bluuebunny/crossref_metadata_2025 huggingface dataset:
Interatomic Forces and Structure of Grain Boundaries
Authors: Vitek V. , de Hosson J. Th. M.
Published: March 2011

Over the past two decades, grain boundary structures have been investigated, with increasing frequency, using computer simulation techniques. The accuracy of the potentials used to describe the interaction between atoms is essential to the success of any computer modelling and practically all these studies have been made assuming that the atoms exert pair-wise forces on each other. This paper discusses the applicability and limitations of this assumption and the validity and applicability of the simulation results obtained with pair-potentials. First, it is shown that certain structural features of grain boundaries are independent of the potential used. Such results form, for example, the basis of the structural unit model which relates the structures of boundaries corresponding to different misorientations. Secondly, the multiplicity of boundary structures and its physical implications are discussed. In particular, we report on the complexities of the structure of Σ=5 [001] twist boundaries and on alternative structures of [111] twist boundaries near the Σ=3 twin orientation, both found by computer modelling. These results, which are of general nature, are compared with experimental observations by X-ray diffraction and transmission electron microscopy and a very good agreement is found. However, exact positions of atoms in calculated structures depend on the potential used. Hence, to study properties sensitively dependent on these positions requires to go beyond the pair-potentials.
Surface Reconstruction of SI(100)
Authors: Weber Thomas A.
Published: March 2011

The reconstruction of the Si(100) surface has been studied using a potential consisting of two- and three-body interactions [1]. Minimum energy quenches of a slab of 320 Si atoms 10 layers thick with periodic boundary conditions in the xy plane found the p(2×l) reconstruction lower in energy than the c(2×2) reconstruction. The potential energy contours for the addition of an adatom to the (100) surface were determined for the unreconstructed surface and for the p(2×l) and c(2×2) reconstructions.
Progress in Spin Glasses and Random Fields – Research with a Special Purpose Computer
Authors: Ogielski A. T.
Published: March 2011

Extensive numerical simulations of random magnetic materials have been recently performed at AT&T Bell Laboratories with a fast specially designed computer. I will discuss certain issues concerning the use of specialized computers in research, and I will review some major results obtained in simulations of a three-dimensional spin glass and an antiferromagnet with random fields.
Hartree-Fock Cluster Computations for Ionic Crystals
Authors: Vail J. M. , Pandey R.
Published: March 2011

The ICECAP code is applied to charged and uncharged color centers in alkali halides and alkaline-earth oxides, to test the usefulness of complete-cation pseudopotentials for reproducing the cluster boundary conditions. The physical model includes consistency up to electrostatic octupole order between the Hartree-Fock cluster and the surrounding infinite shell-model lattice. The total energy of the system is determined variationally, including distortion and polarization of the cluster and lattice, and LCAO-MO gaussian-localized cluster wave functions. Electronic states with the lattice unrelaxed are also analysed, yielding color-center optical transition energies. Furthermore, consistency between quantum (cluster) and classical (shell-model) descriptions of the perfect lattice is tested.
Theoretical Investigation of the Jahn-Teller Vibronic 1E ⊗ ɛ State in the Neutral Vacancy of Silicon
Authors: Malvido J. C. , Madhavan P. V. , Whitten J. L.
Published: March 2011

A method for constructing Jahn-Teller coupled vibronic states is developed by projecting distorted electronic eigenstates onto undistorted states and, with the aid of irreducible tensor methods, the force constants can be identified with reduced matrix elements of the normal mode expansion of the vibrational Hamiltonian. A scheme is then realized for estimating the force constants as well as the total vibronic energy from the calculated energie of the distorted electronic states. An application of the method to the 1 E ⊗E vibronic state of the neutral silicon vacancy is presented as an illustration
Vibrational Properties of the π-Bonded Chain Model of the Si(111)2×l Surface
Authors: Alerhand O. L. , Allan D. C. , Mele E. J.
Published: March 2011

A tight-binding theory is used to study vibrational excitations of the π-bonded chain model of the Si(111)2×l surface. Some aspects of the surface phonon spectrum are discussed. We study the charge fluctuations driven by the vibrational excitations and the surface conductivity associated with the phonons. We find that a longitudinal optical phonon on the surface chains dominates the surface conductivity.
Defect Behaviour in Oxides
Authors: Cormack A. N. , Catlow C. R. A. , Lewis G. V. , Freeman C. M.
Published: March 2011

We describe computer-based atomistic simulation studies of defect behaviour in oxides. In illustrating the value of the technique, contact with experiment is discussed through comparison with measured energies of ion migration and other energies. Since the success of these methods is dependent on the extent to which the interatomic potentials used provide a realistic model of the material, consideration is given to transferability of potentials, especially to tenary compounds where the widely adopted practice of fitting potential parameters to available crystal data is not feasible. Our principal examples will include ionic conductivity in gadolinium zirconate, electronic defect properties of BaTiO3 and grossly nonstoichiometric rutile.
Simulation of Equilibrium Segregation in Alloys Using the Embedded Atom Method
Authors: Foiles Stephen M.
Published: March 2011

