bluuebunny/crossref_metadata_2025 huggingface dataset:
Short and Long-Range Ordering of (Ni0.67Cr0.33)1-xFex Alloys Under Electron Irradiation
Authors: Frely E. , Beuneu B. , Barbu A. , Jaskierowicz G.
Published: April 2011

(Ni0.67Cr0.33)1-xFex alloys with x = 0, 5 and 10 at.%, have been irradiated at temperatures between 300°C and 500°C with the electrons of a 2.5MeV Van de Graaff accelerator and of a 1MeV High Voltage Electron Microscope (HVEM). All of them have been successively ordered at short and at long range under irradiation. The transition temperature is 525°C for Ni0.61Cr0.34Fe0.05 and 445°C for Ni0.59Cr0.31Fe0.10. An Inconel sample irradiated up to 1 d.p.a. in the 1MeV microscope did not show any superlattice peak although its composition is very close to the 10% iron model alloy. The kinetics of ordering has been followed by resistivity measurements and fitted by the Dienes kinetic model.
Atom Transport in Nickel by Displacement Cascades for Spatially Dependent Displacement Rate and Sink Strength
Authors: Wollenberger H. , Fielitz P. , Macht M.-P. , Naundorf V.
Published: April 2011

Atom transport under irradiation is determined by the concentration of freely migrating defects, which depends on the dynamical equilibrium between production and annihilation rates. In order to determine effective values of both of these quantities for the case of ion irradiation, spatially resolved self-diffusion measurements were performed on single crystals of nickel which contained several thin tracer layers at different depths. By fitting the solution of a diffusion equation to the depth dependent measurements effective fractional production rates of freely migrating defects and effective sink strengths have been obtained.
Boron Transient Enhanced Diffusion in Heavily Phosphorus Doped Silicon
Authors: Huang M. B. , Myler U. , Simpson T. W. , Simpson P. J. , Mitchell I. V.
Published: April 2011

A study has been made of B transient enhanced diffusion (TED) in heavily P-doped Si using secondary ion mass spectroscopy (SIMS) and positron annihilation spectroscopy (PAS). The Pdoped silicon was implanted with boron ions of 40 keV energy to a dose of 3 x 1014 cm-2, and then annealed at temperatures ranging from 700–1000°C in a N2 ambient for varying durations. As P doping concentration increased from 3 x 1019 to 1 x 1020 cm-3, boron diffusivity and the immobile boron fraction decreased. Our experimental results are inconsistent with the predictions of the Fermi-level model and suggest that the clustering between B atoms and Si interstitials should be invoked in order to explain the immobile portion of the B peak during TED.
Neutron Damage in Reactor Pressure-Vessel Steel Examined with Positron Annihilation Lifetime Spectroscopy
Authors: Cumblidge Stephen E. , Motta Arthur T. , Catchen Gary L.
Published: April 2011

We have used positron annihilation lifetime spectroscopy to study the development of damage and annealing behavior of neutron-irradiated reactor pressure-vessel steels. We irradiated samples of ASTM A508 nuclear reactor pressure-vessel steel to fast neutron 172 fluences of up to 1017 n/cm2, and we examined these samples using positron annihilation lifetime spectroscopy (PALS) to study the effects of neutron damage in the steels on positron lifetimes. Non-irradiated samples show two positron lifetimes: a 110 ps component corresponding to annihilations in the bulk material, and a 165 ps lifetime corresponding to annihilations in dislocation defects. The irradiated samples show an additional lifetime component of 300 ps in the PAL spectra and an increase in the proportion of annihilations with a 165 ps lifetime, suggesting that vacancies and vacancy clusters are present in the material after room temperature irradiation. The samples were then annealed to temperatures ranging from 210° C to 450° C. The positron lifetimes introduced by neutron damage disappear after annealing the samples at 280° C.
Radiation-Induced Segregation in Alloy X-750
Authors: Kenik E. A.
Published: April 2011

The microstructural and microchemical evolution of an Alloy X-750 heat under neutron irradiation has been studied in order to understand the origin of irradiation-assisted stress corrosion cracking. Both clustering of point defects and radiation-induced segregation (RIS) at interfaces and boundaries have been observed. Although no significant changes in the precipitate structure were observed, boundaries exhibited additional depletion of Cr and Fe and enrichment of Ni.
Defect Diffusion During Annealing of Low-Energy Ion-Implanted Silicon
Authors: Bedrossian P. J. , Caturla M -J. , Diaz De La Rubia T.
Published: April 2011

We present a new approach for investigating the kinetics of defect migration during annealing of low-energy, ion-implanted silicon, employing a combination of computer simulations and atomic-resolution tunneling microscopy. Using atomically-clean Si(111)-7×7 as a sink for bulk point defects created by 5 keV Xe and Ar irradiation, we observe distinct, temperature-dependent surface arrival rates for vacancies and interstitials. A combination of simulation tools provides a detailed description of the processes that underdy the observed temperature-dependence of defect segregation, and the predictions of the simulations agree closely with the experimental observations.
Radiation Effects in Glass Waste Forms for High-Level Waste and Plutonium Disposal
Authors: Weber W. J. , Ewing R. C.
Published: April 2011

