bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the Radionuclide Coprecipitation-Solid Solution Formation. The UO2(S)-La(OH)3(S) Coprecipitation as an Analogue for The UO2(S)-Pu(OH)3(S) System
Authors: Bruno Jordi , Grenthe Ingmar , Muñoz Maria
Published: March 2011

The UO2(s)-La(OH)3(s) coprecipitation equilibria have been studied in 0.5 M NaClO4 medium, at 25°C under anoxic conditions. The data obtained in the pH range between 2 and 5, and at different initial La(III)/U(IV) ratios (10%,5%,3%,2% and 1%), is explained by applying the Doerner-Hoskins logarithmic law. The same law can also be used to describe previously collected UO2(s)-Pu(OH)3(s) coprecipitation data. A method is proposed which uses the logarithmic distribution constants and the thermodynamic quantities for the pure phases to describe the solubility of radionuclides under repository conditions.
Analysis of Colloid Transport
Authors: Travis B. J. , Nuttall H. E.
Published: March 2011

The population balance methodology is described and applied to the transport and capture of polydispersed colloids in packed columns. The transient model includes particle growth, capture, convective transport, and dispersion. We also follow the dynamic accumulation of captured colloids on the solids. The multidimensional parabolic partial differential equation was solved by a recently enhanced method of characteristics technique. This computational technique minimized numerical dispersion and is computationally very fast. The FORTRAN 77 code ran on a VAX-780 in less than a minute and also runs on an IBM-AT using the Professional FORTRAN compiler. The code was extensively tested against various simplified cases and against analytical models.

The packed column experiments by Saltelli et al. were re-analyzed incorporating the experimentally reported size distribution of the colloid feed material. Colloid capture was modeled using a linear size dependent filtration function. The effects of a colloid size dependent filtration factor and various initial colloid size distributions on colloid migration and capture were investigated. Also, we followed the changing colloid size distribution as a function of position in the column.

Some simple arguments are made to assess the likelihood of colloid migration at a potential NTS Yucca Mountain waste disposal site.
Diffusion and Permeability Based Sorption Measurements in Intact Rock Samples
Authors: Bradbury Michael H. , Stephen I. G.
Published: March 2011

Distribution ratios have been determined for Sr, Cs and Tc (as pertechnetate) over a range of concentrations for a Darley Dale sandstone by three different methods: crushed rock batch tests, with W/R ratio and particle size range as independent variables, diffusion-sorption and permeability-sorption experiments on intact rock samples. Comparisons of Rd - values obtained from batch and diffusion-sorption experiments indicate that crushed rock tests can overestimate sorption by as much as one or two orders of magnitude.
An Analogue Validation Study of Natural Radionuclide Migration in Crystalline Rocks using Uranium-Series Disequilibrium Studies
Authors: Smellie J. A. T. , MacKenzie A. B. , Scott R. D.
Published: March 2011

Concentrations and isotope ratios of natural decay series radionuclides have been studied in three contrasting crystalline rock drillcore sections intersecting water-conducting fractures deep in the bedrock. Radioactive disequilibria resulting from rock-water interactions were observed in two of the cores. These indicated uranium migration along distances of 40 cm or more on a timescale of 106 years in conjunction with thorium immobility under the same conditions. Fracture surface minerals showed a high affinity for radionuclide retardation and a limit of about 3 cm is suggested for the migration of radionuclides from fracture fluids into the saturated rock. This limit may correspond to enhanced matrix porosities resulting from earlier hydrothermal activity along the same channels.
Nucleation of Internal Melt During Pulsed Laser Irradiation
Authors: Peercy P. S. , Thompson Michael O. , Tsao J. Y. , Poate J. M.
Published: March 2011

Real-time measurements of the molten layer thickness and simultaneous measurements of the melt duration at the surface reveal that melt nucleates internally when Si implanted with low solid-solubility impurities such as In is melted with a 30 nsec laser pulse at 694 nm. Internal nucleation of melt was observed for all energy densities examined. Furthermore, at energy densities insufficient to melt the entire amorphous layer, internal nucleation of melt is followed by an explosive-like process in which a buried molten layer propagates toward the irradiated surface.
Femtosecond Dynamics of Highly Excited Semiconductors
Authors: Shank Charles V. , Downer Michael C.
Published: March 2011

The advent of femtosecond optical pulse techniques has provided new opportunities for the investigation of the dynamical properties of highly excited semiconductors. In this paper we describe recent investigations of delayed Auger heating in Si.
Laser Induced Oxidation of Heavily Doped Silicon
Authors: Fogarassy E. , White C.W. , Lowndes D.H. , Narayan J.
Published: March 2011

We have investigated the incorporation of oxygen into heavily doped silicon during UV excimer laser irradiation. For the case of repetitive laser irradiations in air, we observe that the amount of oxygen incorporated into Si depends markedly on the dopant. For As and Sb implanted silicon, there is no anomalous oxygen incorporation. By contrast, increasing amounts of 0 are incorporated into In implanted silicon as a function of number of laser shots. The incorporation of 0 is associated with degradation of the optical and structural properties of the surface, and a deep diffusion of the dopant. This behavior is believed to be partly related to specific chemical reactions between oxygen and indium present in the surface at high concentrations as the result of dopant segregation during solidification.
Cross-Sectional Tem Characterization of Structural Changes Produced In Silicon By One Micron Picosecond Pulses
Authors: Smirl Arthur L. , Boyd Ian W. , Boggess Thomas F. , Moss Steven C. , Pinizzotto R.F.
Published: March 2011

