bluuebunny/crossref_metadata_2025 huggingface dataset:
A Perspective about the Application of Quality of Context in U-Learning Environments
Authors: Nunes Felipe Becker , Herpich Fabricio , Voss Gleizer Bierhalz , Medina Roseclea Duarte
Published: May 2016

U-Learning environments collects context information relative to user's preferences and needs, but this information is typically very volatile. For this reason, Quality of Context is aimed at treating this information by applying quality parameters. This chapter aims to help the reader understand how the quality of context information can be treated in U-Learning environments, which are the main theoretical bases, technologies that support them and what are the methods, advantages and disadvantages related to this approach. In addition, specific cases of development and application of technologies and strategies involving Quality of Context are presented to illustrate all the concepts described. The results of usability testing related to the SUS questionnaire showed that the developed environment described in the case of study operated satisfactorily, based on the assessments made by the group of users who tested the modules and their operation.
Using Fuzzy Control Methods for Increasing the Energy Efficiency of Buildings
Authors: Mpelogianni Vassiliki , Groumpos Peter P.
Published: May 2016

The energy sector worldwide faces significant challenges that everyday become even more acute. Innovative technologies and energy efficiency measures are nowadays well known and widely spread, and the main issue is to identify the more effective and reliable in the long term. In order to do so the decision maker has to compensate many factors. This article investigates the feasibility of the application of new intelligent control methods in modeling and controlling the performance of a building. For the first time a performance comparison of Fuzzy Logic vs Fuzzy Cognitive Maps (FCMs) theories is performed and interesting results are presented. Multi-level intelligent controllers to manage the various parts of a building's automation and increase its energy efficiency are presented. For the first time the Building Energy Management System has been modeled using FCMs. Simulation studies with real environmental data have been performed and useful results have been obtained and discussed. Challenging future research topics are provided.
Antenna Design and Direction of Arrival Estimation in Meta-Heuristic Paradigm
Authors: Dey Nilanjan , Ashour Amira S.
Published: May 2016

Antennas are considered as a significant component in any wireless system. There are numerous factors and constraints that affect its design. Therefore, recently several algorithms are developed to allow the designers optimize the antenna with respect to numerous different criteria, general constraints and the desired performance characteristics. In recent years there has been an increasing attention to some novel evolutionary techniques, such as Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Ant Colony Optimization (ACO), Bacteria-Foraging (BF), Biogeography Based Optimization (BBO), and Differential Evolution (DE) that used for antenna optimization. The current study discussed three popular population-based meta-heuristic algorithms for optimal antenna design and direction of arrival estimation. Basically, single and multi-objective population-based meta-heuristic algorithms are included. Besides hybrid methods are highlighted. This paper reviews antenna array design optimization as well as direction of arrival optimization problem for different antennas configurations.
Metallurgical Failure Analysis of Intramedullary Nail Used for Femoral Fracture Stabilization
Authors: Ghiban Brandusa , Antoniac Iulian , Dan Gheorghe , Ghiban Alexandru , Ene Razvan
Published: May 2016

Currently orthopedics challenge is the use of intramedullary nails to straighten diaphyseal femoral fractures. In this paper it was conducted a case study on an intramedullary nail used for femoral fracture stabilization, in the case of one young patient. The evolution was unfavorable to the fracture site and the implant failed after three month of first surgical intervention. Intramedullary nail dimensions were 300mm length and 10mm in diameter. The following investigations were made in order to establish the failure causes: determination of the chemical composition through spectral analysis, macrostructural analysis using stereomicroscopy, optical microstructural analysis using optical microscopy, fractographic analysis using scanning electron microscopy. The final conclusions showed that the metallic biomaterial used for manufacturing the intramedullary nail was approximately an austenitic stainless steel AISI 316L, but with major microstructural defects. Macro-structural analysis revealed the presence of two zones of cracking, which are very rare at austenitic stainless steels. Also breaking with a fragile character has radial front tear propagation. In longitudinal section, cracks were evidenced due to the extraction operation and also the presence of corrosion products was shown. From fractographic analysis it was determined that intramedullary nail failure was predominantly through the mechanism of brittle fracture that took place at the point of maximum bending of the implant fragile.
New Concept in Cranioplasty Based on Biomaterials Performance in Various Clinical Cases
Authors: Mohan Dumitru , Nica Dan A. , Mohan Aurel , Feder Bogdan , Ciurea Alexandru Vlad
Published: May 2016

Today, there are four known types of grafts for cranioplasty: autogenic grafts (the same bone is reused such) such as bone from cranium, ribs, shinbones, shoulder blades, sternum or ilia, allogenic grafts (the graft originates from another human) such as cartilage, xenogenic grafts (grafts transplanted from animals ex: bovines, pigs, etc.) and alloplastic gra fts (graft consisting of inorganic material) such as celluloid, Polymethylmethacrylate-PMMA, polyetheretherketone-PEEK, hydroxyapatite, polyethylene, silicone, ceramic and other derivatives; metallic implants such as Aluminium, Gold, Silver, Lead, Platinum, Titanium, Tantalum and their alloys. In this paper, the authors perform a comprehensive review of how the techniques have evolved from classic metals to modern biopolymers and how the modern technology will impact the future of cranial reconstruction. Also, comparative aspects related to the use of modern biopolymers like PMMA and PEEK in cranioplasty will be revealed based on surgical experience and clinical cases. Modern technology enables neurosurgeons to understand the threedimensional anatomy of the skull and defect and allows them to be able to create implants perfectly tailored to the size and shape of the defect without neglecting the volumetry of the skull. The best materials of today appear to be PEEK due to their excellent mechanical properties other properties like non-immunogenicity, non-oncogenicity, sterility, biological tolerance and an acceptable price range.
Tissue Reaction to Subcutaneous Implantation of SuperEBA (Reinforced Zinc Oxide Cement) Used as Root-End Filling Material: A Histological Study in Rats
Authors: Iliescu Alexandru Andrei , Petcu Cristian Marian , Petcu Ileana Cristiana , Gheorghiu Irina Maria , Iliescu Andrei , Stan Mihaela Georgiana , Zurac Sabina Andrada
Published: May 2016

