bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of PMAC-Based Multifunctional Combined CNC Machine
Authors: Huo Meng You , Xu Jin Quan , Zhang Jian Hua , Ai Xing , Hu Yu Jing
Published: March 2009

This paper presents a PMAC-based combined CNC machine that integrates technologies of ultrasonic machining, electrical discharge machining and high speed grinding. As a multifunctional machine, it can provide diverse machining methods for different materials. For hard and brittle materials, it can conduct ultrasonic machining and high-speed grinding respectively or in a combined form; for conductive hard and brittle materials, electrical discharge machining with or without ultrasonic vibration could be implemented. Driven by AC servomotors, the mechanical structure of
the vertical machine is mainly composed of a cross workbench for work piece handling, and a spindle head for tool feeding or high speed rotating. Besides those mentioned above, the system management program, the pulse power generator as well as the ultrasonic generator are also analyzed in this paper. Experimental results show that this machine has a wide range of application indeed and is suitable for various materials processing.
Error Estimate of Approximate Double Circular Arc Interpolated Method for Curve Smoothing
Authors: Zhang Zi Qiang , Yan Qiu Sheng , Zheng Zhi Dan , Chen Shao Bo
Published: March 2009

Approximate Double Circular Arc Interpolated Method which was put forward by author, is different from other circular arc interpolated methods in demanding only the corner between normal directions of each circular arcs at intersection point are less than designated allowed value but not demanding contiguous circular arcs are tangent, and makes the calculating be predigested. In order to estimate error of the method, emulated calculating is carried out, namely the course of curve being obtained by reverse engineering is simulated in this paper. The results show: if space between measure points is about 0.1mm in curve being obtained by reverse engineering, then, the most departure of smoothing results from original curve is 0.552μm for the stated example. Influence of the error on NC machining is quite small, so it can meet the needs of NC machining.
Fatigue Crack Growth Tests on Carbon Fibre Reinforced Aluminium Matrix Composites
Authors: Karcagi Rita , Lukács János
Published: March 2009

Composite materials combine the advantages of their components. Carbon fibre
reinforced composites are used in construction where reduced weight is critical. To produce carbon fibre reinforced composites, aluminium alloys can be the matrix. Advantageous properties of aluminium matrix composites – good toughness, low weight – are applied in aerospace and automotive industry. Because aluminium alloys are not reactive to carbon, therefore the coating of the fibres can solve the problem. Nickel coated and chemically treated carbon fibres were used to producing of aluminium matrix composites. The investigated composite materials were prepared by pressure infiltration. The influence of treating of carbon fibres was examined on the fracture mechanical properties of aluminium matrix composites. Three types of matrix materials, three types of carbon fibres and four types of surface treatment were studied. Fatigue crack growth tests were performed under mode I loading condition and the failure mechanisms of the composite materials were investigated. Test results belonging to different coated fibres were compared, and our results were compared with the results from the literature, too.
Advanced Structural Steels in the Hungarian Steel Industry
Authors: Verő Balázs , Zsámbók Dénes , Horváth Ákos , Dobránszky János , Kopasz László , Hirka József
Published: March 2009

At the beginning of the third millennium, the world’s annual steel production reached
900 million tons. Flat products account for the majority of the production. It is also known that around three times the amount used today would be needed if the mechanical properties of the steels produced would have stagnated on the level characteristic of the 1930s and 40s. The history of the development and production of HSLA steel in Hungary dates back to the beginning of the 1960s. For the construction of the new Erzsébet Bridge, research workers at Danube Steelworks and at Steel Industry Research Institute developed the Ti micro-alloyed steel MTA50. In the study, we will summarise the history of the development of steels of the 700MPa strength category, thereafter we will introduce the main features of the project running within the scope of the National Research and Development Programme aimed at the development of DP- and TRIP-steels, and we will finally
report on the results of the first year of the three-year project.
The Mechanism of Intragranular Ferrite Nucleation on Inclusion in Steel
Authors: Yang Zhi Gang , Zhang Chi , Pan T.
Published: March 2009

The intragranular ferrite, which renders fabrication of fine-microstructure and improves toughness of welds in ultra-fine grain steels, is often observed to nucleation on non-metallic inclusion. The mechanism of this nucleation is related to the interfacial energy between austenite, ferrite with inclusions, the solute depletion zone around the inclusions and the strain energy due to different thermal coefficients between matrix and inclusions, et al. The interfacial energy of iron
with nitrides and carbides is crucial to promote the ferrite nucleation on such as VN. On the other hand, the composition change in local austenite is probably the control reason for ferrite on MnS and Ti2O3. The thermal strain energy is calculated to be far less than the driving force for phase transformation and not effective to promote ferrite nucleation unless at very small undercoolings.
Electrical and Physical Properties of Al and Nb Doped PbTiO3 Ceramic Thin Films
Authors: Zhang Bo Ping , Li Jing Feng , Dong Yan , Iijima Takashi
Published: March 2009

A series of Pb(Ti1-xAlx)O3, Pb(Ti1-xNbx)O3 and Pb(Ti1-xAlx/2Nbx/2)O3 thin films were fabricated onto Pt/Ti/SiO2/Si(100) substrates using a chemical solution deposition process. The dielectric constant of the Pb(Ti1-xAlx)O3 thin films increased with increase of aluminum content, while a maximum dielectric constant value was observed for the Pb(Ti1-xNbx)O3 and Pb(Ti1 xAlx/2Nbx/2)O3 thin films when the doping contents were 10 and 20 mol%, respectively. The dielectric constant of the Pb(Ti0.8Al0.1Nb0.1)O3 thin film is about 600, being two times higher than those of Pb(Ti0.9Al0.1)O3 and Pb(Ti0.9Nb0.1)O3 thin films. The Pb(Ti0.8Al0.1Nb0.1)O3 thin film showed less than 10-7 A/cm2 current density at ±150 kV/cm, being superior to the leakage property of the PbTiO3, Pb(Ti0.9Al0.1)O3 and Pb(Ti0.9Nb0.1)O3 thin films. The co-doping of aluminum and niobium is more effective to increase the dielectric and ferroelectric properties as compared with the individual aluminum or niobium doping.
Effect of Pressure on Melting Temperature of Silicon and Germanium
Authors: Yang C.C. , Jiang Qing
Published: March 2009

