DENSITY-FUNCTIONAL CALCULATIONS OF THE STRUCTURE AND PROPERTIES OF IMPURITIES AND DISLOCATIONS IN SEMICONDUCTORS

A local density functional cluster method is used to investigate the s tructure of dislocations in Si and GaAs as well as the interaction of P and O impurities with dislocations in Si. The 90-degrees partial in Si is found to be strongly reconstructed but P impurities are strongly bound to the dislocation and inhibit this reconstruction. O impuritie s are also attracted to the core but form stable di-interstitial oxyge n complexes there. These results can account for the strong pinning ef fects observed in plastically deformed Si containing these impurities. In GaAs, the 90-degrees Ga(g) (beta) partial is strongly reconstructe d in the same way as in Si, but the As(g) (alpha) partial is not. This may account for the higher mobility observed for As(g) partials over Ga(g) ones.