Micropipes in silicon carbide crystals: Do all screw dislocations have open cores?

Micropipes in a 6H-SiC semiconductor wafer were studied by scanning electron and atomic force microscopy. The screw dislocations intersecting the wafer's surface were located by etch pitting, and their Burgers vectors determined by x-ray topography. The etch pits were eroded into smooth craters by ion beam etching to expose levels of dislocation line from inside the sample's bulk. There a micropipe's diameter is distant from surface relaxation effects. Hollow cores (micropipes) were observed at the base of the craters whose screw dislocations had Burgers vectors of magnitude three multiples of the c-lattice parameter and higher. Screw dislocations with 1c and 2c Burgers vectors had no associated micropipes.