bluuebunny/crossref_metadata_2025_split huggingface dataset:
SiC Film Deposited by Pulsed Excimer Laser Ablation
Authors: Tench R. J. , Balooch M. , Connor A. L. , Bernardez L. , Olson B. , Allen M. J. , Siekhaus W. J. , Olander D. R. 
Published: March 2011

ABSTRACTThin films of β- SiC were grown on Si substrates by excimer laser pulse ablation of bulk SiC. The films were examined by Auger electron, X-ray, and photoelectron spectroscopies. The film was smooth as monitored by scanning electron microscopy. Scanning electron and scanning tunneling microscopy showed inclusions in the deposited SiC film and laser ionization mass analysis detected SiC dimers in the vapor plume emitted from the target.
Surface Composition Changes and Ablation Dynamics in Excimer Laser Irradiated CdTe
Authors: Brewer P. D. , Zinck J. J. , Olson G. L. 
Published: March 2011

ABSTRACTWe have investigated the dynamics of KrF excimer laser ablation of CdTe and the fluence dependent changes in surface stoichiometry that accompany the laser ablation process. The composition of the CdTe surface was reversibly controlled between stoichiometric and a Te-rich condition by varying the laser fluence over the range from 15–65 mJ/cm2. The primary species ejected from the irradiated surface were Cd atoms and Te2 molecules. Their velocity distributions as measured by time-of-flight mass spectrometry were found to be Maxwellian. From the analysis of the velocity distributions, the preferential desorption of surface atoms, and the reversible nature of the process, we conclude that the desorption is due to a photo-thermal mechanism which mediates the competition between Te2 formation and desorption and the desorption of Cd atoms.
The Role of the Species Formed in Pecvd Systems on the Density of States of a-Si:H Films
Authors: Martins R. , Rodrigues L. , Vieira M. , Fortunato E. , Santos M. , Dirani E. , Carvalho N. , Baía I. , Guimarães L. 
Published: March 2011

ABSTRACTHere the species detected by a quadropole mass analyser and resulting from the decomposition of SiH4 induced by a plasma [using a diode-like PECVD (Plasma Enhanced Chemical Vapour Deposition) system, in which has been varied the following experimental conditions: temperature of the substrate (Ts); deposition pressure (pd); power density (dp) and electrode geometries], have been correlated with the electro-optical properties and Density of States (DOS), inferred from Constant Photocurrent Measurements (CPM). The mass spectra analysis reveal the existence of atomic and molecular hydrogen as well as on the SiH3 and SiH2 species whose ratios are strongly dependent on electrode geometries used, that also roles the adequated deposition conditions for producing good quality materials. Thus, for the recessed electrode we observe an enhancement on plasma density at low self bias voltage (Vdc), leading to the production of high quality films at Ts = 180 °C, using moderate dp and pd in the range of 75–80 mtorr, with Vdc ≃ 8 V. On the other hand, for the grid electrode we observe an enhancement in molecular hydrogen at growth surface for high Ts, leading to the production of the best films for Ts in the range of 280–300 °C, using dp ≃ 25 mWcm−3, pd ≃ 100 mtorr and Vdc ≃ 30 V. For both electrodes we observe that high bombardment is important for getting microstructures, defect free and dense. The CPM data show that DOS increases with pd indicating that the enhancement on the number of collisions in the gas phase lead to the increase on chain polymerization formation. We also observe that the hydrogen coverage onto the growth surface is important for activating the growth mechanism, producing homogeneous material with a low DOS.
Thermal Equilibration Between Band Tail and Near Surface Defect States in Hydrogenated Amorphous Silicon and Silicon-Germanium Alloys
Authors: Aljishi Samer , Jin Shu , Ley Lothar , Wagner Sigurd 
Published: March 2011

ABSTRACTWe employ total yield photoelectron spectroscopy to measure the density of occupied states at the clean a-SixGe1_x:H alloy surface. The near surface defect states are observed to lie at 0.57 eV above the valence band edge with a density of 4×l017 cm−3, independent of Ge content. The valence band tail characteristic energy is also measured to be independent of alloy composition with an average value of 54 meV. We demonstrate that thermodynamic equilibrium at the surface between weak bonds (forming the valence band tail) and the dangling bonds provides an excellent description of the experimental data and explains why the surface state density in a-Si:H cannot be lowered below the 1011 to 1012 cm−2 range.
Structure of a-Si:H/SnO2 Interface Characterized By Xps
Authors: Koinuma H. , Nakano M. , Gonda S. 
Published: March 2011

