bluuebunny/crossref_metadata_2025 huggingface dataset:
The Cumulative Beta Decay and the Effect of Electron Radiation on a Simulated HLW Sintered Glass
Authors: Bevilacqua A.M. , de Bernasconi N.B. Messi , Russo D.O. , Prastalo S. , Sanfilippo M. , Heredia A.D. , Sterba M.E.
Published: April 2011

The first aim of the work was to calculate, by means of the computer codes ORIGEN2. 1, ITS 3.0 and TRIM95, the beta/gamma cumulative dose and displacements produced by the fission products hold in the high level wastes (HLW) from reprocessed CANDU spent fuel, up to one million years, with a burnup of 7,000 MWd/tU and a cooling time of 20 years. Based on that results were calculated and graphically presented the mean electron energy (β−, internal conversion and Auger) and the cumulative beta events and ionization dose due to electrons, per metric ton of heavy metal and per cubic centimeter of the sintered HLW glass form, as a function of the time up to one million year.
On the Behavior of Uranium Dioxide Toward Aqueous Corrosion: Incidence of Electronic Stopping of Fission Fragments
Authors: Choffel C. , Garrido F. , Thomé L. , Dran J.-C. , Nowickit L. , Turos A.
Published: April 2011

The scenario of spent fuel direct storage in a deep geological repository is currently under consideration in many countries. In this approach the nuclear fuel — mainly uranium dioxide —acts as a first barrier towards fission fragment and actinide release. Although the access of water in such a repository is rather unlikely, evaluating the safety of a disposal requires the knowledge of the mechanisms and kinetics of alteration and dissolution of the nuclear fuel in groundwaters. Despite the fact that the reported litterature on the topic is really extensive, it is still a challenging problem due to the complexity of the system: the used nuclear fuel cannot identify with uranium dioxide itself due to both radiation damage and modification of the matrix composition during reactor operation. Parametric studies in well-defined conditions on simple systems are therefore of prime importance in order to determine the relevant parameters involved in the structural transformations of the uranium-oxygen-water systenL The aim of the present work was to study the incidence of the electronic stopping of fission fragments on the behavior of nuclear fuel towards leaching in deionized water under oxidative conditions. Several features were of special interest: (i) quantification of the damage induced by swift-heavy ion irradiation prior to aqueous corrosion; (ii) stoichiometry and oxygen depth concentration of the alterated surface region; (iii) structural transformation of the crystalline structure induced by incorporation of additional O atoms; (iv) comparison between unirradiated and irradiated samples
Packaging of High Burnup UO2 and MOX Spent Fuel Considering Temperature Restrictions in the Near Field of a Repository
Authors: McGinnes D.F. , Schneider J. W.
Published: April 2011

The direct disposal of spent fuel is one of the options considered in the Swiss high level waste management program. One of the important questions, within this program, is the heat generation from high-burnup UO2and MOX spent fuels. Depending on the repository boundary conditions (e.g. ambient temperatures at depth, thermal properties of the host rock etc.), on the maximum temperatures allowed in the near field and on the heat output of the fuel, it may not always be possible to completely fill the conceptual waste canister. The aim of this paper is to address the potential loading of spent fuel into canisters for different possible repository heat loading restrictions
TEM Study of Neutron Irradiated Synroc
Authors: Smith Katherine L. , Blackford Mark G. , Lumpkin Gregory R.
Published: April 2011

Synroc is a candidate waste form for the immobilisation of high level radioactive waste (HLW)[1]. It is polyphase titanate ceramic principally comprised of zirconolite, hollandite perovskite and rutile (nominally CaZrTi2O7, (BaxCsy)[(Ti3+, Al)2x+y(Ti4+)8−2x−y]O16), CaTiO3and TiO2respectively). Waste species substitute into the three former phases. In particular, actinides (ACTs) substitute onto the Ca and Zr sites in zirconolite and the Ca site in perovskite. Consequently over time, these phases will suffer alpha-recoil and alpha particle damage while hollandite and rutile will suffer alpha particle damage. The effect of radiation damage on the structure and consequently on the durability of Synroc's constituent phases is important to predictive modelling of Synroc's behaviour in the repository environment and risk assessment.
Evolution of an Engineered Barrier Under Thermal Gradient During the STRIPA Experiments: Influence of the Clay Texture on the Element Transfers
Authors: Pozo C. , Jullien M. , Poinssot C.
Published: April 2011

Hydrothermal experiments on saturated barrier were conducted for 6 months and 4 years in the granite of the STRIPA mine (Sweden). The French clay Fo-Ca 7 (80 % Kaolinite/Smectite mixed-layer) was compacted (25 MPa) and placed around a steel heater in a 20 cm diameter borehole. The temperature was about 170°C at contact with the heater and only 80°C at clay/granite interface, thus giving a thermal gradient around 10°C/cm
LiNO3 Addition to Cement Which Prevents Aluminum Corrosion
Authors: Matsuo T. , Izumida T. , Hironaga M. , Horikawa Y. , Shiomi T.
Published: April 2011

