Relative stability of H^T vs. H* and H₂^T vs. H*₂ in c-C, Si, Ge, and α-Sn and their consequences

Ab-initio Hartree-Fock calculations of the relative stability of tetrahedral interstitial (H^T) and bond-centered interstitial (H*) hydrogen in c-C, Si, Ge, and α-Sn reveal that H* is more stable than H^T in c-C and Si but less stable than H^T in Ge and α-Sn. This change in relative stability affects the amount of H⁺ present, since H⁺ is a bond-centered species. This in turn affects the penetration kinetics of H into bulk Si vs. Ge under plasma exposure conditions and the ability of H to passivate shallow dopants. Significant differences in both properties have been reported. Ourresults are also consistent with the differences in muon kinetics between Si and Ge observed by μSR. We also calculate the relative stability of hydrogen dimers (H₂^T molecule and the H₂^* complex) in the same hosts.