bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Induced Nanostructure Formation on a Surface of CdZnTe Crystal
Authors: Medvid Arthur , Mychko A. , Pludons A. , Naseka Yu.
Published: May 2010

For the first time, a new PL band at 1.8718 eV is observed after irradiation of Cd1-xZnxTe (x = 0.1) crystal by Nd:YAG laser at intensity 12.0 MW/cm2. The origin of this PL band we connect with formation of strongly enriched layer by Zn atoms at the irradiated surface of the sample due to a themogradient effect. Self-organizing structures of nanometer size are observed on the surface of a CdZnTe crystal (x = 0.1) irradiated by strongly absorbed Nd:YAG laser radiation at intensities 4.0-12.0 MW/cm2. The effect of exciton quantum confinement manifested by a shift to higher energies of the A0,X exciton line in the photoluminescent spectrum is present in structures of 10–15 nm in diameter at the top of nanohills. A graded band gap structure with optical window is formed on the top of nanohills.
Effect of SiC Nanoparticles Dispersion on the Microstructure and Mechanical Properties of Electroplated Sn-Bi Solder Alloy
Authors: Lee Chang Woo , Shin Y.S. , Yoo S.H.
Published: May 2010

The effect of SiC nanoparticle dispersion was investigated for microstructure change and mechanical properties of Sn-Bi electroplated alloys. The diameters of SiC nanoparticle in this study were 45-55 nm. The SiC nanoparticles were mixed with Sn-Bi electroplating and then the nanoparticles were dispersed with ultrasonic vibrator. After the dispersion, the SiC dispersed Sn-Bi alloys were electroplated on Cu deposited Si wafer. The microstructure and mechanical properties of the sample were evaluated by FE-TEM, FE-SEM, EDS, and shear tester. For TEM observation, the specimens were prepared by ultramicrotome and FIB. The SiC nanoparticles were well-dispersed in Sn-Bi alloy. SiC particles were located near grain boundaries or grain inside. The average grain size of the solder alloy was decrease about 30% compared with the grain size of Sn-Bi alloy prepared in the same condition. Due to the grain refinement and dispersion hardening by SiC nanoparticles, the SiC dispersed Sn-Bi alloy is expected to obtain high reliability and joining strength when it applied to interconnection materials.
Self-Diffusion in Magnetron-Sputtered Nanocrystalline Fe Films
Authors: Chakravarty S. , Tietze U. , Lott D. , Horisberger M. , Stahn Jochen , Lalla N.P. , Schmidt Harald
Published: May 2010

Self-diffusion in magnetron sputtered nanocrystalline Fe films was investigated by neutron reflectometry on [natFe(10 nm)/57Fe(5 nm)]20 isotope multilayers between 310 and 510°C. The determined diffusivities corresponding to diffusion length between 0.8 – 2.1 nm are time dependent and decrease by more than two orders of magnitude during isothermal annealing. This behaviour can be attributed due to the annihilation of frozen-in point defects, formed during sputtering. For very long annealing times of more than 8 days the diffusivities above 400°C are in good accordance with the volume diffusivities on single crystals given in the literature. However, at temperatures below 400°C the diffusivities are higher than extrapolated literature data, indicating that defect annihilation is still an ongoing process. Furthermore, a comparison of diffusivities obtained for nanocrystalline Fe films prepared by magnetron sputtering and ion beam sputtering, respectively, is presented and discussed.
Effect of Alumina Additives on the Crystallite Size and Lattice Strain of Nanocrystalline Hydroxyapatite Obtained by Dry Mechanochemical Process
Authors: Sanayei M. , Nasiri-Tabrizi Bahman , Ebrahimi-Kahrizsangi Reza , Shokuhfar Ali
Published: May 2010

Hydroxyapatite (HAp) is an important bioactive ceramic that possessing beneficial biocompatibility and osteoconductivity resulting in bonding to human bone tissues. The dry mechanochemical process is widely used to prepare nanometer HAp. However, little research has been carried out concerning the correlation between adding alumina and the structural changes during the mechanochemical process. In this research, special attention was paid to the effect of alumina additive on the crystallite size and lattice strain of nanocrystalline HAp. Characterization was accomplished by using powder X-ray diffraction (XRD). The obtained data demonstrated that the diffraction lines corresponding to the HAp phase became broad and weak with increasing alumina additive. In fact, the nanocrystalline HAp with high crystallinity degree can be synthesized in the proper amounts of alumina additive via mechanochemical method. Furthermore, an increase of alumina additive led to increase in lattice strain and decrease in size of the powder grain.
Synthesis and Characterization of Ga Doped SiO2 Nanoparticles by a Reverse Micelle and Sol–Gel Processing
Authors: Kim Min Yeong , Chu Min Cheol , Cho Seong Jai , Bae Dong Sik
Published: May 2010

Ga doped SiO2 nanosized particles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles and the thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethyl orthosilicate(TEOS) within the micro-emulsion. The average size of synthesized Ga doped SiO2 nanoparticles were about in the size range of 10-15 nm and Ga particles 2-5 nm. The effects of synthesis parameters, such as the molar ratio of water to TEOS, and the molar ratio of water to surfactant, are discussed.
Application of ZnO Nanoparticles EM Wave Detector Prepared by Sol-Gel and Self-Combustion Techniques
Authors: Yahya Noorhana , Daud Hanita , Tajuddin Nurulhuda Ali , Daud Hasnah Mohd , Shafie Afza , Puspitasari Poppy
Published: May 2010

