First-principles, spin-polarized local-density-functional calculations were used to model interstitial iron (Fei) and its complexes with substitutional Al in dilute SixGe1−x alloys (x<8%). Both the effect of direct bonding between Fei or FeiAl with Ge atoms in the x → 0 limit, and the evolution of the defect properties with the alloy composition, were considered. It was found that Fei preferred Si-rich regions, but when placed near a Ge atom, its (0/+) level was shifted toward the conduction band. However, the ionization energy of Fe(+/2+)-Al− was only slightly changed by the presence of neighboring Ge atoms in the proximity. It was also found that indirect alloying effects shift the donor levels of Fei and FeAl at a fast rate toward the valence band. The acceptor levels, however, remain approximately at the same distance from Ev.

First-Principles Study of Fe and FeAl Defects in SiGe Alloys. A.Carvalho, J.Coutinho, R.Jones, J.Goss, M.Barroso, P.R.Briddon: Physical Review B, 2008, 78[12], 125208 (10pp)