bluuebunny/crossref_metadata_2025 huggingface dataset:
Negative Capacitance Phenomena in CZT Room Temperature Radiation Detectors
Authors: Hassan Mahmoud A.
Published: March 2009

CdZnTe , Cadmium zinc telluride (CZT) is an interesting room temperature radiation detector. This research paper is reporting a negative capacitance behavior of CZT detectors at bias voltages around 60V. Initially at 0V, the CZT capacitance is positive and decreases with bias voltage increase. At around 60V, the measured capacitance approaches zero, then with small voltage increase , capacitance value reverses sign and starts to increase in the negative direction with
increasing bias voltage . This effect is stable at 100 kHz. The behavior of low and other quality detectors can differ, low quality detectors can show negative capacitance at low bias voltages and low frequencies. The initial explanation of this phenomena is due to non-uniform distribution of impurities inside the bulk material.
Fabrication and Characterisation of Reverse Proton Exchange Optical Waveguides in Neodymium Doped Lithium Niobate Crystals
Authors: Domenech M. , Lifante G. , Cussó F. , Parisi A. , Cino A.C. , Riva Sanseverino S.
Published: March 2009

In this work, the complete fabrication process which combines Proton Exchange (PE) and Reverse Proton Exchange (RPE) in Neodymium doped LiNbO3 channel waveguides is reported. To produce the PE-RPE channel waveguides the fabrication of dielectric SiO2 masks had to be implemented. For this propose, we adopted a technique based on the Ion Plating Plasma Assisted Deposition of SiO2 followed by the standard ultraviolet photolithographic patterning. On the other
hand, we determined the main optical and spectroscopic properties of Nd3+ ions in the channel waveguides including the study of the lifetime as function as the polarisation.
Optical Properties of GaN on Si Substrate Using Plasma-Assisted MOCVD Technique in the Infrared and Visible Regions
Authors: Hashim M. Roslan , Oh S.A. , Ng Sha Shiong , Zainuriah Hassan , Ibrahim Kamarulazizi , Barmawi M. , Sugianto  , Budiman M. , Arifin P.
Published: March 2009

In this paper, we report the characteristics of GaN heteroepitaxial films grown on Si(111)at 700oC using plasma-assisted metalorganic chemical vapour deposition (PA-MOCVD). In this growth technique, H2 plasma was used in addition to N2 plasma. Two sets of samples with different buffer layers were used, i.e. GaN and AlN buffer layers. In the infrared region both samples exhibit similar reststrahlen band shape. However the sample with GaN buffer layer exhibits better optical
properties in the visible region compared with its counterpart. This is attributed to its better structural bulk and surface properties.
Investigation of the SiC Transistor and Diode Nuclear Detectors at 8 MeV Proton Irradiation
Authors: Strokan Nikita B. , Ivanov Alexander M. , Savkina N.S. , Lebedev Alexander A. , Kozlovski Vitalii V. , Syväjärvi Mikael , Yakimova Rositza
Published: March 2009

Nuclear-particle detectors based on SiC with a structure composed of an n+-type
substrate, a p-type epitaxial layer, and a Schottky barrier are studied. Structures with a ~10-µm-thick 6H-SiC layer exhibit transistor properties, whereas those with a ~30-µm-thick 4H-SiC layer exhibit diode properties. It is established that a more than tenfold amplification of the signal is observed in the transistor-type structure. The amplification is retained after irradiation with 8-MeV protons with a dose of at least 5 × 10 13 cm –2 ; in this case, the resolution is ≤ 10%. Amplification of the signal was
not observed in the structures of diode type. However, there were diode-type detectors with a resolution of ≈ 3%, which is acceptable for a number of applications, even after irradiation with the highest dose of 2 × 10 14 cm.
Homoepitaxial Growth on 4H-SiC (03-38) Face by Sublimation Close Space Technique
Authors: Yoneda S. , Furusho Tomoaki , Takagi H. , Ohta S. , Nishino Shigehiro
Published: March 2009

For preliminary step toward fabrication of MOSFET using 4H-SiC 8) 3 (03 prepared by sublimation method, epitaxial growth of device quality 4H-SiC on 4H-SiC (0001) 8.0° off substrate was carried out and investigated. Smooth and specular surface of 4H-SiC (0001) plane was obtained by optimum growth condition. And epitaxial growth on 4H-SiC 8) 3 (03 and ) 8 3 (03 substrates were carried out with optimum growth conditions of 4H-SiC (0001). Smooth and specular surface was obtained on 4H-SiC 8) 3 (03 and ) 8 3 (03 plane. Growth rate of epilayers of 4H-SiC (0001), 8) 3 (03 and ) 8 3 (03 face were same. Oxidation rate of 4H-SiC (0001), ) 1 (000 , 8) 3 (03 and ) 8 3 (03 face was investigated. The oxidation rate was different depending on the faces. It was observed that the difference of oxidation rate of 8) 3 (03 and ) 8 3 (03 is mainly due to the difference of polarity similar to the case of reported for (0001) and ) 1 (000 .
Large Area SiC Epitaxial Layer Growth in a Warm-Wall Planetary VPE Reactor
Authors: Burk Albert A. , O'Loughlin Michael  J. , Paisley Michael J. , Powell Adrian R. , Brady M.F. , Müller Stephan G. , Allen S.T.
Published: March 2009

