bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Equilibration and Growth of Doped Amorphous Silicon
Authors: Kakalios J. , Street R. A. , Tsai C. C. , Weisfield R. 
Published: March 2011

AbstractThe relation between the thermal equilibration of the defect structure in n-type doped hydrogenated amorphous silicon (a-Si:H) and the deposition conditions has been investigated. When the deposition rate is increased by raising the rf power the equilibration time constants become longer, though the thermal equilibrium processes are qualitatively similar to those in samples grown under optimal conditions. Models relating the slower equilibration rate to the deposition-induced microstructure are explored.
Influence of Plasma Excitation Frequency on Deposition Rate and on Film Properties for Hydrogenated Amorphous Silicon
Authors: Curtins H. , Wyrsch N. , Favre M. , Prasad K. , Brechet M. , Shah A. V. 
Published: March 2011

AbstractThe preparation of hydrogenated amorphous silicon by the radio-frequency (RF) glow discharge technique is shown to be strongly dependent on the plasma excitation frequency. We have investigated the influence of this parameter on the deposition rate, on the hydrogen content and on the opto-electronic properties of the amorphous silicon films, over the range 25 to 150 MHz. A large variation of the deposition rate is observed, while most of the material properties remain practically unchanged. The results should be of considerable interest for mass production of low-cost amorphous silicon thin film devices.
Preparation and Properties of Hydrogenated Amorphous Silicon Produced by Plasma-Enhanced Chemical Vapor Decomposition of Silane
Authors: Tokuda K. L. , Adler D. , Reif R. 
Published: March 2011

AbstractWe have investigated the properties of several hydrogenated amorphous silicon (a-Si:H) films prepared by the plasma-enhanced chemical vapor decomposition (PECVD) of silane. This reactor is singular because it operates at pressures as low as 10 mTorr and uses infrared lamps to heat the growth environment. Structural characterization showed that all the samples were amorphous. Most films had hydrogen concentrations about 5%, optical gaps near 1.6 eV, and neutral dangling-bond concentrations of the order of 5 × 1016 Cm−3. Electrical activation energies were typically in the range 0.5 – 0.6 eV and the photoconductivity under ∼100 mW/cm2 white light was 10−4 (Ω-cm)−1. The dark conductivity was near 10−8(Ω-cm)−1. No significant change in dark conductivity or photoconductivity occurred after several hours of exposure to light.
High Quality Amorphous Silicon Prepared by Catalytic Chemical Vapor Deposition (CTL-CVD) Method
Authors: Matsumura Hideki 
Published: March 2011

AbstractA new method of producing high quality hydrogenated amorphous silicon (a-Si:H) and its compound films is presented. An SiH4 and H2 gas mixture is decomposed without using any plasmas or photochemical excitation, but using only thermal and catalytic reactions between deposition gas and a heated tungsten catalyzer. Photoconductivity of a-Si:H films produced by, this method reaches 10−3 (Ωcm)−1 and photosensitivity exceeds 105 for illumination of AM-1 light of 100 mW/cm2, highly efficient boron- or phosphorus-doping into the films is achieved, and also the optical band gap of the films is easily controlled without apparent degradation of the properties by adding GeH4 gas to the deposition gas.
Interaction of Reactive Species Obtained by G-D Silane Decomposition with Si(111) and a-Si:H Surfaces
Authors: Cruz S. A. , Mendez-Rosales V. M. 
Published: March 2011

AbstractWe calculate the average surface potential barrier for incorporation of H, Si, SiHb (n=1–4) into films of a-Si:H as well as crystalline Si(111) surfaces. In the first case a local amorphous configuration for the surface is employed through a representative cluster(Si29 H1 0 ) forming 5, 6, 7 Si atom rings. For the crystalline surface, several layers of Si atoms are considered. Pairwise superposition of combined Morse and Thomas-Fermi-Moliére interatomic potentials is assumed for the total interaction between the incoming species and the surface.
Photoluminescence in Hydrogenated Silicon-Germanium Alloys
Authors: Ranganathan R. , Gal M. , Viner J. M. , Taylor P. C. 
Published: March 2011

