bluuebunny/crossref_metadata_2025 huggingface dataset:
High Temperature Capacitive Pressure Sensor Employing a SiC Based Ring Oscillator
Authors: Meredith Roger D. , Neudeck Philip G. , Ponchak G.E. , Beheim Glenn M. , Scardelletti M.C. , Jordan J.L. , Chen Liang Yu , Spry David J. , Krasowski Michael J. , Hunter Gary W.
Published: May 2012

Smart sensor systems that can operate at high temperatures are required for a range of aerospace applications such as propulsion [1]. For future aerospace propulsion systems to meet the requirements of decreased maintenance, improved performance, and increased safety, the inclusion of intelligence into the propulsion system design and operation is necessary. This implies the development of sensor systems able to operate under the harsh environments present in an engine. Likewise, applications such as Venus exploration missions require systems that can operate in the harsh environments present on the Venus planetary surface. More sensor systems added to the aircraft increases the number of wires and the associated weight, complexity, and potential for failure. Thus, there is a need not only for high temperature sensors and electronics, but also for high temperature wireless technology. This implies the integration of sensors, electronics, wireless circuits, and power into a single system. In this paper, we demonstrate a significant step towards this goal, i.e., for the first time the integration of a pressure sensor with a SiC JFET logic-gate ring oscillator that operates at 500 °C; the sensor output signal is extracted from the small-signal ring oscillation frequency detected at the powersupply end of the DC power wires.
10 kV SiC Power MOSFETs and JBS Diodes: Enabling Revolutionary Module and Power Conversion Technologies
Authors: Das Mrinal K. , Grider David , Leslie Scott , Raju Ravi , Schutten Michael , Hefner Allen
Published: May 2012

The majority carrier domain of power semiconductor devices has been extended to 10 kV with the advent of SiC MOSFETs and Schottky diodes. Twenty-four MOSFETs and twelve JBS diodes have been assembled in a 10 kV half H-bridge power module to increase the current handling capability to 120 A per switch without compromising the die-level characteristics. For the first time, a custom designed system (13.8 kV to 465/√3 V solid state power substation) has been successfully demonstrated with these state of the art SiC modules up to 855 kVA operation and 97% efficiency. Soft-switching at 20 kHz, the SiC enabled SSPS represents a 70% reduction in weight and 50% reduction in size when compared to a 60 Hz conventional, analog transformer.
SiC JFET Power Modules for Reliable 250°C Operation
Authors: Sheridan David C. , Casady Jeff B. , Autry Tracy , Aguirre Rizal , Lee Victor , Johnson R. Wayne , Palmer Michael J. , Scofield James
Published: May 2012

An all SiC 600V / 6 m hermetic half-bridge power module has been developed to operate at ambient temperatures of 200oC and with junction temperatures near 250oC. The modules use SiC trench JFET technology and can output over 100A at Tj=250oC. Double pulsed switching was performed up to temperatures of 150oC with a measured total switching energy of 0.73mJ
Investigation of Basal Plane Dislocation Reduction/Elimination by Molten KOH-NaOH Eutectic Etching Method
Authors: Song Hai Zheng , Sudarshan Tangali S.
Published: May 2012

An optimized molten KOH-NaOH eutectic etching method is developed to reveal defects in highly n-doped SiC substrates and to pre-treat the substrate prior to epitaxial growth. Different from the conventional KOH etching method, by way of eutectic method, the basal plane dislocation (BPD) conversion in the subsequent epitaxial growth is independent of the etch pit size pre-generated on the substrate. Even with a short period (~3 minutes) of pretreatment which does not generate any visible etch pits or degradation of surface morphology on the substrate, an epilayer with low BPD density -2 is still achieved. This simple and non-destructive method shows high potential to be practically employed as one of the basic pretreatment steps to the substrates in SiC epitaxial growth in order to achieve very low or free BPD density.
A 450°C High Voltage Gain AC Coupled Differential Amplifier
Authors: Yang Jie , Fraley John , Western Bryon , Schupbach Marcelo , Lostetter Alexander B.
Published: May 2012

APEI, Inc. designed, fabricated and tested a high gain AC coupled differential amplifier based on a custom-built silicon carbide (SiC) vertical junction field effect transistor (VJFET). This SiC differential amplifier is capable of high temperature operation up to 450 °C, at which a high differential voltage gain of more than 47 dB is maintained. This high gain AC coupled differential amplifier can be integrated with harsh environment sensors that deliver weak AC output signals to improve signal quality and noise immunity.
300C Capable Digital Integrated Circuits in SiC Technology
Authors: Patil Amita , Rao Naresh , Tilak Vinayak
Published: May 2012

This paper pertains to development of high temperature capable digital integrated circuits in n-channel, enhancement-mode Silicon Carbide (SiC) MOS technology. Among the circuits developed in this work are data latch, flip flops, 4-bit shift register and ripple counter. All circuits are functional from room temperature up to 300C without any notable degradation in performance at elevated temperature. The 4-bit counter demonstrated stable behavior for over 500 hours of continuous operation at 300C.
Direct Frequency Modulation of a High Temperature Silicon Carbide Oscillator
Authors: Brennan Daniel , Vassilevski Konstantin , Wright Nicolas G. , Horsfall Alton B.
Published: May 2012

This paper reports on direct frequency modulation of a RF Colpitts oscillator, realised from silicon carbide devices and proprietary components, capable of transmitting sensor data whilst operating at 300°C. Utilizing a reversed biased Schottky diode as a varactor in an LC oscillator, it is possible to modulate the frequency of an RF carrier by applying external voltage signals. These experiments have shown that a 10V bias will increase the frequency by as much as 10%, however signals as low as 10mV are easily detectable with standard silicon receivers.
Fabrication of Silicon Carbide Thin Film as a Stabilizing Layer for Improving the Stability of Porous Silicon Photodiodes
Authors: Naderi Nima , Hashim Md. Roslan
Published: May 2012

