bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Impurities on the Kinetics of Nucleation and Growth in Amorphous Silicon
Authors: Roth J. A. , Olson G. L.
Published: March 2011

The effects of intentionally introduced impurities on the crystallization time, nucleation rate and crystallite growth velocity during solid phase random crystallization of amorphous Si thin films have been determined. Films deposited in UHV onto oxidized Si wafers were subjected to multiple energy ion implantation to introduce uniform distributions of P, B, As, O or F at 0.1–1.0 at.%. Crystallization times and growth velocities were determined over the temperature range 650 to 850°C from time-resolved reflectivity measurements, and nucleation rates were determined from these data using a classical, steady state nucleation and growth model. Strong impurity effects are observed: P, B and As all decrease the nucleation rate but accelerate the growth of crystallites, whereas both 0 and F retard growth while enhancing nucleation. The largest effects are for P, which reduces the nucleation rate more than 100 times at 1% concentration, and F, which increases the rate by roughly the same amount.
Surface Alloys of Icosahedral AlMnSi with Phason Distortions
Authors: Follstaedt D. M. , Knapp J. A.
Published: March 2011

The microstructures produced by electron-beam melting and by ion-beam mixing Al/Mn and Al/Mn/Si layers on Si substrates are examined. The treatments were found to incorporate Si from the substrate into the surface alloy. Several phases formed, depending on treatment, including α- and β-AlMnSi, μ-AlMn (epitaxial on Si{111}), and amorphous and icosahedral AlMnSi. The observed microstructures relate the novel icosahedral phase to other phases and elucidate its formation kinetics. Diffraction patterns from large icosahedral grains (up to 5 μm) show distortions in the position and shape of weak (but not strong) reflections, as predicted for phason defects in a quasicrystalline lattice, one of the structures proposed for icosahedral phases.
Ion Implantation and Annealing of Oxides
Authors: White C. W. , Boatner L. A. , Sklad P. S. , Mchargue C. J. , Pennycook S. J. , Aziz M. J. , Farlow G. C. , Rankin J.
Published: March 2011

Ion implantation damage and annealing results are presented for a number of crystalline oxides. In A12 O3, the amorphous phase produced by ion bombardment of the pure material first crystallizes in the (crystalline) γ phase. This is followed by the transformation of γ-Al2 O3 to α-A12O3 at a well defined interface. The activation energy for the growth of α alumina from γ is 3.6 eV/atom. In CaTiO3, the implantation-induced amorphous phase transforms to the crystalline phase by solid-phase epitaxy (SPE). ZnO is observed to remain crystalline even after high implantation doses at liquid nitrogen temperatures. The near surface of KTaO3 is transformed to a polycrystalline state after implantation at room temperature or liquid nitrogen temperature.
Mg Implantation and Characterization of Sapphire Surfaces
Authors: Jardine A. P. , Mukhopadhyay S. Mitra , Blakely J. M.
Published: March 2011

Mg ion-implantation of A12O3 wafers followed by air annealing at high temperatures was investigated as a way to provide bulk doped samples for studies of Mg surface segregation and its effect on surface mass transport. SIMS was used to analyse Mg concentrations in implanted and unimplanted near-surface regions and in the bulk. It was found that the concentration of Mg decreases dramatically with depth from both surfaces of an annealed wafer and is also observed in the bulk. These observations are attributed to bulk diffusion of the Mg combined with equilibrium surface segregation. Surface mass transport associated with the (1120) surface of an A12 O3 single crystal wafer doped and equilibrated by such a method was studied by the grating decay method; the Mg doped sample showed a decay rate in air higher than that in the undoped wafer by a factor of ∼ 2.4 at 1500°C.
Transient Enhanced Diffusion in B+ and P+ Implanted Silicon
Authors: Pennycook S. J. , Culbertson R. J.
Published: March 2011

We report the transient enhanced diffusion of supersaturated phosphorus in ion-implanted SPE grown Si. Precipitation proceeds rapidly to a metastable SiP phase, which can be converted to an orthorhombic form or redissolved by subsequent heat treatment. The effects are strongly temperature dependent, and consistent with the trapped interstitial model. The behavior of different dopants follows their relative interstitialcy diffusion coefficients. The results suggest that ion implantation induced point defects dominate over thermally activated point defects during low temperature and certain rapid thermal processing, controlling dopant deactivation and diffusion in crystalline or amorphous silicon, and can also affect the SPE growth rate.
Simulation Studies of Collision Cascades in Liquid in Targets
Authors: Loi D. Y. , Shapiro M. H. , Tombrello T. A. , Garrison B. J. , Winograd N.
Published: March 2011

Multiple interaction computer simulations have been used to determine the properties of collision cascades in liquid In targets induced by normally incident 5 keV Ar+ ions. Below the first atomic layer the cascade becomes Thompson-like relatively quickly. However, within the first atomic layer the angular distribution of moving atoms became forward peaked by 150 fs and remained so until,∼300 fs. Energy and angle resolved (EARN) spectra were calculated for the ejected atoms. The peak of the energy distribution shifted to lower energies at larger ejection angles, and the angular distributions became broader for lower energy particles. Both results agree with recent experimental data, and with a simple model proposed bg Garrison. Our results suggest that the detailed structure of the surface layer is very important in the sputtering process.
Atomic Beam Interactions with Silicon (111) Surfaces: A Molecular Dynamics Study
Authors: Dodson Brian W. , Taylor Paul A.
Published: March 2011

