bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thin Films of CoSi2 Co-Deposited onto Si1-xGexAlloys
Authors: Goeller Peter T. , Boyanov Boyan I. , Sayers Dale E. , Nemanich Robert J. 
Published: September 2012

AbstractCobalt disilicide films have been formed on strained epitaxial Si0.80Ge0.20/Si(100) alloys via co-deposition of silicon and cobalt. Co-deposition is shown to improve the epitaxy and prevent the phase segregation commonly observed with the formation of Co/SiGe contacts using other methods such as the direct deposition of cobalt onto SiGe or the sequential deposition of a silicon sacrificial layer and cobalt onto SiGe. EXAFS measurements at the cobalt K edge indicate that co-deposited films annealed at 500–700° C are indeed crystalline CoSi2 throughout this temperature range. The XRD patterns of the co-deposited films do not exhibit any of the CoSi2 (111), (220) or (311) peaks normally associated with other preparation methods. The sheet resistance and r.m.s. roughness of the CoSi2 films increase monotonically with annealing temperature. These results indicate that co-deposited films are epitaxial to the (100)-oriented SiGe substrate and suggest that low thermal budget, low resistivity contacts to strained SiGe can be grown with this method. Issues related to the presence of Ge at the CoSi2/substrate interface will be discussed.
Investigation of Cu-Ge/Gaas Metal-Semiconductor Interfaces for Low Resistance Ohmic Contacts
Authors: Oktyabrsky Serge , Borek M.A. , Aboelfotoh M.O. , Narayan J. 
Published: September 2012

AbstractChemistry and interfacial reactions of the Cu-Ge alloyed ohmic contacts to n-GaAs with extremely low specific contact resistivity (6.5×10-7 Ω·cm2 for n~1017 cm-3) have been investigated by transmission electron microscopy, EDX and SIMS. Unique properties of the contact layers are related to the formation (at Ge concentration above 15 at.%) of a polycrystalline layer of ordered orthorhombic ε1-Cu3Ge phase. Formation of the ε1-phase is believed to be responsible for high thermal stability, interface sharpness and uniform chemical composition. The results suggest that the formation of the ζ- and ε1,-Cu3Ge phases creates a highly Ge-doped n+-GaAs interfacial layer which provides the low contact resistivity. Layers with Ge deficiency to form ζ-phase show nonuniform intermediate layer of hexagonal β-Cu3As phase which grows epitaxially on Ga{111} planes of GaAs. In this case, released Ga diffuses out and dissolves in the alloyed layer stabilizing the ζ-phase which is formed in the structures with average Ge concentration of as low as 5 at.%. These layers also exhibit ohmic behavior.
Effects of the Substrate Pretreatments on the Leakage Current in the Low-Temperature Poly-Si TFTs
Authors: Kim Tae-Kyung , Lee Byung-Il , Ihn Tae-Hyung , Joo Seung-Ki 
Published: September 2012

AbstractPoly-Si TFT’s were fabricated on the glass substrate by the Metal Induced Lateral Crystallization(MILC). Before deposition of the active a-Si thin films(1000 Å), the glass substrate was pretreated in three different ways such as oxidation of a-Si(100 Å), oxide buffer layer deposition(1000 Å), and ion mass doping of the glass substrates. The leakage current at reverse bias could be reduced by one order of magnitude by the substrate pretreatment. Field effect mobility of n-channel TFT’s was 108cm2/Vsec, subthreshold slope and on/off current ratio were 0.7 V/dec. and about 106, respectively.
A Study of the Interaction between Cu3Ge and (100) Si, and its Effect on Electrical Properties
Authors: Borek M.A. , Oktyabrsky S. , Aboelfotoh M.O. , Narayan J. 
Published: September 2012

