bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of the Bonding Structure on Disorder and Band-Tails in a-B:H
Authors: Bernhard N. , Eberhardt K. , Schubert M. B. , Bauer G. H. 
Published: March 2011

ABSTRACTA thorough investigation of plasma-CVD amorphous hydrogenated boron (a-B:H) has been conducted with the main emphasis on how in this amorphous semiconductor the variation of the coordination number in comparison to a-Si:H influences the structural disorder and density of states in the band tails. a-B:H was deposited from different concentrations of B2 H6 diluted in H2 by both DC- and RF-plasma-CVD. The influence of the change of substrate temperature, pressure, flow and deposition power on the structural, optical and electronic properties of the material was examined. Raman-scattering and IR-absorption reveal the clear non-crystallinity of the deposited films. Almost all samples show some photoconductivity with a σphoto/σdark ratio from 10-1 to 3×101. Although a strong influence of some of the deposition parameters on bandgap and refractive index, hydrogen content, dark and photoconductivity was observed, the density of states in the band tails as measured by PDS was relatively high, showing always a rather flat Urbach slope of about 180 – 220 meV. An explanation for this unexpected almost uniform huge Urbach slope might be that even in the amorphous state the behaviour of boron is still dominated by its electron deficiency character which leads to a certain amount of three centre bonds (as seen in IR-absorption) and results in comparison to amorphous hydrogenated silicon in even stronger constraints of the amorphous network and obviously in more potential fluctuations.
Transient Simulations of Amorphous Silicon Devices
Authors: Hack M. , Shaw J. G. 
Published: March 2011

ABSTRACTWe have developed a numerical simulation program (MANIFEST) which calculates the time-dependent behaviour of one and two dimensional amorphous silicon devices. Our model solves the complete set of transport equations for both electrons and holes and fully includes the appropriate time dependent occupation functions for the traps in the band gap of the amorphous silicon. These traps are assumed to obey Shockiey-Read-Hall kinetics. We have simulated the transient behaviour of pin and nin diodes, both in the dark and under illumination, as well as the characteristics of thin film transistors. Our initial results are in good agreement with experimental data.
A New Device Model of Amorphous Silicon Thin-Film Transistor for Circuit Simulation
Authors: Choi Hong S. , Park Jin S. , Oh Chang H. , Joo In S. , Kim Yong S. , Han Min K. , Choi Yearn I. , Yun Jung G. , Park Won K. , Kim Woo Y. 
Published: March 2011

ABSTRACTWe present a new analytical model of amorphous silicon thin-film transistor (a-Si TFT) suitable for circuit simulators such as SPICE. The effects of localized gap state distributions of a-Si as well as temperatures on the a-Si TFT performances have been fully considered in the presented model. The parameters used in SPICE, such as transconductance, channel-length modulation, and power factor of source-drain current, are evaluated from the measured current-voltage and capacitance-voltage characteristics by employing the proposed extraction method. It has been found out that the analytical model is in good agreement with experimental data at both room temperature and elevated temperature and successfully implemented in a widely used circuit simulator.
Reactive Ion Etched MO/CR Source-Drain Metallization for Amorphous Silicon Thin Film Transistors
Authors: Kwasnick R. F. , Possin G. E. , Saia R. J. 
Published: March 2011

ABSTRACTA novel two step reactive ion etch (RIE) process is described for the etching of bilayer Mo/Cr source-drain metallization on hydrogenated amorphous silicon (a-Si:H) inverted-staggered thin film transistors. The Cr acts as an etch stop during Mo etching, and is thin enough (∼3 0 nm) that only a small thickness of underlying a-Si is removed during the Cr etch. The resulting Mo/Cr profile is sloped, compared to the more vertical and somewhat uncontrolled slope that is achieved with Mo wet etch. Very similar transistor behavior was observed for both Mo wet etched and Mo/Cr reactive ion etched source-drain metallization. The major advantage of this process over wet etching of Mo source-drain is improved step coverage of subsequently deposited layers due to the less vertical sidewall slope.
Influence of the Gate Bias and Temperature on Positive Charge Generation in TFT Gate-Quality Amorphous Silicon Nitride Films
Authors: Kanicki Jerzy , Sankaran Mythili 
Published: March 2011

