bluuebunny/crossref_metadata_2025 huggingface dataset:
Graphene Layers on Silicon Carbide Studied by Raman Spectroscopy
Authors: Röhrl Jonas , Hundhausen Martin , Emtsev Konstantin V. , Seyller Thomas , Ley Lothar
Published: March 2009

We present a micro-Raman spectroscopy study on single- and few layer graphene (FLG)
grown on the silicon terminated surface of 6H-silicon carbide (SiC). On the basis of the 2D-line (light
scattering from two phonons close to the K-point in the Brillouin zone) we distinguish graphene
mono- from bilayers or few layer graphene. Monolayers have a 2D-line consisting of only one
component, whereas more than one component is observed for thicker graphene layers. Compared to
the graphite the monolayer graphene lines are shifted to higher frequencies. We tentatively ascribe the
corresponding phonon hardening to strain in the first graphene layer.
Dual-Pearson Approach to Model Ion-Implanted Al Concentration Profiles for High-Precision Design of High-Voltage 4H-SiC Power Devices
Authors: Mochizuki Kazuhiro , Onose Hidekatsu
Published: March 2009

We demonstrate a Dual-Pearson approach to model ion-implanted Al concentration
profiles in 4H-SiC for high-precision design of high-voltage power devices. Based on the Monte
Carlo simulated data for 35-400 keV implantation, we determine the nine Dual-Pearson parameters
and confirm precise reproduction of profiles of 1015-1021 cm-3 Al with sufficient smoothness. This
leads to a direct incorporation of implanted Al profiles into a device simulator. The influence of dose
and energy on channeling is also discussed from the view point of implantation-induced disorder in
4H-SiC.
Detection and Characterization of Defects Induced by Ion Implantation/Annealing Process in SiC
Authors: Nagano Masahiro , Tsuchida Hidekazu , Suzuki Takuma , Hatakeyama Tetsuo , Senzaki Junji , Fukuda Kenji
Published: March 2009

Defect formation during the ion-implantation/annealing process in 4H-SiC epilayers is
investigated by X-ray topography, KOH etching analysis and transmission electron microscopy.
Nitrogen and phosphorus ions are implanted in the 4H-SiC epilayers and then activation annealing is
performed at 1670 °C. Linearly arrayed or clustered extended defects are found to be formed during
the implantation/annealing process by comparing X-ray topography images taken before and after the
process. It is confirmed that the defect arrays are formed underneath a shallow groove on the surface
and consist of a high density of basal-plane Shockley-type stacking faults.
Compensation Effects in 7 MeV C Irradiated n-Doped 4H-SiC
Authors: Izzo Gaetano , Litrico Grazia , Calcagno Lucia , Foti Gaetano , La Via Francesco
Published: March 2009

The defects produced by irradiation with 7 MeV C+ induce a change in the electrical properties of
4H-SiC Schottky diodes. Capacitance-voltage and Current-voltage characteristics of the diodes
fabricated in epilayers doped with different nitrogen concentrations were monitored before and
after irradiation with different fluences. The Capacitance-voltage curves show free carrier
compensation after low fluence irradiation and it was found that the reduction of carriers per ion
induced vacancy increases with nitrogen content. The forward current-voltage characteristics of
the diodes show an increase in the series resistance after irradiation. This change is mainly related
to the high compensation occurring around the end of the ion range.
TEM Observation of SiO2/4H-SiC Hetero Interface
Authors: Matsuhata Hirofumi , Senzaki Junji , Nagai Ichiro , Yamaguchi Hirotaka
Published: March 2009

The SiO2/4H-SiC hetero-interface was observed using TEM in plan-view geometry. Local
roughening of the SiO2/4H-SiC hetero-interface accompanied with local generation of basal-plane
dislocations in SiC was observed. In some places, local variations in film thickness of SiO2 as well as
the presence of extra carbon and particle-like contrast asociated with the generation of basal-plane
dislocations in SiC was observed. The influence of these defect regions on MOSFET properties is
discussed.
Influence of Metallization Annealing on Channel Mobility in 4H-SiC MOSFET on Carbon Face
Authors: Harada Shinsuke , Kato Makoto , Yatsuo Tsutomu , Fukuda Kenji , Arai Kazuo
Published: March 2009

4H-SiC MOSFET on carbon face exhibits the high channel mobility when the gate oxide is
formed by pyrogenic wet oxidation. However, this improvement is not proof against the metallization
annealing which is indispensable in the fabrication of the SiC power MOSFETs. We develop the
alternative metallization process suitable for the high channel mobility on the carbon face. The
metallization annealing in hydrogen ambient has much effect to suppress the degradation of the
channel mobility. The lateral MOSFET with the ohmic contact formed by hydrogen annealing
exhibits the high channel mobility which is comparable to the channel mobility of the lateral
MOSFET formed without metallization annealing.
Electrically Detected Magnetic Resonance Studies of Processing Variations in 4H SiC Based MOSFETs
Authors: Cochrane Corey J. , Lenahan Patrick M. , Lelis Aivars J.
Published: March 2009

We apply electrically detected magnetic resonance (EDMR) to variously processed 4H
SiC MOSFETs from two vendors. Although, the EDMR line shapes observed are nearly the same
for vendor 1 devices subjected to a nitric oxide (NO) anneal and devices without it, the relationship
between EDMR and gate voltage differs greatly between these samples. Furthermore, the EDMR
response versus gate bias varies dramatically. EDMR results from a third device produced by a
second vendor are very different from those provided by the first vendor. This result implies that
significantly different defect populations are present in devices fabricated by different vendors.
The Preparation of World-Class Single Crystal Silicon Carbide Wafers Using High Rate Chemical Mechanical Planarization Slurries
Authors: White Michael L. , Reggie Stan , Naguib Nevin , Nicholson Kenneth , Gilliland Jeffrey , Walters Alicia
Published: March 2009

