Carbon, dopant, and vacancy interactions in germanium

Electronic structure calculations have been used to study the interaction of carbon with isolated substitutional dopants (boron, phosphorus, or arsenic), vacancies, and dopant-vacancy pairs in germanium. For comparison, equivalent defects were examined in silicon. The calculations employed a plane-wave basis set and pseudopotentials within the generalized gradient approximation of density functional theory. The results predict a range of different association preferences, with carbon being strongly bound in some cases and unbound in others. For example, in germanium, the carbon-vacancy cluster is weakly bound whereas in silicon it is more strongly bound. Conversely, dopant-carbon pairs are not stable in either germanium or silicon compared to their isolated components. If, however, they are formed during implantation, they will act as strong vacancy traps. Details of clusters comprised of a dopant, carbon, and vacancy are also discussed with respect to their formation by the association of a vacancy or cluster pair. (C) 2007 American Institute of Physics.