Local modes of hydrogen defects in Si:Ge and Ge:Si

We give an overview of the results obtained from joint experimental and theoretical studies of H in Si-rich (Si:Ge) and Ge-rich (Ge:Si) SiGe. Si:Ge and Ge:Si implanted at low temperatures with H+ and/or D+ have been studied by in situ infrared absorption spectroscopy. The states of isolated H and H dimers in dilute SiGe have also been investigated by ab initio theory. Four configurations of positively charged bond-centered H (HBC+) have been identified both in Si:Ge and in Ge:Si. Interestingly, the infrared spectrum arising from HBC+ centers in Ge:Si is a mirror image of that observed for Si:Ge, which is a direct result of the opposite sign of the strain field induced by Si-Ge bonds on the lattice of Si:Ge and Ge:Si materials. We found that, unlike Ge in Si:Ge, the Si atoms in Ge:Si are efficient trapping sites for H, resulting in the appearance of H anti-bonded to Si at low temperatures and H dimers in the form of Ge-HBC⋯Si-HAB defects at room temperature.