The retrograde filling is a critical step to a successful outcome of the endodontic surgery. Despite the progress in the technology of novel root-end filling materials, zinc oxide-eugenol cement superEBA is still preserving its clinical value on long-term basis. The study aimed to reconsider the tissue response to the initial irritating effect of this material. Silicon tubes filled with superEBA were subcutaneously implanted for 120 days in white Wistar rats which were afterwards sacrificed. The connective tissue surrounding the superEBA implants revealed fibroblast proliferation and a definite reparatory process without inflammatory reaction. A non-specific tissue healing in progress around the implants, without calcifications, necrosis, and apoptosis was also described after 4 months. SuperEBA proved on animal model that its cytotoxicity is reducing gradually in time until no adverse reaction is observed. The reduced content in eugenol compared to other surgical zinc oxide cements and the benefic effect of o-ethoxybenzoic acid are the support to reconsider SuperEBA as a biocompatible retrograde filling material.
Computational Study of Physicochemical Properties of the Monomers Used in Stomatology
Authors: Opri Mirela , Amzoiu Emilia , Manolea Horia Octavian , Rîcă Radu
Published: May 2016

Monomers used in dentistry allow tackling shrinkage problem during polymerization of dental composites.These monomers may cross biomembranes, a phenomenon that can lead to various toxic responses. An important factor that express the lipophilicity of these compounds is the partition coefficient. This parameter allows assessment of the solubility of a monomer to another and, generally, of a material to another.Computational partition coefficients study of water / octanol for a series of monomeric compounds analyzed showed the contribution of chemical structures dependent descriptors of substances on this parameter. The purpose of the assessment of these molecular descriptors is to show their importance in the partition of the substances studied in two phases aqueous and lipid (n-octanol).This allows optimization of the action of compounds activity very useful in finding new monomers used in dental reconstruction.
Large Area Silicon Carbide Photodiode, and Monolithic Readout Design and Fabrication
Authors: Akturk Akin , Cusack Brendan , Goldsman Neil
Published: May 2016

We are in the process of designing and fabricating a very large area (> 4mm2) and extremely low dark current silicon carbide ultraviolet photodiode with a readout circuitry monolithically fabricated on the same die. This is a large area silicon carbide based active pixel sensor (APS), capable of measuring low power density deep ultraviolet photons as well as low energy particles. To this end, we have already fabricated several large area photodiodes with low dark current values and large ultraviolet responsivities. We here report the electrical and optical measured performance of various size photodiodes we have fabricated.
Ion Implanted 4H-SiC UV Pin-Diodes for Solar Radiation Detection – Simulation and Characterization
Authors: Matthus C.D. , Erlbacher Tobias , Burenkov Alexander , Bauer Anton J. , Frey Lothar
Published: May 2016

This paper describes the fabrication, characterization, and simulation of 4H-SiC pin-photodiodes for solar UV radiation detection. The devices were produced with an aluminum implanted emitter unlike most previously published detectors which use epitaxy for all applied doping regions (see e.g. [1-3]). They were electrically characterized at different temperatures with and without UV-illumination and afterwards a spectral analysis of the photocurrent was performed. A quantum efficiency up to 55% at 260 nm will be shown. Furthermore, the capability of the diodes for visible blind sun UV monitoring e.g. within a building, is demonstrated.
Studies on Floating Contact Press-Pack Diodes Surge Current Capability
Authors: Banu Viorel , Berthou Maxime , Montserrat Josep , Jordà X. , Millan José , Godignon Philippe
Published: May 2016

This work reports experimental results on surge current capability of press-pack SiC diodes: Schottky, JBS and PIN. Our investigation showed a strong improvement of electro-thermal performances of the surge current capability for the 5.5 kV JBS diodes by using press-pack encapsulation. The surge current failure analysis for the press-pack SiC diodes is described together with a simplified unidimensional model for the temperature evaluation at the failure point.
Development of a Wire-Bonding-Less SiC Power Module Operating over a Wide Temperature Range
Authors: Sato Shinya , Tanisawa Hidekazu , Anzai Takeshi , Takahashi Hiroki , Murakami Yoshinori , Kato Fumiki , Watanabe Kinuyo , Sato Hiroshi
Published: May 2016

In this paper, we describe a power module fabricated using SiC metal–oxide–semiconductor field-effect transistors (MOSFETs). A C-R snubber is integrated into this power module for reduction of the surge voltage and dumping of the voltage ringing. The four SiC MOSFETs are sandwiched between active metal copper (AMC) substrates. The surfaces of the SiC MOSFETs are attached to AMC substrates by Al bumps, owing to which the power module shows low inductance. Moreover, this power module ensures credibility and reliability at higher operating temperatures beyond 200 °C. The switching characteristics of the module are studied experimentally for high-temperature and high-frequency operations.
SPICE Modeling of Advanced Silicon Carbide High Temperature Integrated Circuits
Authors: Akturk Akin , Goldsman Neil , Ahyi Ahayi , Dhar Sarit , Cusack Brendan , Park Minseo
Published: May 2016