The pressure-dependent melting temperature of bulk Si, bulk Ge and nanocrystalline (nc) Si are predicted by the Clapeyron equation where the pressure-dependent volume difference is modeled by introducing the effect of surface stress induced pressure. The predictions are found to be consistent with the present experimental and other theoretical results.
Optimal Operational Conditions during Production of Lead-Calcium-Tin Anodes for Improve Their Mechanical Properties
Authors: Camurri Carlos , Araneda Eugenia , Pagliero Antonio , Dille Jean
Published: March 2009

Previous works have shown that a minimum yield strength s0 of 58 MPa for leadcalcium- tin anodes of 6 mm thickness and a nominal composition of 0.7% Ca and 1.3% Sn are required to avoid early deformations and distortions during their operation in copper electrowinning cell. This s0 value for the anodes is associated with a terminal cold rolling process and a further precipitation hardening prior to their installation in the electrowinning cells. The objectives of the present work are to determine the alloy recrystallization temperature according to Ca and Sn contents, the maximum cold rolling temperature and the aging time required to obtain the desired mechanical quality. The results indicate that recrystallization temperature ranges between 120 and 150°C, according to the anode composition. To reach the desired deformation and precipitation hardening and consequently a yield strength of 58 MPa, the maximum cold rolling temperature is 45°C and the minimum aging time, 30 days.
Enhancement of Ductility in Aluminum Alloys by the Control of Transition-Metal Solutes during Thermo-Mechanical Processing
Authors: Saimoto Shigeo , Cao S. , Mishra Raja K.
Published: March 2009

Predictions of chromium additions to aluminum alloys to stabilize the deformation debris products were examined. Additions of 0.22 wt. % Cr to AA6063 extrusion alloys manifested enhanced formability under bending and precision-strain-rate-sensitivity tensile testing indicated that the stacking fault energy was reduced. The debris products were more resistant to dynamic recovery resulting in enhanced ductility at 27 °C and the solute-drag effect of Mg was dramatically manifested in the Haasen plot.
Grain Refinement and Mechanical Properties of a Metastable Austenitic Fe-Cr-Ni-Mn Alloy
Authors: Ma Yunqing , Jin Jae Eun , Lee Young-Kook
Published: March 2009

A lot of works for developing the structural nano-materials have been performed all
over the world in recent years. Severe deformation techniques like HPT, ECPA and ARB have been applied to different materials such as Al, Cu, Ti and several steels. Such techniques greatly reduced the grain size and improved the yield and tensile strengths. However, the elongation of the materials is greatly decreased due to the small amount of work hardening, and these techniques do not seem suitable for the mass production. Therefore, this study has been carried out as a fundamental research for developing austenitic steels with high strength and good elongation using a conventional rolling and annealing processes. Fe-0.1%C-10%Cr-5%Ni-8%Mn alloy was melted, homogenized, hot rolled, and cold rolled at room temperature to transform γ austenite to α ’ martensite. After that, the specimens were annealed just above its reverse transformation finish temperature (Af) to obtain the fine reversed austenite grains. The grain size of the metastable austenitic steel was successfully refined to less than 200nm by repeating rolling and annealing processes. The resultant nanocrystalline material shows not only high strength but also large elongation because the work hardening ability is enhanced by the strain-induced martensitic transformation during the tensile test.
Grain Refinement in AZ91E Magnesium Alloy by Thermo-Mechanical Treatments
Authors: Yamamoto Atsushi , Ikeda Masahiko , Tsubakino Harushige
Published: March 2009

In order to improve poor formability in magnesium alloy, grain refinement has been
attempted on AZ91E alloy by a thermo-mechanical treatment. Specimens were firstly cold-rolled at 10 %, then solution heat treated at 673 K for 86.4 ks, and hot-rolled at 573 K with about 5 % for four passes, or hot-rolled at 20 % with one pass. The rolled specimens were finally heat treated at 473 to 673 K for 3.6 to 36 ks. Microstructures in the starting material characterized by grain boundary precipitates and aluminum rich regions with about 180 µm in grain size were changed into fine
grained microstructures with about 10 to 30 µm in diameter, in which precipitates of Mg17Al12 were uniformly distributed. Although the specimen was prepared by rolling, the (0001) texture was not so remarkable.
Phase Transition during Slow Heating in the Mixture Insert Metal Using TLP Bonded Interlayer
Authors: Kim Sung Wook , Lee Chang Hee
Published: March 2009

This study was carried out to investigate the effect of heating rate on the phase transition between additive base metal powder and liquid insert metal during transient liquid phase (TLP) diffusion bonding of Ni-based superalloy GTD-111. Heating rates studied were 10, 1, 0.5 and 0.1°Cs-1 in high vacuum conditions (3×10-5 torr) by means of a high frequency induction furnace. When heated at lower than 0.5°Cs-1, the transition of dissolution to solidification occurred during heating. In the case of very slow heating, the dissolution quickly finished at a lower temperature, and solidification soon started. The separated grains of additive base metal powders supplied the lager interface area for the diffusion of boron. Solidification transition temperatures of liquid phase were affected by the increase of diffusion interface and of duration time during slow heating. A minimum heating rate required to heat insert materials to a normal TLP isothermal bonding temperature of GTD-111 (≈1150°C) without a dissolution-solidification transition during heating should be higher than 1°Cs-1.
Photoelectrochemical Measurements on Cathodically Electrodeposited Films of Cadmium and Zinc Chalcogenide Compounds
Authors: Bouroushian M. , Kosanovic T.
Published: March 2009

