bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoluminescence Studies of a Quantum Well Modulated by Faceting on Gaas (110) Surfaces
Authors: Tomiya S. , Reaves C. M. , Krishnamurthy M. , Wassermeier M. , Bimberg D. , Petroff P. M. , DenBaars S. P.
Published: March 2011

Step bunching during epitaxial growth results in the transformation of a vicinal surface into a periodic array of micro-facets. Molecular beam epitaxial growth on the vicinal GaAs (110) surface exhibits this phenomenon which has primarily been characterized by electron microscopy. GaAs quantum wells with AlAs barriers were grown on GaAs(110) substrates vicinal 0.5-2· towards [010]. The faceting on the vicinal surface creates two distinct quantum well thicknesses. While most of the quantum well is 96Å thick, it broadens at the faceted regions. This thickness modulation produces two distinct luminescence peaks. By using temperature dependent photoluminescence, we have observed trends in exciton mobility. The exciton mobility decreases at low temperatures for the 1.0° and 2.0° samples, indicating a scattering mechanism. We will discuss interface roughness and other sources of scattering.
Interfacial Atomic Structure in Heteroepitaxial β-SiC on TiC Substrates
Authors: Chien Fen-Ren , Nutt S. R. , Carulli J. , Buchan N. , Yoo W. S. , Mailloux P. M.
Published: March 2011

Thin epitaxial films of β-SiC were grown on (100), (111) and (112) TiC substrates and the interfaces were characterized by HREM. The (111) interface was abrupt and atomically flat, while the (112) interface was composed of {111} facets and steps. The (100) orientation did not result in epitaxial growth of SiC, a phenomenon attributed to the poor match of atomic positions in SiC and TiC on the (100) plane, although the lattice parameters are relatively close. A model for the atomic structure of the stable (111) interface is proposed based on comparison with HREM images of the interfaces.
Kinetic Roughening in Epitaxial Growth of Bcc (110) Films
Authors: Fritzsche Helmut , Gradmann Ulrich
Published: March 2011

For the epitaxial growth of bcc(110) metals on bcc(110) metal substrates, there is a general tendency for roughening by formation of quasi-periodic ridges along [001], with up-and-down staircases in the [110] direction. It can be detected by high angular resolution Spot Profile Analysis (SPA)-LEED, as has been done previously by Hahn et al. for the case of W(110) on W(110). We found this kinetic facetting for Fe(110) on Fe(110), where it can be described by the model of layer restricted diffusion (LRD) epitaxy. We observed the same phenomenon for Fe(110) on W(110), Fe(110) on Cr(110), Cr(110) on W(110) and Cr(110) on Fe(110). In this paper, we present data for Fe(110) on Cr(110). The change between sharp single spots for in-phase energies to double spots for out-of-phase energies documents the staircase facet structure; it can be used to measure a vertical strain in the films.
The Role of Vertical Exchange in the Growth of GaAs/AlAs Lateral and Vertical Superlattices
Authors: Lorke Axel , Krishnamurthy Mohan , Petroff Pierre M.
Published: March 2011

We report on the formation of lateral superlattices in short period vertical GaAs/AlAs superlattices. To explain the observed self-organized phase separation, we propose a model of vertical intermixing, driven by the exchange of Ga on the surface with impinging Al atoms. The model correctly describes the formation of lateral superlattices for both integer and fractional monolayer deposition. It also predicts a far-reaching intermixing at GaAs-AlAs interfaces. Insitu RHEED studies of the initial growth stage of both GaAs-AlAs and AlAs-GaAs interfaces support the assumption of an asymmetric exchange at the growing surface and confirm the longrange Ga migration predicted by the model.
Irradiation Effects of Ar-Cluster Ion Beams on Si Surfaces
Authors: Takaoka G. H. , Sugahara G. , Hummel R. E. , Northby J. A. , Sosnowski M. , Yamada I.
Published: March 2011

The effects of energetic Ar cluster ion impacts on Si(111) surfaces have been studied for cluster energies up to l5keV. The mean cluster size was about 1000 atoms, and the smaller sizes could be systematically excluded. Si samples irradiated at different cluster ion energies were analyzed by RBS, ellipsometry, and differential reflectometry. Implantation of Ar in samples irradiated with cluster ions was found by RBS to be detectable, but very small in comparison with samples irradiated with monomer ions of the same energy. The thickness of the damage layer as measured by both ellipsometry and differential reflectometry was also much smaller in the cluster ion irradiated samples.
Investigation of Damage Induced by Low Energy Focused Ion Beam Irradiation in GaAs
Authors: Kosugi Toshihiko , Yuba Yoshihiko , Gamo Kenji
Published: March 2011

Defects induced by Ga focused ion beam (FIB) irradiation at an energy between 0.1 and IkeV have been characterized by means of deep level transient spectroscopy (DLTS) and related capacitance measurements. Seven different kinds of defect centers were resolved and two centers at 0.33 and O.56eV below the conduction band were dominant in the 100eV Ga implanted sample at doses up to 1015/cm2. Induced defect centers were observed to distribute over the region far beyond the theoretical ion range, which resulted from defect migration during the irradiation. Low energy irradiation induced defects were readily annealed out during low temperature heat treatment in contrast to those induced by high energy irradiations.
The Influence of an In-Situ Electric Field on H+ and He+ Implantation Induced Defects in Silicon
Authors: Ravi J. , Erokhin Yu. , Koveshnikov S. , Rozgonyi G.A. , White C.W.
Published: March 2011

