bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared Characterization of PMMA-SiO2 Hybrid Glasses Obtained by Sol-Gel Process
Authors: Díaz-Flores L.L. , Rodríguez A. S. López , SifuentesGallardo P. , Rivera M.A. Hernàndez , Romo M.a Garnica , Bernal R. , Yáñez-Limón J.M.
Published: April 2011

This work is about the production of hybrid coatings of the system SiO2-PMMA (PMMA, polymethylmethacrylate). These materials have interesting mechanical and chemical properties useful for anticorrosive and wear resistance applications. SiO2-PMMA hybrids were obtained by the sol-gel traditional process, using tetraethylorthosilicate (TEOS) and methylmethacrylate (MMA) by Aldrich Co, as starting reagents. The SiO2:PMMA ratio was varied from 0:1 to about 1:1 at air atmosphere deposition. The coatings were obtained on acrylic sheets and silicon wafers. A diversity of coatings with chemical composition ranging from SiO2 and PMMA to obtain the SiO2-PMMA hybrids were obtained. Infrared (IR) and atomic force microscopy (AFM), were performed to determinate structural and morphological behavior.
Thermoluminescence of Beta Particle Irradiated LiMgF3:X (X=Ce, Er)
Authors: Muñoz I. C. , Brown F. , Baldenevro R. I. , Orante-Barrón V. R. , Cruz-Vázquez C. , Furetta C. , Bernal R.
Published: April 2011

The thermoluminescence (TL) properties of beta particle irradiated Ce and Er doped LiMgF3 phosphors are presented. Pellet-shaped samples were prepared by cool-pressing 74 μm size particle powder, followed by thermal annealing at 700 °C during 5 h in air atmosphere. Some samples were irradiated with beta particles in the dose range from 8 up to 128 Gy. The sensitivity of Er doped samples was greater than the one of Ce-doped. In both cases, a 2 % mol of dopant concentration was used. The TL fading was between 19 % for Ce-doped samples, and 24 % for the Er-doped. The integrated TL increases as dose increases, with no saturation clues. The TL sensitivity of samples exhibited a loss in successive irradiation – readout cycles.
Thermal Stability of Pt Nanoparticles Supported on WOx/Al2O3 for n-Heptane Hydroconversion
Authors: Contreras J. L. , Fuentes G.A. , Salmones J. , Zeifert B.
Published: April 2011

The thermal stabilization of γ-Al2O3 using W+6 ions has been found useful to the synthesis of Pt/Al2O3 catalysts. The sequential impregnation method was used to study the effect of W6+ upon Pt/ γ-Al2O3 reducibility, Pt dispersion, Raman spectroscopy and n-heptane hydroconversion. The W/Pt atomic ratios varied from 3.28 to 75. We found that the W6+ ions delayed reduction of a fraction of Pt+4 atoms beyond 773 K. At the same time, W6+inhibited sintering of the metallic crystallites once they were formed on the surface. For the sample with a W/Pt atomic ratio of 3.28, W6+ did not inhibit the H2 reduction of Pt oxides even below of 773 K, the Pt oxides were reduced completely, however, the Pt dispersion decreased for this sample with respect to the Pt/γ-Al2O3 catalyst. After reduction at 1073 K, sequential samples impregnating Pt on WOx/γAl2O3 were more active and stable during n-heptane hydroconversion than monometallic Pt/γAl2O3 catalyst. Selectivities for dehydrocyclization, isomerization and Hydrocracking changed significantly when the W/Pt atomic ratio and reduction temperature increased. Initial and final reaction rates were more sensitive to reduction temperature. W6+ ions promoted high thermal stability of Pt crystallites when sequential catalysts were reduced at 1073 K and deactivation of bimetallic catalysts reduced at 773 K and 1073 K was less than the deactivation of Pt/Al2O3 catalyst.
Synthesis of Sulfated Pt/ZrO2 Catalysts Using Different Precipitants for n-Hexane Hydroisomerization
Authors: Yu Guo-Xian , Panl Wei , Zhou Xiao-Long , Chen Li-Fang , Wang Jin-An
Published: April 2011

Ammonia (AOH), dimethylamine (DME) and triethanolamine (TEA) as precipitants were used to prepare Pt-SO42-/ZrO2 catalysts, and the crystalline structures, textural structures and surface acid properties of the catalyst samples were characterized and n-hexane hydroisomerization activity over the samples were investigated. DME and TEA as the precipitants would delay the crystallization process. The organic amines were difficult to remove during the washing process, leading to the rinsing times increase, which probably decreased the catalyst BET area. Super Lewis acid sites in SZ catalysts would play very important roles in catalytic hydroisomerization activity.
Utilization of Solar Energy and Atmospheric Oxygen in the Photodregradation of Diesel in Water by Cu/TiO2 Catalysts
Authors: Manriquez Ma. , Corro Grisel , Hernandez J. Gonzalo
Published: April 2011

Photocatalytic destruction of the water soluble diesel fraction (WSF) was performed using Cu/TiO2 catalysts. Inexpensive and clean solar light and atmospheric oxygen were used as the energy source and oxidant, respectively. We investigated the effect of Cu species on the formation of a doping energy level between the conduction and valence band in TiO2. Photocatalytic reactions were investigated by monitoring the evolution of WSF as a function oftime of solar irradiation by UV-vis and FTIR spectroscopic techniques. The photocatalytic process in the presence of 5%Cu/TiO2 catalyst, is shown to be quantitatively efficient in the destruction of the water-soluble diesel fraction. The total destruction of water-soluble compounds originating from diesel residues indicates that photocatalysis can be employed for WSF treatment.
Hydrogen Production by Steam Reforming of Methanol over New Ag-Au(1-D)-CeO2 Catalyst
Authors: Pérez-Hernández R. , Gutiérrez-Martínez A. , Gutiérrez-Wing C.
Published: April 2011