Zinc oxide (ZnO) has found many important applications such as optoelectronic devices, sensors and varistors. The challenging part however is synthesizing ZnO nanoparticles and its utilisation as EM detectors. Sol-gel and self-combustion techniques were chosen in this study due to the ability to produce single phase and nano-size samples. The starting mixture consists of 10 grams of zinc (II) nitrate, Zn(NO3)2.6H2O salt which was dissolved in 50 mL of nitric acid, HNO3.The solution was stirred at 250 rpm continuously for 1 day. The mixture was then gradually heated for every 15 minutes until it combusted at 110oC for the self-combustion technique. For the sol-gel technique, the dissolved mixture was heated at 40oC, 50oC, 60oC and 70oC until the gelatine was formed. After the drying process, the as-prepared samples were annealed at 100oC and 200 oC for 1 hour for each technique. Characterizations were performed by using X-Ray Diffraction (XRD), Raman Spectra and Scanning Electron Microscopy (SEM).The XRD analysis showed a major peak of [101] plane at 2Ө for the self-combustion technique and the sol-gel technique. Raman results for the samples prepared via sol-gel and self-combustion techniques had shown the major peak of ZnO that is located at the Raman shifts of 437.67 cm-1. Using the Scherrer equation, single crystal nano particle of ZnO was successfully obtained in the range of 38.49 nm to 50.70 nm for the sample prepared via the sol gel technique. By the self-combustion technique, the average dimension of the as-prepared sample is in the range of 34-49 nm. Further heat treatment resulted in a major change of the Raman shift corresponding to the single phase ZnO nano particles. The best samples were used as electromagnetic (EM) detectors. The EM detectors are polymer based composite which were prepared using a casting technique.
Deposition of Nano Sized Titanium Nitride on H11 Tool Steel Using Active Screen Plasma Nitriding Method
Authors: Yazdani Arash , Soltanieh Mansour , Aghajani Hossein , Rastegari Saeed
Published: May 2010

Active screen plasma nitriding (ASPN) is an emerging surface engineering technology that offers many advantages over the conventional DC plasma nitriding (DCPN). In this research, plasma nitriding of H11 tool steel, using titanium active screen was investigated. Samples were plasma nitrided at 550oC, for 10 and 20 h with 3 different gas mixtures of H2/N2% = 3, 4, 5. The coating microstructure and phase analysis were investigated using Scanning Electron Microscopy (SEM) and X-ray Diffraction techniques. The dominant phase in the compound layer was TiN. With increasing processing time, the layer thickness was increased. According to SEM results, the sample surface was formed of nano sized and particulate titanium nitride particles. It was shown that with increasing H2% in gas mixtures, better surface quality, golden yellow color, was obtained. Also, the intensity of TiN peaks and layer thickness were increased significantly.
Zirconium – Based Ceramic Targets for Producing Nanocrystalline Coatings Resistant to Heat and Thermal Creep
Authors: Olszyna Andrzej Roman , Kostecki Marek
Published: May 2010

Technology of thermal ceramic barriers (TBC) has been chiefly designed for materials with a single thermal barrier of the 7YSZ type. A high content of Y2O3 ensures a good phase stability of the YSZ material. In search for other alternative materials suitable for TBC, the material most often examined is modified zirconium oxide. The modification consists of stabilizing the ZrO2 powder with Y2O3 and doping it with La, Gd and Nd. This paper presents the results of studies on producing cathodic zirconium oxide-based ceramic targets intended for depositing refractory heat-resistant nano-crystalline TBC coatings. The targets are characterized by a high density (close to its theoretical value) and have a homogeneous phase and chemical structure.
Optimization for Development of Carbon Nanotubes Using Taguchi Method at Constant Temperature
Authors: Sufian Suriati , Yusup Suzana , Ahmadun Fakhru'l Razi
Published: May 2010

In this study, an optimization of floating catalyst chemical vapor deposition (FC-CVD) using Taguchi method is done in developing multiwall nanotubes (MWNTs) at constant temperature. The reaction is run at the temperature of 850°C in atmospheric pressure with ferrocene as the catalyst precursor and benzene as the carbon feedstock. By applying Taguchi’s method as the design of experiment, three parameters: namely reaction time, hydrogen flow rate and catalyst weight have been varied during the optimization of the experiment. The results show that the BET specific surface area increases as the reaction time increases, the degree of graphitization reduces as the mass of the catalyst increases and the relative value of amorphous carbon to graphite carbon decreases as the hydrogen flow rate increases.
Consolidation Process in Near Net Shape Manufacturing of Armstrong CP-Ti/Ti-6Al-4V Powders
Authors: Yamamoto Yukinori , Kiggans Jim O. , Clark Michael B. , Nunn Stephen D. , Sabau Adrian S. , Peter William H.
Published: May 2010

This paper summarizes our recent efforts to develop the manufacturing technologies of consolidated net-shape components by using new low-cost commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy powders made by the Armstrong process. Fabrication processes of net shape/ near net shape components, such as uniaxial die-pressing, cold isostatic pressing (CIP), sintering, roll compaction and stamping, have been evaluated. The press-and-sinter processing of the powders were systematically investigated in terms of theoretical density and microstructure as a function of time, pressure, and temperature. Up to 96.4% theoretical density has been achieved with the press-and-sinter technology. Tensile properties of the consolidated samples exhibit good ductility as well as equivalent yield/ultimate tensile strengths to those of fully consolidate materials, even with the presence of a certain amount of porosity. A consolidation model is also under development to interpret the powder deformation during processing. Net shape components made of the Armstrong powder can successfully be fabricated with clearer surface details by using press-and-sinter processing.
Effect of Oxygen on Phase Precipitation and Mechanical Functionality in Ti-29Nb-13Ta-4.6Zr
Authors: Niinomi Mitsuo , Nakai Masaaki , Akahori Toshikazu , Tsutsumi Harumi
Published: May 2010

