bluuebunny/crossref_metadata_2025 huggingface dataset:
RHEED Observation of Tin Atomic Chains Formation on Vicinal Gallium Arsenide Plane
Authors: Senichkin Aleksey , Bugaev Aleksandr , Mokerov Vladimir
Published: April 2011

In the present work by means of measurements of RHEED intensity the research of the arrangement of tin atoms on vicinal surfaces of GaAs crystals was carried out. The orientation of crystals was close to (001). The intensity of diffracted electrons was measured in different points of the diffraction picture to reveal the arrangement of tin atoms on terraces or on edges of terraces. It was shown that tin atoms may decorate edges of terraces and thus form chains. Concentrations of tin atoms located on terraces and their edges were established. It was revealed, that tin atoms decorate edges of terraces only at rather high temperatures of a substrate.
A Hydrogen-Bonding Based Approach to Fabricate Polymer/Inorganic Nanoparticle Multilayer Film
Authors: Hao Encai , Lian Tianquan
Published: April 2011

A new hydrogen-bonding based route for layer-by-layer fabrication of polymer/inorganic nanoparticle multilayer thin films was developed. Surface modification of inorganic nanoparticles can provide functional groups on the particle surface, e.g. pyridine, carboxyl, and flavin. A polymer/inorganic nanoparticle multilayer film can be fabricated in a layer-by-layer manner using the hydrogen-bonding interaction between the functional groups on the surface of nanoparticles and polymers. The multilayer buildup was monitored by UV-visible spectroscopy, which showed a linear increase of the film absorbance with the number of adsorbed nanoparticle layers. FTIR spectroscopy was used to verify hydrogen bonding between polymer and nanoparticles, which is believed to be the driving force for the formation of polymer/nanoparticle multilayer thin films.
Fabrication of Multilayer Films Using a Spinning Process
Authors: Cho Jinhan , Char Kookheon , Hong Jong-Dal , Lee Ki-Bong
Published: April 2011

We introduce a method to build up organic/organic and organic/inorganic multilayer films composed of cationic poly(allylamine hydrochloride) (PAH) and negatively charged poly(sodium 4-styrenesulfonate) (PSS) or inorganic cadmium sulfide (CdS) nanoparticles using a spinning process. Since the deposition of each layer is made at a high spinning speed, the adsorption time for the formation of a homogeneous thin layer takes only 8 to 15 seconds. The adsorbed film thickness per bilayer can be easily controlled from about 5Å to 40Å by varying the spinning speed (Ω) and the mole concentration of polyelectrolytes. We also demonstrated with X-ray reflectivity that the alternating organic/inorganic ultrathin films fabricated by the spin SA process retain highly ordered internal structure in comparison with those prepared by the conventional SA process.
Monte Carlo Simulation of Vapour Deposition of Nonstoichiometric Amorphous Silica
Authors: Burlakov V. M. , Tsukahara Y. , Briggs G. A. D. , Sutton A. P.
Published: April 2011

Monte Carlo simulation of deposition of nonstoichiometric amorphous SiOx nanolayers from vapor phase onto a polymer surface is reported. The model developed is based on the network properties of silica and takes into account dangling bonds arising during the real process of deposition. The model is validated via comparison of the radial- and bond angle distribution functions for the simulated Si and SiO2 structures with those obtained from experiment for bulk materials. Porosity of the simulated amorphous layer is characterized by the relative volume of pores and the ratio of the pore surfaces to the pore volume. We found that porosity strongly depends on nucleation sites density (NSD) on the polymer substrate. At NSD lower than 1 nm−2 the porosity may reach as much as 30% of the layer volume, while at NSD higher than 4 nm−2 it decreases down to 3-7%. Possible implications of the obtained results are discussed.
Elastic Properties of Diamond-Like Amorphous Carbon Films Grown by Computer Simulation of Ion-Beam Deposition Process
Authors: Belov A.Yu. , Jäger H.U.
Published: April 2011

Atomic-scale calculations were performed for the first time to investigate mechanical properties of amorphous carbon films grown by a realistic simulation of ion-beam deposition. The simulated films have a thickness of a few nanometers and reproduce the main structural features of real films, with the bulk content of sp3 bonded atoms varying from 35 to 95%, depending on the ion energy (E = 20-80 eV). Employing empirical interatomic potentials for carbon, the average bulk stresses as well as the atomic-level stress distributions were calculated and analysed. The bulk stresses were found to depend not only on the ion energy, but also on the film quality, in particular, on such structural inhomogeneities as local fluctuations of the sp3 fraction with the depth. The local variation of the bulk stress from the average value considerably increases as the local content of sp2 bonded atoms increases. Elastic constants of amorphous carbon films were also computed using the method of inner elastic constants, which allows for the stress dependence of elastic constants to be analysed. The variation of Young's modulus as a function of the lateral bulk stress in an amorphous film is demonstrated.
STM characterization of Cu thin films grown by direct ion deposition
Authors: Pomeroy Joshua M. , Couture Aaron , Jacobsen Joachim , Hill Colin C. , Sethna James P. , Cooper Barbara H. , Brock Joel D.
Published: April 2011