Experimental results are presented for SiC epitaxial layer growths employing a largearea, 7x3-inch, warm-wall planetary SiC-VPE reactor. This high-throughput reactor has been optimized for the growth of uniform 0.01 to 30-micron thick, specular, device-quality SiC epitaxial layers with background doping concentrations of <1x1014 cm-3. Multi-layer device profiles such as Schottky, MESFETs, SITs, and BJTs with n-type doping from ~1x1015 cm-3 to >1x1019 cm-3, p-type
doping from ~3x1015 cm-3 to >1x1020 cm-3, and abrupt doping transitions (~1 decade/nm) are regularly grown in continuous growth runs. Intrawafer layer thickness and n-type doping uniformities of <1% and <5% s/mean have been achieved. Within a run, wafer-to-wafer thickness and doping variation are ~±1% and ~±5% respectively. Long term run-to-run variations while under process control are approximately ~3% s/mean for thickness and ~5% s/mean for doping.
Latest results from an even larger 6x4-inch (100-mm) reactor are also presented.
Characteristics of Trench-Refilled 4H-SiC P-N Junction Diodes Fabricated by Selective Epitaxial Growth
Authors: Li Can Hua , Losee Peter A. , Seiler Joseph , Chow T. Paul , Bhat I.
Published: March 2009

Selective nitrogen doping of 4H-SiC by epitaxial growth using TaC as the high
temperature mask has been demonstrated. Nomarski optical microscope and scanning electron microscope (SEM) were used to characterize selective growth of SiC. In addition, 250µm square shaped p-n junction diodes by selective n type epitaxial growth on p type epi layer were fabricated. The refilled fingers with different width were designed to vary the periphery/area (P/A) ratio. The effects of P/A ratio on the current-voltage (J-V) characteristics have been investigated. The ideality factor extracted from J-V characteristics is ≈2 at temperature range of 25-275°C, which indicates that the Shockley-Read-Hall recombination is the dominant mechanism in the conduction region. The reverse leakage current did not show dependence on P/A ratio for trench refilled diodes. The room temperature reverse leakage current density at 100V is less than 3.5×10-7 A/cm2 for all diodes. Also, the reverse leakage current did not increase significantly with temperature up to 275°C. The breakdown voltages measured at room temperature are about 450V and 400V for diodes without and with fingers, respectively.
Lateral Epitaxial Overgrowth of 3C-SiC on Si Substrates by CVD Method
Authors: Sugishita S. , Shoji A. , Mukai Yoshihiko , Nishiguchi Taro , Michikami K. , Isshiki Toshiyuki , Ohshima Satoru , Nishino Shigehiro
Published: March 2009

Lateral epitaxial overgrowth (LEO) is known as method of defects reduction for GaN. LEO is expected to reduce crystal defects on hetero-epitaxial growth of 3C-SiC. (100) Si substrate patterned with SiO2 mask was used as the substrate. Before CVD process, V shape crater was made on Si surface by HCl etching. And growth condition of CVD was optimized. Single crystal of 3C-SiC was grown laterally on SiO2 layer. Cross-sectional transmission electron microscopic observation indicated that crystal quality of LEO region was single and no defect crystal.
Planar Defects, Voids and their Relationship in 3C-SiC Layers
Authors: Méndez David , Aouni A. , Araujo Daniel , Ferro Gabriel , Monteil Yves , Bustarret Etienne
Published: March 2009

One of the problems with Si(001)/3C-SiC templates is that they involve highly
defective interfaces due to the presence of misfit dislocations, voids and planar defects that degrade the SiC layer quality. A way to accommodate the high lattice mismatch between these materials and reduce the voids density is to carbonize the Si substrate before the epitaxial growth. In this contribution an alternative way to reduce planar defects density is presented by analyzing the relationship between planar defects and voids. Planar view and cross section transmission electron microscopy micrographs show a diminution of planar defects in the regions surrounding the voids. Due to the lower elastic energy over the voids
and/or to a lateral growth in these regions, the generation of planar defects is partially deactivated, improving locally the crystalline quality of the SiC layer. The introduction of such cavities can be thus seen as a new parameter of Si/SiC templates design.
Suppression of the Twin Formation in CVD Growth of (111) 3C-SiC on (110) Si Substrate
Authors: Nishiguchi Taro , Nakamura Mitsutaka , Nishio Koji , Isshiki Toshiyuki , Ohshima Satoru , Nishino Shigehiro
Published: March 2009

Chemical vapor deposition of (111) 3C-SiC on (110) Si substrate was carried out, and the effect of the substrate off-axis introduced on (110) Si substrate for suppressing the twin formation in 3C-SiC hetero-epitaxial layers was investigated. From the growth on hemispherically polished (110) Si substrate, it was found that the off-axis toward the [001] Si axis had a noble effect for suppressing the twin formation, while the off-axis toward the [110] Si axis was ineffective. The growth of single 3C-SiC crystal containing few double positioning boundaries, which are related with the twin formation, was demonstrated on the (110) Si substrate 3° off-axis toward the [001] Si axis. Transmission electron microscopic observation
revealed that double positioning boundaries on the (110) Si substrate off-axis toward the [001] Si axis were nearly eliminated within the initial a few hundreds nano meter in thickness.
Comparative Evaluation of Free-Standing 3C-SiC Crystals
Authors: Polychroniadis Efstathios K. , Balloud Carole , Juillaguet Sandrine , Ferro Gabriel , Monteil Yves , Camassel Jean , Stoemenos J.
Published: March 2009

The evolution of defects versus thickness has been investigated in three different freestanding 3C-SiC samples, using TEM (Transmission Electron Microscopy) and LTPL (Low Temperature Photo-Luminescence) spectroscopy. In all samples, the stacking fault density reduces rapidly within the first 20 µm of the growth. Then it remains constant, at about 5x103 cm-1 up to the end. This behavior is attributed to the easy generation of stacking faults, even under a very low
thermal stress, as in-situ experiments reveal. On the opposite the elimination of inversion domains, by bending boundaries during the growth, is found to be sample dependant. This is in good agreement with LTPL results.
Two-Dimensional Model of Conjugate Heat and Mass Transport in the Isothermal Chemical Vapour Infiltration of 3D-Preform by SiC Matrix
Authors: Kulik V.I. , Kulik A.V. , Ramm M.S. , Nilov A.S. , Bogdanov M.V.
Published: March 2009

