bluuebunny/crossref_metadata_2025 huggingface dataset:
Rheological and Fatigue Properties of Asphalt Binders Containing Anti-Rut Agents
Authors: Liu Kuang Yi , Dong Jian Zhong , Liu Rong Mao , Zheng Liang
Published: February 2014

Modification of asphalt binders has increasingly become the norm in designing optimally performing pavement. In this paper, an anti-rut agent was used as a modifier to add into base asphalt and its effects on the property of the asphalt were investigated. A shear blender was used to ensure a good distribution of the anti-rut agent. The conventional physical properties test and Dynamic Shear Rheometer (DSR) test were used to evaluate the properties of the asphalt. The results showed that the softening point and rutting parameter increases significantly, the ductility and penetration decrease due to the introduction of the anti-rut agent. Besides, the result of fatigue test showed that excess anti-rut agent may lead a deterioration in the fatigue life. Key word: Anti-rut agent; Rutting parameter; Rheological property; Fatigue life.
Utilization of Steel Slag as Aggregates for Porous Asphalt Mixture
Authors: Li Can Hua , Xiang Xiao Dong , Zhou Xi Ying , Tu Xiao Qian
Published: February 2014

Steel slag is a byproduct, making up a portion of 15-20% of iron output. Most of them are deposited in slag storing yards and thus results in many serious environment problems in China. This paper aims to explore the feasibility of utilizing steel slag as aggregates in porous asphalt mixtures. Open-graded friction course (OGFC), a permeable and porous asphalt mixture, was evolved in this paper. Residual stability ratio test, tensile strength ratio test, seepage test and rutting test got used in the research. Results showed that OGFC with steel slag as coarse aggregate had good performances.
Construction Technique and Quality Control of Sup-25 Asphalt Mixture Used in Hao-Tong Highway
Authors: Cui Peng , Sang Yang , Li Bao Quan , Zhang Hai Xia
Published: February 2014

In this paper, the asphalt mixture proportions for Hao-Tong highway was investigated using Sup25 gradation design method. Marshall Test was applied to estimate performance of asphalt concrete. Based on the actual project application, the methods of construction technology and construction quality control of Sup25 asphalt mixture were discussed in this paper. The test results showed that water permeability, degree of compaction and rutting of the Sup25 asphalt mixture layer meet the requirements of Chinese specification.
Application of Superfine Aggregate in Corrosion Resist of Hydraulic Concrete
Authors: Ci Jun , Sun Zhao Xiong , Ge Yi Xiong
Published: February 2014

According to the vulnerable erosion ability of the ordinary hydraulic concrete, we adopt the method which adding both with superfine slag and super plasticizer to form the high performance concrete.The experiment about concrete erosion was carried out between the high performance concrete and the ordinary hydraulic concrete, the corrosion mechanism was studied respectively from the macro perspective and the micro perspective.From the experiment results we can conclude that the high performance concrete can resistance the sulfate attack which with the SO42- concentration almost reached 20250 mg/L,it has better erosion resistance than the ordinary hydraulic concrete.
Life Cycle Assessment of External Thermal Insulation Composite System Based on Rock Wool Board
Authors: Li Zhu , Gong Xian Zheng , Wang Zhi Hong , Liu Yu
Published: February 2014

Although external wall thermal insulation layer protects the major structure effectively and is capable of the prolonging of the service life of the structure, building thermal insulation material production brings environmental impact in some degree. In this research, quantitative analysis and evaluation of resources consumption and pollutant emission caused by materials on external wall were carried out based on Life Cycle Assessment (LCA). The results show that, the environmental load brought by rock wool board production has a decisive influence on the total environmental load of the external thermal insulation system production.
Study on Treatment Processes and Basic Performance of Steel Slag-Rice Husk Ash Complex Cementitious Material
Authors: Chen Lin , Cai Jun , Li Bao Quan , Zhang Xin Yan
Published: February 2014

In this paper, a novel composite cementitious material was prepared by using steel slag and rice husk ash. The appreciate treatment processes of composite cementitious material prepared were investigated. At same time its basic performance of cement mortar, such as water demand ratio, setting time, soundness and strength were also investigated and discussed. Experimental results show that the cementitious materials prepared has good basic properties with appreciate treatment processes. It concluded that the properly treated steel slag and rice husk ash can be used to prepare cementitious material.
Utilization of Waste Rubber Powder in Semi-Flexible Pavement
Authors: Huang Chong , Hong Jin Xiang , Lin Jun Tao , Deng Cheng , Li Lin
Published: February 2014

The central concept of semi-flexible pavement (SFP) is to combine the best qualities of concrete and asphalt pavement by means of filling the voids of the large gap asphalt mixture (LGAM) with good fluidity grout. The major purpose of this study is to determine the feasibility of utilizing waste rubber powder in the grout so as to reduce the stiffness of the semi-flexible pavement. In this paper, seven kinds of grout were prepared by adding different volume dosage of the waste rubber powder and seven kinds of SFP were also prepared. By means of rutting, dynamic elastic modulus and low-temperature cracking performance tests, the performances of SFP were compared. The experimental results illustrated that the waste rubber powder was suitable to the semi-flexible pavement material. With the dosage of rubber powder increased, the anti-rutting, dynamic modulus of SFP decreased, but the low-temperature cracking of SFP was improved. Preferably, the volume dosage of the waste rubber powder should be not more than 20%.
Influence of Nano-SiO2 and Nano-TiO2 on Early Hydration of Calcium Sulfoaluminate Cement
Authors: Ma Bao Guo , Li Hai Nan , Zhu Yan Chao , Han Lei , Li Xiang Guo
Published: February 2014

