Christophe Raynaud

Bio: Christophe Raynaud is an academic researcher from University of Lyon. The author has contributed to research in topics: Diode & Silicon carbide. The author has an hindex of 18, co-authored 99 publications receiving 1335 citations. Previous affiliations of Christophe Raynaud include Institut national des sciences Appliquées de Lyon.

State of the art of high temperature power electronics

Abstract: High temperature power electronics has become possible with the recent availability of silicon carbide devices. This material, as other wide-bandgap semiconductors, can operate at temperatures above 500 °C, whereas silicon is limited to 150-200 °C. Applications such as transportation or a deep oil and gas wells drilling can benefit. A few converters operating above 200 °C have been demonstrated, but work is still ongoing to design and build a power system able to operate in harsh environment (high temperature and deep thermal cycling).

Silica films on silicon carbide: a review of electrical properties and device applications

Abstract: This paper reviews the present knowledge on silica films (SiO2) on silicon carbide (SiC). First, kinetic of thermal oxidation of SiC is described, and the effects of a great number of parameters (various SiC polytypes, substrate type, substrate orientation...) are discussed. Mainly, thermal oxides grown on SiC are close to stoichiometric silica and the oxidation rate depends on the terminal face of the SiC monocrystal. The next four sections discuss the electrical properties of the oxide, and of the oxide/SiC interface, and especially the effects of materials and technological process on the interface state density and the effective oxide charge (Section 5), and the origin of the interface states are discussed in detail (Section 6). Oxides grown on n-type SiC have electrical properties (in terms of dielectric strength, leakage currents, interface trap, and oxide charges) measured by means of metal-oxide-semiconductor (MOS) structures, similar to oxides grown on silicon. Until recently, p-type SiC MOS structures have had a large equivalent oxide charge and larger interface state densities in spite of many efforts, compared to silicon MOS structures. It seems nevertheless that recent studies have improved the SiO2/SiC interfacial quality. Aluminum, carbon and alkali species are ihs main suspected contaminants. Finally, Section 7 presents the applications of oxide films in SE-based devices: MOS capacitors and MOS field effect transistors (MOSFETs) for microelectronics, MOSFETs for power electronics, and some applications using silica layers as a passivation layer. In spite of a smaller than required carrier mobility in the inversion layer, MOS field effect transistors (MOSFETs) have been demonstrated to operate up to 650 degreesC and integrated circuits based on NMOS and PMOS technologies have been successfully operated up to 300 degreesC. Vertical power MOSFETs are also of importance but their performances are still limited by a specific on-resistance larger than device requirements. The effect of charges present in the oxide on the electrical properties of high voltage diodes is also briefly discussed.

Thermal Stability of Silicon Carbide Power Diodes

Abstract: Silicon carbide (SiC) power devices can operate at much higher junction temperature than those made of silicon. However, this does not mean that SiC devices can operate without a good cooling system. To demonstrate this, the model of a merged p-i-n Schottky (MPS) SiC diode is presented, and its parameters are identified with experimental measurements. This model is then used to study the ruggedness of the diode regarding the thermal runaway phenomenon. Finally, it is shown that, where a purely unipolar diode would be unstable, the MPS structure brings increased stability.

Barrier height determination of SiC Schottky diodes by capacitance and current-voltage measurements

Abstract: Extractions of barrier heights of 6H and 4H-SiC Schottky diodes have been performed on structures with various gate metallization, using both capacitance-voltage (C-V) and current-voltage (I-V) measurements. The sum of the two barriers extracted by C-V measurements on both n-type and p-type materials is found to be higher than the band gap energy E-G, whereas the one extracted by I-V is less than E-G. However, above room temperature, temperature variations of barrier heights are in agreement with the variations of E-G. We have also computed theoretical I-V characteristics using a two-barrier height model. By taking account of temperature variations of a large number of parameters, e.g., the carrier mobility, free carrier concentration, and barrier height, we have achieved a good fit with experimental data. The model is shown to be valid for n-type Schottky diodes over a wide range of temperatures (from 100 to 500 K).

