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 structure 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 impurities are also attracted to the core but form stable di-interstitial oxygen complexes there. These results can account for the strong pinning effects observed in plastically deformed Si containing these impurities. In GaAs, the 90-degrees Ga(g) (beta) partial is strongly reconstructed 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.