Plan and cross-sectional transmission electron microscopy (TEM) has been used to examine the various bulk and surface structural changes observed in crystalline silicon following melting caused by the absorption of 1-μm pulses that are 4 ps in duration. We show for the first time that for picosecond excitation polycrystalline Si (p-Si), rather than singlecrystal Si, is always formed when the melt resolidifies. Specifically, cross-sectional TEM analyses indicate that a thin layer of fine-grained p-Si is formed at the interface of the melted region with the bulk. When the incident fluence is more than 10% above the melting threshold, the region between the surface and the fine-grained p-Si regrows as largergrain p-Si. This is the first reported observation of a large-grain p-Si layer on a fine-grain p-Si base in crystalline material. If the incident fluence is less than 10% above threshold, the region near the surface resolidifies as amorphous Si, but the narrow layer of fine-grained p-Si remains at the interface with the single crystal material. Present models for resolidification must be modified to account for these features.
Time-Resolved Optical Studies of Picosecond Laser Interactions With Gaas Surfaces
Authors: Liu J.M. , Malvezzi A.M. , Bloembergen N.
Published: March 2011

The interactions of picosecond laser pulses at 532 nm wavelength with GaAs surfaces have been studied with time-resolved reflectivity and transmission measurements at three probe wavelengths. At fluences below the melting threshold, the laser-generated electron-hole plasma is limited to a density below ≈1020cm−3. The high reflectivities of molten GaAs observed at fluences above the tlhreshold have a wavelength dependence inconsistent with a simple Drude model for a metallic GaAs molten layer. At high fluences, the evolution of a laser-induced vapor cloud is observed.
Dynamical Laser Desorption Process of Ionic Clusters In Group Iv Elements
Authors: Kasuya A. , Nishina Y.
Published: March 2011

Emission of ionic clusters from surfaces of group IV elements has been analyzed by means of time-of-flight measurements under nitrogep laser irradiation in its peak intensity ranging from 50 to 200 MW/cm with pulse duration of 10 ns. The measurements on Si, Ge and β-Sn with a straight flight tube show a continuous distribution of spectra in the flight time corresponding to the mass-to-charge ratio between 1 and 2 in units of the singly charged atom of respective elements. The line shape analysis indicates that emitted ions immediately after laser excitation are coagulated in the form of large clusters having nearly an equal mass-to-charge ratio between 5/4 and 3/2. They eventually decompose into monoatoms and their ions in a time scale of 10 ps as confirmed by a quadrupole mass analysis. These results are in remarkable contrast with the case of graphite which exhibits a series of sharp spectral peaks. The clear distinction between graphite and other group IV elements is attributed to the intrinsic difference in their chemical bonds under highly excited conditions.
Amorphous Gallium Produced By Pulsed Excimer Laser Irradiation
Authors: Fröhlingsdorf J. , Stritzker B.
Published: March 2011

Pure crystalline Ga films (α-Ga, β-Ga) have been irradiated at low temperatures (≤ 20 K) with an Excimer laser. By measuring the superconducting transition temperature Tc and the residual resistivity ≤o, the resulting Ga phases (α-Ga, β-Ga, a-Ga) can be identified.

Both crystalline Ga phases can be transformed into the amorphous phase.

The threshold energy density for the β→ a transition depends on the film thickness, whereas the α →. a transition occurs always at about 225 mJ/cm2 This behavior is in agreement with earlier observations that a-Ga can grow on top of the in-phase but not on the β-phase.

The results of laser quenching are compared with other non-equilibrium techniques for the production of a-Ga, such as vapor quenching and low temperature ion iradiation.
Self And Ion Beam Annealing of P,Ar, And Kr In Silicon
Authors: Cannavo S. , Ferla A. La , Campisano S.U. , Rimini E. , Ferla G. , Gandolfi L. , Liu J. , Servidori M.
Published: March 2011

The damage produced by high current density ∿l0µA/cm2 implants of 120 keV P+ into <111> and <100> silicon wafers, 500 °m thick, has been investigated in the fluence range 1×l01 5/cm2-l×l016 /cm2 by ion channeling and by transmission electron microscopy. For both orientations the thickness of the damage layers increases with the fluence up to 2×1015 /cm2 and then decreases. The rate of regrowth is a factor two faster for the <100> with respect to the <111> oriented Si crystals. Similar ratios have been found in pre-amorphized samples and irradiated with Kr+ ions in the temperature range 350°C-430°C. The TEM analysis reveals the presence of hexagonal silicon and of twins in small amounts for both orientations. The beam induced epitaxial growth depends also on the species present in the amorphous layer. A comparison between self-annealing and beam annealing in Si <100> preamorphized with Ar+ or P+ shows a noticeable retardation of the growth rate in the presence of Ar+.
Mev Ion Induced Modification of The Native Oxide of Silicon
Authors: Headrick R.L. , Seiberling L.E.
Published: March 2011

We have studied the native oxide of silicon (110) and the changes roduced by MeV ion bombardment using transmission ion channeling of 5.9 MeV9Be, and Elastic Recoil Detection Analysis (ERDA). Transmission channeling was used to measure interfacial nonregistered Si and adsorbed C and 0. ERDA was used to measure the surface concentration of H. MeV ions were found to cause an increase in the interfacial nonregistered silicon which saturates at approximately one monolayer. Rapid desorption of hydrogen was observed. The effect of 2 keV electrons on the silicon native oxide was also studied by Auger Electron Spectroscopy.
Nonlinear Optics And Surface Science
Authors: Shen Y. R.
Published: March 2011

