bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Bio-Mineralization of BCP with Compensation of Calcium and Phosphate Ions
Authors: Zheng Hua De , Wang Ying Jun , Ma Qiang , Ning Cheng Yun , Chen Xiao Feng
Published: March 2009

In the present study, an Intelligent Multi-parameter Simulated Evaluation in vitro （IMSE system） was used to study the deposition properties of apatite formation on the surface of biphasic calcium phosphate porous ceramic (BCP) from static and dynamic r-SBF. Results showed that apatite formed on the surface of BCP from static and dynamic r-SBF differed between each other. In static r-SBF, ions were transferred by diffusion, which could not compensate the consuming of calcium ions, and mist apatite layer was formed on the surface of samples. But in the dynamic r-SBF, simulated fluid was adjusted precisely and flowed forcedly, the concentrations of ions were homogeneous; with the compensation of ions, calcium and phosphate were supersaturated, and the free energy of apatite formation was negative, bone-like apatite sheets were formed on the surface of samples.
Evaluation of Precision Machining Characteristics for MAP of Magnesium Alloy
Authors: Lee Jung In , Kwak Jae Seob , Kang Dae Min
Published: March 2009

. It is very difficult to polish the surface of magnesium materials because of its explosion and fragility properties. Magnetic Abrasive Polishing (MAP) process is one of the nontraditional machining technologies newly developed. In the MAP process, a cutting tool that consists of ferrous particles and nonferrous abrasives under oil lubricant is flexible. Because of this flexibility, the tool can remove a very small amount of material from a workpiece and better surface can be produced after polishing the workpiece. In this study, the MAP of a magnesium material was performed. In the experimental verification, design of experimental method was performed to evaluate parameters’effect of the MAP on polishing results of the magnesium material. As a result, it was seen that the MAP was very useful for finishing the magnesium material.
Phosphate and Stannate Chemical Conversion Coatings Formed on AZ91D Alloys
Authors: Yang Xiang Jie , Jin Hua Lan
Published: March 2009

The morphology and the mass change of the AZ91D alloys matrix after pretreatment, the morphology and the phase composition of chemical conversion coatings formed by phosphate and stannate were studied using scanning electron microscope, X-ray diffraction and the mass loss method. The corrosion resistance of the coatings were studied by salt spay test and damp heat test. The results show that the phase composition of matrix before and after pretreatment is almost changeless and the mass diminishes a litter, the deep micro flaw appears near between α-Mg and β phase during acidic pickling. The phosphate chemical conversion coating is mainly composed of Mg, MgO and some amorphous phase, and the stannate conversion coating is crystal structure and mainly composed of Mg, Al12Mg17 and MgSnO3•3H2O. Results from salt spay test and damp heat test indicate that the two coatings also can provide good protection for the magnesium alloy matrix, and stannate is better than phosphate.
Production and Properties of a 90%Si-Al Alloy for Electronic Packaging Applications
Authors: Yu Kun , Li Chao , Yang Jun , Cai Zhi Yong
Published: March 2009

The high silicon content Si-Al alloy is a typical heat dissipation material that used in the electrical packaging field. A spray forming process wais used to produce a 90%Si-Al alloy specimen as a heat dissipation material in the present study. Then the spray formed 90%Si-Al specimens weare hot pressed at 1000°C with different pressure ranged from 2MPa to 10MPa to increase their density. The physical properties of the experimental alloy specimen weare measured. And the microstructure wass are observed by using optical microscopy and scanning electronic microscopy. The results showed that the Spray forming wais suitable forto producinge a 90%Si-Al alloy. With hot pressure of 10MPa, the relative density value of 90%Si-Al reachedcan obtain 94%. The typical physical properties such as the thermal conductivity, coefficient of thermal expansion and electrical conductivity of 90%Si-Al alloy are acceptable as a heat dissipation material for many electronic packaging applications.
Research on Corrosion Resistance of Mg-Al-Sr Alloy
Authors: Wu Tong , Peng Xiao Dong , Wang Dong Ya , Xie Wei Dong
Published: March 2009

The corrosion properties of Mg-Al-Sr alloy was characterized with comparison to AZ91D alloy. With the addition of Mg-Sr master alloy, the grain size of Mg alloy refined and the corrosion resistance was improved. The experimental results indicated that the formation of small amount of Al4Sr phase was favorable to improve the corrosion resistance. However, with the increase of Al4Sr stripy phase, the area ratio of cathode to anode will increase, resulting in the decrease of corrosion resistance potential.
Quantitative Evaluation of Wall Thinning of Metal Pipes by Microwaves
Authors: Lu Yang , Liu Lin Sheng , Ishikawa Masaharu
Published: March 2009

In this paper, a method which can inspect a metal pipe in a large scale and measure the wall thinning remotely was demonstrated. A microwave network analyzer was employed to generate microwave signals propagating in the pipe where the frequency was swept from 47.38 to 47.47 GHz. A copper pipe with inner diameter of 17 mm, 1 mm wall thickness, 900 mm length, and connected with joints having the length of 17 mm and values of thickness reductions from 3 to 80% wall thickness was measured. By building up a resonance model for the microwave signals propagating in the metal pipe, and by analyzing the resonance results of the microwave signals at the receiving port, a nondestructive method was derived to determine the degree of the wall thinning in the pipe. By comparing the experimental results with the evaluation results obtained by the theoretical analysis, it is shown that the errors of the evaluation are less than 0.5% of the pipe diameter. It indicates that high precision for remote detection and quantitative evaluation of wall thinning can be achieved by using this nondestructive method.
A Method for Improving Compressive Residual Stress of Small Holes Surface by Water-Jet Cavitation Peening
Authors: Han B. , Ju Dong Ying
Published: March 2009

