Positron 2D-ACAR study of divacancies in Si: Experiments and theory

Two-dimensional angular correlation of annihilation (2D-ACAR) for divacancies in Si with definite charge states (V₂⁰, V₂^1- and V₂^2-) are studied theoretically and experimentally. The 2D-ACAR for the various charge states shows almost isotropic and very close to each other. However, using a specimen with aligned divacancies (V₂^1-), we have obtained a small but definite anisotropy in the 2D-ACAR. All these features are well reproduced by first principles calculations based on the two-component density-functional theory. Furthermore calculated anisotropies for the different charge states show systematic changes arising from the bonding character of the divacancy electrons. Theoretical 2D-ACAR is also presented for monovacancies. The present calculation and experiment demonstrate that the 2D-ACAR is an effective tool to provide microscopic information about vacancy-type defects.