A variety of electrochemical and electrical techniques is employed in order to determine useful parameters of the optical behaviour of thin semiconducting films. In particular, this work is intended to the characterization of cathodically electrodeposited binary and ternary cadmium and zinc selenides and tellurides by photoelectrochemical (PEC) tests. Typical solid-state techniques, such as reflection, laser assisted photoreflection, resistivity and Hall effect measurements are used as well. A plain relation between crystal structure/film morphology and PEC behavior is established so long as the electrochemical preparation method is capable to explicitly control the deposit structure. In certain cases, a particular charge transfer mechanism in the semiconductor, associated with the existence of a nanostructure, is shown to result in higher photoconversion efficiencies as compared to larger-grained films.
Amorphous Structure of Poly(Propylene Glycol) Electrolytes
Authors: Goulart Silva Glaura , Souza Patterson Patrício de , Silveira Mizher Ana Júlia , Pimenta Marcos A.
Published: March 2009

Changes in glass transition and ionic association of PPG/LiClO4 samples with increasing salt concentration have been studied using temperature modulated differential scanning calorimetry (TMDSC)and micro Raman spectroscopy, respectively. PPG, of average molar mass of 3000, was used as host for LiClO4 over the range O:Li = 35 – 4. The analysis of the Raman band, obtained at room temperature, associated with the ν1 symmetric stretching mode of ClO4 - anions, shows the presence of ionic association (ion pair) for electrolytes with salt concentration higher than O:Li = 8. The glass transition changes in the electrolytes were investigated using the differential of heat capacity with respect to temperature [dCp/dT], obtained from TMDSC. The analysis of the dCp/dT signal, by fitting with Gaussian curves, showed that there is a glass transition splitting in samples with concentrations higher than O:Li = 16, which indicates the presence of nanoheterogeneities in these amorphous electrolytes. Raman results pemit to affirm that this nanoheterogeneities were associated mainly with solvent separated ion pairs regions of different concentrations, and not with aggregate of ionic species.
Preparation and Characterization of TeO2 Based Glasses
Authors: Pedlíková J. , Zavadil J. , Prochazková Olga , Kaluzny J.
Published: March 2009

Binary and ternary TeO2 based oxy-chloride glass systems have been prepared and characterised by absorption and low-temperature photoluminescence spectroscopy, and by the measurements of dc electrical conductivity. Prepared glasses exhibit transmittance 75-80% in a broad transmission range 0.3 – 6.5µm with modest shift of upper absorption edge to longer wavelength as heavier ions are introduced into the system. Electronic transitions between 4f-4f inner shells of Pr3+ ions embedded into the host glass have been investigated in a wide temperature
range as a function of used precursors used for doping. The temperature dependence of dc electrical conductivity exhibits Arrhenius plots with the single activation energy. PACS codes 81.05.Kf, 78.20.Ci, 78.55.Hx
Space Charge Studies of Aged XLPE Using Combined Isothermal and Thermostimulated Current Measurements
Authors: Carmo Lança M. , Neagu Eugen R. , Marat-Mendes José N.
Published: March 2009

Space charge in electrically aged cross-linked polyethylene (XLPE) was studied using a procedure combining isothermal and non-isothermal measurements of charge and discharge currents. Aging is carried out using an AC field while immersing the disk-shaped samples in an ionic aqueous solution at constant temperature. After aging the samples were isothermally DC charged and discharged. Next a non-isothermal experiment with constant heating rate was performed (FTSDC). Finally the sample was kept at the highest temperature in order to completely discharge the polymer. The space charge introduced in the XLPE during aging can be analyzed from the study of the FTSDC spectra. The thermogram (FTSDC) shows a very broad peak. The peak is attributed to trapped space charge in traps with long relaxation times. It is possible to decompose it into three or four individual peaks and obtain the corresponding activation energies. The results were compared with previous ones obtained for LDPE (low density polyethylene) aged under similar conditions.
Growth and Properties of GaN/Si Heterojunction
Authors: Zainuriah Hassan , Ng Sha Shiong , Chew G.L. , Yam F.K. , Abdullah Mat Johar , Hashim M. Roslan , Ibrahim Kamarulazizi , Kordesch M.E.
Published: March 2009

Gallium nitride (GaN) is a highly promising wide band gap semiconductor with applications in high power electronic and optoelectronic devices. Thin films of GaN are most commonly grown in the hexagonal wurtzite structure on sapphire substrates. Growth of GaN onto silicon substrates offers a very attractive opportunity to incorporate GaN devices onto silicon based integrated circuits. Although direct epitaxial growth of GaN films on Si substrates is a difficult task (mainly due to the 17% lattice mismatch present), substantial progress in the crystal quality can be achieved using a buffer layer. A full characterization of the quality of the material needs to be assessed by a combination of different techniques. In this work, a detailed characterization study of GaN thin film grown on Si(111) with AlN buffer layer by low pressure metalorganic chemical vapor deposition (LP-MOCVD) was carried out. Post deposition analysis includes scanning electron microscopy (SEM), x-ray diffraction (XRD), Hall and infrared (IR) spectroscopy techniques. The IR spectra were compared to the calculated spectra generated with a damped single harmonic oscillator model. Through this method, a complete set of reststrahlen parameters (such as ε∞, S, wTO, γ) of the GaN epilayer were obtained. Our results show that the GaN film has a single crystalline structure. Current-voltage characteristics (I-V) of this GaN/Si heterojunction were measured at room temperature. Rectification behavior was observed for this anisotype heterojunction. The electrical characteristics of Ni Schottky barriers on this unintentionally doped n-type film were also investigated. The barrier height of Ni/GaN Schottky barriers has been determined to be 0.93 eV by I-V measurement.
Electroluminescence from GaInAsP/InP VCSEL
Authors: Ulug Asiye , Karabulut Melek Tuncay
Published: March 2009

