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Germanium hydrogen pairs in silicon

The Covalent Materials Consortium is working on the ab initio studies of covalently bonded materials (AIMPRO). Spin-polarised SC local density functional pseudopotential techniques using real space basis set. (P. Briddon et al)

Hydrogen in a dilute SiGe alloy is contrasted with hydrogen in Si and Ge. Structural, vibrational and electronic properties of crystalline alloys containing 1.6% Ge complexed with single hydrogen atoms are considered. The behaviour of bond-centred hydrogen is found to be weakly perturbed, when compared to hydrogen in pure Si.

Compared to Si, H⁺ near to isolated Ge_s is found to be degenerate in energy, suggesting that such complexes are only present at low temperatures where the role of entropy and the migration of H are not relevant. The vibrational modes of these complexes are found to be similar to those of H in silicon, but shifted downwards in frequency by the nearby Ge atom. The effect of Ge on the electrical levels of H is to weakly perturb the acceptor and donor levels compared to those of H in Si. Multiple trapping sites are found for H⁺ near to Ge_s.