This paper investigates the effect of silicon carbide (SiC) thin film as a stabilizing layer on porous silicon (PS) in metal–semiconductor–metal (MSM) photodiodes. Photo-assisted pulsed electrochemical etching method was used to produce the PS layers with large pore density and small crystallite size. As–prepared PS surface was modified with acetylene gas flow in a thermal process (750°C) in order to replace the hydrogen termination by Si–C bonds which is more stable. During the thermal carbonization, carbon atoms penetrated into the silicon lattice forming a thin (~4 nm) SiC layer. Because of high inertness of silicon carbide thin film, thermally carbonized porous silicon layer (TC-PS) was found to be more stable than the freshly prepared PS surfaces. A small reduction in specific surface area was found after carbonization which is due to the small size of acetylene molecules. The FTIR measurements confirmed the presence of SiC bonds in the TC-PS sample. The photocurrent of the fabricated photodiodes based on as-grown PS was lowered under prolonged green laser radiation (532nm, 5mW), but devices based on TC-PS showed more stable I-V characteristics under the same condition even for 120 min of laser exposure.
Low Defect Density Bulk AlN Substrates for High Performance Electronics and Optoelectronics
Authors: Raghothamachar Balaji , Dalmau Rafael , Moody Baxter , Craft H. Spalding , Schlesser Raoul , Xie Jin Qiao , Collazo Ramón , Dudley Michael , Sitar Zlatko
Published: May 2012

Using the physical vapor transport (PVT) method, single crystal boules of AlN have been grown and wafers sliced from them have been characterized by synchrotron white beam X-ray topography (SWBXT) in conjunction with optical microscopy. X-ray topographs reveal that the wafers contain dislocations that are inhomogeneously distributed with densities varying from as low as 0 cm-2 to as high as 104 cm-2. Two types of dislocations have been identified: basal plane dislocations and threading dislocations, both having Burgers vectors of type 1/3<112-0> indicating that their origin is likely due to post-growth deformation. In some cases, the dislocations are arranged in low angle grain boundaries. However, large areas of the wafers are nearly dislocation-free and section X-ray topographs of these regions reveal the high crystalline perfection.
Performance Comparison of GaN Power Transistors and Investigation on the Device Design Issues
Authors: Lee Chwan Ying , Chen Yung Hsiang , Lee Lurng Shehng , Hung Chien Chung , Yen Cheng Tyng , Lin Suh Fang , Xuan Rong , Kuo Wei Hung , Ku Tzu Kun , Tsai Ming Jinn
Published: May 2012

One normally-on N-channel AlGaN/GaN device and two types of normally-off GaN devices have been studied. The normally-on device with Sapphire substrate shows good Idsat and breakdown characteristics, but the gate leakage current is quite large. The first normally-off GaN hybrid metal insulator semiconductor – high electron mobility transistor (MIS-HEMT) grown on Si substrate exhibits good performance with positive threshold voltage of 3V and the breakdown voltage of over 1800V. However the second normally-off GaN MOSFET structure is rather difficult to exhibit good blocking characteristic compared to GaN MIS-HEMT device due to inadequate device design.
Design of High-Performance Synchronous Buck DC-DC Converters Using GaN Power HEMTs
Authors: Shenai Krishna , Shah Krushal
Published: May 2012

Simple, physics-based, and accurate circuit models are reported for GaN power HEMTs and inductors; these models are then used to design high-performance chip-scale synchronous buck (SB) power converters to provide agile point-of-load (POL) low-voltage ( down to 1V) high-current (up to 10A) power to portable mobile devices from a battery. Excellent agreement between the measured and simulated results is demonstrated for load regulation for a 19V/1.2V, 800 kHz SB converter; for comparison, the same converter performance using the best commercially available state-of-the-art silicon power MOSFETs is also evaluated. It is shown that the conventional approach used for estimating power loss of a SB power converter is in error; a new application-specific Figure of Merit (FOM) for power switches is proposed that accounts for both input and output switching losses.
Density Functional Simulations of Transition Metal Terminated (001)-Diamond Surfaces
Authors: Tiwari Amit Kumar , Goss Jonathan P. , Briddon Patrick R. , Wright Nicolas G. , Horsfall Alton B.
Published: May 2012

The chemical termination of diamond strongly impacts its electron affinity and thermal stability. We have performed density functional calculations examining up to a monolayer of selected transition metals (Ti, V, Ni and Cu) on the 2×1 reconstructed (001) surface. We find that addition of the carbide forming species, Ti and V, results in significantly higher binding adsorption energies at all surface coverages relative to those of the non-carbide-forming species. For monolayer coverage by Cu or Ni, and sub-monolayer coverage by Ti and V, we observe a negative electron affinity. We propose that based upon the electron affinities and binding energies, metal coated 2×1 reconstructed (001) diamond surfaces are promising candidates for electron emitters.
Diamond Vertical Schottky Barrier Diode with Al2O3 Field Plate
Authors: Umezawa Hitoshi , Nagase Masanori , Kato Yukako , Shikata Shinichi
Published: May 2012

A field-plate structure is applied to vertical diamond Schottky barrier diode. A sputtered Al2O3 with 0.2 µm thickness is utilized for field-plate insulator. Fabricated diamond VSBD shows low leakage characteristics. Accordingly, the breakdown voltage is improved from 900V to 1,800V.
CdGeN2 and ZnGe0.5Sn0.5N2: Two New Nitride Semiconductors with Band Gaps in the Blue-Green
Authors: Punya Atchara , Lambrecht Walter R.L.
Published: May 2012

