Phosphorous clustering in germanium-rich silicon germanium

The formation of clusters consisting of donor atoms and lattice vacancies can deleteriously affect the performance of silicon germanium devices. In the present study results from electronic structure calculations are evaluated using mass action analysis to identify the extent to which phosphorous-vacancy clusters form in germanium-rich silicon germanium. Although it is energetically favourable to form clusters containing up to four phosphorous atoms, clusters are only important at lower temperatures. At such temperatures the formation of the cluster, in which four phosphorous atoms are tetrahedrally coordinated around a vacancy, is especially stable. At high temperatures unbound vacancies and phosphorous atoms are dominant.