bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of M Centers in InP
Authors: Wager J. F. , Vechten J. A. Van
Published: March 2011

Simple atomic models are proposed for three metastable centers in InP, which have been called “M centers”. All undergo “large lattice relaxation” and emit or absorb multiple electrons on changing atomic configuration. The one which has been most thoroughly studied is called M and is introduced by MeV electron irradiation. The second, called M:P, is present in as grown device quality InP and is a problem for MISFET devices. The third, called M:Fe, is present in Fe doped InP that has been processed at high T to produce a p+ region. Our model for M consists of a V−InP+In defect complex in one configuration and 2P+In + V+p in the other configuration. Transformation between these two configurations occurs by nearest neighbor hopping of a P atom between vacant sites. The “negative U” character of the M center is a simple consequence of the P atom hop. Our model for the M:P center is a V+p one configuration and a V−InIn−p in the other, the transformation occurs by In atom hopping. For the M:Fe center we tentatively propose Fe−In + V−In in one configuration and Fe−In V+PP+In for the other, the transformation again occurring by P atom hopping. It is also possible that the Fe occupies a bond centered interstitial position, Fe−2bc, in the first configuration and Fe−InV+P in the second, the transformation occurring by Fe atom motion. A distinction between these two possibilities can be made with a pressure dependence measurement. It is noted that the activation energies for these transformations support the Ballistic Model for vacancy migration.
Identification of the Double Acceptor States of Some Transition Metal Impurities in GaAs
Authors: Hennel A.M.
Published: March 2011

The double acceptor states of chromium, cobalt and nickel were identified by means of the optical and transport measurements under external fields such as hydrostatic pressure, uniaxial stress and magnetic field. The axial fields enable us to observe optical line splittings, which give information about defect symmetries. This technique has been used to identify a double acceptor state of nickel in the GaAs energy gap. High pressure eliminates a degeneracy between defect levels and crystal bands. This leads to activation of new charge states of some impurities. In the case of chromium and cobalt impurities, their double acceptor levels were found to be degenerate with the conduction band of GaAs. A trend existing for the energies of the double acceptor levels permits us to conclude that there will be no other acceptors among the transition metal impurities in GaAs.
High Resolution Transmission Electron Microscopy of Proton Implanted Gallium Arsenide
Authors: Sadana D. K. , Zavada J. M. , Jenkinson H. A. , Sands T.
Published: March 2011

High resolution transmission electron microscopy (HRTEM) has been performed on cross-sectional specimens from high dose (1016 cm−2) H+ implanted (100) GaAs (300 keV at room temperature). It was found that annealing at 500°C created small (20-50Å) loops on {111} near the projected range (Rp)(3.2 μm). At 550-600°C, voids surrounded by stacking faults, microtwins and perfect dislocations were observed near the Rp. A phenomenological model explaining the observed results is proposed.
A Study of Co and Mn in ZnO Varistors
Authors: Pike G. E. , Seager C. H. , Dosch R. G.
Published: March 2011

ZnO varistors are polycrystalline materials which have highly non—linear current/voltage characteristics controlled by depletion regions around the grain boundaries. Dissolved transition metals at concentrations of about 1 at.% are required to achieve this large nonlinearity, but their role is unclear. To address this issue we have usedthe technique of photothermal deflection spectroscopy to measure the optical absorption of varistors containing Co or Mn, both common dopants. Prominent peaks and edges appear in the spectra, and are associated with substitutional Co2+and Mn2+ ions whose ground states are deep within the ZnO bandgap. Electro— and photoluminescence spectra show Stokes shifted peaks for some of these transitions. The spectral dependence of the photoconductivity shows that some of the absorption features correspond to ionization of the impurities. This result is used to show how the dark impact ionization of these impurities due to a high applied voltage can contribute to the current/voltage nonlinearity.
Dry—Processing Induced Isolation—Degradation in GaAs Integrated Circuits
Authors: Chang M.F. , Lee C.P. , Sheng N.H. , Kirkpatrick C.G. , Chen R.T.
Published: March 2011

Our study shows that the isolation—degradation in semi—insulating GaAs substrate is closely related to dry—processes during the device fabrication. It was found that EL2, the major electron trap in undoped LEC semiinsulating GaAs, could be passivated by plasma—assisted etchings or depositions. The passivation of EL2 causessurface leakage and leads to crosstalk in GaAs ICs.
Role of Electron Microscopy in Semiconductor Electronic Defects Analysis
Authors: Petroff P. M.
Published: March 2011

A review of the Transmission Electron Microscopy and Scanning Transmission Electron Microscopy techniques used for electronic defect identification is presented. The structural, chemical and STEM based spectroscopy methods for electronic defect analysis are discussed along with selected examples.
EBIC Spectroscopy - A New Approach to Microscale Characterization of Deep Levels in Semi-Insulating GaAs
Authors: Li C.-J. , Sun Q. , Lagowski J. , Gatos H.C.
Published: March 2011

