bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Rotational Dynamics of Liquids Confined in Nanopores
Authors: Korb J.-P. , Malier L. , Cros F. , Xu Shu , Jonas J. 
Published: April 2011

ABSTRACT2H NMR relaxation times of selectively deuterated polar molecules confined to a set of calibrated nanoporous silica glasses are reported. These experiments, combined with the consideration of different time scales in the theory of surface relaxation, show how confinement effects can provide detailed information on the rotational dynamics of temporarily adsorbed liquid layers in presence of biphasic fast exchange.
Fluid and Protein Motion in Monomolecular and Bilayer Films Overlying Sublayers of Finite Depth
Authors: Stone H.A. 
Published: April 2011

ABSTRACTMotion of a monolayer, bilayer or other surface film is affected by the presence of a surrounding fluid phase. Several recent experimental and theoretical studies have examined this viscous coupling with particular attention given to situations where the subphase provides the dominant resistance to motion. This research is summarized and the translation of a membrane-bound particle over a sublayer of finite depth is considered.
Electron Spin Resonance of Hydrogenated Amorphous Silicon Alloyed with Sulfur
Authors: Yan Baojie , Taylor P. C. 
Published: April 2011

ABSTRACTElectron spin resonance (ESR) and light-induced electron spin resonance (LESR) measurements were performed on sulfur-doped hydrogenated amorphous silicon (a-SiS:H). At low S doping levels (H2S/SiH4 ≤ 10−3 in gas phase), the ESR and LESR line shapes are similar to those observed in undoped a-Si:H. The dark spin density generally increases with S doping and reaches 5×1016 cm−3 at H2S/SiH4 ≈ 10−3. On the other hand, at high S concentration, the dark spin density increases significantly with S concentration. The ESR and LESR line shapes become identical and asymmetric, a fact that implies the ESR and LESR signals result from the same kind of ESR center. Since S doping is very inefficient, the ESR signals probably are due to defects instead of trapped carriers in band tails. The asymmetry of the ESR and LESR line shapes at high sulfur concentration may result from either more than one type of defect or an asymmetry in the g tensor of a single defect. The photo-excitation of H-passivated, S-related defects could also contribute to the LESR.
Hydrogen Populations in PECVD a-Si:H,D
Authors: Cull T. S. , Kernan M. J. , Chan P. H. , Fedders P. A. , Leopold D. J. , Norberg R. E. , Wickboldt P. , Paul W. 
Published: April 2011

ABSTRACTProton NMR and deuteron NMR (DMR) have been used to measure hydrogen populations in a series of PECVD a-Si:H,D films. The sharp DMR doublet from Si-D is fitted and subtracted out. The residual spectra then show specific signatures for molecular D2 and HD. The fitting procedures yield quantitative measures of Si-bonded and molecular species. A particular comparison is made between a pair of films prepared as the powered and unpowered electrodes in the same plasma deposition. Both silicon-bonded and molecular populations axe significantly different in the two films and correlate with photoresponse products ημT and with IR as well as other materials characterizations.
Determination of the Density of States in Semiconductors from Transient Photoconductivity
Authors: Main C. 
Published: April 2011

ABSTRACTThis paper discusses the techniques we have developed to analyse the photo-response of amorphous semiconductors to transient optical excitation to determine the energy distribution of gap states (DOS). We highlight the difficulties arising from a direct ‘single point’ approach using the instantaneous transient photocurrent i(t) when there is significant structure in the DOS or in the presence of recombination. Frequency domain methods which involve measurement of the amplitude I(ω) and phase φ(ω)of the steady ac photocurrent in response to ac excitation are shown to overcome these problems, but include other, experimental shortcomings. The paper describes a solution which combines the best features of time and frequency domain methods. The method involves numerical Fourier transformation of the time sampled impulse response i(tk) into a complex ac response (ω n), followed by analysis for gap-state distribution. Essentially, the method succeeds since it folds in information from the whole of the measured response for each energy considered. Other advantageous features include applicability to semiconductors exhibiting dispersive or non-dispersive transport, and to pre- and post- recombination regimes of the transient photocurrent, without modification. The features of this analytical method are demonstrated with computer simulated and experimental transient photocurrent data for a-Si:H.
Spin Dependent Photoinduced Absorption in a-Si:H
Authors: Schultz N. , Vardeny Z. V. , Taylor P. C. 
Published: April 2011

