bluuebunny/crossref_metadata_2025 huggingface dataset:
Renaissance and Progress in Nitride Semiconductors - My Personal History of Nitride Research -
Authors: Akasaki Isamu
Published: April 2011

Wide bandgap group-III nitride semiconductors are currently experiencing the most exciting development. High brightness blue and green light emitting diodes (LEDs) are commercialized, and UV and blue laser diodes (LDs), high-speed transistors (TRs) and UV photodetectors (PDs) with low dark current, which will be able to operate in harsh environments, have been demonstrated. In this paper, renaissance and progress in crystal growth and conductivity control of nitride semiconductors in the last quarter century are reviewed as the groundwork for all of those high-performance devices. My personal history of nitride research will be also introduced.
Dynamics of Ga Clusters on GaAs(001) Surface
Authors: Tsukamoto Shiro , Koguchi Nobuyuki
Published: April 2011

Dynamics of Ga clusters and GaAs epitaxial growth on a GaAs (001) surface were successfully observed by a system in which scanning tunneling microscopy (STM) and molecular beam epitaxy (MBE) were incorporated into one unit rather than in separate chambers. With the substrate temperature of 528°C, reflection high-energy diffraction (RHEED) patterns showed a (4×6) Ga-stabilized surface reconstruction and dynamics of steps and islands were clearly observed. The detaching and attaching of small Ga clusters might cause the change of steps and islands. It seems that the small Ga clusters migrated with the diameter of about 0.8 to 1.2 nm and around the steps and islands. These clusters could be observed only when they were detached from or attached to the steps and islands. Moreover, even under the substrate temperature of 440 oC and the As4 partial pressure of 2×10−6 torr, STM images were clearly observed. After 0.1 ML Ga was additionally supplied to the sample by migration enhanced epitaxy mode, step flow growth occurred, resulting in an additional GaAs layer grown on the B-step side. Moreover, the c(4×4) As-stabilized surface reconstruction was moderate. It seems that there is an equilibrium additional layer of As amorphous adatoms on the c(4x4) surface reconstructions.
Electromigration in Epitaxial Copper Lines
Authors: Goindi H.S. , Shin C.S. , Frederick M. , Shusterman Y. , Kim H. , Petrov I. , Ramanath G.
Published: April 2011

Copper is becoming the metal of choice for interconnect applications in integrated circuits due to its lower electrical resistivity and higher electromigration (EM) resistance. The effects of grain size, preferred orientation, and interfacial layers, on electromigration in Cu lines are, however, not yet well understood. In this paper, we compare the EM characteristics of epitaxial Cu(111) lines with that of polycrystalline lines with a (111) texture. We also investigate the effects of Ta, TaN and TiN interfacial underlayers and Cu crystal quality on the EM response of epitaxial Cu(001) lines. EM tests were carried out on 2-μm-wide Cu lines at a constant current density between 0.02 and 3.5 MA/cm2 in an Ar ambient at 300 °C. Our results indicate that EM resistance of both (111) and (001) epitaxial lines have a higher mean time to failure (MTTF) than polycrystalline Cu lines. The presence of a TiN or TaN interfacial layer increases the MTTF in Cu(001) films, while a Ta underlayer degrades EM resistance. X-ray diffractograms indicating a smaller full-width-at-half-maximum of Cu(001) films on nitride underlayers suggest that lower defect densities in these Cu films is the likely reason for improved EM resistance. Both (111) and (100) orientations fail by formation of faceted voids.
The Effect of Pb on the Interface Structure of Fe/Cr(100) Metallic Multilayers
Authors: Kim Kyu-Young , Kamiko Masao , Oh Sang-Mun , Lu Guang-Hong , Yamamoto Ryoichi
Published: April 2011

We investigated the differences in the interface structures and magnetotransport properties between surfactant-mediated multilayers and normal ones. From the observations of RHEED and High-Resolution X-ray diffraction patterns, we confirmed that the surfaces of Fe/Cr(100) multilayers with Pb are flatter and the interfaces are sharper than one without Pb, which means that Pb operates as an effective surfactant. The magnetoresistance(MR) ratio of the multilayers prepared with Pb was larger than that of the multilayers prepared without Pb. The change of resistance with magnetic field was larger for the multilayers with a surfactant.
Surface structure and metal epitaxy: Ag/Cu(111)
Authors: Umezawa Kenji , Nakanishi Shigemitsu , Gibson Walter M.
Published: April 2011

We have investigated the growth of 3 ML (mono-layer) of Ag on Cu(111) for substrate temperatures from 170 through 640 K by using time of flight-impact collision ion scattering spectroscopy (TOF -ICISS). Two different types of epitaxial growth exist: Ag [112]//Cu[112](type-n) and Ag [112]//Cu[112] (type-r).The growth modes of the Ag thin films on Cu(111) surfaces depend strongly on the temperature during deposition with the Ag(111) planes having a preferred orientation of either type-n growth mode or type-r growth mode as a function of theCu substrate temperature. The experimental results concerning Ag/Cu(111) show many similarities to those in the previous study of Au/Ni(111). This would suggest that an observed oscillation in the growth mode, dependent on the substrate temperature during deposition may a general phenomenon on solid surfaces, in cases of large misfit since it has now been seen for both Au/Ni(111) and Ag/Cu(111) systems.
Molecular Orientation in The Peptide Self-Assembled Monolayers
Authors: Fujita Katsuhiko , Yokoyama Ryuichi , Tsutsui Tetsuo
Published: April 2011

Self-assembled monolayer (SAM) of peptides is investigated in terms of the correlation of their molecular orientation and the dipolar interactions. The used helical peptides containing a disulfide group on the terminal, which can form SAMs on a gold substrate, were synthesized. The molecular orientation was estimated from the reflection absorption IR intensity ratio of amide I and amide II bands which have transition moment almost parallel and perpendicular to the molecular axis, respectively. The adsorption behavior and layer thickness were determined by surface plasmon resonance.

