bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of the Amorphous-to-Microcrystalline Transition during Silicon Film Growth at Increased Rates: Extensions of the Evolutionary Phase Diagram
Authors: Ferlauto Andre S. , Rovira Pablo I. , Koval Randy J. , Wronski Christopher R. , Collins Robert W. 
Published: April 2011

ABSTRACTThe microstructural and phase evolution of silicon films (Si:H) prepared by low temperature (200°C) rf plasma-enhanced chemical vapor deposition (PECVD) with hydrogen dilution of silane has been studied using real time spectroscopic ellipsometry (RTSE) and atomic force microscopy (AFM). Both RTSE and AFM support the concept of an evolutionary phase diagram that describes different regimes of bulk layer thickness and H2-dilution ratio R within which predominantly amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) films are obtained. In this study, the evolutionary phase diagram has been extended to identify four separate growth regimes: (i) a-Si:H with a smooth surface and a stable roughness layer thickness, (ii) a-Si:H with a rougher surface and an unstable roughness layer thickness, (iii) mixed-phase (a+μc)-Si:H, and (iv) fully-coalesced (single-phase) μc-Si:H. Based on this framework, the effect of increased rf power to achieve higher deposition rates in the rf PECVD process was investigated.
Comparative Fluctuation Microscopy Study of Medium-Range Order in Hydrogenated Amorphous Silicon Deposited by Various Methods
Authors: Voyles P. M. , Treacy M. M. J. , Jin H-C. , Abelson J. R. , Gibson J. M. , Yang J. , Guha S. , Crandall R. S. 
Published: April 2011

ABSTRACTWe have characterized by fluctuation electron microscopy the medium-range order of hydrogenated amorphous silicon thin films deposited by a variety of methods. Films were deposited by reactive magnetron sputtering, hot-wire chemical vapor deposition, and plasma enhanced chemical vapor deposition with and without H2 dilution of the SiH4 precursor gas. All of the films show the signature of the paracrystalline structure typical of amorphous Si. There are small variations in the degree of medium-range order with deposition method and H content. The PECVD film grown with high H2 dilution contains Si crystals ∼5 nm in diameter at a density of ∼109 cm−2. The amorphous matrix surrounding these crystals shows no difference in mediumrange order from the standard PECVD film. This supports explanations of the resistance of the H-dilution material to light-induced degradation that depend only on the presence of crystalline grains without modifications of the amorphous matrix.
Topological Signatures of Medium Range Order in Amorphous Semiconductor Models
Authors: Treacy M. M. J. , Voyles P. M. , Gibson J. M. 
Published: April 2011

ABSTRACTThe topological local cluster (or Schläfli cluster) concept of Marians and Hobbs is used to detect topologically crystalline regions in models of disordered tetrahedral semiconductors. We present simple algorithms for detecting both Wells-type shortest circuits and O'Keeffe-type rings, which can be used to delineate alternative forms of the Schläfli cluster in models.
Influence of the Fermi Energy on Si–H Vibrational Modes in Amorphous and Microcrystalline Silicon
Authors: Nickel N. H. , Lengsfeld P. 
Published: April 2011

ABSTRACTThe influence of boron and phosphorous doping and the effect of structural changes on hydrogen bonding in a-Si:H and µc-Si are investigated using Raman spectroscopy. Information on H bonding is obtained from Si-H stretching local vibrational modes (LVM's). In n-type and undoped a-Si:H the LVM's of isolated Si-H near 2000 cm−1 and clustered Si-H around 2100 cm−1 can be clearly distinguished. In heavily B doped a-Si:H, however, the LVM at 2100 cm−1 disappears. A structural change from a-Si:H to µc-Si gives rise to an additional mode centered at 1911 cm−1. Similar LVM's are observed in poly-Si containing platelets.
T-Site-Trapped Molecular Hydrogen in a-Si:H
Authors: Norberg R. E. , Leopold D. J. , Fedders P. A. , Borzi R. , Chan P. H. , Herberg J. , Tomic N. 
Published: April 2011

ABSTRACTProton-29Si double resonance NMR measurements on high quality plasma-enhanced chemical vapor deposition a-Si:H deposited from SiH4 show that more than one third of the contained hydrogen is present as H2 molecules residing in the amorphous equivalent of T sites. The NMR signal from these trapped H2 appears in the narrow 4 kHz proton line, which arises from the less clustered hydrogen population. Very little of the molecular component is in the broad ~24 kHz line, which arises mostly from clustered hydrogen tightly bonded to silicon.
A Study of Non-Infrared-Active Hydrogen Bonding in a-Si:H Thin Film using combined Calibrated Temperature Desorption Spectroscopy and FTIR
Authors: Santjojo DJ. , Cornish J.C.L. , Talukder M.O.G. 
Published: April 2011

