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

Silicon codoped with aluminum and iron is investigated by electron paramagnetic resonance. Three spectra of trigonal, two of orthorhombic and two of monoclinic symmetry are detected and interpreted as being associated with iron- and aluminum-related defects. Most of the spectra are known but the analysis presented here supplemented by the observation of two additional spectra of trigonal and monoclinic symmetry, respectively, suggests alternative interpretations. We give evidence that the three trigonal spectra arise from three charge states of one and the same trigonal Fe-Al pair. Particularly, the trigonal spectrum, that can be described by a paramagnetic center with a spin S = 1, is associated with the corresponding acceptor state. A calculation of effective 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 same charge state of a complex consisting of two iron atoms and one aluminum atom. The resonances are consistently explained as transitions within the two energetically lowest Kramers doublets of a spin 5/2 system with a large zero-field splitting.