bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of TEDREC Phenomena for 4H-SiC Pin Diode with p/n Type Drift Layer
Authors: Nakayama Koji , Hemmi Tetsuro , Asano Katsunori
Published: March 2013

Temperature dependence simulations of forward characteristics for 4H-SiC pin diodes with Shockley-type stacking faults are performed in order to investigate the mechanism of the TEDREC phenomena. The forward voltage drops of both n-type and p-type drift layers at room temperature increase as the length of the Shockley-type stacking fault increases. When the diodes are compared to each other at the same temperature, the differences between the forward voltage drops do not change significantly up to 150 oC, but the differences suddenly narrow in the range from 150 °C to 200 °C. The Shockley-type stacking fault prevents current from flowing at room temperature. The current, however, flows throughout the drifted diode when the temperature is raised.
AlGaN/GaN Based HEMTs on SiC/Si-Substrates: Influences on High Frequency Performance
Authors: Jatal Wael , Tonisch Katja , Baumann Uwe , Schwierz Frank , Pezoldt Joerg
Published: March 2013

Al0.35Ga0.65N/GaN- and Al0.2Ga0.8N/AlN/GaN-heterostructures high electron mobility transistors (HEMTs) with a gate length (LG) varying from 1.2 to 0.08 µm were fabricated on silicon Si(111) substrates using a 3C-SiC transition layer. Metal organic chemical vapour deposition (MOCVD) was used to growth the AlGaN-heterostructures and a low pressure chemical vapour deposition (LPCVD) to create the 3C-SiC(111) transition layer preventing Ga-induced melt back etching and Si-out diffusion. Reduced Al content and an AlN interlayer improved the device performance. The HEMTs with LG=0.08µm had a maximum drain current density of 1.25 A/mm and a peak extrinsic transconductance of 400 mS/mm. A unity current gain cut-off frequency (ƒT) of 180 GHz and maximum frequency (ƒmax) of 70 GHz were measured on these devices.
1 MHz Resonant DC/DC-Converter Using 600 V Gallium Nitride (GaN) Power Transistors
Authors: Wienhausen Arne Hendrik , Kranzer Dirk
Published: March 2013

Gallium Nitride (GaN) is known to provide the opportunity of producing power transistors with remarkable electrical properties, such as low on-state resistance and low switching energies. This paper demonstrates how the use of GaN power transistors along with the possibility of raising the switching frequency can lead to a significant reduction of volume, weight and production costs of a power converter while maintaining high efficiency. A 1 kW resonant LLC converter using 600 V GaN power transistors is presented.
Optimising the Growth of Few-Layer Graphene on Silicon Carbide by Nickel Silicidation
Authors: Escobedo-Cousin Enrique , Vassilevski Konstantin , Hopf Toby , Wright Nick G. , O’Neill Anthony , Horsfall Alton B. , Goss Jonathan , Cumpson Peter
Published: March 2013

Few-layers graphene films (FLG) were grown by local solid phase epitaxy on a semi-insulating 6H-SiC substrate by annealing Ni films deposited on the Si and C-terminated faces of the SiC. The impact of the annealing process on the final quality of the FLG films is studied using Raman spectroscopy. X-ray photoelectron spectroscopy was used to verify the presence of graphene on the sample surface. We also demonstrate that further device fabrication steps such as dielectric deposition can be carried out without compromising the FLG films integrity.
Study of Carbonization Process on Surface of Si Substrate in High Vacuum Region with Hydrocarbon Gas
Authors: Watanabe Yukimune , Shinoda Keisuke , Tsukahara Masahiro , Shimada Hiroyuki , Furusawa Masahiro , Horikawa Tsuyoshi , Kamimura Kiichi
Published: March 2013

The formation mechanism of a carbonized layer was investigated under low-pressure and low-temperature process conditions. The initial carbonized layer under those conditions was formed epitaxially using the silicon atoms sublimated from substrate and the carbon atoms of the gas source. This result is suggested from the consideration of pit formation mechanism at the Si/SiC interface. After the initial layer was formed, the carbonized layer grew by the diffusion process of the carbon atoms through the crystal defects in the initially formed layer. This is suggested from that the thickness of the carbonized layer increases linearly with the square root of the process time. The growth rate seemed to be determined by the concentration of carbon atoms taken into the SiC.
Surface Preparation of 4° Off-Axis 4H-SiC Substrate for Epitaxial Growth
Authors: Li Xun , Hassan Jawad , Kordina Olof , Janzén Erik , Henry Anne
Published: March 2013

Results of surface preparation on Si-face 4° off-cut 4H-SiC substrates are presented in this paper. The influences of two types of etchants, i.e. hydrogen chloride (HCl) and only hydrogen (H2), were investigated by Nomarski microscopy and AFM. The experiments were performed in a hot wall CVD reactor using a TaC coated susceptor. Four etching temperatures, including 1580 °C, 1600 °C, 1620 °C and 1640 °C, were studied. In-situ etching with only H2 as ambient atmosphere is found to be the optimal way for the SiC surface preparation. Using HCl at temperature higher than 1620 °C could degrade the substrates surface quality.
Study of the Effects of Growth Rate, Miscut Direction and Postgrowth Argon Annealing on the Surface Morphology of Homoepitaxially Grown 4H Silicon Carbide Films
Authors: Camarda Massimo , Canino Andrea , Fiorenza Patrick , Severino Andrea , Anzalone Ruggero , Privitera Stefania , La Magna Antonino , La Via Francesco , Vecchio Carmelo , Mauceri Marco , Litrico Grazia , Pecora Antonino , Crippa Danilo
Published: March 2013

we study the surface morphology of homoepitaxially grown 4H silicon carbide in terms of growth rate, miscut direction of the substrate and post growth argon thermal annealings. All the results indicate that the final surface morphology is the result of a competition between energetic reorganization and kinetic randomness. Because in all observed conditions energetic reorganization favors surface ondulations (“step bunching”), out-of-equilibrium conditions are one of the keys to favor the reduction of the surface roughness to values below ~0.5 nm. We theoretically support these results using kinetics superlattice Monte Carlo simulations (KslMC)
Growth Rate and Surface Morphology of 4H-SiC Single Crystal Grown under Various Supersaturations Using Si-C Solution
Authors: Komatsu Naoyoshi , Mitani Takeshi , Takahashi Tetsuo , Okamura Masayuki , Kato Tomohisa , Okumura Hajime
Published: March 2013

