ELECTRON-PARAMAGNETIC-RESONANCE OF IRON-RELATED AND ALUMINUM-RELATED DEFECTS IN SILICON

Silicon codoped with aluminum and iron is investigated by electron par amagnetic resonance. Three spectra of trigonal, two of orthorhombic an d two of monoclinic symmetry are detected and interpreted as being ass ociated with iron- and aluminum-related defects. Most of the spectra a re known but the analysis presented here supplemented by the observati on of two additional spectra of trigonal and monoclinic symmetry, resp ectively, suggests alternative interpretations. We give evidence that the three trigonal spectra arise from three charge states of one and t he same trigonal Fe-Al pair. Particularly, the trigonal spectrum, that can be described by a paramagnetic center with a spin S = 1, is assoc iated with the corresponding acceptor state. A calculation of effectiv e g' values shows that the ground states of the neutral orthorhombic, the neutral trigonal, and the positively charged trigonal Fe-Al pairs are orbital doublets (4E,5E). Both monoclinic spectra belong to the sa me charge state of a complex consisting of two iron atoms and one alum inum atom. The resonances are consistently explained as transitions wi thin the two energetically lowest Kramers doublets of a spin 5/2 syste m with a large zero-field splitting.