Low energy (5–20 eV) atomic beam-surface interactions have been studied using a molecular dynamics technique. Silicon atoms are directed at an unreconstructed (111) silicon substrate either perpendicular to the surface or at grazing angles of incidence from 10–35°. The Si-Si interaction is treated using an empirical many-body silicon potential so that the effects of covalent bonding are included. At general beam orientations relative to the surface, low energy atoms are rapidly adsorbed at the surface, whereas at higher energies they either bounce off the surface or penetrate into the substrate. However, when the surface component of beam momentum is parallel to a (100) symmetry direction, Si atoms, under certain conditions, are found to channel along the surface rows, resulting in very little local excitation of the surface geometry and only gradual energy loss. The vertical momentum is carried away by substrate lattice vibrations, and the particle is guided along the surface by interaction with the atoms making up the surface ‘half-channels’. This surface channeling effect offers considerable promise for delicate control of the beam-induced annealing/growth of non-equilibrium surface geometries, and thus for high-quality growth at low temperatures.
The Competition between Ion Beam Induced Epitaxial Crystallization and Amorphization in Silicon: The Role of the Divacancy
Authors: Linnros J. , Elliman R. G. , Brown W. L.
Published: March 2011

The transition from ion induced epitaxial crystallization to planar amorphization of a preexisting amorphous layer in silicon has been investigated. The conditions for dynamic equilibrium at the transition were determined for different ion species as a function of dose rate and temperature. The critical dose rate for equilibrium varies exponentially with 1/T, exhibiting an activation energy of ∼1.2 eV. Furthermore, for different ions, the critical dose rate is inversely proportional to the square of the linear displacement density created by individual ions. This second order defect production process and the activation energy, which is characteristic of divacancy dissociation, suggest that the accumulation of divacancies at the amorphous/crystalline interface controls the balance between crystallization and amorphization.
Annealing Kinetics during Rapid and Classical Thermal Processing of Laser and Implantation Induced defects in Silicon
Authors: Adekoya W. O. , Muller J. C. , Siffert P.
Published: March 2011

The annealing behaviour of electrically-active defects in-duced in virgin n-type silicon by-Nd-Yag Laser (1.6 J cm−2,0.53 μm) irradiation has been investigated with Deep Level Transient Spectroscopy (DLTS). The observed defects : E(0.32 eV), E(0.45 eV) and E(0.53 eV) are characteristic of laser treated silicon, and have been reported by a number of workers. Using a rapid thermal furnace at 600°C for durations between 10 and 60s, we have observed a linear decrease in the concentration of these defects, and for times T > 60s, they are seen to disappear. A similar result was obtained in studies carried out on both vir-gin and implanted p-type silicon. This is in sharp contrast to the classical furnace annealing which requires much longer du-rations (20–30 min) at the same temperature (600 °C) in order to obtain the same results. A study of the annealing kinetics for the E(0.32 eV ;σn = 8 × 10−16 cm−2) level between 500 and 650°C in steps of 50°C for the two processes confirms this tendency for all processing temperatures, and shows a difference in ac-tivation energy of practically the same order of magnitude as the ionization energy of the defect (i.e. = 0.31 eV). Induced defects in high temperature > 1000°C in rapid thermal processed (RTA) n-type Si, also annealed out after a further 600°650 °C, 60 s RTA treatment. These results suggest that defect annealing is not a purely thermal mechanism, and lend strong support to the idea of an ionization induced enhancement.
Sulfur Segregation in Ion-Implanted and RTA'd Silicon
Authors: Herring R. A. , Clearfield H. M.
Published: March 2011

The segregation of 6 Mev S-implanted Si during RTA between 700 and 1200 °C has been closely studied. A model has been proposed in which self-interstitial atoms induce S to segregate into the bulk Si at ∼700°C and vacancies induce S to segregate towards the implanted surface at the higher temperatures. The binding energy between the SIA and S has been measured to be ∼0.5 eV.
UV Photon-Assisted Refractory Metal Deposition
Authors: Kovall G. A. , Matthews J. C. , Solanki R.
Published: March 2011

We have been investigating deposition of tungsten and molybdenum films at lover temperatures than conventional CVD processes with the aid of ultraviolet photons. The photon source is a high intensity, medium-pressure mercury lamp. W and Mo films have been deposited from their respective hexacarbonyls. W films have also been obtained by photon enhanced reduction of tungsten hexafluoride. In all cases films were deposited over 75 mm diameter substrates, which included quartz, silicon dioxide, and silicon wafers. The deposition system, conditions and the properties of the photodeposited films are presented.
Microfabrication Technologies for Advanced VLSI Devices
Authors: Horiike Y. , Yoshikawa R. , Okano H. , Nakase M. , Komano H. , Takigawa T.
Published: March 2011

Recent progress in microfabrication technologies for advanced VLSI devices, such as 16M and 64MDRAM, is presented. First, an EB delineator with a vector-scanned VSB on a moving stage has been developed for printing 0.25 μm patterns employing PMMA, high dose exposure, and 50 KeV EB. Optical lithography also has been extended toward lower submicron geometry. A Krf excimer laser reduction projection system, using a quartz/CaF2 lens, resolves successfully 0.35 μm patterns. Ga field ion beam technology has been developed with new applications in fuse-cutting of redundancy and in optimizing sense amplifier by cutting transistor gates in the SRAM device. For fine line etching technology, collimated reactive ions produced by 10-3 Torr magnetron discharge achieves deep Si trench etching and tapered Al etching by using a polymer deposition process in addition to the original thin sidewall film. Finally, a damage-free excimer laser etching process has been developed which can etch n+ poly-Si with resist mask and with pattern transfer using an optics down to 0.5 μm and 0.9 μm resolutions respectively.
Laser Photochemical Vapor Deposition of Ge Films (300 ≤ T ≤ 873 K) from GeH4: Roles of Ge2H6 and Ge
Authors: King K. K. , Tavitian V. , Geohegan D. B. , Cheng E. A. P. , Piette S. A. , Scheltens F. J. , Eden J. G.
Published: March 2011