We have investigated growth rate and surface morphology of 4H-SiC single crystal grown from Si-C solution with various supersaturation levels at growth temperature in the range from 1840 to 2140 °C. The growth rate depends linearly on the amount of supersaturated carbon, irrespective of the growth temperature. This indicates that the growth is limited by the transfer of solute element onto the crystallization front. The adequate condition for stable solution growth are discussed with respect to high growth rate and surface morphology.
Amorphous Silicon Carbide Film Formation at Room Temperature by Monomethylsilane Gas
Authors: Habuka Hitoshi , Tsuji Masaki , Ando Yusuke
Published: March 2013

The silicon carbide thin film formation process, completely performed at room temperature, was developed by argon plasma and a chemical vapor deposition using monomethylsilane gas. Silicon-carbon bonds were found to exist in the obtained film, the surface of which could remain specular after exposure to hydrogen chloride gas at 800 oC. The silicon dangling bonds formed at the silicon surface by the argon plasma are considered to react with the monomethylsilane molecules at room temperature to produce the amorphous silicon carbide film.
Defect Revelation and Evaluation of 4H Silicon Carbide by Optimized Molten KOH Etching Method
Authors: Dong Lin , Zheng Liu , Liu Xing Fang , Zhang Feng , Yan Guo Guo , Li Xi Guang , Sun Guo Sheng , Wang Zhan Guo
Published: March 2013

We have studied the defects on 4H-SiC substrates and epilayers by using molten KOH defect selective etching. It is found that adding Na2O2 into molten KOH at the etched temperature enables the revelation of dislocations on n+ and semi-insulating substrates, whereas purely molten KOH is sufficient to obtain good etched pattern on p+ substrates. Related statistical data on dislocation densities of n+, p+ and semi-insulating substrates are also presented. The morphological defects commonly observed on the epilayers are finally investigated and it is shown that some important structural features can be revealed by molten KOH method.
Morphology Optimization of Very Thick 4H-SiC Epitaxial Layers
Authors: Yazdanfar Milan , Stenberg Pontus , Booker Ian D. , Ivanov Ivan.G , Pedersen Henrik , Kordina Olof , Janzén Erik
Published: March 2013

Epitaxial growth of about 200 µm thick, low doped 4H-SiC layers grown on n-type 8° off-axis Si-face substrates at growth rates around 100 µm/h has been done in order to realize thick epitaxial layers with excellent morphology suitable for high power devices. The study was done in a hot wall chemical vapor deposition reactor without rotation. The growth of such thick layers required favorable pre-growth conditions and in-situ etch. The growth of 190 µm thick, low doped epitaxial layers with excellent morphology was possible when the C/Si ratio was below 0.9. A low C/Si ratio and a favorable in-situ etch are shown to be the key parameters to achieve 190 µm thick epitaxial layers with excellent morphology.
3C-SiC Growth on (001) Si Substrates by Using a Multilayer Buffer
Authors: Canino Andrea , Severino Andrea , Piluso Nicolò , La Via Francesco , Privitera Stefania , Alberti Alessandra
Published: March 2013

3C-SiC shows encouraging physical properties for the development of low cost high power compatible silicon based technology. The fundamental capability of grown 3C-SiC on silicon substrates leads to the possibility of a full integration of Si based process technologies. This is the driving force for the efforts for development a high quality heteroepitaxial film. The fundamental issue is the reduction of defects and stress due to the lattice mismatch between the 3C-SiC epilayer and the Silicon substrate. In this paper we show a way to reduce macroscopic structural features and to enhance the material quality and the surface quality by simply using a process based on a multilayer (ML) buffer structure with n++ and n doping alternation. This process leads to an evident improvement of both surface roughness, morphology and crystal quality.
Heteroepitaxial Growth of 3C-SiC on Polar Faces of 6H-SiC Substrates, TEM Investigations
Authors: Lebedev Sergey P. , Lebedev Alexander A. , Sitnikova Alla A. , Kirilenko Demid A. , Seredova Natasha V. , Tregubova Alla S. , Scheglov Mikhail P.
Published: March 2013

Abstract Results of an epitaxial growth of 3C-SiC epilayers on Si (0001) and C(000¯1) faces of hexagonal 6H-SiC substrates are described. TEM study of grown layers as well as interface between cubic and hexagonal polytypes is presented. Difference between the layers on the Si and C faces are discussed.
Plasma Treatment of 3C-SiC Surfaces
Authors: Attolini Giovanni , Rotonda P.M. , Cornelissen C. , Mazzera Margherita , Bosi Matteo
Published: March 2013

Surfaces of cubic silicon carbide (3C-SiC), grown by vapour phase epitaxy with silane and propane as precursors, were treated with plasma to remove residual species deposited during the growth procedure and the sample cooling down, or due to atmospherical contamination. The impurity traces were investigated with optical absorption spectroscopy. No morphology changes due to the plasma exposure were observed.
Structural Characterization of 3C-SiC Grown Using Methyltrichlorosilane
Authors: Bosi Matteo , Attolini Giovanni , Pécz Béla , Zolnai Zsolt , Dobos László , Martínez Oscar , Jiang Liu Di , Taysir Salim
Published: March 2013