Two-dimensional model of conjugate heat and mass transport in Chemical Vapour
Infiltration (CVI) process was developed. The model was used for simulation of Isothermal CVI production of SiC matrix composite. Flow pattern, thermal field and distributions of species concentrations in the gas region of the reactor and in the porous preform were analysed. Temperature and species concentration distributions were found to be noticeably non-uniform. The non-uniformity of parameter distributions leads to non-uniform densification of the preform both
along the preform thickness and height.
Pressure Effect on the Elastic Properties of SiC Polytypes
Authors: Davydov Sergey Y.
Published: March 2009

The pressure dependences of the second-order elastic constants ij C and the velocity of sound in 3C-SiC and 2H-SiC crystals are calculated in the framework of the Keating model with the additional assumption that the central α and the noncentral β force constants are linear functions of external hydrostatic pressure. Grüneisen parameters for the different acoustic modes of 3C-SiC have been also calculated. The third –order elastic constants ijk C for 3C-SiC are determined from the dependences of ij C on the pressure.
High Al-Doping of SiC Using a Modified PVT (M-PVT) Growth Set-Up
Authors: Müller Ralf , Künecke Ulrike , Weingärtner Roland , Schmitt Holger , Desperrier Patrick , Wellmann Peter J.
Published: March 2009

Several highly aluminum doped SiC bulk crystals were grown with a modified PVT (MPVT) method. To facilitate 4H-SiC formation, growth was conducted on the C-face. The samples were investigated using Hall measurements in the Van-der-Pauw geometry. Lowest room temperature values for specific resistivities were 0.09 Ωcm for 6H-SiC and 0.2 Ωcm for 4H-SiC, which are to our knowledge the lowest values yet reported in literature. Thus, resistivity values of < 0.2 Ωcm, which are required for substrates in high power device applications, could be demonstrated for 4HSiC. Remarkably, in very highly doped samples the type of conduction could not be determined by Hall measurements.
Defect Characterization of 4H-SiC Bulk Crystals Grown on Micropipe Filled Seed Crystals
Authors: Kato Tomohisa , Kojima Kazutoshi , Nishizawa Shin Ichi , Arai Kazuo
Published: March 2009

We report defects study in 4H-SiC bulk crystals grown by sublimation method on
micropipe filled seed crystals oriented (0001) on-axis. The seed crystals of 1~3 inch in diameter were prepared from the large 4H-SiC bulk crystals. Before the sublimation growth, micropipes of the seed crystals were filled with epilayers grown by micropipe filling technique of CVD method. We confirmed about 95% of micropipes perfectly disappeared in the grown crystal. The mechanism of the
micropipe extinction was also defined by defect analysis.
Electronic Levels Induced by Irradiation in 4H-Silicon Carbide
Authors: Castaldini Antonio , Cavallini Anna , Rigutti L. , Nava Filippo
Published: March 2009

The effects of irradiation with protons and electrons on 4H-silicon carbide epilayers were investigated. The particle energy was 6.5 and 8.2 MeV. The electronic levels associated with the irradiation-induced defects were analyzed by current-voltage characteristics and deep level transient spectroscopy measurements up to 700 K. In the same temperature range the apparent free carrier concentration was measured by capacitance-voltage characteristics to monitor possible
compensation effects due to the deep level associated to the induced defects. Introduction rate, enthalpy and capture cross-section of such deep levels were compared and some conclusions about the nature of the defects were drawn.
Capacitance Spectroscopy Study of High Energy Electron Irradiated and Annealed 4H-SiC
Authors: Alfieri Giovanni , Monakhov Edouard V. , Linnarsson Margareta K. , Svensson Bengt Gunnar
Published: March 2009

Deep level transient spectroscopy (DLTS) was employed to investigate the annealing behaviour and thermal stability of radiation induced defects in nitrogen doped 4H-SiC epitaxial layers, grown by chemical vapor deposition (CVD). The epilayers have been irradiated with 15 MeV electrons and an isochronal annealing series has been carried out. The measurements have been performed after each annealing step and six electron traps located in the energy band gap range
of 0.42-1.6 eV below the conduction band edge (Ec) have been detected.
Comparative Study of 4H-SiC Irradiated with Neutrons and Heavy Ions
Authors: Kalinina Evgenia V. , Kholuyanov G. , Onushkin G. , Davydov D.V. , Strel'chuk Anatoly M. , Konstantinov Andrey O. , Hallén Anders , Skuratov V.A. , Kuznetsov Andrej Yu.
Published: March 2009

The influence of the irradiation with neutrons, Kr+ (245 MeV) and Bi+ (710 MeV) ions on the optical and electrical properties of high-resistivity, high-purity 4H-SiC epitaxial layers grown by chemical vapor deposition was investigated using photoluminescence and deep-level transient spectroscopy. Electrical characteristics were studied using Al and Cr Schottky barriers as well as p+-n-n+ diodes fabricated by Al ion implantation on this epitaxial layers. It was found that both
"light" neutrons and high energy heavy ions introduced identical defect centers in 4H-SiC. So, even at extremely high density of the ionization energy of 34 keV/nm, typical for Bi+ ion bombardment, damage structure formation in SiC single crystal is governed by energy loss in elastic collisions.
Characterization of 4H-SiC Epitaxial Layers by Microwave Photoconductivity Decay
Authors: Kumar R.J. , Losee Peter A. , Li Can Hua , Seiler Joseph , Bhat I. , Chow T. Paul , Borrego J.M. , Gutmann Ronald J.
Published: March 2009

A Microwave Photoconductivity Decay (M-PCD) technique which senses changes insample conductivity as carriers recombine following excitation by a laser pulse, has been used to determine the minority carrier recombination lifetime from the decay rate of carriers in 4H-SiC epitaxial layers. Decay times varying from 60 ns to 500 ns have been measured, with the decay increasing with thickness. Device simulations show that I-V characteristics of pin diodes fabricated with these epitaxial layers are compatible with the observed decay times.
Excitation Power Dependence of Al-Related Features in the LTPL Spectra of 4H-SiC
Authors: Zielinski Marcin , Balloud Carole , Juillaguet Sandrine , Boyer Bernard , Soulière Véronique , Camassel Jean
Published: March 2009