We propose a new approach to the defect characterization in semiinsulating (SI) GaAs which combines the high spatial resolution and scanning capability of the Electron Beam-Induced Current (EBIC) mode of Scanning Electron Microscopy (SEM) with the advantages of optical and thermal spectroscopies employed in the identification of deep levels. In the PHOTO-EBIC approach a DC electron beam and a chopped subbandgap monochromatic light impinge on the SI GaAs through a semi-transparent Au electrode. The photoinduced modulation of the EBIC as a function of the subbandgap energy of incident photons constitutes a structure which corresponds to the photoionization of deep levels. In the thermally stimulated EBIC (TS-EBIC) the deep levels are filled at low temperature by the excess carriers generated by an electron beam. Subsequently, the changes of EBIC as a function of temperature constitute a spectrum of peaks which correspond to different deep levels. The peak position determines the deep level energy while the magnitude of peaks can be used for the assessment of the relative concentration of deep levels located within the small volume probed by the electron beam.
Local Vibrational Mode Spectroscopy of Impurities in Semiconductors
Authors: Newman R. C.
Published: March 2011

Infrared band—mode and LVM absorption is illustrated for a range of impurities and impurity—complexes in silicon and gallium arsenide. We discuss the effects of changes in the local force constants and contributions to the dipole moment resulting from displacements of host lattice atoms. The difficulties in establishing absolute calibrations relating the strength of the absorption to the concentration of defects are highlighted. Our purpose is to show how the measurements lead to characterization of crystals and how they complement other diagnostic techniques to evaluate effects of irradiation, heat treatments, diffusions etc.
Optical Properties of the Pb Center at the Si/SiO2 Interface
Authors: Edwards Arthur H. , Fowler W. Beall
Published: March 2011

We present theoretical results for the optical prooerties of the Pb center at the Si/SiO2 interface. Using wave functions obtainec from semiempirical (MINDO/3) cluster calculations, we have calculated electric dipole matrix elements connecting the singly occupied (neutral) defect state to the unoccupied conduction-band-like states, as well as those connecting the occupied valence-band-like states to the singly occupied defect state and to the unoccupied defect state. We predict the absorption cross section for excitation from the valence band to the unoccupied state to be of order 10−19 cm2 and that for excitation from the valence band to the occupied state and from the occupied state to the conduction band to be an order of magnitude larger. We also predict that the absorption will in some cases be strongly dependent on the direction of the polarization. Effects of symmetry lowering in the oxide and of distortions in the silicon are discussed.
Comparison of the Optical Cross Section for the Si Dangling Bond in a- Si:H and At the c - Si/SiO2 Interface
Authors: Jackson W. B. , Johnson N. M.
Published: March 2011

The optical properties of the trivalent silicon dangling bond defect in hydrogenated amorphous silicon and at the Si/SiO2 interface are compared. While both defects give rise to ambipolar deep levels within the gap, significant differences in the optical properties between the two systems are found. The absorption in a-Si:H is significantly stronger and is dominated by a transition from the defect to the conduction band while the absorption at the interface is dominated by hole emission. The average dipole matrix element squared is roughly independent of energy in both systems with a magnitude of ∼30Å2. Implications of these results for optical measurements in other silicon systems are discussed.
A Dynamic Jahn-Teller Effect in the ESR Spectrum of the N1 Centre in Diamond
Authors: Loubser J.H.N. , Wyk J.A. Van
Published: March 2011

The N1 centre in Type Ia diamonds is a di-nitrogen centre with S = ½. One nitrogen's interaction with the unpaired electron at room temperature gives a large splitting, All = 46.4 G, A ⊥ = 32.2 G with <111> symmetry while the hyperfine splitting due to the other one has <110> symmetry with parameters All = 2.95 ±.03 G, A⊥ = 2.81 ±.03 G. As the temperature is increased averaging effects start; first some hyperfine lines broaden at about 150°C and disappear at 200°C. At still higher temperatures new lines appear and at about 850°C the averaging process is completed. The interpretation of the dynamics leads to a model of a non-planar N-C-C-N configuration with the electron jumping between the two N-C bonds. The measured activation energy is 0.4 eV which is about midway between the measured values for a similar effect in the isolated nitrogen centre, P1, (E = 0.7eV) and the N-C-N, W7, centre (E = 0.24 eV).
Cross-Sectional Transmission Electron Microscopy of Defects in Beta Silicon Carbide Thin Films
Authors: Carter C.H. , Edmond J.A. , Palmour J.W. , Ryu J. , Kim H.J. , Davis R.F.
Published: March 2011

Techniques have been developed at NCSU for fabricating cross-sectional transmission electron microscopy (XTEM) foils from monocrystalline beta silicon carbide thin films grown by chemical vapor deposition. The results of the TEM observations are utilized to discern the efficacy of the various processing parameters in terms of film quality and defect structure as well as oxidation, ion implantation and annealing procedures.
Physics of Deep Levels
Authors: Dow John D.
Published: March 2011

The physics of deep levels is reviewed, with emphasis on the qualitative physics that has been elucidated as a result of the ideas of Lannoo, Lenglart, Hjalmarson, Vogl, Wolford, Hsu, Sankey, Allen, and others.
Thermodynamics of Deep Levels in Semiconductor
Authors: Vechten J.A. van
Published: March 2011

Thermodynamnies is obviously central to the ultimate goal ol an exquisite control of the electronic properties of scmiconducting devices and to the uinderstanding this will require. It should also be useful for the subsidiary goal of the firm identification of the various electrically active defects. This subsidiary goal will not be achieved unless adequate attention is paid to the reactions among the various atomic and ionization states of the defects, the electrons and the holes.
Special Aspects of Diffusion in Metallic Thin Films
Authors: Gupta D.
Published: March 2011