LiNO3 addition to cement was examined to prevent hydrogen gas generation from metallic aluminum in dry active wastes during waste solidification and under circumstances of underground water penetration into the land disposal site. And its reaction mechanism was identified by some chemical analyses. The volume of the hydrogen gas generation with LiNO3 addition was 10% as much as that without LiNO3, by formation of the insoluble Li-Al preservation film on aluminum. After the land disposal of waste forms, LiNO3 would be expected to be effective to prevent aluminum corrosion as long as the cement forms keep their alkaline character, and when it became ineffective, the circumstances around the waste forms can be made less corrosive for aluminum. The aluminum corrosion at that time would be as much as 10% of that without LiNO3 addition.
Preparation of a-Si:H and a-SiGe:H I-Layers for Nip Solar Cells at High Deposition Rates Using a Very High Frequency Technique
Authors: Jones S.J. , Deng X. , Liu T. , Izu M.
Published: April 2011

The 70 MHz Plasma Enhance Chemical Vapor Deposition (PECVD) technique has been tested as a high deposition rate (10 A/s) process for the fabrication of a-Si:H and a-SiGe:H alloy ilayers for high efficiency nip solar cells. As a prelude to multi-junction cell fabrication, the deposition conditions used to make single-junction a-Si:H and a-SiGe:H cells using this Very High Frequency (VHF) method have been varied to optimize the material quality and the cell efficiencies. It was found that the efficiencies and the light stability for a-Si:H single-junction cells can be made to remain relatively constant as the i-layer deposition rate is varied from 1 to 10 Å/s. Also these stable efficiencies are similar to those for cells made at low deposition rates (1 Å/s) using the standard 13.56 MHz PECVD technique. For the a-SiGe:H cells of the same i-layer thickness, use of the VHF technique leads to cells with higher currents and an ability to more easily current match triple-junction cells prepared at high deposition rates which should lead to higher multi-junction efficiencies. Thus, use of this VHF method in the production of large area a- Si:H based multi-junction solar modules will allow for higher i-layer deposition rates, higher manufacturing throughput and reduced module cost.
Effect of Excitation Frequency on the Performance of Amorphous Silicon Alloy Solar Cells
Authors: Yang J. , Sugiyama S. , Guha S.
Published: April 2011

We have studied amorphous silicon alloy solar cells made by using a modified-very-highfrequency glow discharge at 75 MHz with a deposition rate of ∼6 Å/s. The solar cell performance is compared with those made from conventional glow discharge at 13.56 MHz with lower deposition rates. Cells made at ∼6 Å/s with 75 MHz showed comparable stabilized efficiency to those made at ∼3 Å/s with 13.56 MHz. The best performance, however, was obtained with ∼1 Å/s, including a stabilized 9.3% a-Si alloy single-junction cell employing conventional glow discharge technique. Using 75 MHz, we have achieved 11.1% and 10.0% initial active-area efficiencies for a-Si alloy and a-SiGe alloy n i p cells, respectively. An initial efficiency of 11.0% has also been obtained in a dual bandgap double-junction structure.
New Method to Determine the a-Si:H Pin Diode Series Resistance by Noise Measurements
Authors: Blecher F. , Seibel K. , Hillebrand M. , Böhm M.
Published: April 2011

The series resistance limits the linearity of photodiodes and decreases the efficiency of solar cells. It is usually determined from IV-measurements for moderate and high forward current density. This method, however, provides only partial information about Rs, since the series resistance depends on the operating point. An alternative method is based on noise measurements. System noise of the measuring system with a low-noise current-voltage converter has been investigated. A new method for extraction of photodiode series resistance from noise measurements is suggested. Noise measurements are carried out for a-Si:H pin diodes. The series resistance of an amorphous pin diode has been extracted for different operating conditions using the new measurement method.
Photocurrent in Microcrystalline Hydrogenated Silicon P-I-N Devices
Authors: Fernandesi M. , Vieirai M. , Maqarico A. , Koynov S. , Fantoni A. , Schwarz R.
Published: April 2011

The photocurrent delivered by microcrystalline hydrogenated silicon p-i-n devices and the spectral response are analysed under different applied bias voltage. The spectral response is extended far beyond 900 nm. Under reverse bias the spectral response is high and essentially unchanged while under increasing forward bias it decreases continuously. For forward bias higher than the open circuit voltage, the usual reversal of the spectral response is not observed and the photocurrent remains negative and almost independent of the bias voltage. A heterojunction model based on the presence of additional local electric fields near the grain boundaries is presented to explain this behaviour. Those fields lead to a strong increase of the recombination at the grain boundaries decreasing the contribution from the photogenerated carriers for the secondary photocurrent. Reverse bias restores the electric field at the interfaces minimizing the influence of the local barriers.
A Novel Room Temperature Infrared Detector Using Micro-Compensated Amorphous Silicon
Authors: Caputo D. , Cesare G. De , Nascetti A. , Palma F.
Published: April 2011

Detection at room temperature of near and medium infrared radiation has been achieved by using micro-doped or micro-compensated amorphous silicon films as intermediate absorber layer in a p-n junction. Extremely low dopant concentrations in the gas mixture have been utilized to achieve micro-doping and micro-compensation. Device operation is based on transitions, induced by the infrared radiation, between extended states in the valence band and defects in the forbidden gap. The absorption process changes electron defect occupancy, giving rise to change in electric field distribution. This effect can be observed as variation of differential capacitance of the structure. Capacitance measurements, performed on two different devices with micro-doped and micro-compensated absorber layer respectively, showed sensitivity to radiation from 900 nm up to 4·5 jim.
Temperature Dependence of Electroluminescence from Nanocrystalline Silicon thin Films
Authors: Toyama T. , Kotani Y. , Shimode A. , Shimizu K. , Okamoto H.
Published: April 2011