3C-SiC layers were grown on Si substrates using standard precursors (SiH4 and C3H8) and by adding methyl trichloro silane (MTS) to the gas phase, with growth temperatures between 1200 and 1300 °C. Characterization of the 3C-SiC layers shows that 3C-SiC grown with MTS has higher polycrystalline and amorphous content as well as lower residual stress.
p-Doped SiC Growth on Diamond Substrate by VLS Transport
Authors: Vo-Ha Arthur , Carole Davy , Lazar Mihai , Tournier Dominique , Cauwet François , Soulière Véronique , Planson Dominique , Brylinski Christian , Ferro Gabriel
Published: March 2013

This work deals with the study of the Selective Epitaxial Growth (SEG) of SiC using the Vapour-Liquid-Solid (VLS) transport on diamond (100) substrate with Al-Si as the liquid phase fed by propane. Morphology, structure and doping type of the SiC deposit were determined. Polycrystalline p-doped 3C-SiC was obtained during the growth. Study of the initial step of growth showed that SiC nucleation occurs without any propane addition but just through the interaction of liquid Al-Si and diamond via a dissolution/precipitation process. This explains the random nucleation and the polycrystalline growth. Despite this, preliminary electrical measurements show encouraging results.
Real-Time Observation of High Temperature Interface between SiC Substrate and Solution during Dissolution of SiC
Authors: Kawanishi Sakiko , Yoshikawa Takeshi , Morita Kazuki
Published: March 2013

Precise morphological control of the interface between SiC and solution during the solution growth of SiC is crucial for obtaining high quality crystals with fewer defects and less step bunching. In this paper, a new technique for real-time observation of the high temperature interface between SiC and solution through the back surface of SiC was developed by focusing on the “wide” bandgap of SiC. Real-time observation of the interface during dissolution of SiC into an Fe-Si solvent alloy was carried out using a digital microscope, and the submicron-height structure of the solid-liquid interface was clearly observed at up to 1773 K. Interface morphologies, such as numerous hexagonal pits which were present at the initial stage of dissolution, followed by preferential dissolution in the lateral direction, were observed.
An Extended EDMR Setup for SiC Defect Characterization
Authors: Gruber Gernot , Koch Markus , Pobegen Gregor , Nelhiebel Michael , Hadley Peter
Published: March 2013

Only a few methods exist to observe, identify, and localize defects in SiC devices. These defects are a major limit for device performance and reliability. Presented is an improved experimental setup to investigate deep level defects using electrically detected magnetic resonance (EDMR). The method applied in this study exploits the simultaneous in-situ electron spin resonance (ESR) measurement of a standard sample (DPPH) to calibrate the magnetic field. The functionality is shown by comparing the data of an ion implanted SiC diode to results from a recent study . The in-situ B-field calibration is found to increase the accuracy of EDMR measurements by a factor of 2.5.
Deep Levels in P-Type 4H-SiC Induced by Low-Energy Electron Irradiation
Authors: Yoshihara Kazuki , Kato Masashi , Ichimura Masaya , Hatayama Tomoaki , Ohshima Takeshi
Published: March 2013

We have characterized deep levels in as-grown and electron irradiated p-type 4H-SiC epitaxial layers by the current deep-level transient spectroscopy (I-DLTS) method. A part of the samples were irradiated with electrons in order to introduce defects. As a result, we found that electron irradiation to p-type 4H-SiC created complex defects including carbon vacancy or interstitial. Moreover, we found that observed deep levels are different between before and after annealing, and thus annealing may change structures of defects.
Diffusion Study of Chlorine in SiC by First Principles Calculations
Authors: Alfieri Giovanni , Kimoto Tsunenobu
Published: March 2013

Using first-principles calculations, we investigated the migration mechanisms of Cl in cubic SiC. The analysis of the formation energies of several defect configurations (isolated interstitials and complex defects), either reported in the literature or calculated in the present study, revealed that three migration mechanisms are possible: Interstitialcy and two different vacancy-mediated mechanisms (both concerted exchange and second-neighbor hop). Our calculations showed that vacancy-mediated diffusion is more energetically favorable than an intersticialcy one and the values of the diffusivity, for both n-type and p-type SiC were also estimated.
Electron Paramagnetic Resonance Studies of Nb in 6H-SiC
Authors: Trinh Xuan Thang , Gällström Andreas , Son Nguyen Tien , Leone Stefano , Kordina Olle , Janzén Erik
Published: March 2013

Defects in unintentionally Nb-doped 6H-SiC grown by high-temperature chemical vapor deposition were studied by electron paramagnetic resonance (EPR). An EPR spectrum with a hyperfine (hf) structure consisting of ten equal-intensity lines was observed. The hf structure is identified to be due to the hf interaction between an electron spin S=1/2 and a nuclear spin of 93Nb. The hf interaction due to the interaction three nearest Si neighbors was also observed, suggesting the involvement of the C vacancy (VC) in the defect. Only one EPR spectrum was observed in 6H-SiC polytype. The obtained spin-Hamiltonian parameters are similar to that of the Nb-related EPR defect in 4H-SiC, suggesting that the EPR center in 6H-SiC is the NbSiVC complex in the neutral charge state, NbSiVC0. Photoexcitation EPR experiments suggest that the single negative charge state of the NbSiVC complex is located at ~1.3 eV below the conduction band minimum.
EPR Study of the Nitrogen Containing Defect Center Created in Self-Assembled 6H SiC Nanostructure
Authors: Kalabukhova Ekaterina N. , Savchenko Dariya , Shanina Bela , Bagraev Nikolai T. , Klyachkin Leonid , Malyarenko Anna
Published: March 2013

