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We investigated the carrot-defect reduction effect by optimizing the buffer layers of 4H-Silion Carbide (SiC) epitaxial wafers. The SiC epitaxial wafer with the 0.5 μm-thick optimized condition-B buffer layer show the carrot-defect density of 0.13 cm-2, since that with the conventional-A buffer layer were 0.68 cm-2. Although the average bunching length with the optimized condition-B buffer layer was 7-times longer than those with the conventional condition-A buffer layer, we could reduce the bunching length by applying the optimized condition-B only to the initial 0.05 μm-thick buffer layer. Finally, with the initial 0.05 μm-thick optimized condition-B buffer layers, we could achieve the SiC epitaxial wafers with only half the carrot-defect densities of those with the conventional condition-A buffer layers, while the average bunching lengths were less than 100 μm. With this condition, we could achieve the estimated yield of 90.1% with 4 x 4 mm chips, while that with the conventional condition-A buffer layer was 81.9%.

For the popularization of SiC power device, improvement on both productivity and quality of 150 mm diameter SiC epitaxial wafer is inevitable. With highly productive 8x150-mm CVD reactor, we have grown epitaxial layer on 4° off 4H-SiC wafer Si-and C-face. Modifying some reactor parts and optimizing growth conditions enabled us to achieve a good balance between high uniformity and smooth surface.

The Ariake Sea, a typical closed bay on the west coast of Kyushu Island, has suffered from several external impacts. However, the relative contribution of the various factors and processes is still unclear. In this study, field observations were conducted inside the artificial tidal flat to model the physical, chemical and ecological attributes of the tidal flat system for the preservation and recovery of the coastal environment in the Ariake Sea. The communities and environment within the artificial tidal flat pond became established within one year of the artificial pond being completed. Meteorological and tidal conditions were found to strongly affect the topography of the pond, particularly the region between the sub-tidal zone to the supra littoral zone, the development of which itself resulted in stabilization of the tidal flat habitat within the pond.

本研究では、有明海を豊饒の海として再生するために、様々考えられている環境悪化要因のなかから、海岸線付近に位置する沿岸干潟域における底質環境の悪化と自然の浄化作用を有する干潟や塩性湿地の喪失という2つの要因に着目し、有明海の沿岸干潟環境の現況を調べるとともに、その改善･再生技術の開発と実証試験及び再生策の事業化に向けた評価手法の検討までを幅広く行なった。