Dislocation related photoluminescence in Si and SiGe is attributed to stable interstitial clusters bound to 60° dislocations. Density functional based total energy calculations in Si give binding energies between 1.5 and 3.6 eV for $I_3$ and $I_4$ clusters with 90° and 30° partials. They possess donor levels around $E_v+0.4\mathrm{}\mathrm{eV}$ which are consistent with deep level transient spectroscopic studies on $p$-Si. It is further suggested that the clusters would act as the obstacles to the movement of dislocations which may have been observed in recent transmission electron microscopy studies.

• Received 21 February 2001

DOI:https://doi.org/10.1103/PhysRevLett.87.187404