Origins of micropipes in SiC crystals

It is argued that micropipes in SiC crystals grown by the physical vapor transport process form independently of screw dislocations. A mechanism involving liquid droplets of silicon containing some carbon or graphite particles is proposed to explain the formation of micropipes. The observed strain fields associated with micropipes are attributed to the presence of screw dislocations in their vicinity. An expression is developed that relates the change in radius of a micropipe to the number of screw dislocations that are eliminated during its expansion.