Oxygen plays very important roles in titanium and its alloys. Solute oxygen in titanium alloys leads to solid solution strengthening, suppressing the precipitation of the athermal omegaor orthorhombic martensite phase, enhancing the formation of the -case, etc. The proper using oxygen is effective to improve the mechanical functionalities of titanium alloys. However, the role of oxygen in titanium alloys is still not well understood. Therefore, the effect of oxygen on the mechanical functionalities such as strength-ductility balance, hardness, and Young’s modulus in Ti-29nb-13Ta-4.6Zr was investigated.
Application of Local Rapid Heat Treatment for Improvement of Microstructure and Mechanical Properties of Titanium Products
Authors: Markovsky Pavlo E.
Published: May 2010

Local Rapid Heat Treatment (LRHT) based on induction-heating methods can be used to form unique location-specific microstructures and properties in commercial titanium alloys while maintaining the bulk of the material in an initial, non-heat-treated condition. The present work is focused on practical aspects of LRHT application for microstructure/ mechanical properties improvement of some parts made of commercial titanium alloys. It is shown, that LRHT application could improve mechanical properties of such complicated part like turbine engine compressor blades, and two made of Ti-6Al-4V and VT22 titanium alloys goods after repair with Electron Beam Physical Vapor Deposition as well as with Build-up Welding.
Characterization of the Microstructure, Tensile and Creep Behavior of Powder Metallurgy Processed and Rolled Ti-6Al-4V-1B Alloy
Authors: Chen Wei , Boehlert Carl J.
Published: May 2010

This work investigated the microstructure and elevated-temperature (400-475oC) tensile and tensile-creep deformation behavior of a powder metallurgy (PM) rolled Ti-6Al-4V-1B(wt.%) alloy. The PM rolled Ti-6Al-4V-1B alloy exhibited a duplex microstructure, and it did not exhibit a strong α-phase texture compared with the PM extruded Ti-6Al-4V-1B alloy. The PM rolled Ti-6Al-4V-1B alloy exhibited greater creep resistance than the PM extruded Ti-6Al-4V-1B alloy as well as the as-cast Ti-6Al-4V-1B alloy.
A Continuous Process to Produce Titanium Utilizing Metallothermic Chemistry
Authors: Withers James , Laughlin John , Elkadi Yasser , DeSilva Jay , Loutfy Raouf O.
Published: May 2010

In the standard Kroll process reaction between the TiCl4 and Mg is at the reactor wall interface that limits the potential to design a continuous process. Many alternatives have been investigated over the past 70 years to engineer a continuous process utilizing metallothermic reduction of TiCl4. Approaches utilizing burner type architectures for continuous processing result in unacceptable very fine Ti powder. A unique process that operates continuously and produces controlled size powder that can be directly utilized in standard powder metallurgy, rapid manufacturing, or substituted for sponge will be discussed.
The Electrolytic Production of Ti from a TiO2 Feed (The DARPA Sponsored Program)
Authors: Withers James , Laughlin John , Elkadi Yasser , DeSilva Jay , Loutfy Raouf O.
Published: May 2010

DARPA instituted an Initiative in Titanium in 2003 to produce titanium, alternatively to the Kroll process, in a billet form for under $4/lb. This DARPA sponsored program has gone into Phase II consisting of utilizing ore/TiO2 as a feed. The TiO2 is carbothermically reduced to a suboxide-carbide (Ti:O:C) which is used anodically to resupply the titanium content in an electrolysis process that deposits titanium in a powder morphology. The deposited powder is uniquely stripped from the cathodes and harvested in a separate stream that permits continuous electrolytic processing to produce titanium at an estimated cost about ½ the Kroll process. Oxygen contents less than 500 ppm are achievable with particle sizes in the desired range for powder metallurgy applications. The process has been demonstrated on a continuous basis and is in the stage of scaling-up to 500 lbs/day.
Electrical Characteristics of MOSFETs Using 3C-SiC with Buried Insulating Layer
Authors: Tanehira Takafumi , Nakano T. , Nakao Motoi
Published: May 2010

Metal oxide semiconductor field effect transistors (MOSFETs) using SiC on insulator (SiC-OI) substrate with the structure of 3C-SiC (100)/SiO2/Si have been fabricated. SiC-OI substrates with SiC thicknesses of 100 nm and 600 nm are employed as starting materials and aluminum ions are implanted for p-regions or channel regions with a multi-implantation technique. Afterward, to form the source and drain regions, phosphorus ions are implanted. The gate oxide layer is grown in dry thermal oxidation, followed by post-oxidation annealing. Nickel is used as a contact material for the source and drain region, and aluminum is used for the gate material. From Id-Vd characteristics, 600 nm SiC-OI MOSFET is superior to 100 nm SiC-OI MOSFET. It is might that the crystalline quality of surface SiC layers affects the performance of MOSFET.
SiC-OI MOSFET is operated successfully for the first time.
10 kV, 10 A Bipolar Junction Transistors and Darlington Transistors on 4H-SiC
Authors: Zhang Qing Chun Jon , Callanan Robert , Agarwal Anant K. , Burk Albert A. , O'Loughlin Michael  J. , Palmour John W. , Scozzie Charles
Published: May 2010

4H-SiC Bipolar Junction Transistors (BJTs) and hybrid Darlington Transistors with 10 kV/10 A capability have been demonstrated for the first time. The SiC BJT (chip size: 0.75 cm2 with an active area of 0.336 cm2) conducts a collector current of 10 A (~ 30 A/cm2) with a forward voltage drop of 4.0 V (forced current gain βforced: 20) corresponding to a specific on-resistance of ~ 130 mΩ•cm2 at 25°C. The DC current gain, β, at a collector voltage of 15 V is measured to be 28 at a base current of 1 A. Both open emitter breakdown voltage (BVCBO) and open base breakdown voltage (BVCEO) of ~10 kV have been achieved. The 10 kV SiC Darlington transistor pair consists of a 10 A SiC BJT as the output device and a 1 A SiC BJT as the driver. The forward voltage drop of 4.5 V is measured at 10 A of collector current. The DC forced current gain at the collector voltage of 5.0 V was measured to be 440 at room temperature.
Optical Insights into the Internal Electronic and Thermal Behavior of 4H-SiC Bipolar Devices
Authors: Werber Dorothea , Aigner Martin , Wachutka Gerhard
Published: May 2010