The photochemical growth of polycrystalline and amorphous Ge films on SiO2, GaAs and NaCl by photodissociating GeH4 with excimer laser radiation in parallel geometry is reported. For substrate temperatures (TS) below the pyrolytic threshold for GeH4 (553 K), two distinct regions of film growth are observed. In the 425< TS < 553 K range, the ultraviolet (UV) laser “seeds” the reactor with Ge2H6 which readily pyrolyzes at the surface, forming several monolayers of Ge which subsequently catalyze the pyrolysis of GeH4. The activation energy (Ea) in this region is the same as that for the normal CVD growth of Ge from GeH4 (Ea = 0.9 eV). If, however, the laser is pulsed throughout the film growth run, Ea falls by a factor of at least 2 and growth is observed for TS as low as 300 K. In this laser sustained region, film growth ceases in the absence of UV laser radiation. These results clearly demonstrate the ability of a UV laser to alter the reactor chemistry and dictate the species responsible for film growth.
Comparison of the Processes Induced by Mercury Lamp and ArF Excimer Laser Photoassisted CVD of a-Si:H Films
Authors: Fuchs C. , Fogarassy E.
Published: March 2011

We compare, in this study, the photoassisted processes for silicon deposition using both a low pressure mercury lamp and an ArF excimer laser for the specific case where the SiH4 gas is sealed in the reaction chamber.
Modelling of Hg(3P1) Photosensitization of SiH4 and Surface Reactions of the SiH3 Radical
Authors: Perrin Jérome , Biroekhuizen Ton
Published: March 2011

We present an experimental study and modelling of gas phase and surface processes involved in mercury-sensitized decomposition of SiH4, leading to hydrogenated amorphous silicon (a-Si:H) film deposition in a parallel plate reactor. The total surface reaction proabability β and the sticking probability s of SiH3 on a growing a-Si:H film are determined in the 40° – 350°C temperature domain. At 100°C β ≈ 0.1 ± 0.01 whereas s ≈ β/4 which reveals an intense radical recombination on the surface. Both β and s increase as a function of temperature. At 350°C β reaches 0.21±0.01. These results are interpreted by a precursor state model for SiH3 adsorption.
Stepwise Monolayer Growth of GaAs by Pulsed Laser Metal Organic Vapor Phase Epitaxy
Authors: Doi Atsutoshi , Aoyagi Yoshinobu , Namba Susumu
Published: March 2011

Atomic layer epitaxy (ALE) of GaAs by pulsed laser metal organic vapor phase epitaxy is reported. Suspension of Ga deposition at 100% coverage is an essential part of the growth mechanism for ideal ALE. This is achieved by a photo-catalytic decomposition of adsorbed trimethylgallium (TMG). Selective enhancement of the decomposition rate for adsorbed TMG on As, with no enhancement for that on Ga is the main reason for suspension of Ga deposition at 100% coverage. A decomposition rate for TMG on As which is about 100 times faster than that on Ga is estimated from a comparison between theory and experiment.
Alternative Reactants for the Laser-Assisted Deposition of Silicon Nitride on Metals.
Authors: Partridge Julian P. , Strutt Peter R.
Published: March 2011

An alternative approach is described for the laser synthesis of silicon nitride layers using relatively innoccuous, non-pyrophoric reactants such as hexamethyltrisilazane. The pyrolysis process produces 2000 A particles of silicon nitride and the reaction mechanisms are invesigated using infrared spectroscopic analyses. The morphology of the deposited layer is critically dependent on process conditions due to considerable differences in the coupling efficiencies of the nitride deposit and the underlying metallic substrate. The existence of a laser-generated plasma above the metal is discussed in the light of microstructural features observed.
The Role of Low-Energy Ion/Surface Interactions During Crystal Growth From the Vapor Phase
Authors: Greene J. E. , Rocketr A. , Sundgren J.-E.
Published: March 2011

Low-energy (often < 100 eV) ion bombardment during thin film deposition is commonly used in such diverse application areas as microelectronics, optical coatings, magnetic recording layers, and hard wear resistant coatings to modify the microstructure and microchemistry of films deposited by a variety of techniques (e.g. sputtering, primary ion deposition, plasma-assisted CVD. and accelerated-beam MBE). Ion irradiation has been shown to affect every phase of deposition including nucleation and growth kinetics, crystal structure and phase stability, the average grain size and degree of preferred orientation of polycrystalline films, the epitaxial temperature of single-crystal films, defect concentrations, elemental incorporation probabilities, surface segregation, and, hence, film properties. As discussed in this brief review, a detailed understanding of many of these processes is beginning to emerge. Effects such as trapping, preferential sputtering, enhanced diffusion, and collisional mixing have been used to interpret and, in some cases, model experimental results. Nevertheless, there are still large gaps in our knowledge of the role of ion bombardment on fundamental processes such as nucleation kinetics.
Reactions of Bare Silicon Cluster Ions: Prototypical Deposition and Etching Versus Cluster Size
Authors: Mandich M. L. , Reents W. D. , Bondybey V. E.
Published: March 2011