Due to the wide band-gap and high thermal conductivity of the 4H polytype of silicon carbide (SiC) as well as the maturity of this polytype’s fabrication processes, 4H-SiC offers an extremely attractive wide bandgap semiconductor technology for harsh environment applications spanning a variety of markets. To this end, 4H-SiC power electronics is gradually emerging as the technology of choice for next-generation power electronics; however, relatively limited progress has been made with regards to silicon carbide integrated circuits (ICs). We address this problem by developing fabrication and design methods for the SiC IC components themselves, as well as complementary SPICE type compact models for these components, and thereby facilitate the development of future SiC ICs and Process Design Kits (PDKs).
Utilization of SiC MOSFETs in Voltage Source Inverter of Inductive Power Transfer Systems for Enduring Capacitive Loads
Authors: Kampitsis Georgios , Gati Eleni , Papathanassiou Stavros , Manias Stefanos N.
Published: May 2016

In this work, the use of SiC MOSFETs is proposed for the implementation of the H-bridge Voltage Source Inverter (VSI) of Inductive Power Transfer Systems (IPTSs) in order to successfully support potential capacitive loading. Conventional power semiconductor devices are prevented from feeding capacitive loads because of the occurrence of current overshoots and voltage spikes due to the reverse recovery phenomenon of the antiparallel diodes. Operation of the VSI under capacitive load can be caused in IPTSs during resonant frequency tracking or misalignment between the coupled coils, due to the existence of resonant circuits. Experiments conducted with both Si and SiC MOSFETs show the superiority of the latter in terms of system stability, endurance in high power and avoidance of catastrophic failure.
Temperature Dependent Stability of Stacking Fault in Highly Nitrogen-Doped 4H-SiC Crystals
Authors: Taniguchi Chisato , Ichimura Aiko , Ohtani Noboru , Katsuno Masakazu , Fujimoto Tatsuo , Sato Shinya , Tsuge Hiroshi , Yano Takayuki
Published: May 2016

The formation of basal plane stacking faults in highly nitrogen-doped 4H-SiC crystals was theoretically investigated. A novel theoretical model based on the so-called quantum well action (QWA) mechanism was proposed; the model considers several factors, which were overlooked in a previously proposed model, and explains well the annealing-induced formation of double layer Shockley-type stacking faults in highly nitrogen-doped 4H-SiC crystals. We further revised the model to consider the carrier distribution in the depletion regions adjacent to the stacking fault and were successful in explaining the shrinkage of stacking faults during annealing at even higher temperatures.
A Highly Efficient 3.3-kV SiC-Si Hybrid Power Module with a Novel SiC JBS Diode and a Si Advanced Trench HiGT
Authors: Yamada Renichi , Kameshiro Norifumi , Toyota Yoshiaki , Hirao Takashi , Yasui Kan , Onose Hidekatsu , Mochizuki Kazuhiro , Miki Hiroshi , Yokoyama Natsuki , Okino Hiroyuki , Matsuhima Hiroyuki , Oda Tetsuo , Hasegawa Jiro , Mori Mutsuhiro
Published: May 2016

A 3.3-kV SiC-Si hybrid module, composed of a low-forward-voltage (VF) SiC junction-barrier-Schottky (JBS) diode and a low-saturation-voltage VCE(sat) Si trench IGBT was fabricated and demonstrated highly efficient operation.
Novel vs Conventional Bipolar Logic Circuit Topologies in 4H-SiC
Authors: Elgabra Hazem , Siddiqui Amna , Singh Shakti
Published: May 2016

Silicon Carbide (SiC) is an attractive candidate for integrated circuits (ICs) in harsh environment applications due to its superior inherent electrical properties. Though current research is geared towards adapting existing silicon based digital logic technologies to 4H-SiC, the true merit of each technology in 4H-SiC has remained unclear. Creating logic technologies specifically for 4H-SiC, taking into account its electrical properties, is an area which remains unexplored. In this paper, we present a novel bipolar logic technology that is designed and optimized for 4H-SiC, and compare its performance with the prevalent bipolar technologies. The results show that the novel logic technology not only compares well with the conventional technologies in performance, but also features simpler design, smaller footprint, and a low transistor count.
3D Integration of Si-Based Peltier Device onto 4H-SiC Power Device
Authors: Furubayashi Yutaka , Tanehira Takafumi , Yonemori Kei , Seo Nobuhide , Kuroki Shin Ichiro
Published: May 2016

We propose 3-D integration of Peltier device onto a power device. In order to transport a heat from the power device, as a suitable material of the Peltier device, silicon was adopted because of its high Seebeck coefficient, high thermal conductivity, and applicability to semiconductor process. Bulk Si-based Peltier devices with conventional shape showed an active thermal transport over a Joule heat at the operation current less than 5 A. 3-D integration of 4H-SiC-based Schottky barrier diodes and Si-based film Peltier device, separated by intrinsic SiC layer, was realized by using conventional Si-based process flow.
Interfacial Disorder of Graphene Grown at High Temperatures on 4H-SiC(000-1)
Authors: Giannazzo Filippo , Nicotra Giuseppe , Deretzis Ioannis , Piazza Aurora , Fisichella Gabriele , Agnello S. , Spinella Corrado , La Magna Antonino , Roccaforte Fabrizio , Yakimova Rositza
Published: May 2016