The influence of the chemical mechanical planarization process on the 4o off-axis 4HN
SiC removal rate for silicon carbide slurry produced by Cabot Microelectronics Corporation (CMC)
has been studied. A detailed kinetic analysis was applied and the linearity of an Arrhenius-like
activation energy plot suggests that the primary removal occurs from particles adhered to the pad
surface.
Novel Use of Columnar Porous Silicon Carbide Structures as Nanoimprint Lithography Stamps
Authors: Leach J.H. , Morkoç Hadis , Ke Yue , Devaty Robert P. , Choyke Wolfgang J.
Published: March 2009

Columnar porous Si-face 6H-SiC substrates were prepared by a photo-electrochemical etching
method and applied as nanoimprint lithography (NIL) stamps. The diameter of the pores in the
porous region was about 20 nm and the center-to-center separation between pores was about 60 nm.
The columnar porous SiC substrates were subjected to a vapor phase silanization treatment whereby
a monolayer of perfluorooctyltrichlorosilane (FOTS) was deposited in order to keep the stamps
from sticking to the substrates during the imprint step. Subsequently, the porous SiC stamps were
used to imprint polymethylmethacrylate (PMMA) at elevated temperatures and pressures. The
imprinted PMMA could then be used to transfer the nanopattern on the columnar porous SiC to
other substrates for various purposes; e.g. templates for GaN regrowth, catalysts for nanowire
growth by vapor-liquid-solid type methods (VLS), etc. SiC is not typically used for NIL stamps
since etch processing of SiC is less mature than that of Si. However, as demonstrated here, there is
no reason why SiC cannot be used as a material for NIL stamps. The superior mechanical properties
to Si make the use of SiC alluring as a master template for NIL processing.
High-Current 10 kV SiC JBS Rectifier Performance
Authors: Imhoff Eugene A. , Hobart Karl D.
Published: March 2009

Forward and reverse bias performance of 10kV, 10A and 20A junction barrier-controlled
Schottky 4H silicon carbide rectifiers are presented. Over a temperature range of 30 to 200°C, the
forward current-voltage curves show a normal Schottky rectifier relationship and the reverse
current-voltage curves show typical PiN blocking. When operated in reverse-blocking at 125°C and
8kV, the 10A JBS rectifiers are notably stable at less than 5μA of leakage current, despite the large
active area of the devices.
5 kV, 9.5 A SiC JBS Diodes with Non-Uniform Guard Ring Edge Termination for High Power Switching Application
Authors: Hu Jun , Li Larry X. , Alexandrov Peter , Wang Xiao Hui , Zhao Jian Hui
Published: March 2009

4H-SiC Junction Barrier Diodes (JBS) diodes were designed, fabricated and tested. The
JBS diodes based on a 45μm thick, 1.4×1015cm-3 doped drift layer with multiple non-uniform spacing
guard ring edge termination showed a blocking voltage of over 5kV. The 5kV JBS diode has a
forward current density of 108A/cm2 at 3.5V and a specific on resistance (RSP_ON) of 25.2mW·cm2,
which is very close to the theoretical RSP_ON of 23.3mΩ·cm2. DC I-V measurement of packaged JBS
diodes showed a forward current of 100A at a voltage drop of 4.3V. A half-bridge inverter with a bus
voltage up to 2.5kV was used to characterize the high power switching performance of SiC JBS
diodes. A large inductance load of 1mH was used to simulate the load of a high power AC induction
motor. Compared to a Si PIN diode module, the SiC JBS package reduces diode turn-off energy loss
by 30% and Si IGBT turn-on energy loss by 21% at room temperature.
Schottky Barrier Diode Fabricated by MOCVD-Grown Epilayer Using Bis-Trimethylsilylmethane Precursor
Authors: Song Ho Keun , Lee Jong Ho , Oh Myeong Sook , Moon Jeong Hyun , Seo Han Seok , Yim Jeong Hyuk , Kwon Sun Young , Kim Hyeong Joon
Published: March 2009

Schottky barrier diode (SBD) was fabricated by MOCVD using bistrimethylsilylmethane
(BTMSM, C7H20Si2) precursor. The 4H-SiC substrates which had different
crystallographic characteristics were used for the comparison of the crystallinity effect on the
electrical properties of the SBDs. From the measurement of the reverse I-V characteristics of the
SBDs with micropipes, it is shown that the origin of the main leakage path and early breakdown (or
ohmic behavior in reverse bias) in 4H-SiC SBDs is the grain boundaries caused by the inclusions or
other defects. The best performance of SBD were shown in the epilayer grown at 1440 oC using
high quality substrate, and the breakdown voltage and reverse leakage current were about 450 V
and 10-9 A/cm2, respectively.
Field-Plate Terminated Pt/n- 4H-SiC SBD Using Thermal SiO2 and Sputter Deposited AlN Dielectric Stack
Authors: Kumta A. , Rusli E. , Xia J.H.
Published: March 2009

Silicon dioxide (SiO2), one of the commonly used dielectrics for field plate terminated
4H-SiC devices suffers from high electric field and premature breakdown due to its low dielectric
constant (k). This problem can be addressed by using high-k dielectrics such as AlN that will reduce
the field and improve the breakdown voltage (VB). Sputter deposited amorphous AlN films with a
thickness (tAl) ranging from 0.05 μm to 1.3 μm have been deposited on 4H-SiC n-type samples with
a 10 μm thick epilayer doped with nitrogen to a concentration of 1.7–3.5×1015/cm3 . The VB of the
diodes was found to improve to as much as 1500 V at tAl = 0.8 μm, which is more than 2 times the VB
of unterminated structures which have a premature breakdown between 600-700 V due to field
enhancement at the diode periphery.
Observation of Crystalline Defects Causing pn Junction Reverse Leakage Current
Authors: Watanabe Tomokatsu , Nakao Yukiyasu , Fujihira Keiko , Miura Naruhisa , Tarui Yoichiro , Imaizumi Masayuki , Oomori Tatsuo
Published: March 2009

