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The present study deals with the application of cluster analysis and principal components analysis (PCA) to a data set of 25 medieval glass fragments (21 of them excavated on the territory of present Bulgaria). The glasses have been analysed using different analytical techniques. The data obtained for the element composition of the glasses were treated for 7 chemical parameters (SiO2, Na2O, K2O, MgO, CaO, Al2O3 and Fe2O3) by means of z‑transformation of the raw data, Ward’s method of linkage and squared Euclidean distance as similarity measure in order to discover appropriate linkage between the glass fragments and between the chemical parameters characterizing them. Thus, the investigated glass artefacts are classified into several patterns depending on their chemical composition and are related to the specific characteristics of the raw materials used for their production and/or the glassmaking technology.

The statistical variability of the static noise margin of a six-transistor bulk complementary metal-oxide-semiconductor static random access memory (SRAM) cell due to random doping fluctuations (RDFs) is investigated via 3-D technology computer-aided design simulations. The SRAM cell is created through 3-D process simulations of the entire cell as a single structure. The process flow is based on a typical 32-nm technology. The effects of RDFs on the cell performance are investigated using the highly efficient statistical impedance field method.

In this paper, we study the impacts of proximity effects on the electrical characteristics Id-Vg and the static noise margin of a six-transistor (6T) bulk complementary metal-oxide-semiconductor (MOS) static random access memory (SRAM) cell using 3-D process and device technology computer-aided design (TCAD) simulations. We show that when a 6T SRAM cell is simulated as a single continuous 3-D structure, effective stresses in channels are reduced due to close proximity of n-channel and p-channel MOS transistors in the cell with respect to simulations of transistors as discrete 3-D structures. Furthermore, we find that doping in channels of SRAM transistors is reduced by well proximity and implant shadowing. Stress and doping proximity effects have opposite contributions to device performance. We estimate the influence of proximity effects for typical 32-nm technology to be more than 10% for certain electrical cell characteristics. We thus conclude that, to accurately predict electrical cell behavior via TCAD simulations, the 6T SRAM cell should be a single continuous 3-D structure, instead of a set of six discrete transistors, which are simulated as individual 3-D devices and connected via a netlist.

International audience; We present a low-temperature time-resolved cathodoluminescence study on (In,Ga)N/GaN quantum wells grown on the (11-22) facets of non-coalesced ELO-GaN. Taking advantage of the quantum confined Stark effect, such structures have been proposed as promising monolithic white light emitters. Here, we show that in order to achieve solar-like white light emission from this kind of structure, one has to pay attention on the respective evolutions of radiative and non-radiative QW exciton decay times along the (11-22) facets.

We report on the current properties of Al1-x InxN (x approximate to 0.18) layers lattice- matched ( LM) to GaN and their specific use to realize nearly strain- free structures for photonic and electronic applications. Following a literature survey of the general properties of AlInN layers, structural and optical properties of thin state- of- the- art AlInN layers LM to GaN are described showing that despite improved structural properties these layers are still characterized by a typical background donor concentration of ( 1 - 5) x 10(18) cm(-3) and a large Stokes shift (similar to 800 meV) between luminescence and absorption edge. The use of these AlInN layers LM to GaN is then exemplified through the properties of GaN/ AlInN multiple quantum wells ( QWs) suitable for near- infrared intersubband applications. A built- in electric field of 3.64MVcm(-1) solely due to spontaneous polarization is deduced from photoluminescence measurements carried out on strain- free single QW heterostructures, a value in good agreement with that deduced from theoretical calculation. Other potentialities regarding optoelectronics are demonstrated through the successful realization of crack- free highly reflective AlInN/ GaN distributed Bragg reflectors ( R > 99%) and high quality factor microcavities ( Q > 2800) likely to be of high interest for short wavelength vertical light emitting devices and fundamental studies on the strong coupling regime between excitons and cavity photons. In this respect, room temperature ( RT) lasing of a LM AlInN/ GaN vertical cavity surface emitting laser under optical pumping is reported. A description of the selective lateral oxidation of AlInN layers for current confinement in nitride- based light emitting devices and the selective chemical etching of oxidized AlInN layers is also given. Finally, the characterization of LM AlInN/ GaN heterojunctions will reveal the potential of such a system for the fabrication of high electron mobility transistors through the report of a high two- dimensional electron gas sheet carrier density ( n(s) similar to 2.6 x 10(13) cm(-2)) combined with a RT mobility mu(e) similar to 1170 cm(2) V-1 s(-1) and a low sheet resistance, R similar to 210 Omega square.

