bluuebunny/crossref_metadata_2025 huggingface dataset:
Phonon-Polariton Propagation, Guidance, and Control in Bulk and Patterned Thin Film Ferroelectric Crystals
Authors: Ward David W. , Statz Eric , Beers Jaime D. , Stoyanov Nikolay , Feurer Thomas , Roth Ryan M. , Osgood Richard M. , Nelson Keith A.
Published: April 2011

Using time resolved ultrafast spectroscopy, we have demonstrated that the far infrared (FIR) excitations in ferroelectric crystals may be modified through an arsenal of control techniques from the fields of guided waves, geometrical and Fourier optics, and optical pulse shaping. We show that LiNbO3 and LiTaO3 crystals of 10–250 μm thickness behave as slab waveguides for phonon-polaritons, which are admixtures of electromagnetic waves and lattice vibrations, when the polariton wavelength is on the order of or greater than the crystal thickness. Furthermore, we show that ferroelectric crystals are amenable to processing by ultrafast laser ablation, allowing for milling of user-defined patterns designed for guidance and control of phonon-polariton propagation. We have fabricated several functional structures including THz rectangular waveguides, resonators, splitters/couplers, interferometers, focusing reflectors, and diffractive elements. Electric field enhancement has been obtained with the reflective structures, through spatial shaping, of the optical excitation beam used for phonon-polariton generation, and through temporal pulse shaping to permit repetitive excitation of a phonon-polariton resonant cavity.
Design of a New Taper for Light Coupling Between a Ridge Waveguide and a Photonic Crystal Waveguide
Authors: Jamois Cécile , Geppert Torsten , Wehrspohn Ralf B.
Published: April 2011

We propose the design of a new taper to improve light coupling between a photonic-crystal-based W1 waveguide and a ridge waveguide of similar width. The taper design is directly deduced from band structure calculations and allows an adiabatic mode conversion. The comparison between light propagation from the ridge waveguide through the W1 waveguide and through the taper, respectively, shows good improvement of the coupling efficiency.
Dispersion Engineering of Photonic Crystal Devices
Authors: Pustai David M. , Chen Caihua , Sharkawy Ahmed , Shi Shouyuan , Murakowski Janusz , Prather Dennis W.
Published: April 2011

We present and experimentally validate self-collimation in planar photonic crystals as a new means of achieving structureless confinement of light in optical devices. We demonstrate the ability to arbitrarily guide and route light by exploiting the dispersive characteristics of the photonic crystal. Propagation loss as low as 2.17 dB/mm is measured, and the experimental validation of routing structures are presented.
Temperature Controlled Scanning Nonlinear Dielectric Microscopy
Authors: Ohara K. , Cho Y.
Published: April 2011

Scanning Nonlinear Dielectric Microscopy (SNDM) can obtain the linear and nonlinear dielectric constant distribution of dielectric and ferroelectric materials with sub-nanometer resolution. In this paper, we present the new type of SNDM which can control the sample temperature (80K-730K) in vacuum (less than 5×10−7 Torr), and its application to measure the surface polarization state on LiTaO3 single crystal.
Room Temperature Dielectric Function of Low Dimensional TlMeX2
Authors: Mamedov Nazim , Wakita Kazuki , Akita Seiji , Nakayama Yoshikazu
Published: April 2011

Room temperature ellipsometric measurements of low dimensional TlMeX2 (Me=Ga, In; X=S,Se,Te) were performed in the photon energy range 1.5–6.5e V.Obtained ellipsometric data were then treated with allowance for optical anisotropy of the above materials. The components of dielectric function tensor were determined. The structures of the obtained dielectric function are interpreted in terms of the angle resolved photoemission and band structure results. The contribution of the atomic states of each atom (Tl, In, Se) in the band states in the point M of the Brillouin zone is traced back using LCAO analysis. An ultraviolet window in the joint density of electronic states of some of TlMeX2 is disclosed and substantiated to be a sign of ferroelectricity at room temperature. For the first time the nanorods of TlMeX2 are demonstrated.
Investigation of Valence State of U, Pu, and Am in Crystalline Host-Phases Using in situ Cathodoluminescence Spectroscopy
Authors: Zamoryanskaya Maria V. , Burakov Boris E. , Garbuzov Vladimir M.
Published: April 2011

Ceramics compounds based on the pyrochlore, (Ca,Gd,Hf,An)2TiO7; zircon, (Zr,An)SiO4, and garnet, (Y,Gd,An‥)3(Al,Ga,An…)5O12, where An = U, Am, Pu, Np, Cm, structures have been investigated to determine their use as durable nuclear waste forms for the immobilization of weapons-grade plutonium and other actinides. U, Pu, and Am were incorporated into synthetic zircon, pyrochlore, and garnet and were investigated using in situ cathodoluminescence (CL) and compared with Ce3+, Ce4+, Eu2+ and Eu3+ in order to determine the valence state of the actinide dopants. The results obtained allow for the identification of Am3+ ions in synthetic zircon and garnet. The CL emission of Am3+ is characterized by narrow bands in the orange-red spectral region and is similar to CL emission of Eu3+ in zircon and garnet. No characteristic CL emission of Pu4+ was observed in zircon, pyrochlore or garnet. This is similar to CL emission of Ce4+, which does not have characteristic CL emission in the visible region of the spectrum. Although ions of Ce3+ were characterized by intense CL emission, no characteristic CL emission of Pu3+ was identified in zircon, pyrochlore, or garnet.