The Embedded Atom Method (EAM) is combined with Monte Carlo simulation techniques to determine the equilibrium segregation at internal defects and surfaces. This approach has been applied in the Ni-Cu alloy system to the calculation of the surface composition profiles and the segregation at an edge dislocation. The surface composition profile of these alloys as a function of distance from the surface is found to vary non-monotonically with the top atomic layer strongly enriched in Cu and the near surface atomic layers enriched in Ni. The compositional variation in the core region of an edge dislocation shows enrichment of Ni in the compressed regions of the partial dislocation core and Cu enrichment in the expanded regions. In addition, the composition changes abruptly at the slip plane of the dislocation.
Defect Structure and Dynamics in Silicon
Authors: Pantelides S. T. , Car R. , Kelly P. J. , Oshiyama A.
Published: March 2011

This paper gives a brief account of recent calculations of equilibrium configurations, formation energies, and migration energies of intrinsic lattice defects (vacancies, self-interstitials) and complexes of dopant impurities (phosphorus, aluminum) with these defects. The results have been used to provide a comprehensive interpretation of low- and high-temperature diffusion data.
Depth-Profiling of Near-Surface Atomic Correlations by Total Reflection of Synchrotron Radiation
Authors: Dosch H. , Wack D. C. , Batterman B. W.
Published: March 2011

We report measurement of Bragg intensities obtained from an Fe3Al(110) single crystal under the condition of total reflection. It is demonstrated that depth-resolved near-surface atomic correlations can be achieved by the independent control of both ocurring grazing angles.
Scanning Optical Fiber Microscope for High Resolution Laser Beam Induced Current Images of Semiconductor Materials
Authors: Ogura M. , Tajima M. , Tokumaru Y.
Published: March 2011

Laser beam induced current images (LBIC) of polycrystalline silicon and liquid encapsulated Czochralski (LEC) GaAs are observed with a new scanning optical fiber microscope (SOFM), which utilizes an optical fiber as a mobile light source. In this system, fine optical probing with the beam diameter less than lm is achieved without requiring severe mechanical precision. A variety of light sources are employed to reveal different defect species. The distribution of deep levels in LEC GaAs is visualized with extrinsic photo-excitation by using a Nd:YAG laser.
Channeling Contrast Microscopy: A Powerful Tool for Examining Semiconductor Structures
Authors: McCallum J. C. , Brown R. A. , Nygren E. , Williams J. S. , Olson G. L.
Published: March 2011

Channeling contrast microscopy with a He+ microbeam has been employed to measure 3-dimensional damage distributions and impurity profiles in ion implanted laser annealed silicon. Refinements to the technique are described, involving construction of a precision goniometer to allow accurate orientation of the microbeam with respect to micron-scale- sample features. We have found that indium diffusion in amorphous silicon is significantly less for laser annealing than with lower temperature furnace annealing. Lateral variations in the extent of crystal growth have also been observed across laser irradiated areas less than 100μm.
Characterization of the DFZ in Silicon Wafers by a Non-Destructive Technique
Authors: Borrego J. M. , Gutmann R. J. , Jensen N. , Lo C. S. , Paz O.
Published: March 2011

This paper presents a non-destructive technique for characterizing The Defect Free Zone (DFZ) of silicon wafers. The method consists in measuring the decay of microwave reflection following the creation of excess carriers by a light pulse. For wafers with similar surface passivation we have found a direct correlation between the transient duration and the size of the DFZ. A computer model of the microwave reflection in silicon wafers with different size of DFZ agrees with experimental observation.
Microstructural Characterization of GaAs Substrates
Authors: Moore T. M. , Matteso S. , Duncan W. M. , Matyi R. J.
Published: March 2011

The defect microstructures of GaAs substrates have been investigated in a multi-technique approach including integral cathodoluminescence (CL), scanning electron acoustic microscopy (SEAM), double crystal x-ray topography (XRT), and defect delineation etch. The XRT, CL, and SEAM studies are of identical areas on
<100> SI GaAs(Cr) grown by the liquid encapsulated Czochralski (LEC) method and by the horizontal Bridgman (HB) method. Correlation was made to the defect structure revealed by defect delineation etching. The samples were also characterized by Fourier transform photoluminescence (FTPL) to qualitatively identify the major transitions contributing to the CL images. The CL, SEAM, XRT, and defect delineation etch images of each material are compared and their different perspectives are discussed.
Recent Progress with Surface Analysis by Laser Ionization
Authors: Becker Christopher H.
Published: March 2011

This paper briefly reviews previous results and developments, then presents new results, using a novel surface analytical technique that uses non-resonant multiphoton ionization (MPI) of neutral atoms and molecules sputtered by an ion beam, or desorbed by an electron beam or laser beam. In this method, which we call surface analysis by laser ionization (SALI), the non-resonant MPI, or “laser ionization,” is coupled with state-of-the-art time-of-flight mass spectrometry to provide extremely sensitive, general, and readily quantifiable surface analysis. Examples are presented for two applications relevant to the semiconductor industry and for the analysis of the near surface region of two specially pretreated stainless steels. A discussion also describes the favorable prospects for implementation of SALI with submicron dimension liquid metal ion beams for microanalysis, including situations with electron beam sensitive samples.
Ion Beam Channeling in Superlattices
Authors: Chu Wei-Kan , Allen W. R. , Picraux S. T. , Ellison J. A.
Published: March 2011

Ion beam channeling analysis has recently been applied to lattice strain measurements on strained-layer superlattices (SLS). In this review talk, we outline three different methods of strain measurement: axial dechanneling, angular scans, and planar resonance. We describe the principles and illustrate them with examples; we also give a detailed theoretical treatment of the planar resonance effect in SLS's.
Pulsed Beams and Ion-Beam Mixing: Metal-Si and Metalmetal Structures
Authors: Mayer J. W. , Fastow R. , Galvin G. , Hung L. S. , Nastasi M. , Thompson M. O. , Zheng L. R.
Published: March 2011

