POSITRON-ANNIHILATION IN DIAMOND, SILICON AND SILICON-CARBIDE

Recent positron lifetime and doppler broadening results on silicon, diamond and silicon carbide are presented in this contribution. In as-grown Czochralski Si ingots vacancies are found to be retained after growth at concentrations typically around 3 x 10(16)/cm(3). 10 MeV electron irradiation of variously doped Si wafers shows that only high doping concentrations well in excess of the interstitial oxygen concentration causes an increase in the amount of monovacancies retained. In porous silicon very long-lived positronium lifetimes in the range 40-90 ns are found. Polycrystalline diamond films contain various types of vacancy agglomerates but these are found to be inhomogeneously distributed from crystallite to crystallite. Electron irradiation of silicon carbide results in two vacancy-related lifetimes which are interpreted as resulting from carbon and silicon vacancies.