AbstractThe reduction in the dimensions of advanced semiconductor devices has brought about the need for new metallization materials with low resistivity and high electromigration resistance. The Cu3Ge, has been suggested as a contact and metallization material due to its low resistivity (6 μΩ-cm), high electromigration resistance, and high chemical stability. We have grown thin films of Cu3Ge on (100) Si by the sequential e-beam deposition of an amorphous Ge layer then a Cu layer, followed by a thermal anneal to crystallize the Cu3Ge film. The Cu-Ge films maintain their low resistivity (10-15 μΩ cm) over a range of anneal temperatures, up to an anneal temperature of 600°C, where a significant increase in resistivity is observed. We have shown that this increase in resistivity is directly related to the structure of the Cu3Ge film and interface. We have observed by cross-sectional transmission electron microscopy (TEM), that films of Cu3Ge form a smooth, atomically sharp interface with (100) Si, up to an anneal temperature of 600°C, where the film agglomerates, and additional compounds are observed. In this paper, we discuss the correlation between microstructure, interface structure and electrical properties of these novel thin film structures.
Electrical Characterization of In Schottky Contacts to Epitaxial n-In0.46Ga0.54P Grown on n+-GaAs by Mocvd
Authors: Marcano N. , Singh A. 
Published: September 2012

AbstractIn/n-In0.46Ga0.54P Schottky diode was fabricated by thermal evaporation of In on chemically etched surface of In0.45Ga0.54P:Si epitaxial layer grown on highly doped n type GaAs. The In metal formed a high quality rectifying contact to In0.46Ga0.54P:Si with a rectification ratio of 500. The direct current-voltage/temperature (I-V/T) characteristics were non-ideal with the values of the ideality factor (n) between 1.26-1.78 for 400>T>260 K. The forward I-V data strongly indicated that the current was controlled by the generation-recombination (GR) and thermionic emission (TE) mechanisms for temperature in the range 260-400 K. From the temperature variation of the TE reverse saturation current, the values of (0.75±0.05)V and the (4.5±0.5)×10-5 Acm-2K-2 for the zero bias zero temperature barrier height (φoo) and modified effective Richardson constant were obtained. The 1 MHz capacitance-voltage (C-V) data for 260 K < T < 400 K was analyzed in terms of the C-2-V relation including the effect of interface layer to obtain more realistic values of the barrier height (φbo). The temperature dependence of φbo was described the relation φbo =(0.86±10.03) - (8.4±0.7)×l0-4T. The values of φoo, obtained by the I-V and C-V techniques agreed well.
Conversion Tunneling in Non-Ideal Schottky Barriers: Virtual Resonance Manifestation and Interface States Influence
Authors: Romanov D.A. , Kalameitsev A.V. , Kovchavtsev A.P. , Subbotin I.M. 
Published: September 2012

AbstractWe have investigated experimentally and theoretically the elastic conversion tunneling of charge carriers in MOS structures Au on p+-InAs with superthin (10-20 Å) oxide film, the structures used in infrared photodetectors. In these structures the Schottky barrier provides near-surface inversion layer. The tunnel current-voltage (I-V) curves obtained at helium temperatures demonstrate the negative differential resistance region (NDR). We develop semiclassical two-band transfer matrix approach to the conversion tunneling analysis in a multilayer structure and calculate on its base the I-V curves dependence on the structure parameters. The NDR occurs to be caused by the motion of the remote quantum level in the inversion layer. The calculated I-V characteristics agree with the experimental ones quite well. The very existence of NDR and the shape of I-V curves depends strongly on the nature of localized electron states at the semiconductor interface. The characteristics of these electron states are used in the calculations as fitting parameters. Therefore, we suggest a new method for the interface states diagnosis.
Theory of Reactive Adsorption on Si(100)
Authors: Doren D. J. , Brown A. Robinson , Konecny R. 
Published: September 2012

AbstractDensity functional calculations on cluster models of Si(100)-2xl have been used to predict reaction mechanisms and energetics for several reactive adsorption processes. Dissociative adsorption of H2, H20, BH3, and SiH4 will be described and compared to available experimental data. Based on these examples, a qualitative theory of mechanisms for dissociative adsorption of hydrides on silicon surfaces will be proposed. These reactions can largely be understood in terms of the electron density distributions in the molecule and surface dimer. On a buckled dimer, there are both electron-rich and electron-deficient sites, which have different chemical interactions with adsorbates. The role of this difference is illustrated in a novel surface Diels-Alder reaction, for which symmetric addition to an unbuckled surface dimer is allowed by orbital symmetry. This reaction creates new reactive surface sites that may be useful for subsequent chemical surface modification.
Multilevel Approaches Toward Monitoring and Control of Semiconductor Epitaxy
Authors: Aspnes D. E. , Dietz N. , Rossow U. , Bachmann K. J. 
Published: September 2012