Calcium sulfoaluminate (CSA) cements were currently receiving a lot of attention because their manufacture produced less CO2 than ordinary Portland cement (OPC). However, it was essential to understand all parameters which might affect the hydration process. This work dealt with the effect of two nanostructured materials, such as nanoSiO2 (NS) and nanoTiO2 (NT), on the properties of CSA pastes during early hydration. Isothermal calorimetry, X-ray diffraction (XRD) and Scanning electron microscopy (SEM) were used to analyze the pastes. Results indicated that the influence of NS and NT on the early hydration of CSA showed different: when NS and NT were added by 5% (mass fraction), the early hydration of CSA cement can be significantly promoted by NS, and slightly accelerated by NT. X-ray diffraction and SEM analysis results showed that both of NS and NT can improve the microstructure of the cement pastes, which made the cement stone more uniform and dense. For the difference, during cement hydration, except for nucleation function, NS had a high pozzolanic activity. Whereas,the effect of NT on microstructure of hardened CSA-cement was mainly due to its seeding effect.
Influence of Sucrose on Hydration Process of Portland Cement
Authors: Li Zheng Hao , Shen Wei Guo , Lan Qing , Lu Zi Li , Cao Liang Hong , Xu Zhi Yuan
Published: February 2014

The sucrose (0.045%) is added in the cement paste, the consistency of Ca2+ and OH- reduce little, the AFt has high solubility product, thus the AFt exists as gel like product which covers the surface of the clinker particles, the sucrose acts as a retarder. When the dosage of the sucrose is 0.24%, the sucrose poisons the hydration of C2S and C3S markedly, so the consistency of Ca2+ and OH- reduce sharply, the AFt has low solubility product, the needle like AFt form a hydration product network and accelerates the setting process, C2S and C3S cannot yield enough C-S-H, the strength development is baffled. It was supposed that there are two dosage threshold values of sucrose on the hydration process, 0.01% is a retardation threshold value accelerating the formation of Aft, while 0.2% is an acceleration threshold value poisoning the hydration of C3S and C2S.
Influence of EVA Copolymer Latex on Cement Hydration and Microstructures of Modifed Mortars
Authors: Zhou Ji , Zhang Can Lin , Jiang Cheng Cheng , Yu Jian Ying
Published: February 2014

This article deals with the effect of ethylene-vinyl acetate (EVA) on cement hydration and microstructures of modified mortars. Ultrasonic pulse velocity (UPV) and chemically bound water are investigated to characterize cement hydration of modified mortars. The addition of EVA decreases the cement hydration before 7 day, and increases cement hydration after 7 day. Cement hydration of EVA-modified mortar is close to pure cement mortar at 28 day. Scanning electron microscope (SEM) analyses show that cement particles are encased by the EVA at early age, which prevents the cement hydration. Hydration products generate in large quantities, and polymer film crosslinks with calcium silicate hydration (C-S-H) after 28 day.
Study on Utilization of Silica-Calcium Tailings in Concrete
Authors: Tian Xiao Wu , Shen Wei Guo , Shan Lai , Cao Liang Hong , Lan Qing , Lu Zi Li
Published: February 2014

The large production of tailings has caused soil, water and air pollution and serious potential safety hazard. The composition, particle morphology, particle size distribution of the silica-calcium tailings are investigated to assess the feasibility of using it in concrete in this paper. The silica-calcium tailings are mainly composed of quartz, calcite and dolomite. The results show that the tailings powder can stimulate the hydration of cement and fill the gradation gap between fine aggregate and cementitious materials in concrete as micronized sand to meet the requirements of concrete. The incorporation of silica-calcium tailings in concrete reduces the ultimate total shrinkage, autogenous shrinkage and drying shrinkage at early age.
Utilization of Steel Slags in the Cement Industry
Authors: Li Jiang Feng , Luo Xiu Cheng , Sun Meng Ke , Shen Wei Guo , Cao Bing , Li Xin Ling
Published: February 2014

The production of steel slag, a byproduct of the steel refining keeps increasing rapidly and it reached 90.42 million tons in 2011 in China, but its comprehensive utilization ratio is only 22% and far less than the ratio of 65% in Europe. Main chemical compositions of steel slag are CaO, SiO2, Al2O3, FeO, Fe2O3, MgO, MnO, P2O5 and so on, C3S, C2S, C3MS2, RO phase are its common minerals. Due to its high reactivity and Ferro content, steel slag has high potential utilization as supplementary hydraulic cementitious materials or cement clinker meal in cement industry. A method of multiple phased sintering was presented, it can break through the bottlenecks for the steel slag using in the cement industry, e.g. volume stability and grindability ,the carbon emission of cement industry is slashed, it is an effective new approach to massively utilize steel slag in cement industry.
SiC Etching and Sacrificial Oxidation Effects on the Performance of 4H-SiC BJTs
Authors: Lanni Luigia , Malm B. Gunnar , Östling Mikael , Zetterling Carl Mikael
Published: February 2014

Performance of 4H-SiC BJTs fabricated on a single 100mm wafer with different SiC etching and sacrificial oxidation procedures is compared in terms of peak current gain in relation to base intrinsic sheet resistance. The best performance was achieved when device mesas were defined by inductively coupled plasma etching and a dry sacrificial oxide was grown at 1100 °C.
Progress in Large-Area 4H-SiC Epitaxial Layer Growth in a Warm-Wall Planetary Reactor
Authors: Thomas Bernd , Hansen Darren M. , Zhang Jie , Loboda Mark J. , Uchiyama Junichi , Toth Timothy J. , Chung Gil Yong , Manning Ian , Quast Jeff P. , Mueller Stephan G.
Published: February 2014