Temperature dependence of electroluminescence (EL) from nanocrystalline Si (nc-Si) has been studied in comparison with that of photoluminescence (PL) from the nc-Si. The similarity is found in the temperature dependence of peak shift between EL and PL excited by ultraviolet light. The blue shift in both peaks is also found when the carrier generation rate is increased. The experimental results are indicative that the peak shifts due to the temperature and the generation rate are based on different mechanisms.
Erbium-Doped A-Si:H Films Fabricated by Standard Pecvd Using Metalorganics
Authors: Feoktistov N.A. , Golubev V.G. , Medvedev A.V. , Pevtsov A.B.
Published: April 2011

1·54 jim light-emitting erbium-doped hydrogenated amorphous silicon films have been fabricated by standard low temperature (200 – 250 °C) PE CVD technique. The films were doped with erbium during the deposition by making use of a new fluorine-containing metalorganic compound Er(HFA)3*DME [where HFA=CF3C(O)CHC(O)CF3, DME=CH3OCH2CH2OCH3]. Photoluminescence spectra of the a-Si(Er):H films were studied within the range 0·6–1·7 pm at both 77 K and 295 K. A photoconductivity was also detected. The photo- to dark conductivity ratio was on the order of 103.
A Study of Silicon Suboxide thin Films by Photoluminescence
Authors: Wang F. , Wolfe D.M. , Hinds B.J. , Lucovsky G. , Platz R. , Wagner S.
Published: April 2011

Silicon suboxide (SiOx1 0<x<2) thin films have been investigated by means of photoluminescence, FTIR and photothermal deflection spectroscopy. Results showed that as the oxygen content in the films increases, the temperature dependence of PL intensity (Ipl) becomes weaker, and the PL peak position (Ep) shifts to the visible with decreasing intensity predominantly due to a decrease in the absorption coefficient. After sequential rapid thermal annealing from 500 to 100°C, Ep shifts simply to low photon energy. However, Ip1 of high oxygen content films first increases with increasing annealing temperature (TRTA), then decreases when TRTA>800°C, in contrast to low oxygen content films whose Ip1 monotonically decreases with TRTA and disappears above 700°C. The results are interpreted in terms of inhomogeneity in the as-deposited films, phase segregation upon annealing, and quantum confinement.
Role of the Collecting Resistive Layer on the Static Characteristics of 2D a-Si:H thin Film Position Sensitive Detector
Authors: Fortunato E. , Martins R.
Published: April 2011

The aim of this work is to present an analytical model able to interpret the role of the thin collecting resistive layer on the static performances exhibited by 2D amorphous silicon hydrogenated pin thin film position sensitive detectors. In addition, experimental results concerning the device linearity and spatial resolution are presented and checked against the predicted values of the analytical model proposed.
Deposition and Evaluation of Micro-Crystalline Silicon for Use in Photoconducting Antennas
Authors: Yarasi Sripathi , Manku Tajinder
Published: April 2011

The importance of micro-crystalline silicon (μc-Si:H) for the photo-conducting dipole antenna application is investigated in this paper. The structural and optical properties of gc-Si:H films prepared by plasma enhanced chemical vapor deposition are studied with Raman spectra, scanning electron microscope, and ellipsometer measurements. The influence of grain size and defects on the opto-electronic characteristics of the photo-conducting dipole antenna is discussed. A sample of the antenna fabricated in our clean room laboratory is reported.
Analysis of Radical Reaction on Growing Surface During Si Epitaxy by Photo-Cvd
Authors: Abe Katsuya , Watahiki Tatsuro , Yamada Akira , Konagai Makoto
Published: April 2011

The growth mechanism of Si film at low temperature on Si(100) by photo-CVD was theoretically analyzed by using reaction models both in the gas phase and on the growing surface. We introduced three surface reactions; the growth of Si from SiH3 radicals, the dangling bond termination by atomic hydrogen and the abstraction of bonding hydrogen by SiH3 radicals. We assumed that the film structure is determined by the hydrogen surface coverage ratio “ø” and the parameters of the surface reaction model were determined from the experimental results. The theoretical analysis explained well the experimental data on the growth rate.
Hydrogenated Amorphous Silicon Germanium Alloys Grown by the Hot-Wire Chemical Vapor Deposition Technique
Authors: Nelson Brent P. , Xu Yueqin , Williamson D.L. , Von Roedern Bolko , Mason Alice , Heck Stephan , Mahan A.H. , Schmitt S.E. , Gallagher A.C. , Webb John , Reedy Robert
Published: April 2011

We successfully grow high-quality hydrogenated amorphous-silicon-germanium alloys (a-SiGe:H) by the hot-wire chemical-vapor deposition (HWCVD) technique using silane and germane gas mixtures. These alloys display electronic properties as good as those grown by the plasma-enhanced chemical-vapor deposition (PECVD) technique, when comparing materials with the same optical bandgaps. However, we grow materials with good electrical properties at high deposition rates—up to 40 Å/s, compared to 1–4 Å/s for PECVD materials. Our alloys exhibit similar trends with increasing Ge content to alloys grown by PECVD. The defect density, the dark conductivity, and the degree of nanostructural heterogeneity (as measured by small-angle X-ray scattering) all increase with increasing germanium content in the alloy. The nanostructural heterogeneity displays a sharp transition between 9 at.% and 14 at.% germanium. PECVD- grown a-SiGe:H alloys exhibit a similar transition at 20 at.% Ge. The photoconductivity and the ambipolar diffusion length of the alloys decrease with increasing germanium content. For a fixed silane-to-germane gas ratio, all material properties improve substantially when increasing substrate temperature (Tsub) from 220°C to 375°C. Increasing Tsub also narrows the optical bandgap and lowers the hydrogen content in the alloys for the same germane-to-silane gas ratio.
Internal Stress and Optical Degradation in a-Si:H Deposited on Glass Substrates
Authors: Nakata Jun-ichi , Miyako Tadayuki , Imao Shozo , Doi Atsutoshi
Published: April 2011