First-principles calculations are presented for CdGeN2 and ZnGe0.5Sn0.5N2 compounds with the orthorhombic structure derived from wurtzite. Lattice constants and internal parameters are obtained from local density approximation full-potential linearized muffin-tin orbital calculations and the quasiparticle self-consistent GW method is used to calculate the band structures. Corrections for zero-point motion and exciton binding energy are included. Both approaches lead to gaps in the blue-green region.
Process and Crucible Modification for Growth of High Doped 4H-SiC Crystal with Larger Diameter
Authors: Park Jong Hwi , Yang Tae Kyoung , Kim Il Soo , Lee Won Jae , Yeo Im Gyu , Eun Tai Hee , Lee Seung Seok , Kim Jang Yul , Chun Myoung Chul
Published: May 2012

The present research was focused to investigate various process parameters influenced on the large 4H-SiC crystal growth on a 6H-SiC seed by PVT method. The crucible diameter along horizontal axial direction and inserted graphite ring was modified to change the growth parameter like the temperature gradient. In the initial stage of growth, foreign polytypes such as 6H/4H were observed on 6H-SiC seed, indicating the growth temperature to be unstable on crystal surface. However, from the middle of growth step, 4H-SiC was successfully formed in the ingot with the modification of growth pressure and a SIMS analysis confirmed the high doping concentration in grown 4H-SiC crystal.
Low Temperature Epitaxy of 3C SiC Using Hexamethyldisilane Precursor on Si <111> Substrates
Authors: Wagner Brian , Oliver James D. , Singh Narsingh B. , King M. , McLaughlin S. , Kahler D. , Knuteson D. , Berghmans A. , Rai R.
Published: May 2012

The CVD growth of SiC thin films using hexamethyldisilane (HMDS) as the singular precursor on Si substrates with an AlN nucleation layer was explored in this study. A statistically designed experiment was used to conclude that growth temperature has the largest impact on crystal quality and surface microstructure. In addition to crystal quality, wafer bow was studied. Crystal quality and growth rate are loosely correlated to wafer bow in our study. SEM surface microstructural analysis of the SiC films shows a changing microstructure with growth temperature consistent changes in measured crystal quality. TEM studies reveal that the films are the 3C polytype having a high density of planar faults.
CVD Heteroepitaxial Growth of 3C-SiC on 4H-SiC (0001) Substrates
Authors: Li Xun , Leone Stefano , Andersson Sven , Kordina Olof , Henry Anne , Janzén Erik
Published: May 2012

This study has been focused on 3C-SiC epitaxial growth on 4H-SiC (0001) on-axis substrates using the standard CVD chemistry. Several growth parameters were investigated, including growth temperature, in-situ etching process and C/Si ratio. High quality single domain 3C epilayers could be obtained around 1350 °C, with propane present during pre-growth etching and when the C/Si ratio was equal to 1. The best grown layer is 100% 3C-SiC and single domain. The net n-type background doping is around 2x1016 cm-3. The surface roughness of the layers from AFM analysis is in the 3 to 8 nm range on a 50x50 μm2 area.
SixCy Thin Films Deposited at Low Temperature by DC Dual Magnetron Sputtering: Effect of Power Supplied to Si and C Cathode Targets on Film Physicochemical Properties
Authors: Medeiros Henrique S. , Pessoa Rodrigo S. , Sagás Júlio C. , Fraga Mariana A. , Santos Lúcia V. , Maciel Homero S. , Massi Marcos , da Silva Sobrinho A.S.
Published: May 2012

A DC dual magnetron sputtering system with graphite (C) and silicon (Si) targets was used to grow stoichiometric and non-stoichiometric silicon carbide (SixCy) thin films at low temperature. Two independently DC power sources were used to enable the total discharge power be shared, under certain proportions, between the Si and C magnetron cathodes. The motivation was to control the sputtering rate of each target so as to vary the stoichiometric ratio x/y of the deposited films. The species content, thickness and chemical bonds of as-deposited SixCy films were studied by Rutherford backscattering spectroscopy (RBS), profilometry analysis and Fourier transform infrared absorption (FTIR), respectively. Overall, the present work reveals a new reliable plasma sputtering technique for low temperature growth of amorphous SixCy thin films with the capability of tuning the degree of formation of a-SiC, a-Si and a-C bonds in the film bulk.
Mn Implantation for New Applications of 4H-SiC
Authors: Linnarsson Margareta K. , Wong-Leung Jennifer , Hallén Anders , Khartsev S.I. , Grishin A.M.
Published: May 2012

Structural disorder and lattice recovery of high dose, manganese implanted, semi-insulating, 4H-SiC have been studied by secondary ion mass spectrometry, Rutherford backscattering in channeling directions, visible-to-near infrared optical spectroscopy as well as with transmission electron microscopy. After heat treatment at 1400 and 1600 °C, a substantial rearrangement of manganese is observed in the implanted region. However, the crystal has not been fully recovered. More disorder remains in the [11 3] compared to the [0001] channel direction. Stacking faults, voids and 3C inclusions are observed in the implanted region. A Mn containing phase has most likely formed.
Diffusion and Gettering of Transition Metals in 4H-SiC
Authors: Danno Katsunori , Saitoh H. , Seki Akinori , Shirai T. , Suzuki Hiroshi , Bessho T. , Kawai Yoichiro , Kimoto Tsunenobu
Published: May 2012

