Polarity- and orientation-related defect distribution in 4H-SiC single crystals

In order to further improve the crystal quality, the influence of polarity and off-orientation on crystallographic perfection of 4H-SiC single crystals was investigated. Micropipe density (MPD), stacking fault density (SFD) and dislocation density (DD) were determined for 2" single crystals grown in (0001) direction 0-7 degrees off towards (1120) and for crystals tip to 1" in diameter grown in (1150) (a) and (1100) (m) directions and using repeated a-face growth (RAF). KOH etching, optical microscopy and X-ray topography were used for the characterization. It is shown that the MPD and DD decrease with increasing off-orientation for the growth in polar directions, respectively, on C- and Si-terminated seeds. A similar behaviour was found for the SFD and DD in non-polar directions with off-orientation towards c-direction. The non-polar crystals were free of micropipes. Nevertheless, while the DD could be reduced up to three orders of magnitude for the growth along non-polar directions, compared with that in c-direction, the SFD continuously increased. RAF is suitable to completely eliminate the micropipes and to reduce slightly the SFD. However, during the final growth step in polar c-direction MPs as well as SFs tend to form again, with a concentration that is comparable with the standard c-plane growth. The results will be discussed in terms of growth mechanism and kinetic aspects. (c) 2006 Elsevier B.V. All rights reserved.