bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alternative Mechanism for Defect Generation in a-Si:H
Authors: Redfield David 
Published: April 2011

ABSTRACTRecombination-driven mechanisms for defect formation do not account well for several experimental facts, and indeed conflict with some facts. To overcome these problems, an alternative mechanism is proposed in which latent defect centers are converted to metastable defects (dangling bonds) without a recombination event. The transitions are driven simply by electron capture at the center with no energy barrier. A new configuration-coordinate diagram expressing this mechanism includes essential configuration-induced changes in the energies of band edges, and accounts for several other previously problematic observations. This carrier-induced mechanism (CIM) is consistent with defect formation in forward bias and defect inhibition in reverse bias, light-enhanced annealing, as well as the usual light-induced and beam-induced formation. For low orħħωthe process starts by ionization of an existing defect.
Origin and Incorporation Mechanism for Oxygen Contaminants in a-Si:H and μc-Si:H Films Prepared by the Very High Frequency (70 MHz) Glow Discharge Technique
Authors: Kroll U. , Meier J. , Keppner H. , Littlewood S. D. , Kelly I. E. , Giannoulès P. , Shah A. 
Published: April 2011

ABSTRACTThe effect of plasma power, reactor outgassing rate and feed gas purity on the oxygen content of amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) layers, prepared by the VHF (70 MHz) glow discharge technique has been investigated. The oxygen concentration in the films was measured by Secondary Ion Mass Spectrometry. The gas purity could be optionally enhanced by the application of a getter-based gas purifier mounted in the gas pipe just before the reactor. The purifier reduces the oxygen contaminants in the feed gas to levels in the ppb range. It was found that oxygen incorporation was enhanced at lower deposition rates. The deposition rate dependence of the oxygen incorporation is in excellent agreement with the proposed incorporation mechanism. Furthermore, the reactor outgassing rate and the purity of the feed gas itself were identified as the main contamination sources for the oxygen contaminants in the deposited a-Si:H films as well as in μc-Si:H films : e.g. at outgassing rates in the range of 10−6 mbar 1 s−1, at least around half of the oxygen detected in both a-Si:H and in the μc-Si:H layers originates from the feed gas if the latter is unpurified. By combining reduced outgassing rates and the use of purified feed gas, a-Si:H and μc-Si:H films with an oxygen concentration of 5×1017cm−3 and 2×1018cm−3, respectively, were deposited. These values both represent the lowest concentrations of oxygen contaminants reported to date for these kinds of materials.
Correlation Between Phototransport and Network Order in a-Si:H
Authors: Morell G. , Katiyar R. S. , Weisz S. Z. , Jia H. , Shinar J. , Balberg I. 
Published: April 2011

ABSTRACTHydrogenated amorphous silicon (a-Si:H) films prepared by the glow discharge (GD) technique show superior optoelectronic properties over those prepared by rf sputtering (RFS). To find out whether this is associated to structural differences in the amorphous network, we have carried out a comprehensive comparison of the Raman spectra of the two types of films grown at different substrate temperatures. The use of two properly chosen excitation radiations allowed the observation of the Raman spectra from the near surface versus that from the bulk of the films. The results show that the short-range order in the bulk of GD films is close to that of the ideal tetrahedral network, having an rms bond angle deviation (Δθ) of ≈9°. In contrast, the smallest value of Δθfound in the RFS films was ≈15°. There is also a short-range order inhomogeneity in both sets of materials that can be reduced significantly by selecting the appropriate substrate temperature. The intermediate-range disorder is relatively small and uniform in GD films, while large differences exist in this parameter between the surface and bulk of RFS films. In general, the results indicate that the short-range order and the inhomogeneity in intermediate-range order present in the RFS films cannot be improved to equal those of GD materials by annealing at temperatures low enough that no substantial hydrogen effusion occurs. These structural differences are argued to be the reasons for the superior phototransport properties of GD over RFS materials and are interpreted in terms of the differences between the two deposition processes.
Numerical Modelling of Time-of-Flight in SCLC-Mode
Authors: Brüggemann Rudolf , Bauer Gottfried H. 
Published: April 2011

