Theory of the hydrogen interstitial impurity in germanium

The self-consistent pseudopotential method is used to study the electronic structure of the hydrogen interstitial impurity in Ge. The impurity is considered to be at the site of tetrahedral symmetry and strong intra-atomic correlation effects are included. It is found that a singly occupied H-$1s$ deep donor state exists, a result consistent with positive muon spin rotation (${\mu }^{+}\mathrm{SR}$) experiments. This state lies at least 1 eV, and perhaps as much as 6 eV, below the Ge valence-band maximum. An examination of the charge density suggests only a small tendency of H to bond with the neighboring Ge atoms. It is tentatively concluded that this deep donor state is the one probed by ${\mu }^{+}\mathrm{SR}$ experiments but that H migrates to impurity- or defectrelated complexes or forms of molecular hydrogen rather than remaining as an isolated interstitial impurity.