AbstractResults of a detailed study of photoluminescence (PL) in the a-Si1−xGex:H system are presented. Many samples exhibit a low energy “tail” to the PL efficiency which is of constant magnitude independent of x. There is a departure from this behavior when a low energy PL peak near 0.8–0.9 eV is present. The position of the low energy PL peak is independent of Ge concentration. It has been suggested that this PL transition is from an electron in the conduction band tail into a silicon dangling bond state. As Ge is added to a-Si:H it is the edge of the conduction band which decreases in energy while the valence band remains relatively constant in energy. It is therefore unlikely that the low energy PL is due to a transition from the conduction band into a silicon dangling bond state because the energy of the silicon dangling bond with respect to the valence band is probably essentially independent of Ge content. If the PL which peaks near 0.8 eV results from a transition which involves a silicon dangling bond, then the transition may be from the dangling bond to the valence band.
Electronic States in Amorphous Solids, Liquids, and Alloys
Authors: Bar-Yam Y. , Adler D. , Joannopoulos J. D. 
Published: March 2011

AbstractWe describe elements of a thermodynamical ensemble theory of electronic states in a variety of disordered systems. Equilibrium energies and kinetics of phase space exploration combine to determiine the ensembles describing disordered systems. Electronic properties are then related to structural energies. This relationship serves to determine the distribution of electronic states present in real materials. Thus we obtain directly electronic properties without a need for detailed microscopic information about the diverse systems. Applications range from the Urbach edge to defect properties providing a unified understanding.
High-Quality a-Si-Based Alloys : a-SiGe Films Fabricated in a Super Chamber and Superlattice Structure a-Si Films Prepared by a Photo-CVD Method
Authors: Tsuda Shinya , Haku Hisao , Tarui Hisaki , Matsuyama Takao , Sayama Katsunobu , Nakashima Yukio , Nakano Shoichi , Ohnishi Michitoshi , Kuwano Yukinori 
Published: March 2011

AbstractIn order to improve the conversion efficiency of a-Si solar cells, high-quality a-Si based alloys of both narrow handgap and wide bandgap were studied.Concerning the narrow bandgap material, we found a particular dependence of film qualities on substrate temperature. In addition, high-quality a-SiGe:H films were obtained by using a super chamber (separated ultra-high vacuum reaction chamber).As for the high-quality wide bandgap material, a-Si/a-SiC superlattice structure films fabricated by a photo-CVD method were studied for the first time. From the analysis of their properties, we found that the superlattice structure p-layer was an active layer for photovoltaic effect. A conversion efficiency of 11.2% has been obtained for a pin a-Si solar cell whose player was of the superlattice structure.
Carbon Local Bonding Configurations in Amorphous Hydrogenated Silicon-Carbon Alloys
Authors: Petrich Mark A. , Reimer Jeffrey A. 
Published: March 2011

AbstractWe present the results of a carbon-13 nuclear magnetic resonance (NMR) study of well-characterized thin films of amorphous hydrogenated silicon carbide. The NMR data detail the distribution of carbon local bonding configurations in films which have carbon-to-silicon ratios less than one. In particular, we show data which clearly identify and quantify non-hydrogenated sp2, or unsaturated, carbon bonding environments.
Temperature Dependence of Optical Properties and Minority Carrier Diffusion Length in a-SiGe:H,F
Authors: Schwarz R. , Dietrich K. , Goedecker S. , Kolodzey J. , Slobodin D. , Wagner S. 
Published: March 2011

AbstractWe report the temperature dependence of several optical parameters of thin films of hydrogenated and fluorinated amorphous silicon alloys (a-SiGe:H,F) between 5 and 95 °C. The absorption coefficient near the optical band gap Eg increases with temperature. From this increase we calculate a temperature coefficient for Eg of −4.5×10−4 eV/K, which is essentially independent of band gap The concomittant change of index of refraction n was determined in the near infrared region from the interference pattern in the reflection spectra. The temperature coefficient dn/n/dT is 0.9×10−4 K−1 for un-alloyed a-Si:H,F and increases with increasing Ge atomic fraction. The changes of Eg and n with temperature are consistent with a simple quantummechanical description of the complex dielectric constant. We also report the temperature dependence of the minority carrier diffusion length in a-SiGe:H,F.
Electronic Transport Properties of a-Si:H,F/a-Si,Ge:H,F Superlattices
Authors: Conde J. P. , Aljishi S. , Shen D. S. , Chu V. , Smith Z E. , Wagner S. 
Published: March 2011

AbstractWe study the dark conductivity σd, dark conductivity activation energy Ea and photoconductivity σph of a-Si:H,F/a-Si,Ge:H,F superlattices both perpendicular and parallel to the plane of the layers. In parallel transport, both the σph and σd are dominated by the alloy layer characteristics with the superposition of carrier confinement quantum effects. In perpendicular transport, the σd shows an interplay of quantum mechanical tunneling through the barriers and of classical thermal emission over the barrier layer and the σph is controlled by the decreasing absorption by the silicon barrier layer as the optical gap Eopt of the structure decreases.We also found that the multilayer structure allows to grow lower gap a-Si,Ge:H,F alloys than achievable under the same deposition conditions for bulk materials. This stabilizing effect allowed us to study low-gap superlattice structures and extract information about these very low gap (<1.2 eV) a- Si,Ge:H,F alloys.
High Conductive a-Si:H/a-SiC:H:F Super Lattice Prepared by a Chemically Controlled Method
Authors: Koinuma H. , Kawasaki M. , Fueki K. 
Published: March 2011

