The mechanism of micropipe nucleation at inclusions in silicon carbide

A model is presented for a possible mechanism of screw dislocation (includi ng micropipe) nucleation in silicon carbide. The model is based on the obse rvation of micropipe nucleation at the sites of foreign material inclusions using synchrotron white beam x-ray topography and transmission optical mic roscopy. It is shown that incorporation of the inclusion into the growing c rystal can lead to deformation of the protruding ledge which constitutes th e overgrowing layer. Accommodation of this deformation into the crystal lat tice leads to the production of pairs of opposite sign screw dislocations w hich then propagate with the growing crystal. Evidence for the existence of such pairs of dislocations is presented. (C) 1999 American Institute of Ph ysics. [S0003-6951(99)01332-7].