ABSTRACTWe report on the illumination time dependence of the generation of positive charge in gate-quality nitrogen-rich amorphous silicon nitride films subjected to sub-bandgap illumination at different temperature in vacuum. The influence of film thickness and gate bias applied during illumination on the generation of positive charge is also described. We have found that a stretched-exponential function, which characterizes dispersive charge transport in silicon nitride, gives the best description of our experimental results.
Deposition and Characterization of Near “Intrinsic” μc-Si Films Deposited by Remote Plasma-Enhanced Chemical-Vapor Deposition - RPECVD
Authors: Williams M. J. , Wang C. , Lucovsky G. 
Published: March 2011

ABSTRACTUndoped films of μc-Si deposited by RPECVD are n-type with a room temperature dark conductivity of ∼6×10-4 S/cm and an activation energy of ∼0.3 eV. This is due to native donor-like defects. We report on the conductivity and photoconductivity of boron-doped μc-Si, with emphasis on low doping levels that are designed to compensate exactly these native donor-like defects. We describe the dark conductivity and the photoconductivity as functions of dark conductivity activation energy and the average boron concentration, and present a model for the photoconductivity based on band off sets between the crystalline and amorphous regions of the μc-Si.
Fast Changes in a-Si:H Solar Cells After Severe Light-Soaking
Authors: Roedern Bolko Von 
Published: March 2011

ABSTRACTThe fast changes observed in the stabilized state of a-Si:H solar cells and modules at temperatures below 70°C are inconsistent with the commonly accepted picture of “defect annealing.” The fast changes observed in the stabilized state, for example when the temperature is altered, are explained in terms of converting the charge state of the dangling bond defects that are already present in the material. It is suggested that the slow degradation of solar cells arises from the creation of new defects and can be described by fitting stretched exponential curves to the solar cell performance data.
Temperature Dependence of Metastable Defect Creation in a-SiNx:H
Authors: Hamed A. , Fritzsche H. , Köhler S. 
Published: March 2011

ABSTRACTLight exposure of multilayers consisting of alternating 2.5 nm thick a-Si:H and about 40 nm thick a-SiNx:H produces a large metastable excess dark conductance. This appears to be due to metastable defects in a-SiNx:H produced by hopping injection of photocarriers from the a-Si:H. They anneal at an equilibration temperature TE∼460°K. These metastable defects are created with the same efficiency between 4K and 300K. The efficiency rapidly falls above 350K. The metastable defects have the same anneal temperature regardless of creation temperature. The mechanism of defect creation will be compared with that in a-Si:H.
Amorphous Silicon Analogue Memory Elements
Authors: Rose M. J. , Hajto J. , LeComber P. G. , Snell A. J. , Owen A. E. , Osborne J. S. 
Published: March 2011

ABSTRACTBoth Cr/p+/V and Cr/p+/Cr devices exhibit fast electrically programmable memory switching with a programmable voltage range, ΔVS, which depends only on the choice of the top metal. Despite a difference in ΔVS, both types of device have very similar electrical properties, but show one major difference in room temperature I-V characteristics, where under certain conditions, discontinuities are observed.
Density of States Spectroscopy in p-Type a-Si:H and a-SiC:H
Authors: Crandall Richard S. , Salamon Stanley J. , Xu Yueqin 
Published: March 2011

ABSTRACTWe derive a closed form expression for differential junction capacitance applicable when the density of states (DOS) varies exponentially with energy. Using this expression, we analyze p/n junction capacitance measurements that probe the DOS in boron doped hydrogenated amorphous silicon and silicon carbide alloy. In both materials we find that the p-layer DOS is described by an exponential increase with energy above the Fermi level.
An Investigation of Spin and Charge States Associated with Metastable Defects in N-Type Hydrogenated Amorphous Silicon
Authors: Rasmussen R. J. , Cohen J. D. , Essick J. M. 
Published: March 2011

ABSTRACTDepletion-width-modulated (DWM) ESR spectroscopy and junction capacitance techniques were employed to investigate deep-defect states in various metastable states of 10 and 80 Vppm PH3-doped a-Si:H. From the joint application of these methods, we enumerate the change in total spin and charge associated with emission of carriers from states within the mobility gap resulting from a modulated bias voltage. We conclude that the magnitude of the modulated spin-to-charge ratio is nearly unity, consistent with earlier similar investigations of n-type a-Si:H, where the D-/D0 transition was shown to dominate. Furthermore, we present results of a previously unreported “quadrature” DWM-ESR signal of large magnitude under a wide range of experimental conditions. Similar related effects are also reported from spin- and capacitance-transient studies. These results clearly demonstrate that the changes in spin significandy lag corresponding changes in charge.
Effects of Temperature and Charge Depletion on the Spin Density in Hydrogenated Amorphous Silicon
Authors: Lee J.-K. , Schiff E. A. 
Published: March 2011