Diffusion of transition metals in 4H-SiC has been investigated by secondary ion mass spectroscopy using epilayers and substrates implanted with titanium (Ti), chromium (Cr), iron (Fe), or nickel (Ni). In the epilayers, Cr, Fe, and Ni atoms have diffused by argon (Ar) annealing at 1780°C for 30 min. In n+ substrates, the diffusivity of the metals is smaller than that in the epilayers, and only Ni has diffused by the annealing. By the Ar or helium implantation following the implantation of transition metals, diffusion of transition metals can be successfully suppressed.
Photoluminescence and Raman Spectroscopy Characterization of Boron- and Nitrogen-Doped 6H Silicon Carbide
Authors: Ou Yi Yu , Jokubavicius Valdas , Liu Chuan , Berg Rolf W. , Linnarsson Margareta K. , Kamiyama Satoshi , Lu Zhao Yue , Yakimova Rositza , Syväjärvi Mikael , Ou Hai Yan
Published: May 2012

Nitrogen-boron doped 6H-SiC epilayers grown on low off-axis 6H-SiC substrates have been characterized by photoluminescence and Raman spectroscopy. The photoluminescence results show that a doping larger than 1018 cm-3 is favorable to observe the luminescence and addition of nitrogen is resulting in an increased luminescence. A dopant concentration difference larger than 4x1018 cm-3 is proposed to achieve intense photoluminescence. Raman spectroscopy further confirmed the doping type and concentrations for the samples. The results indicate that N-B doped SiC is being a good wavelength converter in white LEDs applications.
Simulation of the Temperature Dependence of Hall Carriers in Al Doped 4H-SiC
Authors: Nath Anindya , Scaburri Raffaele , Rao Mulpuri V. , Nipoti Roberta
Published: May 2012

A global minima search weighted and non-weighted least squares algorithm has been employed for a comparative study of various possible models to describe electrical properties of high dose Al implanted 4H-SiC. A wide range of experimental data has been taken from literature to demonstrate validation of the model. It was found that a single activation energy level, a temperature dependent Hall scattering factor and a degeneracy factor equal to 4 lead to a satisfactory fitting of experimental Hall data up to an Al substitutional density of 1020cm 3 in 4H SiC.
Elimination of Deep Levels in Thick SiC Epilayers by Thermal Oxidation and Proposal of the Analytical Model
Authors: Kawahara Koutarou , Suda Jun , Kimoto Tsunenobu
Published: May 2012

It has been clarified that Z1/2 center, a well known deep level as a lifetime killer, can be reduced to the concentration below 1011 cm-3 by thermal oxidation or C+ implantation plus Ar annealing. In this study, the authors investigate the trap-reduction phenomena systematically (experimentally), and propose a model to analyze the phenomena. Furthermore, prediction of the defect distributions is realized by solving a diffusion equation in accordance with the trap reduction model. This analytical model can explain almost all experimental data: oxidation-temperature dependence, oxidation-time dependence, and initial-Z1/2-concentration dependence of the defect reduction. Based on these results, the authors accomplish to eliminate the Z1/2 center to a depth of 100 μm in the sample with a relatively high initial-Z1/2-concentration of 1013 cm-3 by thermal oxidation at 1400°C for 16.5 h.
Excitation Properties of Silicon Vacancy in Silicon Carbide
Authors: Gali Adam
Published: May 2012

Isolated point defects possessing high spin ground state and below-band-gap excitation may play a key role in realizing solid state quantum bits in semiconductors which are the basic building blocks of quantum computers. Silicon vacancy in silicon carbide provides these features making it a feasible candidate in this special and emerging field of science. However, it has been not clarified what is the exact nature of the luminescence of silicon vacancy detected in hexagonal polytypes. This is the first crucial step needed to understand this basic defect in silicon carbide. We report density functional theory based calculations on silicon vacancy defect. Based on the obtained results we identify the silicon vacancy related photoluminescence signals with the negatively charged defect.
Local Thermal Expansion and the C-C Stretch Vibration of the Dicarbon Antisite in 4H SiC
Authors: Devaty Robert P. , Yan Fei , Choyke Wolfgang J. , Gali Adam , Kimoto Tsunenobu , Ohshima Takeshi
Published: May 2012

The C-C stretch vibration associated with the dicarbon antisite in 4H SiC has been observed out to the fifth harmonic in the low temperature photoluminescence spectrum. The anharmonicity is accounted for reasonably well by fits to the data based on the Morse potential. We combine the observations from experiment, the analytically tractable Morse potential, and results obtained from first principles calculations on this defect to obtain an estimate of the thermal expansion coefficient of the C-C bond. This local thermal expansion coefficient is considerably smaller than the linear thermal expansion coefficient of bulk 4H SiC, in striking contrast with the recent result for the nitrogen-vacancy center in diamond that the local thermal expansion coefficient is larger than the bulk value.
Defects in an Electron-Irradiated 6H-SiC Diode Studied by Alpha Particle Induced Charge Transient Spectroscopy: Their Impact on the Degraded Charge Collection Efficiency
Authors: Iwamoto Naoya , Koizumi Atsushi , Onoda Shinobu , Makino Takahiro , Ohshima Takeshi , Kojima Kazutoshi , Koike S. , Uchida Kazuo , Nozaki Shinji
Published: May 2012

Defects in electron-irradiated 6H-SiC diodes have been studied by single alpha particle induced charge transient spectroscopy and deep level transient spectroscopy (DLTS) in order to identify critical defects responsible for the charge collection efficiency (CCE) decreased by high-energy electron irradiation. The defect X2 detected by the charge transient spectroscopy and the electron trap Ei detected by the DLTS had a similar activation energy of around 0.50 eV. In addition, the annealing at 200oC completely removed defects X2 and Ei, and restored the CCE. The defect X2 is attributed to the electron trap Ei, and responsible for the decreased CCE.
Comparison of Post-Growth Carrier Lifetime Improvement Methods for 4H-SiC Epilayers
Authors: Booker I.D. , Hassan Jawad , Hallén Anders , Sveinbjörnsson E.Ö. , Kordina Olof , Bergman Peder
Published: May 2012