The CL study of U-doped garnet and pyrochlore allow for the identification of the presence of two forms of uranium: the uranyl ion, (UO2)2+, and tetrahedral complex, (UO4)2−. Ions of U4+ did not have characteristic CL emission in the visible region. The study of pyrochlore samples doped simultaneously with 238Pu and 238U revealed that CL intensity of the uranyl ion increases with increasing dose of self irradiation from the 238Pu. It was assumed that self-irradiation might cause the change of actinide valence state.
Competition Between Internal and Surface Crystallization in Glass-ceramics Developed for Actinides Immobilization
Authors: Loiseau Pascal , Caurant Daniel , Majerus Odile , Baffier Nöel , Fillet Catherine
Published: April 2011

Glass-ceramic matrices containing zirconolite (nominally CaZrTi2O7) as the only crystalline phase in their bulk can be considered as good candidates for actinide-rich nuclear wastes (containing minor actinides or Pu) immobilization. In this study, three different methods are envisaged and compared to prepare such waste forms using neodymium as trivalent actinides surrogate. Independently on the preparation method, zirconolite is shown to be the only crystalline phase to nucleate in the bulk. However, crystallization of silicate phases (titanite CaTiSiO5 + anorthite CaAl2Si2O8) can occur from samples surface and can compete with zirconolite crystallization. The effect of the crystal growth thermal treatment duration (2–300 h) at high temperature (1050–1200°C) on glass-ceramics structure and microstructure is studied. In the oxides system studied here, it appears that zirconolite is not thermodynamically stable in comparison with titanite but, for kinetics reasons, such transformation will not occur during waste forms disposal.
Behavior of Uranium Dioxide: Chemistry and Catalysis in the UO2-water System
Authors: Devoy Jérôme , Haschke John , Cui Daqing , Spahiu Kastriot
Published: April 2011

Interactions during extended exposure of UO2 to 2:1 H2+O2 mixtures at room temperature and 0.13 bar pressure are investigated in an effort to describe chemical and kinetic behavior of spent fuel following contact with groundwater. Oxidation of UO2 to UO2+x by O2 occurs initially when oxide is directly exposed to the gas mixture or submerged in water, but immersion is accompanied by a 25-fold reduction in the rate. The initial rate is proportional to [O2]2 for gasphase oxidation and to [O2]1.5 for the submerged oxidation. Continued measurement during direct oxide-gas contact indicates sequential reactions in which the UO2+x product is further oxidized by H2O and ultimately reacts with H2 to form an oxide hydride.
Evaluation of Corrosion Processes Affecting the Performance of Alloy 22 as a Proposed Waste Package Material
Authors: Cragnolino Gustavo A. , Dunn Darrell S. , Pan Yi-Ming
Published: April 2011

This paper presents recent work on evaluating localized corrosion and stress corrosion cracking, two corrosion processes that are important to the long-term performance of Alloy 22 (58Ni-22Cr-13Mo-3W-4Fe). This alloy is the material preferred by the U.S. Department of Energy (DOE) for the outer container of the waste package to be used in the proposed high-level radioactive waste repository at Yucca Mountain, Nevada. It was found that both welded and thermally aged materials are more susceptible to localized corrosion in chloride solutions at temperatures above 60 EC than the mill-annealed material. This observation suggests that welding and certain post-welding operations may decrease the estimated life of the waste packages. However, no stress corrosion crack growth was observed in concentrated chloride solutions and simulated, concentrated groundwater at 95 EC when precracked compact tension specimens were tested under both constant and cycling loading.
The Impact of Cementitious Materials on the Corrosion of Copper Canisters
Authors: King Fraser , Werme Lars
Published: April 2011

Cementitious materials could be used in an underground repository as seals, bulkheads, grouts, or to provide a smooth surface for vehicles in the rooms and tunnels during repository construction. There is a possibility that an alkaline plume could be released from the cementitious materials in the repository and impact the corrosion behaviour of the canisters. The available literature information on the corrosion and electrochemical behaviour of copper in alkaline environments has been reviewed. Alkaline conditions promote passivation of the canister, whereas the presence of chloride groundwaters supports general dissolution. Localized corrosion due to an alkaline plume is considered to be unlikely because the protectiveness of the passive film (as measured by the difference between the corrosion and pitting potentials) increases with increasing pH.
The Use of Natural Uranium Decay Series Studies in Support of Understanding Redox Conditions at Potential Radioactive Waste Disposal Sites
Authors: Tullborg Eva-Lena , Smellie John A. T. , MacKenzie Angus B.
Published: April 2011

Uranium is a redox-sensitive element which occurs naturally in the bedrock and groundwaters in Fennoscandia, and can be used, in conjunction with its decay series descendants, to indicate groundwater redox conditions. Not only can contemporary conditions be characterised, but evidence of past changes (e.g. during the last glaciation some 10 ka ago) can be preserved in minerals which coat the fracture walls along groundwater pathways. Uranium decay series data for groundwaters and solid fracture phases from the site of the Äspö Hard Rock Laboratory and its near vicinity are presented and discussed in the context of redox conditions.
Gate Overlapped Lightly Doped Drain Poly-Si TFTs Employing 45° Tilt Implant For Source and Drain
Authors: Lee Jae-Hoon , Shin Moon-Young , Shin Heesun , Nam Woo-Jin , Han Min-Koo
Published: April 2011

