Papers by Author: Koji Nishio

Abstract: Epitaxial growth of AlN was carried out by MOVPE method on SiC/Si buffered substrates prepared by using various Si surfaces of (110), (211) and (001). Cross-sectional HRTEM analyses of the interfaces between SiC buffer layer and AlN epitaxial layer disclosed characteristic nanostructures related growth mechanism on the each substrate. In the case of Si(110) and Si(211) substrate, hexagonal AlN grew directly on SiC(111) plane with AlN(0001) plane parallel to it. In contrast, growth on Si(001) substrate gave complicate structure at AlN/SiC interface. Hexagonal AlN didn’t grow directly but cubic AlN appeared with a pyramidal shape on SiC(001). When the cubic AlN grew 10nm in height, structure of growing AlN crystal changed to hexagonal type on the pyramidal {111} planes of cubic AlN.

Abstract: 4H-SiC was grown on 4H-SiC (1100) substrates by sublimation boule growth, and transmission electron microscopic investigation was carried out. Two basal-plane-dislocations in the same basal plane (the BPD pair), whose dislocation line extend toward the [1100] growth direction, were observed as aligned along [0001]. The density of the BPD pairs along [0001] was in the same order with that of the stacking faults in the sample. A threading screw-dislocation was observed in between aligned BPD pairs. It is proposed that the interaction between stacking faults and threading screw-dislocations on the grown surface generates the BPD pairs. Since a high density of stacking faults is inherent to the growth on the substrates perpendicular to (0001), keeping an atomically flat grown surface is important to prevent the generation of the threading screw-dislocations, and thus to suppress the generation of the BPD pairs in case of the growth on (1100) and/or (11 2 0) substrates.

Abstract: In our previous study, we reported that a metastable phase with high Ca/P molar ratio appeared in the temperature range from 700 οC to 800οC
The purpose of this study is to investigate the crystallographic relationship between the metastable phase and HAp matrix. Ca-def HAp was annealed at 500-1000' ο C in air. High-resolution transmission electron microscopic (HRTEM) observations were performed along the [010], [110] and [001] zone axes in order to investigate the structure of the metastable phase. From HRTEM images and results of the analysis of selected area electron diffraction patterns along [010], [110] and [001] zone axes, the lattice constants of the metastable phase were analyzed into a=2.86nm, b=0.94nm, and c=0.69nm of an orthorhombic crystals system.

Abstract: Chemical vapor deposition of (111) 3C-SiC on (110) Si substrate was carried out, and the effect of the substrate off-axis introduced on (110) Si substrate for suppressing the twin formation in 3C-SiC hetero-epitaxial layers was investigated. From the growth on hemispherically polished (110) Si substrate, it was found that the off-axis toward the [001] Si axis had a noble effect for suppressing the twin formation, while the off-axis toward the [110] Si axis was ineffective. The growth of single 3C-SiC crystal containing few double positioning boundaries, which are related with the twin formation, was demonstrated on the (110) Si substrate 3° off-axis toward the [001] Si axis. Transmission electron microscopic observation revealed that double positioning boundaries on the (110) Si substrate off-axis toward the [001] Si axis were nearly eliminated within the initial a few hundreds nano meter in thickness.

Abstract: Interfaces between a Si(110) substrate and 3C-SiC crystals grown hetero-epitaxially by CVD were investigated by cross-sectional transmission electron microscopy. Gas flow condition during the carbonization process affects the roughness of the substrate surface and there is an optimum condition to preserve the flat surface. High quality 3C-SiC crystals grew only on the flat substrate, with crystallographic relationship of Si[1-10]//SiC[1-10] and Si[001]//SiC[1-1 - 2], because the well-lattice-match relationship was limited in a two-dimensional region at the SiC(111)/Si(110) interface. Using the optimum condition, some kinds of roughness at an atomic scale remained on the surface of the substrate. Nanoscopic observation of the crystals grown on an off-axis substrate revealed the influence of the roughness on the epitaxial growth and the defects generation at the interface.

Abstract: Hetero-epitaxial CVD growth of 3C-SiC on a Si(110) substrate gives a (111) crystal with low defects density. However, double positioning growth often disturbs growth of a single crystal. The growth on an off-axis Si(110) substrate suppressed propagation of the double positioning defects in the grown layer effectively. Cross-sectional transmission electron microscopy revealed the details of the suppression process on the off-axis substrate. The suppression mechanism and the origin of the defects formation at double positioning boundaries were interpreted by the growth model based on an anisotropic growth rate on (111) plane of 3C-SiC.