A Ag-Au(1-D)-CeO2 catalyst was prepared by precipitation method using Ag-Au nanowires and Ce(NO3)3·6H2O as precursors. The catalytic activity of the catalysts was evaluated in a steam reforming of methanol (SRM) reaction from 250 to 475 °C. 100 % of methanol conversion was observed at 450 °C together with high H2 selectivity. This study evidenced that the use of 1-D metallic nanostructures could be used as an active phase on a CeO2 matrix for steam reforming of methanol for H2 generation to be used as fuel.
Synthesis of Acetone and Acetaldehyde from Propane-Butane Mixture
Authors: Dossumov Kusman. , Tungatarova Svetlana. A.
Published: April 2011

Supported polyoxide catalysts on the base of Mo and W, as well as natural Kazakhstan's clays were tested in the process of oxidative conversion of propane and propane-butane mixture. The influence of reaction temperature, contact time, composition and percentage of the active component of catalyst were determined. The important petrochemical products - acetone (500-550°) and acetaldehyde (300-350°) were the main liquid products of reaction on natural Kazakhstan's clays and also on clays modified by Mo, Bi, Cr and Ga ions.
HgCdTe Surface Cleanup and Etch Using a Remote Hydrogen Plasma
Authors: Smith Patricia B.
Published: April 2011

Dry passivation of HgCdTe with ZnS or CdTe using physical or chemical vapor deposition can be improved by incorporating an in situ plasma cleanup of the HgCdTe surface prior to the deposition. Contamination at the HgCdTe/ dielectric interface from ambient oxide and hydrocarbon residues may lead to fixed charge in capacitor or diode device structures. In addition, the oxides of HgCdTe are known to be thermally unstable. Removal of the surface contamination layer is advantageous for producing a consistent and electrically reliable interface. We describe the interaction of a remotely generated H2 or H2/Ar plasma (2.45 GHz, 600W) with HgCdTe, using ex-situ and in-situ ellipsometry, and atomic force microscopy. This work represents the first effort to characterize a low damage HgCdTe surface cleanup process which is compatible with vacuum in-situ passivation.
The Growth Of High-Quality MCT Films by MBE Using in Situ Ellipsometry
Authors: Svitashev K.K. , Dvorwetsky S.A. , Shvets V.A. , Mardezhov A.S. , Sidoroy YU.G. , Nis I.E. , Varavin V.S. , Liberman V. , Remesnik V. G.
Published: April 2011

The ellipsometry and RHEED study of MCT grown on (112) CdTe and GaAs by MBE was carried out. The dependence of ellipsometric parameter on composition is evaluated. As shown we can measure the growth rate, the roughness changing, initial temperature and composition by ellipsometry in situ. We investigated the evolution of roughness of film surface. We observed the appearance of surface roughness at initial stage of MCT growth under various composition (XcdTe0÷0.4). The following growth in optimal growth condition (including constancy of substrate temperature) gives us the smoothing of the surface and supplies us the high-quality MCT films. It is found that under constant temperature of substrate heater we can not grow the thick, perfect film of MCT. The concentration, mobility and life time of carriers in MCT films were respectively: n=1.8*1014 ÷8.2*1015cm−3, μn=44000÷370000cm2 V−1 s−1, τ=40÷220ns;p=1.8*1015÷8.4*1015 cm−3, μp=215÷284 cm2V−1 s−1 τ=12÷20ns.
Differentially Strained P-Doped Quantum well Infrared Photodetector
Authors: Kuroda R.T. , Garmire E.
Published: April 2011

In this paper, we discuss a differentially strained p-doped quantum well infrared photodetector that achieves high performance specifications. We examine key device specifications for a 9 and 18 μm infrared detector. We calculate that through differential strain, these novel detectors have improved gain and substantially reduced dark current over previous quantum well infrared photodetectors, while being able to detect normal incident light.
Recent Developments in High Resistivity Detector-Grade CdTe
Authors: Hage-Ali M. , Siffert P.
Published: April 2011

We present a brief review of results concerning the doping or compensation of CdTe by different elements like halogen, group IV, hydrogen and 3d transition elements for high resistivity materials. Comparison with theoretical models and discussion of results under this light is provided.
Progress in Cd1−xZnxTe (CZT) Radiation Detectors
Authors: Butler J. F. , Doty F. P. , Apotovsky B. , Friesenhahn S. J. , Lingren C.
Published: April 2011

Results of a program to improve the performance of Cd1−xZnxTe detectors by adjusting growth parameters to achieve low-strain, high purity low defect crystals, investigating surface effect phenomena and contacting methods, and establishing reproducible manufacturing methods are reviewed and discussed. Processing and fabrication methods were developed which are applicable throughout the composition range. Energy spectra for room temperature Cd1−xZnxTe detectors exhibit resolutions (FWHM) from 2.16 keV at 14 keV to 6.9 keV at 122 keV. An energy resolution of 910 eV at 5.9 keV was achieved at −25 C. Stable ohmic contacts and gamma ray detection for ZnTe are reported for the first time. Applications of Cd1−xZnxTe to nuclear medicine and X-ray fluorescence are discussed. New gamma ray imagers using Cd1-−ZnxTe detector arrays are described, and imaging data for a 32 × 32 monolithic array of 1 mm2 elements on a 42mm × 42mm substrate are presented.
Characterization of Doped GexSi1−x Multiple Quantum well Structures for far- IR Detectors
Authors: Greve D. W. , Misra R. , Strong R. , Schlesinger T.E.
Published: April 2011