We propose a short channel gate overlapped lightly doped drain (GOLDD) poly-Si TFT employing 45° tilt implant for source and drain (S/D) regions without any additional ion doping or mask. Oblique-incident ELA activation is performed to activate both n+ S/D and n- LDD regions as well as cure junction defects. The proposed poly-Si TFT can suppress the anomalous leakage current, and exhibit the better reliability against the hot-carrier stress.
Metal induced crystallization of SiGe at 370°C for monolithically integrated MEMS applications
Authors: Sedky Sherif , Baert Kris , Hoof Chris Van , Wang Yi , Biest Omer Van Der , Witvrouw Ann
Published: April 2011

Over the last decade SiGe has been proposed as a structural material for low thermal budget microelectromechanical systems (MEMS) that can be post-processed on top of standard CMOS driving and controlling electronics [1-6]. There are several ways to decrease the deposition temperature of SiGe and at the same time preserve the desired physical properties for MEMS as low electrical resistivity, high quality factor, economical growth rate and low mean stress and strain gradient. The conventional approach to reduce the crystallization thermal budget is to increase the germanium content to 60%, or more, using conventional Low Pressure Chemical Vapor Deposition (LPCVD) [1-3]. In this case highly conductive polycrystalline films can be realized, but the strain gradient is relatively high. This can be eliminated by furnace annealing at 450°C [2], which might introduce damage to the underlying circuits such as in the case of Cu/low k CMOS. This problem can be alleviated using excimer pulsed laser annealing [7, 8], which has been attractive for low thermal budget applications such as thin film transistors (TFT) [9], solar cells fabricated on glass substrates [10] and for monolithic integration of MEMS devices on top of standard driving electronics using SiGe as an active material [8, 11]. Also the use of hydrogenated microcrystalline SiGe allows for a low thermal budget [12]. In addition, metal induced crystallization has recently been proposed to enhance the crystallization of silicon at temperatures as low as 500°C, and the realized devices had outstanding performance compared to those employing conventional solid-phase crystallization [13]. This technique enhances crystallization by two methods. First, it has been observed that depositing SiGe on top of a thin Al or Ni layer, has a polycrystalline micro-structure close to the metal/ SiGe interface [11]. Annealing this film for a long period (is determined by the annealing temperature), results in metal diffusion and a subsequent crystallization of the film. Finally, when the metal is diffused completely through out the film, it can be etched away. The main disadvantage of this approach is that the mean stress is highly compressive and this might affect the functionality of surface micromachined structures [13].
Characterization of the Bulk Recombination in Hydrogenated Amorphous Silicon Solar Cells
Authors: Deng J. , Pearce J.M. , Vlahos V. , Collins R.W. , Wronski C.R.
Published: April 2011

Dark forward bias current, JD-V, characteristics offer a probe for characterizing carrier recombination and the defect states in the intrinsic layers of hydrogenated amorphous silicon (a-Si:H) solar cells. Detailed studies were carried out on such characteristics for the cells with optimized p/i interfaces and high quality i-layers in which the current transport is bulk recombination dominated. It was found that the diode quality factor n is not a constant with bias voltages as has been generally considered. Instead, it can be best described through the bias dependent differential diode quality factors, n(V) = [kT/q]−1[d(lnJD)/dV]−1, whose magnitude and shape reflect the gap state distribution in the corresponding bulk i-layers. The n(V) characteristics obtained on cell structures with both hydrogen diluted and undiluted i-layers have been utilized in characterizing the differences in the distribution of defect states in the two i-layers both in annealed state as well as after creating light induced defects. In the characterization of the Staebler-Wronski Effect (SWE) using JD-V characteristics, a newphenomenon is observed – relaxation of light induced defect states created by 1 sun illumination at 25°C, which is also found in the follow-on studies on the photo-conductivities of corresponding thin films.
Microcrystalline Silicon Solar Cell Deposited Using Modified Very-High-Frequency Glow Discharge and Its Application in Multi-junction Structures
Authors: Yue Guozhen , Yan Baojie , Owens Jessica M. , Yang Jeffrey , Guha Subhendu
Published: April 2011

We have used the modified very-high-frequency glow discharge technique to deposit hydrogenated microcrystalline silicon (m c-Si:H) solar cells at high rates for use as the bottom cell in a multi-junction structure. We have investigated c-Si:H single-junction, a-Si:H/ c-Si:H double-junction, and a-Si:H/a-SiGe:H/m c-Si:H triple-junction solar cells and achieved initial active area efficiencies of 7.7%, 12.5%, and 12.4%, respectively. Issues related to improving material properties and device structures are addressed. By taking advantage of a lower degradation in m c-Si:H than a-Si:H and a-SiGe:H alloys, we have minimized the light induced effect in multi-junction structures by designing a bottom-cell-limited current mismatching. As a result, we have obtained a stable active-area cell efficiency of 11.2% with an a-Si:H/a-SiGe:H/μ c-Si:H triple-junction structure.
Deposition of Optimal a-Si:H and a-SiGe:H by HWCVD Using the Same Filament Temperature and Substrate Temperature
Authors: Mahan A.H. , Xu Y. , Gedvilas L.M.
Published: April 2011

The incorporation of high Ge content a-SiGe:H into a low bandgap solar cell device commonly involves the use of bandgap (Ge) profiling. In previous work using the hot wire (HWCVD) technique, device quality low bandgap (ETauc= 1.25eV) a-SiGe:H films were deposited at low Tsub(∼200-250°C) filament operating at Tfil∼ 1750-1800°C. However, higher bandgap films containing little or no Ge and deposited under the same low temperature (Tsub,Tfil) conditions were of decidedly inferior quality to those deposited using higher temperatures (Tfil∼2000°C,Tsub∼360°C) solar cell with an efficiency ∼ 5.85% was fabricated using these materials, it was clear that our best ‘end point’ materials alloying at this low Tfilseverely limits film reproducibility and filament lifetime. This work explores deposition of device quality low bandgap a-SiGe:H and (high bandgap) a-Si:H, both at the same low Tsub, using a tantalum (Ta) filament operating at low Tfil. Film material properties are presented.
Extension of the Constant Photocurrent Method to Determine Densities of Occupied and Unoccupied Localised States
Authors: Main Charlie , Reynolds Steve , Zrinŝcak Ivica , Merazga Amar
Published: April 2011

