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

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The local vibrational modes arising from single interstitial hydrogencentres in Si, Si-rich SiGe, Ge-rich SiGe, and Ge crystals are modelledby an ab initio supercell method. The stress response of the 1998 and1794 cm−1 bands that appear in proton-implanted Si and Ge samples is wellreproduced, further confirming their assignment to bond-centredH+ defects. It isshown that H− in Ge is anti-bonded to a Ge atom, and is likely to be considerably less mobile than in Si. AlthoughH+ is not trapped by the minority species in both Si-rich and Ge-rich alloys, we find thatH− can be stabilized by forming anti-bonded H–Si structures.