Prototypical silicon deposition and etching reactions have been observed in gas phase reactions of size selected bare silicon cluster ions at room temperature. Laser evaporation of bulk silicon just outside the ion cell of a Fourier transform mass spectrometer produces abundant positive and negative silicon cluster ions. These cluster ions are trapped inside the cell for subsequent study of their bimolecular reactivity with various neutral reagents. Deposition type reactions occur with silanes, e.g. CH3SiH3, and increase the number of silicon atoms in the cluster. Etching reactions occur in reactions with certain halogen or oxygen containing reagents. For example, NO2 and XeF2 react to destroy the silicon clusters by sequential loss of a silicon atom. Overall the reactivity of small silicon cluster ions correlates with chemistry which occurs at two distinct types of dangling bonds in the clusters: either a lone pair of electrons or a single unpaired electron.
The Kinetic Energy and Angular Distribution of Sputtered Polyatomic Molecules: Outline and Applications
Authors: Haring R. A.
Published: March 2011

Kinetic energy and angular distribution measurements give information about the emission mechanism of desorbed particles. For a sputtering mechanism, the energy and angular distribution is usually assumed to be of the form: Φ(E,θ)∝ E cosθ/(E+U)3 . This expression is valid for sputtered atoms and cannot be immediately applied to the sputtering of molecules, where the energy is shared between internal and external degrees of freedom. A model is presented for the kinetic energy and angular distribution of sputtered polyatomic molecules. The formalism is related to an earlier model for sputtered clusters by Können, Tip and De Vries [1]. It is assumed that the individual atoms of a molecule are given an initial momentum according to linear collision cascade properties. If the molecule does not dissociate, it is treated as an entity and carried as such through a planar surface potential barrier. The model shows a continuous transition from a fragmentation dominated behaviour at high kinetic energies to a collision-cascade-like behaviour at low kinetic energies of the sputtered molecules. The model is compared with experimental data on sputtering of Kr2, SiCl and SiF.
The Role of Single and Multi-Electron Excitations in Electron Stimulated Desorption
Authors: Avouris P H. , Bozso F. , Rossi A. R.
Published: March 2011

We investigate the nature of the electronic transitions which lead to the desorption of ions from adsorbate-covered metal and semiconductor surfaces. F+ desorption from F/Si occurs via a Knotek-Feibelman mechanism, while H+ desorption from H/Si and O+ from CO/metals involve multi-electron transitions. The desorption of CO+ from CO/metals and NO+ from NO/Si apparently occurs via a simple Menzel-Gomer-Redhead mechanism.
Laser-Chemical Deposition and Etching on the Metallization Level of Integrated Circuits
Authors: Johnson A. Wayne , Greenberg K. E.
Published: March 2011

Laser-controlled chemical deposition and etching techniques were used to modify integrated circuits. This work used a pulsed laser to initiate and control the etching, by chlorine gas, of aluminum conductors. New conducting paths were then formed by laser-chemical vapor deposition of highly-doped silicon from silane and diborane. Improved conductivity of laser-deposited connectors was achieved by the selective deposition of tungsten on the silicon. These techniques were used to “rewire” an integrated circuit allowing the full evaluation of the corrected circuit design.
Photopatterning of Metal Oxide Catalyst in Porous Glass
Authors: Luong John C. , Borrelli Nick F. , Schreurs Jan W. H. , Morse Dave L.
Published: March 2011

It is well recognized that Vycor brand porous glass impregnated with a photosensitive organometallic compound can be used to produce refractive index patterns upon photolysis [1–3]. For instance, a metal carbonyl such as Mn2(CO)10 adsorbed into the porous glass matrix has been used to photopattern high resolution phase gratings albeit with low diffraction efficiencies due to the low refractive index change (Δn) so produced [1].
A High Resolution TEM Study of In-Situ Surface Oxidation of Indium III–V Semiconductors
Authors: Smith David J. , Petford-Long Amanda K.
Published: March 2011

Electron irradiation of InP, InAs and InSb crystals within the electron microscope causes the crystallization of nearsurface amorphous material and the oxidation of bulk crystalline material. The material most commonly found in both regions is cubic In2O3, although small regions (< 5 nm) of the corresponding In-c 6mpound semiconductors are sometimes recrystallized. The observations are consistent with desorption of the anion species due to electron-beam-stimulated processes, with subsequent oxidation of residual In metal.
A Model for Silicon Dendrite Growth During Laser/Plasma Deposition from a Silane Discharge
Authors: Anderson Harold M. , Hargis Philip J.
Published: March 2011

