NATURAL INTRINSIC EX CENTER IN THERMAL SIO2 ON SI - O-17 HYPERFINE INTERACTION

The atomic structure of the intrinsic EX defect naturally generated in thermal SiO2 on Si has been analyzed by electron spin resonance on 51 % O-17 enriched (111)Si/SiO2 structures. Although the hyperfine struct ure could be only partly observed, the results indicate that the EX ce nter is an excess-oxygen defect, the defect core incorporating several O atoms which appear not to be entirely equivalent sites with regard to hyperfine interaction. The emanating working model is a Si vacancy in SiO2, where an unpaired electron is delocalized over the four borde ring O atoms, resulting in an effectively pure s state, which is subje ct to Si-29 superhyperfine interaction with neighboring Si sites.