ABSTRACTThe dependence of the spin density upon temperature and charge depletion is calculated based on the standard defect model in a-Si:H of a D-center with positive, neutral, and negative charge states. The results are compared with recent measurements of depletion width modulated spin densities and temperature-dependent spin densities. It is shown that the initial charge density assumed for the defect system substantially affects conclusions regarding electronic correlation energies drawn from the measurements.
Surface Processes Limiting the High Rate Deposition of High Electronic Quality a-Si
Authors: Veprek S. , Anibacher O. , Riickschloβ M. 
Published: March 2011

ABSTRACTAmorphous silicon of a high electronic quality with Odatk 10-10, σPh ≈ 1·10-4 (Ωcm)-3 and density of gap states of about 0.3 to 2.1016 eV-1cm-3 is deposited at rates up to 17 Å/sec. The rate limiting steps are identified and their control via the plasma parameters is explained. This allows one to establish the fundamental scaling parameters for large-area high-rate deposition of a-Si. Long term stability of the films in terms of postoxidation and photode-gradation is briefly addressed.
Hydrogen Dilution effects on Amorphous Hydrogenated Silicon (a-Si:H) Prepared by Glow Discharge Near Room Temperature
Authors: Cheung Man Ken , Petrich Mark A. 
Published: March 2011

ABSTRACTWe report here the first phase of our attempt to deposit “device-quality” a-Si:H films by glow discharge near room temperature (50 °C). We have found that, at a low rf power density (40 mW/cm2) and high hydrogen/silane ratios (≥ 2), film quality is not uniquely determined by the substrate temperature, Ts. The microstructure of our low hydrogen content films as revealed by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies is similar to that of “device-quality” films deposited at standard Ts. The next phase of our work is to ascertain whether or not similar IR and NMR characteristics between our low Ts films and the standard Ts films imply also similar opto-electronic properties.
Optical Properties of Random Multilayers of Amorphous A-Si:H/A-Si3N4+x:H and the Classical Localization
Authors: Nitta Shoji , Ogawa Kohji , Furukawa Takehiro , Itoh Takashi , Nonomura Shuichi 
Published: March 2011

ABSTRACTIn the optical reflectance spectrum of the random multilayers of a-Si:H/a-Si3N4+x:H, it is observed an anomalous peak which is explained by the classical localization of light propagation. The following two subjects are discussed in this report; (a). The Kramers-Kronig transformation is done including the anomalous disorder-related reflectance peak. Extra absorption coefficients Δα are obtained by this analysis. Energy dependence of the localization length 1(hv) of light propagation are obtained by 1(hv)=1/Δα(hv). (b). The other is the experiment on scaling where the ratio of the disorder and the average layer thickness is kept constant but the size of each layer is changed in each experiment
Surface Absorption Below the Band Gap in a-Si:H Using Photoluminescence Absorption Spectroscopy
Authors: Gu S. Q. , Nitta S. , Taylor P. C. 
Published: March 2011

ABSTRACTPhotoluminescence absorption spectroscopy or PLAS has been used to measure the below gap absorption in a-Si:H at 77 K. As the absorption probed by this technique is composed of contributions from the bulk and the surfaces of the a-Si:H, we have developed an improved sample structure to separate these two contributions. Two kinds of interface have been investigated: a-Si1−xNx:H/a-Si:H and a-Si1−xOx:H/a-si:H. For the studies ofa-Si1−xNx:H/a-Si:H.x, two samples have been employed. The first sample consisted of an a-Si1−xNx:H/a-Si:H/a-Si:H/a-Si1−xNx:H/NiCr layered structure; the second one had a similar structure except that the a-Si:H layer was interrupted periodically by two thin (100 A°) a-Si1−xNx:H layers to increase the contribution of the interface absorption. A shoulder of the absorption around 1.2 eV for the second sample, which was not found in the first one, is probably due to the interfaces between a-Si:H and a-Si1−xNx:H. All samples were light-soaked using an Ar+ laser (5145 A°). The increases in the absorption measured by PLAS at 77 K are essentially the same as the results of PDS at 300 K, which suggests that the interfaces do not contribute to the light-induced absorption.
Fundamental Consideration on Carrier Transport in Amorphous Silicon Superlattices
Authors: Jiang Y. L. , Hwang H. L. 
Published: March 2011