We compare two methods for post-growth improvement of bulk carrier lifetime in 4H-SiC: dry oxidations and implantations with either 12C or 14N, followed by high temperature anneals in Ar atmosphere. Application of these techniques to samples cut from the same wafer/epilayer yields 2- to 11-fold lifetime increases, with the implantation/annealing technique shown to give greater maximum lifetimes. The maximum lifetimes reached are ~5μs after 12C implantation at 600°C and annealing in Ar for 180 minutes at 1500°C. Higher temperatures give decreased lifetimes, a result which differs from reports in literature.
High-Resolution Time-Resolved Carrier Lifetime and Photoluminescence Mapping of 4H-SiC Epilayers
Authors: Booker I.D. , Hassan Jawad , Janzén Erik , Bergman Peder
Published: May 2012

We present a comparison between time-resolved carrier lifetime mappings of several samples and integrated near band edge intensity photoluminescence mappings using a pulsed laser. High-injection conditions and as-grown material are used, which generally allow for the assumption of a single exponential decay. The photoluminescence intensity under these circumstances is proportional to the carrier lifetime and the mappings can be used to detect lifetime-influencing defects in epilayers and give an estimate of the carrier lifetime variation over the wafer. Several examples for the defect detection capability of the system are given.
Correlation of Extended Defects on Carrier Lifetime in Thick SiC Epilayers
Authors: Mahadik Nadeemullah A. , Stahlbush Robert E. , Caldwell Joshua D. , O'Loughlin Michael  J. , Burk Albert A.
Published: May 2012

The effect of extended defects on carrier lifetime was investigated in 140 um thick 4H-SiC epilayers using whole wafer ultraviolet photoluminescence (UVPL) and microwave photoconductive decay (uPCD) mapping. Half-loop arrays (HLA) seen in the UVPL images showed a corresponding lifetime degradation in the same region, even before expansion of the HLAs to form SFs. Lifetime lowering was also seen for a defect comprising of a small 3C-SiC inclusion with a larger misoriented 4H-SiC region. Additionally, formation of slip planes after high temperature annealing was observed, which consequently shows a lifetime reduction in that region.
Characterization of Annealed HPSI 4H-SiC for Photoconductive Semiconductor Switches
Authors: Hettler Cameron , Sullivan III William W. , Dickens James
Published: May 2012

Annealing of high purity semi-insulating (HPSI) 4H-SiC is investigated as a method to improve bulk photoconductive semiconductor switches through recombination lifetime modification. Five samples of HPSI 4H-SiC were annealed at 1810 °C for lengths of time ranging from 3 to 300 minutes. The recombination lifetime of the unannealed and annealed samples was measured using a contactless microwave photoconductivity decay (MPCD) system. The MPCD system consists of a 35 GHz continuous microwave probe and a tripled Nd:YAG pulsed laser. The recombination lifetime was increased from 6 ns, as received, up to 185 ns by annealing for 300 minutes. To experimentally verify switch improvements, identical switches from unannealed and annealed material were fabricated and tested at low voltage. The unannealed device generated a 15 ns pulse with a 2 ns rise-time. The annealed device conducted for upwards of 300 ns with a comparable 2 ns rise-time. The increased recombination lifetime resulted in lower on-state resistance and increased energy transfer.
Identification of the Basal Plane Component of the Burgers Vector of Small Dislocations in 6H SiC Using Birefringence Microscopy
Authors: Hoa Le Thi Mai , Ouisse Thierry , Seiss M. , Chaussende Didier
Published: May 2012

Using 6H SiC wafers including regions with a varying residual stress, the birefringence pattern of almost vertical dislocations is measured and modeled. We show that it is possible to identify the basal plane component of "small" dislocations by a quantitative fit of the birefringence pattern. Combining birefringence and etch pit detection after KOH etching shows that most of the vertical dislocations are of a mixed nature, exhibiting both an edge and a screw component.
Effects of Nitrogen Doping on the Morphology of Basal Plane Dislocations in 4H-SiC Epilayers
Authors: Zhang Xuan , Nagano Masahiro , Tsuchida Hidekazu
Published: May 2012

Morphologies of BPDs in 4H-SiC epilayers with different nitrogen doping concentrations are explained in detail. While BPDs in low-doped epilayers have the typical morphology of gliding dislocations responding to stress, BPDs in highly doped ([N]≥1.0×1018 cm-3) epilayers are straight and tilt away from [11-20]. Structures of BPDs are further studied by weak-beam TEM.
Deflection of Threading Dislocations with Burgers Vector c/c+a Observed in 4H-SiC PVT–Grown Substrates with Associated Stacking Faults
Authors: Byrapa Sha Yan , Wu Fang Zhen , Wang Huan Huan , Raghothamachar Balaji , Choi Gloria , Sun Shun , Dudley Michael , Sanchez Edward , Hansen Darren M. , Drachev Roman , Mueller Stephan G. , Loboda Mark J.
Published: May 2012

A review is presented of Synchrotron White Beam X-ray Topography (SWBXT) studies of stacking faults observed in PVT-Grown 4H-SiC crystals. A detailed analysis of various interesting phenomena were performed and one such observation is the deflection of threading dislocations with Burgers vector c/c+a onto the basal plane and associated stacking faults. Based on the model involving macrostep overgrowth of surface outcrops of threading dislocations, SWBXT image contrast studies of these stacking faults on different reflections and comparison with calculated phase shits for postulated fault vectors, has revealed faults to be of basically four types: (a) Frank faults; (b) Shockley faults; (c) Combined Shockley + Frank faults with fault vector s+c/2; (d) Combined Shockley + Frank faults with fault vector s+c/4.
Conversion Mechanism of Threading Screw Dislocation during SiC Solution Growth
Authors: Ujihara Toru , Kozawa Shigeta , Seki Kazuaki , Alexander Alexander , Yamamoto Yuji , Harada Shunta
Published: May 2012