ABSTRACTThe interface structure of a-Si:H films deposited by glow discharge decomposition of Si2H6 on SnO2 was characterized on an atomic scale with the use of in situ XPS. The method analyzes the variation of the intensity of photoelectron emission originating from the bottom SnO2 layer and transmitting through the upper a-Si:H layers of various thicknesses. It was evaluated that a-Si:H was partially oxidized as it grew to a thickness of about 15 A, while the SnO2 bottom layer was reduced to metallic Sn and SnOx (0 < x < 2) states as deep as 2 A and 12 A from the interface, respectively,
Experimental Determination for the Transition Temperature Between Ballistic and Hopping Controlled Recombination in a-Si:H
Authors: Zvanut M. E. , Wang K. , Han D. , Silver M. 
Published: March 2011

ABSTRACTThe transient forward bias current of a-SI:H p-i-n diodes has been measured as a function of temperature and voltage. The transient shows an initial decay followed by a substantial rise which suggests a large value for the ratio of the carrier lifetime to the transit time as demonstrated by Shapiro. We found that both the time at which the rise begins and the ratio of the final saturated current to the minimum current increase with decreasing temperature for temperature greater than a characteristic temperature, Tc. For T < Tc, both the time and the ratio abruptly decrease with temperature. We attribute this change in temperature dependence to a change in the transport kinetics from ballistic to hopping controlled recombination.
The Influence of Tunneling Transitions on Recombination and Photoconductivity of a-Si:H
Authors: Cleve B. , Thomas P. 
Published: March 2011

ABSTRACTSpin dependent photoconductivity measurements provide evidence for the existence of tunneling transitions from localized tail states into the dangling bond recombination centers. These processes can be included approximately into the conventional model based on rate equations. Satisfactory values for the activation energy of the photoconductivity at low temperatures are obtained. Our model produces thermal quenching and an enhancement of the photoconductivity with rising dark Fermi level.
Effect of the Depletion Region of a-Si:H Schottky Diodes on the Time-of-Flight Mobility-Lifetime Product
Authors: Wyrsch N. , Roca i Cabarrocas P. , Wagner S. , Viret V. 
Published: March 2011

ABSTRACTThe effect of the depletion region in amorphous silicon Schottky diodes on the mobility-deep trapping lifetime product μτ of electrons has been investigated using transient photoconductivity techniques. We varied the laser wavelength of the exciting laser in time-of-flight (TOF) measurements. The results are correlated with measurements of the internal field by means of the charge collection efficiency, and with measurement of the deep-trapping time by the Delayed-Field TOF technique (DFTOF). We find that the electron μτ decreases from the bulk toward the top surface.
Amorphous Hydrogenated Silicon P-I-N Solar Cells Grown from Hydrogen-Diluted Silane
Authors: Bennett Murray S , Tu Jacob C 
Published: March 2011

ABSTRACTWe investigated p-i-n solar cells in which the i-layer was grown from hydrogen-diluted silane. The deposition parameters which were varied include flow rates, deposition pressure and power, and the degree of hydrogen dilution. We found that high quality devices could be made in which the i-layer was grown under a wide range of deposition conditions but that over this range neither the initial performance nor the stability of the devices differed significantly from those of cells having the same structure, but in which the i-layer was deposited from SiH4 with no H2-dilution.
Properties of Catalytic-Cvd Amorphous Silicon-Germanium (a-SiGe:H)
Authors: Matsumura Hideki , Yamaguchi Masaaki , Morigaki Kazuo 
Published: March 2011

ABSTRACTHydrogenated amorphous silicon-germanium (a-SiGe:H) films are prepared by the catalytic chemical vapor deposition (Cat-CVD) method using a SiH4, GeH4 and H4 gas mixture. Properties of the films are investigated by the photo-thermal deflection spectroscopy (PDS) and electron spin resonance (ESR) measurements, in addition to the photo-conductive and structural studies. It is found that the characteristic energy of Urbach tail, ESR spin density and other photo-conductive properties of Cat-CVD a-SiGe:H films with optical band gaps around 1.45 eV are almost equivalent to those of the device quality glow discharge hydrogenated amorphous silicon (a-Si:H).
B(Ch3)3 as P Layer Doping Gas
Authors: Shen D. S. , Chatham H. , Schropp R. E. I. 
Published: March 2011

