bluuebunny/crossref_metadata_2025 huggingface dataset:
Inappropriate Toothbrushes Selection Alter Composite Dental Material Restoration Surface Roughness: A Preliminary Study
Authors: Oktaviana Elylla , Ardhani Retno , Yulianto Heribertus Dedy Kusuma
Published: May 2016

Introduction. Regular dental plaque control by means of chemically and mechanically methods are among efforts to improve oral health and hygiene. Mechanical cleansing using toothbrush is still the gold standard for continually removing of dental plaque. But on the other hand, inappropriate selection of toothbrushes type selection promotes alteration on dental material restoration surface. Toothbrushes with different degree of stiffness are readily available on market and are classified as hard, medium, and soft. Mechanical friction due to regular movement of the toothbrush with various degree of stiffness was predicted as factor that related with surface roughness alteration on dental material restoration. Nowadays, resin composite material is still declared as the material of choice to repair dental hard tissue damage due to caries activity. However, it has been found that the irregularity of surface promotes bacterial adhesion and biofilm deposition, whereas the smooth surface does not favor bacterial deposition. The progress of bacterial deposition promotes secondary caries on the margin between material restoration and teeth. The aim of this in vitro study was to evaluate the influence of brushing treatment by means of three different toothbrushes on the surface of resin-based compositesExperimental. Specimens were prepared from experimental RBCs with 5 mm diameter and 2 mm thick. Specimens were divided equally into 3 different groups (group A, B, and C). Each group has 5 numbers of specimens. Group A was treated with hard toothbrush, and group B as well as C were treated with medium and soft toothbrush respectively. The toothbrush was mounted in the customized mechanically brushing machine to control the force and number of cycle during specified time. Brushing cycle and time for all groups was conducted for 1000 times of brushing in 60 minutes. Surface roughness resulted from mechanically brushing is evaluated by means of profilometer device.Results and Discussion. The results of the preliminary study shows that there is a differences of surface roughness between groups. The value of roughness varied among all group, and the highest number of roughness were found in group A (> 0.2 micrometres).Conclusions. This result implies brushing with hard toothbrush preferentially has greater risk of surface damage and become pronounce factor of secondary caries.
Effect of Infiltration with Ferric Oxide Containing Glass on the Color and Mechanical Properties of Zirconia
Authors: Park Sang Won , Oh Gye Jeong , Jang Kyung Jun , Ji Min Kyung , Kim Ji Hyun , Kim Jin Won , Ban Jae Sam , Lim Hyun Pil , Yun Kwi Dug , Kim Min Ji , Park Chan
Published: May 2016

This study was to examine the effects of ferric oxide contents, which is one of the components of a newly developed glass, on the color and mechanical strengths of zirconia surfaces after glass infiltration. The composition of bioactive glass contained: SiO2–Al2O3–Na2O–MgO–BaO–CaO–Nb2O5–TiO2–Fe2O3. 84 presintered zirconia discs (diameter 15 mm, height 1.2 mm) were prepared. The experimental groups were divided into 6 groups by Fe2O3 contents of 0, 1, 1.5, 2.0, 2.5 and 2.9 wt%. Non-glass infiltrated zirconia was used as a control. Bioactive glass was coated on the presintered zirconia disc by a spin coating and infiltrated into zirconia by complete sintering at 1450°C for 2 hr. The color of the specimens was measured using a digital spectrophotometer and biaxial flexural strength and fracture toughness was compared. The colors of glass infiltrated zirconia were from yellow to yellowish orange according to ferric oxides contents and those were within the range of natural teeth colors. The mechanical properties of glass infiltrated zirconia were not inferior to those of zirconia. Glass infiltration with ferric oxide into zirconia can improve the color and mechanical properties of zirconia and be applicable for dental purpose.
Fabrication of Bioactive Stainless Steel by the Function of Apatite Nuclei
Authors: Yabutsuka Takeshi , Karashima Ryoki , Takai Shigeomi , Yao Takeshi
Published: May 2016

Micropores were formed on the surfaces of stainless steel (SUS) by sandblasting methods and Apatite Nuclei (AN) were formed in the pores. By this treatments, a bioactive SUS was fabricated. Apatite-forming ability of the SUS was evaluated by immersing in an acellular simulated body fluid. Formation of bonelike apatite was induced on the surface of the SUS within 1 day. High bonding strength of the bonelike apatite layer was achieved by a mechanical interlocking effect between the bonelike apatite formed in the pores and the SUS specimen.
Cytocompatiblity of Ceramic Nanoparticles to Various Types of Cells
Authors: Abe Shigeaki , Iwadera Nobuki , Mutoh Mami , Katsurayama Tomohiko , Morimoto Shino , Nakanishi Ko , Akasaka Tsukasa , Inoue Satoshi , Yawaka Yasutaka , Iida Junichiro , Yoshida Yasuhiro
Published: May 2016

In this study, we investigated the cytocompatibility of ceramic nanoparticles on different types of cells. All ceramics nanoparticles investigated in this study except Copper oxide (CuO) exhibited good cytocompatibility and cell viability (90% or more) even at 20 ppm concentration. In contrast, CuO nanoparticles caused cell inflammation, and their effect depended on their particle size. Confocal fluorescence microscopy measurements indicated that some particles had penetrated into the cells. These results indicate that except CuO nanoparticles, all other ceramic nanoparticles reported herein exhibited excellent cytocompatibility even for lung epithelial cells.
Hollow Shells Development and Characterization for Cells Carrying Purpose
Authors: Miramond Thomas , Borget Pascal , Moreau Françoise , Fellah Borhane , Daculsi Guy
Published: May 2016