AbstractVarious optical techniques have been developed over the last few years to allow real-time analysis of regions of importance for semiconductor epitaxy, in particular the unreacted and reacted parts of the surface reaction layer (SRL) and the near-surface region of the sample. When coupled with emerging microscopic methods of calculating optical properties, these approaches will allow several levels of control beyond that which has been currently demonstrated.
Investigation of electric fields, interface charges, and conduction band offsets at ZnSe/GaAs heterojunctions with a novel photoreflectance technique
Authors: Dougherty D. J. , Fleischer S.B. , Warlick E. L. , House J. L. , Petrich G. S. , Ho E. , Kolodziejski L. A. , Ippen E. P. 
Published: September 2012

AbstractZnSe/GaAs heterojunctions were investigated by contactless electroreflectance and photoreflectance techniques. Negative surface charge densities on the order of 1012 cm-2 were observed for films grown on n-type GaAs indicating a large contribution to the conduction band barrier between the materials due to band bending. The conduction band offset was also measured using a new photoreflectance technique involving a tunable pump laser.
Optical Investigations of InAs Growth on GaAs and Lasing in Singly and Multiply Stacked Island Quantum Boxes
Authors: Kalburge A. , Ramachandran T. R. , Heitz R. , Xie Q. , Chen P. , Madhukar A. 
Published: September 2012

AbstractWe report on the optical investigations of InAs growth on GaAs. In-situ STM/AFM studies show the presence of features 2-4 ML high, which we call quasi-3D (Q3D) clusters, well in advance of 3D island formation. Though the photoluminescence (PL) emission from these Q3D clusters is in the same wavelength regime as that from well developed 3D islands, they show characteristic differences in the PL excitation spectra and temperature dependence of PL, distinguishing them clearly from the 3D islands. Finally, we discuss the lasing observed from lasers containing single and five sets of InAs layers grown with conditions in which the in-situ STM/AFM studies show only 3D islands.
Metrology of Very Thin Silicon Epitaxial Films using Spectroscopic Ellipsometry
Authors: Chen Weize , Reif Rafael 
Published: September 2012

AbstractNon-destructive silicon epitaxial film thickness measurements have been performed using spectroscopic ellipsometry (SE) in the visible to near infrared range. The epitaxial films were grown by CVD at 700 – 900°C. It is shown that SE can simultaneously determine the epitaxial film thickness, the native oxide thickness, and the substrate dopant concentration. The epitaxial film thicknesses measured by SE are in excellent agreement with results of secondary ion mass spectrometry (SIMS). The dopant concentrations measured by SE also agree well with SIMS results for n-type substrates, but are consistently higher than SIMS values for p-type substrates. This study shows that spectroscopic ellipsometry could be used in semiconductor manufacturing environments as a viable non-destructive technique for sub-0.5 μm silicon epitaxial film thickness measurement.
Nonradiative recombination on Si surfaces during anodic oxidation in fluoride solution
Authors: Rappich J. , Timoshenko V. Yu. , Dittrich Th. 
Published: September 2012

AbstractThe anodic oxidation of p-Si(100) in aqueous NH4F solution is investigated in-situ by photoluminescence (PL) with short N2-laser pulses as a function of pH at constant potential. The PL intensity depends sensitively on the modification of the Si surface and on the change of the oxidation rate during current oscillations. The interruption of the anodic oxidation at the maximum of a current oscillation peak leads to a current transient which shows typical features of oxide removal and hydrogenation for two different oxide thicknesses. This makes it possible to realize an intermediate state of the Si surface with a coexisting hydrophilic (oxide) and hydrophobic (hydrogenated) part.
Advanced Lithography for Nanofabrication
Authors: Hui Frank Y.C. , Eres Gyula 
Published: September 2012

