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, stacking-fault density and dislocation density were determined for 2″ single crystals grown in the <00▪¯1> direction 0–7° off towards <11▪0> and for crystals up to 1″ in diameter grown in <11▪0>(a) and <1¯1▪0>(m) directions and using repeated a-face growth. KOH etching, optical microscopy and X-ray topography were used for the characterization. It was shown that the micropipe density and dislocation density decrease with increasing off-orientation for the growth in polar directions, respectively, on C- and Si-terminated seeds. A similar behavior was found for the stacking-fault density and dislocation density in non-polar directions with off-orientation towards c-direction. The non-polar crystals were free of micropipes. Nevertheless, while the dislocation density could be reduced up to 3 orders of magnitude for the growth along non-polar directions, compared with that in c-direction, the stacking-fault density continuously increased. Repeated a-face growth was suitable to completely eliminate the micropipes and to reduce slightly the stacking-fault density. However, during the final growth step in polar c-direction micropipes as well as stacking faults tend to form again, with a concentration that was comparable with the standard c-plane growth. The results were explained in terms of growth mechanism and kinetic aspects.

Polarity- and Orientation-Related Defect Distribution in 4H-SiC Single Crystals. H.J.Rost, M.Schmidbauer, D.Siche, R.Fornari: Journal of Crystal Growth, 2006, 290[1], 137-43