ABSTRACTNon-infrared-active hydrogen bonding species were investigated by analyzing the infrared spectra and the calibrated temperature desorption spectroscopy (CTDS) spectra of hydrogen released during degassing of hydrogenated amorphous silicon thin films. Samples were degassed gradually using a linear temperature ramp (0.5°C/s). Each stage corresponds to a temperature at which the hydrogen effusion peaks can be found (~ 340°C, ~ 500°C and ~ 610°C). Differences in the amounts of hydrogen obtained from the FTIR spectra and the CTDS measurement correspond to the non-infrared-active, occluded hydrogen.
Influence of the Grain Boundary Band Offset on Charge Transport Mechanism in Microcrystalline Silicon Analysed by Numerical Simulation
Authors: Fantoni Alessandro , Vieira Manuela , Schwarz Reinhard 
Published: April 2011

ABSTRACTMicrocrystalline silicon is a two-phase material composed of grains of crystalline silicon embedded in an amorphous silicon tissue. The boundary regions between the crystalline grains and the amorphous matrix are treated similarly to a heterojunction interface.The band offset at the grain boundaries causes the appearance of local electric field peaks, variables in intensity and direction. We present results obtained with two dimensional simulations of a μc-Si:H p-i-n junction in short circuit condition. Charge transport mechanism is described by the internal electric configuration assumed by the junction in thermodynamic equilibrium and illuminated with monochromatic radiations. Different configurations of the band offset at the grain boundaries are also considered and related to the transport properties in microcrystalline silicon
On the Role of Charged Defect States and Deep Traps in the Photocarrier Drift and Diffusion in a-Si:H
Authors: Stradins Paul , Matsuda Akihisa 
Published: April 2011

ABSTRACTThe drift and diffusion in the presence of charged defects and photocarriers trapped in the tail states is re-examined. In continuity equations, diffusive and drift currents are related to free particles while the Poisson equation includes all charges. In order to make use of ambipolar diffusion approximation, the mobilities and diffusion coefficients should be attributed to the total electron and hole populations making them strongly particle-number dependent. Due to the asymmetry of the conduction and valence band tails, almost all trapped electrons reside in negatively charged defects (D−). A simple model of photocarrier traffic via tail and defect states allows to establish the effective mobility values and coefficients in Einstein relations. In a photocarrier grating experiment, grating of D− is counterbalanced by the grating of trapped holes. Nevertheless, electrons remain majority carriers, allowing the measurement of minority carrier diffusion length, but analysis is needed to relate the latter with μτ product.
Simulation and Design of Amorphous Silicon Thin-Film Transistors for Driving Color Detectors
Authors: Caputo D. , Colalongo L. , Irrera F. , Lemmi F. , Palma F. 
Published: April 2011

ABSTRACTPractical use of amorphous silicon stacked-junction color detectors in large-area arrays requires periodic readout of the photo-charge stored in the capacitance of the device by a transient technique of sensing. In any stacked-junction devices, color information is obtained by the “self-biasing” process: during an integration time, the three junctions independently lose charge; during the readout pulse, the capacitances of the three junctions in electrical series are re-charged. Equilibrium is reached after a few cycles, when the charge integrated in a cycle by each junction is the same, and equals the readout charge. The amount of charge is determined by the reverse biased junction and accounts for the light intensity.Dimensioning the amorphous silicon Thin Film Transistor (TFT) used as a pixel switch for the detector is a critical part of the project of a color imager. The actual design determines the self-bias process duration and the readout accuracy. The typical large thickness difference between the detector junctions makes the constraints for the switching process extremely demanding: since a greater capacitance is expected in the thinner top junction detecting blue radiation, the on-resistance must be reduced. Since the front junction does not ensure full rejection of green and red light, a calculation must be performed to extract the information on blue radiation. This requires further precision in the readout process.In this work we present a simulation study of the self-biasing process. Both a-Si:H TFT and the a-Si:H p-i-n-i-p two-color detectors are simulated by a finite-elements two-dimensional simulator ensuring a correct modeling of both the devices. Simulations allow to study in detail the timing and the accuracy of the self-biasing process. Including electrostatic capacitance and trapped charge, a set of design rules for the TFT is achieved in terms of on-state design. Similar considerations can be extended to the case of ATCD three-color detectors.
Fast growth of amorphous silicon layers by amplitude modulation PECVD
Authors: Biebericher A. C. W. , Bezemer J. , Weg W. F. van der , Goedheer W. J. 
Published: April 2011