ABSTRACTWe have studied photoexcitation dynamics in undoped a-Si:H from 80 K to 300 K by the techniques of photoluminescence (PL), photoinduced absorption (PA) and their respective versions of optically detected magnetic resonance, namely PLDMR and PADMR. Both PL and PA spectra are composed of low and high energy bands, respectively. Using their respective temperature dependences we correlate the low energy PA band (∼ 0.4 eV) to the high energy PL band (∼1.3 eV) and the high energy PA band (∼ 1 eV) to the low energy PL band (∼ 0.8 eV). We also found that the PADMR spectrum is composed of three main contributions: a narrow resonance at g ∼ 2 (FWHM = 15 G), a broad resonance at g ∼ 2 (160 G) and a narrow asymmetric resonance at g ∼ 4 (20 G). By measuring their photon energy spectrum we found that the g ∼ 4 and the broad g ∼ 2 resonances are correlated with each other and therefore are due to trapped electron-hole pairs in the triplet spin configuration.
Fluctuating Defect Density Probed with Noise Spectroscopy in Hydrogenated Amorphous Silicon
Authors: Verleg P.A.W.E. , Uca O. , Dijkhuis J. I. 
Published: April 2011

ABSTRACTResistance fluctuations have been studied in hydrogenated amorphous silicon in the temperature range between 300 K and 450 K. The primary noise source has a power spectrum of approximately 1/f and is ascribed to hydrogen motion. Hopping of weakly bound hydrogen is thermally activated at such low temperatures with an average activation energy of 0.85 eV. The attempt rate amounts to 7 · 1012 s−1.
Experimental Determination of the Distribution of Tail States of Hydrogenated Amorphous Silicon: A Transient Photocurrent Analysis
Authors: Webb D. P. , Chan F. Y. M. , Zou X. C. , Chan Y. C. , Lam Y. W. , Lin S. H. , O'Leary S. K. , Lim P. K. 
Published: April 2011

ABSTRACTRecent experimental developments have cast doubt on the validity of the common assumption that the distribution of tail states of hydrogenated amorphous silicon exhibits a single exponential functional form. We employ transient photocurrent decay measurements to determine this distribution of tail states. In our approach, however, we determine the distribution of tail states directly from the experimental data, without assuming, a priori, a specific functional form. It is found that these experimental results are consistent with other more recent experimental determinations of the distribution of tail states, suggesting the possibility of deviations from a single exponential distribution of tail states in hydrogenated amorphous silicon.
Ambipolar Phototransport (μτe = μτh) Observed as an Intrinsic Property of a-SiGe:H
Authors: Wickboldt Paul , Pang Dawen , Paul William , Chen Joseph H. , Chen Chih-Chiang , David Cohen J. 
Published: April 2011

ABSTRACTA study is presented of a series of high quality PECVD a-Si0.33Ge0.67 films, produced by cathodic deposition, in which small concentrations of PH3, B2H6 or air impurities were added during deposition. The quantum efficiency-mobility-lifetime product (ημτ) increases, and the ambipolar diffusion length (Lamb) decreases monotonically with dopant concentration for both PH3 and B2H6. This result is strong evidence that for these films neither photocarrier is dominant (μτe= μτh) at zero doping. This result is very different from what has been typically observed by other researchers, that the electron is the dominant photocarrier for undoped a-SiGe:H.Drive level capacitance (DLC) measurements of these alloys show an unusual behavior of being temperature-independent, and the dark conductivity activation energy is maximum for zero doping. It is proposed that all of these unusual properties are due to the unusually low impurity concentration of these films, and that these properties are, in fact, the intrinsic properties for a-SiGe:H alloys. To verify this, films were prepared with a calibrated and controlled air leak introduced during deposition. As the air leak was increased, the film properties changed to typical behavior. Even for air concentrations as low as 2 ppm (gas phase), the transport measurements showed changes consistent with a shift in the Fermi level toward the conduction band.
Electronic transport and structure of microcrystalline silicon deposited by the VHF-GD technique
Authors: Goerlitzer M. , Beck N. , Torres P. , Kroll U. , Keppner H. , Meier J. , Koehler J. , Wyrsch N. , Shah A. V. 
Published: April 2011