This paper examines the use of Constant Photocurrent (CPM) measurements on thin film semiconductors, employing steady (DC) and modulated (AC) sub-gap illumination, to determine the density of localised states (DOS) in the bandgap. AC and DC measurements often result in different apparent absorption spectra. It is demonstrated that it is possible not only to extract information from the respective 'absorption' spectra, on the DOS below the Fermi level - i.e. occupied states, but also on the density of unoccupied states above the Fermi level. The ability to discriminate between these two groups of states by using DC and AC modulated sub-gap light arises from the frequency dependence of the different excitation pathways by which free electrons can be produced. AC modulated excitation will reveal absorption associated with transitions from occupied states into the conduction band, while DC excitation will include transitions from the valence band into unoccupied defect states, followed by slow thermal emission to the conduction band. We examine the temperature dependence of the CPM spectra and present a simple analysis of the DC and AC absorption spectra which allows the two regions of the DOS, above and below the Fermi level, to be determined.
Hydrogen Injection in ETP Plasma Jet for Fast-Deposition of High-Quality a-Si:H
Authors: Petit A.M.H.N. , Swaaij R.A.C.M.M. van , Sanden M.C.M. van de
Published: April 2011

We have used a cascaded-arc expanding thermal plasma (ETP) to produce thin films of amorphous silicon at high growth rates (> 3 nm/s). Here, we present a study of the effect on material properties of hydrogen injection in the nozzle, i.e., at the exit of the arc where the plasma expands into the reactor chamber. The advantage of using extra H2 in the nozzle is that the plasma chemistry and pressure in the arc remain unchanged, whilst higher growth rates and a material with low defect densities can be obtained.

We observe that with an increase of substrate temperature the growth rate decreases due to densification of the material. This densification is accompanied by a reduction of the hydrogen content and of the microstructure parameter. Further we observe that hydrogen content decreases with higher growth rate. A strong relation is found between the light conductivity and the microstructure parameter indicating a large void fraction in samples grown at low temperature.

We have been able to grow a-Si:H material, with H2 in the nozzle, at 350°C and 3 nm/s with a light conductivity of 1.2 × 10−5 Ω1cm−1, which can be suitable for solar-cell application.
Recessed and Epitaxially Regrown SiGe(B) Source/Drain Junctions with Ni salicide contacts
Authors: Isheden Christian , Hellström Per-Erik , Radamson Henry H. , Östling Mikael
Published: April 2011

Integration issues concerning recessed epitaxial SiGe(B) source/drain junctions formed by selective Si etching followed by selective epitaxial growth of in situ heavily B-doped Si1−xGex are presented. The concept is beneficial compared to conventional ion implanted junctions, since dopant activation above the solid solubility in Si can be obtained. When integrated in the PMOS process flow, the resulting Si1−xGex layer is very rough. Several possible causes for low quality epitaxy are discussed and improvements are proposed. It is suggested that the dopant type and/or concentration in the silicon substrate can have an effect on the process.
On the “Life” of {113} Defects
Authors: Cherkashin N. , Calvo P. , Cristiano F. , Mauduit B. de , Claverie A.
Published: April 2011

In this paper, we present a new set of conditions which can be used for imaging {113} defects. These conditions have the advantage of allowing the simultaneous imaging of all the variants of the defects. They can be used for building up accurate size-histograms or for checking the occurrence of the different variants. Making use of these conditions, we revisit the well- known experiments of the dissolution of the {113} defects and pinpoint some specific features of defect evolution during annealing which were not evidenced in previous works. The new results are discussed and are definitely found to be well-explained in the framework of a non- conservative Ostwald ripening.
Strain Relaxation of Ion-implanted Strained Silicon on Relaxed SiGe
Authors: Crosby R. T. , Jones K. S. , Law M. E. , Saavedra A. F. , Hansen J. L. , Larsen A. N. , Liu J.
Published: April 2011

The relaxation processes of strained silicon films on silicon-rich relaxed SiGe alloys have been studied. Experimental structures were generated via Molecular Beam Epitaxial (MBE) growth techniques and contain a strained silicon capping layer of approximately 50 nm. The relaxed SiGe alloy compositions range from 0 to 30 atomic% germanium. Samples received two distinct types of silicon implants. A 12 keV Si+ implant at a dose of 1×1015 atoms/cm2 was used to generate an amorphous layer strictly confined within the strained Si cap. An alternate 60 keV Si+ implant at a dose of 1×1015 atoms/cm2 was employed to create a continuous amorphous layer extending from the sample surface to a position 50 nm into the bulk SiGe material. The strain relaxation and regrowth processes are quantified through High Resolution X-Ray Diffraction (HRXRD) rocking curves and Cross-sectional Transmission Electron Microscopy (XTEM). The role of injected silicon interstitials upon the strain relaxation processes at the Si/SiGe interface after annealing at 600°C is investigated.
Ni Silicide Morphology On Small Features
Authors: Chamirian Oxana , Lauwers Anne , Kittl Jorge A. , Dal Mark Van , Potter Muriel De , Vrancken Christa , Lindsay Richard , Maex Karen
Published: April 2011