In certain cases, the incidence energy of constituent atoms activates an atomistic insertion mechanism, which decreases the surface roughness of metal thin films. In an effort to probe this effect, homoepitaxial copper films were grown using a mass/energy selected direct ion deposition technique that allows precise control of the incidence energy. Surface roughness is measured using a Scanning Tunneling Microscope (STM) within the same UHV surface analysis system. The activation of the insertion mechanism near 20 eV triggers smoother crystal growth. The beneficial effects begin to be obscured by adatom/vacancy creation near 30 eV. A sophisticated Kinetic Monte Carlo/Molecular Dynamics (KMC-MD) model supports this interpretation.
Synthesis and Crystal Chemistry of New Transition Metal Tellurium Oxides in Compounds Containing Lead and Barium
Authors: Wedel Boris , Sugiyama Katsumasa , Itagaki Kimio , Müller-Buschbaum Hanskarl
Published: April 2011

During the past decades the solid state chemistry of tellurium oxides has been enriched by a series of quaternary metallates. Interest attaches not only to the chemical and physical properties of these compounds, but also to their structure, which have been studied by modern methods. The partial similarity of earth alkaline metals and lead in solid state chemistry and their relationships in oxides opens a wide field of investigations. Eight new compounds in the systems Ba-M-Te-O (M= Nb, Ta) and Pb-M-Te-O (M = Mn, Ni, Cu, Zn) were prepared and structurally characterized: Ba2Nb2TeO10, Ba2M6Te2O21 (M = Nb, Ta) and the lead compounds PbMnTeO3, Pb3Ni4.5Te2.5O15, PbCu3TeO7, PbZn4SiTeO10 and the mixed compound PbMn2Ni6Te3O18. The structures of all compounds are based on frameworks of edge and corner sharing oxygen octahedra of the transition metal and the tellurium. Various different channel structures were observed and distinguished. The compounds were prepared by heating from mixtures of the oxides, and the single crystals were grown by flux method or solid state reactions on air. The synthesis conditions were modified to obtained microcrystalline material for purification and structural characterizations, which were carried out using a variety of tools including powder diffraction data and refinements of X-ray data. Relationships between lead transition metal tellurium oxides and the earth alkaline transition metals tellurium oxides are compared.
Resistive Anomaly Relevant to Nd Moments in the Antiferromagnetic Phase of the Bandwidth-Controlled Manganites
Authors: Kuwahara H. , Noda K. , Kawasaki R.
Published: April 2011

We have investigated the electronic and magnetic properties of (Nd1−ySmy)0.45Sr0.55MnO3(0≤y≤1) crystals, in which one-electron bandwidth (W ) is systematically decreased from the parent compound (y=0) with increase of y. We have found remarkable magnetic phase transition concerning the change of rare-earth (RE) moments in low temperatures below 25 K. The subtle drop in resistivity superimposed upon the spin-valve like magnetoresistance (MR) was observed for the isothermal MR measurements, e.g. δρ(H)|ρ(H')≍4.7% at 3.5 T and 4 K. The phase transition fields corresponding to these concomitant magnetic and resistive changes monotonically decrease with temperature and disappear above ∼25 K. It turned out that the resistive drop is due to the field-induced increase of magnetic moments ofRE ions from magnetization measurements. The field-induced phase transition from the small moment state to the large one in RE ions can be explained in terms of energy level crossing between the crystal-field-split J multiplets by the Zeeman effect.
Competitive Adsorption of O2 and H2O at the Neutral and Defective SnO2 (110) Surface
Authors: Slater Ben , Catlow C. Richard A. , Williams David E. , Stoneham A. Marshall
Published: April 2011

Using first principles techniques we have examined the relative physisorption/chemisorption energetics of neutral molecular water and oxygen at the most thermodynamically stable surface (110) of tin dioxide. We find that water binds more strongly to the perfect surface at 5 co- ordinate tin sites than oxygen. However, binding of both water and oxygen at bridging oxygen vacancies in the defective surface is comparable. In the context of gas-sensing behaviour at moderate temperatures (∼300K), we propose that the Mars and van Krevelen [1] re-oxidation reaction will slow when the partial pressure of water is high, since the number of favourable adsorption sites will effectively decrease. In addition, one would expect that the surface conductivity will increase, since the re-oxidation reaction will be hindered.
Towards Stabilized 10% Efficiency of Large-Area (> 5000cm2) a-Si/a-SiGe Tandem Solar Cells using High-Rate Deposition
Authors: Okamoto Shingo , Terakawa Akira , Maruyama Eiji , Shinohara Wataru , Tanaka Makoto , Kiyama Seiichi
Published: April 2011

This paper reviews recent progress in large-area a-Si/a-SiGe tandem solar cells in Sanyo. Much effort has been devoted to increasing both the stabilized efficiency and the process throughput. A key issue in increasing the stabilized efficiency is thinner i-layer structure with an improved optical confinement effect. High-rate deposition of the i-layers has been investigated using rf (13.56MHz) plasma-CVD method while keeping the substrate temperature below 200 °C. A high photosensitivity of 106 of a-Si:H films maintain up to the deposition rate (Rd) of 15 Å/s by optimizing hydrogen dilution and other deposition conditions. It is of great importance to utilize the effect of hydrogen dilution which can reduce the incorporation of excess hydrogen in the films. The world's highest conversion efficiency of 11.2% has been achieved for a large-area (8252cm2) a-Si/a-SiGe tandem by combining the optimized hydrogen dilution and other solar cell related technologies.
Defect Creation by Electron Beam Irradiation in Amorphous Silicon Nitride Films Compared with That by Light Soaking
Authors: Shimizu Tatsuo , Kawashima Yuji , Kumeda Minoru
Published: April 2011