AbstractA novel method for generating lateral features by patterning the naturally forming surface hydride layer on Si is described. Because of the relatively strong chemical bonding between silicon and hydrogen, the hydride layer acts as a robust passivation layer with essentially zero surface mobility at ordinary temperatures. A focused electron beam from a scanning electron microscope was used for patterning. Upon losing the hydrogen passivation the silicon surface sites become highly reactive. Ideally, the lifetime of such a pattern in a clean environment should be infinite. Deliberate exposure of the entire wafer to a suitable gas phase precursor results in selective area film growth on the depassivated pattern. Linewidths and feature sizes of silicon dioxide on silicon below 100 nm were achieved upon exposure to air. The silicon dioxide is robust and allows effective pattern transfer by anisotropic wet-chemical etching. In this paper, the mechanism of hydrogen desorption and subsequent pattern formation, and the factors that govern the ultimate pattern resolution will be discussed.
Chemical Characterization by FT-IR Spectrometry and Modification of the Very First Atomic Layer of A TiO2 Nanosized Powder
Authors: Baraton M.-I. , Merhari L. , Chancel F. , Tribout J. 
Published: September 2012

AbstractNanosized powders exhibit high specific surface areas resulting in enhanced reactivities. Surface tailoring by controlled adsorption of molecules can thus be conveniently performed and more easily monitored by surface-sensitive techniques. In situ and ex situ grafting procedures of hexamethyldisilazane (HMDS) on nanosized titania (n-TiO2) powder were carried out and studied by Fourier transform infrared spectrometry (FT-IR). In addition to a decrease of the hydrophilic OH groups, the vibration analysis revealed hydrophobic CH3 groups on the grafted samples. Co-adsorption of CO and H2O on the differently grafted samples showed a large reduction of water effect compared to the as-received n-TiO2 powder. Modulation of infrared transmitted energy by controlled adsorption of O2 and CO made it possible to qualitatively compare the electronic properties of the surface-tailored samples.
In-Situ Etch to Improve Chemical Beam Epitaxy Regrown AlgaAs/GaAs Interfaces for HBT Applications
Authors: Hsin Y.M. , Li N. Y. , Tu C. W. , Asbeck P. M. 
Published: September 2012

AbstractWe have studied the etching effect of AlxGa1-xAs (0≤ x ≤ 0.5) by trisdimethylaminoarsenic (TDMAAs) at different substrate temperatures, and the quality of the resulting etched/regrown GaAs interface. We find that the etching rate of AlxGa1-x As decreases with increasing Al composition, and the interface trap density of the TDMAAs etched/regrown interface can be reduced by about a factor of 10 as deduced from capacitance-voltage carrier profiles. A smooth surface morphology of GaAs with an interface state density of 1.4×l011 cm−2 can be obtained at a lower in-situ etching temperature of 550°C. Moreover, by using this in-situ etching the I-V characteristics of regrown p-n junctions of Al0.35Ga0.65As/Al0.25Ga0.75As and Al0.35Ga0.65As/GaAs can be improved.
Gas Migration in MX80 Buffer Bentonite
Authors: Horseman S. T. , Harrington J. F. , Sellin P. 
Published: September 2012

ABSTRACTControlled flow-rate gas injection experiments have been performed on
pre-compacted samples of KBS-3 specification M×801 buffer
bentonite using helium as a safe replacement for hydrogen. By simultaneously
applying a confining pressure and backpressure, specimens were
isotropically-consolidated and fully water-saturated under pre-determined
effective stress conditions, before injecting gas using a syringe pump.
Ingoing and outgoing gas fluxes were monitored. All tests exhibited a
conspicuous threshold pressure for breakthrough, somewhat larger than the
sum of the swelling pressure and the backpressure. All tests showed a
post-peak negative transient leading to steady-state gas flow. Using a
stepped history of flow rate, the flow law was shown to be nonlinear. With
the injection pump stationary (i.e. zero applied flow rate), gas pressure
declined with time to a finite value. When gas flow was reestablished, the
threshold value for gas breakthrough was found to be significantly lower
than in virgin clay. There is strong evidence to suggest that the capillary
pressure for the penetration of interparticle pore space of buffer bentonite
is of such a magnitude that normal two-phase flow is impossible. Gas entry
and breakthrough is therefore accompanied by the development of microcracks
which propagate through the clay from gas source to sink. The experiments
suggest that these pathways open under high gas pressure conditions and
partially close if gas pressure falls, providing a possible explanation of
the nonlinearity of the flow law.
Determination of Porewater Chemistry in Compacted
Bentonite
Authors: Lehikoinen J. , Muurinen A. , Melamed A. , Pitkänen P. 
Published: September 2012

