First principles study of GeSi exchange mechanisms at the Si(001) surface

Based on density functional theory calculations, we show that an isolated Ge adatom on Si(001) triggers an exchange mechanism involving three atoms, which leads to the formation of a Si adatom and a mixed SiGe surface dimer. The activation energy calculated from first principles is sufficiently low (0.8 eV) to make such a process viable down to the lowest temperature (330 K) at which intermixing was reported. A second mechanism, with a higher barrier, is also proposed and shown to possibly contribute to the incorporation of Ge into deeper layers as experimentally observed at higher temperatures. © 2008 American Institute of Physics