The molecular orientation depended on the dipolar interaction between the peptide molecules and between the peptide dipole and its image. The molecular direction against the substrate affects the orientation probably due to the interaction between the peptide dipole and Au-S polarization. This speculation is supported by the fact that the orientation difference by the molecular direction became smaller when the spacer from the helix body to the disulfide group is longer. The results indicate that the careful molecular design and optimal preparation condition of SAMs allow formation of well-organized and predetermined structure of nano-architecture even by use of large and complex molecules.
Mechanisms in embedded selective epitaxy and overgrowth of an integrated laser/modulator quantum well structure using MOMBE and MOVPE
Authors: Kröner Philipp , Baumeister Horst , Gessner Roland , Rieger Josef , Schier Michael , Veuhoff Eberhard , Marti Othmar , Heinecke Harald
Published: April 2011

Lateral integration of optoelectronic devices comprising strained multiple quantum well (MQW) structures can most successfully be accomplished by selective area epitaxy using metal organic molecular beam epitaxy (MOMBE). We optimized the growth parameters with respect to a planar butt coupling and sharp, flat MQW interfaces in an integrated MQW laser / MQW modulator structure. Defect generation in metal organic vapor phase epitaxy (MOVPE) overgrown cladding layers is analyzed and shown to contain information about the quality of the buried butt coupling. A ridge waveguide structure has successfully been fabricated from an optimized integrated laser / modulator structure.
Computational Study of Polymerization in Carbon Nanotubes
Authors: Stuart Steven J. , Dickson Brad M. , Sumpter Bobby G. , Noid Donald W.
Published: April 2011

Molecular dynamics simulations of ethylene polymerization have been performed using a chemically realistic, reactive potential. These simulations have been performed in the bulk liquid and in the interior of both (10,10) and (7,7) nanotubes as a means of investigating the effects of nanoscale confinement on the polymerization reaction. The structure of the resulting polymer was found to be similar in the bulk and in the (10,10) tube at the elevated temperatures investigated, while only very small oligomers were formed in the (7,7) tube. The reaction rate was substantially reduced in the nanotubes, when compared to the bulk, primarily as a result of spatial interference due to reaction products. These simulations have implications for the possible use of nanotubes as synthetic reaction vessels, as well as for the general understanding of association reactions in confined spaces.
Flow, Diffusion, Dispersion, and Thermal Convection in Percolation Clusters: NMR Experiments and Numerical FEM/FVM Simulations
Authors: Kimmich Rainer , Klemm Andreas , Weber Markus , Seymour Joseph D.
Published: April 2011

Based on computer-generated templates, percolation objects were fabricated. Random-site, semi-continuous swiss cheese, and semi-continuous inverse swiss-cheese percolation models above the percolation threshold were considered. The water-filled pore space was investigated by nuclear magnetic resonance (NMR) imaging and in the presence of a pressure gradient, by NMR velocity mapping. The percolation backbones were determined using velocity maps. The fractal dimension of the backbones turned out to be smaller by about 17 % than that of the complete cluster. As a further relation of interest, the volume-averaged velocity was calculated as a function of the probe volume radius. In a certain scaling window, the resulting dependence can be represented by a power law. The experimental results favorably compare to computer simulations with the finite-element method (FEM) or the finite-volume method (FVM). Thermal convection in percolation clusters of different porosities was studied using the NMR velocity mapping technique. The velocity distribution is related to the convection roll size distribution. The maximum velocity as a function of the porosity clearly visualizes a closed-loop percolation transition if the Rayleigh number conditions are appropriate. Percolation theory suggests a relationship between the anomalous diffusion exponent and the fractal dimension of the cluster,i.e.between a dynamic and a structural parameter. Interdiffusion between two compartments initially filled with H2O and D2O, respectively, was examined by proton imaging. The results confirm the theoretical expectation. Finally, advection driven dispersive transport was investigated in the large Péclet number limit. The superdiffusive transport anomaly was demonstrated and discussed in terms of the non-local advection-diffusion and the fractional diffusion theories.
Friction and the Continuum Limit – Where is the Boundary?
Authors: Zhu Yingxi , Granick Steve
Published: April 2011

The no-slip boundary condition, believed to describe macroscopic flow of low-viscosity fluids, overestimates hydrodynamic forces starting at lengths corresponding to hundreds of molecular dimensions when water or tetradecane is placed between smooth nonwetting surfaces whose spacing varies dynamically. When hydrodynamic pressures exceed 0.1-1 atmospheres (this occurs at spacings that depend on the rate of spacing change), flow becomes easier than expected. Therefore solid-liquid surface interactions influence not just molecularly-thin confined liquids but also flow at larger length scales. This points the way to strategies for energy-saving during fluid transport and may be relevant to filtration, colloidal dynamics, and microfluidic devices, and shows a hitherto-unappreciated dependence of slip on velocity.
Hydrocarbon Reactions in Carbon Nanotubes: Pyrolysis
Authors: Stuart Steven J. , Dickson Brad M. , Noid Donald W. , Sumpter Bobby G.
Published: April 2011