A key challenge in the permanent disposal of high-level waste (HLW), plutonium residues/scraps, and excess weapons plutonium in glass waste forms is the development of predictive models of long-term performance that are based on a sound scientific understanding of relevant phenomena. Radiation effects from β-decay and α-decay can impact the performance of glasses for HLW and Pu disposition through the interactions of the α-particles, β-particles, recoil nuclei, and γ-rays with the atoms in the glass. Recently, a scientific panel convened under the auspices of the DOE Council on Materials Science to assess the current state of understanding, identify important scientific issues, and recommend directions for research in the area of radiation effects in glasses for HLW and Pu disposition. The overall finding of the panel was that there is a critical lack of systematic understanding on radiation effects in glasses at the atomic, microscopic, and macroscopic levels. The current state of understanding on radiation effects in glass waste forms and critical scientific issues are presented.
Ion Irradiation-Induced Amorphization in the MgO-Al2O3-SiO2 System: A Cascade Quenching Model
Authors: Wang S. X. , Wang L. M. , Ewing R. C.
Published: April 2011

The ion beam-induced crystalline-to-amorphous transition was studied for crystalline phases in the MgO-A12O3-SiO 2 system. Samples were irradiated with 1.5 MeV Xe+ at temperatures from 15 to 1023 K, and the dose required for amorphization was determined by in situ transmission electron microscopy. Based on a cascade quenching model, we propose that irradiation-induced amorphization is closely related to glass formation. The rate of crystallization from a melt is the controlling factor in determining the susceptibility to amorphization and glass formation. From the analysis of cascade quenching evolution, we have derived a simple relation between amorphization dose and temperature. A quantitative parameter, S0, that describes the susceptibility to amorphization is derived that considers the crystalline structure, field strength, and phase transition temperature.
Thermal Neutron Irradiation of LiNbO3 Crystals Doped with Hf and Hfmg
Authors: Marques J. G. , Kling A. , Soares J. C. , Silva M. F. Da , Diétguez E. , Agullö-Löpez F.
Published: April 2011

The effects of irradiation with thermal neutrons on LiNbO3 single crystals doped with Hf and Hf,Mg were studied with ion beam and hyperfme interaction techniques, using Hf as a probe. In crystals where Hf occupies both Li and Nb sites, the fraction in Nb sites is strongly reduced after irradiation. The initial situation is recovered after thermal annealing at 973 K, in air.
Formation of Alkali Metal Layers at the Surface of Electron-Irradiated Alkali Halides
Authors: Paparazzo E. , Zema N. , Moretto L.
Published: April 2011

Scanning Auger microscopy (SAM) and reflected electron energy loss microscopy (REELM) have been used to study the chemical modifications induced by 10-keV electron bombardment at the surface of the alkali halides: LiF, NaF, NaCl and KI. Auger spectra show that the alkali-to-halogen surface ratio increases with irradiation time, although they provide no conclusive evidence as to the chemical nature of the damage layer. Conversely, REELM analysis clearly reveals the formation of alkali metal through the occurrence of characteristic bulk plasmon peaks and surface plasmon peaks, which can also be used to image the lateral distribution of the damage layer to nearly submicron spatial resolution. Some unexpected signals are observed, deriving from combination of surface plasmon excitations with bulk plasmon excitations, and tentatively interpreted as arising from the inhomogeneous morphology of the alkali metal layer.
Electron and X-Ray Photon Radiation Effects on Surfaces of Lead Silicate Glasses
Authors: Wang Paul W.
Published: April 2011

Radiation effects on insulators have been extensively studied in terms of radiation induced damage. However, little work has concentrated on in situ surface modification during irradiation and the evolution of surface relaxation after the termination of irradiation. In this work, 1.3 keV electrons and 1.2536 keV Mg Kα X-ray photons were applied to investigate radiation effects on surface structural changes during irradiation and relaxation. The microstructure and composition of lead silicate glass were investigated in situ in an ultra-high-vacuum (UHV) environment by X-ray Photoelectron Spectroscopy (XPS). Similar surface radiation effects were observed using both types of radiation which included permanent metallic lead separation from the glass network resulting from Pb-O bond breaking, bimodal distribution of the 0 is XPS signal due to bridging and non-bridging oxygens, gradual increase of total lead and silicon concentrations and gradual decrease of oxygen concentration during relaxation. Different radiation effects for electron beam and X-ray photons were also observed. For photon irradiation, silicon and lead continuously accumulated while the oxygen on the surface continuously decreased during irradiation and relaxation. In the case of electron irradiation, both silicon and lead were depleted from the surface during irradiation and accumulated during relaxation. Opposite concentration changes were observed for oxygen; it increased during irradiation and decreased during relaxation. The experimental results are discussed in terms of charge effects, secondary electron yield, field-enhanced diffusion, non-bridging oxygens and nucleation of metallic lead.
Radiation Effects Of Vacuum Ultraviolet Laser Photons on Silicon Dioxide
Authors: Kurosawa K. , Herman P. R. , Kurmaev E. Z. , Shamin S. N. , Galakhov V. E. , TakigawA Y. , Sasaki W. , Yokotani A.
Published: April 2011

The argon excimer laser provides 9.8-eV photons that readily surmount the electronic bandgap energy of SiO2 (∼9.0 eV), directly generating excitons in a single-photon absorption process. We have shown by Si L2,3 (Si 3s→2p) X-ray emission spectroscopy, Si 2p X-ray photoelectron spectroscopy and Raman spectroscopy that this absorption process is responsible for silicon precipitation in the silica. The X-ray emission studies further show that the silicon precipitates are crystalline, forming in highest concentration in 120–230 nm layer beneath the laserirradiated surface. Silicon precipitation was not observed on samples irradiated with 146-nm krypton excimer radiation due to a smaller 8.5-eV photon energy that is below the silica bandgap.
Improvement of the Nucleation and Growth of Thin Film Phosphors for Electroluminescent Flat Panel Displays
Authors: Moss T.S. , Espinoza B.F. , Dye R.C.
Published: April 2011