A major crystalline defect which causes a pn junction reverse leakage current has been
identified. A faintish stripe defect (FSD), the main cause of the leakage current, was observed in
about 90% of the current leak points of our pn diodes. Double shell pits were observed at the edge
of the FSD after molten KOH etching, indicating that the FSD is elongated on a basal plane and
crosses the epilayer surface. The FSDs are sorted into several groups in terms of the shapes and
arrangements of the etch pits. A cross-sectional TEM image of an FSD shows an eight-hold stacked
structure, demonstrating that the defect contains a stacking fault. Etch pit observation after
repetitive RIE of an epilayer revealed that FSDs originate both in threading dislocations in SiC
substrates and from an SiC epitaxial growth process itself.
Fatigue Properties of Steels with Ultrasonic Attrition Treated Surface Layers
Authors: Uusitalo J. , Karjalainen L. Pentti , Retraint Delphine , Palosaari M.
Published: March 2009

Severely deformed surface layers have been created by ultrasonic attrition technique on four steel sheets to investigate their influence on fatigue behaviour. A low-carbon (0.05%) ferritic steel and a medium-carbon (0.47%) normalized ferritic-pearlitic steel were selected to study the effect of carbon content on fatigue properties of carbon steels. Two stainless steels, Type 316L and Type 301LN, were also tested to study the influence of stability of the austenitic structure. Microstructural features were characterized by hardness measurements, X-ray diffraction and optical and electron microscopy. Fatigue properties were determined in flexural bending in the range 104 to 107 cycles. Crack nucleation and propagation stages were followed. In the attrition treatment thin severely deformed surface layers were found to form. Highly increased hardness was measured in these layers, especially for stainless steels, where also strain-induced martensite was formed. Drastic improvement in fatigue resistance was observed for all steels due to the surface nanocrystallization treatment.
Texture and High-Angle Boundary Formation during Deformation Processing
Authors: McNelley Terry R. , Swaminathan S. , Su J.Q. , Zhilyaev Alex P.
Published: March 2009

Among the phenomena leading to formation of high-angle boundaries during deformation processing at low homologous temperatures is the subdivision of prior grains and formation of deformation bands. Evidence for this phenomenon during processing of AA2004, a superplastic aluminum alloy, is reviewed; fragmentation of deformation bands leads to equiaxed grains and high-angle boundaries that support superplasticity. In addition to subdivision, groups of grains undergo lattice rotation toward one or the other variant of the β orientation fibers during plane-strain deformation of pure aluminum by ambient temperature rolling. The formation of equiaxed grains from banded structures during simple shear by equal channel angular pressing (ECAP) is also considered.
Failure at Elevated Temperatures: Influence of Dynamic Restoration
Authors: McQueen H.J.
Published: March 2009

Inherent failure mechanisms at elevated temperature are primarily wedge crack growth at triple junctions arising from differential grain boundary (GB) sliding at higher stresses and pore formation on sliding boundaries due to vacancy diffusion at lower stresses and higher T. The behaviours of these mechanisms have been ascertained in creep where they can be studied over long periods. They continue to operate in hot working although their effects per unit strain have been reduced by decrease in fractional contribution of GB sliding. Dynamic recovery (DRV) significantly develops a stable substructure that strongly mitigates stress concentration. In alloys of austenitic steel, Ni and Cu, dynamic recrystallization (DRX) aids DRV in reducing stress concentrations and the migrating GB isolate fissures so they cannot propagate. Solutes and precipitates generally reduce ductility by diminishing DRV and DRX. Large particles and inclusions, notably on GB, introduce new sources of fissure nucleation, lowering ductility; solidification segregation and low melting constituents, especially if they spread along the GB, create severe problems.
Study of Unsupported and Al2O3 or SiO2-Supported Nickel Molybdate for Oxireforming of Ethane
Authors: Boukhlouf Hamza , Benrabaa R. , Barama S. , Barama A.
Published: March 2009

The nickel molybdate unsupported and supported on alumina or silica were prepared by co-precipitation and co-precipitation/impregnation methods and calcined in air at 550°C for 15h. The textural and structural properties of the solids have been studied using Brunner-Emmett-Teller surface analyze (BET), X-ray diffraction (XRD), Laser Raman Spectroscopy (LRS), scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDX), temperature-programmed reduction (TPR) and Atomic absorption spectroscopy (AAS). The catalytic activity measurements were performed in a fixed bed quartz reactor under the following experimental conditions: P = 1 atm, Tr = 470- 650 °C, C2H6/O2 = 2 and Wcat = 0.1g. XRD, confirmed par LRS analysis, showed the presence of -NiMoO4 and -NiMoO4 phases. The second one was only observed with the Al2O3 support. The Ni molybdate is a very selective catalyst in oxireforming of ethane with a selectivity consisted between 85 and 100%.
Electrical Properties Dependent on Schottky Diode Pd/PSC-pSi(100) Based on Hydrocarbon Gas Sensor
Authors: Keffous A. , Kechouane M. , Kerdja Tahar , Belkacem Y. , Bourenane K. , Menari H. , Maoudj M. , Boukezzata A.
Published: March 2009