This paper presents an investigation of the morphological and structural properties of graphene (Gr) grown on SiC(000-1) by thermal treatments at high temperatures (from 1850 to 1950 °C) in Ar at atmospheric pressure. Atomic force microscopy and micro-Raman spectroscopy showed that the grown Gr films are laterally inhomogeneous in the number of layers, and that regions with different stacking-type (coupled or decoupled Gr films) can coexist in the same sample. Scanning transmission electron microscopy and electron energy loss spectroscopy shoed that a nm-thick C-Si-O amorphous layer is present at the interface between Gr and SiC. Basing on these structural results, the mechanisms of Gr growth on the C-face of SiC under these annealing conditions and the role of this disordered layer in the suppression of epitaxy between Gr and the substrate have been discussed.
The Role of Porous Graphite Plate for High Quality SiC Crystal Growth by PVT Method
Authors: Shin Hee Won , Lee Hee Jun , Kim Hwang Ju , Lee Dong Hoon , Park Mi Seon , Jang Yeon Suk , Lee Won Jae , Yeo Im Gyu , Chun Myong Chuel , Lee Si Hyun , Kim Jung Gon
Published: May 2016

The present research is focused to investigate a role of the porous graphite (PG) plate that could improve the quality of 4H-SiC crystal. The grown crystal in porous graphite inserted crucible showed the lower intensity of Al, B and Ti impurity concentration than SiC crystal grown in conventional crucible. The porous graphite plate before and after the growth process has been investigated by a Raman spectroscopy and a photoluminescence spectrum (PL). According to the analysis result, it was confirmed that the porous graphite plate had the effect of suppressing impurities supplied to SiC single crystal during the growth process.
Modified Epitaxial Graphene on SiC for Extremely Sensitive and Selective Gas Sensors
Authors: Eriksson Jens , Puglisi Donatella , Strandqvist Carl , Gunnarsson Rickard , Ekeroth Sebastian , Ivanov Ivan G. , Helmersson Ulf , Uvdal Kajsa , Yakimova Rositza , Lloyd Spetz Anita
Published: May 2016

Two-dimensional materials offer a unique platform for sensing where extremely high sensitivity is a priority, since even minimal chemical interaction causes noticeable changes in electrical conductivity, which can be used for the sensor readout. However, the sensitivity has to be complemented with selectivity, and, for many applications, improved response- and recovery times are needed. This has been addressed, for example, by combining graphene (for sensitivity) with metal/oxides (for selectivity) nanoparticles (NP). On the other hand, functionalization or modification of the graphene often results in poor reproducibility. In this study, we investigate the gas sensing performance of epitaxial graphene on SiC (EG/SiC) decorated with nanostructured metallic layers as well as metal-oxide nanoparticles deposited using scalable thin-film deposition techniques, like hollow-cathode pulsed plasma sputtering. It is demonstrated that under the right modification conditions the electronic properties of the surface remain those of graphene, while the surface chemistry can be tuned to improve sensitivity, selectivity and speed of response to several gases relevant for air quality monitoring and control, such as nitrogen dioxide, benzene, and formaldehyde.
Trapping States in SiO2/GaN MOS Capacitors Fabricated on Recessed AlGaN/GaN Heterostructures
Authors: Fiorenza Patrick , Greco Giuseppe , Iucolano Ferdinando , Parisi Antonino , Reina Santo , Patti Alfonso , Roccaforte Fabrizio
Published: May 2016

In this work, the different nature of trapping states in metal-oxide-semiconductor (MOS) capacitors fabricated on recessed AlGaN/GaN heterostructures has been investigated. In particular, the origin of both fast and slow states has been elucidated by frequency dependent conductance measurements. Using post deposition annealing in forming gas, which is known to induce hydrogen incorporation at the interface, allowed to ascribe the fast traps (with characteristic response time in the range of 5–50 μs) to SiO2/GaN interface states and the slow traps (50–100 μs) to “border traps” located few nanometers inside the SiO2 layer. The results can be useful to predict the behavior of GaN switching devices, like hybrid MOSHEMTs.
Visualization of Polarization and Two Dimensional Electron Gas Distribution in AlGaN/GaN Heterostructure Using Scanning Nonlinear Dielectric Microscopy
Authors: Hirose Kotaro , Chinone Norimichi , Cho Yasuo
Published: May 2016

AlGaN/GaN heterostructure was observed using scanning nonlinear dielectric microscopy, which can measure both carrier and polarization profile in AlGaN/GaN heterostructure. As a result, GaN spontaneous polarization and AlGaN polarization which was sum of spontaneous polarization and piezoelectric polarization were clearly distinguished. Moreover, two dimensional electron gas was observed at the AlGaN/GaN interface. These results show that scanning nonlinear dielectric microscopy is useful method for evaluation of two dimensional electron gas profile and polarization profile in AlGaN/GaN heterostructure.
Advances in Fast Epitaxial Growth of 4H-SiC and Defect Reduction
Authors: Tsuchida Hidekazu , Kamata Isaho , Ito Masahiko , Miyazawa Tetsuya , Uehigashi Hideyuki , Fukada Keisuke , Fujibayashi Hiroaki , Naitou Masami , Hara Kazukuni , Osawa Hitoshi , Sugiura Toshikazu , Kozawa Takahiro
Published: May 2016

This paper reports on recent advances in 4H-SiC epitaxial growth toward high-throughput production of high-quality and uniform 150 mm-diameter 4H-SiC epilayers by enhancing of growth rates, improving uniformity and reducing defect densities. A vertical single-wafer type SiC epitaxial reactor is employed and high-speed wafer rotation is confirmed as effective, not only for enhancing growth rates without increasing the source gas supply but also improving thickness and doping uniformities. The current levels of reducing particle-induced defects, in-grown stacking faults, basal plane dislocations and the Z1/2 center (carbon vacancies) are reviewed.
Study and Optimization of a 600V Pseudo-Vertical GaN-on-Silicon Rectifier by Finite Element Simulations
Authors: Souguir-Aouani Amira , Thierry-Jebali Nicolas , Tournier Dominique , Yvon Arnaud , Collard Emmanuel , Planson Dominique
Published: May 2016