Internal stress in a-Si:H films prepared by plasma chemical vapor deposition was studied in connection with optical degradation or Staebler-Wronski effect (SWE). It was found that the stress increased with increasing discharge power density (0.03 ∼ 1.5 W/cm2) of silane, accompanied by increase in the introduction rate of SWE. These results imply that highly decomposed radical species due to high discharge power density dominate the surface reaction. Consequently, larger stress and larger introduction rate of SWE are brought about in the films. The stress also slightly increased at lower power density (< 0.03 W/cm2), suggesting that neutral silane molecules take part in the reaction at these power density.
Microcrystalline Silicon Growth: Deposition Rate Limiting Factors
Authors: Hamma S. , Colliquet D. , Cabarrocas P. Rocai
Published: April 2011

Microcrystalline silicon films were deposited on corning glass substrates both by the standard hydrogen dilution and the layer-by-layer (LBL) technique. In-situ UV-visible spectroscopic ellipsometry measurements were performed to analyze the evolution of the composition of the films.The change of the hydrogen plasma conditions by increasing the pressure in the LBL process leads to a faster kinetic of crystallization and to an increase of the deposition rate by a factor of two. The increase of the pressure and the decrease of the inter-electrode distance allowed to increase the deposition rate from 0.26 to 3 Å/s in the hydrogen dilution technique. Interestingly enough, the crystalline fraction of the films remains higher than 50%. However, as the deposition rate increases the growth process results in a slower kinetic of crystallization with a long range evolution of the film composition (up to 0.5 νm).
Photo-Leakage-Current Analysis of Poly-Si TFT by Using Rear Irradiation OBIC Method
Authors: Wakagi Masatoshi , Ookubo Tatsuya , Ando Masahiko , Kawachi Genshiro , Mimura Akio , Minemura Tetsuroh
Published: April 2011

Photo-leakage-current of poly-Si (polycrystalline Si) TFFs has been investigated by using the rear irradiation OBIC (Optical Beam Induced Current) method. In the case of the offset gate TFIs, it was found that the photo-leakage-current was generated in the offset region of the drain electrode side. In order to reduce the photo-leakage-current, low concentration phosphor (P) was doped in the offset region, which corresponds to LDD (Lightly Doped Drain) structure. In the LDD TFT, the photo leakage current at the offset region decreased remarkably, because of the reduction of hole transportation in this region.
Effect of Plasma Treatment on Crystallization Behavior of Amorphous Silicon Films
Authors: Pangal K. , Sturm J.C. , Wagner S.
Published: April 2011

The crystallization of amorphous silicon (a-Si:H) deposited by plasma enhanced chemical vapor deposition (PECVD) by thermal annealing is of great interest for display and silicon-on-insulator (SOI) technologies, though long anneal times (about 20 hrs) at 600 °C are typically required. We report that a room temperature hydrogen plasma exposure in a parallel plate diode type Reactive Ion Etcher (RIE) can reduce this crystallization time by a factor of five. This plasma enhanced crystallization can be spatially controlled by masking with patterned oxide, so that both amorphous and polycrystalline areas can be realized simultaneously at desired locations. This effect is due to the creation of seed nuclei at the surface, which enhance crystallization rates.
Low Temperature Vibrational Properties of Amorphous Silicon
Authors: Crandall R. S. , Iwaniczko E. , Mahan A. H. , Liu X. , Pohl R.O.
Published: April 2011

We present internal friction and shear modulus measurements of amorphous silicon (a-Si) and germanium (a-Ge) films. The temperature independent plateau in internal friction below 10 K, common to all amorphous solids, also exists in these films. However, its magnitude which depends critically on the deposition method is smaller than found for all other amorphous solids. In particular, hydrogenated a-Si with about 1 at. % H prepared by hot-wire chemical-vapor-deposition leads to an internal friction nearly three orders of magnitude smaller than observed for all other amorphous solids. The internal friction increases after the hydrogen is removed by effusion.
Absorption Strengths of Si-H Vibrational Modes in Hydrogenated Silicon
Authors: Beyer W. , Ghazala M.S. Abo
Published: April 2011

Infrared absorption data of various Si:H samples involving several series of a-Si:H films as well as µc-Si:H and c-Si:H samples were analyzed to obtain ratios of the absorption strengths A of the Si-H stretching modes at 2000 and 2100 cm−1 and of the Si-H wagging mode at 640 cm−1. Hydrogen effusion measurements were used to obtain the absolute values of A. The results suggest essentially equal absorption strengths for the two Si-H stretching modes and a ratio of wagging and stretching absorption strengths independent of hydrogen density NH. Films with predominant 2100 cm−1stretching absorption show a stronger sample dependence of A than observed for samples with predominant 2000 cm−1absorption. A slight increase of the absorption strength of the Si-H wagging and stretching modes with rising hydrogen concentration is observed for a-Si:H films and is attributed to the decrease of the refractive index. Enhanced A values of µc-Si:H samples compared to a-Si:H samples point to the presence of molecular hydrogen.
Performances of Nano/Amorphous Silicon Films Produced by Hot Wire Plasma Assisted Technique
Authors: Ferreira I. , Águas H. , Mendes L. , Fernandes F. , Fortunato E. , Martins R.
Published: April 2011