As a novel surface strengthening technique, Water-jet cavitation peening has been applied to improve the fatigue life by inducing the compressive residual stress in the near surface layer of mechanical components. Compared with conventional shot peening, one advantage of WCP is that the complicated and tiny surface can be peened more easily. In this study, the small holes with various diameters and depths in the SUS304 stainless steel specimens were treated by WCP. In order to estimate its strengthening capability to the small holes, the surface residual stress and the depth distributions in the near surface layer of the small holes were measured by X-ray diffraction method. The experimental results show that WCP can successfully improve the near surface compressive residual stress of small holes. The maximum of surface compressive residual stress of WCP state is up to around –450 MPa. The dept of compressive residual stress zone is up to around 125 μm.
Visualization of Stress Distribution Using Smart Mechanoluminescence Sensor
Authors: Wang Wen Xue , Matsubara T. , Takao Y. , Imai Y. , Xu Chao Nan
Published: March 2009

This paper describes a study on the application of smart mechanoluminescence (ML) sensor to structures for the visualization of stress distribution. Smart thin film sensor of ML material SrAl2O4:Eu/polyme is coated on the surface of structure. The sensor will emit visual light when the structure is subjected to deformation. The light intensity is proportional to the strain energy density and the equivalent strain of the stressed material based on the energy viewpoint and experimental facts. The distribution of visual light intensity is recorded using CCD camera or ordinary camera. Then the stress distribution can be evaluated from the distribution of visual light intensity based on solid mechanics and the relationship between light intensity and equivalent strain. Compression test of a disk with coated SrAl2O4:Eu/epoxy film sensor is conducted to compare the visual light distribution with the stress distribution obtained from finite element analysis. Furthermore, tensile test of a rectangular specimen with a coated SrAl2O4:Eu/polymer film sensor is performed to demonstrate the relationship between visual light intensity and strain. Experimental and numerical results show that the smart sensor of ML material SrAl2O4:Eu/polymer is an effective strain sensor to directly visualize the stress distribution in real time.
Material Selection and Design for Moisture Damage of HMA Pavement
Authors: Huang Jun Feng , Wu Shao Peng , Ma Li Xing , Liu Zhi Fei
Published: March 2009

Moisture damage is a primary mode of distress occurring in hot mix asphalt (HMA) pavements. Usually, the acid aggregate like gneiss must use some anti-stripping additive to resist water damage. Hydrated lime is best known as an anti-stripping additive since 1910. The purpose of this paper is to look at some aspects of the effects of aggregate chemical properties and hydrated lime on the dynamic mechanics and stripping behavior of hot mix asphalt. Two types of aggregates evaluated in this study were limestone and gneiss. The effects of the aggregates type were evaluated on four different aggregate gradations which were composed with the two aggregates in different proportion. And the hydrated lime has been used for HMA pavements to mitigate moisture-related damage in gneiss asphalt mixture. Laboratory tests for different asphalt mixture include Marshall Test, Frozen-thaw Cycle Test, Dynamic Modulus Test (DMT) and Indirect Tensile Fatigue Test (ITFT). Testing data and analyses demonstrated that different aggregate gradations have different mechanical properties. Hydrate lime has greatly contributed to moisture damage resistance in acid aggregate gneiss and enhanced the dynamic modulus. The modified with hydrated lime mixture composed with coarse gneiss aggregate and fine limestone aggregate also has better performance of the mixture against rutting, fatigue and thermal cracking. It can be concluded from ITFT tests that the fatigue life (load cycle times) of additive hydrated lime asphalt concrete is more than neat ones. At last, we can conclude that the selection and design that modified with hydrated lime and fine limestone aggregate replace acid aggregate could create multiple benefits in asphalt mixtures.
Germanium Incorporation during PVT Bulk Growth of Silicon Carbide
Authors: Hens Philip , Künecke Ulrike , Konias Katja , Hock Rainer , Wellmann Peter J.
Published: March 2009

Silicon carbide as a material for electronic devices still has substantial problems concerning its structural quality and defects. It has been shown that dopants can have a big influence on structural properties like polytype stability and dislocation statistics [1]. We will discuss the effect of an isoelectronic dopant in silicon carbide. Germanium, being a member of the 4th group in the periodic table of elements like silicon and carbon, will not influence the electrical properties of the material such as e.g. aluminum. In our experiments we reached concentrations of up to 1*1020 cm-3. We have observed an impact on the polytype stability during sublimation growth with in-situ germanium incorporation. We investigated an influence on the dislocation statistics during growth and, hence, varying germanium concentration. We found only a slight decrease in mobility during Hall measurements but no severe changes in electrical properties of the material.
Towards Large Area (111)3C-SiC Films Grown on Off-Oriented (111)Si
Authors: Severino Andrea , Anzalone Ruggero , Bongiorno Corrado , Italia M. , Abbondanza Giuseppe , Camarda Massimo , Perdicaro L.M.S. , Condorelli Giuseppe , Mauceri Marco , La Via Francesco
Published: March 2009