ABSTRACTThe application of time-of-flight (TOF) in the space charge limited current (SCLC) mode to a-Si:H pin-diodes has led to the discovery of new features in the current transients. An alternative to analytic models, our numerical modelling describes the specific nature of amorphous semiconductors by taking into account the interaction of free carriers with tail states and the contribution of trapped carriers to the space charge. Typical features of experimental SCLC-TOF-currents such as a cusp in the transient can be reproduced. We confirm the concept of ‘effective thickness’ for the determination of the transit time. At high injection intensity only a small fraction of the charge can be collected. Bimolecular recombination via tail states and surface recombination is identified as a loss mechanism that competes with recombination via dangling bonds. The post-transit behaviour of electron-TOF is dominated by holes emitted from the valence band (vb) -tail. The density of states distribution from post-transit-spectroscopy (PTS) shows features of the vb-tail. Finally, hole SCLC-TOF shows a different behaviour from electron SCLC-TOF.
Defect Properties of Cathode Deposited Glow Discharge Amorphous Silicon Germanium Alloys
Authors: Zhong Fan , Chen Chih-Chiang , David Cohen J. , Wickboldt Paul , Paul William 
Published: April 2011

ABSTRACTWe have characterized the deep defect densities and their energy distributions for a series of a-Si1-xGex:H alloys with large Ge content (0.57< × < 1.00) prepared by the cathode deposited glow discharge method. Our results indicate markedly superior properties for these samples. A small Urbach tail slope (about 45meV) was found for all samples in this alloy range. The defect densities were either obtained directly from the drive-level capacitance profiling or deduced from the sub-band-gap optical spectra. Both are substantially lower than the trend line determined from previous studies of a-Si1-xGex:H samples produced by conventional glow discharge and by Photo-CVD methods. However, the relation between the total defect densities and the optical spectra in the cathodic samples obeys the same defect formation model that has been used to successfully predict the defect densities in other types of a-Si1-xGex:H material.
Wide GAP a-SiC:H Alloys for Novel Photovoltaic-Electrochromic Window Coatings
Authors: Bullock John N. , Xu Yueqin , Benson David , Branz Howard M. 
Published: April 2011

ABSTRACTSelf-powered “smart” windows utilize an electro-optic transmittance modulator based on electrochromic (EC) thin films that exhibit reversible and controlled changes in optical properties with an applied voltage between 0.7 and 2.0 V. Existing window designs require an external electrical connection, which may be economically unfeasible. This problem is solved by the tandem photovoltaic-electrochromic device, in which a wide-gap amorphous silicon-based alloy photovoltaic device is deposited together with an electrochromic optical transmittance modulator in a monolithic device on a single substrate. In this paper, we discuss our proposed monolithic photovoltaic-electrochromic device.We also present studies of transparent, wide-gap (1.8 to 2.2 eV) amorphous silicon-carbon thin films and p-i-n devices designed for use in the photovoltaic-electrochromic device. These photovoltaic cells can operate at low current (<1 mA/cm2) because a total injected charge of only 60 μC/cm2 will darken the EC layer to a visible transmission of 5%, but they need a high open-circuit voltage (>1.0 V) and high transparency (≈70%). We present our progress toward these design targetxxss.
Deposition of Polysilicon Films by Hot-Wire CVD at Low Temperatures for Photovoltaic Applications
Authors: Puigdollers J. , Bertomeu J. , Cifre J. , Andreu J. , Delgado J. C. 
Published: April 2011

ABSTRACTPolysilicon (poly-Si) thin films have been obtained using hot-wire chemical vapor deposition (HWCVD) from silane-hydrogen mixtures. The films were prepared at low substrate temperatures (down to 200°C) and at very high deposition rates (up to 40 Å/s). They showed good crystalline properties and no amorphous phases were detected. The films can also be efficiently doped by adding diborane or phosphine to gas phase. In this paper, an overview of the properties of the poly-Si films, intrinsic and p and n-doped, deposited at our laboratory by HWCVD is presented and discussed. The properties of the material and the features of the deposition technique which are interesting for their application in photovoltaics are emphasized.
Application of the Defect Pool Model in Modelling of a-Si:H Solar Cells
Authors: Zeman Miroslav , Tao Guoqiao , Trijssenaar Marcel , Willemen Joost , Metselaar Wim , Schropp Ruud 
Published: April 2011

