bluuebunny/crossref_metadata_2025_split huggingface dataset:
Defects in Photo-Assisted CBE-Grown GaAs
Authors: Goodhew Peter J. , Beanland R. , Farrell T. 
Published: March 2011

ABSTRACTExcimer laser light has been used to achieve the maximum growth rate of GaAs in a chemical beam epitaxy system when temperatures were more than a hundred degrees below the normalgrowth temperature. Secondary electron and transmitted electron microscopy of material grown using laser assistance shows the presence of surface ripples aligned with crystallographic directions. Layers grown at the lowest temperatures using a high fluence of excimer laser light contain a high density of small dislocation tangles (>1011 cm-−2 ). Lower fluences have no effect on the microstructure of the material.
Competitive Pairing and the Chemistry of Coadsorbed Hydrogen and Halogens on Ge(100)
Authors: Yang Yuemei L. , Cohen Stephen M. , D'Evelyn Mark P. 
Published: March 2011

ABSTRACTThe chemistry of coadsorbed H and X (X=C1, Br) on semiconductor surfaces is important in epitaxial growth of silicon from chlorosilanes and of SixGe1−x alloys, in hydrogenating/ halogenating cycles in atomic layer epitaxy, and also provides an interesting model system, yet has received little attention to date. We have investigated the interaction of HC1 and HBr with Ge(100) by temperature-programmed desorption, and find that H2, HCl and HBr each desorb with near-first-order kinetics near 570–590 K and that GeCl2 and GeBr2 desorb with near-second-order kinetics near 675 K and 710 K, respectively. Analysis of the desorption kinetics of H2 and HX provides evidence that adsorbed H and X atoms pair preferentially in a qualitatively similar way as H atoms adsorbed alone on Ge(100)2×1 or Si(100)2×1 and that pairing of H+X occurs in competition with pairing of H+H.
Properties of Single-Crystalline SiC Films Grown on Si by Low-Pressure Chemical Vapor Deposition at 750°C
Authors: Golecki I. , Marti J. , Reidinger F. 
Published: March 2011

ABSTRACTMonocrystalline, epitaxial cubic (100) SiC films have been grown on (100) Si substrates at 750°C, the lowest temperature reported to date, by low-pressure chemical vapor deposition, using methylsilane, SiCH3H3, a single precursor with a Si:C ratio of 1:1, and H2. Hexagonal SiC films were obtained with the aid of a remote H2plasma, which also increased the deposition rate through a reduction in the activation enthalpy. The films were characterized by means of transmission electron microscopy, single- and double-crystal X-ray diffraction, infra-red absorption, ellipsometry, thickness measurements, four-point probe measurements, and other methods. Based on X-ray diffractometry, the crystalline quality of our β-SiC films is equivalent to that of commercial films of similar thickness. We describe the novel growth apparatus and the properties of the films.
Channel Layer Surface Modifications in a-Si:II thin Film Transistors With Oxide/Nitride Dielectric Layers
Authors: He S. S. , Stephens D. J. , Hamaker R. W. , Lucovsky G. 
Published: March 2011

ABSTRACTWe have fabricated normal and inverted staggered a-Si:H thin film transistors, TFTs, using silicon oxide/nitride double layer dielectrics. Significant improvements in the electrical performance of these TFTs have been obtained by integrating additional processingsteps into the usual processing cycles. These include; i) a pre-deposition nitridation ofthe a-Si:H surface for the top-gate devices, and ii) a post-deposition passivation of thea-Si:H surface (i.e., the back of the channel region) for the bottom-gate structures. Improvements in the electrical properties of the a-Si:H TFTs resulting from these additionalprocessing steps are discussed.
Chemical Beam Epitaxy of GaP Using Triethylgallium and Tertiarybutylphosphine
Authors: Kelliher James T. , Bachmann Klaus J. 
Published: March 2011

ABSTRACTIn this paper we report the growth of GaP/Si heterostructures by metalorganic chemical beam epitaxy (MOCBE), including information on a MOCBE system custom built for this work. The gallium source was triethylgallium and the phosphorus source was tertiarybutylphosphine. The range for GaP epitaxy is 260 <T< 375°C. Methods of characterization included scanning electron microscopy (SEM), Auger electron (AES), X-ray photoelectron (XPS) and Rutherford backscattering (RBS) spectroscopies.
Decomposition Kinetics of Tetraethoxysilane on SiO2
Authors: Todd Bradley G. , Hudson John B. , Wu Peter K-C. 
Published: March 2011

