bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Reaction Mechanisms Governing the Selective Area Growth of III-V Compound Semiconductors by Chemical Beam Epitaxy
Authors: Davies G J , Skevington P J , Levoguer C L , French C L , Foord J S
Published: March 2011

Previous studies have helped elucidate the underlying mechanisms for selective area epitaxy in chemical beam epitaxy by investigating the reactions of triethylgallium (TEG) on a silicon nitride surface. However no explanation was produced as to why selective growth is lost at low temperatures or high Gp V beam fluxes. This question is addressed in this paper which examines the interaction between TEG and As2 on the silicon nitridesurface. In the absence of arsenic, TEG adsorbs with a low sticking probability on the dielectric. Adsorbed species mainly desorb rather than decompose, and any Ga produced on the surface becomes converted to a nitride form; no free Ga is produced hence GaAs growth cannot occur. Arsenic is found to form a weakly adsorbed phase on the nitride surface. Reaction with co-adsorbed TEG results in the formation of GaAs. Adsorbed As also is efficient in increasing the reactive sticking probability of TEG.The results provide further insight into the reaction mechanisms governing selected area epitaxy.
Aluminum CVD for Interconnect Thin Films
Authors: Speckman Donna M.
Published: March 2011

Aluminum thin films were deposited by chemical vapor deposition on SiO2 substrates using trimethylamine alane (TMAA) in a standard low pressure CVD reactor system, with argon as a carrier gas. Film quality and morphology were found to be a sensitive function of reactor flow dynamics. High purity films were obtained with resistivities of ∼5.0 μΩ-cm and grain sizes of 1–2 μm in diameter, but many of these films also exhibited aluminum whiskers, which caused VLSI processing problems. The CVD aluminum films exhibited conformal deposition over 0.5μm topographies, and also demonstrated electromigration lifetimes comparable to those of sputtered aluminum films. Aluminum films deposited using TMAA were also found to be selective at 90°C for titanium oxide.
Influence of a RF Plasma on the Nucleation of Aluminum Using N-Trimethylamine-Alane (TMAA) as Precursor
Authors: Weber A. , Bringmann U. , Schiffmann K. , Klages C.-P.
Published: March 2011

Aluminum films deposited on silicon with MOCVD methods generally exhibit a high surface roughness due to the hindered nucleation. To decrease the nucleation barrier a pretreat-ment of the wafer with TiCl4 vapor as a chemical activator is commonly suggested.

This work examines the influence of a rf hydrogen plasma on the nucleation of aluminum onSi and SiO2 using TMAA as precursor.

Atomic force microscopy (AFM) was used to determine the surface roughnesses and crystallite sizes of the aluminum deposits. Without plasma activation the nucleation barrier on Si(111) is substantially higher than on oxidized Si and therefore the pretreatment of the wafer plays an important role. The hydrogen plasma causes a substantial increase of the nucleus density leading to deposits with lower surface roughnesses compared to conventionalMOCVD aluminum. The influence of the substrate on the nucleation is almost “switched off” by the plasma activation and the grain sizes of Al on Si (111) and SiO2 differ only slightly. Relatively smooth films with a resistivity of 2.7 μΩcm are obtainable by employing a plasma activated nucleation step followed by a thermal MOCVD process. The increased nucleation rate is discussed in terms of kinetic effects of plasma activation.
Selectivity and Copper CVD From CuI β-Diketonates: Importance of Gas Phase Chemistry
Authors: Chiang C.-M. , Dubois L. H.
Published: March 2011

The gas phase chemistry of CuI(hexafluroacetylacetonateXvinyltrimethylsilane),Cu(hfac)(vtms), was investigated using molecular beam techniques. Mass spectrometric and infrared spectroscopic data clearly show that Cu(hfac)2 is produced at nozzle temperatures in excess of 500 K. This result suggests that Cu(hfac)(vtms) undergoes a thermally induced disproportionation reaction in the gas phase to yield CuII (hfac)2, vtms, and atomic copper. As a consequence, copper CVD from CuIβdiketonates is deprived of its inherent selectivity.
Reactor Issues Important for the Deposition of Selective Tungsten by Chemical Vapor Deposition Using the SiH4 Reduction of WF6
Authors: Kotecki David E. , Colgan Evan G. , Rose Alan
Published: March 2011