Energy deposition and heat-flow determine the temperature distributions in pulsed-beam irradiated structures. In laser irradiated Si, transient conductance measurements indicated a liquid/solid interface velocity of 2.8 m/sec during crystallization in agreement with a heat flow model. With pulsed ionbeam annealing of metal-Si structures, melting starts at the interface; epitaxial NiSi2 layers have been formed. Ion-beammixing experiments on polycrystalline and epitaxial Au-Ag bilayers show that intermixing is more pronounced in the polycrystalline structures as is the case with thermal annealing. Superlattice structures are formed in the epitaxial structures.
Effect of Ion Irradiation on the Formation of Ni, Cr and Pt Silicide
Authors: Wielunski Leszek S. , Lien Chuen-Der , Liu Bai-Xin , Nicolet Marc-A.
Published: March 2011

The influence of Xe+, As+ and Si+ irradiation on the Ni, Cr and Pt-silicide formed upon subsequent thermal annealings has been investigated. Helium MeV backscattering spectrometry and x-ray diffraction have been used to analyze the samples. The effect of silicon-metal interface contamination has been observed using an intentionally formed thin silicon oxide layer. The oxide layer was thick enough to prevent thermal silicide formation in unirradiated samples. In irradiated samples, the silicide forms thermally in spite of the presence of this oxide layer for Ni and Cr, but not for Pt. Similar results were obtained for Xe+, As+ and Si+ irradiations. We attribute this effect to ion mixing of the interfacial layer. The differences between results obtained with Ni, Cr and Pt are discussed. These results demonstrate that a low-dose irradiation can render the process of silicide formation upon thermal annealing tolerant to interfacial impurities. On the other hand, we also show that ion irradition can inhibit Pt and Ni silicide formation.
Structure and Properties of Single Crystal Al2O3 Implanted with Chromium and Zirconium
Authors: Mchargue C. J. , Naramoto H. , Appleton B. R. , White C. W. , Williams J. M.
Published: March 2011

Single crystals of Al2O3 were implanted with chromium and zirconium to fluences of 1 × 1016 to 1 × 1017 ions cm−2. Rutherford backscattering-channeling studies showed the surface layers to be damaged but crystalline with the implanted ions randomly distributed. The microhardness and indentation fracture toughness were higher for the random solutions than for conventionally formed solid solutions. Changes in structure and properties caused by annealing in air at temperatures up to 1800°C were studied.
Metastable Percolation Phase Formation in Lif Implanted with Alkali Ions
Authors: Davenas J. , Thevenard P. , Dupuy C.
Published: March 2011

The formation of a continuous metallic layer in the doped region of LiF crystals implanted at low temperature, has been explained by the formation of bridges between next neighbouring alkali ions of the lattice around-each implanted ion. For a critical concentration of implanted ions it is possible to show using statistical arguments that conducting chains are formed by the union of these links, according to a percolation mechanism. We show that the assumption of a distribution of isolated implanted ions at low temperature is justified by the observation of their precipitation when the crystal is warmed up to room temperature. The transformation of the metallic optical absorption into the colloidal band associated with precipitates of implanted ions is correlated with the transition from a conducting state to an insulating state of the implanted layer. We show that this evolution towards an equilibrium situation may be reversed by a reirradiation, which is used as an external perturbation and that the conducting state associated with dispersed implanted ions is then once again obtained.
Implantation into Covalent Polymeric Materials
Authors: Weber David C. , Brant Patrick , Carosella Carmine A.
Published: March 2011

Ion implantation has been used to modify the organic semiconducting polymer, polyacetylene, (CH)x, and the semimetal, graphite, Cx. Implantation results in the formation of a unique polymer-fluorine interaction. This interaction leads to increased conductivity. The implantation also made the “doped” (CH)x resistant to the usual air oxidation which normally occurs with the conventionally doped polymers.
Surface Modification and Radiation-Induced Segregation
Authors: Rehn L. E.
Published: March 2011

Large changes in the distributions of alloying components have been observed in a wide variety of alloys during ion bombardment. This metastable, radiation-induced segregation (RIS) results from the preferential transport of alloying components by defect fluxes. Since the number of radiationinduced defects can exceed the number of implanted ions by several orders of magnitude, RIS can be highly efficient in modifying near-surface alloy compositions. In this paper, the general features of RIS are described. Aspects which are pertinent to the modification of materials by ion beams are emphasized. Examples are given of surface modifications which utilize RIS effects.
Electrical Properties of the Ion-Implanted Pd1−x Bx System
Authors: Mendoza-Zelis L. , Traverse A. , Chaumont J. , Bernas H. , Dumoulin L.
Published: March 2011

The resistivity (and resistivity temperature dependence) of low temperature B implanted Pd films was measured at B concentrations up to x ֮0.55. Both properties indicate that the evolution of the system towards an amorphous structure sets in at about x ֮0.30 (the deep eutectic composition). The previous discovery of superconductivity by Stritzker and Becker at high values of x is confirmed. Annealing properties of the system were also investigated.
Study of Metastable Fe-W Films
Authors: Göltz Gerhard , Fernandez Rouel , Nicolet Marc-A. , Sadana Devendra K.
Published: March 2011