ABSTRACTBasic consideration of parameters including electron de Broglie wavelength, resonant tunneling time (τr) and inelastic scattering tunneling (τi) were studied to identify the intrinsic tunneling properties of amorphous double—barrier (DB) structure. The order of magnitude of τr/τi. of amorphous DB structure is about 5 to 12 which is far beyond that of crystalline case which is 1 to 2. The transmissivity versus applied voltage or versus electron energy were calculated to identify the influence of barrier height, barrier thickness and electron effective mass. The influence of carrier distribution will also be discussed.
Reducing the Saturated Defect Density- in a-Sl:H by Post-Growth Anneals
Authors: Yoon J. H. , Xu X. , Kotharay M. , Wagner S. 
Published: March 2011

ABSTRACTThe saturated light-induced defect density Nsat in a-Si:H was studied as a function of deposition temperature and of pre-light-soaking anneals. The deposition temperature and annealing affect the microstructure, which we characterize by the Si-H and Si-H2 infrared absorption intensities. We find correlations between Nsat and the initial defect density, the Urbach energy, the hydrogen concentration and the fraction of H in SiH4 groups. Annealing before light-soaking can reduce the saturated defect density substantially.
Assessment of Weak Si-Si Bond Breaking Mechanisms of the Staebler-Wronski Effect
Authors: Biswas R. , Kwon I. , Soukoulis C. M. 
Published: March 2011

ABSTRACTThe mechanisms of the Staebler-Wronski effect are investigated by examining the stability of computer-generated amorphous hydrogenated silicon networks with a molecular dynamics approach. Models with both monohydride and dihydride species are examined. A new Si-H interatomic potential is utilized for the simulations. A localized excitation is used to model the non-radiative transfer of photo-excited carrier energy to the lattice. The a-Si:H model with only monohydride species is stable to bond-breaking excitations. The a-Si:H model with both monohydride and dihydride species is less stable and exhibits, after local excitations, higher energy dangling bond states that can however be easily annealed away.
Mechanism of Ion Transport in Cooled and Supercooled Water at High Pressure
Authors: Nakahara M. , Takisawa N. , Osugi J. 
Published: March 2011

ABSTRACTAs predicted by the Hubbard-Onsager continuum dielectric friction theory for ionic mobility in solution, the observed pressure coefficient of the difference ζ between the observed ionic drag coefficient and the Stokes law friction (4πηR), is negative for the small ion Li+ even at low temperatures where the water structure is highly developed. For the large ion Cs+, however, it is positive at any temperature in contrast to the theoretical prediction, its magnitude being larger at lower temperatures and pressures. The anomaly is shown also by the medium-sized ion K+ below room temperature. The passing-through-cavities (PTC) mechanism has been proposed to explain the limitations of the continuum theory.
Thermodynamic Properties of the Alkali Metals at High Pressures and High Temperatures
Authors: Boehler Reinhard 
Published: March 2011

ABSTRACTThe melting temperatures of Li, Na, K, Rb, and Cs versus pressure were measured to 32 kbar in a piston cylinder apparatus with hydrostatic pressure medium and in situ pressure measurements. The accuracies in pressure and temperature are ± 0.4 % and ± 0.25° C, respectively. Substantial deviation from measurements using solid, non-hydrostatic pressure media is observed. The adiabat, (δT/δP)s,was measured to 32 kbar and 400°C by adiabatic compression. Ln (δT/δP)s is a linear function of volume with good consistency in the slopes. (δT/δP)s changes insignificantly at the liquid-solid phase transitions. The Grüneisen parameters, calculated from γ = Bs/T (δT/δP)s, decreases with pressure and temperature. Bs is the adiabatic bulk modulus. The γ-volume curves show strong curvature and γ tends to become volume independent at compressions of about 30 %. γ increases by several percent at the liquid-solid transition.
Condie Process
Authors: Ritter N. , Avitzur B. 
Published: March 2011