ABSTRACTElectronic transport parallel and perpendicular to growth direction has been studied in a series of microcrystalline silicon samples obtained by various dilutions of silane in hydrogen. It is clearly shown that the transport properties (dark conductivity, drift mobility, ambipolar diffusion length and photoconductivity) under dark and under illumination conditions are enhanced as the dilution is increased. Furthermore, these films exhibit no degradation upon light-soaking. X-Ray diffraction patterns of the samples confirm that there is a correlation between the amount of crystalline fraction in the samples and the transport properties, as well as a preferential orientation along the growth direction. A similar correlation is found with the shift of the Si-H stretching mode peak of the infrared spectra (IR). Because transport properties have been measured by different techniques (dark conductivity, ambipolar length and photoconductivity in the direction perpendicular to growth direction, drift mobility in the direction parallel to growth direction), no statement can be made about a possible anisotropy in transport, as it would be expected from the columnar shape of the crystallites.
Direct Nucleation of Crystalline SiGe on Substrates by Reactive Thermal CVD with Si2H6 and GeF4
Authors: Yoshizawa Fumio , Shiota Kunihiro , Inoue Daisuke , Hanna Jun-ichi 
Published: April 2011

ABSTRACTPolycrystalline SiGe (poly-SiGe) film growth by reactive thermal CVD with a gaseous mixture of Si2H6 and GeF4 was investigated on various substrates such as Al,Cr, Pt, Si, ITO, ZnO and thermally grown SiO2.In Ge-rich film growth, SEM observation in the early stage of the film growth revealed that direct nucleation of crystallites took place on the substrates. The nucleation was governed by two different mechanisms: one was a heterogeneous nucleation on the surface and the other was a homogeneous nucleation in the gas phase. In the former case, the selective nucleation was observed at temperatures lower than 400°C on metal substrates and Si, where the activation of adsorbed GeF4 on the surface played a major role for the nuclei formation, leading to the selective film growth.On the other hand, the direct nucleation did not always take place in Si-rich film growth irrespective of the substrates and depended on the growth rate. In a growth rate of 3.6nm/min, the high crystallinity of poly-Si0.95Ge0.05in a 220nm-thick film was achieved at 450°C due to the no initial deposition of amorphous tissue on SiO2 substrates.
Transport and Recombination Channels in Undoped Microcrystalline Silicon Studied by ESR and EDMR
Authors: Will D. , Lerner C. , Fuhs W. , Lips K. 
Published: April 2011

ABSTRACTWe present a detailed study of ESR and spin-dependent transport (EDMR) on μc-Si. We identify to different types of defects at g=2.0055(±3) and g=2.0044(±5) and study their influence on transport and recombination by stepwise annealing the samples. We find that transport is not controlled by defects if ND<1018 cm−3. For ND>1018cm−3 a dramatic decrease of the conductivity is found and we identify a hopping contribution in transport. To explain our ESR and EDMR results we propose a simple model where most defects are distributed at the surface of the columns and transport is along percolation paths. We also observe minor metastable changes of the defect density which are assigned to adsorption of atmospheric oxygen.
Correlation Between Surface Morphology and Lattice Orientation of Microcrystalline Silicon
Authors: Kondo M. , Nishimiya T. , Saitoh K. , Ohe T. , Matsuda A. 
Published: April 2011

ABSTRACTThe surface morphology and preferential orientation of μc-Si:H has been studied on c-Si substrate in relation to the Si-H bonding mode. Epitaxy-like growth is observed on Si (001) substrate at a moderate temperature and under low ion bombardment, while the surface is significantly roughened. With increasing or decreasing the temperature or increasing the ion bombardment, the lattice orientation is randomized and an amorphous component is increased, resulting in the reduction of the surface roughness. The growth mode is intimately related to the Si-H bonding configuration. The epitaxy-like growth is collapsed accompanying the disappearance of the surface Si-H 2,3 mode. The resemblance of these phenomena to the low temperature MBE is discussed.
Real-Time ESR Observation During Film Growth of a-Si:H
Authors: Yamasaki S. , Umeda T. , Isoya J. , Tanaka K. 
Published: April 2011