ABSTRACTThe increasing complexity of hydrogenated amorphous silicon (a-Si:H) based solar cells requires continuous extending and testing of the computer models which are used for their simulation. The calculation of the defect states density in the bandgap of a-Si:H based on the defect pool model (DPM) has been rally implemented in the ASA (Amorphous Semiconductor Analysis) computer program developed at Delft University of Technology. We used the technique of inverse modelling to verify the DPM and to calibrate it by fitting the dark and illuminated J-V characteristics of a single-junction a-Si:H solar cell fabricated at Utrecht University. The DPM was also used in simulating the absorption coefficient of a-Si:H layers. Using the DPM for the defect states distribution, a good agreement between simulated and measured data was obtained. The values of the material parameters needed for obtaining the best fits are more realistic than using a conventional model for the defect states distribution.
A Totally Wet Etch Fabrication Technology for Amorphous Silicon Thin Film Transistors
Authors: Miri Amir Masoud , Chamberlain Savvas G. 
Published: April 2011

ABSTRACTWe developed a totally wet etch processing technology for the fabrication of inverted staggered amorphous silicon thin-film transistors (TFTs) and circuits. In this technology we take advantage of highly etch selective KOH and HF base solutions for amorphous silicon and silicon nitride layers. Our technology is simple, reproducible, fully compatible with positive photo-resist lithography techniques, and suitable for mass production of amorphous silicon TFT based circuits. Using this process, we fabricated thin film transistors which have an effective mobility of 0.83 cm2 V−1 s−1, threeshold voltage of 2V and on/off current ratio of 107. In this paper we discuss the details of our fabrication process and report on the chemical conditions of the etching and deposition processes.
Excimer Laser Annealed Poly-Si TFT Technologies
Authors: Okumura Fujio , Sera Kenji , Tanabe Hiroshi , Yuda Katsuhisa , Okumura Hiroshi 
Published: April 2011

ABSTRACTThis paper describes the excimer laser annealed (ELA) poly-Si TFT technologies in terms of excimer laser annealing of Si films, the leakage current, and the TFT stability. A laser energy density and a shot dependencies of TFT characteristics was analyzed by TEM, SEM, and Raman. The mobility increases with increasing not only the energy density but also the shot density. The mobility increase with the energy density is due to the grain size enlargement. On the other hand, the mobility increase up to 10 to 20 shots is due to a decrease of defects, including small grains, grain boundaries and defects inside grains. The contribution of grain-growth is small. The ELA TFT has a micro-offset structure to reduce the leakage current. Moreover, we have proposed a dynamic leakage current reduction structure. The combination of these technologies provides a sufficiently small leakage current for AMLCDs. The stability of the gate insulator was analyzed. The TFT shows negative threshold voltage shift under gate bias stress. This is due to water penetration and the subsequent field activated chemical reaction in the gate insulator. The dissociation of Si-OH bonds with hydrogen-bonded water was a fundamental contributor. The shift was suppressed sufficiently by hydrogen passivation. Obtained ELA TFTs;s have mobilities of over 100 cm2/Vsec, threshold voltages of less than 3 V, effective leakage currents of less than 10−13 A, and are stable more than 10 years.
Defect-Engineered Graded GexSi1-x Buffers on Si (001) with Extreme Low Threading Dislocation Density
Authors: Kissinger G. , Morgenstern T. , Morgenstern G. , Erzgräber H. B. , Richter H. 
Published: April 2011

AbstractStepwise equilibrated graded GexSii-x (x≤0.2) buffers with threading dislocation densities between 102 and 103 cm−2 on the whole area of 4 inch silicon wafers were grown and studied by transmission electron microscopy, defect etching, atomic force microscopy and photoluminescence spectroscopy.
A Study of Gettering Efficiency and Stability in Czochralski Silicon
Authors: McHugo Scott A. , Weber E. R. , Mizuno M. , Kirscht F. G. 
Published: April 2011

