- 第2回 物理工学科教室談話会（講師：Prof.T. Kimoto）
日時： 2016年5月12日(木) 13:30-15:00
場所：工学部6号館 2階 62号講義室
講師：Prof. T. Kimoto
所属：Dept. of Electronic Science & Engineering, Kyoto University
題目：Material Science in SiC Power Devices
Abstract：Power semiconductor devices have attracted increasing attention as key components in a variety of power conversion systems. Although the performance of Si power devices has remarkably been improved, silicon carbide (SiC) (and gallium nitride (GaN)) is promising for advanced low-loss and fast power devices, which can substantially outperform Si-based power devices. Through recent progress in SiC growth and device technologies, production of 600 –1700 V SiC Schottky barrier diodes and power MOSFETs has started, and remarkable improvement of energy efficiency has been demonstrated in real systems such as power supplies, air conditioners, photovoltaic power converters, and railcars. In spite of the promising potential of SiC power devices, basic understanding of material science associated with SiC is still very poor, leading to the lack of guidelines for defect control and thereby further improvement of device performance/reliability. In this seminar, several important topics including the oxide/semiconductor interface, carrier lifetimes, and high-field phenomena in SiC are reviewed.
SiC power MOSFETs are an ideal power switch owing to the low on-resistance and fast switching. However, the interface properties of SiO2/SiC MOS structures are still far from a satisfactory level, severely affecting the performance and reliability of SiC power MOSFETs. To understand the MOS physics, the interface defects have been characterized by several unique techniques, and the correlation with channel mobility has been established. Control of carrier lifetimes in SiC is a key technology for SiC bipolar devices such as PiN diodes, thyristors, and IGBTs. The author’s group identified the lifetime-killing defect in SiC and revealed its microstructure; that is carbon monovacancy. The carbon vacancy defects can be almost completely eliminated or intentionally generated by several techniques. By combination of these processes, control of carrier lifetimes in SiC has been demonstrated.
Junction breakdown is mainly governed by impact ionization caused by high-energy carriers under high electric field. The author’s group fabricated unique diode structures and succeeded to accurately determine the electron and hole impact ionization coefficients in the wide electric field and temperature ranges. A few unusual behaviors
are observed in impact ionization coefficients, and these phenomena may be attributed to a unique electronic band structure of SiC.
- 第1回 物理工学科教室談話会（講師：Inti Sodemann）
講師：Inti Sodemann (Massachusetts Institute of Technology)
題目：Particle-hole symmetric phases in multicomponent Landau levels
概要：The picture of fractional quantum Hall states as liquids of composite particles made from electrons bound to fluxes has evolved over the years as a central paradigm in the understanding of these phases. A recent proposal on the compressible phase that arises in half-filled Landau levels allows to consistently incorporate the particle-hole symmetry by viewing the composite fermion as a Dirac particle. In turn, the natural habitat for this Dirac composite fermion is the surface of a chiral topological insulator protected by an anti-unitary particle-hole symmetry with a single Dirac cone. In this talk I will describe generalizations of these ideas to the case of N-component landau levels, such as those arising in quantum Hall bilayers (N=2) and graphene (N=4). When multi-component Landau levels are half filled they can be viewed as the surface of a chiral topological insulator with N Dirac cones. I will describe gapped phases that respect the particle-hole symmetry and are top
ologically ordered and discuss their potential experimental realization.