The diffusion processes in thin films are largely controlled by their microstructure and chemistry. In this publication, we discuss briefly how the recently devel-oped experimental techniques coupled with the available analytical treatments have been able to characterize these processes. Actually a hierarchy of diffusion rates along the atomic defects in thin films, namely the vacancies, grain-boundaries and dislocations, has been found. The interactions of solutes present in thin films with the atomic defects in altering the diffusion rates are discussed. It has also been possible to measure diffusion in amorphous metallic alloy films and its features are described. Finally, we outline the general principles for modifying diffusion in thin films to achieve the desired technological objectives.
The Structure of Si and Ge Deposited by Ion Beam Sputtering
Authors: Windischmann H. , Cavese J. M. , Collins R. W. , Harris R. D. , Gonzalez-Hernandez J.
Published: March 2011

The crystallinity for silicon and germanium films deposited by ion beam sputtering (IBS) as a function of substrate temperatures was determined using Raman spectroscopy, spectroscopic ellipsometry, electrical conductivity and x-ray diffraction measurements. The results show that IBS silicon crystallizes between 300–350°C while germanium crystallizes between 20–200°C. Reasonably good agreement is obtained among the four distinctively different characterization techniques in identifying the onset of crystallinity. A direct relationship is observed between the substrate temperature required for crystallization and the log of the operating pressure for various deposition techniques. Energetic particle stimulation during film growth appears to reduce the crystallization temperature at a given operating pressure. Raman data show that the crystallization temperature depends on the deposition rate. A graded structure is observed in films deposited above 300°C, probably due to oxygen contamination.
Thin Films of Diamond-Like Carbon
Authors: Kerwin David B. , Daudin Bruno , Dubus Michel , Fontenille J. , Robinson Raymond S. , Spain Ian L.
Published: March 2011

Thin films of hard, diamond-like, carbon have been deposited on glass, silicon and sapphire substrates using three different ion beam deposition techniques: (a) ion beam sputter-deposition from a graphite target, (b) sputter-deposition with simultaneous bombardment of the growing film using a second ion beam, (c) primary ion deposition using a beam extracted from an Ar-hydrocarbon plasma. Structural, mechanical optical and electrical properties were measured. It was found that the hydrogen content controlled the internal (compressive) stress and that relatively stress-free films contained ,∼ 30 atomic % H (average). The H content could be correlated with the H/C arrival ratio from the gas phase. Optical absorption and luminescence measurements gave a band gap of '∼, 1 ev with band-tailing. Resistivity measurements and their temperature dependence fitted variable range hopping models. Hardnesses were ≿ 7 Mohs. The properties of the films were consistent with a mixture of sp3 and sp2 bonds in an amorphous, hydrogenated structure.
Electronic Properties of Thin PD Overlayers on Au(111): Relationship to Chemisorption Properties
Authors: Shena Xinyin , Frankel D. J. , Hermanson J. , Lapeyre G. J. , Smith R. J.
Published: March 2011

We present results for the electronic structure and chemical properties of thin Pd films grown epitaxially on Au(lll) single-crystal substrates. Photoemission spectroscopy is used to monitor the development of the Pd d-bands near the Fermi energy (EF ) as a function of overlayer thickness. The state density aF E is relatively small for the single Pd monolayer (ML), but increases monotonically with overlayer thickness, resembling the bulk Pd electronic structure for films thicker than 5 ML. At the same time we observe that the 1 ML Pd film is iner with respect to CO chemisorption, while the multilayer films readily chemisorb CO, similar to bulk Pd. We examine possible models for the inert behavior of the Pd monolayer, based on related slab calculations which show the substrate-induced modification of the electronic structure in the overlayer.
Capillary Instabilities in Thin, Polycrystalline Films
Authors: Srolovitz David J. , Safran S. A.
Published: March 2011

Thin films can break up into islands only if they are perturbed by substrate-intersecting perturbations. Grain boundary grooves and vertex pits are typical defects which nucleate holes in these films. Holes which exceed a critical size - proportional to the ratio of the film thickness to the equilibrium contact angle - grow, eventually disconnecting the film.
The Structural Properties of Sputtered Zinc Oxide
Authors: Hickernell Fred S.
Published: March 2011

X-ray diffraction, chemical etching and electron microscopy are useful in delineating the microstructural properties of c-axis normal oriented polycrystalline zinc oxide films, sputter deposited on amorphous substrates. Dense ZnO films with high crystalline content and low etch rates have a strong piezoelectric effect and low surface acoustic wave and guided optical wave propagation loss. The structural properties are dependent upon substrate conditions, deposition parameters and the type of sputtering system used. Scanning electron microscope examination of the surface and side fractures of high quality ZnO films show smooth continuous upper surface and side regions with no vertical fiber grain structures apparent. Light chemical etching reveals surface defects consisting of uniformly distributed conical shaped etch pit structures with a lateral to vertical etch ratio of 3 to 1. A correlation has been made between film structure and single crystal zinc oxide. The structural picture which emerges is that of a predominantly positive polarity (0001) upper surface layer with localized negative polarity (0001) fiber grain inversions. The sputter conditions which lead to low defect density films are a high substrate temperature, high deposition rate and low reactive gas pressures to promote the adatom mobility necessary for the preferred (0001) zinc face growth. Post deposition laser and thermal annealing can be used to reduce stress in the films and improve their guided optical wave properties.
Electrcn Trapping/Detrapping in Thin SiO2 Under High Fields
Authors: Wu N. R. , Chiao S. , Wang C. , Bhushan B. , Yang C. Y.
Published: March 2011