Triplet center with spin state S = 1 is detected in the EPR spectrum of the self-assembled 6H SiC nanostructure obtained by non-equilibrium boron diffusion into the n-type 6H SiC epitaxial layer (EL) under conditions of the controlled injection of the silicon vacancies at the temperature of T = 900°C. From the analysis of the angular dependences of the EPR spectrum and the numerical diagonalization of the spin Hamiltonian, the value of the zero-field splitting constant D and g-factor are found to be D = 1140•10-4см-1 and gpar = 1.9700, gper = 1.9964. Based on the hyperfine (hf) structure of the defect originating from the hf interaction with one 14N nuclei, the large value of the zero-field splitting constant D and technological conditions of the boron diffusion into the n-type 6H SiC EL, the triplet center is tentatively assigned to the defect center consisting of nitrogen atom and silicon vacancy.
Kinetic Monte Carlo Simulation of Impurity Effects on Nucleation and Growth of SiC Clusters on Si(100)
Authors: Lubov Maxim N. , Pezoldt Joerg , Trushin Yuri V.
Published: March 2013

The influence of attractive and repulsive impurities on the nucleation process of the SiC clusters on Si(100) surface was investigated. Kinetic Monte Carlo simulations of the SiC clusters growth show that that increase of the impurity concentration (both attractive and repulsive) leads to decrease of the mean cluster size and rise of the nucleation density of the clusters.
On Peculiarities of Defect Formation in 6Н-SiC Bulk Single Crystals Grown by PVT Method
Authors: Emelchenko Gennadi A. , Zhokhov Andrey A. , Tartakovskii Ilya I. , Maksimov Andrey A. , Steinman Edward A.
Published: March 2013

The structural defects in the single 6H-SiC crystals grown by the PVT method have been studied by the scanning electron microscopy, Raman scattering and photoluminescence techniques. The formation mechanism of the defects, micropipes and parasitic polytypes 4H and 15R, observed in the single 6H-SiC crystal has been proposed.
The Formation of New Periodicities after N-Implantation in 4H- and 6H-SiC Samples
Authors: Zekentes Konstantinos , Tsagaraki Katerina , Breza Aikaterini , Frangis Nikolaos
Published: March 2013

The purpose of the present study is to study the crystal periodicities that appear in 4H- and 6H-SiC material after the implantation with nitrogen and prior to post-implantation annealing. High Resolution X-Ray diffraction (HRXRD) and Transmission Electron Microscopy (TEM) have been employed towards this purpose. Extra peaks at smaller, than the main (00n) peak, diffraction angles in HRXRD scans and extra spots in the electron diffraction patterns have been observed due to the presence of these periodicities. Higher lattice constant periodic structures are apparently formed from the implanted nitrogen ions located at interstitial sites and disappear after the annealing and the resulting positioning of nitrogen atoms in substitutional sites.
A Comparison of Free Carrier Absorption and Capacitance Voltage Methods for Interface Trap Measurements
Authors: Suvanam Sethu Saveda , Usman M. , Gulbinas K. , Grivickas V. , Hallén Anders
Published: March 2013

This paper aims to establish a new method to characterize the interface between 4H-SiC and passivating dielectric layers. The investigations are made on MOS test structures utilizing Al2O3 and SiO2 dielectrics on 4H-SiC. These devices are then exposed to various fluences of Ar+ implantation and then measured by the new method utilizing optical free carrier absorption (FCA) technique to assess the interface traps. A program has been developed using MATLAB to extract surface recombination velocity (SRV) at the oxide/epi-layer interface from the optical data. Capacitance-voltage (CV) is done to extract the density of interface traps (Dit) and a comparison was made. It is observed that SiO2 samples show a large rise of SRVs, from 0.5×104 cm/s for a reference sample to 8×104 cm/s for a fluence of 1×1012 cm-2, whereas Al2O3 samples show more stable SRV, changing from 3×104 cm/s for the un-irradiated reference sample to 6×104 cm/s for a fluence of 1×1012 cm-2. A very similar trend is observed for Dit values extracted from CV measurements and it can therefore be concluded that the FCA method is a suitable technique for the interface characterization.
Study of Terminated Species on 4H-SiC (0001) Surfaces Planarized by Catalyst-Referred Etching
Authors: Bui Pho Van , Sadakuni Shun , Okamoto Takeshi , Arima Kenta , Sano Yasuhisa , Yamauchi Kazuto
Published: March 2013

Our group has developed a novel abrasive-free planarization technique known as catalyst-referred etching (CARE). It can produce flat, undamaged, and smooth SiC surfaces with a root-mean-square roughness of less than 0.1 nm over a whole wafer. This study investigates the etching mechanism of CARE by performing X-ray photoelectron spectroscopy (XPS) measurements to determine the termination species of CARE-processed SiC surfaces. We compared XPS spectra of a CARE-processed surface with those of an as-received SiC surface that had been treated with 50% HF solution. XPS spectra of the CARE-processed wafer contain the F 1s core level, whereas those of an as-received SiC wafer surface did not. This indicates that F anions play an important role in the etching process of CARE.
Electrical Impact of the Aluminum P-Implant Annealing on Lateral MOSFET Transistors on 4H-SiC N-Epi
Authors: Noll Stefan , Scholten Dick , Grieb Michael , Bauer Anton J. , Frey Lothar
Published: March 2013

In this work we investigate the effect of the aluminum p-well implant annealing process on the electrical properties of lateral 4H-SiC MOSFET transistors. The interface trap concentration was measured by quasi-static capacitive voltage (QSCV) and negative bias stress measurements on MOSFETs. We found that higher annealing temperatures significantly reduce the trap density in the lower bandgap, and as a consequence the threshold voltage drift of the transistor after negative stress is reduced.
Edge Termination Design Improvements for 10 kV 4H-SiC Bipolar Diodes
Authors: Nguyen Duy Minh , Huang Runhua , Phung Luong Viet , Planson Dominique , Berthou Maxime , Godignon Philippe , Vergne Bertrand , Brosselard Pierre
Published: March 2013