The choice of off-axis (111) Si substrates is poorly reported in literature despite of the ability of such an oriented Si substrate in the reduction of stacking faults generation and propagation. The introduction of off-axis surface would be relevant for the suppression of incoherent boundaries. We grew 3C-SiC films on (111) Si substrates with a miscut angle from 3° to 6° along <110> and <11 >. The film quality was proved to be high by X-Ray diffraction (XRD) characterization. Transmission electron microscopy was performed to give an evaluation of the stacking fault density while pole figures were conducted to detect microtwins. Good quality single crystal 3C-SiC films were finally grown on 6 inch off-axis (111)Si substrate. The generated stress on both 2 and 6 inch 3C-SiC wafers has been analyzed and discussed.
Growth of 4H-SiC Single Crystals on 6H-SiC Seeds with an Open Backside by PVT Method
Authors: Tymicki Emil , Grasza Krzysztof , Racka Katarzyna , Raczkiewicz Marcin , Łukasiewicz Tadeusz , Gała Maciej , Kościewicz Kinga , Diduszko Ryszard , Bożek Rafał
Published: March 2009

4H-SiC single crystals grown by the seeded physical vapour transport method have been investigated. These crystals were grown on 6H-SiC seeds. The influence of the seed temperature, form and granulation of SiC source materials on the stability and efficiency of the 4H polytype growth have been investigated. A new way of the seed mounting - with an open backside - has been used. Crystals obtained were free of structural defects in the form of hexagonal voids. The crystalline structure of SiC crystals was investigated by EBSD (Electron Backscatter Diffraction) and X-Ray diffraction methods. Moreover, defects in crystals and wafers cut from these crystals were examined by optical, scanning electron and atomic force microscopy combined with KOH etching.
A Comparative Study of the Morphology of 3C-SiC Grown at Different C/Si Ratios
Authors: Attolini Giovanni , Watts Bernard Enrico , Bosi Matteo , Rossi Francesca , Riesz Ferenc
Published: March 2009

A comparative study of the morphology of 3C-SiC films prepared with different C:Si ratios is presented. The silane precursor controls the growth rate at all values of C:Si ratio but combined of observations using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) indicates that the C:Si ratio is critical in determining the grain size and at values of C:Si close to 1 texturing and faceting become evident. Makyoh Topography reveals various surface defects, a slight mesoscale roughness and bending of the epiwafers.
Low Temperature Growth of 3C-SiC Film on Si (111) by Plasma Assisted CVD
Authors: Shimizu Hideki , Kato Akira
Published: March 2009

In order to demonstrate the formation of 3C-SiC film on Si (111) at low substrate temperature, the effects of C3H8 on the crystallinity of the films on Si (111) have been investigated by changing the flow rate of C3H8 at the substrate temperature of 850 °C. Oriented polycrystalline 3C-SiC film grew under the C/Si of 3 – 5 with a-C. It is suggested that etching effects of growing surface by hydrogen radicals generated from C3H8 decomposition is lowered by lowering the substrate temperature. The crystallinity has been investigated by reflection electron diffraction (RED) and a X-ray diffraction (XRD). The thickness and the surface roughness of the films were investigated by an ellipsometric measurement.
P-Type 3C-SiC Grown by Sublimation Epitaxy on 6H-SiC Substrates
Authors: Lebedev Sergey P. , Lebedev Alexander A. , Abramov Pavel L. , Bogdanova Elena V. , Nel'son D.K. , Oganesyan Gagik A. , Tregubova Alla S. , Yakimova Rositza
Published: March 2009

Highly doped p-3C-SiC layers of good crystal perfection have been grown by sublimation epitaxy in vacuum. Analysis of the photoluminescence (PL) spectra and temperature dependence of the carrier concentration shows that at least two types of acceptor centers at ~EV + 0.25 eV and at EV + 0.06-0.07 eV exist in the samples studied. A conclusion is made that layers of this kind can be used as p-emitters in 3C-SiC devices.
Searching for Ge Clusters inside 3C-SiC Layers Grown by Vapor-Liquid-Solid Mechanism on 6H-SiC Substrates
Authors: Marinova Maya , Tsiaousis Ioannis , Frangis N. , Polychroniadis Efstathios K. , Kim-Hak Olivier , Lorenzzi Jean , Ferro Gabriel
Published: March 2009

The use of Ge very rich Si-Ge liquid phase during the heteroepitaxial growth of 3C-SiC on Si-face, on-axis 6H-SiC(0001) substrate by vapour-liquid-solid mechanism leads to the formation of Ge based precipitates inside the 3C layer. These Ge based features are investigated by TEM and atomic models of the Ge clustering are proposed by means of high resolution TEM image simulation. Conventional TEM shows only a few small precipitates sparsely distributed near the interface, as well as dislocations and stacking faults starting from the interface in an almost regular manner. High resolution TEM shows fine structural imperfections in the form of Guinier Preston zones also near the interface. It is concluded that the high Ge content creates an enlargement of the SiC lattice leading to a misfit with the substrate. This could be the driving force for the formation of all the observed features.
Graphene Formation on SiC Substrates
Authors: VanMil Brenda L. , Myers-Ward Rachael L. , Tedesco Joseph L. , Eddy Charles R. , Jernigan Glenn G. , Culbertson James C. , Campbell Paul M. , McCrate J.M. , Kitt S.A. , Gaskill D. Kurt
Published: March 2009

Graphene layers were created on both C and Si faces of semi-insulating, on-axis, 4H- and 6H-SiC substrates. The process was performed under high vacuum (<10-4 mbar) in a commercial chemical vapor deposition SiC reactor. A method for H2 etching the on-axis substrates was developed to produce surface steps with heights of 0.5 nm on the Si-face and 1.0 to 1.5 nm on the C-face for each polytype. A process was developed to form graphene on the substrates immediately after H2 etching and Raman spectroscopy of these samples confirmed the formation of graphene. The morphology of the graphene is described. For both faces, the underlying substrate morphology was significantly modified during graphene formation; surface steps were up to 15 nm high and the uni-form step morphology was sometimes lost. Mobilities and sheet carrier concentrations derived from Hall Effect measurements on large area (16 mm square) and small area (2 and 10 m square) samples are presented and shown to compare favorably to recent reports.
AFM and Raman Studies of Graphene Exfoliated on SiC
Authors: Tiberj Antoine , Martin Marta , Camara Nicolas , Poncharal P. , Michel T. , Sauvajol J.L. , Godignon Philippe , Camassel Jean
Published: March 2009