This work presents the impact analysis of physical and geometrical parameters on the on-resistance and the breakdown voltage in order to optimize a 600 V pseudo-vertical GaN/Si Schottky rectifier. The results by finite element simulations indicate that the most influent parameter on the resistance is the thickness of the n+ layer. Regarding reverse specifications, simulations show that a good efficiency of the “Mesa + Guard Ring” is achieved for a guard ring doping concentration higher than Na=5×1017 cm-3.
Growth of Crack-Free GaN on Si HEMTs with Fe-Doped GaN Using Un-Doped GaN Interlayer
Authors: Era Atsushi , Hatakenaka Susumu , Okazaki Hiroyuki , Kamo Yoshitaka , Nishida Takehiro , Watanabe Hiroshi
Published: May 2016

We show the influence of Fe-doping upon bowing and cracking in GaN-on-Si based high-electron-mobility transistors (HEMTs) and report how to prevent from bowing and cracking. In-situ reflectance measurements revealed that stress relaxation occurred during the growth of GaN:Fe on Al0.25Ga0.75N, resulting in the wafer bowing and cracking. In-situ measurements and transmission electron microscope images showed that the relaxation was caused by the 3D growth of GaN:Fe and the propagation of threading dislocations. To suppress the relaxation, a 100 nm-thick un-doped GaN interlayer was inserted between GaN:Fe and Al0.25Ga0.75N. As a result, a crack-free low-bow surface was obtained for GaN-on-Si HEMTs with GaN:Fe.
HVPE GaN Growth on 4H SiC and Die Dicing
Authors: Usikov Alexander , Kurin Sergey , Barash Iosif , Roenkov Alexander D. , Antipov Andrei , Khait Oleg , Medvedev Oleg , Helava Heikki , Makarov Yuri
Published: May 2016

Hydride Vapor Phase Epitaxy (HVPE) was used to grow 1-4 μm thick undoped GaN layers on 4H-SiC and sapphire substrates. To adjust mechanical strain and crack formation in the GaN/SiC samples, the AlGaN-based buffer layer was grown at low temperature (920-980°C) and the GaN layer was grown at a higher temperature (1000-1040°C). Laser scribing through the GaN layer or the SiC substrate was applied to fabricate dies from the GaN/SiC and GaN/sapphire samples. The laser irradiation passing through the GaN layer to the sapphire substrate or through the SiC substrate to the GaN layer, along two orthogonal directions created a net of micro-cavities in sapphire and melted grooves in SiC that promote easy breakage of the sample into rectangular dies.
High-Speed Solution Growth of Single Crystal AlN from Cr-Co-Al Solvent
Authors: Watanabe Shota , Nagaya Masashi , Takeuchi Yukihisa , Aoyagi Kenta , Harada Shunta , Tagawa Miho , Ujihara Toru
Published: May 2016

We achieved a high growth rate in solution growth of AlN single crystal by suppressing unintentional precipitations near the surface of solvent and by increasing the equilibrium nitrogen concentration in the solvent. In order to suppress unintentional precipitations, we made the solvent supersaturated just above the surface of the substrate by optimizing the composition of the solvent and the temperature distribution based on thermodynamic numerical analysis. In particular, we focused on interactions between nitrogen or aluminum and solvent elements, leading to the increase of the equilibrium nitrogen concentration. We selected chromium and cobalt due to their high affinity with nitrogen or aluminum. Consequently, we successfuly achieved growth rate as high as 200 μm/h in maximum.
Voids-Free 3C-SiC/Si Interface for High Quality Epitaxial Layer
Authors: Anzalone Ruggero , Piluso Nicolo , Reitano Riccardo , Alberti Alessandra , Fiorenza Patrick , Salanitri Marco , Severino Andrea , Lorenti Simona , Arena Giuseppe , Coffa Salvo , La Via Francesco
Published: May 2016

A study of the carbonization process and of a low temperature buffer layer on the Cubic Silicon Carbide (3C-SiC) epitaxial growth has been reported in this work. From this study it has been evidenced the importance of the C/H2 ratio and of the buffer layer process on the voids formation at the 3C-SiC/Si interface. From our study, the influence of the voids the wafer curvature is highlighted. It has been observed that decreasing the density of these voids, decreases the stress of the 3C-SiC film; consequently, the wafer curvature is reduced.
Analysis and Reduction of Stacking Faults in Fast Epitaxial Growth
Authors: Uehigashi Hideyuki , Fukada Keisuke , Ito Masahiko , Kamata Isaho , Fujibayashi Hiroaki , Naitou Masami , Hara Kazukuni , Osawa Hitoshi , Kozawa Takahiro , Tsuchida Hidekazu
Published: May 2016

We have developed a single-wafer vertical epitaxial reactor which realizes high-throughput production of 4H-SiC epitaxial layer (epilayer) with a high growth rate [1,2]. In this paper, in order to evaluate the crystalline defects which can affect the characteristics of devices, we investigated the formation of variety of in-grown stacking faults (SFs) in detail. Synchrotron X-ray topography, photoluminescence (PL) and transmission electron microscopy are employed to analyze the SFs and the origins of the SF formation are discussed. The result in reducing in-grown SFs in fast epitaxial growth is also shown.
Elimination of BPD in 5~30um Thick 4H-SiC Epitaxial Layers Grown in a Warm-Wall Planetary Reactor
Authors: Feng Gan , Sun Yong Qiang , Qian Wei Ning , Lv Li Ping , Zhao Jian H. , Tsai D. , Raghunathan M. , Fei Y.
Published: May 2016

