Hartree- Fock Cluster Study of Interstitial Transition Metals in Silicon

Results are presented of a Hartree-Fock cluster study of interstitial Ti, V, Cr, and Mn impurities in sili-con. A SilO cluster models the nearest Si atoms around a tetrahedral interstitial site in crystalline Si. The dangling bonds of the Si atoms are saturated by hydrogens. The effect of the Si core electrons is repre-sented by an effective potential. Characteristic for the electronic structure of the low-lying states of the neutral, singly positive, and doubly positive ions in silicon is the presence of fairly delocalized but still pre-dominantly transition-metal (3d)-like orbitals of t2 and e symmetry. For all ions the energy of the weighted average of the terms belonging to a configuration is lowest for the configuration with maximum occupation of the t2 orbitals. Ground states with maximum spin multiplicity are found for all ions, except Tio. 1