Papers by Author: Shunta Harada

Abstract: The dislocation behavior during bulk crystal growth on the 4H-SiC (000-1) C-face using the solution method was investigated. A 2 inch wafer with a 4° off angle was fabricated from a bulk crystal grown by the TSSG method, and the dislocations in the crystal were evaluated using synchrotron X-ray topography and TEM observation. From the topograph images, it was found that the TSD density remarkably decreased as the growth progressed. Furthermore, the TEM observation suggested that TSD decreases as the threading dislocations convert to in-plane defects toward the center of the crystal. Conventionally, it was considered that conversion of threading dislocations hardly occurs in solution growth on the C-face. However, it is thought that this phenomenon was not observable because the conversion efficiency is remarkably low. We speculate that dislocations may be transformed by suddenly making macrosteps during bulk growth.

Abstract: We achieved the growth of extremely-high quality SiC crystal with two-step solution method with specially-designed seed crystals. The two-step growth consists of 1^st step growth on Si-face for the reduction of threading dislocations and 2^nd step growth on C-face for the reduction of basal plane dislocations and thickening. In this method, we can make the dislocation density extremely low, while the polytype easily changes during growth due to the absence of spiral hillocks originating from threading screw dislocation (TSD). In this study, we prepared specially designed seed crystals for both 1^st and 2^nd growth steps to provide steps continuously. In the seeds, a few TSDs exist at the upper-side of the step structure. Consequently, we demonstrated the suppression of the polytype transformation during the C-face growth with extremely low-dislocation-density crystal. Accordingly, we successfully obtained extremely low-dislocation density 4H-SiC with TSD, TED and BPD density of 11, 385 and 28 cm^-2.