ABSTRACTHydrogenated amorphous silicon has been deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) with a square wave amplitude modulated rf signal of 50 MHz. We studied the dependence of the deposition rate on the modulation frequency, using optical emission spectroscopy and plasma modeling. We observed an enhancement in deposition rate by modulating the plasma. This behavior is explained by the characteristics of the electronenergy distribution during the periodical onset of the plasma. According to a one-dimensional fluid model, high-energy electrons cause a large production of radicals at the onset. The heating occurs over the whole plasma volume, leading to an increase of the homogeneity of the layers. The discharge structure is changed completely. A comparison is made between results obtained at 13.56 MHz and at 50 MHz deposition voltages.
Wide Bandgap ≥1.8eV Amorphous Silicon for Solar Multijunction Cell and Image Sensor Applications
Authors: Kolodziej Andrzej , Krewniak Pawel , Tadeusiewicz Ryszard 
Published: April 2011

ABSTRACTThis paper discusses the use of wide bandgap a-Si:H prepared by reactive magnetron sputtering (RMS) in low temperature and hydrogen control process deposition for multijunction cell applications. Primarily technological experiments are presented. The studies were carried out on a-Si:H films and TCO / n+ a-Si:H / i a-Si:H / Nickel Schottky barrier structures with i layer thicknesses ranging between 0.1 and 0.5 μm, using AFM, X-ray small angle and Raman spectroscopy, and optical transmission and reflection measurements after a degraded steady state. The properties exhibited by the films obtained in various ways are compared. In particular, fill factor dependence on light, field, and thickness is presented for RMS films.
Solar-Cell Suitable μc-Si Films Grown by ECR-CVD
Authors: Birkholz M. , Conrad E. , Lips K. , Selle B. , Sieber I. , Christiansen S. , Fuhs W. 
Published: April 2011

ABSTRACTThe preparation of μc-Si films from SiH4-H2 mixtures by electron-cyclotron resonance (ECR) CVD at deposition temperatures ≤ 400°C on foreign substrates is reported. Deposition conditions were identified for which Si films with a high degree of crystallinity were grown as was confirmed by Raman spectroscopy. A factorial analysis was carried out, for which the influence of deposition temperature, microwave power, hydrogen dilution and total pressure on film growth were investigated. Samples of optimized crystallinity were prepared in a lowpressure and high-hydrogen dilution regime. In-plane grain sizes were measured by TEM and found to be on the order of 10 - 12 nm. Next to the optimization of crystallinity several sources of impurity contamination during film deposition were identified and eliminated. Intrinsic μc-Si layers could be prepared under these conditions that exhibited a dark conductivity σd of 2 × 10-7 S/cm and photosensitivity σph/σd of 150. It is concluded that ECR CVD is capable of producing intrinsic layers with electronic properties as necessary for use in state-of-the-art n-i-p μc-Si solar cells.
Si + SiH4 Reactions and Implications for Hot-Wire CVD of a-Si:H: Computational Studies
Authors: Muller Richard P. , Holt Jason K. , Goodwin David G. , Goddard William A. 
Published: April 2011

ABSTRACTGas phase chemistry is believed to play an important role in hot-wire CVD of amorphous silicon, serving to convert the highly-reactive atomic Si produced at the wire into a less-reactive species by reaction with ambient SiH4. In this paper, we use quantum chemistry computations (B3LYP/cc-pvTZ) to examine the energetics and rates of possible gas-phase reactions between Si and SiH4. The results indicate that formation of disilyne (Si2H2) is energetically favorable. Unlike other products of this reaction, Si2H2 does not require collisional stabilization, and thus this species is the most likely candidate for a benevolent precursor that participates in the growth of high-quality Si films.
Effect of Ramp Annealing to Ni Induced Lateral Crystallization of Amorphous Silicon
Authors: Shivani S. , Poon M.C. , Chan M. , Ko P.K. 
Published: April 2011