ABCTRACT

Silicidation of small features of various geometries and sizes using Ni-silicide was studied. Effects of dopants, surface preparation and silicidation parameters on silicide morphology were investigated. It was found that Ni silicide thickness and quality of the silicide/silicon interface (presence of NiSi2 pyramids) are dependent on the area dimensions and geometry. NiSi formed on narrow lines is thicker compared to wide areas. We found that pyramids of epitaxial NiSi2 protruding into the Si substrate are formed during the silicidation of undoped, boron-doped and BF2-doped active areas. The presence of pyramids was not observed on As-doped silicon. Rough interface due to the pyramids could be the reason for a more pronounced linewidth dependence of leakage current in the case of p+/n diodes. A higher density of pyramids was found on narrow lines (below 0.2μm) and particularly islands structures. No pyramids were found when a Ge preamorphisation implant was used.
Effect of Ge-rich Si1−zGez Segregation on the Morphological Stability of NiSi1−uGeu Film Formed on Strained (001) Si0.8Ge0.2 Epilayer
Authors: Yao H.B. , Chi D.Z. , Tripathy S. , Chow S.Y. , Wang W.D. , Chua S. J. , Sun H.P. , Pan X.Q.
Published: April 2011

The germanosilicidation of Ni on strained (001) Si0.8Ge0.2, particularly Ge segregation, grain boundary grooving, and surface morphology, during rapid thermal annealing (RTA) was studied. High-resolution cross-sectional transmission electron microscopy (HRXTEM) suggested that Ge-rich Si1−zGez segregation takes place preferentially at the germanosilicide/Si1−xGex interface, more specifically at the triple junctions between two adjacent NiSi1−uGeu grains and the underlying epi Si1−xGex, and it is accompanied with thermal grooving process. The segregation process accelerates the thermal grooving of NiSi1−uGeu grain boundaries at the interface. The segregation-accelerated grain boundary grooving has significant effect on the surface morphology of NiSi1−uGeu films in Ni-SiGe system.
Technology Computer Aided Design of Ultra-shallow Junctions in Si Devices Formed by Laser Annealing Processes
Authors: Magna Antonino La , Alippi Paola , Privitera Vittorio , Fortunato Guglielmo , Camalleri Marco , Svensson Bengt
Published: April 2011

The simulation of laser annealing, applied to the formation of ultra-shallow junctions in Si, is discussed. Our effort is developing tools capable to aid the process integration issue. The numerical approach deals with a double problem: 1) the interaction between the irradiated transistor structure and the laser light, 2) the non-equilibrium evolution of the thermal field, molten regions and dopant density. Here we present a complete methodology: the calculated heat source distribution, induced by the irradiation, is used as input of a phase-field approach for the simulation of the thermal phase and impurity fields. We solved numerically the phase field equations in two dimensional structures, considering as an initial status the generic material modification due to an ion implant process. We present various simulation results obtained in MOS structures with different geometry. With the support of the simulation results we discuss the problematic and the perspectives of the excimer laser annealing process application in the fabrication of MOS devices.
The Effect of Fluorine Implantation on Boron Diffusion in Metastable Si0.86 Ge0.14
Authors: El Mubarek Huda A. W. A. , Wang Yun , Bonar Janet M. , Hemment Peter , Ashburn Peter
Published: April 2011

This paper investigates the effect of varying F+ implantation energy on boron thermal diffusion and boron transient enhanced diffusion (TED) in metastable Si0.86Ge0.14 by characterising the diffusion of a boron marker layer in samples with and without P+ and F+ implants. The effect of two F+ implantation energies (185keV and 42keV) was studied at two anneal temperatures 950°C and 1025°C. In samples implanted with P+ & 185keV F+, the fluorine suppresses boron transient enhanced diffusion completely at 950°C and suppresses thermal diffusion by 25% at 1025°C. In samples implanted with P+ & 42keV F+, the fluorine does not reduce boron transient enhanced diffusion at 950°C. This result is explained by the location of the boron marker layer in the vacancy-rich region of the fluorine damage profile for the 185keV implant but in the interstitial-rich region for the 42keV implant. Isolated dislocation loops are seen in the SiGe layer for the 185keV implant. We postulate that these loops are due to the partial relaxation of the metastable Si0.86Ge0.14 layer.
Thermal Stability and Electrical Properties of Ag(Al) Metallization
Authors: Kim Hyunchul C. , Theodore N. David , Mayer James W. , Alford Terry L.
Published: April 2011

The thermal stability and electrical resistivity of Ag(Al) alloy thin films on SiO2 are investigated and compared to pure Ag thin films by performing various analyses: Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), transmission electron microscopy (TEM), and four-point probe. The susceptibility to agglomeration of Ag on SiO2 layer is a drawback of Ag metallization. Ag(Al) thin films show good thermal stability on SiO2 layer without any diffusion barrier. The films are stable up to 600 °C for 1 hour in vacuum. Electrical resistivity of as-deposited Ag (5 at % Al) thin film is slightly higher than that of pure Ag thin film. However, the resistivity of Ag(Al) samples annealed at high temperatures (up to 600 °C for 1 hour in vacuum) remains constant due to the improvement of thermal stability (large reduction of agglomeration). This finding can impact metallization for thin film transistors (TFT) for displays, including flexible displays, and high-speed electronics due to lower resistivity value compared to Cu thin film.
New hybrid low-k dielectric materials prepared by vinylsilane polymerization
Authors: Kang Jung-Won , Kim Byung Ro , Kang Gwi-Gwon , Moon Myung-Sun , Choi Bum-Gyu , Ko Min-Jin
Published: April 2011