The deposition of CaGa2S4:Ce has been accomplished using a commercial liquid delivery system on two substrate surfaces: ZnS and SrS. However, the film deposited on ZnS was not of satisfactory quality because of the formation of an amorphous layer and a high amount of residual porosity within the deposition. The use of a SrS layer on top of the ZnS improved the nucleation by reducing the interfacial energy between the substrate and deposition. It greatly reduced the porosity in the coating and reduced the formation of the amorphous layer. The crystallinity of the CaGa2S4 400 peak was also increased by a factor of ten when a layer of SrS was used. Further, the FWHM of the 400 peaks from the two depositions was not significantly different, indicating that the crystallite size and strain was approximately the same. The B40 was increased by a factor of two, from 1.84 cd/m2 for ZnS to 3.67 cd/m2 for SrS. This increase is an improvement in the performance of the films and is attributable to the increase in the crystallinity. To utilize these improvements, the ability to deposit both the SrS and CaGa2S4:Ce layers within the same reactor has been developed.
Nonlinear Optical Microscopy for Imaging Patterned Self-Assembled Monolayers
Authors: Smilowitz L. , Jia Q.X. , Yang X. , Li D.Q. , McBranch D. , Robinson J.M.
Published: April 2011

We have used the inherent surface sensitivity of second harmonic generation (SHG) to develop an instrument for nonlinear optical (NLO) microscopy of surfaces and interfaces. This optical technique is ideal for imaging nanometer thick self-assembled monolayers (SAM's) which have been patterned using photolithographic techniques. In this paper we demonstrate the application of SHG microscopy to patterned SAM's of the noncentrosymmetric molecule calixarene and discuss other potential applications for this new technique.
Scaling Properties of Submonolayer Growth Including Evaporation and Defects
Authors: Larralde H. , Jensen P. , Meunier M. , Pimpinelli A.
Published: April 2011

We present a model for thin film growth by particle deposition that takes into account the possible evaporation of the particles deposited on the surface as well as the effect of point defects. Our focus is on the early formation kinetics of two-dimensional islands on the surface, in particular in the scaling properties of the maximum number of islands formed on the surface. Most of our results are obtained through the analysis of rate equations describing the system. They are supported by simple scaling arguments and are confirmed by extensive computer simulations. We find significant differences with previous studies of this system which arise from different physical hypotheses concerning the mechanisms of island growth in the presence of evaporation.
The Effect of Si Additions on the Epitaxial Growth of Gel−x Cx Alloys on Si(100)
Authors: Yang Bi-Ke , Weil J. D. , Krishnamurthy M.
Published: April 2011

We report on the differences in the epitaxial growth mechanisms between Ge1−xCx (O<x<0.1) and Ge1−x−ySixCy (x=0.2, 0<y<0.05) alloys grown on Si(100) using low temperature( 200°C) molecular beam epitaxy. Thin films (50˜65nm) were characterized in situ by RHEED and ex situ by transmission electron microscopy and x-ray diffraction. With increasing C concentration, the microstructure of both Ge and GeSi alloys changes from 2D layer growth to 3D islanding. The d400 spacing of the relaxed alloys decreases marginally, with a maximum of 1at.% C being substitutionally incorporated. Ge-C films with higher C content have a high density of planar defects, typically twins and stacking faults. The addition of 20% Si does not appear to increase the amount of substitutional C in the films. Rather, the additions of 20% Si to Ge-C alloys somehow seems to enhance the tendency for the formation of planar defects.
Kinetic Model for Layer-By-Layer Homoepitaxial Growth
Authors: Trofimov V. I. , Mokerov V. G. , Shumyankov A. G.
Published: April 2011

The new kinetic model for homoepitaxial growth on a singular surface is presented. The model combines a familiar rate equations approach and a concept of a feeding zone that allows to connect the growth processes in neighbouring monolayers. The model involves the irreversible 2D nucleation, growth and coalescence of the islands in each growing monolayer and consists of an infinite set of coupled rate equations for the adatom and island densities and coverage in successive monolayers. With using this model the temporal evolution of the surface morphology (rms roughness and RHEED intensity) is studied. It is shown that the growth mode is fully determined by a single dimensionless parameter μ = D/J where D and J are the normalized surface diffusion coefficient and deposition flux, respectively. There exist five regions of m corresponding different growth regimes varying from smooth 2D layer-by-layer growth at sufficiently high values of μ (>108) to very rough Poisson-like random deposition growth at μ<10−4. The extension of the model to the case of heteroepitaxy is also discussed.
Vacancy Diffusion Kinetics on Si(111) and (001) Surfaces Studied by Scanning Reflection Electron Microscopy
Authors: Watanabe Heiji , Ichikawa Masakazu
Published: April 2011