Results are presented for epitaxial SiC layers grown on 100 mm and 150 mm wafers suitable for power devices by CVD using a VP2800WW multi-wafer reactor with 10×100mm and 6×150mm configurations. We have demonstrated continuous improvement in uniformity for thickness and doping, as well as in defect reduction in standard epitaxy on 100 mm wafers. Thickness and doping sigma/mean values of <1.5% and <8%, respectively, could be routinely achieved. Doping and thickness measurements of 30 μm layer growth show results similar to standard epilayer growth. The averaged projected site yields of 80% for 5x5 mm2 and of 96% for 2x2 mm2 correspond to a low epitaxial defect density of <1 cm="" sup="">-2 in 30μm thick epilayers. Epilayer structures for bipolar devices like PiN diodes and BJTs are shown. The interface regions between nitrogen doped and aluminum doped layers show an abrupt transition of dopant concentration. Wafer quality of 100 mm and 150 mm material is presented as an important base factor for excellent epitaxial layer quality. It is shown that 150 mm substrates exhibit TSD and BPD densities very similar to the 100 mm materials. Site counts for TSDs and BPDs on sample wafers show dislocations densities of 500 cm-2 and 300 cm-2, respectively. After CVD process optimization, a thickness uniformity (sigma/mean) of <1.5% and a doping uniformity of <13% was achieved on epitaxial layers on 150mm.
Effect of Current-Spreading Layer Formed by Ion Implantation on the Electrical Properties of High-Voltage 4H-SiC p-Channel IGBTs
Authors: Deguchi Tadayoshi , Katakami Shuji , Fujisawa Hiroyuki , Takenaka Kensuke , Ishimori Hitoshi , Takasu Shinji , Takei Manabu , Arai Manabu , Yonezawa Yoshiyuki , Fukuda Kenji , Okumura Hajime
Published: February 2014

High-voltage SiC p-channel insulated-gate bipolar transistors (p-IGBT) utilizing current-spreading layer (CSL) formed by ion implantation are fabricated and their properties characterized. A high blocking voltage of 15 kV is achieved at room temperature by optimizing the JFET length. An ampere-class p-IGBT exhibited a low forward voltage drop of 8.5 V at 100 A/cm2 and a low differential specific on-resistance of 33 mΩ cm2 at 250 °C, while these values were high at room temperature. For further reduction of the forward voltage drop in the on-state and temperature stability, the temperature dependence of the JFET effect and carrier lifetime in p-IGBTs are investigated. Optimization of the JFET length using an epitaxial CSL, instead of applying ion implantation and lifetime enhancement, could lead to a further reduction of the forward voltage drop.
Discriminating High k Dielectric Gas Sensors
Authors: Roy Sandip Kumar , Vassilevski Konstantin V. , O'Malley Christopher J. , Wright Nick G. , Horsfall Alton B.
Published: February 2014

High temperature gas sensors for the detection of harmful gases under extreme conditions have been demonstrated. Here, we show the detection and selective response of two SiC based MIS sensor structures with HfO2 and TiO2 high κ dielectric layers to two different hydrogen containing gases. The structures utilise a Pt catalytic gate contact and a high-κ dielectric that was grown on a thin SiO2 layer, which was thermally grown on the Si face of epitaxial 4H SiC. The chemical characteristics of MIS capacitors have been studied in N2, O2, H2 and CH4 ambients at 573K. The data show a positive flatband voltage shift for oxygen and methane with respect to the nitrogen baseline, whilst hydrogen shows a negative shift. The response for the TiO2 based sensor is significantly larger than that of the HfO2 based device for hydrogen, enabling discrimination of gases within a mixture.
Two Packaging Solutions for High Temperature SiC Diode Sensors
Authors: Brezeanu Gheorghe , Draghici Florin , Badila Marian , Craciunoiu Florea , Pristavu Gheorghe , Pascu Razvan , Bernea Florin
Published: February 2014

A partially electrically isolated package with a gold wire and fully isolated solution with a metallic piston, respectively, are designed and tested for high temperature sensors (400°C) based on SiC Schottky barrier diodes (SBD). Electrical behavior and sensor performance are very close for both packaging solutions. The stress due to contact pressure and higher cost are some disadvantages for pressure contact technology.
Silicon Carbide Field Effect Transistors for Detection of Ultra-Low Concentrations of Hazardous Volatile Organic Compounds
Authors: Puglisi Donatella , Eriksson Jens , Bur Christian , Schütze Andreas , Lloyd Spetz Anita , Andersson Mike
Published: February 2014

Gas sensitive silicon carbide field effect transistors with nanostructured Ir gate layers have been used for the first time for sensitive detection of volatile organic compounds (VOCs) at part per billion level for indoor air quality applications. Formaldehyde, naphthalene, and benzene have been used as typical VOCs in dry air and under 10% and 20% relative humidity. A single VOC was used at a time to study long-term stability, repeatability, temperature dependence, effect of relative humidity, sensitivity, response and recovery times of the sensors.
C-Face Epitaxial Growth of 4H-SiC on Quasi-150-mm Diameter Wafers with High Throughput
Authors: Nishio Johji , Kudou Chiaki , Tamura Kentaro , Masumoto Keiko , Kojima Kazutoshi , Ohno Toshiyuki
Published: February 2014

C-face epitaxial growth of 4H-SiC was investigated considering the use as drift layers of high blocking voltage SiC power MOSFETs, such as 3.3 kV, using a multiple-wafer epitaxy system. As high as 50.9 μm/h was achieved as the growth rate while maintaining specular surface within quasi-150 mm-diameter wafers. Also, it has been found that the background carrier concentration could be lowered enough to control the desired n-type doping concentration of nitrogen. In addition, high-throughput has been confirmed by comparing the current data with the recent results reported.
Pressure Dependence of Thermal Contact Resistance between Copper Heat Sink and Copper DBC Surfaces in SiC Power Device Packages
Authors: Toth Pal Zsolt , Hammam Tag , Nee Hans Peter
Published: February 2014