Xenon irradiation of Fe-W multilayers at room temperature (R.T.) can produce two types of metastable states: low doses (< 1 × 1016 Xe/cm2 ) extend the equilibrium solid solubility of W in Fe and vice versa, maintaining the equilibrium b.c.c. lattice structure of Fe and W; at high doses (> 1 × 1016 Xe/ cm2 ) and in the vicinity of the composition Fe70W30, amorphization can occur. In comparison, RF sputter-deposited FexWl-x films were amorphous over the whole range (0.35<x < 0.79) investigated. The recrystallization temperatures of these amorphous layers exceed 600°C for 15 min vacuum annealing. Whereas Fe-W compounds always form during thermal annealing, these compounds are normally not found after Xe-irradiation of multilayers.
Structural and Mechanical Properties of Ion Implanted Al and Cu
Authors: Moine P. , Delafond J.
Published: March 2011

Tensile deformation experiments on Al single crystals and parallel microstructural studies by T.E.M. on specimens directly thinned prior to a Zn+ ion implantation have been carried out. An uniform concentration of 7 at % Zn has been obtained on 1200Å thick layers by implantation using multiple energies. The temperature ranges of metastable phase of these samples are different from bulk Al-Zn alloys of identical concentration. Room and 80°C temperature thermal treatments leading to an important precipitation hardening in bulk alloys do not produce any significant mechanical modification in implanted Al single crystals. T.E.M. observations do not show any supplementary scattering around Bragg spots. On the contrary, we observe the direct appearance of precipitates at 135°C and 150°C after some days annealing.

High cycle reversed load fatigue test in vacuum show significant modifications of surfacedamage of an oxygen implanted copper specimen.
Superconducting Critical Temperatures of C-Implanted Al5 Structure V-Si
Authors: Gavaler J. R. , Braginski A. I. , Manocha A. S. , Appleton B. R. , White C. W. , Williams J. M.
Published: March 2011

A series of A15 structure V-Si films were sputtered with compositions ranging from approximately V90Si10 to V75Si25 . The as-deposited critical temperature onsets were between ~ 8 and 17K. Carbon levels of up to 5 at.%(average) were implanted and the films subsequently annealed at various temperatures between 650 and 1050°C. No Tc's above 17K were obtained in the C-implanted films. However enhancements of as much as ~ 9K, from ~ 8 to 17K, in highly Si-deficient films indicated that carbon was incorporated into the A15 structure of these films to form pseudo-binary V-Si-C alloys. Experimental details are given and some reasons why Tc values greater than 17K were not obtained are discussed.
Pulsed Ion Beam Annealing Of Nickel Thin Films on Silicon
Authors: Chen L.J. , Hung L.S. , Mayer J.W. , Baglin J.E.E.
Published: March 2011

High power pulsed ion beams have been applied to anneal nickel thin films on silicon. RBS and TEM have been performed to study ion beam induced effects. With Ba+ion beams at energy densities greater than 0.7 J/cm2and H+beams above about 1.3 J/cm2, cellular structures were found. At about 0.6 J/cm2for Ba+(about 1.0 J/cm2for H+), epitaxial NiSi2was formed. At lower energy densities, polycrystalline layers containing a mixture of silicide phases were observed. With ion beam annealing, melting starts at the Ni/Si interface and epitaxy was found at energy densities well below that required to melt Ni or crystalline Si.
Optical Imaging and Information Storage in Ion Implanted Ferroelectric Ceramics
Authors: Peercy P. S. , Land C. E.
Published: March 2011

Photographic images can be stored in ferroelectric-phase lead lanthanum zirconate titanate (PLZT) ceramics using a novel photoferroelectric effect. These images are nonvolatile but erasable and can be switched from positive to negative by application of an electric field. We have found that the photosensitivity of ferroelectric PLZT is dramatically improved by ion implantation into the surface exposed to image light. For example, the intrinsic photosensitivity to near-UV light is increased by as much as four orders of magnitude by coimplantation with Ar and Ne. The increased photosensitivity results from implantation-induced decreases in dark conductivity and dielectric constant in the implanted layer. Furthermore, the increased photoferroelectric sensitivity has recently been extended from the near-UV to the visible spectrum by implants of Al and Cr. Ion-implanted PLZT is the most sensitive, nonvolatile, selectively-erasable image storage medium currently known.
Rapid Annealing of Implant Damage Using Thermal Radiation
Authors: Fulks R. T. , Russo C. J. , Downey D. F. , Hanley P. R. , Stacy W. T.
Published: March 2011

The rapid annealing of implant damage using thermal radiation has been shown to be a production-worthy method of achieving good activation and minimal dopant redistribution of implanted species. The method involves the shuttered exposure of a standard 3" or 4" silicon wafer to a uniform thermal radiation front produced by a graphite heater for short times (10–30 sec). The propagation of residual damage observed by TEM is significantly less than that produced by furnace annealing and device structures annealed have electrical characteristics comparable to standard furnace anneals.
The Microstructure of Silicon-on-Insulator Structures Formed by High Dose Oxygen Ion Implantation
Authors: Pinizzotto R.F. , Vaandrager B.L. , Lam H.W.
Published: March 2011

