POSITRON-ANNIHILATION IN A METAL-OXIDE-SEMICONDUCTOR STUDIED BY USINGA PULSED MONOENERGETIC POSITRON BEAM

The positron annihilation in a metal-oxide semiconductor was studied b y using a pulsed monoenergetic positron beam. Lifetime spectra of posi trons were measured as a function of incident positron energy for a po lycrystalline Si (100 nm)/SiO2 (400 nm)/Si specimen. Applying a gate v oltage between the polycrystalline Si film and the Si substrate, posit rons implanted into the specimen were accumulated at the SiO2/Si inter face. From the measurements, it was found that the annihilation probab ility of ortho-positronium (ortho-Ps) drastically decreased at the SiO 2/Si interface. The observed inhibition of the Ps formation was attrib uted to an interaction between positrons and defects at the SiO2/Si in terface.