Long-wavelength vertical cavity surface emitting lasers (VCSELs) operating in the 1.3 µm to 1.5 µm wavelength range are considered the best candidate for the future low-cost reliable light sources in fiber communications. However, the room temperature performance of GaInAsP/InP long-wavelength InP lattice matched material system falls below the shortwavelength VCSELs. In this work we present the results of our studies concerning I-V and electroluminescence measurements on GaInAsP/InP structure with distributed Bragg reflectors. The device lased at 0.98 µm at room temperature.
SiC Materials and Technologies for Sensors Development
Authors: Godignon Philippe
Published: March 2009

Silicon Carbide has proven its strong interest for power and high frequency devices but it also has superior characteristics for application in the sensors and MEMS fields. The characteristic requirements of the starting material are different from that of power devices since the level of defects is not so critical while the layer stress is important especially in 3C-SiC on Si. The keyprocess for MEMS fabrication is the etching, which is progressing thanks to ICP process improvements. A perfect control of the etching step could allow the obtention of nano-resonators in
SiC with fairly superior characteristics to the Si ones. Other electrical sensors for high temperature application such as gas sensors or Hall sensors have been also successfully developed taking profit of the deep etching process improvement and high temperature contact developments.
High Energy Resolution Detectors Based on 4H-SiC
Authors: Ivanov Alexander M. , Kalinina Evgenia V. , Kholuyanov G. , Strokan Nikita B. , Onushkin G. , Konstantinov Andrey O. , Hallén Anders , Kuznetsov Andrej Yu.
Published: March 2009

The spectrometric characteristics of the detectors based on 4H-SiC using 4.8-7.7 MeV a-particles were determined. The Cr Schottky barriers with areas of 1×10-2 cm2 were performed^by vacuum thermal evaporation on 4H-SiC epitaxial layers grown by chemical vapor deposition (CVD) with thickness 26 and 50 µm. The concentrations of the uncompensated donors into CVD epitaxial layers were (6-10) ×1014 cm-3, that allowed to develop a detector depletion region up to
30 µm using reverse bias of 400 V. The energy resolution less than 20 keV (0.34%) for lines of 5.0- 5.5 MeV was achieved that is twice as large of the resolution of high-precision Si-based detectors prepared on specialized technology. The maximum signal amplitude of 4H-SiC - detectors corresponding to the average electron-hole pair generation energy was found to be 7.70 eV.
Structural Improvement of Seeds for Bulk Crystal Growth by Using Hot-Wall CVD of 4H-SiC
Authors: Wagner Günter , Schulz D. , Doerschel J.
Published: March 2009

Growth of 4H-SiC epitaxial layers has been performed in a horizontal hot-wall CVD (chemical vapor deposition) reactor using the silane-propane-hydrogen system. Two inch 4H-SiC, C-face wafers with an off-cut angle of about 7° towards <11 2 0> direction have been used as substrates. Micropipe dissociation has been investigated by varying the carbon-silicon (C/Si) ratio in
the source gas atmosphere. Depending on the C/Si ratio the micropipes propagate into the layer without changing their image (C/Si > 1) or they dissociate in separate dislocations leaving a scar like formed surface region (C/Si £ 1). The substrates including epitaxial layers of reduced micropipe density were used as seeds for bulk crystal growth. If a micropipe is once closed in an epilayer grown at a low C/Si ratio, it is not opened in the subsequent growth process at high temperature.
Aluminium Doping of 4H-SiC Grown with HexaMethylDiSilane
Authors: Sartel C. , Soulière Véronique , Zielinski Marcin , Monteil Yves , Camassel Jean , Rushworth S.
Published: March 2009

We report on the study of the p-type doping of 4H-SiC material using
HexaMethylDiSilane/TriMethylAluminium/Propane (HMDS/TMA/P) system in place of the usual Silane/TriMethylAluminium/Propane (S/TMA/P) precursors. The influence of growth parameters such as TMA flow, growth rate or C/Si ratio is investigated. The aluminium incorporation level is deduced from both by C(V) (mercury probe) and SIMS measurements. The presence of aluminium in the layers is confirmed by non-destructive optical micro-Raman experiments. Good quality p-type, aluminium doped 4H-SiC layers can be grown using
HMDS/TMA/P system. The amount of aluminium in the layers can be controlled by choosing the growth conditions and an aluminium concentration as high as 2x1019 at.cm-3 has been reached.Finally, comparing the two HMDS/TMA/P and S/TMA/P systems, no difference in aluminium incorporation has been found.
Development of Epitaxial SiC Processes Suitable for Bipolar Power Devices
Authors: Sumakeris Joseph J. , Das Mrinal K. , Ha Seoyong , Hurt Edward , Irvine Kenneth G. , Paisley Michael J. , O'Loughlin Michael  J. , Palmour John W. , Skowronski Marek , McD. Hobgood H. , Carter Jr. Calvin H.
Published: March 2009

