Showing papers on "Silicon carbide published in 2015"

Material science and device physics in SiC technology for high-voltage power devices

Abstract: Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600?1700 V) SiC Schottky barrier diodes (SBDs) and power metal?oxide?semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.

Coherent control of single spins in silicon carbide at room temperature

Abstract: Defects in silicon carbide have recently been proposed as bright single-photon sources. It is now shown that they can be used as sources of single electron spins having long coherence times at room temperature. Spins in solids are cornerstone elements of quantum spintronics1. Leading contenders such as defects in diamond2,3,4,5 or individual phosphorus dopants in silicon6 have shown spectacular progress, but either lack established nanotechnology or an efficient spin/photon interface. Silicon carbide (SiC) combines the strength of both systems5: it has a large bandgap with deep defects7,8,9 and benefits from mature fabrication techniques10,11,12. Here, we report the characterization of photoluminescence and optical spin polarization from single silicon vacancies in SiC, and demonstrate that single spins can be addressed at room temperature. We show coherent control of a single defect spin and find long spin coherence times under ambient conditions. Our study provides evidence that SiC is a promising system for atomic-scale spintronics and quantum technology.

Silicon carbide-free graphene growth on silicon for lithium-ion battery with high volumetric energy density

Abstract: Silicon is receiving discernable attention as an active material for next generation lithium-ion battery anodes because of its unparalleled gravimetric capacity. However, the large volume change of silicon over charge–discharge cycles weakens its competitiveness in the volumetric energy density and cycle life. Here we report direct graphene growth over silicon nanoparticles without silicon carbide formation. The graphene layers anchored onto the silicon surface accommodate the volume expansion of silicon via a sliding process between adjacent graphene layers. When paired with a commercial lithium cobalt oxide cathode, the silicon carbide-free graphene coating allows the full cell to reach volumetric energy densities of 972 and 700 Wh l−1 at first and 200th cycle, respectively, 1.8 and 1.5 times higher than those of current commercial lithium-ion batteries. This observation suggests that two-dimensional layered structure of graphene and its silicon carbide-free integration with silicon can serve as a prototype in advancing silicon anodes to commercially viable technology. The volume expansion of silicon is a big problem in lithium-ion batteries with silicon anodes. Here, the authors report direct graphene growth on silicon nanoparticles, which effectively mitigates the problem, leading to excellent electrochemical performance.

Isolated electron spins in silicon carbide with millisecond coherence times

Abstract: Optically detected magnetic resonance experiments show that single spins having a coherence time on the millisecond scale can be isolated in divacancy defects in silicon carbide at low temperature.

Silicon carbide: A unique platform for metal-oxide-semiconductor physics

Abstract: A sustainable energy future requires power electronics that can enable significantly higher efficiencies in the generation, distribution, and usage of electrical energy. Silicon carbide (4H-SiC) is one of the most technologically advanced wide bandgap semiconductor that can outperform conventional silicon in terms of power handling, maximum operating temperature, and power conversion efficiency in power modules. While SiC Schottky diode is a mature technology, SiC power Metal Oxide Semiconductor Field Effect Transistors are relatively novel and there is large room for performance improvement. Specifically, major initiatives are under way to improve the inversion channel mobility and gate oxide stability in order to further reduce the on-resistance and enhance the gate reliability. Both problems relate to the defects near the SiO2/SiC interface, which have been the focus of intensive studies for more than a decade. Here we review research on the SiC MOS physics and technology, including its brief history, the state-of-art, and the latest progress in this field. We focus on the two main scientific problems, namely, low channel mobility and bias temperature instability. The possible mechanisms behind these issues are discussed at the device physics level as well as the atomic scale, with the support of published physical analysis and theoretical studies results. Some of the most exciting recent progress in interface engineering for improving the channel mobility and fundamental understanding of channel transport is reviewed.

Engineering near-infrared single-photon emitters with optically active spins in ultrapure silicon carbide.

Abstract: Vacancy-related centres in silicon carbide are attracting growing attention because of their appealing optical and spin properties. These atomic-scale defects can be created using electron or neutron irradiation; however, their precise engineering has not been demonstrated yet. Here, silicon vacancies are generated in a nuclear reactor and their density is controlled over eight orders of magnitude within an accuracy down to a single vacancy level. An isolated silicon vacancy serves as a near-infrared photostable single-photon emitter, operating even at room temperature. The vacancy spins can be manipulated using an optically detected magnetic resonance technique, and we determine the transition rates and absorption cross-section, describing the intensity-dependent photophysics of these emitters. The on-demand engineering of optically active spins in technologically friendly materials is a crucial step toward implementation of both maser amplifiers, requiring high-density spin ensembles, and qubits based on single spins.