We have analyzed a single-wafer chemical vapor deposition (CVD) reactor used for the selective deposition of tungsten (W) by the silanc (SiH4) reduction of tungsten hcxafluoride (WF6). Results from a reactor model, which incorporates simplified heterogeneous reaction chemistry, arc compared to experimental data obtained from the same reactor to provide insight and understanding into reactor performance and define some of the trade-offs in the design of the reactor. A reactor for this process must provide: acold-wall temperature to suppress homogeneous reactions, a uniform wafer temperature to ensure uniform stress and resistivity in deposited films, and a uniform flux of SiH4 to the wafer surface to ensure uniform thickness of films. Maintaining a small internal volume in the reaction chamber was found to be beneficial for reducing both the quantity of rcactant gas at elevated temperatures and the residence time of the gas in the reactor, both of which lead to improved selectivity.
Defects in Photo-Assisted CBE-Grown GaAs
Authors: Goodhew Peter J. , Beanland R. , Farrell T.
Published: March 2011

Excimer 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

The 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

Monocrystalline, 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

We 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

In 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

The 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

Films 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

A 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

We 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

This 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

Spectroscopic 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

We 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

Porous 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

We 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

Rapid 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

Porous 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

We 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

We 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

The 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

We 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

Heavily 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

Organic-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

A 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

The 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

Microcrystalline 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.
Microstuctural Evolution and Substrate Selectivity in Pecvd μc-Si
Authors: Parsons Gregory N. , Boland John J. , Tsang James C.
Published: March 2011

We discuss a process for selective area deposition of microcrystalline silicon (μc-Si) using plasma enhanced chemical vapor deposition at low substrate temperature (<300°C) using time modulated silane flow in a hydrogen plasma. We discuss selectivity and deposition rate on a variety of substrates with process conditions important for manufacturing applications, and show a distinct microstructural evolution in the initial nucleation layers using Raman spectroscopy that correlates with the transition from selective to non-selective growth. Atomic hydrogen discriminates between different degrees of bond strain in the nucleii formed on different substrates, and can increase the crystallinity fraction in films deposited at low temperatures by modifying the kinetics of bulk-like bond formation.
Crystallinity Analysis of Amorphous-Crystalline Mixed Phase Silicon films Using Exafs Method
Authors: Wakagi Masatoshi , Kaneko Toshiki , Ogata Kiyoshi , Nakano Asao
Published: March 2011

The crystalline phase fraction (Xc) of amorphous-crystalline mixed phase Si films prepared by thermal annealing of a-Si:H films and by plasma CVD and chemical annealing methods was investigated by the EXAFS method. The EXAFS spectra of these films were represented by linear-combination of a-Si:H and c-Si EXAFS spectra. The values of Xc were analyzed by least-square curve fitting. The crystallinity was also analyzed by a Raman scattering method measured from both sides of the films. Then, the Xc values analyzed by the Raman method were calibrated by the EXAFS analysis results.
Modeling of Boron Diffusion in Polysilicon-On-Silicon Layers
Authors: Sultan Akif , Batra Shubneesh , Lobo Melvyn , Park Keunhyung , Banerjee Sanjay
Published: March 2011