The influence of in-situ electronic perturbations on defect generation during 150 keV proton implantation into biased silicon p-n junctions has been investigated. The concentration and spatial distribution of the deep traps were characterized using a modification of the double corelation deep level transient spectroscopy technique (D-DLTS). With the in-situ electric field applied, a decrease in concentration of vacancy-related, as well as H-related, traps was observed. 500 keV He+ implantation was also performed to supplement the above studies and to differentiate any passivation effects due to hydrogen. A model based on the charge states of hydrogen and vacancies was used to explain the observed behaviour.
Dislocation Loops in Spinel Crystals Irradiated Successively with Deep and Shallow Ion Implants
Authors: Ai Rebecca X. , Bordes Nicole , Cooper Elizabeth A. , Sickafus Kurt E. , Ewing Rodney C. , Nastasi Michael
Published: March 2011

This study examines the influence of microstructural defects on irradiation damage accumulation in the oxide spinel. Single crystals of the compound MgAl2O4 with surface normal [111] were irradiated under cryogenic temperature (100°K) either with 50 keV Ne ions (fluence 5.0 × 1012/cm2), 400 keV Ne ions (fluence 6.7 × 1013cm2) or successively with 400 keV Ne ions followed by 50 keV Ne ions. The projected range of 50 keV Ne ions in spinel is ~50 nm (“shallow”) while the projected range of 400 keV Ne ions is ~ 500 nm (“deep”). Transmission electron microscopy (TEM) was used to examine dislocation loops/ defect clusters formed by the implantation process. Measurements of the dislocation loop size were made using weak-beam imaging technique on cross-sectional TEM ion-implanted specimens. Defect clusters were observed in both deep and shallow implanted specimens, while dislocation loops were observed in the shallow implanted sample that was previously irradiated by 400 keV Ne ions. Cluster size was seen to increase for shallow implants in crystals irradiated with a deep implant (size ~8.5 nm) as compared to crystals treated only to a shallow implant (size ~3.1 nm).
Layer by Layer Amorphization in Si: Temperature, Ion Mass and Flux Effects
Authors: Battaglia A. , Romano G. , Campisano S.U.
Published: March 2011

The layer-by-layer amorphization process is explored in a temperature range in which the kinetics of crystallization can be neglected. It has been found that the pure amorphization rate increases exponentially as the substrate temperature is decreased with an apparent activation energy of 0.48 eV. Moreover the rate increases with both the ion flux and the energy deposited into elastic collisions. A phenomenological model is proposed to explain the experimental results.
Microstructures of Si Surface Layers Implanted with Cu
Authors: Follstaedt David M. , Myers Samuel M.
Published: March 2011

The microstructures of Si ion-implanted with Cu have been characterized by TEM after annealing. For 1.2 at.%, the Cu is trapped at planar defects, but for 10 at.%, η-Cu3Si forms, allowing Cu to diffuse at its equilibrium solubility. These observations allow proper evaluation of the binding energies of Cu to previously formed internal cavities (2.2 eV) and η-Cu3Si (1.7 eV). The η-Cu3Si in the 10 at.% layer catalyzes oxidation of the Si. The microstructures also indicate that Si implanted with ~2 at.% Cu reforms epitaxially with embedded defects after 8 hr. at 700°C, but for ~10 at.% Cu, epitaxy is not recovered after 6 hours at 600ºC.
Ion Beam Induced Structural and Electrical Modifications in Crystalline and Amorphous Silicon
Authors: Coffa S. , Battaglia A. , Priolo F.
Published: March 2011

The mechanisms of defect accumulation and dynamic annealing in ion-implanted crystalline and amorphous Si are elucidated by performing conductivity and Raman spec-trascopy measurements in-situ during ion irradiation. In amorphous Si the entire gamut of defect structures has been characterized by analyzing the annealing kinetics from 77 K to ~ 800 K both during and after irradiation. Moreover the modifications in the electronic properties of crystalline Si produced by ion-irradiation have been investigated. The use of in-situ techniques in combination with transmission electron microscopy and deep-level transient spectroscopy allowed us to demonstrate the correlation between structural and electrical defects produced by ion-irradiation in Si.
Barrier Effect of Retrograde Well Against Ion-Induced-Charge Carriers
Authors: Sayama Hirokazu , Kishimoto Takehisa , Takai Mikio , Kimura Hiroshi , Ohno Yoshikazu , Sonoda Ken-Ichiro , Kotani Norihiko , Satoh Shin-Ichi
Published: March 2011

The charge collection efficiency of a diode with a retrograde well was estimated using focused ion beam irradiation at 400 keV and 2 MeV. The retrograde well was found to effectively suppress a collection of charge carriers created by energetic particles. The charge collection efficiency of the diode with the retrograde well was ~ 25 % lower than that with the conventional well when 400 keV ~ 2 MeV protons were irradiated normal to diodes. This result was in good agreement with device simulation.
Ion Beam Processing of InGaAsP
Authors: Pearton S.J. , Abernathy C.R. , Wisk P.W. , REN F.
Published: March 2011

The activation kinetics of Si+ and Be+ ions implanted into InGaAsP (λ = 1.3 µm) grown by MOMBE were studied over a variety of doses (5 × 1012 - 5 × 1014 cm-2), annealing times (3-60 sec) and temperatures (575-750°C). Maximum doping concentrations of ~2 × 1019 cm-3 were obtained for both Si+ and Be+, with activation energies for electrical activation of 0.58 eV and 0.39 eV, respectively. Multiple energy F+ or H+ implants can be used to produce high resistance layers for isolation purposes - maximum sheet resistances of ~8 × 106 Ω/□or ~106 Ω/□ for initially p+or n+ InGaAsP, respectively, were obtained for F+ implants followed by annealing near 450 °C. Smooth, anisotropic dry etching of the InGaAsP was obtained with low pressure CH4/H2/Ar discharges with the etch rates being independent of conductivity type or doping levels.
Formation of Shallow Energy Levels in Mn+ Implanted GaAs with Extremely Low Background Impurity Concentration
Authors: Shen Honglie , Makita Yunosuke , Yamada Akimasa , Niki Shigeru , Iida Tsutomu , Shibata Hajime , Fons Paul , Obara Akira
Published: March 2011