The kinetics of vacancy diffusion on Si(111) and (001) surfaces are studied by using scanning reflection electron microscopy (SREM). Two types of layer-by-layer etching (reversal of step-flow growth and two-dimensional vacancy island nucleation) are observed during lowenergy Ar ion irradiation (500 eV) at elevated substrate temperatures. This means that vacancies created by low-energy ion impact diffuse on the surfaces, and are annihilated at the step edges. Although isotropic vacancy diffusion is observed on Si(111), anisotropic vacancy diffusion along the dimer rows and preferential vacancy annihilation at the SB steps are observed on Si(001). This anisotropic vacancy diffusion results in single-domain formation. The diffusion length of vacancies is estimated from the width of the denuded zones, which are formed on both sides of the atomic steps by thermal heating after the introduction of vacancies at room temperature. The activation energy of 3.0±0.2 eV obtained for Si(111) corresponds to the potential barrier both for surface adatom diffusion and for lateral binding energy to release adatoms from the step edges. For Si(001) surfaces, the activation energy obtained for vacancy diffusion along the dimer rows is 2.3±0.2 eV. The vacancy diffusion model mediated by dimer vacancy complexes, rather than by single-dimer vacancies, best accounts for our experimental results.
Shallow Donor Formation In Hydrogen-Implanted Silicon
Authors: Tokuda Yutaka , Iwata Hiroyuki , Ito Akira
Published: April 2011

Formation of shallow donors has been studied in 100-keV hydrogen-implanted n-type silicon with a dose of 1×1015 cm−2. Annealing experiments are made in the temperature range 100 to 800°C. Gold Schottky contacts are fabricated on these samples to obtain carrier concentration profiles. The hydrogen profiles are measured by secondary ion mass spectroscopy. In the annealing temperature range 350 to 450°C, an increase of the carrier concentration is observed near the surface region with almost flat depth profiles. The well- known hydrogen-related donors (1st shallow donors) disappear around 400°C, while shallow donors (2nd shallow donors)observed here decrease above 500 °C. Hydrogen profiles show almost no change in the 2nd donor formation temperatures, although hydrogen starts to outdiffuse at 250°C. This indicates that the 2nd shallow donors are related to hydrogen atoms and to implantation-induced damage. The implantation-induced defects trap diffusing hydrogen atoms, which leads to the formation of the 2nd shallow donors.
Vibrational Spectroscopy Of Gold Hydrogen Complexes In Silicon
Authors: Evans M. J. , Gornstein M. G. , Stavola Michael
Published: April 2011

Several vibrational bands have been observed in the region 1750–1900 cm−1 for n-type silicon into which gold and hydrogen had been introduced by high temperature diffusion. This paper focuses primarily on a defect which gives rise to bands at 1813.3 and 1827.1 cm−1. This center contains a single hydrogen atom and has two charge states in the gap with trigonal symmetry. We propose a tentative model in which this complex contains a substitutional Au atom and a single hydrogen atom at one of two possible antibonding sites, bonded either to Au or to Si. A defect observed previously in Si samples doped with Pt and H which gives rise to hydrogen stretching bands at 1880.7 and 1897.2 cm−1 has similar properties to the Au-H complex discussed here, suggesting that these defects have the same structure. Other hydrogenstretching modes observed in Si samples that contain Au and H are also discussed.
Dislocation Interactions And Their Impact On Electrical Properties Of GeSi-Based Heterostructures
Authors: Ringel S. A. , Grillot P. N.
Published: April 2011

Substantial improvements in the quality of relaxed, heteroepitaxial GeSi layers have occurred in the past few years due to both the development of compositionally-graded buffer layers and to an improved understanding of strain-relaxation in lattice-mismatched epitaxy, which have led to low dislocation densities within these layers. As a result, high performance GeSi devices have been achieved which has fueled yet greater device design flexibility through the use of relaxed GeSi layers over a wider range of alloy compositions and lattice constants. A complete understanding of the properties of all defects that result from strain-relaxation is essential to realize high performance and reliable devices, especially as the lattice-mismatch strain becomes more severe. While the structural properties of dislocations in relaxed GeSi layers have been studied in detail, the electronic properties of these defects and their consequences on the overall electrical properties of relaxed GeSi layers are not well understood. In this paper, we show that for high quality (low dislocation density) relaxed layers, clusters of intrinsic point defects formed by dislocation interaction, rather than the dislocations themselves, now dominate the deep level spectrum. We further show that these defects reduce the electronic material quality for films grown by UHVCVD at low temperatures (650 °C) in comparison to films grown at temperatures > 800 °C even though all films have similarly low threading dislocation densities. Using DLTS, spreading resistance, EBIC and Hall effect measurements, these defects are shown to introduce a low concentration of hole traps from Ev, + 0.05 to Ev + 0.30 eV that compensate and type convert nominally undoped GeSi layers grown at 650 °C to p-type. Annealing studies indicate that these defects anneal out at ∼ 750 – 800 °C(2w, hich is accompanied by conductivity type reversal to ntype, elimination of compensation and increased diffusion length. These observations, in addition to the precise position of each energy level, closely correlate with earlier results on plasticallydeformed bulk Si, suggesting that these defect complexes are of intrinsic origin. We conclude that strain-relaxation in graded heterostructures causes considerable dislocation interaction which introduces point defect complexes associated with dislocations that, in addition to threading dislocation density, must now be considered as an important factor for achieving high electronic quality, relaxed GeSi layers.
Growth Induced Alignment Of The First Neighbor Shell Of CAs In AlxGa1−xAs
Authors: Zheng J. -F. , Stavola Michael , Abernathy C. R. , Pearton S. J.
Published: April 2011

We have discovered a growth-induced alignment of the Al and Ga first neighbors of CAs, acceptors in AlxGa1−xAs grown by metalorganic molecular beam epitaxy. This growth induced alignment has been detected from the polarization dependence of the C atom's vibrational absorption bands that the alignment gives rise to. The alignment of the first neighbor shell of CAs also gives rise to aligned CAs-H complexes when the C is passivated by H. This leads to polarized H-stretching absorption bands which have also been observed. The growth-induced alignment provides information which helps us to assign the complicated CAsvib rational spectrum observed in the AlxGa1−xAs alloys.
Characterization Of APB's In GaP
Authors: Cohen Dov , Carter C. Barry
Published: April 2011