10 kV class 4H-SiC bipolar diodes have been fabricated. Two different edge terminations (Mesa/JTE or MESA/JTE with JTE rings) with two different junction bend radius have been designed and tested. Measurement results show that the inclusion of JTE rings improve the edge termination efficiency. The measurements indicate also a better reverse performance of diodes with larger bend radius.
Formation of Epitaxial Defects by Threading Screw Dislocations with a Morphological Feature at the Surface of 4º Off-Axis 4H-SiC Substrates
Authors: Aigo Takashi , Ito Wataru , Tsuge Hiroshi , Yashiro Hirokatsu , Katsuno Masakazu , Fujimoto Tatsuo , Yano Takayuki
Published: March 2013

In this paper, we present the formation of extended epitaxial defects, such as carrot defects, from threading screw dislocations (TSDs) with a morphological feature at the surface of the substrates. It was confirmed using highly sensitive surface observation, atomic force microscopy (AFM) and KOH etching that the surface roughness around a TSD was observed as the morphological feature and TSDs with such a morphological feature formed extended epitaxial defects with high frequency of appearance compared to usual TSDs without any features. The density of TSDs with such morphological feature depended on the polishing methods. Furthermore, we observed that the formation and shapes of extended defects from TSDs with such morphological feature were affected by step-bunching at the surface of the epilayers.
Laplace Transform Deep Level Transient Spectroscopy Study of the EH6/7 Center
Authors: Alfieri Giovanni , Kimoto Tsunenobu
Published: March 2013

We employed Laplace transform deep level transient spectroscopy (LDLTS) for the resolution of the EH6/7 center in n-type 4H-SiC epilayers. Our results suggest that this technique is effective in separating the emission rates of the EH6 and EH7 levels. From the Arrhenius dependence of the emission rates we could estimate the energy position of EH6 and EH7 as 1.39 and 1.49 eV below the minimum of the conduction band edge, respectively. Generation of of EH6 and EH7 centers by low-energy electron irradiation (dose dependence) was also investigated. At last, a double pulse Laplace DLTS is performed in order to show the electric filed dependence of the emission rates of EH6 and EH7.
Origin Analyses of Obtuse Triangular Defects in 4deg.-Off 4H-SiC Epitaxial Wafers by Electron Microscopy and by Synchrotron X-Ray Topography
Authors: Yamashita T. , Matsuhata H. , Miyasaka Y. , Ohshima H. , Sekine M. , Momose K. , Sato T. , Kitabatake M.
Published: March 2013

Triangular shaped defects with obtuse-angles at tops and long bases are often observed in surfaces of epitaxial films. We have investigated the origins of them, and it became clear that these defects without clear origins were formed by contaminations of tantalum carbide particles. Formations of micro-order pipes at the origin points of these defects were also observed. These micro-order pipes did not accompany strain and dislocations around them, though their appearances were very similar to the ones so-called micro-pipes.
Characterization of Diverse Gate Oxides on 4H-SiC 3D Trench-MOS Structures
Authors: Banzhaf Christian T. , Grieb Michael , Trautmann Achim , Bauer Anton J. , Frey Lothar
Published: March 2013

This study focuses on the characterization of silicon dioxide (SiO2) layers, either thermally grown or deposited on trenched 100 mm 4H-silicon carbide (SiC) wafers. We evaluate the electrical properties of silicon dioxide as a gate oxide (GOX) for 3D metal oxide semiconductor (MOS) devices, such as Trench-MOSFETs. Interface state densities (DIT) of 1*1011 cm-2 eV-1 under flat band conditions were determined using the hi-lo CV-method [1]. Furthermore, current-electric field strength (IE) measurements have been performed and are discussed. Trench-MOS structures exhibited dielectric breakdown field strengths up to 10 MV/cm.
Effects of a Post-Oxidation Annealing in Nitrous Oxide on the Morphological and Electrical Properties of SiO2/4H-SiC Interfaces
Authors: Swanson Lukas K. , Fiorenza Patrick , Giannazzo Filippo , Roccaforte Fabrizio
Published: March 2013

This work reports on the morphological, structural and electrical effects of a nitrous oxide (N2O) ambient post-oxidation annealing (POA) of the SiO2/4H-SiC interface. In particular, a conventional electrical characterization of MOS capacitors showed that nitrous oxide POA reduces the presence of both fixed oxide charge and the density of interface states. A local atomically flat interface was observed by transmission electron microscopy with only a moderate step bunching observed at a macroscopic scale. A novel nanoscale characterization approach via scanning spreading resistance microscopy resolved local electrical changes induced at the SiC surface exposed to N2O POA. This result subsequently revealed additional insight into the mechanism for the improved device performance subjected to N2O POA treatment.
The Effect of Modified Crucible Design and Seed Attachment on SiC Crystal Grown by PVT
Authors: Jung Jung Young , Lee Sang Il , Park Mi Seon , Lee Doe Hyung , Lee Hee Tae , Lee Won Jae , Hong Soon Ku , Chun Myong Chuel
Published: March 2013

The present research was focused to investigate the effect of internal crucible design that influenced the 4H-SiC crystal growth onto a 6H-SiC seed by PVT method. The crucible design was modified to produce a uniform radial temperature gradient in the growth cell. The seed attachment was also modified with a use of polycrystalline SiC plate. The crystal quality of 4H-SiC single crystals grown in modified crucible and grown with modified seed attachment was revealed to be better than that of crystal grown in conventional crucible. The full width at half maximum (FWHM) values of grown SiC crystals in the conventional crucible, the modified seed attachment and the modified crucible were 285 arcsec, 134 arcsec and 128 arcsec, respectively. The micropipe density (MPD) of grown SiC crystals in the conventional crucible, the modified seed attachment and the modified crucible were 101ea/cm^2, 81ea/cm^2 and 42ea/cm^2, respectively.
Sublimation Growth of AlN and GaN Bulk Crystals on SiC Seeds
Authors: Mokhov E.N. , Wolfson A.A. , Helava H. , Makarov Yuri
Published: March 2013