A model for dendrite growths in polycrystalline Si films formed during laser/plasma deposition with a silane discharge and a pulsed KrF laser has been developed. The model assumes a thin (less than 10 nm) amorphous silicon (a-Si) film is deposited on a substrate prior to phase transformation due to laser heating. The observed dendritic structure of the overall polycrystalline Si films is attributed to Si crystals shooting from an excessively supercooled Si liquid bath. Supercooled liquid forms since the melting point for a-Si can be reached at relatively low KrF laser fluences. Latent heat evolved at the solid-liquid interface induces an interface temperature higher than that of the melt and the requisite negative temperature gradient for absolute bath supercooling. Since the formation of an undercooled liquid by fast melting a-Si is also an important first step in explosive crystal regrowth studies, these results may have important implications for crystal growth and transient annealing. A conical approximation model is used in this study to characterize the stability of the dendrite tip in terms of local temperature gradients, i.e., the degree of undercooling at the tip of the parabolic dendrite. The degree of undercooling and hence the tip radius appears to be significantly affected by small changes in the laser fluence. Stability criteria lead to a relationship between regrowth velocity, V, and the tip radius, R, of the form VR2= constant. The size and stability of the dendrite tip is determined from a balance between the destabilizing force due to thermal diffusion and the stabilizing capillary force. Based on the observed tip radii formed at laser fluences from 0.13 to 0.25 J/cm2, the model predicts regrowth velocities in a range between 2.0 and 20 m/s – values consistent with transient annealing studies of a-Si
Oxygen Exchange Phenomena in SIO2 During Microwave-Discharge Plasma Oxidation
Authors: Kimura Shin-Ichiro , Murakami Eiichi , Warabisako Terunori , Mitani Eisuke , sunami Hidho
Published: March 2011

The oxygen migration process during microwave-discharge plasma oxidation of Si is investigated using 18O as a tracer. The exchange phenomena between migrating oxygen and its counterpart in SiO2 are observed. When plasma grown oxide (Si 18O2) is further oxidized in 18O-enriched plasma. 18O is observed both at the SiO2 /Si interface and in the bulk of Si16O2. For the reversed case. i.e. Si18 O2 is oxidized in 18O plasma, the total amount of pre-existing 18O decreases. The suppression of 18O is more drastic in the surface region. These oxygen distributions indicate that oxygen migrates toward the interface accompanied by oxygen exchange.
Fine Line Patterning By Focused Ion Beam Induced Decomposition of Palladium Acetate Films
Authors: Harriott L. R. , Cummings K. D. , Gross M. E. , Brown W. L. , Linnros J. , Funsten H. O.
Published: March 2011

Fine conducting features have been produced on Si and SiO2 substrates by irradiation of spin-on palladium acetate, [Pd(O2CCH3)2]3 films with a submicron focused ion beam. The exposures were made with a 20 keV Ga+, focused to a 0.2 micrometer spot. Electrical conductivity measuremnents were made on the resultant features as a function of ion dose for linewidths of one and ten micrometers. The sheet conductivity in the two cases was comparable and increased dramatically in the dose range between 2×1014 and 5×1014 ions/cm2. The conductivity of the exposed lines was further increased after heating in a hydrogen atmosphere. Measurements of carbon and oxygen content indicate that even at the highest ion doses a significant amount of organic material remains. Results are compared to those for 2 MeV He+ and Ne+ broad beam exposures. Potential applications are also discussed.
The Composition and Interfacial Properties of Cvd Tungsten Films
Authors: Yang C. , Mehta S. , Davies P.
Published: March 2011

CVD tungsten has been under active investigation as a contact barrier, as a material for contact fill and via fill, and as an interconnect metal for VLSI applications [1].
Materials Surface Processing with Excimer Lasers
Authors: Elliott David J. , Piwczyk Bernhard P.
Published: March 2011

The continued reduction of VLSI circuit geometries together with increasingly higher levels of circuit integration create the demand for new circuit fabrication technologies. One of the limitations of current IC fabrication technology is the use of high temperature processing. High temperatures severely distort silicon wafers, causing loss of geometry control and a subsequent reduction of device yield. Excimer laser technology, at very short ultra-violet wavelengths offers the possibility of extremely low temperature processing, including the following major applications: Photoresist exposure, photoresist ablation over alignment marks, annealing and etching. In addition, applications in circuit personalization and fiber optics appear as very promising new applications for excimer laser technology in the electronics industry.
Electrical Characterization of Some Native Insulators on Germanium
Authors: Gregory O. J. , Crisman E. E. , Pruitt Lisa , Hymes D. J. , Rosenberg James J.
Published: March 2011

Preliminary characterization of two native insulators on germanium is reported. A technique for preparing oxide by a room temperature chemical technique (wet chemical oxidation) is described. Compositional data based on IR transmission and ellipsometry, as well as characteristics of MOS capacitors based on this film are given. Also, compositional and electrical characterization of nitrided atmospheric pressure oxides are reported here. These films have very low fixed charge and interface state densities, and show excellent potential for use as gate insulators in a germanium MOS technology.
Nanometer Lithography for Quantum Scale Devices
Authors: Cook Charles F. , Kwiatkowski Joseph H. , Smith Doran D. , Berkowitz Harry L.
Published: March 2011

Electron-beam lithography that has the capability of writing high-resolution nanometer features in semiconductors will be required to fabricate next-generation quantum scale devices, such as nanometer gate mini-FET's, lateral quantum-well arrays, or metal grid radiators,which have feature sizes from 100 nm (1000 A) to 15 nm (150 A). A Philips EM 420T scanning transmission, electron microscope (STEM) has been modified to write nanometersize features in gallium arsenide. For this STEM we have developed a high-speed beam blanker and pattern generator (PG) that is resist speed limited. The maximum writing field size is 100 by 100 micrometers; within this field size, the smallest addressable step is approximately 1.8 nm (18 A). A HP-9845 is used to supply data for the PG and for computer-aided design of the devices to be written. Pattern transfer from the resist to GaAs is completed by using the liftoff method. As a result of this capability, we have patterned more than one million dots in a prototype 80 by 80 micrometer solid state radiator. The dots have diameters down to 15 nm (150 A), which requires an e-beam writing time of less than 30 minutes.
Microfabrication of Field Emission Devices for Vacuum Integrated Circuits using Orientation Dependent Etching
Authors: Campisi G. J. , Gray H. F.
Published: March 2011