This work reports on the performances of undoped and n doped amorphous/nano-crystalline silicon films grown by hot wire plasma assisted technique. The film's structure (including the presence of several nanoparticles with sizes ranging from 5 nm to 50 nm), the composition (oxygen and hydrogen content) and the transport properties are highly dependent on the filament temperature and on the hydrogen dilution. The undoped films grown under low r.f. power (≍ 4 mWcm−2) and with filament temperatures around 1850 °K have dark conductivities below 10−1Scm−1, optical gaps of about 1.5 eV and photo-sensitivities above 105, (under AM3.5), with almost no traces of oxygen content. N- doped silicon films were also fabricated under the same conditions which attained conductivities of about 10−2Scm−1.
Interconnect Capacitance Extraction in Large-Area a-Si Imaging Systems
Authors: Pham H.H. , Nathan A.
Published: April 2011

We present a new numerical extraction method for the quasi-static parasitic coupling capacitances associated with geometric overlapping in amorphous silicon (a-Si) thin film transistors (TFTs) and interconnect addressing lines in large-area a-Si imaging systems. The capacitance is extracted using a recently developed computational technique, based on exponential expansion of the Green's function, which offers a quick and accurate means of computing the three-dimensional potential and electric field, and hence, the charge distribution and capacitance. The technique can be used for effectively dealing with the extreme geometry TFT and interconnect structures (where layer thicknesses are much smaller than the other physical dimensions), the floating potential of the glass substrate, and multidielectric media, all of which are typical to large-area a-Si imaging electronics.
NMR Detection of New Hydrogen Populations in Amorphous and Crystalline Silicon
Authors: Borzi R. , Cull T. S. , Fedders P. A. , Leopold D. J. , Norberg R. E. , Boyce J. B. , Johnson N. M. , Ready S. E. , Walker J.
Published: April 2011

Deuteron magnetic resonance (DMR) has been used to further examine hydrogen (deuteron) populations in amorphous-silicon (a-Si) and in n-type crystalline silicon (x-Si). In both a-Si and x-Si DMR shows central components arising at least in part from isolated molecular deuterium and sharp doublet features from Si-bonded hydrogen (D). Our new results include the observation in x-Si of molecule-specific DMR multiple echoes from trapped ortho-D2. A second new result is the observation in x-Si of a substantialn Si-bonded D population with splittings between 46 and 80 kHz and perhaps arising from (deuterated) hydrogen bond-centered and antibonding configurations.
Wandering Dangling Bond Model for Staebler-Wronski Effects
Authors: Ikeda Masatoshi , Kitagawa Akio , Suzuki Masakuni
Published: April 2011

A new model for Staebler-Wronski effects is proposed. Defect pairs of (D°:D+) or (D°:D°) as a precursor of neutral dangling bonds are produced by electron-phonon interactions. Most of the defect-pairs immediately rebond after creation, but some of them separate resulting in wandering dangling bonds. The separation and the wandering take place through bond-switching. When wandering dangling bonds collide, most of them make covalent bonds via defect-pairs. The rate equations based on these processes are given and annealing effects on photo-generated dangling bonds are studied.
Light-Excited Structural Instability of a-Si:H
Authors: Kong G.L. , Zhang D.L. , Yue G.Z. , Wang Y.Q. , Liao X.B.
Published: April 2011

With the accumulation of experimental data, it has been recognized by many that the light-induced metastable change of a-Si:H, Staebler-Wronski effect (SWE), may be related to a structural instability of the whole a-Si:H network. However, direct evidence of such a structural change is still lacking. In the present paper, the efforts of our laboratory in this direction will be reviewed, including the light-induced changes of Si-H bond absorption, low frequency dielectric response, and an apparent photo-dilation effect.
Bonded Hydrogen Atom Participation in Metastable Defect Formation in Hydrogenated Amorphous Silicon
Authors: Lucovsky G. , Yang H.
Published: April 2011

This paper proposes intrinsic reaction pathways for generation of metastable defects in hydrogenated undoped or intrinsic amorphous silicon (i-a-Si:H). Since these pathways involve only silicon (Si) and hydrogen (H) atoms, this approach is valid for device grade materials in which concentrations of oxygen (0) atoms, and nitrogen-hydrogen (N-H) groups are present at concentrations below about 1019 cm−3. Ab initio calculations demonstrate that the proposed generation pathway reactions are exothermic with relatively small reaction barriers (< 0.4 eV).
Effect of Nh3/SiH4 Gas Ratios of Top Nitride Layer on Stability and Leakage in a-Si:H Thin Film Transistors
Authors: Murthy R.V.R. , Ma Q. , Nathan A. , Chamberlain S.G.
Published: April 2011