We report an investigation of few layers graphene exfoliated on SiC. Using AFM and Raman spectroscopy, we find that the graphene thickness determined from the normalized intensity of Raman lines significantly depart from the one obtained using XPS.
Investigation of Graphene Growth on 4H-SiC
Authors: Castaing A. , Guy Owen James , Lodzinski Michal , Wilks S.P.
Published: March 2009

This paper reports the investigation of epitaxial graphene growth on 4H-SiC substrates. Growth has been performed under ultra high vacuum (UHV) conditions at temperatures ranging from 1150 to 1250°C, and the formation of the graphene layer has been monitored using X-ray photoelectron spectroscopy (XPS). A gradient of 100°C in temperature was introduced across the sample in order to grow a wide range of thicknesses along the sample. Atomic force microscopy (AFM) of the surface shows that the epitaxial graphene layer follows the topography of the bulk material and introduces very little surface roughness. This paper also reports the electrical characterisation of the graphene layers.
Formation of Different Carbon Phases on SiC
Authors: Pezoldt Joerg
Published: March 2009

Carbon is able to crystallise in different allotrope modifications. They mainly differ in the dominating bindings formed in dependence on the hybridization sp, sp2 and sp3 of the carbon atoms. The present work demonstrates the formation of two different forms of car¬bon allotropes by heating both polar surfaces of on axis 6H-SiC(0001) and 6H-SiC(000 ) crystals to temperatures above 1600°C. In consequence of the structural evolution graphite-like (sp2-hybridised) and carbine-like (sp-hybridised) allotropic carbon modifications were obtained.
Effect of Source and Drain Contacts Schottky Barrier on 3C-SiC Nanowire FETs I-V Characteristics
Authors: Rogdakis Konstantinos , Lee Seoung Yong , Kim Dong Joo , Lee Sang Kwon , Bano Edwige , Zekentes Konstantinos
Published: March 2009

In this work, SiC nanowire (NW) FETs are prepared and their electrical measurements are presented. From the samples fabricated on the same substrate, various I-Vs shapes are obtained (linear, non linear symmetric, and asymmetric). With the assistance of simulation, we show that this is a result of different values of Schottky Barrier Heights (SBH) at Source (S) / Drain (D) contacts of FETs. An origin for this might be a non uniformity in annealing, NW doping level and high interface traps density (that pins the Fermi level) as well as the high sensitivity of the metal-NW contacts to local surface contaminations.
Textile Solar Cells Based on SiC Microwires
Authors: Greulich-Weber Siegmund , Zöller M. , Friedel B.
Published: March 2009

The solar cell concept presented here is based on 3C-SiC nano- or microwires and conju¬gated polymers. Therefore the silicon carbide wires are fabricated by a sol-gel route including a car-bothermal reduction step, allowing growth with predetermined uniform diameters between 0.1 and 2μm and lengths up to several centimetres. The design of our photovoltaic device is therein based on a p-i-n structure, well known e.g. from silicon photovoltaics, involving an intrinsic semiconduc¬tor as the central photoactive layer, sandwiched between two complementary doped wide-bandgap semiconductors giving the driving force for charge separation. In our case the 3C-SiC microwires act as the electron acceptor and simultaneously as carrier material for all involved components of the photovoltaic element.
Influence of Structural Defects on Carrier Lifetime in 4H Epitaxial Layers, Studied by High Resolution Optical Lifetime Mapping
Authors: ul Hassan Jawad , Bergman Peder
Published: March 2009

Thick 4H-SiC epitaxial layers have been characterized using high-resolution lifetime mapping. The lifetime maps are obtain by the detection of photoluminescence decay of the band gap emission. Full wafers mappings with 200 m resolution reveal lifetime variations that can be associated with structural defects replicated from the substrate, and variations in epitaxial growth conditions due to the susceptor design. High resolution mapping over smaller regions with down to 20 m step size, reveals local lifetime reductions associated with different structural defects in the epitaxial layer. Identified defects that influence the lifetime are the carrot defect, different types of in-grown stacking faults, and an unidentified defect associated with a pair of basal plane dislocations on the surface. Also clusters of threading screw dislocations, probably originating from a dissociated micropipe in the substrate, are found to reduce the lifetime.
Laser Deflection Measurements for the Determination of Temperature and Charge Carrier Distributions in 4H-SiC Power Diodes
Authors: Werber Dorothea , Wachutka Gerhard
Published: March 2009

A change of the electron and hole densities n and p and of the lattice temperature T modulates the real optical refractive index nopt of the device under test. In the forward conducting state the electron and hole distributions n(x) and p(x) in the i-region of the device are generated by the action of carrier injection from the n- and p-emitters. The device is locally heated by Joule and recombination heat, leading to a temperature distribution T(x). The gradients of temperature and charge carrier densities cause a spatial modulation of the real refractive index nopt(x). A laser beam transmitted orthogonally to the direction of current flow of the device is deflected by the gradient of nopt(x). Concurrent deflections caused simultaneously by the carrier gradients on the one side and by the temperature gradient on the other side can be discriminated by their different time constants.
Two Dimensional X-Ray Diffraction Mapping of Basal Plane Orientation on SiC Substrates
Authors: Palisaitis Justinas , Bergman Peder , Persson P.O.Å.
Published: March 2009