Two different optical measurement techniques have been combined in one single experimental platform to provide detailed insight into the interior of 4H-SiC bipolar devices with respect to their coupled electronic and thermal behavior: First, free carrier absorption (FCA) measurements yield time-resolved electron and hole densities profiles during turn-on and under stationary conditions; and second, light deflection measurements provide information about the gradients of the electron and hole densities as well as that of the temperature gradient. The full measurement process is also simulated on the computer as “virtual experiment” on the basis of high-fidelity physical device models. Investigations on high-blocking 4H-SiC bipolar diodes exemplify the optical probing methodology and the numerical simulation.
Fast Switch-Off of High Voltage 4H–SiC npn BJTs from Deep Saturation Mode
Authors: Ivanov Pavel A. , Levinshtein Michael E. , Palmour John W. , Agarwal Anant K. , Zhang Q. Jon
Published: May 2010

In this paper, very fast switch-off of high voltage 4H–SiC npn Bipolar Junction Transistors (BJTs) driven in deep saturation regime is reported. It is shown that the switch-off time can be as short as 4 ns if a reverse base current pulse is applied that provides forced minority carrier sweep out from the base.
Operation of Silicon Carbide BJTs Free from Bipolar Degradation
Authors: Konstantinov Andrei O. , Domeij Martin , Zaring Carina , Keri Imre , Svedberg Jan Olov , Gumaelius Krister , Östling Mikael , Reimark Mats
Published: May 2010

The mechanisms of bipolar degradation in silicon carbide BJTs are investigated and identified. Bipolar degradation occurs as result of stacking fault (SF) growth within the low-doped collector region. A stacking fault blocks vertical current transport through the collector, driving the defective region into saturation. This results in considerable drop of emitter current gain if the BJT is run at a reasonably low collector-emitter bias. The base region does not play any significant role in bipolar degradation. Long-term stress tests have shown full stability of large-area high-power BJTs under minority carrier injection conditions provided the devices are fabricated using low Basal Plane Dislocation (BPD) material. However, an approximately 20% current gain compression is observed for the first 30-60 hours of burn-in under common emitter operation, which is related to instability of surface recombination in the passive base region.
Temperature Modeling and Characterization of the Current Gain in 4H-SiC Power BJTs
Authors: Buono Benedetto , Ghandi Reza , Domeij Martin , Malm B. Gunnar , Zetterling Carl Mikael , Östling Mikael
Published: May 2010

The current gain of 4H-SiC BJTs has been modeled using interface traps between SiC and SiO2 to describe surface recombination, by a positive temperature dependence of the carrier lifetime in the base region and by bandgap narrowing in the emitter region. The interface traps have been modeled by one single level at 1 eV above the valence band, with capture cross section of 1 × 10-15 cm2 and concentration of 2 × 1012 cm-2. The temperature behavior of SiC BJTs has been simulated and the results have been compared with measurements. An analysis of the carrier concentration has been performed in order to describe the mechanisms for fall-off of the current gain at high collector current. At room temperature high injection in the base and forward biasing of the base-collector junction occur simultaneously causing an abrupt drop of the current gain. At higher temperatures high injection in the base is alleviated by the higher ionization degree of the aluminum dopants, and then forward biasing of the base-collector junction is the only acting mechanism for the current gain fall-off at high collector current. This mechanism and the negative temperature dependence of the carrier mobility can also explain the reduction of the knee current for gain fall-off with increasing temperature. Simulations with different emitter widths have been also performed and analyzed to characterize the emitter size effect. Higher current density caused by reducing the emitter width introduces higher carrier recombination in the emitter region, leading to a reduction of the current gain.
Use of SiCl4 as Silicon Precursor for Low-Temperature Halo-Carbon Epitaxial Growth of 4H-SiC
Authors: Kotamraju Siva Prasad , Krishnan Bharat , Melnychuk Galyna , Koshka Yaroslav
Published: May 2010

Chlorinated silicon precursor SiCl4 was investigated as an alternative to SiH4 with HCl addition as a source of additional chlorine in order to suppress the homogeneous nucleation during the low-temperature epitaxial growth at 1300°C. The homogeneous nucleation in the gas phase was further reduced compared to SiH4+HCl growth. The process window for obtaining good epilayer morphology during the CH3Cl/SiCl4 growth was found to correspond to Si supply-limited mode. At lower values of C/Si ratio formation of Si-rich polycrystalline islands/droplets took place. At high C/Si ratio, formation of polycrystalline SiC was the source of morphology degradation. The process window became increasingly narrower at higher Rg, which limited the possibility of significantly increasing Rg at such low growth temperatures. Generation of triangular defects became significant at Rg above 5-6 μm/hr, even when a nearly-optimal value of C/Si ratio was used. Similar experiments were conducted using C3H8, a more traditional precursor, instead of the halo-carbon precursor CH3Cl. While a similar growth rate could be achieved for the same SiCl4 flow rate, much lower values of the C/Si ratio were required. The morphology with C3H8 was worse within the process window. The C/Si process window for the C3H8/SiCl4 growth was much narrower compared to the CH3Cl/SiCl4 growth, and the window essentially disappeared at Rg > 3 4 μm/hr.
Electrical and Thermal Performance of 1200 V, 100 A, 200°C 4H-SiC MOSFET-Based Power Switch Modules
Authors: Scofield James D. , Merrett Joseph Neil , Richmond Jim , Agarwal Anant K. , Leslie Scott
Published: May 2010