Defect creation by electron beam irradiation is compared with that by light soaking in a-Si1-xNx:H films. For the film with x=0.06, the ESR spin density increases by 20-keV electron beam irradiation without changes in the g-value. However, for the film with x=0.47, the ESR spin density increases with accompanying the decrease in the g-value from 2.0042 to 2.0034. The decrease in the g-value can be explained by increasing number of N atoms at the backbond site of the Si atom having the dangling bond. Light soakings does not change the g-value of the ESR signals of the films.
Structural Properties of Microcrystalline Si Solar Cells
Authors: Luysberg M. , Scholten C. , Houben L. , Carius R. , Finger F. , Vetterl O.
Published: April 2011

The structural properties of nip-µc-Si:H solar cells are investigated by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. Different structural compositions are obtained by variation of the gas mixture during preparation by plasma enhanced chemical vapour deposition. Nucleation and growth of the n-layer onto textured TCO substrate was found to be similar to the growth on glass substrates. The growth of the i-layer follows a local epitaxy. This implies that the structure of the n-layer is of special importance regarding the control of the microstructure in microcrystalline Si nip solar cells.
Improved interface between front TCO and microcrystalline silicon p-i-n solar cells.
Authors: Vallat-Sauvain E. , Faÿ S. , Dubail S. , Meier J. , Bailat J. , Kroll U. , Shah A.
Published: April 2011

The microstructure of microcrystalline silicon p-layers on zinc oxyde (ZnO) has been studied by Transmission Electron Microscopy (TEM). ZnO has been characterised by X-Rays diffraction and by Scanning Electron Microscopy (SEM). These reveal that the ZnO surface topography consists of regular pyramids with a (110) preferential crystallographic growth axis. High Resolution TEM observations indicate that the p- layer growth starts at the top of the ZnO pyramids. This results, for fully microcrystalline p-layers, in a decreased thickness at the bottom of the ZnO pyramids. When the p-layer is fully microcrystalline, no amorphous incubation layer could be observed between ZnO and p-silicon layer. Moreover, the high crystallinity of the p-layers in microcrystalline p-i-n devices is accompanied by an increased fill-factor in the I-V characteristics.
Microcrystalline Silicon Thin-Film Solar Cells Prepared at Low Temperature
Authors: Nasuno Y. , Kondo M. , Matsuda A.
Published: April 2011

Hydrogenated microcrystalline silicon (µc-Si:H) p-i-n solar cells have been prepared using a conventional RF plasma-enhanced chemical vapor deposition (PECVD) method at a low process temperature of 140 °C. The low temperature deposition of µc-Si:H has been found to be effective to suppress the formation of oxygen-related donors that cause a reduction in open circuit voltage (Voc) due to shunt leakage. We demonstrate the improvement of Voc by lowering the deposition temperature down to 140, while suppressing the reduction in high short circuit current density (Jsc) and fill factor (FF). A high efficiency of 8.9% was obtained using an Aasahi-U substrate. Furthermore, by optimizing textured structures on ZnO transparent conductive oxide (TCO) substrates, an efficiency of 9.4% (Voc=0.526V, Jsc=25.3mA/cm2, FF=0.710) was obtained. In addition, relatively high efficiency of 8.1% was achieved using VHF (60MHz) plasma at a deposition rate of 12 Å/s. Thus, this low temperature deposition technique for µc-Si:H is promising for both high efficiency and high rate deposition of µc-Si:H solar cells.
Evolution of the Mobility Gap with Thickness in Hydrogen-Diluted Intrinsic Si:H Materials in the Phase Transition Region and Its Effect on p-i-n Solar Cell Characteristics
Authors: Koval R.J. , Pearce J.M. , Ferlauto A.S. , Collins R.W. , Wronski C.R.
Published: April 2011

Insights into the growth processes and evolution of microstructure in intrinsic hydrogenated silicon (Si:H) films obtained from real-time spectroscopic ellipsometry (RTSE) are extended to the characterization of the optoelectronic properties of the corresponding solar cells. To assess the effects of transition regions from the amorphous to mixed microcrystalline phases, cell structures with and without such regions at different depths in the i-layer from the p-contact have been investigated. Experimental results are presented that clearly demonstrate changes in the mobility gap, Eµ, of the materials as their microstructure evolves with thickness, further supporting the important effect of the hydrogen dilution ratio R (R[H2]/[SiH4]) on the transition between the amorphous and microcrystalline phases. Light J-V characteristics at room temperature and dark J-V characteristics at different temperatures were measured on p(a-SiC:H:B)-i(Si:H)-n(µc-Si:H:P) solar cell structures with i-layers of different thicknesses and R values. The mobility gaps of both the amorphous and microcrystalline intrinsic-layer materials as well as those of the transition layers are obtained from dark J(V,T) measurements. Using numerical simulation, both the light and the dark J-V characteristics are self-consistently modeled assuming sharp changes in the mobility gaps at the intrinsic layer transition thicknesses determined by RTSE.
Defect Density Profiling in Light-Soaked and Annealed Hydrogenated Amorphous Silicon Solar Cells
Authors: Crandall Richard S. , Yang Jeffrey , Guha Subhendu
Published: April 2011