AbstractGettering efficiencies and stabilities of internal gettering sites for metallic impurities in high and low carbon doped silicon have been compared with ramped and standard two-step pre-annealing conditions. This study was intended to compare two proposed techniques to shorten the long low temperature nucleation step in the standard Hi-Lo-Hi internal gettering site formation treatment. Specifically, we compare the affect of carbon and a ramped annealing sequence on oxygen precipitate formation and gettering effectiveness. Our results show both techniques accelerate oxygen precipitation, however, only the low carbon ramped materials produced efficient and stable gettering sites. The high carbon materials did not with either annealing treatment. This disparity in performance is due to a difference in the oxygen precipitate’s strain field. The precipitates in the low carbon material possessed a high strain field with strain-induced defects while in the high carbon material they were strain-free with no defects. These results indicate the strain stabilizes the gettered impurity such that the gettering rate is increased and stability is enhanced.
Hydrogen Passivation of Shallow Dopants in InP Studied by Photoluminescence Spectroscopy
Authors: Balasubramanian Sathya , Kumar Vikram 
Published: April 2011

ABSTRACTThe effect of hydrogenation on the photoluminescence (PL) of InP : Mg, InP : Zn and undoped n-InP is presented. An increase in the near band edge pl intensity due to passivation of non-radiative centers was observed in all the samples. A donor - acceptor pair transition was observed before hydrogenation in the InP : Mg sample and after hydrogenation in the InP : Zn sample due to the acceptor deactivation. In n-InP the enhancement of donor bound exciton after hydrogenation points to the absence of donor passivation.
Atomic Hydrogen in GaN
Authors: Neugebauer Jürg , Van de Walle Chris G. 
Published: April 2011

ABSTRACTBased on extensive first-principles total-energy calculations we study the electronic structure, atomic geometry and energetics of atomic hydrogen in cubic GaN. All charge states of hydrogen (H+, H0, H-) are examined. For H- the gallium tetrahedral interstitial site is energetically most stable. All other sites are much higher in energy, indicating a high diffusion barrier for H- in GaN. H+ favors positions on a sphere with a radius of ≈ 1 Å and a nitrogen atom in the center. Among these positions the nitrogen antibonding site is energetically most stable. An unexpectedly large negative-U effect (U = —2.5eV) indicates that H0 is unstable.
Inversion of Conductivity in p-Si after Ion Treatment
Authors: Buzynin Alexander N. , Luk–yanov Albert E. , Osiko Vyacheslav V. , Voronkov Vladimir V. 
Published: April 2011

AbstractThe results of electric parameters studies of silicon samples with unusual p-n junctions are presented. The junctions appeared after the treatment of homogeneous p-Si wafers by 1–5 keV energy argon ion irradiation at the temperature below 100°C and without doping by any n-type impurities. The model of this phenomena is discussed.
Probing Metal Defects in CCD Image Sensors
Authors: McColgin William C. , Lavine J. P. , Stancampiano C. V. 
Published: April 2011

AbstractWe have investigated the role of heavy metals in causing visible pixel defects in Charge Coupled Device (CCD) image sensors. Using a technique we call dark current spectroscopy, we can probe for deep-level traps in the active areas of completed image sensors with a sensitivity of 1 × 109 traps/cm3 or better. Analysis of histograms of dark current images from these sensors shows that the presence of traps causes quantization in the dark current. Different metal traps have characteristic dark current generation rates that can identify the contaminant trap. By examining the temperature dependence of the dark current generation, we have calculated the energy levels and generation cross sections for gold, iron, nickel, and cobalt. Our results show the relationship of these traps to the “white spot” defects reported for image sensors.
Electronic Properties of Ideal and Interface-Modified Metal-Semiconductor Contacts
Authors: Mönch Winfried 
Published: April 2011

AbstractBarrier heights in metal-semiconductor contacts may be modified by interlayers. The effects of atomic interlayers are due to interface dipoles. With the restriction to nearest-neighbor interactions and monovalent interlayer atoms, they may be described as interface molecules which consist of an interlayer and a substrate atom. If the interlayers are thicker than a few atomic layers their two interfaces with the metal and with the semiconductor will be non-interacting. Both types of interfaces are described by the model that interface-induced gap states determine the alignment of the bands and the electronegativity difference describes the charge transfer across the interface. The present paper discusses and analyzes experimental data for H-modified diamond and silicon, Al/Si/GalnP, and metal/ Si3N4/Si Schottky contacts.
High Temperature I-V and C-V Characteristics of a Al/n-GaAs/In Schottky Barrier Type Device
Authors: Singh A. , Marcano N. 
Published: April 2011