Doped GexSi1−x/Si multiple quantum well structures have been grown by UHV/CVD and characterized by various techniques. SIMS and X- ray confirm the intended modulation of germanium and boron concentrations, and photoluminescence has been used to assess material quality. Strong free- carrier absorption has been observed at normal incidence in some samples. The results suggest that doping intermediate between 4 × 1018 cm−3 and 4 × 1019 cm−3 is necessary for useful detectors.
Undoped Lec GaAs as an Infrared Bolometer Detector
Authors: Estill S , Brozel M. R.
Published: April 2011

Undoped LEC GaAs grown with very low residual acceptor concentration is often low resistivity with an activation energy for conduction of 0.43 eV. We demonstrate that this material can form a very sensitive bolometer element and show how large two dimensional bolometer arrays might be fabricated from this material.
Growth of MBE-Codeposited IrSi3 on Si(111) and Si(100)
Authors: Gibson Gary A. , Lange Davis A. , Falco Charles M.
Published: April 2011

We have used Molecular Beam Epitaxy (MBE) to successfully grow films that are predominantly IrSi3 on both Si(111) and Si(100) substrates by codeposition of Si and Ir in a 3:1 ratio. Bragg-Brentano and Seemann-Bohlin x-ray diffraction reveal that polycrystalline IrSi3 films form as low as 450 °C. This is the lowest temperature yet reported for growth of this iridium silicide phase. These x-ray diffraction techniques, along with Transmission Electron Microscope (TEM) diffraction and in situ Low Energy Electron Diffraction (LEED), show that at higher deposition temperatures codeposition can form IrSi3 films on Si(111) that consist predominantly of a single epitaxial growth orientation. Ion beam channeling and x-ray rocking curves show that the epitaxial quality of IrSi3 films deposited on Si(111) is superior to that of IrSi3 films deposited on Si(100). We also present evidence for several new epitaxial IrSi3 growth modes on Si(111) and Si(100).
Low Temperature Pl Characterization of Lpee Grown GaSb and GaInAsSb Epilayers
Authors: Iyer S. , Hegde S. , Bajaj K.K. , Abul-Fadl Ali , Mitchel W.
Published: April 2011

We have investigated the low temperature (4.5 K) photoluminescence (PL) spectra of GaSb and GaInAsSb layers. The layers were grown by liquid phase electro-epitaxial (LPEE) technique. Several bound excitomc transitions were observed both in GaSb and GaInAsSb layers. Shift in the PL peak energy corresponding to the band to band transition with temperature was determined. The linear part of the shift above 100K, exhibited a slope of -0.3 meV/K.
The Burstein-Moss Shift in Quantum Confined Infrared Materials
Authors: Ghatak Kamakeya P. , De Badal
Published: April 2011

In this paper we have investigated the Burstein-Moss shift in quantum wires and dots of III-V and II-VI materials on the basis of Kane and Hopfield models for the appropriate carrier dispersion laws. It is found taking Hg1−xCdxTe, In1−xGax AsyP1−y lattice matched to InP and CdS as examples that the Burstein-Moss shift exhibits oscillatory dependences for quantum wires and dots of the said materials with respect to doping and film thickness respectively. Besides, the numerical value of the same shift is greatest in quantum dots and least in quantum wires. In addition, the theoretical analysis is in agreement with the experimental datas as given elsewhere.
Extending HgCdTe Photovoltaic Detector Technology to Cutoff Wavelengths of 17 μm
Authors: Krueger E. E. , Pultz G. N. , Maschhoff K. R. , Tobin S. P. , Norton P. W. , Rutter J. H. , Reine M. B.
Published: April 2011

We are developing two-layer LPE P-on-n HgCdTe photovoltaic detector arrays with cutoff wavelengths out to 17 μm for a NASA spaceborne infrared radiometer. These bilinear multiplexed arrays will operate at 60 K, and must achieve sensitivities approaching the background limit for a background photon flux of 2×1015 photons/cm2-sec. The detectors must operate at reverse bias voltage to interface with silicon CMOS multiplexer circuits, and must exhibit low 1/f noise.

This paper reviews progress toward these demanding requirements. The limiting junction current mechanisms for HgCdTe photodiodes at these very long cutoff wavelengths are reviewed. Data are presented for both CdTe-passivated and ZnS-passivated arrays at 60 K with cutoff wavelengths of 15.4−16.9 μm. Average R0A products of 13 ohm-cm2 and quantum efficiencies of 89% have been achieved for cutoff wavelengths of 15.4 μm at 60 K. These array data demonstrate the potential for VLWIR PV HgCdTe to meet the requirements for advanced NASA applications.
Cyclic CVD for Preparation of Silicon Films of Adjustable Structure
Authors: Koynov Svetoslav , Grebner Stefan , Fischer Thomas , Schwarz Reinhard
Published: April 2011

Two versions of a deposition method referred to as CYCLIC-CVD are presented. Both are based on the repetition of cycles involving two steps: a) a thin a-Si:H layer deposition and b) a hydrogen plasma treatment. In the first version the cycles consist of a thermal CVD deposition step at 500–550 °C followed by a hydrogen plasma step. Device quality a-Si:H films of less than 3 at.% hydrogen content have been prepared. In the second version, which we call Closed Chamber CVD (CC-CVD) the deposition step is done by conventional PE CVD. However, the hydrogenation step is performed with closed reactor chamber. The latter step provides conservation of silicon mass at an equilibrium between H-etching and redeposition. As a result, μc-Si films of high crystallinity are produced with a high overall deposition rate.
Optimization of a Dual-Mode RF / Microwave Plasma for Amorphous thin film Deposition
Authors: Etemadi R. , Leroy O. , Drevillon B. , Godet C.
Published: April 2011