Growth techniques of high quality AlN and GaN bulk crystals on SiC seeds by sublimation sandwich method are presented. GaN crystals were grown in the temperature range of 1100-1250 °C and with addition of ammonia (NH3) to prevent GaN decomposition. GaN powder or metallic Ga was used as the source. AlN crystals up to 2 inch diameter have been grown on SiC seeds in the temperature range of 1950 -2050 0С. Kinetic mechanisms and transport features in the sandwich cell are discussed. The achieved high crystal quality has allowed producing semiconductor devices on their basis, in particular, ultraviolet LEDs
ICP Etching of 4H-SiC Substrates
Authors: Biscarrat Jerome , Michaud Jean François , Collard Emmanuel , Alquier Daniel
Published: March 2013

Due to its inert chemical nature, plasma etching is the most effective technique to pattern SiC. In this paper, dry etching of 4H-SiC substrate in Inductively Coupled Plasma (ICP) has been studied in order to evaluate the impact of process parameters on the characteristics of etching such as etch rate and trenching effect. Key process parameters such as platen power and ICP coil power prove to be essential to control the SiC etch rate. On the other hand, the ICP coil power and the working pressure mainly master the trenching effect. Our results enlighten that high etch rate with minimal trenching effect can be obtained using high ICP coil power and low working pressure.
Pressureless Silver Sintering Die-Attach for SiC Power Devices
Authors: Hascoët Stanislas , Buttay Cyril , Planson Dominique , Chiriac Rodica , Masson Amandine
Published: March 2013

Pressureless silver sintering is an interesting die-attach technique that could overcome the reliability limitations of the power electronic devices caused by their packaging. In this paper, we study the manufacturing parameters that affect the die attach: atmosphere, drying time, heating ramp rate, sintering temperature and duration. It is found that sintering under air gives better results, but causes the substrates to oxidize. Sintering under nitrogen keeps the surfaces oxide-free, at the cost of a weaker attach.
Solar-to-Hydrogen Conversion Efficiency of Water Photolysis with Epitaxially Grown p-Type SiC
Authors: Yasuda Tomonari , Kato Masashi , Ichimura Masaya , Hatayama Tomoaki
Published: March 2013

Solar-to-hydrogen conversion efficiencies of water photolysis with epitaxially grown p-type 4H-, 6H- and 3C-SiC were estimated in the two electrode system. For all the polytypes, the efficiency with a Pt counter electrode in the two electrode system was very low compared with those in the three electrode system. However, when Ni was used as a counter electrode in the two electrode system, photocurrents were as large as the three electrode system. The estimated efficiencies seem to depend on the bandgap of SiC polytypes, and the highest solar-to-hydrogen conversion efficiency was 0.38% with 3C-SiC.
Remarkable Increase in Surge Current Capability of SiC Schottky Diodes Using Press Pack Contacts
Authors: Banu Viorel , Godignon Philippe , Jordá Xavier , Perpinya Xavier , Millan José
Published: March 2013

This work presents experimental results on surge current capability of SiC Schottky diodes performed on free floating press-pack encapsulation technologies. For the tests, we used a home-made workbench. The aim of our studies is to improve the current robustness and power density of Silicon Carbide (SiC) devices able to operate at temperatures over 300C°. Various technological approaches have to be considered, mainly on the interconnection technique and metallization layers in order to improve the power density and temperature operation of the diodes. Our investigation showed a strong improvement of electro-thermal performances, and especially the surge current capability that is almost doubled by using press-pack encapsulation.
Reverse Leakage Currents in High-Voltage 4H-SiC Schottky Diodes
Authors: Ivanov Pavel A. , Grekhov Igor V. , Potapov Alexander S. , Il'inskaya Natalya D. , Kon'kov Oleg I. , Samsonova Tatyana P.
Published: March 2013

High-voltage 4H-SiC Schottky Barrier Diodes (SBDs) and Junction Barrier Schottky (JBS) diodes have been fabricated and evaluated. Current-voltage (I-V) characteristics were measured in a wide temperature range. All diodes fabricated showed nearly ideal forward behavior. For SBDs with Schottky Barrier Height (SBH) of 1.12 eV, the reverse I–V characteristics are described well by the thermionic emission model (at voltages varying from several mV to 2 kV and temperatures ranging from 361 to 470 K) if barrier lowering with increasing band bending is taken into account. For SBDs with SBH of 1.53 eV, no thermionic current was detected in reverse direction at temperatures below ~500 K. The leakage currents appeared only at high reverse voltages and elevated temperatures. The analysis of reverse I-V characteristics allowed to propose dislocation related mechanism of current flow due to the local injection of electrons from metal to semiconductor. It is shown that defect related leakage currents can be significantly reduced by JBS-structure.
On-State and Switching Performance Comparison of A 600 V-Class Hybrid SiC JFET and Si Superjunction MOSFETs
Authors: Tamaki Tomohiro , Ishida Shinya , Tomizawa Yoshikazu , Nakamura Hiroyuki , Shirai Yasuhiro , Akiyama Satoru , Shimizu Haruka , Yokoyama Natsuki
Published: March 2013

We compare the on-state and switching performance of a 600 V-class Hybrid SiC junction field effect transistor (HJT) and Si superjunction MOSFETs (SJ-MOSs), both of which are packaged in TO-3P full-mold package, as a function of operating frequency. The maximum load current is limited by the package power dissipation rating determined by the maximum junction temperature. Since the HJT is composed of a SiC JFET and a low voltage Si MOSFET, the allowable maximum junction temperature of the HJT is the same as that of SJ-MOSFETs, namely 150 °C. The experimental results show that the maximum operating current of the HJT is comparable to that of SJ-MOSs, but the EMI noise of the HJT is much suppressed due to lower dV/dt.
Experimental Study of Short-Circuit Capability of Normally-off SiC-BGSITs
Authors: Takatsuka Akio , Tanaka Yasunori , Yano Koji , Yatsuo Tsutomu , Arai Kazuo
Published: March 2013