The fundamental ingredient lacking in solar cell modeling is the spatial distribution of defects. To gain this information, we use drive-level capacitance profiling (DLCP) on hydrogenated amorphous silicon solar cells. We find the following: Near the p-i interface the defect density is high, decreasing rapidly into the interior, reaching low values in the central region of the cell, and rising rapidly again at the n-i interface. The states in the central region are neutral dangling-bond defects whose density agrees with those typically found in similar films. However, those near the interfaces with the doped layers are charged dangling bonds in agreement with the predictions of defect thermodynamics. We correlate the changes in solar cell efficiency owing to intense illumination with changes in the defect density throughout the cell. Defects in the central region of the cell increase to values typically found in companion films. We describe the measurements and interpretation of DLCP for solar cells with the aid of a solar cell simulation.
Photoluminescence Study of Self-Limiting Oxidation in Nanocrystalline Silicon Quantum Dots
Authors: Arai Kenta , Omachi Junichi , Nishiguchi Katsuhiko , Oda Shunri
Published: April 2011

We have studied photoluminescence (PL) of surface oxidized nanocrystalline silicon quantum dots (QDs) for various oxidation periods and temperatures. With increasing oxidation period, the surface oxide grows and the Si QD core shrinks initially, then retardation of the oxidation process occurs which is ascribed to compressive stress at the interface between Si QD core and oxide. Upon oxidation, the PL spectrum peak shifts toward the shorter wavelength side followed by retardation of the blueshift or even manifestation of the redshift. The origin of PL is due to the localized excitons at the interface between Si QD core and oxide or amorphous SiOx (a-SiOx) formed at the interface. The blueshift is associated with the increased quantum con.nement or increased bandgap of a-SiOx. The redshift is due to the stress e.ect of the bandgap of Si QD core or a-SiOx. We have successfully confirmed the effect of compressive stress associated with the self-limiting oxidation by PL measurement.
Carrier transport and photogeneration in large area p-i-n Si/SiC heterojunctions
Authors: Louro P. , Vygranenko Yu. , Schwarz R. , Fernandes M. , Vieira M. , Gloeckner J. , Schubert M.
Published: April 2011

Glass/ZnO:Al/p (SixC1−x:H)/i (Si:H)/n (SixC1−x:H)/Al (0<x<1) heterojunction cells were produced by PE-CVD at low temperature. Junction properties, carrier transport and photogeneration are investigated from illuminated current- and capacitance- voltage characteristics and spectral response measurements, in dark and under different illumination conditions. For the heterojunction cells high series resistance around 106 ω and atypical J-V characteristics are observed leading to poor fill factors, also it was observed that the responsivity decreases with the increase of the light bias intensity. For the homojunction the behaviour is typical of a non optimised p-i-n cell and the responsivity varies only slightly with the light bias conditions. A numerical simulation gives insight into the transport mechanism suggesting that in the heterojunctions and in dark conditions the transport mechanism depends almost exclusively on field-aided drift while under illumination it is dependent mainly on the diffusion of free carriers.
Microcrystalline Germanium Carbide: A New, Almost Direct Gap, Thin Film Material for Photovoltaic Energy Conversion
Authors: Dalal Vikram L. , Herrold Jason T.
Published: April 2011

We report on the growth and electrical and optical properties of micro- and poly- crystalline Ge1−x Cxfilms. This is a new material which does not exist in nature. The films were grown using ECR plasma techniques under conditions of low pressure and high power from a mixture of germane, methane and hydrogen. The bandgap of the material could be varied from that of c-Ge (∼0.7 eV) to almost 1.15 eV by changing the methane/germane ratio. X ray diffraction and Raman measurements indicated good crystallinity in the film. The optical absorption spectrum of the film resembles that of c-Ge, with a near direct bandgap, implying that as C is added, both the central and the L valley in the conduction band move up simultaneously, while maintaining a small (∼0.15 eV) separation between the two. The Hall mobility was measured to be 70 cm2/V-sec. The films were doped n- type using phosphine, and p- type using diborane. P-n junctions with good rectification characteristics were fabricated. Because of its excellent optical absorption, this material may be suitable for photovoltaic applications, particularly for tandem junction cells. We have also observed that grain size can be controlled using H etching, and have observed distinct changes in optical properties related to quantum size effects in c-Ge films.
Porous silicon thin film gas sensor
Authors: Ferreira I. , Fortunato E. , Martins R.
Published: April 2011

The performances of amorphous and nano-crystalline porous silicon thin films as gas detector are pioneer reported in this work. The films were produced by the hot wire chemical vapour deposition (HW-CVD). These films present a porous like-structure, which is due to the uncompensated bonds and oxidise easily in the presence of air. This behaviour is a problem when the films are used for solar cells or thin film transistors. For as gas detectors, the oxidation is a benefit, since the CO, H2 or O2 molecules replace the OH adsorbed group. In the present study we observe the behaviour of amorphous and nano-crystalline porous silicon thin films under the presence of ethanol, at room temperature. The data obtained reveal a change in the current values recorded by more than three orders of magnitude, depending on the film preparation condition. This current behaviouris due to the adsorption of the OH chemical group by the Si uncompensated bonds as can be observed in the infrared spectra. Besides that, the current response and its recover time are done in few seconds.
Structural Characterization of SiF4, SiH4 and H2 Hot-Wire-Grown Microcrystalline Silicon Thin Films with Large Grains
Authors: Gutierrez J. J. , Inglefield C. E. , An C. P. , DeLong M. C. , Taylor P. C. , Morrison S. , Madan A.
Published: April 2011