Bioceramics draw attention in bone tissue engineering field since their biomimetic properties regarding bone attribute. In this context, a concept of smart bioceramics granules made of Hydroxyapatite have been set up, enhancing surface area available to body fluids containing proteins and cell adhesion for bone forming respectively thanks to microporosities and macropore concavities. New “hollow shell” granules were developed and assessed by physico-chemical characterizations, in-vitro experiments and in-vivo implantation in comparison with classical round granules. This new original galenic formulation showed promising potential in cell carrying and osteoconduction matter.
Bioceramic Drug Delivery System for Cancer Treatment and Regenerative Medicine
Authors: El-Ghannam Ahmed
Published: May 2016

Silica-calcium-phosphate composite (SCPC) is a drug delivery platform that has successfully demonstrated the ability to bind and release several therapeutics including antibiotics, peptides, anticancer drugs, and growth factors. It has successfully demonstrated a unique capacity for bone regeneration. The present studies address the effect of the phosphate and silicate functional groups on drug binding and controlled release kinetics of Cisplatin (Cis). Moreover, the roles of ceramic composition and resorbability on rhBMP2 release kinetics and bone regeneration in a critical size calvarial defect in rabbit is presented.
Conversion of Marine Structures to Calcium Phosphate Materials: Mechanisms of Conversion Using Two Different Phosphate Solutions
Authors: Macha Innocent J. , Grossin David , Ben-Nissan Besim
Published: May 2016

Marine structure, coralline materials were converted to calcium phosphate using two different phosphate solutions. The aim was to study the conversion mechanisms under acidic and basic environment at moderate conditions of temperature. Crystal growth and morphology of converted corals were characterized by XRD and SEM respectively. The results suggested that under acidic conditions (H3PO4), dissolution and precipitation control and direct the crystal formation and morphology in which transition from plate like to rod like hydroxyapatite structure was favoured. Metastable phase such as monetite formed and transformed to HAp during reaction. During the first hour of the dissolution a monetite and hydroxyapatite mixture precipitates and then the full conversion to hydroxyapatite is observed. On the other hand, under basic conditions (NH4)2HPO4, just diffusional surface conversion of the calcium carbonate structure of coralline materials to hydroxyapatite and a very small amount of tri-calcium phosphate is observed. The mechanism can be classified as the solid-state topotactic ion-exchange reaction mechanism.
Production of Apatite from Snail Shells for Biomedical Engineering Applications
Authors: Ekren Nazmi , Gunduz Oguzhan , Celik Sibel , Ayata Bilge , Sahin Yesim Muge , Chou Joshua , Ben-Nissan Besim , Salman S. , Gokce Hasan , Oktar Faik Nuzhet
Published: May 2016

Bioceramics is very important application for dental and orthopedic procedures. Beside all these normal procedures traffic accidents are requiring increasing number of graft, prostheses and orthosis applications. Bioceramics can be produced from local and natural sources with various methods. Those can be produced from various bone structures through calcination (at high temperatures) or with diluted hydrochloric acid (HCl) application & freeze drying. Beside these methods calcite and aragonite structures like from sea shells and egg shells bioceramic production can be realized through mechanochemical processing via a simple hot-plate or ultrasonic equipment. A fresh water snail shell (Zebra Nerite Snail - Neritinanatalensis) was prepared as bioceramic production source. The resulting hydroxyapatite (HA) powders were obtained without any impurities. At two varying temperature of 865 and 885 °C the snail shells was transformed to HA bioceramics. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential thermal analysis (TG/DTA) were evaluated.
Adhesion Properties of an Apatite Film Deposited on Dentine Using Er:YAG Laser Ablation Method
Authors: Yamamoto Ei , Kato Nobuhiro , Yoshikawa Kazushi , Yasuo Kenzo , Yamamoto Kazuyo , Hontsu Shigeki
Published: May 2016

Tooth enamel cannot be naturally reconstructed once it is destroyed immoderately. Therefore, the restoration of enamel is important in dental treatment. Hydroxyapatite (HAp) can potentially be used for a novel dental biomaterial to repair the enamel. We have proposed a tooth restoration technique with intraoral laser ablation method. A thin layer of HAp was deposited on dentin surface in the atmosphere by ablation phenomenon using an Er:YAG (Erbium: Yttrium-Aluminum-Garnet) laser irradiated to the target of α-tricalcium phosphate (α-TCP). Then, the deposited layer was hydrolyzed by dripping pure water on its surface in order to create HAp film. The adhesive strength between the HAp film and dentin was evaluated by quasi-static tensile tests. As a result of the mechanical evaluation, the adhesive strength was greater than approximately 3.8 MPa. It is clear that the HAp film created by the Er:YAG laser ablation method is attached tightly to the dentin.
Basic Properties of PMMA Reinforced Using Ceramics Particles of ZrO2-Al2O3-SiO2 Coated with Two Types of Coupling Agents
Authors: Hasratiningsih Zulia , Cahyanto Arief , Takarini Veni , Karlina Elin , Djustiana Nina , Febrida Renny , Usri Kosterman , Faza Yanwar , Hardiansyah Andri , Purwasasmita Bambang Sunendar
Published: May 2016

In this study, novel composites materials composed of polymethyl methacrylate (PMMA) reinforced ZrO2-Al2O3-SiO2 filler system were developed. Zirconia-alumina-silica filler system were synthesized through sol-gel technique. Chitosan and trimethoxypropilsilane (TMPS) were used to modify the composites system. The resulting composites material were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and hardness test. SEM images displayed the composites particles in nanometer size with minor agglomeration. The XRD results revealed the presence of cubic and tetragonal phase of zirconia and also monoclinic silica phases in the composites system. These crystallographic characteristic could affect the mechanical properties of the composites. The hardness value for un-modified composites was 15.27 ± 0.25 VHN and for TMPS 19.43 ± 1.89 VHN and chitosan modification 18.75 ± 2.05 VHN, respectively. Therefore, these novel composites materials composed of PMMA reinforced filler system of zirconia-alumina-silica would provide the potential to apply in dental technology.
Comparison of Bottom-Up and Top-Down 3C-SiC NWFETs
Authors: Choi Ji Hoon , Bano Edwige , Henry Anne , Attolini Giovanni , Zekentes Konstantinos
Published: May 2016