We investigated the short-circuit capabilities of 1.2 kV normally-off SiC buried gate static induction transistors (SiC-BGSITs). The maximum short-circuit energy was found to be 35.6 J/cm2, which is twice that of normally-on SiC-BGSITs and 3.3–5.6 times higher than that of the Si-IGBTs. The maximum short-circuit time was 590 μs. It is concluded that these high short-circuit capabilities result from saturation characteristics of the normally-off SiC-BGSITs.
15 kV, Large Area (1 cm2), 4H-SiC p-Type Gate Turn-Off Thyristors
Authors: Cheng Lin , Agarwal Anant K. , Capell Craig , O'Loughlin Michael J. , Lam Khiem , Zhang Jon , Richmond Jim , Burk Albert A. , Palmour John W. , Ogunniyi Aderinto , O’Brien Heather , Scozzie Charles
Published: March 2013

In this paper, we report our recently developed 1 cm2, 15 kV SiC p-GTO with an extremely low differential on-resistance (RON,diff) of 4.08 mΩ•cm2 at a high injection-current density (JAK) of 600 ~ 710 A/cm2. The 15 kV SiC p-GTO was built on a 120 μm, 2×1014/cm3 doped p-type SiC drift layer with a device active area of 0.521 cm2. Forward conduction of the 15 kV SiC p-GTO was characterized at 20°C and 200°C. Over this temperature range, the RON,diff at JAK of 600 ~ 710 A/cm2 decreased from 4.08 mΩ•cm2 at 20°C to 3.45 mΩ•cm2 at JAK of 600 ~ 680 A/cm2 at 200°C. The gate to cathode blocking voltage (VGK) was measured using a customized high-voltage test set-up. The leakage current at a VGK of 15 kV were measured 0.25 µA and 0.41 µA at 20°C and 200°C respectively.
Preparation and Characterization TiO2 Aerogel Fibers
Authors: Lv Miao , Qin Guo Tong , Wei Wei
Published: March 2013

TiO2 aerogel fibers have been fabricated by electron span combined supercritical drying technique. Polyvinylpyrrolidone (PVP)/TiO2 composite fibers are prepared by electrospinning PVP and TiO2 precursor Ti (OC4H9)4. TiO2 aerogel fibers are obtained by supercritical drying PVP/TiO2 composite fibers using ethanol as media. Structural of the aerogel fibers was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and N2 adsorption at 77 K. The effect of mass ratio of PVP/TiO2 was investigated. SEM shows that pore structure of nanofibers was well developed, with the diameter of nanofibers about 2 μm. N2 adsorption/desorption data show that the highest surface area of aerogel fibers reached 241.6 m2/g with the average pore diameter about 10 nm. The aerogel fibers were anatase type TiO2.
Preparation of Persimmon Tannins Immobilized on Collagen Adsorbent and Research on its Adsorption to Cr(VI)
Authors: Cui Jian , Wang Zhong Min , Liu Feng Lei , Dai Pei Bang , Chen Ran , Zhou Huai Ying
Published: March 2013

Persimmon tannins (PT) were immobilized on a matrix of collagen fiber by cross-linking of glutaraldehyde. The adsorption behaviours to Cr (VI) on PT were investigated including the effects of initial pH, initial concentration of Cr (VI), temperature, adsorbent dosage, adsorption kinetics and the recycling performance of PT adsorbents. The results showed that pH value had a major influence in adsorption. PT showed a strong adsorbability to Cr (VI) in the pH range of 1.0 to 3.0, whereas the effect of temperature on the adsorption was comparatively weaker. The adsorption equilibrium could be well described by Freundlich equation. PT adsorption efficiency of Cr (VI) reached 98.04% and the maximum equilibrium adsorption capacity of Cr (VI) was up to 49.01 mg/g at 303 K with a pH value of 2.0, 100 mg/L of initial concentration of Cr (VI) and 0.1g of adsorbent dosage. The adsorption data could be well fitted by pseudo-second-order rate model. PT adsorbents were characterized by FTIR and EDS. The analysis indicated that the adsorption mechanism was mainly contributed by redox adsorption.
Synthesis, Microstructure, and Dielectric Properties of Mn-Doped 0.33BaTiO3-0.67BiFeO3 Multiferroic Solid Solutions
Authors: Hang Qi Ming , Shan Feng , Zhu Jian Min , Zhu Xin Hua
Published: March 2013

In this work, 0.33BaTiO3-0.67BiFeO3 multiferroic ceramics doped with x mol% MnO2 (x= 0.1-1.0) were fabricated by solid-state reaction method, and their microstructure and dielectric property were also investigated. The perovskite phase structure of the solid solutions was confirmed by X-ray diffraction patterns, and the formation of minor impure phase of Bi2Fe4O9 was prevent effectively by Mn-doping. With increasing the Mn-doped concentration, the dielectric constants of Mn-doped 0.33BaTiO3-0.67BiFeO3 multiferroic ceramics first increased, and reached a maximum value of 340 (measured @1MHz) at the Mn-doped concentration of 0.60 mol%, and then decreased. On the other hand, the dielectric losses first decreased, and reached the minimum value at the Mn-doped concentration of 0.30 mol%, and then increased along with increasing the Mn-doped concentrations. The ferroelectric domain structures in the Mn-doped 0.33BaTiO3 - 0.67BiFeO3 multiferroic ceramics with rhombohedral symmetry were also revealed by TEM image and selected area electron diffraction patterns, and tweed-like domain structures were observed.
A Device for Measuring High-TC Superconductor Transition Temperature with Electric Transport and AC Susceptibility Methods Based on Small Cryocooler Cooling
Authors: Wang San Sheng , Ning Xiao Shuai , Chu Xiang Hua , Li Hua
Published: March 2013