The process of the epitaxial growth of 4H-SiC has been optimized to obtain higher ratio of conversion of BPDs to the TEDs on 100 mm substrates in a warm-wall planetary reactor. 100% BPD conversion ratio was successfully obtained with excellent surface morphology under optimized growth process. The high efficiency of the optimized growth process in BPD conversion is independent of the initial surface conditions and BPD density of the substrates.
Formation and Reduction of Large Growth Pits on 100 mm 4° 4H-SiC
Authors: Sun Yong Qiang , Feng Gan , Kang Jun Yong , Qian Wei Ning , Lv Li Ping , Li Yi Yang , Li Kai Xi , Zhao Jian H.
Published: May 2016

The large growth pits (LGPs) dependence of substrate quality, growth rate, and C/Si ratio have been discussed in the 4H-SiC epitaxial growth on 100 mm N-type 4H-SiC Si-face substrates misoriented by 4° toward [11-20] with a warm-wall planetary reactor. The formation and reduction of LGPs have been investigated by adjusting the growth process parameters. With the optimized process, the perfect surface morphology with lower LGPs density has been obtained on the high quality substrate.
Improvement on 150 mm 4H-SiC Epitaxial Wafer Quality
Authors: Masuda Tatsuya , Miyasaka Akira , Norimatsu Jun , Tajima Yutaka , Muto Daisuke , Momose Kenji , Osawa Hitoshi
Published: May 2016

For the popularization of SiC power device, improvement on both productivity and quality of 150 mm diameter SiC epitaxial wafer is inevitable. With highly productive 8x150-mm CVD reactor, we have grown epitaxial layer on 4° off 4H-SiC wafer Si-and C-face. Modifying some reactor parts and optimizing growth conditions enabled us to achieve a good balance between high uniformity and smooth surface.
Smooth 4H-SiC Epilayers Grown with High Growth Rates with Silane/Propane Chemistry Using 4° Off-Cut Substrates
Authors: Lilja Louise , Hassan Jawad , Janzén Erik , Bergman J. Peder
Published: May 2016

4H-SiC epilayers with very smooth surfaces were grown with high growth rates on 4° off-cut substrates using standard silane/propane chemistry. Specular surfaces with RMS values below 0.2 nm are presented for epilayers grown with growth rates up to 30 μm/h using horizontal hot-wall chemical vapor deposition, with up to 100 μm thickness. Optimization of in-situ etching conditions and C/Si ratio are presented.
Optical Nuclear Spin Polarization of Divacancies in SiC
Authors: Ivády Viktor , Szasz Krisztian , Falk Abram L. , Klimov Paul V. , Christle David J. , Koehl William F. , Janzén Erik , Abrikosov Igor A. , Awschalom David D. , Gali Ádám
Published: May 2016

We demonstrate optically pumped dynamic nuclear polarization (DNP) of 29Si nuclear spins that are strongly coupled to paramagnetic color centers in 4H- and 6H-SiC. We observe 99%±1% degree of polarization. By combining ab initio theory with the experimental identification of the color centers’ optically excited states, we quantitatively model how the polarization derives from hyperfine-mediated level anticrossings. In addition, we developed a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process. These results lay a foundation for SiC-based quantum memories, nuclear gyroscopes, and hyperpolarized probes for magnetic resonance imaging.
Limitations in Very Fast Growth of 4H-SiC Crystals by High-Temperature Gas Source Method
Authors: Hoshino Norihiro , Kamata Isaho , Tokuda Yuichiro , Makino Emi , Sugiyama Naohiro , Kojima Jun , Tsuchida Hidekazu
Published: May 2016

Limitations in the very fast growth of 4H-SiC crystals are surveyed for a high-temperature gas source method. The evolution of macro-step bunching and void formation in crystal growth is investigated by changing the partial pressures of the source gases and crystal rotation speeds. The variation in macro-step formation depending on radial positions, where step-flow or spiral growth governs, of a grown crystal is also revealed. Based on the relation between growth conditions and macro-step bunching, a trade-off between growth rate enhancement and crystal quality and a method to improve such trade-off are discussed. Nitrogen at a high concentration under very high growth rates in the high-temperature gas source method is also investigated.
Boron-Implanted 3C-SiC for Intermediate Band Solar Cells
Authors: Ma Quan Bao , Galeckas Augustinas , Azarov Alexander , Thøgersen Annett , Carvalho Patricia Almeida , Wright Daniel N. , Diplas Spyros , Løvvik Ole Martin , Jokubavicius Valdas , Liu Xin Yu , Sun Jian Wu , Syväjärvi Mikael , Svensson Bengt Gunnar
Published: May 2016

Sublimation-grown 3C-SiC crystals were implanted with 2 atomic percent of boron ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 8.5×1016 atoms/cm2. The samples were then annealed at 1400, 1500 and 1600 °C for 1h at each temperature. The buried boron box-like concentration profile can reach ~2×1021 cm-3 in the plateau region. The optical activity of the incorporated boron atoms was deduced from the evolution in absorption and emission spectra, indicating possible pathway for achieving an intermediate band behavior in boron doped 3C-SiC at sufficiently high dopant concentrations.
Doping of 4H-SiC with Group IV Elements
Authors: Krieger M. , Rühl Maximilian , Sledziewski Tomasz , Ellrott Gunter , Palm Theresa , Weber Heiko B. , Bockstedte Michel
Published: May 2016