ABSTRACTThe decomposition of tetraethoxysilane (TEOS) on a thermally grown SiO2 surface has been studied using molecular beam scattering, with mass spectrometric detection and time of flight techniques. Decomposition was characterized over a range of temperatures from ambient to 1100 K using a mass spectrometer having a line of sight to the sample surface. Time of flight measurements were used to characterize parent and product species and to determine surface residence time. The initial step in the decomposition process at low temperatures is the loss of one ethoxy ligand to produce triethoxysilane, ethylene and possibly water as gas phase products. At temperatures above 850 K there is a change in the rate limiting process and an abrupt increase in the decomposition probability. Observed kinetics are explained in terms or an adsorbed molecular precursor mechanism.
Deposition, Annealing, and Characterization of Tantalum Pentoxide Films
Authors: Treichel H. , Mitwalsky A. , Tempel G. , Zorn G. , Kern W. , Sandier N. , Lane A. P. 
Published: March 2011

ABSTRACTFilms of tantalum pentoxide (Ta2O5) have been fabricated by use of different precursor materials, deposition techniques and annealing procedures. Several analytical methods were appliedto study the layers. Fundamental properties and new data are reportedand related to practical features that are of importance in device design and manufacturing of advanced, highly integrated devices. This overview may facilitate the choice of an optimal combination of precursor, deposition technique and corresponding annealing procedure for aspecific application of these films in microelectronics, since the electrical properties reveal the potential of Ta2O5 films for the use in 64Mbit and 256Mbit DRAM devices as high dielectric constant material.
The Deposition of Silicon Oxide Films by LPCVD at Temperatures as Low as 100°C from a New Liquid Source
Authors: Hochberg K. , Roberts David A. 
Published: March 2011

ABSTRACTA precursor for the LPCVD of silicon oxide films has been developed that extends the low temperature deposition range to 100°C. The chemical, 1,4 disilabutane (DSB), produces silicon oxide depositions similar to those of the higher temperature silane and diethylsilane (DES) processes. Optimum DSB processes require pressures below 300 mTorr, similar to silane, in contrast to DES pressures above 600 mTorr at 350°C. This results in poorer conformalities than those of DES, but the step coverages are still superior to those from silane oxides. The DSB films are low stress, carbon-free oxide layers that are suitable for temperature-sensitive underlayers and substrates such as photoresist, plastics, GaAs, and HgCdTe.
Chemistry at Polyimide-Metal Interfaces: In Situ FTIR Studies of Polymer Curing Processes and Thermal Stability
Authors: Lu Jiong-Ping , Volfson David , Trusell Fred , Jensen Klavs F. 
Published: March 2011

ABSTRACTWe report in-situ Fourier transform infrared (FTIR) reflection-absorption studies of curing chemistry of polyimide thin films on Crand Cu surfaces, and of the thermal stability of the resulting thin film interfaces when exposed to air at elevated temperatures. The polyimide investigated is based on 4,4'-(hexafluoroisopropylidene)bis(phthalicanhydride)-4,4'-bis(4-aminophenoxy)-biphenyl. The imidization process takes place at temperatures higher than 90°C anda small amount of anhydride is generated during curing. This by-product is converted to imide at temperatures above 250°C. Complete imidization is achieved after curing at 300°C on Cr substrates, while evidence for incomplete curing on Cu is observed under the same conditions. Thermal stability studies with Cr and Cu substrates show that thermal decomposition of thin (∼1000Å) polyimide filmsoccurs on Cu when the film is exposed to air at 200°C, while the polyimide is stable on Cr.
Large Area Plasma Enhanced Chemical Vapor Deposition of Nonstoichiometric Silicon Nitride
Authors: Kuo Yue 
Published: March 2011

ABSTRACTThis paper presents results on PECVD of low refractive index silicon nitride in a large area system. Film deposition characteristics, suchas deposition rate and thickness uniformity, were investigated over awide range of process parameters, such as gas composition, power, pressure, and N2 pressure. Film properties, such as RI, absorbance, stress, and etch rate, have also been studied. A general model, which includes both the deposition and etching mechanisms, has been developed to explain these results. This model could explain the film uniformity issue in the process.
Growth of Dielectric Thin Films by Irradiation of Condensed Molecular Precursors with Synchrotron Radiation
Authors: Strongin D. R. , Moore J. F. , Ruckman M. W. , Strongin M. 
Published: March 2011

