Magnetic Resonance of Oxygen-Related Defects in Silicon

ABSTRACTThe electron spin resonance (ESR) of a number of vacancy-oxygen complexes created in electron irradiated Si containing oxygen is briefly reviewed. In these centers the unpaired spin density is highly localised (50–70%) on two Si sites within the complex. The ESR spectra of several paramagnetic thermal donors (TD+) formed by annealing oxygen-rich Si at 450 °C for one to several hundred hours are reviewed as well as recent experiments under uniaxial stress from which for the ground state a 2 valley effective mass-like wavefunction was derived. Results of electron nuclear double resonance (ENDOR) experiments on the TD+ ESR line “NL8” are presented for the first time. They reveal that all TD's identified in IR-spectroscopy are superimposed in the NL8 ESR line and that upon growth of the TD the structure of the core and the symmetry of the TD's is not changed. The hyperfine interactions with up to 7 shells of Si nuclei of 5 TD+'s were determined. Their size and tensor orientations are consistent with the two-valley effective mass-like wavefunction. 4 TD's identified in ENDOR could be correlated with IR-bands from growth kinetics. Although the ENDOR experiments so far do not yet lead to a detailed TD model, the model possibilities are narrowed down considerably by these results. The core must consist of nuclei with very low magnetic abundancy. It is tentatively suggested, that the core contains an O2 molecule.