In this paper we report the electrical and thermal performance characteristics of 1200 V, 100 A, 200°C (Tj), SiC MOSFET power modules configured in a dual-switch topology. Each switch-diode pair was populated by 2 x 56 mm2 SiC MOSFETs and 2 x 32 mm2 SiC junction barrier Schottky (JBS) diodes providing the 100 A rating at 200°C. Static and dynamic characterization, over rated temperature and power ranges, highlights the performance potential of this technology for highly efficient drive and power conversion applications. Electrical performance comparisons were also made between SiC power modules and equivalently rated and packaged IGBT modules. Even at a modest Tj=125°C, conduction and dynamic loss evaluation for 20kHz, Id=100A operation demonstrated a significant efficiency advantage (38-43%) over the IGBT components. Initial reliability data also illustrates the potential for SiC technology to provide robust performance in harsh environments.
Demonstration of High Temperature Bandgap Voltage Reference Feasibility on SiC Material
Authors: Banu Viorel , Brosselard Pierre , Jordá Xavier , Godignon Philippe , Millan José
Published: May 2010

This work demonstrates that a stable voltage reference with temperature, in the 25°C-300°C range is possible with SiC. This paper reports the simulated and experimental results as well and a practical and simplified vision on the principles of thermally compensated voltage reference circuits, usually named bandgap references. For our demonstration, we have used SiC Schottky diodes. The influence of the barrier height and the ideality factor on the voltage reference and a comparison between simulated and experimental results are also presented.
System Improvements of Photovoltaic Inverters with SiC-Transistors
Authors: Kranzer Dirk , Reiners Florian , Wilhelm Christian , Burger Bruno
Published: May 2010

In this paper the system improvements of PV-inverters with SiC-transistors are demonstrated. The basic characteristics of engineering prototypes of normally-off SiC-JFETs and SiC-MOSFETs were measured and their differences in the application are considered. To demonstrate the improvement in PV-inverter performance, a 5 kW single-phase and a three-phase full bridge inverter with normally-off SiC-JFETs were developed at Fraunhofer ISE. Different switching frequencies up to 144 kHz were applied and the impact on production costs and inverter performance was rated under the aspects of an industrial product development. This means, the influences on the efficiency and power density. In this work, a world record in PV-inverter efficiency of 99 % was achieved in a single-phase inverter and for the three-pase inverter, the power density was tripled with respect to commercially available state of the art PV-inverters.
AlN Substrates and Epitaxy Results
Authors: Makarov Yuri , Chemekova T.Yu. , Avdeev O.V. , Mokhov N. , Nagalyuk S.S. , Ramm M.G. , Helava Heikki
Published: May 2010

AlN substrates are produced by Physical Vapor Transport (PVT) growth of AlN bulk single crystals followed by post growth processing of the crystals (calibration, slicing, lapping, and polishing). The AlN substrates are suitable for epitaxial growth. The substrates may be used for development of devices such as ultra violet (UV) light emitting diodes (LEDs) and laser diodes (LDs), Piezo-Electric Transducers, SAW devices, RF Transistors, etc.
Free Standing AlN Single Crystal Grown on Pre-Patterned and In Situ Patterned 4H-SiC Substrates
Authors: Yazdi Gholam Reza , Vassilevski Konstantin , Córdoba José M. , Gogova Daniela , Nikitina Irina P. , Syväjärvi Mikael , Odén Magnus , Wright Nicolas G. , Yakimova Rositza
Published: May 2010

Free standing AlN wafers were grown on pre-patterned and in situ patterned 4H-SiC substrates by a physical vapor transport method. It is based on the coalescence of AlN microrods, which evolve from the apex of SiC pyramids grown on the SiC substrate during a temperature ramp up for in situ patterned substrate and SiC pyramids formed by reactive ion etching (RIE). This process yields stress-free (according XRD and Raman results) AlN single crystals with a thickness up to 400 µm and low dislocation density.
Deep-Level Defects in AlN Single Crystals: EPR Studies
Authors: Ilyin Ivan V. , Soltamova Alexandra A. , Soltamov V.A. , Khramtsov V.A. , Mokhov E.N. , Baranov P.G.
Published: May 2010

Electron paramagnetic resonance (EPR) at X-band (9.4 GHz) and Q-band (35 GHz) have been used to study defects in two samples of AlN monocrystals, grown by a sublimation sandwich method. These investigations reveal the presence of Fe2+ impurities in the reddish sample. The spectra of substitutional Fe2+ are highly anisotropic and could be observed even up to the room temperature. After illumination the signals showing the DX behavior were detected in the same sample. We assume these signals to arise due to the presence of the shallow donor center namely the isolated substitutional oxygen ON occupying the nitrogen position. In the second slightly amber-coloured sample EPR measurements before and after X-ray showed the presence of a deep-donor center which was assumed to be nitrogen vacancy VN. Based on thermoluminescence measurements the depth of the level was estimated to 0.45-0.5 eV.
Characteristics of Diamond SBD’s Fabricated on Half Inch Size CVD Wafer Made by the “Direct Wafer Fabrication Technique”
Authors: Shikata Shinichi , Umezawa Hitoshi , Yamada Hideaki , Tsubouchi T. , Mokuno Yoshiaki , Chayahara Akiyoshi
Published: May 2010