ABSTRACTThe boron doped p-layer is a critical part of a-Si:H solar cells. Trimethylboron (B(CH3)3) has been suggested to be a better doping gas and has a better thermal stability than B2H6. Single junction a-Si:H solar cells and a-Si:H/a-Si:H tandem cells with the p-layers deposited using B(CH3)3 have resulted in conversion efficiencies of 11.4% and 10.4%, respectively. Using these new p+-layers, we also reached 10% efficiencies in single junction a-Si:H solar cells with the i-layer deposited at a high deposition rate of ∼ 2 nm/s from either SiH4 or Si2H6 as a source gas.
The Influence of Doping on the Electronic Properties of Hydrogenated Amorphous Silicon.
Authors: Herm D. , Wetzel H. , Kunst M. 
Published: March 2011

ABSTRACTThe results of transient photoconductivity and photoinduced absorption measurements in lightly phosphorus and boron doped (0-10 ppm ) a-Si:H films at T = 300 K are presented. From the observed increase of minority carrier trapping with doping it is concluded that even light doping leads to a strong increase of the density of deep traps. Furthermore an abrupt change of the behaviour of the transient photoconductivity between 2 ppm and 3 ppm B2H6 is observed. This change may be interpreted as the transition to a p-type semiconductor.
Hydrogen Bonding, and Microvoids in a-Si:H: a Proton NMR Study
Authors: Zheng M. , VanderHeiden E.J. , Taylor P.C. , Shinar R. , Mitra S. , Shinar J. 
Published: March 2011

ABSTRACTThe cw proton NMR spectra, spin lattice relaxation times Tx and free induction decay times T*2 were measured in various a-Si:H films deposited by rf-sputtering. All spectra exhibited broad and narrow components, of T*2 ∼ 20 and 45 μsec, respectively. In samples deposited at high rf power, the ratio of the integrated intensities of the broad and narrow lines was ∼ 1.5. These samples, which apparently contain mainly bulk monohydride bonds and a low volume fraction of microvoids, exhibit long-range H motion. In a sample deposited at low rf power, this ratio was ∼ 3. These samples, which contain significant dihydride and microvoid content, show a dramatic suppression of the long-range H motion. The T1 of both types of samples exhibits a clear minimum at ∼ 30 K, indicative of relaxation by H2 trapped in microvoids. The absolute values of T1, however, are smaller in the sample deposited at low rf power (0.1 sec at the minimum as opposed to 0.3 to 1.0 sec at the minimum), apparently due to a larger ratio of molecular hydrogen to bonded hydrogen. After annealing for 24 hours at 294°C, the ratio of broad-to-narrow components increases to > 10 in all samples, and the magnitudes of the T1 minima increase to about 1 sec in all samples.
Long Range Hydrogen Motion, Evolution, and Bonding in a-Si:H and a-Ge:H
Authors: Shinar R. , Wu X.-L. , Mitra S. , Shinar J. 
Published: March 2011

ABSTRACTThe results of secondary ion mass spectrometry and IR studies of hydrogen diffusion in a-Si:H and a-Ge:H are reviewed and discussed. In a-Si:H, the diffusion is significantly slower at low total H content. The exponent α of the power-law time dependent diffusion constant D(t) = Doo(ωt)−α does not decrease with temperature as 1-T/To. D(tL), for constant diffusion length L, thus deviates from an Arrhenius behavior. The “apparent” activation energy Ea and prefactor Do derived from lnD(tL) vs 1/T yield a Meyer-Neldel relation Do = Aooexp(Ea/kToo) irrespective of L, H content, or microstructure. Aoo ≅ 3.3 × 10−14cm2/s and Too ≅ 730K for 2.5 × 10−5 ≤ Do ≤ 102cm2/s and 1.3 ≤ Ea ≤ 2.2eV. The preliminary results on a-Ge:H are similar, with Aoo ≅ 1.3 × 10−15cm2/s and Too = 530K. It is suspected that deviations from an exponential distribution of H site energies, structural relaxation, and deep H trapping sites related to microvoids may all contribute to the deviation of α from a 1-T/To behavior. Measurements following prolonged annealing suggest structural relaxation that affects H-site energies.
Effect of Thermal Equilibration on Dark- and Photo-Conductivities in Undoped Amorphous Silicon-Germanium Alloys
Authors: Liu J. Z. , Shen D. S. , i Cabarrocas P. Roca , Park H. , Wagner S. 
Published: March 2011