We have performed 2D X-ray diffraction mapping of the SiC lattice basal plane orientation over full 2” SiC substrates. Measurements of the omega angle were made in two perpendicular directions <11-20> and <1-100>, which gives the complete vectorized tilt of the basal planes. The Mapping revealed two characteristic bending behaviors on measured commercial wafers. The first is characterized by large variations in omega angle across the wafer in both crystallographic directions. The continuously changing omega angle in both directions gives the wafer an apparent rotationally symmetric bending which is concave towards the growth direction. The second characteristic behavior is seen in wafers with lower degree of omega angle variation. The variations in this type of wafers are not changing linearly, but are bending the basal planes with two-fold symmetry.
Carrier Generation Lifetime in 4H-SiC Epitaxial Wafers
Authors: Chung Gil Yong , Loboda Mark J. , Marninella M.J. , Schroder D.K. , Isaacs-Smith Tamara , Williams John R.
Published: March 2009

The pulsed MOS-C (Metal Oxide Semiconductor-Capacitor) technique was used to measure generation lifetimes in 4H-SiC epitaxial wafers. The ratio of generation to recombination lifetime has been investigated to understand the dominant defect for generation lifetime. The EH6/7 defect level is considered to limit generation lifetime and field enhanced emission is proposed to explain extremely large variation of generation lifetime in a small area. Generation lifetime is limited by dislocations when they are above a threshold density of about 106cm-2. Generation lifetimes measured on 4 and 8 degree off-cut angle epi-substrates are very comparable.
Minority Carrier Lifetime Measurements in Specific Epitaxial 4H-SiC Layers by the Microwave Photoconductivity Decay
Authors: Ottaviani Laurent , Palais Olivier , Barakel Damien , Pasquinelli Marcel
Published: March 2009

We report on measurements of the minority carrier lifetime for different epitaxial 4H-SiC layers by using the microwave photoconductivity decay (µ-PCD) method. This is a non-contacting, non-destructive method very useful for the monitoring of recombination processes in semiconductor material. Distinct samples have been analyzed, giving different lifetime values. Transmittance and absorption spectra have also been carried out. The n-type layers, giving rise to a specific absorption peak near 470 nm, are not sensitive to optical excitation for the used wavelengths, as opposite to p-type layers whose lifetime values depend on thickness and doping.
Direct Observation of Lifetime Killing Defects in 4H SiC Epitaxial Layers via Spin Dependent Recombination in Transistors
Authors: Cochrane Corey J. , Lenahan Patrick M. , Lelis Aivars J.
Published: March 2009

We have identified a magnetic resonance spectrum associated with minority carrier lifetime killing defects in device quality 4H SiC.
Defect Status in SiC Manufacturing
Authors: Berkman Elif , Leonard R.T. , Paisley Michael J. , Khlebnikov Y. , O'Loughlin Michael  J. , Burk Albert A. , Powell Adrian R. , Malta D.P. , Deyneka E. , Brady M.F. , Khlebnikov I. , Tsvetkov Valeri F. , Hobgood H.McD. , Sumakeris Joseph J. , Basceri C. , Balakrishna Vijay , Carter Jr. Calvin H. , Balkas C.
Published: March 2009

Availability of high-quality, large diameter SiC wafers in quantity has bolstered the commercial application of and interest in both SiC- and nitride-based device technologies. Successful development of SiC devices requires low defect densities, which have been achieved only through significant advances in substrate and epitaxial layer quality. Cree has established viable materials technologies to attain these qualities on production wafers and further developments are imminent. Zero micropipe (ZMP) 100 mm 4HN-SiC substrates are commercially available and 1c dislocations densities were reduced to values as low as 175 cm-2. On these low defect substrates we have achieved repeatable production of thick epitaxial layers with defect densities of less than 1 cm-2 and as low as 0.2 cm-2. These accomplishments rely on precise monitoring of both material and manufacturing induced defects. Selective etch techniques and an optical surface analyzer is used to inspect these defects on our wafers. Results were verified by optical microscopy and x-ray topography.
Nucleation and Growth of 3C-SiC Single Crystals from the Vapor Phase
Authors: Chaussende Didier , Eid Jessica , Mercier Frédéric , Madar Roland , Pons Michel
Published: March 2009

The conditions to succeed in growing 3C-SiC single crystals are first, make available large 3C-SiC seeds and second, develop a suitable growth process. In this paper, we will address those two issues by reviewing the most recent results in the field. Nucleation, growth, structural quality and doping results will be presented. New insights on 3C bulk growth will be discussed with respect to a future development of real bulk 3C-SiC ingots.
Accurate Measurements of Second-Order Nonlinear-Optical Coefficients of Silicon Carbide
Authors: Sato Hiroaki , Shoji Ichiro , Suda Jun , Kondo Takashi
Published: March 2009

Second-order nonlinear-optical coefficients of 4H and 6H-SiC have been measured with the wedge technique. Using high-quality (11-20) samples as well as performing rigorous measurements and analyses, the three independent components, d31 (= d32), d15 (= d24), and d33, have been accurately determined. We have found that the nonlinear-optical coefficients are nearly the same between the measured 4H and 6H-SiC samples within the experimental accuracy; d31 = 5.4 pm/V, d15 = 6.2 pm/V, and d33 = 9.7pm/V.
Electrical and Mechanical Properties of Post-Annealed SiCxNy Films
Authors: Fraga Mariana A. , Massi M. , Oliveira I.C. , Cruz N.C. , Dos Santos Filho S.G.
Published: March 2009