Manganese ions implantation into ultrapure GaAs layers grown by molecular beam epitaxy were investigated by photoluminescence technique systematically in a wide range of manganese concentration up to 1×1020cm-3. Five shallow emission bands denoted by (Mn°, X), “G”, “G' “ “H” and (D, A)2 are formed in the implanted layers in addition to the well known Mn impurity related emission at ~880nm. With increasing manganese concentration to 1×1019cm-3, “G” exhibits no energy shift, suggesting that “G” is different from the behavior of [g-g] emission that is commonly formed in shallow acceptor (such as C) incorporated ultrapure GaAs. (Mn°, X), “G” and “G' “ present no energy shift with increasing excitation intensity, while “H” and (D, A)2 indicate peak energy shift greatly showing typical donor-acceptor pair characteristics. “G” and (Mn°, X) are found to hold similar radiative origin which is different from “G”. Temperature dependence measurement reveals that emission “G” has a thermal activation energy of 5.4meV.
Ion Beam Surface Modification for Achieving Rectification in Gold-Aluminum Nitride-Silicon Junctions
Authors: Stacy T. , Liaw B. Y. , Khan A. H. , Zhao G. , Charlson E. M. , Charlson E. J. , Meese J. M. , Prelas M. , Wragg J. L. , Chamberlain J. E. , White H. W.
Published: March 2011

Low energy ion bombardment has been utilized to fabricate rectifying contacts on aluminum nitride grown on single crystal silicon substrates. Bombardment of aluminum nitride with methane was followed by sputter deposition of gold contacts. To our knowledge, this is the first report of rectifying contact formation on aluminum nitride. Scanning electron micrographs show that the initially ordered aluminum nitride surface is significantly altered with low energy methane ion beam exposure. Electrical measurements made on samples which had been partially masked during implantation indicate that rectification is a result of the ion bombardment.
Nonlinear Optical Materials Synthesized by Ion Implantation: Metal Quantum Dots in Transparent Dielectrics
Authors: Haglund Richard F. , Osborne D. H. , Yang LI , Magruder R. H. , White C. W. , Zuhr R. A.
Published: March 2011

Composites consisting of nanometer-size metal clusters embedded in a host dielectric can be synthesized by implanting metal ions in either glassy or crystalline substrates. The size and size distributions of the nanoclusters can be controlled by varying the parameters either of the ion-implantation process or subsequent annealing. The nonlinear optical response of these quantum-dot composites can be modeled as that of independent electrons confined to a spherical potential well; experimental data on relaxation times compares favorably with this simple picture. Optical figures-of-merit of these materials suggest potential for applications in nonlinear waveguide devices, particularly since ion implantation is compatible with device-fabrication processes. The basic features of these materials are illustrated from experiments on Cu and Pb clusters in silica.
The Effect of Si, F Implantation on the Formation and Light Emitting Properties of Porous Silicon
Authors: Wang Lianwei , Lin Chenglu , Liu Ping , Zhou Zuyao , Zou Shichang
Published: March 2011

The effect of ion implantation on the formation and light emitting properties of porous silicon is reported. Si + , F+ ions were implanted into silicon wafers before electrochemical etching process. The experiments showed that porous structure can be formed on the wafer containing amorphous layer, while the porosity distribution with the depth changed greatly compared with the anodized crystalline Si. The implantation of F+ ions greatly affects the formation mechanism. The creation of point defects leads to red-shift in photoluminescence measurements.
Host Guest Interactions in Ti-Implanted Silica, Borosilicate and Aluminosilicate Glasses
Authors: Henderson D. O. , Morgan S. H. , Mu R. , Collins W. E. , Magruder R. H. , White C. W. , Zuhr R. A.
Published: March 2011

Titanium oxide glasses exhibit a significant nonlinear optical response which is attributed to the large polarizability of the Ti ion. Ion implantation is a unique method for incorporating polarizable ions in glass hosts and allows for tailoring the nonlinear optical properties of the material for potential device applications in all optical switching and planar waveguide technology. However, at the molecular level, the linear and nonlinear properties of ion implanted glasses are governed by interactions between the glass host and the implanted ion, radiation damage, and ion-glass chemistry. In order to probe the host-guest interactions, we have measured the infrared and optical spectra for Ti implanted in silica, borosilicate, and aluminosilicate glasses. The infrared and optical spectra indicate that the host-guest interactions and defect concentration differ significantly for the three glasses investigated.
Nano-Structure Ge Formed in Thin Film SiO2 Using Ion Implantation
Authors: Phillips J.R. , Hellman Olof C. , Kobayashi N. , Makita Yunosuke , Shibata Hajime , Yamada A. , Fons P. , Tsai Yushin , Niki Shigeru , Hasegawa Masataka , Iida Tsutomu
Published: March 2011