In this paper we present the study of a Schottky diode gas sensing by using porous SiC films with palladium as a catalytic metal. The Schottky diodes were used for the first time for hydrocarbon (C2H6) gas sensing. The properties of the porous SiC films formed by electrochemical method were investigated by scanning electron microscopy (SEM). The electrical measurements were made at room temperature (295 K) in different ambient. The effect of the porous surface structure was investigated by evaluating electrical parameters such as the ideality factor (n), barrier height (Bp) and series resistance (Rs). The porous layer significantly affects the electrical properties of the Schottky diodes. Analysis of current-voltage (I-V) characteristics showed that the forward current might be described by a classical thermal emission theory. The ideality factor determined by the I–V characteristics was found to be dependent on the SiC thickness. For a thinner SiC layer (0.16 µm), the electrical parameters n was found around 1.135, 0.7041 eV for a barrier height and 45  for a series resistance, but for a thicker one (1.6 µm) n, Bp and Rs were 1.368, 0.7756 eV and 130 , respectively. The low value of the series resistance obtained using Cheung’s method clearly indicated the high performance of the Schottky diode for thinner SiC layer. This effect showed the uniformity of the SiC layer. Finally, sensitivity around 66 % and selectivity of the sensors were reached by using the PSC layer at low voltages below 0.5 Volt.
On Topographic Properties of Semiconductor Surfaces and Thin Film Systems
Authors: Jurečka Stanislav , Kobayashi Hikaru , Takahashi Masao , Brunner Róbert , Madani Mohammad , Pinčík Emil
Published: March 2009

The microroughness of the semiconductor/oxide interface substantially influence properties of the whole structure. In our work Si/SiO2/SiOx structures were prepared by using low temperature nitric acid oxidation technique and by the electron gun technique and then the whole structure was passivated by the HCN technique. In the present study we investigate the surface morphology evolution during the creation of the SiO2/SiOx double-layer and after the passivation steps. Surface roughness properties are studied by the fractal geometry methods. The complexity of analysed surface is sensitive to the oxidation and passivation steps and the proposed fractal complexity measure values enable quantifying of the fine surface changes.
Characterization of a-C:H Thin Films Deposited from C2H4 by PECVD Microwave Discharge
Authors: Kihel M. , Clergeraux R. , Sahli Salah , Escaich D. , Segui Y. , Raynaud Patrice
Published: March 2009

Some investigations on physico-chemical properties of hydrogenated amorphous carbon (a-C:H) thin films deposited from C2H4 precursor have been carried out. The films were elaborated in a Microwave Multipolar Plasma reactor excited at Distributed Electron Cyclotron Resonance (MMP-DECR). The effects of the plasma power on the electrical and structural characteristics of the deposited films have been evaluated. It appeared that for low plasma power ( 400 W), the deposition rate and the hydrogen concentration increases, whereas the Csp2 concentration remains constant. Beyond 400 W, the deposition rate and the hydrogen concentration reach saturation levels and the Csp2 concentration decreases. In contrast, the film density decreased with the increase of the plasma power. Below 400 W, the dielectric constant decreased with the increase of the plasma power, however, beyond 400 W its value remained almost constant. The correlation between film characterization and properties shows that the permittivity is driven by the film density and the film structure.
Effect of TiN/CrN Multilayer Coating by Cathodic Arc Deposition on Wear and Corrosion Behaviours of AZ91D Magnesium Alloy
Authors: Tian Lin Hai , Liu Er Qiang , Fan Ai Lan , Qin Lin , Liu Dao Xin , Tang Bin , Pan Jun De
Published: March 2009

TiN/CrN multilayer coating was deposited on AZ91D magnesium alloy by pulsed bias cathodic arc PVD process. Effects of the coating on wear and corrosion behaviours of magnesium alloy were investigated. The stick-tearing for adhesion evaluation, nanoindentation for hardness measurement, ball-on-disc testing for wear tests, and potentiodynamic polarization for corrosion tests were used. The results show that the friction coefficient is decreased and the wear resistance is improved remarkably by TiN/CrN multilayer coating on AZ91D magnesium alloy. The corrosion resistance of the alloy is increased at a certain degree.
Experimental and Numerical Studies of Welded Tubes Formability
Authors: Ayadi A. , Cherouat Abel , Rezgui Mohammed Ali , Mezghani Najeh
Published: March 2009

This paper presents a numerical methodology which aims to improve 3D welded tube hydroforming formability. This methodology is based on elastoplastic constitutive equations accounting for non-linear anisotropic hardening. The experimental study is dedicated to the identification of material parameters (the parent and the heat-affected zones) using the global measure response of tube displacement, thickness evolution and internal pressure expansion. Applications are made to study numerically the effect of the anisotropic parameters, the hardening flow and the heat-affected zone shape on the hydro-formability of welded tubes.
Snoek Relaxation in bcc Metals and High Damping β-Ti Alloys
Authors: Yin Fu Xing , Yu Li Ming , Ping De Hai , Iwasaki Satoshi
Published: March 2009

The Snoek relaxation, a specific point-defect induced anelastic relaxation phenomenon, is characteristic of an internal friction peak in bcc metals with interstitial solutes. Such internal friction mechanism has not been applied in the development of high damping alloy while grain boundary and twin boundary featured anelastic relaxations are applied in some high damping alloys. In this paper, the fundamental principles and experimental results concerning the Snoek relaxation are reviewed, and the feasibility to apply the Snoek relaxation mechanism into high damping alloys is discussed. Due to the peak-shape behavior in the Snoek relaxation type damping, composition design of a high damping alloys should takes temperature position, broadness and also peak height into account. Ti-Nb-O and Ti-V-Cr-O alloys are designed and fabricated by CCLM casting in our laboratory. It is conformed that the damping behaviors of the alloys are of Snoek relaxation type showing obvious frequency and temperature dependence. While the broadened damping peak caused by the substitutional solutes is advantage to improve the temperature stability of damping capacity, a large concentration of interstitial solute and texture control are required to improve the reduced damping capacity.
Abrupt Softening Phenomenon in a Shape Memory CuAlNi Single Crystal under Uniaxial Compression
Authors: Sun Li , Huang W.M.
Published: March 2009

