight degradation was found for annealing temperatures up to 850 °C. As reason for the increased thermal stability, the suppression of As loss during the annealing by the SPS was identified.