Cross-sectional and plan view transmission electron microscopy and high resolution scanning electron microscopy have been used to characterize the microstructure of silicon-on-insulator formed by high dose oxygen ion implantation. The complete microstructure was observed to be composed of a series of distinct zones. The top silicon layer was {100} single crystal with a very low dislocation density. The second layer was a mixture of fine grained polysilicon and amorphous SiO2. The third layer was pure SiO2 , followed by a second mixed layer. Finally, there was a layer of {100} silicon with an extremely high dislocation density. Some of the dislocations extended as far as 1 μm into the Si substrate. The relative widths of the layers were found to depend on the total ion fluence. The oxide layer did not occur for low doses and the two mixed layers merged into one zone. At high doses, the silicon-silicon dioxide interfaces are abrupt due to internal oxidation.
Saturation, Exchange and Retention of Implanted D/H Ions in Fused Silica
Authors: Doyle B. L. , Arnold G. W.
Published: March 2011

Elastic recoil detection techniques have been used to measure hydrogen isotope profiles in fused silica implanted with 20 keV H and/or D ions. Saturation is obtained for both H and D implantations at a concentration of 2.2 × 1021 ions/cm3. H and D exchange are observed for saturated samples subsequently implanted with a different H isotope. A previously developed local mixing model of H-trapping has been extended to include retrapping and beam-induced detrapping for application to these studies. This theoretical analysis provides a good fit to the H/D saturation and isotope exchange behavior. Isochronal annealing shows that both H and D are released in a single stage centered about 550°C.
Ion Beam Deposition of Amorphous Carbon Films With Diamond Like Properties
Authors: Angus John C. , Mirtich Michael J. , Wintucky Edwin G.
Published: March 2011

Carbon films were deposited on silicon, quartz, and potassium bromide substrates from an ion beam. Growth rates were approximately 0.3 μm/hour. The films were featureless and amorphous and contained only carbon and hydrogen in significant amounts. The density and carbon/hydrogen ratio indicate the film is a hydrogen deficient polymer. One possible structure, consistent with the data, is a random network of methylene linkages and tetrahedrally coordinated carbon atoms.
A Comparison of Atomic Mixing Behaviour of Cu- Au and Cu- W Systems for Room Temperature and Low Temperature Irradiation
Authors: Wang Z.L. , Westendorp J.F.M. , Doorn S. , Saris F.W.
Published: March 2011

300 keV Kr ion irradiations with doses varying from 2× 1015 to 2× 1016 at/cm2 have been applied to initiate mixing of Cu-Au and Cu-W systems. As under normal thermodynamic conditions the Cu-Au system is miscible whereas the Cu-W system is not, the comparison of both systems provides a test for the current theories on ion-beam mixing. A pronounced difference in mixing phenomena is observed for both systems; in the Cu-Au system atomic displacements are one order of magnitude larger than those in the Cu-W system. In addition, a drastic temperature dependence of ion-beam mixing in the Cu-Au system has been found. The mixing is suppressed by lowering the substrate temperature during irradiation. These results show that radiation enhanced diffusion is the mechanism underlying the ion-beam mixing of Cu and Au. Results for the Cu-W system are consistent with a collisional mixing model.
Temperature Dependence of Ion Beam Mixing in Al
Authors: Picraux S.T. , Follstaedt D. M. , Delafond J.
Published: March 2011

The atomic mixing of evaporated Al/Sb films and of Al/Ag films on Al<110> crystal substrates by 400 keV Xe ion beams has been investigated. Concentration depth profiles were measured in situ by 1.5 MeV He scattering as a function of Xe fluence from 2 to 32×1015 Xe/cm2. The initial mixing rates are similar at 85 and 300 K; mixing proceeds by rapid motion of Al (≈15 Al/Xe) into and uniformly through the thickness of the Sb film and by a slow motion of Sb (≈0.5 Sb/Xe) into the Al<110> substrate. More rapid Sb mixing into Al occurs for polycrystalline Al. The rate for Al into Sb slows at concentrations approaching the stable AlSb phase. Appreciably higher rates of Sb mixing into Al (2.2 to 2.8 Sb/Xe) occur at 575 K. Mixing rates for the highly soluble system, Al/Ag, are compared to the nearly insoluble Al/Sb at 85 and 300 K. Appreciably higher rates are found for Ag than for Sb, suggesting the influence of chemical driving forces even at these low temperatures.
Inadequacy of the Conventional View of Hydrogenated Amorphous Silicon
Authors: Adler D. , Silver M. , Shaw M. P. , Cannella V.
Published: March 2011

The conventional view of the electronic structure of hydrogenated amorphous silicon is: (1) the material is characterized by a mobility gap of about 1.8 eV, with exponential band tails due to disorder and deep defect states arising from silicon dangling bonds (T3 centers); (2) substitutional doping occurs because of the formation of chargedimpurity/dangling-bond pairs, e.g. P4+ – T3-, at the substrate temperature; (3) the effective correlation of the T3 center is about 0.4 eV; (4) T3o centers are the predominant recombination center; (5) the three intrinsic ESR signals are due to electrons on T3o centers, electrons in the conduction band tail, and holes in the valence band tail. It is the purpose of this paper to demonstrate that this model is in sharp disagreement with an array of basic experimental data, and much of the evidence presented in its favor is based on self-inconsistent logic. We conclude that it is very likely that large concentrations of charged intrinsic defect pairs are present in all hydrogenated amorphous silicon films.
Electronic Transport in Hydrogenated Amorphous Silicon
Authors: Silver M. , Adler D. , Shaw M. P. , Cannella V. , McGill J.
Published: March 2011