Thermal contact resistances have been measured in an experiment emulating heat transfer from a SiC die to a cooled heat sink through a heat spreader and a DBC structure. The major surface-dependent parameters are the surface roughness, surface hardness, and planarity. The measured thermal contact resistances are in agreement with theoretical values. When investigating DBC copper surfaces a second interface between the bonded Cu to AlN has to be taken into account.
Silicon Carbide Transistors for IC Design Applications up to 600 °C
Authors: Maralani Ayden , Lien Wei Cheng , Zhang Nuo , Pisano A.P.
Published: February 2014

Low power Silicon Carbide (SiC) devices and Integrated Circuits (ICs) in conjunction with SiC or Aluminum Nitride (AlN) sensing elements will enable sensing functions in high temperature environments up to 600 °C where no silicon based devices or circuits have been able to survive in that temperature range. In power electronics applications, existence of low power SiC devices and IC technologies will significantly aid the development of high power density power modules in which total weights and cooling systems sizes are reduced. This paper will be evaluating the performances of the fabricated low power SiC device candidates (JFET and BJT) for SiC-based analog ICs design for high temperature and power electronics applications.
Latest SiC Epitaxial Layer Growth Results in a High-Throughput 6×150 mm Warm-Wall Planetary Reactor
Authors: Burk Albert A. , Tsvetkov D. , O'Loughlin Michael  J. , Ustin S. , Garrett L. , Powell A.R. , Seaman J. , Partin N.
Published: February 2014

Latest results are presented for SiC-epitaxial growths employing a novel 6x150-mm/10x100-mm Warm-Wall Planetary Vapor-Phase Epitaxial (VPE) Reactor. The increased throughput offered by this reactor and 150-mm diameter wafers, is intended to reduce the cost per unit area for SiC epitaxial layers, increasing the market penetration of already successful commercial SiC Schottky and MOSFET devices [1]. Increased growth rates of 30-40 micron/hr and short <2 hr fixed-cycle times (including rapid heat-up and cool-down ramps), while maintaining desirable epitaxial layer quality were achieved. Increased quantities of 150-mm epitaxial wafers now allow statistical analysis of their epitaxial layer properties. Specular epitaxial layer morphology was obtained, with morphological defect densities <0.4 cm-2, consistent with projected 5x5 mm die yields averaging 93% for Si-face epitaxial layers between 10 and 30 microns thick. Intrawafer thickness and doping uniformity are good, averaging 1.7% and 5.1% respectively. Wafer-to-wafer doping variation has also been significantly reduced from ~12 [5] to <3% s/mean. Initial results for C-face growths show excellent morphology (97%) but poor doping uniformity (~16%). Wafer shape is relatively unchanged by epitaxial growth consistent with good epitaxial temperature uniformity.
High Temperature Electrical Characterization of 4H-SiC MESFET Basic Logic Gates
Authors: Alexandru Mihaela , Banu Viorel , Florentin Matthieu , Jordá Xavier , Vellvehi Miguel , Tournier Dominique
Published: February 2014

Due to our demonstrated stable Tungsten-Schottky barrier at elevated temperatures, and also thanks to our technological process maturity regarding SiC-Schottky contact fabrication, we have implemented the digital logic gates library adopting a normally-on MESFET topology. In this paper we present new experimental results showing the thermal behavior up to 300oC of 4H-SiC logic gates library, monolithically integrating normally-on MESFETs and epitaxial resistors. The implemented SiC devices are based on important CMOS features and are specially designed for large ICs device integration density.
Stability and Reactivity of [11-20] Step in Initial Stage of Epitaxial Graphene Growth on SiC(0001)
Authors: Kageshima Hiroyuki , Hibino Hiroki , Yamaguchi Hiroshi , Nagase Masao
Published: February 2014

The energetics for the Si desorption and the C adsorption at a [11-20] step on SiC(0001) surface are studied using the first-principles calculation. It is found that the [11-20] step is stable and nonreactive. The stability of the step is thought to govern the surface morphology during the graphene formation. It is shown that the Si pressure and the temperature are the control parameters for the surface morphology and the graphene quality.
Optimizing the Vacuum Growth of Epitaxial Graphene on 6H-SiC
Authors: Hopf Toby , Vassilevski Konstantin , Escobedo-Cousin Enrique , Wright Nick G. , O'Neill Anthony G. , Horsfall Alton B. , Goss Jonathan P. , Barlow Anders , Wells George , Hunt Michael
Published: February 2014

Multilayer epitaxial graphene has been grown on the Si-face of 6H-SiC on-axis commercial substrates under high vacuum conditions and at growth temperatures up to 1900 °C, utilizing the standard sublimation growth technique and a modified SiC rapid thermal annealing system which allows for excellent control of heating and cooling ramp rates. The peak growth temperature and total growth time during the graphene growth step, along with the temperature of the initial substrate etch step, were all systematically varied in order to ascertain their effect on the formation of epitaxial graphene films on the SiC surface. Modifying the substrate etch temperature was found to have a significant impact on the morphology of the SiC substrate, with a uniform step structure only developing across the surface within a narrow temperature band. Furthermore, changing the values of the peak temperature or the growth time during the growth step were both shown to have a large effect on the resultant materials properties of the graphene films.
Backside Monitoring of Graphene on Silicon Carbide by Raman Spectroscopy
Authors: Fromm Felix , Hundhausen Martin , Kaiser Michl , Seyller Thomas
Published: February 2014