The until-now demonstrated SiC-Nanowire Field Effect Transistors (NWFETs) have exhibited poor performance due to the high residual doping of the NWs as well as the bad interface with the gate dielectrics. Top-down NWs have been used for the SiC NWFETs fabrication on the basis of low-doped 3C-SiC material and eliminating, thus, the first reason. The transistors with top-down grown NWs exhibited three orders of magnitude higher current and transconductance values with respect to SiC NWFETs with bottom-up grown NWs. Nevertheless, it was not possible to switch-off the transistors showing the importance of interface with the gate dielectrics.
SiC for Biomedical Applications
Authors: Saddow Stephen E. , Frewin Christopher L. , Araujo Cespedes Fabiola , Gazziro Marioa , Bernadin Evans , Thomas Sylvia
Published: May 2016

Silicon carbide is a well-known wide-band gap semiconductor traditionally used in power electronics and solid-state lighting due to its extremely low intrinsic carrier concentration and high thermal conductivity. What is only recently being discovered is that it possesses excellent compatibility within the biological world. Since publication of the first edition of Silicon Carbide Biotechnology: A Biocompatible Semiconductor for Advanced Biomedical Devices and Applications five years ago [1], significant progress has been made on numerous research and development fronts. In this paper three very promising developments are briefly highlighted – progress towards the realization of a continuous glucose monitoring system, implantable neural interfaces made from free-standing 3C-SiC, and a custom-made low-power ‘wireless capable’ four channel neural recording chip for brain-machine interface applications.
Large Area Visible Blind 4H-SiC p+/N UV Photodiode Obtained by Aluminium Implantation
Authors: Sciuto Antonella , Mazzillo Massimo , Di Franco Salvatore , Roccaforte Fabrizio
Published: May 2016

4H-SiC junction photodiodes, obtained by aluminium (Al) ion- implantation on low doped n-type epilayers are widely characterized observing an extremely low dark current density < 1 nA/cm2 at -100 V up to 90°C, a peak responsivity of 0.11 A/W at 280 nm corresponding to a quantum efficiency of 50% and a visible blindness > 103. The absence of optically active defects and pairs recombination centers was monitored by electro-optical and Emission Microscopy measurements.
Application of 25mΩ SiC MOSFETs in a 10kVA Grid-Connected AC/DC Converter
Authors: Piasecki Szymon , Rabkowski Jacek , Kaźmierkowski M.P.
Published: May 2016

This paper presents a grid-connected 10 kVA AC/DC converter built with 25mΩ SiC MOSFETs. The converter design process was based on an optimization procedure, which was applied to find the parameters that provide efficiency of 98.5% and power density of 3 kWA/dm3. The 10 kVA prototype, including LCL filter, was built and tested in various operation modes showing very good performance and high efficiency. The AC/DC converter is also able to act as an active power filter compensating high-order harmonics of the grid current caused by diode rectifier.
Large Area 4H SiC Products for Power Electronic Devices
Authors: Manning Ian , Zhang Jie , Thomas Bernd , Sanchez Edward , Hansen Darren , Adams Daniel , Chung Gil Yong , Moeggenborg Kevin , Parfeniuk Christopher , Quast Jeffrey , Torres Victor , Whiteley Clinton
Published: May 2016

Efforts to develop 150 mm 4H SiC bare wafer and epitaxial substrates for power electronic device applications have resulted in quality improvements, such that key metrics match or outperform 100 mm substrates. Total dislocation densities and threading screw dislocation densities measured for 150 mm wafers were ~4100 cm-2 and ~100 cm-2, respectively, compared with values of ~5900 cm-2 and ~300 cm-2 measured for 100 mm wafers. While median basal plane dislocation counts in 150 mm samples exceed those of the smaller platform, a nearly 45% reduction was realized, resulting in a median density of ~3900 cm-2. Epilayers grown on 150 mm substrates likewise exhibit quality metrics that are comparable to 100 mm samples, with median thickness and doping sigma/mean values of 1.1% and 4.4%, respectively.
The Interaction between Graphene and the SiC Substrate: Ab Initio Calculations for Polar and Nonpolar Surfaces
Authors: Deretzis Ioannis , Giannazzo Filippo , La Magna Antonino
Published: May 2016

Notwithstanding the graphitization of SiC under high thermal treatment can take place for all SiC surfaces, the quality of the resulting graphene as well as its structural and electrical characteristics strongly depend on the SiC face where growth has taken place. In this paper we use the density functional theory to analyze the structural and electronic properties of epitaxial graphene grown on three different SiC planes. Calculations are presented for the (6√3×6√3)R30°-reconstructed SiC(0001) surface (Si face) as well as the nonpolar SiC(11-20) and SiC(1-100) planes. We argue that the formation of a strongly-bound interface buffer layer is an exclusive property of the SiC(0001) surface. Moreover, our results indicate that nonpolar planes give rise to graphene with a nearly ideal low-energy spectrum.
Metal/P-GaN Contacts on AlGaN/GaN Heterostructures for Normally-Off HEMTs
Authors: Greco Giuseppe , Iucolano Ferdinando , Giannazzo Filippo , Di Franco Salvatore , Corso Domenico , Smecca Emanuele , Alberti Alessandra , Patti Alfonso , Roccaforte Fabrizio
Published: May 2016