We present a survey of the most important factors relating to an epitaxial SiC growth
process that is suitable for bipolar power devices. During the last several years, we have advanced our hot-wall SiC epitaxial growth technology to the point that we can support the transition of bipolar power devices from demonstrations to applications. Two major concerns in developing a suitable epitaxial technology are epilayer uniformity and extended defect density. Our state-of-theart capability permits the realization of 1-cm2 area devices with exceptional yields. Another major
concern is the stability of bipolar devices during forward conduction. We have developed proprietary substrate and epilayer preparation technologies that have essentially eliminated Vf drift as a significant barrier to the exploitation of SiC based bipolar devices.
Modified Physical Vapor Transport Growth of SiC - Control of Gas Phase Composition for Improved Process Conditions
Authors: Wellmann Peter J. , Straubinger Thomas L. , Desperrier Patrick , Müller Ralf , Künecke Ulrike , Sakwe Sakwe Aloysius , Schmitt Holger , Winnacker Albrecht , Blanquet Elisabeth , Dedulle Jean Marc , Pons Michel
Published: March 2009

We review the development of a modified physical vapor transport (M-PVT) growth technique for the preparation of SiC single crystals which makes use of an additional gas pipe into the growth cell. While the gas phase composition is basically fixed in conventional physical vapor transport (PVT) growth by crucible design and temperature field, the gas inlet of the MPVT configuration allows the direct tuning of the gas phase composition for improved growth conditions. The phrase "additional" means that only small amounts of extra gases are supplied in
order to fine-tune the gas phase composition. We discuss the experimental implementation of the extra gas pipe and present numerical simulations of temperature field and mass transport in the new growth configuration. The potential of the growth technique will be outlined by showing the improvements achieved for p-type doping of 4H-SiC with aluminum, i.e. [Al]=9⋅1019cm-3 and ρ<0.2Ωcm, and n-type doping of SiC with phosphorous, i.e. [P]=7.8⋅1017cm-3.
Optical Spectroscopy as a Tool for Observation of Porous SiC Graphitization
Authors: Shuman V.B. , Savkina N.S.
Published: March 2009

We have studied effects of thermal treatment in vacuum and wet oxidation on the optical transmission of SiC samples with porous layer on the Si face in the visible and near infrared spectral range. An analysis of changes in the absorption coefficient shows that the process of graphitization in vacuum begins at a temperature below 700°C and can be observed at wet oxidation at 1000°C.
Progress and Limits of the Numerical Simulation of SiC Bulk and Epitaxy Growth Processes
Authors: Pons Michel , Blanquet Elisabeth , Dedulle Jean Marc , Ucar M. , Wellmann Peter J. , Danielsson Örjan , Ferret Pierre , Di Cioccio Lea , Baillet Francis , Chaussende Didier , Madar Roland
Published: March 2009

Modeling and simulation of the SiC growth process is sufficiently mature to be used as a training tool for engineers as well as a decision making tool, e.g. when building new process equipment or up-scaling old ones. It is possible to simulate accurately temperature and deposition distributions, as well as doping. The key of success would be the combined use of simulation, experiments and characterization in a "daily interaction". The main limitation in SiC growth modeling is the accurate knowledge of physical, thermal, radiative, chemical and electrical data for the different components of the reactor. This is the weakest link in developing completely predictive models. In addition, the link between the thermochemical history of the grown material and its structure and defects still needs further development and input of experimental data.
XRDT Study of Structural Defects of 6H-SiC Crystals
Authors: Agrosì G. , Fregola R.A. , Monno A. , Scandale Eugenio , Tempesta G.
Published: March 2009

X-Ray Diffraction Topography (XRDT) and Optical Microscopy (OM) are adopted to study extended structural defects in 6H-SiC bulky crystals. Topographs are taken by means of White Beam Synchrotron Radiation Source (WB-SRS-XRDT) and by means of monochromatic radiation (MoKα1) with conventional source (Lang method). All studied samples are characterised by the presence of linear defects, dislocations and microchannels, uniformly distributed in the crystal. Such defects draw a net of independent systems of parallel lines, with different orientation and different contrast widths. Micro-channels are parallel to the c axis, whereas dislocations are perpendicular or nearly parallel to the c axis. The last are unit screw dislocations. It has been concluded that the growth mechanism is driven by screw dislocations and that channels results from the coalescence of parallel dislocations.
PVT-Growth and Characterization of Single Crystalline 3C-SiC on a (0001) 6H-SiC Substrate
Authors: Polychroniadis Efstathios K. , Mantzari Alkyoni , Freudenberg A. , Wollweber Jürgen , Nitschke R. , Frank Thomas , Pensl Gerhard , Schöner Adolf
Published: March 2009

The aim of the present work is to grow 3C-SiC on (0001) 6H-SiC seeds using the
Physical Vapour Transport (PVT) method and to study the electrical and structural properties of the grown material. Photoluminescence (PL)-mappings reveal that the overgrown layer consists predominantly of the 3C-SiC polytype and capacitance-voltage (C-V) measurements result in a net nitrogen donor concentration of 1x1016cm-3. Transmission Electron Microscopy (TEM)
observations also confirm that the overgrown layer is of the 3C-SiC polytype having the cubic [111] crystallographic direction parallel to the c-axis of the 6H-SiC substrate. In some cases, twin crystals of 3C-SiC are formed immediately after the interface and, in a few cases, small 6H-SiC inclusions are observed in the cubic film having the same orientation as the substrate. The film near the substrate/overgrown interface shows a high density of defects such as dislocations and stacking faults (SF’s), which propagate into the overgrown layer. Finally although there is a rapid decrease of the defect density within the first 60 µm from the interface, the SF density remains almost constant within the last 100 µm below the surface.
Midgap Levels in As-Grown 4H-SiC Epilayers Investigated by DLTS
Authors: Danno Katsunori , Kimoto Tsunenobu , Matsunami Hiroyuki
Published: March 2009

