Positron annihilation 2D-ACAR study of irradiation-induced defects in Si

A positron annihilation method constitutes the most characteristic feature to demonstrate directly the lattice vacancy (hereinafter referred to vacancy) independent of the added elements, the electrical conductance and the charge state of them. The method can detect hole, divacancy and vacancy cluster. The divacancy is introduced into the single crystal sample by using the electron radiation with 15 MeV at room temperature. For 2D-ACAR spectrum of the perfect crystal,the maximum peak to valley showed 12.3% of the peak height of 2D-ACAR spectrum. It was clear from the measurement results of sample with the neutral divacancy (V2deg) that 2D-ACAR spectra of divacancy are isotropic and stable at the different charged states. 2D-ACAR spectra are calculated by using the first principle to the neutral divacancy. The results of the theoretical calculation are very agreed with those of observation and they are very isotropic. (S.Y.)