Antiphase boundaries in GaP crystals epitactically grown on Si (001) have been characterized using transmission electron microscopy. Convergent-beam electron diffraction was used to identify the antiphase-related grains. The antiphase boundaries were observed to adopt facets parallel to specific crystallographic orientations. Furthermore, stacking-fault-like contrast was observed along the interface suggesting that the domains may be offset from one another by a rigid-body lattice translation.
Low Temperature Photoluminescence Properties Of In-Situ Zn Doped InP Layers Grown By Lp-Mocvd
Authors: Moon Y. B. , Si S. K. , Yoon E. , Kim S. J.
Published: April 2011

In situ Zn-doped InP layers are grown by low pressure metalorganic chemical vapor deposition at 620°C. Hole concentration increases with dopant flow rate, but reaches a saturated hole concentration of approximately 1.5 × 1018/cm3. Differently from the Zn-diffused InP case, photoluminescence (PL) of the in situ Zn doped InP shows band edge peak, e/D-A peak and distant D-A peak up to the hole concentration of 7.6 × 1017/cm3. These results can be explained by less generation of interstitial Zn atoms during in situ doping. PL characteristics of the in situ Zn-doped InP at the saturated hole concentration is extensively studied to explain its compensation mechanism. Two new deep bands, presumably responsible for the hole saturation behavior, are observed for the first time.
Defect States In p-ZnSe:N Grown By MOVPE
Authors: Fujita Shizuo , Ogata Ken-Ichi , Kawaguchi Daisuke , Peng Zhi Gang , Fujita Shigeo
Published: April 2011

Concentration and origin of defect states in p-type nitrogen-doped ZnSe (p-ZnSe:N) grown by metalorganic vapor-phase epitaxy (MOVPE) are discussed by means of timeresolved photoluminescence and deep level transient spectroscopy. Thermal annealing, which is a useful tool for realizing p-type conductivity, results in deep defect states which seem to be associated with Zn vacancies and with nitrogen acceptors. By lowering the annealing temperature, the trap concentrations can be successfully reduced without seriously sacrificing the acceptor activation efficiency, although further reduction of Zn vacancies is pointed out as a remaining requirement for the improvement of quality of MOVPE-grown p-type layers.
Identification Of The Native Vacancy Defects In ZnSxSe1−x And MgyZn1−y SxSe1−x by Positron Annihilation
Authors: Saarinen K. , Laine T. , Skog K. , Oila J. , Hautojärvi P. , Rakennus K. , Uusimaa P. , Salokatve A. , Pessa M.
Published: April 2011

We show how positron annihilation can distinguish vacancies in the different sublattices of a compound semiconductor by performing experiments in ZnSxSe1−x and Mgy Zn1−ySxSe1−x layers. We identify the Se vacancies (Vse) in N-doped and the Zn vacancies (Vzn) in Cl-doped material by the shape of the core electron momentum distribution. The charge of the defect involving VSe is neutral or negative in the p-type alloys, suggesting that the Se vacancy is complexed with an acceptor. The concentration of the VSe complexes is high (≥ 1018 cm−3 ), indicating that their role is important in the electrical compensation of p-type ZnSxSe1−x and MgyZn1−y SxSe1−x.
Electrical Characterization Of Nitrogen Acceptors In p-ZnSe/p-GaAs Grown By Molecular Beam Epitaxy
Authors: Seghier D. , Gislason H.P.
Published: April 2011

Using current-voltage measurements, deep-level transient spectroscopy and admittance spectroscopy we investigated nitrogen doped ZnSe grown on p-GaAs substrates by molecular beam epitaxy. Three major hole traps were observed with energy levels at 0. 11, 0.46, and 0.56 eV from the valence band. We attribute the level at 0.11 eV to a nitrogen acceptor. No other direct observations of this important acceptor level in p-ZnSe have been reported in the literature so far. The two remaining levels may originate from the nitrogen doping process. In addition, reverse current-voltage characteristics of the ZnSe/GaAs heterojunction show a hysteresis at low temperature and a soft saturation. At a constant reverse bias the current increases slowly until it reaches a steady state value. This behavior is attributed to a slow voltage-induced barrier lowering due to the presence of mismatch interface states. Therefore, these analyses are of a major interest for applications of ZnSe/GaAs based devices and illustrates the necessity of improving the growth conditions of such structures.
Hrtem Characterization of 6H-15R Polytype Boundaries in Silicon Carbide Grown by Physical Vapor Transport
Authors: Sanchez E. K. , Graef M. De , Qian W. , Skowronski M.
Published: April 2011

The interface between 6H and 15R polytypes of silicon carbide, grown by Physical Vapor Transport, was studied by high-resolution transmission electron microscopy. The sample was investigated in cross-section cut perpendicular to the [11.0] irection. The atomic stacking sequence at the interface of the polytypes was determined. Polytype boundaries with orientations parallel and perpendicular to the 6H c-axis were investigated. Stacking faults associated with low angle grain boundaries in both 6H and 15R regions were observed and the 15R regions systematically showed a higher fault density than the 6H regions.
Behavior Of The Potential N-Type Dopants P And As In Diamondafter Low Dose Ion Implantation
Authors: Hofsäss H. , Dalmer M. , Restle M. , Ronning C. , Bharuth-Ram K. , Quintel H. , Isolde-Collaboration The
Published: April 2011

