Superscrew dislocations in silicon carbide: Dissociation, aggregation, and formation

An approach to precisely determine the magnitude and the sign of Burgers vectors of superscrew dislocations (including elementary screw dislocations and micropipes) in silicon carbide (SiC) single crystals has been developed. The histogram of Burgers vector values associated with micropipes follows Gaussian distribution with most possible absolute Burgers vector value of about 100 A for both 4H and 6H SiC. Superscrew dislocations are quasistable. Their transformations, such as dissociation, coalescence, and aggregation, follow the principle of Burgers vector conservation and energetically favored behavior. The coalescence of dislocations with same-sign Burgers vectors is less likely to occur during the growth. Finally, a possible mechanism of mismatched coalescence between multiple nucleation sites is proposed to understand the formation of micropipes with large Burgers vectors at the early stage of SiC bulk growth. (c) 2006 American Institute of Physics.