Abrupt softening phenomenon was observed in a shape memory CuAlNi single crystal upon uniaxial compression. Sudden martensite variant(s) reorientation was found to be the reason behind this anomalous behavior. The significance of this finding is twofold. On one hand, it clearly demonstrates that the stress induced transformation can follow a sequence of the phase transformation (martensitic transformation, austenite to martensite) and then reorientation (from one martensite variant to another). On the other hand, the anomalous softening provides a good evidence for explaining the propagation of the phase transformation front.
Characterization of Radiation Hard Silicon Materials
Authors: Luukka Panja , Härkönen Jaakko , Tuovinen Esa , Czellar Sandor , Eremin Vladimir , Li Zheng , Tuominen Eija , Verbitskaya Elena
Published: March 2009

Segmented silicon detectors are widely used in modern high-energy physics (HEP) experiments due to their excellent spatial resolution and well-established manufacturing technology. However, in such experiments the detectors are exposed to high fluences of particle radiation, which causes irreversible crystallographic defects in the silicon material. Since 1990’s, considerable amount of research has gone into improving the radiation hardness of silicon detectors. One very promising approach is to use magnetic Czochralski silicon (MCz-Si) that has been found to be more radiation hard against charged hadrons than traditional Float Zone silicon material (Fz-Si) used in the current HEP applications. Other approaches include operating the devices at cryogenic temperatures and designing special detector structures such as p-type detectors or semi-3D detectors. In order to demonstrate that the developed technologies are suitable for the HEP experiments, it is necessary to extensively characterize the potentially radiation hard detectors. We have an excellent instrument for this, the Cryogenic Transient Current Technique (C-TCT) measurement setup, which is an effective research tool for studying heavily irradiated silicon detectors. With the C-TCT setup it is possible to extract the full depletion voltage, effective trapping time, electric field distribution and the sign of the space charge in the silicon bulk in the temperature range of 45-300 K. This article
Effect of Additional Element and Heat Treating Temperature on the Microstructure and Mechanical Behaviour of Ag Thin Film
Authors: Ju Dong Ying , Ishiguro S. , Hasegawa K. , Arizono T.
Published: March 2009

For Ag film used for storage media, it is required to have heat-resistant, anti-constant temperature, anti-constant humidity characteristics and corrosion resistance, while the high reflectivity of Al is maintained. An Ag thin film (additive elements Pd, Cu and P) was produced on glass substrates and various heat treatments were conducted. Then, the fine structure on this thin film was observed by AFM, and fine structure evaluation in the inside was carried out by in-plane diffraction and X-ray diffraction. In addition, residual stress analysis was performed. These results were compared and examined, and the fine structure and physical properties in a metallic thin film were evaluated.
Amperometric Biosensors Equipped with Enzyme Micelle Membrane Using Polymaleimidostyrene as Stabilizer
Authors: Wang Xiu Yun , Uchiyama Shunichi
Published: March 2009

This paper describes recent advances in the development of bioelectrochemistry research which is focused on the advanced design and preparation of enzyme-based amperometric biosensors, as well as the functional structure and principle. Particular emphasis is directed to the discussion and exploration of electrochemical biosensors based on novel functional polymer, polymaleimidostyrene (PMS), as effective immobilization support and stabilizer. The sulphydryl and amino groups of enzymes react with maleimide groups of PMS. As a result, various enzymes can be easily modified on the electrode surface. First topic is PMS-based enzyme-micelles which are dispersed in the polystyrene film prepared on the electrode surface. The structure and morphology of enzyme-micelles membranes were characterized by scanning electron microscope. Second topic is bio-functionalization of electrode surface using enzyme-immobilized PMS. Electrochemical and bioelectrocatalytic properties of enzyme-micelle membranes were examined by various electrochemical techniques. These enzyme-micelle-based electrochemical biosensors exhibited good sensitivity and selectivity for the detections of urea, uric acid, L-ascorbic acid, glucose and toxic phenol compounds. The prospects and further developments in this exciting interdisciplinary field are also suggested.
Growth of Single Crystal 3C-SiC(111) on a Poly-Si Seed Layer
Authors: Locke Christopher , Frewin Christopher L. , Wang Jing , Saddow Stephen E.
Published: March 2009

A novel method for growing highly-crystalline 3C-SiC on an oxide release layer via a poly-Si seed layer is reported. Silicon carbide’s potential role as a ubiquitous material for MEMS fabrication lies in its dual role as an electronic and mechanical material. Unfortunately, due to residual stresses and crystal defects stemming from the large lattice constant mismatch and the thermal expansion coefficient difference between SiC and Si, the use of SiC in Si-based MEMS fabrication techniques has been very limited. The growth of 3C-SiC on a poly-Si seed layer deposited on oxide on (111)Si substrates (i.e., p-Si/ SiO2/(111)Si) provides an alternative fabrication method to expensive, traditional SOI bonding techniques for producing free-standing 3C-SiC MEMS structures. 3C-SiC grown with a poly-Si seed layer on SiO2 should experience reduced residual stress and far fewer defects due to the compliance of the SiO2 layer. Although poly-Si is utilized as a seed layer in this process, a well-ordered monocrystalline 3C-SiC layer was achieved and the process and film properties reported.
Role of Substrate Misorientation in Relaxation of 3C-SiC Layers on Silicon
Authors: Zielinski Marcin , Portail Marc , Roy Sebastien , Kret S. , Chassagne Thierry , Nemoz M. , Cordier Yvon
Published: March 2009