Midgap levels in 4H-SiC epilayers have been investigated by DLTS. The EH6/7 center (Ec-1.55 eV) is the dominant deep level as observed in DLTS spectra from n-type epilayers. The activation energy of EH6/7 center is unchanged regardless of applied electric fields, indicating that the charge state of EH6/7 center may be neutral after electron emission (acceptor-like). A DLTS spectrum
for a p-type epilayer in the temperature range from 90 to 830 K is dominated by two peaks, D center and a deep trap at 1.49 eV from the valence band edge. Minority carrier traps have been also investigated by DLTS using pn diodes. Two minority carrier traps with activation energies of 1.0 eV and 1.43 eV have been detected.
Electrical Properties of p-Type In-Situ Doped vs. Al-Implanted 4H-SiC
Authors: Pernot Julien , Contreras Sylvie , Camassel Jean , Robert Jean-Louis
Published: March 2009

We report a detailed investigation of the electrical properties of p-type 4H-SiC. In the
range 100 K-800 K we show that, both, the temperature dependence of the hole concentration and Hall mobility is satisfactorily described using the relaxation time approximation. Performing a detailed comparison of in-situ vs. implantation doping, we evidence an incomplete activation of the dose (about 50 ±10 %) with apparition of a large number of compensating centres in the implanted
layers.
Hall Effect in the Channel of 3C-SiC MOSFETs
Authors: Krieger M. , Pensl Gerhard , Bakowski Mietek , Schöner Adolf , Nagasawa Hiroyuki , Abe Masayuki
Published: March 2009

Temperature-dependent Hall effect investigations in the channel of lateral 3C-SiC
LDDMOSFETs with nitrogen(N)-implanted source/drain regions are conducted. The free electron concentration and the electron Hall mobility are independently determined. A maximum electron Hall mobility of 75 cm2/Vs is observed. The gate oxide withstands electric field strengths up to 5 MV/cm. A high density of interface states of a few 1013 cm-2eV-1 close to the 3C-SiC conduction band edge still lowers the performance of the MOS device.
A New Model for the DI-Luminescence in 6H-SiC
Authors: Rauls E. , Gerstmann Uwe , Pinheiro M.V.B. , Greulich-Weber Siegmund , Spaeth Johann Martin
Published: March 2009

In a combined theoretical and experimental work, we have investigated the
common DI photoluminescence in 6H-SiC material. We present an atomistic model which is able to explain the annealing behavior, i. e. the correlation with the silicon vacancy, the local vibrational modes and the excitonic-like character observed.
The VSiCSi(SiCCSi) Complex in Electron-Irradiated 6H-SiC
Authors: Pinheiro M.V.B. , Rauls E. , Gerstmann Uwe , Greulich-Weber Siegmund , Spaeth Johann Martin
Published: March 2009

We identify the VSiCSi(SiCCSi) complex in electron-irradiated 6H-SiC samples. Based on the analysis of new photo-excited EPR spectra, and supported by theoretical calculations, it was possible to establish its microscopic structure and to conclude that this complex is formed from the first product of the Si-vacancy annealing, the VSiCSi complex (also known as P6/P7 centers).
Kinetic Aspects of the Interstitial-Mediated Boron Diffusion in SiC
Authors: Bockstedte M. , Mattausch Alexander , Pankratov Oleg
Published: March 2009

Using an ab initio method we analyze the mechanisms of the boron diffusion with emphasis on the role of the intrinsic interstitials. It is shown that the boron diffusion is dominated by a kick-out mechanism. The different effect of silicon and carbon interstitials gives rise to kinetic effects. A preference for a kick-in of the boron interstitial into the carbon lattice sites is found. Kinetic effects reported in co-implantation experiments and in-diffusion experiments are explained by our findings.
Hydrogen-Saturated SiC-Surfaces: Model Systems for Studies of Passivation, Reconstruction and Interface Formation
Authors: Seyller Thomas
Published: March 2009

Hydrogenation of SiC surfaces was carried out by annealing in ultra-pure hydrogen at temperatures of around 1000°C. The hydrogenated surfaces were studied using a variety of techniques and show exceptional properties which are discussed in the light of earlier studies of Si and SiC surfaces and interfaces.
First Principles Simulations of SiC-Based Interfaces
Authors: Catellani A. , Cicero G. , Righi M.C. , Pignedoli C.A.
Published: March 2009

We review some recent investigations on prototypical SiC-based interfaces, as obtained from first-principles molecular dynamics. We discuss the interface with vacuum, and the role played by surface reconstruction in SiC homoepitaxy, and adatom diffusion. Then we move to the description of a buried, highly mismatched semiconductor interface, the one which occurs between SiC and Si, its natural substrate for growth: in this case, the mechanism governing the creation of a
network of dislocations at the SiC/Si interface is presented, along with a microscopic description of the dislocation core. Finally, we describe a template solid/liquid interface, water on SiC: based on the predicted structure of SiC surfaces covered with water molecules, we propose (i) a way of nanopatterning cubic SiC(001) for the attachment of biomolecules and (ii) experiments to reveal the
local geometry of adsorbed water.
ALD Deposited Al2 O3 Films on 6H-SiC(0001) after Annealing in Hydrogen Atmosphere
Authors: Gao Kun Yuan , Seyller Thomas , Emtsev Konstantin V. , Ley Lothar , Ciobanu Florin , Pensl Gerhard
Published: March 2009

Atomic Layer Deposited Al2O3 films on hydrogen-terminated 6H-SiC(0001) were
annealed in hydrogen atmosphere and characterized by admittance spectroscopy measurement and photoelectron spectroscopy (PES). The resultant density of interface trap (Dit) from admittance spectroscopy measurement is reduced near mid gap, but increases strongly towards the conduction band edge. Systematic PES measurements show that hydrogen annealing introduces Si4+ as a new component besides Si0 and Si+. Using different electron escape depths for photon electrons, depth profiling of Si in its different oxidation states was performed. The result indicates the formation of a top SiO2 layer and a rougher interfacial layer containing more Si+ and Si4+ which could be responsible for the strong increase of Dit just below the conduction band edge.
SiC/SiO2 Interface States: Properties and Models
Authors: Afanas'ev Valeri V. , Ciobanu Florin , Dimitrijev Sima , Pensl Gerhard , Stesmans Andre
Published: March 2009