Recently, a systematic comparison of SIMS measurements with LTPL (Low Temperature Photoluminescence) spectra led us to propose a straightforward empirical calibration of the LTPL intensity versus Al content in 4H-SiC samples. In the present work we analyze the effect of the LTPL excitation power on the intensity of the Al-related features. We examine the influence of the excitation conditions on the calibration curve and determine the limitations of the method.
Defect Evolution in Ion Irradiated 6H-SiC Epitaxial Layers
Authors: Ruggiero Alfonso , Zimbone M. , Roccaforte Fabrizio , Libertino Sebania , La Via Francesco , Reitano Ricardo , Calcagno Lucia
Published: March 2009

Deep-Level Transient Spectroscopy and room temperature photoluminescence were used to characterise a 6H-SiC epitaxial layer irradiated with 10 MeV C+ and to follow the defect annealing in the temperature range 300-1400 °C. The intensity of luminescence peak at 423 nm, related to band to band transitions, decreases after irradiation and it is slowly recovered after annealing in the temperature range 1000-1400 °C. The DLTS spectra of low temperature annealed samples show the presence of several overlapping traps, which anneal and evolve at high
temperatures. After 1200 °C a main level at Ec-0.43 eV (E1/E2) is detected. The comparison between luminescence and DLTS results indicates that the defect associated with the E1/E2 level is mainly responsible for the luminescence quenching after irradiation.
Probing of the Wave Function of Shallow Donors and Acceptors by EPR in SiC Crystals with Changed Isotopic Composition
Authors: Muzafarova Marina V. , Ilyin Ivan V. , Mokhov E.N. , Baranov P.G. , Ber B.Ya. , Ionov A.N. , Kop'ev P.S. , Kaliteevskii M.A. , Godisov O.N. , Kaliteevskii A.K.
Published: March 2009

The conclusion which is drawn from the EPR line broadening and narrowing of the N
shallow donor in an isotope enriched and non-enriched 4H-SiC and 6H-SiC crystals along with previous ENDOR results shows that the spin-density distribution over the C and Si nuclei differs between the 4H-SiC and 6H-SiC polytypes. The main part of the spin density in 4H-SiC is located on the Si sublattice. In contrast, in 6H-SiC the main part of the spin density is located on the C sublattice. An explanation for the difference in the electronic wave function of the N donor in 4HSiC
and 6H-SiC can be found in the large difference in the band structure of two polytypes and in the position of the minima in the Brillouin zone.
Effective-Mass Theory of Shallow Donors in 4H-SiC
Authors: Ivanov Ivan G. , Stelmach A. , Kleverman Mats , Janzén Erik
Published: March 2009

The one-valley effective-mass approximation is developed for the case of uniaxial
crystals with indirect bandgap and applied to the donor states in 4H-SiC. Good agreement is found between the theory and experiments providing data on the electronic states of the shallowest nitrogen donor in 4H-SiC. The ionization energy of this donor is deduced to be 61.35 ± 0.2 meV.
Analysis of SiC Islands Formation during First Steps of Si Carbonization Process
Authors: Méndez David , Aouni A. , Araujo Daniel , Bustarret Etienne , Ferro Gabriel , Monteil Yves
Published: March 2009

The effect of the temperature at which the carbon source is introduced in the
reactor on the early stages of the carbonization process is analyzed here. Three samples heated up to 1150°C with propane introduction temperatures (Tintro) of 725, 1030 and 1100°C are analyzed by transmission electron microscopy and attenuated total reflectance. The size of the SiC nuclei increases with Tintro. There is also an effect on the strain of the resulting carbonization layer. The electron diffraction pattern of the sample with the highest Tintro shows a fully relaxed 3C-SiC layer, while no evidence of SiC relaxation is present in low Tintro samples where the SiC islands seems to be pseudomorphic.
The Search for Near Interface Oxide Traps - First-Principles Calculations on Intrinsic SiO2 Defects
Authors: Knaup J.M. , Deák Peter , Gali Adam , Hajnal Z. , Frauenheim Thomas , Choyke Wolfgang J.
Published: March 2009

The density of interface traps (Dit) in thermally oxidized SiC is unacceptably high for MOS device fabrication. The most severe problem is posed by the extremely high concentration of slow acceptor states near the conduction band edge of 4H-SiC. These states are attributed to near interface traps originating from (probably intrinsic) defects in the oxide. Here a systematic theoretical search is presented for possible defects in the oxide with an appropriate acceptor level. Supercell calculations using a hybrid functional approach (and resulting in a correct gap) on defects in alpha-quartz exclude the oxygen vacancy and the oxygen interstitial, as possible candidates. In contrast, these calculations predict interstitial silicon to have an acceptor level in the appropriate range. The carbon interstitial in silica has an acceptor level somewhat deeper than that. Occupation of these levels give rise to significant rearrangement of the environment, leading to a more extended
defect structure.
Epitaxial Deposition of Silicon Carbide Films in a Horizontal Hot-Wall CVD Reactor
Authors: Veneroni Alessandro , Omarini Fabrizio , Masi Maurizio , Leone Stefano , Mauceri Marco , Pistone Giuseppe , Abbondanza Giuseppe
Published: March 2009