In this paper, we present a comprehensive study of microcrystalline silicon thin film samples deposited by a novel growth process intended to maximize their grain size and crystal volume fraction. Using Atomic Force Microscopy, Raman spectroscopy, and x ray diffraction the structural properties of these samples were characterized qualitatively and quantitatively. Samples were grown using a Hot-Wire Chemical Vapor Deposition process with or without a post-growth hot-wire annealing treatment. During Hot-Wire Chemical Vapor Deposition, SiF4 is used along with SiH4 and H2 to grow the thin films. After growth, some samples received an annealing treatment with only SiF4 and H2 present. These samples were compared to each other in order to determine the deposition conditions that maximize grain size. Large microcrystalline grains were found to be aggregates of much smaller crystallites whose size is nearly independent of deposition type and post-annealing treatment. Thin films deposited using the deposition process with SiF4 partial flow rate of 2 sccm and post-growth annealing treatment had the largest aggregate grains ∼.5 µm and relatively high crystal volume fraction.
VHF Large Area Plasma Processing on Moving Substrats
Authors: Kuske J. , Stephan U. , Terasa R. , Brechtel H. , Kottwitz A.
Published: April 2011

The production of amorphous and microcrystalline silicon, e.g. for solar cells, requires large area, high-deposition rate plasma reactors. Increasing the frequency from the conventional 13.56MHz up to VHF has demonstrated higher deposition and etch rates and lower particle generation, a reduced ion bombardement and lower breakdown, process and bias voltages. But the use of VHF for large area systems leads to some problems. The non-uniformity of deposition rate increases due to the generation of standing waves and evanescent waveguide modes at the electrode surface. One possibility to process large area substrates is the use of a one-dimensional extended, homogeneous plasma source in combination with a moving substrate. The requirements, which result from the deposition process and from the RF-engineering, corresponds with the developed plasma source, using deposition frequencies in the VHF-range (50-100 MHz), almost perfectly.

Using a source of 550mm length experiments were done with 81.36MHz at RF power densities of 70-180mW/cm2, silane/ hydrogen pressures of 5-30Pa and flow rates of 10-300sccm. The measured potential distribution error was ±2%. Optical emission spectroscopy delivered discharge intensity errors of ±3-10%. Deposition rates up to 20µm/h for amorphous silicon (60Å/s) and film thickness inhomogenities less than ±5% were achieved (with an area of the moved substrate of 30cm–30cm). Experimental results of the film properties will be discussed in relation to the deposition parameters and compared with complementary experiments, carried out on a small scale equipment with excitation frequencies up to 165 MHz.
Electrical Properties of Solid Phase Crystallized Silicon Films
Authors: Watanabe Tadashi , Watakabe Hajime , Sameshima Toshiyuki
Published: April 2011

In this study, the carrier mobility and density for solid phase crystallized (SPC) silicon films fabricated at 600 °C for 48 hours are analyzed by free carrier optical absorption. The carrier mobility is 40 cm2/Vs for SPC films doped with 6×1019-cm−3-phosphorus atoms. This analysis suggests the SPC films have fine crystalline grains closed to single crystalline silicon. In addition, initial carrier density was 3×1019 cm−3, which increased to 6×1019 cm−3by XeCl excimer laser irradiation of 500mJ/cm2. The inactivated regions in SPC films are reduced by laser irradiation. However, the electrical conductivity after laser irradiation for SPC films doped with 6×1018-cm−3-phosphorus atoms decreased from 3.3 to 0.018 S/cm as laser energy density increased to 500mJ/cm2. On the other hand, the electrical conductivity increased from 14.7 to 31.3 S/cm with similar increase of laser energy density after H2O vapor heat treatment at 260°C for 3 hours with 1.3 MPa. Furthermore, the characteristics of n-channel TFTs fabricated with initial SPC films as well as SPC films which was irradiated by laser at 425mJ/cm2 are also researched. The threshold voltage is decreased from 3.8 to 2.0 V by laser irradiation. Threshold voltages of both cases are decreased from 3.8 to 2.4 V for no-laser irradiation and from 2.0 to 0.8 V for laser irradiation, after H2O vapor heat treatment at 310°C for 1 hour with 9.0MPa. Based on the above trial, the defect reduction method combining laser irradiation and H2O vapor heat treatment has proved to be very effective for SPC films and SPC TFTs.
Influence of chemical bath deposition parameters on the formation of CuInS2 / Zn(Se,O) junctions for thin film solar cells
Authors: Chaparro A.M. , Gutiérrez M.T. , Herrero J. , Klaer J.
Published: April 2011

Thin film solar cells of CuInS2/Zn(Se,O)/ZnO configuration have been studied as a function of the Zn(Se,O) buffer layer deposition parameters. Deposition of the buffer films was carried out by the chemical bath deposition (CBD) method, at different bath temperatures and compositions, and followed in situ with a quartz crystal microbalance. The CBD conditions were chosen to grow Zn(Se,O) buffer layers under different kinetic regimes but maintaining the same buffer thickness. The cells have been characterised with current-voltage and quantum efficiency measurements. Light soaking effects and medium term stability have been checked. It is found that Zn(Se,O) grown under predominant electroless kinetics gives rise to buffer films richer in oxygen, which allow for higher fill factors, higher efficiencies (around 10%) and stability of the cells. These cells show however lower open circuit potential. On the other hand, Zn(Se,O) buffers grown under chemical regime become richer in selenium, which gives rise to cells with higher open circuit potential, but lower fill factor, conversion efficiency and stability. Light soaking effects are also more important with the chemically grown buffers.
High-Energy Electron and Proton Irradiation of Cu(In,Ga)Se2Heterojunction Solar Cells
Authors: Jasenek A. , Boden A. , Weinert K. , Balboul M. R. , Schock H. W. , Rau U.
Published: April 2011