Amorphous SiCxNy films have been deposited on (100) Si substrates by RF magnetron sputtering of a SiC target in a variable nitrogen-argon atmosphere. The as-deposited films were submitted to thermal anneling in a furnace under argon atmosphere at 1000 °C for 1 hour. Composition and structure of unannealed and annealed samples were investigated by RBS and FTIR. To study the electrical characteristics of SiCxNy films, Metal-insulator-semiconductor (MIS) structures were fabricated. Elastic modulus and hardness of the films were determined by nanoindentation. The results of these studies showed that nitrogen content and thermal annealing affect the electrical, mechanical and structural properties of SiCxNy films.
High Temperature Solution Growth on Free-Standing (001) 3C-SiC Epilayers
Authors: Tanaka Ryo , Seki Kazuaki , Ujihara Toru , Takeda Yoshikazu
Published: March 2009

Solution growth was performed using a free-standing (001) 3C-SiC epilayer as a seed crystal at a growth temperature of 1700°C. The seed crystal was prepared by a CVD method on the undulated Si substrate. 3C-SiC stably grew on the (001) seed crystal. However, dark stripes from the seed crystal to the grown crystal along {111} planes were clearly observed. The stripes were due to the high-density stacking faults extended from the stacking faults in the 3C-SiC epilayer that were induced during the CVD growth on Si substrate.
Defects in 4H-SiC Layers Grown by Chloride-Based Epitaxy
Authors: Beyer Franziska Christine , Pedersen Henrik , Henry Anne , Janzén Erik
Published: March 2009

Chloride-based 4H-SiC epitaxial layers were investigated by DLTS, MCTS and PL. The DLTS spectra of the as grown samples showed dominance of the Z1/2 and the EH6/7 peaks. For growth rates exceeding 100 µm/h, an additional peak occurred in the DLTS spectra which can be assigned to the UT1 defect. The shallow and the deep boron complexes as well as the HS1 defect are observed in MCTS measurements. The PL spectra are completely dominated by the near band gap (NBG) emission. No luminescence from donor-acceptor pair occurred. The PL line related to the D1 centre was weakly observed. In the NBG region nitrogen bound exciton (N-BE) and free exciton (FE) related lines could be seen. The addition of chlorine in the growth process gives the advantage of high growth rates without the introduction of additional defects.
Photo-EPR Studies on Low-Energy Electron-Irradiated 4H-SiC
Authors: Carlsson Patrick , Son Nguyen Tien , Pedersen Henrik , Isoya Junichi , Morishita Norio , Ohshima Takeshi , Itoh Hisayoshi , Janzén Erik
Published: March 2009

Photoexcitation electron paramagnetic resonance (photo-EPR) was used to determine deep levels related to the carbon vacancy (VC) in 4H-SiC. High-purity free-standing n-type 4H-SiC epilayers with concentration of intrinsic defects (except the photo-insensitive SI1 center) below the detection limit of EPR were irradiated with low-energy (200 keV) electrons to create mainly VC and defects related to the C sublattice. The simultaneous observation of and signals, their relative intensity changes and the absence of other defects in the sample provide a more straight and reliable interpretation of the photo-EPR results. The study suggests that the (+|0) level of VC is located at ~EC–1.77 eV in agreement with previously reported results and its single and double acceptor levels may be at ~ EC–0.8 eV and ~ EC–1.0 eV, respectively.
C-V and DLTS Analyses of Trap-Induced Graded Junctions: The Case of Al+ Implanted JTE p+n 4H-SiC Diodes
Authors: Fabbri Filippo , Moscatelli Francesco , Poggi Antonella , Nipoti Roberta , Cavallini Anna
Published: March 2009

Capacitance versus Voltage (C-V) and Deep Level Transient Spectroscopy (DLTS) measurements of Al+ implanted p+n diodes with Al+ implanted Junction Termination Extension are here studied. These diodes present C-V characteristics like graded junction for low forward bias values, i.e. > 0.4 V , or like abrupt junctions for large reverse bias, i.e. between 0.4V and -10V. The depth range of the graded junction, computed by the capacitance values, is much larger than the simulated tail of the ion implanted Al+ profile. DLTS spectra have been measured both in injection and standard configuration and always show minority carrier traps in the temperature range 0-300K. Three are the minority carrier related peaks, one attributed to the Al acceptor and the others to the D and D1 defects. The depth distribution of these hole traps will be discussed with respect to the apparent carrier concentration, obtained by C-V analysis.
Far-Action Radiation Defects and Gettering Effects in 4H-SiC Implanted with Al Ions
Authors: Kalinina Evgenia V. , Zamoryanskaya M.V. , Kolesnikova E.V. , Lebedev Alexander A.
Published: March 2009

Structural features of 4H-SiC structures with CVD epitaxial layers, subjected to high-dose Al ion implantation and short high-temperature pulse annealing, have been studied using secondary-ion mass-spectroscopy, transmission electron spectroscopy, local cathodoluminescence and cathodoluminescence imaging on cross-sectionally cleaved surfaces of the structures. An accelerated diffusion of radiation defects, a “long-range action effect”, with a diffusion coefficient of 10 -9 cm2 s-1 after high-dose Al ion implantation and the gettering effect after subsequent pulsed thermal annealing have been observed for the first time. After a short high-temperature annealing, the quality of the starting material is improved in the course of formation of implantation-doped p+-n junctions due to defect gettering. As a result of the decrease in the concentration of optical active defect centers as well of deep centers by an order of magnitude in CVD layer, an increase in the diffusion length of minority carriers (Lp) by a factor of 1.5-2 was obtained.
Observation of SiC Oxidation in Ultra-Thin Oxide Regime by In Situ Spectroscopic Ellipsometry
Authors: Takaku Toshiyuki , Hijikata Yasuto , Yaguchi Hiroyuki , Yoshida Sadafumi
Published: March 2009