The present production processes for epitaxial SiC do not allow the matching of productivity with the material quality requested by the microelectronics market. Here, to respond to such a demand, a combined experimental and multi-scale – multi-hierarchy modeling approach was adopted. Models allow to verify a priori the role of process operative parameters on the performance ones for both
the final product and of the process itself, like growth rate uniformity, film stoichiometry and dopants incorporation, homogeneous nucleation of particulate, microdefects and film morphology. Specifically, in this work the developing of a lumped deposition mechanism is addressed
SiC and III-Nitride Growth in Hot-Wall CVD Reactor
Authors: Janzén Erik , Bergman Peder , Danielsson Örjan , Forsberg Urban , Hallin Christer , Hassan Jawad , Henry Anne , Ivanov Ivan G. , Kakanakova-Georgieva A. , Persson P.O.Å. , Wahab Qamar-ul
Published: March 2009

The Hot-Wall CVD reactor was developed for the thick epitaxial SiC layers needed for high voltage power devices but its inherent better properties – better cracking efficiency of the precursor gases and better lateral and vertical temperature homogeneity – should also influence the growth of other materials such as the III-nitrides. We will give some examples of thick SiC layers grown on either off- or on-axis substrates with this technique. We will also show that high-quality
III-nitride materials can be grown.
Surface Preparation of 6H-SiC Substrates by Electron Beam Annealing
Authors: Agueev Oleg A. , Avdeev Sergey P. , Svetlichnyi Alexander M. , Konakova Raisa V. , Milenin Victor V. , Lytvyn Petr M. , Lytvyn Oksana S. , Okhrimenko Olga B. , Soloviev Stanislav I. , Sudarshan Tangali S.
Published: March 2009

An effect of electron beam annealing (EBA) on both surface morphology and
characteristics of test Ti/n-6H-SiC contacts was investigated. It was found that the mean roughness of the n-6H-SiC surface decreased from 3.43 nm to 1.35 nm and the surface sheet resistance increased from 3.1 to 4.0 Ω/sq after EBA. The Ti/n-6H-SiC contacts formed on substrates after EBA exhibited ohmic properties, while the same contacts formed on the un-annealed samples were Schottky contacts with the barrier height of 0.63 eV and ideality factor of 1.92.
Increased Growth Rate in a SiC CVD Reactor Using HCl as a Growth Additive
Authors: Myers-Ward Rachael L. , Kordina Olof , Shishkin Z. , Rao Shailaja P. , Everly R. , Saddow Stephen E.
Published: March 2009

Hydrogen chloride (HCl) was added to a standard SiC epitaxial growth process as an additive gas. A low-pressure, hot-wall CVD reactor, using silane and propane precursors and a hydrogen carrier gas, was used for these experiments. It is proposed that the addition of HCl suppresses Si cluster formation in the gas
phase, and possibly also preferentially etches material of low crystalline quality. The exact mechanism of the growth using an HCl additive is still under investigation, however, higher growth rates could be obtained and the surfaces were improved when HCl was added to the flow. The film morphology was studied using SEM and AFM and the quality with LTPL analysis, which are reported.
Ni-Silicide Contacts to 6H-SiC: Contact Resistivity and Barrier Height on Ion Implanted n-Type and Barrier Height on p-Type Epilayer
Authors: Moscatelli Francesco , Scorzoni Andrea , Poggi Antonella , Canino Mariaconcetta , Nipoti Roberta
Published: March 2009

Recently Ni/SiC contacts have been studied in order to achieve very low contact
resistivity (rc) values on n-type SiC. In this work contact resistivity values of Ni-silicide contacts to n-type ion implanted 6H-SiC are analyzed aiming at extracting the Schottky Barrier Height (SBH). The n-type ion implanted 6H-SiC specimens were annealed at 1300, 1500, 1650°C for 20 min in a
high purity Ar ambient. The rc values have been extracted from Transmission Line Method (TLM) measurements in the range of temperatures 25-290°C. The rc values are in the range 1-5×10-5 Wcm2 depending on the annealing temperature. The SBH fBn has been extracted by exploiting the dependence of the contact resistivity on the temperature. By using the field emission model, the value obtained for fBn on our samples is in the range 1.1-1.3 eV depending on the annealing
temperature. The SBH on p-type 6H-SiC has been evaluated on Schottky diodes by means of both IV and C-V measurements. A value of qfBp= (1.75±0.05) eV has been obtained on p-type SiC through the C-V method. The average SBH extracted from I-V data collected at room temperature is (1.19±0.03) eV and this value increases as a function of the temperature until (1.50±0.01) eV at 290°C. Differences between values of SBH extracted from I−V and from C−V measurements are explained in terms of inhomogeneous barrier height
Characterization of Electrical Contacts on Polycrystalline 3C-SiC Thin Films
Authors: Castaldini Antonio , Cavallini Anna , Rossi Marco , Cocuzza M. , Ricciardi Carlo
Published: March 2009

We report on the investigation of electrical properties of polycrystalline 3C-SiC thin
films deposited on oxidized Si by low pressure chemical vapor deposition (LPCVD) to obtain bi-layer structures [Si(100)/SiO2/poly 3C-SiC] for pressure sensors and micro-electromechanical system (MEMS) applications.
Polycrystalline 3C-SiC films have been preliminary characterized in their compositional, structural, morphological and electrical properties. Moreover, metal contact definition has been carefully optimized by transmission line method (TLM) analyses performed at different temperatures. We focuses the attention on the evaluation of the bulk resistivity (ρ), the specific contact resistivity (ρc) and their behavior dependence on the temperature because these are the
characteristics of major importance for the fabrication of pressure sensors or MEMS.
Structure and Morphology of 4H-SiC Wafer Surfaces after H2-Etching
Authors: Soubatch S. , Saddow Stephen E. , Rao Shailaja P. , Lee W.Y. , Konuma M. , Starke Ulrich
Published: March 2009