AbstractAl/n-GaAs Schottky barrier type diode was fabricated by thermal deposition of Al on chemically etched polished surface of (100) n-GaAs at a pressure of 4×10−6 Torr. Back ohmic contact to n-GaAs was prepared by thermal deposition of In, followed by a 90 min. anneal in Ar atmosphere at 390° C. The C−2 vs V characteristics were quite linear for reverse bias voltages in the range 0-4 V. Over the temperature range 300–360 K, the values of the barrier height and the net carrier density (Nd-Na), obtained from the C−2-V data, were in the range 1.33–1.26 V and 4.3×l0−16-5.0×l0−16 cm−3, respectively. The forward I-V data over the temperature range 300–400 K, indicated that the electrical current across the Al/n-GaAs Schottky junction was transported by the mechanisms of generation-combination (GR) in the space charge, thermionic emission (TE) and ohmic leak current. A value of (1.20±0.04) V for the zero bias barrier height was deduced from the temperature dependence of the TE reverse saturation current. The barrier height deduced from the I-V data was practically independent of temperature. The 20% change in Nd-Na with temperature, obtained from the C-V data, and important contributions of the GR and leak currents to the total forward current, suggested the presence of defect levels in the surface space charge layer in n-GaAs, which may be responsible for the discrepancy in the values of the barrier height obtained from the I-V and C-V data.
Reversible and Irreversible Light-Induced Change of Photoluminescence in Porous Silicon
Authors: Choi Suk-Ho , Mun Byoung-Hun 
Published: April 2011

AbstractWe have investigated the light-induced change of photoluminescence(PL) and its recovery in porous silicon. The exposure of the porous silicon to continuous laser light in vacuum results in the quenching of the PL intensity, which is almost fully recovered by simply keeping the samples in vacuum or in air at room temperature for a few days. When the light exposure is done in air, the PL spectra of the samples with initial PL peak at 800 nm are blue-shifted to the peak position at 740 nm and the samples with the initial PL spectrum peaked at 740 nm shows only a rise of PL intensity without any change of its peak position. Fourier transform infrared(FTIR) studies suggest that the light-induced change of PL in air is a irreversible process and occurs as a result of optically induced replacement of some of the Si-H bonds with O-Si-H bonds or adsorption of oxygen with hydrogen loss.
Bls Studies of Exchange Coupling in The Iron Whisker/Cr/Fe System
Authors: Cochran J.F. , Totland K. , Heinrich B. , Venus D. , Govorkov S. 
Published: April 2011

ABSTRACTBrillouin light scattering (BLS) and magneto-optic Kerr effect have been carried out on a series of specimens consisting of a Fe(001) whisker substrate upon which thin Cr(001) and Fe(001) layers have been deposited by means of molecular beam epitaxy in ultrahigh vacuum. The Fe film was 20 monolayers (ML) thick, and the Cr(001) films were grown having various thicknesses. It is demonstrated that BLS thin film frequencies measured in the saturated magnetic state with the thin film magnetization parallel with the applied magnetic field can be used to obtain the exchange coupling strength between the thin film and whisker magnetizations both for antiferromagnetic coupling and for ferromagnetic coupling, provided that the ferromagnetic coupling is not too strong. It is also shown that the coupling strength is extremely sensitive to the quality of the chromium growth: a small deterioration in the growth conditions has been found to reduce the exchange coupling by nearly a factor of two.
First Principles Calculation of Electrical Conductivity and Giant Magnetoresistance of ColCu Multilayers
Authors: Butler W. H. , Zhang X.-G. , Nicholson D. M. C. , Maclaren J. M. 
Published: April 2011

ABSTRACTWe show that the Kubo formula can be used to calculate the non-local electrical conductivity of layered systems from first principles. We use the Layer Korringa Kohn Rostoker method to calculate the electronic structure and the Green function of Co/Cu/Co trilayers within the local density approximation to density functional theory. This Green function is used to calculate the conductivity through the Kubo formula for both majority and minority spins and for alignment and anti-alignment of the Co moments on either side of the Cu spacer layer. This allows us to determine the giant magnetoresistance from first principles. We investigate three possibilities for the scattering in Co/Cu/Co: (1) equal electron lifetimes for Cu, majority spin Co, and minority spin Co, (2) equal electron lifetimes for majority and minority Co, weaker scattering in Cu and spin dependent interfacial scattering, (3) electron lifetimes for majority and minority spin cobalt proportional to their Fermi energy densities of states and spin dependent interfacial scattering.