In this paper, the electrical properties of different metal/p-GaN contacts (Ti/Al, TiN/Ti/Al and Ni/Au) have been investigated to get a deeper understanding of the behavior of p-GaN/AlGaN/GaN heterostructures for normally-off HEMTs. In particular, the study of the temperature dependent current-voltage characteristics allowed to identify the dominant carrier transport mechanism at the metal/p-GaN interface (Thermionic Field Emission). From the fit of the experimental current-voltage data it was possible to determine the Schottky barrier height values for the three systems, 2.08 eV (Ti/Al), 1.57 eV (TiN/Ti/Al) and 1.89 eV (Ni/Au). Hence, choosing the highest barrier height contact (Ti/Al) as gate electrode on a p-GaN/AlGaN/GaN heterostructure, optimized based on simulations, allowed to obtain devices with a normally-off behavior and a positive Vth of +1.3 V.
Tri-Gate Al0.2Ga0.8N/AlN/GaN HEMTs on SiC/Si-Substrates
Authors: Jatal Wael , Baumann Uwe , Jacobs Heiko O. , Schwierz Frank , Pezoldt Joerg
Published: May 2016

A nanochannel array structure was applied to realize enhancement-mode high electron mobility transistors based on AlGaN/AlN/GaN-heterostructures grown on Si substrates using a SiC transition layer. The fabricated nanochannel array HEMT, consisting of 78 channels connected in parallel with a channel width of 100 nm defined by electron-beam lithography and dry etching, shows a threshold voltage of 0.35 V. The high electron mobility transistors with LG= 0.2 μm had a maximum drain current density of 445 mA/mm and a peak extrinsic tranconductance of 235 mS/mm. A unity current gain cut-off frequency of 30 GHz and maximum oscillation frequency of 40 GHz were measured on these devices.
Design and Optimization of AlGaN Solar-Blind Double Heterojunction Ultraviolet Phototransistor
Authors: Bai Yun , Shen Hua Jun , Li Chengzhan , Tang Yi Dan , Liu Xin Yu
Published: May 2016

The n-p-i-n AlGaN solar-blind ultraviolet double heterojunction phototransistor (DHPT) with internal gain is proposed and optimized in this paper. The dependences of spectral responsivity and quantum gain on structure parameters of the AlGaN DHPT are simulated in detail. Then, the polarization effect of AlGaN heterojunction on the performance of AlGaN DHPT is also investigated. Results show that positive polarization charge would enhance the photoresponse of the device, whereas the negative polarization charge would reduce the photoresponse significantly. The reasons for the polarization effect on performance of AlGaN DHPT are discussed.
Optimization of the Silicidation and Growth Processes for 3C-SiC Heteroepitaxy on Diamond Substrate
Authors: Soulière Véronique , Carole Davy , Ferro Gabriel
Published: May 2016

This work reports on the CVD heteroepitaxial growth of 3C-SiC layers on diamond (100) substrates. To obtain good layer quality, the growth procedure involves a “silicidation” step consisting in depositing a silicon layer by CVD on the diamond substrate, in order to elaborate a very thin SiC buffer layer. 3C-SiC growth is then performed on this SiC seeding layer. Silicidation and growth parameters have been studied in order to improve the quality and the morphology uniformity of the heteroepitaxial layer. The study points out the role of liquid silicon during the growth process.
Advances in 3x150 mm Hot-Wall and 6x150 mm Warm-Wall SiC Epitaxy for 10kV-Class Power Devices
Authors: O'Loughlin Michael , Burk Albert , Tsvetkov Denis , Ustin Scott , Palmour John W.
Published: May 2016

Initial results from a custom, 3x150 mm horizontal hot-wall, SiC Vapor-Phase epitaxial growth reactor (VPE), with full planetary motion are reported. Epitaxial layer properties are compared with those grown on previously reported 1x150 mm hot-wall and 6x150 mm warm-wall reactors for epitaxial wafers of up to 100 microns thickness. The median intra-wafer thickness and doping uniformity (σ/mean) for the 3x150 mm reactor are 0.9% and 6.10%, respectively. The intra-run thickness and doping variation are 0.18% and 1.01%. The projected 5x5 mm useable area for layers of nominal 5 to 30 μm thickness for all the reactor configurations (as measured by a Candela CS2 optical surface analyzer) are approximately 92%, corresponding to an effective defect density of about 0.35 cm-2. Useable areas as high as 86.5% and 1-2 nm rms roughness have been observed for layers of over 100 μm thickness. Initial morphological results using a higher resolution, LaserTec SICA6X confocal differential interference contrast (CDIC) microscope, are also presented.
Effect of H2 Carrier Gas on CVD Growth Rate for 4H-SiC Trench Filling
Authors: Ji Shi Yang , Kojima Kazutoshi , Kosugi Ryoji , Saito Shingo , Sakuma Yuuki , Matsukawa Yasuko , Yonezawa Yoshiyuki , Yoshida Sadafumi , Okumura Hajime
Published: May 2016

The effect of H2 carrier gas on the growth rate during the trench filling using CVD epitaxial growth was investigated in a wide pressure range (10∼38 kPa). It is found that, in the entire pressure range, reducing H2 flow rate can increase the filling rate (the growth rate inside trench) and the filling efficiency (the thickness ratio between epilayer on trench bottom and mesa top), which means a high productivity and a low risk of void defects. The filling rate and efficiency of ∼1.5 μm/h and ∼18 respectively was achieved at 38 kPa.
Structure of Straight-Line Defect and its Effect on the Electrical Properties of Schottky Barrier Diodes
Authors: Kamei Koji , Guo Ling , Momose Kenji , Osawa Hitoshi
Published: May 2016