Raman spectroscopy is commonly applied for studying the properties of epitaxial graphene on silicon carbide (SiC). In principle, the Raman intensity of a single graphene layer is rather low compared to the signal of SiC. In this work we follow an approach to improve the Raman intensity of epitaxial graphene on SiC by recording Raman spectra in a top-down geometry, i.e. a geometry in which the graphene layer is probed with the excitation through the SiC substrate [1]. This technique takes advantage of the fact, that most of the Raman scattered light of the graphene is emitted into the SiC substrate. We analyze in detail the top-down measurement geometry regarding the graphene and SiC Raman intensity, as well as the influence of aberration effects caused by the refraction at the air/SiC interface.
Fast 4H-SiC Epitaxial Growth on 150 mm Diameter Area with High-Speed Wafer Rotation
Authors: Fujibayashi Hiroaki , Ito Masahiko , Ito Hideki , Kamata Isaho , Naitou Masami , Hara Kazukuni , Yamauchi Shoichi , Suzuki Kunihiko , Yajima Masayoshi , Mitani Shin Ichi , Suzuki Katsumi , Aoki Hirofumi , Nishikawa Koichi , Kozawa Takahiro , Tsuchida Hidekazu
Published: February 2014

A single wafer type 150 mm vertical 4H-SiC epitaxial reactor with high-speed wafer rotation was developed. The rotation of the wafer at high speed significantly enhances the growth rate, and high growth rates of 40–50 μm/h are possible on 4°off-cut 4H-SiC substrates. In addition, a low defect density and smooth surface without macro step bunching can be achieved. Excellent uniformity of thickness and doping concentration was obtained for a 150 mm wafer at a high growth rate of 50 μm/h.
Commercialization of High 600V GaN-on-Silicon Power Devices
Authors: Parikh Primit , Wu Yi Feng , Shen Li Kun
Published: February 2014

With power conversion losses endemic in all areas of electricity consumption, broadlycategorized into motion control (accounting for around 50% of total electrical energy use), lighting,air conditioning, and information technology, consumers, governments and utilities are finding waysto achieve higher efficiency. Manufacturers of data servers, telecom systems, solar power invertersand drives for motor control are focused on reducing power conversion losses while simultaneouslyshrinking the size of power systems. Although silicon has historically been the base device materialused by the power conversion industry, it is rapidly reaching its physical performance limits. GaNsemiconductors solutions reduce power conversion loss by over 50% in a significantly smaller formfactor and at a lower cost, when device design, fabrication technology and application design areholistically combined to deliver superior end products.
Evaluation of Degradation due to Electron Irradiation of Si1-xCx S/D n-type MOSFETs
Authors: Hori Masato , Asai Yuki , Yoneoka Masashi , Tsunoda Isao , Takakura Kenichiro , Nakashima Toshiyuki , Gonzalez Mireia B. , Simoen Eddy , Claeys Cor
Published: February 2014

To solve the problem of the limitation to improve device performance in standard Si integration technologies and to develop radiation-harsh devices, the irradiation effects of Si1-xCx source/drain (S/D) n-type metal oxide semiconductor field effect transistors (n-MOSFETs) have been investigated. It is shown that the drain current and the maximum electron mobility of Si1-xCx n-MOSFETs decrease by electron irradiation. The reduction of the device performance can be explained by the radiation-induced lattice defects in the devices. However, the electron mobility enhancement effect by adding C remained after an electron irradiation up to 5×1017 e/cm2.
Development of Homoepitaxial Growth Technique on 4H-SiC Vicinal Off Angled Substrate
Authors: Kojima Kazutoshi , Masumoto Keiko , Ito Sachiko , Nagata Akiyo , Okumura Hajime
Published: February 2014

We have investigated key factors for controlling the polytype and surface morphology of 4H-SiC homoepitaxial growth on less than 4o off-axis substrates. In addition, we characterized the crystal quality and surface quality of the epitaxial layer of an entire 3-inch vicinal off angled substrate. The results suggested that the control of surface free energy, control of the vicinal off angle itself, and high temperature growth, is highly important in controlling the surface morphology and polytype stability of the epitaxial layer grown on a vicinal off angled substrate. We also obtained a high-quality epitaxial layer grown on a 3-inch vicinal off angle substrate, which was comparable to those on 4o off-axis substrates.
Effect of Facet Occurrence on Polytype Destabilization during Bulk Crystal Growth of SiC by Seeded Sublimation
Authors: Tsavdaris Nikolaos , Ariyawong Kanaparin , Chaix-Pluchery Odette , Dedulle Jean Marc , Sarigiannidou Eirini , Chaussende Didier
Published: February 2014

We report on polytype destabilization during bulk crystal growth of Silicon Carbide by seeded sublimation method. Polytype transitions are experimentally obtained and a thermodynamic analysis using classical 2D nucleation theory is used towards the understanding of the experimental results. Whether it is a thin lamella or an inclusion, it is found that the polytype transitions systematically occur on the (0001) facet. This suggests that the polytype switch takes place through classical 2D nucleation at the facet. We will show that two criteria must be fulfilled for the occurrence of a foreign polytype: i) minimization of nucleation energy and ii) presence of a facet. This is directly depending on the crystal shape (convex or concave) and its evolution with growth time.
Dependence of the Growth Parameters on the In-Plane Distribution of 150 mm φ Size SiC Epitaxial Wafer
Authors: Kudou Chiaki , Tamura Kentaro , Nishio Jyouji , Masumoto Keiko , Kojima Kazutoishi , Ohno Toshiyuki
Published: February 2014

