First principles study of aluminum-oxygen complexes in silicon

The atomic structure and electronic properties of aluminum-related defect complexes in silicon are investigated using first-principles calculations. Various configurations of Al-O complexes containing interstitial and substitutional Al atoms and interstitial O atoms are studied. We find that interstitial Al atoms induce deep gap states. The formation energies of interstitial AlO complexes could be much lower than that of interstitial Al under oxygen-rich conditions. We propose that the formation of Al-O complexes may explain the experimental observation that the coexistence of Al and O results in reduced lifetime in Si wafers.