ABSTRACTIn-situ electron-spin-resonance (ESR) measurements of film growth of hydrogenated amorphous silicon (a-Si:H) using a remote hydrogen plasma technique have been performed. The Si dangling-bond signal in a-Si:H during and after deposition has been detected, in addition to the gas-phase ESR signals both of atomic hydrogen and photo-excited SiHx molecules. Dynamic changes of the Si dangling-bond signal intensity were observed when the deposition started and stopped, which has suggested the existence of a subsurface region with higher spin density than that in the bulk region.
Structural Properties of a-Ge1-xCx:H Alloys Prepared by the RF Sputtering Technique
Authors: Marques F. C. , Vilcarromero J. , Freire F. L. 
Published: April 2011

ABSTRACTStructural and mechanical properties of hydrogenated amorphous germanium carbon (a-Ge1-xCx:H) alloys are presented. The films were prepared by the rf-co-sputtering technique using a graphite/germanium composed target. The carbon and germanium relative concentrations were determined by RBS, and the total hydrogen concentration by ERDA measurements. An increase in the optical gap was measured for low carbon content (0 < × < 0.15). For higher values of x the optical gap is almost constant. Infrared transmission absorption spectra show several absorption bands related to Ge-C stretching, C-Hn (n = 1,2,3) and Ge-H stretching and bending modes. The mechanical internal stress was strongly affected by the incorporation of carbon. The trends of the optical gap, refractive index, infrared absorption and mechanical stress as a function of the carbon content suggest that the high carbon concentration alloys have polymeric and/or graphite-like contribution in their structure.
Defect Formation Mechanism During PECVD of a-Si:H
Authors: Maeda Keiji , Umezu Ikurou 
Published: April 2011

ABSTRACTDefect formation mechanism in a-Si:H during PECVD at substrate temperature below 250°C is considered to be breaking of weak bonds in the Urbach tail. To break weak bonds, an extra energy is necessary. This energy is supplied by the reaction energy of SiH3 precursor at the growing surface incorporating SiH2 into the network. The defect density is experimentally shown to be proportional to a product of the energy supply frequency, i.e., SiH2 density, and the weak bond density which is obtained by the Urbach energy. By analysis using the configurational coordinate diagram the energy level of the broken weak bond is determined to be 0.2 eV above the valence band mobility edge. There is similarity of the defect formation mechanism during deposition to that of the Staebler-Wronski effect.
High-Rate Deposition of a-Si:H Films in 55 kHz Glow Discharge: Growth Mechanisms and Film Structure
Authors: Budaguan B. G. , Aivazov A. A. , Sazonov A. YU , Popov A. A. , Berdnikov A. E. 
Published: April 2011

ABSTRACTThe 55 kHz GD technique allowed the high-rate deposition of a-Si:H films (up to 30 A/s) with good electronic properties in spite of inhomogeneous structure. In this work, we investigated the growth mechanisms and the correlation between plasma parameters and film structure. The electrical parameters of discharge, the properties of plasma and of the films were investigated with using of wide range of methods (optical emission spectroscopy, mass-spectrometry, IR-spectroscopy, atomic force microscopy).The films were deposited in an industrial reactor of diode type with both non-grounded electrodes used as substrate holders. The deposition mechanism in this case includes the alternation of growth phases when the negatively charged particles reach the anode (at a moment) during the first half-period of an oscillation of electric field, and the improvement of growing surface under the influence of the bombardment by positive ions during the second half-period. It is shown that the increase of the power increases the ionic flux leading to the increase of the size of structural inhomogeneities. The pressure influences the energy of positive ions, and, therefore, the hydrogen content and its bonding form on the growing surface.
Ion Bombardment and Disorder in Amorphous Silicon
Authors: Sidhu L. S. , Gaspari F. , Zukotynski S. 
Published: April 2011

ABSTRACTThe effect of ion bombardment during growth on the structural and optical properties of amorphous silicon are presented. Two series of films were deposited under electrically grounded and positively biased substrate conditions. The biased samples displayed lower growth rates and increased hydrogen content relative to grounded counterparts. The film structure was examined using Raman spectroscopy. The transverse optic like phonon band position was used as a parameter to characterize network order. Biased samples displayed an increased order of the amorphous network relative to grounded samples. Furthermore, biased samples exhibited a larger optical gap. These results are correlated and attributed to reduced ion bombardment effects.
Amorphous Silicon-Carbon Alloys and Amorphous Carbon from Direct Methane and Ethylene Activation by ECR
Authors: Conde J. P. , Chu V. , Giorgis F. , Pirrt C. F. , Arekat S. 
Published: April 2011