ABSTRACTLaboratory experiments were performed to study the interaction between
groundwater and compacted sodium bentonite (Volclay MX-80). The solutions
used were the fresh and saline groundwater simulants. The experiments were
carried out in aerobic and anaerobic conditions at elevated temperature. Of
main interest in the present study were the chemical changes in the reacting
solution, bentonite porewater. and bentonite itself. The results for major
cations display a principal difference between the interactions with fresh
and saline solutions, while the differences between aerobic and anaerobic
conditions within each solution case seem to be minor. The experimental
results for the bentonite-water equilibria were interpreted in terms of a
multi-site surface complexation model and the computer program HYDRAQL. The
apparent diffusivities for sodium and sulphate in bentonite samples
sandwiched between two filterplates were also determined.
Experimental Study on Scale Effects of Bentonite / Sand Mixtures
on Gas Migration Properties
Authors: Hokari Toshiyuki , Okihara Mitsunobu , Ishii Takashi , Ishii Takao , Ikuse Hiroyuki 
Published: September 2012

ABSTRACTGas migration properties of bentonite/sand mixtures for a large-scale
structure were estimated on the basis of laboratory test results obtained
with small test specimens. Water and gas migration tests were carried out to
clarify scale effects on migration properties of the mixtures.
Near-Field Thermal-Hydrological Behavior for Alternative
Repository Designs at Yucca Mountain
Authors: Buscheck Thomas A. , Nitao John J. , Ramspott Lawrence D. 
Published: September 2012

ABSTRACTThree-dimensional calculations that explicitly represent a realistic mixture
of waste packages (WPs) are used to analyze decay-heat-driven
thermal-hydrological behavior around emplacement drifts in a potential
high-level waste facility at Yucca Mountain. Calculations, using the NUFT
code, compare two fundamentally different ways that WPs can be arranged in
the repository, with a focus on temperature, relative humidity, and
liquid-phase flux on WPs. These quantities strongly affect WP integrity and
the mobilization and release of radionuclides from WPs. Point-load spacing,
which places the WPs roughly equidistant from each other, thermally isolates
WPs from each other, causing large variability in temperature, relative
humidity, and liquid-phase flux along the drifts. Line-load spacing, which
places WPs nearly end to end in widely spaced drifts, results in more
locally intensive and uniform heating along the drifts, causing hotter,
drier, and more uniform conditions. A larger and more persistent reduction
in relative humidity on WPs occurs if the drifts are backfilled with a
low-thermal-conductivity granular material with hydrologie properties that
minimize moisture wicking.
Application of Interaction Matrices in Performance Assessment -
the Fuel Matrix as an Example
Authors: Sellin Patrik , Bruno Jordi , Cera Ester 
Published: September 2012

ABSTRACTIn a safety analysis of a repository for high level nuclear waste, it is of
primary importance to identify and document all processes that are acting on
the repository system. An interaction matrix methodology have been applied
to the spent fuel subsystem. The purpose of this application is to identify,
structure and rank the Process System and to discuss how the identified
processes can be treated.
Optimization of Lanthanide Borosilicate Frit Compositions for
the Immobilization of Actinides Using a Plackett-Burman/Simplex Algorithm
Design
Authors: Mesko M. G. , Meaker T. F. , Ramsey W. G. , Marra J. C. , Peeler D. K. 
Published: September 2012

ABSTRACTImmobilization by vitrification is one potential disposition option for a
portion of the United States' excess plutonium inventory. Research has been
performed at the Savannah River Site (SRS) to determine the optimum
composition of a lanthanide borosilicate frit for the vitrification of
plutonium using a Plackett-Burman design and simplex algorithm as a
statistical tool. This technique uses various response variables to rank and
optimize a composition. The variables used in this study correspond to
homogeneity, durability, actinide solubility and devitrification after
heat-treatment.The optimized frit composition was determined using a constant
ThO2 loading of 20 wt%. No noticeable trends were followed
with respect to the individual components which may indicate a relatively
robust system able to accommodate variations in the feed.Batches containing various loadings of ThO2 were melted to
determine if actinide solubility was improved in the optimized composition
compared to that of a similar lanthanide borosilicate glass. No noticeable
improvement in ThO2 solubility was realized as a result of using
this optimization technique.