The recent status of applications of nonlinear optics to surface science is reviewed. The basic theory of wave mixing on a surface layer, and the possibility of using various nonlinear optical processes for surface probing are briefly discussed. Emphasis is on surface second harmonic generation, which is shown with many illustrations to be a rather unique and versatile tool for surface studies.
Amorphization And Recrystallization Processes In Monocrystaline Beta Silicon Carbide Thin Films
Authors: Edmond J.A. , Withrow S.P. , Kong H.S. , Davis R.F.
Published: March 2011

Individual, as well as multiple doses of 27Al+, 31p+, 28Si+, and 28Si+ plus 12C+ were implanted into (100) oriented monocrystallne β-SiC films+. A critical energy of =16 eV/atom required for the amorphization of β-SiC via implantation of Al and P was determined using the TRIM84 computer program for calculation of damage-energy profiles coupled with results of RBS/ion channeling analyses. In order to recrystallize amorphized layers created by the individual implantation of all four ion species, thermal annealing at 1600, 1700, or 1800°C was employed. Characterization of the recrystallized layers was performed using XTEM. Examples of SPE regrown layers containing; 1) precipitates and dislocation loops, 2) highly faulted, microtwinned regions, and 3) random crystallites were observed.
Ion Implantation At Elevated Temperatures
Authors: Lam Nghi Q. , Leaf Gary K.
Published: March 2011

A kinetic model has been developed to investigate the synergistic effects of radiation-enhanced diffusion, radiation-induced segregation and preferential sputtering on the spatial redistribution of implanted solutes during implantation at elevated temperatures. Sample calculations were performed for Al+ and Si+ ions implanted into Ni. With the present model, the influence of various implantation parameters on the evolution of implant concentration profiles could be examined in detail.
Binary And Ternary Amorphous Alloys of Ion-Implanted Fe-Ti-C
Authors: Follstaedt D. M. , Knapp J. A.
Published: March 2011

The microstructure of Fe implanted with up to 50 at.% C was found to consist of hexagonal iron carbide precipitates oriented with respect to the Fe matrix. For higher C concentrations, an amorphous phase forms. This concentration dependence is explained in terms of the lattice structure of the iron carbide. In Ti-implanted Fe, substitutional Ti was found in the bcc Fe lattice for concentrations ≤ 15 at.% Ti. The work of others suggests that amorphous phases form for ≥ 33 at.% Ti. These results are discussed in terms of concentration boundaries of the ternary Fe(Ti,C) amorphous phase.

Ion beam alloying methods are currently being used to form metastable alloys [1], both for fundamental investigations of such alloys as well as for potential use to improve physical properties of components [2]. An important consideration in metal alloys is what phase will form upon implantation; one aspect of this question is to determine when amorphous phases will form. Rules are currently being advanced to predict alloy systems which will yield amorphous phases. By using ion irradiation and ion beam mixing as well as ion implantation, such rules can be evaluated over entire composition ranges.

To gain insight into amorphous phase formation, we have studied Fe alloys implanted with C, Ti and Ti + C. The Fe(C) alloys exhibit compound precipitation and amorphous phase formation; the precipitation and the concentrations at which the amorphous phase appears can be accounted for by considerations of the structure of the hexagonal carbide which forms. Based on conventional uses of the Fe(C) system, such alloys may be useful for improving mechanical properties by implanting C into ferrous components. Iron implanted with Ti is examined to a limited extent here, but by including ion irradiation studies by others [3], a more complete characterization of Fe(Ti) alloys is obtained. The microstructures of Fe(C) and Fe(Ti) are examined along with the known composition limits of amorphous Fe(Ti,C) alloys, which are important for their improved mechanical properties [2]. Taken together, a more complete determination of amorphous phase formation in this ternary system is obtained.
Collision Cascades, Ionization, Spikes And Energy Transfer
Authors: Brown W. L.
Published: March 2011

The collisions of an individual energetic ion in a solid set atoms of the solid in motion and excite electronic states. The moving atoms collide with others to form a collision cascade and the electronic excitation also forms a branched trail around the track of the ion. If the densities of the energy deposition in either of these modes is high the result is called a “spike”. The low density regimes of collision and ionization cascades and evidence for the transition to non-linear high density spikes are summarized. The understanding of the latter is still quite incomplete as is also understanding of the transfer of energy between the kinetic and the electronic modes, particularly at high energy densities.
Laser Recrystallization of Mocvd Poly-Gaas on Insulating Substrates
Authors: Bao X.M. , Huang X.F. , Han P. , Yin J.M.
Published: March 2011

Poly-GaAs films have been grown on amorphous insulating substrates by MOCVD technique. The films were analyzed using TEM, X-ray diffraction, AES and ESCA measurements. The results show that poly-GaAs films are flat, bright and close in texture and stoichiometric. The grain size is about 200Å. The film contains trace impurities such as Si,O and C. They are evenly distributed in the film. The poly-GaAs films were crystallized by CW Ar+ laser with a increase of grain size from 200Å to 40 µm. Schottky barrier diodes of good I-V characteristics were made on the laser recrystallized GaAs films.
Solid Phase Epitaxial Recrystallization of Sos, with Applications to Submicrometer Cmos and Bipolar Devices
Authors: Vasudev P.K.
Published: March 2011