The preparation of amorphous insulating films containing nanometer-scaled structures of semiconductors has attracted increased attention since the observation of room temperature emission of light from films containing indirect-bandgap semiconductors such as Ge and Si. While most experimental reports on these Si and Ge nano-scale structures have been based on thin films created using sputter-deposition, in this study we have used conventional ion implantation of Ge to create the non-equilibrium mixture of materials that, upon annealing, develops a nano-crystallite phase embedded in the amorphous matrix. The presence of clusters that are difficult to image in TEM, in addition to microcrystallites, is an issue of interest since the source of light emission is still controversial. The second phase is formed from excess amounts of the semiconductor, in this case added by implantation. In this paper the formation and size distribution of the Ge nano-structures was characterized using Raman scattering and transmission electron microscopy (TEM). Similarly to reported sputtered film results, Raman spectra suggest Ge clusters that are not well formed crystallites may be present for anneals at low temperatures and in unannealed films. For annealing temperatures exceeding 600°C, a mixture of amorphous-like clustering and nano-crystallites may result, depending on the volume fraction of Ge. For low dose samples it was found that temperature and time of annealing could be used to manipulate the nucleation behavior of the nano-crystallites.
Oriented Si and Ge Nanocrystals Formed in Al2O3 by Ion Implantation and Annealing
Authors: White C.W. , Budai J.D. , Withrow S.P. , Pennycook S.J. , Hembree D.M. , Zhou D.S. , Vo-Dinh T. , Magruder R.H.
Published: March 2011

Ion implantation followed by thermal annealing in a reducing atmosphere has been used to create a high density of oriented Si and Ge nanocrystals in (0001) AI2O3. Both types of nanocrystals are three-dimensionally aligned with respect to the AI2O3 matrix, but the orientational relationships are different, and the two types of nanocrystals have different shapes in AI2O3. Implantation of Si and Ge in fused silica also produces nanocrystals, but in this case, the nanocrystals are randomly oriented relative to each other.
First Results from the Los Alamos Plasma Source Ion Implantation Experiment
Authors: Rej D. J. , Conrad J. R. , Faehl R. J. , Gribble R. J. , Henins I. , Horswill N. , Kodali P. , Nastasi M. , Reass W. A. , Shamim M. , Sridharan K. , Tesmer J. R. , Walter K. C. , Wood B. P.
Published: March 2011

A new facility is operational at Los Alamos to examine plasma source ion implantation on a large scale. Large workpieces can be treated in a 1.5-m-diameter, 4.6-m-Jong plasma vacuum chamber. Primary emphasis is directed towards improving tribological properties of metal surfaces. First experiments have been performed at 40 kV with nitrogen plasmas. Both coupons and manufactured components, with surface areas up to 4 m2, have been processed. Composition and surface hardness of implanted materials are evaluated. Implant conformality and dose uniformity into practical geometries are estimated with multidimensional particle-in-cell computations of plasma electron and ion dynamics, and Monte Carlo simulations of ion transport in solids.
A New Computationally-Efficient 2-D Model for Boron Implants into (100) Single-Crystal Silicon
Authors: Morris Steven J. , Yang Shyh-Horng , Lim David H. , Tasch AL. F.
Published: March 2011

In this paper, the first comprehensive and computationally-efficient two-dimensional model is reported for boron implants into (100) single-crystal silicon with explicit dependence on energy, dose, implant angles, mask height, mask orientation, and rotation of the wafer during the implant. The model and its implementation into SUPREM 4 are described, and where possible, the explicit dependencies are illustrated.
Visualization of Ion Channeling of (100)Si and Si1-xGex Epitaxial Grown Layers on Silicon
Authors: Xu M. , Atzmon Z. , Schroer A. , Wilkens B. , Mayer J.W.
Published: March 2011

Three dimensional visualization of ion channeling spectra was obtained by computer graphics in order to observe the crystalline quality and the strain state of thin films. Pure (100)Si and Si1-xGex (x=0.10, 0.18) layers, epitaxially grown on (100)Si substrates, were channeled along the <110> crystal axis with the 2 MeV He++ ion beam in a UHV target chamber. The data were interpolated using a standard bicubic tensor product B-spline surface with uniform knot sequences in x and y directions. With this modeling technique we have shown the orientation of the major planes in a diamond crystal and the angular displacement of the Ge signal in the SiGe epilayer relative to the Si substrate signal due to the presence of tetragonal distortion in the epilayer.
Recent Progress in SOI Materials and Devices for VLSI Applications
Authors: Hosack H. H.
Published: March 2011

Silicon-On-Insulator (SOI) technology [1-4] has been shown to have significant performance and fabrication advantages over conventional bulk processing for a wide variety of large scale CMOS IC applications. Advantages in radiation environments has generated significant interest in this technology from military and space science communities [5,6]. Possible advantages of SOI technology for low power, low voltage and high performance circuit applications is under serious consideration by several commercial IC manufacturers [7,8].
Damage Accumulation in MgAl2O4 Crystals by Xe Ion Irradiations
Authors: Yu N. , Nastasi M. , Hollander M.G. , Evans C.R. , Maggiore C.J. , Sickafus K.E. , Tesmer J.R.
Published: March 2011

We have studied the damage kinetics in single crystal MgAl2O4 (spinel) with (100) orientation under 370 keV Xe ion irradiations at temperatures of -100 and 400 C. In-situ Rutherford Backscattering Spectrometry (RBS) and ion channeling have been used to monitor the damage accumulation in spinel following sequential Xe ion irradiations. A significant temperature effect on the irradiation damage has been found. Channeling data show that at -100 C, the irradiated spinel layer reaches the same level as in a random spectrum at a dose of 8×1015 Xe/cm2 (20 DPA for peak damage), while at 400 C, the near surface region (50 nm) remains single-crystalline up to 2×1016 Xe/cm2.
Experimental Study of Precipitation Processes in Oxygen Implanted Silicon
Authors: Weber R. , Yankov R. , Müller R. , Skorupa W. , Reiss S. , Heinig K.-H.
Published: March 2011