Spin-on Low-K materials are potentially very attractive as interconnection materials in a wide range of semiconductor structures. In this work, new organic-inorganic hybrid materials synthesized by vinylsilane polymerization were proposed. According to compositions and additional fabrications, dielectric constants of these materials were evaluated to be 2.3∼3.1. The hardness was 2.0GPa after 430°C curing. These materials had good adhesion strength such that fracture toughness on silicon wafer was 0.22 MPam0.5 without any adhesion promoters. This result indicates that these organicinorganic hybrid materials are very promising candidates for low-K dielectrics.
Scanning Near-Field Microwave Probe for In-line Metrology of Low-K Dielectrics
Authors: Talanov Vladimir V. , Moreland Robert L. , Scherz André , Schwartz Andrew R. , Liu Youfan
Published: April 2011

We have developed a novel microwave near-field scanning probe technique for non-contact measurement of the dielectric constant of low-k films. The technique is non-destructive, noninvasive and can be used on both porous and non-porous dielectrics without any sample preparation. The probe has a few-micron spot size, which makes the technique well suited for real time low-k metrology on production wafers. For dielectrics with k<4 the precision and accuracy are better than 2% and 5%, respectively. Results for both SOD and CVD low-k films are presented and show excellent correlation with Hg-probe measurements. Results for k-value mapping on blanket 200mm wafers are presented as well.
Chemical Routes to Improved Mechanical Properties of PECVD Low K Thin Films
Authors: Bilodeau S.M. , Borovik A.S. , Ebbing A.A. , Vestyck D.J , Xu C. , Roeder J.F. , Baum T.H.
Published: April 2011

Increasing the elastic modulus and hardness of low K films is one of the key challenges towards integration of these materials into future integrated circuits. Several approaches are explored for increasing the hardness of carbon doped oxide (CDO) dielectrics. Several low K precursors and their mixtures specifically chosen to enhance the hardness (H) and modulus (E) of CDO films through chemically induced cross-linking. Composition and FTIR measurements suggest the presence of C-C and C-Si cross-linking with concurrent observation of improved film hardness and modulus at relatively low deposition temperatures. Films deposited at 373°C using diethoxy-methyl-oxiranyl have a hardness and modulus of 2.5 GPa and 18.1 GPa respectively. Films deposited at 180°C using tetramethylcyclotetrasiloxane (TMCTS) and 25% hardener have hardness and modulus of 1.5 GPa and 9.4 GPa, respectively. These film properties are significantly higher than those observed for TMCTS alone under similar deposition conditions. Based on these results a low temperature process with 25% hardener and 75% TMCTS combined with a porogen was used to produce a porous film with a k<2.5 and a hardness of 0.72GPa.
Thermomechanical Stresses in Copper Interconnect/Low-κ Dielectric Systems
Authors: Shen Y.-L. , Ege E. S.
Published: April 2011

Numerical simulations of thermal stresses in copper interconnect and low-κ dielectric systems are carried out. The analyses include two- and three-dimensional finite element modeling of the interconnect structure. Various combinations of metal, oxide and polymer-based low-κ dielectric schemes are considered in the simulation. The evolution of stresses and deformation pattern in copper, barrier layers, and the dielectrics are critically assessed.
Dry Etch and Wet Clean Process Characterization of Ultra Low-k (ULK) Material Nanoglass®E
Authors: Murthy B. Ramana , Chang C.K. , Ahilakrishnamoorthy  , Chen Y.W. , Naman Ananth
Published: April 2011

NANOGLASS®E (NGE) ultra low-k (ULK) dielectric material, with a k-value of ∼2.2, was integrated for 130 nm Cu/ULK interconnect process technology. This work deals with the characterization of reactive ion etching (RIE) and wet chemical processing of this film. Blanket films were characterized for etch rate, surface roughness, k-value change and chemical compatibility. Trench etching and post etch wet clean processes were developed and optimized enabling process integration for single damascene structures. Trench etch processes were evaluated for two etch schemes viz., etching under - photo resist and etching under hardmask. The details of each scheme will be described and advantages observed will be discussed. To evaluate effect of wet clean processes three different formulations were used. After formation of single damascene wafers, metal comb and serpentine structures were measured for metal continuity and bridging. Electrical continuity was achieved for long serpentine structures with 0.18μm/0.18μm line width/spacing. Based on voltage ramp test results the film was found to be sensitive to certain plasma etch conditions.
The Influence of Temperature and Concentration on Copper Deposition Kinetics in Supercritical Carbon Dioxide
Authors: Zong Yinfeng , Watkins James J.
Published: April 2011

The kinetics of copper deposition by the hydrogen-assisted reduction of bis(2,2,7- trimethyloctane-3,5-dionato)copper in supercritical carbon dioxide was studied as a function of temperature and precursor concentration. The growth rate was found to be as high as 31.5 nm/min. Experiments between 220 °C and 270 °C indicated an apparent activation energy of 51.9 kJ/mol. The deposition kinetics were zero order with respect to precursor at 250 °C and 134 bar and precursor concentrations between 0.016 and 0.38 wt.% in CO2. Zero order kinetics over this large concentration interval likely contributes to the exceptional step coverage obtained from Cu depositions from supercritical fluids.
Charge trapping and scattering by extrinsic gas dopants in tris(8-hydroxyquinoline) aluminum (Alq3)
Authors: Fong H.H. , So S.K.
Published: April 2011