Vacuum integrated circuits and field emission (FE) devices with geometries on the micron and submicron scale have been discussed as alternatives to solid state devices for high speed and hostile environment application as well as for miniature electron sources for CRTs. These miniaturized vacuum devices have been developed on the basis of the advances in micromachining technology, i.e. orientation-dependent etching (ODE) of lithographically patterned silicon. This paper describes the ODE methods used to fabricate pyramidal electron emitter points 1.5 μm high, with radius of curvature of 20 to 100 nm from <100> silicon. In order to reduce operating voltages, an integral extraction electrode (grid) was fabricated by a self-aligned technique. With a single gate mask level the extraction and planar collector structures were fabricated on chip, to form a planar vacuum triode. The final mask step provided the flexibility for fabricating a variety of planar vacuum integrated circuit elements.
Scanning Tunneling Microscopy and Spectroscopy of Semiconductor Surfaces
Authors: Demuth J. E. , Hamers R. J. , Tromp R. M.
Published: March 2011

The principles of scanning tunneling microscopy and its application to study silicon surfaces are briefly reviewed. Scanning tunneling microscopy “topographs” contain both geometric information about the locations of atoms at the surface as well as about the charge densities of surface localized states. We describe procedures by which these two components can be distinguished so as to produce images of the surface electronic states with atomic resolution. This ability to spatially resolve the surface electronic structure provides new information to understand the local structure and nature of bonding, and in some cases can be used as a means to chemically image specific features of the surface.
Hot Electron Relaxation in Quantum Wells
Authors: Lyon S. A.
Published: March 2011

Hot electron relaxation in bulk semiconductors has been studied for several decades, but only through recent advances in crystal growth has it become possible to investigate the ther-malization of hot quasi-two-dimensional carriers in quantum wells. These same advances have opened the possibility of constructing various semiconductor devices which rely on hot electrons for their operation. We discuss experimental results on the energy relaxation of hot electrons in GaAs/AlGaAs quantum wells. The experiments make use of optical spectroscopy for determining the carrier distribution. In particular, steady-state hot photoluminescence measurements have been employed with modulation-doped quantum wells in order to minimally perturb the system by the photoexcited carriers. Both the relaxation of very energetic electrons and the cooling of a hot thermalized carrier distribution are considered. The quantum well results are compared to results from similar experiments with bulk GaAs.
Theoretical Considerations on the Growth of Metallic Crystalline Superlattices
Authors: Van Der Merwe J. H. , Braun M. W. H.
Published: March 2011

We deliberate on the conditions favorable to the growth of metallic crystalline superlattices (MCS) with (111) f.c.c./(110) b.c.c. interfaces. We use, with some motivation, equilibrium criteria (i) to justify the occurrence of the Kurdjumov-Sachs (KS) and Nishiyama-Wassermann (NW) orientations, and to show with analyses which also allow for elastic relaxation, that only the NW orientation that occurs at n.n. distance ratios in the interval 0.8 ≲ bf.c.c / ab.c.c ≲ 1.0 can yield the regular orientational relationships required for high quality MCS; ahd(ii) to show that, for the acquisition of the required smoothness of the interfaces, which is mainly determined by the growth mode - monolayer-by-monolayer (FM = Frank-van der Merwe) or island nucleation and growth (VW ≊ Volmer-Weber) mode - it is desirable to use material combinations with small surface free energy mismatch. Only then can VW growth (which inevitably occurs in each superlattice period) at relatively high supersaturation be FM-like and with low density of defects.
Structure Studies of Thin Amorphous Films by Synchrotron X-Ray Absorption and Analytical Electron Microscopy.
Authors: Heald S. M. , Tafto J.
Published: March 2011

We combine the techniques of EXAFS and XANES using synchrotron x-rays, and the corresponding techniques using electron energy loss spectroscopy (EXELFS and ELNES) to characterize and study the local atomic arrangement in thin amorphous films. These probes are complementary in that x-rays are best suited for absorption edges above 3 keV and electron energy loss spectroscopy for low energy edges, and thus this combination is very useful for amorphous materials containing both low and high Z elements. We use in addition transmission electron microscopy, electron diffraction, and electron energy loss spectroscopy in the low energy loss region. Results from amorphous T1O2 and amorphous SnO2 made by reactive sputtering are presented.
Anomalous Magneto-Optical and Magnetic Behavior in a Two-Dimensional Magnetic Semiconductor Superlattice MnSe/ZnSe
Authors: Lee D. , Chang S.-K. , Nakata H. , Nurmikko A. V. , Kolodziejski L. A. , Gunshor R. L.
Published: March 2011

The growth by molecular beam epitaxy (MBE) of ultrathin layer II-VI compound semiconductors with magnetic constituents has opened new possibilities in the study of both lower dimensional electronic and magnetic phenomena. Some aspects of the latter are presented here with the zincblende MnSe/ZnSe superlattice as the test system. Initial indicators suggest that interfaces play a key role in determining the magnetic character of the heterostructure.
Photo Effects in Doping Modulated Amorphous Semiconductors
Authors: Fritzsche H.
Published: March 2011