The puzzles regarding the magnitude of the free electron mobility in hydrogenated amorphous silicon are examined. It is suggested that highlevel double injection produces a metastable increase in the carrier mobility by neutralizing positively and negatively charged defect states thereby eliminating long-range potential fluctuations. Since these defect states cannot be neutralized under low-level or single injection, they both contribute to the modulation of the conduction band and increase the freecarrier scattering. If the latter is the predominant scattering mechanism, the neutralization of charged defects directly leads to a mobility increase under double-injection conditions. We discuss the various implications of this model, and present recent experimental results in agreement with these ideas.
Room Temperature Light Induced Electron Spin Resonauce In Undoped Hydrogenated Amorphous Silicon (a-Si:H)
Authors: Pandya R. , Zafar S. , Schiff E. A.
Published: March 2011

The effects of illumination upon the absorption electron spin resonance spectrum of the dangling bond defect system have been studied in undoped amorphous hydrogenated silicon (a-Si:H). A small shift of the inhomogeneous envelope of the system towards higher g-value is observed at roomtemperature. The shift is not accompanied by a significant change in the signal. Results are reported which indicate that this shift is not due to illumination induced heating of the specimen or calibration changes of the spectrometer. The results may be related to previously reported optical bias effects upon transient photocurrent and photoinduced absorption studies.
Capacitance-Voltage Characteristics of Metallic Gate/Oxide/a-Si:H Mos Structures
Authors: Schropp Ruud E. I. , Snijder Jan , Verwey Jan F.
Published: March 2011

The density of states (DOS) has for the first time been calculated throughout the entire bandgap region of undoped amorphous silicon from quasi-static capacitance-voltage (QSCV) measurements using MOS structures. The QSCV DOS is compared with the DOS obtained by the field-effect method. It is shown, that the coexistence of states of a different nature at the same bandgap level can be revealed by the temperature dependence of low frequency MOS CV measurements.
Transport Measurements in LPCVD Amorphous Silicon Obtained from Disilane.
Authors: Manfredotti C. , Gervino G. , Montaldi L. , Nastasi U. , Murri R. , Schiavulli L.
Published: March 2011

Measurements of high temperature conductivity on a-Si:H obtained by LPCVD from Si2H6 at temperatures between 450 and 500 °C indicate clearly a change on the activation energy from 0.9 - 1.0 eV to 0.55 - 0.6 eV around 600 °K.

The results are not strongly different from those obtained in GD a- SiH4:however, the coefficent of the energy shift of the mobility edge with temperature is greater by a factor of 2, while the average extension of the tail state distribution at T= 0 °K is roughly a factor 1.5 larger. The main discrepancy concerns the pre-exponential factor, which is one or two orders of magnitude larger, giving a product (NcukT)of the order of 1021 cm-1 s-1. By assuming a conduction mobility two orders of magnitude larger than the maesured Hall mobility one obtains a value for N which is only a factor four times larger than what currently assumed for a-Si:H.
Density-of-States Distribution In Disilane LPCVD Deposited Amorphous Silicon as Determinated By SCLC
Authors: Manfredotti C. , Gervino G. , Montaldi L. , Varesio R. , Zanini A. , Nastasi U.
Published: March 2011

I-V characteristics have been measured in a-Si:H films deposited from Si2 H6 by LPCVD and have been analyzed according to a direct method. DOS distribution is thickness-dependent, similarly to what has been found on SiH deposited films, with values at Fermi level ranging from below 1016 cm-3 eV-1 up to 1018 cm-3 eV-1. Deposition temperature, at least in the interval 450 - 500°C, does not seem to affect DOS distribution. Hydrogen content is pratically constant in all the films. The only possible conclusion is that only thickness influences DOS distribution and that only for thickness larger than 0.8 μm it is possible to get densities at Fermi level below 1016 cm-3 eV-1.
Thickness Dependence of the Optical and Electrical Properties of Thin A-Si:H Films
Authors: Demichelis F. , Mezzetti E. , Mpawenayo P. , Tagliaferro A. , Tresso E. , Bourquard S. , Rava P. , Mea G. Della , Mazzoldi P.
Published: March 2011

Optical and electrical properties are investigated as a function of thickness for two sets of samples of a-Si:H films deposited respectively by RF magnetron sputtering and by RF glow discharge under the same conditions. The hydrogen concentration, the transmittance and reflectance spectra in the UV-visible-NIR and the resistivity were measured for both sets of samples. Relationships between index of refraction, absorption coefficient, imaginary part of the dielectric constant, optical band gap, resistivity and the thickness are found and interpreted. The thickness dependence of these parameters is related to the larger amount of inhomogeneities present in sputtered samples with respect to glow discharge samples.
Frequency-Dependent Noise in Hydrogenated Amorphous Silicon
Authors: Bathaei F. Z. , Anderson J. C.
Published: March 2011

Flicker noise, due to trapping and emission from states in the mobility gap, leads to a spectrum in which noise power is proportional to 1/fn. Experimentally we find 0.6 <n<1.1 for an Si:H film in an n+-i-n4 structure. Theoretical development allows the extended state electron mobility, and the density of states at the conduction band edge to be obtained. Similar measurements on Schottky diodes provide the distribution of the localized state density in the mobility gap.
The Effect of Light Soaking on the Photoconductivity Response in A-SI:H
Authors: Changhua Qiu , Wenhao Wu , Shifu Zhao , Daxing Han
Published: March 2011