Single-photon emitting diode in silicon carbide.

Abstract: Electrically driven single-photon emitting devices have immediate applications in quantum cryptography, quantum computation and single-photon metrology. Mature device fabrication protocols and the recent observations of single defect systems with quantum functionalities make silicon carbide an ideal material to build such devices. Here, we demonstrate the fabrication of bright single-photon emitting diodes. The electrically driven emitters display fully polarized output, superior photon statistics (with a count rate of >300 kHz) and stability in both continuous and pulsed modes, all at room temperature. The atomic origin of the single-photon source is proposed. These results provide a foundation for the large scale integration of single-photon sources into a broad range of applications, such as quantum cryptography or linear optics quantum computing.

Magnetic field and temperature sensing with atomic-scale spin defects in silicon carbide

Abstract: Quantum systems can provide outstanding performance in various sensing applications, ranging from bioscience to nanotechnology. Atomic-scale defects in silicon carbide are very attractive in this respect because of the technological advantages of this material and favorable optical and radio frequency spectral ranges to control these defects. We identified several, separately addressable spin-3/2 centers in the same silicon carbide crystal, which are immune to nonaxial strain fluctuations. Some of them are characterized by nearly temperature independent axial crystal fields, making these centers very attractive for vector magnetometry. Contrarily, the zero-field splitting of another center exhibits a giant thermal shift of −1.1 MHz/K at room temperature, which can be used for thermometry applications. We also discuss a synchronized composite clock exploiting spin centers with different thermal response.

Predicting Two-Dimensional Silicon Carbide Monolayers

Abstract: Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1–x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1–x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1–x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. More...

Enhanced thermal conductivity for polyimide composites with a three-dimensional silicon carbide nanowire@graphene sheets filler

Abstract: A rigid three-dimensional structure composed of silicon carbide (SiC) nanowire@graphene sheets (3DSG) was prepared using a high frequency heating process. The polyamide acid was then infused into the three-dimensional structure and imidized at 350 °C. The thermal conductivity of polyimide (PI)/3DSG composites with 11 wt% filler addition can be up to 2.63 W m−1 K−1, approximately a 10-fold enhancement when compared with the results obtained using neat PI. Furthermore, the 3DSG shows a better synergistic effect in thermal conductivity improvement, relative to a simple mixture of SiC nanowires and graphene sheets (GSs) fillers with the same additive content. The reinforced thermal properties can be attributed to the formation of efficient heat conduction pathways among GSs.

Ionization-induced annealing of pre-existing defects in silicon carbide

Abstract: A long-standing objective in materials research is to effectively heal fabrication defects or to remove pre-existing or environmentally induced damage in materials. Silicon carbide (SiC) is a fascinating wide-band gap semiconductor for high-temperature, high-power and high-frequency applications. Its high corrosion and radiation resistance makes it a key refractory/structural material with great potential for extremely harsh radiation environments. Here we show that the energy transferred to the electron system of SiC by energetic ions via inelastic ionization can effectively anneal pre-existing defects and restore the structural order. The threshold determined for this recovery process reveals that it can be activated by 750 and 850 keV Si and C self-ions, respectively. The results conveyed here can contribute to SiC-based device fabrication by providing a room-temperature approach to repair atomic lattice structures, and to SiC performance prediction as either a functional material for device applications or a structural material for high-radiation environments.

Mechanical behavior of zirconium diboride–silicon carbide–boron carbide ceramics up to 2200 °C

Abstract: The mechanical properties of hot pressed zirconium diboride–silicon carbide–boron carbide (ZrB2–SiC–B4C) ceramics were characterized from room temperature up to 2200 °C in an argon atmosphere. The average ZrB2 grain size was 3.0 μm. The SiC particles segregated into clusters, and the largest clusters were >30 μm in diameter. The room temperature flexural strength was 700 MPa, decreasing to 540 MPa at 1800 °C and to 260 MPa at 2200 °C. The strength was controlled by the SiC cluster size up to 1800 °C. At higher temperatures, strength was controlled by formation of liquid phases, and precipitation of large BN and B–O–C–N inclusions. The mechanical behavior of these materials changes at ∼1800 °C, meaning that extrapolation of properties from lower temperatures is not accurate. Mechanical behavior in the ultra-high temperature regime was dominated by impurities and changes in microstructure. Therefore, the use of higher purity materials could lead to significant improvements in ultra-high temperature strength.