Molecular dynamics simulations have been used to study the pyrolysis of eicosane (C2042 both in the gas phase and when confined to the interior of a (7,7) carbon nanotube. A reactive bond-order potential was used to model the thermal decomposition of covalent bonds. The unimolecular dissociation is first-order in both cases. The decomposition kinetics demonstrate Arrhenius temperature dependence, with similar activation barriers in both geometries. The decomposition rate is slower by approximately 30% in the confined system. This rate decrease is observed to be a result of recombination reactions due to collisions with the nanotube wall.
Synthesis, Structure and Magnetic Properties of Monoclinic Nb12O29
Authors: Waldron J. E. L. , Green M. A.
Published: April 2011

The synthesis, structure and magnetic properties of monoclinic Nb12O29 are described. The synthesis of a pure bulk sample is difficult due to the large number of other similar phases. It is achieved by rapid reduction of H-Nb2O5 with Nb metal. The compound is shown to undergo a charge ordering transition at low temperature which provokes long range magnetic order in an intriguing one dimensional arrangement.
Temperature Dependence of Magnetic Compton Profile in DyCo5
Authors: Miyagawa Hayato , Watanabe Yasuhiro , Koizumi Akihisa , Sakai Nobuhiko , Mizumaki Masaichiro , Sakurai Yoshiharu , Nakamura Tetsuya , Nanao Susumu
Published: April 2011

Magnetic Compton profiles (MCPs) of a DyCo5.4 single crystal were measured at 10 K, 200 K and 300 K. The temperature dependence of the spin moment, which is deduced from the areas under the normalized MCPs, is significantly different from that of the total magnetization measured by a superconducting quantum interference device (SQUID). This difference is due to the presence of a substantial amount of the orbital moment on a Dy site that does not contribute to the magnetic Compton scattering cross section. The analysis of the MCPs reveals that the absolute value of the spin moment increases with increasing temperature and that the spin magnetic moment of the conduction electrons has an opposite sign to the total spin magnetization in the covered range of temperature.
High Oxidation State Alkali-Metal Late-Transition-Metal Oxides
Authors: Currie David B. , Hector Andrew L. , Raekelboom Emmanuelle A. , Owen John R. , Weller Mark T.
Published: April 2011

Li2NaCu2O4 has been prepared by solid state reaction under high-pressure (250 Atm) oxygen. A structural study, using time-of-flight powder neutron diffraction on a sample made with 7Li, shows a material isostructural with Li3Cu2O4, with sodium occupying the octahedral and lithium the tetrahedral A-cation sites. A 7Li MAS-NMR study of Li3Cu2O4, Li2NaCu2O4 and Li2CuO2 has been used to confirm the Li/Na site ordering.
Effect of Strained Si-Si Bonds in Amorphous Silicon Incubation Layer on Microcrystalline Silicon Nucleation
Authors: Fujiwara Hiroyuki , Kondo Michio , Matsuda Akihisa
Published: April 2011

In order to investigate microcrystalline silicon (μc-Si:H) nucleation from the hydrogenated amorphous silicon (a-Si:H) phase, we performed a H2-plasma treatment of a-Si:H layers deposited at different temperatures. In the H-treatment experiment, the formation process of an infrared peak at ∼1937 cm-1, assigned to SiHn (n=1∼2) complex, is studied, as the SiHn complex is proposed to be a precursor for the μc-Si:H nucleation. With increasing the a-Si:H deposition temperature, the total amount of the SiHn complex formed by the H treatment increased. Nucleation of μc-Si:H under high H2-dilution conditions showed a clear relationship with the SiHn complex formed by the H treatment. The SiHn complex formation process, in terms of strained Si-Si bond breaking by H, is discussed.
New experiments on the relationship between light-induced defects and photoconductivity degradation
Authors: Heck Stephan , Branz Howard M.
Published: April 2011

We report experimental results that help settle apparent inconsistencies in earlier work on photoconductivity and light-induced defects in hydrogenated amorphous silicon (a-Si:H) and point toward a new understanding of this subject. After observing that light-induced photoconductivity degradation anneals out at much lower T than the light-induced increase in deep defect density, Han and Fritzsche[1] suggested that two kinds of defects are created during illumination of a-Si:H. In this view, one kind of defect degrades the photoconductivity and the other increases defect sub-bandgap optical absorption. However, the light-induced degradation model of Stutzmann et al.[2] assumes that photoconductivity is inversely proportional to the dangling-bond defect density. We observe two kinds of defects that are distinguished by their annealing activation energies, but because their densities remain in strictlinear proportionduring their creation, the two kinds of defects cannot be completely independent.

