Universality of the Bond-Breaking Mechanism in Defect Bistability: Observation of Open Volume in the Deep States of In and Ga inCdF2

Positron annihilation experiments reveal an open-volume defect in the deep state atomic configurations of bistable donors In and Ga in ${\mathrm{CdF}}_2$. The size of the open volume is at least half of a monovacancy. The results are similar to those obtained previously for the $\mathrm{DX}$ centers in the covalent system ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$. It is therefore likely that the bond-breaking mechanism (substitutional to interstitial atomic motion) responsible for metastability of point defects in covalent semiconductors is more universal and its validity extends to highly ionic compounds, similar to ${\mathrm{CdF}}_2$.