Commercial on-axis wafers of 4H-SiC(0001) were etched in a standard reactor for chemical vapor deposition (CVD) using molecular hydrogen flux in order to improve the structure and morphology of the surface. The substrate temperature during etching was varied from 1400 to 1600°C. Characterization of the surface morphology was performed using optical and atomic force microscopy (AFM). Low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy
(XPS) were also used to examine the surface structure and chemical composition of the samples. The sample of best quality was obtained for an etching temperature of 1400°C. Its surface is ° × 30 ) 3 3 ( R reconstructed and covered by an ordered “silicate” layer. Increasing the substrate temperature during etching to 1500°C leads to enhanced step-bunching and the formation of macroterraces. At 1600°C distinct depressions appear on the surface, presumably from etching of structural defects such as screw dislocations. Subsequent annealing at 1000°C in ultra-high vacuum (UHV) removes the surface oxide and produces the ° × 30 ) 3 3 ( R surface phase of clean 4HSiC(
0001).
Reactive Ion Etching Induced Surface Damage of Silicon Carbide
Authors: Xia Jun Hai , Rusli E. , Gopalakrishnan R. , Choy S.F. , Tin Chin Che , Ahn J. , Yoon S.F.
Published: March 2009

Reactive ion etching of SiC induced surface damage, e.g., micromasking effect induced coarse and textured surface, is one of the main concerns in the fabrication of SiC based power devices [1]. Based on CHF3 + O2 plasma, 4H-SiC was etched under a wide range of RF power. Extreme coarse and textured etched surfaces were observed under certain etching conditions. A super-linear relationship was found between the surface roughness and RF power when the latter was varied from 40 to 160 W. A further increase in the RF power to 200 W caused the surface roughness to drop abruptly from its maximum value of 182.4 nm to its minimum value of 1.3 nm. Auger electron spectroscopy (AES) results revealed that besides the Al micromasking effect, the carbon residue that formed a carbon-rich layer, could also play a significant role in affecting the surface roughness. Based on the AES results, an alternative explanation on the origin of the coarse surface is proposed.
Forward-Bias Degradation in 4H-SiC p+nn+ Diodes: Influence of the Mesa Etching
Authors: Camara Nicolas , Thuaire Aurelie , Bano Edwige , Zekentes Konstantinos
Published: March 2009

The defects were investigated in p+nn+ 4H-SiC diodes by observing the forward-biasinduced light emission through the substrate. The spatial intensity distribution, the temporal evolution and the spectral content of the electroluminescence (EL) signal have been measured in order to detect, identify and understand the defect formation during forward-bias application. It was found that, exept from the dislocations inside the epilayers, mesa etching is a main cause for the
formation of extended defects. To our knowledge, for the first time, reduction of mesa-etchinginduced defects is shown in this investigation.
Realisation of Large Area 3C-SiC MOSFETs
Authors: Schöner Adolf , Bakowski Mietek , Ericsson Per , Strömberg Helena , Nagasawa Hiroyuki , Abe Masayuki
Published: March 2009

Lateral MOSFET devices with varying size from a single unit cell to 3x3 mm2 containing 1980 unit cells have been realised using two basic technologies; lateral trench MOSFET (LTMOS) with epitaxially grown source and drain, and lateral MOSFET with lightly doped drain (LDDMOS) having implanted source and drain regions. The LDDMOS devices had blocking capability of 100 V and the channel mobility in the range of 10 cm2/Vs in {-110} current flow direction and of
5 cm2/Vs in {110} current flow direction. The properties of both fabricated MOSFET types, LTMOS and LDDMOS, are dominated by a high density of interface states of the order of 1×1013 cm-2eV-1. Both the drain current and the leakage current scale linearly with the device size up to the maximum investigated device size of 3x3 mm2. No size limiting defects have been observed
contrary to what is often the case in 4H-SiC material.
Homoepitaxial Growth of 4H-SiC Using CH3Cl Carbon Precursor
Authors: Koshka Yaroslav , Lin Huang De , Melnychuck Galyna , Mazzola Michael S. , Wyatt Jeffery L.
Published: March 2009

The results of the initial experiments with halogenated carbon precursor chloromethane (CH3Cl) for epitaxial growth of 4H-SiC are presented. The growth rate for mirror-like morphology was easily increased up to about 7 µm/hr at C-rich conditions without detectable surface morphology degradation. Further increase of the silane flow resulted in island formation. The growth with the traditional silane-propane system at the same conditions (and optimized Si/C ratio) produced a very different result, with the growth rate decreasing from upstream to downstream, and morphology degradation taking place for much lower growth rate than in CH3Cl growth. Consequently, the epitaxial growth with chloromethane appears to have significantly different kinetics of the gas-phase precursor decomposition and different mechanisms of the surface reactions, which favors the step-flow growth. In addition, these preliminary data indicated that the maximum achievable growth rate corresponding to the good surface morphology may be noticeably larger for the CH3Cl+SiH4+H2 growth system.
Improved Surface Morphology and Background Doping Concentration in 4H-SiC(000-1) Epitaxial Growth by Hot-Wall CVD
Authors: Wada Keiji , Kimoto Tsunenobu , Nishikawa Kimito , Matsunami Hiroyuki
Published: March 2009

4H-SiC layers have been homoepitaxially grown on off-axis 4H-SiC(000-1) under various conditions by horizontal hot-wall CVD. Improvement of surface morphology and reduction of background doping concentration have been achieved. Surface morphology grown on the (000-1) C face strongly depends on the C/Si ratio at 1500 °C, and hillock-like surface defects can be eliminate by increasing growth temperature to 1600 °C. Site-competition behavior is clearly observed under
low-pressure growth conditions even on the (000-1) C face. The lowest doping concentration has been determined to be 6.0x1014 cm-3. A trial of high-speed growth on the (000-1) C face and deep level analysis are also discussed.
High-Purity Versus High-Defect-Density Semiinsulating Substrates for SiC MESFET: Simulation of Device Characteristics
Authors: Koshka Yaroslav , Sankin Igor
Published: March 2009