Germanium (Ge) doping of 4H silicon carbide (SiC) has recently attracted attention because a conductivity-enhancing effect was reported. In this work, we report on an experimental and theoretical approach to elucidate this effect. Ge and tin (Sn) – a second candidate of group IV elements – have been implanted into n-type 4H-SiC. Despite the expected isoelectric nature of Ge and Sn, a more efficient annealing of implantation-induced defects was observed compared to noble gas implantation with identical simulated initial implantation damage. In particular, a strong reduction of the prominent Z1/2 defect was observed. Density functional theory calculations under equilibrium conditions show that Ge is mainly incorporated on a substitutional silicon lattice site without creating new charge transition levels in the bandgap. The low abundance of other Ge-related defects suggests that kinetic mechanisms should be responsible for the observed effect of group IV doping.
High Temperature Solution Growth of SiC by the Vertical Bridgman Method Using a Metal Free Si-C-Melt at 2300 °C
Authors: Fahlbusch Lars , Schöler Michael , Mattle Patrick , Schnitzer Sarah , Khodamoradi Hossein , Iwamoto Naoya , Svensson Bengt Gunnar , Wellmann Peter J.
Published: May 2016

We developed a solution growth process related to the combination of the Vertical Bridgman and Vertical Gradient Freeze in a metal free Si-C melt at growth temperatures of 2300 °C. For this procedure we present a detailed description of the growth process and discuss the influence of different growth parameters on the surface morphology and growth rate. So far, we managed to grow SiC layers with a thickness up to 300 μm. The characterization of the crystal morphology was carried out using SEM images and the metal concentration was estimated using SIMS.
Formation and Annihilation of Carbon Vacancies in 4H-SiC
Authors: Ayedh Hussein M. , Bobal Viktor , Nipoti Roberta , Hallén Anders , Svensson Bengt Gunnar
Published: May 2016

The carbon vacancy (VC) is a major point defect in high-purity 4H-SiC epitaxial layers limiting the minority charge carrier lifetime. In layers grown by chemical vapor deposition techniques, the VC concentration is typically in the range of 1012 cm-3 and after device processing at temperatures approaching 2000 °C, it can be enhanced by several orders of magnitude. In the present contribution, we show that the cooling rate after high-temperature processing has a profound influence on the resulting VC concentration where a slow rate promotes elimination of VC. Further, isochronal annealing of as-grown and as-oxidized epi-layers protected by a carbon-cap was undertaken between 800 °C and 1600 °C. The results reveal that thermodynamic equilibrium of VC is established rather rapidly at moderate temperatures, reaching a VC concentration of only a few times 1011 cm-3 after 40 min at 1500 °C. Hence, the concept of eliminating VC’s by annealing at moderate temperatures under C-rich equilibrium conditions shows great promise and enables re-annealing of high-temperature processed wafers, in contrast to the procedures commonly used today to eliminate VC. In-diffusion of carbon interstitials and out-diffusion of VC’s are discussed as the kinetics processes establishing the thermodynamic equilibrium
Lifetime Measurement in n-Type 4H-SiC by Mean of the Microwave Phase-Shift
Authors: Berenguier Baptiste , Palais Olivier , Bertaina Sylvain , Ottaviani Laurent , Lyoussi A.
Published: May 2016

During the past years, our team developed an original lifetime measurement method for semiconductors wafers, called microwave phase-shift (µW-PS). It was successfully employed to determinate bulk lifetime and surface recombination velocities on silicon. We recently adapted the method to silicon carbide (SiC), using a continuous UV laser and acousto-optic modulator. The theory is presented, using the standard continuity equation in n-type 4H-SiC. The proposed measurement setup firstly allows to estimate a bulk lifetime ranging from 2.3 to 6.7 µs.
Effect of Aluminum during the High Temperature Solution Growth of Si-Face 4H-SiC
Authors: Chaussende Didier , Parent-Bert Lucile , Shin Yun Ji , Ouisse Thierry , Yoshikawa Takeshi
Published: May 2016

Using a sessile drop method, investigation of the surface reconstruction of a Si-face, 4°off (0001) 4H-SiC surface in contact with pure silicon or Al-Si alloys has been carried out in the 1600-1800°C temperature range. In pure silicon and at 1600°C, the surface evolves with a two stage process: i) a fast step-bunching leading to parallel macrosteps and ii) a slower step leading equilibrium morphology, composed of (0001), (10-1n) and (01-1n) facets. Increasing the temperature to 1800°C or adding a few percents of aluminium drastically enhance the first stage, but strongly reduce the second one.
Observation of Pair Structures of Threading Dislocation and Surface Defect in 4H-SiC Wafer by Mirror Projection Electron Microscopy
Authors: Isshiki Toshiyuki , Hasegawa Masaki
Published: May 2016

Two types of shallow surface defects associated with treading dislocation were found out by using mirror projection electron microscope. One was single groove with a dimension of about 4 nm in depth, 2 μm in width and 15 μm in length, named “as nanogroove”. The other was a shallow groove at 1.3nm in depth being between pair of hillocks at 2-3 nm in height and 1.5 μm in distance, named as “nanohillock pair”. Dislocations combined with the defects were found out by micro-KOH etching method with low-energy scanning electron microscopy. The dislocations were identified by g-b analysis using scanning transmission electron microscopy as threading edge dislocations converted from basal plane dislocation at bulk-epi layer interface or within epi layer.
Electrical Properties of Defects in 4H-SiC Investigated by Photo-Induced-Currents Measurements
Authors: Privitera Stefania , Litrico Grazia , Camarda Massimo , Piluso Nicolo , La Via Francesco
Published: May 2016

In this paper we have studied the connection between crystal quality and electrical transport in 4H-SiC by simultaneous micro-photoluminescence (μPL) and photocurrent (PC) measurements. We have used a focused HeCd laser at 325 nm (i.e. above bandgap) to measure with a spatial resolution of few microns both the μPL spectra and the I-V characteristics in 4H-SiC/Ni Schottky diodes. We found that the PC signal acquired along a defect can give information on its spatial distribution in depth. The minority carrier lifetime has been also estimated and its dependence on the emission wavelength has been determined for several stacking faults.
Cross Section and Plan View STEM Analysis on Identical Conversion Point of Basal Plane Dislocation to Threading Edge Dislocation of 4H-SiC
Authors: Sato Takahiro , Orai Yoshihisa , Isshiki Toshiyuki , Fukui Munetoshi , Nakamura Kuniyasu
Published: May 2016