Diamond is a hopeful candidate for power switching device which can operate at high temperature as a “Cooling system free” device, yet at a high current. Recently we have developed a 3D diamond CVD growth method coupled with a sophisticated “direct wafer fabrication technique” to fabricate diamond wafer without slicing. Currently, half inch size single crystal diamond substrates are available for R&D of diamond device. Using this technique, we have increased the device fabrication size from 3x3mm2 to half inch wafer. In this paper, we present the results of measurements on the first device fabricated on a half inch size CVD substrate. We have carried out the first device characteristics mapping for diamond, and have observed the influence of substrate characteristics on the SBD characteristics.
Doping Concentration and Surface Morphology of 4H-SiC C-Face Epitaxial Growth
Authors: Lee Kung Yen , Lee Shin Yi , Huang Chih Fang
Published: May 2010

This research is focused on the influence of high C/Si ratios and low pressure on n-type doping concentration and surface defects of 4H-SiC C-face epilayers. N-type doping concentration decreases as C/Si ratio increases from 3.0 to 4.0 and pressure reduces from 100 mbar to 50 mbar; defect densities decrease as pressure increases at both C/Si ratios of 3.0 and 4.0. RMS roughness is about 0.21 nm for all C-face samples, independent of C/Si ratios of 3.0 and 4.0 and pressure from 50 mbar to 100 mbar. However, the influence of growth temperature on doping concentration and surface defects can not be clearly observed in this work.
Thermally Induced Surface Reorganization of 3C-SiC(111) Epilayers Grown on Silicon Substrates
Authors: Portail Marc , Chassagne Thierry , Roy Sebastien , Moisson Catherine , Zielinski Marcin
Published: May 2010

We investigate by means of Atomic Force Microscopy and Scanning Electron Microscopy the surface modifications of 3C-SiC(111)/Si epilayers induced by thermal annealing performed under hydrogen or argon atmosphere. We explore the effects of these treatments both on as grown and polished epilayers. Owing to an important initial surface roughness, the annealing has few impact on as grown films. On polished epilayers, a surface reorganization via the formation of a regular array of steps is evidenced. The proper effect of each gas on the surface reorganization is discussed.
SiC Nanowires Grown on 4H-SiC Substrates by Chemical Vapor Deposition
Authors: Krishnan Bharat , Kotamraju Siva Prasad , Sundaresan Siddarth G. , Koshka Yaroslav
Published: May 2010

Growth of SiC nanowires on commercial 4H-SiC substrates by chemical vapor deposition is reported. The main objective was to explore a possibility of reproducing the substrate polytype in order to obtain SiC NWs specifically composed of the hexagonal 4H-SiC polytype. The growth experiments were conducted in a hot-wall CVD reactor with H2 as the carrier gas, SiCl4 as the silicon source, and CH3Cl as the carbon source. Vapor-liquid-solid (VLS) growth mode was enabled by using metal nano-particle on the surface of the 4H-SiC substrates. Formation of nanowires or bigger nano-cones was achieved depending on the temperature and the metal catalyst used. Only SiC phase with no presence of Si was confirmed by X-ray diffraction for the growth temperatures down to 1050°C. The low temperature photoluminescence spectra measured on as-grown NWs showed clear 4H-SiC nitrogen bound excitons in some of the samples, particularly when in-situ N2 doping was used. The density of stacking faults detected by TEM strongly depended on the growth conditions.
Temperature and Injection Level Dependencies of Carrier Lifetimes in p-Type and n-Type 4H-SiC Epilayers
Authors: Hayashi Toshihiko , Asano Katsunori , Suda Jun , Kimoto Tsunenobu
Published: May 2010

Temperature and injection level dependencies of carrier lifetimes in p-type and n-type 4H-SiC epilayers have been investigated. The carrier lifetimes have been measured by differential microwave photoconductance decay measurements at various injection levels and temperatures. In both p-type and n-type epilayers, the carrier lifetimes gradually increased with increasing the injection level except for the very high injection condition. And the carrier lifetimes exhibited continuous increase with elevating the temperature for both epilayers. The carrier lifetime reached 3.3 µs in p-type and 4.2 µs in n-type epilayers at 250°C and an injection level of 1.8x1016 cm-3.
Increase of SiC Substrate Resistance Induced by Annealing
Authors: Straubinger Thomas L. , Woodin Richard L. , Witt T. , Shovlin J. , Dolny Gary M. , Sasahara P. , Schmitt Erwin , Weber Arnd Dietrich , Casady Jeff B. , Casady Janna R. B.
Published: May 2010

We report here an anisotropic increase in SiC bulk resistivity by annealing at 1150 °C, and discuss the implications for SiC devices. The increase in resistivity is resistivity dependent and can be (at least) partially reversed by a subsequent anneal at higher temperature. Ideal device performance is achievable with appropriate annealing steps during device processing.
Modeling of Boron Diffusion and Segregation in Poly-Si/4H-SiC Structures
Authors: Mochizuki Kazuhiro , Shimizu Haruka , Yokoyama Natsuki
Published: May 2010

Boron diffusion in boron-doped poly-Si/nitrogen-doped 4H-SiC structure was investigated by combining a reported model of poly-Si diffusion sources with the authors’ model of boron diffusion in 4H-SiC. By taking the limited supply of carbon interstitials at heterointerfaces into account, we determined a segregation coefficient of 4 to 8 and an activation energy of 0.20 eV in the temperature range of 650 to 1000°C.
Dislocation Conversion and Propagation during Homoepitaxial Growth of 4H-SiC
Authors: Kallinger Birgit , Thomas Bernd , Polster Sebastian , Berwian Patrick , Friedrich Jochen
Published: May 2010