Single crystal (100) silicon substrates were implanted at 300 keV with substoichiometric oxygen doses ranging from 1 × 1016 to 1 × 1017 cm-2. Samples were annealed for 2 hours over the temperature range from 1100°C to 1250°C and were subsequently analysed by both cross sectional transmission electron microscopy (XTEM) and scanning electron microscopy (SEM). The nucleation and growth of oxide precipitates within the implanted layer was followed during annealing. The emphasis was placed upon studying the process of Ostwald ripening which is known to play an important role in the formation of the incipient buried layer. Besides, a clear trend of the SiO2 precipitates to arrange in well defined regions was revealed and this was attributed, as distinct from the earlier claims, to an inherent process of self organisation.
Synthesis of (SIC)3N4 Films by Ion Implantation
Authors: Uslu C. , Lee D. H. , Berta Y. , Park B. , Thadhani N. N. , Poker D. B.
Published: March 2011

We have investigated the synthesis of carbon-silicon-nitride compounds by ion implantation. In these experiments, 100 keV nitrogen ions were implanted into polycrystalline β-SiC (cubic phase) at various substrate temperatures and ion doses. These thin films were characterized in detail by x-ray diffraction with a position-sensitive detector, transmission electron microscopy with chemical analysis, and Rutherford backscattering spectroscopy. The as-implanted samples show a buried amorphous layer at a depth of 170 nm. The peak concentration of nitrogen saturates at approximately 45 at. % with doses above ~9.0×1017 N/cm2 at 860°C. These results suggest formation of a new phase by nitrogen implantation into β-SiC.
Low Energy Ion Beam Assisted Deposition of Low Resistivity Aluminum Using TMAA
Authors: Yan H. Q. , Wang H. , Steckl A. J.
Published: March 2011

Thermal deposition and Ga+ ion beam assisted deposition of Al using TMAA have been studied. At temperatures between 95ºC and 105ºC, where thermal deposition is negligible, the introduction of a low energy Ga+ ion beam (8 to 10 keV) produces selective deposition. Ion beam seeding followed by ion beam irradiation during TMAA flow leads to consistent selectivity at this temperature range. The lowest resistivity of selectively deposited Al film is 7 µΩ-cm, only 2.5 times the bulk Al resistivity. The selective deposition rate is about 300Å/min. Depositions at higher temperature produced very low resistivity Al films, but with a decreasing selectivity ratio. X-ray diffraction showed that deposited Al films are polycrystalline, with very small FWHM.
Details of the Defect Profile in Self-ion Implanted Silicon
Authors: Zhang P.X. , Goldberg R.D. , Mitchell I.V. , Schultz P.J. , Lockwood D.J.
Published: March 2011

Raman spectra excited at two laser wavelengths are used to study the damage in self-implanted silicon. It was found that the contributions from the damaged surface crystalline and a-Si layers can be distinguished and separated, based on the different light absorption coefficients. A defect-activated low frequency band in the damaged surface crystalline Si layer was revealed. In totally amorphized samples the Raman spectra excited by 457.9 and 647.1 nm show different scattering intensity ratios for the optical- and acoustic-like-phonons. This novel result seems to indicate a depth dependent variation of the disordering in the amorphous layer.
Development of an Atomic Oxygen Source for Thin Oxide Film Formation
Authors: Inoue S. , Kawagoe Y , Yamanishi K. , Tanaka M.
Published: March 2011

Atomic oxygen promotes the oxidation of thin films. The authors developed a silent discharge type atomic oxygen source for thin oxide film formation. The atomic oxygen source consists of a quartz discharge tube and two cylindrical electrodes that are attached to the outside wall of the tube. The atomic oxygen concentration is estimated to be 3%.

The atomic oxygen source was installed in an ICB (Ionized Cluster Beam) apparatus and applied to the formation of Er-Ba-Cu-0 thin films. By introducing the atomic oxygen during deposition, a film showing superconductivity at 81K was obtained when the substrate temperature was 570ºC. Also the substrate temperature to obtain a film showing superconductivity at 77K was estimated to be 50 °C lower than that for obtaining superconducting film formation in an atmosphere of 6% ozone. The atomic oxygen source was also applied to SrTiO3 thin film formation. Electrical properties of this film were examined and compared with those of films prepared in an atmosphere of 6% ozone. The dielectric constant of SrTiO3 film was improved from 60 to 180 by introducing atomic oxygen instead of 6% ozone. Therefore the atomic oxygen source was proven to be advantageous for thin oxide film formation.
Hard Carbon Films with Various Microstructure Prepared by Ion Assisted Evaporation
Authors: Ullmann J. , Weber A. , Falke U.
Published: March 2011

For a deeper understanding of the creation of carbon films the hydrogen-free ion assisted evaporation (IAE) method with neon species was used. Variation of the ion parameters energy and ion to neutral arrival ratio, delivering the necessary energy for modification of the film growth, results in different microstructures investigated with EELS, HRTEM and TED as well as different microhardnesses measured by dynamical Vickers indentation. A possible film growth mechanism is proposed based on an ion etching of mainly sp2-bonded carbon surface atoms and on defect dominated structure modification below the surface depending on the ion energy
TiOxCy Thin Film Deposition by CO2+-Ion Beam Sputtering of Titanium
Authors: KEMPF BERTILO E.
Published: March 2011