A constant alternating current stressing technique is employed to study the electron trapping and detrapping cha~acteristics
within a layer of thin silicon dioxide (˜.100 Å). A two-charge centroid model is proposed to explain the trapping/detrapping phenomena under high electric fields. The oxide breakdown mechanism induced by the local field of trapped electrons is also discussed.
Minority Carrier Injection and Series Resistance Effects in Hydrogenated Amorphous Silicon Schottky Barrier Diodes
Authors: Kanicki Jerzy
Published: March 2011

The minority-carrier injection and series resistance effects on the electrical properties of a-Si:H Schottky barrier diodes are described. The conductivity modulation was observed, for the first time, in metal/HOMOCVD a-Si:H contacts. Its effect on capacitance-voltage characteristics are discussed. The minority-carrier injection ratio is estimated from current-voltage characteristics as a function of total forward current for different metals. It is shown that these effects cannot be neglected in the interpretation of the AC and DC measurements. The caution, therefore, must be taken when using a-Si:H diodes structures to obtain the fundamental physical parameters characterizing either the interface or bulk properties of amorphous semiconductors.
Electronic and Optical Properties of A—(Si, Ge):H Alloys
Authors: Daial Vikram , Booker James F. , Leonard Mark
Published: March 2011

We describe the preparation and electronic and optical properties of amorphous (Si, Ge) alloys. A—(Si, Ge):H alloys were prepared by glow discharge decomposition of SiH4 and GeH4. The bandgap was varied between 1.78 and 1.42 eV by changing the GeH4:SiH4 ratio in the gas phase. We find a distinct influence of growth temperature on electronic properties. Films grown at low temperatures (200–250C) tendto have much lower photo conductivity than films grown at higher temperatures (300–325C). The electron (μ τ) products of high temperature films are general> 1X10–7 cm2/V. We also obtain very sharp valence band tails in a—(Si, Ge):H alloys, with slopes of ∼ 40 meV. The hole (μ τ) product is generally ∼1–2X10–8 cm2/V. All these properties suffer a catastrophic decline when bandgap is reduced below about 1.5 eV.
Preparation of α-(Si.Ge):H Alloys by D.C. Glow Discharge Deposition
Authors: Slobodin D. , Aljishi S. , Schwarz R. , Wagner S.
Published: March 2011

We report the preparation of α-(Si.Ge):H alloy films by decomposition of SiF4, GeF4, and H2 in a d.c. glow discharge. Germanium is incorporated very efficiently from GeF4. The germanium content and optical gap canbe controlled by varying the GeF4 flow while keeping the SiF4 and H2 flows constant. The films, all prepared at 300 ºC substrate temperature, exhibit high photo- to dark-conductivity ratios for compositions of up to -25% germanium.
Amorphous Silicon—Germanium Deposited by Photo—CVD
Authors: Itozaki H. , Fujita N. , Hitotsuyanagi H.
Published: March 2011

Hydrogenated amorphous silicon germanium (a—SiGe:H) films were deposited by photo—chemical vapor deposition (Photo—CVD) of SiH4 and GeH4 with mercury sensitizer. Their band gap was controlled from 0.9 eV to 1.9 eV by changing the gas ratio of SiH4 and GeH4. High quality opto—electrical properties have been obtained for thea—SiGe:H films by Photo—CVD. Hydrogen termination and microstructure of a-SiGe:H were investigated by infrared absorption and transmission electron microscopy. Ana—Si:H solar cell and an a—Si:H/a—SiGe:H stacked solar cell were made, each of which has conversion efficiency 5.3% and 5.1%, respectively.
Properties of A—Sin:H Films Prepared by Glow Discharge of Si2H6—Nh3 Gas Mixture
Authors: Kojima Y. , Narikawa S. , Matsuyama T. , Imada E. , Nojima H. , Hayakawa T. , Ehara S.
Published: March 2011

The electrical and optical properties of a—SiNx:H films prepared by the glow discharge of Si2H6-NH3 gas mixture have been investigated in a wide range of the molar ratio of NH3 to Si2H6 The maxima of the dark—and the photo—conductivity are observed at the molar ratio of about 10-1. At this molar ratio the deposition rate is about33 Å/sec. The optical gap and the compositional ratio of nitrogen to silicon change smoothly from those of a—Si:H to those of a—Si3N4. It is found that the valency control is possible in a—SiNx:H films prepared at a high deposition rate.
Hydrogenated Amorphous Silicon Films by the Pyrolysis of Disilane(1)
Authors: Chu T. L. , Chu Shirley S. , Ang S. T. , Lo D. H. , Duong A. , Hwaung C. G. , Book L.
Published: March 2011

The thermal decomposition of disilane in a hydrogen or helium flow has been used for the deposition of hydrogenated amorphous silicon (a-Si:H) films on the surface of several substrates at 450°-500°C. The concentration of disilane in the reaction mixture has been found to affect strongly the deposition rate and the photoconductivity of a-Si:H films. The AMI conductivity of a-Si:H films increases with increasing disilane concentration and approaches lO−5(ohm-cm)−l at disilane concentrations higher than about 4%, and the conductivity ratio is about lO5. The density of gap states in CVD a-Si:H films have been determined by the photothermal deflection spectroscopy, capacitancetemperature, capacitance-frequency, and space-charged-limited current measurements with similar results.
High Performance A–Si Solar Cells and Narrow Bandgap Materials
Authors: Nakano Shoichi , Kishi Yasuo , Ohnishi Michitoshi , Tsuda Shinya , Shibuya Hisashi , Nakamura Noboru , Hishikawa Yoshihiro , Tarui Hisaki , Takahama Tsuyoshi , Kuwano Yukinori
Published: March 2011

High performance a-Si solar cells were developed. A conversion efficiency of 11.5% was achieved for a textured TCO/p-SiC/in/Ag structure with a size of 1 cm2 using the high quality i-layer fabricated by a new consecutive, separated reaction chamber apparatus. A conversion efficiency of 9.0% was obtained with a size of 10cm × 10cm. A high quality a-SiGe:H:F, which is a new narrow bandgap material for a-Si solar cells, was fabricated by a glow discharge decomposition of SiF4 + GeF4 + H2.