ABSTRACTNickel Metal-Induced-Lateral-Crystallization (MILC) has been used to enlarge the grain size and improve the quality of (poly-Si) Thin-Film-Transistors (TFTs). However, the MILC temperature is still low and the grain size is still small. The feasibility of forming very large grains (single crystal like) from amorphous silicon (a-Si) by combining MILC with ramp annealing has been studied. It has been found that the grain size after ramp annealing is remarkably enhanced and can reach of the order of several ten's of microns. The velocity of MILC with ramp annealing is faster than that of MILC with isothermal annealing. The grain size becomes maximal at around 625°C/2hrs, and saturates at higher temperatures of 625- 1000°C. The effect of temperature, time and other parameters has also been studied in order to maximize the grain size and quality. MILC with ramp annealing at 625°C can greatly lower the process time and reduce the need of subsequent annealing to enhance the grain size. The new technology can have numerous novel applications such as providing a low cost alternative to form silicon-on-insulator (SOI) substrates and a breakthrough for high performance TFTs and novel multi-layers SOI like devices and circuits.
Concentration and Stress Evolution During Electromigration in Passivated Al(0.25 at. % Cu) Conductor Lines
Authors: Kao H.-K. , Cargill G. S. , Hu C.-K. 
Published: April 2011

AbstractWe have used x-ray microbeam fluorescence and diffraction for in-situ measurements of electromigration-induced Cu diffusion and stress evolution in passivated, polycrystalline 10[.proportional]m-wide, 200[.proportional]m-long Al(0.25 at.% Cu) conductor lines. Cu migration is in the direction of the electron flow and is determined by the direction and magnitude of the current and by the temperature during electromigration. The effective charge and diffusivity of Cu in Al(Cu) have been obtained from analysis of the Cu concentration profiles. The evolution of electromigration-induced strains normal to the sample surface has been monitored by x-ray microbeam diffraction. A linear strain profile developed after about 9 hrs of electromigration with 1.5[.dotmath]105 A/cm2 at 300°C, corresponding to 3MPa/[.proportional]m equi-biaxial stress. From the Cu profile measured at the same time, the critical Cu concentration for significantly slowing down Al grain boundary diffusion is estimated to be ∼0.15 at. %. These data also confirm that downstream Cu transport is accompanied by a counter flow of Al in the upstream direction.
Curing Study of Hydrogen Silsesquioxane Under H2/N2 Ambient
Authors: Liou Huey-Chiang , Dehate Evan , Duel Jerry , Dall Fred 
Published: April 2011

AbstractThin film properties of hydrogen silsesquioxane (HSQ) cured at different temperature under N2 and H2/N2 ambients have been studied. In this study, it was found that compared to an N2 ambient, film curing in an H2/N2 ambient will impact HSQ properties when the temperature is 400°C – 500°C. H2/N2 ambient can be used to minimize the dielectric constant while increasing modulus of the films. The data indicates that H2 can minimize the oxidation of the HSQ films and maintain the dielectric properties.
Properties of Tin Thin Films Deposited by Alcvd as Barrier for Cu Metallization
Authors: Satta Alessandra , Beyer Gerald , Maex Karen , Elers Kai , Haukka Suvi , Vantomme A. 
Published: April 2011

AbstractIn advanced multi-level metallization schemes, the application of copper as interconnect metal requires the prevention of Cu diffusion into the active area and into interlevel dielectrics by total encapsulation of Cu with barrier films. Critical requirements for diffusion barriers are very small thicknesses, low resistivity, low deposition temperature and conformality on high aspect ratio trenches and vias. For this application, we have studied TiN films deposited by atomic layer chemical vapour deposition (ALCVD) at 400°C and 350°C. This paper discusses the ALCVD TiN films properties and compares them to the properties of TiN deposited by ionized physical vapour deposition (I-PVD).The ALCVD TiN deposited at 400°C exhibits a resistivity comparable to I-PVD TiN resistivity. However, the ALCVD films deposited at 350°C show higher resistivity. The Cl residue in ALCVD films is 1.5% at 400°C and 3% at 350°C. The microstructure is fine-grained. A very high level of conformality on trenches characterizes the ALCVD TiN films. We believe this property gives a clear advantage over the sputtered I-PVD TiN since its coverage in high aspect ratio trenches and vias is expected to be limited for the future devices interconnection scheme.
Optimal Design of Reactors for Metalorganic Vapor Phase Epitaxy of Group III Nitrides
Authors: Pawlowski R. P. , Theodoropoulos C. , Mountziaris T.J. , Moffat H.K. , Han J. , Thrush E. J. 
Published: April 2011

