Papers by Author: Taro Nishiguchi

Abstract: This article describes the analysis of the polytype transformation of SiC ingot. We analyzed the sample by Raman spectroscopy and TEM observation. The result of the analysis shows the polytype is transformed from 4H-SiC to 6H-SiC, and then returned to 4H-SiC. We found that the direction of the c-axis is not the same as the growth direction of the ingot. And also we found the existence of 8H-SiC at the interface between 6H-SiC and 4H-SiC region by the selected area diffraction pattern and confirmed it by HR-TEM observation.

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: The advantage of room-temperature photoluminescence (PL) mapping was demonstrated for nondestructive detection of stacking faults (SFs) in off-oriented 4H-SiC epitaxial and bulk wafers. In mapping of the SF-related emission at 2.9 eV on the wafers, the SFs in the surface region appeared as a bar-shaped pattern with the long side perpendicular to the off-cut direction. The use of 266 nm light excitation is essential to detect the SF pattern in the bulk wafers because of its shallow penetration depth. The dark lines crossing the bar-shaped patterns in the epitaxial wafers are ascribable to the basal plane dislocation located close to the SF-planes.

Abstract: Growth of 4H-SiC bulk crystals on 4H-SiC {03-38} seeds was done. 4H-SiC {03-38} is obtained by inclining the c-plane toward <01-10> at a 54.7 degrees angle. Growth on the 4H-SiC {03-38} seed has the potential to achieve high quality crystals without micropipes and stacking faults. Micropipe-free c-plane 4H-SiC wafers were achieved by growth on the 4H-SiC {03-38} seed. A transmission X-ray topograph image of the micropipe free c-plane wafer revealed that there are no macroscopic defects with displacements.

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.

Abstract: Lateral epitaxial overgrowth (LEO) is known as method of defects reduction for GaN. LEO is expected to reduce crystal defects on hetero-epitaxial growth of 3C-SiC. (100) Si substrate patterned with SiO2 mask was used as the substrate. Before CVD process, V shape crater was made on Si surface by HCl etching. And growth condition of CVD was optimized. Single crystal of 3C-SiC was grown laterally on SiO2 layer. Cross-sectional transmission electron microscopic observation indicated that crystal quality of LEO region was single and no defect crystal.