In our measurements of photoconductivity and defect absorption (constant photocurrent method) during 25°C light soaking and during a series of isochronal anneals between 25 < T < 190°C, we find that the absorption measured with E ≤1.1 eV, first increases during annealing, then exhibits the usual absorption decrease found for deeper defects. The maximum in this absorption at E ≤1.1eV occurs simultaneously with a transition from fast to slow recovery of photoconductivity. The absorption for E ≤1.1eV showstwodistinct annealing activation energies: the signal rises with about 0.87 eV and falls with about 1.15 eV. The 0.87 eV activation energy roughly equals the activation energy for the dominant, fast, recovery of photoconductivity. The 1.15 eV activation energy roughly equals the single activation energy for annealing of the light-induced dangling bond absorption.
Contributions of D0 and non-D0 Gap States to the Kinetics of Light Induced Degradation of Amorphous Silicon under 1 sun Illumination
Authors: Pearce J. , Niu X. , Koval R. , Ganguly G. , Carlson D. , Collins R.W. , Wronski C.R.
Published: April 2011

Light induced changes to 1 sun degraded steady state (DSS) have been investigated on hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells and corresponding films fabricated with and without hydrogen dilution of silane. Striking similarities are found for the degradation kinetics, between the electron mobility lifetime (μτ) products and the corresponding fill factors (FF). These correlations that exist for both intrinsic materials at temperatures between 25 and 100°C, are present for the DSS as well as in the kinetics, which exihibit distinctly different dependence on temperature. No such correlations are present between μτ, FF and densities of D0 defects, measured with subgap absorption α(E) at 1.2eV, and electron spin resonance (ESR). The creation of non-D0 defects is also clearly indicated by the temperature dependence of the kinetics and the changes in the shape of α(E) with the results suggesting the presence of more than one mechanism for the creation of light induced defects associated with the Staebler-Wronski effect (SWE).
Investigation of Light-Induced Defect Depth Profile in Hydrogenated Amorphous Silicon Films
Authors: Shimizu S. , Stradins P. , Kondo M. , Matsuda A.
Published: April 2011

We report direct measurement of depth profile of light induced defects (LIDs) in hydrogenated amorphous silicon (a-Si:H) films. These depth profiles were measured by ESR measurements combined with layer-by-layer precise wet etching technique. We discuss those LIDs depth profiles in relation to the spatial depth distribution of photocarriers generation and recombination profiles, as well as the defect creation efficiency. In case of uniformly absorbed light, the light induced defects creation takes place uniformly in depth of the a-Si:H film. In case of nonuniformly absorbed light, the LIDs depth profile is spatially wider than photocarrier generation rate profile G(x), and depends on G(x) sublinearly. Moreover, the LID depth profile agrees well with the photocarrier direct recombination rate profile rather than the profile of total recombination rate or that through defects. The obtained results suggest that the LIDs creation takes place at local site where the photocarriers recombine directly.
Is interstitial hydrogen playing a role in the Staebler-Wronski effect ?
Authors: Longeaud C. , Roy D.
Published: April 2011

We have studied the density of states (DOS) of many different series of a-Si:H samples prepared in radio-frequency powered deposition systems. Samples were obtained from decomposition of pure silane or of mixtures of silane with argon, helium or hydrogen. The DOS were investigated in the as-deposited, light-soaked and annealed states. For all the samples the light-soaking behaviour is almost the same: 2 min of light-soaking are enough to increase the deep states density and after full saturation both the deep states and the conduction band tail exhibit a large increase. The effect of the annealing process is sample dependent, the DOS being restored for some samples or almost insensitive to the annealing process in some cases. To explain all these results, we propose a mechanism of light-soaking/annealing in which interstitial H2 molecules and voids play a major role.
Two-Dimensional Amorphous Silicon Color Sensor Array
Authors: Lemmi F. , Mulato M. , Ho J. , Lau R. , Lu J. P. , Street R. A.
Published: April 2011

This paper reports on the first full realization and characterization of a two-dimensional array of amorphous silicon (a-Si:H) color sensors, addressed by integrated amorphous silicon-based thin-film transistors (TFTs). The array includes 512 × 512 pixels with 75-µm pitch, or about 340 dpi. Each pixel features a color sensor realized by a p-i-n-i-p stack of doped and undoped a-Si:H layers, and the TFT. The color sensors are made of two back-to-back p-i-n diodes, which selectively sense the illumination according to the polarity of the applied bias voltage. The sensor layers are grown on top of the TFTs to improve the array fill factor. The p-in-i-p sensor stack is mesa-isolated into single sensors to reduce cross-talk.

Images are acquired using two bias voltages and yield the red and blue/green components of the original with a good color separation. A color image is reconstructed using the information from the two images acquired. Aside from a color bias, which is expected for a two-color reconstruction, the imaging system works well. In particular, the array shows very low leakage currents, which enable a very large dynamic range and sensitivity. In the response of the array to a light pulse, the bottom thick diode ensures a fast drop in the signal after the flash, while the top thin diode exhibits some residual image lag.
The Determination of Optoelectronic Properties of Microcrystalline andAmorphous Silicon Films
Authors: Kunst Marinus , Aichberger Susanne von , Thom Wilhelm , Wünsch Frank
Published: April 2011

The study and characterization of the (opto)electronic properties of a-Si:H and µSi filmsby contactless transient photoconductivity measurements is presented. The importance ofminority carrier trapping is shown for the example of a-Si:H films prepared with different dopinglevels. It is shown that the microwave mobility determined by these measurements is a versatiletool for the characterization of the films. Examples are given by the study of µ Si filmsproduced by laser crystallization of a-Si:H films and the optimization of the substratetemperature for the Hot Wire deposition of µ Si films.
Integrated Optical and Electrical Modeling of a-Si:H Based Solar Cells
Authors: Zeman Miro , Swaaij René A.C.M.M. van , Heuvel Joost J.G. van den , Metselaar Wim
Published: April 2011