ABSTRACTSpectroscopic evidence is presented that shows that boron nitride andaluminum oxide can be synthesized by exposing a condensed layer of molecular precursors to synchrotron radiation. In the A12 O3 circumstance a condensed layer of trimethylaluminum (TMA)and water at 78 K on a silver substrate produces pure layers of aluminum oxide. Using the same condensed layer technique boron nitride is produced by exposing a solid matrix of diborane and ammonia to synchrotron radiation. Near edge x-ray absorption fine structure and core level photoelectron spectroscopies are used to characterize the A12 O3 and BN layers, which were typically 30Å thick. During the formation of aluminum oxide the carbon component inthe alkylaluminum precursor is completely removed during irradiation as a volatile methane product which was detected by mass spectrometry. In the absence of synchrotron radiation the molecular precursors in both the aluminum oxide and boron nitride systems show evidence of some interactions within the solid, but upon warming to near room temperature (260 K) the layers desorb from the substrate.
Small-Angle X-Ray Scattering from Light Emitting Porous Silicon and Siloxene
Authors: Franz H. , Petrova-Koch V. , Muschik T. , Lehmann V. , Peisl J. 
Published: March 2011

ABSTRACTWe studied the microstructure of two types of light emitting porous silicon (PS), as-etched and rapid thermal oxidized and of material prepared according to the siloxene recipe by Small-Angle X-Ray Scattering (SAXS). In all three types of samples we found particles with nanometer dimensions. The average particle size in as-etched PS is ingood agreement with results achieved by TEM and X-ray diffraction. Shape analysis shows, that the PS skeleton consists of cylindrical shaped particles with an average heigth of 20Å and a diameter of 40 Å.
Fine Structure of Visible Light Emitting Porous Silicon
Authors: Nakagawa Kiyokazu , Nishida Akio , Shimada Toshikazu 
Published: March 2011

ABSTRACTPorous Si formed by anodization is studied by means of high-resolution scanning electron microscopy, optical microscopy, micro-photoluminescence spectroscopy, high-resolution transmisson electron microscopy, and micro-Raman spectroscopy. Surface morphologies of porous Si films are varied by changing the anodization conditions. High-resolution scanning electron microscopy measurements show that in all these films, porous Si fine structures of visible photoluminescent regions, which are confirmed with optical microscopy and micro-photoluminescence spectroscopy, are composed of particlelike structure of various sizes from several nm to several tens of nm. Transmission electron microscopy shows that these particles are composed of single-crystal Si spheres covered with an oxide layer. The peak of the Raman spectrum from the particlelike structure is shifted to lower energy and is wider than that for bulk Si, possibly due to lattice expansion around large surface fractions. These results suggest that the effective photoluminescence of porous Si is due to three-dimensional carrier confinement in quantum boxes.
Some Perspectives on the Luminescence Mechanism Via Surface-Confined States of Porous Si
Authors: Koch F. , Petrova-Koch V. , Muschik T. , Nikolov A. , Gavrilenko V. 
Published: March 2011

ABSTRACTWe elaborate on the explanation of radiative emission involving surface-confined states on the nanocrystallites of porous Si. After reviewing the evidence for the existence of such states, we give a model description of the origin of visible luminescence in porous Si. The model accounts for different spectral luminescence bands with distinct energies and relaxation times.
Microcrystallites in Oxidized Porous Silicon
Authors: Lehmann V. , Cerva H. , Jobst B. , Petrova-Koch V. , Kux A. , Muschik Andt. 
Published: March 2011

ABSTRACTRapid thermal oxidation of porous silicon leads to desorbtion of hydrogen from the inner surface and formation of a thin oxide layer. Despite this dramatic change in the chemical composition oxidized microporous silicon (miPS) shows photoluminescence (PL) in the visible region. This is contradictory to the idea that the observed PL originates from chemical compounds like siloxene or polysilane, which would require a certain stoichiometry. If silicon microcrystallites are still present in the oxidized miPS, the observed luminescence can be explained in terms of a quantum confinement effect. It is the purpose of this work to prove the existence of microcrystallites in oxidized miPS using electron microscopy and X-ray diffraction.
Light-Emitting nm-Size Silicon Using Electrochemical Anodization and Oxidation
Authors: Ito Toshimichi , Ohta Toshimichi , Motoi Kenji , Arakaki Osamu , Hiraki Akio 
Published: March 2011