The persistent photoconductivity (PPC) observed between 200 and 400K in npnp doping modulated hydrogenated silicon (a-Si:H) having individual layer thicknesses between 200 and 600Å iS compared with similar effects in compensated a-Si:H and in amorphous silicon/silicon nitride multilayers. The thermal activation barrier against creation of PPC in these materials, the low quantum efficiency, and the very slow recombination at 300K and higher temperatures suggest the presence of special traps that are spatially or energetically removed from the excess majority carriers. The PPC is accompanied by strongly nonohmic effects which exhibit similar metastabilities and long decay times.
Effects of Indium on the Properties of N-Type CdS Thin Films Deposited by Spray Pyrolysis
Authors: Kim Y. T. , Park S. C. , Chung S. K.
Published: March 2011

Effects of the doping level of indium impurity on electrical and optical properties of the CdS thin films, prepared with solution-sprayed method have been studied. The density of free carriers can be raised to an order of magnitude higher than that of non-doped case by increasing doping level of indium up to 0.01mole-% while indium doping does not significantly change the mobility from its value in non-doped samples. The optical energy gap is decreased with increasing indium content while the thermal activation energy remains unchanged. The experimental results are discussed in terms of the self compensation and radiative recombination phenomena.
Optical Properties of Pseudomorphic InxGa1−xAs Quantum Wells
Authors: Anderson N. G. , Lo Y. C. , Kolbas R. M.
Published: March 2011

The luminescence properties of MBE-grown pseudomorphic InxGa1−xAs—GaAs quantum-well structures are examined as a function of photoexcitation intensity and temperature. The structures examined consist of single In0.28Ga0.72As or (isolated) multiple In0.16Ga0.84As pseudomorphic wells sandwiched between thick, unstrained GaAs confining layers. Low-temperature photoluminescence spectra for these samples, which range in quantum-well thickness from 17 Å to 50 Å, consist of a single feature attributable to transitions associated with n = 1 electron and j = 3/2, Mj = 3/2 > - hole states. Spectral widths of these peaks are very narrow (7–11 meV), even for a heavily spike-doped sample (Si, ND ∼ 1018 spike-doped at well center). Emission intensities for the quantum-well structures are studied as a function of excitation intensity over the range 3 × 102 ≤ Pex ≤ 6 x 1O4 W/cm2, and one of the samples (x = 0.16, 50 Å undoped wells) prepared as a laser structure is shown to support stimulated emission at an excitation intensity < 104 W/cm2. The excellent luminescence properties of these structures are shown to degrade rapidly with increasing temperature, with radiative efficiencies dropping more than two orders of magnitude over the temperature range 20K – 180K. One possible explanation for this behavior is proposed.
Properties of Gold Films on Aluminum Alloy Substrates Prepared by Ionized Cluster Beam Deposition Process
Authors: Hashimoto Yoichi , Maeyama Yoshitaka , Machida Kazumichi
Published: March 2011

The deposition of gold film onto aluminum alloy substrate was attempted by the Ionized Cluster Beam(ICB) deposition process. The adhesive strength, reflectivity, and geometrical accuracy(conformance to specifications) were evaluated for the films deposited under various acceleration voltages and substrate temperatures. The film-substrate interface was examined by Auger electron spectroscopy and x-ray diffraction. A gold film with reflectivity of 99.2 % and an adhesive strength of over 4–0 N/mm2 was obtained by ICB deposition at room temperature. It was established that a high adhesive strength can be achieved by ICB deposition even if a surface oxide layer on the substrate remains.
Defects in Superlattices Under Pressure
Authors: Hong Run-Di , Jenkins David W. , Ren S. Y. , Dow John D.
Published: March 2011

We report theoretical calculations of deep levels in GaAs/AlxGa1−xAs superlattices under hydrostatic pressure. We predict phase diagrams for DX centers: for a given composition x there is a function p(a), which relates pressure p and GaAs quantum-well width a, and defines a phase boundary between two regions: one in which DX is a deep trap in the fundamental band gap and another in which the DX deep level lies in the conduction band.
The Effects of Surface and Interface Depletion Regions on the Photoconductivity of a-Si:H in Surface Cell Structures
Authors: Parsons GN , Kusano C , Lucovsky G
Published: March 2011

We have studied the optical, electrical and photoelectronic properties of a-Si:H thin films in surface cell structures. We have concluded that upward band bending in the form of depletion layers at the film surface and film oxide glass interface causes the electrical properties to display a thickness dependence. We find that the measured values of the quantum efficiency, mobility, lifetime product, hereafter nuT, also displays a thickness dependence. We show how the limiting bulk values for nuT and other electronic properties can be determined.
The Growth of Silicon Oxide Films by Remote Plasma Enhanced CVD
Authors: Tsu DV , Lucovsky G
Published: March 2011

We have grown films of silicon oxide by remote Plasma Enhanced CVD (remote PECVD). By changing the fraction of O3 in a plasma excited O3/He mixture that is mixed with a fixed flow of SiH4 diluted with Ar, we can deposit films which are either Si-rich, stoichiometric or Si-deficient. These changes are accompanined by differences in the incorporation of bonded hydrogen which occurs in SiH groups in Si-rich films and SiOH groups in Si-deficient films.
Enhancement of Photocarrier Lifetime Due to Charge Separation in a-Si:H/a-Ge:H Superlattices
Authors: Wronski C. R. , Tiedje T. , Abeles B.
Published: March 2011

