Tsunenobu Kimoto 교수

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 mate

A discussion is presented of a buying- and selling-time prediction system for stocks on the Tokyo Stock Exchange and the analysis of internal representation. The system is based on modular neural networks. The authors developed a number of learning algorithms and prediction methods for the TOPIX (Tokyo Stock Exchange Prices Indexes) prediction system. The prediction system achieved accurate predictions, and the simulation on stocks trading showed an excellent profit

A comprehensive introduction and up-to-date reference to SiC power semiconductor devices covering topics from material properties to applicationsBased on a number of breakthroughs in SiC material science and fabrication technology in the 1980s and 1990s, the first SiC Schottky barrier diodes (SBDs) were released as commercial products in 2001. The SiC SBD market has grown significantly since that time, and SBDs are now used in a variety of power systems, particularly switch-mode power supplies a

Abstract Major features of silicon carbide (SiC) power devices include high blocking voltage, low on-state loss, and fast switching, compared with those of the Si counterparts. Through recent progress in the material and device technologies of SiC, production of 600–3300 V class SiC unipolar devices such as power metal-oxide-semiconductor field-effect transistors (MOSFETs) and Schottky barrier diodes has started, and the adoption of SiC devices has been demonstrated to greatly reduce power loss

Effects of surface defects on performance of kV-class 4H- and 6H-SiC epitaxial p-n junction diodes were investigated. The perimeter recombination and generation, instead of the bulk process, are responsible for forward recombination current and reverse leakage current of the diodes, respectively. Mapping studies of surface morphological defects have revealed that triangular-shaped defects severely degrade high-blocking capability of the diodes whereas shallow round pits and scratch give no direc

4H-SiC(0001), (0001), and (1120) have been directly oxidized by N 2 O at 1300°C, and metal–oxide–semiconductor (MOS) interfaces have been characterized. The interface state density has been significantly reduced by N 2 O oxidation on any face, compared to conventional wet O 2 oxidation at 1150°C. Planar n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) fabricated on 4H-SiC(0001), (0001) and (1120) faces have shown effective channel mobilities of 26, 43, and 78 cm 2 /Vs, resp

Growth of SiC on off-oriented 6H-SiC{0001} substrates was quantitatively analyzed based on the theory proposed by Burton, Cabrera, and Frank (BCF theory). By measuring the critical growth conditions where the growth mode changed from step-flow to two-dimensional nucleation, the surface diffusion lengths of adatoms on 6H-SiC(0001)Si and (0001̄)C faces were calculated with the model. Although the nucleation rate was much higher on (0001̄)C faces, the surface diffusion length was longer on (0001̄)C

Step bunching in chemical vapor deposition of 6H– and 4H–SiC on off-oriented {0001} faces is investigated with cross-sectional transmission electron microscopy. On an off-oriented (0001)Si face, three Si–C bilayer-height steps are the most dominant on 6H–SiC and four bilayer-height steps on 4H–SiC. In contrast, single bilayer-height steps show the highest probability on a (0001̄)C face for both 6H– and 4H–SiC epilayers grown with a C/Si ratio of 2.0. The increase of C/Si ratio up to 5.0 induces

Growth of SiC on off-oriented 6H-SiC{0001} substrates was performed between 1100 and 1500 °C. Homoepitaxial growth of 6H-SiC was achieved at temperatures as low as 1200 °C, utilizing step-flow growth. Twinned crystalline 3C-SiC was grown at 1100 °C; this result can be ascribed to suppressed surface migration of adsorbed Si species at the lower temperature, and to the occurrence of two-dimensional nucleation on terraces. The C/Si ratio significantly effected the surface morphology and growth rate

The growth mechanism in chemical vapor deposition (CVD) of silicon carbide (SiC) on off-oriented SiC{0001} substrates (step-controlled epitaxy) is reviewed. In step-controlled epitaxy, SiC growth is controlled by the diffusion of reactants in a stagnant layer. Critical growth conditions where the growth mode changes from step-flow to two-dimensional nucleation are predicted as a function of growth conditions using a model describing SiC growth on vicinal {0001} substrates. Step bunching on the s

High-purity and thick 4H–SiC(0001) epilayers have been grown by a horizontal hot-wall chemical vapor deposition (CVD) system, which was designed and built at the authors’ group. The background donor concentration has decreased by reducing pressure during CVD, and a low donor concentration of 1–3×1013 cm−3 was achieved by CVD growth at 80 Torr. The free exciton peaks dominated in low- and room-temperature photoluminescence spectra without titanium or point-defect related peaks. The electron mobil

Abstract Carrier lifetimes in n‐type 4H‐SiC epilayers have been investigated by differential microwave photoconductance decay measurements. Through a correlation study between lifetime and various deep levels, the Z 1/2 and/or EH 6/7 centers have been identified as effective recombination centers. When the Z 1/2 (and EH 6/7 ) concentration is higher than 10 13 cm –3 , the inverse carrier lifetime is in proportion to the trap concentration, and the lifetime increases with increasing excitation in

Step bunching and terrace widening on 6H– and 4H–SiC epilayers on vicinal {0001} faces have been studied with atomic force microscopy (AFM) and transmission electron microscopy (TEM). Macroscopically, hill-and-valley structures are observed on off-oriented (0001)Si faces, whereas surfaces are rather flat on off-oriented (0001̄)C faces. High-resolution TEM analysis revealed that 3 bilayer-height steps are dominant on 6H–SiC and 4 bilayer-height steps on 4H–SiC. The distribution of step height and