POSITRON-ANNIHILATION IN DIAMOND, SILICON AND SILICON-CARBIDE

Recent positron lifetime and doppler broadening results on silicon, di amond and silicon carbide are presented in this contribution. In as-gr own Czochralski Si ingots vacancies are found to be retained after gro wth at concentrations typically around 3 x 10(16)/cm(3). 10 MeV electr on irradiation of variously doped Si wafers shows that only high dopin g concentrations well in excess of the interstitial oxygen concentrati on causes an increase in the amount of monovacancies retained. In poro us silicon very long-lived positronium lifetimes in the range 40-90 ns are found. Polycrystalline diamond films contain various types of vac ancy agglomerates but these are found to be inhomogeneously distribute d from crystallite to crystallite. Electron irradiation of silicon car bide results in two vacancy-related lifetimes which are interpreted as resulting from carbon and silicon vacancies.