A new dual-plasma (surface wave-coupled microwave and capacitively-coupled radiofrequency) PECVD reactor for high growth rate of Amorphous insulating alloys is being developped. A high flexibility for thin film materials synthesis is expected, because the energy of the ion bombardment can be monitored independently from the microwave plasma chemistry. In situ diagnostics (Optical EMission Spectroscopy and Spectroscopie Ellipsometry) are used for the optimization of the dual-Mode plasma deposition of hydrogenated Amorphous silicon a-Si:H and silicon oxides a-SiOx:H (with 0 ≤ × ≤ 2). The growth of stoichiometric oxide at 3.3 nm / s has been achieved.
A Unified Description of the Density of States for Hydrogen and Electrons in Amorphous Silicon
Authors: Deane S.C. , Powell M.J.
Published: April 2011

We derive the hydrogen density of states for hydrogenated Amorphous silicon (a-Si:H), which is completely consistent with the electronic density of states for the defect pool model. If silicon dangling bond energies are distributed in energy, as in a defect pool model, then the hydrogen density of states becomes quite complex, with the hydrogen binding energy dependent on the Fermi level and dangling bond transition energy. We demonstrate that the electronic density of states for dangling bonds is almost identical to our previous defect pool model, while the hydrogen density of states can account for the results of hydrogenation-dehydrogenation experiments. The effective hydrogen correlation energy is variable, being negative for most hydrogen binding sites, but positive for most defect sites.
Molecular Dynamics Studies of Diamondlike Amorphous Carbon
Authors: Fedders P. A. , Drabold D. A.
Published: April 2011

First principles molecular dynamics methods are used to construct supercells for diamondlike Amorphous carbon, to study its properties, and to compare and contrast it with a-Si. As with recent lab fabricated material, these supercells contain no hydrogen. Several structural models are introduced and the topological, electronic, and vibrational properties are discussed. In particular, in spite of the presence of 3-fold coordinated sites and no hydrogenation, we have obtained a supercell sample that has a gap of about 2.5 eV containing no defect states. To our knowledge, ours is the only theoretical work that agrees with recent experiments in this respect. We explore the nature of defects in the Amorphous network and, in particular, the atomistic origin of the clean gap in unhydrogenated C but not in unhydrogenated Si.
Fabrication of Highly Stable a-Si:H from Chlorinated Precursors
Authors: Azuma M. , Yokoi T. , Shimizu I.
Published: April 2011

High quality a-Si:H was fabricated from SiH2Cl2 by ECR hydrogen plasma at high growth rate (>15 A/s). After sticking the precursors, SiHnClm (n+m≤3), stable Si-network was formed by chemical reactions enhanced on the heated substrate due to strong interaction between Cl and H bonded with Si. The defect densities of 3×1015 and 3×1016 cm3 were obtained for the films in the as-grown and the saturated states after light soaking, respectively. In these stable films, a surprisingly large amount of voids (2–10 vol%) was found by the simulation of the spectra of pseudo-dielectric constant measured by spectral ellipsometry.
Metastable Defect Kinetics in Hydrogen Passivated Polycrystalline Silicon
Authors: Nickel N. H. , Street R. A. , Jackson W. B. , Johnson N. M.
Published: April 2011

The temperature dependence of the dark conductivity, σD, of unhydrogenated and hydrogen passivated polycrystalline silicon (poly-Si) films was Measured. While σD of unhydrogenated poly-Si did not exhibit any influence of thermal treatment prior to the measurement, striking effects were observed in hydrogenated poly-Si films. Below 268 K a cooling-rate dependent metastable change of σD is observed. The dark conductivity increases by more than 8 orders of magnitude. This frozen-in state is metastable: Annealing and a slow cool restore the temperature dependence of the relaxed state. The time and temperature dependence of the relaxation reveal that this process is thermally activated with 0.74 eV. The lack of the quenching metastability in unhydrogenated poly-Si is direct evidence that the metastable changes in σD are due to the formation and dissociation of an electrically active hydrogen complex, in the grain-boundary regions.
New Model for Local H-Atom Bonding Re-Arrangements Associated with the Staebler-Wronski Effect in a-Si:H and a-Si:H-Based Alloys
Authors: Lucovsky G. , Williams M.J. , Cho S.M. , Jing Z. , Whitten J.L.
Published: April 2011

Many photoelectronic properties of a-Si,N:H alloys prepared by remote PECVD (RPECVD) from two N-atom source gases - N2 and NH3 - are the same; however, the photo-induced changes in the electrical properties in alloys with -2.1 eV bandgaps are ∼3 to 5 times greater in alloys deposited from NH3, which display Si-NH, as well as SiH bonding. Based on this result, we show that bonding groups important in the Staebler-Wronski effect include (i) ≡SiH, and nearest-neighbor (ii) ≡Si-NH-Sis and/or ≡Si-O-Sis in which the respective N and O-atoms make H-bonds with the sSiH group. The model, based on ab-initio calculations, includes a H-exchange reaction in which trapping of photo-generated holes promotes a transfer of the H-atom from the ^SiH group to a nearest-neighbor ≡Si-NH-Si≡ creating (i) a Si-dangling bond (Si*) and (ii) a Metastable (≡Si-NH2-Si≡) + group. Calculations indicate that neutral (≡Si-NH2≡Sis) ° is unstable, so that relaxation of (≡Si-NH2-Si≡) + groups can occur by trapping of a thermally-released (trapped) electron during a post-light-soaking thermal-anneal. The same type of model is developed for hole/electron trapping-induced H-atom transfer between ≡SiH and ≡Si-0-Si≡ groups in other a-Si:H Materials.
Relationship Between Plasma Chemistry and Electron Trapping rate in Plasma-Deposited Silicon Nitride
Authors: Smith Donald L
Published: April 2011