CMOS/SOS devices and circuits were fabricated in 0.3-µm-thick epitaxial silicon-on-sapphire (SOS) films. Two solid phase epitaxial recrystallization techniques (DSPE* and SPEAR**) reduced the total microtwin concentrations in the Si layers more than ten- fold, while increasing electron and hole inversion layer mobilities between 30 and 45%. Leakage currents were substantially reduced in all SPEAR devices and in n-channel DSPE transistors, with some increase observed for p-channel DSPE devices. Drive currents and subthresholds slopes also showed significant improvement in both n- and p-devices. Propagation delays below 75 ps were obtained for CMOS/SOS inverters with Lef = 0.5 µm. The application of DSPE and SPEAR techniques to 0.3-µm SOS films will extend the scaling of CMOS/SOS to circuits with very large scale integration (VLSI) complexity.
High-Quality Thin Si Film By Spe Regrowth on Epitaxially Grown Spinel
Authors: Kimura Takafumi , Yamawaki Hideki , Arimoto Yoshihiro , Ikeda Kazuto , Ihara Masaru , Ozeki Masashi
Published: March 2011

A high-quality thin Si layer on epitaxial spinel(MgO·Al2O3) on Si substrate has been developed. It was obtained by the solid phase epitaxial (SPE) regrowth of amorphous Si with Si seed islands on the epitaxially grown spinel. The SPE-Si layer on the epitaxial spinel was superior to conventional Si on sapphire (SOS) in stacking-fault density, Hall mobility, and contamination from the insulating materials. The SPESi layer has low stacking-fault density of 10–50 cm-2, even for 0.4 μm thickness. This value is eight orders of magnitude less than that of Si on epitaxial spinel obtained by vapor phase epitaxial (VPE) growth with SiH4. The SPE-Si also has high electron Hall mobility of 880 cm2/V-s for n=5×l016 cm-3, for 1-μm-thick Si. This value is about 85% of that in bulk Si, and is higher than that in Si on spinel grown by VPE-growth and SOS. (100) spinel layer was grown on (100) Si substrate by a MgCI2-Al-HCI-CO2-H2 VPE growth system. After thermal oxidation, Si seed islands were grown on the spinel by the pyrolysis of SiH4. Amorphous Si was deposited on the Si seed islands by chemical vapor deposition (CVD) of SiH4. The SPE-Si layer was obtained by regrowth of the amorphous Si in a hydrogen atmosphere.
Reduction of Ca and F Segregated at the Surface of a Si/CaF2/Si(100) Structure By Solid Phase Epitaxy of Si
Authors: Sasaki Masayoshi , Onoda Hiroshi , Hirashita Norio
Published: March 2011

Epitaxial Si films have been grown on single crystalline CaF2 on (l00)Si substrates by molecular beam epitaxy(MBE) or combination of MBE and solid phase epitaxy(SPE) of deposited amorphous Si(a-Si). It has been found that Ca and F segregate at the surface of the Si grown by MBE. The high energy electron diffraction (RHEED) patterns from the Si surface show the superstructures which are caused by the existence of Ca and F at the Si surface. To reduce the segregation effect, SPE process has been successfully applied to Si epitaxy. The Si SPE performed on top of the MBE Si layer reduces the Ca concentration at the Si surface by an order of magnitude, although the segregation effect is not completely suppressed.
Silicon on Insulator Formed By O+ OR N+ Ion Implantation
Authors: Hemment P.L.F.
Published: March 2011

The synthesis of buried layers of SiO2 and Si3N4, by ion implantation is reviewed. This process, which may be used to form device worthy silicon-on-insulator (SOI) structures, involves (i) implantation of O+ or N+ ions and (ii) high temperature processing to achieve defect annealing and chemical segregation of the implanted species.
Properties of Thin Films After Focused Beam Processing
Authors: Campbell I.H. , Fauchet P.M.
Published: March 2011

A Raman microprobe is used to detect the changes in crystallinity, stress and homogeneity on thin films of SOI irradiated by a single laser pulse. Maximum, isotropic, planar tensile stress increased from 5x109 dyn/cm2 to 12x109 dyn/cm2 in the processed area and stress of 8x109 dyn/cm2 was observed 20 μm beyond the damaged region. Crystallite sizes of 50 Å to greater than 300 Å were observed inside the processed area. Results obtained with different pulsed laser frequencies are compared and significant differences in the processing effects are observed.
Mechanical Properties of Ga1–xInxAs
Authors: Guruswamy S. , Hirth J.P. , Faber K.T.
Published: March 2011

Substantial solid solution strengthening of GaAs by In acting as InAs4 units has recently been predicted. This strengthening could account for the reduction of dislocation density in GaAs single crystals grown from the melt. High temperature hardness measurements up to 700ºC have been carried out on (100) GaAs and Ga0.9975 In0.0025 As wafers. Results show a significant strengthening effect in In—doped GaAs even at concentration levels of about 0.2 wt%. A temperature independent flow stress region is observed for both these alloys. The In—doped GaAs shows ahigher plateau stress level compared to the undoped GaAs. The results are consistent with the solid solution strengthening model.
Minority Carrier Lifetime Studies in Halogen Lamp Recrystallized Soi Films
Authors: Chantre A. , Ronzani D. , Vu D. P.
Published: March 2011

We report a detailed investigation of minority carrier generation processes in halogen lamp recrystallized SOI films. Various kinds of materials have been analyzed in order to assess the roles of the different crystallographic imperfections present in the layers (precipitates, subgrain boundaries, interfaces). We conclude that generation lifetimes inprecipitate-free material are controlled by subgrain boundaries, and show that 100 μs lifetimes can be measured in defect-free regions of SOI obtained using a defect localization technique.
An Analytical Model for the Threshold Voltage of Polysilicon Mosfet's
Authors: Anwar A.F.M. , Khondker A.N.
Published: March 2011

