First-principles calculations of the self-interstitial cluster I4 in Si

The I-4 cluster model, which is recently proposed as primarily self-interstitial clustering in Si [N. Arai et al., Phys. Rev. Lett. 78, 4265 (1997)], has been examined using the ab initio pseudopotential method based on the local density-functional theory. All the bonds are well reconstructed with enough bond charge and relatively small bond distortions. The formation energy per self-interstitial is 1.5 eV. This value is less than one half of that of isolated self-interstitials, although this is fairly larger than that of extended self-interstitial agglomerates such as {113} planar defects. The I-4 cluster has no electronic states inside the minimum band gap, which is consistent with no previous experimental identification. The present results quantitatively support the possible existence of the I-4 clusters as primary clusters or embryos of extended agglomerates. [S0163-1829(99)00535-4].