We analyze in detail the evolution of curvature of 3C-SiC layers grown on vicinal silicon substrates. A common feature of (100) and (111) oriented layers is a strongly asymmetric wafer bending that may suggest an anisotropic stress relaxation within the layer. A comparative study of the curvature, lattice parameter, surface morphology and structural defects for the off-angles ranging from 0.5° to 6° is performed in order to confirm or disprove this hypothesis. We find a homogeneous, tensile in-plane lattice deformation. We also show the correlation of the orientation of the high and low curvature axes with the morphology and defect pattern of the layer.
Characterization of 6H-SiC Single Crystals Grown by PVT Method Using Different Source Materials and Open or Closed Seed Backside
Authors: Racka Katarzyna , Tymicki Emil , Raczkiewicz Marcin , Grasza Krzysztof , Kozubal Michal , Jurkiewicz-Wegner Elzbieta , Jakieła Rafał , Brzozowski Andrzej , Pawłowski Mariusz , Piersa Miroslaw , Sadło J. , Krupka Jerzy
Published: March 2009

n- and p-type 6H-SiC single crystals grown by PVT method using different charge materials – poly-SiC sinter or fresh SiC powder – have been studied. An open or closed seed backside during the growth processes have been applied. In the former, a distinct decrease backside etching of the seed was observed. Crystals have been extensively characterized with respect to their purity, quality and electrical properties using complex experimental methods. For the n-type boule an axially and radially homogeneous resistivity ~0.11 cm at 300 K was observed. Electrical properties of the p-type crystal, i.e., high room-temperature resistivity of 239 cm, were affected by compensation effects between residual donors (nitrogen and oxygen) and acceptors (mainly boron).
Dislocation-Induced Birefringence in Silicon Carbide
Authors: Ouisse Thierry , Chaussende Didier , Auvray Laurent , Pernot Etienne , Madar Roland
Published: March 2009

The dislocation-induced birefringence of Silicon Carbide (SiC) is analytically and quantitatively modelled by using the adequate SiC data. A good agreement can be obtained between theory and experiment, provided that a background residual (uniaxial) stress is added to the local dislocation-induced stress. Observations are compatible with or predictable from the Burgers vector values, so that birefringence reveals an interesting tool for probing the nature of the dislocations associated, e.g., to micropipes, also faster than and complementary to the more involved transmission electron microscopy (TEM) technique.
Wafer Level Recombination Carrier Lifetime Measurements of 4H-SiC PiN Epitaxial Wafers
Authors: Chung Gil Yong , Loboda Mark J. , MacMillan Mike F. , Wan Jian Wei
Published: March 2009

Effective recombination lifetimes of 4H-SiC PiN epitaxy wafers are measured by -PCD (microwave photoconductive decay) system at wafer level. Lifetimes measured in presence and absence of the p+ layer show lower lifetime values with p+ layer present. This is attributed to high recombination rate at p+/n- interface. Lifetimes at various buffer thicknesses show lower values at the buffer layer of about 50 m due to high interface recombination rate resulting from rougher surface of the buffer layer. Lifetimes of PiN wafers from interrupted and continuous p+/n- growth are very comparable.
Investigation of Thermal Properties of Heavily Doped 4H-SiC Crystals by a Picosecond Transient Grating Technique
Authors: Ščajev Patrik , Kadys Arunas , Jarašiūnas Kęstutis
Published: March 2009

We applied a picosecond dynamic grating technique for investigation of thermal diffusivity, sound velocity, thermo-optic and photoelastic coefficients in heavily doped 4H-SiC substrates. Spatial modulation of thermal properties was achieved by intraband carrier absorption at excitation by an IR picosecond laser pulse (1064 nm) and subsequent carrier thermalisation. Decay of dynamic grating at its various periods and sample temperatures was monitored at 532 nm wavelength. The thermal diffusivity DT = 0.94 cm2/s, thermo-optic coefficient dn/dT = 3.610–5 K-1 and effective photoelastic constant = – 0.10 were determined at 300 K. DT value increased at lower temperatures and saturated below 100 K. Temperature dependences of thermo-optic coefficient and thermal expansion were found in good correlation with heat capacity peculiarities.
Microhardness of 6H- and 4H-SiC Substrates
Authors: Eddy Charles R. , Wu Ping , Zwieback Ilya , VanMil Brenda L. , Myers-Ward Rachael L. , Tedesco Joseph L. , Souzis Andrew E. , Gaskill D. Kurt
Published: March 2009

Knoop microhardness assessments were conducted on a variety of 6H- and 4H-SiC substrates to assess any appreciable differences that may need to be considered in wafer manufacture and general application. Nitrogen-doped, vanadium-doped and unintentionally doped (UID) substrates with both on-axis and 8° off-axis orientations were assessed. In general, the Knoop hardness values fell in the 2000 to 2500 kg/mm2 range (equivalent to approximately 20 to 25 GPa). Hardness values measured in the <1100> crystal direction were significantly higher than in the <11-20> direction. Undoped and vanadium-doped samples were harder than nitrogen-doped samples. For both 6H and 4H nitrogen-doped samples, the hardness was as much as 10% higher for 8° offcut wafers than for on-axis.
Investigation of the Metal–Insulator Transition in n-3C-SiC Epitaxial Films
Authors: Lebedev Alexander A. , Abramov Pavel L. , Agrinskaya Nina V. , Kozub Ven I. , Kuznetsov Alexey N. , Lebedev Sergey P. , Oganesyan Gagik A. , Chernyaev A.V. , Shamshur Dmitrii , Skvortsova Maria O.
Published: March 2009

n-type 3C-SiC films have been grown by sublimation epitaxy on hexagonal silicon carbide substrates. The low-temperature conductivity and magnetoresistance of the films have been studied in relation to their doping level and structural perfection. It was found that a metal--insulator transition occurs in the n-3C-SiC layer at concentrations Nd - Na ≤ 3 1017 cm-3.
Identification of the Negative Di-Carbon Antisite Defect in n-Type 4H-SiC
Authors: Gali Adam , Umeda T. , Janzén Erik , Morishita Norio , Ohshima Takeshi , Isoya Junichi
Published: March 2009