A photo-CVD method was investigated in order to improve the interface properties of a–Si solar cells. A conversion efficiency of 11.0% was obtained with a solar cell in which the p-layer is fabricated by the photo-CVD method. a-SiGe:H films were fabricated by the photo-CVD method for the first time as a narrow bandgap material for multi-bandgap a-Si solar cells.
Light-Induced Metastable Defects in a-Si:H: Towards an Understanding
Authors: Stutzmann Martin , Jackson Warren B. , Tsai Chuang Chuang
Published: March 2011

The dependence of the creation and the annealing of metastable dangling bonds in hydrogenated amorphous silicon on various material parameters will be discussed in the context of a recently proposed model. After a brief review of the kinetic behaviour governing defect creation and annealing in undoped a- Si:H, a number of special cases will be analyzed: the influence of alloying with O, N, C, and Ge, changes introduced by doping and compensation, and the role of mechanical stress. Finally, possibilities to increase the stability of a-Si:H based devices will be examined.
Continued Development of R.F. Sputtered a-Si:H Thin-Film Transistors Towards an All-Sputtered Device
Authors: Allison J. , Turner D.P. , Cousins D.C.
Published: March 2011

Prototype thin film transistors have previously been fabricated by r.f. magnetron sputtering of a-Si:H on to CVD Si02 using a crystalline silicon gate. These devices exhibited an on/off current ratio of four orders of magnitude for gate voltages as low as 10 volts. This demonstrated the suitability of the sputtered layer for liquid crystal display applications.

The use of a crystalline substrate negates the advantages of using a thin film,such as large area capability and low cost, so we have turned our attention to the provision of a sputtered dielectric. Several candidate materials have been considered, including Si02, Si3N4, Ta205, AIN and Ti02. We present the characteristics of our first all-sputtered transistor utilising an Si02 gate,and assess the dielectric properties and potential of other materials, with emphasis on the silicon oxynitride system.
Amorphous Silicon Linear Image Sensor
Authors: Ozawa T. , Takenouchi M. , Tomiyama S.
Published: March 2011

Document width linear image sensor arouse strong and wide interest as a compact image reading component for facsimile and other document readers. Among those, a-Si:H is excellent in stability and light sensitivity. The photosensing element of those sensors have a sandwich-like structure which consist of Cr/i-a-Si:H/ITO. In this structure, i-a-Si:H/ITO shows good shottky contact resulting high photo to dark current ratio and fast photoresponse. We have been developing linear image sensor of A4 and B4 size with resolutions of 8dot/mm and l6dot/mm and had applied successfully to facsimile and image input terminals.
Amorphous Si:H Heterojunction Photodiode and its Application to a Compact Scanner
Authors: Kaneko S. , Kajiwara Y. , Okumura F. , Ohkubo T.
Published: March 2011

This paper reports heterojunction photodiode properties and its application to a compact scanner. The photodiode has ITO / p-a-SiC:H / a-Si:H / metal structure. This diode has high photo to dark current ratio and small photocurrent saturation voltage, because of the excellent blocking characteristics for a heterojunction with large built in potential. Moreover, a-Si:H / metal contact has been investigated. A contact linear image sensor has been fabricated using the heterojunction photodiode array and compact optical system. Performance tests showed excellent results. Good reproduced images have been obtained.
Electrical and Optical Properties of PECVD Amorphous Silicon Grown at Low Frequencies
Authors: Piper W.W. , Possin G.E.
Published: March 2011

The semiconducting properties of a-Si are ideally suited for making a switch to control the matrix addressing of an array of liquid crystal pixels. This investigation explores the differences between a-silicon deposited by plasma enhanced chemical vapor deposition at 13.56MHz and at 60KHz. The bonded hydrogen concentration, the index of refraction and the optical band gap of a-Si have been measured. The device used to explore the field effect mobility of a-Si is an inverted staggered FET fabricated on a glass substrate with conventional photolithography.
Photoemission Studies of Amorphous Silicon/Germanium Heterojunctions
Authors: Evangelisti F. , Modesti S. , Boscherini F. , Fiorini P. , Quaresima C. , Capozi M. , Perfetti P.
Published: March 2011

The heterostructures obtained by growing a-Ge on a-Si:H and a-Si have been investigated by synchrotron radiation photoemission. We measured valence band and core level spectra on the heterostructures grown in situ under ultrahigh-vacuum conditions. A step-by-step monitoring of possible band-bending changes during the interface formation enabled us to determine unambiguously the band discontinuities. The measured values of the valence band discontinuity were 0.2 ± 0.1 eV for a-Si:H/a-Ge and 0.0 ± 0.1 eV for a-Si/a-Ge, respectively. Evidence was found for the formation of abrupt interfaces without interdiffusion.
Electrical and Structural Properties of Grain Boundary in Polycrystalline Si
Authors: Young R. T. , Narayan J. , Chang Y. K.
Published: March 2011

