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We investigated the effect of the solution flow on crystalline morphology in the off-axis 4H-SiC solution growth. In particular, we focused on the relation between the Si solution flow and step flow directions. In step parallel flow in which the solution drifted transversely to the step flow direction of the off-axis substrate, it was possible to attain a better surface morphology than in the flow in which the solution drifted toward the other direction. Furthermore, it was found that the surface morphology was found to be improved as the solution flow velocity increased. These improvements in the morphological stability are presumed to be caused by aligning the solute concentration fluctuation along the steps.

We performed top-seeded solution growth of 4H-SiC for obtaining longer length crystal. Si-Cr and Si-Ti melts were used as solvents. Meniscus formation technique was applied to the present study. Special attention was paid to improve the process stability during long-term growth. One of major technological problems in the solution growth is that the precipitation of polycrystalline SiC which hiders the stable single crystal growth. Another problem is the fluctuation of supersaturation at the growth interface during the growth. Through the optimization of growth process conditions, we have successfully grown 4H-SiC single crystals up to 14 mm long with three-inch-diameter, and evaluated their crystalline quality.

The solution growth behavior of silicon carbide (SiC) by a temperature difference method using Fe–Si solvent below 1773 K was investigated to clarify the dominant factor affecting growth kinetics. Solution growth experiments were conducted both under the suppression of buoyancy convection and under forced convection controlled by rotating the seed and supply source substrates. In addition, the fluid flow in the solution was estimated by numerical analysis. When buoyancy convection was suppressed, a ridge of SiC grew on the seed substrate only around the edge of the contact area with the solution, which was affected by Marangoni flow generated by the large temperature gradient. Under forced convection in the solution by substrates rotation, lateral growth of SiC was observed over the entire region of the contacting area. Growth rates of SiC of 60–160 μm/h were obtained for various temperature conditions and were increased proportionally by increasing the supersaturation of carbon at the growth interface. It was thus clarified that the mass transfer of carbon in the solution was the rate-determining step of the solution growth process of SiC.

In this study, we have investigated the rate-limiting process of 4H-SiC solution growth using Si-Cr based melt, and have tried high-speed growth. It is revealed that the rate-limiting process of SiC growth under our experimental condition is interface kinetics, which can be controlled by such factors as temperature and supersaturation of carbon. By enhancing the interface kinetics, SiC crystal has been grown at a high rate of 2 mm/h. The FWHM values of X-ray rocking curves and threading dislocation density of the grown crystals are almost the same as those of seed crystal. Possibility of high-speed and high-quality growth of 4H-SiC has been indicated.

4H-SiC single crystal with 3-inch diameter was grown by top seeded solution growth (TSSG) technique. We used a new convection control member called “Immersion Guide (IG)” which causes the high and homogenous fluid flow in the solution. As a result, we achieved relatively high growth rate and morphological stability

We report the results of the systematic investigation into correlations between energetics and hexagonal stacking configurations for carbon, silicon, SiC, BN, AlN, GaN, and InN polytypes with sp3-bonded networks. The atomistic geometry, energetics, and electronic structure for these compounds with up to the periodic stacking length of L = 8 have been carefully calculated based on the density functional theory within the generalized gradient approximation (GGA). Using the Axial Next-Nearest-Neighbor Ising model extracted from the GGA calculations, we have also studied the energetics for more than 6 million kinds of nonequivalent stacking polytypes with up to L = 30, whose configurations have been deduced by the efficient polytype generation algorithm [E. Estevez-Rams and J. Martinez-Mojicar, Acta Crystallogr., Sect. A: Found. Crystallogr. 64, 529 (2008)], and illustrated some trends of structural and energetic properties for these compounds.

Crystallinity of 4H-SiC bulk crystal obtained by solution growth technique was characterized mainly by KOH etching of the off-ground and serially ground specimen. Marked reduction of basal plane dislocation, threading edge and screw dislocations during the growth of on-axis crystal was confirmed. Cross-sectional TEM observation revealed the rapid reduction behavior of threading dislocations microscopically. AFM observation of as-grown morphology showed that screw dislocation dipoles is related to the reduction of threading screw dislocations and single domain formation, which is essential for establishing the high crystallinity.

We have grown high-quality long cylindrical (12 mm thick) 4H-SiC bulk crystals by the meniscus formation technique, which was first applied for the solution growth of bulk SiC. It enabled long-term growth by suppressing parasitic reactions such as polycrystal precipitation around the seed crystal. In addition, we could control the growth angle from −22° to 61° by adjusting the meniscus height. The thickness of the grown cylindrical crystals was 12 mm, which is the largest reported until now, and corresponded to a growth rate of 0.6 mm/h. Smooth morphology growth was maintained on the (000-1) C-face. In cross-sectional transmission optical microscopy images, few solvent inclusions and voids were observed. XRD measurements revealed that the FWHM values of the grown crystals were almost the same as those of the seed crystal.

We attempted the traveling solvent method (TSM) growth of SiC on 6H-SiC(0001) substrates using Si and Si-M (M=Ti, Cr and Dy) solvents at growth temperatures of 1500-1800°C. It was confirmed that 4H-SiC polytype was extremely stabilized in the highly carbon dissolved liquid phase. 4H-SiC growth on 6H-SiC, i.e. hetropolytype epitaxial growth, was observed only from Si-Dy solvent. The Dy content above 60at% was necessary to obtain 100% 4H-SiC polytype.