New features of the ASA software package are described that allow the analyses of the performance of hydrogenated amorphous silicon (a-Si:H) based solar cells with rough interfaces and buffer and graded layers. Using the updated version of ASA improved understanding of i) the effect of the front and back contact roughness on the external quantum efficiency and the absorption of light in the individual layers of a-Si:H solar cells and ii) the role of band gap grading of the intrinsic a-SiGe:H layer in a solar cell is obtained. The simulated results using the ASA package agree well with measured data on solar cells and are used to give insight into the behavior of the internal parameters of the solar cells.
Evidence for Long-range Hydrogen Motion in a-Si:H under Room-temperature Illumination Using Raman Scattering of Amorphous Tungsten Oxide Overlayer
Authors: Cheong Hyeonsik M. , Lee Se-Hee , Nelson Brent , Mascarenhas Angelo , Deb Sayten K.
Published: April 2011

We demonstrate that one can detect minuscule amounts of hydrogen diffusion out of a-Si:H under illumination at room temperature, by monitoring the changes in the Raman spectrum of amorphous tungsten oxide as a function of illumination. The Staebler-Wronski effect, the light-induce creation of metastable defects in hydrogenated amorphous silicon (a-Si:H), has been one of the major problems that has limited the performance of such devices as solar cells. Recently, Branz suggested the hydrogen collision model that can explain many aspects of the Staebler-Wronski effect. One of the main predictions of this model is that the photogenerated mobile hydrogen atoms can move a long distance at room temperature. However, light-induced hydrogen motion in a-Si:H has not been experimentally observed at room temperature. We utilized the high sensitivity of the Raman spectrum of electrochromic a-WO3 to hydrogen insertion to probe the long-range motion of hydrogen at room temperature. We deposited a thin (200 nm) layer of a-WO3 on top of a-Si:H, and under illumination, a change in the Raman spectrum was detected. By comparing the Raman signal changes with those for control experiments where hydrogen is electrochemically inserted into a-WO3, we can estimate semiquantitatively the amount of hydrogen that diffuses out of the a-Si:H layer.
Formation of Polycrystalline Silicon Films Using Electrical-Current-Induced Joule Heating
Authors: Andoh Nobuyuki , Takahashi Hiroyuki , Sameshima Toshiyuki
Published: April 2011

Electrical current induced joule heating method was applied to crystallization of 50 nm-thick amorphous silicon films formed on glass substrates. Voltages were applied to silicon films connected with a capacitance in parallel. Irradiation with 5 ns-pulsed-laser melted films partially and caused electrical current induced joule heating because of reduction of electrical resistance. Lateral grain growth with 12.6 µm was realized using the tapered-shaped-electrodes to apply voltages to silicon films with a capacitance of 0.33 µF. For 2.6×1017cm−3phosphorus-doped films, analysis of temperature change in the electrical conductivity gave that defect states at grain boundaries was low of ∼1017cm−3.
Photoluminescence Characterisation of Ion Implanted CdTe
Authors: Halliday D. P. , Potter M. D. G. , Boyle D. S. , Durose K.
Published: April 2011

We have ion implanted a series of dopants into single crystal CdTe. The influence of the impurities on the CdTe has been studied by low temperature photoluminescence spectroscopy. The impurities studied are: O, Cl, Cu, S, Na and Sb, and were selected because of their potential importance in thin film CdTe/CdS photovoltaic devices. Each impurity was implanted to give a smooth gaussian distribution in the first few microns of material with a doping density of 1×1015cm−3. Low temperature photoluminescence spectra were recorded from each sample and compared with an undoped sample. The PL features observed in each sample are discussed and the data is compared to an earlier photoluminescence study of thin film CdTe/CdS photovoltaic device structures.
Flexible and monolithically integrated CIGS-Modules
Authors: Kessler F. , Herz K. , Powalla M. , Hartmann M. , Schmidt M. , Jasenek A. , Schock H. W.
Published: April 2011

Monolithically integrated Cu(In,Ga)Se2-mini-modules (CIGS) have been fabricated on polymer as well as on metal foils. Preferred foils with view on costs and physical properties were ferritic steel, titanium, Fe/Ni-alloys (e.g. Kovar®) and polyimide as the only appropriate low temperature candidate. The metal substrates were isolated by multiple layers of SiOx and Al2O3 which served both as diffusion barrier against substrate elements and dielectric barrier. Small area cell efficiencies of 13.8% on ferritic steel foils and 10.6% on polymer foils (both without antireflective coating) were obtained. First monolithically integrated submodules of up to 10×10cm2 substrate area were fabricated both on ferritic steel and polyimide substrates. Different patterning methods have been applied and matched to the respective substrate materials.
A Detailed Study of Cu(In,Ga)Se2 Thin Films by Electron-Beam-Induced-Current and Cathodoluminescence
Authors: Romero M.J. , Hasoon F.S. , Al-Jassim M.M. , Garcia R. , Noufi R.
Published: April 2011