We have studied the lattice sites of P and As impurities in natural IIa diamond after room temperature ion implantation at very low doses of 1011 P/cm2 and ≤ 1013 As/cm2 and subsequent annealing. We implanted radioactive 33P and 73Se/73As probe atoms and used the sensitive emission channeling technique to determine the impurity lattice sites. In this technique the channeling effects of emitted decay electrons are measured for different crystal axes. By comparison with calculated electron emission distributions the fractions of emitter atoms on different lattice sites can be quantitatively determined. After annealing of the implanted samples above 900°C we find high substitutional fractions of 70 ± 10 % for 33P and 55 ± 5 % for 73As.
Optical And Electrical Characterisation Study Of SICL4 Reactive Ion Etched Gaas
Authors: Murtagh M. , Ye Shu-Ren , Masterson H.J. , Beechinor J.T. , Crean G.M. , Auret F.D. , Deenapanray P.N.K. , Meyer W.E. , Goodman S.A. , Myburg G.
Published: April 2011

In this study 1016cm−3 n-type epitaxial GaAs was reactive-ion-etched (RIE) in a parallel plate type reactor as a function of rf power and gas pressure using a SiCl4 plasma. The sample matrix followed a 3 level 3 factorial statistical experimental design. Photoreflectance (PR) was employed to characterise the etch induced modification to the electronic band structure at the fundamental band-edge transition. Variable angle spectroscopic ellipsometry (VASE) and photoluminescence (PL) optical diagnostic techniques are also employed to characterise the plasma processed GaAs. PR results detail a decrease in the surface electric field (Fs) with etch severity arising from an RIE induced electron trap that increases in concentration with energetic ion sputtering. For the highest rf power densities PR further distinguishes between reactant desorption and adsorption limited etching regimes. VASE and PL data reveal the extent and degree of surface modification of the etched substrates. Atomic-Force-Microscopy showed the etched surfaces to have an average roughness, Ra of 15nm. Optical characterisation data are correlated with electrical measurements using fabricated Schottky barrier diodes for deep-level-transient spectroscopy (DLTS) as well as current-voltage and capacitance-voltage (CV) analysis. CV results detail a reduced surface carrier concentration after RIE while DLTS revealed the emergence of six electron trap defect levels. One of the two prominent RIE induced trap levels exhibited similar DLTS behaviour as that produced after ion bombardment of n-type (Si) GaAs.
Characterization of PECVD Deposited Fluorosilicate Glass (FSG) After CMP and Cleaning
Authors: Mordo D. , Goswami I. , Malik I. J. , Mallon T. , Emami R. , Withers B.
Published: April 2011

A characterization of Plasma-Enhanced CVD Fluorinated Silicate Glass (FSG) is presented. This study investigates the behavior of FSG film in the Chemical Mechanical Polishing (CMP) environment and compares those characteristics to undoped TEOS (UTEOS), Thermal Oxide and Si-Rich oxide capped FSG films. The removal rate, refractive index (RI), surface roughness, contact angle, water content by FTIR and thermal desorption spectroscopy (TDS) were studied.

The FSG films are polished ˜ 10% faster than the undoped PECVD oxide films. Their composition was slightly changed after CMP as can be seen by the minor increase in the RI. A layer of Si-Rich oxide (SRO) was found to have a stabilizing effect on the FSG film during CMP and post CMP cleaning operations, and thus can be used in the intermetal dielectric schemes that require low dielectric constant FSG layers.
Poly(Arylene Ethers) as Low Dielectric Constant Materials for ULSI Interconnect Applications
Authors: Vrtis Raymond N. , Heap Kelly A. , Burgoyne William F. , Robeson Lloyd M.
Published: April 2011

Poly(arylene ethers)s are low dielectric constant organic spin on materials. PAE-2, which is a non-fluorinated poly(arylene ether), exhibits a dielectric constant below 3.0, thermal stability greater than 425 °C as well as excellent adhesion to Si, SiO2, and Al. These are the major atributes which makes it a very attractive candidate for integration as an interlevel or inter-metal dielectric material (ILD). Material properties including dielectric constant, thermal stability, moisture absorption, and mechanical analysis will be discussed.
Comparison of Three Low Dielectric Constant Organic Polymers
Authors: Case C. B. , Case C. J. , Kornblit A. , Mills M. E. , Castillo D. , Liu R.
Published: April 2011

Three low dielectric constant organic polymers are being investigated for possible use in a conventional, subtractive etch, multi-level metal process with PVD Al plugs. Material properties, physical properties, planarization ability and etch chemistries are compared, as well as the possibility of using these materials in a low temperature PVD A1 plug process.
Preliminary Electrical Characterization of Pulsed-Plasma Enhanced Chemical Vapor Deposited Teflon-like Thin Films
Authors: Labelle Catherine B. , Limb Scott J. , Gleason Karen K. , Burns James A.
Published: April 2011

Pulsed-rf excitation of hexafluoropropylene oxide (HFPO) has been used to deposit films with chemical compositions similar to poly(tetrafluoroethylene) (PTFE). Films were deposited at pulse cycles of 10/20, 10/50, 10/200, and 10/400 ms on/ms off and analyzed using electron spin resonance spectroscopy (ESR). All four films produced similar broad ESR spectra, with an average width at maximum slope of ˜60 G and a g-value of 2.0045. The concentration of free electrons in a sample decreased with increasing pulse off time. This behavior can be modeled by the reaction of a free radical with a gas species, assuming that free radicals are generated only during the pulse on time. The films' dielectric constants were found to decrease from 1.99 to 1.95 for pulse off times increasing from 20 to 400 ms.
Influence of the Cure Process on the Properties of Hydrogen Silsesquioxane Spin-On-Glass
Authors: Többen D. , Weiganda P. , Shapiro M.J. , Cohen S.A.
Published: April 2011