Characterization and Implementation of Dual-SiC MOSFET Modules for Future Use in Traction Converters

Abstract: Silicon (Si) insulated-gate bipolar transistors are widely used in railway traction converters. In the near future, silicon carbide (SiC) technology will push the limits of switching devices in three directions: higher blocking voltage, higher operating temperature, and higher switching speeds. The first silicon carbide (SiC) MOSFET modules are available on the market and look promising. Although they are still limited in breakdown voltage, these wide-bandgap components should improve traction-chain efficiency. Particularly, a significant reduction in the switching losses is expected which should lead to improvements in power–weight ratios. Nevertheless, because of the high switching speed and the high current levels required by traction applications, the implementation of these new modules is critical. An original method is proposed to compare, in terms of stray inductance, several dc bus-bar designs. To evaluate the potential of these new devices, a first set of measurements, based on a single-pulse test-bench, was obtained. The switching behavior of SiC devices was well understood at turn-off and turn-on. To complete this work, the authors use an opposition method to compare Si-IGBT and SiC-MOSFET modules in voltage source inverter operation. For this purpose, a second test-bench, allowing electrical and thermal measurements, was developed. Experimental results confirm the theoretical loss-calculation of the single-pulse tests and the correct operation of up to three modules directly connected in parallel. This analysis provides guidelines for a full SiC inverter design, and prospects for developments in traction applications are presented.

Conformal deposition of silicon carbide films

Abstract: Disclosed are methods and systems for providing silicon carbide films. A layer of silicon carbide can be provided under process conditions that employ one or more silicon-containing precursors that have one or more silicon-hydrogen bonds and/or silicon-silicon bonds. The silicon-containing precursors may also have one or more silicon-oxygen bonds and/or silicon-carbon bonds. One or more radical species in a substantially low energy state can react with the silicon-containing precursors to form the silicon carbide film. The one or more radical species can be formed in a remote plasma source.

Wide-Bandgap-Based Power Devices: Reshaping the power electronics landscape

Abstract: For the last few years, the virtues of power devices based on gallium nitride (GaN) and silicon carbide (SiC) technologies have been well promoted. Now, with the availability of qualified devices from multiple suppliers and falling prices due to the rise in production and the use of larger substrates, more designers are adopting widebandgap (WBG)-based power devices in their new designs to get to the next level of performance, while others are looking to replace the maturing silicon (Si) with more robust emerging technologies.

Modeling of Wide-Bandgap Power Semiconductor Devices—Part II

Abstract: Wide bandgap power devices have emerged as an often superior alternative power switch technology for many power electronic applications. These devices theoretically have excellent material properties enabling power device operation at higher switching frequencies and higher temperatures compared with conventional silicon devices. However, material defects can dominate device behavior, particularly over time, and this should be strongly considered when trying to model actual characteristics of currently available devices. Compact models of wide bandgap power devices are necessary to analyze and evaluate their impact on circuit and system performance. Available compact models, i.e., models compatible with circuit-level simulators, are reviewed. In particular, this paper presents a review of compact models for silicon carbide power diodes and MOSFETs.

Ultrahigh-Voltage SiC p-i-n Diodes With Improved Forward Characteristics

Abstract: Silicon carbide (SiC) p-i-n diodes having five different n−-layer ( $i$ -layer) thicknesses from 48 to $268~\mu $ m are fabricated. The forward characteristics of SiC p-i-n diodes are significantly improved by carrier-lifetime enhancement. After this improvement, the differential on-resistance is inversely proportional to the square root of current density for all the diodes with different thicknesses of n−-layer. As a result, the forward current density–voltage characteristics can be approximately expressed by a parabolic function, as in the case of Si p-i-n diodes. Using a 268- $\mu $ m-thick n−-layer, the lifetime enhancement, and an improved space-modulated junction termination extension structure, a very high blocking voltage over 26.9 kV and low differential on-resistance of 9.7 m $\Omega \cdot $ cm $^{2}$ are achieved.

Enhanced electrical conductivity of silicon carbide ceramics by addition of graphene nanoplatelets

Abstract: The paper describes the fabrication by liquid-phase spark plasma sintering (SPS) of composites of dense silicon carbide (SiC) with up to 20 vol.% graphene nanoplatelets (GNPs), and discusses the relationships between composition, microstructure and electrical conductivity. The structural integrity of the GNPs is preserved during the whole process, as observed by Raman spectroscopy. The effects of the applied pressure (50 MPa) during SPS result in the preferential orientation of the GNPs perpendicular to the pressing axis and anisotropic electrical behaviour. The electrical conductivity measured in the direction perpendicular to the SPS pressing axis is 4 to 6 times higher than the parallel counterpart. The conductivity increases up to three orders of magnitude with increasing GNPs fraction, reaching values of 4380 S m −1 at room temperature for materials with 20 vol.% GNPs. The conduction mechanism of the composite is analysed as a function of the GNPs content.