電解質溶液の液膜厚みが10～100 μmの場合の腐食速度は酸素拡散律速となる．更に液膜厚みが10 μm以下となった場合には液膜への酸素溶解速度が律速となる．このような薄液膜下におけるガルバニック腐食の数値解析モデルの開発を行った．このモデルでは，酸素のSalting-out効果，及び導電率，酸素溶解度と酸素溶解速度の温度依存性を考慮した．Fe/Znガルバニック電極を用いた塩水噴霧試験（SST）とサイクル腐食試験（CCT）を行い，ガルバニック電流の測定を行った．ガルバニック電流は，乾燥湿潤過程において最大値を示した．実測されたガルバニック電流は，数値解析結果と良く一致した．CCTにおける液膜厚みを数値解析により推定した結果，ガルバニック電流が最大となる液膜厚みは3～10 μmであった．

The purpose of this study is to clarify the effect of dry and wet processes on the mechanisms of edge corrosion of hot dip 55 mass% Al–Zn alloy coated steel sheet. The corrosion tests employed were continuous salt-spray tests and cyclic corrosion tests using NaCl solution or artificial seawater. It was confirmed that the edge corrosion is suppressed during the salt-spray test using artificial seawater. Furthermore, the suppression was not prevented by dry and wet processes. In order to reveal the corrosion mechanisms, the galvanic current and the cathodic polarization curves at exposed steel were measured and the corrosion products were characterized. It is suggested that the artificial seawater forms anti-corrosive corrosion products and that suppress the cathodic reaction on the steel which is exposed on the shear cut edge. The corrosion products are not changed by dry and wet processes. The numerical analysis also revealed the influence of the dry and wet process on edge corrosion.

Hot-dip 55%Al–Zn alloy coated steel sheet has superior corrosion resistance both on flat panel and near shear cut edge in various atmospheric environments. However, the corrosion often occurs near the shear cut edge in continuous wet conditions, for example, NaCl solution spray test (SST, JIS Z2371), and this has been explained by galvanic model. In this paper, it is clarified that the corrosion near shear cut edge is suppressed by artificial sea water and its second ingredient, MgCl2.To make clear the corrosion mechanisms on MgCl2 suppression of the corrosion near shear cut edge, the measurement of cathodic polarization curve on the Fe electrode after the corrosion test using a AZ/Fe/AZ galvanic electrode, the estimation of corrosion products by numerical analysis in consideration of the substances migration and the precipitation reactions, and the analysis of corrosion products by FT-IR spectroscopy were conducted. As a result, in the galvanic condition, it is clarified that Mg(OH)2 precipitates on the Fe exposed cut edge. Moreover, the corrosion near shear cut edge is suppressed by the effect of the cathodic reaction suppression of Mg(OH)2.

We have grown thick AlN epilayers on SiC substrates by a new solution growth technique using Cu solvents under atmospheric pressure nitrogen. By using growth apparatus based on CZ growth system with inductive heating, we have grown AlN single crystalline layers of which thickness were more than 200 μm on (4H,6H)-SiC substrates at relatively low growth temperatures such as 1600 °C-1800 °C. Inch-size self standing AlN crystals were also prepared by removing the SiC substrate. TEM observation, ω-scan XRD measurement and cathode luminescence spectroscopy were conducted to characterize the crystallinity of the obtained AlN layers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We performed solution growth of SiC single crystals from Si-Ti-C ternary solution using the accelerated crucible rotation technique (ACRT). It was confirmed that the growth rate exceeding 200 μm/hr was achievable by several ACRT conditions. This high growth rate might be due to the enhancement of the carbon transport from the graphite crucible to the growth interface using the ACRT. Moreover, the incorporation of inclusions of the Si-Ti solvent in the grown crystal was significantly suppressed by using the ACRT. It was thought that the intensive convection near the growth interface resulted in not only the marked increase of SiC growth rate but also the superior homogeneity in the surface morphology. It was concluded that faster stable growth can be accomplished in the SiC solution growth using the ACRT.

Synthesis of single crystalline AlN has long been the subjects of intensive studies since it has exceptional properties suitable for the substrate materials for optoelectronic and electronic devices. The solution growth technique has some advantages over the sublimation growth technique. Its growth temperature is generally much lower than that of the sublimation growth. The obtained crystal is believed to show superior crystallinity since it is grown under nearly equilibrium condition. In the present study we have developed a new solution growth technique using Cu and Ti as solvents under atmospheric pressure of nitrogen. By using this solution, we have grown AlN single crystalline layer on 6H-SiC substrate at relatively low growth temperatures such as 1600-1800 °C. The thickness of the grown layer was larger than 30 μm. TEM observation revealed the fairly low dislocation density such as 10 5 /cm 2 in the obtained AlN layers.

The effect of hydrogen doping on luminescence properties of ZnO was investigated. Hydrogen was incorporated in the ZnO crystal by irradiation with an inductively coupled plasma (ICP), in particular, the pulse modulated mode operation of ICP, and the luminescence spectra and hydrogen concentration of the resultant samples were analyzed. A hydrogenated region of 20–100 nm was formed at the sample surface by the irradiation and the concentration of hydrogen was 1017–1018 cm−3. Hydrogen doping improved the ultraviolet emission efficiency of all the samples, and the degree of improvement depended on the initial state (impurity concentration) of the original samples. The most significant improvements were recorded for the sample lightly contaminated with Cu, Al, and Li. The correlation between impurity concentration and hydrogen doping effects is discussed from the viewpoint of charge transfer between hydrogen and the other impurities.