A device for measuring high-TC superconducting transition temperature in a small cryocooler is described which allows a samples temperature to fall steadily from room temperature to 45K. This cryocooler not only meets the high-TC superconductors measurement requirements, but also yields accurate measurement results under ambient conditions. In this device, two measurement methods for measuring high-TC superconducting transition temperature are applied: the electric transport and the AC susceptibility. The former adopts a four-wire method to eliminate the contact resistance between the leads and the sample. During the measurement process the current reversal method for datum processing is applied to eliminate the thermoelectric voltages; this ensures the repeatability error less than 0.4K in the measurement of the superconducting transition temperature. The AC susceptibility method adopts a lock-in amplifier to provide an AC voltage signal for the primary coil, and then lock-in amplifier is used to measure the electrical signals of the secondary coil according to the AC magnetic susceptibility values. The advantage of this device is that by merely changing the position of the sample in the vacuum chamber, the R-T curve and the χ-T curve of a superconducting sample in the same temperature range can be automatically recorded, which provides reliable data for high-TC superconductor transition curve measurement.
Degradation of Porosity and Enhanced Critical Current Density in MgB2 with a Toluene-Treatment Boron Powder
Authors: Pan Xi Feng , Yan Guo , Liu Xiang Hong , Feng Yong , Zhang Ping Xiang , Zhao Yong , Mastumoto Akiyoshi , Kumakura Hiroshi
Published: March 2013

A series of MgB2 bulks with different porosity have been successfully prepared by in-situ solid-state reaction at ambient pressure with a toluene-treatment boron powder. The mass density reaches 1.86 g cm-3 at the most compact MgB2 bulk, which has an imporous microstructure, excellent grains coupling, clean grain boundaries and nanosized grains (100~200 nm). Our results reveal that the porosity of MgB2 can be significantly depressed by tuning the residual toluene content and heat treatment temperature in this way. Due to the degradation of porosity and thus the enhancement on grains connectivity and grains boundary pinning, the critical current density, Jc and irreversible fields Birr of MgB2 are significantly improved. For the best sample, at 20K, 4T and 10K, 6T, the Jc reach 2400 and 3700 A cm-2, which is higher than normal porous sample by a factor of 20 and 8, respectively; and the Birr at 20 K reaches 5.10 T.
Influence of Repeated Tensile Stress on Determining the Critical Tensile Stress/Strain of Copper Reinforced Bi-2223/Ag Tapes
Authors: Jing Li Wei , Zhang Guo Min , Li Jin Cheng , Wu Xin , Liu Qi
Published: March 2013

Critical stress/strain is an important parameter to describe the transport property of superconductors under mechanical stress. The critical stress/strain of specified superconductor should be gotten before the superconductor is applied to manufacture devices. Determination of the critical stress/strain of specified superconductor is related to the chosen reduction percentage of the critical current under monotonic mechanical stress. However, in practical applications, superconductor also withstands repetitive mechanical stresses. Therefore, the influence of repetitive mechanical stress on the critical current or N value should be considered when the critical stress/strain of the superconductor is determined. Therefore, in this paper, the electrical transport property of copper reinforced Bi-2223/Ag tapes under both monotonic and repetitive tensile stress was studied theoretically and experimentally. Based on analysis of the change of critical current and N value under monotonic and different repetitive tensile stresses, the critical stress and strain of this superconductor tape were proposed.
Effect of Sintering Conditions on the Phase Formation and Microstructure of Bi-2223/Ag/Ni Composite-Sheathed Tapes
Authors: Chen Xing Pin , Liu Meng , Yu Xiao Wei , Li Ming Ya
Published: March 2013

Effect of sintering conditions in the first heat treatment on the phase and microstructure evolution of Bi-2223/Ag/Ni composite-sheathed tapes fabricated by powder-in-tube method was studied. Samples were sintered at different temperatures for different time in an atmosphere of 14.5% O2. The results showed that this higher O2 atmosphere improved the content of Bi-2223 phase. XRD and SEM results showed that Bi-2223 content increased with the extension of the dwelling time. Meanwhile, the sintering temperature had significant influence on the Bi-2223 content and secondary phase dimensions as well. With the increase of the sintering temperature, the Bi-2223 content reached to a maximum at 834. With further increase of sintering temperature, the Bi-2223 phase was decomposed to Bi-2212 and others secondary phases.
Preparing Ultrathin MgB2 Thin Film by Ex Situ Annealing of Mg-B Precursor Film
Authors: Dai Qian , Ma Ruo Run , Feng Qing Rong , Zhang Huai , Yang Qian Qian , Nie Rui Juan , Wang Fu Ren
Published: March 2013

Ultrathin MgB2 film is essential for the fabrication of MgB2 superconducting single photon detectors (SSPDs). In this paper, we prepared 20nm and 10nm MgB2 film using ex-situ annealing of Mg-B multilayer method. The precursor films were prepared by electron beam evaporation. A flowing Mg vapour and H2 was introduced in the annealing process to keep MgB2 thin film thermodynamically stable. The annealing temperature was between 680 and 740 and annealing time was 1-10min. 20nm MgB2 films on MgO(111) substrates had the critical temperature (Tc) of 32.2K. The films grew along c-axes direction. As the substrate changed to SiC(001) and Al2O3(001), Tc decreased to 30.3K and 10.2K respectively. For 10nm MgB2 film on SiC(001) substrate, Tc was 24.2K. The self-field critical current density for 10nm and 20nm film on SiC(001) substrate was 2.1×106A/cm2 and 2.3×106A/cm2, respectively. AFM image showed that the film had a flat surface with mean roughness of 0.899nm for 10nm MgB2 film.