We report a study of self-assembled GaN/AlN quantum dots (QDs) grown by metalorganic vapor phase epitaxy. We have investigated the impact of the AlN template quality on the nucleation of QDs obtained by the so-called Stranski-Krastanov growth mode transition. It is shown that the AlN epilayer deposited on GaN exhibits different relaxation steps. A rather inefficient plastic relaxation first occurs in the early few nanometers. Then, as the growth proceeds cracks are generated to further release the elastic energy. However, Raman spectroscopy indicates that strain relaxation takes place only nearby the cracks. Consequently, a third relaxation process occurs as the AlN layer thickness still increases. It is characterized by V-shape pits at the AlN surface likely originating from opening of threading dislocation terminations. Atomic force microscopy and micro-photoluminescence studies indicate that these topological defects act as preferential nucleation centers competing with the GaN QD formation. (c) 2007 Elsevier B.V. All rights reserved.

Nous presentons ici une methode tres simple de realisation de reseaux d'amplitude de pas sub-micronique sur des films polymeres a base de carbazole deposes sur des substrat de silice. Les reseaux sont fabriques en irradiant avec un faisceau laser a 193 nm un masque de phase place au contact du film. La qualite des reseaux obtenus permet desormais d'envisager la realisation de micro-cavites lasers de type planaire permettant de selectionner une emission laser monomode autour de 400 nm.

We report on a clear experimental demonstration of the presence of biexciton recombination in high quality GaN/AlGaN quantum wells, thus opening the way to relevant improvements of the performances of GaN based devices. The samples have been grown by metalorganic vapor phase epitaxy optimizing the deposition conditions to strongly reduce the Al fluctuations in the barriers. This leads to a photoluminescence broadening of only 5 meV at a temperature of 10 K for an Al content in the barriers of 5%. The biexciton binding energy if found to be of the order of 9 meV. The recombination kinetics show that the exciton and biexciton components are not thermalized at low temperature allowing to extract the intrinsic lifetimes of the two components. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A physically based simulation methodology provides fast and practical EM lifetime prediction. We identified an “EM-aware” region to define the length dependence of Cu-lines under high current stress. For eventual calibration of 2× nm node Cu-lines, we analyzed the sensitivity trends of vacancy and void profiles as well as the mass transport mechanisms using a 3D TCAD tool. This includes electron flow dependency to explain line and via depletion effects for void formations under various EM stress conditions. We report a non-linearity in the length dependence on the EM failure jL product at ~9000 A/cm and a slight temperature dependence on the Blech Threshold (jL)c at ~2000 A/cm extracted at 300°C in the EM aware region.

The reliability of complex interconnect structures at all levels of the chip integration hierarchy has become a major concern due to the use of fine feature sizes, diverse materials, and complex 3D architectures. Reliability issues range from stress related failures such as dielectric cracking and interface debonding during manufacturing to electrical and mechanical failures such as electromigration and void formation during operation. This paper summarizes computational results obtained using a unified physics-based 3D simulation framework.

Light-emitting diodes (LEDs) were fabricated in gallium nitride with two embedded photonic crystals (PhCs), creating a waveguide with a highly confined, strongly excited, and well-extracted fundamental mode. This structure improves upon previous PhC LED designs by reducing the extraction length of the fundamental mode and establishing a path to designs with very low absorption losses. Optical output was measured with angular-resolved electroluminescence. The extraction length of the fundamental mode was measured to be 21–39 lm along the PhCs’ C-M directions, which is much shorter than values reported for single-PhC devices. This structure opens the way to more efficient LEDs and lasers.