A special type of high angle grain boundary with mirror symmetry of the crystallographic orientation between the two grains is examined electrically and structurally. Transmission electron microscopy investigations show the nonuniform nature of the grain boundary. Both coherent and incoherent regions are observed along the boundary plane, and the types of dislocations and their densities vary from place to place. Electrical measurements of the boundary properties indicate no measurable barrier height. Heat treatment of the sample in an oxygen atmosphere at 950°C for 30 min did not change the boundary resistance. However, recombination effects are enhanced after boron diffusion. When pulsed laser radiation was used to process this material, it was found that the grain boundary structures were modified by laser-induced surface melting, i.e., incoherent boundaries were converted to coherent boundaries in the melted region.
Characterization of Grain Boundaries in Polycrystalline GaAs
Authors: Spencer Michael G. , Schaff William J. , Ken Wagner D.
Published: March 2011

Examination of capacitance transients arising from the emission or capture of electrons at a charged GaAs grain boundary reveal for the first time the existence of discrete interface levels. The position of these levels in the bandgap and their associated capture cross sections are determined from the transients.
Grain Boundary Passivation in Polycrystalline Silicon : A D.L.T.S. Study
Authors: Srivastava Prakash C. , Bourgoin Jacques C.
Published: March 2011

After treatment in a deuterium plasma, the D.L.T.S. spectrum associated with grain boundaries in p–type Si is found to reduce to a narrow band centered at 0.32 ± 0.02 eV with a total density of 5 ⨉ 1015 cm−2 . However, the capture cross-section, measured to be ∼ 2 × 10−20 cm2 , is 10 times larger than the apparent cross-section associated with the states present in unpassivated material.
Ebic/Tem Investigation of Defects in Solar Cell Silicon
Authors: Ast Dieter G. , Cunningham Brian , Strunk Horst
Published: March 2011

Two examples are given of the application of EBIC and HVTEM to the study of defects in silicon.

An hexagonal dislocation network in a coherent first order twin boundary in WEB silicon shows a three fold symmetry when imaged by EBIC. The observed variation of the minority carrier lifetime at the nodes is consistent with a model which assumes that jogs are particularly strong recombination sites at a dislocation.

EBIC and STEM observations on unprocessed and processed EFG ribbon show that the phosphorus diffused junction depth is not uniform, and that a variety of chemical impurities precipitate out during processing. Two kinds of precipitates are found i) 10 nm or less in size, located at the dislocation nodes in sub-boundary like dislocation arrangements formed during processing and ii) large precipitates, the chemical composition of which has been partially identified. These large precipitates emit dense dislocations tangles into the adjacent crystal volume.
An Enhanced Photoresponse at Dislocation Subgrain Boundaries Revealed by X-Ray Topography of Polysilicon Solar Cells
Authors: Johnson S.M. , Armstrong R.W. , Rosemeier R.G. , Storti G.M. , Lin H.C. , Regnault W.F.
Published: March 2011

An enhanced photoresponse at dislocation subgrain boundaries (in comparison with grain boundaries and dislocation-associated twin boundaries) is attributed to an increased junction depth at their positions relative to the value of the minority carrier diffusion length, Ln. For reasonably pure material, Ln is determined by the dislocation density. The dislocation microstructure of polysilicon solar cells is advantageously studied by means of the several x-ray topography techniques.
High Resolution Electron Microscopy of Grain Boundaries in Silicon
Authors: Cunningham B. , Ast D.
Published: March 2011

The lattice imaging technique has been used to study grain boundaries in annealed, chemically vapor deposited (CVD) silicon. The majority of the grain boundaries are Σ*=3, 9 or 27, i.e. they are all twin related, and have boundary planes which coincide with high density planes of the appropriate coincidence site lattice (CSL). Asymmetric Σ=27 boundaries are found to be dissociated on an atomic scale into faceted Σ=3 boundaries and Σ=9 boundaries. No dissociation of the Σ=27 boundaries is observed when the boundary planes are symmetric.
Theory of Mosfet Operation in Small-Grain Polysilicon
Authors: Depp S. W. , Huth B. G. , Juliana A. , Koepcke R. W.
Published: March 2011

The operation of a MOSFET transistor fabricated in undoped, small-grain polysilicon is considered, and a model is developed which can predict threshold and drain current as a function of gate voltage. A two-dimensional calculation is described for the band-bending under the influence of a gate potential with the assumption that the grain boundaries are repetitive and oriented at right angles to the gate-oxide/polysilicon interface. Both hole and electron traps are assumed present at the grain boundaries and are coincident in energy with the intrinsic Fermi level at room temperature. An energy barrier to the flow of carriers is present in the undoped polysilicon, and the magnitude of this energy barrier is dependent on the gate voltage. The band-bending occurs over much shorter distances than the intrinsic Debye length, and the trapped charge at the grain boundaries behaves very similarly to the charged impurities in a depletion model. The two-dimensional model can be approximated by a one-dimensional calculation for the band-bending by making the assumption that the trapped charge is uniformly distributed throughout the grain. The results of this calculation can be used to calculate the magnitude of the free carriers in the channel region. Using this information, the dependence of the potential barrier on gate voltage, and the gradual channel approximation for an FET, one can compute the drain current vs. gate voltage, and the results of these calculations are given for parameters used in fabricating actual devices. Finally, experimental results are compared with the model for typical transistors fabricated in undoped, small-grain polysilicon.
Electronic Properties of ZnO Varistors: A New Model
Authors: Pike G. E.
Published: March 2011