Silicon nitride deposited by plasma-enhanced chemical vapor deposition (PECVD) from SiH4 and NH3 is not crystalline Si3N4 with a specific stoichiometric ratio, but rather SiNxHy, an Amorphous network in which the N/Si ratio can vary from zero in Amorphous Si (a-Si) to almost two. The rate at which injected electrons are trapped in SiNxHy decreases by over 103 when N/Si is increased from 4/3 to the N saturation point, and the trapping centers are therefore likely to be Si dangling bonds. Trapping is undesirable in semiconductor devices except in memory applications, because it shifts the device's flat-band voltage, although in a-Si thin-film transistors (TFT's) the nitride trapping rate can easily be made Much smaller than the rate of electron trapping in deep states of the a-Si. When deposition plasma chemistry is driven to the N-saturation point, SiNxHy has a trapping rate lower than that of the best PECVDSiO2, although this is still 104 above that of thermal oxide grown on single-crystal Si. N-saturated deposition requires not only a high NH3/'SiH4 feed ratio, but also sufficient plasma power to activate the NH3 so that it will completely consume the SiH4 in formation of the tetra-aminosilane [Si (NH2) 4] precursor molecule. Then, the Si in the Amorphous network becomes entirely bonded to N rather than to both H and N, and NH groups act like O does in SiO2 to lower the coordination of the network and thus avoid dangling bonds.
Effects of Intermittent Deposition on the Defect Density in a-Si:H
Authors: Kamei Toshihiro , Hata Nobuhiro , Matsuda Akihisa
Published: April 2011

Effects of intermittent deposition on the defect density in hydrogenated Amorphous silicon (a-Si:H) are investigated at various substrate temperatures by using a mechanical shutter, while maintaining the discharge continuously. The intermittent deposition experiments, where monolayer growth and intermission (waiting time) are repeated in cycles, enable us to study surface dangling bond (DB) recombination and thermal hydrogen desorption separately from other reactions on the growth surface. The defect density in films prepared at lower substrate temperatures decreases with the waiting time, while that deposited at higher substrate temperatures increases with the waiting time.
The Interpretation of the Constant Photocurrent Method in Terms of Deep Defect Density of States in A-SI.H
Authors: Siebke Frank , Stiebig Helmut
Published: April 2011

The constant photocurrent Method (CPM) is often used to measure the sub-bandgap absorption for the determination of the defect density. However, the absolute value of the derived defect density depends on the method of data analysis and the calibration factor. Normally the calibration factor is obtained from electron spin resonance (ESR) but the defect pool model gives rise to doubt whether ESR detects the same defects as CPm. Therefore, we propose combined total-yield photoelectron spectroscopy (TYPES) and CPM Measurements on n-type a-Si:H to determine the calibration factor. Furthermore, we calculate CPM spectra by extending an approach to simulate photoconductivity, taking into account the full set of optical transitions, and compare the results with standard evaluation Methods.
Structural, Optical and Electrical Properties of  μc-Si:H Very Thin Films Deposited by the VHF-GD Technique
Authors: Flückiger Roger , Meier J. , Shah A. , Catana A. , Brunel M. , Nguyen H. V. , Collins R. W. , Carius R.
Published: April 2011

In this paper we present new results for very thin
 μc-Si:H films (< 350 Å) deposited at low temperature (170 C) by the Very High Frequency - Glow Discharge technique (VHF-GD) at 70 MHz. First, the effect of boron doping on the growth and electrical properties of μc-Si:H very thin films is investigated, leading to an optimised value of about 0.6 % (B2H6/SiH4). Structural properties of an optimised thickness series ranging from 100 to 350 Å are studied using TEM, Raman, grazing angle X-ray diffraction/reflection and spectroscopie ellipsometry. Further, a columnar structure growth model for these very thin
-type μc-Si:H films will be proposed.
Characterization and Optimization of The Tco/a-Si:H(,B) Interface for Solar Cells by In-Situ Ellipsometry and Sims/XPS Depth Profiling
Authors: Wanka H.N. , Lotter E. , Schubert M.B.
Published: April 2011

The chemical reactions at the surface of transparent conductive oxides (SnO2, ITO and ZnO) have been studied in silane and hydrogen plasmas by in-situ ellipsometry and by SIMS as well as XPS depth profiling. SIMS and XPS of the interface reveal an increasing amount of metallic phases upon lowering a-Si:H growth rates (controlled by plasma power), indicating that the ion and radical impact is more than compensated by protecting the surface by a rapidly growing a-Si:H film. Hence, optical transmission of TCO films as well as the efficiency of solar cells can be improved if the first few nanometers of the p-layer are grown at higher rates. Comparing a-Si:H deposition on top of different TCOs, reduction effects on ITO and SnO2 have been detected whereas ZnO appeared to be chemically stable. Therefore an additional shielding of the SnO2 surface by a thin ZnO layer has been investigated in greater detail. Small amounts of H are detected close to the ZnO surface by SIMS after hydrogen plasma treatment, but no significant changes occur to the optical and electrical properties. In-situ ellipsometry indicates that a ZnO layer as thin as 20 nm completely protects SnO2 from being reduced to metallic phases. This provides for shielding of textured TCOs, and hence rising solar cell efficiencies, too. Regarding light trapping efficiency we additionally investigated the smoothing of initial TCO texture when growing a-Si:H on top by combining atomic force microscopy and spectroscopie ellipsometry.
An Exploratory Survey of p-Layers for a-Si:H Solar Cells
Authors: Li Y.-M. , Jackson F. , Yang L. , Fieselmann B.F. , Russell L.
Published: April 2011

The window layer (p-layer) critically affects the conversion efficiency of a-Si:H based p-i-n type solar cells. This paper surveys possible alternative window materials in comparison with the standard boron doped a-SiC:H p-layer. A novel wide-gap amorphous silicon alloy, a-Si:F:H, will be shown to be a good alternative p-layer. As an example of nontraditional p-layer, boron based alloys (e.g., a-B:H) exhibit notable photovoltaic action in a-Si:H solar cells. We comment on attempts to deposit μc-Si alloy window layers on textured TCO-coated glass substrates.
High-Growth Rate a-Si:H Deposited by Hot-Wire CVD
Authors: Brogueira P. , Chu V. , Conde J.P.
Published: April 2011