We investigate radiation-induced defects in high-efficiency Cu(In,Ga)Se2/CdS/ZnO heterojunction solar cells after 1-MeV electron and 4-MeV proton irradiation. We use electron and proton fluences of more than 1018cm−2and up to 1014cm−2, respectively. The irradiation experiments performed at three independent electron irradiation facilities consistently prove the superior radiation resistance of these Cu(In,Ga)Se2devices compared to other types of solar cells. The reduction of the solar cell efficiency in all experiments is predominantly caused by a lossΔVOCof the open circuit voltageVOC. An analytical model describesΔVOCin terms of radiation-induced defects enhancing recombination in the Cu(In,Ga)Se2absorber material. From our model we extract the defect introduction rates for recombination centers in Cu(In,Ga)Se2for the respective particles and energies. Isochronal annealing stepsfully recover VOCof the irradiated Cu(In,Ga)Se2solar cells. Exposure to temperatures of approx. 400 K are sufficient to restore the initialVOCwithin less than 5 %, even after excessive irradiation. The annealing process displays an activation energy ofEA= 1.1 eV. Admittance spectroscopy directly reveals the generationandthe annealing of radiation-induced defects.
Comparative study of the structural and optical properties of CIS films prepared by RFmagnetron sputtering and selenization of elemental layers
Authors: Cunha António F. , de Azevedo M.M. Pereira , Ferrão Ricardo J.O. , Lourenço A.A.C.S. , Boemare Claude
Published: April 2011

We report on a study where the properties of films obtained by RF-magnetron sputtering and by Selenization of elemental precursor layers are analysed by Raman scattering, x-ray diffraction and optical measurements. Three routes were followed to prepare CIS films on glass. CIS type-I was prepared by selenization at various temperatures, CIS type-II was prepared by RF-magnetron sputtering on room temperature substrate followed by annealing at 450°C in air for 10 min and CIS type-III was prepared by RF-magnetron sputtering on a substrate at a temperature ranging from 200°C up to 500°C with a post-deposition annealing in the same conditions as for CIS type-II. Correlating the results from x-ray diffraction with the Raman scattering and optical measurements it was possible to establish unequivocally the formation of CIS with the chalcopyrite structure for CIS type-I at 400°C. Through the same procedure it was possible to establish a way to produce CIS type-II with the chalcopyrite structure. A high density of defects was inferred from the transmission results. Finally the growth dynamics of CIS type-III was studied. It was observed a structural/compositional transition around substrate temperature of 300°C. It was observed that all the films had a sphalerite structure even for the highest substrate temperatures. It was establish the need for a post-deposition annealing to obtain CIS type-III with the chalcopyrite structure. The Raman scattering was found to be a very sensitive technique that allowed us to uncover a difference in the CIS type-I and II with the chalcopyrite structure.
Engineered tantalum aluminate and hafnium aluminate ALD films for ultrathin dielectric films with improved electrical and thermal properties
Authors: Clark-Phelps Robert B. , Srivastava Anuranjan , Cleveland Lance , Seidel Thomas E. , Sneh Ofer
Published: April 2011

Continued scaling of device dimensions requires deposition of high-quality thin films with a thickness of 50 angstroms or less. Nucleation effects in typical CVD processes make it difficult to achieve continuous films in this thickness regime. Atomic layer deposition (ALD), a technique developed over 25 years ago but applied to IC processing only recently, enables deposition of ultra-thin films with atomic-scale precision. This technique offers 100 percent step coverage of high aspect ratio features, as-deposited films which are amorphous and free of pinholes, excellent within-wafer uniformity and wafer-to-wafer uniformity, and favorable electrical properties. Moreover, ALD offers the opportunity to engineer material properties by creating layered structures (nanolaminates) and mixtures (alloys) which combine advantageous properties of different materials. These last features may be critical in efforts to replace silicon dioxide as the industry's dielectric workhorse if no single material emerges as a suitable direct replacement. The nanolaminate capability of ALD will be discussed with physical and electrical data on nanolaminates of aluminum oxide with tantalum pentoxide and aluminum oxide with hafnium oxide. Individual nanolaminate layers can be varied from tens of angstroms to as little as 1-2 atomic layers. Data for Al2O3/Ta2O5and Al2O3/HfO2alloys will also be presented demonstrating the ability to create materials with controlled, variable composition. The alloy and nanolaminate capabilities enable the creation of graded interfaces and atomically smooth transitions between different materials. Prospects for application of these materials to gate stacks and capacitors will be assessed.
Electricaland Structural Characteristics Of Ultra-Thin TiO2/Ti-Si-O Stacked Gate Insulator Formed by Rf Sputtering Technique
Authors: Koyama M. , Kaneko A. , Koike M. , Fujiwara I. , Yabuki M. , Yoshiki M. , Koike M. , Nishiyama A.
Published: April 2011