The effect of the type of the silica gel pore structure on the surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process has been examined applying N-2 sorption and X-ray photoelectron spectroscopy techniques. The nickel catalyst precursors with identical composition (SiO2/Ni = 1.0) has been synthesized by precipitation of Ni(NO3)(2) center dot 6H(2)O solution with Na2CO3 solution on the three types of silica gel with different pore structures. It is shown that the usage of the silica gel supports with different texture as source of SiO2 causes different location of Ni-species into the support pores and on the external surface area. The XPS data confirm the formation of surface species with different strength of interaction and different dispersion. These surface characteristics of the precursors will predetermine the formation of the active nickel metallic phase as well as the mass transfer of the reactants and products to and from the catalytic sites.

We report on the dependence on temperature of the homogeneous and inhomogeneous broadening of the fundamental transition of single polar GaN/AlN quantum dots (QDs). Stranski-Krastanov QDs have been grown by molecular beam epitaxy using NH3 as a nitrogen source, with a very low surface density. Low temperature (LT) microphotoluminescence measurements have been performed on 200 nm wide mesas in order to isolate the luminescence of single QDs. The linewidth is found to vary from 590 mu eV at 4 K up to 1350 mu eV at 65 K in a dot of 6 monolayer height. Though the LT linewidth is still dominated by spectral diffusion, the temperature dependent broadening up to 50 K is mainly accounted for by interactions between excitons and acoustic phonons through a coupling coefficient value nearly two orders of magnitude larger than its counterpart in InAs QDs. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Lightly-doped-drain MOS transistors with an inverse-T-gate and an active polysilicon spacer are investigated. The application of these devices in VLSI integrated circuit fabrication is examined from a practical point of view. It is shown that in comparison to the minimum gate length of a conventional transistor the designed gate length can be decreased, with the double spacer width. The results of the ring-oscillator measurements show that the increase in overlap capacitance is not a restriction for circuit application of these devices.

An analytical model for the estimation of the minimum channel length which ensures a long channel behaviour in the MOS transistor is presented. The two-dimensional doping of the region under the gate is taken into account in the calculations. The model can be used in the case of graded-drain devices. Some of the results obtained are compared with those published in the literature.

We report on the experimental achievement of narrow ultraviolet excitonic and biexcitonic emission from GaN/AlGaN quantum wells. The very large biexciton binding energy (up to 12 meV) inhibits thermalization between the two species allowing to study the recombination kinetics of the biexciton gas. By performing resonant and nonresonant time resolved measurements, we elucidate the interplay between biexciton formation and exciton acoustic-phonon mediated relaxation within localized states.

The influence of thermally excited vibrations on vibronic spectra (absorption, CARS excitation profile and resonance background) has been modelled for polyatomic molecules in solution. It is shown that for a model describing some polymethine compounds, the spectra depend only slightly on temperature except in the case of a resonance background and an excitation profile of vibrations with a relatively high value of the origin shift parameter (Δ > 1). The investigations of low-frequency vibrations by resonance CARS to giving information about some molecular parameters is proposed.

The authors report on the achievement of optically pumped III-V nitride blue microdisk lasers operating at room temperature. Controlled wet chemical etching of an AlInN interlayer lattice matched to GaN allows forming inverted cone pedestals. Whispering gallery modes are observed in the photoluminescence spectra of InGaN/GaN quantum wells embedded in the GaN microdisks. Typical quality factors of several thousands are found (Q>4000). Laser action at similar to 420 nm is achieved under pulsed excitation at room temperature for a peak power density of 400 kW/cm(2). The lasing emission linewidth is down to 0.033 nm.

Shrinking feature sizes, novel device designs as well as stress engineering increase the need for three- dimensional process and device simulations. We present several application examples for full 3D process and device simulations using Sentaurus TCAD, including a 3D NMOSFET with shallow trench isolations (STI), a PMOSFET device with SiGe pockets for stress engineering (similar to the structure presented in Ref. [1]) and a Omega-FinFET (similar to structures presented in Refs. [2,3]). TCAD simulations of the full process flow as well as of the electrical device characteristics are performed. We also show examples of 3D oxidation simulations with Sentaurus Process.