Thermal oxidation process of silicon carbide in ultra-thin oxide regime has been studied by performing in-situ and real time spectroscopic ellipsometry. We found the thermal oxidation at 700°C forms no or extremely thin interface layers between SiC and oxide layers. In contrast, the oxidation at 850°C forms an interface layer of around 1 nm in thickness, having similar thickness and optical constants of the interface layers formed by the oxidation at higher temperature than 1000°C. To make clear the conditions no interface layer is formed, i.e., whether low temperature growth or thin oxide thickness is crucial, we have performed the oxidation at 850°C in the reduced oxygen pressure. Based on the results of these experiments, we discussed the origin of the formation of interface layers as well as the oxidation mechanism of SiC.
Impact of a Treatment Combining Nitrogen Plasma Exposure and Forming Gas Annealing on Defect Passivation of SiO2/SiC Interfaces
Authors: Watanabe Heiji , Watanabe Yuu , Harada Makoto , Kagei Yusuke , Kirino Takashi , Hosoi Takuji , Shimura Takayoshi , Mitani Shuhei , Nakano Yuki , Nakamura Takashi
Published: March 2009

We propose a treatment combining nitrogen plasma exposure and forming gas annealing (FGA) to improve the electrical properties of SiO2/SiC interfaces. Although conventional FGA at 450°C alone is not effective for reducing interface traps and fixed charges, our combination treatment effectively reduces both even at moderate temperatures. We achieved further improvement by applying our treatment at higher (over 900°C) FGA temperatures, including lower interface state density (Dit) values for both deep and shallow energy levels (1 - 4 x 1011 cm-2eV-1). Considering that nitrogen incorporation promotes hydrogen passivation of interface defects, a possible mechanism for the improved electrical properties is that interface nitridation eliminates carbon clusters or Si-O-C bonds, which leads to the formation of simple Si and C dangling bonds that can be readily terminated by hydrogen. We therefore believe that our treatment is a promising method for improving the performance of SiC-based MOS devices.
Oxidation Process of SiC by RTP Technique
Authors: Kwietniewski N. , Gołaszewska Krystyna , Piotrowski T.T. , Rzodkiewicz W. , Gutt Tomasz , Sochacki M. , Szmidt Jan , Piotrowska Anna
Published: March 2009

The kinetics of 4H-SiC thermal oxidation by RTP technique and the properties of thin thermal oxide was reported. The thickness of the thermal oxide was determined by spectroscopic ellipsometry and confirmed by electrical measurements. The conductance method was applied to analyse the surface states parameters. The lifetime, density and cross-section of the surface traps were extracted for as-fabricated MOS capacitors and after thermal annealing processes.
Impact of Carbon Cap Annealing on Gate Oxide Reliability on 4H-SiC (000-1) C-Face
Authors: Harada Shinsuke , Kato Makoto , Ito Sachiko , Suzuki Kenji , Ohyanagi Takasumi , Senzaki Junji , Fukuda Kenji , Okumura Hajime , Arai Kazuo
Published: March 2009

Reliability of the gate oxide is influenced by the device structure and the processes. In the SiC MOSFET, the surface morphology is degraded by the high temperature activation RTA, and the degradation is remarkable on the n+ source region. This study develops the method to suppress the degradation of the reliability of the gate oxide on the carbon face. By utilizing the carbon cap for the RTA and the high density O2 plasma etching to remove the carbon cap, the reliability is drastically improved both on the un-implanted and the implanted surfaces. Especially, the degradation of the reliability is perfectly suppressed on the un-implanted surface.
Reliability of Large-Area Gate Oxide on the C-Face of 4H-SiC
Authors: Hatakeyama Tetsuo , Kono Hiroshi , Suzuki Takuma , Senzaki Junji , Fukuda Kenji , Shinohe Takashi , Arai Kazuo
Published: March 2009

This paper discusses the issues regarding reliability of large-area (up to 9mm2) gate oxide on the C-face of 4H-SiC. We first show that the initial failure in TDDB characteristics of large area gate oxide is strongly correlated with the surface-defect density. Using wafers with low surface-defect density wafers, scaling analysis of the area-dependence of TDDB characteristics has been performed. It has shown that the reliability of a large area gate oxide is dominated by initial and random failures. Further, we have shown that, by optimizing the temperatures of post-oxidation anneal in hydrogen atmosphere, the random failures of TDDB characteristics are substantially reduced.
Nano-Electro-Structural Evolution of Ni-Si Ohmic Contacts to 3C-SiC
Authors: Eriksson Jens , Roccaforte Fabrizio , Giannazzo Filippo , Lo Nigro Raffaella , Moschetti Giuseppe , Raineri Vito , Lorenzzi Jean , Ferro Gabriel
Published: March 2009