The effects of various ambient gases (N2, O2, H2O) to the electron mobility of tris(8-hydroxyquinoline) aluminum, Alq3, were examined. For a clean Alq3, the electron transport is non-dispersive and essentially trap-free as revealed by optical time-of-flight measurements. At 295K, the electron mobility (μe) spans the range 0.2-1×10−6cm2V−1s−1 when the field varies from 0.4-0.9 MV cm−1. Exposing the sample to oxygen dosages in the range 1-100 Torr.s does not cause any noticeable changes in μe. The effect of oxygen on μe can be observed only at much higher oxygen dosages (>105 Torr.s). In contrast, exposing pristine Alq3 to moisture of same dosages causes a gradual reduction in μe by a factor of 4. It is proposed that oxygen diffuses into Alq3 during exposure and subsequently acts as charge scattering centers for externally injected free electrons. On the other hand, water induces charge traps at high dosages. Moisture control appears to be the most critical factor for the long-term operation of Alq3-based organic light-emitting diodes.
a-Si TFT OLED Fabricated on Low-Temperature Flexible Plastic Substrate
Authors: Sarma Kalluri R.
Published: April 2011

Active matrix organic light emitting diode (AM OLED) display fabricated on a flexible plastic substrates has a potential for being lower cost, lighter weight, lower power and highly rugged with superior image quality, compared to the current glass substrate based AM LCDs. Amorphous silicon (a-Si) technology offers the potential for fabricating the required active matrix backplanes on low temperature (< 150°C) plastic substrates for producing flexible AM OLED displays. We have developed low-temperature a-Si TFT processes, and backplane electronics designs to fabricate and successfully demonstrate AM OLEDs using 4”-size flexible plastic substrates. Flexible AM OLED test displays with sizes up to 2×2-inch and resolutions up to 80 cgpi equivalent have been designed and fabricated. The required enabling technologies and fabrication and evaluation of these displays are discussed.
A Simple Explanation on the Crystallization Kinetics of a Cw Laser Crystallization of Amorphous Silicon
Authors: Park Seong Jin , Kang Sang Hoon , Ku Yu Mi , Jang Jin
Published: April 2011

We have studied a CW laser crystallization (CLC) of various-shaped a-Si patterns on glass with changing scanning speed and laser power. The crystallized region inside the patterns showed 3 distinct regions, which is distinguished by their grain size; fine grains of several tens of nanometers near the edge of the pattern, very large grains over a few micrometers at the center of the pattern, so called Sequential Lateral Crystallization region and large grains about a micrometer or less between SLC and fine grain regions. This phenomenon is due to the formation of 2-D temperature gradient inside the pattern. One is the temperature gradient between the edge and center; the temperature of outer region is lower than that of inner region during or right after a CW laser scanning. The other is the temperature gradient along the scan direction; the temperature of starting region of a CW laser scanned area is lower than that of ending region. The former contributes mainly to make molten silicon area inside a pattern, and the latter induces lateral growth along the scan direction to make long grains in SLC region.
Flexible Substrate Based Gas Sensors for Air Pollution Monitoring
Authors: Dmitriev S. , Duca Gh. , Dementiev I. , Craciun A.
Published: April 2011

In the given report we present results of investigation of possibility to produce gas sensors on flexible substrates (polymer roll base). As gas sensitive materials were chosen glass chalcogenide semiconductors on the base of solid solutions of (As2S3)x-(As2Se3)1−x (where x=0; 0.3; 0.5; 0.7 and 1.0) and also solid solutions of As-Tl-S-Se system. Thin films of the mentioned above materials were deposited on lavsan roll film by means of thermal evaporation under vacuum conditions 10-5 Torr. At the thickness of 1-2 um the deposited layers are possessed the specific resistance in the range of 1010-1014 Ohm.cm on dependence on chemical composition.

The change of conductivity of these films in the presence of gas impurity in atmosphere was used as sensitive parameter. Gas sensitive characteristics of obtained structures were tested with such toxic and inflammable environmental pollutant gases as carbon monoxide, methane, nitrogen dioxide, hydrogen and other. All measurements of gas sensitivity were performed at room temperature. For further increase of the gas sensitivity and selectivity the very thin layer of Pd was deposited onto the surface of semiconductor layer. The last one has allowed to increasing the gas sensitive characteristics by order.

Through routine technology mode ready gas sensors were created. Dimensions of the developed gas sensitive elements were 1000×1000×350 μm.
High Quality Gate Insulator for Very-Low Temperature Poly-Si TFT Employing Nitrous Oxygen Plasma Pre-Treatment
Authors: Shin Moon Young , Han Sang-Myeon , Lee Min-Cheol , Shin Hee-Sun , Han Min-Koo , Kwon Jang-Yeon , Noguchi Takashi
Published: April 2011

We have proposed nitrous oxide (N2O) plasma pre-treatment in order to reduce the oxide charge densities as well as to increase the breakdown field of silicon dioxide film for flexible display. Our experimental results show that the proposed treatment improved both the flat-band voltage from –3V to –1.8V and the breakdown voltage of gate oxide from 7MV/cm to 9.5MV/cm, respectively. The proposed treatment also improved poly-Si TFT characteristics such as low sub-threshold swing of 0.43V/dec.
Role of Coincident Site Lattice Boundaries in Creep and Stress Corrosion Cracking
Authors: Was G.S. , Alexandreanu B. , Andresen Peter , Kumar Mukul
Published: April 2011