An analytical model is developed to describe quantitatively the increase in the threshold voltage of n-channel polysilicon (poly-Si) MOSFET's. The model takes into account charge-coupling between the gate and grain boundary traps. This charge-coupling appears in Poisson's equation and a charge neutrality equation. A drift-diffusion mode of conduction is used to describe the turn-on characteristics that occur beyond the strong inversion threshold.
Dependence of A-Si:H Tfts Performances on Deposition and Process Parameters
Authors: Chartier E. , Szydlo N. , Boulitrop F. , Proust N. , MagariÑO J.
Published: March 2011

Amorphous silicon TFTs have been realized using several plasma-CVD systems which differ in the conception of the reactor: hot or cold walls, and from the frequency used: 400 kHz and 13.56 MHz. Silicon nitride has been used as insulator. Inverted and direct staggered structures with different channel dimensions (0.5 ≤ W/L ≥ 20) are compared. High performance TFTs with mobility from 0.5 to 0.7 cm2V−1s−1 for inverted and from 0.1 to 0.4 cm2V−1s−l for direct staggered TFTs have been optimized by a full study of the insulator semiconductor and source/drain contact properties.
Photoluminescence and Photoconductivity Studies on a-Si:H
Authors: Mendoza-Alvarez Julio G. , Torres Gerardo , Gonzalez-Hernandez J.
Published: March 2011

It has been previously reported that intense illumination on a-Si:H induces luminescence fatigue. The effect of light soaking on the photoconductivity of this material is also known. In this work, studies of photoluminescence (PL) at 10°K shows that the intensity of the main peak at 1.3eV can be correlated with the decrease in the photoconductivity (PC) of the sample. Similar to the PC, the effects of light soaking on the PL spectrum are reversible; annealing at 200°C fully restore the PL spectrum. Our results indicate that the light-induced radiative defects are also involved in the carrier recombination mechanism. By measuring the PL spectrum at temperatures in the range from 10 to 120°K, the activation energy for the non-radiative process has been determined in both light-soaked and heat-dried states.
Improvement of Wetting of Silicon on Insulator During Lamp Zone Melting Using Plasma Nitridation
Authors: Haond M. , Dutartre D. , Pantel R. , Straboni A. , Vuillermoz B.
Published: March 2011

In the preparation of SOI films by Zone Melting Recrystallization (ZMR) a cap layer is necessary to avoid the beading up of a silicon film when it is molten over silicon. This is a consequence of a bad wetting of liquid Si on SiO2. We report the successful application of a plasma nitridation treatment of the capping oxide. We compare the behaviour of the liquid silicon films during ZMR for different capping structures. The modification of the interface is investigated by using Auger analysis. We show that a range of nitrogen accumulation at the interface provides a good wetting.
Large Grain Growth of Silicon Films on Low Temperature Glass Substrates
Authors: Bleil C. E. , Troxell J. R.
Published: March 2011

Argon laser recrystallization of silicon films deposited on low temperature glass substrates offers the potential for development of large scale matrix addressable displays incorporating on-glass line drivers and logic circuitry. In order to achieve this promise, the challenge of containing molten silicon, at 1685 K, in close proximity to a glass substrate (Corning 7059) which has an annealing temperature of 914 K, must be met. We have successfully recrystallized areas of several squared millimeters of 500 nm thick silicon films without cracking on 7059 glass substrates. This was achieved by the incorporation of multiple film layers interposed between the silicon and the glass substrate, which serve to control the thermal gradients which occur during the recrystallization process. Grains in the recrystallized films are typically 10µm wide and several hundred µm long, achieved using a laser spot size of approximately 70 µµµµm diameter and a scan rate of 15 cm/s. Comparable results were obtained for a wide range of laser powers, from 7.5 to 9.2 W.
Crystallization Of Amorphous Silicon During Thin Film Gold Reaction
Authors: Hultman Lars G. , Psaras P. A. , Hentzell H.T.G.
Published: March 2011

The crystallization of α-Si in α-Si(50nm) and Au(5nm) thin film bi-layers has been investigated during heat treatment in a transmission electron microscope (TEM). When crystallization of α-Si first begins at 130°C the Au-Si alloy reflections observed at lower temperatures vanish and several new reflections from metastable Au-Si compounds occur. Dendritically growing islands of poly-Si are observed after heating at 175°C. If the samples are held constant at 175°C for ten minutes, the poly-Si islands grow together. The formation of poly-Si depends on the diffusion of Au into α-Si and the formation of metastable Si-Au compounds. After crystallization Au segregates to the front and back surface of the poly-Si film.
Interfacial Reactions Between Amorphous W-Si Thin Films And Polycrystalline Overlayers
Authors: Thomas R. E. , Perepezko J. H. , Wiley J. D.
Published: March 2011