AbstractMetalorganic Vapor Phase Epitaxy (MOVPE) has emerged as the technique of choice for growing thin films and structures of group III-nitrides. The objective of this work is to address the optimal design of vertical rotating disk and stagnation flow MOVPE reactors in order to achieve film thickness uniformity over large area substrates. Gas inlets that preserve the axial symmetry and enable alternating feeding of the precursors through coaxial rings were studied. The growth of GaN films from trimethyl-gallium and ammonia was used as a typical example. A fundamental reaction-transport model of the MOVPE process including gas-phase reactions and gas-surface interactions has been developed. The model was validated through comparison with growth rate data obtained from both research-scale and industrial-scale reactors. Performance diagrams for industrial-scale stagnation flow and rotating disk reactors were developed by varying the reactor geometry and operating conditions to identify regions of uniform film growth.
Composition and Structure of Sputter Deposited Erbium Hydride thin Films
Authors: Adams D.P. , Romero J.A. , Rodriguez M.A. , Floro J.A. , Banks J.C. 
Published: April 2011

AbstractErbium hydride thin films are grown onto polished, a-axis α Al2O3 (sapphire) substrates by reactive ion beam sputtering and analyzed to determine composition, phase and microstructure. Erbium is sputtered while maintaining a H2 partial pressure of 1.4 ×10−4 Torr. Growth is conducted at several substrate temperatures between 30 and 500°C. Rutherford backscattering spectrometry (RBS) and elastic recoil detection analyses after deposition show that the H/Er areal density ratio is approximately 3:1 for growth temperatures of 30, 150 and 275°C, while for growth above ∼430 °C, the ratio of hydrogen to metal is closer to 2:1. However, x-ray diffraction shows that all films have a cubic metal sublattice structure corresponding to that of ErH2. RBS and Auger electron spectroscopy confirm that sputtered erbium hydride thin films are relatively free of impurities.
Room Temperature Growth of Indium Tin Oxide Films By Ultraviolet-Assisted Pulsed Laser Deposition
Authors: Craciun V. , Craciun D. , Chen Z. , Hwang J. , Singh R.K. 
Published: April 2011

AbstractThe characteristics of indium tin oxide (ITO) films grown at room temperature on (100) Si and Coming glass substrates by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique have been investigated. The most important parameter, which influenced the optical and electrical properties of the grown films, was the oxygen pressure. For oxygen pressure below 1 mtorr, films were metallic, with very low optical transmittance and rather high resistivity values. The resistivity value decreased when using higher oxygen pressures while the optical transmittance increased. The optimum oxygen pressure was found to be around 10 mtorr. For higher oxygen pressures, the optical transmittance was better but a rapid degradation of the electrical conductivity was noticed. X-ray photoelectron spectroscopy investigations showed that ITO films grown at 10 mtorr oxygen are fully oxidized. All of the grown films were amorphous regardless of the oxygen pressure used.
Improvement Of Cavitation Erosion Resistance and Corrosion Resistance Of Brass by Laser Surface Modification
Authors: Tam K. F. , Cheng F. T. , Man H. C. 
Published: April 2011

AbstractLaser surface modification of brass (Cu-38Zn-1.5Pb) using AISiFe and NiCrSiB alloy was achieved by using a 2kW continuous wave Nd-YAG laser with the aim of improving the cavitation erosion resistance and corrosion resistance. The alloying powder was preplaced on the brass substrate by thermal spraying to a thickness of 350µm, followed by laser beam scanning to effect melting, mixing and alloying. A modified surface was achieved by overlapping of adjacent tracks. The cavitation erosion resistance and the anodic polarization characteristics of the laser surface modified specimens in 3.5% NaCI solution at 23°C were studied by means of a 20kHz ultrasonic vibrator at a peak to peak amplitude of 60µm and a potentiostat respectively. The cavitation erosion resistance of the specimens modified with AlSiFe and NiCrSiB was improved by a factor of 3 and 7 respectively, compared with that of the brass substrate. Potentiodynamic test, however, indicated that the corrosion resistance of specimens modified with AlSiFe deteriorated, as reflected by a shift of the polarization curve towards higher current densities. On the other hand, the corrosion resistance of specimens modified with NiCrSiB was significantly improved, as evidenced by the presence of a passive region (from −175 mV to −112 mV) and a reduction in the anodic current density by at least an order of magnitude compared with the substrate at the same anodic potential. The hardness profile and the compositional profile were measured using a Vickers hardness tester and EDX respectively. The microstructure and the surface morphology of the specimens were investigated with the aid of SEM and optical microscopy.