Hydrogen silsesquioxane spin-on-glass (SOG) is regarded as a potential low-k material for multilevel metallization (MLM) schemes. In this work we report on the properties of films which have been cured at different temperatures covering the range from 350°C to 850°C. It is found that the material remains in its microporous structures at the lower temperature while it can be strongly densified at increased thermal budgets. The slope of the dielectric constant indicates that care ought to be taken in subsequent metallization anneals in order to preserve the low-k values observed.
Deposition and Characterization of Porous Silica Xerogel Films
Authors: Jin Changming , List Scott , Yamanaka Stacey , Lee Wei William , Taylor Kelly , Hsu Wei-Yung , Olsen Leif , Luttmer J.D. , Havemann Robert , Smith Douglas , Ramos Teresa , Maskara Alok
Published: April 2011

The continued scaling of device feature size demands the use of low permittivity intermetal dielectric materials. Porous silica xerogel films have low dielectric permittivity through the incorporation of micropores into the SiO2 network. A feasible xerogel process has been developed. Crack-free and uniform silica xerogel films up to two microns in thickness with targeted porosity were readily coated. Xerogel materials completely filled 0.3 μm wide gaps with a 2:1 aspect ratio. MOSCAP measurements revealed a low permittivity and high dielectric breakdown strength. The dielectric breakdown strength is expected to be higher than that of ambient air because the average pore size of in the xerogel film is much smaller than the mean free path of the ambient air. Surface treated xerogel films were found to be hydrophobic as indicated by the absence of adsorbed moisture peaks in FTIR spectra. Xerogel films maintained their porosity after deposition of dense capping layers and a subsequent process under 700 atm Ar pressure at 400 °C. Test structures containing xerogel were successfully planarization with CMP and went through a tungsten plug deposition process without delamination nor collapsing. These results reflect the reasonable mechanical strength of xerogel films.
Characterization of a‐SiNx Thin Film Deposited By Inductively Coupled Plasma Enhanced Chemical Vapor Deposition
Authors: Han Sang‐Soo , Jun Byung‐Hyuk , No Kwangsoo , Bae Byeong‐Soo
Published: April 2011

Silicon nitride thin films are deposited at low temperature using the inductively coupled plasma enhanced chemical vapor deposition.(ICP‐CVD) N2 and SiH4 gases are used as reactant gases for deposition of silicon nitride thin films with low hydrogen content. Composition, refractive index, and hydrogen content of the films were examined with variation of N2 flow rate, RF power and substrate temperature. As N2 flow rate and RF power increase and substrate temperature is lowered, N/Si ratio is reduced producing higher refractive index of the film. Hydrogen content of the films is calculated by FTIR spectroscopy and is much less than those of the films deposited by conventional PECVD using SiH4/N2 gases since N2 gas is used instead of NH3 gas. Total hydrogen content is constant regardless of RF Power and N2 flow rate. However, the hydrogen content decreases with increasing substrate temperature due to the release of hydrogen at high temperature.
Direct Observation of Mobile Protons in SiO2 Thin Films: Potential Application in a Novel Memory Device
Authors: Vanheusden K. , Warren W.L. , Devine R. A. B. , Fleetwood D. M. , Schwank J. R. , Winokur P. S. , Lemnios Z. J.
Published: April 2011

In this work we show that annealing of silicon/silicon‐dioxide/silicon structures in forming gas (N2:H2; 95:5) above 500°C leads to spontaneous incorporation of mobile H+ ions in the buried SiO2 layer. We demonstrate that, unlike the alkali ions feared as killer contaminants in the early days, the space charge distribution of these mobile protons within the buried oxide layer can be very well controlled and easily rearranged with relatively high speed at room temperature. The hysteresis in the flat band voltage shift provides a unique vehicle to study proton kinetics in silicon dioxide thin films. It is further shown how this effect has great potential as the basis for a reliable nonvolatile FET memory device that is expected to be competitive with state‐of‐the‐art Si‐based memory technologies. The power of this novel device is its simplicity; it requires few processing steps, all of which are standard in Si integrated‐circuit fabrication.
Correlation of Electrical and Physical Properties of SIMOX BOX Affected by Various Implantation Parameters
Authors: Yoon J. U. , Kim G. N. , Krska J‐H Y. , Chung J. E. , Allen L. P. , Goodson K. , Kaeding O. , Nauka K.
Published: April 2011

The impact of two implant parameters, namely the implant substrate temperature and implant beam current, on the physical and electrical properties of SIMOX buried oxide are investigated. Three implant substrate temperatures, 540 °C, 590 °C, and 640 °C and three beam current, 45 mA, 55 mA, 65 mA, are investigated. Results from thermal conductivity and surface photovoltage measurements show no apparent differences between samples. Results from interface roughness shows a decreasing trend as the substrate temperature and beam current increases. For the samples with different implant temperatures, the high‐field conduction shows an opposite dependence for top‐interface versus substrate injection. This behavior can be explained by the conservation of silicon in the buried oxide. Correlation of surface photovoltage and high‐field conduction shows weak positive dependency while that of interface roughness and high‐field conduction shows dependency only when the sets of temperature variation and beam current variation are decoupled.
Soft X-ray Si 2p core-level spectra of H8Si8O12 physisorbed on Si(111)-H: additional experimental evidence regarding the binding energy shift of the HSi03 fragment
Authors: Zhang K. Z. , Banaszak Holl Mark M. , McFeely F. R.
Published: April 2011