Titanium metal is sputtered by ion beams using a Kaufman-type ion source with carbondioxide as working gas. Deposition takes place on watercooled substrates of silicon and InP. The films obtained are amorphous; they adhere excellently. SEM-pictures reveal a featureless dense fracture and a smooth surface. Despite a carbon content of 9 at % the films are highly transparent in the visible and near infrared wavelength range. Refractive indices center around 2.15 at values typically found for amorphous TiO2. The electrical properties are characterized by dielectric constant of ε = 26 ± 3, leakage current densities at breakdown of jL = 3.65 . 10-3 A/cm2 and breakdown fields EB > 1 MeV/cm.
Fabrication of W/C Multilayers by Direct Ion Beam Deposition
Authors: Ito K. , Nishimoto K. , Watanabe K. , Kataoka I. , Widmann Frédéric
Published: March 2011

The multilayer structures of tungsten and carbon for soft x-ray mirrors were fabricated by the low energy (<100eV) direct ion beam deposition method with various depositing ion energies. The layered structures were observed by cross sectional TEM. The undulated structures were found in the layered structures of the depositing ion energy of 6OeV and lOOeV. It becomes larger as the depositing ion energy increases, and the undulation of the upper layers was larger than that of the under layers. The undulation seems to increase in each carbon layer. These results are quite different from the results of evaluation of thick monolayer films in the previous work. Then, the interfacial composite layer was evaluated by XPS. The tungsten carbide layer was found at the W/ C interface on the C layer. However, we can not find such layer at the interface on the W layer. This result can be explained by the difference of the momentum of the depositing ion.
Intra-Cascade Surface Recombination of Point Defects During Ion Bombardment of Ge (001)
Authors: Floro J. A. , Kellerman B. K. , Chason E. , Picraux S. T. , Brice D. K. , Horn K. M.
Published: March 2011

Low energy Ar and Xe ion bombardment of Ge (001) produces large numbers of point defects on the Ge surface and in the near-surface regions. Defect concentrations on the surface are detected and quantified in real time during bombardment using in situ Reflection High Energy Electron Diffraction (RHEED). We report the energy dependence of the defect yield for 70–500 eV Ar and Xe ion bombardment, and the temperature dependence of the defect yield (defects/ion) during 200 eV ion bombardment. The defect yield drops rapidly as the substrate temperature during bombardment is varied from 175 K to 400 K. We attribute the yield reduction to surface recombination of adatoms and vacancies produced in the same collision cascade.
Parameter Extraction from the Reverse I-V and C-V Characteristics of an Epitaxial p-InP/Au Schottky Diode
Authors: Singh A. , Cova P. , Masut R. A.
Published: March 2011

Epitaxial p-InP/Au Schottky diodes were fabricated by evaporation of Au onto Zn doped epitaxial layers of InP grown by MOVPE, on a highly doped InP substrate. The reverse current-voltage (Ir-Vr) and 1 MHz capacitance-voltage (C-V) characteristics of the Au/p-InP diodes were measured in the temperature range 220-393 K. At all temperatures, soft reverse current-voltage characteristics were observed, which may be due to the decrease in the effective Schottky barrier height (øbr) with the increase of Vr. The voltage dependence of the reverse current was well described in terms of the interface layer thermionic emission (ITE) model which incorporates the effects of applied reverse voltage drop and the transmission coefficient across the interface layer and image force lowering of the barrier height into the thermionic emission theory. A self consistent iteration and least square fitting technique was used to obtain the zero bias barrier height (øbo) and interface layer capacitance (Ci) from the Ir-Vr data. Both, the Ir-Vr and the C-V data were analyzed under the assumption of reverse bias voltage independence of the charge trapped in the interface states, which was supported by our experimental data. The values of øbo obtained from the C-V measurements agreed well with those obtained from the Ir-Vr data for a value of 0.45 AK−2cm−2 for the effective Richardson constant (Aeff).
The Interface for Cryogenic-Processed Metal/Inp
Authors: He L. , Anderson W.A. , Palmer J. , Shi Z.
Published: March 2011

Au and Pd Schottky contacts to n-InP produce extremely high barrier heights and low leakage currents when deposition is on a substrate cooled to 77K. Extensive chemical and structural analyses indicate that this process causes the metal film to be continuous at 50Å, much better than in standard processing. Stoichiometry of InP near the surface is better maintained with this process. A thin P:O compound may exist at the interface which also contributes to a high barrier height.
Changing PL Intensity from GaAs/Al0.3Ga0.7As Heterostructures due to the Chemisorption of SO2: Effects of Heterostructure Geometry
Authors: Geisz J.F. , Kuech T.F. , Ellis A.B.
Published: March 2011

Chemical adsorption of gases onto semiconductor surfaces results in a change in the density of electronic surface states. The corresponding change in the number of surface charges gives rise to a measurable change in the bulk charge distribution within the semiconductor. This phenomenon forms the basis of a novel solid-state chemical sensor device using the intensity of photoluminescence (PL) as a measurement technique. We have observed changes in the PL intensity from MOVPE-grown GaAs/Al0 3Ga0 7As heterostructures due to the chemisorption of SO2 onto “photowashed” GaAs surfaces. The photowashing technique is believed to reduce the density of preexisting surface states by removing As from the GaAs surface oxide. The PL signal-to-noise ratio and PL sensitivity characteristics of these chemical sensors may be dramatically improved by varying semiconductor structure. We have observed a range of PL enhancements upon exposure to 0.6% SO2 in flowing N2 from heterostructure layers with various thicknesses and doping densities. These results are explained by comparison with a FEM numerical model derived to correlate the relative PL intensity from various heterostructures to the surface charge density.
Improved Adhesion of P-doped SiO2-Interface Layers on InP by Low-Temperature Damage-Free Plasma-CVD
Authors: Riemenschneider R. , Hartnagel H.L. , Kräutle H.
Published: March 2011