ABSTRACTPorous silicon oxidized by thermal, anodic and plasma processes has been investigated mainly using transmission microscopy, ion scattering techniques for compositional depth analysis (including H) and photoluminescence (PL) measurements. Suitable thermal oxidation of PS can increases in PL peak energy: the largest peak energy attained in the present study is 2.6eV (475nm). In the case of anodic oxidation, PL excitation spectra measured suggest the presence of some effect other than the quantum confinement effect at the initial oxidation stage while the latter may be effective at the subsequent anodic oxidation stage and in the thermal oxidation process. Electroluminescence was also observed from the oxidized porous silicon.
Effects of Surface Treatments on the Photoluminescence of Porous Si and a Suggested Mechanism for the Photoluminescence
Authors: Yamada Masao , Kondo Kazuaki , Sasaki Takae , Takazawa Akira , Tamura Tetsuro 
Published: March 2011

ABSTRACTWe report how vacuum annealing and dry oxidation affect the photoluminescence (PL) properties of porous Si. Vacuum annealing weakens the intensity of as-prepared porous Si, whereas, oxidation using dry oxygen at 5 Torr increases the intensity remarkably above 800 °c. Blue shifts as large as 100 nm are also observed for temperatures between 800 °C and 1000 °c. The photoluminescence decay patterns of both as-prepared and dry-oxidized porous Si excited by a nitrogen laser pulse are not exponential, but are fitted well by two exponential decays with lifetimes ranging from a few nanoseconds to over 100 nanoseconds. Further, those decay patterns do not change with changing excitation power by more than three orders of magnitude. These studies suggest that (l) hydrogen termination (with some fluorine termination) on the porous Si surface is not always necessary to get photoluminescence, (2) low surface defect densities are essential to increase the photoluminescence intensity, and (3) the radiative recombination path is not a direct interband transition, but, due to quantum size effects, it may go through some luminescence centers lying In the widened band gap.
The Role of Si-H, Si-H2 and Oxygen in the Photoluminescence of Porous Si.
Authors: Lavine J. M. , Bellezza A. J. 
Published: March 2011

ABSTRACTWe have observed no correlation between the presence or absence of the FTIR spectral lines at 669 and 2089 cm-1 (Si-H) and at 912 and 2112 cm-1(Si-H2) and the photoluminescent output of porous Si. We have observed no correlation between the presence or absence of PL output and the growth of the Si-O-Si line at 1105 cm-1. As a result we suggest that surface passivation plays no role in the PL output. We also suggest that the growth of the Si-O-Si line at 1105 cm-1under photo-oxidative conditions results in the alteration of the backbone of a Si-backboned species and not in the attachment of O at the surface.
An Electrochemical Study of Porous Silicon
Authors: L'ecuyer J. D. , Farr J. P. G. 
Published: March 2011

ABSTRACTThe I-V and impedance characteristics of p and n-type silicon electrodes in HF solutions have been determined. Three different I-V regimes are observed, one of which is associated with the on-set of localized dissolution. The formation of porous silicon takes place via a surface state mediated charge transfer mechanism. The position of the main recombination-generation center is estimated at 400 mV above the valence band edge. Localized dissolution is initiated at or close to active adsorption sites. It is then favoured because of geometrical field enhancement effects. Porous silicon has a surface chemistry that can be significant in luminescence.
Luminescence Activation of Porous Silicon by Post-Anodization Treatment
Authors: Kux A. , Muller F. , Koch F. 
Published: March 2011

ABSTRACTWe prepare “nonluminescing” porous Si by electrochemical etching (50 mA/cm2 in 50% HF diluted 1:1 with ethanol) of 1 Ω(100) p-type wafers in the absence of light in order to study the subsequent luminescence activation by postprocessing. The treatments are: photochemical etching, ageing under ambient conditions, thermal oxidation. The study reveals remarkable inhomogeneities in the depth distribution of the luminescence and allows us to comment on the relative importance of particle size, spin density and chemical composition for the luminescence.
Intense RT Visible Photoluminescence from Anodized Amorphous and Nanocrystalline Silicon Films
Authors: Bustarret E. , Bruyere J. C. , Muller F. , Ligeon M. 
Published: March 2011

ABSTRACTHeavily Boron-doped micrometer-thick amorphous (a-Si:B:H) or nanocrystalline (nc-Si) silicon layers have been deposited on a variety of conductive substrates by the 50 KHz PECVD of SiH4 / B2H6 / H2 mixtures at 320°C. These films have been partially electro-oxidized in a HF solution and then anodically oxidized in water in a manner similar to that yielding luminescent porous monocrystalline silicon layers (PcSL). Although the anodized films are x-ray amorphous, they yield intense luminescence properties at room temperature very similar to those of anodically oxidized PcSL with a similar vibrational spectrum. In both anodically oxidized materials, aging is shown to improve the external quantum efficiency. In amorphous anodized layers, optical microscopy under UV excitation showed strongly luminescent strain-related heterogeneities (20 μ,m in diameter) connected by non luminescent channels. The incidence of our results on the current debate about the origin of visible room-temperature luminescence in porous silicon and Si:O:H systems is discussed.
Organic-Inorganic Junctions formed on Porous Silicon: Isolation of a Surface Configuration primary to the Luminescence Mechanism.
Authors: Cottrell T. R. , Benziger J. B. , Yee J. C. , Chunt J. K. M. , Bocarslyt A. B. 
Published: March 2011