Interactions between amorphous metal thin films and either a substrate or an overlayer can limit their effectiveness as diffusion barriers. We have found in previous studies that Au and Al polycrystalline thin films in contact with amorphous W-Si lowers the crystallization temperature of the a-(W-Si) by at least 100C. In contrast Cu and Mo have no apparent effect on the stability of the amorphous layer. The mechanisms leading to premature crystallization are not well understood. Amorphous W .72Si.28 was deposited by D.C. sputtering onto single crystal Si substrates. Overlayers of Al were then evaporated onto the W-Si. Using Auger electron spectroscopy depth profiling coupled with cross-section TEM, we have studied interfacial reactions between the amorphous layer and polycrystalline Al. Auger profiling results show that in the case of Al overlayers, W and Si diffuse out of the a-(W-Si) into the Al where WAl12 forms. These results can be explained in the context of three binary diffusion couples, W-Si, W-Al, Al-Si, and the individual interactions associated with these couples.
Bombardment-Induced Mixing of Mo Films on Si
Authors: Van Ommen AH. , Willemsen M.F.C. , Boudewijn PR. , Reader A. H.
Published: March 2011

We studied ion beam mixing of thin Mo films on monocrystalline Si by As “implantation at room temperature. The results differ significantly from those obtained for implantation at elevated temperature (T > 200°C). where ion beam mixing results in hexagonal MoSi2 formation. Room temperature implantation results in the formation of an amorphous mixed layer. The composition of this layer varies with depth from Mo-rich to Si-rich. The mixed layer thickness increases linearly with implanted dose and energy. An increase of the implantation temperature with 100°C gives rise to a factor of 2 larger mixed layer thickness and to the formation of amorphous MoSi2 near the interface with Si. These phenomena indicate that at elevated temperature ion beam mixing is controlled by radiation-enhanced diffusion whereas, at room temperature ballistic mixing is the dominant mechanism.
Epitaxial Formation of Rare Earth Silicides by Rapid Annealing
Authors: Knapp J. A. , Picraux S. T.
Published: March 2011

Rapid electron beam and lamp heating have been used to form thin epitaxial films of rare-earth suicides by reacting overlayers of the rare earths with (111) Si substrates. Of the metals Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, all but Gd are found to form epitaxial suicide layers by rapid solid-phase reaction, while suicides of Gd, Dy, Tm, Yb and Lu have been formed epitaxially by liquid phase reaction. For all but Er this is the first demonstration of epitaxial growth on Si. Details obtained from ion beam channeling analysis and transmission electron microscopy confirm the expected epitaxial structure and also show that the Si vacancies in the suicide form an ordered superlattice, rather than a random array as had been assumed before.
Formation Of Stacking Fault Tetrahedra During Epitaxial Growth of Silicon and Germanium-Silicon Layers on {111} Silicon Substrates
Authors: Brasen D. , Nakahara S. , Bean J. C.
Published: March 2011

Transmission electron microscopy was used to characterize defects formed in silicon (Si) and germanium-silicon (Ge-Si) alloy layers grown sequentially by molecular-beam epitaxy (MBE) on {111} Si substrates. Stacking fault tetrahedra (SFT) were found to form in these epitaxial layers. In addition, the apex of the SFT are seen to be pointing down toward the Si substrate, with most of the SFT tips converging exactly at the Si/Si and the Ge-Si/Si interfaces. Diffraction contrast experiments using various two-beam conditions have shown that the stacking faults bounding the SFT are of intrinsic (vacancy) type. In the case of a Si layer on the Si substrate, it is reasoned that the SFT are caused by impurities on the surface of the Si substrate prior to deposition. However, in the Ge-Si layer, it is believed that the formation of the S FT is due to local stresses caused by the structural ordering/phase separation of the Ge atoms.
The Electronic Properties of Epitaxial Calcium Fluoride-Silicon Structures
Authors: Smith T. P. , Phillips J. M. , People R. , Gibson J. M. , Pfeiffer L. , Stiles P. J.
Published: March 2011

The characterization of electronic devices using epitaxial CaF2 on Si is described. In addition, the growth and annealing techniques used to obtain high quality epitaxial films are discussed. In particular, the results of using rapid thermal annealing to improve the epitaxial quality of CaF2 films are presented in detail.

The electronic and electrical properties of these structures are very promising. Epitaxial CaF2 films with breakdown fields as high as 3 × 106 V/cm and interface trap densities as low as 7 × 1010cm-2eV-1 have been fabricated. In addition, minority carrier dominated trapping has been observed at the CaF2 /Si interface. Finally, the material properties of these structures, as determined by Rutherford backscattering, channeling, and electron microscopy, are discussed and correlated with their electronic properties.
MBE Growth of an Epitaxial Insulator-Metal-Semiconductor Structure: CaF2/CoSi2/Si(111)
Authors: Phillips Julia M. , Augustyniak W. M.
Published: March 2011

We report the first successful growth of an epitaxial insulator-metal-semiconductor structure. A layer of metallic CoSi2, followed by a layer of insulating CaF2 have been grown by molecular beam epitaxy on Si(111). The epitaxial quality of the CaF2 layer improves upon rapid thermal annealing, while the already excellent crystallinity of the CoSi2 layer is unaffected. The lattice of the CoSi2 is rotated 180° with respect to the Si lattice while the CaF2 lattice is aligned with the Si lattice.
Theimddynamically Stable Metal / III-V Compound-Semiconductor Interfaces
Authors: Stanley Williams R. , Lince Jeffrey R. , Tsai Thomas C. , Pugh John H.
Published: March 2011

Chemical reactions that occur at a metal/III-V compound-semiconductor interface should be minimized if the change in Gibbs free energy of the bulk materials with respect to any possible reaction products is positive. However, the large positive change in entropy caused by vaporization of the highly volatile group V elements is a very important contribution to the Gibbs free energy of these systems, especially at higher temperatures. Thus, a particular metal/III-V compound-semiconductor interface may be thermody-namically stable at one temperature, but unstable with respect to sublimation of elemental group V species at a higher temperature if the enthalpy change for the reaction is positive. Examination of bulk phase diagrams makes it possible to rationalize the reaction products observed and to predict which will be the most stable interface for any particular metal/III-V system.
First Phase Nucleation And Growth Of Titanium Disilicide With An iPhasis On The Influence Of Oxygen
Authors: Van Houtum Harrie J. W. , Raaijmakers Ivo J. M. M.
Published: March 2011