Silicon carbide (SiC) power devices are expected to be useful in low-loss power conversion equipment in wide-ranging industrial areas. 4H-SiC Schottky barrier diodes (SBDs) and metal oxide semiconductor field-effect transistors (MOSFETs) have been launched on the commercial market, and many results obtaining outstanding performance of 4H-SiC switching devices have been reported [1-. Presently, SiC chip cost is a big problem preventing an increase in market penetration of such commercial devices. Therefore, 150 mm size wafers are urgently required reducing the cost per unit area for SiC epitaxial layers. Recently, some SiC wafer vendors announced that 150 mm SiC substrate would be released [4, and some groups have reported results of epitaxial growth on 150 mm SiC substrate [6-9].
50 μm-Thick 100 mm 4H-SiC Epitaxial Layer Growth by Warm-Wall Planetary Reactor
Authors: Sun Yong Qiang , Feng Gan , Li Zhe Yang , Lv Li Ping , Luo Jin Yun , Wu Jin Bo , Li Yi Yang , Zhang Jian Hui
Published: February 2014

Homo-epitaxial growth of 50 μm-thick 4H-SiC on 4° off-axis 100 mm substrates have been demostrated by using a commercial warm-wall multi-wafer planetary reactor (Aixtron 2800 G4). With optimized process, epitaxial layer with an average thickness of 48.146 μm and doping level of 8.39×1014/cm3 are obtained. The thickness uniformity with an edge exclusion of 5 mm are 1.30% (σ/mean) and 2.17% (max-min/max+min), and the doping level uniformity are 4.66% (σ/mean) and 6.95% (max-min/max+min), respectively. Surface roughness of the as-grown 50 μm-thick epitaxial layer has an RMS value of 0.606 nm with one step bunching on the 20×20 μm2 areas. This initial effort on thick 4H-SiC homoepitaxial growth indicates that this comercial multi-wafer planetary reactor has the potential for mass production of SiC epiwafers for 5000 V and above power devices.
Revisiting the Thermochemical Database of Si-C-H System Related to SiC CVD Modeling
Authors: Sukkaew Pitsiri , Ojamäe Lars , Danielsson Örjan , Kordina Olof , Janzén Erik
Published: February 2014

Chemical vapor deposition of silicon carbide (SiC-CVD) is a complex process involving a Si-C-H system wherein a large number of reaction steps occur. To simulate such a system requires knowledge of thermochemical and transport properties of all the species involved in the process. The accuracy of this information consequently becomes a crucial factor toward the correctness of the outcome prediction. The database on thermochemical properties of well-known species such as small hydrocarbons has been established over decades and it is accurate and easily accessible. On the other hand, the database for less frequently used species such as organosilicons is still under development. Apart from the accuracy issue, a consistency in acquiring procedures, whether theoretical or experimental, is another factor controlling the final error of the simulated outcome. In this work, the thermochemical data for several important growth species for SiC CVD using the SiH4/CxHy/H2 system has been calculated. For the most part an excellent agreement is seen with previously reported data, however for the organosilicons a larger deviation is detected and in particular for the CH3SiH2SiH species which shows a stark deviation from the CHEMKIN database.
Simulation Studies on Giant Step Bunching in 4H-SiC Epitaxial Growth: Cluster Effect
Authors: Ishida Yuuki , Yoshida Sadafumi
Published: February 2014

We have developed the computer simulation including cluster effect and Schwoebel effect and investigated the conditions generating GSB using the simulation. We have demonstrated that the simulation developed can reproduce GSB. We have found for the occurence of GSB that there exists a threshold value of the surplus flux rate of Si-or C-source gases not contributing to growth, which depends on the flux rate of each source gas, namely the boundary between with and without GSB. It is noted that this boundary does not depend on the off-angle of substrates. We have also found the mechanism for explaining the occurrence of wavy surface morphplogy.
Simulations of SiC CVD - Perspectives on the Need for Surface Reaction Model Improvements
Authors: Danielsson Örjan , Kordina Olof , Janzén Erik
Published: February 2014

Simulations of SiC chemical vapor deposition is an excellent tool for understanding, improving and optimizing this complex process. However, models used up to date have often been validated for one particular set of process parameters, often in the silicon limited growth regime, in one particular growth equipment. With chlorinated precursors optimal growth condition is often found to take place at the border between carbon limited and silicon limited regimes. At those conditions the previous models fail to predict deposition rates properly. In this study we argue that molecules like C2H2, C2H4 and CH4, actually might react with the surface with much higher rates than suggested before. Comparisons are made between the previous model and our new model, as well as experiments. It is shown that higher reactivities of the hydrocarbon molecules will improve simulation results as compared to experimental findings, and help to better explain some of the trends for varying C/Si ratios.
Impurity Behavior of High Purity SiC Powder during SiC Crystal Growth
Authors: Shin Dong Geun , Son Hae Rok , Heo Sun , Kim Byung Sook , Han Jung Eun , Min Kyung Suk , Lee Dong Hwa
Published: February 2014

Two kinds of SiC powder having a different impurity contents and particle size were prepared by carbothermal reduction under different conditions from traditional process for controlling the purity of product. SiC single crystal was grown in the RF heating PVT machine at the temperature above 2,100 °C. After crystal growth, boule was cut to wafers in 1mm thickness and fine polished using diamond abrasive slurry. The impurity in the powder and wafer was analyzed using glow discharged mass spectroscopy (GDMS). Major impurities in the SiC wafer were aluminum, boron, iron and titanium which were accorded in the SiC powder and these impurities were decreasing in proportional to those in the powder. However, behavior of each elemental impurity was different from each other during the crystal growth. In case of boron was increased after crystal growth while aluminum decreased. In case of titanium and boron were higher in the wafer than in the powder. It can be explained to other impurity source such as graphite crucible and insulation felt.
Simulation Studies on Giant Step Bunching Accompanying Trapezoid-Shape Defects in 4H-SiC Epitaxial Layer
Authors: Ishida Yuuki , Yoshida Sadafumi
Published: February 2014