One-step synthesis of Si@C nanoparticles by laser pyrolysis: high-capacity anode material for lithium-ion batteries.

Abstract: Carbon-covered silicon nanoparticles (Si@C) were synthesized for the first time by a one-step continuous process in a novel two stages laser pyrolysis reactor. Crystallized silicon cores formed in a first stage were covered in the second stage by a continuous shell mainly consisting in low organized sp2 carbon. At the Si/C interface silicon carbide is absent. Moreover, the presence of silicon oxide is reduced compared to materials synthesized in several steps, allowing the use of such material as promising anode material in lithium-ion batteries (LIB). Auger Electron Spectroscopy (AES) analysis of the samples at both SiKLL and SiLVV edges proved the uniformity of the carbon coating. Cyclic voltammetry was used to compare the stability of Si and Si@C active materials. In half-cell configuration, Si@C exhibits a high and stable capacity of 2400 mAh g–1 at C/10 and up to 500 mAh g–1 over 500 cycles at 2C. The retention of the capacity is attributed to the protective effect of the carbon shell, which avoids d...

Characterization of a Silicon IGBT and Silicon Carbide MOSFET Cross-Switch Hybrid

Abstract: A parallel arrangement of a silicon (Si) IGBT and a silicon carbide (SiC) MOSFET is experimentally demonstrated. The concept referred to as the cross-switch (XS) hybrid aims to reach optimum power device performance by providing low static and dynamic losses while improving the overall electrical and thermal properties due to the combination of both the bipolar Si IGBT and unipolar SiC MOSFET characteristics. For the purpose of demonstrating the XS hybrid, the parallel configuration is implemented experimentally in a single package for devices rated at 1200 V. Test results are obtained to validate this approach with respect to the static and dynamic performance when compared to a full Si IGBT and a full SiC MOSFET reference devices having the same power ratings as for the XS hybrid samples.

Quantum Hall resistance standards from graphene grown by chemical vapour deposition on silicon carbide

Abstract: Replacing GaAs by graphene to realize more practical quantum Hall resistance standards (QHRS), accurate to within 10−9 in relative value, but operating at lower magnetic fields than 10 T, is an ongoing goal in metrology. To date, the required accuracy has been reported, only few times, in graphene grown on SiC by Si sublimation, under higher magnetic fields. Here, we report on a graphene device grown by chemical vapour deposition on SiC, which demonstrates such accuracies of the Hall resistance from 10 T up to 19 T at 1.4 K. This is explained by a quantum Hall effect with low dissipation, resulting from strongly localized bulk states at the magnetic length scale, over a wide magnetic field range. Our results show that graphene-based QHRS can replace their GaAs counterparts by operating in as-convenient cryomagnetic conditions, but over an extended magnetic field range. They rely on a promising hybrid and scalable growth method and a fabrication process achieving low-electron-density devices. The quantum Hall effect in GaAs-based devices defines resistance standards accurate to within one part in 10−9 at magnetic fields close to 10 T. Here, Lafont et al. demonstrate such accuracies over an extended magnetic field range at 1.4 K in chemically vapour-deposited graphene on silicon carbide.

Development of Ultrahigh-Voltage SiC Devices

Abstract: Ultrahigh-voltage silicon carbide (SiC) devices [p-i-n diodes and insulated-gate bipolar transistors (IGBTs)] and switching test have been investigated. As a result, we have succeeded in developing a 13-kV p-i-n diode, 15-kV p-channel IGBT, and 16-kV flip-type n-channel implantation and epitaxial IGBT with a low differential specific on-resistance ( R $_{\rm diff,on}$ ). It was revealed that a power module fabricated using a nanotech resin, Si3N4 ceramic substrate, and W base plate was suitable for ultrahigh voltage and high temperature. A switching test was carried out using a clamped inductive load circuit, which indicated that the energy loss of a circuit with ultrahigh-voltage SiC devices is lower than that of Si devices.

Approaching Truly Freestanding Graphene: The Structure of Hydrogen-Intercalated Graphene on 6H-SiC(0001)

Abstract: X-ray measurements of its vertical absorption height indicate that hydrogen-intercalated graphene on silicon carbide is effectively free-standing.