Much of the research on ZnO varistors has concentrated on the explanation of their dc current-voltage characteristics. However, varistors also have unusual ac properties which can be technologically important, and must be described by any comprehensive model. In an ideal varistor with identical grain boundaries throughout, there should be no dispersive capacitance at zero bias. In real varistors this capacitance varies considerably with frequency. This dispersion has two causes, charge trapping in the depletion regions and differing grain boundary barriers. Calculations for each process are given. For voltages well below the varistor breakdown value, the low frequency capacitance increases with applied voltage. At even higher voltages the capacitance turns over and becomes negative. All of these effects can be described with a double depletion layer/thermionic emission model. The anomalous capacitance behavior with bias is due to the modulation of the potential barriers by charge trapping at the grain boundaries. In the varistor breakdown regime minority carriers created by impact ionization are important.
Degradation of Zinc Oxide Varistors
Authors: Takahashi Ken , Miyoshi T. , Maeda K. , Yamazaki T. , Ohwada S.
Published: March 2011

The effect of ambient gases on degradation and rejuvenation of ZnO varistors was investigated from the viewpoint of voltage-current characteristics. Ambient oxygen gas suppressed increases in the leakage current during ac biasing, while it rejuvenated degraded samples. The time dependence of rejuvenation indicated that ion migrations, possibly the desorption and adsorption of oxygen ions at the grain boundaries, occur reversibly in degradation and rejuvenation. Moreover, a noticeable difference was observed between V–I curve shapes after ac biasing in nitrogen and in oxygen atmospheres.
The Electrical Activity at Twin Boundaries in Silicon
Authors: Cunningham B. , Strunk H.P. , Ast D.G.
Published: March 2011

Although coherent twin boundaries in silicon are electrically inactive, dislocations in the boundaries can act as efficient recombination centers for minority carriers. Different twin boundary dislocation arrangements have been studied by EBIC and TEM. It is found that the observed EBIC contrast is dependent not only on the arrangement of the dislocations in the boundaries but also on the inclination of the boundaries to the surface. It is shown that different defect configurations can produce similar EBIC contrast.
Space Charge Contribution To Solute Segregation Near Grain Boundaries
Authors: Yan M. F. , Cannon R. M. , Bowen H. K.
Published: March 2011

The interaction potentials between solutes and grain boundaries in ionic solids are identified as [1] the electrostatic interaction between the charged solutes and grain boundaries and [2] the elastic energy due to size misfit of solutes in the matrix. Equilibrium solute distribution is calculated from the defect distributions leading to the minimum free energy. Space charge distributions near interfaces during kinetic processes are evaluated. We analyze the limiting case of constrained equilibrium in which the vacancy distribution and degree of solute-vacancy association satisfy a minimum free energy under the constraint of no solute redistribution.
Effects on Fissure Calcite by Recharge Water - Some Problems Related to 14C-Dating of Groundwater
Authors: Tullborg Eva-Lena
Published: March 2011

The modelling of water flow in the bedrock is of especial importance for safetyassessementof radioactive waste disposal in crystalline rocks. Age dating of the water has been tried for the validation of ground water transport models. Thus, several tritium and 14C-analyses have been carried out on water samples from deep boreholes drilled within SKB's (Swedish Nuclear Fuel and Waste Management Company) study sites. However, several processes will influence the final content of 14C in the groundwater measured and correction for enrichment and dilution are hard to carry out. Another contribution to the understanding of recharge water transport by using frequency and stable isotope analyses of calcite fissure fillings is suggested.
Chemical Thermodynamic Data Set for Minerals Associated With Granite
Authors: Muller A. B. , Fritz B. , Wyman A. , Snellman M.
Published: March 2011

The OECD Nuclear Energy Agency is coordinating the development of a critically reviewed CODATA compatible chemical thermodynamic data base for ten radioelements important to various areas of nuclear technologies. Such a data base in itself is insufficient for modeling the speciation and solubility behaviour of radioelements in natural rock/water systems. Data must also be available for describing the rock phases present, which determine to a large extent the physico-chemical environment. Since a number of NEA Member countries are contemplating nuclear waste disposal in granitic environments, a data base for seventy-three minerals associated with granite is presented here, as a complement to the data base work on radioelements.
Weathered Basalt Glass: A Natural Analogue for the Effects of REACTION Progress on Nuclear Waste Glass Alteration
Authors: Grambow B. , Jercinovic M. J. , Ewing R. C. , Byers C. D.
Published: March 2011

Laboratory experiments alone cannot be used to verify models for the long-term release of radionuclides from nuclear waste glasses. Basalt glasses have been proposed as an appropriate natural analogue for the long-term validation of release models [1]. Their analogous behavior has been demonstrated in laboratory experiments in which both types of glasses display similar reaction rates, alteration products and surface layer morphologies [2,3]. This paper illustrates how empirical data from natural occurrences of basalt glass can be interpreted by a model which is developed to describe the reaction progress of the corrosion of nuclear waste form borosilicate glass [4,5].
Dissolution of Basaltic Glass in Seawater : Experiments and Thermodynamic Modelling
Authors: Crovisier J. L. , Fritz B. , Grambow B. , Eberhart J. P.
Published: March 2011