In this paper, we have reported an attempt to decrease equivalent oxide thickness (EOT) of TiO2gate insulator by thinning the amorphous layer formed at the TiO2/Si interface. We have decreased the thickness of the TiO2/Si interfacial layer to as little as 1.6 nm by suppressing the oxygen flow rate during the TiO2 sputtering. It was confirmed that the dielectric constant of the interfacial layer revealed higher value than that of SiO2, depending on the sputtering condition. Titanium in the interfacial layer, which was responsible for the polarization enhancement, was explicitly identified by high spatial resolution TEM-EELS. As a result, EOT of 1.3 nm was realized by TiO2/Ti-Si-O stacked gate insulator without any degradation in the electrical characteristics.
A Study on the Polycrystalline Silicon Germanium Gate Electrode Fabrication Technology for Cobalt Silicide Process
Authors: Sato Hidekazu , Sukegawa Takae , Mori Toshifumi , Suzuki Kousuke , Mori Haruhisa
Published: April 2011

This paper reports the dependence on the concentration of the germanium (Ge) in polycrystalline silicon (poly-Si) cap layer on the polycrystalline silicon germanium (poly-SiGe) for low resistivity cobalt disilicide (CoSi2) formation. Particularly, we investigate the relationship between sheet resistance of CoSi2 films and concentration of Ge in cap-Si layer. The excellent value of sheet resistance (∼6 / ) is achieved by Ge concentration in cap-Si layer controlled at 2% or less for 90nm length CoSi2/poly-Si/poly-SiGe gate structure. This result indicates that conventional Co silicide process technology can be readily used even for poly-SiGe gate structure.
X-Ray Techniques for Silicides
Authors: Tweet Douglas J. , Maa Jer-shen , Hsu Sheng Teng
Published: April 2011

Previously we have found that the addition of a thin layer of Co between Ni and the Si substrate dramatically improves the thermal stability of the resulting silicide. Here we describe the use of four different x-ray techniques to obtain complementary information on film structure, providing a possible explanation for the observed thermal stability.
Stability Improvement of Nickel Silicide with Co Interlayer on Si, Polysilicon and SiGe
Authors: Maa Jer-shen , Tweet Douglas J. , Ono Yoshi , Stecker Lisa , Hsu Sheng Teng
Published: April 2011

Thermal stability of nickel silicide is improved by adding a thin Co interlayer at Ni/Si interface. After high temperature anneal, the low sheet resistance of silicide and the low junction leakage of the ultra-shallow junction show the lack of film degradation. The transformation to disilicide phase occurred at a lower temperature. At 850°C, interface shows the truncated facet structure extended 100° to 200° below silicide/Si interface. With Co addition, nickel silicide formed on polysilicon and on SiGe films also show improved thermal stability and low sheet resistance. Formation temperature of disilicide phase occurred at lower temperature in all these cases.
An Experimental and Computational Study of the Elastic-Plastic Transition in Thin Films
Authors: Lilleodden Erica T. , Zimmerman Jonathan A. , Foiles Stephen M. , Nix William D.
Published: April 2011

Nanoindentation studies of thin metal films have provided insight into the mechanisms of plasticity in small volumes, showing a strong dependence on the film thickness and grain size. It has been previously shown that an increased dislocation density can be manifested as an increase in the hardness or flow resistance of a material, as described by the Taylor relation [1]. However, when the indentation is confined to very small displacements, the observation can be quite the opposite; an elevated dislocation density can provide an easy mechanism for plasticity at relatively small loads, as contrasted with observations of near-theoretical shear stresses required to initiate dislocation activity in low-dislocation density materials. Experimental observations of the evolution of hardness with displacement show initially soft behavior in small-grained films and initially hard behavior in large-grained films. Furthermore, the small-grained films show immediate hardening, while the large grained films show the ‘softening’ indentation size effect (ISE) associated with strain gradient plasticity. Rationale for such behavior has been based on the availability of dislocation sources at the grain boundary for initiating plasticity. Embedded atom method (EAM) simulations of the initial stages of indentation substantiate this theory; the indentation response varies as expected when the proximity of the indenter to a Σ79 grain boundary is varied.
Deformation Microstructure of Cold Gas Sprayed Coatings
Authors: Borchers C. , Stoltenhoff T. , Gäartner F. , Kreye H. , Assadi H.
Published: April 2011

Cold Gas Spraying is a new coating technique, in which the formation of dense, tightly bonded coatings occurs only due to the kinetic energy of high velocity particles of the spray powder. These particles are still in the solid state as they impinge on the substrate. Adiabatic heating after impingement can cause local shear instabilities and jet formation. The local microstructure is strongly dependant on local stress state and temperature rise. A variety of different microstructures is observed by TEM. The results are compared with modelling of the spray process.
SiC-Si Grooved Surface Bonding
Authors: Agrunova Tatiana S. , Grekhov Igor V. , Kostina Lioudmila S. , Tur'yanskii Alexander G. , Pirshin Igor V. , Prudnikov Ilya R. , Kostin Konstantin B.
Published: April 2011

SiC Lely platelets and SiC epilayers on large area SiC substrates were directly bonded to non-oxidized grooved surface silicon wafers in order to obtain structures prospective for the design of power bipolar devices with wide band-gap emitter junctions. The reported capabilities of grooved interfaces to reduce elastic strain and intrinsic sources of an interfacial potential barrier were utilized. The influence of surface morphology on the structural perfection of the bonded samples was studied in detail by X-ray and AFM techniques. As compared to traditional bonding technology, experimental data showed an easier smooth-to-grooved surface bonding accomplished in the formation of the boundary with better continuity and strength. For 2 in. diameter SiC wafers with root mean square height of roughness σ=16 Å and lateral coherence length L=1.8 μm bonding continuity not smaller than 90% was reached, while the crystals with σ=30 Å, L=5 μm failed to bond to Si even under an external force.
Monocrystalline Si Films from Transfer Processes for Thin Film Devices
Authors: Bergmann Ralf B. , Berge Christopher , Rinke Titus J. , Werner Jürgen H.
Published: April 2011