In the present study we have modeled the diffusion of boron in single crystal silicon from an ion-implanted polysilicon film deposited on a single crystal silicon substrate. Modeling has been done for both BF2 and boron implants in the polysilicon layer. A new phenomenological model for a diffusivity has been implemented in the PEPPER simulation program using an effective concentration-dependent diffusivity approach. The effective diffusivities of boron in single crystal silicon have been extracted using Boltzmann-Matano analysis. The modeling has been implemented for a wide range of furnace anneal conditions (800°C to 950°C, from 30 min. to 6 hours), and implant conditions (BF2 doses varied from 5×1015 to 2×10'16 cm-2 at 70 keV, boron dose of 5×1015 cm-2 at 20 keV).
Raman Studies of Heavily Doped Polycrystalline Si Films Prepared by Excimer-Laser-Annealing of Doped a-Si:H
Authors: Savage M. E. , JaYamaha U. , Compaan A. , Aydinli A. , Shen Dashen
Published: March 2011

Extremely heavily doped polycrystalline silicon films were prepared by multiple-pulse XeCl excimer laser annealing of hydrogenated amorphous silicon films. The as-grown films used here included five types: intrinsic, boron-doped, phosphorous-doped, and carbon alloyed with and without boron doping. Raman studies reveal that the annealed films prepared from the boron or phosphorous doped a-Si:H have high carrier activation and display the interference lineshape (Breit-Wigner-Fano) of the discrete phonons (Si-Si and Si-B modes) interacting with the continuum of the single particle electronic Raman scattering. The Raman lineshapes indicate concentrations of ∼1 × 1021 cm3. This is confirmed by dark conductivities exceeding 100 S/cm in the annealed boron-doped and phosphorous-doped layers.
Si Film Growth by Supercooling of a Molten Si Alloy Film
Authors: Wallace R. L. , Yi J. , Anderson W. A.
Published: March 2011

A method is described for the deposition of large-grain polysilicon films at low substrate temperatures. This technique uses precipitation from a thin molten prelayer of Si-Au or Si-Au which is supersaturated with Si from a DC magnetron sputter gun. Typical growth temperatures are 600° C for the Si-Al layer, and 500° C for the Si-Au layer. Growth rates of 6 μm/hr have been achieved, though higher rates seem possible. Films of 20 μm thickness and grain size up to several hundred μm have been grown on SiO2 and sheet Mo substrates using Au and Al as the “solvent” metals. The proposed model for film growth was confirmed by cross-section EDS studies of the film/substrate interface. Film crystallinity was confirmed by etching studies, X-ray diffraction, and selected area diffraction. Preferential nucleation has been achieved using a patterned suicide forming metal (Cr,Ni) on RuO2, coated oxidized wafer. A loss mechanism of the solvent metal during growth was observed.
Polysilicon thin Films and Devices Produced by Low-Temperature (600°C) Furnace Crystallisation of Hydrogenated Amorphous Silicon (a-Si:H)
Authors: Dyer T. E. , Marshall J. M. , Pickin W. , Hepburn A. R. , Davffis J. F.
Published: March 2011

In this work, we report on the electronic properties of polysilicon thin films and devices realised via furnace crystallisation of undoped a-Si: H. The onset of crystallisation, degree of amorphisation and average grain size are determined by UV reflectivity and electron microscopy. Grain size is found to increase with decreasing a-Si:H substrate temperature, and a maximum areal grain size of 0.4μm2 is obtained. Optical absorption, DC conductivity and transient photoconductivity measurements are employed to examine carrier transport mechanisms. We observe a Meyer-Neldel relationship between the DC conductivity prefactor σ0 and activation energy Eσ. A plasma hydrogenation treatment of the as-crystallised films results in an order of magnitude increase in the DC conductivity and a similar increase in photoconductivity. This is consistent with a shift of the Fermi level position 0.06 eV towards the conduction band. Additionally, analysis of the transient photoconductivity infers a reduced density of states. We discuss the implications of our results for polysilicon TFT optimisation.
Phosphorus Glass Doping of Polycrystalline Silicon During Rapid Thermal Annealing
Authors: Hartiti Bouchaib , Slaoui Abdelilah , Stuck Roland , Muller Jean-Claude , Siffert Paul
Published: March 2011