We present a study of the optoelectronic and structural properties of a-Si:H deposited by Hot-Wire chemical vapor deposition (HW-CVD) from SiH4 and H2 at “Medium” (Tfil ≃ 1500°C) and “high” (Tfil ≃ 1900 °C) filament temperatures. For each tungsten filament temperature regime, the following deposition parameters are varied: (i) pressure (p ∼ 10−2 — 0.5 Torr); (ii) substrate temperature (Tsub ∼ 180 — 270 °C); (iii) silane flow rate (FsiH4 ∼ 1 — 10 ccm) and (iv) hydrogen flow rate (FH2 ∼ 0 — 10 seem). Films deposited at Tfil ∼ 1900 °C in a low pressure regime (p ∼ 2.7 × 10−2Torr) using flows of 5 sccm for both H2 and SiH4 had high deposition rates (rd ∼ 8 Ås−1). These films showed an optical bandgap, E9Tauc ≃ 1.7 eV, a dark conductivity σd ∼ 10−8Scm−1 with an activation energy Eα,σd ≃ 0.8 eV, and photoconductivity σph ≥ 10−5Scm−1 (σph ∼ 10−5). Films deposited at Tju = 1500 °C and p ≃ 0.3 Torr, showed 1.7 < E9Tauc < 2 eV, 10−5 < σd < 10−3Scm−1, 0.2 < Eα,σ d < 0.5 eV and σph/Σd < 102. For the same Tfit and p ∼ 3 × 10−2 — 0.1 Torr, the films show 1.7 < E9Tauc < 2 eV, 10−3 < Σd < 10−1Scm−1 and σph/σd < 1. Films deposited using molybdenum and rhenium filaments at Tfil ≃ 1900 °C show E9Tauc ≃ 1.7 eV and σd ∼ σph ∼ 10−7Scm−1
Saturation Behavior and Thermal Annealing Recovery of Light-Induced Degradation in a-SiGe:H Alloy Solar Cells
Authors: Guha S. , Xu X. , Yang J.
Published: April 2011

We have studied the saturation behavior and thermal annealing recovery of light-induced degradation in amorphous silicon-germanium (a-SiGe:H) alloy solar cells with various Ge contents. In contrast to amorphous silicon (a-Si:H) alloy cells, a-SiGe:H alloy cells with high microvoid density show similar thermal annealing behavior to those with lower microvoid density. Infrared studies show that unlike a-Si:H alloys, a-SiGe:H alloys with higher microvoid density do not show higher hydrogen or dihydride content. Moreover, even with a Ge-content of 41 %, there is saturation in degradation after light soaking for 1000 hours.
Non-Local Recombination in “Tunnel Junctions” of Multijunction Amorphous Si Alloy Solar Cells
Authors: Hou Jingya , Xi Jianping , Kampas Frank , Bae Sanghoon , Fonash S. J.
Published: April 2011

This paper analyzes the charge transport in “tunnel junctions” of amorphous Si Material based multijunction solar cells and proposes some guidelines for making good “tunnel junctions” based on the analysis. The Mechanism of the current flow in these “tunnel” junctions is recombination. However, the recombination mechanism is not the usual localized recombination but is non-localized recombination. The energy analysis shows that the usual localized recombination will cause a large energy loss and result in much lower energy conversion efficiency and Voc than the experimentally measured values. In non-local recombination, opposite charge carriers located at different locations can recombine by tunneling into a defect state. Based on this Mechanism, a good “tunnel junction” should be thin, with a large defect state density in the middle region of the “tunnel junction”. Broad tail states material and a thin layer small band gap material in tunnel junctions may improve the non-local recombination by providing more intermediate states for charge to tunnel through.
Investigation of Shunt Resistances in Single-Junction a-Si:H Alloy Solar Cells
Authors: Lord Kenneth R. , Walters Michael R. , Woodyard James R.
Published: April 2011

Dark current-voltage characteristics of one hundred twenty single-junction a-Si:H alloy solar cells were studied. Parametric Modelling of dark I-V Measurements was used to determine some of the cell parameters. Average shunt resistances were 31 to 1200 kΩ for intrinsic layer thicknesses of 200 to 800 nm, respectively. Current switching was observed during dark I-V Measurements; the current in the reverse-bias region varies approximately as the square of the voltage following the onset of switching. The I-V characteristics in the switched mode are not understood. Voltage history and scan rate play a role in dark I-V characteristics.
AD-Layer for Spatial Control of Light Induced Degradation on Pin Devices
Authors: Vieira M. , Fantoni A. , Fortunato E. , Lavareda G. , Martins R.
Published: April 2011

In this work we report experimental results on light induced metastability of a-Si:H p.i.n. devices with different Microscopic/Macroscopic structures and we discuss them in terms of improved stability through spatial control of charged defects grown during light exposure. By placing a thin (few Å) intrinsic layer (i') between both p/i and i/n a-Si:H interfaces we are able to reduce the effective degradation rate through spatial modification of the electric field profile in the device. The electronic transport and the stability changes that accompany the change in Microstructure (R) and hydrogen content (CH) of the i- and i'-layer, were monitored throughout the entire light induced degradation process and compared with the corresponding μτ product (for both carriers) inferred through steady state photoconductivity and Flying Spot Technique (FST) Measurements. Results show that the degradation rate is a function of CH and R of both layers and can be correlated with the density of microvoids and di-hydride bonding. Since the i'- layers have a higher Cfj bonded mainly as SiH1 radicals (R≈0.4), they act as an hindrance to the growth of the defect, in the active region, generating “gettering centers” whose localisation and density are tailored in such a way that they will control spatially the electric field profile during light exposure.

