Models of core reconstruction for the 90 degrees partial dislocation in semiconductors

We compare the models that have been proposed in the literature for the ato mic structure of the 90 degrees partial dislocation in the homopolar semico nductors, silicon, diamond, and germanium. In particular, we examine the tr aditional single-period and our recently proposed double-period core struct ures. Ab initio and tight-binding results on the core energies are discusse d, and the geometries are compared in the light of the available experiment al information about dislocations in these systems. The double-period geome try is found to be the ground-state structure for all three materials. We a ddress boundary-condition issues that have been recently raised concerning these results. The structures of point excitations (kinks, solitons, and ki nk-soliton complexes) in the two geometries are also reviewed.