Cu(In,Ga)Se2 (CIGS) thin films were deposited using the three-stage process. At the third stage, an amount of Indium was added to the CIGS that is greater than the standard used in processing high-efficient CIGS solar cells. The effects of Indium excess and substrate temperature were then investigated by electron-beam-induced-current (EBIC) and cathodoluminescence (CL). The addition of more indium compared to the standard noticeably affects the ZnO/CdS/CIGS heterojunction. On the other hand, the substrate temperature primarily affects the luminescence behavior of these films. It is suggested than In enrichment and Na incorporation play a main role in the electronic properties of the film. From these results, the efficiencies obtained for this set of CIGS cells are finally understood.
Fabrication of CuInSe2 Solar Cells by the Evaporation of Binary Selenide Compounds
Authors: Lee Doo Youl , Yun Jae Ho , Ahn Byung Tae , Yoon Kyung Hoon , Song Jinsoo
Published: April 2011

CuInSe2 films were prepared by the three-stage process using the evaporation of In2Se3, Cu2Se and Se. In the third stage, the depth of Cu-poor surface region was precisely adjusted by the control of the evaporation rate of In2Se3 and Se. The interface between Cu-poor surface region and stoichiometric CuInSe2 film was characterized using AES, microEDAX, and RBS. The 9.59% efficiency was achieved in the 0.16 cm2 area cell. The efficiency is the same level of the CIS cell prepared using the element coevaporation, opening up the application of binary compounds for highly efficient Cu(In,Ga)Se2 cells.
Annealing time and collection efficiency in electrodeposited CdS/CdTe solar cells
Authors: Agostinelli G. , Dunlop E.D. , Ebner B. , Gibson N.
Published: April 2011

This paper presents a detailed analysis of the spatially resolved evolution of External Quantum Efficiency of electrodeposited CdS/CdTe solar cells as a function of the duration of the post-deposition annealing process which promotes n to p-type conversion of electrodeposited CdTe. Strips of 30×4 cm were cut from deposited plates at various stages of the fabrication process and processed into cells. Annealing treatments were carried out on these strips at 400°C for times ranging from 1 to 120 minutes. 130 spectral response curves (in the range of 300 to 900 nm) have been measured to trace temporal evolution and spatial non-uniformity of the materials and extrapolate parameters such as effective diffusion lengths, evolution of the collection profiles, and junction depth. Correlation between these parameters suggests that recrystallisation does not take place uniformly but progresses through the film. The analysis of structural vs. optical parameters along the cells provides evidence for spatial non-uniformities of the state of crystallisation of as-deposited and annealed material. Poor performance has been observed near the edges of the cells where material is resistant to recrystallisation.
Materials and Physical Properties of Novel High-k and Medium-k Gate Dielectrics
Authors: Liu Ran , Zollner Stefan , Fejes Peter , Gregory Rich , Lu Shifeng , Reid Kim , Gilmer David , Nguyen Bich-Yen , Yu Zhiyi , Droopad Ravi
Published: April 2011

Rapid shrinking in device dimensions calls for replacement of SiO2 by new gate insulators in future generations of MOSFETs. Among many desirable properties, potential candidates must have a higher dielectric constant, low leakage current, and thermal stability against reaction or diffusion to ensure sharp interfaces with both the substrate Si and the gate metal (or poly-Si). Extensive characterization of such materials in thin-film form is crucial not only for selection of the alternative gate dielectrics and processes, but also for development of appropriate metrology of the high-k films on Si. This paper will report recent results on structural and compositional properties of thin film SrTiO3 and transition metal oxides (ZrO2and HfO2).
Plastic Deformation of Thin Metal Foils without Dislocations and Formation of Point Defects and Point Defect Clusters
Authors: Kiritani Michio , Yasunaga Kazufumi , Matsukawa Yoshitaka , Komatsu Masao
Published: April 2011

Evidence for plastic deformation of crystalline metal thin foils without dislocations is presented. Direct observation during deformation under an electron microscope confirmed the absence of the operation of dislocations even for heavy deformation. In fcc metals including aluminum, deformation leads to the formation of an anomalously high density of vacancy clusters, in the form of stacking fault tetrahedra. The dependency of vacancy cluster formation on temperature and deformation speed indicates that the clusters are formed by the aggregation of deformation-induced vacancies. Conditions required for the absence of the dislocation mechanism are explained, and a new atomistic model for plastic deformation of crystalline metals is proposed.
Structure and mechanical behavior relationship in nano-scaled multilayered materials
Authors: Sergueeva A. , Mara N. , Mukherjee A.K.
Published: April 2011

Multilayered foils with 10%Cu/90%Ni and different bi-layer thickness (100-1000 nm) have been fabricated by electrodeposition. TEM and x-ray diffraction analysis indicate discrete layer formation and a (100) textured structure. The maximum tensile strength (590 MPa) is obtained for foils with the smallest layer thickness. Preliminary results on high temperature deformation show a strong dependence of strength and plasticity on layer thickness.
Molecular dynamics simulations of wafer bonding
Authors: Scheerschmidt Kurt
Published: April 2011

Molecular dynamics simulations using empirical potentials have been employed to describe atomic interactions at interfaces created by the macroscopic wafer bonding process. Investigating perfect or distorted surfaces of different semiconductor materials as well as of silica enables one to study the elementary processes and the resulting defects at the interfaces, and to characterize the ability of the potentials used. Twist rotation due to misalignment and bonding over steps influence strongly the bondability of larger areas. Empirical potentials developed by the bond order tight-binding approximation include ∏-bonds and yield enhanced interface structures, energies, and transferability to new materials systems.
Electrical characterisation of UHV-bonded silicon interfaces
Authors: Reznicek A. , Senz S. , Breitenstein O. , Scholz R. , Gösele U.
Published: April 2011

Direct wafer bonding can be used to mechanically and electrically connect semiconductors. In our experiments two 100 mm diameter (100) Si wafers (n-doping: 1014 cm−3) are first cleaned by standard chemical cleaning (RCA 1, 2). The surface is terminated by hydrogen after a HF dipping. The wafers are prebonded in air to protect the surface. After introduction into the ultra high vacuum (UHV) system the wafers are separated again. The hydrogen termination is released in a heating chamber. RHEED confirmed a surface reconstruction. The wafers are then cooled down to room temperature and bonded in UHV. The bonding energy is very close to the bulk bonding energy.