We have investigated the “straight-line defect,” which has not been classified separately and is quite similar to the carrot defect. We found that the straight-line defect differed structurally from the carrot defect. The presence of a particle on the substrate-epi layer interface seemed to be the cause of the defect; a layer of poly-type (3C-SiC) extended from the particle to the epi-layer surface. The straight-line defect likely resulted from shape change from the 3C-SiC triangular defect. This change in shape from triangular to straight-line defects depended on the C/Si ratio. To investigate the electrical characteristics, we fabricated a Schottky barrier diode (SBD) structure on a silicon carbide (SiC) epi wafer. With application of a high voltage, destruction occurred on both the upstream and the downstream side of the step flow of straight-line defects in the reverse voltage test. This reverse direction characteristic differed from that observed with triangular defects.
In Situ Cleaning Process of Silicon Carbide Epitaxial Reactor for Removing Film-Type Deposition Formed on Susceptor
Authors: Mizuno Kosuke , Habuka Hitoshi , Ishida Yuuki , Ohno Toshiyuki
Published: May 2016

The in situ cleaning process of a silicon carbide epitaxial reactor was developed using chlorine trifluoride gas for removing the film-type silicon carbide deposition formed on a susceptor. By adjusting the etching temperature to less than 330 °C, the formed silicon carbide films could be removed without significant damage to the susceptor.
Investigation of Mo Defects in 4H-SiC by Means of Density Functional Theory
Authors: Csóré András , Gällström Andreas , Janzén Erik , Gali Ádám
Published: May 2016

We investigated Molybdenum (Mo) defects in 4H silicon carbide (SiC). This system can be suitable candidate for in vivo biomarker applications since it shows photoluminescence (PL) in the near-infrared (NIR) region. In order to reveal the origin of this Mo-related PL center we carried out ab initio density functional theory (DFT) calculations on two microscopic models.
Photoluminescence of 10H-SiC
Authors: Henry Anne , Yano Hiroshi , Hatayama Tomoaki
Published: May 2016

The photoluminescence of the near band gap emission of 10H-SiC is revealed for the first time and detected just below 3.0 eV. The crystallinity thus polytype of the sample is controlled with transmission electron microscope analyses and Laue diffraction. On the photoluminescence spectra up to eight sharp lines are associated to the non-phonon lines of the nitrogen bound exciton even if ten are expected in 10H-SiC. Phonon replicas of these non-phonon lines are observed at lower energy with energy separations similar than those in other hexagonal SiC polytypes. At moderate temperature free-exciton replicas are also observed which allow the determination of the excitonic band gap at 3020.6 meV, value in agreement with the hexagonality of 10H-SiC of 40%. The binding energies associated to the nitrogen bound-excitons are determined as well as the ionization energies of the nitrogen donors in the 10H-SiC polytype.
Correlation of Lifetime Mapping of 4H-SiC Epilayers with Structural Defects Using Synchrotron X-Ray Topography
Authors: Goue O.Y. , Yang Yu , Guo J.Q. , Raghothamachar Balaji , Dudley Michael , Hosteller J.L. , Myers-Ward Rachael L. , Klein Paul B. , Gaskill D. Kurt
Published: May 2016

Lifetime maps for two 4H-SiC epi-wafers (samples 1 and 2) were recorded using microwave photoconductive decay (μPCD) measurements and correlated with the type and distribution of structural defects mapped by synchrotron X-ray topography (white beam and monochromatic). Sample 1 showed lower lifetime inside one of its higher doped facet regions and along its edges. The low lifetime in the facet region was associated with the presence of a high density of multi-layered Shockley stacking faults (SFs) and low angle grain boundaries (LAGBs). These stacking faults are likely double Shockley stacking faults (DSSFs) and probably nucleated from scratches present on the substrate surface and LAGBs present in that region, propagating during epilayer growth. In contrast, sample 2 showed a reduced carrier lifetime in the middle region associated with a network of interfacial dislocations (IDs) and half loop arrays (HLAs) originating from 3C inclusions that are generated during epilayer growth. Along the edges of both samples, overlapping triangular defects, microcracks and BPD loops lowered lifetime.
Deep Level Characterization of 5 MeV Proton Irradiated SiC PiN Diodes
Authors: Alfieri Giovanni , Mihaila Andrei , Ayedh Hussein M. , Svensson Bengt Gunnar , Hazdra Pavel , Godignon Philippe , Millan José , Kicin S.
Published: May 2016

In this contribution, we report on the electrical characterization of point defects in 4H-SiC p+in diodes. Ten electrically active levels have been detected in the base region of the devices, by employing Deep Level Transient Spectroscopy (DLTS) and Minority Carrier Transient Spectroscopy (MCTS). Of these ten levels, six are majority carrier traps, in the 0.1-1.7 eV energy range below the conduction band edge, and four were minority carrier traps located in the 0.13-0.4 eV energy range above the valence band edge. We found that, during DLTS measurements, both majority and minority carrier traps can be detected and we explain this by considering the behavior of the quasi-Fermi levels. At last, we studied the impact of proton irradiation on the minority charge carrier lifetime.
Fluorescent P-Type 4H-SiC Grown by PVT Method
Authors: Zhuo Shi Yi , Liu Xi , Gao Pao , Huang Wei , Yan Cheng Feng , Shi Er Wei
Published: May 2016

Fluorescent SiC, which contains donor and acceptor impurities with optimum concentrations, can work as a phosphor for visible light emission by donor-acceptor-pair (DAP) recombination. In this work, 3 inch N-B-Al co-doped fluorescent 4H-SiC crystals are prepared by PVT method. The p-type fluorescent 4H-SiC with low aluminum doping concentration can show intensive yellow-green fluorescence at room temperature. N-B DAP peak wavelength shifts from 578nm to 525nm and weak N-Al DAP emission occurred 403/420 nm quenches, when the temperature increases from 4K to 298K. The aluminum doping induces higher defect concentration in the fluorescent crystal and decreases optical transmissivity of the crystal in the visible light range. It triggers more non-radiative recombination and light absorption losses in the crystal.
Modelling of Effective Minority Carrier Lifetime in 4H-SiC n-Type Epilayers
Authors: Kaminzky Daniel , Kallinger Birgit , Berwian Patrick , Rommel Mathias , Friedrich Jochen
Published: May 2016