The paper presents the application of a computer particle simulation program for understanding and visualizing dielectrophoresis. Dielectrophoresis, a phenomenon, where non-charged polarizable dielectric cell sized objects experience electrostatic forces in spatially non-uniform electric fields. Using an appropriate model, based on particle interactions through Coulomb force, it is possible to carry out simulations that accurately match analytical data.

The apparent expression of MOST threshold voltage distribution with arbitrary mask-level gate length is obtained. It is shown that calculated and experimental distributions are in good agreement in the case of a short channel device.

In the original publication of ‘Assessing the Impacts of Citizen Deliberations on the Health Technology Process’ the title was published incorrectly. The correct title should be: Assessing the Impacts of Citizen Deliberations on the Health Technology Assessment Process. The publisher regrets this error.

Crack-free lattice-matched Al 0.85 In 0.15 N/GaN heterostructures were grown on sapphire substrates with barrier thicknesses up to 100 nm which exhibit very high polarization-induced electron sheet density ( cm −2 ) located at the heterointerface. These layers have been further processed as high electron mobility transistors (HEMTs). Optical characterization of these structures was carried out by photoluminescence and microphotoluminescence (PL) for different biased voltages. The insertion of an InGaN back-barrier unambiguously reveals that spatially direct optical recombinations occur within the AlInN alloy. Since the GaN excitonic bandgap is very sensitive to local temperature changes, the PL technique allows mapping very precisely the actual local temperature distribution in biased HEMT devices. For a gate length of 1.5 m temperatures up to 1130 K were found at a drain-source voltage of 20 V thus indicating the presence of a hot phonon bath.

We report on time-resolved photoluminescence measurements carried out along the thickness gradient of two types of GaN/AlGaN quantum wells with low Al content in the barriers (5% and 9%, respectively). A reduction of the biexciton binding energy with increasing well thickness is observed, as a result of the reduced quantum confinement and the increasing impact of the quantum confined Stark effect. In the sample with 5% Al content in the barriers, for thicknesses of the well region larger than similar to 9 monolayers, the biexciton binding energy is found to be smaller than that measured for bulk GaN. (c) 2008 American Institute of Physics.

The authors report on the achievement of narrow ultraviolet emission using GaN∕AlGaN quantum wells grown by metal organic vapor phase epitaxy. The origin of the inhomogeneous broadening of the emission is explained by means of micro-photoluminescence and atomic force microscopy measurements. The effect of the well/barrier interface roughness on the linewidth is found to be marginal, while the impact of Al composition fluctuations of the barriers is highly critical. Emission linewidths as small as 5meV at 10K are obtained by decreasing the aluminum concentration fluctuations in the AlGaN barrier.

The authors report on the micron scale characterization of a monolithic GaN microcavity (MC) with lattice matched AlInN/GaN distributed Bragg reflectors by means of a microtransmission setup. This technique allows extracting very high quality factors (Q up to 2800), in accordance with theoretical predictions, contrary to what was previously reported for nitride based MCs. Furthermore, two-dimensional mappings of the MC transmission spectrum allow probing the disorder in this MC. The direct relationship between an increased disorder and a reduction in the Q factor is clearly observed. (c) 2006 American Institute of Physics.

We report a thorough study of the growth of self-assembled GaN∕AlN quantum dots (QDs). These QDs were grown on sapphire substrates using the Stranski-Krastanov (SK) growth mode by means of low-pressure metal organic vapor phase epitaxy. The influence of the V∕III ratio on the QD height, shape, and density is studied. Emissions above (3.8eV) and below (2.8eV) the band gap of GaN are observed for small dots (1.3nm) and large ones (4.4nm), respectively. Special emphasis was given to the SK growth mode transition and the parameters influencing the QD formation. The two-dimensional–three-dimensional transition is studied continuously by photoluminescence mapping showing its high sensitivity to the V∕III ratio.