AbstractAmorphous super lattices composed of a-Si:H and a-SiC:H:F layers were continuously prepared from a gas miture of CF4 and either SiH4 or Si2 H6 by the pulsed plasma and photo (PP&P) CVD method. The method utilizes the difference in photochemical reactivity of the source gases for the formation of layered structure. The layered films prepared by using Si2H6 as silicon source under the condition that they had optical gaps up to 2.0 eV were found to show photoconductivities higher not only than those of a-SiC:H:F films prepared from the same gas mixture by the continuous plasma and photo hybrid CVD but also than those of a-Si:H films by the photo CVD. From the comparison of optical and electrical properties of super lattices prepared, the photoconductivity of the films is suggested to be primarily dependent on the quality of barrier layer rather than on the quality of well layer.
The Characteristics of Amorphous Silicon TFT and its Application in Liquid Crystal Display
Authors: Chikamura T. , Hotta S. , Nagata S. 
Published: March 2011

AbstractAn amorphous silicon TFT particularly suited for the full color liquid crystal display driver has been developed and reported here. Various fundamental factors involved in the a-Si TFT, such as the effects of structure, materials, and the method of fabrications were reviewed and investigated in terms of the field effect mobility, the threshold voltage and the reliabilities. An inverted-staggered TFT structure was employed for the purpose wherein the interface states between two layers was successfully lowered by employing the successive deposition procedures of SiNx gate insulator on the a-Si layer. Proper ohmic contacts and the blocking of hole injections were accomplished by forming a n+ layer between the a-Si layer and the source/drain metal electrodes which consists of a double layer of Al/MoSi2 in order to prevent the aluminum diffusion into the a-Si layer during the 300°C heat treatment at the succeeding fabrication processes. The degradation of display images due to the high intensity backlights was minimized by employing a light shielding layer and by making the thickness of a-Si layer 200 Å against the direct sunlight of up to 100,000 luxes. Stable actual performances of TFT for more than 4000 hours at 80 °C were confirmed. The development of a color LCD TV driven by this TFT is also reported.
Large Scale and Large Area Amorphous Silicon Thin Film Transistor Arrays for Active Matrix Liquid Crystal Displays
Authors: Miki H. , Kawamoto S. , Horikawa T. , Maejima T. , Sakamoto H. , Hayama M. , Onishi Y. 
Published: March 2011

AbstractThe preparation and properties of hydrogenated amorphous silicon thin film transistor arrays for active matrix liquid crystal displays are reported. The effect of amorphous silicon film preparation conditions on the field effect mobility of thin film transistors was investigated. The dry etching rate of silicon nitride film was studied.The thin film transistor arrays have 408 ˜ 640 transistors on the first version and 450 ˜ 640 ˜ 3 transistors on the second version. The liquid crystal panel fabricated using the first version arrays showed good characteristics.
States in the Gap of Doped and Undoped a-Si:H Studied by Photomodulation Spectroscopy
Authors: Zhou T. X. , Vardeny Z. , Tauc J. 
Published: March 2011

AbstractThe steady state photomodulation spectrum, its temperature and excitation intensity dependences have been studied in phosphorous doped and undoped a-Si:H. The spectra are analyzed in terms of photocarriers trapped in band-tail states and dangling bonds (DB) defects in undoped samples and impurities and charged DB states introduced by doping in P-doped samples. In undoped a-Si:H we found that the two DB energy levels D± are symmetrically located about midgap with an effective correlation energy Ueff of 0.6±0.2eV. In P-doped a-Si:H D− is pushed toward midgap by about 0.25 eV and Ueff = 0.4±0. 2 eV.
Deep States in a-Si:H - Changes with Doping and Applied Stress.
Authors: Kočka J. , Vanéček M. 
Published: March 2011

AbstractRecent Constant Photocurrent Method (CPM) results and a new model of a-Si:H density of states are briefly reviewed. The small but systematic changes of subgap absorption (α) with the applied external stress have been found. When light-soaking is done under the applied stress the strong increase of α is observed. The μτ (mobility-lifetime) versus α duality is demonstrated. The increase of the dangling bond density, combined with the change of its charge state, is used for the explanation of duality. The light induced creation of dangling bond-impurity intimate pairs is speculated to be the driving force for the Fermi level shift.
Time-of-Flight Measurements in a-Si:H Between Room Temperature and 130° C°
Authors: Shen D. S. , Aljishi S. , Smith Z E. , Conde J. P. , Chu V. , Wagner S. 
Published: March 2011