Solution growth is considered to be a powerful method for high quality SiC crystals. This work reports that the conversion process from a threading screw dislocation into a few Frank partial dislocations in basal planes was investigated by synchrotron X-ray topography. This process was effectively assisted by step-flow growth on off-oriented (0001) seed crystals. The Frank partials were not extended into the crystal grown toward the [0001] direction perpendicular to the basal plane. Thus, the conclusion of this study suggests the use of off-oriented seed crystal is important to improve crystal quality.
Surface Morphology of Leakage Current Sources of 4H-SiC Schottky Barrier Diodes by Atomic Force Microscope
Authors: Katsuno Takashi , Watanabe Yukihiko , Ishikawa Tsuyoshi , Fujiwara Hirokazu , Konishi Masaki , Morino Tomoo , Endo Takeshi
Published: May 2012

The leakage current sources of 4H-SiC Schottky barrier diodes (SBDs) were analyzed using atomic force microscopy (AFM) to determine the surface morphology. Nanosized circular cone shaped pits (nanopits), which depth were distributed from 5 to 70 nm, were observed at the leakage current sources. The leakage currents of 4H-SiC SBDs generate at the nanopits due to the concentration of the electrical field strength. The positions of nanopits correspond to the positions of threading dislocations (TDs), which were identified from molten potassium hydroxide (KOH) etching.
Dislocation Formation in Epitaxial Film by Propagation of Shallow Dislocations on 4H-SiC Substrate
Authors: Ishikawa Yukari , Sato Koji , Okamoto Yoshihiro , Hayashi Noritaka , Yao Yong Zhao , Sugawara Yoshihiro
Published: May 2012

Shallow defects, which were induced by mechanical treatment, on 4H-SiC wafers were investigated. The density and the distribution in depth of shallow defects on the wafers were depended on wafer venders. Most of serious defects such as dislocation array (DA), triangular stacking fault (TRSF) and triangular defect (TRD) in epitaxial film were demonstrated to be caused by shallow dislocations on the surface of the wafers. Revised mechanical polish can reduce the densities of DA, TRSF and TRD in epitaxial film.
Photoluminescence Study of the Driving Force for Stacking Fault Expansion in 4H-SiC
Authors: Hirano Rii , Sato Yuki , Tajima Michio , Itoh Kohei M. , Maeda Koji
Published: May 2012

We investigated expansion velocities of Shockley stacking faults (SSFs) in 4H-silicon carbide under laser illumination using photoluminescence methods. The experiments showed that the velocity of SSF expansion or the glide velocity of SSF-bounding 30°-Si(g) partial dislocations (PD) is supralinearly dependent on the excitation intensity. We estimated sample temperature by analyzing the broadening of band-edge emission and concluded that the lattice heating by laser illumination is not the cause of the enhanced dislocation glide. The supralinear dependence can be accounted for by a photo-induced sign reversal of the effective formation energy of SSF acting as the driving force of SSF expansion under the illumination.
Luminescence Imaging of Extended Defects in SiC via Hyperspectral Imaging
Authors: Caldwell Joshua D. , Lombez Laurent , Delamarre Amaury , Guillemoles Jean Francois , Bourgoin Brice , Hull Brett A. , Verhaegen Marc
Published: May 2012

Over the past decade, improvements in silicon carbide growth and materials has led to the development of commercialized unipolar devices such as Schottky diodes and MOSFETs, however, much work remains to realizing the goal of wide-scale commercialization of both unipolar and bipolar devices such as pin diodes or IGBTs, for high applications requiring high powers, operating in elevated temperatures or radiation environments or for many fast switching applications. Despite the great strides that have been made in reducing extended and point defect densities during this period, such defects still remain and with the push to lower off-cut angle substrates are in many cases seeing increases in prevalence. Thus, spectroscopic and imaging techniques for locating and identifying these defects are in high demand. Luminescence imaging and spectroscopy have both been utilized heavily in such work, yet simultaneously obtaining corresponding spectroscopic and spatial information from such defects is problematic. Here we report on hyperspectral imaging of electroluminescence from SiC pin diodes, whereby a stack of luminescence images are collected over a wide spectral range (400-900 nm), thereby providing the ability to both image distinct features and identify their corresponding spectral properties. This process is also equally applicable to collecting either photo- or electroluminescence from other materials or devices emitting in either the UV-Vis or NIR spectral range, as well as to reflectance, transmission or other imaging techniques.
Ab Initio Calculation of Mechanical Properties of Stacking Fault in 3C-SiC: Effect of Stress and Doping
Authors: Umeno Yoshitaka , Yagi Kuniaki , Nagasawa Hiroyuki
Published: May 2012

We carry out ab initio density functional theory calculations to investigate the fundamental mechanical properties of stacking faults in 3C-SiC, including the effect of stress and doping atoms (substitution of C by N or Si). Stress induced by stacking fault (SF) formation is quantitatively evaluated. Extrinsic SFs containing double and triple SiC layers are found to be slightly more stable than the single-layer extrinsic SF, supporting experimental observation. Effect of tensile or compressive stress on SF energies is found to be marginal. Neglecting the effect of local strain induced by doping, N doping around an SF obviously increase the SF formation energy, while SFs seem to be easily formed in Si-rich SiC.
On the Twin Boundary Propagation in (111) 3C-SiC Layers
Authors: Marinova Maya , Andreadou Ariadne , Mantzari Alkyoni , Polychroniadis Efstathios K.
Published: May 2012