The deposition of thin films on III-V compound semiconductors is encountered with various interfacial problems. We present a new approach using a modified plasma technique in a phosphorous ambient at substrate temperatures ranging from 250 to 350 °C which covers two import aspects: Firstly, a good insulator quality due to the plasma process. Secondly, an appropriate surface pre-treatment and defect passivation by a phosphine-like cleaning process using a solid phosphorous source. The analysis of the film adhesion yields improved adhesive properties due to the high activation energy of a plasma process for surface reactions, and by preventing a phosphorus-related defects. The phosphorous concentration in the SiO2 films has to be adapted in order to prevent electrical degradation of the SiO2-InP interface. The influence of phosphorous deficiency and excess phosphorous will be discussed.
Thermally Driven In-Situ Removal of Native Oxide Using Anhydrous Hydrogen Fluoride
Authors: Apte Pushkar P. , Park Heungsoo , Saraswat Krishna C. , Helms C. R.
Published: March 2011

In-situ native-oxide removal is critical for epitaxial single-crystal silicon deposition, for polysilicon emitters and contacts and for ultrathin gate dielectric films in integrated circuit (IC) fabrication. We have developed an in-situ, thermally-driven, anhydrous hydrogen fluoride (AHF)-based native-oxide removal technique in which the wafer is treated by AHF at low temperatures (300-400°C) and a short (10 sec) 950°C ‘spike’ in AHF-H2 immediately prior to Si deposition. This process removes native oxides formed by standard wet cleans such as HC1:H202 and NH4OH:H202, as well as native oxides formed by the clean-room ambient. Further, the technique is an effective pre-clean for both polysilicon and epitaxial silicon deposition. This flexibility, combined with other salient features such as simplicity and a low thermal budget, make the process eminently suited for IC fabrication.
Chemical Modification of Surface Steps on SI(111) Vicinal Wafers: a Bonding Model for Phase Changes in Second Harmonic Generation
Authors: Jing Z. , Lucovsky G. , Whitten J. L.
Published: March 2011

There have been several studies of second harmonic generation (SHG) from chemically-modified vicinal Si(111) wafers. The SH fields contain one-fold (ψ) and three-fold (3ψ) symmetry contributions, which originate respectively from the terrace and surface step atoms. The phase of these contributions are different for native oxides, and are a function of the frequency of the incident radiation, ω. To identify the origin of these different phases for the terrace and step SH fields, we use a classical anharmonic oscillator model based on two assumptions: (a) a significant fraction of Si atoms at the steps have dangling bonds when oxides are formed below ∼850°C, and (b) these step atoms are linked to atoms at the bottom of the steps by O-Si-O groups following annealing at >900°C.
Ultra Thin Sacrificial Diffusion Barriers - Control of Diffusion Across the Cu-SiO2 Interface
Authors: Kirchner Eric , Murarka S.P. , Eisenbraun E. , Kaloyeros A.
Published: March 2011

In a copper-SiO2 dielectric multilevel interconnection scheme a diffusion barrier is needed between the metal and the dielectric to prevent the diffusion of Cu into SiO2 when subjected to thermal treatments and high electric bias. Ultra thin layers (50–100Å) of Al and Ti are being investigated for use as the required diffusion barrier as well as an adhesion promoter between Cu and SiO2 The results of our investigations, using C-V, resistance, and XPS measurements, will be presented and discussed. It will be shown that both Al and Ti reduce the SiO2 surface leading to a metal, oxygen, and Si bonded layer which acts as diffusion barrier under applied electrical bias of 1.5 MV/cm at temperatures as high as 250–300°C. Upper layers of Al and Ti are consumed by reaction with Cu. Such reactions increase the electrical resistivity and corrosion resistance of Cu (especially with Al). The results and the applicability of such barriers in practical cases will be presented and discussed.
Thermal and Electromigration Effects on the Surface and Aluminum/Aluminum Oxide Interface of Aluminum Metallizations
Authors: Ramseyer George O. , Beasock Joseph V. , Sylla William K. , Walsh Lois H.
Published: March 2011

Thermal and electromigration effects on the thicknesses of aluminum oxide at the aluminum-1% silicon/thermal silicon dioxide interface were quantitatively determined by AES. Void sites corresponded with thinner aluminum oxide thicknesses at this interface. Changes in surface topography and grain structure were quantitatively determined for thermally annealed aluminum-1% silicon metallizations by AFM.
Electrical, Magnetic and Mechanical Properties of Nanocrystalline Nickel
Authors: Aus M.J. , Szpunar B. , Erb U. , Palumbo G. , Aust K.T.
Published: March 2011

The electrical, magnetic and mechanical properties of bulk nanocrystalline nickel produced by pulse-electrodeposition are reviewed and discussed in the context of nanoprocessing as a distinct form of grain boundary engineering to develop soft magnetic materials with improved performance characteristics.
Enhanced Ionic Conduction at the Film/Substrate Interface in LiI Thin Films Grown on Sapphire(0001)
Authors: Lubben D. , Modine F. A.
Published: March 2011

The ionic conductivity of LiI thin films grown on sapphire(0001) substrates has been studied in situ during deposition as a function of film thickness and deposition conditions. LiI films were produced at room temperature by sublimation in an ultra-high-vacuum system. The conductivity of the Lil parallel to the film/substrate interface was determined from frequency-dependent impedance measurements as a function of film thickness using Au interdigital electrodes deposited on the sapphire surface. The measurements show a conduction of ∼5 times the bulk value at the interface which gradually decreases as the film thickness is increased beyond 100 nm. This interfacial enhancement is not stable but anneals out with a characteristic log of time dependence. Fully annealed films have an activation energy for conduction (σT) of ∼0.47 ± .03 eV, consistent with bulk measurements. The observed annealing behavior can be fit with a model based on dislocation motion which implies that the increase in conduction near the interface is not due to the formation of a space-charge layer as previously reported but to defects generated during the growth process. This explanation is consistent with the behavior exhibited by CaF2 films grown under similar conditions.
Switching and Negative Capacitance in Thin Amorphous SiC-Si Heterojunction Diode
Authors: Sohn K. , Lee H.
Published: March 2011

