Magnetic Resonance of Oxygen-Related Defects in Silicon
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MAGNETIC RESONANCE OF OXYGEN-RELATED DEFECTS IN SILICON
J. MICHEL, J.R. NIKLAS AND J.-M. SPAETH University of Paderborn, Fachbereich 6, Physik, Warburger Str. 100 A, D-4790 Paderborn, Federal Republic of Germany
ABSTRACT The electron spin resonance (ESR) of a number of vacancy-oxygen complexes In created in electron irradiated Si containing oxygen is briefly reviewed. 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 02 molecule.
1.
INTRODUCTION
In silicon containing oxygen two kinds of paramagnetic centers have been observed. One kind is generated after electron or neutron irradiation at room temperature and is due to a radiation damage effect. These centers require the creation of one or several vacancies, which are trapped by oxygen. The atomic structures of several such defects have clearly been identified. The electronic structure is that of rather highly localised unpaired electrons and the observed hyperfine (hf) data were interpreted successfully by a LCAO expansion of the wavefunction [1-9]. These centers will be reviewed briefly in the first section. The second kind of paramagnetic oxygen-related centers is generated when oxygen-rich Si is annealed. By annealing at temperatures between 400 to about 550 °C the so-called 'thermal donors' (TD) are formed. TD's were first reported in 1958 [10] and were thought to be oxygen aggregates. They are hitherto still of unknown atomic structure despite of many subsequent attempts to determine it. Potentially, magnetic resonance is a powerful tool to unravel the structure of a defect. In the case of the TD's, this goal has not yet been reached. Recently, however, a substantial progress was made. In the major part of this paper recently published ESR results are reviewed and for the first time the results of electron nuclear double resonance (ENDOR) experiments are reported
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