The present study reports on the propagation of twin boundaries in (111) 3C-SiC by means of conventional (CTEM) and high resolution transmission electron microscopy (HRTEM). The investigated 3C-SiC layers were homoepitaxially grown by Chemical Vapour Deposition (CVD) on layers previously grown by Vapor Liquid Solid (VLS) mechanism on 6H-SiC substrates. At the initial stages of growth the usual twin boundary that occurs is an incoherent {-211} Σ3 one. It transforms to more energetically favorable cases by several ways: (i) The initial {-211} boundary turns 90º, to a fully coherent (111) interface, forming microtwins; (ii) A step-like interface occurs with facets along the (111) and the {-211} planes; (iii) It transforms in a fourfold twin complex propagating to the surface.
Defect Structures at the Silicon/3C-SiC Interface
Authors: Hens Philip , Müller Julian , Spiecker Erdmann , Wellmann Peter J.
Published: May 2012

In all heteroepitaxial systems the interface between substrate and layer is a crucial point. In this work SEM and TEM studies on the interface between silicon substrate and cubic silicon carbide (3C-SiC) layers obtained by chemical vapor deposition (CVD) are presented. A clear connection between process parameters, like the design of substrate cleaning, and the heating ramp, and resulting defect structures at the substrate-layer interface could be found. Whereas the process step of etching in hot hydrogen for oxide removal is crucial for avoiding the generation of closed voids of type 2, the design of the temperature ramp up to growth temperature during carbonization influences the interface roughness. Here a fast ramp helps to obtain a flat interface.
Sub-Bandgap Light-Induced Carrier Generation at Room Temperature in Silicon Carbide MOS Capacitors
Authors: DasGupta Sandeepan , Armstrong Andrew , Kaplar Robert , Marinella Matthew , Brock Reinhard , Smith Mark , Atcitty Stanley
Published: May 2012

Carrier generation characteristics in n-type substrate SiC MOS capacitors induced by sub-bandgap energy light are reported. The generation rate is high enough to create an inversion layer in ~20 minutes with monochromatic light (front side illumination) of energy 2.1 eV in 4H-SiC for electric fields smaller than 1 MV/cm. Generation and recovery results strongly indicate involvement of a metastable defect whose efficiency as a generation center increases under hole-rich and decreases under electron-rich conditions. The generation dependence on bias history and light energy shows the defect to have properties consistent with the metastable silicon vacancy / carbon vacancy-antisite complex (VSi / Vc - CSi).
Silicon Carbide-Silicon Dioxide Transition Layer Mobility
Authors: Salemi Shahrzad , Akturk Akin , Potbhare Siddharth , Lelis Aivars J. , Goldsman Neil
Published: May 2012

We present transition layer electron mobility versus field curves for several 4H-SiC/SiO2 structures, simulated by a newly developed Monte Carlo simulator that uses density of states calculated by density functional theory (DFT). Our calculations show that among all structures, abrupt SiC/SiO2 has the highest transition layer mobility.
Two-Way Tunneling Model of Oxide Trap Charging and Discharging in SiC MOSFETs
Authors: Lelis Aivars J. , Habersat Daniel B. , Green Ronald , Goldsman Neil
Published: May 2012

A two-way tunneling model describing simultaneous oxide trap charging and discharging in SiC MOSFETs is presented, along with a comparison with experimental results. This model can successfully account for the variation in threshold-voltage instability observed as a function of bias-stress time, bias-stress magnitude, and measurement time.
Influence of Threading Dislocations on Lifetime of Gate Thermal Oxide
Authors: Yamamoto Kensaku , Nagaya M. , Watanabe H. , Okuno E. , Yamamoto T. , Onda S.
Published: May 2012

The reliability of gate oxides is a fundamental issue for realizing SiC MOSFETs. Many reports said that crystal defects shorten the lifetime of the gate oxide. And, epi defects, the basal plane dislocations and threading screw dislocations (TSD) are considered killer defects. However, because of the high TSD density of commercial SiC wafers, the exact relationship between other kinds of dislocations with lifetime has not been revealed. On the other hand, RAF wafers that we developed have low TSD density, so it is easy to evaluate the relationship between other kinds of dislocations and lifetime. By using RAF wafers, in this study, we clarified the relationship between the lifetime of the gate oxide and crystal defects. We fabricated MOS diodes and measured their lifetimes by TDDB (Time Dependent Dielectric Breakdown) measurement. The breakdown points were defined by the photo-emission method. Finally, we classified the defects by TEM (Transmission Electron Microscopy). As the results, it was clarified that threading edge dislocation (TED) decreases the lifetime as does TSD, which earlier reports said. The lifetime of the gate oxide area, in which a TED is included, was shorter by one order of magnitude than a wear-out breakdown. And, the TSD was two orders.
Strain Build-Up, Swelling and Stacking Fault Formation in Implanted 4H-SiC
Authors: Barbot Jean François , Leclerc S. , Tromas Christophe , Audurier Valerie , Declémy Alain , Texier Michael , Beaufort Marie France
Published: May 2012

Ion implantation into 4H-SiC induces a local gradient of strain which increases with the nuclear energy losses. With the increase of temperature the strain tends to become uniform in the whole implanted area requiring the migration of particles. In case of helium implantation, defects are more stabilized and their evolutions observed post thermal annealing are concomitant with the surface swelling. The local modifications imputed to the ion process lead to the formation and the pile-up of stacking faults in the highly damaged region.
SiC Growth by Solvent-Laser Heated Floating Zone
Authors: Woodworth Andrew A. , Neudeck Philip G. , Sayir Ali , Spry David J. , Trunek Andrew J. , Powell J. Anthony
Published: May 2012