In this paper, we present measurement results of stability and leakage current characteristics in inverted staggered hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) for different compositions of the top (passivation) nitride (a-SiNx:H). Here, we varied the deposition parameters, i.e., the ammonia (NH3) to silane (SiH4) gas ratio, of the passivation material for fixed composition of the (nitrogen-rich) gate nitride. When stressed with a prolonged gate bias, the observed shift in both threshold voltage (VT) and leakage current was largest in samples where the gas ratio (R = NH3/SiH4) was small. In the samples considered, R varied from 5 to 25. The shift in VT can be attributed to injection of energetic carriers from the a-Si:H and their subsequent trapping in the top a-SiNx:H layer. The trapping is reduced when the layer is nitrogen-rich.
Excitation Energy Dependence of Photoinduced Absorption in Intrinsic a-Si:H
Authors: Schultz N. , Vardeny Z.V. , Taylor P.C.
Published: April 2011

We have studied subgap absorption of intrinsic a-Si:H induced by below- and above-gap photo-excitation. We find very similar photoinduced subgap absorption spectra when excited with 2.4 eV or 1.2 eV light. Both spectra exhibit a power-law dependence on laser intensity ΔT ∼ 1a, where a is 0.5 and 0.7 for 2.4 and 1.2 eV excitation energy, respectively. This behavior indicates a change in the recombination mechanism as a function of excitation energy. The PA spectrum excited at 1.2 eV shows a strong dependence on bias illumination. Bias illumination bleaches the absorption according to a power-law as ΔT = c(Ebias)·Iβ, where β is approximately 0.85 and independent of probe energy and bias energy. The parameter c(Ebias) increases superlinearly with bias illumination energy for Ebias > 1.7 eV.
The Intuitive Thermalisation Model Compared to Explicit Multiple Trapping Calculations
Authors: Feist H. , Aichberger S. v. , Kunst M.
Published: April 2011

A simple model (the HTMT model) describing the interaction of excess mobile charge carriers with an exponential bandtail is presented. The new model differs from the commonly used intuitive thermalization (TROK) model only by the definition of the demarcation energy. By comparison of the results of the TROK and the HTMT model with numerical calculation of the interaction it is shown that the HTMT model yields an adequate description, whereas the TROK model does not reproduce the absolute values and also has a deviating time dependence at higher temperatures. The origin of these differences is discussed.
Odmr Measurements of Microcrystalline Silicon
Authors: Malten C. , Carius R. , Finger F. , Yamasaki S.
Published: April 2011

Undoped microcrystalline silicon films of high crystalline volume fraction were studied by optically detected magnetic resonance (ODMR). Luminescence energies peak at 0.88 eV and emission at 1.3 eV arising from amorphous tissue is negligible. Recombination involving dangling bonds (g=2.0052, g=2.0043) in disordered regions or crystallites and shallow states near the conduction band (g= 1.998) in the crystalline parts of the material are observed. At temperatures below 30 K a very broad feature of approximately 1000 G width is observed, possibly originating from two separate resonances with high g-values of g=2.1 and g=2.08. We suggest the origin to be of hole-states near or in the valence band. No evidence for excitonic recombination was found. Frequency response indicates ODMR lifetimes of all resonances in the range of 10−5s to 10−4s.
Application of Thin-Film Micromachining on Glass
Authors: Boucinha M. , Chu V. , Conde J.P.
Published: April 2011

Three dimensional microstructures have been made on glass substrates using surface micromachining techniques. Bridge structures were fabricated using both hydrogenated amorphous silicon and microcrystalline silicon. A low density silicon nitride with an etch rate of 100 Å/s in buffered HF was used as the sacrificial layer. As an example of how micromachining can be applied to large area electronics, thin film transistors (TFT) with the dielectric replaced by an air-gap were fabricated. The electrical characteristics of the first working devices are presented.
Deposition of Highly Conductive n+ Silicon Film for a-Si:H Thin Film Transistor
Authors: Kuo Yue , Latzko K.
Published: April 2011

Plasma enhanced chemical vapor deposition of phosphorus-doped n+ silicon film over a wide range of process conditions has been studied. The deposited films were characterized with SIMS, Raman, and XRD. An unusually abrupt change of resistivity over a small SiH4(1% PH3) flow rate has been observed and was correlated to the variation of the film's morphology from amorphous to micrycrystalline. The grains are less than 50 Å in size and has strong <111> orientation. Amorphous silicon thin film transistors with microcrystalline n+ source and drain contacts have consistently good device characteristics. However, the contact resistance is comparable to the channel resistance when the channel length approaches 1 micrometer.
The Influence of Electrons From the Filament on the Material Properties of Hydrogenated Amorphous Silicon Grown by the Hot-Wire Chemical Vapor Deposition Technique
Authors: Nelson Brent P. , Wang Qi , Iwaniczko Eugene , Mahan A.H. , Crandall R.S.
Published: April 2011

We observe that under certain conditions, hydrogenated amorphous silicon grown by the hotwire chemical-vapor deposition technique has dark conductivities varying by several orders of magnitude across the same film. Similarly, the ambipolar diffusion lengths fluctuate significantly in these films, yet there is not much evidence of a corresponding structural change. We attribute this electronic nonuniformity to electrons from the filament reaching insulating substrates and charging the substrate negatively in some regions, thus causing films to grow with inferior material properties in those regions. The effect diminishes with increasing substrate temperature, where the film itself may be conductive enough to remove charge reaching the growing surface. Wellgrounded, conducting substrates seem to be immune from this effect. We reduce this effect by putting a conductive grid on insulating substrates, of close enough spacing to remove the charge, and measure the material properties of the film grown between the conductive elements of the grid.
New Excimer Laser Crystallization in the Lattice Shape to Improve the Uniformity of Electrical Characteristics of Poly-Si TFT
Authors: Jeon Jae-Hong , Park Cheol-Min , Park Kee-Chan , Lee Min-Cheol , Han Min-Koo
Published: April 2011