The reaction of basalt glasses with natural waters were proposed as analog systems to the long-term alteration of nuclear waste glasses in the geosphere [1].
Oxidation of Candu UO2 Fuel by the Alpha-Radiolysis Products of Water
Authors: Shoesmith D. W. , Sunder S. , Johnson L. H. , Bailey M. G.
Published: March 2011

The oxidation of CANDU fuel (UO2) by the alpha-radiolysis products of water has been investigated using electrochemical and X-ray photoelectron spectroscopic-experiments. Experiments with O2 and H2O2, two of the expected products of radiolysis of water, indicate that the rate of oxidation of UO2 by H2O2 is about 200 times faster than by dissolved oxygen. Oxidation by both H2O2 and O2 shows pH dependence. Possible reaction paths for the oxidation of UO2 by radiolysis products are discussed.
Structural Changes in 238Pu-Substituted Zirconolite on Recovery from the Metamict State
Authors: Clinard F. W. , Livak R. J. , Hobbs L. W. , Rohr D. L.
Published: March 2011

238Pu-substituted zirconolite (CaPuTi2O7) was held at ≈350 K for a time sufficient to allow self-irradiation damage to convert the material to the metamict condition. Samples were then stored at 875 K, while dimensional and microstructural changes were monitored by dilatometry and transmission electron microscopy. Densification proceeded sporadically over a period of ≈400 days, attaining a final value of 4 vol% as a result of crystallization. The material was found to be friable at an intermediate stage of recovery, apparently as a result of internal strains. Evidence is presented that CaPuTi2O7 can exist in more than one metamict state, depending on extent of prior damage and thermal history.
Some Aspects on the Use of Iron Canisters for HLW
Authors: Neretnieks Ivars
Published: March 2011

Iron canisters for high level nuclear waste embedded in compacted bentonite in deep geologic repositories will corrode forming hydrogen gas. The equilibrium pressure (when corrosion would stop) has been estimated to be between 500 and 1000 atm. under repository conditions. As this is much higher than the lithostatic pressure (weight of rock overburden) the gas must be allowed to escape before it disrupts the repository. Escape by diffusion alone is not sufficient but recent experiments have demonstrated that the larger pores in the bentonite are blown free of water and let the gas escape before excessive pressures build up.

The potential effect of a capillary breaking layer (CBL) has been explored. A fine layer nearest the canister (e.q. quartz sand) would have much lower capillary suction pressures than the bentonite clay and would keep the water out as long as there is sufficient overpressure. As long as the CBL is void of liquid water no radionuclides can escape, even if the canister is penetrated.
HLW Container Corrosion in Geological Disposal Conditions
Authors: Helie Max , Plante Georges
Published: March 2011

In order to prevent a possible return of activity to the biosphere, the current concept for High Level Waste disposal is to build a multi barrier system consisting of a slow leaching waste form, the waste container, backfilling materials and the geological formation. The main threat to the integrity of the container is aqueous corrosion and two concepts are currently accepted, one based on a thin “corrosion resistant” overpack, the other on a thick “corrosion allowance” canister.
Simulation of Water Transport in Heated Rock Salt
Authors: Schlich M. , Jockwer N.
Published: March 2011

This paper summarizes computer simulation studies on water transport in German rock salt. Based on JOCKWERS's experimental investigations on water content and water liberation, the object of these studies was to select a water transport model, that matches the water inflow which was measured in some heater experiments in the Asse Salt Mine. The main re-sult is, that an evaporation front model, with Knudsen-type vapor transport combined with fluid transport by thermal expansion of the adsorbed water layers in the non evaporated zone, showed the best agreement with experi-mental evidence.
234U/230TH Ratio as an Indicator of Redox State, and U, TH, and RA Behavior in Briney Aquifers
Authors: Laul J. C. , Smith M. R. , Hubbard N.
Published: March 2011

The234U/230Th ratio serves as an in-situ indicator of the redox state in groundwater aquifers. The higher this ratio, the more U there is in the +6 valance state and thus a less reducing environment. Radium sorption is retarded in the shallow aquifer and is dependent on the CaSO4content and the redox state. Relative to Ra, U and Th are highly sorbed. The total retardation factor for Th is ∼1400 and mean sorption time for228Th is ∼10 days in the shallow zone. The desorption rate of Ra is significantly slower in the shallow than in the deep aquifer. There is no effect of colloids in brines.
Influence of Redox Environments on the Geochemical Behaviour of Radionuclides
Authors: Bidoglio G. , Avogadro A. , Plano A. De
Published: March 2011

Studies were carried out on the effect of redox conditions on the release from simulated vitrified HLW of Np-237, Pu-238 and Tc-99 and their migration through columns packed with site-specific porous material representative of clay and salt aquifers. Results obtained under oxic and anoxic conditions are compared. The release rates of Np, Pu and Tc were found to be lower in the absence of air than with oxygenated groundwaters. Speciation studies showed that neptunium and technetium were released in the oxidized forms Np(V) and Tc(VII) even under the investigated anoxic conditions where reduced species are thermodynamically more stable. In spite of that, a stronger interaction was observed when the leachate was passed through the column in the absence of air. A surface reduction process accounts for the observed behaviour. Under more reducing conditions, plutonium appears to be present in the tetravalent state in colloidal form.