Self-Interstitial in Germanium

Low-temperature radiation damage in $n$- and $p$-type Ge is strikingly different, reflecting the charge-dependent properties of vacancies and self-interstitials. We find, using density functional theory, that in Ge the interstitial is bistable, preferring a split configuration when neutral and an open cage configuration when positively charged. The split configuration is inert while the cage configuration acts as a double donor. We evaluate the migration energies of the defects and show that the theory is able to explain the principal results of low-temperature electron-irradiation experiments.

Figure 1

Configuration-coordinate diagram for the self-interstitial. All energies shown are in eV and were calculated in the ${\mathrm{Ge}}_{329}{\mathrm{H}}_{172}$ cluster, using S as marker. Coordination numbers of the interstitial atom(s) are given in superscript, brackted. Ge-Ge bonds within 10% of the bulk bond length were considered.