Synchrotron topography studies of the operation of double-ended Frank-Read partial dislocation sources in 4H-SiC

Synchrotron White Beam X-ray Topography (SWBXT) has been used to image and analyze a distinctive stacking fault pattern observed in 4H-SiC wafers. The pattern often consists of a six-pointed star comprised of multiple layers of rhombus-shaped stacking faults with three different fault vectors of the Shockley type bounded by 30° Shockley partial dislocations. Formation of this stacking fault pattern is associated with a micropipe at its center which can act as nucleation sites for dislocation half-loops belonging to the primary basal (1/311-20(0001)) slip system and occasionally the secondary prismatic (1/311-20{1-100}) slip systems. In this case, the rhombus-shaped Shockley type stacking faults are nucleated on the basal plane by dissociation of 1/311-20 pure screw dislocations cross-slipped from the prismatic plane and subsequent expansion caused by glide of the leading partial and locking of the trailing partial by interaction with 60° 1/3-2110 dislocations on the basal plane. Based on these observations, a formation mechanism involving the operation of a double-ended Frank-Read partial dislocation source has been proposed. In the limit, this glide and cross-slip mechanism leads to 4H to 3C polytype transformation in the vicinity of the micropipe by a mechanism similar to that proposed by Pirouz and Yang (1993) [21].