Quantitative assessment of the influence of deep traps in semiinsulating (SI) SiC
substrates on transient behavior and substrate leakage current of SiC MESFET is reported. Twodimensional device simulation confirmed that favorable reduction of the current-collapse happens when a fully depleted buffer is used. Simultaneously, the high-purity buffer causes an undesirable increase of the current bypassing the physical channel. A similar and even more pronounced effect is observed when very high purity SI substrates are used. The deep level-induced transient behavior
disappears for the concentration of deep acceptor traps below the order of 1x1015 cm-3. However, this low trap concentration results in a virtual inability to pinch-off the channel even at very high gate biases. It has been demonstrated that the electric field preventing electron injection from thechannel into the substrate is very sensitive to the initial charge state of the traps prior to device biasing, which in turn is determined by the energy position of the deep levels in the substrate.
Current Gain of 4H-SiC Bipolar Transistors Including the Effect of Interface States
Authors: Domeij Martin , Danielsson Erik , Lee Hyung Seok , Zetterling Carl Mikael , Östling Mikael
Published: March 2009

The current gain (b) of 4H-SiC BJTs as function of collector current (IC) has been investigated by DC and pulsed measurements and by device simulations. A measured monotonic increase of b with IC agrees well with simulations using a constant distribution of interface states at the 4H-SiC/SiO2 interface along the etched side-wall of the base-emitter junction. Simulations using only bulk recombination, on the other hand, are in poor agreement with the measurements. The interface states degrade the simulated current gain by combined effects of localized recombination and trapped charge that influence the surface potential. Additionally, bandgap narrowing has a significant impact by reducing the peak current gain by about 50 % in simulations.
1000 V, 30 A SiC Bipolar Junction Transistors and Integrated Darlington Pairs
Authors: Krishnaswami Sumi , Agarwal Anant K. , Capell Craig , Richmond Jim , Ryu Sei Hyung , Palmour John W. , Balachandran S. , Chow T. Paul , Baynes Stephen , Geil Bruce , Jones Kenneth A. , Scozzie Charles
Published: March 2009

1000 V Bipolar Junction Transistor and integrated Darlington pairs with high current
gain have been developed in 4H-SiC. The 3.38 mm x 3.38 mm BJT devices with an active area of 3 mm x 3 mm showed a forward on-current of 30 A, which corresponds to a current density of 333 A/cm2, at a forward voltage drop of 2 V. A common-emitter current gain of 40 was measured on these devices. A specific on-resistance of 6.0 mW-cm2 was observed at room temperature. The onresistance
increases at higher temperatures, while the current gain decreases to 30 at 275°C. In addition, an integrated Darlington pair with an active area of 3 mm x 3 mm showed a collector current of 30 A at a forward drop of 4 V at room temperature. A current gain of 2400 was measured on these devices. A BVCEO of 1000 V was measured on both of these devices.
Low and High Temperature Performance of 600V 4H-SiC Epitaxial Emitter BJTs
Authors: Balachandran S. , Chow T. Paul , Agarwal Anant K.
Published: March 2009

The paper presents a study of the different aspects of the temperature dependent
performance of a 4H-SiC epi-emitter Bipolar Junction Transistor particularly the low temperature performance. Some critical device physics related factors that affect the forward active performance of the device are explored and the device behavior is modeled up to 100K. We present for the first time the experimental low-temperature (down to 100K) performance of 4H-SiC epi-emitter BJTs and the determination of the temperature beyond which the current gain starts to increase with temperature. We have also corroborated these results with 2-dimensional device simulations.
Optimisation of Heterostructure Bipolar Transistors in SiC
Authors: Chen Chia Ching , Horsfall Alton B. , Wright Nicolas G. , O'Neill Anthony G.
Published: March 2009

We present the results of a simulation study on the behaviour of 3C-SiC bipolar
transistors fabricated using a 6H-SiC heterojunction emitter. We show that despite the potential barrier originating in the discontinuity of the conduction bands, that npn devices offer a higher common emitter gain in comparison to pnp devices. The base voltage corresponding to the maximum gain of the device is controlled by the tunnelling of carriers across the collector-base junction and is different for both npn and pnp devices.
Lifetime Control of the Minority Carrier in PiN Diodes by He+ Ion Implantation
Authors: Tanaka Yasunori , Kojima Kazutoshi , Takao Kazuto , Okamoto Mitsuo , Kawasaki Megumi , Takatsuka Akio , Yatsuo Tsutomu , Arai Kazuo
Published: March 2009

This paper reports the first demonstration of the lifetime control of the minority carrier in 4H-SiC PiN diodes by He+ ion implantation. In this work, we fabricated 4H-SiC PiN diodes with the epitaxial junction and the blocking voltage of 2.6kV, precisely corresponding to the theoretical blocking voltage calculated from the doping concentration (4.0x1015/cm2) and the thickness of the
drift layer (16.5 µm). He+ ion implantation was performed with the energy and the dose of 400kV and 1.0x1013-2.0x1014/cm2, respectively. We observed no different characteristics in the blocking voltage (2.6kV) and leakage current (<10µA@2.5kV) between the PiN diodes with/without He+ ion implantation. However, we confirmed the improvement of the current recovery characteristics in the diodes with He+ ion implantation.
Investigation of Microwave Switching 4HSiC pin Diodes in the 20-500 °C Temperature Range
Authors: Boltovets Mykola S. , Basanets Volodymyr V. , Camara Nicolas , Krivutsa Valentyn A. , Zekentes Konstantinos
Published: March 2009

The switching characteristics of 4Н-SiС p-i-n diodes with 6 µm long i-region were
investigated in the 20÷500 °С temperature ranges. It is shown that the diode reverse current increases with temperature and does not exceed 10-7 А at temperature of 500 °С (UR = 100 V). The diode resistance rF at forward current of 40 mA decreases as temperature increases from 20 up to 500 °С. The effective minority charge carrier lifetime in the i-region (τр) was determined from the
diode switching (from forward current to reverse voltage) characteristics; it was about 5 ns. As temperature increases from 20 up to 500 °С, τр increases by a factor of 3. We discuss the possibility of application of such diodes (i) in microwave switching facilities and (ii) as temperature sensors. A comparison is made between the parameters of 4Н-SiС p-i-n diodes and those of Si p-i-n diodes
with comparable values of calculated blocking voltage.
Mechanical and Thermal Properties of Silicon Nitride Hot Pressed with Adding Rare-Earth Oxides
Authors: Choi Dae Ho , Moon Byung Kyu , Sung Rak Joo , Kim Seung Ho , Niihara Koichi
Published: March 2009