ABSTRACTWe report the effect of thermal equilibration on the dark- and photo- conductivities of an un-doped a-Si,Ge:H,F with optical gap of 1.47 eV. Annealing at high temperature and subsequent quenching can freeze in the equilibrium configuration at the annealing temperature. The characteristic glass-like transition behavior of the conductivities was observed and used to estimate a freeze-in temperature of about 140°C. As the annealing temperature increases above the freeze-in temperature, the frozen-in dark- and photo- conductivities decrease, the photo- to dark- conductivity ratio increases, and the photoconductivity-generation rate exponent increases. These changes in conductivities are explained by a model calculation, which assumes that the quenching introduces new defect states to die lower energy flanks of the Gaussian defect distributions.
Capacitance Studies of Metastable States in Light-Soaked, Quench-Cooled, and Bias-Annealed N-Type Hydrogenated Amorphous Silicon
Authors: Leen Thomas M. , David Cohen J. , Gelatos Avgerinos V. 
Published: March 2011

ABSTRACTWe have investigated the metastable states produced in n-type a-Si:H samples by 3 kinds of treatments: light soaking followed by partial annealing, fast (quench) cooling, and bias-annealing. We employed voltage pulse photocapacitance to examine the deep defect state distribution, ND, and drive level capacitance profiling to determine the occupied conduction bandtail states NBT. Our results indicate that: (1) Although the most heavily doped films exhibit a larger increase in ND with light soaking than the corresponding decrease in NBT (consistent with some proposed defect creation reactions), in more lightly doped films we observe significant changes in NBT for much smaller corresponding differences in ND; (2) for quench cooling we observe increases by factors of up to over 2 in NBT without any measurable changes in ND for all samples; and (3) we observe increased NBT in bias annealed samples with no changes in ND. All of these results are inconsistent with a purely silicon bond breaking mechanism for metastable defect creation. We consider a significant contribution from a dopant activation mechanism which does not involve changes in ND).
Electron Trapping in Amorphous Silicon - A Quantum Molecular Dynamics Study
Authors: Yang Lin H. , Kalia Rajiv K. , Vashishta Priya 
Published: March 2011

ABSTRACTQuantum molecular dynamics (QMD) simulations provide the real-time dynamics of electrons and ions through numerical solutions of the time-dependent Schrodinger and Newton equations, respectively. Using the QMD approach we have investigated the localization behavior of an excess electron in amorphous silicon at finite temperatures. For time scales on the order of a few picoseconds, we find the excess electron is localized inside a void of radius ∼ 3 Å at finite temperatures.
An Extension of the Embedded Atom Method
Authors: Pasianot R. , Savino E. J. , Rao S. , Farkas D. 
Published: March 2011

For the class of materials in which covalent effects are important, there is still no simple and reliable scheme, adapted to computer simulations, that can handle angle de- pendent forces. Either they are based on the introduction of three body (or higher) [1] interactions, or demand unphysical behavior from the many body functions used [2,3]. In the first case, computer efficiency is considerably low due to the large amounts of calculations required; in the second case a negative curvature of the embedding function must be assumed for materials in which the Cauchy pressure is negative, and this is contrary to the current interpretations of that function.In the present work we derive a method to introduce many body shear forces, suited to computer simulations, which is free from the shortcomings mentioned above.
Structural and Electronic Properties of Narrow Gap Zincblende and Chalcopyrite Compounds
Authors: Pascale T.M. de , Meloni F. , Serra M. , Massidda S. , Continenza A. , Freeman A. J. 
Published: March 2011

ABSTRACTIndium compounds and corresponding epitaxially grown superlattices have provided good single crystals suitable for accurate experimental measurements and have added new interest to the study of the constituent bulk semiconductors and the II-IV-V2 chalcopyrite crystal phases. This paper reports results of structural and electronic properties of narrow gap binary and ternary semiconductors determined selfconsistently from first principles using both the full potential linearized augmented plane wave (FLAPW) and norm-conserving pseudopotentials (PP) total-energy methods.
Dislocation Glide in Ice Hi
Authors: Fairbrother Peter J. , Heggie Malcolm I. , Jones Bob 
Published: March 2011