The existence of a TiSi2phase in the C49 (ZrSi2) structure prior to formation of the stable low resistivity C54 TiSi2structure has been justified for Ti-Si thin film diffusion couples after low temperature (500°C to 650°C) anneal. The transition temperature (Ttr) to the C54 phase is shown to be dependent on layer thickness, thinner films yielding higher Ttr. We could not detect an influence of oxygen on Ttr. Moreover the growth rate of C49 TiSi2is independent of oxygen contamination in the Ti layer up to a mean concentration of 23 at.%. It is postulated that the transition from the C49 to the C54 phase actually is a recrystallization process.
Interface States at Au/Gaas Schottky Contacts
Authors: Werner J. , Ploog K.
Published: March 2011

We present a new method for the characterization of traps at the interfacial layer of metal/semiconductor contacts. The method is based on measurements of the ac-admittance of Schottky contacts over a wide frequency range. The frequency dependence is analyzed within a new Trap Transistor Model which explains the ac-behavior as well as the dc-characteristics. In particular we propose that the ac-current across the interface consists of capacitive as well as of conductive parts. We are able to deduce the density of trap states at the majority carrier Fermi level as well as the capture cross section of the traps. The model is applied to Au/GaAs-Schottky contacts. We find a weak energy dependence for the density of interface states as well as for their capture cross section within the energy range of 0.45eV to 0.57eV below the conduction band edge.
Refractory Silicide Schottky Contacts To Gaas
Authors: Yokoyama N. , Ohnishi T. , Nakamura T. , Nishi H.
Published: March 2011

Refractory suicides form high temperature stable Schottky contacts to GaAs. This finding enabled us to develop self-aligned GaAs MESFETs, thereby enabling the development of today's GaAs ICs. This paper reviews electrical and metallurgical studies on refractory-metal/GaAs and refractory-metal-si licide/GaAs interfaces. We emphasize the fact that W5Si3/GaAs contacts have extremely stable electrical properties even after annealing at temperatures up to 850°C. Crystallographical properties of the W5S3 film on GaAs, investigated by x-ray and TEM measurement techiques, are also covered. We found that the Schottky electrical characteristics are not affected by whether the film is amorphous or crystalline.
Interface Reactions and Electrical Behaviour of Ni-AuGe Contacts on GaAs
Authors: Botha A P , Relling E
Published: March 2011

Interdiffusion and reaction in the GaAs/AuGe/Ni and GaAs/Ni/AuGe/Ni thin film systems have been investigated, using Auger Electron Spectroscopy depth profiling and Rutherford Backscattering Spectrometry. The roles of the individual metal layers were determined by studying the GaAs/AuGe, GaAs/Ni and GaAs/Ni/AuGe subsystems. It was found that the interfacial layer in the GaAs/Ni/AuGe/Ni contact scheme prevents Ge from diffusing away from the interface. In this way more efficient doping of the GaAe is possible. Current-Voltage measurements indicate that this layer structure forms a good ohmic contact to GaAs.
The Phase Formation Sequence In Titanium-Silicon Thin Films
Authors: Beyers Robert , Sinclair Robert
Published: March 2011

The reliable use of TiSi2 in integrated circuit metallizations will depend in part on an intimate knowledge of the effects of processing variables — such as annealing time, temperature, and ambient — on the phase formation sequence. For this reason, transmission electron microscopy has been used to investigate the formation of TiSi2 thin films on silicon substrates [1]. For films formed either by reacting titanium with a silicon substrate or by sintering a codeposited (Ti + 2 Si) mixture, we find that a high resistivity (∼60 μΩcm), metastable phase — TiSi2(C49 or ZrSi2 structure) — forms prior to the desired low resistivity (∼15 μΩcm), equilibrium phase — TiSi2(C54 structure). In titanium-silicon diffusion couples, a thin layer of TiSi is also present on top of the metastable TiSi2- For processing temperatures above 550°C, the available data suggest that the metastable TiSi2 forms first and acts as a template for subsequent nucleation of the TiSi phase. In codeposited (Ti + 2 Si) films, TiSi2(C49 structure) is the only intermediate phase. The temperature at which the C49 structure transforms to the C54 structure increases significantly as the film impurity content increases. Differences in earlier reports of TiSi2 formation [2–5] appear to be resolved if x-ray diffraction peaks attributed to Ti5Si3 and TiSi were actually from the metastable TiSi2
Microscopic Model of Metal-Semiconductor Contacts and Semiconductor Heterojunctions
Authors: Mailhiotand C. , Duke C. B.
Published: March 2011

A microscopic many-electron model is utilized to calculate the self-consistent one-electron potential in the vicinity of a metal-semiconductor or semiconductor-semiconductor interface. The boundary conditions ensuring thermal, mechanical and electron-transfer equilibrium are imposed explicitly. Numerical calculations predict the validity of Schottky's phenomenological boundary condition for metal-semiconductor contacts and the applicability of the electron affinity rule for semiconductor heterojunctions. The occurrence of interfacial atomic rearrangements and/or chemical reactions is incorporated into the model via the inclusion of charge centers near the interface.
Electrical Transport in thin Silicide Films
Authors: Hensel J. C.
Published: March 2011