AbstractThe drift mobility μd and the mobility-lifetime product μτ in undoped a-Si:H have been studied up to 130°C. The electron μde is temperature-activated with Eae = 0.13 to 0.16 eV. The electron (μτ)e increases with temperature T. For hole transport, we observe the transition from dispersive to non-dispersive transport with increasing T. The hole μdh is ∼ 1/100 of μde, and is activated with Eah = 0.34 to 0.48eV. The hole (μτ)h does not change much with T. A computer simulation demonstrates the high sensitivity of μd to the band tail width.
Crystal Structure Refinements of Rhombohedral Symmetry Materials Containing Boron-Rich Icosahedra
Authors: Morosin B. , Aselage T. L. , Feigelson R. S. 
Published: March 2011

ABSTRACTThe crystal structures of several icosahedral boron-containing compounds have been refined using MoKα intensity data. Preparation of crystals differs from previous procedures, with boron carbide grown from molten copper and boron arsenide by arsenic vapor transport. The structures consist of icosahedral units bonded together with direct B-B bonds as well as other linkage units (B-C-B and As-As chains).
Rapid Isothermal Annealing of N-Implanted 6H-SiC Layers Used for Fabrication of p-n Photodiodes
Authors: Pensl Gerhard , Helbig Reinhard , Zhang Hong , Ziegler Gonther , Lanig Peter 
Published: March 2011

ABSTRACTIon implantation of 14N and Rapid Isothermal Annealing (RIA) were employed to achieve n-type doping in epitaxial-grown 6H-SiC layers. The electrical properties of the implanted films were investigated by Hall effect measurements in order to optimize the annealing parameters. In comparison with standard furnace annealing (1470°C/7min), the annealing parameters for the RIA process could be considerably reduced (1050°C/4min). Based on planar technique, implanted p-n junctions were fabricated. The temperature dependence of I-V characteristics and of the quantum efficiency of photodiodes were studied. The maximum of the quantum efficiency at γ=330 nm reaches values of 35% at 400°C.
Electrical Properties of 3C-SiC and its application to FET
Authors: Yoshida S. , Endo K. , Sakuma E. , Misawa S. , Okumura H. , Daimon H. , Muneyama E. , Yamanaka M. 
Published: March 2011

ABSTRACTElectrical and luminescent properties of nondoped, and N-doped n-type 3C-SiC layers epitaxially grown on Si(100) by chemical vapor deposition were studied. Nondoped n-type epilayers with carrier concentration of 1×1016cm−3 and the Hall mobility of 750cm2/Vs at room temperature have the activation energy of donors, Ed=2OmeV, which is different from that of the donors in the N-doped layers. The photoluminescence spectra of nondoped layers are different from those of N-doped ones. These results suggest that the donors in the unintentionally doped n-type 3C-SiC are not due to N impurities. 45–70 % of N-donors in the N-doped epilayers are compensated.Schottky-barrier and MOS-type field-effect transistors have been fabricated from 3C-SiC. The transistor operations of MESFETs and MOSFETs were studied at elevated temperatures up to 440°C. Transconductances of 1.7mS/mm and 0.15mS/mm for MESFET and 0.8 and 0.05mS/mm for MOSFET at room temperature and 440°C, respectively, were obtained. The drain currentvoltage characteristics of both the FETs at room temperature did not change in the least after heating up to 440°C in the air.
AES Studies of the M/SiC Interface with Metal Carbide Formers
Authors: Zeller M. V. , Bellina J. , Saha N. , Filar J. , Hargraeves J. , Will H. 
Published: March 2011

ABSTRACTAfter Nichrome, Ni, Cr, and Au/Ta films are deposited onto single crystals of cubic SiC, their reactivities at the metal-semiconductor interface are studied by Auger Electron Spectroscopy. For all metals except Ni, metal carbides are detected at the interfaces. Initially these carbides tend to promote adhesion and limit the reaction with the substrate. Annealing at or above 450°C causes Ni to diffuse into the SiC and the Ta and Cr films to migrate through the capping material and away from the SiC, thereby delaminating. Development of the secondary phases at interface severely complicates the interpretation of the depth profiling data and with the uniformity of the contact film. These phases seem to be initiated at SiC defect sites where the reaction kinetics are considerably different and may be minimized with improved SiC substrates.
Predictions on the Physical Properties of Amorphous Carbon-Tin Semiconducting Alloys I Structure and Optical Properties
Authors: Mpawenayo Prosper 
Published: March 2011