Trapezoid-shape (T-S) defects on epilayer surfaces, which include two kinds of the giant step bunching (GSB), are one of killer defects for MOSFETs. We have investigated the generation mechanism of the two GSBs using "step kinetics simulator" we developed. The simulator has reproduced the behavior of the GSBs. Based on results from the simulation, we have discussed the generation mechanism of the two GSBs.
The Influence of the Carbonization Mechanisms on the Crystalline Quality of the Carbonization Layer for Heteroepitaxial Growth of 3C-SiC
Authors: Watanabe Yukimune , Horikawa Tsuyoshi , Kamimura Kiichi
Published: February 2014

The carbonized layer for a buffer layer strongly influences the crystalline quality of the 3C-SiC epitaxial films on the Si substrates. The growth mechanism of the carbonized layer strongly depended on the process conditions. The surface of silicon substrate was carbonized under the pressure of 7.8 × 10-3 Pa or 7.8 × 10-2 Pa in this research. Under the relatively low pressure of 7.8 × 10-3 Pa, the carbonized layer was grown by the epitaxial mechanism. The crystal axis of the carbonized layer grown under this pressure was confirmed to coincide with the crystal axis of the Si substrate from the results of the selected area electron diffraction (SAED) analysis. Under the relatively high pressure condition of 7.8 × 10-2 Pa, the carbonized layer was grown by the diffusion mechanism. The result of the SAED pattern and the XTEM image indicated that this layer consisted of small grainy crystals and their crystal axes inclined against the growth direction. It was confirmed that the crystalline quality of the SiC film deposited on the carbonized layer grown by the epitaxial mechanism is better than that deposited on the layer grown by the diffusion mechanism.
A Study of the Intermediate Layer in 3C-SiC/6H-SiC Heterostructures
Authors: Lebedev Alexander A. , Zamoryanskaya Maria V. , Davydov Sergey Yu. , Kirilenko Demid A. , Lebedev Sergey P. , Sorokin Lev M. , Shustov Denis B. , Shcheglov Mikhail P.
Published: February 2014

Transmission electron microscopy and the cathodoluminescence method have been used to study the transition region in 3C-SiC/6H-SiC heterostructures. It is shown that this region is, as a rule, constituted by alternating 3C-SiC and 6H-SiC layers, with possible inclusion of other silicon carbide polytypes. An assumption is made that this structure of the transition region can be explained in terms of the spinodal decomposition model
Characterization of Ge-Doped Homoepitaxial Layers Grown by Chemical Vapor Deposition
Authors: Sledziewski Tomasz , Beljakowa Svetlana , Alassaad Kassem , Kwasnicki Pawel , Arvinte Roxana , Juillaguet Sandrine , Zielinski Marcin , Soulière Véronique , Ferro Gabriel , Weber Heiko B. , Krieger M.
Published: February 2014

We have investigated the electrical properties of n-type 4H-SiC in-situ germanium-doped homoepitaxial layers grown by chemical vapor deposition. Germanium is an isoelectronic impurity and, therefore, not expected to contribute to the conductivity. However, Hall effect measurements taken on samples with and without germanium revealed an enhanced mobility by a factor of ≈2 at T ≈ 55 K in the germanium-doped sample despite equal free electron concentration and equal compensation. Deep level transient spectroscopy (DLTS) measurements taken on germanium-doped samples reveal negative peaks indicating the presence of charged extended defects.
Persistent Conductivity in n-Type 3C-SiC Observed at Low Temperatures
Authors: Beljakowa Svetlana , Hauck Martin , Bockstedte Michel , Fromm Felix , Hundhausen Martin , Nagasawa Hiroyuki , Weber Heiko B. , Pensl Gerhard , Krieger M.
Published: February 2014

Persistent conductivity in n-type 3C-SiC is investigated in a wide temperature range down to 3 K by Hall effect, admittance spectroscopy, low temperature photoluminescence (LTPL) and Raman spectroscopy. We propose a model, which clearly explains the persistent behavior of the electron density n below 50 K. It is experimentally verified that the persistent conductivity results from doped SF bunches, which can be considered as nanopolytype inclusions in 3C-SiC.
Minority Carrier Transient Spectroscopy of As-Grown, Electron Irradiated and Thermally Oxidized p-Type 4H-SiC
Authors: Alfieri Giovanni , Kimoto Tsunenobu
Published: February 2014

A total of nine electrically active levels have been detected in as-grown and electron irradiated p-type 4H-SiC epilayers. These traps are found in the 0.32-2.26 eV energy range, above the valence band edge (EV). Of these, six are majority carrier traps whereas three are minority carrier traps. We found that thermal oxidation affects the concentrations of two midgap levels, the majority carrier trap, labeled HK4 and the minority carrier trap identified as EH6/7. The analysis of the irradiation energy and dose dependence of the concentration of these two traps, rules out the possibility that they may share the same origin.
Oxidation Induced ON1, ON2a/b Defects in 4H-SiC Characterized by DLTS
Authors: Booker Ian D. , Abdalla Hassan , Lilja Louise , Hassan Jawad , Bergman Peder , Sveinbjörnsson E.Ö. , Janzén Erik
Published: February 2014