Preliminary results show improvements in film's stability when the interfacial layer is included. So future progress toward more stable and efficient a-Si:H solar cells will depend on a careful engineering design of the devices.
a-Si TFT Technologies for AM-LCDS
Authors: Ibaraki Nobuki
Published: April 2011

A technical trend for a-Si TFTs is their application to large-size, high-pixel density AM-LCDs such as XGA, EWS, and HDTV. In order to realize these LCDs, the TFT device characteristics must be improved. Future technologies, which will be necessary to fabricate TFTs with improved characteristics are as follows

(1) Fully self-aligned TFT technology: A SA-TFT structure reduces the feedthrough voltage caused by parasitic capacitance due to gate/source overlap. This results in an improved picture quality and a higher aperture ratio. Fabrication of such a structure would require ion doping technology.

(2) Ion doping technology: This non-Mass-separated implantation technique has large area doping capability and much higher doping speed compared to conventional ion implantation technique. The Major problems with the ion doping technique is the implantation of unwanted species which deteriorate the quality of source/drain and channel regions of TFTs.
Surface and Interface Modification of Copper for Electronic Application
Authors: Lanford W. A. , Ding P. J. , Hymes S. , Murarka S. P.
Published: April 2011

Before copper will be used in the manufacture of microelectronic circuits, a number of its surface and interface properties have to be addressed. These include corrosion resistance, adhesion to dielectrics, and ability to block the transport of copper ions from the metal into adjacent materials. Different schemes have been explored to meet copper's material properties needed for electronic application. For surface modification, these include ion implantation, plasma treatments, formation of surface silicides, and annealing of copper films doped with other elements. For interface control, most schemes have involved deposition of an adhesion/barrier film. The present paper will discuss our present understanding of the mechanisms that govern surface and interface passivation. Special attention will be given to schemes that might lead to both surface and interface passivation in the same process.
A New Electrical Model for Calculating the Sheet Resistance Parameter in Alloyed Ohmic Contacts
Authors: Reeves Geoffrey K. , Barry Harrison H.
Published: April 2011

This paper briefly reviews the standard Transmission Line Model (TLM) commonly used to measure the specific contact resistance ρc and the sheet resistance Rsk beneath a planar ohmic contact. In the case of an alloyed ohmic contact, a more realistic three layer (Tri-Layer Transmission Line Model (TLTLM)) can be used for the analysis. This model is based on three layers (metal layer, alloyed semiconductor layer and the unalloyed semiconductor layer) and the two interfaces between them. By using appropriate TLTLM parameters, it is possible to calculate the sheet resistance Rsk that has been experimentally derived from the standard TLM. The new TLTLM model predicts that values of Rsk greater and less than Rsh (the unmodified epitaxial layer sheet resistance) are possible in agreement with experimentally reported observations.
Studies on the Interface of TiN/n-GaAs
Authors: Jie Ho , Gaolong Jin , Liwu Lu , Zhenjia Xu , Lichun Zhang
Published: April 2011

Recent reports on refractory metal nitrides/n-GaAs Schottky contacts have demonstrated that improved electrical performance can be obtained after annealing at temperature between 750 and 850°C . It is thought that a p+-type layer should be responsible for this phenomenon, which may be generated by N or N related defects. In this paper, the role of nitrogen in SI-GaAs and n-GaAs has been investigated by Hall effect and DLTS measurements. No evidence of the formation of a p+-type layer has been observed. A deep energy level of Ec-0.36eV which is thought to be related to N and an enhanced effect of N on the density of EL2 level were observed. DLTS and SIMS techniques were used to study the interface of TiN/n-GaAs Schottky contacts. The Ti3+(3d1)/Ti2+(3d2) single acceptor level at Ec-0.21 eV was observed, but the EL2 donor level is dominant. Combining the experimental results, a discussion is made about the reasons for the improvements of electrical performance after annealing.
Optimization of Pd/Zn/Pd/Au Ohmic Contacts to p-Type inGaAs/ InP
Authors: W Leech Patrick , Reeves Geoffrey K.
Published: April 2011

The electrical properties of Pd/Zn/Pd/Au based ohmic contacts to p-type In0 47Ga0 53As/ InP with an interposed superlattice of 50Å In047Gao 53As/ 50 Å InP have been investigated. In this study, several configurations of the Pd/Zn/Pd/Au metallization were fabricated with varying thicknesses of the Zn and interfacial Pd layers in the range 0 to 400 Å. The lowest values of specific contact resistance, ρc, were 1.2 x 10-5 Ω cm2 as-deposited and 7.5 x 106 Ω cm2 for samples annealed at 500 °C. In the as-deposited structures, ρc was reduced by an increase in thickness of both the Zn and Pd layers to 300 Å. For annealed samples, a critical thickness of the Zn ≥ 50 Å and Pd ≥ 100 Å layers was required in order to significantly reduce the magnitude of ρc. These results are consistent with a model of Pd/Zn contacts based on Zn doping of the interface. Studies of thermal stability of the contacts at 400 °C and 500 °C have shown that the Zn/Pd/Au and Pd/Zn/Pd/Au configurations were significanty lower in ρc at extended ageing times than the Pd/Au contacts.
Copper Metallization Manufacturing Issues for Future ICs
Authors: Gutmann Ronald J. , Paul Chow T. , Gill William N. , Kaloyeros Alain E. , Lanford William A. , Murarka Shyam P.
Published: April 2011

Copper metallization for on-chip multilevel interconnects is receiving increasing attention for future generations of ICs, with advantages of low line resistance, low interconnect delay, high electromigration resistance and, possibly, overall back-end process simplicity. However, copper introduces a set of processing and manufacturing issues which must be addressed in the research and development phases of the technology. This paper summarizes the most likely processing steps for integrating copper metallization into IC technology and presents the manufacturing issues (materials, unit processing and process integration issues) that need to be addressed.
Selective Copper Cvd on Diamond Surfaces Using Self-Assembled Monolayers
Authors: Potochnik Stephen J. , Hsu David S. Y. , Calvert Jeffrey M. , Pehrsson Pehr E.
Published: April 2011