We identify the negatively charged dicarbon antisite defect (C2 core at silicon site) in electron irradiated n-type 4H-SiC by means of combined electron paramagnetic resonance (EPR) studies and first principles calculations. The pair of HEI5 and HEI6 EPR centers (S = 1/2, C1h symmetry) are associated with the cubic and hexagonal dicarbon antisite defects, respectively. This assignment is based on the comparison of the measured and calculated hyperfine tensors of 13C and 29Si atoms. We investigated the creation and annihilation of this defect as a function of electron-dose and annealing temperature.
Defects in High Energy Ion Irradiated 4H-SiC
Authors: Izzo Gaetano , Litrico Grazia , Severino Andrea , Foti Gaetano , La Via Francesco , Calcagno Lucia
Published: March 2009

The defects produced by 7.0 MeV C+ irradiation in 4H-SiC epitaxial layer were followed by Deep Level Transient Spectroscopy, current-voltage measurements and Transmission Electron Microscopy in a large fluence range (109-51013 ions/cm2). At low fluence (109 -1010 ions/cm2), the formation of three main level defects located at 0.68 eV, 0.98 eV and 1.4 eV below the conduction band edge is detected. The trap concentration increases with ion fluence suggesting that these levels are associated to the point defects generated by ion irradiation. In this fluence range the leakage current of the diodes does not change. At higher fluence an evolution of defects occurs, as the concentration of traps at 0.68 eV and 1.4 eV decreases, while the intensity of the level at 0.98 eV remains constant. In this fluence range complex defects are formed and an increase of a factor five in the leakage current is measured.
Anti-Site Defects are Found at Large Distances from Localised H and He Ion Implantations
Authors: Steeds John W. , Peng N. , Sullivan W.
Published: March 2009

1 MeV ion implantations of 4H SiC have been performed to various doses with ion probes of 5 µm diameter. Defect introduction has been studied by microscopic photoluminescence.
Surface Morphology Improvement and Repeatable Doping Characterization of 4H-SiC Epitaxy Grown on 4° Off-Axis 4H-SiC Wafers
Authors: Sunkari Swapna G. , Das Hrishikesh , Hoff Carl , Koshka Yaroslav , Casady Janna R. B. , Casady Jeff B.
Published: March 2009

4H Silicon Carbide (4H-SiC) has a great potential for low-loss power devices due to its superior electrical properties. However, the increase in demand for the power devices requires high quality SiC substrates and epitaxial layers. Mercury probe Capacitance Voltage (Hg CV) measurement is a well known procedure to characterize epi layers grown on SiC substrates, due to its non-destructive technique. However, careful calibration of the tool is very important for repeatable and accurate measurements. Here we present very close repeatability of Hg CV within 2.4% (standard deviation 0.7%), between different Solid State Measurements (SSM) setups compared with Ni Schottky (NiS) CV. In addition to growing uniformly doped epi layers, high surface quality of the epi layer is also needed for improved device performance. Improved process conditions resulted in a smooth epi with a surface roughness Ra 1.2 nm for a 6 µm thick epi layer. Molten Potassium Hydroxide (KOH) etching analysis also revealed a significant correlation between the surface roughness and epi defects.
Analysis of Forward Current-Voltage Characteristics of Non-Ideal Ti/4H-SiC Schottky Barriers
Authors: Ivanov Pavel A. , Potapov Alexander S. , Samsonova Tat'yana P.
Published: March 2009

Forward current-voltage characteristics of non-ideal Ti / 4H-SiC Schottky barriers with ideality factor n = 1.1 - 1.2 have been analyzed. The non-ideality is considered as a result of formation of a thin intermediate dielectric layer between the deposited titanium layer and 4H-SiC. Using experimental current-voltage characteristics, the electro-physical characteristics of Ti contacts such as the energy barrier height, the thickness of the intermediate layer and the energy distribution of the interface trap density are determined.
Characterization of the SiO2/SiC Interface with Impedance Spectroscopy
Authors: Sobas Pawel A. , Grossner Ulrike , Svensson Bengt Gunnar
Published: March 2009

Using impedance spectroscopy (IS) for the characterization of SiO2/4H-SiC (MOS) structures, insight on the capacitive and resistive contributions in different physical regions of the MOS structures is obtained. Changing the DC bias conditions, semiconductor, interface as well as oxide traps can be detected. The MOS capacitance, as extracted from IS data, is different from the one obtained using capacitance voltage (CV) measurements, due to the possibility of distinguishing different charge transfer processes using IS. For instance, in the investigated capacitors, a clear contribution is revealed from ionic conduction processes at bias voltages close to zero.
4H-SiC Oxide Characterization with SIMS Using a 13C Tracer
Authors: Fronheiser Jody , Matocha Kevin , Tilak Vinayak , Feldman Leonard C.
Published: March 2009