This paper reviews our recent studies of electrical transport in thin suicide films. Resistivity as a function of temperature, Hall effect, and magnetoresistance have been characterized for CoSi2 and NiSi2 and in conjunction with band theory provide estimates of important electronic parameters, viz. carrier densities and carrier scattering lengths. Resistivity data for TiSi2 and TaSi2 are included. Also examined in resistivity are (i) effects produced by ion bombardment which show CoSi2 to have an unusual susceptibility to radiation damage and (ii) classical size effects in the very thin film regime which show the boundary scattering to be principally specular. As an application we describe a Si/CoSi2/Si heterostructure transistor recently developed.
Crystallization Of Amorphous Tungsten Disilicide. Stacking Faults And Resistivity
Authors: LeGoues F. K. , d'Heurle F. M. , Joshi R. , Suni Ilka
Published: March 2011

Films of WSi, have been investigated by electron microscopy after annealing at different temperatures. It is shown that films annealed at 550°C contain a high density of stacking faults. The crystalline identity of these stacking faults has been established. Undoubtedly the high density of stacking faults is the cause of the resistivity maximum observed in films annealed at 550°C.
Implantation Induced Charge Trapping and Interface States Generation in Si-SiO2 System
Authors: Wong H. , Cheung N. W.
Published: March 2011

Constant-voltage stressing has been used to investigate the damage of SiO2 and the Si/SiO2 interface induced by silicon implantation through polysilicon/SiO2/P-Si structures annealed at 950°C. The implant doses used were from 5×1011cm-2 to 1014cm-2. Although no detectable interface states density was observed after the annealing for implant doses less than 2×1013cm-2, interface states generation, hole trapping, and electron trapping were found to be greatly enhanced by the Si implantation. The interface states density generation rate was found to increase with higher implant doses. The density of hole trapping centers saturated at a value of 3×1012cm-2 for implant doses higher than 2×1012cm∼-2. The density of electron trapping centers was found to increase with implant dose, while the associated trapping cross section was much smaller than that of the unimplant oxide.
The Oxidation Behavior of the √3×√3 Ag and Au/Si(111) Surfaces at Room Temperature Studied by Photoemission
Authors: Yeh J. J. , Friedman D. J. , Cao R. , Hwang J. , Nogami J. , Lindau I.
Published: March 2011

The differences of the room temperature oxidation behavior of ordered Ag/Si(111) and Au/Si(111) surfaces were studied by surface sensitive soft x-ray photoemission spectroscopy obtained with synchrotron radiation. Si surfaces covered with a monolayer of Ag or Au, once annealed to display a √3×√3 LEED pattern, were believed to be passivated against oxidation according to earlier reports. This work shows that these two surfaces oxidize but in a different way. Up to 104 L O2 exposures, the observed valence band of the Au/Si surface's valence band electron energy distribution curve is almost identical to that of the surface before oxygen exposure. But the corresponding Si 2p core level spectrum shows a small chemically shifted component indicating an initial stage of the formation of Si oxide. Thi3 chemically shifted signal becomes a strong peak at -3.7 eV below the clean Si position, characteristic of SiO2, after subsequent O2 exposures up to 1010 L. The Ag/Si system behaves in a similar fashion, but oxide growth saturates at 108 L, and the final oxides formed include a distribution of suboxides in addition to SiO2. Clearly, oxide formation is not prohibited by the presence of the ordered Au or Ag metal overlayer but delayed. Although the onset of oxidation is delayed compared to that for the clean Si surface, due to the metal-silicon bonding, the oxide formation is much faster once the surface starts to oxidize.
Dopant Redistribution During Silicide Formation
Authors: Ohdomari I. , Konuma K. , Takano M. , Chikyow T. , Kawarada H. , Nakanishi J. , Ueno T.
Published: March 2011

After the review of dopant redistribution phenomena observed during formation of near noble metal suicides, we describe the results of our recent experiments to get a better understanding of a mechanism of the dopant redistribution phenomenon in Si substrates. The key factors to understand the dopant redistribution are dopant segregation at the suicide/ Si interface due to lower solubility limit of dopants in suicides, enhanced diffusion of dopants into the Si substrate at much lower temperatures than the ordinary thermal diffusion, and electrical activation of the redistributed dopants. The results of As and carrier concentration measurements before and after Pd2Si formation to make clear the third factor show that the electrical activity of the redistributed As atoms in Si is strongly dependent on the initial activity before Pd2Si formation which is controlled by the temperature for the pre-annealing of As implanted Si.

Shrinkage of extrinsic dislocation loops introduced by As implantation and subsequent annealing have been observed after Pd2Si formation, which is a good evidence of vacancy generation during Pd2Si formation. The role of the vacancies and interstitials on the second factor, the enhanced diffusion, has also been discussed. Finally we list a few issues to be answered in future by more detailed works in order to get a complete understanding of the redistribution phenomenon.
Pulsed Lasek Atom Probe Analysis of Stoichiometry Variations in GaAlAs
Authors: Grovenor C.R.M. , Cerezo A. , Smith G.D.W.
Published: March 2011

The recent development of Pulsed Laser Atom Probe (PLAP) analysis has allowed routine analysis of the composition of a wide range of semiconducting materials. This paper presents results on the analysis of stoi chiometry variations in MOCVü GaAlAs layers demonstrating that accurate analysis of aluminium concentration fluctuations can be achieved with this technique.