ABSTRACTThe process of conventional hydrostatic extrusion limits the length of the billet that can be extruded to a length somewhat shorter than that of the chamber. Production units are also limited to pressures of about 8,000 Kg/cm2. Thus the reduction that can be affected in one pass of hydrostatic extrusion of mildly tough materials like low carbon steels or copper is limited to no more than 75% R.A., if the extrusion is performed at room temperature. For subsequent passes, each previous extrudate must be cut to suitable length so it will fit again into the chamber.The Condie process (Austen, U.S. Pat. #3,999,415) provides the means to perform extrusion through several dies, one die at a time, in one loading of the chamber. In the present model, only two dies are loaded into the chamber together with the billet. A short length is first extruded through the first die, while the second die is kept free to move idly with the extrudate. Then extrusion through the first die ceases and the billet is forced to extrude through the second die. As the second die approaches the first die and the intermediate diameter section shortens, the extrusion stops. Thus, one cycle of a finite length is completed. But, the accumulated reduction from billet to extrudate is large, similar to the reduction obtainable by a single die from a chamber of twice as high a pressure.
High Pressure Method for Identification of Crystal Elastic Imperfections - Generation of Defects in Silicon Single Crystals Under Pressure
Authors: Jung J. , Lefeld-Sosnowska M. 
Published: March 2011

ABSTRACTNew method for identification of the kind of elastic stress-free crystal imperfections which are not visible by standard X-ray and electron microscopy methods was presented. The method is based on the high pressure annealing creating large stresses at defect sites,followed by X-ray topography. This method was applied in structural defects studies of high quality silicon single crystals and allowed to determine the composition and structure of precipitates in silicon.
Investigation of Carbon Vapor Pressure at Very High Temperatures and Pressures with the Aid of Laser Heating
Authors: Scheindlin M.A. 
Published: March 2011

For several decades the behavior of carbon and carbonaceous materials has been observed with unvarying interest. Well known are two polymorphous modifications of carbon, namely, graphite and diamond, each possessing unique physicochemical properties which make them attractive for extensive utilization in numerous industries.The history of carbon studies at high temperatures and pressures produced quite a few examples of ingenious experimental techniques and experimenter's skill, however, many of those studies only resulted in the emergence of new, hard-to-solve problems. This is precisely the case with the melting and vaporization of graphite.
Equation of State for Fluid and Solid Hydrogen-Isotopes H2, D2, and T2
Authors: Shimizu Hiroyasu 
Published: March 2011

ABSTRACTThe calculations of the P-V isotherms of fluid hydrogen isotopes H2 , D2 , and T2 up to their freezing pressures at 200, 300 and 500 K have been performed for 4 kinds of intermolecular potentials by using the modified hard-sphere variational perturbation theory with a quantum correction. By comparing the results with the 300 K experimental equation of state, it has turned out that the agreement is good for the potentials of Silvera-Goldman and Nellis et al. except near the freezing point of H2 . The quantum pressures were estimated, and their dependences on volume, molecular mass, and temperature are discussed quantitatively. We discuss the discrepancy of the P-V isotherms between experiments by Brillouin scattering and theoretical results for H2 near the freezing point, including the recent solid isotherms to higher pressures.
Experimental Measurements of the Solubility of Hydrocarbons in Compressed Natural Gas Under Pressure (10 – 100 MPa) and Temperature (50 – 150°C).
Authors: Nogaret E. , Tufeu R. , Le Neindre B. 
Published: March 2011

ABSTRACTAn apparatus to measure phase equilibria under pressure is described. The composition of the gas phase was determined using a high pressure, high temperature sampling cell. We have found that compressed natural gas is a very good solvent of hydrocarbons. A possible application of this study is the understanding of processes which lead to migration of oil and the location of oil and gas fields.
Surface Segregation of Boron During Si-MBE Growth
Authors: Sardela M. R. , Ni W. -X. , Ekberg J. O. , Sundgren J. -E. , Hansson G. V. 
Published: March 2011

ABSTRACTBoron doping, using an elemental boron source during molecular beam epitaxial growth of silicon, has been studied. The boron flux was provided by a high temperature source heated by radiation and electron bombardment. The maximum boron deposition rate used was 1×1012 cm−2 s−1 at an estimated B temperature of 1950 °C. For growth at a substrate temperature of 650 °C, there is very little surface segregation when the doping level is in the range 1×1016-1×1019 cm−3. For very high boron to silicon flux ratio (>7×10−3) there is a strong surface segregation that results in surface accumulation of boron. This initially leads to a 2×2 reconstruction of the Si (100) surface, and further surface segregation during growth results in roughening of the surface due to the creation of (311)-facets. In a separate set of experiments, the surface segregation was studied using in situ Auger electron spectroscopy of predeposited layers of boron that were gradually covered by Si capping layers. Strong and surface coverage dependent surface segregation was observed both in the case of Si (100) and (111) substrates.