Mechanical and thermal properties of Si3N4 ceramics with various rare-earth oxides
(La2O3, CeO2, Lu2O3, Dy2O3, Sm2O3, Nd2O3, Yb2O3, and RuO2) were investigated. Flexural strength of silicon nitride with addition of 5vol% Nd2O3, CeO2, Dy2O3, and Sm2O3 showed higher value than that of silicon nitride with Lu2O3 and La2O3 added because they form denser microstructure and smaller elongated grain. Thermal conductivity of silicon nitride with an addition
of 5vol% RuO2 was more enhanced than that of silicon nitride added with Nd2O3, Sm2O3, and Dy2O3 because the addition of RuO2 depressed grain growth. It is also associated with lattice oxygen governing thermal conductivity of Si3N4 when added rare-earth oxides.
Effect of Warm Rolling on Microstructure and High Temperature Mechanical Behavior of a Nano-Structured Al-8Fe-2Mo-2V-1Zr Alloy
Authors: Kim Won Yong , Park Jae Sung , Kim Mok Soon
Published: March 2009

Mechanical properties of a nano-structured Al-8Fe-2Mo-2V-1Zr alloy produced by spray forming and subsequent hot-extrusion at 420°C were investigated in terms of tensile test as a function of temperature. Warm rolling was adapted as an additional process to expect further refinement in microstructure. Well-defined equiaxed grain structure and finely distributed dispersoids with nano-scale in particle size were observed in the spray formed and hot extruded sample (as-received
sample). The average grain size and particle size were measured to 500 nm and 50 nm, respectively. While it was found that warm rolling gives rise to precipitate fine dispersoids less than 10 nm without influencing the grain size of matrix phase, in the temperature range of RT∼150°C, distinguishable changes in ultimate tensile strength were not found between the as-received and warm-rolled samples. At elevated temperatures ranging from 350 to 550°C, warm-rolled sample showed a higher value of elongation than as-received one although similar values of elongation were observed between two samples at temperatures lower than 350°C.
The Influence of Electric Current Pulses on the Microstructure of Magnesium Alloy AZ91D
Authors: Yang Yuan Sheng , Zhou Quan , Hu Zhuang Qi
Published: March 2009

The microstructure evolution of magnesium alloy AZ91D solidified with different
electric current pulses and cooling rates was investigated and a new method, Low-voltage Electric Current Pulses (LVECP), to produce semi-slurry magnesium alloy was developed in this paper. The experimental results showed that the electric current pulses during solidification changed morphology of dendrites and the equiaxed, non-dendritic grains formed. The size of the primary a-Mg particles in semi-solid AZ91D alloy and the sphericity of the particles decreased with increase of discharging the voltage and treating time of LVECP. The increase of the cooling rate
during the solidification of AZ91D alloy with LVECP promoted the formation of finer a-Mg particles, but the value of the sphericity of the particles rised. The formation of equiaxed, nondendritic structure by LVECP might be attributed to the electric current pulses increase the nucleation rate, restrained growth of the dendrites, and made dendrite arms remelted during the solidification of AZ91D alloy.
Thixotropic Mg Alloys through Liquidus and Sub-Liquidus Casting
Authors: Le Qi Chi , Cui J. , Xia Kenong
Published: March 2009

Several Mg alloys were processed to achieve the thixotropic microstructure of
non-dendritic, globular primary grains for semisolid forming using a novel method that does not require stirring. The alloys were poured at their liquidus temperatures or about ten degrees below the liquidus temperatures using either batch or semi-continuous casting. Although the compositions of the alloys had considerable effects on details of the resulting microstructure, generally fine, equiaxed primary grains were obtained by controlling the resting time, casting speed and cooling rate. The lower casting temperatures and addition of calcium were effective in preventing burning of Mg without using a protective atmosphere. This new method has great
potential for industry applications.
Effect of Stabilised ZrO2, Al2O3 and TiO2 on Sintering of Hydroxyapatite
Authors: Mezahi F.Z. , Harabi Abdelhamid , Zouai S. , Achour S. , Bernache-Assollant Didier
Published: March 2009

In this work, the hydroxyapatite was prepared from cortical bone after calcination at 700°C during 1 hour. In order to improve mechanical properties of HA, 5 wt% of the ZrO2 (stabilized with 12.0 wt% CeO2), Al2O3 and TiO2 were added to HA powder as a reinforcing phase. All the powders were sintered at 1300°C for 2 hours. The XRD was utilized to identify the phases composition. It was found that the initial calcined powder is hydroxyapatite with the following chemical composition Ca5(PO4)3OH. In addition, the phenolphthalein test has put into evidence the existence of free CaO. For powders containing ZrO2, the XRD spectra has showed a little percent of formed b-tricalcium phosphate (b-TCP); the HA was decomposed to (b-TCP) and CaO which forms with ZrO2 the calcium zirconate (CaZrO3). Nevertheless, in powders containing TiO2, the XRD spectra showed that a partial decomposition of HA to b-TCP was occurred with formation of calcium titanium oxide (CaTiO3). However, for powders containing Al2O3, a nearly full decomposition of HA to b-TCP was occurred, the free Al2O3 was present. Finally, it has been found that HA composites containing a large amount of b-tricalcium phosphate are resorbale than HA composites containing a small amount of b-TCP and they were not well densified. The microhardness values of HA- ZrO2 composites were greater than those of HA- Al2O3 and HATiO2 composites.