We present an extended model for the simulation of the effective minority carrier lifetime in 4H-SiC epiwafers after optical excitation. This multilayer model uses measured values (such as doping profile, point defect concentration and capture cross sections, epilayer thickness) as input parameters. The bulk lifetime and the diffusion constant are calculated from the actual time dependent excess carrier profiles, resulting in more realistic transients having different decay regimes than in other models. This enables a better understanding of optical lifetime measurements.
Study of Nanoscale Inhomogeneities in Silicon Carbide Crystals via Small-Angle X-Ray Scattering
Authors: Logunov Mikhail , Neverov Vladimir , Mamin Bari , Skvortsov Denis , Sidorov Roman
Published: May 2016

The structure of 4H-SiC and 6H-SiC monocrystals’ nanoscale defects was studied by the small-angle X-ray scattering (SAXS) method. Analysis of dispersion indicatrices has shown the presence of inhomogeneities in the form of linear fractals in silicon carbide crystals of 6H and 4H polytypes, mass fractals in 6H polytype and inhomogeneities partition’s fractal surface in 4H polytype.
Mapping of Threading Screw Dislocations in 4H n-Type SiC Wafers
Authors: Ellison Alexandre , Sörman Erik , Sundqvist Björn , Magnusson Björn , Yang Yu , Guo Jian Qiu , Goue Ouloide , Raghothamachar Balaji , Dudley Michael
Published: May 2016

X-ray topography shows that selective KOH etching after CVD growth of n-type epilayers on highly N doped 4H SiC substrates can be used to reliably map pure and mixed Threading Screw Dislocations (TSD). The influence of the mapping grid density and the wafer position in the crystal on the average TSD density are investigated. A reliable mapping of TSD contributed to the development of 100mm SiC wafers with average TSD density down to 200 cm-2.
Controlling the Carbon Vacancy Concentration in 4H-SiC Subjected to High Temperature Treatment
Authors: Ayedh Hussein M. , Nipoti Roberta , Hallén Anders , Svensson Bengt Gunnar
Published: May 2016

The carbon vacancy (VC) is the major charge carrier lifetime limiting-defect in 4H-SiC epitaxial layers and it is readily formed during elevated heat treatments. Here we describe two ways for controlling the VC concentration in 4H-SiC epi-layer using different annealing procedures. One set of samples was subjected to high temperature processing at 1950 °C for 3 min, but then different cooling rates were applied. A significant reduction of the VC concentration was demonstrated by the slow cooling rate. In addition, elimination of the VC’s was also established by annealing a sample, containing high VC concentration, at 1500 °C for a sufficiently long time. Both procedures clearly demonstrate the need for maintaining thermodynamic equilibrium during cooling.
Ion Implantation Defects in 4H-SiC DIMOSFET
Authors: Fontana Enzo , Piluso Nicolo , Russo Alfio , Lorenti Simona , Marcellino Cinzia M. , Coffa Salvo , La Via Francesco
Published: May 2016

In this paper the influence of point defects generated by the ion implantation process in 4H-SiC DIMOSFET has been studied in detail. The point defects generated by the source or body implantation process have been detected by micro-photoluminescence and the effect of these defects on the electrical characteristics of the DIMOSFET has been studied. In particular it has been observed that a reduction of the source ion implanted dose produces a large reduction of point defects in the source region and a considerable improvement of the electrical characteristic of the DIMOSFET.
Accuracy of the Energy Distribution of the Interface States at the SiO2/SiC Interface by Conductance Method
Authors: Noguchi Munetaka , Iwamatsu Toshiaki , Amishiro Hiroyuki , Watanabe Hiroshi , Nakata Shuhei , Kuroiwa Takeharu , Yamakawa Satoshi
Published: May 2016

The electrical characteristics of the SiC metal-oxide-semiconductor field effect transistor (MOSFET) have been limited by large amount of states at the SiO2/SiC interface. In this study, the accuracy of the energy level of the interface states extracted by hypothetical high frequency extreme, which is conventionally used, is experimentally examined. Conductance measurements at low temperature between 65 K and 100 K reveal that the extracted energy distribution of the interface states at nitrided SiO2/SiC interface close to the conduction band edge depends on the measurement temperature. It is demonstrated that conductance method at 65K enables us more accurate evaluation of the interface states at the SiO2/SiC interface and found that the interface states density (Dit) of nitride SiO2/SiC interface is over 1013 cm-2eV-1 at energy level of 0.1 eV below the conduction band edge.
Mechanisms of Nitrogen Incorporation at 4H-SiC/SiO2 Interface during Nitric Oxide Passivation – A First Principles Study
Authors: Ettisserry Devanarayanan , Goldsman Neil , Akturk Akin , Lelis Aivars J.
Published: May 2016

In this work, we investigate the behavior of Nitrogen atoms at 4H-Silicon Carbide (4H-SiC)/Silicon dioxide (SiO2) interface during nitric oxide passivation using ab-initio Density Functional Theory. Our calculations suggest different possible energetically favorable and competing mechanisms by which nitrogen atoms could a) incorporate themselves into the oxide, just above the 4H-SiC substrate, and b) substitute for carbon atoms at the 4H-SiC surface. We attribute the former process to cause increased threshold voltage instability (hole traps), and the latter to result in improved effective mobility through channel counter-doping, apart from removing interface traps in 4H-SiC power MOSFETs. These results support recent electrical and XPS measurements. Additionally, Nitric Oxide passivation is shown to energetically favor re-oxidation of the 4H-SiC surface accompanied by the generation of oxygen vacancies under the conditions considered in this work.
Nondestructive and Local Evaluation of SiO2/SiC Interface Using Super-Higher-Order Scanning Nonlinear Dielectric Microscopy
Authors: Chinone Norimichi , Kosugi R. , Tanaka Yasunori , Harada Shinsuke , Okumura Hajime , Cho Yasuo
Published: May 2016