The transfer of thin monocrystalline silicon films to foreign substrates is of great interest for a number of applications such as silicon on insulator devices, active matrix displays and thin film solar cells. We present a transfer approach for the fabrication of monocrystalline Si films on foreign substrates based on the formation ofquasi-monocrystallineSi-films. Our transfer approach is compatible with high temperature processing such as epitaxial growth at 1100°C, thermal oxidation and phosphorous diffusion. Reuse of Si host wafers is demonstrated by the subsequent epitaxial growth of three monocrystalline Si films on a single host wafer. Monocrystalline Si films with a thickness of 15 µm and a diameter of 3” are transferred to glass and flexible plastic substrates. The typical light point defect density in films transferred from virgin wafers ranges between 10 to 100 cm−2, while stacking fault and dislocation densities are ≤ 100 cm−2. The minority carrier diffusion length in the epitaxial Si films is around 50 µm.
A New Double Laser Recrystallization Technique to Induce Ultra-Large Poly-Si Grains
Authors: Lee Minghong , Moon Seungjae , Hatano Mutsuko , Grigoropoulos Costas P.
Published: April 2011

A new double laser recrystallization technique that can produce lateral grains of tens of micrometers is presented. A nanosecond laser (excimer or Nd:YLF laser) and a pulse modulated Ar+ laser are used in the experiment. The effect of different parameters on lateral grain growth is investigated. These parameters include the time delay between the two lasers, the excimer laser fluence, the Ar+ laser power and the pulse duration. This process has wide process window and is insensitive to both the excimer laser fluence and the Ar+ laser power fluctuations. Preheating and melting of the a-Si film with the Ar+ laser before firing the excimer laser is found to be necessary for inducting lateral grain growth. The transient excimer laser irradiation is believed to generate nucleation sites for initiating the subsequent lateral grain growth. The solidification dynamics of the process is probed by high spatial and temporal resolution laser flash photography. A lateral solidification velocity of about 10 m/s is observed.
Structure and Characteristics of Strained-Si-On-Insulator (Strained-SOI) MOSFETs
Authors: Takagi Shin-ichi , Tezuka Tsutomu , Sugiyama Naoharu , Mizuno Tomohisa , Kurobe Atsushi
Published: April 2011

Abstrct:

Strained-Si MOSFET is an attractive device structure to be able to relax several fundamental limitations of CMOS scaling, because of high electron and hole mobility and compatibility with Si CMOS standard processing. In this paper, we present a new device structure including strained-Si channel, strained-SOI MOSFET, applicable to CMOS under sub-100 nm technology nodes. The main feature of this device is that thin strained-Si channel/relaxed SiGe hetero-structures are formed on buried oxides. The principle and the advantages are described in detail. The strained-SOI MOSFETs, whose electron and hole mobility is 1.6 and 1.3 times, respectively, higher than in conventional MOSFETs, have successfully been fabricated by combining the SIMOX technology with re-growth of strained Si films. We also present novel fabrication techniques to realize ultra-thin SiGe-on-Insulator (SGOI) virtual substrates with high Ge content, including Ge condensation due to oxidation of SGOI with lower Ge content. Strained-Si/SGOI structures with total thickness of 21 nm and Ge content of 56 % have been fabricated by oxidizing SiGe films on conventional SOI substrates and re-growing strained-Si films.
Integration Challenges for Double-Gate MOSFET Technologies
Authors: Maszara W.P.
Published: April 2011

Device modeling data and some early experiments suggests that fully depleted MOSFET devices where channel is controlled by two opposing gates or one gate that surrounds most or the entire channel, will provide better scaling than the classic devices with one gate on one side of the channel. However, formation of such devices requires complex, non-conventional and sometimes exotic geometry and processing, ranging from wafer bonding to selective lateral ‘tunnel’ epitaxy, to selectively wet-etched channels with triangular cross-section. Classic single-gate transistors have been recently demonstrated with reasonable performance at 20-15 nm of physical gate length. Double-gate transistors with their process integration complexity will likely become a viable alternative for smaller geometries. This paper will discuss various approaches to realization of those multi-gate fully depleted devices and their process integration challenges for sub-15 nm gates.
LPCVD Deposition Techniques for Nanograin sub-10nm Polysilicon Ultra-thin Films
Authors: Ecoffey Serge , Bouvet Didier , Ionescu Adrian M. , Fazan Pierre
Published: April 2011

This paper investigates the limits of a low pressure chemical vapour deposition (LPCVD) technique for the deposition of a nanometre scale ultra-thin polysilicon (poly-Si) film with sub-10nm grain sizes. Three different processes using pure silane (SiH4) in a standard horizontal hot-wall reactor are presented: (i) a direct poly-Si deposition, (ii) a Hemispherical Silicon Grain (HSG) deposition and (iii) an amorphous silicon (a-Si) deposition followed by a thermal crystallization anneal. The direct poly-Si deposition gives a minimum film thickness achievable around 20 nm with grain sizes ranging from 20 to 30 nm. The HSG deposition process leads to the formation of grains with diameters varying from 5 to 50 nm and heights ranging from 5 to 20 nm. The best results are obtained with the third process (a-Si / crystallization), which allows the formation of 6 nm poly-Si thick films with grain sizes ranging from 10 to 20 nm.