The hydridospherosiloxane cluster H8Si8012 has been physisorbed onto Si(111)-H and soft X-ray Si 2p core-level photoemission spectra obtained. The results of these experiments provide strong support for previous binding energy assignments of HSi03 moieties at -3.6 eV.
Gate Electrode Effects On Dielectric Breakdown Of SiO2
Authors: Toriumi Akira , Mitani Yuichiro , Satake Hideki
Published: April 2011

We discuss the gate electrode effects on SiO2 degradation in MOS structures. The gate electrode material was poly‐silicon, but the impurity doping procedure was varied in terms of species and concentrations. First, the origin of the substrate hole current observed in n‐MOSFETs, by injecting electrons from the silicon substrate, is discussed in terms of oxide thickness and gate electrode doping species, because the dielectric breakdown is closely related to the total hole fluence in the oxide. The effects of the gate electrode on the oxide network structure and on the Si/SiO2 interface are also experimentally investigated. Finally, the experimental results obtained for Qbd of different gate electrode MOSFETs are shown, including the polarity dependence of Qbd. Furthermore, the percolation analysis to explain the polarity dependence is introduced, since the dielectric breakdown process is really stochastic.
Characterization of Plzt on Platinum Electrodes for High Density Fram Application
Authors: Choi YongSoo , Choe SooDoo , Kim SeungHyun , Kim ChangEun , Yang DooYoung
Published: April 2011

A new sol‐gel route to obtain PLZT thin film was developed by combining the advantage of 2‐methoxyethanol as a solvent and acetylacetone as a chelating agent. The sol maintained the same stable state as that of fresh synthesized sol even after 60 days of aging. The PLZT films spin coated onto a Pt/Ti/SiO2 substrate with 15% Pb excess and 7.5% La added sol showed well developed rosette microstructure of uniform grain sizes(0.3 ‐ 0.5 μm) and gave well behaved ferroelectric properties with the values of Ps, Pr, and Ec of 40 μC/cm2, 15 μ C/cm2, and 20 kV/cm respectively at 5V after 650 °C and above annealing. The degradation in polarization of 2.5% La doped PLZT thin film was found to be less than 20% up to 1012 cycles
The Optical Properties of Channel Waveguides in Batio3 Thin Films
Authors: Block B. A. , Wessels B. W. , Gill D. M. , Conrad C. W. , Ho S. T.
Published: April 2011

BaTiO3 epitaxial films have been prepared on (001) MgO substrates by metalorganic chemical vapor deposition. The as‐deposited 0.2 μm thick films had a surface roughness of 12 nm. Channel waveguides were fabricated from the films and the optical throughput measured. To differentiate the surface scattering loss from the internal scattering loss, waveguides were also prepared with a surface planarization step to reduce the surface roughness to 2.5 nm. The waveguide loss was greatly reduced for the planarized waveguides. The results indicate that surface and side wall roughness accounted for the majority of the waveguide loss. Grain boundary grooving lead to surface roughness and routes to overcome this problem are discussed.
Assembly of thin Film Dielectrics by Sequential Adsorption Reactions of Unilamellar Inorganic Colloids
Authors: Fang Mingming , Kim Chy Hyung , Sutorik Anthony C. , Kaschak David M. , Mallouk Thomas E.
Published: April 2011

Several layered inorganic materials (e.g. KCa2Nb3O10, KTiNbO5, and CsPb2Nb3O10) were prepared and their alkali cations exchanged by in aqueous acid. A fraction of the interlayer protons of HCa2Nb3O10 and HTiNbO5 can be replaced by tetra-n-butylammonium (TBA+), by reaction with TBA+OH. Intercalation of a sufficient amount of TBA+ causes complete exfoliation, and single, nanometer-thick sheets of these materials are thus obtained. By sequential adsorption of these two-dimensional colloidal polyanions and polymeric cations, monolayer sheets of layered perovskites can be stacked on silicon surfaces to give thin films of any desired thickness. The layered materials, the exfoliated colloids, and the thin film multilayers on silicon were studied by X-ray diffraction, transmission electronic microscopy (TEM), ellipsometry, and atomic force microscopy (AFM). The dielectric properties of the related bulk materials were measured, and are also discussed.
Effect of Reactive Nitrogen Gas on the Electrical and Optical Properties of Rf-Sputtered Amorphous Carbon Films
Authors: Lee Kwang Bae , Lee Duck Jung , Shin Yong Woo
Published: April 2011

We have investigated the changes in the temperature dependence of the dc conductivity and the optical gap with nitrogen content in amorphous carbon nitride (a-C:N) films, in order to find the effect of nitrogen doping on the electrical and optical properties of amorphous carbon films. Specimens were deposited onto borosilicate glass substrates by the rf magnetron sputtering method using Ar and N2 as a sputtering gas and a reactive one, respectively. The values of the activation energy of the dc conductivity, Ea, of these films are 0.3∼0.8 eV and those of the optical gap, Eg, are 0.8∼ 1.4 eV. Both values decrease with increasing nitrogen content, which is due to the increase of the concentration or average size of sp islands segregated into the sp matrix by nitrogen doping. From the investigation of the behavior of both Ea and Eg in accordance with the nitrogen content, we discuss the three subsequent shifts of band edge and Fermi level, accompanied with the subsequent changes of microstructure in a-CN films by nitrogen doping.