ABSTRACTOrganic-inorganic junctions were formed between porous silicon and various conjugated conducting polymers, poly(3-methylthiophene) and polypyrrole. Schottky type barriers were observed between the conducting polymers in their doped state and p and n-type porous silicon. In their undoped state the conducting polymers behave like p-type semiconductors. Consistent with this, ohmic contacts were observed between undoped conducting polymers and p-type porous silicon while rectifying behavior typical of a p-n junction was observed for conducting polymers deposited onto n-type porous silicon. During characterization of the porous silicon substrate, an investigation of the surface chemistry revealed a strong correspondence between solution pH and the luminescence intensity of porous silicon. Surface titration experiments were performed on p and n-type porous silicon and the results indicate that a monoprotic surface acid with a pKa between 3–4 is a primary component in the luminescence mechanism of porous silicon.
Calculation of the Energy Spectrum of NANÖ-Meter-Sized Silicon
Authors: Gavrilenko Vladimir , Vogl Peter , Koch Frederick 
Published: March 2011

ABSTRACTA large number of experiments on porous silicon has reliably demonstrated that the onset of optical absorption is shifted to energies significantly above the band edge of bulk Si. This increased transparency of the small nanometer-sized crystallites with their H-covered surfaces is a fact that asks for theoretical interpretation. Handwaving arguments about quantum size effect can only be a qualitative guide.We present here a tight binding calculation of a Si slab with nanometer dimensions covered with hydrogen. This is a model system for one-dimensional confinement. We consider the effect on the electron energy structure, the total and local densities of states of Si covered with hydrogen in two phases: monohydride - Si : H (2×1) symmetric dimer, and dihydride phases - Si : Hi (1×1) A total energy minimization method in the framework of the self-consistent tight binding theory has been used to investigate the structural reconstruction of the Si -surface after the adsorption of hydrogen. We find, that the band gap of the slab covered with H on both sides (monohydride phase) shifts to higher energies (typically ∼1.8 eV for 1.16 nm thick slab). The adsorption of hydrogen removes all the electronic states from the gap for both phases investigated. In nanometer sized slabs the lowest electronic states in the conduction band are localized on the surface Si—atoms, in contrast to thicker slabs. We discuss the implication of this model calculation to light emission in porous Si.
Transport and Microstructure of Microcrystalline Silicon Alloys
Authors: Lucovsky G. , Wang C. , Williams M. J. , Chen Y. L. , Mauer D. M. 
Published: March 2011

ABSTRACTThe microstructure and electrical properties of μc-Si and μc-Si,C prepared by remote plasma-enhanced chemical-vapor deposition, PECVD, are reviewed. The microstructure has been characterized by transmission electron microscopy, TEM, infrared, IR, absorption and Raman scattering. The electrical properties were characterized by temperature-dependent dark-conductivity measurements. These studies have explained significant quantitative differences between the carrier transport properties of μc-Si and μc-Si,C alloys in terms of a band offset model for the interfacial potential steps between the amorphous and crystalline constituents of these material systems.
Highly Textured Microcrystalline Si-Thin film Fabricated by Layer-by-Layer Technique
Authors: Ishihara Shun-Ichi , He Deyan , Akasaka Tetsuya , Arak Yuzoh , Nakata Masami , Shimizu Isamu 
Published: March 2011

ABSTRACTMicrocrystalline silicon with high crystallinity was fabricated on a glass substrate at a rather low temperature (320 C) by alternately repeating the deposition of Si thin layer 10 nm thick from fluorinated precursors and the treatment with atomic hydrogen. Hydrogen content was reduced to 0.5 at% or less. According to the in situ ellipsometric observation, the sticking of precursors followed the reactions for the construction of the ordered structure with the aid of atomic hydrogen. In addition, the defects were passivated efficiently with the treatment down to 4×1016 spins/cm3. A marked improvement was simultaneously verified in the efficiency of the substitutional P-doping in the films fabricated by this layer-by-layer technique.