Vibrational properties of elemental hydrogen centres in Si, Ge and dilute SiGe alloys

The local vibrational modes arising from single interstitial hydrogen centres in Si, Si-rich SiGe, Ge-rich SiGe, and Ge crystals are modelled by an ab initio supercell method. The stress response of the 1998 and 1794 cm ^-1 bands that appear in proton-implanted Si and Ge samples is well reproduced, further confirming their assignment to bond-centred H⁺ defects. It is shown that H^- in Ge is anti-bonded to a Ge atom, and is likely to be considerably less mobile than in Si. Although H⁺ is not trapped by the minority species in both Si-rich and Ge-rich alloys, we find that H^- can be stabilized by forming anti-bonded H-Si structures.