Status of silicon carbide (SiC) as a wide-bandgap semiconductor for high-temperature applications: A review

Abstract: Silicon carbide (SiC), a material long known with potential for high-temperature, high-power, high-frequency, and radiation hardened applications, has emerged as the most mature of the wide-bandgap (2.0 eV ≲ Eg ≲ 7.0 eV) semiconductors since the release of commercial 6HSiC bulk substrates in 1991 and 4HSiC substrates in 1994. Following a brief introduction to SiC material properties, the status of SiC in terms of bulk crystal growth, unit device fabrication processes, device performance, circuits and sensors is discussed. Emphasis is placed upon demonstrated high-temperature applications, such as power transistors and rectifiers, turbine engine combustion monitoring, temperature sensors, analog and digital circuitry, flame detectors, and accelerometers. While individual device performances have been impressive (e.g. 4HSiC MESFETs with fmax of 42 GHz and over 2.8 W mm−1 power density; 4HSiC static induction transistors with 225 W power output at 600 MHz, 47% power added efficiency (PAE), and 200 V forward blocking voltage), material defects in SiC, in particular micropipe defects, remain the primary impediment to wide-spread application in commercial markets. Micropipe defect densities have been reduced from near the 1000 cm−2 order of magnitude in 1992 to 3.5 cm−2 at the research level in 1995.

Intrinsic SiC/SiO2 Interface States

Abstract: The energy distribution of electron states at SiC/SiO 2 interfaces produced by oxidation of various (3C, 4H, 6H) SiC polytypes is studied by electrical analysis techniques and internal photoemission spectroscopy. A similar distribution of interface traps over the SiC bandgap is observed for different polytypes indicating a common nature of interfacial defects. Carbon clusters at the SiC/SiO 2 interface and near-interfacial defects in the SiO 2 are proposed to be responsible for the dominant portion of interface traps, while contributions caused by dopant-related defects and dangling bonds at the SiC surface are not observed.

Polarity of oxide surfaces and nanostructures

Abstract: Whenever a compound crystal is cut normal to a randomly chosen direction, there is an overwhelming probability that the resulting surface corresponds to a polar termination and is highly unstable. Indeed, polar oxide surfaces are subject to complex stabilization processes that ultimately determine their physical and chemical properties. However, owing to recent advances in their preparation under controlled conditions and to improvements in the experimental techniques for their characterization, an impressive variety of structures have been investigated in the last few years. Recent progress in the fabrication of oxide nano-objects, which have been largely stimulated by a growing demand for new materials for applications ranging from micro-electronics to heterogeneous catalysis, also offer interesting examples of exotic polar structures. At odds with polar orientations of macroscopic samples, some smaller size polar nano-structures turn out to be perfectly stable. Others are subject to unusual processes of stabilization, which are absent or not effective in their extended counterparts. In this context, a thorough and comprehensive reflexion on the role that polarity plays at oxide surfaces, interfaces and in nano-objects seems timely.This review includes a first section which presents the theoretical concepts at the root of the polar electrostatic instability and its compensation and introduces a rigorous definition of polar terminations that encompasses previous theoretical treatments; a second section devoted to a summary of all experimental and theoretical results obtained since the first review paper by Noguera (2000 J. Phys.: Condens. Matter 12 R367); and finally a discussion section focusing on the relative strength of the stabilization mechanisms, with special emphasis on ternary compound surfaces and on polarity effects in ultra-thin films.

Degradation of hexagonal silicon-carbide-based bipolar devices

Abstract: Only a few years ago, an account of degradation of silicon carbide high-voltage p-i-n diodes was presented at the European Conference on Silicon Carbide and Related Compounds (Kloster Banz, Germany, 2000). This report was followed by the intense effort of multiple groups utilizing varied approaches and subsequent progress in both fundamental understanding of this phenomenon and its elimination. The degradation of SiC p-i-n junctions is now well documented to be due to the expansion of Shockley-type stacking faults in the part of the devices reached by the electron-hole plasma. The faults can gradually cover most of the junction area, impeding current flow and, as a result, increasing the on-state resistance. While in most semiconductors stacking faults are electrically inactive, in hexagonal silicon carbide polytypes (4H- and 6H-SiC) they form quantum-well-like electron states observed in luminescence and confirmed by first-principles calculations. The stacking-fault expansion occurs via motion of 30° sil...

Materials Science Forum

Abstract: Properties and Application of Geopolymers Vol. 841 (/MSF.841 /book) Development and Investigation of Materials Using Modern Techniques Vol. 840 (/MSF.840/book) Superplasticity in Advanced Materials ICSAM 2015 Vols. 838-839 (/MSF.838-839/book) 12th International Conference on High Speed Machining Vols. 836-837 (/MSF.836-837/book) Sintering Fundamentals II Vol. 835 (/MSF.835/book) Advanced Machining Technologies: Traditions and Innovations Vol. 834 (/MSF.834/book) Applied Materials and Technologies Vol. 833 (/MSF.833/book) Emerging Functional Materials: Book (/MSF.841/book) Papers (/MSF.841)