Basal Plane Dislocations (BPDs) in SiC are thought to cause degradation of bipolar diodes with blocking voltages > 2kV by triggering the formation and expansion of stacking faults during device operation. Hence, low N doped, thick epitaxial layers without BPDs are urgently needed for the realization of long-term stable SiC bipolar diodes. Such epilayers can be achieved if the conversion of the BPD into another harmless dislocation type is supported by proper epitaxial growth parameters and use of vicinal (off-cut) substrates. In this work, the influence of the substrate’s off-cut angle and of the epilayer thickness on BPD density and surface morphology were investigated. The BPD densities of epilayers grown on 2° and 4° off-cut substrates were very low compared to growth on 8° off-axis substrates. X-Ray Topography has proved that all the Threading Dislocations (TD) propagate from the substrate to the epilayer and that BPDs in the substrate convert to Threading Edge Dislocations (TED) in the epilayer, i.e. the dislocation density (DD) of the substrate determines the epilayer’s DD. The conversion of BPDs is supported by the presence of bunched steps as for growth of thick layers on 2° and 4° off-cut substrates.
Single Shockley Stacking Faults in As-Grown 4H-SiC Epilayers
Authors: ul Hassan Jawad , Bergman Peder
Published: May 2010

An extended structural defects which locally drastically reduces the carrier lifetime, has been observed in as-grown epilayers. A combination of back polishing, etching in molten KOH and optical microscopy revealed the geometrical structure of the stacking fault inside the epilayer. The fault started close to the epi-substrate interface, expanded initially rapidly but changed geometry after some time and reduced in size during further growth. The optical spectrum as well as the temperature dependence from this fault is identical to the emission from the single Shockley stacking faults previously only observed and formed in the bipolar diodes during forward voltage operation.
Microstructural Characterization of Epitaxial Cubic Silicon Carbide Using Transmission Electron Microscopy
Authors: Chayasombat Bralee , Kimata Y. , Kato T. , Tokunaga Tomoharu , Sasaki Katsuhiro , Kuroda Kotaro
Published: May 2010

Microstructures of switch-back epitaxy cubic silicon carbide (3C-SiC) before and after Al ion implantation were investigated by transmission electron microscopy (TEM). Stacking faults aligned along the {111} were observed in 3C-SiC. A surface bulge was observed in some regions and planar defects were observed under the bulge region. After ion implantation of 3C-SiC, defects were observed to be distributed up to a depth approximately 500 nm from the surface.
Characteristics of Porous 3C-SiC Thin Films Formed with Nitrogen Doping Concentrations
Authors: Kim Kang San , Chung Gwiy Sang
Published: May 2010

This paper describes the characteristics of porous 3C-SiC with in-situ N-doping concentrations. Polycrystalline (poly) 3C-SiC thin films were deposited on p-type Si (100) substrates by APCVD using hexamethyildisilane (HMDS: Si2(CH3)6). The porous 3C-SiC (pSiC) was achieved by anodized with 380 nm UV-LED. The characteristics of the N2 doped pSiC were evaluated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and photo luminescence (PL). Average pore diameter is about 50 nm and etched area was increased with N2 doping rate. These results are attributed to decrease the crystallinity by N2 doping. The band gaps of poly 3C-SiC films and porous 3C-SiC films were 2.5 eV and 2.7 eV, respectively.
Thermal Stability of Defect Centers in n- and p-Type 4H-SiC Epilayers Generated by Irradiation with High-Energy Electrons
Authors: Reshanov Sergey A. , Beljakowa Svetlana , Zippelius Bernd , Pensl Gerhard , Danno Katsunori , Alfieri Giovanni , Kimoto Tsunenobu , Onoda Shinobu , Ohshima Takeshi , Yan Fei , Devaty Robert P. , Choyke Wolfgang J.
Published: May 2010

This paper comprises a systematic study of the thermal stability of defect centers observed in n- and p-type 4H-SiC by deep level transient spectroscopy (DLTS); the defects are generated by irradiation with high-energy electrons of 170 keV or 1 MeV.
Shallow Defects Observed in As-Grown and Electron-Irradiated or He+-Implanted Al-Doped 4H-SiC Epilayers
Authors: Beljakowa Svetlana , Reshanov Sergey A. , Zippelius Bernd , Krieger M. , Pensl Gerhard , Danno Katsunori , Kimoto Tsunenobu , Onoda Shinobu , Ohshima Takeshi , Yan Fei , Devaty Robert P. , Choyke Wolfgang J.
Published: May 2010

Aluminum-doped 4H-SiC samples were either irradiated with high-energy electrons (170 keV or 1 MeV) or implanted with a box-shaped He+-profile. Admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS) were employed to search for defect centers. AS spectra of as-grown as well as of electron-irradiated (170 keV or 1 MeV) 4H-SiC epilayers reveal the Al acceptor (ΔE(Al) = 200 meV) and an unknown defect (ΔE(SB) = 177 meV), while AS spectra of the He+-implanted and annealed sample show in addition to the Al-acceptor two energetically deeper acceptor-like defect centers (ΔE(RE3) = 255 meV and ΔE(KR3) = 375 meV). The KR3-center is not directly formed by the He+-implantation, it requires an annealing process. The DLTS spectra of the He+-implanted and annealed sample resolve a double-peak structure of the KR3-defect (ΔE(KR3A) = 380 meV and ΔE(KR3B) = 410 meV).
Elastic Waves in Nano-Columnar Porous 4H-SiC Measured by Brillouin Scattering
Authors: Devaty Robert P. , Clouter Maynard J. , Ke Yue , Choyke Wolfgang J.
Published: May 2010