We show that the use of phosphorus doped spin-on glasses as diffusion source is an attractive approach for the formation of shallow junctions in polycrystalline silicon materials. Moreover, this very simple doping process using a glass film can be fruitfully associated to rapid thermal annealing.
Crystallization of A-Si Films on Low-Melting-Point Glass Substrates
Authors: Park W. K. , Chae G. S. , Givargizov E. I. , Limanov A. B. , Kiselev A. N.
Published: March 2011

Results of experiments on crystallization of thin (50 to 200 nm) amorphous Si films initially deposited onto glass substrates by different techniques (PECVD, LPCVD) and treated by different lasers (argon, excimer, or Cu-vapor) are given. The films treated are characterized by in-plane and cross-sectional TEM, and by microdiffraction. Some conclusions about mechanisms of the crystallization are made.
GaAs Quantum Dots by MOCVD
Authors: Fukui Takashi , Ando Seigo
Published: March 2011

New GaAs quantum dots called tetrahedral quantum dots (TQDs) were fabricated using selective area metalorganic chemical vapor deposition (MOCVD). GaAs sub-micron crystals were completely buried in AlGaAs with single growth run without any processing damage at heterojunction interface. The substrates were SiO2 masked (111)B GaAs, which are partially etched free of SiO2 over triangular area using electron beam lithograpy and reactive ion etching techniques. First, truncated tetrahedral AlGaAs buffer layers with {110} facet sidewalls were grown in triangular area. Next, GaAs TQDs were sequentially grown on the top of AlGaAs. Finally, AlGaAs layers were overgrown on the resulting tetrahedral structures. The shape of GaAs tetrahedron was measured by an atomic force microscope(AFM). The size of bottom triangle of GaAs TQDs were estimated to be 20 nm. The size fluctuation was about 2%, which means that uniformity of selective area growth is excellent. Photoluminescence of GaAs TQDs buried in AlGaAs was measured at 8.5K. A clear emission peak from GaAs TQDs was observed at 810 nm. The energy shift from the GaAs emission peak is 19meV, which agrees well with the calculation. The results suggest that the selective area MOCVD method is very promising to fabricate GaAs quantum dots.
Two-Dimensional Damage Distributions Induced by Localized Ion Implantations
Authors: Faye M. M. , Laanab L. , Beauvillain J. , Claverie A. , Vieu C. , Benassayag G.
Published: March 2011

A general method is presented for calculating the spatial distribution of damage generated by localized implantation in semiconductors. Implantation through masks and focused ion beam implantation in GaAs are simulated and compared to cross-sectional transmission electron microscopy observations. An excellent agreement is obtained when a depth-dependent lateral straggle is considered. Arbitrarily shaped mask edges and different compositions for the mask and the substrate are included in the calculations as well as realistic current profiles of the ion spot in the case of focused ion beam implantations. Simulations and experiments clearly demonstrate the potential application of localized implantations to fabricate lateral quantum nanostructures.
A Scanning Tunneling Microscopy Study of Mbe-Grown GAAS(001)-Faceted Surfaces
Authors: Maboudian R. , Bressler-Hill V. , Wang X.-S. , Pond K. , Petroff P. M. , Weinberg W. H.
Published: March 2011

Scanning tunneling microscopy (STM) and reflection high-energy diffraction (RHEED) have been employed to investigate the morphology of faceted GaAs(001) surfaces grown by molecular beam epitaxy (MBE). The RHEED pattern monitored during the growth indicates that the faceting corresponds to (711)A planes. The STM images obtained on these surfaces reveal predominantly a (2×4) local ordering, although unusual (2×3) and (2×6) structures have also been observed. The atom-resolved imaging of the (2×4) structure indicates that the unit cell consists of two As dimers and two missing dimers, identical to the structure obtained on the flat As-rich GaAs(001)-(2×4) surface. Furthermore, islands on the surface are found to be anisotropie, with a shape anisotropy of about 4:1 for step A to step B. The anisotropy is explained in terms of the difference in step edge reactivity.
Luminescence Study of Wet Chemically Etched InP/InGaAs-Submicron-Structures
Authors: Jacobs B. , Zull H. , Forchel A. , Gyuro I. , Speier P. , Zielinski E.
Published: March 2011