Measurements of whole n-n wafers showed a linear relationship of voltage and current at a low current density of 0.05 A/cm2. The current flow is inhomogeneous, which is visible in IR- thermography images. Above 0.1 V the current density first saturates, but increases super- linearly for higher voltages. The electrical properties of a grain boundary can be modeled by a double Schottky barrier. The barrier height decreases with increasing applied voltage. C-V measurements show a strong dependence of capacitance on frequency, temperature and applied voltage.

The capacitance increases with higher temperature and lower frequency. The interface state density can be estimated from the low temperature and high frequency capacitance limit as Dit = 1·1011 cm−2 eV−1 assuming a constant density of states.

We can conclude that in order to avoid the undesirable effect of the potential barrier and trap states at the bonding interface a high doping near the interface is required for the application of wafer bonding to devices with a high current density across the bonded interface.
Field Emission Characteristic of Silicon Cathodes Coated with GaN Nanoparticles
Authors: Hajra M. , Chubun N.N. , Chakhovskoi A.G. , Hunt C.E. , Liu K. , Murali A. , Risbud S H. , Tyler T. , Zhirnov V.
Published: April 2011

Arrays of p-type silicon micro-emitters have been formed using a subtractive tip fabrication technique. Following fabrication, the emitter surface was coated with GaN nanoparticles and nanocrystalline diamond by a dielectrophoresis deposition technique. The emitters were evaluated and compared before and after the surface treatment using I-V measurements in the diode configuration. The phosphor screen, used as the anode, was spaced nominally about 70 µm from the cathode. The field emission characteristics were measured in a high vacuum chamber at a pressure range between 10−5and 10−8Torr. The results suggest that the emitters benefit from coating the surface with nanocrystalline diamond in terms of reduction in the turn on voltage, GaN coating increase the turn on voltage. Both diamond and GaN improved the emission uniformity in the region of the low voltage operation.
Performances Presented by Large Area ZnO Thin Films Deposited by Spray Pyrolysis
Authors: Nunes Patrícia , Marques Antonio , Fortunato Elvira , Martins Rodrigo
Published: April 2011

In this work we present the results of a study on the uniformity of ZnO thin films produced by spray pyrolysis. The properties of the thin films depend essentially on the carrier gas pressure and gas flow used. The best films for optoelectronic applications were obtained with a carrier gas pressure of 2 bar and solution flow of 37 ml/min. The velocity of the nozzle affects essentially the uniformity of the ZnO thin films. However this important characteristic of the large area thin films is independent of the nature (doped and undoped) of the thin film and exhibits a high dependence on the variation of the temperature along the substrate.
Charge Carrier Transport in a-Si:H/a-SiC:H Heterojunction with Blocking Layer
Authors: Vygranenko Yu. , Fernandes M. , Louro P. , Mačarico A. , Vieira M.
Published: April 2011

This paper presents a one-dimensional numerical simulation of the charge carrier transport and photogeneration within a p-i-n (a-Si:H) homojunction and a p(a-SiC:H)/i (a-Si:H)/n (a-SiC:H) heterojunction with weakly-doped n-layers. A good matching between the simulated J-V characteristics and the corresponding experimental curves has been achieved for both configurations. By analysing the simulated band diagrams, electric field

distributions, the electron and hole current densities, and the free carrier population profiles we conclude that in short-circuit mode the carrier transport is different in the homojunction and heterojunction due to band offsets.
Silicon Field Emitter Arrays Integrated with MOSFET Devices
Authors: Hong Ching-yin , Akinwande Akintunde I.
Published: April 2011

We report a metal oxide semiconductor field effect transistor (MOSFET) controlled field emission array (FEA) device. The device uses a lateral double diffused MOSFET (LD-MOSFET) to control electron supply to the surface. The FEAs were fabricated using isotropic etch of silicon, oxidation sharpening and chemical mechanical polishing. The LD-MOSFETs have a threshold voltage of 0.48V while the FEAs have a turn-on voltage of 28V. Analysis using the FN formulation indicates that a silicon tip radius of 11 nm would fit the FEA IV data. The tip radius from the electrical data is very close to the average tip radius of 10 nm obtained from transmission electron microscope (TEM) analysis. The IV characterization of the MOSFET/FEA demonstrated control of electron emission by the MOSFET gate voltage.
Grain Quality Enhancement of Nickel-Crystallized Polysilicon Film in Quantum-Wire-Like Structures
Authors: Wang Hongmei , Jagar Singh , Zhan N. , Cheng C. F. , Poon M. C. , Chan Mansun
Published: April 2011

Methods for forming high quality re-crystallizing polysilicon films are being actively studied due to their ability to provide significant improvement to polysilicon Thin-Film-Transistors (TFT). Recently, a simple Metal-Induced-Lateral-Crystallization (MILC) method with nickel, together with high temperature annealing, can result in single crystal like polysilicon film [1]. TFTs fabricated on this so-called Large-grain Silicon-On-Insulator (LPSOI) can achieve SOI MOSFET performance especially for making small dimension devices. This paper reports that the polysilicon grain quality can be further enhanced by crystallizing the polysilicon film into the shape of long-wire.