This paper reports on the macro- and nanoscale electro-structural evolution, as a function of annealing temperature, of nickel-silicide Ohmic contacts to 3C-SiC, grown on 6H-SiC substrates by a Vapor-Liquid-Solid (VLS) technique. The structural and electrical characterization of the contacts, carried out by combining different techniques, showed a correlation between the annealing temperature and the electrical characteristics in both the macro- and the nanoscale measurements. Increasing the annealing temperature between 600 and 950 °C caused a gradual increase of the uniformity of the nanoscale current-distribution, with an accompanying reduction of the specific contact resistance from 5 x 10-5 to 8.4 x 10-6 Ωcm2. After high temperature annealing (950 °C) the structural composition of the contacts stabilized, as only the Ni2Si phase was detected. A comparison with previous literature findings suggests a superior crystalline quality of the single domain VLS 3C-SiC layers.
On the Formation of Ni-Based Ohmic Contacts to n-Type 4H-SiC
Authors: Kuchuk Andrian V. , Kladko V.P. , Piotrowska Anna , Ratajczak Renata , Jakieła Rafał
Published: March 2009

In this study, the formation of Ni, Ni-rich Ni2Si and Si-rich NiSi2 ohmic contacts to n-type 4H-SiC are investigated. The Ni/n-SiC ohmic contact with resistance rc ~ 4.2×10-4 Ω cm2 is formed after annealing at 1050oC. For Ni2Si/n-SiC, the contact resistances were rc ~ 4×10-4 Ωcm2 and rc ~ 3.5×10-4 Ωcm2 after annealing at 1000 and 1050oC, respectively. The non-ohmic I-V characteristics are observed for NiSi2/n-SiC contact even after annealing at 1050oC. The features of ohmic contact formation for Ni-based metallization to 4H n-SiC are discussed.
Process Optimization for High Temperature SiC Lateral Devices
Authors: Soueidan Maher , Lazar Mihai , Nguyen Duy Minh , Tournier Dominique , Raynaud Christophe , Planson Dominique
Published: March 2009

Complementary lateral structures, N-JFETs, P-JFETS and bipolar diodes, have been implemented in p and n-type 4H-SiC wafers with epilayers. The device were optimized using finite element code MEDICITM simulations, based on ion implanted and etched Reduced-Surface-Field structures. Two Ti/Ni alloy composition are found to form ohmic contacts compatibles with high temperature device operation. 900°C and respectively 1000°C post-metallisation annealing during 2min are necessary. The presence of a graphite layer is determined by XPS (X-ray photon spectroscopy) analyses at the metal-semiconductor interface. On the fabricated p and n-type lateral JFETs, in blocking state, breakdown voltage as high as 600V are obtained.
HCl Etching Behavior on Low-Tilt-Angle and Step-Free 4H-SiC Surfaces
Authors: Trunek Andrew J. , Powell J. Anthony , Neudeck Philip G. , Mrdenovich M.
Published: March 2009

We report on new observations made, when 4H-SiC, Si-face substrate mesas, having either low tilt-angle (< 1°) with steps or step-free top surfaces, were exposed to three separate HCl etching conditions for five minutes at temperatures of 1130°C, 1240°C and 1390°C. We observed that HCl was ineffective at 1130°C, as etching was incomplete with abundant surface contamination. At 1240°C, screw dislocations were aggressively etched by HCl, while multiple shallow flat-bottomed etch pits were formed on step-free mesa surfaces. At 1390°C, step-flow etching dominated as large etch pits were formed at screw dislocations and previously step-free surfaces etched inward from mesa edges to form parallel rows of organized steps.
The Effect of Slurry Composition and Flatness on Sub-Surface Damage and Removal in Chemical Mechanical Polishing of 6H-SiC
Authors: Lee Gi Sub , Hwang Hyun Hee , Son Chang Hyun , Choi Jung Woo , Lee Won Jae , Shin Byoung Chul , Seo Jung Doo , Ku Kap Ryeol , Jeong Hae Do
Published: March 2009

The effect of slurry composition and wafer flatness on a material removal rate (MRR) and resulting surface roughness which are evaluation parameters to determine the CMP characteristics of the on-axis 6H-SiC substrate were systematically investigated. 10 x 10 mm2 6H-SiC substrates and 2-inch SiC wafers fabricated from the ingot grown by a conventional physical vapor transport (PVT) method are used for this study. The SiC substrate after the CMP process using slurry added oxidizers into slurry consisted of KOH-based colloidal silica and nano-size diamond particle exhibited the significant MRR value and a fine surface without any surface damages. SiC wafers having high bow value after the CMP process exhibited large variation in surface roughness value compared to wafer with low bow value. The CMP-processed SiC wafer having a low bow value of 10m was observed to result in the MRR value of 0.15 m/h and the mean height (Ra) value of 0.772Ǻ.
Residual Stress Measurement on Hetero-Epitaxial 3C-SiC Films
Authors: Anzalone Ruggero , Locke Christopher , Severino Andrea , Rodilosso Davide , Tringali Cristina , Foti Gaetano , Saddow Stephen E. , La Via Francesco , D'Arrigo Giuseppe
Published: March 2009

The fabrication of SiC MEMS-based sensors requires new processes able to realize microstructures on bulk material or on the SiC surface. The hetero-epitaxial growth of 3C-SiC on silicon substrates allows one to overcome the traditional limitations of SiC micro-fabrication. This approach puts together the standard silicon bulk microfabrication methodologies with the robust mechanical properties of 3C-SiC. Using this approach we were able to fabricate SiC cantilevers for a new class of pressure sensor. In the present research, chemical vapour deposition (CVD) in the low pressure regime of 3C–SiC on silicon substrates was carried out using silane (SiH4), propane (C3 H8) and hydrogen (H2) as the silicon supply, carbon supply and gas carrier, respectively. The resulting bow in the MEMS structures was evaluated optically and the residual stress in the films calculated using the modified stoney equation and determined to be approximately 300 MPa.