We report measured and calculated frequencies of elastic waves propagating in columnar porous 4H-SiC, an analytically tractable system. The sample was prepared using photo-electrochemical etching followed by mechanical polishing. The frequencies were measured using Brillouin scattering spectroscopy in backscattering geometry. The effective elastic constants, ordinary and extraordinary indices of refraction, and mass density, all obtained using effective medium models, are used to calculate the frequencies. Although the quasistatic limit is not strongly satisfied, the agreement between the measured and calculated values is good.
Nitridation of the SiO2/SiC Interface by N+ Implantation: Hall versus Field Effect Mobility in n-Channel Planar 4H-SiC MOSFETs
Authors: Moscatelli Francesco , Poggi Antonella , Solmi Sandro , Nipoti Roberta , Armigliato Aldo , Belsito Luca
Published: May 2010

In this paper the electrical and structural characteristics of n-MOSFETs fabricated on 4H SiC with a process based on nitrogen (N) implantation in the channel region before the growth of the gate oxide are reported for low (5x1018 cm-3) and high (6x1019 cm-3) N concentration at the SiO2/SiC interface. The electron mobility and the free carrier concentration in the MOSFET channel were evaluated by Hall effect measurement. The MOSFETs with the higher N concentration had the best electrical characteristics in terms of threshold voltage and field effect mobility, in spite of a lowering of the electron mobility in the channel. The latter is a negative drawback of the fabrication process that probably can be ascribed to an incomplete recovery of the implantation damage or to a high density of interstitial N atoms present in the channel region. In fact, the MOSFETs with the superior electrical performances were fabricated with the higher N+ dose and the shorter thermal oxidation time. However, no evidence of extended defects, clusters or nano-particles in SiC at the interface with the gate oxide was found in every SiC MOSFETs devices observed by electron transmission microscopy
Significant Decrease of the Interface State Density by NH3 Plasma Pretreatment at 4H-SiC (000-1) Surface and its Bond Configuration
Authors: Iwasaki Yoshinori , Yano Hiroshi , Hatayama Tomoaki , Uraoka Yukiharu , Fuyuki Takashi
Published: May 2010

We have investigated NH3 plasma pretreatment for Si- and C-face 4H-SiC and characterized interface properties and bond configuration. It is revealed that the NH3 plasma pretreatment is effective to reduce interface state density on C-face. From X-ray photoelectron spectroscopy (XPS) measurements, N- and H-related C bonds were observed. N and H passivate C-related defects and dangling bonds, resulting in improved interface properties.
Improved 4H-SiC MOS Interface Produced by Oxidized-SiN Gate Oxide
Authors: Moon Jeong Hyun , Yim Jeong Hyuk , Seo Han Seok , Kim Chang Hyun , Lee Do Hyun , Cheong Kuan Yew , Bahng Wook , Kim Nam Kyun , Kim Hyeong Joon
Published: May 2010

We have investigated the electrical and physical properties of the oxidized-SiN with or without post oxidation annealing (POA) in N2 gas. A significant reduction in interface-trap density (Dit) has been observed in the oxidized-SiN with N2 POA for 60 min if compared with other oxides. The reason for this has been explained in this paper.
Analysis of the Formation Conditions for Large Area Epitaxial Graphene on SiC Substrates
Authors: Yakimova Rositza , Virojanadara Chariya , Gogova Daniela , Syväjärvi Mikael , Siche D. , Larsson Karin , Johansson Leif I.
Published: May 2010

We are aiming at understanding the graphene formation mechanism on different SiC polytypes (6H, 4H and 3C) and orientations with the ultimate goal to fabricate large area graphene (up to 2 inch) with controlled number of monolayers and spatial uniformity. To reach the objectives we are using high-temperature atmospheric pressure sublimation process in an inductively heated furnace. The epitaxial graphene is characterized by ARPES, LEEM and Raman spectroscopy. Theoretical studies are employed to get better insight of graphene patterns and stability. Reproducible results of single layer graphene on the Si-face of 6H and 4H-SiC polytypes have been attained. It is demonstrated that thickness uniformity of graphene is very sensitive to the substrate miscut.
Quasi-Freestanding Graphene on SiC(0001)
Authors: Speck Florian , Ostler Markus , Röhrl Jonas , Jobst Johannes , Waldmann Daniel , Hundhausen Martin , Ley Lothar , Weber Heiko B. , Seyller Thomas
Published: May 2010

We report on a comprehensive study of the properties of quasi-freestanding monolayer and bilayer graphene produced by conversion of the (6√3×6√3)R30° reconstruction into graphene via intercalation of hydrogen. The conversion is confirmed by photoelectron spectroscopy and Raman spectroscopy. By using infrared absorption spectroscopy we show that the underlying SiC(0001) surface is terminated by hydrogen in the form of Si-H bonds. Using Hall effect measurements we have determined the carrier concentration and type as well as the mobility which lies well above 1000 cm2/Vs despite a significant amount of short range scatterers detected by Raman spectroscopy.
Defect Control in Growth and Processing of 4H-SiC for Power Device Applications
Authors: Kimoto Tsunenobu , Feng Gan , Hiyoshi Toru , Kawahara Koutarou , Noborio Masato , Suda Jun
Published: May 2010

Extended defects and deep levels generated during epitaxial growth of 4H-SiC and device processing have been reviewed. Three types in-grown stacking faults, (6,2), (5,3), and (4,4) structures, have been identified in epilayers with a density of 1-10 cm-2. Almost all the major deep levels present in as-grown epilayers have been eliminated (< 1x1011 cm-3) by two-step annealing, thermal oxidation at 1150-1300oC followed by Ar annealing at 1550oC. The proposed two-step annealing is also effective in reducing various deep levels generated by ion implantation and dry etching. The interface properties and MOSFET characteristics with several gate oxides are presented. By utilizing the deposited SiO2 annealed in N2O at 1300oC, a lowest interface state density and a reasonably high channel mobility for both n- and p-channel MOSFETs with an improved oxide reliability have been attained.