The temperature dependences of response time tr and steady state photoconductivity (PC) were used to deduce the DOS at energies above the dark Fermi level. The tr and PC of annealled state A and light soaked state B were measured from 115K to 300K. Light soaking causes degradation of PC. Compared with state A, the PC response of state B is faster at low temperatures, but is slower at high temperatures. The difference between state A and state B was interpreted by a decrease of shallow traps and an increase of deep traps.
A 29Si-NMR Investigation of Amorphous Hydrogenated Silicon Nitride
Authors: Petrich Mark A. , Livengood Rhett E. , Reimer Jeffrey A. , Hess Dennis W.
Published: March 2011

We present the results of a spectroscopic study of amorphous hydrogenated silicon nitride. The nitride was prepared by plasma enhanced chemical vapor deposition and was studied with infrared absorption (IR) and solid-state nuclear magnetic resonance (NMR) spectroscopies. This nitride film shows a particularly interesting distribution of hydrogen: hydrogen atoms are nearly exclusively bound to nitrogen.
Photoelectronic Properties of a-Si:Sex and a-Si:Tex Thermally Evaporated Films.
Authors: Wakim F. G.
Published: March 2011

The presence of selenium (Se) or Telurium (Te) in amorphous silicon films seems to improve the quality of these films by reducing the number of unsatisfied or dangling bonds and changing the optical gap and thermal activation energy. The thermal activation energies of a-Si:Sex and a-Si:Tex were always larger than that of a-Si films. The measured optical gap can be tailored to some value between 0.8 eV and 1.8 eV depending on the use of Se or Te and on the relative concentrations. The presence of Se or Te in a-Si films seems to have the same effect as that of hydrogen in a-Si films prepared by glow discharge of silane and used in solar cells.
The Effect of Deposition Procedure on the Conductivity of Hydrogenated Amorphous Silicon Multilayer Films.
Authors: Moddel G. , Su F.-C. , Vanier P. E.
Published: March 2011

The conductivity of multilayer P-doped amorphous hydrogenated silicon (a-Si:H) thin films is measured for films prepared with different, deposition procedures. Multilayer films are deposited by plasma enhanced CVD following a procedure in which the plasma is extinguished and the deposition chamber is filled with air or argon after the deposition of each layer. These films are compared to films grown in continuous deposition runs. The technique provides a direct means to determine the effects of continuous versus interrupted deposition and to analyze oxide interface and bulk gap state densities. Exposing the layers to air between depositions produces deleterious effects whereas the effect of argon exposure are slight. Literature values for the density of states in oxidized a-Si:H are used to provide evidence for a defective layer in very thin P-doped a-Si:H having a defect density of over 1013 cm−2 eV−1 approximately 0.3 eV below the transport level.
Electron and Hole Transport Perpendicular to the Planes of a-Si:H/ a-Si, Ge:H Compositional Superlattices
Authors: Kolodzey J. , Aljishi S. , Schwarz R. , Shen D.-S. , Quinlan S. , Lyon S. A. , Wagner S.
Published: March 2011

Drift mobilities, drift mobility-lifetime products and minority carrier diffusion lengths perpendicular to the planes of a-Si:H, F/a-Si0.35,Ge0.65:H, F superlattices have been measured over a range of well sublayer widths. The transport data suggest a transition from scattering dominated transport in states at the top of the barriers for short superlattice periods to recombination dominated transport at the bottom of the wells for large periods. The characteristic period for this transition is ˜3 nm.
Parameters Affecting Light-Induced Excess Conductivity in Amorphous Silicon Doping-Modulated Multilayers
Authors: Su F.-C. , Levine S. , Vanier P. E.
Published: March 2011

The phenomenon of light-induced excess conductivity (LEC) which occurs in a-Si:H npnp doping-modulated multilayers is found experimentally to be dependent on several different factors. The concentrations of the dopants in n-type and p-type layers affect the Fermi level position, the height of the barriers, and also the density of defects. These parameters are altered by different choices of inert gas diluent (Ar or He) and substrate temperature T. For a given set of deposition conditions, the LEC effect can be maximized by varying the layer thickness. With undiluted silane at T = 250 °C, the effect was relatively small, reaching a maximum in relatively thick layers (540 Å). The largest effects were obtained for films deposited from silane diluted in helium, using thinner (330 Å) layers. However, for films deposited from silane diluted in argon, thS magnitude of the effect and optimum layer thickness was intermediate (440 Å). When Ts was varied, a minimum in LEC was found near 200–250° C. The influence of Sinternal field was examined by using nini, pipi and npnp multilayers. The internal field is a necessary factor to observe a large LEC effect. A compensated film shows a small LEC effect.
Observation and Study of Wavelength Dependence of The Open-Circuit Voltage In a-Si:H BASED p-i-n SOLAR Cells
Authors: Gorn M. , Kniffler N. , Winterling G.
Published: March 2011

The spectral dependence of Voc is studied in a-Si:H based p-i-n junctions by using chopped monochromatic light. A dispersion ΔVoc = Voc(blue) - Voc(red) is observed which depends systematically on a low level doping of the central layer. While ΔVoc is largest and positive in phosphorous doped cells it is negative in boron doped cells. Voc is found to be enhanced by an additional white bias light.