Selective chemical vapor deposition (CVD) of conductive, adherent copper films was achieved on single-crystal and polycrystalline diamond substrates modified with a ligating aminosilane and a Pd-based catalyst. Only isolated copper particles deposited on hydrogenated or aminosilane-coated diamond substrates without Pd. The Pd catalyst enhanced selectivity by a factor of 103 to 104. Copper CVD was performed in a cold-walled chamber at 446-456 K and 8x10-3 Pa using hexafluoroacetylacetonate-Cu-trimethylvinylsilane in H2 (1:1). Surfaces were characterized with x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Patterned Cu features were formed by exposing the aminosilane films to patterned ultraviolet (193 nm) radiation prior to Pd-catalyst addition and Cu CVD.
Deposition of Conductive Titanium Sub-Oxide Films by Reactive Ion-Beam Sputtering
Authors: Grigorov K.G. , Benhocine A.H. , Bouchier D. , Meyer F.
Published: April 2011

Titanium monoxide films were deposited on silicon by reactive ion beam sputtering from a Ti target. The film composition was measured in situ by Auger electron spectrometry. It was observed that oxygen content in the deposit does not depend on the substrate temperature, up to 600 °C. Synthesized TiO films had a cubic structure with a lattice parameter of 4.17 Å, which confirmed that the O/Ti concentration ratio in the films was very close to the expected value. The films were found to be conductive, with a resistivity value equal to 170 μΩ cm. They had a yellowish metallic appearence and a very smooth surface. Sequences of annealings at increasing temperatures were performed under ultra-high-vacuum. No AES signal from silicon was observed up to a temperature of 700 °C.
Simulation of Collimated Titanium Nitride Physical Vapor Deposition using EVOLVE
Authors: Toprac Anthony J. , Wang Shi-Qing , Schlueter Jim , Cale Timothy S.
Published: April 2011

Simulation of the physical vapor deposition (PVD) of titanium nitride (TiN) in micronscale contacts was performed using EVOLVE, a physically-based model of non-continuum
mass transport. Simulations of uncollimated TiN PVD using a sub-unity sticking coefficient of 0.6 provide accurate model predictions of experimental data. Using this value in simulations of PVD with a 1:1 aspect ratio collimator results in a significant underprediction of titanium nitride deposition in the feature bottom in comparison to the experimental results. This under-prediction was compensated for empirically by adjusting
a “beaming” coefficient to produce good model predictions of the experimental data.
Development of A Silane Rich CVD Tungsten Process
Authors: Tripathi Sanjay , Moghadam Farhad
Published: April 2011

The economics of manufacturing is driving the use of larger wafer sizes. At the same time smaller device geometries place more stringent requirements on film properties. Maintaining tight control of metal film properties in larger reactors presents unique challenges in the development of manufacturing worthy processes. This paper presents the development of a CVD tungsten process that was necessitated by the requirement for stable deposition uniformity with the conversion of wafer sizes from 6“ to 8”. The scaled up version of the 6“ process was rendered obsolete in the 8” tool due to unacceptable drifts in deposition uniformity.

Fluorine build up in the reaction chamber from the silane (SiH4) and hydrogen (H2) reduction of tungsten hexafloride (WF6) was identified to be the main cause for the process instability. We discuss how the problem was identified and how the new process was developed. Data on the uniformity of deposited films, collected over several hundred wafers with the old process and the new process show the new process to be superior. Device yield and electrical parameter data show the new process to be at least as good as the previous process.
Focused Ion Beam: Advanced Technique for Device Modification
Authors: Abramo Marsha , Hahn Loren
Published: April 2011

Focused ion beam (FIB) technology is used to modify circuits for early-product design debug; it also has the capability to create probe points to underlying metallurgy, allowing device characterization while maintaining full functionality. These techniques provide critical feedback to designers for rapid verification of proposed design changes.

Current FIB technology has its limitations because of redeposition of sputtered material; this phenomena may induce vertical electrical shorts and limit the achievable aspect ratio of a milled via to 6:1. Therefore, innovative enhancements are required to provide modification capability on planar chip technology which may utilize up to five levels of metallurgy. The ability to achieve high-aspect-ratio milling is required to access underlying circuitry. Vias with aspect ratios of 10:1 are necessary in some cases.

This paper reviews a gas-assisted etching (GAE) process that enhances FIB milling by volatilizing the sputtered material, examines the results obtained from utilizing the GAE process for high-aspect-ratio milling, and discusses selectivity of semiconductor materials (silicon, aluminum, tungsten and silicon dioxide).
The Selectivity of Reactive Ion Etch of Ga0.5LIn0.49P/Gaas
Authors: Wu J.W. , Chan S.H. , Lin K.C. , Chang C.Y. , Chang E.Y.
Published: April 2011

The Ga0.51In0.49p/GaAs system has better desired property (ΔEC >ΔEV) than the conventional AlGaAs/GaAs system for heterojunction bipolar transistor (HBT) application. However, in the fabrication of HBTs, a precise control of the etch of the epilayer is very important. In this study, CH4/H2 and BCl3/SF6 were used for the reactive ion etch of the Ga0.51In0.49P/GaAs. It is found that the etch rate of Ga0.51In0.49P could be higher than that of GaAs with CH4/H2 gas mixture under appropriate etching conditions. While in the case of BCl3/SF6, the etching rate of GaAs could be much higher than that of the Ga0.51In0.49P. By properly using CH4/H2 and BCl3/SF6, the fabrication of Ga0.51In0.49P-based device using reactive ion etch could be easily achieved.