Abstarct

The new laser annealing technique to control the surface morphology and microstructure of poly-Si film is proposed. Compared with the conventional laser annealing technique where the laser beam is irradiated on the whole area of active layer, our new method make the laser beam transmitted locally onto the active amorphous silicon (a-Si) layer. Using the masking window in grid shape, the active layer is recrystallized in the lattice shape during the laser irradiation. By the optical microscope and scanning electron microscopy (SEM), we observed the orderly pattern, which consists of amorphous and poly-Si regions. In our new poly-Si film, the rough surface morphology, which is shown in conventional sample, could not be found. Furthermore we fabricated a poly-Si TFT utilizing the active poly-Si film recrystallized by our new method. The new poly-Si TFT showed much higher ON current than the conventional poly-Si TFT, although the leakage current is relatively high. The excellent ON characteristics may be attributed to the uniform surface morphology. After hydrogenation, the electrical characteristics of our new polySi TFT was improved considerably and this device may be applied successfully to the active matrix liquid crystal displays (AMLCD's).
Thin-Film Transistors Fabricated With Poly-Si Films Crystallized by Microwave Annealing
Authors: Choi YongWoo , Lee JeongNo , Jang TaeWoong , Ahn ByungTae
Published: April 2011

Solid phase crystallization has the advantages of low cost and excellent uniformity but the crystallization temperature is too high to use glass as a substrate. Using microwave annealing, we crystallized a-Si films at 550 °C within 3 h, which is much shorter than the annealing time at 600 °C of furnace annealing. We fabricated TFTs with poly-Si films crystallized by microwave annealing at low temperature and obtained the characteristics slightly better than or at least comparable to the TFTs by furnace annealing in spite of smaller grain size. This may be due to the improvement of surface roughness of poly-Si film. The poly-Si TFTs with PECVD a-Si film showed better characteristics than the TFTs with LPCVD a-Si film because of larger grain size and smoother Si/SiO2 interface.
Low-Temperature Formation of SiNx Gate Insulator for Thin-Film Transistor Using CAT-CVD Method
Authors: Izumi A. , Ichise T. , Matsumura H.
Published: April 2011

Silicon nitride films prepared by low temperatures are widely applicable as gate insulator films of thin film transistors of liquid crystal displays. In this work, silicon nitride films are formed around 300 °C by deposition and direct nitridation methods in a catalytic chemical vapor deposition system. The properties of the silicon nitride films are investigated. It is found that, 1) the breakdown electric field is over 9MV/cm, 2) the surface state density is about 1011cm−2eV−1 are observed in the deposition films. These result shows the usefulness of the catalytic chemical vapor deposition silicon nitride films as gate insulator material for thin film transistors.
Role of RF Power and Gas Mixture in Some Optical and Photoluminescence Properties of Dual-Plasma a-C:H Films
Authors: Heitz T. , Godet C. , Bouree J.E. , Drevillon B. , Chu V. , Conde J.P. , Clerc C.
Published: April 2011

Electronic properties of polymer-like hydrogenated amorphous carbon films, grown in a RF-assisted microwave plasma reactor, have been studied using optical absorption and photoluminescence spectroscopies. Using a Forouhi-Bloomer parametrization of π-π* transitions, two regimes are evidenced for increasing C atom density : a decrease of the optical gap Eππ* at constant (H/H+C) content attributed to sp2C clustering, followed by some H elimination with minor changes in Eππ* due to cross-linking of polymer chains. The photoluminescence efficiency in the visible range (peak at ≈ 2.3 eV) is found to decrease over four orders of magnitude at the onset of the cross-linking regime. This quenching is attributed to stress-induced non-radiative centers.
All Printed Bistable Reflective Displays: Printable Electrophoretic Ink and All Printed Metal-Insulator-Metal Diodes
Authors: Park Jaeyong , Jacobson Joseph M.
Published: April 2011

We have printed Metal-Insulator-Metal Diodes onto flexible substrates using hybrid polymer and metal-metal oxide inks. Successful device structures were printed by means of several processes including 1] a two step process of Ta in polymer matrix with thermally grown oxide followed by printed Cr in polymer and 2] a one step process of pre-oxidized Ta microparticles in polymer. Back-to-back diode I-V characteristics were demonstrated with tunable turn-on voltages between 5V and 100V. Coupled with a fully printable bistable, electronically addressable electrophoretic ink which we have developed, such systems open the way for all printed, reflective, bistable electronic displays.
Effects of Ultraviolet-Light on Polyimide Films for Liquid Crystal Alignment
Authors: Gong Shaoqin , Kanicki Jerzy , Ma Lan , Zhong John Z. Z.
Published: April 2011

UV-light effects on the polyimide films have been studied by characterizing the film property changes and by measuring the liquid crystal pretilt angle. Infrared, UV-visible and X-ray photoelectron spectroscopy measurements indicate that bond-breaking and oxidation occur during broadband UV-illumination of the film in the air. Free radicals are formed during UV-illumination as evidenced by the analysis of electron spin resonance spectra. Surface tension and polarity are increased after UV-illumination based on the contact angle measurements. While the pretilt angle on the rubbed polyimide film is decreased after nonpolarized UV-illumination, polarized UV-light generates a relatively small pretilt angle on a nonrubbed surface.
Structure of Ions in Liquid-Crystalline Materials
Authors: Naemura Shohei , Nakazono Yuji , Nishikawa Kenichi , Sawada Atsushi , Kirsch Peer , Bremer Matthias , Tarumi Kazuaki
Published: April 2011