Properties of defects encountered at the oxidized surfaces of silicon carbide (SiC) suggest their origin to be different from the dangling-bond-type defects commonly observed in the oxidized silicon. Among different models of these SiC/oxide interface states advanced during the past decade, two have received substantial experimental support. This first one is the “carbon cluster”
model, which ascribes the traps with energy levels in the SiC bandgap to inclusions of elemental carbon formed during the SiC surface treatment and subsequent oxidation. The second model invokes intrinsic defects of SiO2 to account for the high density of interface states in the energy range close to the conduction band of SiC. Achievements in reducing the SiC/SiO2 defect density are discussed.
Interface States in SiO2/4H-SiC(0001) Interfaces from First-Principles: Effects of Si-Si Bonds and of Nitrogen Atom Termination
Authors: Ohnuma Toshiharu , Tsuchida Hidekazu , Jikimoto Tamotsu , Miyashita Atsumi , Yoshikawa Masahito
Published: March 2009

First-principles calculations for the abrupt SiO2/4H-SiC interfaces accounting for Si-Si bonding and Nitrogen atom termination have been performed. Interface states due to Si-Si bonds appear at the valence band edge. Interface states at the midgap vanish when N atom terminates the Si dangling bond, but the interface states arising from the Si-N bonds appear at the valence band edge at the same time.
Structural and Electronic Properties of Si1-xCxO2
Authors: Justo João F. , Silva Cesar R.S. da , Pereyra I. , Assali Lucy V.C.
Published: March 2009

There is growing interest in understanding the properties of SiC-SiO2 interfaces,
which can be formed by oxidation of silicon carbide surfaces. Here, we used variable cell shape ab initio molecular dynamics to investigate the structural and electronic properties of crystalline phases of silicon oxycarbide which could appear within such interfaces. We find that carbonoxygen single bonds may remain stable inside a silicon oxide matrix. For the Si2CO6 compound, there are at least two crystalline phases, both having large bulk modulii and wide bandgaps.
Observation of Deep Level Centers in 4H and 6H Silicon Carbide Metal Oxide Semiconductor Field Effect Transistors
Authors: Meyer David J. , Dautrich Morgen S. , Lenahan Patrick M. , Lelis Aivars J.
Published: March 2009

Utilizing an very sensitive electron spin resonance (ESR) technique, spin dependent recombination (SDR) we have identified interface and near interface trapping centers in 4H and 6H SiC/SiO2 metal oxide semiconductor field effect transistors (MOSFETs). We extend our group’s earlier observations on 6H devices to the more technologically important 4H system and find that several centers can play important roles in limiting the performance of SiC based
MOSFETs.
Development of the Novel Electron Bombardment Anneal System (EBAS) for SiC Post Ion Implantation Anneal
Authors: Shibagaki Masami , Kurematsu Yasumi , Watanabe Fumio , Haga Shigetaka , Miura Kuniaki , Suzuki Tomoyuki , Satoh Masataka
Published: March 2009

We develop the rapid thermal anneal system of the implanted SiC, Electron Bombardment Anneal System (EBAS), which is able to heat up to 1900 oC with a rate of 320 oC/min in vacuum. Using this novel system, the annealing of N+ implanted SiC samples (total dose: 2.4 x 1015 cm-2, thickness: 220 nm) at 1900 oC for 0.5 min results in a low sheet resistance of 1.39 x 103 ohm/sq. with
extremely low roughness of the surface (RMS value: 0.32 nm). It is also demonstrated that EBAS can anneal the sample with low electric power consumption.
Ar Annealing at 1600°C and 1650°C of Al+ Implanted p+/n 4H-SiC Diodes: Analysis of the J-V Characteristics Versus Annealing Temperature
Authors: Bergamini Fabio , Moscatelli Francesco , Canino Mariaconcetta , Poggi Antonella , Nipoti Roberta
Published: March 2009

We report on the electrical characterization of Al+ implanted p+/n 4H-SiC diodes via a planar technology. Hot implantation at 400°C and post implantation annealing at 1600°C and 1650°C in high purity Argon ambient were done for the realization of p+/n diodes. The current voltage characteristics of the p+/n diodes and the resistivity of the implanted layer were measured at room temperature. The majority of the 136 measured diodes had a turn on voltage of 1.75 V for both annealing temperatures. The 1600°C annealed diodes showed an almost exponential forward
characteristic with ideality factor equal to 1.4, an average reverse leakage current density equal to (4.8 ± 0.1)×10-9 A/cm2 at –100 V, and a break down voltage between 600 and 900V. The 1650°C annealed diodes often had forward “excess current component” that deviates from the ideal forward exponential trend. The average reverse leakage current density was equal to (2.7 ± 0.5)×10-8 A/cm2
at –100 V, and the breakdown voltage was between 700 and 1000V, i.e. it approached the theoretical value for the epitaxial 4H-SiC layer.
J-V Characteristics of Al+ Ion Implanted p+/n 4H-SiC Diodes Annealed in Silane Ambient at 1600°C
Authors: Bergamini Fabio , Rao Shailaja P. , Saddow Stephen E. , Nipoti Roberta
Published: March 2009