The deep levels ON1 and ON2a/b introduced by oxidation into 4H-SiC are characterized via standard DLTS and via filling pulse dependent DLTS measurements. Separation of the closely spaced ON2a/b defect is achieved by using a higher resolution correlation function (Gaver-Stehfest 4) and apparent energy level, apparent electron capture cross section and filling pulse measurement derived capture cross sections are given.
Diffusion of Alkali Metals in SiC
Authors: Linnarsson Margareta K. , Hallén Anders
Published: February 2014

Diffusion of lithium, sodium and potassium in SiC has been studied by secondary ion mass spectrometry. The alkali metal diffusion sources have been introduced by ion implantation. Subsequent anneals have been carried out in vacuum or in Ar atmosphere in the temperature range 700 °C - 1500 °C for 5 min to 16 h. The bombardment-induced defects in the vicinity of the ion implanted profile are readily decorated by the implanted . In the bulk, the diffusing alkali metals are most likely trapped and detrapped at boron and/or other defects during diffusion. The diffusivity of the studied alkali metals decreases as the mass increases, Li+<Na+<K+, but the sodium mobility in SiC is substantial already at 1100 °C.
On Photoelectrical Properties of 6H-SiC Bulk Crystals PVT-Grown on 6H- and 4H-SiC Substrates
Authors: Liaugaudas Gediminas , Jarašiūnas Kęstutis , Tsavdaris Nikolaos , Sarigiannidou Eirini , Chaussende Didier
Published: February 2014

Free carrier lifetimes and diffusion coefficients were determined in 6H-SiC bulk crystals grown by PVT on 6H-and 4H-SiC seeds varying the temperature from 300 K to 650 K and at excess carrier densities ΔN0 from 1017 cm-3 to 1019 cm-3. Carrier generation was achieved by using a single or two-photon absorption of picosecond pulses at 351 and 532 nm, respectively. Fast and slow recombination transients revealed the decay time of free carriers and the presence of deep acceptor traps. The thermal trap activation energy Ea = 0.33 eV was determined in the 6H/4H sample and ascribed to the boron, while the presence of deeper traps is suggested in the 6H/6H sample. At room temperature and reaching conditions of trap saturation regime (ΔN0 1019 cm3), both crystals revealed the bipolar diffusion coefficient Da 4 cm2/s. For comparison, we also determined the photoelectrical parameters in commercial 6H-SiC crystals grown by the Lely and PVT techniques.
Driving Force of Stacking Fault Expansion in 4H-SiC PN Diode by In Situ Electroluminescence Imaging
Authors: Konishi Kazuya , Yamamoto Shigehisa , Nakata Shuhei , Toyoda Yoshihiko , Yamakawa Satoshi
Published: February 2014

We evaluate the velocity of stacking faults (SFs) expansion under various current and temperature levels on the pn diodes by electroluminescence (EL) observation in situ. The driving force of the SFs expansion is analyzed on the basis of the experimental results. The velocity of the SFs expansion increases in proportional to the current density at the every junction temperature levels. The activation energy for the velocity of the SFs expansion is estimated.
Dislocation Revelation for 4H-SiC by Using Vaporized NaOH: A Possible Way to Distinguish Edge, Screw and Mixed Threading Dislocations by Etch Pit Method
Authors: Yao Yong Zhao , Ishikawa Yukari , Sugawara Yoshihiro , Sato Koji , Danno Katsunori , Suzuki Hiroshi , Sakamoto Hidemitsu , Bessho Takeshi , Yamaguchi Satoshi , Nishikawa Koichi
Published: February 2014

In this paper, we report a newly developed dislocation-revealing etch pit method for 4H-SiC single crystal, which can distinguish edge (TED, Burgers vector b=a), elementary screw (TSD, b=1c) and mixed (TMD, b=c+a) threading dislocations. In this method, vaporized NaOH gas was used to etch the Si-face of a SiC wafer at substrate temperature around 950 °C. By a side-by-side comparison between the optical images of the etch pits and the X-ray topographic (XRT) images, it has been found that threading dislocations (TDs) in SiC could be revealed as hexagonal etch pits with distinct geometrical features (shape, size and facet orientation) depending on their Burgers vectors. Based on these results, we consider this etch pit method as an easily-operated and inexpensive technique to categorize TDs, and it may help to promote our understanding on the different roles that these types of TDs have played in the performance degradation of SiC power devices.
TEM Observation of Defect Structure of Low-Energy Ion Implanted SiC
Authors: Kameda Toshimasa , Tomita Atsuo , Matsui Takaaki , Isshiki Toshiyuki
Published: February 2014

The aim of this review is to present the observation of low-energy ion implanted SiC and annealing them by using TEM. By detail analyses of the TEM images and results of SRIM, ion implanted SiC was classification four structure depending on the ion concentration in a few ten nm shallow region. This results suggest that crystal structure in a few nm shallow region can be controled by concentration of the ion implant. And SiC was re-crystallized single poly-type after annealed at 1500°C. But, defects in end of amorphous region affect to recover the damaged structure .
Characterization of Damage Induced by Electric Discharge Machining and Wiresawing with Loose Abrasive at Subsurface of SiC Crystal
Authors: Ishikawa Yukari , Yao Yong Zhao , Sato Koji , Sugawara Yoshihiro , Okamoto Yoshihiro , Hayashi Noritaka
Published: February 2014

The damage induced at the cut surface of SiC crystal by slicing were investigated by Raman scattering method and transmission electron microscopy. Electric discharge machining (EDM) predominately forms cracks, silicon, carbon and 3C-SiC by 6H-SiC pyrolysis and wiresawing with loose abrasive (WSLA) induces triangular crystal disordered area, stacking faults and dislocation loop bundles by stressing at the cut surfaces of SiC crystal.