Both steady-state current and dielectric-loss measurements were performed on a liquid-crystalline material, 4-(trans-4-pentylcyclohexyl)benzonitryl, in an isotropic liquid phase, which provide information on generation and behavior of ions, dominating DC and AC conductivity, respectively. The frequency dependence measurements of dielectric-loss can successfully estimate such characteristics of ions as total quantity of electricity, diffusion constant (mobility), and the size. With help of chemical analysis like ion chromatography and semi-empirical quantum chemical computation, the majority of ions, especially dominating AC conductivity, were estimated to be inorganic cations with Stokes' radius of around 2 × 10−8(cm), either naked or hydrated, and solvated ions with Stokes' radius of around 5 × 10−8(cm), most probably with the liquid-crystalline molecules at the solvation number of 1.2 in average. The present microscopic investigation of conduction mechanism is of great help for development of liquid-crystalline materials, especially for use in sophisticated displays with excellent picture quality.
Electroluminescent Displays
Authors: King Christopher N.
Published: April 2011

This paper will review the electrical and optical properties of both monochrome and color electroluminescent (EL) displays. A simple electrical model for thin film electroluminescent (TFEL) device operation will be presented and used to describe the luminance and power consumption of TFEL devices. The basic material characteristics desirable for EL phosphors will be described. Progress in the development of monochrome and color EL displays will be presented including TFEL and Active Matrix EL devices and phosphors.
Stepped Gate Polysilicon Thin-Film Transistor for Large Area Power Applications
Authors: Aschenbeck J. , Chen Y. , Clough F. , Xu Y. Z. , Sankara Narayanan E. M. , Milne W. I.
Published: April 2011

For the first time, we report a new poly-Si stepped gate Thin Film Transistor (SG TFT) on glass. The Density of States extracted from measured I-V characteristics has been used to evaluate the device performance with a two dimensional device simulator. The results show that the three-terminal SG TFT device has a switching speed comparable to a low voltage structure and the high on-current capability of a metal field plate (MFP) TFT and the potential for comparable breakdown characteristics.
Electron Beam Degradation of Sulfide-Based Thin-Film Phosphors for Field Emission Flat Panel Displays
Authors: Abrams B.L. , Trottier T.A. , Swart H.C. , Lambers E. , Holloway P.H.
Published: April 2011

The change in cathodoluminescence (CL) brightness and changes in surface chemistry of the thin film phosphor, SrS:Ce, have been investigated using a scanning Auger electron spectrometer and an Oriel optical spectrometer. The data for SrS:Ce were compared to ZnS:Cu, Al, Au and Y2O2S:Eu powders all collected in a stainless steel UHV chamber with gas pressures of 10−6 Torr O2. In the presence of a 2kV primary electron beam, the amounts of C and S on the surface decreased while the oxygen concentration increased. As a result, ZnO, Y2O3 and presumably SrOx formed. This change in surface chemistry coincided with a decrease in CL brightness. SrS degraded much faster than ZnS or Y2O2S. The model for this degradation process suggests that the primary electron beam dissociated physisorbed molecules to reactive atomic species. These atomic species reacted with surface S and C, carrying them away and leaving behind an increasingly more impenetrable layer. Threshold voltage experiments were conducted to reveal where it becomes possible to measure the CL. This threshold voltage should be affected by the oxide layer discussed above. The implications for vacuums in an FED FPD will be discussed.
Advances in the Growth of SrS Thin Films by Pulsed Laser Deposition
Authors: Piqué A. , Auyeung R. C. Y. , Chrisey D. B. , Justus B. , Huston A. , Revaya R. E. , Frazier B.
Published: April 2011

High quality luminescent thin films of strontium sulfide (SrS) doped with rare earths have been grown using Pulsed Laser Deposition (PLD). SrS films ranging in thicknesses from 0.05 to 2 µm. were deposited on MgO (001) and glass substrates. Deposition parameters such as growth temperature and H2S background gas pressure were varied and their effect on the structure, morphology and luminescence of the films was evaluated. The PLD grown films all showed texture and were highly oriented when deposited on MgO substrates as determined by their XRD spectra. Optical microscopy, SEM and AFM analysis were used to study the films' surface morphology. The thermally and optically stimulated luminescence properties of these films were evaluated as well. The data indicates that these materials may be useful for optical data storage applications.
Cobalt and Nickel for Improved Aluminum-Indium Tin Oxide Contact Metallurgy in Polysilicon TFT Display Applications
Authors: Howell Robert S. , Saha Sambit K. , Hatalis Miltiadis K.
Published: April 2011

Among the issues associated with the fabrication of polysilicon thin film transistor (TFT) active matrix displays is the contact resistance between indium tin oxide (ITO) pixel electrodes and the aluminum data lines. We have investigated the use of Co and Ni for use as barrier layers between the Al and ITO in order to provide good ohmic contacts. For comparison, a titanium barrier layer has also been used and measured. A thin, 10 nm Co layer sufficed to provide good ohmic contacts in an ITO-Co-Al stack, while a thicker layer was required in the case of Ni in order to form a similar good ohmic contact. The contacts have been characterized using resistance measurements in conjunction with X-ray photo-electron spectroscopy (XPS) and X-ray diffraction (XRD) in order to correlate the electrical results with the physical metallurgy of the contacts.