We have investigated the optical properties of wet chemically etched InP/InGaAs-wires and dots with widths between 100 nm and 10 μm for different excitation densities. We observe that the non radiative recombination centers at the etched sidewalls can be saturated already at moderate excitation densities about 100 W/cm2. Avoiding saturation effects we obtain a surprisingly large sidewall recombination velocity of 107 cm/sec at 77 K. The comparison of wire and box structures shows that there is no significant difference in the quantum efficiency of both types of structures down to a geometrical size of 160 nm.
Preparation and Chemical Investigation of Porous Silicon
Authors: Poulin S. , Diawara Y. , Currie J. F. , Yelon A. , Gujrathi S. C. , Petrova-Koch V.
Published: March 2011

We have begun a systematic study of the chemistry of light emitting porous Si (LEPOS) using X-ray photoemission spectroscopy and time-of-flight elastic recoil nuclear scattering. The relation of chemical composition to preparation parameters and its evolution with rapid thermal annealing in N2:H2 and in vacuum were studied. The relation between chemical and photoluminescence properties and stability was investigated. The composition of LEPOS is extremely sensitive to preparation conditions and to subsequent treatment. The concentration of C and F in addition to Si, H and O vary with thermal treatment conditions and with time after preparation. However, preparation under the cleanest possible conditions increase both reproducibility and stability.
Magnetopolarons in Quantum-Well Wires
Authors: Wendler L. , Haupt R. , Chaplik A. , Hipólito O. , Osório F.
Published: March 2011

The interaction of quasi-one-dimensional electrons and longitudinal-optical (LO) phonons, placed in a perpendicular magnetic field is calculated. Results are presented for the polaron correction to the Landau levels and the polaron cyclotron mass.
Solution Precipitation of CdSe Quantum Dots
Authors: Kagan Cherie R. , Cima Michael J.
Published: March 2011

Synthesis of CdSe quantum dots with a high degree of monodispersity is achieved by nucleation from a supersaturated solution followed by growth to the desired particle size. The effects of temperature on the kinetic mechanisms of nucleation and growth were observed. A reaction vessel equipped with a low thermal mass internal heating element enabled controlled ramping of the solution temperature during the reaction. Nanocrystallite diameter is determined by the reaction time and the solution temperature during particle growth.

A method was developed to fabricate ∼1μm thick glass films containing ∼3 vol% CdSe quantum dots. A sol was prepared by mixing a silica organosol with a nanocrystallite dispersion of CdSe and was applied to amorphous quartz substrates by spin-coating. The sols were dried at elevated temperatures in a nitrogen atmosphere. Optical absorbance and fluorescence measurements of the glass film were used to characterize the optical properties of the embedded nanocrystallites. Comparison of the excitonic absorbance of the quantum dot dispersion and the doped glass film shows that particle monodispersity is maintained upon incorporation into the dielectric matrix. Stokes shifts in the band-to-band fluorescence relative to the film absorbance were measured. Shifts in the wavelength of the excitonic absorbance and fluorescence were observed upon incorporation of the quantum dots into the glass film and upon heat treating the glass film to elevated temperatures.
Photoluminescence Excitation Spectroscopy of Cd SxSe(1-x) Nanoparticles
Authors: Stokes Edward B. , Persans Peter D.
Published: March 2011