Coherent Raman spectra for resonance pumping conditions and a three-frequency variant were claculated for polyatomic molecules. A model based on density of states and displaced harmonic oscillators was used. The contributions of different intermediate vibrational levels in the electronic state S1 to the resonance Raman susceptiblity χ and the interference of χ with a non-resonant electronic background are discussed. It is shown that many intermediate levels belonging to S1 and corresponding to two excited vibrations (the relevant Raman vibration and either one of the others) influence the spectrum significantly, in contrast to the case with absorption. The asymmetry of the Raman line is due mainly to the interference with a non-resonant background. The method used takes into account the influence of the interference of neighbouring lines on the line shape and also the possible deformation of the lines by the dispersion of the Raman polarizability. The results are in qualitative agreement with known experimental data for some dyes.

Model calculations of coherent Raman spectra under resonance pumping conditions for polyatomic molecules have been carried out. The influence of the resonance background, which originates from the ‘extra’ resonance term of the resonance vibronic transition S0S1, is demonstrated. According to the calculations, the coherent anti-Stokes Raman scattering (CARS) spectra for ωa = 2ωp−ωs are slightly changed when the resonance background is taken into account. The background contribution to the coherent Stokes Raman scattering (CSRS) for ωs = 2ωp−ωa is higher. It is shown that a line reshaping associated with the concentration changes contains information about the relaxation parameters of the molecules, especially about the dephasing Γ.

In the treatment of absorption spectra and Raman excitation profiles of polyatomic molecules, relaxation constants appear as ‘soft’ parameters. It is shown that the spectra of non-linear Raman scattering under resonance pumping conditions are sensitive to variations in the relaxation constants and the number of active vibrations, especially when ‘extra’ resonances are included. This is demonstrated by calculations of coherent Stokes Raman scattering spectra carried out using the density of states model and displaced independent harmonic oscillators. The use of non-linear Raman spectra for checking the reliability of the model descriptions of S0–S1 transitions is proposed.

A polysilicon sealed pad oxide local oxidation process has been investigated. The oxidation mask in this method has a polysilicon frame formed along the perimeter of a conventional mask pattern by a self-aligned technique. This technology is completely free of “bird's beak” formation which is particularly important for increasing the packing density.

A new transistor structure with inverse-T gate and active polysilicon spacer (APOS) is presented. The spacer is formed from doped polysilicon and is in electrical contact with both the transistor gates and the polysilicon interconnections. The effective extension of the polysilicon lines is calculated and good agreement with the experimental results is achieved.

In-depth optical spectroscopic studies of single polar GaN/AlN quantum dots (QDs) grown by molecular beam epitaxy are carried out by means of low-temperature microphotoluminescence. Luminescence linewidths as low as 700 mu eV are obtained allowing thorough characterization of the QD electronic properties. Biexciton emission is observed for a wide range of dot size. It is shown that the binding energy (E-XX(b)) exhibits two regimes. The main one is governed by the dot height through the quantum confined Stark effect leading to a variation of E-XX(b) from +3 meV for the smallest dots to -11 meV for the largest ones. A secondary variation of opposite sign is demonstrated for dots having the same height but different lateral size.

We report the observation of well-resolved A and B excitonic resonances in the reflectivity spectra of a wedged GaN/AlGaN quantum well (QW) with 5% Al content in the barriers for different well thicknesses. For the thicker well cases, the energy splitting between the A and B excitons is larger than the one found for bulk GaN. However, the A-B exciton energy splitting decreases with decreasing well thickness, accordingly to the delocalization of the electron and hole wave functions in very thin QWs, as supported by theoretical simulations. Moreover, we used time-resolved photoluminescence measurements to investigate the recombination dynamics of the two excitonic states demonstrating the existence of a thermodynamic equilibrium between the two populations at a sample temperature of 10 K.

The authors report the realization of InGaN/GaN light emitting diodes (LEDs) with an electrical injection design suitable for vertical cavity surface emitting lasers. Controlled oxidation of an AlInN interlayer lattice matched to GaN allows confining the injected current in a 3 mu m diameter aperture. Submicron-scale characterization of the current flow and optical properties is achieved by means of microelectroluminescence measurements. LEDs can be safely driven, in continuous mode operation, up to current densities higher than 20 kA/cm(2). (c) 2007 American Institute of Physics.