Cross section and plan view dislocation analysis at the conversion point of a basal plane dislocation (BPD) into a threading edge dislocation (TED) in a silicon carbide epitaxial wafer was developed using a newly modified multi directional scanning transmission electron microscopy (STEM) technique. Cross section STEM observation in the [-1100] direction, found a conversion point located 5.5 μm from the surface, where two dislocation lines in the basal plane convert into one dislocation line nearly along the hexagonal c axis was observed. Using plan view STEM observation along the [000-1] direction, it is confirmed that the dislocation lines are two partial dislocations of a BPD and one TED by g·b invisibility analysis. This new technique is a powerful tool to evaluate the fundamental dislocation characteristics of power electronics devices.
An Ultrafast I-V Measurement Technique Accounting for Capacitive and Leakage Currents in Reverse Mode for SiC Power Devices
Authors: Fonder Jean Baptiste , Brosselard Pierre , Tournier Dominique , Berthou Maxime , Vergne Bertrand
Published: May 2016

An ultrafast I-V measurement technique has been developed to measure simultaneously C-V and leakage parameters of SiC power devices. After considering the coupled contribution of both static (leakage current) and dynamic (capacitive current) aspects with respect to high dV/dt voltage ramps, a time-based characterization is detailed and validated on SiC Junction Barrier Schottky (JBS) power diodes.
Dipole Type Behavior of NO Grown Oxides on 4H–SiC
Authors: Haasmann Daniel , Moghadam Hamid Amini , Han Ji Sheng , Aminbeidokhti Amirhossein , Iacopi Alan , Dimitrijev Sima
Published: May 2016

In this paper, we present surprising MOS capacitor C–V bias instability observed in NO-grown oxides, with distinctly different behavior compared to that of conventional NO-annealed oxides on 4H-SiC. Using sequential back-and-forth and bias-temperature stress C–V measurements, it was demonstrated that the C–V shift direction of NO-grown oxides was opposite to that of NO-annealed oxides. A model based on bias-temperature stress orientated near-interfacial dipoles is proposed to explain this unique behavior of NO-grown oxides.
Measurement Issues Affecting Threshold-Voltage Instability Characterization of SiC MOSFETs
Authors: Green Ronald , Lelis Aivars J. , Habersat Daniel B.
Published: May 2016

This work focuses on measurement issues that affect the accuracy of positive bias temperature instability measurements of SiC power MOSFETs using a conventional sweep technique to characterize the threshold voltage, VT. Threshold-voltage shifts occurring during stress are readily recoverable during the measurement, resulting in an underestimation in VT degradation. Recovery of VT due to gate-stress relaxation before or during the measurement was a major source of measurement error that was mitigated by performing an immediate sweep down in gate voltage, VGS, from the stress bias toward threshold. Allowing the gate bias to drop to zero just prior to measuring by sweeping VGS positively resulted in smaller observed degradation due to VT recovery. This result is important, especially in cases where the gate stress has to be completely removed before making any electrical measurements. The VT shift caused by bias stress can quickly recover and yield test results that underestimate the effect of the applied stress. A full recovery of VT was observed following a positive gate bias stress for conditions where the gate was either subject to a negative gate voltage for a few seconds, or when VGS was maintained at zero volts for several minutes.
Accurate Doping Density Determination in SiC with Constant Surface Potential Corona Charging; Industry Ready Alternative to Hg-CV
Authors: Savtchouk Alexandre , Wilson Marshall , Lagowski Jacek , Czett Andor , Buday Csaba
Published: May 2016

We present a refined non-contact doping density determination in silicon carbide that incorporates 3 novel features: (1) constant surface potential method of corona charging into depletion; (2) vibrating Kelvin probe measurement of depletion surface voltage and voltage compensation maintaining constant surface potential, and (3) a unique self-consistent procedure for data analysis. The results obtained on epitaxial SiC demonstrate up to 3 times improved accuracy and enhanced repeatability giving 1σ in 10 repeats of 0.05% and 0.1% for doping in e15cm-3 and e19cm-3 range, respectively. An enhanced charging range enables measurement of high doping density in the e19cm-3 range and to achieve larger depth in doping profiling. With these refinements, a non-contact doping metrology for SiC represents an industry ready alternative to Hg-CV.
A Surprising Result: “Bulk” SiC Defects in the Negative Bias Instability in 4H-SiC MOSFETs
Authors: Anders Mark A. , Lenahan Patrick M. , Lelis Aivars J.
Published: May 2016

We utilize electrically detected magnetic resonance and “on-the-fly” elevated temperature stressing to examine the effects of negative bias temperature stress on defects within the “bulk” SiC, that is, below the SiC/SiO2 interface. We observe generation of two temperature-dependent defects; one has a two (or three) line spectrum with lines separated by about 61 (30) Gauss when the SiC/SiO2 interface is perpendicular to the magnetic field and very slightly less, about 59 (30) Gauss when the SiC/SiO2 interface is parallel to the field. The second spectrum has a single line with zero-crossing g = 2.0118 when the magnetic field is nearly perpendicular to the SiC/SiO2 interface; the g-value drops to about 2.0016 with the field parallel to the SiC/SiO2 interface. We also observe strong evidence for hydrogen motion within the “bulk” SiC, as both spectra broaden significantly at elevated temperature, with broadening at both high and low fields and frequencies.