The SiO2/SiC interface is characterized for carbon accumulation using the carbon isotope 13C as a marker layer combined with secondary ion mass spectroscopy (SIMS). SiC was epitaxially grown using an isotopically enriched propane source and subsequently oxidized to a thickness required to consume the entire 13C layer. Mass specific depth profiles through the oxide film yield residual carbon concentrations at or below 3x1011 cm-2. The depth resolution of SIMS and natural abundance of 13C in the bulk SiC film limit sensitivity but allow us to set a limit of 2.5x1014 cm-2 carbon build up at or near the interface.
Transient Currents Induced in 6H-SiC MOS Capacitors by Oxygen Ion Incidence
Authors: Iwamoto Naoya , Onoda Shinobu , Ohshima Takeshi , Kojima K. , Kawano K.
Published: March 2009

Single event transient currents induced in 6H-SiC MOS capacitors are measured by using oxygen ions. Charges collected from the samples are calculated by the transient currents. Applying the drift-diffusion model to the charges, the diffusion length of electron is estimated. Transient currents induced in the gamma ray irradiated MOS capacitors are also investigated. No significant change in the transient currents is observed after gamma ray irradiation.
Thick Epitaxial Layers Growth by Chlorine Addition
Authors: La Via Francesco , Izzo Gaetano , Camarda Massimo , Abbondanza Giuseppe , Crippa Danilo
Published: March 2009

The growth rate of 4H-SiC epi layers has been increased up to 100 µm/h by chlorine addition. The epitaxial layers grown with this process have been characterized by electrical, optical and structural characterization methods. Very thick (> 100 µm) epitaxial layer has been grown and the Schottky diodes realized on these layers have good yield (> 87%) with a low defect density (10/cm2). This process gives the opportunity to realize very high power devices with breakdown voltages in the range of 10 kV or X-Ray and particle detectors with a low cost epitaxy process.
Comparison between Polishing Etching of On and Off-Axis C and Si-Faces of 4H-SiC Wafers
Authors: Kościewicz Kinga , Strupiński Wlodek , Olszyna Andrzej Roman
Published: March 2009

Crystallographic quality of the epitaxial layers depends on the process temperature, partial pressures of active components and the surface polarity and also on the crystallographic quality of the subsurface layer resulting from the preparation of the substrate. The polishing etching in hydrogen-propane atmosphere of 4H-SiC substrate of different orientations and polarity was studied. The optimization of the polishing etching has been achieved with respect to the flow of C3H8, the duration and the temperature of the process. The investigation of the surface of SiC substrate before and after in situ polishing-etching in H2+C3H8 atmosphere was carried out by Nomarski interference contrast microscopy (DIC) and atomic force microscope (AFM).
Spectroscopic Measurement of Electric Discharge Machining for Silicon Carbide
Authors: Sugimoto Tatsunori , Noro Toshiya , Yamaguchi Satarou , Majima Hideyoshi , Kato Tomohisa
Published: March 2009

Diamond saw is generally used to make the silicon carbide (SiC) wafers from ingots, but it takes long time for cutting. We have used the electric discharge machining (EDM) to cut SiC. The cutting speed of EDM for SiC is almost 10 times faster than the diamond saw, and the surface roughness is 1/10 for the diamond saw. EDM cut SiC by the plasma produced between the wire and SiC material. The emissions from EDM plasma may involve much information for EDM cutting. We monitored the total light intensity by a photodiode, and observed the spectrum of the emission from EDM plasma by a visible spectroscopy. The discharge gas used helium and argon. In both discharges, the light emission was observed when the current was not zero. Also, many lines were observed Si I, Si II and C I from the SiC sample, and Cu I and Zn I from the wire. And, the electron temperature of EDM plasma was estimated to be under several eV because the observed lines were almost the emission from atoms. Also, the scars, which show the copper-alloy wire was hurt by discharge, were observed from the wire.
SiC Power Devices: Product Improvement Using Diffusion Soldering
Authors: Holz Matthias , Hilsenbeck Jochen , Otremba Ralf , Heinrich Alexander , Türkes Peter , Rupp Roland
Published: March 2009

SiC power devices have reached a high market penetration, especially for high-voltage applications like switch mode power supplies. In the past, however, the superior material properties like, e.g., good thermal conductivity, have often not been put to full use due to the limitations of current packaging techniques. Especially the inferior thermal conductivity of current die attach materials have been an obstacle to realise the full potential of SiC technologies. In this paper, we describe in detail the use of diffusion solder for the die attach of SiC chips. Replacing the conventional solder layer by a thin metal stack for diffusion soldering, the thermal conductivity of the device is significantly improved. In addition, we show the positive impact of diffusion soldering on the assembly process and on the device reliability. These results are interesting for, both, SiC diodes and switches.
Single Crystal and Polycrystalline 3C-SiC for MEMS Applications
Authors: Henry Anne , Janzén Erik , Mastropaolo Enrico , Cheung Rebecca
Published: March 2009

Cantilever resonators have been fabricated from two types of materials, single crystal and polycrystalline 3C-SiC films. The films have been grown in a hot-wall chemical vapor deposition reactor on 100 mm diameter p-type boron-doped (100) Si wafer without rotation of the wafer. The crystal structure of the films have been accessed with X-ray diffraction. The cantilever devices have been fabricated using a one-step etch and release process; the beam length has been varied between 50 and 200 µm. Resonant frequencies in the range 110 KHz – 1.5 MHz and 50 – 750 KHz have been obtained for single crystal and polycrystalline SiC devices, respectively. Furthermore, the experimental resonance frequencies have been used to calculate the Young’s Modulus E for the two different types of SiC. The single crystal SiC, possessing a very high Young’s Modulus (446 GPa), should be an optimal material for RF-MEMS applications.