SiO2/SiC interface was investigated by using super-higher-order (SHO) scanning nonlinear dielectric microscopy (SNDM) with high spatial resolution. Comparison of non-oxidized and thermally oxidized 4H-SiC wafer (Si-face) revealed that only 5 min oxidation makes the interface quality spatially inhomogeneous. Next four SiC wafers treated under different post oxidation annealing (POA) conditions in NO ambient (three “with” and one “without” POA) were also compared. Using SHO-SNDM, local capacitance-voltage (C-V) curves were obtained. The local C-V curve obtained in sample with POA was more close to ideal C-V curve compared to the C-V curves obtained in the sample without POA. In addition, two-dimensional normalized SNDM images taken on the four SiC wafers were observed, which showed that the spatial deviation of interface state was reduced by the POA treatment. Moreover, standard deviations s of the normalized SNDM images were calculated. Then, very strong correlations between σ and interface-state density Dit as well as channel electron mobility μFE were observed.
Bulk Growth of Large Area SiC Crystals
Authors: Powell Adrian R. , Sumakeris Joseph J. , Khlebnikov Yuri , Paisley Michael J. , Leonard R.T. , Deyneka Eugene , Gangwal Sumit , Ambati Jyothi , Tsevtkov V. , Seaman Jeff , McClure Andy , Horton Chris , Kramarenko Olek , Sakhalkar Varad , O’Loughlin M. , Burk Albert A. , Guo J.Q. , Dudley Michael , Balkas Elif
Published: May 2016

The growth of large diameter silicon carbide (SiC) crystals produced by the physical vapor transport (PVT) method is outlined. Methods to increase the crystal diameters, and to turn these large diameter crystals into substrates that are ready for the epitaxial growth of SiC or other non homogeneous epitaxial layers are discussed. We review the present status of 150 mm and 200 mm substrate quality at Cree, Inc. in terms of crystallinity, dislocation density as well as the final substrate surface quality.
An Investigation of SiC Schottky Contact Barrier Inhomogeneity for Temperature Sensing Applications
Authors: Pristavu Gheorghe , Brezeanu Gheorghe , Badila Marian , Draghici Florin , Pascu Razvan , Craciunoiu Florea
Published: May 2016

This paper proposes a method of characterizing silicon carbide Schottky diodes with inhomogeneous contacts in temperature sensing applications. Using the energy activation technique, temperature intervals where the effective barrier height is constant are determined. Unlike the conventional barrier which increases with temperature for inhomogeneous diodes, the effective barrier has physical meaning and can be used for sensor performance evaluation. The utility of effective barrier analysis is confirmed on fabricated Ni/4H-SiC Schottky diodes with different annealing conditions and different degrees of barrier non-uniformity. The good agreement between calculated and experimental data proves the suitable behavior of inhomogeneous diodes as sensors for different temperature ranges.
Relationship between C-Face Defects and Threshold-Voltage Instability in C-Face 4H-SiC MOSFETs Studied by Electrically Detected Magnetic Resonance
Authors: Kim Geon Woo , Arai Ryo , Ma S.J. , Okamoto Mitsuo , Yoshioka Hironori , Harada Shinsuke , Makino Takahiro , Ohshima Takeshi , Umeda Takahide
Published: May 2016

We present EDMR (electrically detected magnetic resonance) observations on “C-face defects” in C-face 4H-SiC MOSFETs. We found that negative threshold-voltage shifts of C-face MOSFETs are increased in association with EDMR signals of C-face defects as well as with the dissociation of hydrogen atoms induced by gamma-ray irradiation.
Negative Bias Temperature Instability of SiC MOSFET
Authors: Yen Cheng Tyng , Hung Hsiang Ting , Hung Chien Chung , Lee Chwan Ying , Lee Heng Yuan , Lee Lurng Shehng , Huang Yao Feng , Cheng Chi Yin , Chuang Pei Ju , Hsu Fu Jen
Published: May 2016

MOSFETs and MOS capacitors (MOSCAPs) have been fabricated on Si-face of 4H-SiC to investigate the negative bias temperature instability (NBTI) characteristics of SiC MOSFETs. The shifts of threshold voltage of MOSFETs ranged from -216mV to -1257mV after stressed by 1000sec of -1V to -15V gate bias, correspondingly. The negative shift of the threshold voltage indicated that there were positive charges piled up at or near the oxide/SiC interface. In the mean time, the flat-band voltage shifts of SiC MOSCAPs using the same oxide after stressed by -15V bias for 28800 sec at 175°C were negligible, due to insufficient supply of holes, thus suggesting that the NBTI observed in this study was primarily participated by hole trapping, instead of electron emission. The time evolution of DVth induced by negative bias stress was found to saturate quickly, also suggesting that positive charges were primarily coming from trapping of pre-existing near-interface oxide traps, instead of generation of interface traps. The DVth induced by negative bias stress was lower at higher temperature which might be attributed to faster recovery of hole trapping at elevated temperature.
Doping Fluctuation and Defect Formation in Fast 4H-SiC Crystal Growth Using a High-Temperature Gas Source Method
Authors: Kamata Isaho , Hoshino Norihiro , Tokuda Yuichiro , Makino Emi , Sugiyama Naohiro , Kojima Jun , Tsuchida Hidekazu
Published: May 2016