The lifetime of photogenerated electrons in a-Ge:H/a-Si:H multilayer structures with layers about 100Å thick, is enhanced by two orders of magnitude above the value in bulk a-Ge:H. This lifetime enhancement effect is explained by charge separation produced by layers, due to the assymmetry in the conduction and valence band offsets at the interfaces. The peak in the electron lifetime as a function of superlattice periodicity is determined by a trade-off between the electron tunneling rate into the a-Si:H barriers and electrostatic repulsion of holes due to photo-induced space charge.
Photoacoustic Measurement of a-Si:H/a-SiNx:H Superlattice Films
Authors: Xiaomei Feng , Hsiangna Liu , Zhichao Wang , Shuye Qiu , Yuliang He
Published: March 2011

Photoacoustic (PAS) and optical transmission spectra were measured on a-Si:H/a-SiNx:H superlattices. The absorption coefficient ∝ in the range 102∼104 cm-1 was obtained by converting the PAS signal to ∝. The enhancement of the PAS peak intensity Qs and the increase in the width of the Urbach edge with decreasing a-Si:H layer thickness are explained as results of quantum size effect in the superlattice structure.
Evaluation of Commercially Available Transformation Toughened Zirconia
Authors: Swab Jeffrey J.
Published: March 2011

Transformation toughened zirconia (TTZ) is a material being considered for use in advanced heat engines. However, at elevated temperatures TTZ materials undergo a phase transformation fron tetragonal to the monoclinic with an associated volume increase of approximately 5%.This transformation results in a loss of strength and fracture toughness. Six commercially available Japanese TTZ materials and one experimental domestic grade were examined for the extent and effect of this phasetransformation after exposure to elevated temperatures (1000 to 1200°C) for times of 100 and 500 hours. Tests completed to date show that all the TTZ materials examined transform and lose strength, but to various degrees. Strength losses after heat treatment at 1000°C for 100 and 500 hours, ranged from a high of 60% to as little as 7%. Additional heattreatments of 500 hours at 1100 and 1200°C were carried out on TTZ's whichhad strength losses of 15% or less after exposure to 1000°C.

Although the major thrust of this program is to examine the effects of high temperatures on TTZ materials, a preliminary examination of the effects of low temperatures on the properties is also being done. A small number of specimens are undergoing treatments at 200°C and ∼.8 MPa water vapor pressure for 50 hours. Early indications are that strength greatly reduced after this treatment.
Weibull Modulus of Toughened Ceramics
Authors: Kendall Kevin , Alford N. McN , Birchall J. D
Published: March 2011

The influence of toughness on the Weibull modulus of ceramics is discussed. It is shown that an increase in toughness does not give a higher Weibull modulus if the ceramic is truly brittle, following the Griffith criterion of fracture. However, R curve behaviour, such as that shown by tetragonal zirconia, by Dugdale material, or by fibrous ceramic composites, leads to an improved Weibull modulus. Theoretical argument and experimental results support these conclusions.
Erosion of a Silicon Carbide Whisker Reinforced Silicon Nitride
Authors: Morrison C. T. , Routbort J. L. , Scatitergood R. O.
Published: March 2011

The steady-state solid particle erosion behavior of hot-pressed Si3N4 reinforced with 0, 10, and 20 weight percent SiC whiskers has been investigated at room temperature using angular alumina particles (63 to 270 μm diameter) as the erodent. The impact angle was varied from 30 to 90 ° and particle velocities were varied from 80 to 140 m/s. These materials were found to be very erosion resistant. However, there was little effect of the SiC whisker reinforcement on either the absolute erosion rate or on the velocity or particle-size exponents for the rates.The lack of a fiber reinforcement effect occurs even though the fiber additions provide an increase in the fracture toughness at high fiber contents. Results on differently processed Si3Na4 .base materials showed that microstructural variations due to processing history have very significant influence on the erosion resistance of the base (matrix) material. The results substantiate the idea that microstructure plays an important, but not fully understood role in the erosion processes for brittle materials.
On Prevalent Whisker Toughening Mechanisms in Ceramics
Authors: Evans A. G. , Rühle M. , Daigleish B. J. , Thouless M. D.
Published: March 2011

Some aspects of whisker toughening are reviewed. It is shown that several important toughened materials have a toughness dominated by the nonlinear bridging of intact whiskers. Such toughening is demonstrated to depend sensitively on the relative fracture resistance properties of the whiskers, the interface and the matrix. It is also shown that, when the interface fracture resistance is low, the frictional sliding behavior of the previously debonded interface and the whisker strength distribution exert a major influence on toughness, in accordance with pull-out phenomena.
Processing and Creep Performance of Silicon Carbide Whisker-Reinforced Silicon Nitride
Authors: Porter John. R. , Lange F. F. , Chokshi A. H.
Published: March 2011

Silicon carbide whisker reinforcement can significantly reduce creep rates in polycrystalline alumina [1], but the system SiC/Al2O3 is thermodynamically unstable in air and oxidizes to mullite during creep testing [2]. The system SiC/Si3N4 was investigated as a potentially more stable, high temperature structural composite. Silicon carbide whiskers were successfully incorporated into a silicon nitride matrix doped with alumina and yttria. Processing involved mixing dispersed slurries of silicon carbide and silicon nitride, adding the dopants as a solution of their nitrates and subsequently increasing the pH to precipitate the additive hydroxides. The resulting slurries were filter pressed at room temperature and hot pressed at 1650°C in graphite dies to full density. X-ray diffraction and transmission electron microscopy confirmed the presence of β-Si3N4, α-SiC and trace quantities of α-Si3N4, confirming that the α-β Si3N4 reaction occurred. An additional, as yet unidentified, minor phase was also detected.

Whisker reinforcement was shown to increase the room temperature flexural strength and fracture toughness but high temperature creep performance was unaffected by whisker reinforcement.