In an effort to grow single crystal SiC fibers for seed crystals the following two growth methods have been coupled in this work: traveling solvent and laser heated floating zone to create the solvent-laser heated floating zone (Solvent-LHFZ) crystal growth method. This paper discusses the results of these initial experiments, which includes, source material, laser heating, and analysis of the first ever SiC crystals (confirmed by synchrotron white beam x-ray topography)
XRD Characterization for Al- and N-Doped 3C-SiC on Si (100) Substrate after Pulsed Excimer Laser Anneal
Authors: Lee Kung Yen , Huang Yan Hao , Huang Chih Fang , Chung Cheng Yueh , Lin Shun Chiu , Zhao Feng
Published: May 2012

This paper characterizes Al, N doped and undoped 3C-SiC samples after pulsed excimer laser anneal by using X-ray diffraction (XRD) and atomic force microscopy (AFM). In order to protect surface morphology, low energy density of 0.2444 J/cm2 per shot was applied to Al and N doped samples. The results show damage recovery is corresponding to the amount of total energy applied to the surface. The peak shift of Bragg diffraction spectra of Al doped samples are almost independent of the amount of total energy. As the energy density is reduced to 0.0667 J/cm2 per shot and applied to undoped samples, the peaks of Bragg diffraction spectra of undoped samples are shifted. However, the peaks of Bragg diffraction spectra of undoped samples annealed with combination of energy densities of 0.0667 and 0.2444 J/cm2 are not shifted.
Origin of the Warpage of 3C-SiC Wafer: Effect of Nonuniform Intrinsic Stress
Authors: Sun Yu , Izumi Satoshi , Sakai Shinsuke , Yagi Kuniaki , Nagasawa Hiroyuki
Published: May 2012

Technique of bulk-like 3C-SiC film (up to 300 µm) growth on undulant-Si substrate is known to be very effective to reduce stacking fault density as well as that of other planar defects. However, freestanding 3C-SiC wafer shows anisotropic warpage involving large convex curvature in the direction perpendicular to the ridge of undulation ([110] direction), and slight concave curvature in parallel direction ([-110] direction), i.e. saddle shape. In this paper the origin of the warpage of the 3C-SiC wafer is investigated. Ex-situ curvature measurements and stress calculation reveal that large compressive intrinsic stress is generated during high-temperature growth process (1623 K) in both parallel and perpendicular directions. In order to investigate the intrinsic stress distribution along the [001] direction, a reactive ion etching (RIE) is conducted for the 3C-SiC on Si substrate to observe the dependence of the SiC/Si system curvature as a function of 3C-SiC thickness. This observation shows that the intrinsic stress component perpendicular to the ridge of undulation presents nonuniform distribution in [001] direction. The remarkable change in the intrinsic stress is observed in the 50 µm-thick region from SiC/Si interface. A finite element method simulation using the obtained intrinsic stress distribution clearly explains that the anisotropic warpage of SiC wafer is induced by the intrinsic stress distribution in quantitative manner. Microstructure change induced by stacking fault reduction process (stacking fault collision) would be the cause of the intrinsic stress variation.
Amorphous Silicon Carbide (α-SiC) Thin Square Membranes for Resonant Micromechanical Devices
Authors: Barnes Andrew C. , Zorman Christian A. , Feng Philip X.L.
Published: May 2012

We report an initial experimental exploration of engineering very thin, suspended amorphous silicon carbide (a-SiC) membranes into vibrating micromechanical devices. We show that micromachined a-SiC thin square membranes can make interesting multiple-mode flexural resonators, with frequency spectra exhibiting many measurable resonant modes over a wide frequency range (100kHz–10MHz) in the low radio frequency (RF) bands. Initial demonstration and preliminary data suggest interesting and rich dynamical, nonlinear, and dissipative properties in these micromechanical resonances. Specifically, for instance, at room temperature (T≈300K) and in moderate vacuum (e.g., ~20mTorr), resonant modes of an a-SiC square membrane (thickness: t≈1.5µm, size: 1mm×1mm) are observed in the ~100kHz–5MHz range, with measured quality factors (Q’s) in the range of ~2,500–9,000.
Amorphous Silicon Carbide as a Non-Biofouling Structural Material for Biomedical Microdevices
Authors: Zorman Christian A. , Eldridge Abigail , Du Jian Gang , Johnston Matt , Dubnisheva Anna , Manley Sargum , Fissell William , Fleischman Aaron , Roy Shuvo
Published: May 2012

This paper details the development of amorphous hydrogenated silicon carbide (a-SiC:H) films as structural material that is resistant to biofouling. The a-SiC:H films were deposited by PECVD and evaluated for their mechanical and anti-biofouling properties. It was found that the as-deposited films exhibited compressive residual stresses that could be converted to moderate tensile stresses upon a post deposition anneal. The amorphous films exhibited a much lower Young’s modulus but similar burst stress when compared to polycrystalline 3C-SiC films of like thickness. The as-deposited a-SiC:H films were more resistant to biofouling than silicon and silicon dioxide surfaces. Coating the a-SiC:H films with polyethylene glycol (PEG) significantly improved the anti-fouling characteristics for extended periods.
Seebeck Coefficient of Heavily Doped Polycrystalline 3C-SiC Deposited by LPCVD
Authors: Lei Man I. , Mehregany Mehran
Published: May 2012

The Seebeck coefficient of heavily-nitrogen-doped n-type polycrystalline 3C-SiC (n-SiC) and platinum (Pt) thin films has been measured from room temperature up to 300 °C by using a microfabricated test structure. At room temperature, the absolute Seebeck coefficient of the n-SiC is -10 μV/°C. With ambient temperature increase, the absolute Seebeck coefficient of the n-SiC is found to gradually increase, reaching -20 μV/°C at 300 °C.