The dispersion data are discussed by considering the contributions to Voc arising from drift in an inhomogeneous field and from carrier diffusion.
Cowparison Studies of Hydrogenated Amorphous Silicon Films Prepared From Silane-Hydrogen and Silmne-Helium Mixtures
Authors: Patel R. I. , Olsen D. J. , Shirck J. R. , Tran N. T.
Published: March 2011

Hydrogenated amorphous silicon films were produced from silane/hydrogen and silane/helium gas mixtures by RF glow discharge. We examined the optical and electrical properties of films produced with these gas mixtures, at various RF power levels and silane fractions. Film quality was analyzed by measuring the dark and photoconductivity, optical band gap, and activation energy. Optical emission spectroscopy was also used as a diagnostic tool for studying the plasma during glow discharge depositions. Experimental results indicate that amorphous silicon films made from silane/helium mixtures exhibit improved optoelectronic properties, higher deposition rates, and higher emission intensity ratios (ISiH/IH) as compared to films produced from silane/hydrogen mixtures. In preparing films from silane/helium mixtures, the onset of dust/powder formation occurs at considerably higher RF powers as compared to silane/hydrogen, thus making this approach an attractive commercial option for depositing films at high rates.
Influence of Transparent Conducting Oxide on Amorphous Silicon Solar Cell Performance
Authors: Walker Chris , Hollingsworth Russell , Cueto Joe del , Madan Arun
Published: March 2011

The use of transparent conducting oxides (TCO) as electrical contacts in a-Si:H solar cells has stimulated interest in the multitude of effects that these layers have on a-Si:H solar cell performance. The study of a-Si:H p-i-n junctions using a TCO contact involves many factors such as, interdiffusion, transmission, reflection, and resistivity. In this paper, we attempt to distinguish between these factors through the role they play in determining the solar cell device performance. Devices were characterized via dark and illuminated current vs. voltage (I-V) measurements, and spectral response. It was found that the properties of the TCO have an important role in influencing FF and Jsc in the devices.
Stability and Efficiency in Amorphous Tandem Solar Cells
Authors: Galluzzi F. , Conte G. , Angelis L. De , Peruzzi R.
Published: March 2011

Theoretical evaluation of stability and efficiency of two-junction two-terminal amorphous tandem solar cells is performed using an analytical model which takes into account not only optical characteristics and transport properties but also photodegradation effects due to dangling bond formation under light exposure.

Requirements for material quality and device design are particularly investigated.
VLSI Processing of Amorphous Silicon Alloy P-I-N Diodes For Active Matrix Applications
Authors: McGill J. , Cannella V. , Yaniv Z. , Day P. , Vijan M.
Published: March 2011

A number of new amorphous silicon alloy microelectronic devices, including LCD active matrix displays, linear image sensors, and thin film multilayer computer memories, have been developed in our company. These applications rely heavily on the quality of the intrinsic semiconductor as well as its ability to withstand the many processing steps used in a modern photolithographic process. In this paper, we present electrical data on amorphous silicon alloy p-i-n diodes after such a process. These devices have an active area of 20μm × 20μm defined using standard photolithographic techniques and etched using a dry etch process. These diodes are characterized by ideality factors (n) of 1.4 and extrapolated reverse saturation current densities of 1013A/cm2h. The diodes exhibit nearly 10 orders of magnitude rectification at ± 3V and the reverse bias current density remains below 10-8 A/cm2 for reverse bias voltages of -15V. In pulsed forward bias, these diodes can be operated at current densities greater than 300A/cm2. Thin film amorphous silicon diodes moreover have the advantage that varying the thickness of the intrinsic layer allows the optimization of parameters such as the capacitance per unit area, the reverse bias current density and the forward bias conductance per unit area. We find that these devices are fully compatible with state of the art VLSI processing techniques and are suitable for applications in integrated circuit structures, for example rectification devices in microelectronic arrays and isolation devices in display matrices.
Short Channel Length Planar Tft's Using Amorphous Silicon Alloys
Authors: Yang M. , Yaniv Z. , Vijan M. , Cannella V.
Published: March 2011

There is a rapid growth of interest in the application of amorphous silicon alloy thin film devices to large area microelectronic circuits. Increased current levels are a constant goal since gains in device current result in proportional gains in power and speed. Mobility limitations in amorphous silicon thin film transistors have directed interest toward short conduction channel devices to achieve higher current levels; furthermore, compatibility with large area processing makes photolithography with 10μm feature size very attractive. Consequently, innovative techniques, which define channel lengths by processing parameters rather than by mask feature size are necessary. Previous work has applied such techniques to vertical structure TFT's which define channel lengths by the vertical height of deposited layers. Here, we report on a technique which achieves short channel lengths in planar structures using etching parameters to define short channel lengths. Amorphous silicon alloy TFTs have been fabricated with channel lengths of ≈2μm which reach currents of lma. These techniques broaden the range of application of amorphous silicon alloy TFTs by providing devices capable of operating at higher currents and higher speeds.
Application of Two-Step Deposition Method To Ultra-Thin a-Si FETs
Authors: Katoh Y. , Sugiura O. , Takeuchi Y. , Uchida Y. , Matsumura M.
Published: March 2011

Two-step deposition method for fabricating ultra-thin a-Si FETs has been investigated theoretically and experimentally. Theoretical relation between field-effect mobility and a-Si layer thickness agreed qualitatively with the experimental results. The mobility of the 15nm-thick FET was drastically improved by an application of the two-step deposition method.