ABSTRACTThe field of geological materials is rapidly opening up to computer modelling and ice poses stimulating new problems. The normal pressure and 0°C form of ice is ice Ih in which the oxygen sublattice is wurtzite. Imagining first that the protons occupy O–O “bond-centre” sites, it is generally believed that in ice Ih these protons are displaced along the bond direction in a correlated fashion such that each oxygen has two close protons (at about 1Å ) and two more distant ones (at about 1.7Å ). The correlated “disorder” of protons causes frustration of certain atomic movements, such as water molecule reorientation (as measured by dielectric relaxation times) and dislocation glide. Frustration can be relieved (and dislocation glide facilitated) by proton order defects, such as ionic defects, like an oxygen surrounded by only one close proton (OH−) or three (H3O+), or Bjerrum defects, like an O–O link with no intervening proton (L defect) or two protons (D defect).We present results of ab initio total energy calculations on the formation of these defects.
Ab Initio Molecular Dynamics of Column IV Microclusters
Authors: Drabold David A. , Klemm Stefan , Sankey Otto F. 
Published: March 2011

ABSTRACTWe report the results of ab-initio molecular dynamics simulations for small clusters of Si and C atoms. Ground-state geometries and vibrational spectra are presented. We also describe a Bayesian spectral estimation technique which we have found to be useful in analyzing molecular dynamics trajectories.
Molecular-Dynamics Study of Grain-Boundary Migration in Metals
Authors: Rickman J. M. , Phillpot S. R. , Wolf D. 
Published: March 2011

ABSTRACTThe migration of a (100) Θ = 43.6° (Σ29) twist grain boundary is observed during the course of a molecular-dynamics (MD) simulation. The migration is investigated by calculating changes in the planar structure factor Sp(k), the orientation of interparticle bonds in the migrating plane, and the motion of the center of mass of planes near the grain boundary. It is found that (a) migration is accompanied by sliding, and (b) each migration step consists of a series of local bond rearrangements. It appears that, as a precursor to migration, Frenkel-like defects are produced at the grain boundary.
Energetics and Configurations of Lattice Defects in CuTi
Authors: Shoemaker James R. , Wesley David , Wharton William R. , Oehrli Michael L. , Sabochick Michael J. , Lam Nghi Q. 
Published: March 2011

ABSTRACTThe energies and configurations of interstitials and vacancies in the ordered compound CuTi were calculated using atomistic simulation. Vacancies created by the removal of either a Cu or Ti atom resulted in a vacant Cu site, with an antisite defect in the latter case. The vacancy at the Cu site was found to be very mobile within two adjacent (001) Cu planes, resulting in two dimensional migration. Interstitials created by inserting either a Cu or Ti atom had complicated configurations containing one or more antisite defects.
First Principles Calculation of Oxygen Ordering in YBa2Cu3O7-y
Authors: Sterne P. A. , Wille L. T. 
Published: March 2011

ABSTRACTWe have performed a number of first principles electronic structure calculations for YBa 2Cu 3O7_y with different oxygen orderings and concentrations. The resulting total energies have been used to assess the applicability of some of the proposed models for oxygen ordering in this system. We find that the results are consistent with an Ising-like model with asymmetric next-neighbor interactions between oxygen sites. We determine effective interaction parameters from the first principles calculations and use them to compute the phase diagram for the system, which is in excellent agreement with experiment for the tetragonal-orthorhombic I transition.
Theoretical Study of a new Transition Sequence in III-V Compounds: High-Pressure Phases of InSb
Authors: García Alberto , Cohen Marvin L. , Zhang S. B. 
Published: March 2011

ABSTRACTA detailed study of the pressure-induced phase transitions at zero temperature in InSb up to 40 GPa using a first-principles pseudopotential total-energy method is presented. In addition to InSb(I) (cubic) and (II) (polar β-Sn), we identify InSb(III) as a hexagonal phase (found earlier for GaSb) and (VI) as a polar bcc phase in agreement with recent experiments. New structural models, orthorhombic polar β-Sn and body-centered orthorhombic, are proposed as candidates for the InSb(IV) and (V) phases based on total-energy minimizations. These findings are compared with recent results for GaAs to illustrate the trends in transition paths among III-V compounds.
First-Principles Interatomic Potentials for Transition Metals and Their Surfaces
Authors: Moriarty John A. , Phillips Robert B. 
Published: March 2011

ABSTRACTFor bulk transition metals, a first-principles generalized pseudopotential theory (GPT) of interatomic potentials has been developed in which the cohesive-energy unctional takes the form of a volume term plus sums over widely transferable two-, three-, and four-ion potentials. The GPT has been further extended to surfaces by making an internal transformation of this functional to an embedded-atom-like format in which the embedding function is identified as the bulk volume term and the atomic volume is replaced by an average electron density. Applications of the bulk and surface GPT to the calculation of structural, vacancy-formation, and surface energies in Cu and Mo, and to the investigation of surface relaxation and reconstruction in Mo are discussed.