ABSTRACTHydrogenated amorphous silicon-carbon alloys are prepared using electron-cyclotron resonance (ECR) plasma-enhanced chemical vapor deposition. Hydrogen is introduced into the source resonance cavity as an excitation gas. Silane is introduced in the main chamber in the vicinity of the plasma stream, whereas the carbon source gases, methane or ethylene, are introduced either with the silane or with the hydrogen as excitation gases. The effect of the type of carbon-source gas, excitation gas mixture and silane-to-carbon source gas flow ratio on the deposition rate, bandgap, subgap density of states, spin density and hydrogen evolution are studied.
Microcrystalline Silicon Germanium: An Attractive Bottom-Cell Material for Thin-Film Silicon-Based Tandem-Solar-Cells
Authors: Ganguly Gautam , Ikeda Tom , Kajiwara Kei , Matsuda Akihisa 
Published: April 2011

ABSTRACTWe have prepared hydrogenated macrocrystalline silicon germanium by plasma enhanced CVD of a mixture of silane and germane gas diluted with hydrogen. The growth conditions have been systematically controlled to obtain large (∼400Å) crystallites of silicon-germanium as observed using Raman scattering and x-ray diffraction. The dangling bond (germanium) density has been reduced to <5×1016 cm−3 at low substrate temperatures (∼150°C). The optical absorption spectra of the 50% Ge containing material is red-shifted compared to microcrystalline silicon, consistent with a reduction of the indirect optical gap to 0.9eV. Schottky type cells fabricated using Au on an n+ crystalline silicon substrate confirm that the long wavelength response is remarkably enhanced in this material.
Improved Amorphous Silicon Alloy Solar Cells for Module Fabrication
Authors: Banerjee A. , Yang J. , Guha S. 
Published: April 2011

ABSTRACTAn initial conversion efficiency of 13.5% has been obtained on a triple-junction triple-bandgap device fabricated in a large-area deposition reactor capable of producing one-square-foot modules. The intrinsic layer of the top cell is a wide bandgap amorphous silicon alloy. The middle and bottom cells employ high quality amorphous silicon-germanium alloy. The high efficiency of the triple-junction cell is attributed to the relative reduction of the optical loss in the top tunnel junction and the improvement in the quality of the middle and bottom component cells. Triple-junction devices with initial efficiency of 13.3% have shown saturation at 11.6% after light soaking. Modules of aperture area 909cm2 have been fabricated using an assembly process similar to the one being currently used in our manufacturing line. The module design consists of onelarge-area, high-current monolithic multijunction device. The status of the small-area devices andmodules is described
Space-Charge-Limited Currents in n-i-n Devices Incorporating Glow-Discharge and Hot-Wire Deposited a-Si:H
Authors: Molenbroek Edith C. , Van Der Werf C. H. M. , Feenstra K. F. , Rubinelli F. , Schropp R. E. I. 
Published: April 2011

ABSTRACTSpace-charge-limited currents have been examined in a wide variety of n-i-n devices. If the devices were completely symmetric, the current-voltage characteristics would be identical for positive and negative bias, but in several devices differences between the two polarities were observed. In order to understand in which part of the device these differences originate, the influence of the contacts and interfaces on the JV characteristics were examined by using different metal top contacts, different n-layers and different i-layers. Ag and Al top contacts gave minor differences between the polarities, whereas with Cr contacts no differences were observed. Incorporation of a defect layer in the i-layer results in asymmetric JV curves. We have observed a small asymmetry in an experimental device, and a large asymmetry using AMPS modeling. N-i-n devices appear to be a sensitive probe for interface defects.
Photocapacitance and Hole Drift Mobility Measurements in Hydrogenated Amorphous Silicon (a-Si:H)
Authors: Nurdjaja Indra , Schiff E. A. 
Published: April 2011

ABSTRACTWe present measurements of the photocapacitance in hydrogenated amorphous silicon (a-Si:H) Schottky barrier diodes under reverse bias. A calculation relating photocapacitance to hole drift mobility measurements is also presented; the calculation incorporates the prominent dispersion effect for holes in a-Si:H usually attributed to valence bandtail trapping. The calculation accounts quantitatively for the magnitude and voltage-dependence of the photocapacitance.