We present photoluminescence excitation spectra for glasses doped with CdSxSe(1-x). The peak of the emission spectrum is blue shifted toward the bandgap as excitation energy flux is increased. Total photoluminescence emission intensity is observed to be significantly enhanced and blue shifted by exciting with photon energies greater than ∼4 eV. A simple model of the nanoparticle band structure is presented to account for the observed spectra.
Nonlinear Optical Properties of Au Colloid-Doped Glasses
Authors: Kadono Kohei , Sakaguchi Toru , Wakabayashi Hajimu , Fukumi Toshio , Yamanaka Hiroshi , Miya Masaru , Tanaka Hiroshi
Published: March 2011

Degenerate four-wave mixing experiments have been performed for Au colloid-doped glasses prepared by melting and sputtering methods. The nonlinear optical properties of the glasses are discussed from viewpoint of the concentration of the Au colloid particles and the thickness of the glasses. We also discuss the dependence of the nonlinear properties on the pulse duration of laser for the measurements, and a very slow relaxation.
Characterisation of Polycrystalline thin Films of Tellurium
Authors: Ray A K , Hogarth C A , Swan R
Published: March 2011

Structural, electrical and optical characterisations were performed on tellurium film deposited under high vacuum conditions on ultrasonically cleaned Corning glass 7059 substrates. SEM and TEM studies reveal the polycrystalline nature of deposited tellurium films. At steady state high field conditions, space charge limited conduction is believed to have occurred due to the existence of a fast decaying density of trapping states in the energy gap. The DC conductivity is believed to exhibit a T-1/ law dependence below room temperature, giving a value of 2×10-l6eV/m3 for conduction states close to the Fermi level. From the power law dependence on frequency of AC conductivity, the barrier for bipolaron hopping is estimated to 0.33eV.Optical absorption in 9nm thick tellurium samples is due to direct transitions both allowed and forbidden producing two edges, the first one at 4eV and the other at about 0.5eV, respectively.
Deposition of Fluorine Doped Tungsten Oxide Thin Films by Atmospheric Pressure Chemical Vapor Deposition
Authors: Proscia James W. , Winter Charles H. , Reck Gene P. , Wen Gang Gang
Published: March 2011

Polycrystalline fluorine doped tungsten oxide thin films were deposited onto glass substrates by reacting tungsten hexafluoride, difluoroethane, and isopropanol. The reaction was performed in an atmospheric pressure chemical vapor deposition reactor at a temperature of approximately 400 °C. The electrical conductivity and spectral properties were suggestive of n-type substitutional doping in which oxygen is partially replaced by fluorine. Temperature dependent resistivity measurements were consistent with the presence of polarons. The films were blue in color with enhanced reflectance and absorbance in the IR. These optical characteristics are potentially useful in improving the solar control properties of glass. Scanning electron microscopy revealed a faceted surface morphology. The fluorine atom concentration decreased when the films were annealed in air.
Quantum Size Effect in Metal Coated Nanoparticles
Authors: Zhou H. S. , Honma I. , Komiyama H. , Haus J. W.
Published: March 2011

In this paper we report the synthesis of Au2S nanoparticles with a gold coating on the surface; the particles are characterized by transmission electron microscopy (TEM), electron diffraction and absorption data. The absorption spectrum is recorded during the gold coating growth process; this data demonstrates a large resonance shift during the growth process. The results are consistent with the growth of a metal shell around the particles; the theoretical model includes electron quantum confinement in the metal shell. The size dependence of the frequency shift, as well as the width of the resonance are consistent with the model.
Paramagnetic Nitrogen Defects in Silicon Nitride
Authors: Warren W. L. , Kanicki J. , Robertson J. , Poindexte E. H.
Published: March 2011

The photocreation mechanisms and properties of nitrogen dangling bonds in amorphous hydrogenated silicon nitride (a-SiNx:H) thin films are investigated. We find that the creation kinetics are strongly dependent on the post-deposition anneal; this thermal process can be described by a simple exponential function which yields an activation energy of 0.8 eV. The compositional dependence of the nitrogen dangling bond center suggests that its energy level lies close to the valence band edge, in agreement with theoretical calculations. This energy level position can explain why a-SiNx:H films often become conducting following a high post-deposition anneal.