ABSTRACTThe theory developed by Coulson, Rushbrooke and Longuet-Higgins (CRLH) on the electron-charge density and the atom-bond polarisability in hetero-atom conjugated systems is used to show that n-electron charge transfer by Sn substitutional incorporation in aC:H would promote the tetrahedral structure. An agreement with Phillips stability criterion is found.
The effective medium theory is then applied for predictions on the dielectric properties of narrow optical band-gap (0,6–1,5 eV) C-Sn alloys. It is suggested that the incorporation of electronegativeelements (F, Cl) would reduce the high sub-bandgap absorption.
Effect of High Temperature Annealing on the Thermoelectric Properties of GaP Doped SiGe
Authors: Vandersande Jan W. , Wood Charles , Draper Susan 
Published: March 2011

ABSTRACTSilicon-germanium alloys doped with GaP are used for thermoelectric energy conversion in the temperature range 300°C - 1000°C. The conversion efficiency depends on Z - S2/ρΛ, a material's parameter (the figure of merit), where S is the Seebeck coefficient, ρ is the electrical resistivity and Λ is the thermal conductivity. The annealing of several samples in the temperature range of 1100°C - 1300°C resulted in the power factor P (=S2/ρ) increasing with increased annealing temperature. This increase in P was due to a decrease in ρ which was not completely offset by a drop in S2 suggesting that other changes besides that in the carrier concentration took place. SEM and EDX analysis of the samples indicated the formation of a Ca- P-Ge rich phase as a result of the annealing. It is speculated that this phase is associated with the improved properties. Several reasons which could account for the improvement in the Power factor of annealed GaP doped SiGe are given.
The Effect of Sm, Eu and Yb on the Thermoelectric Properties of Th3P4,-Type Lanthanum Sulfide
Authors: Nakahara J. F. , Beaudry B. J. , Gschneidner K. A. , Takeshita T. , Laboratory Ames 
Published: March 2011

ABSTRACTThe Th3P4-type lanthanum sulfides are n-type semiconductors and a continuous series of solid solutions is found between the compositions of La3S4 and La2S3. These materials are attractive for use in high temperature thermoelectric applications because of their high melting points, low thermal conductivities and their inherent ability to vary the electron concentration from a maximum of 6.02 × 1021 cm−3 for La3S4 to zero for La2S3 (i.e., self-doping). In this study, La3S4 compounds in which trivalent La has been partially substituted by divalent Sm, Eu or Yb (La3−xMxS4 , x = 0.1 to 0.9) have been prepared by the pressure assisted reaction sintering method and were found to have the Th3P4 structure. The thermoelectric properties (Seebeck coefficient and electrical resistivity) were measured as a function of temperature and the optimum composition was found for x between 0.2 and 0.3 in which the electrical power factor was a maximum at 1000°C.
Effect of the Microstructure on the Thermoelectric Properties of Polycrystalline Lanthanum Chalcogenides
Authors: Lockwood A. , Wood C. , Vandersande J. , Zoltan A. , Parker J. , Danielson L. , Alexander M. , Whittenberger D. 
Published: March 2011

ABSTRACTSmall amounts of second phase materials can have important effects on the thermoelectric properties of polycrystalline γ-La3-xX4 (X-S, Te; 0<x<l/3). Microscopic examination by SEM of hot pressed La3–xTe4 samples has revealed from 1–5 vol. % of La202Te, an amount which is not detected by x-ray powder diffraction measurements. This amount of La202Te resulting from oxygen contamination can reduce the concentration of electrons by as much as 10% to 75% below the electron concentration calculated for single phase La3–xTe4 in the composition range of greatest interest. Small amounts of second phase materials can also lower the lattice thermal conductivity by scattering low frequency phonons These results indicate that microstructural effects should be considered when electrical and thermal properties of polycrystalline materials are analyzed.
Refractory Films from Spin-Cast Polyacrylonitrile
Authors: Renschler C. L. , Sylwester A. P. 
Published: March 2011

ABSTRACTPolyacrylonitrile (PAN) films have been spin-cast and pyrolyzed to produce thin (500–1500 Å) carbon films. These films have higher electrical conductivities than carbon films produced by other methods at similar temperatures. The conductivity can be varied by at least four orders of magnitude by changing the pyrolysis temperature. UV, IR, and Raman spectroscopies were used to investigate the chemical structure of the films during different stages of processing.