The crystallization procedure started with a regular Nickel-Induced-Lateral-Crystallization (NILC) process at 560 °C as described in [1]. The film was then etched into narrow wires, which were parallel to the direction of nickel propagation. The NILC second anneal at 900 °C was then performed on these silicon wire. Through surface energy anisotropy stimulated grain expansion in the NILC high-temperature second annealing, enhanced grain quality beyond that on planar polysilicon film.

Transistor fabricated on these wire is similar to gate-all-around structure as that of FinFET [2]. Much better scalability to the deep submicron region was observed for these wire transistors than regular planar TFTs formed on the same NILC film. Experimental results showed that a wide transistor formed by the parallel combination of the quantum wire transistors much higher current drive than a TFT on the same NILC film with equivalent width.
A Model for Heterogeneous Nucleation and Growth of Silicon Nanoparticles on Silicon Dioxide from Disilane
Authors: Leach William T. , Zhu Jian-Hong , Ekerdt John G. , Mashiro Supika , Sakai Junro , Kawshima Takayuki
Published: April 2011

A model is presented that describes silicon nanoparticle deposition in terms of disilane decomposition on silicon dioxide, adatom diffusion, nucleation, nanoparticle growth and coalescence. Total nanoparticle densities are output as a function of time, and segregation of nanoparticles into subsets with common size allows size distributions to be reported for all times during the simulation. Model parameters are fit to low pressure chemical vapor deposition data with disilane pressures ranging from 5×10−4 to 5×10−3 Torr and surface temperatures from 510 to 570 °C. Simulations are used to explain how growth pressure and surface temperature influence incubation time, nanoparticle density and size distribution.
Size Effects Determined from Tensile Tests of Perforated MEMS Scale Specimens
Authors: Chasiotis Ioannis , Knauss Wolfgang G.
Published: April 2011

A systematic study of small-scale size effects has been conducted on elliptically perforated specimens with minimum radius of curvature of 1 micron. This study aimed at assessing the dependence of failure stress at the tip of a notch on varying: (a) stress concentration for constant radius of curvature, (b) radius of curvature of micro-notches relative to the material grain size and constant stress concentration. The experiments demonstrate a strong influence of notch radius on the failure strength of MEMS scale specimens, while the effect of the stress concentration factor is of rather secondary importance. The local failure strength at the tip of a notch increases when the radius of curvature becomes smaller, which is in accordance with the probabilistic nature of failure. When the notch radius becomes as small as 1 micron (only three times larger than the grain size) then a strong size effect is observed. This effect becomes moderate for larger radii of curvature, up to 8 microns (25 times the grain size), when the failure stress at the notch tip almost reaches the tensile strength recorded for 50 micron wide samples.
Micromachined Nanoparticulate Ceramic Gas Sensor Array on Mems Substrates
Authors: Heule Martin , Gauckler Ludwig J.
Published: April 2011

In most MEMS applications, dust and particles are avoided with considerable endeavor. However, for many applications such as gas sensors, powders of functional ceramics would often provide better performance than corresponding thin film layers. There are abundant ways to synthesize powders with well defined chemical composition, phase and size distribution, whereas the processing parameters for thin-film preparation often are limited. Specifically where the functionality is based on a chemical reaction on surfaces, nanoscaled powders with a high specific surface area have proven useful. This is the case for tin oxide gas sensors that exhibit a drop in electrical resistivity induced by the combustion of the analyte gas. Soft lithography was used for the fabrication of mesoscaled powder-based ceramic structures. In this paper, we present the integration of small tin oxide microstructures with an effective gas-sensing area of 10 by 30 νm2 on a micro-hotplate substrate. Such a substrate can heat the ceramic sensor to operating temperatures quickly with low power consumption. A whole array of sensors can be integrated on one micro-hotplate. Processing steps to prepare the sensor array on the micro hot plate are presented and discussed concerning processing sequence, sensitivity towards 1000 to 1500 ppm hydrogen and power consumption. Additionally, effects of grain growth due to on-chip annealing of the ceramic nanostructure were observed.
Charge Transport in Low Stress Si-rich Silicon Nitride Thin Films
Authors: Habermehl S. , Carmignani C.
Published: April 2011

Field dependent bulk charge transport in Si-rich, low stress silicon nitride thin films is studied in correlation to the local atomic Si-N bond strain. Across a range of film compositions varying from fully stoichiometric Si3N4 to Si-rich SiN0.54, Poole-Frenkel emission is determined to be the dominant charge transport mechanism with the Poole- Frenkel barrier height found to decrease concomitantly from 1.10 to 0.52 eV. Across the same composition range the local residual Si-N bond strain, as measured by FTIR spectroscopy, is observed to vary from 0.006 to –0.0026. Comparison of the barrier height to the residual strain reveals a direct correlation between the two quantities. It is concluded that reductions in the Poole-Frenkel barrier height are a manifestation of compositionally induced strain relief at the molecular level. Reductions in the barrier height result in increased Poole-Frenkel emission detrapping rates and consequently higher leakage currents in Si-rich films.