Al+ implanted p+/n 4H-SiC diodes were realized via planar technology. The p+/n
junctions were obtained by hot implantation at 400°C, followed by a post implantation annealing at 1600°C in Silane ambient. 136 diodes and other test structures were measured: the current voltage^curves and the resistivity of the implanted layer were investigated at room temperature. The majority of the measured diodes had a turn on voltage of about 1.75 V, a forward characteristic with exponential trend and ideality factor equal to 1.2, and a very low spread in the distribution of the
reverse leakage current values at –100V. The average reverse leakage current value is (9.7 ± 0.4) × 10-9 A/cm2. The breakdown voltage of these diodes approached the theoretical value for the use epitaxial 4H-SiC layer, i.e. 0.75 – 1.0 kV. All these positive results are penalized by the high resistivity value of the implanted Al+ layer, which amounts to 11 W·cm that is one order of
magnitude higher than the desired value.
The Role of Formation and Dissolution of C Clusters on the Oxygen Incorporation during Dry Thermal Oxidation of 6H-SiC
Authors: Radtke C. , Baumvol Israel J.R. , Ferrera B.C. , Stedile Fernanda Chiarello
Published: March 2009

The mechanisms of oxygen incorporation during dry thermal oxidation of 6H-SiC wafers were investigated. Isotopic tracing of oxygen was performed by sequential oxidations in dry O2 enriched or not in the 18O isotope and subsequent determinations of the 18O profiles. The results obtained with SiC substrates were compared with those of Si, evidencing different mechanisms of oxygen incorporation and transport. The gradual nature of the SiO2/SiC interface was also evidenced. A probable explanation for this gradual SiO2/SiC interface is shown to be the formation
of C clusters during oxidation.
4H-SiC MOS Structures Fabricated from RTCVD Si Layers Oxidized in Diluted N2O
Authors: Pérez-Tomás Amador , Tournier Dominique , Godignon Philippe , Mestres Narcis , Millan José
Published: March 2009

Thin (~10nm) Si layers have been deposited using Rapid Thermal CVD at temperatures ranging 950°C-1050°C. RTCVD deposited Si layers have been oxidized using N2O at 1300°C during relatively short times (15min) to produce SiO2 layers of 20-30nm. The interfacial characteristics of N2O oxidized RTCVD layers have been studied using the conductance method, showing a reduced traps density and a low band bending fluctuation when compared with conventional N2O grown oxides on 4H-SiC substrates. The surface topology of these layers has also
been analyzed evidencing an adequate topography with low roughness.
Effects of N2O Anneal on Channel Mobility of 4H-SiC MOSFET and Gate Oxide Reliability
Authors: Fujihira Keiko , Tarui Yoichiro , Ohtsuka Kenichi , Imaizumi Masayuki , Takami Tetsuya
Published: March 2009

The effect of N2O anneal on channel mobility of inversion-type 4H-SiC n-channel
MOSFET has been systematically investigated. It is found that the mobility increases with increasing anneal temperature from 900 to 1150°C. The highest field effect mobility of 30 cm2/Vs is achieved by 1150°C anneal for 3 h, which is about 20 times higher than that for non-annealed MOSFET. In order to investigate the oxide reliability, TDDB measurement has been performed on SiO2 grown on n-type
4H-SiC. The oxide lifetime is found to be drastically improved by N2O anneal.
Electrical Properties of Aluminium Oxide Films Grown by Atomic Layer Deposition on n-Type 4H-SiC
Authors: Avice Marc , Grossner Ulrike , Monakhov Edouard V. , Grillenberger Joachim , Nilsen Ola , Fjellvåg Helmer , Svensson Bengt Gunnar
Published: March 2009

In this study, electrical properties of Al2O3 deposited by Atomic Layer Deposition
(ALCVD) on n-type 4H-SiC were investigated. Metal-Oxide-Semiconductor (MOS) capacitors were characterized by various electrical techniques such as Capacitance-Voltage (CV), Current- Voltage (IV) and Deep Level Transient Spectroscopy (DLTS) measurements. Two different oxidants, H2O and O3, have been used for the oxide deposition. After deposition, the flat-band
voltage shift is much less using O3 than H2O (~ 7V versus ~ 20V). Annealing treatment has been carried out at different temperatures in Ar atmosphere up to 700°C. Whereas the flat-band voltage
shift can be reduced by annealing, the leakage current remains rather high.
Characterization of 4H-SiC MOS Structures with Al2O3 as Gate Dielectric
Authors: Paskaleva A. , Ciechonski R.R , Syväjärvi Mikael , Atanassova E. , Yakimova Rositza
Published: March 2009

The electrical properties of Al2O3 as a gate dielectric in MOS structures based on n- and p-type 4H-SiC grown by sublimation method have been investigated and compared to the properties of similar structures utilizing SiO2. The electrically active defects in the structures are studied by CV method. The results show that the type as well as spatial and energy distribution of defects in Al2O3/SiC and SiO2/SiC samples are different. The structures with Al2O3 on p-type 4H-SiC demonstrate much better C-V characteristics than the p-type 4H-SiC/SiO2 structures.
4H-SiC MOSFETs Using Thermal Oxidized Ta2Si Films as High-k Gate Dielectric
Authors: Pérez-Tomás Amador , Godignon Philippe , Mestres Narcis , Montserrat Josep , Millan José
Published: March 2009

Oxidized Ta2Si layers have been used as high-k dielectric layer for 4H-SiC MOSFETs. The gate insulator was grown by dry oxidation of 40nm deposited Ta2Si during 1h at 1050oC. The dielectric constant obtained from 4H-SiC MIS capacitors is ~20 with an insulator thickness of 150nm. These devices exhibit adequate subthreshold, saturation and drive characteristics. For the MOSFETs fabricated on a p-implanted and annealed region, a peak mobility up to 45cm2/Vs has
been extracted. The specific on-resistance of this device is 29mW·cm2 at room temperature with VDS=0.2V and VGS=14V.