POSITRONIUM FORMATION IN SIO2-FILMS GROWN ON SI SUBSTRATES STUDIED BYMONOENERGETIC POSITRON BEAMS

The annihilation characteristics of positrons in SiO2 filMS grown on S i substrates were studied by using monoenergetic positron beams. Doppl er broadening profiles of the annihilation radiation and lifetime spec tra of positrons were measured as a function of incident positron ener gy for SiO2 (166 nm)/Si specimens fabricated by thermal oxidation. Fro m the measurements, it was found that about 90% of positrons implanted into the SiO2 film annihilate from positromium (Ps) states. This fact was due to the trapping of positrons by open-space defects and a resu ltant enhanced formation of Ps in such regions. For the SiO2 film grow n at 650-degrees-C, the lifetime of ortho-Ps was found to be shorter t han that in the film grown at 1000-degrees-C. This result suggests tha t the volume of open-space defects in the SiO2 film decreased with dec reasing the growth rate of the SiO2 film.