The heterojunction diode of amorphous SiC-pSi with barrier contacts in which the interface layer, a-SiC, is much less than 100 nm and contains considerable defect densities, exhibited bistable switching with memory. Either state was maintained over weeks without bias. A high-impedance state switched to a low-impedance state with the transient on-state when a threshold voltage was exceeded. After application of current pulses, a low-impedance switched to a high-impedance state. In C-V Measurement, novel negative capacitance phenomenon in the entire bias range which has not been reported yet was demonstrated. Experimental results show that this negative capacitance is due to the inductive reactance. This phenomenon presents the possibility of replacing inductor even at zero bias.
Photodarkening Effect Dependent on Alkaline Metal Dopants in Semiconductor - Doped Glass
Authors: Yanagawa T. , Nakano H.
Published: March 2011

This report clearly shows that the photodarkening effect in semiconductor-doped glasses comes from the color center formation of alkaline silicate glass. It also discusses the cause of response time shortening after darkening. It seems that fast and stable responses can be obtained with a specific alkaline metal composition, showing a change in the dielectric properties and also a drastic decrease in the ion conductivity based on the mixed-alkali effect. After-darkening phenomena, such as the absorption increase in all transparent region of the glass, the appearance of electron spin resonance (ESR) arising from the formation of glass color centers, and matrix glass changes observed with a field emission scanning electron microscope (FE-SEM), are distinctly shown.
Structural and Electrical Properties of BaTio3 Thin Films Grown on p-Si Substrates with Different Device Designs
Authors: Chang L. H. , Jia Q. X. , Anderson W. A.
Published: March 2011

RF magnetron sputtering of BaTiO3 on (100) p-Si was performed to produce a high-quality BaTiO3/p-Si interface and BaTi03 insulator gates with high dielectric constant and low leakage current. Through different processing and device designs, different capacitor structures, including single layer amorphous, single layer polycrystalline and bi-layer amorphous on polycrystal-line, were investigated in this study. Raman spectroscopy showed the optical phonon modes of the BaTiO3 thin films with different structures. The structural properties of the films were characterized by X-ray diffraction. Using both the quasistatic and the high-frequency capacitance-voltage measurements, the interface-trap density was estimated at high 1011 eV−1 cm−2. The relative dielectric constant of the composite structure was controlled in a range from 30 to 130. The leakage current density was as low as 8×10−10 A/cm2 at a field intensity of (2±0.5)×105 V/cm. Breakdown voltage varied from 5x105 to 2×106 V/cm.
Effect of Doping on the Interface States in Au Schottky Contact to p-In0.21Ga0.79As Grown on GaAs by Metal Organic Vapour Phase Epitaxy
Authors: Singh A. , Cova P. , MASUT R. A.
Published: March 2011

Epitaxial p-In0.21Gao0.79As/Au Schottky barrier type diodes were fabricated by evaporation of Au on chemically etched surfaces of In0.21Ga0.79As:Zn layers grown on highly doped GaAs substrate by MOVPE. 1 MHz capacitance-voltage (C-V) and Capacitance-frequency (C-f) measurements were performed in the frequency range 1 KHz-1 MHz at room temperature in Au Schottky diodes made on four epitaxial In0.2 Ga0.79As:Zn samples with doping concentrations between 6×1014cm−3 and 4×1017 cm−3. Under forward bias, a large frequency dispersion in the junction capacitance was observed which was attributed to the interface states in thermal equilibrium with the semiconductor. The interface states capacitance extracted from the C-f data was analyzed in terms of Lehovec's theoretical model of interface state continuum with single time constant, and the characteristic parameters of the interface states (energy density (Nss), relaxation time (τ) and hole capture cross-section (σh)) were determined. In the samples with doping concentration in the range 1.5×1017-4.3×1017 cm−3, Nss was about an order of magnitude higher than in the sample having a doping concentration of 5.8×1014 cm−3. Over the interface states energy range 0.40-0.65 eV, Nss decreased exponentially with energy in the highly doped samples and σh increased with energy in all the samples.
Solid-State Reactions of a 3D-Transition Metal-Ti/Al2O3 System
Authors: Suenaga Seiichi , Koyama Miho , Arai Shinji , Nakahashi Masako
Published: March 2011

An interfacial mechanism for reactions between a Me-Ti thin film (Me=3d transition metals; Cu,Ni) and an A12O3 substrate is newly proposed. It has been clarified that Me3Ti3O (diamond cubic of Fd3m), which is formed as an intermediate phase in both the Cu-Ti/Al2O3 and Ni-Ti/Al2O3 systems, is responsible for the bonding between Me and A12O3. The solid-state reactions of the Me-Ti bilayer film/Al2O3 system were studied with Auger electron spectroscopy (AES) and X-ray diffraction (XRD) to clarify the interfacial reaction between Me-Ti and the A12O3 substrate. Me3Ti3O was observed at the interface between A12O3 and Me after annealing. Me3Ti3O was formed by oxidation of the Me-Ti compounds. The oxygen which reacted with the Me-Ti compounds has been found to be generated from the reduction of the A12O3 substrate.