This paper investigates the quality of 4H-SiC crystals grown at a very fast growth rate (> 2.5 mm/h) using a high-temperature gas source method. Differences in nitrogen doping efficiency were clarified in facet and step-flow regions. In case for growth in the macro-step bunching mode, doping fluctuation and void formation were observed in the macro-step bunching region. Propagation of threading screw dislocations (TSDs) in the grown crystal was also investigated by synchrotron X-ray topography.
Time Resolved Gate Oxide Stress of 4H-SiC Planar MOSFETs and NMOS Capacitors
Authors: Domeij Martin , Buono Benedetto , Gumaelius Krister , Allerstam Fredrik
Published: May 2016

Lateral SiC MOSFETs and NMOS capacitors were fabricated and electrically evaluated for channel mobility, DIT and gate oxide breakdown. Time resolved measurements of VTH and VFB drift during gate bias stress were performed resulting in logarithmic time dependence for moderate stress time and temperature. Gate bias stress was also carried out during 20 hours at temperatures up to 225 C. Stress times resulting in a VTH shift of 500 mV were determined and an activation energy EA=0.86 eV was extracted for the VTH drift.
Improvement of SiO2/4H-SiC Interface Quality by Post-Oxidation Annealing in N2 at High-Temperatures
Authors: Chanthaphan Atthawut , Cheng Yen Hung , Hosoi Takuji , Shimura Takayoshi , Watanabe Heiji
Published: May 2016

The efficient and practical method for SiO2/4H-SiC interface improvement using post-oxidation annealing (POA) in pure N2 ambient was studied by means of x-ray photoelectron spectroscopy (XPS) analysis and electrical characterization. SiC-MOS capacitors with slope-shaped thermal oxides were used to investigate optimal conditions for interface nitridation. It was found that the amount of nitrogen atoms incorporated into the interfaces increased when raised the annealing temperature up to 1400°C, and thin oxide (< 30 nm) was used. Furthermore, N2-POA at 1400°C was proven to be very promising as equivalent to NO-POA in terms of reduced interface state density of SiC-MOS devices.
Irradiation and Post-Annealed nMOSFETs with Al Implanted P-Well: Limit of Robustness
Authors: Cabello Maria , Florentin Matthieu , Alexandru Mihaela , Schmidt Bernd , Rebollo Jose , Montserrat Josep , Millan José , Godignon Philippe
Published: May 2016

The electrical behaviour of irradiated and post-irradiation annealed nMOSFETs with an implanted p-type body and having a N2O oxynitrided gate oxide is analysed in this work. This study reveals the existence of a “threshold fluence” which might change the predominant SiO2/SiC interface charge trapping type from donors to acceptors at a given energy. The irradiation fluence and energy limit that guaranty a normal or improved operation of the MOSFETs are also given.
Processing and Characterization of MOS Capacitors Fabricated on 2°-Off Axis 4H-SiC Epilayers
Authors: Vivona Marilena , Fiorenza Patrick , Sledziewski Tomasz , Gkanatsiou Alexandra , Krieger M. , Chassagne Thierry , Zielinski Marcin , Roccaforte Fabrizio
Published: May 2016

In this work, the electrical properties of SiO2/SiC interfaces onto a 2°-off axis 4H-SiC layer were studied and validated through the processing and characterization of metal-oxide-semiconductor (MOS) capacitors. The electrical analyses on the MOS capacitors gave an interface state density in the low 1×1012 eV-1cm-2 range, which results comparable to the standard 4°-off-axis 4H-SiC, currently used for device fabrication. From Fowler-Nordheim analysis and breakdown measurements, a barrier height of 2.9 eV and an oxide breakdown of 10.3 MV/cm were determined. The results demonstrate the maturity of the 2°-off axis material and pave the way for the fabrication of 4H-SiC MOSFET devices on this misorientation angle.
High-Mobility SiC MOSFETs with Alkaline Earth Interface Passivation
Authors: Lichtenwalner Daniel J. , Pala Vipindas , Hull Brett , Allen Scott , Palmour John W.
Published: May 2016

Alkaline earth elements Sr and Ba provide SiO2/SiC interface conditions suitable for obtaining high channel mobility metal-oxide-semiconductor field-effect-transistors (MOSFETs) on the Si-face (0001) of 4H-SiC, without the standard nitric oxide (NO) anneal. The alkaline earth elements Sr and Ba located at/near the SiO2/SiC interface result in field-effect mobility (μFE) values as high as 65 and 110 cm2/V.s, respectively, on 5×1015 cm-3 Al-doped p-type SiC. As the SiC doping increases, peak mobility decreases as expected, but the peak mobility remains higher for Ba interface layer (Ba IL) devices compared to NO annealed devices. The Ba IL MOSFET field-effect mobility decreases as the temperature is increased to 150 °C, as expected when mobility is phonon-scattering-limited, not interface-trap-limited. This is in agreement with measurements of the interface state density (DIT) using the high-low C-V technique, indicating that the Ba IL results in lower DIT than that of samples with nitric oxide passivation. Vertical power MOSFET (DMOSFET) devices (1200V, 15A) fabricated with the Ba IL have a 15% lower on-resistance compared to devices with NO passivation. The DMOSFET devices with a Ba IL maintain a stable threshold voltage under NBTI stress conditions of-15V gate bias stress, at 150 °C for 100hrs, indicating no mobile ions. Secondary-ion mass-spectrometry (SIMS) analysis confirms that the Sr and Ba remain predominantly at the SiO2/SiC interface, even after high temperature oxide annealing, consistent with the observed high channel mobility after these anneals. The alkaline earth elements result in enhanced SiC oxidation rate, and the resulting gate oxide breakdown strength is slightly reduced compared to NO annealed thermal oxides on SiC.