Density-functional study of small interstitial clusters in Si: Comparison with experiments

Local density functional calculations are carried out on models of tri- and tetra-self-interstitial clusters in Si. Electrical levels and local vibrational modes (LVMs) of the defects are found. The latter are compared with recent experiments detailing the isotopic shifts of LVM frequencies associated with phonon replicas of the W- and X-photoluminescence lines, attributed to ${\mathrm{I}}_3$ ad ${\mathrm{I}}_4$, respectively. While the ground state ${\mathrm{I}}_4$ structure accounts well for the measured optical and electrical data, the most stable ${\mathrm{I}}_3$ aggregates either show no gap states, or the lack for LVMs that could be linked with the W-line. Instead, this optical center can be linked to a metastable form of ${\mathrm{I}}_3$.

Figure 1

The ${\mathrm{I}}_3$ and ${\mathrm{I}}_4$ structures considered. For clarity, Si atoms at the defect core are represented as gray spheres.