Interfaces control many properties in engineering materials, several of which are critical to the integrity of the engineering structure. In single phase, solid solution, austenitic alloys, grain boundaries are often the weak link, displaying susceptibility to creep, corrosion and stress corrosion cracking. As such, grain boundary structure control affords the opportunity to improve the overall performance of alloys in a variety of applications. The role of coincident site lattice boundary (CSLB) enhancement and grain boundary connectivity is examined for how it affects the response of an alloy to stress and the environment. Specifically, the effect of grain boundary character on creep, grain boundary sliding, intergranular stress corrosion cracking, and irradiation assisted stress corrosion cracking in austenitic nickel-base (high purity Ni-Cr-Fe and alloy 600) and iron-base (high purity Fe-Cr-Ni and 304 stainless steel) alloys and for ferritic- martensitic alloy T91 is discussed.
Expressions for the effective diffusivity in materials with interphase boundaries
Authors: Belova Irina V. , Murch Graeme E.
Published: April 2011

We address the problem of calculating the long-time-limit effective diffusivity in stable two- phase polycrystalline material. A phenomenological model is used where the high diffusivity interphase boundaries are treated as connected “coatings” of the individual grains. Derivation of expressions for the effective diffusivity with segregation is made along Maxwell lines. Monte Carlo simulation using lattice-based random walks is used to test the validity of the expressions. It is shown that for the case analysed the derived expressions for the effective diffusivity are in very good agreement with simulation results. The equivalent of the Hart equation is also derived. It is shown to be in poor agreement with simulation results.
Dewetting on the Surface of Rutile
Authors: Gilliss Shelley R. , Ravishankar N. , Barry C.
Published: April 2011

After annealing a continuous SiO2 film on the (001) surface of TiO2, the film dewets and then spreads to form a complex pattern. The final droplet morphology displays a densely branching morphology similar to those seen in computer-simulated models. It is proposed that Bénard-Marangoni convection cells form within the film before dewetting occurs. The formation of Bénard-Marangoni convection cells prior to dewetting results in the uniform size and spacing of the droplets on the surface. These convection cells form at temperature when the TiO2 substrate dissolves into the SiO2 thin film. The change in composition results in regions of differing surface tensions and therefore leads to the formation of the convection cells.
Atomic-Scale Simulation of Grain Boundary Kinetics during Recrystallization
Authors: Trautt Z. , Upmanyu M.
Published: April 2011

We present two-dimensional molecular dynamics (MD) simulations of symmetric tilt grain boundary kinetics, driven by stored energy of deformation. The latter is introduced by prescribing a well-defined gradient in dislocation density across a flat grain boundary. Bicrystals simulations reveal that the boundary motion, albeit jerky, increases linearly with simulation time. We also employ a control simulation to extract the driving force for motion, which then yields a unique boundary mobility. Preliminary comparisons with curvature driven boundary migration for misorientations 30° and 22.78° suggest that misorientation dependence of boundary migration is significantly less anisotropic, in turn implying that the mechanism of motion itself is different.
Synthesis and Characterization of ZnO Nanoparticles
Authors: Abhulimen I. U. , Chen X. B. , Morrison J. L. , Rangari V. K. , Bergman L. , Das K.
Published: April 2011

Nanoparticles of ZnO were synthesized using a sonochemical technique. Sonochemistry arises from an acoustic cavitation phenomenon, that is, the formation, growth and implosive collapse of bubbles in a liquid medium. The ultraviolet photoluminescence (PL) studies of the samples showed a strong PL intensity and a significant blue shift relative to the PL of the bulk. Shifts up to 70 meV were observed and attributed to a confinement effect. Scanning electron microscopy indicated roughly spherical particles, ∼160 nm in diameter. However, nano-platelets and rods were observed in transmission electron micrographs. Preliminary electrical measurements indicated a highly resistive nature of the nanoparticulate material.
Growth, Characterization, and Application of High Al-content AlGaN and High Power III-Nitride Ultraviolet Emitters
Authors: Ren Z. , Jeon S.-R. , Gherasimova M. , Cui G. , Han J. , Peng H. , Song Y. K. , Nurmikko A. V. , Zhou L. , Goetz W. , Krames M. , Cho H.-K.
Published: April 2011

A study of Si-doped and Mg-doped AlxGa1-xN up to × ∼ 50 % and the characteristics of ultraviolet (UV) light emitting diodes (LEDs) with emission wavelengths at 340 nm and 290 nm are reported. By using grading super-lattices (SLs) before n-type AlGaN growth, surface roughness is much improved. Resistivity of 2.9×10-2 Ωcm and free electron concentrations of 2.9×10 cm- are achieved for n-type Al0.45Ga0.55N. The viability of effective p-type doping is defined by a minimum concentration of Mg required to offset the background impurities and, more importantly, a maximum limit above which inversion domains and structural defects start to nucleate, accompanied by a rapid degradation of electrical transport. Resistivity of 10 Ωcm and free hole concentrations above 1017 cm−3 are achieved for AlxGa1-xN up to × ∼ 50 % within an optimum window of Mg incorporation. Output powers up to 1.5 mW from small area 340 nm LEDs (< 100 μm diameter) and 110 μW from 290 nm LEDs (100 μm diameter) directly off a planar chip have been achieved under DC condition. For large area encapsulated lamp (1×1 mm2 device area and 0.52 mm2 mesa area), output power of 79 mW from 340 nm LEDs and 8.5 mW from 290 nm LEDs are achieved under pulse mode (1kHz, 2% duty factor).