The annihilation characteristics of positrons in oxide/Si structures were studied, by using a mono-energetic positron beam, at temperatures ranging from 50K to ambient. The positrons formed positronium in the oxide film, and annihilated from localized states in open spaces. Positronium formation was suppressed at temperatures below 100K. This was attributed to the trapping of positrons by point defects in the oxide film at low temperatures. The depth distributions of such traps were not homogeneous, and the concentrations in the central region of the oxide films were higher than those in the regions which were near to the surface or the interface. The use of mono-energetic positrons for the detection of point defects provided unique information on the depth distributions of hole traps in SiO2 films.

A.Uedono, T.Moriya, S.Tanigawa, T.Kawano, Y.Ohji: Journal of Applied Physics, 1995, 78[5], 3269-73